Data for: \"Laboratory-grown crust in planktic foraminifera Neogloboquadrina pachyderma; insights into resolving inaccuracies in polar palaeotemperature estimates\"

Data corresponding to article \"Laboratory-grown crust in planktic foraminifera Neogloboquadrina pachyderma; insights into resolving inaccuracies in polar palaeotemperature estimates\" by: A. Westgård, M. M. Ezat, F. E. Sykes, G. L. Foster, J. Meilland, 4, T. B. Chalk, J. A. Milton
Abstract: Proxy based records of past changes in the polar ocean-cryosphere-climate system can provide invaluable constraints on ongoing and future climate change. However, the dominant planktic foraminiferal species in polar regions, Neogloboquadrina pachyderma, exhibits considerable intra- and inter-test heterogeneity in Mg/Ca and potentially other elemental ratios, compromising their utility as palaeothermometers and tracers of other environmental variables such as carbonate chemistry. In particular, N. pachyderma often exhibits a thick “crust” characterised by low Mg/Ca calcite outside its higher Mg/Ca internal “lamellar calcite”. The cause of this heterogeneity is currently uncertain, but it is variably ascribed to environmental change via depth migration or to a “vital effect” related to variations in biomineralisation mechanism/foraminiferal physiology. To help resolve this issue, we performed large scale culturing experiments of N. pachyderma under controlled environmental conditions and used Laser Ablation ICP-MS to study the intra-shell variability in trace element ratios. We document, for the first time, that in laboratory-grown N. pachyderma the calcite crust has lower Mg/Ca, Na/Ca, and B/Ca than the inner lamellar calcite even when both components are grown in equivalent environmental conditions. This implies that the crust and lamellar calcite of N. pachyderma are deposited via contrasting biomineralisation strategies, not only resulting in distinct geochemical compositions for multiple elements, but also in different sensitivities to changing environmental conditions. Given the crust constitutes a large, but variable percentage of a specimen’s final shell weight, this complicates the application of proxies using this and other similar species. It is therefore recommended that future studies either apply in situ techniques, such as applied here, to analytically separate the crust from lamellar calcite, or target specimens with only one component to avoid the complicating influence of this “vital effect” on environmental reconstruction.

本数据集对应论文《浮游有孔虫（planktic foraminifera）厚壳新抱球虫（Neogloboquadrina pachyderma）的实验室培养壳层：解析极地古温度估算偏差的研究》，作者为A. Westgård、M. M. Ezat、F. E. Sykes、G. L. Foster、J. Meilland、4、T. B. Chalk、J. A. Milton。

摘要：基于代用指标的极地海洋-冰冻圈-气候系统过去变化记录，可为当前及未来气候变化研究提供极为宝贵的约束依据。然而，极地海域优势浮游有孔虫（planktic foraminifera）物种厚壳新抱球虫（Neogloboquadrina pachyderma）在镁钙比（Mg/Ca）及其他潜在元素比值上存在显著的壳内与壳间异质性，这削弱了其作为古温标及碳酸盐化学等其他环境变量示踪剂的应用价值。尤为特别的是，该物种通常会在自身高镁钙比的内层层状方解石（lamellar calcite）外部形成一层以低镁钙比方解石为特征的厚实“壳层”。目前这种异质性的成因尚不明确，现有研究将其不同程度归因于物种垂直迁徙引发的环境变化，或是与生物矿化机制/有孔虫生理变化相关的“生命效应（vital effect）”。为解决这一问题，本研究在可控环境条件下开展了大规模的厚壳新抱球虫培养实验，并采用激光剥蚀电感耦合等离子体质谱法（Laser Ablation ICP-MS）分析其壳内微量元素比值的异质性。本研究首次证实，在实验室培养的厚壳新抱球虫中，即便壳层方解石与内层层状方解石形成于相同的环境条件，前者的镁钙比、钠钙比（Na/Ca）与硼钙比（B/Ca）仍低于后者。这表明厚壳新抱球虫的壳层方解石与内层层状方解石通过截然不同的生物矿化策略形成，二者不仅在多种元素的地球化学组成上存在显著差异，对环境变化的敏感性也各不相同。由于壳层在个体最终壳体重量中占比可观但存在波动，这给该物种及其他类似物种的代用指标应用带来了干扰。因此，建议未来研究要么采用本研究使用的原位分析技术，将壳层方解石与内层层状方解石分离后再开展分析，要么仅选取仅含单一壳体成分的标本作为研究对象，以规避该“生命效应”对环境重建结果的干扰。