Recent analytical advances enable stable potassium (K) isotopes to serve as a promising geochemical tracer of paleoceanography. Preserved calcified fossils in marine carbonate sediments have the potential to act as important archives of ancient seawater. However, little is known about the magnitude, direction, and mechanism of K isotope fractionation between marine carbonates and seawater. To investigate isotope fractionation between biogenic carbonates and modern seawater, we measured K concentration, phase, and isotopic composition in calcified skeletons from a variety of calcifying species. Samples included deep-sea corals, hermatypic corals, bivalves, gastropods, brachiopods, and planktonic foraminifera recovered globally over the past ten years in habitats with temperatures varying from 2 to 29 ⁰C. Our results show that the δ⁴¹K values of the calcified organisms varied significantly, ranging from -0.72±0.11 to 0.94±0.04‰. Among studied samples, deep-sea corals exhibit the largest isotopic variability and the lowest δ⁴¹K, ranging from -0.72±0.11 to 0.28±0.09‰. Hermatypic corals display a moderate δ⁴¹K range from -0.20±0.07 to 0.37±0.10‰. Bivalves display δ⁴¹K values falling within a wide range from 0.04±0.05 to 0.94±0.04‰, including the highest δ⁴¹K observed. Gastropods exhibit δ⁴¹K values between -0.42±0.06 and -0.12±0.06‰, while brachiopods express δ⁴¹K values from -0.30±0.05 to 0.24±0.06‰. Limited foraminifera samples (n=2) reveal δ⁴¹K values of 0.15±0.06 to 0.21±0.06‰. Based on synchrotron-based atomic analyses, K in biogenic carbonates is dominantly hosted in amorphous K₂CO₃, calcite-like and aragonite-like K phases, and intracrystalline organic matrices of varying proportions. The K isotopic composition in studied marine biogenic carbonates does not exhibit strong temperature dependence in general but is linked to skeletal K phases. This phase-control potentially indicates a first-order biological control on skeletal K incorporation, partitioning, and associated K isotope fractionation. This appears to reflect a substantial “vital effect” role; i.e., physiological modification of the environmental information recorded in calcifying organisms. Observed substantial variations in δ⁴¹K call for additional attentions before using marine biogenic carbonates to interpret ancient seawater δ⁴¹K composition. In sum, physiological modulation substantially complicates the interpretation of marine carbonate δ⁴¹K records through time. Future studies should include species-specific calibration with complementary synchrotron data to refine K isotope applications for paleoceanography.

最近的分析进展使稳定的钾（K）同位素成为有希望的古海洋地球化学示踪剂。海洋碳酸盐沉积物中保存的钙化化石有可能成为古代海水的重要档案。但是，关于海洋碳酸盐和海水之间钾同位素分馏的大小，方向和机理知之甚少。为了研究生物碳酸盐与现代海水之间的同位素分馏，我们测量了来自各种钙化物种的钙化骨架中的K浓度，相和同位素组成。样本包括在过去十年中在温度从2到29⁰C不等的栖息地中全球范围内回收的深海珊瑚，带血珊瑚，双壳类，腹足类，腕足类和浮游有孔虫。我们的结果表明，δ钙化生物的⁴¹ K值变化很大，范围为-0.72±0.11至0.94±0.04‰。在所研究的样品，深海珊瑚 表现出最大的同位素变率和最低的δ ⁴¹ K，范围从-0.72±0.11至0.28±0.09‰。造礁珊瑚显示适度δ ⁴¹从-0.20±0.07至0.37±0.10‰K范围之外。双壳类显示δ ⁴¹落下的K值在宽范围内从0.04±0.05到0.94±0.04‰，包括最高δ ⁴¹ ķ观察。腹足表现出δ ⁴¹的K值-0.42±0.06 -0.12和±0.06‰之间，而腕足表达δ ⁴¹从-0.30±0.05的K值0.24±0.06‰。有限有孔虫样品（n = 2）揭示δ ⁴¹K值为0.15±0.06至0.21±0.06‰。根据基于同步加速器的原子分析，生物碳酸盐中的K主要存在于非晶K ₂ CO ₃，方解石样和文石样K相以及不同比例的晶内有机基质中。研究的海洋生物碳酸盐中的K同位素组成通常不表现出强烈的温度依赖性，但与骨架K相相关。该相控可能潜在地表明骨骼K掺入，分配和相关的K同位素分级的一级生物学控制。这似乎反映出实质性的“重大 影响”作用；即对钙化生物中记录的环境信息进行生理修改。在δ观察实质性变化⁴¹利用海洋生物碳酸盐解释古海水之前ķ呼吁更多的关注δ ⁴¹ K组成。总之，生理调制基本上复杂海相碳酸盐的δ的解释^41个ķ记录通过时间。未来的研究应包括具有互补同步加速器数据的特定物种校准，以完善钾同位素在古海洋学中的应用。