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Accurate estimates of surface mass balance over the Greenland ice sheet (GrIS) would contribute to understanding the cause of recent changes and would help to better estimate the future contribution of the GrIS to sea‐level rise. Given the limitations of in‐situ measurements, modeling, and remote sensing, it is critical to explore the opportunity to merge the available data to better characterize the spatial and temporal variation of the GrIS surface mass balance (SMB). This work utilizes a particle batch smoother data assimilation technique that yields SMB estimates that benefit from the snow model Crocus and a 16‐day albedo product derived from satellite remote sensing data. Comparison of the results against in‐situ SMB measurements shows that the assimilation of the albedo product reduces the root mean square error of the posterior estimates of SMB by 51% and reduces bias by 95%. Plain Language Summary: Greenland ice sheet (GrIS) is losing mass through ice discharge from outlet glaciers and surface processes (e.g., meltwater runoff, sublimation, and evaporation). Recent studies suggest that meltwater runoff will be the dominant mass loss process over the GrIS in the future as it will increase under climate warming. Accurate estimates of the GrIS surface mass balance (SMB) are a critical objective, which, despite its importance, continues to contain large uncertainties from significant errors in forcing data as well as model errors. This work uses a data assimilation framework (which has not been used in estimation of the GrIS SMB) and a satellite‐derived 16‐day albedo product to produce a reanalysis estimates of SMB along the Kangerlussuaq transect (K‐transect) stations in west Greenland. We used the K‐transect in‐situ SMB measurements to validate our results over the 2000–2014 hydrological year. The data assimilation technique (i.e., particle batch smoother) reduces the spatial root‐mean‐square error of SMB over the K‐transect stations by 51% from 858 millimeter water equivalent (mmWE) to 423 mmWE and the bias in the estimates by 95%, from −70 to 3.5 mmWE. It was shown that this methodology has the potential to resolve the spatial variability of the surface processes along the K‐transect stations and in particular of the bare ice surface albedo that is not resolved by the model at a resolution of 25 km (i.e., the model uses a constant bare ice albedo). The results suggest that the methodology can be applied over the entire GrIS using MODIS albedo observations to generate an improved reanalysis of SMB estimates. Key Points: A data assimilation method was used to generate a reanalysis estimates of the surface mass balance of the Greenland ice sheet along the K‐transect stationsA particle batch smoother technique was used to condition the prior estimates of surface mass balance on 16‐day MODIS albedoResults show that the assimilation of albedo reduces the root mean square error of the surface mass balance estimates by 51% [ABSTRACT FROM AUTHOR]

The article discusses a study which described the placement of Greenland ice sheet ablation measurements in a multi-decadal context. Topics covered include the purpose of the Programme for Monitoring of the Greenland Ice Sheet (PROMICE), the collection of observational records to determine the 1961-1990 reference climate and the measurements of ice ablation along the ice-sheet margin.

Intense rainfall events significantly affect Alpine and Alaskan glaciers through enhanced melting, ice-flow acceleration and subglacial sediment erosion, yet their impact on the Greenland ice sheet has not been assessed. Here we present measurements of ice velocity, subglacial water pressure and meteorological variables from the western margin of the Greenland ice sheet during a week of warm, wet cyclonic weather in late August and early September 2011. We find that extreme surface runoff from melt and rainfall led to a widespread acceleration in ice flow that extended 140 km into the ice-sheet interior. We suggest that the late-season timing was critical in promoting rapid runoff across an extensive bare ice surface that overwhelmed a subglacial hydrological system in transition to a less-efficient winter mode. Reanalysis data reveal that similar cyclonic weather conditions prevailed across southern and western Greenland during this time, and we observe a corresponding ice-flow response at all land- and marine-terminating glaciers in these regions for which data are available. Given that the advection of warm, moist air masses and rainfall over Greenland is expected to become more frequent in the coming decades, our findings portend a previously unforeseen vulnerability of the Greenland ice sheet to climate change. [ABSTRACT FROM AUTHOR]

