As the climate changes, the deep ocean is warming

The subtropical North Atlantic. Credit: Marie-Jose Messias

New research reveals that much of the “excess heat” in the subtropical North Atlantic Ocean (below 700 metres) is trapped in the deep ocean.

Nearly all of the heat generated by human activity has been absorbed by the oceans. Researchers showed that in the subtropical North Atlantic (25°N), 62% of the warming between 1850 and 2018 occurred in the deep water.

Deep ocean temperatures will rise by 0.2°C in the next 50 years, according to researchers from Exeter University and the University of Brest.

Temperature increases in the ocean can have a wide range of effects on marine ecosystems and chemistry, as well as sea-level rise.

According to Dr. Marie-José Messias of the University of Exeter, as the Earth’s surface heats up, it’s critical to know how that heat is redistributed inside the ocean’s interior, all the way down to Earth’s deepest layers, in order to gauge the planet’s increasing “energy imbalance.

Besides discovering that the deep ocean is retaining most of this surplus heat, our research demonstrates how ocean currents transport heat to different places.

“We discovered that this shift was a crucial factor in the North Atlantic’s warming,” the authors write.

The Atlantic Meridional Overturning Circulation (AMOC) was the focus of their research (AMOC).

Atmospheric Moisture Exchange (AMOC) is an ocean conveyor belt that moves warm water from the tropical regions north to the deep ocean.

The study’s findings demonstrate the significance of AMOC-mediated warmth transmission between regions.

According to Dr. Messias, the surplus heat from the Southern Hemisphere waters is now accounting for nearly a quarter of the total heat in the North Atlantic.

Chemical “tracers”—compounds whose composition can be used to track ocean changes in the past—were used in this investigation.

Nature magazine Communications Earth & Environment published the study entitled “The redistribution anthropogenic excess heat is a fundamental driver in the North Atlantic’s warming..”

Further information: The redistribution of anthropogenic excess heat is a key driver of warming in the North Atlantic, Communications Earth & Environment (2022). DOI: 10.1038/s43247-022-00443-4

Journal information: Communications Earth & Environment

Source: University of Exeter