The team focused on the Antarctic Cold Reversal, a temporary cooling event that occurred despite broader warming in the southern hemisphere. Sediment cores from the Bransfield Strait revealed preserved sedimentary ancient DNA (sedaDNA), enabling scientists to confirm Phaeocystis blooms that had previously escaped detection due to the lack of microfossils. These findings demonstrate that extensive winter sea ice followed by intense spring melt created ideal conditions for algal growth.
"Our study shows that these algal blooms contributed to a significant reduction in global atmospheric CO2 levels during a climatically important transition phase characterized by high sea ice extent," said lead author Josefine Friederike Weiss of AWI. Evidence included elevated barium-to-iron ratios in sediments, a marker for strong biological productivity.
The researchers highlight that greater winter sea ice expansion meant more meltwater in spring, which fertilized surface waters and fueled blooms. These processes influenced food webs, nutrient cycles, and long-term carbon storage in the deep ocean. By efficiently transporting carbon downward, Phaeocystis played an outsized role in stabilizing past climate.
However, today these algae face existential risk. Rapid sea ice decline in Antarctica threatens Phaeocystis populations, with cascading consequences for ecosystems and the climate system. While other algae such as diatoms may expand, the shift could reduce oceanic carbon storage and destabilize food chains. Additionally, Phaeocystis produces dimethyl sulphide, a gas that enhances cloud formation and planetary cooling. Its decline could weaken this natural climate regulation mechanism.
The study underscores how sedimentary DNA, combined with traditional geochemical analyses, provides a powerful tool for reconstructing past climate events. This approach reveals the pivotal role of microbial life in regulating atmospheric CO2 and offers critical insights for predicting future climate pathways.
Research Report:Carbon drawdown by algal blooms during Antarctic Cold Reversal from sedimentary ancient DNA
Related Links
Alfred Wegener Institute
Beyond the Ice Age
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