Mean Annual Temperature Estimates Research Articles

Seasonal variability in Arctic temperatures during early Eocene time

As a deep time analog for today's rapidly warming Arctic region, early Eocene (52–53 Ma) rock on Ellesmere Island in Canada's High Arctic (∼ 79°N.) preserves evidence of lush swamp forests inhabited by turtles, alligators, primates, tapirs, and hippo-like Coryphodon. Although the rich flora and fauna of the early Eocene Arctic imply warmer, wetter conditions than at present, the quantification of Eocene Arctic climate has been more elusive. By analyzing oxygen isotope ratios of biogenic phosphate from mammal, fish, and turtle fossils from a single locality on central Ellesmere Island, we infer early Eocene Arctic temperatures, including mean annual temperature (MAT) of ∼ 8 °C, mean annual range in temperature of ∼ 16.5–19 °C, warm month mean temperature of 19–20 °C, and cold month mean temperature of 0–3.5 °C. Our seasonal range in temperature is similar to the range in estimated MAT obtained using different proxies. In particular, relatively high estimates of early Eocene Arctic MAT and SST by others that are based upon the distribution of branched glycerol dialkyl glycerol tetraether (GDGT) membrane lipids in terrestrial soil bacteria and isoprenoid tetraether lipids in marine Crenarchaeota fall close to our warm month temperature, suggesting a bias towards summer values. From a paleontologic perspective, our temperature estimates verify that alligators and tortoises, by way of nearest living relative-based climatic inference, are viable paleoclimate proxies for mild, above-freezing year-round temperatures. Although for both of these reptilian groups, past temperature tolerances probably were greater than in living descendants.

A climatic and taxonomic comparison between leaf litter and standing vegetation from a Florida swamp woodland

One method to determine past climate has been the use of leaf morphological characteristics of fossil leaves quantified using modern climate and canopy leaf characteristics. Fossil assemblages are composed of abscised leaves, and climate may be more accurately determined by using leaves from leaf litter instead of the canopy. To better understand whether taphonomic processes make a difference in this relationship, a north-central Florida woodland was sampled to determine the morphologically based climate estimates from these leaves. Leaves from woody, dicotyledonous plants were collected and identified, then compared using presence/absence data and analyzed using several linear regression equations and the CLAMP data set. Although the majority of standing vegetation was reflected in leaf litter, some inconsistencies were observed, which may reflect plant community structure or sampling technique. Mean annual temperature (MAT) and growing season precipitation (GSP) were estimated from leaf litter morphological characters and living leaves. Overall, values for MAT estimated from litter and living leaves were cooler than actual MATs, although several accurate and high estimates were obtained depending on the predictive method used. Estimated GSP values were higher than actual GSPs. Statistically, no difference was observed between MAT and GSP estimates derived from leaf litter vs. estimates derived from living leaves, with one exception.

Oxygen isotope ratios in fossil wood cellulose: Isotopic composition of Eocene- to Holocene-aged cellulose

We measured the δ18O of cellulose (δ18Ocel) extracted from fossil wood collected at 9 sites in the northern and southern hemispheres as a potential source of information about precipitation δ18O (δ18Oppt) in the past and paleotemperatures. The samples had been buried in fluvial sediments for periods of time ranging from ca. 45 million to 250 years. At the oldest localities (high latitude, Eocene- through Pliocene-age sites in Canada and Russia), mean annual temperature (MAT) estimates derived from the modern relationship between MAT and δ18Ocel are 6–16°C lower than the MAT estimates derived from other biological proxies. Estimates of Pleistocene and Holocene mean annual temperatures are close to the modern values at those sites. These results are consistent with other recent findings that the MAT/δ18Oppt relationship across North America was not constant throughout the Cenozoic. Paleo-δ18Oppt estimates derived from fossil cellulose and the modern North American relationship between δ18Ocel and δ18Oppt are within the current annual range of δ18Oppt values at all locations. The middle Eocene δ18Oppt we determined from arctic cellulose samples (−21.9‰) is consistent with river water δ18O determined in two other studies (−19.1‰ to −22‰). These findings provide some evidence that a precipitation δ18O signal may be retained in wood cellulose during millions of years of burial, and that latitudinal patterns in δ18Oppt may not have changed much during the past 45Ma. These interpretations depend, of course, on the assumption that the isotopic composition of the cellulose has not changed during burial, an assumption for which it is difficult to gather direct evidence. XRD analysis shows that the crystalline form of the fossil cellulose we used to estimate paleoprecipitation δ18O and paleo-MAT is the same as that of modern cellulose, and that the samples are free of quartz and iron oxide contaminants that result in negative errors in measured δ18Ocel.

