Marine bacterial community structure and function have been observed to shift during fluctuating environmental conditions, suggesting that distinct members of the community adapt to the abundance and composition of available nutrients and carbon. We measured changes in bacterial diversity and metabolic response of natural microbial consortia during early degradation of complex sources of particulate organic carbon (POC) in polar waters. The bacterial populations were representative of spatially disconnected communities, having been collected from the chlorophyll maximum and bottom waters of the Bering Strait and Chukchi Sea, respectively. Shifts in community composition, nitrogen assimilation and proteomic expression of the free-living Arctic bacteria were followed in ten-day, parallel incubation experiments with natural and isotopically labeled algal amendments under near in situ conditions. Based upon 16S rRNA gene sequencing and detailed biochemical composition, we are examining if initial bacterial community structure and succession impact early POC degradation kinetics. Additionally, we are investigating if there are phylogenetic niches for metabolic function driving POC degradation by western arctic marine bacteria.