Quantitative Palaeoclimate Reconstructions Research Articles

Tsuga leaves from the Neogene Baoshan Basin in southwest China and their palaeoecological implications

Tsuga (Endl.) Carrière (Pinaceae) has a rich fossil record represented by pollen, leaves, wood and seed cones. Although fossil leaves of the genus have been widely documented, most of them have not been examined microscopically, which may limit their taxonomic resolution. In this study, three-dimensionally preserved leaves and leaf fragments of Tsuga from the Neogene (latest Miocene to Pliocene) Baoshan Basin in western Yunnan, southwest China, were examined both morphologically and micromorphologically. The fossil leaves are characterized by flattened and bifacial shape, round to obtuse apex and petiolate base, adaxially sunken and abaxially elevated midvein, adaxial surface without stomata and with elongated, smooth-margined epidermal cells, and abaxial surface with two stomatal bands along the midvein, each stomatal band consisting of 6–8 longitudinal stomatal lines. Based on comparisons with extant species of the genus, we found that the fossil leaves show the closest affinity to Tsuga dumosa (D. Don) Eichler, an extant species growing in the modern western Yunnan. As modern species of Tsuga prefer humid conditions, our fossil find suggests a humid climate in the Baoshan Basin at the time of fossil deposition, probably due to the influence of the Indian summer monsoon from the southwest. This is consistent with previous results of quantitative palaeoclimate reconstructions using spore/pollen fossil assemblages. Our study provides new fossil evidence for the origin of modern conifer diversity in southwest China. It highlights the importance of microscopic studies in the taxonomic resolution of fossil leaves of Pinaceae.

Quantification of Middle to Late Holocene precipitation in the Gonghe Basin, northeastern Qinghai-Tibetan Plateau, from the geochemistry of aeolian surface soil

The Northeastern Qinghai-Tibetan Plateau (QTP) is situated in the climatically sensitive intersection of the Asian summer and winter monsoons and the westerlies. However, due to the lack of a well-defined relationship between aeolian deposits and climatic factors in this region, there are few quantitative palaeoclimate reconstructions from these deposits. This deficiency prevents a comprehensive understanding of the precipitation history of the alpine and arid/semi-arid intermontane basins in this region, although the regional landscape is dominated by deserts/dunefields. We studied the relationship between two geochemical indices, C (the ratio of (Fe + Al + Mn + Cr + Co + Ni) to (Ca + Mg + Na + K + Sr + Ba)) and Re (the ratio of (CaO + MgO + K2O + Na2O) to (Fe2O3+MnO2)) of the aeolian topsoils and potential modern climatic variables across the Gonghe Basin in the northeastern QTP. We found that the mean annual precipitation (MAP) is the dominant climatic control of the variations of C and Re in the surface aeolian deposits, accounting for 70.9% and 53.1% of the total explained variances, respectively. Accordingly, we established two climofunctions based on C and Re to quantitatively reconstruct the MAP evolution during the Middle–Late Holocene, from the alternating aeolian sand-palaeosol sequences in the Gonghe Basin. The results revealed five intervals of enhanced MAP, with similar results obtained from the two sections, which document millennial–centennial-scale climatic fluctuations during the Middle–Late Holocene. These fluctuations are consistent with climate records from tree rings and lake sediments in this region, within the dating errors. This consistency supports the reliability of our methodology of quantitative reconstruction based on geochemical climofunctions for aeolian deposits. Our findings demonstrate a robust approach for the quantitative reconstruction of palaeo-precipitation using geochemical parameters from aeolian topsoils in an alpine and arid/semi-arid intermontane basin, and they provide new evidence for understanding significant Holocene environmental events recorded in different geological archives within the transitional region of the monsoon and the westerlies.

