A remnant of glacial seawater preserved in the pore fluids of sediment cores from the Maldives Inner Sea provided an opportunity to investigate the stable strontium isotopic composition (δ88/86Sr) of the ocean during the Last Glacial Maximum and explore the usefulness of δ88/86Sr as a tracer of early marine diagenesis. We used paired measurements of δ88/86Sr and radiogenic Sr isotope ratios (87Sr/86Sr) in pore fluids and surrounding carbonate sediments to constrain the diagenetic history of the preserved glacial water mass at IODP Sites U1466 and U1468. These pore fluid profiles document variability in δ88/86Sr in a shallow marine setting, revealing distinct diagenetic processes dominating within different depth intervals. We find evidence for isotope fractionation during secondary calcite precipitation at intermediate depths and observe that in aragonite-dominated settings, fractionation during recrystallization may be obscured by the dissolution of aragonite in the uppermost sediments. Correcting for the effect of carbonate recrystallization on pore fluid Sr concentration ([Sr]) and isotopic composition, we estimate that glacial seawater [Sr] was higher (∼98μM) and δ88/86Sr lower (∼0.32‰) compared to the modern ocean, consistent with hypotheses attributing the present-day disequilibrium of the ocean Sr budget to glacial/interglacial changes in shelf carbonate weathering and burial. Our results provide evidence that the ocean [Sr] and δ88/86Sr are sensitive to carbon cycle changes on timescales much shorter than its residence time (∼2 Myr) and demonstrate that pore fluid δ88/86Sr measurements are a useful addition to multi-tracer studies of diagenesis in complex marine systems.

中文翻译：

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稳定和放射性锶同位素追踪残余冰川海水的组成和成岩作用改变


马尔代夫内海沉积物岩心孔隙液中保存的冰川海水残余物为研究末次冰盛期海洋稳定的锶同位素组成 （δ88/86Sr） 和探索 δ88/86Sr 作为早期海洋成岩作用示踪剂的有用性提供了机会。我们使用孔隙液和周围碳酸盐沉积物中 δ88/86Sr 和放射 Sr 同位素比值 （87Sr/86Sr） 的配对测量来限制 IODP 站点 U1466 和 U1468 保存的冰川水团的成岩历史。这些孔隙流体剖面记录了浅海环境中 δ88/86Sr 的变化，揭示了在不同深度区间内占主导地位的不同成岩过程。我们发现了在中等深度的次生方解石沉淀过程中同位素分馏的证据，并观察到在以文石为主的环境中，再结晶过程中的分馏可能会被文石在最上层沉积物中的溶解所掩盖。校正碳酸盐再结晶对孔隙液 Sr 浓度 （[Sr]） 和同位素组成的影响，我们估计与现代海洋相比，冰川海水 [Sr] 更高 （∼98μM），δ88/86Sr 更低 （∼0.32‰），这与将当今海洋 Sr 预算的不平衡归因于大陆架碳酸盐风化和埋藏的冰川/间冰期变化的假设一致。我们的研究结果提供了证据，证明海洋 [Sr] 和 δ88/86Sr 在比其停留时间 （∼2 Myr） 短得多的时间尺度上对碳循环变化很敏感，并表明孔隙流体 δ88/86Sr 测量是复杂海洋系统中成岩作用多示踪研究的有用补充。