ИСТИНА

We quantify, for the first time, the ice discharge contribution of every glacier in the Arctic (excluding the Greenland Ice Sheet) to the ocean, also known as frontal ablation. Frontal ablation occurs from the combination of ice flow into the ocean, and ice gain/loss from terminus advance/retreat. This is needed to quantify the relative importance of mass loss from surface mass balance (i.e. snowfall minus meltwater runoff) vs mass loss to the ocean to better constrain glacier contributions to sea level rise, map iceberg production patterns, and improve understanding of ice-ocean interactions. We calculate frontal ablation by combining glacier velocity, thickness, and terminus-position observations derived from satellites and airborne campaigns from 2000 to 2020. Ice velocity is derived from the NASA ITS_LIVE mission, which uses Landsat 5, 7, and 8 imagery to quantify ice motion. Images from the same satellites are used to quantify glacier terminus changes from 2000 to 2010 and from 2010 to 2020. Glacier thickness observations are derived from airborne campaigns including NASA’s Operation IceBridge, and, where thickness observations are not available, we use model outputs from Farinotti et al. (2019). These observations are combined along manually drawn flux gates in a custom python script to quantify frontal ablation for the 1444 marine-terminating glaciers in the Northern Hemisphere. Average pan-Arctic frontal ablation for 2000-2020 is -79 ± 30 Gt a-1, of which terminus retreat accounts for approximately one third. The regions with the most discharge in ascending order are Svalbard, Russia, Alaska, Greenland (excluding the ice sheet), Canada, and Iceland/Jan Mayen. We find that 110 glaciers ceased to be marine-terminating between 2000 and 2020. The 40 glaciers with the highest frontal ablation rate contribute ~50% of total pan-Arctic frontal ablation, while the 284 biggest contributing glaciers (20%) account for 90% of total Arctic frontal ablation.