ALBERT

Description: [1]  Glaciers are strongly retreating and thinning in Patagonia. We present new inferences about the climatic situation and the surface mass balance on the Northern Patagonia Icefield in the past and the future using a combined modeling approach. Thesimulations are driven by NCAR/NCEP Reanalysis and ECHAM5 data, which were physically downscaled using the Weather Research and Forecasting regional climate model and simple sub-grid parameterizations. The surface mass balance model was calibrated with geodetic mass balance data of three large non-calving glaciers and with point mass balance measurements. An increase of accumulation on the Northern Patagonia Icefield was detected from 1990-2011 as compared to 1975-1990. Using geodetic mass balance data, calving losses from the Northern Patagonia Icefield could be inferred which doubled in 2000-2009 as compared to 1975-2000. The 21st century projection of future mass balance of the Northern Patagonia Icefield shows a strong increase in ablation from 2050 on and a reduction of solid precipitation from 2080, both due to higher temperatures. The total mass loss in the 21th century is estimated to be 617 ± 50 Gt with strongly increasing rates towards the end of the century. The prediction of the future mass balance of the Northern Patagonia Icefield includes several additional sources of errors due to uncertainties in the prediction of future climate and due to possible variations in ice dynamics which might modify the geometry of theicefield and change the rate of mass losses due to calving.

Description: Isotope records of atmospheric CH4 can be used to infer changes in the biogeochemistry of CH4. One factor currently limiting the quantitative interpretation of such changes are uncertainties in the isotope measurements stemming from the lack of a unique isotope reference gas, certified for δ13C-CH4 or δ2H-CH4. We present a method to produce isotope reference gases for CH4 in synthetic air that are precisely anchored to the VPDB and VSMOW scales and have δ13C-CH4 values typical for the modern and glacial atmosphere. We quantitatively combusted two pure CH4 gases from fossil and biogenic sources and determined the δ13C and δ2H values of the produced CO2 and H2O relative to the VPDB and VSMOW scales within a very small analytical uncertainty of 0.04‰ and 0.7‰, respectively. We found isotope ratios of −39.56‰ and −56.37‰ for δ13C and −170.1‰ and −317.4‰ for δ2H in the fossil and biogenic CH4, respectively. We used both CH4 types as parental gases from which we mixed two filial CH4 gases. Their δ13C was determined to be −42.21‰ and −47.25‰ representing glacial and present atmospheric δ13C-CH4. The δ2H isotope ratios of the filial CH4 gases were found to be −193.1‰ and −237.1‰, respectively. Next, we mixed aliquots of the filial CH4 gases with ultrapure N2/O2 (CH4 ≤ 2 ppb) producing two isotope reference gases of synthetic air with CH4 mixing ratios near atmospheric values. We show that our method is reproducible and does not introduce isotopic fractionation for δ13C within the uncertainties of our detection limit (we cannot conclude this for δ2H because our system is currently not prepared for δ2H-CH4 measurements in air samples). The general principle of our method can be applied to produce synthetic isotope reference gases targeting δ2H-CH4 or other gas species.