Whenweanalyzethesaltsalinity(盐浓度)ofoceanwaters,wefindthatitvariesonlyslightlyfromplacetoplace.Nevertheless,someofthesesmallchangesareimportant.Therearethreebasicprocessesthatcauseachangeinoceanicsalinity.Oneoftheseisthesubtractionofwaterfromtheoceanbymeansofevaporation.Inthismanner,thesalinityisincreased,sincethesaltstaysbehind.Ifthisiscarriedtotheextreme,ofcourse,whitesaltwouldbeleftbehind;this,bytheway,ishowmuchofthetablesaltweuseisactuallyobtained.
Theoppositeofevaporationisprecipitation,suchasrain,bywhichwaterisaddedtotheocean.Heretheoceanisbeingdiluted(稀释)sothatthesalinityisdecreased.Thismayoccurinareasofhighrainfallorincoastalregionswhereriversflowintotheocean.Thussalinitymaybeincreasedbythesubtractionofwaterbyevaporation,ordecreasedbytheadditionoffreshwaterbyprecipitation.
Normally,inhotregionswherethesunisverystrong,theoceansalinityissomewhathigherthanitisinotherpartsoftheworldwherethereisnotasmuchevaporation.Similarly,incoastalregionswhereriversdilutethesea,salinityissomewhatlowerthaninotheroceanicareas.
Athirdprocessbywhichsalinitymaybealteredisassociatedwiththeformationandmeltingofseaice.Whenseawaterisfrozen,thedissolvedmaterialsareleftbehind..Inthismanner,seawaterdirectlybeneathfreshlyformedseaicehasahighersalinitythanitdidbeforetheiceappeared.Ofcourse,whenthisicemelts,itwilltendtodecreasethesalinityofthesurroundingwater.
IntheWeddellSea,thedensestwaterintheoceanisformedasaresultofthisfreezingprocess,whichincreasesthesalinityofcoldwater.Thisheavywatersinksandisfoundinthedeeperportionoftheoceansoftheworld.
26.Thispassagemainlytellsusabout_______.
A.theanalysisofthesalinityofoceanwaters
B.thecausesofthevariationinoceanicsalinity
C.theimportanceofthechangesinoceanicsalinity
D.thedifferentformsofsaltsinoceanwaters
27.Itcanbeknownfromthepassagethatincreaseinthesalinityofoceanwateriscaused
by______.
A.meltingofseaiceB.precipitation
C.evaporationD.supplementofsalt
28.Whichofthefollowingisnotthecauseofthedecreaseintheoceanicsalinity?
A.Precipitation.B.Rainandsnow.
C.Formationofice.D.Additionofwaterbyrivers.
29.WhichofthefollowingstatementsisTRUEaccordingtothepassage?
A.Oceanicsalinityhasgreateffectonsealife.
B.Manyfactorscombinetocausechangesinoceanicsalinity.
C.Themovementofthewaterisrelatedtotheamountofsalt.
D.Thetemperatureofthewaterhasmuchtodowiththeoceanicsalinity.
30.ThepurposeofmentioningtheWeddellSeais_______.
A.togiveanexampleofcold-watersalinity
B.topointoutthelocationofdeepwaters
C.tomakeacomparisonbetweenhot-watersalinityandcold-watersalinity
D.toshowthatthewaterintheWeddellSeavariesinsalinityfromplacetoplace
