PP31F-01
Putting Current North America Drought Conditions into a Multi-Century Perspective. Part 1: Constructing the Paleo Drought Dataset
Drought is an important climatological phenomenon which has significant socioeconomic and environmental impacts. Several drought indices have been developed to quantify drought, but all of them rely on meteorological observations taken at instrumented in situ weather stations. The instrumental record for drought monitoring in the U.S. extends back only about a hundred years, and the record is even shorter in other countries such as Canada and Mexico. Recurrence intervals and water management compacts (for example, the Colorado River Basin domestic or Rio Grande international compacts) based upon such short records may not be built upon the true climatology of a region. Reliable drought information can be derived from paleoclimatic data such as tree- rings, thus enabling researchers and decision-makers to assess drought variability and impacts over a multi- century period. Previous work has developed research-quality paleoclimatic drought reconstructions which have been used in retrospective analyses but, until now, such data bases have not been used comprehensively in operational monitoring. Part 1 of this paper describes the development of the reconstructed paleoclimatic Palmer drought index gridded dataset for North America from tree-ring data. Part 2 of this paper describes how the reconstructed paleoclimatic data base is blended with a 20th century instrumental-based Palmer drought index gridded dataset for operational drought monitoring applications across North America.
PP31F-02
Putting Current North America Drought Conditions Into a Multi-Century Perspective. Part 2: Using the Blended Product in Operational Drought Monitoring
Drought is an important climatological phenomenon which has significant socioeconomic and environmental impacts. Several drought indices have been developed to quantify drought, and all of them rely on meteorological observations taken at instrumented in situ weather stations. The instrumental record for drought monitoring in the U.S. extends back only about a hundred years, and the record is even shorter in other countries such as Canada and Mexico. As a result, recurrence intervals and water management compacts (for example, the Colorado River Basin domestic or Rio Grande international compacts) based upon such short records may not be built upon the long-term climatology of a region. Reliable drought information can be derived from paleoclimatic data such as tree-rings, thus enabling researchers and decision-makers to assess drought variability and impacts over a multi-century period. Previous work has developed research-quality paleoclimatic drought reconstructions which have been used in retrospective analyses but, until now, such data have not been used comprehensively in operational monitoring. Part 1 of this paper describes the development of the reconstructed paleoclimatic Palmer drought index gridded dataset for North America from tree-ring data. Part 2 of this paper describes how the reconstructed paleoclimatic data base is blended with a 20th century instrumental- based Palmer drought index gridded dataset for operational drought monitoring applications across North America.
PP31F-03
14C-Dating and Paleoclimate Reconstruction Using the Holocene Tufa Developed in Ehime Prefecture, Southwestern Japan.
Tufas are freshwater carbonates widely developed in limestone areas under temperate and tropical climates. The stable isotopic and the other chemical properties of the tufas changes with climatic conditions. Because of the relatively high depositional rate and development of annual lamination, the tufas can be ideal paleoclimatic archives that supply high-resolution records on the past temperature and precipitation change. We have analysed 1.45 m-thick paleo-tufa section along a stream in Seiyo City in Ehime Prefecture, SW Japan. We determined the ages of the deposits by carbonate 14C because the section lacks suitable material for 14C dating of organic carbon and for U-Th dating. We collected ten samples from the section and measured the 14C composition by benzene-liquid scintillation counting. To evaluate initial value of dead carbon proportion (dcp), we also analyzed the recent tufa. The paleo-tufa section appears a clear discontinuity that devides the section into the lower part (sample of ps-1 to 4, 80 cm thick) and the upper part (ps-5 to 10, 65 cm). Annual lamination of 1-3 mm thick is clearly developed in the upper part, but obscure in the lower part. The 14C value of the recent tufa is -37.7 ‰ (vs. NIST) and corresponding to the apparent age of 309 B.P. On the other hand, the 14C values of the paleo-tufas range from - 410.7 ‰ in the lowermost sample (ps-1) to -242.6 ‰ in the uppermost sample. Assuming that initial dcp of the recent tufa can be applied to the paleo-tufa samples, the 1.45 m-section was considered to have been deposited from 3940 to 1900 B.P. The assumed age of the sample below the discontinuity (ps-4) was 3300 B.P. This suggests that the depositional rate of the 80-cm-thick lower part was approximately 1 mm/year. Both of oxygen and carbon stable isotopic values increased from the oldest sample (-7.30 and -10.96 ‰, respectively) to the youngest sample (-6.99 and -6.85 ‰, respectively). This might be ascribed to the cooling trend in this period. Carbon stable isotopic value of the recent tufa is as low as -9.87 ‰ that may indicate a warmer condition than 1900 B.P. However, a slightly higher oxygen isotopic value (-6.68 ‰) of the recent tufa may have resulted from cooling if the water isotopic value have been stable in the last thousands years.
