Metrics to Quantify the Contributions of Different Size Fractions to the Particle Size Distribution Based on Measurements in Arctic Waters

Rick A Reynolds, University of California San Diego, Scripps Institution of Oceanography, La Jolla, CA, United States, Hugh Runyan, Scripps Institution of Oceanography, UC San Diego, La Jolla, CA, United States and Dariusz Stramski, University of California San Diego, Scripps Institution of Oceanography, La Jolla, United States
The size distribution of suspended particles influences several processes in aquatic ecosystems, including light propagation, trophic interactions, and biogeochemical cycling. The shape of the particle size distribution (PSD) is commonly modeled as a single-slope power law for optical and ecological applications, which can be further used to estimate the relative contributions of different planktonic size classes to particle number, area, and volume. We use a dataset of 168 high size-resolution PSD measurements in Arctic oceanic waters to examine variability in the shape of the PSD over the particle diameter range 0.8 to 120 μm. A value of −3.6 ± 0.33 was obtained for the average slope of a power law fitted over this size range, consistent with other studies. Our analysis indicates, however, that this model has significant limitations in adequately parameterizing the complexity of the PSD, and performs poorly in predicting the relative contributions of different size fractions such as those based on pico-, nano-, and micro-plankton size classes. Similarly, median particle size was also generally a poor indicator of size class contributions. The results indicate that alternative percentiles of the cumulative distribution function may provide better metrics to capture the overall shape of the PSD and to quantify the contributions of different size fractions.