A regional data-constrained coupled ocean-sea ice general circulation
model and its adjoint are used to investigate mechanisms controlling the
volume transport variability through Bering Strait during 2002 to 2013.
Comprehensive time-resolved sensitivity maps of Bering Strait transport
to atmospheric forcing can be accurately computed with the adjoint along
the forward model trajectory to identify spatial and temporal scales
most relevant to the strait's transport variability. The simulated
Bering Strait transport anomaly is found to be controlled primarily by
the wind stress on short time-scales of order 1 month. Spatial
decomposition indicates that on monthly time-scales winds over the
Bering and the combined Chukchi and East Siberian Seas are the most
significant drivers. Continental shelf waves and coastally-trapped waves
are suggested as the dominant mechanisms for propagating information
from the far field to the strait. In years with transport extrema,
eastward wind stress anomalies in the Arctic sector are found to be the
dominant control, with correlation coefficient of 0.94. This implies
that atmospheric variability over the Arctic plays a substantial role in
determining Bering Strait flow variability. The near-linear response of
the transport anomaly to wind stress allows for predictive skill at
interannual time-scales, thus potentially enabling skillful prediction
of changes at this important Pacific-Arctic gateway, provided that
accurate measurements of surface winds in the Arctic can be obtained.
The novelty of this work is the use of space and time-resolved
adjoint-based sensitivity maps, which enable detailed dynamical, i.e.
causal attribution of the impacts of different forcings.