AnevaluationofpHandNO3sensordatafromSOCCOMfloatsandtheirutilizationtodevelopoceaninorganiccarbonproducts

AsummaryofdiscussionsandrecommendationsoftheCarbonWorkingGroup(CWG)oftheSouthernOceanCarbonandClimateObservationsandModelingproject(SOCCOM)

March2016

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AnevaluationofpHandNO3sensordatafromSOCCOMfloatsandtheirutilizationtodevelopoceaninorganiccarbonproducts

R.Wanninkhof1,K.Johnson2,N.Williams3,J.Sarmiento4,S.Riser5,E.Briggs6,S.Bushinsky4,B.Carter5,7,A.Dickson6,R.Feely7,A.Gray4,L.Juranek3,R.Key4,L.Talley6,J.Russel8,andA.Verdy61.AtlanticOceanographicandMeteorologicalLaboratoryofNOAA,MiamiFL2.MontereyBayAquariumResearchInstitute,MossLandingCA3.OregonStateUniversity,CorvallisOR4.PrincetonUniversity,PrincetonNJ5.UniversityofWashington,Seattle,WA6.ScrippsInstitutionofOceanography,UCSD,LaJollaCA7.PacificMarineEnvironmentalLaboratoryofNOAA,SeattleWA8.UniversityofArizona,TucsonAZTableofcontent: PageRecommendationsandfindings 31.Introduction 42.Biogeochemicalsensorsonfloats 5Typesoffloats 6 DetailsofsensorsonSOCCOMfloats 7Frequencyofprofilingmeasurements 103.Performanceofsensors 124.Sensordeployments,calibration,validationandchecks 125.Recommendedconstantsforinorganiccarbonsystemparameters 136.pHcomparisonsbetweenbottleandfloatdata 167.UtilizingmultiplelinearregressionstoadjustpHandNO3sensorsonfloats188.Datamanagementandqualitycontrol/adjustments 209.Productdevelopment 2110.Outlook 23AppendixA.Chargeforthecarbonworkinggroup(CWG)ofSOCCOM 25References 28

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AnevaluationofpHandNO3sensordatafromSOCCOMfloatsandtheirutilizationtodevelopoceaninorganiccarbonproducts

Recommendationsandfindings:TheCarbonWorkingGroup(CWG)oftheSouthernOceanCarbonandClimateObservationsandModeling(SOCCOM)projectistaskedwithprovidingrecommendationsforacquisitionandqualitycontrolofdatafrombiogeochemicalsensorsonSOCCOMfloats:CWGFindings

Ø TheNO3andpHsensorsonfloatsareindevelopmentstagebutrapidlyreachingthepointofprovidingqualitydatatostudykeybiogeochemicalprocessesintheSouthernOcean.

Ø Thereisanimprovedunderstandingandremediesofissuescausingdriftinthebiogeochemicalsensors.

Ø ThetransitionfromanadhocadjustmentprocedureofpHandNO3toasystematicapproachhandledbydatacentersiswelllaidoutandprogressing.

Ø TheaccuraciesoffloatO2,NO3andpHdataafterappropriateadjustmentsare2µmolkg-1,0.5µmolkg-1,and0.01,respectively.

Ø NO3andpHdatafromtheprofilingfloatsinSOCCOMcanbeadjustedasneededusingMultiLinearRegression(MLR)algorithmsbasedonqualitybottledatafrom1000-2100dbarintheregion(seeeqns.3and4)towithinthelevelofcurrentinstrumentaluncertainties.

CWGRecommendations

Ø Allsamplesbroughtbacktoshorefromfloatdeploymentvalidationcastsshouldbeanalyzedfortotaldissolvedinorganiccarbon,DIC,inadditiontopHandtotalalkalinity,TAlk.

Ø ContinuedacquisitionandassemblyofhighqualityinorganiccarbondatafromCTD/bottlecastsiscriticalforqualitycontroloffloatsensors,modelvalidationandalgorithmdevelopment/improvement.

Ø AconsistentsetofdissociationconstantsandachemicalmodelshouldbeusedforcalculatinginorganiccarbonsystemparametersasdescribedinTable4.

Ø ItisimperativethatthetemperatureandpressuredependenceofpHsensors,andtheircorrespondencetotheappropriatepHscalesisfurtherstudiedindetail.

Ø ContinuedstudyandimprovementofadjustmentapproachesandincorporationoftheseeffortsintoaroutineapproachfollowingArgoguidelinesisneeded.

Ø Continuedstudyandimprovementindeploymentprocedures,physicalconfigurationofsensors,sensordesignandqualitycontrolisneeded.

Ø AccommodationisneededforupdatedprotocolsinArgotoprocessthebiogeochemicalandbiologicaldatausingseparatefilesanddataacquisitioncenterspriortomergingofphysicalandbiogeochemicaldata.

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1.Introductioni.PurposeofdocumentTheSouthernOceanCarbonandClimateObservationsandModeling(SOCCOM)projectisrevolutionizingoureffortstoinvestigatetheSouthernOcean.Thenewapproaches,inparticulartheutilizationofbiogeochemicalsensorsonfloats,requireacarefuluncertaintyanalysisandclearprocedurestocreateusefulproducts.Thecarbonsystemworkinggroup(CWG)ofSOCCOMischargedtoaddresstheseissueswithregardstothemeasuredandderivedinorganiccarbonsystemparameters:totalalkalinity(TAlk),totaldissolvedinorganiccarbon,(DIC),partialpressureofCO2(pCO2),andpH.TheonlyinorganiccarbonsystemparameteracquiredfromtheSOCCOMfloatsispH,theothersarecalculatedthroughdifferentmeansasdescribedbelow.Thisdocumentisanauthoritativeoverviewofprocedurestoadjustsensorsforoffsetsanddrift,andtouseofthefloatdatatocreateproducts,suchasregionalfieldsofinorganiccarbonparameters.ii.TheCWGandSOCCOMobjectivesThecarbonworkinggroupactivitiesarepartoftheoverallobjectivesofSOCCOM.SOCCOMisfocusedonunlockingthemysteriesoftheSouthernOceananditsinfluenceonclimate.SOCCOMisawell-structuredprogramwiththreemajorthemesofobservation,modelingandbroaderimpacts.TheCWGaddressestheobservationthemewithfocusoncreatingfieldsofcarbonsystemparameters,suchascarbonatemineralsaturationstates.AfulldescriptionofthechargeoftheCWGisprovidedinAppendixA.TherecommendationsandimplementationwillalsobenefitthecarboncyclemodelsoftheSouthernOceanthroughimprovedconstraints.TheCWGwillhavesignificantbroaderimpactsastheproceduresandapproachesdescribedcanbeutilizedtoimprovethequalityandproductsresultingfromfloatsequippedwithbiogeochemicalsensorsocean-wide.iii.OutlineofdocumentThisdocumentprovidesrecommendationsandguidelinestoadjustandcheckdatafrombiogeochemicalsensorsonprofilingfloats,inparticularpHandNO3sensorsbasedonempiricalapproachesandmodels.Theadjusteddataalongwithmodelsofdifferentlevelsofsophisticationareusedtodeterminethelargerscalefieldsofthebiogeochemicalparametersofinterest.Thefirstsectionofthedocumentdescribesthesensorsonfloatsandtheirpre-cruisecalibrationandtypicalbehaviorwhenfirstdeployedwithfocusontheNO3andpHsensors.ThisisfollowedbyadescriptionofthepHmeasurementandthederivationofcarbonsystemparametersandtheiruncertainties.AdjustmentproceduresoftheNO3andpHsensorsaredescribedbasedonmultiplelinearregression(MLR)algorithmsderivedfromthevalidationcruisesandotherhighqualitybottledata.ThefinalsectiontouchesuponthecarbonproductsthatwillbeproducedaspartoftheSOCCOMprojectusingdifferentempiricalapproaches.

