An official website of the United States government
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 of subglacial discharge and ocean temperature. The relationship is tested, calibrated and validated using datasets of terminus position, subglacial discharge and ocean temperature covering the full ice sheet and surrounding ocean from the period 1960–2018. We demonstrate a statistically significant link between multi-decadal tidewater glacier terminus position change and submarine melting and show that the proposed parameterization 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-emission RCP2.6 scenario. In contrast, a high-emission RCP8.5 scenario results in a median retreat of 4.2 km, with a quarter of tidewater 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.
more »
« less
Calving as a Source of Acute and Persistent Kinetic Energy to Enhance Submarine Melting of Tidewater Glaciers
Abstract Calving icebergs at tidewater glaciers release large amounts of potential energy. This energy—in principle—could be a source for submarine melting, which scales with near‐terminus water temperature and velocity. Because near‐terminus currents are challenging to observe or predict, submarine melt remains a key uncertainty in projecting tidewater glacier retreat and sea level rise. Here, we study one submarine calving event at Xeitl Sít’ (LeConte Glacier), Alaska, to explore the effect of calving on ice melt, using a suite of autonomously deployed instruments beneath, around, and downstream of the calving iceberg. Our measurements captured flows exceeding 5 m/s and demonstrate how potential energy converts to kinetic energy . While most energy decays quickly (through turbulence, mixing, and radiated waves), near‐terminus remains elevated, nearly doubling predicted melt rates for hours after the event. Calving‐induced currents could thus be an important overlooked energy source for submarine melt and glacier retreat.
more »
« less
- PAR ID:
- 10647877
- Publisher / Repository:
- American Geophysical Union
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 52
- Issue:
- 19
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract. The frontal flux balance of a medium-sized tidewater glacier in westernGreenland in the summer is assessed by quantifying the individual components(ice flux, retreat, calving, and submarine melting) through a combination ofdata and models. Ice flux and retreat are obtained from satellite data.Submarine melting is derived using a high-resolution ocean model informed bynear-ice observations, and calving is estimated using a record of calvingevents along the ice front. All terms exhibit large spatial variability alongthe ∼5 km wide ice front. It is found that submarine melting accountsfor much of the frontal ablation in small regions where two subglacialdischarge plumes emerge at the ice front. Away from the subglacial plumes,the estimated melting accounts for a small fraction of frontal ablation.Glacier-wide, these estimates suggest that mass loss is largely controlled bycalving. This result, however, is at odds with the limited presence oficebergs at this calving front – suggesting that melt rates in regionsoutside of the subglacial plumes may be underestimated. Finally, we arguethat localized melt incisions into the glacier front can be significantdrivers of calving. Our results suggest a complex interplay of melting andcalving marked by high spatial variability along the glacier front.more » « less
-
Abstract Frontal ablation, the combination of submarine melting and iceberg calving, changes the geometry of a glacier's terminus, influencing glacier dynamics, the fate of upwelling plumes and the distribution of submarine meltwater input into the ocean. Directly observing frontal ablation and terminus morphology below the waterline is difficult, however, limiting our understanding of these coupled ice–ocean processes. To investigate the evolution of a tidewater glacier's submarine terminus, we combine 3-D multibeam point clouds of the subsurface ice face at LeConte Glacier, Alaska, with concurrent observations of environmental conditions during three field campaigns between 2016 and 2018. We observe terminus morphology that was predominately overcut (52% in August 2016, 63% in May 2017 and 74% in September 2018), accompanied by high multibeam sonar-derived melt rates (4.84 m d −1 in 2016, 1.13 m d −1 in 2017 and 1.85 m d −1 in 2018). We find that periods of high subglacial discharge lead to localized undercut discharge outlets, but adjacent to these outlets the terminus maintains significantly overcut geometry, with an ice ramp that protrudes 75 m into the fjord in 2017 and 125 m in 2018. Our data challenge the assumption that tidewater glacier termini are largely undercut during periods of high submarine melting.more » « less
-
Abstract At tidewater glaciers, the ocean supplies heat for submarine ice melt and the glacier supplies freshwater that impacts ocean circulation. Models that employ buoyant plume theory are widely used to represent the effects of subglacial discharge on both glacier melt and freshwater export, but a scarcity of observations means that these models are largely unvalidated. The challenges and inherent risks of working near actively calving glaciers make it difficult to collect in situ observations. This study, conducted at Xeitl Sít’ (LeConte Glacier) in southeast Alaska, reports the first observations of velocity and geometry of the upwelling core of a subglacial discharge plume. This subglacial discharge plume rises along an overcut ice face, with vertical velocities in excess of 1 m s−1, and a plume shape consistent with subglacial discharge emerging from a narrow outlet. Buoyant plume theory, as commonly applied, fails to replicate the observed entrainment, underestimating the plume's volume flux by more than 50%. Large eddy simulations reveal that over half of this mismatch can be attributed to the overcut slope of the ice, which enhances entrainment. Enhanced mixing near the grounding line may account for the additional entrainment. Accurate representation of plume geometry and entrainment is critical for understanding plume‐driven melt of the terminus and the initial mixing of glacial meltwater as it is exported into the ocean.more » « less
-
Abstract. Changes in ocean temperature and salinity are expected to be an important determinant of the Greenland ice sheet's future sea level contribution. Yet, simulating the impact of these changes in continental-scale ice sheet models remains challenging due to the small scale of key physics, such as fjord circulation and plume dynamics, and poor understanding of critical processes, such as calving and submarine melting. Here we present the ocean forcing strategy for Greenland ice sheet models taking part in the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6), the primary community effort to provide 21st century sea level projections for the Intergovernmental Panel on Climate Change Sixth Assessment Report. Beginning from global atmosphere–ocean general circulation models, we describe two complementary approaches to provide ocean boundary conditions for Greenland ice sheet models, termed the “retreat” and “submarine melt” implementations. The retreat implementation parameterises glacier retreat as a function of projected subglacial discharge and ocean thermal forcing, is designed to be implementable by all ice sheet models and results in retreat of around 1 and 15 km by 2100 in RCP2.6 and 8.5 scenarios, respectively. The submarine melt implementation provides estimated submarine melting only, leaving the ice sheet model to solve for the resulting calving and glacier retreat and suggests submarine melt rates will change little under RCP2.6 but will approximately triple by 2100 under RCP8.5. Both implementations have necessarily made use of simplifying assumptions and poorly constrained parameterisations and, as such, further research on submarine melting, calving and fjord–shelf exchange should remain a priority. Nevertheless, the presented framework will allow an ensemble of Greenland ice sheet models to be systematically and consistently forced by the ocean for the first time and should result in a significant improvement in projections of the Greenland ice sheet's contribution to future sea level change.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1029/2025GL117900
