Soluble, Colloidal, and Particulate Iron Across the Hydrothermal Vent Mixing Zones in Broken Spur and Rainbow, Mid-Atlantic Ridge

Abstract

The slow-spreading Mid-Atlantic Ridge (MAR) forms geological heterogeneity throughout the ridge system by deep crustal faults and their resultant tectonic valleys, which results in the existence of different types of hydrothermal vent fields. Therefore, investigating MAR hydrothermal systems opens a gate to understanding the concentration ranges of ecosystem-limiting metals emanating from compositionally distinct fluids for both near-field chemosynthetic ecosystems and far-field transport into the ocean interiors. Here, we present novel data regarding onboard measured, size-fractionated soluble, colloidal, and particulate iron concentrations from the 2018 R/V L’Atalante – ROV Victor research expedition, during which samples were taken from the mixing zone of black smokers using a ROV-assisted plume sampling. Iron size fractionation (<20, 20–200, and >200nm) data were obtained from onboard sequential filtering, followed by measurement via ferrozine assay and spectrophotometric detection at 562nm. Our results showed the persistent presence of a nanoparticulate/colloidal phase (retained within 20–200nm filtrates) even in high-temperature samples. A significant fraction of this phase was retrievable only under treatment with HNO3 – a strong acid known to attack and dissolve pyrite nanocrystals. Upon mixing with colder bottom waters and removal of iron in the higher parts of the buoyant plume, the larger size fractions became dominant as the total iron levels decreased, but it was still possible to detect significant (micromolar) levels of nanoparticulate Fe even in samples collected 5m above the orifice in the rising plume. The coolest sample (<10°C) still contained more than 1μM of only nitric acid-leachable nanoparticle/colloidal, at least 200 times higher than a typical Fe concentration in the non-buoyant plume. Our results support previous reports of dissolved Fe in MAR vent plumes, and we propose that this recalcitrant Fe pool – surviving immediate precipitation – contributes to maintaining high hydrothermal iron fluxes to the deep ocean.

Nanoparticulate apatite and greenalite in oldest, well-preserved hydrothermal vent precipitates

“…Accounting for errors in the dissolution rate (up to approximately one order of magnitude), this lifetime is far shorter than particle settling times expected for nanoparticulate material, which, through Stokes Law, equates to 0.18 m/year for a 100-nm FAP particle. By analogy to other nanoparticulate phases identified in modern hydrothermal plumes ( 63 ), these particles would be expected to reside in the oceanic water column for several years and, more likely, decades. Thus, we conclude that the preservation of FAP particles implies that seawater was at or above saturation with respect to FAP to arrest the thermodynamic drive for dissolution.…”

High Precision Femtosecond Laser Ablation ICP‐MS Measurement of Benthic Foraminiferal Mn‐Incorporation for Paleoenvironmental Reconstruction: A Case Study From the Plio‐Pleistocene Caribbean Sea

“…While the source of Mn in the Caribbean waters is not well‐constrained, emerging evidence from seafloor hydrothermal vents indicates that high concentrations of dissolved‐Mn(II) and Mn(III) in ocean waters and Mn‐oxide deposits are mainly related to hydrothermal activities (Middag, de Baar, Laan, & Klunder, 2011). Mn(II) in hydrothermal plumes may have longer oxidation half‐lives than much of the other trace metals (e.g., iron, copper, zinc) dispersing over a distance of more than 4,000 km from the vent (Gartman & Findlay, 2020; Resing et al., 2015; Yücel et al., 2021). Being surrounded by the Lesser Antilles Volcanic Arc (LAVA) in the east, and the Central American Volcanic Arc (CAVA) in the west, the Caribbean Sea may receive Mn from volcanic sources (Homoky et al., 2011) and hydrothermal inputs (Frank et al., 2006) (Figure 1a).…”

Inorganic Fe-O and Fe-S oxidoreductases: paradigms for prebiotic chemistry and the evolution of enzymatic activity in biology

“…Iron oxide and sulfide nanocolloids are abundant on Earth and can be found in diverse habitats, including soils, water, rocks and living organisms ( Cornell and Schwertmann, 2003 ; Jolivet et al, 2006 ; Rickard and Luther, 2007 ; Sagnotti, 2007 ; Navrotsky et al, 2008 ; Konishi et al, 2012 ; Guo and Barnard, 2013 ; Posth et al, 2014 ; Maher, 2016 ; Claudio et al, 2017 ; Yuan et al, 2020 ; Huang, 2022b ). These encompass diverse environments such as high pH hydrothermal vents ( Lough et al, 2019 ; Yücel et al, 2021 ), ice sheets ( Hawkings et al, 2014 ), fly ash and street dust ( Yang et al, 2016b ; Gonet and Maher, 2019 ). Remarkably, they are also found in magnetosomes from Magnetotactic Bacteria (MTB) ( Pósfai et al, 2013 ; Uebe and Schüler, 2016 ; Goswami et al, 2022 ), as well as in other biogenic iron minerals ( Posth et al, 2014 ).…”

“…These nanocolloids form through various mechanisms ( Guo and Barnard, 2013 ), resulting in a range of sizes, shapes, and structures ( Xie et al, 2018 ). Iron sulfide nanocolloids are prevalent in hydrothermal vent plumes ( Findlay et al, 2019 ; Yücel et al, 2021 ) and can be found in many marine sediments ( Rickard and Luther, 2007 ; Gu X. et al, 2020 ; Subramani et al, 2020 ). Geological evidence indicates that secondary pyrrhotite, pyrite, greigite, mackinawite and green rust (fougerite) may have existed as nanocolloids during the Hadean and early Archean era, a time period that predates and overlaps with the emergence of proteins and primitive life forms ( Holland, 2007 ; Raiswell and Canfield, 2012 ; Bekker et al, 2013 ; Catling, 2013 ; Halevy et al, 2017 ; Goswami et al, 2022 ).…”