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2.BiogeochemicalsensorsonfloatsTheArgoprofilingfloatprogramstartedintheearly1990'swithanambitiousgoalofdeployingaglobalarrayoffloatsequippedwithtemperature(T),salinity(S),andpressure(P)sensors.Itsprimaryobjectivewastodeterminechangesinoceanheatcontentintheupper1500m.TheoverallvisionofArgoistogreatlyexpandourknowledgeofchangesintheoceanwith"greatlyimprovedcollectionofobservationscapabilitiesinsidetheoceanthroughincreasedsamplingofoldandnewquantitiesandincreasedcoverageintermsoftimeandarea"1.Thecurrentprogramhaswell-definedobjectivesalongwithgooddissemination,qualitycontrol,anddatamanagementprotocols,anddatafromtheArgoprogramisnowusedinoverscientific200publicationsperyear.ThegreatsuccessofArgo,theurgentneedtostudytrendsinothervariablesinachangingocean,andrapidadvancesinsensortechnologyhaveinspiredresearcherstoincorporatenovelsensorsontotheprofilingfloatplatforms.Oxygensensorswerethefirsttobeusedextensively(Körtzingeretal.2004)andarenowdeployedonabout5%oftheglobalfloatarray(seeFigure1forfloatpositions).Thesensorsarewellbehavedandwithproperprecautionsyielddatabelievedtobeaccuratetowithin1%(≈2µmolkg-1).OxygendataprocessingprotocolsareclosetoroutinebutArgobiogeochemicalsensordatastillfollowadifferentqualitycontrolpaththancoreArgodata.ThebiogeochemicalsensorsofprimaryinteresttothisdiscussionareNO3andpH.WealsoconsiderpropertiesthatareestimatedorcalculatedfromtheseandotherArgomeasurements(e.g.aragonitesaturationΩA,TAlk,andDIC).TheO2sensorsarealsodiscussedasO2dataareusedextensivelytoestimatethecarbonsystemparameters.TheO2sensorsserveasanexampleofacomparativelymatureefforttodeploynovelbiogeochemicalsensorsontheArgoplatform.

1http://www.argo.ucsd.edu

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Figure1.LocationsofallfloatsreportingthroughtheWorldMeteorologicalOrganization’sGlobalTelecommunicationsSystem(GMS)forJanuary20162(top)andfloatsequippedbiogeochemicalsensorsasofSeptember20153(bottom)TypesoffloatsFivetypesoffloatsarecommonlydeployedintheArgoprogram(APEX,Navis,SOLOII,Provor,andNOVA).SOCCOMexclusivelyusesAPEXandSea-BirdNAVISfloatsattimeofwriting.TheNAVISfloatswithbiogeochemicalsensorsareastandardproductofSeabirdElectronicsandcanbepurchasedwithuserspecifiedconfigurations.Theyareinthelatestagesofdevelopmentandnotyetconsideredfullymature(asoftheendof2015).TheTeledyneWebbResearch(TWR)APEXfloatsaredeployedbytheUniversityofWashington(UW)andaretheprimaryplatformfordeployingthebiogeochemicalsensorsdescribedbelow.However,theAPEXfloatwiththeBGCsensorsusedinSOCCOMisnotastandardproductofTWRandisnotcommerciallyavailable.SOLOIIfloatsareextensivelydeployedbyWHOIandSIOforthecoreArgoarray,buttheyhavenotyetbeenadaptedtocarryavarietyofBGCsensors.Theplatformshavenoappreciableeffectonthedatafromthebiogeochemicalsensors,otherthanthatsomefloatshavepH,NitrateandO2sensorsinapumpedwatercircuit4.Thismayimpactsensoroperation.OxygensensorsinthepumpedstreamprecludeO2aircalibrationsandanecdotalevidencesuggestsmorefoulingissueswiththenitratesensorswhentheyareinapumpedloop.

2http://www.argo.ucsd.edu/statusbig.gif3http://argo.jcommops.org/maps.html4Theplacementinapumpedwatercircuitistominimizefouling.However,someresultssuggestthat,tothecontrary,thisisnotoptimalforthepHandNO3sensors.Theyarebeingrepositionedtohavedirectexposuretoseawater.

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DetailsofsensorsonSOCCOMfloats5Temperature(T),Pressure(P),andconductivity/"salinity"(C/S)sensorsarethecoresensorsontheArgoprofilingfloatsandhavehighaccuracy.AlloftheArgoandSOCCOMfloatscarrySea-Bird(SBE)pressure,temperatureandconductivitysensors.Conductivitysensorssometimesexperienceslowdriftratesthatarecorrectedforinthedelayedqualitycontrol(QC)processusingsalinityclimatologies6.ThetemperaturesintheArgoprofilesareaccurateto±0.002°C.Pressuresarenominallyaccurateto±2.4dbar,buttheymayalsodrift.Pressurevaluesareadjusted,ifneeded,innearreal-timebasedontheknownpressurewhenthesensorisatthesurface.Forsalinitytheaccuracyis0.005basedonpropagationofuncertaintiesinconductivityandtemperature.ThefactoryspecificationsoftheSBEsensorsareprovidedinTable1.---------------------------------------------------------------------------------------------------------------------Table1.Accuracyanddriftofthetemperature,Pressure,andconductivitysensorsasprovidedbythemanufacturer(Sea-BirdSBE)a.Sensor CalibrationStandard Initialaccuracy TypicaldriftT(˚C) ITS-90 0.002 0.0002˚Cy-1C(S/m) IAPSO/OSIL 0.0005 0.0002(S/m)y-1P(dbar) Deadweight&Pref 2 0.8dbary-1a:basedonapresentationbySRisertotheCWGon9/15/2015.---------------------------------------------------------------------------------------------------------------------ThreetypesofO2sensorsarecurrentlydeployedonSOCCOMfloatsthatallworkonthesameprinciplereferredtoasoptodes.TheseopticalO2sensorsconsistofasemi-permeablemembrane,sensingelement,light-emittingdiode(LED)andphotodetector.Thesensingelementcontainsaluminescentdyethatisimmobilizedinagelmatrix.WhenexposedtobluelightfromtheLED,thedyeeitherluminescesorisquenchedbyinteractionwithO2.Somesensorsalsoemitaredlightasareferencetoenhancestability.Thisredlightissimplyreflectedbackbythedye.Theintensityorlifetimeofthereturnedluminescenceismeasuredbyaphoto-detector.BecausetheintensityofresponsedriftsrelativelyquicklySBE63sandAanderaaoptodesonlyusethedecaylifetimetocalculatethedissolvedoxygenconcentration.ThequantitymeasurediscloselyrelatedtothepartialpressureofO2andthesensorcanmeasuretheO2inairaswell,thereforofferingauniquewaytocalibratethesensorwhenthefloatsurfaces(Johnsonetal.,2015).

