Showing papers on "World Ocean Atlas published in 2013"

World ocean atlas 2013. Volume 1, Temperature

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World ocean atlas 2013. Volume 4, Dissolved inorganic nutrients (phosphate, nitrate, silicate)

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Evaluation of the carbon cycle components in the Norwegian Earth System Model (NorESM)

Abstract: . The recently developed Norwegian Earth System Model (NorESM) is employed for simulations contributing to the CMIP5 (Coupled Model Intercomparison Project phase 5) experiments and the fifth assessment report of the Intergovernmental Panel on Climate Change (IPCC-AR5). In this manuscript, we focus on evaluating the ocean and land carbon cycle components of the NorESM, based on the preindustrial control and historical simulations. Many of the observed large scale ocean biogeochemical features are reproduced satisfactorily by the NorESM. When compared to the climatological estimates from the World Ocean Atlas (WOA), the model simulated temperature, salinity, oxygen, and phosphate distributions agree reasonably well in both the surface layer and deep water structure. However, the model simulates a relatively strong overturning circulation strength that leads to noticeable model-data bias, especially within the North Atlantic Deep Water (NADW). This strong overturning circulation slightly distorts the structure of the biogeochemical tracers at depth. Advancements in simulating the oceanic mixed layer depth with respect to the previous generation model particularly improve the surface tracer distribution as well as the upper ocean biogeochemical processes, particularly in the Southern Ocean. Consequently, near-surface ocean processes such as biological production and air–sea gas exchange, are in good agreement with climatological observations. The NorESM adopts the same terrestrial model as the Community Earth System Model (CESM1). It reproduces the general pattern of land-vegetation gross primary productivity (GPP) when compared to the observationally based values derived from the FLUXNET network of eddy covariance towers. While the model simulates well the vegetation carbon pool, the soil carbon pool is smaller by a factor of three relative to the observational based estimates. The simulated annual mean terrestrial GPP and total respiration are slightly larger than observed, but the difference between the global GPP and respiration is comparable. Model-data bias in GPP is mainly simulated in the tropics (overestimation) and in high latitudes (underestimation). Within the NorESM framework, both the ocean and terrestrial carbon cycle models simulate a steady increase in carbon uptake from the preindustrial period to the present-day. The land carbon uptake is noticeably smaller than the observations, which is attributed to the strong nitrogen limitation formulated by the land model.

MAREDAT: towards a world atlas of MARine Ecosystem DATa

Abstract: . We present a summary of biomass data for 11 plankton functional types (PFTs) plus phytoplankton pigment data, compiled as part of the MARine Ecosystem biomass DATa (MAREDAT) initiative. The goal of the MAREDAT initiative is to provide, in due course, global gridded data products with coverage of all planktic components of the global ocean ecosystem. This special issue is the first step towards achieving this. The PFTs presented here include picophytoplankton, diazotrophs, coccolithophores, Phaeocystis, diatoms, picoheterotrophs, microzooplankton, foraminifers, mesozooplankton, pteropods and macrozooplankton. All variables have been gridded onto a World Ocean Atlas (WOA) grid (1° × 1° × 33 vertical levels × monthly climatologies). The results show that abundance is much better constrained than their carbon content/elemental composition, and coastal seas and other high productivity regions have much better coverage than the much larger volumes where biomass is relatively low. The data show that (1) the global total heterotrophic biomass (2.0–4.6 Pg C) is at least as high as the total autotrophic biomass (0.5–2.4 Pg C excluding nanophytoplankton and autotrophic dinoflagellates); (2) the biomass of zooplankton calcifiers (0.03–0.67 Pg C) is substantially higher than that of coccolithophores (0.001–0.03 Pg C); (3) patchiness of biomass distribution increases with organism size; and (4) although zooplankton biomass measurements below 200 m are rare, the limited measurements available suggest that Bacteria and Archaea are not the only important heterotrophs in the deep sea. More data will be needed to characterise ocean ecosystem functioning and associated biogeochemistry in the Southern Hemisphere and below 200 m. Future efforts to understand marine ecosystem composition and functioning will be helped both by further archiving of historical data and future sampling at new locations. Microzooplankton database: doi:10.1594/PANGAEA.779970 All MAREDAT databases: http://www.pangaea.de/search?&q=maredat

