Abstract Brachiopods present a key fossil group for Phanerozoic palaeo-environmental and palaeo-oceanographical reconstructions, owing to their good preservation and abundance in the geological record. Yet to date, hardly any geochemical proxies have been calibrated in cultured brachiopods and only little is known on the mechanisms that control the incorporation of various key elements into brachiopod calcite. To evaluate the feasibility and robustness of multiple Element/Ca ratios as proxies in brachiopods, specifically Li/Ca, B/Ca, Na/Ca, Mg/Ca, Sr/Ca, Ba/Ca, as well as Li/Mg, we cultured Magellania venosa, Terebratella dorsata and Pajaudina atlantica under controlled experimental settings over a period of more than two years with closely monitored ambient conditions, carbonate system parameters and elemental composition of the culture medium. The experimental setup comprised of two control aquariums (pH0 = 8.0 and 8.15, T = 10 °C) and treatments where pCO2 − pH (pH1 = 7.6 and pH2 = 7.35), temperature (T = 16 °C) and chemical composition of the culture medium were manipulated. Our results indicate that the incorporation of Li and Mg is strongly influenced by temperature, growth effects as well as carbonate chemistry, complicating the use of Li/Ca, Mg/Ca and Li/Mg ratios as straightforward reliable proxies. Boron partitioning varied greatly between the treatments, however without a clear link to carbonate system parameters or other environmental factors. The partitioning of both Ba and Na varied between individuals, but was not systematically affected by changes in the ambient conditions. We highlight Sr as a potential proxy for DIC, based on a positive trend between Sr partitioning and carbonate chemistry in the culture medium. To explain the observed dependency and provide a quantitative framework for exploring elemental variations, we devise the first biomineralisation model for brachiopods, which results in a close agreement between modelled and measured Sr distribution coefficients. We propose that in order to sustain shell growth under increased DIC, a decreased influx of Ca2+ to the calcifying fluid is necessary, driving the preferential substitution of Sr2+ for Ca2+ in the crystal lattice. Finally, we conducted micro-computed tomography analyses of the shells grown in the different experimental treatments. We present pore space – punctae – content quantification that indicates that shells built under increased environmental stress, and in particular elevated temperature, contain relatively more pore space than calcite, suggesting this parameter as a potential novel proxy for physiological stress and even environmental conditions.

中文翻译：

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将微量元素和微量元素掺入培养的腕足动物：生物矿化模型的新见解对代理应用的影响

摘要 腕足类动物保存良好，地质记录丰富，是显生宙古环境和古海洋学重建的关键化石群。然而，迄今为止，几乎没有任何地球化学替代物在培养的腕足动物中得到校准，并且对控制各种关键元素掺入腕足动物方解石的机制知之甚少。为了评估多种元素/钙比率作为腕足动物代理的可行性和稳健性，特别是 Li/Ca、B/Ca、Na/Ca、Mg/Ca、Sr/Ca、Ba/Ca 以及 Li/Mg，我们在两年多的时间里，在受控实验设置下培养 Magellania venosa、Terebratella dorsata 和 Pajaudina atlantica，并密切监测环境条件、碳酸盐系统参数和培养基的元素组成。实验设置包括两个控制水族箱（pH0 = 8.0 和 8.15，T = 10 °C）和处理，其中 pCO2 - pH（pH1 = 7.6 和 pH2 = 7.35）、温度（T = 16 °C）和化学成分培养基被操纵。我们的结果表明，Li 和 Mg 的掺入受温度、生长效应以及碳酸盐化学的强烈影响，使 Li/Ca、Mg/Ca 和 Li/Mg 比率作为直接可靠的替代物的使用变得复杂。不同处理之间的硼分配差异很大，但与碳酸盐系统参数或其他环境因素没有明确的联系。Ba 和 Na 的分配因人而异，但不受环境条件变化的系统影响。我们强调 Sr 作为 DIC 的潜在代理，基于培养基中 Sr 分配和碳酸盐化学之间的积极趋势。为了解释观察到的依赖性并提供用于探索元素变化的定量框架，我们设计了第一个腕足动物生物矿化模型，这导致建模和测量的 Sr 分布系数之间的密切一致。我们提出，为了在 DIC 增加的情况下维持壳生长，必须减少 Ca2+ 流入钙化液，从而推动 Sr2+ 优先取代晶格中的 Ca2+。最后，我们对不同实验处理中生长的贝壳进行了显微计算机断层扫描分析。我们提出了孔隙空间 - punctae - 含量量化，表明贝壳在增加的环境压力下建造，