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Chemical and Physical Features of Seawater and the World Ocean “Water, water everywhere…and nor a drop to drink!” -from Rime of the Ancient Mariner by Samuel Taylor Coleridge (1798) • We discussed that much of our water is not drinkable due to elevated salinity and impurities Only 1 part in 10,000 of water is easily accessible for drinking and irrigation. • However, between 85-95% of many organisms are comprised of mostly water. • We will discuss what water is and how it’s composition influences the marine environment, animals in it, and humans. Freshwater • Water that is relatively pure, with very few dissolved salts • Freshwater occurs in: • Lakes, rivers, streams, groundwater, glaciers, rainwater, soil, water vapor in the atmosphere (In contrast, ocean water is salty because salts from land run into it and stay there as surface water evaporates.) Water: Unique Properties • We know that water consists of two atoms of hydrogen and one atom of oxygen (H2O) • Water molecules are held together by electrochemical hydrogen bonds (fairly weak) Freshwater • Only 2.5% of the planet’s water is freshwater, and only 1% of that exists on Earth’s surface. Figure 14.1 •Water, ice, and vapor exist on earth. •In a special instance you can see them all at once. •Try an ice cube on the counter on a hot summer day! Hydrogen bonding permits water to change phase when energy is added or taken away. Water: The Universal Solvent • Water dissolve many things and is known as the universal solvent, esp. salts. • Again, H+ bonding plays a role hear by interacting with other charged atoms. • The oceans consist of (by mass): • 96.5% water • 3.0% sodium and chlorine ions (table salt, Na+ and Cl–) • 0.5% other salts Figure 13.3 How does seawater get this way?? • Coastal waves, rain, and other sources of weathering erode rocks and move sediments into the ocean. • Other sources of minerals include hydrothermal vents and even aquaculture! Tridacnid clam: James Fatherree Salinity • All in all the total amount of salt dissolved in seawater, or salinity, is about 35 ppt. • The concentrations of individual salts don’t vary much either, due to the rule of constant proportions*. • Therefore, even if marine organisms are exposed to changes in total salinity, the changes in individual ion concentration remains similar. *R.C.P.: Relative amounts of the various ions in seawater are always the same. Scientists use Niskin bottles and “messengers” to sample water at depth. • Water density varies with salinity and temperature. • If salinity or temperature increase, so does the density of the water. Need more samples... No problem. “Rosettes,” or multiple sampling arrays may be deployed to take measurements at multiple depths.. Alternatively, different tools may be attached to the sample array providing a multitude of readings to be made in a single drop! Hey, it beats doing it by hand! • Dissolved gasses such as CO2 and N2 can be measured in addition to O2. Of course, if you have LOTS of cash, the satalites have come a long way. Seawater also does other cool stuff! Light transmission -loose color at depth Pressure -increases 1 atmosphere for each 10 m increment OUCH! Part II: Ocean Circulation Water Motion and the Earth • The ocean never truly stops moving. Just ask Russell Crowe! • Much of the circulation we might experience actually occurs at the surface. • Wind drives much of the “ocean motion,” but something else plays a role, earth’s rotation. • This is known as the Coriolis Effect. Bench view Your view Homeland Security’s View! Another point of view… Notice that no matter what direction you are turning, the “deflective” force is still clockwise in the North and counter-clockwise in the South! Wind Patterns Wind Patterns • Ultimately, the power of the wind evolves from the sun and it’s affect on the air temperature. • Hot air rises because it is less dense and vice versa. • As air moves up (or out of the way) other air rushes inward to occupy the existing “space” • Air is bent by the Coriolis Effect just like water, therefore… Convection cells created by rising and sinking air are responsible for much of our sailing history. Surface Currents • All major surface currents are driven by the wind. • Again, Coriolis Effect causes the surface waters to track toward the right (N. hemisphere). • Progressive spiraling caused by shallower currents pushing on deeper currents results in Ekman Spirals. • As spirals continue, wind shear becomes less and less at depth. • Eventually, deep currents travel ~90° to the wind direction. The final result: formation of gyres. El Niño and other large fluctuations can occur. Ultimately this type of circulation affects the average temperatures in oceans in both hemispheres. • Since the ocean is three dimensional most currents are only viewed as surface events. • We know that dense water sinks. Stratification takes place during each season. • Thermoclines may result when mixing of upper, intermediate and deep layers do not mix well. Occasionally, large changes in surface water temperature facilitates complete mixing of ocean depths, resulting in overturn of the water column. Waves and Tides Waves, the result of surface winds, have been responsible for many changes, some beneficial and some destructive. Technically, the water never moves! Surf is created as energy from the wave bunches and changes shape near the shore. One benefit of waves and tides. Some waves are just plain mean!! How do tides happen?? Gravitational forces by the moon and the sun pulling on water cause the rise and fall of tides. Since the earth rotates and the moon and sun, pull, tides occur at several intervals throughout the day.