DOCSLIB.ORG

The South Atlantic: an Overview of Results from 1983-88 Research

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
The South Atlantic: an Overview of Results from 1983-88 Research FEATURE THE SOUTH ATLANTIC: AN OVERVIEW OF RESULTS FROM 1983-88 RESEARCH By Arnold L. Gordon ~ EACH of the major ocean basins is unique, but the Initiative (SAARI) meeting repoll are available from South Atlantic is unrivaled in its number of singular Dr. Garzoli at Lamont-Doherty Geological Observa- features. In its polar region are formed intermediate tory, Palisades, NY, 10964. What follows is an and bottom water masses that cool and lower the abbreviated account of the primary results in the salinity of much of the global ocean. The subtropical SAAR1 report. Names mentioned here without at- region has an eastern boundary that doesn't quite tributive dates refer to the report, in which additional extend to the latitude of maximum westerlies, allow- information and extensive references may be ob- A curious ing thernmcline communication with its counterpart tained: an abbreviated list of references is included at feature of the in the South Indian Ocean. Within the Argentine the end of the article. Basin of the South Atlantic one can sample deep Large Scale Circulation South Atlantic is water from the North Atlantic, deep and intermediate A curious feature of the South Atlantic is the the northward heat water from the Pacific, and bottom water formed in northward heat flux across 30°S, a consequence of the Weddell Sea. These water masses spread and the global thermohaline circulation cell driven by flux across 30°S vigorously mix within tiffs cosmopolitan basin and formation of North Atlantic Deep Water (NADW). throughout much of the South Atlantic. In the classical description, southward-moving Perhaps the most startling attribute of the South NADW is replaced by an upper layer return rio,:,' Atlantic is the significant equalorward heat flux derived from Pacific water, with the introduction of within the subtropical region. Estimates range from Antarctic Intermediate and Subantarctic Mode Wa- 18 to 86 x I()~W for the northward heat flux across ter (AAIW/SAMW: the latter terrn coined by Mc- the 8°S to 32°S belt. Associated with this flux is a Cartney ). Gordon (1986) suggested that at least some strong thennohaline circulation, as upper layer water of the return flow is derived from the thermocline spreads northward to compensate the southward water of the Indian Ocean, which has access to the export of colder North Atlantic Deep Water (NADW), South Atlantic around the southern tip of Africa. The The METEOR expedition of the 1920s and the relative influence of the wann and salty Indian water work during the International Geophysical Year (IG Y) and the colder and fresher Pacific water is crucial to of the late 1950s provide a glimpse of the large scale the larger scale climate system, because the Atlantic features of the South Atlantic Ocean. In the last five meridional heat and fresh water fluxes are very years there has been a surge in our appreciation of the sensitive to the ratio of the volume fluxes of the two South Atlantic phenomena, mainly because of an water types. Gordon suggested that up to 50~ of the Office of Naval Research Accelerated Research Ini- required flow could be derived from the Indian tiative entitled "'The Southern Ocean," which was Ocean pathway. primarily directed toward improvement of the de- The SAAR1 research does indeed present evi- scription of the subtropical South Atlantic. The pro- dence of Indian Ocean water intrusion into the South gram focused on the poleward "corners" of the sub- Atlantic (Olson and Evans, 1986; Gordon et al., tropical gyre: the separation of the Brazil Current and 1987). It is still unknown what part of that inflow its confluence with the Malvinas or Falkland Current eventually contributes to cross equatorial transport in in the southwest, and the Agulhas Retroflection and the upper ocean and what part returns to the Indian Benguela Current in the southeast. Ocean along a surface route south of the Agulhas In May 1988, a meeting was organized by Silvia Retroflection. The Agulhas "'leakage" into the Atlan- Garzoli to discuss the program accomplishments. tic Ocean need not involve thermohaline forcing at Copies of the South Atlantic Accelerated Research all, because purely wind-driven models of the Agulhas Retroflection reveal transfer of Indian Ocean water A. L. Gordon, Latnont-Dohertv Geoloc, ical Ohservato#p;. Pah- into the Atlantic (cf. Fig. 3, p. 16). xade,~, N.Y 10964. :With conttibutio~t,~ fiom particq~ant,~ in the The application of inverse methods to data from ONR-sponsored Soztt/t ,.trio/trio rdsedrch l~VOk,#'dnt: S. Bennett, D. the International Geophysical Year (IGY) reveals no Boudra, O. Brown, R.Evans, R. Fine. S. Garzoh, J. Luyten, M. McCartne>. D. Olson, G. Roden. T. Whitw'orth, P. Zemba. significant Indian Ocean flow into the Atlantic 1 2 OCEANOGRAPHY,NOVEMBER.1~)88 Figure 2: The Brazil Current, the western boundary current Atlantic in a regton known as the Brazil-Malvinas Cop~/luence. associated with the subtropical gyre in the South Atlantic Ocean. Warmest smface waters (approx. 