Modelling the fate of Hollow Glass Microspheres deployed for Arctic sea ice albedo modification.

Loss of sea ice is both a response to climate change and a driver of further warming, due to the lower albedo of open water. Covering strategic areas of Arctic sea ice with a thin layer of Hollow Glass Microspheres (HGMs) has been proposed as an intervention to slow, or even reverse, loss of ice. Toxicological studies have identified effect limits for HGMs in both pelagic and benthic species. The current study provides context for those toxicological studies, by estimating environmental concentrations if HGMs are deployed as suggested. Two different models were used, a vertical-dimension water-column model and a three-dimensional transport model. With the water-column model, we assume an initial surface concentration of 70 g/m2 of HGMs, and horizontally homogeneous conditions over large areas. HGMs were found to distribute throughout the surface mixed layer with concentrations from around 5 mg/L at the surface, to below 1 mg/L at 25 m depth. In the three-dimensional model, we considered HGMs applied to an ice floe of area 20 km2, to correspond to a field trial in the Arctic. Near the initial location, average concentrations in the top 20 m of the water column were around 0.5 mg/L after 5 days. In both cases considered, concentrations of HGMs in the surface mixed layer are such that adverse effects on copepods are likely. Given that the melting season in the Arctic also coincides with a period of high biological activity, it is possible that application of HGMs could have detrimental effects on the Arctic ecosystem.