Ifthesalinity(含盐量)ofoceanwatersisanalyzed,itisfoundtovaryonlyslightlyfromplacetoplace.Nevertheless,someofthesesmallchangesareimportant.Therearethreebasicprocessesthatcauseachangeinoceanicsalinity.Oneoftheseisthesubtractionofwaterfromtheoceanbymeansofevaporation--conversionofliquidwatertowatervapor.Inthismanner,thesalinityisincreased,sincethesaltsstaybehind.Ifthisiscarriedtotheextreme,ofcourse,whitecrystalsofsaltwouldbeleftbehind.
Theoppositeofevaporationisprecipitation(降水),suchasrain,bywhichwaterisaddedtotheocean.Heretheoceanisbeingdiluted(稀释)sothatthesalinityisdecreased.Thismayoccurinareasofhighrainfallorincoastalregionswhereriversflowintotheocean.Thussalinitymaybeincreasedbythesubtractionofwaterbyevaporation,ordecreasedbytheadditionoffreshwaterbyprecipitationorrunoff(形成地表水部分的降水).
Normally,intropicalregionswherethesunisverystrong,theoceansalinityissomewhathigherthanitisinotherpartsoftheworldwherethereisnotasmuchevaporation.Similarly,incoastalregionswhereriversdilutethesea,salinityissomewhatlowerthaninotheroceanicareas.
Athirdprocessbywhichsalinitymaybealteredisassociatedwiththeformationandmeltingofseaice.Whenseawaterisfrozen,thedissolvedmaterialsareleftbehind.Inthismanner,seawaterdirectlybeneathfreshlyformedseaicehasahighersalinitythanitdidbeforetheiceappeared.Ofcourse,whenthisicemelts,itwilltendtodecreasethesalinityofthesurroundingwater.
IntheWeddellSea,offAntarctica,thedensestwaterintheoceansisformedasaresultofthisfreezingprocess,whichincreasesthesalinityofcoldwater.Thisheavywatersinksandisfoundinthedeeperportionsoftheoceansoftheworld.
Choosecorrectanswerstothequestion:
1.Thebesttitleofthepassagecanbe“_____”.
A.TypicalOceansandTheirRespectiveFeatures
B.TheCausesoftheChangesinSalinityofOceanWater
C.DifferentOceansHaveDifferentSalinity
D.ThePrecipitationandEvaporationofOceans
2.Whichofthefollowingprocesseswillincreasesalinityofoceanwaters?
3.Accordingtothispassage,thesea_islikelytohavethelowestsalinity.
4.TheWeddellSea_____.
A.isagoodexampleofincreasedsalinityinfreezingseawater
B.ismuchlargerinareathantheArcticoceans
C.hasamuchlowersalinitynowthanever
D.hasthedenserwaterinitsupperparts
5.Coastalregionsarementionedascaseswhere_____.
A.seawaterislesssaltybecausefreshwaterjoinsin
B.riverscarryindustrialexhaustintosea
C.seaicetendstomeltmorequicklythaninthecenterofoceans
D.heavywatersinkstothedeeperportionsoftheoceans
