Oral Session 6

Phytoplankton and total particle size distributions in the Western Arctic Ocean: Links with the bulk spectral particulate absorption coefficients of seawater

Optical properties of natural assemblages of particles and phytoplankton suspended in the ocean can provide insights into their responses to environmental changes. The particle size distributions exert an influence on respective particulate optical properties, yet the study of such relationships is often restricted owing to the lack of comprehensive measurements on oceanographic cruises. We examined the particle and phytoplankton size distributions (1 to 50 μm for both), the bulk light absorption coefficients, the absorption efficiency factors and cross-sections using data collected from Arctic waters as part of the NASA ICESCAPE2011 cruise. For the density function of particle number concentrations, a ratio of phytoplankton to the total particles in the pico size range was generally small (0.09 ± 0.12). In contrast, significant variations in the nano and micro size ranges were observed. Our results showed that the bulk total particles and phytoplankton absorption coefficients are strongly influenced by variability in their respective mean absorption cross-sections. Variations of the mean absorption cross-sections were further influenced primarily by the mean absorption efficiency factors. For phytoplankton, the efficiency factor was well correlated with a product of the mean phytoplankton cell diameter and the intracellular concentration of chlorophyll-a. Variations in the mean phytoplankton diameter were low (4.96 ± 1.97 μm). We observed a tight relationship between the imaginary part of the refractive index in the red band of chlorophyll-a and the intracellular chlorophyll-a concentration. This result was consistent with previous laboratory experiments of single phytoplankton species.

Atsushi Matsuoka, University of New Hampshire, USA, https://orcid.org/0000-0002-6327-9948

Rick Reynolds, Scripps Institution of Oceanography, University of California San Diego, USA

Dariusz Stramski, Scripps Institution of Oceanography, University of California San Diego, USA

Samuel Laney, NOAA Pacific Marine Environmental Laboratory, USA

Heidi Sosik, Woods Hole Oceanographic Institution, USA

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