Complex sentence: In the North it met the Arctic Ocean; the islands of Novaya Zemlya, Kolguyev and Vaigach also belonged to it, but the Kara Sea was reckoned to Siberia.
Split into simpler sentences: In the North it met the Arctic Ocean. The islands of Novaya Zemlya, Kolguyev and Vaigach also belonged to it, but the Kara Sea was referred to Siberia.