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Published January 30, 2009 | public
Journal Article

Dissolution kinetics of biogenic silica collected from the water column and sediments of three Southern California borderland basins


Understanding biogenic silica (bSi) dissolution kinetics in margin environments is important in assessing the global silicon cycle, a cycle closely linked to the global carbon cycle. This understanding is also essential to answer the question of whether bSi content in marine sediment is a valid indicator of productivity in the overlying surface ocean. In this study, plankton tow, sediment trap, and sediment samples were collected at sites in three Southern California borderland basins. Batch dissolution experiments with plankton tow and sediment trap materials (conducted in the laboratory at 22 °C) showed linear dissolution kinetics, from which mean dissolution rate constants of 0.05 d^(−1) for plankton tow samples and 0.07 d^(−1) for sediment trap samples could be calculated. The dissolution rate constants for both types of samples showed seasonal variability but not the same seasonal patterns. Faster dissolution was observed with sediment trap samples collected at 800 m than at 550 m. With sediment multi-core samples, non-linear dissolution kinetics was observed, which complicates the direct comparison of dissolution rates. Nonetheless, dissolution appeared to be slower for the sediments samples than for samples collected from the water column and to decrease with depth in the sediments. Rate constants for surface sediment (0–0.5 cm) were at least 3–5 times less, and sediments at depths > 2 cm had rate constants at least 6–13 times less than those for material sinking to the sediment surface at these sites. Dissolution experiments conducted with Santa Barbara Basin surface sediment samples amended with dissolved aluminum (Al) and San Pedro Basin trap samples amended with enriched detrital materials (obtained by leaching bSi from sediment samples) suggested that dissolution was inhibited by Al and that the sediments from the different basins varied in the extent of Al release.

Additional Information

© 2008 Elsevier B.V. Received 5 July 2008; revised 2 December 2008; accepted 3 December 2008. Available online 10 December 2008. This project is supported by the National Science Foundation (Grant OCE-0351498 to Suvasis Dixit and Janet G. Hering and Grant OCE-0351169 to William M. Berelson and Douglas E. Hammond). Efforts of the captains and crews of the R/V New Horizon and R/V Seawatch made this work possible. Sediment trap materials from SBB were kindly supplied by Dr. R. Thunell and E. Tappa. Additional shiptime and sediment traps were made available by Drs. T. Michaels and D. Capone. The assistance of W. Beaumont, R. Schwartz and L. Collins in laboratory and field efforts is appreciated.

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