The Atlantic Ocean near Bermuda is warmer and more acidic than ever, 40 years of observations show

Decade-long warming of the oceans that affects ocean circulation, decreasing oxygen levels that contribute to changes in salinification and nutrient supply, and ocean acidification are just some of the challenges facing the world’s oceans.

In 1988, a comprehensive and sustained time series of ocean observations, called the Bermuda Atlantic Time Series Study (BATS), began at a site approximately 80 km southeast of the island of Bermuda. There, scientists take monthly samples of the physics, biology and chemistry of the surface and depths of the ocean.

In a new article published in Frontiers of Marine Sciencethe researchers have now presented the latest results of this monitoring effort.

“We show that the ocean surface in the subtropical North Atlantic Ocean has warmed by about 1°C over the past 40 years. In addition, ocean salinity has increased and it lost oxygen,” said author Professor Nicholas Bates. Oceanian researcher at the Bermuda Institute of Ocean Science, a unit of the Julie Ann Wrigley Global Futures Laboratory at Arizona State University (ASU) and professor in the ASU School of Ocean Futures. “Additionally, ocean acidity increased between the 1980s and the 2020s.”

Hot, salty, deoxidized, sour

At the BATS monitoring station, ocean surface temperatures have increased by about 0.24°C each decade since the 1980s. In total, the ocean today is about 1°C warmer than it was. at 40 years old. Over the past four years, ocean temperatures have also increased more sharply than in previous decades, the researchers found.

Not only have the monitored waters become warmer, but also saltier on the surface, meaning more salt is dissolved in the water. Like surface temperature, this salinity has increased disproportionately in recent years, according to the most recent data.

“We suspect this is part of broader, more recent trends and changes in ocean temperatures and environmental changes, such as atmospheric warming and the hottest years in the world,” Bates said.

At the same time, data indicates that over the past 40 years, the amount of oxygen available to living aquatic organisms has decreased by 6%. Acidity values ​​have also changed: the ocean is now 30% more acidic than it was in the 1980s, leading to lower carbon ion concentrations. This can, among other things, affect the ability of shelled organisms to maintain their shells.

“The ocean chemistry of surface waters in the 2020s is now outside the seasonal range observed in the 1980s and the ocean ecosystem now lives in a different chemical environment than a few decades ago,” he said. explained Bates. “These changes are due to the absorption of anthropogenic CO₂ of the atmosphere.”

Importance of long-term data

Collecting data over extended periods of time is important for predicting future changes in conditions. “These observations provide insight into the rate of change in the recent past in ocean warming and chemistry. They provide key insights into future changes over the coming decades,” Bates said. “They are also evidence of the regional and global environmental changes and existential challenges we will face as individuals and societies in the near future.”

The monitoring stations providing data for the present study are just two of many long-term sustained ocean time series sites located throughout the world’s oceans. Stations off the coast of Hawaii, the Canary Islands, Iceland and New Zealand also play a key role in monitoring long-term ocean changes. At some of these stations, similar processes were observed, highlighting the challenges and complexity of understanding the long-term interactions between ocean warming, salinification and acidification, the researchers said.