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Science 101: Ocean Science
The Vast Unknown
It is unlikely that an airplane equipped with the most up-to-date maps could crash into an undiscovered mountain. How could a mountain thousands of feet tall be missing from a map? Yet on January 7, 2005, a mere 400 miles (644 km) from its base on Guam, a U.S. Navy submarine ran into an uncharted seamount. According to official charts, the sub was cruising through water around 6,000 feet (1,829 m) deep. One crew member died and 23 others were injured.
Although the ocean covers almost three-quarters of Earth's surface and makes up more than 90 percent of the habitable area, or biosphere, surprisingly little is known about it. The surfaces of the Moon and Jupiter have been mapped more thoroughly than the floor of the sea has.
Understanding the ocean matters. It matters because the ocean plays a major role in determining climate and weather. It matters because we use the oceans day in and day out for transportation, food, medicine, and pleasure. It matters because billions are spent exploring space while our own backyard is relatively unexplored. And it matters because what we learn by studying the oceans is just so fascinating.
One Ocean, Many Regions
Looked at from the shore, the ocean may appear to stretch unchanging to the horizon. Except for those bodies of water surrounded by land, all the world's oceans are connected. Yet just as there are distinct regions of the surface world—rain forests, tundra, and prairies, for example—there are distinct regions within the ocean. And just like terrestrial organisms, some ocean creatures travelthe world, while others are restricted to very particular conditions. To understand and protect the vast diversity of life in the ocean, we need to understand and protect the vast diversity of habitats and processes that support it.
Location, Location, Location
The ocean can be divided into two basic regions: the pelagic zone, or water column, and the benthic zone, or seafloor. There are further divisions within those two zones based on depth and proximity to shore. The pelagic zone is divided into coastal (neritic) zones and oceanic zones (those away from the influence of land), and into the mesopelagic, bathypelagic, and abyssal pelagic zones, in order of increasing depth.
The divisions of the benthic zone begin high on shore in the supralittoral, or splash, zone, which is rarely if ever covered with water. Then there is the intertidal zone, regularly submerged and exposed as the tides rise and fall, followed by the sublittoral, or subtidal zone, which extends to the edge of the continental shelf. The deepest zones are the abyssal and the hadal. The hadal zone encompasses the very deepest areas, in the trenches or anywhere below 19,800 feet (6,000 m).
These place-based divisions reflect physical differences, such as the amount of freshwater input or annual changes in temperature, that have a profound influence on the biology and chemistry of each underwater region.
From the perspective of organisms that need light to make energy (that is, plants and other photosynthesizing organisms), there are two distinct zones in the ocean. One is the photic, or sunlit, zone, and the other is the aphotic, or lightless zone. Yet another division reflects changing water chemistry and density. Water that is warmer or less salty is less dense than cooler or saltier water, and water that is less dense tends to stay at the surface. Between the surface and deep zones is the pycnocline, or zone of rapidly changing density. Although invisible to us, the pycnocline is a very real boundary for the small creatures that make up the majority of life in the oceans.
Currents form another set of boundaries in the ocean. The water is full of planktonic organisms, or organisms that are weak swimmers. Traveling against or even crossing major currents can be impossible for these beings.
Ocean zones can also be categorized based on the dominant features of particular communities. On land, there are forests of trees; in the oceans, there are kelp forests. On land, there are tall-grass prairies; in the oceans, there are sea-grass meadows. Some communities, such as mangrove forests and salt marshes, straddle the area between land and sea. Other examples of ocean communities include coral reefs, mussel reefs, hydrothermal vents, and methane seeps. Each type of community is distinct, offering a unique set of opportunities and challenges for the organisms that live there.
The Teeming Hordes
Envision a world in which some animals as well as plants remain fixed to the ground, getting food by grabbing passersby or filtering it from the air around them. Imagine that not just the ground but the air itself was full of life—microscopic organisms invisible to the naked eye but whose presence colored the air, innumerable jellyfish, odd-looking snails with wings. Imagine that at night, the vast majority of these animals could produce their own light, flashing signals to one another through the dark. This is the world of the oceans. They are full of life—some of it familiar, some of it bizarre, and much of it still unknown.
Taxonomists divide animals into about 33 major groups, called phyla. Each phylum represents a distinct body plan. The difference between phyla is much greater than the difference between species within an individual phylum. Out of all these phyla, only one has no representatives in the ocean: the little velvet worms called onychphorans. By contrast, 14 phyla are found only in the ocean. The large-scale diversity of animals in the oceans far outshines that on land. Even though the number of identified species on land is much higher than that in the oceans, this number is deceptive, as new ocean organisms continue to be discovered. For example, in 1988, scientists realized that what had been viewed as just two species of commercially valuable deep-sea crabs was really 18 different species. Every year brings similar findings—in 2001, a 23-foot (7 m) squid unlike any . . .Science 101: Ocean Science. Copyright © by Jennifer Hoffman. Reprinted by permission of HarperCollins Publishers, Inc. All rights reserved. Available now wherever books are sold.