The Stratification Maxima of the Seasonally Varying Surface Layer in the Arctic Ocean’s Beaufort Gyre

Abstract

The Beaufort Gyre region of the Arctic Ocean is strongly stratified at the base of the wintertime mixed layer, which impedes the vertical transport of heat, energy, and other tracers. Ice-Tethered Profiler observations during 2004-2018 were used to characterize and investigate the seasonal and interannual variability of the strength, depth, density, and thickness of this highly stratified layer at the base of the mixed layer. This includes investigating the remnant stratification maximum, which formed when the summer mixed layer shoaled. Seasonally, the stratification maximum was never in a steady state. It was largest in October (4.8 × 10⁻³ 𝑟𝑎𝑑²/𝑠𝑒𝑐²) and decreased during all winter months (to 2.3 × 10⁻³ 𝑟𝑎𝑑²/𝑠𝑒𝑐² in June), indicating that surface forcing and interior vertical mixing were never in equilibrium during the year. Interannually, the period from 2011-2018 had a higher stratification maximum than then the period from 2005-2010 regardless of the season. The remnant stratification maximum was consistently weaker than the winter stratification maximum from which it formed. The initial evolution of the remnant stratification maximum is used to estimate an effective vertical diffusivity of order 10⁻⁶𝑚²/𝑠. No significant geographic variability was found, in part due to high temporal and small scale variability of the stratification maximum layer. Implications for heat transport through to the sea ice cover are discussed.