The UK experienced a marine heatwave of unprecedented intensity in June 2023, signaling a rising threat to its marine ecosystems and highlighting the urgent need for improved monitoring and preparedness.
Climate change is increasing global temperatures as well as the frequency, intensity, and duration of extreme temperature anomalies.
A recent study reveals that while the UK has historically avoided severe marine heatwaves (MHWs), an unprecedented, intense but short-lived MHW struck UK waters in June 2023, signaling a shift in marine climate risks. The research highlights increasing frequency of these events, particularly in the southern North Sea, with potential compound effects on marine ecosystems due to simultaneous low oxygen conditions.
Marine heatwaves—periods of at least 5 days of unusually high sea surface temperatures—pose significant threats to marine biodiversity and fisheries worldwide. Understanding their occurrence and impacts in UK waters is critical for preparing the region’s marine management and conservation strategies.
The study was conducted by researchers from the National Oceanography Centre in the United Kingdom, including Zoe Louisa Jacobs and colleagues, and was published on October 4, 2024, in the journal Frontiers in Marine Science.
The team combined satellite remote sensing data of sea surface temperatures from 1983 to 2023 with biogeochemical model outputs to analyze marine heatwaves and cold spells across the Northeast Atlantic, focusing on the UK and surrounding waters. They examined frequency, duration, intensity, and spatial patterns of these temperature extremes, as well as concurrent changes in chlorophyll-a concentrations, oxygen levels, and acidity.
Results show that the UK is not a global hotspot for marine heatwaves or cold spells, but the southern North Sea stands out for frequent extreme temperature events and associated biogeochemical changes, such as “blue waves” (low chlorophyll-a) and “green waves” (high chlorophyll-a). Notably, the southern North Sea and English Channel may experience year-round episodes where marine heatwaves coincide with low near-bottom oxygen levels, creating compound stressors that could harm benthic ecosystems. The June 2023 heatwave, although intense with temperature anomalies up to 4°C, lasted only 16 days and occurred offshore, limiting its ecological impact compared to longer events elsewhere. However, the study confirms a clear trend of increasing marine heatwave frequency and duration in UK waters over recent decades.
The authors caution that while the study uses comprehensive satellite and model data, limitations to the accuracy of models include the relatively short duration of the most intense recent events and the complexity of local drivers such as atmospheric heatwaves and ocean currents. Biological impacts remain under-documented, and further ecological monitoring is needed to fully understand consequences for sensitive habitats like seagrass beds and cold-water corals.
These findings underscore the urgent need for the UK to develop robust policies and preparedness plans for marine heatwaves, learning from regions that have already experienced severe impacts. As climate change drives ocean warming, the likelihood of more frequent and intense marine heatwaves threatens marine biodiversity, fisheries, and the blue economy. The study highlights the importance of integrated monitoring of physical and biogeochemical conditions to anticipate and mitigate compound extreme events.
Why it matters.
The UK is entering a new era of marine climate extremes, with marine heatwaves becoming more common and potentially more damaging. This research provides a crucial foundation for understanding and managing these emerging risks to the UK’s marine environment.
References:
Study:
Jacobs, Z. L., Jebri, F., Wakelin, S., Strong, J., Popova, E., Srokosz, M., & Loveridge, A. (2024). Marine heatwaves and cold spells in the Northeast Atlantic: what should the UK be prepared for? Frontiers in Marine Science, 11, 1434365. https://doi.org/10.3389/fmars.2024.1434365
Further reading:
Cornes, R. C., et al. (2023). Long-term trends in sea surface temperature around the UK. Environmental Research Letters, 18(2), 024022.
Hobday, A. J., et al. (2016). A hierarchical approach to defining marine heatwaves. Progress in Oceanography, 141, 227-238.
Smale, D. A., et al. (2019). Marine heatwaves threaten global biodiversity and the provision of ecosystem services. Nature Climate Change, 9(4), 306-312.
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