Quantitative Paleoclimatic Reconstructions Research Articles

Investigating paleoclimate and current climatic controls at Lago Argentino using sediment pixel intensity time series

The quantity and characteristics of sediment deposited in lakes are affected by climate to varying extents. As sediment is deposited, it provides a record of past climatic or environmental conditions. However, determining a direct relationship between specific climatic variables and measurable sediment properties, for instance between temperature and sediment optical reflectance, is complex. In this study, we investigate the suitability of sediment reflectance, recorded as sediment pixel intensity (PxI), as a paleoclimate proxy at a large ice-contact lake in southern Patagonia, Lago Argentino. We also evaluate whether sediment PxI can be used to investigate the present-day climatic drivers of sedimentation across Lago Argentino. First, we show that sediment PxIs relate to underlying sediment composition, and are significantly correlated with XRF-derived major element composition. Secondly, we find that PxIs correlate with both austral summer temperatures and wind speeds, but not with precipitation. PxI timeseries reach the p<0.1 correlation significance threshold for use as a paleo-wind proxy in as many as 6 cores and a paleo-temperature proxy in up to 4 cores. However, high spatial variability and the non-unique relationship between PxI and both temperature and wind speed challenges the necessary assumption of stationarity at Lago Argentino. While not suitable as a paleoclimatic proxy, correlations between PxI and instrumental climate data do chronicle current climatic controls on sediment deposition at Lago Argentino: high summer temperatures enhance settling of coarse, optically dark grains across the lake basin by promoting ice melt and lake stratification, while high wind speeds reduce the settling of fine, optically bright grains in the ice-proximal regions by transporting sediment-rich waters away from the glacier fronts. The assumptions required for quantitative paleoclimatic reconstruction must be carefully evaluated in complex lacustrine environments, but records unsuitable for use as proxies might nevertheless yield valuable information about the drivers of modern sedimentary transport and deposition.

Periodicity of the Southern Annular Mode in Southern Patagonia, insight from the Lago Argentino varve record

Climatic variability across a large fraction of the Southern Hemisphere is controlled by the Southern Annular Mode and associated latitudinal shifts in the Southern Westerly Wind belt. In Patagonia, these changes control the large-scale temperature and precipitation trends – and resulting glacier surface mass balance. Our understanding of recent changes in this climatic oscillation is, however, limited by the number of paleo-environmental records in the mid to high-latitude Southern Hemisphere. Here, we first use a synthetic proxy record to demonstrate that periodicity may be preserved in a wider range of records than can be used for quantitative paleoclimatic reconstructions. We then analyze a 5000-year-long sedimentation record derived from Lago Argentino, a 1500 km2 ice-contact lake in Southern Patagonia. We extract a mass accumulation rate and greyscale pixel intensity record from 28 cores across all of Lago Argentino's main depositional environments. We align the mass accumulation rate and pixel intensity records to a common time axis through multivariate dynamic-time-warping, and investigate their spectral properties using the multi-taper Lomb Scargle periodogram. We find statistically significant spectral peaks at 200 ± 20, 150 ± 16, and 85 ± 9 years in two thirds of mass accumulation rate and one third of the pixel intensity records. These periodicities reveal the centennial periodicity of the Southern Annular Mode, which is the key climatic driver of sedimentation at Lago Argentino.

Lithochemical parameters in equilibrium systems of modern sedimentation in lakes and on the sea shelf

