Lemon Creek Glacier Research Articles

Applicability of Relatively Low-Cost Multispectral Uncrewed Aerial Systems for Surface Characterization of the Cryosphere

This paper investigates the ability of a relatively low cost, commercially available uncrewed aerial vehicle (UAV), the DJI Mavic 3 Multispectral, to perform cryospheric research. The performance of this UAV, where applicable, is compared to a similar but higher cost system, the DJI Matrice 350, equipped with a Micasense RedEdge-MX Multispectral dual-camera system. The Mavic 3 Multispectral was tested at three field sites: the Lemon Creek Glacier, Juneau Icefield, AK; the Easton Glacier, Mt. Baker, WA; and Bagley Basin, Mt. Baker, WA. This UAV proved capable of mapping the spatial distribution of red snow algae on the surface of the Lemon Creek Glacier using both spectral indices and a random forest supervised classification method. The UAV was able to assess the timing of snowmelt and changes in suncup morphology on snow-covered areas within the Bagley Basin. Finally, the UAV was able to classify glacier surface features using a random forest algorithm with an overall accuracy of 68%. The major advantages of this UAV are its low weight, which allows it to be easily transported into the field, its low cost compared to other alternatives, and its ease of use. One limitation would be the omission of a blue multispectral band, which would have allowed it to more easily classify glacial ice and snow features.

Seismic Mapping of Subglacial Hydrology Reveals Previously Undetected Pressurization Event

AbstractUnderstanding the dynamic response of glaciers to climate change is vital for assessing water resources and hazards, and subglacial hydrology is a key player in glacier systems. Traditional observations of subglacial hydrology are spatially and temporally limited, but recent seismic deployments on and around glaciers show the potential for comprehensive observation of glacial hydrologic systems. We present results from a high‐density seismic deployment spanning the surface of Lemon Creek Glacier, Alaska. Our study coincided with a marginal lake drainage event, which served as a natural experiment for seismic detection of changes in subglacial hydrology. We observed glaciohydraulic tremor across the surface of the glacier that was generated by the subglacial hydrologic system. During the lake drainage, the relative changes in seismic tremor power and water flux are consistent with pressurization of the subglacial system of only the upper part of the glacier. This event was not accompanied by a significant increase in glacier velocity; either some threshold necessary for rapid basal motion was not attained, or, plausibly, the geometry of Lemon Creek Glacier inhibited speedup. This pressurization event would have likely gone undetected without seismic observations, demonstrating the power of cryoseismology in testing assumptions about and mapping the spatial extent of subglacial pressurization.

Ice thickness estimates of Lemon Creek Glacier, Alaska, from active-source seismic imaging

AbstractLemon Creek Glacier, a temperate valley glacier in the Juneau Icefield of Southeast Alaska, is the site of long running (>60 years) glaciological studies. However, the most recent published estimates of its thickness and subglacial topography come from two ~50 years old sources that are not in agreement and do not account for the effects of years of negative mass balance. We collected a 1-km long active-source seismic line on the upper section of the glacier parallel and near to the centerline of the glacier, roughly straddling the equilibrium-line altitude. We used these data to perform joint reflection-refraction velocity modeling and reflection imaging of the glacier bed. We find that this upper section of Lemon Creek Glacier is as much as 150 m (~65%) thicker than previously suggested with a large overdeepening in an area previously believed to have a uniform thickness. Our results lead us to reinterpret the impact of basal motion on ice flow and have a significant impact on expectations of subglacial hydrology. We suggest that further efforts to develop a whole-glacier model of subglacial topography are necessary to support studies that require accurate models of ice thickness and subglacial topography.

