Air and Sea Carbon Dioxide Exchange in Coastal Zones - Essay Example

Air and Sea Carbon Dioxide Exchange in Coastal Zones Abstract Oceans and atmosphere contain various gases that get exchanged with one another because of many factors such as pressure, wind speed and velocity and temperature change. Carbon dioxide is one of the most crucial gases that is exchanged between air and seawater in coastal zones because of gas pressure, temperature and wind. Carbon dioxide is required by land and oceanic living beings due to which, it travels to and from oceans and atmosphere. After entering from the atmosphere to the seawater, the carbon dioxide changes into different components such as carbonic acid, carbonates and bicarbonates and while entering back into the atmosphere, it changes back to carbon dioxide. Oceans have higher ratio of carbon dioxide as compared to atmosphere. Marine organisms like planktons, seaweeds and microscopic creatures require carbon dioxide for their growth while plants on land require carbon dioxide for their growth. Introduction Gases are present in our atmosphere as well as in oceans. These gases get mixed with one another as an exchange takes place between the two mediums regarding the gases present in them. Our atmosphere contains a number of gases such as nitrogen, oxygen, carbon dioxide and many other gases (Tokoro, et al 2007). Likewise, the oceans also contain a number of different gases that get emitted into the air. Carbon dioxide from the atmosphere that is naturally created as well as fabricated because of man’s effort enters the seawaters and the oceans pay no hindrance in accepting the carbon dioxide from the atmosphere (Tokoro, et al 2007). Carbon dioxide is the most prominent gas that can be observed during the exchange of various gases between air and sea. This paper explains the exchange of carbon dioxide between air and sea in the coastal zones. There are various reactions that take place with the exchange of carbon dioxide between sea and air and it is only because of the reactions that the gas exchange seems possible. The exchange takes place because of a number of factors that affect the exchange such as wind speed and velocity, environmental factors, temperature and pressure. Coastal zones are important sites to notice the exchange of gases between atmosphere and seawater. A descriptive account of air and sea carbon dioxide exchange in the coastal zones can be found in this paper, as the purpose of this paper is to inform about this exchange. Discussion Carbon dioxide is present in the atmosphere in a less amount as compared to other gases of the atmosphere such as nitrogen and oxygen due to which, it is also known as a trace gas (Prentice, et al., 2001). The role, which carbon dioxide plays in enabling people and living beings to live on earth cannot be negated. Carbon dioxide works in the atmosphere to maintain a suitable environment for the residents of the earth. The heat that is fenced within the earth’s atmosphere is because of carbon dioxide that is required to maintain life on earth (Revelle and Suess, 1957). Carbon dioxide works in form of a greenhouse gas that keeps the capacity of trapping heat within the earth’s atmosphere. The carbon dioxide that is present in the form of a trace gas and is reduced in ratio is enough to keep suitable heat required for the earth’s atmosphere (Ducklow and McAllister, 2004). Carbon dioxide works as a trapper of heat only when it is present in the atmosphere, once it enters the waters of the oceans; it loses its capability of trapping heat (Prentice, et al., 2001). Carbon dioxide shows efficiency in being exchanged between air and water because of its quick movement between atmosphere and sea water. Because of its rapid movement to and from the seawaters, a large number of its ratio is present in the ocean. According to Prentice, et al. (2001), the seawaters contain nearly ninety-three percent of the total carbon dioxide. This ratio of carbon dioxide continues travelling to and from the seawaters. Carbon dioxide plays an important role during photosynthesis and enables plants to live and make their own food. Plants inhale carbon dioxide due to which, they continue to live (Revelle and Suess, 1957). However, when there is no sunlight, plants exhale carbon dioxide due to which, it becomes a part of the atmosphere. Carbon dioxide is also created or fabricated by human beings as they use carbon dioxide for their life related needs such as annihilating forests, burning firewood, oil or petroleum for their transportation and industrial working (Prentice, et al., 2001). Like atmospheric carbon dioxide is used and created by living beings on lands, similarly, it is created and employed by oceanic creatures such as animals and plants (Prentice, et al., 2001). The ratio of carbon dioxide in the atmosphere remains constant because if some of the carbon dioxide is taken by the oceanic creatures and seawaters, some other part of atmosphere takes carbon dioxide again to make the ratio constant (Prentice, et al., 2001). Many oceanic creatures and marine living being take in carbon dioxide similar to the land creatures. Oceanic seaweeds and other categories of plants take in carbon dioxide to create their food for their survival and take out oxygen that is used by sea animals for their sustenance. Like atmospheric carbon dioxide, oceanic carbon dioxide also has a cycle with the help of which, it gets into the atmosphere and then back to the ocean. The ocean is much rich in carbon dioxide as compared to atmosphere as it contains extensive amount