Marine particle size-fractionation indicates organic matter is processed by differing microbial communities on...

Area of Science:

• Marine microbial ecology
• Biogeochemical cycles
• Oceanography

Background:

• Particulate organic matter (POM) sinking flux is crucial for the ocean's biological carbon pump and carbon export.
• Particle-associated microbes form "hotspots" of activity, influencing POM fate.
• Previous studies using sediment/gel traps primarily captured sinking particles.

Purpose of the Study:

• To investigate variations in particle-associated microbial communities across different particle size fractions (0.2-1.2, 1.2-5, 5-20, >20 μm) down to 500 m depth.
• To compare microbial communities on sinking and suspended particles using in situ pumps.
• To examine the diagenetic state of size-fractionated particles using isotopic signatures.

Main Methods:

• Collection of particles using in situ pumps at the Bermuda Atlantic Time-series Study site.
• Analysis of microbial communities associated with four distinct particle size fractions.
• Isotopic analysis to assess the diagenetic state of particles.

Main Results:

• Distinct microbial communities were found on different particle sizes.
• Community composition showed similar changes with depth across all particle size categories, contrary to prior research.
• Isotopic analysis revealed significant differences in particle composition by size and depth, indicating microbial and grazing transformations.

Conclusions:

• Particle size influences microbial community structure.
• Consistent community shifts with depth across particle sizes suggest long particle residence times or rapid microbial succession.
• Coupling microbial and isotopic data reveals unique successional patterns and organic matter transformation processes in marine particles.