Future Evolution of Greenland's Marine‐Terminating Outlet Glaciers

Abstract

Mass loss from the Greenland ice sheet (GrIS) has increased over the last two decades in response to changes in global climate, motivating the scientific community to question how the GrIS will contribute to sea‐level rise on timescales that are relevant to coastal communities. Observations also indicate that the impact of a melting GrIS extends beyond sea‐level rise, including changes to ocean properties and circulation, nutrient and sediment cycling, and ecosystem function. Unfortunately, despite the rapid growth of interest in GrIS mass loss and its impacts, we still lack the ability to confidently predict the rate of future mass loss and the full impacts of this mass loss on the globe. Uncertainty in GrIS mass loss projections in part stems from the nonlinear response of the ice sheet to climate forcing, with many processes at play that influence how mass is lost. This is particularly true for outlet glaciers in Greenland that terminate in the ocean because their flow is strongly controlled by multiple processes that alter their boundary conditions at the ice‐atmosphere, ice‐ocean, and ice‐bed interfaces. Many of these processes change on a range of overlapping timescales and are challenging to observe, making them difficult to understand and thus missing in prognostic ice sheet/climate models. For example, recent (beginning in the late 1990s) mass loss via outlet glaciers has been attributed primarily to changing ice‐ocean interactions, driven by both oceanic and atmospheric warming, but the exact mechanisms controlling the onset of glacier retreat and the processes that regulate the amount of retreat remain uncertain. Here we review the progress in understanding GrIS outlet glacier sensitivity to climate change, how mass loss has changed over time, and how our understanding has evolved as observational capacity expanded. Although many processes are far better understood than they were even a decade ago, fundamental gaps in our understanding of certain processes remain. These gaps impede our ability to understand past changes in dynamics and to make more accurate mass loss projections under future climate change. As such, there is a pressing need for (1) improved, long‐term observations at the ice‐ocean and ice‐bed boundaries, (2) more observationally constrained numerical ice flow models that are coupled to atmosphere and ocean models, and (3) continued development of a collaborative and interdisciplinary scientific community.

Meltwater‐Enhanced Nutrient Export From Greenland's Glacial Fjords: A Sensitivity Analysis

“…To understand potential impacts of increased melting and discharge on coastal ecosystems, we need to understand the time scales of change at Greenland's calving fronts (e.g., Catania et al, 2020). Many of Greenland's tidewater glaciers rest on prograde slopes (the bed shallowing inland, Millan et al, 2018), such as Mogens Heinesen in SE Greenland and Savissuaq Glacier in NW Greenland (Morlighem et al, 2017).…”

Greenland liquid water runoff from 1979 through 2017

“…Over the past decades, liquid runoff from Greenland has increased (Mernild and Liston, 2012;Bamber et al, 2018;Trusel et al, 2018;Perner et al, 2019). When that runoff leaves the ice sheet and enters fjords and coastal seas, it influences a wide range of physical (Straneo et al, 2011;An et al, 2012;Mortensen et al, 2013;Bendtsen et al, 2015;Cowton et al, 2015;Mankoff et al, 2016;Fried et al, 2019;Cowton et al, 2019;Beckmann et al, 2019), chemical (Kanna et al, 2018;Balmonte et al, 2019), and biological (Kamenos et al, 2012;Kanna et al, 2018;Balmonte et al, 2019) systems (Catania et al, 2019). The scale of impacts ranges from the ice-ocean boundary to the distal open ocean (Gillard et al, 2016).…”

“…The scale of impacts ranges from the ice-ocean boundary to the distal open ocean (Gillard et al, 2016). The influence of freshwater on multiple domains and disciplines (Catania et al, 2019) is the reason several past studies have estimated runoff at various 15 km resolution) and the Regional Atmospheric Climate Model (RACMO; Noël et al (2019), 5.5 km resolution) and runoff, R, is defined by…”

Automated Terminus Detection for Greenland's Peripheral Marine-Terminating Glaciers

“…This strategy could be expanded by calculating terminus positions along additional flowlines. In contrast, the box method (Walsh et al, 2012;Moon and Joughin, 2008;McNabb and Hock, 2014;Catania et al, 2020) evaluates terminus change in terms of a single area change value. shows the median misfits between the automated and manual delineations by image condition for both the 10% (52 out of the 512 − see section 2.5.2) of manual delineations excluded from the optimization algorithm development and the full manual dataset.…”

“…The marine-terminating glaciers in southeast Greenland, particularly, have been observed to undergo rapid retreat in response to oceanic forcing (Seale et al, 2011;Howat et al, 2008;Howat and Eddy, 2011;Walsh et al, 2012;Sole et al, 2011). From 2001-2005, Seale et al (2011 observed synchronous retreat in marine-terminating glaciers south of 69 and potentially vary between glaciers, subsurface ocean warming increases terminus undercutting caused by submarine melting and reduces resistance to ice flow provided by sea ice and icebergs adjacent to the terminus, resulting in increased rates of ice discharge at glacier calving fronts (Benn et al, 2007;Straneo et al, 2012;Catania et al, 2020). Surface melting also contributes to undercutting when it is routed underneath the glacier (as subglacial discharge) and discharged at the glacier's grounding line (Fried et al, 2018;Slater et al, 2018).…”