Rapid submarine melting driven by subglacial discharge, LeConte Glacier, Alaska

Motyka, R. J.; Dryer, W. P.; Amundson, J. M.; Truffer, Martin; Fahnestock, M. A.

doi:10.1002/grl.51011

Cited by 142 publications

(169 citation statements)

References 29 publications

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“…These are quite extreme conditions that might be met by some previous studies (e.g. Motyka et al, 2013Motyka et al, , 2003 but certainly not all. The implication is that, in many cases, the heat storage term cannot be neglected -it must be evaluated directly or at least averaged in time to reduce its amplitude.…”

Section: Storage Of Heat and Saltmentioning

confidence: 84%

“…Other approaches employ both heat and salt budgets and retain more components of the budgets (e.g. Motyka et al, 2003;Rignot et al, 2010;Xu et al, 2013;Motyka et al, 2013). In all cases, the storage terms ( / ), surface heat fluxes ( ) and fluctuating transports ( 2 / 2 ) have been neglected.…”

Section: Across Greenland's Fjords: Previous Methods and Future Studiesmentioning

confidence: 99%

“…A variety of methods have been employed to extract a certain part of the velocity field. In some cases, the raw snapshots of velocity and water properties are used to calculate cross-section transport (Xu et al, 2013;Motyka et al, 2003Motyka et al, , 2013Rignot et al, 2010). In others, geostrophic velocities are calculated from water properties (Johnson et al, 2011;Inall et al, 2014) or a high frequency mode is removed from the velocity field (Sutherland and Straneo, 2012).…”

Section: Measuring a Mean Velocity Profilementioning

confidence: 99%

“…A growing number of studies attempt to infer submarine melt rates from measurements of ocean heat transport in the fjords where outlet glaciers terminate (Motyka et al, 2003;Johnson et al, 2011;Sutherland and Straneo, 2012;Rignot et al, 2010;Christoffersen et al, 2011;Motyka et al, 2013;Xu et al, 2013;Inall et al, 2014;Mortensen et al, 2014). Water properties and velocity, usually measured over a brief period, are used to estimate ocean heat transport through a fjord cross-section.…”

Section: Introductionmentioning

confidence: 99%

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Dynamics of Greenland�s glacial fjords

Jackson¹

2016

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Glacial fjords form conduits between glaciers of the Greenland Ice Sheet and the North Atlantic. They are the gateways for importing oceanic heat to melt ice and for exporting meltwater into the ocean. Submarine melting in fjords has been implicated as a driver of recent glacier acceleration; however, there are no direct measurements of this melting, and little is known about the fjord processes that modulate melt rates. Combining observations, theory, and modeling, this thesis investigates the circulation, heat transport, and meltwater export in glacial fjords.While most recent studies focus on glacial buoyancy forcing, there are other drivers -e.g. tides, local wind, shelf variability -that can be important for fjord circulation. Using moored records from two major Greenlandic fjords, shelf forcing (from shelf density fluctuations) is found to dominate the fjord circulation, driving rapid exchange with the shelf and large heat content variability near the glacier. Contrary to the conventional paradigm, these flows mask any glacier-driven circulation in the non-summer months. During the summer, when shelf forcing is reduced and freshwater forcing peaks, a mean exchange flow transports warm Atlantic-origin water towards the glacier and exports glacial meltwater.Many recent studies have inferred submarine melt rates from oceanic heat transport, but the fjord budgets that underlie this method have been overlooked. Building on estuarine studies of salt fluxes, this thesis presents a new framework for assessing glacial fjord budgets and revised equations for inferring meltwater fluxes. Two different seasonal regimes are found in the heat/salt budgets for Sermilik Fjord, and the results provide the first time-series of submarine meltwater and subglacial discharge fluxes into a glacial fjord.Finally, building on the observations, ROMS numerical simulations and two analytical models are used to investigate the dynamics of shelf-driven flows and their importance relative to local wind forcing across the parameter space of Greenland's fjords. The fjord response is found to vary primarily with the width relative to the deformation radius and the fjord adjustment timescale relative to the forcing timescale. Understanding these modes of circulation is a step towards accurate modeling of ocean-glacier interactions.