Abstract. The work combines physicochemical and statistical modeling in the description of marine and continental salt water bodies. Sedimentary systems consist of aluminosilicate, carbonate and organogenic source material. Paleoclimatic changes are traditionally considered in the time scale. However, the real fluctuation amplitude of the target natural parameter is usually absent or has insufficient resolution for quantitative paleoclimatic reconstructions. Accessible quantitative analysis of time series is based on mineralogy and geochemistry of bottom sediments. Ahalytical complex includes X-ray phase diagnostics of minerals, SEM and XRF analysis of bulk chemical composition, isotopic dating and counting of annual rhythms. Modern high-resolution techiquem like scanning XRF SR with a measurement step of 1 mm successfully provides the necessary synchronization between analytical data and instrumental seasonal-annual observations. Multiple regression methods are used to calculate the transfer functions for transforming the elemental composition of sediments into time series of the desired target environment. Additional physicochemical equilibrium estimates of sedimentation were calculated, confirming the convergence of the parameters of the selected multisystem (rock + liquid + gas) with environmental conditions. For equilibrium systems, time series of absolute values of the desired parameters, such as temperature, salinity, pH, redox environment, etc., were calibrated with synchronous weather and climate fluctuations. In particular, the reconstruction of marine sediments opened up the prospect of studying the periodicity of ice-free periods in the Arctic Ocean, using quantitative estimates of external conditions from the lithochemistry of bottom sediments.

A quantitative paleoclimatic reconstruction of the non-analogue environment of oxygen isotope stage 3: new data from small mammal records of southwestern Germany

Ensuring comparability between results is a key goal of all paleoecological reconstructions. Quantitative estimates of meteorological variables, as opposed to relative qualitative descriptions, provide the opportunity to compare local paleoenvironmental records against global estimates and incrementally build regional paleoclimatic records. The Bioclimatic Method provides quantitative and qualitative estimates of past landscape composition and climate along with measures of statistical accuracy by applying linear discriminant functions analysis and transfer functions to faunal taxonomic abundance data. By applying this method to the rodent data from Geißenklösterle and Hohle Fels, two Paleolithic cave sites located in the Ach Valley of southwestern Germany, we classify the regional vegetation according to Walters’ zonobiome model. We also present new estimates of meteorological variables including mean annual temperature, mean annual precipitation, and vegetative activity period of the Ach Valley for the period spanning ~ 60,000 to 35,000 cal BP. The results suggest the Ach Valley contained a non-analogous landscape of arctic tundra and temperate deciduous woodland with occasional arid steppe expansion. Meteorological estimates suggest the climate was significantly colder during the Middle and Upper Paleolithic than today, with higher annual precipitation and dramatic temperature shifts between seasons. These results fit well with climatic reconstructions from Switzerland and the Netherlands based on a variety of proxies. They also provide further evidence of a localized climatic response within southwestern Germany to the stadial-interstadial shifts preceding the Heinrich 4 event. Finally, these results reinforce our previous claims that climatic volatility was not a driving force in the loss of Neanderthal groups throughout the Swabian Jura during OIS 3.

Application of a Diatom Transfer Function to Quantitative Paleoclimatic Reconstruction — A Case Study of Yunlong Lake, Southwest China

Although diatom records from lake sediments have been used for quantitative paleoclimatic reconstruction, their validity and sensitivity have rarely been tested rigorously. At Yunlong Lake, an alpine lake in Southwest China, we studied the seasonal succession of diatom assemblages to produce a mean surface water temperature (MSWT) transfer function. In addition, based on the spatial distribution of surface diatom assemblages with water depth, we produced a diatom-water depth (WD) transfer function. Combined with the analysis of diatom assemblages in a sediment core (YL2013-A), changes in surface water temperature and water level over the last ∼100 years were quantitatively reconstructed using the diatom-based transfer functions. Comparison with records of regional meteorology and reservoir water capacity revealed that the diatom-based lake water level reconstruction is a sensitive indicator of short-term fluctuations in precipitation, and it also reflects a long-term stepwise rise in water level caused by the impounding and large-scale extension of the reservoir. In addition, the diatom-inferred MSWT is consistent with the changes in air temperature prior to large-scale human disturbance of the site. However, after the extension of the reservoir, although the regional air temperature continued to increase, the water temperature decreased substantially. This suggests that the large increase in lake water volume in the short term led to a decrease in the average water temperature, which in turn led to the occurrence of a diatom bloom in the cold season. The results demonstrate that diatom transfer functions based on modern observations of the same lake has a high environmental sensitivity and can be used for the quantitative reconstruction of regional climate change. Overall, our findings provide a foundation for the use of lake diatom records for quantitative paleoclimatic reconstruction on various timescales.

