Most of the contained fluid is salt water, or brine, since its dissolved salt content may be higher than in sea water.
(Most of the contained fluid; is; salt water, or brine; since its dissolved salt content may be higher than in sea water) (its dissolved salt content; may be; higher than in sea water)
Most of the contained fluid its dissolved salt content
is may be
salt water, or brine since its dissolved salt content may be higher than in sea water
higher than in sea water