Mixed Layer Depth Variability in Coastal Waters of British Columbia, Canada

Mixed layer depth is examined for the waters off the coast of British Columbia, Canada, in the Northeast Pacific. The output of a 32 year (1979-2010), hindcast is used, as well as a large series of CTD and ARGO float profiles. The numerical simulation is done with a local implementation of the Regional Ocean Modelling System (ROMS) with relatively high vertical resolution (60 sigma layers). The seasonal cycle of the mixed layer depth is first determined, highlighting the strong contrast between the waters of the offshore, shelf and marginal areas. The year to year variability of the near surface stratification is then examined for both the numerical simulations and observations. In particular, the regional impact of the El Nino signal (e.g. in 1998) on the upper water column structure is evident in the observations and is captured by the numerical model.