Bacterial incorporation of relict carbon in the hydrothermal environment of Guaymas Basin
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Radiocarbon analyses of bulk carbon and individual organic compounds are presented for the hydrothermal environment of the Rebecca’s Roost vent in the southern trough of the Guaymas Basin hydrothermal field. The Delta(14)C values of CO, and CH4 in the hottest hydrothermal fluids (317 degrees C) are nearly “radiocarbon dead” (-944 parts per thousand and -923 parts per thousand, respectively). In contrast, the Delta(14)C values of sediments and individual fatty acids (-418 parts per thousand to -227 parts per thousand) obtained from a bacterial mat located south of the vent site are similar to values previously reported for hydrothermal petroleum in this environment and are more depleted in C-14 than overlying waters. Hydrothermal fluids moving through the sediments appear to supply C-14 of intermediate age to the bacteria. This carbon may take the form of, or may be supplied by processes similar to, the generation of hydrothermal petroleum. Although the bacterial mat visibly was dominated by Beggiatoa spp., such mats are known to include numerous other species. Individual compound data show that preaged carbon is being consumed by the integrated bacterial assemblage. Values of delta(13)C and Delta(14)C indicate that petroleum-derived carbon is incorporated directly into fresh bacterial biomass. Subsequently, some of this newly synthesized material also is consumed by heterotrophs, as eukaryotic sterols from the same sample also have C-14-depleted values (Delta(14)C = -136 parts per thousand to -110 parts per thousand). Therefore, the entire system may operate as a complex consortium to transform relict carbon back into biomass. Bacterial consumption of relict carbon occurs despite the ample supply of fresh carbon delivered from the productive, overlying water column. Copyright (c) 2005 Elsevier Ltd.