Ocean: The largest of the five “oceans,” the Pacific stretches from the Arctic to the Southern Ocean and from east of Asia and Australia to the Americas. It covers more area than all the land on Earth combined and is more than double the surface area of the Atlantic Ocean. It also wins the deepest point in the ocean contest with the Mariana Trench, which is nearly 11 kilometers (about 7 miles) deep.
Atlantic Ocean: This next largest ocean lies between the Americas and the continents of Europe and Africa. It’s home to the Bermuda Triangle, the Sargasso Sea, the Gulf Stream, and the hurricanes that rattle the Caribbean Islands and the southern and eastern coasts of the U.S. The North Atlantic is by far the most thoroughly explored, best understood, and most heavily fished of the five “oceans.”
Indian Ocean: Nestled between Africa (to the west) and Australia (to the east) and between Asia (to the north) and the Southern Ocean (below it), the Indian Ocean ranks third in surface area but first in warmth.
Southern Ocean: The Southern Ocean is relatively small, but its average depth is greater than the average depth of any of the other four oceans — four to five kilometers (2.5 to 3 miles) deep! It’s best known for its strong, sustained easterly winds, its huge waves (due to the strong, sustained winds), and its frigid environment; during its winter, nearly the entire surface of the Southern Ocean is frozen. It’s also home to the world’s largest ocean current — the Antarctic Circumpolar Current — and it is chock full of nutrients.
Arctic Ocean: Surrounding the North Pole and bordering the northern edges of North America, Asia, and Europe is the Arctic Ocean. Most of it is located within the Arctic Circle, from the North Pole down to about 70 degrees northern latitude. It’s the smallest and shallowest of the five “oceans,” and for most of the year, most of its surface area consists of ice 1 to 10 meters (3 to 33 feet) thick. The Arctic Ocean is best known for its wildlife (including polar bears, whales, and seals) and for its natural resources (primarily oil).
©John Wiley & Sons, Inc.
FIGURE 1-1: The ocean’s five “oceans.”
Recognizing the ocean zones
Oceanographers have divided the ocean into zones to better understand and describe the physical characteristics of the ocean, the ecosystems (biological communities) in each zone, and the inhabitants of those ecosystems. Zoning can be simple, such as dividing the ocean into two zones — photic and aphotic:
Photic (light): The top 200-meter (650-foot) layer of the ocean through which enough light penetrates enabling photosynthesis to occur. (Photosynthesis is the process of using the sun’s energy to produce food from carbon dioxide and water.)
Aphotic (dark): The part of the ocean from 200 meters down to the bottom, where it’s totally dark.
Another simple zoning system involves dividing the ocean into pelagic and benthic layers:
Pelagic (top): The water above the ocean floor.
Benthic (bottom): The seafloor and the thick layer of sediments below the seafloor.
In Chapter 4, we cover two more-detailed approaches to zoning the ocean — one that divides it into five horizontal layers (like layers of a cake) based on depth, and another that divides it into three vertical zones from coast to open ocean.
Dropping in on the different ecosystems
An ecosystem is a biological community of organisms interacting with their physical environment as a whole. Think of it as a mostly self-contained, self-reliant neighborhood with a diverse population. Land-based ecosystems include grasslands, deserts, rainforests, and wetlands. Common marine ecosystems include coral reefs, estuaries (where fresh water and salt water mix), kelp (seaweed) beds and forests, mudflats, rocky shores, sandy shores, seagrass meadows, and more. Lesser known ecosystems develop near the bottom of the deep sea and include communities that form around hydrothermal vents (which spew hot, mineral-rich water that some bacteria feed on), whale falls (literally, dead whales that sink to the bottom), and cold seeps (where methane gas is released that some bacteria and archaea feed on).
What’s so fascinating about ecosystems is that the community of residents that live within them evolved together, adapting to the unique conditions of a particular place as well as each other. In Chapter 5, we explore numerous marine ecosystems and introduce you to the plants, animals, and other organisms typically found in each.
Going with the Flow: The Physical Properties of the Ocean
Even without all the wonderful living organisms that call it home, the ocean is amazing. In fact, it is very much like a living thing itself; it breathes, it moves, it’s constantly changing, and it interacts with everything around it — land, water, and air. It plays a huge role in controlling Earth’s climate and making the weather, and it distributes heat and nutrients around the globe, making the entire world more habitable for every living thing.
In this section, we get physical by focusing on the salt in seawater, the various processes that maintain a steady flow of water around the world, and the interactions among land, sea, and air.
Getting up to speed on the water cycle
While plants and animals have life cycles, water has a life cycle of its own. Following the rule of “what goes up must come down,” the life cycle of water, commonly referred to as the hydrologic cycle, describes the way water travels around the globe from ocean to air to land and back again to the ocean (see Figure 1-2).
©John Wiley & Sons, Inc.
FIGURE 1-2: The hydrologic (water) cycle.
Water is a wonderous element which can take on three different states of being. It can exist in a solid state (ice), a liquid form (water), or a gaseous state (steam), in which it evaporates and becomes vapor (humidity). When humid air is cooled, the water forms droplets and falls back to the earth as precipitation — in either liquid form (as rain) or in solid form (as snow or hail).
Knowing what makes seawater salty
Why are most lakes, rivers, ponds, and streams all freshwater, whereas the ocean is salty? Mostly because of the water cycle. Most of the salt in the ocean comes from freshwater rivers and runoff from land. As the water moves over the land and rocks and through the earth, it picks up minute traces of salt and other minerals, which it then carries to and deposits in the ocean.
When water evaporates from the ocean, the salt remains, while the water vapor either precipitates over the ocean or is carried over and deposited as precipitation on land, where it washes more minerals into the
