Holocene dynamics of the southern westerly winds over the Indian Ocean inferred from a peat dust deposition record

Chuxian Li*, Jeroen E. Sonke, Gaël Le Roux, Nathalie Van der Putten, Natalia Piotrowska, Catherine Jeandel, Nadine Mattielli, Mathieu Benoit, Giles F.S. Wiggs, François De Vleeschouwer

*Corresponding author for this work

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Abstract

The southern westerly winds (SWW) play a major role in climate variability in Southern Hemisphere mid- and high-latitudes, regulating rainfall, ocean circulation, and the Southern Ocean carbon sink. Despite their importance, little is known about millennial scale changes in the SWW and how they have influenced the climate system in the past and interacted with the Earth's surface elements, such as dust, nutrients and carbon. Here we present a dust record from a 6.6 kyr old peat core in Amsterdam Island (AMS) situated at the northern edge of the SWW (37°S) in the Southern Indian Ocean. Mineral dust flux was used to track atmospheric dust production, long-distance transport and subsequent deposition. Dust provenance was determined from rare earth element (REE) and Nd isotopic signatures (εNd) in the peat core, compared with a reference dataset of Southern Hemisphere dust sources. Using a multi-proxy mixing model, the εNd and REE ratios show a relatively uniform mixture of ca. 40% local, 15% Southern African and 45% Southern South American dust sources since 6.6 cal kyr BP. However, from 1910 AD onwards, there is a doubling in the contribution from Southern Africa (32%). Two mineral dust flux minima occur at 6.2–4.9 cal kyr BP and 3.9–2.7 cal kyr BP, interpreted as periods with equatorward-shifted and/or strengthened SWW at the northern edge of the wind belt. Conversely, periods of higher dust flux at 6.6–6.2 cal kyr BP, 4.9–3.9 cal kyr BP, and 1.4 cal kyr BP onwards are interpreted as poleward-shifted and/or weakened SWW. These interpretations are based on the findings that higher (lower) wind speeds lead to enhanced (less) removal of distal dust on the way to AMS, by wet deposition and turbulence. Published Holocene SWW records at the northern edge of the wind belt (33–41°S) covering South-America, Southern-Africa and Australia, show much variability over the last 6.6 kyr. We suggest this reflects complex regional climate variability in the different SH longitudinal sectors, indicating that SWW are not zonally homogeneous at the northern edge of the wind belt. The recent shift in dust provenance is not accompanied by enhanced total dust deposition at AMS. We therefore suggest that human impact (e.g., land use changes) and drier climate conditions in Southern Africa have led to enhanced dust mobilization.

Original languageEnglish
Article number106169
Pages (from-to)1-13
Number of pages13
JournalQuaternary Science Reviews
Volume231
Early online date28 Jan 2020
DOIs
Publication statusPublished - 1 Mar 2020

Funding

Many thanks for the support of the Mission 66 of Amsterdam Island, without which the field trip could not have been possible. We are grateful to Svante Björck (Lund University, Sweden), Bart Klink and Elisabeth Michel (both Laboratoire des sciences du climat et de l’environnement, LSCE, France) for their valuable assistance during fieldwork. A very special thanks to Alain Quivoron and Hubert Launay for their continuous directive and logistical support during and after fieldwork on Amsterdam Island. Combined fieldwork was funded by the French Polar Institute (IPEV, Brest, France) through the IPEV Programmes 1066 “PARAD” (to F. De Vleeschouwer) and 1065 PALATIO (to N. Van der Putten and E. Michel). We are grateful to Nina Marchand ( IPEV ) for the logistical support, Cédric Marteau for access to protected areas of the TAAF Nature Reserve, and Olivier Magand and Isabelle Jouvie (Institut de Géosciences et de l’Environnement in Grenoble, France) for collecting the local soil samples. We thank the members of the Dust Observations for Models (DO4) team for access to field samples from southern Africa. We are grateful to Dominic Hodgson (British Antarctic Survey) for his very helpful discussions and comments on the draft. Thanks to Jan-Berend Stuut (Royal Netherlands Institute for Sea Research, NIOZ, the Netherlands) for the Australian samples (shown in supplementary information) and his comments on the draft. We are grateful to Marie-José Tavella, David Baqué, Camille Duquenoy, Aurélie Marquet, and Stéphanie Mounic (Observatoire Midi-Pyrénées, France) for their help with sample analysis. Some of the radiocarbon ages were obtained as part of the Idex Peat3 project of the University of Toulouse and through the national service support: Artemis- INSU-CNRS (to G. Le Roux). Chuxian Li’s PhD is supported by a scholarship from the Chinese Scholarship Council.

FundersFunder number
Chinese Scholarship Council
Dominic Hodgson
Institut de G?osciences et de l'Environnement
Laboratoire des Sciences du Climat et de l'Environnement
China Scholarship Council
Université de Toulouse
Institut Polaire Français Paul Emile Victor
Koninklijk Nederlands Instituut voor Onderzoek der Zee

    Keywords

    • Amsterdam Island
    • Anthropogenic activities
    • Dust sources
    • Peat
    • Southern westerly winds

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