Late Quaternary changes in surface productivity and oxygen minimum zone (OMZ) in the northwestern Arabian Sea; micropaleontologic and sedimentary record at ODP Site 728A

Online Access: Get full text
doi: 10.1007/s12040-011-0011-7
Author(s): Rai, Ajai K.; Das, S. S.
Author Affiliation(s): Primary:
University of Allahabad, Department of Earth and Planetary Sciences, Allahabad, India
Volume Title: Proceedings of the Indian Academy of Sciences: Earth and Planetary Sciences
Source: Proceedings of the Indian Academy of Sciences: Earth and Planetary Sciences, 120(1), p.113-121. Publisher: Indian Academy of Sciences, Bangalore, India. ISSN: 0253-4126 CODEN: PISAA7
Note: In English. 70 refs.; illus.
Summary: 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. In general, the interglacial periods are characterized by low sediment accumulation rates than the glacial intervals. On an average, the total biogenic carbonate percentages were higher during interglacial and during periods of higher surface productivity. Most terrigenous material was trapped on shelf during intervals of high sea level stands of interglacial, whereas more erosion of shelf increased the sedimentation rates during glacial periods. In addition, the fragmentation record may be the result of changes in intensity and vertical distribution of the OMZ with time. During glacial intervals, the lower boundary of the OMZ probably was in a shallower position than during interglacial periods, when dissolution increased as a result of higher organic production. The higher rates of sinking organic matter result into a stronger OMZ as oxygen is used to disintegrate the organic matter. This process lowers the pH of water which results into increased dissolution of calcium carbonate. Copyright 2011 Indian Academy of Sciences
Year of Publication: 2011
Research Program: ODP Ocean Drilling Program
Key Words: 24 Surficial Geology, Quaternary Geology; Arabian Sea; Cenozoic; Foraminifera; Globigerina; Globigerinacea; Globigerinidae; Indian Ocean; Invertebrata; Leg 117; Microfossils; Northwestern Arabian Sea; ODP Site 728; Ocean Drilling Program; Oxygen minimum zone; Paleoecology; Protista; Quaternary; Rotaliina; Upper Quaternary; Upwelling
Coordinates: N174042 N174042 E0594934 E0594933
Record ID: 2012071117
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data supplied by Springer Verlag, Berlin, Federal Republic of Germany