Sea-level rises at Heinrich stadials of early Marine Isotope Stage 3: Evidence of terrigenous n-alkane input in the southern South China Sea

The timing of suborbital-scale sea-level fluctuations within Marine Isotope Stage 3 (MIS 3) remains a matter of debate. We use a set of co-registered signals of the sediment core MD05-2897 from the southern South China Sea (SCS) to evaluate the phase relationship between sea-level fluctuations and climatic events during early MIS 3. During Heinrich Stadials 6, 5a and 5 (HS6, HS5a, HS5), planktonic foraminiferal δ18O values of core MD05-2897 increased by 0.8–1.0‰ due to an enrichment of δ18O in precipitation and/or a reduction of monsoon precipitation. The alkenone-derived sea surface temperature (U37K′-SST) recorded 1.0–2.0 °C cooling signatures during wintertime of HS6, HS5a and HS5, which were attributed to a stronger influx of cold surface waters from the northern SCS driven by the strengthened winter monsoon. Therefore, a combination of foraminiferal δ18O and U37K′-SST results well documents these Heinrich stadials of the East Asian monsoon climate. Moreover, we find that the terrigenous n-alkane abundance of core MD05-2897, which is independent of changes in vegetation types around the southern SCS throughout MIS 3, is potentially an indicator for relative sea-level changes on suborbital timescale. The n-alkane abundance was relatively higher during the first half of HS6, HS5a and HS5 and afterward significantly decreased during the second half of these Heinrich stadials. This may suggest relatively lower sea level at the beginning of Heinrich stadials and sea-level rises afterward. Our new results add to the growing body of evidence that the timing of millennial-scale sea-level rises during early MIS 3 was simultaneous with Heinrich stadials.