The forward cascade of sea ice floes in the Weddell Sea

Abstract Sea ice is a material composed of polydisperse floes whose geometries evolve in response to conditions in the surrounding ocean and atmosphere. Due to sparse observations, quantifying the influences of basin-wide forcings on floe behavior has remained a challenge, and past studies have instead focused on finer-scale dynamics in driving the summer break up of the pack. Here, we combine high-resolution altimetry and imagery to characterize the life cycle of floes in the Weddell Sea, which we link to large-scale dynamics inferred from sea ice age estimates across the gyre. We demonstrate that basin-wide solar heating and oceanic circulation govern the floe size and thickness distributions during break up, in a forward cascade involving synoptic, mesoscale and floe-scale forcings fracturing ice into increasingly smaller pieces. This cascade is arrested by lateral erosive processes acting at the sub-floe scale, as evidenced by the three-dimensional rounding of floes during summer. We hypothesize that projected basin-scale changes over the next decades may accelerate the forward cascade of sea ice and result in smaller floes that are more vulnerable to melt.