2. List of the measurements performed at Mace Head:

3. The CO2 and Radon in-situ data performed by LSCE are available on: www.ipsl.jussieu.fr/services/Observations/fr/RAMCES.htm AGAGE continuous time series are available on: NOAA/CMDL data obtained from the weekly flask samples are available on: www.cmdl.noaa.gov/ccgg/

4. CO2 is measured continuously at Mace Head since 1992 with a non-dispersive infra-red analyzer. Each point represents an hourly average calculated from one observation per second. The instrument is calibrated against a suite of five high pressure tanks filled in with known CO2 mixing ratio. These five tanks have been calibrated at LSCE in agreement with the international reference scale from the World Meteorological Organisation (WMO).

5. The short term CO 2 variability observed at Mace Head depends on the origin of the air masses. In oceanic conditions the CO 2 concentration is very stable. When continental air masses are sampled we observe short term variability which relate to the local and regional carbon sources (both anthropogenic and biospheric). We have developped a scheme to classify each hourly mean as representative of either oceanic or continental air mass. This data selection scheme is based on local meteorological information, and on the hourly CO 2 standard deviation. Separation of continental and marine air masses

6. Different origin of the air mass...delivers different CO 2 signals. marine continental

7. From the continuous CO 2 time series we deduce two dataset which are representative of oceanic and continental air masses. In the continental dataset the objective is to select only episodes which are representative of large scale carbon fluxes. The two selected dataset represent on average 30% and 10% of the complete time series respectively. They are both distributed to the international data centers. The remaining part of the time series represents the data which are representative of local events. These local data have for example been used by Biraud et al., 2002 to calculate the CO 2 emissions from Ireland.

9. The seasonal cycles infer from the two Mace Head dataset (oceanic and continental) are significantely different. In the middle figure on the next page we have subtracted from each time series the reference marine boundary layer values (those values are calculated from the marine site part of the global monitoring network). We observe a systematic offset between the two time series at Mace Head, with higher CO 2 mixing ratios in the continental time serie (CBC) compared to the marine time series (RBC). This offset is due to the CO 2 emissions in Europe. It is maximum in wintertime because in addition to the emissions from human activities, at this time of the year the biosphere also acts as a net source of CO 2. In the RBC-Marine Boundary layer time serie we observe two CO2 minimum in Spring and Autumn. This signal indicate that the North Atlantic represent a strong carbon sink at these periods. This seems confirmed by the air/sea fluxes deduced from oceanic data sets obtained from scientific cruises.