Premium
Stable isotope evidence for alternative bacterial carbon sources in the Gulf of Mexico
Author(s) -
Kelleyl Cheryl A.,
CofJin Richard B.,
Cifuentes Luis A.
Publication year - 1998
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.1998.43.8.1962
Subject(s) - phytoplankton , oceanography , organic matter , environmental science , transect , isotopes of carbon , carbon cycle , dissolved organic carbon , seawater , environmental chemistry , salinity , total organic carbon , carbon fibers , ecology , ecosystem , geology , chemistry , nutrient , biology , materials science , composite number , composite material
In temperate coastal waters, it is generally assumed that carbon cycling is primarily supported by phytoplankton production, having δ 13 C values ranging from −22 to −18‰. In a transect leading out from the Mississippi River, riverine and seawater δ 13 C endmembers of particulate organic matter have previously been measured at −25.5 and −20.0‰, respectively. In addition, δ 13 C values of dissolved organic carbon in the northern Gulf of Mexico range from −24.7 to −19.6‰, with the more 13 C‐depleted values from fresher waters. Assumptions about coastal transport of dissolved organic matter predict that the bacterial δ 13 C values should fall along the conservative salinity mixing line between terrestrial and marine carbon sources. However, in the field survey presented here, δ 13 C values of bacteria in coastal regions of the Gulf of Mexico adjacent to the Mississippi River are considerably 13 C‐depleted, with values as low as −33‰. These isotope values suggest that carbon from sources other than phytoplankton production or terrestrial organic matter are supporting the production of the bacterial assemblage. Possibilities include the incorporation of carbon derived from light hydrocarbons from seep areas and the chemoautotrophic processes of methane oxidation and nitrification. These 13 C‐depleted stable isotope data are evidence that bacterially assimilated carbon in the northern Gulf of Mexico may be seasonally uncoupled to surface phytoplankton production.