Ancestor born in Oslo emigrated to Queenstown, Ire

Hello, I'm hoping that someone can give me some leads about my ggrandfather Thomas Johnson born in Oslo in 1853. He emigrated to Ireland (Queenstown, now Cobh) and married Catherine Sullivan of Cobh in 1870. On the marriage certificate he lists his father as John Johnson, farmer. Any information that you can offer would be appreciated. Thank you. Mary Lou Skillin