We present the δ¹¹B of well‐preserved brachiopod fossils coupled with geochemical modeling to examine how seawater boron responded to abrupt and dynamic climate changes in the Late Paleozoic. The Late Carboniferous, a time of major coal formation and glacioeustatic sea level changes, is characterized by relatively stable brachiopod δ¹¹B of 15–17‰, similar to values seen in modern brachiopods. Brachiopod δ¹¹B dropped by ~5‰ in the early Permian and then restabilized at a new value of 10‰ within a few million years. Mass balance models of seawater δ¹¹B reproduced the overall trends in our brachiopod data but failed to capture the large drop in δ¹¹B in the early Permian. Published seawater ⁸⁷Sr/⁸⁶Sr and δ^44/40Ca data based on brachiopod shells also shift to lower values in the early Permian, suggesting a common control on all three seawater isotope systems. The Permian terrestrial record of evaporites and eolian deposits suggests a prolonged reduced delivery of dissolved weathering products to the ocean, accounting for the change in seawater ⁸⁷Sr/⁸⁶Sr. This reduced weathering, in turn, led to increased atmospheric CO₂ and lowered seawater pH, which may have significantly decreased major removal mechanisms for seawater calcium and boron leading to declines in both isotope systems. We propose that boron removal via coprecipitation in carbonates and adsorption onto clay minerals was significantly diminished due to a reduction in the availability of the borate aqueous species caused by lowered seawater pH.

中文翻译：

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横跨石炭纪-二叠纪气候过渡的腕足动物δ11B记录

我们目前的δ ¹¹加上地球化学模拟研究海水中的硼如何应对在晚古生代突然和动态的气候变化保存完好的腕足动物化石的B中。晚石炭世，主要煤炭形成和glacioeustatic海平面变化的时间，特点是相对稳定的腕足δ ¹¹ 15-17乙‰，类似于现代的腕足看到值。腕足δ ¹¹乙方在早二叠世下降〜5‰，然后以10中的几百万年来的新值‰重新稳定。海水δ的质量平衡模型¹¹乙转载我们的腕足数据的总体趋势，但未能捕获δ大幅下降¹¹二叠纪早期B。已公布的海水⁸⁷基于腕足动物壳的Sr / ⁸⁶ Sr和^δ44 / ⁴⁰ Ca数据在二叠纪早期也转移到较低的值，这表明对所有三个海水同位素系统都采取了相同的控制措施。二叠纪的蒸发岩和风积沉积记录表明，溶解的风化产物向海洋的输送减少了，这是海水⁸⁷ Sr / ⁸⁶ Sr的变化的原因。这种风化的减少反过来又导致了大气CO _2的增加海水pH值降低，这可能显着降低了海水钙和硼的主要去除机理，从而导致两种同位素系统均下降。我们认为，由于海水pH值降低导致硼酸盐水溶液种类的可用性降低，因此通过碳酸盐中的共沉淀和吸附在粘土矿物上的除硼作用大大减少。