When a tourist party goes to Antarctica whether part of a trip organized by a travel agency or a adventurous party going by themselves, who should them report to? Is there anything as immigration laws governing Antarctica? Does any country require that their own citizens or any person that will one day ever enter their territory as tourist or resident report any travel to Antarctica?
This has been addressed over at Travel StackExchange: Does one need a visa to visit Antarctica? and Non-AT country citizen visiting Antarctica by non-AT country registred vessel (yacht) — do I need a permit and why? To summarize and expand on those two links:
If your home country is a signatory of the Antarctic Treaty, or your expedition departs from such a country, or your ship is registered in such a country, you generally will require a permit from the appropriate authorities in that country in order to visit. These are needed so that these countries can comply with Article VII.5 of said treaty:
Each Contracting Party shall, at the time when the present Treaty enters into force for it, inform the other Contracting Parties, and thereafter shall give them notice in advance, of
(a) all expeditions to and within Antarctica, on the part of its ships or nationals, and all expeditions to Antarctica organized in or proceeding from its territory; ...
In general, cruise ships that travel to Antarctica will take care of these permits for their passengers. However, if you are traveling by private vessel, you will need to apply for such a permit in the pertinent country or countries.
If, on the other hand, you are neither a citizen of, traveling on a vessel registered in, or departing from a country that is a signatory of the Antarctic Treaty, it is basically terra nullius for you. You can travel there without any permission whatsoever. It is, however, not recommended. Note also that most of the countries that are in any way "close" to Antartica are signatories to the treaty. I suppose you could leave from Madagascar or Namibia if you really wanted to avoid getting a permit.
Edit: The laws that govern actions in the Antarctic are individual to each country. This means that if you do something in the Antarctic that you shouldn't have done, and your expedition is for whatever reason governed by one of the AT signatories, it is up to the law enforcement officials of that country to prosecute you.
As an example, let's take Canada. As part of the ratification of the Antarctic Treaty system, Canada enacted the Antarctic Environmental Protection Act. The laws in this act require any Canadians or Canadian vessels visiting Antarctica to acquire a permit; prohibit mining; prohibit activities that harm or disturb native plants or animals; prohibit damaging historic sites; and regulate many other things as well. Penalties for violating these laws include fines up to 2,000,000 CAD for individuals and up to 12,000,000 CAD for corporations. Individuals can also be imprisoned for up to five years. (These are the maximum penalties for second & further offenses; penalties for first offenses are generally lower.)