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Paleoclimate records can be valuable for both reconstructing Earth's past climate history and in the evaluation of climate models, but these records can vary greatly in quality, with significant differences [...]

The late Miocene and Pliocene Beaufort Formation and equivalent units throughout the Canadian Arctic Archipelago captured a rich record of landscape evolution, Arctic paleoclimatology, and paleo-ecosystem changes caused by a [...]

We discuss the DISORT-based radiative transfer pipeline ('CRISM_LambertAlb') for atmospheric and thermal correction of MRO/CRISM data acquired in multispectral mapping mode (~200 m/pixel, 72 spectral channels). Currently, in this phase-one version of the system, we use aerosol optical depths, surface temperatures, and lower atmospheric temperatures, all from climatology derived from Mars Global Surveyor Thermal Emission Spectrometer (MGS-TES) data and from surface altimetry derived from MGS Mars Orbiter Laser Altimeter (MOLA). The DISORT-based model takes the dust and ice aerosol optical depths (scaled to the CRISM wavelength range), the surface pressures (computed from MOLA altimetry, MGS-TES lower atmospheric thermometry, and Viking-based pressure climatology), the surface temperatures, the reconstructed instrumental photometric angles, and the measured I/F spectrum as inputs, and then a Lambertian albedo spectrum is computed as the output. The Lambertian albedo spectrum is valuable geologically because it allows the mineralogical composition to be estimated. Here, I/F is defined as the ratio of the radiance measured by CRISM to the solar irradiance at Mars divided by [pi]; if there was no martian atmosphere, I/F divided by the cosine of the incidence angle would be equal to the Lambert albedo for a Lambertian surface. After discussing the capabilities and limitations of the pipeline software system, we demonstrate its application on several multispectral data cubes--particularly, the outer reaches of the northern ice cap of Mars, the Tyrrhena Terra area that is northeast of the Hellas basin, and an area near the landing site for the Phoenix mission in the northern plains. For the icy spectra near the northern polar cap, aerosols need to be included in order to properly correct for the C[O.sub.2] absorption in the [H.sub.2]O ice bands at wavelengths near 2.0 [micro]m. In future phases of software development, we intend to use CRISM data directly in order to retrieve the spatiotemporal maps of aerosol optical depths, surface pressure, and surface temperature. This will allow a second level of refinement in the atmospheric and thermal correction of CRISM multispectral data. Index Terms--Atmospheric propagation, infrared spectroscopy, remote sensing, software verification and validation.

The Neogene Meyer Desert Formation, Sirius Group, at Oliver Bluffs in the Transantarctic Mountains, contains a sequence of glacial deposits formed under a wet-based glacial regime. Within this sequence fluvial deposits have yielded fossil plants that, along with evidence from fossil insects, invertebrates and palaeosols, indicate the existence of tundra conditions at 85[degrees]S during the Neogene. Mean annual temperatures of c. -12 [degrees]C are estimated, with short summer seasons with temperatures up to +5 [degrees]C. The current published date for this formation is Pliocene, although this is hotly debated. Reconstructions produced by the TRIFFID and BIOME 4 vegetation models, utilizing a Pliocene climatology derived from the HadAM3 General Circulation Model (running with prescribed boundary conditions from the US Geological Survey PRISM2 dataset), also predict tundra-type vegetation in Antarctica. The consistency of the model outputs with geological evidence demonstrates that a Pliocene age for the Meyer Desert Formation is consistent with proxy environmental reconstructions and numerical model reconstructions for the mid-Pliocene. If so, the East Antarctic Ice Sheet has behaved in a dynamic manner in the recent geological past.

