Marine heatwaves during winter

Subject – Environment

Context – Marine heatwaves during winter could have dire impacts on New Zealand fisheries and herald more summer storms.

Concept –

The ocean around New Zealand is getting warmer, and extreme warming events have become more frequent over the past years.
These marine heatwaves can have devastating impacts on ocean ecosystems. When they happen in summer, they usually receive a lot of attention. But those happening during winter, when the ocean is cooler, are often ignored.
Yet, these winter events can affect the spawning and recruitment of fish and other sea animals, and in turn have significant impacts on aquaculture and fisheries.
Marine heatwaves are defined as periods of five days or more of ocean temperatures in the top 10% of local average values for the time of year.
During winter 2021, surface waters were on average 0.3℃ (±0.75) warmer than usual, with peaks occasionally reaching +4.2℃.

Changes across the southwest Pacific affect New Zealand

We know ocean temperatures are warming faster during winter than summer around New Zealand and across the wider subtropical southwest Pacific Ocean. The warming has become particularly evident since 2010 and has manifested in the emergence of the “Southern Blob”.
This ocean hotspot is centred northeast of New Zealand and has been linked to drought in both South America and New Zealand.
The current rate of warming in the Southern Blob exceeds natural variability, implying a contribution from human-induced climate change. Along with changes in the regional atmosphere, this large-scale process increases the likelihood of winter marine heatwaves around New Zealand.
Our research shows the deepest and longest-lasting marine heatwaves in the Tasman Sea are typically driven by ocean currents — in contrast to shallower summer marine heatwaves, which are driven by the atmosphere.
The warmer-than-normal winter ocean temperatures in the Tasman and coastal seas around New Zealand send warning signals about what the summer may bring. On top of impacts on coastal ecosystems, marine heatwaves also affect extreme weather and make floods and tropical storms over New Zealand more likely during the coming summer.

Moana Project

The Moana Project is a 5-year $11.5 million MBIE Endeavour ocean research initiative.
It aims to improve understanding of coastal ocean circulation, connectivity and marine heatwaves to provide information that supports New Zealand’s seafood industry.
The project includes outstanding research organisations in New Zealand and overseas, and partners with Whakatōhea iwi to support their rohemoana interests in the Bay of Plenty.