World Ocean Atlas Research Articles

Endemicity and climatic niche differentiation in three marine ciliated protists

AbstractThe biogeographic pattern of single‐celled eukaryotes (protists), including ciliates, is poorly understood. Most marine species are believed to have a relatively high dispersal potential, such that both globally distributed and geographically isolated taxa exist. Primary occurrence data for three large, easily identified ciliate species, Parafavella gigantea, Schmidingerella serrata, and Zoothamnium pelagicum, and environmental data drawn from the National Oceanic and Atmospheric Administration's World Ocean Atlas were used to estimate each species’ spatial and environmental distributions using Maxent v3.3.3k. The predictive power of the models was tested with a series of spatial stratification studies, which were evaluated using partial receiver operating characteristic (ROC) statistics. Differences between niches occupied by each taxon were evaluated using background similarity tests. All predictions showed significant ability to anticipate test points. The null hypotheses of niche similarity were rejected in all background similarity tests comparing the niches among the three species. This article provides the first quantitative assessment of environmental conditions associated with three species of ciliates and a first estimate of their spatial distributions in the North Atlantic, which can serve as a benchmark against which to document distributional shifts. These species follow consistent, predictable patterns related to climate and environmental biochemistry; the importance of climatic conditions as regards protist distributions is noteworthy considering the effects of global climate change.

Quantification of last glacial-Holocene net primary productivity and upwelling activity in the equatorial eastern Atlantic with a revised modern dinocyst database

In order to better explore quantitative reconstructions of net primary productivity (NPP) conditions using a dinoflagellate cyst (dinocyst)-based transfer function method, we revised the tropical Atlantic modern dinocyst database n = 208 (Marret et al., 2008). Modern assemblages from the worldwide dinocyst atlas (Zonneveld et al., 2013) were added to provide a better geographical coverage of the South Atlantic Ocean. The environmental dataset was updated using the World Ocean Atlas 2013 for sea-surface temperature (SST) and sea-surface salinity (SSS) data, as well as for 1997–2017 mean NPP values recorded during SeaWifs and MODIS spatial programs. New environmental datasets were tested using anomalies regarding mean latitudinal SST as a potential index to track past upwelling activity. Finally, preindustrial NPP values, simulated with the IPSL-CM5A-LR model developed at the Institut Pierre Simon Laplace (IPSL) have been added to the dinocyst environmental database to provide NPP values consistent with the mean age of “modern” dinocyst assemblages. The transfer function method using the updated modern database was then applied to fossil dinocyst assemblages of core KZAI-01, retrieved off the Congo River mouth and covering the last 43.2 kyr. Our results indicate a dominant orbital forcing, with higher primary productivity values reconstructed during precession minima (MIS 3 and the last deglaciation) and enhanced by a maximum of obliquity during the last deglaciation and the Holocene. The synchronicity between high upwelling intensity and high terrigenous inputs during high NPP period (e.g. during the last Deglaciation) highlighted the prevalent role of river-induced upwelling activity, which is specific to the Congo River. These results have improved our understanding of the environmental forcing leading to major trophic changes in the intertropical area.

The roles of mixed layer depth in affecting chemical and biological characteristics of Makassar straits, Indonesia

Mixed Layer Depth (MLD) is able to determine the amount of light and nutrients abundance for the growth of phytoplankton, its known that phytoplakton pigments are the main absorbers and light scatterers in the ocean. Location wich has deeper MLD and large seasonal variations are the most productive areas, also could have blooming or the maximum growth of large phytoplankton occurring in the existence of a limited number nutrients for several days. The aims of this study are to understand the characteristics of the MLD and it roles to the abundance of Chlorophyll and nutrient in Indonesia Through-Flow/ITF (Indonesia: “ARLINDO”), specifically the area along Makassar Strait. The Chlorophyll and oceanographic parameters were obtained based on measuring by CTD in TIMIT 2016 expedition. The MLD was deep (~43 m) in the northern part of the transect (around Central Sulawesi Island) and shoaled progressively until about 13 m in the southern transect (the Southern Makassar Strait). The Chlorophyll-a (Chl-a) concentration show a decline pattern from the north to the south transects with the maximal Chl-a is 0.37 mg/m3. Nutrient parameters in southern Makassar Strait studied were NODC (National Oceanographic Data Center) data from WOA (World Ocean Atlas), it can indicated a correlation between nutrient (Nitrate) with Chlorophyll. The mean correlation in mixing layer for whole area is 0.78, showing that Nitrate concentration is highly related proportional to Chlorophyll abundance, while below the mixing layer, correlation value is -0.52, indicating the inverse relation between Chlorophyll and nutrient. Based on those correlation, and assumption that the source of Chlorophyll is from phytoplankton, it can be concluded that phytoplankton needs Nitrate in its metabolism process as well as other productivities reason in mixing layer, while in depth below the mixing layer, growth of phytoplankton is no longer depends on concentration of Nitrate nutrient.

