This is the main conclusion of a study led by the ICM-CSIC that shows that the flux of biogenic particles travelling to the ocean floor in the coastal areas of the Antarctic region is as intense during autumn as in summer, the season of greatest export until now.
Researchers from the Institut de Ciències del Mar (ICM-CSIC), in collaboration with the IDEAL Center (Chile) and the Chilean Antarctic Institute (INACH), detected an unprecedented phenomenon at the Antarctic coast: during autumn, the biogenic particle flux to the seabed can be as intense as in summer, when it was considered until now, that the majority of the annual export of organic carbon (>85%) occurred in this polar environment.
To carry out the research, data were acquired from a sediment trap that collected the particle flux over 153 days, between February and June 2019, off the western coast of the Antarctic Peninsula. The results are included in a study recently published in the journal Scientific Reports, which provides new evidence of how climate change is transforming the phytoplankton bloom calendar in the Antarctic.
According to the study, due to changes in wind patterns and the presence of sea ice around the Antarctic Peninsula, phytoplankton still find conditions to thrive during the autumn, when normally the phytoplankton bloom decreases drastically, and, consequently, there is an “out of season” organic carbon flux.
“We have observed, for the first time, that there is an of organic carbon flux to the seabed aligned with high primary production in autumn, which has not been observed anywhere else in the Antarctic,” explains Enrique Isla, researcher at ICM-CSIC and lead author of the study. In this sense, Isla points out that this will probably be the new temporal pattern of carbon transport, at least for the coastal zone, due to climate change.
A transforming ecosystem
The data show that the particulate organic carbon (POC), biogenic silica, and total mass fluxes during autumn did not show significant differences compared to the summer values. Moreover, the collected fluxes exceeded those observed for deeper and offshore Antarctic environments, indicating a high export capacity of phytoplankton and organic matter from shallow coastal environments to the open sea.
On the other hand, the dominant phytoplankton functional group during autumn was centric diatoms such as Chaetoceros and Thalassiosira, whereas in summer, pennate diatoms (Pseudo-nitzschia, Cocconeis) predominated. According to the scientific team, this change reveals a seasonal transition in planktonic communities and confirms the extension of the biologically active period.
Krill, an ally against climate change
A substantial portion of the POC is transported in the form of Antarctic krill faecal pellets (euphausiids), which act as an effective sedimentation vehicle. These pellets represent up to 60% of the carbon exported in the water column, being especially efficient due to their density and rapid sedimentation rates.
“This organic matter flux is energy for the seabed fauna and, at the same time, enhances atmospheric CO₂ immobilization into the sea floor sediment, a process that mitigates climate change effects,” emphasizes Isla.
Global implications
The study expands our knowledge of polar marine ecosystems and highlights the need to reassess the role of Antarctic coastal zones in the global carbon budget. As climate change alters natural primary production calendars, understanding how these ecosystems respond is also key to projecting future environmental scenarios.
“The study results could have implications for accurately modelling the global carbon cycle, as they suggest that the contribution of Antarctic coastal zones may be currently underestimated,” the authors conclude.