Chemical and Physical Properties of Seawater Chapter 3, p 44 - 68 Specifics Properties of water Ocean Circulation Waves and Tides Brainstorm with a partner! Unique properties of water All 3 states of matter on Earth Very polar molecule Weak hydrogen bonds Evaporation Liquid à Gas Hydrogen bonds broken Density and temperature Temperate and State Less dense as a solid than a liquid. Habitat and insulation for organisms H+ bonds result in higher melting and freezing temp. Latent heat of melting Latent heat of melting – the amount of heat required to melt a substance Absorbs A LOT of heat when it melts – Hydrogen bonds break, but motion of molecules does not speed up until all of the ice melts. It takes A LOT of energy to break hydrogen bonds! Heat Capacity Water is able to absorb a lot of heat with a relatively small increase in temperature HIGH heat capacity – amount of heat needed to raise a substance’s temperature by a given amount Important for marine organisms Not exposed to rapid changes in temperatures Latent heat of evaporation One of highest of all substances on Earth Only fastest moving molecules can break hydrogen bonds and evaporate Molecules left behind in the liquid phase have a lower temperature – evaporative cooling Water Cycle Properties of Seawater Water is the universal solvent Ion dissociation Seawater Salinity – total amount of salt dissolved in seawater Not just Na+ and Cl- Lots of salts! See p. 48, Table 3.1 Where do the salts come from? Where might ion concentrations of seawater differ from the normal amounts? Salinity, Temperature, Density More salty = More dense Lower temperature à more dense Measuring temperature and salinity at specific points in the ocean – Niskin bottles Let’s take a look! Temperature Profile Temperature and salinity at several depths at once; above is a temperature profile or thermocline (zone of rapid temperature change). SST Satellite Images Current Conditions Temperature and Salinity SST of NE coast of the United States. Do you know the current? Dissolved Gases Oxygen (O2) – not very soluble Most released through photosynthesis Amounts also dependent upon respiration Carbon Dioxide (CO2) – more soluble 80% of dissolved CO2 is in ocean Nitrogen (N2) Dissolve at surface of water or gases released into air Gas dissolves best in cold water Oxygen Content of Ocean High oxygen content near the sea surface Low oxygen at mid-depth Increase in oxygen in the water ~ 1 km water below sea level CO2 in the Ocean How is the fact that 80% of the world’s CO2 is found in the ocean affecting our oceans? CO2 Emissions CO2 is much more soluble than oxygen because it reacts chemically when it dissolves CO2 makes up more than 80% of the dissolved gas in the ocean, compared to less than 0.04% of air Ocean stores more than 50x as much total CO2 as the atmosphere. Light Conditions CO2 + H2O + sun energy à C6H12O6 + O2 C6H12O6 + O2 à CO2 + H2O + energy Must have the right light conditions to fuel photosynthesis! Light levels change with depth. Visible Light Spectrum Colors of the Ocean Photos courtesy of www. science.nasa.gov Depth of 30 m: Only blue light remains: (a)Under natural lighting this sea star appears light blue, with the tips of the arms almost black. (b)A flash reveals the sea star’s true colors. Light Zones 1. Photic zone – sunlit, 200 meters below the surface of the ocean 2. Twilight zone - from about 200 - 2000 meters below the surface. 3. Abyssal zone – no sunlight, from 2000 - 5000 meters below the surface to the bottom of the ocean. Light Penetration of Surface Waters Gathering Data Pressure in the Ocean Organisms on land are under 1 atm (14.7 lbs/sq in or psi) at sea level. The weight of all the air above them. Marine organisms are under the weight of water as well as the atmosphere. Since water is much heavier than air, marine organisms are under much more pressure than those on land. As the pressure increases, gases are compressed. Gas -filled structures inside organisms like air bladders, floats, and lungs shrink or collapse. Limits depth range of organisms We need special equipment to go deep or special instruments that can withstand pressure Pressure in the Ocean Ocean Circulation Currents move ocean waters around the world’s oceans at different depths Currents circulate heat, nutrients, pollution, and organisms Great affects on earth’s climate New Gulf Current The Coriolis Effect www.oceanservice.noaa.gov If the Earth did not rotate on its axis, the atmosphere would only