title: North Pacific seasonality and the glaciation of North America 2.7 million years ago.
abstract: In the context of gradual Cenozoic cooling, the timing of the onset of significant Northern Hemisphere glaciation 2.7 million years ago is consistent with Milankovitch's orbital theory, which posited that ice sheets grow when polar summertime insolation and temperature are low. However, the role of moisture supply in the initiation of large Northern Hemisphere ice sheets has remained unclear. The subarctic Pacific Ocean represents a significant source of water vapour to boreal North America, but it has been largely overlooked in efforts to explain Northern Hemisphere glaciation. Here we present alkenone unsaturation ratios and diatom oxygen isotope ratios from a sediment core in the western subarctic Pacific Ocean, indicating that 2.7 million years ago late-summer sea surface temperatures in this ocean region rose in response to an increase in stratification. At the same time, winter sea surface temperatures cooled, winter floating ice became more abundant and global climate descended into glacial conditions. We suggest that the observed summer warming extended into the autumn, providing water vapour to northern North America, where it precipitated and accumulated as snow, and thus allowed the initiation of Northern Hemisphere glaciation.
authors.affiliation: Geoforschungszentrum Potsdam (GFZ), 14473 Potsdam, Germany. haug@gfz-potsdam.de
authors.forename: Gerald H
authors.initials: GH
authors.lastname: Haug
authors.forename: Andrey
authors.initials: A
authors.lastname: Ganopolski
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Sigman
authors.forename: Antoni
authors.initials: A
authors.lastname: Rosell-Mele
authors.forename: George E A
authors.initials: GE
authors.lastname: Swann
authors.forename: Ralf
authors.initials: R
authors.lastname: Tiedemann
authors.forename: Samuel L
authors.initials: SL
authors.lastname: Jaccard
authors.forename: Jörg
authors.initials: J
authors.lastname: Bollmann
authors.forename: Mark A
authors.initials: MA
authors.lastname: Maslin
authors.forename: Melanie J
authors.initials: MJ
authors.lastname: Leng
authors.forename: Geoffrey
authors.initials: G
authors.lastname: Eglinton
mesh_terms: D001110:Arctic Regions; D003081:Cold Climate; D017377:Diatoms / Q000737:chemistry / Q000378:metabolism; D019015:Geologic Sediments / Q000737:chemistry; D049690:History, Ancient; D046448:Ice Cover; D010100:Oxygen / Q000032:analysis; D010140:Pacific Ocean; D012621:Seasons; D012623:Seawater / Q000737:chemistry; D012914:Snow; D013696:Temperature; D013997:Time Factors
chemical_list: D010100:Oxygen