Linkages Between East China Sea Deep‐Sea Oxygenation and Variability in the East Asian Summer Monsoon and Kuroshio Current Over the 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 the increased productivity driven by 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 that enhanced EASM precipitation and KC upwelling directly influenced organic export flux and bottom water oxygen content in the ECS. The ECS bottom water was suboxic during Marine Isotope Stage (MIS) 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 relative abundances of 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 KC variability over the past 400 kyr.

Organic carbon burial and their implication on sea surface primary productivity in the middle Okinawa Trough over the past 200 ka

“…The average Dd 13 C P-B is -0.18% during MIS 6, compared with the average ratio of 0.77% during MIS 1-5. The dramatic depletion in d 13 C G. ruber during MIS 6 are also recorded in adjacent IODP site U1429 (Vats et al, 2021). Furthermore, the Dd 13 C P-B ratio remains stable during MIS 1-5, and no glacial-interglacial cycle is identified.…”

“…During MIS 2 and MIS 6, the sea level is similar (Figure 4G). But the subsurface KC upwelling is strong during MIS 2, and weak during MIS 6 (Vats et al, 2021). During MIS 6, Oligotrophic KC and weak subsurface upwelling led to poor-nutrient surface water.…”

Sediment depositional pattern in the northern Japan Sea over the last 1200 ka and its linkages to orbital forcing

“…The comparison of pyrite abundance with the last ~800 ka sea level change (Spratt & Lisiecki, 2016) shows a relatively higher abundance of pyrite during the period of higher sea level in the last 800 ka (Figure 6). The higher productivity causes a stronger oxygen minimum zone in the shallow and marginal sea (Das et al, 2017; Vats et al, 2021) and increased iron availability in the Japan Sea supports pyrite formation.…”

“…The higher productivity causes a stronger oxygen minimum zone in the shallow and marginal sea (Das et al, 2017;Vats et al, 2021) and increased iron availability in the Japan Sea supports pyrite formation.…”

“…Hilgen et al (2020) reported a low amplitude cycle having periods of 168 and 221 kyr surrounding 200 kyr cycles. The inflow of TWC modulates the 23 kyr cycle in the Japan Sea (Das et al, 2021;Vats et al, 2020Vats et al, , 2021, and global ice volume changes modulate the 41 kyr cycle in the Japan Sea. This is the first record that shows the presence of 228 kyr cycles in the Pleistocene record of the Japan Sea, which suggests the sediment depositional pattern in the Japan Sea was influenced by 200 kyr cycles.…”