Results from air sampling
Methane
At Neumayer, methane mixing ratio has been measured on high-volume air samples since 1986 and on flask samples since 1994 by the IUP-Heidelberg (PI: Ingeborg Levin). Methane increased (globally) by approximately 100 ppb over the last 25 years. Interestingly, the growth rate decreased continuously from about 10-15 ppb 1/yr in the 1980s to about 5 ppb 1/yr in the 1990s and finally fluctuates around zero since about the year 2000 but rising again afterward. This trend in the CH4 growth rate indicates that, between 2000 and 2007, the sources of this greenhouse gas approach an equilibrium with its sinks (photochemical oxidation). Not yet finally clarified, increasing emissions associated with growing population agriculture and energy demand, possibly caused increase methane concentrations after 2007 again in both hemispheres. The distinct sinusoid like seasonal cycle of methane with minimum mixing ratios during austral summer is caused by the seasonality of the photochemical CH4 oxidation
Carbon dioxide
Whole air samples to determine long-term concentration trends of greenhouse gases and their isotopic composition are taken by the IUP-Heidelberg (PI: Ingeborg Levin). The long-term increase of CO2, caused by an ongoing input of CO2 from fossil fuel burning and land-use change into the atmosphere, was almost linear over the last decade (growth rate 1.8 ppm 1/yr), however, large inter-annual variations are obvious. For example in 1997/98 during a strong El Niño period a positive CO2 anomaly was observed which is accompanied by a significant decrease of delta 13C-CO2, indicating unusually large continental biogenic CO2 emissions during this period.
14CO2 samples were collected atNeumayer since 1983. The long-term Δ14C decrease observed is mainly caused by oceanic uptake of bomb 14CO2 and by the ongoing in put of 14C-free fossil fuel CO2 into the atmosphere. The Neumayer Δ14CO2 level was slightly lower than that at Jungfraujoch (47°N) in the early years, due to the strong 14CO2 disequilibrium flux between the atmosphere and circum-Antarctic surface ocean water. However, in the last five years the north-south difference has changed sign as 14C-free fossil fuel CO2 emissions are steadily increasing in particular in the northern hemisphere.
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Sulphur hexafluoride
Global observations of tropospheric SF6: Symbols and left axis: Atmospheric SF6 mixing ratios (given in ppt = parts per trillion, i.e. pico moles of SF6 per mole of dry air) observed in the Northern and Southern Hemispheres. The overlapping flask and cylinder data from Neumayer are virtually indistinguishable. Lines and right axis: SF6 growth rates calculated from de-seasonalized measurements.
Sulfur hexafluoride (SF6) is almost exclusively emitted into the atmosphere by man and mainly used in electric switch gear and for degassing molten reactive metals. Due to its extremely long atmospheric life time of more than 1000 years, almost all SF6 remains in the atmosphere. Consequently, starting around 1970, mixing ratios persistently increased by several percent per year during the last three decades. The linear trend observed over the last decade indicates a virtually constant emission rate since 1995. Sulfur hexafluoride is also an excellent tracer to validate atmospheric transport models as the distribution of its sources is well known and mainly restricted to the Northern Hemisphere. From the well-established north-south difference of SF6 mixing ratios, a mean inter-hemispheric exchange time of 1 to 1.5 years can be deduced.
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