A climatology‐based quality control procedure for profiling float oxygen data

Abstract: [1] Over 450 Argo profiling floats equipped with oxygen sensors have been deployed, but no quality control (QC) protocols have been adopted by the oceanographic community for use by Argo data centers. As a consequence, the growing float oxygen data set as a whole is not readily utilized for many types of biogeochemical studies. Here we present a simple procedure that can be used to correct first-order errors (offset and drift) in profiling float oxygen data by comparing float data to a monthly climatology (World Ocean Atlas 2009). Float specific correction terms for the entire array were calculated. This QC procedure was evaluated by (1) comparing the climatology-derived correction coefficients to those derived from discrete samples for 14 floats and (2) comparing correction coefficients for seven floats that had been calibrated twice prior to deployment (once in the factory and once in-house), with the second calibration ostensibly more accurate than the first. The corrections presented here constrain most float oxygen measurements to better than 3% at the surface.

Analysis of deep-layer and bottom circulations in the South China Sea based on eight quasi-global ocean model outputs

Abstract: This study is a preliminary analysis of the South China Sea (SCS) deep circulations using eight quasi-global high-resolution ocean model outputs. The goal is to assess models' ability to simulate these deep circulations. The analysis reveals that models' deep temperatures are colder than the observations in the World Ocean Atlas, while most models' deep salinity values are higher than the observations, indicating models' deep water is generally colder and saltier than the reality. Moreover, there are long-term trends in both temperature and salinity simulations. The Luzon Strait transport below 1500 m is 0.36 Sv when averaged for all models, smaller compared with the observation, which is about 2.5 Sv. Four assimilated models and one unassimilated (OCCAM) display that the Luzon deep-layer overflow reaches its minimum in spring and its maximum in winter. The vertically integrated streamfunctions below 2400 m from these models show a deep cyclonic circulation in the SCS on a large scale, but the pattern is different from the diagnostic streamfunction from the U.S Navy Generalized Digital Environment Model (GDEM-Version 3.0, GDEMv3). The meridional overturning structure above 1000 m is similar in all models, but the spatial distribution and intensity below 1500 m are quite different from model to model. Moreover, the meridional overturning below 2400 m in these models is weaker than that of the GDEMv3, which indicates a deep vertical mixing process in these models is biased weak. Based on the above evaluation, this paper discusses the impacts of T/S initial value, topography, and mixing scheme on the SCS deep circulations, which may provide a reference for future model improvement.

Biogeographical patterns of phytoplankton community size structure in the oceans

Abstract: Aim Develop a biogeographical classification of phytoplankton size distributions for the Atlantic Ocean and predict the global phytoplankton size composition based on prevailing environmental conditions. Location Atlantic Ocean and Global Ocean Methods Using phytoplankton size composition data, nutrient concentrations (nitrite+nitrate, phosphate, and silicate), irradiance, temperature and zooplankton abundances of the Atlantic Meridional Transect programme,we derived and tested an environmental classification method of phytoplankton size distribution with a k-means clustering technique. We then used principal component and Dirichlet multivariate regression analyses to disentangle the relative influence of different environmental conditions on the phytoplankton size composition. Subsequently, we evaluated different probabilisitic models and selected the most parsimonious one to estimate the global phytoplankton size distributions in the world oceans based on global climatology data of the World Ocean Atlas 2009. Results Based only on prevailing environmental conditions and without a priori knowledge concerning, for example, the position of oceanic fronts, the primary productivity, the distribution of organisms or any geographical information, our classification method captures the size structures of phytoplankton communities across the Atlantic. We find a strong influence of temperature and nitrite+nitrate concentration on the prevalence of the different size classes, and we present evidence that both factors may act independently on structuring phytoplankton communities. While at low nitrite+nitrate concentrations temperature has a major structuring impact, at high nitrite+nitrate concentrations its influence is reduced. Finally, we show that the global distribution of phytoplankton community size structure can be predicted by a probabilistic model based only on temperature and

Tsunami speed variations in density‐stratified compressible global oceans

Abstract: [1] Tsunami speed variations in the deep ocean caused by seawater density stratification is investigated using a newly developed propagator matrix method that is applicable to seawater with depth-variable sound speeds and density gradients For a 4 km deep ocean, the total tsunami speed reduction is 044% compared with incompressible homogeneous seawater; two thirds of the reduction is due to elastic energy stored in the water and one third is due to water density stratification mainly by hydrostatic compression Tsunami speeds are computed for global ocean density and sound speed profiles, and characteristic structures are discussed Tsunami speed reductions are proportional to ocean depth with small variations, except in warm Mediterranean seas The impacts of seawater compressibility and the elasticity effect of the solid earth on tsunami traveltime should be included for precise modeling of transoceanic tsunamis

