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Just as the UK is in the midst of a new marine heatwave, new analysis has been published of the unprecedented sea surface temperatures of up to 5 °C higher than normal off northwest Europe in June last year.

A new by a consortium of British and Irish institutions, including the Scottish Association for Marine Science (SAMS) in Oban, showed the region experienced its longest recorded category II marine heatwave (16 days). This means temperatures around the British Isles reached a 16°C peak in June instead of 13.5°C. 

�鶹ӰԺoceanographer Prof. Mark Inall, a co-author on the paper, said: “Our study showed the marine heatwave developed quickly due to high-pressure weather conditions including reduced levels of cloud cover, strong sunshine levels, weak winds and tropical air. Additionally, the high pressure suppressed wave activity resulting in little mixing through the water column, allowing the sea surface water to warm quickly.”

A feedback mechanism from the sea to the land, caused by a warming ocean heating the air above, contributed to record-breaking mean temperatures for the UK and heavier rainfall through stronger, warmer and more moist sea breezes. 

Prof. Inall added: “An intriguing aspect of this study is that the extreme marine heatwave was shown to then warm the air, and contribute to a heatwave in parts of the UK – marine temperatures matter to UK’s towns and cities.

“Our findings suggest that such high sea surface temperatures will become commonplace by the middle of the century, without strong mitigation to slow the rise of greenhouse gas emissions.” 

The UK is currently experiencing another marine heatwave, which began on since May 16^th.

Co-author Dr Sam Jones is an oceanographer at SAMS, which contributed data from an autonomous underwater robot called a glider. The glider was patrolling the north-east Atlantic at the time of the heatwave last June. He said: “Gliders are similar to having a mobile thermometer in the ocean interior.

“Satellites are great at measuring the sea surface ‘skin’ over a large area and the shallowest fixed mooring sensors we have are about 50 metres’ depth, so gliders can fill in the gaps and do so in great detail. For example, we were able to ascertain that the warming event last June was exclusively in the upper 40 metres of the sea, at least in its early stages. Below that, temperatures were fairly typical.”

The paper – “” – is published in Communications Earth and Environment. 

The study involved a consortium of scientist from the Met Office, Plymouth Marine Laboratory; the University of Exeter; National Oceanography Centre; Scottish Association for Marine Science; Marine Institute (Ireland); the Marine Directorate of the Scottish Government; and the University of Bristol.