New Zealand Southern Alps Blanketed by Red Australian Dust During 2019/2020 Severe Bushfire and Dust Event

Episodic deposition of light absorbing impurities on glaciers reduces albedo and exacerbates snow melt. In 2019/2020 a devastating Australian bushfire and desert dust event combined with favorable meteorological conditions transported an unprecedented mass of impurities across the Tasman Sea turning the Southern Alps of Aotearoa New Zealand red. Here we use time lapse cameras, airmass back trajectories, snow impurity geochemistry, and remote sensing to quantify the timing, provenance, and mass deposition of the event. Deposited in late November 2019, the impurities were dominated by mineral dust with a distinct southeastern Australian geochemical fingerprint. The event deposited ∼4,500 ± 500 tons of red dust to Southern Alps permanent snow and ice with a mean dust mass concentration of 6.5 ± 0.7 g m−2. A southeast Australian desert dust storm generated by the same type of meteorological conditions as the 2020 New Year bushfires was the main driver of the glacier discoloration. Plain Language Summary In 2019/2020, snow on the Southern Alps of Aotearoa New Zealand changed color from white to red overnight. While New Zealand air quality dropped following the severe 2020 New Year Australian bushfire event, the glacier discoloration was caused by a desert dust storm and weather conditions that transported an extraordinary amount of red dust from southeastern Australia across the Tasman Sea in late November 2019. Understanding the source and amount of dust deposited to the Southern Alps is required to assess the impact on glacial melt and snow biology. Key Points Dust deposition to Southern Alps occurred in late November 2019 from Australian bushfire and desert dust storm event Dust geochemical fingerprint and airmass back trajectories pinpoint a southeastern Australian provenance Approximately 4,500 tons of red dust are estimated to have been deposited to the Southern Alps