Sound and Pressure

     Sound travels nearly 5 times faster underwater than through air.  In water, sound is transmitted by water molecules; since water molecules are densely packed (more so than molecules in air), they transmit sound more quickly.  Because sound waves travel more efficiently underwater than light waves, marine organisms frequently rely on sound (hearing), much more so than light (vision).  Blues Whales produce deep rumbling sounds; deep, low-pitched sounds that are the loudest noise produced by any animal.  You will feel a Blue Whale vocalization before you ever hear it!  Whale vocalizations can travel over entire ocean basins!

(Taken by professor McNamara)

     Another factor that changes dramatically with depth is pressure Pressure = Force/Area (P=F/A).  Organisms on land are exposed to 1 atmosphere of pressure at sea level.  Marine organisms, on the other hand, are under the weight of the water above them and as well as the atmosphere.  Pressure increases dramatically with depth; for every 10 meters of increased depth, another atmosphere is added.  As pressure increases, gases are compressed.  Gas-filled structures inside organisms which provide more buoyancy than the storage of body lipids, such as AIR BLADDERS and lungs shrink or collapse under the pressure.  This limits the depth range of many organisms.  Others have evolved physiological adaptations to survive in the depths (we'll come back to this).          

Every 10 meters = +1 atmosphere of pressure



Dissolved Gases in Seawater and Light Energy Wave Lengths

     Gases in the air dissolve easily in seawater at the oceans surface.  Organisms living in the ocean require these dissolved gases to survive.  The major gases in seawater are Nitrogen (N2), Oxygen (O2), and Carbon Dioxide (CO2).  Nitrogen and Oxygen always naturally occur as N2 and O2 because they are 2 out of the 7 DIATOMIC ELEMENTS.  The 7 diatomic elements are Bromine (Br2), Iodine (I2), Nitrogen (N2), Chlorine (Cl2), Hydrogen (H2), Oxygen (O2), and Fluorine (F2). Diatomic elements mean these elements are present in the gaseous state as molecules composed of 2 atoms.  Nitrogen constitutes ~48% of the dissolved gases in seawater.  Nitrogen is essential for organisms and can be a limiting factor for PHYTOPLANKTON.  Phytoplankton are unicellular microscopic plant-like organisms that utilize sunlight to photosynthesize like trees or plants do on land.  Most dissolved Nitrogen is unusable since it exists as N2 gas, a form that cannot be assimilated by most organisms.  Oxygen constitues ~36% of the gases dissolved in seawater.  Oxygen is essential to all AEROBIC life forms.  Life forms that use aerobic respiration (you and i) are generating energy by the full oxidation of nutrients through Krebs cycle where Oxygen is the final electron acceptor.  What this means is English is your body uses nutrients in the air (when you breathe) with Oxygen to react with the nutrients so the electrons get transported to your cells throughout your body for energy to survive.  Dissolved Oxygen comes from photosynthesis and the DIFFUSION from the atmosphere.  Diffusion simply means having a substance naturally move down it's concentration gradient from high to low.  For example, you stand in the front of the line.  You spray perfume on yourself.  You smell it first because it is so highly concentrated.  I'm behind you in line so I smell it second, the person behind me smells it third and so on and so forth until the substance hits it's equilibrium.  Gases such as Oxygen dissolve better in cold water than in warm water, and so concentrats are highest in polar waters and in cold, deep seawater.  Carbon Dioxide (CO2) comprises ~15% of the dissolved gases in seawater and is much more soluble in seawater than Oxygen.  CO2 reacts chemically with water when it dissolves to create Carbonic Acid H2CO3, there fore seawater can hold a tremendous amount of CO2.  (Carbon Dioxide) CO2 + (Water) H2O ---> (Carbonic Acid) H2CO3.  The ocean stores 50 times as much CO2 as the atmosphere. 

CO2 is used near the surface and produced at depths.  O2 is produced near the surface and used at depth.  Notice the difference!

