Seasonality of halogen deposition in polar snow and ice

Abstract

Abstract. The atmospheric chemistry of iodine and bromine in Polar regions is of interest due to the key role of halogens in many atmospheric processes, particularly tropospheric ozone destruction. Bromine is emitted from the open ocean but is enriched above first-year sea ice during springtime bromine explosion events, whereas iodine emission is attributed to biological communities in the open ocean and hosted by sea ice. It has been previously demonstrated that bromine and iodine are present in Antarctic ice over glacialinterglacial cycles. Here we investigate seasonal variability of bromine and iodine in polar snow and ice, to evaluate their emission, transport and deposition in Antarctica and the Arctic and better understand potential links to sea ice. We find that bromine and iodine concentrations and Br enrichment (relative to sea salt content) in polar ice do vary seasonally in Arctic snow and Antarctic ice. Although seasonal variability in halogen emission sources is recorded by satellitebased observations of tropospheric halogen concentrations, seasonal patterns observed in snowpack are likely also influenced by photolysis-driven processes. Peaks of bromine concentration and Br enrichment in Arctic snow and Antarctic ice occur in spring and summer, when sunlight is present. A secondary bromine peak, observed at the end of summer, is attributed to bromine deposition at the end of the polar day. Iodine concentrations are largest in winter Antarctic ice strata, contrary to contemporary observations of summer maxima in iodine emissions. These findings support previous observations of iodine peaks in winter snow strata attributed to the absence of sunlight-driven photolytic re-mobilisation of iodine from surface snow. Further investigation is required to confirm these proposed mechanisms explaining observations of halogens in polar snow and ice, and to evaluate the extent to which halogens may be applied as sea ice proxies.

Evaluating the impact of blowing snow sea salt aerosol on springtime BrO and O<sub>3</sub> in the Arctic

“…A similar increase of Br − in snowfall samples after polar sunrise was reported at Alert by Toom-Sauntry & Barrie (2002). Furthermore, Spolaor et al (2013Spolaor et al ( , 2014 found a strong 455 seasonal variability of Br − in polar firn at both Arctic and Antarctic sites, with greater Br − values in spring/summer compared to winter.…”

Halogen-based reconstruction of Russian Arctic sea ice area from the Akademii Nauk ice core (Severnaya Zemlya)

“…Satellite measurements have documented a rapid decrease in recent Arctic summer sea ice area (Comiso, 2011;Stroeve et al, 2007). During the last 10 years, the four lowest September sea ice minima of the last 35 years have been recorded (Arctic Sea-Ice Monitor -IJIS, www.ijis.iarc.uaf.…”

Imprint of Arctic sea ice cover in North-Greenland ice cores

“…This is compatible with reported seasonality from ice core record (Maselli et al, 2017), with Satellite measurements (Begoin et al, 2010) and modelling studies (Yang et al, 2005), which show a Bromine and Bromine enrichment maximum during the summer months despite the decrease in atmospheric BrO flux observed over summer induced by the reduction of 375 young sea ice and ice salinity due to melting (Maselli et al, 2017). The discrepancy is probably a result of the lag between bromine-containing particles becoming airborne and thus allowing bromine to become enriched above the seawater ratio compared to Na + , and the final deposition (Spolaor et al, 2014).…”

“…It is interesting to notice that the area immediately around Greenland with higher concentration of BrO in the atmospheric column reported by GOME-2 BrO (Spolaor et al, 2014) is indeed the eastern coastal side of Greenland between 75 and 79 ° 420 N, making B17 an ideal site to capture the regional variability of local sea ice extent.…”