Strontium to calcium ratios in the marine gastropod Conus ermineus: Growth rate effects and temperature calibration

Here we investigate the potential of Sr/Ca ratios in the marine gastropod Conus ermineus for reconstructing seawater temperatures. We present annually resolved records of Sr/Ca and δ18O for four shells collected alive from the Flower Garden Banks National Marine Sanctuary in the Gulf of Mexico. Our results show that variations in Sr/Ca and δ18O covary with the in situ seasonal temperature cycle. Sr/Ca and temperature are positively correlated, in contrast with the inverse relationship found in inorganically precipitated aragonite. The seasonal Sr/Ca variability is superimposed on a long‐term trend of increasing Sr/Ca with age. Both the seasonal and long‐term ontogenetic changes in Sr/Ca are associated with variations in growth rate, defined here as the shell linear extension rate (LER); the seasonal variability in LER is superimposed on a long‐term decrease with ontogeny. Thus the covariance of Sr/Ca ratios with temperature and LER suggests that Sr incorporation is likely driven by temperature influence on growth rate, rather than by thermodynamic effects. Unlike the seasonal variability, the ontogenetic effect is characterized by inverse covariation between Sr/Ca and LER, suggesting that Sr/Ca variability is not controlled by growth rate alone, but probably by two different biomineralization mechanisms, one related to temperature and the other related to age. We use the seasonal Sr/Ca signal of four shells to construct a temperature calibration. To minimize the ontogenetic effects, we separate the records into juvenile and adult growth stages and calculate the Sr/Ca‐temperature (T) relationships: Juvenile: Sr/Ca (mmol mol−1) = 0.042 (±0.008) * T (°C) + 0.24 (±0.21) (R2 = 0.66) Adult: Sr/Ca(mmol mol−1) = 0.072 (±0.014) * T (°C) − 0.05 (±0.34) (R2 = 0.68) Applying the calibration to a single specimen provides mean annual temperature estimates within ±1°C of the in situ temperature record but resolves the seasonal variability only within ±3.5°C. The large error in the seasonal estimates reflects the high variability among specimens. To reduce the uncertainty on seasonal temperatures, we propose combining records from multiple shells to generate an average temperature record. The potential of this approach needs, however, to be validated in other locations.

Antarctic climate at the Eocene/Oligocene boundary — climate model sensitivity to high latitude vegetation type and comparisons with the palaeobotanical record

Simulated climate for the Antarctic continent using the GENESIS (Version 2.1) Global Climate Model with 34 Ma boundary conditions is shown to be highly sensitive to polar vegetation type. Six experiments were run using different levels of atmospheric CO 2, orbital configurations, ice sheet geometries and vegetation types to assess model sensitivity to Antarctica being covered with either a needle leaf evergreen forest or tundra. Simulations using 2× pre-industrial levels of CO 2 (combined mean annual temperature (MAT) − 19 °C) are about 7 °C cooler than minimum estimates from the Antarctic Cenozoic plant record (MAT − 12 to 15 °C). However, simulations using 3× CO 2 (MAT − 7 °C) are in good agreement with our empirical estimates of mean annual temperature. With ice sheets and orbits set up to represent early Oligocene interglacial conditions, the tundra climate is significantly cooler than the evergreen forest climate, with local, austral summer averages up to 6 °C cooler in non-glaciated areas and continental averages ∼2.5 °C cooler. In the model this is mainly due to higher albedo and decreases in net radiation and sensible and latent heat flux, especially during spring and summer. Feedbacks between coastal and continental cooling, marginal sea surface temperatures and sea ice also appear to be significant. A review of the late Palaeocene to earliest Miocene plant fossil record in the Antarctic Peninsula and Ross Sea regions shows that the vegetation was in transition ∼34 Ma, from a relatively diverse, mainly evergreen forest to a tundra vegetation. The modelled sensitivity of continental temperatures to a change from forest to tundra suggests vegetation-climate feedbacks during the Eocene–Oligocene transition played a significant role in the initial rapid glaciation of the continent.

