Mechanisms of Lateral Spreading in a Near-Field Buoyant River Plume Entering a Fjord

Observations collected from a fast-flowing buoyant river plume entering the head of Doubtful Sound, New Zealand, were analysed to examine drivers lateral spreading. The near-field is characterised by flow speeds over 2 ms −1 , and strong stratification ( N > 0.1 s −2 ), resulting in enhanced shear which supports elevated turbulence dissipation rates (ϵ 10 −3 W kg ). Estimates spreading derived trajectories Lagrangian GPS surface drifters cross-plume hydrographic transects. Lateral latter compared favourably with estimates control volume technique previous study. was driven baroclinic pressure gradient toward base plume. However, underestimated drifters. A convergence near-surface barotropic concentrated within core. combination internal stress mixing at layer, presence steep fjord sidewalls likely reduced rate relative theoretical rate. width observations provided evidence scale-dependent dispersion followed 4/3 power law. Two models dispersion, examined assess capable representing observed An analytical horizontal shear-flow model generated that consistent law dispersion. Therefore, appeared be dominant mechanism thus spreading, layer.