To better understand the association between barium (Ba) and silicon (Si) at ocean margins, we collected filtered seawater samples along the Congo River plume at the coast of Congo and Gabon and along an off-shelf section at 3°S, complemented by three freshwater samples collected directly from the Congo River. The water samples from the Congo margin were collected during GEOTRACES cruise GA08 with German RV Meteor (M121) in November-December 2015 with a stainless steel CTD rosette and a towed fish for surface waters. Congo River freshwater samples were taken upstream by boat in May, July and October 2017 near the center of the river at ~6°S and ~12.5°E (stations 12.1-12.3). We determine for the first time Ba and Si stable isotopes at the Congo River-dominated Southeast Atlantic margin. Based on these data we evaluate the contribution of Congo River plume to Ba and Si budgets in the South East Atlantic Ocean, and the association between Ba and Si at the Congo margin.

Dissolved barium (Ba) concentration and its stable isotopes, dissolved silicon (Si) concentration and its stable isotopes, and calculated Ba values based on global, South Atlantic or regional (this study area) Si-Ba correlations. Ba is defined as the deviation of dissolved Ba concentration from the Ba-Si linear relationship.