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Seasonal Variations in the Siliciclastic Fluxes to the Western Philippine Sea and Their Impacts on Seawater ε Nd Values Inferred From 1 Year of In Situ Observations Above Benham Rise
Author(s) -
Xu Zhaokai,
Li Tiegang,
Colin Christophe,
Clift Peter D.,
Sun Rongtao,
Yu Zhaojie,
Wan Shiming,
Lim Dhongil
Publication year - 2018
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1029/2018jc014274
Subject(s) - foraminifera , siliciclastic , oceanography , geology , water column , plankton , water mass , precipitation , seawater , paleontology , geography , sedimentary depositional environment , structural basin , meteorology , benthic zone
The Sr and Nd isotopic compositions of siliciclastic sediments and the Nd isotopic compositions of planktonic foraminifera are investigated in sediment trap samples collected in 2015 at water depths of 500 and 2,800 m to (1) track the seasonal changes in the sources and transport patterns of siliciclastic sediments to Benham Rise, (2) constrain the Nd isotopic compositions of the planktonic foraminifera throughout the water column, and (3) assess the influences of lithogenic inputs on the Nd isotopic compositions of the water masses. We demonstrate that volcanic matter and eolian dust are derived primarily from Luzon Island and the Ordos Desert, respectively. In addition, we show that reduced precipitation over Luzon Island and the weakened East Asian winter monsoon intensity result in mass fluxes from Luzon Island and the eastern Asian deserts to the sea, respectively, that are weaker in the winter than in the spring. Furthermore, the ε Nd values of the foraminifera collected at a water depth of 500 m change slightly in 2015, suggesting negligible impacts of lithogenic Nd inputs characterized by significant seasonal flux variations. In contrast, the ε Nd values of the planktonic foraminifera collected at a water depth of 2,800 m are systematically more radiogenic and appear to display seasonal variability. Such results suggest the rapid modification of ε Nd values during the settling of planktonic foraminifera by the precipitation of Mn coatings derived from water masses at deposition depths, with greater contributions of colder water masses originating from the volcanic Luzon Island margin during the winter.