The Oceans and Atmospheric Regulation

Theoceans and the global carbon cycle

The oceans play a key role in the global carbon cycle. Photosynthesis by phytoplankton generates organic compounds of aqueous carbon dioxide. Eventually, some of the biogenic matter sinks into deeper water, where it undergoes decomposition and oxidation back into carbon dioxide. This process transfers carbon dioxide from the surface water and sequesters it in the ocean deep water. As a consequence, atmospheric concentrations of CO2 can be maintained at a lower level than otherwise. This mechanism is known as a 'biologic pump'; long-term changes in its operation may have caused the rise in atmospheric C02 at the end of the last glaciation. Ocean biomass productivity is limited by the availability of nutrients and by light. Hence, unlike the land biosphere, increasing CO2 levels will not necessarily affect ocean productivity; inputs of fertilizers in river runoff may be a more significant factor. In the oceans, the carbon dioxide ultimately goes to produce carbonate of lime, partly in the form of shells and the skeletons of marine creatures. On land, the dead matter becomes humus, which may subsequently form a fossil fuel. These transfers within the oceans and lithosphere involve very long time scales compared with exchanges involving the atmosphere.

Упражнение 9.

Выберите из текста Oceans and carbon dioxide 10–15 основных, с точки зрения смысловой нагрузки, слов (ключевые слова). Определите, к каким частям речи они относятся.

Упражнение 10.

Переведите текст письменно. (Контрольное время – 30 минут)

The atmosphere and the surface ocean waters are closely connected both in temperature and in CO2 concentrations. The atmosphere contains less than 1.7 per cent of the CO2, held by the oceans, and the amount absorbed by the surface ocean water rapidly regulates the concentration in the atmosphere. The absorption of CO2 by the oceans is greatest where the water is rich in organic matter or where it is cold. Thus the oceans are capable of regulating atmospheric CO2, of changing the greenhouse effect and of contributing to climate change. The most important aspect of carbon cycle linking atmosphere and ocean is the difference between the partial pressure of CO2 in the lower atmosphere and that in the upper oceanic layer. This results in atmospheric CO2 being dissolved in the oceans and in some of this being subsequently converted into particulate carbon, mainly through the agency of plankton, ultimately sinking to form carbon-rich deposits in the deep ocean as part of a cycle lasting hundreds of years. Thus two of the major effects of ocean surface warming would be to increase its СО2 equilibrium partial pressure and to decrease the abundance of plankton. Both of these effects would tend to decrease the oceanic uptake of CO2 and therefore to increase its atmospheric concentration, thereby producing a positive feedback (i.e. enhancing) effect on global warming. However, the operation of the atmosphere-ocean system is sufficiently complex that, for example, global warming may so increase oceanic convective mixing that the resulting imports of cooler water and plankton into the surface layers might exert a break (i.e. negative feedback) on the system warming.

Упражнение 11.

Составьте 5 общих вопросов к тексту The Oceans and Atmospheric Regulation.

Упражнение 12.

(Парная работа) Ответьте на вопросы, составленные в упражнении 11.

Дата добавления: 2014-12-27