Periodical breakdown of the Arabian Sea oxygen minimum zone caused by deep convective mixing
Published:January 01, 2002
Gert Jan Reichart, Juriaan Nortier, Gerard Versteegh, Willem Jan Zachariasse, 2002. "Periodical breakdown of the Arabian Sea oxygen minimum zone caused by deep convective mixing", The Tectonic and Climatic Evolution of the Arabian Sea Region, P. D. Clift, D. Kroon, C. Gaedicke, J. Craig
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The northern Arabian Sea is at present characterized by a pronounced oxygen minimum zone (OMZ) with oxygen concentrations reaching values as low as 2 μm between 150 and 1250 m. This intense mid-water OMZ results from high annual organic particle fluxes and a moderate rate of thermocline ventilation. Sediment studies have shown that the intensity of the northern Arabian Sea OMZ has fluctuated on Milankovitch and sub-Milankovitch time scales, in conjunction with changes in either surface water productivity or thermocline ventilation. Here we evaluate the role of convective mixing in the periodical breakdown of the OMZ by reconstructing the density gradient for periods showing a well-ventilated water column. For this reason we reconstructed sea surface temperatures and salinities for the last 70 ka based on alkenone thermometry and δ18O analyses on planktic and benthic foraminifers. For the studied time span thermocline ventilation by intermediate water formation in the northern Arabian Sea is a viable mechanism to explain observed fluctuations in the intensity of the OMZ. We postulate that the necessary decrease in the vertical density gradient during well-ventilated periods resulted from intensified winter monsoonal winds in combination with effects caused by glacio-eustacy.
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The Tectonic and Climatic Evolution of the Arabian Sea Region
Over long periods of time the tectonic evolution of the solid Earth has been recognized as the major control on the development of the global climate system. Tectonic activity acts in one of two different ways to influence regional and global climate: (i) through the opening and closing of oceanic gateways and its effect on the circulation patterns in the global ocean; (ii) through the growth and erosion of orogenic belts, resulting in changes in oceanic chemistry and disruption of atmospheric circulation. The Arabian Sea region has several features that make it the best area for studies of climate and palaeoceanographic responses to tectonic activity, most notably in the context of the South Asian monsoon and its relationship to the growth of high topography in the adjacent Himalayas and Tibet.
The Tectonic and Climatic Evolution of the Arabian Sea Region brings together a collection of recent studies on the area from a wide group of international contributors. The paper range from high resolution, Holocene palaeoceanographic studies of the Pakistan margin to regional tectonic reconstructions of the ocean basin and surrounding margins throughout the Cenozoic. Marine geophysics, stratigraphy, isotope chemistry and neotectonics come together in a multidisciplinary approach to the study of interactions of land and sea. while much work remains to be done to understand fully the tectonic and climatic evolution of the Arabian Sea, a great deal has been achieved since the last major review, as detailed in the 26 contributions. This volume is essential reading for palaeoceanographers, sedimentologists and geophysicists. It will also be interest to structural geologists and those working in the petroleum industry.