Size speciation of dissolved trace metals in hydrothermal plumes on the Southwest Indian Ridge

Ziming Fang; Wen-Xiong Wang

doi:10.1016/j.scitotenv.2021.145367

Size speciation of dissolved trace metals in hydrothermal plumes on the Southwest Indian Ridge

Sci Total Environ. 2021 Jun 1:771:145367. doi: 10.1016/j.scitotenv.2021.145367. Epub 2021 Jan 23.

Authors

Ziming Fang¹, Wen-Xiong Wang²

Affiliations

¹ Hong Kong Branch of the Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), School of Energy and Environment, State Key Laboratory of Marine Pollution, City University of Hong Kong, Kowloon, Hong Kong, China; Research Centre for the Oceans and Human Health, City University of Hong Kong Shenzhen Research Institute, Shenzhen 518057, China.
² Hong Kong Branch of the Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), School of Energy and Environment, State Key Laboratory of Marine Pollution, City University of Hong Kong, Kowloon, Hong Kong, China; Research Centre for the Oceans and Human Health, City University of Hong Kong Shenzhen Research Institute, Shenzhen 518057, China; Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou 511458, China. Electronic address: wx.wang@cityu.edu.hk.

PMID: 33548727
DOI: 10.1016/j.scitotenv.2021.145367

Abstract

Determining the size speciation and chemical transformation of trace metals is of paramount in order to better assess the impact of hydrothermal activities on the ocean metal budgets. In this study, we examined the concentration and size speciation of dissolved trace metals (i.e. Mn, Fe, Cu, Ni, Mo, As, Pb, Cd) in the hydrothermal plumes of two vent fields (i.e. Longqi and Tiancheng) on the Southwest Indian Ridge. The majority of dissolved Mn (75-100%) in the buoyant and non-buoyant plumes were presented as soluble Mn (<1 kDa), while dissolved Fe in the buoyant plume contained considerable colloidal Fe (54-95%). More than 66% of hydrothermally dissolved Fe was removed in the buoyant plume within a short distance of dispersion. Except for the samples most proximal to the fluid source, concentrations of Cu, Ni and Mo in the plumes were comparable to those of the background seawater and independent of the plume dilution. Concentrations of dissolved As and Pb in the buoyant plume of the Tiancheng field were higher than those of the Longqi field, resulting from the scavenging of As in the Longqi field and the release of Pb from metal sulfide dissolution in the Tiancheng field. Concentrations of dissolved Cd in the non-buoyant plume were nearly identical to the background seawater and soluble Cd was dominant (75-92%) in the soluble phase. In contrast, 33-96% (or 0.024-0.085 μg/kg) of dissolved Cd was removed in the buoyant plume and the remaining dissolved Cd was mainly in colloidal phase (up to 96%), suggesting that hydrothermal plume was likely an important sink of oceanic Cd and colloidal ligands played an important role in the stabilization of hydrothermal Cd. Our study has demonstrated the very dynamic nature of trace metal speciation in hydrothermal vent fluids.

Keywords: Hydrothermal plume; Size speciation; Southwest Indian Ocean; Trace metal.