Marine Microgels

The ocean plays a critical role in global carbon cycling: it handles half of the global primary production, yielding the world's largest stock of reduced organic carbon (ROC) that supports one of the world's largest biomasses. However, the mechanisms whereby ROC becomes mineralized remain unresolved. This review focuses on laboratory and field observations that dissolved organic carbon (DOC) self-assembles, forming self-assembled microgels (SAGs). Self-assembly has ∼10% yield, generating an estimated global seawater SAG budget of ∼10¹⁶ g C. Transects at depths of 10–4,000 m reveal concentrations of ∼10⁶ to ∼3 × 10¹² SAG L⁻¹, respectively, forming an estimated ROC stock larger than the global marine biomass. Because hydrogels have ∼1% solids (10 g L⁻¹), whereas seawater DOC reaches ∼10⁻³ g L⁻¹, SAGs contain ∼10⁴ more bacterial substrate than seawater. Thus, microgels represent an unsuspected and huge micron-level ocean patchiness that could profoundly influence the passage of DOC through the microbial loop, with ramifications that may scale to global cycles of bioactive elements.