Late Quaternary Monsoonal Variations in the Western Arabian Sea Based on Cross-Spectral Analyses of Geochemical and Micropalaeontological Data (ODP Leg 117, Core 728A)

  1. P. L. de Boer2 and
  2. D. G. Smith3
  1. W. G. H. Z. ten Kate,
  2. A. Sprenger,
  3. T. N. F. Steens and
  4. C. J. Beets

Published Online: 29 APR 2009

DOI: 10.1002/9781444304039.ch12

Orbital Forcing and Cyclic Sequences

Orbital Forcing and Cyclic Sequences

How to Cite

ten Kate, W. G. H. Z., Sprenger, A., Steens, T. N. F. and Beets, C. J. (1994) Late Quaternary Monsoonal Variations in the Western Arabian Sea Based on Cross-Spectral Analyses of Geochemical and Micropalaeontological Data (ODP Leg 117, Core 728A), in Orbital Forcing and Cyclic Sequences (eds P. L. de Boer and D. G. Smith), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304039.ch12

Editor Information

  1. 2

    Utrecht, The Netherlands

  2. 3

    London, UK

Author Information

  1. Geomarine Centre, Institute of Earth Sciences, Free University, de Boelelaan 1085, 1081 HV Amsterdam, The Netherlands

Publication History

  1. Published Online: 29 APR 2009
  2. Published Print: 28 JAN 1994

ISBN Information

Print ISBN: 9780632037360

Online ISBN: 9781444304039

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Keywords:

  • Late Quaternary monsoonal variations in western Arabian Sea;
  • seasonal upwelling;
  • aeolian intensity proxies;
  • power spectra of SPECMAP (solid curve);
  • proxy for intensity of OMZ

Summary

ODP Hole 728A (Leg 117), located at a semi-enclosed slope basin on the continental margin of Oman, underlies a seasonally monsoon-enhanced upwelling zone. The sediment composition reflects past environmental fluctuations which are linked to variations in the monsoon system. These include seasonal upwelling, palaeoproductivity, variation in the extent of the OMZ and aeolian input. The top-most Pleistocene (21.5 m; 524 ka) was sampled at 25-cm intervals for micropalaeontological, geochemical and stable isotope analyses.

Twelve of the micropalaeontological and geochemical variables determined have been used as proxy indicators. These are assumed to be directly related to wind strength (Ti, Cr), biological productivity (CaCO3, TOC, U, Ba, Br and I), intensity of the OMZ (planktonic foraminiferal tests whole–fragments ratio) and upwelling-induced productivity (δ13C Globigerina bulloides – δ13C Neogloboquadrina dutertrei). Examination for coherence and phase relationship with the SPECMAP stacked δ18O record, using cross-spectral analyses, has revealed that productivity proxies vary in concert with OMZ proxies, and are coherent with the orbital cycles of the Milankovitch model. However, upwelling and aeolian intensity proxies may not be related directly to the orbital parameters, but show instead a more complicated behaviour.