Abstract
Abstract. The initiation and evolution of the Cordilleran Ice Sheet are relatively poorly constrained. International Ocean Discovery Program (IODP) Expedition 341 recovered marine sediments at Site U1417 in the Gulf of Alaska (GOA). Here we present alkenone-derived sea surface temperature (SST) analyses alongside ice-rafted debris (IRD), terrigenous, and marine organic matter inputs to the GOA through the late Pliocene and early Pleistocene. The first IRD contribution from tidewater glaciers in southwest Alaska is recorded at 2.9 Ma, indicating that the Cordilleran Ice Sheet extent increased in the late Pliocene. A higher occurrence of IRD and higher sedimentation rates in the GOA during the early Pleistocene, at 2.5 Ma, occur in synchrony with SSTs warming on the order of 1 ∘C relative to the Pliocene. All records show a high degree of variability in the early Pleistocene, indicating highly efficient ocean–climate–ice interactions through warm SST–ocean evaporation–orographic precipitation–ice growth mechanisms. A climatic shift towards ocean circulation in the subarctic Pacific similar to the pattern observed during negative Pacific Decadal Oscillation (PDO) conditions today occurs with the development of more extensive Cordilleran glaciation and may have played a role through increased moisture supply to the subarctic Pacific. The drop in atmospheric CO2 concentrations since 2.8 Ma is suggested as one of the main forcing mechanisms driving the Cordilleran glaciation.
Highlights
During the Neogene, the global climate transitioned from relatively warm to cooler conditions that enabled the development of ice masses in both hemispheres (Zachos et al, 2001)
To late Pliocene average sea surface temperature (SST) at Site U1417 were approximately 1.7 ◦C warmer than modern, while Pliocene and Pleistocene SSTs at Site U1417 are similar to the modern range observations (e.g. NOAA WOA13; Boyer et al, 2013; Fig. 2a)
The SST evolution from the Pliocene to the early Pleistocene in the subarctic northeast and eastern to mid-latitude North Pacific is very different from the North Atlantic, with a colder Pliocene than early Pleistocene
Summary
During the Neogene, the global climate transitioned from relatively warm to cooler conditions that enabled the development of ice masses in both hemispheres (Zachos et al, 2001). The Mid-Piacenzian Warm Period (MPWPl; 3.3–3.0 Ma) interrupts this cooling trend, with global temperatures around 2–3 ◦C above pre-industrial levels (Jansen et al, 2007; Haywood and Valdes, 2004) and more intense warming at higher latitudes (Haywood et al, 2013; Dolan et al, 2015). The later onset (oNHG) or intensification (iNHG) of the Northern Hemisphere glaciation is marked by the expansion of the Laurentide, Greenland, and Scandinavian ice sheets around 2.5 Ma, as indicated by ice-rafted debris (IRD) records from the North Atlantic Ocean (i.e. Shackleton et al, 1984) and the advance of the Cordilleran Ice Sheet at 2.7 Ma inferred from a terrestrial
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