JOURNAL OF QUATERNARY SCIENCE (2010) 25(5) 828–829Copyright # 2010 John Wiley & Sons, Ltd.Published online in Wiley InterScience(www.interscience.wiley.com). DOI: 10.1002/jqs.1420

Correspondence

Reply to Comment: A Last GlacialMaximum pollen record fromBodmin Moor showing a possiblecryptic northern refugium insouthwest England

ANN KELLY, DAN J. CHARMANand REWI M. NEWNHAM (2010)Journal of Quaternary Science 25: 296–308

We are grateful to Scourse (2010, this issue) for drawing atten-tion to the uncertainty that we ourselves felt when confrontedwith the palynological data and the sequence of acceleratormass spectrometric 14C and optically stimulated luminescence(OSL) age estimates from Dozmary Pool mire. We agree thatalternative explanations to the cryptic refugia hypothesis arepossible and sought to identify and assess these in the discus-sion section of the paper. We deliberately used the term ‘pos-sible cryptic northern refugium’ in the title to draw attention tothe uncertainty associated with the data from this intriguingand (so far) unique site from the region.

Scourse raises four issues in preferring an alternative expla-nation to possible local presence of trees: (1) the low pollenconcentrations; (2) pollen taphonomy and the origin of thesediments; (3) comparisons with modern pollen spectra fromtundra environments; (4) reworking from local sediments.Here, we comment briefly on each of these issues in turn, buthave grouped our comments under issues relating to the pollendata sources and those related to the sedimentary processes asthey affect the record.

Pollen concentration and long-distancetransport

While accepting that pollen concentrations were low through-out the pre-Holocene record from Dozmary Pool, they werenonetheless of sufficient volume to allow counts of > 300 totalland pollen (TLP) per sample in most cases. Presenting a con-centration diagram for the main taxa together with the pollendiagram may have provided some clarification, although pol-len concentrations can be highly misleading unless supportedby a fine-resolution chronology that accounts satisfactorily forvariations in sediment accumulation rates. For the record, we

would like to report an error in Fig. 4 (p. 302) of the originalpaper, which shows an incorrect curve for pollen concentra-tion. The correct version is shown here in Fig. 1. Pollen concen-trations are low but not quite as low as suggested by Scourse(2010), with average values for TLP in pollen assemblage zone(PAZ) 1 and 3 at around 5000 grains cm�3.

We agree that the results published by Frechette et al. (2008)show that present-day pollen from Picea forest may travel hun-dreds of kilometres to become incorporated within the sedi-ments of Arctic lakes. While we accept that the elevatedPicea percentages could be explained at least partly by this pro-cess, we do not believe it is possible to demonstrate conclu-sively that long-distance transport is the only explanation forthe Dozmary data, based on the modern pollen rain percentagedata from high-latitude regions.

Taphonomy and reworking

The origin of the Dozmary sediments is something of a puz-zle, but based on the mineralogy we speculated that theminerogenic fraction was mainly a product of springs feedingthe lake and carrying kaolinite. The source of the pollen isunclear and it could be from contemporary pollen rain andsurface flow from the small (<1 km2) catchment (includinga long-distance component), or springs and/or solifluctioncarrying small amounts of pollen from earlier sediments,including the potential aeolian deposits as suggested byScourse. As was noted by Scourse (2010), we suggestedreworking as a contributory process. The disagreement isover the extent of its influence on the pollen content of thesediments. Three lines of evidence suggest that reworkingcannot be the sole explanation for the pollen spectra. First,the chronological data show good agreement between OSLand radiocarbon ages and most of the dates fall in a conform-able sequence. Although the error bars on the OSL age arewide, it seems unlikely that the OSL age would be the sameas the radiocarbon age in reworked sediments. More likely,the radiocarbon age would be older than the OSL age, assum-ing the OSL sample was adequately zeroed during deposi-tion. The two outlier radiocarbon ages are at the base andwithin a zone (PAZ 2) we proposed as being likely subjectto reworking. If the entire sediment was reworked, it is unli-kely that the remaining dates would form a conformablesequence. Second, the good physical condition of the major-ity of grains suggests that the pollen were contemporaneouswith the sediments accumulating in the lake. Finally, particlesize analysis of the sediments (unpublished) did not indicateevidence of ‘pulses’ of sediment delivery and the coniferouspollen shows a continuous rather than an intermittent pre-sence through PAZ 1 and 3. Reworking might be expectedto result in a more variable set of changes through time.