5Fromhttp://sio-argo.ucsd.edu/RG_Climatology.html)andhttp://www.argo.ucsd.edu/Data_FAQ.html6http://www.jcommops.org/Apps/WebObjects/Argo.woa/wo/OR63C76oBdZD8I3GtmaI1g/1.0.0.41.1.1

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ForthefloatsdeployedduringSOCCOMtheSBE63andAanderaaOptode38307and4330modelshavebeenused.AsshowninTable2belowtheyhavesimilarcharacteristics.TheimportantdifferenceisthattheSBE63isplumbedintothewaterloopthatalsohousestheconductivitysensorandthereforcannotmakeoxygenmeasurementsinairwhenitsurfaces.Theseairmeasurementsofferanaccuratecalibrationvalueifatmosphericpressureandwatervaporpressureareknownattimeofsurfacing.Airimmediatelyabovetheoceanisgenerallyat100%relativehumidity,sothatthewatervaporpressurecanbecalculatedfromairtemperature,salinity,andatmosphericpressure.Theseopportunisticcalibrationsinairwhenthefloatsurfacesofferameanstoadjustforsmalldrifts(Bushinskyetal.,2016).Theaircalibrationshaveimprovedaccuraciesto2µmolkg-1comparedtothefactoryspecificationsinTable2.Theaccuracyislimitedprimarilybyknowledgeofthebarometricpressureatthelocationthefloatreachesthesurface.---------------------------------------------------------------------------------------------------------------------Table2.SummaryoffloatO2sensorperformancebasedprimarilyonmanufacturers'specificationsa.

a:FromapresentationofS.RisertotheCWG(9/15/2015)---------------------------------------------------------------------------------------------------------------------TheNO3sensorsonAPEXfloatsareInSituUltravioletSpectroscopy(ISUS)sensorsbuiltandcalibratedatMBARI.TheNAVISfloatshaveSUNAsensorsbuiltandcalibratedbySatlantic.TheSUNAV2(SubmersibleUltravioletNitrateAnalyzer)isachemical-freeUVnitratesensorbasedontheISUSnitratemeasurementtechnologydevelopedatMBARI.ISUSandSUNAhavethesamemainopticalcomponents,butSUNAhastheopticalpathconfigureddifferently.ThedescriptionbelowisadoptedfromJohnsonetal.(2013).Nitrateabsorbslightintheultravioletwithpeakabsorptionmaximumnear200nmwitha

7The3830sensorswereusedinthe12"pre-SOCCOM"floatsdeployedduringP16Sin2014.TheyarenolongerusedinSOCCOMfloats

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moderatelystrongmolarabsorptivity.ThedeepUVabsorptionspectrumofseawaterisdominatedbythecombinedsignalfromnitrateandbromide,withamuchsmallercontributionfromdissolvedorganicmatterthatisseparatedbymeasurementsatmultiplewavelengths.TheISUSmakesasingleUVspectralscanwiththelampon(lightscan)andlampoff(darkscan).Thelightanddarkscansareused,alongwithreferencespectralintensitiesfromsimilarscansofdeionizedwatermadeinthelaboratory,tocomputetheabsorbancespectrumfrom200to400nm.Theabsorbancespectrumisusedwiththeconcurrenttemperatureandsalinitytocomputenitrateusingthetemperaturecompensated,salinitysubtractedalgorithm(SWwithT/Scorr.).TheobservedsalinityandtemperatureareusedtopredicttheUVspectrumduetobromide.Thecorrectedspectrumthencontainsonlycomponentsduetonitrateandanapproximatelylinearbaselineduetoorganicmatterandinstrumentaldrift.Allspectraldataistelemeteredtoshoresuchthatnitrateconcentrationscanberecomputedasnecessary.Theaccuracyofthesensorisabout2μM,andthiscanbeimprovedthroughinsituadjustments.Errorsinnitrateconcentrationareconstantoffsetsovertheentireverticalprofilesuchthattheerroratthereferencedepthcanbeaddedbacktotheentireprofileandamuchhigher-qualitysetofnitratedatacanbeobtained.Theadjusteddatahaveaccuraciesontheorderof0.5μM,relativetothereferencevalue.---------------------------------------------------------------------------------------------------------------------Table3.AccuracyoftheSUNANitratesensorinseawatera,b withT/S

corr.b withoutT/Scorrection

Detectionlimit 0.5μM 2.0μMAccuracy(greaterof) ±2μM or±10%ofreading Precision(shortterm) 0.3μM 1.0μMDrift(perhourlamptime)c 0.3μM 2.4μMa:Fromhttp://satlantic.com/sites/default/files/documents/2015_datasheet_SUNAV2.pdfb:Thesevaluesarewithappropriatecorrectionsforsalinityandtemperaturec:Duringatypicalprofilethelampisactivated70secondsoratotalof5.5hoursfora5-yeardeployment---------------------------------------------------------------------------------------------------------------------The(SBE/Satlantic)pHsensorisanewbiogeochemicalsensoranditisthefirstinorganiccarbonsystemparameterroutinelydeployedonprofilingfloats.TodatethepHsensorsontheSOCCOMAPEXfloatshaveallbeenbuiltatMBARIaspartofatechnologytransferagreement.ToensureasmoothtransitionfromsensorsconstructedatMBARItocommercialversions,theMBARIsensorswillbegraduallysubstitutedwithcommerciallybuiltsensorsofsimilardesign,beginningwiththedeploymentofSBEpHsensorsonNavisfloats.MeasurementofpHusingIonSensitiveFieldEffectTransistor(ISFET)technologyissummarizedinMartzetal.(2010)andbrieflydescribedhere.TheISFETisametaloxidesemiconductorfieldeffecttransistor(MOSFET).Theconductionchanneliscoveredbya

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thininsulatinglayerofamphotericmaterial.ThepHofthesolutionattheinsulator/solutioninterfacecontrolsthesite-bindingprotonation/deprotonationstateoftheinsulatormaterialand,hence,thesurfacechargeattheinterface.TheinterfacialchargedeterminesthestrengthoftheelectricfieldintheconductionchanneloftheFET,locatedbetweenthesourceanddrain.TheISFETsusedinSOCCOMareoperatedbyapplyingaconstantdrainsourcecurrent.AconventionalreferenceelectrodeisusedinconjunctionwiththeISFET.Itisasolid-statechlorideion-selectiveelectrode(Cl-ISE)withverylittlepressurehysteresis.TheapproximatesalinitysensitivityfortheFET|CI-ISEis0.013pHsalinity–1(Martzetal.,2010).TheISFETsensordeployedonprofilingfloatsiscalledtheDeep-SeaDuraFETpHsensor.ThepHisreportedonthetotalprotonscale(pHT).Itcanoperateatpressuresto2000mdepthintheocean.ThereforethesystemmustbecalibratedforpHmeasurementsthroughlargetemperatureandpressuregradients.TheintegratedDeep-SeaDuraFETincludesapressuretolerant,solid-stateAgClreferenceelectrodeCI-ISEdescribedabove.Theoutputofthesensorisavoltage,VRSthatisrelatedtoH+ionactivity,temperatureandpressureby:

VRS=k0+k2(T-273.15)+f(P,T)-RT/Fln(aH+aCl-)T,P (1)

=k0+k2(T-273.15)+f(P,T)-RT/F[ln(mH,fmCl)+ln(γHγCl)T,1+V$ HClP/RT] (2)

k0isthereferencepotential.k2isthetemperaturedependenceofVRS.f(P)isthepressurecoefficientofthesensor.Unlikeaconventionalelectrode,thek0andk2valuesoftheISFETcontaintermsassociatedwithFETdesign,semiconductorprocessingandpowerapplicationvalues.Thereforethek0andk2valuesmustbedeterminedforeachindividualsensor.

Giventheuncertaintyofcoefficientsineqn.(2)overtherangeofTandPintheoceantheuncertaintycantranslatetoa0.01pHerrorduetopressureat2000dbarpressureand0.015duetotemperature.Asaresult,theestimatedpHTvaluescanhavebiasesontheorderof0.02atpressuresnear2000dbar,basedonpropagationofpossibleerrorsduetouncertaintiesinTandPdependence.

InitialdeploymentsoffloatswithpHshowedameanrateofdrift,diagnosedasthechangebetweenpHobservedbelow1000mdepthandtheexpectedpHatthisdepth,of-0.036pHyr-1.However,withappropriatesensorconditioning,inparticularequilibrationoftheAgClreferenceelectrode(CI-ICE)withbromideinseawater,thisdriftcanbedecreasedby5-fold.(K.Johnson,pers.com.).