Explaining mass balance and retreat dichotomies at Taku and Lemon Creek Glaciers, Alaska

AbstractWe reanalyzed mass balance records at Taku and Lemon Creek Glaciers to better understand the relative roles of hypsometry, local climate and dynamics as mass balance drivers. Over the 1946–2018 period, the cumulative mass balances diverged. Tidewater Taku Glacier advanced and gained mass at an average rate of +0.25 ± 0.28 m w.e. a–1, contrasting with retreat and mass loss of −0.60 ± 0.15 m w.e. a−1 at land-terminating Lemon Creek Glacier. The uniform influence of regional climate is demonstrated by strong correlations among annual mass balance and climate data. Regional warming trends forced similar statistically significant decreases in surface mass balance after 1989: −0.83 m w.e. a–1 at Taku Glacier and −0.81 m w.e. a–1 at Lemon Creek Glacier. Divergence in cumulative mass balance arises from differences in glacier hypsometry and local climate. Since 2013 negative mass balance and glacier-wide thinning prevailed at Taku Glacier. These changes initiated terminus retreat, which could increase dramatically if calving begins. The future mass balance trajectory of Taku Glacier hinges on dynamics, likely ending the historic dichotomy between these glaciers.

Insights into combined radiogenic and stable strontium isotopes as tracers for weathering processes in subglacial environments

This study reports stable and radiogenic strontium isotope behaviour in the dissolved load and suspended sediments from the subglacial outflow of the Lemon Creek glacier (Juneau Ice Field, Alaska) over a single melt season. In situ measurements (discharge, total alkalinity, pH and conductivity) are combined with elemental concentrations, X-ray diffraction (XRD) analysis and radiogenic strontium isotope measurements to interpret the variations observed in stable strontium isotopic ratios.The stable Sr isotope composition (88Sr/86Sr ratio expressed as δ88/86Sr, ‰) of the dissolved load averages 0.31±0.05‰, and is heavier than both the suspended sediment 0.18±0.03‰, as well as local bedrocks ~0.20 to 0.26‰. We attribute the enrichment of heavier isotopes in the dissolved load to the uptake of lighter Sr isotopes by secondary weathering minerals, driving the dissolved load to heavier values. X-ray diffraction (XRD) analysis confirms the presence of clays in the suspended sediments and thermodynamic modelling suggests the presence of iron oxy-hydroxide phases. Although it is not possible to completely rule out the effect of dissolution of primary minerals in controlling Sr isotopic compositions of the dissolved load, our data indicate that the extent of secondary mineral formation likely plays a significant role. The preferential weathering of minerals such as biotite (consistent with the mineralogical assemblages found in the suspended sediments), as well as the potential presence of radiogenic calcites from metacarbonates (derived from the Yukon-Tanana terrain), may be driving the small seasonal shifts in 87Sr/86Sr of the dissolved load to more radiogenic compositions, from 87Sr/86Sr(DL)=0.71048 to 0.710647.Using the combination of stable and radiogenic strontium isotopes to investigate weathering processes shows that radiogenic Sr isotopes provide information regarding weathering of primary phases. While the stable Sr isotope data appear to record information regarding the extent of secondary mineral formation, where secondary minerals incorporate the light isotopes, driving the dissolved load to heavy values.

Implications for post-comminution processes in subglacial suspended sediment using coupled radiogenic strontium and neodymium isotopes

Enhanced physical weathering rates in subglacial systems promote high levels of comminution, transport, and deposition of fine-grained sediment within the subglacial drainage network. The impact of shifts in sediment loads from variations in meltwater flux, and their effects on downstream ecosystems, remains poorly quantified and places a fundamental importance on our ability to characterize subglacial depositional environments. Here, for the first time, we assess the seasonal evolution of the subglacial suspended sediment using coupled radiogenic strontium (87Sr/86Sr) and neodymium (143Nd/144Nd) isotopic ratios with elemental ratios and in situ measurements. Weathering rates in fluvial and riverine systems have been traditionally assessed using radiogenic isotopic tracers: 143Nd/144Nd ratios relate to the crustal age whereas 87Sr/86Sr ratios relate to age and preferential mineral dissolution. Thus relative shifts in these ratios will allow us to characterize distinct sediment transport networks. We apply this technique to the Lemon Creek Glacier (LCG), Alaska, USA, and to the Athabasca Glacier (AG), Alberta, CA. At the LCG, the 143Nd/144Nd values range from εNd of −4.6 (0.9) to −8.7 (0.2), which suggests a poorly mixed sediment flux. However, the greatest period of variability may correlate with the drainage of a supraglacial lake and suggests caution should be exerted in time-scale 143Nd/144Nd provenance studies that may be affected by climatic disturbances. In contrast, limited variation is observed within the AG 143Nd/144Nd seasonal record. A consistent, direct relation between the Rb/Sr elemental ratio and the 87Sr/86Sr ratio proves interesting as it enables us to unravel incongruent weathering trends in the radiogenic Sr record. Correlation between the 87Sr/86Sr and total discharge suggests that the process is partially controlled by mantling of the bedrock, which can be detected using post-comminution ages. While the subglacial structure may be enabled by the subglacial till beneath the AG, our study supports the use of Sr-Nd as a new proxy in the subglacial environment.

