Subglacial discharge‐driven renewal of tidewater glacier fjords

Carroll, Dustin; Sutherland, David A.; Nash, Jonathan D.; Catania, G. A.; Stearns, L. A.

doi:10.1002/2017jc012962

Cited by 74 publications

(112 citation statements)

References 91 publications

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“…UMI features a 210‐m down‐fjord sill extending slightly above the grounding line depth. While warm water inflows would persist here absent of external forcing, recent MITgcm simulations find that seasonal subglacial discharge draws deep Atlantic water over shallow sills even for glaciers grounded below the sill depth (Carroll et al, ).…”

Section: Discussionmentioning

confidence: 99%

Reconciling Drivers of Seasonal Terminus Advance and Retreat at 13 Central West Greenland Tidewater Glaciers

et al. 2018

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The majority of Greenland tidewater glaciers undergo a seasonal cycle in terminus position, characterized by wintertime advance and summertime retreat. Understanding mechanisms that control seasonal cycles can help elucidate how tidewater glaciers regulate dynamic ice loss on longer timescales. However, controls on terminus position are numerous and complex. To address this, we compare time series of satellite‐derived terminus positions for tidewater glaciers in central west Greenland with observations of environmental forcings, including runoff at the grounding line, mélange presence, and, where available, ocean temperature in the proglacial fjord. We show that for most glaciers, seasonal terminus positions are more sensitive to glacial runoff than mélange or ocean thermal forcing. The strength of this relationship differs for two end‐member glacier types in the region, defined by their terminus geometry and dominant calving style. First, we find a strong relationship between magnitudes of runoff and terminus retreat at tidewater glaciers with shallow grounding lines (<400 m) that calve primarily through small‐magnitude serac failures. At these glaciers, subglacial plumes drive submarine melt and locally enhance retreat, causing heterogeneous position change across the terminus and local embayments where seasonal terminus changes are largest. In contrast, deep termini susceptible to buoyant flexure retreat sporadically through full ice thickness calving events less dependent on runoff. While less common, these glaciers deliver larger ice fluxes to the ocean. With predicted surface melt increases and diminished mélange coverage in a warming climate, our results reveal the impact of environmental forcings on diverse tidewater glacier systems in the region.

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Section: Discussionmentioning

confidence: 99%

Reconciling Drivers of Seasonal Terminus Advance and Retreat at 13 Central West Greenland Tidewater Glaciers

et al. 2018

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“…It is likely that CTWs are a major mechanism for exchange in broad fjords in general. The summertime observations of CTWs in SE Greenland Inall et al () and West Spitsbergen Inall et al () indicate that they are not a winter‐specific phenomenon, while the results of Carroll et al () indicate that they can be generated by sill‐tide interactions. While the strong, along‐shelf winds characteristic of SE Greenland in winter are a trigger for CTW driven exchange, this is not a necessary condition and we thus anticipate this behavior in broad fjords elsewhere.…”

Section: Discussionmentioning

confidence: 99%

Influence of Barrier Wind Forcing on Heat Delivery Toward the Greenland Ice Sheet

Fraser

Inall

2018

JGR Oceans

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A high‐resolution numerical hydrodynamic model of Kangerdlugssuaq Fjord and the adjacent southeast Greenland shelf region was constructed in order to investigate the dynamics of fjord‐shelf exchange. Recent studies have suggested that rapid exchange flows, driven by along‐shelf barrier wind events, are the dominant agent of exchange between fjord and shelf. These events are prone to occur during the winter, when freshwater forcing is minimal and observations of the fjord interior are scarce. Subglacial freshwater discharge was held at zero, so that any buoyancy‐driven overturning circulation was driven by melting alone. The model described a geostrophically balanced background flow transporting water masses between the fjord mouth and the glacier terminus, indicating that rotational effects are of order‐one importance. Barrier wind events were found to trigger coastally trapped internal wave activity within fjord, temporarily enhancing exchange and vertical mixing, and causing warm water to oscillate in the along‐fjord direction. These internal waves were also found to enhance the background flow via Stokes' drift. Heat delivery through the fjord mouth was smaller than that recorded in summer observations, however the system is more effective at delivering this heat to the head of the fjord. There exists the potential for wintertime melting at the ice‐ocean interface to be significant to the same order as summertime melting.

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“…One of the key questions is how hydrographic changes observed at the entrance of a fjord are transmitted through the fjord system to the glacier terminus (Mortensen et al, ). Models of conceptual fjord systems show a strong impact of warm coastal water on glacier dynamics (e.g., Carroll et al, ). However, validation of these conceptually modeled fjord systems is often lacking as seasonal observations from fjords in Greenland are sparse, and only a few fjord systems have been studied extensively year‐round, for example, Young Sound (Boone et al, ; Rysgaard & Glud, ), Godthåbsfjord (Mortensen et al, , ), Sermilik, and Kangerlussuaq Fjords (Jackson et al, ).…”

Section: Introductionmentioning

confidence: 99%

Local Coastal Water Masses Control Heat Levels in a West Greenland Tidewater Outlet Glacier Fjord

et al. 2018

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Fjords form the gateway between the open ocean and the Greenland Ice Sheet (GIS) and consequently play a crucial role for the stability of the Ice Sheet. Hydrographic observations, especially with seasonal resolution, from these fjords are limited making it difficult to assess linkages between the fjord, coastal water masses, and freshwater discharge from GIS. Here we present a decade‐long monthly hydrographic time series from a southwest Greenland fjord in direct contact with GIS. Our observations reveal significant temporal and spatial water mass variations related to coastal, glacial, and atmospheric dynamics. During winter, the fjord circulation is dominated by seasonal dense coastal inflows and the timing of these inflows determines intermediate and deepwater temperatures. During summer, runoff from GIS leads to a pronounced freshening of the fjord. In general, the fjord's seasonal circulation system damps the seasonal variation in temperature in the fjord. This leads to a seasonal temperature range in the intermediate layer in the inner part of the fjord that is half the observed range at the fjord entrance. Changes in mean water temperatures in the intermediate layer seem predominantly linked to local coastal water masses, where cold winter/warm summer events decrease/increase the mean water temperatures. Consequently, these events play an important role in heat transport toward glacier termini.

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Subglacial discharge‐driven renewal of tidewater glacier fjords

Cited by 74 publications

References 91 publications

Reconciling Drivers of Seasonal Terminus Advance and Retreat at 13 Central West Greenland Tidewater Glaciers

Reconciling Drivers of Seasonal Terminus Advance and Retreat at 13 Central West Greenland Tidewater Glaciers

Influence of Barrier Wind Forcing on Heat Delivery Toward the Greenland Ice Sheet

Local Coastal Water Masses Control Heat Levels in a West Greenland Tidewater Outlet Glacier Fjord

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