of carbon dioxide for the needs of oceanic life. The process with the help of which, carbon dioxide travels to and from the seawater is known as molecular diffusion. Molecular diffusion takes place when the pressure of carbon dioxide is unequal in the atmosphere and ocean water (Prentice, et al., 2001). When atmospheric pressure of carbon dioxide is elevated, it is diffused into the seawater and when oceanic pressure of carbon dioxide is elevated, it is diffused into the atmosphere. As already mentioned that oceans contain more carbon dioxide as compared to atmosphere, therefore, the carbon dioxide entering the ocean water goes through reactions and various products are created such as carbonates, bicarbonates and carbonic acid (Prentice, et al., 2001). Due to the reactions and transformation of carbon dioxide into other components, the pressure of carbon dioxide is reduced (Ducklow and McAllister, 2004). As a result, the process of exchange continues to happen. The oceanic plants need carbon dioxide for their development and a food web is also created as some creatures eat other creatures due to which, carbon dioxide circulates from and into the ocean. Carbon dioxide is required by oceanic and land plants and other creatures both during various life processes due to which, it is obtained by the plants and other creatures of both habitats. The efficacy of carbon dioxide in the lives of oceanic and land creatures cannot be negated (Prentice, et al., 2001). The microscopic life of the oceans also make use of carbon dioxide due to which, more and more carbon dioxide is required by the marine life. The carbon dioxide taken by the marine life is provided back to the atmosphere and then taken again for survival of the marine life (Ducklow and McAllister, 2004). Because of this continuous exchange of carbon dioxide, a fixed ratio of carbon dioxide is maintained in the ocean and atmosphere and this constant ratio helps in the survival of land and oceanic life. Gases move in two ways; from the atmosphere into the oceans and from the oceans into the atmosphere.  The critical factor, which determines this gaseous exchange, is the difference in the concentration of the gases between air and water and the speed of the wind at that particular time (ABE, et al 2010).  This exchange is important to our climate and the quality of the air we breathe. Our climate is dependent on how much carbon dioxide there is in the atmosphere since it directly contributes to global warming. Over most of the ocean, the movement of man-made carbon dioxide is from the air to the sea due to physical and biological processes which occur in seawater allowing the oceans to efficiently take up carbon dioxide (Beman 2001). Once carbon dioxide enters seawater, it reacts with the carbonate ions (CO32-) which are present to from hydrogen carbonate (HCO3-).  This moves the reaction to the right and allows more carbon dioxide to enter from the atmosphere as illustrated below. Planktons, which are marine plants also take up carbon dioxide biologically through photosynthesis and convert it to plant material.  Seaweeds also inhale carbon dioxide and exhale oxygen and provide the animals with oxygen that they require for their survival. Wind speed is a basic factor in carbon dioxide exchange and generally, the faster the wind, the more gas exchange occurs. This is because such high winds produce big waves making the surface of the sea rough and mix up the waters below.  As the waves break, they introduce billions of bubbles into the surface waters and these bubbles transfer gases from the atmosphere into the water. These same bubbles mix up the water thus helping gases escape from the water and enter the atmosphere (Spokes 2003). According to Revelle and Suess (1957), the carbon dioxide that enters into the oceans in the coastal zones can be reason of fuel combustion by human beings. Some of the carbon dioxide enters the oceanic waters as a natural process but some of it enters the oceans due to extensive usage of fuels for daily day-to-day processes that acquire us to make use of carbon dioxide for our easy living. Revelle and Suess (1957) describe that the rate of carbon dioxide in the atmosphere and in the oceanic waters is increasing day by day due to extensive fuel combustion requirements of human beings. Revelle and Suess (1957) inform that a portion of “3.9 * 10-3” of carbon dioxide that is present in the earth’s atmosphere gets added every year because of smouldering fossil fuels artificially, which is done by human hand. The carbon dioxide that is created because of fossil fuels combustion, is observed by the oceanic waters or it goes to biosphere (Revelle and Suess 1957). The oceanic matter contains storage of organic material, which contains nearly seven percent of carbon (Revelle and Suess 1957). The carbon dioxide that is present in water is reduced or minimized because of the process of photosynthesis and it is generated or created because of the oxidation process that takes place in oceanic. Due to oxidation and photosynthesis, the carbon dioxide that is located in the water is present in a balanced ratio (Revelle and Suess 1957). This balance enables carbon dioxide to maintain in a certain ratio. However, massive fuel combustion misbalances the ratio of carbon dioxide. Other environmental factors that affect the gas exchange include rainfall, which increases the emission of gases from the ocean, sea ice that alters the rate of exchange and water temperature (Hara, et al 1998). Precipitation causes the air sea gas exchange to increase manifold due