UC San Diego

Abstract: Climate‐related environmental change has been suggested to alter Arctic phytoplankton community composition. Development and application of capabilities to characterize Arctic phytoplankton community composition from optical measurements including satellite ocean color observations is essential for monitoring such changes over extended spatiotemporal scales. We analyzed concurrent measurements of phytoplankton pigment composition and optical absorption spectra (aph) from research cruises in the Chukchi and Beaufort Seas. A diagnostic pigment analysis (DPA) was used to differentiate phytoplankton communities in terms of dominant phytoplankton size classes (PSCs) defined by cell size, that is, pico‐ (<2 μm), nano‐ (2–20 μm), and microphytoplankton (>20 μm). The DPA results were used along with aph measurements to examine a capability to distinguish between pigment‐based PSCs using solely the optical data of aph. Our results reveal that the spectral absorption properties of micro‐dominated phytoplankton assemblages differ significantly from other phytoplankton communities. Simple aph band ratios involving spectral bands available on multispectral satellite ocean color sensors are shown to provide a useful optical metric to distinguish between micro‐dominated and non‐micro‐dominated communities with a minimum success rate of 70% relative to reference pigment‐based classification. The pigment‐based and aph‐based classifications also showed consistent biogeography within the investigated region, with relatively high occurrence of micro‐dominated samples in the Chukchi Sea and rare occurrence in the Beaufort Sea. The aph‐based classifications provide a potential optical approach to examine changes in phytoplankton community composition in western Arctic seas, especially the relative prevalence of micro‐dominated or non‐micro‐dominated phytoplankton communities.