New insights into the current- and past hydrology of the north-western subtropical Pacific Ocean over the past 25 kyr, based on investigations of the Nd isotopic composition of seawater and deep-sea sediments from the northern South China Sea

• Main Author: Wu, Qiong
• Other Authors: Géosciences Paris Sud (GEOPS), Université Paris-Sud - Paris 11 (UP11)-Centre National de la Recherche Scientifique (CNRS), Université Paris Sud - Paris XI, Christophe Colin
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: HAL CCSD 2014
• Subjects: Authigenic phases; Paleohydrology; Last glacial period; Nd isotopic composition; Seawater; South China Sea; Philippine Sea; Hydrology; Holocene; Foraminifera; Nepheloid layers; Composition isotopique du Nd; Holocène; Paléohydrologie; Dernière période glaciaire; Phases authigéniques; Foraminifères; Couche néphéloïde; Hydrologie; Mer des Philippines; Mer de Chine du Sud; Eau de mer; [SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry; [SDU.STU.PG]Sciences of the Universe [physics]/Earth Sciences/Paleontology; [SDU.STU.CL]Sciences of the Universe [physics]/Earth Sciences/Climatology; [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography; Pacific; Planktonic foraminifera
• Online Access: https://tel.archives-ouvertes.fr/tel-01362508; https://tel.archives-ouvertes.fr/tel-01362508/document; https://tel.archives-ouvertes.fr/tel-01362508/file/VD2_WU_QIONG_08092014.pdf

The aim of this study is to reconstruct the evolution of the hydrology of the western subtropical North Pacific Ocean by using εNd proxy analysed on foraminifera and dispersed authigenic ferromanganese oxide precipitates in sediments from deep-sea cores collected in the northern SCS. Before using the εNd proxy on deep sea sediments of the SCS, Nd of 16 seawater profiles collected in the northern South China Sea (SCS) and the Philippine Sea were investigated to establish the εNd distribution of water masses along the tropical western Pacific and the SCS that, until now have not been documented. εNd values for mid- and deep-water masses of the Philippine Sea and the SCS range from -2.7 to -4.4 and generally increase slightly with water depth. In the Philippine Sea, εNd values for the North Pacific Intermediate Water (NPIW) reach- 2.7±0.4 at mid-depths (500 to 1400 m). Below ~1800 m, the Pacific Deep Water (PDW) is characterized by less radiogenic Nd (-4.1±0.5) indicating the instrusion of southern sourced water masses. For most of the stations in the Northern SCS, water masses below 1500m (PDW) display homogenous εNd values (~ -4.1) similar to those of the PDW in the Philippine Sea. εNd values for the South China Sea Intermediate Water (SCSIW, 500-1500m) vary from -3.0 to -3.9 as a result of the vertical mixing of the NPIW with the PDW in the SCS. Seawater εNd values for the SCS (~5.3 to -7.0) display local modification in areas where the water lies above sediment drift deposit systems. This implies that “boundary exchange” with unradiogenic sediments (around~11) may occur temporally and spatially and does not modify he Nd isotopic composition of the PDW in the Northern SCS. In a second step, seawater εNd extracted from cleaned planktonic foraminifera G. ruber has been investigated on core MD05-2904, collected at a deph of 2000m on the north-western margin of the SCS. This study was undertaken in order to reconstruct hydrological variations since the LGM in the western subtropical North Pacific. The εNd records ...