Climatic reconstruction at the early Miocene La Rinconada mine (Ribesalbes-Alcora Basin, eastern Spain) based on Coexistence Approach, CLAMP and LMA analysis

The early Miocene La Rinconada mine from eastern Iberian Peninsula contains a rich megafloral assemblage with abundant leaf fossils from a single stratigraphic level of the sedimentary succession. This has provided a good opportunity to undertake detailed comparative quantitative palaeoclimate reconstruction using different approaches, namely the Coexistence Approach (CA), Climate Leaf Analysis Multivariate Programme (CLAMP) and Leaf Margin Analysis (LMA). Considering the results of all techniques used, the palaeoclimate estimates are the following: mean annual temperature (MAT) CA = 10–16.5 °C/CLAMP = 11.48 °C, warmest month mean temperature (WMMT) CA = 25–26.4 °C/CLAMP = 23.31 °C, coldest month mean temperature (CMMT) CA = 4.3–4.8 °C/CLAMP = 0.84 °C, mean annual precipitation (MAP) CA = 1217–1297 mm, mean precipitation of the wettest month (MPWet) CA = 116–164 mm and mean precipitation of the warmest month (MPWarm) CA = 118–131 mm. Temperature and precipitation values obtained through CLAMP, LMA and CA indicate the occurrence of a wet and warm climate the whole year around with marked seasonality for rainfall and temperature but without a summer-dry regime. The climatic values obtained in the La Rinconada mine are in well accordance with other Burdigalian and late Burdigalian–early Langhian sites from the Iberian Peninsula (e.g. S 141 Borehole) and Central-Southern Europe (e.g. Holedeč, Čermníky, Přívlaky, Bílina Delta, Manisa-Soma, Spanokhorion and the Evia Island), suggesting the absence of a clear latitudinal gradient in temperature and precipitation for this period in Europe. This climate is consistent with the plant communities described in the area from taxonomic studies and IPR analysis.

Late Oligocene climate and floristic diversity of Assam, Northeast India

Late Oligocene is considered as the last significant globally warm climate. In India, the Makum Coalfield has exposures of sediments which were deposited at a low latitude of 10–15° N during the late Oligocene. Here, we report a diverse assemblage of fossil leaves and fruits. The assemblage envelops 18 leaf and 9 fruit morphotypes. The floristic assemblage indicates a warm and humid climate during the deposition of the sediments. The quantitative palaeoclimate reconstruction indicates that the leaf morphological traits were dominantly adapted to Indonesian–Australian type of monsoon.

Environmental changes of the stadial/interstadial type during the Late Saalian (MIS-6) – Multi-proxy record at the Wola Starogrodzka site, central Poland

Marine, lacustrine and terrestrial records from many sites located in various regions of the world suggest that the climate amelioration at the end of MIS-6 (Late Saalian) was interrupted by the short-termed cooling just prior to the MIS-6/MIS-5e boundary (Saalian/Eemian). This climatic event might be similar to the transition between interstadial conditions of the Allerød and stadial conditions of the Younger Dryas at the end of the Last Glacial (MIS-2). On the other hand, the results of quite numerous palaeobotanical studies show no stadial-interstadial oscillations below the Saalian/Eemian boundary, but reflect the gradual improvement of climate and increasing density of vegetation at that time. In western and central Europe, environment changes at the end of the Late Saalian are poorly recognized. Therefore, each new record illustrating this part of the Late Pleistocene is extremely important. We examined two profiles at the Wola Starogrodzka site, central Poland, by high-resolution analyses of pollen, Cladocera, plant macroscopic remains, mineral grain size and distribution, and organic matter content. The studied sequences represent the closing phase of the Late Saalian (in Poland called the Warta Stage of Odranian), and the early to middle part of the Eemian Interglacial. Change of the stadial-interstadial-stadial type at the end of the Late Saalian was registered both in aquatic and terrestrial environment. The recorded interstadial was correlated with Zeifen interstadial, while the following stadial – with the Kattegat stadial. Quantitative palaeoclimate reconstruction based on pollen data (modern analogue technique) showed the change in mean annual temperature by ca. 3 °C at that time.

