Chemical coupling with the atmosphere
Of the greenhouse gases, carbon dioxide is perhaps the most important because of its links to human activities. Since the Industrial Revolution, atmospheric carbon dioxide has risen by 30 percent, while average global temperatures have climbed about 0.5°C. On average, carbon dioxide resides in the atmosphere about 100 years before it settles into the ocean, or is taken out of the atmosphere by plants. The oceanic removal of carbon dioxide from the atmosphere has a cooling affect on global temperatures.
Over geological time, most of the world's carbon (more than 90 percent) has settled into the ocean. There are many physical and biological processes that result in chemical exchanges between the ocean and the atmosphere, and between the upper ocean and the deep ocean. Carbonate chemistry regulates much of the transfer of carbon dioxide from air to sea; but biological processes, such as photosynthesis which turns carbon dioxide into organic material, also play an important role. Over time, organic carbon settles into the deep oceana process referred to as the "biological pump." The upper ocean has lower concentrations of total carbon than the deep ocean as a result of this pump. But if the ocean were completely mixed from top to bottom, as could happen if its "thermohaline" (heat and salt) circulation system was disrupted, much of this carbon could be churned up toward the surface. The ocean could become a source, rather than a sink, of carbon dioxidea phenomenon that would have a catastrophic impact on global temperatures.
Worldwide, winds transport about 1010 kilograms of dust on any given daythis is roughly equivalent to the mass of three supertanker ships. Windblown dust from soils and desert sands are rich in iron that, when it settles into the ocean, serves as "fertilizer" for phytoplankton. Global climate models suggest that as temperatures rise, the interiors of continents will become hotter and drier, which would result in greater amounts of dust being blown out to sea. In turn, more iron dust settling in the ocean would greatly enhance phytoplankton productivity, thus slowing the rate of carbon dioxide increase in the atmosphere. In summary, in continental dust, nature may have a negative feedback mechanism that it uses to delay or even reverse global warming trends.
Return:Ocean and Climate
Physical coupling with the atmosphere
Ocean and atmosphere move because they are fluid. The speed and direction of air and sea currents are determined primarily by air temperature gradients. As heat rises and eventually escapes the ocean to warm the overlying atmosphere, it creates air temperature gradients and, consequently, winds. In turn, winds push against the sea surface and drive ocean current patterns. Over time, a complex system of currents was established whereby the ocean transports a tremendous amount of heat toward the poles. Because heat escapes more readily into a cold atmosphere than a warm one, the northward flow of ocean and air currents is enhanced by the flow of heat escaping into the atmosphere and, ultimately, into outer space.
The ocean has a high temperature and momentum "inertia," or resistance to change. Relative to the atmosphere, it has a very slow circulation system, so changes in its systems generally occur over much longer timescales than in the atmosphere, where storms can form and dissipate in a single day. The ocean changes over periods from months to years to decades, whereas the atmosphere changes over periods of minutes to hours to days. The interactions between ocean and atmosphere are fully nonlinear, and occur over decades, which is why their "dialogue" is so hard to interpret.
New climate models provide an excellent way to crack the code. Recently, scientists have suggested that the atmosphere provides the means for the ocean to extend its reach globally and set off, like dominoes, chains of meteorological events. During the 1997-98 El Niño, for example, the we witnessed record levels of rainfall in southern Californiawhere it is normally arid desert. Just before the onset of an El Niño, we see the tropical Indian Ocean warm dramatically. Then the warming seems to propagate across the Pacific. About 9 months into an El Niño, the new trade wind patterns cross over South America and change the current patterns of the tropical Atlantic, bringing drought to Brazil, where there is normally lush rain forest, and the African Sahel. Other scientists have theorized that ocean temperatures oscillate between hot and cold, like some decadal climatic pendulum swing. It becomes clear that there is an almost mechanistic system by which the ocean drives climate change, which is why it was dubbed by scientists as the "global heat engine."