Titre du document / Document title

Methyl bromide : Ocean sources, ocean sinks, and climate sensitivity

Auteur(s) / Author(s)

ANBAR A. D. ⁽¹⁾ ; YUNG Y. L. ⁽¹⁾ ; CHAVEZ F. P. ;

Affiliation(s) du ou des auteurs / Author(s) Affiliation(s)

⁽¹⁾ Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, ETATS-UNIS

Résumé / Abstract

The oceans play an important role in the geochemical cycle of methyl bromide (CH₃Br), the major carrier of O₃-destroying bromine to the stratosphere. The quantity of CH₃Br produced annually in seawater is comparable to the amount entering the atmosphere each year from natural and anthropogenic sources. The production mechanism is unknown but may be biological. Most of this CH₃Br is consumed in situ by hydrolysis or reaction with chloride. The size of the fraction which escapes to the atmosphere is poorly constrained ; measurements in seawater and the atmosphere have been used to justify both a large oceanic CH₃Br flux to the atmosphere and a small net ocean sink. Since the consumption reactions are extremely temperature-sensitive, small temperature variations have large effects on the CH₃Br concentration in seawater, and therefore on the exchange between the atmosphere and the ocean. The net CH₃Br flux is also sensitive to variations in the rate of CH₃Br production. We have quantified these effects using a simple steady state mass balance model. When CH₃Br production rates are linearly scaled with seawater chlorophyll content, this model reproduces the latitudinal variations in marine CH₃Br concentrations observed in the east Pacific Ocean by Singh et al. [1983] and by Lobert et al. [1995]. The apparent correlation of CH₃Br production with primary production explains the discrepancies between the two observational studies, strengthening recent suggestions that the open ocean is a small net sink for atmospheric CH₃Br, rather than a large net source. The Southern Ocean is implicated as a possible large net source of CH₃Br to the atmosphere. Since our model indicates that both the direction and magnitude of CH₃Br exchange between the atmosphere and ocean are extremely sensitive to temperature and marine productivity, and since the rate of CH₃Br production in the oceans is comparable to the rate at which this compound is introduced to the atmosphere, even small perturbations to temperature or productivity can modify atmospheric CH₃Br. Therefore atmospheric CH₃Br should be sensitive to climate conditions. Our modeling indicates that climate-induced CH₃Br variations can be larger than those resulting from small (±25%) changes in the anthropogenic source, assuming that this source comprises less than half of all inputs. Future measurements of marine CH₃Br, temperature, and primary production should be combined with such models to determine the relationship between marine biological activity and CH₃Br production. Better understanding of the biological term is especially important to assess the importance of non anthropogenic sources to stratospheric ozone loss and the sensitivity of these sources to global climate change.

Revue / Journal Title

Global biogeochemical cycles   ISSN 0886-6236   CODEN GBCYEP 

Source / Source

1996, vol. 10, n^o1, pp. 175-190 (1 p.1/4)

Langue / Language

Anglais

Editeur / Publisher

American Geophysical Union, Washington, DC, ETATS-UNIS  (1987) (Revue)

Mots-clés anglais / English Keywords

world ocean ; air-sea interface ; hydrochemistry ; sea water ; models ; prediction ; climate ; geochemical cycle ; bromides ; methane ; stratosphere ; production ; hydrolysis ; chlorides ; consumption ; temperature ;

Mots-clés français / French Keywords

Océan ; Interface air mer ; Hydrochimie ; Eau mer ; Modèle ; Prévision ; Climat ; Cycle géochimique ; Bromure ; Méthane ; Méthane (bromo) ; Stratosphère ; Production ; Hydrolyse ; Chlorure ; Consommation ; Température ;

Mots-clés espagnols / Spanish Keywords

Océano ; Interfase aire mar ; Hidroquímica ; Agua mar ; Modelo ; Previsión ; Clima ; Ciclo geoquímico ; Bromuro ; Metano ; Estratosfera ; Producción ; Hidrólisis ; Cloruro ; Consumo ; Temperatura ;

Localisation / Location

INIST-CNRS, Cote INIST : 21109, 35400004482734.0110