Dataset: seep isotopes
Deployment: AT15-44

Average stable isotopic signatures (d15N and d13C) for carbonate rocks and animals collected during AT 15-44 at various methane seep sites on the Costa Rica margin. The values are averages, not actual measurements.  Researchers needing the raw data should seek them from llevin@ucsd.edu.

Animal tissues were sorted, processed and analysed according to methods in Levin & Mendoza.

Levin, L. A. & Mendoza, G. (2007) "Community structure and nutrition of deep methane seep macroinfauna from the Aleutian Margin and Florida Escarpment, Gulf of Mexico."  Mar. Ecol. 28, 131-151. (doi:10.1111/j.1439-0485.2006.00131.x)

For further information, see:

Lisa A. Levin, Victoria J. Orphan, Greg W. Rouse, Anthony E. Rathburn, William Ussler III, Geoffrey
S. Cook, Shana K. Goffredi, Elena M. Perez, Anders Waren, Benjamin M. Grupe, Grayson Chadwick and
Bruce Strickrott.(2012) "A hydrothermal seep on the Costa Rica margin: middle ground in a continuum of reducing ecosystems" Proc. R. Soc. B published online 7 March 2012. doi: 10.1098/rspb.2012.0205

From Final Report:

At Costa Rica, carbonate organic matter content was high (0.5 to 3.5%).  Organic matter in the carbonates had d 13C signatures of -65o/oo to -23o/oo indicating a varied methane contribution to the C pool. Faunal isotopic signatures ranged broadly, from -101o/oo to -10o/oo for d13C and -12 to +18 for d 15N.   They revealed strong trophic resource partitioning among mollusk and polychaete species. A broad range of d 13C  signatures reflect use of a variety of microbial food resources, often within a single rock.  Very light d 13C signatures (mean -92o/oo, n=18) in an abundant dorvilleid polychaete (Dorvillea sp.) in the most sulfidic carbonates provides evidence of a carbonate endolithofauna that may rely primarily on archaeal carbon. Intense grazing of rocks by lepetopsid limpets  many with isotopic evidence for methane-derived C, apparently exerts strong top-down control on the distribution of protists and smaller invertebrates.

At Hydrate Ridge, inorganic d13C values of carbonates ranged from -26o/oo to -54o/oo, whereas the rock organic d13C spanned a much broader range (from -19o/oo to -71o/oo.).  Within a rock the two values were not correlated and there were no significant isotopic differences on average between active and inactive carbonates, although inactive values were less variable.      Natural abundance animal carbon isotope signatures ranged from -17o/oo to -88o/oo, with average values of animals (per rock) showing no significant difference between active and inactive sites (P-0.232). However, carbonate d13C org (P=0.002) and d15N (animal P=0.005) were isotopically lighter on rocks designated as active, relative to those designated as inactive.