Phytoliths as quantitative indicators for the reconstruction of past environmental conditions in China I: phytolith-based transfer functions

This study investigated the distribution of phytolith assemblages in China from surface soil samples at 243 sites along significant ecological and climatic gradients to develop transfer functions for quantitative reconstruction of palaeoenvironment. Canonical correspondence analysis (CCA) and detrended correspondence analysis (DCA) were used to determine the main environmental variables influencing phytolith distributions. The results reveal that mean annual precipitation (MAP) is the dominant variable controlling the spatial distribution of phytoliths, which accounts for 39% of the total variance. Mean annual temperature (MAT), relative humidity (Humi), and annual evaporation (VAP) are another three significant variables, accounting for 6%, 10%, and 5%, respectively, of the total variance in phytolith distributions. Transfer functions, based on weighted averaging plus partial least squares (WA-PLS), were developed for MAP ( R - boot 2 = 0.90 , root-mean-square-error of prediction (RMSEP)=148 mm), MAT ( R - boot 2 = 0.84 , RMSEP=2.52 °C), Humi ( R - boot 2 = 0.75 , RMSEP=6.36%) and VAP ( R - boot 2 = 0.59 , RMSEP=327 mm). Overall, our results confirm that phytoliths can provide reliable and robust estimates of MAP, MAT, Humi and VAP. Thus, WA-PLS is a robust calibration method for quantitative palaeoenvironmental reconstruction based on phytolith data.

Correlations of climate and plant ecology to leaf size and shape: potential proxies for the fossil record

The sizes and shapes (physiognomy) of fossil leaves are widely applied as proxies for paleoclimatic and paleoecological variables. However, significant improvements to leaf-margin analysis, used for nearly a century to reconstruct mean annual temperature (MAT), have been elusive; also, relationships between physiognomy and many leaf ecological variables have not been quantified. Using the recently developed technique of digital leaf physiognomy, correlations of leaf physiognomy to MAT, leaf mass per area, and nitrogen content are quantified for a set of test sites from North and Central America. Many physiognomic variables correlate significantly with MAT, indicating a coordinated, convergent evolutionary response of fewer teeth, smaller tooth area, and lower degree of blade dissection in warmer environments. In addition, tooth area correlates negatively with leaf mass per area and positively with nitrogen content. Multiple linear regressions based on a subset of variables produce more accurate MAT estimates than leaf-margin analysis (standard errors of ±2 vs. ±3°C); improvements are greatest at sites with shallow water tables that are analogous to many fossil sites. The multivariate regressions remain robust even when based on one leaf per species, and the model most applicable to fossils shows no more signal degradation from leaf fragmentation than leaf-margin analysis.

Oxygen isotope and paleobotanical estimates of temperature and 18O-latitude gradients over North America during the early Eocene

