Palaeoenvironmental record of glacial lake evolution during the early Holocene at Sokli,NE Finland

The development of a glacial lake impounded along the retreating, northeastern ice margin of the Fennoscandian Ice Sheet during the last deglaciation and environmental conditions directly following the early Holocene deglaciation have been studied in NE Finland. This so‐called Sokli Ice Lake has been reconstructed previously using topographic and geomorphologic evidence. In this paper a multiproxy approach is employed to study a 3‐m‐thick sediment succession consisting of laminated silts grading into gyttja cored in Lake Loitsana, a remnant of the Sokli Ice Lake. Variations in the sediment and siliceous microfossil records indicate distinct changes in water depth and lake size in the Loitsana basin as the Sokli Ice Lake was drained through various spillways opening up along the retreating ice front. Geochemical data (XRF core‐scanning) show changes in the influence of regional catchment geochemistry (Precambrian crystalline rocks) in the glacial lake drainage area versus local catchment geochemistry (Sokli Carbonatite Massif) within the Lake Loitsana drainage area during the lake evolution. Principal component analysis on the geochemical data further suggests that grain‐size is an additional factor responsible for the variability of the sediment geochemistry record. The trophic state of the lake changed drastically as a result of morphometric eutrophication once the glacial lake developed into Lake Loitsana. The AMS radiocarbon dating on tree birch seeds found in the glaciolacustrine sediment indicates that Lake Loitsana was deglaciated sometime prior to 10 700 cal. a BP showing that tree Betula was present on the deglaciated land surrounding the glacial lake. Although glacial lakes covered large areas of northern Finland during the last deglaciation, only few glaciolacustrine sediment successions have been studied in any detail. Our study shows the potential of these sediments for multiproxy analysis and contributes to the reconstruction of environmental conditions in NE Finland directly following deglaciation in the early Holocene.     

Grounding‐line dynamics during the last deglaciation of Kveithola,W Barents Sea,as revealed by seabed geomorphology and shallow seismic stratigraphy

A marine geophysical study reveals a complex deglaciation pattern in the Kveithola trough, W Barents Sea. The data set includes multibeam swath bathymetry and sub‐bottom sediment profiler (chirp) data acquired for the whole extent of a palaeo, marine‐terminating ice stream, along with high‐resolution single‐channel seismic data from chosen profiles. The multibeam data show a geomorphic landform assemblage characteristic of ice streams. The results of a combination of seismic and chirp unit stratigraphy reveal that the seabed geomorphology is governed by a deeper‐lying reflector. The reflector dominates surface expressions of several subglacial and ice‐marginal units, each connected to a separate episode of ice‐margin stillstand/advance. Analysis of the combined data set has resulted in a conceptual model of the ice‐stream retreat. The model depicts complex deglaciation of a small, confined ice‐stream system through episodic retreat. It describes the formation of several generations of grounding‐zone systems, characterized by high meltwater discharges and the deposition of fine‐grained grounding‐line fans. The inferred style of grounding‐zone deposition in Kveithola deviates from that of other accounts, and is suggested to be intermediate in the previously described continuum between morainal banks and grounding‐line wedges. The results of this paper have implications for grounding‐zone theory and should be of interest to modellers of grounding‐line dynamics and ice‐stream retreat.     

Thallium removal through adsorption onto ionic liquid-impregnated solid support: influence of the impregnation conditions

This article presents the use of ionic liquid in the removal process of thallium ions using solid–liquid extraction by impregnating ionic liquid (1-n-hexyl-3-methylimidazolium chloride) onto an inorganic solid support (Florisil). The influence of impregnation was studied in order to improve the adsorption capacity of the material obtained. Impregnation was realized with the help of a rotavapor. Stirring time and temperature used were varied. Ionic liquid-impregnated materials obtained at different conditions of impregnation were characterized using scanning electron microscopy, energy-dispersive X-ray analysis, and Fourier transform infrared spectroscopy. In order to determine the most efficient adsorbent material, the materials obtained were used in the removal process of thallium ions from aqueous solutions, varying the initial concentration of thallium ions and the stirring time used in the adsorption process. It was observed that for the improving the adsorption capacity of the obtained ionic liquid-impregnated material, it is not necessary to increase the stirring time of the impregnation process but to increase the temperature. The experimental data obtained in the adsorption process were fitted with the Langmuir isotherm. Adsorption of thallium ions onto Florisil impregnated with 1-n-hexyl-3-methylimidazolium chloride ionic liquid corresponds to a pseudo-second-order kinetic model.     

Scientific detector workshop 2022 on-sky performance verification of near-infrared e−APD technology for wavefront sensing and demonstration of e−APD pixel performance to improve the sensitivity of large science focal planes

Near-infrared adaptive optics as well as fringe tracking for coherent beam combination in optical interferometry require the development of high-speed sensors. Because of the high speed, a large analog bandwidth is required. The short exposure times result in small signal levels which require noiseless detection. Both requirements cannot be met by state-of-the-art conventional CMOS technology of near-infrared arrays as has been attempted previously. A total of five near-infrared SAPHIRA 320 × 256 pixel HgCdTe e⁻APD arrays have been deployed in the wavefront sensors and in the fringe tracker of the VLTI instrument GRAVITY. The current limiting magnitude for coherent exposures with GRAVITY is m_k = 19, which is made possible with ADP technology. New avalanche photo-diode array (APD) developments since GRAVITY include the extension of the spectral sensitivity to the wavelength range from 0.8 to 2.5 μm. After GRAVITY a larger format array with 512 × 512 pixels has been developed for both AO applications at the ELT and for long integration times. Since dark currents of <10⁻³ e⁻/s have been demonstrated with 1Kx1K e⁻APD arrays and 2Kx2K e⁻APD arrays have already been developed, the possibilities and adaptations of e⁻APD technology to provide noiseless large-format science-grade arrays for long integration times are also discussed.