Present day Jakobshavn Isbræ (West Greenland) close to the Holocene minimum extent

Geometric Controls of Tidewater Glacier Dynamics

“…To test our idealized results in a real-world setting, we instead turn to model simulations from Jakobshavns Isbrae's (JI) evolution in the Holocene (Kajanto et al, 2020). We focus on a simulation of the retreat of JI from a sill at the fjord mouth of Jakobshavn Isfjord, to a point inland of today's GL position.…”

“…We focus on a simulation of the retreat of JI from a sill at the fjord mouth of Jakobshavn Isfjord, to a point inland of today's GL position. This model retreat is forced using a step reduction in the equilibrium line altitude early in the Holocene (experiment SE_CM in Kajanto et al (2020)). While this is a sensitivity experiment not meant to reflect the actual evolution of JI (Kajanto et al, 2020), it is convenient for our purposes since it produces a long-lasting, dynamic retreat.…”

“…In particular, this concerns the friction coefficient, which we assume spatially uniform to isolate the signal of the dynamic component of ice loss, regardless of where the glacier is situated in the fjord. Given that water availability is typically higher at the bed compared to at the fjord et al, 2018a;Kajanto et al, 2020) for instance, may reduce the potential of basal perturbations to stabilize the glacier relative to lateral perturbations. This may be one reason why Q GL /S values for lateral perturbations were found to be higher than the ones for basal perturbations, and why no glacier could be enforced to retreat over bumps.…”

“…Rates of ice discharge from the Greenland Ice Sheet are likely to exceed their Holocene (last 12,000 yrs) maxima this century (Briner et al, 2020;Kajanto et al, 2020), and parts of Antarctica are on the brink of irreversible mass loss (Garbe et al, 2020). Consequently, major natural and societal challenges related to changes in the terrestrial cryosphere of the high latitudes lay ahead.…”

“…The real-world example Jakobshavn Isbrae. a) Topography of Jakobshavn Isfjord with approximate present-day glacier front, and centerline along which profiles shown in b) of the wetted area S and its along-fjord change dS are calculated; c) zoom to area where JI is enclosed between fjord walls, with yellow circles showing all modeled grounding line positions in this section(Kajanto et al, 2020); d) dS profile in the same section of the fjord with grounding line positions indicated; e) QGL/S in this section with grounding line positions and a polynomial fit (blue dotted line). The opposing trends in dS (d) and QGL/S (e) as indicated by the arrows demonstrate qualitatively that the negative relationship QGL/S over dS can be found in this complex setting.…”