    
     One of the most biologically important properties of seawater is it transparency, allowing sunlight to penetrate into water.  This is vital because all photosynthetic organisms need light to grow and survive.  Sunlight contains all the colors of the rainbow, but not all the colors penetrate seawater equally.  Light waves with shorter wavelengths contain more energy and penetrate deeper than those with longer wavelengths.  However,  by 300 meters, even blue light has been absorbed and darknes prevails.  The thin film of sunlit water at the top of the surface zone is the PHOTIC ZONE and is dependent on the amount of suspended material in the water.
     <100 meters in open ocean
     <40 meters in the coastal
     <600 meters in the clear tropical regions

Aphotice Zone!!!!

Deep sea Shrimp are red.
Blue light reaches the deepest
so Shrimp are red so they
can't be seen!
Their eggs are red too!
(Taken by Professor McNamara
on research trip.)

Ocean below the photic zone lies in blackness.  Except for light generated by living organisms, the region is in pertetual darkness.  This dark water beneath the photic zone is known as the APHOTIC ZONE.  Unlike the photic zone, the aphotic zone is dark, cold, and has high pressure.                          

                                

The Oceans Heat Capacity and Salinity

Water is the solvent.  NaCl (salt) is the solute.

     Water has a high HEAT CAPACITY.  Heat capacity is the amount of heat needed to raise the temperature of 1 gram of a substance by 1 degree Celsius.  Water's specific heat is 4.186 joule/gram*C.  Because of water's high heat capacity, marine organisms do not experience sudden swings in temperature that may occur on land.  Water's hydrogen bonds makes it an excellent SOLVENT.  A solvent is a substance, usually a liquid, capable of dissolving another substance.  Water can dissolve more things than any other natural substance.
     The oceans contain enough salt to cover the entire planet with a layer more than 500 feet thick!  The salts in sea water comes from the chemical weathering of rocks and the OUT-GASSING of hydrothermal vents.  Out-gassing is the release of adsorbed or occluded gasses or water vapor, usually by heating.  The amount of a solid materical dissolved in water is a measure of it's SALINITY.  The salinity of sea water is typically 3.5%, or more commonly, salinity is referred to as "parts per thousand" (3.5%=35%o).  A salinity of 3.5% indicates that sea water contains 96.5% pure water and 3.5% SOLUTES.  A solute is the substance that is dissolved in a solution.  Only 6 ions (Chlorine Cl-, Sodium Na+, Magnesium Mg2+, Calcium Ca2+, Potassium K+, and Sulfate SO42-)compose 99% of the solids dissolved in sea water, and of these Sodium (Na+) and Chloride (Cl-) account for 85%.  Salinity also influences the density of sea water; the saltier the water the denser it is.  The density of sea water therefore depends on it's salinity and it's temperature. 

Next lecture I will discuss dissolved gasses in sea water.                     

Physical and Chemical Properties of Sea Water

Hydroden Bonding (+ with - charges)

Water is the only substance that occurs naturally in all three phases: solid, liquid, and gas.  In liquid water, HYDROGEN BONDS hold most of the molecules together. A hydrogen bond is a weak attraction of a hydrogen atom (H+) with an electronegative atom such as nitrogen (N-3), oxygen (O-2), or flourine (F-).  As water cools, the movement of the molecules slows and they pack together more tightly.  This is why cold liquid water is DENSER than warm water.  Density is a measure of how much of some entity is within a fixed amount of space.  Density=Mass(g)/Volume(L).  Water freezes when the molecules move so slowly that the hydrogen bonds 'take-over'; locking the molecules into a 3-dimensional pattern.  The same mass of water now occupies more volume as ice than as liquid water, so ice is les dense than liquid water and floats.  This is extremely unusual and very important for aquatic organisms living on, in, or beneath the ice.  In ice, the water molecules are held together by the hydrogen bonds in the ice crystal.  When ice melts, energy (in the form of heat) is required to break the hydrogen bonds, and to increase the speed of the molecules.  Because of the hydrogen bonds, more heat is required to melt ice or to convert liquid water into water vapor; giving water a high HEAT CAPACITY.

The next lecture I will discuss heat capacity.