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Climate of the Past An interactive open-access journal of the European Geosciences Union
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Volume 13, issue 12
Clim. Past, 13, 1791-1813, 2017
https://doi.org/10.5194/cp-13-1791-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Clim. Past, 13, 1791-1813, 2017
https://doi.org/10.5194/cp-13-1791-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 13 Dec 2017

Research article | 13 Dec 2017

A multi-proxy analysis of Late Quaternary ocean and climate variability for the Maldives, Inner Sea

Dorothea Bunzel1, Gerhard Schmiedl1, Sebastian Lindhorst1, Andreas Mackensen2, Jesús Reolid1, Sarah Romahn1, and Christian Betzler1 Dorothea Bunzel et al.
  • 1Center for Earth System Research and Sustainability (CEN), Institute for Geology, University of Hamburg, 20146 Hamburg, Germany
  • 2Alfred Wegener Institute (AWI), Helmholtz Centre for Polar and Marine Research, 27568 Bremerhaven, Germany

Abstract. As a natural sediment trap, the marine sediments of the sheltered central part of the Maldives Inner Sea represent an exceptional archive for paleoenvironmental and climate changes in the equatorial Indian Ocean. To evaluate the complex interplay between high-latitude and monsoonal climate variability, related dust fluxes, and regional oceanographic responses, we focused on FeAl, TiAl and SiCa ratios as proxies for terrigenous sediment delivery and total organic carbon (TOC) and Br XRF counts as proxies for marine productivity. Benthic foraminiferal fauna distributions, grain size and stable δ18O and δ13C data were used for evaluating changes in the benthic ecosystem and changes in the intermediate water circulation, bottom water current velocity and oxygenation.

Our multi-proxy data record reveals an enhanced dust supply during the glacial intervals, causing elevated FeAl and SiCa ratios, an overall coarsening of the sediment and an increasing amount of agglutinated benthic foraminifera. The enhanced dust fluxes can be attributed to higher dust availability in the Asian desert and loess areas and its transport by intensified winter monsoon winds during glacial conditions. These combined effects of wind-induced mixing of surface waters and dust fertilization during the cold phases resulted in an increased surface water productivity and related organic carbon fluxes. Thus, the development of highly diverse benthic foraminiferal faunas with certain detritus and suspension feeders was fostered. The difference in the δ13C signal between epifaunal and deep infaunal benthic foraminifera reveals intermediate water oxygen concentrations between approximately 40 and 100µmolkg−1 during this time. The precessional fluctuation pattern of oxygen changes resembles that from the deep Arabian Sea, suggesting an expansion of the oxygen minimum zone (OMZ) from the Arabian Sea into the tropical Indian Ocean with a probable regional signal of strengthened winter-monsoon-induced organic matter fluxes and oxygen consumption further controlled by the varying inflow intensity of the Antarctic Intermediate Water (AAIW). In addition, the bottom water oxygenation pattern of the Maldives Inner Sea reveals a long phase of reduced ventilation during the last glacial period. This process is likely linked to the combined effects of generally enhanced oxygen consumption rates during high-productivity phases, reduced AAIW production and the restriction of upper bathyal environments in the Inner Sea during sea-level lowstands. Thus, our multi-proxy record reflects a close linkage between the Indian monsoon oscillation, intermediate water circulation, productivity and sea-level changes on orbital timescale.

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We investigated a sediment core from the Maldives to unravel the interaction between equatorial climate and ocean variability of the past 200 000 years. The sedimentological, geochemical and foraminiferal data records reveal enhanced dust, which was transported by intensified winter monsoon winds during glacial conditions. Precessional fluctuations of bottom water oxygen suggests an expansion of the Arabian Sea OMZ and a varying inflow of Antarctic Intermediate Water.
We investigated a sediment core from the Maldives to unravel the interaction between equatorial...
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