Gross Primary Production of Antarctic Landfast Sea Ice: A Model‐Based Estimate

Much of the Antarctic coast is covered by seasonal landfast sea ice (fast ice), which serves as an important habitat for ice algae. Fast‐ice algae provide a key early season food source for pelagic and benthic food webs, and contribute to biogeochemical cycling in Antarctic coastal ecosystems. Summertime fast ice is undergoing a decline, leading to more seasonal fast ice with unknown impacts on interconnected Earth system processes. Our understanding of the spatiotemporal variability of Antarctic fast ice, and its impact on polar ecosystems is currently limited. Evaluating the overall productivity of fast‐ice algae has historically been hampered by limitations in observations and models. By linking new fast‐ice extent maps with a one‐dimensional sea‐ice biogeochemical model, we provide the first estimate of the spatio‐seasonal variability of Antarctic fast‐ice algal gross primary production (GPP) and its annual primary production on a circum‐Antarctic scale. Experiments conducted for the 2005–2006 season provide a mean fast ice‐algal production estimate of 2.8 Tg C/y. This estimate represents about 12% of overall Southern Ocean sea‐ice algae production (estimated in a previous study), with the mean fast‐ice algal production per area being 3.3 times higher than that of pack ice. Our Antarctic fast‐ice GPP estimates are probably underestimated in the Ross Sea and Weddell Sea sectors because the sub‐ice platelet layer habitats and their high biomass are not considered. Plain Language Summary Antarctic landfast sea ice (fast ice) is sea ice fastened to the coastline of Antarctica and provides a prolific habitat for microalgae. These ice algae are ecologically important because their production takes place early in the season when water column primary production is low. By combining a new satellite data set and a biogeochemical sea‐ice algal growth model, this study provides the first estimate of circum‐Antarctic fast‐ice algal production: 2.8 million tonnes of carbon per year, which is about 12% of the total Antarctic sea‐ice algal production. The mean algal primary production per area in fast ice is 3.3 times higher than that of pack ice. Key Points First estimate of circum‐Antarctic landfast sea‐ice annual gross primary production, with a focus on the 2005–2006 season Mean landfast sea‐ice algal primary production is 2.8 TgC/y, representing 12% (range 5%–19%) of total Southern Ocean ice algal productivity Mean modeled landfast sea‐ice algal production per ar