Johan Renaudie

The Eocene–Oligocene transition (EOT) was a critical interval of global cooling and circulation change that reshaped marine ecosystems. However, current knowledge of diatom diversity and community dynamics during this interval relies mainly on biostratigraphic compilations, which largely document common species and thus likely underestimate true diversity. This study provides a more complete picture of Southern Ocean diatom communities across the EOT by using comprehensive quantitative surveys from four sites spanning the Atlantic and Indian Ocean sectors. Results reveal a consistent pattern across sites, with two major shifts in community composition around 37–36 and 34 Ma, linked to major environmental change. Following a prolonged interval of diversification without substantial extinction in the late Eocene, we identify a pronounced extinction event approximately 1 Myr after the Eocene–Oligocene boundary (E–O, ∼33.9 Ma). This suggests that significant changes in surface ocean conditions lagged the boundary and varied across the Southern Ocean. These findings highlight the interplay between global climate changes and local environmental factors in shaping diatom communities. By capturing detailed patterns of diatom diversity and extinction, our study improves our understanding of past ecological responses.

Marine diatoms couple the global carbon and silicon cycles, and their fossil record tracks oceanographic and climatic changes in deep-time. The Eocene/Oligocene Transition (EOT) marks the onset of Antarctic glaciation and major ocean reorganization and is a key interval in diatom evolutionary history. Although high-latitude plankton responses to polar cooling are extensively studied, it remains challenging to determine how cooling-driven changes in circulation, stratification and nutrient supply propagated and shaped low-latitude assemblages. Here we reconstruct species-level diatom diversity from exhaustive full-assemblage counts and integrate these data with diatom and radiolarian productivity from Deep Sea Drilling Project (DSDP) Site 366 (Sierra Leone Rise, equatorial Atlantic) spanning 38–32 Ma. Diatom diversity at DSDP 366 varies in step with Southern Ocean diversity records across the same interval. Extinction rates and community-structure metrics indicate a major reorganization of tropical diatom communities that is consistent with changes in upper-ocean stratification. We identify a sharp shift in community structure at ~33.5 Ma, pointing to a rapid ecological response in the earliest Oligocene.

The digital revolution has transformed palaeontology through the development of openly accessible, community-driven databases that underpin some of the most complex and large-scale empirical studies of the history of life on Earth. These systems safeguard high-effort, volunteered data and have revealed major macroevolutionary patterns, including the ‘Big 5’ mass extinctions. These efforts also represent remarkable global scientific and financial investment, which is continually required to support the next generation of databases and associated research. Here we conducted a survey of 118 palaeontological and allied Earth science databases, analysing their diversity dynamics, including origination and extinction rates. We show that approximately 85% of all community-curated databases have lifespans of less than 15 years, putting decades of investment at risk. We show that database creation effort has increased in the past 30 years, with peaks in database loss related to 5-year funding cycles. We advocate for strategies to enhance database longevity, including sustained funding models, stronger institutional support and modular backend architectures that better link international community databases to each other and to fossil specimens.

The Eocene/Oligocene Transition represents a period of profound changes in diatom productivity and evolutionary history within the Cenozoic era. Unraveling how these changes correlate with climatic shifts during this transition is crucial for understanding the potential role of diatoms in the cooling trends observed at the Eocene/Oligocene boundary (∼ 33.9 Ma). Current research predominantly relies on bulk opal accumulation measurements to assess productivity dynamics, which fails to distinguish the contribution of different biosiliceous (e.g., diatom versus radiolarian) plankton to total biogenic silica productivity. Furthermore, despite the fundamental role of community composition and diversity in diatom productivity and carbon sequestration, these factors are often not incorporated in existing studies focusing on the late Paleogene diatom productivity. The main objective of our work is to explore the potential roles of diatom communities in the Late Eocene climatic changes by focusing on diatom- and radiolarian-specific productivity across multiple Southern Ocean sites, rather than bulk opal measurements, and by incorporating total diatom abundance into the analysis of diatom diversity evolution throughout the Eocene/Oligocene transition. By quantifying diatom and radiolarian abundances across four Southern Ocean sites in the Atlantic and Indian Ocean sectors, and analyzing diatom productivity through recent reconstructions of diatom diversity from approximately 40–30 Ma interval, our findings reveal a significant increase in diatom abundance coupled with notable shifts in community diversity. These changes suggest a potential ecological shift, likely associated with the development of stronger circum-Antarctic currents in the Late Eocene. Such shifts could have influenced the efficiency of the biological carbon pump by enhancing organic carbon export to the deep ocean and thus potentially contributing to reduced atmospheric CO2 levels. While our findings indicate that the expansion of diatoms may have been a part of the mechanisms underlying the Late Eocene cooling, they also highlight the importance of integrating diatom diversity and community evolution into diatom productivity research. Furthermore, our results offer valuable insights into the complex relationship between diatom abundance and diversity in the geological record, reflecting the intricate interplay of environmental and climatic factors.

