Deep ocean warming investigated in the subtropical North Atlantic Ocean

A research team from the University of Exeter has investigated deep ocean warming in the North Atlantic Ocean.

What causes deep ocean warming?

The majority of the ‘excess heat’ stored in the subtropical North Atlantic Ocean has been discovered in the deep ocean, which is approximately 700 metres below the surface.

Scientists have estimated that 90% of ocean warming has been caused by humans; the study revealed that 62% of this warming – measured from 1850 to 2018 – is held deep in the subtropical North Atlantic Ocean (25°N).

This study is titled: ‘The redistribution of anthropogenic excess heat is a key driver of warming in the North Atlantic,’ and was recently published in the journal, Nature.

Additionally, this study utilised temperature records and chemical tracers, which are compounds whose make-up can be utilised to uncover past changes in the ocean.

How will this escalate in the coming years?

A collaborative team including researchers from the University of Exeter and the University of Brest has estimated that deep ocean warming will increase by a further 0.2°C in the next 50 years. This is considered detrimental by scientists because ocean warming can have a variety of consequences, including sea-level rise, changing ecosystems, currents and chemistry, as well as deoxygenation.

“As our planet warms, it is vital to understand how the excess heat taken up by the ocean is redistributed in the ocean interior all the way from the surface to the bottom, and it is important to take into account the deep ocean to assess the growth of Earth’s ‘energy imbalance’,” explained Dr Marie-José Messias, from the University of Exeter.

“As well as finding that the deep ocean is holding much of this excess heat, our research shows how ocean currents redistribute heat to different regions. We found that this redistribution was a key driver of warming in the North Atlantic.”

How do the currents impact this?

In order to gain further information about how the currents impacted the deep ocean warming detected by scientists, they studied the system of currents known as, the Atlantic meridional overturning circulation (AMOC).

Taking this into consideration during the experiment was useful, as the AMOC works like a conveyer belt, and carries warm water from the tropics in the North, which is where the colder, more dense water sinks into the deep ocean and spreads slowly to the South.

Thus, these findings highlight the importance of deep ocean warming, demonstrating transference from one AMOC region to another.

Dr Messias concluded: “Excess heat from the Southern Hemisphere oceans is becoming important in the North Atlantic – now accounting for about a quarter of excess heat.”

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