On the seasonal freshwater stratification in the proximity of fast‐flowing tidewater outlet glaciers in a sub‐Arctic sill fjord

Mortensen, John; Bendtsen, Jørgen; Motyka, R. J.; Lennert, Kunuk; Truffer, Martin; Fahnestock, M. A.; Rysgaard, Søren

doi:10.1002/jgrc.20134

Cited by 130 publications

(233 citation statements)

References 18 publications

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“…The lack of a fresh surface layer in the February profile means that the plume reaches the surface more easily, while use of the September profile produces only very minor differences relative to the default 5 August profile (Figs 7c-g). Observations by Mortensen and others (2013) suggest that the fresh surface layer is well established by late June and that the August profile is therefore likely representative of the stratification for much of the summer. In May and early June, it is possible that the fresh surface layer is absent (Mortensen and others, 2013); however, our modelling suggests that this makes it easier for a plume to reach the surface, thus lowering the critical discharge needed for the plume to reach the fjord surface and strengthening our conclusions regarding the distributed nature of subglacial discharge.…”

Section: Sensitivitiesmentioning

confidence: 99%

“…Observations by Mortensen and others (2013) suggest that the fresh surface layer is well established by late June and that the August profile is therefore likely representative of the stratification for much of the summer. In May and early June, it is possible that the fresh surface layer is absent (Mortensen and others, 2013); however, our modelling suggests that this makes it easier for a plume to reach the surface, thus lowering the critical discharge needed for the plume to reach the fjord surface and strengthening our conclusions regarding the distributed nature of subglacial discharge. In summary, our analysis suggests that seasonal changes in stratification do not affect our conclusions.…”

Section: Sensitivitiesmentioning

confidence: 99%

“…In our plume modelling, we use ambient fjord conditions sampled on 5 August 2009 (Figs 3c, d) ∼35 km from the terminus of KNS (Mortensen and others, 2013). The significant distance from the terminus means that the stratification at the calving front could differ from the profile we use; dense ice mélange prevented detailed surveying of the fjord closer to the terminus.…”

Section: Sensitivitiesmentioning

confidence: 99%

“…The significant distance from the terminus means that the stratification at the calving front could differ from the profile we use; dense ice mélange prevented detailed surveying of the fjord closer to the terminus. The ambient fjord conditions also show a seasonal evolution with a freshening of water close to the surface during the summer months (Mortensen and others, 2013). To test how plume dynamics respond to seasonal changes in fjord stratification, we ran BPT with ambient profiles from 8 February and 15 September 2009 (Figs 7a, b).…”

Section: Sensitivitiesmentioning

confidence: 99%

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Spatially distributed runoff at the grounding line of a large Greenlandic tidewater glacier inferred from plume modelling

et al. 2017

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ABSTRACT. Understanding the drivers of recent change at Greenlandic tidewater glaciers is of great importance if we are to predict how these glaciers will respond to climatic warming. A poorly constrained component of tidewater glacier processes is the near-terminus subglacial hydrology. Here we present a novel method for constraining near-terminus subglacial hydrology with application to marine-terminating Kangiata Nunata Sermia in South-west Greenland. By simulating proglacial plume dynamics using buoyant plume theory and a general circulation model, we assess the critical subglacial discharge, if delivered through a single compact channel, required to generate a plume that reaches the fjord surface. We then compare catchment runoff to a time series of plume visibility acquired from a time-lapse camera. We identify extended periods throughout the 2009 melt season where catchment runoff significantly exceeds the discharge required for a plume to reach the fjord surface, yet we observe no plume. We attribute these observations to spatial spreading of runoff across the grounding line. Persistent distributed drainage near the terminus would lead to more spatially homogeneous submarine melting and may promote more rapid basal sliding during warmer summers, potentially providing a mechanism independent of ocean forcing for increases in atmospheric temperature to drive tidewater glacier acceleration.

