Acidification of the Arctic Ocean greater than expected

The Arctic Ocean will absorb more _CO2 this century than most climate models have calculated so far. This also significantly increases the expected acidification. This is confirmed by a study by climate researchers from the University of Bern and ENS in Paris. Ocean acidification threatens organisms with calcareous shells, such as mussels or marine snails, and can thus have serious effects on the entire food chain.

The world’s oceans absorb large amounts of human-emitted CO₂ from the atmosphere. The additional CO₂ absorbed leads to acidification of the oceans, which is already observed today. This consequence of climate change mainly affects organisms with calcareous shells and skeletons, such as mussels, sea urchins, starfish and corals. Among the world’s oceans, it is the Arctic Ocean in which acidification has progressed the most.

A study just published in the renowned journal “Nature” by the Bernese climate scientist Jens Terhaar and colleagues from the Ecole Normale Supérieure (ENS) in Paris shows that the acidification of the Arctic Ocean is likely to be much higher than expected. The study found that the smallest of the seven oceans in the world will absorb 20 percent more_CO2 by the end of this century, assuming that greenhouse gas growth is proceeding unchecked. “This leads to a much higher acidification, especially at a depth of between 200 and 1000 metres,” explains Jens Terhaar, member of the group for ocean modelling at the Oeschger Center for Climate Research at the University of Bern. This depth area is an important retreat for many marine life forms.

Consequences for the entire food chain
The acidification of the seas directly affects all living beings that form calcareous shells. In acidified sea water, sufficient calcium carbonate is missing as a component of calcareous skeletons for shells, snails, sea urchins and phytoplankton, among others. “Our results suggest,” says co-author Lester Kwiatkowski, “that for shellfish, adapting to acidification in the Arctic Ocean is becoming increasingly difficult.” If these animals are lost in the food chain, this is likely to have a negative impact on the entire food chain, including fish and marine mammals.

New method allows more reliable predictions
The international research team’s study found that model calculations of _CO2 absorbed by the Arctic Ocean lead to very different results depending on the climate model. The researchers succeeded in establishing a physical relationship across all models between the current density of seawater on the surface and the associated formation of deep water.

Greater deep water formation leads to greater transport of CO₂ into the interior of the ocean and thus to a higher acidification. The density of the surface water thus serves as an indirect indicator for the acidification of the Arctic Ocean. With the help of measurements of the sea water density, this connection enables researchers to reduce the previous uncertainties of the model calculations. Thus, the team was able to give far better estimates of the extent of future acidification.

Greater deep water formation leads to greater transport of CO₂ into the interior of the ocean and thus to a higher acidification. The density of the surface water thus serves as an indirect indicator for the acidification of the Arctic Ocean. With the help of measurements of the sea water density, this connection enables researchers to reduce the previous uncertainties of the model calculations. Thus, the team was able to give far better estimates of the extent of future acidification.

Source: University of Bern