25°C) are coded in red. The flows southward along the continental margin r(South America sulfate temperature decreases are color-coded through yellow to a point off Argentina and Uruguay where, in the mean, it and green: the dark blue shows the coldest water (approv. 9 ° C). separates fi'om the coast at about 36°S. The cold.fi'esh subantarc- The image was taken at a time when the Brazil Current was in its tic water in the Malvinas or Falkland Current meets the warm. southward extension and a large anticyclonic (warm) eddy or saline Brazil Current. and both turn eastward into the open rin~ was being./brined. (Rintoul, 1988). Gordon et al. (1987), using 1983 fresher when the Drake Passage route is favored? data, found 10 Sv of Agulhas water entering the Might this have important feedback to the production Atlantic (1 Sv = 106m3 s-~). Whitworth and Nowlin rate of NADW? (1987) calculated nearly 20 Sv of inflow using the The South Atlantic subtropical gyre has an elon- 1983/84 Ajax data set, which is subject to eddy gated crest stretching across the ocean near 30 °- aliasing because of a several month hiatus between 35°S. The gyre is marked at its poleward edge by the cruise legs. In her Ph.D. thesis, Bennett evaluated the Antarctic Circumpolar Current. The northern limb of 1985 CTD data from the Agulhas Retroflection and the subtropical gyre consists of a broad sweep to- found that only 2.8 Sv of water warmer than 9°C wards the northwest. In the northeastern comer of the flowed from the Indian into the Atlantic Ocean; her South Atlantic there is a weak cyclonic (clockwise) re-evaluation of the 1983 data set lowered the esti- gyre, described by Bosley and Gordon. The gyre is mate for that year to 6.3 Sv. formed by the South Equatorial Counter Current and If the Gordon suggestion is correct, it points to a the Angola Current, which flows southward along potentially significant climate issue: Might the At- the African coast. J. Reid clarified this complex lantic become warmer and saltier during periods pattern by defining the absolute geostrophic circula- when the Agulhas route is favored, versus colder and tion of the South Atlantic. OCEANOGRAPHY-NOVEMBER, 1988 13 The large scale circulation and the distribution of was in the process of separation, whereas the south- eddy' variability in the near surface layers of the ern one had been separated for at least a month and South Atlantic are another focus of research, pursued had been modified by the late winter atmosphere. by Olson. The dynamic height field relative to the These modified warm core eddies may not re-coa- 2000db level and surface velocities flom the SAARI lesce with the main thennocline, and hence they and FGGE drifter data sets show thai the 2000db represent a potentially significant salt flux into the reference level is best lk)r the eastern portion of the subantarctic zone of the South Atlantic. basin: however, that reference level clearly is inade- At depth, the most saline NADW is associated quate along the Brazilian coast, where the actual with the western meander of the Brazil Current. The level of no motion probably is higher in the water NADW continues tlowing south, beneath the Malv- column (cf. Fig. 1, p. 15). The drifter tracks also inas Current. which indicates that the separation of reveal the closed anticyclonic flows near the mid- the deep western boundary current need not be coher- Atlantic ridge that appear in most descriptions of the ent with the shallower thermocline separation lati- South Atlantic circulation. tude: this further complicates the definition of the BraziI-Malvinas Connuenee Brazil Current. Contrasting water masses are brought together in Piola and Gordon presented a detailed picture of the Argentine Basin by' a layer cake of boundary the AAIW/SAMW in the Argentine Basin. The ~, currents: The eddy-rich BraziI-Malvinas (Falkland) density interval 27.05 to 27.20 kg in 3 in the suban- Confluence dominates the upper layer, with deeper tarctic zone of the northern Drake Passage is charac- meridional flow involving NADW, Circumpolar terized by two water types with potential tempera- Deep Water and Antarctic Bottom Water. At the tures of 3.7 ° and 4.8~C, respectively: both have meeting, there was not complete agreement as to the salinity of approximately 34.2 ppt. Thermohaline Contrasting exact definition of the Brazil Current, but in general, characteristics are modified by, winter sea-air inter- water masses are reference to the Brazil Current is confined to its action near Burdwood Bank and by' mixing with the thermocline expression.
