The OT Background to Jesus' Baptism

Ian Paul has an interested discussion here on the OT background to Jesus' baptism focusing particularly on Matthew's account. 

I would make just one minor comment concerning Paul's statement that, "Contrary to all artistic depiction (including the mosaic above from Ravenna), what happens next occurs after Jesus has ‘gone up out of the water’, in other words, once he has left the river and is on the bank once more." While the text does state, "Jesus came up immediately from the water" (NASB), this does not have to mean that he would have have to have go to shore. For example, one could say that "a whale came up out of the water." Furthermore, the idea of "immediately" (εὐθὺς) seems more naturally to refer to coming up out from under the water than hastening back to shore. So, I am not sure certainty is warranted in either case.