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Papers by Jonathan Kingslake
Geophysical Research Letters
A primary question driving glaciological research today is: how much and how fast will global sea... more A primary question driving glaciological research today is: how much and how fast will global sea-level rise due to Antarctic Ice Sheet mass loss (Scambos et al., 2017)? The Amundsen Sea Embayment in West Antarctica has long been considered geometrically prone to collapse (Clarke & Lingle, 1977; Hughes, 1981). Thwaites Glacier (Figure 1), the largest glacier in the Amundsen Sea Embayment and the glacier projected to contribute the most to sea-level rise in West Antarctica beyond the next century, is likely in the early stages of this marine ice-sheet instability (Joughin et al., 2014; Rignot et al., 2014; Shepherd et al., 2012). The pacing of Thwaites Glacier retreat remains uncertain in part due to poorly constrained solutions for the parameters that control glacier sliding. Assumptions underlying the mechanics that define the boundary condition at the ice-bed interface affect the glacier's modeled response to ocean forcing, increasing glaciological sources of uncertainty in predictions of the West Antarctic Ice Sheet's contribution to sea level over decadal timescales (Brondex et al., 2019). To simulate catchment-scale glacier discharge and retreat, time-evolving prognostic ice-flow simulations must define the boundary condition at the ice-bed interface, usually as part of a diagnostic optimization experiment. It is customary to assume the velocity normal to the bed is zero-ice cannot penetrate the bed. The form of the friction law, also described as the sliding law, or sliding relation in the literature, is then typically defined to
Observations of near-surface firn density and ice layer stratigraphy collected on the Greenland i... more Observations of near-surface firn density and ice layer stratigraphy collected on the Greenland ice sheet are rare. This dataset contains information about twenty-four shallow firn cores drilled in the percolation zone in southwest Greenland between 2017 and 2019. Seven cores ranged between 2.9 and 6.3 meter (m) depth, with the remaining seventeen cores extending to 10–27 m depths. Each core has data on density, ice layer stratigraphy, and type of material (i.e. snow, firn, or ice). Quality control was performed on all data to replace erroneous data. More details including uncertainty analysis are provided in the method section and in Rennermalm et. al., (2021). The dataset includes the following files Core_meta_data.csv : File with metadata about each core, including location, site name, retrieval date, investigators, and other information Explanation_of_core_variables.csv : File with explanation of the variables reported in the core data files Core data files: For each core two fi...
AGU Fall Meeting Abstracts, Dec 1, 2020
AGU Fall Meeting Abstracts, Dec 15, 2020
AGU Fall Meeting Abstracts, Dec 1, 2019
<p>Rising sea levels in the 21<sup>st</sup... more <p>Rising sea levels in the 21<sup>st</sup> century threaten coastal communities with inundation, yet projecting the relative and global mean sea level response to climate warming is complex. Lack of contemporary analogues for future climate dynamics has turned attention to periods in the geologic past that can illuminate how Earth’s climate system reacts to temperature forcing. Recent evidence suggests the Antarctic and Greenland ice sheets may have retreated inland of their present-day extents during the mid-late Holocene (~8-3 ka), then readvanced until the pre-industrial. These findings have highlighted the utility of the mid-Holocene—when summer temperatures in the northern hemisphere may have neared 4 degrees hotter than preindustrial levels—as a partial analogue for future warming.</p><p>Here we present a new probabilistic estimate of mid-Holocene global mean sea level (GMSL). We construct an ensemble of global ice sheet reconstructions for the last 80 kyr that spans a range of possible mid-Holocene GMSL scenarios. We predict relative sea level from each model accounting for glacial isostatic adjustment and using a range of solid earth structures. We then compare these predictions to 10,733 postglacial sea-level indicators and weigh the GMSL curves from each ice model using data-model fits. The constraints placed on mid-Holocene global mean sea level clarify climate dynamics during this critical interval in Earth’s recent history, and enable new estimates of post-glacial Antarctic ice volume and the likelihood of mid-Holocene West Antarctic ice sheet readvance.</p><p> </p>
AGU Fall Meeting Abstracts, Dec 1, 2019
EGU General Assembly Conference Abstracts, Apr 1, 2018
