Oceans uptake of carbon ‘widely underestimated’

Researchers have discovered that, compared to previous predictions, there is more than twice the amount of ocean carbon uptake between the atmosphere and oceans

The world’s oceans soak up a large majority of carbon dioxide emissions from human activities. By absorbing carbon dioxide (CO2), the ocean reduces the amount of warming those emissions would otherwise cause.

Absorbing carbon dioxide increases the acidity of seawater, which can harm shell-building creatures and other marine life.

Previous estimates of the movement of carbon (known as ‘flux’) between the atmosphere and oceans have not accounted for temperature differences at the water’s surface and a few metres below.

The new study, led by the University of Exeter, includes this – and finds significantly higher net flux of carbon uptake into the oceans.

It calculates CO2 fluxes from 1992 to 2018, finding up to twice as much net flux in certain times and locations, compared to uncorrected models.

A small difference in ocean surface temperature

Andrew Watson from Exeter’s Global Systems Institute, said: “Half of the carbon dioxide we emit doesn’t stay in the atmosphere but is taken up by the oceans and land vegetation ‘sinks’.

“Researchers have assembled a large database of near-surface carbon dioxide measurements – the Surface Ocean Carbon Atlas, that can be used to calculate the flux of CO2 from the atmosphere into the ocean.

“Previous studies that have done this have, however, ignored small temperature differences between the surface of the ocean and the depth of a few metres where the measurements are made.

“Those differences are important because carbon dioxide solubility depends very strongly on temperature.

The study used satellite data to correct the differences in temperature, which resulted in a substantially larger flux going into the ocean.

The calculated difference in ocean carbon uptake results to about 10% of global fossil fuel emissions.

Jamie Shutler of the Centre for Geography and Environmental Science at the University of Exeter, added: “Our revised estimate agrees much better than previously with an independent method of calculating how much carbon dioxide is being taken up by the ocean.

“That method makes use of a global ocean survey by research ships over decades, to calculate how the inventory of carbon in the ocean has increased.

“These two ‘big data’ estimates of the ocean sink for CO2 now agree pretty well, which gives us added confidence in them.”