circulate back and forth between the poles and the equator The Coriolis Effect www.oceanservice.noaa.gov Because the Earth rotates on its axis, circulating air is deflected toward the right in the Northern Hemisphere and toward the left in the Southern Hemisphere. This deflection is called the Coriolis effect. Wind Patterns Winds in atmosphere are driven by heat energy from the sun. Equator is warmer than poles – more heat energy absorbed here Less dense hot air rises Cooler air replaces it Wind is formed! Remember, winds to not travel straight, they are bent by Coriolis Effect Trade Winds 30°N Doldrums 30°S Air near equator is warmed by solar heating and rises. Air from higher latitudes moves in over the Earth’s surface to replace the rising air, creating winds. The TRADE WINDS are deflected by the Corliolis effect and approach the Equator at an angle of about 45°. Ekman Transport If the ocean current is regarded as layered, then each deeper layer moves more slowly than the overlying layer. Global Wind Patterns The major wind patterns are created by the rising of sun-warmed air and the sinking of cold air. How do the continents effect the wind patterns? Major Surface Currents Ocean Gyres Created by wind-driven surface currents Moderate climate by bringing warm water north and cold water south Thermoclines Depth profiles for salinity, temperature, and density What is a thermocline and how does it develop? Seasonal vs. permanent thermoclines Temperature Profile Stable water column = less dense shallow and more dense deeper Unstable water column = surface water sink and mixes with deeper water DOWNWELLING Polar regions in winter Ocean Mixing These two water masses originate at the surface in the extreme North and South Atlantic, then sink and spread along the bottom. Thermohaline Circulation The movement (circulation) of water in the ocean over great distances that is driven by changes in density Changes in density determined by temperature and salinity. “Fingerprint” of the water mass is how currents are tracked Circulation of the Ocean The Great Ocean Conveyor – Global current pattern Deep circulation of the oceans is part of the global pattern known as great ocean conveyor. This constantly replenishes the oxygen supply to the depths. Waves Water particles do not move along with a wave but instead move in circles. When under the crest they move up and forward with the wave, then they are pulled back down. As wave after wave passes, the water and anything floating in or on it moves in circles. Waves Fetch - the span of open water over which the wind blows Fetch is important in determining the size of waves Wind starts the wave which eventually settles out into a swell as it gets farther from the source of wind. What kind of waves are these? Waves -Storm winds generate seas, peaked with waves with relatively flat troughs. - When the waves reach shallow water, they get higher and shorter (closer together). They become unstable and break, expending their energy on the shoreline. - Water particles under swells have the ideal circular motion. - In shallower water the influence of the bottom causes the particle motion to flatten out into a back and forth movement known as surge Tides Gravitational pull of the moon and sun and by the rotations of the earth, moon, and sun. The moon and earth are held together by gravitational attraction. The moon’s gravity is strongest on the side of the earth closest to the moon. Centrifugal force produced by the earth’s motion causes water to bulge outward, away from the moon. On the side of the earth closest to the moon, the gravitational pull overcomes the centrifugal force and pulls the water into a bulge toward the moon. How does a grunion (Leuresthes tenuis) use the tide? Tides Because the moon moves while the earth is rotating, a full tidal cycle takes 50 minutes longer than the 24 hrs it takes the earth to make a complete rotation. Tides 1. Spring Tide - The tidal bulges are largest, and therefore the tidal range is greatest, when the moon and sun are in line - new and full moon. 2. Neap Tide - Tidal ranges smallest when moon and sun are puling at right angles, which occurs when the moon is in quarter. Tides Semidiurnal tides – 2 high tides and 2 low tide per day Bay of Fundy How tides work: great demo Tides Worldwide distribution of semidurinal (2H, 2L), mixed semidiurnal (2H and 2L of different heights), and diurnal (1H, 1L) tides.
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