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LinkingPugetSoundPrimaryProductiontoStratificationandAtmosphericDriversonSeasonaltoInter-decadalScales

ParkerMacCready1*

NeilBanas2

February1,20161SchoolofOceanography,UniversityofWashington,Box355351,Seattle,WA98195-5351,USA2DeptofMathematicsandStatistics,UniversityofStrathclyde,26RichmondSt,GlasgowG11XQ,UK*Contact:pmacc@uw.edu

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ABSTRACTThepopulationsofChinookandCohosalmoninPugetSoundhavedeclinedsubstantiallyinrecentdecades.Workingfromthehypothesisthatthisdeclinewascausedbychangesinfoodavailability,datafromdifferentsourceswasanalyzedtoseeiftherewereclearchangesoverthisperiodinphysicaldrivers(rivers,winds,sunshine),waterconditionsinPugetSound(stratification),andphytoplanktonabundanceandbloomtiming.Timeseriesofthesepropertieswereconstructedfromallreadilyavailabledatasources,eachhavingdifferentsamplingfrequencyandduration.Short,irregularlysampled,andinfrequentrecords,especiallyforphytoplankton,hindertheanalysis,makingitdifficulttocharacterizeanomaliesintheseasonalcycleofchlorophyllandestablishitsrelationtoforcingvariables.Windmixinghaspotentialasapredictivevariable,butmoreanalysisisneeded.IntroductionOverthepastseveraldecadesChinookandCohosalmonpopulationsintheSalishSeahavedecreasedmarkedly.CohosmoltsurvivalinPugetSoundandtheStraitofGeorgiadeclinedbyfactorofthreeormoreovertheperiod1977-2010(Zimmermanetal.2015).Incontrast,nearbycoastalCohoshowedvariableorevenincreasingsurvival.ThefactthatbothregionsaresubjecttosimilarlargescaleclimaticforcingsuggeststhatchangestoconditionswithintheSalishSeamayberesponsible.WithintheSalishSeatherearelongtermrecordsofbothenvironmentalandecosystempropertiesintheStraitofGeorgia,andthesepointto“regimeshifts”aroundthelate1970’s,mid1980’s,andmid1990’s(PerryandMasson2013).Inparticulartheyidentifysixvariablesthatarestatisticallyrelatedtotheseregimeshifts:“seasurfacetemperature,windspeed,theNorthPacificGyreOscillationindex,humanpopulationsurroundingtheStraitofGeorgia,recreationalfishingeffort,andthenumberofhatcheryreleasesofChinooksalmon(Oncorhynchustshawytscha)intotheStrait.”OneclearclimaticsignalisthatSSTintheStraitofGeorgiaincreasedfrom10.5°Cto12°Covertheperiod1971-2007.Bottomwatertemperatureincreasedaswell,byasimilaramount(Richeetal.2014).Ithasbeensuggestedthatbottom-uppressuresuchaschangeinfoodavailabilityhasledtothedeclineinSalishSeaChinookandCoho(Zimmermanetal.2015).Thismotivatesthecurrentstudy,whereweexplorevariationofphytoplanktonabundanceinPugetSound,undertheassumptionthatitwillinturncontrolzooplanktonabundanceandhencesmoltsurvival.Therearechallengestothisgoal.PugetSoundhasfewerlong-termdatarecordsthantheStraitofGeorgia,sothestrategyofthisprojectistoattempttocorrelatephysicaldriverssuchasriverflowandweather(whichhaverelativelylongrecords)tophytoplankton(forwhichdatarecordsarerelativelyshort).AsimilarapproachhasbeenshowntoworkintheStraitofGeorgia(AllenandWolfe2013)wherethetimingofthespringbloomhasbeensuccessfullypredictedusingprimarilywindspeedandcloudiness.The

