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Historical response of SI for European tree birches ( B. pendula and B. pubescens ) to global atmospheric CO 2 increase from 287 to 356 ppmv. The training set includes mean SI values for herbarium material ( F ) collected in The Netherlands and Denmark in the period 1843 – 1995 and leaf remains from living peat ( छ ) in The Netherlands, formed in the period 1952 – 1995 (17). Historical CO 2 concentrations of 315 – 356 ppmv are mean spring-season values from Mauna Loa monitoring (http: ͞͞ cdiac.esd.ornl.gov ͞ ndps ͞ ndp001.html), and concentrations of 287 – 315 ppmv are representative values derived from shallow Antarctic ice cores (http: ͞͞ cdiac.esd.ornl.gov ͞ trends ͞ co2 ͞ siple.htm). For analytical method, see text. Regression statistics: n ϭ 63; slope ϭ Ϫ 0.0846. Goodness-of-fit linear model: R 2 ϭ 0.78, R adj 2 ϭ 0.78. Analysis of variance
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By applying the inverse relation between numbers of leaf stomata and atmospheric CO2 concentration, stomatal frequency analysis of fossil birch leaves from lake deposits in Denmark reveals a century-scale CO2 change during the prominent Holocene cooling event that occurred in the North Atlantic region between 8,400 and 8,100 years B.P. In contrast...
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... strongly stimates rely of Holocene on CO 2 measured atmospheric in air CO extracted 2 concentrations from Ant- arctic ice cores. Records for the past millennium indicate significantly reduced CO 2 levels from A.D. 1550 to 1800, which are temporally related to the historical Little Ice Age climate deterioration (1, 2). By contrast, Antarctic ice-core data do not clearly support a temperature–CO 2 correlation during the eight earlier short-term cooling pulses that punctuated Holocene climatic conditions in the North Atlantic region with a period- icity of Ϸ 1,500 years (3). Only the so-called 8.2-ka-B.P. cooling event has been associated with a long-term, modestly declining CO 2 trend recognized in the Taylor Dome record (2). This most prominent century-scale instability of Holocene climate is re- flected as a negative ␦ 18 O excursion in Greenland ice cores (4, 5) as well as in a variety of marine and terrestrial proxy records indicative of pronounced modifications of regional temperature and ͞ or precipitation regimes in the North Atlantic region (3, 4, 6–11). The instability is related to a brief episode of massive release of meltwater associated with the final demise of the Laurentian ice sheet (12). The conventional iced-based concept of relatively stabilized CO 2 concentrations during the greater part of the Holocene is challenged increasingly by stomatal frequency analysis of fossil leaves (13–15). Species of C 3 plants are often characterized by a plastic phenotype capable of consistent adjustment of numbers of leaf stomata in response to changes in ambient CO 2 concen- tration (16–18). Identification of a CO 2 -sensitive gene involved in stomatal development in Arabidopsis thaliana demonstrates the genetic control of the response (19). As a corollary of this responsiveness, stomatal frequency analysis of fossil leaves en- ables the detection and quantification of atmospheric CO 2 changes at different time scales (14, 17–25). High-resolution analysis of tree leaves buried in Lateglacial and Holocene peat and lake deposits suggests temporal correlation between global CO 2 dynamics and Northern Hemisphere temperature. In Eu- rope and North America, reconstructed CO 2 fluctuations (14, 15, 20) appear to parallel well documented ␦ 18 O and chrinomid- based temperature changes associated with the Younger Dryas stadial and the Preboreal Oscillation, the first of the Holocene climatic instabilities occurring at Ϸ 11,000 calendar years B.P. (26). Both Younger Dryas and Preboreal Oscillation are not apparent in the CO 2 record of Antarctic ice (2, 27), which may be due to generally low temporal resolution of Lateglacial and early Holocene CO 2 data from Antarctica. To corroborate the concept of a coupling between recurrent Holocene cooling pulses and CO 2 fluctuations, we document stomatal frequency data that constrain timing and magnitude of CO 2 shifts associated with the prominent 