Alaskan marine transgressions record out-of-phase Arctic Ocean glaciation during the last interglacial

Louise Farquharson,Daniel Mann,Guido Grosse,Tammy Rittenour,Benjamin Jones,Pamela Groves

doi:10.1130/g40345.1

Abstract

Ongoing climate change focuses attention on the Arctic cryosphere’s responses to past and future climate states. Although it is now recognized the Arctic Ocean Basin was covered by ice sheets and their associated ﬂoating ice shelves several times during the Late Pleistocene, the timing and extent of these polar ice sheets remain uncertain. Here we relate a relict barrier-island system on the Beaufort Sea coast of northern Alaska to the isostatic effects of a previously unrecognized ice shelf grounded on the adjacent continental shelf. A new suite of optically stimulated luminescence dates show that this barrier system formed during one or more marine transgressions occurring late in Marine Isotope Stage 5 (MIS 5) between 113 ka and 71 ka. Because these transgressions occurred after the warmest part of the last interglacial (ca. 123 ka) and did not coincide with the global eustatic sea-level maximum during MIS 5e, this indicates Arctic ice sheets developed out-of-phase with lower-latitude sectors of the Laurentide and Fennoscandian ice sheets. We speculate that Arctic ice sheets began development during full interglacial conditions when abundant moisture penetrated to high latitudes, and low summer insolation favored glacier growth. These ice sheets reached their full extents at interglacial-glacial transitions, then wasted away at the heights of mid-latitude glaciations because of moisture limitations.

Highlights

Changes in glacier extent and relative sea level (RSL) along the Beaufort Sea coast of Alaska during Marine Isotope Stage (MIS) 5 at ca. 130–71 ka (Lisiecki and Raymo, 2005; Shakun et al, 2015) provide insights into how the Arctic cryosphere responded to climate states different from those of the present
What could have caused marine transgressions reaching 10 m above present sea level thousands of years after the MIS 5e peak in eustatic sea level? Tectonism can be excluded, given the long-term stability of this trailing continental margin (Grantz et al, 1994; Shephard et al, 2013). Both involving glacial isostatic adjustment: (1) collapse of a glacial forebulge generated by the Laurentide Ice Sheet (Fig. 3A), and (2) localized isostatic depression under the grounded margin of an ice shelf in the Beaufort Sea (Fig. 3B)
The Optically stimulated luminescence (OSL)-constrained sedimentological and geomorphological evidence presented here indicates that marine transgressions occurred along Alaska’s Beaufort Sea coastline after the peak warmth and eustatic transgression of the last interglacial

Summary

Introduction

Changes in glacier extent and relative sea level (RSL) along the Beaufort Sea coast of Alaska during Marine Isotope Stage (MIS) 5 at ca. 130–71 ka (Lisiecki and Raymo, 2005; Shakun et al, 2015) provide insights into how the Arctic cryosphere responded to climate states different from those of the present. Changes in glacier extent and relative sea level (RSL) along the Beaufort Sea coast of Alaska during Marine Isotope Stage (MIS) 5 at ca. Peak global interglacial conditions occurred during MIS substage 5e Two other periods of low global ice volume occurred during MIS substages 5a and 5c between ca. We hypothesize that raised marine deposits along the Arctic coast of Alaska provide insights into the timing and extent of Arctic Ocean Basin (AOB) glaciation during this period, when Milankovitch radiative forcing was intermediate between full-glacial and full-interglacial conditions and prompted unique responses in high-latitude glaciers (Svendsen, 2004). Surficial deposits on the Arctic Coastal Plain of northern Alaska (Fig. 1) provide an archive of marine, alluvial, glacial, and aeolian deposits that span much of the Cenozoic (Dinter et al, 1990). One of the most striking geomorphic features on this coastal plain is a relict barrier-island system

Results

Discussion

Conclusion