To Ba or not to Ba: Evaluating water column excess particulate barium as a proxy for water column respiration

Science Highlights

14 November 2025

Rahman and co-workers (2025, see reference below) examine the relationship between pBaxs (excess particulate barium (Ba), in other words particulate Ba in excess of that predicted from crustal values) and organic matter respiration in the water column along the GEOTRACES GA03 North Atlantic and GP16 Eastern Tropical Pacific transects. Others have proposed pBaxs as a respiration proxy, and this new work now examines the pBaxs proxy across two ocean basins and different biogeochemical provinces. Furthermore, the authors test the pBaxs proxy against respiration rates calculated using 230Thorium‐normalized particulate organic carbon (POC) fluxes in the water column.

Respiration rates estimated from pBaxs were significantly different between biogeochemical provinces (i.e., gyre vs. oxygen deficient zone stations). Also, rate estimates using depth weighted average pBaxs concentrations and Th‐normalized POC fluxes in the 100–500 m interval agreed well within biogeochemical provinces where comparisons could be made. Thus, average pBaxs concentrations provide reasonable respiration rate estimates in the 100–500 m depth interval, providing a viable alternative if other methods are not available.

Figure: Comparison of pBaxs-based respiration rates (mmol C/m2/d, grey bars) calculated using Equations 1-3 (for Baresidual = 180 pmol/L) and Th-normalized particulate organic carbon respiration rates (estimated by subtracting the minimum flux at ∼500 m from the maximum in the 100–500 m zone, black bars) at individual stations along GP16. Mean pBaxs-based and Th-normalized rates for oxygen deficient zone and gyre stations are also presented.

Reference:

Rahman, S., Shiller, A. M., Anderson, R. F., Hayes, C. T., & Pavia, F. (2025). To Ba or not to Ba: Evaluating water column excess particulate barium as a proxy for water column respiration. Global Biogeochemical Cycles, 39, e2025GB008671. Access the paper: https://doi.org/10.1029/2025GB008671

Latest highlights

Contrasting organic carbon  remineralisation rates revealed by particulate excess barium in the North Pacific and South China Sea

Yuan and co-workers quantify organic carbon remineralisation in the twilight zone of the China Sea using particulate excess barium as a proxy…

Sedimentary controls on seawater nickel distributions and nickel isotope compositions: a two steps study

Nickel isotopic mass balance in the ocean stands among the less understood so far…

23 million years of productivity reconstructed in the Central Pacific Ocean using past and modern proxies

Using diverse geochemical proxies, Chu and colleagues analysed an iron–manganese crust to reconstruct central Pacific productivity over the past 23 million years.

Lead isotopes reveal that hydrothermal variability is driven by Sea‐Level change and transient magmatism

De and colleagues present the first millennial-scale reconstruction of hydrothermal variability at a mid-ocean ridge using lead isotopes from iron-manganese coatings…

Rechercher