Degradation of internal organic matter is the main control on pteropod shell dissolution after death

The potential for preservation of thecosome pteropods is thought to be largely governed by the chemical stability of their delicate aragonitic shells in seawater. However, sediment trap studies have found that significant carbonate dissolution can occur above the carbonate saturation horizon. Here we present the results from experiments conducted on two cruises to the Scotia Sea to directly test whether the breakdown of the organic pteropod body influences shell dissolution. We find that, on the timescales of three to thirteen days, the oxidation of organic matter within the shells of dead pteropods is a stronger driver of shell dissolution than the saturation state of seawater. Three to four days after death, shells became milky white and nano‐SEM images reveal smoothing of internal surface features and increased shell porosity, both indicative of aragonite dissolution. These findings have implications for the interpretation of the condition of pteropod shells from sediment traps and the fossil record, as well as for understanding the processes controlling particulate carbonate export from the surface ocean.

有壳翼足类（thecosome pteropods）的保存潜力，被认为主要受控于其脆弱的文石质壳体在海水中的化学稳定性。然而沉积物捕获器研究发现，碳酸盐饱和层以上仍可发生显著的碳酸盐溶解现象。本文报道了两次前往斯科舍海（Scotia Sea）航次的实验结果，以直接验证翼足类有机躯体的降解是否会对壳体溶解产生影响。研究结果显示：在3至13天的时间尺度下，死亡翼足类壳体内部有机质的氧化作用对壳体溶解的驱动强度，高于海水的碳酸盐饱和状态。死亡后3至4天，壳体变为乳白色；纳米扫描电镜（nano-SEM）成像结果显示，壳体内表面特征趋于平滑，且壳体孔隙度升高，二者均为文石溶解的典型表征。上述发现对于解读沉积物捕获器及化石记录中的翼足类壳体状态具有重要参考意义，同时也有助于理解调控表层海洋颗粒碳酸盐输出的相关过程。