PHYCASO - Phytoplankton evolution and carbonate dynamics during past regimes in the Southern Ocean (IODP Expedition 392)

由于人类活动导致的气候崩溃和栖息地破坏，第六次大规模灭绝事件的威胁，对海洋物种和生态系统的长期前景的影响现在至关重要。球石藻（也被称为钙质纳米浮游生物）是一种丰富的真核单细胞浮游植物，广泛分布于阳光照射的上层海洋，是海洋生态系统食物链的基础。这些微小的生物沉淀出大量形状精美的碳酸钙鳞片（球石——由钙和碳结合而成），形成一层被称为球球的保护性盔甲。当这些微小的浮游生物死亡时，它们的骨骼开始落到海底，形成富含碳的沉积物，并填充化石记录。通过研究保存完好的颗石藻化石群落，我们可以了解海洋生物的进化和多样性，并重建过去的环境条件，以预测现代群落将如何应对正在发生的和未来的气候变化。国际海洋发现计划远征392号将在南大洋的阿古拉斯高原钻探跨越白垩纪到第四纪早期的深海沉积物，这是地球历史上的一个关键时期，代表了从温暖和高二氧化碳状态到更冷的“冰库”世界的长期转变。这些都与类似于当今全球变暖的扰动有关，但对海洋初级生产和碳酸盐发育的确切影响仍然难以捉摸。本研究旨在通过记录球岩藻的多样性、进化形态变化和积累速率，并将其与地质丰富的球岩藻物种的pCO2代用指标进行比较，以确定球岩藻（浮游生物）进化和中上层原生碳酸盐生成与南大洋古气候的关系。了解这种关系是预测气候变化对当今海洋生态系统功能影响的关键。

Given the threat of a sixth mass extinction event as a result of human-based climate breakdown and habitat disruption, implications about the long-term outlook of marine species and ecosystems are now of paramount importance. Coccolithophores (also known as calcareous nannoplankton) are an abundant group of eukaryotic unicellular phytoplankton that are widespread in the sunlit upper oceans and represent the base of the food chain in marine ecosystems. These miniscule organisms precipitate a multitude of elaborately shaped scales of calcium carbonate (coccoliths- composed of bonded calcium and carbon) to form a protective armour known as a coccosphere. When these microscopic plankton die, their skeletons begin to fall to the ocean floor forming carbon-rich sediments and populating the fossil record. Studying the preserved communities of fossil coccolithophores, we can understand the evolution and diversity of marine life through time and reconstruct past environmental conditions that played out to predict how modern communities will respond to ongoing and future climatic changes. International Ocean Discovery Program Expedition 392 will drill deep-sea sediments in the Agulhas Plateau, Southern Ocean that span Cretaceous to early Quaternary time, a key interval in Earth's history that represents a long-term transition from warm and high CO2 states into much cooler 'icehouse' worlds with large Antarctic ice sheets. These are related to perturbations similar to the present-day global warming, but the precise impact on the oceanic primary production and carbonate development still remains elusive. In this research, we aim to produce records of diversity, evolutionary morphological change, and accumulation rate and compare these with pCO2 proxies of geologically abundant coccolith species to determine the relationship between coccolithophore (plankton) evolution and pelagic primary carbonate production with the palaeoclimate in the Southern Ocean. An understanding of this relationship is key to predicting the impact of climate change on the functionality of the present-day oceanic ecosystems.