A new chemical analyzer for in situ measurement of nitrate and total sulfide over hydrothermal vent biological communities

A new submersible chemical analyzer, ALCHIMIST (AnaLyseur CHIMique In SiTu) , based on colorimetric detection and flow injection analysis (EIA), was ad apted to allow in situ measurements of nitrate + nitrite (N + N) and total dissolved sulfide (Sigma S) in the deep sea hydrothermal environment. Befor e in situ trials, the influence of hydrostatic pressure and temperature on the analytical responses was examined under simulated conditions (1-300 X 1 0(5) Pa, 5-25 degrees C). First trials were performed during dives of the Remotely Operated Vehicle ( ROV), VICTOR 6000, over the Lucky Strike hydrothermal vent field (Mid-Atlan tic Ridge). ALCHIMIST, installed on the ROV, enabled simultaneous N + N and Sigma S calibration and measurements at 1650 m depth, at a rate of 22 anal yses per hour. At depth, the precision of the in situ Sigma S and N + N mea surements is estimated to be, respectively, 1.1% and 0.8%. The detection li mit is 0.8 mu M for Sigma S and 0.5 mu M for N + N. At a vent site of the Lucky Strike area, ALCHIMIST enabled to resolve, at t he decimeter scale, the chemical gradients which characterize the patchy di stribution of hydrothermal fauna. Additionally, temperature-concentration r elationships offered further information on the processes controlling the c hemistry of the habitats. Like former in situ analyzers used in this field, this new instrument should be valuable to characterize the physico-chemica l characteristics of vent fauna environment. (C) 2000 Elsevier Science B.V. All rights reserved.