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Sample records for holocene infilling processes

  1. Holocene Infilling History of Tampa Bay, Florida

    NASA Astrophysics Data System (ADS)

    Brooks, G. R.; Larson, R. A.; Cronin, T.; Willard, D.

    2007-05-01

    Tampa Bay is a shallow, sediment-starved estuary located along the central Florida Gulf coast. Based upon sedimentologic, biostratigraphic, and geochronologic analyses of 120 sediment cores and 190 surface sediment samples, karst-controlled basins located in the mid to upper estuary were found to contain a continuous sedimentary record documenting the Holocene sea-level rise and infilling history. The basal unit sampled in cores consists of organic-rich and/or carbonate-rich sediments containing freshwater fauna. Interpreted as lake deposits, the surficial sediments of these units were dated at approximately 8-9 ka suggesting that isolated sinkhole lakes occupied the region prior to being flooded by the Holocene sea-level rise. Overlying the lake deposits, dm-scale, organic-rich muds containing brackish water fauna, represent the transition from fresh to marine conditions as sea level flooded the region. The flooding surface itself is generally undefined, but sometimes represented by a mm-scale layer of shell fragments likely representing a lag deposit. Age dates bracketing this layer show that flooding occurred approximately 6-7 ka. Overlying sediments consist of 3-4 m of organic-rich, sandy muds with typical estuarine fauna. Age dates from the base of this unit indicate estuarine conditions became established approximately 5.5-6 ka. The modern expression of karst basins is a series of shallow, bathymetric depressions, likely reflecting the historically slow rate (0.030-0.065 cm/yr) of fine- grained sediment accumulation. These shallow depressions continue to function as fine-grained sediment sinks, but are now rapidly filling as the rate of accumulation has dramatically increased by approximately one order-of-magnitude (0.16-0.32 cm/yr) within the past 100 years, likely due to human activities.

  2. High Resolution Seismic Study of the Holocene Infill of the Elkhorn Slough, Central California

    EPA Science Inventory

    The seismic analysis of the sedimentary infill of the Elkhorn Slough, central California, reveals a succession of three main seismic units: U1, U2, U3, with their correspondent discontinuities d2, d3. These units are deposited over a paleorelief representing the channel location ...

  3. Recording of the Holocene sediment infilling in a confined tide-dominated estuary: the bay of Brest (Britanny, France)

    NASA Astrophysics Data System (ADS)

    Gregoire, Gwendoline; Le Roy, Pascal; Ehrhold, Axel; Jouet, Gwenael; Garlan, Thierry

    2016-04-01

    Modern estuaries constitute key areas for the preservation of sedimentary deposits related to the Holocene period. Several previous studies using stratigraphic reconstructions in such environments allowed to characterise the major parameters controlling the Holocene transgressive sequence and to decipher their respective role in the sedimentary infill: (1) the evolution of main hydrologic factors (wave or tide-dominated environment), (2) the sea level fluctuation and (3) the morphologies of the bedrock and the coastline. Nevertheless, the timing of the transgressive deposits and the detailed facies need to be precise in regard to the stratigraphic schemes. The Bay of Brest (Western Brittany, France) offers the opportunity to examine these points and to compare with previous studies. It constitutes an original tide-dominated estuary that communicates to the open sea (Iroise Sea) by a narrow strait. Two main rivers (Aulne and Elorn) are connected to a submerged paleovalleys network that was incised in the Paleozoic basement during lowstands and still preserved in the present morphology. It delineates the central basin surrounded by tidal flat located in sheltered area. The analysis of high and very-high resolution seismic lines recorded through the whole bay combined with sediment cores (up to 4.5 m long) and radiocarbon dating allow to precise the architecture and the timing of the thick Holocene coastal wedge. It is preserved from the valley network to the shore and presents a longitudinal variability (downstream-upstream evolution). The infill is divided into two successive stages (corresponding to the transgressive and highstand system tracts) which laterally evolve from the paleo-valley to the coast. Two units constitute the transgressive system tract. The oldest, dated from 8200 to 7000 cal B.P. is composed of fine-grained, organic-rich tidal flat deposits located in the sheltered area and organised in levees on the terrace bordering the paleo-valley. A tidal

  4. Infilling of the Hudson River Estuary During the Late Holocene (3000ka to Present): Implications for Estuarine Stratigraphic Models

    NASA Astrophysics Data System (ADS)

    McHugh, C. M.; Pekar, S. F.; Ryan, W. B.; Carbotte, S.; Bell, R.; Burckle, L.

    2002-12-01

    Estuaries are widely preserved in the geologic record and the estuarine fill, contained between non-marine sediment, provides an excellent temporal marker for continental margin studies. Estuarine stratigraphic models have provided a framework within which to interpret the estuarine fill. However, estuarine systems differ greatly in the shape of their valleys, the tectonic boundaries they cross, and in sediment supply so that their position in the geologic record may be out of sequence with that predicted by the models. New insights into estuarine systems and models are provided by the Hudson River Estuary (HRE; New York State) based on >150 cores and grab sediment samples and acoustic images documenting in great detail how the HRE filled its earlier excavated valley during the latest Holocene (3ka to present). Radiocarbon and 137-Cs radioisotope ages, borehole, and core data document the sedimentation patterns of the estuary. Diatom assemblages provide estimates of the shallowing-upwards of the estuary as its basin filled with sediments. The three areas of the stratigraphic model present in the HRE, include zones formed within inner fluvial and outer marine areas, (containing coarse-grained, sands and gravels), and a central area (containing fine-grained, silts and clays), that are nearly filled with little room for sediments to accumulate at or near sea-level. This has resulted in sedimentary bypass for almost the entire length the estuary. South of Kingston, fine-grained sediments have ceased accumulating when the bottom approaches wave base. Upstream from Kingston, final filling occurs as sediments fill in the remaining accommodation, forming islands. This should result in the export of sediment to the coastal zone. Instead, localized areas of sediment trapping still exist, which are related to the Hudson Valley Highlands and to the location of the estuarine turbidity maximum that hold large volumes of sediment. As a result minor volumes of Recent sediment are

  5. Biostratinomic processes for the development of mud-cast logs in Carboniferous and Holocene swamps

    SciTech Connect

    Gastaldo, R.A.; Demko, T.M.; Liu, Yuejin; Keefer, W.D.; Abston, S.L. )

    1989-08-01

    Prostrate trees are common features of fossil forest litters, and are frequently preserved as mud-casts. Specimens of Carboniferous mud-cast trees and a mud-filled incipient cast of a Holocene Taxodium have been investigated to determine the biostratinomic processes responsible for their formation. These processes are complex. Hollowing of tree trunks may take place during life or by degradation after death. Once the trunk has fallen, the hollow cavity is supported by surrounding wood and/or bark tissues and acts as a conduit for sediment-laden waters. Leaf litter may be preserved on bedding surfaces. The infilling sequence of horizontal, parallel bedded, fine-grained sediment is deposited from suspended load during multiple overbank flooding events. These results differ from experimentally produced pith casts in which the sediment grain size is of fine sand. In Holocene specimens, alluvial mud within the log may provide a substrate for infaunal invertebrates. No evidence of infaunal burrowing in Carboniferous analogues exists.

  6. Boston Infill Schools.

    ERIC Educational Resources Information Center

    Stull, Don; Heder, Lajos

    Concepts and recommendations are presented regarding a proposed system of dispersed classroom clusters or 'infill schools'. These small independent urban schools would be housed in prefabricated structures developed for infill housing in Boston. The infill unit uses pre-designed building components and can be constructed in a few weeks. The infill…

  7. The organic and mineral matter contents in deposits infilling floodplain basins: Holocene alluviation record from the Kłodnica and Osobłoga river valleys, southern Poland

    NASA Astrophysics Data System (ADS)

    Wójcicki, K. J.; Marynowski, L.

    2012-07-01

    The work examines the timing and environmental conditions of floodplain sedimentation in the valleys of the upland Kłodnica and piedmont Osobłoga rivers in the Upper Odra River basin. A distribution of 52 14C-ages shows relatively high floodplain sedimentation at the Late Glacial-Holocene transition, more stable floodplain environments since the Early (in the Kłodnica Valley) and Middle Holocene (in the Osobłoga Valley) and a gradual increase in floodplain deposition in the Late Holocene (since < 3.4 kyr BP). Organic matter [OM] and mineral matter [MM] fluctuations were correlated with variables responsible for the activation of erosion (i.e. vegetation changes, human impact and hydrological events) as well as factors affecting the local record of sedimentation (i.e. valley morphology, hydrologic conditions and episodes of local erosion). A clear relationship is shown between an increase in alluviation and climate- or human-induced extension of unforested areas. The deposition of mineral-rich sediments increases rapidly during periods characterized by non-arboreal pollen values exceeding approximately 8% in pollen diagrams. On the other hand, the results obtained do not confirm significant interactions between Holocene changes in forest composition and alluviation. Despite the settlement of agrarian groups, the sedimentary record of human activity in the Osobłoga catchment is very poor during the Neolithic and early Bronze Age. A large-scale alluviation of the Osobłoga and Kłodnica valleys was initiated during the settlement of people of the Lusatian culture from the middle Bronze Age and escalated in the early Middle Ages and Modern Times. The deposition of products of soil erosion was limited to between ca. 1.9-1.2 kyr BP, probably due to demographic regression during the Migration Period. Comparison of OM/MM fluctuations with phases of increased fluvial activity does not show a relationship between Holocene wetter phases and catchment sediment yield

  8. Paleontological interpretations of crater processes and infilling of synimpact sediments from the Chesapeake Bay impact structure

    USGS Publications Warehouse

    ,; Edwards, L.E.; Litwin, R.J.

    2009-01-01

    Biostratigraphic analysis of sedimentary breccias and diamictons in the Chesapeake Bay impact structure provides information regarding the timing and processes of late-stage gravitational crater collapse and ocean resurge. Studies of calcareous nannofossil and palynomorph assemblages in the International Continental Scientific Drilling Program (ICDP)-U.S. Geological Survey (USGS) Eyreville A and B cores show the mixed-age, mixed-preservation microfossil assemblages that are typical of deposits from the upper part of the Chesapeake Bay impact structure. Sparse, poorly preserved, possibly thermally altered pollen is present within a gravelly sand interval below the granite slab at 1392 m in Eyreville core B, an interval that is otherwise barren of calcareous nannofossils and dinocysts. Gravitational collapse of watersaturated sediments from the transient crater wall resulted in the deposition of sediment clasts primarily derived from the nonmarine Cretaceous Potomac Formation. Collapse occurred before the arrival of resurge. Low pollen Thermal Alteration Index (TAI) values suggest that these sediments were not thermally altered by contact with the melt sheet. The arrival of resurge sedimentation is identified based on the presence of diamicton zones and stringers rich in glauconite and marine microfossils at 866.7 m. This horizon can be traced across the crater and can be used to identify gravitational collapse versus ocean-resurge sedimentation. Glauconitic quartz sand diamicton dominates the sediments above 618.2 m. Calcareous nannofossil and dinoflagellate data from this interval suggest that the earliest arriving resurge from the west contained little or no Cretaceous marine input, but later resurge pulses mined Cretaceous sediments east of the Watkins core in the annular trough. Additionally, the increased distance traveled by resurge to the central crater in turbulent flow conditions resulted in the disaggregation of Paleogene unconsolidated sediments. As a

  9. Paleontological interpretations of crater processes and infilling of synimpact sediments from the Chesapeake Bay impact structure

    USGS Publications Warehouse

    Self-Trail, Jean M.; Edwards, Lucy E.; Litwin, Ronald J.

    2009-01-01

    Biostratigraphic analysis of sedimentary breccias and diamictons in the Chesapeake Bay impact structure provides information regarding the timing and processes of late-stage gravitational crater collapse and ocean resurge. Studies of calcareous nannofossil and palynomorph assemblages in the International Continental Scientific Drilling Program (ICDP)–U.S. Geological Survey (USGS) Eyreville A and B cores show the mixed-age, mixed-preservation microfossil assemblages that are typical of deposits from the upper part of the Chesapeake Bay impact structure. Sparse, poorly preserved, possibly thermally altered pollen is present within a gravelly sand interval below the granite slab at 1392 m in Eyreville core B, an interval that is otherwise barren of calcareous nannofossils and dinocysts. Gravitational collapse of water- saturated sediments from the transient crater wall resulted in the deposition of sediment clasts primarily derived from the nonmarine Cretaceous Potomac Formation. Collapse occurred before the arrival of resurge. Low pollen Thermal Alteration Index (TAI) values suggest that these sediments were not thermally altered by contact with the melt sheet. The arrival of resurge sedimentation is identified based on the presence of diamicton zones and stringers rich in glauconite and marine microfossils at 866.7 m. This horizon can be traced across the crater and can be used to identify gravitational collapse versus ocean-resurge sedimentation. Glauconitic quartz sand diamicton dominates the sediments above 618.2 m. Calcareous nannofossil and dino-flagellate data from this interval suggest that the earliest arriving resurge from the west contained little or no Cretaceous marine input, but later resurge pulses mined Cretaceous sediments east of the Watkins core in the annular trough. Additionally, the increased distance traveled by resurge to the central crater in turbulent flow conditions resulted in the disaggregation of Paleogene unconsolidated sediments. As

  10. How do how internal and external processes affect the behaviors of coupled marsh mudflat systems; infill, stabilize, retreat, or drown?

    NASA Astrophysics Data System (ADS)

    Carr, J. A.; Mariotti, G.; Wiberg, P.; Fagherazzi, S.; McGlathery, K.

    2013-12-01

    Intertidal coastal environments are prone to changes induced by sea level rise, increases in storminess, and anthropogenic disturbances. It is unclear how changes in external drivers may affect the dynamics of low energy coastal environments because their response is non-linear, and characterized by many thresholds and discontinuities. As such, process-based modeling of the ecogeomorphic processes underlying the dynamics of these ecosystems is useful, not only to predict their change through time, but also to generate new hypotheses and research questions. Here, a three-point dynamic model was developed to investigate how internal and external processes affect the behavior of coupled marsh mudflat systems. The model directly incorporates ecogeomorphological feedbacks between wind waves, salt marsh vegetation, allochthonous sediment loading, tidal flat vegetation and sea level rise. The model was applied to examine potential trajectories of salt marshes on the Eastern seaboard of the United States, including those in the Plum Island Ecosystems (PIE), Virginia Coast Reserve (VCR) and Georgia Coastal Ecosystems (GCE) long term ecological research (LTER) sites. While these sites are undergoing similar rates of relative sea level rise (RSLR), they have distinct differences in site specific environmental drivers including tides, wind waves, allochthonous sediment supply and the presence or absence of seagrass. These differences lead to the emergence of altered behaviors in the coupled salt marsh-tidal flat system. For marsh systems without seagrass or significant riverine sediment supply, conditions similar to those at PIE, results indicated that horizontal and vertical marsh evolution respond in opposing ways to wave induced processes. Marsh horizontal retreat is triggered by large mudflats and strong winds, whereas small mudflats and weak winds reduce the sediment supply to the salt marsh, decreasing its capability to keep pace with sea level rise. Marsh expansion and

  11. The TALE Infill Array

    NASA Astrophysics Data System (ADS)

    Bergman, Douglas

    2009-05-01

    The TALE Infill Array in conjunction with the TALE Tower Detector will provide hybrid coverage of the cosmic ray energy spectrum down to 3x10^16 eV. It will consist of about 100, two square meter scintillators on the surface spaced at 400 m; and 24 buried twelve square meter scintillators. The combination of surface and underground detectors will allow for the determination of the muon content of showers and thus give a handle on cosmic ray composition.

  12. Holocene sedimentation processes and environmental changes along the Namibian coastline

    NASA Astrophysics Data System (ADS)

    Schüller, Irka; Belz, Lukas; Wilkes, Heinz; Wehrmann, Achim

    2016-04-01

    The regional oceanic and atmospheric circulation patterns strongly control environmental conditions in southern Africa. Changes in the system may have significant consequences on climate and related processes. The hyper arid coast of Namibia is mainly influenced by (1) the cold Benguela upwelling, (2) the Benguela current and (3) the Angola current. The Benguela current transports the cool, upwelling water from south to north and interacts with the warm, contrary flowing Angola current at the Angola-Benguela Front (ABF). Today the ABF is located around the Namibian-Angolan border with minor seasonal changes. Therefore, climate and environment at the Namibian coast are affected by the cold water conditions. It is known evidently that the location of the ABF changed during the Holocene over several latitudes and enabled warm water species to expand their range farther south. Several (paleo-) lagoons (coastal salt pans) exist along the Namibian coastline. Most of them are already barred and filled by longshore sediment transport processes. Tidal flooding and active sedimentation processes are restricted to the southernmost lagoons. Two different types of sediments occur. The northern pans contain well sorted, siliciclastic medium sands. Fine-layered alternation refers to changes in mineral composition. The southern pans are dominated by typical tidal sediments with a high amount of benthic fauna (mainly bivalves and gastropods). At Cape Cross the distinct shift between both facies is documented in the cores. Age determinations of core material prove a very fast sediment filling of the distinct lagoons with high sedimentation rates. However, the age of closure differs from lagoon to lagoon. Northern pan sediments are much older (Cape Cross: ~ 5000 a BP) than southern (Sandwich Bay and Conception Bay: 1800 - 300 a BP). Additional information are supported by river clay deposits (~ 36600 a BP) and fossil reed systems (~ 47900 a BP) in Conception Bay and peat deposits at

  13. Catchment clearing accelerates the infilling of a shallow subtropical bay in east coast Australia

    NASA Astrophysics Data System (ADS)

    Coates-Marnane, Jack; Olley, Jon; Burton, Joanne; Sharma, Ashneel

    2016-06-01

    Understanding processes that govern the transport and distribution of terrestrial sediments to and within bays is critical for interpreting the drivers of long-term changes in these ecosystems. On the east coast of Australia increased soil erosion and sediment delivery following extensive land clearing in the contributing catchments, associated with European settlement, is highlighted as a key driver of the decline of numerous nearshore habitats including seagrass meadows and in-shore coral reefs. Here we use optical, radiocarbon and radionuclide dating to estimate mass accumulation rates and type of terrestrial sedimentation in central Moreton Bay during the Holocene. We compare the long-term rates of infilling within the central basin with the recent past and show a 3-9 fold increase in sediment accretion over the last 100 years compared to the long term (last ∼ 1500 to 3000 yrs) average. Infilling during the Holocene is not spatially uniform, with preferential deposition occurring within the now submerged palaeochannels of the Brisbane and Pine rivers. We suggest that modern turbidity regimes in Moreton Bay are the result of the compounded effect of both a historical increase in fine sediment supply and a rapid decline in the effective storage capacity of the basin.

  14. Infilling missing hydrological data - methods and consequences

    NASA Astrophysics Data System (ADS)

    Bardossy, A.; Pegram, G. G.

    2013-12-01

    Hydrological observations are often incomplete - equipment malfunction, transmission errors and other technical problems lead to unwanted gaps in observation time series. Furthermore, due to financial and organizational problems, many observation networks are in continuous decline. As an ameliorating stratagem, short time gaps can be filled using information from other locations. The statistics of abandoned stations provide useful information for the process of extending records. In this contribution the authors present different methods for infilling gaps using: - nearest neighbours - simple and multiple linear regression - black box methods (fuzzy and neural nets) - Expectation Maximization - Copula based estimation The methods are used at different time scales for infilling precipitation from daily through pentads and months to years. The copula based estimation provides not only an estimator for the expected value, but also a probability distribution for each of the missing values. Thus the method can be used for conditional simulation of realizations. Observed precipitation data from the Cape region in South Africa are used to illustrate the intercomparison of the methodologies. The consequences of using [or not using] infilling and data extension are illustrated using a hydrological modelling example from South-West Germany.

  15. Testing of clay tile infilled frames

    SciTech Connect

    Flanagan, R.D.; Bennett, R.M.; Burdette, E.G.; Goodpasture, D.W.

    1992-08-21

    Several large-scale static tests of clay tile infilled frames were recently conducted. For in-plane racking tests, the effects of cyclic loading, varying frame stiffness, varying infill size, infill offset from frame centerline, and single and double wythe infill construction were investigated. Out-of-plane tests examined infilled frame response to inertial loadings and inter-story drift loadings. Multiple loadings were performed to determine in-plane strength and stiffness degradation from both out-of-plane loadings. To determine constitutive properties of the infills, prism compression, mortar compression and various unit tile tests were performed.

  16. NATURAL ARSENIC CONTAMINATION OF HOLOCENE ALLUVIAL AQUIFERS BY LINKED TECTONIC, WEATHERING, AND MICROBIAL PROCESSES

    EPA Science Inventory

    Linked tectonic, geochemical, and biologic processes lead to natural arsenic contamination of groundwater in Holocene alluvial aquifers, which are the main threat to human health around the world. These groundwaters are commonly found a long distance from their ultimate source of...

  17. Basin infilling of a schematic 1D estuary using two different approaches: an aggregate diffusive type model and a processed based model.

    NASA Astrophysics Data System (ADS)

    Laginha Silva, Patricia; Martins, Flávio A.; Boski, Tomász; Sampath, Dissanayake M. R.

    2010-05-01

    processes. In this viewpoint the system is broken down into its fundamental components and processes and the model is build up by selecting the important processes regardless of its time and space scale. This viewpoint was only possible to pursue in the recent years due to improvement in system knowledge and computer power (Paola, 2000). The primary aim of this paper is to demonstrate that it is possible to simulate the evolution of the sediment river bed, traditionally studied with synthetic models, with a process-based hydrodynamic, sediment transport and morphodynamic model, solving explicitly the mass and momentum conservation equations. With this objective, a comparison between two mathematical models for alluvial rivers is made to simulate the evolution of the sediment river bed of a conceptual 1D embayment for periods in the order of a thousand years: the traditional synthetic basin infilling aggregate diffusive type model based on the diffusion equation (Paola, 2000), used in the "synthesist" viewpoint and the process-based model MOHID (Miranda et al., 2000). The simulation of the sediment river bed evolution achieved by the process-based model MOHID is very similar to those obtained by the diffusive type model, but more complete due to the complexity of the process-based model. In the MOHID results it is possible to observe a more comprehensive and realistic results because this type of model include processes that is impossible to a synthetic model to describe. At last the combined effect of tide, sea level rise and river discharges was investigated in the process based model. These effects cannot be simulated using the diffusive type model. The results demonstrate the feasibility of using process based models to perform studies in scales of 10000 years. This is an advance relative to the use of synthetic models, enabling the use of variable forcing. REFERENCES • Briggs, L.I. and Pollack, H.N., 1967. Digital model of evaporate sedimentation. Science, 155, 453

  18. Semiarid landscapes response to Aeolian processes during Holocene in Baikal Region

    NASA Astrophysics Data System (ADS)

    Dan'ko, Lidia; Opekunova, Marina

    2010-05-01

    Arid and semiarid landscapes play a significant role in global climate, biogeochemical, and hydrological processes. Regional analysis of the past aeolian processes is essential for improve our understanding of how various landscape and ecosystems responded to climate change in the past. Our investigation presents details on sand dunes and on loess-like sediments. The study areas are situated in the northern part of Baikal Region (Eastern Siberia). In its depressions, the so-called Barguzinskaya and Tunkinskaya Valley surrounded mountain ranges local dunefieds and loess-like sediments have developed. Present climate in the study areas is continental, characterized by low precipitation(mean annual 250-450 mm) and wide annual range of temperature. Field investigations indicate that the Holocene deposits of the Barguzinskaya and Tunkinskaya Valley are sealed the pedo-sedimentary interface. The analytical results suggest that one's represents a changeover from intensified soil formation to accelerated aeolian dust accumulation. The original content of calcium carbonate and gypsum at the base of some sections of loess-like sediments indicates the aeolian origin of these sediments. In whole, the soil horizons are a proof for humid phases. The change was forced by climatic aridity. Absolute dating of the organogenic components of soils (14C) indicate the age positions of the arid and humid climate phases. Our results indicate not only 1-4 long-time episodes of aeolian dust accumulation during the Holocene, but shot-time aeolian accumulation episodes, that were specific for Late Holocene. For example, in the Tunkinskaya Valley the Late Holocene soil formation replaced by aeolian deposit at 1700 - 1900, 800 and 200-250 years ago, in the Barguzinskaya Valley - about 3100 - 2900, 2300 and 600 years ago. It can be concluded that a periodical formation of the aeolian deposits in the semiarid landscapes during Holocene can be postulated. Aeolian and loess-like sediments of the

  19. Fracturing improvements enhance infill drilling

    SciTech Connect

    Miller, B.J.; Gillstrom, R.L.

    1995-12-31

    The production history of a one thousand well field extension drilled in the early 1980`s showed that additional wells could not be drilled at current oil prices and oil recovery. Step out drilling and production history showed that an additional one hundred infill and development wells could be drilled if the recovery could be increased. Multiple production logs indicated the upper half of the zone was not open at the well bore. Thus, if the upper zone could be more effectively completed, the well recovery had the potential to be increased to a level where future development would be feasible. The low reservoir pressure and high permeability contrast requirements demanded that a much higher viscosity fluid system needed to be used that also had the ability to clean up easily. The nitrogen foam frac yielded these desired characteristics. Five infill wells were drilled in 1991 and 1993 utilizing a nitrogen foam frac system. Production from the wells has shown a projected ultimate recovery from the wells of approximately twice the original wells.

  20. Masonry infill performance during the Northridge earthquake

    SciTech Connect

    Flanagan, R.D.; Bennett, R.M.; Fischer, W.L.; Adham, S.A.

    1996-03-08

    The response of masonry infills during the 1994 Northridge, California earthquake is described in terms of three categories: (1) lowrise and midrise structures experiencing large near field seismic excitations, (2) lowrise and midrise structures experiencing moderate far field excitation, and (3) highrise structures experiencing moderate far field excitation. In general, the infills provided a positive beneficial effect on the performance of the buildings, even those experiencing large peak accelerations near the epicenter. Varying types of masonry infills, structural frames, design conditions, and construction deficiencies were observed and their performance during the earthquake indicated. A summary of observations of the performance of infills in other recent earthquakes is given. Comparison with the Northridge earthquake is made and expected response of infill structures in lower seismic regions of the central and eastern United States is discussed.

  1. Holocene hillslope processes and deposits in two U-shaped mountain valleys in western Norway

    NASA Astrophysics Data System (ADS)

    Laute, K.; Beylich, A. A.

    2012-04-01

    This doctoral research project is integrated in the Norwegian Research Council (NFR) funded SedyMONT-Norway Project within the ESF EUROCORES TOPO-EUROPE SedyMONT (Timescales of sediment dynamics, climate and topographic change in mountain landscapes) Programme. Research is carried out within two steep, U-shaped and glacier-connected tributary valleys (Erdalen and Bødalen) on the western side of the Jostedalsbreen ice cap in western Norway. Contemporary denudative processes in both valley systems include rock and boulder falls, avalanches, slush flows, debris flows, creep processes, wash- and chemical denudation and fluvial transport of solutes, suspended sediments and bedload. The main aims of this research project which are approached within a Holocene to contemporary timescale are: (i) to investigate the spatio-temporal variability of Holocene hillslope development, (ii) to analyse more specificly the morphometric influences and geomorphic consequences of the Little Ice Age (LIA) glacier advance on selected hillslope systems within defined headwater areas in both valleys, (iii) to study morphometric and meteorological controls of contemporary denudative slope processes as well as (iv) to quantify the rates of sediment delivery from headwater areas and its changes over time. A process-based approach is applied using a variety of different methods and techniques. Focus is on different temporal (Holocene to contemporary) and spatial (selected hillslope systems, headwater areas and entire valley system) scales. The applied methods include orthophoto- and topographical map interpretation, GIS and DEM computing, geomorphological fieldmapping and hillslope profile surveying complemented by relative dating techniques (lichenometry and dendrochronology), geophysical investigations and terrestrial laser scanning (LIDAR). For monitoring contemporary rates of slope processes a designed monitoring programme (running since 2009) with a wide spectrum of instrumentation; e

  2. From Late Miocene to Holocene: Processes of Differentiation within the Telestes Genus (Actinopterygii: Cyprinidae)

    PubMed Central

    Dubut, Vincent; Fouquet, Antoine; Voisin, Adrien; Costedoat, Caroline; Chappaz, Rémi; Gilles, André

    2012-01-01

    Investigating processes and timing of differentiation of organisms is critical in the understanding of the evolutionary mechanisms involved in microevolution, speciation, and macroevolution that generated the extant biodiversity. From this perspective, the Telestes genus is of special interest: the Telestes species have a wide distribution range across Europe (from the Danubian district to Mediterranean districts) and have not been prone to translocation. Molecular data (mtDNA: 1,232 bp including the entire Cyt b gene; nuclear genome: 11 microsatellites) were gathered from 34 populations of the Telestes genus, almost encompassing the entire geographic range. Using several phylogenetic and molecular dating methods interpreted in conjunction with paleoclimatic and geomorphologic evidence, we investigated the processes and timing of differentiation of the Telestes lineages. The observed genetic structure and diversity were largely congruent between mtDNA and microsatellites. The Messinian Salinity Crisis (Late Miocene) seems to have played a major role in the speciation processes of the genus. Focusing on T. souffia, a species occurring in the Danube and Rhone drainages, we were able to point out several specific events from the Pleistocene to the Holocene that have likely driven the differentiation and the historical demography of this taxon. This study provides support for an evolutionary history of dispersal and vicariance with unprecedented resolution for any freshwater fish in this region. PMID:22479629

  3. Estuarine infill and coastal progradation, southern van diemen gulf, northern Australia

    NASA Astrophysics Data System (ADS)

    Woodroffe, C. D.; Mulrennan, M. E.; Chappell, J.

    1993-03-01

    There are several estuaries associated with the pronouncedly seasonal rivers which drain northwards from the Middle Proterozoic sandstone Arnhem Land plateau, and the Tertiary Koolpinyah land surface, into the macrotidal van Diemen Gulf, in the Northern Territory of Australia. The Holocene development of these, investigated in greatest detail for the South Alligator River with an upland catchment of > 10,000 km 2. through drilling, palynology and radiocarbon dating, comprises both estuarine infill and coastal progradation. Three phases of estuarine infill can be recognised: (i) a transgressive phase (8000-6800 years B.P.) of marine incursion; (ii) a big swamp phase (6800-5300 years B.P.) of widespread mangrove forest development; and (iii) a sinuous/cuspate phase of floodplain development since 5300 years B.P., during which the tidal river has meandered and reworked earlier estuarine sediments. Since 6000 years B.P., the South Alligator coastal plain has prograded at a decelerating rate, with two phases of chenier ridge formation. A similar pattern of estuarine infill, and decelerating coastal plain progradation, is demonstrated for the Adelaide and Mary Rivers, both with catchments of > 6000 km 2. The southern shore of van Diemem Gulf appears to have changed its overall position little during the last 2000 years. The major source for the clay, silt and fine sands which have infilled the estuary and coastal plain has been from seaward. Dispite the similarity of development, coastal sediment build up has had different effects on the morphology of each tidal river. The Adelaide has undergone a major diversion and no longer flows directly into van Diemen Gulf, but occupies a former fluvial course, and the Mary has been blocked entirely, and its former estuarine palaeochannels have been infilled with tide-transported sediment.

  4. Solar cycles or random processes? Evaluating solar variability in Holocene climate records

    PubMed Central

    Turner, T. Edward; Swindles, Graeme T.; Charman, Dan J.; Langdon, Peter G.; Morris, Paul J.; Booth, Robert K.; Parry, Lauren E.; Nichols, Jonathan E.

    2016-01-01

    Many studies have reported evidence for solar-forcing of Holocene climate change across a range of archives. These studies have compared proxy-climate data with records of solar variability (e.g. 14C or 10Be), or have used time series analysis to test for the presence of solar-type cycles. This has led to some climate sceptics misrepresenting this literature to argue strongly that solar variability drove the rapid global temperature increase of the twentieth century. As proxy records underpin our understanding of the long-term processes governing climate, they need to be evaluated thoroughly. The peatland archive has become a prominent line of evidence for solar forcing of climate. Here we examine high-resolution peatland proxy climate data to determine whether solar signals are present. We find a wide range of significant periodicities similar to those in records of solar variability: periods between 40–100 years, and 120–140 years are particularly common. However, periodicities similar to those in the data are commonly found in random-walk simulations. Our results demonstrate that solar-type signals can be the product of random variations alone, and that a more critical approach is required for their robust interpretation. PMID:27045989

  5. Solar cycles or random processes? Evaluating solar variability in Holocene climate records.

    PubMed

    Turner, T Edward; Swindles, Graeme T; Charman, Dan J; Langdon, Peter G; Morris, Paul J; Booth, Robert K; Parry, Lauren E; Nichols, Jonathan E

    2016-04-05

    Many studies have reported evidence for solar-forcing of Holocene climate change across a range of archives. These studies have compared proxy-climate data with records of solar variability (e.g. (14)C or (10)Be), or have used time series analysis to test for the presence of solar-type cycles. This has led to some climate sceptics misrepresenting this literature to argue strongly that solar variability drove the rapid global temperature increase of the twentieth century. As proxy records underpin our understanding of the long-term processes governing climate, they need to be evaluated thoroughly. The peatland archive has become a prominent line of evidence for solar forcing of climate. Here we examine high-resolution peatland proxy climate data to determine whether solar signals are present. We find a wide range of significant periodicities similar to those in records of solar variability: periods between 40-100 years, and 120-140 years are particularly common. However, periodicities similar to those in the data are commonly found in random-walk simulations. Our results demonstrate that solar-type signals can be the product of random variations alone, and that a more critical approach is required for their robust interpretation.

  6. Late Pleistocene and Holocene depositional trends, processes, and history of Astoria deep-sea fan, Northeast Pacific

    USGS Publications Warehouse

    Nelson, H.

    1976-01-01

    The asymmetrical Astoria Fan (110 ?? 180 km) developed off the Columbia River and Astoria submarine canyon during the Pleistocene. Morphology, stratigraphy, and lithology have been outlined for a Pleistocene turbidite, and a Holocene hemipelagic sedimentary regime to generate geologically significant criteria for comparison with ancient equivalent deposits. Both gray silty clay of the Late Pleistocene and olive-gray clay of the Early Holocene are interrupted by turbidites. The few deeply incised fan valleys of the more steeply sloping upper fan contain thick, muddy and very poorly sorted sand and gravel beds that usually have poorly developed internal sedimentary structures. The numerous shallower fan valleys and distributaries of the flatter middle and lower fan contain thick, clean, and moderately sorted medium to fine sands that are vertically graded in texture, composition and well-developed internal sedimentary structures. Tuffaceous turbidites (containing Mazama ash, 6600 B.P.) can be traced as thick deposits (ca. 30-40 cm) throughout the Astoria Channel system and as thin correlative interbeds (ca. 1-2 cm) in interchannel areas. Similarly, sand/shale ratios are high throughout the fan valleys and the middle and lower fan areas of distributaries, but are low in the upper-fan interchannel areas. These depositional trends indicate that high-density turbidity currents carry coarse traction loads that remain confined in upper but not lower fan valleys. Fine debris selectively sorts out from channelized flows into overbank suspension flows that spread over the fan and deposit clayey silt. A high content of mica, plant fragments, and glass shards (if present) characterizes deposits of the overbank flows, a major process in the building of upper fan levees and interchannel areas. In the Late Pleistocene, turbidity currents funneled most coarse-grained debris through upper channels to depositional sites in middle and lower fan distributaries that periodically shifted

  7. The late devensian and holocene evolution of Barmouth Bay, Wales

    NASA Astrophysics Data System (ADS)

    Larcombe, Piers; Jago, Colin F.

    1994-03-01

    A marine seismic and sedimentological investigation of the Late-Devensian and Holocene sediments of Barmouth Bay, North Wales, was undertaken to reconstruct late-glacial and Holocene sedimentary environments, and to evaluate post-glacial sedimentation rates. In the last glacial, the Devensian, many Welsh estuaries were the sites of valley glaciers flowing from the Welsh Ice cap onto the modern inner-shelf. At Barmouth, the Mawddach valley glacier flowed into the present inner-shelf of Cardigan Bay. The modern courses of the Mawddach Estuary and the river Gwril were overdeepened by erosive sub-glacial flows, and are later infilled by a coarse-grained sub-glacial and pro-glacial infill sequence. With late-glacial relative sea-level rise and retreat of the Welsh Ice, the Mawddach valley tidewater glacier became grounded and confined to the valley. Re-equilibration of the ice profile occurred, and a morainal complex was formed at its toe. In the early Holocene, the morainal complex formed the seaward boundary of a sheltered nearshore basin where fine-grained, partly organic, sediments were deposited in a lagoonal or estuarine environment. Holocene reworking of the sediments by shallow-marine processes has formed a lag surface to the morainal complex, and has introduced gravel of Irish Sea Ice character from offshore. Wave action has formed a shingle coastal barrier, narrowing the mouth of the modern estuary. A shoreface-attached sand wedge, which attains a maximum thickness of 4 m beneath the modern ebb-tidal delta, overlies the lag surface and onlaps the coastal barrier. Since 8-9 ky BP, the mean sediment accumulation rate of estuarine and shallow-marine sediments has been 2.3-3.1 mm/yr, roughly equivalent to the long-term mean rate of sea-level rise for Cardigan Bay. This mean rate masks rapidly increasing accumulation rates in the Mawddach Estuary in the last 5-6 ky, which now may be 82 mm/yr, and which are due to reworking of shoreface and barrier sands into the

  8. Anthropogenic triggers for Late Holocene soil erosion in the Jebel Toubkal, High Atlas, Morocco

    NASA Astrophysics Data System (ADS)

    Fletcher, William; Hughes, Philip

    2016-04-01

    The Assif n'Imserdane valley, located in the Jebel Toubkal area of the High Atlas, Morocco, is a highly dynamic geomorphological setting. The valley was glaciated during the Late Pleistocene, and subsequently experienced a catastrophic rock avalanche leading to the formation of one of the largest mass movement landforms in North Africa. Recent research (Hughes et al., GSA Bulletin 126: 1093-1104) has dated the formation of the rock avalanche to the mid-Holocene at 4.5 ± 0.5 ka. Here, we examine the sedimentological (organic matter content, magnetic susceptibility, particle size and XRF) and palaeoecological (pollen and spores, non-pollen palynomorphs (NPPs), microcharcoal and conifer tracheid fragments) record of a small infilled basin located adjacent to a Late Pleistocene moraine and close to the rock avalanche in the Arroumd sector. The deposits, primarily fine-grained and minerogenic with a low concentration of organic microfossils including pollen, coprophilous ascospores, wood and charcoal microfragments, are enriched in fine silts and ferrimagnetic minerals, consistent with erosional sources from surrounding slope soils. Two radiocarbon dates on fine charcoal recovered from the deposit indicate that the infill event occurred during the first millennium AD (after 430 - 640 AD). As such, the deposits point to a phase of slope instability and erosion that is not linked to either deglaciation processes or to the mid-Holocene rock avalanche. Instead, the nature and timing suggest that an anthropogenic trigger of degradation to the natural vegetation cover may be implicated. The record casts light on a previously undocumented phase of landscape instability in the dynamic setting of the Assif n'Imserdane valley, and highlights the potential for further exploration of small infilled basins in the High Atlas to illuminate the geoecological history of this semi-arid mountain region.

  9. Infill and mire evolution of a typical kettle hole: young ages at great depths (Jackenmoos, Austria)

    NASA Astrophysics Data System (ADS)

    Götz, Joachim; Salcher, Bernhard

    2015-04-01

    Kettle holes are very common features in proglacial environments. Myriads of small, often circular shaped lakes are indicative of dead ice slowly melting out after the collapse of glaciers and subsequent burial of glaciofluvial sediments. Many of these lakes transformed into mires during the Postglacial and the Holocene. Still, little is known about the mechanisms leading to mire formation in such environments. We aim to analyse the shape and the postglacial history of infilling and peat accumulation of a typical dead ice kettle using 2D resistivity surveying, core-drilling, 14C dating and palynologic analyses. The kettle hole mire is located within a small kame delta deposit just south of the LGM extend of the Salzach Piedmont glacier (Austria/Germany). Today, the mire is a spot of exceptional high biodiversity and under protection. Sediment core samples extracted in the deepest (c. 10-14 m) and central part of the kettle directly overly lacustrine fine sediments and yielded young ages covering the subatlantic period only. Young ages are in agreement with palynologic results comprising e.g. pollen of secale (rye) and juglans (walnut). However, these deposits are situated beneath a massive water body (10 m), only covered by a thin floating mat. A second, more distally situated drill core indicates the thinning of this water body at the expense of peat deposits covering the Late Glacial to Middle Holocene. Multiple 2D resistivity data support drilling information and enabled us to reconstruct the shape of the basin. The transition from lacustrine sediments to the water body above is characterised by a sharp increase in resistivity. Furthermore, the resistivity pattern within the entire kettle indicates an increase towards the centre, most probably as a result of the changing nutrient content. The postglacial evolution of the mire is in agreement with the concept of "floating mat terrestrialisation", representing a horizontal growth of the floating mat from the edges

  10. Large-scale testing of structural clay tile infilled frames

    SciTech Connect

    Flanagan, R.D.; Bennett, R.M.

    1993-03-18

    A summary of large-scale cyclic static tests of structural clay tile infilled frames is given. In-plane racking tests examined the effects of varying frame stiffness, varying infill size, infill offset from frame centerline, and single and double wythe infill construction. Out-of-plane tests examined infilled frame response to inertial loadings and inter-story drift loadings. Sequential in-plane and out-of-plane loadings were performed to determine the effects of orthogonal damage and degradation on both strength and stiffness. A combined out-of-plane inertial and in-plane racking test was conducted to investigate the interaction of multi-directional loading. To determine constitutive properties of the infills, prism compression, mortar compression and various unit tile tests were performed.

  11. Experimental testing of hollow clay tile infilled frames

    SciTech Connect

    Flanagan, R.D. ); Bennett, R.M.; Barclay, G.A. . Dept. of Civil Engineering)

    1992-02-27

    A common building construction of the Oak Ridge Y-12 Plant is structural steel framing with infilled unreinforced hollow clay tile walls. A comprehensive program is underway to evaluate the resistance of this construction to natural phenomena loadings, particularly earthquake. This paper presents the results of the first series of large-scale infilled frame tests which were statically loaded in-plane to failure. Varying frame to infill stiffness was examined within the range of actual building construction.

  12. Seismic safety assessment of existing masonry infill structures in Nepal

    NASA Astrophysics Data System (ADS)

    Chaulagain, Hemchandra; Rodrigues, Hugo; Spacone, Enrico; Varum, Humberto

    2016-06-01

    Reinforced concrete (RC) buildings in Nepal are constructed with RC frames and masonry infill panels. These structures exhibit a highly non-linear inelastic behavior resulting from the interaction between the panels and frames. This paper presents an extensive case study of existing RC buildings in Nepal. Non-linear analyses were performed on structural models of the buildings considered as a bare frame and with masonry infill, in order to evaluate the influence of infill walls on the failure mechanisms. Five three-storey buildings with different structural configurations and detailing were selected. The effect of masonry infill panels on structural response was delineated by comparing the bare-framed response with the infill response. Seismic performance is evaluated with regard to global strength, stiffness, energy dissipation, inter-storey drift, and total deflection of the structure. A parametric analysis of structures with masonry infill is also performed. For this, the influence of different material properties is studied, namely diagonal compressive stress, modulus of elasticity and tensile stress of masonry infill panels. Study results show that masonry infill increases the global strength and stiffness of the structures; it decreases the inter-storey drift and hence the total displacement of the structure. The results quantify the influence of the infill panels on structural response and, in particular, the effect of the diagonal compressive strength of the masonry wall.

  13. Late Pleistocene and Holocene aeolian sedimentation in Gonghe Basin, northeastern Qinghai-Tibetan Plateau: Variability, processes, and climatic implications

    NASA Astrophysics Data System (ADS)

    Qiang, Mingrui; Jin, Yanxiang; Liu, Xingxing; Song, Lei; Li, Hao; Li, Fengshan; Chen, Fahu

    2016-01-01

    Although stratigraphic sequences of aeolian deposits in dryland areas have long been recognized as providing information about past environments, the exact nature of the environmental processes they reflect remains unclear. Here, we report the results of a detailed investigation of eight outcrop sections in the Gonghe Basin, northeastern Qinghai-Tibetan Plateau. Measurements of sediment grain-size and chemical composition indicate that the deposits are primarily of aeolian origin, consisting of interbedded, well-sorted sand, silty sand, loess and/or palaeosol; however, their occurrence varies from site to site. Fossil dune sands mainly occur in or close to the currently stabilized or semi-stabilized dune fields, whereas loess is distributed along the downwind marginal areas. This pattern of basin-scale differentiation was controlled mainly by spatial variability of sediment supply due to the antecedent sedimentary patterns within the basin. Together with previously-published optically stimulated luminescence (OSL) ages, 24 new OSL dates are used to elucidate the history of aeolian activity and its relationship to climatic changes. There is no apparent relationship between past dune activity and downwind loess deposits. Deposition of silty sand probably occurred during past phases of windy, dry and cold climate in the Late Pleistocene. However, climatic factors alone cannot explain the occurrence of silty sand deposition. This is because the deposition of silty sand was always preceded by episodes of fluvial deposition prior to river incision, thereby indicating the importance of an 'activated' sediment supply associated with fluvial processes. Deposition of well-sorted sand occurred episodically, not only during the Late Pleistocene, but also during the early- to mid-Holocene. Vegetation conditions, controlled either by the occurrence of intervals of moisture deficit during the Late Pleistocene or by changes in the balance between precipitation and

  14. No-infill 3D Printing

    NASA Astrophysics Data System (ADS)

    Wei, Xiao-Ran; Zhang, Yu-He; Geng, Guo-Hua

    2016-09-01

    In this paper, we examined how printing the hollow objects without infill via fused deposition modeling, one of the most widely used 3D-printing technologies, by partitioning the objects to shell parts. More specifically, we linked the partition to the exact cover problem. Given an input watertight mesh shape S, we developed region growing schemes to derive a set of surfaces that had inside surfaces that were printable without support on the mesh for the candidate parts. We then employed Monte Carlo tree search over the candidate parts to obtain the optimal set cover. All possible candidate subsets of exact cover from the optimal set cover were then obtained and the bounded tree was used to search the optimal exact cover. We oriented each shell part to the optimal position to guarantee the inside surface was printed without support, while the outside surface was printed with minimum support. Our solution can be applied to a variety of models, closed-hollowed or semi-closed, with or without holes, as evidenced by experiments and performance evaluation on our proposed algorithm.

  15. Holocene aeolian development in Central Spain; chronology, regional correlations and causal processes

    NASA Astrophysics Data System (ADS)

    García-Hidalgo, José F.; Temiño, Javier; Segura, Manuel

    2007-10-01

    Extensive areas in the southern part of the Duero Tertiary Basin (Central Spain) are covered by aeolian sands. Presently, the aeolian system is relict but in its origin and development it can be described as a "wet aeolian system". Climatic and environmental changes during the Holocene are typified by alternating humid and arid periods. These are recorded in the sedimentary record as either organic-rich sandy palaeosols or clean aeolian sand, respectively. Palaeosol dating (12 radiocarbon dated samples) and stratigraphical and sedimentological analysis of several dunefields in quarries and boreholes allow the distinction of four periods of palaeosol development since the Allerød. Aeolian sediments commonly rest on fluvial deposits, which were themselves the major source area for aeolian sands. These fluvial deposits have an age of about 14,000 cal yr BP. The first phase of aeolian activity postdates these fluvial sediments and has an upper age of about 12,000-11,700 cal yr BP, probably corresponding to the last cold oscillation of the Lateglacial (Younger Dryas). The second phase ranges from about 11,500 to 9500 cal yr BP, during which period the majority of dunes in the Tierra de Pinares area formed. This is also a major phase of aeolian activity in other areas of the Iberian Peninsula. A third and probably discontinuous phase of aeolian activity took place between 6800 and about 3000 cal yr BP. The age for this phase is supported by the presence of Visigothic burial sites covered by aeolian sands. The presence of charred material and degraded slipfaces clearly indicate stabilisation by vegetation and the final degradation of the aeolian system at the end of the fourth aeolian phase (990-540 cal yr BP). Minor aeolian activity has also occurred subsequently in this area, since aeolian sand movement was even reported in the 20th century. The aeolian phases can be tentatively correlated with aeolian phases in Europe. Aeolian activity tends to occur regionally during

  16. Late Holocene coastal wetlands change, Mississippi Sound, Alabama: Short-term vs. long-term patterns and processes

    SciTech Connect

    Davies, D.J.; Smith, W.E. . Environmental Geology Div.)

    1994-03-01

    Wetlands occupy much of the low-lying mainland coast in Mississippi Sound, Alabama, grading from Spartina salt marsh (48.8 km[sup 2]) to fresh water marshes (13.5 km[sup 2]) to forested wetlands (123.4 km[sup 2]) (Rathbun et al, 1987). These wetlands are undergoing rapid short-term (years to decades) net acreage loss due to headland shoreline erosion. In contrast, long-term (centuries to millennia) change in marsh area is largely due to submergence from Holocene transgression and local subsidence. The Sound overlies drowned Pleistocene-Holocene coastal sediments; existing salt marshes likely developed after inundation of paleomarshes cored at a MHW depth of [minus]3 to [minus]7 m in the mid-Sound (C[sup 14] dates of 4--7,000 Y.B.P.). Geomorphic evidence indicates the primary cause of short-term loss of salt marsh is localized erosion of its seaward edge, rather than submergence. A low (< 1 m) intertidal scarp and narrow sandy beach on open Sound shorelines indicate episodic storm erosion. Linear open Sound shorelines formed by wave modification, in contrast to typically less modified protected shores; nearshore Sound bathymetry shows a gently seaward sloping possible wave-cut terrace. Marsh erosion rates are due to several processes including water energy (background as well as seasonal storms); cohesiveness of marsh sediments; and health of marsh flora. Orientation of the shoreline relative to southerly wind-forced waves during passage of winter cold fronts may be the primary factor. While today's short-term rates of overall vertical coastal inundation are relatively low, the development of new marsh acreage is also negligible. As sediment influx from coastal streams is low, it may be difficult to sustain present marsh acreage should sea level rise accelerate.

  17. 5. DETAIL OF MUD INFILL (MIXED WITH STRAW), LATHS AND ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    5. DETAIL OF MUD INFILL (MIXED WITH STRAW), LATHS AND STRUCTURAL COMPONENTS (CORNER POST, SILL AND STUD), SOUTHEAST CORNER OF EAST SIDE OF ORIGINAL SECTION. - Thomas Threlkeld House, Benson Pike, Shelbyville, Shelby County, KY

  18. 58. THIRD LEVEL, WORKING HOUSE SECTION, DETAIL OF INFILLED CONVEYOR ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    58. THIRD LEVEL, WORKING HOUSE SECTION, DETAIL OF INFILLED CONVEYOR WHICH LED TO STANDARD MILL; LOOKING NORTH - Northwestern Consolidated Elevator "A", 119 Fifth Avenue South, Minneapolis, Hennepin County, MN

  19. 8. DETAIL, FIRST FLOOR, INFILL SECTION, SOUTH (FRONT) ROOM, LOOKING ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    8. DETAIL, FIRST FLOOR, INFILL SECTION, SOUTH (FRONT) ROOM, LOOKING SOUTH (UP) AT PORTION OF EARLY PANELED CEILING ABOVE LATER ACOUSTICAL TILE CEILING - 90 Broad Street (Commercial Building), Charleston, Charleston County, SC

  20. Strength and stiffness reduction factors for infilled frames with openings

    NASA Astrophysics Data System (ADS)

    Decanini, Luis D.; Liberatore, Laura; Mollaioli, Fabrizio

    2014-09-01

    Framed structures are usually infilled with masonry walls. They may cause a significant increase in both stiffness and strength, reducing the deformation demand and increasing the energy dissipation capacity of the system. On the other hand, irregular arrangements of the masonry panels may lead to the concentration of damage in some regions, with negative effects; for example soft story mechanisms and shear failures in short columns. Therefore, the presence of infill walls should not be neglected, especially in regions of moderate and high seismicity. To this aim, simple models are available for solid infills walls, such as the diagonal no-tension strut model, while infilled frames with openings have not been adequately investigated. In this study, the effect of openings on the strength and stiffness of infilled frames is investigated by means of about 150 experimental and numerical tests. The main parameters involved are identified and a simple model to take into account the openings in the infills is developed and compared with other models proposed by different researchers. The model, which is based on the use of strength and stiffness reduction factors, takes into account the opening dimensions and presence of reinforcing elements around the opening. An example of an application of the proposed reduction factors is also presented.

  1. Glacial isostatic adjustment and Holocene to contemporary source-to-sink fluxes in valley-fjord systems in western Norway

    NASA Astrophysics Data System (ADS)

    Beylich, Achim A.; Laute, Katja; Liermann, Susan

    2013-04-01

    architecture of major storage elements (talus cones, valley infills, deltas at the outlets of both drainage basins) using different geophysical methods like georadar and seismic refraction surveys are carried out to improve the quantitative knowledge on Holocene process rates and sedimentary budgets. Detailed geomorphological mapping is conducted and interpreted in combination with digital elevation models and data. The U-shaped valley morphometry is the main control of Holocene denudational surface processes in both Erdalen and Bødalen. Stepped longitudinal valley profiles within the drainage basin systems have caused that glacial isostatic adjustment has not had significant effects on surface denudational processes in the middle and upper parts of both Erdalen and Bødalen. In Erdalen the more clearly defined stepped longitudinal valley profile has resulted in larger storage (especially in larger volumes of Holocene valley infill and talus cones) and in a lower level of slope-channel coupling as compared to Bødalen. As a result, the glacial inheritance of topography is the most important factor controlling valley development since the LGM and sediment storage capacity is primarily conditioned by valley morphometry. Different periods within the Holocene with varying intensity of denudational surface processes can be identified and the glacially sculpted topography has not yet adapted to denudational surface processes acting under Holocene environmental conditions. Under the present-day environmental conditions mechanical denudation dominates over chemical denudation. Surface process rates are moderate to low, and the valley systems are altogether supply-limited. The process and denudation rates from the Erdalen and Bødalen drainage basins are compared with rates from other SedyMONT test sites (transport-limited drainage basin systems located in the Alps), and with denudational process rates in other cold environment drainage basin systems worldwide through the SEDIBUD

  2. Reconstructing Holocene changes in the Southern Hemisphere westerly winds: Integrating modern processes and paleoclimate data from New Zealand's southern fjords

    NASA Astrophysics Data System (ADS)

    Hinojosa, J.; Moy, C. M.; Wilson, G. S.; Stirling, C. H.

    2013-12-01

    The Southern Hemisphere westerly winds are an important component of the global carbon cycle due to their influence on Southern Ocean CO2 flux. In addition, the winds influence mid-latitude storm tracks, thereby controlling moisture balance over much of New Zealand's South Island and other Southern Hemisphere regions. Fiordland, New Zealand is an ideal locale to investigate Holocene changes in westerly wind behavior: It sits at the northern margin of the wind field maximum, is sensitive to latitudinal and strength fluctuations of the winds, and is the location of numerous fjord sub-basins with high sedimentation rates (up to 3 mm/yr). Due to the strong positive relationship between wind speed and regional rainfall, reconstructions of past precipitation and fjord circulation can inform us of past westerly wind behavior. These processes can be observed through changes in the rate of organic carbon delivery from land: When precipitation is high, more terrestrial organic carbon is delivered to the fjords, while low precipitation shifts the balance toward accumulation of marine organic carbon. An important first step towards reconstructing past westerly wind variability is to characterize the distribution and cycling of carbon throughout different depositional settings in the fjords to determine the optimal location for the development of paleoclimate records. Here, we present a geochemical characterization of surface sediments and the water column throughout the region and apply this understanding to sediment cores. During three field seasons in 2012 and 2013, we collected surface sediments, particulate organic matter, and piston cores from 10 different fjords spanning 44-46° S. Our results suggest that organic carbon in the fjord basins largely follows a two-end-member mixing model, drawing from marine and terrestrial end-member sources. We see consistent down-fjord trends in carbon and nitrogen concentrations and isotopes measured from surface sediments and

  3. Holocene Palaeoenvironment on Kamchatka

    NASA Astrophysics Data System (ADS)

    Diekmann, B.; Chapligin, B.; Dirksen, O.; Dirksen, V.; Hoff, U.; Meyer, H.; Nazarova, L.

    2013-12-01

    In the scope of the German-Russian research programme KALMAR (Kurile-Kamchatka and Aleutean Marginal Sea-Island Arc Systems: Geodynamics and Climate Interaction in Space and Time), Holocene lake-sediment records and peat sections were investigated on Kamchatka, to infer environmental changes related to subpolar climatic processes in the northwestern Pacific realm at the eastern Siberian margin. The research strategy followed a multi-proxy approach, using fossil bioindicators (diatoms, chironomids, pollen), stable-isotope geochemistry of diatoms, sedimentology, tephra chronology, and radiocarbon dating. The oldest sediments were retrieved from former proglacial Lake Sokoch, situated at the treeline at 495 m a.s.l. in the Ganalsky Ridge of southern central Kamchatka. Lacustrine sediment records and peat sections of mid- to late Holocene age were recovered from the up to 25 m deep Two-Yurts Lake and neighbouring smaller forest lakes and onshore areas, situated in a former proglacial basin at 275 m a.s.l. at the eastern flank of the Central Kamchatka Mountain Chain, the Sredinny Ridge. Our findings give evidence of longterm climate changes that suggest the existence of a warm and humid early Holocene climate optimum between roughly 9.0 and 4.5 ka BP, followed by climate deterioration of the neoglacial epoch in concert with summer cooling, glacial advances, and enhanced continentality. Two strong cooling episodes punctuated late Holocene climate development between 4.5 and 3.5 ka BP and during the last millennium, marking the prelude of neoglacial cooling and the Little Ice Age. This general development of Holocene climate on Kamchatka is in line with environmental changes in the neighbouring Sea of Okhotsk, where the pattern of sea-ice dynamics is consistent with early Holocene warmth and Neoglacial climate cooling. While the marine records from the Sea of Okhotsk mainly reflect winter conditions, our findings show that summer climate on Kamchatka shows a similar trend

  4. Numerical analysis for in-plane behavior of infilled frames

    SciTech Connect

    Jamal, B.D.; Bennett, R.M.; Flanagan, R.D.

    1992-02-27

    A nonlinear finite element study was conducted for the Y-12 Plant to evaluate the in-plane behavior of masonry infilled steel frames. ABAQUS was used to develop the finite element model and perform a parametric analysis. The model was verified by comparing the results with the experimental program series carried out at the University of Brunswick, Canada. The initial stiffness could be matched using an elastic model with an interface element. The ultimate load could be matched using the ABAQUS nonlinear concrete model for the infill. A softened interface was used to account for the localized mortar crushing that tends to occur at the corners of infilled frames. This model was used to match the secant stiffness at approximately 50% of the ultimate load. A parametric study was performed on the initial stiffness. Results indicated that an appropriate equivalent strut could closely match the behavior.

  5. Shake table testing of structural clay tile infilled frames

    SciTech Connect

    Bennett, R.M.; Fowler, J.J.; Flanagan, R.D.

    1996-03-08

    Two steel frames with structural clay tile infills were tested under simulated seismic loads in both the out-of-plane and in-plane direction. Out-of-plane testing showed that infill panels separate from their bounding frame, and respond at their own natural frequency during a seismic excitation. Due to arching, the panels remain stable. In-plane seismic testing showed similar behavior patterns to previous static testing. The natural frequency was adequately predicted using a piecewise linear equivalent strut analytical method. The structure was then subjected to over one thousand cycles of loading using a sine sweep before failure.

  6. Numerical methods for analysis of clay tile infills

    SciTech Connect

    Flanagan, R.D.; Tenbus, M.A.; Bennett, R.M.

    1993-10-20

    Recent Department of Energy requirements have led to a comprehensive evaluation of the industrial facilities at the Oak Ridge Y-12 Plant. The structures consist of simply connected steel frames infilled with structural clay tile walls. The objective of the evaluation was to determine the stability of the unreinforced infills, and whether they provide the lateral capacity necessary to resist the moderate seismic hazard at the site. Due to lack of information on the behavior of structural clay tile infills, various large-scale tests were performed to investigate the in-plane, out-of-plane and combined in-plane and out-of-plane behavior. The results of these tests are briefly summarized, and the development of analytical guidelines based on these tests is given. Little interaction between in-plane and out-of-plane loads was observed, both in terms of stiffness and strength. Out-of-plane stability can be examined panel by panel based on arching action. Inter-story drift does not appear to present a stability problem for the type of infill construction investigated. In-plane behavior may be adequately modeled with a nonlinear compression strut. A typical building is chosen for an illustrative application. The methodology and results of the seismic analysis are presented for this structure.

  7. The long-term evolution of intertidal mudflats in the northern Netherlands during the Holocene; natural and anthropogenic processes

    NASA Astrophysics Data System (ADS)

    Vos, Peter C.; van Kesteren, Wessel P.

    2000-09-01

    At present, intertidal mudflats form only a minor part of the tidal area of the Wadden Sea. During the Holocene, however, the extent of intertidal mudflats was much larger, as is indicated by abundant mud layers in the coastal sequence of the northern Netherlands. In this paper, a new model for the long-term coastal evolution of the northern Netherlands is presented and the (natural/anthropogenic) origin of the intertidal mudflats is discussed. The Fivel palaeo-tidal basin (NE Groningen) serves as foundation of this model, with time steps in reconstruction of more than 1000 years. Shorter duration events are ignored. The driving force in the coastal evolution during the early Holocene was the rapid sea-level rise. The Pleistocene valley systems of the Northern Netherlands drowned and became tidal basins. In their inner parts intertidal mudflats evolved. The coastline was situated about 10-15 km north of the present-day Wadden Sea islands and the tidal range along the coastline was smaller (microtidal, ca. 1.0 m, 7500 BP, as against mesotidal, 1.8-2.4 m, today). As energy conditions were moderate, the intertidal mudflats were partly covered by salt-marsh vegetation (`rooted mud layers'). Due to increasing tidal range, since about 6200 BP the vegetation cover disappeared from the intertidal mudflats (`non-rooted mud layers'). After 5000 BP, the marshes of the tidal basins started to prograde seaward, mainly as a result of the declining sea-level rise rate. On the other hand, the island coast retreated landward, so that the back barrier land-sea gradient became narrower and steeper. This steeping of the land-sea gradient together with the further increase in the tidal range caused an increase in energy in the tidal basins (local tidal currents and wave action). Because of this natural process, the intertidal sandflats expanded at the expense of the mudflats, and around 2000 BP the sandflats bordered the salt-marsh area. Mudflats were largely lost. Penetration of the

  8. Seismic stratigraphy as indicator of late Pleistocene and Holocene sea level changes on the NE Brazilian continental shelf

    NASA Astrophysics Data System (ADS)

    Aquino da Silva, André G.; Stattegger, Karl; Schwarzer, Klaus; Vital, Helenice

    2016-10-01

    The late Pleistocene Holocene stratigraphic architecture on the northeastern Brazilian continental shelf off the Parnaíba Delta has been explored by high-resolution seismic profiles. The seismic surveys reveal the widespread distribution of incised valleys of different size in offshore continuation of the present-day Parnaiba delta. According to morphology two channel types can be distinguished: U-shaped channels in the eastern part and V-shaped channels in the western part. The stratigraphic successions were grouped into four seismic units separated by different seismic boundaries. The characteristics of the seismic boundaries and internal reflectors of the seismic units were used to distinguish between marine and riverine deposits. The incised-valleys architectural elements were used to link sedimentation processes and variations in base level from late Pleistocene channel avulsion and channel infill in the lowermost course of the paleo-Parnaíba River to marine sediments of the present-day inner shelf. The change of the depositional environments in relation to deglacial sea-level rise is compared to incised valley infills of the Mekong River and Red River systems in Southeast Asia.

  9. Holocene loess deposition and soil formation as competing processes, Matanuska Valley, southern Alaska

    USGS Publications Warehouse

    Muhs, D.R.; McGeehin, J.P.; Beann, J.; Fisher, E.

    2004-01-01

    Although loess-paleosol sequences are among the most important records of Quaternary climate change and past dust deposition cycles, few modern examples of such sedimentation systems have been studied. Stratigraphic studies and 22 new accelerator mass spectrometry radiocarbon ages from the Matanuska Valley in southern Alaska show that loess deposition there began sometime after ???6500 14C yr B.P. and has continued to the present. The silts are produced through grinding by the Matanuska and Knik glaciers, deposited as outwash, entrained by strong winds, and redeposited as loess. Over a downwind distance of ???40 km, loess thickness, sand content, and sand-plus-coarse-silt content decrease, whereas fine-silt content increases. Loess deposition was episodic, as shown by the presence of paleosols, at distances >10 km from the outwash plain loess source. Stratigraphic complexity is at a maximum (i.e., the greatest number of loesses and paleosols) at intermediate (10-25 km) distances from the loess source. Surface soils increase in degree of development with distance downwind from the source, where sedimentation rates are lower. Proximal soils are Entisols or Inceptisols, whereas distal soils are Spodosols. Ratios of mobile CaO, K2O, and Fe2O3 to immobile TiO2 show decreases in surface horizons with distance from the source. Thus, as in China, where loess deposition also takes place today, eolian sedimentation and soil formation are competing processes. Study of loess and paleosols in southern Alaska shows that particle size can vary over short distances, loess deposition can be episodic over limited time intervals, and soils developed in stabilized loess can show considerable variability under the same vegetation. ?? 2004 University of Washington. All rights reserved.

  10. Effects of Holocene vegetation change on soils across the forest-grassland transition, northern Minnesota, and implications for erosion processes

    NASA Astrophysics Data System (ADS)

    Mason, Joseph; Kasmerchak, Chase; Keita, Hawa; Liang, Mengyu; Gruley, Kristine

    2016-04-01

    Boundaries between forest and grassland in the midlatitudes and their shifts in response to Holocene climatic change, provide opportunities to detect effects of life on landscapes. In northern Minnesota, USA, paleoecological research has documented that grassland and/or savanna expanded eastward in the dry early to middle Holocene. In the late Holocene, forest cover expanded westward at the expense of savanna and grassland. We studied soils at 20 sites spanning the forest-grassland transition. A dramatic change in soil morphology coincides approximately, though not exactly, with that transition as recorded in 1870s-1880s land surveys, suggesting that soils change rapidly in response to forest expansion (we are attempting to constrain the timescale of response through radiocarbon dating of deep soil organic matter in which stable C isotopes record past presence of grassland). The key changes from grassland to forest are loss of organic matter below a thin surface A horizon and greatly enhanced mobility and downward translocation of clay - particularly smectite - in forest soils. This results in upper soil horizons that have relatively low smectite content and low microaggregate stability (as detected through laser diffraction analysis of aggregate disintegration in laboratory experiments), especially below the thin A horizon. The best explanation for this change appears to involve differences in how OM is added to and accumulated in the soil under forest and grassland; soil acidity and base saturation change more gradually eastward along a gradient more likely to reflect climate than vegetation. Evidence of bioturbation (especially gopher burrowing) is much more common at former grassland sites. In addition to mixing OM downward in the soil, burrowing moves detrital carbonates upward, probably enhancing OM accumulation and aggregate stability. Research on geomorphic response to Holocene climatic change in the Midwestern US has often emphasized higher potential

  11. View from intersection. Ninestory reinforced concrete building infilled with brick. ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    View from intersection. Nine-story reinforced concrete building infilled with brick. The street facades on beaubien and east grand are faced with stone accents and elaborate brick work. Brick pilasters run the entire height of the building. Steel tiebacks are apparent running up the height of the building on the east side. The large tower appears at the northeast and southeast corners - Detroit Storage Company, 2937 East Grand Boulevard, Detroit, MI

  12. Lacunae infills for in situ treatment of historic glazed tiles

    NASA Astrophysics Data System (ADS)

    Mendes, Marta T.; Esteves, Lurdes; Ferreira, Teresa A.; Candeias, António; Tennent, Norman H.; Rodrigues, José Delgado; Pereira, Sílvia R. M.

    2016-05-01

    Knowledge of current conservation materials and methods together with those adopted in the past is essential to aid research and improve or develop better conservation options. The infill and painting of tile lacunae are subjected to special requirements mainly when used in outdoor settings. A selection of the most commonly used materials was undertaken and performed based on inquiries to practitioners working in the field. The infill pastes comprised organic (epoxy, polyester), inorganic (slaked lime, hydraulic lime and zinc hydroxychloride) and mixed organic-inorganic (slaked lime mixed with a vinylic resin) binders. The selected aggregates were those most commonly used or those already present in the commercially formulated products. The infill pastes were characterised by SEM, MIP, open porosity, water absorption by capillarity, water vapour permeability, thermal and hydric expansibilities and adhesion to the ceramic body. Their performance was assessed after curing, artificial ageing (salt ageing and UV-Temp-RH cycles) and natural ageing. The results were interpreted in terms of their significance as indicators of effectiveness, compatibility and durability.

  13. Robust, functional nanocrystal solids by infilling with atomic layer deposition

    SciTech Connect

    Liu, Yao; Gibbs, Markelle; Perkins, Craig L.; Tolentino, Jason; Zarghami, Mohammad H.; Bustamante, Jr., Jorge; Law, Matt

    2011-12-14

    Thin films of colloidal semiconductor nanocrystals (NCs) are inherently metatstable materials prone to oxidative and photothermal degradation driven by their large surface-to-volume ratios and high surface energies. The fabrication of practical electronic devices based on NC solids hinges on preventing oxidation, surface diffusion, ripening, sintering, and other unwanted physicochemical changes that can plague these materials. Here we use low-temperature atomic layer deposition (ALD) to infill conductive PbSe NC solids with metal oxides to produce inorganic nanocomposites in which the NCs are locked in place and protected against oxidative and photothermal damage. Infilling NC field-effect transistors and solar cells with amorphous alumina yields devices that operate with enhanced and stable performance for at least months in air. Furthermore, ALD infilling with ZnO lowers the height of the inter-NC tunnel barrier for electron transport, yielding PbSe NC films with electron mobilities of 1 cm² V-1 s-1. Our ALD technique is a versatile means to fabricate robust NC solids for optoelectronic devices.

  14. Holocene alluvium around Lefkosia (Nicosia), Cyprus: An archive of land-use, tectonic processes, and climate change

    USGS Publications Warehouse

    Newell, W.L.; Stone, B.; Harrison, R.; ,

    2004-01-01

    Holocene alluvium of the Pedhicos River around Lefkosia (Nicosia), Cyprus, was studied. Alluvial stratigraphy was found to present serial flood deposits underlying river terraces and an extensive alluvial fan. It was found that the stratigraphy and geomorphology of the alluvium can be interpreted to distinguish not only the effects of climate change, but also land-use change, and the impact of particular engineering works. It was suggested that details of the physical properties of the flood deposit sequences and paleosols can contribute to modeling various geophysical and engineering properties and in predicting response to vertical acceleration during earthquakes.

