147 Climate, Ocean and Environmental Changes Through Earth History: From Marine and Terrestrial Proxies to Model Assessments (Posters)

This session brings together marine and terrestrial proxies and modelling to reconstruct rapid ocean, environment, and climate events, and shifts between long-term climate/ocean/environment states, within the context of normal variability throughout Earth history.

Monday, 20 October 2025
8:00 AM - 5:30 PM
HBGCC, Hall 1

Controls on the Barium Isotopic Composition of Authigenic Carbonates at Methane Seeps

Paper number: 147-16
Program: Technical Sessions
Time: 8:45 AM – 8:45 AM

Authors

Abstract

The barium (Ba) isotopic composition of carbonate minerals (δ138Bacarb) is a promising new geochemical tracer for past Ba cycling. However, further study of the potential influence of early diagenetic processes on δ138Bacarb records remains an important avenue for this new tracer’s development. Marine methane seep environments are sites of intense Ba cycling during early diagenesis. Seeps may be responsible for much of the flux of Ba from the sedimentary subsurface into seawater, while the authigenic carbonate minerals precipitating at seeps may represent an archive of Ba cycling. This study presents δ138Bacarb data of authigenic carbonate collected at eight methane seeps from the South China Sea and the Gulf of Mexico. The obtained δ138Bacarb values range widely between −0.15‰ to 0.37‰. Under conditions of low upward flux of Ba, identified by low Ba/Ca ratios of carbonate minerals (<100 mmol/mol), δ138Bacarb values exhibit a negative covariation with Ba content, suggesting variable transitions between the influence of seawater (low Ba/Ca and high δ138Ba) and the influence of sediments (high Ba/Ca and low δ138Ba). Aragonite-dominated carbonates tend to show higher δ138Bacarb values than high-Mg calcite-dominated carbonates. This pattern suggests a greater influence of seawater during aragonite precipitation caused by its formation at shallower depths compared to high-Mg calcite. Accordingly, low δ138Bacarb values and relatively high Ba/Ca molar ratios are interpreted to reflect the release of Ba from sediments. However, under conditions of increased upward flux of Ba, seep carbonates display highly variable δ138Bacarb values independent of Ba/Ca molar ratios, suggesting that additional processes (i.e. re-precipitation of 134Ba-enriched barite) control porewater barium isotope compositions. Taken together, these new observations showcase the complexity of Ba isotope systematics at marine seeps, governed by the mixing of Ba from different sources and mineral dissolution and authigenesis (carbonate minerals and barite).

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-412964

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