FrequencyofprofilingmeasurementsThepHandNO3sensorsareloggedontheupcastofthefloatwithadefault10-daycycleApproximately65measurementsaretakenontheupwardprofilewiththeAPEXfloats.ThisrateisdeterminedbypowerrequirementsoftheNO3sensorandlimitationsoftheelectronics.Themeasurementspacingisvariabletocapturerelevantfeatureswith

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nominally100-mintervalsfrom1500to1000m;50mfrom1000to400m;20mfrom400to360m;10mfrom360to100m;and5-mintervalsfrom100mto5m.TheassociatedT,S,andO2dataareprovidedatthesamedepthsinthedatafiles.TheNAVISfloats,withmoremodernelectronics,arecapableofmuchhigherverticalresolution.TheyprovidepH,oxygenandbio-opticalmeasurementsat2-meterspacingintheupper1000m.NitrateremainsatthesameresolutionobtainedwithAPEXfloats.ExamplesoftwoprofilesofO2andpHfromSOCCOMAPEXfloat9254areprovidedinFigure2.

Figure2.Profilesofoxygen(blue)andpHT(red)fromfloat9254at39˚S,155˚W,for11/21/2015(opensymbols)and12/01/2015(closedsymbols),illustratingthedepthresolution,andtherapidbutcoherentchangesinbiogeochemicalparametersintheupper

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watercolumnduringtheAustralSpring/Summer(dataobtainedon12/05/2015fromhttp://soccom.princeton.edu/soccomviz.php).3.PerformanceofsensorsBasedoninformationonthesensorsprovidedaboveandthemeasurementsinthefieldtodatewecanprovideanassessmentoftheperformanceofthesensors.Thisisnotexact,asonlylimitedinsituvalidationispossible.Moreover,sensorsandtheshoresidepreparationsandcalibrationroutinesarestillbeingimproved.Table4providesanassessmentofcurrentestimatesofperformanceofthesensorsbasedonmanufacturersspecificationsandcalibrationsinlaboratoryandothervenues.---------------------------------------------------------------------------------------------------------------------Table4.SensorresponseandcurrentestimatesofaccuracyofsensorsduringdeploymentParameter Accuracy Stability(drift)P 2dbar 0.8yr-1T 0.002˚C 0.0002yr-1S 0.005 0.01yr-1O2 2µmol/kg 0.6µmolyr-1NO3 0.5µmol 0.3μMyr-1(a)pH .01 -0.036yr-1(b)(a):Basedona1-hourtotallampusageoverayear(≈52profiles)(seeTable3).(b):FromMartzetal.(2010),newconditioningapproacheshavedecreasedthisdrifttolessthan0.007yr-1---------------------------------------------------------------------------------------------------------------------Thereareslightdifferencesinsetupsandtypesoftheinstrumentsdeployedbutoveralltheyshouldhavesimilarperformance.Animportantdifferenceisifthesensorsareplumbedintoawatercirculationsystemorexposeddirectlytotheoceanwater.ThecirculationsystemprecludestheaircalibrationoftheO2sensor,butshouldimprovetheresponsetimeofthesensor.Thecirculationloopshaveananti-foulingagentbuttheNitrate(opticalsensor)appearstohaveotherfoulingissuesintheloop.CurrentlyallthebiogeochemicalsensorsontheAPEXfloatsarebeingtestedwithsensorsdirectlyexposedtoseawater.4.Sensordeployments,calibration,validationandchecksLaboratorycalibrationofsensorshasbeenchallengingduetodifficultiesrecreatingtheenvironmentatseawhenthesensorsaredeployed.O2sensorsareroutinelycheckedinthelaboratory.FortheAPEXfloatstheO2sensorsarecomparedside-by-sidewithacalibratedlaboratorysensorofthesamemakeandmodel.pHsensorsarecheckedpriortodeploymentinartificialseawaterbutduetodifferencesinchemicalconstituentsbetweenartificialseawaterandrealseawater,appreciableadjustmentsarenecessary.NO3sensorsarecheckedinthelaboratoryaswellbutwhileoverallresponseandgeneralbehaviorofthesensorcanbechecked,mostdatarequireanadjustmentoncedeployed.

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ThevalidationCTD/bottlecaststhatarepartoftheusualSOCCOMprotocolatthetimeoffloatdeploymentareanimportantmeanstocheckthesensorswhentheyaredeployedandtodetermineappropriateadjustments.Thefirstprofilefromthefloatoftendoesnotcorrespondwellwiththebottledatafromthecastbecausethesensorssometimesexperiencedriftduringtheirinitialprofile,notablytheNO3sensor.TheO2sensorsgenerallydonotundergoacheckagainstthecalibrationcast,inpartbecausethesensorsshowgoodagreementbetweenlabbasedcalibrationvaluesandthedeploymentvalues.However,forthesakeofconsistency,similarchecksandadjustmentsshouldbemadeforO2,pHandNO3sensors.ThedeploymentcastisagoodqualitativecheckfordriftandoffsetsbutcurrentlyadjustmentstopHandNO3sensorvaluesareperformedbasedontheMLRsdevelopedfromdeploymentcastsandotherhighqualitybottledataintheSouthernOcean(seesection7).ThepHandNO3sensorsroutinelyneeda"soakingtime"ofafewprofilesduringwhichthereisappreciabledrift.Thedriftisattributedtoseveralfactors.ForNO3itappearsthattheopticalwindowcouldbedirtiedbyorganicsduringstorageandtransport.ForpHtheAgClinthereferenceelectrodereactswithBrinseawateruntilequilibriumbetweenAgClandAgBrintheelectrodeisobtained.CleaningproceduresofopticalwindowsandlongersoakingtimesofpHsensorsinrealseawaterinthelaboratoryarecurrentlybeinginvestigatedasaviablemeanstodecreaseinitialdrift.OncetheNO3sensorstabilizesfromlargedriftthereisasmallerresidualdrift(seeTable3).ThustheNO3sensoradjustmentofteninvolvesanadjustmentforoffsetsoonafterdeploymentfollowed,atalatertime,bycorrectionforalongertimedrift.Theadjustmentsaredoneinanopportunisticfashionbasedonknowledgeofclimatologiesandstoichiometriesbetweenparameters.TheprimaryadjustmentsaredoneatdepthbasedontheWorldOceanAtlasWOA,otherclimatology,orasrecommendedforSOCCOMbyaMLRalgorithm(section7).ForNO3sensorsdeployedinsubtropicalregions(e.g.,nearBATS)wheresummertimenitratevaluesinthesurfacearezero,asecondcalibrationcheckisbasedonthezeroconcentrationinthemixedlayer.DriftovertimeisdeterminedandcorrectedbasedoncomparisonoffloatandMLRalgorithmatdepth(1000-2100m)wherenitrateislinearlyregressedagainsttemperature,salinity,pressureandoxygen:NO3=a+bT+cS+dP+eO2,wherethecoefficientsaredeterminedfromcruisedatainthearea.5.RecommendedconstantsforinorganiccarbonsystemparametersAdjustmentofpHsensorsissignificantlymorechallengingthanforothersensorsandrequiresinformationonthedissociationoftheinorganiccarbonspeciesinseawater.ThisCO2systeminformationisalsonecessarytocreateinorganiccarbonproductsfromthepHfloatdata.pHsensorsonthefloatsmeasurethepHatinsitutemperatureandpressurewhichisdifferentfromthecalibrationandvalidationsampleswhichareanalyzedatconstanttemperatureand1atm.ThesensorsmeasurethefreeH+ionsanditismostappropriatetoexpressthepHonthefreescale(K.Johnson,pers.com.).ThepHsamplesfromCTD/Bottlecastsaremeasuredatconstanttemperature(usually20or25˚C)onthetotalscaleinaship'slaboratory.OnselectoccasionspHisnotmeasuredonboardbutratherdeterminedalongwithTAlkonbottlesamplesshippedtotheshoresidelaboratory

