Loihi Seamount, hydrothermal Helium-3 and dissolved iron sources and their dispersion within the Pacific Ocean

As part of the GEOTRACES cruise GP15, Jenkins and co-workers (2020, see reference below) observed large water column anomalies in helium isotopes and trace metal concentrations above the Loihi Seamount (~19°N, 154°W) that extends along the GP15 track for hundreds of kilometers. Expanding their data with historical ones, they observe that the Loihi Helium-3 (3He) and dissolved iron (dFe) “signal” was propagating at depth of 1100 m within ∼100 – 1000 km of Loihi, characterized by a distal dFe:3He ratio of ∼4 ×106. Contrastingly, no major methane input was observed. Modeling the regional circulation allowed these authors to estimate a hydrothermal 3He source from Loihi of 10.4 ±4.2 mol a−1 and a corresponding dFe flux of ∼40 Mmol a−1. On a larger scale, they simulate that the Loihi-influenced waters (enriched in He and Fe) eventually upwell along the west coast of North America, also extending around 1000 km into the northwest Pacific Ocean, which could play a role in fertilizing the subpolar North Pacific Ocean.

Figure: (a) A map showing the distribution of 3He anomalies at a depth of 1100 m in the subtropical North Pacific (note the eastward plume emanating from Hawaii) and the GEOTRACES GP15 station locations (red stars), (b) the location of the stations closest to the Loihi source, (c) the size of the 1100 m 3He anomaly observed during GP15 (red stars) and previous stations (black dots), and (d) modelled upwelling intensities for the Loihi source.


Jenkins, W. J., Hatta, M., Fitzsimmons, J. N., Schlitzer, R., Lanning, N. T., Shiller, A., Buckley, N. R., German, C. R., Lott, D. E., Weiss, G., Whitmore, L., Casciotti, K., Lam, P. J., Cutter, G. A., Cahill, K. L. (2020). An intermediate-depth source of hydrothermal 3He and dissolved iron in the North Pacific. Earth and Planetary Science Letters, 539, 116223. DOI: https://doi.org/10.1016/j.epsl.2020.116223

Latest highlights

Science Highlights

Loss of old Arctic sea ice increases methylmercury concentrations

Researchers from the SCRIPPS, the Stockholm Natural Museum and the Mediterranean Institute of Oceanography show the importance of sea ice composition on methylmercury budgets


Science Highlights

Estimating Atmospheric Trace Element Deposition Over the Global Ocean

A recently developed method based on the natural radionuclide Be-7 has provided a means to estimate the bulk atmospheric trace element deposition velocity

Science Highlights

Dissolved gallium unravels Pacific and Atlantic waters in the Arctic Ocean

Whitmore and co-workers demonstrate that the dissolved gallium distribution provide a better water source deconvolution than the nutrient tracers


Science Highlights

Precise estimate of the mercury export from the Arctic to the Atlantic Ocean

Using new observations acquired during GEOTRACES Arctic cruises, a refined arctic mercury budget has been established