scholarly journals Large-scale geographic patterns of pelagic copepods in the southwestern South Atlantic

2020 ◽  
Vol 204 ◽  
pp. 103281 ◽  
Author(s):  
Eduardo Marcelo Acha ◽  
María Delia Viñas ◽  
Carla Derisio ◽  
Daniela Alemany ◽  
Alberto R. Piola
Keyword(s):  
Large Scale ◽  
South Atlantic ◽  
Geographic Patterns ◽  
Pelagic Copepods

MODELING THE SOUTH ATLANTIC OCEAN FROM MEDIUM TO HIGH RESOLUTION

2014 ◽  
Vol 31 (2) ◽  
Author(s):  
Mariela Gabioux ◽  
Vladimir Santos da Costa ◽  
Joao Marcos Azevedo Correia de Souza ◽  
Bruna Faria de Oliveira ◽  
Afonso De Moraes Paiva
Keyword(s):  
High Resolution ◽  
Atlantic Ocean ◽  
Large Scale ◽  
South Atlantic ◽  
Surface Relaxation ◽  
The South ◽  
Small Surface ◽  
Basic Model ◽  
Basic Set ◽  
Set Up

Results of the basic model configuration of the REMO project, a Brazilian approach towards operational oceanography, are discussed. This configuration consists basically of a high-resolution eddy-resolving, 1/12 degree model for the Metarea V, nested in a medium-resolution eddy-permitting, 1/4 degree model of the Atlantic Ocean. These simulations performed with HYCOM model, aim for: a) creating a basic set-up for implementation of assimilation techniques leading to ocean prediction; b) the development of hydrodynamics bases for environmental studies; c) providing boundary conditions for regional domains with increased resolution. The 1/4 degree simulation was able to simulate realistic equatorial and south Atlantic large scale circulation, both the wind-driven and the thermohaline components. The high resolution simulation was able to generate mesoscale and represent well the variability pattern within the Metarea V domain. The BC mean transport values were well represented in the southwestern region (between Vitória-Trinidade sea mount and 29S), in contrast to higher latitudes (higher than 30S) where it was slightly underestimated. Important issues for the simulation of the South Atlantic with high resolution are discussed, like the ideal place for boundaries, improvements in the bathymetric representation and the control of bias SST, by the introducing of a small surface relaxation. In order to make a preliminary assessment of the model behavior when submitted to data assimilation, the Cooper & Haines (1996) method was used to extrapolate SSH anomalies fields to deeper layers every 7 days, with encouraging results.

scholarly journals Use of recent geoid models to estimate mean dynamic topography and geostrophic currents in South Atlantic and Brazil Malvinas confluence

2012 ◽  
Vol 60 (1) ◽  
pp. 41-48
Author(s):  
Alexandre Bernardino Lopes ◽  
Joseph Harari
Keyword(s):  
Numerical Model ◽  
Large Scale ◽  
Singular Spectrum Analysis ◽  
Satellite System ◽  
South Atlantic ◽  
Dynamic Topography ◽  
Geostrophic Currents ◽  
Mean Dynamic Topography ◽  
Level Model

The use of geoid models to estimate the Mean Dynamic Topography was stimulated with the launching of the GRACE satellite system, since its models present unprecedented precision and space-time resolution. In the present study, besides the DNSC08 mean sea level model, the following geoid models were used with the objective of computing the MDTs: EGM96, EIGEN-5C and EGM2008. In the method adopted, geostrophic currents for the South Atlantic were computed based on the MDTs. In this study it was found that the degree and order of the geoid models affect the determination of TDM and currents directly. The presence of noise in the MDT requires the use of efficient filtering techniques, such as the filter based on Singular Spectrum Analysis, which presents significant advantages in relation to conventional filters. Geostrophic currents resulting from geoid models were compared with the HYCOM hydrodynamic numerical model. In conclusion, results show that MDTs and respective geostrophic currents calculated with EIGEN-5C and EGM2008 models are similar to the results of the numerical model, especially regarding the main large scale features such as boundary currents and the retroflection at the Brazil-Malvinas Confluence.

scholarly journals A Hydroclimatological Analysis of Precipitation in the Ganges–Brahmaputra–Meghna River Basin

