The Water Planet

nWater covers about 71% of the Earth’s surface. Considering the depth and volume, the world’s oceans provide more than 99% of the biosphere – the habitable space on Earth.

nThe vast majority of water on
Earth can’t be used directly for
drinking, irrigation, or industry
because it’s salt water.

nAs the population increases,
so does the need for water.

ØPart of the solution to meeting
this demand lies in understanding
what water is, where it goes,
and how it cycles through nature.

The Polar Molecule

nWater is a simple molecule; the way it’s held together
gives it unique properties.

ØThe hydrogen atoms bond to the oxygen atoms with
a covalent bond.

ØA covalent bond is formed by atoms sharing electrons.
This makes water a very stable molecule.

nA molecule with positive and negative charged ends
has polarity and is called a polar molecule.

ØThe water molecule’s polarity allows it to bond
with adjacent water molecules.

ØThe positively charged hydrogen end of one water molecule
attracts the negatively charged oxygen end of
another water molecule.

nThis bond between water molecules is
called a hydrogen bond.

The Effects of Hydrogen Bonds

nBeing a polar molecule, water has these characteristics:

ØLiquid Water. The most important characteristics of the hydrogen bonds is the ability to make water a liquid at room temperature. Without them, water would be a gas.

ØCohesion/Adhesion. Because hydrogen bonds attract water molecules to each other, they tend to stick together. This is cohesion. Water also sticks to other materials due to its polar nature. This is adhesion.

ØViscosity. This is the tendency for a fluid to resist flow.
The colder water gets, the more viscous it becomes.
It takes more energy for organisms to move through it,
and drifting organisms use less energy to keep
from sinking.

ØSurface Tension. A skin-like surface formed due to
the polar nature of water. Surface tension is water’s
resistance to objects attempting to penetrate its surface.

The Effects of Hydrogen Bonds (continued)

ØIce Floats: as water cools enough to turn from a liquid into solid ice, the hydrogen bonds spread the molecules into a crystal structure that takes up more space than liquid water, so it floats.

nIf ice sank, the oceans would be entirely frozen – or at least substantially cooler – because water would not be able to retain as much heat.

nThe Earth’s climate would be colder – perhaps too cold for life.

Solutions and Mixtures in Water

nA solution occurs when the molecules of one substance are homogeneously dispersed among the molecules of another substance.

nA mixture occurs when two or more substances
closely intermingle, yet retain their individuality.

Salts and Salinity

nSalinity includes the total quantity of all dissolved
inorganic solids in seawater.

nSodium chloride (rock salt or halite) is the most
common and abundant sea salt.

nScientist’s measure salinity in various ways –
expressed in parts per thousand (‰).

nThe ocean’s salinity varies from near zero at river
mouths to more than 40‰ in confined, arid regions.

nThe proportion of the different dissolved salts
never change, only the relative amount of water.

The Colligative Properties of Seawater

nColligative properties are properties of a liquid that may be altered by the presence of a solute and are associated primarily with seawater. Pure water doesn’t have colligative properties. Fresh water, with some solutes, can have colligative properties to some degree.

nThe colligative properties of seawater include:

ØAbility to conduct an electrical current. A solution that can do this is called
an electrolyte.

ØDecreased heat capacity. Takes less heat to raise the temperature of seawater.

ØRaised boiling point. Seawater boils at a higher temperature than pure fresh water.

ØDecreased freezing temperature. Seawater freezes at a lower temperature than fresh water due to increased salinity.

ØSlowed evaporation. Seawater evaporates more slowly than fresh due to the attraction between ions and water molecules.

ØAbility to create osmotic pressure. Liquids flow or
diffuse from areas of high concentration to areas of
low concentration until the concentration equalizes.
Osmosis occurs when this happens through a
semi-permeable membrane, such as a cell wall.
Because it contains dissolved salts, water in seawater
exists in lower concentration than in fresh water.

The Principle of Constant Proportions

nIn seawater no matter how much the salinity varies, the proportions
of several key inorganic elements and compounds do not change.
Only the amount of water and salinity changes.

ØThis constant relationship of proportions in seawater is called the principle of constant proportions.

ØThis principle does not apply to everything dissolved in seawater – only the
dissolved salts.