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Section: Sensitivitiesmentioning

confidence: 99%

Section: Sensitivitiesmentioning

confidence: 99%

Section: Sensitivitiesmentioning

confidence: 99%

Section: Sensitivitiesmentioning

confidence: 99%

See 2 more Smart Citations

Spatially distributed runoff at the grounding line of a large Greenlandic tidewater glacier inferred from plume modelling

et al. 2017

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“…To isolate which water body is driving subaqueous melt, we calculate the temperature and salinity loss due to the melting of glacier ice with reference to the Gade-slope (Gade, 1979;Holland and Jenkins, 1999;Mortensen et al, 2013;Straneo et al, 2011. Given a potential temperature for glacier ice (θ i ) at the front, we define an effective potential temperature (θ eff ) of the corresponding virtual water type by calculating the energy required to melt a unit weight of ice as follows:…”

Section: Identification Of Interaction Processesmentioning

confidence: 99%

Ice–ocean interaction and calving front morphology at two west Greenland tidewater outlet glaciers

et al. 2014

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Abstract. Warm, subtropical-originating Atlantic water (AW) has been identified as a primary driver of mass loss across the marine sectors of the Greenland Ice Sheet (GrIS), yet the specific processes by which this water mass interacts with and erodes the calving front of tidewater glaciers is frequently modelled and much speculated upon but remains largely unobserved. We present a suite of fjord salinity, temperature, turbidity versus depth casts along with glacial runoff estimation from Rink and Store glaciers, two major marine outlets draining the western sector of the GrIS during 2009 and 2010. We characterise the main water bodies present and interpret their interaction with their respective calving fronts. We identify two distinct processes of iceocean interaction which have distinct spatial and temporal footprints: (1) homogenous free convective melting which occurs across the calving front where AW is in direct contact with the ice mass, and (2) localised upwelling-driven melt by turbulent subglacial runoff mixing with fjord water which occurs at distinct injection points across the calving front. Throughout the study, AW at 2.8 ± 0.2 • C was consistently observed in contact with both glaciers below 450 m depth, yielding homogenous, free convective submarine melting up to ∼ 200 m depth. Above this bottom layer, multiple interactions are identified, primarily controlled by the rate of subglacial fresh-water discharge which results in localised and discrete upwelling plumes. In the record melt year of 2010, the Store Glacier calving face was dominated by these runoff-driven plumes which led to a highly crenulated frontal geometry characterised by large embayments at the subglacial portals separated by headlands which are dominated by calving. Rink Glacier, which is significantly deeper than Store has a larger proportion of its submerged calving face exposed to AW, which results in a uniform, relatively flat overall frontal geometry.

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Ice-dammed lake drainage cools and raises surface salinities in a tidewater outlet glacier fjord, west Greenland

Kjeldsen

Mortensen

Bendtsen

et al. 2014

J. Geophys. Res. Earth Surf.

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The drainage of ice-dammed lakes in the form of outburst floods in Greenland is detected regularly by remote sensing, and these events are expected to occur more frequently in a warmer climate. However, their impact on ice sheet stability and neighboring water bodies is still unknown. In this interdisciplinary study, we investigate lake drainages from the Greenland Ice Sheet into a west Greenland fjord by analyzing simultaneous time series of satellite observations and direct hydrographic measurements of temperature and salinity in the fjord. Satellite images show that, in general, lake drainages have occurred quasiperiodically during the last decade. A particular sequence of drainage events was observed by satellite in 2009 and was analyzed together with the first direct hydrographic observations. Signs of ice-dammed lake drainages were observed by a downstream mooring located just below the intertidal zone. The release of freshwater occurred at the fjord subsurface at a tidewater outlet glacier. The downstream in-water sequence of property changes in relation to these drainage events was observed as an almost immediate decrease in surface layer temperature (~2°C) followed within a week by the arrival of a high-saline pulse (~+5 units) with elevated salinity lasting for several days during the passage. During lake drainages, large amounts of relatively warm and saline intermediate water are brought to the near-surface layers by entrainment processes near the glacier front, and this influences the hydrography of the fjord but also impacts the ecosystem through upwelling of nutrient-rich intermediate water.

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On the seasonal freshwater stratification in the proximity of fast‐flowing tidewater outlet glaciers in a sub‐Arctic sill fjord

Cited by 130 publications

References 18 publications

Spatially distributed runoff at the grounding line of a large Greenlandic tidewater glacier inferred from plume modelling

Spatially distributed runoff at the grounding line of a large Greenlandic tidewater glacier inferred from plume modelling

Ice–ocean interaction and calving front morphology at two west Greenland tidewater outlet glaciers

Ice-dammed lake drainage cools and raises surface salinities in a tidewater outlet glacier fjord, west Greenland

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