Imprint of a dissolved cobalt basaltic source on the Kerguelen Plateau

[摘要] Processes of cobalt (Co) entrainment from shelf sediments over the KerguelenPlateau were studied during the KEOPS (Kerguelen Ocean Plateau comparedStudy) in order to explain the exceptionally high dissolved cobaltconcentrations that have been measured in the surface waters above theKerguelen Plateau, and in intermediate and deep waters above its easternslope. Lateral advection and dissolution of Co contained in basalt sedimentsaround Heard Island, a main source of lithogenic Co in the study area, wereshown to imprint the process of surface enrichment over the plateau.Dissolved Co enrichment was strongest at the intercept of the eastern slopewith intermediate and deep waters, probably due to more efficientmobilisation of the sediments in the slope current, in addition to advectionof Co-enriched and low-oxygenated ocean water masses.

In surface waters, the strong sedimentary Co inputs were estimated to bemuch higher than biological Co uptake in phytoplankton blooms, underliningthe potential use of dissolved cobalt as tracer of the natural ironfertilization above the Kerguelen Plateau. Based on a simple steady-statebalance equation of the external input of dissolved iron over the plateau,the fertilization of iron inferred by using dissolved Co as a tracer ofbasalt sources is estimated to be 28 × 10² ± 21 × 10² t yr⁻¹in surface waters of the Kerguelen Plateau. This estimate isconsistent with preceding ones (Zhang et al., 2008; Chever et al., 2010), andthe calculated iron supply matches with the phytoplankton demand (Sarthou etal., 2008).

[学科分类] 地球化学与岩石