Middle Holocene Climate Oscillations Recorded in the Western Dvina Lakeland

Although extensive archeological research works have been conducted in the Serteya region in recent years, the Holocene climate history in the Western Dvina Lakeland in Western Russia is still poorly understood. The Neolithic human occupation of the Serteyka lake–river system responded to climate oscillations, resulting in the development of a pile-dwelling settlement between 5.9 and 4.2 ka cal BP. In this paper, we present the quantitative paleoclimatic reconstructions of the Northgrippian stage (8.2–4.2 ka cal BP) from the Great Serteya Palaeolake Basin. The reconstructions were created based on a multiproxy (Chironomidae, pollen and Cladocera) approach. The mean July air temperature remained at 17–20 °C, which is similar to the present temperature in the Smolensk Upland. The summer temperature revealed only weak oscillations during 5.9 and 4.2 ka cal BP. A more remarkable feature during those events was an increase in continentality, manifested by a lower winter temperature and lower annual precipitation. During the third, intermediate oscillation in 5.0–4.7 ka cal BP, a rise in summer temperature and stronger shifts in continental air masses were recorded. It is still unclear if the above-described climate fluctuations are linked to the North Atlantic Oscillation and can be interpreted as an indication of Bond events because only a few high-resolution paleoclimatic reconstructions from the region have been presented and these reconstructions do not demonstrate explicit oscillations in the period of 5.9 and 4.2 ka cal BP.

Vegetation History and Precipitation Changes in the NE Qinghai‐Tibet Plateau: A 7,900‐years Pollen Record From Caodalian Lake

AbstractThe northeastern Qinghai‐Tibet Plateau is strongly influenced by the East Asian summer monsoon (EASM), the Indian summer monsoon (ISM) and the westerlies. However, how these various circulation systems interacted in the region during the Holocene, and the nature of the associated environmental impacts, are unclear and even controversial. Here we present a high‐resolution pollen record from Caodalian Lake since 7.9 ka (1 ka = 1,000 cal yr BP), which is used to reconstruct the regional vegetation history and climatic changes. In addition, we use a novel procedure for pollen‐based quantitative paleoclimatic reconstruction to characterize the evolution of precipitation at Caodalian Lake and nearby Qinghai Lake. The results suggest that mean annual precipitation (Pann) is the most significant factor controlling the fossil pollen record at both sites, and the Pann reconstructions are well correlated with each other (r = 0.72, p &lt; 0.001). A synthesis of the Pann records from the two sites indicates that the precipitation in the region began to increase before 10 ka, reached a maximum during 10–5 ka, and gradually decreased thereafter. We propose that the pattern of precipitation evolution in the Qinghai Lake basin resulted from the combined effects of the ISM and EASM, with a precipitation maximum of 10–7 ka for the ISM and 7–5 ka for the EASM; both systems contributed to the regional precipitation maximum during 10–5 ka. Our well‐dated and unambiguous Pann record also provides the opportunity to reconcile paleoenvironmental reconstructions derived from different paleoenvironmental proxies from the Qinghai Lake basin.

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.

