Oceanographers, including Rice University’s Sven Kranz, have discovered a significant connection between small-scale microbial processes and ecosystemwide dynamics, offering new insight into the mechanisms driving marine carbon storage.
Research conducted across multiple ocean regions showed that conditions in the upper ocean, such as nutrient availability and microbial interactions, play a crucial role in shaping the carbon-rich particles that sink into the deep ocean. These particles continue to reflect surface ecosystem dynamics, even at great depths, influencing how carbon is ultimately stored, according to a recent press release from Florida State University. The findings were published Nov. 24 in the Proceedings of the National Academy of Sciences.
Given that the ocean is the Earth’s largest active carbon sink, absorbing carbon dioxide from the atmosphere and storing it for long periods, understanding these processes has significant implications for the global carbon cycle.
“Our findings show that the story of marine carbon doesn’t end when particles sink,” said Kranz, an associate professor of biosciences. “The imprint of the surface ecosystem persists deep in the ocean, meaning we need to rethink how those particles carry and store carbon throughout the water column.”
Kranz’s lab focuses on phytoplankton ecology and biogeochemistry, studying how different phytoplankton groups respond to changes in carbon dioxide, light intensity and nutrient availability as well as how biochemical processes such as photosynthetic pathways, carbon acquisition and protein regulation shape those responses.
Understanding complex transformations
On land, plants absorb carbon dioxide, converting it into organic matter and oxygen through photosynthesis. This same process is performed by tiny, ocean-dwelling plants called phytoplankton, which establish the base of the complex marine food web. The organic matter produced in this system ranges from microscopic particles unable to be seen with the naked eye to particles as thick as a nickel.
Some of these particles sink from the sunlit surface into the ocean’s depths, effectively removing carbon from the atmosphere and storing it for decades to millennia; as this organic matter descends, it undergoes complex transformations that have long puzzled scientists.
“Understanding these changes is critical, as the rate and extent to which they occur determine how long this carbon is locked away,” Heather Forrer, a doctoral graduate at FSU and first author of this study, said in the release.
These transformations are driven by microorganisms or microbes, which influence organic matter’s sinking rate by reshaping or degrading the particles. The research team collected sinking particles from the Gulf of Mexico, California Current ecosystem and tropical Indian Ocean to examine molecular changes as they descend into the deep ocean.
Maglab Research
Using the National MagLab’s advanced ultrahigh-resolution mass spectrometer, which harnesses a powerful magnetic field to identify molecules with extreme precision, the researchers for the first time were able to directly compare the molecular composition of sinking particles collected in different ocean regions at different depths.
They found that in nutrient-rich regions such as California’s upwelling region, where particles are produced and sink quickly, more “fresh” carbon reached greater depths with very little molecular change, suggesting a strong carbon sequestration pathway.
By contrast, nutrient-poor regions like the Gulf feature slower-sinking particles, which are more extensively processed by microbes, showing greater molecular changes since formation and contributing less effectively to carbon storage.
The air we breathe and Earth’s climate are largely controlled by the ocean and the processes investigated in this publication. By better understanding these fine-scale processes, we gain a clearer picture of how the ocean functions today and more accurately predict how resilient these marine carbon storage pathways are in a warming world, Forrer said.
Collaboration and support
Co-authors of this paper include FSU professor of oceanography Michael Stukel; FSU professor of oceanography and environmental science Robert Spencer; Amy Holt, an FSU alumna and postdoctoral fellow at the University of Alaska Southeast; Amy McKenna, an analytical chemist with the National MagLab’s Ion Cyclotron Resonance Facility and Colorado State University; and Huan Chen, a National MagLab research faculty member.
This research was supported by the National Science Foundation-funded California Current Ecosystem Long-Term Ecological Research and Bluefin Larvae in Oligotrophic Ocean Foodwebs, Investigation of Nutrients to Zooplankton projects and the National Oceanic and Atmospheric Administration’s RESTORE Science Program.