Southeast Greenland Research Articles

Firn aquifer water discharges into crevasses across Southeast Greenland

AbstractIn Southeast Greenland, summer melt and high winter snowfall rates give rise to firn aquifers: vast stores of meltwater buried beneath the ice-sheet surface. Previous detailed studies of a single Greenland firn aquifer site suggest that the water drains into crevasses, but this is not known at a regional scale. We develop and use a tool in Ghub, an online gateway of shared datasets, tools and supercomputing resources for glaciology, to identify crevasses from elevation data collected by NASA's Airborne Topographic Mapper across 29000 km2of Southeast Greenland. We find crevasses within 3 km of the previously mapped downglacier boundary of the firn aquifer at 20 of 25 flightline crossings. Our data suggest that crevasses widen until they reach the downglacier boundary of the firn aquifer, implying that crevasses collect firn-aquifer water, but we did not find this trend with statistical significance. The median crevasse width, 27 meters, implies an aspect ratio consistent with the crevasses reaching the bed. Our results support the idea that most water in Southeast Greenland firn aquifers drains through crevasses. Less common fates are discharge at the ice-sheet surface (3 of 25 sites) and refreezing at the aquifer bottom (1 of 25 sites).

Aeromagnetic expression of the central Nagssugtoqidian Orogen, South-East Greenland

The Paleoproterozoic Nagssugtoqidian Orogen is one of the principal tectonic features related to the assembly of Nuna, extending across Greenland from east to west and forming an orogenic belt separating the North Atlantic Craton on the south from the Rae Craton on the north. In South-East Greenland, the Ammassalik Intrusive Complex (AIC) (∼1910 to 1870 Ma) occupies the central part of the orogenic belt, was formed by subduction- and magmatic arc-related processes, and has significant potential for undiscovered deposits of critical minerals. Previous interpretations of aeromagnetic data have been hindered by terrain effects, and we use a novel mix of geophysical analysis tools to develop new tectonomagmatic interpretations of the central Nagssugtoqidian Orogen in South-East Greenland. These interpretations extend into areas covered by ocean and ice. Results show that Archean rocks of the juxtaposed North Atlantic (Isertoq Terrane) and Rae (Kuummiut Terrane) Cratons are relatively weakly magnetized (with the exception of rocks of the Schweizerland Terrane) and have a NW-striking structural fabric that likely formed or was enhanced during the Nagssugtoqidian Orogeny. The AIC is structurally complex, with weakly magnetized metasedimentary rocks, and both weakly and strongly magnetized intrusions, arrayed in a NW-striking tectonic fabric. The strongly magnetized intrusions are largely concealed and distributed in a broader and more spatially complex fashion than previously known, suggesting that additional areas may be considered for mineral exploration. Strongly magnetized NW-striking dikes are imaged within the AIC, where they are spatially closely related to the strongly magnetized intrusions, and extend southward into the North Atlantic Craton (Isertoq Terrane). This spatial pattern of arc magmatism is consistent with previously developed models of SW-directed subduction that preceded collision during the Nagssugtoqidian Orogeny. The strongly magnetized Ammassalik Batholith (∼1670 Ma) and related intrusions form a cluster of plutons within ∼ 50 km of the Nagssugtoqidian suture. Their tectonomagmatic setting is unknown, although are speculatively related to delamination of a lithospheric keel formed during the Nagssugtoqidian Orogeny ∼ 200 m.y. prior. Numerous strongly magnetized NNE-striking Paleogene dikes, related to the opening of the Atlantic Ocean, are imaged cutting most other geologic units.

