The surface temperature of the Southern Ocean varies very little, ranging from 1 °C (33.8 °F) to 1.8 °C (35.2 °F).[4] During the summer sea ice covers 4,000,000 square kilometres (1,500,000 sq mi) of ocean.[5] The continental shelf surrounding the mainland is 60 kilometres (37 mi) - 240 kilometres (149 mi) wide. The depth of the seafloor in this area ranges from 50 metres (164 ft) - 800 metres (2,625 ft), with an average of 500 metres (1,640 ft). After the shelf the continental slope descends to abyssal plains at 3,500 metres (11,483 ft) - 5,000 metres (16,404 ft) deep.