Trophic regions of a hydrothermal plume dispersing away from an ultramafic‐hosted vent‐system: Von Damm vent‐site, Mid‐Cayman Rise

Abstract

[1] Deep-sea ultramafic-hosted vent systems have the potential to provide large amounts of metabolic energy to both autotrophic and heterotrophic microorganisms in their dispersing hydrothermal plumes. Such vent-systems release large quantities of hydrogen and methane to the water column, both of which can be exploited by autotrophic microorganisms. Carbon cycling in these hydrothermal plumes may, therefore, have an important influence on open-ocean biogeochemistry. In this study, we investigated an ultramafic-hosted system on the Mid-Cayman Rise, emitting metal-poor and hydrogen sulfide-, methane-, and hydrogen-rich hydrothermal fluids. Total organic carbon concentrations in the plume ranged between 42.1 and 51.1 mM (background = 43.2 AE 0.7 mM (n = 5)) and near-field plume samples with elevated methane concentrations imply the presence of chemoautotrophic primary production and in particular methanotrophy. In parts of the plume characterized by persistent potential temperature anomalies but lacking elevated methane concentrations, we found elevated organic carbon concentrations of up to 51.1 mM, most likely resulting from the presence of heterotrophic communities, their extracellular products and vent larvae. Elevated carbon concentrations up to 47.4 mM were detected even in far-field plume samples. Within the Von Damm hydrothermal plume, we have used our data to hypothesize a microbial food web in which chemoautotrophy supports a heterotrophic community of microorganisms. Such an active microbial food web would provide a source of labile organic carbon to the deep ocean that should be considered in any future studies evaluating sources and sinks of carbon from hydrothermal venting to the deep ocean.

Spatially resolved sampling reveals dynamic microbial communities in rising hydrothermal plumes across a back-arc basin

“…Microorganisms are ecological lynchpins in deepocean hydrothermal ecosystems, as they fuel symbiosis (Petersen et al, 2012), dominate near-vent food webs (Bennett et al, 2013) and mediate biogeochemical processes in plumes that are of significance to the greater oceans (Kadko, 1993;Toner et al, 2009;Wu et al, 2011;Li et al, 2014b). Yet, our understanding of the ecology of hydrothermal plume microorganisms and their relationship to those of the seafloor and surrounding water column is still in its infancy .…”

The influence of vent systems on pelagic eukaryotic micro-organism composition in the Nordic Seas

“…Previous studies suggest that the vents have an effect and contribute to increased carbon production (Atkins 2000;Wakeham et al 2001;Hügler and Sievert 2011;Bennet et al 2013). However, the effect of ventspecific biodiversity has remained largely unexplored.…”

“…This conclusion is strengthened by the high protistan diversity described in López-García et al (2007). Bennet et al (2013) also found an increase in total organic carbon (TOC) compared to surrounding waters. These studies suggest that vents can be positive for protists, possibly due to increased food availability our data on vent systems in the Nordic Seas did not clearly identify any effect on the microplankton community.…”

“…Although eukaryotic micro-organisms in Nordic Seas plumes have not been studied before, several other studies have focused on the effect of hydrothermal plumes from other parts of the world on both the mesozooplankton (Berg and Van Dover 1987;Burd and Thomson 1995;Burd et al 2002;Vinogradov and Vereshchaka 2005;Olsen et al 2013) and the microplankton (Atkins 2000;López-García et al 2007;Bennet et al 2013). While hydrothermal vents clearly contribute to increasing the available metabolic energy, how this increased energy affects the biodiversity remains unclear.…”

“…These micro-organisms support diverse assemblages of eukaryotes (Bennet et al 2013), which in turn become the source of energy to higher trophic levels such as mesozooplankton (e.g. Kaartvedt et al 1992;Burd et al 2002;Olsen et al 2013).…”