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Section: Storage Of Heat and Saltmentioning

confidence: 84%

Section: Across Greenland's Fjords: Previous Methods and Future Studiesmentioning

confidence: 99%

Section: Measuring a Mean Velocity Profilementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Dynamics of Greenland�s glacial fjords

Jackson¹

2016

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“…how much freshwater is contributed by melt− ing ice, or how currents affect drifting ice distribution (e.g. Motyka et al 2013;Straneo et al 2011). They are, however, usually limited in space to the profiles taken, and in time to the actual surveys.…”

Section: Introductionmentioning

confidence: 99%

Two-element acoustic array gives insight into ice-ocean interactions in Hornsund Fjord, Spitsbergen

Głowacki¹,

Deane²,

Moskalik³

et al. 2015

Polish Polar Research

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Glacierized fjords are dynamic regions, with variable oceanographic conditions and complex ice−ocean interactions, which are still poorly understood. Recent studies have shown that passive underwater acoustics offers new promising tools in this branch of polar research. Here, we present results from two field campaigns, conducted in summer 2013 and spring 2014. Several recordings with a bespoke two−hydrophone acoustic buoy were made in different parts of Hornsund Fjord, Spitsbergen in the vicinity of tidewater glaciers to study the directionality of underwater ambient noise. Representative segments of the data are used to illustrate the analyses, and determine the directions of sound sources by using the time differences of arrivals between two horizontally aligned, broadband hydrophones. The results reveal that low frequency noise (< 3 kHz) is radiated mostly from the ice cliffs, while high−frequency (> 3 kHz) noise directionality strongly depends on the distribution of floating glacial ice throughout the fjord. Changing rates of iceberg production as seen for example in field photographs and logs are, in turn, most likely linked to signal amplitudes for relevant directions. These findings demonstrate the potential offered by passive acous− tics to study the dynamics of individual tidewater glaciers.

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Alaska tidewater glacier terminus positions, 1948–2012

2014

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A significant portion of the world's glacier ice drains through tidewater outlets, though much remains unknown about the response to recent climate change of tidewater glaciers. We present a 64 year record of length change for 50 Alaska tidewater glaciers. We use U.S. Geological Survey topographic maps to provide a base length for glaciers before 1970. Using all available cloud-free Landsat images, we manually digitize calving front outlines for each glacier between 1972 and 2012, resulting in a total of more than 10,000 outlines. Tidewater glacier lengths vary seasonally; focusing on the 36 glaciers terminating in tidewater throughout the study period, we find a mean (± standard deviation) seasonal variation of 60 ± 85 m a −1 . We use these oscillations to determine the significance of interannual changes in glacier length. All 36 glaciers underwent at least one period (≥1 year) of significant advance or retreat; 28 glaciers underwent at least one period of both significant advance and retreat. Over the entire period 1948-2012, 24 of these glaciers retreated a total (± uncertainty) of 107.95 ± 0.29 km, 11 advanced a total of 7.71 ± 0.20, and one (Chenega Glacier) did not change significantly. Retreats and advances are highly variable in time; several glaciers underwent rapid, short-term retreats of a few years duration. These retreats occurred after large changes in summer sea surface temperature anomalies; further study is needed to determine what triggered these retreats. No coherent regional behavior signal is apparent in the length record, although two subregions show a coherence similar to recent observations in Greenland.

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Rapid submarine melting driven by subglacial discharge, LeConte Glacier, Alaska

Cited by 142 publications

References 29 publications

Dynamics of Greenland�s glacial fjords

Dynamics of Greenland�s glacial fjords

Two-element acoustic array gives insight into ice-ocean interactions in Hornsund Fjord, Spitsbergen

Alaska tidewater glacier terminus positions, 1948–2012

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