NSF Award
2414673
The Eocene (56-33.9 Ma) was a time of profound climatic variability as Earth transitioned from the hothouse, ice-free conditions of the early Eocene, to the warmhouse of the middle Eocene, to the coolhouse of the Oligocene, characterized by lower temperatures and the development of permanent ice sheets on Antarctica. Based on these large changes in Earth’s climate, it is reasonable to assume that the composition of the pelagic calcifier ecosystem in the Eocene changed in response to evolving patterns of ocean circulation, continental weathering, and cooling temperature, but there are few Eocene data available to test this assumption. The proposed research will reconstruct changes of the South Atlantic subtropical gyre ecosystem from the early Eocene to the early Oligocene, and it will determine how these changes impacted carbonate production at the surface and its preservation at the seafloor. Data will be generated using sediment cores collected below the oligotrophic waters of the South Atlantic subtropical gyre during the International Ocean Discovery Program Expeditions 390C and 393 (Sites U1557 and U1558). These data will improve the societal understanding of the evolution of the carbon cycle under different climatic regimes. This research will also generate the first complete Eocene record of pelagic carbonate communities and carbonate accumulation rates for the western South Atlantic Ocean, which remains a poorly studied region during a key interval of the Cenozoic. Broader impact activities include the support for two early career researchers, and an outreach program that will promote the participation of high school students from disadvantaged backgrounds in summer research experiences. Additionally, several undergraduate and graduate students will be involved in research activities.<br/><br/><br/>On geological time scales, the biologically-mediated production of calcium carbonate at the ocean surface and the burial of this calcium carbonate at the seafloor influence the marine chemistry and, indirectly, the CO2 concentration in the atmosphere. Thus, these processes are important components of the carbon cycle. However, their evolution through time is not well constrained, in particular with oligotrophic systems, which are less productive but cover vastly more area than upwelling regions. The goal of this project is to study how oligotrophic pelagic calcifier communities evolved during a time characterized by different temperatures and CO2 concentrations in the atmosphere (i.e., Eocene) and how these changes have affected carbonate burial at the seafloor. Specifically, the investigators will test the following hypotheses:<br/><br/>1) Surface carbonate productivity changed from the early Eocene to the early Oligocene (~56-32 Ma);<br/>2) These changes were connected to changes in the composition of the pelagic calcifier ecosystem;<br/>3) Changes in the pelagic calcifier ecosystems were driven by changes in surface currents;<br/>4) Above the carbonate compensation depth, carbonate burial was not impacted by deep-ocean circulation. <br/><br/>The investigators will evaluate project hypotheses by generating and interpreting mass accumulation rates of planktic foraminifera and calcareous nannoplankton (the main producers of carbonate found in deep sediments), planktic foraminiferal assemblages and percent fragmentation, and benthic foraminiferal accumulation rate from two new International Ocean Discovery Program sites drilled in the western south Atlantic, Sites U1557 and U1558.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
