MGGD Research Areas


Marine hydrothermal systems and the deep-subseafloor biosphere

Nowhere is the connection between the geophysics of earth’s interior and the geochemical, biological, and physical processes of the ocean more direct than at mid-ocean ridge crests and sites of mid-plate volcanism. Fluid-rock interactions, hydrothermal venting and resultant hydrothermal plumes provide the most dramatic linkages between the geophysical processes controlling crustal accretion and the flux of energy and mass to the overlying waters. MGGD researchers study many facets of these hydrothermal systems including: i) the geochemical implications of plate tectonics; ii) seawater-ocean crust interactions; iii) the discharge of high and low temperature hydrothermal fluids; and iv) the formation and dispersion of hydrothermal plumes within the deep ocean water column. We are interested in both the geochemical and geomicrobiological implications of hydrothermal systems. Study sites include both mid-plate seamounts and active volcanoes and hydrothermally active mid-ocean ridge systems, as well as subduction zones (e.g., serpentinite mud volcanoes).

The existence of an extensive subseafloor biosphere associated with the hydrothermal circulation occurring within sediment-buried basement on ridge flanks is currently subject to intense discussion and growing research. Efforts to test deep subseafloor biosphere hypotheses are obviously problematic due to the severe inaccessibility of this environment. Consequently, MGGD researchers are active in developing new way to access the deep subseafloor biosphere: i) advancing the quality of access to this environment utilizing new generation IODP (Integrated Ocean Drilling Program) CORK observatories; ii) large scale sediment buried microbial (tracer) transport experiments; and iii) in situ microbial geochemical/ecology studies.

Mud volcano thumbnail photo.

The Shinkai-6500 manned submersible, operated by JAMSTEC, samples a spring discovered on the summit of a serpentinite mud volcano (South Chamorro Seamount) at 13° 47' N in the Mariana Forearc that was subsequently drilled on ODP Leg 195 in 2001. Water originating from the top of the subducting Pacific plate at ~25 km below the seafloor is seeping from the top of the mountain, where it maintains a chemosynthetic community of Archaea and bacteria and macrofauna including mussels, small tubeworms, and whelks. [photo by M. Mottl]

Tripod thumbnail photo.

Deployed from the ROV Jason-II, the SOEST-developed MANIP (Micro Adjustable Non Intrusive Profiler) collects in situ geochemical microprofiles of an iron-oxidizing hydrothermal microbial mat at Loihi Seamount, on the submerged flanks of the island of Hawai‘i.

Sediment thumbnail graphic.

Increasing evidence indicates that a deep microbial biosphere exists throughout much of the sediment buried ocean crust (basement rock). It is expected that this biosphere is not homogeneous, but varies with basement age, fluid recharge rates, temperature and degree of rock weathering. This cartoon illustrates a hypothetical relationship among fluid flow, temperature and redox zones within the buried basement crust, as influenced by the recharge (seawater flows into subsurface basement) and discharge (subsurface fluids flow outward) zones associated with exposed rocky outcrops on the flanks of a mid-ocean ridge. Dashed arrows represent advective fluid flow and small solid arrows indicate diffusive flow. (Modified from Wheat et al. 2002)

Seafloor eruption thumbnail graphic.

Intense particle plumes were formed following a seafloor eruption on the East-Pacific Ridge, near 9° 50' in early 2006. Figure is a contour plot of light attenuation (Δc; m-1) versus depth and latitude for an along axis (ridge summit) tow-yo cast. Δc intensity is represented by colors. Density (sigma-theta; kg m-3) contours (solid black lines) are superimposed over Δc. The dotted line indicates the saw-toothed tow pattern of the CTD-transmissometer-bottle rosette instrument package. The deepest density line indicates localized areas of instability in the lower part of the water column; the strong correlation between the vertical structures in Δc and the deep density contour line suggests strong localized hydrothermal venting is driving the entrainment and subsequent rise of ambient bottom water.

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