Sea surface temperatures around Aotearoa in 2022 and 2023 were the hottest ever recorded, according to new data from Stats NZ.
Since 1982, oceanic sea-surface temperatures have increased by up to 1.05°C, and coastal sea-surface temperatures by up to 1.35°C. The new data also cover marine heatwaves, finding the Western North Island region experienced heatwave conditions for 89 percent of the year, the highest among the nine coastal regions measured.
A second Stats NZ dataset found that the amount of phytoplankton has tended to decrease in our northern waters and increase down south since 1998. However, since 2019, almost all areas have seen these numbers drop. Phytoplankton are the base of marine food-webs and can help remove carbon dioxide from the atmosphere.
The Science Media Centre asked experts to comment.
Dr Matt Pinkerton, Principal Scientist – Marine Ecology & Remote Sensing, NIWA, comments:
“Things are getting hotter because of climate change – we knew that already – but the accelerating pace of warming of the oceans around New Zealand is surprising. The rate of ocean surface warming round New Zealand is now outstripping the global average threefold in some areas and twice on average. This disrupts the narrative that New Zealand is well placed to avoid the worst that climate change will bring. More warming brings more marine heatwaves and the increase in these abnormally hot events since 2010 is dramatic.
“It’s the biological response that really matters though: how will our coastal ecosystems, shellfish, fisheries, seabirds and marine mammals be affected by this heating? Counterintuitively, the easiest biological thing to observe are the microscopic plants at the base of the ocean food-chain and the ‘primary production’ of their growth. In warmer ocean areas, warming is known to be bad for primary production, but this unwanted consequence has usually been offset by the positive effect of warming on primary production in cooler waters. No longer. Since about 2019, ocean warming has been accompanied by dropping indicators of primary production in all ocean areas. Oceanic primary production indicators fell to record low levels in 2023, with potentially dire effects for fish, seabirds and marine mammals.”
Conflicts of interest: Member of the MfE technical Advisory Group on marine indicators. Author of reports to MfE for temperature and ocean productivity indicators. Reviewer for MfE of “Our Marine Environment 2019”
Dr Christopher Cornwall, Lecturer in Marine Biology, School of Biological Sciences, Victoria University of Wellington, comments:
“The release of the updated changes in sea surface temperatures highlight a worrying trend within Aotearoa New Zealand’s waters and the global ocean. Increasing seawater temperatures due to global warming have large ramification for marine life within Aotearoa. The report by Stats New Zealand touches on the increasing durations of marine heatwaves. Intense marine heatwaves can cause large scale ecological change by killing habitat-forming species such as kelp here in Aotearoa. Previous intense marine heatwaves have caused mortality of southern bull kelp in the Canterbury and on the West Coast. However, the effects of these marine heatwaves on the majority of marine life within our oceans are poorly understood. It is highly likely that both the background warming and more frequent, intense, and longer marine heatwaves are already working to permanently alter these marine ecosystems within Aotearoa. For example, we have around 1100 species of macroalgae in Aotearoa. For the majority of these species, their ranges within our waters will be altered before they can be described, and it is possible that some will go extinct in the near-term future.”
No conflicts of interest.
Dr Georgia Grant, Climate Scientist, GNS Science, comments:
“As our atmosphere continues to warm with increasing greenhouse gases, it isn’t surprising the surface of the ocean warms with it, in fact approximately 90% of climate warming has been absorbed by the ocean already. If we didn’t have the ocean air temperatures would be >20°C higher.
“At times in the past, the Southwest Pacific experienced ocean surface temperatures nearly double the global average temperature anomaly three million years ago when carbon dioxide levels similar to today were sustained. It’s important for New Zealanders to be aware that, even if global warming is kept to 2°C above pre-industrial temperatures in line with the Paris target (which the world is not on track to meet), we should expect higher ocean temperatures here. As an island nation, the ocean dictates much of our weather, and increasing ocean temperatures are one of the factors as to why storms like Cyclone Gabrielle are expected to increase in severity under climate warming.”
No conflicts of interest.
Ben Knight, Marine Biophysical Scientist, Cawthron Institute, comments:
“Trends in water temperatures and primary productivity provide useful information to help understand the magnitude of changes that are happening in Aotearoa New Zealand’s marine environment. Mean temperature trends presented in this analysis indicate mean warming of our marine waters of up 1.5°C in the past 30 years in important coastal regions, such as Fiordland. Such temperature changes can have a huge impact on New Zealand’s marine species, affecting the distribution of mobile species and potentially causing stress to sessile species, such as iconic the shallow-water dwelling Black Coral (Antipathella fiordensis) that inhabits Fiordland.
“Chlorophyll-a, the marine pigment associated with phytoplankton, described as primary production in this study, also show evidence of changes around New Zealand. These microscopic algae form the base of marine foodwebs, supplying the underlying energy to support the growth and maintenance of New Zealand’s marine species. However, phytoplankton can also cause harm if toxic, or harmful, algal species occur. Consequently, understanding any changes to the solar-powered organisms that provide the basis of life, and the potential for harm, in our marine waters is extremely important.
“Previous studies have noted the connection between warming seas and the potential for changes to land run-off, and deepwater, nutrient flows to surface waters that can affect both the quantity and species of phytoplankton occur. This study highlights increases in primary productivity in most coastal locations. At Cawthron we have seen evidence of increasing harmful algal bloom events in some species occurring around New Zealand which may be coincident with such changes. In contrast, recent negative anomalies in the waters around New Zealand have been observed, having the potential to impact ocean foodwebs and carbon storage processes. Consequently, this analysis is very helpful in contributing information on the drivers of changes that are occurring around New Zealand.
No conflicts of interest declared.
Dr Joe Prebble, Paleontologist, GNS Science, comments:
“The different productivity response north and south of New Zealand as the oceans warm is really interesting, and a feature of the different ocean circulation patterns and distribution of nutrients north and south of New Zealand. The 20-year trends observed in ocean productivity in subtropical waters (east of the north island), are broadly consistent with what has been predicted from earth systems models over the last decade. These predict small declines in surface nutrients, chlorophyll a and integrated primary productivity. In contrast, for Subantarctic waters south of New Zealand, the productivity response predicted by models, and observed in records of past warm climates is more ambiguous – the productivity response of the Southern Ocean to future warming is far from certain.”
No conflicts of interest.
ENDS.