Submesoscale flows are energetic motions on scales of several kilometers that may lead to substantial vertical motions. Here we present satellite and ship radar as well as underway conductivity-temperature-depth and Acoustic Doppler Current Profiler observations of a cyclonic submesoscale filament in the marginal ice zone of Fram Strait. The filament created a 500-m thin and 50-km long sea ice streak and extends to >250-m depth with a negative/positive density anomaly within/below the halocline. The frontal jets of 0.5 m/s are in turbulent thermal wind balance while the ageostrophic secondary circulation in places appears to subduct Atlantic Water at >50 m/day. Our study reveals the submesoscale dynamics related to sea ice shapes that can be sensed remotely and shows how submesoscale dynamics contribute to shaping the marginal ice zone. It also demonstrates the co-occurrence and mixing of water masses over short horizontal scales, which has implications for ocean and sea ice models and understanding of patch formation of planktonic organisms.