  15. Evaluation and analysis of the performance of masonary infills during the Northridge earthquake

    SciTech Connect

    Bennett, R.M.; Fischer, W.L.; Flanagan, R.D.; Tenbus, M.A.

    1996-02-01

    Observations were made of the behavior of masonry infills in structural frames during the Northridge earthquake, and an analytical technique was developed for analyzing infilled frame structures. Infills near the epicenter suffered significant damage, but in several cases contributed to the seismic resistance and life safety performance. Older infill buildings in downtown Los Angeles experienced intensity of shaking similar to that expected in central/eastern United States earthquakes. The infills experienced some cracking, but otherwise complemented the lateral resistance of the weak building frames. This suggests infill frame buildings in moderate seismic zones may provide at least life safety functions without the need for expensive retrofit. A developed analytical technique was used to analyze two buildings for which the observed behavior and records from the Northridge earthquake were available. The analytical technique was based on using a piecewise linear equivalent strut for the infill. Parameters for the strut were obtained by examining the results of a wide variety of experimental infill tests. The strut method is easy to incorporate in standard linear analyses, and converges quite rapidly. The strut method was applied to two structures that had records from the Northridge earthquake. Very favorable comparisons between the analytical method and observed response were obtained. Recommendations were made concerning evaluation of the vulnerability of infills to earthquakes, and the construction of infills.

  16. Efficient infill sampling for unconstrained robust optimization problems

    NASA Astrophysics Data System (ADS)

    Rehman, Samee Ur; Langelaar, Matthijs

    2016-08-01

    A novel infill sampling criterion is proposed for efficient estimation of the global robust optimum of expensive computer simulation based problems. The algorithm is especially geared towards addressing problems that are affected by uncertainties in design variables and problem parameters. The method is based on constructing metamodels using Kriging and adaptively sampling the response surface via a principle of expected improvement adapted for robust optimization. Several numerical examples and an engineering case study are used to demonstrate the ability of the algorithm to estimate the global robust optimum using a limited number of expensive function evaluations.

  17. Infilling and interpolation of precipitation at different temporal scales in South Africa

    NASA Astrophysics Data System (ADS)

    Pegram, Geoff; Bárdossy, András

    2014-05-01

    Hydrological observations are often incomplete - equipment malfunction, transmission errors and other technical problems lead to unwanted gaps in observation time series. Furthermore, due to financial and organizational problems, many observation networks are in continuous decline. As an ameliorating stratagem, short time gaps can be filled using information from other locations or other variables, such as circulation patterns. The statistics of abandoned stations provide useful information for the process of extending records. In this contribution the authors present a comparison of different methods for infilling gaps using: - nearest neighbours - simple and multiple linear regression - black box methods (fuzzy rules and neural nets) - Expectation Maximization - Copula based estimation The methods are used at different time scales for infilling precipitation from daily through pentads and months to years. The copula based estimation provides not only an estimator for the expected value, but also a probability distribution for each of the missing values. Thus the method can be used for conditional simulation of realizations. Observed precipitation data from the Cape region in South Africa are used to illustrate the intercomparison of the methodologies. An outlook suggesting how to use these data for spatial interpolation concludes the presentation.

  18. Global Change in the Holocene

    NASA Astrophysics Data System (ADS)

    Alverson, Keith

    2004-05-01

    Many people, even perhaps the occasional Eos reader, associate the term ``global change'' with warming caused by mankind's recent addiction to fossil fuels. Some may also be well aware of enormous global changes in the distant past uninfluenced by humans; for example, Pleistocene ice ages. But was there any ``global change'' between the end of the last ice age and the onset of industrialization? The answer to this question is addressed early-in the title, even-in the new book Global Change in the Holocene. I don't suggest anyone stop reading after the title, though; the rest of the book is both highly informative and a real pleasure to read. The opening chapter tells us that the Holocene is certainly not, as sometimes charged, a ``bland, pastoral coda to the contrasted movements of a stirring Pleistocene symphony.'' Rather, it is a ``period of continuous change.'' Melodious language aside, the combination of sustained and high-amplitude climatic variability and a wealth of well-preserved, precisely datable paleoclimate archives make the Holocene unique. Only by studying the Holocene can we hope to unravel the low-frequency workings of the Earth system and the degree to which humans have changed our world. This book sets out to teach the reader how to obtain the relevant data and how to use it to do much more than showing static analogues of possible future climate states. It challenges researchers to discern in their data the effects of the dynamic processes underlying coupled variability in the Earth's climate and ecosystems. These processes continue to act today, and it is through providing an understanding of these system dynamics in the Holocene that paleo-environmental studies can make the greatest contribution to future-oriented concerns.

  19. Strontium Distribution Coefficients of Basalt and Sediment Infill Samples from the Idaho National Engineering and Environmental Laboratory, Idaho

    SciTech Connect

    M. N. Pace; R. C. Bartholomay; J. J. Rosentreter

    1999-07-01

    The U.S. Geological Survey and Idaho State University, in cooperation with the U.S. Department of Energy, are conducting a study to determine and evaluate strontium distribution coefficients (Kds) of subsurface materials at the Idaho National Engineering and Environmental Laboratory (INEEL). The purpose of this study is to aid in assessing the variability of strontium Kds at the INEEL as part of an ongoing investigation of chemical transport of strontium-90 in the Snake River Plain aquifer. Batch experimental techniques were used to determine Kds of six basalt core samples, five samples of sediment infill of vesicles and fractures, and six standard material samples. Analyses of data from these experiments indicate that the Kds of the sediment infill samples are significantly larger than those of the basalt samples. Quantification of such information is essential of furthering the understanding of transport processes of strontium-90 in the Snake River Plain aquifer and in similar environments.

  20. Tender mooring for infill drilling operations: A case study

    SciTech Connect

    1997-04-01

    The Tapis-pump platform is a four-leg jacket structure located 230 ft south of the Tapis-D platform and connected to it by a walkway bridge. All crude production (360,000 B/D) from Esso Production Malaysia Inc. (EPMI) wells in the South China Sea offshore Terengganu is piped to the Tapais-pump platform for pumping to an onshore terminal. The continuous operation of this platform is essential. The Tapis-D platform is a manned production platform that also acts as a central communication center and emergency response command center for EPMI`s offshore operations in the South China Sea. A total of nine wells is planned for an infill drilling program at the Tapis-D platform. The rig selected for this infill drilling program is a self-erecting tender-assisted rig that uses an eight-point wire rope mooring system. Eleven pipelines are connected to the Tapis-pump/Tapis-D platform complex. All the pipelines were laid on the seafloor without any special external protection and were not tied down or anchored. The paper describes the planning of the mooring system for drilling.

  1. Influence of Reservoir Infill on Coastal Deep Water Hypoxia.

    PubMed

    Linker, Lewis C; Batiuk, Richard A; Cerco, Carl F; Shenk, Gary W; Tian, Richard; Wang, Ping; Yactayo, Guido

    2016-05-01

    Ecological restoration of the Chesapeake through the Chesapeake Bay total maximum daily load (TMDL) requires the reduction of nitrogen, phosphorus, and sediment loads in the Chesapeake watershed because of the tidal water quality impairments and damage to living resources they cause. Within the Chesapeake watershed, the Conowingo Reservoir has been filling in with sediment for almost a century and is now in a state of near-full capacity called . The development of the Chesapeake TMDL in 2010 was with the assumption that the Conowingo Reservoir was still effectively trapping sediment and nutrients. This is now known not to be the case. In a TMDL, pollutant loads beyond the TMDL allocation, which are brought about by growth or other conditions, must be offset. Using the analysis tools of the Chesapeake TMDL for assessing the degree of water quality standard attainment, the estimated nutrient and sediment loads from a simulated dynamic equilibrium infill condition of the Conowingo Reservoir were determined. The influence on Chesapeake water quality by a large storm and scour event of January 1996 on the Susquehanna River was estimated, and the same storm and scour events were also evaluated in the more critical living resource period of June. An analysis was also made on the estimated influence of more moderate high flow events. The infill of the Conowingo reservoir had estimated impairments of water quality, primarily on deep-water and deep-channel dissolved oxygen, because of increased discharge and transport of organic and particulate inorganic nutrients from the Conowingo Reservoir. PMID:27136155

  2. Influence of Reservoir Infill on Coastal Deep Water Hypoxia.

    PubMed

    Linker, Lewis C; Batiuk, Richard A; Cerco, Carl F; Shenk, Gary W; Tian, Richard; Wang, Ping; Yactayo, Guido

    2016-05-01

    Ecological restoration of the Chesapeake through the Chesapeake Bay total maximum daily load (TMDL) requires the reduction of nitrogen, phosphorus, and sediment loads in the Chesapeake watershed because of the tidal water quality impairments and damage to living resources they cause. Within the Chesapeake watershed, the Conowingo Reservoir has been filling in with sediment for almost a century and is now in a state of near-full capacity called . The development of the Chesapeake TMDL in 2010 was with the assumption that the Conowingo Reservoir was still effectively trapping sediment and nutrients. This is now known not to be the case. In a TMDL, pollutant loads beyond the TMDL allocation, which are brought about by growth or other conditions, must be offset. Using the analysis tools of the Chesapeake TMDL for assessing the degree of water quality standard attainment, the estimated nutrient and sediment loads from a simulated dynamic equilibrium infill condition of the Conowingo Reservoir were determined. The influence on Chesapeake water quality by a large storm and scour event of January 1996 on the Susquehanna River was estimated, and the same storm and scour events were also evaluated in the more critical living resource period of June. An analysis was also made on the estimated influence of more moderate high flow events. The infill of the Conowingo reservoir had estimated impairments of water quality, primarily on deep-water and deep-channel dissolved oxygen, because of increased discharge and transport of organic and particulate inorganic nutrients from the Conowingo Reservoir.

  3. Glacial to Holocene climate changes in the SE Pacific. The Raraku Lake sedimentary record (Easter Island, 27°S)

    NASA Astrophysics Data System (ADS)

    Sáez, Alberto; Valero-Garcés, Blas L.; Giralt, Santiago; Moreno, Ana; Bao, Roberto; Pueyo, Juan J.; Hernández, Armand; Casas, David

    2009-12-01

    Easter Island (SE Pacific, 27°S) provides a unique opportunity to reconstruct past climate changes in the South Pacific region based on terrestrial archives. Although the general climate evolution of the south Pacific since the Last Glacial Maximum (LGM) is coherent with terrestrial records in southern South America and Polynesia, the details of the dynamics of the shifting Westerlies, the South Pacific Convergence Zone and the South Pacific Anticyclone during the glacial-interglacial transition and the Holocene, and the large scale controls on precipitation in tropical and extratropical regions remain elusive. Here we present a high-resolution reconstruction of lake dynamics, watershed processes and paleohydrology for the last 34 000 cal yrs BP based on a sedimentological and geochemical multiproxy study of 8 cores from the Raraku Lake sediments constrained by 22 AMS radiocarbon dates. This multicore strategy has reconstructed the sedimentary architecture of the lake infilling and provided a stratigraphic framework to integrate and correlate previous core and vegetation studies conducted in the lake. High lake levels and clastic input dominated sedimentation in Raraku Lake between 34 and 28 cal kyr BP. Sedimentological and geochemical evidences support previously reported pollen data showing a relatively open forest and a cold and relatively humid climate during the Glacial period. Between 28 and 17.3 cal kyr BP, including the LGM period, colder conditions contributed to a reduction of the tree coverage in the island. The coherent climate patterns in subtropical and mid latitudes of Chile and Eastern Island for the LGM (more humid conditions) suggest stronger influence of the Antarctic circumpolar current and an enhancement of the Westerlies. The end of Glacial Period occurred at 17.3 cal kyr BP and was characterized by a sharp decrease in lake level conducive to the development of major flood events and erosion of littoral sediments. Deglaciation (Termination

  4. Reconstructing climate processes driving variability in precipitation sources from mid to late Holocene speleothem δ18O records from the Southwest US

    NASA Astrophysics Data System (ADS)

    Wong, C. I.; Nusbaumer, J. M.; Banner, J.

    2015-12-01

    Independent co-variation of speleothem δ18O values and other moisture-sensitive speleothem proxies (e.g., growth rate, trace element concentrations) in recently published Holocene stalagmite records from Texas and New Mexico suggest a decoupling between precipitation amounts and precipitation sources over the southwest US. There is, however, limited understanding of the relation between precipitation sources and precipitation amounts and the climate processes governing variability in the region's precipitation sources. To address this, we use source water tags to track precipitation derived from Pacific and Atlantic Oceans during a simulation of modern (1975-2013) climate. We find distinct patterns in the spatial distribution of the fraction of Pacific-derived winter precipitation are associated with unique atmospheric states. High pressure ridging reflected by 500 hPa geopotential heights result in weaker zonal winds and stronger northerly winds over the western US. Under these conditions, Pacific-derived moisture propagates further to the east, and Atlantic-derived moisture is suppressed over southern US. Conversely, 500 hPa geopotential heights that are latitudinally streamline result in strong zonal winds across the entire US. Under these conditions, the fraction of West Pacific-derived precipitation is limited to higher latitudes, and the fraction of far East Pacific- and Atlantic-derived precipitation is enhanced across the Southwest and Southern US, respectively. Further analysis of this data set will assess the teleconnections that link the distinct atmospheric conditions over the US with the state of the ocean and atmosphere over the Pacific and Atlantic Oceans. The results will be applied to reconstructing variability in the climate dynamics governing moisture transport to the southwest US during the mid to late Holocene as reflected by speleothem δ18O records in the region.

  5. Horizontal spacing, depletion, and infill potential in the Austin Chalk

    SciTech Connect

    Kyte, D.G.; Meehan, D.N.

    1996-12-31

    There have been more than 4500 laterals drilled in the Austin Chalk. This paper looks at estimated ultimate recoveries (EUR) on a barrels/acre basis for these Austin Chalk wells. Baffels/acre recoveries were computed by estimating ultimate per-well recoveries, drilled density and the impact of vertical production. The data were then analyzed for depletion and infill potential. Certain areas were selected for further study using an artificial neural network. The network was built and used to study the effects of parameters such as lateral length, first production date, structure of the Austin Chalk, etc. on these recoverable barrel/acre numbers. The methodology and regional results of the study are reviewed with detailed analyses shown in selected areas.

  6. Holocene to contemporary source-to-sink fluxes in a valley-fjord system in western Norway: Erdalen and Bødalen site project (SedyMONT - IP Norway)

    NASA Astrophysics Data System (ADS)

    Beylich, A. A.; Laute, K.; Liermann, S.

    2012-04-01

    estimate bedload transport rates in both valleys. The volume and composition of lake sediments are studied using echo-sounder, georadar and different coring techniques. Investigations on volumes and architecture of storage elements (talus cones, valley infills, deltas) using different geophysical methods like georadar and seismic refraction surveys are carried out to improve the quantitative knowledge on Holocene process rates and sediment budgets. Detailled geomorphological mapping is performed and interpreted in combination with digital elevation models and data. The U-shaped valley morphometry is the main control of Holocene denudative processes in both Erdalen and Bødalen. In Erdalen the more clearly defined stepped longitudinal valley profile results in a larger storage (larger volume of Holocene valley infill) and an altogether lower level of slope-channel coupling as compared to Bødalen. Different periods within the Holocene with varying intensity of denudative processes can be identified. Under the present-day environmental conditions mechanical denudation dominates over chemical denudation. Process rates are altogether moderate to low, and the valley systems are altogether supply-limited. The process and denudation rates from Erdalen and Bødalen are compared with rates from the other SedyMONT test sites (Alps) (http://www.sedymont.eu), and with denudative process rates in other cold environment catchment systems worldwide through the SEDIBUD Programme (http://www.geomorph.org/wg/wgsb.html).

  7. Infilling stratigraphy of macrotidal tide-dominated estuaries. Controlling mechanisms: Sea-level fluctuations, bedrock morphology, sediment supply and climate changes (The examples of the Seine estuary and the Mont-Saint-Michel Bay, English Channel, NW France)

    NASA Astrophysics Data System (ADS)

    Tessier, Bernadette; Billeaud, Isabelle; Sorrel, Philippe; Delsinne, Nicolas; Lesueur, Patrick

    2012-11-01

    This article presents a synthesis of recent works performed on two macrotidal tide-dominated estuaries located along the southern coast of the English Channel, the Seine estuary and the Mont-Saint-Michel Bay (NW France). On the basis of very high resolution seismic data combined with sediment cores and AMS dating, these works allow reconstructing the Holocene infill of such singular estuaries, yet rarely documented in the literature. Rate in sea-level rise, bedrock morphology, sediment supply are the main controlling factors of the general infill pattern. Both infills are composed of two units, the transgressive systems tract (TST) and highstand systems tract (HST). The maximum flooding surface (MFS) is dated around 6500 cal BP when the Holocene sea-level rise slowed down, and corresponds to the main architectural change. The TST is poorly preserved compared with the HST that constitutes the main depositional unit, making this incised valley fill deviating from the classical models. The HST is composed above the axis of the incised valley of a highly wandering estuarine channel belt characterized by deep tidal reworking throughout its building. On the margin of this high-energy estuarine system, the HST is made of wave-dominated barriers, tidal flats and offshore tidal banks.. They constitute dominantly aggradational systems, the aggradation rate of which is in accordance with the rate of sea-level rise from 6500 cal BP onwards. Consequently, the impacts of the rapid climate changesthat characterized mid- to late Holocene times can be preserved in these marginal successions. Various sedimentary and geometrical signatures indicate that periodic enhanced storminess episodes, probably related to the Bond Cold Events (~ 1500 years periodicity), are responsible for the most drastic environmental changes in these macrotidal tide-dominated settings. The role of long term tidal cycles as well as the impact of human activities are also considered.

  8. A Holocene history of dune-mediated landscape change along the southeastern shore of Lake Superior

    USGS Publications Warehouse

    Loope, Walter L.; Fisher, Timothy G.; Jol, Harry M.; Anderton, John B.; Blewett, William L.

    2004-01-01

    Causal links that connect Holocene high stands of Lake Superior with dune building, stream damming and diversion and reservoir impoundment and infilling are inferred from a multidisciplinary investigation of a small watershed along the SE shore of Lake Superior. Radiocarbon ages of wood fragments from in-place stumps and soil O horizons, recovered from the bottom of 300-ha Grand Sable Lake, suggest that the near-shore inland lake was formed during multiple episodes of late Holocene dune damming of ancestral Sable Creek. Forest drownings at ~3000, 1530, and 300 cal. years BP are highly correlated with local soil burial events that occurred during high stands of Lake Superior. During these and earlier events, Sable Creek was diverted onto eastward-graded late Pleistocene meltwater terraces. Ground penetrating radar (GPR) reveals the early Holocene valley of Sable Creek (now filled) and its constituent sedimentary structures. Near-planar paleosols, identified with GPR, suggest two repeating modes of landscape evolution mediated by levels of Lake Superior. High lake stands drove stream damming, reservoir impoundment, and eolian infilling of impoundments. Falling Lake Superior levels brought decreased sand supply to dune dams and lowered stream base level. These latter factors promoted stream piracy, breaching of dune dams, and aerial exposure and forestation of infilled lakebeds. The bathymetry of Grand Sable Lake suggests that its shoreline configuration and depth varied in response to events of dune damming and subsequent dam breaching. The interrelated late Holocene events apparent in this study area suggest that variations in lake level have imposed complex hydrologic and geomorphic signatures on upper Great Lakes coasts.

  9. Holocene to contemporary fluvial sediment fluxes and budgets of two glacier-fed valley-fjord systems in the Nordfjord area, western Norway

    NASA Astrophysics Data System (ADS)

    Liermann, S.; Beylich, A. A.; Hansen, L.

    2012-04-01

    This PhD project is part of the NFR funded Norwegian Individual Project within the ESF SedyMONT (Timescales of sediment dynamics, climate and topographic change in mountain landscapes) TOPO-EUROPE program. Two neighboring glacier-fed valley-fjord systems (Erdalen & Bødalen) with a different topographic inheritance from Pleistocene glaciations are compared. It is of special interest how the different valley morphometries have influenced Holocene to contemporary sediment fluxes and budgets. To understand the spatial and temporal sediment flux variability during the Holocene the main focus lays on i) quantification and analysis of storage element volumes for estimation of Holocene sedimentation rates and sediment yields, ii) analysis of the spatial and temporal sediment flux variability, iii) analysis of the linkages between sediment transfer and storage, iv) analysis of controlling factors for postglacial, sub-recent and contemporary sediment fluxes and v) construction of Holocene to contemporary sediment budgets for Erdalen and Bødalen. The analysis of sedimentary fluxes and budgets as well as their controls at different timescales (Holocene to contemporary) is a basis for the assessment of complex landscape responses of Holocene to recent changes in temperature, precipitation and runoff. For constructing sediment budgets at a small-catchment scale (50-100 km2) it is necessary to integrate the temporal and spatial variations of supply of material from sediment sources, sediment transport and storage and to identify, how far the different system components are coupled to each other. Both valleys are instrumented with a year-round monitoring system (runoff, suspended and solute transport) for analyzing fluvial sediment fluxes. The results enable to link sediment transport and runoff (events) and the spatial and temporal variability of sediment transport processes. In addition, glacier sediment supply and its spatial variability in Erdalen and Bødalen is monitored

  10. Postglacial sedimentary infill of the Bricial peatland (Cantabrian Mountains, Spain)

    NASA Astrophysics Data System (ADS)

    Correia, Antonio; Ruiz-Fernández, Jesús; Oliva, Marc; Fernández, Antonio; García-Hernández, Cristina; Gallinar, David

    2016-04-01

    Bricial is a peatland located in a glaciokarst depression of the Western Massif of the Picos de Europa (NW Spain). The depression is 425 m long and 245 m wide, and it is surrounded by moraines built during the stage of glacial expansion after the maximum advance within the Last Glaciation. In contrast to what happens in other karstic depressions existing in this massif (e.g. Comeya), the thickness and sedimentary infill of this depression is still unknown. With the purpose of better knowing the depression's structure, two electrical resistivity tomographies (ERT)s with different lengths across the Bricial depression were conducted along perpendicular directions; the shortest ERT was done in a NNE-SSW direction with an electrode spacing of 2 m and a total length of 78 m; the longest ERT was done in a WNW-ESE direction with a 5 m electrode spacing and a total length of 195 m. Both ERTs used 40 electrodes in a Wenner configuration. The two ERTs were done in such way that they intersected near an 8 m deep borehole drilled in the area in 2006. A two-dimensional electrical inversion software was used for inverting the apparent electrical resistivity data obtained during the field work into two-dimensional models of electrical resistivity of the ground. The models are a representation of the distribution of the electrical resistivity of the ground to depths of about 14 m along the shortest ERT and 35 m along the longest. In both geoelectrical models the electrical structure is approximately horizontal at the surface (i.e., between 3 to 5 m depth) and is more complex as depth increases. Low resistivity values prevail in most part of the profiles, which is consistent with the sedimentary sequence collected in the area. The 8 m long sedimentary sequence collected from Bricial consists of homogeneous organic-rich sediments. The base of the sequence was dated at 11,150 ± 900 cal yr BP. Taking into account the sedimentation rates and the data inferred from the electrical

  11. RC Infilled Frame-RC Plane Frame Interactions for Seismic Resistance

    NASA Astrophysics Data System (ADS)

    Arulselvan, Suyamburaja; Subramanian, K.; Perumal Pillai, E. B.; Santhakumar, A. R.

    Experimental investigation was planned and conducted to study the influence of brick masonry infill in a reinforced cement concrete frame. The analytical methods available needs validation by comparison with experimental results and more accurate methods of analysis like finite element analysis has to be used for the above purpose. In this study, RC frame with middle bay brick infilled representing a five-stories, three bay building in quarter-scale has been taken for experimental investigation and the available methods of theoretical analysis and finite element analysis using ANSYS software for the frames have been carried out. Until the cracks developed in infills, the contribution of the infill to both lateral stiffness and strength was very significant. The change in lateral stiffness, strength, ductility and natural period of the framed structure due to the presence of infills change the behaviour of the building under seismic action. The object of this study was to investigate the behaviour of such infilled frames under seismic loads. For this purpose, five stories, three bay frames with central portion infilled with brick were tested under static cyclic loading simulating seismic action. Analytical works was done to understand the stiffness, strength and behaviour of these types of frames.

  12. Holocene Lake Records on Kamchatka

    NASA Astrophysics Data System (ADS)

    Diekmann, Bernhard; Biskaborn, Boris; Chapligin, Bernhard; Dirksen, Oleg; Dirksen, Veronika; Hoff, Ulrike; Meyer, Hanno; Nazarova, Larisa

    2014-05-01

    The availibility of terrestrial records of Holocene palaeoenvironmental changes in eastern Siberia still is quite limited, compared to other regions on the northern hemisphere. In particular, the Kamchatka Peninsula as an important climate-sensitive region is very underrepresented. Situated at the border of northeastern Eurasia, the maritime-influenced terrestrial setting of Kamchatka offers the potential to pinpoint connections of environmental changes between the periglacial and highly continental landmasses of eastern Siberia and the sub-Arctic Pacific Ocean and Sea of Okhotsk. The study region lies at the eastern end-loop of the global thermohaline ocean conveyor belt and is strongly affected by atmospheric teleconnections. Volcanic, tectonic, and glacial processes overprint palaeoenvironmental changes in addition to primary climate forcing. In order to widen our understanding of plaeoclimate dynamics on Kamchatka, sediment cores from different lake systems and peat sections were recovered and analysed by a multi-proxy approach, using sedimentological and geochemical data as well as fossil bioindicators, such as diatoms, pollen, and chironomids. Chronostratigraphy of the studied records was achieved through radiocarbon dating and tephrostratigraphy. Sediment cores with complete Holocene sedimentary sequences were retrieved from Lake Sokoch, an up to six metre deep lake of proglacial origin, situated at the treeline in the Ganalsky Ridge of southern central Kamchatka (53°15,13'N, 157°45.49' E, 495 m a.s.l.). Lacustrine sediment records of mid- to late Holocene age were also recovered from the up to 30 m deep Two-Yurts Lake, which occupies a former proglacial basin at the eastern flank of the Central Kamchatka Mountain Chain, the Sredinny Ridge (56°49.6'N, 160°06.9'E, 275 m a.s.l.). In addition to sediment coring in the open and deep Two-Yurts Lake, sediment records were also recovered from peat sections and small isolated forest lakes to compare

  13. Holocene, subrecent and contemporary source-to-sink fluxes in a valley-fjord system, Erdalen and Bødalen site project (SedyMONT - Norway)

    NASA Astrophysics Data System (ADS)

    Beylich, Achim A.

    2010-05-01

    infills, deltas) using different geophysical methods like georadar and seismic refraction surveys are carried out to improve the quantitative knowledge on Holocene process rates. Detailed geomorphological mapping is performed and interpreted in combination with digital elevation models and data. The process and denudation rates in Erdalen and Bødalen are compared with process and denudation rates in the other SedyMONT test sites (Alps) (http://www.sedymont.eu) and with other cold environment catchments worldwide through the global SEDIBUD Programme (http://www.geomorph.org/wg/wgsb.html).

  14. Documentation of Computer Program INFIL3.0 - A Distributed-Parameter Watershed Model to Estimate Net Infiltration Below the Root Zone

    USGS Publications Warehouse

    ,

    2008-01-01

    This report documents the computer program INFIL3.0, which is a grid-based, distributed-parameter, deterministic water-balance watershed model that calculates the temporal and spatial distribution of daily net infiltration of water across the lower boundary of the root zone. The bottom of the root zone is the estimated maximum depth below ground surface affected by evapotranspiration. In many field applications, net infiltration below the bottom of the root zone can be assumed to equal net recharge to an underlying water-table aquifer. The daily water balance simulated by INFIL3.0 includes precipitation as either rain or snow; snowfall accumulation, sublimation, and snowmelt; infiltration into the root zone; evapotranspiration from the root zone; drainage and water-content redistribution within the root-zone profile; surface-water runoff from, and run-on to, adjacent grid cells; and net infiltration across the bottom of the root zone. The water-balance model uses daily climate records of precipitation and air temperature and a spatially distributed representation of drainage-basin characteristics defined by topography, geology, soils, and vegetation to simulate daily net infiltration at all locations, including stream channels with intermittent streamflow in response to runoff from rain and snowmelt. The model does not simulate streamflow originating as ground-water discharge. Drainage-basin characteristics are represented in the model by a set of spatially distributed input variables uniquely assigned to each grid cell of a model grid. The report provides a description of the conceptual model of net infiltration on which the INFIL3.0 computer code is based and a detailed discussion of the methods by which INFIL3.0 simulates the net-infiltration process. The report also includes instructions for preparing input files necessary for an INFIL3.0 simulation, a description of the output files that are created as part of an INFIL3.0 simulation, and a sample problem that

  15. Application of Integrated Reservoir management and Reservoir Characterization to Optimize Infill Drilling

    SciTech Connect

    B. Pregger; D. Davies; D. Moore; G. Freeman; J. Callard; J.W. Nevans; L. Doublet; R. Vessell; T. Blasingame

    1997-08-31

    Infill drilling if wells on a uniform spacing without regard to reservoir performance and characterization foes not optimize reservoir development because it fails to account for the complex nature of reservoir heterogeneities present in many low permeability reservoirs, and carbonate reservoirs in particular. New and emerging technologies, such as geostatistical modeling, rigorous decline curve analysis, reservoir rock typing, and special core analysis can be used to develop a 3-D simulation model for prediction of infill locations.

  16. Application of Integrated Reservoir Management and Reservoir Characterization to Optimize Infill Drilling

    SciTech Connect

    1998-03-12

    Infill drilling if wells on a uniform spacing without regard to reservoir performance and characterization foes not optimize reservoir development because it fails to account for the complex nature of reservoir heterogeneities present in many low permeability reservoirs, and carbonate reservoirs in particular. New and emerging technologies, such as geostatistical modeling, rigorous decline curve analysis, reservoir rock typing, and special core analysis can be used to develop a 3-D simulation model for prediction of infill locations.

  17. Application of Integrated Reservoir Management and Reservoir Characterization to Optimize Infill Drilling

    SciTech Connect

    1998-01-01

    Infill drilling if wells on a uniform spacing without regard to reservoir performance and characterization foes not optimize reservoir development because it fails to account for the complex nature of reservoir heterogeneities present in many low permeability reservoirs, and carbonate reservoirs in particular. New and emerging technologies, such as geostatistical modeling, rigorous decline curve analysis, reservoir rock typing, and special core analysis can be used to develop a 3-D simulation model for prediction of infill locations.

  18. OPTIMIZATION OF INFILL DRILLING IN NATURALLY-FRACTURED TIGHT-GAS RESERVOIRS

    SciTech Connect

    Lawrence W. Teufel; Her-Yuan Chen; Thomas W. Engler; Bruce Hart

    2004-05-01

    A major goal of industry and the U.S. Department of Energy (DOE) fossil energy program is to increase gas reserves in tight-gas reservoirs. Infill drilling and hydraulic fracture stimulation in these reservoirs are important reservoir management strategies to increase production and reserves. Phase II of this DOE/cooperative industry project focused on optimization of infill drilling and evaluation of hydraulic fracturing in naturally-fractured tight-gas reservoirs. The cooperative project involved multidisciplinary reservoir characterization and simulation studies to determine infill well potential in the Mesaverde and Dakota sandstone formations at selected areas in the San Juan Basin of northwestern New Mexico. This work used the methodology and approach developed in Phase I. Integrated reservoir description and hydraulic fracture treatment analyses were also conducted in the Pecos Slope Abo tight-gas reservoir in southeastern New Mexico and the Lewis Shale in the San Juan Basin. This study has demonstrated a methodology to (1) describe reservoir heterogeneities and natural fracture systems, (2) determine reservoir permeability and permeability anisotropy, (3) define the elliptical drainage area and recoverable gas for existing wells, (4) determine the optimal location and number of new in-fill wells to maximize economic recovery, (5) forecast the increase in total cumulative gas production from infill drilling, and (6) evaluate hydraulic fracture simulation treatments and their impact on well drainage area and infill well potential. Industry partners during the course of this five-year project included BP, Burlington Resources, ConocoPhillips, and Williams.

  19. Spatial and temporal variability in sedimentation rates associated with cutoff channel infill deposits: Ain River, France

    USGS Publications Warehouse

    Piegay, H.; Hupp, C.R.; Citterio, A.; Dufour, S.; Moulin, B.; Walling, D.E.

    2008-01-01

    Floodplain development is associated with lateral accretion along stable channel geometry. Along shifting rivers, the floodplain sedimentation is more complex because of changes in channel position but also cutoff channel presence, which exhibit specific overflow patterns. In this contribution, the spatial and temporal variability of sedimentation rates in cutoff channel infill deposits is related to channel changes of a shifting gravel bed river (Ain River, France). The sedimentation rates estimated from dendrogeomorphic analysis are compared between and within 14 cutoff channel infills. Detailed analyses along a single channel infill are performed to assess changes in the sedimentation rates through time by analyzing activity profiles of the fallout radionuclides 137Cs and unsupported 210Pb. Sedimentation rates are also compared within the channel infills with rates in other plots located in the adjacent floodplain. Sedimentation rates range between 0.65 and 2.4 cm a -1 over a period of 10 to 40 years. The data provide additional information on the role of distance from the bank, overbank flow frequency, and channel geometry in controlling the sedimentation rate. Channel infills, lower than adjacent floodplains, exhibit higher sedimentation rates and convey overbank sediment farther away within the floodplain. Additionally, channel degradation, aggradation, and bank erosion, which reduce or increase the distance between the main channel and the cutoff channel aquatic zone, affect local overbank flow magnitude and frequency and therefore sedimentation rates, thereby creating a complex mosaic of sedimentation zones within the floodplain and along the cutoff channel infills. Last, the dendrogeomorphic and 137Cs approaches are cross validated for estimating the sedimentation rate within a channel infill. Copyright 2008 by the American Geophysical Union.

  20. Project evaluates POSC specifications for infill drilling. [Petrochemical Open Software Corp

    SciTech Connect

    Zahniser, D.L. ); Merritt, R.W. ); Chan, C.K. )

    1994-05-16

    A project is under way to build data-loading tools and create an integrated oil and gas production data base using specifications developed during the last 3 years by the Petrotechnical Open Software Corp. (POSC). The Industry Pilot Project (IPP) Phase 1 is a collaborative effort between seven oil companies. The participating oil companies have provided a large set of data from a producing North American oil and gas field and money, hardware, and personnel. Many companies have already streamlined their infill drilling processes and receive significant incremental benefits. But current information technology can often be a stumbling block. Cross-disciplinary use of information is the key goal of these streamlining efforts, but much time is lost in finding, reformatting, accessing, and determining the quality of data. This project sets out to prove how POSC specifications can help reduce the cost and time for developing a field, improved the quality of the decision-making process, minimize the number of communication barriers and, most importantly, change technology from a hurdle to a seamless step. The project demonstrates that POSC specifications are an enabling technology that can dramatically improve the way oil companies and suppliers operate.

  1. Holocene fire dynamics in Fennoscandia

    NASA Astrophysics Data System (ADS)

    Clear, Jennifer; Seppa, Heikki; Kuosmanen, Niina; Molinari, Chiara; Lehsten, Veiko; Allen, Katherine; Bradshaw, Richard

    2015-04-01

    Prescribed burning is advocated in Fennoscandia to promote regeneration and to encourage biodiversity. This method of forest management is based on the perception that fire was much more frequent in the recent past and over a century of active fire suppression has created a boreal forest ecosystem almost free of natural fire. The absence of fire is thought to have contributed to the widespread dominance of Picea abies (Norway spruce) with the successive spruce dominated forest further reducing fire ignition potential. However, humans have altered the natural fire dynamics of Fennoscandia since the early- to mid-Holocene and disentangling the anthropogenic driven fire dynamics from the natural fire dynamics is challenging. Through palaeoecology and sedimentary charcoal deposits we are able to explore the Holocene spatial and temporal variability and changing drivers of fire and vegetation dynamics in Fennoscandia. At the local-scale, two forest hollow environments (<20km apart) were analysed for high resolution macroscopic charcoal and pollen analysis and their fire and vegetation history are compared to identify unique and mutual changes in disturbance history. Pollen derived quantitative reconstruction of vegetation at both the local- and regional-scale identifies local-scale disturbance dynamics and large-scale ecosystem response. Spatio-temporal heterogeneity and variability in biomass burning is explored throughout Fennoscandia and Denmark to identify the changing drives of fire dynamics throughout the Holocene. Palaeo-vegetation reconstructions are compared to process-based, climate driven dynamic vegetation model output to test the significance of fire frequency as a driver of vegetation composition and dynamics. Early-Holocene fire regimes in Fennoscandia are driven by natural climate variations and fuel availability. The establishment and spread of Norway spruce is driven by an increase in continentality of climate, but local natural and anthropogenic

  2. Holocene environmental change at the oasis of Tayma

    NASA Astrophysics Data System (ADS)

    Engel, Max; Brückner, Helmut; Wellbrock, Kai; Pint, Anna; Grottker, Matthias; Voss, Peter; Ginau, Andreas; Klasen, Nicole; Frenzel, Peter

    2013-04-01

    The oasis of Tayma in northwestern Saudi Arabia has a rich cultural heritage comprising a large number of historic buildings and artefacts from the late Neolithic onwards. Extensive groundwater resources and the location at a branch of the Incense Road connecting south Arabia and the eastern Mediterranean determined the site's importance in Antiquity. This paper reports about Holocene environmental change at Tayma setting the frame for the interpretation of the archaeological record. Humid conditions during the early Holocene are inferred for the Arabian Peninsula (AP) based on the investigation of sabkhas, palaeo-lakes, sand dunes, wadis, speleothems and marine sediments. Most of these climate archives are located in the southern and southeastern part of the AP, where a northward shift of the Intertropical Convergence Zone (ITCZ) triggered increased rainfall at the onset of the Holocene. At Tayma, where the influence of the ITCZ shift can be excluded, the sedimentary infill of a sabkha basin, the micro- and macrofaunal record, a digital elevation model based on DGPS measurements, and 14C-AMS data indicate the presence of a perennial lake with a minimum depth of 13 m, a stored water volume of 1.16 107 m3 and a surface of 18.45 km2 between 10,000-9000 cal BP. Foraminiferal test malformations and the shape of sieve pores on ostracod valves were used to detect trends in palaeo-salinity and ecological stress conditions. Contraction of the lake at least after 8500 cal BP is a response to a long-term aridisation trend subsequent to the early Holocene. Based on the hydrological water balance equation, quantitative data on minimum palaeo-rainfall during the early Holocene humid period were determined. Input parameters for the equation are the minimum lake level, lake surface and lake volume during the peak of the early Holocene humid period as well as palaeo-evapotranspiration, groundwater infiltration, and surface runoff. A perennial lake in the endorheic basin of the

  3. Holocene sea level history, modern-day vertical uplift and forebulge evolution: further constraints on the GIA process over the North American continent

    NASA Astrophysics Data System (ADS)

    Roy, K.

    2015-12-01

    The intense cycles of glaciation and deglaciation that have characterized Earth's climate over the past 900,000 years have had a profound impact on the Earth system. The significant imprints that the related variations in surface mass load have had on sea level history and the Earth's shape can be employed to constrain models of the glacial isostatic adjustment (GIA) process. These models rely on two fundamental inputs, namely a history of ice-sheet loading and a representation of the variation of viscosity in the lithosphere and in the mantle. Especially important GIA related observables include Global Positioning System (GPS) observations of the movement of the solid Earth's surface and inferences of past relative sea level evolution. Depending on the region from which they originate, these data provide information on different model characteristics. In particular, while the relative sea level constrained relaxation occurring near former centers of glaciation can be relatively easily parametrized to facilitate an inversion for mantle viscosity, the same process in the regions of forebulge collapse is much more complex but nevertheless provides essential further constraints upon mantle viscosity. In this paper, we examine how recently available high-quality datasets of relative sea level evolution from the U.S. East coast (Engelhart et al., Geology, 2011) and the North American Pacific coast (Engelhart et al., QSR, 2015) can be employed, together with an extensive dataset of space-geodetic observations of present-day vertical uplift of the crust over North America (Peltier et al., JGR - Solid Earth, 2015), to further improve the latest state-of-the-art ICE-6G_C (VM5a) model (Peltier et al., JGR - Solid Earth, 2015). It will be demonstrated that the high quality of the data does not only provide further constraints on radial variations of viscosity in the mantle, but also on the history of the deglaciation that occurred over North America after the Last Glacial

  4. Analysis of dynamic testing performed on structural clay tile infilled frames

    SciTech Connect

    Fowler, J.J.

    1994-12-18

    The behavior of two structural clay tile infilled frames subjected to dynamic loading is investigated. The testing was performed by USACERL using a biaxial shake table machine on which two framed infills were spaced nine feet apart and connected by steel trusses and an eight inch concrete roof slab. The infills were composed of structural clay tile block which were laid with the cores horizontal. The specimen was loaded in both the out-of-plane and in-plane directions using a site specific time history record. The testing focused on determining frame and panel load-deflection behavior, acceleration amplification, and frequency degradation characteristics. The out-of-plane tests resulted in little degradation of frequency which means there was little loss of stiffness. There was no evidence of the infill {open_quotes}walking-out{close_quotes} of the steel frame; in fact the infill still had substantial stability after completion of the out-of-plane tests. As a result of the gradual increase in ground motion in the in-plane testing, the stiffness of the specimen gradually decreased. Strength and stiffness characteristics obtained from the dynamic testing were comparable to results and behavior seen in static tests. Degradation in the panel was much more rapid under the stronger ground motions which were produced during the sine sweep tests.

  5. Tectonic Complexity within Volcanically Infilled Impact Features on Mercury

    NASA Astrophysics Data System (ADS)

    Byrne, Paul; Klimczak, Christian; Blair, David; Ferrari, Sabrina; Solomon, Sean; Freed, Andrew; Watters, Thomas; Murchie, Scott

    2013-04-01

    Extensional tectonic deformation on Mercury is almost entirely restricted to impact features that host volcanic smooth plains. However, tectonic landforms within such features vary enormously in structural complexity. Here, we describe the progression in tectonic complexity within four representative volcanically flooded impact sites — a "ghost crater," the Mozart basin, the Rembrandt basin, and the Caloris basin — together with the implications of recent numerical modeling for the Caloris basin in particular, the largest recognized impact feature on the innermost planet. Ghost craters are volcanically buried impact features marked by a ring of tectonic landforms. Interior to many ghost craters are graben of no preferred orientation that divide the plains infill into polygonal blocks. The 235-km-diameter Mozart basin (centered at 7.8°N, 169.6°E) contains graben and ridges within its peak ring. Wrinkle ridges deform the basin center and are enclosed by an annulus of basin-circumferential graben. Outward from this annulus to the peak ring, mixed-orientation graben form a less-organized pattern. This general tectonic configuration is also observed within the similarly sized Raditladi and Rachmaninoff basins. Rembrandt basin (centered at 33.5°S, 88°E; diameter 715 km) has a basin floor heavily deformed by extensional and contractional structures. Basin-radial graben and ridges form fan-like patterns that are bounded by a mix of circumferential ridges and graben. Local clusters of ridges with mixed orientations lay farther outward on the southwestern and eastern portions of the interior smooth plains. The greatest tectonic complexity occurs within the 1,640-km-diameter Caloris basin, centered at 30°N, 161°E. A basin-radial graben set termed Pantheon Fossae originates from a point near the basin center and extends over half-way to the basin rim. Here, the Pantheon Fossae graben are bound by circumferential graben that form a near-complete annulus. Outward of

  6. Holocene carbonate sedimentation in Aitutaki Lagoon, Cook Islands, South Pacific

    SciTech Connect

    Richmond, B.M.; Hein, J.R.

    1987-05-01

    Aitutaki, an almost-atoll in the Southern Cook Islands, is characterized by a shallow enclosed lagoon. Sediment distribution within the lagoon can be broadly placed into three sedimentary-bathymetric provinces. (1) A low-relief reef rim (< 2 m deep), including sand flats and washover fans, is comprised mostly of clean sand and gravel. (2) The majority of the lagoon floor, which lies between 3 and 6 m water depth, is dominated by sand and silt; coral-algal patch reefs are common with densities greater than 500 reefs/km/sup 2/. Sediment commonly is coarser grained near the patch reefs. (3) Enclosed and elongate-sinuous topographic lows (basins) up to 10 m deep are marked by coral-algal reef growth along their margins. These features are typically narrow, less than 100 m wide, and are U-shaped in cross section and infilled by carbonate and terrigenous muds. High-resolution continuous seismic profiling and limited drilling indicate that differences in thickness of Holocene sediment result from primary irregularities in the pre-Holocene basement surface. Aitutaki was formed by late Miocene volcanism, with a post-edifice building mid-Pleistocene (0.77 Ma) volcanic episode. Two islets within the lagoon are also of volcanic origin, and sinuous coral ridges which extend for several kilometers probably developed on Quaternary lava flows. The coral ridges and meandering enclosed basins appear to be unique to Aitutaki in the Cook Islands.

  7. Sediment infilling and wetland formation dynamics in an active crevasse splay of the Mississippi River delta

    USGS Publications Warehouse

    Cahoon, Donald R.; White, David A.; Lynch, James C.

    2011-01-01

    Crevasse splay environments provide a mesocosm for evaluating wetland formation and maintenance processes on a decadal time scale. Site elevation, water levels, vertical accretion, elevation change, shallow subsidence, and plant biomass were measured at five habitats along an elevation gradient to evaluate wetland formation and development in Brant Pass Splay; an active crevasse splay of the Balize delta of the Mississippi River. The processes of vertical development (vertical accretion, elevation change, and shallow subsidence) were measured with the surface elevation table–marker horizon method. There were three distinct stages to the accrual of elevation capital and wetland formation in the splay: sediment infilling, vegetative colonization, and development of a mature wetland community. Accretion, elevation gain, and shallow subsidence all decreased by an order of magnitude from the open water (lowest elevation) to the forest (highest elevation) habitats. Vegetative colonization occurred within the first growing season following emergence of the mud surface. An explosively high rate of below-ground production quickly stabilized the loosely consolidated sub-aerial sediments. After emergent vegetation colonization, vertical development slowed and maintenance of marsh elevation was driven both by sediment trapping by the vegetation and accumulation of plant organic matter in the soil. Continued vertical development and survival of the marsh then depended on the health and productivity of the plant community. The process of delta wetland formation is both complex and nonlinear. Determining the dynamics of wetland formation will help in understanding the processes driving the past building of the delta and in developing models for restoring degraded wetlands in the Mississippi River delta and other deltas around the world.

  8. Sediment infilling and wetland formation dynamics in an active crevasse splay of the Mississippi River delta

    NASA Astrophysics Data System (ADS)

    Cahoon, Donald R.; White, David A.; Lynch, James C.

    2011-08-01

    Crevasse splay environments provide a mesocosm for evaluating wetland formation and maintenance processes on a decadal time scale. Site elevation, water levels, vertical accretion, elevation change, shallow subsidence, and plant biomass were measured at five habitats along an elevation gradient to evaluate wetland formation and development in Brant Pass Splay; an active crevasse splay of the Balize delta of the Mississippi River. The processes of vertical development (vertical accretion, elevation change, and shallow subsidence) were measured with the surface elevation table-marker horizon method. There were three distinct stages to the accrual of elevation capital and wetland formation in the splay: sediment infilling, vegetative colonization, and development of a mature wetland community. Accretion, elevation gain, and shallow subsidence all decreased by an order of magnitude from the open water (lowest elevation) to the forest (highest elevation) habitats. Vegetative colonization occurred within the first growing season following emergence of the mud surface. An explosively high rate of below-ground production quickly stabilized the loosely consolidated sub-aerial sediments. After emergent vegetation colonization, vertical development slowed and maintenance of marsh elevation was driven both by sediment trapping by the vegetation and accumulation of plant organic matter in the soil. Continued vertical development and survival of the marsh then depended on the health and productivity of the plant community. The process of delta wetland formation is both complex and nonlinear. Determining the dynamics of wetland formation will help in understanding the processes driving the past building of the delta and in developing models for restoring degraded wetlands in the Mississippi River delta and other deltas around the world.

  9. The effect of prior out-of-plane damage on the in-plane behavior of unreinforced masonry infilled frames

    SciTech Connect

    Henderson, R.C.; Jones, W.D.; Burdette, E.G.; Porter, M.L.

    1993-08-25

    In order to address the effect of prior out-of-plane damage on the in-plane behavior of unreinforced masonry infills, two full-scale (24 feet tall by 28 feet long) structural clay tile infills and one frame-only (no infilling) were constructed and tested. The infilled frame, consisting of two wide flange columns surrounded by masonry plasters and an eccentric wide flange purlin, was identical to many of the infills located at the Oak Ridge Y-12 Plant. The masonry infill was approximately 12.5 inches thick and was composed of individual four- and eight-inch hollow clay tile (HCT) units. One of the infill panels was tested out-of-plane by four quasi-static actuators -- two on each column. The test structure was deflected out-of-plane equally at all four actuator locations in order to simulate the computed deflection path of the top and bottom chords of a roof truss framing into the columns at these locations. Prior to the infill testing, a bare frame was loaded similarly in order to determine the behavior and stiffness contribution of the frame only. Following the out-of-plane test of the infilled panel, the structure was loaded in-plane to failure in order to ascertain residual strength. A second, identical infilled frame was then constructed and tested in-plane to failure. In this way, in-plane behavior with and without prior out-of-plane damage could be established and compared. For both out-of-plane and in-plane testing, reversed-cyclic quasi-static loading was used in order to obtain full tension/compression hystereses. Also, natural frequencies of the first infilled panel were determined before and after the out-of-plane testing. This paper describes the test series and discusses the conclusions pertinent to the effect of out-of-plane cracking on in-plane stiffness and behavior.

  10. Surface-geophysical techniques used to detect existing and infilled scour holes near bridge piers

    USGS Publications Warehouse

    Placzek, Gary; Haeni, F.P.

    1995-01-01

    thin as 2-ft thick. Scour-hole geometry, the thickness of fill material in scour holes, and riverbed deposition were detected using this technique. Processing techniques were applied after data collection to assist with the interpretation of the data. Data were transferred from the color Fathometer, CSP, and GPR systems to a personal computer, and a commercially available software package designed to process GPR data was used to process the GPR and CSP data. Digital filtering, predictive-deconvolution, and migration algorithms were applied to some of the data. The processed data were displayed and printed as color amplitude or wiggle-trace plots. These processing methods eased and improved the interpretation of some of the data, but some interference from side echoes from bridge piers and multiple reflections remained in the data. The surface-geophysical techniques were applied at six bridge sites in Connecticut. Each site had different water depths, specific conductance, and riverbed materials. Existing and infilled scour holes, exposed pier footings, and riverbed deposition were detected by the surveys. The interpretations of the geophysical data were confirmed by comparing the data with lithologic and (or) probing data.

  11. Assessing bioturbation using micromorphology and biosilicate evidence: A case study of the early-Holocene Brady Soil, central Great Plains, USA

    NASA Astrophysics Data System (ADS)

    Woodburn, T. L.; Hasiotis, S. T.; Johnson, W. C.

    2012-12-01

    The Old Wauneta Roadcut site in southwestern Nebraska exhibits a 1.2 meter-thick exposure of the Brady Soil, a buried paleosol which formed within loess during the Pleistocene-Holocene transition. Excavation of the loess-paleosol sequence has revealed considerable bioturbation by plant roots, invertebrates, and small vertebrates. Bioturbation was not restricted to a single time period, but occurred continually throughout soil development, as evidenced by differing sediment fills and crosscutting relationships. The Brady Soil is an accretionary soil within the uppermost part of the Last Glacial Maximum Peoria Loess. At the base of the solum, the Bkb horizon exhibits an increased illuvial clay and carbonate content, and contains extensive, small (~2cm width), backfilled burrows typically produced by cicada nymphs (Cicadidae) or beetle larvae. The most stable period of the Brady Soil is expressed by the dark (9.8 YR 4/1), thick Ab horizon. This is overlain by an ACb horizon, where soil formation was being extinguished by the onset of Holocene-age Bignell Loess deposition. Within the upper solum and Bignell Loess, a shift in biota activity occurs as indicated by the large burrow (6-12 cm width) and chamber (30-40 cm width) systems observed. Trace sizes suggest that a burrowing rodent, such as the prairie dog (Cynomys sp.) or ground squirrel (Spermophilus sp.), was responsible for their creation. Soil micromorphology was used to distinguish sediment-size classes, mineralogy, and clay morphology of specific loess deposits and soil horizons in order to track displacement of sediment through the profile due to bioturbation. Five block samples were taken in undisturbed sediment and soil horizons for thin-section analysis. Twelve additional samples of burrow cross-sections or bioturbated sediment were analyzed for comparison. Soil features produced by faunal and floral activity were differentiated from features produced by pedologic processes through the identification and

  12. Study on the effect of the infill walls on the seismic performance of a reinforced concrete frame

    NASA Astrophysics Data System (ADS)

    Zhang, Cuiqiang; Zhou, Ying; Zhou, Deyuan; Lu, Xilin

    2011-12-01

    Motivated by the seismic damage observed to reinforced concrete (RC) frame structures during the Wenchuan earthquake, the effect of infill walls on the seismic performance of a RC frame is studied in this paper. Infill walls, especially those made of masonry, offer some amount of stiffness and strength. Therefore, the effect of infill walls should be considered during the design of RC frames. In this study, an analysis of the recorded ground motion in the Wenchuan earthquake is performed. Then, a numerical model is developed to simulate the infill walls. Finally, nonlinear dynamic analysis is carried out on a RC frame with and without infill walls, respectively, by using CANNY software. Through a comparative analysis, the following conclusions can be drawn. The failure mode of the frame with infill walls is in accordance with the seismic damage failure pattern, which is strong beam and weak column mode. This indicates that the infill walls change the failure pattern of the frame, and it is necessary to consider them in the seismic design of the RC frame. The numerical model presented in this paper can effectively simulate the effect of infill walls on the RC frame.

  13. Welding of pyroclastic conduit infill: A mechanism for cyclical explosive eruptions

    NASA Astrophysics Data System (ADS)

    Kolzenburg, S.; Russell, J. K.

    2014-07-01

    Vulcanian-style eruptions are small- to moderate-sized, singular to cyclical events commonly having volcanic explosivity indices of 1-3. They produce pyroclastic flows, disperse tephra over considerable areas, and can occur as precursors to larger (e.g., Plinian) eruptions. The fallout deposits of the 2360 B.P. eruption of Mount Meager, BC, Canada, contain bread-crusted blocks of welded breccia as accessory lithics. They display a range of compaction/welding intensity and provide a remarkable opportunity to constrain the nature and timescales of mechanical processes operating within explosive volcanic conduits during repose periods between eruptive cycles. We address the deformation and porosity/permeability reduction within natural pyroclastic deposits infilling volcanic conduits. We measure the porosity, permeability, and ultrasonic wave velocities for a suite of samples and quantify the strain recorded by pumice clasts. We explore the correlations between the physical properties and deformation fabric. Based on these correlations, we reconstruct the deformation history within the conduit, model the permeability reduction timescales, and outline the implications for the repressurization of the volcanic conduit. Our results highlight a profound directionality in the measured physical properties of these samples related to the deformation-induced fabric. Gas permeability varies drastically with increasing strain and decreasing porosity along the compaction direction of the fabric but varies little along the elongation direction of the fabric. The deformation fabric records a combination of compaction within the conduit and postcompaction stretching associated with subsequent eruption. Model timescales of these processes are in good agreement with repose periods of cyclic vulcanian eruptions.

  14. Prediction of the Fundamental Period of Infilled RC Frame Structures Using Artificial Neural Networks

    PubMed Central

    Asteris, Panagiotis G.; Tsaris, Athanasios K.; Cavaleri, Liborio; Repapis, Constantinos C.; Papalou, Angeliki; Di Trapani, Fabio; Karypidis, Dimitrios F.

    2016-01-01

    The fundamental period is one of the most critical parameters for the seismic design of structures. There are several literature approaches for its estimation which often conflict with each other, making their use questionable. Furthermore, the majority of these approaches do not take into account the presence of infill walls into the structure despite the fact that infill walls increase the stiffness and mass of structure leading to significant changes in the fundamental period. In the present paper, artificial neural networks (ANNs) are used to predict the fundamental period of infilled reinforced concrete (RC) structures. For the training and the validation of the ANN, a large data set is used based on a detailed investigation of the parameters that affect the fundamental period of RC structures. The comparison of the predicted values with analytical ones indicates the potential of using ANNs for the prediction of the fundamental period of infilled RC frame structures taking into account the crucial parameters that influence its value. PMID:27066069

  15. Masonry Infilling Effect On Seismic Vulnerability and Performance Level of High Ductility RC Frames

    NASA Astrophysics Data System (ADS)

    Ghalehnovi, M.; Shahraki, H.

    2008-07-01

    In last years researchers preferred behavior-based design of structure to force-based one for designing and construction of the earthquake-resistance structures, this method is named performance based designing. The main goal of this method is designing of structure members for a certain performance or behavior. On the other hand in most of buildings, load bearing frames are infilled with masonry materials which leads to considerable changes in mechanical properties of frames. But usually infilling wall's effect has been ignored in nonlinear analysis of structures because of complication of the problem and lack of simple logical solution. As a result lateral stiffness, strength, ductility and performance of the structure will be computed with less accuracy. In this paper by use of Smooth hysteretic model for masonry infillings, some high ductile RC frames (4, 8 stories including 1, 2 and 3 spans) designed according to Iranian code are considered. They have been analyzed by nonlinear dynamic method in two states, with and without infilling. Then their performance has been determined with criteria of ATC 40 and compared with recommended performance in Iranian seismic code (standard No. 2800).

  16. Masonry Infilling Effect On Seismic Vulnerability and Performance Level of High Ductility RC Frames

    SciTech Connect

    Ghalehnovi, M.; Shahraki, H.

    2008-07-08

    In last years researchers preferred behavior-based design of structure to force-based one for designing and construction of the earthquake-resistance structures, this method is named performance based designing. The main goal of this method is designing of structure members for a certain performance or behavior. On the other hand in most of buildings, load bearing frames are infilled with masonry materials which leads to considerable changes in mechanical properties of frames. But usually infilling wall's effect has been ignored in nonlinear analysis of structures because of complication of the problem and lack of simple logical solution. As a result lateral stiffness, strength, ductility and performance of the structure will be computed with less accuracy. In this paper by use of Smooth hysteretic model for masonry infillings, some high ductile RC frames (4, 8 stories including 1, 2 and 3 spans) designed according to Iranian code are considered. They have been analyzed by nonlinear dynamic method in two states, with and without infilling. Then their performance has been determined with criteria of ATC 40 and compared with recommended performance in Iranian seismic code (standard No. 2800)

  17. Holocene aridification of India

    NASA Astrophysics Data System (ADS)

    Ponton, Camilo; Giosan, Liviu; Eglinton, Tim I.; Fuller, Dorian Q.; Johnson, Joel E.; Kumar, Pushpendra; Collett, Tim S.

    2012-02-01

    Spanning a latitudinal range typical for deserts, the Indian peninsula is fertile instead and sustains over a billion people through monsoonal rains. Despite the strong link between climate and society, our knowledge of the long-term monsoon variability is incomplete over the Indian subcontinent. Here we reconstruct the Holocene paleoclimate in the core monsoon zone (CMZ) of the Indian peninsula using a sediment core recovered offshore from the mouth of Godavari River. Carbon isotopes of sedimentary leaf waxes provide an integrated and regionally extensive record of the flora in the CMZ and document a gradual increase in aridity-adapted vegetation from ˜4,000 until 1,700 years ago followed by the persistence of aridity-adapted plants after that. The oxygen isotopic composition of planktonic foraminifer Globigerinoides ruber detects unprecedented high salinity events in the Bay of Bengal over the last 3,000 years, and especially after 1,700 years ago, which suggest that the CMZ aridification intensified in the late Holocene through a series of sub-millennial dry episodes. Cultural changes occurred across the Indian subcontinent as the climate became more arid after ˜4,000 years. Sedentary agriculture took hold in the drying central and south India, while the urban Harappan civilization collapsed in the already arid Indus basin. The establishment of a more variable hydroclimate over the last ca. 1,700 years may have led to the rapid proliferation of water-conservation technology in south India.

  18. Holocene aridification of India

    USGS Publications Warehouse

    Ponton, C.; Giosan, L.; Eglinton, T.I.; Fuller, D.Q.; Johnson, J.E.; Kumar, P.; Collett, T.S.

    2012-01-01

    Spanning a latitudinal range typical for deserts, the Indian peninsula is fertile instead and sustains over a billion people through monsoonal rains. Despite the strong link between climate and society, our knowledge of the long-term monsoon variability is incomplete over the Indian subcontinent. Here we reconstruct the Holocene paleoclimate in the core monsoon zone (CMZ) of the Indian peninsula using a sediment core recovered offshore from the mouth of Godavari River. Carbon isotopes of sedimentary leaf waxes provide an integrated and regionally extensive record of the flora in the CMZ and document a gradual increase in aridity-adapted vegetation from ???4,000 until 1,700 years ago followed by the persistence of aridity-adapted plants after that. The oxygen isotopic composition of planktonic foraminifer Globigerinoides ruber detects unprecedented high salinity events in the Bay of Bengal over the last 3,000 years, and especially after 1,700 years ago, which suggest that the CMZ aridification intensified in the late Holocene through a series of sub-millennial dry episodes. Cultural changes occurred across the Indian subcontinent as the climate became more arid after ???4,000 years. Sedentary agriculture took hold in the drying central and south India, while the urban Harappan civilization collapsed in the already arid Indus basin. The establishment of a more variable hydroclimate over the last ca. 1,700 years may have led to the rapid proliferation of water-conservation technology in south India. Copyright 2012 by the American Geophysical Union.

  19. Rapid deglacial and early Holocene expansion of peatlands in Alaska.

    PubMed

    Jones, Miriam C; Yu, Zicheng

    2010-04-20

    Northern peatlands represent one of the largest biospheric carbon (C) reservoirs; however, the role of peatlands in the global carbon cycle remains intensely debated, owing in part to the paucity of detailed regional datasets and the complexity of the role of climate, ecosystem processes, and environmental factors in controlling peatland C dynamics. Here we used detailed C accumulation data from four peatlands and a compilation of peatland initiation ages across Alaska to examine Holocene peatland dynamics and climate sensitivity. We find that 75% of dated peatlands in Alaska initiated before 8,600 years ago and that early Holocene C accumulation rates were four times higher than the rest of the Holocene. Similar rapid peatland expansion occurred in West Siberia during the Holocene thermal maximum (HTM). Our results suggest that high summer temperature and strong seasonality during the HTM in Alaska might have played a major role in causing the highest rates of C accumulation and peatland expansion. The rapid peatland expansion and C accumulation in these vast regions contributed significantly to the peak of atmospheric methane concentrations in the early Holocene. Furthermore, we find that Alaskan peatlands began expanding much earlier than peatlands in other regions, indicating an important contribution of these peatlands to the pre-Holocene increase in atmospheric methane concentrations. PMID:20368451

  20. The coupled δ 13C-radiocarbon systematics of three Late Glacial/early Holocene speleothems; insights into soil and cave processes at climatic transitions

    NASA Astrophysics Data System (ADS)

    Rudzka, D.; McDermott, F.; Baldini, L. M.; Fleitmann, D.; Moreno, A.; Stoll, H.

    2011-08-01

    The coupled δ 13C-radiocarbon systematics of three European stalagmites deposited during the Late Glacial and early Holocene were investigated to understand better how the carbon isotope systematics of speleothems respond to climate transitions. The emphasis is on understanding how speleothems may record climate-driven changes in the proportions of biogenic (soil carbon) and limestone bedrock derived carbon. At two of the three sites, the combined δ 13C and 14C data argue against greater inputs of limestone carbon as the sole cause of the observed shift to higher δ 13C during the cold Younger Dryas. In these stalagmites (GAR-01 from La Garma cave, N. Spain and So-1 from Sofular cave, Turkey), the combined changes in δ 13C and initial 14C activities suggest enhanced decomposition of old stored, more recalcitrant, soil carbon at the onset of the warmer early Holocene. Alternative explanations involving gradual temporal changes between open- and closed-system behaviour during the Late Glacial are difficult to reconcile with observed changes in speleothem δ 13C and the growth rates. In contrast, a stalagmite from Pindal cave (N. Spain) indicates an abrupt change in carbon inputs linked to local hydrological and disequilibrium isotope fractionation effects, rather than climate change. For the first time, it is shown that while the initial 14C activities of all three stalagmites broadly follow the contemporaneous atmospheric 14C trends (the Younger Dryas atmospheric 14C anomaly can be clearly discerned), subtle changes in speleothem initial 14C activities are linked to climate-driven changes in soil carbon turnover at a climate transition.

  1. Infilling missing precipitation records - A comparison of a new copula-based method with other techniques

    NASA Astrophysics Data System (ADS)

    Bárdossy, András; Pegram, Geoffrey

    2014-11-01

    Infilling missing data might be an unpleasant and tedious task, but is necessary for analysis and water resources management, so it should not be done in a lackadaisical manner. The important thing about the infilled values is that they need to be as good as possible, because poor infilling is likely to lead to poor decisions. Traditionally, a range of methods is routinely employed, e.g. Nearest Neighbor substitution through to Kriging, but few methods attach a quality estimate to the infilled values. In this paper a new copula based method is developed for infilling missing daily and monthly rain gauge data and is compared against six other commonly used methods, in a semi-arid environment with a range of rain-rates and interstation distances, in the Southern Cape region of South Africa. For daily data it is clear that the copula-based methods are superior to the others in terms of point estimation and have the added benefit of providing an estimate of the precision of the interpolation, not provided by the others. In our case, the addition of atmospheric circulation patterns designed to add information for infilling has a relatively small positive effect on the quality of the estimation. The main reason for this is that a small number of wet days does not allow a good estimation of the conditional distribution of precipitation amounts; we note that the average probability of a dry day in this region is 86%. An improvement of the estimate of the probability of a dry day was however observed. In other regions, with a higher number of wet days, an atmospheric Circulation Pattern (CP) based method is likely to lead to further improvements. Using copula-based methods, the estimated probabilities of a dry day correspond well to the observed frequencies of dry days. The monthly data yield the same conclusion, with the qualification that the Expectation Maximisation [EM] algorithm performs as well as the copula method (because of the low count of dry months in this

  2. An experimental investigation on the ultimate strength of epoxy repaired braced partial infilled RC frames

    NASA Astrophysics Data System (ADS)

    Dubey, Shailendra Kumar Damodar; Kute, Sunil

    2014-09-01

    Due to earthquake, buildings are damaged partially or completely. Particularly structures with soft storey are mostly affected. In general, such damaged structures are repaired and reused. In this regard, an experimental investigation was planned and conducted on models of single-bay, single-storey of partial concrete infilled reinforced concrete (RC) frames up to collapse with corner, central and diagonal steel bracings. Such collapsed frames were repaired with epoxy resin and retested. The initiative was to identify the behaviour, extent of restored ultimate strength and deflection of epoxy-retrofitted frames in comparison to the braced RC frames. The performance of such frames has been considered only for lateral loads. In comparison to bare RC frames, epoxy repaired partial infilled frames have significant increase in the lateral load capacity. Central bracing is more effective than corner and diagonal bracing. For the same load, epoxy repaired frames have comparable deflection than similar braced frames.

  3. Structure and origin of Holocene cold events

    NASA Astrophysics Data System (ADS)

    Wanner, Heinz; Solomina, Olga; Grosjean, Martin; Ritz, Stefan P.; Jetel, Markéta

    2011-10-01

    The present interglacial, the Holocene, spans the period of the last 11,700 years. It has sustained the growth and development of modern society. The millennial-scale decreasing solar insolation in the Northern Hemisphere summer lead to Northern Hemisphere cooling, a southern shift of the Intertropical Convergence Zone (ITCZ) and a weakening of the Northern Hemisphere summer monsoon systems. On the multidecadal to multicentury-scale, periods of more stable and warmer climate were interrupted by several cold relapses, at least in the Northern Hemisphere extra-tropical area. Based on carefully selected 10,000-year-long time series of temperature and humidity/precipitation, as well as reconstructions of glacier advances, the spatiotemporal pattern of six cold relapses during the last 10,000 years was analysed and presented in form of a Holocene Climate Atlas (HOCLAT; see http://www.oeschger.unibe.ch/research/projects/holocene_atlas/). A clear cyclicity was not found, and the spatiotemporal variability of temperature and humidity/precipitation during the six specific cold events (8200, 6300, 4700, 2700, 1550 and 550 years BP) was very high. Different dynamical processes such as meltwater flux into the North Atlantic, low solar activity, explosive volcanic eruptions, and fluctuations of the thermohaline circulation likely played a major role. In addition, internal dynamics in the North Atlantic and Pacific area (including their complex interaction) were likely involved.

  4. INFIL1D: a quasi-analytical model for simulating one-dimensional, constant flux infiltration

    SciTech Connect

    Simmons, C.S.; McKeon, T.J.

    1984-04-01

    The program INFIL1D is designed to calculate approximate wetting-front advance into an unsaturated, uniformly moist, homogeneous soil profile, under constant surface-flux conditions. The code is based on a quasi-analytical method, which utilizes an assumed invariant functional relationship between reduced (normalized) flux and water content. The code uses general hydraulic property data in tabular form to simulate constant surface-flux infiltration. 10 references, 4 figures.

  5. The Role of Conjoining (Tie) Channels in Lowland Floodplain Development and Lake Infilling

    NASA Astrophysics Data System (ADS)

    Rowland, J. C.; Dietrich, W. E.; Day, G.; Lepper, K.; Wilson, C. J.

    2003-12-01

    In simple models of lowland river systems, water and sediment enter the main stem via tributary and secondary channels and are only redistributed to the floodplain during overbank and crevasse splay events. Along numerous river systems across the globe, however, water and sediment are regularly exchanged between the river and off river water bodies via stable, narrow channels. These channels, known as tie channels on the Fly River in Papua New Guinea and batture channels along the lower Mississippi, are largely overlooked but important components of floodplain sediment dispersal where they exist. These channels become pathways of sediment dispersal to the floodplain system when elevated river stages force sediment-laden flows into the off-river water bodies. On the Fly River, it is estimated that about 50% of the sediment delivery to the floodplain is via these channels, and along low gradient tributary channels during flood driven flow reversals. During low flow, tie channels serve to drain the floodplain. With the outgoing flows, large amounts sediment can be carried and lost to the floodplain; floodplain lakes progressively infill with sediment as the mouth of these channels steadily prograde lakeward. These lake deposits not only become significant stratigraphic components of floodplains (traditionally referred to as clay plugs), but are important local sinks recording hundreds to thousands of years of river history. As with all sinks, the proper interpretation of these stratigraphic records requires understanding the processes by which sediment is delivered to the sink and how these processes alter the paleohydraulic and climatic signals of interest. We have conducted field investigations of conjoining channels in Papua New Guinea (the Fly and Strickland Rivers), Louisiana (Raccourci Old River ~ 65 km upriver of Baton Rouge) and Alaska (Birch Creek). These field investigations include extensive surveys of both cross and along channel morphological trends

  6. Out-of-plane behavior of hollow clay tile walls infilled between steel frames

    SciTech Connect

    Butala, M.B.; Jones, W.D.; Beavers, J.E.

