# Salinity and density relationship with temperature

### Density of Ocean Water - Windows to the Universe

Salinity-Temperature-Density Relationships Handout. Questions Seawater density is a function of both temperature and salinity. The density increases with. The average temperature of the sea is about 2°C. The average surface temperature is about 17°C. Increasing the mass by adding salt increases the density. The density of water increases as the salinity increases. The density of seawater ( salinity greater than ) increases as temperature decreases at all.

The gravitational force G of the earth pulls downward and is proportional to the mass of an object. The gravitational force on an object is also called weight.

The force due to gravity is greater on objects that are more massive, or weigh more. The buoyant force B of water pushes up. In the third century B.

He observed that the volume of water pushed out of a tub, or displaced, by an object was equal to the volume of the object. The buoyant force of the water is equal to the weight of the water displaced. An object accelerates when the forces on that object are unequal.

Although acceleration is commonly used to describe an object that is speeding up, the scientific definition of acceleration means changing speed.

An accelerating object can be speeding up or slowing down. An object will always move in the direction of the greater force. An object may accelerate downwards sink or upwards rise in a body of water. Salinity and density share a positive relationship.

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• The Ocean and Temperature
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As density increases, the amount of salts in the water—also known as salinity, increases. Various events can contribute to change in the density of seawater.

Salinity can decrease from the melting of polar ice or increase from the freezing of polar ice. Evaporation increases salinity and density while the addition of freshwater decreases salinity and density.

The Mississippi delta The ocean water is constantly churning underneath, bringing nutrients up to the top. The difference in density of cold water versus density of warmer water is responsible for ocean currents and upwelling. This slightly heavier density is another contributing factor to upwelling as it causes the water molecules to roll over each other.

## Properties of the sea: salinity and temperature

Salinity is usually 35 ppt parts per thousandbut can range from ppt and is highest in the northern Red Sea. The Red Sea When the temperature, density or salinity of a layer changes rapidly, this region is referred to as a cline. Thermoclines, or areas of rapid change in temperature, familiar to most people who enjoy swimming in the ocean, are the most important due to their effect on planktonic ecosystems and primary producers.

Areas of rapid change in density are pycnoclines and areas of rapid change in salinity are haloclines. Thermoclines occur a short distance offshore when the shallow surface water is heated by the sun, resulting in warm, less dense, water staying at the surface and the sinking of cold, dense water. A seasonal thermocline is formed when surface water is cooled, and sinks to the bottom resulting in a mixing of the layers.

The approaching cool weather impacts primary production in the euphotic zone by cooling the surface water and bringing phytoplankton with nutrients to the creatures below. Shorter days and lower angles of sunlight limit the growth rate of the phytoplankton, which in turn limits the primary production and growth rate of organisms higher on the food chain.

The waters turn from blue to green as the increase in the number of phytoplankton dissolving inorganic nutrients causes an increase in chlorophyll biomass. Herbivorous zooplankton biomass also begins to increase, providing food for an entire food web above that depend on the energy they provide.

## Temperature Salinity Diagram – Effect of Temperature on Salinity

During the summer, the phytoplankton absorb most of the dissolved inorganic nutrients from the surface waters and are consumed by the zooplankton, decreasing the rate of photosynthesis.

Vertical mixing ceases and phytoplankton, which remain in the upper layers, become nutrient-limited. Given two layers of water with the same salinity, the warmer water will float on top of the colder water. However, temperature has a greater effect on the density of water than does salinity. Hence, a layer of water pycnocline with higher salinity can actual float on top of water with lower salinity if the layer with higher salinity is quite a bit warmer than the lower salinity layer.

The temperature of the ocean decreases significantly as you go to the bottom of the ocean. So, the density of ocean water increases somewhat proportionately as you go to or toward the bottom of the ocean.

### Water Density Calculator

The deep ocean is layered with the most dense water on bottom and the lightest water on top. Circulation in the depths of the ocean is horizontal, a result of deviations in density in constrast to surface circulation which is a product of surface winds. That surface level movement is to some degree vertical and horizontal, perhaps swirling, but within the same general density layer.