The different climatic response of pedogenic hematite and ferrimagnetic minerals: Evidence from particle-sized modern soils over the Chinese Loess Plateau

In recent years, increasing interest in loess studies has focused on qualitative and quantitative paleoclimatic reconstruction using the imperfect antiferromagnetic mineral hematite. However, the linkage between the hematite formation and climatic variables remains controversial. Here we present the results of a comprehensive investigation of the magnetic properties and statistical analysis of a suite of clay and silt fractions of modern soil samples from 179 sites across the Chinese Loess Plateau (CLP) and adjacent regions. Our objective was to clarify the relationships between modern climatic variables and pedogenic hematite, as well as pedogenic ferrimagnetic minerals. First-order reversal curve measurements were also conducted on representative particle-sized subsamples from a N-S transect to understand the differences in magnetic mineralogy between the two fractions. Our results show that pipette extraction separates the fine-grained superparamagnetic (SP) and most of the single-domain (SD) magnetic grains into the clay fraction, and that the remaining silt fraction displays the magnetic properties of coarse pseudo-single domain (PSD) or a mixture of multidomain (MD)/PSD and a few SD particles. Only the pedogenic clay fraction shows a strong correlation with climatic variables. The application of redundancy analysis helps to distinguish the climate variables controlling the formation of ferrimagnetic minerals and hematite during pedogenesis. On the CLP, pedogenic ferrimagnetic minerals are sensitive to mean annual precipitation, while pedogenic hematite formation is preferentially dependent on mean annual temperature. The confirmation of the temperature-dependent nature of hematite on the CLP provides a new possibility for quantitatively reconstructing the paleotemperature history of Chinese loess/paleosol sequences.

A novel procedure for pollen-based quantitative paleoclimate reconstructions and its application in China

Traditionally, the evaluation of pollen-based quantitative paleoclimate reconstructions focuses on the ability of calibration sets to infer present climatic conditions and/or the similarity between fossil and modern assemblages. Objective criteria for choosing the most appropriate climate parameter(s) to be reconstructed at a specific site are thus lacking. Using a novel approach for testing the statistical significance of a quantitative reconstruction using random environmental data, in combination with the advantageous large environmental gradients, abundant vegetation types and comprehensive modern pollen databases in China, we describe a new procedure for pollen-based quantitative paleoclimatic reconstructions. First, the most significant environmental variable controlling the fossil pollen assemblage changes is identified. Second, a calibration set to infer changes in this targeted variable is built up, by limiting the modern ranges of other environmental variables. Finally, the pollen-based quantitative reconstruction is obtained and its statistical significance assessed. This novel procedure was used to reconstruct the mean annual precipitation ( P ann) from Gonghai Lake in the Lvliang Mountains, and Tianchi Lake in the Liupan Mountains, on the eastern and western fringe of the Chinese Loess Plateau, respectively. Both P ann reconstructions are statistically significant ( p <0.001), and a sound and stable correlation relationship exists in their common period, showing a rapid precipitation decrease since 3300 cal yr BP. Thus, we propose that this procedure has great potential for reducing the uncertainties associated with pollen-based quantitative paleoclimatic reconstructions in China.

Hydrogen isotope ratios of moss cellulose and source water in wetlands of Lake Superior, United States reveal their potential for quantitative paleoclimatic reconstructions

The hydrogen isotopic composition of organic substrates provides valuable information on past hydrological changes. To explore whether quantitative information can be obtained from this proxy, we measured D/H ratios of cellulose extracted from mosses inhabiting both hollow and hummock sites in three swales located near Lake Superior, United States. These isotope ratios were compared to those of potential water sources, namely swale, moss, and ground water, to evaluate whether cellulose D/H ratios reflect those of its water sources. For that evaluation, we relied on a better mechanistic understanding of the isotopic fractionation occurring during cellulose synthesis in plants as well as the relative simplicity of moss physiology in regard to water use strategies and a dataset that combines published D/H ratios for modern moss cellulose. We found that moss cellulose δD values for hollow species (−118.1±8.5‰) were significantly depleted (p=0.016) in D by 8‰ in relation to those for hummock species (−110.1±8.1‰), possibly due to an averaging effect taking place in hollow species. In addition, we found that 40% of the hydrogen in cellulose from hollow species probably experienced isotopic exchange with the surrounding cell water, and this percentage is not statistically different from that (42%) obtained from an analysis of published data on modern moss cellulose. This analysis also reveals that the fraction of hydrogen in modern moss cellulose that is subjected to isotope exchange falls within a relatively narrow range (±3%). Using this range and a mechanistic model, we were able to estimate source water δD values using those measured for moss cellulose, and these estimates were statistically indistinguishable from the measured δD values of moss and swale water. Further, the ratios of δD/δ18O of moss cellulose of hollow species yielded values that are similar to those reported for the local meteoric water line, thus adding a potential source of paleo-hydrological reconstructions from moss cellulose. Consequently, our combined results suggest not only that moss cellulose D/H ratios reflect those of source water, but that the latter values can be estimated fairly precisely from cellulose D/H ratios using a relatively simple mechanistic model. However, the accuracy of this model hinges on assumptions that need to be tested further to corroborate its widespread applicability.

