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Reproduced from The Living Ocean, SeaWiFS Project, NASA Life in the Oceans - Studying Global Ocean Colour from Space Covering about seventy percent of the Earth's surface, the Oceans are central to the continued existence of life on our planet. The Oceans are where life first appeared on Earth. The largest creatures On Earth (whales) and the smallest (bacteria and viruses) live in the oceans. We rely on the ocean for many things, including food: water transportation, recreation, minerals, and energy. Oceans store energy. When ocean currents change, they cause changes in global weather patterns and can cause droughts, floods, and storms. However our knowledge of our oceans is limited. Ships, coastlines, and islands provide places from which we can observe, sample, and study small portions of Oceans. But we can only look at a very small part of the global ocean this way. We need a better place from which to study oceans. Space provides this place. Satellites circling the Earth can survey an entire Ocean in less than an hour. These satellites can "look" at clouds to study the weather, or at the sea surface (when it's not cloudy) to measure the sea's surface temperature, wave heights, and direction of waves. Some satellites use radar to "look" through the clouds at the sea surface. One other important characteristic that we can see from space is the color of the ocean. Changes in the color of ocean water over time or across a distance on the surface provide valuable information.
The Ocean isn't just blue - What we see from space We see color when light is reflected by objects around us. White light is made up of a spectrum or combination of colors, as in a rainbow. When light hits the surface of an object, these different colors can be reflected or absorbed in differing intensities. The color we see depends on which colors are reflected and which are absorbed. For example, a book that appears red to us absorbs more of the green and blue parts of the white light shining on it, and reflects the red parts of the white light. When we look at the ocean from space, we see many different shades of blue. Using instruments that are more sensitive than the human eye, we can measure carefully the fantastic array of colors of the ocean. Different colors may reveal the presence and concentration of phytoplankton, sediments, and dissolved organic chemicals. Phytoplankton are smaIl, single-celled ocean plants, smaller than the size of a pinhead. These plants contain the chemical chlorophyll. Plants use chlorophyll to convert sunlight into food using a process called photosynthesis. Because different types of phytoplankton have different concentrations of chlorophyll, they appear as different colors to sensitive satellite instruments such as the Sea-viewing Wide Field-of-View Sensor (SeaWiFS). Thus, looking at the color of an area of the ocean allows us to estimate the amount and general type of phytoplankton in that area, and tells us about the health and chemistry of the ocean. Comparing images taken at different periods tells us about changes that occur overtime.
Phytoplankton - A little link in a big chain Why are phytoplankton so important? These small plants are the beginning of the food chain for most of the planet. As phytoplankton grow and multiply, small fish and other animals eat them as food. Larger animals then eat these smaller ones. The ocean fishing industry finds good fishing spots by looking at ocean color images to locate areas rich in phytoplankton. Phytoplankton, as revealed by ocean color, frequently show scientists where ocean currents provide nutrients for plant growth. ln addition, the plants show where pollutants poison the ocean and prevent plant growth, and where subtle changes in the climate-warmer or colder more saline or less saline-affect phytoplankton growth. Since phytoplankton depend upon specific conditions for growth, they frequently become the first indicator of a change in their environment.
Besides acting as the first link in the food chain, phytoplankton are a critical part of ocean chemistry. The carbon dioxide in the atmosphere is in balance with Carbon dioxide in the ocean. During photosynthesis phytoplankton remove carbon dioxide from sea water, and release oxygen as a by-product. This allows the oceans to absorb additional carbon dioxide from the atmosphere. If fewer phytoplankton existed, atmospheric carbon dioxide would increase.
No one yet knows how much carbon the oceans and land can absorb. Nor do we know how the Earth's environment will adjust to increasing amounts of carbon dioxide in the atmosphere. Studying the distribution and changes in global phytoplankton using ocean color and other tools will help scientists find answers to these questions.
The Earth is unique to our solar system: it can sustain life. Without the Earth's atmosphere, our planet would become extremely cold and barren of life. The atmosphere consists of nitrogen (about 70 percent) and oxygen (about 20 percent). The other ten percent consists mostly of carbon dioxide, water vapor, and several "trace" gases such as neon and argon. Like the glass roof and walls of a greenhouse, the Earth's atmosphere keeps its surface much warmer than it would be without the "greenhouse effect." How? Energy from the sun arrives as short-wavelength radiation (light), while the Earth emits long-wavelength (infrared) energy back into space. The hotter an object is, the shorter the wavelength of the radiation it emits. The short-wavelength sunlight easily penetrates the atmosphere and warms the Earth. However some of the long-wavelength energy emitted from the Earth is absorbed by the atmosphere before it escapes into space. Carbon dioxide, water vapor and other gases in the atmosphere are responsible for absorbing escaping long-wavelength energy. Thus, the Earth keeps some of the heat that would otherwise have been lost to space.
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