The “biological pump,” in which carbon is utilized by organisms at the surface and transferred to ocean depths away from contact with the atmosphere, is one of the most significant components of the Southern Oceanic carbon cycle, according to new research. The study was published in PNAS by researchers from the University of Hawai’i at Mnoa and NOAA’s Pacific Marine Environmental Laboratory.
The Southern Ocean, also known as the Antarctic Ocean, absorbs approximately 40% of the total amount of human-generated carbon dioxide (CO2) emissions and 60%–90% of the excess heat trapped by greenhouse gases in the atmosphere. As a result, the Southern Ocean helps slow the rate of climate change. One of the most important aspects of oceanography is comprehending how the Southern Ocean absorbs CO2. However, the remote and harsh conditions of the Southern Ocean make it difficult for scientists to accurately characterize the process of carbon cycling.
Yibin Huang and Andrea Fassbender from NOAA’s Pacific Marine Environmental Laboratory collaborated with assistant professor of oceanography Seth Bushinsky from the UH Mnoa School of Ocean and Earth Science and Technology (SOEST) to lead the scientific team. For the first time, they looked at data from more than 60 autonomous profiling floats over a ten-year period to quantify the role that tiny phytoplankton, or phytoplankton, play in the Southern Ocean’s CO2 absorption from the atmosphere by producing various kinds of biogenic (brought about by living organisms) carbon. Each kind of biogenic carbon contrastingly affects carbon trade and the trading of CO2 between the air and sea.
“Our research employs a recently developed method for estimating the production and export of distinct biogenic carbon pools at ocean basin scales in order to monitor how marine ecosystems function and their response to future climate change,”
Lead author Huang, a Cooperative Institute for Marine and Atmospheric Research .
Because a change in the rate at which biogenic carbon is stored in ocean waters could result in more CO2 remaining in the atmosphere and potentially affect the rate of climate change, it is crucial to comprehend how much carbon is captured in the interior of the ocean by the biological pump and how this influences the amount of CO2 taken up by the ocean.
According to lead author Huang, a scientist at the Pacific Marine Environmental Laboratory who works for the Cooperative Institute for Marine and Atmospheric Research, oceanographers have long faced the challenge of simultaneously monitoring the three distinct types of carbon produced by biological activity. He stated that scientists typically treat total carbon production as a black box due to the complexity of traditional methods.
“To monitor how marine ecosystems function and their response to future climate change, our study applies a recently developed method for estimating the production and export of distinct biogenic carbon pools in a cost-effective manner and at ocean basin scales,” Huang stated.
How phytoplankton extract carbon from the atmosphere Through the unique Southern Ocean circulation south of 35 degrees south latitude, physical and biological processes interact to shape regional biogeochemistry that has an impact on the interior of the global ocean. Deep waters that are rich in dissolved inorganic carbon come into contact with the atmosphere thanks to the predominant upwelling that occurs south of the Antarctic Circumpolar Current. The profound waters are additionally rich in supplements, which fuel natural movement cresting during spring and summer. Some species of phytoplankton use dissolved inorganic carbon to make their exoskeletons, and when they die, they transport it to the bottom.
While tiny fish thrive in this rich, cold water, they can’t completely use accessible supplements and the disintegrated inorganic carbon brought to the surface during upwelling. Locally, some of the dissolved inorganic carbon escapes into the atmosphere. Large-scale circulation then transports the unused nutrients toward the equator, fueling a significant portion of the biological production in the subtropics and tropics. The slower growth of phytoplankton during the winter, when deep-water mixing is at its peak, influences the Southern Ocean’s seasonal pattern of carbon cycling.
The paper focuses on quantifying how much dissolved inorganic carbon these tiny organisms use and how the natural carbon export process affects the modern CO2 exchange between the ocean and air.
The researchers discovered that while particulate inorganic carbon production reduces CO2 uptake by approximately 270 million tons per year, organic carbon production captures approximately 3 billion tons of carbon annually, which is approximately one quarter of all human emissions. Contrasts in how much each kind of carbon is created from north to south across the Southern Sea impact what the natural siphon means for nearby air-ocean CO2 trade.
Without the activity of microscopic fish consuming carbon during the southern side of the equator’s developing season, the Southern Sea would be a CO2 source for the climate, the researchers said.
According to Fassbender, who is also an adjunct professor at the University of California, Santa Cruz, “understanding year-to-year variability in biogenic carbon production may be of central importance to understanding variability in the overall Southern Ocean carbon sink.” This is because phytoplankton play such an important role in the modern Southern Ocean carbon sink.
She stated, “Expanding persistent year-round observations from biogeochemical profiling floats would serve as a cost-effective method to monitor the biological pump globally and throughout the Southern Ocean.”
More information: Yibin Huang et al, Biogenic carbon pool production maintains the Southern Ocean carbon sink, Proceedings of the National Academy of Sciences (2023). DOI: 10.1073/pnas.2217909120
