Significant contribution of small icebergs to the freshwater budget in Greenland fjords

Rezvanbehbahani, S.; Stearns, L. A.; Keramati, Ramtin; Shankar, S.; Veen, C. J. van der

doi:10.1038/s43247-020-00032-3

Cited by 20 publications

(31 citation statements)

References 26 publications

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“…The small contribution of subglacial discharge and direct glacier melt is supported by findings from other West Greenland fjords, which show that the majority of glacial modification takes place along the fjord -through, for example, iceberg melt -while direct melt from the glacier terminus and subglacial discharge are a small contributor (Mortensen et al, 2020;Muilwijk et al, 2021). Our model slightly underestimates the surface cooling and freshening, which we assume to be due to the exclusion of runoff to the surface of the fjord (Mernild et al, 2015), or possibly due to underestimated contribution from small icebergs by the power law size distribution (Rezvanbehbahani et al, 2020).…”

Section: Iceberg Modification In Ilulissat Icefjordmentioning

confidence: 84%

Impact of icebergs on the seasonal submarine melt of Sermeq Kujalleq

Kajanto,

Straneo,

Nisancioglu

2022

Preprint

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Abstract. The role of icebergs in narrow fjords hosting marine terminating glaciers in Greenland is poorly understood, even though icebergs provide a substantial freshwater flux that can exceed the subglacial discharge. Iceberg melt is distributed at depth, contributing to fjord stratification, thus impacting melt and dynamics of the glacier front. We model the high-silled Ilulissat Icefjord in Western Greenland with the MITgcm ocean model, using the IceBerg package to study the effect of icebergs on fjord properties, and compare our results with available observations from 2014. We find the subglacial discharge plume to be the primary driver of the seasonality of circulation, glacier melt and iceberg melt. Icebergs are necessary to include to correctly understand the properties of Ilulissat Icefjord, since they modify the fjord in three main ways: First, icebergs cool and freshen the water column within their vertical extent; Second, icebergs depress the neutral buoyancy depth of the plume and the outflow route of glacially modified water; Third, icebergs modify the deep basin, below their vertical extent, due to both increased entrainment of glacially modified water into the fjord, and iceberg modification of the incoming ambient water. Furthermore, the depressed neutral buoyancy depth of the plume limits melt to the deep section of the front of Sermeq Kujalleq (Jakobshavn Isbræ) even during peak summer, and thus promotes undercutting. We postulate that the impact of icebergs on the neutral buoyancy depth of the plume is a key mechanism connecting iceberg melange and glacier calving, independent of mechanical support.

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Section: Iceberg Modification In Ilulissat Icefjordmentioning

confidence: 84%

Impact of icebergs on the seasonal submarine melt of Sermeq Kujalleq

Kajanto,

Straneo,

Nisancioglu

2022

Preprint

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“…In separate simulations, we assign maximum iceberg keel depths of 50 m, 150 m, 250 m, 350 m and 450 m, whilst maintaining the c1 concentration and the -2 power law exponent. We then vary the size-frequency distribution power law exponent from -1.6 to -2.1 in increments of 0.1 (covering the range observed to date in Greenland's fjords (Rezvanbehbahani et al, 2020;Sulak et al, 2017)), whilst retaining the c1 concentration and the 300 m maximum keel depth.…”

Section: Iceberg-ocean Interactionmentioning

confidence: 99%

“…Several recent studies have identified icebergs as a substantial freshwater source in some of Greenland's fjords, with iceberg freshwater volumes comparable to or greater than ice sheet runoff (Enderlin et al, 2016(Enderlin et al, , 2018Jackson and Straneo, 2016;Moon et al, 2017;Moyer et al, 2019;Rezvanbehbahani et al, 2020). Furthermore, modelling of one of these fjords suggests that including the heat and salt fluxes https://doi.org/10.5194/tc-2021-323 Preprint.…”

Section: Introductionmentioning

confidence: 99%

“…associated with submarine iceberg melting increases greatly the model's ability to reproduce observed glacier-adjacent water properties (Davison et al, 2020). However, iceberg concentration, keel depth, and size-frequency distribution likely vary hugely between fjords as well as over time, though observations of icebergs at the fjord scale are sparse (Enderlin et al, 2016;Moyer et al, 2019;Rezvanbehbahani et al, 2020;Sulak et al, 2017). As such, it is likely that the effect of icebergs on glacier-adjacent water properties will also vary both spatially (i.e.…”

