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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.dsr.2006.05.007 Byline: J.W. Fleeger (a), K.R. Carman (a), P.B. Weisenhorn (a), H. Sofranko (a), T. Marshall (a), D. Thistle (b), J.P. Barry (c) Keywords: Carbon dioxide; Meiobenthos; Nematodes; Size distribution; Biovolume; Monterey Canyon Abstract: One proposal for ameliorating global warming is to sequester large amounts of carbon dioxide in the deep ocean, but the environmental consequences of sequestration for sediment-dwelling animals are poorly known. In a previous publication, we reported that [approximately equal to]80% of benthic copepods were killed in an experimental release of CO.sub.2 off northern California at 3262m. The effects of this release on nematodes are reported here. We examined samples of nematodes taken inside two 'corrals' into which CO.sub.2 was directly injected (providing an extreme endpoint for CO.sub.2 exposure) and taken near to and far from this CO.sub.2 source. After 30 days, pore-water pH was unchanged ([approximately equal to]7.8) at the sediment-water interface far ([approximately equal to]40m) from corrals, but pH profiles were reduced by [approximately equal to]0.75 near ([approximately equal to]2m) corrals. Corral pH was highly acidic (5.4 in a measurement from a subsequent experiment). Fifty randomly selected nematodes from each of four vertical layers from the 14 cores were photographed. They were assigned to a tail group (based on morphology), and individual biovolume was estimated from measurements of body length and width. Although nematode abundance (expressed as total nematodes and by tail group) was not affected, length, width, and individual biovolume significantly differed between near and far samples. Median nematode biovolume examined across tail group and core layer increased by [approximately equal to]48% inside and near corrals. Differences between near and corral samples were always less than differences between near and far samples. However, nematode length:width ratio did not differ between near and far, and the shapes of length, width, and biovolume frequency distributions were similar in all samples. We postulate that the nematode community throughout the upper 3cm suffered a high rate of mortality after exposure to CO.sub.2, and that nematodes were larger because postmortem expansions in body length and width occurred. Decomposition rates were probably low and corpses did not disintegrate in 30 days. The observable effects of a reduction in pH to about 7.0 after 30 days were as great as an extreme pH reduction (5.4), suggesting that 'moderate' CO.sub.2 exposure, compared to the range of exposures possible following CO.sub.2 release, causes high mortality rates in the two most abundant sediment-dwelling metazoans (nematodes and copepods). Author Affiliation: (a) Department of Biological Sciences, Louisiana State University, Baton Rouge, LA 70803-1725, USA (b) Department of Oceanography, Florida State University, Tallahassee, FL 32306-4320, USA (c) Monterey Bay Aquarium Research Institute, Moss Landing, CA 95039, USA Article History: Received 4 August 2005; Revised 17 May 2006; Accepted 20 May 2006

Hydrogen sulfide discharge at cold seep sites is recorded as enrichment in the barium to calcium (Ba/Ca) ratio in shells of vesicomyid clams collected live from cold seeps in Monterey Canyon and the Cascadia margin. A direct relationship between increased Ba fluxes from cold seeps and Ba incorporation into shells was established for the Cascadia margin site. For the Monterey canyon site, a 2-yr episode of high fluid flow centered on 1992 was inferred from coherent changes in the Ba/Ca profiles of three Calyptogena kilmeri shells. Comparison with precipitation and [[delta].sup.18]O data indicates that this high-flow period may have been driven by an increase in rainfall after the 1988--1990 California drought. High-resolution records preserved in clam shells are shown to be useful in elucidating characteristics, history, and possible mechanisms driving fluid discharge at continental margin seeps, thus establishing their potential use as paleotracers of fluid seepage events.

The effects of C[O.sub.2] on nematode tailgroup abundance and body size, shape and biovolume spectra are examined and these measurements are considered to detect the changes in deep=sea nematode communities. The effects of a reduction in pH to about 7.0 after 30 days is found to be as great as an extreme pH reduction, suggesting that 'moderate' C[O.sub.2] exposure, compared to the range of exposures possible following C[O.sub.2] release, causes high mortality rates in the two abundant, sediment-dwelling metazoans.