Acidification of the Bay of Biscay

The challenge

Ocean acidification is another effect of climate change that is already being observed in the Bay of Biscay. It can particularly affect organisms that depend on calcium carbonate to form shells, skeletons or protective structures, such as bivalves, crustaceans or cold-water corals. It was necessary to check whether rising atmospheric CO₂ was also altering ocean chemistry in this region.

The solution

AZTI led a study based on more than 21,700 pH measurements taken between 2002 and 2022 at three coastal stations, in the layers between the surface and a depth of 100 metres. This made it possible to analyse how pH has changed over two decades and to compare its behaviour at different points along the coast.

The results

• A sustained decline in pH was detected in Basque coastal waters, confirming that rising atmospheric CO₂ is also altering ocean chemistry in this region.
• pH is falling by between 0.022 and 0.041 units per decade, at rates slightly higher than the global average.
• Similar values at all three stations analysed, which points to a homogeneous pattern of acidification along the coastal strip of the southeast of the Bay of Biscay.
• If the current trend continues, no severe effects are expected in the coming decades. However, acidification can act in combination with other factors linked to climate change: warming waters, oxygen loss, sea-level rise and extreme events.
• pH monitoring is a key indicator of marine climate change. It reinforces the importance of maintaining long-term monitoring networks to understand how this process evolves locally and to guide mitigation, adaptation and marine management measures.