Palaeoceanography of the Banda Sea, and Late Pleistocene initiation of the Northwest Monsoon

Abstract

This paper details the Late Quaternary palaeoceanography of the Banda Sea based on analysis of core SHI 9016, located east of Timor. This core is located below the pathway of the Indonesian Throughflow, at a depth of 1805 m bsl. Planktonic foraminifera assemblages, the δ18O and δ13C of the foraminifer Globigerinoides ruber, and the total carbonate content of each sample were used to reconstruct the vertical structure of the water column through the past ∼ 80,000 yr. Today, the core site is characterised by high sea-surface temperature and high precipitation, which results in the formation of a low-salinity boundary layer. Sea-surface temperature estimates down core indicate minimal cooling during the last glacial maximum. Mean sea-surface temperatures ranged between 29.8°C and 26.6°C for the past ∼ 80,000 yr; sea-surface seasonality never increased above 3°C. In addition, the abundance of the planktonic foraminifera Neogloboquadrina dutertrei, Neogloboquadrina pachyderma, and Globigerinoides quadrilobatus indicates that the mixed layer (the low-salinity boundary layer of the Throughflow) thinned during Marine Isotope Stages 3 and 2. This enhanced a deep chlorophyll maximum (DCM) layer. The Northwest Monsoon was less intense for about 60,000 yr and then 'switched on' at ∼ 15,000 cal yr BP. This thickened the mixed layer, reducing the DCM, and increased SST seasonality in the Banda Sea.