Biogenic and inorganic calcium carbonates contain considerable amounts of internal water, both as free and organically associated water. The oxygen isotopic compositions (δ¹⁸O) of internal water and hosting carbonate are analysed for various carbonates before and after heating at 175°C for 90 minutes. During heating, the δ¹⁸O values of internal water significantly increase in biogenic aragonites and speleothem calcite, whereas the δ¹⁸O carbonate values were lowered. Correspondingly, an aragonitic bivalve’s clumped isotope distribution (Δ₄₇) changed during heating, increasing reconstructed paleotemperatures. In contrast, an inorganic aragonite crystal, containing a comparable amount of internal water, showed no oxygen isotope exchange, and its Δ₄₇ values remained unaltered during heating, implying there is a link between internal oxygen isotope exchange and Δ₄₇ resetting. This alteration process occurred without any detectable transformation from aragonite to calcite. Our results therefore reveal a mechanism that facilitates oxygen isotope exchange between biogenic aragonite and its internal water, whilst simultaneously resetting the Δ₄₇ values, without affecting mineralogy. Future studies may therefore apply coupled water–carbonate analyses to scrutinize these kinds of diagenetic alteration processes. It appears that in biogenic aragonites, more carbonate is available for exchange reactions with the internal water reservoir than in inorganic aragonites, a feature that can be attributed to the distribution of organic‐associated water and/or high surface area fluid‐inclusions. This water‐aragonite exchange occurs at lower temperatures than those required for solid‐state bond reordering at the same timescale, and thus likely has occurred earlier during the burial of biogenic aragonites.

中文翻译：

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内部水有助于生物文石中结块同位素的热复位

生物和无机碳酸钙含有大量的内部水，既是游离水又是有机缔合水。氧同位素组成（δ ¹⁸ O）的内部水和托管碳酸盐之前和在175℃下加热90分钟后分析了各种碳酸盐。在加热期间，δ ¹⁸的内部水O值显著增加在生物文石和方解石钟乳石，而δ ¹⁸ ö碳酸值降低。相应地，一个文石质双壳类的结块同位素分布（Δ ₄₇）在加热过程中发生了变化，从而提高了重建的古温度。与此相反，无机文石晶体，含有的内部水相当量，没有显示出氧同位素交换，其Δ ₄₇值在加热过程中保持不变，这意味着有内部氧同位素交换和Δ之间的链路₄₇复位。发生了这种变化过程，没有从文石到方解石的任何可检测到的转变。因此，我们的结果表明，有利于生物文石和其内部的水之间的氧同位素交换的机制，而同时复位所述Δ ₄₇值，而不会影响矿物学。因此，未来的研究可能会应用水-碳酸盐耦合分析来仔细研究这些成岩作用的改变过程。与无机文石相比，在生物文石中似乎有更多的碳酸盐可用于与内部水库进行交换反应，这一特征可归因于有机缔合水和/或高表面积流体包裹体的分布。这种水-文石交换的温度低于在相同时间范围内固态键重新排序所需的温度，因此很可能发生在埋葬生物文石的过程中。