Arsenic and Antimony in Hydrothermal Plumes from the Eastern Manus Basin, Papua New Guinea

Zhigang Zeng,Haiyan Qi,Xiaoyuan Wang,Bowen Zhu

doi:10.1155/2018/6079586

Abstract

Studies on the concentrations of arsenic (As) and antimony (Sb) in seawater columns are very important for tracing hydrothermal plumes and understanding fluid characteristics of seafloor hydrothermal systems. The total As, Sb, Mn, and Cl− concentrations of three hydrothermal plume seawater column samples have been studied at Stations 18G, 18K, and 18B in the eastern Manus back-arc basin, Bismarck Sea, Papua New Guinea. At Stations 18G and 18K, the plumes above North Su and near the Suzette site in the SuSu Knolls hydrothermal field are both enriched in As, Sb, and Mn and depleted in Cl, as a result of contribution of As-Sb-Mn-enriched and Cl-depleted vent fluid outputs to the hydrothermal plume, which is most likely generated in the subseafloor by fluid-rock interaction, magma degassing, or phase separation (boiling of hydrothermal fluid). The plume at Station 18B is enriched in As, Sb, Mn, and Cl, suggesting that As-Sb-Mn-Cl-enriched fluid discharges from vents, which have been generated by fluid-rock interaction. The concentrations of As and Sb anomalous layers, like manganese (Mn), are higher than those of the other layers in the three hydrothermal plume seawater columns. As and Sb with Mn showed a positive correlation (R2>0.8, p<0.05), and the distributions of As and Sb within the hydrothermal plume are not controlled by particle adsorption or biogeochemical cycles, suggesting that As and Sb, like Mn, can be used to detect and describe the characteristics of hydrothermal plumes in seawater environment. In addition, anomalous layer with As/Sb ratio lower than those of ambient seawater at the same temperature is found in the eastern Manus basin, suggesting that the As/Sb ratio may also act as an effective tracer reflecting the effect of hydrothermal activity on As and Sb in the seawater column.

Highlights

Hydrothermal plumes are potent tools for locating, characterizing, and quantifying seafloor hydrothermal discharge
At Station 18B, As, Sb, and Cl in the seawater profile are enriched relative to ambient seawater, and the maximum concentrations occur at 1641 m BSL, which is consistent with the Mn and temperature anomalies in the hydrothermal plume water column (Table 1, Figure 3)
The profile of Mn concentration parallels that of the lower temperature anomaly at Station 18G, where the Mn concentration increases continuously from ∼1300 m BSL to 1492 m BSL (Figure 2(b)), with the maximum occurring at 1492 m BSL and reaching 36.3 nM (Mn is about 4 times the ambient seawater value (9.3 nM), Table 1)

Summary

Introduction

Hydrothermal plumes are potent tools for locating, characterizing, and quantifying seafloor hydrothermal discharge. Since 1990, studies on hydrothermal plumes in the eastern Manus back-arc basin have been carried out. During the 21st cruise of Research Vessel (R/V) Akademik Mstislay Keldysh in April–June 1990, all seawater columns studied in the Manus basin showed turbidity anomalies (up to 1880 nephels, at 1600 m below sea level (BSL)), as well as anomalies in dissolved Mn (up to 44.8 nM, at 1975 m BSL) and in biogeochemical parameters (CO2-assimilation up to 0.07 mM⋅day−1, at 1950 m BSL; CH4-oxidation up to 3.30 nM⋅day−1, at 2150 m BSL) [14]. In NovemberDecember 1990, large scale triple-layered buoyant plumes were revealed from seawater column anomalies of CH4

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Conclusion