Sunday, 25 October 2015

Entering the last week

Having the checkered flag of our Lake Hamana piston coring mission in sight, we can already look back at many days of hard work and dedication. However, we still need to complete a few things.

We have been sampling sediment from four consecutive sites along a N-S transect within the lake’s central basin, north of the tidal delta. Two of these sites are entirely finished (site 1 and 2), whereas we still have to take six more 2 m piston core sections from the northern two sites (site 3 and 4).   

Location map of Lake Hamana (left) and bathymetry of the lake basin with indication of our coring sites, yellow ones are finished, red ones still need to be completed (right)

At every site we collect a total of nine cores. First of all, a short gravity core has to be taken in order to retrieve a relatively undisturbed top section. Then, we start piston coring in a first hole, acquiring sections from 0-2 m, 2-4 m, 4-6 m and 6-8 m. Afterwards, 1 m overlap sections can be gathered from a second hole, which is closely spaced to the first one. Overlaps comprise sections from 1-3 m, 3-5 m, 5-7 m and 7-9 m. Ideally, one drilling hole should be sufficient if no stratigraphic gaps existed between individual sections. Unfortunately, we can never be sure of this continuity, due to restrictions that are inherent to the piston coring system, tidal influences on the lake/platform level, drift as a result of strong currents and waves... With these nine cores, we can eventually reconstruct one complete composite core.

Schematic representation of  cores that need to be collected on each site

Our work on Lake Hamana is not just limited to hammering and getting mud tubes out of the barrel. Maintenance of the equipment is as, if not more important, because coring is impossible with corroded, rusty material that is clogged with sediment and salt crystals. After all, we are working on a brackish lake. Moreover, unexpected material failure due intensive use and other problems can unpleasantly stall our coring operations. Maintenance, reparations, modifications, problem-solving… are thus key words for time gaps in between coring and often have to be executed on our 3x4 m floating platform, which is not always that evident!

Hammering, hammering and some more hammering... there is no escaping it!
Cleaning the empty liner before inserting it into the barrel
Getting the coring barrel ready for use
Checking if the piston is still working properly, a crucial task
Some more platform maintenance
We also need to maintain ourselves with a good lunch...

... and even more importantly, a nice cup of coffee once in a while!

Luckily, our coring team’s spirit is still alive and we will give it our all during these last few days! 

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