I want to calculate, which land areas of my elevation raster data set are under a specific elevation height. The open sea with pixel values of 0 should not be included in the analysis. I want to convert the pixel values of only the open sea (and not the landmass) from 0 to noData, how can I do this without clipping or masking my raster with boundary shapefiles of the coastline or the country?
Your technical issue is quite easy to solve. Using the raster calculator you can use a conditionnal statement
Con("yourraster"!=0 , "yourraster")
Which will replace all 0 by NoData ( "condition": your raster is different from 0, "if true": you use the value of your raster, "if false" is left void, so it will be NoData)
Conceptually, this is another problem because some land pixels have an elevation equal (or even below) 0 (e.g. a large part of the Netherlands or the "dead sea" area). So this rule could be problematic and the use of an external mask is recommended. It depends on your knowledge of your data (do small water bodies in your DEM have a positive elevation) and study area (any land area below sea level ? )