Internal Waves in the Western Arctic Ocean
Dosser, Hayley Victoria
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The importance of internal waves in the Western Arctic Ocean is assessed using a combination of observations from Ice-Tethered Profilers drifting in the Canada Basin between Fall 2005 and Fall 2014 and numerical simulations of internal wave propagation and stability in measured stratifications typical of the Western Arctic. The Ice-Tethered Profiler dataset provides the first decade-long record, with broad spatial coverage, for the near-inertial internal wave field in the Arctic Ocean. Since the Ice-Tethered Profiler sampling pattern only marginally resolves the near-inertial frequency, complex demodulation is used to estimate wave amplitudes from vertical isopycnal displacements. Using this technique, a seasonal cycle in average near-inertial wave vertical displacement amplitude is identified for the upper ocean. Waves are largest during summer when sea-ice extent and speed are at a minimum, with a second peak in early winter associated with strong storms. Seasonal variations in wave amplitude are connected to changes in sea-ice properties that affect how readily the ice responds to wind forcing. In addition to seasonal variability, near-inertial wave amplitude has a slight increasing trend paralleling the decline in sea-ice extent over the last decade. Variance in the distribution of wave amplitudes doubled between 2005-2007 and 2012-2014, with larger-than-average waves generated more frequently in both summer and winter. Numerical solutions for the vertical structure of internal waves propagating through observed stratification profiles from the Canada Basin indicate that the double-diffusive staircase within the Atlantic Water layer significantly modifies the internal wave field, causing reflection for discrete vertical wavenumber bands and amplifying wave energy at depths where constructive interference occurs. Near-inertial internal waves of average amplitude are predicted to be stable within the Atlantic Water layer, but the fraction of larger-than-average waves that are potentially shear unstable has more than doubled over the last decade. An increase in episodic internal wave mixing events is predicted in the Canada Basin. The internal wave field in the Western Arctic Ocean will likely continue to evolve as sea-ice extent and thickness decline, and multiyear ice is replaced by first-year ice.
- Oceanography