Vom inneren Schelf zur Tiefsee: Ablagerungsräume am Westrand der antarktischen Halbinsel

Aim of this study was to describe and characterize three typical West Antarctic Peninsula continental margin depositional environments. Seismic, downhole and laboratory tools and techniques were applied to record physical and chemical proxies for a mulifacetted and differenciated understanding of the particular environments. 1) A detailed seismostratigraphic characterisation of the unique Antarctic inner and outer shelf along the passive margin of the West Antarctic Peninsula has been complemented by logging informations that are tied to the seismic profiles via a new continuous depth vs. velocity profile. Sealevel fall overcompensated by increased isostatic subsidence due to ice build-up that affected the continent and the adjacent shelfs is the most likely explanation for time synchronous start of topset preservation at ~2.8 Ma observed in Antarctic Peninsula and East Antarctic shelf records in conjunction with Nothern Hemnisphere Glaciation. 2) Seismostratigraphic Model of Palmer Deep based on seismic Deep Tow Boomer records. 3) Large mounts on the continental rise along the Antarctic Peninsula margin between 63°S and 69°S and within 200 km of the shelf break are interpreted as sediment drifts, separated by turbidity current channels. Using a special standardized moving window counting routine the spatial facies information data has been transformed into a regional Antarctic Peninsula ice volume indicator curve that is in good agreement with the Lear et al., 2000 data over the past 10 Ma. This regional ice volume curve for the Antarctic Peninsula is the most significant finding of this thesis. All evaluated proxy data prove that the early Pliocene was a time of reduced global- and Antarctic ice volume (-70%) and sea ice extent. Never before and after during the last 10 Ma was palaeo productivity higher at the rise than during this time. During the late Miocene the ice sheet was highly dynamic with frequent advances and retreats. Starting at 3.2 Ma in concert with the Northern Hemisphere Glaciation the ice sheet became a permanent feature occupying the shelf during most of the glacial half cycles

Nearly diffraction limited FTIR mapping using an ultrastable broadband femtosecond laser tunable from 1.33 to 8 µm

Micro-Fourier-transform infrared (FTIR) spectroscopy is a widespread technique that enables broadband measurements of infrared active molecular vibrations at high sensitivity. SiC globars are often applied as light sources in tabletop systems, typically covering a spectral range from about 1 to 20 µm (10 000 - 500 cm−1) in FTIR spectrometers. However, measuring sample areas below 40x40 µm2 requires very long integration times due to their inherently low brilliance. This hampers the detection of ultrasmall samples, such as minute amounts of molecules or single nanoparticles. In this publication we extend the current limits of FTIR spectroscopy in terms of measurable sample areas, detection limit and speed by utilizing a broadband, tabletop laser system with MHz repetition rate and femtosecond pulse duration that covers the spectral region between 1250 - 7520 cm−1 (1.33 - 8 µm). We demonstrate mapping of a 150x150 µm2 sample of 100 nm thick molecule layers at 1430 cm−1 (7 µm) with 10x10 µm2 spatial resolution and a scan speed of 3.5 µm/sec. Compared to a similar globar measurement an order of magnitude lower noise is achieved, due to an excellent long-term wavelength and power stability, as well as an orders of magnitude higher brilliance

Rainfall threshold for initiating effective stress decrease and failure in weathered tephra slopes

Rainfall is one of the most important triggers of slope failure. Weathered pyroclastic (tephra) deposits are especially vulnerable to slope failure because they commonly form slopes of high porosity and high clay content. Empirically derived thresholds for the triggering of landslides are commonly based on rainfall conditions and have been widely applied in volcanic soils. However, so far only few researchers utilized pore water pressure in the slope as additional variable for the threshold calibration. Here, we derived a new rainfall threshold for initiating the decrease in effective stress in the slope by analyzing a long-term record of rainfall and piezometer data from a slide-prone coastal area in northern New Zealand that consists of clayey, halloysitic tephra deposits. The level of effective stress decrease increased with rainfall intensity and duration. We observed highest effective stress decrease of up to 36% during rainfall events that triggered landslides in our study area. The effective stress threshold exhibits a satisfactory predictive capability. The probability of correctly predicting a decrease in effective stress is 53%. The effective stress threshold contributes towards the implementation of the decrease in effective stress into rainfall thresholds for the occurrence of landslides

A new attraction-detachment model for explaining flow sliding in clay-rich tephras

Altered pyroclastic (tephra) deposits are highly susceptible to landsliding, leading to fatalities and property damage every year. Halloysite, a low-activity clay mineral, is commonly associated with landslide-prone layers within altered tephra successions, especially in deposits with high sensitivity, which describes the post-failure strength loss. However, the precise role of halloysite in the development of sensitivity, and thus in sudden and unpredictable landsliding, is unknown. Here we show that an abundance of mushroom cap–shaped (MCS) spheroidal halloysite governs the development of sensitivity, and hence proneness to landsliding, in altered rhyolitic tephras, North Island, New Zealand. We found that a highly sensitive layer, which was involved in a flow slide, has a remarkably high content of aggregated MCS spheroids with substantial openings on one side. We suggest that short-range electrostatic and van der Waals interactions enabled the MCS spheroids to form interconnected aggregates by attraction between the edges of numerous paired silanol and aluminol sheets that are exposed in the openings and the convex silanol faces on the exterior surfaces of adjacent MCS spheroids. If these weak attractions are overcome during slope failure, multiple, weakly attracted MCS spheroids can be separated from one another, and the prevailing repulsion between exterior MCS surfaces results in a low remolded shear strength, a high sensitivity, and a high propensity for flow sliding. The evidence indicates that the attraction-detachment model explains the high sensitivity and contributes to an improved understanding of the mechanisms of flow sliding in sensitive, altered tephras rich in spheroidal halloysite