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mechanisticlinkthispredictionreliesonisthatthespringbloomintheStraitofGeorgiatendstobeinitiatedassoonasthereisasignificantbreakfromtheverticalmixingofwinterstorms,allowingasurfacedensitystratificationthatkeepsphytoplanktonintheeuphoticzoneatthesametimeasthereisenoughsunshinetosupportabloom.HereweanalyzedatarecordsinPugetSoundofverydifferentlengthsandfrequencies:Atmosphericforcing: 1948-presentRiverflow: 1980-presentMarineWaterTemperatureandSalinity(monthly): 1991-presentMarineWaterChlorophyll(monthly): 2002-presentMarineWaterTemperature,Salinity,andChl(dailyorbetter): 2005-presentOfthese,thefinalcategoryof“dailyorbetter”watercolumnmeasurementswouldbethemostuseful,buttherecordsaretooshorttocorrelatewithsalmondeclinesontheirown.Ourapproachisinsteadtolookforwaysthatthelongerrecordsmaybeleveragedtoextendourpredictionsofphytoplankton(takingchlorophyllconcentrationasaproxyforphytoplanktonbiomass).Specifically,weseektotesttheprimaryhypothesisthatseasonalorinterannualvariationsinchlorophyllmaybepredictedusingsomecombinationofdensitystratification,windmixing,andsunshine.Asecondaryhypothesisisthatdensitystratificationmaybepredictedusingriverflow.Theprimaryhypothesisamountstoanextremelysimplifiedecosystemmodel,onethatattemptstousecorrelationasasubstituteformoremechanisticmodelssuchanNPZD(Nutrients,Phytoplankton,Zooplankton,Detritus)nutrient-cyclingmodelembeddedinadetailedcirculationmodel(Banasetal.2009;Davisetal.2014).Wefindthat,whilewearenotabletodisprovetheprimaryhypothesis,wealsoareunabletouseexistingdatatomakepredictions.Inparticularwefindnomeaningfulcorrelationsbetweenmonthlyanomaliesofsunshineorstratificationwithmonthlychlorophyllanomalies.Here“anomaly”isdefinedasthedeviationfromthemeanannualcycle,whichisstrongforallvariables.IntheMethodssectionwegivedetailsofthedatagatheringandprocessing.ThecorrelationbetweenvariablesispresentedinResults,andsomethoughtsaboutfuturedirectionsaregivenintheDiscussion.MethodsHerewepresentthedetailsofthedatasourcesused,atalevelthatismeanttoinformfutureresearcherswhowanttousethedataforotherpurposes.Rivers

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FlowdatacanbedownloadedfromtheUSGSformostriversaroundPugetSoundfromhttp://waterdata.usgs.gov/nwis/.Pythoncodewaswrittentoautomatethisandflowdatafrom1980-2015wasdownloadedfortheSkagit,Snohomish,Stillaguamish,Columbia,Puyallup,Duwamish,Nisqually,Deschutes,Skokomish,Duckabush,Dosewallips,HammaHamma,Cedar,NooksackandSamishrivers(Fig.1).Inmostcasesdataonriverflowisavailableforamuchlongertimespan,e.g.backto1940fortheSkagit.Dataforsomeriversdoesnotextendbackto1980intheUSGSonlinefiles:theColumbiastartsin1992,theDeschutesstartsin1991,andtheSamishstartsin1997.Inlate2009theUSGSstoppedreportingSkokomishdataduringhighflowconditions.Thiscanbecircumventedusingacombinationofnearbygaugedrivers,butwasnotdoneforthisproject.Insomecasestheriversarenotgauged,orhavesignificantwatershedareabelowthegauge.AlternategaugesandscalingfactorshavebeendevelopedbytheWashingtonStateDept.ofEcology(Mohamedalietal.2011)andthesewereusedtocreatethefinalstreamflowrecordsusedinthisproject.Dailyflowdatafor1980-2012fromtheFraserRiverwasdownloadedbyhandfromEnvironmentCanadathroughthewebsitehttp://wateroffice.ec.gc.ca/search/search_e.html?sType=h2oArcusingrivercode08MF005.Datafor2013and2014,absentfromtheonlinearchive,wasprocuredbyspecialrequesttoEnvironmentCanada,and2015camefromanarchivecompiledfromFraserdailyflowthatise-maileddailytoMacCreadybyEnvironmentCanadaaspartofanotherproject.

Figure1.MaporriversenteringPugetSound,fromhttp://pubs.usgs.gov/fs/2011/3083/,showingthelocationofmajorrivers.

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Figure2.Annualcycleofflowinselectedriversusedinthestudy.Allyearsareplottedwiththingraylines,andaveragesofalldataasthickblacklines.Theyear2015ishighlightedinredandexemplifiesthelargeanomaliespossible,inthiscasethemuch-reducedspringfreshetduetolowsnowpackinthewinterof2014-15.Datafromallriverswasprocessedusingpythonintoacommonformatwithdailyfrequency.AtmosphereWeatherdatawasobtainedfromthreesources.DailyweatherobservationsfromnearSeaTacAirportweredownloadedbyhandfromhttp://www.ncdc.noaa.gov/cdo-web/datasets/GHCND/stations/GHCND:USW00024233/detail,whichgoesbackto1948.AsisapparentinFig.3,therecordiscompleteforprecipitationandtemperature,butonlyshorter,non-overlappingsegmentsareavailableforvariablesrelatedtosunshineandwind.Asaresultthisdatawasnotusedinthelateranalysis,exceptasground-truthfortheotherweatherdatasources.