Study of ocean thermal energy resources in Para’baya, West Sulawesi

Ocean thermal is one of the renewable energy resources. In 1981, a design of Ocean Thermal Energy Conversion (OTEC) pilot power plant was proven could produce electricity. The performance of OTEC depends on the possible temperature differences of the warm and cold seawater, at least 20°C. In the coastal of Para’baya, this requirement can be satisfied since the distance to reach the 1000 m depth is less than 10,000 m from the shore. The result of ocean thermal power calculation in Makassar Strait shows that Para’baya could produce higher power than any other place in west coast of Sulawesi, with an average power output of 120.35 kW. This ocean thermal study, in the coast of Para’baya, used sea surface temperatures (SST) data from the result of Long-term Indonesian Throughflow Model Simulation (LITHMOS) over 24 years (1982 – 2006), and sea temperature data at 1000 m depth from the World Ocean Atlas (WOA) 2009. The result shows that ocean thermal energy distributions in the Makassar Strait were affected by the combination of gust, wind direction, and sun position which varies in each season. Maximum ocean thermal power is reached during the first transitional season (March, April, May) with output power of 128 kW, and the minimum power is achieved during the dry season (June, July, August) with an output power of 114 kW.

Identification of Decapterus sp. potential fishing grounds in Java and Western Kalimantan Seas

Decapterus sp. is one of the main targeted species for small pelagic fish in Java and western Kalimantan Seas (Karimata Strait and South China Sea). Decapterus sp. mainly catch at around 40-70 meters depth. They live in warm waters (more than 26°C) with salinity greater than 30 ppt, pH greater than 7.75, and concentration of dissolved oxygen (DO) greater than 4.2 ml/l. Datas were obtained from World Ocean Atlas 2013, NCEP, and result of numerical model. The aim of the research was to investigate the seasonal variation of decapterus sp. potential fishing ground. The results show that variation of seasonal oceanographic conditions has an impact to the potential fishing ground pattern of decapterus sp. The catching prediction area was at 20 m depth, except when second transition season which was at 40 meters depth. Fishing period should be done during the rainy season according to the widest area of potential fishing ground.

Estimating Oxygen in the Southern Ocean Using Argo Temperature and Salinity

AbstractAn Argo‐based estimate of oxygen (O2) at 150 m is presented for the Southern Ocean (SO) from temperature (T), salinity (S), and O2 Argo profiles collected during 2008–2012. The method is based on a supervised machine learning algorithm known as random forest (RF) regression and provides an estimate for O2 given T, S, location, and time information. The method is validated by attempting to reproduce the Southern Ocean State Estimate (SOSE) O2 field using synthetic data sampled from SOSE. The RF mapping shows skill in the majority of the domain but is problematic in some of the boundary regions. Maps of O2 at 150 m derived from observed profiles suggest that SOSE and the World Ocean Atlas 2013 climatology may overestimate annual mean O2 in the SO, both on a global and basin scale. A large regional bias is found east of Argentina, where high O2 values in the Argo‐based estimate are confined closer to the coast compared to other products. SOSE may also underestimate the annual cycle of O2. Evaluation of the RF‐based method demonstrates its potential to improve understanding of O2 annual mean fields and variability from sparse O2 measurements. This implies the algorithm will also be effective for mapping other biogeochemical variables (e.g., nutrients and carbon). Furthermore, our RF evaluation results can be used to inform the design of future enhancements to the current array of O2 profiling floats.