Glacial/interglacial dynamics during the Quaternary were suggested to be mainly driven by obliquity (41-kyr periodicity), including irregularities during the last 1 Myr that resulted in on average 100-kyr cycles. Here, we investigate this so-called Mid-Pleistocene Transition via model-based deconvolution of benthic δ18O, redefining interglacials by lack of substantial northern hemispheric land ice outside of Greenland. We find that in 67%, 88% and 52% of the obliquity cycles during the early, middle and late Quaternary, respectively, a glacial termination is realized leading to irregular appearances of new interglacials during various parts of the last 2.6 Myr. This finding suggests that the proposed idea of terminations leading to new interglacials in the Quaternary as obliquity driven with growing influence of land ice volume on the timing of deglaciations during the last 1 Myr might be too simple. Alternatively, the land ice-based definition of interglacials needs revision if applied to the entire Quaternary. This study presents a new definition of interglacials during the Quaternary. The authors find the appearance of interglacials is in general following the 41-kyr cycle of obliquity with various exceptions, suggesting a more complex physical mechanism triggering glacial terminations. [ABSTRACT FROM AUTHOR]

We present twenty-three years (1993-2016) of automatic weather station (AWS) data, collected along the K-transect near Kangerlussuaq in west Greenland. The transect runs from east to west, roughly perpendicular to the ice sheet edge at about 67° N. The K-transect originated from the Greenland Ice Margin Experiments (GIMEX), held in the summers of 1990 and 1991. Until recently, surface mass balance and ice velocity measurements were performed at nine locations along the K-transect, of which four are equipped with AWS: two in the ablation zone at approximately 500 m and 1,000 m asl, one at the approximate equilibrium-line altitude (~1,500 m asl), and one in the lower accumulation zone (~1,850 m asl) at distances of 5, 38, 88, and 140 km from the ice edge, respectively. Here, we present an overview of the various AWS types and their data corrections, quality, and availability, including a preliminary trend analysis. Recent increases in temperature and radiation components are associated with the frequent occurrence of anti-cyclonic conditions in west Greenland, resulting in clear skies and relatively warm summers. Strong melt concurs with a decrease in winter accumulation, lowering the surface albedo of the ice sheet. The AWS situated at 1,500 m asl, the former equilibrium-line altitude (ELA), observed almost a doubling of the summertime net shortwave radiation since 2004; as a result, the ELA along the K-transect has been steadily increasing and is currently situated well above 1,700 m asl. [ABSTRACT FROM AUTHOR]

Over the past decade, ice loss from the Greenland Ice Sheet increased as a result of both increased surface melting and ice discharge to the ocean. The latter is controlled by the acceleration of ice flow and subsequent thinning of fast-flowing marine-terminating outlet glaciers. Quantifying the future dynamic contribution of such glaciers to sea-level rise (SLR) remains a major challenge because outlet glacier dynamics are poorly understood. Here we present a glacier flow model that includes a fully dynamic treatment of marine termini. We use this model to simulate behaviour of four major marine-terminating outlet glaciers, which collectively drain about 22 per cent of the Greenland Ice Sheet. Using atmospheric and oceanic forcing from a mid-range future warming scenario that predicts warming by 2.8 degrees Celsius by 2100, we project a contribution of 19 to 30 millimetres to SLR from these glaciers by 2200. This contribution is largely (80 per cent) dynamic in origin and is caused by several episodic retreats past overdeepenings in outlet glacier troughs. After initial increases, however, dynamic losses from these four outlets remain relatively constant and contribute to SLR individually at rates of about 0.01 to 0.06 millimetres per year. These rates correspond to ice fluxes that are less than twice those of the late 1990s, well below previous upper bounds. For a more extreme future warming scenario (warming by 4.5 degrees Celsius by 2100), the projected losses increase by more than 50 per cent, producing a cumulative SLR of 29 to 49 millimetres by 2200.