why has the temperature of the Arctic Ocean changed during the last 40 years?

Question

a. sea ice produced more salt, causing the cold ocean water to sink
b. less snow falls in the Arctic now then 40 years ago
c. more sunlight now reaches Earth than in the past
d. sea ice has melted, allowing more sunlight to hit the ocean

Answer 1

d. sea ice has melted, allowing more sunlight to hit the ocean