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closeProper controls?
Posted by schadtc on 08 Jul 2013 at 00:08 GMT
For an important set of samples like this, I would like to see better control samples. Seems to me that they should have had both samples from the drilling fluid and samples of meltwater from higher up in the core above the accretion ice. From the methods it appears the the only control samples were from laboratory water (more of an extraction control, rather than a sample collection/integrity control.
"Two control samples (purified water, 18.2 MΩ, <1 ppb total organic carbon; and the same water, autoclaved and subjected to concentration by ultracentrifugation) also were processed using the same protocols"
RE: Proper controls?
sorogers replied to schadtc on 09 Jul 2013 at 21:40 GMT
We performed analyses on two control samples. One was autoclaved reverse osmosis water from our lab that was subjected to ultracentrifugation, as with the ice core meltwater samples, and then taken through exactly the same procedures as the ice core meltwater samples. The second control was reverse osmosis water taken through the same process as the ice core meltwater samples, except it was not subjected to ultracentrifugation. All of the sequence that matched accession numbers from GenBank that were also those indicated in the meltwater samples were removed from further analysis. Also, any other sequences from the meltwater that was closest to those same species were removed from further analysis. Additionally, sequences that were similar to those from repetitive elements, cloning vectors, and intergenic regions were removed from further analysis. We did review a list of organisms that had been found in drilling fluid from the Vostok ice core, but did not find any of these organisms represented in our dataset. This has been true for our other studies of Vostok ice core sections, both accretion ice and glacial ice. Our decontamination and washing procedure apparently removes all of those contaminants.