The study, published in 'Nature Climate Change', investigates how climate variability affects different layers of ocean-dwelling phytoplankton, focusing on both surface and subsurface communities. According to the research, subsurface phytoplankton biomass has increased over the last decade in response to rising ocean temperatures, while surface phytoplankton show reduced chlorophyll levels, though their total biomass remains stable.
The study utilized 33 years of data from the Bermuda Atlantic Time-series Study (BATS) in the Sargasso Sea, revealing that the surface mixed-layer, a region of turbulence at the ocean's surface, has become shallower as the oceans warm.
"It's important to understand these trends because phytoplankton are the foundation of the marine food web, and play a key role in removing carbon dioxide from the atmosphere," said Dr. Johannes Viljoen from the University of Exeter.
He added, "Our findings reveal that deep-living phytoplankton, which thrive in low-light conditions, respond differently to ocean warming and climate variability compared to surface phytoplankton."
"We typically rely on satellite observations to monitor phytoplankton, but the subsurface is hidden from satellite view. Our study highlights the limitations of satellite observations, and underscores the urgent need for improved global monitoring of phytoplankton below what satellites can see."
Co-author Dr. Bob Brewin noted, "Changes at the base of the food web can have cascading effects on marine life, from tiny zooplankton to large fish and marine mammals."
"So the future of phytoplankton will have major implications for biodiversity, as well as climate change."
Dr. Viljoen stressed the importance of continuing to monitor these deep phytoplankton to better understand ongoing, often unnoticed changes in the ocean. "Continued monitoring of these deep-living phytoplankton will help scientists better understand ongoing changes in the ocean that might otherwise go unnoticed," he said.
The research was supported by a UKRI Future Leader Fellowship awarded to Dr. Brewin.
Research Report:Climate variability shifts the vertical structure of phytoplankton in the Sargasso Sea
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