A new reconstruction of winter and summer temperatures in the Low Countries (the present-day Netherlands and Belgian Flanders), based upon documentary evidence from AD 764 to 1705 and extended by observations to 1998, is compared with relevant paleo series from the European network. The Low Countries Temperature (LCT) reconstruction is well supported by existing evidence in both seasons from about 1300 onwards, on timescales ranging from annual to centennial. The spectral analysis confirms that the dominant oscillations in the LCT have counterparts in the independent data and that most of the periodicities characteristic for the instrumental segment of the LCT are preserved in the reconstruction. Throughout this period of reliable reconstruction there was no detectable inhomogeneity of the variances in either seasons. Prior to about 1300, there are few sources that can be used to evaluate LCT. It was possible to add some support for the LCT on decadal and centennial timescales for the 12th and 13th centuries. However, there is no independent data for the first three centuries of the reconstruction. The LCT series exhibits significant season-dependent variability on bidecadal and centennial timescales. The seasonality is particularly remarkable in the 10th and 15th centuries which were--on average--warm in the summer and cold in the winter. The 20th century was by far (three standard errors) the warmest century of the last millennium in terms of winter temperatures, while the 13th century was warmest in terms of summer temperatures (by the narrow margin of one standard error). In both seasons, the coldest centennial period was centered around 1600. The present results place the reconstructed LCT series within the existing paleoclimatic network, and provide an insight into temperature variability in the Low Countries through the centuries.

Mass-balance relationships of 10 major elements in a Vertisol climosequence and chronosequence formed on alluvial terraces on the Texas Gulf Coastal Plain indicate that the soils develop characteristic element translocation patterns in response to climatic forcing and reach mass-flux equilibrium within a relatively short period of time. Vertisols within the climosequence (age 35 ka, 800-1500 mm mean annual precipitation [MAP]) approach a net mass flux of ~-16% ([+ or -] 3%) of parent element contents, corresponding to a weathering-flux of -1.0 x [10.sup.-3] to -1.3 x [10.sup.-3] g [cm.sup.-2] [yr.sup.-1], when MAP exceeds 900 mm. Net mass-flux assessments in a Vertisol chronosequence (0.4-35 ka, 1000 mm MAP) show that this equilibrium is achieved within 5-6 k.y. Below 900 mm MAP, positive net mass fluxes indicate that Vertisol profiles are gaining material (at a rate of 0.2 x [10.sup.-3] g [cm.sup.-2] [yr.sup.-1]). Vertisols forming in drier MAP areas approach equilibrium with climate by different mechanisms and at different rates, compared to their wetter counterparts, and may not be as sensitive to millennial-scale climate shifts. Keywords: Vertisols, mass-balance relationships, net-mass flux analysis, climate sensitivity.

An empirical-statistical climate-glacier model is used to reconstruct Late Pleistocene climate conditions in the south-central Andes of northern Chile (29-30[degrees]S). The model was tested using modern climate data and the results compare favorably with key glaciological features presently observed in this area. Using several glaciers at 29[degrees]S as case studies, the results suggest an increase in annual precipitation ([DELTA]P = 580 [+ or -] 150 mm, today 400 mm), and a reduction in annual mean temperature ([DELTA]T = -5.7 [+ or -] 0.7[degrees]C). These data suggest full glacial LGM (Last Glacial Maximum) conditions for the maximum glacier advances at 29[degrees]S, a scenario that is asynchronous with the timing of maximum advances north of the Arid Diagonal (18-24[degrees]S) where late-glacial climate was moderately cold but very humid. The reconstructed case study glaciers at 29[degrees]S do not allow conclusions to be drawn about the seasonality of precipitation. However, comparison with regional paleodata suggests intensified westerly winter precipitation and a stable position for the northern boundary of the westerlies at ~27[degrees]S. However, the meridional precipitation gradients were much steeper than today while the core area of the Arid Diagonal remained fixed between 25-27[degrees]S.

Geocarb III, a model depicting paleolevels of atmospheric carbon dioxide, contains revisions that emphasize factors influencing CO(2) uptake via continental weathering. These factors include surface temperature and runoff, silicate and volcanic weathering, weathering effects of angiosperms and gymnosperms, land area, and global water discharge.

