Abstract
Abstract. Although it has been demonstrated that the speed and magnitude of the recent Arctic sea ice decline is unprecedented for the past 1450 years, few records are available to provide a paleoclimate context for Arctic sea ice extent. Bromine enrichment in ice cores has been suggested to indicate the extent of newly formed sea ice areas. Despite the similarities among sea ice indicators and ice core bromine enrichment records, uncertainties still exist regarding the quantitative linkages between bromine reactive chemistry and the first-year sea ice surfaces. Here we present a 120 000-year record of bromine enrichment from the RECAP (REnland ice CAP) ice core, coastal east Greenland, and interpret it as a record of first-year sea ice. We compare it to existing sea ice records from marine cores and tentatively reconstruct past sea ice conditions in the North Atlantic as far north as the Fram Strait (50–85∘ N). Our interpretation implies that during the last deglaciation, the transition from multi-year to first-year sea ice started at ∼17.5 ka, synchronously with sea ice reductions observed in the eastern Nordic Seas and with the increase in North Atlantic ocean temperature. First-year sea ice reached its maximum at 12.4–11.8 ka during the Younger Dryas, after which open-water conditions started to dominate, consistent with sea ice records from the eastern Nordic Seas and the North Icelandic shelf. Our results show that over the last 120 000 years, multi-year sea ice extent was greatest during Marine Isotope Stage (MIS) 2 and possibly during MIS 4, with more extended first-year sea ice during MIS 3 and MIS 5. Sea ice extent during the Holocene (MIS 1) has been less than at any time in the last 120 000 years.
Highlights
IntroductionThe connection between Arctic sea ice and bromine was first identified through an anticorrelation between springtime ground level ozone (O3) and filterable bromine air concentrations (Barrie et al, 1988)
bromine enrichment (Brenr) as a potential indicator of past sea ice conditionsThe connection between Arctic sea ice and bromine was first identified through an anticorrelation between springtime ground level ozone (O3) and filterable bromine air concentrations (Barrie et al, 1988)
At Renland, such a consistent correlation is not present, and Brenr is at times lower during warmer climate periods. We suggest that this difference originates from the fact that during warm periods, the relative FYSI-to-OW influence is greater at NEEM than at Renland, the latter being mostly dominated by OW conditions in the North Atlantic
Summary
The connection between Arctic sea ice and bromine was first identified through an anticorrelation between springtime ground level ozone (O3) and filterable bromine air concentrations (Barrie et al, 1988). Large bromine oxide (BrO) column enhancements and simultaneous tropospheric ozone depletion were later found in Antarctica (Kreher et al, 1997). Satellite observations reveal geographically widespread “bromine explosions”, i.e. the sudden increase in atmospheric bromine concentrations during springtime occurring in both polar regions (Chance, 1998; Richter et al, 1998; Wagner and Platt, 1998). The mechanism proceeds via springtime photochemical heterogeneous reactions that lead to the activation of bromide, followed by the release and exponential increase in gas-phase bromine species in the polar troposphere (Vogt et al, 1996).
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