Comprehensive inverse model constrains the application of beryllium-7 as a deposition tracer

26 March 2026

Measurements of beryllium-7(⁷Be) activity in surface waters provide a promising approach for quantifying the deposition of aerosol-bound elements at the ocean surface. In this application, it is generally assumed that (i) the fraction of marine ⁷Be in particulate form is negligible and/or (ii) the interactions between particulate and dissolved ⁷Be in seawater can be ignored. However, these assumptions have been questioned by the work of Grenier et al. (2023, see Science Highlight) based on samples collected along the GEOVIDE GA01 section.

In the present study, Lerner and colleagues (2025, see reference below) test these assumptions using a comprehensive model that includes vertical advection, vertical diffusion, gravitational settling, radioactive decay, atmospheric deposition, and the reversible exchange between dissolved and particulate ⁷Be. By using an inverse method, they showed that their model can reproduce reasonably well the ⁷Be activity data collected at two stations of the GEOVIDE cruise (one station in the East Greenland-Irminger Current and the other in the southern Labrador Sea). However, while ⁷Be data from the East Greenland–Irminger Current can be reproduced without consideration of adsorption and/or desorption processes, reversible exchange or desorption needs to be considered in order to fit the ⁷Be profiles observed in the southern Labrador Sea. At the latter station, reversible exchange results in a significant imbalance between the surface deposition and water-column inventory of dissolved, but not total (dissolved + particulate), ⁷Be. Thus, the authors conclude that reversible exchange could be neglected when total ⁷Be, but not dissolved ⁷Be, is applied as a deposition tracer.

**Figure**: a) Map showing the locations of ⁷Be sampling stations (black circles) in the southern Labrador Sea and the East Greenland-Irminger Current, with arrows providing a schematic of surface circulation and the cross-black circle depicting a region of deep convection in the Labrador Sea. b-e) Difference between modeled and observed values of total ⁷Be activity (b,d) and particulate ⁷Be activity (c,e) with horizontal bars showing ± 1 standard deviation. The comprehensive model of ⁷Be cycling (yellow) reproduces the data at both stations, while model skill deteriorates at the southern Labrador Sea station when reversible exchange (cyan) or desorption processes (green) are excluded.

References:

Lerner, P., Grenier, M., Marchal, O., & van Beek, P. (2025). An inverse modelling approach to constrain ⁷Be cycling in the subpolar North Atlantic. Deep Sea Research Part I: Oceanographic Research Papers, 220, 104465. Access the paper: 10.1016/j.dsr.2025.104465

Grenier, M., van Beek, P., Lerner, P., Sanial, V., Souhaut, M., Lagarde, M., Marchal, O., & Reyss, J. L. (2023). New insights on the ⁷Be cycle in the ocean. Deep Sea Research Part I: Oceanographic Research Papers, 194, 103967. Access the paper: 10.1016/j.dsr.2023.103967

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