Hydrothermal trace metal release and microbial metabolism in the northeastern Lau Basin of the South Pacific Ocean

Natalie R Cohen,Abigail E Noble,Christopher R German,Tyler J Goepfert,Nicholas J Hawco,John P Mccrow,Carl H Lamborg,Andrew E Allen,Tristan J Horner,Dawn M Moran,Matthew R Mcilvin,Mak A Saito

doi:10.5194/bg-18-5397-2021

Abstract

Abstract. Bioactive trace metals are critical micronutrients for marine microorganisms due to their role in mediating biological redox reactions, and complex biogeochemical processes control their distributions. Hydrothermal vents may represent an important source of metals to microorganisms, especially those inhabiting low-iron waters, such as in the southwest Pacific Ocean. Previous measurements of primordial 3He indicate a significant hydrothermal source originating in the northeastern (NE) Lau Basin, with the plume advecting into the southwest Pacific Ocean at 1500–2000 m depth (Lupton et al., 2004). Studies investigating the long-range transport of trace metals associated with such dispersing plumes are rare, and the biogeochemical impacts on local microbial physiology have not yet been described. Here we quantified dissolved metals and assessed microbial metaproteomes across a transect spanning the tropical and equatorial Pacific with a focus on the hydrothermally active NE Lau Basin and report elevated iron and manganese concentrations across 441 km of the southwest Pacific. The most intense signal was detected near the Mangatolo Triple Junction (MTJ) and Northeast Lau Spreading Center (NELSC), in close proximity to the previously reported 3He signature. Protein content in distal-plume-influenced seawater, which was high in metals, was overall similar to background locations, though key prokaryotic proteins involved in metal and organic uptake, protein degradation, and chemoautotrophy were abundant compared to deep waters outside of the distal plume. Our results demonstrate that trace metals derived from the NE Lau Basin are transported over appreciable distances into the southwest Pacific Ocean and that bioactive chemical resources released from submarine vent systems are utilized by surrounding deep-sea microbes, influencing both their physiology and their contributions to ocean biogeochemical cycling.

Highlights

The central Pacific Ocean encompasses several biogeochemical regimes, including low-nitrate surface waters in the subtropical gyres and high-nitrate, yet low-iron waters in the equatorial upwelling zone (Cohen et al, 2021a; Moore et al, 2013, 2001; Saito et al, 2014)
We present the full-depth dissolved trace metal section to address whether hydrothermal activity previously measured in the northeastern edge of the Lau Basin is associated with trace metal input, and we leverage the MetZyme protein data set to determine whether surrounding microbes were sensitive to distal hydrothermal-plume geochemistry
The South Equatorial Pacific Intermediate Water is associated with a deepening of the thermocline evident in macronutrient and trace metal nutriclines, with on average < 0.15 nM dFe, < 0.6 nM dZn, < 0.6 nM dCu, < 3.1 nM dNi, < 80 particulate metal (pM) dCd, and < 25 pM dCo persisting to 300 m in the South Pacific (Fig. 1)

Summary

Introduction

The central Pacific Ocean encompasses several biogeochemical regimes, including low-nitrate surface waters in the subtropical gyres and high-nitrate, yet low-iron waters in the equatorial upwelling zone (Cohen et al, 2021a; Moore et al, 2013, 2001; Saito et al, 2014). Towards the South Pacific Ocean, little dust input from continental sources combined with low macronutrient concentrations results in low primary productivity and reduced biological carbon export to the deep ocean (Jickells et al, 2005). In this region, active hydrothermal venting may be an important source of trace metals, such as iron, to surrounding microorganisms. The chemicals most concentrated in vent fluids include iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), methane, and sulfides They reach millimolar to micromolar concentrations compared to the picomolar to nanomolar range typical of background seawater and are used as energy sources for chemosynthetic microbial communities that sustain rich food webs (Bruland and Lohan, 2003; Tivey, 2007). Trace metal concentrations within these plumes generally decrease with distance from the hydrothermal source as a result of dilution and removal processes that include both abiotic precipitation and microbial uptake (Cowen et al, 1990; Gartman and Findlay, 2020)

Methods

Results

Conclusion