Density of water

density = mass/volume  units: g/cm 3 (= g/ml = kg/L) Effect of Temperature on Density  density of water - @ 4 oC and 1 atm pressure  fresh:1.000 g/cm 3 (by definition!) Density and Stratification  sea: 1.027 g/cm 3 (on average)
what determines water density?  temperature – inverse relationship the major players of the ocean’s layers  lower temp = higher density  higher temp = lower density  salinity – direct relationship  lower sal = lower density  higher sal = higher density  pressure  water is essentially (but not exactly) incompressible  but at very high pressures (deep depths) – pressure increases density  sea level would be ~30-50 m higher without pressure effect

Ocean surface temperature
often called sea surface temperature or SST
strongly correlates with latitude because insolation (amount of sunlight striking Earth’s surface) is high at low latitudes & low at high latitudes
surface ocean isotherms (lines of equal temperature)  generally trend east-west  except where deflected toward poles or equator by currents  warm water carried poleward on western side of ocean basins  Gulf Stream, Kuroshio Current – Northern Hemisphere  Brazil Current, East Australia Current – Southern Hemisphere  cooler water carried equatorward on eastern side of ocean basins  Canary Current, California Current – Northern Hemisphere  Benguela Current, Peru Current – Southern Hemisphere
SST overall pattern  highest in the tropics (~25-29 oC) where insolation is highest  decreases poleward with decreasing insolation  negative temperatures in Arctic Ocean & around Antarctica

1 Ocean abyssal temperature

cold and dense  colder than 4 oC (remember Challenger expedition)  colder = more dense  remember temperature-density relationship for seawater  temperature of maximum density is right at freezing point (~ -1.91 oC)
smaller temperature range than SST  <1 oC – 2.5 oC @ 4000 m depth  overall, from ~1000 m and below, most temperatures are 2 o – 4oC
more uniform distribution than SST  isolation from insolation (read that twice!)  still, some patterns can be discerned  colder near Antarctica  warmer in North Atlantic  warmest in isolated basins (due to diffusion of heat over time)  Caribbean Sea basin  Philippine Sea basin

Predict-a-profile Produce-a-profile kinda like whack-a-mole How did we do? except you don’t actually
warm surface waters ≈ 2% of ocean volume hit anything
thermocline waters ≈ 18% of ocean volume
deep waters ≈ 80% of ocean volume near near near near Alaska Antarctica Alaska Antarctica

Polar Temperate Region Tropics Temperate Region Polar Polar Temperate Region Tropics Temperate Region Polar ("high ("mid-latitudes") ("low latitudes") ("mid-latitudes") ("high ("high ("mid-latitudes") ("low latitudes") ("mid-latitudes") ("high latitudes") latitudes") latitudes") latitudes")

0 0 0 warm surface waters warm surface waters 0 ve r cool to warm warm to very warm cool to warm ld pycnocline and permanent thermocline y o 1000 co 1000 1000 1000 ld

to

2000 co 2000 2000 2000 ld very cold deep waters very cold to c 3000 3000 3000 3000

Water Depth (m) very cold very cold very cold Water Depth (m) 4000 4000 4000 4000

5000 5000 5000 5000 70 oN 60 ooooooooooooooN 50 N 40 N 30 N 20 N 10 N 0 10 S 20 S 30 S 40 S 50 S 60 S 70 S 70 oN 60 ooooooooooooooN 50 N 40 N 30 N 20 N 10 N 0 10 S 20 S 30 S 40 S 50 S 60 S 70 S

2 Explain-a-profile thermocline in tropics

What does this mean? Tropical Waters
The permanent thermocline (low latitudes)
warm, less dense surface layer over very cold and dense deep waters extends from the base of 32 41 50 59 68 77 86 °F
the permanent thermocline is the interval through which temperature the surface mixed layer decreases rapidly with increasing water depth 0 5 1015 20 25 30 °C near near (~75-150 m) to ~1000 m 0 Alaska Antarctica water depth. Polar Temperate Region Tropics Temperate Region Polar seasonal ("high ("mid-latitudes") ("low latitudes") ("mid-latitudes") ("high latitudes") latitudes")
The depth of the mixed (summer) thermocline 0 warm surface waters warm surface waters 0 layer is a function of mixing pycnocline and permanent thermocline (homogenization) of the 500 permanent 1000 1000 thermocline warmed surface waters (~150-1000 m) 2000 2000 downward by day-to-day very cold deep waters winds and storms, waves 3000 3000 1000 and surface currents. Water Depth (m) cold deep waters 4000 4000 below thermocline

5000 5000 (below pycnocline) o oooooooooooooo 70 N 60 N 50 N 40 N 30 N 20 N 10 N 0 10 S 20 S 30 S 40 S 50 S 60 S 70 S 1500

Growth of thermocline in mid-latitudes Seasonal Thermocline Temperate Waters
Winter storms tend to be (mid-latitudes) NOTE: applies to mid-latitude temperate regions only bigger/stronger than 32 41 50 59 68 77 °F summer storms.
March – winter cooling of surface waters has destroyed 0 5 10 15 20 25 °C seasonal thermocline, vertical mixing is taking place
Therefore the mixed layer 0 summer mixed layer (0-75 m) 75 m
May – surface waters winter mixed layer (0-150 m) tends to be deeper during 150 m seasonal begin to warm, weak winter months. (summer) thermocline forms
Summer heating causes thermocline 500 permanent
June – surface layer the creation of a seasonal thermocline increasingly shallow thermocline (a steeper (~150-1000 m) and isolated from temperature gradient than deeper waters; ther-

during the winter). 1000 1000 m mocline strengthens pronounced seasonality cold deep waters
August – thermocline below thermocline reaches maximum is the hallmark of (below pycnocline) the mid-latitudes
Decay of thermocline occurs August – January, as surface 1500 waters increasingly cool and mix with deeper waters

3 thermocline in polar regions Salinity and the halocline

A permanent thermocline is Polar Waters
Salinity changes with latitude due
In some areas of the ocean, (high latitudes) to variations in precipitation and surface water and deep water are absent in polar regions 32 41 50 °F evaporation with latitude. separated by a halocline , a zone of rapid change of salinity with because surface waters are
Highest ocean salinity is between water depth. 0 5 10 °C 20-30 o north and south of the very cold and deep waters 0
The thermocline and halocline are very cold. equator, because evaporation combine to form the pycnocline exceeds precipitation there. (which is mighty fine).
Therefore, there is little
Low salinity at the equator and
Water stratification (layering) temperature contrast (or poleward of 30 o results from within the ocean is most 500 evaporation being less than pronounced at the latitudes gradient) between polar no permanent precipitation. between 40 oN and 40 oS. surface and deep waters. thermocline (surface waters
A small seasonal (summer) are cold, deep waters are cold)

thermocline forms but (m) depth water 1000 vertical mixing occurs basically year-round.

temperature salinity density 1500 = “thermo” = “halo” = “pycno”

Fun with dots on plots o Temperature ( C) Density ( σ t ) 0 5 10 15 20 25 23 24 25 26 27 28 0 warm surface 0 less dense surface waters waters 500 thermocline 500 pycnocline

1000 1000

1500 1500 very cold dense 2000 deep waters 2000 deep waters

2500 2500 Water Depth (in meters) Depth Water (in Water Depth (in meters) Depth Water (in 3000 3000

3500 3500

4000 4000 32 41 50 59 68 77 1.023 1.024 1.025 1.026 1.027 1.028 Temperature ( oF) Density (g/cm 3)

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