Marne-Nordsee is an Amt ("collective municipality") in the district of Dithmarschen, in Schleswig-Holstein, Germany. Its seat is in Marne. It was formed on 1 January 2008 from the former Amt Marne-Land, the town Marne and the municipality Friedrichskoog.
The Amt Kirchspielslandgemeinde Marne-Nordsee consists of the following municipalities (with population in 2005):