Carbon dioxide oceanic sink

Fan, S., Gloor, M., Mahlman, J., Pacala, S., Sarmiento, ]., Takahashi, T., and Tans, P. (1998). A large terrestrial carbon sink in North America implied by atmospheric and oceanic carbon dioxide data and models. Science 282, 442-446. 

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.)...

Carbon dioxide mainly enters the oceans from the atmosphere. It dissolves in the cold surface waters around the north and south poles. When these cold waters sink, they carry the carbon deep into the oceans where it can be stored for hundreds of years. Because of their ability to store carbon, the oceans are known as a carbon sink. The sea as a carbon sink has become increasingly important in recent decades because human activity is adding increasing amounts of carbon dioxide to the atmosphere, and much of it ends up in the sea. According to the National Aeronautics and Space Administration (NASA), almost half of the carbon added to the atmosphere hy fossil fuel burning ends up sequestered in the ocean. 

Carbon dioxide mainly exits the oceans at the interface with the atmosphere. Warm surface waters easily release carbon dioxide into the atmosphere. When warm waters rise to the surface, mainly near the equator, carbon dioxide is transferred from the water to the air. Because of this, the sea is a source of carbon for the carbon cycle as well as a carbon sink. 

Another way to increase Earth s ability to store carbon is by creating new, artificial carbon sinks that would trap excess carbon gas produced by human activity before it enters the atmosphere. The carbon dioxide would be collected and placed in a new location for controllable, long-term storage. Scientists have already experimented with two new carbon sink locations, one deep in the ocean, the other underground. In each case, carbon is forcefully injected into its new reservoir for long-term storage. 

Table 3.10 exemplifies the calculation of C02 sinks into the vegetation cover of Russia. Such calculations using the GMNSS demonstrate the dynamics of the C02 flux mosaic in the atmosphere-plant-soil system. Knowledge of this mosaic makes it possible to assess the role of specific types of soil-plant formations in the regional balance of carbon, and on this basis to calculate the global fluxes of carbon dioxide across the atmosphere-land border. Similar calculations are also possible for the atmosphere-ocean system. 

What are the likely future changes in concentrations of carbon dioxide, methane, and other carbon-containing GHGs in the atmosphere as well as changes in the sources and sinks of carbon on land and in the ocean ... 

Moore, J. K., Abbott, M. R., Richman, J. G., Nelson, D. M. (2000). The Southern Ocean at the last glacial maximum A strong sink for atmospheric carbon dioxide. Global Biogeochem. Cycles 14, 455-475. 

Hesshaimer V., Heimann M., and Levin I. (1994) Radiocarbon evidence for a smaller oceanic carbon-dioxide sink than previously believed. Nature 370, 201-203. 

A second top-down method for determining oceanic and terrestrial sinks is based on spatial and temporal variations in concentrations of atmospheric CO2 obtained through a network of flask air samples (Masarie and Tans, 1995 Cooperative Atmospheric Data Integration Project—Carbon Dioxide, 1997). Together with models of atmospheric transport, these variations are used to infer the geographic distribution of sources and sinks of carbon through a technique called inverse modeling. 

One of the most important components of the chemical perspective of oceanography is the carbonate system, primarily because it controls the acidity of seawater and acts as a governor for the carbon cycle. Within the mix of adds and bases in the Earth-surface environment, the carbonate system is the primary buffer for the aridity of water, which determines the reactivity of most chemical compoimds and solids. The carbonate system of the ocean plays a key role in controlling the pressure of carbon dioxide in the atmosphere, which helps to regulate the temperature of the planet. The formation rate of the most prevalent authigenic mineral in the environment, CaCOs, is also the major sink for dissolved carbon in the long-term global carbon balance. 

Ocean disposal options fall into several categories, as illustrated in Fig. 1. One is to dilute the dissolved CO2 at a depth below the mixed layer. Carbon dioxide can be stored using this method for decades to centuries, but capacities are limited. Another approach is to form lakes of CO2 at the bottom of the ocean. Below 2700 m, compressed CO2 is denser than seawater and sinks to the bottom. In addition, CO2 reacts with seawater to form a clathrate, a cage structure with approximately six water molecules per C02- Clathrates are solids that can form at temperatures slightly higher than the melting point of water and thus form spontaneously in the presence of liquid CO2 near the bottom of the ocean. However, they are not stable, and as a result, they dissolve into ocean water once the... 

NCREASING USE OF FOSSIL FUELS (petroleum, coal, and gas) will continue to load the atmosphere with carbon dioxide beyond the apparent capacity of the plant and oceanic sinks to absorb the gas. There has been an estimated 15% increase in atmospheric carbon dioxide since the turn of the century (/). An active response to this worldwide problem is to capture and chemically convert the carbon dioxide at its source of production. Ironically, these conversion processes must be powered by nonfossil fuel sources (solar or nuclear) to achieve a net reduction in atmospheric carbon dioxide. 

FIGURE 17.16 Sources of carbon dioxide emission in the United States. Note that not all of the emitted CO2 enters the atmosphere. Some of it is taken up by carbon dioxide sinks," such as the ocean. 

In the atmosphere, CO2 is affected by processes that operate on different time scales, including interaction with the silicate cycle (for more details, see Bashkin and Howarth, 2002), dissolution in the oceans, and annual cycles of photosynthesis and respiration (see also Section 4). The relative effect of these processes is described below taking into account the interrelationship between sources and sinks of carbon dioxide in the Asian region. Here, it is important to note that carbon dioxide is not reactive with other atmospheric species its MRT is three years (Figure 5). This value is largely determined by exchange with seawater (see below). 

Discuss the actual and potential role of ocean waters as a sink of carbon dioxide. Indicate the limitations of CO2 dissolving in sea waters. 

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. 

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