Key Takeaways
- Research reveals significant changes in phytoplankton species in the Southern Ocean, influenced by climate change.
- Satellite data and in-situ samples demonstrate a decline in diatoms and an increase in cryptophytes and haptophytes since 1997.
- These shifts may weaken the ocean’s carbon sequestration ability, highlighting the need for ongoing monitoring of marine ecosystems.
Climate-Induced Changes in Southern Ocean Phytoplankton
A recent study published in Nature Climate Change examines the impact of climate change on phytoplankton in the Southern Ocean, utilizing 25 years of satellite and ocean sample data. Researchers combined records from the European Space Agency’s Climate Change Initiative (CCI), including sea surface temperature, ocean color, and sea ice extent, with markers from over 14,000 in-situ samples. Lead researcher Alexander Hayward, an Earth System Scientist at the Danish Meteorological Institute, noted that machine-learning models enabled the team to track changes in various phytoplankton groups.
Key observations indicate a notable reduction in diatoms—critical single-celled algae known for their carbon absorption—on the Antarctic continental shelf from 1997 to 2023. In contrast, cryptophytes experienced significant population growth since 2017, alongside moderate increases in diatoms across the region except for West Antarctica, where they continued to decline. Additionally, haptophytes saw an uptick on the continental shelf before 2017.
Smaller phytoplankton groups like cryptophytes and haptophytes increased during the study, particularly after 2016, which marked a sharp decrease in sea ice. This environmental change enabled diatom populations to begin rebounding due to improved light availability and altered nutrient dynamics.
Diatoms account for 46% of Southern Ocean phytoplankton, while haptophytes make up 32%. Diatoms play a vital role in carbon sequestration due to their silica shells, which sink to the ocean floor, effectively transporting carbon. They are also a primary food source for krill, which are crucial to the diets of larger marine animals.
The study utilized satellite data from the Copernicus Sentinel-3, which measures light reflected off the ocean surface to infer phytoplankton populations indirectly. Though the satellite cannot differentiate between species, it facilitates the monitoring of chlorophyll levels, which are essential for understanding phytoplankton dynamics.
Research on phytoplankton is vital for comprehending climate change, as their biomass and pigment diversity are classified as essential climate variables. Ongoing studies, such as the Phyto-CCI project initiated by ESA, aim to generate comprehensive records of phytoplankton types using advanced satellite analysis to better monitor marine ecosystems and their role in climate regulation.
Hayward emphasized that declining diatom populations could weaken the biological carbon pump, critically affecting carbon dioxide transport to the ocean depths. This underscores the urgency for enhanced research and observation efforts in this sensitive ecosystem, as even microscopic changes could have significant implications for global climate systems.
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