|Session:||Large-scale ocean properties: science, observations and impacts (02A)|
Error Estimation of the Regional Mean Sea Level Trends From Altimetry Data
Ablain, M1; Prandi, P1; Lombard, A2; Bronner, E2
The global mean sea level (MSL) provided by satellite altimetry (TOPEX/Poseidon and Jason-1) is used as the reference to calculate the ocean elevation. From these data updated with the best geophysical corrections and the best altimeter data, a global rate of 3.4 mm is obtained over the 15 year period from 1993 to 2009 applying the post glacial rebound (MSL aviso website http://www.jason.oceanobs.com/msl). Besides, the regional sea level trends bring out an inhomogeneous repartition of the ocean elevation with local MSL slopes ranging from +/- 10 mm/year.
Current and Future of Tropical Ocean Climate Study (TOCS) and Triangle Trans-Ocean Buoy Network (TRITON) Buoy Array
Ando, Kentaro1; Ishihara, Yasuhisa2; Mizuno, Keisuke1; Masumoto, Yukio1; Baba, Shoichiro2; Hase, Hideaki1; Hasegawa, Takuya1; Horii, Takanori1; Iskandar, Iskhaq1; Kashino, Yuji1; Takahashi, Naoko2; Takahashi, Yukio2; Ueki, Iwao1; Yamaguchi, Masayuki2
This paper describes the past, current and future activities of both scientific TOCS project and technical and operational TRITON buoy project in JAMSTEC. These two projects have been linked each other for the purpose to promote the understanding ocean climate variations and ocean circulations in the Indo-Pacific regions, and to contribute to monitor El Nino/Southern Oscillation (ENSO) phenomena with the TAO array in the Pacific Ocean. The scientific TOCS project started in 1993 aimed originally to understand surface ocean circulation in the western Pacific by using sub-surface ADCP moorings in the western boundary and on the equator. In this project, we have also joined international efforts to maintain the TAO array, and routinely serviced the TAO array along 165E, 156E, 147E and 138E lines in 1993-1999. In 1998, the replacement of TAO-ATLAS buoy to TRITON buoys along 156E, 147E, 138E has started. After the data comparison between TRITON buoys and ATLAS buoys along 156E in 1999, TRITON buoy array became part of the present TAO/TRTION buoy array starting 2000. In the Indian Ocean, we have been deploying one subsurface ADCP mooring at 0-90E since 2000 in the TOCS project. Two TRITON buoys at 1.5S-90E and 5S-95E have also been deployed since 2001. The dataset of surface current profile by ADCP has been accumulated for last 8 years, the longest time series in the Indian Ocean.
In more than 15 years activity, many scientific results regarding to the variations in the western Pacific Ocean and the eastern Indian Ocean could be obtained mainly from above mentioned moored buoy data and ship observation data, and these scientific results have been contributed to better understanding of the ocean climate variations such as the El Nino/Southern Oscillation phenomena and the Indian Ocean Dipole mode. For example, the datasets of ADCP current profiles and subsurface temperature and salinity data of TRITON buoys in the eastern Indian ocean could capture the ocean variability associated with three Indian Ocean Dipole modes occurred in 2006, 2007, and 2008.
The TRITON buoy project is the corporative project with the TOCS project in terms of buoy operations and developments of buoy technology. In 1998, original TRITON buoy was developed and tested by a Japanese heavy industry company. However, due to several disadvantages such as difficulties to deploy and recover by smaller vessel etc., we have developed a new smaller and lower cost surface buoy with flexibility in modifying electric system, named m-TRITON buoy system. This buoy is currently used in the Indian Ocean RAMA array at 1.5S-90E and 5S-95E, and will be used for the new site at 8S-95E in 2009.
In future, in cooperation with CLIVAR/GOOS/IOP activity in the Indian Ocean, we will expand our RAMA sites with m-TRITON buoys in the south-eastern Indian Ocean, and will contribute to complete the RAMA array. In the western Pacific, we will continue maintenance of the current TRITON sites, and also stimulate participations of other institutions to the TAO/TRITON array by providing buoys and/or ship-time as in a framework of international efforts. Two programs will contribute to better understanding of tropical warm pool climate variations, which may play important role in overarching from the Indian Ocean to Pacific Ocean.
The HOAPS-3 satellite climatology of global freshwater flux
Bakan, S.1; Andersson, A.2; Klepp, C.2; Schulz, J.3
1Max-Planck-Inst. f. Meteorologie, Hamburg, GERMANY;
2University of Hamburg, GERMANY;
3DWD, Offenbach, GERMANY
The proper knowledge of the global water cycle is crucial for successful climate system understanding and modeling in order to answer questions like “What is the temporal and spatial variability of essential water cycle components ?” or “How does the global water cycle develop in a warming world ?” With the ability to derive ocean latent heat flux and precipitation from satellite data with acceptable accuracy and frequent global coverage, a climatological assessment of the crucial processes has become possible. The HOAPS-3 climatology (Hamburg Ocean Atmosphere Parameters and Fluxes from Satellite Data) contains fields of precipitation, surface fluxes and related atmospheric parameters over the global ice-free ocean between 1987 and 2005. Except for the AVHRR Pathfinder SST, all basic state variables needed for the derivation of the fluxes are calculated from SSM/I passive microwave radiometer measurements. A sophisticated processing chain, including multi-satellite averages, inter-sensor calibration, an efficient sea ice detection procedure, and well validated retrieval algorithms make HOAPS a suitable data set for climatological applications as well as for case studies. Gridded 0.5 degree monthly, pentad and twice daily data products are freely available from www.hoaps.org. On a global scale, HOAPS-3 shows, that the average evaporation since 1987 exceeds rain rate over the ocean systematically with almost negligible yearly cycle and small monthly variations. The globally averaged evaporation shows a continuous increase during the study period, especially in the subtropics. Precipitation does not exhibit any significant global trend. Regionally some reduction in the subtropics and a substantial increase in the ITCZ and over the southern mid latitude oceans can be seen, but no significant change over the northern oceans. Comparison with similar satellite and reanalysis fields of the same period exhibit remarkable similarities and differences in the temporal developments of global evaporation and precipitation with a substantial range of results for the E-P balance over global oceans.
Observing System for Turkish Straits System
Besiktepe, S1; Jarosz , E2
1NATO Undersea Research Center, ITALY;
2Naval Research Laboratory, Oceanography Division, Stennis Space Center, UNITED STATES
Exchange flows through straits play important role on the evolution of the water masses in the basins connected by straits. Observations of the water exchange in the straits provide information about the evolution of the water mass properties in the basin as well as providing information on the water properties in the straits. An efficient observing system must take into account the wide variety of dynamical processes which occur over the multiplicity of time and space scales. Observations of flow and water mass properties in the straits require resolving important spatial and temporal time scales in the processes occurring in and near straits. In this paper, observing system designed for Turkish Straits System (TSS) shown as an example for using different platforms and sensor as a part of integrated observing system. The Turkish Straits System provides an opportunity to observe dynamical processes over a wide variety of time and space scales known to occur in many straits of the world. Complex non-linear processes of two-way exchange flows, hydraulic controls, dense water overflows and jets, turbulent mixing and entrainment, locally and remotely driven motions reflecting ocean-atmosphere interactions in adjacent basins as well as locally, occur in this region of a relatively small size. The Turkish Straits System is an excellent and challenging area to observe all these processes above issues, while its manageable size provides excellent opportunities for conducting at-sea experiments. Observing System which consists of in-situ and satellite platforms, covering different scales of motion from the Black Sea to the Aegean Sea in the TSS are used to monitor the physical and bio-optical properties of the waters during September 2008 and February 2009 by NATO Undersea Research Center (NURC). Large scale hydrographic surveys carried out by the R/V Alliance provide a complete synoptic view of the hydro-physical variables in the Black Sea, Marmara Sea and the Aegean Sea. Sub-mesoscale and turbulence (microstructure) measurements were carried out in the Istanbul and Canakkale Straits and their outflows to adjacent seas where these scales are important to resolve the dynamical details of the flow. In order to resolve sub-mesoscale features, towed systems, CTD chains mobilized and used to make measurements at strategic locations to observe flow details. Currents, sea-level, temperature and salinity measurements obtained from fixed moorings to quantify mechanisms of two-way transports through the TSS, to study their variability over different time scales (from hourly to seasonal), and to estimate mean, seasonal, and synoptic exchange rates in the Istanbul and Canakkale Straits. Concurrent time-series of satellite data obtained during the experiment used to support in-situ measurements and identify transport and plankton activity patterns. Knowledge gained from these exercises could offer the opportunity to understand the strait dynamical processes in other parts of the world ocean and develop predictive capabilities for these processes. The enclosed geometry of the Marmara Sea, connected to the adjacent basins through two narrow, highly restrictive straits with hydraulically-controlled flows offers a unique opportunity in terms of experimental control. On the other hand, the complexity of the flow and mixing processes in the region are also in many ways unique: some essential details are either experimentally difficult to capture or not adequately handled by existing ocean models which are often geared for open ocean or relatively simpler coastal areas. The processes are often not sufficiently understood to design experiments or develop models that will address all the problems in unison.
Monitoring deep convection combining altimetry and modelling: Application to the Labrador and Mediterranean Sea.
