Abstract The oceanic redox state has played an essential role in the evolution of life on earth, and oceanic “anoxic events” have been proposed as one of the causal mechanisms for mass extinctions. During the mid-Cretaceous, oceanic anoxic events (OAEs) occurred several times and had a substantial impact on the biosphere. Planktic foraminifers are marine planktons with calcite tests, and their shells constitute approximately 30%–80% of modern deep-marine calcite; thus, they play a key role in the global carbon cycle. Previous studies have reported that at, or near, the times of major Cretaceous OAEs, planktic foraminifers have a high turnover (extinction and speciation) rate. However, the precise impact of anoxic conditions on the evolutionary trend of planktic foraminifers remained obscure. In this study, we investigate this by assessing the extinction/speciation rate of planktic foraminifers around OAEs. Our results suggest that the development of anoxia during OAEs would not have had a direct effect on the evolutionary trend (i.e., species number and turnover ratio). Two foraminiferal turnovers occurred around OAE1a and OAE2, however, all five turnover peaks seem to be largely associated with a relatively short-term (0.5–3 Myr) eustatic curve. Decreasing species numbers of planktic foraminifers are associated with a relatively lower sea eustatic level (second-order; ~20 Myr) and a small latitudinal temperature gradient around OAE1b, which are not anoxic conditions. Changes in oceanographical parameters (i.e., surface biological productivity, water column structure, carbonate chemistry, and nutrients) related to lowering sea-levels might have had a significant effect on foraminiferal evolutionary trends.

中文翻译：

---

是什么推动了白垩纪浮游有孔虫的进化趋势：海洋缺氧事件（OAE）直接影响了它？

摘要 海洋氧化还原状态在地球生命演化过程中发挥了重要作用，海洋“缺氧事件”被认为是物种大灭绝的原因之一。在白垩纪中期，海洋缺氧事件（OAEs）发生了多次，对生物圈产生了重大影响。浮游有孔虫是经方解石试验的海洋浮游生物，其贝壳约占现代深海方解石的30%～80%；因此，它们在全球碳循环中发挥着关键作用。先前的研究报告称，在或接近白垩纪 OAE 的主要时期，浮游有孔虫的更新（灭绝和物种形成）率很高。然而，缺氧条件对浮游有孔虫进化趋势的确切影响仍然不清楚。在这项研究中，我们通过评估 OAE 周围浮游有孔虫的灭绝/物种形成率来对此进行调查。我们的结果表明，OAE 期间缺氧的发展不会对进化趋势（即物种数量和周转率）产生直接影响。OAE1a 和 OAE2 周围发生了两次有孔虫周转，然而，所有五个周转峰似乎都与相对短期（0.5-3 Myr）的eustatic 曲线相关。浮游有孔虫物种数量的减少与相对较低的海平面（二级；~20 Myr）和 OAE1b 周围的小纬度温度梯度有关，这不是缺氧条件。海洋学参数的变化（即表面生物生产力、水柱结构、碳酸盐化学、