Benthic foraminiferal paleoceanography of the South China Sea over the last 40,000 years

Abstract

Benthic foraminifera in gravity and piston cores from two sites of the northern and southern slopes of the South China Sea (SCS) were analyzed to evaluate changes in surface productivity and deep-water mass characteristics over the last 40,000 years. Our observations suggest that changes in organic carbon flux, that is food supply, and chemical and/or physical properties of the ambient water mass may be the two primary and intercorrelated factors controlling the distribution patterns of benthic foraminifera. When organic carbon flux increased above 3.5 g C m −2 yr −1 in the southern SCS during the last glacial maximum and in the northern SCS during the first part of the Holocene around 10 ka B.P., a group of detritus feeders including Bulimina aculeata and Uvigerina peregrina dominated the benthic foraminiferal assemblage as shown by relative abundance (%) and accumulation rates. This may reflect episodes of increased surface productivity, possibly induced by increased input of nutrients from nearby river runoff. Suspension feeders such as Cibicidoides wuellerstorfi and a group of `opportunistic' species including Oridorsalis umbonatus, Melonis barleeanum and Chilostomella ovoidea gradually became more abundant than detritus feeders as soon as the organic carbon flux decreased to 2.5–3.5 g C m −2 yr −1. Similar glacial to interglacial changes in relative abundance and accumulation rates were observed in both cores for a number of species, including Eggerella bradyi, Globocassidulina subglobosa, Astrononion novozealandicum, Sphaeroidina bulloides and Cibicidoides robertsonianus. These changes were not correlated to the distribution patterns of organic carbon in both cores and may have been related to yet unspecified changes in chemical and/or physical properties of the ambient water mass, independent of changes in organic carbon flux.