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Abstract

Hydrothermal vents have been identified as a key source of trace elements supporting ocean ecosystems. The density and extent of the early plume control the pathways connecting the plume to the surface. Hydrothermal vents generate buoyant water which rises, entraining deep water, until reaching neutral buoyancy. The prevailing view is that the plume then spreads horizontally a few kilometres until constrained by rotation. Here we present a unique observational data set from three Hydrothermal systems consisting of: high horizontal resolution, 100m, Tow-Yo sections; and microstructure profiles. These observations show plumes with horizontal extents much less than a rotational constraint implying a process dispersing the plume time scales shorter than rotation. We calculate the Ertel potential vorticity from the observations to reveal regions of low PV with susceptibility to sub-mesoscale instabilities. Diagnostics reveal that the plume is primed for all three forms of instability: convective instability in the rising plume leading to vertical exchange; centrifugal instability in the upper core of neutrally buoyant plume leading to horizontal exchange; and symmetric instability on the flanks of the plume leading to slantwise exchange. We then show strongly enhanced turbulent mixing within the plume compared to typical deep ocean values, 1000 times larger than background. Finally, we apply a linear mixing model which shows that the plume fluid mixes as strongly when at neutral depth as during the rising phase. In combination these results, in contrast to previous views, present a picture of an intensely dynamic plume rapidly transferring hydrothermal tracers throughout the region.