A GEOPHYSICAL TRANSECT ACROSS THE ARCTIC OCEAN COLLECTED FROM THE US COAST GUARD ICEBREAKER HEALY

COAKLEY, Bernard, Department of Geology and Geophysics, University of Alaska, 900 Yukon Drive, Fairbanks, AK 99775-5789, [email protected], KRISTOFFERSEN, Yngve, Department of Earth Science, University of Bergen, Allegaten 41, Bergen, N-5007, Norway, and HOPPER, John, Department of Geology and Geophysics, Texas A&M University, College Station, TX 77843

The history of the Arctic Ocean is preserved in the pattern of plateaus and sub-basins that segment it and written in the sediments beneath the seafloor. While it is clearly an oceanic basin, to date there is only a single mutually agreed upon plate boundary, the Gakkel Ridge. As a result, reconstructions of the paleogeography of the northern hemisphere prior to Cenozoic times are largely hypothetical. Identifying Arctic plate boundaries will begin the process of deciphering the tectonic history of the Mesozoic Arctic Ocean. This history will provide the context for better understanding the large tectonic features continental margin features that have recently begun to be well mapped. In turn, what is learned from the marine geology will provide critical information towards understanding the terrestrial geologic evolution of major features in the northern hemisphere (e.g., the Brooks Range and North Slope of Alaska and the Chukchi Shelf).

During the late Summer of 2005 the US Coast Guard icebreaker Healy undertook a research cruise across the Arctic Ocean. During this cruise, the ship collected continuous multi-beam bathymetry, sub-bottom profiler and gravity anomaly data. As ice conditions permitted, multi-channel seismic reflection and refraction data were collected. The source consisted of two 250 cubic inch airguns. The shots were received by a 200-300 m long streamer (16 to 24 channels) and nearly 100 sonobuoy deployments.

Data collected in the Amerasian Basin show a pervasive mantled sedimentary layer, consistent with tectonic inactivity of this basin.Some locations lack this layer, suggesting localized erosion by bottom currents.

The stratigraphic record of the Arctic Ocean is revealed in the ~2200 km of multi-channel seismic reflection data collected during this cruise. These sediments contain a unique paleo-oceanographic and climatic record. Very little of the Cenozoic and almost none of the Mesozoic record has been directly sampled. Deciphering this history will complement the sediment and ice cores taken at lower latitudes and extend the limited historical time series for the high arctic, making it possible to study truly global paleo-climate for the first time.