The Arctic Ocean.docx

The Arctic Ocean.docx

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TheArcticOcean

TheArcticOcean

Source:

NOAA.IceisthedominantfeatureofArcticmarineecosystems.Itcontinuouslysculptsthecoastallandscapeandactsasamajorlimitingfactortoallbiologicalactivity.TwodistinctzonesaredistinguishedintheArcticregionbasedonice:

theArcticBasinmarineregionischaracterizedbytheyear-roundpresenceofseaice,whiletheotherArcticsubregionshaveice-freeperiodsrangingfromlessthanamonthtouptofourmonths.TheArcticcoast（includingislands）encompasses68%ofCanada'scoastline,stretching165,000kilometers（km）fromJamesBayandBaffinIslandtotheYukon.Theregionexhibitsawiderangeofcoastallandformsandreliefsfashionedbytheprocessesofvolcanism,glaciation,faultingandfolding.Thetidalrangeisgenerallylessthan0.5meter（m）inthenorthernandwesternsectorsbutincreasesto1.0-5.0mintheeastandsouth.

ArcticSeaIce

（Source:

BiodiversityInstituteofOntario）

TheArcticOceanwatersaresocoldthattheydevelopathicklayerofseaiceonthesurfaceduringmostoftheyear.ThecoldwatersoftheArcticwouldseemtobeinhospitableforlife,butarichecosystemispresent.

SeaIceFormation

（Source:

BiodiversityInstituteofOntario）

Saltlowersthefreezingtemperatureofwater,sothatseawaterfreezesatabout-2°C,whereaspurewaterfreezesat0°C.WhentheairtemperaturedropsintheArctic,athicklayerofseawaterbecomesreadytofreezeallatonce.Thefirstsignsoffreezingarechangesincolorandtextureasmillionsoftinyfloatingiceneedlesform,creatingadense“soup”calledfrazilice.Asthetemperaturefallsfurther,thefrazilicethickensandtrapspocketsofsaltyseawater,orbrine,withinitslayerscreatingaslushymixturecalledgreaseice.Eventuallythegreaseiceaccumulates,reachingathicknessofupto1m.Inresponsetogravity,thepocketsofbrinemovedownward,andwithinafewweeksaccumulateinthelowerlayers.Asaresulttheiceatthesurfacecontainslittlesalt.Theirremovalfromtheupperlayersincreasesitsfreezingpoint,aidingthechangefromgreaseicetosolidice.Seaicethusfreezessolidfromthetoplayerdown.Eventually,allofthesaltwaterisdrainedandtheicelayerisfrozensolidintopackice.Duringthewinter,theareaoftheArcticOceancoveredwithpackiceexpandstoformacontinuousvastsheet.Whenmeltingoccursinthespringandsummer,thepackiceretreatsandbreaksupintosmallerpieces.

（Source:

BiodiversityInstituteofOntario）

TypesofSeaIce

TherearetwoformsofpackiceintheArctic.Thewintericepackconsistsofannualice,whichmeltsinthespringandfreezesagaininthefall.Multiyearice,whichremainsfrozenthroughoutthesummer,formsfarthernorthintworegions:

InthecentralpartoftheArcticOcean,thereisthemassivepermanentpolarpack,otherwiseknownastheArcticorpolaricecap,thatslowlyrotatesclockwiseasaunit.Thesummericepack,whichmakesuptheotherregionofmultiyearice,surroundsthepermanentpolarpack,andbreaksupinthesummer.ThesebrokenpiecesoficeblockmanyofthechannelsbetweentheArcticislandsyear-round.

（Source:

BiodiversityInstituteofOntario）

MultiyearIce

（Source:

BiodiversityInstituteofOntario）

Multiyeariceremainsfrozenyear-round,butstillgoesthroughacycleofchanges.Thesurfacelayerofthisicemeltsinthesummerandthewaterthendrainsthroughporesintheicetothebottom.Thissalt-freemeltwaterremainsfloatingbeneaththeiceatopthedensersaltwater.Inthewinter,themeltwaterrefreezesasalayeronthebottomofthepackice.Oneyearatatime,thelayerstravelupwardinacontinuouscycleoflossandreplacement.Thiscyclepreventsthemultiyearicefromthickeningindefinitely.MultiyeariceformsthepermanentpolarpackinthecenteroftheArcticOcean,aswellasthesummericepackthatsurroundsthepermanentpolaricepack,andbreaksupinthesummer.Unlikeannualice,thesummericepacknevercompletelymelts.

AnnualIce

（Source:

BiodiversityInstituteofOntario）

Annualicetypicallyreachesathicknessofabout2metersoverthewinter.ThistypeofpackicebeginstoformbythemiddleofSeptember,andbytheendofOctobertheicefieldisalmostsolidalongthecoasts.Aswinterprogresses,theannualiceextendsoffshore,connectingsomeislandswithasolidsheetofseaice.ThethicknessoftheiceincreasesuntilMayatwhichpointitbeginstothaw,withshallowbluepoolsformingontheicesurface.Risingsummertemperaturescausetheicetomeltfurtherandeventuallyitbreaksup.Cracksformthatsoonwidenintochannelsorleadsthatseparatetheicepackintochunkscalledfloes.Floessometimescollidewitheachother,andbreakintomanypieces.IcebreakupoccursinearlyJulyinthelowArctic,andattheendofthemonthinthehighArctic.TheicedensitydeclinesuntillateAugust,butbymid-Septemberthefreezingcyclebeginsagain.

