Suspended particle and bacterial maxima in Peruvian coastal waters during a cold water anomaly

Simultaneous optical, biological and chemical analyses of coastal waters off Peru were made during a period characterized by anomalously cold surface waters and weak wind-driven coastal upwelling. Particle size distributions and the microbial and chemical nature of the intermediate nepheloid layers provide strong evidence that bacteriol growth, settling and offshore transport of particles are major processes controlling the particulate structure of the nearshore waters. The data also support previous suggestions that mid-depth maxima in suspended particles associated with nitrite maxima have a large bacterial component. Further, these results demonstrate the effectiveness of in situ optical methods for detection and quantification of the bacterial component of particle size distributions. While some features were similar to the particulate structures observed previously in Peruvian coastal waters, the data show the region to have significant temporal and spatial variability.