Area Of Greenland Research Articles

Climate‐Driven Changes in Dissolved Organic Carbon and Water Clarity in Arctic Lakes of West Greenland

AbstractTo assess climate‐mediated terrestrial‐aquatic linkages in Arctic lakes and potential impacts on light attenuation and carbon cycling, we evaluated lake responses to climate drivers in two areas of west Greenland with differing climate patterns. We selected four lakes in a warmer, drier area to compare with four lakes from a cooler, wetter area proximal to the Greenland Ice Sheet. In June from 2013–2018, we measured epilimnetic water temperature, 1% depth of photosynthetically active radiation (PAR), dissolved organic carbon (DOC), specific ultraviolet absorbance (SUVA254), DOC‐normalized absorbance at 380 nm (a*380), and chlorophyll a. Interannual coherence of 1% PAR and DOC was particularly high for lakes within the warmer, drier area. This coherence suggests forcing of Arctic lake features by a large‐scale driver, likely climate. Redundancy analysis showed that monthly average precipitation, winter North Atlantic Oscillation (NAO) index (NAOW), spring average air temperature, and spring average precipitation influenced the lake variables (p = 0.003, adj. R2 = 0.58). In particular, monthly average precipitation contributed to increases in soil‐derived DOC quality metrics and chlorophyll a and decreased 1% PAR. Interannual changes in lake responses to climate drivers were more apparent in the warmer, drier area than the cooler, wetter area. The interannual lake responses within and between areas, associated with climate trends, suggest that with ongoing rapid climate change in the Arctic, there could be widespread impacts on key lake responses important for light attenuation and carbon cycling.

Tri Hita Karana-based green environment building management model

The development of tourism in Bali has a positive impact on improving people’s welfare and national economic development. This is followed by a negative impact on the environment in development activities, namely land use change and declining green land area, which in turn did not reflect sustainable development. Therefore, tourism development efforts must also be balanced with efforts to prevent negative impacts to maintain sustainability is and based on local cultural values. Green building environmental management is one aspect in the application of international standard, namely the Greenship issued by the Green Building Council Indonesia. The purpose of this study is to create green building environmental management model based on Tri Hita Karana, one of the local wisdoms of Balinese culture, consisting of Parahyangan, Pawongan and Palemahan. The study is conducted on several hotel buildings in Bali and using multiple linear regression tests. It shows that the application of environmental management aspects of green buildings had a significant effect of 75.3 percent on Palemahan, 20.2 percent on Pawongan and 5.1 percent on Parahyangan. The aspect of advanced waste management which is one of the aspects of environmental management of green buildings has the highest influence of 35.3 percent on Palemahan.

Polycyclic aromatic hydrocarbons in urban Greenland soils of Nanjing, China: concentration, distribution, sources and potential risks.

