Beaded streams are widespread in permafrost regionsand are considered a common thermokarst landform.However, little is known about their distribution, how andunder what conditions they form, and how their intriguingmorphology translates to ecosystem functions and habitat.Here we report on a circum-Arctic survey of beaded streamsand a watershed-scale analysis in northern Alaska using remotesensing and field studies.We mapped over 400 channelnetworks with beaded morphology throughout the continuouspermafrost zone of northern Alaska, Canada, and Russiaand found the highest abundance associated with mediumto high ground-ice content permafrost in moderately slopingterrain. In one Arctic coastal plain watershed, beaded streamsaccounted for half of the drainage density, occurring primarilyas low-order channels initiating from lakes and drainedlake basins. Beaded streams predictably transition to alluvialchannels with increasing drainage area and decreasingchannel slope, although this transition is modified by localcontrols on water and sediment delivery. The comparisons ofone beaded channel using repeat photography between 1948and 2013 indicate a relatively stable landform, and 14C datingof basal sediments suggest channel formation may beas early as the Pleistocene–Holocene transition. Contemporaryprocesses, such as deep snow accumulation in riparianzones, effectively insulate channel ice and allows for perennialliquid water below most beaded stream pools. Becauseof this, mean annual temperatures in pool beds are greaterthan 2 C, leading to the development of perennial thaw bulbsor taliks underlying these thermokarst features that rangefrom 0.7 to 1.6 m. In the summer, some pools thermally stratify,which reduces permafrost thaw and maintains cold-waterhabitats. Snowmelt-generated peak flows decrease rapidly bytwo or more orders of magnitude to summer low flows withslow reach-scale velocity distributions ranging from 0.01 to0.1ms-1, yet channel runs still move water rapidly betweenpools. The repeating spatial pattern associated with beadedstream morphology and hydrological dynamics may provideabundant and optimal foraging habitat for fish. Beadedstreams may create important ecosystem functions and habitatin many permafrost landscapes and their distribution anddynamics are only beginning to be recognized in Arctic research.
