By Alan Brenner
The International Ocean Discovery Program has three main core repositories. They are located in Japan, the United States, and Europe. The European repository in Bremen, Germany is responsible for the Arctic and Atlantic sea-floor cores. The IODP has been known as the DSDP (Deep-Sea Drilling Project and ODP (Ocean Drilling Project).
The Bremen repository takes about 30 hours to reach by plane from Canberra, and it is worth the journey. Upon arrival in Bremen, the first stop is to rub the donkey’s hoof on the statue of the Bremen town musicians, from the Brothers Grimm fairy tale.
After this tourist duty is completed, take the tram to the Universtat Bremen which is home to the largest marine sediment core repository in the world. In the cold-storage at Marum, massive walls of sediment core casings are arranged by expedition and cruise number. Cores are split into a working half and an archive half. More than one hole may are drilled at a site to provide earth-scientists with a continuous record of spliced material. Initially, the working halves are sampled, while either the working or archive halves are used for non-destructive analysis.
The primary objective for the visit to the Marum, was to take ~70 meters worth of U-Channels from a single sediment core from the Western Mediterranean. For reference, this is about a million year’s worth of sedimentation in this location. Secondly, X-ray Fluorescence Scanning needed be done to get an idea of various elemental counts down each section of core at centimeter intervals.
The core of interest was taken nearly 20 years ago from the Mediterranean and has dewatered over that time which meant that taking UChannels was difficult because a channel could not simply be pressed into the sediments – they were too resistant. To overcome this, a knife was used to cut grooves into the sediment and it was then possible to press the channel in. After insertion of UChannel into the middle of the core, a wire was pulled underneath the channel, the filled UChannel pulled out, and a lid capped to the top.
We have an XRF at the ANU RSES, but it was important to do the count-scans before taking out the ‘U-channels’. Taking measurements with the Scanner on the sediments in the original liner are more reliable then scans taken on the U-Channel because there has been less disturbance at that point. Scans are run at 1 cm resolution for each of 3 ‘runs’ (50, 30, 10kVs).
These yield a suite of heavy (Ba), medium(Br, Zr, Sr, Rb), and light (Al, Si, K, Ca, Ti, Mn, Fe) elemental counts.
As mentioned previously, there are many types of analyses that can be done on marine sediments. Some of these are non-destructive, and others are destructive. Even though destruction sounds like a negative thing, the data yielded from said procedure can be invaluable. For me, it is difficult to reconcile that such invaluable material is to be ‘destroyed’, but taking into account that sediment cores have a shelf life on the order of decades and it makes logical sense to do good science on them before their expiration date.
Some of the experiments that I will be doing for my PhD involve the destruction of a few grams of sediment per data point, but the data obtained from this are Mediterranean-temperatures from the distant past. I will post more on this procedure in a future installment. Thanks for reading!