    1991-08-16

    Several buildings at Y-12 Plant rely on unreinforced hollow clay tile walls (HCTW) infilled between unbraced, non-moment resisting steel frames to resist natural phenomena forces, seismic and wind. One critical building relies on moment resisting steel frames in one direction while relying on unreinforced HCTWs infilled between the columns in the orthogonal direction to resist these forces. The HCTWs must act as shear walls while maintaining out-of-plane lateral stability. In assessing the safety of these buildings to seismic forces, several models to study the in- and out-of-plane effects were made and analyzed. The study of the moment resisting steel framed building indicated that bending stresses in the walls were induced by building drift and not by inertial forces per se. The discovery of this phenomenon was some what of a surprise in that the analysis performed is not typically used in design of these structures. The study indicated that the walls began to crack at their interface with the foundation at a low ``g`` level and that horizontal cracking at different elevations continued until the walls exhibited little bending resistance. This paper presents results of the study for out-of-plane behavior of unreinforced HCTWs infilled between adjacent moment resisting steel frames and discusses the problems of assessing the in-plane behavior given the horizontal cracks induced by building drift in the out-of-plane direction.

  7. Holocene to contemporary fluvial sediment budgets in small glacier-fed valley-fjord systems (ESF-NRF SedyMONT - Norway Project, SedyMONT, TOPO-EUROPE)

    NASA Astrophysics Data System (ADS)

    Liermann, Susan; Beylich, Achim A.; Rubensdotter, Lena; Hansen, Louise

    2010-05-01

    link sediment transport and runoff (events) and the spatial and temporal variability of sediment transport processes. In addition, several channel test stretches in the two catchments are defined. Channel surveys include seasonally repeated channel morphometry studies and pepple counts for bedload transport and storage estimations. Sediment traps are deployed to indentify different sediment sources using grain size and SEM analysis. Lake sediment investigations are focused on i) quantifying post-Little Ice Age to contemporary sedimentation rates, ii) the temporal variability of process rates and iii) the detection and analysis of sediment sources. Sediment cores are retrieved in defined lakes within Erdalen and Bødalen. Geophysical methods (Georadar, Geoseismic) are applied for calculation of the total valley infills and for interpretation of the stratigraphic architecture, with the goal to define the controlling factors for the postglacial sediment storage within the two glacially eroded valleys. This research contributes to the understanding of controls of Holocene to contemporary sedimentary processes and budgets in formerly glaciated steep mountain environments. This presentation was supported by the EUROCORES programme TOPO-EUROPE of the European Science Foundation.

  8. Prompt transgression and gradual salinisation of the Black Sea during the early Holocene constrained by amino acid racemization and radiocarbon dating

    NASA Astrophysics Data System (ADS)

    Nicholas, William Anthony; Chivas, Allan R.; Murray-Wallace, Colin V.; Fink, David

    2011-12-01

    The restricted environment of the Black Sea is particularly sensitive to climatic and oceanographic fluctuations, owing to its connection with the Mediterranean Sea via the narrow Bosphorus Strait. The exact mechanism and timing of the most recent connection between these water bodies is controversial with debate on the post-glacial history of the Black Sea being dependent on radiocarbon dating for numerical ages. Here we present new 23 accelerator mass spectrometer (AMS) radiocarbon ages on peat and bivalve molluscs, supported by the first amino acid racemization (AAR) dating of bivalve molluscs ( n = 66) in the Black Sea. These data indicate infilling of the Black Sea during the early Holocene from an initial depth 107 m below sea-level, and 72 m below that of the Bosphorus Sill. These data combined with a review of previous radiocarbon ages has enabled a unique perspective on the post-glacial Black Sea. A sea-level curve based on conventional and AMS radiocarbon ages on peat and AMS-based ages on Dreissena sp. shells indicate the water-level in the earlier lake phase continued, until the early Holocene, to be lower than the Bosphorus Sill after the Younger Dryas ended. However, the absence of AMS-dated mollusc ages from the shelves of this basin older than the Younger Dryas is suggestive of sub-aerial exposure of the shelves, and comparatively lower water-levels when the Younger Dryas began. Thus post-glacial outflow from the Black Sea occurred through a lowered or open Bosphorus seaway. Basin-wide radiocarbon ages on peat indicate a prompt increase in water-level from that of the pre-existing and unconnected palaeo-lake during the earliest Holocene (9600-9200 cal a BP). Mass colonisation of the Black Sea by Mediterranean taxa did not occur until salinity had risen sufficiently, a process which took 1000 a or more from the initial transgressive event. This gradual change in salinity contrasts with the prompt transgression which would have taken ˜400 a to occur.

  9. Mediterranean Holocene climate, environment and human societies

    NASA Astrophysics Data System (ADS)

    Holmgren, Karin; Gogou, Alexandra.; Izdebski, Adam.; Luterbacher, Juerg.; Sicre, Marie-Alexandrine; Xoplaki, Elena

    2016-03-01

    This paper introduces the reader to a special issue of articles that explores links and processes behind societal change, climate change and environmental change in a Holocene perspective in the Mediterranean region. All papers are, by purpose, co-authored by scientists representing different disciplines. The cross-cutting theme has been to reach beyond simple explanations of potential climate-society relationships and advance our understanding on how to improve research methods and theories in the field. The thirteen papers in this issue address these questions in three different ways, by i) conceptual/methodological approaches; ii) review papers; and iii) case studies.

  10. The Telescope Array Low-Energy Extension (TALE) Infill Ground Array

    NASA Astrophysics Data System (ADS)

    Belz, J.

    The physics goals of the The Telescope Array Low-Energy Extension (TALE) include the hybrid measurement of spectrum and composition of cosmic rays down to energies below 1017 eV. To achieve composition measurements from observation of extensive air showers, a ground array detector must have the ability to distinguish the muonic and electromagnetic components of a shower. Here, we consider the design issues relevant to the infill ground array component of the TALE hybrid detector, and present results of prototype studies as well as preliminary detector designs and the envisioned array layout.

  11. Application of Integrated Reservoir Management and Reservoir Characterization to Optimize Infill Drilling.

    SciTech Connect

    1998-01-15

    A total of 18 wells, 14 producers and 4 injection wells, were drilled and completed during the Field Demonstration portion of the project. These 18 wells are all currently in service, with the producing wells going on-line between May and September 1996, and the injection wells going into service between August and December 1996. Current Unit production is approximately 3,100 BOPD, of which approximately 800 BOPD is being contributed from the 14 Project 10-acre producing wells (Figure 1). A revision in the Statement of Work was approved to allow for the drilling of additional 10-acre infill wells or injection well conversions as budget constraints allow.

  12. Application of Integrated Reservoir Management and Reservoir Characterization to Optimize Infill Drilling

    SciTech Connect

    Fina Oil and Chemical Company

    1999-11-03

    The eighteen 10-acre infill wells which were drilled as part of the field demonstration portion of the project are all currently in service with no operational problems. These wells consist of fourteen producing wells and four injection wells. The producing wells are currently producing a total of approximately 376 bopd, down from a peak rate of 900 bopd. The four injection wells are currently injecting a total of 140 bwipd. Unit production is currently averaging approximately 2,600 bopd, 12,000 bwpd and 18,000 bwipd.

  13. Impediments and constraints in the uptake of water sensitive urban design measures in greenfield and infill developments.

    PubMed

    Sharma, Ashok K; Cook, Stephen; Tjandraatmadja, Grace; Gregory, Alan

    2012-01-01

    Water sensitive urban developments are designed with integrated urban water management concepts and water sensitive urban design measures. The initiatives that may be included are the substitution of imported drinking water with alternative sources using a fit-for-purpose approach and structural and non-structural measures for the source control of stormwater. A water sensitive approach to urban development can help in achieving sustainability objectives by minimising disturbance to ecological and hydrological processes, and also relieve stress on conventional water systems. Water sensitive urban developments remain novel in comparison with conventional approaches, so the understanding and knowledge of the systems in regards to their planning; design; implementation; operation and maintenance; health impacts and environmental impacts is still developing and thus the mainstream uptake of these approaches faces many challenges. A study has been conducted to understand these challenges through a detailed literature review, investigating a large number of local greenfield and infill developments, and conducting extensive consultation with water professionals. This research has identified the social, economic, political, institutional and technological challenges faced in implementing water sensitive urban design in greenfield and infill developments. The research found in particular that there is the need for long-term monitoring studies of water sensitive urban developments. This monitoring is important to validate the performance of novel approaches implemented and improve associated guidelines, standards, and regulatory and governance frameworks, which can lead to mainstream acceptance of water sensitive urban development approaches. The dissemination of this research will help generate awareness among water professionals, water utilities, developers, planners and regulators of the research challenges to be addressed in order to achieve more mainstream acceptance of

  14. Incidence, Mechanisms, and Severity of Game-Related High School Football Injuries across Artificial Turf Systems of Various Infill Weight

    PubMed Central

    Meyers, Michael Clinton

    2016-01-01

    Objectives: Today’s new generations of artificial turf are increasingly being installed to duplicate or exceed playing characteristics of natural grass. Rather than playing on the polyethylene turf fibers, shoe: surface interaction actually occurs between the cleat and the various proprietary sand/rubber infill composites of varying weight. At this time, the influence of surface infill weight on football trauma is unknown. Therefore, this study was conducted to quantify incidence, mechanisms, and severity of game-related high school football trauma across artificial turf systems of various infill weight. Methods: Artificial turf systems were divided into four sand/rubber infill weight groups based on lbs per square foot: (A) > 9.0, (B) 6.0 - 8.9, (C) 3.1 - 5.9 and, (D) 0.0 - 3.0. A total of 52 high schools participating across four states over 5 competitive seasons were evaluated for injury incidence, injury category, time of injury, injury time loss, player position, injury mechanism and situation, primary type of injury, injury grade and anatomical location, field location at time of injury, injury severity, head, shoulder, and lower extremity trauma, elective imaging and surgical procedures, cleat design, turf age, and environmental factors. Results: Of the 1,467 high school games documented, 494 games (33.7%) were played on infill (A), 404 (27.5%) on infill (B), 379 (25.8%) on infill (C), and 190 (13.0%) on infill (D). A total of 3,741 injuries were documented, with significantly lower total injury incidence rates (IIR), [18.4 (95% CI, 18.0-18.7) vs 27.5 (26.8-27.9) vs 33.5 (32.7-34.0) and 23.7 (22.7-24.4)], substantial IIRs [3.4 (95% CI, 3.0-3.8) vs 6.6 (6.2-7.1), 8.5 (8.2-8.9) and 6.5 (5.8-7.1)], trauma from shoe: surface interaction during contact [4.6 (95% CI, 4.1-5.0) vs 7.5 (7.0-7.9), 6.4 (5.9-6.9) and 6.9 (6.2-7.5)], playing surface impact trauma [2.4 (95% CI, 2.1-2.8) vs 4.9 (4.4-5.4), 6.1 (5.6-6.6) and 4.4 (3.7-5.1)], and less total elective imaging

  15. Rapid assessment for seismic vulnerability of low and medium rise infilled RC frame buildings

    NASA Astrophysics Data System (ADS)

    Al-Nimry, Hanan; Resheidat, Musa; Qeran, Saddam

    2015-06-01

    An indexing method for rapid evaluation of the seismic vulnerability of infilled RC frame buildings in Jordan is proposed. The method aims at identifying low and medium rise residential buildings as safe or in need of further detailed evaluation. Following a rapid visual screening, the building is assigned a Basic Capacity Index (BCI); five performance modifiers are identified and multiplied by the BCI to arrive at the Capacity Index (CI) of the building. A Capacity Index lower than a limit CI value indicates that the screened building could experience moderate earthquake damage whereas a higher value implies that minor damage, if any, would take place. To establish the basic evaluation parameters; forty RC frame buildings were selected, designed and analyzed using static nonlinear analysis and incorporating the effect of infill walls. Effects of seismicity, local site conditions, horizontal irregularities (setbacks and re-entrant corners), vertical irregularities (soft story at ground floor level) and overhangs on the seismic performance of local buildings were examined. Assessment forms were designed and used to evaluate and rank 112 sample buildings. About 40% of the surveyed buildings were found to be in need of detailed evaluation to better define their seismic vulnerabilities.

  16. Feedback Loop of Data Infilling Using Model Result of Actual Evapotranspiration from Satellites and Hydrological Model

    NASA Astrophysics Data System (ADS)

    Murdi Hartanto, Isnaeni; Alexandridis, Thomas K.; van Andel, Schalk Jan; Solomatine, Dimitri

    2014-05-01

    Using satellite data in a hydrological model has long been occurring in modelling of hydrological processes, as a source of low cost regular data. The methods range from using satellite products as direct input, model validation, and data assimilation. However, the satellite data frequently face the missing value problem, whether due to the cloud cover or the limited temporal coverage. The problem could seriously affect its usefulness in hydrological model, especially if the model uses it as direct input, so data infilling becomes one of the important parts in the whole modelling exercise. In this research, actual evapotranspiration product from satellite is directly used as input into a spatially distributed hydrological model, and validated by comparing the catchment's end discharge with measured data. The instantaneous actual evapotranspiration is estimated from MODIS satellite images using a variation of the energy balance model for land (SEBAL). The eight-day cumulative actual evapotranspiration is then obtained by a temporal integration that uses the reference evapotranspiration calculated from meteorological data [1]. However, the above method cannot fill in a cell if the cell is constantly having no-data value during the eight-day periods. The hydrological model requires full set of data without no-data cells, hence, the no-data cells in the satellite's evapotranspiration map need to be filled in. In order to fills the no-data cells, an output of hydrological model is used. The hydrological model is firstly run with reference evapotranspiration as input to calculate discharge and actual evapotranspiration. The no-data cells in the eight-day cumulative map from the satellite are then filled in with the output of the first run of hydrological model. The final data is then used as input in a hydrological model to calculate discharge, thus creating a loop. The method is applied in the case study of Rijnland, the Netherlands where in the winter, cloud cover is

  17. The Birougou Mountains: Forested throughout the Holocene

    NASA Astrophysics Data System (ADS)

    Pietsch, S. A.; Tanga, J.-J.; Ngok-Banak, L.

    2009-04-01

    The Congo basin with an area of ~400 million ha harbours the second largest tropical forest complex of the world which covers ~60% of the area. Besides tropical rain forest the savannah biome comprises the second naturally abundant ecosystem type. During the Holocene (20.000 yrs. BP - Modern Times) the distribution of forest and savannas changed with changing climate and during the last glacial maximum (~20.000 yrs. BP) most of the Congo basin was covered by savannas and the Congolian rain forests were confined to refuge areas. Later the distribution between savannas and rainforest changed with changing climate, whereby in some regions rainforest and savannas replaced each other while on some sites one vegetation type persisted. During drier periods of the Holocene the rain forest biome was confined to refuge areas, which formed a conservation reservoir for forest re-extension during more humid, i.e. forest favourable, climatic periods. In order to understand the dynamics of the forest/savannah replacement process reference states of patches of stable savannah or stable rain forest are needed. Within this paper we will describe a patch of stable rain forest vegetation located at the Birougou Mountains in Gabon, and demonstrate that rain forest vegetation has continuously persisted since the Holocene climate optimum dated at around ~6.000 yrs. B.P. by using the signature of stable Carbon isotope discrimination of photosynthesis. Savannah grasses follow the C4-type of photosynthesis while forest vegetation exhibits C3 photosynthesis. Accordingly they differ in the d13C ratios of carbon incorporated into biomass. Soil organic Carbon originates from decomposition of litter inputs. d13C values along a vertical soil profile thus indicate persistence or past changes in vegetation cover. 14C age of soil humic acids, indicate the mean residence time of soil organic carbon. Results indicate that at the Birougou mountains (in contrast to other parts of the Congo basin) litter

  18. Lateglacial and early Holocene climates of the Atlantic margins of Europe: Stable isotope, mollusc and pollen records from Orkney, Scotland

    NASA Astrophysics Data System (ADS)

    Whittington, Graeme; Edwards, Kevin J.; Zanchetta, Giovanni; Keen, David H.; Bunting, M. Jane; Fallick, Anthony E.; Bryant, Charlotte L.

    2015-08-01

    The margins of mainland Europe, and especially those areas coming under the influence of North Atlantic weather systems, are ideally placed to record changing palaeoclimates. Cores from an infilled lake basin at Crudale Meadow in Mainland, Orkney, revealed basal deposits of calcareous mud ('marl') beneath sedge peat. Stable isotope, palynological and molluscan analyses allowed the establishment of palaeoenvironmental changes through the Devensian Lateglacial and the early Holocene. The δ18Omarl record exhibited the existence of possibly four climatic oscillations in the Lateglacial (one of which, within event cf. GI-1c, is not often commented upon), as well as the Preboreal Oscillation and other Holocene perturbations. The cold episodes succeeding the Preboreal Oscillation were demarcated conservatively and one of these (event C5, ˜11.0 ka) may have previously been unremarked, while the putative 9.3 and 8.2 ka events seem not to produce corresponding palynologically visible floristic changes. The events at Crudale Meadow are consistent with those recorded at other sites from Britain, Ireland and elsewhere, and can be correlated with isotopic changes shown by the Greenland ice cores. The multi-proxy approach enriches the environmental reconstructions from the site, although the synchronicity of the response of the various proxies is sometimes equivocal, depending upon the time period concerned, taphonomy, and the nature of the deposits. The site may contain the most northerly Lateglacial isotope record from northwest Europe, and it has yielded one of the best archives for the demonstration of abrupt early Holocene events within Britain.

  19. Holocene vegetation dynamics in the northeastern Rub' al-Khali desert, Arabian Peninsula: a phytolith, pollen and carbon isotope study

    NASA Astrophysics Data System (ADS)

    Parker, A. G.; Eckersley, L.; Smith, M. M.; Goudie, A. S.; Stokes, S.; Ward, S.; White, K.; Hodson, M. J.

    2004-10-01

    The Holocene vegetation history of the Arabian Peninsula is poorly understood, with few palaeobotanical studies to date. At Awafi, Ras al-Khaimah, UAE, a 3.3 m lake sediment sequence records the vegetation development for the period 8500 cal. yr BP to 3000 cal. yr BP. 13C isotope, pollen and phytolith analyses indicate that C3 Pooid grassland with a strong woody element existed during the early Holocene (between 8500 and 6000 cal. yr BP) and became replaced by mixed C3 and C4 grasses with a strong C4 Panicoid tall grass element between 5900 and 5400 cal. yr BP. An intense, arid event occurred at 4100 cal. yr BP when the lake desiccated and was infilled by Aeolian sand. From 4100 cal. yrBP the vegetation was dominated by C4 Chloridoid types and Cyperaceae, suggesting an incomplete vegetation cover and Aeolian dune reactivation owing to increased regional aridity. These data outline the ecosystem dynamics and carbon cycling in response to palaeomonsoon and north-westerly variability during the Holocene. Copyright

  20. Repeated catastrophic valley infill following medieval earthquakes in the Nepal Himalaya.

    PubMed

    Schwanghart, Wolfgang; Bernhardt, Anne; Stolle, Amelie; Hoelzmann, Philipp; Adhikari, Basanta R; Andermann, Christoff; Tofelde, Stefanie; Merchel, Silke; Rugel, Georg; Fort, Monique; Korup, Oliver

    2016-01-01

    Geomorphic footprints of past large Himalayan earthquakes are elusive, although they are urgently needed for gauging and predicting recovery times of seismically perturbed mountain landscapes. We present evidence of catastrophic valley infill following at least three medieval earthquakes in the Nepal Himalaya. Radiocarbon dates from peat beds, plant macrofossils, and humic silts in fine-grained tributary sediments near Pokhara, Nepal's second-largest city, match the timing of nearby M > 8 earthquakes in ~1100, 1255, and 1344 C.E. The upstream dip of tributary valley fills and x-ray fluorescence spectrometry of their provenance rule out local sources. Instead, geomorphic and sedimentary evidence is consistent with catastrophic fluvial aggradation and debris flows that had plugged several tributaries with tens of meters of calcareous sediment from a Higher Himalayan source >60 kilometers away.

  1. Reconstructing the infilling history within Robert Sharp Crater, Mars: Insights from morphology and stratigraphy

    NASA Astrophysics Data System (ADS)

    Brossier, J.; Le Deit, L.; Hauber, E.; Mangold, N.; Carter, J.; Jaumann, R.

    2015-10-01

    Robert Sharp (133.59°E, -4.12°N) is a 150 km diameter impact crater , located in the equatorial region of Mars, near Gale Crater, where the MSL rover Curiosity landed in August 2012. Using orbital data, an iron chlorine hydroxide named akaganéite that typically forms in highly saline and chlorinated aqueous environments on Earth has been detected in Robert Sharp crater [1]. Interestingly, akaganéite has also been detected in Gale Crater from the ground [2,3]. In order to reconstruct the paleo-environments in the region, we produce a geological map of Robert Sharp(Fig.1). Crater counts provide time constraints on its infilling history.

  2. Repeated catastrophic valley infill following medieval earthquakes in the Nepal Himalaya

    NASA Astrophysics Data System (ADS)

    Schwanghart, Wolfgang; Bernhardt, Anne; Stolle, Amelie; Hoelzmann, Philipp; Adhikari, Basanta R.; Andermann, Christoff; Tofelde, Stefanie; Merchel, Silke; Rugel, Georg; Fort, Monique; Korup, Oliver

    2016-01-01

    Geomorphic footprints of past large Himalayan earthquakes are elusive, although they are urgently needed for gauging and predicting recovery times of seismically perturbed mountain landscapes. We present evidence of catastrophic valley infill following at least three medieval earthquakes in the Nepal Himalaya. Radiocarbon dates from peat beds, plant macrofossils, and humic silts in fine-grained tributary sediments near Pokhara, Nepal’s second-largest city, match the timing of nearby M > 8 earthquakes in ~1100, 1255, and 1344 C.E. The upstream dip of tributary valley fills and x-ray fluorescence spectrometry of their provenance rule out local sources. Instead, geomorphic and sedimentary evidence is consistent with catastrophic fluvial aggradation and debris flows that had plugged several tributaries with tens of meters of calcareous sediment from a Higher Himalayan source >60 kilometers away.

  3. Repeated catastrophic valley infill following medieval earthquakes in the Nepal Himalaya.

    PubMed

    Schwanghart, Wolfgang; Bernhardt, Anne; Stolle, Amelie; Hoelzmann, Philipp; Adhikari, Basanta R; Andermann, Christoff; Tofelde, Stefanie; Merchel, Silke; Rugel, Georg; Fort, Monique; Korup, Oliver

    2016-01-01

    Geomorphic footprints of past large Himalayan earthquakes are elusive, although they are urgently needed for gauging and predicting recovery times of seismically perturbed mountain landscapes. We present evidence of catastrophic valley infill following at least three medieval earthquakes in the Nepal Himalaya. Radiocarbon dates from peat beds, plant macrofossils, and humic silts in fine-grained tributary sediments near Pokhara, Nepal's second-largest city, match the timing of nearby M > 8 earthquakes in ~1100, 1255, and 1344 C.E. The upstream dip of tributary valley fills and x-ray fluorescence spectrometry of their provenance rule out local sources. Instead, geomorphic and sedimentary evidence is consistent with catastrophic fluvial aggradation and debris flows that had plugged several tributaries with tens of meters of calcareous sediment from a Higher Himalayan source >60 kilometers away. PMID:26676354

  4. Acceptance and Angular Resolution of an Infill Array for the Pierre Auger Surface Detector

    SciTech Connect

    Medina, C.; Gomez Berisso, M.; Allekotte, I.; Etchegoyen, A.; Supanitsky, D.; Medina-Tanco, G.

    2007-02-12

    The Pierre Auger Observatory has been designed to study the highest-energy cosmic rays in nature (E {>=} 1019 eV). The determination of their arrival direction, energy and composition is performed by the analysis of the atmospheric showers they produce. The Auger Surface Array will consist of 1600 water Cerenkov detectors placed in an equilateral triangular grid of 1.5 km. In this paper we show how adding a ''small'' area of surface detectors at half the above mentioned spacing would make it possible to lower the detection threshold by one order of magnitude, thus allowing the Observatory to reach lower energies where the cross-over from galactic to extragalactic sources is expected. We also analyze the angular resolution that can be attained with such an infill array.

  5. Late Holocene vertical deformation, Yellowstone National Park, Wyoming

    SciTech Connect

    Locke, W.W.; Meyer, G.A.

    1985-01-01

    Volcano-tectonic deformation has been measured within the Yellowstone caldera using precision leveling techniques. The shorelines represent originally horizontal planes, accumulated deformation of which can be observed as vertical displacement and tilt. Dating of the shorelines allows the calculation of average rates of deformation since and between episodes of shoreline formation. Shoreline elevations projected to perpendiculars to isolines on contemporary uplift correlate well for 12 km across the perpendiculars. Projections to parallels are nearly horizontal for 5 km. 1985 fieldwork will extend this line to 20 km. Both correlations imply that the pattern of contemporary uplift is an accurate model for late Holocene deformation. Maximum late Holocene rates of deformation, as determined form minimum /sup 14/C dates, are 50-75% of contemporary rates. This suggests that late Holocene deformation has 1) been episodic (50-75% of the time), 2) been oscillatory (75-90% up, 10-25% down), or 3) occurred at an increasing rate through time. Tilt and uplift rates are similar, implying little downcutting at the outlet, and rates between shorelines are similar to those since shoreline formation, implying nearly constant average rates of deformation in the past 2500 years. Local deformation has been significant throughout the late Holocene. Episodic deformation in a graben 1 km across has controlled the location of the lake outlet, thus water level. Sharp local warping has deformed some shorelines by 1 mm/yr. These faults may relate to volcanic processes or to the regional tectonic regime.

  6. Holocene coastal glaciation of Alaska

    NASA Astrophysics Data System (ADS)

    Calkin, Parker E.; Wiles, Gregory C.; Barclay, David J.

    2001-01-01

    Holocene fluctuations of the three cirque glaciers on the Seward Peninsula and five groups of tidewater- and land-terminating glaciers along the northernmost Gulf of Alaska, provide a proxy record of late Holocene climatic change. Furthermore, the movements of the coastal glaciers were relevant to late Holocene native American migration. The earliest expansion was recorded about 6850 yr BP by Hubbard Glacier at the head of Yakutat Bay in the Gulf of Alaska; however, its down-fjord advance to the bay mouth was delayed until ˜2700 BP. Similarly, expansions of the Icy Bay, Bering, and McCarty glaciers occurred near their present termini by ˜3600-3000 BP, compatible with marked cooling and precipitation increases suggested by the Alaskan pollen record. Decrease in glacier activity ˜2000 BP was succeeded by advances of Gulf coastal glaciers between 1500 and 1300 BP, correlative with early Medieval expansions across the Northern Hemisphere. A Medieval Optimum, encompassing at least a few centuries prior to AD 1200 is recognized by general retreat of land-terminating glaciers, but not of all tidewater glaciers. Little Ice Age advances of land-based glaciers, many dated with the precision of tree-ring cross-dating, were centered on the middle 13th or early 15th centuries, the middle 17th and the last half of the 19th century A.D. Strong synchrony of these events across coastal Alaska is evident.

  7. Transverse, supraglacially derived crevasse infillings in a Pleistocene ice-sheet margin zone (eastern Poland): Genesis and sedimentary record

    NASA Astrophysics Data System (ADS)

    Godlewska, Anna; Terpiłowski, Sławomir

    2012-08-01

    The so-called 'crevasse infillings' in the marginal zone of the Saalian ice sheet in eastern Poland are atypical relief forms for lowlands glaciated in the Pleistocene. They are located on a high of the Cretaceous/Palaeogene substratum and form isolated ridges arranged in trains parallel to the former ice-sheet margin, i.e., transverse to the movement of the ice sheet. The sedimentary succession of the crevasse infillings consists mainly of undeformed glaciodeltaic deposits. We propose a model of the crevasse infilling development in three phases against the background of ice mass dynamics: 1) ice-sheet advance over a high of the substratum — compressive ice flow that bumped against the high's slope and enrichment of the ice with debris; 2) an overriding of the substratum high by ice masses — a tensional ice-flow regime resulted in significant crevassing; and 3) ice mass stagnation — low energy, supraglacial deltaic sedimentation in isolated ponds between disintegrated ice blocks under frozen bed conditions. Considering this genesis, we suggest classifying these forms as kames instead of crevasse infillings.

  8. Complex Holocene Sedimentation and Erosion in Deep Basins of Lake Superior

    NASA Astrophysics Data System (ADS)

    Colman, S. M.; Wattrus, N. J.

    2006-12-01

    Little sediment accumulates on the lake floor of most of the Laurentian Great Lakes in water less than about 100 m deep. Such sediment is thought to be resuspended by waves and currents and "focused" onto the deeper lake floor. New high-resolution CHIRP seismic-reflection data in central Lake Superior suggests that Holocene sedimentation has been considerably more complex there. The late- and post- glacial stratigraphy in Lake Superior consists of glacial-lacustrine red varves overlain by gray varves. The glacial-lacustrine section is capped by poorly laminated, fine-grained, gray Holocene muds. In many areas, the entire post-glacial section is cut by polygonal fractures and faults related to dewatering or syneresis. Our new seismic-reflection data from water depths of 150-250 m indicate that the upper surface of the varved section is extensively eroded, both by planation of varves draped over bathymetric highs and by widespread channeling. The cause of this pervasive erosion is not known, but it may be related to the sudden opening of a low outlet from the lake as the continental ice sheet retreated. Within the Holocene section, small to medium sized (2-4 m deep, 100-300 m wide) channels are formed, in some cases overlying the older channels in the varved section. Commonly, the Holocene channels cut directly into the underlying varved section. Both of these types of channels are partially to fully filled with Holocene sediments. Dipping reflections within the Holocene section suggest considerable complexity in Holocene sedimentation. Large parts of the study area contain only thin (<1 m) Holocene section and large areas contain none at all. All of these observations indicated a much more complex set of Holocene erosional and depositional processes in deep water than those implied by the simple focusing mechanism.

  9. Timing and magnitude of the Caribbean mid-Holocene highstand

    NASA Astrophysics Data System (ADS)

    Ashe, E.; Khan, N.; Horton, B.; Brocard, G. Y.; Dutton, A.; Engelhart, S. E.; Kopp, R. E.; Hill, D. F.; Peltier, W. R.; Scatena, F. N.

    2015-12-01

    We present a database of published and new relative sea-level (RSL) data for the past 13 ka, which constrains the Holocene sea-level histories of the Caribbean coast of Central and South America (Florida Keys, USA to Guyana) and the Bahamas and Greater and Lesser Antilles islands. Our evaluation of mangrove peat and Acropora palmata sea-level indicators from geological investigations provides 503 sea-level index points and 242 limiting dates. We subdivide the database into 21 regions based on the availability of data, tectonic setting, and distance from the former Laurentide ice sheet. Most index points (75%) and limiting dates (90%) are <8 ka, although there is an unusual temporal distribution with the greatest amount of the data (~28%) occurring between 6-8 ka. We reassess and screen radiocarbon and U/Th ages of mangrove peat and coral data. We use the stratigraphic position (overburden thickness) of index points account for sediment compaction, and use the paleotidal model of Hill et al. (2011) to account for Holocene changes in paleotidal range. A noisy-input Gaussian process regression model calculates that the rates of RSL change were highest during the early Holocene (3-8 mm/yr) and have decreased over time (< 2 mm/yr), which is related to the reduction of ice equivalent meltwater input and collapse of the proglacial forebulge during the Holocene. The sea-level reconstructions demonstrate that RSL did not exceed the present height (0 m) during the Holocene in the majority of locations, with the exception of a small highstand (<2 m) on the northern coast of South America along the Orinoco Delta and Suriname/Guyana located furthest away from the former Laurentide Ice Sheet. The different sea-level histories are an ongoing isostatic response to deglaciation of the Laurentide Ice Sheet and suggest subsidence resulting from collapse of the proglacial forebulge reaches further south than previously considered.

  10. Field Investigations of Landscape Development in southeast Spain for use in Modeling Holocene (8,000 - 1,500 yr) Agropastoral Landuse and Landscape Interactions

    NASA Astrophysics Data System (ADS)

    Dimaggio, E. N.; La Roca, N.; Arrowsmith, J. R.; Diez-Castillo, A.; Bernabeu, J.; Barton, C. M.

    2007-12-01

    -rich paleosols. Small remnant surfaces mapped as Terrace Z (below Terrace A) were observed within the main barrancos and indicate a later, brief accumulation period with subsequent incision to the modern channel. Holocene landscape development in the Penaguila appears to have progressed from a period of stability to slope denudation with aggradation (stream infilling) followed by rapid incision which initiated sometime near the time of occupation. This change from a low relief alluvial surface to one cut by narrow channels may have been an important shift for local populations. Their response to that environmental modification may be associated with the horticulturalist to agricultural intensification noted in the archaeological record. Tighter chronology and better understanding of the driving processes for barranco incision and hollow formation will improve our ability to correlate the changing landscape with land use practices. Such an improved correlation leads to better understanding of human-landscape interactions.

  11. Simulated Atlantic Multidecadal Oscillation during the Holocene

    NASA Astrophysics Data System (ADS)

    Wei, W.; Lohmann, G.

    2011-12-01

    In this study, the Atlantic Multidecadal Oscillation (AMO) under different boundary conditions during the Holocene, i.e. orbital change, greenhouse gas concentration, the Laurentide ice sheet and its melting, are examined in several long-term simulations using the Earth system model COSMOS. The simulated AMO indices exhibit a quasi-multidecadal periodicity, consistent with the typical 50-80 year cycle of the AMO indicated by the observation data. A warm phase of the AMO accompanies a hemispheric scale warming in the NH, with the maximum warming over the North Atlantic and part of the Arctic. Such a warming favors more evaporation and thus more precipitation over most part of the North Atlantic, especially enhancing the Atlantic intertropical convergence zone. Concerning the forcing mechanism of the AMO, the most common believed physical process involves the variation of the Atlantic meridional overturning circulation (AMOC). Although a fully understanding of such a process is beyond the scope of this study, our results show the strong correlation between the AMO index and AMOC index on multidecadal timescales and, during a warm phase of the AMO, the AMOC is intensified significantly. The climate influence of the AMO during the Holocene demonstrates that there is no remarkable change in its spatial pattern under different climate background conditions, which further reveals that the AMO is an internal variability of the climate system. However, we imply that this influence can be distinguished regarding the regional scale feature and its magnitude. It has been supported by a previous study, which suggests that the regional response to the AMO can be modulated by orbitally induced shifts in large-scale ocean-atmosphere circulation. Moreover, we argue that the climate influence of the AMO might be amplified by a vigorous background climate condition, in particular during a cold period.

  12. Late Quaternary valley infill and dissection in the Indus River, western Tibetan Plateau margin

    NASA Astrophysics Data System (ADS)

    Blöthe, Jan H.; Munack, Henry; Korup, Oliver; Fülling, Alexander; Garzanti, Eduardo; Resentini, Alberto; Kubik, Peter W.

    2014-06-01

    The Indus, one of Earth's major rivers, drains large parts of the NW Himalaya and the Transhimalayan ranges that form part of the western Tibetan Plateau margin. In the western Himalayan syntaxis, where local topographic relief exceeds 7 km, the Indus has incised a steep bedrock gorge at rates of several mm yr-1. Upstream, however, the upper Indus and its tributaries alternate between bedrock gorges and broad alluvial flats flanked by the Ladakh and Zanskar ranges. We review the late Quaternary valley history in this region with a focus on the confluence of the Indus and Zanskar Rivers, where vast alluvial terrace staircases and lake sediments record major episodes of aggradation and incision. New absolute dating of high-level fluvial terrace remnants using cosmogenic 10Be, optically and infrared stimulated luminescence (OSL, IRSL) indicates at least two phases of late Quaternary valley infilling. These phases commenced before ˜200 ka and ˜50-20 ka, judging from terrace treads stranded >150 m and ˜30-40 m above modern river levels, respectively. Numerous stacks of lacustrine sediments that straddle the Indus River >200 km between the city of Leh and the confluence with the Shyok River share a distinct horizontal alignment. Constraints from IRSL samples of lacustrine sequences from the Leh-Spituk area reveal a protracted lake phase from >177 ka to 72 ka, locally accumulating >50-m thick deposits. In the absence of tectonic faulting, major lithological differences, and stream capture, we attribute the formation of this and other large lakes in the region to natural damming by large landslides, glaciers, and alluvial fans. The overall patchy landform age constraints from earlier studies can be reconciled by postulating a major deglacial control on sediment flux, valley infilling, and subsequent incision that has been modulated locally by backwater effects of natural damming. While comparison with Pleistocene monsoon proxies reveals no obvious correlation, a late

  13. Geodynamic evolution and sedimentary infill of the northern Levant Basin: A source to sink-perspective

    NASA Astrophysics Data System (ADS)

    Hawie, N.

    2013-12-01

    Nicolas Hawie a,b,c (nicolas.hawie@upmc.fr) Didier Granjeon c (didier.granjeon@ifpen.fr) Christian Gorini a,b (christian.gorini@upmc.fr) Remy Deschamps c (remy.deschamps@ifpen.fr) Fadi H. Nader c (fadi-henri.nader@ifpen.fr) Carla Müller Delphine Desmares f (delphine.desmares@upmc.fr) Lucien Montadert e (lucien.montadert@beicip.com) François Baudin a (francois.baudin@upmc.fr) a UMR 7193 Institut des Sciences de la Terre de Paris, Université Pierre et Marie Curie/ Univ. Paris 06, case 117. 4, place Jussieu 75252 Paris Cedex 05, France b iSTEP, UMR 7193, CNRS, F-75005, Paris, France c IFP Energies nouvelles, 1-4 avenue du Bois Préau 92852 Rueil Malmaison Cedex, France d UMR 7207, Centre de Recherche sur la Paleobiodiversité et les Paleoenvironnements. Université Pierre et Marie Curie, Tour 46-56 5ème. 4, place Jussieu 75252 Paris Cedex 05, France e Beicip Franlab, 232 Av. Napoléon Bonaparte, 95502 Rueil-Malmaison, France Sedimentological and biostratigraphic investigations onshore Lebanon coupled with 2D offshore reflection seismic data allowed proposing a new Mesozoic-Present tectono-stratigraphic framework for the northern Levant Margin and Basin. The seismic interpretation supported by in-depth facies analysis permitted to depict the potential depositional environments offshore Lebanon as no well has yet been drilled. The Levant region has been affected by successive geodynamic events that modified the architecture of its margin and basin from a Late Triassic to Middle Jurassic rift into a Late Cretaceous subduction followed by collision and Miocene-Present strike slip motion. The interplay between major geodynamic events as well as sea level fluctuations impacted on the sedimentary infill of the basin. During Jurassic and Cretaceous, the Levant Margin is dominated by the aggradation of a carbonate platform while deepwater mixed-systems prevailed in the basin. During the Oligo-Miocene, three major sedimentary pathways are expected to drive important

  14. Holocene paleoenviroments of northwest Iowa

    SciTech Connect

    Baker, R.G.; Bettis, E.A. III; Schwert, D.P.

    1996-05-01

    This paper presents the biotic, sedimentary, geomorphic, and climatic history of the upper part of the Roberts Creek Basin, northeastern Iowa for the late-glacial and Holocene, and compares these records with a C-O isotopic sequence from Coldwater Cave, 60 km northwest of Roberts Creek. the biotic record (pollen, vascular plant and bryophyte macrofossils, and insects) is preserved in floodplain alluvium that underlies three constructional surfaces separated by low scarps. Each surface is underlain by a lithologically and temporally distinct alluvial fill. The highest surface is underlain by the Gunder Member of the Deforest Formation, dating from 11,000 to 4000 yr BP; beneath the intermediate level is the Roberts Creek Member, dating from 4000 to 400 yr BP; and the lowest level is underlain by the Camp Creek Member, deposited during the last 380 yr. Pollen and plant macrofossils in the alluvial fill show that a typical late-glacial spruce forest was replaced by Quercus and Ulmus in the early Holocene. This early-to-middle Holocene forest became dominated by medic elements such as Acer saccharum, Tila americana, Ostyra virginiana, and Carpinus caroliniana as late as 5500 yr BP; in contrast, the closest sites to the west and north were at their warmest and driest were covered by prairie vegetation between 6500 and 5500 yr BP. After 5500 yr BP, the forest in the roberts Creek area was replaced by prairie, as indicated by a rich assemblage of plant macrofossils, although only Ambrosia and Poaceae became abundant in the pollen record. The return of Quercus {approx} 3000 BP (while nonarboreal pollen percentages remained relatively high) indicates the oak savanna prevailed with little change until settlement time. 83 refs., 17 figs., 5 tabs.

  15. High-resolution multi-proxy reconstruction of Lake Ighiel (Western Carpathians, Romania): processes and controlling factors of lacustrine dynamics during the mid and late Holocene

    NASA Astrophysics Data System (ADS)

    Haliuc, Aritina; Veres, Daniel; Hubay, Katalin; Begy, Robert; Brauer, Achim; Hutchinson, Simon; Braun, Mihaly

    2016-04-01

    Concerns about current and prospective environmental change have increased the interest in past climate variability and its impact on the bio-hydro-atmosphere and human society. Acting as high-resolution terrestrial archives, lacustrine sediments are the result of the complex interaction between internal and external forcing and an important tool in efforts to resolve questions related to the palaeoclimatic and palaeoenvironmental conditions of the recent past. Here we discuss a new, high-resolution sedimentary record from the Romanian Carpathians (central-eastern Europe). Lake Ighiel (46° 10'50"N, 23° 22'00"E) is a small lake located in a mid-altitude mountain belt (Trascau Mountains) at an altitude of 924 m ( lake maximum depth 9 m; catchment area 487 ha). We employ detailed 210Pb and 14C dating coupled with high-resolution X-ray fluorescence scanning (μ-XRF) measurements, long-core sedimentary logging, environmental magnetic proxies (susceptibility, natural and induced remanences) in an attempt to trace the 6000 years evolution of lake-catchment system. More specifically, we discuss: i) the temporal evolution of the main sedimentation phases of the lake based on sedimentological, geochemical and magnetic proxies; ii) the amplitude and interplay of processes (natural and/or anthropogenic) controlling the depositional environment through time; iii) assess the contribution of each controlling factors and reconstruct the evolution of lacustrine system and palaeoclimate forcing using multivariate statistics. The sedimentary record can be divided into six phases based on alternating high and low detrital fluxes, oscillating lacustrine productivity and redox conditions. A series of detrital events (5200; 4800; 5400; 5250; 4500; 4050; 3800; 3500; 3250; 3050; 2650; 2350; 2250; 1400; 1100; 500; 100 cal yr BP) were identified by microfacies analyses and X-ray fluorescence scanning (μ-XRF) analysis. These events are reflected in most of the parameters and appear

  16. Basin Dynamics and Sedimentary Infilling of Miocene Sandstone Reservoir Systems In Eastern Tunisian African Margin

    NASA Astrophysics Data System (ADS)

    Bédir, Mourad; Khomsi, Sami

    2015-04-01

    Most of hydrocarbon accumulations and aquifers within the Cap Bon, Gulf of Hammamet and Sahel basins in eastern tunisian foreland are reservoired within the Upper Miocene Birsa and Saouaf sandstones and shales Formations. In the gulf of Hammamet, these sandstones constitutes oil and gas fields and are exploited on anticline highs and described as varying from shoreface to shallow marine and typically exhibit excellent reservoir quality of 30% to 35% porosity and good permeability from 500 to 1100 md. In addition, the fracturing of faults enhanced the reservoir quality potential. In contrary, the same hydrocarbon reservoirs are important hydrogeologic ones in the Cap Bon and Sahel basins with huge amount of hundred millions of cubic meters of water only partially exploited. Integrated wire line logging correlations, seismic sequence stratigraphic, tectonics and outcrop geologic analogue studies had permitted to highlight the basin structuring and sedimentary environments of sequence deposits infilling of the reservoir distribution between high platforms to subsiding graben and syncline basins bounded by deep-seated transtensive and transpressive flower faults. Seven third order sequence deposits limited by downlap prograding and onlap/toplap aggrading/retrograding system tracts extend along the eastern margin around the three basins by facies and thickness variances. System tracts exhibit around high horst and graben a channelized and levee infillings extending from 100 meters to more than a kilometer of width. They present a stacked single story and multistory channels types showing space lateral and vertical migrations along NE-SW, E-W and N-S directions. Paleogeographic depositional reservoir fair maps distribution highlight deltaic horst domain with floodplain and incised valley of fluvial amalgamed and braided sandstones distributary channels that occupy the high folded horsts. Whereas folded horst-graben and syncline borders domain of Shelf prodelta are

  17. Seismic Evaluation and Preliminary Design of Regular Setback Masonry Infilled Open Ground Storey RC Frame

    NASA Astrophysics Data System (ADS)

    Hashmi, Arshad K.

    2016-06-01

    Current seismic code presents certain stringent factors for defining frame as regular and irregular. Thereby these stringent factors only decide the type of analysis (i.e. equivalent static analysis or dynamic analysis) to be done. On the contrary, development of new simplified methods such as pushover analysis can give lateral load capacity of any structure (e.g. regular or irregular frame etc.) easily. Design by iterative procedure with the help of pushover analysis for serviceability requirement (i.e. inter storey drift limitation) provided by present seismic code, can provide an alternative to present practicing procedure. Present paper deals with regular setback frame in combination with vulnerable layout of masonry infill walls over the frame elevation (i.e. probable case of "Vertical Stiffness Irregularities"). Nonlinear time history analysis and Capacity Spectrum Method have been implemented to investigate the seismic performance of these frames. Finally, recently developed preliminary design procedure satisfying the serviceability criterion of inter storey drift limitation has been employed for the preliminary design of these frames.

  18. Origin and deformation of Holocene shoreline terraces, Yellowstone Lake, Wyoming

    SciTech Connect

    Meyer, G.A.; Locke, W.W.

    1986-08-01

    Geodetic surveys within the Yellowstone caldera have documented active uplift that is most likely caused by magmatic processes in the upper crust. Along the northeast shore of Yellowstone Lake, maximum relative uplift rates are 10 mm/yr for the period 1923-1975. However, information on deformation prior to historic instrumental records has been lacking. In this study, closely spaced data on elevations of postglacial shoreline terraces around the north end of Yellowstone Lake reveal complex tilting. Though most Holocene deformation is probably magma related, the pattern of shoreline tilting deviates significantly from the historic pattern of roughly symmetric inflation of the caldera. Along the northeast shore, where tilt directions of historic and shoreline deformation are similar, differential uplift of a > 2500-yr-old terrace is roughly 10 m; this gives a maximum uplift rate of 4 mm/yr. These unique Holocene terraces may exist due to episodic deformation because vertical movements affecting the lake outlet directly control lake level.

  19. Holocene paleoenvironments of Northeast Iowa

    USGS Publications Warehouse

    Baker, R.G.; Bettis, E. Arthur; Schwert, D.R.; Horton, D.G.; Chumbley, C.A.; Gonzalez, Luis A.; Reagan, M.K.

    1996-01-01

    This paper presents the biotic. sedimentary, geomorphic, and climatic history of the upper part of the Roberts Creek Basin, northeastern Iowa for the late-glacial and Holocene, and compares these records with a C-O isotopic sequence from Coldwater Cave. 60 km northwest of Roberts Creek. The biotic record (pollen, vascular plant and bryophyle macrofossils. and insects) is preserved in floodplain alluvium that underlies three constructional surfaces separated by low scarps. Each surface is underlain by a lithologically and temporally distinct alluvial fill. The highest surface is underlain by the Gunder Member of the Deforest Formation, dating from 11 000 to 4000 yr BP; beneath the intermediate level is the Roberts Creek Member, dating from 4000 to 400 yr BP; and the lowest level is underlain by the Camp Creek Member, deposited during the last 380 yr. Pollen and plant macrofossils in the alluvial fill show that a typical late-glacial spruce forest was replaced by Quercus and Ulmus in the early Holocene. This early-to-middle Holocene forest became dominated by mesic elements such as Acer saccharum, Tilia americana, Ostrya virginiana, and Carpinus caroliniana as late as 5500 yr BP; in contrast, the closest sites to the west and north were at their warmest and driest and were covered by prairie vegetation between 6500 and 5500 yr BP. After 5500 yr BP, the forest in the Roberts Creek area was replaced by prairie, as indicated by a rich assemblage of plant macrofossils, although only Ambrosia and Poaceae became abundant in the pollen record. The return of Quercus ??? 3000 BP (while nonarboreal pollen percentages remained relatively high) indicates that oak savanna prevailed with little change until settlement time. The bryophyte assemblages strongly support the vascular plant record. Rich fen species characteristic of boreal habitats occur only in the late-glacial. They are replaced by a number of deciduous-forest elements when early-to-middle Holocene forests were

  20. Assessing metal contamination from construction and demolition (C&D) waste used to infill wetlands: using Deroceras reticulatum (Mollusca: Gastropoda).

    PubMed

    Staunton, John A; Mc Donnell, Rory J; Gormally, Michael J; Williams, Chris D; Henry, Tiernan; Morrison, Liam

    2014-11-01

    Large quantities of construction and demolition waste (C&D) are produced globally every year, with little known about potential environmental impacts. In the present study, the slug, Deroceras reticulatum (Mollusca: Gastropoda) was used as the first biomonitor of metals (Ag, As, Ba, Cd, Co, Cr, Cu, Mn, Mo, Ni, Pb, Sb, Se, Ti, Tl, V and Zn) on wetlands post infilling with construction and demolition (C&D) waste. The bioaccumulation of As, Ba, Cd, Co, Sb, Se and Tl were found to be significantly elevated in slugs collected on C&D waste when compared to unimproved pastures (control sites), while Mo, Se and Sr had significantly higher concentrations in slugs collected on C&D waste when compared to known contaminated sites (mining locations), indicating the potential hazardous nature of C&D waste to biota. Identifying exact sources for these metals within the waste can be problematic, due to its heterogenic nature. Biomonitors are a useful tool for future monitoring and impact studies, facilitating policy makers and regulations in other countries regarding C&D waste infill. In addition, improving separation of C&D waste to allow increased reuse and recycling is likely to be effective in reducing the volume of waste being used as infill, subsequently decreasing potential metal contamination.

  1. Holocene loess and paleosols in central Alaska: A proxy record of Holocene climate change

    SciTech Connect

    Bigelow, N.H.; Beget, J.E.

    1992-03-01

    Episodic Holocene loess deposition and soil formation in the sediments of the Nenana valley of Central Alaska may reflect Holocene climate change. Periods of loess deposition seem to correlate with times of alpine glacier activity, while paleosols correspond to times of glacial retreat These variations may reflect changes in solar activity Stuiver and Braziunas, 1989. Other mechanisms, such as orbitally forced changes in seasonality, volcanism, and atmospheric C02 variability may also have affected Holocene climates and loess deposition.

  2. Infilling and flooding of the Mekong River incised valley during deglacial sea-level rise

    NASA Astrophysics Data System (ADS)

    Tjallingii, Rik; Stattegger, Karl; Wetzel, Andreas; Van Phach, Phung

    2010-06-01

    The abrupt transition from fluvial to marine deposition of incised-valley-fill sediments retrieved from the southeast Vietnamese shelf, accurately records the postglacial transgression after 14 ka before present (BP). Valley-filling sediments consist of fluvial mud, whereas sedimentation after the transgression is characterized by shallow-marine carbonate sands. This change in sediment composition is accurately marked in high-resolution X-ray fluorescence (XRF) core scanning records. Rapid aggradation of fluvial sediments at the river mouth nearly completely filled the Mekong incised valley prior to flooding. However, accumulation rates strongly reduced in the valley after the river-mouth system flooded and stepped back. This also affected the sediment supply to deeper parts of the southeast Vietnamese shelf. Comparison of the Mekong valley-filling with the East Asian sea-level history of sub- and inter-tidal sediment records shows that the transgressive surface preserved in the incised-valley-fill records is a robust sea-level indicator. The valley was nearly completely filled with fluvial sediments between 13.0 and 9.5 ka BP when sea-level rose rather constantly with approximately 10 mm/yr, as indicated by the East Asian sea-level record. At shallower parts of the shelf, significant sediment reworking and the establishment of estuarine conditions at the final stage of infilling complicates accurate dating of the transgressive surface. Nevertheless, incised-valley-fill records and land-based drill sites indicate a vast and rapid flooding of the shelf from the location of the modern Vietnamese coastline to the Cambodian lowlands between 9.5 ka and 8.5 ka BP. Fast flooding of this part of the shelf is related with the low shelf gradient and a strong acceleration of the East Asian sea-level rise from 34 to 9 meter below modern sea level (mbsl) corresponding to the sea-level jump of melt water pulse (MWP) 1C.

  3. Infilling of Cobble Substrate used by White Sturgeon on the Nechako River, at Vanderhoof BC

    NASA Astrophysics Data System (ADS)

    Zimmermann, A. E.; Argast, T.; Sary, Z.

    2013-12-01

    Nechako white sturgeon are experiencing a recruitment failure, which has been attributed to the failure of eggs and larvae to survive as a result of changes in the substrate at the locations where they are known to spawn. As part of the overall recovery effort initiative, cobble substrate was placed at two locations to provide clean spawning substrate. Subsequently, the condition of the substrate has been investigated using an underwater camera and freeze core sampling. These observations have shown that coarse sand and fine gravels (fine bedoad) have in-filled the coarse substrate where it was placed along the inside corner of the bends, while placed substrate located on the outside of the bends has remained free of this size fraction. This observation has lead to the quandary: Is placed cobble substrate on the outside corner of the bends not being filled in with fine bedload because fine bedload is not moving past these sites, or are post-regulation flood flows sufficient to ensure fines remain suspended and are not deposited in the interstitial spaces? To assess this question a number of field based techniques will be used in August of 2013 during high flows to examine the movement of fine bedload. The techniques employed will include an underwater camera, P61 suspended sediment sampler, a HellySmith and KAROLYI bedload sampler and an ADCP with RTK for bottom tracking. The intent is to examine the movement of fine bedload across the channel at a number of potential spawning sites. The poster will summarize the observations to date about the movement of fine bedload at the spawning sites, and discuss the implications for spawning substrate improvement efforts.

  4. Multiple thermal maxima during the Holocene

    SciTech Connect

    Davis, O.K.

    1984-08-10

    The astronomical theory of climatic change provides an alternative to the traditional chronology for Holocene climatic change, which calls for one thermal maximum about 6000 years ago. The theory predicts a series of maxima during the Holocene, one for each season. Because the relation of the perihelion to the spring equinox changes with a 22,000-year period, late summer insolation would have been greatest 5000 years ago, whereas early summer insolation would have been greatest 13,000 years ago. Climatic reconstructions based on the response of ecosystems to late summer climate indicate a later Holocene thermal maximum than paleoclimatic data sensitive to early summer climate. In southern Idaho, three different vegetation types indicate thermal maxima at different times during the Holocene, depending on the climatic variable controlling each type. 28 references, 2 figures.

  5. Early Holocene hydrology and environments of the Ner River (Poland)

    NASA Astrophysics Data System (ADS)

    Kittel, Piotr; Płóciennik, Mateusz; Borówka, Ryszard K.; Okupny, Daniel; Pawłowski, Dominik; Peyron, Odille; Stachowicz-Rybka, Renata; Obremska, Milena; Cywa, Katarzyna

    2016-03-01

    The Ner River valley (central Poland) underwent substantial transformation during the Weichselian-Holocene transition as a result of fluvial processes and climate changes, resulting in the establishment of its present shape in the Holocene. A multiproxy study based on organic deposits from a palaeochannel fill (Lutomiersk-Koziówki) shows that after the channel was cut off during the late glacial termination, it became a shallow oxbow, fed by local springs. In the Boreal period, the oxbow lake was also fed by precipitation and became a telmatic environment overgrown by rush and swamp vegetation. Finally, it was covered by overbank deposits. The first flooding phase (9900-9600 cal. BP) was followed by the accumulation of overbank sediments (after 9500 cal. BP) and flooding increased after ca. 9300-9000 cal. BP. Pollen data provide information on the regional vegetation context for local and regional changes. In the Atlantic period, an increase in both summer and winter temperatures is inferred from the pollen data, corresponding to an expansion of thermophilous deciduous forests. While in general, flooding phases of the Early Holocene are poorly recognised in Eastern Europe, the Lutomiersk-Koziówki site may be considered as one of the reference points for this phenomenon in the region.

  6. Middle Holocene thermal maximum in eastern Beringia

    NASA Astrophysics Data System (ADS)

    Kaufman, D. S.; Bartlein, P. J.

    2015-12-01

    A new systematic review of diverse Holocene paleoenvironmental records (Kaufman et al., Quat. Sci. Rev., in revision) has clarified the primary multi-centennial- to millennial-scale trends across eastern Beringia (Alaska, westernmost Canada and adjacent seas). Composite time series from midges, pollen, and biogeochemical indicators are compared with new summaries of mountain-glacier and lake-level fluctuations, terrestrial water-isotope records, sea-ice and sea-surface-temperature analyses, and peatland and thaw-lake initiation frequencies. The paleo observations are also compared with recently published simulations (Bartlein et al., Clim. Past Discuss., 2015) that used a regional climate model to simulate the effects of global and regional-scale forcings at 11 and 6 ka. During the early Holocene (11.5-8 ka), rather than a prominent thermal maximum as suggested previously, the newly compiled paleo evidence (mostly sensitive to summer conditions) indicates that temperatures were highly variable, at times both higher and lower than present, although the overall lowest average temperatures occurred during the earliest Holocene. During the middle Holocene (8-4 ka), glaciers retreated as the regional average temperature increased to a maximum between 7 and 5 ka, as reflected in most proxy types. The paleo evidence for low and variable temperatures during the early Holocene contrasts with more uniformly high temperatures during the middle Holocene and agrees with the climate simulations, which show that temperature in eastern Beringia was on average lower at 11 ka and higher at 6 ka than at present (pre-industrial). Low temperatures during the early Holocene can be attributed in part to the summer chilling caused by flooding the continental shelves, whereas the mid-Holocene thermal maximum was likely driven by the loss of the Laurentide ice sheet, rise in greenhouse gases, higher-than-present summer insolation, and expansion of forest over tundra.

  7. The late-Holocene progradation of the Mahakam Delta, Indonesia - A case study of tidal, tropical deltas

    NASA Astrophysics Data System (ADS)

    Dalman, R.; Ranawijaya, D.; Missiaen, T.; Kroonenberg, S.; Storms, J.

    2011-12-01

    branch, indicating a strong spatial differentiation in subsidence or in paleobathymetry. The outbuilding of the fluvial distributaries provided the shallow, sheltered and vegetated areas which allowed rapid aggradation and progradation of the tide-dominated delta plain. Records of avulsions are not found in the Mahakam Delta due to the rapid infill of the delta and floodplain, inhibiting the creation of a possible superelevation of the fluvial channels. The tidal plain processes are sufficiently capable of trapping sediment and consequently aggrading to keep up with the fluvial distributaries. Additionally, the tidal discharge in the main distributaries and strong bank stabilising vegetation have kept the main distributaries in place during the entire progradational event. Little to no lateral shifting has occurred over the entire period despite the large number of distributaries active currently. In general channel networks in tidal deltas with strong vegetation seem to be dominantly controlled by mouthbar induced bifurcations and not by nodal avulsions or lateral migration.

  8. Assessment of quantitative Holocene temperature reconstructions based on multiple proxies from the sediment record of Lake Loitsana, Sokli, NE Finland

    NASA Astrophysics Data System (ADS)

    Shala, S.; Helmens, K. F.; Luoto, T. P.; Salonen, J. S.; Väliranta, M.; Weckström, J.

    2014-12-01

    Four biotic proxies (pollen, plant macrofossils chironomids and diatoms) are employed to quantitatively reconstruct variations in mean July air temperatures (Tjul) at Lake Loitsana, NE Finland, during the Holocene. The aim: assessing the reliability of these temperature reconstructions and the timing of highest Tjul. The reconstructed Tjul values are evaluated in relation to local-scale/site-specific processes associated to the Holocene lake development at Loitsana, as these factors have been shown to significantly influence the fossil assemblages found in the Lake Loitsana sediments. Our study shows that the reconstructions are influenced, at least to some extent, by local factors, and highlights the benefit of using multi-proxy data in Holocene climate reconstructions. While pollen-based temperatures follow the classical trend of gradually increasing early Holocene Tjul with a mid-Holocene maximum July warming, the aquatic/wetland assemblages reconstruct higher than present Tjul already during the early Holocene, i.e. at the peak of summer insolation. We conclude that the relatively low early Holocene July temperatures recorded by the terrestrial pollen are the result of site-specific factors possibly combined with a delayed response of the terrestrial ecosystem compared to the aquatic ecosystem.

  9. Multiproxy evidence of Holocene climate variability from estuarine sediments, eastern North America

    USGS Publications Warehouse

    Cronin, T. M.; Thunell, R.; Dwyer, G.S.; Saenger, C.; Mann, M.E.; Vann, C.; Seal, R.R.

    2005-01-01

    We reconstructed paleoclimate patterns from oxygen and carbon isotope records from the fossil estuarine benthic foraminifera Elphidium and Mg/ Ca ratios from the ostracode Loxoconcha from sediment cores from Chesapeake Bay to examine the Holocene evolution of North Atlantic Oscillation (NAO)-type climate variability. Precipitation-driven river discharge and regional temperature variability are the primary influences on Chesapeake Bay salinity and water temperature, respectively. We first calibrated modern ??18 Owater to salinity and applied this relationship to calculate trends in paleosalinity from the ??18 Oforam, correcting for changes in water temperature estimated from ostracode Mg /Ca ratios. The results indicate a much drier early Holocene in which mean paleosalinity was ???28 ppt in the northern bay, falling ???25% to ???20 ppt during the late Holocene. Early Holocene Mg/Ca-derived temperatures varied in a relatively narrow range of 13?? to 16??C with a mean temperature of 14.2??C and excursions above 16??C; the late Holocene was on average cooler (mean temperature of 12.8??C). In addition to the large contrast between early and late Holocene regional climate conditions, multidecadal (20-40 years) salinity and temperature variability is an inherent part of the region's climate during both the early and late Holocene, including the Medieval Warm Period and Little Ice Age. These patterns are similar to those observed during the twentieth century caused by NAO-related processes. Comparison of the midlatitude Chesapeake Bay salinity record with tropical climate records of Intertropical Convergence Zone fluctuations inferred from the Cariaco Basin titanium record suggests an anticorrelation between precipitation in the two regions at both millennial and centennial timescales. Copyright 2005 by the American Geophysical Union.

  10. Lateglacial and early Holocene climates of the Atlantic margins of Europe: Stable isotope, mollusc and pollen records from Orkney, Scotland

    NASA Astrophysics Data System (ADS)

    Whittington, Graeme; Edwards, Kevin J.; Zanchetta, Giovanni; Keen, David H.; Bunting, M. Jane; Fallick, Anthony E.; Bryant, Charlotte L.

    2015-08-01

    The margins of mainland Europe, and especially those areas coming under the influence of North Atlantic weather systems, are ideally placed to record changing palaeoclimates. Cores from an infilled lake basin at Crudale Meadow in Mainland, Orkney, revealed basal deposits of calcareous mud ('marl') beneath sedge peat. Stable isotope, palynological and molluscan analyses allowed the establishment of palaeoenvironmental changes through the Devensian Lateglacial and the early Holocene. The δ18Omarl record exhibited the existence of possibly four climatic oscillations in the Lateglacial (one of which, within event cf. GI-1c, is not often commented upon), as well as the Preboreal Oscillation and other Holocene perturbations. The cold episodes succeeding the Preboreal Oscillation were demarcated conservatively and one of these (event C5, ∼11.0 ka) may have previously been unremarked, while the putative 9.3 and 8.2 ka events seem not to produce corresponding palynologically visible floristic changes. The events at Crudale Meadow are consistent with those recorded at other sites from Britain, Ireland and elsewhere, and can be correlated with isotopic changes shown by the Greenland ice cores. The multi-proxy approach enriches the environmental reconstructions from the site, although the synchronicity of the response of the various proxies is sometimes equivocal, depending upon the time period concerned, taphonomy, and the nature of the deposits. The site may contain the most northerly Lateglacial isotope record from northwest Europe, and it has yielded one of the best archives for the demonstration of abrupt early Holocene events within Britain.

  11. Influence of Holocene stratigraphic architecture on ground surface settlements: A case study from the City of Pisa (Tuscany, Italy)

    NASA Astrophysics Data System (ADS)

    Sarti, Giovanni; Rossi, Veronica; Amorosi, Alessandro

    2012-12-01

    The Holocene stratigraphic architecture of modern coastal and deltaic plains has peculiar characteristics that may influence ground surface settlements. In the Pisa urban area, the inhomogeneous spatial distribution of geotechnically weak layers, typically formed during the mid-late Holocene (highstand) coastal progradation, is inferred to be responsible for urban ground settlement and building damage, as evidenced by the tilt of several surface structures, among which the famous Leaning Tower of Pisa is the most prominent. On the basis of integrated stratigraphic, sedimentological and geotechnical data from a wide georeferenced database, three facies associations with high deformability potential (Units 1-3) are identified in the uppermost 30 m as opposed to depositional facies (Units 4-5) with higher geotechnical strength. Whereas Unit 1 represents a thick, laterally extensive lagoonal clay deposit, the overlying highly deformable units (Units 2-3) show more discontinuous spatial distribution controlled by the Holocene paleohydrographic evolution of the Arno coastal plain. Unit 2, dated between the Neolithic and the Etruscan age (ca. 5000-2000 yr BP), is composed of swamp clays and silty clays recording lagoon infilling due to Arno Delta progradation. Units 3 and 4, which consist of wet levee deposits and stiff floodplain clays, respectively, formed during the subsequent phases of alluvial plain construction started around the Roman age (from ca. 2000 yr BP). Whereas Units 3 and 4 are recorded within the uppermost 5 m, fluvial and distributary channel sands (Unit 5) cut the underlying deltaic-alluvial succession at various stratigraphic levels, down to Unit 1. The spatial distribution of these units gives rise to three, locally juxtaposed, stratigraphic motifs in Pisa underground, reflecting different potential risks for settlement under building loads. We show how lateral changes in stratigraphic architecture account for the irregular spatial distribution of

  12. A new model evaluating Holocene sediment dynamics: Insights from a mixed carbonate-siliciclastic lagoon (Bora Bora, Society Islands, French Polynesia, South Pacific)

    NASA Astrophysics Data System (ADS)

    Isaack, Anja; Gischler, Eberhard; Hudson, J. Harold; Anselmetti, Flavio S.; Lohner, Andreas; Vogel, Hendrik; Garbode, Eva; Camoin, Gilbert F.

    2016-08-01

    found in the lagoon of nearby Tahaa, which are supposed to be induced by elevated cyclone activity. Correspondingly, enhanced erosion and run-off from the volcanic hinterland as well as lower lagoonal salinity would be associated with intense rainfall during repeated cyclone landfall. Increased amounts of coarse-grained sediment from marginal reef areas would be transported into the lagoon. However, Ti/Ca and Fe/Ca ratios as proxies for terrigenous sediment delivery have incessantly declined since the mid-Holocene. Also, benthic foraminiferal faunas do not validate reef-to-lagoon transport of sediment. Alternatively, the apparent onset of higher hydrodynamic energy conditions can be explained by more permanent southeast trade winds and higher-than-present sea level, which are supposed for the mid-late Holocene in the south Pacific. Sustained winds would have flushed higher amounts of open ocean water into the lagoon enhancing primary productivity and the amount of pelagic organisms within the lagoon while lowering lagoonal salinity. We propose the shift towards coarser-grained sedimentation patterns during the mid-late Holocene to reflect sediment-load shedding of sand aprons due to oversteepening of slopes at sand apron/lagoon edges during times of stronger trades and higher-than-present sea level of the Highstand Systems Tract, which led to redeposition of sediment even within the lagoon center. Modern conditions including a sea-level fall to modern level were reached ca. 1000 years BP, and lagoonal infill has been determined to a large part by fine-grained carbonate-dominated sediments produced within the lagoon and derived from the marignal reef. Infill of lagoonal accommodation space via sand aprons is estimated to be up to six times higher than infill by lagoonal background sedimentation and emphasizes the importance of the progradation of sand aprons. Contrary to the commonly supposed assumption that coarse-grained sediment layers within fine-grained lagoonal

  13. A new model evaluating Holocene sediment dynamics: Insights from a mixed carbonate-siliciclastic lagoon (Bora Bora, Society Islands, French Polynesia, South Pacific)

    NASA Astrophysics Data System (ADS)

    Isaack, Anja; Gischler, Eberhard; Hudson, J. Harold; Anselmetti, Flavio S.; Lohner, Andreas; Vogel, Hendrik; Garbode, Eva; Camoin, Gilbert F.

    2016-08-01

    deposits found in the lagoon of nearby Tahaa, which are supposed to be induced by elevated cyclone activity. Correspondingly, enhanced erosion and run-off from the volcanic hinterland as well as lower lagoonal salinity would be associated with intense rainfall during repeated cyclone landfall. Increased amounts of coarse-grained sediment from marginal reef areas would be transported into the lagoon. However, Ti/Ca and Fe/Ca ratios as proxies for terrigenous sediment delivery have incessantly declined since the mid-Holocene. Also, benthic foraminiferal faunas do not validate reef-to-lagoon transport of sediment. Alternatively, the apparent onset of higher hydrodynamic energy conditions can be explained by more permanent southeast trade winds and higher-than-present sea level, which are supposed for the mid-late Holocene in the south Pacific. Sustained winds would have flushed higher amounts of open ocean water into the lagoon enhancing primary productivity and the amount of pelagic organisms within the lagoon while lowering lagoonal salinity. We propose the shift towards coarser-grained sedimentation patterns during the mid-late Holocene to reflect sediment-load shedding of sand aprons due to oversteepening of slopes at sand apron/lagoon edges during times of stronger trades and higher-than-present sea level of the Highstand Systems Tract, which led to redeposition of sediment even within the lagoon center. Modern conditions including a sea-level fall to modern level were reached ca. 1000 years BP, and lagoonal infill has been determined to a large part by fine-grained carbonate-dominated sediments produced within the lagoon and derived from the marignal reef. Infill of lagoonal accommodation space via sand aprons is estimated to be up to six times higher than infill by lagoonal background sedimentation and emphasizes the importance of the progradation of sand aprons. Contrary to the commonly supposed assumption that coarse-grained sediment layers within fine

  14. CHRONOLOGICAL CONSTRAINTS ON FLUID CIRCULATION IN MESOZOIC FORMATIONS OF THE EASTERN PART OF THE PARIS BASIN INFERRED FROM U-Pb DATING OF SECONDARY INFILLING CARBONATES

    NASA Astrophysics Data System (ADS)

    Pisapia, C.; Deschamps, P.; Hamelin, B.; Buschaert, S.