Temporal and Spatial Variability of Global Upper Ocean Freshwater Content

Observational salinity data from the Global Temperature and Salinity Profile Program (GTSPP) are used to identify temporal and spatial variability of the upper ocean freshwater content (FWC). First, the optimal spectral decomposition (OSD) is used to build up monthly synoptic temperature and salinity data set from January 1990 to December 2009 on 1oA—1o grids and the same 33 vertical levels as the World Ocean Atlas 2005. Then, the monthly varying upper layer FWC fields (F) with four different layer thicknesses (surface to 50, 100, 300, and 700 m depths) are obtained.

Determination of Dynamic Ocean Topography Using the Minimum Energy State

Geostrophic balance represents the minimum energy state in a linear system with conservation of potential vorticity. On the base of that, a minimum energy state (MES) method is proposed to determine dynamic topography (η) and in turn the absolute geostrophic velocity from hydrographic data through finding η to minimize a functional, . Numerical approach leads to a set of well-posed linear algebraic equations of η at grid points. Feasibility and advantage of the MES method are illustrated using the three-dimensional (T, S) data of the NOAA National Centers for Environmental Information (NCEI) World Ocean Atlas 2013 version 2 for the North Atlantic Ocean (100oW-6oW, 7oN-72oN) on 1o 1o grids.

An inventory of Arctic Ocean data in the World Ocean Database

Abstract. The World Ocean Database (WOD) contains over 1.3 million oceanographic casts (where cast refers to an oceanographic profile or set of profiles collected concurrently at more than one depth between the ocean surface and ocean bottom) collected in the Arctic Ocean basin and its surrounding marginal seas. The data, collected from 1849 to the present, come from many submitters and countries, and were collected using a variety of instruments and platforms. These data, along with the derived products World Ocean Atlas (WOA) and the Arctic Regional Climatologies, are exceptionally useful – the data are presented in a standardized, easy to use format and include metadata and quality control information. Collecting data in the Arctic Ocean is challenging, and coverage in space and time ranges from excellent to nearly non-existent. WOD continues to compile a comprehensive collection of Arctic Ocean profile data, ideal for oceanographic, environmental and climatic analyses (https://doi.org/10.7289/V54Q7S16).

A parallel FP-growth algorithm on World Ocean Atlas data with multi-core CPU

According to the complexity of ocean data, this paper adopts a parallel mining algorithm of association rules to explore the correlation and regularity of oxygen, temperature, phosphate, nitrate and silicate in the ocean. After the marine data is interpolated, this paper utilizes the parallel FP-growth algorithm to mine the data and then briefly analyzes the mining results of the frequent itemsets and association rules. The relationship between the parallel efficiency and the core number of CPU is analyzed through datasets with different scales. The experimental results indicate that the acceleration effect is ideal when each thread scored 200,000–300,000 data, which leads to more than 1.2 times of performance improvement.

Propagation of the Semidiurnal Internal Tide: Phase Velocity Versus Group Velocity

AbstractThe superposition of two waves of slightly different wavelengths has long been used to illustrate the distinction between phase velocity and group velocity. The first‐mode M2 and S2 internal tides exemplify such a two‐wave model in the natural ocean. The M2 and S2 tidal frequencies are 1.932 and 2 cycles per day, respectively, and their superposition forms a spring‐neap cycle in the semidiurnal band. The spring‐neap cycle acts like a wave, with its frequency, wave number, and phase being the differences of the M2 and S2 internal tides. The spring‐neap cycle and energy of the semidiurnal internal tide propagate at the group velocity. Long‐range propagation of M2 and S2 internal tides in the North Pacific is observed by satellite altimetry. Along a 3,400 km beam spanning 24°–54°N, the M2 and S2 travel times are 10.9 and 11.2 days, respectively. For comparison, it takes the spring‐neap cycle 21.1 days to travel over this distance. Spatial maps of the M2 phase velocity, the S2 phase velocity, and the group velocity are determined from phase gradients of the corresponding satellite observed internal tide fields. The observed phase and group velocities agree with theoretical values estimated using the World Ocean Atlas 2013 annual‐mean ocean stratification.

