A local sniper has asked for help tracking down a hidden wraith. Scan the ice to reveal the cloaked enemy.
Use the proximity indicator to locate the cloaked wraith. Once you've scanned it, the sniper will kill it with one shot. At the Pathfinder's request, the "mystery sniper" will reveal himself and allow you to approach him at the nearby sentry point. Go and have a conversation with him to complete the task.
The name "White Death" is an allusion to the Finnish sniper Simo Häyhä, who was nicknamed White Death by Soviet soldiers. Häyhä amassed a body count of over 500 during the course of the Winter War.