A novel method for sea ice reconstructions using satellite calibration of bromine enrichment records in Arctic ice cores

Paleo-records such as marine sediments and ice cores are commonly used to extend our knowledge about past sea-ice cover during the period prior to instrumental observations. Several studies (Spolaor et al., 2016, Saiz Lopez and Von Glasow, 2012) have identified bromine in ice cores as a potential proxy for past sea ice conditions. During polar springtime, in fact, the photochemical recycling of bromine is extremely efficient over first year sea ice (FYSI), resulting in enhanced concentrations of inorganic gas phase bromine (e.g. BrO) compared to the ocean surface, multi-year sea ice or snow-covered land. This process is known as “bromine explosion” and is detected by satellite sensors and in-situ observations from early March
to late May. After emission, the BrO plume is frequently carried for several days by high-latitude cyclones in the lower troposphere until it reaches land and falls in the form of bromine enriched snow compared to seawater Br/Na ratio.  Here, we present the first statistical validation of this proxy using satellite sea ice observations. By combining bromine enrichment (relative to seawater, Br_enr) records from three Greenlandic ice cores with satellite sea ice imagery over a span of three decades, we demonstrate its efficacy. During the satellite era (1984–2016), Brenr values in the ice cores show significant correlations with first-year sea ice formed in the Baffin Bay and Labrador Sea, confirming that gas-phase bromine enrichment processes, which predominantly occur over sea ice surfaces, are the primary drivers of the Brenr signal in ice cores. Furthermore, to evaluate Br_enr’s ability to capture historical sea ice variability, we compare 20th-century Arctic sea ice historical records and proxy data with reconstructions derived from an autoregressive–moving-average (ARMA) model. The results show overall strong agreement. While further improvements are needed—such as site-specific calibrations and detailed studies on bromine transport dynamics—this study introduces a novel quantitative method for reconstructing past seasonal sea ice variability using bromine enrichment in ice cores