Empirical estimates of climate parameters such as mean annual temperature (MAT) are essential to describe both ancient climate and to ground truth climate model simulations of past climates. In terrestrial settings, no single proxy record is able to provide detailed temporal yet geographically widespread information, and it thus becomes essential that paleoclimatic information obtained from different proxies be comparable. As an example of how to compare estimates, and to illustrate what can be learned by doing so, we measured oxygen isotope ratios of phosphate in the tooth enamel of fossil mammals and the body scales of freshwater fish in order to estimate the mean annual temperature (MAT) in which they lived. The samples were collected from Paleogene rocks of the Bighorn, Green River, and Powder River basins of Wyoming. Earliest Eocene samples provide MAT estimates that are similar to MAT estimates for the same times and areas obtained from leaf margin analysis. Furthermore, isotopic data from the Paleocene Eocene Thermal Maximum (PETM), which has not yet yielded fossil floras, indicate a significantly higher MAT of 26°C. We also used temperature estimates obtained by both methods to investigate paleoelevation and to reconstruct geographic patterns of MAT over North America for the early Eocene. Larger Laramide basins have higher temperatures and lower inferred elevations compared to associated volcanic highlands where cooler temperatures are consistent with substantial elevations. In turn, latitudinal gradients in temperature indicate that warming centered on polar regions played an important role during the Eocene “hothouse”. Lastly, we show that the reconstructed Eocene relation between oxygen isotope ratios of precipitation and MAT is significantly different from the modern relation between these two variables. Because the relation has changed over time, the modern correlation should not be used to estimate paleo-MAT from measurements of oxygen isotope ratios in fossil material.

Late Cretaceous and Paleocene terrestrial climates of New Zealand: Leaf fossil evidence from South Island assemblages

Univariate and multivariate leaf morphology‐based analysis of leaf fossil assemblages from localities in the South Island of New Zealand provide quantitative paleoclimate estimates for the terrestrial Late Cretaceous and Paleocene. Favourable growing conditions with a cool to mild temperate climate are inferred for the youngest pollen zone in the Late Cretaceous (PM2) with moderately high precipitation and high dicotyledonous angiosperm diversity. Mean annual temperature estimates of c. 12–16 and c. 7–11°C were produced from northwest Nelson and North Otago PM2 Zone assemblages, respectively. These different temperature estimates most likely reflect differences in age, although geographic differences may also be a factor. Consistent data from three Paleocene assemblages suggest cool‐temperate conditions. Mean annual temperature estimates of c. 6–12°C were produced from these Paleocene assemblages. They also had lower dicotyledonous leaf diversity than the Late Cretaceous assemblages, no more than 30 different angiosperm leaf forms.

Paleoclimatic Condition Inferred from the Tertiary Plant Megafossil Assemblages from Northern Thailand

Physiognomic analysis using CLAMP technique of Wolfe (1933) was performed to two plant megafossil assemblages from northern Thailand intramontane basins to obtain quantitative data on the mean annual temperature (MAT), cold month and warm month mean temperatures (CMMT & WMMT) and growing season precipitation (GSP). The assemblage from Ban Pa Kha (BPK), a subbasin of Li Basin, dated as Late Oligocene, consists of 30 types of woody dicotyledonous leaves along with infructescence and inflorescence of alders and winged-seed of maple, as well as conifers. Physiognomic analysis of the fossil angiosperm leaves implies a MAT of 17.60°C, CMMT and WMMT of 7.5 and 27.80°C, and GSP of 324.5cm. Its composition and physiognomic feature correspond well with Notophyllous Broad-leaved Evergreen Forest of Wolfe (1979). Assemblage from Mae Lai basin (ML) of late Early to middle Middle Miocene age consists of 36 types of dicotyledonous leaves with no component of “Laurasian montane element” proposed by Morley (1999). Climate variables obtained are a MAT of 19.20°C, CMMT and WMMT of 12.5 and 26.30°C, and GSP of 214.7cm. Although MAT estimate is slightly lower than expected, floristic composition of ML can be comparable to Paratropical Rain Forest of Wolfe (1979). MAT estimates indicate the warming trend from the BPK to the ML time. CMMT estimate from BPK is 5 degree lower than that of ML, whereas WMMT is even higher in BPK. This suggests that decrease of mean annual range of temperature, caused mainly by an increase of CMMT, result in the reduction of temperate elements and expansion of paratropical evergreen forests by at least Middle Miocene. GSP estimates indicate perhumid Late Oligocene climate and humid but much smaller precipitation in the Mae Lai time. This change might be ascribed to uplifting Tibetan plateau and the onset of monsoonal climate before the Mae Lai time.

