Oceanography 101, Richard Strickland! ! Lecture 20! ! © 2006 University of Washington Oceanography 101, Richard Strickland! ! Lecture 20! ! © 2006 University of Washington Tidal Currents in Puget Sound Puget Sound • Flood from • One big estuary Pacific and – Surface salinity away hugs S shore from rivers 26-29 g/kg of Juan de • Near rivers brackish, Fuca Strait salinity <10 g/kg – Coriolis effect – Subsurface salinity 30 -31 g/kg depending • Ebb hugs N on season shore • Inflowing ocean water • Zoom in on salinity ~32 Admiralty • Many small estuaries Inlet below 1 2 Oceanography 101, Richard Strickland! ! Lecture 20! ! © 2006 University of Washington Oceanography 101, Richard Strickland! ! Lecture 20! ! © 2006 University of Washington Net Puget Sound Circulation Net Puget Sound Circulation Net surface flow = seaward Net Net surface subsurface outflow flow = landward Entrainment & tidal pumping of deep Puget Sound water into surface outflow Net entrainment of deep ocean water into subsurface waters Source: Thomson 1994 3 4 Oceanography 101, Richard Strickland! ! Lecture 20! ! © 2006 University of Washington Oceanography 101, Richard Strickland! ! Lecture 20! ! © 2006 University of Washington Puget Sound Sub-Basins Puget Sound Sub-Basins • Whidbey Basin • Hood Canal – No sill – Sill under floating bridge – 2/3 of all the fresh water – Long, narrow, deep that enters the Sound – Thin layer of low-salinity • Skagit, Stillaguamish, water at surface Snohomish Rivers – Strong stratifcation – Strong stratification – Weak mixing – Weak tidal mixing – Fjord • Tides must make hairpin turn at south end of Whidbey Island – Salt Wedge 5 6 Oceanography 101, Richard Strickland! ! Lecture 20! ! © 2006 University of Washington Oceanography 101, Richard Strickland! ! Lecture 20! ! © 2006 University of Washington Puget Sound Sub-Basins Main Basin Stratification • Main Basin • Low-salinity (<26 g/kg) water in surface layer – Sill at Admiralty Inlet – Upper 50 meters – Long, deep • Higher-salinity (<29 g/kg) water in subsurface – Not so narrow layer – Moderate tidal mixing – Moderate stratification – Broad halocline – Partially mixed Source: Collias, McGary & Barnes 1974 7 8 Oceanography 101, Richard Strickland! ! Lecture 20! ! © 2006 University of Washington Oceanography 101, Richard Strickland! ! Lecture 20! ! © 2006 University of Washington Main Basin Stratification Puget Sound Sub-Basins • Schematic time series animation of Main • Admiralty Inlet Basin salinity & net estuarine currents – (also Tacoma Narrows, etc.) • Sill zone – Shallow, rough bottom topography – Fast currents, strong vertical mixing – Weak stratification – Well mixed Admiralty Inlet Seattle Tacoma Narrows Salt water Halocline Fresh water 9 10 Oceanography 101, Richard Strickland! ! Lecture 20! ! © 2006 University of Washington Oceanography 101, Richard Strickland! ! Lecture 20! ! © 2006 University of Washington Admiralty Inlet Admiralty Inlet • Entrance to Puget • Entrance to Puget Sound from Juan Sound from Juan de Fuca Strait de Fuca Strait – Flood reaches 4+ – Ebb reaches 4+ knots knots – Eddies form along – Eddies form along irregular shoreline irregular shoreline – From “Tide Prints” – Drawn from Puget by McGary & Sound model Lincoln 1977 • Ocean lab • Pacific Science Center 11 12 Oceanography 101, Richard Strickland! ! Lecture 20! ! © 2006 University of Washington Oceanography 101, Richard Strickland! ! Lecture 20! ! © 2006 University of Washington Admiralty Inlet Currents Puget Sound Sub-Basins • Well-mixed = net seaward (ebb) flow • South Sound – Sill at Tacoma Narrows Source: http://tbone.biol.sc.edu/tide/ – Nisqually River – Numerous inlets, channels & Flood small streams – Generally weak tidal mixing Ebb – Difficult to categorize as a Net (average) flow = 0.5 kt ebb (seaward) whole • Areas of salt wedge, well- mixed, partially mixed 13 14 Oceanography 101, Richard Strickland! ! Lecture 20! ! © 2006 University of Washington Oceanography 101, Richard Strickland! ! Lecture 20! ! © 2006 University of Washington Flushing in Estuaries Flushing in Estuaries • Gradual replacement of water in estuary • Flushing rate = time to 100% replace volume – Inflowing river & ocean waters flushed to sea – (Inter)tidal prism P = average volume – Removes pollutants, replaces nutrients & O2 entering & leaving over tidal cycle – Average volume of estuary V ÷ tidal prism P = # tidal cycles to flush total volume of estuary 15 16 Oceanography 101, Richard Strickland! ! Lecture 20! ! © 2006 University of Washington Oceanography 101, Richard Strickland! ! Lecture 20! ! © 2006 University of Washington Flushing in Estuaries Puget Sound Basin Flushing Wednesday, September 20, 2006 • Why care about Hood Canal fish • Estuary type is related to suffocate flushing rate? Humans could play part in flushing – Removes pollutants low oxygen levels – Strong stratification, weak By ROBERT McCLURE from estuary to P-I REPORTER mixing ocean Scientists are scrambling • = Poor flushing to document what – Replenishes oxygen appears to be the most • Salt Wedge (Whidbey Basin) in deep water widespread fish kill to • Fjord (Hood Canal) date in Hood Canal, the Weak stratification, strong • Poor flushing deep and poorly flushed – mixing – Buildup of pollutants waterway that researchers say suffers • Well mixed = Good flushing – Fish die of low from oxygen levels at • Tacoma Narrows oxygen their lowest ebb in at least five decades. • Admiralty Inlet 17 18 Oceanography 101, Richard Strickland! ! Lecture 20! ! © 2006 University of Washington Oceanography 101, Richard Strickland! ! Lecture 20! ! © 2006 University of Washington Puget Sound Basin Flushing Puget Sound Basin Flushing • Moderately stratification. • Hood Canal dead zone moderate mixing – Caused in part by human sewage disposal – = Very well flushed – Malfunctioning septic tanks – Main Basin – Very slow flushing time = 1 year or longer • Basins are connected • Main Basin: so far, so good – Whidbey, Hood Canal, South – Receives (treated) sewage of 2.5 million people Sound connect to ocean via – Fast flushing time = 1–3 months Main Basin & Juan de Fuca • New sewage discharge planned for Edmonds – Longer flushing time than – Keep it out of the Whidbey Basin one large basin • Potential for another Hood Canal • Must flush through Main Basin • Strong stratification, poor flushing 19 to reach ocean 20 Oceanography 101, Richard Strickland! ! Lecture 20! ! © 2006 University of Washington Puget Sound Basin Flushing • Keep sewage discharge out of Whidbey Basin – Well-mixed Admiralty Inlet likely path of discharge from Edmonds site • Weak tidal flushing in Whidbey Basin 21.