Abstract
AbstractHistorically tide gauge (TG) data have been used to estimate global sea level rise. Critical to the analysis of TG records is the assumption that the TG sites are stable and not affected by vertical land motion (VLM). We analyze century‐long TG records from New Zealand that have been affected by VLM due to both major and transient earthquake events at a regional level as well as local instabilities. Using combined GPS and precise leveling, we estimate relative VLM between the GPS and TG of up to 1 mm/year. Based on 15–20 years of GPS data, the effect of seismic activity and slow slip events has uplifted sites by up to 0.8 mm/year on average in Wellington and Dunedin. Updated estimates of long‐term relative sea level (RSL) at four New Zealand TGs, as well as an estimate of RSL at a new fifth TG (New Plymouth), are determined using data through 2013—an additional 13 years compared to the previous study. The VLM corrected RSL rates gives our best estimate absolute sea level of +1.45 ± 0.28 mm/year (1891−2013). It is important that absolute sea level derived from RSL rates include realistic estimates of VLM, especially at TG sites that are close to plate boundaries, located in seismically active regions, affected by glacial isostatic adjustment, land ice loss, or gas/oil/water extraction.
Highlights
The long‐term trend in global mean sea level (GMSL) is recognized as an important indicator of climate change
It is important that absolute sea level derived from relative sea level (RSL) rates include realistic estimates of vertical land motion (VLM), especially at tide gauge (TG) sites that are close to plate boundaries, located in seismically active regions, affected by glacial isostatic adjustment, land ice loss, or gas/oil/water extraction
At Dunedin, the vGPS is based on the OUSD site, which ironically, is closer to the TG than the TG and cGPS antenna site (TGGPS) receiver (DUNT). (This anomaly is something of an historical accident that acts as a constraint on the quality of this result.) Using the OUSD rate based on the
Summary
The long‐term trend in global mean sea level (GMSL) is recognized as an important indicator of climate change. Larger‐ scale regional VLM such as tectonic activity needs to be accounted for; otherwise, the resulting estimate of the mean sea level trends will be biased It is only in the last two decades that space geodetic techniques such as GPS have allowed VLM to be measured to a precision better than 1 mm/year (e.g., Beavan, Denys, et al, 2010; Lidberg et al, 2010). New Zealand has an important part to play in these global studies Does it have four long‐term (over 120 years) TG records, but it borders the Southland Front/Southland Current, which in turn affects sea level variability at local and regional scales (Wunsch et al, 2007). No GPS measurements are available to quantify VLM at the TG sites prior to 2000, Table 1 (bottom half) lists all earthquakes with M > 7 that have occurred between 1855 and 2003, which may potentially have
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