Spring and summer profiles of dissolved and particulate barium (Ba) from WOCE SR3 line (145°E) in the Southern Ocean are compared and seasonal evolutions discussed. Fluxes are estimated from mass conservation equations and from differences in reservoir contents between seasons. Subtraction of barium is observed at mesopelagic depths (upper 600 m) and appears to exceed up to tenfold the combined local build-up and the deep-ocean fluxes of particulate Ba, pointing towards significant dissolution to take place in intermediate and deep waters. Although regression analyses identify silicate as the major predictor of dissolved Ba, Ba and silicate are clearly uncoupled in surface waters where Ba behaves more similar to nitrate, excluding diatoms as users of Ba. Moreover, we observe a southward decrease in the Ba vs. silicate regression slopes driven by the conditions in intermediate and deep waters and mainly marked by the location of the Polar Front. These findings corroborate existing knowledge about the predominant control by barite formation and dissolution on the oceanic Ba cycle. It suggests a decreased dissolution of barite south of the Polar Front as compared to the situation in the Polar Front Zone and the Subantarctic Zone. This is in agreement with the fact that, except for deep waters, the Antarctic Circumpolar Current water column is oversaturated with respect to barite, in contrast to the situation north of the Polar Front, where the whole water column is undersaturated [Jeandel C., B. Dupre, G. Lebaron, C. Monnin and J.F. Minster, 1996. Longitudinal distributions of dissolved barium, silica and alkalinity in the western and southern Indian Ocean. Deep-Sea Res. 1, 43 (1), 1-31; Monnin, C., C. Jeandel, T. Cattaldo and F. Dehairs, 1999. The marine barite saturation state of the world's ocean. Mar. Chem., 65, 253-261]. |