8.2-ka-B.P. cooling event. We analyzed leaves of European tree birches ( Betula pubescens and Betula pendula ) preserved in cores of gyttja deposits from Lake Lille Gribsø, North of Copenhagen, Denmark (55°58 Ј 43 ЈЈ N; 12°18 Ј 52 ЈЈ E). Well preserved leaf remains occur continually through an interval corresponding to the period between Ϸ 8,700 and Ϸ 6,800 calendar years B.P. Temporal control is provided by a series of six accelerator mass spectrometry 14 C chronologies mea- sured on single leaves (Table 1). Stomatal frequency can be expressed in terms of stomatal density and stomatal index (SI): SI ϭ (stomatal density ͞ [stomatal density ϩ epidermal cell density]) ϫ 100. In contrast to stomatal density, SI reflects stomatal frequency indepen- dently of variation in epidermal cell size related to light intensity, temperature, or nutrient and water availability. In angiosperm leaves, therefore, mean SI is the more sensitive parameter for detecting stomatal frequency responses to changing CO 2 levels (28, 29). Effects of variation within and between leaves can be eliminated by using large data sets (17, 18, 28). Leaves of B. pendula and B. pubescens display essentially similar SI patterns and can be treated therefore as a single category in stomatal frequency analysis (18). There is sufficient evidence from field studies and experiments that CO 2 -induced trends in mean SI for Betula leaves are not disturbed significantly by environmental factors other than CO 2 (30, 31). Standardized, computer-aided determination of stomatal pa- rameters on leaf cuticles was performed on a Leica Quantimet 500C ͞ 500 ϩ image-analysis system. Measured parameters in- clude stomatal density and epidermal cell density (including guard cells). Counting areas are restricted to stomata-bearing alveoles. Calculated SIs are mean values for up to seven leaves per data point. Seven digital images (field area, 0.035 mm 2 ) per leaf were analyzed (standard deviations are constant after seven counts). We used the rate of historical CO 2 responsiveness of the European tree birches (Fig. 1) to quantify early Holocene SI-based CO 2 levels. Our approach of inferring an unknown value of a quantitative variable (CO 2 ͞ x 0 ) from the quantitative response of a single taxon (SI birch ͞ y) meets the basic require- ments for a classical linear regression, which allows a better performance at the extremes and with slight extrapolation (32–34). The reconstructed CO 2 record shows a fluctuating pattern (Fig. 2). Inferred CO 2 minima with averages of Ϸ 275 ppm by volume (ppmv) occur at Ϸ 8,680 years B.P. and between Ϸ 8,430 and Ϸ 8,040 years B.P.; prominent maxima with values of 300– 325 ppmv occur at Ϸ 8,640 years B.P. and between Ϸ 7,920 and Ϸ 7,270 years B.P. The series of low CO 2 concentrations around 8,300 years B.P. follow a declining trend of Ϸ 25 ppmv within a time interval of Ͻ 100 years. This interval ends with a return to levels Ͼ 300 ppmv after Ϸ 300 years. Timing and duration of the century-scale CO 2 excursion are in harmony with the proxy records for the 8.2-ka-B.P. cooling event embracing a period of 200 – 300 years between Ϸ 8,400 and Ϸ 8,100 years B.P. (3 – 12). The SI signals thus indicate a temporal association between the 8.2-ka-B.P. cooling and atmospheric CO 2 concentration. The exact phase relationship between changes in temperature and CO 2 cannot be determined yet. Our CO 2 reconstructions reflect rapid changes with a signif- icantly greater magnitude than the smooth and modest atmo- spheric CO 2 decline to values Ϸ 260 ppmv inferred from the low-resolution Taylor Dome ice-core record (Fig. 2). The data also confirm the regular occurrence of early Holocene atmo- spheric CO 2 concentrations well above 300 ppmv, unknown from Antarctic ice cores but common in leaf-based time series (9, 14). These apparent controversies between leaf-based and ice-based CO 2 data have not been resolved yet (ref. 35; see text at www.sciencemag.org ͞ cgi ͞ content ͞ full ͞ 286 ͞ 5446 ͞ 1815a). It should be noted that early Holocene records from Greenland ice cores have repeatedly indicated rapidly fluctuating CO 2 levels including values Ͼ 300 ppmv (36, 37). At present, the Antarctic record is usually considered to be reliable, so that discrepancies are ascribed to CO 2 enrichment