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doi:10.2204/iodp.sp.341.2011 AbstractGlobal climate during the Neogene to Quaternary is distinguished by the transition into a colder, more variable world dominated by the onset and intensification of major Northern Hemisphere glaciations and is associated with an increase in erosion rates and sediment delivery to basins. The effects of this increased erosion may be profound, as worldwide analyses of orogenic belts have shown that earth systems cannot be considered to be the product of a series of distinct, decoupled tectonic and climatic processes. Rather, there is complex interplay between deformation, exhumation, and climate systems. Exhumation plays a key role in controlling the regional distribution of metamorphic rocks, local climate change, and development of structures throughout an orogen. As tectonic processes influence regional climate by raising mountains that enhance orographic precipitation patterns and intensity, the Neogene–Quaternary climate transition likely affected tectonic processes through changes in erosion rates, which redistributed mass and subsequently altered stresses in orogenic wedges. Analytical models examining the coupling between glacial erosion and orogenic processes reveal that glacial erosion can significantly modify the patterns and rates of erosion in an orogenic wedge. A critical question is, at what stage of the deteriorating Neogene climate is an orogen ultimately driven into subcriticality? Does this lead to increased exhumation in the glaciated core of a mountain belt, enhanced topographic relief, and migration of the locus of sediment accumulation to the toes of an orogen that impacts deformation patterns? Addressing the linkages between global climate change, modification of the dynamics of surficial processes, and subsequent tectonic responses requires integrated studies of orogenic systems in areas that exemplify specific end-members of the problem. The Gulf of Alaska borders the St. Elias orogen of Alaska and Canada, the highest coastal mountain range on Earth and the highest range in North America. This orogen is <30 Ma in age, and mountain building occurred during a period of significant global climate change, allowing this expedition to examine the response of an orogenic system to the establishment of a highly erosive glacial system. Additionally, the implications of the Neogene glacial growth in the circum-North Pacific are far-reaching, beyond a tectonic response to increased glacial erosion and exhumation. As climate determines the timing and patterns of precipitation, it controls glacial dynamics, erosion, and sediment/meltwater and chemical fluxes to the ocean. Establishing the timing of northwestern Cordilleran ice sheet (NCIS) advance–retreat cycles in southern Alaska will address a major challenge in Quaternary paleoclimatology, which is to know the extent to which glacial-age climate change was a synchronous worldwide event and what the driving mechanisms were for potentially propagating millennial-scale warming–cooling cycles around the globe. Evidence of substantial changes in surface productivity in the Gulf of Alaska since the Last Glacial Maximum indicates that millennial-scale climate change and eustasy in the northeast Pacific Ocean has a first-order effect on primary productivity. Thick Pleistocene glacimarine deposits of the Gulf of Alaska continental margin contain a rich history of climate change recorded in both proxy climate data and sediment accumulation rates that can help decipher the architecture of massive late Tertiary and Quaternary high-latitude Northern Hemisphere continental margin sedimentary sequences. Exceptionally high rates of glacigenic sediment accumulation in this region also allow for development of a paleomagnetic record of geomagnetic field variability on submillennial scales to assess geomagnetic persistence, a signature of the mantle’s influence on the geodynamo and the paleomagnetic record. Integrated Ocean Drilling Program (IODP) Expedition 341, which combines IODP Proposal 686-Full and ancillary proposal letter (APL)-786 will drill a cross-margin transect to investigate the northeast Pacific continental margin sedimentary record formed during orogenesis during a time of significant global climatic deterioration in the Pliocene–Pleistocene, which led to the development of the most aggressive erosion agent on the planet, a temperate glacial system. Sedimentary provenance and paleoclimatic, glacimarine, and structural sedimentary indicators tied to a multicomponent chronology will be used to generate detailed records of changes in the locus and magnitude of glacial erosion, degree of tectonic shortening, and sediment and freshwater delivery to the coastal ocean and their impact on oceanographic conditions in the Gulf of Alaska, and the resulting continental margin stratigraphic record on the interaction of these processes. Because the oceanographic processes in the Gulf of Alaska directly impact the Bering Sea, Expedition 341 will strongly complement IODP Expedition 323 by addressing the late Neogene evolution of continental glaciation and freshwater and nutrient inputs, but in a more proximal source to glacial drivers of many of these processes. Major objectives of planned drilling in the Gulf of Alaska are as follows:
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