Hyperthermal events are a key element in understanding Palaeogene climate history, but many of these events other than the prominent Palaeocene–Eocene Thermal Maximum are poorly understood and studied. Two hyperthermal events that occurred in the middle to late Palaeocene include the Latest Danian Event (LDE) and the Early Late Palaeocene Event (ELPE). Most studies of these events focus on calcareous nannofossils and foraminifera, as well as geochemical data and astronomical tuning, but, to date, none consider biosiliceous production and flux. We therefore present eight records of biosiliceous fluxes, supported by geochemical data, from the Atlantic, Pacific, and Indian ocean sites spanning parts of the Palaeocene. Our results show pronounced variability in biosiliceous fluxes through the Palaeocene, with a peak at the time of the LDE. Establishing a link between the ELPE and biosiliceous flux variability through this time interval is more challenging, but the occurrence of peaks in biosiliceous fluxes after this event may indicate a global response of biogenic silica to several short-term biotic events, including the ELPE.

Climate and ecosystem dynamics vary across timescales, but research into climate-driven vegetation dynamics usually focuses on singular timescales. We developed a spectral analysis–based approach that provides detailed estimates of the timescales at which vegetation tracks climate change, from 10 ¹ to 10 ⁵ years. We report dynamic similarity of vegetation and climate even at centennial frequencies (149 ⁻¹ to 18,012 ⁻¹ year ⁻¹ , that is, one cycle per 149 to 18,012 years). A breakpoint in vegetation turnover (797 ⁻¹ year ⁻¹ ) matches a breakpoint between stochastic and autocorrelated climate processes, suggesting that ecological dynamics are governed by climate across these frequencies. Heightened vegetation turnover at millennial frequencies (4650 ⁻¹ year ⁻¹ ) highlights the risk of abrupt responses to climate change, whereas vegetation-climate decoupling at frequencies >149 ⁻¹ year ⁻¹ may indicate long-lasting consequences of anthropogenic climate change for ecosystem function and biodiversity.

Diatoms are the key players in the present-day global biogeochemical cycles. Yet, the diatom flux response to the dynamically changing climates of the Palaeogene has long been subject to divergent interpretations. We present a synthesis of Palaeogene deep-sea diatom-bearing sediment occurrences in time and space in order to gain new insight into inter-basin and latitudinal distribution of diatom accumulation zones from the Cretaceous–Palaeogene boundary to the Oligocene–Miocene transition. Our dataset includes 189 sites drilled in the Atlantic, Pacific, and Indian oceans and in the Arctic. It suggests that the number and distribution of deep-sea diatom-bearing sediment occurrences are mainly controlled by the nutrient availability and ocean circulation. Climate appears to have only an indirect correlation with our results, which may be linked to the expansion of the Antarctic Ice Sheet during the Oligocene global cooling. A comparison of our results with the temporal distribution of shallow marine diatomite occurrences (Figus et al., 2024a) suggests that the increase in the number of deep-sea diatom-bearing sediment occurrences (particularly in the Atlantic) during the diatomite gap (∼ 46 to ∼ 44 Ma) in shallow marine settings is indirectly related to the tectonic reorganizations occurring during this period: palaeogeographic changes caused the cessation of shallow marine diatomite deposition and increased nutrient availability in the oceans through continental weathering intensification. We also challenge the previous views on geographic shifts in the key loci of biogenic silica accumulation, which generally indicate that as global cooling progressed through middle and late Eocene, the Southern Ocean was gradually becoming the key biogenic silica sink. Our synthesis shows – albeit in a non-quantitative perspective – that through most of the Palaeogene, low to mid-latitude areas, especially in the Atlantic Ocean, were the locus of widespread biogenic silica deposition and burial.

