Title
Centennial to millennial-scale changes in oxygenation and productivity in the Eastern Tropical South Pacific during the last 25,000 years
Date Issued
01 January 2016
Access level
open access
Resource Type
journal article
Author(s)
Salvatteci R.
Ortlieb L.
Druffel E.
Boussafir M.
Schneider R.
Publisher(s)
Elsevier Ltd
Abstract
Oxygen minimum zones (OMZ) have expanded in all tropical oceans during the last 50 years resulting in habitat contraction and considerable changes in marine biogeochemistry. However, for a better understanding of the OMZ dynamics under the current climate change, two questions are relevant: 1) how do the magnitude and temporal changes in oceanic dissolved oxygen of the last few decades compare to the natural variability on longer timescales, and 2) what were the local and remote factors driving OMZ changes in the past. In the present study we use a stacked record covering the last 25 kyr from the Eastern Tropical South Pacific (ETSP) OMZ to reconstruct changes in oxygenation and productivity. We use a suite of proxies including the presence of laminations, redox sensitive metals (U, Mo, Re, Ni and Cu), total organic carbon and δ15N measurements. Water column denitrification and sediment redox conditions show pronounced centennial to millennial-scale variability during the last 25 kyr, with oxygenation levels as low as at present. Global cold periods at different timescales such as the Last Glacial Maximum (23-19 kyr BP) and the Little Ice Age (1500-1850 AD) were associated with a weak OMZ and low export production, while warm intervals such as the deglaciation, part of the Medieval Climate Anomaly and the last 100 years are associated with a stronger OMZ and high export production. Water column denitrification and sediment redox conditions were strongly coupled during the last 25 kyr BP apart from one remarkable exception: during the Antarctic Cold Reversal, sediments were less reducing but the water column denitrification was high resulting in a strong but shallow OMZ. This may have been produced by an enhanced Antarctic Intermediate Water flow. Contrary to our expectations and modeling predictions for the next few decades, we observe a weak ETSP-OMZ during the warm mid-Holocene, which may have been the result of a stronger Walker Circulation that brought oxygen-rich waters to intermediate depths off Peru via Equatorial undercurrents. In combination with other paleoceanographic reconstructions, our results show that oxygenation variability in the ETSP-OMZ was influenced by ocean circulation changes in the Tropical Pacific, high latitude oceanographic and climatic changes, and local productivity.
Start page
102
End page
117
Volume
131
Language
English
OCDE Knowledge area
Ecología
Subjects
Scopus EID
2-s2.0-84946600106
Source
Quaternary Science Reviews
ISSN of the container
02773791
Sponsor(s)
We deeply thank the “Institut de Recherche pour le Développement” for granting a PhD scholarship to RS during which most of the analyses were done. We deeply thank Bo Thamdrup, chief scientist of the Galathea-3 expedition (Leg 14), and Bente Lomstein, who conducted the core sampling onboard the RV Vaedderen. We also sincerely thank F. Le Cornec, J. Cottet and I. Djouraev (IRD-Bondy and LOCEAN) for their most appreciated help with the ICP-MS analyses. We thank P. Martinez for providing the SCOPIX and photograph images. We thank F. Scholz and B. Schneider for constructive discussions. We are grateful to R. Gingold ( sweepandmore.com ) for a thorough revision of the manuscript. The AMS radiocarbon measurements were obtained by the “Laboratoire de mesures de C-14” LMC14 (UMS2572, CEA-CNRS-IRD-IRSN-Ministère de la Culture), Gif-sur-Yvette, France, through the IRD financial and technical support to this laboratory and the UCI Keck Carbon Cycle AMS Laboratory. We are grateful to the “ FONDECYT ” grant for the “Maestria en Ciencias del Mar that supported this research. We acknowledge support from the PALEOTRACES and PALEOPROXUS projects, and the Chaire croisée PROSUR, all partly supported by IRD. This work is a contribution of Sonderforschungsbereich 754 “Climate–Biogeochemistry interactions in the tropical ocean” ( www.sfb754.de ), which is supported by the Deutsche Forschungsgemeinschaft.
Sources of information:
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