Canadian Arctic sea ice reconstructed from bromine in the Greenland NEEM ice core.

Andrea Spolaor,Paul Vallelonga,Clara Turetta,Jacopo Gabrieli,Alfonso Saiz-Lopez,Niccolò Maffezzoli,Dorthe Dahl-Jensen,Kumiko Goto-Azuma,Carlos A Cuevas,Carlo Barbante,Giulio Cozzi

doi:10.1038/srep33925

Abstract

Reconstructing the past variability of Arctic sea ice provides an essential context for recent multi-year sea ice decline, although few quantitative reconstructions cover the Holocene period prior to the earliest historical records 1,200 years ago. Photochemical recycling of bromine is observed over first-year, or seasonal, sea ice in so-called “bromine explosions” and we employ a 1-D chemistry transport model to quantify processes of bromine enrichment over first-year sea ice and depositional transport over multi-year sea ice and land ice. We report bromine enrichment in the Northwest Greenland Eemian NEEM ice core since the end of the Eemian interglacial 120,000 years ago, finding the maximum extension of first-year sea ice occurred approximately 9,000 years ago during the Holocene climate optimum, when Greenland temperatures were 2 to 3 °C above present values. First-year sea ice extent was lowest during the glacial stadials suggesting complete coverage of the Arctic Ocean by multi-year sea ice. These findings demonstrate a clear relationship between temperature and first-year sea ice extent in the Arctic and suggest multi-year sea ice will continue to decline as polar amplification drives Arctic temperatures beyond the 2 °C global average warming target of the recent COP21 Paris climate agreement.

Highlights

A seasonal cycle in polar atmospheric bromine was first discovered in the 1980s by Sturges and Barrie[1] with higher bromine concentrations observed during Arctic spring
Snow deposited at NEEM originates primarily from the south-west with long-range aerosol transport associated with emission sources in northern North America and Asia[34,35]
Marine aerosols in northwest Greenland originate from the Canadian Arctic and Baffin Bay sectors[36] and as such are considered the dominant source locations of Br deposited at the NEEM site

Summary

Introduction

A seasonal cycle in polar atmospheric bromine was first discovered in the 1980s by Sturges and Barrie[1] with higher bromine concentrations observed during Arctic spring. Seasonal variability in bromine enrichment has been observed in surface snow samples from Antarctica (Law Dome17) and the Arctic (Northwest Greenland[17], Svalbard[18], Severnaya Zemlya[19]). Such enrichment beyond seawater compositions consistently occurs in spring/ summer and is consistent with photochemical recycling processes linked to FYSI. Ice core-based reconstructions of precipitation moisture sources, dust transport and sea salt proxies[31] indicate large-scale atmospheric and oceanic circulation changes occurring through the Bølling-Allerød and Younger Dryas glacial termination sequence and point to a key role for changes in North Atlantic Ocean surface conditions[32]

Methods

Results

Conclusion