Archive:Physical properties of the oceans
Part of the Ocean engineering course offered by the Wikiversity Department of Naval Architecture & Ocean Engineering, School of Engineering and the Engineering and Technology Portal
Lesson Outline
1. Overview 2. Temperature 3. Density 4. Salinity 5. Chemistry
Lecture
Overview
The oceans of Earth are vast and wild. Our primordial soup, they provide many of the facets that we refer to as existence. The weather of earth is controlled by the heat capacity and circulatory heat transfer mechanisms of the ocean currents. Many of our mineral assets, our foodstuffs and all of our fresh waters have passed through the oceans at some time.
Temperature
The temperature of the oceans is not a constant, nor is it uniform throughout the oceanic mass. Sunlight imparts its energy to the ocean surfaces all summer long, and in response the ocean heats and holds that energy. Once winter comes, the oceans release that warmth back into the atmosphere in accordance with their heat capacity. This is why it is warmer near the coast in winter, and cooler in summer. Just as the ocean may act as climate control for a local area, the oceans provide convective heat transfer as they circulate, providing climatic adjustment for every latitude via the Thermohaline Circulation. These currents are responsible for the cool weather along the US Atlantic coast, and the balmy high-latitude climate of the Mediterranean. The oceans in the Northern hemisphere are usually warmer in January, long after the summer has passed, and coolest in April, after most of their heat has been given off to the cold winter skies.
Similarly, the temperature of the ocean is not uniform at all depths. Any swimmer may recognize the temperature differential between the water at the surface, where the sunlight is incident, and that deeper water that is much cooler. At medium depths however, there is a greatly increased temperature differential, and the water below a certain point is much cooler than the water above it. This sharp differential is called the thermocline, and is present in most ocean environments, although greater in the tropics and in temperate regions during summer and nearly nonexistent in polar regions. In shallow waters, the cold air of winter can cool the surface so quickly that the water will actually "turn over", reversing the thermocline. The dependence of the thermocline upon salinity and density will be discussed further with those topics.
Density
The makeup of the oceans is paramount to all these functions. The ocean is composed of primarily water, however the chemical and biological sediments carried by rivers are present too, as are similar constituents formed from the falling of rain through pollution and the remnants of aquatic life cycles. All of this material amounts to a watery mixture often referred to as salt water, yet more accurately described as saline. Salinity is the measure of how much material is mixed in with water. Density in the oceans is a function of salinity, represented by the following equation:
Assignments
Activities: 1. Select your favorite region of the oceans and research the physical properties of that area 2. Using your newfound knowledge of the subject, why can't freshwater fish live in saltwater environments?
Readings: Reading 1. - Peruse the appropriate sections of Wikibooks:Introduction to Oceanography
Study guide: 1. Wikipedia article:Temperature 2. Wikipedia article:Density 3. Wikipedia article:Salinity 4. Wikipedia article:Chemistry 5. Wikipedia article:Marine geology 6. Wikipedia article:Oceanography 7. Wikipedia article:Chemical oceanography 8. Wikipedia article:Physical oceanography