FLUID DYNAMICS – OCEAN CHEMISTRY SALINITY, TEMPERATURE, DENSITY

SALINITY OF THE OCEAN Average salinity of ocean water is 35 ppt or, 35 grams salt for every 1,000 grams of water. Most common ions in seawater are chloride, sodium, and potassium Increases in salinity make seawater more dense, causing it to sink relative to fresher water.

VARIABLES AFFECTING OCEAN SALINITY Increase in salinity results from :  Evaporation  formation of sea ice (glaciers) Decrease in salinity results from:  precipitation  runoff  melting of sea ice (glaciers)

VARIABLES AFFECTING OCEAN SALINITY: High evaporation creates high salinity (low and middle latitudes). River runoff and glacial melt decrease salinity. Icepack accumulation increase salinity of ocean water by removing fresh water from the ocean.

HALOCLINE Depth zone of sharp salinity change from low salinity to high salinity

OCEAN TEMPERATURE The densest water sinks so the ocean is typically layered or stratified. Deep water is typically cold and dense. Surface water is warm and “light”. Temperature and density water profiles are usually mirror images of each other. The effect of cold temperatures and high salinity creates dense, sinking water masses at high latitudes.

OCEAN TEMPERATURE The surface layer is m deep (also known as the mixed layer), the intermediate layer is 1,000-1,500m deep, and the deep/bottom layer lie below 1,500ft deep.

THERMOCLINE Thermoclines are the sudden changes in temperature over depth intervals. They marks the boundary between warm surface water and cold, deeper water. The strongest effects are in the tropics. Thermoclines may not be present in very high latitudes.

THERMOCLINE

THERMOHALINE CIRCULATION Water columns are stable unless wind and wave energy stirs it up causing warm surface water to become more dense and sink. This is called downwelling. Intense downwelling is when a large volume of water sinks (salinity and temperature don’t change) and this water mass has a “fingerprint” in which oceanographers can use to follow the movement, or circulation, of water masses over great distances. This form of circulation is called thermohaline circulation – driven by changes in density which is in turn is determined by temperature and salinity.

WARM AND COLD CURRENTS

SALINITY AND TEMPERATURE Water that has high salinity freezes below 0°C (32°F) This is why salt is used to melt the snow/ice on road pavement. The saltier the brine, the lower its freezing point. This is also why salt traditionally was added to the water–ice mixture used to make ice cream.

ANALYZING TEMPERATURE AND SALINITY GRAPHS

HOW DO LIVING ORGANISMS REGULATE SALINITY LEVELS? Elodea cells in fresh water Elodea cells in 10% salt solution What do you notice about the cells of the elodea in the salt solution?

DIFFUSION Molecules moving from areas of high concentration to areas of low concentration and eventually reaches equilibrium. Ex: Occurs in the exchange of oxygen into muscles from the blood cells in the blood stream Concentration all on one side of the membrane Equilibrium has been reached; same # of molecules on each side

CELL MEMBRANE Selectively permeable: allows some substances to enter and leave the cell but prevents others from doing so. Protects cell from losing common ions in seawater, as well as organic molecules (proteins) Allows water and small molecules to pass Outside of cell Inside of cell (cytoplasm) Cell membrane Proteins Protein channel Lipid bilayer Carbohydrate chains

OSMOSIS Diffusion of water across a selectively permeable membrane. Also moves to reach equilibrium and move from an area of high concentration to low concentration. If salt content is higher inside the cell, water will move in, and vice versa

Isotonic Solution Hypertonic Solution Hypotonic Solution SOLUTIONS

EXAMPLE OF OSMOSIS

OSMOCONFORMERS Organisms whose internal concentrations change as the salinity of water changes (narrow range) They usually stay where the salinity of the water matches that of their fluids If placed in fresh water, cells will swell up and burst because of osmotic flow of water into their cells How do living organisms regulate salinity levels?

OSMOREGULATORS Control internal concentrations to adapt to different salinities by adjusting the concentrations of solutes in their body fluids. (wide range) Only the amount of solutes needs to be the same, not the exact same amounts Ex: Redfish