I think the situation as to pronunciation as it exists today has been pretty well covered by your other answers.
But I wonder if you might have found information about this from a source that was thinking more in terms of long term history. Withycombe's The Oxford Dictionary of English Christian Names
and Miriel as common alternative spellings of Muriel
in medieval times, and says that the modern English surnames Merrell and Merrill
sometimes derive from an ancestress named Muriel
. This implies to me that back in medieval England the pronunciation of the first syllable of Muriel
rhymed more with the modern word "fur" than it does with "pure". In other words, original Muriel
didn't have that y-consonant sound in the first syllable that English speakers use today. Perhaps that somehow got into the name when it was revived in the 19th century.
And if back in medieval times some there were dialects where "ur" turned to "air", that would explain how the Merrill
is related to Muriel
Finally, in the dialect of most of the United States, Meriel
would today be pronounced about the same, just as most Americans west of New Jersey pronounce Mary
, merry, and marry the same. So perhaps the idea that Mariel
is ultimately a variation of Muriel
comes from some American linking them through the medieval spelling Meriel
? Just a thought. :)