The net rate of snow accumulation b is predicted to increase over large areas of the Antarctica a... more The net rate of snow accumulation b is predicted to increase over large areas of the Antarctica and Greenland ice sheets as the climate warms. Models disagree on how this will affect the thickness of the firn layer-the relatively low-density upper layer of the ice sheets that influences altimetric observations of ice-sheet mass change and paleo-climate reconstructions from ice cores. Here we examine how b influences firn compaction and porosity in a simplified model that accounts for mass conservation, dry firn compaction, grain size evolution, and the impact of grain size on firn compaction. Treating b as a boundary condition and employing an Eulerian reference frame helps to untangle the factors controlling the b-dependence of firn thickness. We present numerical simulations using the model as well as simplified steady-state approximations to the full model, to demonstrate how the downward advection of porosity and of grain size are both affected by b, but have opposing impacts on firn thickness. The net result is that firn thickness increases with b and that the strength of this dependence increases with the surface grain size. We also quantify the circumstances under which porosity-and grain-size-advection balance exactly, which counter-intuitively renders steady-state firn thickness independent of b. These findings are qualitatively independent of the stress-dependence of firn compaction and whether the thickness of the ice-sheet is increasing, decreasing, or steady. They do depend on the grain-size dependence of firn compaction. Firn models usually ignore grain-size evolution, but we highlight the complex effect it can have on firn thickness when included in a simplified model. This work motivates future efforts to better observationally constrain the rheological effect of grain size in firn. 1 Introduction Firn is snow that has persisted for at least one full year on the surface of a glacier or ice sheet. In the absence of significant surface melting, firn is transformed into glacial ice through dry firn compaction. As it is buried by subsequent snow fall, the vertical load of the overlying material compacts firn until it becomes glacial ice (e.g., Cuffey and Paterson, 2010). Understanding firn compaction is important for dating gases trapped in ice cores (e.g.
Journal of Glaciology, 2021
The influence of surface melt on the flow of Greenland's largest outlet glaciers remains poor... more The influence of surface melt on the flow of Greenland's largest outlet glaciers remains poorly known and in situ observations are few. We use field observations to link surface meltwater forcing to glacier-wide diurnal velocity variations on East Greenland's Helheim Glacier over two summer melt seasons. We observe diurnal variations in glacier speed that peak ~6.5 h after daily maximum insolation and extend from the terminus region to the equilibrium line. Both the amplitude of the diurnal speed variation and its sensitivity to daily melt are largest at the glacier terminus and decrease up-glacier, suggesting that the magnitude of the response is controlled not only by melt input volume and temporal variability, but also by background effective pressure, which approaches zero at the terminus. Our results provide evidence that basal lubrication by meltwater drives diurnal velocity variations at Greenland's marine-terminating glaciers in a similar manner to alpine glacier...
Journal of Glaciology, 2021
Refreezing of meltwater in firn is a major component of Greenland ice-sheet's mass budget, bu... more Refreezing of meltwater in firn is a major component of Greenland ice-sheet's mass budget, but in situ observations are rare. Here, we compare the firn density and total ice layer thickness in the upper 15 m of 19 new and 27 previously published firn cores drilled at 15 locations in southwest Greenland (1850–2360 m a.s.l.) between 1989 and 2019. At all sites, ice layer thickness covaries with density over time and space. At the two sites with the earliest observations (1989 and 1998), bulk density increased by 15–18%, in the top 15 m over 28 and 21 years, respectively. However, following the extreme melt in 2012, elevation-detrended density using 30 cores from all sites decreased by 15 kg m−3 a−1 in the top 3.75 m between 2013 and 2019. In contrast, the lowest elevation site's density shows no trend. Thus, temporary build-up in firn pore space and meltwater infiltration capacity is possible despite the long-term increase in Greenland ice-sheet melting.
Journal of Glaciology, 2021
Firn compaction models inform mass-balance estimates and paleo-climate reconstructions, but curre... more Firn compaction models inform mass-balance estimates and paleo-climate reconstructions, but current models introduce key uncertainties. For example, models disagree on the dependence of density and compaction on accumulation rate. Observations of compaction to test these models are rare, partly because in situ methods for measuring englacial strain are time-consuming and expensive. Moreover, shallow measurements may confound strain due to compaction with strain due to ice-sheet flow. We show that phase-sensitive radio-echo sounder (pRES) systems, typically deployed to measure sub-shelf melting or ice-sheet deformation, can be used to measure firn compaction and test firn models. We present two complementary methods for extracting compaction information from pRES data, along with a method for comparing compaction models to pRES observations. The methods make different assumptions about the density structure and vary in their need for independent density measurements. Compaction profi...