Seasonal Variation of Thermocline Depth: Consequence on Nutrient Availability in the Ivorian Coastal Zone

Faced with the threat of overfishing in Africa, this study was initiated in the coastal zone of Côte d'Ivoire to understand the nutrients availability as function of variation in the depth of thermocline. Data from the ocean bank, World Ocean Atlas (WOA), were used in the ODV software during the twelve months of 2009 taken at 5.5°W/4.5°N (station coordinates). ODV software has allowed to make seasonal analysis, from vertical profiles and latitudinal analysis from the coast toward the sea through some parameters such as temperature, nitrate, phosphate and oxygen. The depth of thermocline, nitracline, phosphacline and oxycline was determined by the seasonal analysis. To evaluate the enrichment intensity of coast towards the sea, latitudinal analysis was investigated using the section profiles (1°S/5°N coordinates). The main results have shown not only the variation in the depth of the thermocline, but also the variation of nitracline, phosphacline and oxycline at different marine seasons. During the cold season, there was an ascent of the thermocline over the surface of water and a strong enrichment from the coast to the sea especially in August. While in hot season, the thermocline was lower and its stability has favoured the stratification of the water column, which prevents the enrichment of the oxygenated surface layer. Analysis of relationships shows that nutrient elements and oxygen change polynomially with temperature.

Thermocline Layers Depth and Thickness in Indonesian Waters when Souteast Monsoon

Termocline layer is effect of the unstabliized water when its stratified and usually with temperature decrease. This Research comprehensively discussed Indonesian waters, especially at a time when ITF flows strengthened in eastern part of Indonesia as compared to the western waters of Indonesia. Therefore, it is necessary to study the changes in the depth and thickness of the thermocline in various Indonesian waters to determine the condition toward oceanographic phenomenon that occurred in Southeast Monsoon. The data used are secondary data obtained from the World Ocean Atlas the form of climatological data. The data used is the temperature (oC) monthly from year 2005 to 2012 in June-August with a spatial resolution 10. The research location is determined based on the division of zoning Regional Fisheries Management or RFM. Location research adjusted for optimize the benefits of this research in pelagic fishing effort. The method used in this research is the analysis of spatial, temporal, and literature studies about the temperature gradient changes. The result show that Thermocline layer in eastern area of Indonesia found deeper than western Indonesia. Thickness of thermocline layer in western area of Indonesia has lower thickness level rather than eastern area of Indonesia.Keywords : Thermocline, Temperature Gradient, dan South East Monsoon, ITF

Impacts of sea-surface salinity in an eddy-resolving semi-global OGCM

To explore the impacts of sea-surface salinity (SSS) on the interannual variability of upper-ocean state, we compare two 10-year runs of an eddy-resolving ocean general circulation model (OGCM): in one, SSS is strongly restored toward a monthly climatology (World Ocean Atlas ’98) and in the other, toward the SSS of a monthly gridded Argo product. The inclusion of the Argo SSS generally improves the interannual variability of the mixed layer depth; particularly so in the western tropical Pacific, where so-called “barrier layers” are reproduced when the Argo SSS is included. The upper-ocean subsurface salinity variability is also improved in the tropics and subtropics even below the mixed layer.To understand the reason for the latter improvement, we separate the salinity difference between the two runs into its “dynamical” and “spiciness” components. The dynamical component is dominated by small-scale noise due to the chaotic nature of mesoscale eddies. The spiciness difference indicates that as expected from the upper-ocean general circulation, SSS variability in the mixed layer is subducted into the thermocline in subtropics; this signal is generally advected downward, equatorward, and westward in the equator-side of the subtropical gyre. The SSS signal subducted in the subtropical North Pacific appears to enter the Indian Ocean through the Indonesian Throughflow, although this signal is weak and probably insignificant in our model.