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Figure3.ObservedweatherdatafromSeaTacairport,forthepast65years.Bluelinesaremonthlyaveragesandredlinesareannualaverages.Three-hourlyfieldsofallrelevantweatherareavailablefor2002-2009ona4kmresolutiongridoverPugetSoundaspartofanarchivecreatedbyMacCreadyforamodelingproject(Giddingsetal.2014)outoftheregionalMM5andWRFnumericalweatherforecastsrunbyCliffMass’groupatUW(Massetal.2003).Thistypeofatmosphericdataisexcellentforourpurposesbecauseofitshighspatialandtemporalresolution,andbecauseitcompareswelltoobservations.However,thetimeperiodisshortforourpurposes.Withsomeworkitcouldbeextendedfrom2009tothepresent,butamorepromisingapproachwouldbetouseoutputfromamuchlongerreanalysis,forexamplethe12kmWRFreanalysisofthePacificNorthwestfor1970-2069byEricSalathé,UWBothel(Salathéetal.2014).Forthisprojecttimeseriesof10mwindspeedanddownwardshortwaveradiation(sunshine)atalocationintheEasternendoftheStraitofJuandeFuca(123°W,48.3°N)wereextracted.A“windmixing”timeserieswascreatedasthesumoftheabsolutevalueofthecubedwindspeeds.Thewindspeedcubedisproportionaltotheworkdonebywindstress(whichvariesaswindspeedsquared).AsimilarindexwasusedinananalysisoftheStraitofGeorgiaspringbloom(AllenandWolfe2013).Boththesunshineandwindmixingserieswerethenaveragedintoweeklybins.ThethirdsourceofatmosphericdatacomesfromtheNCEP(NationalCentersforEnvironmentalPrediction,partofNCAR,http://www.esrl.noaa.gov/psd/data/gridded/data.ncep.reanalysis.html)reanalysisproducts.Monthlymeansat2.5°resolution(verycoarseforourpurposes,about250km)areavailableasfarbackas1948.ForthisprojectwedownloadedmonthlymeansofSurfaceDownwardShortwaveRadiationFlux(essentiallyameasureof

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howsunnyitis,includingtheeffectsofclouds.Datawereobtainedfromhttp://www.esrl.noaa.gov/psd/data/gridded/data.ncep.reanalysis.derived.surfaceflux.html.Examplesofrecordsfromthissourcearepresentedaspartofthecombinedanalysisbelow.AcomparisonofNCEPshortwavefluxandSeaTacobservedsunshineareshownonFig.4,showingthattheNCEPfieldshaveatleastmoderateskillinthiscrudecomparison.

Figure4.Twenty-yearcomparisonofmonthly“sunshine”anomaliesforNCEP(downwardshortwaveradiation)andSeaTacobservations(%sunshine),plottedastimeseries(left)andascatterplot(right).Thesignalsarepositivelycorrelatedbutonlyweakly,socautionisadvisablewhenusingNCEP.Finally,three-hourlyreanalysisproductsat32kmresolutionfromtheNARR(NCEPNorthAmericanRegionalReanalysis,http://www.esrl.noaa.gov/psd/data/gridded/data.narr.html)modelareavailablefrom1979onwards,butwerenotusedforthisprojectbecauseofthesubstantialtimethatwouldhavebeenrequiredfordownloading.PugetSoundWaterColumnDatafromCTDCastsThedatasourcemostcentraltothisanalysisisthemonthlyCTDcaststhathavebeentakenbytheWashingtonStateDepartmentofEcologyaspartoftheirAmbientMonitoringProgram.Qualitydataareavailableonlinefrom1991onwardsfrom37corestations,29ofwhichareinPugetSound(Fig.5).Olderdataexistsbutmaybeoflowerqualityandsowasnotused.Datafrom13ofthesestationswasdownloadedas.csvfilesfromhttps://fortress.wa.gov/ecy/eap/marinewq/mwdataset.asp.Atthetopoftheformchoosethestationandatthebottomchoose"csv"and"allyears"andthen"getfile."Thespecificstationsused,andsomecommentsondataqualityare:

• BLL009_0,BellinghamBay• BUD005_0,BuddInlet• DNA001_0,DanaPassage

o 2001deepTbadinJulyo 2002shallowslowvalueFeb,shallowTspikeOct

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o 2006lotsoflittleT,sspikesalldepths,manymonths• HCB004_0,HoodCanalinLynchCove• PSB003_0,MainBasinoffSeattle

o 1994salinityspike4mFeb/Maro 2007manyT,sspikes,especiallydeep

• HCB003_0,HoodCanal,middleofmainchannel(HammaHammaR.)• SAR003_0,middleofWhidbeyBasin• GOR001_0,GordonPoint-SouthPugetSound• PSS019_0,SouthWhidbeyBasin-offEverett• CRR001_0,CarrInlet• ADM002_0,AdmiraltyInletjustoutsidePugetSound

Figure5.LocationsandcodesofEcologylongtermCTDstations.TheEcologyCTDdatahasvaluesevery0.5mfromneartheseasurfacetonearthebottom.Oftendataspikesappearednearthebottomofcastsandthesewereremovedinprocessing.Inadditionanumberofcastsappearedtohaverepeateddepthswithslightlydifferentvalues,perhapsbecauserepeatcastsweremistakenly

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placedinthearchivetogether.Allprocessingwasdoneinpython.ExamplesofcastsattwoofthestationsareshowninFig.6.

