Data from: Evolutionary ecology of Early Paleocene planktonic foraminifera: size, depth habitat and symbiosis

The carbon stable isotope (δ13C) composition of the calcitic tests of planktonic foraminifera has an important role as a geochemical tracer of ocean carbon system changes associated with the Cretaceous/Paleogene (K/Pg) mass extinction event and its aftermath. Questions remain, however, about the extent of δ13C isotopic disequilibrium effects and the impact of depth habitat evolution on test calcite δ13C among rapidly evolving Paleocene species, and the influence this has on reconstructed surface-to-deep ocean dissolved inorganic carbon (DIC) gradients. A synthesis of new and existing multispecies data, on the relationship between δ13C and δ18O and test size, sheds light on these issues. Results suggest that early Paleocene species quickly radiated into a range of depths habitats in a thermally stratified water column. Negative δ18O gradients with increasing test size in some species of Praemurica suggest either ontogenetic or ecotypic dependence on calcification temperature that may reflect depth/light controlled variability in symbiont photosynthetic activity. The pattern of positive δ13C test-size correlations allows us to (1) identify metabolic disequilibrium δ13C effects in small foraminifera tests, as occur in the immediate aftermath of the K/Pg event, (2) constrain the timing of evolution of foraminiferal photosymbiosis to 63.5 Ma, ∼0.9 Myr earlier than previously suggested, and (3) identify the apparent loss of symbiosis in a late-ranging morphotype of Praemurica. These findings have implications for interpreting δ13C DIC gradients at a resolution appropriate for incoming highly resolved K/Pg core records.浮游有孔虫（planktonic foraminifera）钙质壳体的碳稳定同位素（δ¹³C）组成，作为与白垩纪/古近纪（K/Pg）集群灭绝事件及其后续过程相关的海洋碳系统变化的地球化学示踪剂（geochemical tracer），具有重要研究价值。然而，目前仍存在诸多待厘清的问题：快速演化的古新世物种中，δ¹³C同位素不平衡效应的影响程度、深度栖息环境演化对壳体方解石δ¹³C的作用，以及上述因素对重建表层-深层海洋溶解无机碳（DIC）梯度的影响。本研究整合全新及已发表的多物种数据，围绕δ¹³C与δ¹⁸O及壳体大小的关联展开分析，为解决上述问题提供了新的视角。研究结果显示，古新世早期物种快速辐射至热分层水柱中的各类深度栖息环境。在部分Praemurica属物种中，壳体δ¹⁸O值随壳体增大呈负向梯度变化，这表明其钙化温度存在个体发育或生态型依赖性，该依赖性或反映了受深度/光照调控的共生体光合活性差异。壳体δ¹³C与大小呈正相关的分布模式，使我们得以：（1）识别出K/Pg灭绝事件发生初期小型有孔虫壳体中的代谢性同位素不平衡δ¹³C效应；（2）将有孔虫光合共生作用的演化时间限定在63.5 Ma，比此前推测的时间早约0.9 Myr；（3）识别出Praemurica属一个晚存续形态型中疑似丧失共生作用的现象。上述发现对于以适配即将问世的高分辨率K/Pg岩心记录的分辨率来解读δ¹³C相关的溶解无机碳梯度具有重要参考意义。