Abstract
Since the later part of the 19th Century, tide gauge records indicate that global sea levels have risen with an average rate of 1.7 ± 0.3 mm/yr. Satellite altimetry records indicate that the rate of sea level rise between 1993 and 2010 was 3.2 ± 0.4 mm/yr. It is currently uncertain if this latter figure is indicative of an increased rate of rise, or the result of a periodic signal. In any event, if the future sea level rise is to be predicted accurately, it is of great importance that changes in the rate of sea level rise be detected as soon as possible.
This study utilises a variety of techniques, including Least Squares and Fast Fourier Transform analyses, to assess the sea level records from New Zealand’s four longest tide gauge stations, located in Auckland, Wellington, Lyttelton and Dunedin, to detect any significant changes in the rate of relative sea level rise. It finds that Wellington’s records demonstrate a relative acceleration of 0.013 ± 0.01 mm/yr2 between 1891 and 2007, which is superimposed over the decadal and interdecadal signals that are present in the records. However, continuous Global Positioning System measurements that have been collected at the site over the past decade indicate the presence of significant tectonic motion in the form of subduction. The records from the Auckland, Lyttelton and Dunedin tide gauges do not demonstrate significant accelerations. The longest significant signals that are present within the sea level records from Auckland, Wellington, and Dunedin have periods in the range of 45 to 50 years.
The establishment of continuous Global Positioning System stations at long-term tide gauge stations is imperative to isolate non-constant vertical deformations from the observed relative rates of sea level rise to detect accelerations, and also to isolate the absolute rate of sea level rise.