Water, water, everywhere Which organisms occur at a given place in the marine environment is determined by the physical and chemical properties of the surrounding water Marine organisms depend on water for metabolic demands, but also as a medium through which they must travel, hunt, reproduce, avoid predation, find mates, etc. The unique properties of water Water is the only substance that occurs naturally in all 3 phases: solid, liquid and gas In liquid water, hydrogen bonds hold most of the molecules together Hydrogen bonds The unique properties of water As water cools, the movement of the molecules slows and they pack together more tightly Colder liquid water is denser than warmer water Water freezes when the molecules move so slowly that the hydrogen bonds take over, locking the molecules into a 3-dimensional pattern Because the same mass of water now occupies more volume as ice than as liquid water, ice is less dense than liquid water and floats Extremely unusual and very important for aquatic (freshwater and marine) organisms living on, in, or beneath the ice! Got water? 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; gives water a high heat capacity; how much heat is needed to raise a substances temperature by 1 degree What does this mean for marine life? Because of waters high heat capacity, marine organisms do not experience sudden swings in temperature that may occur on land (although shallow water ecosystems are more vulnerable) Because of waters hydrogen bonds, water is also an excellent solvent; water can dissolve more things than any other natural substance Ion in solution Salt crystal Seawater The oceans contain enough salt to cover the entire planet with a layer more than 500 feet thick! The salts in seawater come from the chemical weathering of rocks (via river flow) and the out-gassing of hydrothermal vents The total amount of solid material dissolved in water is a measure of its salinity Salinity of seawater The salinity of seawater is typically 3.5% A salinity of 3.5% indicates that seawater contains 96.5% pure water and 3.5% solutes Only 6 ions compose 99% of the solids dissolved in seawater, and of these sodium and chloride account for 85% More commonly, salinity is referred to as parts per thousand or (3.5% = 35) Could you please pass the salt The salinity of water greatly affects the organisms that live in it Most marine organisms will die in freshwater, and vice versa (well come back to this) Salinity also influences the density of seawater; the saltier the water, the denser it is The density of seawater therefore depends on its salinity and its temperature Dissolved gases in seawater Gases in the air easily dissolve in seawater at the oceans surface Organisms living in the ocean require these dissolved gases to survive The major gases in seawater are: Nitrogen (N 2 ) Oxygen (O 2 ) Carbon dioxide (CO 2 ) Dissolved gases in seawater: Nitrogen Nitrogen constitutes ~48% of the dissolved gases in seawater Nitrogen is essential for organisms and can be a limiting factor for phytoplankton Most dissolved Nitrogen is unusable since it exists as N 2 gas, a form that cannot be assimilated by most organisms Nitrogen can be a pollutant when added to seawater in large quantities! Dissolved gases in seawater: Oxygen Oxygen constitutes ~36% of the gases dissolved in seawater Oxygen is essential for all aerobic life forms Dissolved oxygen comes from photosynthesis and diffusion from the atmosphere Gases, such as oxygen, dissolve better in colder water than in warm water, and so concentrations are highest in polar waters and in colder, deeper seawater Dissolved gases in seawater: Carbon Dioxide Carbon dioxide comprises ~15% of the dissolved gases in seawater and is much more soluble in seawater than oxygen CO 2 reacts chemically with water when it dissolves forming H 2 CO 3 (carbonic acid), therefore seawater can hold a tremendous amount of CO 2 The ocean stores 50 times as much CO 2 as the atmosphere! CO 2 is used near the surface and produced at depth O 2 is produced near the surface and used at depth Let there be light! One of the most biologically important properties of seawater is its transparency, allowing sunlight to penetrate into the 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 Wavelength (nm) 10 5 nm Increasing energy Visible light 650 nm 10 3 nm 1 nm10 3 nm10 6 nm 1 m 10 3 m Radio waves Micro- waves Infrared X-rays UV Gamma rays 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 darkness prevails You light up my life Where light penetrates, photosynthesis proceeds; very important! 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