    2009-12-01

    The French agency for nuclear waste management (ANDRA) developed an Underground Research Laboratory in the Mesozoic formations of Eastern part of the Paris Basin (France) to assess the feasibility of a high-level radioactive wastes repository in sedimentary formations. The target host formation is a low-porosity detrital argillite (Callovo-Oxfordian) embedded between two shelf limestones formations (of Bajocian-Bathonian and Oxfordian-Kimmeridgian ages). These formations are affected by fracture networks, likely inherited mainly from the Eocene-Oligocene extension tectonics, also responsible of the Rhine graben formation in the same region. The limestones have very low permeability, the primary and secondary porosity being infilled by secondary carbonated minerals. The inter-particle porosity is filled with euhedral calcite spar cements. Similarly, macro-cavities and connected micro-fractures are almost sealed by euhedral calcite. Geochemical evidences (δ18O) suggest that the secondary carbonates likely derived from a common parent fluid (Buschaert et al., 2004, Appl. Geochem. (19) 1201-1215p). This late carbonated precipitation phase is responsible for the intense cementation of the limestone formations and bears witness of a major phase of fluids circulation that marked the late diagenetic evolution of the system. Knowledge of the chronology of the different precipitation phases of secondary minerals is thus of critical importance in order to determine the past hydrological conditions of the geological site. The aim of this study is to provide chronological constraints on the secondary carbonate mineral precipitation using U/Th and U/Pb methods. Analyses are performed on millimeter to centimeter scale secondary calcites collected within fractures outcropping in the regional fault zone of Gondrecourt and in cores from the ANDRA exploration-drilling program. Preliminary U-Th analyses obtained on secondary carbonates from surface fractures infillings yield secular

  15. Human impact and Holocene climatic change in the archaeological site 'Piani della Corona

    NASA Astrophysics Data System (ADS)

    Pelle, Teresa; Scarciglia, Fabio; La Russa, Mauro F.; Natali, Elena; Tinè, Vincenzo

    2010-05-01

    A pedoarchaeological study was carried out in the archaeological site "Piani della Corona", located on a wide terrace at 500 m a.s.l. along the southwestern coast of Calabria, in southern Italy. The archaeological excavations exhumed an extensive settlement related to old to medium Bronze Age phases and traces of late Neolithic human colonization. On the basis of archaeological finds the pedostratigraphic succession can be partly dated. It consists of soils with variable features and andic properties, which include yellowish-brown (in places more reddish), deep argillic (Bt) horizons with variable amounts of clay coatings in pores and dark brown infillings of soil material rich in organic matter, in places overlaid by thin, severely truncated, brown to dark brown, organic-mineral (A) horizons. These layers include late Neolithic ceramic artefacts (Diana style facies) and typical incineration burials found in biconical vases, that can be referred to 6500-5000 years BP. The prehistoric layers are widely overlaid and strongly superimposed by a paleosurface of the early to medium Bronze age. This surface is affected by many pole holes left by large rectangular, apsidal wooden huts (not preserved), ploughed furrows, excavated cisterns, ditches and trenches, often filled by organic-rich dark brown material. Also hearths with charcoal remains, burials, vases and other diagnostic ceramic fragments occur. The upper portion of the pedostratigraphic succession consists of thicker brown A horizons, that appear cyclically ploughed during historical times (archaeologically not well dated as a consequence of their reworking for agricultural practices), with abrupt irregular boundaries often entering the underlying horizons. Micromorphological observations confirmed the presence of clay coatings within pores of Bt horizons, showing that they represent relict features (i.e. related to inactive illuvial processes, at present), as often fragmented and with smooth-banded to grainy

  16. Holocene climate less stable than previously thought

    NASA Astrophysics Data System (ADS)

    deMenocal, Peter; Bond, Gerard

    Until recently, Holocene climate was thought to be extremely stable with none of the abrupt variations that characterize the cold climates of glacial times [Dansgaard et al., 1993]. New terrestrial, marine, and ice core data, however, document abrupt changes during the warm interglacial climate of the last 12,000 years. These newly developed Holocene paleoclimate records indicate that the Holocene was punctuated by a series of millennial-scale (1000-2000 year) cooling events, the most recent of which was the Little Ice Age (LIA) between approximately 1500 and 1800 A.D. Historical evidence indicates that the estimated ˜1°-2°C LIA ooling was ufficient to choke European ports with sea ice, freeze European rivers (as graphically recorded in the 1565 painting “Winter Landscape” by Pieter Bruegel), force abandonment of Viking colonies in Greenland, and cause glaciers to overrun alpine villages [Bradley and Jones, 1995]. Although these Holocene cooling events were not as large as the well-known glacial Heinrich events and Dansgaard-Oeschger climate instabilities [Bond et al., 1996; Dansgaard et al., 1993], they nonetheless document dramatic climate swings during the “climatically stable” Holocene.

  17. Tracking Nile Delta vulnerability to Holocene change.

    PubMed

    Marriner, Nick; Flaux, Clément; Morhange, Christophe; Stanley, Jean-Daniel

    2013-01-01

    Understanding deltaic resilience in the face of Holocene climate change and human impacts is an important challenge for the earth sciences in characterizing the full range of present and future wetland responses to global warming. Here, we report an 8000-year mass balance record from the Nile Delta to reconstruct when and how this sedimentary basin has responded to past hydrological shifts. In a global Holocene context, the long-term decrease in Nile Delta accretion rates is consistent with insolation-driven changes in the 'monsoon pacemaker', attested throughout the mid-latitude tropics. Following the early to mid-Holocene growth of the Nile's deltaic plain, sediment losses and pronounced erosion are first recorded after ~4000 years ago, the corollaries of falling sediment supply and an intensification of anthropogenic impacts from the Pharaonic period onwards. Against the backcloth of the Saharan 'depeopling', reduced river flow underpinned by a weakening of monsoonal precipitation appears to have been particularly conducive to the expansion of human activities on the delta by exposing productive floodplain lands for occupation and irrigation agriculture. The reconstruction suggests that the Nile Delta has a particularly long history of vulnerability to extreme events (e.g. floods and storms) and sea-level rise, although the present sediment-starved system does not have a direct Holocene analogue. This study highlights the importance of the world's deltas as sensitive archives to investigate Holocene geosystem responses to climate change, risks and hazards, and societal interaction.

  18. Vegetation and carbon cycle dynamics in Holocene

    NASA Astrophysics Data System (ADS)

    Rachmayani, R.; Prange, M.; Schulz, M.

    2009-04-01

    Holocene climate has been relatively well investigated with global climate models. Ruddiman suggested that the growth of atmospheric carbon dioxide during the Holocene recorded in the Taylor Dome ice core is a result of profound human impact on climate due to slash-and-burn agricultural practice during the Neolithic period. A series of numerical time slice experiments using the comprehensive global climate model CCSM3 (Community Climate System Model, version 3) has been carried out to study orbitally driven climate variability during the Holocene. The importance of biogeophysical feedbacks between vegetation and climate as well as the role of terrestrial carbon storage in atmospheric carbon dioxide dynamics will be analyzed. The results will be compared to other climate models in order to address some aspects of the Ruddiman hypothesis on exceptional long-term atmospheric carbon dioxide increase during the Holocene. To this end, the land model component of CCSM3 has been improved. The improvements lead to a better simulation of global forest cover and net primary production. Key words Climate, CCSM3, Holocene, Vegetation

  19. Sensitivity of northern peatland carbon dynamics to Holocene climate change

    NASA Astrophysics Data System (ADS)

    Yu, Zicheng; Beilman, David W.; Jones, Miriam C.

    In this paper, we evaluate the long-term climate sensitivity and global carbon (C) cycle implications of northern peatland C dynamics by synthesizing available data and providing a conceptual framework for understanding the dominant controls, processes, and interactions of peatland initiation and C accumulation. Northern peatlands are distributed throughout the climate domain of the boreal forest/taiga biome, but important differences between peatland regions are evident in annual temperature vs. precipitation (T-P) space, suggesting complex hydroclimatic controls through various seasonal thermal-moisture associations. Of 2380 available basal peat dates from northern peatlands, nearly half show initiation before 8000 calendar years (cal years) B.P. Peat-core data from sites spanning peatland T-P space show large variations in apparent C accumulation rates during the Holocene, ranging from 8.4 in the Arctic to 38.0 g C m-2 a-1 in west Siberia, with an overall time-weighted average rate of 18.6 g C m-2 a-1. Sites with multiple age determinations show millennial-scale variations, with the highest C accumulation generally at 11,000-8000 cal years B.P. The early Holocene was likely a period of rapid peatland expansion and C accumulation. For example, maximum peat expansion and accumulation in Alaska occurred at this time when climate was warmest and possibly driest, suggesting the dominant role of productivity over decomposition processes or a difference in precipitation seasonality. Northern peatland C dynamics contributed to the peak in atmospheric CH4 and the decrease in CO2 concentrations in the early Holocene. This synthesis of data, processes, and ideas provides baselines for understanding the sensitivity of these C-rich ecosystems in a changing climate.

  20. The effect of Holocene changes in relative sea level on the morphology of rocky coasts

    NASA Astrophysics Data System (ADS)

    Trenhaile, Alan S.

    2010-01-01

    A mathematical wave and weathering model was used to study the effect of Holocene changes in relative sea level (RSL) on rock coast development. Model runs were made for fast- and slow-eroding coasts in macro- and mesotidal environments using Holocene RSL records from Sweden, northeastern USA, southwestern Britain, central Japan, western Africa, and southern Australia. A further series of otherwise identical runs were made with constant sea level. Changes in RSL determined the amount of time that marine processes have operated within the modern intertidal zone, and rates of wave attenuation and erosion continue to be influenced by subtidal morphology that developed in most areas when RSL was rising to its present level. The model suggested that although tidal range is also important, Holocene RSL changes promoted subhorizontal platform development in Australasia and over much of the Southern Hemisphere, and sloping platforms over much of the Northern Hemisphere. Shore platforms may have been partly inherited from earlier periods in the Holocene, when RSL was similar to today's. Nevertheless, most platforms continue to be eroded at all tidal levels. Where geological and wave conditions are less favourable, erosion in the lower intertidal zone has essentially terminated in areas where RSL rose to its present position, whereas erosion only occurs today in the lower intertidal zone in places where RSL rose to above its present level in the middle Holocene.

  1. The impact of climate changes during the Holocene on vegetation in northern French Guiana

    NASA Astrophysics Data System (ADS)

    Freycon, Vincent; Krencker, Marion; Schwartz, Dominique; Nasi, Robert; Bonal, Damien

    2010-03-01

    The impact of climatic changes that occurred during the last glacial maximum and the Holocene on vegetation changes in the Amazon Basin and the Guiana Shield are still widely debated. The aim of our study was to investigate whether major changes in vegetation (i.e. transitions between rainforests and C 4 savannas) occurred in northern French Guiana during the Holocene. We measured variations in the δ 13C of soil organic matter at eight sites now occupied by forest or savannah. The forest sites were selected to cover two regions (forest refugia and peneplains) which are thought to have experienced different intensities of disturbance during the latest Pleistocene and the Holocene. We found that none of the forest sites underwent major disturbances during the Holocene, i.e. they were not replaced by C 4 savannahs or C 4 forest savannahs for long periods. Our results thus suggest that tropical rainforests in northern French Guiana were resilient to drier climatic conditions during the Holocene. Nevertheless, geographical and vertical variations in the 13C of SOM were compatible with minor changes in vegetation, variations in soil processes or in soil physical properties.

  2. Earliest Holocene south Greenland ice sheet retreat within its late Holocene extent

    NASA Astrophysics Data System (ADS)

    Carlson, Anders E.; Winsor, Kelsey; Ullman, David J.; Brook, Edward J.; Rood, Dylan H.; Axford, Yarrow; LeGrande, Allegra N.; Anslow, Faron S.; Sinclair, Gaylen

    2014-08-01

    Early Holocene summer warmth drove dramatic Greenland ice sheet (GIS) retreat. Subsequent insolation-driven cooling caused GIS margin readvance to late Holocene maxima, from which ice margins are now retreating. We use 10Be surface exposure ages from four locations between 69.4°N and 61.2°N to date when in the early Holocene south to west GIS margins retreated to within these late Holocene maximum extents. We find that this occurred at 11.1 ± 0.2 ka to 10.6 ± 0.5 ka in south Greenland, significantly earlier than previous estimates, and 6.8 ± 0.1 ka to 7.9 ± 0.1 ka in southwest to west Greenland, consistent with existing 10Be ages. At least in south Greenland, these 10Be ages likely provide a minimum constraint for when on a multicentury timescale summer temperatures after the last deglaciation warmed above late Holocene temperatures in the early Holocene. Current south Greenland ice margin retreat suggests that south Greenland may have now warmed to or above earliest Holocene summer temperatures.

  3. Towards a mechanical failure model for degrading permafrost rock slopes representing changes in rock toughness and infill

    NASA Astrophysics Data System (ADS)

    Mamot, Philipp; Krautblatter, Michael; Scandroglio, Riccardo

    2016-04-01

    The climate-induced degradation of permafrost in mountain areas can reduce the stability of rock slopes. An increasing number of rockfalls and rockslides originate from permafrost-affected rock faces. Discontinuity patterns and their geometrical and mechanical properties play a decisive role in controlling rock slope stability. Under thawing conditions the shear resistance of rock reduces due to lower friction along rock-rock contacts, decreasing fracture toughness of rock-ice contacts, diminishing fracture toughness of cohesive rock bridges and altered creep or fracture of the ice itself. Compressive strength is reduced by 20 to 50 % and tensile strength decreases by 15 to 70 % when intact saturated rock thaws (KRAUTBLATTER ET AL. 2013). Elevated water pressures in fractures can lead to reduced effective normal stresses and thus to lower shear strengths of fractures. However, the impact of degrading permafrost on the mechanical properties of intact or fractured rock still remains poorly understood. In this study, we develop a new approach for modeling the influence of degrading permafrost on the stability of high mountain rock slopes. Hereby, we focus on the effect of rock- and ice-mechanical changes along striking discontinuities onto the whole rock slope. We aim at contributing to a better rock-ice mechanical process understanding of degrading permafrost rocks. For parametrisation and subsequent calibration of our model, we chose a test site (2885 m a.s.l.) close by the Zugspitze summit in Germany. It reveals i) a potential rockslide at the south face involving 10E4m³ of rock and ii) permafrost occurrence due to ice-filled caves and fractures. Here we combine kinematic, geotechnical and thermal monitoring in the field with rock-mechanical laboratory tests and a 2D numerical failure modeling. Up to date, the following results underline the potential effects of thawing rock and fracture infill on the stability of steep rock slopes in theory and praxis: i. ERT and

  4. Amateur football pitches: mechanical properties of the natural ground and of different artificial turf infills and their biomechanical implications.

    PubMed

    Zanetti, Elisabetta M; Bignardi, Cristina; Franceschini, Giordano; Audenino, Alberto L

    2013-01-01

    Artificial turf is being used more and more often. It is more available than natural turf for use, requires much less maintenance and new products are able to comply with sport performance and athletes' safety. The purpose of this paper is to compare the mechanical and biomechanical responses of two different artificial turf infills (styrene butadiene rubber, from granulated vehicle tires, and thermoplastic rubber granules) and to compare them to the performance of natural fields where amateurs play (beaten earth, substantially). Three mechanical parameters have been calculated from laboratory tests: energy storage, energy losses and surface traction coefficient; results have been correlated with peak accelerations recorded on an instrumented athlete, on the field. The natural ground proved to be stiffer (-15% penetration depth for a given load), and to have a lower dynamic traction coefficient (-48%); the different kinds of infill showed significantly different stiffnesses (varying by more than 23%) and damping behaviour (varying by more than 31%). In running, peak vertical accelerations were lowest in the artificial ground with thermoplastic rubber granules, while, in slalom, both artificial grounds produced higher horizontal peak accelerations compared to the natural ground. Results are discussed in terms of their implications for athletic performance and injury risk. PMID:23230960

  5. Geomorphological evolution of Mediterranean enclosed depressions in the Late glacial and Holocene: The example of Canohès (Roussillon, SE France)

    NASA Astrophysics Data System (ADS)

    Carozza, Jean-Michel; Llubes, Muriel; Danu, Mihaela; Faure, Elodie; Carozza, Laurent; David, Mélodie; Manen, Claire

    2016-11-01

    The origin and evolution of the enclosed depressions (pans) of southern France during the period from the Late Glacial to the Holocene are discussed on the basis of new stratigraphical, geophysical and chronological (14C) data from the Canohès depression (Roussillon, Southern of France) and its nearby environment. The Canohès depression is non-karstic, excavated from Pliocene arkosic sands that were shaped by eolian erosion during cold stages of the Middle and Upper Pleistocene. The timing and controlling factors of eolian carving of the depression are discussed on the basis of geomorphological data, surrounding alluvial terrace chronology, preserved ledge within the depression and alluvial infill of the depression. Formation of the depression was controlled, locally, by climate variability and its consequences on vegetation and water table position and, regionally, by the sea base level. The enclosed depression probably started to form during MIS 6, reaching its maximum depth during MIS 2. Climate variability in the region is recorded in the depression's infill. The basal deposits are of fluvial origin and record the increase of moisture and temperature during the Early Late-Glacial. The first lacustrine deposits are observed during the Bölling/GI-1e stage, while continental sedimentation and drying occurred during the Alleröd and Younger Dryas stages. During the Early and Middle Holocene, lacustrine conditions prevailed, except during short periods of drying. The specific evolution of the Canohès depression as regards other such formations is discussed in light of regional deglaciation and climate chronology. A regional synthesis of eolian erosion is proposed.

  6. Cyclic steps in proglacial delta fronts: New insights from Upper Pleistocene-Holocene successions, St. Lawrence Estuary and Gulf, Québec, Canada

    NASA Astrophysics Data System (ADS)

    Dietrich, Pierre; Ghienne, Jean-François; Normandeau, Alexandre; Lajeunesse, Patrick

    2015-04-01

    Proglacial delta fronts in both present-day systems and in the sedimentary record frequently include sand-sized, upstream-migrating bedforms. Although several studies have recently monitored their sediment dynamics, their formative processes are still matter to debate. Here we report on two Pleistocene-Holocene proglacial deltaic successions located on the North Shore of the St. Lawrence Estuary and Gulf, Québec, Canada. Owing to a well-constrained pattern of glacio-isostatic rebound, these now-emerged successions are characterized by accurate palaeo-bathymetric reconstructions. In our case study, we describe backstepping (upstream-migrating) cross strata lying on delta foresets at shallow bathymetries ranging from 10 m to deeper part, reaching in places 50 m. Cross strata, interpreted as being deposited by Froude-supercritical cyclic steps, are characterized by steep mean dips (up to 13°) and short-wavelength (10-20 m) undulations. They form backstepping assemblages of massive to faintly laminated sand bounded on either side by downslope-dipping erosive surfaces on which strata onlap and are truncated upslope and downslope respectively. Graded sand beds, sheared flamed mud layers, matrix- to clasts-supported pebbles or sand intraclasts occasionally occur. In a first case study located in the St. Lawrence Estuary (Portneuf), cyclic steps are borne by gently-sloped (2-3°) foresets deposits at depositional depth less than 50 m. Related sand includes graded beds, thin (5-10 mm) muddy interbeds and terrestrial organic debris. In a second delta located in the Gulf of St. Lawrence (Moisie River), backstepping, faintly laminated gravelly sand beds are directly overlain by pebbly topsets constituted by the subaqueous termination of a sandur. They are in addition either sharply truncated or are passing gradually downslope to regular, steep-sloped gilbert-like delta foresets. Scour infills with backsets are commonly associated with these strata that were deposited at very

  7. Estuarine fluvial floodplain formation in the Holocene Lower Tagus valley (Central Portugal) and implications for Quaternary fluvial system evolution

    NASA Astrophysics Data System (ADS)

    van der Schriek, Tim; Passmore, David G.; Rolão, Jose; Stevenson, Anthony C.

    2007-11-01

    We present a brief synthesis of the Quaternary fluvial record in the Lower Tagus Basin (central Portugal), concentrating on factors controlling infill and incision. The Holocene part of the record forms the focus of this paper and guides the questioning of the basic assumptions of the established Quaternary fluvial evolution model, in particular the link between sea-level change and fluvial incision-deposition. We suggest that several incision-aggradation phases may have occurred during glacial periods. Major aggradation events may overlap with cold episodes, while incision appears to concentrate on the warming limb of climate transitions. The complex stratigraphy of the Quaternary record in the Lower Tagus valley is influenced by repeated base-level and climate changes. This paper submits the first chronostratigraphic framework for valley fill deposits in the Lower Tagus area. Sea-level rise forced aggradation and controlled deposition of the fine-grained sedimentary wedge underlying the low-gradient Lower Tagus floodplain. Investigations have focused on the lower Muge tributary, where rapidly aggrading estuarine and fluvial environments were abruptly established (∼8150 cal BP) as sea level rose. Base level at the valley mouth controlled the upstream extent of the fine-grained backfill. Tidal environments disappeared abruptly (∼5800 cal BP) when the open estuary at the Muge confluence was infilled by the Tagus River. The decrease and final still stand of sea-level rise led to floodplain stabilisation with peat (∼6400-5200 cal BP) and soil formation (∼5200-2200 cal BP). Localised renewed sedimentation (∼2200-200 cal BP) is linked to human activity.

  8. Early Holocene lake ecosystem development in the southern Baltic lowlands

    NASA Astrophysics Data System (ADS)

    Słowiński, Michał; Ott, Florian; Kramkowski, Mateusz; Noryśkiewicz, Agnieszka M.; Zawiska, Izabela; Dräger, Nadine; Theuerkauf, Martin; Hass, Christoph; Obremska, Milena; Błaszkiewicz, Mirosław; Kordowski, Jarosław; Tjallingii, Rik; Rzodkiewicz, Monika; Schwab, Markus; Brauer, Achim

    2016-04-01

    The first millennia of the Holocene are characterized by gradual and rapid environmental changes following the warming at the beginning of the Holocene superimposed by short-term climatic instability. Landscape evolution during this period occurred at different time scales due to specific response times of landscape compartments like vegetation succession, soil formation and permafrost thawing. As a consequence, a spatiotemporally heterogeneous pattern of changes occurred particularly in regions close to the margins of the continental ice sheets like the Baltic region. Regional atmospheric circulation patterns were affected by cold catabatic winds from the remains of the Fennoscandian ice sheet. The ongoing deglaciation further influenced the regional climate through meltwater release and related changes in the North Atlantic thermohaline circulation. Both effects declined with the progressive ice sheet melt down. Additionally, the land-sea distribution in the North Sea changed drastically during the final melting phase of the glacial ice sheets. The Baltic Sea development is even more complex due to the strong glacio-isostatic adjustments effects that resulted in open and closed water stages affecting the entire Baltic realm. Consequently, the early Holocene interval of sediment records from the southern Baltic lowlands are not considered as straightforward palaeoclimate archives but need to be interpreted in a broader context. We present five partly varved lake records from northern Poland all including an intriguing highly organic-rich interval interrupting biochemical calcite precipitation at about the same time between 10.5 and 10.2 cal kyr BP. These sediment records have been correlated by independent age models based on varve counting, AMS 14C dating, biostratigraphy and tephrochronology. We present multi-proxy records of early Holocene sediments and our preliminary interpretation suggests hydrological processes as the main reason for the intriguing shifts

  9. Holocene sedimentary environments in Smeerenburgfjorden, Spitsbergen

    NASA Astrophysics Data System (ADS)

    Heggdal Velle, Julie; Forwick, Matthias; Hass, H. Christian; Sverre Laberg, Jan; Vorren, Tore O.; Nielsen, Tove; Solheim, Anders

    2013-04-01

    Multi-proxy analyses of six sediment cores and analyses of swath bathymetry and chirp data were integrated to elucidate the Holocene sedimentary processes and palaeoenvironments in Smeerenburgfjorden, northwest Spitsbergen. Three basins separated by two sills define the present-day large-scale bathymetry. A transverse ridge in the innermost part of the fjord represents the Little Ice Age (LIA) maximum position of Smeerenburgbreen. Slide scars along the fjord sides and mass transport deposits in the basins indicate repeated mass wasting. Recessional moraines deposited during the last deglaciation suggest a mean annual retreat rate of 140 m/year. Another set of recessional moraines deposited between the maximum LIA position of Smeerenburgbreen and its present day terminus indicate a mean retreat rate of the ice front of ~87 m/year. Strong out-fjord decreasing trends in magnetic susceptibility and Fe-content indicate that these properties are related to material originating from the Hornemantoppen granite in the catchment of Smeerenburgbreen and are, thus, useful proxies for the reconstruction of the activity of the glacier. Relatively little ice rafting, most likely related to warmer surface water conditions, occurred between 8650 and 7350 cal. years BP. Ice rafting from both sea-ice and icebergs increased around 6200 cal. years BP and peaked at ~5200 cal. years BP, associated with a regional cooling. Smeerenburgbreen became more active around 2000 cal. years BP. It probably retreated during the Roman Warm Period (50 BC - AD 400) and advanced during the Dark Ages Cold Period (AD 400 - 800). From AD 1300 - 1500 (late Medieval Warm Period), ice rafting, sedimentation rates and productivity increased in the inner fjord. The Little Ice Age was characterised by reduced ice rafting, possibly linked to an increased sea-ice cover suppressing iceberg drift. An increase in Ice Rafted Debris (IRD) commencing around AD 1880 is suggested to represent the beginning of

  10. Holocene coastal paleoenvironmental record, Bay of Brest

    NASA Astrophysics Data System (ADS)

    Fernane, Assia; Gandouin, Emmanuel; Goslin, Jérôme; Penaud, Aurélie; Van Vliet lanoë, Brigitte

    2013-04-01

    Coastal areas are sensitive environments regarding the risk of submersion and the impact on biodiversity induced by salinity changes. These areas thus provide good palaeocecological archives to monitor palaeo sea level changes and the associated adaptation of different biological communities. The north-western coast of France has poorly been investigated regarding its Holocene palaeoecological signatures (Morzadec-Kerfourn, 1974; Naughton et al., 2007). Chironomids have been recognized to be an efficient tool for palaeoclimate and palaeosalinity reconstructions in lakes (Brooks, 2006), and more recently in river floodplains (Gandouin et al, 2006). In this study, environmental changes related to both climate processes and human disturbances, were reconstructed over the last 5000 years, based on pollen and chironomid assemblages from two coastal cores retrieved at Pors Milin (Brittany, NW France). The sedimentary sequences consist of terrestrial peaty layers interdigited with marine clastic deposits. The study area is composed by a sandy beach, truncating the peat, limited by a high sandy bar, and a back marsh developed at + 4 m NGF. Pollen and chironomid results reveal that anthropogenic factors would mainly control environmental changes that occurred in this sector. The disappearance of many chironomid taxa (inhabitants of main river channel) and the dramatic fall in diversity may have been induced by the development of the Merovingian forest clearance at Pors Milin. Indeed, we suggest that the development of agriculture, the river embankment and the draining of wetlands may explain the chironomid habitat loss and the subsequent fall of biodiversity. This change in faunal assemblages occurred synchronously with a decrease in the "arborean / non arborean" pollen ratio reflecting the land opening of the watershed. Several nitrophilous and anthropogenic pollen taxa reinforce our hypothesis concerning the development of agricultural and livestock farming activities at

  11. Holocene glacier history from alpine speleothems, Milchbach cave, Switzerland

    NASA Astrophysics Data System (ADS)

    Luetscher, M.; Hoffmann, D. L.; Frisia, S.; Spötl, C.

    2011-02-01

    Mountain glaciers and their sediments are prominent witnesses of climate change, responding sensitively to even small modifications in meteorological parameters. Even in such a classical and thoroughly studied area as the European Alps the record of Holocene glacier mass-balance is only incompletely known. Here we explore a novel and continuous archive of glacier fluctuations in a cave system adjacent to the Upper Grindelwald Glacier in the Swiss Alps. Milchbach cave became partly ice-free only recently and hosts Holocene speleothems. Four coeval stalagmites show consistent petrographic and stable isotopic changes between 9.2 and 2.0 ka which can be tied to abrupt modifications in the cave environment as a result of the closing and opening of multiple cave entrances by the waxing and waning of the nearby glacier. During periods of Holocene glacier advances, columnar calcite fabric is characterized by δ18O values of about -8.0‰ indicative of speleothem growth under quasi-equilibrium conditions, i.e. little affected by kinetic effect related to forced degassing or biological processes. In contrast, fabrics formed during periods of glacier minima are typical of bacterially mediated calcite precipitation within caves overlain by an alpine soil cover. Moreover, δ18O values of the bacterially mediated calcite fabrics are consistent with a ventilated cave system fostering kinetic fractionation. These data suggest that glacier retreats occurred repeatedly before 5.8 ka, and that the amplitudes of glacier retreats became substantially smaller afterwards. Our reconstruction of the Upper Grindelwald Glacier fluctuations agrees well with paleoglaciological studies from other sites in the Alps and provides a higher temporal resolution compared to traditional analyses of peat and wood remains found in glacier forefields.

  12. Holocene climate change in Arctic Canada and Greenland

    NASA Astrophysics Data System (ADS)

    Briner, Jason P.; McKay, Nicholas P.; Axford, Yarrow; Bennike, Ole; Bradley, Raymond S.; de Vernal, Anne; Fisher, David; Francus, Pierre; Fréchette, Bianca; Gajewski, Konrad; Jennings, Anne; Kaufman, Darrell S.; Miller, Gifford; Rouston, Cody; Wagner, Bernd

    2016-09-01

    This synthesis paper summarizes published proxy climate evidence showing the spatial and temporal pattern of climate change through the Holocene in Arctic Canada and Greenland. Our synthesis includes 47 records from a recently published database of highly resolved Holocene paleoclimate time series from the Arctic (Sundqvist et al., 2014). We analyze the temperature histories represented by the database and compare them with paleoclimate and environmental information from 54 additional published records, mostly from datasets that did not fit the selection criteria for the Arctic Holocene database. Combined, we review evidence from a variety of proxy archives including glaciers (ice cores and glacial geomorphology), lake sediments, peat sequences, and coastal and deep-marine sediments. The temperature-sensitive records indicate more consistent and earlier Holocene warmth in the north and east, and a more diffuse and later Holocene thermal maximum in the south and west. Principal components analysis reveals two dominant Holocene trends, one with early Holocene warmth followed by cooling in the middle Holocene, the other with a broader period of warmth in the middle Holocene followed by cooling in the late Holocene. The temperature decrease from the warmest to the coolest portions of the Holocene is 3.0 ± 1.0 °C on average (n = 11 sites). The Greenland Ice Sheet retracted to its minimum extent between 5 and 3 ka, consistent with many sites from around Greenland depicting a switch from warm to cool conditions around that time. The spatial pattern of temperature change through the Holocene was likely driven by the decrease in northern latitude summer insolation through the Holocene, the varied influence of waning ice sheets in the early Holocene, and the variable influx of Atlantic Water into the study region.

  13. The ghosts of mammals past: biological and geographical patterns of global mammalian extinction across the Holocene

    PubMed Central

    Turvey, Samuel T.; Fritz, Susanne A.

    2011-01-01

    Although the recent historical period is usually treated as a temporal base-line for understanding patterns of mammal extinction, mammalian biodiversity loss has also taken place throughout the Late Quaternary. We explore the spatial, taxonomic and phylogenetic patterns of 241 mammal species extinctions known to have occurred during the Holocene up to the present day. To assess whether our understanding of mammalian threat processes has been affected by excluding these taxa, we incorporate extinct species data into analyses of the impact of body mass on extinction risk. We find that Holocene extinctions have been phylogenetically and spatially concentrated in specific taxa and geographical regions, which are often not congruent with those disproportionately at risk today. Large-bodied mammals have also been more extinction-prone in most geographical regions across the Holocene. Our data support the extinction filter hypothesis, whereby regional faunas from which susceptible species have already become extinct now appear less threatened; they may also suggest that different processes are responsible for driving past and present extinctions. We also find overall incompleteness and inter-regional biases in extinction data from the recent fossil record. Although direct use of fossil data in future projections of extinction risk is therefore not straightforward, insights into extinction processes from the Holocene record are still useful in understanding mammalian threat. PMID:21807737

  14. The ghosts of mammals past: biological and geographical patterns of global mammalian extinction across the Holocene.

    PubMed

    Turvey, Samuel T; Fritz, Susanne A

    2011-09-12

    Although the recent historical period is usually treated as a temporal base-line for understanding patterns of mammal extinction, mammalian biodiversity loss has also taken place throughout the Late Quaternary. We explore the spatial, taxonomic and phylogenetic patterns of 241 mammal species extinctions known to have occurred during the Holocene up to the present day. To assess whether our understanding of mammalian threat processes has been affected by excluding these taxa, we incorporate extinct species data into analyses of the impact of body mass on extinction risk. We find that Holocene extinctions have been phylogenetically and spatially concentrated in specific taxa and geographical regions, which are often not congruent with those disproportionately at risk today. Large-bodied mammals have also been more extinction-prone in most geographical regions across the Holocene. Our data support the extinction filter hypothesis, whereby regional faunas from which susceptible species have already become extinct now appear less threatened; they may also suggest that different processes are responsible for driving past and present extinctions. We also find overall incompleteness and inter-regional biases in extinction data from the recent fossil record. Although direct use of fossil data in future projections of extinction risk is therefore not straightforward, insights into extinction processes from the Holocene record are still useful in understanding mammalian threat. PMID:21807737

  15. Tracking Nile Delta Vulnerability to Holocene Change

    PubMed Central

    Marriner, Nick; Flaux, Clément; Morhange, Christophe; Stanley, Jean-Daniel

    2013-01-01

    Understanding deltaic resilience in the face of Holocene climate change and human impacts is an important challenge for the earth sciences in characterizing the full range of present and future wetland responses to global warming. Here, we report an 8000-year mass balance record from the Nile Delta to reconstruct when and how this sedimentary basin has responded to past hydrological shifts. In a global Holocene context, the long-term decrease in Nile Delta accretion rates is consistent with insolation-driven changes in the ‘monsoon pacemaker’, attested throughout the mid-latitude tropics. Following the early to mid-Holocene growth of the Nile’s deltaic plain, sediment losses and pronounced erosion are first recorded after ~4000 years ago, the corollaries of falling sediment supply and an intensification of anthropogenic impacts from the Pharaonic period onwards. Against the backcloth of the Saharan ‘depeopling’, reduced river flow underpinned by a weakening of monsoonal precipitation appears to have been particularly conducive to the expansion of human activities on the delta by exposing productive floodplain lands for occupation and irrigation agriculture. The reconstruction suggests that the Nile Delta has a particularly long history of vulnerability to extreme events (e.g. floods and storms) and sea-level rise, although the present sediment-starved system does not have a direct Holocene analogue. This study highlights the importance of the world’s deltas as sensitive archives to investigate Holocene geosystem responses to climate change, risks and hazards, and societal interaction. PMID:23922692

  16. Regional flow in the Baltic Shield during Holocene coastal regression

    USGS Publications Warehouse

    Voss, Clifford I.; Andersson, Johan

    1993-01-01

    The occurrence of saline waters in the Baltic Shield in Sweden is consistent with ongoing but incomplete Holocene flushing and depends on the geometry and connectivity of conductive structures at both regional and local scales, and on the surface topography. Numerical simulation of regional variable-density fluid flow during Holocene land-rise and coastal regression shows that the existence of any old saline water, whether derived from submarine recharge in regions below Sweden's highest postglacial coastline or geochemical processes in the crystalline rock, is an indication either of slow fluid movements through the bedrock over long times, or of long travel distances through fracture systems before arriving at measurement points. During the land-rise period, regional flow is not affected by the variable density of fluids in the upper few kilometers of the shield, and the topography of the water table is the only driving force. The spatial distribution of meteoric flushing water and pre-Holocene waters may be complex, with the possibility of relatively fresh water in fracture zones below salty units even at depths of a few kilometers. The domination of the topographic driving force implies that deep saline water is not necessarily stagnant, and significant flow may be expected to occur in well-connected horizons even at depth. Local topography variation and fracture zone location combine to create a complex flow field in which local topographic driving forces extend to considerable depth in some areas, whereas regional topographic forces predominate in others. Thus, a pattern may be difficult to discern in measurements of the regional salinity distribution, although it is clear that the coastal region is the major zone of discharge for deeper pre-Holocene fluids. During the land-rise period, the regional flow field equilibrates with changing climatic conditions and coastal positions, while the distribution of flushing water and older water lags and will

  17. A mid to late Holocene history of floodplain and terrace reworking along the middle Delaware River valley, USA

    NASA Astrophysics Data System (ADS)

    Stinchcomb, Gary E.; Driese, Steven G.; Nordt, Lee C.; Allen, Peter M.

    2012-10-01

    This study tests and refines the traditional floodplain development model for the partly confined middle Delaware River valley, which has shown that the main channel was relatively stable and flanked by a 6000-8000 year old, vertically accreting alluvial terrace. The Holocene alluvial processes and history presented here in 6 fluvial phases were reconstructed using morphostratigraphy, 36 profile descriptions, 332 grain size analyses, and 82 14C ages from soil trenches, auger borings, and archaeological excavations. Fluvial phases I-III largely validate previous reconstructions showing a late Pleistocene (I: > 10.7 ka) braided stream transition into an early Holocene wandering stream with prolonged floodplain stability (II: 10.7-8 ka), followed by early-middle Holocene erosion and then deposition (III: 8-5 ka). The early and middle Holocene changes in alluvial stratigraphy and sedimentology broadly correlate with climatically derived Holocene subdivisions, suggesting climate change partly controls alluvial response along the middle Delaware River valley. This study documents for the first time a middle Holocene episode of channel incision occurring sometime between 6.0 and 5.0 ka. Although the results reconfirm that the majority of alluvial landforms are composed of vertical accretion deposits, we present here new evidence of oblique, abandoned channel, and lateral accretion deposits inset to similar landforms with different formation histories (i.e., polycyclic terrace development), depicting a river valley that has experienced floodplain and terrace reworking. The majority of floodplain and terrace reworking occurs during the late-middle and late Holocene phases IV-VI (5.5-0 ka), following the middle Holocene incision event. These phases demonstrate floodplain reworking processes in the form of channel abandonment, stripping, flood channeling, and convex bank erosion. The subsequent space filled rapidly with evidence of multistory soil formation, and eventually

  18. Field Demonstration of Horizontal Infill Drilling Using Cost-effective Integrated Reservoir Modeling--Mississippian Carbonates, Central Kansas

    SciTech Connect

    Saibal Bhattacharya

    2005-08-31

    Mississippian carbonate reservoirs have produced in excess of 1 billion barrels of oil in Kansas accounting for over 16% of the state's production. With declining production from other age reservoirs, the contribution of Mississippian reservoirs to Kansas's oil production has risen to 43% as of 2004. However, solution-enhanced features such as vertical shale intervals extending from the karst erosional surface at the top introduce complexities/compartmentalizations in Mississippian carbonate reservoirs. Coupled with this, strong water drives charge many of these reservoirs resulting in limited drainage from vertical wells due to high water cuts after an initial period of low water production. Moreover, most of these fields are operated by small independent operators without access to the knowledge bank of modern research in field characterization and exploitation/development practices. Thus, despite increasing importance of Mississippian fields to Kansas production, these fields are beset with low recovery factors and high abandonment rates leaving significant resources in the ground. Worldwide, horizontal infill wells have been successful in draining compartmentalized reservoirs with limited pressure depletion. The intent of this project was to demonstrate the application of horizontal wells to successfully exploit the remaining potential in mature Mississippian fields of the mid-continent. However, it is of critical importance that for horizontal wells to be economically successful, they must be selectively targeted. This project demonstrated the application of initial and secondary screening methods, based on publicly available data, to quickly shortlist fields in a target area for detailed studies to evaluate their potential to infill horizontal well applications. Advanced decline curve analyses were used to estimate missing well-level production data and to verify if the well produced under unchanging bottom-hole conditions--two commonly occurring data

  19. Sea level changes in the Holocene

    SciTech Connect

    Tanner, W.F. )

    1993-03-01

    Beach ridge data provide much information on the history of sea level changes through all of Holocene time. Two data sets start at about 12,000 B.P., one of them essentially continuous to now with data every 40--50 yrs. Another starting at 7,600 B.P. is continuous to the present. Others span the last 3,200 years. These records agree reasonably closely, and show the Little Ice Age (since 1,200 A.D.). The sea level changes in these data include the following: (a) Early Holocene crisis, about 8,000 B.P. The Swedish (Baltic Sea) record ends about this time, the Hudson Bay record starts at roughly this time, and the Danish record has a 300--500-year gap at about this time. From the latter, it appears that sea level rose sharply, shortly before 8,000 B.P., and fell again shortly after 8,000 B.P. These were the largest changes in Holocene time. The vertical change may have been as much as 12--18 meters, and the rate of change as much as 5--8 cm/yr, perhaps the maximum possible. In stable areas, evidence for these changes are now 25--30 meters below sea level. (b) Early Holocene general rise, up to about 8,000 B.P. Evidence for this is now known only on uplifted coasts. (c) Middle Holocene high, 2 m above present MSL 7,000--5,500 B.P. (d) Middle Holocene low, 3--4 m below present MSL 5,000--3,500 B.P. (e) Several changes up to 2 meters, especially since 3,000 B.P. In general, rates of change have been close to 1 cm/yr (major exceptions noted above). The only persistent interval was that between beach ridges; each ridge and its associated swale seem to have been built by a sea-level rise-and-fall couplet, having dimensions so small (perhaps 5--30 cm) that they could be overlooked easily on tide-gauge records. The average apparent time interval was 35--50 years.

  20. Holocene deceleration of the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    MacGregor, Joseph A.; Colgan, William T.; Fahnestock, Mark A.; Morlighem, Mathieu; Catania, Ginny A.; Paden, John D.; Gogineni, S. Prasad

    2016-02-01

    Recent peripheral thinning of the Greenland Ice Sheet is partly offset by interior thickening and is overprinted on its poorly constrained Holocene evolution. On the basis of the ice sheet’s radiostratigraphy, ice flow in its interior is slower now than the average speed over the past nine millennia. Generally higher Holocene accumulation rates relative to modern estimates can only partially explain this millennial-scale deceleration. The ice sheet’s dynamic response to the decreasing proportion of softer ice from the last glacial period and the deglacial collapse of the ice bridge across Nares Strait also contributed to this pattern. Thus, recent interior thickening of the Greenland Ice Sheet is partly an ongoing dynamic response to the last deglaciation that is large enough to affect interpretation of its mass balance from altimetry.

  1. Holocene deceleration of the Greenland Ice Sheet.

    PubMed

    MacGregor, Joseph A; Colgan, William T; Fahnestock, Mark A; Morlighem, Mathieu; Catania, Ginny A; Paden, John D; Gogineni, S Prasad

    2016-02-01

    Recent peripheral thinning of the Greenland Ice Sheet is partly offset by interior thickening and is overprinted on its poorly constrained Holocene evolution. On the basis of the ice sheet's radiostratigraphy, ice flow in its interior is slower now than the average speed over the past nine millennia. Generally higher Holocene accumulation rates relative to modern estimates can only partially explain this millennial-scale deceleration. The ice sheet's dynamic response to the decreasing proportion of softer ice from the last glacial period and the deglacial collapse of the ice bridge across Nares Strait also contributed to this pattern. Thus, recent interior thickening of the Greenland Ice Sheet is partly an ongoing dynamic response to the last deglaciation that is large enough to affect interpretation of its mass balance from altimetry. PMID:26912699

  2. The Alpine ?Iceman? and Holocene Climatic Change

    NASA Astrophysics Data System (ADS)

    Baroni, Carlo; Orombelli, Giuseppe

    1996-07-01

    The finding of a prehistoric mummified corpse at the upper edge of the accumulation area of an alpine glacier, together with its unique set of artifacts, provided new information on glacier dimensions during the little-known phases of major glacier shrinkage that characterized the warmest parts of the Holocene. The sudden burial of the corpse in a permanent snow cover occurred 5300-5050 cal yr B.P., indicating a significant climatic change that induced glacier expansion at the beginning of Neoglaciation. New geomorphologic data and two AMS 14C ages from buried soils suggest that the present glacier size, following over 100 yr of shrinkage, is comparable to that immediately preceding Neoglaciation. Therefore, we can deduce that the current global climatic warming may have interrupted the environmental conditions prevailing in the Alps during Neoglacial time, restoring characteristics similar to those prevailing during the climatic optimumthat were never achieved during the second half of the Holocene.

  3. Introduction to Holocene environmental change in Kamchatka

    NASA Astrophysics Data System (ADS)

    Brooks, S. J.; Diekmann, B.; Jones, V. J.; Hammarlund, D.

    2015-11-01

    This volume brings together a collection of papers on Holocene environmental change in the Kamchatka Peninsula, in the Russian Far East. Much of the work that appears in these papers was completed under the auspices of two major research activities: a UK NERC-funded project Influence of global teleconnections on Holocene climate in Kamchatka, which dealt with the analysis of lake records collected during the Swedish Beringia 2005 expedition organised by the Swedish Polar Research Secretariat; and a Russian-German multidisciplinary research project KALMAR - Kurile-Kamchatka and Aleutian Marginal Sea-Island Arc Systems: Geodynamic and Climate Interaction in Space and Time, funded by the German Federal Ministry of Education and Research (BMBF).

  4. Holocene fault scarps near Tacoma, Washington, USA

    USGS Publications Warehouse

    Sherrod, B.L.; Brocher, T.M.; Weaver, C.S.; Bucknam, R.C.; Blakely, R.J.; Kelsey, H.M.; Nelson, A.R.; Haugerud, R.

    2004-01-01

    Airborne laser mapping confirms that Holocene active faults traverse the Puget Sound metropolitan area, northwestern continental United States. The mapping, which detects forest-floor relief of as little as 15 cm, reveals scarps along geophysical lineaments that separate areas of Holocene uplift and subsidence. Along one such line of scarps, we found that a fault warped the ground surface between A.D. 770 and 1160. This reverse fault, which projects through Tacoma, Washington, bounds the southern and western sides of the Seattle uplift. The northern flank of the Seattle uplift is bounded by a reverse fault beneath Seattle that broke in A.D. 900-930. Observations of tectonic scarps along the Tacoma fault demonstrate that active faulting with associated surface rupture and ground motions pose a significant hazard in the Puget Sound region.

  5. The Caribbean conundrum of Holocene sea level.

    NASA Astrophysics Data System (ADS)

    Jackson, Luke; Mound, Jon

    2014-05-01

    In the tropics, pre-historic sea-level curve reconstruction is often problematic because it relies upon sea-level indicators whose vertical relationship to the sea surface is poorly constrained. In the Caribbean, fossil corals, mangrove peats and shell material dominate the pre-historic indicator record. The common approach to reconstruction involves the use of modern analogues to these indicators to establish a fixed vertical habitable range. The aim of these reconstructions is to find spatial variability in the Holocene sea level in an area gradually subsiding (< 1.2 mm yr-1) due the water loading following the deglaciation of the Laurentide ice sheet. We construct two catalogues: one of published Holocene sea-level indicators and the other of published, modern growth rates, abundance and coverage of mangrove and coral species for different depths. We use the first catalogue to calibrate 14C ages to give a probabilistic age range for each indicator. We use the second catalogue to define a depth probability distribution function (pdf) for mangroves and each coral species. The Holocene indicators are grouped into 12 sub-regions around the Caribbean. For each sub-region we apply our sea-level reconstruction, which involves stepping a fixed-length time window through time and calculating the position (and rate) of sea-level (change) using a thousand realisations of the time/depth pdfs to define an envelope of probable solutions. We find that the sub-regional relative sea-level curves display spatio-temporal variability including a south-east to north-west 1500 year lag in the arrival of Holocene sea level to that of the present day. We demonstrate that these variations are primarily due to glacial-isostatic-adjustment induced sea-level change and that sub-regional variations (where sufficient data exists) are due to local uplift variability.

  6. Holocene environmental and parasequence development of the St. Jones Estuary, Delaware (USA): Foraminiferal proxies of natural climatic and anthropogenic change

    USGS Publications Warehouse

    Leorri, E.; Martin, R.; McLaughlin, P.

    2006-01-01

    The benthic foraminiferal record of marshes located along western Delaware Bay (St. Jones Estuary, USA) reflects the response of estuaries to sea-level and paleoclimate change during the Holocene. System tracts are recognized and within them parasequences based on sedimentological and foraminiferal assemblages identification. The parasequences defined by foraminiferal assemblages appear correlative with rapid Holocene climate changes that are of worldwide significance: 6000-5000, 4200-3800, 3500-2500, 1200-1000, and 600??cal years BP. Following postglacial sea-level rise, modern subestuaries and marshes in the region began to develop between 6000 and 4000??years BP, depending on their proximity to the mouth of Delaware Bay and coastal geomorphology. Initial sediments were fluvial in origin, with freshwater marshes established around 4000??years BP. The subsequent sea-level transgression occurred sufficiently slowly that freshwater marshes alternated with salt marshes at the same sites to around 3000??years BP. Locally another two transgressions are identified at 1800 and 1000??years BP respectively. Marine influence increased in the estuaries until 600??years BP (Little Ice Age), when regression occurred. Sea-level began to rise again during the mid-19th Century at the end of the Little Ice Age, when marshes became established. The presence of a sand lens in the upper and middle estuary and the reduction in the number of tests in the top samples in cores from the same area also suggest an anthropogenic influence. The estuary infill resulted in a sharp transgressive sequence, represented by salt marsh foraminiferal assemblages in the upper part of the cores. The increase in marsh foraminifera in both areas suggests an increase in marine influence that might be due to the transgression beginning at the end of the Little Ice Age about 150-180??years ago coupled with anthropogenic straightening of the channel in 1913. ?? 2006 Elsevier B.V. All rights reserved.

  7. Anthropogenic climate change has driven Lake Superior productivity beyond the range of Holocene variability

    NASA Astrophysics Data System (ADS)

    OBeirne, M. D.; Werne, J. P.; Hecky, R. E.; Johnson, T. C.; Katsev, S.; Reavie, E. D.

    2013-12-01

    Recent studies have noted that changes in Lake Superior's physical, chemical and biological processes are apparent - including a warming of the surface waters at a rate twice as great as the surrounding airshed in the last 20 years. These changes are often difficult to perceive as cause for concern when not placed within a historical context. In this study, bulk C and N abundance and stable isotope composition was determined on sediments from three piston and corresponding gravity cores, representing a record of lake-wide paleoproductivity trends spanning the Holocene. These data are compared with the same measurements on eight multi-cores sampled at high resolution spanning the past ~200 years, which allows for the historical comparison with recent (1800 A.D. to present) productivity trends. Throughout the Holocene, Lake Superior experienced a slow, steady increase in productivity consistent with conventional lake ontogeny. During the last 200 years, however, the Lake Superior basin has undergone biogeochemical changes that are unique in the context of the Holocene. Lake-wide sedimentary bulk organic carbon data indicate increasing primary production between 1900 and present, as indicated by a ~2‰ increase in δ13Corg. In contrast,δ15Norg values, which increased throughout the Holocene, become progressively 15N-depleted after 1900, likely due to atmospheric deposition of NOx from fossil fuel combustion. The most recent increases in primary productivity are likely a response to increasing water temperatures, leading to longer ice-free periods as previously documented in Lake Superior.

  8. Holocene linkages between char, soot, biomass burning and climate from Lake Daihai, China

    NASA Astrophysics Data System (ADS)

    Han, Y. M.; Marlon, J. R.; Cao, J. J.; Jin, Z. D.; An, Z. S.

    2012-12-01

    Black or elemental carbon (EC), including soot and char, are byproducts of anthropogenic fossil-fuel and biomass burning, and also of wildfires. EC, and particularly soot, strongly affects atmospheric chemistry and physics and thus radiative forcing; it can also alter regional climate and precipitation. Pre-industrial variations in EC as well as its source areas and controls however, are poorly known. Here we use a lake-sediment EC record from China to reconstruct Holocene variations in soot (combustion emissions formed via gas-to-particle conversion processes) and char (combustion residues from pyrolysis) measured with a thermal/optical method. Comparisons with sedimentary charcoal records (i.e., particles measured microscopically), climate and population data are used to infer variations in biomass burning and its controls. During the Holocene, positive correlations are observed between EC and an independent index of regional biomass burning. Negative correlations are observed between EC and monsoon intensity, and tree cover inferred from arboreal pollen percentages. Abrupt declines in temperature are also linked with widespread declines in fire. Our results 1) confirm the robustness of a relatively new method for reconstructing variations in EC; 2) document variations in regional biomass burning; 3) support a strong climatic control of biomass burning throughout the Holocene; and 4) indicate that char levels are higher today than at any time during the Holocene.

  9. Late Holocene climate: Natural or anthropogenic?

    NASA Astrophysics Data System (ADS)

    Ruddiman, W. F.; Fuller, D. Q.; Kutzbach, J. E.; Tzedakis, P. C.; Kaplan, J. O.; Ellis, E. C.; Vavrus, S. J.; Roberts, C. N.; Fyfe, R.; He, F.; Lemmen, C.; Woodbridge, J.

    2016-03-01

    For more than a decade, scientists have argued about the warmth of the current interglaciation. Was the warmth of the preindustrial late Holocene natural in origin, the result of orbital changes that had not yet driven the system into a new glacial state? Or was it in considerable degree the result of humans intervening in the climate system through greenhouse gas emissions from early agriculture? Here we summarize new evidence that moves this debate forward by testing both hypotheses. By comparing late Holocene responses to those that occurred during previous interglaciations (in section 2), we assess whether the late Holocene responses look different (and thus anthropogenic) or similar (and thus natural). This comparison reveals anomalous (anthropogenic) signals. In section 3, we review paleoecological and archaeological syntheses that provide ground truth evidence on early anthropogenic releases of greenhouse gases. The available data document large early anthropogenic emissions consistent with the anthropogenic ice core anomalies, but more information is needed to constrain their size. A final section compares natural and anthropogenic interpretations of the δ13C trend in ice core CO2.

  10. The infill timing of a quaternary intermontane basin: new chrono-stratigraphic and palaeoenvironmental data by a 900 m deep borehole from Campochiaro (central-southern Apennine, Italy)

    NASA Astrophysics Data System (ADS)

    Amato, Vincenzo; Aucelli, Pietro P. C.; Cesarano, Massimo; Cifelli, Francesca; Leone, Natalia; Mattei, Massimo; Russo Ermolli, Elda; Petrosino, Paola; Rosskopf, Carmen M.

    2016-04-01

    The axial zone of the central-southern Apennine (Molise sector), is characterized by the presence of several quaternary tectonic depressions (Venafro, Isernia, Carpino, Sessano, Boiano and Sepino), generally NW-SE and NE-SW elongated, filled by very thick fluvial-marshy successions. Transtensive and extensional tectonic phases, alternating by relative stable tectonic periods with prevailing climatic variation induced processes, contributed to the infilling. In fact, during Early Pleistocene, the transtensive tectonic phases and, from the end of Early Pleistocene, the extensional tectonic phases, were responsible to enhance the subsidence into the basins, thanks to the activity of the high angle faults, generally NW-SE, NESW and E-O oriented, influencing also their environmental and sedimentary evolution. Between the late Middle Pleistocene and the early Upper Pleistocene, the subsidence reduced, and alluvial plain and alluvial fans environments improved. In the last years, several studies on the Boiano intermontane basin, bounded at south by Matese massif, were carried out. A detailed morpho-stratigraphic and tectonic evolution of the basin was proposed since Middle Pleistocene (MIS 13, 500 ka BP), thanks to field surveys and boreholes facies analyses, supported by Ar/Ar datings, tephrostratigraphical and pollen data. However, still now, the presence of Early Pleistocene eposits was only supposed. Succession. A deep continuous core (900 m) was carried out in the Campochiaro sector of the basin. Facies analyses, supported by preliminary paleomagnetic and tephrostratigraphic data, allow us to recognize the top of the prequaternary bedrock (Molise Flysch, Miocene) at 240 m of depth and to divide the whole succession in 4 main stratigraphic units. From the bottom to the top, the infilling is made of: Unit 1 (240-150 m), presenting lacustrine-palustrine environments, alternating clays and clayey-silts layers, constrained to Early Pleistocene; Unit 2 (150-123 m

  11. Single Foraminifera Reconstructions of Equatorial Pacific Variability from the Late Glacial Maximum to the Holocene

    NASA Astrophysics Data System (ADS)

    Ford, H. L.; Ravelo, A. C.; Polissar, P. J.

    2011-12-01

    The tropical Pacific ocean is the largest source of global climate interannual variability today. Climate model simulations of future warming exhibit widely divergent behavior indicating an incomplete understanding of the factors that dictate tropical climate variability. Past records of tropical Pacific variability are one approach to deepening our understanding of tropical climate change processes and improving predictions of future change. Here we reconstruct tropical Pacific variability from the Last Glacial Maximum (LGM) and from the Holocene at ODP Sites 806 and 849, located in the western equatorial Pacific warm pool (WEP) and eastern equatorial Pacific cold tongue (EEP), respectively. In order to reconstruct sea surface temperature (SST) variability, individual specimens of G. sacculifer were analyzed for Mg/Ca values via laser ablation (Photon Machines Analyte.193 with HelEx sample cell) coupled with a Thermo ElementXS ICP-MS (LA-ICP-MS). At WEP Site 806, average SST of the single shell analyses was cooler, by about 3°C, in the LGM compared to the Holocene, but the standard deviation of analyses was similar in the two time periods. Thus, it may be that average, minimum, and maximum SSTs in the WEP are controlled by radiative processes throughout the year, perhaps related to lower greenhouse gas forcing in the LGM. For EEP Site 849, the average SST of the single shell analyses was also cooler, by about 2°C, but, unlike WEP Site 806, the standard deviation of the analyses was less in the LGM compared to the Holocene. Most notably, at EEP Site 849, the coldest of single shell SST analyses were similar in the LGM and Holocene samples. In contrast, the warmest single shell SSTs were cooler in the LGM sample compared to the Holocene. In the modern ocean, about 80% of the SST variance at EEP Site 849 is related to the seasonal cycle, thus our data may indicate that the primary difference between conditions in the Holocene and LGM was that the warm season was

  12. Temporal and spatial variation of infilling processes in a landslide scar in a steep mountainous region, Japan

    EPA Science Inventory

    The duration of the soil-depth recovery needed for reoccurrence of landslides at a given site is much longer than the return period of rainfall needed to generate sufficient pore water pressure to initiate a landslide. Knowledge of the soil development rate in landslide scars is ...

  13. Evolution of the solar irradiance during the Holocene

    NASA Astrophysics Data System (ADS)

    Vieira, L. E. A.; Solanki, S. K.; Krivova, N. A.; Usoskin, I.

    2011-07-01

    Context. Long-term records of solar radiative output are vital for understanding solar variability and past climate change. Measurements of solar irradiance are available for only the last three decades, which calls for reconstructions of this quantity over longer time scales using suitable models. Aims: We present a physically consistent reconstruction of the total solar irradiance for the Holocene. Methods: We extend the SATIRE (Spectral And Total Irradiance REconstruction) models to estimate the evolution of the total (and partly spectral) solar irradiance over the Holocene. The basic assumption is that the variations of the solar irradiance are due to the evolution of the dark and bright magnetic features on the solar surface. The evolution of the decadally averaged magnetic flux is computed from decadal values of cosmogenic isotope concentrations recorded in natural archives employing a series of physics-based models connecting the processes from the modulation of the cosmic ray flux in the heliosphere to their record in natural archives. We then compute the total solar irradiance (TSI) as a linear combination of the jth and jth + 1 decadal values of the open magnetic flux. In order to evaluate the uncertainties due to the evolution of the Earth's magnetic dipole moment, we employ four reconstructions of the open flux which are based on conceptually different paleomagnetic models. Results: Reconstructions of the TSI over the Holocene, each valid for a different paleomagnetic time series, are presented. Our analysis suggests that major sources of uncertainty in the TSI in this model are the heritage of the uncertainty of the TSI since 1610 reconstructed from sunspot data and the uncertainty of the evolution of the Earth's magnetic dipole moment. The analysis of the distribution functions of the reconstructed irradiance for the last 3000 years, which is the period that the reconstructions overlap, indicates that the estimates based on the virtual axial dipole

  14. Basement depth and sedimentary infill from deep seismic reflection data at the western tip of the offshore Corinth Rift

    NASA Astrophysics Data System (ADS)

    Beckers, Arnaud; Tripsanas, Efthymios; Hubert-Ferrari, Aurélia; Beck, Christian; Sakellariou, Dimitris

    2015-04-01

    The Corinth rift is a young continental rift located in central Greece. The active part of the rift forms an E-W striking depression - the Gulf of Corinth - that is the deepest in its central part. Extensive seismic surveys have imaged the basin's basement and allowed to estimate the total extension across most of the Gulf except its western tip. Extension is high in the central part and decreases westward and eastward, as reflected in the present-day bathymetry. Two decades of GPS measurements have shown that the extension rate increases westwards from ~5 to 10-15 mm yr-1, but this is not consistent with the long term pattern. However, no data allowed so far to estimate the basement depth at the western tip of the Gulf, where the geodetic extension rate is the largest. Such data would allow to check the apparent inconsistency between the present rate and the long-term estimates of crustal extension. We present here an unpublished multichannel seismic line dating from 1979 and crossing the western tip of the Gulf of Corinth. The line is 22 km long and strikes WNW-ESE, from the Mornos delta to the West-Channel fault. A Maxipulse source has been used, allowing to image the basement below the synrift sedimentary infill. To the east, a ~1.6 km deep basin is imaged between the southern margin of the Gulf and an inactive south-dipping fault located between the Aigion and the Trizonia faults. The sedimentary infill consists in an alternation between basin-focused bodies made of incoherent reflections and more extensive high-amplitude reflectors. Attributing this alternation to eustatic variations give an age of 300-350 ka to the oldest well imaged deposits. Northwest of the Trizonia fault, the basement is imaged at shallower depth, i.e. ~450 m. The western tip of the seismic line reaches the Mornos delta, close to the northern shoreline. There, the depth to the basement is larger, reaching ~1.2 km. The infill is made of 3 units : on the basement lies a thin unit of

  15. Influence of vegetation on the infilling of a macrotidal embayment: examples from salt marshes and shingle spit of the Baie de Somme (North France)

    NASA Astrophysics Data System (ADS)

    Le Bot, Sophie; Forey, Estelle; Lafite, Robert; Langlois, Estelle

    2015-04-01

    As many estuaries in the English Channel, the Baie de Somme is currently filling with a mean seabed elevation between 1.3 and 1.8 cm/yr. Embankments and polders, as well as sea level rise, increase this natural accretion process, which leads to important modifications of environment uses. Interactions between vegetation and sediment dynamics constitute a key-point to consider, in order to better understand the infilling processes in estuaries. To estimate the effect of vegetation on these processes, two particular environments have been studied in the bay: (i) the mid salt marsh covered with Halimione portulacoides, associated with a silty sedimentation, and (ii) the shingle spit, that closes the bay from the South, on which the sea kale (Crambe maritime), a protected pioneer species, develops. Salt marshes progress with a rate of 5-10 m/yr (mean value calculated on the 1947-2011 period). Sedimentological analysis have been conducted on 9 cores (50cm long) collected in three Halimione communities of the bay. They are associated with a silty-dominated (38-84 micrometer) sedimentation under the influence of decantation processes. Rhythmicity is observed in the sedimentation, due to the repetition of a two-layer pattern, that includes a dark layer composed of vegetal rests and that would represent annual sedimentation. Annual sedimentation rates (0.7 to 5.8 cm/yr) are consistent with mean values previously recorded. The shingle spit progresses to the North under the influence of the littoral drift at a rate of 7 m/yr (mean value calculated on the 1947-2011 period). Sea kales are observed on parts formed since several years, above the level of the highest astronomical tides. TLS surveys and sedimentation bars have allowed to measure erosion/sedimentation volumes at the scale of the spit and of sea kale individuals, during spring 2013. Individuals of this species facilitate the trapping of sand, transported by winds from the intertidal flats. Sea kale thus contributes

  16. Holocene carbon dynamics and climate forcing of two subarctic minerotrophic fens

    NASA Astrophysics Data System (ADS)

    Mathijssen, P.; Aurela, M.; Blaauw, M.; Juutinen, S.; Lohila, A.; Niemelä, E.; Tuittila, E.; Tuovinen, J.; Väliranta, M.

    2013-12-01

    Historical data on three dimensional peatland development patterns, carbon (C) dynamics and radiative forcing may aid us to understand peatland - climate-related feedback mechanisms. We investigated vertical and horizontal peat growth patterns of two subarctic fens, Lompolonjänkkä (Western Finnish Lapland) and Kiposuo (Eastern Finnish Lapland). We calculated C accumulation rates and, based on these and modern gas measurements, we estimated historical CO2 and CH4 fluxes. Past C budgets and radiative forcing were reconstructed. The C accumulation rates of Lompolojänkkä fen and Kiposuo fen varied between ranges 3 - 47 and 2 - 27 g C m-2 a-1, respectively. Plant macrofossil analyses suggest that fen plant communities have changed only a little throughout the Holocene and accordingly we assume only minor variation in CH4 emissions. However, C uptake rates varied and showed extended periods of low C uptake between 8 and 2 kcal BP in Lompolojänkkä and between 9 and 4 kcal BP in Kiposuo. These periods of low C uptake coincide with warm and dry climate conditions. Lateral expansion of Lompolojänkkä was fast after peatland initiation, which happened through infilling, and during the last two millennia, but expansion was slow between 6 and 3 kcal BP. Kiposuo started to initiate simultaneously over a large area mainly on mineral soil. Subsequent lateral expansion has been negligible. In conclusion the reconstructed C dynamics suggest that the mid Holocene dry and warm conditions slowed down peat growth and C accumulation. This was especially striking in Lompolonjänkkä. Both fens had a positive radiative forcing (RF) effect to the atmosphere after the peat initiation. The RF turned negative after c. 700 years from the initiation in Lompolonjänkkä and after c. 1500 years in Kiposuo. Afterwards the radiative forcing continued to decrease until the present, reaching current radiative forcing of -1.33 x 10-8 W m-2 (Lompolonjänkkä) and -0.77 x 10-8 W m-2 (Kiposuo

  17. A new varved late Glacial and Holocene sediment record from Lake Jelonek (North Poland) - preliminary results

    NASA Astrophysics Data System (ADS)

    Kramkowski, Mateusz; Filbrandt-Czaja, Anna; Ott, Florian; Słowiński, Michał; Tjallingii, Rik; Błaszkiewicz, Mirosław; Brauer, Achim

    2015-04-01

    Anually laminated (varved) lake deposits are suitable natural archives for reconstructing past climatic and environmental changes at seasonal resolution. A major advantage of such records is that varve counting allows constructing robust and independent chronologies, a key challenge for paleoclimate research. Recently, a new annually laminated sediment record has been obtained from Lake Jelonek, located in the eastern part of the Pomeranian Lakeland in northern Poland (Tuchola Pinewoods). The lake is surrounded by forest and covers an area of 19,9 ha and has a maximum depth of 13,8 m. Three overlapping series of 14,3 m - long sediment records have been cored with an UWITEC 90 mm diameter piston corer from the deepest part of the lake. A continuous master composite profile has been established comprising the entire postglacial lacustrine sediment infill. Preliminary analyses including micro-facies analyses on thin sections from selected intervals as well as X-ray fluorescence element scanning (µ-XRF) reveal that the sediments are to a large part annually laminated. Here we present detailed varve models for different sediment intervals and discuss high-resolution geochemical variation in the entire sediment record. A preliminary age model based on radiocarbon dating and major biostratigraphical boundaries based on pollen data will be presented as well. These data will form the fundament for the planned multi-proxy study for detailed reconstructions of climatic and environmental variability during the late glacial and Holocene in the southern Baltic. This study is a contribution to the Virtual Institute ICLEA (Integrated Climate and Landscape Evolution Analysis) funded by the Helmholtz Association and National Science Centre Poland NCN 2011/01/B/ST10/07367.

  18. Comparing modelled fire dynamics with charcoal records for the Holocene

    NASA Astrophysics Data System (ADS)

    Brücher, Tim; Brovkin, Victor; Kloster, Silvia; Marlon, Jennifer; Power, Mitch

    2014-05-01

    An Earth System model of intermediate complexity, CLIMBER-2, and land surface model JSBACH that includes dynamic vegetation, carbon cycle, and fire regime are used for simulation of natural fire dynamics through the last 8,000 years. To compare the fire model results with the charcoal reconstructions, several output variables of the fire model (burned area, carbon emissions) and several approaches of model output processing are tested. The z-scores out of charcoal dataset have been calculated for the period 8,000 to 200 BP to exclude a period of strong anthropogenic forcing during the last two centuries. The model analysis points mainly to an increasing fire activity during the Holocene for most of the investigated areas, which is in good correspondence to reconstructed fire trends out of charcoal data for most of the tested regions, while for few regions such as Europe the simulated trend and the reconstructed trends are different. The difference between the modeled and reconstructed fire activity could be due to absence of the anthropogenic forcing in the model simulations, but also due to limitations of model assumptions for modeling fire dynamics. For the model trends, the usage of averaging or z-score processing of model output resulted in similar directions of trend. Therefore, the approach of fire model output processing does not effect results of the model-data comparison. Global fire modeling is still in its infancy; improving our representations of fire through validation exercises such as what we present here is thus essential before testing hypotheses about the effects of extreme climate changes on fire behavior and potential feedbacks that result from those changes. Brücher, T., Brovkin, V., Kloster, S., Marlon, J. R., and Power, M. J.: Comparing modelled fire dynamics with charcoal records for the Holocene, Clim. Past Discuss., 9, 6429-6458, doi:10.5194/cpd-9-6429-2013, 2013.

  19. High rates of bedload transport measured from infilling rate of large strudelscour craters in the Beaufort Sea, Alaska

    USGS Publications Warehouse

    Reimnitz, Erk; Kempema, E.W.

