Impacts of Australian bushfires on New Zealand glacial environments

The size of Aotearoa’s glaciers is extremely sensitive to changes in temperature and precipitation, which has led to an alarming retreat over recent decades. Fresh snow and ice have high albedo – a measure of how much solar radiation is reflected from the surface of a material without being absorbed. However, when top layers of snow and ice become contaminated with impurities, the albedo is significantly reduced, leading to greater absorption of the Sun’s energy and increased ice melting. There are two important sources of impurities: wind-blown dust and airborne particles containing smoke and ash; and the growth of microbial populations, such as algae, on the surface of the ice and snow. Importantly, there appears to be a relationship between growth of these microbial communities and increased deposition of airborne particles.

Hunting for snow algae on the Price Range, Westland. Phot credit: Phil Novis, Manaaki Whenua-Landcare Research

The Australian bushfires in 2019-2020 produced substantial quantities of black carbon and airborne contaminants over Aotearoa, dramatically changing the colour of snowfields and glaciers in the Southern Alps. Glacial microbial communities also darken glacier surfaces. A combination of these factors could reduce albedo of glaciers in Aotearoa and increase melt rates. However, the magnitude of these effects, as well as the interaction between microbial growth and black carbon deposition, are not well known, and current models for glacier melting do not take them into account. Dr Novis and Dr Petherick will determine the effect of light-absorbing airborne contaminants from Australian bushfires and microbial communities on the melting of Aotearoa glacial systems – both individually and through their interactions. This study will provide the basis for future work on the effects of impurities on glacier melting.

Dr Lynda Petherick sampling a wetland core from Tasmania. Photo credit: Dr Patrick Moss