Temporal variability of the waters of Pelorus Sound, South Island, New Zealand

Abstract

Dynamics of the flow in Pelorus Sound (41°S, 174°E) are discussed in terms of previously reported observations and new observations in October 1976. Asymmetry in the tidal elevation and flow is caused primarily by co‐oscillating over‐tides generated outside the Sound by non‐linear effects on the fundamental 12.42‐hour tide in Cook Strait. Variations in the phase of the tidal flow with depth result both from frictional energy dissipation of the flow on the mudflats near the head of Pelorus Sound and from internal tides. Internal tides were not as clearly developed in October 1976 as in August 1974. Generation of observed seiching in Kenepuru Sound is probably also connected to the phase difference between the surface and bottom flows near the confluence of Kenepuru and Pelorus Sounds. Salt transport during periods when the Sound has a clear vertical structure is mainly by advection. Extreme examples occur with peak freshwater inflow, when a thin layer of low‐salinity surface water moves rapidly seawards. After sustained periods of low freshwater inflow the isohalines are nearly vertical in the outer sound and horizontal diffusion becomes important.