The correct answer is option 2 - Kuroshio Current.

The Kuroshio Current is a strong ocean current that flows along the western coast of Japan. It is often referred to as the "black current" because of its dark waters. The Kuroshio Current is one of the strongest ocean currents in the world, with average speeds of about 2 to 4 knots. It carries warm water from the tropics towards the north, contributing to the warm climate and biodiversity of Japan.

Option 1 - Gulf Stream, is a powerful warm ocean current that flows from the Gulf of Mexico along the eastern coast of North America. Although it is also a large current, it is not referred to as the "black current" due to its clear blue waters.

Option 3 - California Current, is a cold ocean current that flows southward along the western coast of North America. It is the eastern limb of the North Pacific Subtropical Gyre. It is also not referred to as the "black current."

Option 4 - Antarctic Current is a cold ocean current that encircles Antarctica. It is not referred to as the "black current" and is located in a different region from the Kuroshio Current.