Water Chemistry Information
Pressure
Air is .1% as dense as water and the ocean pressure is directly proportional to its depth and acts in all directions within the water <- ->^
The atmospheric pressure is 1kg/cm2 (14.7lbs/sq in)= 1 ATM. An increase of 1 atm for each 33' or 10m and at 30m (100') the pressure is 4atm (1atm/10m + 1atm for air). Mariana trench 11,034m (36192')= 1000atm.
This is known as hydrostatic pressure and because of it, many organisms restricted to particular level or depth and those that can go to all areas have evolved adaptations to compensate for the change.
Density
Salt water is 800x greater in density than air (supports big organisms) The density is affected by temperature. As water cools, water molecules move closer, increasing density..2. 4'C max density (1g/cm3) 3. cooler decreases density..ice= .92g/cm3 and is less dense so it floats. Some organisms have glycoprotein in their blood lowering freezing point of their internal fluid.
Temperature: Water has a high heat capacity...ability to resist rapid temperature changes and is transferred by convection. Temperature is the most important physical factor in the marine environment limiting the distribution of ocean life by effecting density, salinity, gas concentration in oceans. There is minimum vertical mixing because warm water (on top) can't replace cold water. The thermocline is a narrow zone between warm surface water and cold bottom water. Temp. effects ectotherms and endotherms.
It also affects the density as does salinity so both salinity and temp. must be considered to work out density. Variation of -2 (28) to +30 (86). Satellites are now used to monitor water temperatures.
Gases
Gases enter the ocean by diffusion from the atmosphere until it reaches saturation level...different for each gas. The most important are O, CO2 and N. Dissolved O2 = aerobic (use O2 and none= anaerobic...used for respiration and corrosion.
O2 makes up 21% of the atmosphere but in the coldest oceans its less than 1% to as much as 9%. O2 comes from photosynthesis in the ocean and this diffuses into the air because water can only hold small amounts of O2. The ocean provides 50% of atmosphere O2. Turbulence increases the amount of O2 that can dissolve in water. Dissolved O2 declines rapidly as depth increases...why?? At the surface as O2 is used, its replaced quickly by photosynthesis and as it deepens, respiration becomes greater than photosynthesis.
Light p63
Used for
photosynthesis by plants with chlorophyll. Much is reflected back
to atmosphere and as wave action increases, more is reflected.
Lots are absorbed by water but 65% of all light is absorbed
within the 1st meter and only 1% gets to 100m. The sunlit area is
the photic zone where 70% of worlds photosynthesis. At the depth
where photosynthesis=rate of respiration its the compensation
depth. Lower area (not sunlit) is the aphotic zone =90% of the
ocean.
Certain wave lengths are absorbed..blue goes far down and this is vital to photosynthesis as most autotrophs use red and blue light.
Photic zone ranges from 1m in estuaries to 100m in open ocean and depends on turbidity. Turbidity increases along the coast as suspended solids increase. This causes a shift of balance because where blue is the predominant absorbed light in crystal clear water, suspended solids enable wavelengths of green to penetrate deeper than blue in coastal waters. The highly productive water of the coast is greenish and estuaries are brownish. The compensation depth is shallower in coastal waters and below this the autotrophs can't get enough light for photosynthesis to meet the energy requirements.
Seawater Composition
Water...the wonderful stuff held together by hydrogen bonds which causes ice to melt at 0 instead of -90. It causes the absorption of lots of heat to melt ice and same to evaporate water...cooling. It allows water to hold heat...heat capacity and the amount of heat needed to change water temperatures help for cooling of the earth.
Water is a solvent for most substances especially salts. The characteristics of seawater are due to the nature of pure water and the materials dissolved in it. The solids in seawater come from two sources, the chemical weathering of rocks washed to the sea by the rivers and the earth's interior through hydrothermal vents.
Major components of seawater vary slightly. Two processes add salts to the ocean--river discharge and water circulations through hydrothermal vents (hotsprings). All ocean water cycles through these vents every 8-12 million years. These work together making seawater, with the springs adding and removing chemicals.
Salinity is expressed as concentration of ions in a liter of water or # of grams of dissolved solids in 1000g of seawater. Seawater 1000g samples have 34.7g of dissolved matter so salinity is expressed as 34.7 ppt (0/000) or 3.47 % . The remaining 96.5% is pure water. There is a rule of constant proportions and the chloride ions make up 55.27% of however much salt is present in a seawater sample. Also even though organisms may be exposed to changes in salinity...rivers rain etc, they don't have to deal with changes in rations of the various ions dissolved in the seawater. Today they can measure electrical conductivity in conjunction with temperature of water sample..conductivity is proportional to salinity.
Although constant, the concentration can change with addition or removal of water. Different in local areas depending on rate of evaporation/precipitation and volume of fresh water dumped. (red sea=40, Mediterranean=38 lack of rain fall and high evaporation. Black Sea=18 Baltic Sea=8..low evaporation and high runoff.
Euryhaline=organism can tolerate large salinities and fluctuation.
Stenohaline can't tolerate large salinity changes.
Vertical change surface layer mixed..uniform beneath the halocine layer. large salinity changes above..The salinity changes with depth.
Worksheets
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