within the Greenland ice (38, 39). However, there is evidence that in polar ice also postdepo- sitional CO 2 depletion could occur, but underlying chemical processes of this potential source of error have not yet been investigated in detail (38, 39). The documented coupling between CO 2 fluctuations and the 8.2-ka-B.P. cooling implies a distinctive involvement of the oceans, where short-term perturbations of sea-surface temper- ature and ͞ or salinity allow rapid CO 2 transfer between the atmosphere and surface waters. Holocene cooling events are generally related to a reduction in the thermohaline circulation, resulting in sea-surface temperature lowering in large parts of the North Atlantic (3, 6). This forcing mechanism is evident particularly for the 8.2-ka-B.P. cooling event, where weakening of the thermohaline circulation was triggered by catastrophic release of Laurentide meltwater (12). By applying a freshwater perturbation over 20 years, a global atmosphere-sea-ice-ocean model simulation of the 8.2-ka-B.P. event produces a 320-year lasting weakening of the North Atlantic thermohaline circulation and 1 – 5 ° C surface cooling over the adjacent continents (40). The reconstructed atmospheric CO 2 reduction of Ϸ 25 ppmv indicates a temporarily enhanced North Atlantic sink for CO 2 at the time of the 8.2-ka-B.P. cooling event. While regional pa- lynological data support temperature changes (11), vegetation reconstructions do not provide evidence of an extended terres- trial sink. The occurrence of global CO 2 fluctuations substanti- ates the interpretation of ␦ 18 O records in ice cores from Ant- arctica and Greenland in terms of globally parallel climate changes on the Northern and Southern Hemispheres (41). The CO 2 fluctuations falsify conclusively the concept of an approx- imate antiphase relation between short-term temperature changes on the two hemispheres that would cause buffering of North Atlantic CO 2 drawdown by the effects of synchronous sea-surface temperature increase in the Southern Ocean (42). It thus may be concluded that leaf-based CO 2 data support a much more dynamic evolution of the Holocene CO 2 regime than previously thought. In effect, there seems to be every indication that the occurrence of Holocene CO 2 fluctuations is more consistent with current observations and models of past global temperature changes than the common notion of a relatively stable CO 2 regime until the onset of the Industrial ...
Citations
... The fish feed conversion factor (FCR) was calculated using the following formula. FCR = Total amount of feed/Total weight gain (17) where, the total amount of food and the measure of weight increase by kilogram. ...
The rapid development of the areas of Notopterus chitala fish ponds in Hau Giang province in recent years has raised a question about greenhouse gas emissions, in the form of total carbon dioxide equivalents (CO 2e). There are many parameters that affect greenhouse gas emissions in a fish pond, such as amount of feed, dissolved oxygen (DO), chemical oxygen demand (COD) in the water, pH, water temperature, windy velocity and sunlight reaching the pond surface. In this study, a System Thinking, Experimental Learning Laboratory with Animation, shortly called as Stella is applied as a visual programming language for system dynamics modelling in order to find the relationship between simulated CO 2 and measured CO 2 in Notopterus chitala fish pond. Three ponds were used for measuring average pH, temperature, feeds, DO, COD and phytoplankton inside the ponds while windy speed and light intensity data were collected from a Weather Station nearby. The results of model calibration and validation showed that the Stella 8.0 can be used as predictable tool for the change in time of CO 2 emission during 240 days of fishing. Model can help fishing farmers to adjust the quantity of feeds and control the water quality in their Notopterus chitala fish ponds to reduce greenhouse gas emissions appropriately.
... Undoubtedly, man does intensify the existing trend, but in about 15 per cent. Such an estimate is supported by a comparative analysis of changes in the carbon dioxide content in the air, now and during the Atlantic Optimum of the Holocene (Wagner et al., 2002;Steinthorsdottir et al., 2013). ...