The Global Mode‐1 S2 Internal Tide

AbstractThe global mode‐1 S2 internal tide is observed using sea surface height (SSH) measurements from four satellite altimeters: TOPEX/Poseidon, Jason‐1, Jason‐2, and Geosat Follow‐On. Plane wave analysis is employed to extract three mode‐1 S2 internal tidal waves in any given 250 km by 250 km window, which are temporally coherent over a 20 year period from 1992 to 2012. Depth‐integrated energy and flux of the S2 internal tide are calculated from the SSH amplitude and a conversion function built from climatological hydrographic profiles in the World Ocean Atlas 2013. The results show that the S2 and M2 internal tides have similar spatial patterns. Both S2 and M2 internal tides originate at major topographic features and propagate over long distances. The S2 internal tidal beams are generally shorter, likely because the relatively weaker S2 internal tide is easily overwhelmed by nontidal noise. The northbound S2 and M2 internal tides from the Hawaiian Ridge are observed to travel over 3500 km across the Northeast Pacific. The globally integrated energy of the mode‐1 S2 internal tide is 7.8 PJ (1 PJ = 1015 J), about 20% that of M2 (36.4 PJ). The histogram of S2 to M2 SSH ratios peaks at 0.4, consistent with the square root of their energy ratio. In terms of SSH, S2 is greater than M2 in 10% of the global ocean and ≥50% of M2 in about half of the global ocean.

Estimating the baroclinic Rossby radius of deformation in the Sea of Okhotsk

The first baroclinic Rossby radius of deformation (R 1) in the Sea of Okhotsk is estimated using the hydrological datasets from the World Ocean Atlas (WOA) 2001 and WOA 2013. It is established that the maximum values of R 1 are observed over the Kuril Basin (18–20 km), and its minimum values (1.5–2 km), over the northern shelf of the Sea of Okhotsk. In the central part of the sea R1 varies from 8 to 10 km. The seasonal variability of R1 for both datasets is characterized by the minima in winter and by the maxima in summer. It was found that on the eastern shelf of Sakhalin Island R 1 reaches the maximum both in November (∼6 km) and in April (∼4-5 km). According to the obtained estimates of R 1, the model grid resolution of 3 to 8 km should be used for the eddy-permitting numerical simulation of circulation in the Sea of Okhotsk, and the model grid resolution from 1.5 to 2 km, for the explicit simulation of mesoscale variability.

Evaluation of Satellite-Altimetry-Derived Pycnocline Depth Products in the South China Sea

The climatological monthly gridded World Ocean Atlas 2013 temperature and salinity data and satellite altimeter sea level anomaly data are used to build two altimeter-derived high-resolution real-time upper layer thickness products based on a highly simplified two-layer ocean model of the South China Sea. One product uses the proportional relationship between the sea level anomaly and upper layer thickness anomaly. The other one adds a modified component ( η M ′ ) to account for the barotropic and thermodynamic processes that are neglected in the former product. The upper layer thickness, in this work, represents the depth of the main pycnocline, which is defined as the thickness from the sea surface to the 25 kg/m3 isopycnal depth. The mean upper layer thickness in the semi-closed South China Sea is ~120 m and the mean reduced gravity is ~0.073 m/s2, which is about one order of magnitude larger than the value obtained in the open deep ocean. The long-term temperature observations from three moored buoys, the conductivity-temperature-depth profiles from three joint cruises, and the Argo measurements from 2006 to 2015 are used to compare and evaluate these two upper layer thickness products. It shows that adding the η M ′ component is necessary to simulate the upper layer thickness in some situations, especially in summer and fall in the northern South China Sea.

A fresh look at the deepwater overflow in the Luzon Strait

On the basis of the latest version of a U.S. Navy generalized digital environment model (GDEM-V3.0) and World Ocean Atlas (WOA13), the hydraulic theory is revisited and applied to the Luzon Strait, providing a fresh look at the deepwater overflow there. The result reveals that: (1) the persistent density difference between two sides of the Luzon Strait sustains an all year round deepwater overflow from the western Pacific to the South China Sea (SCS); (2) the seasonal variability of the deepwater overflow is influenced not only by changes in the density difference between two sides of the Luzon Strait, but also by changes in its upstream layer thickness; (3) the deepwater overflow in the Luzon Strait shows a weak semiannual variability; (4) the seasonal mean circulation pattern in the SCS deep basin does not synchronously respond to the seasonality of the deepwater overflow in the Luzon Strait. Moreover, the deepwater overflow reaches its seasonal maximum in December (based on GDEM-V3.0) or in fall (October–December, based on the WOA13), accompanied by the lowest temperature of the year on the Pacific side of the Luzon Strait. The seasonal variability of the deepwater overflow is consistent with the existing longest (3.5 a) continuous observation along the major deepwater passage of the Luzon Strait.