Dissolved Solids in Seawater

nNext to hydrogen
and oxygen, chloride
and sodium are the
most abundant
chemicals in seawater.

Determining Salinity, Temperature, and Depth

nIf you know how much you have of any one seawater chemical, you can figure out the salinity using the principle of constant proportions.

nChloride accounts for 55.04% of dissolved solids – determining a sample’s chlorinity is relatively easy.

nThe formula for determining salinity is based on the chloride compounds:

salinity ‰ = 1.80655 x chlorinity ‰

Sample of seawater is tested at 19.2‰ chlorinity:

salinity ‰ = 1.80655 x 19.2‰

salinity ‰ = 34.68‰

nMost commonly, salinity is determined with a salinometer.
This device determines chlorinity and calculates
the salinity based on the water’s electrical conductivity. It is accurate.

nThe primary tool to measure the properties of seawater is
the conductivity, temperature, and depth (CTD) sensor. The CTD
profiles temperature and salinity with depth.

nAnother less accurate way to determine salinity is with a refractometer.

Why the Seas Are Salty

nA source of sea salts appears to be minerals and chemicals eroding and dissolving into fresh water flowing into the ocean.

nWaves and surf appear to contribute by eroding coastal rock.

nHydrothermal vents change
seawater by adding some
materials while removing others.

nScientists believe these
processes all counterbalance
so the average salinity of
seawater remains constant.

nThe ocean is said to be in
chemical equilibrium.

Salinity, Temperature, and Water Density

nAlthough the ocean’s average salinity is about 35‰, it isn’t uniform.

nPrecipitation and evaporation have opposite effects on salinity.

ØRainfall decreases salinity by adding fresh water.

ØEvaporation increases salinity by removing fresh water.

ØFreshwater input from rivers lowers salinity.

ØAbundant river input and low evaporation results in salinities well below average.

nSalinity and temperature also vary with depth.

ØDensity differences causes water to separate into layers.

ØHigh-density water lies beneath low-density water.

nWater’s density is the result of its temperature and salinity characteristics:

ØLow temperature and high salinity are features of high-density water.

ØRelatively warm, low-density surface waters are separated from cool, high-density deep waters by the thermocline, the zone in which temperature changes rapidly with depth.

ØSalinity differences overlap temperature differences and the transition from low-salinity surface waters to high-salinity deep waters is known as the halocline.

ØThe thermocline and halocline together make the pycnocline, the zone in which density increases with increasing depth.

Salinity, Temperature, and Water Density (continued)

Acidity and Alkalinity

npH measures acidity or alkalinity.

nSeawater is affected by solutes. The relative concentration of positively charged hydrogen ions and negatively charged hydroxyl ions determines the water’s acidity or alkalinity.

ØIt can be written like this:

nAcidic solutions have a lot of hydrogen
ions, it is considered an acid with a
pH value of 0 to less than 7.

nSolutions that have a lot of hydroxyl
ions are considered alkaline. They are also
called basic solutions. The pH is higher
than 7, with anything over 9 considered a
concentrated alkaline solution.

Acidity and Alkalinity (continued)

nSeawater is fairly stable, but pH changes with
depth because the amount of carbon dioxide
tends to vary with depth.

ØShallow depths have less carbon dioxide
with a pH around 8.5.

nThis depth has greatest density of photosynthetic
organisms which use the carbon dioxide, making
the water slightly less acidic.

ØMiddle depths have more carbon dioxide and
the water is slightly more acidic with a lower pH.

nMore carbon dioxide present from the respiration of
marine animals and other organisms, which makes
water somewhat more acidic with a lower pH.

ØDeep water is more acidic with no photosynthesis
to remove the carbon dioxide.

nAt this depth there is less organic activity, which results in a decrease in respiration and carbon dioxide. Mid-level seawater tends to be more alkaline.

ØAt 3,000 meters (9,843 feet) and deeper, the water becomes more acidic again.

nThis is because the decay of sinking organic material produces carbon dioxide, and there are no photosynthetic organisms to remove it.

Biogeochemical Cycles

nProportions of organic elements in seawater differ from the proportions of sea
salts because:

ØThe principle of constant proportions does not apply to these elements.

