DOCSLIB.ORG

Transport Variability of the Brazil Current from Observations and a Data Assimilation Model

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Transport Variability of the Brazil Current from Observations and a Data Assimilation Model Ocean Sci., 14, 417–436, 2018 https://doi.org/10.5194/os-14-417-2018 © Author(s) 2018. This work is distributed under the Creative Commons Attribution 4.0 License. Transport variability of the Brazil Current from observations and a data assimilation model Claudia Schmid1 and Sudip Majumder1,2 1National Oceanic and Atmospheric Administration, Atlantic Oceanographic and Meteorological Laboratory, Miami, Florida, USA 2Cooperative Institute for Marine and Atmospheric Studies, University of Miami, Miami, FL, USA Correspondence: Claudia Schmid ([email protected]) Received: 6 July 2017 – Discussion started: 4 August 2017 Revised: 1 March 2018 – Accepted: 14 May 2018 – Published: 7 June 2018 Abstract. The Brazil Current transports from observations the meridional transport and the sea level pressure explain and the Hybrid Coordinate Model (HYCOM) model are ana- 36 and 15 % of the covariance, respectively. Overall, the re- lyzed to improve our understanding of the current’s structure sults indicate that SAM, SASD, and El Niño–Southern Os- and variability. A time series of the observed transport is de- cillation have an influence on the transport of the Brazil Cur- rived from a three-dimensional field of the velocity in the rent. South Atlantic covering the years 1993 to 2015 (hereinafter called Argo & SSH). The mean transports of the Brazil Cur- rent increases from 3.8 ± 2.2 Sv (1 Sv is 106 m3 s−1) at 25◦ S to 13.9 ± 2.6 Sv at 32◦ S, which corresponds to a mean 1 Introduction slope of 1.4 ± 0.4 Sv per degree. Transport estimates derived from HYCOM fields are somewhat higher (5.2 ± 2.7 and The circulation in the South Atlantic has been studied exten- 18.7 ± 7.1 Sv at 25 and 32◦ S, respectively) than those from sively because it is an important part of the Atlantic Merid- Argo & SSH, but these differences are small when compared ional Overturning Circulation, which consists of a northward with the standard deviations. Overall, the observed latitude transport of relatively warm and fresh upper-ocean water of dependence of the transport of the Brazil Current is in agree- southern origin across the equator into the northern North At- ment with the wind-driven circulation in the super gyre of the lantic and a southward transport of relatively cold and salty subtropical South Atlantic. A mean annual cycle with high- deep water from the North Atlantic into the South Atlantic. est (lowest) transports in austral summer (winter) is found A summary of the circulation in the South Atlantic as well as to exist at selected latitudes (24, 35, and 38◦ S). The signif- the pathways of the flow and its role in the Atlantic Merid- icance of this signal shrinks with increasing latitude (both ional Overturning Circulation has been presented by Schmid in Argo & SSH and HYCOM), mainly due to mesoscale and (2014) and many others (references can be found in Schmid, interannual variability. Both Argo & SSH, as well as HY- 2014). COM, reveal interannual variability at 24 and 35◦ S that re- Herein, the focus is on the structure and variability of the sults in relatively large power at periods of 2 years or more Brazil Current, which is the western boundary current of in wavelet spectra. It is found that the interannual variabil- the subtropical gyre in the South Atlantic. This subtropical ity at 24◦ S is correlated with the South Atlantic Subtropical gyre is largely governed by the Sverdrup equation (Pond and Dipole Mode (SASD), the Southern Annular Mode (SAM), Pickard, 1983) and is part of the super gyre (Gordon et al., and the Niño 3.4 index. Similarly, correlations between SAM 1992; de Ruijter, 1982) which connects the subtropical circu- and the Brazil Current transport are also found at 35◦ S. Fur- lation in the South Indian and South Atlantic oceans. Mostly, ther investigation of the variability reveals that the first and the Brazil Current follows the shelf break quite closely, but second mode of a coupled empirical orthogonal function of it is impacted by mesoscale variability along its pathway that can give rise to meanders that separate it from the shelf break Published by Copernicus Publications on behalf of the European Geosciences Union. 418 C. Schmid and S. Majumder: Brazil Current transport temporarily (e.g., Schmid et al., 1995; Biló et al., 2014; Mill 18° S et al., 2015; Lima et al., 2016). As the Brazil Current reaches the confluence with the Malvinas Current, it is forced away 20 from the shelf break and ultimately feeds into the eastward 22 South Atlantic Current (e.g., Gordon, 1989; Garzoli, 1993; 24 Maamaatuaiahutapu et al., 1998). Just prior to this eastward 26 turn the southward transport increases due to the contribu- 28 tion from the Malvinas Current. Determining the source and 30 variability of the Malvinas Current (e.g., Vivier and Provost, 1999; Spadone and Provost, 2009) as well as what happens 32 east of the confluence is beyond the scope of this study. 