Carbon budget of sea‐ice algae in spring: Evidence of a significant transfer to zooplankton grazers

Abstract

The fate of ice‐bottom algae, before and after release from the first‐year sea ice into the water column, was assessed during the period of ice‐algal growth and decline in Resolute Passage (Canadian Arctic). During spring 1992 (from April to June), algae in the bottom ice layer and those suspended and sinking in the upper water column (top 15 m) were sampled approximately every 4 days. Ice‐bottom chlorophyll a reached a maximum concentration of 160 mg m−2 in mid‐May, after which it decreased to lower values. In the water column, chlorophyll a concentrations were low until the period of ice‐algal decline (∼0.1 mg m−3), with most biomass in the <5‐μm fraction. In both the suspended and sinking material, large increases of algal biomass occurred at the beginning of June, following the release of ice‐algae into the water column. The input of ice‐algal derived carbon to the upper water column and the proportions exported through sinking or remaining in suspension were assessed using a carbon budget for the two periods of ice‐algal growth and decline. For each period the output terms closely balanced the input. The carbon budget showed that most of the biomass introduced into the upper water column remained suspended (>65% of total export) and that ice‐algae were ingested by under‐ice grazers after release from the ice. These results stress the importance of ice algae for pelagic consumers during the early stages of ice melt and show that the transfer of ice algae to higher trophic levels extends beyond the period of maximum algal production in the ice bottom.