Study finds high GHG emissions could turn continental shelves in Antarctic Marine Protected Areas severely acidic by 2100

A new study has raised concerns about the rising acidity levels of the continental shelves in Antarctic Marine Protected Areas (MPA) under high levels of greenhouse gas emissions. Carbon emissions from human activities may be vertically mixed with ocean waters in coastal regions, resulting in severe acidification at all water levels, it suggested. 

Shallow, underwater areas extending from the edge of continents known as continental shelves are expected to see more severe acidification than the open ocean. The study, Severe 21st-century ocean acidification in Antarctic Marine Protected Areas, was published in journal Nature Communications on January 4, 2024.

Read more: Not just oceans, freshwater bodies are turning acidic as well

The ocean helps to mitigate the effects of global warming by absorbing some of the carbon dioxide gas (CO2) that is released into the atmosphere. This comes at a cost to ocean health because the uptake of anthropogenic CO2 causes changes in ocean chemistry, known as ocean acidification, which can be harmful to marine ecosystems.

If we continue with moderate to high levels of greenhouse gas emissions, ecosystems in the shallow continental shelf seas in proposed and established MPAs could experience significant ocean acidification by 2100. Under the intermediate and high emission scenarios, the acidification could be severe. 

For the high and very high emissions scenarios, there will be a widespread lack of aragonite (a type of carbonate mineral) saturation in the proposed and established MPAs by the end of the century. The undersaturation will extend from the ocean’s surface to its depths. This undersaturation implies that organisms such as pteropods that form aragonite won't be able to find places with stable conditions for their shells.

The pH scale could decline by up to 0.36 (on the total scale) for the top 200 metres of the ocean by 2100, the study projected. The study, led by Cara Nissen from University of Colorado, concluded that widespread aragonite undersaturation will occur by the end of the century under the three highest emission scenarios.

Given the cumulative threat to marine ecosystems from environmental change and activities such as fishing, the researchers called for strong emission-mitigation efforts and further management strategies to reduce pressures on ecosystems, such as the continuation and expansion of Antarctic MPAs.

Read more: Increasing ocean acidity will hit the marine food chain, says study

Designed to protect the unique high-latitude Southern Ocean biodiversity, a network of MPAs is being developed by the Commission for the Conservation of Antarctic Marine Living Resources. 

MPAs have been established at the South Orkney Islands Southern Shelf and in the Ross Sea region, with three additional MPAs proposed in the Weddell Sea, East Antarctica and along the western Antarctic Peninsula. If realised, this network of MPAs would protect around 60 per cent of Antarctic shelf waters.

India will continue to support setting up two MPAs in Antarctica to protect marine life and its ecosystem services, Jitendra Singh, Union minister of state (independent charge) for science and technology and earth sciences, told Down To Earth on March 27, 2023.