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Mission | |||||||
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Leg
4 Leg
Summary: Leg 4 will use the ROV to compare the
ecology and evolution of hydrothermal vent
communities at three main localities along
a line of transition between the sediment covered vents in the Guaymas
Basin to the basaltic vent field on the East Pacific Rise at 21º N. Vent
communities will be surveyed for comparison at each site using the ROV’s
video camera. Biological samples will be collected with the ROV
manipulator arm, push cores, water sampling bottles, and a suction
sampler. This material will be used in studies of ecology, physiology,
genetics, and species diversity. This research should reveal some of the
fundamental relationships between vent fauna, vent site characteristics,
and cold seep communities. The leg 4 coordinator is Dr. Robert Vrijenhoek
from MBARI, and the Mexican collaborator is Luis Soto from Universidad
Nacional Autonoma de Mexico. History
& Purpose: A
multidisciplinary team of biologists, chemists, and geologists will
characterize ecological changes between a basaltic hydrothermal field on
the East Pacific Rise (EPR, 21°N) and the massively sedimented
hydrothermal field in Guaymas Basin (27°N). We will also explore the
Tamayo Fracture Zone, a potential transition zone between these areas.
In
contrast, Guaymas Basin hydrothermal vents differ markedly from EPR vents
to the south. Only five vent-endemic species are shared between Guaymas
hot vents and 21°N, which are only 500 km apart. Species that are shared
between these disparate sites (Riftia
pachyptila, Paralvinella grasslei, Provanna
laevis, and Amphisamytha
galapagensis) appear to comprise a complex associated with sulfide
edifices and focused hydrothermal flow. Many
of the non-overlapping species, like the tubeworm Escarpia
spicata and several vesicomyid clams, found in Guaymas Basin also
occur at cold-seeps in the Gulf of California and along the continental
margin from Costa Rica to Oregon. The obvious difference between Guaymas
Basin and 21°N on the EPR is the presence of 200–600 m of sediment
covering active spreading centers in the Gulf of California. Hydrothermal
fluids passing through this sediment carry the chemical signatures of
mantle volatiles from below. However, the sediments also carry a complex
mixture of biogenic hydrocarbons, which in turn support a complex
microbial community. In contrast, hydrothermal communities at basaltic
sites along the East Pacific Rise are supported primarily by volcanically
produced sulfides.
Participants from MBARI, the Childress lab (UC-Santa Barbara), and Mexican collaborators plan to gather benthic samples for geological, chemical, physiological, genetic, and species diversity studies from four localities. |