HR: 16:40h
AN: PP14A-03    [Abstracts]
TI: How Sensitive is the Asian Monsoon System to Remote Forcing?: A Perspective from the late Quaternary Bay of Bengal and Arabian Sea Regions
AU: * Stoll, H M
EM: hstoll@williams.edu
AF: Williams College, Geoscience Dept, Williamstown, MA 01267, United States
AU: * Stoll, H M
EM: hstoll@williams.edu
AF: University of Oviedo, Dept. Geologia, Oviedo, 33005, Spain
AU: Vance, D
EM: dvance@bristol.ac.uk
AF: University of Bristol, Dept. of Earth Sciences, Bristol, BS81RJ, United Kingdom
AU: Arevalos, A
EM: alicia_arevalos@yahoo.com
AF: Williams College, Geoscience Dept, Williamstown, MA 01267, United States
AU: Shimizu, N
EM: nshimizu@whoi.edu
AF: Woods Hole Oceanographic Institute, Dept. of Geology, Woods Hole, MA 02543, United States
AU: Burke, A
EM: burke.andrea@gmail.com
AF: Williams College, Geoscience Dept, Williamstown, MA 01267, United States
AU: Ziveri, P
EM: patrizia.ziveri@falw.vu.nl
AF: Vrije University, Earth Science Dept., Amsterdam, 1081HV, Netherlands
AB: Over the Quaternary has the Asian monsoon system responded predominantly to regional climate drivers such as orbital changes in summer insolation and the land-sea pressure gradient, or global climate boundary conditions such as the extent of northern hemisphere(NH) ice sheets and snow cover? Our paleorecords from the Bay of Bengal and Arabian Sea reveal contrasting influence of the NH ice sheets. Seawater Nd isotopic ratios in the northern Bay of Bengal, reconstructed from planktic foraminifera, are sensitive to the degree of northward penetration of the Asian summer monsoon precipitation into the nonradiogenic terranes of the Himalayas. Shifts in river sources from the more northerly Ganges-Brahmaputra watershed to the more southerly Arakan coastal river systems respond dominantly to ITCZ movement driven by Northern Hemisphere cooling during 100 ky glacial-interglacial cycles. A nonlinear correlation of epsilon Nd with ice volume suggests that ITCZ movement responds to aerial coverage of ice sheets and snow rather than to ice thickness and volume as expected from albedo forcing. These data add support to recent general circulation models of which in this region show strong ITCZ response to Northern Hemisphere ice coverage. A small component of Nd isotopic variation on precessional timescales corresponds to ITCZ movement within the southern Irrawaddy and Arakan coastal systems. There is a strong connection between ITCZ movement and productivity even in a non-upwelling system such as the Bay of Bengal. In the northernmost Bay of Bengal, productivity indicators from Sr-Ca ratios in coccoliths and from Ba-Ti ratios of sediments exhibit principally glacial-interglacial variability consistent with the epsilon Nd record. Higher productivity during interglacials may reflect either higher riverine nutrient sources or stronger wind- driven eddy pumping. In the more southerly Andaman Sea, Sr-Ca ratios in coccoliths reveal productivity variations dominantly on precessional scales. Highest productivity occurs during the period of high summer insolation, which appears to drive local river nutrient influx. In the upwelling system of the Arabian Sea, productivity has long been used as an indicator of the intensity of monsoon winds. In prior studies, suppression of precessional productivity peaks during glacial conditions has been interpreted as evidence for distal (ice sheet or interhemispheric SST contrast) modulation of the monsoon system in the Arabian Sea. Using a new productivity signal which is set in the photic zone, the Sr-Ca ratio of coccoliths, we infer productivity peaks at 10 and 32 ky coherent with precessional summer insolation maxima. The surface-set coccolith productivity record contrasts with biogenic accumulation rate (AR) based productivity indicators in the same core which do not exhibit a 32 ky peak. Some prior evidence for dominantly 100ky cyclicity in Arabian Sea AR-based productivity records may need to be reconsidered in terms of preservational rather than productivity effects.
DE: 1040 Radiogenic isotope geochemistry
DE: 3305 Climate change and variability (1616, 1635, 3309, 4215, 4513)
DE: 3344 Paleoclimatology (0473, 4900)
DE: 4855 Phytoplankton
DE: 4926 Glacial
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting