Oceans For Dummies. Joseph Kraynak

molten rock (imagine heating a rock till it melts — that’s HOT). Convection currents in the molten rock move the plates at three to five centimeters (one to two inches) per year. (See Chapter 6 for more about plate tectonics.)

      Plate tectonics are also responsible for creating most tsunamis. Whenever land shifts at the bottom of the ocean or an underwater volcano erupts, the resulting displacement of water can send a wave thousands of miles across the ocean in a matter of only a few hours. (See Chapter 16 for more about waves and tsunamis.)

      Riding waves, tides, and currents

      Ocean water is constantly in motion thanks to a variety of forces, including the rotation of Earth; the gravitational fields of the sun, Earth, and moon; wind; and variations in the temperature and salinity of ocean water.

      On a cosmic scale, the interaction of the Earth’s, moon’s, and sun’s gravitational forces cause tides that move water toward and away from coastlines once or, more often, twice daily.

      At the ocean’s surface, wind, along with other forces (including Earth’s rotation and variations in water temperature and salinity) drive the formation of large rotating waters called gyres that generally spin clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere. (And no, this has no effect on the direction water swirls down your bathtub drain.)

Below the surface, differences in water density drive currents. Near the poles, when water freezes at the surface, it leaves behind its salt. This colder, saltier water near the surface is denser than the warmer, fresher water below it, so it dives down, hits the seafloor, and heads toward the equator. As this cold water moves down and away from the poles, warmer surface water rushes in toward the poles to replace it, resulting in a continuous current that transports water, heat, and nutrients around the globe. This process is called thermohaline circulation, and the resulting system of currents is called the global ocean conveyor belt. It is one of the many reasons the poles are so important. They literally drive our entire ocean system, supporting marine life (and seafood) all around the globe.

      See Chapter 16 for more about waves, tides, currents, and gyres and how water, heat, and nutrients are circulated around the world via ocean currents.

      Recognizing the ocean’s role in climate control and weather

      The ocean plays a critical role in keeping our planet at a steady temperature as it transports heat (and energy) around the globe. Of course, it’s not that simple, and the ocean doesn’t do this all by itself; it works together with the atmosphere and land to create our climate and influence the ever-changing weather patterns:

       Climate: The prevailing weather over a long period of time (usually more than 30 years), such as tropical (warm and wet), desert (hot dry), polar (cold and dry), and temperate (neither extremely hot nor extremely cold).

       Weather: Atmospheric conditions over a short period of time in respect to temperature, sunshine, storms, wind, and precipitation (rain, snow, sleet, hail).

      The impact of the ocean on weather is most dramatic when the ocean releases some of its energy in the form of a tropical cyclone (a hurricane, cyclone, or typhoon). See Chapter 17 for more about how the ocean influences climate and weather.

Meeting the Ocean’s Inhabitants

      The ocean is teeming with life, from coastline to open ocean and from surface to seafloor. These living beings can be broken down into six groups (technically known as kingdoms) — Plants, Animals, Protists, Fungi, Archaebacteria, and Eubacteria. In this book, we break them into three groups — microbes (generally too small to see with the naked eye), plants (and other organisms that require sunlight for energy and growth), and animals. Each of these groups can be broken down further; for example, the animal kingdom includes simple invertebrates (such as sponges and jellies), mollusks (such as snails and clams), crustaceans (such as crabs and lobsters), fish, reptiles, birds, and mammals.

      In this section, we cover the bare bones of taxonomy — the classification system used to assign organisms to specific groups — and introduce you to the groups of organisms we cover in Part 3.

      Recognizing strength in numbers: Marine microorganisms

      Microorganisms are (mostly) life-forms too small to see with the naked eye. Many of these are smaller than the cells that make up our bodies, but what they lack in size, they more than make up for in numbers. The ocean is home to an estimated 44 octillion microbes — more than all the stars in the known universe. Perhaps more amazing is that microbes comprise somewhere between 90 and 98 percent of the marine biomass (the total mass of all marine life)! These microorganisms can be broken down into four groups:

       Viruses are infectious agents that invade cells and use them to replicate. They’re not even classified as living beings (burn!).

       Bacteria are single-celled organisms that have a cell wall but no nucleus (a container for most of the cell’s genetic material) or organelles (specialized structures in a cell that perform various functions).

       Protists are single-celled organisms equipped with a nucleus and organelles. They’re not animals, plants, or fungi, but some are similar to plants in that they perform photosynthesis, some are similar to animals in that they move around and eat stuff, and some are more of a cross between the two — moving around, eating stuff, and performing photosynthesis.

       Fungi are single-celled or multicelled organisms that feed on organic matter. They include yeasts, molds, mushrooms, and toadstools.

       Microorganisms are a vital component of oceans. They serve as producers, making food for consumers at the bottom of food chains, and they serve as decomposers, breaking down animal waste into chemicals that can be reused. See Chapter 7 for more about microbes and the important roles they play.

      Going green with marine plants and plant-like organisms

      Oceans aren’t exactly known for their floral arrangements, but they do have a few recognizable plants and plenty of other important photosynthetic microorganisms that provide food, oxygen, and habitats for other marine organisms. Here’s a list of some of the more notable marine plants and photosynthetic organisms covered in Chapter 8:

       Phytoplankton are single-celled photosynthetic organisms sometimes described as “floating plants.” Most are single-cell algae (micro-algae), but phytoplankton also include a type of photosynthetic bacteria called cyanobacteria.

       Macro-algae are several species of macroscopic, multicellular marine algae commonly referred to as “seaweed.” They look like plants and can be very large, but they have no vascular system for distributing nutrients. All the cells that make up the seaweed absorb liquids and nutrients from the surrounding water.

       Seagrass is a plant, complete with a vascular system, leaves, roots, and rhizomes (just like lawn grass); they’re pollinated under water, and they produce seeds.

       Mangroves are highly salt-tolerant trees and shrubs that grow along shorelines in tropical locations. In addition to providing food, shelter, and