Sea-surface temperature variability in the Southeast Pacific during the last glacial, interglacial cycle and relationships to paleoenvironmental changes in central and southern Chile [Elektronische Ressource] / vorgelegt von Jérôme Kaiser

Informations

• Publié par: universitat_bremen
• Publié le: 01 janvier 2005
• Nombre de lectures: 18
• Langue: English
• Poids de l'ouvrage: 5 Mo

Extrait

SEA-SURFACE TEMPERATURE VARIABILITY IN THE SOUTHEAST
PACIFIC DURING THE LAST GLACIAL-INTERGLACIAL CYCLE
AND RELATIONSHIPS TO PALEOENVIRONMENTAL CHANGES IN
CENTRAL AND SOUTHERN CHILE

















Dissertation zur Erlangung des Doktorgrades am Fachbereich
Geowissenschaften der Universität Bremen
















Vorgelegt von


Jérôme KAISER
Bremen, November 2005










Kaiser, Jérôme 1. November 2005


DFG-Research Centre Ocean Margins, Universität Bremen, Leobenerstrasse, 28334 Bremen,
Germany




Erklärung





Hiermit versichere ich, dass ich

1. die Arbeit ohne unerlaubte fremde Hilfe angefertigt
habe,

2. keine anderen als die von mir angegebenen Quellen
und Hilfsmittel benutzt habe und

3. die den benutzten Werken wörtlich oder inhaltlich
entnommenen Stellen als solche kenntlich gemacht
habe.





Bremen, den 1. November 2005


Jérôme Kaiser
















Acknowledgments


This work wouldn’t have been what it is without Frank Lamy first of all. So I really want
to thank Frank for his interest and enthusiasm in this work, as well as for his very human and
friendly being. I’m grateful also to Dierk Hebbeln, especially for his always-helpful advices. I
think I have been lucky to have such supervisors. I further thank Ralf Tiedemann for assessing
this work together with Dierk.

A lot of people contribute more or less directly to this work. Helge Arz and Emmanuel
Chapron are acknowledged for their helpful ideas and discussions. I had a lot of good time
with Ralph Kreutz in the lab. It has been a nice way to learn about these “little guys”. I’m
also grateful to Marcus Elvert and Enno Schefuss for their help, advices and lights on the
basis of (bio)geochemistry. Konrad Hughen and Nick Drenzek are thanked for the opportunity
they gave me to work at the WHOI for some months. Thanks also to Marco Mohtadi, Jan-
Berend Stuut, Ricardo De Pol-Holz, Julio Sepulvada and others co-workers on the Chilean
climate history.

Research was part of these three last years, but another important time was the one to
decompress and “talk-a-lot-to-say-nothing”. I want to bow all my friends from France,
Switzerland and Germany, but especially Rik, Marius and Xavier. My parents have also their
place here as they were always supporting me in all my choices and desires. Finally, my main
thanks and feelings go to Ina who had had to bear my humors and Latin way of life …

And thanks for all the fishes !!



















1. INTRODUCTION 1
1.1 Late Quaternary climate variability: Northern and Southern Hemispheres 1
1.2 Contributions of the Southeast Pacific 3
1.3 Objectives 6
2. OCEANOGRAPHIC, ATMOSPHERIC AND PHYSIOGRAPHIC SETTINGS 8
2.1 Sea-surface and deep oceanic circulation in the Southeast Pacific 8
2.2 The southern Westerly winds, or Westerlies 11
2.3 Geology and vegetation cover of the Chilean hinterland 13
3. METHODOLOGY 17
3.1 Stratigraphy17
3.2 Alkenone-based sea-surface temperature reconstruction 18
3.3 Sea-surface salinity reconstruction 22
3.4 X-ray fluorescence measurement 24
3.5 Long-chain n-alkanes 24
4. MANUSCRIPTS26
4.1 Antarctic timing of surface water changes off Chile and Patagonian Ice Sheet 26
response
(F. Lamy, J. Kaiser, U. Ninnemann, D. Hebbeln, H. Arz and J. Stoner)
4.2 A 70-kyr sea-surface temperature record off southern Chile (ODP Site 1233) 42
(J. Kaiser, F. Lamy and D. Hebbeln)
4.3 Variability of sea-surface temperatures off Chile and the dynamics of the Patagonian 66
Ice Sheet during the last glacial period based on ODP Site 1233
(J. Kaiser, F. Lamy, H. Arz and D. Hebbeln)
4.4 The last deglaciation off southern Chile at a sub-centennial resolution: interactions of 84
the Patagonian Ice Sheet, sea-surface temperatures and alkenone productivity
(J. Kaiser, F. Lamy, U. Ninnemann, D. Hebbeln and H. Arz)
4.5 Southeast Pacific sea-surface circulation and vegetation changes in central Chile 95
during the last 40 kyr
(J. Kaiser, F. Lamy, E. Schefuss, R. De Pol-Holz and D. Hebbeln)
4.6 Melting of the Patagonian Ice Sheet and deglacial perturbations of the nitrogen cycle 111
in the Eastern South Pacific
(R. De Pol-Holz, O. Ulloa, L. Dezileau, J. Kaiser, F. Lamy and D. Hebbeln)
5. SUMMARY AND CONCLUSIONS 120
6. PERSPECTIVES124
7. BIBLIOGRAPHY126