Bouffard, J.1; Pascual, A.1; Beranger, K.2; Herrmann, M.3
3Météo-France / CNRM, FRANCE
The center of the Labrador Sea and the North Western Mediterranean (NWM) are characterized by weak stratification and, in winter exposed to intense buoyancy loss due to atmospheric forcing generating open-sea convections. The Deep Convections (DC) is a key-process of the oceanic circulation, costly to monitor in situ and under the influence of climate change. Our study is a first step toward monitoring DC combining remote-sensing and models. In this respect, oceanic simulations of the Mediterranean and Labrador circulation were performed respectively for the 1999–2007 and 1960-2001 period. DC are realistically modelled, and the Sea Surface Elevation (SSE) is in agreement with altimetric data. Numerical results show a strong correlation (>0.9) between the annual DC characteristics and the winter SSE. From that, we propose a simple method to monitor DC long term evolution using only altimetry. Our method, applied to the longest available altimetric time-series, represents correctly the variability of DC both in the NWM and Labrador Sea between 1994 and 2008
Variability of the equatorial Atlantic cold tongue
Brandt, Peter1; Bourlès, Bernard2; Dengler, Marcus1; Caniaux, Guy3; Goni, Gustavo4; Lumpkin, Rick4; Reason, Chris5; Rouault, Mathieu5; Johns, William E.6
4NOAA/AOML, UNITED STATES;
5University of Cape Town, SOUTH AFRICA;
6RSMAS, UNITED STATES
Climate fluctuations in the tropical Atlantic sector are dominated by two distinct patterns of coupled ocean/atmosphere variability. These modes of variability, collectively referred to as tropical Atlantic variability (TAV), are tightly phase locked to the pronounced Atlantic seasonal cycle and vary on interannual to decadal timescales. During boreal spring, when the equatorial Atlantic is uniformly warm, conditions are favorable for the development of an interhemispheric gradient of sea surface temperature (SST) anomalies often referred to as the meridional mode. The so-called zonal mode is frequently viewed as the Atlantic counterpart of the Pacific El Nino Southern Oscillation (ENSO) and is most pronounced during boreal summer coinciding with the seasonal development of the eastern equatorial cold tongue. The interannual variability of SST in the cold tongue during boreal summer is closely linked to rainfall variability in the countries surrounding the Gulf of Guinea and in the northeast region ("Nordeste") of Brazil. Cold tongue SST is controlled by different oceanic and atmospheric processes, among them are surface heat fluxes, vertical mixing, mean and eddy advection. A multinational observational program is at place in the frame of the Tropical Atlantic Climate Experiment (TACE) including shipboard and moored measurements as well as measurements from autonomous floats, drifters and gliders. Within this program the year-to-year variability of the central and eastern equatorial upper ocean heat budget and SST will be quantitatively linked to the different oceanic and atmospheric processes at work.
CLIVAR Global Ocean Observation and Synthesis Activities
National Oceanography Centre, Southampton, UNITED KINGDOM
The overall mission of CLIVAR, the Climate Variability and Predictability Project of the World Climate Research Programme (WCRP) is to observe, simulate and predict the Earth’s climate system, with a focus on ocean-atmosphere interactions. CLIVAR has established its Global Synthesis and Observations Panel (GSOP) to develop, promote and seek to implement strategies for global ocean synthesis efforts, building on previous experiences and developments, eventually leading to a fully coupled reanalysis with atmosphere, ocean. land and cryosphere models. The panel is also responsible for the definition and (in collaboration with relevant bodies) fulfillment of CLIVAR's global needs for sustained observations. To do this it works closely with CLIVAR’s regional ocean basin panels on the one hand and international bodies such as Global Ocean Observing System, the Ocean Observations Panel for Climate and the Joint WMO-IOC Technical Commission on Oceanography and Marine Meteorology on the other.
One of the main contributions of GSOP to CLIVAR science is its evaluation of the current generation of ocean synthesis/reanalysis products providing guidance on their use for study of the global ocean circulation. This evaluation has led to several improvements in the products. Notably it has led to several papers comparing different ocean synthesis products and thus to first specifications of uncertainties in ocean syntheses. An “Ocean Synthesis Directory” provides community links to global ocean synthesis data.
GSOP is engaging through its ocean synthesis project in decadal forecast experiments. One key element is for ocean synthesis groups to provide updated datasets to be used for the decadal prediction experiments. GSOP is also currently in the process of providing all available ocean syntheses as initial conditions for decadal prediction experiments. First such experiments are ongoing and show some success. Possibilities of coupled data assimilation are also being explored. These efforts are currently only just spinning up and will grow over the coming years.
The panel co-sponsors (with the International ocean carbon Coordination project and the International Geosphere-Biosphere Programme’s Surface-Ocean / Lower Atmosphere Study- Integrated Marine Biogeochemistry and Ecosystem Research Carbon Coordination Group) the Global Ocean Ship-based Hydrographic Investigations Panel (GO_SHIP). GO_SHIP brings together interests from physical hydrography, carbon, biogeochemistry, Argo, OceanSITES, and other users and collectors of hydrographic data to develop a strategy for ship-based repeat hydrographic observations post CLIVAR. This activity includes the review and an update of the WOCE hydrographic manual. More widely, GSOP is also seeking to organize the production of an update to the 2002 WOCE Global Data Set v3 to include observations made between the WOCE era and the end of 2010.
This poster will provide illustrations of the work of GSOP including the outputs from ocean synthesis intercomparisons, CLIVAR links to ocean carbon activities and GSOP’s role, with others, in promoting the sustained global ocean observation network.
Deep ocean observing system over middle and long time scale: the E2M3A site in the Southern Adriatic
Cardin, V.R.; Bensi, M.; Gaèiæ , M.
Istituto Nazionale di Oceanografia e di Geofisica Sperimentale - OGS, ITALY
The open-ocean convection has been considered the engine of the global conveyor belt. It is a mechanism forming new dense and oxygenated waters, and it riggers the solubility and the biological pump. Among the few zones in the world interested by the open-ocean convection, the South Adriatic is a small but key area for the intermediate and deep thermohaline cell of the Eastern Mediterranean. There, the Adriatic Dense Water ADW formed prevailing by the open-ocean vertical convection , becomes the main component of the Eastern Mediterranean Deep Water (EMDW). This process takes place in the South Adriatic Pit (SAP) in the centre of the cyclonic gyre. The extension of the vertical mixing, varies on the interannual and decadal time-scales in function of the air-sea heat fluxes and the pre-conditioning vertical density structure.
The high spatio-temporal variability of the deep convection and its interaction with other processes makes difficult it study. Oceanographic cruises provide a good spatial coverage but lack in temporal resolution. The need of high temporal sampling to resolve events and rapid processes and the long sustained measurement of multiple interrelated variables from sea surface to seafloor can be solve by the use of moorings located in specific areas as the Southern Adriatic Pit.
In the framework of the Italian VECTOR project a deep-sea mooring (41°29.7N, 17°42.1E) containing CT sensors at five depths, an upward looking 150 kHz ADCP and an Aanderaa current meter RCM11 was located in the vertical convection area. Moreover, two sediment traps were positioned at 168 m and 1174 m on the mooring line. This mooring configuration permits to individuate water mass formation, measuring simultaneously physical and chemical parameters. The mooring is still in the water and new upgrades will be done in the framework of the European project EuroSITES during 2009. The deployment of pCO2 sensor together with a pH sensor within the mixed layer will allow to estimate the Carbon system at the site. The deployment of a surface buoy will allow the real data transfer from the platform to the land station.
Here, data recorded in the period between end-November 2006 and October 2008 covering two consecutive year with pre-conditioning and deep convection periods will be presented . Surface chlorophyll a obtained from the SeaWiFS data is a good indicator of the vertical mixing patch as demonstrated earlier, and here it has been used in determining the patch position with respect to the mooring location and its geometry.
WCRP CLIVAR and ocean observations
National Oceanography Centre, Southampton, UNITED KINGDOM
The overall mission of CLIVAR, the Climate Variability and Predictability Project of the World Climate Research Programme (WCRP) is to observe, simulate and predict the Earth’s climate system, with a focus on ocean-atmosphere interactions. CLIVAR is a long-term, 15 year, programme which began its implementation phase in 1998. Its role is to provide international coordination in areas of science that progress our understanding of climate variability and change and climate prediction. Implementation of CLIVAR is carried out through the activities of its regional panels (one for each of the ocean basins, and one each for the American and Asian-Australian monsoon and African climate systems) and through its global modelling, observational and synthesis groups. Modelling activities within CLIVAR are focussed on coupled numerical model experiments on seasonal, decadal and centennial timescales, including prediction of the response to both natural and anthropogenic forcing. Special attention is given to assessing and improving predictions and facilitating their applications to society. A key question is how anthropogenic climate change will both be influenced by and modulate climate variability and what are the implications for prediction out to decades and longer.
CLIVAR has overall responsibility for the role of the oceans in climate within WCRP. Sustained ocean observations (as well as ocean process studies) provide key inputs to CLIVAR activities and CLIVAR seeks to stimulate the continued development of the Ocean Observing System in collaboration with the Global Ocean Observing System, the Ocean Observations Panel for Climate and the Scientific Committee on Antarctic Research. It does this through the activities of its Atlantic, Pacific, Indian and Southern Ocean Basin Panels and its Global Synthesis and Observation Panel (GSOP). CLIVAR was an early co-sponsor (with the Global Ocean Data Assimilation Experiment) of Argo and is, for example, co-sponsor of OceanSITES, the PIRATA array and the developing Indian Ocean sustained ocean observing network.
Ocean modelling is an integral part of the work of CLIVAR’s coupled modelling and seasonal prediction working groups for which ocean observations are needed both for model initialization and validation. A key activity within CLIVAR, carried out by GSOP is the coordinated application of data assimilation systems to provide and intercompare integrated ocean syntheses. These have the potential to provide initial conditions for climate predictions on seasonal to decadal timescales (coordinated by CLIVAR’s seasonal and coupled modelling working groups) and for validation and comparison of coordinated ocean-ice reference experiments by CLIVAR’s group on ocean model development. Ocean observations also have a role in CLIVAR’s wider activities in monsoon and African climate prediction.
This poster will summarize the key ocean-related activities of CLIVAR from the perspective of the role of sustained ocean observations in research on climate variability and change. It will provide a backdrop to posters describing the ocean-observation-related work of CLIVAR’s ocean basin panels and GSOP in more detail.