Quantitative climatic reconstruction of the Last Glacial Maximum in China

Quantitative paleoclimatic reconstruction is crucial for understanding the operation and evolution of the global climate system. For example, a quantitative paleoclimatic reconstruction for the Last Glacial Maximum (18±2 ka 14C, LGM) is fundamental to understanding the evolution of Earth’s climate during the last glacial-interglacial cycle. Previous quantitative palaeoclimate reconstructions in China are generally based on statistical comparison of modern pollen assemblages and modern climate data. These methods are based on the premise that vegetation-climate interactions remain the same through time, and implicitly assume that the interactions are independent of changes in seasonality and atmospheric CO2 concentration. However, these assumptions may not always be valid, which may affect the reconstructions. Here, we present the results of a quantitative study of the LGM climate of China based on an improved inverse vegetation model which incorporates physiological processes combined with a new China Quaternary Pollen Database. The results indicate that during the LGM, mean annual temperature (ANNT), mean temperature of the coldest month (MTCO) and mean temperature of the warmest month in China were lower by ~5.6±0.8, ~11.0±1.6 and ~2.6±0.9°C, respectively, compared to today, and that the changes in ANNT were mainly due to the decrease of MTCO. The ANNT decrease in southern China was ~5.5±0.5°C. Mean annual precipitation was lower by ~46.3±17.8 mm compared to today and was especially low in northern China (~51.2±21.4 mm) due to the decrease in summer rainfall. Comparison of our results with recent outputs from paleoclimatic modelling reveals that while the latter are broadly consistent with our estimated changes in mean annual climatic parameters, there are substantial differences in the seasonal climatic parameters. Our results highlight the crucial importance of developing seasonal simulation on paleoclimatic models, as well as the need to improve the quality of paleoclimatic reconstructions based on proxy records from geological archives.

Habitat, climate and potential plant food resources for the late Miocene Shuitangba hominoid in Southwest China: Insights from carpological remains

The late Miocene is a sub-epoch when hominoids became rare worldwide but managed to survive in a few refugia. Investigating the living conditions of the late Miocene hominoids is therefore crucial for a better understanding of how they survived in those refugia. In this study, we present relevant palaeobotanical evidence regarding the habitat, climate and possible plant food resources for the Shuitangba hominoid (Lufengpithecus cf. lufengensis) from the late Miocene Zhaotong Basin, Southwest China. A total of 14 plant taxa were recognized from carpological remains newly recovered from the Zhaotong Basin, among which ten taxa were not reflected in the previous pollen record. These new plant taxa expand our knowledge of the flora and indicate how diverse the ecosystem in the late Miocene Zhaotong Basin was. Based on our carpological taxa, we hypothesize that the Shuitangba hominoid lived in a stratified mixed forest composed of trees, shrubs, lianas, herbs and grasses, near a lake occupied by various aquatic plants. The quantitative palaeoclimate reconstruction using the Coexistence Approach (CoA) indicates that the late Miocene Zhaotong Basin had a mean annual temperature (MAT) of 11.3–17.6°C and a mean annual precipitation (MAP) of 1042–1547mm, suggesting a mildly warm and humid climate for the Shuitangba hominoid. It also indicates that the hominoid had warm and wet summers but cool and dry winters, under the influence of the Asian monsoon. Edible and nutritious fruits and seeds of a considerable size, e.g., nuts of Carya and Corylus, fruits of Euryale and Trapa, were possibly exploited by the Shuitangba hominoid. The harder fruits, e.g., nuts of Carya and Corylus, might have benefited the hominoid as a fallback resource in winter when foods were scarce.

The Last Glacial Maximum in the central North Island, New Zealand: palaeoclimate inferences from glacier modelling

Abstract. Quantitative palaeoclimate reconstructions provide data for evaluating the mechanisms of past, natural climate variability. Geometries of former mountain glaciers, constrained by moraine mapping, afford the opportunity to reconstruct palaeoclimate, due to the close relationship between ice extent and local climate. In this study, we present results from a series of experiments using a 2-D coupled energy balance–ice flow model that investigate the palaeoclimate significance of Last Glacial Maximum moraines within nine catchments in the central North Island, New Zealand. We find that the former ice limits can be simulated when present-day temperatures are reduced by between 4 and 7 °C, if precipitation remains unchanged from present. The spread in the results between the nine catchments is likely to represent the combination of chronological and model uncertainties. The majority of catchments targeted require temperature decreases of 5.1 to 6.3 °C to simulate the former glaciers, which represents our best estimate of the temperature anomaly in the central North Island, New Zealand, during the Last Glacial Maximum. A decrease in precipitation of up to 25 % from present, as suggested by proxy evidence and climate models, increases the magnitude of the required temperature changes by up to 0.8 °C. Glacier model experiments using reconstructed topographies that exclude the volume of post-glacial ( < 15 ka) volcanism generally increased the magnitude of cooling required to simulate the former ice limits by up to 0.5 °C. Our palaeotemperature estimates expand the spatial coverage of proxy-based quantitative palaeoclimate reconstructions in New Zealand. Our results are also consistent with independent, proximal temperature reconstructions from fossil groundwater and pollen assemblages, as well as similar glacier modelling reconstructions from the central Southern Alps, which suggest air temperatures were ca. 6 °C lower than present across New Zealand during the Last Glacial Maximum.

