Barium distribution across the Southern Ocean frontal system in the Crozet–Kerguelen Basin

Abstract

We investigated the dissolved and excess particulate Ba distribution (Ba xs, an estimate of biogenic Ba considered to consist mainly of barite [BaSO 4]) across the complex frontal system of the Crozet–Kerguelen Basin (Southern Ocean; 42–47°S, 62–65°E). Ba xs profiles show the characteristic mesopelagic maximum (depth range between 150 and 400 m) reaching up to 1000 pM in the Subantarctic Zone and Subtropical Front, the highest value observed for Southern Ocean mesopelagic waters. Dissolved Ba (concentrations between 38 and 104 nM) correlates with silicate and alkalinity, but the regression is not perfect, reflecting the involvement of different biogenic carriers in the control of the water column distribution of these compounds. Dissolved Ba in the upper 500 m appears strongly influenced by cross-frontal exchanges, involving both northward and southward transport of water masses. In the mesopelagic waters (150–400 m) of the Polar Front Zone, a dissolved Ba depletion faces the Ba xs maximum. This depletion appears mainly maintained by cross-frontal advection of waters containing less Ba and originating north of the Subantarctic Front. Overall, no clear evidence that precipitation of barite reflected by the occurrence of Ba xs maxima does measurably influence the distribution of dissolved Ba was found.