The South Atlantic: Present and Past Circulation

644 Pages·1996·47.255 MB·English

by  Prof. Dr. Gerold Wefer, Prof. Dr. Wolfgang H. Berger, Prof. Dr. Gerold Siedler, Dr. David J. Webb (auth.)

The
South Atlantic
Present and Past Circulation
With 346 Figures and 42 Tables
, Springer
PROF. DR. GEROLD WEFER ISBN-13: 978-3-642-80355-0
Universitat Bremen
Fachbereich Geowissenschaften
Klagenfu.rter StraBe
28359 Bremen elP-Data applied for
Germany
Die Deutsche Bibliothek -CIP-Einheitsaufnahme
The South Atlantic: present and past circulation I
PROF. DR. WOLFGANG H. BERGER Gerold Wefer ... - Berlin; Heidelberg; New York; Barcelona;
Budapest; Hong Kong; London; MaiJand; Paris; Santa Clara;
Scripps Institution of Oceanography Singapur; Tokio: Springer 1996
ISBN-13: 978-3-642-80355-0 e-ISBN-13: 978-3-642-80353-6
Geological Research Division
DOl: 10.1007/978-3-642-80353-6
University of California, San Diego NE: Wefer, Gerold
La Jolla, CA 92093-0215
USA This work is subject to copyright. All rights are reserved, whether
the whole or part of the material is concerned, specifically the rights
of translation, reprinting, reuse of illustrations, recitations,
broadcasting, reproduction on microfilm or in any other way, and
storage in data banks. Duplication of this pUblication or parts thereof
PROF. DR. GEROLD SIEDLER is permitted only under the provisions of the German Copyright
Law of September 9. 1965, in its current version, and permission
Institut fUr Meereskunde an der
for use must always be obtained from Springer-Verlag. Violations
Christian-Albrechts-Universitat
are liable for prosecution under the German Copyright Law.
Abteilung Meeresphysik
© Springer-Verlag Berlin Heidelberg 1996
Diisterbrooker Weg 20
Softcover reprint of the hardcover 1st edition 1996
24105 Kiel
Germany The use of general descriptive names, registered names, trademarks,
etc. in this publication does not imply, even in the absence of a
specific statement, that such names are exempt from the relevant
protective laws and regulations and therefore free general use.
DR. DAVID J. WEBB
Typesetting: cameraready by authors
Southampton Oceanography Centre Cover Design: E. Kirchner, Heidelberg
Empress Dock
SPIN: 10050853 3213136-543210
Southampton S014 3ZH
United Kingdom Printed on acid free paper
The South Atlantic Gerold Wefer • Wolfgang H. Berger
Gerold Siedler • David J. Webb
Springer
Berlin
Heidelberg
New York
Barcelona
Budapest
Hong Kong
London
Milan
Paris
Santa Clara
Singapore
Tokyo
Preface
In the summer of 1994 (Aug. 15 - 18) about 220 oceanographers and paleoceanographers from
Western Europe, the USA, Africa, South America, Russia and Lithuania met at Bremen University to
present and discuss the results of recent research on present and past circulation in the South Atlantic.
The symposium was organised by Gerold Siedler (University of Kiei) and Gerold Wefer (University
of Bremen), assisted by a "Scientific Programme Committee", which included W.H. Berger, K.
Herterich, N.G. Hogg, Y. Ikeda, J.H.F. Jansen, J.R.E. Luetjeharms, J. Merle, R.G. Peterson, and DJ.
Webb. The local organisation was in the hands of Barbara Donner.
A symposium on the South Atlantic seemed timely and appropriate because the results from a number
of recent projects in oceanography and marine geosciences needed to be integrated into existing knowl
edge. Thus, monitoring programs have been in operation since 1991 as part oft he World Ocean Circu
lation Experiment (WOCE). These programs included studies of the meridional water-mass and heat
transports, the western boundary currents, and deep-and bottom-water transports in the Brazil Basin.
Also comprehensive studies are being carried out in the context ofIGBP Core Projects PAGES (Past
Global Changes) and JGOFS (Joint Global Ocean Flux Study), generating new data for the various
current and production systems of the South Atlantic.
