Dissolved iron at subnanomolar levels in the Southern Ocean as determined by ship-board analysis Original Research Article

The biogeochemistry of iron was investigated in remote waters of the Antarctic ocean in the austral summer of 1995/1996. A sensitive flow injection analyser, based on in-line preconcentration and luminol chemiluminescence detection (FIA-CL), was used for underway surface measurements and vertical profiling during a fine scale survey in the Polar Front (PF) in the Atlantic sector of the Southern Ocean. Results indicated a dynamic environment with dissolved iron concentrations ranging from 0.05 to 0.3 nM. Distributions are consistent with chlorophyll a and fCO2 suggesting a coupling with these parameters. The highest iron concentrations (0.3 nM) were found where chlorophyll a abundance was highest and CO2 undersaturation the most pronounced. The vertical distribution (upper 500 m) revealed a nutrient type distribution with low subsurface values (0.1 nM) gradually increasing to ∼0.3 nM at depth.