PP43C-1529
The Past is a Guide to the Future? Comparing Middle Pliocene Vegetation With Predicted Biome Distributions for the 21st Century
The Middle Pliocene geological stage, ca. 3.6 to 2.6 million years ago, represents an interval of time in which Earth experienced greater global warmth. In order to evaluate the degree to which the Middle Pliocene can be used as a ‘test bed' for future warming, we compare a newly developed Middle Pliocene biome reconstruction with simulated global biome distributions for the mid and late 21st century. The Middle Pliocene biome reconstruction is based on an internally consistent dataset of 202 palaeobotanical sites and predictions from a state-of-the-art coupled climate-vegetation model (HadAM3-TRIFFID-BIOME4), the output of which is used to provide biome estimates for data sparse regions. For the Middle Pliocene, both the vegetation reconstruction and model predictions indicate a generally warmer and moister climate than today. Evergreen taiga as well as temperate forest and grasslands shifted northward resulting in a significantly reduced area of tundra vegetation. Warm-temperate forests (with subtropical taxa) spread in Middle and Eastern Europe and tropical savannas and woodland expanded in Africa and Australia at the expense of deserts. Middle Pliocene biome distributions are compared (globally and on a regional scale) with two new predictions of equilibrium vegetation conditions for the early 21st Century (around 2020, ~ 400ppmv CO2 in the atmosphere) and end of the 21st Century (~ 560ppmv CO2 in the atmosphere), to examine similarities and discrepancies in biome distributions. Our comparison between reconstruction and prediction will contribute to a better understanding of the past and future impact of increased atmospheric CO2 on vegetation and climate.
PP43C-1530
Late Pliocene enhancement of Greenland glaciation: CO2 vs. direct tectonic forcing
Loss of mass from the Greenland ice sheet (GrIS), and in particular the associated sea level rise, is one possible impact of anthropogenic global warming which is of fundamental concern. Therefore, significant effort has recently been applied to modelling the future response of the GrIS to increasing or elevated greenhouse gas concentrations. However, it is currently not known what fundamental forcing mechanisms or critical thresholds have determined the evolution of the GrIS in the past, in particular on geological timescales. In this paper, we address this issue by testing three alternative hypotheses used to explain the enhancement of Greenland glaciation in the Late Pliocene. (1) the "Panama Hypothesis", whereby ocean circulation changes following the formation of the Panama Isthmus enhanced poleward transport of moisture and brought more snowfall to the incipient GrIS; (2) the "Rockies Hypothesis" whereby changes in atmospheric circulation via storm track and Rossby wave deflection, following the uplift of the Rockies, led to cooling over Greenland ; and (3) the "CO2 Hypothesis" whereby decreasing CO2 in the Mid and Late Pliocene led to a global cooling. We use the UK Met Office GCM, HadCM3, and the UK ice sheet model, GLIMMER, and carry out Pliocene and pre- industrial simulations with various combinations of prescribed boundary conditions, in order to elucidate the relative importance of CO2 vs. direct tectonic forcings in controlling the evolution of the GrIS. The study indicates that the decrease in atmospheric CO2, from the elevated values of the mid-Pliocene to lower values of the Quaternary, drove a significant enhancement of Greenland glaciation, which was further increased by climate-ice sheet-vegetation feedbacks, resulting in a GrIS similar to that observed today. Conversely, it shows that climatic shifts associated with the tectonically-driven closure of the Panama Seaway and uplift of the Rockies were not large enough to contribute significantly to enhanced Greenland glaciation.
PP43C-1531
Permanent El Nino Conditions and Meridional Expansion of the Tropical Ocean Warm-Water Pool in the Early Pliocene: Modeling Global Impacts with an Atmospheric GCM
As new data emerges, our interpretation of the early Pliocene climate continually evolves. More and more data from the last few years indicate a persistence of a significantly reduced zonal temperature gradient in the equatorial Pacific, which is associated with climate conditions usually referred to as a "permanent El Niño". Here, data from a variety of regions in both Pacific and Atlantic oceans are collected to reconstruct the meridional temperature gradient in the ocean during the early Pliocene. Our results indicate a substantial reduction in the meridional temperature gradient from the equator to the subtropics (in comparison with today's climate) and a large poleward expansion of the warm-water pool in the tropical Pacific. The implications of a reduced meridional temperature gradient are studied with an atmospheric general circulation model forced with hypothetical surface temperature boundary conditions, representative of our new understanding of the early Pliocene. Changes in the global circulation and precipitation patterns are explored, along with inferences about the ocean heat transports. The Walker circulation is virtually removed by the imposed SST boundary conditions. The latitudinal extent of the Hadley cell increases only slightly, but the strength of the Hadley circulation is substantially reduced, which results in a weakening of the poleward heat transport by the atmosphere in the low- to mid- latitudes. The issue of the poleward heat transport in the early Pliocene is discussed in the context of the "Pliocene Paradox" (Fedorov et al, 2006). Further, the sensitivity of the modeling results to different choices of the surface boundary conditions is explored.