Since 1989 the Colloborative Research Centre (Sonderforschungsbereich) No. 261 at the Univer
sity of Bremen ("The South Atlantic in the Late Quaternary: Reconstruction of material budget and
current system") has carried out extensive geological, geophysical and geochemical investigations on
the various current and production systems ofthe South Atlantic. The central theme of this research is
the reconstruction of current and productivity systems in the South Atlantic for the last 300,000 years.
The International Ocean Drilling Program is currently planning operations in the South Atlantic,
for example offthe coasts of Angola and Namibia, using the ddlling vessel "Joides Resolution" (Leg
175). We hope the results presented here will help in the planning of the expedition and later in evalu
ating the results.
A key aim ofthe organisers was to provide a forum in which people could integrate the results com
ing from both oceanographic and geological studies. The South Atlantic is an ideal region for this pur
pose. As the connecting link between the Antarctic and the North Atlantic, the South Atlantic plays a
crucial role with regard to the heat budget of the North Atlantic and to the biogeochemical budget of
the global ocean. Water from the South Atlantic moves north across the equator at shallow depths
replacing North Atlantic Deep Water (NADW), which forms in the northern North Atlantic due to cooling
of salty surface waters, and moves south at depth.
Investigations of sediments have revealed that the production ofNADW decreased during glacials
when, in its place, there was probably more intermediate water production reaching to greater depths.
The reduction or possibly the complete interruption ofNADW production during glacial periods may
have been directly caused by a decrease in energy and salt inputs from the South Atlantic, resulting
from changes in surface circulation as well as changes in the Agulhas Current system and the Antarctic
Circumpolar Current. Thus changes occurring further south and in other ocean can influence the cli
mate of the North Atlantic via the South Atlantic heat transfer system.
The South Atlantic also plays a decisive role in the coupling of oceanic processes between the Ant
arctic and lower latitudes. The Antarctic water belt is of major significance for global climate as it sup
plies large regions of ocean with intermediate and bottom water. While the North Atlantic is influ
enced by the South Atlantic through the input ofw arm near-surface water, the input ofNADW into the
Southern Ocean and the Antarctic Circumpolar Current is one of the determining factors of the ocea
nography oft he Antarctic. It is probable that the formation of Antarctic Intermediate and Bottom Water
VI Preface
is greatly enhanced by the upwata flow of warm, salt-enriched deep water, which hinders sea-ice for
mation and delivers salt for increased density after cooling.
Approximately 40 lectures were given during the four-day symposium on various aspects of ocea
nography and paleoceanography of the South Atlantic, and over 140 poster presentations helped
to illustrate recent research findings and provided a basis for discussions. Oceanographic and
paleoceanographic topics were deliberately mixed in the morning sessions so as to present as broad a
spectrum of information as possible to the neighbouring disciplines. Lively interdisciplinary discus
sions took place after the lectures, during the breaks as well as during the poster sessions, whereby
geologists gained insight into processes, and oceanographers expanded their appreciation for the range
of possible states ofthe system.
Encouragement of this type of exchange guided selection of the papers for publication in this book.
Thus, there is an emphasis on the more general contributions, and on those with interdisciplinary im
plications. The papers have also benefited from detailed reviews by P.M. Saunders, R.G. Peterson, A.
Gordon, L. Talley, K. Herterich, B. Barnier, W. Roether, D. Smythe-Wright, M. Rhein, J.R.E.
Lutjeharms, W. Curry, A. Mix, R. Schneider, F. Jansen, L. Labeyrie, T. Bickert, C. Robert and V. Ittekkot.
The symposium on the South Atlantic was supported by several international organisations, includ
ing the Oceanography Society (TOS), the international WOCE Scientific Steering Group and the Sci
entific Committee on Oceanic Research (SCOR). Financial backing was provided by the German Re
search Foundation (DFG) as well as by the Senate ofthe Free and Hanseatic City of Bremen. Technical
support was given by Dr. B. Donner, S. Middendorf, A. Grimm-Geils, G. Meinecke and V.Diekamp.