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ofA.DicksonofSIO.Tocomparethebottledatawiththesensordataandapplyadjustmentstothesensordata,carbonatedissociationconstantsandachemicalmodelneedtobeapplied.DetailsofthebasicinorganiccarbonchemistryandrecommendedanalysisprocedurescanbefoundinDicksonetal.(2007).Herewefocusonusingdiscretebottlesamplesatfixedtemperatureand1atmpressuretoadjustinsitupHsensordata.Excel®andMATLAB®routinesarereadilyavailabletoperformtheconversions.Thetemperatureandspeciesconversionsrequireachemicalmodelandtwoinorganiccarbonsystemspecies(DIC,TAlk,pH,orpCO2)(e.g.Pierrotetal.2006).TherecommendedconstantsforSOCCOMeffortsareprovideinTable5.Theyareconsideredthemostconsistentbasedoncurrentknowledge,butthemainpurposeoftherecommendationisforconsistency.Thatis,allSOCCOMproductsshouldbebasedonthesameconstantssuchthatdisagreementsinresultsorinterpretationsarenotcausedbyproductsbeingdevelopedusingdifferentconstants.---------------------------------------------------------------------------------------------------------------------Table5.RecommendedconstantsforcalculatinginorganiccarbonsystemparametersinSOCCOM,includingtemperatureandpressurenormalizations.Carbonatedissociationconstants(1)pHT(2) Totalscale(molkg-1seawater)pK0(3): SolubilityWeiss&Price(1980)pK1andpK2(4)Luekeretal.(2000)usingpHTAssociatedconstants(5)pK(B) DissociationconstantboricacidDickson,(1990)pK(HF) DissociationconstantforhydrofluoricacidofPerez&Fraga(1987)pK2P,pK3P(6) 2ndand3rddissociationconstantsphosphoricacidDicksonetal.,(2007)Pressure(7) Pressurecorrectionsforvariousacid-basedissociationconstantsas

implementedinCO2SYSTB TotalboroninseawaterparameterizedwithsalinityLeeetal.,(2010)KHSO4(8) Dickson(1990)ΩAr,ΩCa(9) AragoniteandCalcitesaturationstatesasprovidedinCO2SYS.(1)TheCO2SYSprogramhasbeenadjustedbyD.Pierrottoaccommodatetheseconstants.

(CO2SYSv2.2).ThefootnotesnotesbelowareadaptedfromA.Dickson,pers.com.(2)Spectrophotometricmeasurementusingpurifiedm-cresolpurpleat25˚Casreference

(Liuetal.,2011).Thesehavebeenverifiedinthelaboratory(at25˚CandS=35)ofA.Dickson,SIOandtheyagreewithLiuetal.to0.002inpH.However,theresultingpHisnotnecessarilyinperfectagreementwiththewaypHisdefinedinthedefinitionofthevariousacid-dissociationconstants.Preliminaryworksuggestsadiscrepancyofabout0.006inpH.IfthisdiscrepancyisaccountedforthenpH,TAlk,andDICareinternallyconsistentwithinlikelyuncertainties.

(3)pK0basedonWeiss(1974),asimplementedintheappendixofWeiss&Price(1980)

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(4)pK1andpK2basedondataofMehrbachetal.(1973),convertedtototalhydrogenionconcentrationscale(Luekeretal.,2000).

(5)Toconverttotalalkalinitytocarbonalkalinityneededincalculations,andtoestimatethehydrogenionactivityfromnon-carbonatespeciesinseawater.ValuesarevalidforS≈20-38,T≈-2to40˚C)

(6)pK2P,pK3PforH3PO4dissociationarebasedonMillero(1995)correctedtopHTscale(seeDicksonetal.,2007)

(7)Pressurecorrectionsforacid-basedissociationconstantsasimplementedinCO2SYS,ThispressuredependenceisbasedonoriginalworkbyCulbersonetal.(1968)ontheequivalentofthefreepHscalewithsubsequentapproximationsofthe∆VofHCO3-basedonthatofHSO4-(K.Johnson,pers.com.).

(8)WatersandMillero(2013)andKhooetal.(1977)showvaluesofKHSO4thataretwiceashighastherecommendedKHSO4ofDickson(1990).TheeffectsofpressureandtemperaturearedifferentforthevariousKHSO4valuesthatwillleadtodifferencesinpHof≈0.01forthedifferentKHSO4valuesonthefreescale

(9)Note,somecurrentbiogeochemicalmodels(e.g.TOPAZ)donotreproducecalculatedvaluesfromCO2SYSusingTAlkandDIC.ThisappearstobeanissuehowCa2+isdetermined.InCO2SYS,Ca2+=293.84*S.

---------------------------------------------------------------------------------------------------------------------ForchecksofotherCO2systemcodesthefollowingtwoexamplesareprovided.TestcasesusingCO2SYSV2.2andconstantsinTable5:Sample400217Station40,P16S(2014)InputvaluesP=1000.3dbarS=34.319T(insitu)=5.720˚CTAlk=2286.4µmolkg-1DIC=2169.1µmolkg-1pHT(20,0)(a)=7.7366PO4=1.82µmolkg-1SiO3=17.8µmolkg-1outputusingTAlkandpHT(20,0)pHT(5.72,1000)=7.9104pHF(5.72,1000))(b)=7.9593DIC=2167.8µmolkg-1fCO2(5.72,1000)=493.4µatmΩAr(5.72,1000)=1.14ΩCa(5.72,1000)=1.79Sample400210Station40,P16S(2014)P=1999.5dbarS=34.581T(insitu)=2.626˚CTAlk=2350.6µmolkg-1DIC=2264.3µmolkg-1

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pHT(20,0)=7.632PO4=2.37µmolkg-1SiO3=82.4µmolkg-1outputusingTAlkandpHT(20,0)pHT(2.62,2000)=7.8062pHF(2.62,2000)=7.8459DIC=2265.9µmolkg-1fCO2(2.63,2000)=576.5µatmΩAr(2.63,2000)=0.74ΩCa(2.63,2000)=1.15(a):pHT(20,0)isthepHonthetotalscaleattemperatureof20˚Candpressureof1atm.(b):pHF(5.72,1000)isthepHonfreescaleattemperatureof5.72˚Candpressureof1000

dbar(98.7atm).pHFiscalculatedfromDICandTAlkwhereDICinturnisdeterminedfromTAlkandpHT(20,0).

6.pHcomparisonsbetweenbottleandfloatdataFortheSOCCOMeffort,useofthetotalpH(pHT)scaleisrecommended.Theotherscalescommonlyusedinseawateraretheseawaterscale(pHsw)andfreescale(pHf)8.AcomprehensivedescriptionofthemetrologyofpHcanbefoundinDicksonetal.(2016).TheDeep-SeaDuraFETpHsensormeasuresthefreehydratedhydrogenionsandpHfwouldbethebestscaleforthissensorinparticularbecausethepressuredependenceofbisulfateioninseawaterisnotwellknowncausinganuncertaintyinthecalibrationofthepHdataatdepthcomparedtothesurfacereference.However,theDuraFETsensorsarecalibratedandvalidatedonthepHTscaleasthisisthescaleofchoiceforspectrophotometricbottlepHmeasurementsinseawater.Table6providesanoverviewofthecalculatedpHat25and0˚Candatboththesurfaceand2000dbarusingdifferentpHscales.ThistableshowsthatthenumericalvaluesofpHTandpHswarequitesimilar,duetothefactthathydrofluoricacidhasasmallcontributiontohydrogenionsinseawater,butthedifferencewiththefreescaleisappreciable.OfparticularnoteisthatthetemperatureandpressuredependenceofthepHfandpHTscalesdifferwhichisacauseofambiguityintheDuraFETpHvaluesreported.WiththeadvancesinpHsensortechnologyacarefulevaluationofthetemperatureandpressuredependenceofpHinseawaterisurgentlyneeded.---------------------------------------------------------------------------------------------------------------------Table6.ComparisonofpHscalesfordifferenttemperaturesandpressuresaS T(˚C) P(dbar) pHsw pHT pHf35 25 0 7.514 7.523 7.635

8 pHf=-log{H+},pHT=-log({H+}+{HSO4-}),andpHsw=-log({H+}+{HSO4-}+{HF0},where{H+}indicatestheactivityoffreehydratedhydrogenions.

