Ocean Acidification

La planète terre est en mauvaise santé. Une étude scientifique vient de réaliser un bilan de neuf différents critères en atteste. Six indicateurs sont déjà dans le rouge et une septième limite planétaire s’apprête à être dépassée, celle concernant l’acidification des océans. C’est inévitable d’ici quelques années mais cela ne doit pas décourager l’action pour limiter les risques.

L’acidification des océans met en danger la biodiversité marine. Getty Images/ Georgette Douwna

Tout commence avec nos émissions de CO2. Les énormes quantités de dioxyde de carbone que nous larguons dans l’atmosphère n’entraînent pas seulement le réchauffement du climat, elles déstabilisent aussi l’équilibre de l’océan. Une partie du CO2 atmosphérique se dissout en effet dans l’eau de via des réactions chimiques naturelles. Depuis le début de la révolution industrielle, environ un tiers du CO2 généré par les activités humaines a été absorbé par les océans.

Le problème c’est que cela engendre leur acidification. Puisque le CO2 est un gaz acide. L’acidification des océans a ainsi déjà augmenté de près de 30 % et si on ne modifie pas nos modes de vie, les modèles de prédiction prévoient une augmentation de 150 % de l’acidité d’ici à 2100.

Dissolution des mollusques et des coraux

Ce phénomène est suivi de près par les scientifiques comme Wolfgang Lucht, spécialiste des systèmes planétaires à l’Institut du climat de Postdam. « Beaucoup de microorganismes mais aussi d’organismes plus gros comme les coraux, construisent leur coquille ou leur squelette à partir de carbonate. Dans un océan plus acide, le carbonate se dissout plus facilement, ils ont donc de bien plus grandes difficultés à former leurs corps », explique-t-il. Comme lorsqu’on utilise du vinaigre pour dissoudre le calcaire, sauf que dans ce cas, ce sont les huîtres, les crabes, les oursins, les homards et les coraux… mais aussi toute une gamme de planctons microscopiques, briques essentielles de la vie sous-marine, qui sont menacés ou au moins fragilisés.

« Cela peut créer d’énormes perturbations dans toute la chaîne alimentaire océanique et on est maintenant très proche de la zone à haut risque où ces changements profonds peuvent arriver », met en garde Wolfgang Lucht. En d’autres termes, il alerte sur le fait qu’une nouvelle limite planétaire s’apprête à être dépassée.

Il y a 15 ans, une équipe scientifique internationale réunie autour du Stockholm Resilience Centre (SRC) a défini le concept des neuf limites planétaires : neuf indicateurs avec des seuils au-delà desquels « les équilibres naturels terrestres peuvent être déstabilisés et les conditions de vie devenir défavorables pour l’humanité », renseigne le Commissariat général au développement durable en France.

En septembre 2023, les chercheurs ont tiré la sonnette d’alarme car six des neuf limites planétaires ont déjà été franchies. Le réchauffement climatique, la chute de la biodiversité, la pollution aux engrais chimiques (les cycles de l’azote et du phosphore), la dégradation des sols, le cycle de l’eau douce, et l’introduction de nouveaux éléments comme les OGM, les nanoparticules ou autres plastiques dans la nature.

Six indicateurs témoins de la santé de la planète déjà dans le rouge

Reste la couche d’ozone et la présence de particules fines (ou aérosols) dans l’atmosphère. Ces deux indicateurs sont encore dans le vert. La limite pour l’acidification des océans s’apprête quant à elle à être franchie « d’ici quelques années » selon Boris Sakschewski, l’un des auteurs principaux du Planetary Health Check, un bilan de santé de la Terre pour faire l’état des lieux des limites planétaires et réactualisé désormais chaque année par l’Institut du climat de Postdam.

Nos modes de vie polluants ont déjà permis l’émission de trop de CO2, qui s’accumule dans l’atmosphère et qui finit par se dissoudre dans les océans. « Il va y rester des dizaines et des centaines de milliers d’années et s’il est difficile de prévoir l’ampleur exacte de l’impact de cette acidification, mais il est certain que cela ne sera pas anodin », explique Wolfgang Lucht, également auteur du Planetary Health Check. Et si certains changements s’annoncent déjà irréversibles, le chercheur appelle à ne pas se laisser gagner par la fatalité. « La meilleure des choses à faire et de limiter nos émissions pour éviter que cela ne devienne pire ».

