A Reassessment of the Role of Atmospheric and Oceanic Forcing on Ice Dynamics at Jakobshavn Isbræ (Sermeq Kujalleq), Ilulissat Icefjord

Abstract

Jakobshavn Isbræ (Sermeq Kujalleq) has been the largest single contributor to mass loss from the Greenland Ice Sheet over the past three decades. Previous research emphasizes the dominant role of oceanic forcing, with the recent advance, deceleration and thickening of Jakobshavn attributed to reduced ocean temperatures. Here, we use satellite imagery and remotely sensed data sets of ice surface velocity, ice surface elevation and ice discharge to extend observations of ice dynamics at Jakobshavn Isbræ between 2018 and 2023. We then use in situ oceanic and meteorological data, in combination with modeled estimates of surface runoff, to explore the potential role of climatic forcing over this 5-year period. Our results show that Jakobshavn began to re-accelerate in 2018, with mean annual near-terminus velocity increasing by 49% between 2018 and 2021. The onset of re-acceleration occurred prior to the arrival of warmer water, and was likely facilitated by the near-terminus being close to flotation and thus highly sensitive to reductions in effective pressure. Such reductions likely resulted from ice surface lowering, driven by both negative surface mass balance and dynamic thinning. During winter 2020/2021, ice velocities remained elevated, with sustained thinning and iceberg calving observed. This unusual behavior corresponded with a significant decrease in rigid mélange extent, likely driven by increased ocean temperatures observed in Disko Bay and Ilulissat Icefjord. This study thus further emphasizes the complexity of climatic forcing at the ice-ocean interface, highlighting that both oceanic and atmospheric forcing must be considered when projecting the future behavior of marine-terminating outlet glaciers.