Carbonate preservation in marine sediments

Observations of carbonate preservation in marine sediments have long been used to infer changes in ocean circulation or biogenic production. When combined with measures of organic carbon rain and calcite accumulation rates, quantitative estimates of changes in preservation can reveal variation in biogenic fluxes, the org. C to calcite flux ratio and saturation state of bottom waters. Here we develop quantitative dissolution proxies for mid to higher latitudes based on foraminiferal test fragmentation. Examining surface sediments, we find that fragmentation in G. bulloides and G. truncatulinoides is linear with increasing seabed dissolution rate and can be used to quantify changes in carbonate preservation. G. truncatulinoides shows a constant relationship of fragmentation to dissolution. However, we observe that, although linear to dissolution rate, the fragmentation in G. bulloides depends on which morphotype is present. Other species, such as G. inflata, have complex responses to increasing dissolution and are less direct preservation indicators.

长期以来，海洋沉积物中碳酸盐保存（carbonate preservation）的观测结果被用于反演海洋环流或生物成因生产力的变化。当与有机碳沉降通量（organic carbon rain）和方解石堆积速率（calcite accumulation rates）的测量数据相结合时，对保存状态变化的定量估算可揭示生物成因通量（biogenic fluxes）、有机碳-方解石通量比及底层水饱和状态的变异。本研究基于有孔虫壳体破碎（foraminiferal test fragmentation），建立了适用于中高纬度的定量溶解替代指标（dissolution proxies）。通过分析表层沉积物，我们发现布氏球房虫（G. bulloides）与截圆抱球虫（G. truncatulinoides）的壳体破碎程度随海底溶解速率升高呈线性相关，可用于定量表征碳酸盐保存状态的变化。截圆抱球虫的壳体破碎程度与溶解作用之间的相关关系为恒定值。但我们注意到，尽管布氏球房虫的壳体破碎程度与溶解速率呈线性相关，但其破碎程度取决于其所对应的形态型（morphotype）。其他类群（如泡抱球虫G. inflata）对溶解作用增强的响应更为复杂，作为直接保存指示物的可靠性相对较差。