Reconstructing past sea ice cover is a fundamental challenge in paleoceanography/paleoclimate research. Conceptual and numerical models of abrupt changes and the role of high vs. low latitudes as the drivers of climate change invoke sea ice as a principle cause of variability, but to date there have been no reliable proxies of past sea ice extent. Understanding the role of sea ice in past changes also critically impacts our understanding of the consequences of future changes in Arctic sea ice cover. This research calibrates and applies a set of new organic biomarkers (IP25 sea ice index, and TEX86 temperature index) to reconstruct changes in sea ice and associated sea surface temperatures from a series of high sedimentation rate cores from the Bering and Chukchi Seas. Specifically, the researchers will 1) produce a high latitude spatial dataset of relative IP25 concentrations and compare the distribution of these compounds with modern sea ice extent, 2) generate a new database of biomarker distributions in surface sediments from high-latitude oceans and compare with known SST variations, and 3) reconstruct past changes in seasonal sea ice and associated sea surface temperatures during the late glacial and Holocene from selected high latitude sites. In addition to the societal relevance of better understanding the role of sea ice extent in climate change, broader impacts include support of a PhD student, summer research projects for undergraduates, and a new faculty member at the University of Texas at Austin.
Normal 0 false false false EN-US X-NONE X-NONE The main research goals of this project were to develop new molecular proxies for reconstructing sea ice variations and to construct records of past changes in sea ice and temperature in the Arctic region. We have measured concentrations of a specific compound synthesized by algae living within sea ice, called IP25, in an extensive set of surface sediment samples from across the modern Arctic seasonal sea ice margin. Comparing these concentrations against instrumental data on the duration of sea ice cover in this area allowed us to test the utility of this sea ice proxy. Our findings indicate that IP25 increases exponentially with sea ice cover and that there are significant nonlinear controls on the sea ice-IP25 relationship. Scaling the IP25 abundance to a proxy for phytoplankton productivity improves the spatial reconstruction of spring-summer sea ice throughout the Atlantic and Pacific sectors of our study, and removed basin-related differences seen in the IP25-sea ice relationship within the Atlantic. Our work shows for the first time that a single index can be applied to different basins across the Arctic (although slight differences in absolute abundances persist between Atlantic and Pacific sites, the slope of the relationship is the same). This modern calibration study provides proof-of-concept that can be applied for down-core sea ice reconstructions using Arctic sediment cores. Records of sea-ice variability from the Chukchi Sea show that sea ice was greatly reduced in the early-mid Holocene relative to the last Glacial period and modern day. On-going global climate change is a significant problem facing society, with some of the greatest impacts occurring at high northern latitudes. This study provides insights into the mechanisms controlling Arctic climate change, particularly sea ice, and gives us a view of long-term variability in the North Pacific climate system, which may help to predict its behavior in the face of continuing anthropogenic warming. In light of recent, apparently anomalous decreases in the seasonal Arctic sea ice cover, this work provides new data on the rate and magnitudes of past changes in sea ice and temperature, as well as the relationships between these two factors, which are crucial for understanding current changes in sea ice cover and Arctic climatology. Improved understanding of global climate change and its potential trajectory in the face of continuing anthropogenic impacts is critical to the ability of society to predict and mitigate the effects of changing climate in the future.
