Past and future response of Greenland's tidewater glaciers to submarine melting

Abstract

The effect of the North Atlantic Ocean on the Greenland Ice Sheet through submarine melting of Greenland's tidewater glacier calving fronts is thought to be a key driver of widespread glacier retreat, dynamic mass loss and sea level contribution from the ice sheet. Despite its critical importance, problems of process complexity and scale hinder efforts to represent the influence of submarine melting in ice sheet-scale models. Here we propose parameterizing tidewater glacier terminus position as a simple linear function of submarine melting, with submarine melting in turn estimated as a function 5 of subglacial runoff and ocean temperature. The relationship is tested, calibrated and validated using datasets of terminus position, runoff and ocean temperature covering the full ice sheet and surrounding ocean from the period 1960-present. We demonstrate a statistically significant link between multi-decadal tidewater glacier terminus position and submarine melting and show that the proposed parameterisation has predictive power when considering a population of glaciers. An illustrative 21st century projection is considered suggesting that tidewater glaciers in Greenland will undergo little further retreat in a low 10 emissions RCP2.6 scenario. In contrast, a high emissions RCP8.5 scenario results in a median retreat of ∼6 km, with 35% of glaciers experiencing retreat exceeding 10 km. Our study provides a long-term and ice sheet-wide assessment of the sensitivity of tidewater glaciers to submarine melting and proposes a practical and empirically validated means of incorporating ocean forcing into models of the Greenland ice sheet.

Dynamic response of the Greenland ice sheet to recent cooling

“…Furthermore, while the results presented here relate specifically to land-terminating margins, it has been argued that the dynamics of tidewater glaciers are a product of both oceanic and atmospheric forcing 77,78 , with the latter potentially driving a positive feedback as a result of its influence upon fjord water circulation and thus submarine melt 77,79,80 . This positive feedback contrasts with our findings at land-terminating margins, indicating that at an ice-sheet scale, the relationship between hydrology and ice dynamics is complex and spatially variable.…”

21st century ocean forcing of the Greenland Ice Sheet for modeling of sea level contribution

“…This latter parameterisation is slightly simpler than that for submarine melting, but is functionally very similar. We note the slight inconsistency of using annual runoff for the submarine melt implementation and summer runoff for the retreat implementation, but we emphasize that this makes no practical difference since annual and summer runoff are very closely related, even in the future projections when the summer becomes longer (Slater et al, 2019).…”

“…estimated as a linear function of parameterised submarine melting (Slater et al, 2019) and is imposed on an ice sheet model through a time-variable ice mask, an approach first suggested by Cowton et al (2018). The submarine melt implementation provides ice sheet modeling groups with more freedom by providing fields of subglacial runoff and ocean properties together with a suggested parameterisation for estimating submarine melt from these quantities.…”

“…where h is grounding line depth (m), q is the annual mean subglacial runoff normalized by calving front area (m d −1 ) and TF is the ocean thermal forcing defined further below. For the retreat implementation we use a slightly different parameterisation (Slater et al, 2019) in which retreat (dL) is expressed as…”

“…where κ is a constant that has been calibrated in Slater et al (2019) and Q is the mean June-July-August subglacial runoff. This latter parameterisation is slightly simpler than that for submarine melting, but is functionally very similar.…”