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| Titel |
Greenhouse gases in the South Atlantic Ocean: recent trends and anomalies from continuous island and shipboard measurements |
| VerfasserIn |
David Lowry, Rebecca Fisher, Mathias Lanoisellé, James France, Euan Nisbet |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250082985
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| Zusammenfassung |
| In-situ observation of tropical and southern Atlantic greenhouse gases is still limited.
Continuous high-precision greenhouse gas measurement by CRDS in the South Atlantic
started in 2010 on Ascension Is. (8Ë S) and near Stanley on East Falkland Is. (52Ë S), and in
2012 on the British Antarctic Survey ship RRS James Clark Ross, which sails annually from
the UK to Antarctica and back. Both the Ascension and Falklands records show sustained
inter-annual growth in both CO2 and CH4. NOAA data from a small number of stations
indicate that Southern Tropical Methane has been increasing since 2007 but that growth is
now slowing. This is confirmed by our new data. Strong CH4 growth of 11 ppb was observed
on Ascension between July 2010 and July 2011 (winter to winter), of 7 ppb/yr from Jan 2011
to Jan 2012 (summer-to-summer) and decreased further to 4 ppb from July 2011 to July
2012. This compares with a fairly constant growth of 4-5 ppb/yr for the Falklands
site.
Isotopic evidence for the causes of the 2010-11 southern hemisphere sub-tropical
methane anomaly is inconclusive. A slight depletion in 13C on Ascension during the period
of growth might indicate that wetland emissions are the dominant cause of the anomaly,
fitting with much higher than average sub-tropical rainfall during recent years,
but a much longer data set is required to isolate the anomaly from the long-term
trend.
On 23 April 2011, Ascension experienced a 20-year event when the ITCZ moved far
south of its normal position. In very clean marine air, in the space of 3 minutes the methane
jumped from a normal autumn southern hemisphere level of 1763 ppb to 1795 ppb, closer to
the concentrations of northern hemisphere spring, settling near to 1800 ppb for six
hours, after which it rapidly fell back to 1760 ppb. Simultaneously CO2 rose from
389 to about 392 ppm, then to 396 ppm before falling back to 388 ppm. During
this period there was very heavy rainfall, with nearly 300 mm on the slopes of
Green Mountain and more than 200 mm in surrounding desert areas. The 35 ppb
magnitude of this methane switch compares with a magnitude of 55 ppb (1825 to
1770 ppb) observed by continuous measurement on-board the James Clark Ross
when crossing the ITCZ from 8Ë N to 8Ë S in October 2010. In this event, high
altitude Northern hemisphere air was moving SE over NW moving trade winds
until the storm brought high level air to ground level. The observations highlight
the usefulness of continuous measurement at such a site and demonstrate that the
meteorological boundary between the hemispheres can on occasion be very sharp. |
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