Cycling of dissolved organic carbon (DOC) was investigated in anoxic sediments of the Santa Monica Basin, California Borderland, by analyzing the concentration and isotopic signatures (D 14 C and d 13 C) of pore-water DOC and dissolved inorganic carbon (DIC), and organic compound classes extracted from the bulk sediments. DOC and DIC increased across the sediment-water interface, indicating net efflux of these solutes out of the sediments. Throughout the depth interval examined (0-30 cm), the D 14 C value of DOC (D 14 C DOC) was similar to, or higher than, that of bulk sedimentary particulate organic carbon (POC), indicating degradation of relatively 14 C-rich components of POC. There were prominent peaks in both D 14-C DOC and D 14 C DIC in the uppermost 2 cm of the sediment column, indicating degradation and remineralization of 14 C-rich, labile organic matter in the near-surface sediments. However, below these sub-surface maxima, D 14 C DOC and D 14 C DIC decreased with depth by $200& and $50&, respectively. Given the diffusive time scales, these decreases were too large to be explained by 14 C loss due to radioactive decay. To help explain these observations, we constructed and implemented a selective degradation model that considers bulk pore-water DOC to be the sum of three kinetically-and isotopically-distinct sub-components. Based on this model, the most reactive DOC fraction, which supported $60% of the DIC production, had a D 14 C value indicating the presence of bomb-14 C. The intermediate fraction had a D 14 C value of $À60& and accounted for most of the pore-water DOC standing stock. The least reactive fraction was virtually non-reactive in these sediments, and had a D 14 C value of $À500&. The benthic DOC flux of this 14 C-depleted, poorly-reactive DOC fraction may represent a source of pre-aged, refractory DOC to the oceans.

ABSTRACT:The flocculation of kaolin suspended in a dilute salt solution was studied as a function of the addition of cationic surfactant and cationic polyacrylamide (CPAM) added separately, consecutively, or simultaneously. Cationic polyacrylamide caused flocculation by bridging when added in low concentrations, but at higher concentrations, charge neutralization became the dominant mechanism and the flocculation rate was highly dependent on the charge density of the polymer. Adsorption of sufficient polymer or surfactant (cetyl pyridinium chloride) prevented immediate adsorption of the other, although surfactant could replace polymer after extended agitation. The adsorption of polymer was greatest when small flocs were formed by charge neutralization or by prolonged shaking.

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