Weddell seals and Leopard seals both birth live young and suckle them. These animals are not native to Antarctica no animal is (except for Penguins) but they come to the continent for the birth and nurturing season, to raise their pups to survival age.
No such mammal lives on the Antarctic continent. Sea leopards and whales may fit your description, and their habitat is the Southern Ocean.
No animal lives on the Antarctic continent: it's too cold and there is no food chain. Sea mammals, including seals and whales visit Antarctica's beaches. Their food chain is at sea, where they live.
There is not a sea animal that breast feeds. A duck has to give birth in the water but does not breast feed.
Humans
A cow
The Antarctic cod, also known as the Antarctic icefish, is primarily a carnivore. It feeds mainly on smaller fish, krill, and other marine organisms. Its diet is predominantly composed of animal matter, which classifies it as a carnivorous species rather than an omnivore.
The definition of a mammal is an animal that gives birth to live young and feeds them milk
The definition of a mammal is an animal that gives birth to live young and feeds them milk
This sort of animal that feeds on carrion is called a "scavenger".
From Wikipedia:"The gut of E. superba can often be seen shining green through the animal's transparent skin, an indication that this species feeds predominantly on phytoplankton."
The Adelie penguin feeds mostly on Antarctic krill, Antarctic silver fish, and Glacial squid. They obviously get it from the ocean.
It all starts like this.... A female animal and a male animal has a baby then the baby feeds on the mother then they are separated then the baby grows up to an adult and then it starts all over again...