Chapter 6 and 7
about 96.5% pure water an d
3.5% dissolved solids and gases (note that important nutrients for
productivity are trace elements in seawater).
What is the source
of some ions (e.g. chloride) that are not common in water entering the
ocean from rivers?
Silica and calcium ions are not as common relative to river water;
where do these go?
water is ~35 parts per
thousand (ppt or 0/00
but varies between 33 to 37 ppt
Water between 0.5 ppt and 17 ppt is called brackish
; >17 ppt is considered seawater
|Salinity can be measured by:
(chlorine, fluorine, bromine and iodine) (1.92%)
- because the proportion of major salts is relatively constant among
seawater samples that vary in salinity.
- Specific (electrical) conductance
- ~Refraction (refractometer)
- ~Specific gravity (hydrometer)
The maximum density of ocean water is at the freezing point which is
lower than pure water (0°C).
Ice is much less dense (0.917 g/cm3
(Salt in water also decreases heat capacity, reduces evaporation rate,
and alters osmotic pressure)
Light in water
Fate of light in
- Reflection - prevented from
water by air-water surface interface
- Scattering - suspended
reflect light at a massive array of angles
- Absorption - diminution of
by transformation into heat energy
Vertical illumination (light
- illumination at some depth as measured by underwater photometer
(often as PAR: photosynthethically-active radiation).
Light is absorbed exponentially with
(a constant percentage of light available is extinguished at each meter)
When plotted as depth vs log % incidence
of light, line is straight in a homogeneous solution.
What would a deflection in the line
Compensation depth -
photosynthesis within a cell at about 1% of incident surface light (the
zone is the region from the surface to where 99% of light has
- an expression of the
optical properties that cause light to be scattered and absorbed rather
than transmitted in a straight line.
Turbidity is primarily caused by total
suspended solids but a direct relationship is varies from system to
Nephlometer (turbidometers) measures
of light scattered at 90°.
Visibility - measure of the depth at
which one can see into the water. Measured using a secchi disc.
What factors affect this measurement?
Visibility can be used to estimate photic
affects the depth of light pentration?
major salts, gases tend to by "nonconservative"
Saturation point of a gas increases with decreasing water temperature.
Why do oxygen and carbon dioxide
concentrations vary with depth in the
Why is pH highest nearer the surface of the ocean?