PP43C-1532 INVITED
PRISM3 Global Paleoclimate Reconstruction: A Global Warming Data Set
The Pliocene Research, Interpretation and Synoptic Mapping (PRISM) Project provides a conceptual model and synoptic view of the earth during the last interval considerably warmer than modern (3.3 to 3.0 Ma) through reconstruction of sea-surface temperature (SST) and other paleoenvironmental parameters. The first PRISM reconstruction, with its foundation in a global network of paleontological analyses, was completed in the early 1990s. Since then, several significant revisions have been released culminating in the PRISM2 data set. The primary goal of PRISM remains a better understanding of the Earth's climate system during the mid-Pliocene, and to that end, includes the development of digital data sets for use with climate models. The new PRISM3 reconstruction, slated to be released early in 2008, has revised SST fields based upon integration of previous and new faunal and floral analyses with new geochemical proxies and biomarkers, a revised vegetation/land cover data set utilizing the BIOME 4 vegetation classification scheme, 3-dimensional land ice distribution based upon ice-sheet model experiments, new sea level estimates based upon stable isotopes and bottom water temperatures, and revised sea-ice distribution. A deep ocean temperature reconstruction, PRISM3D, adds a 3- dimensional component, which can be used for initiating coupled ocean-atmosphere GCM simulations. PRISM3 is a collaborative effort between the U.S. Geological Survey (USGS), National Science Foundation (NSF), National Aeronautics and Space Administration (NASA), British Antarctic Survey (BAS), and several national and international academic institutions (Columbia University, Duke University, George Mason University, University of Leeds and University of Leicester).
PP43C-1533
A Rare Early Pliocene Record of Paleoclimate from North-central Indiana, USA
The Early Pliocene is a critical period in Earth history, representing warm Earth conditions immediately prior to the development of extensive northern hemisphere glaciation. It thus may provide the best available analog for predicting the climate changes associated with continued global warming. Unfortunately, there are few interior continental records for the early Pliocene from the eastern half of North America and subsequently very little is known about the conditions characterizing climate of this region. The Early Pliocene (4-5 Ma) Pipe Creek Sinkhole (PCS) includes the sediment fill of a complex karst environment that developed in north-central IN (Lat 40° 27' 16", Long 85° 47' 31"). The PCS contains a well-preserved record of sedimentation that includes lacustrine strata with an abundant and diverse fauna and flora that collectively provides a valuable record of paleoclimate from the late Tertiary. Previous research indicates that the floral types are broadly consistent with late Tertiary habitat reconstructions of the US Great Plains. Micromorphologic and stratigraphic analysis of PCS sediments indicate that there are at least three distinct facies present. The underlying red facies is an oxidized silty-clay package that is not fossiliferous. An immature paleosol with root traces represents the pedogenic modification of the red facies and indicates a change in the environment of deposition. The highly fossiliferous lacustrine facies includes abundant quartz sand grains that are not present in the red facies. Geochemical analysis of PCS pond sediment total organic carbon (TOC) derived from vascular land plants sources (based on samples with C/N ratios >20) have δ13 C (PDB) isotope values ranging from -15‰ to - 26.2‰ and a mean value of -22.4‰. The red facies averages 0.1% TOC and has δ13 C values averaging -20.0‰, whereas the paleosol δ13 C values average -24.2‰. These values suggest the presence of a mixture of C3 and C4 plants in the ecosystem. The mean value of PCS fossil wood is - 25.2‰, which is consistent with water-stressed growing conditions. Collectively these records indicate that the region represented by the PCS watershed was substantially dryer during the Early Pliocene than today.
