Abstract
Capes and cape-associated shoals represent sites of convergent sediment
transport, and can provide points of relative coastal stability,
navigation hazards, and offshore sand resources. Shoal evolution is
commonly impacted by the regional wave climate. In the Arctic, changing
sea-ice conditions are leading to (1) longer open-water seasons when
waves can contribute to sediment transport, and (2) an intensified wave
climate (related to duration of open water and expanding fetch). At
Blossom Shoals offshore of Icy Cape in the Chukchi Sea, these changes
have led to a five-fold increase in the amount of time that sand is
mobile at a 31-m water depth site between the period 1953-1989 and the
period 1990-2022. Wave conditions conducive to sand transport are still
limited to less than 2% of the year, however - and thus it is not
surprising that the overall morphology of the shoals has changed little
in 70 years, despite evidence of active sand transport in the form of
1-m-scale sand waves on the flanks of the shoals which heal ice keel
scours formed during the winter. Suspended-sediment transport is
relatively weak due to limited sources of mud nearby, but can be
observed in a net northeastward direction during the winter (driven by
the Alaska Coastal Current under the ice) and in a southwestward
direction during open-water wind events. Longer open-water seasons mean
that annual net northeastward transport of fine sediment may weaken,
with implications for the residence time of fine-grained sediments and
particle-associated nutrients in the Chukchi Sea.