Inter-related sediment trap studies at 9-10°N East Pacific Rise: Larval Transport and Hydrothermal Plume Biogeochemistry


DOEI Funded Research: 2008


At mid-ocean ridges, hydrothermal activity discharges chemically-enriched fluids from the seafloor that sustain vibrant and enigmatic biological communities reliant upon the chemical energy available from these systems for life.  While individual hydrothermal systems and their inter-relationships with the geologic processes that underpin them and the biologic communities that they host are becoming increasingly well understood, a novel line of research asks: what are the relationships between these seafloor hydrothermal systems and the wider deep ocean? That is the focus of this study.

To conduct such research we have chosen to collaborate at a particularly well characterized vent-area on the East Pacific Rise which, over the past 10-15 years, has become probably the best understood and characterized seafloor hydrothermal field worldwide.  Globally, it is believed that, on-average, the entire volume of the world’s oceans must be cycled through hot, recently formed oceanic crust at Mid-Ocean Ridges every 10 Million years.  Consequently, because the fluids emitted from hydrothermal vents then mix with seawater in turbulent plumes that dilute the fluid in a ratio of ~10,000:1, it follows that the entire volume of the ocean must be mixed through these plumes every thousand years or so.  This is the same time-scale for circulation of deepwater around the floor of all the world’s deep ocean basins.  At any given vent-site we know that the chemical reactions in hydrothermal plumes both modify the chemical fluxes from the vent-fluids (through precipitation) and impact broader chemical ocean budgets (some chemical species become enriched from vent-input, others are removed from seawater through reactions with the vent-products).  Consequently, we suspect that processes in hydrothermal plumes may impact global-scale ocean chemical budgets.

We also recognize that the processes in hydrothermal plumes are not purely abiotic.  Larvae from hydrothermal communities at the seafloor must disperse away from the source to colonize new sites and also to re-populate sites (as at EPR 9-10°N) after they have been disrupted by episodic eruption events.  These recolonization events have the potential to change the community structure from that which existed prior to the eruption.  On much smaller length scales, even the plume-particles previously described as minerals or chemical precipitates should more accurately be described as suspended biofilms that support a previously overlooked host of microbial life.

To begin to investigate the significance of plume-processes to the global ocean we have deployed a series of time series sample-collection devices (sediment traps) nested within an array of instruments that measured the flow along and across the EPR mid-ocean ridge over a 12 month period (21 samples from each of 5 different depths and locations).  We are now ready to begin to analyze these samples using state-of-the-art biological and geochemical techniques so that, when coupled with the corresponding physical circulation data (already funded as a separate study), we can start to elucidate the impact of this specific hydrothermal system on the wider, open, deep-ocean.