    1982-01-01

    Strudel scours are craters as much as 20 m wide and 4 m deep, that are excavated by vertical drainage flow during the yearly spring flooding of vast reaches of fast ice surrounding arctic deltas; they form at a rate of about 2.5 km^-2 yr^-1. Monitoring two such craters in the Beaufort Sea, we found that in relatively unprotected sites they fill in by deposition from bedload in 2 to 3 years. Net westward sediment transport results in sand layers dipping at the angle of repose westward into the strudel-scour crater, whereas the west wall of the crater remains steep to vertical. Initially the crater traps almost all bedload: sand, pebbles, and organic detritus; as infilling progresses, the materials are increasingly winnowed, and bypassing must occur. Over a 20-m-wide sector, an exposed strudel scour trapped 360 m3 of bedload during two seasons; this infilling represents a bedload transport rate of 9 m3 yr^-1 m^-1. This rate should be applicable to a 4.5-km-wide zone with equal exposure and similar or shallower depth. Within this zone, the transport rate is 40,500 m3 yr^-1, similar to estimated longshore transport rates on local barrier beaches. On the basis of the established rate of cut and fill, all the delta-front deposits should consist of strudel-scour fill. Vibracores typically show dipping interbedded sand and lenses of organic material draped over very steep erosional contacts, and an absence of horizontal continuity of strata--criteria that should uniquely identify high-latitude deltaic deposits. Given a 2- to 3-year lifespan, most strudel scours seen in surveys must be old. The same holds true for ice gouges and other depressions not adjusted to summer waves and currents, although these features record events of only the past few years. In view of such high rates of bottom reworking of the shallow shelf, any human activities creating turbidity, such as dredging, would have little effect on the environment. However, huge amounts of transitory material

  20. Holocene sedimentation at Corkscrew Swamp (Collier Co. ): A model for the origin and evolution of the present wetland-dominated regime of south Florida

    SciTech Connect

    Stone, P.A. ); Duever, M.J.; Meeder, J.F. )

    1993-03-01

    A two-layer peat-over-marl (calcitic mud) sequence characterizes Corkscrew Swamp, a swamp/marsh complex in northern Big Cypress Swamp. The marl began depositing about 10,600 BP and based upon the regional modern analog represents a marsh (grassy) environment of relatively short seasonal flooding, rather than a marl lake. The marsh succeeded formerly dry land of full-glacial times on a long-emerged marine-sand and limestone peninsula. About 5,700 BP peat deposition began by the development of longer-flooded wetland, either marsh or woody swamp vegetation. Both shifts (Pleistocene/Holocene and mid-Holocene) represent onsets of wetter conditions, either episodically or by slowly passing critical thresholds, under control of climate and sea level (hydrologic baselevel). With the rise in average water level at and following each shift, in part by feedback from sediment infilling of the shallow (ca. 2.5m) mineral-substrate basin, the wetland and its deposit expanded upslope, both vertically and outward. A younger basal-peat date (3,900 BP) occurs toward the periphery. Some local topographic alteration by peat fire about 500 BP persists and affects the modern swamp vegetation. A wide swamp-to-marsh shift in other parts may have a similar cause. The shorter record yet revealed for the northern Everglades shows the same two-stage sequence, similar timing in peatland development, wetland and sediment expansion, and long-term (but there different) influences of local peatland topographic alteration. Many wetland areas in South Florida data from a mid-Holocene shift (7,000--4,000 BP).

  1. Holocene evolution of the western Orinoco Delta, Venezuela

    USGS Publications Warehouse

    Aslan, A.; White, W.A.; Warne, A.G.; Guevara, E.H.

    2003-01-01

    The pristine nature of the Orinoco Delta of eastern Venezuela provides unique opportunities to study the geologic processes and environments of a major tropical delta. Remote-sensing images, shallow cores, and radiocarbon-dating of organic remains form the basis for describing deltaic environments and interpreting the Holocene history of the delta. The Orinoco Delta can be subdivided into two major sectors. The southeast sector is dominated by the Rio Grande-the principal distributary-and complex networks of anastomosing fluvial and tidal channels. The abundance of siliciclastic deposits suggests that fluvial processes such as over-bank flooding strongly influence this part of the delta. In contrast, the northwest sector is represented by few major distributaries, and overbank sedimentation is less widespread relative to the southeast sector. Peat is abundant and occurs in herbaceous and forested swamps that are individually up to 200 km2 in area. Northwest-directed littoral currents transport large volumes of suspended sediment and produce prominent mudcapes along the northwest coast. Mapping of surface sediments, vegetation, and major landforms identified four principal geomorphic systems within the western delta plain: (1) distributary channels, (2) interdistributary flood basins, (3) fluvial-marine transitional environments, and (4) marine-influenced coastal environments. Coring and radiocarbon dating of deltaic deposits show that the northern delta shoreline has prograded 20-30 km during the late Holocene sea-level highstand. Progradation has been accomplished by a combination of distributary avulsion and mudcape progradation. This style of deltaic progradation differs markedly from other deltas such as the Mississippi where distributary avulsion leads to coastal land loss, rather than shoreline progradation. The key difference is that the Orinoco Delta coastal zone receives prodigious amounts of sediment from northwest-moving littoral currents that transport

  2. Holocene record of glacier variability from lake sediments reveals tripartite climate history for Svalbard

    NASA Astrophysics Data System (ADS)

    van der Bilt, Willem; Bakke, Jostein; Vasskog, Kristian; D`Andrea, William; Bradley, Raymond; Olafsdottir, Sædis

    2016-04-01

    The Arctic is responding sensitively to ongoing global climate change, warming and moistening faster than any other region on the planet. Holocene proxy paleoclimate time series are increasingly used to put this amplified response in perspective by understanding Arctic climate processes beyond the instrumental period. Glaciers rapidly respond to climate shifts as demonstrated by their current demise around the world. This response has a composite climate signature, marked by shifts in hydroclimate (winter precipitation) as well as (summer) temperature. Attendant changes in glacier size are recorded by variations in glacigenic rock flour that may be deposited in downstream lakes. Here, we present a Holocene reconstruction of glacier activity, based on sediments from Hajeren, a glacier-fed lake on northwest Spitsbergen in the High Arctic Svalbard archipelago. Owing to undisturbed sediments and robust age control, we could resolve variability on a sub-centennial scale. To ensure the accurate detection of glacier activity, we applied a toolbox of physical, magnetic and geochemical proxies in conjunction with multivariate statistics. Our findings indicate a three-stage Holocene climate history for Svalbard, driving by melt water pulses, episodic Atlantic cooling and a decline in orbitally driven summer insolation. Correspondence between inferred advances, including a Holocene glacier maximum around 9.5 ka BP, suggests forcing by the melting LIS during the Early Holocene. Following a late Holocene Thermal Maximum around 7.4 ka BP, glaciers disappeared from the catchment. Glaciers reformed around 4.2 ka BP during the regional onset of the Neoglacial, supporting previous findings. This transition did, however, not mark the onset of persistent glacier activity in the catchment, but a series of centennial-scale cycles of growth and decay, including events around 3.3 and 1.1 ka BP. As orbitally driven insolation declined towards the present, the glaciation threshold

  3. Holocene Carbon Fluxes and Palaeoproductivity in Aquatic Ecosystems: a Multiproxy, Palaeolimnological Approach

    NASA Astrophysics Data System (ADS)

    Mackay, A. W.; Leng, M. J.; Morley, D. W.; Piotrowska, N.; Rioual, P.; Swann, G. E. A.

    2014-12-01

    inputs mediated by taiga forest expansion and fluvial input into the lake. Minima in Holocene palaeoproductivity are coincident with peaks in hematite stained grains in North Atlantic sediments, a proxy for ice-rafted debris, highlighting tight linkages via teleconnection processes between changes in the North Atlantic and remote central Asia.

  4. Assessment of Holocene soil erosion rates on the loess plateau in East Poland using sedimentary archives from closed depressions

    NASA Astrophysics Data System (ADS)

    Kołodyńska-Gawrysiak, Renata; Poesen, Jean; Gawrysiak, Leszek

    2016-04-01

    Closed depressions (CDs) are typical geomorphological features of the European loess belt. They are closed sedimentation basins that enable the estimation of long-term soil erosion rates for different land use environments. This study was conducted in eastern Poland (Nałęczów Plateau). In this region CDs are rather small landforms and the area of 70% of all CDs does not exceed 1500 m2. The study objective was to assess Holocene soil erosion rates in the loess plateau based on a quantitative analysis of colluvial sediments deposited in CDs. Two representative CDs were selected for this study: one CD is located in an old (long-term) forest and the other is situated in a long-term agricultural land. The maximum depth of the CD in the forest, the mean slope gradient and area of the corresponding catchment are 4.9 m, 3.410 and 7568 m² respectively. For the CD in agricultural land these values are 3.2 m, 2.760 and 5156 m² respectively. In both CDs several dozen of drillings and two trenches (2 m long, 1m wide, 2 m deep) were made in the deepest point of the CDs. Mean long-term soil erosion rates were calculated based on the stratigraphy of the soil-sediment sequence infilling the CDs. C-14 and OSL datings of soils and colluvial sediments within the CDs were obtained. For the long-term agricultural used catchment of the CD it was calculated that since 6.31 ± 0.35 ka BP the mean annual soil loss due to water and tillage erosion is 0.63-0.7 t/ha/year or 279.3 mm. In the prehistoric period since 6.31 ± 0.35 ka BP until 1026-1162 AD the mean annual soil erosion rate amounted to 0,10-0.11 t/ha/year or 41.5 mm. During the last ca. 1000 years mean soil erosion rates increased to 3.99-4.63 t/ha/year or 249.2 mm. Results of long-term soil erosion rates (calculated using colluvial sediment sequences in CDs) from agricultural catchments in the loess regions of eastern Poland (this study) and Central Belgium (Gillijns et al. 2005) are quite similar. For the forested catchment

  5. Holocene variation in spatial scales of vegetation pattern in the upper Great Lakes

    SciTech Connect

    Graumlich, L.J. ); Davis, M.B. )

    1993-04-01

    Continental-scale patterns of vegetation change during the Holocene clearly record the influence of climatic change, but the factors are less clearly defined. To characterize the scales of processes determining vegetation patterns during the Holocene, 52 pollen sites were analysed in the upper Great Lakes region. Pollen percentage data for pine, Pinus; oak, Quercus; and birch, Betula were interpolated from samples bracketing four target years (500, 2500, 4500, and 6500 yr BP). Each target year shows broad trends in pollen abundance that correspond to climatic gradients. The three genera differ in the magnitude and pattern of residual variation. Oak residuals are relatively small in magnitude, while pine and birch residuals are relatively large and show greater local variability. Spatial correlograms of Oak corroborate the mapped data in indicating the dominance of region-wide trends. In contrast the birch and pine correlograms indicate that factors operating at scales of 150 to 300 km are as important as region-wide trends in governing pollen abundances. The structure of the correlograms for birch and pine pollen changes through time, with birch showing a more patchy spatial pattern in the mid-Holocene (4500 and 6500 yr BP) as compared to the late-Holocene (500 and 2500 yr BP). Pine shows a more strongly autocorrelated in the mid-Holocene. Our results suggest that substrate, an environmental constraint on vegetation at scales of tens to hundreds of kilometers, has been important in governing the spatial distribution of birch and pine in the upper Great Lakes region. The changing distribution of birch and pine is attributed, in part, to changes in the relative abundance of ecologically dissimilar species within these genera. Further, these observations suggest that spatial scales of tree abundances are dynamic and that constraints imposed by substrate vary in importance in response to long-term climatic variation. 75 refs., 5 figs., 1 tabs.

  6. Aragonite infill in overgrown conceptacles of coralline Lithothamnion spp. (Hapalidiaceae, Hapalidiales, Rhodophyta): new insights in biomineralization and phylomineralogy.

    PubMed

    Krayesky-Self, Sherry; Richards, Joseph L; Rahmatian, Mansour; Fredericq, Suzanne

    2016-04-01

    New empirical and quantitative data in the study of calcium carbonate biomineralization and an expanded coralline psbA framework for phylomineralogy are provided for crustose coralline red algae. Scanning electron microscopy (SEM) and energy dispersive spectrometry (SEM-EDS) pinpointed the exact location of calcium carbonate crystals within overgrown reproductive conceptacles in rhodolith-forming Lithothamnion species from the Gulf of Mexico and Pacific Panama. SEM-EDS and X-ray diffraction (XRD) analysis confirmed the elemental composition of these calcium carbonate crystals to be aragonite. After spore release, reproductive conceptacles apparently became overgrown by new vegetative growth, a strategy that may aid in sealing the empty conceptacle chamber, hence influencing the chemistry of the microenvironment and in turn promoting aragonite crystal growth. The possible relevance of various types of calcium carbonate polymorphs present in the complex internal structure and skeleton of crustose corallines is discussed. This is the first study to link SEM, SEM-EDS, XRD, Microtomography and X-ray microscopy data of aragonite infill in coralline algae with phylomineralogy. The study contributes to the growing body of literature characterizing and speculating about how the relative abundances of carbonate biominerals in corallines may vary in response to changes in atmospheric pCO2 , ocean acidification, and global warming. PMID:27037582

  7. Nonlinear finite element model updating of an infilled frame based on identified time-varying modal parameters during an earthquake

    NASA Astrophysics Data System (ADS)

    Asgarieh, Eliyar; Moaveni, Babak; Stavridis, Andreas

    2014-11-01

    A model updating methodology is proposed for calibration of nonlinear finite element (FE) models simulating the behavior of real-world complex civil structures subjected to seismic excitations. In the proposed methodology, parameters of hysteretic material models assigned to elements (or substructures) of a nonlinear FE model are updated by minimizing an objective function. The objective function used in this study is the misfit between the experimentally identified time-varying modal parameters of the structure and those of the FE model at selected time instances along the response time history. The time-varying modal parameters are estimated using the deterministic-stochastic subspace identification method which is an input-output system identification approach. The performance of the proposed updating method is evaluated through numerical and experimental applications on a large-scale three-story reinforced concrete frame with masonry infills. The test structure was subjected to seismic base excitations of increasing amplitude at a large outdoor shake-table. A nonlinear FE model of the test structure has been calibrated to match the time-varying modal parameters of the test structure identified from measured data during a seismic base excitation. The accuracy of the proposed nonlinear FE model updating procedure is quantified in numerical and experimental applications using different error metrics. The calibrated models predict the exact simulated response very accurately in the numerical application, while the updated models match the measured response reasonably well in the experimental application.

  8. Infilling of missing rainfall and streamflow data in the Shire River basin, Malawi - A self organizing map approach

    NASA Astrophysics Data System (ADS)

    Mwale, F. D.; Adeloye, A. J.; Rustum, R.

    A major requirement for the assessment, development and sustainable use of water resources is the availability of good quality hydrological time series data of sufficiently long duration. However, it is not uncommon to find data that are riddled with gaps, characterized by questionable quality and short durations. Sometimes, the data are just not available. Such situations are most prevalent in developing countries and the consequence is a high degree of uncertainty in the assessed characteristics of water management schemes and ultimately its ineffectual performance. Thus dealing with these problems is an important exercise in hydrological analyses. This paper focuses on the multivariate infilling of gaps for rainfall and streamflow data in the Shire River basin in Malawi, using a self organizing map (SOM) approach, which is a form of unsupervised artificial neural networks. The results show that this approach can produce reliable estimates of hydro-meteorological data thus offering promise for reducing the uncertainties associated with the use of insufficient data for water resources assessment.

  9. Infilled masonry walls contribution in mitigating progressive collapse of multistory reinforced concrete structures according to UFC guidelines

    NASA Astrophysics Data System (ADS)

    Helmy, Huda; Hadhoud, Hamed; Mourad, Sherif

    2015-09-01

    A structure is subjected to progressive collapse when an element fails, resulting in failure of adjoining structural elements which, in their turn, cause further structural failure leading eventually to partial or total collapse. The failure of a primary vertical support might occur due to extreme loadings such as bomb explosion in a terrorist attack, gas explosion and huge impact of a car in the parking area. Different guidelines such as the General Services Administration (GSA 2003) and the Unified Facilities Criteria (UFC 2009) addressed the structural progressive collapse due to the sudden loss of a main vertical support. In the current study, a progressive collapse assessment according to the UFC guidelines is carried out for a typical ten-story reinforced concrete framed structure designed according to codes [(ACI 318-08) and (ASCE 7-10)] for minimum design loads for buildings and other structures. Fully nonlinear dynamic analysis for the structure was carried out using Applied Element Method (AEM). The investigated cases included the removal of a corner column, an edge column, an edge shear wall, internal columns and internal shear wall. The numerical analysis showed that simplification of the problem into 3D bare frames would lead to uneconomical design. It was found for the studied case that, the infilled masonry walls have a valuable contribution in mitigating progressive collapse of the reinforced concrete framed structures. Neglecting these walls would lead to uneconomical design.

  10. High density infill in cracks and protrusions from the articular calcified cartilage in osteoarthritis in standardbred horse carpal bones.

    PubMed

    Laverty, Sheila; Lacourt, Mathieu; Gao, Chan; Henderson, Janet E; Boyde, Alan

    2015-01-01

    We studied changes in articular calcified cartilage (ACC) and subchondral bone (SCB) in the third carpal bones (C3) of Standardbred racehorses with naturally-occurring repetitive loading-induced osteoarthritis (OA). Two osteochondral cores were harvested from dorsal sites from each of 15 post-mortem C3 and classified as control or as showing early or advanced OA changes from visual inspection. We re-examined X-ray micro-computed tomography (µCT) image sets for the presence of high-density mineral infill (HDMI) in ACC cracks and possible high-density mineralized protrusions (HDMP) from the ACC mineralizing (tidemark) front (MF) into hyaline articular cartilage (HAC). We hypothesized and we show that 20-µm µCT resolution in 10-mm diameter samples is sufficient to detect HDMI and HDMP: these are lost upon tissue decalcification for routine paraffin wax histology owing to their predominant mineral content. The findings show that µCT is sufficient to discover HDMI and HDMP, which were seen in 2/10 controls, 6/9 early OA and 8/10 advanced OA cases. This is the first report of HDMI and HDMP in the equine carpus and in the Standardbred breed and the first to rely solely on µCT. HDMP are a candidate cause for mechanical tissue destruction in OA. PMID:25927581

  11. First Infilling of the Venda Nova II Unlined High-Pressure Tunnel: Observed Behaviour and Numerical Modelling

    NASA Astrophysics Data System (ADS)

    Lamas, Luís N.; Leitão, Noemí S.; Esteves, Carlos; Plasencia, Nadir

    2014-05-01

    The underground structures of the Venda Nova II reversible hydroelectric power scheme present features that make it an interesting case study. Worthy of mention are the inclination and length of the unlined pressure tunnel, the high water head and the great depth of the powerhouse cavern. In projects of this type, the main effect of the internal water pressure in the pressure tunnel is the establishment of seepage from the tunnel into the rock mass, which can reach the adits and the powerhouse cavern. This seepage is influenced by several factors, such as the geometry of the underground openings, the rock mass properties—namely, the joints characteristics—and the stress state resulting from the excavation and from the internal water pressure. This article presents the main features of the underground structures of the Venda Nova II scheme and a detailed description of the observed behaviour during the first infilling of the pressure tunnel. A three-dimensional multi-laminated numerical model of the rock mass hydromechanical behaviour was developed to help understand the observed behaviour. The model assumptions in regard to the geometry of the openings, the jointing pattern, the rock mass hydraulic and mechanical behaviour, as well as the hydromechanical interaction, are described. Results obtained with the numerical model are presented and compared with the observed behaviour. Finally, the validity and importance of the numerical tools for the interpretation of the rock mass hydromechanical behaviour is discussed.

  12. High Density Infill in Cracks and Protrusions from the Articular Calcified Cartilage in Osteoarthritis in Standardbred Horse Carpal Bones

    PubMed Central

    Laverty, Sheila; Lacourt, Mathieu; Gao, Chan; Henderson, Janet E.; Boyde, Alan

    2015-01-01

    We studied changes in articular calcified cartilage (ACC) and subchondral bone (SCB) in the third carpal bones (C3) of Standardbred racehorses with naturally-occurring repetitive loading-induced osteoarthritis (OA). Two osteochondral cores were harvested from dorsal sites from each of 15 post-mortem C3 and classified as control or as showing early or advanced OA changes from visual inspection. We re-examined X-ray micro-computed tomography (µCT) image sets for the presence of high-density mineral infill (HDMI) in ACC cracks and possible high-density mineralized protrusions (HDMP) from the ACC mineralizing (tidemark) front (MF) into hyaline articular cartilage (HAC). We hypothesized and we show that 20-µm µCT resolution in 10-mm diameter samples is sufficient to detect HDMI and HDMP: these are lost upon tissue decalcification for routine paraffin wax histology owing to their predominant mineral content. The findings show that µCT is sufficient to discover HDMI and HDMP, which were seen in 2/10 controls, 6/9 early OA and 8/10 advanced OA cases. This is the first report of HDMI and HDMP in the equine carpus and in the Standardbred breed and the first to rely solely on µCT. HDMP are a candidate cause for mechanical tissue destruction in OA. PMID:25927581

  13. High density infill in cracks and protrusions from the articular calcified cartilage in osteoarthritis in standardbred horse carpal bones.

    PubMed

    Laverty, Sheila; Lacourt, Mathieu; Gao, Chan; Henderson, Janet E; Boyde, Alan

    2015-04-28

    We studied changes in articular calcified cartilage (ACC) and subchondral bone (SCB) in the third carpal bones (C3) of Standardbred racehorses with naturally-occurring repetitive loading-induced osteoarthritis (OA). Two osteochondral cores were harvested from dorsal sites from each of 15 post-mortem C3 and classified as control or as showing early or advanced OA changes from visual inspection. We re-examined X-ray micro-computed tomography (µCT) image sets for the presence of high-density mineral infill (HDMI) in ACC cracks and possible high-density mineralized protrusions (HDMP) from the ACC mineralizing (tidemark) front (MF) into hyaline articular cartilage (HAC). We hypothesized and we show that 20-µm µCT resolution in 10-mm diameter samples is sufficient to detect HDMI and HDMP: these are lost upon tissue decalcification for routine paraffin wax histology owing to their predominant mineral content. The findings show that µCT is sufficient to discover HDMI and HDMP, which were seen in 2/10 controls, 6/9 early OA and 8/10 advanced OA cases. This is the first report of HDMI and HDMP in the equine carpus and in the Standardbred breed and the first to rely solely on µCT. HDMP are a candidate cause for mechanical tissue destruction in OA.

  14. Holocene Monsoon variability in East Africa: a marine perspective

    NASA Astrophysics Data System (ADS)

    Romahn, S.; Mackensen, A.; Groeneveld, J.; Pätzold, J.

    2012-12-01

    The processes that control past monsoon variability in the East African Tropics during the Holocene are poorly understood. Especially the role of Sea Surface Temperatures (SST) controlling East African Rainfall on millennial timescales, as it is observed on decadal timescales, is currently intensely debated. In addition, it has been suggested recently that the longitudinal migration of the Congo Air Boundary (CAB) modulates East African precipitation on a regional scale as well [Tierney et al., 2011]. Here, we present a high-resolution marine sediment record for the past 12 kyrs from offshore Tanzania, close to the Rufiji River delta, to contribute to the current debate from a marine point of view. We reconstructed past SST and δ18Oseawater, derived from planktic foraminiferal Mg/Ca and δ18O, and past Sea Surface Salinity (SSS) variations, derived from planktic foraminiferal Ba/Ca-ratios. In the vicinity of river deltas, Ba/Ca-ratios have potential to record precipitation changes in the rivers' catchment area. Our records show that East African precipitation, derived from Ba/Ca-ratios, roughly varies in concert with Indian Ocean SST, suggesting higher Indian Ocean SST to be an important prerequisite for stronger precipitation, and hence an intense monsoon episode in East Africa. We calculated the difference (ΔSST) between our record of Indian Ocean SST and SST of the tropical Atlantic [Weldeab et al., 2005], showing that ΔSST variability resembles the isotopic pattern of the Kilimanjaro ice core record [Thompson et al., 2002]. We suggest this to be the consequence of a longitudinal movement of the CAB over the African Continent, changing the trajectory of Indian Ocean moisture into the continent and therefore affecting the δ18O of the East African rainout. Thompson, L. G., et al. (2002), Kilimanjaro Ice Core Records: Evidence of Holocene Climate Change in Tropical Africa, Science, 298, 589-593. Tierney, J. E., et al. (2011), Late Quaternary behavior of the

  15. Application of integrated reservoir management and reservoir characterization to optimize infill drilling. Annual technical progress report, June 13, 1996--June 12, 1997

    SciTech Connect

    Nevans, J.W.; Pregger, B.; Blasingame, T.; Doublet, L.; Freeman, G.; Callard, J.; Moore, D.; Davies, D.; Vessell, R.

    1997-08-01

    Infill drilling of wells on a uniform spacing, without regard to reservoir performance and characterization, does not optimize reservoir development because it fails to account for the complex nature of reservoir heterogeneities present in many low permeability reservoirs, and carbonate reservoirs in particular. New and emerging technologies, such as geostatistical modeling, rigorous decline curve analysis, reservoir rock typing, and special core analysis can be used to develop a 3-D simulation model for prediction of infill locations. The purpose of this project is to demonstrate the application of advanced secondary recovery technologies to remedy producibility problems in typical shallow shelf carbonate reservoirs of the Permian Basin, Texas. Typical problems include poor sweep efficiency, poor balancing of injection and production rates, and completion techniques that are inadequate for optimal production and injection.

  16. Application of Integrated Reservoir Management and Reservoir Characterization to Optimize Infill Drillings. Annual technical progress report, June 13, 1996 to June 12, 1998

    SciTech Connect

    Nevans, Jerry W.; Blasingame, Tom; Doublet, Louis; Kelkar, Mohan; Freeman, George; Callard, Jeff; Moore, David; Davies, David; Vessell, Richard; Pregger, Brian; Dixon, Bill

    1999-04-27

    Infill drilling of wells on a uniform spacing, without regard to reservoir performance and characterization, does not optimize reservoir development because it fails to account for the complex nature of reservoir heterogeneities present in many low permeability reservoirs, and carbonate reservoirs in particular. New and emerging technologies, such as geostatistical modeling, rigorous decline curve analysis, reservoir rock typing, and special core analysis can be used to develop a 3-D simulation model for prediction of infill locations. Other technologies, such as inter-well injection tracers and magnetic flow conditioners, can also aid in the efficient evaluation and operation of both injection and producing wells. The purpose of this project was to demonstrate useful and cost effective methods of exploitation of the shallow shelf carbonate reservoirs of the Permian Basin located in West Texas.

  17. Middle Holocene Unconformity in Seneca Lake, NY

    NASA Astrophysics Data System (ADS)

    Curtin, T. M.; Crocker, M.; Loddengaard, K.

    2008-12-01

    The post-glacial history of the Finger Lakes, NY have involved several changes in lake levels throughout the latest Pleistocene and Holocene, resulting from the changing position of the retreating Laurentide ice sheet, river outlet position, glacial rebound, and water balance. Previous studies of high-resolution seismic reflection profiles from three Finger Lakes define a middle Holocene erosional surface at water depths as great as 26 m in the northern end of each of lake. There are two proposed hypotheses to explain the origin of the observed erosional surfaces: 1) subaerial erosion during a lake lowstand and 2) erosion resulting from increased internal seiche activity. To evaluate these hypotheses, we examined a series of 2 to 5 m long piston cores collected along a north-south transect from one of the Finger Lakes, Seneca Lake. Cores were correlated using distinctive changes in the profiles of grain size, loss-on-ignition, and magnetic susceptibility. We recognize a significant erosional unconformity of early to middle Holocene sediment at modern depths <60 m because portions of the normal deepwater sediment sequence were missing in cores and were commonly replaced by a thin zone of sand and abraded shells (bivalves, gastropods). At water depths >60 m, the unconformity continues as a conformable zone. We attribute the unconformity to wave abrasion and nearshore current winnowing of the shoreface during a lowstand. With an assumption of an effective 20 m wave base, the depth to the low level lake surface responsible for the unconformity is estimated to be 40 m. The age of the unconformity is ~6 ka, based on radiocarbon ages of lithologic boundaries in the sediment cores. Because the unconformity grades into a conformable zone in deepwater cores that display no change in lithology, we hypothesize that the large-scale lake level drop is likely not the result of climate change, but rather a change in accommodation space in the northern portion of the lake basin due

  18. Late Holocene stable-isotope based winter temperature records from ice wedges in the Northeast Siberian Arctic

    NASA Astrophysics Data System (ADS)

    Opel, Thomas; Meyer, Hanno; Laepple, Thomas; Dereviagin, Alexander Yu.

    2016-04-01

    The Arctic is currently undergoing an unprecedented warming. This highly dynamic response on changes in climate forcing and the global impact of the Arctic water, carbon and energy balances make the Arctic a key region to study past, recent and future climate changes. Recent proxy-based temperature reconstructions indicate a long-term cooling over the past about 8 millennia that is mainly related to a decrease in solar summer insolation and has been reversed only by the ongoing warming. Climate model results on the other hand show no significant change or even a slight warming over this period. This model-proxy data mismatch might be caused by a summer bias of the used climate proxies. Ice wedges may provide essential information on past winter temperatures for a comprehensive seasonal picture of Holocene Arctic climate variability. Polygonal ice wedges are a widespread permafrost feature in the Arctic tundra lowlands. Ice wedges form by the repeated filling of thermal contraction cracks with snow melt water, which quickly refreezes at subzero ground temperatures and forms ice veins. As the seasonality of frost cracking and infill is generally related to winter and spring, respectively, the isotopic composition of wedge ice is indicative of past climate conditions during the annual cold season (DJFMAM, hereafter referred to as winter). δ18O of ice is interpreted as proxy for regional surface air temperature. AMS radiocarbon dating of organic remains in ice-wedge samples provides age information to generate chronologies for single ice wedges as well as regionally stacked records with an up to centennial resolution. In this contribution we seek to summarize Holocene ice-wedge δ18O based temperature information from the Northeast Siberian Arctic. We strongly focus on own work in the Laptev Sea region but consider as well literature data from other regional study sites. We consider the stable-isotope composition of wedge ice, ice-wedge dating and chronological

  19. Application of Integrated Reservoir Management and Reservoir Characterization to Optimize Infill Drilling

    SciTech Connect

    P. K. Pande

    1998-10-29

    Initial drilling of wells on a uniform spacing, without regard to reservoir performance and characterization, must become a process of the past. Such efforts do not optimize reservoir development as they fail to account for the complex nature of reservoir heterogeneities present in many low permeability reservoirs, and carbonate reservoirs in particular. These reservoirs are typically characterized by: o Large, discontinuous pay intervals o Vertical and lateral changes in reservoir properties o Low reservoir energy o High residual oil saturation o Low recovery efficiency

  20. Extending the Anthropocene? Synthesizing Land Use and land cover data for the Holocene, a new global working group

    NASA Astrophysics Data System (ADS)

    Morrison, K. D.

    2015-12-01

    Outside the geophysical sciences, the concept of the Anthropocene has been enthusiastically received. Its meaning, however, has been expanded beyond its original compass to suggest that humans have only recently had a significant impact on global processes. This is unfortunate, since paleoecological and archaeological data suggest significant anthropogenic transformation of land cover and land forms by the mid-Holocene. A new working group, LandCover 6k, is working to aggregate and synthesize global land use and land cover data across the Holocene in order to address these transformations more precisely.

  1. Using self-organizing maps to infill missing data in hydro-meteorological time series from the Logone catchment, Lake Chad basin.

    PubMed

    Nkiaka, E; Nawaz, N R; Lovett, J C

    2016-07-01

    Hydro-meteorological data is an important asset that can enhance management of water resources. But existing data often contains gaps, leading to uncertainties and so compromising their use. Although many methods exist for infilling data gaps in hydro-meteorological time series, many of these methods require inputs from neighbouring stations, which are often not available, while other methods are computationally demanding. Computing techniques such as artificial intelligence can be used to address this challenge. Self-organizing maps (SOMs), which are a type of artificial neural network, were used for infilling gaps in a hydro-meteorological time series in a Sudano-Sahel catchment. The coefficients of determination obtained were all above 0.75 and 0.65 while the average topographic error was 0.008 and 0.02 for rainfall and river discharge time series, respectively. These results further indicate that SOMs are a robust and efficient method for infilling missing gaps in hydro-meteorological time series. PMID:27282595

  2. Late Holocene eolian fossilization of Podzols in Northeastern Germany

    NASA Astrophysics Data System (ADS)

    Hirsch, Florian; Raab, Thomas; Schneider, Anna; Wechler, Klaus-Peter

    2016-04-01

    The North European lowland has been formed by glacial and periglacial processes in the Late Pleistocene. Multiple reshaping since the Late Glacial considerably changed the landscape up to and including especially historic times. Sediment sequences and (fossilized) soils can improve our understanding of Late Quaternary landscape development, but mapping of buried soils and surfaces is often limited to single outcrops. Ongoing archaeological rescue excavations in the pre-field of the open-cast mine Cottbus-Nord (northeastern Germany) with dense excavation trenches in an about 10 ha dune and drift sand area reveal multilayered sediment sequences with fossilized soils and sediments from the Late Pleistocene to the Late Holocene. Archaeological findings ranging from Mesolithic flint stones to an about 200 year old ceramics in eolian sediments covering plow horizons and wheel tracks suggest that eolian relocation of sandy material was intensive about 200 years ago. Still unpublished OSL dating underline the intense eolian activity. Recent studies showed that between the 15Th to the 19Th century an iron smelter 5 km to the west of our study site was supplied with charcoal, which was produced in a forest 5 km east to our study site. Our current findings about Late Holocene eolian activity raise the question if this eolian reshaping of the landscape is connected with the operation of the iron smelter either directly by transport or bog iron ore winning or indirectly by population pressure caused by the prospering iron smelter. Our ongoing research indicates, that already for historic land-use off-site effects causing further landscape changes have to be considered.

  3. Transient coupling relationships of the Holocene Australian monsoon

    NASA Astrophysics Data System (ADS)

    McRobie, F. H.; Stemler, T.; Wyrwoll, K.-H.

    2015-08-01

    The northwest Australian summer monsoon owes a notable degree of its interannual variability to interactions with other regional monsoon systems. Therefore, changes in the nature of these relationships may contribute to variability in monsoon strength over longer time scales. Previous attempts to evaluate how proxy records from the Indonesian-Australian monsoon region correspond to other records from the Indian and East Asian monsoon regions, as well as to El Niño-related proxy records, have been qualitative, relying on 'curve-fitting' methods. Here, we seek a quantitative approach for identifying coupling relationships between paleoclimate proxy records, employing statistical techniques to compute the interdependence of two paleoclimate time series. We verify the use of complex networks to identify coupling relationships between modern climate indices. This method is then extended to a set of paleoclimate proxy records from the Asian, Australasian and South American regions spanning the past 9000 years. The resulting networks demonstrate the existence of coupling relationships between regional monsoon systems on millennial time scales, but also highlight the transient nature of teleconnections during this period. In the context of the northwest Australian summer monsoon, we recognise a shift in coupling relationships from strong interhemispheric links with East Asian and ITCZ-related proxy records in the mid-Holocene to significantly weaker coupling in the later Holocene. Although the identified links cannot explain the underlying physical processes leading to coupling between regional monsoon systems, this method provides a step towards understanding the role that changes in teleconnections play in millennial-to orbital-scale climate variability.

  4. Affordable Cold Climate Infill Housing with Hybrid Insulation Approach, Wyandotte, Michigan (Fact Sheet)

    SciTech Connect

    Metzger, C.; Lukachko, A.; Grin, A.; Bergey, D.

    2013-11-01

    Even builders who are relatively new to energy-efficient construction can consistently reach a target whole house airtightness of 1.5 air changes per hour at 50 Pascals (ACH50) with high R-value enclosures that use a hybrid insulation approach. The City of Wyandotte, Michigan, started a construction program in 2010 to build affordable, energy-efficient homes on lots in existing neighborhoods. A goal of the program was to engage local builders in energy-efficient construction and be able to deliver the new houses for less than $100/ft2. By the end of 2012, approximately 25 new houses were built by five local builders under this program. To help builders consistently achieve the airtightness target, a local architect worked with researchers from Building Science Corporation, a U.S. Department of Energy Building America team, to develop a technology specification with several key pieces. A high R-value wall and roof assembly made use of 2 ?6 advanced framing and a hybrid insulation approach that included insulating sheathing to control thermal bridging and closed cell spray polyurethane foam insulation (ccSPF) for its airtightness and vapor control benefits. This approach allows the air barrier to be completed and tested before any finishing work occurs, ensuring that problems are spotted and corrected early in the construction process.

  5. Reconstruction of glacier variability from lake sediments reveals dynamic Holocene climate in Svalbard

    NASA Astrophysics Data System (ADS)

    van der Bilt, Willem G. M.; Bakke, Jostein; Vasskog, Kristian; D'Andrea, William J.; Bradley, Raymond S.; Ólafsdóttir, Sædis

    2015-10-01

    The Arctic is warming faster than anywhere else on Earth. Holocene proxy time-series are increasingly used to put this amplified response in perspective by understanding Arctic climate processes beyond the instrumental period. However, available datasets are scarce, unevenly distributed and often of coarse resolution. Glaciers are sensitive recorders of climate shifts and variations in rock-flour production transfer this signal to the lacustrine sediment archives of downstream lakes. Here, we present the first full Holocene record of continuous glacier variability on Svalbard from glacier-fed Lake Hajeren. This reconstruction is based on an undisturbed lake sediment core that covers the entire Holocene and resolves variability on centennial scales owing to 26 dating points. A toolbox of physical, geochemical (XRF) and magnetic proxies in combination with multivariate statistics has allowed us to fingerprint glacier activity in addition to other processes affecting the sediment record. Evidence from variations in sediment density, validated by changes in Ti concentrations, reveal glaciers remained present in the catchment following deglaciation prior to 11,300 cal BP, culminating in a Holocene maximum between 9.6 and 9.5 ka cal BP. Correspondence with freshwater pulses from Hudson Strait suggests that Early Holocene glacier advances were driven by the melting Laurentide Ice Sheet (LIS). We find that glaciers disappeared from the catchment between 7.4 and 6.7 ka cal BP, following a late Hypsithermal. Glacier reformation around 4250 cal BP marks the onset of the Neoglacial, supporting previous findings. Between 3380 and 3230 cal BP, we find evidence for a previously unreported centennial-scale glacier advance. Both events are concurrent with well-documented episodes of North Atlantic cooling. We argue that this brief forcing created suitable conditions for glaciers to reform in the catchment against a background of gradual orbital cooling. These findings highlight the

  6. Holocene ENSO Reconstructions from Molecular Rain Gauges

    NASA Astrophysics Data System (ADS)

    Sachs, J. P.; Zhang, Z.; Smittenberg, R.; Saenger, C.; Pahnke, K.; Koutavas, A.

    2005-12-01

    The response ENSO to the mean climate state is poorly understood. Paleoclimate records of ENSO variability under different climate boundary conditions are needed to validate models but remain few and far between. Most existing records are from single cores or locations, are constructed from a single paleo-environmental proxy, and span a short time interval. In light of this paucity of data we are constructing a continuous history of ENSO-related rainfall anomalies, spanning the Holocene, from a wide diversity of settings across the equatorial Pacific, using a multitude of biomarker and molecular isotopic (D/H, 13C/12C) measurements. During 2004-2005 we collected sediment cores from equatorial lakes, bogs, hypersaline basins, and marine sediments in Palau (western Pacific), Kiribati and the Galapagos (central Pacific), and the Panama Basin (eastern Pacific). Each location was specifically targeted for its centrality in one of three zones of anomalous ENSO-related rainfall. Each water body cored was targeted for its sensitivity to rainfall variations. Many of the cores have sediment accumulation rates, derived from Pb-210 and C-14, that exceed 1 m/kyr, permitting decadal resolution. Here we report on our findings to date. Biomarker and molecular D/H records of drought in Palau, high lake levels in the Galapagos, and diminished Andean runoff to the Panama Basin indicate a late Holocene increase in El Nino frequency and/or intensity.

  7. Holocene Hydrologic Changes in the Tropical Pacific

    NASA Astrophysics Data System (ADS)

    Sachs, J. P.; Zhang, Z.; Smittenberg, R.; Saenger, C.; Sachse, D.

    2006-12-01

    The tropical Pacific Ocean plays a central role in the climate system by providing massive fluxes of sensible and latent heat to the atmosphere that have the potential to drive global climate changes. Though some abrupt climate events in the late Pleistocene and Holocene were likely forced from the North Atlantic region, it is entirely possible that some had their trigger in the tropics. A paucity of paleoclimate records from the tropical Pacific region has hampered efforts to evaluate this possibility. Here we present highly resolved and well-dated molecular and isotopic records of rainfall from Palau (western Pacific), Kiribati (central Pacific) and Galapagos (eastern Pacific) lake sediments that indicate large hydrologic changes on decadal to millennial time scales throughout the Holocene. We note that some of the largest events in our records occurred during the last millennium. Implications for the mean state of the tropical climate, the position of the inter-tropical convergence zone (ITCZ), and the El Nino-Southern Oscillation (ENSO) system will be addressed.

  8. Welding of Pyroclastic Conduit Infill: A Mechanism for Cyclical Explosive Eruptions

    NASA Astrophysics Data System (ADS)

    Kolzenburg, Stephan; Russell, James K.

    2014-05-01

    Vulcanian style eruptions are small to moderate sized singular to cyclical events commonly having volcanic explosivity indices (VEI) of 1-3. They produce pyroclastic flows, disperse tephra over considerable areas and can occur as precursors to larger (e.g. Plinian) eruptions. Here we present a study on the evolution of the physical properties (strain, porosity, permeability and ultrasonic wave velocities) of breadcrust bombs recovered from the deposits of the 2350 B.P. eruption of Mt Meager, BC, Canada. These accessory lithics are fragments of welded intra vent deposits formed during compaction and deformation processes operating in the shallow (less than 2 km) conduit. The deformation experienced by these samples is a combination of compaction within the conduit and post-compaction stretching associated with the subsequent eruption. Our results highlight a profound directionality in the measured physical properties of these samples related to the deformation-induced fabric. Gas permeability varies drastically with increasing strain and decreasing porosity along the compaction direction of the fabric. However, permeability varies little along the elongation direction of the fabric. Similarly, ultrasonic wave velocities increase along the compaction direction and remain unaffected along the direction of fabric stretching; Poisons ratio increases along the fabric stretching direction. We combine these physical property measurements with models describing the timescales of porosity loss and to explore the timescales of permeability reduction and re-pressurization of the edifice. Modelling results and reconstruction of the deformation history also suggest the potential for a low-cost technique for monitoring the pressure build-up within volcanic systems based on fumarolic activity.

  9. Late Holocene volcanism at Medicine Lake Volcano, northern California Cascades

    USGS Publications Warehouse

    Donnelly-Nolan, Julie M.; Champion, Duane E.; Grove, Timothy L.

    2016-01-01

    Late Holocene volcanism at Medicine Lake volcano in the southern Cascades arc exhibited widespread and compositionally diverse magmatism ranging from basalt to rhyolite. Nine well-characterized eruptions have taken place at this very large rear-arc volcano since 5,200 years ago, an eruptive frequency greater than nearly all other Cascade volcanoes. The lavas are widely distributed, scattered over an area of ~300 km2 across the >2,000-km2 volcano. The eruptions are radiocarbon dated and the ages are also constrained by paleomagnetic data that provide strong evidence that the volcanic activity occurred in three distinct episodes at ~1 ka, ~3 ka, and ~5 ka. The ~1-ka final episode produced a variety of compositions including west- and north-flank mafic flows interspersed in time with fissure rhyolites erupted tangential to the volcano’s central caldera, including the youngest and most spectacular lava flow at the volcano, the ~950-yr-old compositionally zoned Glass Mountain flow. At ~3 ka, a north-flank basalt eruption was followed by an andesite eruption 27 km farther south that contains quenched basalt inclusions. The ~5-ka episode produced two caldera-focused dacitic eruptions. Quenched magmatic inclusions record evidence of intrusions that did not independently reach the surface. The inclusions are present in five andesitic, dacitic, and rhyolitic host lavas, and were erupted in each of the three episodes. Compositional and mineralogic evidence from mafic lavas and inclusions indicate that both tholeiitic (dry) and calcalkaline (wet) parental magmas were present. Petrologic evidence records the operation of complex, multi-stage processes including fractional crystallization, crustal assimilation, and magma mixing. Experimental evidence suggests that magmas were stored at 3 to 6 km depth prior to eruption, and that both wet and dry parental magmas were involved in generating the more silicic magmas. The broad distribution of eruptive events and the relative

  10. Late Holocene volcanism at Medicine Lake Volcano, northern California Cascades

    USGS Publications Warehouse

    Donnelly-Nolan, Julie M.; Champion, Duane E.; Grove, Timothy L.

    2016-05-23

    Late Holocene volcanism at Medicine Lake volcano in the southern Cascades arc exhibited widespread and compositionally diverse magmatism ranging from basalt to rhyolite. Nine well-characterized eruptions have taken place at this very large rear-arc volcano since 5,200 years ago, an eruptive frequency greater than nearly all other Cascade volcanoes. The lavas are widely distributed, scattered over an area of ~300 km2 across the >2,000-km2 volcano. The eruptions are radiocarbon dated and the ages are also constrained by paleomagnetic data that provide strong evidence that the volcanic activity occurred in three distinct episodes at ~1 ka, ~3 ka, and ~5 ka. The ~1-ka final episode produced a variety of compositions including west- and north-flank mafic flows interspersed in time with fissure rhyolites erupted tangential to the volcano’s central caldera, including the youngest and most spectacular lava flow at the volcano, the ~950-yr-old compositionally zoned Glass Mountain flow. At ~3 ka, a north-flank basalt eruption was followed by an andesite eruption 27 km farther south that contains quenched basalt inclusions. The ~5-ka episode produced two caldera-focused dacitic eruptions. Quenched magmatic inclusions record evidence of intrusions that did not independently reach the surface. The inclusions are present in five andesitic, dacitic, and rhyolitic host lavas, and were erupted in each of the three episodes. Compositional and mineralogic evidence from mafic lavas and inclusions indicate that both tholeiitic (dry) and calcalkaline (wet) parental magmas were present. Petrologic evidence records the operation of complex, multi-stage processes including fractional crystallization, crustal assimilation, and magma mixing. Experimental evidence suggests that magmas were stored at 3 to 6 km depth prior to eruption, and that both wet and dry parental magmas were involved in generating the more silicic magmas. The broad distribution of eruptive events and the relative

  11. Determining the concentration of individual eruptive events of the CAMP: Distinguishing interflow hiatuses from subterranean alteration and void infilling.

    NASA Astrophysics Data System (ADS)

    Olsen, P. E.; Kent, D. V.; Et-Touhami, M.

    2012-04-01

    More important than the total volume of eruptives in a LIP is the concentration in time of individual eruptions with timescales relevant for environmental change. In CAMP lavas, interflow sedimentary and reddened levels are interpreted as evidence of significant time between flows of hundreds to thousands of years allowing soil development and sediment deposition. Additionally, cross-cutting or enclosed sediment bodies, and basalt and sediment mixtures are interpreted as clastic intrusions and phreatic mixing (peperites). Here we show that most such occurrences are more consistent with post-emplacement alteration and void infill by sediment. Criteria for recognizing void fillings in cross-cutting, enclosed or mixed basalt include: 1) paleo-horizontal sediment stratification independent of basalt clasts or void walls - i.e., geopedal; 2) presence of clasts alien to underlying units such as lithic clasts or bones, the latter analogous to karst occurrences; 3) presence of current structures such as ripples; 4) lack of basalt chill margins; and 5) preserved stratigraphy related to overlying units. Criteria for recognizing flow-contact-parallel sediment bodies and reddened and altered contacts as post-emplacement alteration and void infill include: 1) reddening and alteration of both the upper surface of the older flow AND the lower surface of the overlying flow (caused by post-emplacement ground-water-flow); 2) presence of clasts derived from the bottom of the overlying flow; 3) location of tabular sediment bodies within blisters and paleosurface-parallel crack-sheets of the older flow, rather than at the contact between flows; and 4) physical connection between paleosurface-parallel sediment bodies and sediment bodies that cross-cutting the younger flow exhibiting post-emplacement features described above. Features that might be indicative of deposition at the land surface but are not include: 1) roots, which can penetrate for tens of meters through sediment

  12. A Siliciclastic-Infilled Sedimentary Basin Within a Large Carbonate Platform, Tampa Bay, Florida

    NASA Astrophysics Data System (ADS)

    Suthard, B. C.; Hine, A. C.; Locker, S. D.; Duncan, D. S.; Morton, R. A.; Hansen, M. E.; Edgar, N. T.

    2002-12-01

    A seismic stratigraphic framework based on over 800 km of seismic reflection data collected within the Tampa Bay estuary and approximately 200 boreholes in and around the estuary shows three separate subsurface regions. In the north-central portion of the bay there is an irregular east-west oriented subsurface trough in the Miocene limestone that reaches depths of 30 m below the seafloor (mbsf). This trough contains steeply dipping clinoforms that indicate it has been filled from the south and east and borehole data show that these clinoforms are siliciclastic sediments. South of the trough in the center of Tampa Bay there is a broad carbonate bedrock high. This area is characterized by less than two meters of siliciclastic sediment cover as well as small-scale shallow karst features (10's m in width and up to 10 m in relief). In the southern portion of the Bay the seismic reflection data shows the Miocene limestone has large-scale warping as well as larger-scale karst features (100's m in width and 30+ m in relief) creating another deep basin (up to 40 mbsf) that has been filled by siliciclastics from the south and the east. The sedimentary basin underlying the modern estuary reveals that accommodation space can form within the center of large carbonate platforms and that this accommodation space may be filled by remobilized siliciclastics. Based upon the age of the underlying limestones, and recent work in south Florida by others, we propose that the Tampa Basin was filled during multiple Late Neogene and Quaternary sea-level fluctuations. Additionally, we speculate that the observed multiple buried sinkholes, and sag-and-warp deformation indicate spatially selective subsurface collapse probably initiated by deep-seated dissolution produced by karst processes. Overlying stratigraphic units subsided as a result of solution collapse, creating a surficial topographic low. This surficial basin may have controlled subsequent non-marine, estuarine and even open marine

  13. Long-term resilience of late holocene coastal subsistence system in Southeastern South america.

    PubMed

    Colonese, André Carlo; Collins, Matthew; Lucquin, Alexandre; Eustace, Michael; Hancock, Y; de Almeida Rocha Ponzoni, Raquel; Mora, Alice; Smith, Colin; Deblasis, Paulo; Figuti, Levy; Wesolowski, Veronica; Plens, Claudia Regina; Eggers, Sabine; de Farias, Deisi Scunderlick Eloy; Gledhill, Andy; Craig, Oliver Edward

    2014-01-01

    Isotopic and molecular analysis on human, fauna and pottery remains can provide valuable new insights into the diets and subsistence practices of prehistoric populations. These are crucial to elucidate the resilience of social-ecological systems to cultural and environmental change. Bulk collagen carbon and nitrogen isotopic analysis of 82 human individuals from mid to late Holocene Brazilian archaeological sites (∼6,700 to ∼1,000 cal BP) reveal an adequate protein incorporation and, on the coast, the continuation in subsistence strategies based on the exploitation of aquatic resources despite the introduction of pottery and domesticated plant foods. These results are supported by carbon isotope analysis of single amino acid extracted from bone collagen. Chemical and isotopic analysis also shows that pottery technology was used to process marine foods and therefore assimilated into the existing subsistence strategy. Our multidisciplinary results demonstrate the resilient character of the coastal economy to cultural change during the late Holocene in southern Brazil.

  14. Long-Term Resilience of Late Holocene Coastal Subsistence System in Southeastern South America

    PubMed Central

    Colonese, André Carlo; Collins, Matthew; Lucquin, Alexandre; Eustace, Michael; Hancock, Y.; de Almeida Rocha Ponzoni, Raquel; Mora, Alice; Smith, Colin; DeBlasis, Paulo; Figuti, Levy; Wesolowski, Veronica; Plens, Claudia Regina; Eggers, Sabine; de Farias, Deisi Scunderlick Eloy; Gledhill, Andy; Craig, Oliver Edward

    2014-01-01

    Isotopic and molecular analysis on human, fauna and pottery remains can provide valuable new insights into the diets and subsistence practices of prehistoric populations. These are crucial to elucidate the resilience of social-ecological systems to cultural and environmental change. Bulk collagen carbon and nitrogen isotopic analysis of 82 human individuals from mid to late Holocene Brazilian archaeological sites (∼6,700 to ∼1,000 cal BP) reveal an adequate protein incorporation and, on the coast, the continuation in subsistence strategies based on the exploitation of aquatic resources despite the introduction of pottery and domesticated plant foods. These results are supported by carbon isotope analysis of single amino acid extracted from bone collagen. Chemical and isotopic analysis also shows that pottery technology was used to process marine foods and therefore assimilated into the existing subsistence strategy. Our multidisciplinary results demonstrate the resilient character of the coastal economy to cultural change during the late Holocene in southern Brazil. PMID:24718458

  15. A Southern Ocean trigger for Northwest Pacific ventilation during the Holocene?

    PubMed Central

    Rella, S. F.; Uchida, M.

    2014-01-01

    Holocene ocean circulation is poorly understood due to sparsity of dateable marine archives with submillennial-scale resolution. Here we present a record of mid-depth water radiocarbon contents in the Northwest (NW) Pacific Ocean over the last 12.000 years, which shows remarkable millennial-scale variations relative to changes in atmospheric radiocarbon inventory. Apparent decoupling of these variations from regional ventilation and mixing processes leads us to the suggestion that the mid-depth NW Pacific may have responded to changes in Southern Ocean overturning forced by latitudinal displacements of the southern westerly winds. By inference, a tendency of in-phase related North Atlantic and Southern Ocean overturning would argue against the development of a steady bipolar seesaw regime during the Holocene. PMID:24509792

  16. A Southern Ocean trigger for Northwest Pacific ventilation during the Holocene?

    PubMed

    Rella, S F; Uchida, M

    2014-02-17

    Holocene ocean circulation is poorly understood due to sparsity of dateable marine archives with submillennial-scale resolution. Here we present a record of mid-depth water radiocarbon contents in the Northwest (NW) Pacific Ocean over the last 12.000 years, which shows remarkable millennial-scale variations relative to changes in atmospheric radiocarbon inventory. Apparent decoupling of these variations from regional ventilation and mixing processes leads us to the suggestion that the mid-depth NW Pacific may have responded to changes in Southern Ocean overturning forced by latitudinal displacements of the southern westerly winds. By inference, a tendency of in-phase related North Atlantic and Southern Ocean overturning would argue against the development of a steady bipolar seesaw regime during the Holocene.

  17. Fine structure of the geomagnetic field of Holocene by the example of the loess sections of the Chirchic river basin of Uzbekistan

    NASA Astrophysics Data System (ADS)

    Stelmakh, A. G.

    2011-12-01

    Climate change and a number of peculiar of exogenous processes in the geological development on our planet for the past 10-13 thousand years can determine the Holocene time as a special stage in the geological history of the Quaternary period.The Holocene deposit in the Chirchic river basin of Uzbekistan has of "dumb" sediments and as result makes difficult to carry the regional correlation. Among researchers there is no consensus compiling stratigraphic schemes of the Holocene in the region due to the lack of reliable of time subdivisions and correlation of loess deposits.This complicates the chronology of Holocene loess deposits in the region. On the other hand, the Holocene loess deposits in Uzbekistan have not been studied in detail by the paleomagnetic method. Using palaeomagnetic method for study these deposits is one of the perspective methods. This method is a most importance by the stratigraphic subdivision of the Holocene deposits. As is well known Holocene time in the geomagnetic scale refers to the geomagnetic epoch of Brunhes. This epoch is direct geomagnetic polarity. To date researchers revealed a number of short-term variability of the geomagnetic field in the Brunhes epoch. We researched fairly complete of stratigraphic sections of Holocene deposit in the Chirchic river basin of Uzbekistan.Holocene deposits are presented by two alluvial cycles and characterize by sediments of the riverbed and by two river terraces. These formations in stratigraphic scheme Uzbekistan are sediments of Syrdariya complex.In studied sections of Holocene deposits in the Chirchic river basin are installed three short deflections of the magnetic field of Earth. We are determined two events of a reversed magnetization and a short excurse. Determination of their age by TL-method shows that they are located on determined of stratigraphic levels. These two events of a reversed magnetization and a short excurse have palaeomagnetic criterions of the correlation "dumb" deposits

  18. Faunal reorganisation in terrestrial mammalian communities: evidence from France during the Lateglacial-Early Holocene transition

    NASA Astrophysics Data System (ADS)

    Bridault, Anne

    2010-05-01

    The Lateglacial-Early Holocene transition is characterized by rapid oscillations between warm and cold episodes. Their impact on ecosystem dynamics was particularly pronounced in north-western Europe where hunter-gatherer societies experienced a succession of environmental transformations, including the expansion and dispersal of biotic communities and changing herbivore habitats. Recent archaeozoological studies and AMS direct dating on mammalian bones/or bone collagen allow to map and precise this process at a supra-regional scale (France). At regional scales (i.e. Paris Basin & Jura-Northern French Alps), results indicate a rapid faunal reorganisation at the end of Lateglacial that will be presented in detail. Composition of faunal assemblages remains then unchanged during the Early Holocene. By contrast, significant herbivore habitat changes are recorded during the Early Holocene by other proxies (pollen data and isotopic data) and a decrease in Red Deer size through time is evidenced by osteometrical analyses. Hypotheses regarding the kind of adaptation process experienced by the faunal communities through time will be presented. Factors that may have controlled the observed changes will be discussed.

  19. Diatom-inferred total phosphorus from dystrophic Lake Arapisto, Finland, in relation to Holocene paleoclimate

    NASA Astrophysics Data System (ADS)

    Luoto, Tomi P.; Nevalainen, Liisa; Kauppila, Tommi; Tammelin, Mira; Sarmaja-Korjonen, Kaarina

    2012-09-01

    A sediment core from Lake Arapisto, Finland, was examined for fossil diatom assemblages to reconstruct changes in Holocene nutrient availability. Our aim was to investigate the long-term relationship between lake trophic status and climate by comparing the diatom-based phosphorus reconstruction with paleoclimatic proxies. Our results showed that the cold early Holocene was characterized by elevated nutrient conditions concurrent with newly exposed fertile ground. As the climate rapidly warmed and ice sheet further retreated, the catchment vegetation developed, which resulted in decreased nutrient flux into the lake. The Holocene Thermal Maximum (HTM), between ~ 8000 and 4000 cal yr BP, was characterized by oligotrophic conditions, which may have been caused by low effective precipitation and stable watershed vegetation. After the HTM, the lake became more productive. There was no particular increase in the trophic state that could be connected to more recent human influence. Although lake productivity has been shown to be affected by temperature, our record indicated that the nutrient dynamics were driven by complex interactions between changes in temperature, precipitation, catchment, and in-lake processes. Understanding of long-term nutrient dynamics and the associated processes can help in resolving relationships between lake productivity and climate during past and present climate changes.

  20. Elucidating the Holocene Relative Sea-Level History of the US Atlantic Coast

    NASA Astrophysics Data System (ADS)

    Engelhart, S. E.; Anderson, C.; Hill, D.; Horton, B. P.; Peltier, W. R.; van de Plassche, O.; Shennan, I.; Thieler, E. R.; Tornqvist, T. E.

    2007-12-01

    There is an urgent need for a re-assessment of the quality of Holocene relative sea-level (RSL) observations from the Atlantic and Gulf coasts of the United States. Holocene RSL data provide an essential benchmark to compare against other records of RSL change in the last 100-150 years. Only high quality sea-level data reveal spatial and temporal variations in crustal movements since the Last Glacial Maximum and provide a vital constraint upon dynamical models of the Glacial Isostatic Adjustment (GIA) process. We require an accurate model of the GIA process to inform the global data set currently being produced on the time dependence of the gravitational field of the planet by the Gravity Recovery and Climate Experiment (GRACE). We have compiled database of 1400 possible sea-level index points for the Atlantic coast of the United States. These unvalidated data contain much scatter due to concepts inherent in their original interpretation. They rarely allow for other factors such as sediment compaction and tidal range variation. Following validation, results from Delaware and North Carolina show a rapid rise in RSL from the early to mid Holocene, with no evidence of sea- level above present. They also differ somewhat from GIA model predictions. Rates of RSL change during the late Holocene divide into three broad zones: (1) Maine to Boston, MA ~ RSL rise of less than 1 mm yr-1; (2) Cape Cod, MA to Maryland ~ RSL rise between 1 and 3 mm yr-1; and (3) North Carolina to South Carolina ~ RSL rise less than 1 mm yr-1. Comparison with tide-gauge records demonstrate an increase of at least 1 mm yr-1 at all sites since AD 1900.

  1. Holocene constraints on simulated tropical Pacific climate

    NASA Astrophysics Data System (ADS)

    Emile-Geay, J.; Cobb, K. M.; Carre, M.; Braconnot, P.; Leloup, J.; Zhou, Y.; Harrison, S. P.; Correge, T.; Mcgregor, H. V.; Collins, M.; Driscoll, R.; Elliot, M.; Schneider, B.; Tudhope, A. W.

    2015-12-01

    The El Niño-Southern Oscillation (ENSO) influences climate and weather worldwide, so uncertainties in its response to external forcings contribute to the spread in global climate projections. Theoretical and modeling studies have argued that such forcings may affect ENSO either via the seasonal cycle, the mean state, or extratropical influences, but these mechanisms are poorly constrained by the short instrumental record. Here we synthesize a pan-Pacific network of high-resolution marine biocarbonates spanning discrete snapshots of the Holocene (past 10, 000 years of Earth's history), which we use to constrain a set of global climate model (GCM) simulations via a forward model and a consistent treatment of uncertainty. Observations suggest important reductions in ENSO variability throughout the interval, most consistently during 3-5 kyBP, when approximately 2/3 reductions are inferred. The magnitude and timing of these ENSO variance reductions bear little resemblance to those sim- ulated by GCMs, or to equatorial insolation. The central Pacific witnessed a mid-Holocene increase in seasonality, at odds with the reductions simulated by GCMs. Finally, while GCM aggregate behavior shows a clear inverse relationship between seasonal amplitude and ENSO-band variance in sea-surface temperature, in agreement with many previous studies, such a relationship is not borne out by these observations. Our synthesis suggests that tropical Pacific climate is highly variable, but exhibited millennia-long periods of reduced ENSO variability whose origins, whether forced or unforced, contradict existing explanations. It also points to deficiencies in the ability of current GCMs to simulate forced changes in the tropical Pacific seasonal cycle and its interaction with ENSO, highlighting a key area of growth for future modeling efforts.

  2. Exploring Holocene climate fluctuations registered in Bosnian stalagmites adopting a multiproxy approach

    NASA Astrophysics Data System (ADS)

    Chiarini, Veronica; Couchoud, Isabelle; Drysdale, Russell; Bajo, Petra; Milanolo, Simone; Hellstrom, John; De Waele, Jo

    2016-04-01

    The central Mediterranean area, a crucial region for present day and future climate change, has been characterised by contrasting patterns between northern and southern climate influences over the Holocene (e.g. Magny et al., 2012; Peyron et al., 2013). Several records from the Italian Peninsula identify this phenomenon: relatively dry conditions experienced during the first half of the Holocene are followed by an increase in moisture in the northern regions, while in the southern portion of the Peninsula the opposite trend occurs. On the Balkan side of the Adriatic Sea, this contrasting pattern is less well documented. The available studies focused on lake sediments show a more gradual and less warm early Holocene and more stable conditions during the early-mid Holocene compared to Italy (Bordon et al., 2009; Vogel et al., 2010). Several speleothems have been collected from Banja Stijena and Govještica Caves (Bosnia and Herzegovina). Preliminary U-Th dating allowed to choose the five most promising samples for further study. Stable oxygen and carbon isotopes have been analysed along the stalagmite growth axes and trace elements of one sample have been investigated. Air-mass back-trajectory analyses of present day precipitation in the area have been performed in association with GNIP rainfall isotope data analyses, with the aim of understanding the parameters driving rainfall stable oxygen isotope composition variations. Considering the impossibility of having a detailed monitoring of cave conditions due to the practical difficulties of identifying the original location of the samples collected, petrographic observations have been coupled with δ13C and δ18O in order to improve the understanding of the environmental processes recorded by these samples, as suggested in Frisia (2015) and Borsato et al. (2015). Here we will present the results of these multiproxy analyses, exploring the potential of these samples in recording regional climate fluctuations and

  3. Mobilization of Arsenic in Groundwater of Holocene Delta, Indian Segment

    NASA Astrophysics Data System (ADS)

    Chatterjee, D.

    2007-12-01

    Recent incidences of high arsenic exposure from drinking water and human suffering in SE Asia notably in Bengal Delta Plain (BDP) appear to be quite different from the global scenario. The source of arsenic in groundwater of BDP is considered to be geogenic and mostly restricted to Holocene sediments. Several models (oxidation of As-rich pyrite, reductive dissolution of Fe(III)-Fe(II) systems, anion exchange of sorbed As mostly phosphate) have been put forward. However, the models have their own weakness and the paper deals with such discrepancies to focus the arsenic sourcing (primary, secondary and tertiary), release mechanism and mobilization in Holocene deltas. The paper also deals with groundwater quality and (hydro) chemistry vis-a-vis alluvial Holocene sediment. The stratigraphic profiling indicates that the shallow aquifers (< 40m) are significant contributors (~91 percent, n = 497) of high arsenic in groundwater. The major hydrochemical features are low Eh (range: - 149-37 mv; mean: - 53mv) and nitrate (range 0.001- 1.72; mean 0.13 mg/L) followed by high alkalinity (range 100 - 630 mg/L; mean 280 mg/L), iron (1.23- 38.4, mean 7.48 mg/L), phosphate (range 0.002 - 3. 99 mg/L; mean 0.56 mg/L), hardness (range 46-490 mg/L; mean 235) and sulphate (0.28 - 48.62 mg/L; mean 6.43 mg/L). Groundwater (hydro) chemistry indicates that the affected aquifers are reducing in nature. The four different local situations (sanitation, surface water bodies, land use and sanitation coupled with eco-system) are identified and most important is sanitation where groundwater arsenic concentration is highest (up to 1180 mg/L) among the different local situation. Arsenic hotspots are identified as a multi-level phenomena and unveiled greater complexities at a deeper level. Morphology and sediment profiling of BDP deltas are influencing arsenic sourcing where sandy useable aquifers are identified with overbank deposits rich in arsenic host environment. Shallow aquifers ( 5-70 m) are

  4. Holocene growth of a mid-Pacific atoll: Tarawa, Kiribati

    NASA Astrophysics Data System (ADS)

    Marshall, J. F.; Jacobson, G.

    1985-04-01

    Cores from ten holes, drilled to a maximum depth of 30 m, on Tarawa atoll in the central Pacific have been utilised in a study of the Holocene development of the atoll. Four dominant lithologies, in descending order, are cay rock, unconsolidated sediment, corals and leached limestone. Petrographic and radiometric age analyses indicate that the Holocene reef has developed on a previous (last interglacial) reef; the latter shows the effects of both vadose and phreatic freshwater diagenesis. Hydrological investigations beneath the present islands indicate the presence of freshwater lenses up to 29 m thick; the modern lenses are unrelated to freshwater diagenetic imprints preserved within the limestones. Vertical accretion rates of 5 8 m/1000 years for the Holocene reef section on Tarawa are significantly higher than rates measured for other Pacific atolls. The dated coral sequences suggest a more rapid rate of sea level rise during the early Holocene, and a relatively earlier stabilisation of sea level than has been suggested previously.

  5. Environmental evolution of the southern Chukchi Sea in the Holocene

    NASA Astrophysics Data System (ADS)

    Gusev, E. A.; Anikina, N. Yu.; Derevyanko, L. G.; Klyuvitkina, T. S.; Polyak, L. V.; Polyakova, E. I.; Rekant, P. V.; Stepanova, A. Yu.

    2014-07-01

    The molluscan shells from three drill and two piston cores obtained in the southern Russian sector of the Chukchi Sea are dated by the AMS 14C measurement method back to 0.8-3.5 and 9.2-10.5 ka. The period of 9-10 ka was marked by increased sedimentation rates related to the transgression onset. The fossils in the lower Holocene section exhibit the successive upward replacement of brackish-water organisms by their marine counterparts. After the opening of the Bering Strait in the middle Holocene, the sedimentation was under influence of the increased bioproductivity of the waters. The climatic optimum in the Chukotka region corresponds to the early Holocene, while the late Holocene was characterized by the wider development of the ice cover on the shelf.

  6. Holocene Relative Sea-Level Changes from Near-, Intermediate-, and Far-Field Locations

    NASA Astrophysics Data System (ADS)

    Walker, J. S.; Khan, N.; Shaw, T.; Ashe, E.; Vacchi, M.; Peltier, W. R.; Kopp, R. E.; Horton, B.

    2015-12-01

    Holocene relative sea-level (RSL) records exhibit spatial and temporal variability that arises mainly from the interaction of eustatic (land ice volume and thermal expansion) and isostatic (glacio- and hydro-) factors. We fit RSL histories from near-, intermediate-, and far-field locations with noisy-input Gaussian process models to assess rates of RSL change from selected study areas. Records from near-field regions (e.g., Antarctica, Greenland, Canada, Sweden, and Scotland) reveal a complex pattern of RSL fall from a maximum marine limit due to the net effect of eustatic sea-level rise and glacial-isostatic uplift with rates of RSL fall as great as -69 ± 9 m/ka. Intermediate-field regions (e.g., mid-Atlantic and Pacific coasts of the United States, Netherlands, Southern France, St. Croix) display variable rates of RSL rise from the cumulative effect of isostatic and eustatic factors. Fast rates of RSL rise (up to 10 ± 1 m/ka) are found in the early Holocene in regions near the center of forebulge collapse. Far-field RSL records exhibit a mid-Holocene highstand, the timing (between 8 and 4 ka) and magnitude (between <1 and 6 m) of which varies across South America, Africa, Asia and Australia regions.

  7. Stable isotope constraints on Holocene carbon cycle changes from an Antarctic ice core.

    PubMed

    Elsig, Joachim; Schmitt, Jochen; Leuenberger, Daiana; Schneider, Robert; Eyer, Marc; Leuenberger, Markus; Joos, Fortunat; Fischer, Hubertus; Stocker, Thomas F

    2009-09-24

    Reconstructions of atmospheric CO(2) concentrations based on Antarctic ice cores reveal significant changes during the Holocene epoch, but the processes responsible for these changes in CO(2) concentrations have not been unambiguously identified. Distinct characteristics in the carbon isotope signatures of the major carbon reservoirs (ocean, biosphere, sediments and atmosphere) constrain variations in the CO(2) fluxes between those reservoirs. Here we present a highly resolved atmospheric delta(13)C record for the past 11,000 years from measurements on atmospheric CO(2) trapped in an Antarctic ice core. From mass-balance inverse model calculations performed with a simplified carbon cycle model, we show that the decrease in atmospheric CO(2) of about 5 parts per million by volume (p.p.m.v.). The increase in delta(13)C of about 0.25 per thousand during the early Holocene is most probably the result of a combination of carbon uptake of about 290 gigatonnes of carbon by the land biosphere and carbon release from the ocean in response to carbonate compensation of the terrestrial uptake during the termination of the last ice age. The 20 p.p.m.v. increase of atmospheric CO(2) and the small decrease in delta(13)C of about 0.05 per thousand during the later Holocene can mostly be explained by contributions from carbonate compensation of earlier land-biosphere uptake and coral reef formation, with only a minor contribution from a small decrease of the land-biosphere carbon inventory.

