CEE 1030 1st Edition Lecture 20 Oceans Earth s hydrosphere 97 2 of earth s water is concentrated in oceans 71 of earth s surface is covered by oceans Salinity salinity concentration of dissolved salts in seawater ocean water has an average salinity of 3 5 of 35 parts per thousand vs freshwater salinity 0 5 Why is seawater salty sodium leached out of seafloor sediments chloride from outgassing of underwater volcanoes and hydrothermal vents salts and other minerals leached out of terrestrial sediments by rainfall and carried to sea by runoff and groundwater Variations in salinity oceans are not uniformly saline less saline where freshwater runoff mixes with sea water from river mouths or melting glaciers more saline in areas with high evaporation and low precipitation and inflow example Dead Sea Ocean currents ocean current any more or less continuous directed movement of ocean water forces earth s rotation wind temperature and salinity difference gravitational pull of moon sun etc influences shape of ocean basin seafloor topography shoreline shape wind direction etc These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Tracking ocean currents 1992 container of 28 000 friendly floatees washed overboard in north pacific ocean Ocean circulation water at different depths e g surface vs deep can move in different directions affected by different forces Oceanography abridged version 1 surface waters are mixed and moved by wind waves tides 2 differences in temperature and salinity in sea water cause differences in density 3 most deep ocean currents are driven by density differences in water coriolis effect Ocean zones depth mixed layer surface zone of ocean warmed by sun and mixed by wind and waves pycnocline transition zone of abrupt vertical density change pelagic zone all open ocean near coast or sea floor benthic zone water near to and significantly affect by coast or sea floor Mixed layer surface waters warmed by sun cooled by wind wind generated waves create turbulence mixing water up to half a wave length in depth some gas exchange with atmosphere at top and with deeper ocean water at bottom Wind generated currents gulf stream wind driven ocean current of warm surface water transports warm water from Caribbean and Gulf of Mexico across Atlantic toward northern Europe Is the gulf stream slowing down NASA pathfinder data from 1992 2002 indicates slowing currents in Northern Atlantic Effects of global warming melting glaciers result in increased freshwater runoff Pycnocline transition from mixed layer to pelagic zone abrupt density change density gradient can be caused by difference in water temperature or salinity or both temperature based pycnocline thermocline salinity based pycnolcine halocline Seawater density density mass of water per unit volume ocean density gradients result from variation in temperature and or salinity saltwater is denser than freshwater cold water is denser than warm water Thermohaline circulation deep ocean currents driven by density differences temperature and salinity flow under ocean surface submarine rivers Vertical water movement downwelling water sinks because of converging currents or because surface water is denser than deep water Deep ocean circulation dense bottom water spreads out and moves around ocean floor coastlines other currents or mid ocean ridges can force deep water back to surface Vertical water movement upwelling deep water rises because it is less dense than surface waters or pulled up to replace surface water driven away by winds Movement of ocean water wind driven and density driven currents Tidal currents gravitational pull of the moon and to a lesser extent the sun cause alternating horizontal movement of surface water types flood current movement of ocean water toward shore as tide rides ebb current movement of ocean water away from shore as tide rides Daily tides moon s gravitational pull causes oceans to bulge simultaneously on side of earth nearest moon nearside side of earth farthest from moon farside Causes of tides moon s direct gravitation pull causes oceans to bulge on earth s nearside gravity weakens with distance so the moon s gravitational pull is stronger on earth s nearside stretches planet very slightly result in tidal bulge on earth s farside earth rotates on axis more rapidly than the moon s position changes tidal bulges stay in place while planet rotates through them most coasts experience two high tides and two low tides each day Tidal cycles spring tides highest of tidal range near time of new and full moons when gravitational forces of moon and sun are added together neap tides lowest tidal range occurs near times of first and third quarters of moon when gravitational forces of moon and sun are offset Influences on tides tides are influenced by shape of coastline topography of ocean floor and other currents Whirlpools and maelstroms whirlpool swirling water produced where opposing currents meet often causes by tides maelstrom is a particularly powerful whirlpool saltstraumen Norway maelstrom up to 10m in diameter and 5m deep forms every 6 hours as tidal currents force their way through fjord Deflection of currents by Earth s rotation coriolis effect a water droplet that leaves the north pole headed toward the equator will arrive slightly west of the intended destination Coriolis effect on currents currents are deflected clockwise in northern hemisphere currents are deflected counter clockwise in southern hemisphere types of currents eddy circular current at ocean surface diameter about 50 200 km gyre rotational circulation forms in ocean basins centered on subtropical high pressure region acceleration causes sea level to fall along coasts Great pacific garbage patch north pacific gyre currents trap and concentrate suspended plastic and other debris garbage patch currently twice the size of Texas