What is the term for the Arctic region north of the tree line?

Which of the following is the coldest temperature ever recorded in Antarctica? What is the world's southernmost active volcano located in Antarctica? What is the term for the unique phenomenon where the sun remains below the horizon for 24 hours in the polar regions? Which mountain range runs along the border between Alaska and Canada? Which of the following research stations is located on the Antarctic Peninsula? What is the name of the largest fjord in the Arctic? What is the name of the famous canyon in Arizona, USA? In which state is the Palo Duro Canyon located?