The existence and uniqueness of algebraic closures is generally proven using Zorn's lemma. A quick Google search leads to a 1992 paper of Banaschewski, which I don't have access to, which asserts that it can be proven using the ultrafilter lemma, which is known to be strictly weaker. Questions:

• Is it known whether the two are equivalent in ZF?
• Would anyone like to give a quick sketch of the construction assuming the ultrafilter lemma? I dislike the usual construction and am looking for others.