Alaska Airlines and Icelandair frequent flier partnership was severed on May 1, 2013, but is now coming back effective October 1, 2015.
Alaska Airlines Mileage Plan and Icelandair Saga members can earn and use miles on each others flights. Alaska MVP Gold members will have access to Saga lounge at the Reykjavik airport.
You can access Alaska Airlines page for this partnership here.
Alaska Airlines Mileage Plan member will receive double miles for Icelandair flights between October 1 – December 15, 2015. There could be similar offer for Icelandair Saga members as well, but there is no information about this partnership returning on their website yet.
Reykjavik is a natural connection point on flights between North America and Europe due to its location. I flew from Toronto to Helsinki on Icelandair last year just before Christmas and had couple of nights stopover in Reykjavik.
Icelandair benefits from Alaska Airlines feeder traffic on its West Coast gateways of Seattle, Vancouver, Portland, and Anchorage.