Areas of the global major river plumes

Abstract: River plumes are the regions where the most intense river-sea-land interaction occurs, and they are characterized by complex material transport and biogeochemical processes. However, due to their highly dynamic nature, global river plume areas have not yet been determined for use in synthetic studies of global oceanography. Based on global climatological monthly averaged salinity data from the NOAA World Ocean Atlas 2009 (WOA09), and monthly averaged salinity contour maps of the East and South China Seas from the Chinese Marine Atlas, we extract the monthly plume areas of major global rivers using a geographic information system (GIS) technique. Only areas with salinities that are three salinity units lower than the average salinity in each ocean are counted. This conservative estimate shows that the minimum and maximum monthly values of the total plume area of the world’s 19 largest rivers are 1.72×106 km2 in May and 5.38×106 km2 in August. The annual mean area of these river plumes (3.72×106 km2) takes up approximately 14.2% of the total continental shelves areaworldwide (26.15×106 km2). This paper also presents river plume areas for different oceans and latitude zones, and analyzes seasonal variations of the plume areas and their relationships with river discharge. These statistics describing the major global river plume areas can now provide the basic data for the various flux calculations in the marginal seas, and therefore will be of useful for many oceanographic studies.

Toward a multivariate reanalysis of the North Atlantic Ocean biogeochemistry during 1998-2006 based on the assimilation of SeaWiFS chlorophyll data

Abstract: . Today, the routine assimilation of satellite data into operational models of ocean circulation is mature enough to enable the production of global reanalyses describing the ocean circulation variability during the past decades. The expansion of the "reanalysis" concept from ocean physics to biogeochemistry is a timely challenge that motivates the present study. The objective of this paper is to investigate the potential benefits of assimilating satellite-estimated chlorophyll data into a basin-scale three-dimensional coupled physical–biogeochemical model of the North Atlantic. The aim is on the one hand to improve forecasts of ocean biogeochemical properties and on the other hand to define a methodology for producing data-driven climatologies based on coupled physical–biogeochemical modeling. A simplified variant of the Kalman filter is used to assimilate ocean color data during a 9-year period. In this frame, two experiments are carried out, with and without anamorphic transformations of the state vector variables. Data assimilation efficiency is assessed with respect to the assimilated data set, nitrate of the World Ocean Atlas database and a derived climatology. Along the simulation period, the non-linear assimilation scheme clearly improves the surface analysis and forecast chlorophyll concentrations, especially in the North Atlantic bloom region. Nitrate concentration forecasts are also improved thanks to the assimilation of ocean color data while this improvement is limited to the upper layer of the water column, in agreement with recent related literature. This feature is explained by the weak correlation taken into account by the assimilation between surface phytoplankton and nitrate concentrations deeper than 50 meters. The assessment of the non-linear assimilation experiments indicates that the proposed methodology provides the skeleton of an assimilative system suitable for reanalyzing the ocean biogeochemistry based on ocean color data.

Comparison of mixed layer depth and barrier layer thickness for the Indian Ocean using two different climatologies

Abstract: The variability of mixed layer depth (MLD) and barrier layer thickness (BLT) has profound implications on energy exchange processes at the air-sea interface. More important is the role of MLD and BLT in the genesis and intensification of weather systems. The physical and chemical changes that take place within these layers have significance on biological productivity of the oceans. In this study, the monthly evolution of MLD and BLT for Indian Ocean was compared using the state-of-art world ocean atlas (WOA) and a recently developed comprehensive ocean atlas [referred to as new climatology (NC)]. The study area comprises the geographical boundaries encompassing 30°N to 60°S and 30°E to 120°E. Qualitative skill assessment of these variables demonstrates that NC is in good agreement with recently reported observational and modelling studies. This brings out the fact that MLD and BLT climatology derived from NC is better than that of WOA.

