Testing planktic foraminiferal shell weight as a surface water [CO32-] proxy using plankton net samples

Planktic foraminiferal size-normalized weight (SNW) has been used as a proxy for both past changes in deepwater dissolution and surface ocean [CO32-], the latter potentially providing a way to evaluate paleoatmospheric pCO(2) variations beyond the ice core records. Here we examine the relationship between SNW in modern planktic foraminifera and surface water [CO32-] in the Arabian Sea using a suite of samples obtained from plankton net casts in surface waters having a large range in their carbon chemistry. Our results reveal substantial interspecies- and intraspecies-specific variations in the strength, gradient, and even sign of this relationship, indicating that [CO32-] does not exert a dominant control on foraminiferal test weight. Similarly, foraminiferal abundance data do not lend support to the hypothesis that SNW responds to optimal growth conditions. Further work is needed, perhaps in laboratory cultures, to determine those environmental factors that are simply correlated with SNW and those that exert control.

浮游有孔虫大小标准化重量（SNW）已被用作深水溶解作用和表层海洋[CO₃²⁻]过去变化的替代指标，后者可能提供一种评估超出冰芯记录的古大气pCO₂变化的方法。在此，我们利用从表层水中浮游生物网采集的一组样本，研究现代浮游有孔虫的SNW与阿拉伯海表层水[CO₃²⁻]之间的关系，这些样本的碳化学性质差异很大。我们的研究结果显示，这种关系在强度、梯度甚至符号上存在显著的种间和种内特异性差异，这表明[CO₃²⁻]对有孔虫壳重没有主要的控制作用。同样，有孔虫丰度数据也不支持SNW对最佳生长条件有响应这一假设。可能需要在实验室培养中开展进一步的工作，以确定那些仅仅与SNW相关的环境因素以及那些起控制作用的环境因素。