Suspended particulate organic material from hydrothermal vent waters at 21° N

Abstract

Ocean floor spreading centres described recently consist of several sites with chemical and biological features unlike any oceanic sites previously known^1–4. The high-pressure and warm-temperature regimes at these sites, coupled with dynamic hydrothermal water circulation, support biological communities that utilize a source of primary production which appears to be non-photosynthetic⁵. A detailed biochemical analysis of the suspended matter at a biologically-active site has been undertaken, with the goal of describing the relationship between microorganisms, benthic organisms and suspended particulate material within these hydrothermal systems. Suspended particulate matter from warm hydrothermal vent waters (5–38°C) of the East Pacific Rise^1–4 (21° N, 106° W) was sampled on the OASIS expedition with an in situ pumping system in April 1982. Particulate organic carbon (POC) and nitrogen (PON) as well as individual organic compound classes from the lipid fraction were analysed to ascertain the sources and composition of the organic matter in this highly productive area. We show here that the particulate organic material (POM) of the vent water was both quantitatively and qualitatively different from the non-vent bottom water. The POC and PON measured within the vent and non-vent waters vary by a factor of 2–5, the higher values being in warm water. The organic matter in the non-vent water was found to be more resistant towards degradation or remineralization than in the vent water, as shown by the C:N ratio and the total lipid:POC ratio. Contributions to the lipid class compounds were assessed using well-known organic compound source biomarkers such as hydrocarbons, fatty alcohols, sterols, triacylglycerols and steryl and wax esters.