Microscopic image of picophytoplankton. Photo: Anabella Aguilera

Project: Carbon export of the smallest phytoplankton

This project investigates the role of small phytoplankton in the carbon cycle of the ocean, through quantifying how much their cells aggregate, how the aggregation process differs between species and what mechanisms drive it. The knowledge is of importance to understand the role of our oceans in the global carbon cycle.

Facts about the project

Project managers
Hanna Farnelid
Other project members
Lisa Winberg von Friesen
Participating organizations
Linnaeus University
The Swedish Research Council's open calls in 2023
1 January 2024 – 31 December 2027
Ecology, Biology and Environmental Science (Department of Biology and Environmental Science, Faculty of Health and Life Sciences)
Research groups
Marine phytoplankton ecology and applications (MPEA)

More about the project

Phytoplankton in the surface layer of the ocean bind carbon dioxide through photosynthesis. Parts of the resulting biomass sink to the bottom of the ocean where it is stored. The amount of carbon that sinks is largely determined by the species composition of phytoplankton, with larger phytoplankton sinking faster than smaller ones.

The smallest phytoplankton (picophytoplankton) have a global distribution and are expected to become more common as the oceans warm due to climate change. Until now, it has been considered that, due to their small size (<2-3 micro meters), picophytoplankton cells have a low sink rate. However, this may be altered if cells clump together and form aggregates. Aggregation could cause picophytoplankton biomass to sink faster than previously thought. The importance of this process as a carbon sink in coastal ecosystems is unknown and the mechanisms behind aggregation of picophytoplankton are not understood.

In this project, sinking aggregates will be collected and examined to study the proportion of picophytoplankton at different depths. Measurements of the amount of sinking aggregates in different seasons and associated species composition will provide detailed information on the importance of picophytoplankton as a carbon sink. Controlled laboratory experiments will be used to study factors affecting aggregation of different key species, providing insight into how aggregation may be affected by environmental change.

Finally, the molecular mechanisms behind aggregation will be mapped. This will allow the identification of interactions between cells that, in turn, affect the ocean carbon sink. This knowledge will provide molecular indicators for a better understanding of the ocean carbon cycle. The results of the project are important for understanding how an increase of picophytoplankton will affect marine ecosystems and enable the integration of these small, but important, organisms into the ocean carbon budget. 

The project is part of the research in the research group Marine phytoplankton ecology and applications, in Linnaeus University Centre for Ecology and Evolution in Microbial model Systems (EEMiS) and in Linnaeus Knowledge Environment: Water.


Schematic diagram: How does aggregation of picophytoplankton work and how does it influence marine carbon flux? Graphics by Lisa Winberg von Friesen
Schematic diagram: How does aggregation of picophytoplankton work and how does it influence marine carbon flux? Graphics by Lisa Winberg von Friesen