Refining upon the climatic background of the Early Pleistocene hominid settlement in western Europe: Barranco León and Fuente Nueva-3 (Guadix-Baza Basin, SE Spain)

The Early Pleistocene sites of Barranco León and Fuente Nueva-3 (Guadix-Baza Basin, SE Spain) have yielded thousands of Mode 1 or Oldowan lithic artifacts (both sites) and one tooth (in layer D, formerly 5 of Barranco León), today considered to be some of the earliest evidence of humans in western Europe at ca. 1.2–1.5 Ma. Previous quantitative paleoclimatic reconstructions based on herpetile assemblages indicated that, during the formation of these two sites, the mean annual temperature and mean annual precipitation were higher than they are now in the southeastern Iberian Peninsula, with lower continentality. Here, we propose new climatic reconstructions where the mean monthly temperature and precipitation and the difference between the four driest months and the four rainiest months are estimated. Climatograms are built in order to specify the distribution and variation of temperature and precipitation during the year, and the Aridity Indices of Gaussen, Lautensach-Mayer, Dantin-Revenga and De Martonne are used to characterize ombroclimatic differences. According to these new climatic parameters, rainfall distribution through the year shows considerably higher precipitation in every season except summer and early autumn, which remain drier and thus consistent with a Mediterranean climate pattern. No change is observed in the duration of the aridity period, which remains four months long. However, the value of the Aridity Index of De Martonne is higher than 20 (subhumid climate) in Barranco León and Fuente Nueva-3, whereas today it is lower than 20 (semi-arid climate), suggesting major changes in the ombroclimatic type. These results yield a more precise scenario for the paleoclimatic conditions that prevailed during the late Early Pleistocene in the Guadix-Baza Basin and permit us to contrast the ages obtained from numerical dating and biochronology. The very warm and humid climate reconstructed for both Barranco León and Fuente Nueva-3 suggests that, in accordance with the numerical dating, these two sites are contemporaneous with the particularly warm interglacial peaks of Marine Isotope Stages 43–49 (i.e. between 1.35 and 1.47 Ma). The similarity between reconstructed climates, the high overlap between their estimated precipitation and between the difference of the driest from the rainiest season suggest that these sites may correspond to the same part of a climatic glacial/interglacial cycle, but because the evolutionary degree of the rodent Mimomys savini shows a slightly more derived state for Fuente Nueva-3 than for Barranco León (i.e a short chronological difference between the two sites), they may correspond to two consecutive warm interglacial peaks.

Stable isotope mass balance of lakes: a contemporary perspective

The theoretical basis for application of stable isotope mass balance of lakes is described for a range of climatic situations including low latitude, high latitude, high altitude, continental and coastal systems, as well as cases where the atmospheric boundary layer is significantly modified by the lake evaporation process. The effects of seasonality on isotopic offset between precipitation and atmospheric vapour and the slope of the local evaporation line are described. Atmospheric feedback and its role in labelling the isotopic composition of the Laurentian Great Lakes and tropical lakes is discussed. Several important considerations are suggested to improve parameterization of quantitative paleoclimatic reconstructions including use of assumptions that are appropriate for the climatic setting, for the atmospheric feedback situation, for salinity, and headwater setting. Potential for use of dual-isotopes to trace past changes in seasonality and input, and a dual-lake index method that can potentially be used to trace connectivity of lakes are presented. In cases where modern or paleo-evaporation systems may be under-defined there are inherent limitations in the degree of quantification that can be attained.

