Investigating the effect of the Coriolis force on internal wave dynamics and flushing of a coastal embayment

Investigating the effect of the Coriolis force on internal wave dynamics and flushing of a coastal embayment Bryan Flood 1 , Mathew Wells 1 , Joelle Young 2 and Erin Dunlop 3 Department of Physical and Environmental Sciences, University of Toronto, Toronto, Canada Ontario Ministry of the Environment and Climate Change, Toronto, Canada Ontario Ministry of Natural Resources and Forestry, Peterborough, Canada bryan.flood@mail.utoronto.ca Abstract Lake Simcoe is a large (SA = 722 km2), mid-latitude (44ᵒ N lat.) lake in Canada that suffers from high nutrient loading and eutrophication. The 42 m deep Kempenfelt Bay on the western side of the lake contains the majority of the cold-water fish habitat and is also prone to end-of-summer hypolimnetic hypoxic conditions. A better understanding of the exchange dynamics of Kempenfelt Bay is essential for enacting long-term water quality improvements. Using high resolution temperature and current velocity field data from 2015, we show that large-amplitude internal waves have a significant impact on the current velocity structure of Kempenfelt Bay. The internal waves act as bellows, pumping water into and out of the embayment. Moreover, the Coriolis force causes the currents to be deflected to the right, resulting in an asymmetrical flow structure with predominantly westerly flows on the north side, and easterly on the south side of the bay. The asymmetry sets up a residual counter clockwise flow in Kempenfelt Bay that could further impact flushing. Introduction Internal wave dynamics in large, mid-latitude lakes are controlled by a complex interplay of Coriolis, geostrophic and buoyancy forces which contribute to the development of complicated physical processes in a lake’s embayments. Exchange between an embayment and the main basin of a lake is often constrained, leading to the development of unique water characteristics within the embayment that are strongly influenced, both spatially and temporally, by its flushing dynamics. Many of the physical processes governing the flushing dynamics of embayments have been previously investigated, such as tidal currents (Kuo and Neilson, 1988; Sanford et al., 1992; Hartnett et al., 2003) and differential heating/cooling (Burling et al., 1999; Wells and Sherman, 2001; Wells and Sealock, 2009). Spatial thermal variations due to upwelling events (baroclinic forcing) have been shown to be the dominant exchange mechanism in bays (Rueda and Cowen, 2005) and harbours (Hamblin and He, 2003; Lawrence et al., 2004) that are connected to the main basin by a narrow channel. In contrast Trebitz et al. (2002) and Hlevca et al. (2015) found that surface seiches (barotropic forcing) can have a significant impact on the flushing and exchange rates of wetlands and shallow natural embayments, particularly when shallower than the thermocline. The influence of baroclinic forcing in the form of internal waves in deep embayments has not received significant attention. This paper aims to address this knowledge gap by investigating the influence of large-amplitude internal waves on the thermal and current velocity profile of a Coriolis-influenced, mid-latitude embayment. VIII th Int. Symp. on Stratified Flows, San Diego, USA, Aug. 29-Sept. 1, 2016