Seasonal variability in the dynamics of marine-terminating outlet glaciers in Greenland

Howat, I. M.; Box, Jason E.; Ahn, Y.; Herrington, Adam; McFadden, E. M.

doi:10.3189/002214310793146232

Cited by 219 publications

(341 citation statements)

References 37 publications

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“…For a number of stable tidewater glaciers in west Greenland, Howat et al [111] reached similar conclusions based on remote sensing of ice velocity 4-6 km from their termini. In stark contrast, Sugiyama et al [66] found a strong correlation between air temperature and ice velocity over two summers at lake-terminating Perito Moreno in Patagonia, indicative of a static hydrological system showing little seasonal evolution, and in which increases in surface melting consistently result in ice acceleration.…”

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

confidence: 58%

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

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

confidence: 58%

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

100

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“…This ice-mélange is believed to exert a small force that is sufficient in preventing the already almost detached vertical ice-lamellas at the calving face from topping over and breaking off and therefore acts to reduce calving rates . This effect provides a potential explanation of seasonal variations in calving rate (Joughin et al 2008a(Joughin et al , 2008cSohn et al 1998;Howat et al 2010;Reeh et al 2001). The fact that for Greenland the onset of spring terminus retreat is correlated well with the disintegration of the ice-mélange supports this mechanism, in particular as the onset is well before surface melt starts.…”

Section: Sea-ice and Ice-mélangementioning

confidence: 79%

“…3 the effect of enhanced basal lubrication by increased surface melting appears in the context of fast flowing outlet glaciers of secondary importance, although it may on short time scales still be significant (Howat et al 2010). The timescales of adjusting the drainge system at the base of a glacier to enhanced delivery of surface melt water are known to be extremely short (days to weeks) which means that enhanced surface melt may in the long-term not affect the flow much or even slow it down (Sundal et al 2011;Schoof 2010;Van de Wal et al 2008).…”

Section: Atmospheric Forcingmentioning

confidence: 99%

Understanding and Modelling Rapid Dynamic Changes of Tidewater Outlet Glaciers: Issues and Implications

Vieli¹,

Nick²

2011

The Earth's Cryosphere and Sea Level Change

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Recent dramatic acceleration, thinning and retreat of tidewater outlet glaciers in Greenland raises concern regarding their contribution to future sea-level rise. These dynamic changes seem to be parallel to oceanic and climatic warming but the linking mechanisms and forcings are poorly understood and, furthermore, large-scale ice sheet models are currently unable to realistically simulate such changes which provides a major limitation in our ability to predict dynamic mass losses. In this paper we apply a specifically designed numerical flowband model to Jakobshavn Isbrae (JIB), a major marine outlet glacier of the Greenland ice sheet, and we explore and discuss the basic concepts and emerging issues in our understanding and modelling ability of the dynamics of tidewater outlet glaciers. The modelling demonstrates that enhanced ocean melt is able to trigger the observed dynamic changes of JIB but it heavily relies on the feedback between calving and terminus retreat and therefore the loss of buttressing. Through the same feedback, other forcings such as reduced winter sea-ice duration can produce similar rapid retreat. This highlights the need for a robust representation of the calving process and for improvements in the understanding and implementation of forcings at the marine boundary in predictive ice sheet models. Furthermore, the modelling uncovers high sensitivity and rapid adjustment of marine outlet glaciers to perturbations at their marine boundary implying that care should be taken in interpreting or extrapolating such rapid dynamic changes as recently observed in Greenland.

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“…The removal of ice from Sermilik Fjord may explain why the sea ice cover in Sermilik Fjord is often mobile, even in winter. Further, it has been found that a dense ice cover (sea ice and icebergs) near outlet glaciers is important for the glacier stability [Amundson et al, 2010] and that reductions in the ice cover correlate with the glacier's retreat [Howat et al, 2010, Walter et al, 2012. Thus, DWE in Ammassalik and Sermilik Fjord could have an impact on the stability of Helheim…”

Section: Modis Visible Images During Individual Events and Analyze Ammentioning

confidence: 99%

“…The removal of sea ice, moreover, might not be confined to the shelf region but could extend into Sermilik Fjord, with possible effects on Helheim glacier, a large Greenland glacier that drains into Sermilik Fjord. In fact, several authors have found a connection between the movement of outlet glaciers and the existence of a dense sea ice and iceberg cover (ice mélange), which exerts a back pressure on the glacier and inhibits calving [Amundson et al, 2010, Howat et al, 2010, Walter et al, 2012. Thus, if downslope wind events remove the local sea ice cover in Sermilik Fjord, they could contribute to the destabilization of Helheim glacier.…”

Section: Introductionmentioning

confidence: 99%

Strong wind events across Greenland�s coast and their influence on the ice sheet, sea ice and ocean

Oltmanns¹

2015

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In winter, Greenland's coastline adjacent to the subpolar North Atlantic and Nordic Seas is characterized by a large land-sea temperature contrast. Therefore, winds across the coast advect air across a horizontal temperature gradient and can result in significant surface heat fluxes both over the ice sheet (during onshore winds) and over the ocean (during offshore winds). Despite their importance, these winds have not been investigated in detail, and this thesis includes the first comprehensive study of their characteristics, dynamics and impacts. Using an atmospheric reanalysis, observations from local weather stations, and remote sensing data, it is suggested that high-speed wind events across the coast are triggered by the superposition of an upper level potential vorticity anomaly on a stationary topographic Rossby wave over Greenland, and that they intensify through baroclinic instability. Onshore winds across Greenland's coast can result in increased melting, and offshore winds drive large heat losses over major ocean convection sites.Strong offshore winds across the southeast coast are unique over Greenland, because the flow is funneled from the vast ice sheet inland into the narrow valley of Ammassalik at the coast, where it can reach hurricane intensity. In this region, the cold air, which formed over the northern ice sheet, is suddenly released during intense downslope wind events and spills over the Irminger Sea where the cold and strong winds can drive heat fluxes of up to 1000 W m −2 , with potential implications for deep water formation. Moreover, the winds advect sea ice away from the coast and out of a major glacial fjord.Simulations of these wind events in Ammassalik with the atmospheric Weather Research and Forecast Model show that mountain wave dynamics contribute to the acceleration of the downslope flow. In order to capture these dynamics, a high model 3 resolution with a detailed topography is needed. The effects of using a different resolution locally in the valley extend far downstream over the Irminger Sea, which has implications for the evolution and distribution of the heat fluxes.

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Seasonal variability in the dynamics of marine-terminating outlet glaciers in Greenland

Cited by 219 publications

References 37 publications

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

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

Understanding and Modelling Rapid Dynamic Changes of Tidewater Outlet Glaciers: Issues and Implications

Strong wind events across Greenland�s coast and their influence on the ice sheet, sea ice and ocean

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