Impact of Fjord Geometry on Grounding Line Stability

Åkesson, Henning; Nisancioglu, Kerim H.; Nick, F. M.

doi:10.3389/feart.2018.00071

Cited by 19 publications

(27 citation statements)

References 96 publications

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“…Tidewater glacier fjord geometry is known to play a role in stabilizing a retreating terminus, by providing a variety of pinning points—for example, constrictions, sills, and bends—which can impede frontal ablation by reducing the area exposed to melting, reduce calving rates by altering near‐terminus stresses, and allow the glacier time to thicken (Åkesson et al, 2018; Amundson & Carroll, 2018; Carr et al, 2014; Catania et al, 2018; Mercer, 1961; Post, 1975). McNabb and Hock (2014) applied the term “step change retreats” to tidewater glacier retreats where constrictions or other factors result in a stillstand of several years or more between periods of rapid retreat.…”

Section: Discussionmentioning

confidence: 99%

“…Rapid retreat often follows-for example, several kilometers in a few years (McNabb & Hock, 2014)-until the terminus stalls in shallower water or at a constriction in the fjord (e.g., Åkesson et al, 2018;Amundson & Carroll, 2018;Catania et al, 2018;Mercer, 1961;Nolan et al, 1995;Post, 1975). Over time, positive mass balance in combination with MB growth can lead to glacier growth and readvance, potentially asynchronous with regional trends (e.g., Taku Glacier: Pelto et al, 2008;Post & Motyka, 1995;Hubbard Glacier: Barclay et al, 2001;Trabant et al, 2003).…”

Section: Introductionmentioning

confidence: 99%

“…Subsequent thinning and retreat from the MB into an overdeepened basin will expose the ice front to greater water depths and thus increase the potential for iceberg calving and submarine melting (e.g., Alley, 1991; Truffer & Motyka, 2016; van der Veen, 1996). Rapid retreat often follows—for example, several kilometers in a few years (McNabb & Hock, 2014)—until the terminus stalls in shallower water or at a constriction in the fjord (e.g., Åkesson et al, 2018; Amundson & Carroll, 2018; Catania et al, 2018; Mercer, 1961; Nolan et al, 1995; Post, 1975). Over time, positive mass balance in combination with MB growth can lead to glacier growth and readvance, potentially asynchronous with regional trends (e.g., Taku Glacier: Pelto et al, 2008; Post & Motyka, 1995; Hubbard Glacier: Barclay et al, 2001; Trabant et al, 2003).…”

Section: Introductionmentioning

confidence: 99%

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Morainal Bank Evolution and Impact on Terminus Dynamics During a Tidewater Glacier Stillstand

et al. 2020

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Sedimentary processes are known to help facilitate tidewater glacier advance, but their role in modulating retreat is uncertain and poorly quantified. In this study we use repeated seafloor bathymetric surveys and satellite-derived terminus positions from LeConte Glacier, Alaska, to evaluate the evolution of a morainal bank and related changes in terminus dynamics over a 17-year period. The glacier experienced a rapid retreat between 1994 and 1999, before stabilizing at a constriction in the fjord. Since then, the glacier terminus has remained stabilized while constructing a morainal bank up to 140 m high in water depths of 240-260 m, with rates of sediment delivery of 3.3 × 10 5 to 3.8 × 10 5 m 3 a −1. Based on repeated interannual surveys between 2016 and 2018, the moraine is a dynamic feature characterized by push ridges, evidence of active gravity flows, and bulldozing by the glacier at rates of up to meters per day. Beginning in 2016, the summertime terminus has become increasingly retracted, revealing a newly emerging basin potentially signaling the onset of renewed retreat. Between 2000 and 2016, the growing moraine reduced the exposed submarine area of the terminus by up to 22%, altered the geometry of the terminus during seasonal advances, and altered the terminus stress balance. These feedbacks for calving, melting, and ice flow likely represent mechanisms whereby moraine growth may delay glacier retreat, in a system where readvance is unlikely.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Morainal Bank Evolution and Impact on Terminus Dynamics During a Tidewater Glacier Stillstand

et al. 2020

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“…Enderlin et al () found that, all else equal, glaciers with wider termini and/or with geometries that widen inland of the terminus are more sensitive to climate perturbations than their narrower counterparts. In fact, inland widening of the fjord may exert stronger control over retreat than the presence or absence of a terminal moraine (Åkesson et al, ).…”

