Briefly, my charge here is to give you an overview of the issues that will be discussed this morning and talk about the purpose of the workshop.--

imageThe first slide is just to remind us why we're here: The Earth is warming, at least that's what the evidence suggests. This graph shows, the average atmospheric temperatures for the last thousand years and here we are in 1998. So there's fairly convincing evidence that we're warming, and there's also very good evidence that carbon dioxide has dramatically increased in the atmosphere since the beginning of the Industrial Revolution.

imageThis slide shows CO2 in the atmosphere for the last 150,000 years. I always like to show the data on this scale because it is quite clear that we're headed for an atmosphere that's very different from what we've experienced in the recent history of the Earth.

imageI'd also like to remind everybody that the reason that CO2 is increasing in the atmosphere is that we've been burning fossil fuel and putting it into the atmosphere, and we've changed our land use practices. Deforestation has also caused an input of CO2 in the atmosphere. So these two inputs are superimposed on this very complex and very dynamic global carbon cycle.

What we're dealing with here is a source problem, and in terms of a long-term sustainable solution to this problem, we really have to keep our focus on where the CO2 is coming from.

imageRecently, people have become interested in the ability of the oceans to draw CO2 out of the atmosphere. The oceans play a critical role in the global carbon cycle. Part of that role involves what is called the "biological pump", and this is really the focus of this three-day workshop.


That simple "down arrow" in the ocean on the previous diagram is really a very complex food web that is the underlying engine for the pump. Phytoplankton, which are microscopic photosynthetic plants in the oceans, draw CO2 out of the sea water and use it in photosynthesis in order to grow. They're eaten by zooplankton, and small animals and fish, and as these organisms respire they convert the phytoplankton biomass back to CO2. Thus there are huge CO2-in/CO2-out fluxes in the surface ocean.

But some fraction of that biomass produced by the phytoplankton finds its way to the deep ocean, where it's regenerated to CO2 - thus creating a concentration gradient of CO2 from the surface to the deep ocean, and maintaining a large reservoir of CO2 in this deep ocean ecosystem. It is well known that the fraction of phytoplankton biomass that makes it to the deep ocean is related to the entire structure of this complex community.

And it's well known that the rate of photosynthesis of the phytoplankton is a function of the amount of nutrients that are available to these cells. Most of those nutrients, especially nitrogen and phosphorus are supplied to the sun-lit surface waters from upwelling of the deep ocean water.

For years we thought that nitrogen and phosphorus were the key nutrients that limited photosynthesis in the oceans, but there were some puzzling observations. Looking at satellite img of the global distribution of phytoplankton biomass, we can see that it varies tremendously. imageWhere you see green and red and yellow, on this map are areas of high phytoplankton biomass, and where you see purple and blue, low phytoplankton biomass. But we have learned that in the equatorial Pacific, the suparctic Pacific, and the Southern ocean, there are much higher levels of N and P than one would expect based on the relatively low phytoplankton biomass. Why aren't these regions more productive?

In other words, if the phytoplankton were utilizing all of the available nitrogen and phosphorus, these regions would have much higher levels of phytoplankton. This was a real enigma to oceanographers for years until the late John Martin developed his iron hypothesis. He proposed that the reason the phytoplankton can't utilize the available nutrients in these areas-- primarily the Equatorial Pacific and the Southern Ocean -- is that there's not enough iron available to them.

Back to Top Page | 1 | 2 | 3 |

American Society of Limnology & Oceanography - © Copyright 2002
Disclaimer & Directions for Downloading
Site Design Credits