Right after you exit the caverns, to the right of the spot, where you resurface.
After you come down into the caverns, turn around towards the entrance and over the layer of ice, climb onto the ledge above.
Enter the tomb by jumping from over the ship's mast to the other side. In the spot, where you can start the mechanism (QTE), on the right, there is the document.
The last document that you read, after you have explored the tomb - it is right next to the Archivist map.