Abstract
Increasing extent and duration of seasonally ice-free area in the
western Arctic Ocean suggests increased air-sea coupling, specifically
fluxes of momentum and heat between the lower atmosphere and the upper
ocean. The dependence of these fluxes on ice concentration and its
dynamical characteristics is still uncertain. As part of the Stratified
Ocean Dynamics of the Arctic (SODA) project, year-long time series of
upper-ocean velocity profiles were obtained across a range of ice
conditions and are used to infer momentum fluxes. We consider the
structure of observed current profiles as a function of sea state and
ice cover. During the summer and in open water with minimal
stratification, the wind forcing is in local equilibrium with surface
gravity waves, and there is a direct transfer of momentum from the
atmosphere to the upper ocean. The presence of ice modifies the momentum
budget through both the inclusion of ice-atmosphere and ice-ocean
stresses, and by damping short surface gravity waves and thus changing
the surface roughness that the atmosphere acts upon. Ice presence is
also associated with increased near-surface stratification, which can
act to decouple the sub-surface ocean from atmospheric forcing. Our
observations show frequent decoupling of a thin surface layer
(<10 m depth), including case studies in which the relatively
fresh surface waters formed by “ice puddles” have entirely different
motion from the relatively salty water a few meters below. Ice formation
in the fall affects both the ocean stratification and the ice
characteristics, leading to competing effects affecting momentum
transfer. Initial results across the annual cycle are presented.