FeMO2 Dive Cruise 2007
Report Day 05 -- Monday 15 October 2007 -- About Oxygen Deprived but Iron Loving Microbes
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FeMO2 Dive Cruise 2007 |
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About 10 pm the chief scientist came to tell us the engineers had found and repaired the engine controller. Once the ship could maintain position again Jason was lowered to the bottom and resumed its work. By this time I was in bed and when I awoke Medea was being brought aboard followed quickly by Jason. The Jason recovery is very efficient and quick - all 10 of the Jason team work to bring the submersible aboard. Jason floats so low in the water that every wave and swell slightly submerges it.
Once aboard and strapped down, the scientists converge on the sample boxes, Niskin bottles and slurp sampler. They retrieve their samples and take them straight to the lab or place them in a refrigerator set at the same temperature as the bottom water here - about 4 degrees Celsius.
A short time later the deep-sea elevator is sent an acoustic signal that causes it to release its anchor weights and it floats to the surface carrying more samples. Among the elevator samples are 2 titanium water samplers designed to capture hot water spewing out of the volcano. The water is analyzed for the major elements dissolved in it. The hot water was originally seawater, but it has percolated through the basalt of Loihi and been heated by the magma below. In fact, it erupts from the volcano the way a hot spring would erupt on land.
The seawater erupting from these hot spring vents has given up some chemicals to the basalt and the basalt has given up some of its chemicals to the hot water. Knowing the original composition of both the water and the basalt allows scientists to calculate how the water and rock reacted and estimate the temperature of the reactions that must have occurred. Because high temperature reactions and low temperature reactions result in differing dissolved chemicals, it is possible to measure the concentration of these chemicals to calculate how much water reacted at high temperature. Olivier tells me that currently the venting water is dominated by low temperature reactions that make the water more acidic and cause it to dissolve iron from the basalt. Loihi vent water is high in CO2 and in iron, two chemical species that the iron oxidizing microbes can use for energy.
On a side note: Loihi, while just a large bump on the side of Mauna Loa is a very big feature in the deep sea. Olivier shows me a map of the volcanic plume, as measured by volcanic Helium dissolved in seawater, extending east from Loihi 2,500 miles across the Pacific to Baja California. The summit of Loihi is about 1,000 meters deep and the greatest concentrations in this plume are found at that depth.
It also should be noted that these microbes are chemoautotrophs (aka chemo-synthesizers), that is, they can make their own food using chemical energy. We are all aware that plants make their own food using solar energy and we call it photosynthesis. But these little microbes can make food using chemical energy and don't need light energy at all. They can do it because the iron dissolved in the vent water is reduced - in other words it is oxygen poor and if given the chance it will react with more oxygen. When the iron reacts with additional oxygen a little energy is released. This reaction happens all the time and we call it rusting and rust is iron oxide. But if microbes with their special metabolism can control the oxidation of the iron, the microbes can capture that energy that is normally lost. With this energy they can make food and grow.
These microbes have been known for a long time in acid environments such as occurs when rain water percolates through mine tailings, but until recently we did not appreciate how common these iron oxidizers were in environments that are not strongly acidic. They can work at near neutral pH. And iron is the fourth most common element in the crust, so they are much more widespread than once thought. They seem to have been overlooked because they are slow growing and therefore easily overwhelmed by competition from faster growing organisms. Where they are most obvious is in the deep ocean where there is little food for competitors and it is dark and cold. With basaltic ocean crust covering about two-thirds of Earth and containing about 10% iron there is a lot of energy for these microbes in the deep, dark sea. With an area this large for these microbes to oxidize iron and make food they are likely a very important part of Earth's iron and carbon chemistry.
Mid-afternoon the scientists make a CTD rosette cast, and then the ship leaves the summit of Loihi to return to the deep vents of Ula Nui. At Ula Nui Jason will be returned to the deep.
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