Palaeoceanography of the last glacial maximum in the eastern Indian Ocean:planktonic foraminiferal evidence

Palaeoceanographic conditions in the eastern Indian Ocean for the last simi lar to 30 kyr are documented by means of planktonic foraminiferal analyses of 10 gravity cores. Quantitative foraminiferal analysis (%), Q-mode factor analysis, the modem analog technique (MAT) and oxygen-isotope analyses are used. A conspicuous increase during the last glacial maximum (LGM) of fora miniferal fragmentation resulting from a more productive Java upwelling sys tem and/or a more corrosive Antarctic Intermediate Water (AAIW) was found a t intermediate water depths (similar to 1000 m). Contrasting Q-mode factors based on foraminifera between today and the LGM suggest changes in the the rmocline depth, sea-surface temperature (SST), upwelling, and the strength of both the Australasian Mediterranean Water (AAMW) and the Indian Central Water (ICW). The decrease in the percentage abundance of shallow-dwelling a nd symbiont-bearing planktonic foraminifera, the increase in percentage of the upwelling-related species Globorotalia cultrata and Neogloboquadrina du tertrei, and factor 3 (dominated by Globorotalia tumida and Globigerinella siphonifera) suggest a stronger Java upwelling system during the LGM. A ste eper, steric latitudinal gradient (in the presence of a weak Leeuwin Curren t), and a geostrophic flow similar to today's is postulated for the LGM, an d this must have prevented upwelling offshore Western Australia. Today's AA MW-ICW sharp front was weaker during the LGM when the AAMW was saltier, coo ler, and nutrient richer and more similar to the ICW. During the LGM, a mor e gentle SST latitudinal gradient over the similar to 16 to similar to 23 d egrees S region contrasts with today's steeper conditions at the AAMW-ICW F ront. Also, for the LGM, a nutrient-rich ICW may explain previously documen ted increases in mass accumulation rates of CaCO3, organic carbon and benth onic foraminifera in a region where the nutricline was deep and within the lower euphotic zone. (C) 1999 Elsevier Science B.V. All rights reserved.