The Late Ordovician glaciation differs from other major Phanerozoic glaciations because of its short duration ([approximately]1 m.y.). A satisfactory explanation for this glaciation must be able to account for its sudden initiation, short duration, and rapid termination; mechanisms operating on tectonic time scales appear to be precluded. Given recent studies of a major perturbation in the carbon cycle during the glaciation, a climate model investigation of the sensitivity of the Late Ordovician climate to changes in atmospheric pCO2 was undertaken. Under the condition of a 4.5 % reduction in solar luminosity, permanent snow cover (taken as a key indicator of potential for glaciation) is dramatically different between five experiments. The range of 18X present atmospheric level C[O.sub.2] (ice free) to 8X ('runaway' icehouse) lies within the uncertainty of previous geochemical estimates of Late Ordovician atmospheric pC[O.sub.2]. The strong sensitivity to the modest direct forcing from pC[O.sub.2] changes is due to the ice-albedo feedback. A plausible increase in organic carbon burial could have drawn down enough atmospheric C[O.sub.2] to have briefly lowered the climate system below a critical glacial inception threshold at the end of the Ordovician. Conversely, a high pC[O.sub.2] is required for the rest of the early Paleozoic, which was essentially ice free.

Continuous loess sequences in China provide not only information for paleoclimatic reconstructions, but also permit the establishment of a reliable absolute time scale for the Quaternary. An empirical relationship is developed between the grain size of the loess and the sedimentation rate in a short, well-dated reference section (step 1). This relationship is extrapolated to the complete Quaternary section (step 2). After derivation of the sedimentation rate (by measuring the grain size) in all the layers of the sequence, the duration of deposition of each layer is obtained (by dividing thickness by sedimentation rate) and subsequently the age of each point in the sequence is calculated (by adding together all the duration values of the overlying layers). The chronology of the extrapolated part of the section obtained in this way is independent of dates provided by other methods and may also be checked by them.

The relationship between paleoclimates and the future climate, while not as simple as implied in the 'paleoanalog' studies of Budyko and others, nevertheless provides sufficient constraints to broadly confirm the climate sensitivity range of theoretical models and perhaps eventually narrow the model-derived uncertainties. We use a new technique called 'paleocalibration' to calculate the ratio of temperature response to forcing on a global mean scale for three key intervals of Earth history. By examining surface conditions reconstructed from geologic data for the Last Glacial Maximum, the middle Cretaceous and the early Eocene, we can estimate the equilibrium climate sensitivity to radiative forcing changes for different extreme climates. We find that the ratios for these three periods, within error bounds, all lie in the range obtained from general circulation models: 2-5 K global warming for doubled atmospheric carbon dioxide. Paleocalibration thus provides a data-based confirmation of theoretically calculated climate sensitivity. However, when compared with paleodata on regional scales, the models show less agreeement with data. For example, our GCM simulation of the early Eocene fails to obtain the temperature contrasts between the Equator and the Poles (and between land and ocean areas) indicated by the data, even though it agrees with the temperature data in the global average. Similar results have been reported by others for the Cretaceous and for the Last Glacial Maximum.

Analysis of the Greenland Ice-Core Project indicates that the last interglacial period before the present one was much less stable. It switched repeatedly between warmer and cooler states, taking as little as a decade to do so and remaining locked in the new state for 70 to 5,000 years, affecting ocean circulation patterns. That period was slightly warmer overall than the present one, raising questions about the effects of global warming.

Pollen evidence suggests that the paleoclimate of the Mediterranean during the Last Glacial Maximum was semi-arid while geomorphological data suggest high lake levels. Using a water-balance model to predict runoff catchment and a biome model to predict vegetation, type the paleoenvironment of Lake Ioannina may be reconstructed. The reconstruction features wet winters and dry summers. Several atmospheric models have the jet stream shifted to the south and the summer drying effects of the cold North Atlantic may have been seasonally reversed by increased storm frequency.

