Ole Andersen (DTU Space, Denmark); Bjarke Nilsson (DTU Space, Denmark)

The breakup and capsizing of large tabular icebergs contribute to significant oceanic wave events that threaten coastal regions. Despite continuous monitoring near glacier walls, monitoring these processes in open ocean environments has remained challenging due to the unpredictable nature and limited access of the capsizing events. We present a pioneering case study of the London-sized iceberg A-76A, whose final months of fragmentation and capsizing were captured by the SWOT satellite as it approached South Georgia Island in 2023. Our findings highlight SWOT’s unique ability to provide two-dimensional, large-scale views of iceberg-induced waves.

We successfully described the waves by their physical characteristics: wavelength (L), wave height (H), and water depth (h). These parameters together define the wave regime, a combination of linearity and dispersiveness, and thus guide the level of complexity required in the wave model. Immediately following the iceberg's impact, waves are expected to be highly nonlinear due to the extreme nature of the generation mechanism. As they propagate outward, these waves undergo energy loss, and their nonlinearity decreases. Over distance and time, wave trains typically become more regular and linear, with longer wavelengths travelling farther from the origin due to dispersion. We use SWOT to verify the regime of the observed waves. We also use a combination of wavelet transformation and the dispersion relationship to estimate the time that has passed since the impact. Investigating the relation between the wave’s propagation time and regime.

This study establishes foundational methods for wave characterisation from the SWOT mission, enhancing understanding of iceberg break-up dynamics and their impact on ocean surface topography.