Analysis of the Sea Level Change in New Zealand

Abstract

We analyse the sea level change in New Zealand using tide-gauge records available for over a century. The least-squares linear regression analysis is applied to estimate the linear and acceleration trends in (annual) mean sea level (MSL) data from tide gauges (TGs) in Auckland, Wellington, Lyttelton and Dunedin. The results reveal that the linear trends in relative sea level at these four TGs are between 1.2 mm/year (TG Dunedin) and 2.1 mm/year (TG Wellington). The relative sea level trend in New Zealand over the last century is estimated to be 1.7 ± 0.1 mm/year. The relative sea level trends are further corrected for the vertical land motions in order to assess the “absolute” sea level rise in New Zealand. The vertical land motions are investigated throughout New Zealand based on the analysis of GPS time series at 101 permanent sites. The GPS solutions are aligned to the ITRF2000 reference frame. The prevailing pattern of vertical motions in New Zealand is dominated by tectonic subsidence in the lower North Island, while the largest tectonic uplift is detected across the central Southern Alps in the South Island. The estimated rates of absolute sea level rise at the four TGs (co-located with GPS) are between 0.4 mm/year (TG Wellington) and 1.8 mm/year (TG Lyttelton). Based on these estimates, the absolute sea level in New Zealand raised over the last century at an average rate of 1.1 ± 0.3 mm/year.