  Active hydrothermal vents provide the surrounding submarine environment with
substantial amounts of matter and energy, thus serving as important habitats
for diverse megabenthic communities in the deep ocean and constituting a
unique, highly productive chemosynthetic ecosystem on Earth. Vent-endemic
biological communities gather near the venting site and are usually not found
beyond a distance of the order of 100 m from the vent. This is surprising
because one would actually expect matter ejected from high-temperature vents,
which generate highly turbulent buoyancy plumes, to be suspended and carried
far away by the plume flows and deep-sea currents. Here, we study this problem
from a fluid dynamics perspective by simulating the vent hydrodynamics using a
numerical model that couples the plume flow with induced matter and energy
transport. We find that both low- and high-temperature vents deposit most vent
matter relatively close to the plume. In particular, the tendency of turbulent
buoyancy plumes to carry matter far away is strongly counteracted by generated
entrainment flows back into the plume stem. The deposition ranges of organic
and inorganic hydrothermal particles obtained from the simulations for various
natural high-temperature vents are consistent with the observed maximum spatial
extent of biological communities, evidencing that plume hydrodynamics exercises
strong control over the spatial distribution of vent-endemic fauna. While other
factors affecting the spatial distribution of vent-endemic fauna, such as
geology and geochemistry, are site-specific, the main physical features of
plume hydrodynamics unraveled in this study are largely site-unspecific and
therefore universal across vent sites on Earth.
