Canary waters turn from carbon sink to CO2 source

Canary waters turn from carbon sink to CO2 source after 2023 marine heatwave

The waters around the Canary Islands have begun emitting more carbon dioxide (CO2) than they can absorb. The culprit? A marine heatwave that battered the archipelago in 2023 – the hottest year on record – which, despite having dissipated, has left a thermal “inertia” in the ocean that is preventing temperatures from dropping back down. Scientists remain uncertain, for now, whether the ocean will ever return to its normal state.

Unprecedented marine heatwave and its lingering effects

This situation is already having tangible consequences on marine ecosystems, which are becoming less hospitable for endemic species and far more attractive to exotic ones, some of which are toxic. In 2023, the waters around the islands suffered an unprecedented marine heatwave that lasted more than 400 days and pushed temperatures to historic highs. That same year, the Canary Islands experienced the warmest period since records began, with an average temperature of 20.1°C and only a quarter of the expected rainfall. This coincided with the appearance of the El Niño phenomenon (ENSO) in the Pacific.

In 2023, thermometers recorded a minimum sea temperature of 19.4°C and a maximum of nearly 27°C. These figures were two degrees higher than what had been recorded in previous years, against a backdrop of normal conditions already affected by climate change.

‘During successive winters the temperature has not dropped as much as it should’

“During successive winters, the temperature has not dropped as much as it should,” confirms Melchor González Dávila, a marine chemist from the Quima group at the University of Las Palmas de Gran Canaria (ULPGC), in an interview with EL DÍA, during the fifth edition of the ‘Un viaje al futuro sostenible de CanBio’ conference, where the results of this project were presented. The project has been studying the impacts of climate change on Canary Islands ecosystems for several years. It is a vast research initiative involving both public universities, the Government of the Canary Islands, and the Loro Parque Foundation.

Specifically, González Dávila explains that in winter, the sea temperature in the Canary Islands would normally not exceed 18.8°C. “Now we are sitting at around 19.4°C,” the researcher highlights. Although this may seem a trivial figure, it is only when placed in context that the gravity becomes clear. “Until now, the sea temperature was increasing at a rate of 0.3 hundredths of a degree per year, and in the last three years it has done so at a rate of 0.3 degrees.” “It’s staggering,” he insists.

According to open data from the Raprocan network, a project of the Spanish Institute of Oceanography (IEO), the current surface temperature of the sea in the Canary Islands stands at 19.29°C.

The ocean around the Canary Islands is no longer a carbon sink

This rise in temperatures has brought with it a notable increase in the concentrations of carbon dioxide in the sea, which has reached its limit as a CO2 sink. “The sea around the Canary Islands no longer acts as a sink, but as a source of carbon dioxide,” reveals González. It is worth remembering that the sea, along with forests and soil, are the most important natural systems for absorbing excess carbon dioxide from the planet.

This means that ocean acidification has accelerated compared to initial forecasts regarding the impact climate change will have on the Canary Islands. “Ocean acidification – the increase in CO2 concentrations that causes a change in its pH – is the silent impact of climate change on the ocean, because we basically can’t see it,” defines Aridane González, an oceanographer at ULPGC.

Threat to endemic species and the blue economy

Although invisible, the increase in this acidification does leave palpable consequences. “It affects everything related to carbonate in the ocean,” González explains, including organisms that have calcareous shells, such as corals, gorgonians, and gerardias. “A more acidified ocean is an ocean where these organisms find it much harder to form their carbonate skeletons and, therefore, they are at risk of even disappearing,” the oceanographer insists.

On the other hand, this change in sea conditions opens the door to invasive, exotic, and some toxic species. “Species of general interest to Canarian ecosystems are disappearing,” explains González. Some of these are as important as the brown algae of the genus Cystoseira, and according to González, “they are practically no longer seen.” As he insists, this has effects on the development of the blue economy – one of the cornerstones of the Canary Islands’ scientific strategy – with impacts on agriculture, fishing, and the development of marine infrastructure.

“Desalination plants, for example, have an optimal range for temperature, and the change in pH affects the quality of the membranes.” “A warmer ocean also affects the safety and social vulnerability of the Canary Islands in this sense,” the researcher concludes.

Approaching a point of no return

The oceans are the largest natural sinks, as they are capable of absorbing almost 50% of the carbon emitted into the atmosphere through organisms such as plankton, corals, and algae. These types of structures are fundamental for balancing emissions from the burning of fossil fuels, industry, and livestock farming. It is precisely anthropogenic climate change that could push them to a limit of no return, meaning they can no longer fulfil that fundamental role as sinks.

Precisely, this is what this research group will begin to study from now on. “Thanks to the time series data, we will be able to reconstruct how carbon absorption in the Canarian sea has changed and see whether, indeed, the ocean of the Canary Islands has reached that point of no return,” González concludes.

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Canary waters turn from carbon sink to CO2 source