Mid-Holocene expansion of the Indian Ocean warm pool documented in coral Sr/Ca records from Kenya

Scientific Reports, vol. 13, pp. 777

Abstract

Proxy reconstructions suggest that mid-Holocene East African temperatures were warmer than today between 8 and 5 ka BP, but climate models cannot replicate this warming. Precessional forcing caused a shift of maximum insolation from boreal spring to fall in the mid-Holocene, which may have favored intense warming at the start of the warm season. Here, we use three Porites corals from Kenya that represent time windows from 6.55 to 5.87 ka BP to reconstruct past sea surface temperature (SST) seasonality from coral Sr/Ca ratios in the western Indian Ocean during the mid-Holocene. Although the Indian monsoon was reportedly stronger in the mid-Holocene, which should have amplified the seasonal cycle of SST in the western Indian Ocean, the corals suggest reduced seasonality (mean 3.2 °C) compared to the modern record (mean 4.3 °C). Warming in austral spring is followed by a prolonged period of warm SSTs, suggesting that an upper limit of tropical SSTs under mid-Holocene conditions was reached at the start of the warm season, and SSTs then remained stable. Similar changes are seen at the Seychelles. Bootstrap estimates suggest a reduction in SST seasonality of 1.3 ± 0.22 °C at Kenya and 1.7 ± 0.32 °C at the Seychelles. SST seasonality at Kenya corresponds to present-day SST seasonality at 55° E-60° E, while SST seasonality at the Seychelles corresponds to present day SST seasonality at ~ 65° E. This implies a significant westward expansion of the Indian Ocean warm pool. Furthermore, the coral data suggests that SST seasonality deviates from seasonal changes in orbital insolation due to ocean-atmosphere interactions.

Authors 12

1. Maike Leupold Aachen Geological Institute

   RWTH Aachen University

   Affiliation as printed

   Geological Institute, RWTH Aachen University, 52062, Aachen, Germany

2. Miriam Pfeiffer corresponding

   Christian-Albrechts-Universität zu Kiel

   Affiliation as printed

   Institute of Geosciences, Kiel University, 24118, Kiel, Germany. miriam.pfeiffer@ifg.uni-kiel.de

   Institute of Geosciences, Kiel University, 24118, Kiel, Germany

3. Takaaki K. Watanabe

   Christian-Albrechts-Universität zu Kiel

   Affiliation as printed

   Institute of Geosciences, Kiel University, 24118, Kiel, Germany

   KIKAI Institute for Coral Reef Sciences, Kikai Town, Kagoshima, 891‑6151, Japan

4. N. Nakamura

   The University of Tokyo · Keio University

   Affiliation as printed

   Department of Earth and Planetary Science, University of Tokyo, Tokyo, Japan

   Faculty of Science and Technology, Keio University, Tokyo, Japan

5. Lars Reuning

   Christian-Albrechts-Universität zu Kiel

   Affiliation as printed

   Institute of Geosciences, Kiel University, 24118, Kiel, Germany

6. Alina Blume Aachen Geological Institute

   RWTH Aachen University

   Affiliation as printed

   Geological Institute, RWTH Aachen University, 52062, Aachen, Germany

7. Tim R. McClanahan

   Wildlife Conservation Society

   Affiliation as printed

   Wildlife Conservation Society, Mombasa, Kenya

8. Mchulla Mohammed

   National Museums of Kenya

   Affiliation as printed

   National Museum of Kenya, PO Box 82412-80100, Mombasa, Kenya

9. Herman Ogoti Kiriama

   Kisii University

   Affiliation as printed

   Kisii University, PO Box 408-40500, Kisii, Kenya

10. Dieter Garbe‐Schönberg

    Christian-Albrechts-Universität zu Kiel · Constructor University

    Affiliation as printed

    Department of Physics and Earth Sciences, Jacobs University Bremen, 28759, Bremen, Germany

    Institute of Geosciences, Kiel University, 24118, Kiel, Germany

11. Andrea Schröder Ritzrau

    Heidelberg University

    Affiliation as printed

    Institute of Environmental Physics, Heidelberg University, 69120, Heidelberg, Germany

12. Jens Zinke

    University of the Witwatersrand · University of Leicester · Curtin University · Australian Institute of Marine Science

    Affiliation as printed

    Australian Institute of Marine Science, Townsville, QLD, 4810, Australia

    Molecular and Life Sciences, Curtin University, Perth, WA, 6102, Australia

    School of Geography, Archaeology and Environmental Studies, University of Witwatersrand, Witwatersrand, South Africa

    School of Geography, Geology and the Environment, University of Leicester, Leicester, LE1 7RH, UK