The earth is slightly flattened at the poles, the poles are a bit closer to the center of the earth than land on the equator, so the earth is not circle but sphere.Due to this reasoning, the North pole and South pole is closer to the core and the other lands are a bit further.The South pole is in Antarctica which is a very high plateau.So the gravity there would be less as compared to that in the North pole. The Earth is slightly flattened at the the North pole, which is in the middle of a deep ocean.The South pole is a continental which tends to be about 50km thick, while the North pole tends to be about 3 km thick.
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