News insights of the hydrology of the Northwestern subtropical Pacific Ocean from εNd investigations of the South China Sea sediments

Abstract:

Seawater Nd isotopic composition (εNd) extracted from planktonic foraminifera G. ruber have been investigated on core MD05-2904 located on the northwestern margin of the South China Sea (SCS) at 2000 m water depth to reconstruct hydrological variations since the Last Glacial Maximum (LGM) of the western subtropical North Pacific that still poorly documented. For the last 25 kyr, εNd values obtained on foraminifera present large range from -4 to -6.7 suggesting large changes in the contribution of the NPDW (εNd = -4) and the UCDW (εNd -6 to -8) in the western Pacific. The glacial εNd values (~ -6.5) are interestingly similar to those obtained in the South Atlantic and in the Indian Ocean during the LGM and indicate a strong northward propagation of the Southern Sourced Water (SSW) in the subtropical western North Pacific. During the deglaciation, εNd records indicate a relatively decreased proportion of the SSW in the deep-water component of the western subtropical Pacific interrupted by two negative excursions of the εNd implying higher proportion of SSW during the time intervals 17 - 15 cal kyr BP and 10 - 8 cal kyr BP coeval to the Heinrich Statial 1 (HS1) and the early Holocene. The seawater εNd record is also well correlated to δ¹³C record obtained on benthic foraminifera Cibicides wuellerstorfi of the SCS and Southern Ocean confirming that εNd record reflect global circulation changes. The negative shifts centered on the Heinrich Statial 1 (HS1) is coeval with an enhanced upwelling in the Southern Ocean associated to pole wards shifts of the southern westerly inducing a enhanced formation of the SSW that propagate to the subtropical western Pacific. The negative excursion of the εNd during the Early Holocene (~10 - 8 cal kyr BP) indicate a relatively higher proportion of the SSW that could be associated to a higher production of the SSW as it was already recently observed in the South Atlantic and/or a possible reduction of the NPIW in the North Pacific induce by an intensification of the summer East Asian monsoon rainfall.