Status of alkenone paleothermometer calibration: Report from Working Group 3

The alkenone unsaturation index, U37K′, has now proven its worth as a tool for paleothermometry. U37K′ measured in most modern sediments throughout the World Ocean can be translated using established calibrations into realistic, seemingly reliable estimates of mean annual temperature at the sea surface (SST). However, it remains mysterious why water temperature estimates based on this biotic index correspond to “mean annual” SST and whether such estimates apply back in geological time. Solving these mysteries is imperative and will require thoughtful, concerted research effort by the biological, chemical, and geological oceanographic community. This report summarizes what is now known about alkenones, in particular, their use in estimating the growth temperature of specific haptophyte algae that synthesize and export these compounds to the marine sediment record. It highlights future field and laboratory research directions that should be taken to clarify and bolster utility of alkenones as a generally valued paleoceanographic tool.

Tropical climates at the Last Glacial Maximum: a new synthesis of terrestrial palaeoclimate data. I. Vegetation, lake-levels and geochemistry

Palaeodata in synthesis form are needed as benchmarks for the Palaeoclimate Modelling Intercomparison Project (PMIP). Advances since the last synthesis of terrestrial palaeodata from the last glacial maximum (LGM) call for a new evaluation, especially of data from the tropics. Here pollen, plant-macrofossil, lake-level, noble gas (from groundwater) and δ18O (from speleothems) data are compiled for 18±2 ka (14C), 32 °N–33 °S. The reliability of the data was evaluated using explicit criteria and some types of data were re-analysed using consistent methods in order to derive a set of mutually consistent palaeoclimate estimates of mean temperature of the coldest month (MTCO), mean annual temperature (MAT), plant available moisture (PAM) and runoff (P-E). Cold-month temperature (MAT) anomalies from plant data range from −1 to −2 K near sea level in Indonesia and the S Pacific, through −6 to −8 K at many high-elevation sites to −8 to −15 K in S China and the SE USA. MAT anomalies from groundwater or speleothems seem more uniform (−4 to −6 K), but the data are as yet sparse; a clear divergence between MAT and cold-month estimates from the same region is seen only in the SE USA, where cold-air advection is expected to have enhanced cooling in winter. Regression of all cold-month anomalies against site elevation yielded an estimated average cooling of −2.5 to −3 K at modern sea level, increasing to ≈−6 K by 3000 m. However, Neotropical sites showed larger than the average sea-level cooling (−5 to −6 K) and a non-significant elevation effect, whereas W and S Pacific sites showed much less sea-level cooling (−1 K) and a stronger elevation effect. These findings support the inference that tropical sea-surface temperatures (SSTs) were lower than the CLIMAP estimates, but they limit the plausible average tropical sea-surface cooling, and they support the existence of CLIMAP-like geographic patterns in SST anomalies. Trends of PAM and lake levels indicate wet LGM conditions in the W USA, and at the highest elevations, with generally dry conditions elsewhere. These results suggest a colder-than-present ocean surface producing a weaker hydrological cycle, more arid continents, and arguably steeper-than-present terrestrial lapse rates. Such linkages are supported by recent observations on freezing-level height and tropical SSTs; moreover, simulations of “greenhouse” and LGM climates point to several possible feedback processes by which low-level temperature anomalies might be amplified aloft.

