Recent sedimentary records from the Arabian Sea |
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| Authors: | B L K Somayajulu D N Yadav M M Sarin |
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| Institution: | (1) Physical Research Laboratory, 380009 Ahmedabad |
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| Abstract: | An attempt is made to understand the redox conditions that prevailed in the north eastern continental margins of the Arabian
Sea and in the nearby deep water regions during the past few centuries using short undisturbed sediment cores. The geochronology
is accomplished using210Pb excess method and the proxy indicators chosen for productivity and associated redox changes are CaCO3, organic matter (OM), Mn and U along with major elements Fe and Al. Such changes in principle are related to high productivity
in the overlying waters which in turn depend on monsoonal intensity that causes upwelling responsible for increase in productivity.
Alongwith the published data on gravity cores from the same region, our measurements suggest the following:
At ∼ 300 m water depth, south of 21°N, the sediment-water interface at depths of ∼ 300 m had been anoxic during the time span
represented by the presently studied cores for approximately ∼ 700y as evidenced by low Mn/Al (< 0.7 × 10−2) and high U/Al (> 10−4) weight ratios. In some adjacent deeper regions, however, the environment turned oxic around ∼ 200 y BP. Whereas both Mn
and Ra were lost to the overlying waters in the anoxic regions (depth ∼340m), the Mn that diffused from deeper sections appears
to have mineralized at the sediment-water-interface. Studies of this type on long undisturbed cores from the margins of the
Arabian Sea and the Bay of Bengal, involving several proxies and geochronology by more than one method are needed to understand
short term environmental (and monsoonal intensity) changes of the recent past with high resolution. |
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| Keywords: | Sedimentary records Arabian Sea lead 210 trace metals productivity monsoons |
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