Beaded streams are widespread in permafrost regions
and are considered a common thermokarst landform.
However, little is known about their distribution, how and
under what conditions they form, and how their intriguing
morphology translates to ecosystem functions and habitat.
Here we report on a circum-Arctic survey of beaded streams
and a watershed-scale analysis in northern Alaska using remote
sensing and field studies. We mapped over 400 channel
networks with beaded morphology throughout the continuous
permafrost zone of northern Alaska, Canada, and Russia
and found the highest abundance associated with medium
to high ground-ice content permafrost in moderately sloping
terrain. In one Arctic coastal plain watershed, beaded streams
accounted for half of the drainage density, occurring primarily
as low-order channels initiating from lakes and drained
lake basins. Beaded streams predictably transition to alluvial
channels with increasing drainage area and decreasing
channel slope, although this transition is modified by local
controls on water and sediment delivery. The comparisons of
one beaded channel using repeat photography between 1948
and 2013 indicate a relatively stable landform, and 14C dating
of basal sediments suggest channel formation may be
as early as the Pleistocene–Holocene transition. Contemporary
processes, such as deep snow accumulation in riparian
zones, effectively insulate channel ice and allows for 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 underlying these thermokarst features that range
from 0.7 to 1.6 m. In the summer, some pools thermally stratify,
which reduces permafrost thaw and maintains cold-water
habitats. Snowmelt-generated peak flows decrease rapidly by
two or more orders of magnitude to summer low flows with
slow reach-scale velocity distributions ranging from 0.01 to
0.1 m s−1
, yet channel runs still move water rapidly between
pools. The repeating spatial pattern associated with beaded
stream morphology and hydrological dynamics may provide
abundant and optimal foraging habitat for fish. Beaded
streams may create important ecosystem functions and habitat
in many permafrost landscapes and their distribution and
dynamics are only beginning to be recognized in Arctic research.
