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On the evolution of the oxygen minimum zone in the Arabian Sea during Holocene time and its relation to the South Asian monsoon
Staubwasser, M.; Dulski, P. (2002). On the evolution of the oxygen minimum zone in the Arabian Sea during Holocene time and its relation to the South Asian monsoon. Geol. Soc. Lond. Spec. publ. 195: 433-443
In: Hartley, A.J. et al. (Ed.) Geological Society Special Publication. Geological Society of London: Oxford; London; Edinburgh; Boston, Mass.; Carlton, Vic.. ISSN 0305-8719, more
Peer reviewed article  

Also published as
  • Staubwasser, M.; Dulski, P. (2002). On the evolution of the oxygen minimum zone in the Arabian Sea during Holocene time and its relation to the South Asian monsoon, in: Clift, P.D. et al. The tectonic and climatic evolution of the Arabian Sea region. Geological Society Special Publication, 195: pp. 433-443, more

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Keywords
    Arabian Sea; Arabian sea; Holocene; Oxygen minimum layer; Thermocline; Marine

Authors  Top 
  • Staubwasser, M.
  • Dulski, P.

Abstract
    The evolution of the oxygen minimum zone within the permanent thermocline of the Arabian Sea (AS) during early and mid-Holocene time was reconstructed from a laminated sediment core taken from the Pakistani continental margin (316 m water depth). A trace metal proxy for water column ventilation (authigenic U) was extracted by principal component analysis from a large dataset of inorganic and total organic carbon (TOC) measurements. This proxy is compared with preservation of lamination and paired benthic-planktonic 14C data. The latter record the Δ14C depth gradient in the AS and may provide a sensitive indicator for ventilation by enhanced surface convection. Laminated sediments were preserved between 10 and 7.5 ka bp on the Pakistani continental margin and accumulated authigenic U independently from TOC accumulation. The inferred reducing conditions in the AS thermocline are in agreement with high palaeoproductivity in the western AS upwelling region. Century-scale variability in northern AS surface hydrography (recorded as δ18O in planktonic foraminifera) is reflected in the accumulation of authigenic U on the Pakistani margin. The agreement of AS surface conditions, which generally reflect the South Asian monsoon (SAM), with ventilation of the OMZ confirms a dominant influence of the SAM and summer monsoon upwelling in particular on AS thermocline ventilation during early Holocene time. However, the preservation of laminated sediments off Pakistan and palaeoproductivity in the western AS disagree before 10 ka cal. bp, and between 7.5 and 5.5 cal. ka bp. Here, the absence of lamination indicates better ventilation of the thermocline, whereas palaeoproductivity in the upwelling region was high. This suggests that other factors may also have contributed in variable proportions to AS thermocline ventilation. At present, these factors include lateral advection of oxygenated Central Indian Water and ventilation by winter surface convection in the northern AS.

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