Microbial communities of the Lemon Creek Glacier show subtle structural variation yet stable phylogenetic composition over space and time.

Glaciers are geologically important yet transient ecosystems that support diverse, biogeochemically significant microbial communities. During the melt season glaciers undergo dramatic physical, geochemical, and biological changes that exert great influence on downstream biogeochemical cycles. Thus, we sought to understand the temporal melt-season dynamics of microbial communities and associated geochemistry at the terminus of Lemon Creek Glacier (LCG) in coastal southern Alaska. Due to late season snowfall, sampling of LCG occurred in three interconnected areas: proglacial Lake Thomas, the lower glacial outflow stream, and the glacier’s terminus. LCG associated microbial communities were phylogenetically diverse and varied by sampling location. However, Betaproteobacteria, Alphaproteobacteria, and Bacteroidetes dominated communities at all sampling locations. Strict anaerobic groups such as methanogens, SR1, and OP11 were also recovered from glacier outflows, indicating anoxic conditions in at least some portions of the LCG subglacial environment. Microbial community structure was significantly correlated with sampling location and sodium concentrations. Microbial communities sampled from terminus outflow waters exhibited day-to-day fluctuation in taxonomy and phylogenetic similarity. However, these communities were not significantly different from randomly constructed communities from all three sites. These results indicate that glacial outflows share a large proportion of phylogenetic overlap with downstream environments and that the observed significant shifts in community structure are driven by changes in relative abundance of different taxa, and not complete restructuring of communities. We conclude that LCG glacial discharge hosts a diverse and relatively stable microbiome that shifts at fine taxonomic scales in response to geochemistry and likely water residence time.

Juneau Icefield Mass Balance Program 1946–2011

Abstract. The annual surface mass balance records of the Lemon Creek Glacier and Taku Glacier observed by the Juneau Icefield Research Program are the longest continuous glacier annual mass balance data sets in North America. Annual surface mass balance (Ba) measured on Taku Glacier averaged +0.40 m a−1 from 1946–1985, and −0.08 m a−1 from 1986–2011. The recent annual mass balance decline has resulted in the cessation of the long-term thickening of the glacier. Mean Ba on Lemon Creek Glacier has declined from −0.30 m a−1 for the 1953–1985 period to −0.60 m a−1 during the 1986–2011 period. The cumulative change in annual surface mass balance is −26.6 m water equivalent, a 29 m of ice thinning over the 55 yr. Snow-pit measurements spanning the accumulation zone, and probing transects above the transient snow line (TSL) on Taku Glacier, indicate a consistent surface mass balance gradient from year to year. Observations of the rate of TSL rise on Lemon Creek Glacier and Taku Glacier indicate a comparatively consistent migration rate of 3.8 to 4.1 m d−1. The relationship between TSL on Lemon Creek Glacier and Taku Glacier to other Juneau Icefield glaciers (Norris, Mendenhall, Herbert, and Eagle) is strong, with correlations exceeding 0.82 in all cases. doi:10.5065/D6NZ85N3

Identification of snow ablation rate, ELA, AAR and net mass balance using transient snowline variations on two Arctic glaciers

