scholarly journals Spatio-temporal patterns of C : N : P ratios in the northern Benguela upwelling regime

2013 ◽  
Vol 10 (6) ◽  
pp. 10459-10489
Author(s):  
A. Flohr ◽  
A. K. van der Plas ◽  
K.-C. Emeis ◽  
V. Mohrholz ◽  
T. Rixen
Keyword(s):  
South Atlantic ◽  
Subtropical Gyre ◽  
Total Alkalinity ◽  
The South ◽  
Concentration Data ◽  
Redfield Ratio ◽  
Dissolved Carbon ◽  
Bottom Waters ◽  
The Mean ◽  
The Impact

Abstract. Dissolved carbon to nutrient ratios in the oceans' interior are remarkably consistent with the classical C : N : P : O2 Redfield ratio of 106 : 16 : 1 : 138 reflecting the mean composition of organic matter photosynthesized in the sunlit surface ocean. Deviations from the Redfield ratio indicate changes in the functioning of the biological carbon pump, which is driven and limited by the availability of nutrients. The northern Benguela coastal upwelling system (NBUS) is known for losses of fixed nitrogen (N = NO3–, NO2– and NH4+) and the accumulation of phosphate (P) in sub- and anoxic bottom waters and sediments of the Namibian shelf. To study the impact on the regional carbon cycle and consequences for the nutrient export from the BUS into the oligotrophic subtropical gyre of the South Atlantic Ocean we measured dissolved inorganic carbon (CT), oxygen (O2), and nutrient concentrations as well as the total alkalinity (AT) in February 2011. Our results indicate that over the Namibian shelf the C : N : P : O2 ratio decreases to 106 : 16 : 1.6 : 138 because of phosphate efflux from sediments. N reduction further increase C : N and reduce N : P ratios in those regions where O2 concentrations in bottom waters are < 20 µmol kg–1. However, off the shelf along the continental margin the mean C : N : P : O2 ratio is again close to the Redfield stoichiometry. Comparing the situation of 2011 with nutrient concentration data measured during 2 cruises in 2008 and 2009 implies that the amount of excess P that is created in the bottom waters on the shelf and its export into the subtropical gyre after upwelling varies through time. The magnitude of excess P formation and export is governed by inputs of excess N along with the South Atlantic Central Water (SACW) flowing into the NBUS from the north as a poleward compensation current. Since excess N is produced by the remineralization of N-enriched biomass built up by N2-fixing organisms, factors controlling N2 fixation north of the BUS need to be addressed in future studies to better understand the NBUS' role as P source and N sink in the coupled C : N : P cycles.

scholarly journals Spatio-temporal patterns of C : N : P ratios in the northern Benguela upwelling system

2014 ◽  
Vol 11 (3) ◽  
pp. 885-897 ◽  
Author(s):  
A. Flohr ◽  
A. K. van der Plas ◽  
K.-C. Emeis ◽  
V. Mohrholz ◽  
T. Rixen
Keyword(s):  
N2 Fixation ◽  
South Atlantic ◽  
Subtropical Gyre ◽  
Total Alkalinity ◽  
Nutrient Concentrations ◽  
The South ◽  
Upwelling System ◽  
Benguela Upwelling ◽  
Bottom Waters ◽  
The Impact

Abstract. On a global scale the ratio of fixed nitrogen (N) and phosphate (P) is characterized by a deficit of N with regard to the classical Redfield ratio of N : P = 16 : 1 reflecting the impact of N loss occurring in the oceanic oxygen minimum zones. The northern Benguela upwelling system (NBUS) is known for losses of N and the accumulation of P in sub- and anoxic bottom waters and sediments of the Namibian shelf resulting in low N : P ratios in the water column. To study the impact of the N : P anomalies on the regional carbon cycle and their consequences for the export of nutrients from the NBUS into the oligotrophic subtropical gyre of the South Atlantic, we measured dissolved inorganic carbon (CT), total alkalinity (AT), oxygen (O2) and nutrient concentrations in February 2011. The results indicate increased P concentrations over the Namibian shelf due to P efflux from sediments resulting in a C : N : P : -O2 ratio of 106 : 16 : 1.6 : 138. N reduction further increase C : N and reduce N : P ratios in those regions where O2 concentrations in bottom waters are < 20 μmol kg−1. However, off the shelf along the continental margin, the mean C : N : P : -O2 ratio is again close to the Redfield stoichiometry. Additional nutrient data measured during two cruises in 2008 and 2009 imply that the amount of excess P, which is created in the bottom waters on the shelf, and its export into the subtropical gyre after upwelling varies through time. The results further reveal an inter-annual variability of excess N within the South Atlantic Central Water (SACW) that flows from the north into the NBUS, with highest N values observed in 2008. It is postulated that the N excess in SACW occurred due to the impact of remineralized organic matter produced by N2 fixation and that the magnitude of excess P formation and its export is governed by inputs of excess N along with SACW flowing into the NBUS. Factors controlling N2 fixation north of the BUS need to be addressed in future studies to better understand the role of the NBUS as a P source and N sink in the coupled C : N : P cycles.

