Modeling Seasonal Variability of Arctic Barotropic and Baroclinic
Diurnal Tides: Implications for the Tide’s Role in Evolving Arctic Ocean
State
Abstract
Diurnal tidal currents are the dominate contributors to diapycnal mixing
in many regions along the pathways for warm Atlantic Water (AW)
circulating within the Arctic Ocean along the continental slope. This
mixing diffuses AW heat and salt into the cooler and fresher
surroundings, including the upper ocean where ocean heat fluxes play a
role in the stability of the ice pack. The strongest diurnal currents
are associated with topographically-trapped vorticity waves, which are
sensitive to stratification and mean flow. In models, these waves are
also sensitive to choices for forcing and geometry. Sensitivity to
background conditions implies that tidal currents and mixing will change
as the Arctic evolves towards a new climate state. Here, as a first step
towards understanding how diurnal tidal currents might change in a
future Arctic Ocean, we describe results from a suite of high-resolution
(dx=2 km) 2-D and 3-D models for Arctic diurnal tides, focusing on their
currents at locations along the AW pathways. We first demonstrate that
accurate representation of barotropic diurnal tides requires forcing
with both open boundary conditions and the direct potential tide. Next,
we use 3-D models with realistic, ocean background stratification and
mean flow to describe the annual cycle of depth-averaged diurnal tidal
currents. Finally, we investigate the baroclinic structure of diurnally
forced waves including the generation of harmonics (semidiurnal and
higher) that can contribute to mixing within the water column. Our
results show that tides should be explicitly included in ocean and
coupled predictive models for the Arctic to represent the feedbacks
between tidal energetics and ocean mean state via mixing.