. Which Generally Occurs As Temperature Increases?

Seawater Properties that Control Density�

Density is defined as the mass of water per unit book and has units of grams per cubic centimeter (thou /cmⁱⁱⁱ ), kilograms per liter (kg/ L) or kilograms per cubic meter (kg/g³).� The density of fresh water at 4� C is one.0000 g/cmⁱⁱⁱ or ane.000 kg/liter or 1000 kg/g³.

Why do you lot remember the mass of water is defined at a specific temperature?

The range of density in the oceans is from virtually 1.020 to 1.070 g/cm³ The changes in density are caused mainly by variations in pressure, salinity and temperature:

� colder h2o more dumbo

� saltier water more dense

� higher pressure level causes density increase - pressure increases with depth due to the mass of water above

Temperature Effects on Density

Temperature changes effect seawater density:� as h2o cools its density increases.� As water cools, H₂O molecules pack more than closely together (considering the molecules are vibrating less at lower temperatures) and take up less volume.� The same number of water molecules in smaller volume results in a higher density.

How much does the seawater density increment upon cooling from 20� to 0�C?�� Seawater density increases from ane.0240 g/cm³ at 20�C to 1.0273 m/cm³ at 0�C at a constant salinity.� Globally, there is an average of about a 20�C temperature decrease from the surface to bottom of bounding main. The density increase with depth caused by the temperature subtract plays the greatest role in determining the density of a sample of h2o.�

Thus the increment in density due to the decreasing temperature with depth dominates over the salinity decrease and makes the deeper water more dense than surface water.� This ways that in most regions the ocean is stable, that is, it will take energy to mix the sea vertically.� This is not necessarily the situation in the polar regions �

Depth vs Temperature

Globally, the entire temperature range for bounding main water ranges from ~ -2�C to +40�C, which is much smaller than the temperature range for air, which varies from -lx�C to +60�C.

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Surface water temperatures vary much more than deep water temperatures.� Most of the body of water is warm at the surface and colder at increasing depths. The region where temperature decrease is greatest with depth is called the thermocline .� The rate of modify of temperature with depth is called the temperature gradient .� The steepness of the depth gradient in temperature depends on location.� It is greatest in the warm tropical body of water (warm at the surface and colder with increasing depth) and least in the common cold polar bounding main (somewhat uniformly cold at the surface and at increasing depths).

Salinity Effects

Salt in seawater makes it denser than freshwater.� How much salt is in seawater? Typically seawater contains between 33 to 37 grams of salt per liter of seawater, although the extremes of salinity tin range from 28 to 40 g/L.� Oceanographers measure salinity in parts per thousand (ppt), thus typical seawater is between 33 to 37 ppt.

To make seawater, start with freshwater and add 35 grams of common salt to one liter (1 kg) of this freshwater (35 grams per one thousand grams).� This resulting seawater is denser than freshwater considering of added mass of dissolved table salt.

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Typically, the salinity decreases from the surface bounding main to deep waters is very small-scale, from about 36 g/L (ppt) at the surface to 35 grand/L (ppt) in the deep water, thus at that place is a very pocket-size density subtract with depth given a constant temperature.

The salinity of seawater likewise affects it�s freezing point temperature.� F reshwater has a freezing point at 0�C.� Seawater�s freezing point is at ~ -2�C.� The freezing point versus salinity explains why it is easier to class ice on a lake (freshwater) than on a bay (seawater).

Density and Water Movement

The density of seawater determines its trend to motility vertically.� If density of water at surface is higher than below, the water will sink to a level of its own density.� This situation the h2o column is �unstable� .

If density of water at surface is lower than below, the h2o will non sink.� In this state of affairs the h2o column is �stable� . � In this situation it takes free energy input (normally from the wind) to "push button" water downward -east.m., similar submerging a rubber duck in bathtub (you supply energy).

Sinking of surface h2o generally occurs where there is common cold air to cool water at surface.� This situation found at loftier latitudes near the poles.� At these polar sites, surface waters absurd and go dumbo plenty to sink thousands of meters.� Sinking of surface waters is a very important mechanism to replenish waters in the �deep sea� .

In contrast, for most of the ocean (within ~50� of the equator) the surface waters are much warmer and less dumbo than the cold waters establish at depth.� Nether these weather condition surface waters practice not sink and thus there is no direct contact with waters in the deep sea.

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What controls surface salinity?� Mainly the relative rates of evaporation versus precipitation. � When the charge per unit of evaporation is greater than the precipitation, then surface ocean salinity increases. � When the rate of precipitation is greater than the rate of evaporation, then the surface ocean salinity decreases.

� Surface heating and atmospheric precipitation promote h2o column stability past lowering the density of surface seawater.

� Cooling and evaporation diminish stability by increasing surface density.�

Pressure Effects

Equally pressure increases, then does water density.� The water molecules pack together tighter as pressure level increases -the pressure increment with depth, due to the weight of the water in a higher place, and causes the greatest density changes in seawater with depth (greater than the density changes due to temperature and salinity changes).

Seawater Profiles vs Depth

Thermocline is a layer within a body of water or air where the temperature changes rapidly with depth. Because water is not perfectly transparent, almost all sunlight is absorbed in the surface layer, which heats upwards. Wind and waves circulate the water in the surface layer, distributing heat within information technology somewhat, and the temperature may exist quite compatible for the showtime few hundred feet. Below this mixed layer, however, the temperature drops very rapidly�perhaps as much every bit 20 degrees Celsius with an additional 150 m (500 ft) of depth. This area of rapid transition is the thermocline.� Below the thermocline, the temperature continues to driblet with depth, but far more gradually. In the Globe's oceans, 90% of the water is beneath the thermocline. This deep sea consists of layers of equal density, beingness poorly mixed.

Pycnocline is a layer where in that location is a rapid change in water density with depth. In freshwater environments such as lakes this density change is primarily caused by water temperature, while in seawater environments such as oceans the density change may exist caused by changes in water temperature and/or salinity.

Halocline is a vertical salinity slope. Because salinity (in concert with temperature) affects the density of seawater, it tin play a part in its vertical stratification.� Essentially, lower salinity water (= lower density) "floats" on meridian of college salinity h2o (= higher density). The magnitude of the resulting density gradient plays an important role in determining the touch of vertical mixing. A potent salinity gradient volition resist mixing, while a weak gradient tin be mixed more than hands.� Typically, sea vertical structure is dictated past temperature effects on density, just salinity and haloclines play a dominant function in certain regions of the world ocean. The sub-Arctic North Pacific is one such region.