Evaluation of a modern-analogue methodology for reconstructing Australian palaeoclimate from pollen

Quantitative palaeoclimate reconstructions are widely used to evaluate climate model performance. Here, as part of an effort to provide such a data set for Australia, we examine the impact of analytical decisions and sampling assumptions on modern-analogue reconstructions using a continent-wide pollen data set. There is a high degree of correlation between temperature variables in the modern climate of Australia, but there is sufficient orthogonality in the variations of precipitation, summer and winter temperature and plant–available moisture to allow independent reconstructions of these four variables to be made. The method of analogue selection does not affect the reconstructions, although bootstrap resampling provides a more reliable technique for obtaining robust measures of uncertainty. The number of analogues used affects the quality of the reconstructions: the most robust reconstructions are obtained using 5 analogues. The quality of reconstructions based on post-1850 CE pollen samples differ little from those using samples from between 1450 and 1849 CE, showing that European post-settlement modification of vegetation has no impact on the fidelity of the reconstructions although it substantially increases the availability of potential analogues. Reconstructions based on core top samples are more realistic than those using surface samples, but only using core top samples would substantially reduce the number of available analogues and therefore increases the uncertainty of the reconstructions. Spatial and/or temporal averaging of pollen assemblages prior to analysis negatively affects the subsequent reconstructions for some variables and increases the associated uncertainties. In addition, the quality of the reconstructions is affected by the degree of spatial smoothing of the original climate data, with the best reconstructions obtained using climate data from a 0.5° resolution grid, which corresponds to the typical size of the pollen catchment. This study provides a methodology that can be used to provide reliable palaeoclimate reconstructions for Australia, which will fill in a major gap in the data sets used to evaluate climate models.

Quantitative reconstruction of precipitation changes on the NE Tibetan Plateau since the Last Glacial Maximum – extending the concept of pollen source area to pollen-based climate reconstructions from large lakes

Abstract. Pollen records from large lakes have been used for quantitative palaeoclimate reconstruction, but the influences that lake size (as a result of species-specific variations in pollen dispersal patterns that smaller pollen grains are more easily transported to lake centre) and taphonomy have on these climatic signals have not previously been systematically investigated. We introduce the concept of pollen source area to pollen-based climate calibration using the north-eastern Tibetan Plateau as our study area. We present a pollen data set collected from large lakes in the arid to semi-arid region of central Asia. The influences that lake size and the inferred pollen source areas have on pollen compositions have been investigated through comparisons with pollen assemblages in neighbouring lakes of various sizes. Modern pollen samples collected from different parts of Lake Donggi Cona (in the north-eastern part of the Tibetan Plateau) reveal variations in pollen assemblages within this large lake, which are interpreted in terms of the species-specific dispersal and depositional patterns for different types of pollen, and in terms of fluvial input components. We have estimated the pollen source area for each lake individually and used this information to infer modern climate data with which to then develop a modern calibration data set, using both the multivariate regression tree (MRT) and weighted-averaging partial least squares (WA-PLS) approaches. Fossil pollen data from Lake Donggi Cona have been used to reconstruct the climate history of the north-eastern part of the Tibetan Plateau since the Last Glacial Maximum (LGM). The mean annual precipitation was quantitatively reconstructed using WA-PLS: extremely dry conditions are found to have dominated the LGM, with annual precipitation of around 100 mm, which is only 32% of present-day precipitation. A gradually increasing trend in moisture conditions during the Late Glacial is terminated by an abrupt reversion to a dry phase that lasts for about 1000 yr and coincides with "Heinrich event 1" in the North Atlantic region. Subsequent periods corresponding to the Bølling/Allerød interstadial, with annual precipitation (Pann) of about 350 mm, and the Younger Dryas event (about 270 mm Pann) are followed by moist conditions in the early Holocene, with annual precipitation of up to 400 mm. A drier trend after 9 cal. ka BP is followed by a second wet phase in the middle Holocene, lasting until 4.5 cal. ka BP. Relatively steady conditions with only slight fluctuations then dominate the late Holocene, resulting in the present climatic conditions. The climate changes since the LGM have been primarily driven by deglaciation and fluctuations in the intensity of the Asian summer monsoon that resulted from changes in the Northern Hemisphere summer solar insolation, as well as from changes in the North Atlantic climate through variations in the circulation patterns and intensity of the westerlies.