Observed Freshening and Warming of the Western Pacific Warm Pool
CRAVATTE, Sophie1; Delcroix, Thierry1; Zhang, Dongxiao2; McPhaden, Michael3; Leloup, Julie4
2PMEL/NOAA, UNITED STATES;
3NOAA-PMEL, UNITED STATES;
4RSMAS, UNITED STATES
Trends in observed sea surface salinity (SSS) and temperature are analyzed for the tropical Pacific during 1955–2003. Since 1955, the western Pacific Warm Pool has significantly warmed and freshened, whereas SSS has been increasing in the western Coral Sea and part of the subtropical ocean. Waters warmer than 28.5°C warmed on average by 0.29°C, and freshened by 0.34 pss per 50 years. Our study also indicates a significant horizontal extension of the warm and fresh surface waters, an expansion of the warm waters volume, and a notable eastward extension of the SSS fronts located on the equator and under the South Pacific Convergence Zone. Mixed layer depth changes examined along 137°E and 165°E are complex but suggest an increase in the equatorial barrier layer thickness. Our study also reveals consistency between observed SSS trends and a mean hydrological cycle increase inferred from Clausius-Clapeyron scaling, as predicted under global warming scenarios. Possible implications of these changes for ocean-atmosphere interactions and El Niño events are discussed.
Developing global long-term altimeter datasets and climatologies of ocean wave measurements
Cromwell, David; Gommenginger, Christine P.
National Oceanography Centre, UNITED KINGDOM
The prime objective of this work is to build long-term climatologies of ocean significant wave height and wave period based on multi-mission satellite altimeter datasets. The development of such global climatologies is driven by the need to validate present day operational wave forecasting systems as well as improve our understanding of the role of waves in atmosphere-ocean dynamics, ocean surface transport and mixing, and facilitate the detection and measurement of global climate change as revealed in ocean wave parameters. Typical applications also include better estimation of ocean-based renewable energy resources and improved estimation of extreme sea states.
The basic methodology is first to calibrate altimeter-derived significant wave height (SWH) and wave period estimates against a network of in situ buoy measurements. In this study, we use primarily buoy data extracted from the National Data Buoy Center (NDBC) database, made available freely online by the US National Oceanic and Atmospheric Administration (http://www.ndbc.noaa.gov).
Altimeter SWH and radar backscatter, sigma-0, are extracted for the whole duration of the TOPEX, ENVISAT and JASON-1 altimeter missions, thus spanning a period of over 15 years. Collocation of altimeter and buoy data is performed here using a maximum time separation of 30 minutes (buoy data are collected hourly) and a range of maximum spatial separations of (a) 50 km; (b) 100 km; and (c) closest collocation up to a maximum of 500 km. The altimeter data are all obtained via the Radar Altimeter Database System (RADS) hosted at Delft University of Technology (http://rads.tudelft.nl/rads/rads.shtml). The SWH is measured directly by the altimeters while the wave period is calculated using the algorithm of Mackay et al. (2008).
An important consideration when dealing with long-term datasets is the development of a robust technique to perform the calibration in time: how do the best-fit parameters change in time, and what is the dependence on both the specified collocation distance and the duration of the collocated dataset for the ODR results? Our initial investigations suggest that 10 days of data provide too few measurements for a reliable calibration. Conversely, although performing the calibration over a year (or longer) typically provides tens of thousands of altimeter-buoy data pairs, leading to a high-precision calibration, it may smooth over potentially significant intra-annual variability.
Next, the calibration is applied to each dataset of along-track altimeter measurements, yielding along-track global estimates of SWH and wave period for each altimeter mission. These along-track data are then gridded using optimal interpolation to a regular temporal and spatial grid (typically monthly and 2x2 deg, respectively) over the global ocean (within the latitude range covered by each satellite altimeter).
Continuation of the work will include the investigation of other collocation techniques, such as the triple collocation between three independent datasets, which leads to estimate of errors on all data sources (Caires & Sterl, 2003). Additional altimeter datasets, from past and emerging missions, will also be incorporated in the study, including data from ERS-2, GFO, JASON-2 and Cryosat-2.
COriolis Re-Analysis (CORA) : a new comprehensive and qualified ocean in-situ dataset from 1990 to 2008
de Boyer Montegut, C.1; Cabanes, C.2; Coatanoan, C.1; Pertuisot, C.1; Petit de la Villeon, L.1; Carval, T.1; Pouliquen, S.1; Le Traon, P.-Y.1
Coriolis is a french programme basically aimed to contribute to the ocean in situ measurements part of the french operationnal system. It has been especially involved in gathering all global ocean in-situ observation data in real time, and developing continuous, automatic, and permanent observation networks. Coriolis data center now produces by the end of 2009 a comprehensive ocean in-situ dataset of temperature/salinity profiles on the global scale and ranging from year 1990 to 2008. This dataset is meant to be used for general oceanographic research purposes, for ocean model validation, and also for initialisation or assimilation of ocean models. Here we first present the observations types and distribution used to build this dataset (argo, gts data, vos ships, nodc historical data...). Then we will review the processing and quality controls that have been applied to the data (e.g. objective analysis to remove outliers and/or some visual checks). In a last part, we show some basic characteristics of the temperature and salinity fields constructed from this dataset.
Spatial and temporal variability of water masses in the 4 AR/IPCC models
Ferrero, B.; Wainer, I.
University of Sao Paulo, BRAZIL
The development and sophistication of numerical models in recent years has allowed to perform many climate system's simulations. Such simulations aim to reproduce the dynamics and variability of the climate and consequently predict future climate and possible climate changes. Oceanic processes such as formation and distribution of water masses have an important role in understanding the oceans as a reservoir of salt, dissolved gases and heat. Considering that changes in such processes may have great impact in global and regional climate this work aims to describe spatial and temporal variability of water masses in the South Atlantic Ocean and Southern Ocean. Data from the numerical simulations used for the preparation of the Intergovernmental Panel on Climate Change Fourth Assessment Report (4AR/IPCC) were used. Four climate models were chosen: ECHAM5/MPI-OM, IPSL-CM4-V1, MIROC3.2, NOAA / GFDL CM2.1. Results from the Climate of the 20th Century (20c3m) and the 1% per year CO2 increase (to doubling) experiment (1pctto2x) were analyzed. All models show a positive trend of temperature and a freshening trend of the Antartic Intemediate Water (AAIW), Circumpolar Deep Water (CDW) and the Antartic Deep Water (AADW). Densities of these water masses become significantly lighter in the 20c3m scenario. In the 1pctto2x scenario in the AAIW and CDW moved to upper layers. Also in this scenario there is a cooling of the AADW, moving this water mass to deeper layers.
Visual Wind Wave Data From VOS: A Substantial Component of Wind Wave Observing System
Grigorieva, Vika; Gulev, Sergey K.
IORAS, RUSSIAN FEDERATION
Visual wave observations (assimilated in ICOADS) are available effectively from the mid 19th century and represent the longest records of wind wave information worldwide taken with a unique observational practice. Visual wave data are characterized by quite strong systematic and random errors. Maximum random observational errors in wins sea height amount to 1 meter with maximum random observational errors in swell height being up to 1.6 meters. Significant uncertainties (both random and systematic) in wind wave periods estimates of up to 2-3 seconds may result from the deviation of the actual observational practices from the guidelines. VOS-based climatological estimates of wave characteristics also suffer from spatially and temporally inhomogeneous sampling with the largest sampling errors (up to 1.5-2 meters in wave height) identified in the poorly observed regions of the Southern Ocean and subpolar Northern Hemisphere. We will present 60-yr climatology of wind waves based on visual observations. It includes estimates of heights and periods of wind sea and swell as well as derived SWH and dominant period along with error estimates. Climatology allows for the analysis of linear trends and patterns of interannual variability in wind wave characteristics worldwide. Analysis of the earlier 20th century records of visual wave data for selected ship routes demonstrated centennial increase of SWH (of 8-10 cm/decade) in the North Pacific, with no significant centennial trends in the Atlantic. Visual VOS data also allow for estimates of extreme wind waves for the last several decades, if only in well sampled North Atlantic and North Pacific mid latitudes. Further prospects for the improvement of the accuracy of visual wind wave data will be discussed. These include installation onboard of selected VOS rolling sensors and recording of ship radar scans for providing alternative data for the validation of visual wave estimates.
Recent Change in Global Sea Surface Layer Salinity Detected by Argo Float Array
Hosoda, Shigeki1; Suga, Toshio2; Shikama, Nobuyuki1; Mizuno, Keisuke1
2Tohoku Univ/JAMSTEC, JAPAN
We investigated surface layer salinity distributions and characteristics of those spatial and temporal variations in the global ice-free ocean. Surface layer salinity is one of the most important measures indicating the accumulated fresh water flux in the ocean. The fresh water flux change, mainly caused by the flux from atmosphere, links strongly to a change of strength in the global hydrological cycle. The deployment of the Argo float is increasing and the Argo float array has allowed us to document changes in global salinity. In the climatology calculated using historical data in 1960-1989, the surface layer salinity is generally lower in the subpolar and tropical regions and higher in the subtropics. We compared the annual averaged surface layer salinity distribution in 2003-2007 with the climatology and found a general enhancement of lower and higher surface layer salinity, except in the North Atlantic Ocean. Since direct observational estimation of evaporation and precipitation (E-P flux) is difficult at the sea surface, estimating the E-P flux from oceanic salinity is an effective alternative. We estimated the changes of basin-scale E-P flux associated with the strength of the global hydrological cycle from the averaged surface layer salinity in 2003-2007. The results show a high probability of increasing the global hydrological cycle in the past 30 years, showing that surface layer salinity change is a useful proxy to detect long-time climate change or trend, such as global warming. We suggest that sustaining Argo float array allow us to detect detailed variation of global surface layer salinity, and blending satellite (SMOS and Aquarius/SAC-D) and in situ observation by the Argo floats makes it possible to understand changes of the global hydrological cycle in detail.
Deep Water Warming and Steric Height Change in the Pacific Ocean
Kawano, T; Doi, T; Kouketsu, S; Uchida, H; Fukasawa, M; Katsumata, K; Kawai, Y
Changes in the heat content in the Pacific Ocean were studied using data from ship-based basin-scale repeat hydrographic surveys. The comparison between results from recent surveys mainly conducted in the 2000s in CLIVAR/IOCCP and previous surveys conducted in World Ocean Circulation Experiment reveals that the heat content in the deep layer has increased in the almost entire Pacific Ocean. In particular, the contribution from the deep ocean below 2000 dbar is estimated as 5% of the total.
