The annual cycle of particulate organic carbon export in Franklin Bay (Canadian Arctic): Environmental control and food web implications

Abstract

As part of the Canadian Arctic Shelf Exchange Study (CASES), we assessed the importance of new production and resuspension in determining the nature and magnitude of the deep (210 m) particulate organic carbon (POC) flux from October 2003 to September 2004 in central Franklin Bay. In spring and summer, phytoplankton production was nutrient‐limited in the stratified surface layer and the initial spring bloom evolved into a subsurface chlorophyll maximum (SCM) at the nutricline. Large herbivorous calanoid copepods intercepted little of the initial bloom but grazed intensely on the SCM. The phytoplankton and fecal pellet fluxes culminated simultaneously in July–August (24 and 23 mg C m −2 d −1 , respectively). The detrital POC flux peaked in September (52 mg C m −2 d −1 ), coincident with wind‐induced resuspension of recently settled POC. In the fall, detrital POC fluxes increased again to 22 mg C m −2 d −1 , following the off‐shelf transport of terrigenous POC carried by the Mackenzie River plume and POC resuspended by wind on the shelf. In winter, the relatively weak POC fluxes (2–7 mg C m −2 d −1 , detrital at 90%) resulted from the settling down of resuspended sediments. We propose a conceptual model in which the ecosystem of Franklin Bay shifts from an algal to a detrital mode according to seasonal changes in the relative importance of fresh and old POC supplies. On the basis of this model, the ecosystem of southeastern Beaufort Sea could evolve toward a less productive equilibrium dominated by sediment resuspension in response to the ongoing reduction of the ice cover.