NOAA/WDS Paleoclimatology - Global Eocene Nannoplankton Assemblage Data

Nannoplankton play a significant role in the global carbon cycle; changes in the composition of the assemblage can influence primary productivity, carbon burial, and ultimately climate. Here counts of nannofossils in Eocene samples document one of the largest nannoplankton assemblage turnovers of the Cenozoic Era. This event is marked by the global expansion of Reticulofenestra at the termination of the early Eocene climatic optimum (EECO), and continues through the progressive cooling to the earliest Oligocene glaciation. To understand the mechanisms driving this assemblage shift we use multivariate statistical techniques and carbon and oxygen isotope records from localities worldwide. We find that the turnover in the global nannofossil assemblage is tied to thermal destratification of the ocean and a coincident decrease in the efficiency of the oceanic biologic pump at the height of the EECO. We propose that increased vertical mixing and increased nutrient supply to surface waters during the EECO caused a shift in the trophic structure towards enhanced productivity, influencing the global nannoplankton population.

超微浮游生物（nannoplankton）在全球碳循环中扮演着至关重要的角色；其组合组成的变化可对初级生产力、碳埋藏乃至全球气候产生影响。本研究通过对全球多地始新世（Eocene）样品中的钙质超微化石（nannofossils）进行计数，记录了新生代（Cenozoic Era）以来规模最大的超微浮游生物化石组合更替事件之一。该事件以早始新世气候适宜期（early Eocene climatic optimum, EECO）末期网球石属（Reticulofenestra）在全球范围内的扩张为标志性特征，并贯穿了从该时期逐步降温直至最早渐新世冰期（Oligocene glaciation）的完整过程。为阐明驱动该化石组合转变的内在机制，我们采用多元统计分析技术，并结合全球多个采样点的碳、氧同位素记录开展研究。结果发现，全球钙质超微化石组合的更替，与早始新世气候适宜期鼎盛时期的海洋热分层瓦解及同期海洋生物泵效率的降低紧密关联。我们提出，早始新世气候适宜期内垂直混合作用增强、表层海水营养供给提升，使得超微浮游生物群落的营养级结构向更高生产力方向转变，进而对全球超微浮游生物种群产生了显著影响。