Radium isotopes to investigate the water mass pathways on the Kerguelen Plateau (Southern Ocean)

Abstract

Abstract Natural iron fertilization promotes the phytoplankton bloom that takes place on the Kerguelen Plateau in the Indian sector of the Southern Ocean. We measured 228Ra (T1/2=5.75 yr) and 226Ra (T1/2=1602 yr) in waters above the Kerguelen Plateau in order to provide information on the water-mass pathways, which in turn could help elucidate the mechanisms controlling iron fertilization in that area. 228Ra activities are extremely low in this region, being in most cases Using the 228Ra profile obtained at station A3, we could estimate the vertical eddy diffusivity (Kz) on the Kerguelen Plateau. Our Kz estimate (1.5×10−4±1.3×10−4 m2/s) compares well with that reported by Park et al. [2008a. Internal tides and vertical mixing over the Kerguelen Plateau. Deep-Sea Research II, doi:10.1016/j.dsr2.2007.12.027] based on CTD/LADCP data. By combining this Kz estimate with the gradient of dissolved Fe observed at A3 [Blain, S., Sarthou, G., Laan, P., 2008. Distribution of dissolved iron during the natural iron fertilization experiment KEOPS (Kerguelen Plateau, Southern Ocean). Deep-Sea Research II, doi:10.1016/j.dsr2.2007.12.028], we calculate a vertical Fe flux of 1.0–14.3 nmol/m2 d.