In order to better study the influence of land use on the concentration and distribution of organic contaminants in urban areas, the concentrations of 16 principal polycyclic aromatic hydrocarbons (PAHs) were determined on soil samples collected at three depths (0~10cm, 10~20cm and 20~30cm) from urban greenland areas of 6functional zones: residential zone (RZ), business zone (BZ), industrial zone (IZ), cultural and educational zone (CZ), urban park (UP) and urban rural forest (URF) of Nanjing, China. Results showed that the average concentration of ∑PAHs in the urban greenland of Nanjing (499.47ng/g) was comparable to the value reported for other cities under similar conditions. Acenaphthene was the dominant compound (46.2% of the ∑PAHs), and low molecular weight PAHs (LPAHs) represented the largest share of ∑PAHs. Concentrations of ∑PAHs in 6 function zones were different, with the highest value in IZ (954.33ng/g) and lowest value in URF (147.81ng/g). The soil showed the highest ∑PAHs contamination in the layer 10~20cm in all zones (on average 547.01ng/g). ∑PAHs of IZ showed the highest values in all soil layers. Isomer ratio and factor analysis were used to determine the source of PAHs in soil. Petroleum combustion (PC), coal and biomass combustion (CBC), mixed (M) and petroleum (P) sources were finally identified as the four main sources of PAHs in Nanjing urban greenland soil, accounting for 50.2%, 14.9%, 8.4% and 6.6%, respectively. Bap toxic equivalent (TEQBap) was used to analyze the ecological risk. TEQBap was 20.59ng/g in total zones (TZ), below the threshold for multipurpose soil of Dutch legislation (32.96ng/g), but 69% of samples exceeded this threshold. TEQBap of different functional zones is ordered as: IZ (43.62ng/g)>RZ (23.89ng/g) > BZ (20.62ng/g) > CZ (19. 93ng/g) > UP (12.97ng/g) > URF (2.01ng/g). In the industrial area, more than 97% of TEQBap depended on seven carcinogenic PAHs (∑PAH7c), which indicated that IZ had high ecological risk. Lifetime risk of cancer (ILCR) model was used to assess the health risk of ∑PAHs. ILCRs ranked as following: children > youth > adults, with soil oral intake determining the highest cancer risk, followed by skin contact and breath intake. ILCRs of children were in high cancer risk range, with values of 3.77 × 10-4 (for boy) and 3.87 × 10-4 (for girl), while ILCRs of youth and adults were in an acceptable range; ILCRs were highest in IZ, followed by RZ, BZ, CZ, UP and URF. The soil PAHs analysis in different function greenland zones of Nanjing showed that land use influenced the concentration and distribution of PAHs in soils. This difference should be taken into account in the urban greenland planning and management to reduce the risks for the environment and human health.

Lichens from Sisimiut in West Greenland and their Climatic Preferences

AbstractA total of 165 lichen taxa collected from Sisimiut in West Greenland in summer 2017 were reported and categorized toward their climatic preferences. Almost 68% of the 165 lichens are more or less equally distributed in continental and oceanic areas of Greenland. More than 26% of the lichens occur most frequently in oceanic areas and more rarely in continental areas. Almost 5% of the lichens occur most frequently in continental areas and more rarely in oceanic areas. Two lichens are distinctly oceanic. No distinctly continental lichens were found in the present investigation. The results are in good accordance with those obtained from similar investigations in West Greenland. Two different climatic scenarios and their influence upon the lichen communities are discussed.

Potential of Passive Microwave around 183 GHz for Snowfall Detection in the Arctic

This study evaluates the potential use of the Microwave Humidity Sounder (MHS) for snowfall detection in the Arctic. Using two years of colocated MHS and CloudSat observations, we develop an algorithm that is able to detect up to 90% of the most intense snowfall events (snow water path ≥400 g m−2 and 50% of the weak snowfall rate events (snow water path ≤50 g m−2. The brightness temperatures at 190.3 GHz and 183.3 ± 3 GHz, the integrated water vapor, and the temperature at 2 m are identified as the most important variables for snowfall detection. The algorithm tends to underestimate the snowfall occurrence over Greenland and mountainous areas (by as much as −30%), likely due to the dryness of these areas, and to overestimate the snowfall occurrence over the northern part of the Atlantic (by up to 30%), likely due to the occurrence of mixed phase precipitation. An interpretation of the selection of the variables and their importance provides a better understanding of the snowfall detection algorithm. This work lays the foundation for the development of a snowfall rate quantification algorithm.

Rapid ablation zone expansion amplifies north Greenland mass loss.

Since the early 1990s, the Greenland ice sheet (GrIS) has been losing mass at an accelerating rate, primarily due to enhanced meltwater runoff following atmospheric warming. Here, we show that a pronounced latitudinal contrast exists in the GrIS response to recent warming. The ablation area in north Greenland expanded by 46%, almost twice as much as in the south (+25%), significantly increasing the relative contribution of the north to total GrIS mass loss. This latitudinal contrast originates from a different response to the recent change in large-scale Arctic summertime atmospheric circulation, promoting southwesterly advection of warm air toward the GrIS. In the southwest, persistent high atmospheric pressure reduced cloudiness, increasing runoff through enhanced absorption of solar radiation; in contrast, increased early-summer cloudiness in north Greenland enhanced atmospheric warming through decreased longwave heat loss. This triggered a rapid snowline retreat, causing early bare ice exposure, amplifying northern runoff.

