@KINGJAMES447: Thor's Mjolnir is like a baby's pacifier. Their both crying without it.
Any other settings you didn't apply that we should know off to be more specific on this battle?
If Aquaman is in capability of either his trident or water hand, AQ wins.
If it's a H2H Combat, Thor wins.
If they're anywhere near water, AQ stomps.
And if it's to the death, Thor wins.
Not true at all. Some of Thor's greatest feats are without his hammer. He's shattered Surfer's fields of the power cosmic with his bare hands and moved the World Engine. His durability is off the charts - As he's waded through the Destroyer's disintegration beams with just his body, taken hits from Celestials, tanked super novas, etc. Thor's mastery over the elements is still more versatile than anything in Aquaman's arsenal, even with the Trident. Thor still has access to the God Blast.
If your talking about if Aquaman has the strength to puncture through Thor and inflict damage then I believe he does. Even though Thor has all the feats in the world and really tough durability, AQ was known to be the only leaguer to pierce through Darkseid and make him bleed and break the ice barrier of Graves which seemed to be indestructible at the time; both are heavily armored with immense amount of durability strength and stamina.
If they are near the water, what will Aquaman do exactly to make this a stomp? Destroy a God with a wave of water? Regardless, Thor can use the winds to carry himself above that or simply send a hurricane to force the waves back, or scoop Arthur up and blast him back out to sea & send him home. Arthur might as well not try swimming back. While Aquaman may have a measure of resistance to electrical attacks, there's no confirmation he can endure the level of power or divine lightning Thor can manipulate. Thor has harmed Elder Gods & Abstracts with that lightning.
I do believe without his hammer he becomes accustomed to weaknesses thus becoming more vulnerable to Aquaman's attacks. Being in water, Aquaman is at his domain and becomes stronger than on land; and equalizing the two in superhuman abilities after being exposed to water. Here are scans of a battle depicting Thor being vulnerable to drowning and the immense pressure of the water.
I am using Namor as an example just to be valid and use relevant scans and knowing that Aquaman is somewhat his equal; although AQ might think otherwise. Here is a scan depicting that Namor, (or any water-dwelling creature in that matter) grows stronger while in the water.
So yes, I do believe Aquaman has full advantage while underwater and think he has the possibilities of winning this match-up. Again, without his hammer, Thor becomes more vulnerable to attacks.