Deploying profiling floats. (Photo credit: Hilary Palevsky)

To address gaps in ocean data and modeling efforts and better understand ocean carbon, oxygen and heat, oceanographers at the University of Hawaiʻi Mānoa were awarded $4.5 million from the nonprofit Schmidt Sciences. They are team members on two of five projects selected by Schmidt Sciences and the Schmidt Ocean Institute to join the Ocean Biogeochemistry Virtual Institute (OBVI).

The five projects will form the inaugural membership of OBVI, which has committed $45 million over the next five years. The research will address the interlinked questions of how rapidly the ocean is gaining heat and carbon while losing oxygen, and the resilience of marine ecosystems in a rapidly warming world.

Unmasking the silent threat to marine life. Discover how rising acidity levels are endangering our oceans and what we can do to protect these vital ecosystems.

Highlights:

• Understand how ocean acidification is affecting coral reefs, shellfish, and other marine organisms.
• Learn about the scientific processes behind ocean acidification and its implications for ocean chemistry.
• Explore the link between ocean acidification and climate change, highlighting the urgent need for action.
• Discover the initiatives and solutions being implemented to combat ocean acidification and protect marine ecosystems.

Introduction:

Imagine a world where the oceans, the lifeblood of our planet, turn into a hostile environment for marine life. This alarming reality is unfolding due to a phenomenon known as ocean acidification. This process is driven primarily by absorbing excess carbon dioxide from the atmosphere, significantly altering the chemistry of our seas. This change in pH levels is detrimental to marine ecosystems, particularly shell-forming organisms like corals and mollusks.

Pineapple sea cucumber underwater Photo: © ead72 – stock.adobe.com

Climate change impacts every corner of the planet, and the ocean is no exception. As climate change raises temperatures and leads to more unpredictable weather patterns, the delicate balance of marine ecosystems is increasingly at risk.

The ocean is the world’s largest carbon sink, absorbing approximately 90% of the excess heat caused by greenhouse gases and taking in 30% of carbon emissions. The carbon stored by the ocean is known as blue carbon. Its health and stability are critical in mitigating the effects of climate change. So, if we don’t prioritise the health of our oceans, we’ll be losing one of our greatest assets in the fight against climate change.

Wrapping up seven years of ocean acidification monitoring and capacity building in the Pacific Islands.

A community’s ability to monitor and understand the ocean is directly tied to that community’s health and well-being.

Ocean Science Equity‘s goal, as one of The Ocean Foundation’s initiatives, is to tackle unequal access to ocean science. We accomplish this by supporting local experts, establishing regional centers, co-designing and deploying affordable equipment, and providing training.

We are wrapping up seven years of ocean acidification capacity building in the Pacific Islands, which began in 2017. In 2020, a public-private partnership between The Ocean Foundation (TOF) and NOAA established a regional training hub — the Pacific Islands Ocean Acidification Centre (PIOAC).

North America’s battle to save the oyster industry from climate change can inform a similar fight in Senegal

A Taylor Shellfish Farms worker harvests oysters in Oyster Bay, Washington. Like other growers along the US Pacific coast, Taylor Shellfish Farms was badly impacted by an upsurge in ocean acidity levels in 2007, and is now collaborating with researchers on monitoring and mitigation. (Image: Ted S Warren / Alamy)

Editor’s note: Ocean acidification is damaging shellfish from West Africa’s Atlantic shores to the Pacific coast of North America. In this the final instalment of a two-part series, Dialogue Earth looks at how lessons learned on the US west coast might help. Read part 1, about Senegal’s shellfish sector, here.

Oregon and Washington are at the centre of the shellfish trade on the west coast of the US. In 2007, the industry was valued at USD 111 million when it came close to collapse.

