That paper is quite difficult to interpret for a non-expert, and isn't focused on just sea ice extent. I'm not sure what they mean by "extent", is it a maximum

That paper is quite difficult to interpret for a non-expert, and isn't focused on just sea ice extent. I'm not sure what they mean by "extent", is it a maximum or an average? Here's a link with some graphs that are easier to understand: https://www.climate.gov/news-features/understanding-climate/understanding-climate-antarctic-sea-ice-extent https://www.climate.gov/news-features/understanding-climate/.... The annual maximum follows the trend you describe, while the annual minimum has been more static and decreased substantially in the last few years.