Nonlinear increase of Greenland Ice Sheet runoff into Disko Bay

Abstract. The Greenland Ice Sheet (GrIS) has experienced accelerated mass loss with record peaks in 2012 and 2019. Despite its role as an important tipping element in the climate system, the GrIS's response to recent warming is poorly understood. Here we use Ba/Ca ratios in coralline algae as a proxy for runoff into Disko Bay which is strongly influenced by the input of meltwater from glaciers connected to the GrIS, particularly from Jakobshavn Glacier – the fastest flowing marine-terminating glacier of the GrIS. The 115-year multispecimen master chronology confirms an unprecedented trend change in runoff beginning in the early 2000s. Statistical trend- and time of emergence analysis of the algal proxy record suggests that in 2007 western GrIS runoff has permanently emerged above the 20th century reference period, while temperature observations have not yet exceeded this threshold. This provides independent evidence for a non-linear accelerated response of the largest GrIS glacier, underscoring modelling results that a tipping point in glacial mass balance might soon be reached. Massive GrIS meltwater influx could intensify upper ocean stratification and contribute to global sea level rise.