Ocean acidification, caused by human activity, is drastically altering the production of marine plankton shells in the Mediterranean Sea. This troubling finding comes from a recent study conducted by the Institute of Environmental Science and Technology of the Universitat Autònoma de Barcelona (ICTA-UAB). The study raises concerns about the negative consequences for marine ecosystems resulting from the decrease in pH levels in the surface ocean. With the increase in anthropogenic carbon dioxide (CO2) emissions, about 25% of CO2 has entered the ocean since the Industrial Revolution. This has changed the water chemistry and led to a phenomenon known as ocean acidification. In collaboration with researchers from the University of St Andrews, the Max Planck Institute of Chemistry, and the Spanish Council for Scientific Research, the ICTA-UAB investigated the impact of CO2-induced changes on a particular group of calcifying planktonic organisms called foraminifera in the Mediterranean Sea.
The western Mediterranean Sea was chosen for the study due to its susceptibility to anthropogenic pressures and climate change. The high alkalinity and fast circulation of water masses in the basin make Mediterranean waters prone to the uptake of anthropogenic carbon. Since the Industrial Revolution, the pH levels in these waters have dropped by 0.08 units, significantly affecting the biogenic calcification of marine plankton. Foraminifera, single-celled marine calcifying zooplankton, reside in the upper ocean and are highly sensitive to climatic and environmental changes. These organisms build shells made of calcium carbonate, which are ideal for studying the long-term impacts of carbon perturbations on marine ecosystems.
The study found that the decline in foraminiferal calcite mass is primarily driven by ocean acidification caused by anthropogenic emissions, while ocean warming may mitigate this effect. Prior to the Industrial Revolution, the shells of planktonic foraminifera were heavier with minimal variations in weight over time. However, the researchers observed an accelerated decrease in shell weight during the 20th century. Additionally, the study revealed that the anthropogenic carbon dioxide signature has already affected the shell chemistry of the planktonic calcifiers.
The acidification of the Mediterranean Sea surface caused by anthropogenic sources has significantly impacted foraminiferal calcification throughout the 20th century. This finding has broader implications for other calcifying planktonic organisms, such as coccolithophores and pteropods, which also reside in Mediterranean surface waters and play critical roles in atmospheric CO2 modulation. As calcifying plankton are essential components of marine food web architecture and biogeochemical cycles, continued ocean acidification will have negative consequences for marine ecosystem services. These include climate regulation, the functioning of ocean ecosystems, and food security. Given these threats, it is crucial to mitigate climate change by reducing CO2 emissions.
The acidification of the Mediterranean Sea due to human activity is already impacting the production of marine plankton shells. This study highlights the alarming consequences of ocean acidification on foraminifera and emphasizes the need to address climate change by reducing CO2 emissions. The findings underscore the importance of protecting marine ecosystems and the services they provide for the overall health and sustainability of our planet. Continued research in this field is necessary to fully understand the extent of the effects of ocean acidification and implement effective mitigation strategies.