SECTION 1. INTRODUCTION



1. INTRODUCTION

1.1 Late Quaternary climate variability: Northern and Southern Hemispheres

The Late Quaternary time-period is characterized by several phases of long-term climate
shifts between glacial and interglacial states, i.e. an oscillation between cold times with the
development of large ice-sheets over the Northern Hemisphere (NH) and Southern
Hemisphere (SH) high-latitudes with low sea-level, and relatively warm periods similar to the
modern climate. The main origin of these cycles is linked to changes in the astronomical
parameters of the Earth (Milankovitch, 1941), involving non-linear responses from
continental ice-sheets and other climate components (Imbrie et al., 1992). The last
glacial/interglacial cycle spanned the previous ~125,000 yr (125 kyr) and is probably the most
thoroughly studied interval of the Earth’s history using a vast variety of proxy records from
both marine and terrestrial archives, as well as modeling studies.
Superimposed on a long-term trend, high and abrupt climate variability on a multi-
millennial to multi-centennial timescale characterize the last glacial period. Ice-cores and
marine records have shown a number of climate oscillations called the Dansgaard-Oeschger
cycles (DO; Dansgaard et al., 1984) and Heinrich events (HE; Heinrich, 1988), involving
temperature changes at the ice surface of as much as 9°C in a few decades (e.g., Severinghaus
and Brook, 1999). Presenting a recurrent pattern with a pacing of ~1-4.5 kyr and 5-10 kyr
respectively, the ultimate origin of these events is still discussed controversially. A number of
processes are being discussed including mechanisms linked to orbital forcing, solar
variability, ice-sheet instabilities, or floods from glacier-dammed lakes (see for a review e.g.,
Alley et al., 2003; Labeyrie et al., 2003), that may involve stochastic resonance of the coupled
ocean-atmosphere system (e.g., Alley et al., 2001; Ganopolski and Rahmstorf, 2002).
Independent of their ultimate origin, it is generally accepted that both DO and HE events
are closely linked to modifications in the thermohaline circulation (THC; Broecker et al.,
1985; see for a review Rahmstorf, 2002). The THC, or global conveyor circulation,
corresponds to a hypothetic, large-scale oceanic surface and deep circulation mode. In the
North Atlantic realm, and to a minor extent around Antarctica, respectively North Atlantic
Deep Water (NADW) and Antarctic Bottom Water (AABW) are formed by sinking of cold
and salty waters. These water masses spread towards the south (NADW) and the north
(AABW), filling the deepest part of the oceans. Most of these deep waters further outcrop
around Antarctica and returns within the surface as warm water to the North Atlantic region
through the Drake and Cape of Good Hope passages. The still predominant explanation for
the aforementioned abrupt climate changes is on the one hand that changes in the hydrological
cycle in the North Atlantic would affect the THC and thus the global heat distribution (e.g.,
Stocker and Wright, 1991; Knutti et al., 2004). On the other hand, it has been proposed that
rapid climate oscillations may also originate from the tropical Pacific, potentially involving a
long-term modulation of inter-annual to decadal climate changes of the eastern tropical
Pacific El Nino–Southern Oscillation (ENSO) (Cane, 1998). Recently, a number of new data
1SECTION 1. INTRODUCTION



sets and modeling studies suggest an important role of the SH high-latitudes within the
millennial-scale climate and ocean variability as well.
An important step for a better understanding of the global pattern of rapid climate changes
during the last glacial was the synchronization of ice-core records from Greenland and
Antarctica using the methane concentrations measured in the ice (Blunier et al., 1998; Blunier
and Brook, 2001). These data provided strong evidences for the so-called thermal see-saw
mechanism (Crowley, 1992; Broecker, 1998; Stocker, 1998) that implies that major cold
phases in the NH (such as HE events) correspond to warmings in the SH (the so-called A
events) and vice versa, involving changes in the THC. Instead of an antiphase the ice-core
data can als