Beyond serpentinization: pathways of low-temperature seawater alteration of peridotite and their links to magnesium and carbon cycling

• Applicant: Dr. Elmar Albers
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 578426775

Hydrothermal alteration of the oceanic lithosphere is generally considered a sink for Mg, directly affecting seawater chemistry and the global Mg budget, which in turn is coupled to the carbonate–silicate cycle and thus to Earth’s long-term C cycle. However, weathering of seafloor peridotite—its low-temperature alteration by seawater at or near the seafloor—has been shown to be a significant Mg source through dissolution of olivine and/or brucite. These mantle peridotites also commonly host low-temperature carbonate mineralizations, often within weathering-related pore space, suggesting that such alteration generates the geochemical and hydrogeological conditions necessary for carbonate precipitation and thereby directly links peridotite weathering to C cycling. While higher-temperature alteration of seafloor peridotite (i.e., serpentinization) and its geochemical fluxes have been extensively studied, low-temperature weathering remains poorly constrained, despite mantle rocks constituting a significant and highly reactive portion of the oceanic lithosphere exposed to continued seawater interaction. Weathering processes are strongly influenced by both bulk composition (e.g., brucite is rare/absent in pyroxene-rich lithologies) and alteration history (e.g., completely serpentinized rocks contain no olivine). I therefore hypothesize that weathering of incompletely serpentinized lithologies has the greatest potential to contribute Mg to seawater while simultaneously raising local alkalinity and facilitating carbonate formation. This project aims to systematically disentangle the roles of lithology and bulk rock composition (lherzolite vs. harzburgite vs. dunite) and alteration state (incompletely vs. fully serpentinized) in controlling weathering and associated carbonate precipitation. I will make use of a unique peridotite collection from the ultraslow-spreading Gakkel Ridge, Arctic Ocean, which enables (i) the investigation of how bulk composition and serpentinization history affect weathering pathways, and (ii) the linking of carbonate formation to rock microstructures, weathering pathways, and reaction progress. I will combine bulk and in situ geochemical analyses, physical property measurements, and advanced 3D digital imaging of microtextures to constrain porosity generation and evolution during peridotite alteration. These techniques, bridging scales from hand specimen to (sub-)micron resolution, are essential to mechanistically constrain reactions and quantify weathering processes. The proposed research will establish geochemical feedbacks between mineral dissolution and carbonate formation under low-temperature seafloor conditions, providing new constraints on how seawater–mantle rock interactions influence global Mg and C cycling.

• DFG Programme: Research Grants