well, you fought that big guy which was some sort of manifestation of the cold (or nature, or whatever, that was also mentioned in the story with the tribe going through the woods) after which you changed the past one last time, by supporting the captain. the captain tried to take off with the chopper or commited suicide, i don't remember exactly. so now he doesn't do that anymore, thus managing to be there when you fall in the ice, at the beginning, and pull you out.

When i did the Chronos-fight part my ending was that i gave the model of the ship to the captain when he comes in with the telegram sent by HQ. In the video i saw a totally different scene which is on the bridge of the ship with different ppl.

Here's how I saw it: In 1981 a scientist leaves his research station in the north pole, heading for a ship that has come to pick him up. Instead of reaching his ship, he stumbles upon the North Wind which has floated dead amongst the ice for years. He fixes errors made by the Northwinds crew and ultimately saves the ship by comforting the captain instead of letting him hear it, which makes the captain not go suicidal. After fixing everything, the captain is there to pick the scientist up in an alternate, "better" timeline.

1: Why are there zombies on the ship?

2: Why can the player influence the past?

3: What is the "time creature" at the end of the game and what was that "time place" in the end?

4: Most importantly, why would the Northern Wind wait for the scientist in 1981 when the original date of the happenings you're supposed to have fixed is years before that date, not to mention that wasn't the ship that was supposed to pick up the scientist.

I figured q1: They were like some sort of ghosts because if you remember you didn't get real damages from them (from melee or bullets) just some freezing effect on screen no blood. One of the ghosts looked exactly the same like in one of the flashbacks (the guy with the towel on his head).
q2: Some paranormal thing like an X-file
q3: According to the save game name "Chronos" it was the god of time or something..?

there are two exits from the cave and a boulder that you can push if you cliimb the other side.
go out through the lower exit, but only enough for them to see you. go back inside before they shoot and climb next to the boulder, but don't push it yet. wait 'til one of the guys comes inside and push the boulder behind him, trapping him inside. he'll face the exit and start shouting for help. go down behind him and climb towards the upper exit from the cave. you'll see the other guy running away to get help which means you can once again run free through the icey fields of the north. and whatever else polar bears do.

squish the guy with the pushable boulder