polymer self-assembly, ion bonds, hydrophobic bonding, phase transition, bacterial colonization, marine carbon cycling
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.