滨珊瑚年分辨率地球化学指标的古气候意义评估

Reef corals are one of the best archives for climatic and environmental changes in tropical oceans. For that many of the geochemical compositions in corals can be adopted in quantitatively reconstruct paleoclimatic and environmental records. Annual change is one of the most commonly concerned objects in paleoclimate studies, and corals generally have clear annual growth bands. In this term, they can provide credible interannual records in climatic and environmental changes. However, most of the troditional geochemical proxies for paleoclimate in corals are established from high resolution (monthly to seasonal) measurements. Seasonal climatic variations are absolutely much larger than those in annual resolution. Uncertainty of the reconstructed records may increase if such proxies are directly adopted in annual resolution reconstructions. Whether these proxies are suitabel to record reliable annual climate and environmentchanges or not is unlcear yet. In this concern, we propose this study aiming at (1) calibrating the generally used paleoclimatic/environmental proxies (such as Sr/Ca, Mg/Ca, 13C/12C,18O/16O and trace elements) with modern climatic and environmental observations by using multiple corals in the same reef and different reefs in annual resolution; (2) evaluating the reability and applicability of these annual proxies; and (3) analyzing the Sr/Ca of 1-2 alive corals spanning the past100-150 years old annual resolution in northern South China Sea to reconstruct the SST records, and verifying their realibility by comparing with other records to further evalution the applicability of these methods.

造礁珊瑚是热带海洋气候环境演变研究的最佳对象，主要因为其地球化学组成可以重建定量的古气候环境变化记录。年际变化是气候环境演变中最常用的指标之一，造礁珊瑚具有清晰的年纹层，可以提供可靠的气候环境年际变化记录。然而传统的珊瑚古气候环境标尺大多建立于季节-月的高分辨，由于年际变化往往要比季节变化幅度小很多，这些常用于反映季节变化的地球化学指标是否能准确地反映年际气候环境变化，目前还存在很多未知数。本项目拟利用现代观测结果拟合和校验同一礁区不同个体，以及不同礁区多个个体的现代滨珊瑚记录，对年分辨率的一些常用珊瑚地球化学古气候环境指标，如Sr/Ca、Mg/Ca比值、13C/12C、18O/16O和微量元素等与温度、盐度及海水化成组成的关系进行标定和校验，评估其可靠性及适用范围。同时，还将分析南海北部1-2个持续生长100-150年的珊瑚的年分辨率Sr/Ca，评估其记录百年尺度年均SST的可靠性。

本项目主要评估南海珊瑚年分辨地球化学组成是否能准确地反映年际气候环境变化及重建100多年来的古海洋环境。分析琼海龙湾礁区2-3个110-153年的珊瑚及三亚鹿回头同一个体的6个17年现代滨珊瑚年生长速率，Sr/Ca、Mg/Ca比值,δ13C、δ18O；三亚持续一年的周分辨率表层海水Sr/Ca，Mg/Ca；还分析了南海不同地区12个活体珊瑚有机物碳氮同位素。结果表明微生长环境可能影响到珊瑚个体的年生长及年均地球化学组成，导致不同岩芯的球化学组成差异较大。生长环境好的珊瑚年均δ13C、δ18O可以较好地记录大气CO2变化，长时间尺度的气候变化信息（如PDO、IPO），而年均Sr/Ca受到陆源输入（海水Sr/Ca变化）及上升流的影响，不能很好地记录年均SST；Mg/Ca主要反映了年均SST，但是也受到生命活动影响。年均生长速率，年均Mg/Ca能较好地记录20世纪以来的全球变暖。此外,南海珊瑚有机物碳(氮)同位素比世界其他各地分别偏低(高),且存在近岸低(高),离岸高(低)的特点,结合发表的数据发现碳氮同位素存在显著的负相关性,认为食物及有机物组成是主要原因。部分成果以合作者的形式发表在国际刊物及国内核心刊物上。