I get what feels like muscle spasms in my upper center/upper left abdomen just below where my ribs split. these are easily felt and visible outside of the skin. what could it be?

Muscle spasms: I think your diagnosis is correct. An irritable superficial nerve or abdominal muscle is most likely causing these abdominal muscle spasms. If widespread muscle spasms or cramping were occurring, I would think of deficiencies of calcium magnesium ,potassium or sodium. However, your localized spasms should subside on their own. If not, see your MD.