Over 40 Years, Disturbing Climate Pattern Arises in Bermuda Waters

The Bermuda Atlantic Time-series Study has, over the course of 40 years, observed considerable warming, salinization, deoxygenation, and acidification of the North Atlantic Ocean. This underscores the significant transformations happening in the world's marine environments.

Information accumulated over four decades highlights changes in the subtropical North Atlantic Ocean near Bermuda where water temperatures have risen by 1°C.

The state of the oceans is in constant flux, with not only marine ecosystems being affected but also terrestrial life. Ocean monitoring stations in the North Atlantic have been diligently recording these changes for years. Researchers are now beginning to reveal current trends, which indicate that the waters near Bermuda have become warmer, saltier, and more acidic, with decreased levels of oxygen, compared to 40 years ago. The researchers stressed the importance of this long-term monitoring effort in forecasting the considerable challenges societies may face in the near future.

The Bermuda Atlantic Time-series Study (BATS) team is located on the BIOS research vessel Atlantic Explorer.

The warming of our oceans over decades, impacting ocean currents, a reduction in oxygen levels influencing sea water salinity and nutrient distribution, and the acidification of the sea are some of the global challenges currently faced by our oceans.

The Bermuda Atlantic Time-series Study (BATS), a comprehensive sustained campaign of oceanic observation, was initiated in 1988 at a location approximately 80 km southeast of Bermuda. Scientists here regularly collect samples of the physical properties, biology, and chemistry of the ocean’s surfaces and depths. Researchers have most recently published the newest findings from this sustained study in Frontiers in Marine Science.

“We demonstrate that over the last 40 years the surface temperature of the subtropical North Atlantic Ocean has increased by around 1°C. The ocean has also become more saline, and oxygen levels have decreased,” states author Prof Nicholas Bates, who studies oceanography at the Bermuda Institute of Ocean Sciences, part of the Julie Ann Wrigley Global Futures Laboratory at Arizona State University (ASU), and works as a professor in the School of Ocean Futures at ASU. "Moreover, the acidity of the ocean has increased from the 1980s to the 2020s."

The BATS team is located on the BIOS research vessel Atlantic Explorer.

The ocean surface temperature at the BATS monitoring station has risen by an average of 0.24°C per decade since the 1980s. This means the ocean is currently around 1°C warmer than 40 years ago. Over the last four years, this rise in temperature has been more rapid than in previous decades, as revealed by the researchers.

The water monitored by these efforts has not only warmed but has also become more saline, indicating an increased concentration of salt in the water. Just like surface temperatures, this salinity has seen a disproportionate increase in recent years. “We believe this indicates a connection to broader, more recent shifts such as ocean temperature and environmental changes and the recent record-breaking warm years,” remarks Bates.

Members of the Bermuda Atlantic Time-series Study (BATS) team aboard BIOS's research vessel, the Atlantic Explorer.

At the same time, the data reveals a decrease in available oxygen for aquatic life by 6% over the last 40 years. Ocean acidity has also increased: the ocean is now 30% more acidic compared to the 1980s, leading to reduced concentrations of carbon ions. Among other impacts, this can hinder the ability of shelled organisms to maintain their shells.

“The 2020s have seen surface waters diverge from patterns observed in the 1980s, resulting in an altered chemical environment for ocean ecosystems compared to a few decades prior,” Bates said. "These changes are a direct result of the absorption of man-made CO2 from the atmosphere."

Bates points out the importance of long-term data collection in predicting future environmental changes. "These observations provide important indications of the pace of recent changes in ocean warming and chemistry and give crucial insight into the changes we may see in future decades. They are testament to regional and global environmental changes and the pressing challenges we as individuals and societies are likely to encounter in the near future."

The BATS team, pictured in the lab.

The monitoring stations providing the data for the present study are just two out of the several long-term sustained ocean time-series sites located throughout the world’s oceans. Stations off Hawaii, the Canary Islands, Iceland, and New Zealand are also key to monitoring long-term oceanic changes. At some of those stations, similar processes have been observed, highlighting the challenges and complexities of understanding the long-term interactions between warming, salinification, and ocean acidification, the researchers said.

Reference: “Forty years of ocean acidification observations (1983–2023) in the Sargasso Sea at the Bermuda Atlantic Time-series Study site” by Nicholas R. Bates and Rodney J. Johnson, 25 October 2023, Frontiers in Marine Science. DOI: 10.3389/fmars.2023.1289931