Atlantic water intrusion triggers rapid retreat and regime change at previously stable Greenland glacier

Ice discharge from Greenland’s marine-terminating glaciers contributes to half of all mass loss from the ice sheet, with numerous mechanisms proposed to explain their retreat. Here, we examine K.I.V Steenstrups Nordre Bræ (‘Steenstrup’) in Southeast Greenland, which, between 2018 and 2021, retreated ~7 km, thinned ~20%, doubled in discharge, and accelerated ~300%. This rate of change is unprecedented amongst Greenland’s glaciers and now places Steenstrup in the top 10% of glaciers by contribution to ice-sheet-wide discharge. In contrast to expected behaviour from a shallow, grounded tidewater glacier, Steenstrup was insensitive to high surface temperatures that destabilised many regional glaciers in 2016, appearing instead to respond to a >2 °C anomaly in deeper Atlantic water (AW) in 2018. By 2021, a rigid proglacial mélange had developed alongside notable seasonal variability. Steenstrup’s behaviour highlights that even long-term stable glaciers with high sills are vulnerable to sudden and rapid retreat from warm AW intrusion.

Corrigendum: Precipitation trends (1958–2021) on Ammassalik island, south-east Greenland

Corrigendum: Precipitation trends (1958–2021) on Ammassalik island, south-east Greenland* Correspondence: jorrit.van-der-schot@uni-graz.at Keywords: same as original articleCorrigendum on: van der Schot J, Abermann J, Silva T, Jensen CD, Noël B and Schöner W (2023), Precipitation trends (1958–2021) on Ammassalik island, south-east Greenland. Front. Earth Sci. 10:1085499. doi: 10.3389/feart.2022.1085499Incorrect Funding In the published article, there was an error in the Funding statement. The financial support of the University of Graz was not addressed. The original text was: “This research has been conducted as part of the Snow2Rain research project, which has been funded by the Earth System Sciences (ESS) research programme of the ÖAW, the Austrian Academy of Sciences.”. The correct Funding statement appears below.FUNDINGThis research has been conducted as part of the Snow2Rain research project, which has been funded by the Earth System Sciences (ESS) research programme of the ÖAW, the Austrian Academy of Sciences. The authors acknowledge the financial support by the University of Graz. The authors apologize for this error and state that this does not change the scientific conclusions of the article in any way. The original article has been updated.

Mechanisms of Heat Flux Across the Southern Greenland Continental Shelf in 1/10° and 1/12° Ocean/Sea Ice Simulations

AbstractThe presence of warm Atlantic water on the Greenland continental shelf has been connected to the accelerated melting of the Greenland Ice Sheet, particularly in the southwest and southeast shelf regions. Results from two high‐resolution coupled ocean‐sea ice simulations that utilized either the 1/10° Parallel Ocean Program (POP) or the 1/12° HYbrid Coordinate Ocean Model (HYCOM) are used to understand the flux of heat on and off the southern Greenland shelf. The analysis reveals that the region of greatest heat flux onto the shelf is southeast Greenland. On the southwestern shelf, heat is mainly exported from the shelf to the interior basins. We identify differences in the shelf break current structure and on‐shelf heat content between the two simulations. Just south of the Denmark Strait, there is a seasonally persistent pattern of multi‐day variability in the cross‐shelf heat flux in both simulations. In the POP simulation, this high‐frequency signal results in net on‐shore heat flux. In the HYCOM simulation, the signal is weaker and results in net off‐shelf heat flux. This variability is consistent with Denmark Strait Overflow eddies traveling along the shelf break.

Pressure-Temperature history of the 1.9 Ga Nagssugtoqidian Orogeny in the Tasiilaq Region, South-East Greenland: Amphibolite facies metamorphism of a Palaeoproterozoic accretionary prism

Pressure-Temperature history of the 1.9 Ga Nagssugtoqidian Orogeny in the Tasiilaq Region, South-East Greenland: Amphibolite facies metamorphism of a Palaeoproterozoic accretionary prism

Deep ocean circulation in the subpolar North Atlantic observed by acoustically-tracked floats

