The world’s oceans are warming at an alarming rate, setting new records in 2023. This has led to the emergence of marine heat waves, which can have catastrophic impacts on marine ecosystems, economies, and coastal communities. While the UK has largely escaped major heat wave events, a short-lived but intense heat wave in June 2023 has raised concerns about the future. Researchers are now characterizing marine heat waves and cold spells around the UK, revealing regional variability and the potential for significant disruption to marine life and industries. As these extreme events are projected to increase, the UK has a unique opportunity to learn from other nations and prepare for the challenges ahead. Marine heat waves and marine ecosystems are crucial topics to understand.
Mapping the Ocean’s Extremes
Analysis from the research team shows that, in contrast with much of the wider North Atlantic ocean, the waters around the UK are not a significant focal point for marine heat waves. The central subpolar gyre and Southern Ocean have by far the most heat wave and cold spell activity. Yet, the image is far more complicated than that when one zooms into regional waters around the UK
Both are most powerful in the North Sea but weakest around continental Europe: heat waves in the southern North Sea and English Channel generally last ~ month and are warm (> 1.5°C additional maximum temperatures), lighter than those in the eastern part of the North Sea which tend to persist for shorter (~2-3 weeks) but exceed 3°C. The marine heat waves live up to five months and happen year round, including in winter. This large variation in the geographical distribution, magnitude, duration of events (and, for some regions), and timing of individual events is likely to account for the distinct absence of a strong signal regarding an increase or decrease in phytoplankton abundance due to HABs.
Effect on Sea Life and Blue Economy.
When these marine heat wave events occur can be crucial for the UK’s marine ecosystems and blue economy. The plants of the sea would be warm enough to exceed their temperature limits causing damage, and likely mortalities under a summer heat wave. But if an event happens in winter or spring, the unseasonably warm conditions could cause phytoplankton to bloom and, thus, help fisheries — or encourage algal blooms that can lead to adverse effects.
When marine heat waves strike the more-shallow southern North Sea and English Channel, they found that local near-bottom oxygen levels tend to be extremely low as well — which adds further stress to benthic ecosystems. This association is most evident during the spring months when the water column is thoroughly mixed but is less apparent during the summer months, when vertical stratification of the water column begins to form.
Getting Ready for the uncertainty to come.
The UK/Ireland marine heat wave of June 2023 is a wake-up call and suggests we should do more targeted research with the aim for better preparedness. While the events here may not be as persistent or severe as those in other parts of the world, scientists expect stiffer competition for resources.
The UK has a golden opportunity to learn from the experiences of other nations and bolster resilience accordingly. Delineating the most high-risk regions, and evaluating their exposure to species and coastal communities, can enable more effective management strategies to be developed ahead of future extreme events. This will be essential in protecting the UK’s marine environment and all of the industries that rely on it, providing a sustainable blue economy for future generations.
