PMEL Publications Abstract
FY 2026
Characterizing the unique chemical imprint of on-axis, lower-temperature hydrothermal flow to the deep ocean (Southern East Pacific Rise, 16.5°–18.0°S)
Moore, L.E., R.M. Bundy, J.A. Resing, S. White, T. Baumberger, P.N. Sedwick, N.J. Buck, A.M. Antriasian, I. Keohane, B.M. Sohst, S.L. Walker, and C.R. German
Geophys. Res. Lett., 53(7), e2025GL120412, doi: 10.1029/2025GL120412, View open access article at AGU/Wiley (external link) (2026)
In addition to high-temperature vents, lower-temperature flow (LTF) (<300°C) is abundant along mid-ocean ridges and contributes globally-important fluxes of heat and water along with largely-unconstrained geochemical influences on the ocean. We examined the impact of on-axis LTF on the chemical composition of the overlying water column (<40 m above seafloor) along the 16.5°–18.0°S sector of the ultrafast-spreading southern East Pacific Rise using autonomous underwater vehicle Sentry surveys and conductivity-temperature-depth rosette casts. LTF sites were typically spatially isolated from high-temperature systems and imparted unique chemical signatures to the overlying ocean. Water column samples impacted by LTF exhibited low particulate iron:sulfur ratios and high methane: total-dissolvable manganese ratios, whereas samples influenced by high-temperature venting exhibited opposite trends. We confirmed that LTF imparts a distinct and measurable chemical signature to the water column, independent from high-temperature vents. Isolated, on-axis LTF will be important to consider when assessing hydrothermal circulation impacts upon ocean biogeochemistry.
Plain Language Summary. Hydrothermal systems are a large source of diverse chemical species to the ocean interior. To date, most studies have focused on high-temperature “black smoker” vent systems, but lower-temperature systems are far more widespread and their chemical imprint on the deep ocean remains largely unknown. Using autonomous underwater vehicle surveys, we located four high-temperature and thirty-six lower-temperature hydrothermal sites along the Southern East Pacific Rise, an ultrafast-spreading mid-ocean ridge. We sampled the water column immediately above the seafloor at six sites, four of which were lower-temperature flow systems and two of which were close to high-temperature “black smoker” vents, and measured dissolved hydrogen and methane, particulate sulfur and iron, and total-dissolvable iron and manganese. Using these measurements, we found that the lower-temperature systems contributed unique, measurable chemical fingerprints to overlying waters that were distinct from those imparted by high-temperature systems. Furthermore, because the lower-temperature systems we sampled were not located near high-temperature vent sources, we conclude that these chemical impacts are as yet unaccounted for in models of seafloor hydrothermal emissions. Our findings indicate that isolated lower-temperature hydrothermal systems should be included in future considerations of the effects of hydrothermal venting on ocean chemistry.