Formation, flow and break-up of ephemeral ice mélange at LeConte Glacier and Bay, Alaska

Amundson, J. M.; Kienholz, Christian; Hager, Alexander O.; Jackson, R. H.; Motyka, R. J.; Nash, Jonathan D.; Sutherland, David A.

doi:10.1017/jog.2020.29

Cited by 16 publications

(38 citation statements)

References 54 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…All observational data has been archived with the NOAA National Centers for Environmental Information at https://www.ncei.noaa.gov/archive/accession/0189574 (Sutherland et al., 2019b). The subglacial discharge model is archived with the Arctic Data Center at https://doi.org/10.18739/A22G44 (Amundson et al., 2017). All MITgcm model output and code for calculating TEF and efflux/reflux budgets are archived with Zenodo at https://doi.org/10.5281/zenodo.6377142 and https://doi.org/10.5281/zenodo.6377200 (Hager et al., 2022a, 2022b).…”

Section: Data Availability Statementmentioning

confidence: 99%

Subglacial Discharge Reflux and Buoyancy Forcing Drive Seasonality in a Silled Glacial Fjord

et al. 2022

Self Cite

View full text Add to dashboard Cite

Fjords are conduits for heat and mass exchange between tidewater glaciers and the coastal ocean, and thus regulate near‐glacier water properties and submarine melting of glaciers. Entrainment into subglacial discharge plumes is a primary driver of seasonal glacial fjord circulation; however, outflowing plumes may continue to influence circulation after reaching neutral buoyancy through the sill‐driven mixing and recycling, or reflux, of glacial freshwater. Despite its importance in non‐glacial fjords, no framework exists for how freshwater reflux may affect circulation in glacial fjords, where strong buoyancy forcing is also present. Here, we pair a suite of hydrographic observations measured throughout 2016–2017 in LeConte Bay, Alaska, with a three‐dimensional numerical model of the fjord to quantify sill‐driven reflux of glacial freshwater, and determine its influence on glacial fjord circulation. When paired with subglacial discharge plume‐driven buoyancy forcing, sill‐generated mixing drives distinct seasonal circulation regimes that differ greatly in their ability to transport heat to the glacier terminus. During the summer, 53%–72% of the surface outflow is refluxed at the fjord's shallow entrance sill and is subsequently re‐entrained into the subglacial discharge plume at the fjord head. As a result, near‐terminus water properties are heavily influenced by mixing at the entrance sill, and circulation is altered to draw warm, modified external surface water to the glacier grounding line at 200 m depth. This circulatory cell does not exist in the winter when freshwater reflux is minimal. Similar seasonal behavior may exist at other glacial fjords throughout Southeast Alaska, Patagonia, Greenland, and elsewhere.

show abstract

Section: Data Availability Statementmentioning

confidence: 99%

Subglacial Discharge Reflux and Buoyancy Forcing Drive Seasonality in a Silled Glacial Fjord

et al. 2022

Self Cite

View full text Add to dashboard Cite

show abstract

“…At LeConte, the seasonal advance usually begins in late fall and typically continues until April/May but sometimes until June (Figure 3) depending on seasonal fjord and meteorological conditions (Amundson et al, 2020;Kienholz et al, 2019). Retreat is likely triggered by the onset of subglacial discharge coupled with warming of deeper, incoming fjord waters, leading to increased submarine melting (Amundson et al, 2020;Jackson et al, 2020;Motyka et al, 2003Motyka et al, , 2013. Several processes drive the summer retreat with U -F < 0 (terminus velocity minus frontal ablation rate), including (1) retreat onto a reverse slope and into an overdeepened basin, increasing buoyancy and thus calving (e.g., Benn et al, 2007;van der Veen, 1996); (2) thinning caused by extensional strain and summer surface ablation further increasing buoyancy; (3) increased subglacial discharge and seasonal warming of fjord waters as well as an expansion in submarine area exposed to melting, which combine to 10.1029/2019JF005359 Journal of Geophysical Research: Earth Surface increase submarine melting (Motyka et al, 2003;Sutherland et al, 2019); and (4) enhanced calving from undercutting by submarine melting (O'Leary & Christoffersen, 2013).…”

