Maria Luisa Sanchez Montes ^1* Erin L. McClymont ² Hirofumi Asahi ³ Joseph Stoner ⁴ Christopher Moy ⁵ Sophie Gleghorn ² Jerry M Lloyd ²

• ¹ Institute for Arctic and Alpine Research, University of Colorado Boulder, Boulder, United States
• ² Durham University, Durham, England, United Kingdom
• ³ University of Fukui, Fukui, Fukui, Japan
• ⁴ Oregon State University, Corvallis, Oregon, United States
• ⁵ Department of Geology, Division of Sciences, University of Otago, Dunedin, Otago, New Zealand

The Pacific Ocean is an important region for carbon storage, where the past ocean-climate interactions are relatively underexplored to explain glacial/interglacial climate variability during the late Pleistocene re-expansion of the Cordilleran Ice Sheet (CIS). We analysed IODP 341 Expedition Site U1418 marine sediment samples in the Gulf of Alaska (GOA) using marine and terrestrial biomarkers to study the periodicity of glacial-interglacial cycles during the last 500 thousand years and reconstruct the North Pacific oceanography and marine productivity. Our sea surface temperatures (SST) results show MIS 4 and MIS 6 are the coldest and freshest glacials and MIS 5 and MIS 1 are the warmest and saltiest interglacials. The glacial-interglacials during the last 200 kyr are best observed due to the increased sedimentation rates in the GOA during the expansion of the CIS, where coccolithophores dominated the productivity export. We observe lower %IRDs during cold MIS 6 than during warm MIS5. During the MIS6-5e transition, the coccolithophore alkenone K37/K38 ratio suggests a different producer. We conclude that during MIS 6, the stratification of the cold and fresh surface ocean helped the CIS grow, and coccolithophores did not take full profit of the nutrient availability in the ocean but contributed to deep carbon storage and climate cooling. During MIS 5, although SSTs were 6 °C warmer, icebergs were more present. We infer that higher coccolithophore abundance with different alkenone configurations suggests that a change in dominant coccolithophore was the result of changes to the available nutrients and contributed to sedimentary carbon storage. This, in turn, contributed to climate cooling despite the warm climate. As the last interglacial (MIS 5e) had similar to modern atmospheric CO2 concentrations, our results bring new understandings on the CIS and GOA possible behaviours under the current changes in climate.