Geophysical Research Letters
A primary question driving glaciological research today is: how much and how fast will global sea... more A primary question driving glaciological research today is: how much and how fast will global sea-level rise due to Antarctic Ice Sheet mass loss (Scambos et al., 2017)? The Amundsen Sea Embayment in West Antarctica has long been considered geometrically prone to collapse (Clarke & Lingle, 1977; Hughes, 1981). Thwaites Glacier (Figure 1), the largest glacier in the Amundsen Sea Embayment and the glacier projected to contribute the most to sea-level rise in West Antarctica beyond the next century, is likely in the early stages of this marine ice-sheet instability (Joughin et al., 2014; Rignot et al., 2014; Shepherd et al., 2012). The pacing of Thwaites Glacier retreat remains uncertain in part due to poorly constrained solutions for the parameters that control glacier sliding. Assumptions underlying the mechanics that define the boundary condition at the ice-bed interface affect the glacier's modeled response to ocean forcing, increasing glaciological sources of uncertainty in predictions of the West Antarctic Ice Sheet's contribution to sea level over decadal timescales (Brondex et al., 2019). To simulate catchment-scale glacier discharge and retreat, time-evolving prognostic ice-flow simulations must define the boundary condition at the ice-bed interface, usually as part of a diagnostic optimization experiment. It is customary to assume the velocity normal to the bed is zero-ice cannot penetrate the bed. The form of the friction law, also described as the sliding law, or sliding relation in the literature, is then typically defined to
Observations of near-surface firn density and ice layer stratigraphy collected on the Greenland i... more Observations of near-surface firn density and ice layer stratigraphy collected on the Greenland ice sheet are rare. This dataset contains information about twenty-four shallow firn cores drilled in the percolation zone in southwest Greenland between 2017 and 2019. Seven cores ranged between 2.9 and 6.3 meter (m) depth, with the remaining seventeen cores extending to 10–27 m depths. Each core has data on density, ice layer stratigraphy, and type of material (i.e. snow, firn, or ice). Quality control was performed on all data to replace erroneous data. More details including uncertainty analysis are provided in the method section and in Rennermalm et. al., (2021). The dataset includes the following files Core_meta_data.csv : File with metadata about each core, including location, site name, retrieval date, investigators, and other information Explanation_of_core_variables.csv : File with explanation of the variables reported in the core data files Core data files: For each core two fi...
AGU Fall Meeting Abstracts, Dec 1, 2020
AGU Fall Meeting Abstracts, Dec 15, 2020
AGU Fall Meeting Abstracts, Dec 1, 2019
<p>Rising sea levels in the 21<sup>st</sup... more <p>Rising sea levels in the 21<sup>st</sup> century threaten coastal communities with inundation, yet projecting the relative and global mean sea level response to climate warming is complex. Lack of contemporary analogues for future climate dynamics has turned attention to periods in the geologic past that can illuminate how Earth’s climate system reacts to temperature forcing. Recent evidence suggests the Antarctic and Greenland ice sheets may have retreated inland of their present-day extents during the mid-late Holocene (~8-3 ka), then readvanced until the pre-industrial. These findings have highlighted the utility of the mid-Holocene—when summer temperatures in the northern hemisphere may have neared 4 degrees hotter than preindustrial levels—as a partial analogue for future warming.</p><p>Here we present a new probabilistic estimate of mid-Holocene global mean sea level (GMSL). We construct an ensemble of global ice sheet reconstructions for the last 80 kyr that spans a range of possible mid-Holocene GMSL scenarios. We predict relative sea level from each model accounting for glacial isostatic adjustment and using a range of solid earth structures. We then compare these predictions to 10,733 postglacial sea-level indicators and weigh the GMSL curves from each ice model using data-model fits. The constraints placed on mid-Holocene global mean sea level clarify climate dynamics during this critical interval in Earth’s recent history, and enable new estimates of post-glacial Antarctic ice volume and the likelihood of mid-Holocene West Antarctic ice sheet readvance.</p><p> </p>
AGU Fall Meeting Abstracts, Dec 1, 2019
EGU General Assembly Conference Abstracts, Apr 1, 2018