  8. A Late Glacial to Holocene record of environmental change from Lake Dojran (Macedonia, Greece)

    NASA Astrophysics Data System (ADS)

    Francke, A.; Wagner, B.; Leng, M. J.; Rethemeyer, J.

    2013-02-01

    A Late Glacial to Holocene sediment sequence (Co1260, 717 cm) from Lake Dojran, located at the boarder of the F.Y.R. of Macedonia and Greece, has been investigated to provide information on climate variability in the Balkan region. A robust age-model was established from 13 radiocarbon ages, and indicates that the base of the sequence was deposited at ca. 12 500 cal yr BP, when the lake-level was low. Variations in sedimentological (H2O, TOC, CaCO3, TS, TOC/TN, TOC/TS, grain-size, XRF, δ18Ocarb, δ13Ccarb, δ13Corg) data were linked to hydro-acoustic data and indicate that warmer and more humid climate conditions characterised the remaining period of the Younger Dryas until the beginning of the Holocene. The Holocene exhibits significant environmental variations, including the 8.2 and 4.2 ka cooling events, the Medieval Warm Period and the Little Ice Age. Human induced erosion processes in the catchment of Lake Dojran intensified after 2800 cal yr BP.

  9. Including new equatorial African data in global Holocene magnetic field models

    NASA Astrophysics Data System (ADS)

    Korte, M.; Brown, M.; Frank, U.

    2012-04-01

    Global paleomagnetic field reconstructions of the Holocene are a useful tool to study the past evolution of the geomagnetic field at the Earth's surface and the core-mantle boundary, or to estimate shielding against galactic cosmic rays. This protection is currently weak over the South Atlantic anomaly, a feature stretching between South America and Africa. Knowledge of the long-term evolution of this anomaly and whether there are preferred longitudinal ranges of weak fields is required for a better understanding of the geodynamo process and to estimate past magnetic shielding, e.g., for any studies involving the production of cosmogenic isotopes. The distribution of archeo- and paleomagnetic data available for global field reconstructions is highly inhomogeneous. It is strongly biased towards Europe and particularly sparse for Africa and South America. New data from these regions are necessary to confirm or improve field descriptions in Holocene spherical harmonic magnetic field models particularly for the evolution of this presently anomalous region. We present new inclination and relative intensity records from two neighbouring lakes in southern Ethiopia: Chew Bahir and Lake Chamo. Measurements were taken on three sediment cores from Chew Bahir, in which the complete Holocene is preserved in the topmost 4 m, and one 17 m long composite profile from Lake Chamo, which spans approximately the last 7 ka. Our age models are constrained by 10 AMS radiocarbon ages through the Holocene. We investigate the influence of these new records on magnetic field models CALS3k.4 and CALS10k.1b by augmenting previously modeled data with our new data and performing the modeling with otherwise unchanged parameters. Model predictions particularly for the equatorial African region and surroundings are compared and differences discussed.

  10. Palaeolimnological reconstructions of mid-late Holocene climate change from South Georgia

    NASA Astrophysics Data System (ADS)

    Van Nieuwenhuyze, Wim; Roberts, Stephen J.; Hodgson, Dominic A.; Verleyen, Elie; Sterken, Mieke; Sabbe, Koen; Vyverman, Wim

    2014-05-01

    South Georgia's position within the Polar Frontal Zone, the core belt of the Southern Hemisphere Westerly Winds, and between Antarctica and the mid-latitudes makes it a key location for studying the main drivers of past and present-day climate variability. We undertook multi-proxy analyses, including fossil diatom, pigment and μ-XRF analysis, of lake and peat cores from two sites: Annenkov Island, on the southern side of South Georgia, and Prince Olav Harbour on the northern coast of South Georgia to determine: 1) which proxies were most suitable for reconstructing Holocene palaeoclimatic change; 2) whether the climate change signals from these proxies were related to natural lake development, local catchment processes such as changes in ice extent, or regional-global scale climatic change. Deglaciation at both sites was completed by c. 7800 cal. yr. B.P. Low nutrient/low productivity environments, which persisted within lakes at both locations until c. 3500 cal. yr. B.P., are indicative of the relatively slow development of lake ecosystems following deglaciation, and suggest high altitude glaciers or persistent ice-cover remained in both catchments well into the mid Holocene. In contrast, the late Holocene (c. 3500 yr to present) was characterized by initially higher, and then highly variable within-lake biological productivity. On Annenkov Island, the late Holocene diatom composition in Fan Lake was dominated by a single species (Cyclotella stelligera), and we have identified four major phases of increased catchment disturbance (represented by Fragilaria capucina peaks in diatom data), some of which coincide with more numerous meltwater input events (identified from Ti and Sr peaks in μ-XRF data). In this poster we examine the links between these meltwater events, results from other proxies, and changes in the climate of the sub-Antarctic region.

  11. Spatially-Explicit Holocene Drought Reconstructions in Amazonian Forests

    NASA Astrophysics Data System (ADS)

    McMichael, C.; Bush, M. B.

    2014-12-01

    Climate models predict increasing drought in Amazonian forests over the next century, and the synergy of drought and fire may lead to forest dieback. El Niño Southern Oscillation (ENSO) and the Atlantic Multi-decadal Oscillation (AMO) are two primary drivers of Amazonian drought, and each process has a spatially distinct manifestation in the Basin. Paleoecological reconstructions can contextualize the forest response to past drought periods. Stalagmite and lake sediment records have documented that the early- to mid-Holocene, i.e. 10,000 - 5000 calibrated years before present (cal yr BP), was among the driest periods of the last 100,000 years in western Amazonia. Climatic conditions became wetter and more similar to the modern climate over the last 4000 cal yr BP, and fires rarely occurred in the absence of human activity. Yet there are currently no drought and fire reconstructions that examine the spatially explicit patterns of drought during the Holocene. Here, we present regional drought histories from southwestern and northeastern sections Amazonia for the last 10,000 years that document the drought-fire dynamics resulting from both climatic processes. Our reconstructions were based on a compilation of dated soil charcoal fragments (N= 291) collected from within Amazonia sensu stricto, which were analyzed by region using summed probability analysis. The compiled soil charcoal dates contained limited evidence of fire over the last 10,000 years in some regions. Fire frequency rose markedly across the Basin, however, during the last 2000 years, indicating an increased human presence. Fire probabilities, and thus droughts, had similar increasing trajectories between southwestern and northeastern Amazonia from 1500-1100 cal yr BP, which decoupled from 1100-740 cal yr BP, and then regained synchronicity from 740-500 cal yr BP. Fire probability declined markedly after 500 yr cal BP, coincident with European arrival to the Americas. Native populations were decimated

  12. Holocene vegetation history from fossil rodent middens near Arequipa, Peru

    USGS Publications Warehouse

    Holmgren, C.A.; Betancourt, J.L.; Rylander, K.A.; Roque, J.; Tovar, O.; Zeballos, H.; Linares, E.; Quade, Jay

    2001-01-01

    Rodent (Abrocoma, Lagidium, Phyllotis) middens collected from 2350 to 2750 m elevation near Arequipa, Peru (16??S), provide an ???9600-yr vegetation history of the northern Atacama Desert, based on identification of >50 species of plant macrofossils. These midden floras show considerable stability throughout the Holocene, with slightly more mesophytic plant assemblages in the middle Holocene. Unlike the southwestern United States, rodent middens of mid-Holocene age are common. In the Arequipa area, the midden record does not reflect any effects of a mid-Holocene mega drought proposed from the extreme lowstand (100 m below modern levels, >6000 to 3500 yr B.P.) of Lake Titicaca, only 200 km east of Arequipa. This is perhaps not surprising, given other evidence for wetter summers on the Pacific slope of the Andes during the middle Holocene as well as the poor correlation of summer rainfall among modern weather stations in the central AndesAtacama Desert. The apparent difference in paleoclimatic reconstructions suggests that it is premature to relate changes observed during the Holocene to changes in El Nin??o Southern Oscillation modes. ?? 2001 University of Washington.

  13. Application of integrated reservoir management and reservoir characterization to optimize infill drilling. Quarterly technical progress report, September 13--December 12, 1997

    SciTech Connect

    1998-07-01

    The eighteen 10-acre infill wells which were drilled as part of the field demonstration portion of the project are all currently in service with no operational problems. These wells consist of fourteen producing wells and four injection wells. The producing wells are currently producing a total of approximately 450 bopd, down from a peak rate of 900 bopd. Unit production is currently averaging approximately 2,700 bopd, 12,000 bwpd and 18,000 bwipd. The paper describes progress on hydraulic fracture design, reservoir surveillance, data analysis procedures, and deterministic modeling and simulation.

  14. Remote sensing and holocene vegetation: History of global change

    SciTech Connect

    D`Antoni, H.L.; Schaebitz, F.

    1995-06-01

    Predictions of the future evolution of the earth`s atmospheric chemistry and its impact on global circulation patterns are based on global climate models (GCMS) that integrate the complex interactions of the biosphere, atmosphere and the oceans. GCMs must be tested beyond the short-term record of climate and environment to insure that predictions are based on trends and therefore are appropriate to support long term policy making. An appropriate timeframe should extend over the Holocene period (the last 10,000 years) when most contemporary climate and environmental processes began. Since its inception in 1916, pollen analysis has successfully reconstructed the paleoecology of the last 10,000 years for many sites around the world, thus providing a powerful time-link between short and long-term processes in the biosphere. However, pollen analytic results cannot be used in physiological models driven by remotely sensed data. Further, modern ecology and climate data are necessary to calibrate pollen analytical models. A new approach to calibration was attempted by D`Antoni and Spanner in 1993. By calibrating modern pollen data southern Patagonia with satellite remote sensing data they produced predictive models of reflectance in the red (RED) and near infrared (NIR) regions of the electromagnetic spectrum.

  15. Late glacial initiation of Holocene eastern Mediterranean sapropel formation.

    PubMed

    Grimm, Rosina; Maier-Reimer, Ernst; Mikolajewicz, Uwe; Schmiedl, Gerhard; Müller-Navarra, Katharina; Adloff, Fanny; Grant, Katharine M; Ziegler, Martin; Lourens, Lucas J; Emeis, Kay-Christian

    2015-01-01

    Recurrent deposition of organic-rich sediment layers (sapropels) in the eastern Mediterranean Sea is caused by complex interactions between climatic and biogeochemical processes. Disentangling these influences is therefore important for Mediterranean palaeo-studies in particular, and for understanding ocean feedback processes in general. Crucially, sapropels are diagnostic of anoxic deep-water phases, which have been attributed to deep-water stagnation, enhanced biological production or both. Here we use an ocean-biogeochemical model to test the effects of commonly proposed climatic and biogeochemical causes for sapropel S1. Our results indicate that deep-water anoxia requires a long prelude of deep-water stagnation, with no particularly strong eutrophication. The model-derived time frame agrees with foraminiferal δ(13)C records that imply cessation of deep-water renewal from at least Heinrich event 1 to the early Holocene. The simulated low particulate organic carbon burial flux agrees with pre-sapropel reconstructions. Our results offer a mechanistic explanation of glacial-interglacial influence on sapropel formation.

  16. Late glacial initiation of Holocene eastern Mediterranean sapropel formation

    NASA Astrophysics Data System (ADS)

    Grimm, Rosina; Maier-Reimer, Ernst; Mikolajewicz, Uwe; Schmiedl, Gerhard; Müller-Navarra, Katharina; Adloff, Fanny; Grant, Katharine M.; Ziegler, Martin; Lourens, Lucas J.; Emeis, Kay-Christian

    2015-06-01

    Recurrent deposition of organic-rich sediment layers (sapropels) in the eastern Mediterranean Sea is caused by complex interactions between climatic and biogeochemical processes. Disentangling these influences is therefore important for Mediterranean palaeo-studies in particular, and for understanding ocean feedback processes in general. Crucially, sapropels are diagnostic of anoxic deep-water phases, which have been attributed to deep-water stagnation, enhanced biological production or both. Here we use an ocean-biogeochemical model to test the effects of commonly proposed climatic and biogeochemical causes for sapropel S1. Our results indicate that deep-water anoxia requires a long prelude of deep-water stagnation, with no particularly strong eutrophication. The model-derived time frame agrees with foraminiferal δ13C records that imply cessation of deep-water renewal from at least Heinrich event 1 to the early Holocene. The simulated low particulate organic carbon burial flux agrees with pre-sapropel reconstructions. Our results offer a mechanistic explanation of glacial-interglacial influence on sapropel formation.

  17. Late glacial initiation of Holocene eastern Mediterranean sapropel formation.

    PubMed

    Grimm, Rosina; Maier-Reimer, Ernst; Mikolajewicz, Uwe; Schmiedl, Gerhard; Müller-Navarra, Katharina; Adloff, Fanny; Grant, Katharine M; Ziegler, Martin; Lourens, Lucas J; Emeis, Kay-Christian

    2015-01-01

    Recurrent deposition of organic-rich sediment layers (sapropels) in the eastern Mediterranean Sea is caused by complex interactions between climatic and biogeochemical processes. Disentangling these influences is therefore important for Mediterranean palaeo-studies in particular, and for understanding ocean feedback processes in general. Crucially, sapropels are diagnostic of anoxic deep-water phases, which have been attributed to deep-water stagnation, enhanced biological production or both. Here we use an ocean-biogeochemical model to test the effects of commonly proposed climatic and biogeochemical causes for sapropel S1. Our results indicate that deep-water anoxia requires a long prelude of deep-water stagnation, with no particularly strong eutrophication. The model-derived time frame agrees with foraminiferal δ(13)C records that imply cessation of deep-water renewal from at least Heinrich event 1 to the early Holocene. The simulated low particulate organic carbon burial flux agrees with pre-sapropel reconstructions. Our results offer a mechanistic explanation of glacial-interglacial influence on sapropel formation. PMID:26028337

  18. Some physical drivers of changes in the winter storm tracks over the North Atlantic and Mediterranean during the Holocene.

    PubMed

    Brayshaw, David James; Hoskins, Brian; Black, Emily

    2010-11-28

    The winter climate of Europe and the Mediterranean is dominated by the weather systems of the mid-latitude storm tracks. The behaviour of the storm tracks is highly variable, particularly in the eastern North Atlantic, and has a profound impact on the hydroclimate of the Mediterranean region. A deeper understanding of the storm tracks and the factors that drive them is therefore crucial for interpreting past changes in Mediterranean climate and the civilizations it has supported over the last 12 000 years (broadly the Holocene period). This paper presents a discussion of how changes in climate forcing (e.g. orbital variations, greenhouse gases, ice sheet cover) may have impacted on the 'basic ingredients' controlling the mid-latitude storm tracks over the North Atlantic and the Mediterranean on intermillennial time scales. Idealized simulations using the HadAM3 atmospheric general circulation model (GCM) are used to explore the basic processes, while a series of timeslice simulations from a similar atmospheric GCM coupled to a thermodynamic slab ocean (HadSM3) are examined to identify the impact these drivers have on the storm track during the Holocene. The results suggest that the North Atlantic storm track has moved northward and strengthened with time since the Early to Mid-Holocene. In contrast, the Mediterranean storm track may have weakened over the same period. It is, however, emphasized that much remains still to be understood about the evolution of the North Atlantic and Mediterranean storm tracks during the Holocene period.

  19. Development of the Holocene Clinoform in the Gulf of Papua

    NASA Astrophysics Data System (ADS)

    Slingerland, R.; Milliman, J. D.; Driscoll, N. W.; Walsh, J. P.; Keen, T. R.

    2004-12-01

    The Gulf of Papua (GoP) off the southeastern coast of Papua New Guinea, is a modern example of a marine foreland basin in mid-life. Loading of the Australian plate by New Guinea is creating accommodation space that is being filled by clastic sediment delivered by rivers draining the central mountains. Collectively, the Fly, Turama, Kikori, and Purari rivers discharge >200 x 106 t/yr into the basin. Filling is both longitudinal (Fly and Turama Rivers) and transverse, creating a crescentic shelf, similar to ancient shelves such as the Miocene shelf of the Alpine foreland. To develop a model for GoP-type shallow-marine shelf processes and products we have collected 21 piston cores, 24 gravity cores, 4000 nmi of CHIRP and 1000 nmi of multi-electrode sparker profiles in the GoP, and conducted numerical experiments with NCOM, the US Navy Coastal Ocean Model. Morphologically the GoP shelf is characterized by three treads and two risers, which define two clinoforms; here we focus on the upper Holocene clinoform whose face extends from ~20 to ~80 m water depth, where it downlaps onto an erosional surface etched into topsets of an older clinoform. The face of the Holocene clinoform undulates along strike in a series of subtle promontories and reentrants. Geometrical relationships of stratal packages suggest that the undulations are caused by progradation of sand/mud lobes across the roll-over and oblique transport down the clinoform. Intercalated on- and off-lapping wedges suggest a multi-stage clinoform growth, with upslope sand-rich build-outs alternating with mud-rich toe of slope build-outs. The latest sediments consist of a subjacent heterolithic facies, deposited during a phase of oblique clinoform growth, overlain everywhere by an acoustically transparent facies that forms an on- and down-lapping toe of the wedge. We assume that this transparent facies represent sediment winnowed from topset strata, suggesting that the rate of clinoform growth has slowed. The causes

  20. Got Varves?: Reconstructing Holocene Climate Change in Seneca Lake, NY

    NASA Astrophysics Data System (ADS)

    Rogers, C. E.; Curtin, T. M.

    2004-12-01

    The sedimentary deposits of Seneca Lake, one of eleven Finger Lakes in New York State, contain a valuable record of post-glacial climate and environmental change. Paleoenvironmental interpretations depend on knowing what transport and depositional processes controlled the formation of the laminae. In this study, we examine Holocene rhythmites in two profundal cores collected from the northern half of Seneca Lake to determine possible mechanisms of formation of the alternating olive gray-black layers. Magnetic susceptibility was measured at a 2 cm interval prior to splitting the ˜5 m cores. Split cores were described, photographed, and sampled for loss-on-ignition and grain size analysis at a 10 cm interval. When possible, core one was sampled on a lamination-by-lamination basis whereas core five was sampled at a one cm interval. Sequential LOI was used to estimate the total organic and carbonate content of sediments. Grain size analyses were performed using a Coulter LS 230 laser diffractometer after removal of calcium carbonate. Temporal control of paleoenvironmental changes in cores will be established by two accelerator mass spectrometer radiocarbon dates. The cores contain proglacial pink clay overlain by Holocene mm- to cm-scale alternating olive gray and black laminations of fine-grained sand and mud. Magnetic susceptibility changes are distinct, ranging from 1-22 x 10-6 SI units in core one and 4-57 x 10-6 SI units in core five. Sediment is dominantly composed of siliciclastic material (50-99 weight %) with varying amounts of calcite (0.1-75 weight %) plus lesser amounts of organic matter (0.5-4.1 weight %). A distinct variation in sediment color, organic matter, and carbonate content, and median grain size (φ 50) occurs in the laminated sediment. The olive gray layers are characterized by well-sorted very fine silt and clay with a φ 50 <6 μ m, high carbonate content (>25%), and low organic matter content (<1%). The black laminae are generally higher in

  1. The Holocene Paleolimnology of Lake Superior

    NASA Astrophysics Data System (ADS)

    Hyodo, A.; Longstaffe, F. J.

    2010-12-01

    This study describes contributions of glacial meltwater to Lake Superior over the last 11,000 cal BP. Rhythmites (interpreted as varves), lithological and mineralogical variations, and radiocarbon dating were used to establish chronostratigraphic correlation among four sediment cores from Lake Superior (Duluth, Caribou and Ile Parisienne basins, Thunder Bay Trough). Glacial sediments were deposited between 10,850 and 8,800 cal BP. The oxygen-isotope compositions of ostracodes record the presence of glacial meltwater in ancient Lake Superior as the Laurentide Ice Sheet waxed and waned. Glacial meltwater was increasingly dominant between ~10,850 and ~9,250 cal BP, particularly as thick varves formed in northern portions of the Lake Superior Basin (10,400-10,200, 9,900 and 9,300-9,200 cal BP). Glacial meltwater supply was reduced in the Thunder Bay Trough between 9,250 and 8,950 cal BP, but returned from 8,950 to 8,800 cal BP. Glacial meltwater flow from the Lake Superior Basin probably bypassed the Huron Basin several times during this period. Final termination of glacial meltwater supply occurred at 8,800 cal BP - coincident with cessation of varve formation and inception of ancient Lakes Agassiz-Ojibway and Houghton. Primary productivity was very low and algal growth occurred under conditions of extreme nitrogen deficiency - as determined using TOC, TN and C/N ratios - until glacial meltwater supply to the Basin was ended. The postglacial sediments are non-calcareous. The diatom silica proxy record shows that oxygen-isotope compositions of water rapidly increased after glacial meltwater termination, reaching -10 per mil during the Holocene Thermal Maximum. The oxygen-isotope compositions of water decreased at 3,000 cal BP in response to the Holocene Neoglacial Interval before gradually rising to Lake Superior’s modern value of -8.7 per mil. Aquatic primary productivity, inferred using TOC, TN, and the carbon- and nitrogen isotope compositions, has increased

  2. Late Glacial and Holocene sedimentary evolution of Czechowskie Lake (Eastern Pomerania, North Central Poland)

    NASA Astrophysics Data System (ADS)

    Kordowski, Jarosław; Błaszkiewicz, Mirosław; Kramkowski, Mateusz; Noryśkiewicz, Agnieszka M.; Słowiński, Michał; Tyszkowski, Sebastian; Brauer, Achim; Ott, Florian

    2015-04-01

    Czechowskie Lake is located in north-central Poland in Tuchola Forest, about 100 kilometers SW away from Gdańsk. In the deepest parts of the lake there are preserved laminated sediments with an excellent Holocene climatic record. The lake has the area of 76,6 ha. Actual water level is at 109,9 m a.s.l. The average depth is 9,59 m, maximal 32 m. It occupies a large subglacial channel, reproduced within the glacifluvial sediments of the last glaciation. The lake has a history reaching back to Pommeranian phase which is proved by analysis of sedimentary succesions in the vicinity of present-day waterbody. Primarily it come to existence as an very variable ice dammed lake but after dead ice and permafrost desintegration it changed into a stable lake. In the terrestrialised part oft the lake and in its litoral zone there were curried out numerous boreholes within limnic and slope sediments. They have been analysed in respect to lithology and structure. Some of them were also investigated palynologically which along with radiocarbon datings allowed to reconstruct major phases of the water level fluctuations. The maximum infilling with the limnic and telmatic sediments reaches over 12 m. In the bottom of the lake there is a marked presence of many overdeepenings with the diameter of dozen or several dozen meters and the depth of up to 10 m with numerous, distinct throughs between them. They favoured the preservation of the lamination in the deepest parts of the lake due to waves hampering and stopping of the density circulation in the lake waterbody. The analysis of limnic sediments revealed considerable spatial and temporal variability mainly in dependance of the area of the water body and water level in time of deposition. In the lake are recorded three distinct phases of lake level decrease. The sedimentary evolution in the isolated minor lake basins showed gradual decrease of mineral and organic deposition in favour for carbonate one although in places separated by

  3. Holocene evolution of a montane lake catchment inferred from multiproxy sediment analysis : climatic and anthropic impacts in french prealps

    NASA Astrophysics Data System (ADS)

    Bajard, Manon; Sabatier, Pierre; Poulenard, Jérôme; David, Fernand; Arnaud, Fabien; Develle, Anne-Lise; Reyss, Jean-Louis; Fanget, Bernard; Malet, Emmanuel; Crouzet, Christian

    2015-04-01

    Lake La Thuile in the Massif des Bauges (874 m a.s.l. French Alps) provides a 18 meters sedimentary sequence. Due to its mid-altitude position, this lake is one of the first to be formed through the glacial retreat and documents the evolution of its catchment since the Late Glacial Maximum. The first 6 meters of the core cover the last 12 000 years, and allowed to study human/climate/environment interactions in a carbonated environment. This study is the first one to investigate a mid-altitude lake in the French Alps for paleoenvironment reconstruction from lake sediment archive. Its altitudinal position presents the advantage to be very accessible to human activities and allows more developed agriculture than in higher altitude. This study aims to determined how and when is expressed the erosive response of such an environment to human settlement. High resolution multiproxy analysis of the first 6 meters including sedimentological, palynological and geochemical data associated to a well-constrained chronology over the Holocene period allows us to understand the respective impacts of both climate and human on the evolution of Lake La Thuile environment. Five major phases of evolution have been highlighted over this period. From 12 000 to 10 000 yr cal. BP, the vegetation is developing with the onset of hardwood species and the disappearance of Pinus. From 10 000 to 4500 yr cal. BP the warmer climatic conditions of the middle of the Holocene allows the forest to densify and the very low sedimentation rate indicates that the forest stabilizes slopes and prevents from the erosion on the watershed. The climate cooling of the Neoglacial period triggers a first erosive phase with a decreasing of the forest around 3300 cal. BP. Human settlements are suggested at La Thuile from 2500 yr cal. BP by palynological evidence of anthropic taxa. The triggered clearing is accompanied by a second erosive phase related to anthropic activities during the Roman period. Erosion

  4. Holocene hydrologic variability in the Sierra Nevada from D/H ratios in leaf waxes

    NASA Astrophysics Data System (ADS)

    Street, J. H.; Sessions, A. L.; Anderson, R. S.; Welker, J. M.; Paytan, A.

    2009-12-01

    Large-scale atmospheric circulation patterns and underlying ocean conditions in the Northeastern Pacific have a strong bearing on continental climate conditions and water availability in California on seasonal to decadal timescales, as demonstrated in the instrumental record. However, the nature and pacing of the relationship between ocean-atmosphere processes and hydrologic variability in California remain poorly understood over longer timescales and during past climate regimes of the Holocene and late Pleistocene, particularly in the large Sacramento-San Joaquin River watershed draining the western Sierra Nevada. The continuous ~20,000-yr sedimentary record recovered from Swamp Lake, a small mid-elevation (1554 m) lake in Yosemite NP, provides a rare opportunity to reconstruct hydrologic variability in the central Sierra Nevada at high resolution (<100 yr) in relation to known or theorized regime shifts in the North Pacific sector and global drivers of climate change. Here we present the results of organic geochemical and isotopic analyses of sedimentary organic matter from this core. In particular, we explore the utility of compound-specific hydrogen isotope (D/H) measurements on leaf-wax n-alkanes extracted from the sediment as a hydrologic tracer. We examine a precipitation isotopes time series (1990-2001) collected in Yosemite near Swamp Lake (NADP station CA99, 1400 m) to assess modern controls (e.g., temperature, storm track, precipitation amount) on the D/H of precipitation, and compare n-alkane D/H values in recent sediments to instrumental and latest Holocene proxy records in order to evaluate the relative contributions of precipitation D/H and local aridity (precipitation v. evapotranspiration) to the D/H signal integrated in sedimentary n-alkanes. Our down-core D/H results suggest a strong sensitivity to atmospheric circulation changes on multiple timescales, which in turn led to altered hydrologic conditions in the Sierra Nevada: (1) A long

  5. Floodplain construction of the Rio Grande at El Paso, Texas, USA: response to Holocene climate change

    NASA Astrophysics Data System (ADS)

    Hall, Stephen A.; Peterson, John A.

    2013-04-01

    The Rio Grande is one of the larger rivers in North America, and the development of its floodplain is related to Holocene climate and climate change. The late Pleistocene through early Holocene channel is characterized by a meander or braided system with lateral cutting and backfilling, resulting in the valley-wide deposition of massive to cross-bedded, fine-to-medium textured sand. The late Pleistocene-early Holocene floodplain is also the sand source for the adjacent Bolson sand sheet. The sand sheet stopped accumulating new sand 5000 yrs ago, an event directly related to the shutting off of the sand supply caused by the deposition of overbank muds that covered and sealed the floodplain surface. During the middle Holocene, the river may have dried intermittently with the floodplain becoming deflated and local sand dunes forming on the floodplain. After 5000 yrs the climate was less arid and the river shifted to a regime of increased flooding and overbank deposition of silt and clay. By 2500 yrs, a late Holocene period of wet climate resulted in further overbank deposition and the formation of a cumulic Mollisol across the floodplain, the Socorro paleosol. The period of wet climate corresponds to the Audubon Neoglacial and active rock glaciers in the southern Rocky Mountains, speleothem growth in nearby caves, and other evidence for wet-cool conditions in the region. After 1000 yrs, the climate became drier, and the deposition and accumulation of overbank muds by the flooding Rio Grande came to a halt. Even though the river has flooded often in historic times, and presumably during late prehistoric times as well, there is little evidence for deposition of overbank sediments on the floodplain since A.D. 1000. Accordingly, the present-day surface of the Lower Valley is ten centuries old. Three channels occur on the US side of the Lower Valley floodplain, and during the past 2500 yrs stream flow has shifted from one to the other by the avulsion process of channel

  6. River response to rapid Holocene environmental change: evidence and explanation in British catchments

    NASA Astrophysics Data System (ADS)

    Macklin, Mark G.; Jones, Anna F.; Lewin, John

    2010-07-01

    Since the late 1980s our understanding of the relationship between climate, land-use and Holocene river development in Britain has changed radically. Conceptually simplistic and data-poor models of people-river environment interaction, many of which considered human activity alone to be the control of Holocene flooding and alluviation, have been replaced by more data-rich models that explain river behaviour in terms of a continuum of climate and anthropogenic drivers, individually operating over a range of temporal and spatial scales. One of the key factors in this paradigm shift has been the significant increase in the number of 14C-dated fluvial units that has itself recently facilitated the application of meta-analysis techniques to large fluvial data sets. These analyses have produced the first probability-based national and regional reconstructions of Holocene flooding in the British Isles that can be correlated with independent, high-resolution hydro-climate records. This paper critically reviews the major findings of this new research focusing on process-based causality relationships in fluvial systems and quantifying how environmental signals are propagated in river basins and preserved in landform and sedimentary sequences. By using cumulative probability density function (CPDF) plots of fluvial 14C dates that have been classified on the basis of sedimentary environment and evidence for changing depositional regime, 17 multi-centennial length periods of flooding and river instability during the Holocene are identified in the UK. The scale and timing of these episodes vary regionally and correlations can be made with a range of climate proxy records, including the North Atlantic drift-ice index, glacier variations in Europe, and mire surface wetness and water-table reconstructions. A new analysis of overbank floodplain sedimentation rates points to an acceleration after ca 1000 cal. BP, which can be related to the agricultural revolution of the Middle Ages

  7. Holocene geologic slip rate for Mission Creek strand of the southern San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Fryer, R.; Behr, W. M.; Sharp, W. D.; Gold, P. O.

    2015-12-01

    depositional timing of the most well-defined alluvial fan, we are currently processing samples for U-series analysis of pedogenic carbonate. We expect this to result in a maximum bound of the Holocene slip rate on the Mission Creek Strand. Future Be-10 exposure age measurements from surface cobbles will independently constrain fan age yielding a complementary Holocene slip rate.

  8. Holocene Relative Sea-Level Changes from the us Atlantic Coast

    NASA Astrophysics Data System (ADS)

    Horton, B.; Engelhart, S. E.; Kemp, A.; Hill, D. F.; Kopp, R. E.

    2013-12-01

    Reconstructions of Holocene relative sea level (RSL) are important for identifying the ice equivalent meltwater contribution to sea-level change during deglaciation and constraining Earth-Ice models of Glacial Isostatic Adjustment. RSL reconstructions provide data for estimating rates of spatially variable and ongoing vertical land motion; a requirement for understanding the variation in modern and late Holocene sea level as recorded by instrumental and proxy records. We explain the methodology employed to reconstruct former sea levels (as laid out by the International Geoscience Programme) and produce sea level index points from the U.S. Atlantic coast. Sea-level index points consist of an estimate of X (age) and Y (the position of former RSL). Where a suite of index points are developed for a locality or region, they describe changes in RSL through time and estimate rates of change. A valid index point must meet the following four criteria: (1) location of the sample is known to within 1 km; (2) the altitude of the sample (and the error associated with measuring that altitude) is known; (3) the indicative meaning and range is estimated; and (4) the age of the sample is calibrated to sidereal years using the latest calibration curves. By applying this standardized approach to existing literature and new samples, a database of 500 sea-level index points was generated for the U.S. Atlantic coast. The data include discrete RSL reconstructions from individual core samples and continuous records of recent (approximately last 3000 years) RSL using ordered samples from a single core of salt-marsh sediment. We corrected the index points for the influence of compaction and paleotidal range changes. The database is sub-divided into 16 regions based on the distance from the Laurentide Ice Sheet and availability of data. We used a spatio-temporal Gaussian process model to identify and characterize persistent phases of sea-level behavior and to estimate rates and sources of

  9. Records from Lake Qinghai: Holocene climate history of Northeastern Tibetan Plateau linking to global change

    NASA Astrophysics Data System (ADS)

    An, Z.; Colman, S.; Zhou, W.; Brown, E.; Li, X.; Jull, T.; Wang, S.; Liu, W.; Sun, Y.; Lu, X.; Song, Y.; Chang, H.; Cai, Y.; Xu, H.; Wang, X.; Liu, X.; Wu, F.; Han, Y.; Cheng, P.; Ai, L.; Wang, Z.; Qiang, X.; Shen, J.; Zhu, Y.; Wu, Z.; Liu, X.

    2008-12-01

    Lake Qinghai (99°36'-100°16'E, 36°32'-37°15'N ) of the north eastern margin of Tibet Plateau is the largest inland lake of China. It sits on the transitional zone of Asian monsoon- arid areas, receives influences of Asian monsoons and Westerlies, thus sensitive to global climate changes. Although previous studies had investigated Holocene climate change of Lake Qinghai area, it is rare to see precise Holocene climatic sequences of Lake Qinghai, nor in-depth discussions on controlling factors of Lake Qinghai climate changes. In Year 2005, with support from ICDP, Chinese Academy of Sciences (CAS), Chinese Ministry of Science and Technology (MOST) and National Science Foundation of China (NSFC), Drilling, Observation and Sampling of the Earths Continental Crust Corporation (DOSECC) and Institute of Earth Environment, Chinese Academy of Sciences (IEECAS) took a series of shallows cores from the southern basin of Lake Qinghai. West sub-basin sediments display Holocene lacustrine feature for the upper 5m, while the 5-18m are interbeded sediments of shallow lake, eolian-lacustrine and eolian loess. Chinese and US scientists with support from NSFC, MOST, CAS and NSF analysed 1F core from west sub-basin depocenter of the south basin with multiple physical, chemical, biological approaches. By comparing with modern process observation records, we obtained proxies that respectfully reflect precipitation, temperature and lake salinity changes, etc., reconstructed high resolution time sequences of magnetic susceptibility, colour scale, grain size, Corg, C/N, δ13Corg, carbonate, δ13C and δ18O of carbonate and ostracodes, elements, char-soot,Uk'37 and %C37:4 as well as pollen of the last 13Ka. They indicate the climatic change history of Lake Qinghai since past 13Ka, and agreeable evidences are found from adjacent tree ring and stalagmite records. Comparison of Lake Qinghai Holocene climate change sequence with those from high altitude ice core, stalagmites and ocean

  10. Hydrodynamics in Holocene Lake Mega-Chad

    NASA Astrophysics Data System (ADS)

    Bouchette, Frédéric; Schuster, Mathieu; Ghienne, Jean-François; Denamiel, Cléa; Roquin, Claude; Moussa, Abderamane; Marsaleix, Patrick; Duringer, Philippe

    2010-03-01

    Holocene Lake Mega-Chad (LMC) was the largest late Quaternary water-body in Africa. The development of this giant paleo-lake is related to a northward shift of the isohyetes interpreted as evidence for an enhanced Monsoon (African Humid Period). Numerous preserved coastal features have been described all around the LMC shore. Such features reveal the main paleo-hydrodynamical tendencies. In the context of a closed water-body like LMC, hydrodynamics are forced mainly by winds. We use a three-dimensional numerical model (SYMPHONIE) to simulate the mean hydrodynamics in LMC under both Harmattan-like (northeasterly trade winds) and Monsoon-like (southwesterly winds) forcings. The northern part of LMC displays coastal features, such as sand spits, that are consistent with the simulations forced by Harmattan-like winds. Geomorphic features related to Monsoon-driven hydrodynamics are not clearly expressed. They could have developed during the early stage of LMC but subsequently reworked. At the time of sand-spit building, Harmattan-like driven hydrodynamics prevailed and related coastal features were preferentially preserved in the sedimentary record.

  11. Early Holocene Great Salt Lake, USA

    NASA Astrophysics Data System (ADS)

    Oviatt, Charles G.; Madsen, David B.; Miller, David M.; Thompson, Robert S.; McGeehin, John P.

    2015-07-01

    Shorelines and surficial deposits (including buried forest-floor mats and organic-rich wetland sediments) show that Great Salt Lake did not rise higher than modern lake levels during the earliest Holocene (11.5-10.2 cal ka BP; 10-9 14C ka BP). During that period, finely laminated, organic-rich muds (sapropel) containing brine-shrimp cysts and pellets and interbedded sodium-sulfate salts were deposited on the lake floor. Sapropel deposition was probably caused by stratification of the water column - a freshwater cap possibly was formed by groundwater, which had been stored in upland aquifers during the immediately preceding late-Pleistocene deep-lake cycle (Lake Bonneville), and was actively discharging on the basin floor. A climate characterized by low precipitation and runoff, combined with local areas of groundwater discharge in piedmont settings, could explain the apparent conflict between evidence for a shallow lake (a dry climate) and previously published interpretations for a moist climate in the Great Salt Lake basin of the eastern Great Basin.

  12. Holocene coastal paleoenvironments in Atlantic Patagonia, Argentina

    NASA Astrophysics Data System (ADS)

    González Bonorino, G.; Bujalesky, G.; Colombo, F.; Ferrero, M.

    1999-11-01

    The Atlantic shoreline in Patagonia, southernmost South America, is a paraglacial coast that has undergone extensive erosion and retreat since the late Pleistocene, releasing a large volume of sand and gravel to southward littoral drift. Despite regional erosive conditions, accretionary landforms developed during the Holocene in three coastal reentrants. These are, from north to south along a 200 km long shoreline stretch: (1) the cuspate foreland that underlies Bustamante Point, in the Rı´o Gallegos Estuary; (2) the cuspate foreland with incipient spit underlying Dungeness Point, in the eastern Strait of Magellan; (3) the San Sebastián Bay tidal flat; and (4) the El Páramo Spit, partly enclosing the San Sebastián Bay. These accretionary landforms contain a record of relative sea level changes for approximately the past 7 ka, and indicate a tectonically driven drop of about 3 m during growth of Bustamante Point and of 1-2 m in the other areas. Differential sea level fall influenced development of the landforms, with slower rates favoring spit development in the south.

  13. Vegetation and soil dynamics under climatic to anthropogenic forcing through the Holocene in Eastern France

    NASA Astrophysics Data System (ADS)

    Doyen, Elise; Vannière, Boris; Gauthier, Emilie; Bichet, Vincent; Berger, Jean-François; Arnaud, Fabien

    2010-05-01

    Small lakes with little catchment areas, and high resolution Holocene sediment infilling, offer the interest to record mainly local perturbation and to study the switch from climatic to anthropogenic forcing. Two cores were extracted from Lake Antre in the Jura Mountains (Eastern France, 798 m a.s.l) and Lake Moras located on a low-elevated plateau from the upper Rhone valley (Eastern France, 304 m a.s.l). Cores taken from the deep zone of the lakes present continuous sedimentary series from the Late-glacial (15 000 cal. BP) for Lake Moras and from the Atlantic chronozone (6000 cal. BP) for Lake Antre. Several archaeological excavations and investigations around Lakes Antre and Moras give evidence of major human occupation during Gallo-roman period, while former settlements are indicating by Pre- and Protohistoric archaeological artifacts. Multi-proxy reconstructions with high temporal resolution were undertaken: vegetation dynamics by pollen analysis, fire history by the quantification of microscopic charcoal and soil erosion by magnetic susceptibility measurements. Before the anthropogenic forcing, during the mid-Holocene environment of both lakes are constituted mainly by a dense mixed oak forest. The first palaeoecological signs of anthropogenic impact on the two sites appear to have been discontinuous and limited. They appear at the early Neolithic (ca 6000 cal .BP) for Lake Moras and during the Bronze Age (4000 to 3000 cal .BP) for Lake Antre. For the both sites, all the proxies indicate an acceleration of human impact around 3000 to 2700 cal. BP i.e. at the transition between the Bronze Age and the beginning of the Iron Age. The dense forest and the Alnus dominated vegetation on borders of lakes are affected by several clearances. The influx of micro-charcoal increases due to the use of the fire for clearing and manage settlements. The development of Poaceae and Anthropogenic Pollen Indicators (API) suggest an expansion of pastures, whereas the farming

  14. Simulated response of the mid-Holocene Atlantic meridional overturning circulation in ECHAM6-FESOM/MPIOM

    NASA Astrophysics Data System (ADS)

    Shi, Xiaoxu; Lohmann, Gerrit

    2016-08-01

    Changes of the Atlantic meridional overturning circulation (AMOC) in the mid-Holocene compared to the preindustrial state are explored in different coupled climate models. Using time-slice integrations by a newly developed global finite-element model ECHAM6-FESOM with unstructured mesh and high resolution, our simulations show an enhanced mid-Holocene AMOC, accompanied by an increase in the ocean salinity over regions of deep water formation. We identify two different processes affecting the AMOC: (1) a more positive phase of North Atlantic Oscillation (NAO) increased water density over the Labrador Sea through anomalous net evaporation and surface heat loss; (2) a decreased import of sea ice from the Arctic causes a freshwater reduction in the northern North Atlantic Ocean. Using the coupled model ECHAM6-MPIOM in T63GR15 and T31GR30 grids, we find that the simulated AMOC has significant discrepancy with different model resolutions. In detail, stronger-than-present mid-Holocene AMOC is revealed by simulations with the T63GR15 grid, which resembles the result of ECHAM6-FESOM, while a decline of the mid-Holocene AMOC is simulated by the low resolution model with the T31GR30 grid. Such discrepancy can be attributed to different changes in Labrador Sea density which is mainly affected by (1) NAO-induced net precipitation and deep water convection, (2) freshwater transport from the Arctic Ocean, and (3) the strength of AMOC itself. Finally, we analyzed available coupled climate models showing a diversity of responses of AMOC to mid-Holocene forcings, most of which reveal positive AMOC changes related to northern high latitudes salinification.

  15. Setting of and mixed carbonate-siliciclastic facies associated with Holocene nearshore sabellid worm reefs, northern Belize

    SciTech Connect

    Mazzullo, S.J.; Burke, C.D.; Dunn, R.K.; bischoff, W.D. )

    1990-05-01

    Communities of sabellid worms (Polychaeta) in northern Belize (mouth of Northern River Lagoon) occur as areally discontinuous, unlithified patch reefs cresting positive features on an irregular depositional topography of Holocene and older sediments. They are found in nearshore marine, moderate energy, tidally influenced environments (intertidal to 60-cm depths) of normal salinity (36%) adjoining subtidal deposits. These colonies, as much as 30 cm thick, are composed of dense thickets of agglutinating worm tubes (1.0 mm diameter, 3.0 cm long) that trap and bind sand to silt-size bioclastic debris and micrite. Worm population density in these communities averages 30 tubes/cm{sup 2}. The antecedent depositional topography beneath the worm reefs and subjacent to adjoining Holocene deposits is characterized by ridges oriented normal to the present shoreline. These ridges are held up by pre-Holocene (latest Pleistocene ) terrigenous sands of probably fluvial distributary origin, occurring at approximately 2.0 m in the subsurface. The overlying Holocene deposits on these ridges are 2.0 m thick and consist of a general upward-coarsening section of terrigenous sandy, carbonate sandy muds to muddy sands punctuated by mangrove peats and capped by the worm reefs. Low areas on the antecedent topography are presently the sites of deposition of deeper subtidal (1.0 m), muddy carbonate sands with some admixed, reworked terrigenous sand. The Holocene section records drowning due to recent (approximately 6 Ka) transgression of the older, lowstand distributary sands on the northern Belize shelf. This mixed carbonate-siliciclastic section and the worm reefs presently are being reshaped and modified by littoral processes.

  16. Holocene cooling culminates in sea ice oscillations in Fram Strait

    NASA Astrophysics Data System (ADS)

    Müller, Juliane; Werner, Kirstin; Stein, Ruediger; Fahl, Kirsten; Moros, Matthias; Jansen, Eystein

    2012-07-01

    A reconstruction of Holocene sea ice conditions in the Fram Strait provides insight into the palaeoenvironmental and palaeoceanographic development of this climate sensitive area during the past 8500 years BP. Organic geochemical analyses of sediment cores from eastern and western Fram Strait enable the identification of variations in the ice coverage that can be linked to changes in the oceanic (and atmospheric) circulation system. By means of the sea ice proxy IP25, phytoplankton-derived biomarkers and ice rafted detritus (IRD) increasing sea ice occurrences are traced along the western continental margin of Spitsbergen throughout the Holocene, which supports previous palaeoenvironmental reconstructions that document a general cooling. A further significant ice advance during the Neoglacial is accompanied by distinct sea ice fluctuations, which point to short-term perturbations in either the Atlantic Water advection or Arctic Water outflow at this site. At the continental shelf of East Greenland, the general Holocene cooling, however, seems to be less pronounced and sea ice conditions remained rather stable. Here, a major Neoglacial increase in sea ice coverage did not occur before 1000 years BP. Phytoplankton-IP25 indices ("PIP25-Index") are used for more explicit sea ice estimates and display a Mid Holocene shift from a minor sea ice coverage to stable ice margin conditions in eastern Fram Strait, while the inner East Greenland shelf experienced less severe to marginal sea ice occurrences throughout the entire Holocene.

  17. Clinal variation of some mammals during the Holocene in Missouri

    NASA Astrophysics Data System (ADS)

    Purdue, James R.

    1980-03-01

    Eastern cottontail ( Sylvilagus floridanus), fox squirrel ( Sciurus niger), and gray squirrel ( Sciurus carolinensis) were examined for clinal variation during the Holocene. Modern samples of all three species displayed strong east-west patterns along the western edge of the eastern deciduous forest: S. floridanus and S. niger decrease and S. carolinensis increases in size. Archeological samples of S. carolinensis from Rodgers Shelter (23BE125), Benton County, Missouri, and Graham Cave (23MT2), Montgomery County, Missouri, indicated an increase in size from early to middle Holocene. Sylvilagus floridanus from Rodgers Shelter decreased in size from early to middle Holocene and then increased during the late Holocene to modern proportions. A literature survey reveals that clinal variation is a common phenomenon among modern homeotherms. In introduced species, clinal variation has developed after relatively few generations, indicating rapid adaptations to environmental conditions; often winter climatic variables are implicated. Morphological variation in the study species during the Holocene is interpreted as a response to changing climates. Studies of morphological clines may lead to another valuable data source for reconstructing past ecologies.

  18. Parasitic diversity found in coprolites of camelids during the Holocene.

    PubMed

    Taglioretti, Verónica; Fugassa, Martín Horacio; Sardella, Norma Haydée

    2015-07-01

    Knowledge of parasitic infections to which fauna was exposed in the past provides information on the geographical origin of some parasites, on the possible dispersal routes and for archaeological fauna on the potential zoonotic risk that human and animal populations could be exposed. The aim of the present study was to examine the gastrointestinal parasite present in camelid coprolites collected from the archaeological site Cerro Casa de Piedra, cave 7 (CCP7), Patagonia, Argentina. Coprolites were collected from different stratified sequences dating from the Pleistocene-Holocene transition to the late Holocene. Paleoparasitological examination revealed the presence of eggs of Trichostrongylidae attributed to Lamanema chavezi or Nematodirus lamae, eggs of three unidentified capillariids, Strongylus-type eggs and oocysts of Eimeria macusaniensis. These parasites affected camelids living in the studied area since the Pleistocene-Holocene transition, about 10,000 years ago. Gastrointestinal parasite fauna of patagonian camelids did not vary significatively from Pleistocene-Holocene transition to late Holocene, although environmental conditions fluctuated greatly throughout this period, as indicative of the strength and the stability of these associations over time. In this study, the zoonotic and biogeography importance of parasites of camelids are also discussed.

  19. Towards a Circum-Antarctic Holocene Paleointensity Record

    NASA Astrophysics Data System (ADS)

    Brachfeld, S.; Kissel, C.; Laj, C.; Willmott, V.

    2005-12-01

    New Holocene geomagnetic paleointensity records have been constructed from the Western Antarctic Peninsula (WAP), Eastern Antarctic Peninsula (EAP), and from the East Antarctic Margin (EAM). The goal of this work is to develop Antarctic paleointensity reference curves for correlation and dating of Antarctic continental shelf sediments. Sediment sequences deposited in fjords and inner shelf basins contain Holocene sections of 3-meters to more than 20-meters, recording the last deglaciation, the paleohistory of ice shelves, and shifting paleoceanographic conditions. However, these records suffer from a lack biogenic calcite for radiocarbon dating. Diatomaceous mud contains sufficient acid insoluble organic matter (aiom) for radiocarbon dating and hence an independent chronology. However, laminated oozes yield shallow inclinations, hence the remanence vector is suspect. Bioturbated diatomaceous mud and diatom-poor muds yield excellent directional records and satisfy the criteria for magnetic uniformity, however the organic content is low and aiom dates can be problematic. Our paleointensity records show the broad pattern of higher intensity during the late Holocene, and lower intensity during the early to middle Holocene, similar to the sinusoidal intensity pattern seen in global absolute and relative paleointensity stacks. Several of the records contain 3 to 4 late Holocene peaks with 1000-year wavelengths that are similar in amplitude and duration to features seen in northern hemisphere lacustrine and marine records. Here we evaluate the local versus regional character of the Antarctic paleointensity records, and the consistency of aiom-dated versus paleointensity-tuned chronologies.

  20. Comparing modeled fire dynamics with charcoal records for the Holocene

    NASA Astrophysics Data System (ADS)

    Bruecher, T.; Brovkin, V.; Kloster, S.; Marlon, J. R.; Power, M. J.

    2013-12-01

    An Earth System model of intermediate complexity, CLIMBER-2, and land surface model JSBACH that includes dynamic vegetation, carbon cycle, and fire regime are used for simulation of natural fire dynamics through the last 8,000 years. To compare the fire model results with the charcoal reconstructions, several output variables of the fire model (burned area, carbon emissions) and several approaches of model output processing are tested. The z-scores out of charcoal dataset have been calculated for the period 8,000 to 200 BP to exclude a period of strong anthropogenic forcing during the last two centuries. The model analysis points mainly to an increasing fire activity during the Holocene for most of the investigated areas, which is in good correspondence to reconstructed fire trends out of charcoal data for most of the tested regions, while for few regions such as Europe the simulated trend and the reconstructed trends are different. The difference between the modeled and reconstructed fire activity could be due to absence of the anthropogenic forcing in the model simulations, but also due to limitations of model assumptions for modeling fire dynamics. For the model trends, the usage of averaging or z-score processing of model output resulted in similar directions of trend. Therefore, the approach of fire model output processing does not effect results of the model-data comparison. Global fire modeling is still in its infancy; improving our representations of fire through validation exercises such as what we present here is thus essential before testing hypotheses about the effects of extreme climate changes on fire behavior and potential feedbacks that result from those changes.

  1. 'Cape capture': Geologic data and modeling results suggest the holocene loss of a Carolina Cape

    USGS Publications Warehouse

    Thieler, E.R.; Ashton, A.D.

    2011-01-01

    For more than a century, the origin and evolution of the set of cuspate forelands known as the Carolina Capes-Hatteras, Lookout, Fear, and Romain-off the eastern coast of the United States have been discussed and debated. The consensus conceptual model is not only that these capes existed through much or all of the Holocene transgression, but also that their number has not changed. Here we describe bathymetric, lithologic, seismic, and chronologic data that suggest another cape may have existed between Capes Hatteras and Lookout during the early to middle Holocene. This cape likely formed at the distal end of the Neuse-Tar-Pamlico fiuvial system during the early Holocene transgression, when this portion of the shelf was fiooded ca. 9 cal (calibrated) kyr B.P., and was probably abandoned by ca. 4 cal kyr B.P., when the shoreline attained its present general configuration. Previously proposed mechanisms for cape formation suggest that the large-scale, rhythmic pattern of the Carolina Capes arose from a hydrodynamic template or the preexisting geologic framework. Numerical modeling, however, suggests that the number and spacing of capes can be dynamic, and that a coast can self-organize in response to a high-angle-wave instability in shoreline shape. In shoreline evolution model simulations, smaller cuspate forelands are subsumed by larger neighbors over millennial time scales through a process of 'cape capture.' The suggested former cape in Raleigh Bay represents the first interpreted geological evidence of dynamic abandonment suggested by the self-organization hypothesis. Cape capture may be a widespread process in coastal environments with large-scale rhythmic shoreline features; its preservation in the sedimentary record will vary according to geologic setting, physical processes, and sea-level history. ?? 2011 Geological Society of America.

  2. Aquatic ecosystem responses to Holocene climate change and biome development in boreal, central Asia

    NASA Astrophysics Data System (ADS)

    Mackay, Anson W.; Bezrukova, Elena V.; Leng, Melanie J.; Meaney, Miriam; Nunes, Ana; Piotrowska, Natalia; Self, Angela; Shchetnikov, Alexander; Shilland, Ewan; Tarasov, Pavel; Wang, Luo; White, Dustin

    2012-05-01

    were also significant, but considerably less important. The potential importance of climate and biome development (tundra, steppe, cold deciduous forest and taiga) on different trophic levels (i.e. chironomid and diatom communities) in lake ESM-1 was also assessed using RDA. Climate predictors had a more significant influence on Holocene chironomid assemblages, especially July insolation at 60 °N, estimates of regional precipitation and estimates of northern hemisphere temperature, while only the development of the taiga biome had a significant impact on these primary consumers. Diatom communities also had a small, but significant influence on Holocene chironomid populations, perhaps linked to variation in faunal feeding strategies. In contrast, climatic and biome predictors explained similar amounts of variation in the Holocene diatom assemblage (approximately 20% each), while chironomids themselves as predictors explained just under 7% of diatom variation. Lake acidity was inferred using a diatom inference model. Results suggest that after deglaciation, the lake did not undergo a process of gradual acidification, most likely due to the presence of continuous permafrost and low levels of precipitation, preventing base cations and dissolved organic carbon entering the lake (except for the period between 1.7 and 0.7 ka BP). We conclude that lakes in continental, boreal regions undergo different models of lake ontogeny than oceanic boreal regions. Unlike other regions discussed, climate is a more important driver of ecosystem change than catchment changes. We also demonstrate that the start of the period coincident with the onset of the Little Ice Age resulted in important thresholds crossed in catchment vegetation and aquatic communities.

  3. Holocene climate variability in Texas, USA: An integration of existing paleoclimate data and modeling with a new, high-resolution speleothem record

    USGS Publications Warehouse

    Wong, Corinne I.; Banner, Jay L.; Musgrove, Marylynn

    2015-01-01

    Delineating the climate processes governing precipitation variability in drought-prone Texas is critical for predicting and mitigating climate change effects, and requires the reconstruction of past climate beyond the instrumental record. We synthesize existing paleoclimate proxy data and climate simulations to provide an overview of climate variability in Texas during the Holocene. Conditions became progressively warmer and drier transitioning from the early to mid Holocene, culminating between 7 and 3 ka (thousand years ago), and were more variable during the late Holocene. The timing and relative magnitude of Holocene climate variability, however, is poorly constrained owing to considerable variability among the different records. To help address this, we present a new speleothem (NBJ) reconstruction from a central Texas cave that comprises the highest resolution proxy record to date, spanning the mid to late Holocene. NBJ trace-element concentrations indicate variable moisture conditions with no clear temporal trend. There is a decoupling between NBJ growth rate, trace-element concentrations, and δ18O values, which indicate that (i) the often direct relation between speleothem growth rate and moisture availability is likely complicated by changes in the overlying ecosystem that affect subsurface CO2 production, and (ii) speleothem δ18O variations likely reflect changes in moisture source (i.e., proportion of Pacific-vs. Gulf of Mexico-derived moisture) that appear not to be linked to moisture amount.

  4. Holocene climate variability in Texas, USA: An integration of existing paleoclimate data and modeling with a new, high-resolution speleothem record

    NASA Astrophysics Data System (ADS)

    Wong, Corinne I.; Banner, Jay L.; Musgrove, MaryLynn

    2015-11-01

    Delineating the climate processes governing precipitation variability in drought-prone Texas is critical for predicting and mitigating climate change effects, and requires the reconstruction of past climate beyond the instrumental record. We synthesize existing paleoclimate proxy data and climate simulations to provide an overview of climate variability in Texas during the Holocene. Conditions became progressively warmer and drier transitioning from the early to mid Holocene, culminating between 7 and 3 ka (thousand years ago), and were more variable during the late Holocene. The timing and relative magnitude of Holocene climate variability, however, is poorly constrained owing to considerable variability among the different records. To help address this, we present a new speleothem (NBJ) reconstruction from a central Texas cave that comprises the highest resolution proxy record to date, spanning the mid to late Holocene. NBJ trace-element concentrations indicate variable moisture conditions with no clear temporal trend. There is a decoupling between NBJ growth rate, trace-element concentrations, and δ18O values, which indicate that (i) the often direct relation between speleothem growth rate and moisture availability is likely complicated by changes in the overlying ecosystem that affect subsurface CO2 production, and (ii) speleothem δ18O variations likely reflect changes in moisture source (i.e., proportion of Pacific-vs. Gulf of Mexico-derived moisture) that appear not to be linked to moisture amount.

  5. Holocene eruptive activity of El Chichón Volcano, Chiapas, Mexico

    USGS Publications Warehouse

    Tilling, Robert I.; Rubin, Meyer; Sigurdsson, Haraldur; Carey, Steven; Duffield, Wendell A.; Rose, William I., Jr.

    1984-01-01

    Geologic and radiometric-age data indicate that El Chichón was frequently and violently active during the Holocene, including eruptive episodes about 600, 1250, and 1700 years ago and several undated, older eruptions. These episodes, involving explosive eruptions of sulfur-rich magma and associated dome-growth processes, were apparently separated by intervals of approximately 350 to 650 years. Some of El Chichón's eruptions may correlate with unusual atmospheric phenomena around A.D. 1300 and possibly A.D. 623.

  6. Lateglacial-Holocene Environment History, Kazakhstan

    NASA Astrophysics Data System (ADS)

    Kremenetski, K.; Velichko, A.

    2007-12-01

    Kazakhstan is located in central Asia between Caspian Sea and Tiang-Shang Mountains. Few well dated holocene sequences from the forest-steppe and steppe belt of Kazakhstan provided information about the vegetation and climate history. Mokhovoe mire was studied in the watershed of Tobol and Ubagan rivers. That's the most thick peat mire in northern Kazakhstan. Sedimentation in the Mokhovoe sequence started ca. 7800 BP. At that time regional vegetation was represented by steppes and birch-poplar forests. Pine penetrated in the Tobol region likely between 6500 and 6000 BP. Pine grew on sand terraces of Tobol River together with birch. At 3000-2900 BP Tilia, Quercus, Ulmus grew in north-west Kazakhstan.The general structure of vegetation was the same as at 6500-6000 BP. At 1900-1500 BP climate became less continental and pine forests with pure pine canopy expanded on sandy terraces of Tobol and Ubagan rivers. Soon after 1500 BP broad-leaved trees were extinct from the regional forests. Pashennoe lake is located in Karkaralinsk mountains in the most elevated part in the south-east part of the Kazakhstan lowhills. Dry grass-wormwood and wormwood steppes were spread in the region at 10500-8200 BP. Picea obovata and Hippophäe rhamnoides occurred in protected parts in intermountain valleys of Karkaralinsk mountains. Salix and Betula also occurred in valleys. Between 8000 and 6000 BP forest vegetation in Karkaralinsk mountains was represented by birch forests. Pine penetrated to Karkaralinsk mountains between 6000 and 5500 BP, but it didn't formed large forests. At the same time the maximal spread of Alnus glutinosa was reconstructed. The general structure of regional vegetation was stable up to. At 1500 BP pure pine forests expanded over Karkaralinsk mountains and around Pashennoe lake. Few lakes were investigated in Borovoe mountains in south of Kokchetav region of Kazakhstan. In early Holocene birch forests dominated in regional vegetation. Pine expanded in Borovoe at ca

  7. A revised Holocene geochronology for the Lower Mississippi Valley

    NASA Astrophysics Data System (ADS)

    Kesel, Richard H.

    2008-10-01

    Data from two locations, 1) a hydrodam site at the Old River Diversion structure south of the latitude of Natchez MS and 2) eight water wells from the latitude of Baton Rouge, LA, are the basis for a revised Holocene geochronology of the Lower Mississippi River floodplain based on 84 radiocarbon dates, analyses of 64 borehole logs, and 75 grain-size analyses, which together provide major insight into questions concerning the complexity of meander belt movement, the influence of the Younger Dryas on the lower valley, and on the Pleistocene/Holocene interface. Following the Younger Dryas, the early Holocene was characterized by periodic flooding and deposition separated by times of little or no deposition.

  8. Impact of Holocene climate variability on Arctic vegetation

    NASA Astrophysics Data System (ADS)

    Gajewski, K.

    2015-10-01

    This paper summarizes current knowledge about the postglacial history of the vegetation of the Canadian Arctic Archipelago (CAA) and Greenland. Available pollen data were used to understand the initial migration of taxa across the Arctic, how the plant biodiversity responded to Holocene climate variability, and how past climate variability affected primary production of the vegetation. Current evidence suggests that most of the flora arrived in the area during the Holocene from Europe or refugia south or west of the region immediately after local deglaciation, indicating rapid dispersal of propagules to the region from distant sources. There is some evidence of shrub species arriving later in Greenland, but it is not clear if this is dispersal limited or a response to past climates. Subsequent climate variability had little effect on biodiversity across the CAA, with some evidence of local extinctions in areas of Greenland in the late Holocene. The most significant impact of climate changes is on vegetation density and/or plant production.

  9. Synchronous interhemispheric Holocene climate trends in the tropical Andes.

    PubMed

    Polissar, Pratigya J; Abbott, Mark B; Wolfe, Alexander P; Vuille, Mathias; Bezada, Maximiliano

    2013-09-01

    Holocene variations of tropical moisture balance have been ascribed to orbitally forced changes in solar insolation. If this model is correct, millennial-scale climate evolution should be antiphased between the northern and southern hemispheres, producing humid intervals in one hemisphere matched to aridity in the other. Here we show that Holocene climate trends were largely synchronous and in the same direction in the northern and southern hemisphere outer-tropical Andes, providing little support for the dominant role of insolation forcing in these regions. Today, sea-surface temperatures in the equatorial Pacific Ocean modulate rainfall variability in the outer tropical Andes of both hemispheres, and we suggest that this mechanism was pervasive throughout the Holocene. Our findings imply that oceanic forcing plays a larger role in regional South American climate than previously suspected, and that Pacific sea-surface temperatures have the capacity to induce abrupt and sustained shifts in Andean climate. PMID:23959896

  10. Synchronous interhemispheric Holocene climate trends in the tropical Andes

    PubMed Central

    Polissar, Pratigya J.; Abbott, Mark B.; Wolfe, Alexander P.; Vuille, Mathias; Bezada, Maximiliano

    2013-01-01

    Holocene variations of tropical moisture balance have been ascribed to orbitally forced changes in solar insolation. If this model is correct, millennial-scale climate evolution should be antiphased between the northern and southern hemispheres, producing humid intervals in one hemisphere matched to aridity in the other. Here we show that Holocene climate trends were largely synchronous and in the same direction in the northern and southern hemisphere outer-tropical Andes, providing little support for the dominant role of insolation forcing in these regions. Today, sea-surface temperatures in the equatorial Pacific Ocean modulate rainfall variability in the outer tropical Andes of both hemispheres, and we suggest that this mechanism was pervasive throughout the Holocene. Our findings imply that oceanic forcing plays a larger role in regional South American climate than previously suspected, and that Pacific sea-surface temperatures have the capacity to induce abrupt and sustained shifts in Andean climate. PMID:23959896

  11. Holocene evolution of Apalachicola Bay, Florida

    USGS Publications Warehouse

    Osterman, L.E.; Twichell, D.C.; Poore, R.Z.

    2009-01-01

    A program of geophysical mapping and vibracoring was conducted to better understand the geologic evolution of Apalachicola Bay. Analyses of the geophysical data and sediment cores along with age control provided by 34 AMS 14C dates on marine shells and wood reveal the following history. As sea level rose in the early Holocene, fluvial deposits filled the Apalachicola River paleochannel, which extended southward under the central part of the bay and seaward across the continental shelf. Sediments to either side of the paleochannel contain abundant wood fragments, with dates documenting that those areas were forested at 8,000 14C years b.p. As sea level continued to rise, spits formed of headland prodelta deposits. Between ???6,400 and ???2,500 14C years b.p., an Apalachicola prodelta prograded and receded several times across the inner shelf that underlies the western part of the bay. An eastern deltaic lobe was active for a shorter time, between ???5,800 and 5,100 14C years b.p. Estuarine benthic foraminiferal assemblages occurred in the western bay as early as 6,400 14C years b.p., and indicate that there was some physical barrier to open-ocean circulation and shelf species established by that time. It is considered that shoals formed in the region of the present barrier islands as the rising sea flooded an interstream divide. Estuarine conditions were established very early in the post-glacial flooding of the bay. ?? 2009 US Government.

  12. Reef-sourced slope deposits, Holocene, Bahamas

    SciTech Connect

    Ginsburg, R.N.; Eberli, G.P.; Harris, P.M.; Slater, R.; Swart, P.K.

    1987-05-01

    Observations and sampling to 350 m from a two-person submersible off Chub Cay, Berry Island, Bahamas, support the idea that the Holocene deep reef is a principal source of talus, now cemented, that foots the windward margins of Great Bahama Bank. At the Chub Cay dive site, a wall extends from 30 to 170 m subsea; below is a low-relief fore reef slope, ca. 50/sup 0/, of limestone veneered with sediment. The upper wall from 30 to 80 m, the deep reef, has a luxuriant growth of corals and a profusion of the calcareous alga halimeda spp. Below 50 m, living coral decreases, and from 80 to 170 m the wall is highly irregular with discontinuous ledges and blind-end caves. At depths from 150 to 170 m, the wall gives way to the fore reef slope whose relative smooth surface dips at 50/sup 0/ to 60/sup 0/ and extends to 350 m. The fore reef is limestone, but its topography resembles that of alluvial fans; rounded ridges rise a few meters above the intervening valleys that are tens of meters wide. The limestone surface has a discontinuous veneer of fine sediment and algal plates, and locally loose cobble and boulder-sized blocks of limestone. A sample of the limestone slope is of well-cemented coral clasts and skeletal sediment. They infer that the deep reef grows outward so rapidly that it caves periodically. The resulting debris bypasses the wall, but some is perched on the steep fore reef slope below where it is soon incorporated into the slope by submarine cementation.

  13. Remote Sensing and Holocene Vegetation: History of Global Change

    NASA Technical Reports Server (NTRS)

    DAntoni, Hector; Schaebitz, Frank

    1995-01-01

    Predictions of the future evolution of the earth's atmospheric chemistry and its impact on global circulation patterns are based on Global Climate Models (GCM's) that integrate the complex interactions of the biosphere, atmosphere and the oceans. Most of the available records of climate and environment are shortterm records (from decades to a few hundred years) with convolved information of real trends and short-term fluctuations. GCM's must be tested beyond the short-term record of climate and environment to insure that predictions are based on trends and therefore are appropriate to support long term policy making. An appropriate timeframe should extend over the Holocene period (the last 10,000 years) when most contemporary climate and environmental processes began. Since its inception in 1916, pollen analysis has successfully reconstructed the paleoecology of the last 10,000 years for many sites around the world, thus providing a powerful time-link between short- and long-term processes in the biosphere. However, pollen analytic results cannot be used in physiological models driven by remotely sensed data. Further, modern ecology and climate data are necessary to calibrate pollen analytical models. These are available for extensive regions in the northern hemisphere, particularly for eastern United States and Canada, and western Europe. In other parts of the world, weather stations are scattered, records extend over a period of only few years, and there are no systematic climate records for large portions of the globe. This is the case of Patagonia in Argentina where a few weather stations are located close to the Atlantic seaports, fewer stations are in towns located near the eastern Andean foothill, and fewer still are scattered on the extensive Patagonian plateau. This problem became evident after completion of the Argentine-German Program of Palynology (PROPAL), a cooperative effort of National University of Mar del Plata (Argentina) and University Bamberg

  14. Holocene sedimentary evolution of a mid-ocean atoll lagoon, Maldives, Indian Ocean

    NASA Astrophysics Data System (ADS)

    Klostermann, Lars; Gischler, Eberhard

    2015-01-01

    Based on detailed analyses of cores covering the lagoon of Rasdhoo Atoll, Maldives, six carbonate facies, one soil, and one peat facies have been identified. The abundance of carbonate and rare opaque grains was quantified with a point counter. X-ray diffractometry was used to measure mineralogical composition of samples. The statistical delineation of facies using cluster analysis was based on point count, mineralogical, and textural analyses. In decreasing abundance, the six carbonate facies are classified as mollusk-coral-algal floatstone to rudstone (30 %), mollusk-coral-red algae rudstone (23 %), mollusk-coral-algal wackestone to floatstone (23 %), mollusk-coral wackestone (13 %), mollusk-coral mudstone to wackestone (9 %), and mollusk mudstone (2 %). The carbonate facies represent lagoonal background sedimentation, mostly consisting of fine sediments, and event sedimentation depositing transported coarse-grained reefal components. Fifty-seven carbonate samples and one peat sample were dated radiometrically, covering the Holocene transgression from 10 kyrs BP until today. Comparing the sediment accumulation data of the lagoon with two local sea-level curves, three systems tracts can be identified: (1) a lowstand systems tract characterized by karst and soil deposition >10 kyrs BP, (2) a transgressive systems tract with peat and carbonate separated by hiatus 10-6.5 kyrs BP, and (3) a highstand systems tract dominated by carbonate sedimentation 6.5-0 kyrs BP and further divided into three stages (6.5-3, 3-1, and 1-0 kyrs BP). During the Holocene transgression, sedimentation rates increased continuously to a maximum of 1.4 m/kyr during 3-1 kyrs BP. Modern (1-0 kyrs BP) mean sedimentation rates average 0.6 m/kyr. A simple calculation suggests that two processes (background sedimentation and sand apron progradation) will probably fill up the accommodation space of the lagoon during the Holocene highstand, but these processes will not suffice to fill the larger

  15. Forces of environmental flux in Central America during the holocene

    SciTech Connect

    Leyden, B. )

    1994-06-01

    A review of palynological and limnological data from Central America serves as a framework for evaluating environmental stability during the Holocene. The magnitude of climatic forcing after the early Holocene has not produced the dramatic changes that spanned the transition to post-glacial conditions. Nevertheless, climatic variability and human disturbance have had a significant impact on the vegetation of the region. This discussion has relevance for broader questions of species diversity and the long-term stability of vegetation associations in the tropics.

