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 study by a consortium of British and Irish institutions led by Met Office scientists, including the Scottish Association for Marine Science (SAMS) and Plymouth Marine Laboratory (PML), 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.
Impacting variables
SAMS oceanographer 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 16th.
Autonomous underwater vehicles, known as gliders, were able to detect the marine heatwave as it happened. Credit: SAMS
New technology
SAMS 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.
Co-author Dr Sam Jones from SAMS said: “Gliders are similar to having a mobile thermometer in the ocean interior and can operate continuously at sea for several months.
“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.”
Prof. Tim Smyth of PML and co-author on the study, said: “Meteorological events, such a marine heatwaves and storms, highlight the importance of having autonomous instruments in the water measuring when we cannot get out to our sampling stations on boats, and at a high enough frequency (hourly), to capture data on these phenomena.”
The paper – “Exceptional atmospheric conditions in June 2023 generated a Northwest European marine heatwave which contributed to breaking land temperature records” – is published in Communications Earth and Environment.