of the light on mixing with the CL reagent system. The
method requires very little sample handling, the reaction
is simple, throughput is high (a 3 min analytical
cycle, seawater sample quanti®ed within 25 min) and
the shipboard limit of detection is 40 pM, which is
below Fe concentrations generally found in openocean
®eld studies. Preliminary results from the shipboard
determination of vertical iron distributions in
the upper water column of the North and South
Atlantic using the FI±CL monitor are also presented