PP43C-1534
A Late Miocene-Pliocene Antarctic Deepwater Record of Cyclic Iron Reduction Events (ODP Leg 178 Site 1095)
The Pacific margin off the Antarctic Peninsula is very sensitive to climate and ice-sheet volume changes. Climatic variations on the continental shelf control regional sedimentary processes and foster the build-up of giant deep- sea sediment drifts. These drifts represent the most proximal continuous sedimentary recorders for West Antarctic ice sheet evolution and glacial-interglacial cyclicity pattern. Sediment physical, geochemical records and x-ray images derived from ODP Site 1095 (Drift 7) were used to identify pattern in glacial-interglacial cyclicity and associated sedimentary and diagenetic processes during late Miocene and Pliocene. Two boundary types dividing half-cycles have been recognized: (1) interglacial-to-glacial transitions are characterized by a sharp boundary and abrupt change in lithology; (2) glacial-to-interglacial transitions can described as a gradual change from a full glacial to a full interglacial stage. A prominent feature of the glacial-to-interglacial transition is the loss of the magnetic susceptibility signal, caused by diagenetic alteration and demagnetization of magnetic iron minerals in a suboxic to anoxic sediment environment. Similar redox processes are described for organic carbon rich Madeira abyssal plain turbidites and Mediterranean sapropels, but are uncommon for vented Circum- Antarctic deep-sea sediments. Iron reduction zones were coupled to the ice sheet collapse at the end of deglaciation phases. Ice sheet collapse and meltwater formation weaken the bottom water formation and convection, but foster short living diatom blooms resulting in high fluxes of organic matter to the seafloor. Iron reduction zones were observed in sixty-four zones of ODP Site 1095 cores. Thus, the sedimentary record of Drift 7 affords an unique opportunity to study cyclic iron reduction events at long time-scales. The occurrence and intensity of those 'diagenetic zones' reflect long-term trends of global climate change and the related variability of primary production and preservation of organic matter. The study describes the complex interaction of Antarctic ice sheet behavior and ocean conditions in warmer late Miocene to Pliocene climate and may serve as an outlook for upcoming changes in the Circum-Antarctic realm in the course of recent global warming.
PP43C-1535
Implications of Seawater Mg/Ca Variability for Plio-Pleistocene Climate reconstruction
Recent reconstructions of Mg and Ca concentrations of seawater indicate that seawater Mg/Ca has changed significantly on time scales of thousands of years. This study examines the implications of adjusting available equatorial Pacific SST records based on Mg/Ca paleothermometry to account for the inferred past variations of seawater Mg/Ca. The results suggest that both the cold and the warm regions of the equatorial Pacific were much warmer during the Upper Pliocene (32-34° C), and that both regions experienced a marked cooling from ~4 Ma to ~0.8 Ma. The new interpretation of foraminiferal Mg/Ca creates a discrepancy with alkenone-based SST records from the eastern equatorial Pacific which might be due to either overestimation of changes in past seawater Mg/Ca or to factors affecting the interpretation of the alkenone-unsaturation index. The adjusted SST records are consistent with the hypothesis that higher levels of greenhouse gases maintained the warmth of the early Pliocene, and that the cooling implied by these records was at least partly driven by a drop in the atmospheric concentration of greenhouse gases. We used the adjusted warm pool record to calculate the level of greenhouse forcing, expressed as atmospheric CO2 concentration, required to explain Pliocene SSTs. Modern warm pool SST at 806B is 29.2° C, whereas peak reconstructed Pliocene SSTs were 34° C. In our calculations, we consider a range of climate sensitivity factors (l = 0.75, 1.3 and 1.5° C per Wm-2) that reflect the range from fast climate feedbacks only to those that include slow geological feedbacks such as ice sheet and surface albedo changes. For l = 0.75, 1.3 and 1.5° C per Wm-2, we estimate Pliocene atmospheric CO2 concentrations to have been 985, 580 and 525 ppm, respectively. For comparison, current estimates of Pliocene pCO2 vary between ~250 ppm and 560 ppm. The two lower values overlap with previously published estimates of Pliocene pCO2. The critical point of this analysis is that the temperature range that we calculate using a variable seawater Mg/Ca curve is not unrealistic, when considered in the context of Pliocene pCO2 estimates.