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]
  • Simulation of Current Dynamics and Disintegration in Drake Passage with the Regional Ocean Modelling System (ROMS)
    Simulation of current dynamics and disintegration in Drake Passage with the Regional Ocean Modelling System (ROMS) OPB205 MODELISATION OF OCEAN CIRCULATION Master Oceanography, first year 2015 – 2016 Project by Maximilian Unterberger, under direction of Mr. Andrea Doglioli (Assistant Professor in Physical Oceanography, Mediterranean Institute of Oceanography) 30 April 2016 OPB205 Maximilian Unterberger Abstract The influences of current dynamics and disintegration on the Drake Passage in the Southern Ocean is expected to be significant. A boundary current that originates in the South Pacific is entering the Drake Passage in the east and disintegrates inside it in a set of anticyclonic eddies. The integration might be essential for the mixing in the passage and the formation of the Circumpolar Deep Water and thus be necessary for the inducement of the Antarctic Circumpolar Current (ACC) which effects the global Meridional Overturning Circulation (MOC). This theory is assembled and further investigated by J. Alexander Brearley et al. (2014). In dependence of their findings, this work focuses on the same dynamic processes in the Drake Passage. With the regional ocean model simulation (ROMS) software, simulations shall give information about the extremely complex regional activities and the possible impact on MOC. Obtained results with ROMS show deep water masses of low salinity and high temperature originated in the east pacific, flowing partly along the Cape horn but mainly entering the passage directly. This indicates the disintegration of Pacific Deep Water. The integrated current is also visible in the passage in form of a major anticyclonic eddy which with similar temperature and salinity properties and an appearance over the whole water column.
    [Show full text]
  • The Structure and Transport of the Agulhas Return Current
    The Structure and Transport of the Agulhas Return Current Isabelle Jane Ansorge Submitted in fulfillment of the requirements of the Master of Science degree Department of Oceanography University of Cape Town 1996 University of Cape Town The copyright of this thesis vests in the author. No quotation from it or information derived from it is to be published without full acknowledgement of the source. The thesis is to be used for private study or non- commercial research purposes only. Published by the University of Cape Town (UCT) in terms of the non-exclusive license granted to UCT by the author. University of Cape Town I ABSTRACT The Agulhas Current flows along the eastern coast of southern Africa as one of the largest western boundary currents in the world's ocean. On overshooting the southern tip of Africa at approximately 20°E, a retroflection loop is formed that causes the current to double back on itself and to fonn the easterly flowing Agulhas Return Current. No focussed investigation to establish the hydrography of this imponant component of global ocean circulation has to date been carried out. To trace the Agulhas Return Current's passage eastwards into the South Indian Ocean, data collected from six CTD hydrographic cruises; AJAX, ARC, SCARC, Marathon, Discovery 164 and SUZIL, as well as from three XBT temperature cruises,· Marion 83, Gallieni 72 and FIBEX, have been analysed. It is shown that the Agulhas Return Current initially flows zonally from 20°-25°E at a latitude approximately 39°30'-40°30'S before forming a planetary wave over the Agulhas Plateau between 25°-28°E.