Figure6.CTDcastdataforallyears,coloredbymonth,attwostations.Fieldsplottedaresalinity,temperature,sigma(densityminus1000kgm-3),chlorophyllconcentration,anddissolvedoxygen.TheupperrowisfromMainBasinoffSeattle,andthelowerrowisfromlowerHoodCanalinLynchCove.Near-surfacestratificationisapparentinbothplaces,asishypoxiaindeepHoodCanalinthelatesummer.Thephytoplanktonbloomextendssomewhatdeeperthanthesurfacelayerdefinedbydensity.TheCTDdatawasthenprocessedtocreateaveragesofalldataaboveandbelow5mdepths.TimeseriesoftheseaveragedpropertiesatallstationsareshowninFig.7.Ofthesepropertieswewillfocusmostlyonthechlorophyll,becauseofitspotentialaszooplanktonfood,and“stratification,”definedhereasthedifferencebetweendensityaveragedbelow5mandthataveragedabove.The5mdepthchosenasthedividinglinebetweensurfaceanddeepwatersissomewhatarbitrary,andisbasedonasubjectiveestimate,afterlookingatallthedata.Otherauthorshaveconstructedstratificationindicesusingslightlydifferenttechniques(Mooreetal.2008;Sutherlandetal.2011;Giddingsetal.2014).Ourtechniquewaschosentominimizenoisewhenappliedtothedataavailable.

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Figure7.Timeseriesofmonthlywatercolumnpropertiesaveragedaboveandbelow5mdepthforallEcologyCTDstationsanalyzed(rows,stationnamesonrightpanels),andforallproperties(columns).Thetimeseriesextendfrom1991to2014fortemperatureandsalinity,butonlybeginin2002forchlorophyll.PugetSoundWaterColumnDatafromProfilingBuoysThefinaldatasourceconsideredcomesfromtheORCAprofilingbuoys(Devoletal.2007).DatawasobtainedintheformofMATLABfilesprovidedonrequestbyWendyReufatUniversityofWashington.Thebuoyshaveaninstrumentpackageonawinchthatisloweredandraisedthroughthewatercolumnseveraltimesaday(Fig.8).Thestationsandtheirlocationsare:

• CI:SouthSound-CarrInlet• HC_DB:HoodCanal-DabobBay• HC_DK:HoodCanal-Duckabush• HC_HP:HoodCanal-Hoodsport• HC_NB:HoodCanal-NorthBuoy• HC_TW:HoodCanal-Twanoh• PW:MainBasin-PointWells

TheresultingtimeseriesaresimilartothoseonecouldcreatefromtheEcologyCTDcasts,buthavemuchbettertemporalresolution.Inparticulartheyareabletoresolvephytoplanktonblooms,whichhavetimescalesofdaystoweeks.IncontrastthemonthlyCTDcastsmayseriouslyunder-sample,orevenmiss,bloomevents.TheORCAdatawasprocessedinthesamewayastheCTDcasts:averagedintobinsaboveandbelow5mdepth.Theresultingtimeseriesfromallsevenstationsare

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showninFig.9.OnelimitationoftheORCAdataisthatthereareonly7stations,4ofwhichareinHoodCanal.

Figure8.Locations(left)ofsixoutofsevenORCAprofilingbuoys,andapictureofabuoy(right).TheDuckabushlocationisnotshown.

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Figure9.Timeseriesfromall7ORCAprofilingbuoys(byrow,stationnamesinleftpanels),withdatafieldsincolumns.Thefluorescencedataisreportedinarbitrary“fluorunits”butweassumeintheanalysisthatthismaybecomparedatleastqualitativelywiththechlorophyllconcentrationfromCTDcasts.Thewatercolumndatafromeachprofilehasbeenaveragedintovaluesabove5m(red)andbelow5m(blue)andsoshouldbedirectlycomparabletotheCTDtimeseries.TheprimaryproblemwithusingtheORCAdataforthisanalysisisevidentinFig.9.Therecordsonlybeginin2005,andareoftenshortandintermittent.Onlytwooftherecords(HoodCanal,atHoodsportandTwanoh)approachadecadeinlength.

