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density of pure water at 4C
1 g/cm³, serves as standard against which density of all other substances can be measured
why is density an important property of ocean water
bc density differences determine the vertical position of ocean water and cause water masses to float or sink, thereby creating deep-ocean currents
Ex. if you put denser water into less dense water, the denser water will sink creating a current
factors affecting seawater density
ocean, like earth’s interior, is layered according to density
as temp increases, seawater density decreases due to thermal expansion = inversely proportional
as salinity increases, seawater density increases
as pressure increases, seawater density increases
**only temp and salinity influence density of surface water bc pressure only influences it when high pressures are encountered, so only very deep in the ocean
**temp has the greatest influence on surface seawater density bc range of surface seawater temperature is greater than that of salinity.
temp and density variation w/ depth
(1) low latitude regions: surface water temps remain relatively constant until a depth of about 300m bc of good surface mixing mechanisms i.e. surface currents, waves, and tides. below 1000m, water’s low temp remains constant down to ocean floor
(2) high-lat regions also shows hardly any variation w/ depth. density is relatively high at surface bc surface water temps are low
density is high below surface too bc temp is also low
cold high-density water forms at surface, sinks, and initiates deep-ocean currents
thermocline
a layer of water beneath the mixed layer in which a rapid change in temp can be measured in the vertical dimension (only in low-lat waters) (300-1000m)
pycnocline
layer of rapidly changing density (300-1000m)
when established in an area, it creates an incredible barrier to mixing between low-density water above and high-density water below
high grvaitational stability, thus physically isolating adjacent layers of water
results from the combined effect of the thermocline and the halocline because temp and salinity influence density
high-latitude graphs of temp and density lack…
thermocline and a pycnocline —> thermo and pycnoclines only exist in low-lat regions, but halocline exists in both
ocean is layered into three distinct water masses based on density
(1) mixed = occurs above a strong permanent thermocline and corresponding pycnocline, water is uniform bc it is well-mixed by surface currents, waves, and tides
(2) upper water: thermocline and pycnocline in relatively low-density layer, well developed throughout the lwo and middle latitudes
(3) deep water: extends from below thermocline/pycnocline to deep-ocean floor
What are the three factors that affect seawater density? Describe how each factor influences seawater density, including which one is the most important.
(1) temp = most important, as temp increases, density decreases bc water expands more
(2) salinity: as salinity increases, density increases
(3) pressure: as pressure increases, density increases
why is there such a close association between (a) the curve showing seawater density variation with ocean depth and (b) the curve showing seawater temp variation with ocean depth?
temp nd density are inversely proportional —> as temp increases, density decreases