PP31F-04
Ecosystem Response to Dansgaard-Oeschger Climate Variability
Abrupt climate variability is a conspicuous feature seen in ice cores, marine sediments and speleothems, especially during marine isotope stage (MIS) 3. Corresponding changes have been observed in a number of terrestrial (lake sediment) archives, however clear evidence for a synchroneity of events and for the response of terrestrial ecosystems to these rapid changes remains ambiguous. Here we report on a multi-proxy study of the lake sediment sequence of Les Echets in France. We show that the lake ecosystem underwent profound cyclic changes alternating between time intervals of higher and lower lake organic productivity, which both resemble and differ from those seen in ice core and marine archives. Our results indicate that although ecosystem response to climate variability was rapid, it was modulated by local factors.
PP31F-05
The FORCLIM Eco-Physiological Growth Model for Planktic Foraminifera: a new Tool to Reconstruct Ecological Niches, Abundance and Potential Depth and Season of Growth for Fossil Foraminifera Species in Ocean Sediment Records
Paleocean hydrological reconstructions derived from planktic foraminifera isotopic ratios (δ18O and δ13C) or trace element ratio (Mg/Ca) are poorly constrained, for lack of precise knowledge on seasonality and water depth of test formation. This is particularly limiting for reconstruction of the thermocline characteristics. Various calibrations have been published, based on statistical correlation with core tops fossil fauna, sediment traps or plankton net collection. We present here what we think is the first eco-physiological model reproducing the growth of different foraminifera species in function of environmental parameter. By reproducing the main physiological rates of foraminifera (nutrition, respiration, symbiotic photosynthesis), this model estimates their growth in function of temperature, light availability and food concentration. The model is now calibrated for the species Neogloboquadrina pachyderma (dextral and sinistral forms), Neogloboquadrina dutertrei, Globigerina bulloides, Globigerinoides ruber, Globigerinoides sacculifer, Globigerinella siphonifera and Orbulina universa. Most of the model parameters are derived from newly performed experimental observations or from published data and only the influence of food concentration (in a Chl a basis) was calibrated with field observations. Using satellite data, the model predict the seasonal distribution of dominant foraminifer species over 576 field observations worldwide with efficiency higher than 60%. Moreover, the growth rate estimated for each foraminifera species can be used as an abundance indicator which allows prediction of the season and water depth at which most of the population has developed. This offers larges perspectives for both actual understanding of foraminifera role in the carbon/carbonate ocean cycle and for better quantification of paleoceanographic proxies. Forclim is a program supported by the Agence Nationale pour la Recherche and Institut National des Sciences de l'Univers, France.
PP31F-06
Faunal Change of Benthic Foraminifera to the Glacial Events during the Mid-Oligocene Interval in the Eastern Equatorial Pacific Sites (ODP Leg 199)
Deep-sea paleoceanographic environments considerably varied in the late Paleogene, in response to the fluctuation of the Antarctic ice volume and to the potentials of deep water formation in the Southern Ocean. Several glacial events with stable oxygen isotopic shift occurred during the Oligocene. Recently, many Oligocene paleoceanographic studies of Site 1218, ODP Leg 199 (the eastern equatorial Pacific Ocean) have been carried out (Coxall et al., 2005; Wade and Palike, 2004; Palike et al., 2006). These studies suggested that various orbital forcing, particularly long eccentricity and ~1.2 m.y.-obliquity amplitude modulation, affected not only glacial events but also the carbonate compensation depth or surface carbonate production via weathering process. Because the drilled section of this site contains well-preserved foraminifera in almost all samples, this section provides the opportunity for conducting a detailed study of faunal change to the Oligocene glacial events. The objectives of our study are to investigate the mid-Oligocene faunal succession (27.0 to 30.5 Ma) of benthic foraminifera and to consider their relation to paleoceanographic changes in the eastern equatorial Pacific Ocean. Based on a factor analysis to benthic foraminiferal fauna at Sites 1218 and 1219 (112 samples), three factor assemblages were recognized. The Factor 2 assemblage is characterized by typical deep-sea taxa under Oligotropic condition, such as Oridorsalis umbonatus, Cibicidoides spp. and Gyroidinoides spp., whereas the Factor 1 assemblage, characterized by Nuttallides umbonifer that is related to Southern Ocean deepwater flow and / or carbonate undersaturation of deep waters. Factor 1 assemblage was common around four glacial events (76Ol-C11r, 73Ol-C10m, 70Ol-C10n and 67Ol-C9n (Palike et al., 2006)). In addition, dominance of the assemblage became continuously after the 73Ol-C10m. Such occurrence suggests that influence of Southern Ocean deepwater flow and/or carbonate undersaturation at this site was increased in every glacial event during the mid-Oligocene interval. In contrast, the Factor 2 assemblage was observed temporally within the dominance of the Factor 1 assemblage in the glacial events. It seems to be caused by enhanced carbonate production from ocean surface that may be related to orbital cycles. Therefore, the changes of both the characteristics of the deep watermass and surface carbonate production due to orbital forcing are responsible to abyssal benthic foraminifera during the mid-Oligocene in the eastern equatorial Pacific Ocean.
