HR: 1330h
AN: GC12A-0152    [PDF]
TI: Millennial-Scale Abrupt Changes in Strength of the Monsoons During the Last Glacial: Event Sequence During Low Latitude Stadial/Interstadial Transitions
AU: * Higginson, M J
EM: mhigginson@umassd.edu
AF: School for Marine Science and Technology, University of Massachusetts Dartmouth, 706 South Rodney French Boulevard, New Bedford, MA 02744 United States
AU: Altabet, M A
EM: maltabet@umassd.edu
AF: School for Marine Science and Technology, University of Massachusetts Dartmouth, 706 South Rodney French Boulevard, New Bedford, MA 02744 United States
AU: Wincze, L
EM: lwincze@brown.edu
AF: Department of Geological Sciences, Brown University, Box 1846, Providence, RI 02912 United States
AU: Herbert, T D
EM: timothy_herbert@brown.edu
AF: Department of Geological Sciences, Brown University, Box 1846, Providence, RI 02912 United States
AU: Murray, D W
EM: dmurray@brown.edu
AF: Center for Environmental Studies, Brown University, 135 Angell Street, Box 1943, Providence, RI 02912 United States
AU: Murray, R W
EM: rickm@bu.edu
AF: Department of Earth Sciences, Boston University, 685 Commonwealth Avenue, Boston, MA 02115 United States
AB: We exploit the unprecedented ability to synchronize two high-resolution sedimentary records from the Oman and Pakistan margins of the Arabian Sea to derive sea surface temperature (SST) gradient estimates over the last 65 Kyr. Millennial-scale cycles in monsoon dominance parallel Dansgaard-Oeschger events recorded in Greenland. Switches occurred during the last glacial period between a strong summer monsoon climate mode (inter-stadials) and an intensified winter monsoon (during stadials). The amplitude of individual monsoon events and Greenland temperature extremes appears broadly comparable, suggesting that the response to, and likely forcing for, such events was quasi-global in nature. The fidelity of the sedimentary nitrogen isotope record has allowed us to identify a 20cm interval at ODP Site 723 on the Oman margin containing a stadial/inter-stadial between 43-42 Kyr BP. We employ sedimentary $\delta^{15}$N, chlorin pigment and alkenone abundances, major and minor element analyses of 2mm samples across this interval to generate a comprehensive, multi-proxy data set to understand the sequence of climatic events, especially the relative intensity of summer and winter monsoons, during these times. A lack of evidence for bioturbation in excess of our sampling resolution facilitates decadal-scale climatic reconstructions. Using a four-component flux-dilution model, we show that the deposition of carbonate decreased in parallel with an increase in TOM flux from stadial to inter-stadial time. This interval is also marked by a significant drop in lithogenic flux, analogous to a similar decrease noted during deglaciation in the western Arabian Sea. Combined with alkenone U$^{K'}_{37}$-derived estimates for SST, we conclude that the climatological shift from stadial to inter-stadial conditions at low latitudes was characterized by several switches in mean monsoon state. The winter monsoon was the dominant mode during maximum stadial conditions, and conversely that the summer monsoon was dominant during maximum interstadial-like conditions. However, each interval was separated by a distinct `inter-monsoon' mode, indicated by a higher continental dust flux but warmer SST. Proxy records for changing bottom-water oxygenation show near-identical results down to the mm-scale, but hint at increased export production leading the onset of anoxia during the stadial/inter-stadial transition. The coherence of all sedimentary signals depicts a wholesale reorganization of the Arabian Sea climate and marine ecosystem over approximately 200 years, an interval that may be associated with monsoon modulation by small oscillations in solar irradiance.
UR: http://www.smast.umassd.edu/cmastweb/biohigginson.html
DE: 1055 Organic geochemistry
DE: 2162 Solar cycle variations (7536)
DE: 3374 Tropical meteorology
DE: 4215 Climate and interannual variability (3309)
DE: 4267 Paleoceanography
SC: Global Climate Change [GC]
MN: 2003 Fall Meeting