In the Solar System, the coming into existence of a peculiar, fully developed atmosphere on Earth was determined by the ‘Great Oxidation Event’ at the turn of the Proterozoic and Palaeozoic. Within about 600 million years, there were large changes in oxygen concentrations in this atmosphere, ranging from 15 to 35 per cent, having been determined by a combination of cosmic-climatic, tectonic-volcanic and biological phenomena. A particular environmental change occurred at the beginning of the 19th century, as a result of the overlap of the end of the natural Little Ice Age and the beginning of anthropogenic warming of the ‘industrial revolution’. According to the author, the rate of human impact on environmental changes is estimated at about 15 per cent. The appearance of mankind brought new changes in the natural environment, including the oxygen content of the air. The current scale of anthropogenic impact justifies the introduction of a new time slice in the planet’s history - the Anthropocene. The functioning of civilisation is conditioned by meeting energy needs, to be implemented by creating a system of energy generators, among which the heat of the Earth should be an important component. The energy generated from this inexhaustible and cost-free geo-resource should be seen as the most ecological among all currently used energy carriers.
... Present-day climatic variability does not reflect the considerable changes that took place in the region at the end of the Quaternary (Partridge et al., 1997;Ganopolski et al., 1998;Claussen et al., 1999;Gasse, 2000;Lancaster et al., 2002;Renssen et al., 2006). Following a hyper-arid phase during the Late Pleistocene around the LGM, the African Humid Period (AHP) extended from the early until the middle Holocene (11.5-5.5 cal kyrs BP), with an arid interval at 8.2 cal kyrs BP (Alley et al., 1997;deMenocal et al., 2000;Wagner et al., 2002) and a second well-established Holocene wet phase at around 6.5 cal kyrs BP, continuing up to 5.5 cal kyrs BP (Claussen and Gayler, 1997; , 1998;Claussen et al., 1999). From the Late Holocene onwards, arid conditions prevailed up to present-day (Claussen et al., 1999;Regard et al., 2006). ...
... It has never been experimentally demonstrated that records in ice cores are reliable in representing the original atmospheric composition. Research has shown that during the Holocene (10,000 years ago) [CO 2 ] fluctuated between 300 and 348 ppm [15][16][17]. These results contrast with those of Barry et al. [18], Dore et al. [19], Feely et al. [20], Blackford & Gilbert [21], Caldeira & Wickett [22], Sabine et al. [23], Takahashi [24] who consider that [CO 2 ] fluctuated between 270 and 280 ppm until the industrial revolution. ...
One of the great contemporary concerns of humanity is the analysis of climate change, that is, of the processes that alter the structure and functioning of the planet as a system and whose causes are inherently related to human activities. The direct relationship between climate change and carbon cycling in ecosystems is increasingly debated. Arrhenius in 1896 may have "planted the seed" of "global warming" when he launched the theory of the "greenhouse" in the planet's atmosphere by CO2 [1]. Several premises are assumed as evidence of global warming, such as: records in the ice core and records of the concentration of carbon dioxide in the atmosphere in the 19th and 20th centuries. It has never been experimentally demonstrated that records in ice cores are reliable in representing the original atmospheric composition. And the objections in the records of [CO2] in the atmosphere by renowned scientists have never been considered by climatologists.
... This inhibition occurred particularly in plants with high maximum stomatal conductance and high stem vulnerability Introduction Morphological features of plant fossils are a well-established source of information about ancient Earth (McElwain, 1998;Royer, 2001;Beerling and Royer, 2002;Franks and Beerling, 2009;Peppe et al., 2011). For example, measurements of leaf fossil characteristics have been used to infer properties of ancient plant physiology (Boyce et al., 2009;Franks and Beerling, 2009;Brodribb and Feild, 2010;Nicotra et al., 2011;Haworth and Raschi, 2014;Montañez et al., 2016;Wilson et al., 2017Wilson et al., , 2020Boyce and Zwieniecki, 2019;White et al., 2020) and greenhouse gas concentrations (Woodward, 1987;McElwain, 1998;Beerling and Royer, 2002;Wagner et al., 2002;Finsinger and Wagner-Cremer, 2009;Franks and Beerling, 2009;Steinthorsdottir et al., 2011;Montañez et al., 2016;Richey et al., 2020Richey et al., , 2021. Recently, these fossil derived properties have been incorporated into ecosystem process models Matthaeus et al., 2021;Richey et al., 2021), and Earth system models to assess terrestrial ecosystem carbon, water, and nitrogen cycles in deep time. ...