To each and all of those involved, our sincere thanks.
Gerold Wefer, Bremen
Wolfgang H. Berger, La Jolla
Gerold Siedler, Kiel
David J. Webb, Southampton
Contents
W.H. Berger & G. Wefer Central Themes of South Atlantic Circulation 1-11
J.R Reid On the Circulation of the South Atlantic Ocean 13-44
W. Roether & A. Putzka Transient-Tracer Information on Ventilation 45-62
and Transport of South Atlantic Waters
L.-L. Fu The Circulation and its Variability of the South 63-82
Atlantic Ocean: First Results from the
TOPEXIPOSEIDON Mission
G. Siedler, T.J. MUller, The Zonal WOCE Sections in the South Atlantic 83-104
R Onken, M. Arhan,
H. Mercier, B.A. King
& P.M. Saunders
K.G. Speer, J. Holfort, South Atlantic Heat Transport at 11 oS 105-120
T. Reynaud & G. Siedler
A.L. Gordon Comment on the South Atlantic's Role in the 121-124
Global Circulation
J .R.E. Lutjeharms The Exchange of Water between the South Indian 125-162
and South Atlantic Oceans
L.V. Shannon & The Benguela: Large Scale Features and Processes 163-210
G. Nelson and System Variability
OJ. Webb The Southern Boundary of the South Atlantic 211-217
L.O. Talley Antarctic Intermediate Water in the South Atlantic 219-238
RG. Peterson,C.S. Johnson, Lagrangian Measurements in the Malvinas 239-247
W. Kraus & RE. Davis Current
N.G. Hogg, W.B. Owens, Circulation in the Deep Brazil Basin 249-260
G. Siedler & W. Zenk
M. Rhein, F. Schott, The Deep Water Regime in the Equatorial 261-271
J. Fischer, U. Send Atlantic
& L. Stramma
C. Andrie Chlorofluoromethanes in the Deep Equatorial 273-288
Atlantic Revisited
VIII Contents
B. Barnier, P. Marchesiello, Modelling the Ocean Circulation in the South 289-304
& A.P. de Miranda Atlantic: A Strategy for Dealing with Open
Boundaries
R. Schlitzer Mass and Heat Transports in the South Atlantic 305-323
Derived from Historical Hydrographic Data
G. Fischer & G. Wefer Long-term Observation of Particle Fluxes in 325-344
the Eastern Atlantic: Seasonality, Changes
of Flux with Depth and Comparison with
the Sediment Record
A.J. van Bennekom Silica Signals in the South Atlantic 345-354
J. Patzold, K. Heidland, On the Bathymetry ofthe Hunter Channel 355-361
W. Zenk & G. Siedler
W.H.Berger & G. Wefer Expeditions into the Past: Paleoceanographic 363-410
Studies in the South Atlantic
G. Grieger & R. Schlitzer Inverse Modelling ofthe Glacial Atlantic 411-422
CirculationSystem: Investigation of Data
Requirements
E. Boyle Chemical Hydrography of the South Atlantic 423-443
& Y. Rosenthal During the Last Glacial Maximum: Cd vs. Ol3C
J.C. Duplessy, L. Labeyrie, High Latitude Deep Water Sources During the 445-460
M. Paterne, S. Hovine, Last Glacial Maximum and the Intensity of the
T. Fichefet, J. Duprat Global Oceanic Cir..culation
& M. Labracherie
G. Wefer; W.H. Berger, Late Quaternary Surface Circulation in the 461-502
T. Bickert, B. Donner, South Atlantic: The Stable Isotope Record
G. Fischer, S. Kemle- and Implications for Heat Transport and
von MUcke, G. Meinecke, Productivity
PJ. MUller, S. Mulitza,
H.-S. Niebler, J. Patzold,
H. Schmidt, R.R. Schneider
&M. Segl
A.C. Mix & A.E. Morey Climate Feedback and Pleistocene Variations 503-525
in the Atlantic South Equatorial Current
The South Atlantic: Present and Past Circulation IX
R.R. Schneider, P.J. MUller, Late Quaternary Surface Temperatures and Pro- 527-551
G. Ruhland, G. Meinecke, ductivity in the East-Equatorial South Atlantic:
H. Schmidt & G. Wefer Response to Changes in TradelMonsoon Wind
Forcing and Surface Water Advection
J.H.F. Jansen, E. Utkes Late Quaternary Movements of the Angola- 553-575
& R.R. Schneider Benguela Front, SE Atlantic, and Implications
for Advection in the Equatorial Ocean
W.B. Curry Late Quaternary Deep Circulation in the 577-598
Western Equatorial Atlantic
T.Bickert & G. Wefer Late Quaternary Deep Water Circulation in the 599-620
South Atlantic: Reconstruction from Carbonate
