GRL paper on Upernavik Isstrøm
Abstract
Tidewater glacier velocity and mass balance are known to be highly responsive to terminus position change. Yet it remains challenging for ice flow models to reproduce observed ice margin changes. Here, using the Ice Sheet Sys- tem Model (ISSM; Larour et al., 2012), we simulate the ice velocity and thickness changes of Upernavik Isstrøm (north-western Greenland) by prescribing a collection of 27 observed terminus positions spanning 164 years (1849– 2012). The simulation shows increased ice velocity during the 1930s, the late 1970s and between 1995 and 2012 when terminus retreat was observed along with negative surface mass balance anomalies. Three distinct mass balance states are evident in the reconstruction: (1849–1932) with near zero mass balance, (1932–1992) with ice mass loss dominated by ice dynamical flow, and (1998–2012), when increased retreat and negative surface mass balance anomalies led to mass loss that was twice that of any earlier period. Over the multi-decadal simulation, mass loss was dominated by thin- ning and acceleration responsible for 70 % of the total mass loss induced by prescribed change in terminus position. The remaining 30 % of the total ice mass loss resulted directly from prescribed terminus retreat and decreasing surface mass balance. Although the method can not explain the cause of glacier retreat, it enables the reconstruction of ice flow and geometry during 1849–2012. Given annual or seasonal ob-
served terminus front positions, this method could be a use- ful tool for evaluating simulations investigating the effect of calving laws.

Reference
K. Haubner, J.E. Box, N.J. Schlegel, E.Y. Larour, M. Morlighem, A.M. Solgaard, K.K. Kjeldsen, S.H. Larsen, E. Rignot, T.K. Dupont, and K.H. Kjær, K. H., Simulating ice thickness and velocity evolution of Upernavik Isstrøm 1849–2012 by forcing prescribed terminus positions in ISSM, The Cryosphere, 12, 1511-1522, https://doi.org/10.5194/tc-12-1511-2018.

Upernavik Isstrøm’s observed margin front positions
Upernavik Isstrøm’s observed margin front positions between 1849 and 2012 (lines) and trimline positions (yellow dots; Kjeldsen et al., 2015). The background image is from Landsat 8 (September 2013). Inset is the location and shape of the Upernavik catchment (red area), determined by 2008/09 surface velocity from Rignot and Mouginot (2012), which define the model domain.