Maritime Polar air masses are cool, moist, unstable thus found over Arctic basin and greenland ice caps.
Explanation:
Air mass is the volume of air defined by temperature and water vapor. Covering hundred and thousands of miles. Cooler are being found over the arctic.
They move southwards along the Rockies into the plains then eastwards. These air masses collect warm and mist winds, originating in north Atlantic. The center of the air mass has high pressure and surrounded by lower air pressure at higher latitudes.
Antarctica and arctic circle are dominated by such air masses
