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doi:10.2204/iodp.sp.302.2004
INTRODUCTION
The Arctic Ocean and its marginal seas play a fundamental role in the global ocean/climate system. The dense, cold, bottom waters of most of the world's oceans, which originate in the Nordic seas, strongly influence global thermohaline circulation, driving world climate. The permanent Arctic sea-ice cover has a tremendous influence on the Earth's albedo and the distribution of fresh water. It varies both seasonally and over longer time periods and thus has a direct influence on global heat distribution and climate. While understanding the history of the Arctic Ocean is critical for climate, ocean-circulation or tectonic models that would be truly global, the logistical difficulties associated with the work in this remote and harsh region have prevented us from gathering the critical data needed to document the role of this key region in the development and maintenance of the global climate system.
Except for the Pleistocene, only isolated, discontinuous intervals of sediments representing Cenozoic time have been sampled by coring. Thus the Arctic Ocean, despite its critical role in global climate evolution, is the only ocean basin whose history is virtually unknown. The complex history of this basin, which receives surface water from the North Pacific, the North Atlantic and the various large rivers which drain northern Eurasia and North America, where water exists in all three phases year round, can only be studied by direct sampling of the sediments which record its history. The sediment sections preserved on the basinal highs have captured a record of the development of the Fram and Bering Straits, varying fluxes of fresh water into the basin, the development of the Arctic sea ice and the history of the high-latitude effects of the Cenozoic glaciation. This information is necessary to fully understand the climate of the Northern Hemisphere, providing a dataset that complements ice and sediment cores collected at lower latitudes.
Five primary sites are proposed (Figure F1) to recover a 450 m-thick sediment sequence and the upper 30 m of the underlying acoustic basement (bedrock) from the crest of the Lomonosov Ridge. The sediment sequence represents a unique archive of the past 50 million years of paleoenvironmental evolution in the central Arctic Ocean, whereas the transition into the acoustic basement and its uppermost parts represents a similarly unique archive of the early tectonic evolution of the Eurasian Basin.
The ACEX program was developed from ODP/IODP Proposal 533 by Jan Backman, Kate Moran, Bernard Coakley, Margo Edwards, Rene Forsberg, Ruth Jackson, Wilfried Jokat, Yngve Kristoffersen, Larry Mayer, Martin Jakobsson, Evgeny Musatov and Nikita Bogdanov. Wilfried Jokat and Yngve Kristoffersen collected all airgun seismic survey data; Bernard Coakley, Margo Edwards and Martin Jakobsson provided high-resolution chirp sonar, sidescan sonar and bathymetry data.