The deep circulation in the subpolar North Atlantic determines the spread and mixing of high latitude climate signals to lower latitudes. However, our current understanding of the subpolar deep circulation has been limited due to relatively sparse observational data. To improve that understanding, we construct gridded fields of mean velocity and eddy kinetic energy (EKE) in the deep (1800–2800 dbar) subpolar North Atlantic using direct velocity measurements from 122 subsurface acoustically-tracked floats that drifted during June 2014–January 2019. The mean velocity field reveals a relatively strong deep boundary current around Greenland and in the Labrador Sea, with a weaker deep boundary current over the eastern flank of the Reykjanes Ridge, and near-zero mean flow over the western flank, implying a discontinuous deep boundary current across the subpolar basin. The deep EKE, albeit with smaller magnitudes, generally resembles the EKE pattern at the ocean surface, including relatively high values along pathways of the North Atlantic Current and west of Greenland where the Irminger Rings are formed. A surprising finding about deep EKE is an elevated band east of Greenland that parallels the coast and is not present in the surface EKE field. This high EKE band is possibly attributed to the combined influence from propagating Denmark Strait Overflow Cyclones, variability of the wind-driven recirculation offshore of southeast Greenland, and/or topographic waves. The float-based flow fields constructed in this study provide an unprecedented quantitative view of the kinematic properties of the large-scale deep circulation in the subpolar North Atlantic. Combined with cross-basin Eulerian measurements, we believe these recent observations provide a benchmark for testing and improving numerical simulations of deep ocean circulation and the Meridional Overturning Circulation, which are urgently needed for climate change predictions.

The vertical atmospheric structure of the partially glacierised Mittivakkat valley, southeast Greenland

Air temperature inversions, a situation in which atmospheric temperature increases with height, are key components of the Arctic planetary boundary layer. The present study investigates the spatial and temporal variations of temperature inversions over different surface types (rock, gravel, snow, ice) along the Mittivakkat valley (southeast Greenland). For this purpose, 113 vertical profiles with high spatio-temporal resolution of air temperature and relative humidity were collected with unoccupied aerial vehicles (UAVs) during a 13-day field campaign in summer 2019. Air temperature inversions were present in 83% of the profiles, of which 24% were surface-based inversions and 76% were elevated inversions. The proglacial area covered with bare rock and gravel induces surface heating and convection during the day and, through interaction with local circulation patterns, leads to the frequent formation of elevated inversions. In contrast, the glacier surface itself acts as a persistent cooling surface and leads to the formation of surface-based inversions. A low-level fog layer that forms under the inversion layer may be causing non-linear vertical ablation gradients on Mittivakkat Gletsjer. Furthermore, we demonstrate that atmospheric measurements using UAVs can better capture small-scale processes than other products like radiosonde or modeled reanalysis data.

Precipitation trends (1958–2021) on Ammassalik island, south-east Greenland

Along with Arctic warming, climate models project a strong increase in Arctic precipitation in the 21st century as well as an increase in the ratio of liquid to total precipitation. In the precipitation-rich region of south-east Greenland, precipitation changes could locally have significant impacts on runoff. However, climate data are sparse in this remote region. This study focuses on improving our understanding of the past precipitation changes on Ammassalik island in south-east Greenland between 1958 and 2021. To assess past changes in air temperature at 2-meter and precipitation, output from a regional polar climate model (RACMO2.3p2) is evaluated with measurements from automatic weather stations in Tasiilaq and on Mittivakkat glacier. In addition, RACMO2.3p2 is used to assess past seasonal changes in air temperature at 2-meter, precipitation amount, precipitation phase and the altitude of the rain/snow boundary. We find that the climate model accurately represents the monthly average observed air temperature at 2-meter. While total precipitation is overestimated, interannual variability of precipitation is properly captured. We report a significant increase of summer temperature at 2-meter of +0.3°C/decade (p<0.01) at Mittivakkat glacier and +0.2°C/decade (p<0.01) in Tasiilaq in 1958–2021. For the subperiod 1990–2019, the trend in annual averages of temperature at 2-meter in Tasiilaq (+0.8°C/decade, p=0.02) corresponds well to known temperature trends on the Greenland Ice Sheet within the same period. On Mittivakkat glacier a significant trend is not detected within this subperiod (+0.2°C/decade, p=0.25). The modelled liquid precipitation ratio on Ammassalik island increased in all summer months (1958–2015) by +2.0/+1.9/+1.8%/decade in June/July/August respectively. In July and August, these trends were stronger at higher elevations. No statistical evidence is found for trends in other seasons. We also identify monthly increases in the altitude of the rain-to-snow boundary (+25/+23/+20 m/decade in July/August/September respectively).

