In a remarkable discovery, researchers have unveiled an “invisible forest” of phytoplankton thriving in a warming section of our ocean. These minuscule drifting organisms play a crucial role in the planet’s “primary production” through photosynthesis.
The University of Exeter‘s latest study delves into the impact of climate variability on phytoplankton communities at both the ocean surface and the “subsurface” layer below. Published in the esteemed journal Nature Climate Change, the findings shed light on the divergent reactions of these two communities to the changing climate.
In the past decade, there has been a remarkable surge in the total biomass of subsurface phytoplankton in response to rising temperatures. At the same time, surface phytoplankton has exhibited a decrease in chlorophyll, resulting in a less vibrant green appearance. Despite this, the overall biomass has remained stable.
These compelling findings, derived from 33 years of data collected by the Bermuda Atlantic Time-series Study (BATS) in the Sargasso Sea, also indicate a significant shallowing of the surface mixed layer as the ocean has undergone rapid warming.
“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 Department of Earth and Environmental Science at Exeter’s Penryn Campus in Cornwall.
“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 added: “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 added: “Continued monitoring of these deep-living phytoplankton will help scientists better understand ongoing changes in the ocean that might otherwise go unnoticed.”
Journal reference:
- Johannes J. Viljoen, Xuerong Sun & Robert J. W. Brewin. Climate variability shifts the vertical structure of phytoplankton in the Sargasso Sea. Nature Climate Change, 2024; DOI: 10.1038/s41558-024-02136-6