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35 0 0 7.876 7.883 7.82435 25 2000 7.443 7.452 7.55235 0 2000 7.793 7.799 7.839a:calculatedusingtheCO2SYSV2.2programwhereTAlk=2300µmolkg-1;DIC=2230µmolkg-1;PO4=2µmolkg-1;andSi=50µmolkg-1---------------------------------------------------------------------------------------------------------------------AnexampleofthemagnitudeofcorrectionsofpHforadepthprofileofacalibrationstation,Station40onP16S,2014whereaSOCCOMfloatswasdeployed,isshowninFigure4.TheredlineisthepHTmeasuredfromCTD/Bottlesamples(20˚C,1atm)andthegreenlineisthecalculatedpHTatinsitutemperatureandpressurewhichwouldbesimilartoapHprofileobtainedfromaSOCCOMpHsensor.Atapressureof1600dbarandinsitutemperatureof3.15˚Cthedifferencebetweenthevalidationdataat20˚C,1atmandinsitupHdatais0.188ofwhich0.242isassociatedwiththetemperaturedifferenceand-0.065isthepressureeffectonpH.Incomparison,thedifferencebetweenmeasuredpHT(20,0)andcalculatedpHT(20,0)fromTAlkandDICfortheshipboardmeasurementis-0.005.

Figure4.ExampleofpressureandtemperatureeffectonpHbasedonaCTD/bottlecastoncruiseP16.TheredlineistheinterpolationofthepHTmeasuredbyspectrophotometry(openredcircles).TheblueopensquaresarethepHTvaluescalculatedfromTAlkandDIC.ThegreenlineisthecalculatedpHTatinsitutemperatureandpressuremimickingafloatprofile.

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Thedashedlinewithcrossesistheeffectofpressurerelativetothemeasureddata,andthedashedlinewithplussymbolsistheeffectoftemperaturerelativeto20˚C.Bothtemperatureandpressureareappreciablecorrectionsthataresensitivetothedissociationconstantsused.TocalculatetheeffectoftemperatureonpHrequiresDICorTAlkasasecondinorganiccarbonparameterbuttheaccuracyofthemeasurementoftheinorganiccarbonparameterhaslittleeffectontheestimate.Forinstance,a1%uncertaintyintheICparameter(DICorTAlk)willtranslatetoanegligibleuncertaintyof0.0005inthepHforaconversionfrom20˚Cto0˚C.ThusforvalidationsamplestakentoshoreforthepurposeofcomparingpH,theTAlkmeasurementneednotbeofhighaccuracy.ThetemperatureeffectonpHisabout0.2%˚C-1onlogscale.Thepressurecorrectionisabout-0.04/1000dbar.Onlyonesetofconstantsisavailableforthiscorrection,anditsuncertaintyisunknown.SincethereareuncertaintiesintheconstantsandconversionsfrominsitupHfromthefloattospectrophotometricpHmeasurementsitisprudenttoattainthehighestqualityDICandTAlkmeasurementsasthesemeasurementscanprovideanindependentestimateofpH.7.UtilizingmultiplelinearregressionstoadjustpHandNO3sensorsonSOCCOMfloatsSeveralapproachescanbeappliedtoadjustthepHandNO3datafromsensorsonthefloatsbutrobustmeanstodosoinsituarelimited.DuringthefirstyearsofSOCCOMitwasrealizedthatapplyingmultiplelinearregressions(MLR)developedfromhighqualityshipboarddataintheregionisapowerfulmeanstodiscernoffsetsinfloatsensorsatdepth.ThepHandNO3sensorsappeartovaryinaconsistentmannerwithinthepressureandtemperaturerangesoverwhichtheyprofile.Thismakesitpossibletoadjusttheprofilebasedonsensor-offsetsobtainedbycomparingthesensormeasurementsatdepthwithMLRscreatedfordepthsof1000-2100dbar.TheMLRsforNO3andpHarecreatedwiththesameindependent/predictorvariables:P,T,S,andO2asthesevariablesaremeasuredoneachofthefloatsthatcarrythepHandNO3sensors.Therefore,eachfloatcontainstheinformationforchecksoftheNO3andpHsensorsonboard.TheoverallapproachtocreatetheMLRsisdescribedinJuraneketal.(2009)withconsiderationofcrosscorrelationandoverfittingissuesthatcanplagueMLRapproaches.Theempiricalmultiplelinearregressionrelationshipsaredevelopedfromcruisedatain2011(S04P)and2014(P16S)intheSouthPacificsouthof45˚Sfordepthfrom1000to2100dbar.Thedepthrangeandassociatednarrowparameterspaceincreasesthegoodnessoffitandavoidsspuriousresultsthatcanoccurwhenindependent/predictorvariablesarerelatedasoftenisthecaseforbiogeochemicalandphysicalparametersintheocean.TheMLRalgorithmsdeterminedoverthe1000to2100mrangeare:

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𝑝𝐻! 𝑇,𝑃 = 1.380+ 1.8020×10!! 𝑂! + 0.17859 𝑆 + 7.4820×10!! 𝑇 − 3.966×10!! 𝑃, 𝑟!= 0.98, 𝑠.𝑑.= 0.004 (3)

𝑁𝑂! = 544− 0.108 𝑂! − 11.4 𝜎! − 4.92 𝑆 − 2.69 𝑇 − 3.14×10!! 𝑃, 𝑟! = 0.85,

𝑠.𝑑.= 0.3 (4)DetailsonthealgorithmscanbefoundinthesupportinginformationofWilliamsetal.(2016).AlgorithmsforpHTutilizingNO3insteadofO2havebeendevelopedaswellwithsimilaruncertaintiesbutsincetheO2sensorsonthefloatsaremoreplentifulandmoreaccurate,thealgorithmswithO2willbeusedexclusivelyforthepurposeoffloatpHadjustment.ForthepHalgorithmsthediscretepHmeasurementsat20or25˚CatthesurfacewerecorrectedtoinsituvaluesusingthedissociationconstantsinTable4.TheoutputsfromalgorithmshavebeencomparedwithindependentcruisedataintheSouthPacific(P18S-2007),SouthernIndianOcean(S04I-2012),andAtlanticOcean(A16S-2014)anddifferencesaregenerallywithinthelimitsof0.01forpHand0.5µmolkg-1forNO3(Figure5).Atthegeographiclimitsandinareasofdeep-waterformationthedifferencestendtoincreaseandthisshouldbetakenintoconsiderationwhenfloatdataareadjustedintheseregions.