Section: Controls On Outlet Glacier Dynamicsmentioning

confidence: 99%

Future Evolution of Greenland's Marine‐Terminating Outlet Glaciers

et al. 2020

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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.

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“…Fjords act as important repositories for glacial-marine sediments deposited by retreating glaciers because once a marineterminating glacier has its grounded margin within a fjord, any sediments expelled from it are often effectively trapped in the narrow basin setting. In addition, fjord geometry strongly influences glacier retreat behaviour because bathymetric sills, fjord constrictions and turns in the fjord planform shape all provide stability either by reducing the flux at the grounding line and/or by providing lateral buttressing (Warren and Hulton, 1990;Hill et al, 2018;Åkesson et al, 2018;Catania et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

Glacial sedimentation, fluxes and erosion rates associated with ice retreat in Petermann Fjord and Nares Strait, NW Greenland

Hogan¹,

Mayer²,

Reilly³

et al. 2019

Preprint

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Abstract. Petermann Fjord is a deep (> 1000 m) fjord that incises the coastline of northwest Greenland and was carved by an expanded Petermann Glacier, one of the six largest outlet glaciers draining the modern Greenland Ice Sheet (GrIS). Between 5–70 m of unconsolidated glacigenic material infills in the fjord and adjacent Nares Strait, deposited as the Petermann and Nares Strait ice streams retreated through the area after the Last Glacial Maximum. We have investigated the deglacial deposits using seismic stratigraphic techniques and have correlated our results with high-resolution bathymetric data and core lithofacies. We identify six seismo-acoustic facies in more than 3500 line-km of sub-bottom and seismic-reflection profiles throughout the fjord, Hall Basin and Kennedy Channel. Seismo-acoustic facies relate to: bedrock or till surfaces (Facies I); subglacial deposition (Facies II); deposition from meltwater plumes and icebergs in quiescent glaciomarine conditions (Facies III, IV); deposition at grounded ice margins during stillstands in retreat (grounding-zone wedges; Facies V); and the redeposition of material down slopes (Facies IV). These sediment units represent the total volume of glacial sediment delivered to the mapped marine environment during retreat. We calculate a glacial sediment flux for the former Petermann Ice Stream as 1080–1420 m3 a−1 per meter of ice stream width and an average deglacial erosion rate for the basin of 0.29–0.34 mm a−1. Our deglacial erosion rates are consistent with results from Antarctic Peninsula fjord systems but are several times lower than values for other modern GrIS catchments. This difference is attributed to fact that large volumes of surface water do not access the bed in the Petermann system and we conclude that glacial erosion is limited to areas overridden by streaming ice in this large outlet glacier setting. Erosion rates are also presented for two phases of ice retreat and confirm that there is significant variation in these rates over a glacial-deglacial transition. Our new fluxes and erosion rates show that the Petermann Ice Stream was approximately as efficient as the palaeo-Jakobshavn Isbrae at eroding, transporting and delivering sediment to its margin during early deglaciation.

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Impact of Fjord Geometry on Grounding Line Stability

Cited by 19 publications

References 96 publications

Morainal Bank Evolution and Impact on Terminus Dynamics During a Tidewater Glacier Stillstand

Morainal Bank Evolution and Impact on Terminus Dynamics During a Tidewater Glacier Stillstand

Future Evolution of Greenland's Marine‐Terminating Outlet Glaciers

Glacial sedimentation, fluxes and erosion rates associated with ice retreat in Petermann Fjord and Nares Strait, NW Greenland

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