It began with a mystery: oyster larvae were dying in their millions in the coastal hatcheries that supply surrounding shellfish farms. Farmers and scientists initially believed they were being ravaged by a bacterial disease. It took a few months to discover the true culprit: the ocean water they had been pumping into their tanks had become more acidic.

In the pursuit of advancing our understanding of the ocean, we face a crucial challenge to facilitate equitable access to ocean skills, knowledge, and technology. Challenge 9 “Skills, knowledge, and technology for all” of the United Nations Decade of Ocean Science for Sustainable Development 2021-2030 (‘Ocean Decade’) stands as a commitment to ensure comprehensive capacity development and equitable access to these resources across all facets of ocean science.

Currently, global disparities persist among nations, with technical infrastructure and capacities concentrated in the Global North. Additionally, there are significant variations in age and gender representation, with only an average of 38% of women involved in the field of ocean science.

The Ocean Decade recognizes these imbalances and the hindrance they pose to scientific progress and the equitable distribution of benefits derived from the ocean. With the aim of addressing these disparities systematically, Ocean Decade Challenge 9 strives to fill the gaps in ocean science recognition, representation, and resource distribution worldwide.

Greenhouse gas levels, surface temperatures, ocean heat and acidification, sea level rise, Antarctic sea ice cover and glacier retreat reached new highs

 iStock photo for representation

The year 2023 smashed multiple climate records with greenhouse gas levels, surface temperatures, ocean heat and acidification, sea level rise, Antarctic sea ice cover and glacier retreat reaching new highs, according to the World Meteorological Organization’s (WMO) State of the Global Climate 2023 report.

“Sirens are blaring across all major indicators… Some records aren’t just chart-topping, they’re chart-busting. And changes are speeding-up,” United Nations Secretary-General António Guterres said in a statement.

The WMO confirmed that the global mean near-surface temperature in 2023 was 1.45 ± 0.12°C above the 1850-1900 average.

This makes it the warmest year in the 174-year observational record, surpassing the previous record holders — 2016 at 1.29 ± 0.12 °C and 2020 at 1.27±0.13 °C — by a clear margin. The past nine years, 2015-2023, were the nine warmest years on record.

Our planet relies on the oceans as climate regulators. At the same time, the effects of our emissions are most evident in the oceans. Today, eutrophication, climate change, ocean acidification, and invasive species are some of the challenges the oceans face.

The Ocean – A key player in climate

The oceans are already significantly impacted by human activity, making them sensitive to further influence from climate change. Habitats of species may disappear, shift, or shrink, while others gain access to new distribution areas. This can lead to a reduction in biodiversity, exacerbating the oceans’ resilience against, for example, climate change.

According to the International Panel on Climate Change (IPCC), over 90 percent of excess heat and between 20 and 30 percent of carbon dioxide emissions have been absorbed by the oceans. Carbon dioxide is absorbed by the oceans as the gas dissolves in water, and phytoplankton in surface waters take it up and bind it in organic material through photosynthesis. Phytoplankton are then consumed by zooplankton, which, along with other organisms, fall towards the ocean floor as marine snow when they die. This process allows large amounts of carbon from the upper layers of the ocean to reach deeper layers which is crucial for the organisms there. The transport of carbon to the bottom also ensures that it remains in the oceans much longer than if it were to stay in the surface layer, potentially leaking carbon dioxide back into the atmosphere.

In the wake of two harsh winter storms, Bill Mook says the shellfish industry must further adapt to climate change, calls for greater mitigation efforts

Bill Mook sells about 4 million market-size oysters annually. To deal with potentially devastating winter storms, Bill Mook has built underground water tanks to protect his inventory. Photo by Clarke Canfield.

The one-two wallop of mid-January storms was an eye-opener to coastal business and property owners along Maine’s long jagged coast. Never before had they seen such widespread destruction and chaos brought on by environmental changes widely considered a result of climate change.

Bill Mook’s eyes, however, were already wide open to the long-term shifts of temperatures and weather patterns. His oyster-farming business has long withstood the impacts of rising sea levels, warming waters, more frequent and intense storms, ocean acidification, harmful bacterial outbreaks — all of which have forced him to adapt to what nature hurls his way.