Seasonal Variation In Sea Level

We treat sea level as if it were fixed and absolute. Places on land are described as being a certain number of meters above sea level. The nickname of Denver as "The Mile-High City", refers to it's altitude above sea level. There are articles online about the seasonal variation in certain places, but I could not find anything about how, I believe, the average sea level across the world must vary by season.

Here is my reasoning:

The northern and southern hemispheres of the earth are far from equal. The northern hemisphere is nearly half land, while the southern hemisphere is only about ten percent land. This means that, during the northern winter, much more water is effectively locked up as ice and snow on land than during the southern winter. While this is not really a vast amount of water in comparison with the volume in the oceans, it does mean that the average sea level across the world can in no way be considered as absolute.

Water that falls on land as rain also contributes to the lowering of overall sea level, since it is water that is not in the oceans. But this rain water returns to the sea much more quickly than water that ends up as ice or snow on land. Even with rain, it must be considered that the average distance that rain falls from the sea, and thus the amount of time that it takes to flow back there through the watershed, is much greater in the northern hemisphere due to the larger land masses.

Furthermore, it appears to me that there must be less rain falling on a given unit of land in the southern hemisphere. Australia is dry, except for it's east coast. The southern part of Africa is also dry. The southern portion of South America is mostly high and narrow. This means that the only large areas of land in the southern hemispheres that do get a lot of rain is the equatorial areas of Africa and South America.

So, I conclude that sea level cannot be considered as absolute but must vary seasonally. Although, this fact is no doubt camoflaged by both tides and the generally rising sea levels due to melting arctic ice during global warming.