A robust history of seawater strontium ([Sr]SW) is critical for understanding the long-term global carbon cycle as it is influenced by the location of carbonate deposition, chemical weathering, and hydrothermal activity. Barite (BaSO4) and celestite (SrSO4) have been shown to exhibit solid-solution such that Sr substitutes for Ba in the mineral barite. If, for marine barite, this substitution occurs in proportion to seawater Sr concentrations, then a temporal record of Sr/Ba ratios in this phase ([Sr/Ba]barite) may be used to reconstruct the history of seawater Sr. This work addresses the potential utility of marine barite as a paleoproxy of [Sr]SW.

Comparisons of Raman spectra of both synthetic (pure) and marine barite (separated from deep-sea sediments) with the spectra of other Sr-bearing phases confirms that natural marine barite samples separated from deep-sea sediments contain trace quantities of Sr. Application of this technique to marine barite separates also provides a means for screening the integrity of samples for paleo-reconstructions. Using knowledge of in situ marine barite precipitation, geochemical models, and [Sr/Ba]barite of samples isolated from a suite of modern sediment cores, it is evident that [Sr]SW is the dominant variable in determining the extent of Sr substitution in marine barite. Although the utility of this proxy is substantiated, until the Ba concentration at the site of barite precipitation can be determined, the Sr/Ba ratio of marine barite can only be applied as a qualitative predictor of changes in seawater Sr concentrations.

Application of this proxy and comparison with known seawater histories provides further evidence that [Sr/Ba]barite responds to changes in [Sr]SW. Glacial-interglacial records of the Sr composition of barite vary systematically over the past 500 kyr and are coherent with changes in sea level. These oscillations in [Sr/Ba]barite could be explained by recrystallization of Sr-rich aragonite to calcite on exposed continental shelves, and the subsequent release and delivery of Sr to the ocean during low sea-stands. A Cenozoic record of [Sr/Ba] barite is also presented. The processes influencing this record are unclear, but interpretations may be complicated by variations in regional scale processes not observed in the modern ocean, post-depositional processes, or insufficient sample resolution.