GRACE and mass budget method reveal decelerated ice loss in east Greenland in the past decade

Excellent progress has been made in characterizing and understanding ice loss in Greenland, but most existing studies used a constant model to describe the long-term trend, preventing a detailed and rigorous understanding of change in the trend. Moreover, the impacts of atmospheric forcing on the trend of ice mass change are not clear. To address these limitations, we propose a piecewise trajectory model to detect the breaking points in the trend of ice mass change and estimate the optimal segmented trends. A breaking point located around 2012.6 was detected in the CW, SW, NE, SE, and the whole Greenland based on Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-on (FO) data and the mass budget method (MBM). Piecewise trend estimates from both methods suggest that the ice loss decelerated dramatically in east Greenland in 2012.6–2021 compared to 2002–2012.6. The GRACE results indicate that the mass loss rate decelerated by 70% (22.1 ± 0.8 to 6.6 ± 1.0 Gt/yr) in the NE and 38% (89.0 ± 1.5 to 55.4 ± 0.7 Gt/yr) in the SE. Though the rates slightly increased in some regions, the Greenland ice loss rate overall decreased from 269.9 ± 1.8 Gt/yr to 217.0 ± 3.3 Gt/yr. Mass budget analysis suggests that this deceleration was mainly caused by increased precipitation in east Greenland, which was associated with persistent positive North Atlantic Oscillation (NAO) phase in 2013–2021. During this positive NAO period, the enhanced westerlies and low-pressure anomaly off southeast Greenland advected more wet warm air to east Greenland and thus caused more precipitation. As the NAO exhibited a strong positive trend in this century, if it persists into the future, precipitation will have a high chance to increase in east Greenland, benefitting Greenland retaining ice.

Increased oceanic dimethyl sulfide emissions in areas of sea ice retreat inferred from a Greenland ice core

Ocean phytoplankton are an important source of dimethyl sulfide, which influences marine cloud formation. Model studies suggest that declines in Arctic sea ice may lead to increased dimethyl sulfide emissions, however observational support is lacking. Here, we present a 55-year high-resolution ice core record of methane sulfonic acid flux, an oxidation product of dimethyl sulfide, from the southeast Greenland Ice Sheet. We infer temporal variations in ocean dimethyl sulfide emissions and find that springtime (April–June) fluxes of methane sulfonic acid correlate well with satellite-derived chlorophyll-a concentration in the Irminger Sea. Summertime (July–September) methane sulfonic acid fluxes were 3 to 6 times higher between 2002–2014 than 1972–2001. We attribute this to sea ice retreat day becoming earlier and a coincident increase in chlorophyll-a concentration in the adjacent open coastal waters.

Geological processes defining the formation of plumasite-type corundum in the Paleoproterozoic Isertoq Terrane, South-East Greenland

