Christin Hilbich

Reconstruction of the Depositional History of the Former Coastal Lagoon of Vilamoura (Algarve, Portugal): A Sedimentological, Microfaunal and Geophysical Approach

Abstract The late Holocene evolution of the former coastal lagoon of Vilamoura was reconstructed according to sediment cores and geophysical profiles. According to sedimentological analyses of the cores, five palaeoenvironmental stages were defined. (1) The pretransgression stage is represented by an erosive surface formed during incision of the river into the basement because of a lower sea level. This palaeosurface was retraced by refraction seismic profiles, showing that the marine transgression took place on a wide plain with several incised channels. (2) The development of an estuary started by transgression into the river valley corresponding to the postglacial sea level rise. Radiocarbon dating indicates a sea level not lower than −4 m at a minimum age of 4716 ± 72 Cal BP. After the transgressive maximum, infilling of the estuary started, beginning with (3) subtidal infilling related to the formation of a sandy barrier followed by (4) supratidal infilling with further accretion of the barrier, changing the previous open bay into a coastal lagoon. (5) Finally, the lagoon was fluvially filled with terrestrial sediments, changing the marine to a fluvial milieu with floodplain deposition. Analysis of benthic foraminiferal and ostracod assemblages revealed additional information about the environmental conditions during evolution of the estuary, which led to a further subdivision of the marine facies into stages with mainly estuarine, lagoonal, or marine influence. The end of the marine stage was dated at 2895 ± 48 Cal BP, indicating a pre-Roman onset of human-induced soil erosion.

Soil Moisture Data for the Validation of Permafrost Models Using Direct and Indirect Measurement Approaches at Three Alpine Sites

In regions affected by seasonal and permanently frozen conditions soil moisture influences the thermal regime of the ground as well as its ice content, which is one of the main factors controlling the sensitivity of mountain permafrost to climate changes. In this study, several well established soil moisture monitoring techniques were combined with data from geophysical measurements to assess the spatial distribution and temporal evolution of soil moisture at three high elevation sites with different ground properties and thermal regimes. The observed temporal evolution of measured soil moisture is characteristic for sites with seasonal freeze/thaw cycles and consistent with the respective site-specific properties, demonstrating the general applicability of continuous monitoring of soil moisture at high elevation areas. The obtained soil moisture data were then used for the calibration and validation of two different model approaches in permafrost research in order to characterize the lateral and vertical distribution of ice content in the ground. Calibration of the geophysically based four-phase model (4PM) with spatially distributed soil moisture data yielded satisfactory two dimensional distributions of water-, ice- and air content. Similarly, soil moisture time series significantly improved the calibration of the one-dimensional heat and mass transfer model COUP, yielding physically consistent soil moisture and temperature data matching observations at different depths.

Multi-methodological reconstruction of the lake level at Morgarten in the context of the history of the Swiss Confederation

In AD 1315, the Habsburgs fought against the Swiss Confederation at Morgarten. Since historical records are very limited, the battle has been the subject of very controversial discussions. Its location and outcome seem likely to have been influenced by the landscape and the size of the Aegeri lake, but only sparse and contradictory information are available. Numerical, semi-quantitative and relative dating techniques were applied to reconstruct the lake’s dimensions and the landscape. Results obtained from radiocarbon dating of mires (last sedimentation phase of the lake), geomorphic mapping, geoelectrics, soil maps (surface age indication) and archaeological findings were pieced together and gave an astonishingly good consensus. In the Lateglacial, the lake level was higher (750–760 m a.s.l.): because of a catastrophic event, it decreased by 25 m. About 5500 BP, the lake level was at 732 m a.s.l., and since the Roman period, it has varied between 724 and 727 m a.s.l. At the time of the battle the lake was at 726 m – that is, about 2 m higher than today. Together with the cooler climate, the greater extension of the fens and larger lake, the valley floor was wet and unpleasant. If a Habsburg army had to cross this region, they would likely have preferred to walk on a more accessible trail along the footslopes (where they probably were attacked). Precise landscape reconstruction provides new input for historical research. Details about the exact location of the battle, however, remain unclear, and the myth of the battle at Morgarten persists.

Analysis Procedures of an ERT Monitoring Network to Assess Mountain Permafrost Degradation Rate

A long-term ERT monitoring network of mountain permafrost in the Swiss Alps allows the detection of ground ice changes. It enables to compare sites of diverse landforms which are characterized by various ground properties. Electrical resistivity is highly sensitive to unfrozen water content present in the pores and to a lesser extent to temperature change. Data quality assessment of the six sites of the ERT monitoring network involves grounding resistance analysis as well as automatic filtering procedures. The combined analysis of borehole temperature and resistivity dataset reveals spatio-temporal ground property changes. This long-term monitoring network enables e.g. to characterize the extent of permafrost thaw and/or melt of ground ice at Schilthorn, to a lesser extent at Stockhorn, and no or very small changes at rock glacier Murtel.