Quantitative reconstruction of mid- to late-Holocene climate in NE China from peat cellulose stable oxygen and carbon isotope records and mechanistic models

There has been an increasing need to reconstruct past climate from proxy records quantitatively and mechanistically. The inverse proxy modeling method stands out as a novel approach to quantitative palaeoclimate reconstructions through integrating process-based models and proxy records, representing a major progress in quantitative palaeoclimatology. It has been proposed to incorporate multiple proxy records to produce a more robust constraint on the climate parameters sought for estimation, and most of the work has been conducted using pollen records in conjunction with vegetation models. Here, I show a worked example of using paired stable oxygen and carbon isotope records of peat cellulose from one single core to infer the climate history in NE China for the last 6000 years through solving a well-posed inverse problem using Bayesian statistics. The quantitative palaeoclimate data obtained in this study may deepen our insight into the dynamics of the East Asian summer monsoon. Mean growing season temperature and relative humidity show millennial-scale fluctuations prior to c. 4000 cal. yr BP; thereafter, centennial-scale fluctuations prevailed, revealing the relative importance of solar activity over tropical ocean–atmosphere interactions in regulating the variability of regional climate during the late Holocene. It appears that there was a prominent out-of-phase relationship between temperature and relative humidity, due probably to the different response of these climate elements to orbital forcing and land cover. This worked example demonstrates the potential of using model–data fusion techniques to produce physically meaningful, mathematically optimal, and geologically sound results.

Low latitude floral assemblage from the Late Oligocene sediments of Assam and its palaeoclimatic and palaeogeographic significance

There are many outcrops of the Tertiary sediments in northeast India and a large number of plant megafossils have been described from there. Among all, the Late Oligocene sedimentary basin of Makum Coalfield is very important because there is no other exposure having such a rich palaeofloral assemblage not only from northeast India but also from the whole country. The assemblage is also important to confirm whether the suturing between the Indian and Eurasian plates was complete to facilitate plant migration or not. All the reported plant fossils clearly indicate the prevalence of tropical climate in the region during the deposition of the sediments. As the majority of taxa occur in tropical evergreen to moist deciduous and littoral and swampy forest, a warm and humid climate may be envisaged in Upper Assam during the Late Oligocene. The abundance of palms and pantropical megathermal plant families in the Makum Coalfield indicate that the cold month mean temperature (CMMT) was not less than 18°C. The quantitative palaeoclimate reconstruction indicates a monsoonal climate during the period with the same intensity as that of the modern day. The absence of Southeast Eurasian elements in the fossil assemblage provides clear evidence that suturing between the Indian and Asian plates was not complete till the Late Oligocene. Several modern analogues of the fossil taxa are now endemic to the Western Ghats which lies in the same palaeolatitude.

