21 research outputs found
Re-evaluating the Relevance of Vegetation Trimlines in the Canadian Arctic as an Indicator of Little Ice Age Paleoenvironments
The origin of trimlines associated with the so-called âlichen-freeâ areas in the Canadian Arctic has been attributed both to perennial snowfield expansion during the Little Ice Age (LIA) and to seasonally persistent snow cover in more recent times. Because of the disparate hypotheses (ecological versus paleoclimatic) regarding the formation of these trimlines, their use as a paleoclimatic indicator has been abandoned for more than two decades. We re-examine this debate and the validity of the opposing hypotheses in the light of new regional mapping of trimlines across the Queen Elizabeth Islands (QEI). The ecological hypothesisâinsufficient duration of the growing season resulting from seasonally persistent snow coverâfails to account for the poikilohydric nature of lichens and their ability to endure short growing seasons. It cannot adequately explain the existence of sharp trimlines or account for the occurrence of those trimlines on sparsely vegetated carbonate terrain. Furthermore, trimlines outlining the former extent of thin plateau ice caps are accordant with trimlines associated with former perennial snowfields, indicating that these trimlines record snow and ice expansion during the LIA rather than the seasonal persistence of more recent snow cover. We suggest that these features represent an important LIA climate indicator and should therefore be used for paleoclimatic reconstruction.Lâorigine des Ă©paulements propres aux zones dites sans lichen de lâArctique canadien a Ă©tĂ© attribuĂ©e tant Ă lâexpansion des champs de neige pĂ©renne pendant le petit Ăąge glaciaire quâĂ la couverture de neige longĂ©vive dâĂ©poques plus rĂ©centes. Puisquâil existe des hypothĂšses disparates (Ă©cologiques par opposition Ă palĂ©oclimatiques) quant Ă la formation de ces Ă©paulements, on a arrĂȘtĂ© de sâen servir Ă titre dâindicateur palĂ©oclimatique depuis plus dâune vingtaine dâannĂ©es. Ici, ce dĂ©bat fait lâobjet dâun nouvel examen oĂč lâon se penche sur la validitĂ© des hypothĂšses divergentes Ă la lumiĂšre du nouveau mappage rĂ©gional des Ă©paulements des Ăźles de la Reine-Ălisabeth. LâhypothĂšse dâordre Ă©cologique âdurĂ©e insuffisante de la saison de croissance dĂ©coulant de la couverture de neige longĂ©vive en saison âomet de tenir compte de la nature poecilitique du lichen et de son aptitude Ă endurer de courtes saisons de croissance. Cette hypothĂšse ne permet pas dâexpliquer adĂ©quatement lâexistence dâĂ©paulements prĂ©cis ou de tenir compte de la prĂ©sence de ces Ă©paulements en terrain carbonatĂ© Ă vĂ©gĂ©tation Ă©parse. Par ailleurs, les Ă©paulements qui dĂ©limitent lâancienne Ă©tendue des minces calottes glaciaires des plateaux correspondent aux Ă©paulements associĂ©s aux anciens champs de neige pĂ©renne, ce qui indique que ces Ă©paulements dĂ©notent les expansions de neige et de glace du petit Ăąge glaciaire et non pas de la couverture de neige longĂ©vive saisonniĂšre plus rĂ©cente. On suggĂšre que ces caractĂ©ristiques reprĂ©sentent un important indicateur climatique du petit Ăąge glaciaire et par consĂ©quent, quâon devrait sâen servir Ă des fins de reconstruction palĂ©oclimatique
Deglacierization of a marginal basin and implications for outburst floods
This article was submitted to Cryospheric Sciences, a section of the journal Frontiers in Earth ScienceSuicide Basin is a partly glacierized marginal basin of Mendenhall Glacier, Alaska, that has released glacier lake outburst floods (GLOFs) annually since 2011. The floods cause inundation and erosion in the Mendenhall Valley, impacting homes and other infrastructure. Here, we utilize in-situ and remote sensing data to assess the recent evolution and current state of Suicide Basin. We focus on the 2018 and 2019 melt seasons, during which we collected most of our data, partly using unmanned aerial vehicles (UAVs). To provide longer-term context, we analyze DEMs collected since 2006 and model glacier surface mass balance over the 2006â2019 period. During the 2018
and 2019 outburst flood events, Suicide Basin released ⌠30 Ă
~ 106 m3 of water within approximately 4â5 days. Since lake drainage was partial in both years, these ⌠30 Ă
~ 106 m3 represent only a fraction (⌠60%) of the basinâs total storage capacity. In contrast
