Dress warmly and in something that allows for movement and work.
Take the shovel and begin to clear the deck. Carefully scoop the snow off the ice layer and move off the deck, then begin at the edge of the ice sheet and very slowly begin to chip away at the ice with the edge of the shovel. There will be small sheets of ice that break away from the main part that can be removed and discarded.
Continue to chip away at the ice until the deck is clear of the ice. If this is taking too long, you can try using pots of hot water to melt the ice enough to break it up and clear it away. A last resort would be to continue using hot water until it all melts.
Take a final step to prevent the problem from returning by spreading a layer of cat litter on the deck. After the cold spell ends this can easily be hosed off and cleaned up.