Carbon dioxide ocean water

Nearly all of the oxygen found on Earth today is produced by biological activity. During the process of photosynthesis, carbon dioxide and water react in the presence of chlorophyll to produce carbohydrates and oxygen. Scientists believe that oxygen was essentially absent from the earth s atmosphere when the planet was first created. As life developed on Earth and photosynthesis became more common, the rate of production increased until the present concentration of oxygen in the atmosphere, the oceans, and the crustal rocks was reached about 580 million years ago. 

Most of the concerns about global warming has been for land based plants. It can be seen from the proceeding paragraphs that the oceanic conversion of calcium carbonate by microorganisms and of carbon dioxide by plankton are perhaps more important in the regulation of our environment. Incidents such as an underwater volcanic explosion may affect this balance since they alter the temperature of water and the concentration of carbon dioxide in water and, consequently, its internal use and release to the atmosphere. 

The most important greenhouse gas at present is not carbon dioxide but water vapour, simply because there is so much of it in the atmosphere (Box 6.1). Volcanoes emit large amounts of water vapour (c. 1 Ttyr-1 Skelton et al. 2003), but even so this flux is minor compared to evaporation from the oceans and evapotranspiration from plants (c.0.25% see Fig. 3.12). In a warmer world, such as during the Cretaceous, the atmosphere can hold more water vapour. However, the extent of the warming caused by extra atmospheric water vapour is difficult to predict because clouds also exhibit an albedo effect, and the balance between the greenhouse and albedo effects varies with cloud type and altitude (Lovelock Whitfield 1982). 

The density of sea-water is almost independent of depth (1.040-1.045 g cm ) whereas that of liquid carbon dioxide increases with depth see Figure 3.9(b). Down to about 2500 m, liquid carbon dioxide is less dense than sea-water and tends to float upwards. At 2500-3000 m, liquid carbon dioxide is neutrally buoyant i.e., a transition zone in which it neither rises nor sinks), dependent on the sea temperature. Deeper than 3000 m, the liquid is denser than sea-water and sinks downwards to the ocean floor, where it accumulates as a lake, over which a solid layer of crystalline hydrates slowly forms as an ice-like combination of carbon dioxide and water. Within its stability range (low temperature, high pressure), solid C02-hydrate would inspire greater confidence as a permanent store than dissolved or liquid carbon dioxide, although there are few data to say how rapidly carbon dioxide would be leached out by sea-water. 

Absorption of CO2 by the ocean plays a large role in global climate. Because carbon dioxide and water form carbonic acid, the H2CO3 concentration in the ocean increases as the water absorbs atmospheric CO2. Most of the carbon in the ocean, however, is in... 

Absorption of CO2 by the ocean plays a large role in global climate. Because carbon dioxide and water form carbonic acid, the H2CO3 concentration in the ocean increases as the water absorbs atmospheric CO2. Most of the carbon in the ocean, however, is in the form of HC03 and CO ions, which form a buffer system that maintains the ocean s pH between 8.0 and 8.3. The pH of the ocean is predicted to decrease as the concentration of CO2 in the atmosphere increases, as discussed in the Chemistry and Life box on ocean acidification in Section 17.5. 

The carbon dioxide and water mixture at the bottom of Lake Nyos is an example of a solution, a homogeneous mixture of two or more substances. Solutions are common— most of the liquids and gases that we encounter every day are actually solutions. When most people think of a solution, they think of a solid dissolved in water. The ocean, for example, is a solution of salt and other solids dissolved in water. Blood plasma (blood that has had blood cells removed from it) is a solution of several solids (as well as some gases) dissolved in water. In addition to these, many other kinds of solutions exist. A solution may be composed of a gas and a liquid (like the carbon dioxide and water of Lake Nyos), a liquid and another liquid, a solid and a gas, or other combinations (see Table 13.1). 

Solutions of gases dissolved in water are common. Club soda, for example, is a solution of carbon dioxide and water, and most liquids exposed to air contain dissolved gases from air. Fish depend on the oxygen dissolved in lake or ocean water for life, and our blood contains dissolved nitrogen, oxygen, and carbon dioxide. Even tap water contains dissolved gases. The solubility of a gas in a liquid is affected by both temperature and pressure. 

In a similar vein, mean seawater temperatures can be estimated from the ratio of 0 to 0 in limestone. The latter rock is composed of calcium carbonate, laid down from shells of countless small sea creatures as they die and fall to the bottom of the ocean. The ratio of the oxygen isotopes locked up as carbon dioxide varies with the temperature of sea water. Any organisms building shells will fix the ratio in the calcium carbonate of their shells. As the limestone deposits form, the layers represent a chronological description of the mean sea temperature. To assess mean sea temperatures from thousands or millions of years ago, it is necessary only to measure accurately the ratio and use a precalibrated graph that relates temperatures to isotope ratios in sea water. 

Molecules am act one another. Fiuni that simple fact spring fundamentally important consequences. Rivers, lakes, and oceans exist because water molecules attract one another and form a liquid. Without that liquid, there would be no life. Without forces between molecules, our flesh would drip off our bones and the oceans would be gas. Less dramatically, the forces between molecules govern the physical properties of bulk matter and help to account for the differences in the substances around us. They explain why carbon dioxide is a gas that we exhale, why wood is a solid that we can stand on, and why ice floats on water. At very close range, molecules also repel one another. When pressed together, molecules resist further compression. 

Carbonic acid is an important natural component of the environment because it is formed whenever carbon dioxide dissolves in lake water or seawater. In fact, the oceans provide one of the critical mechanisms for maintaining a constant concentration of carbon dioxide in the atmosphere. Carbonic acid takes part in two successive proton transfer equilibria ... 

An important example of non-linearity in a biogeochemical cycle is the exchange of carbon dioxide between the ocean surface water and the atmosphere and between the atmosphere and the terrestrial system. To illustrate some effects of these non-linearities, let us consider the simplified model of the carbon cycle shown in Fig. 4-12. Ms represents the sum of all forms of dissolved carbon (CO2, H2CO3, HCOi" and... 

Fig. 11-16 Partial pressure of CO2 in surface ocean water along the GEOSECS tracks (a) the Atlantic western basin data obtained between August 1972 and January 1973 (b) the central Pacific data along the 180° meridian from October 1973 to February 1974. The dashed line shows atmospheric CO2 for comparison. The equatorial areas of both oceans release CO2 to the atmosphere, whereas the northern North Atlantic is a strong sink for CO2. (Modified with permission from W. S. Broecker et al. (1979). Fate of fossil fuel carbon dioxide and the global carbon budget, Science 206,409 18, AAAS.)...

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