Impacts of Indonesian Throughflow on seasonal circulation in the equatorial Indian Ocean

Impacts of the Indonesian Throughflow (ITF) on seasonal circulation in the equatorial eastern Indian Ocean are investigated using the ocean-only model LICOM by opening and closing ITF passages. LICOM had daily forcing from NCEP reanalysis data during 2000-2011. It can reproduce vertical profiles of mean density and buoyancy frequency of World Ocean Atlas 2013 data. The model also simulates well annual oscillation in the central Indian Ocean and semiannual oscillation in the eastern Indian Ocean of sea level anomalies (SLA) using satellite altimeter data, as well as the semiannual oscillation of surface zonal equatorial currents of Ocean Surface Current Analyses Real Time current data in the equatorial Indian Ocean. The wave decomposition method is used to analyze the propagation and reflection of equatorial long waves based on LICOM output. Wave analysis suggests that ITF blockage mainly influences waves generated from the Indian Ocean but not the Pacific Ocean, and eastern boundary reflections play an important role in semiannual oscillations of SLA and zonal current differences in the equatorial Indian Ocean associated with ITF. Reconstructed ITF-caused SLA using wave decomposition coefficient differences between closed and open ITF-passage experiments suggest both Kelvin and Rossby waves from the first baroclinic mode have comparable contributions to the semiannual oscillations of SLA difference. However, reconstructed ITF-caused surface zonal currents at the equator suggest that the first meridional-mode Rossby wave has much greater contribution than the first baroclinic mode Kelvin wave. Both reconstructed sea level and zonal currents demonstrate that the first baroclinic mode has a greater contribution than other baroclinic modes.

Overview of the Ocean Climatology and Its Variability in the Azores Region of the North Atlantic Including Environmental Characteristics at the Seabed

Obtaining a comprehensive knowledge of the spatial and temporal variations of the environmental factors characterising the Azores region is essential for conservation and management purposes. Although many studies are available for the region, there is a need for a general overview of the best available information. Here, we assembled a comprehensive collection of environmental data and briefly described the ocean climatology and its variability in the Azores. Data sources used in this study included remote sensing oceanographic data for 2003-2013 (sea surface temperature, chlorophyll-a concentration, particulate inorganic carbon and particulate organic carbon), derived oceanographic data (primary productivity and North Atlantic oscillation index) for 2003-2013, and in situ data (temperature, salinity, oxygen, phosphate, nitrate and silicate) obtained from the World Ocean Atlas 2013. We have produced 78 geographic datasets of environmental data for the Azores region that were deposited at the World Data Center Pangaea and also made available at the SIGMAR Azores website. As with previous studies, our results confirmed a high spatial, seasonal and inter-annual variability of the marine environment in the Azores region, typical of mid latitudes. For example, lower sea surface temperature was found in the northern part of the study area coinciding with higher values for chlorophyll-a concentration, net primary production, and particulate organic and inorganic carbon. Higher values for some of these parameters were also found on island slopes and some seamounts. Compiled data on the environmental conditions at near-seabed revealed some notable variations across the study area (e.g. oxygen and nutrients) and with depth (e.g. temperature, salinity, and oxygen). Knowledge of these patterns will help improve our understanding of the distribution of many deep-sea organisms such as fish, cold-water corals and sponges, thereby supporting the implementation of marine spatial planning and other management measures. It should be noted, that the assembled datasets suffer from a number of limitations related to the accuracy of remote sensing and global bathymetry data, or to the limited and unevenly distributed historical environmental observations. Accordingly, an effective global network of observing systems for detecting oceanic change with adequate accuracy and precision is still required.