GSEES Hour (Dr. Leonid Polyak)

Date: July 14, 2009, 17:00-
Place: Humanities and Social Sciences Classroom Building, 1st Floor, Room W103 (N10W7)

Lecturer: Dr. Leonid Polyak (Ohio State University)
Title: "Arctic Ocean history and the Climate Change"

Abstract
Climate change in the Arctic demands especially close attention today as average temperatures in the Arctic over the past 30 years have increased at almost twice the rate of the planet as a whole. One of the first and clearest indicators of the ongoing change is the dramatic shrinkage of summer Arctic sea-ice cover that reached startling levels in 2007. Climate models based on these observations suggest that the Arctic is rapidly moving toward a new, low-ice or even seasonally ice-free state. This state has not been witnessed in human history and is capable of accelerating the current rate of climatic change through Earth's ice-albedo feedback. The Arctic change could also lead to an abrupt climate shift through an increase in freshwater export that could perturb the North Atlantic overturning. Large inter-agency programs have been launched to monitor ongoing change and to develop models for predicting its magnitude and direction. However, to understand the full range of variability for future Arctic climate and ocean system, we need to explore longer-term paleoclimatic records with a special focus on low-ice periods of the recent geological past. Sediment cores from the Arctic Ocean provide the best archives that represent the long-term history of Arctic sea-ice extent and circulation. However, tapping these sedimentary archives faces many difficulties including the logistical problems of operating in an ice-capped ocean and scientific problems in interpreting Arctic sedimentary data. Several recent expeditions in the Arctic Ocean provide new, high-quality marine geological material with which to characterize past variations in ice cover and oceanographic conditions. The 2004 Arctic Coring Expedition (ACEX) for the first time performed deep-sea drilling in the central Arctic Ocean and obtained a long sedimentary record extending to the significant part of the Cenozoic (~55 million years). For a wider geographic coverage with a focus on the most recent, Quaternary paleoenvironments, the 2005 Healy-Oden Trans-Arctic Expedition (HOTRAX) retrieved >20 sediment cores averaging 12 meters in length from a complete transect across the Arctic Ocean and several high-resolution cores from the Alaskan margin. For a more comprehensive characterization of seafloor history, sediment cores are combined with multibeam bathymetric surveys and chirp-sonar subbottom profiling. The talk will overview results from these and related expeditions that improve our understanding of the history of the Arctic Ocean system and implications for future changes.

Dr. Polyak is invited by GCOE Invitation Fellowship Program.