Negative Impacts on a Complex Ecosystem
The ocean supports the livelihood of over three billion people. It also provides the main protein source for one billion people worldwide.
However, marine heatwaves negatively impact this complex ecosystem. These events cause devastating effects to marine life and our society. Due to climate change, marine heatwaves are becoming more frequent, more intense, and longer lasting.
What is a Marine Heatwave?
Heatwaves, or periods of unusually warm temperatures, occur not just on land, but also in the ocean. Unlike heatwaves on land, marine heatwaves can persist for many weeks or months. They extend over much larger areas and may warm the ocean to depths of hundreds of metres.
As climate change causes our planet to warm, marine heatwaves are becoming more frequent, more intense, and longer lasting. In fact, the number of marine heatwaves has doubled since 1982 and most recently we have seen extreme events in the North Atlantic, Antarctica, and around the Mediterranean.
What Causes a Marine Heatwave?
Marine heatwaves are caused by a range of ocean processes acting either separately or in combination. There are two main drivers:
- Surface heat flux: This is heating from the atmosphere. It tends to occur when an atmospheric high-pressure system sits above a region of water for an extended period. Marine heatwaves driven by surface heat flux tend to be shallower and shorter in duration.
- Advection: This is the movement of warmer waters into the region by ocean currents. Heatwaves driven by advection can be deeper and longer in duration.
Oceanic mixing processes play a key role in their occurrence, intensity, and persistence.
Diagram above: Ocean Mixing Process. Source: Holbrook, Scannell, Sen Gupta et al. (2019) 'A global assessment of marine heatwaves and their drivers'. Nature Communications 10, 2624.
Why Care About Marine Heatwaves?
Marine heatwaves can (and increasingly do) negatively impact this complex ecosystem. They cause damage including:
- Coral bleaching
- Harmful algal blooms
- Kelp and seagrass dieback
- Disease and mortality in invertebrates
- Location shifts in fish species
The knock-on effects have caused economic losses in the order of millions to billions of pounds.
The impacts of marine heatwaves are not confined to the ocean itself; they can also affect our weather. They can fuel powerful tropical cyclones, called hurricanes in the North Atlantic. They have also been associated with heavy precipitation. This is a result of warm ocean temperatures favouring strong evaporation, which increases the probability of strong rainfall events over land.
It is critical we understand the science behind them.
How Do We Know They're Happing and Changing?
Every day since the early 1980s, satellites have been monitoring sea surface temperatures. This allows researchers to study marine heatwaves from space.
Back down on planet Earth, measurements are taken by instruments on board ships and on permanent ocean observatories. There are also global networks of autonomous robots and floating instruments continuously collecting ocean data throughout the water column.
The general increase in marine heatwave frequency, intensity, and duration has been witnessed in all these observing systems. The increasing mean global temperature is one of the main drivers, but changing current systems are also responsible.
NOC's Research Into Marine Heatwaves
NOC advances research into marine heatwaves to ultimately protect people and economic infrastructure from these marine-related disasters. This includes studies on the causes, variability, ecological, and climate impacts of marine heatwaves.
One important question focuses on the predictability of marine heatwaves. If we can forecast when and where they might occur, marine industries can make decisions to adapt and mitigate their impacts.
A new study by the NOC has revealed where marine heatwave events are most likely to occur in UK waters for the first time. Led by NOC's Dr Zoe Jacobs, the study shows there are regional marine heatwave hotspots in the Southern North Sea and English Channel. Events here are weaker than in other areas around the UK, but they last longer.
Above: UK Marine Heatwave Map
What Facilities Monitor Marine Heatwaves?
NOC enables sustained ocean observations through the maintenance of facilities including the Porcupine Abyssal Plain Sustained Observatory (PAP) and the ARGO network. In addition to maintaining long-term ocean observatories, scientists at NOC develop innovative, state-of-the-art models and use these tools to better understand and predict marine heatwaves.
Test Your Knowledge
Take the plunge and explore the world of marine heatwaves! Test your knowledge of these ocean events, their causes, and the impact they have on marine life and our planet. Can you keep your cool?
Start QuizHow many people rely on the ocean for their primary source of protein?
What is a marine heatwave?
How has the frequency of marine heatwaves changed since 1982?
Which of the following is NOT a consequence of marine heatwaves?
What are the two main drivers of marine heatwaves?
How are marine heatwaves monitored?
What is the role of the ARGO network in studying marine heatwaves?
Why is it important to predict marine heatwaves?
Further Resources
Live Data from the Porcupine Abyssal Plain (PAP)
Data from Argo Floats
Data from the British Oceanographic Data Centre (BODC)
Key Publications
A stakeholder-guided marine heatwave hazard index for fisheries and aquaculture
Exceptional atmospheric conditions in June 2023 generated a northwest European marine heatwave which contributed to breaking land temperature records
Berthou, Ségolène; Renshaw, Richard; Smyth, Tim; Tinker, Jonathan; Grist, Jeremy P. 
ORCID: https://orcid.org/0000-0003-1068-9211; Wihsgott, Juliane Uta; Jones, Sam; Inall, Mark; Nolan, Glenn; Berx, Barbara; Arnold, Alex; Blunn, Lewis P.; Castillo, Juan Manuel; Cotterill, Daniel; Daly, Eoghan; Dow, Gareth; Gómez, Breogán; Fraser-Leonhardt, Vivian; Hirschi, Joel J.-M.; Lewis, Huw W.; Mahmood, Sana; Worsfold, Mark.
2024
Exceptional atmospheric conditions in June 2023 generated a northwest European marine heatwave which contributed to breaking land temperature records.
Communications Earth & Environment, 5 (1).
10.1038/s43247-024-01413-8
2024
Article
Marine heatwaves and cold spells in the Northeast Atlantic: what should the UK be prepared for?
Jacobs, Zoe Louisa ORCID: https://orcid.org/0000-0001-7348-0699; Jebri, Fatma ORCID: https://orcid.org/0000-0002-7048-0068; Wakelin, Sarah ORCID: https://orcid.org/0000-0002-2081-2693; Strong, James ORCID: https://orcid.org/0000-0001-8603-097X; Popova, Ekaterina ORCID: https://orcid.org/0000-0002-2012-708X; Srokosz, Meric ORCID: https://orcid.org/0000-0002-7347-7411; Loveridge, Alexandra.
2024
Marine heatwaves and cold spells in the Northeast Atlantic: what should the UK be prepared for?
Frontiers in Marine Science, 11.
10.3389/fmars.2024.1434365
2024
Article
Dive Deeper: NOC's Marine Heatwaves Research
NOC scientists use long-term observations and advanced computer models to study the causes and consequences of marine heatwaves. We combine satellite data, deep-sea observatories, robotic floats, and numerical models to monitor the ocean and simulate marine heatwave events, helping predict their impact and support adaptation.