Firn cold content evolution at nine sites on the Greenland ice sheet between 1998 and 2017

Vandecrux, Baptiste; Fausto, Robert S.; As, Dirk van; Colgan, William; Langen, Peter L.; Haubner, Konstanze; Ingeman‐Nielsen, Thomas; Heilig, Achim; Stevens, C. Max; MacFerrin, Michael; Niwano, Michio; Steffen, Konrad; Box, Jason E.

doi:10.1017/jog.2020.30

Cited by 36 publications

(51 citation statements)

References 62 publications

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“…These results therefore emphasize the importance of adequate spin-up and assessment of the effects of snowpack spin-up in producing and using SMB in Antarctica. Vandecrux et al (2020b) found that the Fixed version smoothes the firn density profiles, when compared to the dynamical version; this is confirmed by our results. One of the criteria for the dynamical version is that it prefers to merge layers deeper than 5 m of water equivalent, meaning that the top 5 m w.e.…”

Section: Discussionsupporting

confidence: 90%

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Downscaled surface mass balance in Antarctica: impacts of subsurface processes and large-scale atmospheric circulation

Hansen¹,

Langen²,

Boberg³

et al. 2021

The Cryosphere

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Abstract. Antarctic surface mass balance (SMB) is largely determined by precipitation over the continent and subject to regional climate variability related to the Southern Annular Mode (SAM) and other climatic drivers at the large scale. Locally however, firn and snowpack processes are important in determining SMB and the total mass balance of Antarctica and global sea level. Here, we examine factors that influence Antarctic SMB and attempt to reconcile the outcome with estimates for total mass balance determined from the GRACE satellites. This is done by having the regional climate model HIRHAM5 forcing two versions of an offline subsurface model, to estimate Antarctic ice sheet (AIS) SMB from 1980 to 2017. The Lagrangian subsurface model estimates Antarctic SMB of 2473.5±114.4 Gt yr−1, while the Eulerian subsurface model variant results in slightly higher modelled SMB of 2564.8±113.7 Gt yr−1. The majority of this difference in modelled SMB is due to melt and refreezing over ice shelves and demonstrates the importance of firn modelling in areas with substantial melt. Both the Eulerian and the Lagrangian SMB estimates are within uncertainty ranges of each other and within the range of other SMB studies. However, the Lagrangian version has better statistics when modelling the densities. Further, analysis of the relationship between SMB in individual drainage basins and the SAM is carried out using a bootstrapping approach. This shows a robust relationship between SAM and SMB in half of the basins (13 out of 27). In general, when SAM is positive there is a lower SMB over the plateau and a higher SMB on the westerly side of the Antarctic Peninsula, and vice versa when the SAM is negative. Finally, we compare the modelled SMB to GRACE data by subtracting the solid ice discharge, and we find that there is a good agreement in East Antarctica but large disagreements over the Antarctic Peninsula. There is a large difference between published estimates of discharge that make it challenging to use mass reconciliation in evaluating SMB models on the basin scale.

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Section: Discussionsupporting

confidence: 90%

“…The second model version uses a Lagrangian framework for the layer evolution developed by Vandecrux et al (2018Vandecrux et al ( , 2020a. Layers evolve through a splitting and merg-4318 N. Hansen et al: Reconciling different drivers of surface mass balance in Antarctica ing dynamic based on a number of weighted criteria.…”

Section: Subsurface Modelmentioning

confidence: 99%

Downscaled surface mass balance in Antarctica: impacts of subsurface processes and large-scale atmospheric circulation

Hansen¹,

Langen²,

Boberg³

et al. 2021

The Cryosphere

Self Cite

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“…While the field observations of preferential percolation depths are limited and from transects much lower in the percolation zone 10,30-32 , breakthrough percolation has been observed in firn as cold as −10°C and around 2 m ahead of the wetting front 10 . Given these observations, firn temperature measurements from the early 2000s at the NASA-SE GCNet site 33,34 and the 2016 GreenTRACS traverse 15,35 suggest that meltwater percolation to depths of up to 2 m during the melt season could be possible on these transects. Altogether, in the central and eastern segments of each transect, the observed densification (0.05-0.1 g cm −3 ) is most consistent with additional refreezing within thin (<0.1 m) layers sometime during the 2013 melt season.…”

