29. July, 2014
The “micro team” has been busy analyzing the microbes living in the sediments thousands of meters below the sea surface. One might think that there couldn’t be much life down there but despite the extreme pressure and freezing temperature (below zero) microbes thrive and can be counted in millions per gram of sediment. Their main food source is organic material produced in surface waters and after passing through the water column it eventually settles on the sea-floor. Some microbes use oxygen (as humans) when they degrade this material, others can “breath” with e.g. iron, nitrate, manganese or sulfate. Others again do not even need organic material but gain energy from catalyzing inorganic reactions such as coupling CO2 and hydrogen to produce water + methane + energy.
Anyways, enough micro nerdines, what I really wanted with this blog was to explain a bit about the way we get the sediments up on the ship in the first place. Basically we lower a long plastic tube (core liner) to the sea floor (read more about the gravity core here). It has a very heavy lead block attached at the top and a “core catcher” allowing sediment to go in but not out, in the other end. Then we penetrate the sea-floor with approximately 4 km/h and retrieve the core onto the ship with a winch. Now, in principle this is a very simple operation, especially when you are operating in regions where the sediment cover is thick and homogenous. This is NOT the case in areas close to hydrothermal/volcanic activity. Here you often find hard layers of volcanic ash within the first couple of meters and thus the core liner breaks and then forever bound to the sea. Another obstacle is “drop stones”. Drop stones are stones that are carried by glaciers during ice ages to the sea, and when the ice retreat (melt) the stones are “dropped” to the seafloor. Here they can lie undisturbed for thousands and million of years until either transported to the subduction zone and melted or hit by a scientist core liner in his or hers attempt to collect sediment samples. The result of the latter is often that the core liner brakes. As you might have guessed this has happened a time or two during this cruise. Normally a broken core liner means a lost core, however, this year the new temperature loggers have saved our core a couple of times, even though the liner broke. The reason is that a steel wire runs all the way from the lowest temperature logger and all the way up to the lead block in the top (this might become clearer if you have a glance at one of the pictures). In effect this means that although the core liner is broken we can still recover it and if we are lucky the liner might still contain sediment all the way up to the braking point.
Preparing the gravity core before deployment. Temperature loggers are fittet on top of the core liner and a steel wire runs along the length of the core liner and are attached in the “bomb” head. Photo: Michael Melcher
Gravity core being deployed from the ship hangar. Photo: Ingunn Thorseth
Broken core liner, but the steel wire connected to the temperature loggers enabled us the save both the loggers and the sediment in the lower half of the core. Photo: Michael Melcher
This was all very good and very helpful but all good things comes to an end and yesterday morning the steel wire gave up and not only the core was lost but all the tree temperature loggers have now found their final resting place at the bottom of the sea 2465 meters below the seafloor and at a temperature of -0.765 (the temperature is obviously nothing more than a qualified estimate from me side).
Retrieval of one broken core liner. The steel wires snapped and the remaining 4 meters of core liner and three temperature loggers are to be found more than 2000 meters below the ship. Photo: Michael Melcher
I must admit that this was not one of the highlights of this cruise, but it did help that we got a beautiful 3.5 meter long core 1.5 hours later at the same site. I also helped that the special group of microbes that we have been searching for was actually present in that core and in very high amounts.How do we know they are present, the alert reader might ask. Basically, we crush all the cells, extract all DNA present in the sample and then we are searching for the genes that we know belongs to this specific type of organisms. When (or if) we have found them we stain the DNA with a fluorescent dye so that we can visualize the DNA. The whole process from the core goes down until we know if we have the organisms of interest takes about 14 hours. Then starts the laborious work of trying to get them to grow in the laboratory but that’s another story.
Visual proof that the organisms of interest are actually present. The fluorescent bands are DNA fragments from the microbes we were searching for. Photo: monsieur Cedric Hamelin
This is by far the only stuff going on in the “micro” lab; Desiree is estimating sulfate reduction rates and Rui are doing both de-nitrification, anammox and nitrification rate measurements.
Michael Melchner transfering microbes from the deep ocean floor to lab cultures and hope that they will grow. Photo: Steffen L Jørgensen
Rui Zhao are preparing de-nitrification experiments inside an anaerobic (without oxygen) gloveback. Photo: Steffen L Jørgensen
Last but certainly not least the geochemist are analyzing the pore water (the water in the sediment) for geochemical composition as soon as the water is extracted from the core.
Pore water is extracted from the sediment cores by deploying rhizon samplers at regular intervals. Photo: Michael Melcher
Their data not only helps us select the right samples for further analysis but enables us to predict what the different microbes are doing in the sediment and how much and how fast they are eating. This might seem trivial and without interest for people outside academia, however, mine damen ünd herren it is of immense importance for you, human kind and all life in general. Their activity level is a key controlling factor in determining the oceans and hence also the atmosphere’s chemical composition. In other words – If these organisms for one reason or another change their activity level significantly, you and I would no be here anymore.
With these dramatic words I will end this blog.