Paper in press: Modeling the marine barium cycle

I’m excited to share that a new study led by Hengdi Liang, ‘Modeling the global oceanic barium cycle and implications for paleoceanographic proxies,’ is out today in Earth and Planetary Science Letters.

As the title suggests, we developed a model of the global oceanic barium cycle and explored what it means for barium-based paleoceanographic proxies. This study was a natural follow-up to the global barium climatology we published in 2023 and it was a really fun project to work on. Collaborating with Hengdi and Seth was great, and I learned a lot about different modeling approaches and how to parameterize biogeochemical processes.

The central question we set out to answer was: What processes control the distribution of barium in the ocean? That led us to investigate where the barium in barite comes from, how and where barite forms and dissolves, the rates of these processes, and whether barite fluxes can be used as a quantitative indicator of ocean productivity. To tackle this, we used the AWESOME OCIM modeling framework, which combines a steady-state ocean circulation (from the Ocean Circulation Inverse Model) with a biogeochemical model of the barium cycle. We then built parameterizations of the key processes known to influence barium cycling and optimized them to fit observational data from GEOTRACES. This approach allowed us to estimate rates for the most important barium-related processes and perform sensitivity tests that helped rule out the significance of others.

Well… What did we find!?

The paper lays out six main conclusions. If you’re interested in more detail, check out the full study here.

1. Seawater—not organic matter—is the dominant barium source for pelagic barite. Organic matter still plays a key role as the substrate for barite precipitation, but the barium itself comes overwhelmingly from seawater—not via organic matter.
2. Most pelagic barite forms in the shallow ocean. In fact, about 50 % forms above 150 meters, and 90 % by 900 meters. While shallower than some earlier estimates, the model reproduces the observed ‘increasing-then-decreasing’ trend also seen in pelagic barite stocks.
3. Roughly two-thirds of barite dissolves in the water column and one-third on the seafloor. This ratio is consistent with prior studies and holds even when varying particle sinking speeds or size classes.
4. Barite dissolution appears constant. Everywhere. Surprisingly, dissolution rates don’t vary much with saturation state. This could point to gaps in thermodynamic models—or suggest an unknown mechanism we don’t fully understand (yet!).
5. The global Ba–Si correlation is driven by ocean circulation—not biogeochemistry. By separating preformed and regenerated components of the dissolved barium and silicon inventories, we found that large-scale circulation—not shared uptake or dissolution processes—is primarily responsible for the barium–silicate correlation in seawater. This suggests that barium is best used as a tracer of deep-water circulation, but not a direct proxy for silicate concentrations.
6. The ratio of barite-to-organic matter arriving at the seafloor varies significantly depending on where you are. This variability limits the utility of barium as a quantitative proxy for organic matter flux, but it still works well as a qualitative indicator of export productivity at individual sites.

I hope this study proves useful (or at least interesting!) for anyone working on barium geochemistry. More broadly, I think it shows how combining observational data from programs like GEOTRACES with machine learning climatologies and tools like the ocean circulation inverse model can provide powerful insights into the processes controlling elemental distributions in the ocean. It’s an exciting time for this kind of research, and I’m looking forward to applying these tools to topics like the barium isotope cycle and other trace elements studied by GEOTRACES.

Citation: Liang, H., Horner, T. J., & John, S. G. (2025). Modeling the global oceanic barium cycle and implications for paleoceanographic proxies. Earth and Planetary Science Letters, 658, 119295, doi:10.1016/j.epsl.2025.119295.