The evolution of woody stems approximately 400 mya (middle Paleozoic) facilitated the expansion of plants and has likely affected carbon and water budgets across much of the terrestrial surface since that time. Stems are a carbon cost/sink and limit water transport from soil to leaves as it must pass through specialized xylem tissue. While leaf fossils have provided a wealth of quantitative data, including estimates of plant water fluxes utilizing biophysically based models, fossil-informed models integrating stem and leaf physiology are lacking. Integrated stem-leaf physiology may distinguish successors to ecological catastrophes like the end of the Late Paleozoic Ice Age (LPIA). The documented collapse of LPIA tropical forests provides an opportunity to assess the importance of woody stems as a key to understanding differences in survivorship among common plant taxa from the Carboniferous to the Permian. Here, we present an analysis of the limits to leaf water supply and plant function for Paleozoic forest plant types due to (1) cavitation-induced embolism and xylem blockage and (2) insufficient sapwood water transport capacity.—collectively defined here as sapwood dysfunction. We first present a modified ecosystem process model (Paleo-BGC+) that includes sapwood dysfunction. Paleo-BGC + is parameterized using measurements obtainable from fossil xylem and therefore applicable to both modern and ancient ecosystems. We then assess the effect of sapwood dysfunction on ecosystem processes based on previously published fossil leaf measurements and a new fossil xylem dataset for plant types present in the Late Paleozoic. Using daily meteorology from a GCM of the late Carboniferous (GENESIS v3) under a Glacial (low-CO2) and an Inter-glacial (high-CO2) scenario, we found that simulated sapwood dysfunction slowed plant water use and reduced carbon storage. This inhibition occurred particularly in plants with high maximum stomatal conductance and high stem vulnerability to embolism. Coincidentally, plants with these traits were predominantly reduced or missing from the fossil record from the Carboniferous to the Permian. Integrating stem and leaf physiology may improve the fidelity of model representations of soil-to-atmosphere water transport through plants, simulations of long-term climate phenomena like the LPIA, and ecosystem projections under future climate change.
... The interpretation of such records needs to be careful since existing overlaps with the ice core record can show local disagreements of up to 100 ppm; instead, applying a LOESS fit can return average concentrations that are broadly in line with ice cores (Cui et al., 2020). In particular, overinterpretation of records from stomatal frequency has led to unsubstantiated claims of fast CO 2 excursions during the last deglaciation (Steinthorsdottir et al., 2013;Köhler et al., 2015) and early Holocene (Wagner et al., 1999;Wagner et al., 2002). Contrastingly, on much longer time-scales of millions of years, leaf-based reconstructions have been very useful in constraining past CO 2 variability, and reinforce CO 2 as a primary climate driver throughout the Phanerozoic Eon (540 Ma -Present; Royer et al. (2001Royer et al. ( , 2004). ...
The successful reconstruction of past atmospheric CO2 concentrations from Antarctic ice cores started in the early 1980s. Each newly published record is the product of painstaking discrete measurements of hand-sized samples from ice cores that can reach more than 3 kilometers of depth. Hence, high-resolution reconstructions of CO2 are usually limited to a specific window of time of the last 800 thousand years (800 ka). Using the EDC ice core, we reconstructed atmospheric CO2 concentrations during Marine Isotope Stage 5 (MIS 5; 135–106 ka). The new dataset covers the penultimate deglaciation, the last interglacial, and the last glacial inception in unprecedented centennial resolution. Our new record shows remarkably stable CO2 concentrations for ten thousand years during MIS 5e. Simultaneously, a series of worldwide climatic changes took place, such as falling temperatures in the oceans and over the poles, growing ice sheets, generalized climate instability in the Northern Hemisphere, and changes in the Earth’s orbital parameters. The lack of marked variability in the CO2 record during this period can be explained by an unusual combination of dynamic carbon fluxes and the lack of a suitable deep ocean storage reservoir. As enigmatic as the plateau is the last glacial inception when CO2 suddenly drops from interglacial levels and resumes its coupling with Antarctic temperature. We propose that a Northern Hemisphere trigger sourced this threshold-like behavior.