Conclusion

The criticisms by Scourse (2010) of our interpretations are wellfounded and, in many ways, represent what may be considereda conventional approach to interpreting the tree pollen com-ponent of Last Glacial Maximum (LGM) pollen assemblagesfrom northwestern Europe. This approach, consistent withtraditional concepts of vegetation response during glacial–interglacial cycles, is long established and continues to guideinterpretations of new data. Indeed, our initial interpretationsof the Dozmary Pool data were more strongly aligned withlong-distance dispersal and reworking.

As we point out in the paper, however, a range of evidenceincluding plant macrofossils, mammalian faunas, phylogeo-

graphic and genetic data, and climate modelling has recentlybeen presented that now makes it pertinent to revisit this con-ventional approach to the interpretation of LGM pollen assem-blages from northwestern Europe. It is for this reason that wefelt compelled to consider an alternative approach to interpret-ing the Dozmary data. We do not claim that this is irrefutableevidence for a northern refugium, but that this hypothesis is oneof several serious competing hypotheses. Taken together withthese other lines of evidence, we certainly do not feel the refu-gium hypothesis should be rejected simply because there isanother plausible and arguably simpler hypothesis available.The direction taken by Occam’s razor depends upon underly-ing assumptions. If we assume that the Dozmary tree pollen arederived from long-distance transport or reworking then thoseexplanations are indeed the simplest and most parsimonious.If we relax this assumption, however, in the light of recent inde-pendent evidence that promotes the plausibility of tree survi-val, would Occam’s razor cut a different path?

Scourse concludes his comments with some further insight-ful suggestions for further work, including interrogation of thepollen content of local head deposits. We also heartily agreethat the rediscovery of Pattison’s site in the River Fowey valley(close to Dozmary Pool) could provide indisputable evidenceof tree survival in the area if the tree remains he describedcould be recovered and dated. We would also suggest thatthe search is widened for sediments of LGM age elsewhere inthe region and offshore to test further the hypotheses we put for-ward to explain the data from Dozmary Pool.

References

Frechette B, Vernal A de, Guiot J, Wolfe AP, Miller GH, Fredskild B,Kerwin MW, Richard PJH. 2008. Methodological basis for quantita-tive reconstruction of air temperature and sunshine from pollenassemblages in Arctic Canada and Greenland. Quaternary ScienceReviews 27: 1197–1216.

Kelly A, Charman DJ, Newnham RM. 2010. A Last Glacial Maximumpollen record from Bodmin Moor showing a possible cryptic north-ern refugium in southwest England. Journal of Quaternary Science25: 296–308.

Scourse JD. 2010. Comment: A Last Glacial Maximum pollen recordfrom Bodmin Moor showing a possible cryptic northern refugiumin southwest England. Journal of Quaternary Science 25: 826–827.

ANN KELLYSchool of Geography

Earth and Environmental SciencesUniversity of Plymouth

Plymouth, UK

DAN J. CHARMANSchool of GeographyUniversity of Exeter

Exeter, UK

REWI M. NEWNHAMSchool of Geography

Environment and Earth SciencesVictoria University of Wellington

Wellington, New Zealand

Figure 1. Concentration values for Picea, Total Land Pollen, TotalPollen, Aquatics and Spores. Note the multiplication factor for thehorizontal axis scales.

Copyright � 2010 John Wiley & Sons, Ltd. J. Quaternary Sci., Vol. 25(5) 827–828 (2010)

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