Distribution and biophysical processes of beaded streams in Arctic permafrost landscapes

[摘要] Beaded streams are widespread in permafrost regions and are considered acommon thermokarst landform. However, little is known about theirdistribution, how and under what conditions they form, and how theirintriguing morphology translates to ecosystem functions and habitat. Here wereport on a circum-Arctic survey of beaded streams and a watershed-scaleanalysis in northern Alaska using remote sensing and field studies. Wemapped over 400 channel networks with beaded morphology throughout thecontinuous permafrost zone of northern Alaska, Canada, and Russia and foundthe highest abundance associated with mediumto high ground-ice contentpermafrost in moderately sloping terrain. In one Arctic coastal plainwatershed, beaded streams accounted for half of the drainage density,occurring primarily as low-order channels initiating from lakes and drainedlake basins. Beaded streams predictably transition to alluvial channels withincreasing drainage area and decreasing channel slope, although thistransition is modified by local controls on water and sediment delivery.The comparisons of one beaded channel using repeat photography between 1948 and2013 indicate a relatively stable landform, and ¹⁴C dating of basalsediments suggest channel formation may be as early as thePleistocene–Holocene transition. Contemporary processes, such as deep snowaccumulation in riparian zones, effectively insulatechannel ice and allowsfor perennial liquid water below most beaded stream pools. Because of this,mean annual temperatures in pool beds are greater than 2 °C,leading to the development of perennial thaw bulbs or taliks underlyingthese thermokarst features that range from 0.7 to 1.6 m. In the summer, somepools thermally stratify, which reduces permafrost thaw and maintainscold-water habitats. Snowmelt-generated peak flows decrease rapidly by two ormore orders of magnitude to summer low flows with slow reach-scale velocitydistributions ranging from 0.01 to 0.1 m s⁻¹, yet channel runs still movewater rapidly between pools. The repeating spatial pattern associated withbeaded stream morphology and hydrological dynamics may provide abundant andoptimal foraging habitat for fish. Beaded streams may create importantecosystem functions and habitat in many permafrost landscapes and theirdistribution and dynamics are only beginning to be recognized in Arcticresearch.

[学科分类] 地球化学与岩石