The steric height change below 2000 dbar averaged over the Pacific Ocean was calculated to be 0.1 mm/year, small but not insignificant contribution to the global steric height increase of 1.9 +/- 0.2 mm/year as estimated from the satellite altimeters and the Gravity Recovery and Climate Experiment (GRACE) space mission. The contribution of thermal expansion was 0.16 mm/year and that of saline contraction was -0.07 mm/year. The steric height below 2000 dbar increased in the western Pacific and decreased in the eastern Pacific. The largest increase was seen in the Southern Oceans and as well as the western boundary region off the coast of Japan.
Long-term variations of Subantarctic Mode Water at 32°S in the Indian Ocean
Kobayashi, Taiyo1; Mizuno, Keisuke1; Suga, Toshio2
2JAMSTEC and Tohoku Univ., JAPAN
Long-term variations of Subantarctic Mode Water (SAMW) at 32°S in the Indian Ocean are examined for 1950-2008 using a time-series mapped objectively from historical hydrographic and Argo data. In the upper part of SAMW (<26.7 sigma-theta), saltier water distributed widely around 1960 is replaced with fresher water in the late 1980s after large-amplitude (over 0.1 in salinity) oscillations with 5-10-year time scales. After 2000 the saltier SAMW occupies the area again. A freshening trend in the density range is difficult to conclusively identify now because of the large variations. Meanwhile, the lower part of SAMW (>26.8 sigma-theta) shows a clear freshening trend; its salinity decreases by over 0.1 since the 1960s. A thick pycnostad of SAMW in the 1960s disappeared in the 1980s. Recently, the thick core recovered and became less dense. These features seem consistent with recent model results showing that SAMW is freshened with large, quick fluctuations due to global warming and natural variation.
A decade of physical and biogeochemical measurements in the northern Indian Ocean
Kumar, Prasanna; Sardesai, Sugandha; Nagappa, Ramaiah
National Institute of Oceanography, INDIA
The northern Indian Ocean consists of two tropical basins (Arabian Sea and Bay of Bengal) and the equatorial region, which comes under the influence of strong monsoonal wind reversal. In response to this forcing, the upper ocean circulation and hydrography show strong seasonality. It was the International Indian Ocean Expedition (IIOE) during 1959 to 1965 that provided the first description of the physical, chemical and biological characteristics of this region. Since then there have been several observational campaigns, both by individual nations as well as through international collaborative efforts, which contributed towards furthering our understanding. The availability of satellite remote sensing data further enhanced our understanding of the basin-wide structure and its variability. In this paper we present the results from 3 national programmes that India under took to address the seasonal variability of physical and biogeochemical parameters since 1992 – (1) the Joint Global Ocean Flux Studies (JGOFS) during 1992-1997 in the Arabian Sea, (2) the Bay of Bengal Process Study (BOBPS) during 2001-2006 and (3) the Equatorial Indian Ocean Process Study (EIOPS) which started in 2005 and will continue until 2012. In the above programmes, measurements were and are being carried out following the JGOFS protocol including in situ incubation for primary productivity measurements. The results showed that the Arabian Sea was the most productive region in the northern Indian Ocean followed by the Bay of Bengal and the equatorial Indian Ocean. The Arabian Sea showed strongest seasonal cycle with blooms occurring during summer (June-September) and winter (November-February). The summer blooms in the Arabian Sea are driven by the upwelling and upward nutrient pumping while winter blooms are by convective mixing that supply nutrients to the euphotic zone. In the Bay of Bengal though the surface chlorophyll biomass showed a weak seasonality, the mesoscale eddies played important role in enhancing the biological productivity through upward-pumping of nutrients. In the EIO, the data collected so far suggest very low chlorophyll biomass and productivity. Though the above observational programmes greatly enhanced our understanding of the coupling between the physical and biogeochemical fields in the northern Indian Ocean over the seasonal time scale, our understanding of the inter-annual variability still remains to be rudimentary. Efforts are needed to develop a sustained regional observational network through international collaboration which would include repeat sections, moored arrays as well as drifters. We discuss the urgency of such an initiative and its benefit to climate change study.
Detection of Natural and Anthropogenic signals in the ocean climate
record using the Met Office EN3 data set
Matt, Palmer1; Good, Simon A.1; Haines, Keith2; Rayner, Nick A.1; Stott, Peter A.1
1Met Office Hadley Centre, UNITED KINGDOM;
2University of Reading, UNITED KINGDOM
We present a method to quantify ocean warming that filters out the natural internal variability from both observations and climate simulations and better isolates externally forced air-sea heat flux changes. As a result, we gain a much clearer picture of the drivers of oceanic temperature changes and are able to detect, for the first time, the effects of both anthropogenic and volcanic influences simultaneously in the observed record. Our analyses are based upon Met Office climate models and the EN3 quality controlled subsurface ocean observations, which include XBT bias corrections and cover the period 1950 to present. We present an overview of the EN3 data sources, quality control procedures and data products. The EN3 dataset is freely available to download and use for research purposes from www.metoffice.gov.uk/hadobs.
Glider measurements around the Vercelli Seamount (Tyrrhenian Sea) in May 2009
Mauri, E.; Bubbi, A.; Brunetti, F.; Gerin, R.; Medeot, N.; Nair, R.; Poulain, P.-M.
Many international projects focus on sea mountains because of their importance on the ecology of the marine environment and of their high level of vulnerability to the global change. Hence the Italian Ministry of University and Research (MUR), sensible to this topic, financed the Tyrrhenian Seamounts Ecosystem Project (TySEc) polarizing the attention on the Vercelli Seamount located in the Northern Tyrrhenian Sea, (41°05'00 N / 10°53'00 E), whose summit reaches 55 m below the sea surface. As part of this integrated study, the Istituto Nazionale di Oceanografia e Geofisica Sperimentale (OGS) operated a Slocum shallow battery-powered glider around the Vercelli seamount from the 23rd to the 30th of May 2009 to sample the physical and bio-chemical characteristics of the water column in its vicinity. The glider "Trieste-1" was programmed to cover an area of roughly 750 km2, above the seamount. It was configured to provide oceanographic data during the ascending phase of the saw tooth path, every 0.75 km. During the entire campaign 300 profiles between 4 and 200 m depth were acquired providing temperature, salinity, oxygen, fluorescence, and turbidity data. Preliminary results derived from the glider data are presented. In addition to the expected thermal stratification and the sub-surface salinity maximum characteristic of the Levantine Intermediate Water, a layer with minimum in salinity and maximum in oxygen concentration is evident near 20 m depth. A sub-surface maximum in chlorophyll concentration and turbidity is also seen between 60 and 80m, just below the surface highly oxygenated layer.
Operational Oceanography at the Naval Oceanographic Office: Real-Time Oceanographic Measurements
May, D. A.; Wahl, R. J.; Myrick, R. K.; Grembowicz, K. P.
Naval Oceanographic Office, UNITED STATES
The Naval Oceanographic Office (NAVOCEANO) currently collects data from a variety of real-time satellite and in situ sensors that are processed into tailored fleet products within hours. Satellite sea surface temperature (SST) data are generated from a variety of polar-orbiting and geostationary satellites including NOAA-18/19, METOP, GOES, and MSG. These data are directly assimilated into operational ocean models in near-real-time and are also used to generate regional fleet support products. Satellite altimeter data are received from Jason-1, Jason-2, and ENVISAT altimeters to maintain continuous sea surface height observations that are assimilated into operational ocean models. Significant wave height and marine wind speed products are also generated to support operational maritime activities. Satellite ocean color data are received from sensors aboard two polar-orbiting satellites, SeaWiFS and MODIS. These data are processed into visibility, chlorophyll, and K532 products for a broad range of fleet support. Each data set described here is routinely checked for accuracy, coverage, and timeliness requirements. In addition, NAVOCEANO deploys profiling floats, drifting buoys, and ocean gliders throughout the world to measure surface and subsurface oceanographic parameters such as temperature, salinity, currents, and optics. These tools enable NAVOCEANO to persistently sample areas of naval interest and, coupled with performance models, provide characterization of the operational environment.
Seasonal Variability of Chl a (SeaWiFS) and SST (MODIS Aqua) off Magdalena State, Colombian Caribbean, 1997-2006
Mejia , L.M.; Franco-Herrera, A.
Fundacion Universidad de Bogota Jorge Tadeo Lozano, COLOMBIA
The productive characteristics of the waters off the Magdalena State, Colombia Caribbean, have not been fully described because of a lack of complete studies performed to evaluate its biological, chemical and physical dynamics over time. Even though remote sensing is a sampling technique that allows data in a long temporal and spatial scale to be obtained, it has not been widely used in the study of ecosystems in the Colombian Caribbean. Therefore, the present study applied this method to compare the potential production of events such as continental water inputs and upwelling, which occur during wet and dry seasons, by obtaining, processing and interpreting 16 km2 monthly average satellite data and images of the sea surface temperature (SST) and chlorophyll a (Chl a) concentration in a total area of 12,553.8602 km2, throughout a time period comprised between 1997 and 2002 and 1997 and 2006 and measured using the MODIS Aqua and SeaWiFS remote sensors, respectively. The study area was divided in three oceanic and three coastal sectors, given the differences in the oceanographic, topographic and continental runoff characteristics of the waters. The analysis of the average air atmospheric temperature, wind speed, precipitation levels and Ekman´s depth, concluded that the duration of the seasons was highly variable, contrary to what was generally thought. A temporal thermal and a Chl a concentration stability was found, which allowed to conclude that although events such as El Niño Southern Oscillation took place within the study time, the capability of the waters to enhance the phytoplanktonic development, remained unaffected over time. With regards to the spatial variability, no thermal differences were found between sectors, while the higher Chl a concentrations found in the further southwestern coastal waters defined them as mesotrophic, which was different to the oligotrophic waters of the coastal northeastern sector and the three oceanic sectors. Continental runoffs were defined as the more powerful event that controls the phytoplanktonic development, especially in the west part of the study area during wet seasons. On the other hand, upwelling events play a comparatively more important role in the water fertilization only far in the eastern extreme, during periods of time in which the continental discharges were low.
