Advances in Understanding Sea-Level Variability around New Zealand

Recent modelling of tides over a large tract of the SW Pacific has provided improved knowledge of the trapped tidal wave around New Zealand. An amphidrome in the semidiurnal solar tide (S₂) off the east coast produces a marked contrast in spring-neap tides between east and west coasts. The interannual and decadal variability in sea level around New Zealand (up to a range of 0.2 m) confirms that the Pacific-wide ENSO system and the effect of the Interdecadal Pacific Oscillation (IPO) are not confined to tropical and sub-tropical, latitudes, but are clearly, but not simply, linked to the southern mid-latitude region straddled by New Zealand. The confounding behaviour of interannual and decadal variability and its non-stationary link with ENSO effects masks the ongoing global sea-level rise. Further advances are now possible with the completion of networks of open-coast sea-level gauges in Australia, Pacific Islands and New Zealand, complemented with satellite altimetry and robust tidal models.