Dissolution and Benthic Stable Isotopes
B. Diekmann, R. Petschick, Clay Mineral Fluctuations in Late Quaternary 621-644
F.x. Gingele, D. FUtterer, Sediments of the Southeastern South Atlantic:
A. Abelmann, U. Brathauer Implications for Past Changes of Deep Water
R. Gersonde & A. Mackensen Advection
Central Themes of South Atlantic Circulation
W. H. Bergerl and G. Wefer
1S cripps Institution o/Oceanography, La Jolla, Ca. 92093, USA
2Universitdt Bremen, Fachbereich Geowissenschaften, 28334 Bremen, Germany
Abstract:The central problem of South Atlantic oceanography and paleoceanography is the exchange
of heat between South and North Atlantic. More specifically, it is the nature of the North Atlantic
heat piracy. Without this heat transfer, northern Europe would have an entirely less clement climate.
The necessity to understand the operation of the Atlantic Heat Conveyor provides the rationale for
studying both physical and historical oceanography of the South Atlantic. The study of present
conditions allows a synoptic view of dynamic interaction of surface- and deep circulation, and
associated productivity patterns. The study of past patterns provides clues to the range of possible
states and rates of change, and to the long-term stability of the system.
Physical and Geological Oceanography: the ocean (except for its sediment) essentially loses
An Emerging Symbiosis all memory of its past. None oftheir !lleasurements
from the water column call for interpretation on
A central problem in oceanography concerns the
time scales beyond the mixing time.
efficiency and stability of the heat transfer from
The reason why history is important is that the
South to North Atlantic, within the general frame
past allows us to see a much greater range of pos
work of global thermohaline circulation (e.g.,
sible states of the ocean-climate system than we
Gordon 1986). The question is vital for climatic
could reasonably imagine when extrapolating from
conditions in northern Europe. In recent years, a
the present ocean. The present ocean emerges as a
sense that ocean circulation is subject to consid
special case of many possible oceans: It is up to the
erable change on rather short time scales (decades
modelers to invent ways to move from one state to
to centuries) has emerged from high-resolution
another without violating basic physics and physi
studies of marine sediments deposited at high rates
cally-based common sense.
of accumulation. Studies of corals also have
proved useful in this regard. A mounting concern The discovery of the (poorly known) bounda
for the sensitivity of the ocean-climate system to ries of reality, then, is the pay-off to the physical
the continuing large-scale introduction of green oceanographers who enter the realm of pale
house gases has focussed attention of both physi oceanography. Atthe same time, their skills at pro
cal and historical oceanographers on this type of viding explanations are being severely tested: The
evidence. There is no question that this is a vital conceptual models of paleoceanographers may be
interface, where the physical and historical ap good and necessary, but they need to be trans
proach will thrive in symbiosis. formed to reflect our quantitative understanding of
Here we argue for a broadening of this inter the system.
face, to include a greater range of time scales in The contents of the symposium here presented
the overlap. But why should physical oceanogra reflect the tentative nature oft he incipient symbio
phers take interest in time scales beyond their lim sis between physical and geological oceanogra
its of measurement? After a few thousand years phers: Each group has started to take interest in the
From WEFER G, BERGER WH, SIEDLER G, WEBB OJ (eds), 1996, The South Atlantic: Present and Past Circulation. Springer-Verlag
Berlin Heidelberg, pp loll