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Tracing Water Masses and Assessing Boundary Scavenging Intensity With Beryllium Isotopes in the Northern South China Sea
Author(s) -
Kong W. Y.,
Zhou L. P.
Publication year - 2021
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1029/2021jc017236
Subject(s) - scavenging , seawater , flux (metallurgy) , oceanography , geology , water column , surface water , isotope , tracer , radionuclide , atmosphere (unit) , atmospheric sciences , environmental science , chemistry , meteorology , biochemistry , physics , organic chemistry , quantum mechanics , environmental engineering , nuclear physics , antioxidant
The cosmogenic radionuclide 10 Be and its stable isotope 9 Be can be used as a tracer for water mass mixing, but such applications are rare in both open oceans and marginal seas. Here we report distributions of dissolved 9 Be and 10 Be concentrations of the seawater in the surface and water columns along a section from shelf to deep basin in the northern South China Sea (SCS). The concentrations of 9 Be and 10 Be in surface waters range between 8.8–43.6 pmol/kg and 118–576 atoms/g, respectively. The 9 Be in the northern SCS is dominantly sourced from river waters, while 10 Be has a prominent input from the western Pacific, resulting in the highest 10 Be/ 9 Be ratio of 10.9 × 10 −8 closest to the Luzon Strait. Along the depth section, the 9 Be concentrations decrease southward while 10 Be concentrations increase with the maximum value of 1,237 atoms/g occurring at 2,843 m depth of Station A10. The 10 Be/ 9 Be ratios are interpreted with consideration of water mixing and boundary scavenging, which reveal evidence of a branch of the intruding Kuroshio Current (>7.7 × 10 −8 ) in subsurface water and a deep cyclonic current (>8.9 × 10 −8 ). A box model yields a sedimentation flux of 10 Be around 1,167 atoms/m 2 /s, that is, 4.6 times of the atmospheric deposition flux, pointing to active boundary scavenging of 10 Be. The residence time of 10 Be in the deep water is estimated to be longer than 79 years in the northern SCS. The beryllium isotopes as a water mass tracer will find wide applications in basins where the endmembers are sufficiently differentiated.