An Intermediate-Depth Source of Hydrothermal ³He and Dissolved Iron In the North Pacific

Authors

W.J. Jenkins, Woods Hole Oceanographic InstitutionFollow
M. Hatta, University of Hawaii at ManoaFollow
J.N. Fitzsimmons, Texas A&M UniversityFollow
R. Schlitzer, Alfred Wegener InstituteFollow
N.T. Lanning, Texas A&M UniversityFollow
Alan E. Shiller, University of Southern MississippiFollow
N.R. Buckley, Old Dominion University
C.R. German, Woods Hole Oceanographic Insitution
D.E. Lott III, Woods Hole Oceanographic Institution
G. Weiss, University of Hawaii at Manoa
L. Whitmore, University of Southern MississippiFollow
K. Casciotti, Stanford UniversityFollow
P.J. Lam, University of California, Santa CruzFollow
G.A. Cutter, Old Dominion UniversityFollow
K.L. Cahill, Woods Hole Oceanographic Institution

Document Type

Article

Publication Date

6-1-2020

Department

Marine Science

School

Ocean Science and Engineering

Abstract

We observed large water column anomalies in helium isotopes and trace metal concentrations above the Loihi Seamount. The ³He/⁴He of the added helium was 27.3 times the atmospheric ratio, clearly marking its origin to a primitive mantle plume. The dissolved iron to ³He ratio (dFe:³He) exported to surrounding waters was 9.3 ± 0.3 × 10⁶. We observed the Loihi ³He and dFe “signal” at a depth of 1100 m at several stations within ∼100 – 1000 km of Loihi, which exhibited a distal dFe:³He ratio of ~4 × 10⁶, 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 volcanic-tectonic origins. In contrast, the proximal and distal dMn:³He ratios were both ~1 × 10⁶, 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 ³He distribution, requiring a hydrothermal ³He source from Loihi of 10.4 ± 4.2 mol a⁻¹, ∼2% of the global abyssal hydrothermal ³He 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.

Publication Title

Earth and Planetary Science Letters

Volume

539

Recommended Citation

Jenkins, W., Hatta, M., Fitzsimmons, J., Schlitzer, R., Lanning, N., Shiller, A. E., Buckley, N., German, C., Lott, D., Weiss, G., Whitmore, L., Casciotti, K., Lam, P., Cutter, G., Cahill, K. (2020). An Intermediate-Depth Source of Hydrothermal ³He and Dissolved Iron In the North Pacific. Earth and Planetary Science Letters, 539.
Available at: https://aquila.usm.edu/fac_pubs/17310