A diver planning to dive to a depth of 100 ft can choose to breathe air that is a mixture of oxygen, nitrogen, and helium. If the total pressure of the air in the tank is 3040 mm Hg , and the partial pressures of O2 and He are 304 mm Hg and 1520 mm Hg , respectively, what is the partial pressure of N2

Mass is the amount of matter in an object.  weight is the measurement of the pull of gravity on an object.  say for example, you travel to the moon which has a different gravitational field compared to the gravitational field of earth. (gravitational fields: earth = 1, moon = 0.165)  now when you are on the moon, the pull of gravity on you is different than on the earth. and as weight is the measurement of the pull of gravity on an object, that means yes, your weight can and will change on the moon.  however, on the moon, on earth or even on jupiter, the amount of mass inside of you remains the same. meaning your physical mass remains constant.  in conclusion it is possible for your weight to change as your mass remains constant. 

Thermohaline circulation and gyres