Evolution of marine gravel dunes on the open shelf under multi-directional currents conditions

On inner continental shelves, a variety of coarse grained bedforms, such as gravel dunes, are shaped by hydrodynamic and morphodynamic processes. The formation evolution bedforms reflect balance between seabed coastal morphology, sediment type availability, regional hydrodynamics. Yet, observing bedform directly in the marine environment is rare, mostly due to lack repeat seafloor mapping surveys. In this study we use bathymetry from 3 surveys over 4 years western Cook Strait/Te Moana-o-Raukawakawa region, New Zealand/Aotearoa. We integrate morphology characterisation with classification modelling, investigate dunes under multi-directional current conditions. reveals morphological changes plan-view dune geometry bifurcation crestlines, maximum observed vertical up m at water depths 60 80 m. However, no migration was detected. Our model shows that most prominent spatially correlated eddy formation, high near-bottom currents, reaching speeds ∼4 s −1 bottom stress >25 N −2 each tidal cycle. demonstrate average conditions region capable mobilising coarse-grained (i.e., sand gravel), indicating multi-year time scales result continuous remobilisation rather than extreme or storm events. findings highly dynamic nature Strait, need for regular, ensure up-to-date information.