海水的盐度(The Salinity of Ocean Waters)

ifthesalinityofoceanwatersisanalyzed,itisfoundtovaryonlyslightlyfromplacetoplace.nevertheless,someofthesesmallchangesareimportant.therearethreebasicprocessesthatcauseachangeinoceanicsalinity.

oneoftheseisthesubtractionofwaterfromtheoceanbymeansofevaporation---conversionofliquidwatertowatervapor.inthismannerthesalinityisincreased,sincethesaltsstaybehind.ifthisiscarriedtotheextreme,ofcourse,whitecrystalsofsaltwouldbeleftbehind.

theoppositeofevaporationisprecipitation,suchasrain,bywhichwaterisaddedtotheocean.heretheoceanisbeingdilutedsothatthesalinityisdecreased.

thismayoccurinareasofhighrainfallorincoastalregionswhereriversflowintotheocean.thussalinitymaybeincreasedbythesubtractionofwaterbyevaporation,ordecreasedbytheadditionoffreshwaterbyprecipitationorrunoff.

normally,intropicalregionswherethesunisverystrong,theoceansalinityissomewhathigherthanitisinotherpartsoftheworldwherethereisnotasmuchevaporation.

similarly,incoastalregionswhereriversdilutethesea,salinityissomewhatlowerthaninotheroceanicareas.

athirdprocessbywhichsalinitymaybealteredisassociatedwiththeformationandmeltingofseaice.whenseawaterisfrozen,thedissolvedmaterialsareleftbehind.inthismanner,seawaterdirectlymaterialsareleftbehind.

inthismanner,seawaterdirectlybeneathfreshlyformedseaicehasahighersalinitythanitdidbeforetheiceappeared.ofcourse,whenthisicemelts,itwilltendtodecreasethesalinityofthesurroundingwater.

intheweddellseaantarctica,thedensestwaterintheoceansisformedasaresultofthisfreezingprocess,whichincreasesthesalinityofcoldwater.thisheavywatersinksandisfoundinthedeeperportionsoftheoceansoftheworld.