Reproductive biology and ecology of the boreoatlantic armhook squid Gonatus fabricii (Cephalopoda: Gonatidae)

Abstract The squid Gonatus fabricii (Lichtenstein, 1818) is the most abundant pelagic cephalopod in the Arctic and the only squid to spend all of its life cycle in this region. Despite being highly abundant, its reproductive biology remains poorly known, and data on large maturing and mature specimens are especially rare. This study, based on extensive material (51 large specimens and >35,000 specimens in all), fills major gaps in the knowledge of the reproductive biology and ecology of G. fabricii. The fecundity of females ranged from 8,862 to 16,200 oocytes, with mature and late maturing specimens having between 8,862 to c. 10,000 and 11,402 oocytes, respectively. Oogenesis was synchronous, and oocyte resorption was observed; resorbed oocytes constituted up to 23.5% of fecundity. Between two to five ripe oocytes were observed, and these were 4.0–5.5 mm in diameter (maximum dimension). Males possessed between 77 and 257 spermatophores (length = 5.8–10.8 mm). Spermatophores were characterized by a cement body with well-developed collar and discs at the oral end, an ejaculatory apparatus longer than the cement body and the lack of a tapered, sharp tip to the cement body. Spermatophore size showed a uniform increase in relation to increasing male size. In newer spermatophores, the length, width and volume of the seminal reservoir also increased. Females possessed between 62 and 84 spermatangia (length = 1.8–2.6 mm); the spermatangia were present on the buccal membranes and lacked special attachment structures. Seminal receptacles were not found on the buccal membranes of females. Our findings are consistent with the hypothesis of geographically restricted spawning in G. fabricii. The study found evidence for one new breeding area in south-eastern Greenland. No differences in sizes at maturity were found between the breeding areas. Such geographically localized reproduction is relatively common in non-deep-water squids, but is much less common in deep-water squids. Localized reproduction may be especially important for G. fabricii because increased food availability in the epipelagic layers would likely increase the survival of epipelagic juveniles, with surface currents potentially aiding in their dispersal.

Very large convergent multi-fluted glacigenic deposits in the NW Highlands, Scotland

We describe two large convergent multi-fluted glacigenic deposits in the NW Highlands, Scotland, and point out their resemblance to a number of landforms emerging from presently deglaciating areas of Greenland and Antarctica. We suggest that they all result from locally sourced sediment being deposited by local ice-flow, which was laterally confined by the margins of much larger adjacent glaciers or ice-streams. The NW Highlands features thus seem likely to be the result of processes active during the latter part of the Devensian Glaciation. One of these deposits, on the peninsula between Loch Broom and Little Loch Broom, is evidently sourced from the west-facing Coire Dearg of Beinn Ghobhlach, but was emplaced in a WNW direction rather than along the WSW fall-line. This suggests that the ice that emplaced it was confined by the margins of large glaciers then occupying the adjacent valleys of Loch Broom and Little Loch Broom. The second much larger and more prominent deposit, in Applecross, is composed of bouldery Torridonian sandstone till emplaced on to glacially scoured bedrock; the only feasible source location for this material is about 12 km distant, which requires that the deposit was carried by ice across the trough of Strath Maol Chalum and emplaced while active ice-streams confined it laterally to its present-day location. This, in turn, requires that ice lay in the Inner Sound between Applecross and Skye to an elevation 400–500 m above present-day sea-level. The Wester Ross Re-advance of 15–14 ka left a fragment of lateral moraine against the most easterly flute and buried the distal end of the flutes with hummocky moraine. We hypothesize that the fluted deposits reflect the locations of the ice-stream margins that constrained deposition of locally derived ice-transported sediment, rather than the flow-lines of the ice-stream itself.

