Biogeochemical Fluxes, Interactions and Biogeochemical Fluxes at 9°N East Pacific Rise: Multi-disciplinary


DOEI Project Funded: 2006

Submarine hot-springs at Mid-Ocean Ridges represent an important source of chemicals that regulate the composition of the oceans and fuel unique ecosystems. After nearly 30 years of study, scientists are becoming increasingly familiar with processes at the seafloor where hot fluids interact with cold oxygen-rich seawater, sustaining thriving communities of exotic fauna, previously unknown to science, that are described as chemo-synthetic because they derive their energy from chemical reactions rather than sunlight. What is less often appreciated, however, is that much of the chemical energy available to sustain such novel life-forms escapes upward away from vent-sites in tall billowing plumes of hot water and fine-grained mineral particles that ascend 100m or more into the overlying water column before dispersing, like smoke from some underwater factory.

One of the key elements in these chemical-energy laden plumes is iron. Iron is an essential micronutrient for marine life yet, typically, it is only present in trace amounts in the deep ocean, despite being one of the most abundant elements on Earth. The exception to that general rule is in hydrothermal fluids where concentrations 1-million fold richer than ordinary seawater are common. The aim of this proposal is to trace the fate of that iron (and other enriched chemicals) in hydrothermal plumes, the microbes that interact with them to derive energy, and the larvae of vent-fauna that are transported within the same plumes. While research submersibles can only visit any one vent-site episodically, hydrothermal fields are continuously changing. We now have sensors that can monitor changes in the temperature of fluids at vents, but biological and chemical sensors are still awaited. To overcome this, we plan to use “sediment trap” sampling devices at two vent-sites on the East Pacific Rise - to collect fluxes of material settling from hydrothermal plumes and, hence, monitor changes in hydrothermal output. Each trap will collect 21 samples over ~1 year (thus, each sample will represent ~2-3 weeks’ output) to determine how chemical, microbial and biological fluxes change with time. This will be especially important if a major earthquake and/or volcanic eruption takes place while our equipment is deployed. Colleagues most familiar with our chosen area have suggested that this is likely and have both fluid temperature sensors and seismic recording devices already deployed. We want to join that experiment because there is a strong body of opinion that holds that MOST hydrothermal discharge is only released under such extreme conditions - by placing our traps in the same location we will be in exactly the right place to address this issue if anything so dramatic occurs.

Even without such an event, our study will still shed new light on important hemicalmicrobiological- mineralogical interactions in hydrothermal plumes and into the cycling of iron in the oceans in general. Further, by studying the input to our traps at two locations, ca.20 miles apart, we will be able to collect the larvae of adult fauna that never stray far from an active ventsite. Using DNA techniques, we will be able to investigate what role plumes play in transporting these larvae away from sites where they are spawned and delivering them to new sites that they can colonise as adults. While we may not be able to fully address all these issues immediately, this project will allow us to collect the right samples to begin this work and to demonstrate its value and viability.