The old Sodankyla church was built in 1689. Nine cores from beams at this church have been measured and archived. Briffa 2008 used one of 9 cores. Why only one of 9? Your guess is as good as mine.
Proving that Briffa only used one of 10 cores isn’t entirely trivial, though I think that it can be proved quite convincingly. At the request of Phil Trans B, Briffa archived his Finnish and Swedish measurement data, but, just to make things interesting, he did so without any metadata saying where the data is from. I sort of like decoding these little puzzles set by the team and I’ve been working at this one and have posted up some reference materials for interested parties.
First, I collated the measurement data archived by Briffa in “Tucson format” (an obsolete 80 column punch-card format) into an R-table. The original data is here. You can download my collation (as an R data frame) as follows:
briffa=tree; dim(briffa) #  188618 4
It’s always handy to make an information file for start and end dates of the cores. This can be done as follows:
Squinting as this information table, the first 431 entries are sorted by decreasing end date; the next 591 are sorted by increasing start date. The original article says that there are 430 samples from Finland and 587 from Sweden. So it appears highly likely that the first 431 entries are from Finland and the last 591 are from Sweden, with a slight inaccuracy either in the table in Briffa et al 2008 or in the SI now provided. The nomenclature is different as well with the first 431 having alphabetical starts, while most of the Swedish series have numerical starts.
The primary references for the Finnish data are Helama et al 2002 (Holocene) and Eronen (Briffa) et al 2002 (Holocene).
The Swedish Tornetrask data (Grudd et al. 2002) and Finnish–Lapland data (Eronen et al. 2002; Helama et al. 2002), for pine (Pinus sylvestris), were combined to create a single Fennoscandia regional chronology.
Eronen et al 2002 mentions IDs passim that have a similar appearance to the Briffa IDs. Some Finnish data pertaining to Helama et al 2002/Eronen et al 2002 has been archived at WDCP/ITRDB, but the archive is unfortunately spotty. The Swedish data (Grudd et al Holocene 2002) is entirely absent from ITRDB, though earlier Schweingruber data from Tornetrask is archived (and there might be some overlap).
I spent some time trying to match IDs numbers and found a few matches and report today on an interesting match for the old Sodankyla church (which is mentioned in Eronen (Briffa) et al 2002), which states:
Samples from the old Sodankyla parish church, nine beams in all, were also used (Lindholm et al., 1999).
Measurement data for Sodankyla church is archived at ITRDB. You can download my collation as follows, which shows that all the series have NGC in their ID format (and lists 9 beams (2 ores each), as in the article (though one ID (0008) is missing).
# NGC0001A NGC0001B NGC0002A NGC0002B NGC0003A NGC0003B NGC0004A NGC0004B NGC0005A NGC0005B NGC0006A NGC0007A NGC0007B NGC0009A NGC0009B NGC0010A NGC0010B
Now let’s look up this code, NGC, in the Briffa information file. This yields one series NGC0003X ending in 1687 (just before 1689 construction).
# 100 NGC0003X 1497 1687
It looked like Briffa (Eronen) et al might have averaged the two cores NGC0003A and NGC0003B and this indeed proved to be the case. The following script yielded the figure shown below:
Helama et al refer to selecting a subset of living trees as follows:
The number of living trees used here to construct the ‘modern’ section of the chronology was limited to 50, in order that the recent era should not be over-sampled.
But there is no mention of “limiting” the number of beams from Sodankyla; quite the opposite. They say that 9 beams were used, but it appears that only one was used. So what happened to the other 8 cores? Not that I understand the need to “limit” the number of modern trees, given that an average is later taken. Surely this creates potential selection bias. How were the 50 series selected? And what was the effect?