  16. A tentative of Holocene sediment budget for the Seulles catchment (western France)

    NASA Astrophysics Data System (ADS)

    Viel, Vincent; Lespez, Laurent; Delahaye, Daniel; Le Gouee, Patrick

    2010-05-01

    Geomorphological and paleoenvironmental researches on Holocene sedimentation in the valleys of Normandy provide evidence for fluvial system changes related to climate and human activities in the Paris basin. Alluvial and colluvial deposits are important as archives of past environments changes. They can be used to construct the temporal frameworks for historical erosion and to give an indication of the past erosion processes. Few studies attempts to make long-term soil erosion and sediment storage in the valley bottom in North-western France. This work put into forward results of a research on Holocene sediment budget. This study focuses in the Seulles catchment (430 km²), located in Normandy at the junction between the Armorican massif (upstream part) and the sedimentary Paris Basin (downstream part). In order to reconstruct the Holocene sediment budget, different approaches were used to quantify sediment deposit within the floodplain, soil erosion rates and colluvial deposition. To characterize and quantify the sediment storage into the valley bottoms, 32 partial or complete cross-sections, regularly placed along the valley bottom, were established. These field investigations allow to evaluate the global bulk of fluvial sediment storage into the catchment. In a second step, the assessment of dry bulk densities permits to convert volumetric data into weight. To establish the chronology of the alluvial filling, 6 drilling cores were realized on selected cross-sections to sample organic material content for AMS radiocarbon dating. In total, 38 dates were obtained at the catchment scale and numerous are in process. In the same way, we evaluated Holocene slope erosion and sediment storage using soils profiles descriptions determined from auger coring transects of two small catchments (15 Km²). Results demonstrate the existence until 2500 BP of two morpho-sedimentary units (a model related to sediments dynamics into the catchment and a second one related to the

  17. Application of integrated reservoir management and reservoir characterization to optimize infill drilling. Quarterly technical progress report, March 13--June 12, 1997

    SciTech Connect

    1997-12-31

    The eighteen 10-acre infill wells which were drilled as part of the field demonstration portion of the project are all currently in service with no operational problems. These wells consist of fourteen producing wells and four injection wells. The producing wells are currently producing a total of approximately 650 bopd, down from a peak rate of 900 bopd. Unit production is currently averaging approximately 3,000 bopd, 12,000 bwpd and 18,000 bwipd. The paper describes progress in core analysis, reservoir surveillance, well stimulation, validation of reservoir characterization (includes thin section analyses, depositional environments, and paleontologic analysis), material balance decline curve analysis, and validation of reservoir simulation (includes geostatistical and deterministic).

  18. Application of integrated reservoir management and reservoir characterization to optimize infill drilling. Quarterly technical progress report, June 13--September 12, 1997

    SciTech Connect

    1997-12-31

    The eighteen 10-acre infill wells which were drilled as part of the field demonstration portion of the project are all currently in service with no operational problems. These wells consist of fourteen producing wells and four injection wells. The producing wells are currently producing a total of approximately 500 bopd, down from a peak rate of 900 bopd. Unit production is currently averaging approximately 2,800 bopd, 12,000 bwpd and 17,000 bwipd. The paper describes progress on core analysis, gas-oil/oil-gas permeability tests, water-oil/oil-water permeability tests, water-gas permeability tests, electrical resistivity measurements, capillary pressure tests, reservoir surveillance, and paleontologic analysis.

  19. A lacustrine record of early Holocene watershed events and vegetation history, Corvara in Badia, Dolomites (Italy)

    NASA Astrophysics Data System (ADS)

    Borgatti, Lisa; Ravazzi, Cesare; Donegana, Marta; Corsini, Alessandro; Marchetti, Mauro; Soldati, Mauro

    2007-02-01

    The early-middle Holocene lacustrine succession of Corvara in Badia (Italian Dolomites, 1521 m a.s.l.) records landslides and other watershed events before the onset of human pressure. The sensitivity of this archive to relate climate change, watershed processes and vegetation dynamics in the catchment has been explored through a stratigraphic study, including the analysis of sedimentological features, magnetic properties, palaeobotanical records and radiocarbon dating. A palaeolake existed between 10.1 k and 7 k cal. yr BP and was surrounded by a dense conifer forest. Long-term forest dynamics driven by ecological processes and by climatic conditions favourable to upward forest expansion is recorded throughout the pollen record. Within the fine clastic sedimentation, distinct layers enriched in organic debris of terrestrial origin have been attributed to instant events produced by mass movements. Their age fits the chronology of large landslide events already known in the catchment, enabling correlation of the field evidence of landslides with the lacustrine record. Landslide frequency is controlled by geological and structural factors, but it is significantly modulated by the centennial-millennial climatic phases that characterise the Holocene in the Alps. The taphonomical properties of pollen and macroremains provided valuable insight on the mechanism of watershed processes. Copyright

  20. Dynamic casting of a graben complex: Syn-sedimentary infill and differential subsidence during the permo-carboniferous; Peace River Embayment, western Canada

    SciTech Connect

    Barclay, J.E. Univ. of Calgary, Alberta ); Krause, F.F. ); Campbell, R.R. Calamity Resources, Calgary, Alberta )

    1991-03-01

    The Carboniferous Stoddart Group and Permian Belloy Formation record infill of a long-lived graben complex in the center of the Peace River Embayment. The Dawson Creek Graben Complex began down-dropping during deposition of the Rundle Group and Golata Formation and reached its maximum during Kiskatinaw time. The overlying Taylor Flat Formation shows graben filling and graben decay; whereas the flat Permian Belloy Formation beds within and beyond graben limits indicate tectonic stability. The complex comprised the larger Fort St. John Graben and satellite Hines Creek, Whitelaw, and Cindy grabens. The grabens consist of kilometer-scale horst and graben blocks bounded by normal faults. The internal blocks subsided at various rates, with differential subsidence occurring in the form of horsts subsiding slower than neighboring grabens. Syn- and post-depositional growth-type normal faults controlled formation and bed thickness, as did inter- and intra-formation unconformities. From these observations, a structural/stratigraphic model can be constructed that explains the complex stratigraphy and depositional interpretations. This model describes a basin dominated by tectonic controls rather than global sea-level events. Syn- and post-sedimentary growth-type block faulting, differential subsidence of fault blocks, sedimentary infill, and unconformity truncation were the major controls on the basin. The model provides an analog to grabens and block-faulted basins of growth-faulted basins occurring elsewhere. The implications of the model to petroleum exploration are that all beds can be correlated by assuming that beds were essentially flat-lying prior to and during faulting. The combination of the block-faulted character and complex facies changes provides many structural and stratigraphic petroleum traps.

  1. Results of a detailed infill lake-sediment survey in the Snow Lake area: Evaluation and comparison of grab sample and short core data

    USGS Publications Warehouse

    Friske, P.W.B.

    1996-01-01

    As part of the Exploration Science and Technology Initiative (EXTECH) program a detailed infill lake-sediment and water survey was undertaken in the Snow Lake area during the fall of 1991. This involved the collection of 346 lake sediment grab samples and concomitant waters. In 1993, additional work was undertaken involving the collection of 23 short cores from selected grab sample sites. The primary objectives of the infill survey and short core work were to: 1) evaluate the effectiveness of lake sediment geochemistry in detecting known mineralization in the Snow Lake area; 2) evaluate and develop new approaches in the use of lake sediment geochemistry; and, 3) define, if possible, new exploration targets. At most sites, data from the cores verify the original grab sample results. However, at a few sites the original anomalous grab sample results are interpreted as being related to contamination as opposed to naturally elevated levels. An unusually thick sequence of contaminated surface sediments with extremely high concentrations of trace metals is a likely contributing factor, a condition which is restricted to lakes in the immediate vicinity of local anthropogenic activity. Collection of lake cores provides a useful new approach to the follow-up of grab sample data and to the application of lake sediment geochemistry, particularly in areas with significant local contamination. Much of the known mineralization in the area is clearly reflected by the lake sediment data. Character of the anomalies mirror the composition of the nearby mineralization. The lake sediment data also identify a number of areas that warrant further investigation, several of which are discussed.

  2. Late Holocene Sea-Level Changes in French Polynesia, South-Central Pacific

    NASA Astrophysics Data System (ADS)

    Camoin, G.; Hallmann, N.; Eisenhauer, A.; Samankassou, E.; Milne, G. A.

    2013-12-01

    Camoin, G.1, Hallmann, N.1, Eisenhauer, A.2, Vella, C.1, Samankassou, E.3, Fietzke, J.2, Milne, G.A.4 1 Aix-Marseille Université, CNRS, IRD, CEREGE UM34, Europôle Méditerranéen de l'Arbois, BP80, 13545 Aix-en-Provence cedex 4, France 2 Helmholtz-Zentrum für Ozeanforschung GEOMAR, Kiel, Wischhofstrasse 1-3, 24148 Kiel, Germany 3 University of Geneva, Rue des Maraîchers 13, CH-1205 Geneva, Switzerland 4 University of Ottawa, Department of Earth Sciences, Ottawa, Ontario, K1N 6N5, Canada Knowledge of the timing and course of sea-level changes provides an essential framework for conceptual models aimed at understanding the dynamics of melting of large ice sheets and their effects on the isostasy of the Earth. The marked variability of local Holocene sea levels, responding both to ice-sheet unloading and the redistribution of water masses in the global ocean, demonstrates the need to constrain geophysical processes that include hydro-isostasy, equatorial ocean syphoning and tectonic movements affecting relative sea-level positions. A regional reconstruction of Late Holocene sea-level changes (i.e., the last 6,000 yrs) in French Polynesia is based on the accurate U-series dating of in situ sea-level indicators (coral colonies including microatolls; bivalves) and their precise vertical and horizontal GPS positioning in five atolls (Fakarava, Hao, Manihi, Rangiroa, Tikehau) from the Tuamotu Archipelago and six high islands (Bora Bora, Mangareva, Maupiti, Moorea, Raivavae, Rurutu) from the Society, Gambier and Austral Archipelagos. These islands provide the opportunity to reconstruct accurately Late Holocene sea-level changes that are well-suited to estimate eustatic and isostatic changes because : 1) they exhibit unique coral reef records including valuable sea-level indicators, such as corals and bivalves in growth position, emerged coral conglomerates and beachrocks, 2) their subsidence rates are negligible for the Late Holocene period, thus excluding any tectonic

  3. Stratigraphic signatures of climatic change during the Holocene evolution of the Tigris Euphrates delta, lower Mesopotamia

    NASA Astrophysics Data System (ADS)

    Aqrawi, Adnan A. M.

    2001-02-01

    Fluctuations in climate, sea level and sedimentation rates, in addition to the neotectonic activity, during the geological evolution of the Tigris-Euphrates delta (in the last 10,000 years) had resulted in the deposition of various sedimentary units. Previously, five main stratigraphic units, with other sub-units, have been identified by the author during the study of the Holocene deltaic successions of Lower Mesopotamia and as based upon the results of petrological, geochemical, palaeontological and radiometric analyses of his PhD dissertation. Each unit has been produced through various depositional and diagenetic processes in addition to the dominant climate. Such processes together have been clearly recorded in the forms of either the authigenic minerals occurring in each sequence, particularly the Ca-Mg carbonates, evaporites and clay minerals, the biological activities represented by shell remains of molluscs, foraminifers and ostracods, or the preservation of organic matters within organic-rich layers. This review discusses the impact climatic changes had on the accumulated sedimentary facies during the Holocene evolution of the Tigris-Euphrates delta. Arid climate dominated the study area in the early Holocene after a long period of the wetter conditions of Pleistocene. Such a climatic change has resulted in the formation of gypcretes rich in palygorskite and dolomite occurring within the calcareous fluvial-plain muds, similar to the modern fluvial plain deposits. However, the sediments were highly admixed with coarser sandy deposits of playa and aeolian sources in the western desertic margins, and with older reworked sands of Zagros foothills to the Northeast of Lower Mesopotamia. During the mid-Holocene marine invasion, when the climate became wetter as well, brackish-water/marine sedimentary sub-units were deposited, overlying the previous fluvial plain deposits. The deposition started with a transitional sub-unit flourishing over the older early

  4. Earthflow sediment production and Holocene sediment record in a large Apennine catchment

    NASA Astrophysics Data System (ADS)

    Simoni, Alessandro; Ponza, Alessio; Picotti, Vincenzo; Berti, Matteo; Dinelli, Enrico

    2013-04-01

    Landscape evolution in active mountain chains can be dominated by gravitational slope movements. This is observed in a large portion of the Reno river catchment, Apennines, Italy, where weak rocks, such as clayshales, are subject to earthflows that control hillslope morphology and supply sediments to the channel network. In this paper, we evaluate the sediment flux generated by earthflows and compare it with Holocene-averaged deposition rates to assess the contribution of mass movements to landscape evolution. Present-day hillslope sediment flux is estimated by combining measured displacement rates (72 inclinometers) and spatial attributes of earthflows and historical frequency of reactivations. Averaged sediment yield (~ 1.6 x 103 t/km2/yr) compares well with similar studies on earthflow-dominated landscapes, despite notable differences in methodology. In the study area, the connectivity between hillslopes and the stream network is well developed and no significant sediment sinks influence the sediment transport processes. We document best estimates of regional sediment fluxes and related uncertainties, based on available data. Coarse limestone fragments, present in the clayshales, are used as a natural sediment tracer to allow a comparison with sedimentation rates taking place at the mouth of the intramontane catchment. Here, available borehole logs, 14C datings and stratigraphic correlations of the alluvial fan are used to obtain an estimate of the deposition that took place during Holocene times. Taking also into account the role of solute transport, sedimentation rates are compared to earthflow sediment production rates. Results show a good agreement and demonstrate that earthflows are the primary mass wasting process in these weak rock lithologies. We document best estimates of regional sediment fluxes and related uncertainties. Present earthflow sediment production outpaces Holocene-averaged sedimentation rates by a factor of two. The gap between sediment

  5. Marked Shore-Parallel Variability in Holocene Sediment Thickness Offshore La Jolla, California

    NASA Astrophysics Data System (ADS)

    Hogarth, L. J.; Driscoll, N. W.; Babcock, J.; Le Dantec, N.; Haas, J.; Inman, D. L.; Masters, P. M.

    2005-05-01

    New CHIRP seismic data indicate that the bathymetry and subsurface structure in the nearshore are not well correlated offshore La Jolla, CA. For example, the thickness of the Holocene transgressive sequence varies along strike in the region from less than 1 m thick offshore Torrey Pines State Reserve in the north to greater than 20 m farther south between the Scripps and La Jolla Canyons. This thickness variability appears to be structurally controlled (i.e., by relief on the transgressive surface). Existing theory and observations show longshore transport of sand in the Oceanside littoral cell occurs from north to south. In the littoral cell sediment is transported by waves and currents and exits the nearshore via the La Jolla submarine canyon system. However, the observed variability in shore-parallel sediment thickness cannot simply be explained by longshore transport. The seismic data, collected in April and November 2002, reveals three areas of relatively thick Holocene sediments: 1) between La Jolla and Scripps canyons, 2) directly north of Scripps Canyon, and 3) within the La Jolla Canyon system on small "inter-canyon highs" or shoals between branches of the canyon. The sediment thickness on the inner shelf systematically thins toward the north away from the canyons. In fact, the observed variability of sediment thickness in the shore-parallel direction (south - north) is larger than that observed cross-shelf (east - west). The spatial correlation of the shoaling transgressive surface and the offshore bathymetric high, together with a left-lateral jog in the right-lateral Rose Canyon Fault in this region, suggest a tectonic control on the shelf morphology that in turn controls Holocene sediment thickness offshore of La Jolla. Convergence as a result of fault geometry engenders uplift and shoaling of the transgressive surface, which also has a bathymetric expression offshore. If correct, this would imply that processes such as wave climate control sediment

  6. New Archeointensities from Mid Holocene Archeological Materials

    NASA Astrophysics Data System (ADS)

    Kapper, K.; Donadini, F.; Hirt, A. M.

    2013-12-01

    Paleointensity variation determined from mid Holocene archeomagnetic samples can improve the understanding of Earth's magnetic field and how it has changed during the past 10 000 years. It is important for models of Earth's magnetic field to fill gaps in archeomagnetic data records prior 1000 BC, which are prevalent in European data sets. New data help to complement regional reference curves, which are useful for dating of archeologic artifacts, e.g., pottery or displaced objects such as tiles, if the paleointensity of the object is known. Due to small temporal resolution and uncertainties in data records, the maximum intensity and maximum rate of change of the geomagnetic field is poorly understood. Stacks of intensity records are assumed to smooth out high frequency features in the secular variation curve such as archeomagnetic jerks and geomagnetic spikes. In previous studies it was shown that archeointensities could be measured from various archeological materials, if they were heated and obtain a pure thermoremanent magnetization. Ceramics or potsherds were the first materials to be used to measure the geomagnetic field intensity. They are usually heated to high temperatures and are abundant. In more recent years it was shown that copper slags can be used as well for archeointensity determinations. These are widespread in Europe, Asia and Africa from about 5000 BC onwards, carry a strong magnetization, and charcoal is usually close by or even embedded in the slag and can be used for radiocarbon dating. Samples from burned soils of archeological fires or hearth remains can have accurate archeointensities, provided that the samples carry a pure thermoremanent magnetization, which usually can be found in the center of the fireplace. But for some sites the center is difficult to locate, and relatively loose material may easily suffer from disturbances. In this study we report on results from archeointensity measurements on 91 specimens made of ceramics, slags, and

  7. Paleosecular variation for understanding young volcanoes of the Holocen

    NASA Astrophysics Data System (ADS)

    Di Chiara, A.

    2015-12-01

    The paleosecular variation of the geomagnetic field had been increasingly recognized as a powerful tool for understating volcanic processes. Based on the assumption that every volcanic unit record instantaneously the local magnetic field while cooling down is implied that the paleomagnetic directions from different and uncorrelated units can be correlated. Moreover, volcanic successions well-constrained in ages represent an invaluable tool for understanding the variations of the geomagnetic field across the time quasi-continuously. When a reference curve describing in detail the paleosecular variations of directions and intensities is available for a given region, the curves can be safely used to constrain the age of uncorrelated volcanic deposits such as lava cooling units, pyroclastic deposits, and ignimbrites. I present here an overview of examples where I used paleomagnetism as a correlating and dating tool: from the Azores Archipelago (Faial and Terceira), to the Trindade Island (Brazil) and Chile. At the Faial island, a Holocene volcanic cone field history was entirely reconstructed by an extensive paleomagnetic investigation, while at Terceira the last historical eruptive event was successfully correlated and reinterpreted. At the remote Trindade Island, paleomagnetic directions helped to propose an age to the more recent Volcano of the island. Finally in the Chilean volcano of LLaima, the directions obtained from one historical flow are compared with expected values from the global models with interesting insights. In the two examples from the Azores Archipelago, the statistical comparison of the mean paleomagnetic full vector values from the studied deposit with the fluctuations of the geomagnetic field described in the reference curve provided a very good tool for age constraints.

  8. Insolation forcing of early Holocene climate in Southern East Africa?

    NASA Astrophysics Data System (ADS)

    Barker, P. A.; Leng, M. J.; Gasse, F.; Johnson, T. C.

    2003-04-01

    Palaeoclimatic investigations in southern Tanzania and from Lake Malawi, has forced a re-evaluation of the processes controlling long-term climate changes in the region (Gasse et al., 2002; Johnson et al., 2002). In Lake Malawi at the last glacial maximum (LGM) abundant diatom periphyton (up to 30% at the LGM) and reduced biogenic silica accumulation in cores M98-1P and M98-2P suggests a low lake level and a relatively dry climate (Gasse et al., 2002). The implication is that orbital forcing of southern hemisphere climate was subservient to glacial boundary conditions (Johnson et al., 2002), in contrast to parts of southern tropical South America (Baker, 2002). The situation during the early Holocene, when orbital configuration should produce dry conditions in the southern tropics, is ambiguous. Carbonates precipitated in the southern basin of Lake Malawi, indicating a lowering of lake level and geochemical proxies from the north basin (biogenic silica and total phosphorus) suggest productivity fell, yet the diatom records from the northern basin are complacent, showing only shifts between different planktonic species. Here we present preliminary oxygen isotope data from diatom silica in an attempt to address the lake’s status at this time and implications for the precipitation-evaporation ratio (P-E). This is the first time this method has been applied to the sediments of a large African lake and some of the issues regarding the climatic calibration of the oxygen isotope ratios will be addressed. We will compare the isotope changes to other indicators from Lake Malawi and elsewhere in the region to investigate to what extent reduced insolation moderated the water balance of lakes in the southern tropics in contrast to the wet phase experienced by the equatorial lakes.

  9. Holocene Deglaciation of the Scandinavian Ice Sheet: Preliminary 10Be Ages

    NASA Astrophysics Data System (ADS)

    Cuzzone, J. K.; Clark, P. U.; Marcott, S. A.; Pekka Lunka, J.; Wohlfarth, B.; Carlson, A. E.

    2012-12-01

    The response of ice sheets to a warming climate is not well understood. Because we are limited in our understanding of present dynamics, reconstructing the deglaciation of former ice sheets allows for a better understanding of how past ice sheets responded to a warming climate along with their contribution to sea-level rise. These reconstructions also serve as critical constraints for ice sheet modeling efforts. Here, we present a suite of new 10Be ages from erratic boulders along three transects spanning southern to northern Sweden and Finland, that improve our understanding of the deglaciation of the Scandinavian Ice Sheet (SIS) beginning ~ 11.7ka through its final demise during the early Holocene. Preliminary dates from southern Finland, beginning at the Salpausselka Youngers Dryas moraine (11.5 ± 0.7 ka, n=2), inland southern Finland near Jyvaskyla (11.5 ± 0.5ka, n=2), and coastal Finland (~60km from Gulf of Bothnia) near Vimpeli (11.5 ± 0.4ka, n=1) indicate a rapid retreat following the Younger Dryas for Southern Finland (~500km within uncertainty of ages). Preliminary dates also exist for Northern Finland, near Inari (10.3 ± 0.5ka, n=2). Additional ages now being processed at PRIME Lab, Purdue University, which will establish a basis for SIS retreat from all sampled sites, will also be presented. These new data will help to constrain the Holocene deglaciation of the SIS and its associated retreat rates, and establish the SIS contribution to Holocene sea level rise, which will improve our understanding of ice-sheet response to a warming climate.

  10. Holocene lake-level fluctuations of Lake Aricota, Southern Peru

    USGS Publications Warehouse

    Placzek, C.; Quade, Jay; Betancourt, J.L.

    2001-01-01

    Lacustrine deposits exposed around Lake Aricota, Peru (17?? 22???S), a 7.5-km2 lake dammed by debris flows, provide a middle to late Holocene record of lake-level fluctuations. Chronological context for shoreline deposits was obtained from radiocarbon dating of vascular plant remains and other datable material with minimal 14C reservoir effects (<350 yr). Diatomites associated with highstands several meters above the modern lake level indicate wet episodes. Maximum Holocene lake level was attained before 6100 14C yr B.P. and ended ???2700 14C yr B.P. Moderately high lake levels occurred at 1700 and 1300 14C yr B.P. The highstand at Lake Aricota during the middle Holocene is coeval with a major lowstand at Lake Titicaca (16?? S), which is only 130 km to the northeast and shares a similar climatology. Comparisons with other marine and terrestrial records highlight emerging contradictions over the nature of mid-Holocene climate in the central Andes. ?? 2001 University of Washington.

  11. Reorganization of the North Atlantic Oscillation during early Holocene deglaciation

    NASA Astrophysics Data System (ADS)

    Wassenburg, Jasper A.; Dietrich, Stephan; Fietzke, Jan; Fohlmeister, Jens; Jochum, Klaus Peter; Scholz, Denis; Richter, Detlev K.; Sabaoui, Abdellah; Spötl, Christoph; Lohmann, Gerrit; Andreae, Meinrat O.; Immenhauser, Adrian

    2016-08-01

    The North Atlantic Oscillation is the dominant atmospheric pressure mode in the North Atlantic region and affects winter temperature and precipitation in the Mediterranean, northwest Europe, Greenland, and Asia. The index that describes the sea-level pressure difference between Iceland and the Azores is correlated with a dipole precipitation pattern over northwest Europe and northwest Africa. How the North Atlantic Oscillation will develop as the Greenland ice sheet melts is unclear. A potential past analogue is the early Holocene, during which melting ice sheets around the North Atlantic freshened surface waters, affecting the strength of the meridional overturning circulation. Here we present a Holocene rainfall record from northwest Africa based on speleothem δ18O and compare it against a speleothem-based rainfall record from Europe. The two records are positively correlated during the early Holocene, followed by a shift to an anti-correlation, similar to the modern record, during the mid-Holocene. On the basis of our simulations with an Earth system model, we suggest the shift to the anti-correlation reflects a large-scale atmospheric and oceanic reorganization in response to the demise of the Laurentide ice sheet and a strong reduction of meltwater flux to the North Atlantic, pointing to a potential sensitivity of the North Atlantic Oscillation to the melting of ice sheets.

  12. Mid-Holocene hydrologic model of the Shingobee watershed, Minnesota

    USGS Publications Warehouse

    Filby, S.K.; Locke, Sharon M.; Person, M.A.; Winter, T.C.; Rosenberry, D.O.; Nieber, J.L.; Gutowski, W.J.; Ito, E.

    2002-01-01

    A hydrologifc model of the Shingobee Watershed in north-central Minnesota was developed to reconstruct mid-Holocene paleo-lake levels for Williams Lake, a surface-water body located in the southern portion of the watershed. Hydrologic parameters for the model were first estimated in a calibration exercise using a 9-yr historical record (1990-1998) of climatic and hydrologic stresses. The model reproduced observed temporal and spatial trends in surface/groundwater levels across the watershed. Mid-Holocene aquifer and lake levels were then reconstructed using two paleoclimatic data sets: CCM1 atmospheric general circulation model output and pollen-transfer functions using sediment core data from Williams Lake. Calculated paleo-lake levels based on pollen-derived paleoclimatic reconstructions indicated a 3.5-m drop in simulated lake levels and were in good agreement with the position of mid-Holocene beach sands observed in a Williams Lake sediment core transect. However, calculated paleolake levels based on CCM1 climate forcing produced only a 0.05-m drop in lake levels. We found that decreases in winter precipitation rather than temperature increases had the largest effect on simulated mid-Holocene lake levels. The study illustrates how watershed models can be used to critically evaluate paleoclimatic reconstructions by integrating geologic, climatic, limnologic, and hydrogeologic data sets. ?? 2002 University of Washington.

  13. Holocene eolian activity in the Minot dune field, North Dakota

    USGS Publications Warehouse

    Muhs, D.R.; Stafford, Thomas W.; Been, J.; Mahan, S.A.; Burdett, J.; Skipp, G.; Rowland, Z.M.

    1997-01-01

    Stabilized eolian sand is common over much of the Great Plains region of the United States and Canada, including a subhumid area of ??? 1500 km2 near Minot, North Dakota. Eolian landforms consist of sand sheets and northwest-trending parabolic dunes. Dunes and sand sheets in the Minot field are presently stabilized by a cover of prairie grasses or oak woodland. Stratigraphic studies and accelerator mass spectrometry radiocarbon dating of paleosols indicate at least two periods of eolian sand movement in the late Holocene. Pedologic data suggest that all of the dune field has experienced late Holocene dune activity, though not all parts of the dune field may have been active simultaneously. Similar immobile element (Ti, Zr, La, Ce) concentrations support the interpretation that eolian sands are derived from local glaciofluvial and glaciolacustrine sediments. However, glaciolacustrine and glaciofluvial source sediments have high Ca concentrations from carbonate minerals, whereas dune sands are depleted in Ca. Because noneolian-derived soils in the area are calcareous, these data indicate that the Minot dune field may have had extended periods of activity in the Holocene, such that eolian abrasion removed soft carbonate minerals. The southwest-facing parts of some presently stabilized dunes were active during the 1930s drought, but were revegetated during the wetter years of the 1940s. These observations indicate that severe droughts accompanied by high temperatures are the most likely cause of Holocene eolian activity.

  14. Holocene fire history reconstruction using Tibetan lacustrine sediments

    NASA Astrophysics Data System (ADS)

    Callegaro, Alice; Kirchgeorg, Torben; Battistel, Dario; Bird, Broxton; Barbante, Carlo

    2016-04-01

    The important role that biomass burning playsin influencing the Holocene'sclimate is still under discussion. The present work gives information about past biomass burning events in the Tibetan Plateau and helps to increase the understanding of the interaction between climate, humans and fire activity during Holocene. Asiatic area is one of the centers of the advent of agriculture and pastoralism, and it is a strategic area for understanding the interaction between human and fire during the Holocene. We reconstructed past biomass burning events and vegetation from sediments collected from lake Paru Co, a small moraine dammed lake located in the Tibetan Plateau at 4845 m above sea level. We extracted lake sediment samples by accelerate solvent extraction and analysed different organic molecular proxies by GC-MS and IC-MS. We used monosaccharide anhydrides, levoglucosan and its isomers, as proxies for biomass burning. These are specific molecular markers originated from the pyrolysis of cellulose showing significant fire events and indicate changes in burned fuel. Furthermore we analysed polycyclic aromatic hydrocarbons (PAH) as additional combustion proxies. For a better understanding of changes in vegetation andof human habitation at the lake shore we analysed n-alkanes and sterols. Comparing the data of this multi-proxy approach used in the studied area with climatic and meteorological literature data, reconstruction and contextualization of past fire events are possible: we can see the agreement between dry climate period and presence of more intense fire events, especially in the Early Holocene.

  15. Mid-Holocene Hydrologic Model of the Shingobee Watershed, Minnesota

    NASA Astrophysics Data System (ADS)

    Filby, Sheryl K.; Locke, Sharon M.; Person, Mark A.; Winter, Thomas C.; Rosenberry, Donald O.; Nieber, John L.; Gutowski, William J.; Ito, Emi

    2002-11-01

    A hydrologic model of the Shingobee Watershed in north-central Minnesota was developed to reconstruct mid-Holocene paleo-lake levels for Williams Lake, a surface-water body located in the southern portion of the watershed. Hydrologic parameters for the model were first estimated in a calibration exercise using a 9-yr historical record (1990-1998) of climatic and hydrologic stresses. The model reproduced observed temporal and spatial trends in surface/groundwater levels across the watershed. Mid-Holocene aquifer and lake levels were then reconstructed using two paleoclimatic data sets: CCM1 atmospheric general circulation model output and pollen-transfer functions using sediment core data from Williams Lake. Calculated paleo-lake levels based on pollen-derived paleoclimatic reconstructions indicated a 3.5-m drop in simulated lake levels and were in good agreement with the position of mid-Holocene beach sands observed in a Williams Lake sediment core transect. However, calculated paleolake levels based on CCM1 climate forcing produced only a 0.05-m drop in lake levels. We found that decreases in winter precipitation rather than temperature increases had the largest effect on simulated mid-Holocene lake levels. The study illustrates how watershed models can be used to critically evaluate paleoclimatic reconstructions by integrating geologic, climatic, limnologic, and hydrogeologic data sets.

  16. Testing solar forcing of pervasive Holocene climate cycles

    NASA Astrophysics Data System (ADS)

    Turney, Chris; Baillie, Mike; Clemens, Steve; Brown, David; Palmer, Jonathan; Pilcher, Jonathan; Reimer, Paula; Leuschner, Hanns Hubert

    2005-09-01

    The temporal and spatial extent of Holocene climate change is an area of considerable uncertainty, with solar forcing recently proposed to be the origin of cycles identified in the North Atlantic region. To address these issues we have developed an annually resolved record of changes in Irish bog tree populations over the last 7468 years which, together with radiocarbon-dated bog and lake-edge populations, extend the dataset back to 9000 yr ago. The Irish trees underpin the internationally accepted radiocarbon calibration curve, used to derive a proxy of solar activity, and allow us to test solar forcing of Holocene climate change. Tree populations and age structures provide unambiguous evidence of major shifts in Holocene surface moisture, with a dominant cyclicity of 800 yr, similar to marine cycles in the North Atlantic, indicating significant changes in the latitude and intensity of zonal atmospheric circulation across the region. The cycles, however, are not coherent with changes in solar activity (both being on the same absolute timescale), indicating that Holocene North Atlantic climate variability at the millennial and centennial scale is not driven by a linear response to changes in solar activity. Copyright

  17. Statistical Downscaling of Last Glacial Maximum and mid-Holocene climate simululations over the Continental United States

    NASA Astrophysics Data System (ADS)

    Mondal, Y.; Chiang, J. C. H.; Koo, M.

    2014-12-01

    We document the creation of new high-resolution temperature and precipitation fields over the continental United States during the Last Glacial Maximum (LGM) and mid-Holocene intended for hind-casting species distributions and other biotic scenarios. Global climate simulations do not have the resolution to capture local climate variability that is needed to model ecological and biological variability. To this end, we use a recently developed statistical downscaling method, Equidistant CDF Matching (EDCDFm), developed by Li et al. (2010) [1] to create synthetic high-resolution estimates of the LGM and mid-Holocene climate over the continental United States. We find that this method works well for temperature but performs poorly for precipitation. This required processing over 1.5 billion time series. To do this, we wrote cluster-computing routines in MATLAB and implemented them on Amazon Elastic Compute Cloud.

  18. Latest Pleistocene and Holocene glacier fluctuations on Mount Baker, Washington

    NASA Astrophysics Data System (ADS)

    Osborn, Gerald; Menounos, Brian; Ryane, Chanone; Riedel, Jon; Clague, John J.; Koch, Johannes; Clark, Douglas; Scott, Kevin; Davis, P. Thompson

    2012-08-01

    Glaciers on stratovolcanoes of the Pacific Northwest of North America offer opportunities for dating late Pleistocene and Holocene glacier advances because tephra and fossil wood are common in lateral moraines and in glacier forefields. We capitalize on this opportunity by examining the Holocene glacial record at Mount Baker, an active stratovolcano in northwest Washington. Earlier workers concluded that glaciers on Mount Baker during the early Holocene were more extensive than during the Little Ice Age and hypothesized that the explanation lay in unusual climatic or hypsometric effects peculiar to large volcanoes. We show that the main argument for an early Holocene glacier advance on Mount Baker, namely the absence of ca 10,000-year-old tephra on part of the south flank of the mountain, is incorrect. Moreover, a lake-sediment core indicates that a small cirque moraine previously thought be of early Holocene age is also likely older than the tephra and consequently of late Pleistocene age. Lateral and end moraines and wood mats ca 2 km downvalley of the present snout of Deming Glacier indicate that an advance during the Younger Dryas interval was little more extensive than the climactic Little Ice Age advance. Tephra and wood between tills in the left lateral moraine of Easton Glacier suggest that ice on Mount Baker was restricted in the early Holocene and that Neoglaciation began ca 6 ka. A series of progressively more extensive Neoglacial advances, dated to about 2.2, 1.6, 0.9, and 0.4 ka, are recorded by stacked tills in the right lateral moraine of Deming Glacier. Intervening retreats were long enough to allow establishment of forests on the moraine. Wood mats in moraines of Coleman and Easton glaciers indicate that Little Ice Age expansion began before 0.7 ka and was followed by retreat and a readvance ca 0.5 ka. Tree-ring and lichen data indicate glaciers on the south side of the mountain reached their maximum extents in the mid-1800s. The similarity between

  19. Holocene multidecadal and multicentennial droughts affecting Northern California and Nevada

    NASA Astrophysics Data System (ADS)

    Benson, Larry; Kashgarian, Michaele; Rye, Robert; Lund, Steve; Paillet, Fred; Smoot, Joseph; Kester, Cynthia; Mensing, Scott; Meko, Dave; Lindström, Susan

    2002-02-01

    Continuous, high-resolution δ18O records from cored sediments of Pyramid Lake, Nevada, indicate that oscillations in the hydrologic balance occurred, on average, about every 150 years (yr) during the past 7630 calendar years (cal yr). The records are not stationary; during the past 2740 yr, drought durations ranged from 20 to 100 yr and intervals between droughts ranged from 80 to 230 yr. Comparison of tree-ring-based reconstructions of climate change for the past 1200 yr from the Sierra Nevada and the El Malpais region of northwest New Mexico indicates that severe droughts associated with Anasazi withdrawal from Chaco Canyon at 820 cal yr BP (calendar years before present) and final abandonment of Chaco Canyon, Mesa Verde, and the Kayenta area at 650 cal yr BP may have impacted much of the western United States.During the middle Holocene (informally defined in this paper as extending from 8000 to 3000 cal yr BP), magnetic susceptibility values of sediments deposited in Pyramid Lake's deep basin were much larger than late-Holocene (3000-0 cal yr BP) values, indicating the presence of a shallow lake. In addition, the mean δ18O value of CaCO 3 precipitated between 6500 and 3430 cal yr BP was 1.6‰ less than the mean value of CaCO 3 precipitated after 2740 cal yr BP. Numerical calculations indicate that the shift in the δ18O baseline probably resulted from a transition to a wetter (>30%) and cooler (3-5°C) climate. The existence of a relatively dry and warm middle-Holocene climate in the Truckee River-Pyramid Lake system is generally consistent with archeological, sedimentological, chemical, physical, and biological records from various sites within the Great Basin of the western United States. Two high-resolution Holocene-climate records are now available from the Pyramid and Owens lake basins which suggest that the Holocene was characterized by five climatic intervals. TIC and δ18O records from Owens Lake indicate that the first interval in the early Holocene

  20. Holocene multidecadal and multicentennial droughts affecting Northern California and Nevada

    USGS Publications Warehouse

    Benson, L.; Kashgarian, Michaele; Rye, R.; Lund, S.; Paillet, F.; Smoot, J.; Kester, C.; Mensing, S.; Meko, D.; Lindstrom, S.

    2002-01-01

    Continuous, high-resolution ??18O records from cored sediments of Pyramid Lake, Nevada, indicate that oscillations in the hydrologic balance occurred, on average, about every 150 years (yr) during the past 7630 calendar years (cal yr). The records are not stationary; during the past 2740 yr, drought durations ranged from 20 to 100 yr and intervals between droughts ranged from 80 to 230 yr. Comparison of tree-ring-based reconstructions of climate change for the past 1200 yr from the Sierra Nevada and the El alpais region of northwest New Mexico indicates that severe droughts associated with Anasazi withdrawal from Chaco Canyon at 820 cal yr BP (calendar years before present) and final abandonment of Chaco Canyon, Mesa Verde, and the Kayenta area at 650 cal yr BP may have impacted much of the western United States.During the middle Holocene (informally defined in this paper as extending from 8000 to 3000 cal yr BP), magnetic susceptibility values of sediments deposited in Pyramid Lake's deep basin were much larger than late-Holocene (3000-0 cal yr BP) values, indicating the presence of a shallow lake. In addition, the mean ?? 18O value of CaCO3 precipitated between 6500 and 3430 cal yr BP was 1.6??? less than the mean value of CaCO3 precipitated after 2740 cal yr BP. Numerical calculations indicate that the shift in the ??18O baseline probably resulted from a transition to a wetter (> 30%) and cooler (3-5??C) climate. The existence of a relatively dry and warm middle-Holocene climate in the Truckee River - Pyramid Lake system is generally consistent with archeological, sedimentological, chemical, physical, and biological records from various sites within the Great Basin of the western United States. Two high-resolution Holocene-climate records are now available from the Pyramid and Owens lake basins which suggest that the Holocene was characterized by five climatic intervals. TIC and ??18O records from Owens Lake indicate that the first interval in the early Holocene

  1. Holocene reef accretion: southwest Molokai, Hawaii, U.S.A.

    USGS Publications Warehouse

    Engels, Mary S.; Fletcher, Charles H.; Field, Michael E.; Storlazzi, Curt D.; Grossman, Eric E.; Rooney, John J.B.; Conger, Christopher L.; Glenn, Craig

    2004-01-01

    Two reef systems off south Molokai, Hale O Lono and Hikauhi (separated by only 10 km), show strong and fundamental differences in modern ecosystem structure and Holocene accretion history that reflect the influence of wave-induced near-bed shear stresses on reef development in Hawaii. Both sites are exposed to similar impacts from south, Kona, and trade-wind swell. However, the Hale O Lono site is exposed to north swell and the Hikuahi site is not. As a result, the reef at Hale O Lono records no late Holocene net accretion while the reef at Hikauhi records consistent and robust accretion over late Holocene time. Analysis and dating of 24 cores from Hale O Lono and Hikauhi reveal the presence of five major lithofacies that reflect paleo-environmental conditions. In order of decreasing depositional energy they are: (1) coral-algal bindstone; (2) mixed skeletal rudstone; (3) massive coral framestone; (4) unconsolidated floatstone; and (5) branching coral framestone-bafflestone. At Hale O Lono, 10 cores document a backstepping reef ranging from ∼ 8,100 cal yr BP (offshore) to ∼ 4,800 cal yr BP (nearshore). A depauperate community of modern coral diminishes shoreward and seaward of ∼ 15 m depth due to wave energy, disrupted recruitment activities, and physical abrasion. Evidence suggests a change from conditions conducive to accretion during the early Holocene to conditions detrimental to accretion in the late Holocene. Reef structure at Hikauhi, reconstructed from 14 cores, reveals a thick, rapidly accreting and young reef (maximum age ∼ 900 cal yr BP). Living coral cover on this reef increases seaward with distance from the reef crest but terminates at a depth of ∼ 20 m where the reef ends in a large sand field. The primary limitation on vertical reef growth is accommodation space under wave base, not recruitment activities or energy conditions. Interpretations of cored lithofacies suggest that modern reef growth on the southwest corner of Molokai, and by

  2. Modelling sea-level data from China and Malay-Thai Peninsula to infer Holocene eustatic sea-level change

    NASA Astrophysics Data System (ADS)

    Bradley, S.; Milne, G.; Zong, Y.; Horton, B.

    2008-12-01

    Late Devensian relative sea-level observations record changes in global sea level driven by a complex interplay between tectonic, isostatic and climatic processes, and as such have been adopted in many previous modelling studies to provide information on spatial and temporal ice sheet history, rheological earth properties, and global meltwater signals. In regions distant from previously glaciated areas (so-called 'far- field sites'), sea-level observations have been used to constrain the rate and magnitude of the global eustatic sea level change, as these data are primarily sensitive to changes in the global meltwater flux (Clark et al. 1978) Constraining the eustatic component of sea level change is useful since it provides a direct measure of past continental ice volume that can be compared to results obtained from oxygen isotope methods. A second application, which is the primary focus of this study, is the inference of eustatic change during the mid-to-late Holocene. Constraining the eustaic signal provides information on both: (i) the rate and timing of major ice melting at the end of the last deglaciation and (ii) the magnitude of melting during the late Holocene. The latter is an important baseline that can be compared to estimates of global sea-level rise in the 20th century. The typical sea-level pattern at far-field locations is characterized by a steady rise to a mid- Holocene highstand, followed by a slow monotonic fall to present day levels. Previous studies have examined the spatial and temporal variations in the Holocene highstand to arrive at estimates of eustatic change in the mid-to-late Holocene (Nadaka and Lambeck 1989; Flemming et al. 1998; Lambeck 2002; Peltier 2002). While the results of these studies are broadly compatible, there remain significant discrepancies and so it is important to consider additional data to improve constraints on the eustatic signal. This study addresses this aim by considering previously un-modelled Holocene sea

  3. Millennial-scale faunal record reveals differential resilience of European large mammals to human impacts across the Holocene

    PubMed Central

    Crees, Jennifer J.; Carbone, Chris; Sommer, Robert S.; Benecke, Norbert; Turvey, Samuel T.

    2016-01-01

    The use of short-term indicators for understanding patterns and processes of biodiversity loss can mask longer-term faunal responses to human pressures. We use an extensive database of approximately 18 700 mammalian zooarchaeological records for the last 11 700 years across Europe to reconstruct spatio-temporal dynamics of Holocene range change for 15 large-bodied mammal species. European mammals experienced protracted, non-congruent range losses, with significant declines starting in some species approximately 3000 years ago and continuing to the present, and with the timing, duration and magnitude of declines varying individually between species. Some European mammals became globally extinct during the Holocene, whereas others experienced limited or no significant range change. These findings demonstrate the relatively early onset of prehistoric human impacts on postglacial biodiversity, and mirror species-specific patterns of mammalian extinction during the Late Pleistocene. Herbivores experienced significantly greater declines than carnivores, revealing an important historical extinction filter that informs our understanding of relative resilience and vulnerability to human pressures for different taxa. We highlight the importance of large-scale, long-term datasets for understanding complex protracted extinction processes, although the dynamic pattern of progressive faunal depletion of European mammal assemblages across the Holocene challenges easy identification of ‘static’ past baselines to inform current-day environmental management and restoration. PMID:27009229

  4. Millennial-scale faunal record reveals differential resilience of European large mammals to human impacts across the Holocene.

    PubMed

    Crees, Jennifer J; Carbone, Chris; Sommer, Robert S; Benecke, Norbert; Turvey, Samuel T

    2016-03-30

    The use of short-term indicators for understanding patterns and processes of biodiversity loss can mask longer-term faunal responses to human pressures. We use an extensive database of approximately 18,700 mammalian zooarchaeological records for the last 11,700 years across Europe to reconstruct spatio-temporal dynamics of Holocene range change for 15 large-bodied mammal species. European mammals experienced protracted, non-congruent range losses, with significant declines starting in some species approximately 3000 years ago and continuing to the present, and with the timing, duration and magnitude of declines varying individually between species. Some European mammals became globally extinct during the Holocene, whereas others experienced limited or no significant range change. These findings demonstrate the relatively early onset of prehistoric human impacts on postglacial biodiversity, and mirror species-specific patterns of mammalian extinction during the Late Pleistocene. Herbivores experienced significantly greater declines than carnivores, revealing an important historical extinction filter that informs our understanding of relative resilience and vulnerability to human pressures for different taxa. We highlight the importance of large-scale, long-term datasets for understanding complex protracted extinction processes, although the dynamic pattern of progressive faunal depletion of European mammal assemblages across the Holocene challenges easy identification of 'static' past baselines to inform current-day environmental management and restoration. PMID:27009229

  5. Holocene vegetation, fire and erosional history of City of Rocks National Reserve, South-Central Idaho

    NASA Astrophysics Data System (ADS)

    Weppner, K.; Pierce, J. L.; Betancourt, J. L.

    2011-12-01

    dominant tree species at CIRO. Field observation indicates that sheetflooding is a dominant erosional process at CIRO with sheetflood deposits accounting for ~40% of total measured Holocene alluvial thickness. Only ~20% of this deposition occurred between ~7-2 ka, suggesting a prolonged period of minimal erosion. Furthermore, during this ~5 ka interval, ~60% of alluvium was deposited as sheetfloods with the remainder deposited as overbank and flood deposits, and no recorded debris flows. We hypothesize that during the drier, warmer and possibly more stable climate of the mid-Holocene, decreased vegetation density on hillslopes suppressed colluvial storage, thus limiting the supply of hillslope material for debris flow production. Hillslopes likely experienced more frequent, yet low-volume, sheetflood erosion. Between ~4-2 ka cal yr BP, cooler and wetter conditions returned, as indicated by midden records from central Idaho. After ~2.2 ka, soil horizon development suggests that increased vegetation density re-stabilized hillslopes. This accumulated colluvium supplied material for episodic, post-wildfire debris flow events.

  6. Modelling Holocene peatland and permafrost dynamics with the LPJ-GUESS dynamic vegetation model

    NASA Astrophysics Data System (ADS)

    Chaudhary, Nitin; Miller, Paul A.; Smith, Benjamin

    2016-04-01

    -1361. - Frolking S, Roulet NT, Tuittila E, Bubier JL, Quillet A, Talbot J, Richard PJH. 2010. A new model of Holocene peatland net primary production, decomposition, water balance, and peat accumulation. Earth Syst. Dynam., 1, 1-21, doi:10.5194/esd-1-1-2010, 2010. - Hilbert DW, Roulet N, Moore T. 2000. Modelling and analysis of peatlands as dynamical systems. Journal of Ecology 88: 230-242. - Kleinen T, Brovkin V, Schuldt RJ. 2012. A dynamic model of wetland extent and peat accumulation: results for the Holocene. Biogeosciences 9: 235-248. - Kokfelt U, Reuss N, Struyf E, Sonesson M, Rundgren M, Skog G, Rosen P, Hammarlund D. 2010. Wetland development, permafrost history and nutrient cycling inferred from late Holocene peat and lake sediment records in subarctic Sweden. Journal of Paleolimnology 44: 327-342. - Loisel J, et al. 2014. A database and synthesis of northern peatland soil properties and Holocene carbon and nitrogen accumulation. Holocene 24: 1028-1042. - Sitch S, et al. 2008. Evaluation of the terrestrial carbon cycle, future plant geography and climate-carbon cycle feedbacks using five Dynamic Global Vegetation Models (DGVMs). Global Change Biology 14: 2015-2039. - Smith B, Prentice IC, Sykes MT. 2001. Representation of vegetation dynamics in the modelling of terrestrial ecosystems: comparing two contrasting approaches within European climate space. Global Ecology and Biogeography 10: 621-637. - Tang J, et al. 2015. Carbon budget estimation of a subarctic catchment using a dynamic ecosystem model at high spatial resolution. Biogeosciences 12: 2791-2808. - Wania R, Ross I, Prentice IC. 2009a. Integrating peatlands and permafrost into a dynamic global vegetation model: 1. Evaluation and sensitivity of physical land surface processes. Global Biogeochemical Cycles 23.

  7. Drivers of Change in a 7300-Year Holocene Diatom Record from the Hemi-Boreal Region of Ontario, Canada

    PubMed Central

    Beck, Kristen K.; Medeiros, Andrew S.

    2016-01-01

    A Holocene lake sediment record spanning the past 7300 years from Wishart Lake in the Turkey Lakes Watershed in the Hemi-Boreal of central Ontario, Canada, was used to evaluate the potential drivers of long-term change in diatom assemblages at this site. An analysis of diatom assemblages found that benthic and epiphytic taxa dominated the mid-Holocene (7300–4000 cal yr BP), indicating shallow, oligotrophic, circum-neutral conditions, with macrophytes present. A significant shift in diatom assemblages towards more planktonic species (mainly Cyclotella sensu lato, but also several species of Aulacoseira, and Tabellaria flocculosa) occurred ~4000 cal yr BP. This change likely reflects an increase in lake level, coincident with the onset of a more strongly positive moisture balance following the drier climates of the middle Holocene, established by numerous regional paleoclimate records. Pollen-inferred regional changes in vegetation around 4000 yrs BP, including an increase in Betula and other mesic taxa, may have also promoted changes in diatom assemblages through watershed processes mediated by the chemistry of runoff. A more recent significant change in limnological conditions is marked by further increases in Cyclotella sensu lato beginning in the late 19th century, synchronous with the Ambrosia pollen rise and increases in sediment bulk density, signaling regional and local land clearance at the time of Euro-Canadian settlement (1880 AD). In contrast to the mid-Holocene increase in planktonic diatoms, the modern increase in Cyclotella sensu lato likely indicates a response to land use and vegetation change, and erosion from the watershed, rather than a further increase in water level. The results from Wishart Lake illustrate the close connection between paleoclimate change, regional vegetation, watershed processes, and diatom assemblages and also provides insight into the controls on abundance of Cyclotella sensu lato, a diatom taxonomic group which has shown

  8. Drivers of Change in a 7300-Year Holocene Diatom Record from the Hemi-Boreal Region of Ontario, Canada.

    PubMed

    Beck, Kristen K; Medeiros, Andrew S; Finkelstein, Sarah A

    2016-01-01

    A Holocene lake sediment record spanning the past 7300 years from Wishart Lake in the Turkey Lakes Watershed in the Hemi-Boreal of central Ontario, Canada, was used to evaluate the potential drivers of long-term change in diatom assemblages at this site. An analysis of diatom assemblages found that benthic and epiphytic taxa dominated the mid-Holocene (7300-4000 cal yr BP), indicating shallow, oligotrophic, circum-neutral conditions, with macrophytes present. A significant shift in diatom assemblages towards more planktonic species (mainly Cyclotella sensu lato, but also several species of Aulacoseira, and Tabellaria flocculosa) occurred ~4000 cal yr BP. This change likely reflects an increase in lake level, coincident with the onset of a more strongly positive moisture balance following the drier climates of the middle Holocene, established by numerous regional paleoclimate records. Pollen-inferred regional changes in vegetation around 4000 yrs BP, including an increase in Betula and other mesic taxa, may have also promoted changes in diatom assemblages through watershed processes mediated by the chemistry of runoff. A more recent significant change in limnological conditions is marked by further increases in Cyclotella sensu lato beginning in the late 19th century, synchronous with the Ambrosia pollen rise and increases in sediment bulk density, signaling regional and local land clearance at the time of Euro-Canadian settlement (1880 AD). In contrast to the mid-Holocene increase in planktonic diatoms, the modern increase in Cyclotella sensu lato likely indicates a response to land use and vegetation change, and erosion from the watershed, rather than a further increase in water level. The results from Wishart Lake illustrate the close connection between paleoclimate change, regional vegetation, watershed processes, and diatom assemblages and also provides insight into the controls on abundance of Cyclotella sensu lato, a diatom taxonomic group which has shown

  9. Micro-facies analyses of late Holocene sediments from the Ein Gedi site (Dead Sea)

    NASA Astrophysics Data System (ADS)

    Neugebauer, I.; Brauer, A.; Schwab, M. J.; Frank, U.; Dulski, P.

    2012-04-01

    Late Holocene Dead Sea sediments of the Ein Gedi profile at the western Dead Sea shore provide high-resolution information about small-scale climatic variations in the Levant. Earlier investigations by Migowski et al. (2004, 2006) demonstrated the high potential of the Ein Gedi site for reconstructing the paleoenvironment of this climate-sensitive region, but also the need for high-resolution analyses. In the study presented here, a multi-proxy approach of micro-facies analyses from thin sections, µXRF element scanning and further magnetic susceptibility measurements allowed detailed analyses of a 2.75m long section from the DSEn composite profile spanning the time from approximately 2 to 4 ka BP. The analysed DSEn sequence of the Dead Sea margin is characterised by a continuous succession of evaporitic varves, composed of alternating detrital and aragonite and/or gypsum layers with intercalated earthquake-induced mixed layers (Marco et al., 1996). In the lower part of the investigated interval a sand deposit is associated to lake-level decline around 3.3 ka BP (Bookman (Ken-Tor) et al., 2004) in the Late Bronze Age. The aim of this study is to establish a detailed high-resolution time series of extreme events and decadal-scale variations in the eastern Mediterranean climate system. Using this data set will further enable determining the influence of the North Atlantic Oscillation and solar irradiation changes on that region. Another objective will be to synchronise the DSEn interval with the new ICDP Dead Sea Deep Drilling Project (DSDDP) cores from the northern deep basin in order to compare sedimentation processes at the Dead Sea shore with those from the deep basin. Bookman (Ken-Tor), R., Enzel, Y., Agnon, A., Stein, M., 2004. Late Holocene lake levels of the Dead Sea. Geological Society of America Bulletin, May/June, 555-571. Marco, S., Stein, M., Agnon, A., 1996. Long-term earthquake clustering: A 50,000-year paleoseismic record in the Dead Sea Graben

  10. Glacial to Holocene climate changes in Easter Island (SE Pacific, 27

    NASA Astrophysics Data System (ADS)

    Sáez, A.; Giralt, S.; Valero-Garcés, B. L.; Moreno, A.; Bao, R.; Pueyo, J. J.; Hernández, A.

    2009-04-01

    Sedimentary architecture and paleoclimate for the last 34 000 cal years BP and human activity during the last 850 years have been reconstructed from the Raraku Lake sediments in Easter Island (SE Pacific, 27°S) using a high-resolution multiproxy study of 8 cores, 36 AMS radiocarbon dates and correlation with previous core studies. The Last Glacial period was characterized by cold and relatively humid conditions between 34 to 28 cal kyr BP. High lake levels and clastic input dominated sedimentation in Raraku Lake and a relatively open forest developed at that time. Between 28 and 17.3 cal kyr BP, including LGM period, colder conditions contributed to a reduction of the tree coverage in the island. The end of Glacial Period occurred at 17.3 cal kyr BP and was characterized by a sharp decrease in lake level conducive to the development of major floods due to the erosion of littoral sediments. The Deglaciation Period (Termination 1) occurred between 17.3 and 12.5 cal kyr BP, characterized by an increase in lake productivity, a decrease in the terrigenous input and a rapid lake level recovery inaugurating a period of intermediate lake levels. During this period, the dominance of algal lamination is interpreted as a warmer climate. The timing and duration of this warming trend in Easter Island broadly agrees with other mid- and low latitude circum South Pacific terrestrial records. The early Holocene was characterized by low lake levels. The lake level dropped during the early Holocene (ca. 9.5 cal kyr BP) and peatbog and shallow lake conditions dominated till mid Holocene, partially caused by the colmatation of the lacustrine basin. During the mid Holocene an intense drought occurred that led to a persistent low water table period, subaerial exposure and erosion of some of the sediments, generating a sedimentary gap in the Raraku sequence, from 4.2 to 0.8 cal kyr BP. The palm deforestation of the Easter Island, attributed to the human colonization at about 850 cal yr

  11. Stable carbon and nitrogen isotopes and amino acids in Holocene sediments of Lake Lonar, central India

    NASA Astrophysics Data System (ADS)

    Menzel, Philip; Gaye, Birgit; Wiesner, Martin; Basavaiah, Nathani; Prasad, Sushma; Stebich, Martina; Anoop, Ambili; Riedel, Nils

    2013-04-01

    Investigations on surface sediments and a sediment core from Lake Lonar in central India were carried out within the framework of the HIMPAC (Himalaya: Modern and Past Climate) programme. The aim was to understand recent productivity, sedimentation, and degradation processes and to reconstruct variations in Holocene lake conditions on the basis of biogeochemical analysis on a 10 m long sediment core retrieved from the centre of Lake Lonar. Located in India's core monsoon zone, Lake Lonar offers valuable information about the climate development of the whole region. The lake is situated at the floor of a meteorite impact structure on the Deccan plateau basalt. The modern lake is characterised by brackish water, high alkalinity, severe eutrophication, and bottom water anoxia. The lake is about 6 m deep and fed by rainfall during the SW monsoon season and three perennial streams. Since no out-flowing stream is present and no seepage loss occurs, the lake level is highly sensitive to the balance of precipitation and evaporation. Here we present C/N, carbon and nitrogen isotope, and amino acid data of bulk organic matter from modern lake and Holocene core sediments. Modern conditions are mainly related to human activity which started to have persistent influence on the biological and chemical lake properties at ~1200 cal a BP. The distribution of δ13C in the modern sediments is driven by the ratio between terrestrial and aquatic organic matter, while δ15N seems to be influenced by redox conditions at the sediment-water-interface with elevated values at shallow oxic stations. Differences in the amino acid assemblages of oxic and anoxic surface sediment samples were used to calculate an Ox/Anox ratio indicating the redox conditions during organic matter degradation. The onset of the monsoon reconstructed from the sediment core occurred at ca. 11450 cal a BP. The early Holocene core sediments are characterised by low sedimentation rate, low aquatic productivity, and

  12. Holocene Changes in Land Cover and Greenhouse-gas Concentrations: Rethinking Natural vs Anthropogenic Causation

    NASA Astrophysics Data System (ADS)

    Roberts, C.

    2008-12-01

    The Holocene has witnessed a switch from a nature-dominated to a human-dominated Earth system. Although globally-significant human impacts (wildfire, megafaunal extinctions) occurred during the late Pleistocene, it was the advent of agriculture that led to the progressive transformation of land cover, and which distinguishes the Holocene from previous interglacial periods. A wide array of data provide clear evidence of local-to-regional human disturbance from ~5 ka BP, in some cases earlier. There is more uncertainty about when the anthropogenic "footprint" became detectable at a global scale, and there has consequently been debate about how much of the pre-industrial increase in atmospheric greenhouse gas concentrations is attributable to human causation, linked to processes such as deforestation (CO2) and wet rice cultivation (CH4). Although there has been recent progress in developing quantitative methods for translating pollen data into palaeo-land cover, such as the REVEALS model of Sugita (Holocene 2007) coupled to GIS, this has yet to be widely applied to existing data bases, and most pollen-based land-use reconstructions remain qualitative or semi-quantitative. Lake trophic status, sediment flux / soil erosion, and microcharcoal records of biomass burning provide alternative proxies that integrate regional-scale landscape disturbance. These proxy data along with documentary sources imply that globally-significant changes in land cover occurred prior to ~250 BP which must have altered atmospheric greenhouse gas concentrations by this time. The polarised debate for and against early anthropogenic impact on global carbon cycling mirrors our industrial-era division between nature and society, both conceptually (e.g. Cartesian dualism) and on the ground (e.g. demarcating land between monoculture agriculture and wilderness). However, for the period before ~1750 AD, this likely represents a false dichotomy, because pre-industrial societies more often formed part

  13. Late glacial-Holocene shelf evolution of the Sea of Marmara west of Istanbul

    NASA Astrophysics Data System (ADS)

    Karakilcik, Hatice; Unlugenc, Ulvi Can; Okyar, Mahmut

    2014-12-01

    We present an investigation the Late Quaternary seismic stratigraphy of the shelf area of the northern the Sea of Marmara extending from its northern coast (between Silivri and Kumkapı) to approximately 100 m depth, using shallow high-resolution seismic reflection data along 73 N-S and 15 E-W lines. Seismic sequence analysis is used to identify the depositional systems, associated sedimentation conditions, and relative sea level changes. Seismic stratigraphic interpretations indicate the presence of four distinct seismic units (SU I, II, III and IV) underlying the shelf area. Seismic units are bounded by erosional unconformities overlying an acoustic basement. Seismic unit I constitutes the acoustic basement (AB), which is characterized by chaotic, subparallel, and wavy reflections that out locally off the rocky shorelines and along the crests of the positive structures where the sedimentary cover is absent. Seismic unit II is interpreted to represent the pre-Holocene deposits and exhibits subparallel reflections. Seismic unit II is interpreted to have been subjected to sub-aerial erosion during the Last Glacial Maximum. Seismic unit III-IV are interpreted to have formed during the Holocene (Flandrian) transgression and have parallel/subparallel internal reflection patterns. The top of seismic unit IV forms the present-day sea floor. As a result of the presence of fill, seismic facies within seismic unit IV reflect differences in depositional processes. The bathymetry of the study area has a close relation with sedimentation dynamics, tectonic, wave and flow dynamics and palaeotopograpy. Particularly, sudden dip changes determined at the shelf area might have been due to fault and/or fault systems that control the bottom topography. Seismic activity in the Sea of Marmara region has a key role the northern branch of the North Anatolian Fault Zone (NAFZ) affecting on the tectonic activity of the study area. The last two earthquakes in İzmit and Duzce, Turkey, in

  14. Atmospheric patterns driving Holocene productivity in the Alboran Sea (Western Mediterranean): a multiproxy approach.

    NASA Astrophysics Data System (ADS)

    Ausin, Blanca; Flores, Jose-Abel; Sierro, Francisco Javier; Cacho, Isabel; Hernández-Almeida, Iván; Martrat, Belén; Grimalt, Joan

    2014-05-01

    This study is aimed to reconstruct productivity during the Holocene in the Western Mediterranean as well as to investigate what processes account for its short-term variability. Fossil coccolithophore assemblages have been studied along with Mg/Ca and Uk'37-estimated Sea Surface Temperature (SST) and other paleoenvironmental proxies. The study site is located in a semi-permanent area of upwelling in the Alboran Sea. This productive cell is of special interest since is closely related to local hydrological dynamics driven by the entering Atlantic Jet (AJ). The onset of this productive cell is suggested at 7.7 ka cal. B.P. and linked to the establishment of the anticyclonic gyres. From 7.7 ka cal. BP to present, the N ratio and accumulation rate of Florisphaera profunda show successive upwelling and stratification events. This alternation is simultaneous to changes in the Western Mediterranean Deep Water (WMDW) formation rate in the Gulf of Lions [Frigola et al., 2007], along with changes in Mg/Ca-estimated SST, relative abundance of reworked nannoliths, pollen grains record [Fletcher et al., 2012] and n-hexacosan-1-ol index. Two scenarios are proposed to explain short-term climatic and oceanographic variability: [1] Wetter climate and weaker north-westerlies blowing over the Gulf of Lions trigger a slackening of the WMDW formation. Consequently, a minor AJ inflows the Alboran Sea leading to less vertical mixing and a deepening of the nutricline and hence, long-term stratification events. [2] Arid climate and stronger north-westerlies enable WMDW reinforcement. In turn, increased AJ triggers vertical mixing and nutricline shoaling, and therefore, productive periods. Finally, changes in atmospheric patterns (e.g. the winter North Atlantic Oscillation; [Olsen et al., 2012]) prove to be useful in explaining the WMDW formation in the Gulf of Lions and associated short-term productivity variations in the Alboran Sea. References Fletcher, W. J., M. Debret, and M. F

  15. On the Filling Process Forming Silicic Segregations: Porous Flow Experiments

    NASA Astrophysics Data System (ADS)

    Zavala, K.; Marsh, B. D.

    2002-05-01

    Silicic segregations are only observed in the upper parts of large diabase sill, lava lakes and gabbroic intrusions. The segregations often have sharp upper contacts and diffuse lower contacts that grade into the host rock texture. We have analyzed over 100 segregation samples from the Ferrar Dolerites of the McMurdo Dry Valleys Antarctica, to investigate the nature of the infilling process. These segregations have compositions that correspond to interstitial liquid present at crystallinities between 59 and 63% and temperatures between 1135o C and 1115 oC. Stratigraphic position, size, textures, and chemical composition relations indicate that silicic segregation represent a form of bimodal differentiation produced by the physical tearing of the upper Solidification Front (SF) due to gravitational instability, (SFI). Previous work (Zavala & Marsh, 2001) showed that large segregations, which are chemically and texturally non-homogeneous and have non-monotonic Si02 profiles form by multiple infilling episodes. In contrast, smaller segregations have homogeneous textures and chemical profiles, formed by perhaps longer single episode of infilling. Because the rate of melt flow forming these segregations is controlled by the resistance to flow through the crystalline matrix we performed a series of porous media flow experiments to investigate the details of the melt transport dynamics of the infilling process.

  16. The regularities of the late Holocene soil formation in the lower don steppes

    NASA Astrophysics Data System (ADS)

    Pesochina, L. S.

    2010-12-01

    The direction and stages of pedogenesis, rate and scales of changeability, and type of evolution of chernozems in the steppes of the Lower Don are ascertained by studying the archaeological monuments of the Bronze Age, Early Iron Age, and Middle Ages. It is shown that the soil formation process was characterized by cyclicity, and evolutional soil transformations took place at the level of subtype. The paper ascertains the polygenetic character of modern chernozems, whose evolution during the second half of the Holocene was predominantly low-contrast, inheriting, and transforming. The processes forming the humus, salt, gypsum, and carbonate profiles, as well as the processes of solonetzization-desolonetzization, were the most dynamic. The fundamental differences in the genesis of different parts of the humus profile are revealed. The role of climatically pulsing solonetzicity in forming the specific Azov chernozems is for the first time ascertained.

  17. Holocene biome shifts in the East Asian monsoon margin region

    NASA Astrophysics Data System (ADS)

    Dallmeyer, Anne; Claussen, Martin; Ni, Jian; Wang, Yongbo; Cao, Xianyong; Herzschuh, Ulrike

    2013-04-01

    East Asia is affected by three major atmospheric circulation systems determining the regional climate and vegetation distribution: The moisture advected by the Indian and East Asian monsoon support the growing of forest in large parts of Eastern China. The influence of the monsoon gets weaker further on the continent yielding a transition of forest to steppe and of steppe to desert in Central East Asia (e.g. Inner Mongolia) where the dry westerly winds prevail. Particularly in these transition zones, vegetation is supposed to be very sensitive to climate change and strong feedbacks are expected in case of climate and vegetation shifts due to large environmental changes (Feng et al., 2006). During mid-Holocene, cyclic variations in the Earth's orbit around the sun led to an enhancement of the Asian monsoon system probably causing strong shifts in the biome distribution. According to reconstructions, the steppe-forest margin moved to the northwest by about 500km (Yu et al., 2000) and the desert area in China and Inner Mongolia was substantially reduced compared to today (Feng et al., 2006). However, in the complex environment of Asia, the locally limited reconstructions may not portray the general vegetation change. To get a systematic overview on the spatial pattern of biome shifts in the Asian monsoon - westerly wind transition zone since mid-Holocene, we use the diagnostic vegetation model BIOME4 and force this model with climate anomalies from different transient Holocene climate simulations performed in coupled atmosphere-ocean-vegetation models. The main aims of this study are to a) get a consistent ensemble of possible changes in biome distribution since the mid-Holocene b) test the robustness of the simulated vegetation changes and quantify the differences between the models, and c) allow for a better comparison of simulated and reconstructed vegetation changes. Preliminary results confirm the general trend seen in the reconstructions. The simulations reveal

  18. Reconstruction of environmental chanees in Holocen in Siberian Arctic, Russia

    NASA Astrophysics Data System (ADS)

    Nazarova, Larisa; Diekmann, Bernhard; Frolova, Larisa; Palagushkina, Olga; Tumanov, Oleg; Nourgaliev, Danis

    2013-04-01

    The study of Arctic palaeoenvironmental records enables qualitative and quantitative estimations of past climate changes and provides basis for prediction of future changes in the region. The timing of Holocene climate events in North Atlantic region is relatively good studied. In contrast to it, at present there are very few quantitative palaeoclimatic data for eastern Siberia and proxy records from northern Eurasia mostly document environmental changes at low temporal resolution, and are derived from pollen studies. Due to relatively small magnitude of temperature changes throughout the Holocene, reconstructions based on a single proxy must be interpreted with caution. More reliable estimate of the Holocene climate changes can be obtained only by averaging results inferred from several proxies. The basis, however, of all quantitative reconstruction approaches are regional calibration datasets from which the empirical reconstruction model (i.e. the transfer function) will be established. A 380 cm long sediment core from Lake Temje (Central Yakutia, North-Eastern Russia) was studied to infer Holocene palaeoenvironmental change in the extreme periglacial setting of eastern Siberia during the last 10,000 yrs. Data on sediment composition were used to characterize changes in the depositional environment during the ontogenetic development of the Lake Temje. The analysis of fossil chironomid remains and statistical treatment of chironomid data by the application of a newly developed transfer functions provided inferences of mean July air temperatures (TJuly) and water depths (WD). We obtained a qualitative and quantitative reconstruction of Holocene climate in Central Yakutia and recognized three stages of palaeoenvironmental changes: The early Holocene between 10 and 8 kyr BP was characterized by colder-than-today and moist summer conditions. Cryotextures in the lake sediments document full freezing of the lake water during the winter time. A general warming trend

  19. Holocene evolution of Dahab coastline - Gulf of Aqaba, Sinai Peninsula, Egypt

    NASA Astrophysics Data System (ADS)

    Magdy, Torab

    2016-04-01

    Dahab was a little Bedouin-village in Sinai Peninsula at the mid-western coast of Gulf of Aqaba approx. 90 km north of Sharm-el-Sheikh City and it means "gold" in Arabic language. But in the past 20 years ago it becomes one of the most tourist sites in Egypt. The basement complex is composed mostly of biotiteaplite-granite, mica-aplitegranite, granodiorite, quartzdiorite, alaskite, and diorite. Based on correlation with similar igneous in the most southern part of Sinai and the Red Sea area. Wadi Dahab composed of igneous and metamorphic rocks and the coastline is formed of the fragments of its rocks, mixed with fragments of coral reef and fluvial deposits of Wadi Dahab. The morphology of Dahab coastline is characterized by hooked marine spit, which composed of fluvial sediments carried by marine current from wadi Dahab mouth, this spit encloses shallow lagoon, but the active deposition on the lagoon bottom will evaluate it into saline marsh. This paper dealing with the evolution of Dahab spit and lagoon during the Holocene in addition to the recent time for last 100 years, and it impacts of the future management of the coast area. The coastline mapping during the period of study depends upon GIS technique for data were collected during field measuring by using total station, aerial photo and satellite image interpretation as well as soil sample dating. Suggested geomorphological evolution of Dahab area during the Holocene depending upon geomorphic investigation of the sedimentological process into 6 stages.

