Waves and mixing in Lake Taupō

Mixing processes in Lake Taupō are driven largely by wind stress that can generate barotropic (surface) and baroclinic (internal) waves. During a 2002 study, a baroclinic wave in the southern basin of Lake Taupō had a setup amplitude greater than 45 m, resulting in upwelling at the southern end of the lake following strong west/southwest winds. Vessel-mounted acoustic Doppler current profiler data showed that this setup wave was associated with southward near-shore currents exceeding 40 cm s⁻¹ at 20 m depth. We postulate that these are upwelling subsurface return currents occurring in Lake Taupō following major setup events, which may subsequently trigger the formation of Kelvin waves within the lake. Observations from 2002 also suggest that the return current advected phytoplankton from the deep chlorophyll maxima in the northern basin into the southern basin, resulting in nongrowth increases in phytoplankton concentrations due to phytoplankton focusing. In another event in 2004, the sediment plume from an extreme flood exhibited a gyre-like form in the lake, driven by wind-induced surface currents. These observations highlight the dynamic interplay between wind forcing, internal wave activity, and basin-scale circulation in Lake Taupō, with important implications for nutrient transport, sediment dynamics, and ecosystem structure.