A process-based, climate-sensitive model to derive methane emissions from natural wetlands: application to 5 wetlands sites, sensitivity to model parameters and climate

Methane emissions from natural wetlands constitutes the largest methane source at present and depends highly on the climate. In order to investigate the response of methane emissions from natural wetlands to climate variations, a 1-dimensional process-based climate-sensitive model to derive methane emissions from natural wetlands is developed. In the model the processes leading to methane emission are simulated within a 1-dimensional soil column and the three different transport mechanisms diffusion, plant-mediated transport and ebullition are modeled explicitly. The model forcing consists of daily values of soil temperature, water table and net primary productivity, and at permafrost sites the thaw depth is included. The methane model is tested using observational data obtained at 5 wetland sites located in North America, Europe and Central America, representing a large variety of environmental conditions. It can be shown that in most cases seasonal variations in methane emissions can be explained by the combined effect of changes in soil temperature and the position of the water table. Our results also show that a process-based approach is needed, because there is no simple relationship between these controlling factors and methane emissions that applies to a variety of wetland sites. The sensitivity of the model to the choice of key model parameters is tested and further sensitivity tests are performed to demonstrate how methane emissions from wetlands respond to climate variations. (orig.)76 refs.Available from TIB Hannover: RR 1347(293) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Possible changes of #delta#"1"8O in precipitation caused by a meltwater event in the North Atlantic

The latest version of the Hamburg atmosphere general circulation model ECHAM-4 is used to investigate how a meltwater event in the North Atlantic might alter the signal of stable water isotopes (H_2"1"8O, HDO) in precipitation. Our results show that such a meltwater event will cause significant changes in the isotopic composition of the precipitation over many parts of the Northern Hemisphere, but also in the tropical Atlantic region. Model simulations suggest that for such a scenario isotope anomalies are not always related to temperature changes, but also to changes in the seasonality of precipitation or the precipitation amount. A changed isotopic composition of evaporating ocean surface waters (caused by a massive meltwater input into the North Atlantic) causes temperature-independent isotope anomalies, too. Changes of the deuterium excess are even more affected by the imposed oceanic isotope anomaly due to the nonlinearity of the evaporation process. (orig.)20 refs.SIGLEAvailable from TIB Hannover: RR 1347(294) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Borehole versus isotope temperatures on Greenland: seasonality does matter

New simulations results of the Hamburg Atmosphere General Circulation Model ECHAM-4 under maximum glacial boundary (LGM) conditions confirm the paleo-temperatures on Greenland determined by borehole thermometry. The disagreement between #delta#"1"8O isotope based temperatures and the borehole temperatures of the LGM is not only reproduced by the model but the simulation results provide a plausible explanation: Paleo-temperatures inferred from #delta#"1"8O measurements in ice cores are biased by a substantially increased seasonality of precipitation over Greenland during the LGM. During the glacial winter a much more zonal circulation prevents the effective transport of moisture to the Greenland ice sheet and therefore reduces the contribution of isotopically strongly depleted winter snow to the annual mean isotope signal. (orig.)SIGLEAvailable from TIB Hannover: RR 1347(295) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman