Successional patterns of (trace) metals and microorganisms in the Rainbow hydrothermal vent plume at the Mid-Atlantic Ridge

Abstract

<p><strong>Abstract.</strong> Hydrothermal vent fields found at mid-ocean ridges emit hydrothermal fluids which disperse as neutrally buoyant plumes. From these fluids seafloor massive sulfides (SMS) deposits are formed which are being explored as possible new mining sites for (trace) metals and rare earth elements (REE). It has been suggested that during mining activities large amounts of suspended matter will appear in the water column due to excavation processes, and due to discharge of mining waste from the surface vessel. Understanding how natural hydrothermal plumes evolve as they spread away from their source and how they affect their surrounding environment may provide some analogies for the behaviour of the dilute distal part of chemically enriched mining plumes.</p> <p>This study on the extensive Rainbow hydrothermal plume, observed up to 25 km downstream from the vent site, enabled us to investigate how microbial communities change in the presence of a natural plume. The (trace) metal and REE content of suspended particulate matter (SPM) was determined using HR-ICP mass spectrometry and the microbial communities of the neutrally buoyant plume, above plume-, below plume-, and near-bottom water and sediment were characterised by using 16S rRNA amplicon sequencing methods. Both vertically in the water column and horizontally along the neutrally buoyant plume, geochemical and biological changes were evident as the neutrally buoyant plume stood out by its enrichments in (trace) metals and REEs, of which the concentrations changed as the plume aged. This was also reflected in the background pelagic system as Epsilonproteobacteria started to dominate and the biodiversity appeared to reduce with distance away from the Rainbow hydrothermal vent field. The Rainbow hydrothermal plume provides a geochemically enriched natural environment, which is a heterogeneous, dynamic habitat that is conducive to ecological changes in a short time span.</p>

Volatile‐Rich Hydrothermal Plumes Over the Southern Central Indian Ridge, 24°49’S: Evidence for a New Hydrothermal Field Hosted by Ultramafic Rocks

“…A sharp increase in dissolved trace metals and gas concentrations of plumes layers 1 and 2 at P8, and P5 indicate the possibility of nearby venting. These values are comparable to concentrations reported for hydrothermal plumes found in the Indian Ocean and elsewhere in global oceans (Boulart et al, 2017;Fang & Wang, 2021;Gamo et al, 2015;Gharib et al, 2005;González-Santana et al, 2020;Haalboom et al, 2019;Kawagucci et al, 2008;Ray et al, 2012Ray et al, , 2020Resing et al, 2009;Schmid et al, 2019;Wang et al, 2012;You et al, 2014;Zhu et al, 2008 and references therein). The δ 3 He (88%) at 2570 m at P5 is the highest reported hydrothermal plume value in the Indian Ocean (Table 1) when compared to hydrothermal plumes above Solitaire vent field (δ 3 He = ∼56%; Kawagucci et al, 2008).…”

A Molecular Approach to Explore the Background Benthic Fauna Around a Hydrothermal Vent and Their Larvae: Implications for Future Mining of Deep-Sea SMS Deposits

“…However, the element/Al ratios of the chalcophile elements were still higher than the ratios measured for the reference locations at 25 km from the vent sites. Plume dispersion in the SE direction was already shown (German et al, 2010;Haalboom et al, 2019), which could explain the enrichment by chalcophiles of the sediments at the SE locations. The element/Al ratios for the sediments collected at locations further away from the vent site (36, 54, 56, and 58) were more similar to the ratios found at the reference locations rather than the NE and SE locations.…”

“…This plume could still be detected up to 50 km away from the vent site, moving predominantly to the north and east, following the contours of the Rainbow Ridge at ∼2,100 m depth (Severmann et al, 2004). Moreover, the plume could be consistently traced up to 25 km away from the vent source based on turbidity measurements and the chemical analysis of water samples (Haalboom et al, 2019). The study of Haalboom et al (2019), showed an enrichment of metals compared to the overlying clear water in the neutrally buoyant plume with a high proportion of chalcophile elements closest to the vent site.…”

“…Moreover, the plume could be consistently traced up to 25 km away from the vent source based on turbidity measurements and the chemical analysis of water samples (Haalboom et al, 2019). The study of Haalboom et al (2019), showed an enrichment of metals compared to the overlying clear water in the neutrally buoyant plume with a high proportion of chalcophile elements closest to the vent site.…”

“…The vent fluids emitted differ for each vent location and are influenced by the underlying host rock (Wetzel and Shock, 2000;Cave et al, 2002). Subsequently, microbial activity alters the metal composition in the plume by scavenging and oxidation (Cowen et al, 1990;Dick et al, 2009) whereas the microbial community itself also show a shifting composition and diversity with distance from the vent site (Haalboom et al, 2019). The fall out of major elements and trace metals as well as organic matter synthesized by the chemosynthetic microbial communities could both affect the benthic communities (Sarrazin et al, 2015;Sen et al, 2016).…”