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8 September 2000

Deep Secrets

Dunn Middle School is off to Catalina Island next week, so the ocean is on my mind. We all know about food chains and recycling, but isn't the ocean different? Here on land, plants and animals live and die, and their waste is quickly recycled back into the food chain by scavengers, especially bacteria and fungi. But in the deep ocean, the detritus of life sinks into the abyss, out of reach. There are scavengers in the depths, but they mostly stay there. How are marine ecosystems possible? Why doesn't the ocean run out of raw materials?


The ocean floor at Catalina Island is rich in life and remarkably clean, thanks to bottom-dwelling decomposers like lobsters and sea cucumbers. The deep ocean is different, and organic material accumulates in the cold dark abyss. But what goes down comes up in the natural process of upwelling. This brings nutrient-rich bottom water back to the surface and back into the food chain. Upwelling zones like Point Conception on the outer edge of the Santa Barbara channel are busy with life. They support the world’s most productive fisheries.

Treebeard and Julie getting ready to do some research at Catalina Island, while DMS students share lunch with
Jean-Michel Cousteau. The wetsuits are as uncomfortable as they (and we) look, but they feel better in the water.

Notes:

We had a great time on our Dunn Middle School trip to Catalina Island. You can read some of the kids' impressions in the DMS Friday Newsnote (22 Sep 2000).

We stayed at the Catalina Environmental Leadership Program (CELP) camp at Howlands Landing on the California side of the island, a few miles from the Catalina Isthmus. This camp is sponsered by Catalina Island Camps and Jean-Michel Cousteau's Ocean Futures Society. It was our good fortune that Jean-Michel Cousteau and marine biologist Dr. Richard Murphy were our guides, along with a great group of naturalists. What a treat! There are photos of our adventure on the DMS Catalina Trip page. It was a special treat for me that the CELP program director, Patrick Bacalis, remembered me as Treebeard from his 6th grade school trip to the Santa Barbara County Schools' Outdoor School many years ago, where I got started teaching kids. That's the real reward for teaching!

In coastal areas like the kelp forests around Catalina Island, there are classic examples of food chains/webs. Giant Kelp uses air bladders to rise to the surface to capture the sun's energy and grow, providing habitat for many fish and other creatures. Kelp Snails eat the kelp. Octopus is a a predator that uses its beak to drill neat holes in the snails' shells and consume them. Fish eat the octopus, utilizing the sun's energy a step or two removed. Animal waste sinks to the bottom and the garbage cleaners of the kelp forest such as lobsters and sea cucumbers take it in. As Dr. Richard Murphy eloquently says, "What comes out of them is cleaner than what went into them." The ocean bottom in these coastal waters seems much cleaner than the forest ecosystems I'm used to. Organic detritus disappears quickly in a classic food chain that we could see on our dives.

The coastal kelp forest is remarkably clean, thanks to bottom-dwelling decomposers like sea cucumbers. That's the
back-end in the picture! "What comes out of them is cleaner than what went into them." Photos by Dr. Richard Murphy.

Deep ocean waters are different. Organic waste sinks beyond the reach of these shallow-water decomposers, away from the sunlight and warmth and oxygen of the surface. Upwelling is an oceanographic process that brings these deep, nutrient-rich waters back to the surface. Upwelling occurs in places like Chile, Point Conception on our central California coast, and West Africa, where winds and currents push the coastal waters away from the coast. When the deep waters are brought back to the surface, they explode with the diversity of life we saw at Catalina. One source on the Web says, "Only about 1/1000 of the oceans' surfaces have natural upwelling, but these areas account for nearly half (44%) of the world's food fish." But that's not enough to sweep the entire ocean floor clean. Organic sediments collect.

We can see layers in the atmosphere in the clouds, which make physical gradients visible. We experience layering in lakes when the surface is warm, but it's freezing cold a few feet down when we jump in! At Mono Lake, Yellowstone, and the Salmon River, there are hot springs that are too hot, and they won't mix with cold water to be comfortable because they stay in separate layers. It's either too hot or too cold because the waters won't mix.

There are layers and sharp gradients in the ocean too. There are many factors:

The deep ocean is cold and dark and anoxic (without oxygen), just the right conditions to produce oil in the depths. The Black Sea gets it's name from the color of its sediments, not its water. The oxygen-rich fresh water surface water from the Danube and other rivers is a cap on deeper, anoxic, salt water. There's no natural upwelling to mix the deep organic sediments with the surface ecosystems that could use them. Here is a place where oil is being made. Similar conditions occured world-wide during the Cretaceous period, and around 60% of our current petroleum reserves are from the Cretaceous Age. When we burn fossil fuels in our homes and cars, it's really the last step in an ancient food chain that goes back many millions of years. We're bringing deep ocean organic sediments back into surface food chains to be used again!

What goes down does finally come up, but there might be a cost when too much comes up at once. When I was a kid in the 50s, there was talk about the coming ice age. Now it's global warming. But there might be a connection. Melting ice caps would produce a lot of fresh water that could make a low density cap on the ocean and stop natural upwelling deep ocean waters from reaching the surface, just like warm El Niño waters ruin the fishery in Chile. This could upset the global "conveyor belt" of ocean currents that distribute extra heat from the equator around the planet. This could actually produce a cooling trend. There's evidence that this has happened before. A recent article in Time Magazine says:

Roughly 12,000 years ago, at the end of the last Ice Age, a natural warming sent freshwater from melting glaciers flowing out of the St. Lawrence River into the North Atlantic, all but shutting down the Gulf Stream and plunging Europe into a 1,300-year deep freeze. The more that becomes known about this period, named the Younger Dryas (after a tundra plant), the more scientists fear that the rapid melting of ice could cause the catastrophe to recur.

I called this stumper "deep secrets", but I didn't really appreciate how deep it goes into the Earth's cycles. Here are some links for further research:

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Copyright © 2000 by Marc Kummel / mkummel@rain.org