알겠습니다 seems to translate to something like "certainly, sir" or "very good, sir" - a formal way to show that you have understood what has been said or asked. Does the 겠 particle here have its normal meaning of a future marker, or does it have some other function?
겠 is an 어미(語尾 - 'Ending') that has five meanings. It is used to:
Convey future prediction/speculation.
Ex: "지금 공부를 시작하면 밤 8시에 끝내겠어요." - "If I begin studying now, I will be able to finish by 8 o'clock.
Convey the intention of the subject of the sentence.
Ex: "나는 하루종일 자겠다.' - "I will sleep all day."
Ex: "이 일은 재가 혼자 다 할 수 있겠습니다." - "I will be able to do this word all by myself."
Make an oblique, euphemistic statement/question in order to offer a suggestion.
Ex: "그 음식 당신 혼자다 드실 수 있겠어요?" - "Will you be able to eat all that food by yourself?"
[The fifth meaning is a hard one to explain - the situations which 겠 Ending is used for are about either A, when a speaker expresses confidence in their conclusive assumption they have reached after a chain of thought, or B, when a speaker makes a rhetorical statement about their current situation. Half of the sentences that uses 겠 that belongs to this category are idioms and proverbs, which makes explanation for this even harder.]
Ex #1: "별꼴을 다 보겠네." - Translated literally, it means "[I'm] seeing all sorts of sights/spectacles." An idiom that has a similar meaning in English would be "Now I've seen everything." This is a rhetorical statement.
Ex #2: "그 사람도 나를 기억하겠지." - "I'm sure that person will remember me." Most (if not all) sentences that starts with "I'm sure..." will belong to this category, the conclusive assumption.
I found out that the phrase "알겠습니다" belongs to the fourth meaning, upon further research. Turns out it can be both statement and question.