Key Words: SST, Chlorophyll a, SeaWiFS, MODIS Aqua, Upwelling, Continental Runoff.
Upper ocean variability of the equatorial Indian Ocean and its relation to chlorophyll pigment concentration
Narvekar, Jayu; Kumar, Prasanna
National Institute of Oceanography, INDIA
Equatorial Indian Ocean (EIO) is characteristically different from the rest of the equatorial regions of the world ocean due to (1) the semi-annual reversal in the winds as well as currents and (2) lack of upwelling. The satellite derived chlorophyll pigment concentration shows that EIO is biologically less productive region in the northern Indian Ocean. The reason for this was explored using the monthly mean climatology of the atmospheric and oceanic parameters in the domain 5oN-5oS and 40o-100oE. The oceanic temperature and salinity data were extracted from 3 sources. Hydro-cast and CTD data from the World Ocean Data base 2005 during the period 1919-2004, Responsible National Oceanographic Data base during 1972-2006 and Argo data during 2002-2008. Meterorological data were extracted from National Oceanographic Centre, UK. In addition to the above data, the in situ nutrient and chlorophyll data were also analyzed. The sea surface temperature (SST) showed a strong semi-annual signal in the western EIO (3.5oC) with peak warming in April and cooling in July-August. This warming was due to the high positive net heat flux whereas the cooling was driven by the upwelling along the western boundary. The central and eastern EIO showed a weak annual signal of amplitude 1oC. The sea surface salinity (SSS) showed a weak annual signal in the western EIO (0.3 psu) with high in winter and low in summer. Towards the central and eastern EIO there was no perceptible seasonality. Both mixed layer depth (MLD) and barrier layer thickness (BLT) also showed a weak annual signal. The MLD was deep during boreal summer (June-August) and shallow during boreal winter. The deep MLD during summer was due to the combined effect of strong winds and low net heat flux. The shallow MLD in winter was driven by weak winds and negative E-P. The net heat flux in summer (May-August) was higher than that of winter. The BLT was thickest in the eastern EIO compared to both central and western EIO, which was closely linked to the presence of low salinity water. The satellite derived chlorophyll concentration was highest along the western EIO and showed a semi-annual cycle of amplitude 0.4 mg/m3. The chlorophyll showed a strong correlation with SST. In the central and eastern EIO chlorophyll values were extremely low and did not show any strong seasonality. The correlation of chlorophyll with SST in these regions was also poor. Thus, the study indicated that the lack of strong seasonality in the chlorophyll pigment concentration and extremely low biomass away from the western boundary arises from lack of nutrient supply from subsurface. Lack of physical processes such as upwelling, eddies or strong wind-driven mixing were unable to break the strong stratification, both thermal as well as haline, in the EIO which inhabited supply of sub-surface nutrients as the nutracline was deep.
Station M in the Norwegisn Sea
Bjerknes Centre for Climate research, NORWAY
Having performed daily oceanographic measurements in the deep Norwegian Sea since 1 October 1948, Ocean Weather Ship Station (OWS) M, at 66N,02E, can present the longest existing homogeneous time series from the deep ocean. Station M is operating above the eastern margin of the Norwegian Sea deep basin where a branch of the Atlantic current is entering the area. The location proved to be strategic both for studying the Atlantic inflow and the Norwegian Sea Deep Water. The OWS M is operated by The Norwegian Meteorological Institute (met.no) and the hydrographic programme is carried out by Geophysical Institute, University of Bergen.
Sustainable monitoring system for ice shelves and polar oceans
Monitoring of the flow of dense water from its formation area towards the abyss of the world oceans is a key issue for climate research. In the Weddell Sea, Antarctica, formation of high salinity shelf water (HSSW) takes place on the Ronne shelf. Underneath the floating Filchner-Ronne ice shelf the HSSW is transformed to Ice Shelf Water (ISW, t<-1.9). The ISW cascade towards the deep Weddell Sea, and its fate in connexion with the formation of the WSBW, and finally AABW, are key issues. In the IPY project the Bipolar Atlantic Thermohaline Circulation (BIAC) we have defined and operate an ocean observing system for the Ice Shelf Water in the southern Weddell Sea. The stations (moorings) are constructed so that they only need to be serviced at ~5 year intervals, and the data are planned to be extracted by ships of opportunity, acoustic communication and via satellites. The running costs will therefore be low, and these climate stations should be operative for several decades.
Monitoring the Tropical Ocean: The Importance of Small Vertical Scale Velocity Features
Richards, Kelvin1; Natarov, Andrei1; Firing, Eric1; Kashino, Yuji2
1University of Hawaii, UNITED STATES;
The tropical oceans are our best monitored regions of the World's Oceans. The observing arrays have been designed to capture the basin--wide variations in the velocity and tracer fields. Here we present recent measurements of the velocity field in the Pacific Ocean. We argue that the present observing system misses a sizable fraction of the structure of the velocity field which potentially contributes significantly to ocean mixing. Figure 1 (upper panel) shows the zonal component of velocity along 156E measured using a high (600kHz) lowered ADCP. A striking aspect of the flow shown is the numerous small vertical scale features superimposed on the major currents. The strength of the small vertical scale features is such that the cores of the EUC and NECC are split into multiple maxima.
Figure 1 (lower panel) shows the data after a high--pass filter has been applied in the vertical and then plotted on constant potential density surfaces at the mean depth of the individual surfaces. Numerous small vertical scale features (SVSs) are present across the width of the section. A number of these features are seen to stretch over more than one sampling location with some being in excess of 100km. Shear spectra averaged over a number of latitudes are shown in Figure 2. Distinct peaks in the shear spectra are seen at vertical wavenumbers ranging from 15-50m. For comparison the spectrum from a moored 150kHz ADCP is also shown. The lower frequency ADCP does not capture the smaller scale features. Potential causes of the SVSs include instability of the current system through inertial and parametric subharmonic instabilities and direct forcing by the wind.
The amplitude of the SVSs is such as to suggest they contribute significantly to both lateral and vertical mixing. The implication is that mixing is controlled by factors other than the shear of the larger scale currents. Little is known, however, of the temporal and spatial variations of the properties of these small scale features and their potential contribution to scale-interactions linking mixing scales to basin-scale dynamics. We propose a series of process studies focussed on elucidating the properties and impact of SVSs combined with a larger scale monitoring. Because of its ease of operation, a lowered high frequency ADCP could be made a part of routine measurements that are at present made in conjunction with maintenance of the tropical arrays.
Decadal Scale Sea-level Validation of the ENSEMBLES Ensemble of Ocean Reanalyses
A new set of global, low-resolution ocean reanalyses over the ERA40 period (1960-2006) has been produced for sake of seasonal to decadal climate prediction within the EC-FP6 ENSEMBLES project. These reanalyses all use ERA40 winds and fluxes as forcing, the EN3 quality-controlled temperature and salinity profiles data base built at the UK Met-Office, and are strongly constrained by the observed Sea Surface Temperature. From those reanalyses produced by several groups (including ECMWF, INGV, UK Metoffice, and CERFACS), a common set of variables (temperature, salinity, velocity, upper ocean heat content, sea level height, mixed layer depth and depth of the 20°C isotherm) have been stored with a common Netcdf format, interpolated on a common 1°x1° resolution, 33 vertical levels grid, and made publicly available at http://ensembles.ecmwf.int/thredds/catalog/ocean/catalog.html. This poster presents a comparative validation of those reanalyses against a set of quality-controled multi-decadal tide gauge sea level measurements. Comparison with each reanalysis ensemble is stratified with respect to the location of the tide gauges. Results classically show that the quality of the reanalyses is better at low latitudes, but that a significant amount of variance of the low frequency signals at mid-latitudes is well reproduced. The north Atlantic is shown as the poorest constrained region, though the observational coverage is relatively important. Differences between reanalyses are also characterised and discussed in the light of the differences of the systems used.
Investigating changes in the Atlantic Waters characteristics along the
Egyptian Mediterranean Coast.
Said, M.A.; Gerges, M.A.; Maiyza, I.A.; Hussien , M.A.; Radwan, A.A.
National Institute of Oceanography and Fisheries, Alexandria, EGYPT
The paper investigates the changes in characteristics of the Atlantic Waters (AW) as they move eastwards along the Egyptian coast in the South-eastern Mediterranean. The study analyzed a long series of temperature, salinity and ót data, collected by several expeditions that were carried out by research vessels of different nationalities, including Egypt, during the period 1959-2008, averaged for the winter and summer seasons. The paper also examined the long-term (50 years) changes that occurred in the characteristics of the water masses off the Egyptian coast as a result of damming the Nile River in 1965 and the subsequent cessation of its discharge into the Mediterranean. These changes were considered in terms of their possible contribution to the observed changes in the characteristics of the AW along the Egyptian coast. The results show that the sea surface temperature of the southeastern Mediterranean waters off the Egyptian coast varied between 16.6-18.5oC in winter, and between 22-28oC in summer. Furthermore, the salinity of the coastal waters off the Egyptian coast has, on average, increased from 26.675 in 1964 before the erection of Aswan Dam, to around 38 in the 1970s and reached more than 39 in 2008. Vertically, only one water mass could be observed in winter in the upper 200 m layer, whereas in summer, three distinct water masses could be observed. The subsurface water mass, which is of Atlantic origin, occupying the 50-150 m layer and characterized by low salinities ranging from < 38.60 to 38.80, runs throughout the study area from west to east and spreads over the range of density between 27.5-28.5 ót. Temperature and salinity anomalies indicated increasing trends for both temperature and salinity that reached 0.62oC/dec and 0.067/dec, respectively for the Mediterranean surface waters. For the Atlantic water, the trends were 0.56oC/dec for temperature and 0.035/dec for salinity. These results confirm that the increase of temperature and salinity of AW with time are attributed to both anthropogenic modifications, especially the Nile damming, and the local climatic changes, which need further investigation.
