High Carbon Dioxide Worlds

Carbon dioxide (CO₂) emissions are rapidly rising leading to warmer oceans, surface ocean acidification, and complex changes in marine biogeochemical cycling. Although it is possible to directly assess the short-term effects of these environmental changes on modern marine ecosystems, examination of similar climatic perturbations in the geologic record are necessary in order to predict how marine ecosystems might respond over longer-term (millennial) timescales. For this reason, the “High CO₂ World” Project examines perturbations to the climate system during exceptionally warm intervals of Earth’s history as recorded in ocean-floor archives. Our main goal is to use a combination of geochemical, micropaleontological, and sedimentological techniques to evaluate potential tipping points and threshold responses to perturbation in warmer worlds, which can be used to improve the robustness and sensitivity of climate models.

Our project predominantly focuses on the high CO₂ world of the early Eocene (~56 to 48 Ma), which is considered one of the best geologic analogues for future climate change. During this interval, generally increasing global temperatures were punctuated by transient warming events of varying magnitudes called “hyperthermals”, which include the Paleocene-Eocene Thermal Maximum (PETM), ETM-2, and ETM-3. Therefore, the early Eocene provides an opportunity to not only examine the long-term effects of climatic perturbations in high CO₂ worlds, but also to assess whether the biogeochemical and ecosystem response is scaled to the magnitude of the perturbation.

One of the best records we have of the early Eocene is from IODP Site U1553 (Campbell Plateau) in the understudied South Pacific Ocean. This site was only recently drilled during Expedition 378 (January – February 2020), and provides an exciting and unique opportunity to examine climatic and ecological responses to warming at southern high latitudes. Our continuous coring and multi-hole approach allowed for the recovery of most of the early Paleogene, and the Eocene at Site U1553, includes a double-cored, expanded PETM interval. This expedition has thus provided meters-worth of new material for high-resolution geochemical (e.g., δ¹⁸O, δ¹³C, Mg/Ca, clumped isotopes) and micropaleontological analyses. Our overall goal is to compare our Site U1553 data to those from legacy DSDP, ODP, and IODP sediment cores at both high as well as low latitudes from the Atlantic, Indian and Pacific Oceans in order to put our findings in a global context.