Reef coral calcification and climate dynamics during the Eocene greenhouse (EOCENE)

全球海洋温度上升和海洋酸化对热带浅水珊瑚礁构成威胁。然而，珊瑚礁珊瑚的适应能力在很大程度上是未知的。值得注意的是，在地质历史的温暖时期，如SPP2299定义的始新世，没有热应力和白化的类似数据。在这里，我们提出了一个全球热的中、晚始新世（45 - 35 Ma，本项目始新世）的珊瑚礁珊瑚研究。我们的项目有三个主要研究目标，与SPP的主题A和B一致：(1)以每月分辨率生成海温和蒸发/降水的多年时间序列，并记录珊瑚-虫黄藻共生的运作。(2)生成平行的物理钙化记录和钙化性能的地球化学指纹图谱，探讨对热等应激源的表达和可能的抵抗。(3)确定发生在准年代际时间尺度上的珊瑚群落部分死亡事件是否由于热浪期间发生的漂白事件。这些结果将与后来的新生代温暖期（如上新世中期）的发现进行比较，以便将我们的结果置于整个新生代气候、海洋学和（生物）地理变化的更广泛框架内。为了实现项目目标，我们将研究来自法国和英国（巴黎盆地）的珊瑚，这些珊瑚在其近乎原始，未被改变的保存方面非常不寻常。野外工作将有助于重建生长生境，并将标本置于地质年代背景中。首次将经典x射线照相（密度测定法）和地球化学指标用于始新世珊瑚的生境条件和钙化流体尺度。为了进一步发挥协同作用，我们启动了波鸿-柏林-莱比锡倡议。在此框架下，STRESS将研究漂白事件的代理文件，而DIAGENESIS将研究早期成岩作用期间代理数据的保存潜力。我们的调查结果将通过为公共电视台（Arte-TV/ZDF）制作纪录片的方式传播给更广泛的公众。除了提供始新世中纬度气候的重要约束外，我们还将获得对今天主导珊瑚礁的分类群（例如Porites）中光增强钙化系统的早期进化阶段的独特见解，并为过去地质时期珊瑚生态系统中的热应激和漂白提供第一个分析证据。这种来自极端气候世界的深度时间视角将为珊瑚抵抗未来海洋变暖和酸化双重压力的机制提供另一种观点。此外，对珊瑚钙化的深入了解将直接有助于对中始新世气候最佳期开始时深海碳酸盐溶解的长期讨论，该气候最佳期是全球钙化通量更多地向被淹没的大陆架上的珊瑚礁生态系统分配的结果。

Globally rising ocean temperatures and ocean acidification pose a threat to tropical shallow-water coral reefs. Yet, the acclimation potential of reef corals is largely unknown. Remarkably, no analogue data of heat stress and bleaching exist from warm periods of the geological past, such as the Eocene defined by SPP2299. Here, we propose a study on reef corals from the globally hot middle and late Eocene (45 – 35 Ma; this project EOCENE). Our project has three principal research objectives, consistent with themes A and B of the SPP: (1) Produce multi-year time-series of SSTs and evaporation/precipitation at monthly resolution and document the operation of the coral – zooxanthella symbiosis. (2) Generate parallel physical calcification records and geochemical fingerprints of calcification performance, to explore the expression of and possible resistance to thermal and other stressors. (3) Determine whether events of partial mortality of the coral colonies occurring on quasi-decadal time-scales were due to bleaching events that happened during heatwaves. The results will be compared to findings from later warm periods in the Cenozoic (e.g. mid Pliocene), to place our results within the broader framework of climatic, oceanographic and (bio)geographic changes through the Cenozoic. To meet the project goals, we will study corals from France and England (Paris Basin) that are extremely unusual in their near-pristine, unaltered preservation. Fieldwork will serve to reconstruct growth habitats and to put specimens into a geochronological context. For the first time, classical X-radiography (densitometry) and geochemical proxies for conditions at the habitat and calcification fluid scales will be applied to corals of Eocene age. For further synergies, we started the Bochum-Berlin-Leipzig initiative. In this frame, STRESS will investigate the proxy documentation of bleaching events and DIAGENESIS will study preservation potentials of proxy data during incipient diagenesis. Dissemination of our findings to the broader public will be ensured through contribution to a documentary for public TV (Arte-TV/ZDF). Besides providing important constraints on Eocene mid-latitude climate, we will gain a unique insight into the early evolutionary stages of the light-enhanced calcification system in taxa that dominate today’s coral reefs (e.g. Porites) and the first analytical evidence for heat stress in coral ecosystems and bleaching in the geological past. This deep-time perspective from a world of climatic extremes will provide an alternative view on the mechanisms underlying coral resistance to the dual stress of future ocean warming and acidification. Moreover, insights into coral calcification will directly contribute to a long-running discussion on deep-sea carbonate dissolution at the onset of the Middle Eocene Climate Optimum having been a result of global calcification fluxes being partitioned more toward reef ecosystems on flooded continental shelves.