Speciation of dissolved copper within an active hydrothermal edifice on the Lucky Strike vent field (MAR, 37°N)

The objective of this study was to determine the concentrations of different fractions of dissolved copper (after filtration at 0.45 μm) along the cold part of the hydrothermal fluid-seawater mixing zone on the Tour Eiffel edifice (MAR). Dissolved copper was analyzed by stripping chronopotentiometry (SCP) after chromatographic C18 extraction. Levels of total dissolved copper (0.03 to 5.15 μM) are much higher than those reported for deep-sea oceanic waters but in accordance with data previously obtained in this area. Speciation measurements show that the hydrophobic organic fraction (C18Cu) is very low (2 ± 1%). Dissolved copper is present mainly as inorganic and hydrophilic organic complexes (nonC18Cu). The distribution of copper along the pH gradient shows the same pattern for each fraction. Copper concentrations increase from pH 5.6 to 6.5 and then remain relatively constant at pH > 6.5. Concentrations of oxygen and total sulphides demonstrate that the copper anomaly corresponds to the transition between suboxic and oxic waters. The increase of dissolved copper should correspond to the oxidative redissolution of copper sulphide particles formed in the vicinity of the fluid exit. The presence of such a secondary dissolved copper source, associated with the accumulation of metal sulphide particles, could play a significant role in the distribution of fauna in the different habitats available at vents.