Water ◽  
2018 ◽  
Vol 10 (10) ◽  
pp. 1359 ◽  
Author(s):  
Scott Curtis ◽  
Thomas Crawford ◽  
Munshi Rahman ◽  
Bimal Paul ◽  
M. Miah ◽  
...  
Keyword(s):  
Interannual Variability ◽  
River Basin ◽  
Significant Relationship ◽  
Large Scale ◽  
Monsoon Rainfall ◽  
Southern Oscillation ◽  
Wave Train ◽  
Principal Component ◽  
South Atlantic ◽  
The Ganges

Understanding seasonal precipitation input into river basins is important for linking large-scale climate drivers with societal water resources and the occurrence of hydrologic hazards such as floods and riverbank erosion. Using satellite data at 0.25-degree resolution, spatial patterns of monsoon (June-July-August-September) precipitation variability between 1983 and 2015 within the Ganges–Brahmaputra–Meghna (GBM) river basin are analyzed with Principal Component (PC) analysis and the first three modes (PC1, PC2 and PC3) are related to global atmospheric-oceanic fields. PC1 explains 88.7% of the variance in monsoonal precipitation and resembles climatology with the center of action over Bangladesh. The eigenvector coefficients show a downward trend consistent with studies reporting a recent decline in monsoon rainfall, but little interannual variability. PC2 explains 2.9% of the variance and shows rainfall maxima to the far western and eastern portions of the basin. PC2 has an apparent decadal cycle and surface and upper-air atmospheric height fields suggest the pattern could be forced by tropical South Atlantic heating and a Rossby wave train stemming from the North Atlantic, consistent with previous studies. Finally, PC3 explains 1.5% of the variance and has high spatial variability. The distribution of precipitation is somewhat zonal, with highest values at the southern border and at the Himalayan ridge. There is strong interannual variability associated with PC3, related to the El Nino/Southern Oscillation (ENSO). Next, we perform a hydroclimatological downscaling, as precipitation attributed to the three PCs was averaged over the Pfafstetter level-04 sub-basins obtained from the World Wildlife Fund (Gland, Switzerland). While PC1 was the principal contributor of rainfall for all sub-basins, PC2 contributed the most to rainfall in the western Ganges sub-basin (4524) and PC3 contributed the most to the rainfall in the northern Brahmaputra (4529). Monsoon rainfall within these two sub-basins were the only ones to show a significant relationship (negative) with ENSO, whereas four of the eight sub-basins had a significant relationship (positive) with sea surface temperature (SST) anomalies in the tropical South Atlantic. This work demonstrates a geographic dependence on climate teleconnections in the GBM that deserves further study.

scholarly journals Ocean Model Diagnosis of Interannual Coevolving SST Variability in the South Indian and South Atlantic Oceans

2005 ◽  
Vol 18 (15) ◽  
pp. 2864-2882 ◽  
Author(s):  
J. C. Hermes ◽  
C. J. C. Reason
Keyword(s):  
Atmospheric Circulation ◽  
Southern Hemisphere ◽  
Large Scale ◽  
Ocean Model ◽  
South Atlantic ◽  
Heat Fluxes ◽  
Global Ocean ◽  
The South ◽  
Sst Variability ◽  
South Indian

Abstract A global ocean model (ORCA2) forced with 50 yr of NCEP–NCAR reanalysis winds and heat fluxes has been used to investigate the evolution and forcing of interannual dipolelike sea surface temperature (SST) variability in the South Indian and South Atlantic Oceans. Although such patterns may also exist at times in only one of these basins and not the other, only events where there are coherent signals in both basins during the austral summer have been chosen for study in this paper. A positive (negative) event occurs when there is a significant warm (cool) SST anomaly evident in the southwest of both the South Indian and South Atlantic Oceans and a cool (warm) anomaly in the eastern subtropics. The large-scale forcing of these events appears to consist of a coherent modulation of the wavenumber-3 or -4 pattern in the Southern Hemisphere atmospheric circulation such that the semipermanent subtropical anticyclone in each basin is shifted from its summer mean position and its strength is modulated. A relationship to the Antarctic Oscillation is also apparent, and seems to strengthen after the mid-1970s. The modulated subtropical anticyclones lead to changes in the tropical easterlies and midlatitude westerlies in the South Atlantic and South Indian Oceans that result in anomalies in latent heat fluxes, upwelling, and Ekman heat transports, all of which contribute to the SST variability. In addition, there are significant modulations to the strong Rossby wave signals in the South Indian Ocean. The results of this study confirm the ability of the ORCA2 model to represent these dipole patterns and indicate connections between large-scale modulations of the Southern Hemisphere midlatitude atmospheric circulation and coevolving SST variability in the South Atlantic and South Indian Oceans.

