HR: 1340h
AN: PP43A-0671    [Abstracts]
TI: Southwest Monsoon (SWM) During The Holocene
AU: * Tiwari, M
EM: tmanish@prl.ernet.in
AF: Planetary and Geosciences Division, Physical Research Laboratory, Navrangpura, Ahmedabad, 380009 India
AU: Ramesh, R
EM: r.ramesh@prl.ernet.in
AF: Planetary and Geosciences Division, Physical Research Laboratory, Navrangpura, Ahmedabad, 380009 India
AU: Bhushan, R
EM: bhushan@prl.ernet.in
AF: Planetary and Geosciences Division, Physical Research Laboratory, Navrangpura, Ahmedabad, 380009 India
AU: Sheshshayee, M
EM: msheshshayee@hotmail.com
AF: Dept. of Crop Physiology, University of Agricultural Sciences, Bangalore, 560065 India
AU: Somayajulu, B
EM: soma@prl.ernet.in
AF: Planetary and Geosciences Division, Physical Research Laboratory, Navrangpura, Ahmedabad, 380009 India
AU: Jull, A
EM: jull@u.arizona.edu
AF: NSF Arizona AMS Facility, The University of Arizona, Tucson, AZ 85721 United States
AU: Burr, G
EM: burr@u.arizona.edu
AF: NSF Arizona AMS Facility, The University of Arizona, Tucson, AZ 85721 United States
AB: Paleomonsoon proxies from the western and eastern Arabian Sea have yielded contrasting results. For example a recent study from the western Arabian Sea (Gupta et al., 2003, Nature, 421, 354-357) has shown that SWM declined during Holocene based on a single proxy viz. declining abundance of G. bulloides (a planktonic foraminifera). In contrast, studies from eastern Arabian Sea along the southwestern coast of India have revealed that SWM strengthened during the above period based on other proxies such as oxygen and nitrogen isotopes (Sarkar et al., 2000, Earth Planet. Sci. Lett., 177, 209-218; Agnihotri et al., 2003, The Holocene, 13, 701-713). To resolve this apparent contradiction, multi-proxy analyses was carried out on a sediment core (SS4018G) selected from the mouth of the Gulf of Aden, Western Arabian Sea (13.2°N, 53.2°E; water depth: 2830 m; core length: 130 cm). Fourteen radiocarbon dates were obtained on handpicked species of planktonic foraminifera employing the Accelerator Mass Spectrometry. These span the past ~19,000 calendar years, and the average sedimentation rate is ~7 cm/kyr. The western Arabian Sea experiences intense productivity due to wind-induced upwelling during the SWM. The proxies analyzed are CaCO₃, organic carbon (C_org), C/N and δ¹⁵N of the sedimentary organic matter alongwith δ¹⁸O and δ¹³C of three species of planktonic foraminifera ( Globigerinoides ruber, Globigerinoides sacculifer and Globorotalia menardii). During the Holocene, the CaCO₃ concentration (weight %) as well as the burial flux exhibits a decreasing trend (akin to calcitic G. bulloides abundance). Had this decrease in calcitic productivity been due to reducing SWM, the organic productivity should have also shown a similar decline. But neither the organic carbon concentration nor its burial flux exhibits a declining trend. Similarly, other organic productivity indicators i.e., δ¹³13C and δ¹⁵N do not decrease and stay more or less uniform during the Holocene. One way to reconcile this contrasting behaviour of proxies is that increasing monsoon strength favours silicate rather than carbonate production. Further, it causes cross equatorial transport of the nutrient poor water along the Somali current due to which the organic productivity indicators do not show a conspicuous increasing trend during the Holocene. Thus the declining calcitic productivity seen in western Arabian Sea during the Holocene could in fact be a manifestation of increasing SWM.
DE: 4901 Abrupt/rapid climate change (1605)
DE: 4924 Geochemical tracers
DE: 4936 Interglacial
DE: 4944 Micropaleontology (0459, 3030)
DE: 4964 Upwelling (4279)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005