Impact of a potential 21st century “grand solar minimum” on surface temperatures and stratospheric ozone

We investigate the effects of a recently proposed 21st century Dalton minimum like decline of solar activity on the evolution of Earth's climate and ozone layer. Three sets of two member ensemble simulations, radiatively forced by a midlevel emission scenario (Intergovernmental Panel on Climate Change RCP4.5), are performed with the atmosphere-ocean chemistry-climate model AOCCM SOCOL3-MPIOM, one with constant solar activity, the other two with reduced solar activity and different strength of the solar irradiance forcing. A future grand solar minimum will reduce the global mean surface warming of 2 K between 1986–2005 and 2081–2100 by 0.2 to 0.3 K. Furthermore, the decrease in solar UV radiation leads to a significant delay of stratospheric ozone recovery by 10 years and longer. Therefore, the effects of a solar activity minimum, should it occur, may interfere with international efforts for the protection of global climate and the ozone layer.

Highly accurate isotope composition measurements by a miniature laser ablation mass spectrometer designed for in situ investigations on planetary surface

An experimental procedure for precise and accurate measurements of isotope abundances by a miniature laser ablation mass spectrometer for space research is described. The measurements were conducted on different untreated NIST standards and galena samples by applying pulsed UV laser radiation (266 nm, 3 ns and 20 Hz) for ablation, atomisation, and ionisation of the sample material. Mass spectra of released ions are measured by a reflectron-type time-of-flight mass analyser. A computer controlled performance optimiser was used to operate the system at maximum ion transmission and mass resolution. At optimal experimental conditions, the best relative accuracy and precision achieved for Pb isotope compositions are at the per mill level and were obtained in a range of applied laser irradiances and a defined number of accumulated spectra. A similar relative accuracy and precision was achieved in the study of Pb isotope compositions in terrestrial galena samples. The results for the galena samples are similar to those obtained with a thermal ionisation mass spectrometer (TIMS). The studies of the isotope composition of other elements yielded relative accuracy and precision at the per mill level too, with characteristic instrument parameters for each element. The relative accuracy and precision of the measurements is degrading with lower element/isotope concentration in a sample. For the elements with abundances below 100 ppm these values drop to the percent level. Depending on the isotopic abundances of Pb in minerals, 207Pb/206Pb ages with accuracy in the range of tens of millions of years can be achieved.

Isotopic effects of nitrate photochemistry in snow: a field study at Dome C, Antarctica

Stable isotope ratios of nitrate preserved in deep ice cores are expected to provide unique and valuable information regarding paleoatmospheric processes. However, due to the post-depositional loss of nitrate in snow, this information may be erased or significantly modified by physical or photochemical processes before preservation in ice. We investigated the role of solar UV photolysis in the post-depositional modification of nitrate mass and stable isotoperatios at Dome C, Antarctica, during the austral summer of 2011/2012. Two 30 cm snow pits were filled with homogenized drifted snow from the vicinity of the base. One of these pits was covered with a plexiglass plate that transmits solar UV radiation, while the other was covered with a different plexiglass plate having a low UV transmittance. Samples were then collected from each pit at a 2–5 cm depth resolution and a 10-day frequency. At the end of the season, acomparable nitrate mass loss was observed in both pits for the top-level samples (0–7 cm) attributed to mixing with the surrounding snow. After excluding samples impacted by the mixing process, we derived an average apparent nitrogen isotopic fractionation (15" app/of role in driving the isotopic fractionation of nitrate in snow.We have estimated a purely photolytic nitrogen isotopic fractionation (15"photo) of -55.8 12.0 ‰ from the difference in the derived apparent isotopic ractionations of the two experimental fields, as both pits were exposed to similar physical processes except exposure to solar UV. This value is in close agreement with the 15" photo value of -47.9 6.8 ‰ derived in a laboratory experiment simulated for Dome C conditions (Berhanu et al., 2014). We have also observed an insensitivity of 15" with depth in the snowpack under the given experimental setup. This is due to the uniform attenuation of incoming solar UV by snow, as 15" is strongly dependent on the spectral distribution of the incoming light flux. Together with earlier work, the results presented here represent a strong body of evidence that solar UV photolysis is the most relevant post-depositional process modifying the stable isotope ratios of snow nitrate at low-accumulation sites, where many deep ice cores are drilled. Nevertheless, modeling the loss of nitrate in snow is still required before a robust interpretation of ice core records can be provided.