Paleogene to early Neogene calcareous nannoplankton biochronology and evolution (IODP Expedition 390/393)

钙质超微浮游植物是一种微小的海洋藻类，可以产生方解石外骨骼(球体/球石)，在地质记录中几乎所有的海洋沉积物中都可以找到这种外骨骼。通过研究国际海洋发现计划(IODP)在海底岩心沉积物中保存的钙质纳米化石，我们可以记录它们随时间的演变，包括物种数量(多样性)、物种形成和灭绝速度以及种群组成的变化。我们可以利用这些信息提供准确的沉积物年龄，这是像IODP JOIDES Resolve这样的深海钻探船的一项重要任务，这些结果将告诉我们是否实现了最初的目标。钙质超微浮游动物对海洋环境的变化特别敏感，特别是海表面温度和营养物质的可获得性，个别物种或群体更喜欢特定的生态位。利用丰富的化石物种，我们能够在给定的时间重建特定地点过去的环境条件。IODP探险390号将驶往南大西洋，从古近纪到新近纪(大约6000万年前到现在)，对深海沉积物进行取芯，这是地球气候历史上的一个关键时期，标志着地球从高二氧化碳、非常温暖的“温室”气候过渡到一个更凉爽的“冰屋”世界，那里有大片南极冰盖，时起时落。在这段深刻的气候变化时期，海洋和陆地领域的环境和生态系统发生了戏剧性的变化。始新世早期(约5600万年至5000万年前)为特征的一系列快速变暖事件，随后是始新世晚期的长期降温，然后是渐新世至中新世早期(约3300万年至2000万年前)的冰川-间冰期旋回。钙质超微浮游植物是当时占主导地位的海洋浮游植物，多样性在始新世达到顶峰，但随后大幅下降，与从温室到冰库的这一重大气候变化相吻合。然而，这种进化变化的确切时间和速度仍然鲜为人知，我们计划更好地了解浮游生物进化和南大西洋古气候变化之间的这种关系。更好地理解这种关系是预测未来气候变化对海洋生物圈和生态系统功能的规模和影响的关键。为了回答这些研究问题，我们首先必须检查我们将钻探的深海岩心是否具有正确的地质时代，是否具有随时间推移的连续记录，以及保存我们所需化石的沉积物类型。这项研究项目将为IODP 390C和395E初步探险钻探的地点提供年龄控制，这将是即将于2022年启航的探险成功的关键。

Calcareous nannoplankton are microscopic marine algae that produce calcite exoskeletons (coccospheres/coccoliths) which can be found in almost all marine sediments in the geological record. By studying the calcareous nannofossils preserved within sediments cored from the sea-floor by the International Ocean Discovery Program (IODP) we can document their evolution through time, including changing number of species (diversity), rates of speciation and extinction, and population compositions. We can use this information to provide accurate ages of the sediments, which is an important task on a deep-sea drilling ship like the IODP JOIDES Resolution, and these results will tell us whether we have achieved our initial objectives. Calcareous nannoplankton are sensitive to changes in ocean environment, particularly sea-surface temperature and nutrient availability, with individual species or groups preferring specific ecological niches. Using the abundance of fossil species, we are able to reconstruct past environmental conditions for a specific location at a given time. IODP Expedition 390 will sail to the South Atlantic Ocean and core deep-sea sediments from the Paleogene to Neogene time interval (around 60 million years ago to present), a key interval in Earth's climate history marking the transition from high CO2, very warm 'greenhouse' climates into a much cooler 'icehouse' world with large Antarctic ice sheets that waxed and waned. This profound interval of climatic change saw dramatic shifts in the environments and ecosystems of the marine and terrestrial realms. A series of rapid warming events, known as hyperthermals, characterise the early Eocene (~56-50 million years ago), followed by long-term cooling through the later Eocene, and then glacial-interglacial cycles through the Oligocene and early Miocene (~33-20 million years ago). Calcareous nannoplankton were the dominant ocean phytoplankton at this time and peaked in diversity in the Eocene but then suffered major decline coinciding with this major climatic change from greenhouse to icehouse. However, the precise timing and speed of this evolutionary change is still poorly known and we plan to better understand this relationship between plankton evolution and palaeoclimatic change in the South Atlantic. A better understanding of this relationship is key to predicting the magnitude and impact of future climate change on the ocean biosphere and ecosystem functions. To answer these research questions, we first have to check that the deep-sea cores that we will drill will be of the right geological age, with continuous records through time, and in sediment types that preserve the fossils we need. This research project will provide the age control for the sites that were drilled by the preliminary IODP Expeditions 390C and 395E and this will be key to the success of the forthcoming expeditions which will sail in 2022.