Plumasite-type corundum occurrences in the Nattivit area in South-East Greenland offer a unique opportunity to study corundum formation in-situ where pegmatites intruded into metamorphosed lherzolite and dunite of the Archean-Paleoproterozoic continental crust. The Nattivit area, located in the Isertoq Terrane of North Atlantic Craton, forms part of the overriding plate during convergence of the Nagssugtoqidian orogen (1910-1840 Ma). New field observations and elemental and isotopic geochemical analysis provide further insights in the history of crustal convergence, its exhumation and how corundum was formed. The continental crust in the area consists of metamorphosed mafic to ultramafic rocks and tonalite-trondhjemite-granodiorite (TTG) gneisses, where the mafic rocks in the Isertoq Terrane yield a εNd TDM model age of 3000–2800 Ma. Dunite and lherzolite sills/dikes intruded the mafic rocks before the intrusion of the TTG sheets. The intrusion ages for the TTG obtained from zircon U-Pb geochronology are 2818 ± 8 Ma, 2760 ± 13 Ma to 2667 ± 7 Ma. U-Pb zircon data, zircon textures and Th/U ratios indicate metamorphism occurred at 2698 ± 7 Ma to 2629 ± 11 Ma, 2500–2400 Ma and 1900–1600 Ma. Whole rock geochemical data of mafic to ultramafic rocks show a continental arc affinity, with negative Ta, Nb and positive Pb anomalies. A metasomatic event at 2390 ± 70 Ma partly reset the isotopic signature in the mafic to ultramafic rocks. A marked absence of ages between 2350 and 2100 Ma in the TTG zircon age populations exists, indicating a period with minimal magmatic and/or metamorphic activity. The metamorphic mineral assemblages of the schist, amphibolite, ultramafic rocks and metasomatic reaction zones in ultramafic rocks indicate upper to medium–high amphibolite facies conditions. Kyanite in the metasomatic reaction zones in ultramafic rocks indicate the higher end of the temperature and pressure range above 4.2–10 kbar and 530–800 °C, similar to estimates from dolerite dikes in the Kitak area. The syn-tectonic pegmatites with an intrusion age of 1843 ± 4 Ma formed corundum. The new data indicate that the pegmatite melt/fluid and the geotectonic setting are defining factors for generating plumasite-type corundum.

Evaluating the biosignature potential of nitrogen concentrations in graphite and associated K-silicates

The oldest remnants of life on Earth from various localities in the Isua supracrustal belt in Greenland date back to >3.7 billion years ago (Ga). They are in the form of graphite, whose biogenicity is controversial. Previous studies used the presence and isotopic composition of nitrogen in graphite from along the Isua belt to argue both for and against biogenicity. To determine if the nitrogen chemistry of graphite can indeed serve as a biosignature, we investigated a hydrothermal graphite deposit from south-east Greenland (1.87–1.82 Ga). We found indications that molar C/N ratios of hydrothermal graphite may be similar to those of biogenic graphite from the Archean rock record, meaning that the nitrogen content of graphite is itself perhaps not diagnostic of ancient life, requiring caution in future studies. However, the hydrothermal graphite deposit also revealed unusually low N concentrations in associated silicates, despite a wide range of K concentrations up to 5 wt%. Using a thermodynamic model of nitrogen speciation in the presence of graphite, paired with previously published partition coefficients for ammonium in K-silicates, we show that abiotic process can explain these low N-concentrations of around 1 μg/g in potassic silicates. Higher concentrations of >10 μg/g, such as those found in graphitic metapelites from the Isua supcracrustal belt, would, however, require an unusually ammonium-rich fluid. Such an ammonium-rich fluid is most easily derived from the breakdown of biomass within sediments prior to graphitization. We therefore conclude that potassic silicates associated with graphite can serve as an indirect biosignature. Our approach supports previous inferences of life on Earth back to at least 3.7 Ga.

A regime shift in the Southeast Greenland marine ecosystem.