AbstractIdentification of the transient snowline (TSL) from high spatial resolution Landsat imagery on Lemon Creek Glacier (LCG), southeast Alaska, USA, and Mittivakkat Gletscher (MG), southeast Greenland, is used to determine snow ablation rates, the equilibrium-line altitude (ELA) and the accumulation-area ratio (AAR). The rate of rise of the TSL during the ablation season on a glacier where the balance gradient is known provides a measure of the snow ablation rate. On both LCG and MG, snow pits were completed in regions that the TSL subsequently transects. This further provides a direct measure of the snow ablation rates for a particular year. TSL observations from multiple dates during the ablation season from 1998 to 2011 at LCG and 1999 to 2012 at MG were used to explore the consistency of the TSL rise and snow ablation rate. On LCG and MG the satellite-derived mean TSL migration rates were 3.8 ± 0.6 and 9.4 ± 9.1 m d−1, respectively. The snow ablation rates were 0.028 ± 0.004 m w.e. d−1 for LCG and 0.051 ± 0.018 m w.e. d−1 for MG estimated by applying a TSL–mass-balance-gradient method, and 0.031 ± 0.004 and 0.047 ± 0.019 m w.e. d−1 by applying a snow-pit–satellite method, illustrating significant agreement between the two different approaches for both field sites. Also, satellite-derived ELA and AAR, and estimated net mass-balance (Ba) conditions were in agreement with observed ELA, AAR and Ba conditions for LCG and MG.

The Response of Taku and Lemon Creek Glaciers to Climate

Surface height and mass balance changes of Taku and Lemon Creek Glaciers within Juneau Icefield, Alaska, are examined to determine the relationship between these parameters and climatic forcing. Both Taku and Lemon Creek Glaciers are located in a maritime climate, but they behave very differently. Taku Glacier, a former tidewater glacier, is ∼70 times larger than Lemon Creek Glacier, and its dynamics are largely a result of the post-tidewater glacier cycle which causes insensitivity to climate change during advance phases. Taku Glacier is advancing at present but its surface height, mass balance, and rate of advance have decreased since 1988. Lemon Creek Glacier, a small alpine glacier, is retreating and has maintained a negative mass balance since 1953. Mass balance records from both Taku and Lemon Creek Glaciers correlate well with temperature and show little correlation with precipitation. The mass balance of these glaciers also correlates with the Pacific Decadal Oscillation (PDO). However, the Lemon Creek Glacier mass balance record shows a stronger correlation with the PDO than that of Taku Glacier. Taku Glacier shows a longer delay in response to warming in Southeast Alaska likely due to post-tidewater glacier dynamics, its large accumulation area ratio (AAR), and its size.

The impact of sampling density on glacier mass balance determination

To assess the impact of sampling density on the determination of a glacier's annual mass balance, we used varying densities of measurements to determine annual mass balance on Columbia Glacier, Washington and Lemon Creek Glacier, Alaska. Mass balance was determined solely from field measurements. The density of the mass balance networks ranged from 1 to 375 points km−2. The smaller networks were subsamples of the highest measurement density network. The results on both glaciers indicate significant improvement in accuracy resulting from increasing the total number of measurements from 1 to 4 points km−2 on Lemon Creek Glacier and 12 to 46 points km−2 on Columbia Glacier. There was no significant improvement in accuracy on the smaller Columbia Glacier for utilizing more than 46 points km−2. On Lemon Creek Glacier there was little improvement in mass balance assessment for a network greater than 4 points km−2. On both glaciers this represented a network of 40 measurement sites. Copyright © 2000 John Wiley & Sons, Ltd.

