Effects of measuring devices and sampling strategies on the interpretation of monitoring data for long-term trend analysis

• Published in: Frontiers in Marine Science
• Main Authors: Fischer, P., Dietrich, Peter, Achterberg, E.P., Anselm, N., Brix, H., Bussmann, I., Eickelmann, L., Flöser, G., Friedrich, M., Rust, H., Schütze, Claudia, Koedel, Uta
• Format: Article in Journal/Newspaper
• Language: English
• Published: Frontiers Media, Lausanne 2021
• Subjects: Precision; accuracy; Sensor selection; Sampling scheme; Environmental Monitoring; Kongsfjorden; Long-term data; Coastal waters; Arctic; Arctic Ocean; Svalbard; Climate change; Global warming; Kongsfjord*
• Online Access: https://www.ufz.de/index.php?en=20939&ufzPublicationIdentifier=25326; https://doi.org/10.3389/fmars.2021.770977

A thorough and reliable assessment of changes in sea surface water temperatures is essential for understanding the effects of global warming on long-term trends in marine ecosystems and their communities. The first long-term temperature measurements were established almost a century ago, especially in coastal areas, and some of them are still in operation. However, while in earlier times these measurements were done by hand every day, current environmental long-term observation stations (ELTOS) are often fully automated and integrated in cabled underwater observatories (UWOs). With this new technology, year-round measurements became feasible even in remote or difficult to access areas, such as coastal areas of the Arctic Ocean in winter, where measurements were impossible just a decade ago. In this context, there is a question over what extent the sampling frequency and accuracy influence results in long-term monitoring approaches. In this paper, we address this with a combination of lab experiments on sensor accuracy and precision and a simulated sampling program with different sampling frequencies based on a continuous water temperature dataset from Svalbard, Arctic, from 2012 to 2017. Our laboratory experiments showed that temperature measurements with 12 different temperature sensor types at different price ranges all provided measurements accurate enough to resolve temperature changes over years on a level discussed in the literature when addressing climate change effects in coastal waters. However, the experiments also revealed that some sensors are more suitable for measuring absolute temperature changes over time, while others are more suitable for determining relative temperature changes. Our simulated sampling program in Svalbard coastal waters over five years revealed that the selection of a proper sampling frequency is most relevant for discriminating significant long term temperature changes from random daily, seasonal, or interannual fluctuations. While hourly and daily sampling could deliver ...