Evaluating Sea-Surface Conditions in the Interglacial Arctic Ocean Using Planktic Foraminiferal Assemblages and Mg/Ca Ratios
Summer sea ice cover in the Arctic Ocean is diminishing rapidly. The rate and extent to which it decreases has implications for shipping, mineral development, climate, and national defense. Models can be used to predict the future with some accuracy, but we know that existing models cannot yet fully reproduce observed changes in sea ice extent. Another approach is to look for analogs in the past. What was the sea cover like in the geologic past? Was the Arctic ice free under previous warm atmospheric conditions? Using independent estimates such as from ice cores, it is known when the Arctic was warm in the past. This project will develop an estimator, or proxy, for sea surface temperature. This is based on single-celled organisms known as foraminifera that live in the surface waters of the ocean. When the proxy indicates that sea surface temperature was higher than the melting point of sea ice, we know that sea ice was not present. In the course of completing this research project, contributions will be made to training the next generation of scientists, as well as to informing the broader population about the Arctic. Partial support of a postdoctoral researcher on this project will allow her to broaden her scientific expertise and international experience. An undergraduate student involved in this work will also receive valuable training in many technical aspects of the research. Collaboration with scientists from several countries will aid in fostering broader international cooperation in the Arctic. Results of this research will enrich the content of courses taught by the principal investigator. Knowledge from this project will be disseminated to both specialists and the broader public through talks, publications in professional and popular journals, and internet blogs. The target audiences will include K-12 students of various grades, as well as parents and educators through the Byrd Polar Research Center Learning Center. Proxy reconstructions of the past warm intervals in the Arctic are needed to compare and contrast with understanding of the ongoing and projected changes in the Arctic marine ecosystem environment. Funds are provided to characterize Arctic paleo sea surface temperatures based on the composition of planktic foraminiferal species and their magnesium/calcium ratios in sediment samples from the Fram Strait (the Arctic-Atlantic gateway) and the central Arctic Ocean. This research will involve close collaboration with several national and international partners to ensure sample exchange, interlaboratory data compatibility, and a broad context for interpretation. Achieving the project goals involves several methodological and data-producing steps, including (1) development of the optimal cleaning/measuring procedure for Mg/Ca analysis on fragile tests of subpolar planktic foraminifers, (2) calibration of Mg/Ca to modern hydrography using improved assemblage-based transfer functions, and (3) reconstruction of paleo temperatures at high-resolution (decadal to century-scale) using Holocene cores from the Fram Strait, as well as warming/ice-reduction events in the central Arctic Ocean (e.g., Marine Isotope Stages 1, 5, and 11). This research will provide insights into the extent of surface warming and sea-ice retreat in the Arctic Ocean during past climate amelioration events, as well as the short-term variability in the export of sea ice and polar waters during the Holocene. It will also contribute to understanding the response of Arctic biota, exemplified by planktic foraminifers, to climatic warming and sea-ice reduction. The resultant data sets will be made available through appropriate public archives.