I was asked whether weight of a submerged object changes. The following is my current understanding of the matter and will likely contain errors. Please correct me, if I made any mistakes.
Because force vectors c and d are of the same value, but have a different direction, they annihilate each other. Force vector a has a lower value than vector b, because the hydro static pressure in a depth $H_1$, which acts on the top of the object, is weaker than the hydro static pressure in depth $H_3$, which acts on the bottom of the object. Adding both vectors together yields the vector of upthrust.
Now, moving the submerged object upwards requires less energy compared to moving the same object upwards on land, because by moving the object upwards (positive change in potential energy), water moves downwards to fill the void (negative change in potential energy).
But what if you have a look at a static object on the sea floor? Since it is resting on the seafloor, there will be no more buoyancy. What remains, however, is the gravitational force of the object + the hydro static pressure acting on the top of the object (a).
According to Newton's third law, the sea ground counteracts the sum of both forces (otherwise the object will continue sinking into the ground).
What I don't get is, will this object resting on the sea floor result in a change of the object's weight when compared to an object that is affected by buoyancy?