Occurrence, distribution and origin of C30 cyclobotryococcenes in a subtropical wetland/estuarine ecosystem

Abstract

A series of C30 branched isoprenoid hydrocarbons with a cyclobotryococcane skeleton were identified in the Florida Coastal Everglades Ecosystem. Nine such C30 alkenes were detected and identified as five-membered ring monocyclic hydrocarbons with an identical parent structure of 7,11-cyclobotryococcane based on their mass spectra and hydrogenation behavior. Previous reports have suggested Botryococcus Braunii or green sulfur bacteria (Chlorobiaceae) as likely sources of these 7,11-cyclobotryococcanes. However, their enriched δ13C values (about -18%) determined in this study and their absence in freshwater marsh environments of the Everglades suggest that an origin from green sulfur bacteria or possibly marine diatoms is more likely. The depth profile of individual C30 cyclobotryococcenes in one sediment core from Florida Bay shows abundant variations in their historical deposition and may indicate long-term changes of their source strength due to variations in local environmental conditions.