Quantifying flow regimes in a Greenland glacial fjord using iceberg drifters

Sutherland, David A.; Roth, George E.; Hamilton, G. S.; Mernild, Sebastian H.; Stearns, L. A.; Straneo, Fiammetta

doi:10.1002/2014gl062256

Cited by 48 publications

(73 citation statements)

References 60 publications

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“…We expect this local wind forcing to drive out-flow in the upper layer of the fjord, as suggested in Sutherland et al (2014a) (see also Moffat, 2014), though it is difficult to separate this effect from that of the shelf winds in our records, since down-slope wind events in Sermilik almost always follow strong along-shore shelf winds.…”

Section: Seasonality: Summer Versus Non-summer Conditionsmentioning

confidence: 56%

“…However, it is contrary to the assumption of most previous studies that iceberg melting is small compared to glacier melting. New techniques, such as inferring iceberg melt-rates from satellites (Enderlin and Hamilton, 2014) or tracking icebergs (Sutherland et al, 2014a), are opening many possibilities for studying the role of icebergs in glacial fjords and for isolating their meltwater contribution. The fjord circulation, mixing, and heat transport from this distributed buoyancy source has not been examined and could have very different impacts than a localized freshwater input at the glacier.…”

Section: Future Directionsmentioning

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: Seasonality: Summer Versus Non-summer Conditionsmentioning

confidence: 56%

Section: Future Directionsmentioning

confidence: 99%

Dynamics of Greenland�s glacial fjords

Jackson¹

2016

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“…While such data provide important information about volumes, distributions and the geographical extent of icebergs, they do not provide information about transport. Measurements of iceberg trajectories in Greenlandic fjords are somewhat limited (Amundson et al, 2010;Sutherland et al, 2014;Andres et al, 2015;FitzMaurice et al, 2016). GPS-based observations in fjords (Sutherland et al, 2014;Sulak et al, 2017) and in Baffin Bay (Wagner et al, 2014;Larsen et al, 2015) are biased toward larger and, presumably, more stable icebergs.…”

Section: Introductionmentioning

confidence: 99%

“…Measurements of iceberg trajectories in Greenlandic fjords are somewhat limited (Amundson et al, 2010;Sutherland et al, 2014;Andres et al, 2015;FitzMaurice et al, 2016). GPS-based observations in fjords (Sutherland et al, 2014;Sulak et al, 2017) and in Baffin Bay (Wagner et al, 2014;Larsen et al, 2015) are biased toward larger and, presumably, more stable icebergs. Larger icebergs have been tagged with GPS trackers both for scientific reasons, as large icebergs have been found to account for most of the solid ice volume in specific fjords (Sulak et al, 2017), as well as logistical reasons.…”

Section: Introductionmentioning

confidence: 99%

“…Larger icebergs have been tagged with GPS trackers both for scientific reasons, as large icebergs have been found to account for most of the solid ice volume in specific fjords (Sulak et al, 2017), as well as logistical reasons. Commercial GPS trackers are typically deployed by helicopter (Sutherland et al, 2014;Larsen et al, 2015;Sulak et al, 2017), which requires a large, stable platform. Furthermore, commercial GPS trackers are relatively expensive and the additional cost of helicopter deployments typically limits the number of units available for deployment.…”

Section: Introductionmentioning

confidence: 99%

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Bergy Bit and Melt Water Trajectories in Godthåbsfjord (SW Greenland) Observed by the Expendable Ice Tracker

et al. 2017

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Icebergs and bergy bits makes up a significant component of the total freshwater flux from the Greenland Ice Sheet to the ocean. Observations of iceberg trajectories are biased toward larger icebergs and, as a result, the drift characteristics of smaller icebergs and bergy bits are poorly understood. In an attempt to fill this critical knowledge gap, we developed the open-source EXpendable Ice TrackEr (EXITE). EXITE is a low-cost, satellite-tracked GPS beacon capable of high-resolution temporal measurements over extended deployment periods (30 days or more). Furthermore, EXITE can transform to a surface drifter when its host iceberg capsizes or fragments. Here we describe basic construction of an EXITE beacon and present results from a deployment in Godthåbsfjord (SW Greenland) in August 2016. Overall, EXITE trajectories show out-fjord surface transport, in agreement with a simple estuarine circulation paradigm. However, eddies and abrupt wind-driven reversals reveal complex surface transport pathways at time scales of hours to days.

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Iceberg meltwater fluxes dominate the freshwater budget in Greenland's iceberg‐congested glacial fjords

Enderlin

Hamilton

Straneo

et al. 2016

Geophysical Research Letters

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135

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Freshwater fluxes from the Greenland ice sheet have increased over the last two decades due to increases in liquid (i.e., surface and submarine meltwater) and solid ice (i.e., iceberg) fluxes. To predict potential ice sheet‐ocean‐climate feedbacks, we must know the partitioning of freshwater fluxes from Greenland, including the conversion of icebergs to liquid (i.e., meltwater) fluxes within glacial fjords. Here we use repeat ~0.5 m‐resolution satellite images from two major fjords to provide the first observation‐based estimates of the meltwater flux from the dense matrix of floating ice called mélange. We find that because of its expansive submerged area (>100 km2) and rapid melt rate (~0.1–0.8 m d−1), the ice mélange meltwater flux can exceed that from glacier surface and submarine melting. Our findings suggest that iceberg melt within the fjords must be taken into account in studies of glacial fjord circulation and the impact of Greenland melt on the ocean.

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Quantifying flow regimes in a Greenland glacial fjord using iceberg drifters

Cited by 48 publications

References 60 publications

Dynamics of Greenland�s glacial fjords

Dynamics of Greenland�s glacial fjords

Bergy Bit and Melt Water Trajectories in Godthåbsfjord (SW Greenland) Observed by the Expendable Ice Tracker

Iceberg meltwater fluxes dominate the freshwater budget in Greenland's iceberg‐congested glacial fjords

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