On the differing growth mechanisms of black-smoker and Lost City-type hydrothermal vents

Abstract

Black smokers and Lost City-type springs are varieties of hydrothermal vents on the ocean floors that emit hot, acidic water and cool, alkaline water, respectively. While both produce precipitation structures as the issuing fluid encounters oceanic water, Lost City-type hydrothermal vents in particular have been implicated in the origin of life on the Earth. We present a parallel-velocity flow model for the radius and flow rate of a cylindrical jet of fluid that forms the template for the growth of a tube precipitated about itself and we compare the solution with previous laboratory experimental results from growth of silicate chemical gardens. We show that when the growth of the solid structure is determined by thermal diffusion, fluid flow is slow at the solid-liquid contact. However, in the case of chemical diffusive transport, the fluid jet effectively drags the liquid in the pores of the solid precipitate. These findings suggest a continuum in the diffusive growth rate of hydrothermal vent structures, where Lost City-type hydrothermal vents favour contact between the vent fluid and the external seawater. We explore the implications for the road to life.

Keywords: chemical gardens; chemobrionics; hydrothermal vents; origin of life.

Figure 1.

Fluid-jet-templated precipitated tubes: (a) oceanic hydrothermal vent of the black-smoker type [1]; the robot arm claw is opened about 15 cm. (b) Lost City hydrothermal vent; this feature, named Ryan, is some 13 m in height [2]. (c) Chemical garden in a laboratory beaker showing the tubular growths of a variety of metal salts placed in a solution of sodium silicate. (d) Overall scanning electron microscopy view of a group of tubes growing from a zinc sulfate seed. (e) Close-up scanning electron microscopy view of one tube displaying its outer wall microstructure.

Figure 2.

Sketch of the model set-up with a fluid jet and recirculation of the fluid in the environment around it. (Online version in colour.)

Figure 3.

Variation of tube radius with flow rate for chemical gardens. Thouvenel et al.’s experimental data [30] for R_c=11 mm, Δρ_i= 115.75 kg m⁻³, μ_i=0.942 mPa s, μ_i/μ_e= 0.942/1.74=0.541, g=9.81 m s⁻² are shown with the prediction from Thouvenal et al. (dashed line) and that of Poiseuille flow, equation (1.5) with dP/dz=0 (dot-dashed line), together with equation (1.4) with dP/dz=0 (dotted line) and with dP/dz=−3 Pa m⁻¹ (solid line). (Online version in colour.)

Figure 4.

Variation of tube radius with flow rate for brinicles. Martin’s experimental data [31] for R_c=10 cm, Δρ_i=0.15 g cm⁻³, μ_i= 1.03 c P, μ_i/μ_e=1, g=981 cm s⁻² are shown with the prediction from Poiseuille flow, equation (1.4) with dP/dz=0 and ${\mu }_{\mathrm{e}}\to \mathrm{\infty }$. (Online version in colour.)