34 Another feature of the circulation in this region is a north- 36 ward flow just east of the Brazil Current that originates near 38° S the confluence and is part of a recirculation cell that feeds -30 -25 -20 -15 -10 -5 0 back into the Brazil Current. This recirculation cell has been Transport [Sv] described earlier (e.g., Stramma, 1989) and has been called the Brazil Current Front (e.g., Peterson and Stramma, 1991) Figure 1. Previously published estimates of the Brazil Current as well as the Brazil Return Current (e.g., Boebel et al., transports as a function of latitude. The line with a slope of about 1997). 1.6 Sv per degree is a fit to the transports measured in 19 to 32◦ S. The transport of the Brazil Current estimated in earlier The sources of the transport estimates are Fisher(1964), Signorini studies varies from north to south (Fig.1). This transport is (1978), Miranda and Castro Filho(1979), Miranda and Castro Filho within 1 to 7 Sv (1 Sv is 106 m3 s−1) between 19 and 22.5◦ S (1981), Evans et al.(1983), Evans and Signorini(1985), Gordon and in the upper 400 to 500 m and increases to about 17 Sv at Greengrove(1986), Garzoli and Garraffo(1989), Gordon(1989), Stramma(1989), Garfield(1990), Peterson(1990), Stramma et al. 28◦ S as the vertical extent and strength of the Brazil Cur- (1990), Zemba(1991), Garzoli(1993), Campos et al.(1995), Maa- rent increases. Farther south the Brazil Current transports are maatuaiahutapu et al.(1998), Müller et al.(1998), Jullion et al. mostly in the range of 10 to 30 Sv. Most of the estimates from (2006), Mata et al.(2012), Garzoli et al.(2013), and Biló et al. earlier studies are based on quasi-synoptic sections, while (2014). some are based on time series from moorings with current meters or inverted echo sounders (IESs). Previous studies of the temporal variability were typi- using climatology (e.g., Garzoli et al., 2013; Majumder et al., cally limited in terms of the length of the time series (e.g., 2016). Rocha et al., 2013) and the number of surveys (e.g., Mata In summary, this study will build on the earlier results with et al., 2012) or derived as a time series at one location (e.g., the focus on improving the knowledge about the mean trans- Goni and Wainer, 2001). In addition, studies based on hy- port of the Brazil Current and its variability. In preparation drographic measurements had to use a level of no motion or for this analysis a monthly observations-based time series of make assumptions about the barotropic flow (e.g., by pre- three-dimensional fields of the horizontal velocity was de- scribing a bottom velocity). The large variations in the trans- rived. This time series covers 23 years with a horizontal grid ports from the previous studies as well as the limited knowl- resolution of 0.5◦. The underlying dynamics of the observed edge about the temporal variability of the Brazil Current mo- variability on seasonal to interannual timescales are studied tivated this study on the characteristics and variability of this in conjunction with several ocean indices and sea level pres- current at a wide range of latitudes. sure as a proxy for the wind field that is forcing the subtrop- Another motivation is that, as is well known, estimates of ical gyre. the Atlantic Meridional Overturning Circulation transports The paper is organized as follows. Section2 describes the derived from various observational products and models of- data and methods. Sections3 and4 analyze the structure and ten reveal similar amplitudes of the variability but can have variability of the Brazil Current transport. Section5 summa- significant differences when the means are compared. For the rizes the results. North Atlantic, this was shown, for example, by Msadek et al. (2014). The same is the case in the South Atlantic. An impor- tant challenge for Atlantic Meridional Overturning Circula- 2 Data and methodology tion transport calculations is the estimation of the transport in the western boundary current (the Brazil Current in the sub- Three oceanic data sets are used herein to derive an absolute tropical South Atlantic). All estimates of this transport face three-dimensional geostrophic velocity field. They are pro- the challenge of deriving the contributions on and often also files of temperature and salinity, subsurface velocities from near the shelf break. Typically, this challenge is resolved by float trajectories, and sea surface heights. In addition, wind fields are needed to estimate the Ekman velocity that needs Ocean Sci., 14, 417–436, 2018 www.ocean-sci.net/14/417/2018/ C.
