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，珊瑚礁的适应潜力在很大程度上是未知的。值得注意的是，不存在类似的热应力和漂白数据，来自地质历史的暖期，如SPP2299定义的始新世。在这里，我们建议对全球炎热的中、晚始新世(45-35 Ma；这个项目始新世)的珊瑚礁进行研究。我们的项目有三个主要研究目标，与战略计划的主题A和主题B相一致：(1)制作每月分辨率的SSTs和蒸发/降水的多年时间序列，并记录珊瑚--虫黄杆菌共生的运作情况。(2)生成平行的物理钙化记录和钙化性能的地球化学指纹，以探索对热和其他应激源的表达和可能的抵抗力。(3)确定在准十年时间尺度上发生的珊瑚群部分死亡事件是否是由于热浪期间发生的漂白事件。这些结果将与新生代后期暖期(如中上新世)的发现进行比较，以将我们的结果置于整个新生代气候、海洋和(生物)地理变化的更广泛框架内。为了达到项目目标，我们将研究来自法国和英国(巴黎盆地)的珊瑚，这些珊瑚在近乎原始、原封不动的保存方面非常不寻常。田野工作将有助于重建生长生境，并将标本放在地质年代学的背景下。经典的X射线照相(密度计量学)和环境条件的地球化学指标和钙化流体标尺将首次应用于始新世时代的珊瑚。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。在这个框架中，STREST将调查漂白事件的代理记录，而DIAGENESIS将研究早期成岩过程中代理数据的保存潜力。将通过为公共电视制作纪录片(ARTE-TV/ZDF)来确保向更广泛的公众传播我们的调查结果。除了提供始新世中纬度气候的重要制约因素外，我们还将对主导今天珊瑚礁(例如Porite)的类群中的光增强钙化系统的早期演化阶段进行独特的洞察，并首次分析珊瑚生态系统中的热应力和地质历史上的漂白。这种来自极端气候世界的深度视角将为珊瑚抵抗未来海洋变暖和酸化双重压力的潜在机制提供另一种观点。此外，对珊瑚钙化的洞察将直接有助于关于始新世中期气候最佳时期深海碳酸盐溶解的长期讨论，这是由于全球钙化通量被更多地分配到被洪水淹没的大陆架上的珊瑚礁生态系统。

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.