| Summary: | Bottom water temperatures in lakes and the near-shore Arctic Ocean are usually below 4°C. If the water depth is shallow enough, the sea/lake ice freezes to the sea/lake bed and may significantly shift the mean annual temperature below zero. The temperature regime below the water is therefore directly dependent on the water depth and small changes can have a huge impact. Measurements of the sediment temperature below shallow water bodies, however, are scarce, and single temperature-chains in boreholes are not sufficient to map the spatial variability. As part of the testing phase of the MOSES project, we tested a new temperature lance to measure temperature profiles in lake sediments. The device is a 1.5m steel lance with 30 sensors at 5cm spacing that can be pushed or hammered into the sediment. The sensors equilibrate to the surrounding sediment or water within 10min, allowing for repeat measurements to cover the spatial variability. During the spring expedition to the Bayelva long-term observatory near Ny Ålesund, Svalbard, in March 2021, we measured the sediment temperature under the Brandallaguna and in the glacial lake Tvillingvatnet near the village of Ny Ålesund. The measurement at Tvilingvatnet was 16h long to allow for analysis regarding equilibration time.
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