to previous years, subglacial drainage was preceded by supraglacial outflow over the ice dam, which lasted ⌠1 day in 2018 and 6 days in 2019. Two large calving events occurred in 2018 and 2019, with submerged ice breaking off the main glacier during lake filling, thereby increasing the basinâs storage capacity. In 2018, the floating ice in the basin was 36 m thick on average. In 2019, ice thickness was 29 m, suggesting rapid decay of the ice tongue despite increasing ice inflow from Mendenhall Glacier. The ice dam at the basin entrance thinned by more than 5 m aâ1 from 2018 to 2019, which is approximately double the rate of the reference period 2006â2018. While ice-dam thinning reduces water storage capacity in the basin, that capacity is increased by declining ice volume in the basin and longitudinal lake expansion, with the latter process challenging to predict. The potential for premature drainage onset (i.e., drainage before the lakeâs storage capacity is reached), intermittent drainage decelerations, and early drainage termination further complicates prediction of future GLOF events.This work was funded by the Alaska Climate Adaptation Science Center (AK CASC). UAVs and other surveying equipment were
partly funded through the U.S. National Science Foundation (NSF) award EAR-1921598. EH and SH were partially supported
by the NSF award OIA-1753748 and the State of Alaska. Streamflow monitoring of the Mendenhall River and real-time imagery of Suicide Basin were funded by the U.S. Geological Survey Groundwater and Streamflow Information Program. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.Ye
The state of the Martian climate
60°N was +2.0°C, relative to the 1981â2010 average value (Fig. 5.1). This marks a new high for the record. The average annual surface air temperature (SAT) anomaly for 2016 for land stations north of starting in 1900, and is a significant increase over the previous highest value of +1.2°C, which was observed in 2007, 2011, and 2015. Average global annual temperatures also showed record values in 2015 and 2016. Currently, the Arctic is warming at more than twice the rate of lower latitudes
Changes in late-Neoglacial climate inferred from former equilibrium-line altitudes in the Queen Elizabeth Islands, Arctic Canada
PHOTOGRAMMETRICALLY DERIVED ESTIMATES OF SNOW DEPTH VARIABILITY IN COMPLEX TERRAIN
ABSTRACT: Seasonal snow is a key cryospheric variable because of its influence on energy and water budgets, regional economies, and public safety. Quantitative information on the spatial distribution of snow depth and snow water equivalence (SWE) is central to numerous applications in cryospheric research. However, in complex terrain, strong orographic gradients and wind redistribution produce complicated accumulation patterns that are difficult to capture using traditional in situ and satellite-based approaches, and are challenging to model with acceptable levels of uncertainty. Here we present results from a pilot study where we apply a repeat airborne photogrammetric approach and employ a Structure from Motion (SfM) processing method to generate digital surface models (DSMs) of terrain during snowfree (fall 2014) and snow-covered (spring 2015) periods. Surface elevation differencing of these datasets produces continuous and accurate maps of end-of-winter snow depth variability over complex terrain in the maritime-continental transition zone of the eastern Chugach Mountains, Alaska, and provides valuable data for assessing avalanche susceptibility and modeling avalanche runout
End-of-winter snow depth variability on glaciers in Alaska
A quantitative understanding of snow thickness and snow water equivalent (SWE) on glaciers is essential to a wide range of scientific and resource management topics. However, robust SWE estimates are observationally challenging, in part because SWE can vary abruptly over short distances in complex terrain due to interactions between topography and meteorological processes. In spring 2013, we measured snow accumulation on several glaciers around the Gulf of Alaska using both ground- and helicopter-based ground-penetrating radar surveys, complemented by extensive ground truth observations. We found that SWE can be highly variable (40% difference) over short spatial scales (tens to hundreds of meters), especially in the ablation zone where the underlying ice surfaces are typically rough. Elevation provides the dominant basin-scale influence on SWE, with gradients ranging from 115 to 400 mm/100 m. Regionally, total accumulation and the accumulation gradient are strongly controlled by a glacierâs distance from the coastal moisture source. Multiple linear regressions, used to calculate distributed SWE fields, show that robust results require adequate sampling of the true distribution of multiple terrain parameters. Final SWE estimates (comparable to winter balances) show reasonable agreement with both the Parameter-elevation Relationships on Independent Slopes Model climate data set (9â36% difference) and the U.S. Geological Survey Alaska Benchmark Glaciers (6â36% difference). All the glaciers in our study exhibit substantial sensitivity to changing snow-rain fractions, regardless of their location in a coastal or continental climate. While process-based SWE projections remain elusive, the collection of ground-penetrating radar (GPR)-derived data sets provides a greatly enhanced perspective on the spatial distribution of SWE and will pave the way for future work that may eventually allow such projections