On the recent contribution of the Greenland ice sheet to sea level change

Abstract

Abstract. We assess the recent contribution of the Greenland ice sheet (GrIS) to sea level change. We use the mass budget method, which quantifies ice sheet mass balance (MB) as the difference between surface mass balance (SMB) and solid ice discharge across the grounding line (D). A comparison with independent gravity change observations from GRACE shows good agreement for the overlapping period 2002-2015, giving confidence in the partitioning of recent GrIS mass changes. The estimated 1995 value of D and the 1958-1995 average value of SMB are similar at 411 and 418 Gt yr −1 , respectively, suggesting that ice flow in the mid1990s was well adjusted to the average annual mass input, reminiscent of an ice sheet in approximate balance. Starting in the early to mid-1990s, SMB decreased while D increased, leading to quasi-persistent negative MB. About 60 % of the associated mass loss since 1991 is caused by changes in SMB and the remainder by D. The decrease in SMB is fully driven by an increase in surface melt and subsequent meltwater runoff, which is slightly compensated by a small (< 3 %) increase in snowfall. The excess runoff originates from lowlying (< 2000 m a.s.l.) parts of the ice sheet; higher up, increased refreezing prevents runoff of meltwater from occurring, at the expense of increased firn temperatures and depleted pore space. With a 1991-2015 average annual mass loss of ∼ 0.47 ± 0.23 mm sea level equivalent (SLE) and a peak contribution of 1.2 mm SLE in 2012, the GrIS has recently become a major source of global mean sea level rise.

Controls on rapid supraglacial lake drainage in West Greenland: an Exploratory Data Analysis approach

“…For the third and fourth aims of the research, we used the EDA branch of statistical analysis (Tukey, 1977) to explore the existing hypotheses of rapid lake drainage, to re-evaluate them in the context of the new dataset, and perhaps to suggest new ones that better explain the observations (Tukey, 1977). EDA contrasts with confirmatory analysis, which involves testing only specific hypotheses, and deterministic analysis, which involves formulating statistical models.…”

“…re-evaluate them with new data and perhaps to propose new hypotheses or to suggest future research directions (Tukey, 1977). The EDA focuses on two locations: the land-terminating Paakitsoq and the marine-terminating Store Glacier regions of West Greenland (Fig.…”

Projections of Future Sea Level Contributions from the Greenland and Antarctic Ice Sheets: Challenges Beyond Dynamical Ice Sheet Modeling

“…In contrast, SMB changes occur across the entire ice sheet and arise from surface processes (evaporation, surface melt, and accumulation). Although surface melting and meltwater runoff are increasingly large components of the Greenland Ice Sheet surface mass balance, they are limited to the margins in Antarctica Enderlin et al, 2014;van den Broeke et al, 2016).…”

Dynamic changes in outlet glaciers in northern Greenland from 1948 to 2015

“…Jakobshavn (Thomas et al, 2011), and Helheim and Kangerdlugssuaq in the south-east Luckman et al, 2006), linearly increasing temperatures after the 1990s increased thinning in the ablation zone, which reduced basal/lateral drag and instigated terminus retreat. In northern Greenland, it is likely that similar increased ice marginal thinning due to negative mass balance (van den Broeke et al, 2016;Khan et al, 2015;Pritchard et al, 2009), may have been the initial condition for increased glacier retreat rates and 20 feedbacks between retreat, acceleration and further dynamic thinning. Another subsequent feedback mechanism may have been surface melt induced hydrofracture, either through water filled crevasses (Benn et al, 2007;Nick et al, 2010), or supraglacial lake drainages through the full ice thickness (e.g.…”

“…Increased thinning rates have taken place in the ablation areas (< 2000 m elevation) around the GrIS since the 1990s (Abdalati 15 et al, 2001;van den Broeke et al, 2016;Krabill et al, 2000). At several glaciers, e.g.…”