Morphodynamics of Eddy-driven submarine dunes in the Queen Charlotte Sound/Tōtaranui, New Zealand

The coastal zones of New Zealand feature substantial sediment deposits accumulated over geological time scales. These sediments are reworked by tidal currents, which are funneled and amplified by the rugged coastal topography, generating eddies. This dynamic process results in the formation of complex dune fields, such as those observed in the outer Queen Charlotte Sound/Tōtaranui. In this paper, we use a comprehensive set of meteo-oceanographic observations and numerical modeling to examine how topographically generated eddies influence the formation and behavior of these dunes. Our analysis examines long-term migration rates and short-term crest dynamics across multiple tidal cycles, revealing how crest oscillations are influenced by bed shear stress and how sediment flux phase shifts correlate with crest heights. Finally, we discuss a hypothesis based on hydrodynamic regimes to explain the discrimination between dune fields with markedly different morphologies in the northwest and southeast of the study area. This paper presents analytical methods and novel insights into the dynamics of a complex dune field, where eddy-driven processes generate diverse dune morphologies within a spatially restricted area. • Tidal eddies drive the formation of submarine dunes in outer Queen Charlotte SoundTōtaranui. • Variations in dune geometrical characteristics arise from contrasting hydrodynamic regimes. • Sediment flux phase shifts control short-term dune crest height changes.