Microbial iron reduction and greenhouse gas production in response to organic matter amendment and temperature increase of periglacial sediments, Bolterdalen, Svalbard

Arctic permafrost soils store substantial reserves of organic matter (OM) from which microbial transformation contributes significantly to greenhouse gas emissions of CH4 and CO2. However, many younger sediments exposed by glacier retreat and sea level change in fjord landscapes lack significant organic carbon resources, so their capacity to promote greenhouse gas emissions is unclear. We therefore studied the effects of increased temperatures (4°C and 21°C) and OM on rates of Fe(III) reduction, CO2 production, and methanogenesis in three different Holocene sedimentary units from a single site within the former marine limit of Adventdalen, Svalbard. Higher temperature and OM addition generally stimulated CH4 production and CO2 production and an increase in Bacteria and Archaea abundance in all units, whereas an equal stimulation of Fe(II) production by OM amendment and an increase in temperature to 21°C was only observed in a diamicton. We observed an accumulation of Fe(II) in beach and delta deposits as well but saw no stimulating effect of additional OM or increased temperature. Interestingly, we observed a small but significant production of CH4 in all units despite the presence of large reservoirs of Fe(III), sulfate, and nitrate, indicating either the availability of substrates that are primarily used by methanogens or a tight physical coupling between fermentation and methanogenesis by direct electron transfer. Our study clearly illustrates a significant challenge that comes with the large heterogeneity on a narrow spatial scale that one encounters when studying soils that have complex histories.publishedVersio

Evaluation of signal mode characteristics near the MOF for the purposes of the over-the-horizon radar

© 2019 IEEE. A comparative assessment of the characteristics of the upper and lower rays near the MOF is carried out. The method of oblique sounding of ionosphere by the chirp signals was used and paths of various lengths were used. It is shown that there are frequencies near the MOF which amplitudes of signals of the upper and lower rays are comparable. The difference between the times of group propagation is in the range of ∼ 40-460 μs, which corresponds to the range of distances of ∼ 15-140 km

Evaluation of signal mode characteristics near the MOF for the purposes of the over-the-horizon radar

© 2019 IEEE. A comparative assessment of the characteristics of the upper and lower rays near the MOF is carried out. The method of oblique sounding of ionosphere by the chirp signals was used and paths of various lengths were used. It is shown that there are frequencies near the MOF which amplitudes of signals of the upper and lower rays are comparable. The difference between the times of group propagation is in the range of ∼ 40-460 μs, which corresponds to the range of distances of ∼ 15-140 km

Study of daily variation of coefficient of paths extension by oblique sounding with the Russian chirp network of ionosphere monitoring

© 2019 IEEE. The results of an experimental study of the extension coefficient of HF radio paths of various lengths and geographical orientations using an oblique sounding continuous chirp signal are presented. The results obtained, together with characteristics of means of oblique sounding and a corrected ionosphere model, make it possible to increase the accuracy of recording the coordinates of aerial targets detected by the OTHR

Study of daily variation of coefficient of paths extension by oblique sounding with the Russian chirp network of ionosphere monitoring

© 2019 IEEE. The results of an experimental study of the extension coefficient of HF radio paths of various lengths and geographical orientations using an oblique sounding continuous chirp signal are presented. The results obtained, together with characteristics of means of oblique sounding and a corrected ionosphere model, make it possible to increase the accuracy of recording the coordinates of aerial targets detected by the OTHR