Antarctic bivalve Limatula hodgsoni as a proxy for ambient oceanographic conditions at McMurdo Sound

bivalves have been used as proxies to reconstruct ancient oceanographic conditions based on the assumption that their shell calcite is precipitated in near isotopic equilibrium with ambient seawater. few studies, however, have tested the presumption of equilibrium precipitation for specimens from polar environments. furthermore, reported isotopic values for polar specimens are largely indicative of disequilibrium precipitation, leading to the conclusion that bivalves living in extreme environments may be poor recorders of ambient oceanography. an analysis of shell chemistry of the antarctic bivalve limatula hodgsoni is compared to the local oceanographic data at cape armitage, mcmurdo sound, to assess the suitability of extreme environment bivalves as environmental proxies. results reveal that significant kinetic fractionation occurs during primary-layer shell secretion, resulting in whole-shell isotopic compositions that do not reflect equilibrium with ambient seawater. secondary-layer shell calcite, however, is less affected by biological fractionation and exhibits isotopic compositions that fall within the range of predicted equilibrium values. additionally, whole-shell concentrations of elements including ba, cd, cr, fe, mn, na, sr, and zn exhibit trends that are interpreted to reflect their relative concentrations in ambient seawater. concentrations of mg and b, however, are found to be largely controlled by physiological processes related to bivalve growth rate. while this study concludes that the shell chemistry of l. hodgsoni does reflect the local oceanographic conditions, the reliability of extreme-environment bivalves should be assessed on a species basis as differences in bivalve physiology and microstructure can significantly influence the degree of equilibrium reflected in shell calcite.

双壳类生物已被用作重建古海洋学条件的代理，基于其贝壳方解石是在与周围海水近乎同位素平衡的状态下沉淀的假设。然而，为数不多的研究检验了极地环境样本平衡沉淀的假设。此外，报道的极地样本同位素值主要指示非平衡沉淀，导致得出结论，生活在极端环境中的双壳类生物可能并不是环境海洋学的良好记录者。对南极双壳类生物Limatula hodgsoni的贝壳化学成分的分析与阿姆斯特朗角、麦克默多 Sound 当地的海洋学数据进行比较，以评估极端环境双壳类生物作为环境代理的适宜性。结果显示，在初级层贝壳分泌过程中发生了显著的动力学分馏，导致全壳同位素组成无法反映与周围海水的平衡。然而，次级层贝壳方解石受生物分馏的影响较小，其同位素组成处于预测平衡值范围内。此外，包括Ba、Cd、Cr、Fe、Mn、Na、Sr和Zn在内的元素的全壳浓度表现出趋势，这些趋势被解释为反映了它们在周围海水中的相对浓度。然而，Mg和B的浓度发现主要受与双壳类生物生长速率相关的生理过程控制。尽管这项研究得出结论，L. hodgsoni的贝壳化学成分确实反映了当地海洋学条件，但应基于物种对极端环境双壳类生物的可靠性进行评估，因为双壳类生物生理学和微观结构的差异可以显著影响贝壳方解石中反映的平衡程度。