An intermediate-depth source of hydrothermal 3He and dissolved iron in the North Pacific

Abstract

We observed large water column anomalies in helium isotopes and trace metal concentrations above the Loihi Seamount. The 3 He/ 4 He of the added helium was 27.3 times the atmospheric ratio, clearly marking its origin to a primitive mantle plume. The dissolved iron to 3 He ratio (dFe: 3 He) exported to surrounding waters was 9.3 ± 0.3 × 10 6. We observed the Loihi 3 He and dFe "signal" at a depth of 1100 m at several stations within ∼100-1000 km of Loihi, which exhibited a distal dFe: 3 He ratio of ∼4 × 10 6 , about half the proximal ratio. These ratios were remarkably similar to those observed over and near the Southern East Pacific Rise (SEPR) despite greatly contrasting geochemical and volcanictectonic origins. In contrast, the proximal and distal dMn: 3 He ratios were both ∼ 1 × 10 6 , less than half of that observed at the SEPR. Dissolved methane was minimally enriched in waters above Loihi Seamount and was distally absent. Using an idealized regional-scale model we replicated the historically observed regional 3 He distribution, requiring a hydrothermal 3 He source from Loihi of 10.4 ± 4.2 mol a −1 , ∼2% of the global abyssal hydrothermal 3 He flux. From this we compute a corresponding dFe flux of ∼40 Mmol a −1. Global circulation model simulations suggest that the Loihi-influenced waters eventually upwell along the west coast of North America, also extending into the shallow northwest Pacific, making it a possibly important determinant of marine primary production in the subpolar North Pacific.

Aerobic and anaerobic iron oxidizers together drive denitrification and carbon cycling at marine iron-rich hydrothermal vents

“…Instead, we can use our results as a starting point for more specific probing of ecological interactions and metabolite exchange within the mat, which may be unique in iron mats because of the affinity of organics for iron. In addition to affecting local biogeochemistry, organic-bound iron and other metabolites are carried by diffusely venting fluid moving through the mat, exported from Lōʻihi in buoyant plumes for 100 s to 1000+ km [ 98 ]. These exported fluids fertilize iron-depleted waters, connecting microbial iron and nutrient cycles across ocean basins.…”

Using Excess 3He to Estimate Southern Ocean Upwelling Time Scales

“…This calculation was in part motivated by interest in the potential role of abyssal marine hydrothermal iron emissions in fueling new primary production in the Southern Ocean. Since it is known that significant fractions of this iron persists in the dissolved phase (Bennett et al, 2008; Boyle & Jenkins, 2008; Jenkins et al, 2020; Resing et al, 2015; Tagliabue et al, 2010) but given that scavenging processes also remove this iron from the dissolved phase (Bergquist & Boyle, 2006; Fitzsimmons et al, 2015, 2017; Hayes et al, 2015), consideration of time scales becomes important. Dissolved iron scavenging is a complicated biogeochemical process, and the determination of these time scales and contributing factors is currently an extremely active research area (Tagliabue et al, 2016; Tagliabue & Resing, 2016).…”

“…Given that the Pacific deep water overturning cell (where the bulk of the hydrothermal injection takes place) occurs below the intermediate waters (~1,000 m; Wijffels et al, 1996Wijffels et al, , 2001, this is a reasonable assumption. Moreover, it has recently been shown that the modest upwelling of 3 He seen in the North Pacific amounts to only~2% of the global flux (Jenkins et al, 2020), making the relative uncertainty in the fraction exiting through the Southern Ocean an upper bound.…”

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

“…Non-buoyant plume Fe is thought to be stabilized in the dissolved state as inorganic metal oxides as well as organic and inorganic colloids and through organic ligand complexation (Bennett et al, 2008;Fitzsimmons et al, 2014Fitzsimmons et al, , 2017Gartman and Findlay, 2020;Hawkes et al, 2013). The next largest 3 He signal in the Pacific Ocean after the southern East Pacific Rise is associated with the Lo'ihi Seamount system, which similarly produces a strong distal Fe plume (Jenkins et al, 2020). It remains to be determined whether trace metals are similarly advected from the northeastern (NE) Lau Basin, where the third-largest hydrothermal 3 He signal in the Pacific Ocean has been measured, extending 2000 km to the northwest and representing the most intense hydrothermal signature in this ocean basin at ∼ 1700 m depth (German et al, 2006;Lupton et al, 2004).…”