Transparent exopolymer particle binding of organic and inorganic particles in the Red Sea: Implications for downward transport of biogenic materials

Abstract. Binding of particulate and dissolved organic matter in the water column by marine gels allows sinking and cycling of organic matter into deeper water of the Red Sea and other marine water bodies. A series of four offshore profiles were made at which concentrations of bacteria, algae, particulate transparent exopolymer particles (p-TEP), colloidal transparent exopolymer particles (c-TEP), and the fractions of natural organic matter (NOM), including biopolymers, humic substances, low molecular weight neutrals, and low molecular weight acids were measured to depths ranging from 90 to 300 m. It was found that a statistically-significant relationship occurs between the concentrations of p-TEP and bacteria while a minimal, non-significant relationship between p-TEP and algae occurs. This likely reflects the low abundance of larger algal species in the study region. Variation in the biopolymer fraction of NOM in relationship to TEP and bacteria suggests that extracellular discharges of polysaccharides and proteins from the bacteria and algae are occurring without immediate abiotic assembly into p-TEP. In the water column below the photic zone, TOC, bacteria, and biopolymers show a generally common rate of reduction in concentration, but p-TEP decreases at a diminished rate, showing that it persists in moving organic carbon deeper into the water column despite consumption by bacteria.