Reliability and resolution of the coexistence approach — A revalidation using modern-day data

The coexistence approach (CA) is widely used to reconstruct palaeoclimates for the Cenozoic. Most published CA analyses relied on climate data for nearest living relatives (NLRs) stored in the Palaeoflora database (PFDB). Here, we used more than two-hundred modern relevés (taxon lists of forest stands) from North American, Caucasian and East Asian forest regions in order to test the ability of CA/PFDB to estimate palaeoclimate. Since only data for mean annual temperature (MAT) are publicly available from the PFDB, we concentrated on this climate parameter. Two criteria were tested: ‘resolution’ and ‘reliability’ of CA/PFDB analyses. The CA assumes that for a given climate parameter (e.g. MAT; mean annual precipitation; coldest month mean temperature etc.) the interval shared by all or nearly all NLRs for a fossil assemblage is best describing the past climatic conditions. Narrow, i.e. well-resolved, intervals are desirable, since they describe most precisely the climate. Our results show that CA/PFDB is unable to reliably reconstruct the actual climates of most of the relevés analysed. CA/PFDB performed best for lowland and mid-altitude stands with MAT of ca. 13–16°C, while producing remarkably incorrect results for warmer lowland stands and cooler stands at higher elevations. This is mainly due to generally incorrect entries of MAT ranges of NLRs in the PFDB. Using corrected MAT tolerances, the reconstructed, low-resolved intervals (3°C in exceptional cases, typically 5–10°C) fall within the actual climates. Hence, only dramatic climate changes are likely to be captured in a CA analysis. This renders the coexistence approach useless for the quantitative reconstruction of palaeoclimate and calls for alternative approaches of investigating past climates by means of fossil plants.

Palaeoclimatic Estimates for the Late Pliocene Based on Leaf Physiognomy from Western Yunnan, China

Based on leaf physiognomy of the Late Pliocene Tuantian megaflora from the Mangbang Formation of Tengchong County in western Yunnan, a quantitative reconstruction of palaeoclimate was performed with Leaf Margin Analysis (LMA) methodology and the Climate-Leaf Analysis Multivariate Program (CLAMP). The latter produced the following parameters: mean annual temperature (MAT) from 17.2 to 17.7°C; warmest month mean temperature (WMMT) from 25 to 25.5°C; coldest month mean temperature (CMMT) from 9.5 to 10.8°C; length of growing season (GRS) from 9.5 to 9.7 months; growing season precipitation (GSP) from 1834.3 to 1901.2 mm; mean monthly growing season precipitation (MMGSP) from 222.4 to 230.5 mm; precipitation during the three consecutive wettest months (3-WET) from 892.1 to 917.8 mm; precipitation during the three consecutive driest months (3-DRY) from 474.5 to 512.8 mm; relative humidity (RH) from 76.7 to 77.8%; specific humidity (SH) from 10.7 to 10.8 g/kg; and enthalpy (ENTHAL) from 31.8 to 32 kj/kg. However, the MAT obtained from the Chinese LMA regression at 18.7°C, is slightly higher than that from CLAMP. The integrated analysis of these data and three adjacent pollen floras in western Yunnan suggests that the Gaoligong Mountains (a southern portion of the Hengduan Mountains) were only raised to modest altitudes in the Late Pliocene.

Quantitative palaeoclimate reconstruction as an inverse problem: A Bayesian inference of late-Holocene climate on the eastern Tibetan Plateau from a peat cellulose δ18O record

There has been a sustained need to quantify past climate changes from proxy records to better understand the driving mechanisms and thus to improve the prediction of the future. Transfer function is an intuitive and frequently used method in this regard. However, this method is unable to provide interpretive and predictive results from proxy records, because physical processes are not included. The inverse proxy modelling method opened up a new avenue for quantitative palaeoclimate reconstructions through the integration of proxy records with deterministic models. It is fundamentally different from the statistical approach, representing a conceptual advance in quantitative palaeoclimatology. Here we demonstrate the potential of this method by placing a mechanistic model and a 6000 year long peat cellulose δ18O record obtained from the high-cold and monsoonal eastern Tibetan Plateau ( c. 3500 m a.s.l.) in a Bayesian paradigm. In this worked example, the marginal posterior probability distributions of palaeoclimate variables such as the δ18O of soil water, temperature, and relative humidity were inferred jointly through the solution to an ill-posed inverse problem using the Markov chain-Monte Carlo method. Our results indicate that the observed variation of the peat cellulose δ18O record in this monsoonal area essentially reflects the changes in the oxygen isotopic composition of soil water, which is closely linked to that of rainfall. Compared with hydrology, temperature and humidity have little influence on the oxygen isotope fractionation of leaf water.

