imageThe FeEx site was about 5 south, 90 degrees west, and is in a region characterized by fast currents on the order of 2 knots. These high flow ocean areas poses a particular challenge to biological and chemical oceanographers trying to do an open ocean enrichment experiment

The first challenge was just trying to track where this patch goes. We deployed a buoy that drifted along with the iron-enriched water and reported the position back to the ship every few minutes. A large shower curtain-like device called a drogue anchored this buoy in the water column.

imageThis buoy then became the reference point around which the iron enrichment experiment was conducted. The other challenge was to find a way to add iron to the surface waters. We did that by filling large tanks, adding iron sulfate. In addition, a imagetracer of sulfuric hexafluoride was added to the tanks that enabled us to detect where iron was applied. We then injected this solution into the surface water at the stern of the ship. So the ship's propeller actually functioned like a blender and the ship acted like a tractor as the boat steamed out across the Equatorial Pacific, laying an enriched patch of iron.

imageTo give you an idea of the scale of this experiment, here is a West Coast example. The size of the patch would represent a significant portion of Monterey Bay, which is a 100 square kilometers.

imageTake a look at this slide which depicts the phytoplankton's ability to harness life's energy, and imagine that this red color represents "happy" phytoplankton and these blue colors represent sad phytoplankton.

As one steams across the patch, one can essentially measure the happiness of the phytoplankton. We find, in fact, where iron was enriched, the photosynthetic ability of the phytoplankton increased to their maximum values within a very short time. Some of the first indications that this experiment was working were achieved after about two hours.


imageIn terms of plant biomass, the dark blue line represents the ship's track as we map out distribution of, in this case, chlorophyll right around the buoy. And you can see that there was essentially a 40-fold increase in chlorophyll concentrations in this area.

imageI'd like also to give you a sense of what it's like to be on the cruise. Many of us have had experiences on board ship, but many of us have had no experience in terms of manipulating a marine environment. This cruise, I think, represented sort of a change in my career as an oceanographer. The results that we found were staggering and, in some cases, gut-wrenching. I'm going to show you what the water looked like as a result.

imageThis is a result of what's supposed to be a zooplankton tow. The mesh size of this net is supposed to be large enough to let the phytoplankton through to capture all of the zooplankton, but you can see that we were bringing up huge wads of phytoplankton in the net--so much so, in fact, that this one square meter of net actually ripped apart under the weight of its contents.

imageThis picture is from a tow that was taken outside the enriched area, and this is from a tow that was taken inside the enriched area.

This is somewhat complicated, but please bear with me. The colors here represent different types of phytoplankton in the enriched area. The panel on the left indicates the population of phytoplankton outside the imageenriched area and those on the right represent those inside. The bottom axis represents size. You can see that before the area is enriched, this environment is characterized by relatively tiny phytoplankton and as one enriches with iron, one gets tremendous bloom of these larger cells.

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