Observing Deep-Water Changes in the Northern North Atlantic
Sarafanov, Artem; Falina, Anastasia; Sokov, Alexey; Gladyshev, Sergey
P.P. Shirshov Institute of Oceanology, RUSSIAN FEDERATION
In 1997-2009, full-depth transatlantic hydrographic section along 60°N between Cape Farewell (Greenland) and the Scottish shelf was repeatedly occupied on board the Russian research vessels. Since 2002 onwards, the section has been repeated annually. The comprehensive dataset thus collected has contributed to the research of the recent and long-term deep-water changes in the region. Our presentation summarizes the main published and work-in-progress results of this research including analyses of decadal hydrographic variability, local water mass formation and regional circulation changes.
New hydrographic scenarios in the Western Mediterranean: a possible monitoring strategy
Schroeder, Katrin1; Gasparini, Gian Pietro1; Sparnocchia, Stefania2
1CNR-ISMAR, Sede di La Spezia, ITALY;
2CNR-ISMAR, Sede di Trieste, ITALY
Biophysical couplings in South Australian shelf waters under conditions of summer upwelling and winter downwelling
Seuront, Laurent1; Leterme, Sophie1; Middleton, John2; Byrne, Shaun2; James, Charles2; Luick, John2; Nedoncelle, Karine1; Paterson, James1; Teixeira, Carlos2; van Dongen-Vogels, Virginie1
1Flinders University, AUSTRALIA;
The Southern Australia Integrated Marine Observing System, or SAIMOS, is one of five nodes operating as part of the Australia-wide Integrated Marine Observing System (IMOS). This is a collaborative program designed to observe Australia's oceans, both coastal and blue-water. Since February 2008 Physical Data has been collected for SAIMOS in both summer and winter months during 8 surveys. The data collected during summer are used to characterise the nature and dynamics of the Kangaroo Island-Eyre Peninsula upwelling system during a record upwelling event in February 2008. During this event a plume of very cool water was observed along the bottom from South of Kangaroo Island to the Eyre Peninsula. This plume dissipated rapidly after the end of upwelling favourable winds and by March 2008 had disappeared entirely from the observations.
The abundance and composition of viral, bacterial and pico- and nanoplankton communities have concurrently been investigated. In summer, the space-time dynamic of viral, bacterial and pico- and nanoplankton communities is generally driven by the plume of upwelled, cool and nutrient rich water that flows across the continental shelf, and is locally heavily influenced by the level of vertical stability of the water column. In winter, the qualitative and quantitative nature of the plankton community is related to the local physical properties of the water column, which include the presence of a dense plume of bottom waters outflowing from the Spencer Gulf, the vertical stability of the water column and the presence of a deep chlorophyll maximum (DCM).
Sustained Observations in the Atlantic and Southern Oceans
Smythe-Wright, Denise; Cunningham, Stuart A; Lampitt, Richard; Kent, Elizabeth; King, Brian; Quartly, Graham; Read, Jane F; Zubkov, Mike
National Oceanography Centre, Southampton, UNITED KINGDOM
The marine environment is large in scale, highly dynamic and relatively inaccessible. It requires sustained observations to obtain meaningful information on environmental changes and their causes. To this end, the National Oceanography Centre, Southampton, through the UK Natural Environment Research Council’s Ocean 2025 programme, supports a number of marine time-series and monitoring studies in the Atlantic and Southern Oceans. Some of these are in conjunction with other UK marine laboratories. The primary aims are to provide data and knowledge on a wide range of ecosystem processes, from ocean circulation to biodiversity. They have been developed not just to provide long-term data sets but also to capture extreme or episodic events and play a key role in the initialisation and validation of models. • The Atlantic Meridional Transect (AMT) aims to understand ocean plankton communities and improve our ability to predict the role of the open ocean in the global carbon cycle. • The Porcupine Abyssal Plain Ocean Observatory focuses on ecosystem behaviour and involves high frequency measurements both in the water column and on the sea floor. • Two arrays of instruments, one at 26°N and one across the Canadian-US continental slope, have been positioned to monitor the Meridional Overturning Circulation (MOC) which is a key component in the way the Atlantic Ocean will respond to climate change. • The extended Ellett Line, a hydrographic section from Scotland to Iceland, crosses important components of the North Atlantic MOC and provides additional knowledge of the North Atlantic’s response to climate change. • The international Argo programme aims to populate the world’s oceans with autonomous profiling floats, contributing to long-range weather forecasts and climate change research. • Antarctic Circumpolar Current monitoring in the Drake Passage provides measurements from a choke point in the global ocean circulation which impacts on the North Atlantic and the MOC. • The integration of increasing sources of historical and operational environmental data provides information on air-sea fluxes and how they are changing on multi-decadal scales, which is critical for monitoring and assessing climate change and improving models. The information from these activities has been integrated into the UK Marine Monitoring Assessment Strategy and has contributed to the UK DEFRA Charting Progress II initiative. The observations also contribute to International GOOS and GMES Acronyms DEFRA Department for Environment, Food and Rural Affairs GOOS – Global Ocean Observing System GMES Global Monitoring for the Environment and Security
Determining the Response of the Tropical Pacific to Global Warming
Soden, B.J.1; Vecchi, G.A.2
1University of Miami, UNITED STATES;
2NOAA/GFDL, UNITED STATES
There is a long-standing debate in the climate community as to how the tropical Pacific will respond to increased greenhouse gases: Will the structure of the time-mean changes in the ocean surface temperature more closely resemble an El Niño or a La Niña? This distinction is of profound significance because conditions in the tropical Pacific affect a range of weather phenomena including tropical cyclone activity, global patterns of drought and flood, agricultural productivity, and oceanic biological activity. There is substantial modeling and observational literature advocating both sides of the debate, and these opposing points of view remain to be reconciled [see Vecchi et al., EOS, 2008: Examining the tropical Pacific's response to global warming, EOS, 89, 81-83 for a summary]. Historical reconstructions of SST trends over the past century are currently unable to resolve this dispute. One reconstruction – HadISST [Rayner et al. 2003] – shows a ‘La Niña-like’ pattern, with an increase in the zonal SST gradient. However, the NOAA extended reconstruction of SST (ERSST) [Smith and Reynolds 2004] exhibits an ‘El Niño-like’ pattern, and is consistent with recent analyses of sea level pressure data indicating a weakening of the Walker circulation. Closer inspection of the contrasting SST reconstructions indicates that the differing behavior between the products arises primarily during two periods around the 1930s and 1980s. These periods are roughly coincident with, respectively, the period of greatest change in “bucket-to-intake” corrections of SST measurements (a correction that differs between the products) and the beginning of satellite infrared SST retrievals (satellite data is used in HadISST, but not in ERSST). We propose that a focused effort be placed towards identifying the specific sources of this discrepancy and the appropriate corrections. Another way forward would be through reconstructions of local temperature and salinity using coral skeletons from the tropical Pacific over the historical record. Currently, there are only a handful of published data sets that can address this issue with conflicting interpretations. A more complete picture of the evolution of tropical Pacific climate of the 20th Century would emerge if additional records from various locations were incorporated using a multi-proxy, synthesized approach [Evans et al., 2002: Paleoceanography, 17, 1006]. Because the discrepancies in the reconstructions of pacific SST arise primarily in two discrete periods, proxy observations spanning these periods could prove particularly useful in helping to reconcile the current observational interpretations.
CLIVAR’s regional basin panels and ocean observations.
Stansfield, Kate1; Caltabiano, Antonio2
1National Oceanography Centre, Southampton, UNITED KINGDOM;
2International CLIVAR Project Office, UNITED KINGDOM
The overall mission of CLIVAR, the Climate Variability and Predictability Project of the World Climate Research Programme (WCRP) is to observe, simulate and predict the Earth’s climate system, with a focus on ocean-atmosphere interactions. Within WCRP, CLIVAR carries overall responsibility for coordinating it’s activities on the role of the oceans in climate. Sustained ocean observations (as well as ocean process studies) provide key inputs to CLIVAR activities and CLIVAR is active, in stimulating the continued development of the Ocean Observing System in collaboration with the Global Ocean Observing System (GOOS), the Ocean Observations Panel for Climate and the Scientific Committee on Antarctic Research (SCAR). It does this through the activities of its Atlantic, Pacific, Indian and Southern Ocean Basin Panels and its Global Synthesis and Observation Panel (GSOP).
This poster will outline the role of CLIVAR’s ocean basin panels in the regional implementation of ocean observation activities. In particular it will illustrate:
Geochemical and physical instrumentation development for characterizing a subglacial aquatic environment in Antarctica
Vogel, S.W.1; Powell, R.D.1; Griffith, I.2; Lawson, T.2; Anderson, K.2; Schiraga, S.A.2; Ludlam, G.2; Oen, J.2
1Northern Illinois University, Analytical Center for Climate and Environmental Change, UNITED STATES;
2DOER Marine - Subsea Robotics and Submersible Systems, UNITED STATES
We are developing a number of instrumentation enabling the study of subglacial environment in Antarctica through narrow kilometer long boreholes. Instrumentation includes: i) slim line Sub-Ice ROV (SIR), ii) Geochemical Instrumentation Package for Sub Ice Environments (GIPSIE) to study geochemical fluxes in water and across the sediment water interface with real-time telemetry for targeted sampling, iii) long term energy-balance mooring system, iv) active source slide hammer sediment corer, and v) integration of a current sensor into the ITP profiler. The instrumentation presented here is likely of interest for a wider science community. Of specific interest for the Ocean Obs community are likely the GIPSIE and the active source sediment corer.
The GIPSIE is a geochemical instrumentation package to study geochemical fluxes across the sediment water interface and with the flux of water inside of a water mass. The GIPSIE includes a number of geochemical sensors (CO2, CH4, dO, NH4, NO3, Si, PO4, pH, redox, T, H2, HS, O2, N2O, CTD, particle size, turbidity, color camera, current meter and automated water sampler). A real-time telemetry system allows user controlled targeted sampling of water for chemical and biological work based on actual measurements and not an automated program. The porewater profiler (pH, redox, T, H2, HS, O2, N2O) can penetrate the upper 50 cm of sediment. A thermal probe extension allowing geothermal flux measurements of the upper 1 to 2m is under consideration as is an in situ porewater sampler.
