High-latitude paleoecological response to early Eocene warming events

As atmospheric carbon dioxide continues to rise at unprecedented rates, it is imperative that we better understand the potential long-term effects of warming on marine communities. Calcareous nannoplankton are likely particularly sensitive to the effects of rising CO₂, and as one of the most important groups of mineralizing phytoplankton, their response to climatic change will have a knock-on effect on both marine food web dynamics and biogeochemical cycling.

As calcareous nannoplankton have a rich global fossil record spanning the last ~220 million years of Earth history, it is possible to examine how they were affected by high CO₂ conditions in the geological past. These data can then be fed into Earth System Models, allowing for better predictions as to how modern communities might be affected by – and recover from – current global climate change. The earliest Eocene ca. 52 - 56 million years ago (Ma) is an excellent case study as to how the Earth system might respond to ‘worst-case’ climate scenarios. Additionally, as the high CO₂ world of the early Eocene was punctuated by transient warming events of different magnitudes and durations, it is possible to examine potential threshold paleoecological responses to warming, as well as the recovery rates following individual events.

Here, we present new high-resolution data documenting changes in early Eocene calcareous nannoplankton community composition from two high-latitude International Ocean Discovery Program (IODP) sites (Site U1553 and Site U1514) in the historically understudied Southern Hemisphere. As well as elucidating how climatically sensitive, high-latitude communities were affected by high CO₂ conditions, direct comparison of our data with published lower latitude records will reveal any ocean basin- or region-specific responses to warming.