Paleotemperature Estimation from Dicotyledonous Wood Anatomical Characters

Following an earlier study documenting the relationships between wood anatomical features and climate, we examine the utility of dicotyledonous wood assemblages in assessing paleoclimate. The wood anatomy of dicotyledons from modern forest sites in North, Central, and South America, England, Africa, Malaysia, and the Pacific islands was used to derive equations to predict site mean annual temperature. The best equations gave estimates within 5 degrees C at validation sites. Because trees are physiologically active over a wide range in temperature throughout the year, it would be surprising if wood anatomical characters were more finely tuned to temperature. Mean annual temperature (MAT) was estimated from five fossil wood assemblages: Yellow-stone, Wyoming (early Eocene); Clarno Nut Beds, Oregon (middle Eocene); Post, Oregon (late Eocene); Vantage, Washington (middle Miocene); and Fejej, Ethiopia (Miocene). We used the two best equations to estimate paleotemperature at each site; the MAT estimates differed by 0.1 degrees C at Fejej and 5.7 degrees C at Yellowstone, with differences intermediate to these at the other fossil sites. Compared to present-day values, the paleotemperature estimates indicate that, at middle latitudes of the Northern Hemisphere, mean annual temperatures were warmer in the Eocene and Miocene, whereas the near-equatorial Fejej site was the same temperature in the Miocene as it is today. Where possible, we compared the MAT estimates obtained using fossil woods with those obtained using fossil leaves, and found discrepancies of up to 13 degrees C. These differences may, in part, reflect the complicating effect of evolutionary trends in wood anatomical characters that may have been independent of climate change.

Estimation of temperature and precipitation from morphological characters of dicotyledonous leaves

The utility of regression and correspondence models for deducing climate from leaf physiognomy was evaluated by the comparative application of different predictive models to the same three leaf assemblages. Mean annual temperature (MAT), mean annual precipitation (MAP), and growing season precipitation (GSP) were estimated from the morphological characteristics of samples of living leaves from two extant forests and an assemblage of fossil leaves. The extant forests are located near Gainesville, Florida, and in the Florida Keys; the fossils were collected from the Eocene Clarno Nut Beds, Oregon. Simple linear regression (SLR), multiple linear regression (MLR), and canonical correspondence analysis (CCA) were used to estimate temperature and precipitation. The SLR models used only the percentage of species having entire leaf margins as a predictor for MAT and leaf size as a predictor for MAP. The MLR models used from two to six leaf characters as predictors, and the CCA used 31 characters. In comparisons between actual and predicted values for the extant forests, errors in prediction of MAT were 0.6°-5.7°C, and errors in prediction of precipitation were 6-89 cm (=6-66%). At the Gainesville site, seven models underestimated MAT and only one overestimated it, whereas at the Keys site, all eight models overestimated MAT. Precipitation was overestimated by all four models at Gainesville, and by three of them at the Keys. The MAT estimates from the Clarno leaf assemblage ranged from 14.3° to 18.8°C, and the precipitation estimates from 227 to 363 cm for MAP and from 195 to 295 cm for GSP.

The use of a resemblance function in the measurement of climatic parameters from the physiognomy of woody dicotyledons

Abstract Wolfe compiled a data set (CLAMP) of the physiognomy of woody dicotyledon leaves with a view to using it to extract climatic information from fossil floras. Attempts made, using these data, to identify and describe the relationship between plant physiognomy and climate, have all searched for a global relationship applicable throughout data space. We investigate the possibility that the relation between climate and physiognomy is so non-linear that only local relationships should be sought. We use a resemblance function to select sites that are physiognomically similar to each unknown site; these similar sites, alone, yield a climatic estimate for the unknown site. Data collected from New Zealand and Australia are then added to Wolfe's data set in order to test this new method. We show that the use of a resemblance function enables us to produce Mean Annual Temperature estimates for all modern sites that lie within 2.6°C of meteorological data for 90% of the sites. This method also allows the objective identification of outliers based on their distance in physiognomic space from their nearest neighbours. When a method is used that searches for a global relationship between physiognomy and climate, the misfit of estimated Mean Annual Temperature for the combined Southern Hemisphere and CLAMP sites is almost twice as great (5°C) as that to the CLAMP sites alone. In contrast, when the resemblance function is used, the RMS misfit of estimated Mean Annual Temperature increases by only 0.2°C. This result demonstrates the robustness of the new method.

