Abstract
Warming of high northern latitudes in the Pliocene (5.33–2.58 Myr ago) has been linked to the closure of the Central American Seaway and intensification of North Atlantic Deep Water. Subsequent cooling in the late Pliocene may be related to the effects of freshwater input from the Arctic Ocean via the Bering Strait, disrupting North Atlantic Deep Water formation and enhancing sea ice formation. However, the timing of Arctic freshening has not been defined. Here we present neodymium and lead isotope records of detrital sediment from the Bering Sea for the past 4.3 million years. Isotopic data suggest the presence of Alaskan glaciers as far back as 4.2 Myr ago, while diatom and C37:4 alkenone records show a long-term trend towards colder and fresher water in the Bering Sea beginning with the M2 glaciation (3.3 Myr ago). We argue that the introduction of low-salinity Bering Sea water to the Arctic Ocean by 3.3 Myr ago preconditioned the climate system for global cooling.
Highlights
Warming of high northern latitudes in the Pliocene (5.33–2.58 million years ago (Myr ago)) has been linked to the closure of the Central American Seaway and intensification of North Atlantic Deep Water
At IODP (Integrated Ocean Drilling Program) Site U1341B (Expedition 323) located at Bowers Ridge in the southern Bering Sea (Fig. 1; Methods; Supplementary Fig. 1; refs 27,28), all three of these surface-water proxies record gradual increases beginning around the time of MIS M2 glaciation at 3.3 Myr ago and continuing to 2.75–2.5 Myr ago (Fig. 2d–f), indicating cooling and/or freshening and increased meltwaterrelated stratification
Previous research on Gulf of Alaska sediments shows the presence of tidewater glaciers in southeastern Alaska since the Late Miocene, with more definitive evidence for glaciers based on the presence of dropstones beginning at 4.2–4.3 Myr ago[49]
Summary
Warming of high northern latitudes in the Pliocene (5.33–2.58 Myr ago) has been linked to the closure of the Central American Seaway and intensification of North Atlantic Deep Water. Subsequent cooling in the late Pliocene may be related to the effects of freshwater input from the Arctic Ocean via the Bering Strait, disrupting North Atlantic Deep Water formation and enhancing sea ice formation. Tectonic shoaling of the CAS may have reached a critical threshold between B4.7 and 4.2 Myr ago[6,7,8,9] that restricted Pacific–Caribbean surface-water exchange and redirected warm, saline waters from the equatorial Atlantic to the North Atlantic These changes in the ocean circulation system are believed to contribute to an initial intensification of the Atlantic Meridional Overturning Circulation (AMOC) and warming of the North Atlantic prior to 3.6 Myr ago[9,10,11,12]. The proposed source for this freshwater is the enhanced flow of Siberian rivers, driven by increased moisture transport to Eurasia by the AMOC7 Another possible source is low-salinity Bering Sea water[6,13,14,15]. We generate Pliocene records of sediment provenance and surface-water properties in the Bering Sea to demonstrate the timing of cryospheric evolution in the Bering/ Alaskan region and clarify the relationship between flow of lowsalinity Bering Sea water to the AO and the late-Pliocene global cooling
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