New Zealand's Sea Temperatures Hit Record Highs, Surpassing Global Averages
Experts warn that the new data dispels the belief that New Zealand is shielded from extreme temperatures and raises concerns for local marine life.
Record Highs and Rising Temperatures
New Zealand's sea temperatures have reached unprecedented levels, surpassing global averages threefold in one region, prompting alarm over the health of the country's marine life and ecosystems. According to new data from Stats NZ, since 1982, oceanic sea-surface temperatures have increased on average between 0.16 – 0.26°C per decade, and between 0.19 – 0.34°C per decade in coastal waters. Every oceanic and coastal region recorded their hottest years ever in either 2022 or 2023.
Regional Disparities
Comparing data from the past 20 years, the rate of ocean surface warming around New Zealand has exceeded the global per-decade average of 0.18°C by twofold. One region, the Chatham Rise, has experienced temperatures three times warmer than the global average, said Matt Pinkerton, a principal scientist at the National Institute for Water and Atmospherics.
Geographical Influences
New Zealand's higher temperatures may be attributed to its geographical position and the way global ocean currents move and carry heat. "New Zealand sits sandwiched between the Pacific, the Tasman Sea, and the Southern Oceans – there's a lot of warming associated in all three of those areas, so we are getting the heat from all directions," explained Pinkerton.
Marine Heatwaves
Marine heatwaves, or prolonged periods of unusual seawater warmth, have also reached new levels. The Western North Island experienced heatwave conditions for 89% of 2022, the highest among coastal regions, while the Tasman Sea spent 61% of the year in a heatwave, the highest among oceanic regions. Even small rises in temperature can disrupt marine ecosystems, causing some species to relocate and increasing disease risks, noted Stuart Jones, environmental and agricultural statistics manager at Stats NZ.
Ecological Impact
Previous intense marine heatwaves in New Zealand have led to mass sea sponge bleaching, die-offs of southern bull kelp, large-scale fish strandings, and penguin deaths. "Intense marine heatwaves can cause large-scale ecological change by killing habitat-forming species such as kelp," said Dr. Christopher Cornwall, a marine biology lecturer at Victoria University of Wellington. Both Cornwall and Pinkerton emphasize that the full extent of how warmer oceans will disrupt ecosystems is still poorly understood, underscoring the need for long-term monitoring to anticipate and plan for changes, especially regarding fishing quotas.
Phytoplankton Decline
A separate Stats NZ dataset revealed a decreasing trend in phytoplankton – microscopic algae forming the base of marine food-webs – in New Zealand's warmer northern waters, suggesting a correlation between the decrease in phytoplankton and rising sea-surface temperatures.
Broader Implications
New Zealanders will also feel the effects of warming seas, as the ocean heavily influences the island nation's weather, said Dr. Georgia Grant, a climate scientist at GNS Science. The world's oceans have absorbed about 90% of the extra heat generated from human-caused climate change. "Increasing ocean temperatures are one of the factors why storms like Cyclone Gabrielle are expected to increase in severity under climate warming," Grant added.