Mass Balance Measurements on the Lemon Creek Glacier, Juneau Icefield, Alaska 1953-1998

Mass Balance Measurements on the Lemon Creek Glacier, Juneau Icefield, Alaska 1953-1998

Mass balance measurements on the lemon creek glacier, juneau icefield, alaska 1953–1998

Annual balance measurements on the Lemon Creek Glacier, Alaska conducted by the Juneau Icefield Research Program (JIRP) from 1953 through 1998 provide a continuous 46 year record. This is one of the nine American glaciers selected in a global monitoring network during the International Geophysical year, 1957/58. These data have been acquired primarily by employing consistent ground methods, conducted on similar annual dates and calculated using comparable methodology. The results have been until now fairly precise, but of uncertain accuracy. An adjunct comparison of topographic surface maps of the glacier made in 1957 and 32 years later in 1989 provides a rough determination of glacier surface elevation changes which are clearly of less precision than the compilation of annual ground data. Airborne surface profiling in 1995, and global positioning system leveling transects in 1996–1998 update the record of surface elevation changes over the past decade. The mean glacier ice thickness reductions suggested by these methods from 1957–1989, from 1957–1995 and from 1957–1998 are −13.2 m, −16.4 m, and −21.7 m, respectively. It is of interest that the geodetic interpretations agree fairly well with the trend of sequential balances from ground‐level stratigraphic measurements. To date, however, the infrequent mapping methods in this study have yielded specific balances averaging between 5 and 11% less than those resulting from our annual on‐site glaciological monitoring. For future studies this can be an important factor. The ground data are, therefore, the ones in which we have most confidence. These show cumulative ice losses of −13.9 m (12.7 m water equivalent w.e.) from 1957–1989, of −19.0 m (−17.1 m w.e.) from 1957–1995, of −24.4 m (22 m w.e.) from 1957–1998, and −24.7 m (22.2 m w.e.) for the total cumulative loss over the full 46 years between 1953 and 1998. Although the balance trend has been increasingly negative it averages −0.48 m/a in w.e. or 0.52 m of ice loss per year.To refine the reliability of density determinations in this data set the effects of internal accumulation from refrozen meltwater producing diagenetic ice structures in the annual firnpack have been taken into account. An unusual dearth of such structures within the 1997/98 firnpack provided a unique opportunity to facilitate application of the probing technique over broad areas of the nv. This added to our ground truth and verified accuracy of the test‐pit measurements used in these long‐term mass balance computations.The glacier's continuing negative mass balance has fueled a terminal retreat of 800 m during the 1953–1998 period. The annual balance trend indicates that despite a higher mean elevation and a higher elevation terminus from thinning and retreat, mean annual balance has been strongly negative since 1977 (−0.78 m/a w.e.). Dramatically increased negative mass balances have occurred in the 1990s, with 1996 and 1997 being the only years on record with no retained accumulation since field observations were initiated in the glacier source areas in 1948.

RECENT TRENDS IN THE LEMON CREEK GLACIER, ALASKA

This paper reports the 1989 re-mapping of Lemon Creek Glacier, Alaska, and, in conjunction with 1948 and 1957 maps of the glacier, calculation of 9-year and 32-year changes of glacier mass and terminal position. As in the earlier maps, the new map is at a scale of 1:10,000 with a 5-m contour interval for the glacier surface. Changes between 1957 and 1989 were determined by use of the geodetic method for determining mass balance. Net water equivalent change was -118.71 × 106 m3. The glacier's respective 1957–1989 area and volume losses were 0.878 × 106 m2 and -131.90 × 106 m3 (14.6%). The terminus retreated an average 700 m.

Mass Balance of West Gulkana Glacier

Mass Balance of West Gulkana Glacier

Historical Variations of Lemon Creek Glacier, Alaska, and Their Relationship to the Climatic Record

AbstractLemon Creek Glacier served as the focus of attention of the Juneau Ice Field Research Project from 1953 through 1958, during which period glaciological and related research was accomplished. This paper provides an historical framework for those studies by (1) considering variations of Lemon Creek Glacier in recent centuries and during millennia since the last ice age, and (2) describing certain relationships which appear to exist between these variations and the climatic record.It is found that Lemon Creek Glacier has been receding intermittently since a maximum c. 1750 and by 1958 had lost c. 25 per cent of the former area. Most rapid recession occurred during the periods 1891–1902 and 1929–58. Behaviour of the glacier since c. 1750 reveals a parallelism with glaciers in most of the regions where temperature trends have been graphed as well as with other glaciers of the Juneau Ice Field. The advances of the 1950’s observed in the Rocky, Cascade and Olympic Mountains do not, however, show up in the Juneau area. Lemon Creek Glacier has not advanced more than 375 m. beyond the 1750 position, if at all, during the last 10,000 yr.

