Palaeoproductivity linked to monsoon variability in the northern slope of the South China Sea from the last 290 kyr: evidence of benthic foraminifera from Core SH7B

Abstract

AbstractA benthic foraminiferal proxy record of 290 kyr, acquired from Core SH7B in the northern continental slope of the South China Sea, was studied to identify the bottom-water environment changes since marine isotope stage (MIS) 8. The changes, including oxygenation and types of organic matter flux to the seafloor, reflect the palaeoproductivity fluctuations linked to monsoon variability. Four assemblages, characterizing different palaeoenvironmental changes, have been recognized by factor and cluster analysis with 32 foraminiferal species in 93 samples (>150 µm size fraction). Assemblage Pyrgo spp.–Hoeglundina elegans mainly dominates during interglacial periods of MIS 7, MIS 5 and MIS 3, suggesting well-oxygenated bottom environments with low sea surface productivity linked to a weak East Asian Winter Monsoon (EAWM). Assemblage Uvigerina spp.–Globocassidulina subglobulosa is composed of a constantly high percentage of shallow infaunal species, occurring in intervals of MIS 4, MIS 5, MIS 7 and MIS 8, which indicates that an enhanced EAWM led to a low seasonality of palaeoproductivity, a constant high flux of fresh and labile marine-derived organic particles to the seafloor and a low oxygen bottom environment. Assemblage Melonis barleeanus–Clavulina spp. is characterized by species that depend on seasonal supplies of more altered refractory organic matter and is mainly distributed in interglacial periods (late MIS 5, MIS 3 and MIS 1), suggesting a high seasonality of palaeoproductivity associated with a seasonal intensification of the EAWM. With low benthic foraminiferal diversity and abundance, assemblage Globobulimina affinis–Chilostomella mediterranensis was identified during the intermediate MIS 8 and early MIS 2. Both substantial input of terrigenous nutrients from an increased river run-off and an increased primary productivity correlated with an enhanced EAWM have led to abundant nutrient supplies and severe bottom-water oxygen depletion. As suggested by the composition of benthic foraminiferal in Core SH7B, changes in bottom-water environments of the northern South China Sea over the last 290 kyr were driven by the fluctuating palaeoproductivity linked to the high variability of the EAWM.