Dust Storm Outbreak in Central Asia After ~3.5 kyr BP

AbstractThe evolution and driving factors underlying dust activity in central Asia remain controversial, particularly in its effects on downwind regions. We present a Holocene dust storm activity record retrieved from the Tarim Basin (TB) and perform linear and nonlinear analyses on dust records from the TB and the Greenland areas. The results indicate a similar response of dust activities to total solar irradiance in both areas, and an outbreak of dust storms in the TB at ~3.5 kyr BP. We suggest that decreasing temperature in high northern latitudes, aided by solar activity change, reached a critical threshold near ~3.5 kyr BP. The resulting steepening of the meridional temperature gradient would have facilitated strengthening and southward shift of the Northern Hemisphere westerly jet, leading to the outbreak of dust storms through intensification of low level wind intensity and prolonged spring conditions in the Asian interior.

A meandering polar jet caused the development of a Saharan cyclone and the transport of dust toward Greenland

Abstract. In this study, we identify a new mechanism by which dust aerosols travel over long distances across the eastern side of the North Atlantic Ocean toward the Arctic. The meandering polar jet was at the origin of both dust emission through cyclogenesis over Northwest Africa and poleward transport of the uplifted dust towards the Arctic, through cut-off circulation. The dust emission was associated with an intense Saharan cyclone that formed over Northwest Africa in early April 2011. The formation of the cyclone was caused by the intrusion into subtropics, of a high-latitude-upper-level trough, linked to the meandering polar jet. The trough initiated cyclogenesis over Northwest Africa after orographic blocking by the Anti-Atlas Mountains. The still meandering polar jet led to the formation of a cut-off low further south with which the Saharan dust-cyclone merged 2 d later and moved northward with the main stream. Beside satellite observations, a simulation at high resolution was performed using the prognostic-dust permitting model MesoNH. The total dust load carried during this event to areas located north of 40∘ N was estimated by the model to be 38 Tg and dust deposition was estimated to be 1.3 Tg. The Saharan dust reaching Greenland was accompanied by warm and moist air masses that caused a rise in surface temperature of about 10 ∘C for more than 3 consecutive days over the southeastern Greenland. Ice melt over this area of Greenland was detected in the brightness temperature observations.

Physical Activity and Active Commuting in Relation to Objectively Measured Built-Environment Attributes Among Adolescents.

Background: The associations between objectively measured built-environment attributes and physical activity (PA) behavior have not been extensively studied in adolescents. This research aimed to analyze the associations between built-environment attributes and moderate to vigorous PA and active commuting among adolescents. Methods: Our sample comprised 465 Spanish adolescents (aged 14-18y) who were recruited from the IPEN Adolescent study. The built-environment attributes around participant's home (0.25-, 0.5-, and 1-km street-network buffers) and moderate to vigorous PA were objectively measured. Results: Net residential density and urban greenland area were positively associated with moderate to vigorous PA in 0.25- and 1-km buffers, respectively, and street intersection density was positively associated with active commuting, both in the 0.5- and 1-km buffers. Conclusion: This study highlights the importance of assessing adolescents' neighborhoods when PA behavior is analyzed and when targeting PA interventions to promote health-enhancing behaviors.

Optimization of urban land-use structure in China's rapidly developing regions with eco-environmental constraints

Economic growth and eco-environmental protection are largely incompatible in the optimization of the urban land-use structure (ULUS) in rapidly developing regions. Here, we attempted to construct a model for optimizing ULUS with the inclusion of uncertain interval values, simultaneously considering the economic growth and eco-environmental protection in rapidly developing regions so as to estimate the elastic interval value of ULUS. The corresponding urban economic and environmental benefits were analyzed. Furthermore, an empirical study of Wuhan city revealed that there are certain counterbalance relationships among commercial land, industrial land and green land: the area of residential land, green land and public land is increasing year by year, and that of industrial land remains basically unchanged, while that of commercial land is decreasing gradually. Therefore, in rapidly developing regions, greater economic benefits from the ULUS are usually obtained at the cost of environmental and ecological benefits.