Historical Variations of Lemon Creek Glacier, Alaska, and Their Relationship to the Climatic Record

AbstractLemon Creek Glacier served as the focus of attention of the Juneau Ice Field Research Project from 1953 through 1958, during which period glaciological and related research was accomplished. This paper provides an historical framework for those studies by (1) considering variations of Lemon Creek Glacier in recent centuries and during millennia since the last ice age, and (2) describing certain relationships which appear to exist between these variations and the climatic record.It is found that Lemon Creek Glacier has been receding intermittently since a maximumc. 1750 and by 1958 had lostc. 25 per cent of the former area. Most rapid recession occurred during the periods 1891–1902 and 1929–58. Behaviour of the glacier sincec. 1750 reveals a parallelism with glaciers in most of the regions where temperature trends have been graphed as well as with other glaciers of the Juneau Ice Field. The advances of the 1950’s observed in the Rocky, Cascade and Olympic Mountains do not, however, show up in the Juneau area. Lemon Creek Glacier has not advanced more than 375 m. beyond the 1750 position, if at all, during the last 10,000 yr.

Surface Movement, Hydrological Change and Equilibrium Flow on Lemon Creek Glacier, Alaska

AbstractLemon Creek Glacier served as the focus of attention of the Juneau Ice Field Research Project from 1953 through 1958. During the International Geophysical Year, it represented one of the glaciological stations in the North American network. This paper presents some of the results of these studies, its purposes being (1) to discuss the 1953–58 annual hydrological budgets, and (2) to test Nielsen’s equations for the equilibrium glacier using 1957 and 1958 movement and hydrological data.It is found that each budget year for the period studied shows a deficit, except 1954–55 which registered a pronounced surplus. The net deficit amounts to 10.32×106m.3of water. The 1956–57 budget was only slightly negative (0.82×106m.3) but that for 1957–58 was strongly negative (8.96×106m.3). Surface flow measurements were made along five transverse profiles, two of which were plotted over one full year. It is believed that the one-year measurements provide a more accurate and realistic picture of glacier flow than is normally available from short summer surveys. Thu glacier appears to be close to equilibrium and to behave in the manner predicted by Nielsen’s theory of equilibrium flow.

Surface Movement, Hydrological Change and Equilibrium Flow on Lemon Creek Glacier, Alaska

AbstractLemon Creek Glacier served as the focus of attention of the Juneau Ice Field Research Project from 1953 through 1958. During the International Geophysical Year, it represented one of the glaciological stations in the North American network. This paper presents some of the results of these studies, its purposes being (1) to discuss the 1953–58 annual hydrological budgets, and (2) to test Nielsen’s equations for the equilibrium glacier using 1957 and 1958 movement and hydrological data.It is found that each budget year for the period studied shows a deficit, except 1954–55 which registered a pronounced surplus. The net deficit amounts to 10.32×106 m.3 of water. The 1956–57 budget was only slightly negative (0.82×106m.3) but that for 1957–58 was strongly negative (8.96×106 m.3). Surface flow measurements were made along five transverse profiles, two of which were plotted over one full year. It is believed that the one-year measurements provide a more accurate and realistic picture of glacier flow than is normally available from short summer surveys. Thu glacier appears to be close to equilibrium and to behave in the manner predicted by Nielsen’s theory of equilibrium flow.

Surface Movement and its Relationship To The Average Annual Hydrological Budget of Lemon Creek Glacier, Alaska

AbstractThe object of the 1957 program of the Juneau Ice Field Research Project on Lemon Creek Glacier was (1) to obtain data on surface movement in the accumulation region, and (2) to relate the movement to the average annual hydrological budget. Results show a net loss of ice over the past four years, although this deficit does not appear to be reflected by the movement of the ice. Lemon Creek Glacier appears to be in approximate equilibrium.