chapter  22
38 Pages

The Bosphorus

TheBosphorusisastraitsome30kilometerslong,runinginthegeneraldirectionnorth-northeasttosouth-southwest,andvaryinggreatlyinwidthfromabout700meters atitsnarrowesttooverthreeandahalfkilometersat itswidestItsaveragedepthatthecenterofthechannelis beween50and75meters,butatonepointitreachesa depthofoveronehundred.Thepredominantsurfacecurrent flowsatarateofthreetofivekilometersperhourfromthe BlackSeatotheMarmara,but,becauseofthesinuosityof thechannel,eddiesproducingstrongreversecurrentsoccupy mostoftheindentationsoftheshore.Averystrongwind mayreversethemainsurfacecurrentandmakeitflow north,inwhichcasethecountereddiesalsochangetheir direction.Atadepthofabout40metersthereisasubsurfacecUITent,calledkanalinTurkish,whichflowsfrom theMarmaranorthtowardtheBlackSea.Itswaters, however,areforthemostpartpreventedfromenteringthe BlackSeabyathresholdjustbeyondthemouthofthe Bosphorus;theselowerwaters,denserandmoresalinethan theupper,areturnedbackbythethreshold,minglewith theupperwaters,andaredrivenbacktowardtheMarmara withthesurfacecurrent.Thelowercurrentisstrongenough sothatundercertainconditions,iffishing-netsarelowered intoit,itmaypulltheboatsnorthwardagainstthesoutherly surfacecurrent.