El Nino and decadal effects on sea-level variability in northern New Zealand: a wavelet analysis

Sea-level data from two sites in northern New Zealand, along with the South ern Oscillation Index (SOI), are analysed for interannual and decadal varia bility using wavelets. The analysis shows, using statistically significant wavelet power, there is a significant relationship between mean sea level ( MSL) and SOI. However, the relationship is highly variable, both in magnitu de and in the range of time-scales over which it occurs. This nonstationari ty necessitates the use of techniques such as wavelets for analysis. An int erdecadal response in MSL around northern New Zealand has been isolated, wi th shifts occurring in 1950 and the late 1970s. This behaviour in MSL appea rs to coincide with shifts in the Pacific Decadal Oscillation, thought prev iously to be largely centred in the North Pacific. A strong correlation bet ween SOI and sea surface temperature (SST) is also demonstrated. This relat ionship appears to be stable in magnitude (a large change in SOI produces a large change in SST) and to occur over the same range of time-scares. More SST and MSL data are required for other parts of New Zealand to determine whether these findings apply elsewhere.