Climate change projections for the surface ocean around New Zealand

ABSTRACT

The future status of the surface ocean around New Zealand was projected using two Earth System Models and four emission scenarios. By 2100 mean changes are largest under Representative Concentration Pathway 8.5 (RCP8.5), with a +2.5°C increase in sea surface temperature, and decreases in surface mixed layer depth (15%), macronutrients (7.5–20%), primary production (4.5%) and particle flux (12%). Largest macronutrient declines occur in the eastern Chatham Rise and subantarctic waters to the south, whereas dissolved iron increases in subtropical waters. Surface pH projections, validated against subantarctic time-series data, indicate a 0.335 decline to ∼7.77 by 2100. However, projected pH is sensitive to future CO₂ emissions, remaining within the current range under RCP2.6, but decreasing below it by 2040 with all other scenarios. Sub-regions vulnerable to climate change include the Chatham Rise, polar waters south of 50°S, and subtropical waters north of New Zealand, whereas the central Tasman Sea is least affected.

KEYWORDS:

• Climate change
• surface ocean
• New Zealand
• Earth System Model
• warming
• ocean acidification
• nutrients
• primary production
• particle flux

Acknowledgements

Thanks to Steven Stuart for downloading the ESM outputs, Judy Lawrence for assisting with stakeholder engagement and Andrew Tait, Daniel Rutledge and Graham McBride for coordination of the CCII programme. We also thank Scott Nodder, Vonda Cummings, Mary Livingston and Di Tracey for comments on the original report, and Phil Sutton, Jonathan Verlade, Lionel Carter, and two unidentified reviewers for comments on the manuscript. We thank Erika Mackay and Mark Tucker for assistance with figures, the Ocean Biology Processing Group for SeaWiFS data (NASA Goddard Space Flight Center, Ocean Ecology Laboratory, Ocean Biology Processing Group; (2014): Sea-viewing Wide Field-of-view Sensor (SeaWiFS) Ocean Color Data, NASA OB.DAAC http://doi.org/10.5067/ORBVIEW- 2/SEAWIFS OC.2014.0.). Thanks also to the World Climate Research Programme’s Working Group on Coupled Modelling for access to the CMIP5 model output (via https://pcmdi.llnl.gov/projects/cmip5/). WOA2009 data accessed via https://www.nodc.noaa.gov/OC5/WOA09/prwoa09.html.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Cliff S. Law http://orcid.org/0000-0002-7669-2475

Graham J. Rickard http://orcid.org/0000-0002-0169-4361

Sara E. Mikaloff-Fletcher http://orcid.org/0000-0003-0741-0320

Matt H. Pinkerton http://orcid.org/0000-0001-7948-720X

Erik Behrens http://orcid.org/0000-0002-9713-7227

Steve M. Chiswell http://orcid.org/0000-0002-5957-3706

Kim Currie http://orcid.org/0000-0003-4252-194X

Additional information

Funding

This work was funded by NZ Ministry of Business, Innovation and Employment (MBIE) Contract C01X1225 (CCII), and NIWA Strategic Investment Funding to CAOA1504 (Ocean Climates), and COOF1502 (Oceans: Primary Production).