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Figure5.ComparisonoftheMLRoutputforpHT(T,P)withmeasuredvaluesnotusedintheMLRdevelopmentintheSouthernOcean.A16SisameridionallineintheSouthAtlanticandP14Sisazonalline(≈62˚S)SouthofAustralia.ThecirclesdepictthesamplingdepthandthosewithcolorlesscentersindicatethattheMLRoutputiswithintheuncertaintylimitsof0.01oftheanalysis.ForSOCCOMallpHandNO3sensordataareadjustedbasedonthealgorithmlistedabove.AdjustmentsareperformedbasedonpHandNO3floatdataacquiredatdepth.ForpHanadditiveadjustmentismadetothereferencepotentialk0(seeeqn.1)toreachcorrespondencewiththealgorithmsvalues.ForNO3theadjustmentisadditivetoitsreportedconcentrationvalue.8.Datamanagement,qualitycontrolandadjustmentsSuccessfulfullimplementationoftheSOCCOMfloatprogramrequiresimprovedefficienciesandprotocolsindataacquisitionandmanagement.ContinuedinteractionswithArgodataacquisitioncenters(DAC)areamusttoassurefullincorporationofbiogeochemicalsensorsandbiologicalsensorsintotheArgodatasuite.ThisisparticularlytrueiftheSOCCOMeffortisconsideredaprecursorofaglobalbiogeochemicalandbiologicalsensorarray.ThechallengesofmakingadevelopmentaleffortlikeSOCCOM,whichrequiresflexibilityandadaptationsbutalsothemorerigidrequirementsofthemorematurearrayaresignificant.Atthesametimepiggy-backingontheArgoarrayisagreatbenefitforlessonslearnedandestablishedinfrastructure.TheSOCCOMbiogeochemicalparametersmeasuredonfloatsO2,NO3andpHwillbetransitionedfrominvestigatorbasedmanagement(K.JohnsonandS.Riserlead)toastreamlinedandconsistentapproachmanagedbytheUniversityofWashington(S.Riser).ThebiogeochemicaldatawillbeprocessedinparallelwiththecoreArgodatafollowingagreementswiththeArgosteeringgroup.

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TheArgoprocessingisasfollows9.Therearethreerelevantfilesthatarecreatedforeachfloat:acore-Argo,B-ArgoandM-Argoprofileandtrajectoryfiles.Thecore-ArgoprofileandtrajectoryfilescontainonlytheCTDdata.Theparametersincludedinacore-Argofilearepressure,temperature,salinity,andconductivity.TheB-files,whereBstandsforbiogeochemistryorbiology,willincludeallotherparametersexcepttemperature,salinity,andconductivity.TheywillincludeallintermediateparametersthatarenecessaryforcalculatingparametersofinterestsuchastheUVspectraforNO3andluminescencedecaytimefortheO2optodes.ThecoreandBfilesarecreatedprimarilyforeaseofcalculatingand,whennecessary,adjustingparameters.ThecoreandBfilesarethenmergedintoM-fileswhichwillbeofmostinteresttoinvestigators.Theywillcontainalloceanvariablesthatthefloatmeasures.ThisfilewillcontaintheconcentrationofinterestforthecoreparametersandparametersfoundintheB-filebutnottheintermediateparameters.Thetransitiontothisnewdataprocessingscheme(calledversion3.1)willbechallengingandpossiblyslowdownthereleaseofbiogeochemicaldatafromfloatswhiletheprotocolsarebeingimplemented.9.ProductdevelopmentApriorityforSOCCOMistoutilizethelargeincreaseinhigh-resolutiondataintheSouthernOceantoestimatethestateofbiogeochemicalproperties,andtheprocessesandratesinvolved.Inparticular,themagnitudeandcausesofseasonalvariabilitywillbeestablishedforthefirsttime.Theyear-roundpresenceoftheprofilingfloatsandabilitytosampleundericewillofferseasonallyandspatiallyunbiasedresults.Twoapproachescanbefollowedfordeterminingfieldsandprocessesinvolvinginorganiccarbonparametersbasedonthefloatandadditionaldata.ThefirstapproachistodetermineTAlkempiricallyfromfloatdataorothermeans.ThederivedTAlkandmeasuredpHfromthefloatcanthenbeusedwiththethermodynamicrelationshipsandconstants(Table4)todetermineanyoftheothercarbonsystemparametersofinterestsuchasDIC,pCO2,ΩArorΩCa.RobustrelationshipsofTAlkandsalinityandtemperaturehavebeenderivedforsurfacewater(Leeetal.,2006;Takahashietal.,2014)basedontheconservativebehaviorofTAlkonregionalscales.Forsubsurface,remineralizationandmixingprecludessimplerelationshipsandmoresophisticatedalgorithmsareestablishedbasedontheglobaloceanwatercolumncarbondataset(GLODAP-2,Keyetal.,2004).Carteretal.(2016)developedanalgorithm(andassociatedMATLABcode)toestimatealkalinityglobally,referredtoas“locallyinterpolatedalkalinityregression.”SpecificalgorithmswillalsobedevelopedfortheSouthernOceanaspartofSOCCOM(Williams,pers.com.)

9www.argo.ucsd.edu/Data_FAQ.html

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Figure6.Diagramofpathwaysfordataflowandqualitychecks.Thebluelinesindicatethedatastreamsusedforinterpretation,thegreenlinesarethepathwaysusedtoadjustthefloatdataandtheredlinesarethepathwaysofqualitycontrolleddataflow.Thedoublearrowsindicatethatthedatarepositoriesbothingestandcontributetothequalitycontrol.Theproceduresinthedashedrectanglearethefocusofthisreport.Notethatmostdepositorieshavemultiplefunctions.Asecondapproachistoestablishempiricalrelationshipswiththeparameterofinterestandpredictorvariablesthatcanbemeasuredonfloats,ordeterminedfrombottledatafromcruisesandappliedtofloatdata.ThisapproachissimilartotheMLRalgorithmsusedtoadjustthepHandNO3dataatdepthforfloats.ThismethoddoesnotnecessarilydependonpHdataorTAlkestimates.However,itdoesassumethattheMLRwithpredictorvariablesthatarenotinorganiccarbonsystemparameterscanfaithfullypredicttheinorganiccarbonsystemparametersofinterestonscalesthatarerelevanttothecarboncycle,fromsub-mesocaletomesoscaleandbeyond;andtimescales,fromseasonalthroughinterannualtodecadalandbeyond.AnyprocessthatchangesthecarbonsystemparameterswithrespecttothosepropertiesusedintheMLRwilldegradetheestimatesof

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theevolvingcarbonsystemparameters.Forexample,inthesurfacemixedlayerfunctionaldependenciescanchangerapidlyduetogastransferandbiologicalproductivityandoftencannotbewellrepresentedbyMLRs.OndecadalscalesanthropogenicCO2increaseswillinvalidateMLRspredictingDIC,pCO2orpH.Whilebothapproachesneedtobeinvestigatedinfull,itisprobablethatparametersthatcanbebetterpredictedinthesurfacelayersuchasTAlkalongwithmeasuredfloatpHwillhavesomeadvantagesoverlarge-scaleMLRapproachesnotusinginorganiccarbonsystemparametersinthesurfacemixedlayer.10.OutlookTheSOCCOMeffortisinitsinfancyandmakingthenecessarypreparationstofullyutilizetheobservationsandmodelswhenfullyinplace.AsofFebruary2016,37,or18%oftheplanned200total,floatsaredeployed;thisnumberwillbecloseto50,or25%,bytheendofMay2016.ImplementationofrobustdatamanagementandbiogeochemicaldataadjustmentschemesisunderwaybutwillrequirecontinuedcloseinteractionwithArgoandsignificantresourcesfromSOCCOM.Asdescribedabove,creativeandrobustapproachesusingmultiplelinearregressionsfromCTD/bottledataareusedtocorrectNO3andpHdatatowithin0.5µMand0.01,respectively,whichiswithincurrentinstrumentspecifications.ContinuedchecksandimprovementsofthealgorithmsutilizingCTD/bottledataandbottlesynthesisproductsthatwillbedeliveredduringtheSOCCOMprojectareadvisable.Further,theprogrammustrigorouslyassesssensorperformanceandfailurestoensurethatsensorreliability,accuracyandprecisionarecontinuouslyimproved.Thiswillminimizethedependenceonadjustmentproceduresandresultindataofevergreaterutility.Biologicaldatafromtheprofilingfloats,"bio-optics",arenotaddressedinthisreportbutwillrequireasimilarscrutinyonsensorperformanceandapproachestoadjustsensorvalues.Asmanyofthebio-opticalparametersarenotstatevariablesandsometimesareoperationallydefinedthiswillbeamuchgreaterchallenge.Uncertaintyestimateswillalsobegreaterandapplicabilitytosomeofthelarge-scalequestionsraisedinSOCCOMwillbelimited.However,theiruseinstudyofseasonalityofthebiologicalcycleandspatialheterogeneity(bothinthehorizontalandvertical)ofbiologicalparameters,andtheirinfluenceontheinorganiccarboncyclewillbeinvaluable.Moreover,thebio-opticalparameterslinkcloselytoseveralofthespacebornemeasurementsofferingthepossibilitytoexpandthe2-Dviewoftheoceansurfacefromspacetoa3-Doreven4-Dviewthatincludestimeanddepthdimensions.AmajorfocusofSOCCOMaspartofunravelingthemysteriesoftheSouthernOceanistovastlyimproveourunderstandingofbiogeochemicalprocessesandassociatedestimatesofbiogeochemicalfieldsintheSouthernOceanasawhole.Themeasurementsandtoolstotacklethislargescaleproblemarebeingdevelopedanddeployedoverthefull6yeartimescaleofthegrant,butitiscriticalthatinitialestimatesbemadeasearlyaspossiblewithasmallsubsetsofthearrayinordertoidentifyandaddressasearlyaspossibleimportantissuessuchasthoseaddressedinthisreport.SimilarquestionshavetobeaddressedwithrespecttomodelsthatwillimprovethroughouttheSOCCOMperiod.