Section: Introductionmentioning

confidence: 99%

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Modelling the effect of submarine iceberg melting on glacier-adjacent water properties

Davison

Cowton

Sole

et al. 2021

Preprint

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Abstract. The rate of ocean-driven retreat of Greenland’s tidewater glaciers remains highly uncertain in predictions of future sea level rise, in part due to poorly constrained glacier-adjacent water properties. Icebergs and their meltwater contributions are likely important modifiers of fjord water properties, yet their effect is poorly understood. Here, we use a 3-D ocean circulation model, coupled to a submarine iceberg melt module, to investigate the effect of submarine iceberg melting on glacier-adjacent water properties in a range of idealised settings. Submarine iceberg melting can modify glacier-adjacent water properties in three principle ways: (1) substantial cooling and modest freshening in the upper ~50 m of the water column; (2) warming of Polar Water at intermediate depths due to iceberg melt-induced upwelling of warm Atlantic Water, and; (3) warming of the deeper Atlantic Water layer when vertical temperature gradients through this layer are steep (due to vertical mixing of warm water at depth), but cooling of the Atlantic Water layer when vertical temperature gradients are shallow. The overall effect of iceberg melt is to make glacier-adjacent water properties more uniform with depth. When icebergs extend to, or below, the depth of a sill at the fjord mouth, they can cause cooling throughout the entire water column. All of these effects are more pronounced in fjords with higher iceberg concentrations and deeper iceberg keel depths. These iceberg melt-induced changes to glacier-adjacent water properties will reduce rates of glacier submarine melting near the surface, but increase them in the Polar Water layer, and cause typically modest impacts in the Atlantic Water layer. These results characterise the important role of submarine iceberg melting in modifying ice sheet-ocean interaction, and highlight the need to improve representations of fjord processes in ice sheet-scale models.

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“…Tournadre and others, 2016; Sulak and others, 2017; Barbat and others, 2019; Neuhaus and others, 2019). Iceberg size distributions can yield a range of useful information: they provide insight on the fundamental processes driving iceberg calving (Benn and Åström, 2018; Cook and others, 2018); they can be useful for assessing iceberg risks to shipping and hydrocarbon infrastructure (Fuglem and others, 1996; Habib and others, 2016); iceberg size distributions have been shown to affect fresh water transport in global ocean models (Stern and others, 2016); and shifts in iceberg size distributions have the potential to alter the timing, magnitude and spatial distribution of ocean freshwater fluxes near glaciers and ice sheets (Enderlin and others, 2016; Rezvanbehbahani and others, 2020).…”

Section: Introductionmentioning

confidence: 99%

Fragmentation theory reveals processes controlling iceberg size distributions

et al. 2021

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Iceberg calving strongly controls glacier mass loss, but the fracture processes leading to iceberg formation are poorly understood due to the stochastic nature of calving. The size distributions of icebergs produced during the calving process can yield information on the processes driving calving and also affect the timing, magnitude, and spatial distribution of ocean fresh water fluxes near glaciers and ice sheets. In this study, we apply fragmentation theory to describe key calving behaviours, based on observational and modelling data from Greenland and Antarctica. In both regions, iceberg calving is dominated by elastic-brittle fracture processes, where distributions contain both exponential and power law components describing large-scale uncorrelated fracture and correlated branching fracture, respectively. Other size distributions can also be observed. For Antarctic icebergs, distributions change from elastic-brittle type during ‘stable’ calving to one dominated by grinding or crushing during ice shelf disintegration events. In Greenland, we find that iceberg fragment size distributions evolve from an initial elastic-brittle type distribution near the calving front, into a steeper grinding/crushing-type power law along-fjord. These results provide an entirely new framework for understanding controls on iceberg calving and how calving may react to climate forcing.

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Significant contribution of small icebergs to the freshwater budget in Greenland fjords

Cited by 20 publications

References 26 publications

Impact of icebergs on the seasonal submarine melt of Sermeq Kujalleq

Impact of icebergs on the seasonal submarine melt of Sermeq Kujalleq

Modelling the effect of submarine iceberg melting on glacier-adjacent water properties

Fragmentation theory reveals processes controlling iceberg size distributions

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