On the time‐mean state of ocean models and the properties of long range acoustic propagation

Abstract: [1] Receptions on three vertical hydrophone arrays from basin-scale acoustic transmissions in the North Pacific during 1996 and 1998 are used to test the time-mean sound-speed properties of the World Ocean Atlas 2005 (WOA05), of an eddying unconstrained simulation of the Parallel Ocean Program (POP), and of three data-constrained solutions provided by the estimating the circulation and climate of the ocean (ECCO) project: a solution based on an approximate Kalman filter from the Jet Propulsion Laboratory (ECCO-JPL), a solution based on the adjoint method from the Massachusetts Institute of Technology (ECCO-MIT), and an eddying solution based on a Green's function approach from ECCO, Phase II (ECCO2). Predictions for arrival patterns using annual average WOA05 fields match observations to within small travel time offsets (0.3–1.0 s). Predictions for arrival patterns from the models differ substantially from the measured arrival patterns, from the WOA05 climatology, and from each other, both in terms of travel time and in the structure of the arrival patterns. The acoustic arrival patterns are sensitive to the vertical gradients of sound speed that govern acoustic propagation. Basin-scale acoustic transmissions, therefore, provide stringent tests of the vertical temperature structure of ocean state estimates. This structure ultimately influences the mixing between the surface waters and the ocean interior. The relatively good agreement of the acoustic data with the more recent ECCO solutions indicates that numerical ocean models have reached a level of accuracy where the acoustic data can provide useful additional constraints for ocean state estimation.

A Global Ocean Reanalysis Product in the China Ocean Reanalysis (CORA) Project

Abstract: The first version of a global ocean reanalysis over multiple decades (1979–2008) has been completed by the National Marine Data and Information Service within the China Ocean Reanalysis (CORA) project. The global ocean model employed is based upon the ocean general circulation model of the Massachusetts Institute of Technology. A sequential data assimilation scheme within the framework of 3D variational (3DVar) analysis, called multi-grid 3DVar, is implemented in 3D space for retrieving multiple-scale observational information. Assimilated oceanic observations include sea level anomalies (SLAs) from multi-altimeters, sea surface temperatures (SSTs) from remote sensing satellites, and in-situ temperature/salinity profiles. Evaluation showed that compared to the model simulation, the annual mean heat content of the global reanalysis is significantly approaching that of World Ocean Atlas 2009 (WOA09) data. The quality of the global temperature climatology was found to be comparable with the product of Simple Ocean Data Assimilation (SODA), and the major ENSO events were reconstructed. The global and Atlantic meridional overturning circulations showed some similarity as SODA, although significant differences were found to exist. The analysis of temperature and salinity in the current version has relatively larger errors at high latitudes and improvements are ongoing in an updated version. CORA was found to provide a simulation of the subsurface current in the equatorial Pacific with a correlation coefficient beyond about 0.6 compared with the Tropical Atmosphere Ocean (TAO) mooring data. The mean difference of SLAs between altimetry data and CORA was less than 0.1 m in most years.

INCOIS Live Access Server: A Platform for Serving the Geospatial Data of Indian Ocean

Abstract: The INCOIS Live Access Server (I-LAS) was setup at Indian National Centre for Ocean Information Services to effectively deliver diversified geospatial products pertaining to Indian Ocean. The I-LAS provides free access to full suite of satellite-derived data products viz., sea surface temperature (SST), surface chlorophyll, surface wind products and number of products derived from objectively analyzed in-situ data. Further model analysis products from GODAS-MOM are also made available. Additionally climatological data sets from World Ocean Atlas 2009 are also made available for inter-comparison and generation of anomalies. Various functionalities for on the fly visualization and downloading of data are in built in to the LAS along with OpenDAP data sharing. Some examples of data usage from the LAS are also presented. It is observed that INCOIS LAS is being extensively used by various users and statistics of data usage is monitored on a regular basis and 100% uptime is maintained.

Performances of Seven Datasets in Presenting the Upper Ocean Heat Content in the South China Sea

Abstract: In this study, the upper ocean heat content (OHC) variations in the South China Sea (SCS) during 1993-2006 were investigated by examining ocean temperatures in seven datasets, including World Ocean Atlas 2009 (WOA09) (climatology), Ishii datasets, Ocean General Circulation Model for the Earth Simulator (OFES), Simple Ocean Data Assimilation system (SODA), Global Ocean Data Assimilation System (GODAS), China Oceanic ReAnalysis system (CORA), and an ocean reanalysis dataset for the joining area of Asia and Indian-Pacific Ocean (AIPO1.0). Among these datasets, two were independent of any numerical model, four relied on data assimilation, and one was generated without any data assimilation. The annual cycles revealed by the seven datasets were similar, but the interannual variations were different. Vertical structures of temperatures along the 18A degrees N, 12.75A degrees N, and 120A degrees E sections were compared with data collected during open cruises in 1998 and 2005-08. The results indicated that Ishii, OFES, CORA, and AIPO1.0 were more consistent with the observations. Through systematic comparisons, we found that each dataset had its own shortcomings and advantages in presenting the upper OHC in the SCS.