Load more

Recommended publications
  • Fronts in the World Ocean's Large Marine Ecosystems. ICES CM 2007
    - 1 - This paper can be freely cited without prior reference to the authors International Council ICES CM 2007/D:21 for the Exploration Theme Session D: Comparative Marine Ecosystem of the Sea (ICES) Structure and Function: Descriptors and Characteristics Fronts in the World Ocean’s Large Marine Ecosystems Igor M. Belkin and Peter C. Cornillon Abstract. Oceanic fronts shape marine ecosystems; therefore front mapping and characterization is one of the most important aspects of physical oceanography. Here we report on the first effort to map and describe all major fronts in the World Ocean’s Large Marine Ecosystems (LMEs). Apart from a geographical review, these fronts are classified according to their origin and physical mechanisms that maintain them. This first-ever zero-order pattern of the LME fronts is based on a unique global frontal data base assembled at the University of Rhode Island. Thermal fronts were automatically derived from 12 years (1985-1996) of twice-daily satellite 9-km resolution global AVHRR SST fields with the Cayula-Cornillon front detection algorithm. These frontal maps serve as guidance in using hydrographic data to explore subsurface thermohaline fronts, whose surface thermal signatures have been mapped from space. Our most recent study of chlorophyll fronts in the Northwest Atlantic from high-resolution 1-km data (Belkin and O’Reilly, 2007) revealed a close spatial association between chlorophyll fronts and SST fronts, suggesting causative links between these two types of fronts. Keywords: Fronts; Large Marine Ecosystems; World Ocean; sea surface temperature. Igor M. Belkin: Graduate School of Oceanography, University of Rhode Island, 215 South Ferry Road, Narragansett, Rhode Island 02882, USA [tel.: +1 401 874 6533, fax: +1 874 6728, email: [email protected]].
    [Show full text]
  • The Brazil Current Transport South of 23°S
    Deep-Sea Research, Vol. 36, No. 4, pp. 639-646, 1989. 0198-0149/89 $3.00 + 0.00 Printed in Great Britain. © 1989 Pergamon Press plc. NOTE The Brazil Current transport south of 23°S LOTHAR STRAMMA* (Received 26 August 1988; in revised form 15 November 1988; accepted 30 November 1988) Al~trnet--Geostrophic computations from historical data across the Brazil Current at 23 ° and 24°S lead to transports of 10.2 and 9.6 Sv, respectively. Data exist from all four seasons at about 24°S, but no seasonal signal can be seen in the baroclinic transport of the Brazil Current there. At 33"S the Brazil Current transport is estimated to be 17.5 Sv. A recirculation cell of 7.5 Sv is found in the western South Atlantic south of 280S. The major problem in computing transport of the Brazil Current is not with determining the correct reference depth, but with the Brazil Current flowing partially over the shelf and therefore not being sampled completely by deep-water hydrographic stations. As long as the vertical distribution of water masses is taken into account for choosing a reference depth, geostrophic computations lead to results consistent with previous estimates. INTRODUCTION Tim Brazil Current has long been known to transport substantially less water than the Gulf Stream (STOMMEL, 1957), its counterpart in the North Atlantic, and, compared to the Gulf Stream, the Brazil Current has been sampled to a much lesser extent. Most transport estimates for the Brazil Current have been in two regions: near Rio de Janeiro and in the Brazil-Falkland Confluence Zone.
