Particulate dimethylsulfoniopropionate and dimethylsulfoxide in relation to iron availability and algal community structure in the Peru Upwelling System

The influence of iron on phytoplankton biogenic sulfur production, physiological status, and community structure in the Peruvian Upwelling System was investigated in September 2000. Vertical profiles of particulate dimethylsulfoniopropionate (DMSPp) and dimethylsulfoxide (DMSOp) were measured at stations along two transects passing from the high-iron waters of the continental shelf, across the Peru trench, to low-iron open-ocean waters. Although chlorophyll a (Chl a) biomass decreased significantly across the shelf, DMSPp and DMSOpconcentrations relative to Chl a were higher at the offshore stations (DMSPp:Chl a 2.3–6.4 times greater and DMSOp:Chl a 2.6–4 times greater). These changes were associated with lower iron concentrations, as well as a shift from diatom-dominated communities to ones dominated by cryptophytes and haptophytes (based on algal pigment concentrations). The results of a shipboard iron-addition incubation experiment were similar to patterns observed on the transects. DMSPp:Chl a ratios decreased with increasing iron and diatoms preferentially outgrew other taxa. The possible role of DMSPpand DMSOpas free radical scavengers (stimulated by iron limitation) was supported by the increased concentrations of these compounds measured under low-iron conditions, as well as by the positive correlations (r2= 0.69 and 0.82, respectively) observed between these compounds and the known antioxidant β-carotene.