Shop Windows to the Universe

Young Voices for the Planet DVD in our online store includes 8 films where students speak out and take action on climate change.
This is a simple density-depth ocean water profile. You can see density increases with increasing depth. The pycnocline are layers of water where the water density changes rapidly with depth. This density-depth profile is typical of what you might expect to find at a latitude of 30-40 degrees south.
Click on image for full size
Windows to the Universe original image

Density of Ocean Water

The density of pure water is 1000 kg/m3. Ocean water is more dense because of the salt in it. Density of ocean water at the sea surface is about 1027 kg/m3.

There are two main factors that make ocean water more or less dense than about 1027 kg/m3: the temperature of the water and the salinity of the water. Ocean water gets more dense as temperature goes down. So, the colder the water, the more dense it is. Increasing salinity also increases the density of sea water.

Less dense water floats on top of more dense water. Given two layers of water with the same salinity, the warmer water will float on top of the colder water. There is one catch though! Temperature has a greater effect on the density of water than salinity does. So a layer of water 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 and decreases as you go to the bottom of the ocean. So, the density of ocean water increases and increases as you go to the bottom of the ocean. The deep ocean is layered with the densest water on bottom and the lightest water on top. Circulation in the depths of the ocean is horizontal. That is, water moves along the layers with the same density.

The density of ocean water is rarely measured directly. If you wanted to measure the density of ocean water, you would have to collect a sample of sea water and bring it back to the laboratory to be measured. Density is usually calculated using an equation. You just need to measure the salinity, temperature and pressure to be able to find density. These measurements are often made with a CTD instrument, where the instrument is placed in the ocean water from a ship or a platform.

Last modified August 31, 2001 by Jennifer Bergman.

Shop Windows to the Universe Science Store!

We have beautiful specimens of banded iron formation in our online store from Nature's Own, along with many other mineral specimens.

Windows to the Universe Community

News

Opportunities

You might also be interested in:

Traveling Nitrogen Classroom Activity Kit

Check out our online store - minerals, fossils, books, activities, jewelry, and household items!...more

Salinity

About 70% of the Earth is covered with water. Over 97% of that water is found in the oceans. Everyone who has taken in a mouthful of ocean water while swimming knows that the ocean is really salty! Dissolved...more

Thermohaline Circulation: The Global Ocean Conveyor

The world has several oceans, the Pacific, the Atlantic, the Indian, the Arctic, and the Southern Ocean. While we have different names for them, they are not really separate. There are not walls between...more

Melting Arctic Sea Ice and the Global Ocean Conveyor

Seawater moves through the Atlantic as part of the Global Ocean Conveyor, the regular pattern by which seawater travels the world’s oceans. The water in the Global Ocean Conveyor circulates because of...more

Arctic Ocean Currents

The majority of the world's population does not live in the Arctic. But even if you don't live in the Arctic, it is very important to understand how the Arctic Ocean works because it has an impact on surrounding...more

Content for Climate Change Education Courses

Looking for online content that can be used for a climate change education course or module? Pages linked below can be used to support an introductory climate change education for either a unit or a full...more

Aquifer

An aquifer is the name for a layer of rock which is capable of holding a large amount of water. Some layers are better at holding water than others, for example a layer of sandstone can hold a good deal...more

Carbonates

Carbonate is a name for rocks and minerals which contain a molecule made of both carbon and oxygen known as CO32-. (CO32- is also known as the molecule carbonate). Limestone is an example of a calcium...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA