Organoclay flocculation as a pathway to export carbon from the sea surface

Area of Science:

• Marine microbial ecology
• Biogeochemistry
• Oceanography

Background:

• Marine microorganisms regulate atmospheric CO2 via the biological carbon pump.
• Continental mineral dust deposition enhances carbon sequestration, but its interaction with marine microbes is poorly understood.

Purpose of the Study:

• To investigate how clay minerals interact with marine microorganisms and dissolved organic matter.
• To determine the impact of these interactions on Transparent Exopolymer Particle (TEP) formation and organoclay flocculation.
• To assess the role of organoclay flocs in carbon sequestration and the marine food web.

Main Methods:

• Microcosm experiment using surface seawater from the Gulf of Maine with varying clay concentrations.
• Analysis of TEP concentration, microbial community composition (16S and 18S rRNA gene sequencing), and phytoplankton abundance.
• Feeding experiments with Calanus finmarchicus using organoclay flocs and phytoplankton to assess fecal pellet characteristics.

Main Results:

• Clay addition significantly increased TEP concentration and formed organoclay flocs.
• Phytoplankton community shifted from dinoflagellates to diatoms, with dinoflagellates being removed in organoclay flocs.
• Organoclay flocs increased fecal pellet sinking velocity in copepods, enhancing potential carbon sequestration.

Conclusions:

• Clay minerals interact with marine dissolved organic matter and microbes to promote organoclay floc formation.
• These flocs enhance the biological carbon pump by removing phytoplankton and facilitating carbon export via zooplankton.
• Dust-derived clay minerals play a crucial role in marine carbon sequestration.