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ResultsCombiningthevariousdatarecordswemayaddresstheoriginalhypothesesofthisproject.Startingfirstwiththe“secondary”hypothesisthatstratificationisrelatedtoriverflow,acorrelationanalysisisshowninFig.10.Thereislargeannualvariationofstratificationatalllocations,changingbyafactorof2to5,althoughsomestratificationisalwayspresent.Thestratificationismodestlycorrelatedwithriverflow,andshowsthestrongestcorrelationneartheSkagitRiverinSaratogaPassage.ThecorrelationcoefficientsshowninthelowerpanelsofFig.10,aremaximumlaggedcorrelations,butthelagissubjecttouncertaintycausedbythebinningprocessandisindistinguishablefrom0months.

Figure10.Comparisonofstratificationandriverflowfor5selectedCTDstation–riverpairs.EachcolumnrepresentsaCTDstation–riverpair.Thetoprowistheaverageannualcycleofallstratificationdataforastation,andthemiddlerowistheaverageannualcycleofriverflow,inmonthlybins.Inthebottomrowarescatterplotsofstratificationversusriverflow,whereeachpointisanindividualmonthlyaverage.Correlationcoefficientsarealsoshowninthesepanels.Movingtotheprimaryhypothesis,weseektofindapatternlinkingenvironmentalvariablesandchlorophyllconcentration.Wedothisatfirstbyliningupallthedataforalocationastimeseries.Inthiscasea“location”meansacombinationofariver,anORCAbuoy,andaCTDstation,aswellasweatherdata.ExamplesareshowninFigs.11and12.

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Figure11.IntegratedtimeseriesforCarrInlet(EcologyCTDstationCRR001,ORCAbuoyCI,theNisquallyRiver,andregionalweatherdata).

• Upperpanel:Chlorophyllaveragedabove(red)andbelow5m(blue)frommonthlyCTDcasts(circles)anddaily-averagedORCAprofiles(lines).TheORCAdataisinuncalibrated“fluorunits.”

• Secondpanel:NisquallyRiverflow.• Thirdpanel:Stratification(averagedensitybelow5mminusaveragedensity

above)frommonthlyCTDcasts(circles)anddaily-averagedORCAprofiles(line).

• Bottompanel:MonthlydownwardshortwaveradiationanomalyfromNCEPreanalysisatapointnearSeattle.Theanomalyiscalculatedbyremovingtheaverageannualcycle.Thisfieldisameasureofhowsunnyamonthwasrelativetotheaverageforthatmonth.

Thefieldsareplottedfor2011-13,eventhoughmanyofthefieldshavemuchlongerrecords.ThetimelimitsarebasedonthelimitsoftheORCAdata.

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Figure12.IntegratedtimeseriesforSouthHoodCanal(EcologyCTDstationHCB003,ORCAbuoyHP=Hoodsport,theSkokomishRiver,andweatherdata).

• Upperpanel:ChlorophyllfrommonthlyCTDcasts(circles)anddaily-averagedORCAprofiles(lines).

• Secondpanel:Windmixing(definedinthetext),calculatedfromMM5/WRF4kmweatherforecasts.Weeklyaverages.

• Thirdpanel:SkokomishRiverflow(floodsareclippedlateintherecord).• Fourthpanel:Stratification.• Bottompanel:MonthlydownwardshortwaveradiationanomalyfromNCEP

reanalysisatapointnearSeattle(filledline).Thesamefieldfromweekly-averagedMM5/WRFfieldsisalsoplotted(blueline).

Thefieldsareplottedfor2006-2009,eventhoughmanyofthefieldshavemuchlongerrecords.Thetimelimitsarebasedonoptimizingtheoverlapoffields.