Two major oceanographic changes have recently propagated through several trophic levels in coastal areas of Southeast Greenland (SEG). Firstly, the amount of drift-ice exported from the Fram Strait and transported with the East Greenland Current (EGC) has decreased significantly over the past two decades, and a main tipping element (summer sea ice) has virtually disappeared since 2003 leading to a regime shift in oceanographic and ecological conditions in the region. The following 20-year period with low or no coastal sea ice is unique in the 200-year history of ice observations in the region, and the regime shift is also obvious in the volume of ice export through the Fram Strait after 2013. In the same period, the temperature of the EGC south of 73.5N has increased significantly (>2°C) since 1980. Secondly, the warm Irminger Current, which advects warm, saline Atlantic Water into the region, has become warmer since 1990. The lack of pack ice in summer together with a warming ocean generated cascading effects on the ecosystem in SEG that are manifested in a changed fish fauna with an influx of boreal species in the south and the subarctic capelin further north. At higher trophic levels there has been an increase in the abundance of several boreal cetaceans (humpback, fin, killer, and pilot whales and dolphins) that are either new to this area or occur in historically large numbers. It is estimated that the new cetacean species in SEG are responsible for an annual predation level of 700,000 tons of fish. In addition, predation on krill species is estimated at >1,500,000 tons mainly consumed by fin whales. Simultaneously, there has been a reduction in the abundance and catches of narwhals and walruses in SEG and it is suggested that these species have been impacted by the habitat changes.

Development and validation of a modified QuEChERS method for extracting polychlorinated biphenyls and organochlorine pesticides from marine mammal blubber

The monitoring of legacy persistent organic pollutants (POPs) in blubber of key sentinel marine mammal species has been conducted using established techniques for decades. Although these methods for polychlorinated biphenyl (PCB) and organochlorine (OC) pesticide determination provide accurate and reproducible results, they possess some drawbacks in terms of cost, time, and a need for large volumes of toxic solvents. QuEChERS (quick, easy, cheap, effective, rugged, and safe) extractions may help address these issues, but have not been applied to marine mammal blubber/adipose. As such, our aim was to develop, validate, and apply a QuEChERS method for the extraction of PCB and OC contaminants in marine mammal blubber. First, we tested multiple solid-phase extraction and clean-up steps to find the approach that provided the cleanest extracts along with consistent and acceptable analyte recovery, accuracy, and precision. QuEChERS extractions followed by two enhanced matrix removal-lipid (EMR-lipid), one primary-secondary amine (PSA), and one silica gel clean-up showed the highest matrix removal and acceptable recoveries of spiked internal (62–97%) and external standards (61–94%). Solvent usage was reduced by ∼393% and extraction time was reduced by ∼25% (from 16 to 12 h). Next, the method was validated using standard reference material (SRM) NIST 1945. Recovery experiments on SRM (n = 5) showed acceptable recovery for 76% and 77% of PCBs and OC pesticides, respectively, and high precision for 73% and 69% of PCBs and OCs, respectively. Finally, the method was used on a set of southeast Greenland killer whales (n = 13), with previously published PCB and OC data. Bland-Altman plots indicated good agreement between QuEChERS and current-use methods for ΣPCBs and some OCs with no significant constant or proportional bias. These results demonstrate that this QuEChERS extraction method represents an effective, lower cost alternative to current-use extractions for PCBs and OCs in blubber, and likely other high-lipid samples.

Long time series of absolute gravity observations in Kulusuk, southeast Greenland

AbstractThis report contains terrestrial absolute gravity measurements performed near the village of Kulusuk in southeast Greenland. It represents an exceptionally long time series of nearly two decades. The measurements began in July 1996 until July 2015. The station is located a few meters beside a permanent GNSS station. The final gravity values (g‐values), more precisely the accelerations due to gravity, are listed along their associated uncertainties. A description of the station, a short explanation on the absolute gravimeter, and the data processing are presented.

Subinertial Variability in Four Southeast Greenland Fjords in Realistic Numerical Simulations

AbstractWe identified the nature and driving mechanisms of subinertial variability (variability at a time scale of several days) in four fjords in Southeast Greenland, in three high‐resolution numerical simulations. We find two dominant frequency ranges in along‐fjord velocity, volume transport of Atlantic Water, and along‐fjord heat transport: one around 2–4 days and one around 10 days. The higher frequency is most prominent in the two smaller fjords (Sermilik Fjord and Kangerdlugssuaq Fjord), while the lower frequency peak dominates in the larger fjords (Scoresby Sund and King Oscar Fjord). The cross‐fjord structure of variability patterns is determined by the fjord's dynamic width, while the vertical structure is determined by the stratification in the fjord. The dominant frequency range is a function of stratification and fjord length, through the travel time of resonant internal Kelvin waves. We find that the subinertial variability is the imprint of Coastal Trapped Waves, which manifest as Rossby‐type waves on the continental shelf and as internal Kelvin‐type waves inside the fjords. Between 50% and 80% of the variability in the fjord is directly forced by Coastal Trapped Waves propagating in from the shelf, with an additional role played by alongshore wind forcing on the shelf.

