Sure, When Hood Canal Freezes Over

Looking across the ice towards the Great Bend

Okay, so no one says that but they might as well... I mean, whoever heard of a body of salt water this far from the poles freezing? That’s what was going through my head as I drove our 20’ aluminum boat into the icy sheet last winter.

It started out as a normal, albeit cold, field day for the Oceanic Remote Chemical Analyzer (ORCA) team.  We launched the M/V Mackinaw at Twanoh State Park and drove out to our research buoy in Lynch Cove to replace the CTD package and repair the winch control box.  We thought we were prepared for a cold day on the water, armed with extra layers, beanies, scarves and multiple pairs of wool socks, but then the snow started.  I always seem to forget how difficult it is to do precise, mechanical work on cold metal instruments with cold metal tools, while constantly being splashed by cold, cold water.  The work was taking much longer than anticipated with all of this cold on cold.  When we eventually finished the required maintenance I pointed the boat toward the ORCA Hoodsport buoy where we were scheduled to work on the router.  As we turned around Sisters Point I noticed a definite line on the water surface ahead of me.  “Weird, that looks just like…”  CRUNCH!!!  

Standing on the bow of the M/V Mackinaw as we try to push our way through the ice

Before I could even finish my thought we were startled with a sudden crash as the Mackinaw tried pushing through a sheet of ice.  I slowed down and carefully backed us out through the path we had just cut, and then motored along the margin to see if there was any way through.  No luck.  A flock of seagulls stood on the ice and watched us while we made a call and sent photos to our incredulous supervisor at the University of Washington.  There was no way we’d be able to continue.  We couldn’t see the end of the ice sheet and even if we made it through we’d lose too much daylight to get any work done.  After a few more minutes playing with the chunks of ice that had broken free of the sheet, we headed back to Twanoh to get our boat out of the cold water.

Snapping some photos while we wait for confirmation to call it a day

Encountering ice in Hood Canal surprised our group but apparently it’s not that strange.  Fresh water that flows from the Skokomish River into Hood Canal tends to float on top of the denser salt water, creating a thin fresh layer.  When temperatures drop this layer can freeze, just like any body of fresh water.  If temperatures stay low for long enough, the ice sheet can reach from shore to shore like we witnessed... I’ve even heard stories of people driving wagons across the canal in previous centuries!

Holding up a piece of our Hood Canal ice sheet

Estuarine Circulation through Hands on Learning

Parker MacCready from the UW School of Oceanography demonstrates injecting dyed fresh or saltwater in various depths and locations of the "Puget Sound"

Tucked away in a beautiful brick building on a canal at the University of Washington (behind a free standing whiteboard in the University of Washington's Old Oceanography Building) is an impressive and powerful visualization tool. A to-scale model of the Puget Sound was built in 1950 by the School of Oceanography and has been used to research and teach tidal and circulation characteristics in our complex estuary.

Water enters the Puget Sound from the Pacific Ocean through the Strait of Juan de Fuca, is mixed up in Admiralty Inlet, then pours over shallow sills into four major fjord-like basins.  Some of these are well mixed and regularly circulated while others are stagnant and stratified.  The system is further complicated by tides, freshwater input from rivers the seasonal appearance of cold, salty water from upwelling along the coast.

Dyed freshwater injected at the "Duckabush River" output forms eddies on the surface as it slowly moves north out of "Hood Canal"

This model is so lasting because it attempts to take some of these complications into account.  For example, a tide machine near the model's "ocean" moves water in and out of the system, taking about one minute to complete each tidal cycle.  Tubes beneath the model constantly trickle freshwater at roughly the same rate and location as main rivers.  The bathymetry of the Sound is represented and exaggerated to allow for the viscosity of the water at this scale.

Students are able to inject either fresh or saltwater mixed with blue dye anywhere in the system and observe what happens.  This week a group of students noticed that fresh water stayed near the surface and tended to move out of the system, toward the "ocean," while dense salt water sank.  The deep salty water would then slowly move into the system or get stuck in various deep pockets like in Dabob Bay, Carr Inlet or just west of Deception Pass.  They also noticed a large difference between the different freshwater inputs.  A few drops of dyed water on the "Skagit River" dissipated into Whidbey Basin almost immediately while dye at the "Snohomish River" input remained for the entire class period.

A bird's eye view over "Whidbey Island" shows fresh water from the "Skagit River" quickly dispersing into the basin while dense salt water is trapped in a deep pocket just outside of "Deception Pass"