Immigration year 1913 was the key:

First Name: Marius
Last Name: Nielsen
Ethnicity: Denmark, Scandinavian
Last Place of Residence: Flegum, Denmark
Date of Arrival: Mar 28, 1913
Age at Arrival: 19y Gender: M Marital Status: S
Ship of Travel: Mauretania
Port of Departure: Liverpool
Manifest Line Number: 0004

Notice the last place of residence: Flegum

On the original his father is Niels Chr. Nielsen, Skovsgaard.

This is the Marius we've found in the Danish parish records born 5. Feb. 1894 in Torslev Parish. If he's also the Marius that married Alma needs to be investigated:-)

Karsten