西北太平洋钡生物地球化学及其对弱光层有机碳再矿化的指示

海洋颗粒钡的形成和变化与有机碳的输出和再矿化有关，因此，钡元素被广泛应用于示踪有机碳再矿化和反演生物生产力，但其原理和机制仍不清晰。近期钡稳定同位素的成功开发有望厘清海洋钡循环中的一些未解问题，如重晶石沉淀是否主导弱光层颗粒钡极大值，并且可为地球化学研究提供新指标。本项目针对重大研究计划第五重点资助方向“西太平洋海水元素循环、沉积过程和古气候记录”，核心科学问题是：海洋弱光层中颗粒钡同位素的分布特征和分馏机制是什么，其变化能否指示有机碳再矿化？主要研究内容包括：（1）分析西北太平洋钡同位素的空间分布、季节变化与分馏效应；（2）评估西北太平洋弱光层有机碳再矿化通量及其重要性；（3）检验颗粒钡同位素指示现代海洋和古海洋碳过程的科学依据。本项目基于钡稳定同位素新视角，有机联系水体碳传输与沉积物碳埋藏，可为解答重大研究计划第二关键科学问题“西太平洋流固界面跨圈层物质与能量交换过程”提供思路和佐证。

The formation and variation of particulate barium (PBa) in the ocean are largely influenced by organic carbon export and remineralization. PBa concentrations are therefore used to quantify the organic carbon remineralization in the twilight zone, and its fluxes to the deep ocean and accumulation rates in sediments are applied to reconstruct export productivity. Enabled by the recent success in the determination of stable Ba isotopic compositions in seawater, Ba isotopes have been suggested helpful to elucidate the biogeochemistry of Ba in the ocean and thus to extend and improve its applicability as a geochemical proxy. .In the framework of the NSFC Major Research Plan “Inter-Sphere Interactions of the Earth System in the West Pacific Ocean”, this project selects the western North Pacific as the study site to examine biogeochemical behavior of Ba isotopes in the twilight zone and its linkage and implication to the organic carbon remineralization and paleoproductivity. The main hypothesis is as follows. Particle adsorption mainly induces a distinct isotope fractionation with heavier dissolved and lighter particulate Ba isotopic compositions in the euphotic zone. During particle sinking and its subsequent decomposition in the twilight zone, the regenerated Ba with low Ba isotopic signatures largely returns to the dissolved pool. Meanwhile, a fraction precipitates as barite in oversaturated microenvironments generating another isotope fractionation, which potentially incorporates productivity signals since higher export and remineralization of organic carbon generally results in elevated barite formation..The major objectives of this proposal are thus (1) to determine the spatial distribution, seasonal variability, and fractionation effect of Ba isotopes in the western North Pacific, (2) to evaluate the organic carbon remineralization flux in the twilight zone of the western North Pacific and its influence on the carbon fixation by biological pump, and (3) to testify whether Ba isotopes can be a useful proxy for carbon export and remineralization in the present and past ocean. Via a new avenue of stable Ba isotopes to link carbon transport in the water column and its burial in sediments, this project can improve our understandings to the second key question of the Major Research Plan that is “the material exchange and energy transfer across a fluid-solid interface in the West Pacific Ocean”.