Impact of warm and moist intrusions on black carbon deposition and summer snow melt in the central Arctic

Warm and moist intrusions (WAMIs) into the central Arctic, predominantly observed in winter and early spring, are becoming more frequent, significantly affecting the region’s near-surface energy budget. This study focuses on the deposition pulses of black carbon (BC) triggered by WAMIs and their subsequent impact on snow properties and melting during the summer, using a modeling approach and comprehensive datasets from the 2019–2020 Multidisciplinary drifting Observatory for the Study of the Arctic Climate (MOSAiC) expedition. Our findings reveal that WAMIs induce episodes of intense BC wet deposition in the central Arctic shoulder season (Nov–Apr) due to transported pollution and moisture. We demonstrate that WAMIs result in exceptionally high BC deposition (> 4 orders of magnitude compared to typical winter/spring conditions) across an area of nearly 1 million km2, approximately 20% of the central Arctic Ocean. Furthermore, we establish a direct connection between these winter/spring BC deposition pulses and subsequent summer increases in absorbed solar energy (> 4 W/m2) and snowpack melt rate (+15%). Despite their sporadic occurrence (only 8% of the time), WAMIs play a significant role in the central Arctic surface energy budget through the BC snow albedo effect.