DeepCHALLA subsampling party at the Universiteit Gent...by Heather Moorhouse

The DeepCHALLA sampling team.

DeepCHALLA is an International Continental Scientific Drilling Programme project investigating ~250,000 years of climate change and ecosystem dynamics in Equatorial East Africa, using lake sediment cores from Challa, a 92m crater lake on the flanks of Mount Kilamanjaro in Kenya/Tanzania. Dr Heather Moorhouse from Lancaster University details her trip to Gent, Belgium where subsampling of the cores was undertaken in order to gather the material ready for analyses of isotopes from bulk organic material and diatoms (algae with silica cell walls), jointly undertaken at Lancaster University and the Stable Isotope Facility, British Geological Survey.

In mid-June, amidst a continental heatwave, scientists across the globe from ten different research institutes, descended on the Department of Limnology in Gent, Belgium to collect subsamples of the drilled sediment cores which totalled ~214 m in length, retrieved from Lake Challa, Kenya/Tanzania earlier in the year. In total 9459 subsamples were collected, of which over 1000 samples were collected by yours truly. Luckily for us subsamplers, the laboratory where we spent our days had air conditioning and boasted a picturesque botanical garden next door; perfect for picnic lunch breaks in the sun.

The success of the sampling can be attributed to the hard-work undertaken by the members of the DeepCHALLA team who visited the National Lacustrine Core Facility (LacCore) in Minneapolis, USA just after the core had been retrieved. Here, the composition of the core was described and logged, and from this, the optimum depths at which to take the samples were meticulously determined, taking care to avoid turbidites (sediment deposits resulting from slope failures), cracks in the sediment and tephra layers; which are a fragmented material emitted from volcanic eruptions (unless of course you are a member of the team from the University of Cambridge who is investigating the nature of the tephra deposits in Challa). The excellent condition of the sediment cores and the well-preserved laminations of the sediment at Challa, caused by changes from diatom-rich deposits to darker organic material, made the subsampling preparation relatively straightforward and ultimately, is what makes this a model dataset to work on.

From L-R: Example of laminated sediment layers and a tephra layer (pinkish band) can be seen; Sediment core with a
 turbidite.

I was amongst the subsamplers who had to extract the amount of sediment required for each analysis from a core section at a given depth. Care had to be taken not to contaminate the sample with material from other depths or layers, harder than it sounds especially when the sediment was crumbly. Different analyses required different sampling resolutions so a chain system was created to maintain a continuous workflow, with different people sectioning different cores and depths at the same time. Once all the samples had been taken from each core section, the holes in the core are infilled with foam to prevent collapsing and contamination of different sediment layers then repackaged and put back in cold storage. We quickly developed an efficient sampling system and our quick pace resulted in us finishing a day early (fantastic chance for sightseeing and sampling the local cuisine of beer (very strong, be warned!) and frites).

Not a bad commute home; Gent at night!

Huge thanks go to Dirk Verschuren, Thijs Van der Meeren, Yoeri Torsy and the rest of the team at the Universiteit Gent who put in the hard graft in organising this sampling event. I eagerly await our next project meeting to see how all the analyses and results are coming along. Now, to get started in the laboratory…

DeepCHALLA is live!