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TheintegratedtimeseriesatCarrInlet(Fig.11)showsaclearlydefinedphytoplanktonbloom,startingaroundAprilorMay,andendinginthefall.Forthepurposesofthisprojectwewouldliketobeabletoidentifydifferencesinbloomtimingorstrengthindifferentyears.Thetimeseriesdemonstratethedifficultyofdoingthiswiththedatainhand.ForexampletheORCArecordssuggeststhatthe2012and2013bloomsweremuchlargerthan2011,butthatwouldbedifficulttoguessfromtheCTDdata.Intermsoftiming,itappearsfromtheCTDdatathatthe2013bloomstartedamonthearlierthantheothertwoyears,butthereisagapinORCAdataatthestartofthe2013bloomthatmakesitimpossibletocorroboratethetiming.ThestratificationinCarrInlethasaclearseasonalcyclethatpeaksaroundthemiddleoftheplanktonbloom,andthestratificationfromORCAprofilesandtheCTDcastsmatchwell.Howevertherearenoclearinter-annualdifferencesinstratification,andhencenoreasontoconcludethatstratificationcontrolsproductivityonthistimescaleinastatisticalsense(thisisaddressedmorebelowinaformalcorrelationanalysis).ThesunshineanomalyfromNCEPshowsthatallthreespringswerelesssunnythanaverage.Overallwemayconcludethatthreeyearsistoofewtobegintounderstandthesystemofphytoplanktonbloomshere.ThismotivatesustotrylookingforsignalsinlongerrecordsusingCTDandweatherdata(andsonotconstrainedbytheshortORCArecords).Thisisdonebelow.TheintegratedtimeseriesinSouthHoodCanal(Fig.12)usesalongerORCArecord,andweaddanadditionaldatasourcefromtheMM5/WRFregionalweatherforecast,bringinginweeklysunshineandwindmixingtimeseries.Herethephytoplanktonbloomsignalhasspringandfallpeaks,withclearinter-annualdifferencesapparentintheORCAdata(2007wasahighproductivityyear,2009waslow).ThereisagapintheCTDdataatthisstation(HCB003)coveringthesecondhalfofthefour-yearperiodshown,butitisclearthatitwouldbeextremelydifficulttoestimatebloomstrengthortimingfrommonthlyCTDcastsatthislocation.Thereissomesuggestionthatthespringbloomstartswhenwindmixingbecomesweakinthespring,andthatthefallbloomisterminatedwhenwindmixingfirstbecomes,howeverwindmixingdoesnotexplainthelowphytoplanktoninmidsummer.Thetwoestimatesofsunshine(bottompanel)donotobviouslyexplaininter-annualdifferencesinproductivity–forexample2007,theyearwithhighestphytoplanktonintheperiod,hadanomalouslylowsunshinebybothNCEPmonthlyvaluesandweeklyMM5/WRFvalues.ItisalsoapparentthatthemonthlyNCEPsunshinevaluesmaymissagreatdealofinformation,andappeartocorrelatepoorlywiththehighresolutionMM5/WRFestimates.Theabovetwoexamplessuggestthat:

• MonthlyCTDcastsmaynotdoaverygoodjobofcapturingphytoplanktonbloomstrengthortiming.

• Windmixingisapromisingfieldtolookat,butcurrentlywearelimitedto2002-9.

• StratificationiswellcapturedbythemonthlyCTDdata,butitisnotclearlythecontrollingfactorinseasonalpatternsofphytoplanktonproduction.

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• Sunshineanomaliesmayormaynotbeuseful.ThesenegativeresultsonthestatisticalrelationshipbetweenstratificationandchlorophyllarestrikinggiventhatwehaveeveryreasontobelieveapriorithatthemechanisticlinkisrealandatleasttransientlyimportantinPugetSound,asinsomanyothertemperatemarineecosystems.Apossibleexplanationforthediscrepancyisamismatchoftimescales,astwofurtherbriefanalysesexplore.First,pastwork(NewtonandVanVoorhis2002)suggeststhatstratificationandincominglightmightbeimportantcontrolsonPugetSoundprimaryproductioninwinterandspring,butsecondarytonutrientlimitationinsummer.Figure13showsmonth-by-monthcorrelationsbetweenstratificationandchlinCarrInletusingmonthlyCTDdata.Wefindnosignificantrelationshipinanyseason,althoughthestatisticalpowerofthisanalysisislow.Second,bothseasonal(Figs.11-12)andmonthly(Fig.13)analysesmightfailtodemonstratearealinfluenceofstratificationonchlorophylliftherelevanttimescaleismuchshorter,i.e.the2–10dscaleofbothweathereventsandindividualphytoplanktonblooms.Thereisanecdotalreasontobelievethismightbethecase.Figure14showstheCarrInletORCAdatareplotted,threeyearssuperimposedbyyearday(andwithanalternatestratificationindex,surface-bottomdensitydifference).Inthisview,theseasonalcycleofstratificationappearsquitesimilaracrossthethreeyears,butwhenwefocusinondailyvaluesApril–May,wefindthreeexamplesof5–10deventsinwhichawell-definedpeakinstratificationbrieflyprecedesawell-definedpeakinintegratedchlorophyll(arrows:twoeventsin2012,onein2013).Thisismechanisticallysatisfyingbut,astheanalysesaboveshow,oflittleuseinpredictingchlstatisticallyonlongerscales.

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Figure13.Monthlychlorophyllanomalyversusmonthlystratificationanomaly,frommonthlyCTDcastsinCarrInlet,plottedbymonth.Theanomaliesarerelativetotheaverageofallvaluesinagivenmonth.

Figure14.Alternateindicesoftidallyaveragedstratification(“drho,”bottom–surfacedensitydifference,insigma-tunits)andchlorophyll(verticallyintegrated,mgm–2)attheCarrInletORCAbuoy,for2011(blue),2012(green),and2013(red).Eachpointrepresentsoneday.Theshadedtimeperiodintheleftpanelsisexpandedintherightpanels.

