The land is greening and the oceans are dying: scientists have discovered a global redistribution of life

American researchers have found that in the period from 2003 to 2021 the ability of plants on land to absorb CO₂ through photosynthesis has increased in the face of a warming climate.

At the same time, ocean algae, especially in tropical waters, have become much less efficient at absorbing carbon. This, according to researchers, is changing the balance of life on the planet. While the land is becoming more productive, marine ecosystems are rapidly degrading.

In the new study, scientists note, that the growth of terrestrial plant activity was somewhat restrained a slight decrease in the intensity of photosynthesis among seaweeds. According to the researchers, these results can help in assessing the state of the planet, managing ecosystems more effectively, and developing better strategies for predicting and solving the climate crisis.

Photosynthesis is carried out by microorganisms, known as primary are the producers, that form the basis of the food chain and support almost all forms of life on the planet. They use sunlight to convert CO₂ into organic matter. These microorganisms return some of the absorbed carbon through a process, called autotrophic respiration. The difference between the carbon absorbed and released is called net primary production.

“Net primary production measures the amount of energy that photosynthetic organisms capture and use to support virtually all life in an ecosystem. As the backbone of food chains, clean primary production determines ecosystem health, provides food and fiber for people, reduces anthropogenic carbon emissions, and helps stabilize the Earth’s climate”, — explains the study’s first author, a researcher in Wenhong Li’s lab at the Nicholas School of the Environment at Duke University, Yulong Zhang.

In previous studies of net primary production, terrestrial and oceanic ecosystems were considered separately. As a result, scientists had no idea how the CO₂ emissions across the planet, and how this affects efforts to slowing down global warming.

In the new study, the researchers analyzed trends and changes in global net productivity throughout the year. They paid special attention to how changes on land correlate with changes in the ocean.

“If you are studying planetary health, you need to consider both terrestrial and marine environments to get a comprehensive view of net primary production. The groundbreaking research that first combined terrestrial and marine primary production has not been substantially updated in more than two decades”, — emphasizes the study’s co-author and head of the department Lee Hill Snowdon Chair in Biology at the Nicholas School, Nicolas Cassard.

Satellite observations provide a continuous picture of the process of photosynthesis of plants and seaweed, called phytoplankton. Specialized satellite instruments measure the greenness of the surface, which reflects the content of the green pigment, chlorophyll, produced by photosynthetic organisms.

After that, computer models estimate clean primary production by combining surface greenness data with other environmental data, including temperature, light conditions, and nutrient variability.

The researchers used 6 different sets of satellite data on net primary production. Three datasets were for land, and three were for the oceans Using statistical methods, they analyzed the annual changes in net primary production for land and separately for the ocean.

They found a significant increase in primary production on land at a rate of 0.2 billion metric tons of carbon per year between 2003 and 2021. This trend was widespread from temperate to boreal (high-latitude) zones, except for the tropics of South America.

What is happening in the oceans?

The researchers found an overall decline in net primary carbon production in the marine environment of about 0.1 billion tons annually over the same period from 2003 to 2021. The largest decrease was observed mainly in in tropical and subtropical oceanic zones, especially in the Pacific Ocean.

To understand the potential impact of environmental factors, the researchers analyzed variables such as light availability, air and sea surface temperature, precipitation, and mixed layer depth — an indicator that reflects the degree to which the upper ocean layer is mixed by wind, waves, and surface currents.

“The shift toward higher primary productivity on land has been driven mainly by crops in higher latitudes, where warming has extended the growing season and created more favorable temperatures, and in temperate regions, where localized moisture, forest expansion and cropland intensification have been observed in some areas,” he emphasized co-author of the study, Professor of Earth and Climate Sciences at the Nicholas School, Wenhun Li

At the same time, in some areas of the ocean, rising temperatures have had the opposite effect. According to Nicholas Kassar, the rise in ocean surface temperatures has likely led to a decline in primary production phytoplankton in tropical and subtropical regions, as warmer waters can be placed on top of the colder ones and interfere with the mixing of nutrients necessary for algae survival.

The researchers also found that while land contributed to the the overall growth of primary production in the world, on climate variability throughout the year, especially during powerful climatic events, such as El Niño and La Niña, were mainly influenced by the ocean. Scientists have found that the primary products formed in the ocean are more responsive to El Niño and La Niña than primary production generated on land.

“A series of La Niña events partly accounted for the change in ocean primary production trend we found after 2015. This discovery highlights the great sensitivity of the ocean to future climate variability”, — says study co-author and researcher of climate dynamics at the Nicholas School, Shineng Hu.

The authors of the study note that their work points to the important role of terrestrial ecosystems to compensate for the decline in net primary production of marine phytoplankton. They add, that Declining net primary production in tropical and subtropical ocean zones, coupled with stagnation on land in the tropics, could weaken the foundation of tropical food chains, with cascading effects on biodiversity, fisheries, and local economies. Over time, these disturbances could pose a threat by impairing the ability of tropical regions to effectively absorb CO₂.

“Whether the decline in ocean primary production will continue, and for how long and to what extent growth on land will be able to compensate for these losses, remains a key unanswered question with serious implications for assessing the state of all living things and developing measures to mitigate climate change Long-term coordinated monitoring of land and ocean ecosystems as integral components of the Earth is essential”, — emphasizes Yulong Zhang.

The results of the study are published in the journal Nature

Source: SciTechDaily