Spatial and seasonal variations in the pelagic–benthic coupling of the southeastern Beaufort Sea revealed by sedimentary biomarkers

Abstract

Photosynthetic pigments and stable isotopes from suspended particulate organic matter (POM) and surface sediment of the southeast Beaufort Sea, including the Mackenzie shelf and the Amundsen Gulf, were studied during fall 2003 and summer 2004. This multiple-biomarker approach led to an increased understanding of spatial and seasonal variation in pelagic-benthic coupling, as these 2 biomarkers reflect inherent differences in the time scales over which they integrate. Sedi- mentary pigments highlighted the importance of local water-column production as a source of phy- todetrital inputs to the sea floor. In the summer, the dominance of diatoms in the water column was reflected in the sediment by the abundance of fucoxanthin, a pigment broadly found in diatoms. In the fall, a more variable suite of sedimentary pigments reflected inputs from smaller cells such as haptophytes and prasinophytes. While stable isotope composition of the POM showed seasonal vari- ations, i.e. a more marine signature in the summer and a more terrestrial signature in the fall, sedi- mentary stable isotopes revealed geographical differences. Sediment on the Mackenzie shelf sug- gested a terrestrial source of organic matter, while in the Amundsen Gulf, sources of organic matter had a more marine origin. Finally, benthic community compositions and activity (sediment carbon demand) seemed affected by both spatial and seasonal variations in organic matter inputs to the ben- thos. This study stresses the importance of both physical factors (water depth and riverine inputs) and biological production (primary productivity and secondary production) in the determination of organic matter inputs to the benthos.