References

CPD

Climate of the Past Discussions

CPD

1814-9359

Copernicus GmbH

Göttingen, Germany

10.5194/cpd-8-669-2012

Contribution of changes in opal productivity and nutrient distribution in the coastal upwelling systems to late Pliocene/early Pleistocene climate cooling

Etourneau

¹ ² Ehlert

³ Frank

³ Martinez

⁴ Schneider

Institut für Geowissenschaften, Universität zu Kiel, Ludewig-Meyn-Str. 10, 24118 Kiel, Germany

LOCEAN, CNRS/UPMC/IRD/MNHN – UMR7159, 4 Place Jussieu, 75252 Paris, France

GEOMAR, Helmholtz Centre for Ocean Research Kiel, Wischhofstrasse 1–3, 24118 Kiel, Germany

EPOC CNRS – UMR5805, Université Bordeaux 1, Avenue des Facultés, 33405 Talence, France

06 03 2012

8 2 669 694

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The global late Pliocene/early Pleistocene cooling (~3.0–2.0 million years ago, Ma) concurred with extremely high diatom and biogenic opal production in most of the major coastal upwelling regions. This phenomenon was particularly pronounced in the Benguela Upwelling System (BUS), off Namibia, where it is known as the Matuyama Diatom Maximum (MDM). Our study focuses on a new diatom silicon isotope (δ30Si) record covering the MDM in the BUS. Unexpectedly, the variations in δ30Si signal follow biogenic opal content, whereby the highest δ30Si values correspond to the highest biogenic opal content. We interpret the higher δ30Si values during the MDM as a result of a stronger degree of silicate utilization in the surface waters caused by high productivity of mat-forming diatom species. This was most likely promoted by weak upwelling intensity dominating the BUS during the Plio/Pleistocene cooling combined with a large silicate supply derived from a strong Southern Ocean nutrient leakage responding to the expansion of Antarctic ice cover and the resulting stratification of the polar ocean 3.0–2.7 Ma ago. A similar scenario is hypothesized for other major coastal upwelling systems (e.g. off California) during this time interval, suggesting that the efficiency of the biological carbon pump was probably sufficiently enhanced in these regions during the MDM to have significantly increased the transport of atmospheric CO2 to the deep ocean. In addition, the coeval extension of the area of surface water stratification in both the Southern Ocean and the North Pacific, which decreased CO2 release to the atmosphere, led to further enhanced atmospheric CO2 drawn-down and thus contributed significantly to late Pliocene/early Pleistocene cooling.

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