Notes on Thompson 1994 – Physical Oceanography of the – Puget Sound – Juan de Fuca Strait System

Major topics: Overview of circulation components: estuarine component (rainfall and snowmelt driven – buoyancy-driven), prevailing winds, sills, tidal forcing, wind forcing, coastal ocean forcing

Basin characteristics St of Georgia (SOG) – partially-mixed, (primary), Rosario Strait, Middle Passage to south (93% of c-x area), Discovery Passage to North (7%), major freshwater source, deep water renewal is seasonal – Fig 6 – most renewal in summer as f(deep water salinity [upwelling off coast]),

Puget Sound (PS) – partially–mixed estuary, several basins separated by sills, 98% of water through Admiralty inlet, 2% through Deception Pass. Skagit River – 60% of freshwater inflow (50% goes into Rosario Strait via Deception Pass, 50% goes into Main Basin of Puget Sound), deep water renewal due to propagation of high salinity water up SJF, mean depth of now velocity in main basin at stn 8 = 56m,

Strait of Juan de Fuca (SJF) – Simple geometry, well-mixed estuary, winds over ocean strongly affect mean circulation, time-averaged sea surface slope across SJF accounts for most of the mean flow (geostrophic pressure gradient), deep water baroclinic PG driven,

Primary forcing mechanisms Estuarine currents: freshwater runoff – hydraulic head -> seaward flow, mixing -> deep-water density gradient and upstream flow, Fraser River the dominant fw input, fw input varies seasonally and annually (highest flow in spring),

Tidal currents: Semi-diurnal, in SOG, two entrances for tides (N and S) create co-oscillation interference pattern, minimum tide and degenerate amphidromic pt near Victoria, and a standing wave elsewhere, mixed-semidiurnal tide, but relative strength of diurnal and semidiurnal components vary spatially within system,

Wind-driven currents: N. Pacific High pressure system (summer) and Aleutian Low (winter) -> south easterly winds in winter, north westerly winds in summer off shore, but great variability within the inshore system, summer onshore breezes blow up the SJF,

Coastal ocean forcing: Ekman transport changes sealevel and influences mean circulation in SJF, results in reversal events in SJF at some times and intrusion of high density deep water at other times, this high salinity water leads to deep water renewal in PS and SOG,

Secondary forcing mechanisms Hydraulic control: Tidal mixing over sills result in recirculation of mean flow, spring-neap cycle important in determining mean flow among basins of PS, but also important is the density difference between deep waters on either side of Admiralty inlet, same thing goes for SOG,

Tidal mixing and nutrient flux: Tidal currents break down stratification in shallow and narrow passages leading to increased mixing of deep water with high nutrient concentrations, 96.6% of nutrients from deep water traveling up SJF, 2.4% from Fraser River,

Low-frequency motions in SOG: Spring-neap variation accounts for a lot of the kinetic energy and some of the residual motion,

Decadal-scale fluctuations: PDO accounts for substantial variability in flow characteristics, mean basin salinity does not vary with PDO because increased salinity of incoming water balanced by increased river flow,

Tidal rectification: Inflow and outflow have different velocities due to different water depths and thus variation in bottom friction (similar to stoke’s drift for gravity waves), this leads to residual currents from tidal rectification,

Numerical modeling Various models detailed

Evidence for transboundary transport Satellite imagery, Drift card deployments, Floatable wreckage (including people!) and oil spills, numerical models, Victoria sewage,

Long-term change Sea-level rise, climate change, precipitation changes, prevailing winds, tidal barrages or other in stream hydro power plants Ideas and questions for discussion:

Create a chart of forcing functions, forces from Navier-Stokes equations, and effects on SOG, SJF, and PS.

(1) Terms and concepts to be defined/explained?

(2) Main point of paper?

(3) Main characteristics that distinguish the three components SOG, SJF, PS)?

(4) Forces – make table

(5) Connection of system to North Pacific?

(6) Role of rivers – What do they do?

(7) What determines nutrient fluxes in SJF?

(8) What is deep-water renewal and how does it happen in SJF, SOG, and PS?

(9) Evidence for trans-boundary transport (drift cards, wreckage, etc).

(10) Discussion of specific figures

E.g., Figs. 14 and 215 – Connection between ocean conditions and flow reversal “What are flow reversals in SJF and what causes them?”

Fig 16 – What is hydraulic control?

Fig. 19 – Nutrient flux