The Relationship Between Submarine Melt and Subglacial Discharge From Observations at a Tidewater Glacier

Jackson, R. H.; Motyka, R. J.; Amundson, J. M.; Abib, Nicole; Sutherland, David A.; Nash, Jonathan D.; Kienholz, Christian

doi:10.1029/2021jc018204

Cited by 21 publications

(24 citation statements)

References 58 publications

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“…With a terminus width of ~1 km and a maximum grounding line depth of 200 m (Sutherland and others, 2019), the dimensions of LeConte Glacier make it a relatively accessible analog for smaller outlet glaciers around the periphery of the Greenland ice sheet. In addition, the springtime oceanic temperature and water column stratification at LeConte Glacier are similar to typical conditions observed in Greenlandic proglacial fjords (Jackson and others, 2022). Throughout the year, the glacial system is exposed to a range of ocean temperatures (4–7°C at depth; Hager and others, 2022) and subglacial discharge (20–350 m 3 s −1 ; Amundson and others, 2020), with outflowing plumes (Motyka and others, 2003) and a recirculation gyre (Kienholz and others, 2019) typically visible in the near-terminus surface waters.…”

Section: Introductionsupporting

confidence: 79%

“…Based on the assumption that submarine melt scales with water velocity adjacent to the ice, melt rates near the location of upwelling subglacial discharge plumes are thought to be higher than those away from discharge outlets (Cowton and others, 2015; Slater and others, 2015; Carroll and others, 2016). Recent work, however, has shown that submarine melt rates can be up to two orders of magnitude higher than those predicted by plume-melt theory (Sutherland and others, 2019; Jackson and others, 2020, 2022), which describes the coupling of buoyant plume theory with a three-equation melt parameterization (Holland and Jenkins, 1999; Jenkins, 2011; Cowton and others, 2015), particularly away from the direct influence of discharge plumes.…”

Section: Introductionmentioning

confidence: 99%

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Persistent overcut regions dominate the terminus morphology of a rapidly melting tidewater glacier

et al. 2023

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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.

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Section: Introductionsupporting

confidence: 79%

Section: Introductionmentioning

confidence: 99%

Persistent overcut regions dominate the terminus morphology of a rapidly melting tidewater glacier

et al. 2023

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“…The relative timing of peaks in discharge and KE hint at a 1-2 day lag between changes in runo↵ and changes in ocean circulation (Fig. 3 B), which could result from inadequate representation of water storage in the glacier runo↵ model (Jansson et al, 2003;Jackson et al, 2022). However, a lag-correlation analysis did not result in higher correlation estimates.…”

Section: Resultsmentioning

confidence: 94%

Internal gravity waves generated by subglacial discharge: implications for tidewater glacier melt

Cusack¹,

Jackson²,

Nash³

et al. 2023

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Submarine melting has been implicated in the accelerated retreat of marine-terminating glaciers globally. Energetic ocean flows, such as subglacial discharge plumes, are known to enhance submarine melting in their immediate vicinity. Using observations and a large eddy simulation, we demonstrate that discharge plumes emit high-frequency internal gravity waves that propagate along glacier termini and transfer energy to distant regions of the terminus. Our analysis of wave characteristics and their correlation with subglacial discharge forcing suggest that they derive their energy from turbulent motions within the discharge plume and its surface outflow. Accounting for the near-terminus velocities associated with these waves increases predicted melt rates by up to 70%. This may help to explain known discrepancies between observed melt rates and theoretical predictions. Because the dynamical ingredients -- a buoyant plume rising through a stratified ocean -- are common to many tidewater glacier systems, such internal waves are likely to be widespread.

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“…Interestingly, both also show that dye injected into the domain with the outflow rapidly spread to regions well beyond the outflowing jet. Indeed, dye concentrations (Figure 9) are fairly uniformly spread across the channel in contrast to the velocity field which exhibits significant lateral shear (Jackson et al., 2017, 2022). In addition, there is considerable downward mixing of the dye into the landward flowing lower layer.…”

Section: Discussionmentioning

confidence: 99%

Parameterizing Subglacial Discharge in Modeling Buoyancy Driven Flow in Tidewater Glacier Fjords

2023

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In tidewater glacier fjords, subglacial discharge drives a significant mixing mechanism near glacier fronts and drives a strong exchange flow. Numerous studies (Cowton et al., 2015; Slater et al., 2017) have utilized a parameterization for buoyant plume theory to force fjord scales systems, but neglect to parameterize the outflowing of the plume away from the glacial wall after it has reached its neutral density. In this study, a new model framework, ROMS‐ICEPLUME, is developed to parameterize the rising and initial outflowing stage of subglacial discharge plumes in the Regional Ocean Modeling System (ROMS). The coupled model applies a novel parameterization algorithm to prescribe the velocity and vertical extent of the outflowing plume, which reduces numerical instability and improves model performance. The model framework is tested with a quasi‐realistic forcing using observations of a subglacial discharge plume hydrographic surveys collected from a Greenland fjord. We find that the new model framework is able to reproduce the strong outflowing plume and the compensating inflow at depth, with a spatial structure that correlates well with in‐situ observations. On the other hand, the model framework without the new parameterization algorithm fails to capture the outflowing plume structure. Thus, our new framework for parameterizing subglacial discharge plumes is an improvement from previous coupled model frameworks, and is a promising tool towards advancing our understanding of circulation in tidewater glacier fjords.

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The Relationship Between Submarine Melt and Subglacial Discharge From Observations at a Tidewater Glacier

Cited by 21 publications

References 58 publications

Persistent overcut regions dominate the terminus morphology of a rapidly melting tidewater glacier

Persistent overcut regions dominate the terminus morphology of a rapidly melting tidewater glacier

Internal gravity waves generated by subglacial discharge: implications for tidewater glacier melt

Parameterizing Subglacial Discharge in Modeling Buoyancy Driven Flow in Tidewater Glacier Fjords

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