Microrheology reveals microscale viscosity gradients in planktonic systems

Area of Science:

• Marine microbial ecology
• Biogeochemistry
• Physical oceanography

Background:

• Planktonic systems exhibit complex microscale dynamics driven by chemical factors.
• Physical parameters, like viscosity, are often overlooked in microbial ecology.
• Biological activity, such as phytoplankton presence, influences the surrounding environment.

Purpose of the Study:

• To investigate the spatial heterogeneity of viscosity in planktonic environments.
• To quantify viscosity changes around phytoplankton and in marine aggregates.
• To understand the implications of viscosity microheterogeneity for microbial processes.

Main Methods:

• Microrheological techniques were employed to measure viscosity at the microscale.
• Viscosity was analyzed in the phycosphere (region around phytoplankton).
• Viscosity was also measured within marine aggregates.

Main Results:

• Significant viscosity increases (up to 40x seawater) were observed around phytoplankton cells, extending up to 30 µm.
• Viscosity gradients were amplified around lysing phytoplankton cells.
• Viscosity within marine aggregates was estimated to be over an order of magnitude higher than in seawater.

Conclusions:

• Microscale viscosity heterogeneity is a significant factor in planktonic systems.
• Altered viscosity affects microbial distribution, resource availability, and ecological interactions.
• These microscale changes have global implications for carbon and nutrient cycling.