Hydrogeomorphic processes of thermokarst lakes with grounded‐ice and floating‐ice regimes on the Arctic coastal plain, Alaska

Abstract

Abstract:Thermokarst lakes cover >20% of the landscape throughout much of the Alaskan Arctic Coastal Plain (ACP) with shallow lakes freezing solid (grounded ice) and deeper lakes maintaining perennial liquid water (floating ice). Thus, lake depth relative to maximum ice thickness (1Ð5-2Ð0 m) represents an important threshold that impacts permafrost, aquatic habitat, and potentially geomorphic and hydrologic behaviour. We studied coupled hydrogeomorphic processes of 13 lakes representing a depth gradient across this threshold of maximum ice thickness by analysing remotely sensed, water quality, and climatic data over a 35-year period. Shoreline erosion rates due to permafrost degradation ranged from <0Ð2 m/year in very shallow lakes (0Ð4 m) up to 1Ð8 m/year in the deepest lakes (2Ð6 m). This pattern of thermokarst expansion masked detection of lake hydrologic change using remotely sensed imagery except for the shallowest lakes with stable shorelines. Changes in the surface area of these shallow lakes tracked interannual variation in precipitation minus evaporation (P E L ) with periods of full and nearly dry basins. Shorter-term (2004Shorter-term ( -2008 specific conductance data indicated a drying pattern across lakes of all depths consistent with the long-term record for only shallow lakes. Our analysis suggests that grounded-ice lakes are ice-free on average 37 days longer than floating-ice lakes resulting in a longer period of evaporative loss and more frequent negative P E L . These results suggest divergent hydrogeomorphic responses to a changing Arctic climate depending on the threshold created by water depth relative to maximum ice thickness in ACP lakes.

Drainage Network Structure and Hydrologic Behavior of Three Lake-Rich Watersheds on the Arctic Coastal Plain, Alaska

“…The role of storage deficit from C. D. ARP ET AL. / 393 the preceding season is an important process for ACP watersheds suggested by Bowling et al (2003) and observed in Landsat timeseries analysis of lake area extent for this region (Jorgenson et al, 2005;Jones et al, 2009a) and other ACP landscapes (Plug et al, 2008;Arp et al, 2011 ). The summer of 2009 was considered very wet and relatively cool and cloudy; the lower storage deficit from 2008 conditions combined with relatively large snowpack likely resulted in the much higher water yield.…”

“…For the purposes of delineating drainage network extent, flow paths for (1) flow-through lakes basins were drawn as straight lines from lake inlets to the lake centroid and to lake outlets, and (2) headwater lake basins were drawn only from the lake centroid to the lake outlet. Additionally, all lakes within these three watersheds, whether connected by stream channels or not, were categorized by depth based on lake ice analysis using synthetic aperture radar (SAR) imagery (RADARSAT-1) from 12 April 2007 following methods in Mellor (1982) and Jeffries et al (1996) and detailed in Arp et al (2011). Lake depth classes are (1) Ͻ2-m depth with 388 / ARCTIC, ANTARCTIC, AND ALPINE RESEARCH bedfast ice, (2) 2-4 m depth with floating ice, and (3) Ͼ4-m depth with floating ice.…”

“…Such Arctic watershed responses to climate change may dominate steeper environments, but what are the long-term responses to climate change that can be expected in low-relief ACP watersheds where lakes and other depression storage dominate runoff behavior? Research that identifies mechanisms of thermokarst lake expansion and drainage linked to historic climate reconstructions (Marsh et al, 2009;Arp et al, 2011;Jones et al, 2011) and future GCM predictions (Pohl et al, 2007) may provide an important basis for such understanding. Refining measurements and predictions of Arctic hydrologic intensification is a key aspect towards comprehending Arctic landscape responses to climate change (Rawlins et al, 2010), yet a more essential component maybe understanding land surface mechanisms that control drainage network structure and ultimately watershed function (Woo et al, 2008;McNamara and Kane, 2009).…”

“…Existing climate and river discharge data from these three watersheds enabled us to examine how these differences in watershed morphology, particularly lake-basin type and extent, produced variable runoff responses in years ranging from extreme drought (2007) to relative deluge (2009). Thus, an analysis of these watersheds will help 386 / ARCTIC, ANTARCTIC, AND ALPINE RESEARCH advance our understanding of Arctic landscapes and hydrologic processes in the present and also serve as a model for future changes in the Arctic with respect to lake expansion, drainage, or drying (Pohl et al, 2007;Arp et al, 2011;Jones et al, 2011) and hydrologic intensification resulting in uncertain runoff responses (Rawlins et al, 2010).…”

Characterization of L-band synthetic aperture radar (SAR) backscatter from floating and grounded thermokarst lake ice in Arctic Alaska

“…Seasonal ice-cover typically starts forming on lake surfaces in late October or early November in Arctic Alaska and grows to a maximum thickness of over one meter to two meters by late March/early April (Mellor 1982;Jeffries et al, 1994;Arp et al, 2011). Some lakes are shallower than 1-2 m and no liquid water remains at maximum seasonal ice thickness, resulting in grounded ice.…”