Compound-Specific Isotope Geochemistry in the Ocean

Compound-specific isotope analysis encompasses a variety of methods for examining the naturally occurring isotope ratios of individual organic molecules. In marine environments, these methods have revealed heterogeneous sources and alteration processes that underlie the more commonly measured isotope ratios of bulk materials, as well as revealing signatures of marine metabolisms that may otherwise be impossible to isolate. Recently, compound-specific isotopic techniques have improved the reconstruction of metazoan diets and revealed a new potential of metazoan biomass as an archive of paleoecological information. Despite six decades of practice and a diversity of applications, the use of compound-specific isotopic techniques remains uncommon in marine studies. This review examines broad theoretical motivations behind compound-specific isotopic approaches, some applications to studies of marine carbon cycling and trophic relationships, and methodological limitations. In coming years, improvements in analytical efficiency and molecular or intramolecular specificity may transform compound-specific isotope analysis into a tool that can be applied more broadly and help to build global oceanographic data sets.