Examining the role of allogenous and autogenous factors in the long-term dynamics of a temperate headwater peatland (southern Québec, Canada)

Plant macrofossil and testate amoebae analyses were conducted on a sedimentary core taken from a headwater peatland located near the summit of a hill at the northern extension of the Adirondack Mountains (Québec, Canada). The aims were to reconstruct the developmental stages of the peatland and to examine the allogenous and autogenous factors associated with its long-term dynamics. Results were compared with a quantitative paleoclimatic reconstruction based on the modern analog technique using pollen data from the same core. The long-term development of the peatland (pond—rich fen—intermediate fen—poor fen—bog) mainly reflects an autogenous hydroseral succession. Active peat accumulation under the relatively dry climate of the Early Holocene suggests that summer temperature was a critical factor in peat accumulation through enhanced biomass production. A major long-term decrease in net peat accumulation rates and a progressive decline of mean water-table depth occurred during the Mid- to Late-Holocene (7900–500calyr BP), even though annual precipitation was abundant at the time. The high summer temperature associated to the highest evapotranspiration rates maintained a low water table which in turn led to strong humification of the peat. A similar, synchronous pattern in vertical peat accumulation dynamics characterized another nearby peatland. Based on these results, we suggest that small peatlands situated atop a watershed and/or within a small watershed are ecosystems sensitive to changes in precipitation and/or evapotranspiration, due to their limited water supply.

Eocene prevalence of monsoon-like climate over eastern China reflected by hydrological dynamics

Hydrological dynamics of sedimentary basins are essential for understanding regional climatic pattern in the geological past. In previous qualitative studies lithologically depending on the occurrence of featured sedimentary rocks, the Eocene climate of China had been subdivided into three latitudinal zones, with one subtropical high-controlled arid zone throughout middle China, and two humid zones respectively in the north and south. However, recent advances on mammalian fauna distribution, plant fossil-based quantitative paleoclimatic reconstruction, and modeling experiment jointly suggest that the relatively humid monsoonal climate might have prevailed over the territory. Here we examine and compare sedimentary sequences of 10 Eocene sections across eastern China, and hence the lake level fluctuations, to discuss the nature of climate type. Our results show that, instead of the categorically zonal pattern, the hydroclimate dynamics is intensified landward. This is demonstrated by the fact that, in contrast to the wide developed coal layers around the periphery, evaporites are growingly occurred endocentrically to the central part of middle China. However, although we have had assumed that all evaporites are indicator of extreme aridity, the highly oscillated climate in the central part of middle China was humid in the majority of the Eocene, distinct from permanent arid as seen in deserts or steppe along modern horse latitude. From the upcountry distribution pattern of the Eocene hydrological dynamics, it appears that the relatively dry climate in central China was caused by the impact of continentality or rain shadow effect under monsoonal, or monsoon-like climate.

Палеокліматичні реконструкції для пізнього плейстоцену рівнинної частини України

The article summarizes the results of quantitative paleoclimatic reconstructions conducted using different methods based on the palinological records of the Upper Pleistocene deposits of the plain part of Ukraine. Quantitative climatic characteristics for the Riss-Wurm interglacial period, Dubno interstadial and the Last Glacial Maximum are provided. It is concluded that primary refugia of thermophilic and hydrophilic trees on the plain areas did not exist during the Last Glacial Maximum. Key words: paleoclimatic reconstructions, Late Pleistocene, Riss-Wurm interglacial period, Dubno interstadial.