Methyl and ethyl nitrate saturation anomalies in the Southern Ocean (36–65°S, 30–70°W)
Claire Hughes A B , Adele L. Chuck A , Suzanne M. Turner A and Peter S. Liss AA Laboratory for Global Marine and Atmospheric Chemistry, School of Environmental Sciences, University of East Anglia, Norwich, NR4 7TJ, UK.
B Corresponding author. Email: claire.hughes@uea.ac.uk
Environmental Chemistry 5(1) 11-15 https://doi.org/10.1071/EN07083
Submitted: 8 November 2007 Accepted: 9 January 2008 Published: 22 February 2008
Environmental Context. The alkyl nitrates are a group of organic compounds that are known to be produced naturally in seawater. The sea-to-air flux of alkyl nitrates is believed to contribute significantly to the ‘odd nitrogen’ reservoir of the atmosphere and to play an important role in regulating tropospheric ozone levels in remote marine regions. Here we expand our knowledge of alkyl nitrate concentration distributions and saturation anomalies to Southern Ocean waters.
Abstract. We report the first coupled atmosphere and seawater alkyl nitrate measurements for the Southern Ocean in the area bounded by 36–65°S, 30–70°W (November/December, 2004). Methyl and ethyl nitrate concentrations in seawater were 3.1–194.9 and 0.3–71.8 pmol L–1, respectively. Atmospheric mixing ratios ranged from 1.0 to 71.5 ppt for methyl nitrate and 0.6 to 16.6 ppt for ethyl nitrate. No correlations between alkyl nitrate distributions, and sea surface temperature, windspeed or chlorophyll a were observed. However, methyl and ethyl nitrate were well correlated in both the air and seawater, which suggests a common source. Calculations based on these observations estimate median saturation anomalies of –40% (–95 to 220%) for methyl nitrate and –11% (–98 to 174%) for ethyl nitrate. Positive saturation anomalies were spatially patchy, which suggests that some methyl and ethyl nitrate production was taking place in isolated areas of the study region. Overall our negative median saturation anomaly values suggest that during late austral spring (2004) the region of the Southern Ocean in which our measurements were made was not a net source of methyl or ethyl nitrate to the atmosphere. These results reinforce previous findings which suggest that whilst the equatorial ocean is a major source of methyl and ethyl nitrates to the atmosphere, higher latitude waters are generally at equilibrium or under-saturated. More measurements are required to assess how representative our results are of other areas of the Southern Ocean.
Additional keywords: biogeochemistry, ozone, trace gases.
Acknowledgements
This work was supported by a Natural Environmental Research Council (NERC) grant (NER/G/S/2003/00024, Liss) awarded as part of the Antarctic Funding Initiative (AFI). The authors would like to acknowledge the help and support of the captain and crew of RRS James Clark Ross crusie JR124, and the assistance of the AFI coordinator Martin Miller.
[1]
E. Atlas ,
W. Pollock ,
J. Greenberg ,
L. Heidt ,
Alkyl nitrates, nonmethane hydrocarbons, and halocarbon gases over the equatorial Pacific Ocean during SAGA 3.
J. Geophys. Res. 1993
, 98, 16933.
| Crossref |
[2]
N. J. Blake ,
D. R. Blake ,
A. L. Swanson ,
E. Atlas ,
F. Flocke ,
F. Sherwood Rowland ,
Latitudinal, vertical, and seasonal variations of C1–C4 alkyl nitrates in the troposphere over the Pacific Ocean during PEM-Tropics A and B: Oceanic and continental sources.
J. Geophys. Res. 2003
, 108, 8242.
| Crossref | GoogleScholarGoogle Scholar |
[3]
A. L. Chuck ,
S. M. Turner ,
P. S. Liss ,
Direct evidence for a marine source of C1 and C2 alkyl nitrates.
Science 2002
, 297, 1151.
| Crossref | GoogleScholarGoogle Scholar | PubMed |
[4]
E. E. Dahl ,
S. A. Yvon-Lewis ,
E. S. Saltzman ,
Saturation anomalies of alkyl nitrates in the tropical Pacific Ocean.
Geophys. Res. Lett. 2005
, 32, L20817.
| Crossref | GoogleScholarGoogle Scholar |
[5]
N. J. Blake ,
D. R. Blake ,
O. W. Wingenter ,
B. C. Sive ,
C. H. Kang ,
D. C. Thornton ,
A. R. Bandy ,
E. Atlas ,
F. Flocke ,
J. M. Harris ,
F. Sherwood Rowland ,
Aircraft measurements of the latitudinal, vertical, and seasonal variations of NMHCs, methyl nitrate, and methyl halides during ACE-1.
J. Geophys. Res. 1999
, 104, 21803.
| Crossref | GoogleScholarGoogle Scholar |
[6]
A. E. Jones ,
R. Weller ,
A. Minikin ,
S. Wolff ,
W. T. Sturges ,
H. P. McIntyre ,
S. R. Leonard ,
O. Schrems ,
S. Bauguitte ,
Oxidized nitrogen chemistry and speciation in the Antarctic troposphere.
J. Geophys. Res. 1999
, 104, 21355.
| Crossref | GoogleScholarGoogle Scholar |
[7]
R. Fischer ,
R. Weller ,
H.-W. Jacobi ,
K. Ballschmiter ,
Levels and patterns of volatile organic nitrates and halocarbons in the air at Neumayer Station (70°S), Antarctica.
Chemosphere 2002
, 48, 981.
| Crossref | GoogleScholarGoogle Scholar | PubMed |
[8]
C. Atherton ,
Organic nitrates in remote marine environments: evidence for long-range transport.
Geophys. Res. Lett. 1989
, 16, 1289.
| Crossref |
[9]
R. M. Moore ,
N. V. Blough ,
A marine source of methyl nitrate.
Geophys. Res. Lett. 2002
, 29, 1737.
| Crossref | GoogleScholarGoogle Scholar |
[10]
E. E. Dahl ,
E. S. Saltzman ,
W. J. Bruyn ,
The aqueous phase yield of alkyl nitrates from ROO+NO: Implications for photochemical production in seawater.
Geophys. Res. Lett. 2003
, 30, 1271.
| Crossref | GoogleScholarGoogle Scholar |
