Workshop Report - Ridge 2000 Program

solid understanding of both the biology and geochemistry of
these systems.
The great spatial and temporal variability in environmental
parameters at hydrothermal vents stands in marked contrast to
that usually encountered in the deep sea, and such conditions
alter physiological. behavioral, reproductive, and dispersal
requirements placed on the organisms. One of the most remarkable
manifestations of this variability is a vent community
strikingly different from the surrounding deep-sea fauna, often
at high taxonomic levels. Detailed studies of mechanisms of
dispersal. the role of geographic isolation in the evolution of
vent communities, the spatial and successional special patterns
at particular vents sites, and the time scale of vent activity
along various ridge segments are critical to our understanding
of the biological and geological consequences of such variability.
Equally important are further studies of the responses
and adaptations of these organisms to, and their impacts on,
these hydrothermal systems on time scales ranging from seconds
to eras and spatial scales ranging from millimeters to global.
OBJECTIVE 6: To determine the distribution and intensity of
mid-ocean hydrothermal venting and the interaction of venting
with the ocean environment.
Hydrothermal plumes which issue from seafloor vents link
the oceanic lithosphere, hydrosphere, and biosphere through
a complex series of physical, chemical, and biological interactions.
Plumes disperse heat and chemical species from
newly-formed ocean crust, thereby modifying the composition
of seawater and the underlying sediments on a global scale.
Plumes influence the distribution of deep sea biota remote
from the vents by providing energy, nutrients, and dispersal
mechanisms. Hydrothermal plumes can be direct indicators of
abyssal currents; however, the flux of buoyant water from
hydrothermal vents also promotes vertical mixing and may even
contribute to deep ocean circulation. Although many early
studies used the plume as an exploration tool for locating new
hydrothermal vents, recent work has shown that the plume can
address fundamental questions regarding the magnitude and scale
of hydrothermal venting.
The character of the plume is determined both by crustal
processes and by the oceanic environment. Changes in the plume
can reflect events with diverse spatial and temporal scales,
such as magma chamber evolution, changes in the subsurface
hydrothermal plumbing, and shifting bottom currents. To understand
these complex interactions, we must study hydrothermal
plumes over a wide range of scales in time and space: from the
scale of the individual vent plume fluctuating over a period of
seconds, up to the 1000-km scale of the large ocean-basin plumes
estimated to contain the integrated output from 100 years of
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