Stratigraphic gaps at northern South China Sea margin reflect changes in Pacific deepwater inflow at glacial Termination II

Abstract

To constrain short-term changes of climate and oceanography in the northern South China Sea (SCS) over interglacial marine isotope stage (MIS) 5.5, we studied planktic and benthic δ 18O records of seven marine sediment cores with a time resolution of 70–700 yr. Using 6-8 tie points the planktic records were tuned to the U/Th chronology of speleothem δ 18O records in China and Europe. The last occurrence of pink Globigerinoides ruber marks the top of Heinrich stadial 11 (HS-11) near 128.4 ka. HS-11 matches a 2300-yr long positive δ 18O excursion by 1.5/0.8‰ both in planktic and benthic δ18O records. Hence half of the planktic δ18O signal was linked to increased upwelling of 18O- and 12C-enriched deep waters in the southwestern SCS. The increase was possibly linked to a strengthened inflow of Pacific deep waters through the Bashi Strait, that form a boundary current along the northern slope of the SCS, building a major sediment drift. At its lower margin near 2300–2400 m water depth (w.d.) Parasound records reveal a belt of modern erosion. At the end of glacial termination 2, stratigraphic gaps deleted HS-11 in core MD05-2904 and subsequent peak MIS 5.5 at ODP Site 1144. Likewise hiatuses probably earmarked all preceding glacial terminations at Site 1144 back to 650 ka. Accordingly, boundary current erosion then shifted ∼300 m upslope to ∼2040–2060 m w.d. These vertical shifts imply a rise in boundary current buoyancy, that in turn may be linked to transient events of North Pacific deepwater formation similar to that traced in SCS and North Pacific paleoceanographic records over glacial termination 1.