Seasonal changes in the sinking export of particulate material under first-year sea ice on the Mackenzie Shelf (western Canadian Arctic)

The sinking export of particulate material under landfast first-year sea ice was studied from the winter period to spring melt on the Mackenzie Shelf, western Canadian Arctic. Short-term particle interceptor traps were deployed at 1, 15, and 25 m under the ice on 16 consecutive occasions from 23 February to 20 June 2004. The sinking material was analyzed for chlorophyll (chl) a, phaeo-pigments, total particulate carbon (TPC), particulate organic carbon and nitrogen (POC and PON), and biogenic silica (BioSi). The sinking fluxes of chl a and BioSi increased steadily after 19 March and until the onset of spring melt (26 May), after which they increased considerably. The contribution of large algae (>5 mu m) to the total chl a sinking flux also increased after 19 March, reflecting an increasing contribution of diatoms to the sinking export of algal material. Accordingly, chl a sinking fluxes at 1 m showed a significant linear relationship with bottom ice chl a biomass. On average, 46% of the chl a exported at 1 m was lost in the upper 25 m. POC was the main component of the TPC sinking fluxes throughout the study. POC sinking fluxes remained fairly stable until the onset of spring melt, after which a considerable increase was observed. High POC:chl a ratios indicated a significant contribution of non-algal material to the sinking POC. The daily sinking loss rate of chl a, POC, and PON from the sea ice and interfacial layer (top 1 m of the water column) varied seasonally and was highest during the winter period. Our results illustrate the continuous downward sinking export of organic material under landfast ice, from winter throughout late spring.