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UI CEE 1030 - Oceans
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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 currents1992: 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), tides2.) 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 AtlanticEffects of global warming - melting glaciers result in increased freshwater runoffPycnocline - 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 currentsTidal 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


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