Impact of fjord dynamics and glacial runoff on the circulation near Helheim Glacier

Straneo, Fiammetta; Curry, Ruth; Sutherland, David A.; Hamilton, G. S.; Cenedese, Claudia; Våge, Kjetil; Stearns, L. A.

doi:10.1038/ngeo1109

Cited by 257 publications

(380 citation statements)

References 21 publications

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“…This shallow depth allows minimal time for a subglacially released meltwater plume to entrain enough ambient ocean water to equilibrate before reaching the surface, which has been observed in deep Greenlandic fjords (cf. Straneo et al 2011;Xu et al 2013;Chauché et al 2014), and could be problematic for this study. Additionally, Kronebreen and Tunabreen's termini are largely mélange-and sea ice-free May-August and have fairly consistent sediment plumes visible at the fjord surface.…”

Section: Study Locationmentioning

confidence: 99%

Quantifying suspended sediment concentration in subglacial sediment plumes discharging from two Svalbard tidewater glaciers using Landsat-8 and in situ measurements

Schild

Hawley

Chipman

et al. 2017

International Journal of Remote Sensing

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Marine-terminating outlet glaciers discharge mass through iceberg calving, submarine melting, and meltwater run-off. While calving can be quantified by in situ and remote-sensing observations, meltwater run-off, the subglacial transport of meltwater, and submarine melting are not well constrained due to inherent difficulties observing the subglacial and proglacial environments at tidewater glaciers. Remote-sensing and in situ measurements of surface sediment plumes, and their suspended sediment concentration (SSC), have been used as a proxy for glacier meltwater run-off. However, this relationship between satellite reflectance and SSC has predominantly been established using land-terminating glaciers. Here, we use two Svalbard tidewater glaciers to establish a well-constrained relationship between Landsat-8 surface reflecance and SSC and argue that it can be used to measure relative meltwater runoff at tidewater glaciers throughout a summer melt season. We find the highest correlation between SSCs and Landsat-8 surface reflectance by using the red + NIR band combination (r 2 = 0.76). The highest correlation between SSCs and in situ field spectrometer measurements is in the 740-800 nm wavelength range (r 2 = 0.85), a spectral range not currently measured by Landsat. Additionally, we find that in situ and Landsat-8 measurements for surface reflectance of SSCs are not interchangeable and therefore establish a relationship for each detection method. We then use the Landsat-8 relationship to calculate total surface sediment load, finding a strong correlation between total surface sediment load and a proxy for meltwater run-off (r 2 ≥ 0.89). Our results establish a new metric to calculate SSCs from Landsat-8 surface reflectance and demonstrate how the SSC of subglacial sediment plumes can be used to monitor relative seasonal meltwater discharge at tidewater glaciers. ARTICLE HISTORY

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Section: Study Locationmentioning

confidence: 99%

Quantifying suspended sediment concentration in subglacial sediment plumes discharging from two Svalbard tidewater glaciers using Landsat-8 and in situ measurements

Schild

Hawley

Chipman

et al. 2017

International Journal of Remote Sensing

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“…Recent work has identified links between subglacial hydrology and ice-ocean interactions; the emergence of subglacial water at the grounding lines of tidewater glaciers plays a key role in drawing warm water along fjords to calving fronts [117] and in the transfer of heat from ocean to ice [118], with potential to promote terminus break-up. The near-terminus subglacial hydrology is also known to modulate the strength of fjord circulation [119] and submarine melting of the calving front [120].…”

Section: The Influence Of Hydrology On Marine Terminating ('Tidewatermentioning

confidence: 99%

Recent Advances in Our Understanding of the Role of Meltwater in the Greenland Ice Sheet System

Nienow

Sole

Slater

et al. 2017

Curr Clim Change Rep

104

100

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Purpose of the Review This review discusses the role that meltwater plays within the Greenland ice sheet system. The ice sheet's hydrology is important because it affects mass balance through its impact on meltwater runoff processes and ice dynamics. The review considers recent advances in our understanding of the storage and routing of water through the supraglacial, englacial, and subglacial components of the system and their implications for the ice sheet. Recent Findings There have been dramatic increases in surface meltwater generation and runoff since the early 1990s, both due to increased air temperatures and decreasing surface albedo. Processes in the subglacial drainage system have similarities to valley glaciers and in a warming climate, the efficiency of meltwater routing to the ice sheet margin is likely to increase. The behaviour of the subglacial drainage system appears to limit the impact of increased surface melt on annual rates of ice motion, in sections of the ice sheet that terminate on land, while the large volumes of meltwater routed subglacially deliver significant volumes of sediment and nutrients to downstream ecosystems. Summary Considerable advances have been made recently in our understanding of Greenland ice sheet hydrology and its wider influences. Nevertheless, critical gaps persist both in our understanding of hydrology-dynamics coupling, notably at tidewater glaciers, and in runoff processes which ensure that projecting Greenland's future mass balance remains challenging.

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“…These studies have provided novel insights into the water masses, stratification, and the spread of glacially modified water (often subsurface) (e.g. Johnson et al, 2011;Straneo et al, 2011;Inall et al, 2014). However,…”

Section: Unknown Dynamics In Glacial Fjordsmentioning

confidence: 99%

“…Most studies are based on synoptic shipboards surveys -icebergs pose major obstacles to moorings -and are primarily focused on summer conditions (e.g. Holland et al, 2008a;Rignot et al, 2010;Straneo et al, 2011;Mortensen et al, 2011;Chauché et al, 2014). These studies have provided novel insights into the water masses, stratification, and the spread of glacially modified water (often subsurface) (e.g.…”

Section: Unknown Dynamics In Glacial Fjordsmentioning

confidence: 99%

“…Limited velocity data indicates that shelf variability may play an important role in driving fjord flows (Rignot et al, 2010;Straneo et al, 2010), though conclusive evidence is absent. Furthermore, most observational studies rely on brief, summer surveys (Holland et al, 2008a;Rignot et al, 2010;Christoffersen et al, 2011;Straneo et al, 2011;Johnson et al, 2011;Xu et al, 2013;Inall et al, 2014) that offer limited insight into drivers of summer variability and no information about non-summer months.…”

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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Impact of fjord dynamics and glacial runoff on the circulation near Helheim Glacier

Cited by 257 publications

References 21 publications

Quantifying suspended sediment concentration in subglacial sediment plumes discharging from two Svalbard tidewater glaciers using Landsat-8 and in situ measurements

Quantifying suspended sediment concentration in subglacial sediment plumes discharging from two Svalbard tidewater glaciers using Landsat-8 and in situ measurements

Recent Advances in Our Understanding of the Role of Meltwater in the Greenland Ice Sheet System

Dynamics of Greenland�s glacial fjords

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