Patterns and consequences of sub-seabed flow on continental margins
Principal Investigator: Jim Barry
Collaborators: Keith Kvenvolden, Tom Lorenson, Jon Martin, Geoff Wheat
This project encompasses ongoing studies at the continental margin and expands the research to other areas. There are two components:
P3A Margin tectonics and fluid flowBeneath the seafloor lies a complex "plumbing system" that channels fluids chemically distinct from seawater. The flow of these fluids tends to be greatest along faults that fracture the margins of continents. When earthquakes occur in these regions, fluid flow surges, then tapers off to seeping levels; thus, tectonic activity appears to be a driving force in regulating sub-seafloor flow. The several cold seeps discovered by MBARI researchers over the last six years in Monterey Bay mostly occur along the traces of major faults. The question of whether fluids there originate from aquifers on land, or from compaction of the soupy sediments that accumulate on the seafloor, remains to be resolved.
The chemical composition of the fluids reflects not only their origins, but the environment through which they traversed before discharging into seawater. The mixing of seep fluids with ocean water causes chemical reactions that produce precipitates. The carbonate slabs and chimneys MBARI geologists have recovered using the ROV Ventana are composed of one type of such precipitates. Geologists would like to know whether the chemical reactions that produce carbonates are continual, or if the processes occur in episodes of short duration in geologic terms or over millennia. As with hydrothermal vents at mid-ocean ridges, cold seeps also sustain biological communities of bacteria, clams, and other organisms, which use the reduced inorganic compounds from the leaking fluids in chemosynthesis.
Institute scientists are addressing such questions within the scope of this project. Building on past MBARI studies of cold seeps, they will compare subseafloor fluids and carbonates from three locations:
P3B Cold seep biology and ecologyStudies of cold seeps in Monterey Bay and elsewhere have revealed considerable variation in their resident animal communities which seems to be associated with differences in the intensity of fluid release. Seeps on the bay seafloor appear to represent a low-flow endpoint in the spectrum of seep habitats around the world and thus are valuable in comparisons with those at other sites. In 1998 institute ecologists will concentrate their investigations on seeps in the axis of the canyon, using the ROV Tiburon to venture into deeper waters, where they expect to find varieties of clams not yet studied. They will also participate in the October expedition to the Santa Barbara Basin. In laboratory studies of clams collected in a range of locations, the biologists will determine variations in clam blood physiology that appear to allow different species to thrive at sites with different environmental chemistries. The Monterey Bay and Santa Barbara findings will be compared with those from studies of seeps with more intense flows in Northern California and Sagami Bay, Japan.
The researchers will also continue documenting the distribution and abundance of cold-seep organisms of all sizes, from bacteria to snails and clams, and compare them to animal communities at non-seep control sites. A new branch of this cold-seep census will focus on foraminiferans, microscopic organisms whose shells are abundant in fossils and carbonates. Sizable numbers of forams exist at cold seeps, but little is known of their role in seep ecology. Other work, with collaborators, will explore important links in the chemical cycling of sulfur, such as processes of sulfate reduction in seep sediment and sulfide uptake by free-living bacteria there.
Last updated: 23 November 2005