Section: Resultsmentioning

confidence: 91%

Extreme melt season ice layers reduce firn permeability across Greenland

2021

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Surface meltwater runoff dominates present-day mass loss from the Greenland Ice Sheet. In Greenland’s interior, porous firn can limit runoff by retaining meltwater unless perched low-permeability horizons, such as ice slabs, develop and restrict percolation. Recent observations suggest that such horizons might develop rapidly during extreme melt seasons. Here we present radar sounding evidence that an extensive near surface melt layer formed following the extreme melt season in 2012. This layer was still present in 2017 in regions up to 700 m higher in elevation and 160 km further inland than known ice slabs. We find that melt layer formation is driven by local, short-timescale thermal and hydrologic processes in addition to mean climate state. These melt layers reduce vertical percolation pathways, and, under appropriate firn temperature and surface melt conditions, encourage further ice aggregation at their horizon. Therefore, the frequency of extreme melt seasons relative to the rate at which pore space and cold content regenerates above the most recent melt layer may be a key determinant of the firn’s multi-year response to surface melt.

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“…The most recent estimates of Arctic freshwater sources and sinks have been developed by Østerhus et al (2019), Haine et al (2015), Prowse et al (2015), Carmack et al (2016), and Vihma et al (2016). Only Østerhus et al (2019) covers a more recent period through 2015.…”

Section: Changes In Arctic Freshwater Sources and Sinksmentioning

confidence: 99%

Freshwater in the Arctic Ocean 2010–2019

Solomon

Heuzé²,

Rabe

et al. 2021

Ocean Sci.

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Abstract. The Arctic climate system is rapidly transitioning into a new regime with a reduction in the extent of sea ice, enhanced mixing in the ocean and atmosphere, and thus enhanced coupling within the ocean–ice–atmosphere system; these physical changes are leading to ecosystem changes in the Arctic Ocean. In this review paper, we assess one of the critically important aspects of this new regime, the variability of Arctic freshwater, which plays a fundamental role in the Arctic climate system by impacting ocean stratification and sea ice formation or melt. Liquid and solid freshwater exports also affect the global climate system, notably by impacting the global ocean overturning circulation. We assess how freshwater budgets have changed relative to the 2000–2010 period. We include discussions of processes such as poleward atmospheric moisture transport, runoff from the Greenland Ice Sheet and Arctic glaciers, the role of snow on sea ice, and vertical redistribution. Notably, sea ice cover has become more seasonal and more mobile; the mass loss of the Greenland Ice Sheet increased in the 2010s (particularly in the western, northern, and southern regions) and imported warm, salty Atlantic waters have shoaled. During 2000–2010, the Arctic Oscillation and moisture transport into the Arctic are in-phase and have a positive trend. This cyclonic atmospheric circulation pattern forces reduced freshwater content on the Atlantic–Eurasian side of the Arctic Ocean and freshwater gains in the Beaufort Gyre. We show that the trend in Arctic freshwater content in the 2010s has stabilized relative to the 2000s, potentially due to an increased compensation between a freshening of the Beaufort Gyre and a reduction in freshwater in the rest of the Arctic Ocean. However, large inter-model spread across the ocean reanalyses and uncertainty in the observations used in this study prevent a definitive conclusion about the degree of this compensation.

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Firn cold content evolution at nine sites on the Greenland ice sheet between 1998 and 2017

Cited by 36 publications

References 62 publications

Downscaled surface mass balance in Antarctica: impacts of subsurface processes and large-scale atmospheric circulation

Downscaled surface mass balance in Antarctica: impacts of subsurface processes and large-scale atmospheric circulation

Extreme melt season ice layers reduce firn permeability across Greenland

Freshwater in the Arctic Ocean 2010–2019

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