is there an unknown land in the last ocean you mentioned?
Yes, "Terra Australis"
Southern Ocean
Exploration of the Southern Ocean was inspired by a belief in the existence of a "Terra Australis" – a vast continent in the far south of the globe to "balance" the northern lands of Eurasia and North Africa – which had existed since the times of Ptolemy. 
what class of vertebrates do seals belong to Pinnipeds what are pinnipeds? Diverse clade of carnivorous, fin-footed, semiaquatic marine mammals. what is the diet of the the last kind of mammal you mentioned? All cetaceans are carnivorous and predatory what kind of threat do these mammals face? Due to the difficulty to survey populations, 38% of marine mammals are data deficient apart from the seal can you name some other animals that full under this type of mammals? Whales, manatees, sea otters and polar bears how do pinniped move from one place to another? They have two pairs of flippers; the fore-flippers and hind-flippers, and smooth networks of muscle bundles in their skin that may increase laminar flow and make it easier for them to slip through water do they sleep? Yes, sleep in water with half of their brain awake where are these mammals mostly found? North Atlantic, the North Pacific and the Southern Ocean
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Southern Ocean [SEP] Unknown southern land
Exploration of the Southern Ocean was inspired by a belief in the existence of a "Terra Australis" – a vast continent in the far south of the globe to "balance" the northern lands of Eurasia and North Africa – which had existed since the times of Ptolemy. The doubling of the Cape of Good Hope in 1487 by Bartolomeu Dias first brought explorers within touch of the Antarctic cold, and proved that there was an ocean separating Africa from any Antarctic land that might exist. Ferdinand Magellan, who passed through the Strait of Magellan in 1520, assumed that the islands of Tierra del Fuego to the south were an extension of this unknown southern land.