The heat and fluid transfer associated with the flanges on hydrothermal venting structures

Abstract

We present a simple model of the heat transfer and fluid flow associated with flanges which have been observed on some of the sulphide structures formed at sites of hydrothermal venting on the Endeavour Segment of the Juan de Fuca Ridge [1]. We show that the majority of the heat transferred by a flange is conducted across its upper surface except in flanges which are vigorously overflowing, in which case it is through convective heat transfer associated with the overflowing. We calculate that the flux of hydrothermal fluid through a typical non-overflowing flange of area 1 m2 and with upper surface temperature in the range 10–80°C is of the order of 10–100 cm3/s with an associated heat flux of 104–105 W. This heat flux is small compared to the largest black smoker plumes at Endeavour, which have a heat flux of the order 107 W. In isolation, in a relatively quiescent environment the hydrothermal plume associated with such a flange would rise about 20–40 m into the overlying stratified water column in comparison to the largest smokers in the Endeavour vent field, which have been observed to ascend about 180 m [2]. Flange-derived plumes may therefore contribute to the production of the thermal and chemical anomalies in the water column below the neutral buoyancy height of the large smoker plumes. Our model of the temperature structure of a flange suggests that only the upper few centimetres of a flange have a temperature below 300°C; this suggests that high temperature (< 110°C) micro-organisms may only thrive in the upper few centimetres of the flange.