scholarly journals Large-scale geographic patterns of mercury contamination in Morocco revealed by freshwater turtles

2017 ◽  
Vol 25 (3) ◽  
pp. 2350-2360 ◽  
Author(s):  
Tahar Slimani ◽  
Mohamed Said El Hassani ◽  
El Hassan El Mouden ◽  
Marine Bonnet ◽  
Paco Bustamante ◽  
...  
Keyword(s):  
Large Scale ◽  
Mercury Contamination ◽  
Freshwater Turtles ◽  
Geographic Patterns

Heme b distributions through the Atlantic Ocean: in situ identification of iron limited phytoplankton

2020 ◽  
Author(s):  
Evangelia Louropoulou ◽  
Martha Gledhill ◽  
Eric P. Achterberg ◽  
Thomas J. Browning ◽  
David J. Honey ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
Large Scale ◽  
North Atlantic Ocean ◽  
Iron Status ◽  
Mean Value ◽  
Particulate Material ◽  
South Atlantic ◽  
Phytoplankton Communities ◽  
The Impact

<p>Heme <em>b</em> is an iron-containing cofactor in hemoproteins that participates in the fundamental processes of photosynthesis and respiration in phytoplankton. Heme <em>b</em> concentrations typically decline in waters with low iron concentrations but due to lack of field data, the distribution of heme <em>b</em> in particulate material in the ocean is poorly constrained. Within the framework of the Helmholtz Research School for Ocean System Science and Technology (HOSST) and the GEOTRACES programme, the authors compiled datasets and conducted multidisciplinary research (e.g. chemical oceanography, microbiology, biogeochemical modelling) in order to test heme <em>b</em> as an indicator of <em>in situ</em> iron-limited phytoplankton. This study was initiated in the North Atlantic Ocean and expanded to the under-sampled South Atlantic Ocean for comparison of the results considering the different phytoplankton populations. Here, we report particulate heme <em>b</em> distributions across the Atlantic Ocean (59.9°N to 34.6°S). Heme <em>b</em> concentrations in surface waters ranged from 0.10 to 33.7 pmol L<sup>-1</sup> (median=1.47 pmol L<sup>-1</sup>, n=974) and were highest in regions with a high biomass. The ratio of heme <em>b</em> to particulate organic carbon (POC) exhibited a mean value of 0.44 μmol heme<em> b</em> mol<sup>-1 </sup>POC. We identified the ratio of 0.10 µmol heme <em>b</em> mol<sup>-1</sup> POC as the cut-off between heme <em>b</em> replete and heme <em>b</em> deficient phytoplankton. By this definition, the ratio heme <em>b</em> relative to POC was consistently below 0.10 μmol mol<sup>-1</sup> in areas characterized by low Fe supply; these were the Subtropical South Atlantic gyre and the seasonally iron limited Irminger Basin. Thus, the ratio heme <em>b</em> relative to POC gave a reliable indication of iron limited phytoplankton communities in situ. Furthermore, the comparison of observed and modelled heme <em>b</em> suggested that heme <em>b</em> could account for between 0.17-9.1% of biogenic iron. This range was comparable to previous culturing observations for species with low heme <em>b</em> content and species growing in low Fe (≤0.50 nmol L<sup>-1</sup>) or nitrate culturing media. Our large scale observations of heme<em> b</em> relative to organic matter suggest the impact of changes in iron supply on phytoplankton iron status.</p>

scholarly journals Large-scale distribution of microbial and viral populations in the South Atlantic Ocean

