Marine Microgels

Abstract

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 approximately10% yield, generating an estimated global seawater SAG budget of approximately 10(16) g C. Transects at depths of 10-4,000 m reveal concentrations of approximately 10(6) to approximately 3 x 10(12) SAG L(-1), respectively, forming an estimated ROC stock larger than the global marine biomass. Because hydrogels have approximately 1% solids (10 g L(-1)), whereas seawater DOC reaches approximately 10(-3) g L(-1), SAGs contain approximately 10(4) 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.

A marine biogenic source of atmospheric ice-nucleating particles

“…The presence of spectral features similar to diatom cell wall fragments and diatom exudates material suggests the presence of diatoms in both SML5 and SML19. It is important to note that marine SMLs 13,18,[56][57][58] , subsurface waters 59 , and biofilms 60 are comprised of a complex mixture of inorganic particles, particulate organic matter in the form of microorganisms, biogenic debris, polysaccharide enriched microgels, lipids, proteins and amino acids. Therefore, the X-ray spectra shown here will not be identical for different SML samples.…”

Dissolved organic matter (DOM) release by phytoplankton in the contemporary and future ocean

“…Over the last two decades there has been considerable interest in the role of large polymers in the ocean (see reviews by Passow, 2002a;Verdugo et al, 2004;Verdugo, 2012). There has been the realization that there is a continuum of organic matter from DOM to POM, with gels and exopolymer particles sharing some of the properties of both POM and DOM.…”

“…TEP are invisible using bright-field light microscopy, but become visible after staining, indicating that TEP contain acid polysaccharides (Ramus, 1977;Passow & Alldredge, 1995). TEP are ubiquitous and play an important role in particle dynamics and carbon cycling in the ocean (see reviews by Passow, 2002a;Burd & Jackson, 2009;Verdugo, 2012). For example, TEP are sticky and affect the further aggregation of particles into larger aggregates that sink rapidly though the water column, affecting the biological carbon pump (Engel, 2000;Passow, 2002a;Thornton, 2002).…”

Broad-scale predictability of carbohydrates and exopolymers in Antarctic and Arctic sea ice

“…These microorganisms produce large quantities of dissolved organic carbon (DOC), often in the form of carbohydrate-rich extracellular polymeric substances (EPS) (7). Microbial EPS exist in a dynamic equilibrium from dissolved polysaccharides (dEPS <0.2 μm) to complex particulate EPS that can form gels on the millimeter to centimeter scale (8). Here we focus on the biologically relevant dissolved carbohydrates (dCHO) that constitute a substantial fraction of the DOC in sea ice (9)(10)(11)(12)(13) (Fig.…”

“…1). dCHO are concentrated from sea ice DOC by dialysis (>8 kDa), with subsequent treatment allowing the definition of four subcomponents of the total dCHO pool: (i) dissolved uronic acids (dUA), produced by ice diatoms and ice bacteria (14)(15)(16), that confer strong cross-linkages between polymer chains (8), forming low solubility EPS complexes within brine channels (8,14,17); (ii) dEPS, produced by sea ice algae (9,12,18,19) and isolated from dCHO by 70% (vol/vol) alcohol precipitation; (iii) a low solubility fraction of dEPS obtained by 30% (vol/vol) alcohol precipitation, containing complex EPS molecules (dEPS complex ), often produced by algae with reduced biological activity or when under physiological stress (9,13,19); and (iv) a fraction of highly soluble carbohydrates that are not considered EPS (dCHO non-EPS ), do not precipitate in alcohol, and are produced by many actively growing ice algae (9,14).…”