Environmental physicists Jens Müller and Nicolas Grube at the Institute of Biogeochemistry and Pollutant Dynamics, ETH Zurich, have developed a groundbreaking 3D model to better understand the extent of ocean acidification caused by increasing atmospheric carbon dioxide levels. In their study, published in Science Advances, the researchers detail how they built and utilized the model to explore how deep ocean acidification has penetrated over the past two centuries, beginning with the industrial revolution.
The impact of rising carbon dioxide (CO₂) levels in the atmosphere is well-known for its role in climate change and global warming. However, the ocean’s response to this phenomenon has been equally concerning. As CO₂ levels rise, a significant portion of the gas is absorbed by the oceans, leading to a chemical reaction that increases the acidity of seawater—a process known as ocean acidification. This acidification is similar to the reaction that occurs when CO₂ dissolves in carbonated beverages, giving them their acidic taste. While this phenomenon has been widely acknowledged, its full extent and depth in the oceans, particularly over time, have not been thoroughly quantified until now.
Müller and Grube’s model aimed to answer a critical question: how far has ocean acidification penetrated since the start of the industrial era? The team’s model simulates the world’s oceans, taking into account ocean currents and the gradual accumulation of CO₂ from the atmosphere over the past 200 years. To achieve this, the researchers used historical CO₂ data from 1800, 1994, 2004, and 2014, and incorporated three key indicators of ocean acidification: proton concentration (which reflects the acidity), pH levels, and aragonite saturation states (important for organisms like corals that rely on calcium carbonate to form shells and skeletons).
The results of the study were alarming. The model showed that ocean acidification had progressively moved deeper into the world’s oceans over the years, with the average depth reaching 1,000 meters by 2014. This depth of acidification is significant because it affects the chemistry of the water at much greater depths than was previously anticipated. For comparison, the effects of acidification were especially pronounced in areas with strong ocean currents, such as the Atlantic Meridional Overturning Circulation (AMOC). In these regions, where ocean currents mix deeper water layers, acidification reached depths as deep as 1,500 meters.
This finding underscores the widespread impact of ocean acidification, which is not just a surface phenomenon but one that is gradually affecting deeper ocean layers as well. This deeper penetration of acidification could have far-reaching consequences for marine ecosystems, particularly those organisms that depend on the mineralization of calcium carbonate. For instance, pteropods, small marine snails that are a vital part of the marine food web, could be at risk. Their shells, composed of calcium carbonate, dissolve in more acidic water, threatening their survival. These creatures serve as an essential food source for many larger marine animals, so their decline could have cascading effects on marine biodiversity.
Müller and Grube’s model also highlights the variability in acidification patterns across different regions of the ocean. While acidification has deepened overall, certain areas experience more rapid changes due to the dynamics of ocean currents and mixing. This can lead to localized hotspots where acidification is more severe and poses greater risks to marine life. The researchers emphasized that these findings suggest that ocean acidification is a more complex and multi-dimensional problem than previously thought, affecting not only surface waters but also the deep ocean, where many marine species reside.
In addition to the direct impacts on marine organisms, the study also raised concerns about the broader implications of deeper ocean acidification for the global carbon cycle. The oceans play a critical role in absorbing CO₂ from the atmosphere, helping to mitigate the effects of climate change. However, as ocean acidification progresses, it may alter the ability of oceans to store carbon, potentially accelerating climate change. This feedback loop could exacerbate the challenges posed by rising atmospheric CO₂ levels, leading to further disruptions in the planet’s climate systems.
Müller and Grube’s research adds an important dimension to our understanding of ocean acidification, emphasizing the need for comprehensive monitoring and mitigation strategies to protect marine ecosystems. Their work also suggests that future efforts to combat climate change should consider not only reducing CO₂ emissions but also addressing the long-term impacts of acidification on ocean health. Given the growing evidence that ocean acidification is a global issue affecting the oceans’ depths, it is crucial to consider these changes when assessing the health and resilience of marine ecosystems.
This study offers a sobering glimpse into the long-term effects of human-induced CO₂ emissions on the oceans, shedding light on how these changes unfold over time and emphasizing the urgent need for action to curb further acidification and protect vulnerable marine life. As scientists continue to monitor these shifts, it will be essential to develop more sophisticated models to predict the future trajectory of ocean acidification and its impact on global biodiversity.