2016 ◽  
Vol 8 (2) ◽  
pp. 305-315 ◽  
Author(s):  
Daniele De Corte ◽  
Eva Sintes ◽  
Taichi Yokokawa ◽  
Itziar Lekunberri ◽  
Gerhard J. Herndl
Keyword(s):  
Atlantic Ocean ◽  
Large Scale ◽  
South Atlantic ◽  
South Atlantic Ocean ◽  
The South

scholarly journals The South Atlantic Subtropical High: Climatology and Interannual Variability

2017 ◽  
Vol 30 (9) ◽  
pp. 3279-3296 ◽  
Author(s):  
Xiaoming Sun ◽  
Kerry H. Cook ◽  
Edward K. Vizy
Keyword(s):  
Interannual Variability ◽  
Annual Cycle ◽  
Large Scale ◽  
Austral Summer ◽  
Southern Annular Mode ◽  
South Atlantic ◽  
Subtropical High ◽  
Interannual Variations ◽  
The South ◽  
The North

ERA-Interim and JRA-55 reanalysis products are analyzed to document the annual cycle of the South Atlantic subtropical high (SASH) and examine how its interannual variability relates to regional and large-scale climate variability. The annual cycle of the SASH is found to have two peaks in both intensity and size. The SASH is strongest and largest during the solstitial months when its center is either closest to the equator and on the western side of the South Atlantic basin during austral winter or farthest poleward and in the center of the basin in late austral summer. Although interannual variations in the SASH’s position are larger in the zonal direction, the intensity of the high decreases when it is positioned to the north. This relationship is statistically significant in every month. Seasonal composites and EOF analysis indicate that meridional changes in the position of the SASH dominate interannual variations in austral summer. In particular, the anticyclone tends to be displaced poleward in La Niña years when the southern annular mode (SAM) is in its positive phase and vice versa. Wave activity flux vectors suggest that ENSO-related convective anomalies located in the central-eastern tropical Pacific act as a remote forcing for the meridional variability of the summertime SASH. In southern winter, multiple processes operate in concert to induce interannual variability, and none of them appears to dominate like ENSO does during the summer.

scholarly journals Atmospheric convergence zones stemming from large-scale mixing

2021 ◽  
Vol 2 (2) ◽  
pp. 475-488
Author(s):  
Gabriel M. P. Perez ◽  
Pier Luigi Vidale ◽  
Nicholas P. Klingaman ◽  
Thomas C. M. Martin
Keyword(s):  
South America ◽  
Large Scale ◽  
Hydrological Cycle ◽  
Moisture Flux ◽  
South Atlantic Convergence Zone ◽  
South Atlantic ◽  
Convergence Zone ◽  
The South ◽  
Atmospheric Flow ◽  
Convergence Zones

Abstract. Organised cloud bands are important features of tropical and subtropical rainfall. These structures are often regarded as convergence zones, alluding to an association with coherent atmospheric flow. However, the flow kinematics is not usually taken into account in classification methods for this type of event, as large-scale lines are rarely evident in instantaneous diagnostics such as Eulerian convergence. Instead, existing convergence zone definitions rely on heuristic rules of shape, duration and size of cloudiness fields. Here we investigate the role of large-scale turbulence in shaping atmospheric moisture in South America. We employ the finite-time Lyapunov exponent (FTLE), a metric of deformation among neighbouring trajectories, to define convergence zones as attracting Lagrangian coherent structures (LCSs). Attracting LCSs frequent tropical and subtropical South America, with climatologies consistent with the South Atlantic Convergence Zone (SACZ), the South American Low-Level Jet (SALLJ) and the Intertropical Convergence Zone (ITCZ). In regions under the direct influence of the ITCZ and the SACZ, rainfall is significantly positively correlated with large-scale mixing measured by the FTLE. Attracting LCSs in south and southeast Brazil are associated with significant positive rainfall and moisture flux anomalies. Geopotential height composites suggest that the occurrence of attracting LCSs in these regions is related with teleconnection mechanisms such as the Pacific–South Atlantic. We believe that this kinematical approach can be used as an alternative to region-specific convergence zone classification algorithms; it may help advance the understanding of underlying mechanisms of tropical and subtropical rain bands and their role in the hydrological cycle.

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