Unhappy with his limited play at the Latvian club team Vilki Rīga, Karsums elected to transfer to the Moncton Wildcats of the QMJHL. He enjoyed a very good rookie season for the Moncton Wildcats, finishing in the top five of both team and league rookie scoring with 53 points (30 goals, 23 assists), and accumulating 76 PIM. Karsums also dominated the 2004 World Junior Ice Hockey Championship Division I tournament, scoring 7 goals and adding 6 assists for 13 points in five games.