The sediment corer is an active source slide hammer corer, allowing penetration of stiffer sediment. The design concept increases the impact force of the slide hammer with penetration to overcome greater sediment strength with depth.
Further information on the technology developments and our sub ice work can be found at http://jove.geol.niu.edu/faculty/svogel/Technology/Technology-index.html
Inventory of anthropogenic carbon in the Atlantic
Steinfeldt, Reiner1; Bullister, John L.2; Rhein, Monika1
1University of Bremen, GERMANY;
2National Oceanic and Atmospheric Administration, UNITED STATES
The Atlantic is an important sink for anthropogenic carbon (Cant). High concentrations of Cant are found not only in surface and central waters, but also in the newly formed North Atlantic Deep Water (NADW). The Cant concentrations are calculated by means of the Transit Time Distribution (TTD) method. The TTD parameters are inferred from CFC data from the WOCE period and the CARINA data set, a collection of carbon relevant parameters measured in the Atlantic within international and national programs. The repeated observations in the North Atlantic clearly indicate a decrease of the carbon uptake of Labrador Sea Water during the last decade. This is only partially compensated by enhanced storage of anthropogenic carbon in the newly formed, lighter Upper Labrador Sea Water. The deeper NADW layers, however, show the expected Cant increase due to the rising atmospheric CO2 concentrations.
Coherent signals between the RAPID array and satellite altimetry
Szuts, Zoltan; Marotzke, Jochem
Max-Planck-Institut für Meteorologie, GERMANY
The RAPID array monitors the vertical density structure at a few locations across the North Atlantic. By contrast, satellite altimetry has much better horizontal resolution but is limited to the surface signal. The first step for combining the advantages of each array, for better resolution of Atlantic circulation, is to investigate the shared or coherent signals in each. The consistency among the arrays indicates not only their accuracy, but also a quantitative assessment of the range of motions to which each responds. We consider three data sets: moored density or geopotential anomalies (GPA) from the RAPID temperature and salinity moorings spanning the Atlantic at 26.5 N, sea surface height (SSH) from satellite altimetry, and bottom pressure (BP) measured at the base of the RAPID moorings, The vertical structure of correlation between GPA and SSH or BP at fixed depth levels describes how the dominant variance is inter-related, while a method for fitting vertical dynamic modes to density anomalies provides a physical mechanism to describe the correlations. Directly at the western boundary, correlation between SSH and GPA is small in magnitude and is slightly surface intensified. In stations to the east - at 500 km from the western boundary and on the western flank of the Mid-Atlantic Ridge - the correlation increases near the surface (to 0.85) and at water depths of 1000-3000 m (0.3-0.5). From the western boundary to the Mid-Atlantic Ridge, the correlation between SSH and both the barotropic and first baroclinic modes also increases by a similar amount. This structure of correlation is mostly explained by an increase in the absolute and relative variance of the first baroclinic mode across the same distance. Away from the boundaries, satellite SSH correlates more strongly with a reconstructed SSH calculated from only the barotropic and first baroclinic modes, compared with a reconstruction from all modes. The relative variance contained in baroclinic modes higher than mode 1 is largest at both boundaries, indicating more complex dynamics at these locations that are poorly resolved by surface measurements. A spectral analysis shows that the SSH and GPA signals are coherent at periods of 10 days and 30-100 days when considered in the vertical, and at periods of 30-100 days for the barotropic and two lowest baroclinic modes when considered against mode number. In contrast to SSH, correlation of GPA with BP is largest at the boundaries and is vertically uniform, but is weak (<0.5) in general. Except at the Mid-Atlantic Ridge, the surface expressions of the barotropic and first baroclinic modes are in phase with BP but have correlations less than 0.5. A spectral analysis between GPA and BP against depth shows coherent periods of 10 days and 30-100 days, while the same analysis against mode number shows coherent periods of 30-100 days for low modes (second baroclinic mode and lower). Signals coherent throughout the full water column also occur at periods of 2-5 days.
Impact of Sea Ice Variability on the Ross Sea Water Masses
Tonelli, Marcos; Wainer, Ilana
University of Sao Paulo, BRAZIL
It has been known for a long time that the ocean plays the most important role on Earth's heat budget, what turns it into a major component of the global climate system. Therefore, many studies have been made to assess whether features climate processes are changing and how may climate itself be affected by these changes. Considering that sea ice is rapidly affected by climate changes and is directly linked to the oceanic overturning circulation, which is responsible for the heat exchange and storage, this work aims to look at the impact of changes in sea ice on deep water masses formation in the Southern Ocean. Results from the 20th century and A1b CCSM3/NCAR simulation (1870 to 2100) were analyzed. Using the Optimum Multiparameter Analysis (OMP) to separate water masses, we have focused on the Ross Sea Ice Shelf Water (ISW) spacial variation along the whole simulation period. Much closely to what have been seen on previous sea ice observational data, model results have shown an important ice coverage increasing trend on the Ross Sea along the late 20th century and the entire 21st century. Simulation results have also shown that the ISW gets shallower during the 20th century and then, due to an important sea ice increase during the 21st century, it gets each time deeper and occupies the deepest layer by 2100 while it flows towards higher latitudes. These results show how observational data assimilation is important to properly simulate the future and understand what we may expect.
Ligurian Sea Observing System; A Multi-platform Approach for Model Development and Validation.
Trees, Charles1; Pennucci, Giuliana1; Scholfield, Oscar2; Arnone, Robert3
1NATO Undersea Research Centre, ITALY;
2Rutgers University, UNITED STATES;
3Naval Research Lab-Stennis, UNITED STATES
Because of the close proximity of NURC to the Ligurian Sea, which provides easy access by research vessels and AUVs, NURC has selected this area to develop and test physical and bio-optical models as well as remote sensing/glider data fusion techniques and adaptive sampling strategies for improved model predictions. The Ligurian Sea is ideal for setting up a regional observing system for model validation and testing as it has some complexity in offshore and near shore areas, river discharge in the eastern region and seasonal variability in current speed and direction and bio-optical variability (Mar-Apr phytoplankton blooms and Sep-Oct oligotrophic conditions, Figures 2a and b). NURC’s fleet of gliders are supported by a Command and Control and 3-D Visualization Centre and for 2010 there are plans to deploy several gliders to spatial map the physical and bio-optical variability of coastal and offshore areas on a continuous basis. Using this multi-platform approach of remote sensing, shipboard measurements and AUVs, a bio-optical model that is coupled to an atmospheric/oceanic model will be developed. The beginning of this effort will start with a modeling workshop in the fall 2009 that describes the framework for such an effort. Other modeling efforts such as NRL-Stennis BIOSPACE (Bio-Optical Studies of Predictability and Assimilation for the Coastal Environment) model (Shulman et al., 2008; AGU Fall Mtg, #OS43C-1303), which is being developed and validated in Monterey Bay, USA, can be tested as to the robust nature and portability using NURC Ligurian Sea regional database.
Mediterranean Sea Level Variations from Altimetry Data and Ocean Circulation Models
Vigo, Isabel1; Sanchéz, José M.1; Trottini, Mario1; Chao, Ben2; Garcia, D.1
1University of Alicante, SPAIN;
2Taiwan Central University, TAIWAN
A complete study of the Mediterranean Sea level Variations (SLV) for the last 16 years is presented. We use mainly multimission altimetry data and simulations from the ECCO Ocean Circulation Model. The seasonal and trend components are analyzed, while the residual variability is explained by means of physical fenomena. The different components of the total SLV are also estimated for the period of study.
Changes in Subduction in the South Atlantic Ocean During the 21st Century in the CCSM3
Wainer, Ilana1; Goes, Marlos2; Gent, Peter3; Bryan, Frank3
1University of São Paulo, BRAZIL;
2Penn State University, BRAZIL;
3National Center for Atmospheric Research, BRAZIL
Water mass formation in the South Atlantic is an important component of ocean ventilation in the southern hemisphere. For example, a large component of Antarctic Intermediate Water (AAIW) is formed in this basin, and much of the Antarctic Bottom Water (AABW) is formed in the Weddell Sea. In this paper, the South Atlantic is defined as the region between the equator and the Antarctic continent. This region is important because it takes up a lot of heat and carbon dioxide from the atmosphere. Therefore, a very important question is how water mass formation will change over the 21st century, especially if formation rates weaken, and the South Atlantic can't take up as much heat and CO2 as it does at present? The Community Climate System Model version 3 (CCSM3) is used to analyze changes in water mass formation rates in the South Atlantic over the 21st century. The model results are first compared to observations over 1950--2000, and shown to be rather good. A major reason to address this question with the CCSM3 is that AAIW and AABW are simulated much better in the generation of climate models used in the fourth report of the International Panel on Climate Change than those used in the third report. The formation rates do not change significantly over the 21st century, but the densities at which water masses form become significantly lighter. This suggests small changes to the rate at which the Southern Ocean takes up heat and carbon dioxide over the 21st century
The Global Ocean Mixing Community - A Progress Update
Wolk, Fabian1; Muench, Robin2; MacKinnon, Jennifer3; St. Laurent, Louis4; Hibiya, Toshi5; McDougall, Trevor6; Burchard, Hans7; Naveira Garabato, Alberto8; Ferron, Bruno9; Kunze, Eric10; Umlauf, Lars7
1Rockland Scientific Inc., CANADA;
2Earth & Space Research, UNITED STATES;
3Scripps Institution of Oceanography, UNITED STATES;
4Woods Hole Oceanographic Institution, UNITED STATES;
5University of Tokyo, JAPAN;
6Commonwealth Scientific and Industrial Research Organisation, AUSTRALIA;
7Leibniz Institute for Baltic Sea Research, GERMANY;
8National Oceanography Centre, UNITED KINGDOM;
9Ifremer Centre de Brest, FRANCE;
10University of Victoria, CANADA
Mixing in the ocean controls the transport of heat, freshwater, dissolved gasses, and pollutants and is linked directly to processes responsible for climate variability and predictability. Turbulent mixing is also of crucial importance for ocean biology, from determining the flow field for the smallest plankton to setting large-scale gradients of nutrient availability. In coastal regions the distribution of nutrients and pollution controls the health of our fisheries as well as the broader coastal ecosystem. Technological improvements over the last five decades have led to several direct and indirect observational methods for the study of mixing in the coastal, arctic and abyssal oceans, as well as in lakes. Recent work suggests that there is considerable spatial and temporal non-homogeneity in deep-ocean mixing. Therefore, an improved understanding of the distribution of deep-ocean mixing intensity, and the physics that drives that distribution, is central to understanding the energetics of the ocean and reducing the uncertainties in global circulation and climate models. The community of ocean mixing scientists is organized through the SCOR affiliated Ocean Mixing Group, which has the mandate to foster and contribute to the development and coordination of international research programs related to ocean mixing. This poster presentation provides an overview of the state of work in the ocean mixing community, the observational challenges, and future efforts to study linkages between ocean mixing and climate variability and coastal ecology.