scholarly journals Meridional changes in the South Atlantic Subtropical Gyre during Heinrich Stadials

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Tainã M. L. Pinho ◽  
Cristiano M. Chiessi ◽  
Rodrigo C. Portilho-Ramos ◽  
Marília C. Campos ◽  
Stefano Crivellari ◽  
...  
Keyword(s):  
Global Climate ◽  
South Atlantic ◽  
Subtropical Gyre ◽  
Climate System ◽  
The South ◽  
Foraminiferal Species ◽  
Ocean Gyres ◽  
Long Term Monitoring ◽  
Term Monitoring

AbstractSubtropical ocean gyres play a key role in modulating the global climate system redistributing energy between low and high latitudes. A poleward displacement of the subtropical gyres has been observed over the last decades, but the lack of long-term monitoring data hinders an in-depth understanding of their dynamics. Paleoceanographic records offer the opportunity to identify meridional changes in the subtropical gyres and investigate their consequences to the climate system. Here we use the abundance of planktonic foraminiferal species Globorotalia truncatulinodes from a sediment core collected at the northernmost boundary of the South Atlantic Subtropical Gyre (SASG) together with a previously published record of the same species from the southernmost boundary of the SASG to reconstruct meridional fluctuations of the SASG over last ca. 70 kyr. Our findings indicate southward displacements of the SASG during Heinrich Stadials (HS) 6-4 and HS1, and a contraction of the SASG during HS3 and HS2. During HS6-4 and HS1, the SASG southward displacements likely boosted the transfer of heat to the Southern Ocean, ultimately strengthening deep-water upwelling and CO2 release to the atmosphere. We hypothesize that the ongoing SASG poleward displacement may further increase oceanic CO2 release.

The impact of mesoscale eddies on the phytoplankton community in the South Atlantic Ocean: HPLC-CHEMTAX approach

2019 ◽  
Vol 144 ◽  
pp. 154-165 ◽  
Author(s):  
Andréa da Consolação de Oliveira Carvalho ◽  
Carlos Rafael B. Mendes ◽  
Rodrigo Kerr ◽  
José Luiz Lima de Azevedo ◽  
Felippe Galdino ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
Phytoplankton Community ◽  
Mesoscale Eddies ◽  
South Atlantic ◽  
South Atlantic Ocean ◽  
The South ◽  
The Impact

scholarly journals The impact of the subtropical South Atlantic SST on South American precipitation

2008 ◽  
Vol 26 (11) ◽  
pp. 3457-3476 ◽  
Author(s):  
A. S. Taschetto ◽  
I. Wainer
Keyword(s):  
South America ◽  
Southern Oscillation ◽  
South Atlantic ◽  
Empirical Orthogonal Functions ◽  
Convergence Zone ◽  
South American ◽  
The South ◽  
Inter Tropical Convergence Zone ◽  
The Impact ◽  
Sst Anomalies

Abstract. The Community Climate Model (CCM3) from the National Center for Atmospheric Research (NCAR) is used to investigate the effect of the South Atlantic sea surface temperature (SST) anomalies on interannual to decadal variability of South American precipitation. Two ensembles composed of multidecadal simulations forced with monthly SST data from the Hadley Centre for the period 1949 to 2001 are analysed. A statistical treatment based on signal-to-noise ratio and Empirical Orthogonal Functions (EOF) is applied to the ensembles in order to reduce the internal variability among the integrations. The ensemble treatment shows a spatial and temporal dependence of reproducibility. High degree of reproducibility is found in the tropics while the extratropics is apparently less reproducible. Austral autumn (MAM) and spring (SON) precipitation appears to be more reproducible over the South America-South Atlantic region than the summer (DJF) and winter (JJA) rainfall. While the Inter-tropical Convergence Zone (ITCZ) region is dominated by external variance, the South Atlantic Convergence Zone (SACZ) over South America is predominantly determined by internal variance, which makes it a difficult phenomenon to predict. Alternatively, the SACZ over western South Atlantic appears to be more sensitive to the subtropical SST anomalies than over the continent. An attempt is made to separate the atmospheric response forced by the South Atlantic SST anomalies from that associated with the El Niño – Southern Oscillation (ENSO). Results show that both the South Atlantic and Pacific SSTs modulate the intensity and position of the SACZ during DJF. Particularly, the subtropical South Atlantic SSTs are more important than ENSO in determining the position of the SACZ over the southeast Brazilian coast during DJF. On the other hand, the ENSO signal seems to influence the intensity of the SACZ not only in DJF but especially its oceanic branch during MAM. Both local and remote influences, however, are confounded by the large internal variance in the region. During MAM and JJA, the South Atlantic SST anomalies affect the magnitude and the meridional displacement of the ITCZ. In JJA, the ENSO has relatively little influence on the interannual variability of the simulated rainfall. During SON, however, the ENSO seems to counteract the effect of the subtropical South Atlantic SST variations on convection over South America.