Despite the centennial-scale resolution achieved with the MIS 5 record, we only tentatively interpret submillennial CO2 features. While building the dataset, we realized that CO2 showed sharp oscillations between neighboring data points, too fast to be fingerprinted by true atmospheric variability. Much of the ensuing work tackled the understanding of CO2 fluctuations at the centimeter scale and how they affected our record. We concludedthat while the high resolution allowed the establishment of precisely timed slope changes, individual fluctuations at the centennial scale were likely the result of fractionation effects during the bubble enclosure process in the ice core.
The measurement device used to reconstruct CO2 at the University of Bern is the end product of decades of accumulated knowledge on how to measure CO2 from ancient air bubbles trapped in polar ice. The centrifugal ice microtome (CIM), continuously developed and improved since 2008, is a dry-extraction technique with state-of-the-art precision and high sample throughput. During this Ph.D., the implemented improvements regarding the CIM related to statistical analysis of different potential sources of error. These finesse allowed for a deeper understanding of the system’s intricacies and increased confidence when interpreting its output concentrations.
... Historic and contemporary records of (daily) weather and weather-related phenomena are complemented by the modern observations of Earth-orbiting satellites that have been available since the later part of the 20th century. However, to form a more complete picture of climate change and its causes and effects, these observations need to be supplemented with proxy records (Van Der Burgh et al. 1993;Kürschner et al. 1996;Hoek and Bohncke 2002;Wagner et al. 2002;Visscher et al. 2004;Kouwenberg et al. 2005;van Hoof etal. 2006;Salzer and Hughes 2007;Donders et al. 2008;Sluijs et al. 2009;Wagner-Cremer et al. 2010a;Cramwinckel et al. 2018;Fischer et al. 2018;Gouw-Bouman et al. 2019;Ahmed et al. 2020). ...
... Betula pubescens trees grow near the edge of the lake while species from the other genera grows on more dry land. The continuous presence of B. pubescens in the area and well-preserved leaf remains in the lake sediments from the early Holocene onwards (Wagner, 1999;Wagner et al., 2002) makes the site suitable for reconstruction of GDD5 based on morphological features of B. pubescens epidermal cells. ...
In recent decades, it has become clear through meteorological observations that
the climate is changing. Particularly the spring season is getting warmer and also
seems to start earlier. Since in the far north the growing season is shorter than in the
temperate latitudes, this advance of spring is more prominent. The ecosystems in
the northern areas are thus more vulnerable to this changes in the spring, because
many natural processes risk to get out of balance. In order to properly understand
these current changes of the growing season, it is necessary to look back in time
to the pre-industrial mode of climate. By doing so we can study how the natural
dynamics of the spring season manifested themselves before the modern period
of warming.
Since there is little to no reliable meteorological data available from before the
industrial revolution, we derive the state of the climate of the past from socalled
palaeoecological proxies, in this case fossil leaves that act as biological
thermometers. With the fossil leaf remains we can reconstruct what the temperature
must have been in the past. Before such proxies work properly, they must be
soundly calibrated and tested. In this PhD research, the degree of undulation in
the circumference of the cell wall of the epidermal cells of birch leaves was used
generate information on the thermal intensity of the growing season, with the
advance of spring as main influencing factor. Dwarf birch cell circumference was
already established in previous studies as a paleo-thermometer for the growing
season. In the present study the downy birch was targeted to broaden the
proxy based on the circumference of the leaf cells. In order to achieve this, plant
physiological experiments performed in Finland, Poland, and Greenland provided
leaf samples grown under natural conditions and artificial warming were studied to
determine the exact responsiveness of birch to temperature. The meaningfulness
of the proxy has also been demonstrated by proving that it is sensitive to minor
annual fluctuations in the large-scale atmospheric system that affects the weather
in the areas around the North Atlantic. After validation and testing on modern leaf
material and from historical herbarium specimen, the proxy has then been used to
reconstruct the intensity of the growing season over roughly the past 1300 years in
Denmark, where the fossil leaves samples have been retrieved from lake sediment
cores. This study has shown that during the last millennium, the natural changes in the growing season have been closely linked to the state of prosperity of the
population, demonstrating the societal importance of changing seasonality. The
strong link between spring season weather on societal and economical welfare in
the past clearly shows that this rapidly changing seasonality regime will also have
to be considered in discussions of future climate change impacts on our societies.