When are leaves good thermometers? A new case for Leaf Margin Analysis

Precise estimates of past temperatures are critical for understanding the evolution of organisms and the physical biosphere, and data from continental areas are an indispensable complement to the marine record of stable isotopes. Climate is considered to be a primary selective force on leaf morphology, and two widely used methods exist for estimating past mean annual temperatures from assemblages of fossil leaves. The first approach, Leaf Margin Analysis, is univariate, based on the positive correlation in modern forests between mean annual temperature and the proportion of species in a flora with untoothed leaf margins. The second approach, known as the Climate-Leaf Analysis Multivariate Program, is based on a modern data set that is multivariate. I argue here that the simpler, univariate approach will give paleotemperature estimates at least as precise as the multivariate method because (1) the temperature signal in the multivariate data set is dominated by the leaf-margin character; (2) the additional characters add minimal statistical precision and in practical use do not appear to improve the quality of the estimate; (3) the predictor samples in the univariate data set contain at least twice as many species as those in the multivariate data set; and (4) the presence of numerous sites in the multivariate data set that are both dry and extremely cold depresses temperature estimates for moist and nonfrigid paleofloras by about 2°C, unless the dry and cold sites are excluded from the predictor set.New data from Western Hemisphere forests are used to test the univariate and multivariate methods and to compare observed vs. predicted error distributions for temperature estimates as a function of species richness. Leaf Margin Analysis provides excellent estimates of mean annual temperature for nine floral samples. Estimated temperatures given by 16 floral subsamples are very close both to actual temperatures and to the estimates from the samples. Temperature estimates based on the multivariate data set for four of the subsamples were generally less accurate than the estimates from Leaf Margin Analysis. Leaf-margin data from 45 transect collections demonstrate that sampling of low-diversity floras at extremely local scales can result in biased leaf-margin percentages because species abundance patterns are uneven. For climate analysis, both modern and fossil floras should be sampled over an area sufficient to minimize this bias and to maximize recovered species richness within a given climate.

Elemental and isotopic proxies of paleotemperature and paleosalinity: Climate reconstruction of the marginal northeast Pacific ca. 80 ka

Isotope (δ 18 O) and minor element (Mg/Ca, Sr/Ca) analyses of a fossil shell of the marine mussel Mytilus trossulus (Gould) from the Whisky Run terrace at Coquille Point, Bandon, Oregon, enable reconstruction of a paleoclimatic profile for the temperate northeastern Pacific ca. 80–85 ka. The Whisky Run terrace is correlative with marine oxygen isotope (δ 18 O) substage 5a, the final sea-level highstand of the last interglacial complex. Herein we provide sea-surface temperature estimates and report on a new technique that allows estimates to be made of δ 18 O of seawater and riverine discharge from the skeletal chemistry of a single mussel shell. Estimates of mean annual temperature from Mg/Ca ratios are lower than those suggested by the accompanying fossil fauna, and significantly lower than present-day conditions. The data also suggest a decrease in the range of seasonal temperature extremes at 80 ka compared to today. Estimates of the fresh-water and seawater δ 18 O end members, −4.5‰ and +0.5‰, respectively, are slightly greater than modern values.

Are paleoclimate estimates biased by foliar physiognomic responses to increased atmospheric CO2?

Physiognomic analysis of fossil angiosperm leaves has provided an important quantitative database of Tertiary terrestrial paleoclimate. However, atmospheric CO 2 level, a critical control on plant growth, may have been higher in the Tertiary. It is thus crucial to investigate whether elevated CO 2 affects leaf physiognomy. In this study, leaves were collected from white oak ( Quercus alba L.) seedlings grown in open-top growth chambers at Oak Ridge National Laboratory. The only physiognomic change noted is an increase in length to width ratio with increasing CO 2 . In the literature, leaf size has been observed to increase, decrease or remain unchanged for woody C 3 species grown in elevated CO 2 . Typically, one sees more variation due to microsite or phenotype than due to CO 2 level. By applying these observed physiognomic trends to two fossil floras, it is argued that estimates of mean annual temperature and growing season precipitation may be biased on the order of 1°C and 20 cm, respectively. These are relatively small effects, as the values are similar to the standard errors of the regression models used to estimate paleoclimate. The lack of data, the variability of response to CO 2 associated with microsite and phenotype, and the question of whether observed short-term trends with elevated CO 2 are sustained make it impossible to propose a correction factor. Adequate sample size and sampling of several sites are the best way to attempt to compensate for CO 2 effects on a given fossil flora until response to CO 2 is better understood.

