Biological oceanography

I generally try to stay within my expertise here, but believe it or not I'm not going to far out of bounds by talking a bit about the ocean and the effects of the oil volcano at the bottom of the Gulf of Mexico. I have a master's degree in environmental policy, and I actually took some marine biology on the way to getting it.

It may surprise most people to learn that most of the ocean is what is called a biological desert -- it has very little biological productivity, and little life. The reason is that unless it is very close to freezing, warm water is less dense than cold water, which means that warmer surface water sits on top of colder water and the layers don't mix. Any possible nutrients that might support photosynthetic organisms and create a base for a food chain therefore sink below the depth where sunlight can reach. In the ocean depths, there are organisms that subsist on stuff that rains down, or on reactive chemicals that spew from hot vents along the mid-Atlantic ridge; but none of these are any fun to eat.

The only productive regions of the ocean, therefore, are cold arctic and antarctic waters -- yep, the cold parts of the ocean are more biologically productive than most of the warm parts, while more temperate waters can have seasonal productivity before the thermocline appears in late spring; upwelling zones, where deep currents hit a rise in the sea floor and shoot water upward (e.g. the Peruvian anchovy fishery); shallow coastal waters; and river estuaries and salt marshes. The latter are particularly important because they are highly productive, relatively sheltered places. Many species spawn there, and their larvae spend some time getting started before heading out to the open ocean.

That is why, bad as the effects of the disaster have already been, this is indeed worse news. Oil washing ashore from Port Fourchon to Grand Isle. "Councilman Tom Capella said this morning that oil from the BP rig explosion has washed up on Elmer's Island just west of Grand Isle. And Councilman Chris Roberts said oil was hitting the beaches in a wide area from Port Fourchon in Lafourche Parish to Grand Isle, which is the southern tip of Jefferson Parish. Even heavier oil can be seen just offshore, Roberts said."

Once those marshes and salt ponds are oiled, they will not come back to life for who knows how long. And the primary productivity they represent is irreplaceable.