Subtropical North Atlantic Ocean more saline and acidic in last 40 years: Study

By Nicholas Bates for The Conversation

New Delhi: The surface temperature of the subtropical North Atlantic Ocean has warmed by around one degree Celsius, scientists have found after monitoring the region for the past 40 years.

Further, the ocean has become more acidic and saline and has lost oxygen, the researchers from Arizona State University in the US have found.

The Bermuda Atlantic Time-series Study (BATS) began in 1988 at a site about 80 kilometres southeast of the island of Bermuda.

The study, published in the journal Frontiers in Marine Science, found that especially in the last four years, the ocean surface temperatures have also risen more sharply, even as they increased by around 0.24 degrees Celsius each decade since the 1980s.

"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 Nicholas Bates, an ocean researcher at the Bermuda Institute of Ocean Sciences at Arizona State University.

The ocean is now 30 per cent more acidic than it was in the 1980s, resulting in lower carbon ion concentrations. This can, among other things, affect shelled organisms' ability to sustain their shells, the researchers said.

Their data also suggested that over these 40 years, the oxygen available to aquatic life has reduced by six per cent.

"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. These changes are due to the uptake of anthropogenic CO2 from the atmosphere," said Bates.

The researchers said that collecting data over extended time periods provide key indications of future changes in the next decades. Bates said that they are also proof of regional and global environmental change and the existential challenges we face as individuals and societies in the near future.

The data for the study was collected from several monitoring stations recording time-series information, including those in Hawaii, the Canary Islands, Iceland, and New Zealand.

Many of these stations have observed similar processes of ocean warming, salinification and acidification, which highlight the challenges and complexities of understanding the long-term interactions between these processes, the researchers said.

(Nicholas Bates is an ocean researcher at the Bermuda Institute of Ocean Sciences at Arizona State University.)