Paleoclimate and paleoelevation of the Oligocene Pitch-Pinnacle flora, Sawatch Range, Colorado

Research Article| May 01, 1996 Paleoclimate and paleoelevation of the Oligocene Pitch-Pinnacle flora, Sawatch Range, Colorado Kathryn M. Gregory; Kathryn M. Gregory 1Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York 10964-8000 Search for other works by this author on: GSW Google Scholar W. C. McIntosh W. C. McIntosh 2New Mexico Bureau of Mines and Mineral Resources, Socorro, New Mexico 87801 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1996) 108 (5): 545–561. https://doi.org/10.1130/0016-7606(1996)108<0545:PAPOTO>2.3.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Kathryn M. Gregory, W. C. McIntosh; Paleoclimate and paleoelevation of the Oligocene Pitch-Pinnacle flora, Sawatch Range, Colorado. GSA Bulletin 1996;; 108 (5): 545–561. doi: https://doi.org/10.1130/0016-7606(1996)108<0545:PAPOTO>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Angiosperm leaves from the Oligocene Pitch-Pinnacle flora, which grew between 32.9 and 29 Ma, are described for the first time. This flora is especially interesting because it grew in a tectonically active region around the time of the precipitous Oligocene temperature drop and thus provides important constraints on paleoclimate and paleoelevation. New multiple regression models are developed from the modern vegetation leaf physiognomy data set of J. A. Wolfe and, when applied to the Pitch-Pinnacle flora, suggest a mean annual temperature (MAT) of 12.7 ± 1.5°C, with cold month and warm month means of 4.5 ± 2.2°C and 20.4 ± 2.5°C, respectively, and a mean annual range of temperature of 18.5 ± 3.8°C. Growing season precipitation is estimated to have been 101 ± 16 cm, with this rain falling mostly during the nongrowing season. When the MAT estimate for the Pitch-Pinnacle flora is combined with MAT estimates for coeval floras from the coast, the implied elevation is either 2–3 km if the flora is pre-Oligocene deterioration, or around 1 km if post-deterioration. Paleodrainage reconstructions suggest the former, but more data are needed to resolve this issue. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Biogeographic, ecological and stratigraphic relationships of the Miocene brown coal floras, Latrobe Valley, Victoria, Australia

Palaeobotanical studies of the brown coal deposits of the Latrobe Valley have contributed significantly towards an understanding of the age of the deposits, existing climatic conditions and detailed depositional environments. This paper re-assesses some past reconstructions for the Early to Mid Miocene coals using recent information on plant distributions and their bioclimatic significance and on a marine incursion model for coal lithotype formation. The brown coal flora is composed overwhelmingly of rainforest taxa that presently cover a range of different environments within the Australasian region. The application of a bioclimatic prediction model to these taxa allows the construction of consistent and quantitative estimates of climates during coal-forming phases. It is considered that rainfall in the area was more than twice the 850 mm received today, with significant seasonal variation. The mean annual temperature estimate of about 19°C, indicating a mesothermal or subtropical environment, is some 2–5C higher than present and higher than previous estimates. It does, however, correspond with sea-surface temperature estimates for the Southern Ocean at this time. The original model of lithotype formation, which suggests that lithotypes conform to a successional sequence from open water in the lightest coloured lithotypes to raised bog in the darkest lithotypes, is considered to be inconsistent with the evidence for lightening upwards sequences within the coals, a central feature of the proposed marine incursion model of coal formation. The two models are reconciled to some degree by a reinterpretation of the palaeobotanical data and by the postulation of climatic rather than autogenic successional control over lithotype formation.