50 chironomids or fewer – corrigendum for Larocque-Tobler et al 2015

Last year, Isabelle Larocque-Tobler and coauthors published a chironomid-inferred August air-temperature reconstruction for the 20th century from a Polish lake in Quaternary Science Reviews. The correlation between instrumental temperature records and the near-annual resolution reconstruction from Lake Żabińskie is remarkably good at 0.74. The mean absolute error is only 0.75°C, considerably lower than the cross-validation uncertainty in the Polish-Canadian calibration set (RMSEP = 2.3 °C).

Yesterday a corrigendum was published, reporting three problems with Larocque-Tobler et al (2015; hereafter LT15).

The chironomid stratigraphy was not consistent with the online data table

More precisely, LT15 used an incorrect version of the chironomid stratigraphy from Lake Żabińskie. The corrigendum reports several taxonomic and other changes between the published stratigraphy and the data now archived at the Palaeoclimate Data Centre (I think this is the first chironomid calibration set to be archived publicly). No explanation of how the wrong data came to be used is given.

The reconstruction obtained from the online data differed from the reconstruction published

More precisely, the reconstruction in LT15 was incorrect as there were several data processing errors including: misspelt taxa (which will then be excluded from the analysis); inclusion of lakes with low chironomid counts; and the inclusion of temperature as a species in the calibration set (this will make much less difference to the reconstruction than one might suppose).

The number of head capsules per sample used for the temperature reconstruction was below 50, the typical number used for temperature inferences (Heiri and Lotter, 2001, Larocque, 2001 and Quinlan and Smol, 2001)

This directly contradicts the claim in LT15 that

At least 50 head capsules (Heiri et al., 2001 and Larocque et al., 2001) were mounted. (Methods 3.1)

If a couple of levels in the stratigraphy had 48 chironomid head capsules rather than the requisite 50, it would matter not. Unfortunately, the counts are often far lower, ranging from 19 to 68.5. A third of counts are below 30 chironomids; only an eighth of are 50 or more. This matters because small counts are expected to have larger counting errors and hence larger reconstruction uncertainties.More importantly, readers must be able to rely upon claims made by the authors.

The corrigendum provides a new stratigraphy and a new August air-temperature reconstruction which is, like the old one, remarkably good.

LT15 has been cited eight times.

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About richard telford

Ecologist with interests in quantitative methods and palaeoenvironments
This entry was posted in Peer reviewed literature, transfer function and tagged , . Bookmark the permalink.

5 Responses to 50 chironomids or fewer – corrigendum for Larocque-Tobler et al 2015

  1. That’s interesting, thanks for highlighting the corrigendum to LT15!!

    It reminds me a little bit of problems encountered with the European Pollen Database (EPD), wheredifferences between the published pollen stratigraphy and the data archived in the EPD for some records were noted (see Fyfe et al, VHA 2009 (<a href="http://link.springer.com/article/10.1007%2Fs00334-009-0215-9&quot; ).
    We also had no explanation of how the different dataset came to be in the Database.
    However, as opposed to the corrigendum in your example, we generally assumed that the published stratigraphy showed the correct datasets, not the Database. But then it is also true that pollen stratigraphies can be “double checked” to some extent by comparison with records from sites located nearby.

  2. Sorry, the web link to the Fyfe et al. (2009) paper is wrong; should be http://link.springer.com/article/10.1007%2Fs00334-009-0215-9

  3. Eli Rabett says:

    Of the eight cites more than most involve one of the authors of the original paper. Thus are paper chains made.

  4. Pingback: The limits of high-resolution quantitative palaeoecology and Larocque-Tobler et al (2015) | Musings on Quantitative Palaeoecology

  5. Pingback: Curious chironomid counts | Musings on Quantitative Palaeoecology

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