PP43C-1536
Estimates of Eastern Equatorial Pacific Sea Surface Temperatures During the Pliocene From Carbonate ‘Clumped Isotope' Thermometry
The early Pliocene (5 to 3 Ma) was an interval in Earth history that was globally warmer than the present; thus, study of the details of Pliocene climate can provide insights into the dynamics of warm climates. There are two competing models of the temperature structure of the tropical Pacific upper-ocean during the early Pliocene: the dynamical ‘ocean thermostat' model [1,2] and the ‘El Padre' (or permanent ‘El Nino') model [3], each of which predict zonal temperature gradients and mean conditions in the Eastern Equatorial Pacific (EEP), and which differ markedly from one another in these predictions. The dynamical ‘ocean thermostat' model predicts an increased temperature contrast between the Western Equatorial Pacific (WEP) and EEP, enhanced thermocline tilt and intensified upwelling under warmer conditions. In contrast, the ‘El Padre' model postulates a collapse of the zonal temperature gradient, reduced thermocline tilt and a reduction in upwelling and/or warmer temperatures of upwelled waters. Existing reconstructions of tropical temperatures produce WEP sea surface temperatures which agree with each other, but yield very different results in the EEP [4,5]. We have reconstructed EEP sea surface temperatures at Ocean Drilling Program (ODP) Site 847 using a few samples spanning key intervals of the last 6 million years using carbonate clumped isotope thermometer [6,7,8]. This technique is based on the temperature dependence of the abundances of 13C-18O bonds in carbonate minerals. Initial measurements of planktonic foraminifera and coccoliths from ODP Site 847 indicate cool EEP sea surface temperatures, supporting models of Pliocene climate that have enhanced zonal temperature gradients, relative to modern. Analyses of Globigerinoides sacculifer (with sac) from sediments indicate calcification temperatures of 20.3°C ± 0.1°C and seawater δ18O values of –0.8‰ ± 0.1‰ from ~6.1 to 5.1 million years ago. Measurements of a mixed coccolith assemblage from the fine fraction of 5.6 Ma sediments show calcification temperatures of 20.4°C ± 2.3°C and seawater δ18O values of –1.4‰ ± 0.6‰. G. sacculifer (with sac) and mixed coccoliths from 1.4 Ma sediments yield calcification temperatures of 22.3°C ± 2.5°C and seawater δ18O values of 1.7‰ ± 0.7‰, and 19.4°C ± 1.8°C and seawater δ18O values of 0.4‰ ± 0.5‰, respectively. Our preliminary findings are consistent with the ‘dynamical ocean thermostat' model. [1] Clement, A., et al., 1996, An Ocean Dynamical Thermostat, J. of Clim., 9, 2190-2196. [2] Cane, M., et al., 1997, Twentieth-Century Sea Surface Temperature Trends, Science, 957-960. [3] Fedorov, A., et al., 2006, The Pliocene Paradox (Mechanisms for a permanent El Nino), Science, 312, 1437-1443. [4] Rickaby, R. and Halloran, P., 2005, Cool La Nina during the warmth of the Pliocene?, Science, 307, 1948-1953. [5] Wara, M., et al. ,2005, Permanent El Nino-like conditions during the Pliocene Warm Period, Science, 309, 758-761. [6] Ghosh, P., et al., 2006, 13C–18O bonds in carbonate minerals: A new kind of paleothermometer, GCA, 70, 1439–1456. [7] Eiler, J. and Tripati, A., 2007, ‘Clumped isotope' thermometry in benthic foraminifera and ostracods: A novel tool for reconstructing deep-ocean temperatures. Fall AGU. [8] Tripati, A., et al. 2007, ‘Carbonate `clumped isotope' thermometry in planktonic foraminifera and coccoliths. Fall AGU.
PP43C-1537
Eirik Drift: Complexity Beneath the Surface
Eirik Drift stands as much as 1800 m above the surrounding seafloor and extends approximately 400 km SW from the southern tip of Greenland. It is largely composed of late Neogene-Recent muddy contourites, and due to high depositional rates it contains a valuable archive of global climate, changes in regional contributions to Northern Component Water (NCW), and local expression of the stratal evolution of giant, elongated drifts. We report on observations based on 1900 km of hi-res MCS profiles we collected across Eirik Drift in Aug-Sept 2002 during cruise Kn166-14. Our interpretations are based on correlations to piston and drill core records collected before, during, and since that cruise. The scarcity of modern mudwaves on the surface of Eirik Drift belies its long history of current-controlled deposition. NCW flowing south through the western Irminger Basin has minimized sedimentation along the SW flank of the Drift since at least the late Miocene, causing NW migration and upward growth of this deposit. SW progradation, often cited in the literature, is not obvious to us. Instead, sediment waves and locally enhanced deposition at the SW extremity of the Drift, near the modern 3400 m isobath, began at the same time as elsewhere in our survey area. The most rapid drift buildup occurred during the early to mid-Pliocene. Higher sedimentation rates and thicker accumulations towards the NE were due to sources providing sediment through channels cut into the Drift near the Greenland margin. Rugged basement topography and extensive sediment failures provided locally steep topography that focused the geostrophically balanced NCW. This led to localized sediment buildups and internally complex growth patterns now hidden beneath a more nearly uniform blanket of post-late Pliocene sediment.
