Facing the gate, climb on the left hand ramp and turn to face the ice on the left. You are going to jump behind the ice, so save your game because it is a"blind" jump. Also, make sure you have 100% of health, because a long drop follows and you will be left with just 10%. Lighting a Flare will definitely help you see clearly in the dark.

Facing the ice, stick to the right hand wall and take a running jump over the ice.

Keep pressing the Jump button along with the right direction key. This will make you jump off the back slippery side of the ice and land on another slide just to the right.

Let go of Jump and press Action to grab the edge. Shimmy to the very left and drop down.