PP31F-07
Simulations of Late Paleozoic Continental Ice Sheets Under Orbital and CO2 Forcing
The late Paleozoic ice age was the most severe glaciation of the Phanerozoic. Contrasting views of the size, duration, and history of this glaciation have been proposed from glaciological and sedimentological evidence. This study utilizes the GENESIS atmospheric general circulation model coupled to a 3-D ice sheet model to investigate the influence of atmospheric CO2 concentrations and orbital parameter variations on Pangean glaciation. Our study investigates the effects of a range of atmospheric CO2 concentrations (140 to 2240 ppm) on late Paleozoic continental glaciation. Additionally, an investigation into the effects of Milankovitch orbital forcing is explored via two independent methods. First, simulations of maximum and minimum insolation orbits were run to determine the largest/smallest equilibrium ice sheet volume achievable under the given CO2 concentration. Second, a transient time-marching scheme was developed to track the ebb and flow of glacial ice sheet volume through full orbital cycles. Our results highlight the important role of atmospheric CO2 in determining the distribution, volume, and stability of late Paleozoic ice sheets. At low CO2 levels (< 560 ppm) our model predicts large (1.47×108 km3 maximum), multi-domed ice sheets across Gondwana under both equilibrium and transient orbital conditions. Under equilibrium forcings, orbital variations produce large ice volume (up to 1.3×108 km3) and sea level (up to 245 m) changes. However, under transient forcing, orbital variations lead to much smaller variations in ice volume that would not generate the sea-level changes requisite for cyclothem deposition. In general, the results presented here present a theoretical framework for the reconstruction of late Paleozoic glaciation and aid in the reconciliation of the disparate views of the Late Paleozoic Ice Age.
PP31F-08
Thermal Transgressions and Phanerozoic Extinctions
A number of significant Phanerozoic extinctions are associated with marine transgressions that were probably driven by rapid ocean warming. The conditions associated with what we call thermal transgressions are extremely stressful to life on Earth. The Earth system setting associated with end-Permian extinction exemplifies an end-member case of our model. The conditions favoring extreme warmth and sea-level increases driven by thermal expansion are also conducive to changes in ocean circulation that foster widespread anoxia and sulfidic subsurface ocean waters. Equable climates are characterized by reduced wind shear and weak surface ocean circulation. Late Permian and Early Triassic thermohaline circulation differs considerably from today's world, with minimal polar sinking and intensified mid-latitude sinking that delivers sulfate from shallow evaporative areas to deeper water where it is reduced to sulfide. Reduced nutrient input to oceans from land at many of the extinction intervals results from diminished silicate weathering and weakened delivery of iron via eolian dust. The falloff in iron-bearing dust leads to minimal nitrate production, weakening food webs and rendering faunas and floras more susceptible to extinction when stressed. Factors such as heat, anoxia, ocean acidification, hypercapnia, and hydrogen sulfide poisoning would significantly affect these biotas. Intervals of tectonic quiescence set up preconditions favoring extinctions. Reductions in chemical silicate weathering lead to carbon dioxide buildup, oxygen drawdown, nutrient depletion, wind and ocean current abatement, long-term global warming, and ocean acidification. The effects of extinction triggers such as large igneous provinces, bolide impacts, and episodes of sudden methane release are more potent against the backdrop of our proposed preconditions. Extinctions that have characteristics we call for in the thermal transgressions include the Early Cambrian Sinsk event, as well as extinction events at the Frasnian-Famennian, end-Devonian, end Permian, Early Toarcian, Cenomanian-Turonian, and end Cretaceous. The Late Paleocene and end Triassic extinctions are still under evaluation. The extinctions associated with the glacio-eustatic sea-level change in the Late Ordovician are not consistent with the conditions of our model.