Weathering in the Glacial Foreland of Southern and Western Greenland

Glaciers physically grind up underlying rock and create fine-grained sediment that has a high potential for chemical weathering. Subsequent weathering of these sediments produces solutes, including nutrients and radiogenic isotopes, which are transported by streams to the world’s oceans where they can impact primary productivity and record past ice sheet activity. Previous research on the geochemistry of bedrock, bedload sediment and stream waters demonstrated that the extent of chemical weathering varies across a transect in western Greenland due to variations in either exposure age or precipitation (Scribner et al., 2015), and that variations in the extent of weathering associated with retreat of the Greenland Ice Sheet (GrIS) may account for observed trends in solutes during the last deglacial period. This project adds a new study area in southern Greenland that has higher precipitation, more vegetation, a different lithology, and a range of exposure ages, to address the leading factors contributing to the extent of weathering. Based on the relative proportions of cations and percent change between Na+K concentrations of bedload to waters, the southern region is undergoing less extensive weathering than the western transect, which suggests that lithology may be an important driver of weathering, and that exposure age and precipitation are less important factors than expected. The results also suggest there are additional factors that contribute to weathering that were not accounted for in this study, such as dissolved organic matter and microbial activity.

Remote sensing image-based analysis of the urban heat island effect in Shenzhen, China

The urban heat island effect is a typical urban climate phenomenon, and the formation and intensity of these phenomena are closely related to the land cover type. Based on Landsat 8 remote sensing images of Shenzhen, China, this study uses a linear spectral mixture model to extract land coverage information, and then analyzes the effects of urban land coverage on the land surface temperature (LST) and heat budget components. The results show that the LST of Shenzhen decreases gradually from northwest to southeast and that the LST of urban impervious surfaces are significantly higher than those of vegetation-covered areas with a difference of 3–4 K, thus demonstrating a significant urban heat island effect. Impervious surfaces and urban vegetation both affect the LST and heat budget components of Shenzhen. The impervious area contributes more to the surface sensible heat, while urban vegetation contributes more to the surface latent heat. The research results show that a very small area of urban green land (vegetation fraction coverage less than 4–8%) exhibits a strong capacity for heat dissipation. In the practice of urban construction, avoiding concentrated impervious areas and increasing urban green land areas represent effective methods of alleviating the urban heat island effect. This study helps to better understand the optimization of urban landscapes and alleviation of the urban heat island effect.

Formation of the Population Structure of the Atlantic Cod Gadus morhua Linnaeus, 1758 in the Quaternary Period

This paper presents a comparative analysis of the variability of genetic characteristics in samples from the largest stocks of the Atlantic cod Gadus morhua Linnaeus, 1758 in the Northeast Atlantic (NEA) and the Northwest Atlantic (NWA) waters. The results of a pairwise estimation of the genetic differentiation, performed using allozyme and microsatellite markers, detected a significant difference between the cod sample from the New England Shelf (NWA) and the cod of the Icelandic–Greenlandic and Norwegian–Barents Sea stocks. At the same time, cod samples from areas of East and West Greenland and samples from the Barents Sea, despite considerable geographic differences, demonstrated a high level of identity according to molecular genetic markers. The peculiarities of the formation of the cod population structure in the Quaternary period are considered in connection with the dynamics of global climatic and oceanological processes.

An altitudinal study of the flora of the inland mountains of South-East Greenland