A Decade of Acoustic Thermometry in the North Pacific
Worcester, P.1; Dushaw, B. D.2
1Scripps Institution of Oceanography, UNITED STATES;
2Applied Physics Laboratory, University of Washington, UNITED STATES
The Acoustic Thermometry of Ocean Climate (ATOC) and North Pacific Acoustic Laboratory (NPAL) projects have demonstrated the sustainable utility of long term measurements of temperature by long range acoustic transmissions. Over the decade 1996-2006, acoustic sources located off central California (1996-1999) and north of Kauai (1996-1999, 2002-2006) transmitted to receivers distributed throughout the northeast and north central Pacific. By traversing O(4-5 Mm) ranges, the acoustic travel times are inherently spatially integrating, which suppresses mesoscale variability and provides a precise measure of ray-path-averaged temperature . The acoustic data provide excellent signal-to-noise ratio measurements of large-scale temperature variability with high temporal resolution. This data type offers information about the large-scale, subsurface temperatures of ocean basins that complements that provided by in situ hydrographic profiles and satellite altimetry. Altimetry, hydrography and acoustic remote sensing offer three largely independent measurements of the ocean in the context of ocean state estimation through data assimilation.
The measured travel times were compared with equivalent travel times derived from four independent estimates of the North Pacific: (i) climatology, as represented by the World Ocean Atlas 2005 (WOA05), (ii) objective analysis of the upper ocean temperature field derived from satellite altimetry and in situ profiles, (iii) an analysis provided by the "Estimating the Circulation and Climate of the Ocean" project as implemented at the Jet Propulsion Laboratory (JPL-ECCO), and (iv) simulation results from a high-resolution configuration of the Parallel Ocean Program (POP) model. The comparisons of time series provide a stringent test of the large-scale temperature variability in the models. The measured and calculated travel times are similar, but they also show significant differences. The differences between the measured and computed acoustic travel times, which are comparable in size to the observed signals, indicate that the acoustic data can provide significant additional constraints for numerical ocean models, as suggested long ago by Munk and Wunsch.
The next logical step from these comparisons is to use acoustic travel times, together with other data, to constrain numerical ocean models. Data assimilation allows rigorous assessment of the contributions the various data types make to constraining model behavior. There are no technical impediments, either observationally or computationally, to the simultaneous use of altimetry, hydrography and acoustic remote sensing in operational ocean state estimation.
Upper Ocean Heat Content Simulated by NCEP GODAS
xue, yan1; Kumar, Arun1; Huang, Boyin1; Behringer, David2
1CPC/NCEP/NOAA, UNITED STATES;
2EMC/NCEP/NOAA, UNITED STATES
Upper ocean heat content (UOHC) is one of the key indicators of climate variability on many time-scales extending from interannual to long-term anthropogenic trends. Since UOHC variability is also associated with SST variability, a better understanding and monitoring of UOHC variability can help us understand, monitor, and forecast, other SST modes such as Indian Ocean Dipole (IOD), Pacific Decadal Oscillation (PDO), Tropical Atlantic Variability (TAV) and Atlantic Multidecadal Oscillation (AMO). An accurate ocean initialization of UOHC variability in coupled climate models will also play a crucial role in emerging decadal climate prediction efforts. The NCEP operational global ocean data assimilation system (GODAS) provides a historical ocean reanalysis from 1979 onward, and maintains a continuous update in near real time (1 day delay). The operational GODAS is based on the GFDL Modular Ocean Model version 3 (MOM.v3) forced by the NCEP Reanalysis 2 (R2) surface fluxes, and a three-dimensional variational scheme that assimilates observed temperature, synthetic salinity and Altimetry sea level. Temperature observations include data from XBTs, TAO/TRITON/PIRATA and Argo profiling floats. Estimations of UOHC variability can be affected by many factors including analysis and assimilation produces, and changes in the input data. For example, the coverage of in situ temperature data was poor at the beginning of the reanalysis, but gradually increased with time and reached a near global coverage since 2005. To quantify uncertainty in the UOHC estimates, a comparison of UOHC in the top 300m and 700m using multiple ocean reanalysis products, which include the operational GODAS (GODAS3), its control simulation (CTL), the experimental GODAS that is identical to the operational GODAS except MOM.v4 was used (GODAS4), and the NODC objective ocean reanalysis based on in situ observations only (NODC), was made. We compared the basin average of the top 300m heat content from the four ocean reanalysis products. In the tropical Pacific, GODAS3 and GODAS4 were close to NODC except during 1979-1985 when the initial adjustment was still taking place, and during 1998-1999 when the discharge of heat content following the 1997/98 El Nino was underestimated. In the tropical Indian Ocean, GODAS3 and GODAS4 agreed well with NODC except during 1979-1984 and 1996-2001. In the tropical Atlantic, GODAS3 and GODAS4 were somewhat warmer than NODC before 2002, but became close to NODC afterwards. In the North Pacific, both GODAS3 and GODAS4 agreed very well with NODC prior to 2005, but started to have cold biases afterwards. In the North Atlantic, GODAS4 agreed with NODC much better than GODAS3 did, suggesting that including the Arctic Ocean in the ocean model is important for realistically simulating the North Atlantic heat content. Once the climatological mean differences were removed, the agreement among the ocean reanalysis products was significantly improved. The data assimilation products (GODAS3 and GODAS4) were superior to CTL in the tropical oceans, particularly in the tropical Indian and Atlantic Ocean. Note that the anomalous UOHC in the North Pacific and North Atlantic was very well simulated by CTL. However, it is puzzling that all the NCEP products started to deviate from NODC significantly since 2005 in the North Pacific where observations were generally plentiful. In the Southern Oceans, there was generally a poor agreement among the NCEP products and NODC. However, the agreement was slightly improved when the MOM.v4 was used. Another way to quantify the uncertainty of UOHC variability is to compare the dominant EOF patterns and their time series in the ocean reanalysis products. Separate EOF analysis will be done in each ocean basin in order to isolate mode of variability associated with the PDO, IOD, TAV and AMO. A consistency among the dominant EOF patterns and time series would be an indication of their robustness in representing the climate signal.
Origin and Variability of the Deep and Abyssal Waters of the Northwest Atlantic
Yashayaev, Igor1; de Jong, Femke2; Dickson, Bob3; Fischer, Jürgen4; Kieke, Dagmar5; Quadfasel, Detlef6; Sarafanov, Artem7; van Aken, Hendrik2
1Bedford Institute of Oceanography, CANADA;
2Royal Netherlands Institute for Sea Research, NETHERLANDS;
3Centre for Environment, Fisheries and Aquaculture Science, UNITED KINGDOM;
4Leibniz Institute of Marine Sciences, GERMANY;
5University of Bremen, GERMANY;
6University of Hamburg, GERMANY;
7P.P. Shirshov Institute of Oceanology, RUSSIAN FEDERATION
The two dense water overflows that cross the Greenland–Scotland Ridge via the Denmark Strait and Faroe–Shetland Channel form the Denmark Strait Overflow Water and Northeast Atlantic Deep Water, respectively, filling the deep and abyssal reservoirs of the subpolar North Atlantic. Changes at depths greater than the limits of open-ocean deep convection (2300 m or so) are primarily controlled by the processes involved in the formation and subsequent modification of these waters, starting with the overflows themselves. Each of the constituent water masses that form the original overflows will carry with them the imprint of time-varying climatic forcing in their source regions and of modifications en route. Their properties will also be subject to alteration by the processes of horizontal and vertical exchange from their spillways to the Labrador Basin and further downstream. The purpose of this presentation is to identify from the hydrographic record those locations that are of primary importance for the transfer of ocean climate ‘signals’ into and between the two spreading overflow plumes, and if possible to trace the influence of these changes downstream to the Newfoundland Basin and beyond in the Deep Western Boundary Current.
Causes, Variability and Consequences of Deep Convection in the Labrador Sea in Recent Years
Yashayaev, Igor1; Yashayaev, Kieke, Dagmar1; Kieke, Dagmar2
1Bedford Institute of Oceanography, CANADA;
2University of Bremen, GERMANY
The causes, strength and consequences of the deep convection that produces Labrador Sea Water (LSW) are analyzed by interpreting hydrographic, moored, profiling float and satellite measurements. Significant changes in the winter atmospheric forcing over the Labrador Sea explain most of the observed variability in the properties and volumes of the newly-formed year classes of LSW. The evolution of this water mass along its exit pathways and the associated signal transfer/transit rates will be described. Combining data from two consecutive occupations of the repeat hydrographic section AR7W conducted in May by Bedford Institute of Oceanography and August by University of Bremen in 2008 and 2009, we estimate the export rates of LSW and examine changes in overall stratification associated with input of salt and heat from the Atlantic sources and freshwater from the Greenland melt and Arctic.