Late Holocene sea-level changes and vertical land movements in New Zealand

ABSTRACT

Coasts in tectonically active regions face varying threat levels as land subsides or uplifts relative to rising sea levels. We review the processes influencing relative sea-level change in New Zealand, and the geological context behind ongoing land movements, focussing on major population centres. Whilst Holocene sea levels have been reconstructed using a variety of techniques, recent work uses salt-marsh microfossil assemblages to reconstruct relative sea-level changes over the past few centuries. For the twentieth century, these proxy-based studies often show enhanced rates of sea-level rise relative to tide-gauge observations. The effects of tectonic subsidence must be considered, alongside vertical and dating uncertainties in the sea-level reconstructions. Global Positioning Systems (GPS) observations for the past few decades show that vertical land movement (VLM) may be influencing rates of relative sea-level rise. However, the short period of GPS observations, during which trends and rates have varied at some localities, raises questions over the longer-term contribution of VLM to sea-level change over the past few centuries and for future projections. We argue that high-resolution palaeo-sea-level reconstructions from salt-marsh sedimentary sequences can help to answer these questions regarding the interplay between sea-level change and VLM at key locations.

KEYWORDS:

• Sea level
• Holocene
• New Zealand
• palaeoenvironment
• climate change
• sea-level rise
• palaeoclimate
• vertical land movement
• tectonics
• palaeoseismicity

Acknowledgements

This review is a contribution to the NZ SeaRise Programme, funded by the Ministry of Business, Innovation and Employment. Special thanks are given to Dr. Alastair Clement and Dr. Paul Denys for their thorough and extremely helpful reviews of the manuscript. We also thank Dr. Ed Garrett (University of York) for his comments on the manuscript, Dr. Marta Marcos (University of the Balearic Islands) for help with generating Figure 3, and Dr. Andrew Rees (Victoria University of Wellington) for assistance with transfer functions. Further thanks are given to Dr. Sigrún Hreinsdόttir (GNS Science) for provision and discussion of unpublished cGPS time series, Prof. Edward Cook (Columbia University) for providing the primary data from the 2002 tree-ring climate reconstructions, as well as Dr. Paolo Stocci (NIOZ), Dr. Jeremy Gibb (Coastal Management Consultancy Ltd., retired), Dr. Susan Schwartz (UC Santa Cruz), Dr. Laura Wallace (GNS Science), Prof. Simon Lamb (Victoria University of Wellington), and Prof. Tim Stern (Victoria University of Wellington), for valuable conversations about aspects of the literature.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

Data sharing is not applicable to this article as no new data were created or analysed in this study.