This video, we're going to talk about the marine pelagic zone as an aquatic biome. And so the marine pelagic zone is also known as the open ocean, and it consists of the entire ocean from the surface down to just above the ocean floor. And so you might recall from our previous lesson videos when we talked about the zonation of marine biomes that we already defined the pelagic zone as the nearshore shallower idic zone plus the offshore deeper oceanic zone. And so this makes the marine pelagic zone the largest biome on earth by far as it's found in all of the world's oceans, and it covers about 3 quarters of the earth's entire surface. Now interestingly enough, the aquatic productivity of the marine pelagic zone actually varies, and this is because of how vast the marine pelagic zone is.
It is enormous. Now what you'll also notice is that here we're showing you a bunch of different gradients that exist with the depth of the ocean water. And so, the first gradient that we have here on the far left is a sunlight gradient, and so there is high sunlight towards the surface. But as you go deeper and deeper into the ocean water, the amount of sunlight gets lower and lower, and eventually, you'll get to an area that's characterized by complete darkness. Now the next gradient that we have here is an oxygen gradient, and it is also going to be a decreasing gradient with depth.
And notice the next gradient that we have is for biomass. Again, it's a decreasing gradient. But interestingly enough, notice that this last gradient is a nutrient gradient. It actually increases with depth, unlike the other three gradients that we just talked about. And the reason for this is because the biomass that's at the surface of the water, when it dies, the dead decaying matter will tend to sink to the bottom of the ocean, and along with it, it will bring nutrients.
And so here, what we're saying in the text is that, generally, there's a decreasing biomass gradient that exists with depth, but there's an increasing nutrient gradient that exists with depth, and that's exactly what we just talked about here. So this here concludes our brief lesson on the marine pelagic zone.
