Late Quaternary changes in surface productivity and oxygen minimum zone (OMZ) in the northwestern Arabian Sea: Micropaleontologic and sedimentary record at ODP site 728A |
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| Authors: | AJAI K RAI S S DAS |
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| Institution: | (1) Shirshov Institute of Oceanology, Russian Academy of Sciences, 36 Nakhimovsky Prospekt, 117997 Moscow, Russia |
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| Abstract: | Changes in the abundance of selected planktic foraminiferal species and some sedimentological parameters at ODP site 728A
were examined to understand the fluctuations in the surface productivity and deep sea oxygenation in the NW Arabian Sea during
last ∼540 kyr. The increased relative abundances of high fertility taxa, i.e., Globigerinita glutinata and Globigerina bulloides mainly during interglacial intervals indicate intense upwelling. Strong SW summer monsoon probably increased the upwelling
in the western Arabian Sea during interglacial intervals and caused high surface productivities due to the lateral transport
of eutrophic waters. Most of the glacial periods (i.e., MIS 2, 4, 6, 8 and 12) are characterized by higher relative abundances
of Neogloboquadrina pachyderma and Neogloboquadrina dutertrei associated with Globigerinoides ruber. The more stratified condition and deep mixed layer due to increased NE winter monsoon are mainly responsible for the higher
relative abundances of N. pachyderma during glacial periods. Some of the glacial intervals (i.e., MIS 6 and 8) are also characterized by pteropod spikes reflecting
deepening of aragonite compensation depth (ACD) and relatively less intense oxygen minimum zone (OMZ) in this region due to
deep sea mixing and thermocline ventilation, and relatively less intense surface productivity during winter monsoon. The interglacial
periods are largely devoid of pteropod shells indicating more aragonite dissolution due to increased intensity of OMZ in the
northwestern Arabian Sea. |
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