卡罗琳海山深海珊瑚钡同位素的垂直分布特征及其古海洋意义研究

Barium (Ba) is considered to be a robust proxy for water mass mixing, nutrient cycle and biological productivity in the modern and past oceans. However, the exact mechanism controlling the biogeochemical behavior of Ba is still unclear and the marine Ba cycle has not been fully understood. Deep-sea corals are distributed throughout the global oceans ranging from ~40 m to ~6000 m depth and they can provide information about geochemical changes as well as an absolute chronology, an excellent archive of oceanographic conditions. The Ba/Ca ratio in calcitic corals skeleton reflects Ba concentrations in ambient seawater. However, the Ba/Ca ratio is difficult to effectively discuss relevant scientific issues. Recent studies have introduced stable Ba isotopes as a novel tracer for ocean process and Ba isotopes could potentially provide insight into the oceanic Ba cycle. In this project, we propose to study the Ba isotopes and Ba/Ca ratios of the 170-1500 m deep-sea corals in Caroline Seamount, and to obtain the vertical distribution characteristics of the deep-sea coral Ba isotopes and Ba/Ca ratios in Caroline Seamount; reconstruct the seawater Ba isotope and Ba concentration by deep-sea coral; extract the climate and environment information of deep-sea coral Ba isotope for exploring the Ba cycle process of Caroline Seamount, and develop the deep-sea coral Ba isotope proxy to trace the ocean nutrient cycle, productivity and water mass mixing process. The successful implementation of this project is expected to provide new information for the Ba cycle, nutrient cycle, substance and energy exchange processes in seamount ecosystem.

钡是现代海洋学和古海洋学中示踪水团混合、营养盐循环和生物生产力的重要指标，海洋钡循环一直是国际研究热点。但是目前，钡的生物地球化学行为及其控制机制仍不清晰，制约了对海洋钡循环的认识。深海珊瑚具有时空分辨率高，定年精确等优势，且其骨骼Ba/Ca比值能定量重建海水钡含量变化，为我们探究海洋钡循环提供了良好的载体。但是，单一钡元素含量的研究难以对相关科学问题进行有效探讨。近年来钡同位素分析技术得到迅速发展，为研究海洋钡循环提供了新的手段。申请人已经获得卡罗琳海山大量珍贵的深海珊瑚样品。本项目拟对卡罗琳海山170-1500米的深海珊瑚进行钡同位素与钡含量研究，获得卡罗琳海山深海珊瑚钡同位素和钡含量垂直分布特征；重建卡罗琳海山海水钡同位素与钡含量演化历史；提取深海珊瑚钡同位素指标气候环境信息，探究卡罗琳海山钡循环过程，发展深海珊瑚钡同位素指标在示踪海洋营养盐循环、生产力和水团混合过程中的应用。

项目系统采集了西太平洋卡罗琳海山、麦哲伦海山、马里亚纳海山和雅浦海山的100米-2000米深度的深海珊瑚样品和马里亚纳海沟万米（5米-10918米）海水样品及南海涠洲岛、台湾南部南湾及越南中部岘港3根现代滨珊瑚样品，并开展了地球化学指标分析工作，完成了深海珊瑚和海水样品Ba/Ca及δ138/134Ba指标，南海滨珊瑚样品月分辨率和年分辨率的Ba/Ca，Sr/Ca和δ138/134Ba分析测试工作。研究发现，西太平洋海山的深海珊瑚主要由文石和方解石两大类组成。两大类深海珊瑚Ba/Ca含量随着水深增加而增加，δ138/134Ba随水深增加而减少。深海珊瑚Ba/Ca和δ138/134Ba能定量记录其生活水深的海水Ba/Ca和δ138/134Ba变化，其中，深海文石珊瑚Ba/Ca与海水分配系数（D=(Ba/Cacoral)/(Ba/Caseawater)）D=2.25±0.35，深海方解石珊瑚Ba/Ca与海水D=1.41±0.44；深海文石珊瑚δ138/134Ba与海水δ138/134Ba分馏值（Δ138/134Ba=δ138/134Bacoral-δ138/134Baseawater）Δ138/134Ba=-0.23±0.12‰；深海方解石珊瑚δ138/134Ba与海水δ138/134Ba分馏值Δ138/134Ba=-0.35±0.12‰。海水温度、pH及水深等因素对珊瑚分配系数和分馏值影响较小。深海珊瑚矿物结构不同，是影响其元素分配系数和分馏值的主要原因，相同矿物结构、不同种属的深海珊瑚与海水具有相似的Ba/Ca分配系数和δ138/134Ba分馏值。深海珊瑚Ba/Ca和δ138/134Ba能定量记录海水Ba/Ca和δ138/134Ba变化，两种指标联用为研究水团运动提供了新的手段。此外，研究发现滨珊瑚Ba/Ca指标可以记录海上石油开采、冬季风强度及土壤侵蚀过程等，为研究历史时期没有资料记录的人类活动，提供了新的指标。本项目共发表资助标注的相关学术论文4篇，包括Geophysical Research Letters, Science Bulletin, Marine Pollution Bulletin, Palaeogeography, Palaeoclimatology, Palaeoecology。