Journal cover Journal topic
Climate of the Past An interactive open-access journal of the European Geosciences Union
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
03 Apr 2017
Review status
This discussion paper is under review for the journal Climate of the Past (CP).
A multi-proxy analysis of late Quaternary Indian monsoon dynamics for the Maldives, Inner Sea
Dorothea Bunzel1, Gerhard Schmiedl1, Sebastian Lindhorst1, Andreas Mackensen2, Jesús Reolid1, Sarah Romahn1, and Christian Betzler1 1Center for Earth System Research and Sustainability (CEN), Institute for Geology, University of Hamburg, Hamburg, D-20146, Germany
2Alfred Wegener Institute (AWI), Helmholtz Centre for Polar and Marine Research, Bremerhaven, D-27568, Germany
Abstract. We present a detailed multi-proxy data record to reveal the late Quaternary changes in marine sedimentation and biogeochemical processes of the upper bathyal Maldives (equatorial Indian Ocean) and how they are related to the benthic ecosystem dynamics. We investigated the sediment core SO-236-052-4 from the central part of the Inner Sea, Maldives, focusing on Fe / Ca and Si / Ca ratios as proxies for terrigenous sediment delivery, as well as Total Organic Carbon (TOC) and Ba / Ca ratios as proxies for marine productivity. Benthic foraminiferal fauna distributions, sortable silt records and stable oxygen and carbon isotope analyses were used for reconstructing the past ecosystem, as well as changes in the intermediate water circulation, bottom water current velocity and oxygenation.

This multi-proxy data record shows an enhanced dust supply during the glacial intervals, represented by increased Fe / Ca and Si / Ca ratios, an overall coarsening of the sediment and 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 fertilisation during the cold phases resulted in increased surface water productivity and related organic carbon fluxes. Thus, the development of highly diverse benthic foraminiferal faunas and the distribution of certain detritus and suspension feeders were fostered.

The difference in the stable carbon isotope signal between epifaunal and deep infaunal benthic foraminifera reveals intermediate water oxygen concentrations between approximately 40 and 100 μmol kg−1. The 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, further controlled by the inflow of the Antarctic Intermediate Water (AAIW). The precessional circulation pattern of the bottom water oxygenation is overprinted by glacial-/interglacial changes resulting in a long phase of reduced ventilation during the last glacial period. The latter process is likely linked to the combined effects of generally enhanced oxygen consumption rates during high-productivity phases, reduced AAIW production and restriction of bathyal environments of the Inner Sea of the Maldives during sea-level lowstands. Thus, this multi-proxy record provide a close linkage between the Indian monsoon oscillation, intermediate water circulation, productivity and sea-level changes on orbital time-scale.

Citation: Bunzel, D., Schmiedl, G., Lindhorst, S., Mackensen, A., Reolid, J., Romahn, S., and Betzler, C.: A multi-proxy analysis of late Quaternary Indian monsoon dynamics for the Maldives, Inner Sea, Clim. Past Discuss., doi:10.5194/cp-2017-54, in review, 2017.
Dorothea Bunzel et al.
Dorothea Bunzel et al.
Dorothea Bunzel et al.


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Short summary
We investigated a sediment core from the Maldives Inner Sea to unravel the interaction between the equatorial climate and ocean variabilities for the past 200,000 years. Therefore we evaluated different sedimentological, geochemical and micropaleontological proxies. We found out that during cold glacial periods enhanced dust supplies influenced the study area, e.g. favoring specific benthic foraminifera. This suggest a close linkage to the strength of the Indian winter monsoon.
We investigated a sediment core from the Maldives Inner Sea to unravel the interaction between...