•The ocean basins are divided into three main Oceans:
•The Pacific Ocean is the largest and deepest (52% of the ocean area, mean
depth of 4028 meters);
•The Indian Ocean (20% area, mean depth of 3897 m) and
•The Atlantic Ocean, the shallowest because of the rather narrow deep basins
(25% area, mean depth of 3332 m).
•The Arctic is considered part of the Atlantic Ocean;
•The southern parts of the three Oceans are referred to as the Southern Ocean.
•The northern hemisphere has less ocean than the southern hemisphere, only about
61% ocean versus 81% for the southern hemisphere.
Freshwater:
how strange!
Polar molecule
hydrogen bonding
Water- a rather light molecule with
strong bonds
How much would sea level
in a 4000 m freshwater
ocean, fall if the 2 and 6°C
reservoirs [r = 0.9998] were
to mix completely to form a
4°C reservoir [r = 1.000]?
Answer: about 80 cm
Column 2
r=1.000
Column 1
r=0.9998
Consequence:
Easy to freeze
a lake
Balance beam
cabelling
4°
2°C
3°
Weights are
the same:
gr1h1=gr2h2
gravity
6°C
5°
sinking
Q = rCp Vol dT°
If V = 1 m3 and dT is 1°C
Qair = (1.293)(1004) = 1,298 joules
Qwater = (1023)(4218) = 4,315,014 joules [over 3000 times larger than air]
1 watt = 1 joule/sec
1 cal = 4.184 joules
So a little change of water temperature balanced by sea-air heat flux can really jolt the atmosphere.
Same true if water phase change is linked to atmosphere temperature. You can play with the numbers.
Gulf Stream
Upwelling of cool subsurface
water
Hot “Warm-Pool”
Cold, polar
•Sea water is about a 3.49%
salt solution [34.9 ppt], the rest
is freshwater.
•The major salt constituent is
Chloride [55%] and sodium
[30.6%]
How salt alters the water properties
Is water colder than -2°C observed?
Yes, at the base of glacial ice shelves of Antarctica.
[melts at seawater Tf, why not 0°C?]
•Sea water is about a 3.49%
salt solution [34.9 ppt], the rest
is freshwater.
•The major salt constituent is
Chloride [55%] and sodium
[30.6%]
•
•
The more saline, the denser the sea
water
Density of sea water is a function of
temperature and salinity, both play
an important role
Ocean Salinity
atmosphere
A
B
E>P
P>E
ocean
A
B
Stratification
•
Waters warmer than 10°C
dominate the sea surface
but do not extend much
below 500 m in the ocean;
the warm waters provide
just a veneer of warmth
over a cold ocean. The
sharp drop off in
temperature with depth is
called the thermocline.
Deeper cold waters derive
their properties at the sea
surface during winter at
high latitude.
Normal SST
El Niño
Ocean Stratification
Take away ideas:
1. Water & Climate: The ocean extends over 70.8% of the earth's surface. The ocean holds
98% of the 1.4 billion cubic kilometers of water on the planet, divided within three major
basins. The high capacity and density of water relative to the atmosphere, and the great
amount of energy required for change of phase of water (solid - liquid - vapor) makes the
ocean a powerful and stabilizing force of the Earth's climate system. One obvious
consequence of the ocean’s influence is the “marine effect”, which acts to attenuate
winter/summer and day/night extremes of air temperature. Another is that the ocean
circulation transfers significant amount of heat from low to higher latitudes, helping the
climate system to attain an approximate steady state condition. The ocean is a key part of the
global hydrological cycle, providing moisture for the atmosphere; ocean circulation of
freshwater balances the net evaporative and precipitation belts.
2. Sea Surface Temperature: The temperature of the sea surface is high (27-30°C) near the
equator, often the maximum value is occurs a few degrees of latitude north of the equator
and low (at the sea water freezing point of –1.9°C) within the polar oceans. However, there
are also changes of sea surface temperature with longitude. Warmer water projects poleward
along the western boundaries of the ocean. The eastern tropical regions of each ocean are
cooler than the western tropical margin. These are due to the movement of seawater in the
horizontal (ocean currents) and vertical (upwelling/sinking) directions. Temperature and
density of ocean water are related inversely: warm water means low density, cold water
means denser seawater. The salt content of the water also affects Ocean density.
3. Sea Surface Salinity: Sea water is about a 3.49% salt solution, the rest is freshwater.
The more saline, the denser the seawater. As the range of salt concentration in the ocean
varies from about 3.2 to 3.8%, oceanographers refer to salt content as 'salinity', express salt
concentration as parts per thousand; 34.9 ppt is the average salinity. As seawater evaporates
the salt remains behind, only the freshwater is transferred from the ocean to the atmosphere.
A region of excess evaporation, such as the subtropics tends to become salty, while the
areas of excess rainfall become fresher. Sea ice formation also removes freshwater from the
ocean, leaving behind a more saline solution. Along the shores of Antarctica this process
produces dense water. Salinity reflects the workings of the hydrological cycle: the
movement of freshwater through the earth/ocean/atmosphere system.
4. Below the Sea Surface: Waters warmer than 10°C dominate the sea surface but do not
extend much below 500 m within the ocean; tropical and subtropical surface water provide
is just a veneer of warmth over a cold ocean; typical deep ocean temperature vary from –1°
to 3°C. The sharp drop off in temperature with depth is called the thermocline. The warm
surface water is generally saltier than the cooler deep or polar waters. The halocline marks
the drop of salinity with depth that accompanies the thermocline. The surface water warmth
overrides the saltiness in governing density, so that the warm surface water regions coincide
with buoyant (less dense) water. In polar regions buoyancy of the surface layer is mainly a
consequence of the freshness of the surface water. Deep cold waters derive their properties
at the sea surface during winter at high latitude.
5. Deep Water Masses: The deep Atlantic is relatively salty (34.9). This water is derived
from the sinking of chilled saline surface water in the northern North Atlantic. The cooling
makes the surface water dense, forcing it to sink, or convect into the deep ocean, and spread
southward at depth. It is called North Atlantic Deep Water (NADW). In contrast the deep
Pacific is lower in salinity (34.7), as it experiences no deep convection of cooled salty surface
water, its surface layer is too fresh and buoyant to sink. Pacific deep water is derived from the
lower salinity water column of the southern ocean. Towards the sea floor, temperatures are
near 0°C marking the presence of Antarctic Bottom Water (AABW) derived from the very
cold (-1.9°C; 34.65)), dense water along the shores of Antarctica. At the base of the
thermocline is the low salinity Antarctic Intermediate Water (AAIW) derived from sinking of
cool (3° to 4°C), low salinity waters (34.4) from 50°- 60°S marking the Antarctic Circumpolar
Current and ocean polar front zone.