The biological availability of Fe has been demonstrated to strongly influence both primary and secondary pro- duction in pelagic as well as coastal upwelling high-nutrient low-chlorophyll (HNLC) regimes. Although nearly all of the dissolved Fe in marine surface waters is thought to be complexed by organic ligands, the character and origin of these Fe-organic complexes remains a mystery. Here we report that the activity of naturally occurring viral populations in an HNLC coastal upwelling system can regenerate sufficient concentrations of dissolved Fe to support the growth of the native phytoplankton community. When combined with studies that have demonstrated that Fe in virus-mediated lysates of heterotrophic bacteria and cyanobacteria is highly bioavailable to model marine plank- ton, our data demonstrate that viral activity in this marine system (and potentially others) is critical to the recycling of organically complexed Fe that supports as much as 90% of primary production in HNLC surface waters.