Albert Barnes Commentary Job 38:16

"Hast thou entered into the springs of the sea? Or hast thou walked in the recesses of the deep?" — Job 38:16 (ASV)

Have you entered into the springs of the sea? The word translated “springs” (נבך nêbek) occurs nowhere else in the Scriptures. It is translated by the Vulgate as “profunda,” the deep parts, and by the Septuagint as πηγὴν pēgēn, “fountains.” The reference seems to be to the deep fountains at the bottom of the sea, which were supposed to supply it with water.

A large portion of the ocean’s water is indeed conveyed to it by rivers and streams that run on the surface of the earth. However, it is also known that there are fountains at the bottom of the ocean. In some places, the amount of water flowing from them is so great that its action is perceptible at the surface. One such fountain exists in the Atlantic Ocean near the coast of Florida.

Or have you walked in the search of the depth? This means, rather, in the deep places or caverns of the ocean. The word translated “search” here (חקר chêqer) means “searching,” investigation, and then an object that is to be searched out, and therefore, that which is obscure, remote, or hidden. It may then be applied to the deep caverns of the ocean, or the bottom of the sea.

This is unsearchable to humans. No line has been found long enough to fathom the ocean, and consequently, what is there is unknown. It is cited, therefore, with great appropriateness as a proof of God’s wisdom, that He could look on the deep caverns of the ocean and was able to search out all that was there.

A sentiment similar to this occurs in Homer, when speaking of Atlas:
Ὅατε θαλάσσης;
Πάσης βένθεα οἷδεν.
Hoate thalassēs;
Pasēs benthea oiden.
Odyssey (Job 1:5).
“Who knows the depths of every sea.”