Summary of Abstract Submission

Abstract Submission No. IO50-02-0010PresentationPoster

CHANGES IN PRODUCTIVITY AND DENITRIFICATION FOR THE PAST 90 KA IN THE EASTERN ARABIAN SEA: CONTROLLED BY MONSOONS OR CIRCULATION?

Pratima. M. Kessarkar*1, V. Purnachandra Rao1, Lina L. Fernandes1, Masood Ahmed2

1 CSIR-National Institute of Oceanography, Dona Paula 403 004, Goa, INDIA
2 CSIR-National Geophysical Research Institute, Uppal Road, Hyderabad, INDIA

ABSTRACT :

Past changes in Indian summer monsoon intensity have often been inferred, using upwelling related proxies from the Arabian Sea and, terrestrial inputs such as monsoon runoff related in the eastern region and wind derived in the western region. Here we present multi-proxy data on AMS dated core from the eastern Arabian Sea covering past 90 ka, using CaCO3, total organic carbon, total nitrogen, 18O of G. ruber ,15N of organic matter, environmental magnetic properties and clay mineralogy. The productivity proxies like CaCO3, total organic carbon, total nitrogen showed distinct variations suggesting there has been change in productivity in this region. The 18O values range between 2.3 and 0.0 , with high glacial-interglacial amplitude  18O of ~2.3. The 15N fluctuates between 3.5 and 7.3 signifying changes in denitrification intensity. Clay minerals show variations between the Marine Isotope Stages (MIS) with lower smectite and high illite at MIS 2 and 4 indicating reduced monsoon. Magnetic susceptibility (MS) values range between 13 and 109 x 10-8m3kg-1 with high values centering mid MIS1, 3 and 5 signifying intensified monsoon. The reduced denitrification intensity suggests reduced monsoon during Heinrich Event 1 (H1) to H7 coinciding with changes in the north Atlantic deep water formations. Putting together it is evident that the water column derived proxies that are influenced by monsoon induced circulation changes do not always correlate well with the land derived proxies based on precipitation variation. This may be due to changes in circulation, interference by regional signals and therefore care should be taken while using these proxies.