Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

Anil K. Gupta ¹, David M. Anderson ²

Affiliations
1 Department of Geology & Geophysics, lndian Institute of Technology, Khar agpur - 721 302, IN
2 NOAA Paleoclimatology Program, 325 Bloadway, Bouldct, CO 80305-3328, USA, US

Abstract

South Asian monsoon is an important part of global climate, affecting large areas of the Indian subcontinent Monsoon is life and death to the people of South Asia as good monsoon is a boon to taimers whereas an unusual monsoon can bring misery to the people through widespread floods and droughts Strong differential heating of the Indian landmass and the latent heat released from piccipitation mainly drive the present day summer monsoon circulation During the northeast (winter) monsoon season, winds are dry and biological productivity in the northern Indian Ocean is low providing little food to the deep-sea In opposition, the intense, wet, monsoonal winds of thc southwest (summer) monsoon cause widespread upwelling and high surface productivity, thus a high supply of organic particles to thc sea floor During high surface productivity, distinct fauna and flora flourish in the surface water column in various parts ot the northern Indian Ocean Study of these monsoon proxics accumulating in layers of sediment over hundreds to millions of years help understand the history of monsoons over various time scales Recent study suggests a mechanistic link between the North Atlantic Ocean and the southwest monsoon at century-millennial time scales during the Holocene, suggesting importance of tropics and high latitude teleconnection On short time scales monsoon variability has also been related to the Indian ocean Sea Surface Temperature (SST), Himalayan-Eurasian snow as well as El Nino-Southern Oscillation(ENSO) This study reviews different aspects of past monsoon variability and its future implications.

Keywords

lndian Ocean, Summer monsoon, Biological productivity, Holocene, Monsoon proxies.

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Moumita Das ¹, Anil K. Gupta ¹, David M. Anderson ²

Affiliations
1 Departrnent of Geology and Geophysics, Indian Institute of Technology, Kharagpur 721 302, IN
2 NOAA Paleoclimatology Program, 325 Broadway, Code E/GC, Boulder, CO 80302, US

Abstract

We analyzed a 1000-year census record of benthic foraminifera in core RC 2730 (water depth 698 m), off the Oman Margin, northwestern Arabian Sea, to understand the influence of surface productivity on bottom water environments in response to changes in the intensity of the southwest (SW) monsoon winds. We employed knowledge of the ecology of recent deep-sea benthic foraminifera from different ocean basins for environmental interpretation of benthic assemblages. Benthic faunal data suggest that the interval 1200 - 1400 A.D. is marked by an increased influx of organic matter to the northwestern Arabian Sea floor that resulted from higher surface productivity during a stronger SW monsoon. This interval corresponds to the Medieval Warm Period and a wet phase in India. The organic flux was low during the Little Ice Age (1450- 1850 A.D.) when the SW monsoon was weak. Over the last millennium, the SW monsoon was weakest during the Maunder Minimum, and since then it has shown a continuous intensification, coinciding with increased surface air temperatures.

Keywords

Last millennium, Foraminifera, Organic flux, Southwest monsoon, Northwestern Arabian Sea.

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