Marine heatwaves & oceanic changes

New Zealand is surrounded by ocean, and both our climate and our climate extremes (such as droughts, heatwaves, floods and tropical storms) are highly impacted by ocean temperatures. The ocean is also changing rapidly – it’s absorbing more heat, ocean currents are shifting, and we’re experiencing longer and more intense marine heatwaves. The more we understand the pace and scale of these changes, the better we can plan to adapt.

In the summer of 2021-22, we saw one of our most intense marine heatwaves, and our work indicated that this will start to become “normal”. Marine heatwaves kill off corals, disturb ecosystems, pose risks to fishing and aquaculture, and contribute to heatwaves on land and other climate extremes across the country. We were also seeing changes to our oceanic system, with fish and marine species seen further south than ever before.

This suite of research examined how the ocean system around New Zealand is changing. Using results from the New Zealand Earth System Model, we sought to understand how the highly fertile environment of the sub-tropical front might change. Future changes will determine the locations of fishing hotspots, influence species’ distribution and provide pathways for invasive species. Improved modelling of the ocean system through this research was intended to feed back into global modelling efforts. We also engaged with other research programmes to make sure climate projections for Aotearoa take into account all current knowledge.

You can find detailed information about the research underway in the drop-downs below.

Key findings:

Modelling findings:

• By 2100, the 40-odd marine heatwave days we currently see in a normal year will increase to between 80 days (low emissions, best-case scenario) and 170 days (high emissions, worst-case scenario).
• For some regions, such as southern tip of the South Island, there is a high chance that marine heatwaves start to last more than a year.  
• In regards to the intensity of future marine heatwaves (or just how warm they will be), for coastal waters, average marine heatwave intensities will increase by 20% (best case) to 100% (double, worst case) by the end of the century.
• For the North Island, this means an average marine heatwave could be between 0.5°C to 2°C more intense than they are today.
• The datasets available through this project range from the complete model variable output (ocean temperature at different depths, horizontal velocities, salinity, etc.) and metrics related to marine heatwaves relevant to research purposes, to locally-specific temperature and heatwave projections most useful for industry members and practitioners. An infosheet describing these datasets can be found here

Observational findings:

• Salinity variability is more important to the Tasman Box than was previously understood, which impacts how the ocean sequesters heat and carbon dioxide and influences primary productivity.

• NIWA gives dire warning about ‘severe’ marine heatwaves, 1News, TVNZ
• Marine heatwaves forecast to devastate, Otago Daily Times
• Marine heatwaves expected to get longer, hotter and more severe, Stuff
• Why scientists are expecting another ‘crappy’ year for glacier melt, NZ Herald
• Marine heatwaves: Why do they make our seas scorch?, NZ Herald
• Major climate modelling effort captures New Zealand’s exceptional oceanic conditions, leading to better climate simulations, Deep South Challenge
• Narrowing in on Southern Ocean eddies, Deep South Challenge

Both industry and recreational fishers [have been] noticing changes in the kinds of species that are caught and where [for some time]. It’s hard to see current fisheries being resilient enough to withstand increases between 80% and 100% of median marine heave wave intensities by the end of the century.

Tony Craig, partner with marine consultancy Terra Moana

Stages of research: