HR: 14:55h
AN: PP13D-04    [Abstracts]
TI: Monsoon Variability In The Western Arabian Sea During Last 10,000 Years BP: A Planktic Foraminiferal Abundances And It's Stable Isotope Records
AU: * Singh, A K
EM: ashutosh@prl.res.in
AF: Physical Research Laboratory, Stable Isotope Lab PGS DN, Physical Research Laboratory Ahmedabad, Ahmedabad, 380009, India
AU: Tiwari, M
EM: tmanish@prl.res.in
AF: Physical Research Laboratory, Stable Isotope Lab PGS DN, Physical Research Laboratory Ahmedabad, Ahmedabad, 380009, India
AU: Tiwari, M
EM: tmanish@prl.res.in
AF: NCAOR, NCAOR, Vasco da Gamma, Goa 403804, Vasco da gama, 403804, India
AU: Sinha, D K
EM: devasinha@yahoo.com
AF: Centre of Advanced Study in Geology, Delhi University, 110007, India, Centre of Advanced Study in Geology, Delhi University, New Delhi-110007, India, New Delhi, 110007, India
AU: Ramesh, R
EM: rramesh@prl.res.in
AF: Physical Research Laboratory, Stable Isotope Lab PGS DN, Physical Research Laboratory Ahmedabad, Ahmedabad, 380009, India
AB: Abstract: The western Arabian Sea responds to the southwest monsoon winds by upwelling colder and nutrient rich waters from the deeper layers, causing a reduction in the sea surface temperature and enhanced biological productivity. A number of paleoclimatic studies have been carried out in this region to elucidate past monsoon variability (Sirocco et al., 1993; Gupta et al, 2003; Tiwari, 2005; Saher et.al.; 2007). Globigerina bulloides, a planktic foraminiferal species normally inhabiting surface ocean waters in temperate latitudes ( Be and Tolderlund , 1977) also becomes abundant at tropical latitudes upwelling occurs, and in these cases its abundance can exceed considerably. The conspicuous fluctuation in the abundance of Gg.bulloides during upwelling and non upwelling intervals is established through several studies ( Thiede and Junger, 1980, Gupta et al, 2003) This robust relation has been used as a proxy for wind velocity at several different times in the past in the Arabian Sea (Anderson et.al., 2002). A significant result from some of these centennially resolved Holocene records is declining abundance of Globigerina bulloides which is paralleled by reduced insolation record and this has been inferred as declining strength of Asian Monsoon. We are presenting here the data from the core SS4018 from near the Gulf of Aden, Western Arabian Sea taken at a water depth of 2830 m, precisely dated by the radiocarbon method using Accelerator Mass Spectrometry on planktonic foraminiferal separates. We have carried out the planktic foraminiferal census counts for each sample to know the relative abundance of key species. In addition to this, we have also employed multi- proxy approach such as oxygen and carbon isotopes of planktic foraminiferal tests, TOC, CaCO3 (%) to strengthen our interpretation and also to understand the relationships amongst the proxies themselves. Abundance of the key planktic foraminiferal species and other proxy records reveal at least 3 major climatic events (M-1, M-2 and M-3) during the last 10,000yrs. The earliest one (M-1) is a major decline in the upwelling intensity during 7.9.-5.6 kyBP. We have observed the lowest abundance of upwelling indicator species (UIS), it goes down from 70(%) to 30(%), mixed dweller (MD) and thermocline dweller (TD) species were showing their maximum abundance and at that time Organic carbon (OC) value revealed the lowest amount. Oxygen stable isotope records were also suggesting the same results. The second event at 5.5-2.2 kyBP (M-2) corresponds to average upwelling. We have observed the 2-3 high peaks of (UIS), on average UIS were showing around 50-55(%) of their abundance during this period, thus we have concluded the moderate intensity of SWM winds during M-2. The third event at last 2ky (M-3), decreasing trend in the strength of the SWM has been observed on the basis of sharp decline in the abundance of UIS and OC amount. For this interval, we have observed the increasing trend in the MD and TD planktic foraminiferal species.
DE: 4200 OCEANOGRAPHY: GENERAL
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting