南海不同种类现代砗磲Sr/Ca特征及其发展为SST替代性指标的潜力

Mollusks are sensitive to surrounding environmental changes in most aquatic settings, and they can provide high-resolution seasonal/monthly archives of environmental variables of regions from tropics to high latitudes. These high-resolution seasonal/monthly archives, in combination with low-resolution marine sediment records, could improve our knowledge of marine paleoclimate and paleoenvironment at different timescales.The marine bivalve, Tridacna spp., is the largest bivalve species, it has hard and dense aragonite shells with daily growth lines in their inner shell layer, an ideal material for high-resolution paleoclimate reconstructions.The oxygen isotope ratios (δ18O) of Tridacna specimens, which calcifies essentially in isotopic equilibrium with surrounding seawater, have been mainly used as the evidence for late Quaternary sea level and temperature changes. However, δ18O of marine biogenic carbonate is influenced by both sea surface temperature (SST) and seawater δ18O, and the interpretation of δ18O as a proxy for SST has large uncertainties, especially in areas with large salinity variations.The Sr/Ca ratio, which has been extensively utilized as paleo-thermometers in corals, in Tridacna specimens has also been investigated recently and the results suggested that the Sr/Ca of Tridacna had the potential to be a SST proxy. However, there are also some doubts about the Tridacna Sr/Ca, such as species difference and individual effects.In this study, the high-resolution Sr/Ca ratios of modern Tridacna specimens in different species, which were collected from the South China Sea in 2013, will be determined by ICP-OES with the main aim to examine the Tridacna Sr/Ca differences within and among species and test the relationship between Tridacna Sr/Ca and environmental parameters.

海洋双壳类具有提供从热带到高纬地区高分辨率（月）气候记录的潜力，是对当前古气候记录的重要补充。砗磲是海洋中最大的双壳类，它的碳酸盐壳体具有年和日生长线，是优良的古气候载体。砗磲共有两属6种，在我国南海均有分布，申请者等前期对南海三种现代砗磲的初步调查显示，砗磲Sr/Ca具有发展为独立温度替代性指标的潜力，但是在将其应用到古气候研究之前，还有很多问题需要进一步确认，比如不同种类砗磲Sr/Ca是否存在种间差异、同种砗磲是否存在种内个体差异等。为探讨这一科学问题，申请者近期在南海采集了4种约20个现代砗磲。本项目计划对这些现代砗磲进行高分辨率Sr/Ca测试，通过对比分析，尝试弄清楚砗磲Sr/Ca的种间差异和种内个体差异，并探讨不同种类砗磲Sr/Ca发展为独立温度替代性指标的可行性，最终还将尝试建立不同种类砗磲Sr/Ca与气候环境信息之间的转换方程，为利用砗磲进行古气候研究提供参考。

本项目计划采集不同种类砗磲，开展砗磲Sr/Ca比值研究，分析种间差异和种内个体差异对砗磲Sr/Ca温度计的影响；通过三年的工作，课题组超额完成了项目计划书拟定的任务。课题组首先在南海西沙采集了多个不同种类的现代砗磲样品，通过对高分辨率Sr/Ca比值变化的分析，发现不同种类砗磲Sr/Ca平均值具有明显差异，但同一种类不同个体砗磲的Sr/Ca平均值非常稳定，可重复性强，不存在明显的个体差异；据此课题组建立了南海不同种类砗磲Sr/Ca温度计方程，该项工作为利用砗磲开展南海全新世高分辨率气候变化研究奠定了基础。进一步的，在现代校准的基础上，课题组额外开展了一系列古气候重建工作，对采自南海北部的多个生长于晚全新世的砗磲进行了Sr/Ca和δ18O分析，重建了南海北部晚全新世不同时段气候特征，并开展了南海北部砗磲和珊瑚古气候记录的集成研究，重建了过去2500年南海北部高分辨率海表面温度变化，并对气候季节性和ENSO活动进行了讨论。项目执行期间，申请人以第一作者/通讯作者发表标注研究论文14篇（项目预期结果为发表SCI论文1-3篇），其中包括在Nature Geoscience、Earth Science Reviews、Climate Dynamics等顶级期刊论文，这些论文目前已被引80余次（Google学术数据）；此外，申请人还在资助期内获得了基金委优青和中科院前沿重点青年拔尖人才项目的资助。