Alarming shifts in ocean health: Less oxygen, more heat and acidity

The Atlantic Ocean has experienced significant changes over the past 40 years, according to the Bermuda Atlantic Time-series Study (BATS). The recent findings from this long-term monitoring effort present a concerning picture of the ocean’s health.

The research project, which was launched in 1988 about 80 kilometers southeast of Bermuda, has been meticulously recording the physics, biology, and chemistry of the ocean’s surface and depths through monthly samples. 

Key insights 

Based on this data, experts found that the Bermuda Atlantic is hotter and more acidic than ever before.

Professor Nicholas Bates is an ocean researcher at the Bermuda Institute of Ocean Sciences, a unit of the Julie Ann Wrigley Global Futures Laboratory at Arizona State University (ASU). 

“We show that the surface ocean in the subtropical North Atlantic Ocean has warmed by around 1°C over the past 40 years. Furthermore, the salinity of the ocean has increased, and it has lost oxygen,” said Professor Bates. “In addition, ocean acidity has increased from the 1980s to the 2020s.”

Surface temperatures

The BATS data reveals that the ocean surface temperatures have increased by about 0.24°C per decade since the 1980s, and this warming trend has accelerated in the last four years. 

Salinity

The ocean’s surface salinity has also increased, particularly in recent years. “We suspect this is part of the broader, more recent trends and changes in ocean temperatures and environmental changes, like atmospheric warming and having had the warmest years globally,” said Professor Bates.

Oxygen

One of the most concerning findings is the reduction in oxygen, which has decreased by 6% over the last 40 years. This decrease has serious implications for ocean health, as well as for marine life.

Acidity

Moreover, the ocean’s acidity has increased by 30% since the 1980s, leading to lower concentrations of carbon ions. This change in ocean chemistry can adversely affect marine organisms, especially those with shells, by hampering their ability to maintain their shells.

Changing ocean chemistry 

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

The importance of long-term data collection in understanding and predicting shifts in ocean health cannot be overstated. 

“These observations give a sense of the rate of change in the recent past of ocean warming and ocean chemistry. They provide key indications of future changes in the next decades,” said Professor Bates. “They also are proof of regional and global environmental change and the existential challenges we face as individuals and societies in the near future.”

Monitoring stations

The BATS monitoring station is one of several long-term sustained ocean time-series sites across the globe. Other key stations are located off Hawaii, the Canary Islands, Iceland, and New Zealand.

The researchers noted that similar ocean processes have been observed at some of those stations, highlighting the challenges and complexities of understanding the long-term interactions between warming, salinification, and ocean acidification.

The study is published in the journal Frontiers in Marine Science.

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