CARAPACE: Calcite-Aragonite transition Across Pacific Atolls from the Cretaceous to the Eocene

甲壳：从白垩纪到始新世横跨太平洋环礁的方解石-文石过渡

• 批准号: NE/W009943/1
• 负责人: Cedric John
• 金额: $ 30.56万
• 依托单位: Queen Mary University of London
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2024
• 资助国家: 英国
• 起止时间: 2024 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FW009943%2F1
• 关键词: CARAPACE; Calcite; Aragonite; transition; Across

We propose a new seagoing research campaign in the Mid Pacific and the Emperor's Seamount Chain regions. Specifically, we are interested in the architecture and geometries of reefs situated atop of ancient volcanoes. In mid-ocean setting, corals and other carbonate producers tend to form significant reefs whenever a shallow substrate is available. As postulated by Darwin in the late 1800's, when the volcanic island sinks into the Earth mantle (a process called subsidence) the reefs keep growing and producing sediments, often forming a carbonate island known as an atoll. Sometimes, atolls can have a lagoon in the middle, where the volcano formerly stood. Interestingly, atolls can live for millions of years, but can also die and drown below the surface of the ocean. Drowned atolls are referred to as "guyots".A series of guyots in the mid Pacific piqued our interest. There the production of reefs extends from the Early Cretaceous (about 110 million years ago) to the Oligocene (about 30 million years ago) and to the present. Interestingly, the chemistry of the ocean has changed dramatically during this period: in the Early Cretaceous, the ocean was known as a 'calcitic sea', where the mineral calcite was preferentially precipitated. Somewhere between 50-30 million years ago, the chemistry of the oceans changed and we are now in an 'aragonitic sea', where most of the carbonate production is dominated by the mineral aragonite. Exactly why the chemistry of the ocean has changed remains only partially known, but a probable cause is that global climate had fundamentally changed from the Early Cretaceous warm, ice-free, high CO2 concentration world to the cold, punctuated glaciations and low CO2 concentration world of the recent past.There are two main things we wish to understand with this campaign. The first being the nature of carbonate production across this calcite to aragonite transition, and how the architecture of the carbonate atolls might have adapted in response to this chemical change. Understanding how past carbonates adapted to a different chemistry of the ocean is crucial for predicting how modern climate change will impact corals and other carbonate producers. For instance, will the change in chemistry force carbonate producers such as corals deeper/shallower in the water column? This would impact the geometry of the atoll. Our second objective is to understand by how much global sea-level might have change across the time interval of interest. Current global warming results in the melting of ice sheets at high-latitude, and dramatic sea-level rise. Looking at past example of sea-level changes allows us to calibrate by how much sea-level rises during global warming events. Quantifying the rate of sea-level change can be achieved in carbonates because the reef is growing very close to sea-level, so if we can track the position of the reef and how it changes through time, we can reconstruct global sea-level. For the Cretaceous to Eocene (our window of interest), this is poorly understood. To achieve our two main objectives, we need to collect data on 6 different drowned atolls (guyots); this ensures that we cover the entire geological period of interest, as each atoll is of a slightly different age. The primary data we will use in this research is known as seismic reflection: we send small seismic waves towards the bottom of the sea, and by reconstructing the time of arrival of the reflected seismic waves we can reconstruct the architecture of the atoll.In the future, we plan to select a few 'best' targets based on our data to go back to these atolls and sample the rocks using deep-sea scientific drilling.

我们建议在太平洋中部和皇帝的海底连锁区进行一项新的海上研究活动。具体来说，我们对位于古代火山的礁石的建筑和几何形状感兴趣。在海洋中部环境中，只要有浅层基板，珊瑚和其他碳酸盐生产商都会往往会形成重要的珊瑚礁。正如达尔文（Darwin）在1800年代后期所假设的那样，当时火山岛沉入地球地幔（一种称为沉降的过程）时，珊瑚礁继续生长和产生沉积物，通常形成一个被称为环礁的碳酸盐岛。有时，环礁可能在中间有一个泻湖，火山以前站在那里。有趣的是，环礁可以生存数百万年，但也可以死亡并淹没在海面以下。淹死的环礁被称为“盖特”。中太平洋中的一系列盖特人激起了我们的兴趣。那里的礁石的生产从白垩纪早期（大约1.1亿年前）延伸到渐新世（大约3000万年前）和现在。有趣的是，在此期间，海洋的化学变化发生了巨大变化：在白垩纪的早期，海洋被称为“钙化海”，矿物方解石在这里优先沉淀。在500-30万年前的某个地方，海洋的化学变化了，我们现在处于“马拉贡海”中，大部分碳酸盐生产都以矿物为主导。确切地说，海洋化学发生变化的原因仅是部分知名的，但可能的原因是，全球气候从早期的白垩纪温暖，无冰，高二氧化碳浓度世界到最近的过去的寒冷，冰2浓度和低二氧化碳浓度世界，我们希望有两种主要的事情来了解这项运动。首先是该方解石到后期过渡的碳酸盐生产的性质，以及如何响应这种化学变化而适应了碳酸盐环礁的结构。了解过去的碳酸盐如何适应海洋的不同化学性质对于预测现代气候变化将如何影响珊瑚和其他碳酸盐生产商至关重要。例如，化学作用力碳酸盐生产商的变化会在水柱中更深/浅的珊瑚产生者吗？这将影响环礁的几何形状。我们的第二个目标是了解全球海平面在关注时间间隔内可能会发生多少变化。当前的全球变暖会导致高纬度的冰盖融化，并急剧上升。看看过去的海平面变化例子，我们可以通过在全球变暖事件中的海平面上升来校准。量化海平面变化的速率可以在碳酸盐中实现，因为礁石的增长非常接近海平面，因此，如果我们可以跟踪礁石的位置以及它如何随着时间的流逝而变化，我们可以重建全球海平面。对于白垩纪到始新世（我们感兴趣的窗口），这是很众所周知的。为了实现我们的两个主要目标，我们需要收集6种不同的溺水环礁（Guyots）的数据；这确保我们涵盖了整个地质时期，因为每个环礁的年龄略有不同。我们将在这项研究中使用的主要数据被称为地震反射：我们向海底发送了较小的地震波，通过重建反射的地震波的到来时间，我们可以在未来的原子中重建建筑。我们计划根据我们的数据来选择一些rocksecific and the Atolls练习，我们计划选择一些最佳目标。