‘Marine heatwaves’ in NZ tracked
Scientists are closely watching unusually warm waters around the North Island’s East Coast — and predict “marine heatwaves” could develop near Canterbury and Otago within days.
Described as an extended period of extremely warm ocean temperatures at a particular location, marine heatwaves can last several months and cover thousands of square kilometres.
“Scientifically, a marine heatwave is defined when the ocean temperature at a given location is in the top 10 per cent of the temperatures typically recorded during that time of year for five days or more,” University of Otago marine scientist Dr Robert Smith explained.
An unprecedented event in 2017-18 fuelled New Zealand’s hottestever summer and came with dramatic consequences.
Glaciers melted as some pockets of ocean off the South Island West Coast warmed to 6C above average, while elsewhere, mussel beds suffered cascading losses and vineyards saw early harvests.
While sea surface temperatures around New Zealand had hovered close to normal over much of the past summer, Smith said a strong marine heatwave developed during late February to the east of the country — and was ongoing.
“This marine heatwave is currently impacting coastlines of the Wairarapa, Hawke’s Bay and the Chatham Islands,” he said, adding it had pushed temperatures more than 2C above normal at times.
“The event has been somewhat unusual in that it also enveloped much of the New Zealand subantarctic zone during March, which is not, given its name, an area one might typically think of as experiencing heatwaves.”
In these ecological hotspots, warmer oceans could be disruptive for species of all kinds, from plankton and seaweed to marine mammals and seabirds.
“They may also have implications for regional fisheries, including those for pa¯ua around the Chatham Islands.”
As part of The Moana Project — a five-year, $11.5 million collaboration aiming to make New Zealand a world leader in ocean-forecasting capability — Smith and fellow Otago researchers are working to get a clearer understanding of the heatwaves and their effects. The project has also seen the launch of a free marine heatwave forecast system.
“At present, we are providing short-range forecasts for up to seven days, of where and when marine heatwaves are likely to occur, for selected coastal sites around New Zealand,” he said.
“These sites include the Hauraki Gulf, Bay of Plenty, Cook Strait and Banks Peninsula. While the present tool gives us a short-range forecast, we are looking at ways to extend these forecasts to a few months using machine learning techniques. This research will help us to forecast these extreme events with more certainty and provide warning to our important ocean industries and coastal communities.”