[zeristor]

If this is the case then the benthic sediments would be of food that hadn’t been eaten far higher up in the water column.

Wouldn’t it be fairly pristine? Ships that sunk, and or whales and fish that expired.

Are whales in the sea referred to as megafauna, or is fauna just for land animals?

Where these waters become more oxygenated they would be a lot more life, oxygen permitting, wouldn’t there?

[pvaldes]

Whales are megafauna, yes. Fauna means anything in the Kingdom Animalia.

[causi]

If it supports very little life then there's very little life to die there and sink.

[kuhewa]

Generally the oxygen minimum zones aren't extending up into the photic layer near the surface which does support a fair amount of life.

[zeristor]

There’s Oxygen near the surface just not further down in the depths.

Whales could swim through an area since the surface to breathe, but could pop their clogs at any time (I assume).

[kuhewa]

Anaerobic microbes will still be able to do a job of it, albeit slower