Pigment signatures of algal communities and their implications for glacier surface darkening

Blooms of pigmented algae darken the surface of glaciers and ice sheets, thereby enhancing solar energy absorption and amplifying ice and snow melt. The impacts of algal pigment and community composition on surface darkening are still poorly understood. Here, we characterise glacier ice and snow algal pigment signatures on snow and bare ice surfaces and study their role in photophysiology and energy absorption on three glaciers in Southeast Greenland. Purpurogallin and astaxanthin esters dominated the glacier ice and snow algal pigment pools (mass ratios to chlorophyll a of 32 and 56, respectively). Algal biomass and pigments impacted chromophoric dissolved organic matter concentrations. Despite the effective absorption of astaxanthin esters at wavelengths where incoming irradiance peaks, the cellular energy absorption of snow algae was 95% lower than anticipated from their pigmentation, due to pigment packaging. The energy absorption of glacier ice algae was consequently ~ 5 × higher. On bare ice, snow algae may have locally contributed up to 13% to total biological radiative forcing, despite contributing 44% to total biomass. Our results give new insights into the impact of algal community composition on bare ice energy absorption and biomass accumulation during snow melt.

Hydrologic modeling of a perennial firn aquifer in southeast Greenland

AbstractA conceptual model, based on field observations and assumed physics of a perennial firn aquifer near Helheim Glacier (southeast Greenland), is evaluated via steady-state 2-D simulation of liquid water flow and energy transport with phase change. The simulation approach allows natural representation of flow and energy advection and conduction that occur in vertical meltwater recharge through the unsaturated zone and in lateral flow within the saturated aquifer. Agreement between measured and simulated aquifer geometry, temperature, and recharge and discharge rates confirms that the conceptual field-data-based description of the aquifer is consistent with the primary physical processes of groundwater flow, energy transport and phase change. Factors that are found to control simulated aquifer configuration include surface temperature, meltwater recharge rate, residual total-water saturation and capillary fringe thickness. Simulation analyses indicate that the size of perennial firn aquifers depends primarily on recharge rates from surface snowmelt. Results also imply that the recent aquifer expansion, likely due to a warming climate, may eventually produce lakes on the ice-sheet surface that would affect the surface energy balance.

Expansion of Firn Aquifers in Southeast Greenland

AbstractSurface melt produces more mass loss than any other process on the Greenland Ice Sheet. In some regions of Greenland with high summer surface melt and high winter snow accumulation, the warm porous firn of the percolation zone can retain liquid meltwater through the winter. These regions of water‐saturated firn, which may persist for longer than one year, are known as firn aquifers, commonly referred to as perennial firn aquifers. Here, we use airborne ice‐penetrating radar data from the Center for Remote Sensing of Ice Sheets (CReSIS) to document the extent of four firn aquifers in the Helheim, Ikertivaq, and Køge Bugt glacier basins with more than six repeat radar flight lines from 1993 to 2018. All four firn aquifers first appear and/or show decadal‐scale inland expansion during this time period. Through an idealized energy‐balance calculation utilizing reanalysis data from the Modèle Atmosphérique Régionale (MAR) regional climate model, we find that these aquifer expansions are driven by decreasing cold content in the firn since the late 1990s and recently increasing high‐melt years, which has reduced the firn's ability for refreezing local meltwater. High‐melt years are projected to increase on the Greenland Ice Sheet and may contribute to the continued inland expansion of firn aquifers, impacting the ice sheet's surface mass balance and hydrological controls on ice dynamics.