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(1 - 2 of 2)
- Title
- Observations of carbon export by small sinking particles in the upper mesopelagic
- Description
- Carbon and nutrients are transported out of the surface ocean and sequestered at depth by sinking particles. Sinking particle sizes span many orders of magnitude and the relative influence of small particles on carbon export compared to large particles has not been resolved. To determine the influence of particle size on carbon export, the flux of both small (11–64 μm) and large (> 64 μm) particles in the upper mesopelagic was examined during 5 cruises of the Bermuda Atlantic Time Series (BATS) in the Sargasso Sea using neutrally buoyant sediment traps mounted with tubes containing polyacrylamide gel layers and tubes containing a poisoned brine layer. Particles were also collected in surface-tethered, free-floating traps at higher carbon flux locations in the tropical and subtropical South Atlantic Ocean. Particle sizes spanning three orders of magnitude were resolved in gel samples, included sinking particles as small as 11 μm. At BATS, the number flux of small particles tended to increase with depth, whereas the number flux of large particles tended to decrease with depth. The carbon content of different sized particles could not be modeled by a single set of parameters because the particle composition varied across locations and over time. The modeled carbon flux by small particles at BATS, including all samples and depths, was 39 ± 20% of the modeled total carbon flux, and the percentage increased with depth in 4 out of the 5 months sampled. These results indicate that small particles (< 64 μm) are actively settling in the water column and are an important contributor to carbon flux throughout the mesopelagic. Observations and models that overlook these particles will underestimate the vertical flux of organic matter in the ocean., Published
- Author
- Durkin
- Title
- Silicic acid supplied to coastal diatom communities influences cellular silicification and the potential export of carbon
- Description
- Microcosm experiments were conducted along the Washington and Oregon coasts in May 2009, May 2010, and July 2010 to determine whether variation in the supply of silicic acid from the Columbia River could influence the silicification and sinking potential of coastal diatom blooms. The chlorophyll a concentration increased similarly in communities incubated with added nitrate or both nitrate and silicic acid, indicating that growth was limited by nitrate availability. Communities that grew in the treatment with added silicic acid and nitrate were more silicified than communities in the treatment with only nitrate added. No difference in community composition was detected between these treatments in three out of four experiments. Isolates of Minutocellus, Cylindrotheca, Thalassiosira, and Odontella were obtained from the microcosm experiment conducted in May 2010 and were maintained in the laboratory in 20 µmol L−1 silicic acid. All four diatom isolates contained ∼ 2.5 times more silica per cell when silicic acid concentration in the media was increased to 80 µmol L−1. The intensity of a fluorescent cellular stain of newly precipitated silica (2-(4-pyridyl)-5{[4-dimethylaminoethyl-aminocarbamoyl)-methoxy]phenyl}oxazole) strongly correlated with silica content among species, but was a less sensitive indicator of changing silicification within a single species. Changes in silicification were not correlated with changes in the transcript abundance of silicic acid transporters. Sinking rates increased roughly 2-fold for cells that contained ∼ 2.5 times more silica. Variation in silicic acid supply alters the silicification of nitrate-fueled coastal diatom blooms and the potential sink of carbon from coastal zones., published
- Author
- Durkin