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A promising profiling setup for in situ measurements in lakes with potentiometric solid-contact ion-selective electrodes (SC-ISEs) and a data processing method for sensor calibration and drift correction are presented. The profiling setup consists of a logging system, which is equipped with a syringe sampler and sensors for the measurement of standard parameters including temperature, conductivity, oxygen and photosynthetically active radiation (PAR). The setup was expanded with SC-ISEs in galvanically separated amplifiers. The potential for high-resolution profiling is investigated by deploying the setup in the eutrophic Lake Rotsee (Lucerne, Switzerland), using two different designs of ammonium sensing SC-ISEs. Ammonium was chosen as a target analyte, since it is the most common reduced inorganic nitrogen species involved in various pathways of the nitrogen cycle and is therefore indicative of numerous biogeochemical processes that occur in lakes such as denitrification and primary production. One of the designs, which uses a composite carbon-nanotube-PVC-based membrane, suffered from sulfide poisoning in the deeper, sulfidic regions of the lake. In contrast, electrodes containing a plasticizer-free methacrylate copolymer-based sensing layer on top of a conducting polymer layer as a transducer did not show this poisoning effect. The syringe samples drawn during continuous profiling were utilized to calibrate the electrode response. Reaction hotspots and steep gradients of ammonium concentrations were identified on-site by monitoring the electrode potential online. Upon conversion to high-resolution concentration profiles, fine scale features between the calibration points were displayed, which would have been missed by conventional limnological sampling and subsequent laboratory analyses. Thus, the presented setup with SC-ISEs tuned to analytes of interest can facilitate the study of biogeochemical processes that occur at the centimeter scale.

We present a new potentiometric sensor principle and a calibration protocol for in situ profiling of dissolved CO with high temporal and spatial resolution in fresh water lakes. The sensor system is based on the measurement of EMF between two solid-contact ion selective electrodes (SC-ISEs), a hydrogen ion selective and a carbonate selective sensor. Since it relies on SC-ISEs, it is insensitive to changes in pressure, thus suitable for in situ studies. Also, as it offers a response time ( t) of <10 s, it allows for profiling applications at high spatial resolution. The proposed optimum in situ protocol accounts for the continuous drift and change in offset that remains a challenge during profiling in natural waters. The fast response resolves features that are usually missed by standard methods like the classical Severinghaus CO probe. In addition, the insensitivity of the presented setup to dissolved sulfide allows also for measurements in anoxic zones of eutrophic systems. Highly resolved CO concentration profiles obtained by the novel and robust SC-ISE setup along with the developed optimum in situ protocol allow investigating hotspots of biogeochemical processes, such as mineralization and primary production in the water column and help improving estimates for CO turnover in freshwater systems.

Biogeochemical processes are often confined to very narrow zones in aquatic systems. Therefore, highly resolved in situ measurements are required to study these processes. Potentiometric solid-contact ion selective electrodes (SC-ISEs) are promising tools for such measurements. SC-ISEs show good performance in analyses under controlled experimental conditions. Very few sensor designs, however, can sustain the challenges of natural water matrices and external environmental conditions during in situ applications. We fabricated ammonium and pH selective SC-ISEs with functionalized multiwalled carbon nanotubes (f-MWCNT) as a solid contact. Their functionality was tested in the laboratory and applied in situ for vertical profiling in a eutrophic lake. Sensors were insensitive to strong redox changes, high sulfide concentrations, and bright daylight conditions during the application in the lake. In addition, sensors are easily fabricated and exhibit short response times (<10 s). The proposed design of SC-ISEs based on f-MWCNTs is quite suitable for high-resolution in situ profiling of ionic species in fresh water lakes.

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Hitherto, no palaeomagnetic data for India are available earlier than the Jurassic, 130 M.y. The remanent magnetic directions of oriented samples from one Jurassic and four pre-Cambrian rock formations in India have now been determined. One pre-Cambrian formation gave very scattered direction : the other four formations gave well-defined directions and their magnetic stability was demonstrated by a.c. and thermal demagnetization. The three pre-Cambrian results enable values of the ancient latitude and orientation of India to be estimated at 500, 600 and 750 M.y., assuming the ancient field to have been an axial dipole.By making use of these new results, together with similar data by other workers for Australia, North America and Europe, it can be shown that, as far as the scanty data goes, the rate of drift in latitudes and orientation of the four continents has been of roughly the same magnitude throughout the period since 750 M.y.

Detailed paleomagnetic measurements have been made on a lava sequence exposed between altitudes of 700 to 1000 meters in the Amarkantak‐Dindori tract on the eastern margin of the Deccan traps. The variation in the direction of remanent magnetism with altitude has been studied. The paleomagnetic data reveal the occurrence of a reversal of the earth's magnetic field at an altitude of about 975 meters at Amarkantak as well as the unstable behavior of the geomagnetic field near the polarity transition. These data are at variance with the observation of the same reversal of magnetic field at an altitude of about 625 meters in the paleomagnetic study of several other vertical sequences in the Deccan traps. The variance is interpreted in terms of an uplift of the Amarkantak region by about 350 meters.

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