Climate signatures on lake and wetland size distributions in arctic deltas

Coastal river deltas are landscapes at significant risk from sea level rise and sediment deprivation (Nienhuis et al., 2020; Syvitski et al., 2009). Arctic deltas are likely more vulnerable than their temperate counterparts due to the presence of thermokarst lakes in permafrost, which are sensitive to rapid Arctic warming (Emmerton et al., 2007; Piliouras & Rowland, 2020; Walker, 1998). Pan-arctic thermokarst lake coverage is responding to warmer temperatures in complex ways, as temperature-driven ground ice loss drives lake growth through retrogressive thaw slumping along lake shorelines (Grosse et al., 2013) but also generates surface and subsurface hydrologic connectivity that can cause lake drainage (Grosse et al., 2013; Jones et al., 2020; Rowland et al., 2011; Yoshikawa & Hinzman, 2003). Observed changes in lake area over the last 50 years have shown both positive and negative trends depending on local hydrology, climate, permafrost zonation, ice content, landscape age, and geomorphic setting (Arp et al., 2011; Chen et al., 2012; Jones et al., 2011; Nitze et al., 2018; Plug et al., 2008; Smith et al., 2005). Irrespective of whether lake coverage is expanding or decreasing, the reorganization of thermokarst lake cover will have significant implications Abstract Understanding how thermokarst lakes on arctic river deltas will respond to rapid warming is critical for projecting how carbon storage and fluxes will change in those vulnerable environments. Yet, this understanding is currently limited partly due to the complexity of disentangling significant interannual variability from the longer-term surface water signatures on the landscape, using the short summertime window of optical spaceborne observations. Here, we rigorously separate perennial lakes from ephemeral wetlands on 12 arctic deltas and report distinct size distributions and climate trends for the two waterbodies. Namely, we find a lognormal distribution for lakes and a power-law distribution for wetlands, consistent with a simple proportionate growth model and inundated topography, respectively. Furthermore, while no trend with temperature is found for wetlands, a statistically significant decreasing trend of mean lake size with warmer temperatures is found, attributed to colder deltas having deeper and thicker permafrost preserving larger lakes.