Climate-Ice Sheet Interactions through the Plio-Pleistocene: Preliminary Results from IODP 341 Expedition (Gulf of Alaska).

Since the Pliocene, global climate history is distinguished by the transition into a colder world, dominated by the onset and intensification of major Northern Hemisphere glaciations which have changed in their duration and intensity. It has been argued that cooling in the surface ocean has been driven by or been conducive to continental ice-sheet growth or influenced by progressive sub-glacial erosion and feedbacks to explain changing ice-sheet extent and dynamics, which may occur independently of climate change and/or the potential regional climate impacts of tectonic uplift. At present, isolating climate as the driver of evolving continental ice volume since the Pliocene is hindered by the limited long term data sets which directly link climate changes to evidence for ice-sheet advance/retreat, erosion, and tectonic evolution over million year timescales. IODP Expedition 341 (May-July 2013) drilled a cross-margin transect from ice-proximal sites on the continental shelf to distal sites in the deep Pacific. This study focuses on the most distal drilled site, (Site U1417, c. 4190 m water depth) which extends through the Pleistocene, Pliocene and Miocene and was targeted due to its rich recorded history of climate change, glaciation and tectonics and which will allow for a more detailed understanding of the interaction between north-east Pacific paleoceanography and the history of the north-west Cordilleran ice sheet, neither of which are fully understood given limited data which pre-dates the Last Glacial Maximum. The focus of this research is to target the evidence for past climate change as recorded in evidence for evolving sea surface conditions including sea surface temperatures (SSTs) and ice rafted debris (IRD) through the Pliocene and Pleistocene. We have reconstructed SSTs during the mid-Pliocene and Plio-Pleistocene Transition (PPT) using the alkenone biomarker proxy, the UK37' index, the relative abundance of C37:4 alkenone and IRD counts and compare our results with evidence for evolving ice-sheet history as determined through the shipboard-generated lithostratigraphy. We consider the interaction between SSTs and IRD proxies and evaluate the influence of climate versus tectonic forcing: Is there a Pliocene-Pleistocene cooling? What is the SST variability? What is the SST-IRD relationship?