Interruption of two decades of Jakobshavn Isbrae acceleration and thinning as regional ocean cools

Khazendar, A.; Fenty, Ian; Carroll, Dustin; Gardner, Alex; Lee, Craig M.; Fukumori, Ichiro; Wang, Ou; Zhang, Hong; Seroussi, Hélène; Möller, D.; Noël, Brice; Broeke, M. R. van den; Dinardo, S. J.; Willis, Josh

doi:10.1038/s41561-019-0329-3

Cited by 119 publications

(169 citation statements)

References 64 publications

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“…Contrary to this, Godthåbsfjord experienced distinct high temperatures in 2010 (Mortensen et al, 2018). Where Khazendar et al (2019) attribute cooling of the regional heat source (i.e., dSPMW) to a slowdown and thickening of Jakobshavn Isbrae in Disko Bay, our observations suggest that a more voluminous BBPW in Disko Bay may be responsible for the cooling by squeezing dSPMW to a deeper depth range.…”

Section: Interannual Variationcontrasting

confidence: 78%

An Updated View on Water Masses on the pan‐West Greenland Continental Shelf and Their Link to Proglacial Fjords

et al. 2020

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The accelerated melt of the Greenland Ice Sheet has been linked to a sudden increase in the presence of warm subsurface coastal water in west Greenland. Yet pathways of warm coastal water along the entire west Greenland coast have remained largely unstudied. Here we present the first, near‐synoptic hydrographic observations at both the continental slope and fjord entrances of the west Greenland coastal system from Cape Farewell (59°N) to Melville Bay (75°N) in summer 2016. We observed a distinct north‐south division in the water mass distribution in west Greenland, approximately partitioned by the northern part of Davis Strait, and a division between the continental slope and fjord entrances. Waters from the regional southern freshwater source with origin in the East Greenland Current that rounds Cape Farewell are not observed to enter Baffin Bay. The regional heat source transported by the West Greenland Current is blocked by Southwest Greenland Coastal Water in the south but the deep connections in the north allow warm deep Subpolar Mode Water to enter fjords. Furthermore, we observed cold and relative saline Baffin Bay Polar Water over the inner part of the banks, periodically reaching as far south as 64°N, suggesting the presence of an undescribed southward current at the Southwest Greenland continental shelf.

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Section: Interannual Variationcontrasting

confidence: 78%

An Updated View on Water Masses on the pan‐West Greenland Continental Shelf and Their Link to Proglacial Fjords

et al. 2020

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“…The record is sparser for 2016, but it is sufficient to indicate that increased thickening occurred during the winter of 2016-17 as the ice tongue advanced and the glacier slowed. As a result, just prior to the summer speedup in 2017, the terminus region was ~35 meter higher than the previous summer (see also Khazendar et al, 2019). Winter thickening continued to outpace summer thinning 195 so that by March 2019, surface elevations near the terminus were only 10 to 20 m lower than those observed during spring of 2011.…”

Section: Elevationmentioning

confidence: 95%

“…With this slowdown, the terminus region transitioned from ~15 m/yr of net annual thinning to ~15 m/yr of thickening (Khazendar et al, 2019). This slowdown coincided with a period of increased surface mass balance and cooler atmospheric and ocean temperatures Khazendar et al, 2019;Mouginot et al, 2019). While it is clear that seasonal variation modulates Jakobshavn Isbrae's flow speed, the causal links to underlying atmospheric and oceanic forcing remain poorly understood.…”

mentioning

confidence: 99%

A Decade of Variability on Jakobshavn Isbrae: Ocean Temperatures Pace Speed Through Influence on Mélange Rigidity

