China's new deep-sea manned submersible Fendouzhe, or Striver, returned to the Mariana Trench on Monday. It retrieved sample-collectors left during last week's mission. The crew said it also carried out other tasks. The Mariana Trench in the western Pacific Ocean is the deepest location on Earth. Last week, the Fendouzhe submersible touched down to a record level below the ocean's surface.