to which, carbon dioxide is able to exchange during rainfall in a maximum ratio. In coastal regions, this exchange can be noticed clearly as during rainfall, the size of droplets and rate of rainfall becomes a reason for a faster air sea carbon dioxide exchange (Upstill-Goddard 2006). With increased temperature, not only the heat enters from the atmosphere into the oceanic water but also helps carbon dioxide and other gases to get exchanged on a faster pace (Upstill-Goddard 2006). Temperature changes also affect air water carbon dioxide exchange in the coastal zones as well as in other oceanic waters. Over time, scientists have tried to explain the basic systems employed in this gas exchange. They have put forward theories and hypotheses such as the GAIA control system and the CLAW hypothesis. The authors’ idea was that if temperature increases, phytoplankton would grow more and produce more DMS, which would subsequently lead to an increase in the amounts of sulphate aerosol in the atmosphere. These aerosols would both directly and indirectly cool the planet, reducing the initial temperature rise in the atmosphere (Wanninkhof 1992).The CLAW hypothesis supports a negative feedback loop where some mechanism acts to counteract the initial change in such a way to maintain the status quo as shown in Figure A. Figure A: A simplified representation of the CLAW Hypothesis. DMS stands for Dimethyl Sulphide and CCN for Cloud Condensation Nuclei (Spokes 2003). Effective exchange of mass and energy between the sea and the atmosphere depends on wind velocity, vertical temperature distribution and the hydrological state of water masses, which are in contact with the air. As wind blows over the sea surface, the sea becomes rough leading to the distortion of its aerodynamics and turbulent mixing of the air above the sea (Hara, et al 1998). Such turbulent mixing of the atmosphere above the sea surface allows for the intense transmission of moisture, momentum and heat between the atmosphere and the sea transferred with aerosol particles, which are produced, on the sea surface. Continental margins are currently thought to be a net sink or source of atmospheric CO2, but this is still debatable. “Recent estimates based on regional studies point to a net CO2 air-to-sea flux in the continental ocean margins. In a recent synthesis paper, it is estimated that the coastal margins constitute a net CO2 sink of 0.36 Pg C yr^-1 to the atmosphere based on mass balance calculations, as well as direct pCO2 measurements” (Beman 2001). This flux is a composite over many estuaries, coastal waters, and intensive upwelling areas, typically supersaturated with respect to CO2 and most open shelf areas, which are probably under saturated. He argues that the net CO2 uptake in the coastal zones is primarily driven by cross-shelf transport from nutrient-rich subsurface waters offshore. Overall, this coastal CO2 flux is a significant sink component in the global carbon cycle, given that the global ocean is believed to absorb nearly 2 Pg C yr^-1 of CO2 at present (Beman 2001). Calcium carbonate acts as a biogeochemical carbon buffer between atmosphere, ocean, and the geo-sphere. Marine calcium carbonate is produced as follows: Ca2+ + 2HCO3- 2CaCO3 + 2H+ This reaction shifts the carbon system equilibrium in seawater toward more acidic conditions, which results in a release of CO2 to the atmosphere. Dissolution of CaCO3 works in reverse to take up CO2. However, in the modern day CO2 released by fossil fuel combustion is higher than the estimated release of CO2 to the atmosphere by shallow water CaCO3. The contribution of the coastal areas to the total oceanic emissions of carbon dioxide gas can be significant on a global scale. The continuous exchange of carbon dioxide between the oceans and the atmosphere affects the atmospheric content and cycling of a range of chemical species, which are related to climate change atmospheric particle formation, ozone layer depletion, acid deposition, eutrophication, photo-oxidation, trace elements and persistent organic pollutants (POPs) (Beman 2001). The flux rates of the trace gases from the coastal waters to the air are much higher than the rates for the open ocean. There are inherent challenges in obtaining homogeneous data for coastal waters making the data available to be fully conclusive since it is difficult to accurately quantify the carbon dioxide gas transfer velocity as, it is influenced by a wide range of environmental variables, most of which are strongly interlinked (Beman 2001). Formal mathematical descriptions are being developed but they are not yet definitive. Conclusion Carbon dioxide is exchanged between ocean water and atmosphere in coastal zones and this exchange takes place because carbon dioxide is required by both the living modes. The oceanic life as well as land life requires carbon dioxide for their growth and survival. Carbon dioxide is inhaled and exhaled in both living environments. The land and oceanic plants inhale carbon dioxide and exhale oxygen that is used by creatures that are dependent on oxygen for their survival. The ratio of carbon dioxide is more in ocean water as compared to atmosphere. When the pressure of gas is more in atmosphere or ocean as compared to each other, it gets exchanged. Many other factors such as wind speed, temperature and diffusion, all contribute to the exchange of carbon dioxide between seawater and atmosphere. Therefore, exchange of carbon dioxide is a phenomenal happening that should be given significance. 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