The likelihood that marine organisms and the ocean environment are already being impacted by ocean acidification is “increasing by the day”, claim scientists close to the subject who, in the wake of new research into the depths acidification is now reaching in marine space, argue that “any assumption we are still within planetary boundaries are just plain wrong”.

It has raised new concerns that, while we still know relatively little about the ocean acidification crisis, evidence is only mounting that the ocean is now operating “far outside of a supposedly safe space.”

Earlier this month, research published in Science Advances surfaced to reshape our current understanding of the severity of ocean acidification, highlighting that while it once was an occurrence assumed only to impact the surface level layers of the ocean, it is in reality sinking into marine regions as deep as 1,500 metres and posing new threats to the marine life and organisms that dwell there, including sea snails and cold-water corals.

It had previously been established that the uptake of carbon dioxide impacts the acidity of the ocean’s surface. Earlier this year, scientists presented an open letter to world leaders at COP16, calling for funds and investment to support research into the impact ocean acidification is having on marine ecosystems and biodiversity. 

Among those to have signed this letter was Professor Steve Widdicombe, director of science at Plymouth Marine Laboratory who told Oceanographic Magazine that given the latest findings into the depths ocean acidification is now reaching, “we should be even more concerned for the health and sustainability of marine life and ecosystems, as well as the services and benefits those ecosystems provide us.”

Leading a team of researchers at Plymouth Marine Laboratory, Professor Widdicombe helped publish a report earlier this year bringing the issue of ocean acidification to the world’s attention. The report came with a call on nations to start unlocking the finances for research into ocean acidification and the impact it was having on the biodiversity within the marine spaces.  

As the world’s largest natural sink of carbon dioxide, the ocean is responsible for the absorption of around one quarter of the world’s annual emissions. As those emissions increase, so too does the impact of ocean acidification. At its most simplistic, acidification occurs when a series of chemical reactions drop the pH levels of the ocean, making it more acidic. This, according to Widdicombe, poses a “serious threat to marine life” whose survival depends on the chemical stability of their ecosystems.

“Carbon is an important ingredient to the ocean’s ecosystem; it’s the mineral that organisms use to build their shells’ it’s heavily relied upon by all sorts of organisms from corals to crabs and lobsters, to mollusks and oysters,” explained Widdicombe.  

“The pH of the ocean is also crucially important, because it can influence the physiology of cells. We have measured the impact of ocean acidification in the laboratory for the past 20 years, and we’ve seen case after case of its negative impact on growing organisms.”

The depths at which ocean acidification is now occurring is raising fresh concerns over the scale of that negative impact. It is well understood that the deeper we dive into the ocean layers, the more fragile and co-dependent ecosystems become. Delicate balances are required to sustain healthy systems. 

Coral reefs, for example, are among those organisms at particular risk. The acidic waters hinder their skeleton-building abilities, resulting in coral bleaching and eventual death. This then creates a domino effect on marine systems dependent on the ecosystems healthy coral provide.

It was the work of Jens Daniel Müller and his colleague, Nicolas Grube at the Federal Institute of Technology Zurich in Switzerland, that brought these newest findings to the scientific community’s attention earlier this month, having developed a 3D reconstruction of how carbon dioxide moves through the ocean, based on global measurements of currents and other circulation patterns. By using this model to estimate how the carbon dioxide the oceans have absorbed since 1800, the team of researchers have been able to illustrate just how greenhouse gas emissions have affected deep-water acidity since the start of the industrial revolution.

What it found was there is a clear indication of acidification down to depths as far as 1,000 metres below the surface across most of the ocean. This went deeper still in some areas, such as the North Atlantic – where the Atlantic Meridional Overturning Current (AMOC) routinely carries carbon from the surface to deeper waters – where acidification has reached depths of 1,500 metres beneath the surface.

“I can’t say I’m surprised to learn about the depths at which ocean acidification is found to be occurring,” continued Professor Widdicombe. “I very much suspected that the more we learned about how ocean acidification was progressing, the more concerning it would reveal to be. The assumption that we are still largely within the planetary boundaries for ocean acidification is plainly wrong, and the ocean is now having to operate outside of a supposedly safe space.”

It’s notable that the most severe worsening of ocean acidification has taken place over the course of the last two decades, accelerating at a pace that both Müller and Grube refer to simply as “remarkable”. 

For scientists at Plymouth Marine Laboratory, it’s a clear indication that efforts to mitigate the impacts of ocean acidification now need to be ramped up before it’s too late.

“Time is running out and substantial carbon emissions reductions are critical,” said Widdicombe. “The longer we wait to take necessary action, the worse the impacts will be. But make sure the action we do take is based on sound evidence and we don’t make the problem worse.

“Our approach should be three-fold: We must stop emitting carbon dioxide into the atmosphere; we must protect and restore natural ecosystems that provide marine ecosystems with greater resilience and promote the natural cycling of carbon; and we must invest in research that could provide potential ways of removing carbon from the ocean.”

Click here for more from the Oceanographic Newsroom.