Improving High Latitude Foraminiferal Paleoproxies: Insights from Northern California Current Modern and Historical Records

Oregon State University, Corvallis OR

Investigators

Abstract

This project will improve our ability to reconstruct past ocean conditions, such as sea surface temperatures, in high-latitude regions. These regions experience a more extreme response to climate change than low-latitude regions. One of the best ways to study past ocean-climate change is by studying fossil plankton called planktic foraminifera or “forams”. Forams are microscopic zooplankton that have existed for over 200 million years and live near the surface of the ocean. As these organisms grow, they build small shells. The shell chemistry records the conditions at the time the shells were formed. When the organism dies, its shell sinks to the seafloor and becomes part of the geological fossil record. Thus, the chemical composition of fossil shells recovered from deep-sea sediments can be used to reconstruct the surface ocean conditions in the past. This study will generate the geochemical-environmental relationships (i.e., calibration equations) used to evaluate fossil foram records. The composition of the shells of living and recently deceased forams collected from the surface ocean will be compared to the conditions and chemical makeup of the seawater they are living in. Samples for this study will include an archive of plankton tow samples from the last decade. Newly collected plankton tow and water samples from throughout the Northern California Current region off the coast of northern California, Oregon, and Washington states will also be studied. Although forams are found globally, this study will focus on constraining geochemical-environmental relationships for species that live in intermediate- to high-latitude regions to better predict how these vulnerable regions will respond to our changing climate. The research team will also investigate how the composition of foram shells may change throughout the organism’s life cycle. This study will help ensure that the calibration equations used to interpret fossil records are accurate. The project includes support for an early career scientist and for undergraduate students. The research team will share the results and scientific process of the research with the public through several public outreach events. The dynamic Northern California Current (NCC) system has been extensively monitored for nearly half a century, through a series of hydrographic transects off the coasts of California, Oregon, and Washington, resulting in a robust archive of plankton tow samples and concurrent environmental data. This study will use historical plankton tow samples, and collect new plankton samples, to further develop a range of trace element/calcium (TE/Ca) paleoproxies for intermediate to high latitude planktic foraminiferal species living in the NCC. Species common to the NCC include temperate and high-latitude genotypes of Globigerina bulloides, Neogloboquadrina pachyderma, N. incompta, N. dutertrei, and Turborotalita quinqueloba. These species are common in higher latitude regions, including the Artic Ocean, where temperature change in response to climate change tends to be greatest. The research objectives are to: 1) establish Mg/Ca-temperature and Na/Ca-salinity calibrations for understudied temperate to polar planktic foraminiferal taxa and investigate the potential for other TE/Ca-environmental relationships, 2) investigate potential vital effects and mechanisms for TE incorporation in planktic foraminiferal shells as they transition from life to death, and 3) characterize the d18O(seawater) signature in the study region and establish species specific seawater foraminiferal calcite isotopic offsets in order to constrain the depth habitats of the study taxa, a critical step to establishing calibrations based on data in a “natural laboratory” setting. The proposed research will further develop novel and existing planktic foraminiferal TE/Ca proxies for use in paleoclimatic and paleoceanographic reconstructions, with particular emphasis on improving our ability to reconstruct past environmental conditions in intermediate to high latitude regions. 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.