Which were accomplishments of russian explorers vitus bering and alexei chirikov?

With his knowledge in navigation cartography, Vitus Jonassen Bering achieved some important goals in those fields, such as:

The description of Bering Strait and Alaska. Bering joined the fleet of Tsar Peter I the Great as a sublieutenant. The Tsar appointed him leader of an expedition to define if there was any land connection between Asia and North America, in order to establish commercial relationships with China around Siberia, and to expand territory to North America. The mapping of much of the Arctic coast of Siberia. In his second expedition, that was carried out during the reign of Empress Anna, and was referred to as the Great Northern Expedition (1733–43).

In Alexei Ilich Chirikov case, being the second in command in Bering’s first and second expeditions.  Some of his accomplishments were:

Mapping Siberia’s Artic Cost.After failing in searching Bering shipwreck, he returned to St Petersburg, where he took part in the mapping of the Kamchatka Peninsula.

Identify and explain two specific cultural or political influences that islamic merchants had on sub-saharan africa.