Revelle factor

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The Revelle factor is a unit of measurement in oceanography .

The Revelle factor describes the ratio of the immediate relative change in the partial pressure of carbon dioxide (CO 2 ) in the liquid phase to the relative change in the total inorganically dissolved carbon DIC (= dissolved inorganic carbon). Immediately this means the chemical equilibrium that is established quickly with dissolved carbonate and bicarbonate, without z. B. the construction or dismantling of calcareous skeletons of marine life. The Revelle factor influences the distribution of CO 2 between the atmosphere and the mixed surface layer and thus the kinetics of CO 2 uptake by the deep water.

The Revelle factor was named after the oceanographer Roger Revelle , who was one of the first scientists to study global warming.

Revelle factor =

thermodynamics

In order to get into the ocean, carbon dioxide gas must convert into one of these components of carbonic acid : carbonate ion, bicarbonate ion or protonated carbonic acid; the product of these chemical solubility constants creates a "back pressure" that limits the rate at which carbon dioxide can get to the ocean surface.

DIC

The type of DIC present in ocean water depends on the alkalinity of the system and is illustrated using the Bjerrum plot below. Carbonate dominates in environments with a higher pH value , whereas carbon dioxide predominates in environments with a lower pH value (acidic environment). Bicarbonate ions are in excess in waters with a medium pH value. As the pH value falls , DIC increasingly changes into CO 2 , which increases the partial pressure of CO 2 (pCO 2 ) and the buffer factor.

An increased buffer factor results in a decreasing buffer effect, which would lead to an increased uptake of CO 2 from the atmosphere, which further reduces the pH value. The graph shows the molar proportion of carbonate species in seawater over the respective pH values, with the salinity set at 5,000 ppm and the temperature at 25 ° C. It should be noted that temperature and salinity influence the presence of carbonate species and can vary regionally and seasonally.

Carbonate Bjerrum.gif

DIC and alkalinity regulate the carbonate- and acid-based chemistry in the world's oceans and their influence on the Revelle factor is no exception.

The ratio of DIC to total alkalinity and the changes in pCO 2 are the main reasons for the variability of the Revelle factor. Higher DIC values ​​result in a lower Revelle factor and, as a result, a greater buffer effect. Higher values ​​of pCO 2 result in a larger Revelle factor, which represents a positive feedback loop and consequently leads to a lower buffer effect. The buffer factor typically ranges between 8 and 13.

Anthropogenic CO 2

The ability of ocean water to absorb excess (anthropogenic) CO 2 is inversely proportional to the Revelle factor. It is therefore possible in today's oceans to determine the concentrations of anthropogenic CO 2 by measuring the Revelle factor; the lower the Revelle factor, the greater the amount of anthropogenic CO 2 . Low revelle factors can typically be seen in warmer tropical to subtropical waters, whereas high revelle factors are found in the colder, high-latitude waters of the North Atlantic. The North Pacific has higher Revelle factors and a lower proportion of anthropogenic CO 2 . This is due to the fact that the alkalinity in the North Pacific is 100 µmol kg −1 lower than in the North Atlantic.

The Revelle Effect

The Revelle effect describes how only a small part of pCO 2 is found in the oceans, even if much larger amounts are introduced into the atmosphere. Depending on the alkalinity of water, DIC is either in the form of CO 3 , HCO 3 or CO 2 . When the pH is high (basic), the Revelle factor is greatest, which is why most of DIC is in the form of HCO 3 or CO 3 , rather than CO 2 . The following therefore applies: The greater the buffer effect (lower Revelle factor), the more DIC is present in the form of CO 2 or HCO 3 , which ultimately reduces the pCO 2 levels in both reservoirs, in the atmosphere as well as in the Ocean.

Individual evidence

  1. ↑ a b [1] 7.3.4.2 Carbon Cycle Feedbacks to Changes in Atmospheric Carbon Dioxide . 2007. Retrieved February 15, 2019.
  2. ^ Eric Egleston, Christopher L. Sabine, François MM Morel: Revelle Revisited. Buffer Factors That Quantify the Response of Ocean Chemistry to Changes in DIC and Alkalinity . In: Science . 4, No. 367, 2010, pp. 1-9. doi : 10.1029 / 2008GB003407 .
  3. ↑ Christopher L. Sabine, Richard A. Feely, Nicolas Gruber, Robert M. Key, Kitack Lee, John L. Bullister, Rik Wanninkhof, CS Wong, Douglas WR Wallace: The Oceanic Sink for CO 2 . (PDF) In: Science . 305, No. 367, September, pp. 367-71. doi : 10.1126 / science.1097403 . PMID 15256665 . Retrieved May 19, 2010.