Treffer: Simulating the Thermal Response of Tidal Sediments by Integrating Numerical Modeling and Field Measurements.

Tidal flat ecosystems hold significant socio‐economic value but are vulnerable to increasingly frequent extreme climate events such as heatwaves. Predicting temperature effects on intertidal sediment ecology and biogeochemistry requires a high‐resolution mechanistic model to simulate sediment thermal responses to weather conditions. Here, we develop an open‐source model that captures sediment temperature dynamics over vertical distances up to 10 m, with sub‐millimeter resolution near the sediment surface. Calibrated with field data from intertidal sediments (muds and sands) in the Oosterschelde tidal bay, the Netherlands, the model successfully reproduces temperature fluctuations from minutes to seasons at depths between 0.05 and 1 m. Key controlling parameters include sediment porosity, thermal properties of the dry sediment, and albedo. Simulated sediment temperatures show pronounced seasonal dynamics in the upper 2–3 m but stay relatively stable at depths between 6 and 10 m. Hence, the sediment seasonally alternates between states of being a heat source (September–March) and a heat sink (March–September) for the overlying water. Muddy sediments exhibit higher temperature than sandy sediments, and longer inundation periods yield more stable sediment surface temperatures. Fine‐scale simulations identified March as the most dynamic month, with sediment surface temperature changing at rates up to 0.68°C min−1 and −0.71°C min−1, and temperature gradients in the top 1 cm reaching up to 4.8°C cm−1 and −8.4°C cm−1. Overall, our model offers a valuable analytical tool for studying estuarine and coastal biogeochemistry, particularly the impacts of climate change on tidal flat ecosystems. Plain Language Summary: Tidal flats are coastal areas that are regularly exposed to air and covered by water due to tidal cycles. These ecosystems are important for coastal protection, biodiversity, and local economies, but are sensitive to extreme weather events, such as heatwaves, which can strongly affect their temperature and ecological function. In this study, we developed a detailed computer model to simulate how sediment temperatures in tidal flats respond to weather conditions over time. The model was calibrated using field data from muddy and sandy tidal flats in the Oosterschelde tidal bay, the Netherlands. Our results show that sediment temperatures near the surface change quickly and over a wide range, roughly by up to 10°C between day and night. The highest daily temperature changes occur in March and the lowest in January. The changes in deeper layers are smaller and occur over seasons. Temperatures at depths greater than about 6 m are relatively stable throughout the year. The model also reveals that muddy sediments and longer periods of water coverage help reduce temperature fluctuations. Understanding how sediment temperatures respond to weather extremes is important for predicting the health of tidal flat ecosystems. Our open‐source model can help researchers and managers assess future risks and support the protection of these valuable coastal environments. Key Points: An open‐source model is developed to predict the vertical temperature dynamics in tidal sediments with high spatial and temporal resolutionAfter calibration, the model matches field data with an outstanding accuracy across scales from minutes to seasons and millimeters to metersThe model identifies March as the most variable month with fastest fluctuations and steepest gradients of near‐surface sediment temperature [ABSTRACT FROM AUTHOR]

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