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Evenwithlimitedfloatdeploymenttodateseveralnuggetsor"firsts"canbeobtainedfromthequality-controlleddata.Thispertainsparticularlytosomeofthefirstbiogeochemicalobservationsinwintertimewhenconditionsaresuchthatship-basedobservationsarechallengingandabilitytosampleunderice.Undericeprocessesaspertainingtobiogeochemistryinseasonalsea-iceregionscannowbedetermined.Biogeochemicalstateestimatescanbevalidatedbyfloatmeasurementsparticularlyforthewintertime.ObservingSystemSimulationExperiments(OSSEs)fornetworkdesigncanbecheckedwiththefloatscurrentlydeployedandthevalidityoftheassumptionusedintheOSSEscanbeverified.ThenextmajordevelopmentforbiogeochemicalinvestigationinSOCCOMwillbethedevelopmentofso-callcarbonproducts,orfieldsofcarbonparameterssuchasTAlk,DIC,ΩArandΩCausingavarietyofapproachesrangingfrominterpolationoffloatdata,toregressionanalysesandnumericalmodels.Byproducingthesefieldsthroughtimekeyprocessessuchasnetcommunityproduction,calcification,andrespirationcanbeinferred.Moreover,thetemporalevolutionofpCO2patternsandsaturationhorizonscanbestudiedandtheroleoftheSouthernOceanasamajoranthropogenicCO2sink.

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AppendixA.Chargeforthecarbonworkinggroup(CWG)ofSOCCOMCHARGEFORTHESOCCOMINORGANICCARBONSYSTEMWORKING(CSW)GROUP[OriginalJuly11,2015;EditedDecember2,2015]RATIONALE-AmajorobjectiveofSOCCOMistoassessthechangingcarbonsinkandassociatedchangesininorganiccarbonintheSouthernoceanthroughutilizationofnewautonomoustechnology.Formanyproperties,suchasaragonitesaturationordissolvedinorganiccarbon,theautonomoussensorsdonotdirectlymeasuretheparametersofinterest.Inparticular,fortheinorganiccarbonsystem,SOCCOMcurrentlymeasuresonlypH.InadditiontotheobservedpH,asecondcarbonparametermustbeobtainedinordertosolvethefullinorganiccarbonsystem.Thiswillbeaccomplishedbyusingstoichiometricand/orstatisticalrelationshipsderivedfromthebottledatasetsavailable.Thesealgorithmswillthenbeappliedatthelocationofthefloatmeasurementsusingtheinsitu[float]data.SuchrelationshipsmayalsobeusedtogeneratepHandothertracerestimatesthatcanbeusedtoqualitycontrolandadjustsensordata.Theoverallapproachwillprovideadatasetwitharesolutionofthatofthefloatobservations.Timeresolutionwillbeontheorderofaweekandspatialresolutionwillbe100’sofkminthehorizontalandmetersintheverticaldownto2000m.SeveralgroupswithinSOCCOMaredevelopingandapplyingthesenovelempiricalapproachestodeterminetheinorganiccarbonsystemparametersofinterestfromtheautonomoussensors.AworkinggroupwithinSOCCOMisdesiredtoexchangeideas;toprovideamechanismtoshareresults;andtoapplytheapproachesinnearreal-timeutilizingtheautonomoussensors.Theworkinggroupaimstofacilitaterapiddisseminationofresultswithsoundinterpretation,providingclearconfidenceintervalsandspecifyingappropriatecaveatsandlimitations.GOALS-Theworkinggroupwilladdressseveralspecificquestionswiththeprincipalgoaltoobtainameasurement-basedestimateofthefullinorganiccarbonsystemincludingpH(measuredandcalculated),DIC,TAlk,pCO2,CO32-,andAragoniteandCalcitesaturationindexes.Theworkinggroupwillengageinthefollowingactivities:1.Assessqualityandissueswiththeindependent[floatbased]variablesincludingdriftandhysteresis:-Nitrate,-Oxygen-pH

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-Temperature-PressurePrioritytask:createaninterpolatedestimateoftheoceanicpHusingalgorithmsfromhighqualityshipboard/laboratoryinorganiccarbonsystemmeasurementsandrelatedparametersthatcanbeusedtotestthebehaviorofthepHsensor.2.DevelopastreamlinedapproachforinitialQCandadjustmentoffloat-basedvariablesandadocumentedapproachforuserstosuggestadjustmentsandflags.3.Documentuncertaintyandvalidity(time,distance,depthrange)ofalgorithms.Aparticularfocuswillbeondistributionoferror/uncertaintyintimeandspace.Prioritytask:ProvideaninterpolatedestimateofalkalinitythatcanbeusedwiththepHsensorsdatatoproduceafirstsetofpapersonthecarbonsystemasdeterminedusingthefloats(includingestimateofuncertainty)Longer-termobjective:ExamineallaspectsofthecarbonsystemmeasurementsandcalculationssoastoproducethehighestqualityestimatesofDIC,pCO2andpH,4.Createabestpracticesmanualforad-hocfloatsensorvalidationsandchecks*[5.ProvideadvicetotheSOCCOMexeconthecoordinationofmanuscriptsandpresentations]*[6.Assessqualityandissueswiththevariablesfromopticalsensorsonfloatstomeasurechlorophyllandbackscatter.]*PossibleactivitiesatalaterpointSOCCOMCarbonWorkingGroupmembers:Briggs,Ellen:surfacewaterpCO2,iceeffectsBushinsky,Seth:floatsensors(oxygen)Carter,Brendan:AlkalinityalgorithmdevelopmentandapplicationDickson,Andrew:shorebaseddiscreteinorganiccarbonsystemmeasurementsFeely,Richard:P16SinorganiccarbondataGray,Alison:algorithmdevelopmentandapplicationJohnson,Ken:floatdataJuranek,Laurie:algorithmdevelopmentandapplicationKey,Bob:Bottledataassembly,includinghistoricaldata;hydrographyRiser,Steve:floatdataTalley,Lynne:P16Smeasurements,CTDhydrographyWilliams,Nancy:algorithmdevelopmentandapplicationSarmiento,Jorge:modelapplicationRussell,Joelle:modelapplicationVerdy,Ariane:BiogeochemicalSouthernOceanStateEstimate(SOSE)

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Wanninkhof:CoordinatorAPPROACH:-Bi-Weeklyteleconferenceswithassignmentsoftasks&reports-Protectedsiteforsharingdataalgorithmsandpreliminaryfindings-Inquiryto[outside]expertsonregimes,approaches,methods,&analyses

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