The distribution of ¹⁰Be and ⁹Be in the South Atlantic

Vertical and surface-water distributions of ¹⁰Be and ⁹Be in the South Atlantic Ocean were studied. The major input of ⁹Be to the surface waters of the region is from the partial dissolution of eolian dusts, with the extent of the dissolution being about seven times that of aluminum from the dust particles. The gradients in surface-water ¹⁰Be concentrations appear to reflect the magnitude of the local precipitation. The imprinting of the surface water signals onto the deep water masses appears rapid, particularly in regions of enhanced productivity. Bottom waters of Antarctic origin have characteristic isotope signatures that can be traced along their advective route into the Guinea Basin of the eastern Atlantic. Elevated ⁹Be concentrations in the Angola Basin are indicative of diagenetic input in this region of restricted circulation. The corresponding anomalous ¹⁰Be in the bottom waters indicates historically lower surface-water ¹⁰Be/⁹Be ratios in the region, perhaps as a result of the further southward penetration of the Inter-Tropical Convergence Zone at those times. The budgets of ¹⁰Be and ⁹Be in the South Atlantic were estimated. The results show that cross-equator transport of ¹⁰Be and ⁹Be from the North Atlantic is 0.3 ± 10²³ atoms/year and 5.7 ± 10⁶ mol/year, respectively, accounting for less than 5% of ¹⁰Be and about 10% of ⁹Be entering the North Atlantic. There is a net export across 50°S to the Antarctic/Indian/Pacific Oceans of 0.9 ± 10²³ atoms/year for ¹⁰Be and 7.5 ± 10⁶ mol/year for ⁹Be. Using ¹⁰Be as a tracer, we evaluate accumulation rates of lithogenic minerals to be 1.7 ± 10¹⁴g/year in the North Atlantic and 4.8 ± 10¹³ g/year in the South Atlantic. While the North Atlantic rate agrees with the observed eolian dust input, the estimated lithogenic flux in the South Atlantic is about twice the eolian input, suggesting that the riverine input of ⁹Be to the open ocean may become non-negligible in areas of low eolian dust flux.