（Source:

BiodiversityInstituteofOntario）

Segmentsoftheicepackthatarefirmlyfrozentotheshoreareknownaslandfastice.Offshorewindspushiceawayfromthecoastcreatingagapofopenwaterbetweenthelandfasticeandthepackice-ashorelead.Thewindsalsopushthepackicefurtherouttosea,causingthedriftingfloestocollideandrideupovereachother,orhummock.Theresultisadistinctridgeofjumblediceblocks.

Theloose,floatingpiecesoficepresentinthesummerscourtheshorelines,preventingmostplantsandanimalsfromsettlinginshallowwater.Thismakestheintertidalzone,theareabetweentheshorelineandthenearshorebottom,muchmorebarrenthanitisinothermarineecosystems.

WheretoFindArcticSeaIce

About12-13millionsquarekilometersoftheArcticBasinarecoveredbyiceinwinter.AdditionalseaicecoversmuchofBaffinBayandHudsonBay,aswellastheLabradorSea.NearlyalloftheArcticandsub-Arcticshoresareice-boundthroughoutthewinter.Bylatesummer,theamountofArcticseaiceisreducedtoabout9millionsquarekilometers.Duringthisseason,loosepackicefromtheArcticmovessouthwardalongtheeastGreenlandcoastandfromBaffinBaydowntheLabradorcoastintothenorthAtlanticOcean.Althoughlanesofwateropeninthesummeralongthemainland,manyofthechannelsintheCanadianarchipelagoremainice-cloggedyear-round.

Polynyas

（Source:

BiodiversityInstituteofOntario）

Apolynyaisalargeareaofopenwatersurroundedbyseaicethatisfoundinthesameregionyearafteryear.Althoughpolynyascanbehundredsofkilometerswide,theirsurfaceareaisfarlessthantheareaofseaicewhichsurroundsthem.However,theopenwatersofpolynyasareveryimportanttolifeintheArcticOcean.Polynyasteemwithanimalandplantlife.Itisonlyhere,wheretheseaiceisabsent,thatthesun’senergydirectlyreachesthewaters.Snowandiceordinarilyreflectmuchofthesun’slightenergy,buttheopenwatersofpolynyasabsorbit.Phytoplanktoninthepolynyausethisenergytoproduceanutrientrichgrazingareaforzooplankton.Feedingonthesesmallanimalsarewhalesandfishesthatinturnfeedseals,walrusesandpolarbears.OftenseenasoasesintheharshclimateoftheArcticmarineenvironment,polynyashaveintriguedscientistsformorethanacentury.

Formation

（Source:

BiodiversityInstituteofOntario）

Polynyasoccurinareaswhereswiftlymovingseacurrentspreventthefreezingofsurfacewater.Manypolynyasaresmall,measuringonlyafewhundredsquarekilometers,andmayfreezeoverattheheightofwinter.Thelargerpolynyas,however,stayopenallwinter,althoughtheymayshrinkinsizeinextremelycoldtemperatures.Adistinctcharacteristicofallpolynyasisthattheyarerecurrent.ThelargestArcticpolynya,NorthWater,occursattheheadofBaffinBay,andislikeaninlandseasurroundedbyice.Thispolynyawasdiscoveredin1616,andisusuallyaboutaslargeasLakeSuperior!

Comparedtothesurroundingair,thewatersofapolynyaaresowarmthatsteambillowsup.Theaveragetemperatureofthewaterswithinapolynyaisabout0°C,anditneverdipsbelow-2°C,thefreezingpointofseawater.Polynyasallowheatfromwarmoceancurrentstoescape;thisisimportantintheregulationoftheEarth’stemperature.

Incalmweather,alayerofnewicecanformacrossapolynyainminutes.Inevitably,astrongwindorwavesmashesthisnewicelayer,drivingitouttoseaandonceagainopeningthesurfaceofthepolynya.Thisprocessoccursrepeatedly,makingpolynyasanimportantsourceofnewArcticseaice.

Leads

（Source:

BiodiversityInstituteofOntario）

Aleadisafractureorlargecrackintheseaicethatresultsinapassagewayofopenwater.Leadsarelessimportanttosealifethantheopenareasofpolynyas,buttheyarestillimportanttomanyorganisms.Leadsprovideimportantarteriesforthenavigationofmarinemammalsandbirds.

Leadscanoccuralmostanywherethatseaiceispackedrelativelyloosely.Theymayappearsuddenly,andtendtoopenandcloseoveraperiodofjustafewhoursfollowingchangesinwindsortides.Thereareplaces,however,wherewide,predictableleadsformbetweenthelandfasticeandthefree-floatingpackice.Theselong-lastingleadsarecreatedbywindsblowingoffshorethatpushiceawayfromthecoast,causingthepackicetoaggregate.Thesedistinctleadsprovideopenwaterfornewiceformation.

Leadscanoftenbedetectedfromagreatdistancebecausetheymakethecloudsabovethemappeardark.Thisoccursbecausetheopenwaterinleadsabsorbssunlight,whichisnormallyreflectedofficeorsnow.Thiscausesadarkstreaktoappearontheunderside