Cool and intriguing point of research and ponderance indeed!
First off let's state the obvious, that outside of Scripture and what little we can gleen from True Science, we cannot answer all things with exact accuracy as we were not there and A LOT of time has passed since then and now. So pardon any speculation on my part.
Now as a note on the 2 unclean and the 7 clean animals taken into the ark. Note that of the clean animals that 7 of each were taken, male and female equally, with the 7th as a sacrifice to God for thanksgiving by Noah and his family for surviving the annhilation of the old wicked Pre-Flood World. You will also notice greater genetic variance within the so-called clean animals than with the so-called unclean animals as the clean animals would have had 3 sets of Patriarch and Matriarch genetics as where the unclean animals had only one pair of common Matriarch and Patriarch genes. You will also note throughout human history how the clean animals consistently are found around human population and even influenced by what you could call artificial selection, or human interference.
Now in terms of the spread of animals, I would say a good example of this is look how the human race itself spread over Earth after the Flood. From the point in Ararat all animals and people are able to spread throughout all the corners of the World quite easily even if we do not infer that the continental plates were broken up as goodly Shrimp pointed out. Though if indeed the plates did break up as inferred by that biblical passage it sure would make things a lot more easier to spread quickly beforehand and would also explain how population groups became geographically and genetically isolated afterwards.
Now in specific terms of the Arctic and Antarctic animals you will notice something very special about these animals, even in this time today. That they are able to swim, and indeed seem to constantly migrate either by swimming or walking over the ice from land to the polar regions. In fact a big problem in regards to climate change today is that the polar bear particularly is having troubles since the ice is disappearing rapidly thus disrupting and bringing hardship to its natural migration cycle.
Now in terms of the variation of life this is a very cool bit of evidence indeed which lends support to Noah's Ark story. You will notice if you look at the Theory of Evolution that that theory is not correct as one type of animal cannot change into another type except by hybridization in which case the offspring is either sterile or is in need of its parent species to continue.
However there is one scientific theory put forth by a goodly monk named Gregor Mendel, the Theory of Heredity (or as we call it today Genetics) which in my opinion have enough weight behind it to be called fact. What genetics shows us is that each animal after its own kind has a vast gene pool. One can isolate members of a specific gene pool either naturally or artifically. Also very interesting to lend support to this theory is members of the same kind can in fact even be reintroduced to their common gene pool seamlessly. This to me would seem to suggest that all animals have a common ancestor like unto themselves (that is to say not all animals come from Darwin's common ancestor of all life and evolved, but rather from a common hereditary set of parents that lived long ago.) This means for instance the Bears all have a common ancestor Bear, you might call this the Matriarch and Patriarch Bear. As the offspring of the Matriarch and Patriarch spread throughout Earth they became naturally isolated thus only breeding with other Bears with the same genetic make-up of eachother thus preserving certain characteristics with eachother.
You could then apply this idea and look at the marsupials in Australia as at some point being naturally isolated and thus having only their specific gene pool restricted to the Land Down Under which would explain why you do not find many varieties of them on Earth, or even in Australia.
You can even apply this principle to the Human Race. We know from anthropology we have 3 distinct anthropological post-Flood root races (very curiously aligning both geographically and genetically with the 3 Patriarchs and Matriarchs of the Bible; Shem, Ham, and Japheth and their wives.) We also know through history and even in today's time that such 3 races have indeed interbred throughout time and will retain characteristics or certain characteristics can be bred out or in given enough generations and time. We also know many of the sub-tribes of these three have at different points become geographically and genetically isolated thus retaining a handful of common characteristics. Example: melanin content, bone structure, certain genetic mutations, etc.
Now also consider that if all kinds of animals have a common Patriarch and Matriarch that it would have been quite easy for all such animals to have fit into The Ark literally as it was written with their many variances coming afterwards thanks to genetic spread, interbreeding, and isolation.
In terms of support for a Global Flood itself we can see quite clearly from the stratification of Earth's layers and from the fact that fossils seem to be jumbled throughout the geologic strata, with some even straddling two strata, that the Earth had to have underwent a very violent, sudden, and catastrophic change with a lot of water to mix things up so much and also to leave deposits to become layers.
Like I said, I do not have all answers since we all live thousands of years after such event, and a good bit of this is my own speculation. Though based on what little confirmable facts we do possess we can infer and ponder quite a bit. Very intriguing either way and I enjoy such ponderance. Kudos to you for raising the point!
