White Paper Title: 
Microbial Biogeography and Biogeochemistry of Hydrothermal Plumes and Seafloor Rock Substrates

Hydrothermal vents are conspicuous oases on the seafloor.  The majority of microbial ecology studies of these systems have focused on life in warm fluids and on active chimneys.  Less is known about hydrothermal plumes, especially in relation to how communities evolve with time within the plume.  Likewise, interest in the cold rock substrates such as basalt and extinct hydrothermal chimneys has only recently come into focus.  Additionally, little is known about the global distribution and dispersal of organisms that reside in plumes and on/in rocks.

Microbial communities in hydrothermal plumes are derived from two opposite end members- undiluted hydrothermal fluids ejected from vents and background ocean water.  The chemical biome that results is thermally similar to the deep ocean, but replete with reduced compounds that are typically absent from those waters.  This creates a unique biome that we know little about.  Early work on the Juan de Fuca Ridge showed that there is a potential within plumes for carbon production rates generating equal amounts of carbon in situ through ammonia (Lam et al. 2004, 2008) and methane (de Angelis et al. 1993) oxidation within plumes to that falling from the photic zone.  Interestingly, this ammonia oxidation appears to be carried out by ammonia oxidizing bacteria, not the ubiquitous ammonia oxidizing archaea, making hydrothermal plumes an interesting biome to study the competition between these organisms.

Recent work has begun to focus on defining microbial populations in plumes as a unique ecosystem (Dick et al. 2010, Sylvan et al. in prep).  Further, work at 9°N EPR showed that plume communities can change drastically on the order of days, and, supporting work from the Juan de Fuca Ridge (e.g. Huber et al. 2007), Epsilonproteobacteria drive overall community diversity and structure in these plumes (Sylvan et al. in prep).  Given the impact of hydrothermal plumes on deep sea geochemistry, it is important to understand the microbial populations and processes specifically within plumes in order to define their impact on deep ocean C, N and P cycling, as well as metal cycling.

Microbial populations on extinct hydrothermal chimneys and basalts have gained attention only recently (e.g. Kato et al 2010; Santelli et al 2008).  These populations are unique from those in the overlying water column, and ecological succession is evident with age of the rock on basalts (Santelli et al. 2009) and active or inactive status on hydrothermal chimneys (Kato et al. 2010; Brazelton et al. 2010).   Tag sequencing results from 9°N EPR recently provided an in depth look at bacterial succession and endemism on these two substrates.  Interestingly, extinct chimney communities contain microbes known to cycle both reduced and oxidized forms of S and N on the same sample.  Given the enormous global reservoir of extinct chimneys and basalts (both seafloor exposed and subsurface), these promise to continue providing fascinating and important discoveries within microbial ecology.  In particular, the microbial weathering of these rocks, releasing elements into the water column (e.g. Edwards et al. 2004), and primary productivity rates (organic C production) are of interest for balancing global elemental budgets.