    [Show full text]
  • Future Changes to the Upper Ocean Western Boundary Currents Across Two Generations of Climate Models Alex Sen Gupta1,2,3*, Annette Stellema1,2,3, Gabriel M
    www.nature.com/scientificreports OPEN Future changes to the upper ocean Western Boundary Currents across two generations of climate models Alex Sen Gupta1,2,3*, Annette Stellema1,2,3, Gabriel M. Pontes4, Andréa S. Taschetto1,2, Adriana Vergés3,5 & Vincent Rossi6 Western Boundary Currents (WBCs) are important for the oceanic transport of heat, dissolved gases and nutrients. They can afect regional climate and strongly infuence the dispersion and distribution of marine species. Using state-of-the-art climate models from the latest and previous Climate Model Intercomparison Projects, we evaluate upper ocean circulation and examine future projections, focusing on subtropical and low-latitude WBCs. Despite their coarse resolution, climate models successfully reproduce most large-scale circulation features with ensemble mean transports typically within the range of observational uncertainty, although there is often a large spread across the models and some currents are systematically too strong or weak. Despite considerable diferences in model structure, resolution and parameterisations, many currents show highly consistent projected changes across the models. For example, the East Australian Current, Brazil Current and Agulhas Current extensions are projected to intensify, while the Gulf Stream, Indonesian Throughfow and Agulhas Current are projected to weaken. Intermodel diferences in most future circulation changes can be explained in part by projected changes in the large-scale surface winds. In moving to the latest model generation, despite structural model advancements, we fnd little systematic improvement in the simulation of ocean transports nor major diferences in the projected changes. Anthropogenic climate change manifests as increases in surface temperature and sea level, rainfall distribution changes and increasing frequency and intensity of certain extreme events1.
    [Show full text]
  • Mapping Climatological Seasonal Variations of Surface Currents in the Tropical Atlantic Using Ship Drifts
    JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 91, NO. C9, PAGES 10,537-10,550, SEPTEMBER 15, 1986 Mapping Climatological Seasonal Variations of Surface Currents in the Tropical Atlantic Using Ship Drifts PHILIP L. RICHARDSON AND DAVID WALSH Woods Hole Oceanographic Institution, Woods Hole, Massachusetts The seasonal variability of current velocities in the tropical Atlantic was studied by grouping ship drift velocity observations into 2ø x 5ø boxes and calculating monthly mean velocity values. These values were used to calculate and map the annual mean velocity, the seasonal variation about the mean, the annual and semiannual harmonics, and the first two empirical orthogonal functions (EOFs). The seasonal variation is primarily zonal in the equatorial band and in the North Equatorial Countercurrent (NECC) and primarily alongshore near the coast of South America. Maxima of seasonal variation of 23 cm/s are centered in the NECC near 6øN, 42.5øW and in the Gulf of Guinea near 2øN, 7.5øW. Most (-80%) of the variance in the NECC and along the western boundary of the area studied has an annual period; most of the variance along the equator in the mid-Atlantic has a semiannual period. Over the whole region, 49% of the seasonalvariance is explained by the annual harmonic, and 69% is explained by a combination of the annual and semiannual harmonics. The second EOF contains 29% of the variance of the data set and shows a simultaneousspeeding (slowing) of the major equatorial currents (the South Equatorial Current (SEC), the North Brazil Current, the NECC, and the Guinea Current) along their principal axes of variation with a concurrent slowing (speeding) of the Guyana Current and the Brazil Current.