PP43C-1538
The Antarctic Ice Sheet during Cenozoic climates: Experiments with a simple climate model.
In order to get more insight into the role of the Antarctic Ice Sheet in global climate during different time slices during the Cenozoic era, a zonal mean climate model is used which incorporates meridional heat transport. The advantage of using a simple climate model is the fast computing time which makes it possible to do many schematic investigations in a relatively short period. This climate model is used to investigate how the Antarctic Ice Sheet's initiation and evolution throughout the Cenozoic is related to several climate forcing parameters (topography, orbital parameters, CO2 concentration). Furthermore, limits to the ice volume and deep-sea temperature contributions to the benthic oxygen isotope record are put.
PP43C-1539
Subsurface geology of Kansai International Airport: sequence related to global glacial – interglacial cycles and island tectonics
Tectonic sedimentary basins aligned in the central part of Japan during Quaternary . Thick sediments deposited in these basins provide useful records of climatic changes and tectonics throughout Quaternary. The Osaka sedimentary basin including Osaka Bay and area of Kansai International Airport is one of them. The Quaternary Osaka sedimentary basin has developed at an eastern contractional bend of a major transcurrent fault system named the Median Tectonic Line, which divides the southwest Japan arc. The thickness of Pliocene – Pleistocene sediments reaches to ca 3500m at the deepest part. These sequences are called the Osaka Group and are distributed in the Osaka Bay and exposed in the surrounding mountain areas. The Osaka Group is characterized by alternating sequences of marine and nonmarine strata. The subsurface sediments of Kansai International Airport (KIA) is composed mainly of Pliocene – Pleistocene sediments, which is characterized by alternating sequences of marine and nonmarine strata related to glacial – interglacial cycles. . The stratigraphy at KIA was established by micropaleontological, tephrochronological and magnetostratigraphical method. The sedimentary sequence at KIX is divided into two main units (Kukojima and Sennanoki Formations in ascending order) with the uncomformity within two units. Although thick marine clay units are mainly of the subsurface sequence, characteristics of coarser sediment units have an important role of moving of water during construction of the reclaimed land.
PP43C-1540
Stratigraphy around Kansai International Airport – reconstruction of the Plio-Pleistocene Osaka Group in the southern Osaka Basin
Tectonic sedimentary basin in Osaka is formed by the activation of fault system with E-W trending fault (MTL and AL) and N-S trending fault (Ikoma fault and Osaka wan fault). This sedimentary basin during Quaternary time is aligned in the central part of Japan (Takemura, 1985). In this basin, thick sedimentary sequences deposited and these are including marine clay deposit. These marine clay deposit are formed at least 15 layers. The stratigraphy of the Osaka Group in the hill areas was summarized on the basis of intercalation of marine clay bed and volcanic ash layers. The stratigraphy of submarine strata at Kansai International Airport is summarized based on correlation of four 400m deep cores obtained during 1994 and 1995, and previous results published by Nakaseko et. al., (1984). In 2007, deep borehole core drilling was carried out at Kansai Airport again. It over 1200m depth and this drilling point is most near central axis in Osaka sedimentary basin. In this study, we are analysis by micropaleontological, tephrochronological and magnetostratigraphical method, and correlated around borehole data. The sequences are called upper group (Kukojima) and lower group (Sennanoki) (Nakaseko et al., 1984). These Kukojima and Sennanoki formations are include marine deposit. In this study, we can analysis deeper part formation and it appeared that deeper deposits are formed in the lake. It means these are non-marine deposit not include marine clay and seems to big lake because of main grain size are silt and sand. In this poster, we would like to show the stratigraphy at center of Osaka basin and its characteristics.