Quantitative reconstruction of palaeoclimate from pollen profiles in northeastern Japan and the timing of a cold reversal event during the Last Termination

AbstractWe reconstructed quantified palaeoclimate changes within two Japanese pollen profiles spanning the Last Termination (LT; 18–10 cal. ka) in an attempt to better understand past monsoon activity. The reconstructed winter climate at the Tashiro mire, which is strongly influenced by the Siberian air mass, showed a weak and a short‐lived cooling event at 11.8–10.6 cal. ka. This event spans part of the Younger Dryas (YD) cooling event in the North Atlantic region, suggesting the latter influenced the Siberian high‐pressure system. In contrast, the summer climate at the Komado mire, which is more influenced by the Pacific air mass, experienced a strong and a prolonged cooling event at 15.5–13.0 cal. ka. The latter event is broadly synchronous with the Antarctica Cold Reversal (ACR) event, and suggests that the Pacific high‐pressure system weakened during this period. The pattern of climate change across East Asia shows that the YD event did not extend beyond the East Asian monsoon front, while the ACR event strongly affected the Pacific high‐pressure system during the LT. We suggest the East Asian monsoon front is an important geo‐climatic boundary between YD‐like and ACR‐like deglacial climate changes. Copyright © 2009 John Wiley & Sons, Ltd.

Holocene climate variability in northernmost Europe

The sediments of a small lake on Nordkinnhalvøya, Finnmark, Norway, were investigated in order to test the hypothesis that this region was sensitive to centennial–millennial climatic fluctuations during the Holocene related to changes in ocean circulation. Sedimentation at the site began during the Younger Dryas, although the site chronology, developed using a series of 14C age measurements, reveals an early Holocene hiatus in accumulation. Pollen analysis confirmed that the regional vegetation responded to Holocene climatic variability at centennial–millennial time scales and provided data used to make quantitative palaeoclimate reconstructions. The latter indicate that marked changes in seasonality characterised Holocene climatic fluctuations. Intervals with warmer summers, higher temperature sums and higher precipitation, but cooler winters and generally reduced moisture availability, alternated with intervals with cooler summers, lower temperature sums, lower precipitation, warmer winters and greater moisture availability. The former conditions were more prevalent between ca 8950 and 3950 cal BP, whereas the latter were predominant before ca 8950 and since ca 3950 cal BP. Sediment geochemistry indicates minerogenic material deposited in the lake was probably derived from two or more distinct sources or transport pathways that differed in their responses to palaeoclimatic conditions. A series of cryptotephras were located, although the small size of the shards rendered them unsuitable for electron microprobe analyses. Time-series analysis of pollen analytical and sediment geochemical data indicates that each exhibits statistically significant periodic behaviour (at periods of ca 190, 410, 1050, 1650 and 1810 yr). The periods detected suggest this behaviour may reflect regional expression of climate system responses to solar variability and/or of effects upon tides and ocean circulation of periodic lunar orbital variation. Comparison with records of fluctuations in ocean thermohaline circulation strength indicate some concordance with respect to timing of warmer and cooler intervals, but also some differences. The 8.2 ka event, that is evident in marine records from the Barents Sea, is clearly expressed by both the palaeovegetation and geochemical records. Distinctive temporal behaviour of the palaeovegetation and of different geochemical components indicates complexity in the underlying causes and mechanisms of regional climatic variability; ocean circulation variability alone cannot account for the complex climatic variability observed.

Testing the climatic estimates from different palaeobotanical methods: an example from the Middle Miocene Shanwang flora of China

The Miocene Shanwang biota from eastern China contains exceptionally well-preserved plant fossils with abundant leaf fossils and palynomorphs co-occurring at several levels in the sedimentary succession. This has provided an ideal opportunity to undertake detailed comparative quantitative palaeoclimate reconstruction, based on both mega- and microfloral assemblages, using various approaches, namely the coexistence approach (CoA), leaf margin analysis (LMA) and Climate Leaf Analysis Multivariate Programme (CLAMP). By applying these approaches to the same dataset and using multiple fossil assemblages from different levels we are able to compare results from the different methods of climate prediction. CLAMP and LMA give consistently lower temperature (mean annual temperature, MAT) predictions than the CoA. Taking errors into account all methods indicate no overall climate change through the sequence studied. Results from CoA show overall agreement in the palaeoclimate parameters obtained using both pollen and leaf datasets indicating a high degree of internal consistency with this method.

