Spatial and Interannual Variability of Antarctic Sea Ice Bottom Algal Habitat, 2004–2019

Abstract

AbstractIn the Antarctic, sea ice algae use the highly dynamic sea ice as a platform for growth. Antarctic sea ice extent has recently been highly variable, first showing a slight increase and then a record decrease starting in 2016. We investigated the response of Antarctic ice algal habitat to variations in sea ice and other environmental forcings during 2004–2019. Combining an ice growth model, remote sensing and reanalysis data, and a radiative transfer model, we assessed whether light penetration to the bottom ice was sufficient for ice algal growth. Trends in the inputs over the 16 years were relatively small: there were no changes in ice thickness or bottom ice melt date, a 6.4% decrease in snow depth, a 1.2% decrease in incident light, and a 0.8°C decrease in air temperatures. Eighty‐one percent of the sea ice cover was habitable by ice algae for ≥14 days each year. The Antarctic has a larger extent and duration of potential ice algal habitat than the Arctic. Over time, the spatially averaged seasonal duration of habitat increased because a higher proportion of each pixel became habitable on average, compensating for the 2016–2019 reduction in sea ice extent. The spatial variability in potential habitat was strikingly high, even within geographic sectors. Bottom ice melt date (bloom termination) far surpassed other environmental factors in explaining variation (45%) in ice algal habitat on the 25 km scale. Because melt date depends on the ice‐atmosphere heat balance, Antarctic ice algal habitat may be highly sensitive to future climate changes.