Linkages between East China Sea Deep-sea Oxygenation and the Variability
of the East Asian Summer Monsoon and Kuroshio Current over last 400,000
years
Abstract
The East China Sea (ECS) seasonally receives a high organic input due to
the terrestrial organic matter influx, which is controlled by the East
Asian Summer Monsoon (EASM), and from increased productivity due to
upwelling of the subsurface Kuroshio Current (KC). Changes in benthic
foraminiferal assemblage composition in combination with
paleoceanographic proxy data (CaCO3 (%), TOC (%), δ13Cpf, and δ18Obf)
are used to reconstruct bottom water oxygenation and organic export flux
variability over the last 400 kyr in the ECS. Multivariate analyses of
benthic foraminiferal census data identified six biofacies
characteristic of varying environmental conditions. These results
suggest enhanced EASM precipitation and KC upwelling directly influenced
bottom water oxygen content and organic export flux in the ECS. The ECS
bottom water was suboxic from MIS (Marine Isotope Stage) 11 to 8;
suboxic to dysoxic between MIS 7 and 6, strongly dysoxic between mid-MIS
5 and 4, and exhibited high variability between MIS 3 and 1. Spectral
analysis of abundance variations of the representative genera
Quinqueloculina (oxic), Bulimina (suboxic), and Globobulimina (dysoxic)
reveals a robust 23 kyr signal, which we attribute to
precessionally-paced changes in surface productivity and bottom water
oxygenation related to EASM and KC variability over the past 400 kyr.