Variability of Internal Wave‐Driven Mixing and Stratification in Canadian Arctic Shelf and Shelf‐Slope Waters

Abstract

Our understanding of ocean mixing is challenged by its patchy, episodic nature and a scarcity of direct measurements, especially in the Arctic Ocean. In this study, we exploit a historical record of nearly 3,000 conductivity‐temperature‐depth profiles collected in the shelf and shelf‐slope waters of the Canadian Arctic Ocean from 2002 to 2016 to characterize the variability of 28,872 internal wave‐driven turbulent dissipation and mixing rate estimates from a finescale parameterization. We find that these estimates of wave‐driven dissipation rates and associated diapycnal diffusivities are generally low, but exhibit wide variability, each spanning several orders of magnitude. We further find that stratification plays a significant role in modulating the mixing rate both vertically and regionally within the study domain. Dissipation rate and diffusivity estimates display a weak seasonal cycle, but no evidence of statistically significant interannual trends over this period. Exceptionally large localized temporal variability appears to dominate other potential underlying patterns. The presence of strong upper ocean stratification combined with predominately weak dissipation rate estimates implies that many regions in the Canadian Arctic Ocean are likely in a molecular or buoyancy‐controlled mixing regime. Even when the concept of a turbulent‐enhanced diffusivity is potentially relevant, most turbulent heat flux estimates out of the Atlantic Water thermocline are smaller than the average value required to close the standardly assumed Arctic Ocean heat budget. In contrast, we find evidence for isolated occurrences of anomalously large heat fluxes, which may disproportionately contribute to the liberation of Atlantic Water heat toward the surface sea ice pack.

Laboratory study of the properties of frazil ice particles and flocs in water of different salinities

“…The overall mean size of frazil ice particles in freshwater of 0.52 mm was slightly larger than in saline water. This value falls within the reported ranges of previous studies of 23 µm to 5 mm (Gosink and Osterkamp, 1983;Daly and Colbeck, 1986;Ye et al, 2004;Clark and Doering, 2006;Mc-Farlane et al, 2015. The average overall mean particle size in saline water was 0.46 mm.…”

“…In a similar series of experiments in the same tank, McFarlane et al (2015) found that the tank-averaged turbulent kinetic energy dissipation rate was ∼ 3.4 × 10 −2 m 2 s −3 at a propeller speed of 325 rpm, and this fell within the range of dissipation rates estimated for rivers in Alberta. Dissipation rates in the ocean range from ∼ 10 −2 to 10 −9 m 2 s −3 (Banner and Morrison, 2018;Wang and Liao, 2016), with a reported lower range in the polar regions ranging from ∼ 10 −3 to 10 −10 m 2 s −3 (Chanona et al, 2018;Scheifele et al, 2018). Therefore, the dissipation rate generated in these experiments falls within the upper limits of values observed in the ocean.…”

“…Phase 1 is defined as the time from when the water reached the freezing temperature (t/t c = 0) to the time when the water reached the maximum supercooling temperature (t/t c = 1.0). The other two phases were defined relative to when the peak number of particles or flocs were observed in the ensemble-averaged time series following Clark and Doering (2006). Phase 2 is defined as the time from t/t c = 1.0 to the time when 90 % of the peak number of particles or flocs is reached (t 90a ).…”

“…Several laboratory and field studies have reported measurements of the size and shape of individual frazil ice particles in freshwater. The reported frazil particles were predominantly disc-shaped with a range of diameters between 23 µm and 5 mm and particle sizes fitting a log-normal particle size distribution in laboratory (Gosink and Osterkamp, 1983;Daly and Colbeck, 1986;Ye et al, 2004;Clark and Doering, 2006;Ghobrial et al, 2012;McFarlane et al, 2015) and field studies (Gosink and Osterkamp, 1983;Richard et al, 2011;Ghobrial et al, 2013;Marko et al, 2015;McFarlane et al, 2017). A limited number of measurements of the shape and size of individual frazil ice particles in saline water have been performed, and, to the best of the authors' knowledge, no studies have reported particle size distributions.…”

Pan-Arctic Ocean Primary Production Constrained by Turbulent Nitrate Fluxes

“…While less sea ice may enhance the input of wind energy into the ocean (Rainville and Woodgate, 2009;Dosser and Rainville, 2016), this energy may be dissipated at shallow depths due to the strong stratification (Lincoln et al, 2016). Reanalysis of conductivity-temperature depth and acoustic Doppler current profiler finestructure data has not shown trends in turbulent mixing in recent decades either (Guthrie et al, 2013;Chanona et al, 2018).…”