ØThese nonconservative constituents have concentrations and proportions that vary independently of salinity owing to biological and geological activity.

nAll life depends on material from the nonliving part of the Earth.

ØThe continuous flow of elements and compounds between organisms (biological form) and the Earth (geological form) is the biogeochemical cycle.

nOrganisms require specific elements and compounds to stay alive.

ØAside from gases used in respiration or photosynthesis, those substances required for life are called nutrients.

nThe primary nutrient elements related to seawater chemistry are carbon, nitrogen, phosphorus, silicon, iron, and a few other trace metals.

nNot all nutrients and compounds cycle at the same rate.

nThe biogeochemical cycle of the various nutrients affects the nature of organisms and where they live in the sea.

Carbon

nCarbon is the fundamental element of life.

nCarbon compounds form the basis for
chemical energy and for building tissues.

ØCarbon dioxide must be transformed into
other carbon compounds for use
by heterotrophs.

nThe movement of carbon between the
biosphere and the nonliving world is
described by the carbon cycle.

Nitrogen

nNitrogen is another element
crucial to life on Earth.

nOrganisms require nitrogen for
organic compounds such as
protein, chlorophyll, and nucleic acids.

nNitrogen makes up about 78% of
the air and 48% of the gases
dissolved in seawater.

Phosphorus and Silicon

nPhosphorus is another element important to life because it is used in the ADP/ATP cycle, by which cells convert chemical energy into the energy required for life.

ØPhosphorus combined with calcium carbonate is a primary component of bones and teeth.

nSilicon is used similarly by some organisms
in the marine environment (including diatoms
and radiolarians) for their shells and skeletons.

ØSilicon exists in these organisms
as silicon dioxide, called silica.

Iron and Trace Metals

nIron and other trace metals fit into the
definition of a micronutrient.

ØThese are essential to organisms for constructing
specialized proteins, including hemoglobin and enzymes.

ØOther trace metals used in enzymes include manganese, copper, and zinc.

Diffusion and Osmosis

nDiffusion is the tendency for a liquid, gas, or solute to
flow from an area of high concentration to an area
of low concentration.

nOsmosis is diffusion through a semipermeable
cell membrane.

nThis has important implications with respect to
marine animals.

ØHypertonic - having a higher salt concentration,
and the water will diffuse into the cells.

nIt is what happens when you put a marine fish into fresh water.

ØIsotonic - when water concentration inside the cell
is the same as the surrounding water outside the
cell. There is no osmotic pressure in either direction.

nMarine fish cells are isotonic.

ØHypotonic - having a lower salt concentration than the surrounding water.

nIt is what happens when you put a freshwater fish into seawater.

Active Transport, Osmoregulators, and Osmoconformers

nOsmosis through a semipermeable
cell membrane is called
passive transport.

ØPassive transport moves materials in
and out of a cell by normal diffusion.

nThe process of cells moving materials
from low to high concentration is
called active transport.

ØActive transport takes energy because
it goes against the flow of diffusion.

Active Transport, Osmoregulators, and Osmoconformers (continued)

nMarine fish that have a regulation process that
allows them to use active transport to adjust
water concentration within their cells
are osmoregulators.

nMarine organisms that have their
internal salinity rise and fall along with
the water salinity are osmoconformers.

Other water properties

nPenetration of light is unaffected by salinity, temperature or pressure

nSound is 5 X faster in water than in air.

World Heat Budget

nInsolation is the radiant solar energy that reaches the earth’s surface

ØExcess at the tropics

ØShortage at the poles

ØDifference transferred by winds and currents

nDuring evaporation and melting heat is absorbed from the surroundings

nDuring condensation and freezing heat is released into the surroundings

Gases

nNitrogen

Ø64% if total dissolved gases

nComes from the atmosphere

nOxygen

Ø34% of total dissolved gases

nComes from the atmosphere and photosynthesis

nCold water holds more oxygen

nCarbon Dioxide

ØHigher concentration than the atmosphere

nHydrogen sulfide

ØWaste product of organic decay

ØProduced by bacteria

Heating Curve of Water

nhttp://netcamp.prn.bc.ca/nuggets/heatingcurve.swf