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DiscussionHerewehavepresentedapreliminaryanalysisofdatasetsavailableastimeseriesforPugetSoundrelatedtophytoplankton,motivatedbythesubstantial,documenteddeclineofChinookandCohosalmonintheSalishSeaoverthepast35years.Usingtimeseriesofenvironmentalphysicalforcingvariables(rivers,sunshine,wind),aphysicalresponsevariable(watercolumnstratification),andabiologicalresponsevariable(chlorophyllconcentration)weattemptedtolookforclearcorrelationsthatwouldexplaininter-annualdifferencesortrendsinphytoplanktonblooms.Theresultofthisinitialanalysisisthatnoclearcorrelationswerefound.ThemaindatalimitationintheanalysisisthatmonthlychlorophyllrecordsthroughoutPugetSoundareonlyavailablefor,atbest,thelast14years,anddailyvaluesonlyforthelast10(inacoupleoflocations).Moreover,whilemonthlyCTDcastsmaybeadequateforcharacterizingtheannualcycleofchlorophyllinthedifferentbasinsofPugetSound,theyarelikelyinadequateforcharacterizinginter-annualdifferencesinbloomtimingorstrength.ItishoweverlikelythatifchlorophyllshowedthesamelineardecreaseoverthepastdecadesasChinookandCohosalmonthiswouldbeevidentfromalongerrecord(say30years)ofmonthlychlorophylldata.Somestrategiesforfutureworkonthisproblemaresuggestedbyouranalysis.Explorationofchangesinwindmixingmaybepromising,andthiscouldbeaccomplishedwithhigh-resolutionreanalysisdatasetsthatexist.Amoresophisticatedecosystemmodelcouldbeused,asopposedtotherelativelycrudecorrelationanalysispresentedhere.IntheStraitofGeorgiathepredictionsofspringbloomtiming(AllenandWolfe2013)reliedonamid-complexity,1-Dwatercolumnbiogeochemicalmodel.TheStraitofGeorgiacasemaybemoreamenabletoa1-Dapproach,becauseitisrelativelyhomogeneousoverabroadarea,whereasPugetSoundischaracterizedbyspatialheterogeneity.Thebrute-forceapproach,arealistic3-Dcirculation-biogeochemistrymodelofPugetSound,isalsolikelytogiveusefulinsights,providedreliableatmospheric,river,andoceanboundaryconditionscanbeassembledforthepast40years.Someofthesearealreadyavailable,andgiventrendsinreanalysisproductsitislikelyotherswillbeavailableinthenearfuture.Thenextstepplannedbyourgroupisacompromisebetweenthe1-Dand3-Dmodelapproaches,a2-D(depthandalong-channeldistance),tidally-averagedmodelforthethalwegfromSouthSoundthroughMainBasintotheStraitofJuandeFuca,inwhichafullNPZDmodelcanbeimplementedandexploredsystematically.Ourinferencefromtheanalysisabove,alongwithmodelinsightsfromWinteretal.(1975)andBanas(2009),isthatstratificationandsurfacelightareimportanttoPugetSoundprimaryproductioninclosecombinationwiththealong-channeladvectionandverticalfluxesassociatedwiththeestuarinecirculation,andthatamodelthatresolvesalltheseaspectsofthephysics(andthecombinedeffectsof

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lightlimitation,nutrientlimitation,andverticalexport/regeneration)ismorelikelytocorrectlypredictphytoplanktonbiomassaccumulationthanastatisticaltreatmentofanyofthesefactorsalone.Thedatacompiledhereformacrucialresourceforcalibrationandvalidationofsuchamodel,andassuchmightyetprovetoprovideabasisforretrospectiveanalysisandfuturepredictionoftrendsinprimaryproduction.AcknowledgmentsThisworkwasfundedbyLongLivetheKings,aspartoftheSalishSeaMarineSurvivalProject.

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REFERENCESAllen,S.E.,andM.a.Wolfe,2013:Hindcastofthetimingofthespringphytoplankton

bloominthestraitofGeorgia,1968-2010.Prog.Oceanogr.,115,6–13,doi:10.1016/j.pocean.2013.05.026.http://dx.doi.org/10.1016/j.pocean.2013.05.026.

Banas,N.S.,E.J.Lessard,R.M.Kudela,P.MacCready,T.D.Peterson,B.M.Hickey,andE.Frame,2009:PlanktonicgrowthandgrazingintheColumbiaRiverplumeregion:Abiophysicalmodelstudy.J.Geophys.Res.,114,C00B06,doi:10.1029/2008JC004993.http://doi.wiley.com/10.1029/2008JC004993.