This paper aims to bring together information from a variety of sources on the vascular flora of the botanically little-known-mountains and nunataks of south-east Greenland between Ammassalik and the Blosseville Kyst (66°-69° N). The paper is based on an analysis of a collection of mainly vascular plants from 111 individual sites of known altitude in the inland mountains between Ammassalik and Kialiip Tasiilaa (Tasilaq) in the south, and around Kangersertuaq (Kangerlussuaq) in the north. The collections were made by 17 predominantly climbing expeditions, with little or no botanical experience, and all but one from r963 to 1992. N01,1e of the sites had previously been visited, and the data are practically all unpublished except as botanical reports in general expedition reports which, for a variety of reasons, are now difficult or almost impossible to consult. Although the climate on the coast can be characterised as low-arctic it becomes progressively drier and colder (i.e. high-arctic) inland. A consequence of this is the presence in the interior of the following species, none previously reported in east Greenland from south of Scoresby Sund (72° N): Minuartia stricta, Melandrium affine, Draba arctica, D. subcapitata, Festuca baffinensis and Poa abbreviata. There is also a cluster of records of Arabis arenicola, otherwise extremely rare in south-east Greenland. 100 vascular plants were recorded from the southern area and 86 from the northern. The highest sites were 2480 m in the south and 2roo m in the north, the former being the highest recorded in the Arctic. These altitudes were somewhat lower than those calculated by regression analyses of the number of species plotted against altitude. It seems very likely that many of the species occurring over about r500 m reach their highest recorded altitudes in the Arctic within the study area. The species are tabulated in order of increasing altitude limits and the altitudinal range is arbitrarily divided into three zones: low 370-1200 m, middle 1200-1800 m and high, above 1800 m. Low-arctic oceanic montane and low- and medium-arctic species preponderate in the lowest zone but with increasing altitude the widespread arctic montane element becomes dominant. Comparison with other areas of Greenland shows that the altitudinal limits are noticeably higher in south-east Greenland. The contrasting geology has no detectable affect on the flora, the best developed vegetation being on south-facing sites with summer melt water. Less exhaustive lists of bryophytes and lichens are included in the Appendices.

Polar Jet Associated Circulation Triggered a Saharan Cyclone and Derived the Poleward Transport of the African Dust Generated by the Cyclone

AbstractIn this study, we identify a new mechanism by which dust aerosols travel over long distances across the eastern side of the North Atlantic Ocean toward the Arctic. The meandering polar jet was at the origin of both dust emission through cyclogenesis over Northwest Africa and poleward transport of the uplifted dust toward the Arctic, through cut‐off circulation. The dust emission was associated with an intense Saharan cyclone that formed over Northwest Africa in early April 2011. The formation of the cyclone was caused by the intrusion into subtropics, of a high‐latitude‐upper‐level trough, linked to the meandering polar jet. The trough initiated cyclogenesis over Northwest Africa after orographic blocking by the Anti‐Atlas Mountains. The still meandering polar jet led to the formation of a cut‐off low further south with which the Saharan dust‐cyclone merged 2 days later and moved northward with the main stream. Beside satellite observations, a simulation at high resolution was performed using the prognostic‐dust permitting model MesoNH. The total dust load carried during this event to areas located north of 40 N was estimated by the model to be 38 Tg and dust deposition was estimated to be 1.3 Tg. The Saharan dust reaching Greenland was accompanied by warm and moist air masses that caused a rise in surface temperature of about 10C for more than 3 consecutive days over the southeastern Greenland. Ice melt over this area of Greenland was detected in the brightness temperature observations.

A brief history of lumpfishing, assessment, and management across the North Atlantic

Abstract This report documents the fishery, assessment, and management of lumpfish (Cyclopterus lumpus) across its distribution range. Targeting lumpfish for their roe on a large scale began in the 1950s in Iceland and Norway and then in Canada in the 1970s and Greenland in the 1990s. When the fishery began, there were few regulations, but limits on vessel size, mesh size, number of nets, and length of the fishing season were gradually implemented over time. Worldwide landings have varied from ca. 2000 to 8000 tonnes of roe between 1977 and 2016. Iceland and Canada accounted for >80% of the landings until 2000. After 2013, Greenland and Iceland accounted for >94%. All countries except Iceland show a decreasing trend in the number of boats participating in the fishery, which is related to several factors: the monetary value of the roe, changes in the abundance of lumpfish, and increasing age of artisanal fishers. Each country has a different combination of data available for assessment from basic landings and fishing effort data to more detailed fishery independent survey indices of abundance. The management of total catch also differs, with an effort-controlled fishery in Iceland and Canada, a total allowable catch (TAC) per boat in Norway, and TAC per area in Greenland. Population abundance is above management targets in Iceland and Norway, but the status is less clear in Greenland and around Denmark/Sweden and appears to be depleted around Canada. Certification by the Marine Stewardship Council was instrumental in the adoption of a management plan in Greenland; however, benefits to the fishers remain unclear. Aspects surrounding the biology of lumpfish, which is poorly understood and requires investigation, include growth rate, natural mortality, and population differentiation. In addition, there is concern about the potential impacts that the recent escalation in production of lumpfish for use as cleaner fish in the aquaculture industry could have on the wild population.

