A ∼200-year relative sea-level reconstruction from the Wellington region (New Zealand) reveals insights into vertical land movement trends

Abstract

The sea-level rise threat to New Zealand's coastal cities is regionally exacerbated due to spatially varying vertical land movement (VLM). At Wellington, the capital city, situated adjacent to a major active plate boundary, strong regional spatial and temporal variability of VLM is indicated by the relatively short (∼25 year-long) continuous Global Navigation Satellite Systems (GNSS) network, but until now longer records of VLM have been lacking. Here, a ∼ 200-year-long relative sea-level reconstruction is presented from Pāuatahanui salt marsh in the northern Wellington region. The foraminifera-based relative sea-level reconstruction indicates that ∼1 ± 0.45 m of sudden uplift occurred during the 1855CE Mw 8.2 Wairarapa earthquake. Following this, Pāuatahanui has experienced a mean rate of relative sea-level rise (1855CE to present) of 1.5 ± 0.6 mm/yr, or 2.4 ± 0.8 mm/yr since the start of the twentieth century, consistent with ongoing subsidence in concert with climate-driven sea-level rise. Further acceleration to >3 mm/yr since the 1990s (with 4 mm/yr also possible if the full 95% confidence range is taken into consideration) is consistent with the globally documented acceleration in sea-level rise, although low model precision hampers confidence in this interpretation. This record is the first of its kind from a tectonically complex setting in New Zealand, shedding light on the effects of the historically significant 1855 earthquake, and fills a gap between millennial-scale and contemporary records of VLM with important implications for future sea-level projections in the region.