Description: Past changes in North Pacific sea surface temperatures and sea-ice conditions are proposed to play a crucial role in deglacial climate development and ocean circulation but are less well known than from the North Atlantic. Here, we present new alkenone-based sea surface temperature records from the subarctic northwest Pacific and its marginal seas (Bering Sea and Sea of Okhotsk) for the time interval of the last 15 kyr, indicating millennial-scale sea surface temperature fluctuations similar to short-term deglacial climate oscillations known from Greenland ice core records. Past changes in sea-ice distribution are derived from relative percentage of specific diatom groups and qualitative assessment of the IP25 biomarker related to sea-ice diatoms. The deglacial variability in sea-ice extent matches the sea surface temperature fluctuations. These fluctuations suggest a linkage to deglacial variations in Atlantic meridional overturning circulation and a close atmospheric coupling between the North Pacific and North Atlantic. During the Holocene the subarctic North Pacific is marked by complex sea surface temperature trends, which do not support the hypothesis of a Holocene seesaw in temperature development between the North Atlantic and the North Pacific.

Description: The Mid Pleistocene Transition (MPT) constitutes a fundamental shift in Earth's climate system from a 41 ka to a 100 ka periodicity in glacial oscillations. The exact timing and mechanism(s) that caused this change from a low- to high-amplitude glacial variability are still under debate and only recently Pena & Goldstein (2014) suggested that a disruption of the thermohaline circulation at about 900 ka BP and a subsequent change in ocean circulation might have acted as a trigger for the onset of 100 ka glacial-interglacial cycles. Most studies targeting the MPT are based on Atlantic sediment records whereas only few data sets are available from the North Pacific (see e.g. Clark et al., 2006 and McClymont et al., 2013 for reviews). IODP Expedition 341 distal deep-water site U1417 in the Gulf of Alaska (subpolar NE Pacific) now provided a continuous sediment record for reconstructing Miocene to Late Pleistocene changes in the sea surface conditions and how these relate to orbital and millennial scale climate variability. Here we present organic geochemical biomarker data covering the 1.5 Ma to 0.1 Ma time interval with special focus on the MPT. Alkenone, sterol, n-alkane and C25 highly branched isoprenoid data are used to reconstruct sea surface temperatures, primary productivity and terrigenous organic matter input (via sea ice, icebergs, meltwater discharge or aeolian transport). In addition, the diatom concentration and the species composition of the diatom assemblage deliver information on changes in palaeoproductivity and nutrient (silicate) availability. A major change in the environmental setting between 1.2 and 0.8 Ma is recorded by the biomarkers. This shift seems to be associated with a significant cooling of the surface waters in the Gulf of Alaska. Matching this shift, a significant change in the main components of the diatom community occurred between 1.2 and 0.8 Ma. References Clark, P.U., Archer, D., Pollard, D., Blum, J.D., Rial, J.A., Brovkin, V., Mix, A.C., Pisias, N.G., Roy, M., 2006. Quaternary Science Reviews, 25, (23–24), 3150-3184. McClymont, E.L., Sosdian, S.M., Rosell-Melé, A., Rosenthal, Y., 2013. Earth-Science Reviews, 123, 173-193. Pena, L.D. and Goldstein, S.L., 2014. Science, 345, 318-322.