Joughin¹,

Shean²,

Smith³

et al. 2019

Preprint

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Abstract. The speed of Greenland’s fastest glacier, Jakobshavn Isbrae, has varied substantially since its speedup in the late 1990s. Here we present observations of surface velocity, mélange rigidity, and surface elevation to examine its behaviour over the last decade. Consistent with earlier results, we find a pronounced cycle of summer speedup and thinning followed by winter slowdown and thickening. There were extended periods of rigid mélange in the winters of 2016–17 and 2017–18, concurrent with terminus advances ~ 6 km farther than in the several winters prior. These terminus advances to shallower depths caused slowdowns, leading to substantial thickening, as has been noted elsewhere. The extended periods of rigid mélange coincide well with a period of cooler waters in Disko Bay. Thus, along with the relative timing of the seasonal slowdown, our results suggest that the ocean’s dominant influence on Jakobshavn Isbrae is through its effect on winter mélange rigidity, rather than summer submarine melting. The elevation time series also reveals that in summers when the area upstream of the terminus approaches flotation, large surface depressions can form, which eventually become the detachment points for major calving events. It appears that as elevations near flotation, basal crevasses can form, which initiates a necking process that forms the depressions. The elevation data also show that steep cliffs often evolve into short floating extensions, rather than collapsing catastrophically due to brittle failure. Finally, summer 2019 speeds are slightly faster than the prior two summers, leaving it unclear whether the slowdown is ending.

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“…For example, benthic foraminiferal data from Disko Bay in western Greenland show a close correlation between Jakobshavn Isbrae terminus positions over the last 100 years and subsurface ocean temperatures (Lloyd et al, ). Further, modern observations indicate widespread terminus retreat and thinning occurring when climate conditions promote elevated submarine melt rates (Catania et al, ; Holland et al, ; Rignot et al, ; Straneo & Heimbach, ) and slowing and thickening occurring when subsurface ocean waters cool (Khazendar et al, ). However, no simple relationship exists between ocean and ice that is shared across glacier‐fjord systems in Greenland (Slater et al, ; Straneo et al, ).…”

Section: Controls On Outlet Glacier Dynamicsmentioning

confidence: 99%

Future Evolution of Greenland's Marine‐Terminating Outlet Glaciers

et al. 2020

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Mass loss from the Greenland ice sheet (GrIS) has increased over the last two decades in response to changes in global climate, motivating the scientific community to question how the GrIS will contribute to sea‐level rise on timescales that are relevant to coastal communities. Observations also indicate that the impact of a melting GrIS extends beyond sea‐level rise, including changes to ocean properties and circulation, nutrient and sediment cycling, and ecosystem function. Unfortunately, despite the rapid growth of interest in GrIS mass loss and its impacts, we still lack the ability to confidently predict the rate of future mass loss and the full impacts of this mass loss on the globe. Uncertainty in GrIS mass loss projections in part stems from the nonlinear response of the ice sheet to climate forcing, with many processes at play that influence how mass is lost. This is particularly true for outlet glaciers in Greenland that terminate in the ocean because their flow is strongly controlled by multiple processes that alter their boundary conditions at the ice‐atmosphere, ice‐ocean, and ice‐bed interfaces. Many of these processes change on a range of overlapping timescales and are challenging to observe, making them difficult to understand and thus missing in prognostic ice sheet/climate models. For example, recent (beginning in the late 1990s) mass loss via outlet glaciers has been attributed primarily to changing ice‐ocean interactions, driven by both oceanic and atmospheric warming, but the exact mechanisms controlling the onset of glacier retreat and the processes that regulate the amount of retreat remain uncertain. Here we review the progress in understanding GrIS outlet glacier sensitivity to climate change, how mass loss has changed over time, and how our understanding has evolved as observational capacity expanded. Although many processes are far better understood than they were even a decade ago, fundamental gaps in our understanding of certain processes remain. These gaps impede our ability to understand past changes in dynamics and to make more accurate mass loss projections under future climate change. As such, there is a pressing need for (1) improved, long‐term observations at the ice‐ocean and ice‐bed boundaries, (2) more observationally constrained numerical ice flow models that are coupled to atmosphere and ocean models, and (3) continued development of a collaborative and interdisciplinary scientific community.

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Interruption of two decades of Jakobshavn Isbrae acceleration and thinning as regional ocean cools

Cited by 119 publications

References 64 publications

An Updated View on Water Masses on the pan‐West Greenland Continental Shelf and Their Link to Proglacial Fjords

An Updated View on Water Masses on the pan‐West Greenland Continental Shelf and Their Link to Proglacial Fjords

A Decade of Variability on Jakobshavn Isbrae: Ocean Temperatures Pace Speed Through Influence on Mélange Rigidity

Future Evolution of Greenland's Marine‐Terminating Outlet Glaciers

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