Evidence for ephemeral middle Eocene to early Oligocene Greenland glacial ice and pan-Arctic sea ice

Aradhna Tripati,Dennis Darby

doi:10.1038/s41467-018-03180-5

Abstract

Earth’s modern climate is defined by the presence of ice at both poles, but that ice is now disappearing. Therefore understanding the origin and causes of polar ice stability is more critical than ever. Here we provide novel geochemical data that constrain past dynamics of glacial ice on Greenland and Arctic sea ice. Based on accurate source determinations of individual ice-rafted Fe-oxide grains, we find evidence for episodic glaciation of distinct source regions on Greenland as far-ranging as ~68°N and ~80°N synchronous with ice-rafting from circum-Arctic sources, beginning in the middle Eocene. Glacial intervals broadly coincide with reduced CO2, with a potential threshold for glacial ice stability near ~500 p.p.m.v. The middle Eocene represents the Cenozoic onset of a dynamic cryosphere, with ice in both hemispheres during transient glacials and substantial regional climate heterogeneity. A more stable cryosphere developed at the Eocene-Oligocene transition, and is now threatened by anthropogenic emissions.

Highlights

Earth’s modern climate is defined by the presence of ice at both poles, but that ice is disappearing
For decades geoscientists have suggested that activity of the cryosphere during the Cenozoic was initiated with the growth of an Antarctic ice sheet ~34 million years ago (Ma), while glacial ice in the Northern Hemisphere formed ~14–6 Ma1,2,4,6,14,18–20,27–32
We examined 2029 detrital anhydrous Fe oxide grains from the sand fraction of middle Eocene to early Oligocene sediments recovered at Ocean Drilling Program (ODP) Site 913 (Fig. 1), located 360 km east of Greenland

Summary

Introduction

Earth’s modern climate is defined by the presence of ice at both poles, but that ice is disappearing. The middle Eocene timing of the initiation of ephemeral Cenozoic bipolar glaciations inferred from Pacific δ18O records has been supported by more direct evidence, such as the discovery in the Arctic of sea-ice associated diatoms[15,17] and iceberg-rafted sediment[8,12,13,15,16] Another piece of evidence has been the study of surface textures of quartz grains recovered from the central Arctic Ocean[13,15,16], which include dissolution and conchoidal fractures, as both are consistent with transport by sea ice and/or glacial ice. The timing of Arctic IRD and sea ice development was shown to be broadly consistent with a major decline in atmospheric CO213 inferred from one proxy reconstruction derived from boron isotope-based estimates of seawater pH42

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Conclusion