南海西沙群岛现代鳞砗磲内外层壳体稳定碳、氧同位素变化特征及其影响因素

Variation and influencing factors ofδ^(13)C andδ^(18)O in the inner and outer layers of modern Tridacna squamosa from the Xisha Islands,South China Sea

砗磲具有清晰的生长纹层,是记录热带海洋气候变化的良好载体,其壳体δ^(18)O、δ^(13)C已广泛应用于第四纪古气候研究。然而,目前大多数研究主要集中在内层壳体,关于外层壳体的研究十分稀少。本研究通过对采自南海西沙群岛浪花礁一个现代鳞砗磲的内外层壳体进行月分辨率δ^(18)O、δ^(13)C测试和内壳日生长纹层扫描,分析内外层壳体δ^(18)O和δ^(13)C的变化特征及其影响因素。结果显示该砗磲外壳δ^(18)O比内壳δ^(18)O更加偏正,但是两者都具有十分相似的变化特征,主要受到海表面温度的控制,表明砗磲内外层壳体δ^(18)O能够可靠地指示气候环境的变化。砗磲内外层壳体δ^(13)C存在较大的差异,其中内壳δ^(13)C具有明显的年周期变化。通过对比分析砗磲内壳δ^(13)C与日生长速率、气候环境参数,发现内壳δ^(13)C的季节变化主要与初级生产力和砗磲自身生命活动有关。砗磲外壳δ^(13)C相对于内壳δ^(13)C较为偏负,表现出持续下降的趋势,且无季节性变化,这可能是由采样路径偏离最大生长轴导致的。

Tridacna shells,known for their distinct growth bands,serve as excellent proxies for recording tropical marine climate changes.Theδ^(18)O andδ^(13)C in Tridacna shells have been applied in the Quaternary paleoclimate research.However,most previous researches focused on the inner layer,while the outer layer received less attention.We conducted a comprehensive analysis at a monthly resolutionδ^(18)O,δ^(13)C tests on both the inner and outer layers,as well as daily growth band scans on the inner layer of modern Tridacna squamosa from the Xisha Islands in the South China Sea.Results reveal that the outer layer exhibited higherδ^(18)O values than the inner layer.In addition,both shells displayed similar variation patterns,being primarily influenced by sea surface temperature(SST),and indicating that theδ^(18)O of the outer layer could reliably indicate climate and environmental changes.In contrast,significant differences inδ^(13)C value were observed between the inner and outer layers.The inner layer displayed a noticeable annual cycle inδ^(13)C value.By comparing the inner layerδ^(13)C,climatic and environmental parameters,and daily growth rate(DGR),we determined that the seasonal variations in inner layerδ^(13)C were linked to the primary productivity and the life activities of Tridacna.Meanwhile,theδ^(13)C of the outer layer,which is relatively negative compared to the inner layer,exhibited a continuous downward trend without seasonal changes.This discrepancy may be attributed to the sampling path deviating from the maximum growth axis.