According to a new study, the world’s oceans are losing their greenness owing to global heating and are causing a decline in marine life and the planet’s ability to absorb carbon dioxide.
The change in the palette of the sea is primarily caused by a shrinkage of phytoplankton, the tiny marine creatures that are specifically responsible for nearly half of the ecosphere’s productivity.
The study findings, which also have the ominous implications for oxygen levels and food chains, are based on a cutting-edge study of daily chlorophyll concentrations in low-to-mid latitude oceans from 2001 to 2023.
Chlorophyl is a green pigment responsible for photosynthesis, the process by which plants, algae and phytoplankton convert sunlight, water, and carbon dioxide into oxygen and glucose, and it is one of the fundamental components of life on Earth.
The authors of the new paper assembled data from satellites and monitoring ships to assess the change in the oceanic color.
They found a significant decline of greens-about 0.35 micrograms per cubic meter each year-over the more than two-decade period of the study.
However, the trend was twice as high in coastal regions and more than four times greater near river estuaries.
They associate this with a loss of ecological resilience of the ocean and find a 0.088% annual decrease in carbon sequestration capacity equivalent to 32 million tons.
One of the authors, Di Long of Tsinghua University in Beijing said, “The decline in surface phytoplankton’s carbon sequestration capacity has profound implications for the carbon cycle.”
The new paper implies that the change was likely induced by increasing temperatures associated with climate change.
However, the heating of the epipelagic zone near the surface has intensified the thermal gradient difference with the colder depths, which is thought to be impeding vertical movement of the nutrients on which the phytoplankton depend.
The earlier studies were less comprehensive, and the paper acknowledges that the situation differs from region to region and can be affected by runoffs from agriculture and other human activity.
It concludes the broader picture of “significant decline” of phytoplankton is clear across the low and mild latitudes.
Following these findings, policymakers need to analyze the marine ecological environment in coastal areas and develop a strategy for careful management of deforestation, sewage discharge and water pollution.
The formidable hurdle is tackling the climate crisis while the world’s natural carbon absorber is losing strength.
The recent decline in marine biological productivity shows that we may face greater emissions reduction pressure and that it will weaken the ocean's capacity to absorb carbon dioxide.
