Assuntos
Mudança Climática/história , Ecossistema , Plantas , Pólen/citologia , Contagem de Células , História AntigaRESUMO
499 I. 499 II. 500 III. 500 IV. 500 V. 500 VI. 501 VII. 502 VIII. 504 504 References 505 SUMMARY: Ancient DNA (aDNA) from lake sediments, peats, permafrost soils, preserved megafaunal gut contents and coprolites has been used to reconstruct late-Quaternary floras. aDNA is either used alone for floristic reconstruction or compared with pollen and/or macrofossil results. In comparative studies, aDNA may complement pollen and macrofossil analyses by increasing the number of taxa found. We discuss the relative contributions of each fossil group to taxon richness and the number of unique taxa found, and situations in which aDNA has refined pollen identifications. Pressing problems in aDNA studies are contamination and ignorance about taphonomy (transportation, incorporation, and preservation in sediments). Progress requires that these problems are reduced to allow aDNA to reach its full potential contribution to reconstructions of Quaternary floras.
Assuntos
DNA Antigo/análise , DNA Antigo/isolamento & purificação , DNA de Plantas/isolamento & purificação , Flores/genética , Fósseis , Paleontologia/métodos , Animais , DNA de Plantas/genética , Flores/anatomia & histologia , Fósseis/anatomia & histologia , Conteúdo Gastrointestinal , Sedimentos Geológicos , Lagos , Pergelissolo , Pólen/genética , SoloRESUMO
Comparisons of climate model hindcasts with independent proxy data are essential for assessing model performance in non-analogue situations. However, standardized palaeoclimate data sets for assessing the spatial pattern of past climatic change across continents are lacking for some of the most dynamic episodes of Earth's recent past. Here we present a new chironomid-based palaeotemperature dataset designed to assess climate model hindcasts of regional summer temperature change in Europe during the late-glacial and early Holocene. Latitudinal and longitudinal patterns of inferred temperature change are in excellent agreement with simulations by the ECHAM-4 model, implying that atmospheric general circulation models like ECHAM-4 can successfully predict regionally diverging temperature trends in Europe, even when conditions differ significantly from present. However, ECHAM-4 infers larger amplitudes of change and higher temperatures during warm phases than our palaeotemperature estimates, suggesting that this and similar models may overestimate past and potentially also future summer temperature changes in Europe.
RESUMO
Parducci et al. (Reports, 2 March 2012, p. 1083) fail to present convincing evidence for glacial survival of Pinus and Picea in northern Scandinavia. Their methodology does not exclude contamination. Additionally, they should consider the lack of suitable habitats, the apparent extinction of both taxa after deglacial warming, and alternative hypotheses for the distribution of the Picea genetic marker haplotype A.
Assuntos
Ecossistema , Fósseis , Camada de Gelo , Picea , PinusRESUMO
Estimates of the radiocarbon age of seawater are required in correlations between marine and terrestrial records of the late Quaternary climate. We radiocarbon-dated marine shells and terrestrial plant remains deposited in two bays on Norway's west coast between 11,000 and 14,000 years ago, a time of large and abrupt climatic changes that included the Younger Dryas (YD) cold episode. The radiocarbon age difference between the shells and the plants showed that sea surface reservoir ages increased from 400 to 600 years in the early YD, stabilized for 900 years, and dropped by 300 years within a century across the YD-Holocene transition.