2. Methodological Considerations

In addition to a review of the scanty available literature commenting on failures, this article principally uses the information obtained from a questionnaire submitted to Quaternary palynologists who, to our knowledge, have, at any time, been active in palynological work in the Iberian Peninsula. An e-mail list of 46 colleagues was built from directories of the APLE (Spanish-speakers Association of Palynologists), the AEQUA (Spanish Association of Quaternarists), the INQUA (International Union for Quaternary Research), and the IFPS (International Federation of Palynological Societies). We also made telephone calls to people who had been leading projects and initiatives related to Iberian palaeoecology. All the collaborators are named as authors of this article. Eight declared not to have found problems with their own analyses, in these cases exclusively conducted with material from peat bogs and lacustrine sediments. The remaining 23 individuals (50% of the list) to whom the questionnaire was sent did not reply.

Why so many failed to participate is perhaps an interesting matter for sociological research that is outside the scope of this article. Possible causes are: lack of records of failed pollen work; a poor tradition of collaborative research; bad experiences with former database initiatives; perhaps even doubts about the need for this work. Some palynologists may also now be retired or deceased. In any case, it seems logical to consider that the number of sites listed here (221) is surely less than the total. In addition, even if there was a regional distribution among the non-answers, and taking into account that several areas of Iberia, like the humid north-west, have been more intensively explored and studied than others (Carrión et al. 2000a; 2008), this article cannot deal with possible geographic trends in sediment sterility. This is unfortunate, because the Iberian Peninsula contains an important physiographical heterogeneity (Vera 2004). Therefore with a more complete dataset, several tendencies might have become detectable.

The methods of sampling and laboratory analysis declared by contributors are the usual ones. Thus, most drilling in lacustrine and peaty sediments was done using Russian, Hiller, piston and window corers and rotary drilling (Birks 1986; Leroy 1990). Only rarely were open sections sampled in accessible peat bogs (Carrión and van Geel 1999). Cave sediment sampling from stratigraphical sections followed Girard (1975); Burjachs et al. (2003), or similar (Dupré 1988). Coprolites were cut open and material from the centre was scraped out to minimise contamination from external surfaces (Carrión et al. 2001a). Sometimes, the totality of the coprolites was treated after cleaning the surface with distilled water (González-Sampériz et al. 2003b). Independent of the materials, laboratory treatment was performed following the classical HCl, HF and KOH method (e.g. Girard and Renault-Miskovsky 1969; Faegri and Iversen 1975; Moore et al. 1991; Bennett and Willis 2001). Mineral separation with heavy liquids (Goeury and de Beaulieu 1979; Dricot and Leroy 1989; Nakagawa et al. 1998) was common not only for minerogenic sediments, but also in organic layers of salt marshes, deltas, lagoonal sediments and lacustrine ones. In other cases, sieving was done at 10 microns and also at a coarser mesh (larger than the largest pollen grain). So, even with presumably pollen-rich sediments, Iberian palynologists tend to use complex concentration methods. Could this tradition be related to a long experience of difficulties with extracting pollen and to the diversity of the sediment when available?

Although it is generally not possible to know whether the best analytical procedure was correctly applied, to blame pollen-analysts for failures of pollen extraction seems a little unrealistic. Certainly, macerating larger samples, using sodium pyrophosphate for clays, and gravity separation to enhance pollen concentration, among other protocols, can solve some problems of concentration (Horowitz 1992). But experimental work (Birks and Birks 1980; Havinga 1984; Tipping 1987; Jones et al. 2007) suggests that, in a number of cases, the absence of pollen can be attributable to the nature of the depositional environment. Our primary goal is informative, that is, once problems with a site are known, the pollen analyst should be free to repeat the analysis or avoid further trials.

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