    [Show full text]
  • Global Ocean Surface Velocities from Drifters: Mean, Variance, El Nino–Southern~ Oscillation Response, and Seasonal Cycle Rick Lumpkin1 and Gregory C
    JOURNAL OF GEOPHYSICAL RESEARCH: OCEANS, VOL. 118, 2992–3006, doi:10.1002/jgrc.20210, 2013 Global ocean surface velocities from drifters: Mean, variance, El Nino–Southern~ Oscillation response, and seasonal cycle Rick Lumpkin1 and Gregory C. Johnson2 Received 24 September 2012; revised 18 April 2013; accepted 19 April 2013; published 14 June 2013. [1] Global near-surface currents are calculated from satellite-tracked drogued drifter velocities on a 0.5 Â 0.5 latitude-longitude grid using a new methodology. Data used at each grid point lie within a centered bin of set area with a shape defined by the variance ellipse of current fluctuations within that bin. The time-mean current, its annual harmonic, semiannual harmonic, correlation with the Southern Oscillation Index (SOI), spatial gradients, and residuals are estimated along with formal error bars for each component. The time-mean field resolves the major surface current systems of the world. The magnitude of the variance reveals enhanced eddy kinetic energy in the western boundary current systems, in equatorial regions, and along the Antarctic Circumpolar Current, as well as three large ‘‘eddy deserts,’’ two in the Pacific and one in the Atlantic. The SOI component is largest in the western and central tropical Pacific, but can also be seen in the Indian Ocean. Seasonal variations reveal details such as the gyre-scale shifts in the convergence centers of the subtropical gyres, and the seasonal evolution of tropical currents and eddies in the western tropical Pacific Ocean. The results of this study are available as a monthly climatology. Citation: Lumpkin, R., and G.
    [Show full text]
  • The Sargassum Invasion of the Eastern Caribbean and Dynamics of the Equatorial North Atlantic
    The Sargassum Invasion of the Eastern Caribbean and Dynamics of the Equatorial North Atlantic Invasión de Sargazo en el Caribe Oriental y la Dinámica en la Zona Ecuatorial del Atlántico Norte L'Invasion de Sargasse dans les Caraïbes Orientales et leur Dynamique dans la Partie Nord de l'Atlantique Ėquatorial DONALD R. JOHNSON1*, DONG S. KO2, JAMES S. FRANKS1, PAULA MORENO1, and GUILLERMO SANCHEZ-RUBIO1 1Center for Fisheries Research and Development, Gulf Coast Research Laboratory, University of Southern Mississippi, Ocean Springs, Mississippi 39564 USA. *[email protected]. [email protected]. [email protected]. [email protected]. 2Ocean Dynamics and Prediction Branch, Naval Research Laboratory, Stennis Space Center, Mississippi 39529 USA. [email protected]. EXTENDED ABSTRACT In the spring and summer of 2011, unprecedented quantities of pelagic sargassum came ashore on many islands of the eastern Caribbean (Figure 1), seriously affecting fishery and tourism industries. Concurrently, pelagic sargassum also washed ashore in massive amounts along the coasts of western Africa (Sierra Leone and Benin) and was spotted in large mats by aircraft off northern Brazil (Széchy et al. 2012). Two species were identified in the invasion: Sargassum natans and Sargassum fluitans, both of which coexist throughout the North Atlantic with large mats and long lines commonly found in the Sargasso Sea (Winge 1923) and in the northern Gulf of Mexico (Comyns et al. 2002). Using satellite tracked mixed- layer drifters during 2010 and 2011 we were unable to connect the Caribbean invasion to the central North Atlantic and the Sargasso Sea. However, from archived results of a numerical circulation model (HYCOM), back-tracking from where landfalls were reported suggested that the sargassum may have bloomed in the north equatorial recirculation region (NERR) where conditions in the spring/summer of 2010 were conducive to growth and consolidation.
    [Show full text]
  • Atlantic Ocean Equatorial Currents
    188 ATLANTIC OCEAN EQUATORIAL CURRENTS ATLANTIC OCEAN EQUATORIAL CURRENTS S. G. Philander, Princeton University, Princeton, Centered on the equator, and below the westward NJ, USA surface Sow, is an intense eastward jet known as the Equatorial Undercurrent which amounts to a Copyright ^ 2001 Academic Press narrow ribbon that precisely marks the location of doi:10.1006/rwos.2001.0361 the equator. The undercurrent attains speeds on the order of 1 m s\1 has a half-width of approximately Introduction 100 km; its core, in the thermocline, is at a depth of approximately 100 m in the west, and shoals to- The circulations of the tropical Atlantic and PaciRc wards the east. The current exists because the west- Oceans have much in common because similar trade ward trade winds, in addition to driving divergent winds, with similar seasonal Suctuations, prevail westward surface Sow (upwelling is most intense at over both oceans. The salient features of these circu- the equator), also maintain an eastward pressure lations are alternating bands of eastward- and west- force by piling up the warm surface waters in the ward-Sowing currents in the surface layers (see western side of the ocean basin. That pressure force Figure 1). Fluctuations of the currents in the two is associated with equatorward Sow in the thermo- oceans have similarities not only on seasonal but cline because of the Coriolis force. At the equator, even on interannual timescales; the Atlantic has where the Coriolis force vanishes, the pressure force a phenomenon that is the counterpart of El Ninoin is the source of momentum for the eastward Equa- the PaciRc.
