Paleo-reconstruction of the Jakobshavn Glacier during the late Holocene using ISSM and Paleo-data of Margin Migration

Abstract:

Recent observations of the Greenland Ice Sheet (GrIS) indicate that much of the recent mass loss is attributed to the speed up and retreat of outlet glaciers, especially near the western coast of Greenland. Because ice margin fluctuation (margin migration) plays a critical role in controlling variations in ice sheet volume, assimilation of margin migration into ice-sheet models is imperative to producing improved dynamic reconstructions of the GrIS, thus leading to less spread in future estimates of its contribution to future sea level change. To achieve this, the Ice Sheet System Model (ISSM) is used to simulate past margin migration by relying on robust paleoclimate archives using radiocarbon and cosmogenic ¹⁰ Be exposure dating of glacial features that are used as assimilation targets of past margin migration over Jakobshavn Isbrae during the Holocene. These records indicate large sensitivities in the ice margin to past climate change, providing a unique opportunity to constrain past unknowns such as basal friction and surface mass balance through data assimilation techniques. Building on existing capabilities in ISSM, we use adjoint inversions and automatic differentiation to present preliminary results of temporal inversions of basal friction and surface mass balance over Jakobshavn during the Holocene based upon ice margin reconstructions. Results from these experiments have implications for understanding the controls on past margin migration, while enhancing our understanding of basal and surface processes important for controlling modern day margin migration, which is a critical constraint for improving modern day spinups.