scholarly journals South Atlantic Surface Boundary Current System during the Last Millennium in the CESM-LME: The Medieval Climate Anomaly and Little Ice Age

Geosciences ◽  
2019 ◽  
Vol 9 (7) ◽  
pp. 299
Author(s):  
Fernanda Marcello ◽  
Ilana Wainer ◽  
Peter R. Gent ◽  
Bette L. Otto-Bliesner ◽  
Esther C. Brady
Keyword(s):  
Little Ice Age ◽  
South Atlantic ◽  
Subtropical Gyre ◽  
Ice Age ◽  
Surface Boundary ◽  
South American ◽  
Last Millennium ◽  
Medieval Climate Anomaly ◽  
The South ◽  
Gyre Circulation

Interocean waters that are carried northward through South Atlantic surface boundary currents get meridionally split between two large-scale systems when meeting the South American coast at the western subtropical portion of the basin. This distribution of the zonal flow along the coast is investigated during the Last Millennium, when natural forcing was key to establish climate variability. Of particular interest are the changes between the contrasting periods of the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA). The investigation is conducted with the simulation results from the Community Earth System Model Last Millennium Ensemble (CESM-LME). It is found that the subtropical South Atlantic circulation pattern differs substantially between these natural climatic extremes, especially at the northern boundary of the subtropical gyre, where the westward-flowing southern branch of the South Equatorial Current (sSEC) bifurcates off the South American coast, originating the equatorward-flowing North Brazil Undercurrent (NBUC) and the poleward Brazil Current (BC). It is shown that during the MCA, a weaker anti-cyclonic subtropical gyre circulation took place (inferred from decreased southern sSEC and BC transports), while the equatorward transport of the Meridional Overturning Circulation return flow was increased (intensified northern sSEC and NBUC). The opposite scenario occurs during the LIA: a more vigorous subtropical gyre circulation with decreased northward transport.

scholarly journals Projected End-of-Century Changes in the South American Monsoon in the CESM Large Ensemble

2020 ◽  
Vol 33 (18) ◽  
pp. 7859-7874
Author(s):  
Ana Claudia Thome Sena ◽  
Gudrun Magnusdottir
Keyword(s):  
South America ◽  
South Atlantic ◽  
Northeastern Brazil ◽  
Southeastern Brazil ◽  
South American ◽  
The South ◽  
Wet Season ◽  
Large Ensemble ◽  
South American Monsoon ◽  
The Mean

AbstractProjected changes in the South American monsoon system by the end of the twenty-first century are analyzed using the Community Earth System Model Large Ensemble (CESM-LENS). The wet season is shorter in LENS when compared to observations, with the mean onset occurring 19 days later and the mean retreat date 21 days earlier in the season. Despite a precipitation bias, the seasonality of rainfall over South America is reproduced in LENS, as well as the main circulation features associated with the development of the South American monsoon. Both the onset and retreat of the wet season over South America are delayed in the future compared to current climate by 3 and 7 days, respectively, with a slightly longer wet season. Central and southeastern Brazil are projected to get wetter as a result of moisture convergence from the strengthening of the South Atlantic low-level jet and a weaker South Atlantic subtropical high. The Amazon is projected to get drier by the end of the century, negatively affecting rain forest productivity. During the wet season, an increase in the frequency and intensity of extreme precipitation events is found over most of South America, and especially over northeastern and southern Brazil and La Plata. Meanwhile, during the dry season an increase in the maximum number of consecutive dry days is found over northeastern Brazil and the northern Amazon.

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