    [Show full text]
  • State of the Climate in 2010
    State of the climate in 2010 Citation Blunden, J., D. S. Arndt, and M. O. Baringer. “State of the Climate in 2010.” Bulletin of the American Meteorological Society 92 (2011): S1-S236. Web. 8 Dec. 2011. © 2011 American Meteorological Society As Published http://dx.doi.org/10.1175/1520-0477-92.6.S1 Publisher American Meteorological Society Version Final published version Accessed Mon Mar 26 14:41:06 EDT 2012 Citable Link http://hdl.handle.net/1721.1/67483 Terms of Use Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. Detailed Terms J. Blunden, D. S. Arndt, and M. O. Baringer, Eds. Associate Eds. H. J. Diamond, A. J. Dolman, R. L. Fogt, B. D. Hall, M. Jeffries, J. M. Levy, J. M. Renwick, J. Richter-Menge, P. W. Thorne, L. A. Vincent, and K. M. Willett Special Supplement to the Bulletin of the American Meteorological Society Vol. 92, No. 6, June 2011 STATE OF THE CLIMATE IN 2010 STATE OF THE CLIMATE IN 2010 JUNE 2011 | S1 HOW TO CITE THIS DOCUMENT __________________________________________________________________________________________ Citing the complete report: Blunden, J., D. S. Arndt, and M. O. Baringer, Eds., 2011: State of the Climate in 2010. Bull. Amer. Meteor. Soc., 92 (6), S1 –S­­­266. Citing a chapter (example): Fogt, R. L., Ed., 2011: Antarctica [in “State of the Climate in 2010”]. Bull. Amer. Meteor. Soc., 92 (6), S161 –S171. Citing a section (example): Wovrosh, A. J., S. Barreira, and R.
    [Show full text]
  • Ecologically Or Biologically Significant Marine Areas (Ebsas) Special Places in the World’S Oceans
    2 Ecologically or Biologically Significant Marine Areas (EBSAs) Special places in the world’s oceans WIDER CARIBBEAN AND WESTERN MID-ATLANTIC Areas described as meeting the EBSA criteria at the CBD Wider Caribbean and Western Mid-Atlantic Regional Workshop in Recife, Brazil, 28 February to 2 March 2012 Published by the Secretariat of the Convention on Biological Diversity. ISBN: 92-9225-560-6 Ecologically or Copyright © 2014, Secretariat of the Convention on Biological Diversity. The designations employed and the presentation of material in this publication do not imply the expression Biologically Significant of any opinion whatsoever on the part of the Secretariat of the Convention on Biological Diversity concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. Marine Areas (EBSAs) The views reported in this publication do not necessarily represent those of the Secretariat of the Convention on Biological Diversity. Special places in the world’s oceans The European Commission support for the production of this publication does not constitute endorsement of the contents which reflects the views only of the authors, and the Commission cannot be held responsi ble for Areas described as meeting the EBSA criteria at the any use which may be made of the information contained therein. CBD Wider Caribbean and Western Mid-Atlantic Regional This publication may be reproduced for educational or non-profit purposes without special permission from the copyright holders, provided acknowledgement of the source is made. The Secretariat of the Convention on Workshop in Recife, Brazil, 28 February to 2 March 2012 Biological Diversity would appreciate receiving a copy of any publications that use this document as a source.
