Geochemical Fingerprinting of Siboglinid Tube Worms: Insights From Stable Isotopes (C, N, and S) and Trace Elements

Abstract

At marine methane seeps, siboglinid tube worms influence the exchange of elements between sediments and seawater and potentially represent a recorder of seep activity. The organ of siboglinids produces the chitin of the tube wall, facilitating the formation of tubes that protect the siboglinid's soft tissue. However, the mechanisms underlying element transfer and isotope fractionation between soft tissue and the chitinous tube are poorly constrained. This study analyzes the carbon, nitrogen, and sulfur isotopes as well as trace elements, including rare earth elements (REEs) and copper (Cu), compositions of tissues and tubes of the siboglinid tube worm Paraescarpia echinospica from the Haima seeps of the South China Sea. The stable isotope values of both tissue and the chitinous tube primarily reflect sulfur oxidation processes and carbon fixation by endosymbiotic sulfur-oxidizing bacteria. The trace element composition of the soft tissue suggests the utilization of light rare earth elements (LREEs) and Cu during aerobic oxidation of methane supposedly performed by epibiotic aerobic methanotrophic bacteria. In contrast, the trace element composition (e.g., REEs, Cu) of the chitinous tube primarily records the influence of diagenetic processes and source effects. The chitinous tube is therefore apparently not a straightforward archive of the local environment and metabolic characteristics of the tube worms. Still, the discrepancies between the information stored in tissue and the chitinous tube may offer some insight for the identification of fossil seep-dwelling tube worms if parts of the chitinous tube are preserved. Integrating element and isotope geochemistry within paleontological studies may consequently enhance our understanding of siboglinid evolution.