Complex sentence: After Polar Star made the initial cut to McMurdo, Krasin assisted by grooming (widening) the thin outer channel (which consisted of first-year ice), while Polar Star broke the thicker, much denser multi-year ice near the station.
Split into simpler sentences: After Polar Star made the initial cut to McMurdo, Krasin assisted by grooming (widening) the thin outer channel, which consisted of first-year ice. Meanwhile, Polar Star broke the thicker, much denser multi-year ice near the station.