    [Show full text]
  • Upper-Level Circulation in the South Atlantic Ocean
    Prog. Oceanog. Vol. 26, pp. 1-73, 1991. 0079 - 6611/91 $0.00 + .50 Printed in Great Britain. All fights reserved. © 1991 Pergamon Press pie Upper-level circulation in the South Atlantic Ocean RAY G. P~-rwtSON and LOTHAR Sa~AMMA lnstitut fiir Meereskunde an der Universitiit Kiel, Diisternbrooker Weg 20, 2300 Kiel 1, F.R.G. Abstract - In this paper we present a literature survey of the South Atlantic's climate and its oceanic upper-layer circulation and meridional beat transport. The opening section deals with climate and is focused upon those elements having greatest oceanic relevance, i.e., distributions of atmospheric sea level pressure, the wind fields they produce, and the net surface energy fluxes. The various geostrophic currents comprising the upper-level general circulation are then reviewed in a manner organized around the subtropical gyre, beginning off southern Africa with the Agulhas Current Retroflection and then progressing to the Benguela Current, the equatorial current system and circulation in the Angola Basin, the large-scale variability and interannual warmings at low latitudes, the Brazil Current, the South Atlantic Cmrent, and finally to the Antarctic Circumpolar Current system in which the Falkland (Malvinas) Current is included. A summary of estimates of the meridional heat transport at various latitudes in the South Atlantic ends the survey. CONTENTS 1. Introduction 2 2. Climatic Elements 2 3. Subtropical and Equatorial Circulation 11 3.1. Agulhas Current Retroflection 11 3.2. Benguela Cmrent 16 3.3. Equatorial Cttrrents 18 3.3.1. Components of the system 18 3.3.2. Angola Basin circulation 26 3.3.3.
    [Show full text]
  • Long‐Term Monitoring of the Brazil Current Trans-Port at 22 S from XBT
    RESEARCH ARTICLE Long‐Term Monitoring of the Brazil Current Transport 10.1029/2018JC014809 at 22°S From XBT and Altimetry Data: Seasonal, Key Points: • Seasonal variability of the BC is out‐ Interannual, and Extreme Variability ‐ of phase with the Sverdrup transport M. Goes1,2 , M. Cirano3 , M. M. Mata4 , and S. Majumder1,2,5 due to baroclinic adjustment • The BC transport variability is 1Cooperative Institute for Marine and Atmospheric Studies (CIMAS), University of Miami, Miami, FL, USA, 2Atlantic associated to the wind stress curl in the western part of the basin and Oceanographic and Meteorological Laboratory, National Oceanic and Atmospheric Administration, Miami, FL, USA, coastal upwelling 3Department of Meteorology, Institute of Geosciences, Federal University of Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil, • In the 2009/2010 event, anticyclonic 4Institute of Oceanography, Federal University of Rio Grande (FURG), Rio Grande, Brazil, 5Now at Department of Marine winds lower the coastal sea level, Sciences, University of Georgia, Athens, GA, USA and warm anomalies increase sea level offshore, strengthening the BC Abstract The seasonal and interannual variability of the Brazil Current (BC) at 22°S is examined using Supporting Information: ‐ • Supporting Information S1 expendable bathythermograph (XBT) transect and satellite altimetry data from 1993 to 2017. The XBT based • Figure S1 mean absolute geostrophic transport of the BC is estimated as 4.7 ± 1.9 Sv, with additional 0.9 ± 0.9 Sv • Figure S2 along the shelf. The strong agreement between the absolute dynamic height and altimetric sea surface height is used in two methods to reconstruct a daily time series of the BC transport since 1993.
    [Show full text]
  • Meridional Changes in the South Atlantic Subtropical Gyre During Heinrich Stadials Tainã M
    www.nature.com/scientificreports OPEN Meridional changes in the South Atlantic Subtropical Gyre during Heinrich Stadials Tainã M. L. Pinho1*, Cristiano M. Chiessi2, Rodrigo C. Portilho‑Ramos3, Marília C. Campos1, Stefano Crivellari2, Rodrigo A. Nascimento4, Ana L. S. Albuquerque4, André Bahr5 & Stefan Mulitza3 Subtropical 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 ofer 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 fuctuations of the SASG over last ca. 70 kyr. Our fndings 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. Subtropical gyres are large systems of anticyclonic upper ocean circulation driven by wind stress curl 1, 2, char- acterized as enormous reservoirs of heat and salt3.
    [Show full text]