The effect of nutrient and temperature changes on coral reef development in the Coral Sea over 12 Ma

珊瑚礁支撑着最复杂的低纬度生态系统，影响着数百万依赖珊瑚礁生存的人的生活。然而，世界各地的珊瑚礁正在经历减少。人类活动驱动的全球变化，如全球变暖、海洋酸化和水质恶化(富营养化)，已被确定为这种死亡的可能罪魁祸首。然而，这些因素的相互作用尚不清楚。随着现代珊瑚礁在地质时间尺度上的发展，一个问题是缺乏新近纪珊瑚种植区SST和生产力的长期记录。我和同事们一起研究了珊瑚海珊瑚礁的历史。据报道，珊瑚礁扩张到中新世晚期(10-11 Ma)。然后，在10~6 Ma之间，生物礁消失，直到中上新世暖期(3.0~3.5 Ma)才重新出现。以前的研究假设，在中新世晚期，寒冷、营养丰富的条件的开始导致了珊瑚礁的丧失。我的研究表明，与中新世晚期相比，那里的环境并没有变得更冷、更富营养，而是比现代的礁石环境更温暖，营养更差。初步的项目结果表明，要了解晚中新世的变化，有必要了解中新世中早期发生的变化。为了做到这一点，我们将查看U1464站点和澳大利亚西北大陆架的露头样本。从20-18 Ma开始，最大的新近纪生物礁之一在西北陆架上发育，11-6 Ma消失。海温、营养物质和当地条件的变化被认为是导致珊瑚礁丧失的原因。在这个项目中，我们将使用生物标志物(TEX86和脂类)来重建18-6 Ma之间SST的变化。因此，我们将既关注晚中新世最大的新近世生物礁系统之一的丧失，也关注西北陆架堡礁开始和顶端的条件。通过这样做，我们希望了解一些主要问题：(1)全球变化是否导致了中新世晚期印度-太平洋地区珊瑚礁的丧失？或者珊瑚礁的丧失是由更多的局部变化驱动的？(2)当珊瑚礁繁盛时，中中新世气候最佳时期的SST变化幅度是多少？重建珊瑚礁出现和消失时的众多事件，将使我们更好地理解是什么在地质时间尺度上驱动珊瑚礁的生长和消退。这将有助于更好地了解未来气候变化对珊瑚礁系统的影响。

Coral reefs support the most sophisticated low-latitude ecosystem and affect the lives of millions of people who depend on them for survival. However, coral reefs worldwide are experiencing a decline. Anthropogenically driven global changes, such as global warming, ocean acidification, and deteriorating water quality (eutrophication), have been identified as possible culprits in this demise. However, the interplay of these factors is unknown. As modern coral reefs developed over geological time scales, one issue is the lack of long-term records of SST and productivity from coral growing regions during the Neogene. Together with my co-workers I studied the history of corals reefs from the Coral Sea. It is published that coral reefs expanded until the Late Miocene (10-11 Ma). Then, between 10-6 Ma, the reefs disappeared and did not re-appear until the Mid-Pliocene warm period (3.0-3.5 Ma). Previous research hypothesized that the onset of cold, nutrient-rich conditions during the Late Miocene drove the loss of reefs. My research shows that instead of being a colder, nutrient-rich environment than during the Late Miocene, temperatures were warmer compared to the modern reef setting and nutrient poor. The initial project results show that it is necessary to understand what happened during the Mid-Early Miocene to understand the changes during the Late Miocene. To do this we will look at Site U1464 and outcrop samples from the NW Shelf of Australia. Beginning around 20-18 Ma one of the largest Neogene reef developed on the NW-Shelf before disappearing at 11-6 Ma. Changes in SST, nutrients and local conditions are thought to drive the coral reef loss. In this project we will use biomarkers (TEX86 and Aliphatic lipids) to reconstruct changes in SST between 18-6 Ma. Therefore, we will look both at the loss of one of the largest Neogene reef systems during the Late Miocene but also look at conditions during the start and apex of the NW Shelf barrier reef. By doing so we hope to understand a number of major questions (1) Did global changes cause the loss of coral reefs across the Indo-Pacific during the Late Miocene? Or was the loss of reefs driven by more local changes? (2) What was the magnitude of the SST change across the Mid-Miocene Climatic Optimum when the reefs were flourishing? Reconstructing numerous events when coral reefs appear and disappear will give us a greater understanding on what drives coral reef growth and retreat on geological timescales. This will help to better understand the impact of future climate change on the reef systems.