The warming of the Earth soon after it formed probably prevented the onset of an interminable glacial climate due to highly reflective carbon dioxide (CO2) clouds and the Sun's much less intense output of heat at the time. The suggestion that an early greenhouse effect stabilized the Earth's climate does not explain why the oceans failed to freeze before the greenhouse gases could accumulate. Paleoclimatic simulations indicate that Earth may have narrowly escaped being rendered uninhabitable by world-wide glaciation thanks to either internal heat or additional greenhouse gases.

Zonal-scale patterns of precipitation change, as reconstructed for the Mid-Pliocene and the two Pleistocene optima, are compared with those generated in standard 2 x C[O.sub.2]-1 x C[O.sub.2] equilibrium experiments by two high-resolution GCMs of equal sensitivities of global precipitation and temperature to C[O.sub.2] doubling. We find that the three warm paleoclimates, despite differences in boundary conditions/forcings, exhibit a similarity in zonal-scale patterns of change for precipitation over land in the Northern Hemisphere (NH); the between-epoch pattern correlation is 0.9 on the average. The two models give marked differences in zonal distribution of precipitation anomalies at mid-latitudes; the between-model pattern correlation for changes of precipitation over NH land is 0.4. The response of precipitation over the NH land area to the NH warming is about 10%/[degrees] C in the paleodata compared to 3%/[degrees] C in the models. The largest model/paleodata discrepancy refers to the present-day desert belt, where a large precipitation anomaly persists in all epochs. North of 50 N, the absolute values of the zonally-averaged precipitation anomalies simulated by both models fall in the range implied by the three warm paleoclimates, but they are systematically lower than the anomalies of the Mid-Pliocene. If our reconstructions are valid and if climate changes in the Mid-Pliocene were driven solely by C[O.sub.2] changes, then our results suggest that models are underestimating the magnitude of the precipitation response, especially in the regions of subtropical deserts; the magnitude of the simulated temperature response at high latitudes is also underestimated. At least part of the reported model/paleodata discordance appears to be due to lack of interactive land surface package in the models examined.

The hypothesis that the rise of the Tibetan plateau helped to lower global temperatures by increasing the quantity of carbon dioxide(CO2)-absorbing silicate rock is questionable. The numerical data underlying this hypothesis are incomplete. Moreover, the implication that CO2 fluctuations are linked to geological weathering is unproven. However, the rebuttal view is that some carbon cycle models do relate to silicate and carbonate weathering. The hypothesis agrees well with the geological data.

A new analysis of oxygen isotope data strengthened the case against the long-accepted Milankovitch theory for what caused the ice ages. This paleoclimatic model holds that recurrent fluctuations in the Earth's orbit triggered the growth of glaciers by reducing the solar radiation reaching the mid-to-high latitudes. However, I.J. Winograd and co-workers examined the oxygen isotope levels from the Devils Hole aquifer in southern Nevada and found that the tested samples were 145,000 years old rather than 128,000 years old as required by the Milankovitch theory.

The freshwater diatom flora of northern Quebec ([greater than] 1,000,000 [km.sup.2]) remains largely unknown. The main purpose of this project is to study the distribution of freshwater diatoms preserved in the surficial sediments of 60 lakes. The lakes are located along a latitudinal transect (from [similar to] 49 [degrees] to 59 [degrees] N along the eastern shores of James Bay and Hudson Bay) that includes steep climatic and vegetational gradients, showing significant changes in diatom assemblage composition and water chemistry across treeline. The development of a surface sediment 'calibration' or 'training' set is a powerful method for determining diatom species-environmental relationships. Multivariate statistical methods are used to gain a better understanding of the relationship between diatoms and their environment. In this study, we used Canonical Correspondence Analysis (CCA) to determine which environmental variables are significant in determining the diatom species distributions.