Manganese distribution in the water column near the Azores Triple Junction along the Mid-Atlantic Ridge and in the Azores domain

Abstract

As part of a multidisciplinary research effort aimed at quantifying mid-ocean ridge processes near the Azores, we conducted a survey of the water column above the mid-Atlantic Ridge (MAR) in the vicinity of the Azores Triple Junction. Manganese is a tracer of hydrothermal activity intimately related to mid-ocean ridge processes. This paper reports on 23 vertical depth profiles that were analyzed for total dissolvable manganese (TDM). TDM inputs attributable to hydrothermal circulation could be observed along the MAR in all of the southern Amar (36°15’N), Famous (36°45’N), and Lucky Strike (37°03′N and 37°17′N) segments and south of the Kurchatov fracture zone (40°10′N). To date, seafloor observations of hydrothermal activity on the seabed have been confirmed at Lucky Strike (37°17′N) and at the Rainbow site (36°14′N). Large-scale TDM distribution features along the axial valley of the MAR include a decrease in TDM concentrations from south to north (36°N to 38°30′N), followed by an increase to 40°N. In the basins within the Azores archipelago, we found the lowest TDM background levels of this study (0.4–0.6 nmol l -1) and, based on our data, no firm evidence for hydrothermal inputs of TDM. In the MAR axial valley, we observe both a more elevated TDM background (0.5–1.0 nmol l -1) and evidence for probable hydrothermal TDM inputs. This suggests that hydrothermal inputs contribute to a low-level chronic TDM plume throughout the axial valley of the MAR between 36° and 40°N.