Morphosedimentary response of a fluvio-estuarine beach to interannual variability in landfast ice dynamics

Abstract

Landfast ice plays a significant role in the morphodynamics of cold coasts and accelerating anthropogenic pressures on coastal sedimentary environments are increasing the complexity of its distribution and behavior. However, understanding its interannual variability and geomorphic role along the wide range of inhabited and uninhabited coastal environments remains a challenge. In fact, the difficulty in obtaining periodic high-resolution field data on its physical properties and their temporal evolution is often a major limitation in developing knowledge on landfast ice processes. Here, we present an approach for improving the monitoring of landfast ice dynamics and its geomorphic impact on sedimentary systems by combining (1) topographic datasets from UAS surveys, (2) hydrometeorological conditions during the freezing season, and (3) observations from time-lapse video. This study was conducted over two contrasting freezing seasons at the urban beach of Tibbits Cove in the fluvial estuary of the St. Lawrence River in a context of a low energy wave environment. Results demonstrate the great ability of the approach for (1) measuring interannual variations in ice thickness, surface ruggedness and volume with high accuracy and (2) constraining geomorphic changes due to ice action. These results also reveal the existence of a strong relationship between the severity of the freezing season and the response of landfast ice to hydrometeorological events in a fetch-limited environment. Consequently, a distinct geomorphic response of the beach was also observed following the opposite winter conditions of 2021 and 2022, where ice processes exported almost three times more sediment during a cold winter than during a mild winter. The overall trend in sediment budgets remained negative following two winters, suggesting an important role for landfast ice in the long-term evolution of the beach. Observations also suggest the prevalence of wave-independent sediment entrainment processes such as basal adfreezing in fetch-limited environments. Other ice-related processes, including ice wallowing and gouging, show a negligible influence on the sediment budget of the system and appear to be less powerful than those described in open coastal environments. Ultimately, expanding the use of this approach could greatly enhance our knowledge of the behavior, processes and products of coastal ice in a constantly changing climate, while informing decision-makers of its important influence on the evolution of geosystems in cold regions.