Insights into the biological darkening of the Greenland Ice Sheet: from fundamental research to a monitoring programme

The ERC Synergy project, DEEP PURPLE, has provided since 2020 crucial information about biological, chemical, and physical processes associated with the ice surface melting of the Greenland ice sheet (GrIS), along with ground truth data of biological impurities on the ice. Biological darkening of the ice is fundamentally important because albedo serves as the primary determinant of the surface melt within the ice sheet under a specific climate. Over the period since the commencement of satellite observations in 1981, there has been a consistent decline in the Greenland ice albedo. DEEP PURPLE has demonstrated that biological growth on the ice is not limited by nutrients and it is very likely that biological darkening of the ice will continue inland on the GrIS as climate becomes warmer. As a result from DEEP PURPLE, the Danish Ministry for Climate, Energy and Utilities has financed PROMBIO since 2023, which is a programme for monitoring biological impurities on the GrIS. PROMBIO has successfully developed a methodology for collecting various impurities, including biological substances, from the surface ice and sampling was implemented across 13 weather stations. The resulting data is integrated into the PROMICE database, which is a well-established monitoring programme measuring the GrIS mass balance in near real-time. PROMBIO and DEEP PURPLE collaborates to enhance coverage of both biological and abiotic impurities, improving our understanding of the interplay between climatic factors and physical, chemical, and biological processes, contributing to more accurate climate models and predictions of future melt rates. The combined data from DEEP PURPLE and PROMBIO indicate that the duration of bare ice is a critical factor in the abundance of biological impurities, and different regions of the Greenland ice sheet exhibit varying primary mechanisms for darkening. These findings underscore the complexity of factors driving ice darkening and highlight the need for continued monitoring to inform climate models and policy decisions. The combined fundamental research and monitoring programme presented here will increase certainty on the predictions of the GrIS melt that can be used in the Intergovernmental Panel on Climate Change.