To improve current estimates of phytoplankton specific carbon in the Ross Sea, we calculated a regionally specific algorithm from in situ particulate organic carbon (POC) concentrations and backscatter sensor data. These data come from three independent Seaglider deployments during the austral summer. Algal-specific POC (Cphyto) accounted for between 19.8-61.0% of total POC in the Ross Sea with an average Cphyto concentration of 84.2 µg C L-1. As a result, Cphyto:chlorophyll a ratios were less than POC:chlorophyll a ratios and ranged from 9.00-257 µg C (µg chlorophyll a) L-1. This regionally-specific method is substantially more accurate (average Cphyto concentrations are 10-78 µg C L-1 greater) than estimates derived from published algorithms. Our findings highlight the value of regionally-specific algorithms for measuring inherent optical properties and how such approaches can inform our current understanding of particulate carbon partitioning and food web dynamics.

• Phytoplankton distributions and primary productivity were assessed off the northern coast of Norway in spring. Biomass and productivity were greatest off the continental shelf during the period of observations. • A satellite climatology showed that blooms usually form on the continental shelf first, and spread to deeper waters from 2-4 weeks after the shelf bloom. • The Calanus finmarchicus population had the potential for removing substantial amounts of chlorophyll each day, but phytoplankton vertical distributions were controlled by passive sinking.