Bay Of Plenty Record Marine Heatwave: A Year Of Hot Waters

Today, marine heatwave conditions in the Bay of Plenty have lasted an unprecedented full year – the longest continuous marine heatwave so far recorded for New Zealand. The warming is part of a record year of upper North Island marine heatwaves, according to Moana Project oceanographer Dr Robert Smith.

“The current marine heatwave in the Bay of Plenty started 9 November 2021,” explains Dr Smith from the University of Otago. “Over the last year, sea surface temperatures have remained on average 1.6°C degrees warmer than the long-term average. Pronounced marine heatwave conditions continued during the winter; the Bay of Plenty never really experienced normal winter ocean temperatures. Instead, water temperatures reached 2.4°C above normal.”

“This warming is unprecedented over at least the past 40 years and is not only affecting the surface. Moana Project temperature observations collected in collaboration with commercial fishers show that noticeable warming has extended to depths of at least 60 metres.”

The warming is part of a wider pattern that has affected the entire upper North Island over the past year.

“While the Bay of Plenty is experiencing the longest marine heatwave that we now have on record, many areas in the North Island have broken local records too. Waters off Cape Reinga / Te Rerenga Wairua experienced marine heatwave conditions for more than 95% of the time in the last year, and off Raglan and Taranaki marine heatwaves persisted more than 80% of the time. In the Hauraki Gulf, 274 days had marine heatwave conditions, which is 75% of the year,” continues Dr Smith.

Even though coastal water warming may seem great for beachgoers, marine heatwaves can adversely affect ocean life, including kelp forests, fish and marine mammals, making ocean data essential for good management.

Bay of Plenty Regional Council’s General Manager of Integrated Catchments, Chris Ingle, says having robust scientific information helps to guide good decision making.

“To build climate resilience, we value sound data from the Moana Project. This information helps us, as regulators, manage the pressures on the marine environment,” Mr Ingle says.

The long running marine heatwave conditions are likely caused by a combination of factors. This includes recent changes in ocean currents that transport heat around northern New Zealand, persistent La Niña conditions in the Pacific Ocean, and broad-scale warming of the upper-ocean around New Zealand driven by climate change.

Ocean temperatures affect not only marine life, but also the general weather we see on land.

Lisa Murray, MetService Head of Weather communications says that marine heatwaves can exacerbate rain events.

“A warmer sea heats the air travelling over it and because warmer air can mean more moisture, we can get more rain.”

With the current La Niña predicted to continue into early 2023, the ongoing marine heatwave conditions are likely to extend throughout the coming summer.

Daily updated Moana Project marine heatwave forecasts are available at https://www.moanaproject.org/marine-heatwave-forecast and an overview of the extent of marine heatwaves over the last year is available at https://www.moanaproject.org/recent-marine-heatwaves.

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