Feeling the cold: atmospheric CO 2 enrichment and the frost sensitivity of terrestrial plant foliage

Quantitative palaeoclimate reconstructions from plant fossils using the nearest living relative (NLR) approach axiomatically assume that the climatic limits of plant distributions have largely remained unchanged over at least the past 250 Myr. However, throughout much of the Mesozoic the atmospheric CO 2 concentration is predicted to have been several times greater than the present day, and long-term (≥5 yr) experimental CO 2 enrichment studies indicate this has the capacity to increase the frost sensitivity of plant foliage by raising the temperature at which leaf tissues freeze. Furthermore, we have been able to document increases in the leaf freezing temperatures of some woody shrub species in response to the rise in atmospheric CO 2 concentration over the past two centuries, suggesting leaf freezing temperatures are sensitive to below ambient CO 2 concentrations. These data imply that a previously unrealised increase in the frost sensitivity of terrestrial plants may have already occurred owing to anthropogenic impacts on the contemporary global carbon cycle. Possible consequences of these findings for palaeotemperatures generated from the application of the NLR technique to a time-series of floras are discussed, with particular attention given to differential effects resulting from the nature of the leaf freezing–CO 2 relationship.

Quantitative reconstruction of palaeoclimate from the Middle Miocene Shanwang flora, eastern China

The fossil leaf flora from the Shanwang Formation, Linqu County, Shandong Province, eastern China, is diverse, abundant, well preserved and discretely spaced, all of which make it suitable for the recognition and application of leaf physiognomic characters. This article is the first study of Chinese Tertiary floras using the CLAMP (Climate Leaf Analysis Multivariate Program) approach. Numerous bedding planes yield leaf assemblages through over 20 m thickness of diatomaceous shales within the Middle Miocene Shanwang Formation. The diatomaceous shales, containing abundant fossils, have been divided into 19 units. A working platform (3×3 m) in the Diatomite Quarry of Shanwang was studied for about 3 months in 1998 and as many fossils as possible were recorded layer by layer. This collecting method, used for the first time in the history of Shanwang research, enabled us to record the presence or absence of megafossils in distinct units so that we could investigate leaf physiognomic characteristics and palaeoclimate for each time interval. Leaf fossils from six units (5, 6, 7, 13, 15 and 16) have been used to estimate palaeoclimate parameters of the Shanwang area using the CLAMP 3B dataset. The predicted climate is that of a lakeside setting, at over 1000 m above sea level and within the 17–15-Ma time interval. Meteorological factors have been estimated using the CLAMP approach, including mean annual temperature (MAT; 9.5–11.2°C), warmest month mean temperature (20.2–22.5°C), growing season length (5.9–6.8 months), mean growing season precipitation (83–165 cm) and relative humidity (73–79%). MAT estimates from leaf margin analysis (LMA) range from 12.5 to 15.2°C, which are a maximum of 4° higher than those from our CLAMP analyses and from previous results of LMA studies of the Shanwang flora (10–13°C). Nearest living relatives (NLR) of other biota (pollen, fish, insects, diatoms, microthyriaceous fungi, etc.) indicate warm and moist temperate to subtropical conditions in the Shanwang area during the Miocene. CLAMP predictions are similar to the climate predicted from NLRs although the MAT prediction is a few degrees cooler. The fact that the Shanwang leaf flora is from a lacustrine sequence may have biased the CLAMP analysis towards cooler (and possibly wetter) climates. The modern Yangtze River valley is a reasonable environmental analogue for the Shanwang Middle Miocene, though Shanwang may have had cooler summers, cooler MAT and less seasonality in rainfall. The climate was essentially constant during deposition of the sequence studied, with possible minor variations in precipitation.