Foraminifer fragmentation counts and sand-size fraction across the K-Pg boundary@en

Pelagic ecosystem function is integral to global biogeochemical cycling, and plays a major role in modulating atmospheric CO2 concentrations (pCO2). Uncertainty as to the effects of human activities on marine ecosystem function hinders projection of future atmospheric pCO2. To this end, events in the geological past can provide informative case studies in the response of ecosystem function to environmental and ecological changes. Around the Cretaceous-Palaeogene (K-Pg) boundary, two such events occurred: Deccan large igneous province (LIP) eruptions and massive bolide impact at the Yucatan Peninsula. Both perturbed the environment, but only the impact coincided with marine mass extinction. As such, we use these events to directly contrast the response of marine biogeochemical cycling to environmental perturbation with and without changes in global species richness. We measure this biogeochemical response using records of deep-sea carbonate preservation. We find that Late Cretaceous Deccan volcanism prompted transient deep-sea carbonate dissolution of a larger magnitude and timescale than predicted by geochemical models. Even so, the effect of volcanism on carbonate preservation was slight compared with bolide impact. Empirical records and geochemical models support a pronounced increase in carbonate saturation state for more than 500 000 years following the mass extinction of pelagic carbonate producers at the K-Pg boundary. These examples highlight the importance of pelagic ecosystems in moderating climate and ocean chemistry.远洋生态系统功能是全球生物地球化学循环的核心组成部分，在调节大气二氧化碳分压（pCO2）方面发挥着关键作用。当前人类活动对海洋生态系统功能影响的不确定性，阻碍了对未来大气pCO2的预测。为此，地质历史时期的相关事件可为研究生态系统功能对环境与生态变化的响应提供极具参考价值的案例。在白垩纪-古近纪（K-Pg）界线前后，发生了两起此类事件：德干大火成岩省（LIP）喷发与尤卡坦半岛的巨型小行星撞击事件。二者均对环境造成扰动，但仅小行星撞击事件与海洋生物大灭绝同期发生。基于此，我们利用这两起事件，直接对比全球物种丰富度发生变化与未发生变化两种情况下，海洋生物地球化学循环对环境扰动的响应差异。我们通过深海碳酸盐保存记录来量化这一生物地球化学响应。研究发现，白垩纪晚期德干火山活动引发的短暂深海碳酸盐溶解现象，其强度与持续时间均超过了地球化学模型的预测值。即便如此，相较于小行星撞击事件，火山活动对碳酸盐保存的影响微乎其微。实测记录与地球化学模型均证实，在K-Pg界线处远洋碳酸盐生产者发生大灭绝后的50余万年里，海水碳酸盐饱和状态出现了显著升高。上述案例凸显了远洋生态系统在调节气候与海洋化学组成方面的重要意义。