HR: 1340h
AN: B43B-0146    [Abstracts]
TI: The Influence of Methane Venting on Benthic Foraminiferal Assemblages in Guaymas Basin, Gulf of California
AU: * Perez, E
EM: geperez@isugw.indstate.edu
AF: Natural History Museum of Los Angeles County, 900 Exposition Blvd., Los Angeles, CA 90007
AU: Herguera, J
EM: herguera@cicese.mx
AF: CICESE, Km 107 Carretera Tijuana-Ensenada , Ensenada, 22860 Mexico
AU: Paull, C
EM: paull@mbari.org
AF: Monterey Bay Aquarium Research Institute, 7700 Sandholdt Road, Moss Landing, CA 95039-9644
AU: Ussler, W
EM: methane@mbari.org
AF: Monterey Bay Aquarium Research Institute, 7700 Sandholdt Road, Moss Landing, CA 95039-9644
AU: Cortina, A
EM: aleixcortina@hotmail.com
AF: CICESE, Km 107 Carretera Tijuana-Ensenada , Ensenada, 22860 Mexico
AB: Fossil foraminifera are critical for paleoenvironmental reconstructions including the study of past episodes of methane venting from gas hydrate reservoirs. However, the use of benthic foraminifera as indicators of methane release remains controversial and more modern analog data is needed to understand the ecology and isotopic signatures of foraminifera in methane seeps. The objective of this investigation was to characterize the species composition and vertical distribution of living benthic foraminifera (rose Bengal stained) along known gradients of present methane venting in order to gain insight into the ecological tolerances and preferences of benthic foraminifera in methane seeps. Vertical distribution patterns are also important in determining carbon isotope variability. Samples were retrieved along the NE transform margin of the Guaymas Basin in the Gulf of California (about 1,582 m). Suites of ROV cores were collected from beds of living calyptogenid clams, tubeworms, and bacterial mats; from a methane venting site evidenced by a continuous stream of gas bubbles; and from control sites. Our data shows that foraminiferal abundance is lower in the methane-influenced sites than in the control sites. Lowest foraminiferal abundance occurs at the bacterial mats, probably caused by higher levels of sulfide. The assemblage is dominated by calcareous species that are characteristic of other organic-rich, oxygen-poor environments (e.g., {\it Uvigerina peregrina, Bulimina mexicana, Buliminella tenuata, Globobulimina pacifica}). The vertical distributions of several species are different from those of conspecifics observed in previous studies of non-seep habitats, with deeper and broader depth ranges for some species at the methane-influenced habitats in this study. Of special interest is the occurrence of {\it Planulina wuellerstorfi}, traditionally considered an epifaunal species, at sediment depths of 6 cm and with density maxima between 1 and 3 cm. This may result from deeper and more widespread microbial food sources at methane-influenced sites compared to non-seep habitats.
DE: 4825 Geochemistry
DE: 4267 Paleoceanography
DE: 4804 Benthic processes/benthos
DE: 3030 Micropaleontology
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting