Reading MaterialPuget Sound CruiseObservations during cruisePuget Sound MorphologyBathymetry (water depth)Hydrography (water properties)Types of river-mouth environments Puget Sound SedimentationMechanisms associated with SedimentationReading Material“River Deltas”from “The Coast of Puget Sound”J.P. Downing, Puget Sound BooksField Trip BWorking cruise in Puget Sound on the Thompson, UW’s oceanographic research vesselWednesdayOctober 24All day(no class)Puget Sound CruiseTime: Depart UW 7AM Oceanography Parking LotReturn UW 9 PM Oceanography Parking LotClothing: foul-weather gear, hat, fleece, good shoesPrepare for cold, wet, windy and muddy conditionsFood: Lunch and dinner onboard shipSpecial dietary needs?Observations during cruiseWater columnCTD = chlorinity, temperature, depthturbidity (suspended sediment)SeabedGrab samples – surface sedimentbox core – 50-cm-long piece of seafloorkasten core – 250-cm-long record of sedimentationSeafloor mappingmultibeam acoustic profilesBelow seafloorseismic profilesPuget Sound MorphologyGlacial Originscour – flow under ice sheetformed depressionse.g., Main Basin, Hood Canal, Lake Washingtonsedimentary deposits – also raised land surfaceglacial tills, outwash deposits, lake depositsold glacial sediment now provides new input to PScliff erosionlandslidesland surface erosionBathymetry (water depth)Shallow entranceglacial origin – moraineoceanographic name – sillprimary sill is Admiralty InletSeveral others divide PS into separate basins (>200 m)Main Basin has 46% of water volumeSinuous shape – result of originSouthern Basin has 29% of shorelinesFluvial (river) sediment supplyfills PS from shorelineWhidbey Basin has 43% of tidelandsHydrography (water properties)Salinity (amount of salt dissolved in water)river water has 0 ppt (parts per thousand)ocean water has ~35 ppt – differs around worldbrackish water at depth in PS – 20-30 pptDensity (low salinity = low density)river plume flows over more dense brackish waterInput of river water - varies with space and timenorthern PS rivers supply the most watersmall input during late summerlarge input during late autumn and winter rainslarge input during spring snowmeltTypes of river-mouth environmentsestuary – semi-enclosed settingriver and salt water meet and mixfjord – estuary with glacial origindeep, with shallow sill near mouthdelta – river mouth receiving much sedimentestuary filled with sedimentshoreline growing seawardPuget Sound SedimentationSources of sedimentshallow – shoreline erosion, landslidesdeep – biological productivity, algal debrismuch carbon decomposes,forming methane gasall depths – river dischargedeltas form near river mouthsriver plume carries sediment deepernear sill – inflow with deep ocean waterMechanisms associated with Sedimentationplume transport – turbid surface waterriver momentum, tides, windflocculation – silt and clay particles form larger aggregates, which sink quicklylandward bottom flow – traps sediment near riverdelta formation – thick deposits near river mouthtopset = tidelandsforeset = steep surface, rapid accumulationbottomset = deep deposits, escape seawardDuwamish deltaIntensely impacted by humansWetlands hardened (landfill, roads, parking lots, buildings)Distributarychannels altered and stabilizeddepth in mDuwamish delta4-m resolution, 5x VENisqually deltanearly natural conditionSeveral distributarychannels bring water and sediment across delta to Puget SoundNisqually Delta, 5x VE3-m resolution, looking SWdepth inmeterspitchyawrollheave&squatpositiontidewater-columnsound
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