Application of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) multispectral imagery to mineral and lithologic mapping in southern West Greenland

Remote sensing data acquired by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) were used for mineral and lithologic mapping at the Sarfartoq carbonatite complex area in southern West Greenland. The geology of the study area consists of carbonatites, fenites, hydrothermal alteration zones, gneisses, alluvial deposits etc. The Adaptive Coherence Estimator algorithm was used to analyze the remote sensing data. The reference spectra were selected from the imagery. The mapping results show the distribution of carbonatite, hydrothermally altered zones, fenite, and sericite. In addition, lichen and tundra green vegetation were also mapped. Due to the moderate spatial resolution of ASTER SWIR bands, it was not possible to detect and map the rock units in some parts of the study area. The study shows the possibilities and limitations of the use of the ASTER multispectral imagery for geological studies in the Arctic regions of West Greenland. The paper is the first reported study on the use of ASTER data for mineral and lithologic mapping in the Arctic regions of West Greenland.

Dual-satellite (Sentinel-2 and Landsat 8) remote sensing of supraglacial lakes in Greenland

Abstract. Remote sensing is commonly used to monitor supraglacial lakes on the Greenland Ice Sheet (GrIS); however, most satellite records must trade off higher spatial resolution for higher temporal resolution (e.g. MODIS) or vice versa (e.g. Landsat). Here, we overcome this issue by developing and applying a dual-sensor method that can monitor changes to lake areas and volumes at high spatial resolution (10–30 m) with a frequent revisit time (∼3 days). We achieve this by mosaicking imagery from the Landsat 8 Operational Land Imager (OLI) with imagery from the recently launched Sentinel-2 Multispectral Instrument (MSI) for a ∼12 000 km2 area of West Greenland in the 2016 melt season. First, we validate a physically based method for calculating lake depths with Sentinel-2 by comparing measurements against those derived from the available contemporaneous Landsat 8 imagery; we find close correspondence between the two sets of values (R2=0.841; RMSE = 0.555 m). This provides us with the methodological basis for automatically calculating lake areas, depths, and volumes from all available Landsat 8 and Sentinel-2 images. These automatic methods are incorporated into an algorithm for Fully Automated Supraglacial lake Tracking at Enhanced Resolution (FASTER). The FASTER algorithm produces time series showing lake evolution during the 2016 melt season, including automated rapid (≤4 day) lake-drainage identification. With the dual Sentinel-2–Landsat 8 record, we identify 184 rapidly draining lakes, many more than identified with either imagery collection alone (93 with Sentinel-2; 66 with Landsat 8), due to their inferior temporal resolution, or would be possible with MODIS, due to its omission of small lakes <0.125 km2. Finally, we estimate the water volumes drained into the GrIS during rapid-lake-drainage events and, by analysing downscaled regional climate-model (RACMO2.3p2) run-off data, the water quantity that enters the GrIS via the moulins opened by such events. We find that during the lake-drainage events alone, the water drained by small lakes (<0.125 km2) is only 5.1 % of the total water volume drained by all lakes. However, considering the total water volume entering the GrIS after lake drainage, the moulins opened by small lakes deliver 61.5 % of the total water volume delivered via the moulins opened by large and small lakes; this is because there are more small lakes, allowing more moulins to open, and because small lakes are found at lower elevations than large lakes, where run-off is higher. These findings suggest that small lakes should be included in future remote-sensing and modelling work.