    [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]
  • Joint Geological Survey/University of Cape Town MARINE GEOSCIENCE UNIT TECHNICAL ^REPORT NO. 13 PROGRESS REPORTS for the YEARS 1
    Joint Geological Survey/University of Cape Town MARINE GEOSCIENCE UNIT TECHNICAL ^REPORT NO. 13 PROGRESS REPORTS FOR THE YEARS 1981-1982 Marine Geoscience Group Department of Geology University of Cape Town December 1982 NGU-Tfc—Kh JOINT GEOLOGICAL SURVEY/UNIVERSITY OF CAPE TOWN MARINE GEOSCIENCE UNIT TECHNICAL REPORT NO. 13 PROGRESS REPORTS FOR THE YEARS 1981-1982 Marine Geoscience Group Department of Geology University of Cape Town December 1982 The Joint Geological Survey/University of Cape Town Marine Geoscience Unit is jointly funded by the two parent organizations to promote marine geoscientific activity in South Africa. The Geological Survey Director, Mr L.N.J. Engelbrecht, and the University Research Committee are thanked for their continued generous financial and technical support for this work. The Unit was established in 1975 by the amalgamation of the Marine Geology Programme (funded by SANCOR until 1972) and the Marine Geophysical Unit. Financial ?nd technical assistance from the South African National Committee for Oceanographic Research, and the National Research Institute for Oceanology (Stellenbosch) are also gratefully acknowledged. It is the policy of the Geological Survey and the University of Cape Town that the data obtained may be presented in the form of theses for higher degrees and that completed projects shall be published without delay in appropriate media. The data and conclusions contained in this report are made available for the information of the international scientific community with tl~e request that they be not published in any manner without written permission. CONTENTS Page INTRODUCTION by R.V.Dingle i PRELIMINARY REPORT ON THE BATHYMETRY OF PART OF 1 THE TRANSKEI BASIN by S.H.
    [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]
  • 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.
    [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]
  • International Ocean Discovery Program Expedition 361 Preliminary Report South African Climates (Agulhas LGM Density Profile)
    International Ocean Discovery Program Expedition 361 Preliminary Report South African Climates (Agulhas LGM Density Profile) 30 January–31 March 2016 Ian R. Hall, Sidney R. Hemming, Leah J. LeVay, and the Expedition 361 Scientists Publisher’s notes Core samples and the wider set of data from the science program covered in this report are under moratorium and accessible only to Science Party members until 30 September 2017. This publication was prepared by the JOIDES Resolution Science Operator (JRSO) at Texas A&M University (TAMU) as an account of work performed under the International Ocean Discovery Pro- gram (IODP). Funding for IODP is provided by the following international partners: National Science Foundation (NSF), United States Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan European Consortium for Ocean Research Drilling (ECORD) Ministry of Science and Technology (MOST), People’s Republic of China Korea Institute of Geoscience and Mineral Resources (KIGAM) Australia-New Zealand IODP Consortium (ANZIC) Ministry of Earth Sciences (MoES), India Coordination for Improvement of Higher Education Personnel, Brazil (CAPES) Portions of this work may have been published in whole or in part in other International Ocean Discovery Program documents or publications. Disclaimer Any opinions, findings, and conclusions or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the participating agencies, TAMU, or Texas A&M Research Foundation. Copyright Except where otherwise noted, this work is licensed under a Creative Commons Attribution License. Unrestricted use, distribution, and reproduction is permitted, provided the original author and source are credited. Citation Hall, I.R., Hemming, S.R., LeVay, L.J., and the Expedition 361 Scientists, 2016.
    [Show full text]
  • JOIDES Resolution Expedition 361 (Southern African Climates) Site
    IODP Expedition 361: Southern African Climates Site U1475 Summary Background and Objectives Site U1475 is located on the southwestern flank of Agulhas Plateau (41°25.61′S, 25°15.64′E), ~450 nmi south of Port Elizabeth, South Africa, in a water depth of 2669 mbsl. The Agulhas Plateau, which was formed during the early stages of the opening of the South Atlantic about 90 Ma (Parsiegla et al., 2008), is a major bathymetric high that is variably coated with sediments (Uenzelmann Neben, 2001). The 230,000 km2 plateau, which ascends up to ~2500 m above the adjacent seafloor, is bounded on the north by the 4700 m deep Agulhas Passage and is flanked by the Agulhas Basin in the west and the Transkei Basin in the northeast. The northern part of the plateau is characterized by rugged topography, while the central and southern part of the plateau exhibits a relatively smooth topography (Allen and Tucholke, 1981) and has greater sediment thickness (Uenzelmann Neben, 2001). A strong water mass transport flows across the Agulhas Plateau region (Macdonald, 1993), which involves the water column from the surface down to Upper Circumpolar Deep Water. The hydrography of the upper ocean is dominated by the Agulhas Return Current, which comprises the component of the Agulhas Current that is not leaked to the South Atlantic Ocean but rather flows eastwards from the retroflection (Lutjeharms and Ansorge, 2001). Antarctic Intermediate Water, below the Agulhas Return Current, also follows the same flow path near South Africa as the Agulhas Current showing a similar retroflection (Lutjeharms, 1996).
    [Show full text]