Constraining barium isotope fractionation in the upper water column of the South China Sea
Constraining barium isotope fractionation in the upper water column of the South China Sea
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南海上部水体中钡同位素分馏的约束
DOI：
10.1016/j.gca.2020.08.008
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发表时间：
2020-11
影响因子：
5
通讯作者：
Martin Frank
中科院分区：
文献类型：
--
作者：
Zhimian Cao;Yating Li;Xinting Rao;Yang Yu;Ed C. Hathorne;Christopher Siebert;Minhan Dai;Martin Frank
海水中稳定Ba同位素组成的测定成功，使Ba同位素成为研究现代和过去海洋物理和地球化学过程的新工具。然而，更好地了解Ba同位素在粒子-海水相互作用过程中的分馏是此类应用的先决条件。本文利用南海北方海域溶解态Ba（DBa和δ 138 BaDBa）和颗粒态Ba（pBabulk和δ 138 BapBabulk）的浓度和同位素组成数据，研究了大洋上部Ba同位素分馏的特征。2010年1月，沿着一条从外大陆架到下斜坡的断面采集了海水和悬浮颗粒样品，用于钡同位素测量。1000 m以下的水柱剖面特征是δ 138 BaDBa随深度的增加而减小，DBa随深度的增加而增加。然而，在整个研究区的上部150 m处，δ 138 BaDBa特征基本上恒定在+0.6‰。相应的δ 138 BaBabulk主要代表海洋或过量颗粒Ba（pH 3）的同位素组成，始终低于δ 138 BaDBabut，其值也恒定在+0.1至+0.2‰之间。这表明，在NSCS外陆架和斜坡上，150 m以上普遍存在相同的Ba同位素分馏过程，导致原位分馏系数恒定为−0.5‰。这一数值与先前报告的开阔海洋和湖泊上层200米处的-0.4至-0.5 ‰的数值一致。此外，我们观察到的颗粒钙，颗粒有机碳和氮，和生物二氧化硅的pbsdistribution的显着差异，表明被动吸附到颗粒上，而不是主动的生物利用是最有可能的主要过程诱导Ba同位素分馏在上部NSCS。恒定的δ 138 Ba-Babulk特征表明，颗粒Ba同位素在DBa转化为Pb的过程中整合了可靠的信息，因此比Pb浓度更可靠地代表了总颗粒通量，其显示了可能受其他过程影响的可变值（例如，颗粒沉降和/或浮游动物摄食），从而反映了水柱中的“快照”过程。我们认为，生物生产力在调节散装悬浮颗粒的表面Ba同位素组成中只起次要作用。然而，Ba同位素在多大程度上可能是现在和过去出口生产力的可靠替代物，需要进一步分析特定Ba载体（如整个水柱和沉积物中的重晶石）的δ 138 Ba特征。
Enabled by the success in the determination of stable barium (Ba) isotopic compositions in seawater, Ba isotopes have been suggested as a novel tool to study physical and biogeochemical processes in the present and past ocean. However, a better understanding of the fractionation of Ba isotopes during particle-seawater interactions is a prerequisite for such applications. In this study, we use an extensive data set of concentrations and isotopic compositions of dissolved Ba (DBa and δ138BaDBa) and bulk particulate Ba (pBabulkand δ138BapBabulk) collected in the northern South China Sea (NSCS) to constrain Ba isotope fractionation in the upper ocean. Seawater and suspended particle samples for Ba isotope measurements were collected in January 2010 along a transect from the outer shelf to the lower slope. The water column profiles reaching depths of 1000 m are characterized by a general decrease of δ138BaDBaand an increase of DBa with depth. However, δ138BaDBasignatures are essentially constant at +0.6‰ in the upper 150 m of the entire study area. The corresponding δ138BapBabulk, which primarily represents the isotopic compositions of oceanic or excess particulate Ba (pBaxs), is consistently lower than δ138BaDBabut also constant at values of +0.1 to +0.2‰. This suggests that the same Ba isotope fractionation process prevails above 150 m on the NSCS outer shelf and slope resulting in a constant in situ fractionation factor of −0.5‰. This value is consistent with previously reported values of −0.4 to −0.5‰ in the upper 200 m of the open ocean and a lake. Moreover, we observe significant differences of pBaxsdistributions from those of particulate calcium, particulate organic carbon and nitrogen, and biogenic silica indicating that passive adsorption onto particles rather than active biological utilization is most likely the primary process inducing Ba isotope fractionation in the upper NSCS. The constant δ138BapBabulksignatures suggest that particulate Ba isotopes integrate reliable information during transformation of DBa to pBaxsand are thus a more robust proxy for total particle fluxes than pBaxsconcentrations, which show variable values potentially affected by other processes (e.g., particle sinking and/or zooplankton grazing) and thus reflects “snapshot” processes in the water column. We contend that biological productivity plays only a subordinate role in regulating the surface Ba isotopic composition of bulk suspended particles. The extent to which Ba isotopes may nevertheless be a reliable proxy for present and past export productivity requires further analyses of the δ138Ba signature of specific Ba carriers such as barite throughout the water column and in the sediments.
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影响因子：
3.8
作者：
K. Zuilen;T. Nägler;T. Bullen
通讯作者：
K. Zuilen;T. Nägler;T. Bullen
影响因子：
56.9
作者：
S. Weldeab;D. Lea;R. Schneider;N. Andersen
通讯作者：
S. Weldeab;D. Lea;R. Schneider;N. Andersen
影响因子：
4.1
作者：
T. Suga;A. Kato;K. Hanawa
通讯作者：
T. Suga;A. Kato;K. Hanawa
影响因子：
5
作者：
K. Zuilen;T. Müller;T. Nägler;M. Dietzel;T. Küsters
通讯作者：
K. Zuilen;T. Müller;T. Nägler;M. Dietzel;T. Küsters
影响因子：
4.4
作者：
González-Muñoz, MT;Fernández-Luque, B;Paytan, A
通讯作者：
Paytan, A