The Eocene/Oligocene Transition represents a period of profound changes in diatom productivity and evolutionary history within the Cenozoic era. Unraveling how these changes correlate with climatic shifts during this transition is crucial for understanding the potential role of diatoms in the cooling trends observed at the Eocene/Oligocene boundary (~33.9 Ma). Current research predominantly relies on bulk opal accumulation measurements to assess productivity dynamics, which fails to distinguish the contribution of different biosiliceous (e.g., diatom versus radiolarian) plankton to total biogenic silica productivity. Furthermore, despite the fundamental role of community composition and diversity in diatom productivity and carbon sequestration, these factors are often not incorporated in existing studies focusing on the late Paleogene diatom productivity. The main objective of our work is to explore the potential roles of diatom communities in the late Eocene climatic changes by focusing on diatom- and radiolarian-specific productivity across multiple Southern Ocean sites, rather than bulk opal measurements, and by incorporating total diatom abundance into the analysis of diatom diversity evolution throughout the Eocene/Oligocene transition. By quantifying diatom and radiolarian abundances across four Southern Ocean sites in the Atlantic and Indian Ocean sectors, and analyzing diatom productivity through recent reconstructions of diatom diversity from approximately 40–30 Ma interval, our findings reveal a significant increase in diatom abundance coupled with notable shifts in community diversity. These changes suggest a potential ecological shift, likely associated with the development of stronger circum-Antarctic currents in the late Eocene. Such shifts could have influenced the efficiency of the biological carbon pump by enhancing organic carbon export to the deep ocean and thus potentially contributing to reduced atmospheric CO₂ levels. While our findings indicate that the expansion of diatoms may have been a part of the mechanisms underlying the late Eocene cooling, they also highlight the importance of integrating diatom diversity and community evolution into diatom productivity research. Furthermore, our results offer valuable insights into the complex relationship between diatom abundance and diversity in the geological record, reflecting the intricate interplay of environmental and climatic factors.

The Eocene/Oligocene Transition represents a period of profound changes in diatom productivity and evolutionary history within the Cenozoic era. Unraveling how these changes correlate with climatic shifts during this transition is crucial for understanding the potential role of diatoms in the cooling trends observed at the Eocene/Oligocene boundary (~33.9 Ma). Current research predominantly relies on bulk opal accumulation measurements to assess productivity dynamics, which fails to distinguish the contribution of different biosiliceous (e.g., diatom versus radiolarian) plankton to total biogenic silica productivity. Furthermore, despite the fundamental role of community composition and diversity in diatom productivity and carbon sequestration, these factors are often not incorporated in existing studies focusing on the late Paleogene diatom productivity. The main objective of our work is to explore the potential roles of diatom communities in the late Eocene climatic changes by focusing on diatom- and radiolarian-specific productivity across multiple Southern Ocean sites, rather than bulk opal measurements, and by incorporating total diatom abundance into the analysis of diatom diversity evolution throughout the Eocene/Oligocene transition. By quantifying diatom and radiolarian abundances across four Southern Ocean sites in the Atlantic and Indian Ocean sectors, and analyzing diatom productivity through recent reconstructions of diatom diversity from approximately 40–30 Ma interval, our findings reveal a significant increase in diatom abundance coupled with notable shifts in community diversity. These changes suggest a potential ecological shift, likely associated with the development of stronger circum-Antarctic currents in the late Eocene. Such shifts could have influenced the efficiency of the biological carbon pump by enhancing organic carbon export to the deep ocean and thus potentially contributing to reduced atmospheric CO₂ levels. While our findings indicate that the expansion of diatoms may have been a part of the mechanisms underlying the late Eocene cooling, they also highlight the importance of integrating diatom diversity and community evolution into diatom productivity research. Furthermore, our results offer valuable insights into the complex relationship between diatom abundance and diversity in the geological record, reflecting the intricate interplay of environmental and climatic factors.