... Another line of evidence has focused on the δ 13 C of alkenones in fossil foraminifera (Seki et al., 2010;Badger et al., 2013;Zhang et al., 2013), although the reliability of this proxy for CO 2 concentrations lower than ∼ 400 ppmv has recently been called into question (Badger et al., 2019). A different line of work relates the density of stomata on fossil plant leaves to atmospheric CO 2 concentration, providing data throughout the Cenozoic (Kürschner et al., 1996;Wagner et al., 2002;Finsinger and Wagner-Cremer, 2009;Beerling and Royer, 2011;Stults et al., 2011;Bai et al., 2015;Hu et al., 2015). This proxy has been the subject of discussion regarding its reliability (Indermühle et al., 1999;Jordan, 2011;Porter et al., 2019), based on its discrepancies with the ice-core record and presently unresolved problems due to the influence of other effects such as evolution, extinction, changes in local environment, and immigration of species, although recent work has gone some way towards resolving these issues (Franks et al., 2014). ...
Understanding the evolution of, and the interactions between, ice sheets and the global climate over geological timescales is important for being able to project their future evolution. However, direct observational evidence of past CO2 concentrations, and the implied radiative forcing, only exists for the past 800 000 years. Records of benthic δ18O date back millions of years but contain signals from both land ice volume and ocean temperature. In recent years, inverse forward modelling has been developed as a method to disentangle these two signals, resulting in mutually consistent reconstructions of ice volume, temperature, and CO2. We use this approach to force a hybrid ice-sheet–climate model with a benthic δ18O stack, reconstructing the evolution of the ice sheets, global mean sea level, and atmospheric CO2 during the late Pliocene and the Pleistocene, from 3.6 million years (Myr) ago to the present day. During the warmer-than-present climates of the late Pliocene, reconstructed CO2 varies widely, from 320–440 ppmv for warm periods to 235–250 ppmv for the early glacial excursion ∼3.3 million years ago. Sea level is relatively stable during this period, with maxima of 6–14 m and minima of 12–26 m during glacial episodes. Both CO2 and sea level are within the wide ranges of values covered by available proxy data for this period. Our results for the Pleistocene agree well with the ice-core CO2 record, as well as with different available sea-level proxy data. For the Early Pleistocene, 2.6–1.2 Myr ago, we simulate 40 kyr glacial cycles, with interglacial CO2 decreasing from 280–300 ppmv at the beginning of the Pleistocene to 250–280 ppmv just before the Mid-Pleistocene Transition (MPT). Peak glacial CO2 decreases from 220–250 to 205–225 ppmv during this period. After the MPT, when the glacial cycles change from 40 to 80 120 kyr cyclicity, the glacial–interglacial contrast increases, with interglacial CO2 varying between 250–320 ppmv and peak glacial values decreasing to 170–210 ppmv.
