TY - THES A1 - Köhler, Torsten T1 - Effiziente Algorithmen für die Optimierung der Therapie-Planung zur regionalen Hyperthermie Y1 - 1998 CY - Potsdam ER - TY - BOOK A1 - Köhler, Torsten T1 - Zur Antennensteuerung bei der Hyperthermie-Behandlung T3 - Preprint / Universität Potsdam, Institut für Mathematik Y1 - 1996 VL - 1996, 12 PB - Univ. CY - Potsdam ER - TY - JOUR A1 - Pirli, Myrto A1 - Hainzl, Sebastian A1 - Schweitzer, Johannes A1 - Köhler, Andreas A1 - Dahm, Torsten T1 - Localised thickening and grounding of an Antarctic ice shelf from tidal triggering and sizing of cryoseismicity JF - Earth & planetary science letters N2 - We observe remarkably periodic patterns of seismicity rates and magnitudes at the Fimbul Ice Shelf, East Antarctica, correlating with the cycles of the ocean tide. Our analysis covers 19 years of continuous seismic recordings from Antarctic broadband stations. Seismicity commences abruptly during austral summer 2011 at a location near the ocean front in a shallow water region. Dozens of highly repetitive events occur in semi-diurnal cycles, with magnitudes and rates fluctuating steadily with the tide. In contrast to the common unpredictability of earthquake magnitudes, the event magnitudes show deterministic trends within single cycles and strong correlations with spring tides and tide height. The events occur quasi-periodically and the highly constrained event sources migrate landwards during rising tide. We show that a simple, mechanical model can explain most of the observations. Our model assumes stick-slip motion on a patch of grounded ice shelf, which is forced by the variations of the ocean-tide height and ice flow. The well fitted observations give new insights into the general process of frictional triggering of earthquakes, while providing independent evidence of variations in ice shelf thickness and grounding. KW - tidally modulated cryogenic seismicity KW - stick-slip motion KW - event recurrence predictability KW - ice-shelf thickness KW - ice-shelf grounding KW - East Antarctica Y1 - 2018 U6 - https://doi.org/10.1016/j.epsl.2018.09.024 SN - 0012-821X SN - 1385-013X VL - 503 SP - 78 EP - 87 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Koebsch, Franziska A1 - Winkel, Matthias A1 - Liebner, Susanne A1 - Liu, Bo A1 - Westphal, Julia A1 - Schmiedinger, Iris A1 - Spitzy, Alejandro A1 - Gehre, Matthias A1 - Jurasinski, Gerald A1 - Köhler, Stefan A1 - Unger, Viktoria A1 - Koch, Marian A1 - Sachs, Torsten A1 - Böttcher, Michael E. T1 - Sulfate deprivation triggers high methane production in a disturbed and rewetted coastal peatland JF - Biogeosciences N2 - In natural coastal wetlands, high supplies of marine sulfate suppress methanogenesis. Coastal wetlands are, however, often subject to disturbance by diking and drainage for agricultural use and can turn to potent methane sources when rewetted for remediation. This suggests that preceding land use measures can suspend the sulfate-related methane suppressing mechanisms. Here, we unravel the hydrological relocation and biogeochemical S and C transformation processes that induced high methane emissions in a disturbed and rewetted peatland despite former brackish impact. The underlying processes were investigated along a transect of increasing distance to the coastline using a combination of concentration patterns, stable isotope partitioning, and analysis of the microbial community structure. We found that diking and freshwater rewetting caused a distinct freshening and an efficient depletion of the brackish sulfate reservoir by dissimilatory sulfate reduction (DSR). Despite some legacy effects of brackish impact expressed as high amounts of sedimentary S and elevated electrical conductivities, contemporary metabolic processes operated mainly under sulfate-limited conditions. This opened up favorable conditions for the establishment of a prospering methanogenic community in the top 30-40 cm of peat, the structure and physiology of which resemble those of terrestrial organic-rich environments. Locally, high amounts of sulfate persisted in deeper peat layers through the inhibition of DSR, probably by competitive electron acceptors of terrestrial origin, for example Fe(III). However, as sulfate occurred only in peat layers below 30-40 cm, it did not interfere with high methane emissions on an ecosystem scale. Our results indicate that the climate effect of disturbed and remediated coastal wetlands cannot simply be derived by analogy with their natural counterparts. From a greenhouse gas perspective, the re-exposure of diked wetlands to natural coastal dynamics would literally open up the floodgates for a replenishment of the marine sulfate pool and therefore constitute an efficient measure to reduce methane emissions. Y1 - 2019 U6 - https://doi.org/10.5194/bg-16-1937-2019 SN - 1726-4170 SN - 1726-4189 VL - 16 IS - 9 SP - 1937 EP - 1953 PB - Copernicus CY - Göttingen ER -