The Arctic OceanWord文件下载.docx

The Arctic OceanWord文件下载.docx

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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

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.

TypesofSeaIce

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

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

MultiyearIce

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

AnnualIce

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

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

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

Formation

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

Aleadisafractureorlargecrackintheseaicethatresultsinapassagewayofopenwater.Leadsarelessimportanttosealifethantheopenareasofpolynyas,buttheyarestillimportanttomanyorganisms.Leadsprovideimportantarteriesforthenavigationofmarinemammalsandbirds.

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

Leadscanoftenbedetectedfromagreatdistancebecausetheymakethecloudsabovethemappeardark.Thisoccursbecausetheopenwaterinleadsabsorbssunlight,whichisnormallyreflectedofficeorsnow.Thiscausesadarkstreaktoappearontheunderside