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Lakes in direct contact with glaciers (ice-marginal lakes) are found across alpine and polar landscapes. Many studies characterize ice-marginal lake behavior over multi-decadal timescales using either episodic ~annual images or multi-year mosaics. However, ice-marginal lakes are dynamic features that experience short-term (i.e., day to year) variations in area and volume superimposed on longer-term trends. Through aliasing, this short-term variability could result in erroneous long-term estimates of lake change. We develop and implement an automated workflow in Google Earth Engine to quantify monthly behavior of ice-marginal lakes between 2013 and 2019 across south-central Alaska using Landsat 8 imagery. We employ a supervised Mahalanobis minimum-distance land cover classifier incorporating three datasets found to maximize classifier performance: shortwave infrared imagery, the normalized difference vegetation index (NDVI), and spatially filtered panchromatic reflectance. We observe physically-meaningful ice-marginal lake area variance on sub-annual timescales, with the median area fluctuation of an ice-marginal lake found to be 10.8% of its average area. The median signal (slow lake growth) to noise (physically-meaningful short-term area variability) ratio is 1.5:1, indicating that short-term variability is responsible for ~33% of observed area change in the median ice-marginal lake. The magnitude of short-term area variability is similar for ice-marginal and nonglacial lakes, suggesting that the cause of observed variations is not of glacial origin. These data provide a new context for interpreting behaviors observed in multi-decadal studies and encourage attention to sub-annual behavior of ice-marginal lakes even in long-term studies.
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Gulf of Alaska ice-marginal lake area change over the Landsat record and potential physical controls
Abstract. Lakes in contact with glacier margins can impact glacierevolution as well as the downstream biophysical systems, flood hazard, andwater resources. Recent work suggests positive feedbacks between glacierwastage and ice-marginal lake evolution, although precise physical controlsare not well understood. Here, we quantify ice-marginal lake area change inunderstudied northwestern North America from 1984–2018 and investigateclimatic, topographic, and glaciological influences on lake area change. Wedelineate time series of sampled lake perimeters (n=107 lakes) and findthat regional lake area has increased 58 % in aggregate, with individualproglacial lakes growing by 1.28 km2 (125 %) and ice-dammed lakesshrinking by 0.04 km2 (−15 %) on average. A statisticalinvestigation of climate reanalysis data suggests that changes in summertemperature and winter precipitation exert minimal direct influence on lakearea change. Utilizing existing datasets of observed and modeled glacialcharacteristics, we find that large, wide glaciers with thick lake-adjacentice are associated with the fastest rate of lake area change, particularlywhere they have been undergoing rapid mass loss in recent times. We observe adichotomy in which large, low-elevation coastal proglacial lakes havechanged most in absolute terms, while small, interior lakes at highelevation have changed most in relative terms. Generally, the fastest-changinglakes have not experienced the most dramatic temperature or precipitationchange, nor are they associated with the highest rates of glacier mass loss.Our work suggests that, while climatic and glaciological factors must playsome role in determining lake area change, the influence of a lake'sspecific geometry and topographic setting overrides these external controls.
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- Award ID(s):
- 1821002
- PAR ID:
- 10291796
- Date Published:
- Journal Name:
- The Cryosphere
- Volume:
- 15
- Issue:
- 7
- ISSN:
- 1994-0424
- Page Range / eLocation ID:
- 3255 to 3278
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/tc-15-3255-2021