Banas,N.S.,2009:Controlsonprimaryproductioninanew,mid-complexitymodelofHoodCanal.Posterpresentation,CoastalandEstuarineResearchFederationconference.Availableonlineathttp://neilbanas.com/projects/lynch.

Davis,K.A.,N.S.Banas,S.N.Giddings,S.aSiedlecki,P.MacCready,E.J.Lessard,R.M.Kudela,andB.M.Hickey,2014:Estuary-enhancedupwellingofmarinenutrientsfuelscoastalproductivityintheU.S.PacificNorthwest.J.Geophys.Res.Ocean.,119,8778–8799,doi:10.1002/2014JC010248.http://doi.wiley.com/10.1002/2014JC010248.

Devol,A.H.,W.Ruef,S.Emerson,andJ.Newton,2007:InSituandRemoteMonitoringofWaterQualityinPugetSound :theORCATime-Series.Environ.Res.Eng.Manag.,1,19–23.

Giddings,S.N.,andCoauthors,2014:HindcastsofpotentialharmfulalgalbloomtransportpathwaysonthePacificNorthwestcoast.J.Geophys.Res.Ocean.,119,2439–2461,doi:10.1002/2013JC009622.

Mass,C.F.,andCoauthors,2003:Regionalenvironmentalpredictionoverthepacificnothwest.Bull.Am.Meteorol.Soc.,84,1353–1366+1328,doi:10.1175/BAMS-84-10-1353.

Mohamedali,T.,M.Roberts,B.Sackmann,A.Whiley,andA.Kolosseus,2011:SouthPugetSoundDissolvedOxygenStudyInterimNutrientLoadSummaryfor2006-2007.

Moore,S.K.,N.J.Mantua,J.P.Kellogg,andJ.A.Newton,2008:Localandlarge-scaleclimateforcingofPugetSoundoceanographicpropertiesonseasonaltointerdecadaltimescales.Limnol.Oceanogr.,53,1746–1758,doi:10.4319/lo.2008.53.5.1746.

Newton,J.A.andK.VanVoorhis,2002:SeasonalpatternsandcontrollingfactorsofprimaryproductioninPugetSound'sCentralBasinandPossessionSound.WashingtonStateDeptofEcology,http://www.ecy.wa.gov/biblio/0203059.html.

Perry,R.I.,andD.Masson,2013:Anintegratedanalysisofthemarinesocial–ecologicalsystemoftheStraitofGeorgia,Canada,overthepastfourdecades,anddevelopmentofaregimeshiftindex.Prog.Oceanogr.,115,14–27,doi:10.1016/j.pocean.2013.05.021.http://dx.doi.org/10.1016/j.pocean.2013.05.021.

Riche,O.,S.C.Johannessen,andR.W.Macdonald,2014:Whytimingmattersinacoastalsea:Trends,variabilityandtippingpointsintheStraitofGeorgia,Canada.J.Mar.Syst.,131,36–53,doi:10.1016/j.jmarsys.2013.11.003.http://dx.doi.org/10.1016/j.jmarsys.2013.11.003.

22

Salathé,E.P.,A.F.Hamlet,C.F.Mass,S.-Y.Lee,M.Stumbaugh,andR.Steed,2014:EstimatesofTwenty-First-CenturyFloodRiskinthePacificNorthwestBasedonRegionalClimateModelSimulations.J.Hydrometeorol.,15,1881–1899,doi:10.1175/JHM-D-13-0137.1.http://journals.ametsoc.org/doi/abs/10.1175/JHM-D-13-0137.1.

Sutherland,D.A.,P.MacCready,N.S.Banas,andL.F.Smedstad,2011:AModelStudyoftheSalishSeaEstuarineCirculation*.J.Phys.Oceanogr.,41,1125–1143,doi:10.1175/2011JPO4540.1.http://journals.ametsoc.org/doi/abs/10.1175/2011JPO4540.1\npapers2://publication/doi/10.1175/2011JPO4540.1.

Winter,D.F.,K.Banse,andG.C.Anderson,1975:ThedynamicsofphytoplanktonbloomsinPugetSound,afjordinthenorthwesternUnitedStates.Mar.Biol.29,139–176.

Zimmerman,M.,J.R.Irvine,M.O’Neill,J.H.Anderson,C.M.Greene,J.Weinheimer,M.Trudel,andK.Rawson,2015:SpatialandTemporalPatternsinSmoltSurvivalofWildandHatcheryCohoSalmonintheSalishSea.Mar.Coast.Fish.Dyn.Manag.Ecosyst.Sci.,7,116–134,doi:10.1080/19425120.2015.1012246.http://www.researchgate.net/publication/277313781_Spatial_and_Temporal_Patterns_in_Smolt_Survival_of_Wild_and_Hatchery_Coho_Salmon_in_the_Salish_Sea.