... These calibration functions have been used to estimate past CO 2 concentrations in the last interglacial (e.g., Rundgren and Bennike, 2002;Rundgren et al., 2005), the last glacial maximum (e.g., Beerling and Chaloner, 1994), the lateglacial (e.g., Beerling et al., 1995;Rundgren and Björck, 2003), and the Holocene (e.g., Rundgren and Beerling, 1999;Wagner et al., 1999;Beerling and Rundgren, 2000;Rundgren and Björck, 2003;Jessen et al., 2007). The taxa used in these reconstructions in Europe have mainly been Salix herbacea (e.g., Beerling et al., 1995;Rundgren and Beerling, 1999;Rundgren and Bennike, 2002), Betula nana (e.g., Beerling, 1993;Rundgren and Björck, 2003;Finsinger and Wagner-Cremer, 2009;Steinthorsdottir et al., 2013), B. pubescens or B. pendula (e.g., Wagner et al., 1999;Wagner et al., 2002;Wagner et al., 2004;García-Amorena et al., 2008), Quercus robur or Q. petraea (e.g., Wagner et al., 2004;Van Hoof et al., 2006), S. cinerea (e.g., McElwain et al., 1995), or Buxus balearica and B. sempervirens (e.g., Rivera et al., 2014). In North America, needles of Pinus flexilis (e.g., Van Der Water et al., 1994), Larix laricina, Picea glauca, and P. mariana, and leaves of Dryas integrifolia (e.g., McElwain et al., 2002) have been used. ...
There has been an upsurge of interest and research activity in trait-based approaches in ecology, biogeography, and macroecology. I discuss if this upsurge has impacted Quaternary botany (the study of plant remains preserved in sediments). I show that ecological attributes (including traits) have played and continue to play an integral part in the interpretation of Quaternary botanical data in terms of reconstructing past environments and interpreting long-term changes in plant assemblages. This use started over 120 years ago and continues to the present. It is unclear if a “new” Quaternary botany based on traits will develop because of the taxonomic limitations of much Quaternary botanical data.
... Another line of evidence has focused on the ratio of different types of alkenones in fossil foraminifera (Seki et al., 2010;Badger et al., 2013;Zhang et al., 2013), although the reliability of this proxy for CO2 concentrations lower than ~400 ppmv has recently been called into question (Badger et al., 2019). 15 A different line of work relates the density of stomata on fossil plant leaves to atmospheric CO2 concentration, providing data throughout the Cenozoic (Kürschner et al., 1996;Wagner et al., 2002;Finsinger and Wagner-Cremer, 2009;Beerling and Royer, 2011;Stults et al., 2011;Bai et al., 2015;Hu et al., 2015). This proxy has been the subject of some discussion regarding its reliability (Indermühle et al., 1999;Jordan, 2011;Porter et al., 2019), based on its discrepancies with the icecore record, and presently unresolved problems due to the influence of other effects such as evolution, extinction, changes in 20 local environment, and immigration of species. ...
Abstract. Understanding the evolution of, and the interactions between, ice sheets and the global climate over geological time is important for being able to constrain earth system sensitivity. However, direct observational evidence of past CO2 concentrations only exists for the past 800 000 years. Records of benthic δ18O date back millions of years, but contain signals from both land ice volume and ocean temperature. In recent years, inverse forward modelling has been developed as a method to disentangle these two signals, resulting in mutually consistent reconstructions of ice volume, temperature and CO2. We use this approach to force a hybrid ice-sheet – climate model with a benthic δ18O stack, reconstructing the evolution of the ice sheets, global mean sea level and atmospheric CO2 during the late Pliocene and the Pleistocene, from 3.6 million years (Myr) ago to the present day. During the warmer-than-present climates of the Late Pliocene, reconstructed CO2 varies widely, from 320–440 ppmv for warm periods such as Marine Isotope Stage (MIS) KM5c, to 235–250 ppmv for the MIS M2 glacial excursion. Sea level is relatively stable during this period, with a high stand of 6–14 m, and a drop of 12–26 m during MIS M2. Both CO2 and sea level are within the wide ranges of values covered by available proxy data for this period. Our results for the Pleistocene agree well with the ice-core CO2 record, as well as with different available sea-level proxy data. During the early Pleistocene, 2.6–1.2 Myr ago, we simulate 40 kyr glacial cycles, with interglacial CO2 decreasing from 280–300 ppmv at the beginning of the Pleistocene, to 250–280 ppmv just before the Mid-Pleistocene Transition (MPT). Peak glacial CO2 decreases from 220–250 ppmv to 205–225 ppmv during this period. After the MPT, when the glacial cycles change from 40 kyr to 80/120 kyr cyclicity, the glacial-interglacial contrast increases, with interglacial CO2 varying between 250–320 ppmv, and peak glacial values decreasing to 170–210 ppmv.