The net rate of snow accumulation b is predicted to increase over large areas of the Antarctica a... more The net rate of snow accumulation b is predicted to increase over large areas of the Antarctica and Greenland ice sheets as the climate warms. Models disagree on how this will affect the thickness of the firn layer-the relatively low-density upper layer of the ice sheets that influences altimetric observations of ice-sheet mass change and paleo-climate reconstructions from ice cores. Here we examine how b influences firn compaction and porosity in a simplified model that accounts for mass conservation, dry firn compaction, grain size evolution, and the impact of grain size on firn compaction. Treating b as a boundary condition and employing an Eulerian reference frame helps to untangle the factors controlling the b-dependence of firn thickness. We present numerical simulations using the model as well as simplified steady-state approximations to the full model, to demonstrate how the downward advection of porosity and of grain size are both affected by b, but have opposing impacts on firn thickness. The net result is that firn thickness increases with b and that the strength of this dependence increases with the surface grain size. We also quantify the circumstances under which porosity-and grain-size-advection balance exactly, which counter-intuitively renders steady-state firn thickness independent of b. These findings are qualitatively independent of the stress-dependence of firn compaction and whether the thickness of the ice-sheet is increasing, decreasing, or steady. They do depend on the grain-size dependence of firn compaction. Firn models usually ignore grain-size evolution, but we highlight the complex effect it can have on firn thickness when included in a simplified model. This work motivates future efforts to better observationally constrain the rheological effect of grain size in firn. 1 Introduction Firn is snow that has persisted for at least one full year on the surface of a glacier or ice sheet. In the absence of significant surface melting, firn is transformed into glacial ice through dry firn compaction. As it is buried by subsequent snow fall, the vertical load of the overlying material compacts firn until it becomes glacial ice (e.g., Cuffey and Paterson, 2010). Understanding firn compaction is important for dating gases trapped in ice cores (e.g.
Journal of Glaciology, 2021
The influence of surface melt on the flow of Greenland's largest outlet glaciers remains poor... more The influence of surface melt on the flow of Greenland's largest outlet glaciers remains poorly known and in situ observations are few. We use field observations to link surface meltwater forcing to glacier-wide diurnal velocity variations on East Greenland's Helheim Glacier over two summer melt seasons. We observe diurnal variations in glacier speed that peak ~6.5 h after daily maximum insolation and extend from the terminus region to the equilibrium line. Both the amplitude of the diurnal speed variation and its sensitivity to daily melt are largest at the glacier terminus and decrease up-glacier, suggesting that the magnitude of the response is controlled not only by melt input volume and temporal variability, but also by background effective pressure, which approaches zero at the terminus. Our results provide evidence that basal lubrication by meltwater drives diurnal velocity variations at Greenland's marine-terminating glaciers in a similar manner to alpine glacier...
Journal of Glaciology, 2021
Refreezing of meltwater in firn is a major component of Greenland ice-sheet's mass budget, bu... more Refreezing of meltwater in firn is a major component of Greenland ice-sheet's mass budget, but in situ observations are rare. Here, we compare the firn density and total ice layer thickness in the upper 15 m of 19 new and 27 previously published firn cores drilled at 15 locations in southwest Greenland (1850–2360 m a.s.l.) between 1989 and 2019. At all sites, ice layer thickness covaries with density over time and space. At the two sites with the earliest observations (1989 and 1998), bulk density increased by 15–18%, in the top 15 m over 28 and 21 years, respectively. However, following the extreme melt in 2012, elevation-detrended density using 30 cores from all sites decreased by 15 kg m−3 a−1 in the top 3.75 m between 2013 and 2019. In contrast, the lowest elevation site's density shows no trend. Thus, temporary build-up in firn pore space and meltwater infiltration capacity is possible despite the long-term increase in Greenland ice-sheet melting.
Journal of Glaciology, 2021
Firn compaction models inform mass-balance estimates and paleo-climate reconstructions, but curre... more Firn compaction models inform mass-balance estimates and paleo-climate reconstructions, but current models introduce key uncertainties. For example, models disagree on the dependence of density and compaction on accumulation rate. Observations of compaction to test these models are rare, partly because in situ methods for measuring englacial strain are time-consuming and expensive. Moreover, shallow measurements may confound strain due to compaction with strain due to ice-sheet flow. We show that phase-sensitive radio-echo sounder (pRES) systems, typically deployed to measure sub-shelf melting or ice-sheet deformation, can be used to measure firn compaction and test firn models. We present two complementary methods for extracting compaction information from pRES data, along with a method for comparing compaction models to pRES observations. The methods make different assumptions about the density structure and vary in their need for independent density measurements. Compaction profi...