M₂ tidal effects in greater Cook Strait, New Zealand

Abstract

The application of an M2 nonlinear numerical tidal model to the shelf seas of central New Zealand (∼38,500 km2 area) is described. It has provided a preliminary assessment of tidal and residual currents, bottom stress, energy dissipation, and the stratification index. The existence of a permanent, tidally driven mesoscale eddy (∼75 km diameter) is predicted north of D'Urville Island. Large spatial gradients in bottom stress qualitatively agree with many features of the surficial sediment distribution. A comparison of all available bulk stratification data with the h/u3 stratification index clearly demonstrates the dominance of tidal versus wind mixing over the control of summer stratification. A potential application of the model to fisheries science is suggested through a comparison of the stratification index contour map and some observations of squid fishing vessel locations.

Tidal circulation in Tasman and Golden Bays: Implications for river plume behaviour

“…The first was to use the results from the Bowman et al (1980) Cook Strait model, the second was to configure EFDC for Cook Strait. The Bowman et al (1980) model was a barotropic model and although reasonable agreement between sea-level measurements around Cook Strait were obtained by these investigators, configuring the three-dimensional Bays model using boundary conditions from the Bowman Cook Strait model did not result in adequate agreement with sea-level measurements within the bays. As a result, EFDC was configured for Cook Strait using known open ocean boundary conditions at either end of Cook Strait.…”

“…Assuming that the observed residuals are good estimates of the long-term tidal residual flows, then the model overestimated the residual flow across the northern boundary (possibly an artefact of the boundary) and predicted a more northerly mean flow along the western side of Tasman Bay. However, because the general aspects of the residual circulation between the observations, Heath (1976) estimate, Bowman et al (1980) estimate, and EFDC are consistent, we consider that we are reasonably close to understanding these flows. The area where the predictions diverge the most is along the western side of Tasman Bay and circulation in this region may oscillate.…”

The Wairarapa Coastal Current

“…Existing estimates of flow through Cook Strait range hugely. For example, Bowman et al (1983) recorded drogues passing southwards through Cook Strait with mean speeds up to 26 cm s~'. Heath (1986) notes that flows are variable on 1-4-week timescales, but made estimates of mean flows over 1 month ranging from 4 cm s~' southwards to 7 cm s"' northwards.…”

The tidal measurements of James Cook during the voyage of theEndeavour

“…In addition, spatial gradients in the tide (e.g. at Cook Strait, Bowman et al, 1980), and the fact that our modern stations will not have been located exactly at Cook's positions, will have introduced some differences. However, these are small factors compared to the estimated uncertainties in Cook's measurements, as shown above.…”