Section: Mb2 and Implications For Glacier Terminus Dynamicsmentioning

confidence: 99%

“…During winter, fjord water temperature decreases, subglacial discharge is minimal, and calving is subdued (Amundson et al, 2020), allowing the glacier to advance toward the morainal bank. At LeConte, the seasonal advance usually begins in late fall and typically continues until April/May but sometimes until June (Figure 3) depending on seasonal fjord and meteorological conditions (Amundson et al, 2020;Kienholz et al, 2019). Retreat is likely triggered by the onset of subglacial discharge coupled with warming of deeper, incoming fjord waters, leading to increased submarine melting (Amundson et al, 2020;Jackson et al, 2020;Motyka et al, 2003Motyka et al, , 2013.…”

Section: Mb2 and Implications For Glacier Terminus Dynamicsmentioning

confidence: 99%

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

et al. 2020

Self Cite

View full text Add to dashboard Cite

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.

show abstract

“…Bolch et al, 2010;Frey et al, 2012;Rastner et al, 2012;Guo et al, 2015;. However, they are less effective for mapping more complex glaciated landscapes such as marine-terminating outlet glaciers, which often contain spectrally similar surfaces like mélange (a mixture of sea ice and icebergs) near their calving fronts (Amundson et al, 2020).…”

Section: Introductionmentioning

confidence: 99%

Image classification of marine-terminating outlet glaciers in Greenland using deep learning methods

2021

View full text Add to dashboard Cite

Abstract. A wealth of research has focused on elucidating the key controls on mass loss from the Greenland and Antarctic ice sheets in response to climate forcing, specifically in relation to the drivers of marine-terminating outlet glacier change. The manual methods traditionally used to monitor change in satellite imagery of marine-terminating outlet glaciers are time-consuming and can be subjective, especially where mélange exists at the terminus. Recent advances in deep learning applied to image processing have created a new frontier in the field of automated delineation of glacier calving fronts. However, there remains a paucity of research on the use of deep learning for pixel-level semantic image classification of outlet glacier environments. Here, we apply and test a two-phase deep learning approach based on a well-established convolutional neural network (CNN) for automated classification of Sentinel-2 satellite imagery. The novel workflow, termed CNN-Supervised Classification (CSC) is adapted to produce multi-class outputs for unseen test imagery of glacial environments containing marine-terminating outlet glaciers in Greenland. Different CNN input parameters and training techniques are tested, with overall F1 scores for resulting classifications reaching up to 94 % for in-sample test data (Helheim Glacier) and 96 % for out-of-sample test data (Jakobshavn Isbrae and Store Glacier), establishing a state of the art in classification of marine-terminating glaciers in Greenland. Predicted calving fronts derived using optimal CSC input parameters have a mean deviation of 56.17 m (5.6 px) and median deviation of 24.7 m (2.5 px) from manually digitised fronts. This demonstrates the transferability and robustness of the deep learning workflow despite complex and seasonally variable imagery. Future research could focus on the integration of deep learning classification workflows with free cloud-based platforms, to efficiently classify imagery and produce datasets for a range of glacial applications without the need for substantial prior experience in coding or deep learning.

show abstract

Formation, flow and break-up of ephemeral ice mélange at LeConte Glacier and Bay, Alaska

Cited by 16 publications

References 54 publications

Subglacial Discharge Reflux and Buoyancy Forcing Drive Seasonality in a Silled Glacial Fjord

Subglacial Discharge Reflux and Buoyancy Forcing Drive Seasonality in a Silled Glacial Fjord

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

Image classification of marine-terminating outlet glaciers in Greenland using deep learning methods

Contact Info

Product

Resources

About