Tracking icebergs with time-lapse photography and sparse optical flow, LeConte Bay, Alaska, 2016–2017

Kienholz, Christian; Amundson, J. M.; Motyka, R. J.; Jackson, R. H.; Mickett, John B.; Sutherland, David A.; Nash, Jonathan D.; Winters, Dylan S.; Dryer, W. P.; Truffer, Martin

doi:10.1017/jog.2018.105

Cited by 18 publications

(40 citation statements)

References 31 publications

(41 reference statements)

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“…This paper focuses on the time series data that were collected during the course of the project and captured the ephemeral ice mélange that was present in the fjord from February to April 2017. Much of the data and methods have been discussed previously; here we describe the key features of the data and methods but refer the reader to Kienholz and others (2019) and Sutherland and others (2019) for further details. Also, we note that all data were recorded (and are presented here) in Coordinate Universal Time (UTC).…”

Section: Study Area and Methodsmentioning

confidence: 99%

“…During ice mélange break-up, the icebergs moved too quickly to be tracked across daily images. Instead of changing our sampling strategy, we instead rely on the results of Kienholz and others (2019), who applied sparse optical flow to track icebergs over short time periods (15–120 s) and used the iceberg velocity fields as proxies for fjord surface currents. Although the workflow was designed to track freely flowing icebergs, it also works well in other applications as long as changes in illumination between successive images are small (i.e., the time-lapse interval is small).…”

Section: Study Area and Methodsmentioning

confidence: 99%

“…Submarine melting accounts for ~25% of the ice that is discharged into the fjord, owing to high ocean thermal forcing (4–7°C at depth) and vigorous subglacial discharge (~200 m 3 s −1 ) (Motyka and others, 2003; Motyka and others, 2013; Sutherland and others, 2019); the remainder is discharged via iceberg calving. Surface currents in the fjord are strongly and consistently influenced by the meltwater plume that rises along the glacier terminus and flows out along the fjord surface (Kienholz and others, 2019).

Fig.…”

Section: Study Area and Methodsmentioning

confidence: 99%

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

et al. 2020

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Ice mélange has been postulated to impact glacier and fjord dynamics through a variety of mechanical and thermodynamic couplings. However, observations of these interactions are very limited. Here, we report on glaciological and oceanographic data that were collected from 2016 to 2017 at LeConte Glacier and Bay, Alaska, and serendipitously captured the formation, flow and break-up of ephemeral ice mélange. Sea ice formed overnight in mid-February. Over the subsequent week, the sea ice and icebergs were compacted by the advancing glacier terminus, after which the ice mélange flowed quasi-statically. The presence of ice mélange coincided with the lowest glacier velocities and frontal ablation rates in our record. In early April, increasing glacier runoff and the formation of a sub-ice-mélange plume began to melt and pull apart the ice mélange. The plume, outgoing tides and large calving events contributed to its break-up, which took place over a week and occurred in pulses. Unlike observations from elsewhere, the loss of ice mélange integrity did not coincide with the onset of seasonal glacier retreat. Our observations provide a challenge to ice mélange models aimed at quantifying the mechanical and thermodynamic couplings between ice mélange, glaciers and fjords.

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Section: Study Area and Methodsmentioning

confidence: 99%

Section: Study Area and Methodsmentioning

confidence: 99%

Fig.…”

Section: Study Area and Methodsmentioning

confidence: 99%

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

et al. 2020

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“…where f j is the 2000-2010 mean observed ice flux (Enderlin et al, 2014;King et al, 2018) and the sum runs over all glaciers j in ice-ocean sector i. This ensures that the largest glaciers are treated as the most important when generating a retreat projection per sector.…”

Section: Averaging Retreat Per Ice-ocean Sectormentioning

confidence: 99%

Twenty-first century ocean forcing of the Greenland ice sheet for modelling of sea level contribution

et al. 2020

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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.

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“…The summer and winter terminus exposures gradually decreased as the morainal bank complex grew (winter exposures were affected to a greater degree). Fjord circulation is generally stratified as noted in (a) and (b), and more variable in winter than in summer (see Kienholz et al, 2019).…”

Section: Sediment Dynamics and Moraine Growthmentioning

confidence: 89%

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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Tracking icebergs with time-lapse photography and sparse optical flow, LeConte Bay, Alaska, 2016–2017

Cited by 18 publications

References 31 publications

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

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

Twenty-first century ocean forcing of the Greenland ice sheet for modelling of sea level contribution

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

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