Last week, we reached 214 meters deep in the sediments of Lake Challa, and the unique record of East African equatorial mud is now complete! I had the opportunity to help out during the night shifts on the barge, and learned that it takes lots and lots of time waiting and staring at supermoons before bringing mud to the surface. During the second night on the barge, we had a few hours of high-speed core retrieving, slicing them up in 1.5 meter long pieces, and preparing them for transport to the lab. After we reached 185 meters on Friday morning, we gave way to the loggers from Germany. These loggers measured the coring hole for a myriad of parameters, and with this data it is easier to tie down all the pieces of core into a master sequence.
After we reached the milestone of successfully coring 214 consecutive meters of sediments (which is really a lot!), a few things needed to be done. After the scanning of the last cores in the lab, we cleared everything out very quickly, and packed the cores for transport to Minnesota, where they will be scanned, opened, and a master sequence will be compiled. We then returned to the lake for more water samples, and before we had to head back home we said our last goodbyes to the lovely Lake Challa. We hope to unravel its secrets in the years to come, starting with preliminary work on some core catchers.
And as the icing on the cake, check out this happy movie on what we did during the night and day shifts on the barge. DeepCHALLA, it has been a blast!
The first meters of core were retrieved from Lake Challa on Monday, and then all radars started moving. The teams for the day and night shifts got together and started their routine. Lunches suddenly became very quiet, as half of the people was on the barge, whereas the night teams were sleeping, and the speculations about how many meters of sediment would be recovered during a shift had started.
The depth record of 21 meters of core collected in 2006 was broken on Tuesday, when the night shift came home with 30 meters of perfectly laminated sediments. The current depth is 120 meter, which roughly corresponds to the past 120.000 years. The drill has hit a hard layer here, which has presumably formed during a low stand of the lake. A second hole has been started, for which a different drilling technique will be used to penetrate this layer and reach the underlying sediment.
Once in the lab, the cores are scanned, and core catchers are opened to take subsamples and to make smear slides. A quick glance through the microscope already reveals beautiful down-core alternations between the two dominating species of diatoms in the lake. Only power outages can stop our smooth workflow, and force us to take a break. And then having to re-scan the core once power is back…
Now that all materials and equipment are on board, the engineers are working hard to prepare the barge for coring. Yesterday, the barge was positioned and anchored at the first drilling site, and a start was made to construct the casing that will protect the drill hole. The casing consists of 3m pieces that need to be weld, so it takes a while to cover the 90m deep water column. Still, rumor goes that the real drilling will start later today…!
In the mean time, we spent a day on the lake to collect a water profile. We filled 143 bottles and vials of Challa water from 13 different depths to analyze the composition of a wide variety of elements when we get back to the lab in Utrecht. Although the presence of H2S below 50m can already be confirmed based on ‘field observations’ (or just the smell of rotten eggs).
Our spare time will be limited once the drilling starts and we have to work our shifts , so we use it now to visit nearby Lake Jipe, Grogan’s Castle, and to dance with the locals.
After a bumpy and dusty ride we have arrived in the Challa Hotel in Taveta, which will be our base during the drilling expedition. The engineers are still busy constructing the barge from which the drilling will happen. The preparations, and especially the transport of all materials (heavy tubing, drill mud, cables, ...) take quite some time due to the steep slopes of the crater and the absence of a decent path up and down the rim. There is an endless amount of porters carrying equipment down the crater to the barge, which is getting more and more prepared for the real work!
in the mean time we have set up the lab in which the cores will be collected, scanned, and subsampled. We have been trained on the core scanner, so we know what to do when cores come in during ours shifts. Loes will work here in the night shift, whereas I am scheduled for the day shift. The variety of nationalities and equipment brought results in an interesting collection of plugs and adaptors, but everything is tested and seems to work (for now), so let the drilling begin!
Lake Challa is a crater lake in equatorial eastern Africa at the foot of Mt. Kilimanjaro. The lake's sediments host an archive of past climatic and ecosystem dynamics of at least the past 250.000 year, or the past two full glacial-interglacial cycles. The DeepCHALLA ICDP project aims to obtain a core to generate high-resolution records of tropical climate variability at inter-annual to millennial timescales.
Loes and Francien from the Organic Geochemistry group at Utrecht University have joined the international group of scientists on the drilling expedition, and will post updates on the project on this blog (internet connection permitting).