QUANTIFYING ALASKAN TECTONIC-CLIMATE FEEDBACKS WITH A DRILL BIT: TERRY PAVLIS’ OFFSHORE LEGACY

Due to the rich datasets provided by the St. Elias Erosion/tectonics Project (STEEP) and decades on onshore research by Terry Pavlis and numerous students and colleagues, Integrated Ocean Drilling Program Expedition 341 sailed offshore Alaska in 2013. This expedition was only possible with a suite of seismic data acquired during STEEP and key hypotheses that could be tested with a drill bit. Three of the major objectives directly attributable to STEEP were to: 1) document tectonic response of an active orogen to late Miocene to recent climate change, 2) establish timing of advance-retreat phases of the northwestern Cordilleran ice sheet to test its relation to dynamics of global ice sheets, and 3) implement a source-to-sink study of glacial-tectonic-oceanographic processes that produced one of the thickest Neogene high-latitude continental margin sequences and the Surveyor Fan. As tribute to Terry Pavlis’ career, here we provide a synthesis of the range of research that grew out of Expedition 341 which targeted each of these three hypotheses. These results include quantification of a threshold at which glacial erosion can overcome tectonic inputs to drive an orogen into a subcritical state, documentation that the Cordilleran ice sheet produces large icesheet fluxes into the north Pacific called Siku events and that ice streams on the Gulf of Alaska shelf can respond to tidewater glacial cycles, and demonstration of how critical the transition from 41 Kyr glacial cycles to 100 Kyr glacial cycles, the mid-Pleistocene transition (MPT), were for development of the Surveyor Fan, Aleutian accretionary prism, and the rupture segment responsible for the 1964 great earthquake. Moreover, these offshore results discovered the Surveyor mass transport deposit preconditioned by glacial sediment flux at the MPT, helped to explain evolution of tectonic boundaries at the Pacific-North America-Yakutat triple junction, and confirm how sedimentation can directly affect patterns of faulting. Together with the results from STEEP, Expedition 341 demonstrates the key insights possible with the Chugach-St. Elias tectonic laboratory to understand the fundamental processes of tectonic-climate interaction at the orogen scale. These insights are a legacy of Terry Pavlis laying the foundation for dozens of researchers to build upon.