  20. Rock Art at the Pleistocene/Holocene Boundary in Eastern South America

    PubMed Central

    Neves, Walter A.; Araujo, Astolfo G. M.; Bernardo, Danilo V.; Kipnis, Renato; Feathers, James K.

    2012-01-01

    Background Most investigations regarding the First Americans have primarily focused on four themes: when the New World was settled by humans; where they came from; how many migrations or colonization pulses from elsewhere were involved in the process; and what kinds of subsistence patterns and material culture they developed during the first millennia of colonization. Little is known, however, about the symbolic world of the first humans who settled the New World, because artistic manifestations either as rock-art, ornaments, and portable art objects dated to the Pleistocene/Holocene transition are exceedingly rare in the Americas. Methodology/Principal Findings Here we report a pecked anthropomorphic figure engraved in the bedrock of Lapa do Santo, an archaeological site located in Central Brazil. The horizontal projection of the radiocarbon ages obtained at the north profile suggests a minimum age of 9,370±40 BP, (cal BP 10,700 to 10,500) for the petroglyph that is further supported by optically stimulated luminescence (OSL) dates from sediment in the same stratigraphic unit, located between two ages from 11.7±0.8 ka BP to 9.9±0.7 ka BP. Conclusions These data allow us to suggest that the anthropomorphic figure is the oldest reliably dated figurative petroglyph ever found in the New World, indicating that cultural variability during the Pleistocene/Holocene boundary in South America was not restricted to stone tools and subsistence, but also encompassed the symbolic dimension. PMID:22384187

  1. Variable Holocene deformation above a shallow subduction zone extremely close to the trench

    PubMed Central

    Thirumalai, Kaustubh; Taylor, Frederick W.; Shen, Chuan-Chou; Lavier, Luc L.; Frohlich, Cliff; Wallace, Laura M.; Wu, Chung-Che; Sun, Hailong; Papabatu, Alison K.

    2015-01-01

    Histories of vertical crustal motions at convergent margins offer fundamental insights into the relationship between interplate slip and permanent deformation. Moreover, past abrupt motions are proxies for potential tsunamigenic earthquakes and benefit hazard assessment. Well-dated records are required to understand the relationship between past earthquakes and Holocene vertical deformation. Here we measure elevations and 230Th ages of in situ corals raised above the sea level in the western Solomon Islands to build an uplift event history overlying the seismogenic zone, extremely close to the trench (4–40 km). We find marked spatiotemporal heterogeneity in uplift from mid-Holocene to present: some areas accrue more permanent uplift than others. Thus, uplift imposed during the 1 April 2007 Mw 8.1 event may be retained in some locations but removed in others before the next megathrust rupture. This variability suggests significant changes in strain accumulation and the interplate thrust process from one event to the next. PMID:26123872

  2. Pollen from accurately dated speleothems supports alpine glacier low-stands during the early Holocene

    NASA Astrophysics Data System (ADS)

    Festi, Daniela; Hoffmann, Dirk L.; Luetscher, Marc

    2016-07-01

    Deciphering pollen assemblages from alpine speleothems holds potential to provide unique information about past vegetation in rapidly changing environments. Here, we reconstruct subsurface aerosol transport at Milchbach cave (Switzerland, 1840 m asl) based on the pollen content of two Holocene stalagmites. We demonstrate that pollen is chiefly associated with bacterially mediated calcite fabrics, typical of a well-ventilated cave system. In contrast, pollen is absent from columnar calcite fabrics confirming that hydrological transport is not a significant process for the incorporation of pollen into speleothems at Milchbach cave. Our results support significant changes in the subsurface ventilation regime, which can be associated with the waxing and waning of Upper Grindelwald glacier. Pollen assemblages obtained from six carbonate sub-samples attest the presence of a mixed deciduous forest in the Grindelwald valley during the early and middle Holocene, in agreement with coeval regional pollen records. This study demonstrates that even small amounts of calcite (0.3-2.8 cm3) are capable of delivering pollen spectra representative of the original vegetation if sufficiently elevated deposition fluxes are provided.

  3. Evidence for Holocene stability of steep slopes, northern Peruvian Andes, based on soils and radiocarbon dates

    USGS Publications Warehouse

    Miller, D.C.; Birkeland, P.W.; Rodbell, D.T.

    1993-01-01

    Radiocarbon dating and soil relationships indicate that landscapes in highaltitude glaciated valleys of the northern Peruvian Andes have been remarkably stable during the Holocene. Radiocarbon dates show that deglaciation was underway by 12 ka, and that slopes and alluvial fans at the bases of slopes were essentially stabilized by at least 8 ka. The soils consist of fine-grained loessial A horizons overlying Bw horizons in gravelly till or alluvial-fan gravel. Following deglaciation, widespread gullying took place in till on the steep (maximum angle: 37??) sideslopes of most valleys; the eroded material was deposited as fans at the bases of the slopes. Loess was then deposited as a fairly uniform blanket across most elements of the landscape. Soil formation began during or following loess deposition, and because soil-profile morphology is sufficiently similar at most sites, soil formation has been a dominant process during much of the Holocene. This remarkable stability, especially for such steep slopes, is attributed to a combination of tight packing of the till, permeability of the capping loess, rapid revegetation following ice retreat, and roots from the present grassland vegetation and possibly former forests. ?? 1993.

  4. Reconstruction of Holocene southern African continental climate using biomarkers from salt pan sediments

    NASA Astrophysics Data System (ADS)

    Belz, Lukas; Schüller, Irka; Wehrmann, Achim; Wilkes, Heinz

    2015-04-01

    The climate system of southern Africa is strongly influenced by large scale atmospheric and marine circulation processes and, therefore, very sensitive to global climate change. Recent publications provided evidence for strong spatial and temporal climate variability in southern Africa over the Holocene. It is of major importance to understand the mechanisms driving the southern African climate system in order to estimate regional implications of current global change. However, proxy datasets from continental geoarchives especially of the semi-arid western Kalahari region are still scarce. A main problem is the absence of conventional continental climatic archives, due to the lack of lacustrine systems. In this study we are exploring the utility of sediments from western Kalahari salt pans, i.e. local depressions which are flooded temporarily during rainfall events. Besides the analyses of basic geochemical bulk parameters including TOC, δ13Corg, TIC, δ13Ccarb, δ18Ocarb, TN, δ15N, the paleo-climatic approach focuses on reconstruction of local vegetation assemblages to identify changes in the ecosystem. This is pursued using plant biomarkers, particularly leaf wax n-alkanes and n-alcohols and their stable carbon and hydrogen isotopic signatures. Preliminary results show prominent shifts in n-alkane distribution and δ13C values of the C33 homologue during late Pleistocene and early Holocene. These shifts correlate to changes of the TOC content. Our data indicate changes in carbon sources which possibly reflect major environmental changes.

  5. Geochemical characterization of a Holocene aeolian profile in the Zhongba area (southern Tibet, China) and its paleoclimatic implications

    NASA Astrophysics Data System (ADS)

    Li, Tuoyu; Wu, Yongqiu; Du, Shisong; Huang, Wenmin; Hao, Chengzhi; Guo, Chao; Zhang, Mei; Fu, Tianyang

    2016-03-01

    The Zhongba area lies in the valley of the Maquan River in southern Tibet, where there are both strong modern aeolian activities and ancient aeolian sand sediments. A Holocene aeolian sand and paleosol profile in the Zhongba area was selected for study and termed (Zhuzhu (ZZ) profile). The chronology of the ZZ profile was established by optically stimulated luminescence (OSL) and accelerator mass spectrometry (AMS) 14C dating. Based on the grain size and geochemical elements of the ZZ profile, the geochemical characterization was analyzed, the Holocene aeolian activity processes were reconstructed in the study area, and the paleoclimatic implications were discussed. The major elements and the chemical indicators are highly correlated with different grain-sizes in the ZZ profile. The evolutionary sequence of the aeolian activities and the paleoclimate in Holocene reveal four stages: before 7.3 ka BP, the climate was warm and wet with weak winds when the sand paleosol developed; at 7.3-3.8 ka BP, the climate turned dry, with strong aeolian activities; at 3.8-0.7 ka BP, the climate became wetter and the winds weakened when the silt paleosol developed; and since 0.7 ka BP, it was cold and dry with strong aeolian activities.

  6. The effect of a dynamic soil scheme on the climate of the mid-Holocene and the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Stärz, Michael; Lohmann, Gerrit; Knorr, Gregor

    2016-04-01

    In order to account for coupled climate-soil processes, we have developed a soil scheme, which is asynchronously coupled to a comprehensive climate model with dynamic vegetation. This scheme considers vegetation as the primary control of changes in physical soil characteristics. We test the scheme for a warmer (mid-Holocene) and colder (Last Glacial Maximum) climate relative to the preindustrial climate. We find that the computed changes of physical soil characteristics lead to significant amplification of global climate anomalies, representing a positive feedback. The inclusion of the soil feedback yields an extra surface warming of 0.24°C for the mid-Holocene and an additional global cooling of 1.07°C for the Last Glacial Maximum. Transition zones such as desert/savannah and taiga/tundra exhibit a pronounced response in the model version with dynamic soil properties. Energy balance model analyses reveal that our soil scheme amplifies the temperature anomalies in the mid-to-high northern latitudes via changes in the planetary albedo and the effective longwave emissivity. As a result of the modified soil treatment and the positive feedback on climate, part of the underestimated mid-Holocene temperature response to orbital forcing can be reconciled in the model.

  7. The effect of a dynamic soil scheme on the climate of the mid-Holocene and the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Stärz, M.; Lohmann, G.; Knorr, G.

    2016-01-01

    In order to account for coupled climate-soil processes, we have developed a soil scheme which is asynchronously coupled to a comprehensive climate model with dynamic vegetation. This scheme considers vegetation as the primary control of changes in physical soil characteristics. We test the scheme for a warmer (mid-Holocene) and colder (Last Glacial Maximum) climate relative to the preindustrial climate. We find that the computed changes in physical soil characteristics lead to significant amplification of global climate anomalies, representing a positive feedback. The inclusion of the soil feedback yields an extra surface warming of 0.24 °C for the mid-Holocene and an additional global cooling of 1.07 °C for the Last Glacial Maximum. Transition zones such as desert-savannah and taiga-tundra exhibit a pronounced response in the model version with dynamic soil properties. Energy balance model analyses reveal that our soil scheme amplifies the temperature anomalies in the mid-to-high northern latitudes via changes in the planetary albedo and the effective longwave emissivity. As a result of the modified soil treatment and the positive feedback to climate, part of the underestimated mid-Holocene temperature response to orbital forcing can be reconciled in the model.

  8. CHAPHOLO (scientific drilling project): Paleolimnological Evaluation of Lake Chapala, western Mexico, During Holocene (CONACYT grant: CB2011-168685)

    NASA Astrophysics Data System (ADS)

    Zarate, P. F.; Fritz, S. C.; Ramirez Sanchez, U.; Gomez Salazar, S.; Ceja Andrade, I.; Priyadarsi Debajyoti, R.; Brenner, M.

    2012-12-01

    CHAPHOLO ( CHAP: Chapala; HOLO: Holocene) has as goal to evaluate paleoenvironmental variations recorded in the sediment of neotectonic Lake Chapala (LCH), western Mexico (20°15.129'N, 103° 02.996'W). The lake lies about 1524 m asl. LCH is the largest lake in Mexico (1,100 kmyr2), but is shallow (zmax = 7.20 m). It is located in a basin belonging to the Citala Rift, the east-west branch of three continental rifts that join to form the so-called Jalisco triple junction. Our working hypothesis is that recent (Holocene) paleolimnological changes in LCH were caused by major climate variations and by minor regional/local processes (e.g. volcanism). We will drill a 40m long core from the lake depocenter, with the objective of recovering a full Holocene record, and likely more, assuming a mean sedimentation rate of 2 mm yr-1. Core chronology will be established using AMS 14C and 210Pb techniques and climate inferences will be made using geochemical, geophysical and micropaleontological proxies. Particularly, we pretend to identify the six "short" fluctuations of climate that characterized the Holocene (Mayewski et al., 2004) and the identification of Mediewal Warm Period and the droughts affected the mayan culture (Hodell et al., 1995). We will verify the application of Ti as a proxy to rainfall (Metcalfe et al., 2010). During the last 10,000 the fact about the dissolution of diatom in LCH sediments must be evaluated (Ryves et al., 2009). The working group is multidisciplinary (Geochemistry, Micropaleontology, Paleolimnology, Geophysics) and involves multiple institutions (Guadalajara University, Mexican National University-UNAM, University of Florida, University of Nebraska-Lincoln). CHAPHOLO is supported by funds from the Mexican government and from the Guadalajara University. The theme of CHAPHOLO is consistent with global environmental programs such as PAGES and CLIVAR. This project will be developed in stages over three years.

  9. Pleistocene and Holocene geomorphological development in the Algarve, southern Portugal

    NASA Astrophysics Data System (ADS)

    Chester, David K.

    2012-06-01

    A detailed chronological framework for Pleistocene and Holocene geomorphology and landscape evolution in the Algarve is proposed. With regards to the Pleistocene, attention has focused on the origin, dating and stratigraphy of the Ludo Formation. Subsuming the classifications of earlier writers, it is now proposed that during the Pliocene a marine transgression occurred across a tectonically controlled basin that was constrained by the mountains of the Algarve interior to the north. Fluvial sands were then deposited in a regressive phase during the late Pliocene/early Pleistocene, while braided streams operating under semi-arid conditions subsequently laid down sands and gravels in the middle and upper Pleistocene. Lying unconformably over the Ludo Formation is an alluvial deposit (Odiáxere gravels and Loulé sands) of late Pleistocene/early Holocene date that is found within the river valleys of the Algarve. In the early-Holocene (ca.10, 000-ca.7000 BP) and early late-Holocene (ca.5000-ca.3000 BP), the situation in the Algarve was one of climatic amelioration (i.e., warmer and wetter conditions), rising sea levels, vegetation colonization, soil development and towards the end of this period trenching of the Odiáxere gravels and Loulé sands. From ca.3000 BP evidence is abundant that humans became important geomorphological agents either acting on their own or in combination with climatic factors. From around 5000 BP, conditions became dryer and, between ca.3000 BP and ca.700 BP, clearance of land by pre-Roman, Roman, and especially Islamic agricultural settlers caused widespread erosion and the deposition of extensive spreads of topsoil dominated sediment within river valleys (i.e., the Holocene terrace) and in coastal estuaries. A period followed up to 1900 CE when agricultural practices were less damaging to the soil, erosion was reduced and the Holocene terrace - together with coastal and estuarine deposits - was incised. In the past century and under

  10. Patagonian and southern South Atlantic view of Holocene climate

    NASA Astrophysics Data System (ADS)

    Kaplan, M. R.; Schaefer, J. M.; Strelin, J. A.; Denton, G. H.; Anderson, R. F.; Vandergoes, M. J.; Finkel, R. C.; Schwartz, R.; Travis, S. G.; Garcia, J. L.; Martini, M. A.; Nielsen, S. H. H.

    2016-06-01

    We present a comprehensive 10Be chronology for Holocene moraines in the Lago Argentino basin, on the east side of the South Patagonian Icefield. We focus on three different areas, where prior studies show ample glacier moraine records exist because they were formed by outlet glaciers sensitive to climate change. The 10Be dated records are from the Lago Pearson, Herminita Península-Brazo Upsala, and Lago Frías areas, which span a distance of almost 100 km adjacent to the modern Icefield. New 10Be ages show that expanded glaciers and moraine building events occurred at least at 6120 ± 390 (n = 13), 4450 ± 220 (n = 7), 1450 or 1410 ± 110 (n = 18), 360 ± 30 (n = 5), and 240 ± 20 (n = 8) years ago. Furthermore, other less well-dated glacier expansions of the Upsala Glacier occurred between ~1400 and ∼1000 and ∼2300 and ∼2000 years ago. The most extensive glaciers occurred over the interval from ∼6100 to ∼4500 years ago, and their margins over the last ∼600 years were well within and lower than those in the middle Holocene. The 10Be ages agree with 14C-limiting data for the glacier histories in this area. We then link southern South American, adjacent South Atlantic, and other Southern Hemisphere records to elucidate broader regional patterns of climate and their possible causes. In the early Holocene, a far southward position of the westerly winds fostered warmth, small Patagonian glaciers, and reduced sea ice coverage over the South Atlantic. Although we infer a pronounced southward displacement of the westerlies during the early Holocene, these conditions did not occur throughout the southern mid-high latitudes, an important exception being over the southwest Pacific sector. Subsequently, a northward locus and/or expansion of the winds over the Patagonia-South Atlantic sector promoted the largest glaciers between ∼6100 and ∼4500 years ago and greatest sea ice coverage. Over the last few millennia, the South Patagonian Icefield has experienced

  11. Holocene sea-level changes in the Falkland Islands

    NASA Astrophysics Data System (ADS)

    Newton, Tom; Gehrels, Roland; Daley, Tim; Long, Antony; Bentley, Mike

    2014-05-01

    In many locations in the southern hemisphere, relative sea level (RSL) reached its maximum position during the middle Holocene. This highstand is used by models of glacial isostatic adjustment (GIA) to constrain the melt histories of the large ice sheets, particularly Antarctica. In this paper we present the first Holocene sea-level record from the Falkland Islands (Islas Malvinas), an archipelago located on the Patagonian continental shelf about 500 km east of mainland South America at a latitude of ca. 52 degrees. Unlike coastal locations in southernmost South America, Holocene sea-level data from the Falklands are not influenced by tectonics, local ice loading effects and large tidal ranges such that GIA and ice-ocean mass flux are the dominant drivers of RSL change. Our study site is a salt marsh located in Swan Inlet in East Falkland, around 50 km southwest of Stanley. This is the largest and best developed salt marsh in the Falkland Islands. Cores were collected in 2005 and 2013. Lithostratigraphic analyses were complemented by analyses of foraminifera, testate amoebae and diatoms to infer palaeoenvironments. The bedrock, a Permian black shale, is overlain by grey-brown organic salt-marsh clay, up to 90 cm thick, which, in a landward direction, is replaced by freshwater organic sediments. Overlying these units are medium-coarse sands with occasional pebbles, up to 115 cm thick, containing tidal flat foraminifera. The sandy unit is erosively overlain by a grey-brown organic salt-marsh peat which extends up to the present surface. Further away from the sea this unit is predominantly of freshwater origin. Based on 13 radiocarbon dates we infer that prior to ~9.5 ka sea level was several metres below present. Under rising sea levels a salt marsh developed which was suddenly drowned around 8.4 ka, synchronous with a sea-level jump known from northern hemisphere locations. Following the drowning, RSL rose to its maximum position around 7 ka, less than 0.5 m above

  12. Holocene vegetation changes through Lac Ledro sediments (Trentino, Italy).

    NASA Astrophysics Data System (ADS)

    Joannin, Sebastien; Vannière, Boris; Galop, Didier; Magny, Michel; Gilli, Adrian; Chapron, Emmanuel; Wirth, Stéfanie; Anselmetti, Flavio; Desmet, Marc

    2010-05-01

    Lake Ledro is part of the French program ANR LAMA (coordinators: M. Magny and N. Combourieu Nebout) which aims to link Holocene paleoenvironmental changes along a north-south transect in Italy. Lake Ledro (652 m a.s.l.; Trentino, north-eastern Italy) is the northward component of the transect. It is located on the southern slope of the Alps and its catchment area covers 131 km2 with mountains culminating at 1500-2000 m. A multi-proxy approach based on biotic and abiotic indicators (lake-level, palynology, geochemistry and geophysic) was developed from deep and littoral cores, including sediment sequences in Early and Middle Bronze Age lake-shore archaeological sites. We aim reconstructing paleoenvironmental changes resulting from both climate and anthropic influences trough the entire Holocene. A deep master core was built after extracting twin cores from a non disturbed sediment zone recognised by seismic-reflexion investigations. The age-depth model is based on 13 AMS 14C ages measured on terrestrial plant macrofossils and the mean temporal resolution for analyses is ca 60 years. Palynological study shows the usual vegetation succession for the southern slope of the Alps. During the first part of the Holocene, abrupt changes are observed in pollen assemblages in relation to changes in other proxies (XRF and Magnetic Susceptibility) and correlate with cold events associated to the deglaciation in the North-Atlantic area. Cool episodes corresponding to the PreBoreal Oscillation (ca 11.3 ka cal BP) and 8.2 ka event are respectively characterized by stopping afforestation and a strong development of Abies in the local ecosystem. During the second part of the Holocene, two declines of arboreal pollen abundance are observed in relation with occurrences in both cereal and anthropic pollen indicators. These two phases are confirmed by increase in soil erosion as indicated by abiotic proxies. They give evidence of two successive steps for human settlement (Early

  13. Estimation of Anthropogenic Conversion of Holocene Wetland Cover.

    NASA Astrophysics Data System (ADS)

    Fluet-chouinard, E.; McIntyre, P. B.; Lehner, B.; Kaplan, J. O.

    2015-12-01

    Wetland conversion (or reclamation) has been practiced since the dawn of civilization to this day, transforming biogeochemical cycles and threatening biodiversity, but record of wetland conversion are sparse and unreliable. A figure that "half of the world's wetlands have been lost since the year 1900" is commonly cited despite its origin as an inadequate extrapolation from the US-Midwest in the 1950s. Recently, earth observation technologies have facilitated measurement of wetland cover but are limited temporally. Alternatively, meta-analyses of historical reclamation records suggest conversion rates exceeding 50% since 1900 but may be biased by the records coming mostly from highly-converted sites in recent times. Large reclamation projects during the early historical period are well known but not reliably quantified, shedding uncertainty on the natural wetland baseline relative to which conversion rates should be measured. Rates of loss based on relatively recent baselines (industrial/pre-settlement) cannot account for conversion prior to the baseline date, and may reinforce the perception of humans have substantially altered natural processes only recently. I estimate global wetland conversion with a geospatial approach based on maps of potential wetland cover and historical land cover (and irrigation) reconstructions, then compare estimates with historical records, thus bringing together the two main lines of evidence. Conversion is estimated as potential wetland areas undergoing change to 'non-natural' land cover, and estimates are contextualized relative to a Holocene natural wetland cover baseline. Potential wetland maps from vegetation and hydrological models that exclude drainage and water abstraction processes are used as they are the closest existing to natural wetland cover, despite being based on current-day climatology. To distinguish more types of reclamation practices than existing land cover classes, the GIS estimates are 'calibrated' regionally

  14. Sedimentary infill dynamic and associated trace element temporal trends in a dam reservoir: evidence of high polluted sediment storage after major flood events (Upper Loire river, France)

    NASA Astrophysics Data System (ADS)

    Dhivert, Elie; Grosbois, Cécile; Desmet, Marc; Coynel, Alexandra; Lefevre, Irène

    2014-05-01

    The Villerest Dam, was built in the Upper Loire river during the early 1980's, 80 km downstream of the most important industrial and coal mining area of the basin. It constitutes an important trap of sediments and associated pollutants since its operation in 1984. A 154 cm long core was sampled in 2010, in a former channel levee in the reservoir. This study highlights (i) important sediment accumulation rate during flood events in the reservoir, (ii) the influence of high discharge events in sedimentary infill in terms of stored sediment quality, geochemical markers and anthropogenic sources influence. Coupling sedimentological analyses and 137Cs datation allows to define 3 sedimentary units in this core. The deepest unit corresponds to transported and/or reworked fluvial sediments undated, the uppermost unit to lacustrine sediments post 1984 and between, to a transition unit resulting from the reservoir water infilling in 1983-1984. In addition, the upper unit shows 3 turbiditic-like layers (of 6, 20 and 13 cm thick) corresponding respectively to 1996, 2003 and 2008 major flood events (more than 20-year flood average daily outflow). These flood sequences result from underflow sedimentary inputs and contribute to 43% of the 151 kg/m² of accumulated sediments since 1984. Over the 1984-2010 period, sediments show a general contamination decrease but major flood events transport highly impacted sediments (highest enrichment factor > 20 for Hg and >10 for Cd and Bi), never reached during interflood periods. During these events, trace elements (TE) are mostly associated to organic fraction and clays. Rich-TE solid sources appear to be only solicited, and/or severely amplified, during important flood events over the recording period. In addition to these pollutants inputs, floods also bring an important detrital fraction, diluting anthropogenic TE signal. In details, flood deposits show variations of sedimentological and geochemical signals delimiting two distinct

  15. Late Holocene tectonics and paleoseismicity, southern Cascadia subduction zone

    USGS Publications Warehouse

    Clarke, S.H.; Carver, G.A.

    1992-01-01

    Holocene deformation indicative of large subduction-zone earthquakes has occurred on two large thrust fault systems in the Humboldt Bay region of northern California. Displaced stratigraphic markers record three offsets of 5 to 7 meters each on the Little Salmon fault during the past 1700 years. Smaller and less frequent Holocene displacements have occurred in the Mad River fault zone. Elsewhere, as many as five episodes of sudden subsidence of marsh peats and fossil forests and uplift of marine terraces are recorded. Carbon-14 dates suggest that the faulting, subsidence, and uplift events were synchronous. Relations between magnitude and various fault-offset parameters indicate that earthquakes accompanying displacements on the Little Salmon fault had magnitudes of at least 7.6 to 7.8. More likely this faulting accompanied rupture of the boundary between the Gorda and North American plates, and magnitudes were about 8.4 or greater.

  16. Dynamics of North Atlantic Deep Water masses during the Holocene

    NASA Astrophysics Data System (ADS)

    Hoogakker, Babette A. A.; Chapman, Mark R.; McCave, I. Nick; Hillaire-Marcel, Claude; Ellison, Christopher R. W.; Hall, Ian R.; Telford, Richard J.

    2011-12-01

    High resolution flow speed reconstructions of two core sites located on Gardar Drift in the northeast Atlantic Basin and Orphan Knoll in the northwest Atlantic Basin reveal a long-term decrease in flow speed of Northeast Atlantic Deep Water (NEADW) after 6,500 years. Benthic foraminiferal oxygen isotopes of sites currently bathed in NEADW show a 0.2‰ depletion after 6,500 years, shortly after the start of the development of a carbon isotope gradient between NEADW and Norwegian Sea Deep Water. We consider these changes in near-bottom flow vigor and benthic foraminiferal isotope records to mark a significant reorganization of the Holocene deep ocean circulation, and attribute the changes to a weakening of NEADW flow during the mid to late Holocene that allowed the shoaling of Lower Deep Water and deeper eastward advection of Labrador Sea Water into the northeast Atlantic Basin.

  17. Late holocene tectonics and paleoseismicity, southern cascadia subduction zone.

    PubMed

    Clarke, S H; Carver, G A

    1992-01-10

    Holocene deformation indicative of large subduction-zone earthquakes has occurred on two large thrust fault systems in the Humboldt Bay region of northern California. Displaced stratigraphic markers record three offsets of 5 to 7 meters each on the Little Salmon fault during the past 1700 years. Smaller and less frequent Holocene displacements have occurred in the Mad River fault zone. Elsewhere, as many as five episodes of sudden subsidence of marsh peats and fossil forests and uplift of marine terraces are recorded. Carbon-14 dates suggest that the faulting, subsidence, and uplift events were synchronous. Relations between magnitude and various fault-offset parameters indicate that earthquakes accompanying displacements on the Little Salmon fault had magnitudes of at least 7.6 to 7.8. More likely this faulting accompanied rupture of the boundary between the Gorda and North American plates, and magnitudes were about 8.4 or greater. PMID:17756070

  18. The Anthropocene is functionally and stratigraphically distinct from the Holocene.

    PubMed

    Waters, Colin N; Zalasiewicz, Jan; Summerhayes, Colin; Barnosky, Anthony D; Poirier, Clément; Gałuszka, Agnieszka; Cearreta, Alejandro; Edgeworth, Matt; Ellis, Erle C; Ellis, Michael; Jeandel, Catherine; Leinfelder, Reinhold; McNeill, J R; Richter, Daniel deB; Steffen, Will; Syvitski, James; Vidas, Davor; Wagreich, Michael; Williams, Mark; Zhisheng, An; Grinevald, Jacques; Odada, Eric; Oreskes, Naomi; Wolfe, Alexander P

    2016-01-01

    Human activity is leaving a pervasive and persistent signature on Earth. Vigorous debate continues about whether this warrants recognition as a new geologic time unit known as the Anthropocene. We review anthropogenic markers of functional changes in the Earth system through the stratigraphic record. The appearance of manufactured materials in sediments, including aluminum, plastics, and concrete, coincides with global spikes in fallout radionuclides and particulates from fossil fuel combustion. Carbon, nitrogen, and phosphorus cycles have been substantially modified over the past century. Rates of sea-level rise and the extent of human perturbation of the climate system exceed Late Holocene changes. Biotic changes include species invasions worldwide and accelerating rates of extinction. These combined signals render the Anthropocene stratigraphically distinct from the Holocene and earlier epochs.

  19. The variability of the North Atlantic Oscillation throughout the Holocene

    NASA Astrophysics Data System (ADS)

    Wassenburg, Jasper; Dietrich, Stephan; Fietzke, Jan; Fohlmeister, Jens; Wei, Wei; Jochum, Klaus Peter; Scholz, Denis; Richter, Detlev; Sabaoui, Abdellah; Lohmann, Gerrit; Andreae, Meinrat; Immenhauser, Adrian

    2013-04-01

    The North Atlantic Oscillation (NAO) has a major impact on Northern Hemisphere winter climate. Trouet et al. (2009) reconstructed the NAO for the last millennium based on a Moroccan tree ring PDSI (Palmer Drought Severity Index) reconstruction and a Scottish speleothem record. More recently, Olsen et al. (2012) extended the NAO record back to 5.2 ka BP based on a lake record from West Greenland. It is, however, well known that the NAO exhibits non-stationary behavior and the use of a single location for a NAO reconstruction may not capture the complete variability. In addition, the imprint of the NAO on European rainfall patterns in the Early and Mid Holocene on (multi-) centennial timescales is still largely unknown. This is related to difficulties in establishing robust correlations between different proxy records and the fact that proxies may not only reflect winter conditions (i.e., the season when the NAO has the largest influence). Here we present a precisely dated, high resolution speleothem δ18O record from NW Morocco covering the complete Early and Mid Holocene. Carbon and oxygen isotopes were measured at a resolution of 15 years. A multi-proxy approach provides solid evidence that speleothem δ18O values reflect changes in past rainfall intensity. The Moroccan record shows a significant correlation with a speleothem rainfall record from western Germany, which covers the entire Holocene (Fohlmeister et al., 2012). The combination with the extended speleothem record from Scotland, speleothem records from north Italy and the NAO reconstruction from West Greenland (Olsen et al., 2012) allows us to study the variability of the NAO during the entire Holocene. The relation between West German and Northwest Moroccan rainfall has not been stationary, which is evident from the changing signs of correlation. The Early Holocene is characterized by a positive correlation, which changes between 9 and 8 ka BP into a negative correlation. Simulations with the state

  20. Late Holocene tephrochronology of the northern Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Björck, Svante; Sandgren, Per; Zale, Rolf

    1991-11-01

    Andesitic and basaltic andesitic tephra layers are abundant in Holocene deposits from the Antarctic Peninsula. Visually discernible tephra horizons occur in three lakes on Livingston Island. Tephra in two other lakes and in a moss bank on Elephant Island, with very low ash concentrations, were detected magnetically. Deception Island is the most likely volcanic source for the tephra. With direct 14C dating, age/depth curves, and cross-correlations at least 14 tephra horizons dating to between ca. 4700 and 250 yr B.P. were identified and now form the basis for a preliminary regional tephrochronology that will be a valuable dating tool for investigating the Holocene climatic history of Antarctica.

  1. A lacustrine carbonate record of Holocene seasonality and climate

    USGS Publications Warehouse

    Wittkop, Chad A.; Teranes, Jane L.; Dean, Walter E.; Guilderson, Thomas P.

    2009-01-01

    Annually laminated (varved) Holocene sediments from Derby Lake, Michigan, display variations in endogenic calcite abundance reflecting a long-(millennial-scale) decrease in burial punctuated with frequent short- (decadal-scale) oscillations due to carbonate dissolution. Since 6000 cal yr B.P., sediment carbonate abundance has followed a decreasing trend while organic-carbon abundance has increased. The correlation between organic-carbon abundance and the sum of March-April-October-November insolation has an r2 value of 0.58. We interpret these trends to represent a precession-driven lengthening of the Holocene growing season that has reduced calcite burial by enhancing net annual organic-matter production and associated calcite dissolution. Correlations with regional paleoclimate records suggest that changes in temperature and moisture balance have impacted the distribution of short- oscillations in carbonate and organic-matter abundance superimposed on the precession-driven trends.

  2. Early Holocene glacier advance, southern Coast Mountains, British Columbia, Canada

    NASA Astrophysics Data System (ADS)

    Menounos, Brian; Koch, Johannes; Osborn, Gerald; Clague, John J.; Mazzucchi, David

    2004-07-01

    Terrestrial and lake sediment records from several sites in the southern Coast Mountains, British Columbia, provide evidence for an advance of alpine glaciers during the early Holocene. Silty intervals within organic sediments recovered from two proglacial lakes are bracketed by AMS 14C-dated terrestrial macrofossils and Mazama tephra to 8780-6730 and 7940- 6730 14C yr BP [10,150-7510 and 8990- 7510 cal yr BP]. Radiocarbon ages ranging from 7720 to 7380 14C yr BP [8630- 8020 cal yr BP] were obtained from detrital wood in recently deglaciated forefields of Sphinx and Sentinel glaciers. These data, together with previously published data from proglacial lakes in the Canadian Rockies, imply that glaciers in western Canada advanced during the early Holocene. The advance coincides with the well-documented 8200-yr cold event identified in climate proxy data sets in the North Atlantic region and elsewhere.

  3. Midwestern Holocene paleoenvironments revealed by floodplain deposits in northeastern Iowa

    USGS Publications Warehouse

    Chumbley, C.A.; Baker, R.G.; Bettis, E. Arthur

    1990-01-01

    Pollen analysis of pond deposits in the upper reaches of a stream from northeastern Iowa, an area beyond the last glacial margin, provides a nearly complete record of vegetational changes during the last 12.5 thousand years. Sixty-one radiocarbon dates provide good chronological control. Spruce forest was replaced by deciduous forest before 9 1 thousand years ago, followed by prairie from 5.4 to 3.5 thousand years ago, and oak savanna from 3.5 thousand years ago until presettlement times. The prairie invasion was nearly 3 thousand years later here than at other sites in Iowa and Minnesota, documenting a late Holocene, rather than an early-middle Holocene, period of maximum warmth and dryness for the southern part of the upper Midwest.

  4. The Anthropocene is functionally and stratigraphically distinct from the Holocene.

    PubMed

    Waters, Colin N; Zalasiewicz, Jan; Summerhayes, Colin; Barnosky, Anthony D; Poirier, Clément; Gałuszka, Agnieszka; Cearreta, Alejandro; Edgeworth, Matt; Ellis, Erle C; Ellis, Michael; Jeandel, Catherine; Leinfelder, Reinhold; McNeill, J R; Richter, Daniel deB; Steffen, Will; Syvitski, James; Vidas, Davor; Wagreich, Michael; Williams, Mark; Zhisheng, An; Grinevald, Jacques; Odada, Eric; Oreskes, Naomi; Wolfe, Alexander P

    2016-01-01

    Human activity is leaving a pervasive and persistent signature on Earth. Vigorous debate continues about whether this warrants recognition as a new geologic time unit known as the Anthropocene. We review anthropogenic markers of functional changes in the Earth system through the stratigraphic record. The appearance of manufactured materials in sediments, including aluminum, plastics, and concrete, coincides with global spikes in fallout radionuclides and particulates from fossil fuel combustion. Carbon, nitrogen, and phosphorus cycles have been substantially modified over the past century. Rates of sea-level rise and the extent of human perturbation of the climate system exceed Late Holocene changes. Biotic changes include species invasions worldwide and accelerating rates of extinction. These combined signals render the Anthropocene stratigraphically distinct from the Holocene and earlier epochs. PMID:26744408

  5. Climate model benchmarking with glacial and mid-Holocene climates

    NASA Astrophysics Data System (ADS)

    Harrison, S. P.; Bartlein, P. J.; Brewer, S.; Prentice, I. C.; Boyd, M.; Hessler, I.; Holmgren, K.; Izumi, K.; Willis, K.

    2014-08-01

    Past climates provide a test of models' ability to predict climate change. We present a comprehensive evaluation of state-of-the-art models against Last Glacial Maximum and mid-Holocene climates, using reconstructions of land and ocean climates and simulations from the Palaeoclimate Modelling and Coupled Modelling Intercomparison Projects. Newer models do not perform better than earlier versions despite higher resolution and complexity. Differences in climate sensitivity only weakly account for differences in model performance. In the glacial, models consistently underestimate land cooling (especially in winter) and overestimate ocean surface cooling (especially in the tropics). In the mid-Holocene, models generally underestimate the precipitation increase in the northern monsoon regions, and overestimate summer warming in central Eurasia. Models generally capture large-scale gradients of climate change but have more limited ability to reproduce spatial patterns. Despite these common biases, some models perform better than others.

  6. Midwestern holocene paleoenvironments revealed by floodplain deposits in northeastern iowa.

    PubMed

    Chumbley, C A; Baker, R G; Bettis, E A

    1990-07-20

    Pollen analysis of pond deposits in the upper reaches of a stream from northeastern Iowa, an area beyond the last glacial margin, provides a nearly complete record of vegetational changes during the last 12.5 thousand years. Sixty-one radiocarbon dates provide good chronological control. Spruce forest was replaced by deciduous forest before 9.1 thousand years ago, followed by prairie from 5.4 to 3.5 thousand years ago, and oak savanna from 3.5 thousand years ago until presettlement times. The prairie invasion was nearly 3 thousand years later here than at other sites in Iowa and Minnesota, documenting a late Holocene, rather than an early-middle Holocene, period of maximum warmth and dryness for the southern part of the upper Midwest.

  7. Current subsidence rates due to compaction of Holocene sediments in southern Louisiana

    USGS Publications Warehouse

    Meckel, T.A.; ten Brink, U.S.; Williams, S.J.

    2006-01-01

    Relative contributions of geologic and anthropogenic processes to subsidence of southern Louisiana are vigorously debated. Of these, shallow sediment compaction is often considered dominant, although this has never been directly observed or effectively demonstrated. Quantitative understanding of subsidence is important for predicting relative sea level rise, storm surge flooding due to hurricanes, and for successful wetland restoration. Despite many shallow borings, few appropriate stratigraphic and geotechnical data are available for site-specific calculations. We overcome this by determining present compaction rates from Monte Carlo simulations of the incremental sedimentation and compaction of stratigraphies typical of the Holocene of southern Louisiana. This approach generates distributions of present compaction rates that are not expected to exceed 5 mm/yr, but may locally. Locations with present subsidence rates greater than the predicted maximum probable shallow compaction rates are likely influenced by additional processes.

  8. Late Holocene land- and sea-level changes in the British Isles: implications for future sea-level predictions

    NASA Astrophysics Data System (ADS)

    Gehrels, W. Roland

    2010-07-01

    Four decades of palaeosea-level research in the British Isles have produced a large dataset of age-altitude curves of postglacial sea-level changes. Patterns of late Holocene relative sea-level change reveal the persistent influence of the British/Irish Ice Sheet and the larger Scandinavian Ice Sheet on contemporary rates of vertical land movements. The Shennan and Horton (2002) map of late Holocene relative land movements has been used in future sea-level rise predictions by the United Kingdom Climate Impact Programme in their 2002 assessment (UKCIP02), but has been mistaken for a map of absolute land movements. In this paper, land-motion data for Britain are extracted from the Shennan and Horton (2002) relative sea-level data, and a new map of crustal land movements is presented which also includes Ireland. This procedure takes into account the regional 20th century sea-level rise (˜0.14 m) and the process of ocean syphoning ( i.e. a global fall in sea level of ˜0.3 mm/yr due to GIA induced ocean-floor lowering and re-distribution of ocean mass). The calculated land-motion rates also depend on the global late Holocene ice-equivalent sea-level change, given by the Intergovernmental Panel on Climate Change as 0.0-0.2 mm/yr. Accounting for these processes reduces the misfit between geological observations of vertical land motion and those independently derived from gravity-aligned Global Positioning System (AG GPS) measurements and shows that UKCIP02 has underestimated land subsidence in southern Britain and over-estimated land uplift in Scotland, both by 0.1-0.2 mm/yr. A best fit between GPS and geological estimates of land movements in Britain is achieved for a global long-term eustatic sea-level fall of ca 0.2 mm/yr, suggesting some global ice expansion in the late Holocene, rather than melt. If this is correct, uplift rates in Scotland would be lower and subsidence rates in southern Britain would be faster (by 0.4-0.5 mm/yr) than estimated by UKCIP02. More

  9. Age and spatial distribution of Holocene permafrost in Norway - model results and implications for glacier-permafrost interaction

    NASA Astrophysics Data System (ADS)

    Lilleoren, K. S.; Etzelmuller, B.; Gisnås, K.; Humlum, O.

    2011-12-01

    Following the last glaciation, cryogenic processes related to valley and cirque glaciers, permafrost and seasonal frost have dominated the Norwegian landscape development in high-mountain environments. This is evident by different landscape and landform features, like rock glaciers, block fields, palsas, ice-wedge polygons and ice-cored moraines. For Scandinavia the present regional distribution of mountain permafrost is reasonably well known, both through ground temperature measurements in boreholes, geophysical soundings and spatial modelling exercises. An important question in this context is the dynamics of permafrost during the Holocene, as a major factor for landscape development and geomorphological processes in high mountain areas of Scandinavia. In the present study mean annual air temperature deviation curves through Holocene have been compiled to drive a 1D heat flow model over the last 10 ka period for several mountain sites in Norway. At each site temperature-monitored boreholes were used to calibrate the model. Both an annual run and a seasonal run including monthly temperature variations were performed for each site. In addition the spatial distribution of permafrost during selected time periods of the Holocene were addressed using an equilibrium permafrost model on a 1*1 km resolution. The results of this study indicate an altitudinal zonation of relative permafrost age in Norway, where permafrost has existed continuously since the deglaciation in the highest areas, while large areas that is underlain by permafrost today were degraded during the Holocene Thermal Maximum (HTM). In all boreholes the deepest simulated permafrost occurred during the Little Ice Age (LIA), and also the largest areal distribution of Holocene permafrost in Norway is connected to the LIA. In addition, there exist a clear connection between the distribution of permafrost and presence of blockfields. These findings have several implications, such as for the subglacial

  10. Wasatch fault zone, Utah - segmentation and history of Holocene earthquakes

    USGS Publications Warehouse

    Machette, Michael N.; Personius, Stephen F.; Nelson, Alan R.; Schwartz, David P.; Lund, William R.

    1991-01-01

    The Wasatch fault zone (WFZ) forms the eastern boundary of the Basin and Range province and is the longest continuous, active normal fault (343 km) in the United States. It underlies an urban corridor of 1.6 million people (80% of Utah's population) representing the largest earthquake risk in the interior of the western United States. The authors have used paleoseismological data to identify 10 discrete segments of the WFZ. Five are active, medial segments with Holocene slip rates of 1-2 mm a-1, recurrence intervals of 2000-4000 years and average lengths of about 50 km. Five are less active, distal segments with mostly pre-Holocene surface ruptures, late Quaternary slip rates of <0.5 mm a-1, recurrence intervals of ???10,000 years and average lengths of about 20 km. Surface-faulting events on each of the medial segments of the WFZ formed 2-4-m-high scarps repeatedly during the Holocene. Paleoseismological records for the past 6000 years indicate that a major surface-rupturing earthquake has occurred along one of the medial segments about every 395 ?? 60 years. However, between about 400 and 1500 years ago, the WFZ experienced six major surface-rupturing events, an average of one event every 220 years, or about twice as often as expected from the 6000-year record. Evidence has been found that surface-rupturing events occurred on the WFZ during the past 400 years, a time period which is twice the average intracluster recurrence interval and equal to the average Holocene recurrence interval.

  11. Holocene climate changes in the Cape Hatteras region

    NASA Astrophysics Data System (ADS)

    Naughton, F.; Keigwin, L. D.; Peteet, D. M.; Desprat, S.; Oliveira, D.; Abrantes, F.

    2013-12-01

    In the last century many studies have been done in various naturally occurring archives to understand the nature, timing and causes of Holocene natural climate oscillations. Most of the available Holocene climatic reconstructions are however, not based on a direct comparison of terrestrial, marine and ice records making it difficult to obtain an accurate understanding of the interactions of the atmosphere-ocean-land systems and their relationship in global climate variability. Few studies based on direct sea land comparison have been reported for some key areas of the eastern North Atlantic but almost none in the western North Atlantic. Here we present a direct comparison between terrestrial (pollen) and marine (planktonic δ18O) proxies from a well dated (ten AMS 14C dates on planktonic foraminifera and seaweed) slope core (KNR 178-2 JPC 32), retrieved close to Cape Hatteras (35°58.58'N, 74°42.77'W, 1006 m). This study provides information on eastern North America vegetation and on the northwestern Atlantic sea surface response to both Holocene long-term and rapid climate changes. Five intervals, marked mainly by changes in temperate trees are associated with long term climate shifts (12000-9150 ka; 9150-7250 ka; 7250-5350 ka; 5350-2800 ka; 2800-700 ka). Over these intervals, several abrupt cooling events are noted, as well as several indications of shifts in moisture. The comparison of our data with those available and unpublished records from several key sites of the North Atlantic region, gives insights into the nature, timing and causes of Holocene climate oscillations in the North Atlantic region and in particular off Cape Hatteras.

  12. Biotic turnover rates during the Pleistocene-Holocene transition

    NASA Astrophysics Data System (ADS)

    Stivrins, Normunds; Soininen, Janne; Amon, Leeli; Fontana, Sonia L.; Gryguc, Gražyna; Heikkilä, Maija; Heiri, Oliver; Kisielienė, Dalia; Reitalu, Triin; Stančikaitė, Miglė; Veski, Siim; Seppä, Heikki

    2016-11-01

    The Northern Hemisphere is currently warming at the rate which is unprecedented during the Holocene. Quantitative palaeoclimatic records show that the most recent time in the geological history with comparable warming rates was during the Pleistocene-Holocene transition (PHT) about 14,000 to 11,000 years ago. To better understand the biotic response to rapid temperature change, we explore the community turnover rates during the PHT by focusing on the Baltic region in the southeastern sector of the Scandinavian Ice Sheet, where an exceptionally dense network on microfossil and macrofossil data that reflect the biotic community history are available. We further use a composite chironomid-based summer temperature reconstruction compiled specifically for our study region to calculate the rate of temperature change during the PHT. The fastest biotic turnover in the terrestrial and aquatic communities occurred during the Younger Dryas-Holocene shift at 11,700 years ago. This general shift in species composition was accompanied by regional extinctions, including disappearance of mammoth (Mammuthus primigenius) and reindeer (Rangifer tarandus) and many arctic-alpine plant taxa, such as Dryas octopetala, Salix polaris and Saxifraga aizoides, from the region. This rapid biotic turnover rate occurred when the rate of warming was 0.17 °C/decade, thus slightly lower than the current Northern Hemisphere warming of 0.2 °C/decade. We therefore conclude that the Younger Dryas-Holocene shift with its rapid turnover rates and associated regional extinctions represents an important palaeoanalogue to the current high latitude warming and gives insights about the probable future turnover rates and patterns of the terrestrial and aquatic ecosystem change.

  13. Holocene reef development where wave energy reduces accommodation

    USGS Publications Warehouse

    Grossman, Eric E.; Fletcher, Charles H.

    2004-01-01

    Analyses of 32 drill cores obtained from the windward reef of Kailua Bay, Oahu, Hawaii, indicate that high wave energy significantly reduced accommodation space for reef development in the Holocene and produced variable architecture because of the combined influence of sea-level history and wave exposure over a complex antecedent topography. A paleostream valley within the late Pleistocene insular limestone shelf provided accommodation space for more than 11 m of vertical accretion since sea level flooded the bay 8000 yr BP. Virtually no net accretion (pile-up of fore-reef-derived rubble (rudstone) and sparse bindstone, and (3) a final stage of catch-up bindstone accretion in depths > 6 m. Coral framestone accreted at rates of 2.5-6.0 mm/yr in water depths > 11 m during the early Holocene; it abruptly terminated at ~4500 yr BP because of wave scour as sea level stabilized. More than 4 m of rudstone derived from the upper fore reef accreted at depths of 6 to 13 m below sea level between 4000 and 1500 yr BP coincident with late Holocene relative sea-level fall. Variations in the thickness, composition, and age of these reef facies across spatial scales of 10-1000 m within Kailua Bay illustrate the importance of antecedent topography and wave-related stress in reducing accommodation space for reef development set by sea level. Although accommodation space of 6 to 17 m has existed through most of the Holocene, the Kailua reef has been unable to catch up to sea level because of persistent high wave stress.

  14. The Holocene paleo-tsunami history of West Australia

    NASA Astrophysics Data System (ADS)

    Scheffers, S. R.; Scheffers, A.; Kelletat, D.; Bryant, E. A.

    2008-06-01

    West Australian coastlines experienced several tsunamis in mid-Holocene times. To expand our knowledge about Holocene tsunami events in West Australia, the authors extended the previously studied spatial scale to include the central- and south-western coastlines. Several of the discovered events were mid- and young Holocene (≤ 1000 yr BP) tsunami impacts on the outer coast of the Cape Range Peninsula. Five hundred kilometres to the south between Cape Cuvier and Point Quobba, additional tsunami evidence exists on top of steep cliffs over a coastal stretch of 30 km. The sedimentary signature of two tsunamis is documented in this area by wide ridges comprised of sand, shell, and clasts (including coral fragments) at heights of 12-30 m asl and 300-500 m inland. Enigmatic boulders (20-100 tons) appear as cliff-top megaclasts up to 100 m inland. Here, radiocarbon dating revealed a minimum of two tsunami events: at 5700 yr BP with waves depositing sandy ridges far inland and at approximately 1000 yr BP with waves depositing boulders originating from the marine environment. As the first dates are congruent with previously published results for the Learmonth region 500 km to the north, we assume that the same mid-Holocene tsunami hits this long coastal section as well. The southwestern coast of West Australia from Cape Naturaliste to Albany also shows signs of impacts by extreme waves. Here, huge granite boulders (80-400 tons) were dislocated and transported to heights up to 10 m above sea level. The most prominent dislocated boulders were positioned at Merchant Rock (Cape Naturaliste National Park), at Islet near Nanarup, and in Cave Bay close to Albany.

  15. Holocene climate changes in southern Greenland: evidence from lake sediments

    NASA Astrophysics Data System (ADS)

    Andresen, Camilla S.; Björck, Svante; Bennike, Ole; Bond, Gerard

    2004-12-01

    A Holocene lake sediment record is presented from Lake N14 situated on Angissoq Island 15 km off the main coast of southern Greenland. The palaeoclimatic development has been interpreted on the basis of flux and percentage content of biogenic silica, clastic material, organic material and sulphur as well as sedimentation rate, moss content and magnetic susceptibility. A total of 43 radiocarbon dates has ensured a reliable chronology. It is argued that varying sediment composition mainly reflects changing precipitation. By analogy with the present meteorological conditions in southern Greenland, Holocene climate development is inferred. Between 11 550 and 9300 cal. yr BP temperature and precipitation increase markedly, but this period is climatically unstable. From 9300 yr BP conditions become more stable and a Holocene climatic optimum, characterised by warm and humid conditions, is observed from 8000 to 5000 cal. yr BP. From 4700 cal. yr BP the first signs of a climatic deterioration are observed, and from 3700 cal. yr BP the climate has become more dry and cold. Superimposed on the climatic long-term trend is climate variability on a centennial time-scale that increases in amplitude after 3700 cal. yrBP. A climatic scenario related to the strength and position of the Greenland high-pressure cell and the Iceland low-pressure cell is proposed to explain the Holocene centennial climate variability. A comparison of the Lake N14 record with a terrestrial as well as a marine record from the eastern North Atlantic Ocean suggests that the centennial climate variability was uniform over large areas at certain times. Copyright

  16. Beaver Activity, Holocene Climate and Riparian Landscape Change Across Stream Scales in the Greater Yellowstone Ecosystem

    NASA Astrophysics Data System (ADS)

    Levine, R.; Meyer, G. A.

    2013-12-01

    Beaver (Castor canadensis) have been part of the fluvial and riparian landscape across much of North America since the Pleistocene, increasing channel habitat complexity and expanding riparian landscapes. The fur trade, however, decimated beaver populations by the 1840s, and other human activities have limited beaver in many areas, including parts of the Greater Yellowstone Ecosystem (GYE). Understanding fluctuations in beaver occupation through the Holocene will aid in understanding the natural range of variability in beaver activity as well as climatic and anthropogenic impacts to fluvial systems. We are developing a detailed chronology of beaver-assisted sedimentation and overall fluvial activity for Odell and Red Rock Creeks (basin areas 83 and 99 km2) in Centennial Valley (CV), Montana, to augment related studies on the long-term effects of beaver on smaller GYE fluvial systems (basin areas 0.1-50 km2). In developing the CV chronology, we use the presence of concentrations of beaver-chewed sticks as a proxy for beaver occupancy. Beaver-stick deposits are found in paleochannel and fluvial terrace exposures. The relative ages of exposures were determined by elevation data from airborne LiDAR and ground surveys. Numerical ages were obtained from 36 14C ages (~30 more are pending) of beaver-stick wood collected during investigation of the stratigraphy. Most beaver-stick deposits are associated with ~ 1 meter of fine-grained sediment, interpreted as overbank deposits, commonly overlying gravelly sand or pebble gravel channel deposits which is consistent with enhanced overbank sedimentation associated with active beaver dams in CV streams. The CV deposits differ from those on smaller GYE streams where beaver-stick deposits are associated with abandoned dams (berms), infilled ponds and laminated sediments. The lack of pond-related deposition associated with CV beaver-stick deposits is consistent with frequent dam breaching (≤ 5 years) in the modern channel of Odell

  17. Holocene Climate and Landscape Interactions in the Lake Titicaca Basin, Peru

    NASA Astrophysics Data System (ADS)

    Rigsby, C. A.; Baker, P. A.; Aldenderfer, M. S.

    2001-12-01

    Fluvial strata and landforms in the Rio Ilave valley (Peru) document a history of Holocene aggradation and downcutting that is correlative with regional climatic events. Periods of aggradation correspond to periods of high (or rising) level in Lake Titicaca, increased sediment accumulation in the Ilave delta, and lacustrine sedimentation in the Rio Desaguadero valley. Downcutting episodes correspond to periods of low level in Lake Titicaca, low or rapidly decreasing sedimentation rates in the Ilave delta, and fluvial activity in the Rio Desaguadero valley. The five terrace tracts (T1 through T5) present in this southwestern Lake Titicaca tributary occur as both paired and unpaired terraces and have average heights from 1.4 m to 24.3 m above the valley floor. Radiocarbon dates from the oldest exposed terrace strata and from the top of T4 suggest that the majority of the fluvial sequence was deposited during the time period from the LGM until about 8300 cal BP - a period of generally high precipitation on the Altiplano and high water level in Lake Titicaca. Increased fluvial/glacial runoff during this time resulted in an increased supply of sediment to the Rio Ilave and high sediment accumulation rates offshore from the Ilave delta. With the input of large volumes of easily eroded volcanic-rich sediment from source areas in the Cordillera Occidental, contemporaneous with high base level (Lake Titicaca), sediment load was sufficient to fill the valley and choke the river system. In embayments behind bedrock constrictions, sediments were deposited to heights in excess of 25 meters above the valley floor (T5). This aggradation was followed by downcutting of the T4 and T3 terraces. Initial downcutting began immediately after precipitation, runoff, and sediment load decreased and base level dropped. Downcutting was likely very rapid and was followed by a period of episodic equilibrium and minor downcutting that included a prolonged period of soil formation between ca

  18. Holocene land cover change on the Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Dallmeyer, A.; Claussen, M.

    2010-12-01

    The Tibetan Plateau is expected to be one of the most climatic sensitive regions of the earth. Due to its large horizontal and vertical extend it has a large influence on the regional as well as global climate. As a heat source for the atmosphere in spring and summer it plays an important role for the onset and maintenance of the Asian summer monsoon and therewith influences one of the strongest monsoon circulations of the world. On the other hand, monsoon related convection above the Plateau leads to large-scale subsiding air-masses and dry climate in the regions north and west of the Plateau. These processes depend to a large part on the land cover as it controls the energy balance at the surface and the strength of the diabatic heat fluxes. Land cover changes on the Tibetan Plateau may thus exert strong influence on the regional and northern hemispheric climate. Therefore it is very important to represent past and future land cover changes correctly in global climate models, not only to understand the mechanism behind these land cover changes, but also to understand past and future climate change in Asia. To assess the performance of the comprehensive Earth system model ECHAM5-JSBACH/MPIOM with respect to the land cover on the Tibetan Plateau, we compare results of a transient numerical experiment with pollen-based vegetation reconstructions from four representative sites on the Plateau, covering the last 6000 years. Generally, the reconstructed and simulated trends are similar for most sites. Data and model show a strong decrease of forests on the Plateau. According to the model results, the averaged forest fraction has been reduced by almost one-third from mid-Holocene (41.4%) to present-day (28.3%) and is replaced by shrub and grass. The model mainly identifies differences in near-surface air temperatures due to an orbital induced insolation change as the reason for the vegetation change. Reconstructions rather indicate decreasing summer monsoon precipitation

  19. Variability of the Brazil Current during the late Holocene

    NASA Astrophysics Data System (ADS)

    Chiessi, C. M.; Mulitza, S.; Groeneveld, J.; Silva, J. B.; Campos, M. C.; Gurgel, M. H.

    2013-12-01

    Our understanding of the centennial-scale variability of the Brazil Current (BC) during the late Holocene is elusive because of the lack of appropriate records. Here we used the Mg/Ca and oxygen isotopic composition of planktonic foraminifera from two marine sediment cores collected at 27 °S and 33 °S off southeastern South America to assess the late Holocene variability in the upper water column of the BC. Our results show in phase fluctuations of up to 3 °C in sea surface temperatures (SST), and 0.8 ‰ in oxygen isotopic composition of surface sea water, a proxy for relative sea surface salinity (SSS). Time-series analyses of our records indicate a cyclicity with period of ca. 730 yr. We suggest that the observed cyclicity reflects variability in the strength of the BC associated to changes in the Atlantic meridional overturning circulation (AMOC). Positive (negative) SST and SSS anomalies are related to a strong (weak) BC and a weak (strong) AMOC. Moreover, periods of peak strength in the BC occur synchronously to weak North Brazil Current, negative SST anomalies in the high latitudes of the North Atlantic, and positive (negative) precipitation anomalies over southeastern South America (equatorial Africa), further corroborating our hypothesis. This study shows a tight coupling between the variability of the BC and the high latitudes of the North Atlantic mediated by the AMOC even under late Holocene boundary conditions.

  20. The pace of East African monsoon evolution during the Holocene

    NASA Astrophysics Data System (ADS)

    Weldeab, Syee; Menke, Valerie; Schmiedl, Gerhard

    2014-03-01

    African monsoon precipitation experienced a dramatic change in the course of the Holocene. The pace with which the African monsoon shifted from a strong early to middle to a weak late Holocene is critical for our understanding of climate dynamics, hydroclimate-vegetation interaction, and shifts of prehistoric human settlements, yet it is controversially debated. On the basis of planktonic foraminiferal Ba/Ca time series from the eastern Mediterranean Sea, here we present a proxy record of Nile River runoff that provides a spatially integrated measure of changes in East African monsoon (EAM) precipitation. The runoff record indicates a markedly gradual middle to late Holocene EAM transition that lasted over 3500 years. The timing and pace of runoff change parallels those of insolation and vegetation changes over the Nile basin, indicating orbitally forced variation of insolation as the main EAM forcing and the absence of a nonlinear precipitation-vegetation feedback. A tight correspondence between a threshold level of Nile River runoff and the timing of occupation/abandonment of settlements suggests that along with climate changes in the eastern Sahara, the level of Nile River and intensity of summer floods were likely critical for the habitability of the Nile Valley (Egypt).

  1. Glaciological reconstruction of Holocene ice margins in northwestern Greenland

    NASA Astrophysics Data System (ADS)

    Birkel, S. D.; Osterberg, E. C.; Kelly, M. A.; Axford, Y.

    2014-12-01

    The past few decades of climate warming have brought overall margin retreat to the Greenland Ice Sheet. In order to place recent and projected changes in context, we are undertaking a collaborative field-modeling study that aims to reconstruct the Holocene history of ice-margin fluctuation near Thule (~76.5°N, 68.7°W), and also along the North Ice Cap (NIC) in the Nunatarssuaq region (~76.7°N, 67.4°W). Fieldwork reported by Kelly et al. (2013) reveals that ice in the study areas was less extensive than at present ca. 4700 (GIS) and ca. 880 (NIC) cal. years BP, presumably in response to a warmer climate. We are now exploring Holocene ice-climate coupling using the University of Maine Ice Sheet Model (UMISM). Our approach is to first test what imposed climate anomalies can afford steady state ice margins in accord with field data. A second test encompasses transient simulation of the Holocene, with climate boundary conditions supplied by existing paleo runs of the Community Climate System Model version 4 (CCSM4), and a climate forcing signal derived from Greenland ice cores. In both cases, the full ice sheet is simulated at 10 km resolution with nested domains at 0.5 km for the study areas. UMISM experiments are underway, and results will be reported at the meeting.

  2. Holocene and Pleistocene pluvial periods in Yemen, southern Arabia

    NASA Astrophysics Data System (ADS)

    Fleitmann, Dominik; Burns, Stephen J.; Pekala, Marek; Mangini, Augusto; Al-Subbary, Abdulkarim; Al-Aowah, Mohammad; Kramers, Jan; Matter, Albert

    2011-04-01

    Arabia is an important potential pathway for the dispersal of Homo sapiens ("out of Africa"). Yet, because of its arid to hyper-arid climate humans could only migrate across southern Arabia during pluvial periods when environmental conditions were favorable. However, knowledge on the timing of Arabian pluvial periods prior to the Holocene is mainly based on a single and possibly incomplete speleothem record from Hoti Cave in Northern Oman. Additional terrestrial records from the Arabian Peninsula are needed to confirm the Hoti Cave record. Here we present a new speleothem record from Mukalla Cave in southern Yemen. The Mukalla Cave and Hoti Cave records clearly reveal that speleothems growth occurred solely during peak interglacial periods, corresponding to Marine Isotope Stages (MIS) 1 (early to mid-Holocene), 5.1, 5.3, 5.5 (Eemian), 7.1, 7.5 and 9. Of these humid periods, highest precipitation occurred during MIS 5.5 and lowest during early to middle Holocene.

  3. Regional aridity in North America during the middle Holocene

    USGS Publications Warehouse

    Dean, W.E.; Ahlbrandt, T.S.; Anderson, R.Y.; Bradbury, J.P.

    1996-01-01

    Increased aridity throughout the Great Plains and Rocky Mountain region during the middle Holocene has been documented from pollen records, aeolian proxy variables in lake cores, and active sand dune migration. Varve calibration provided by a continuously varved record of the Holocene from a core from Elk Lake, northwestern Minnesota, shows that the influx of aeolian elastic material increased beginning about 8 ka and ended about 3.8 ka, with peak aeolian activity at about 6 ka. If aeolian influx to Elk Lake corresponds in time to aeolian influx in other lakes and to maximum dune activity in Minnesota dune fields, then the varve calibration in Elk Lake provides precise time calibration of periods of peak aeolian activity in Minnesota. Palaeowind studies from the Minnesota dune fields show that the dominant wind direction when the dunes were active was from the northwest, the same as the dominant wind direction in dune fields throughout the Great Plains and Rocky Mountains. If the mid-Holocene aeolian activity in Minnesota was driven by an increase in westerly zonal winds, then the varve calibration can be extended to more precisely determine the timing of activity of dunes over a much broader area. We suggest that an increase in the westerly zonal wind field might have a solar-geomagnetic cause.

  4. The Nile Delta: climate pacing and vulnerability to Holocene change

    NASA Astrophysics Data System (ADS)

    Marriner, Nick; Flaux, Clément; Morhange, Christophe; Stanley, Jean-Daniel

    2014-05-01

    Deltas are potentially important sentinels to investigate climate-driven changes in palaeohydrology and human impacts, but, paradoxically, have often been overlooked as palaeoclimate records. In this paper, we present two time-series from the Nile Delta to probe both millennial and centennial-scale changes in deltaic hydrogeomorphology over the past 8000 years. In a global Holocene context, the long-term decrease in Nile Delta accretion rates is consistent with insolation-driven changes in the 'monsoon pacemaker', attested throughout the mid-latitude tropics. Using a second record we suggest that, at shorter timescales, many of the major phases of deltaic modification were mediated by climate events linked to El Niño Southern Oscillation- type (ENSO) variability. In the final part of the paper, we propose that following the early to mid-Holocene growth of the Nile's deltaic plain pronounced deltaic erosion is first recorded after ~4000 years ago, the corollaries of falling sediment supply and an intensification of anthropogenic impacts from the Pharaonic period onwards. The study highlights the importance of the world's deltas as sensitive archives to investigate Holocene geosystem responses to climate change, risks and hazards, and societal interaction.

  5. A Holocene paleomagnetic record from Fish Lake, Oregon.

    NASA Astrophysics Data System (ADS)

    Ziegler, L. B.; Stoner, J. S.; Abbott, M. B.; Finkenbinder, M. S.; Hatfield, R. G.; Konyndyk, D.; Reilly, B.; Hillman, A. L.

    2014-12-01

    Paleo-geomagnetic observations provide fundamental models of the core and the geodynamo that cannot other- wise be obtained. Data and modeling studies are beginning to show that regions of concentrated magnetic flux (flux lobes) on the Core-Mantle boundary, those observed historically and others only hinted at from the short historical record, impose a structure on the geomagnetic field that may govern at least some components of geo- magnetic change. Accumulating evidence suggests that this structure reflects the influence of the lower mantle, yet this structure and the evolution of the geomagnetic field within it, even for the Holocene, are only beginning to be- come apparent. Comparison of specific, well-dated Holocene timeseries of PSV (sedimentary and archeomagnetic) inclination, declination, and paleointensity at key locations can provide intriguing insight when viewed through the lens of the known historical and assumed millennial flux lobes. A limiting factor for these studies is the uneven distribution of high quality data with independent chronologies, with Europe and the North Atlantic having better constrained data sets than North America. To begin to fill this data gap, we present initial results from an ongoing study of the paleomagnetic record from Fish Lake, Oregon. Initial evaluation of directions and intensity along with the construction of an independent chronology allow us to assess and build upon prior results to constrain the evolution of the North American flux lobe and refine our understanding of paleo-geomagnetic change during the Holocene.

  6. Late Weichselian to Holocene paleoenvironments in the Barents Sea

    NASA Astrophysics Data System (ADS)

    Ivanova, Elena V.; Murdmaa, Ivar O.; Duplessy, Jean-Claude; Paterne, Martine

    2002-11-01

    Paleoceanographic changes since the Late Weichselian have been studied in three sediment cores raised from shelf depressions along a north-south transect across the central Barents Sea. AMS radiocarbon dating offers a resolution of several hundred years for the Holocene. The results of lithological and micropaleontological study reveal the response of the Barents Sea to global climatic changes and Atlantic water inflow. Four evolutionary stages were distinguished. The older sediments are moraine deposits. The destruction of the Barents Sea ice sheet during the beginning of the deglaciation in response to climate warming and sea level rise resulted in proximal glaciomarine sedimentation. Then, the retreat of the glacier front to archipelagoes during the main phase of deglaciation caused meltwater discharge and restricted iceberg calving. Fine-grained distal glaciomarine sediments were deposited from periodic near-bottom nepheloid flows and the area was almost permanently covered with sea ice. The dramatic change in paleoenvironment occurred near the Pleistocene/Holocene boundary when normal marine conditions ultimately established resulting in a sharp increase of biological productivity. This event was diachronous and started prior to 10 14C ka BP in the southern and about 9.2 14C ka in the northern Barents Sea. Variations in sediment supply, paleoproductivity, sea-ice conditions, and Atlantic water inflow controlled paleoenvironmental changes during the Holocene.

  7. Early Holocene glaciation on Mount Baker, Washington State, USA

    NASA Astrophysics Data System (ADS)

    Thomas, Paul A.; Easterbrook, Don J.; Clark, Peter U.

    2000-07-01

    The relation between radiocarbon-dated tephras and glacial moraines on the south flank of Mount Baker, Washington, records evidence of an early Holocene glacier advance. Scoria that erupted from a local cinder cone 8420±70 14C yr BP (9450±100 cal yr) occurs immediately in front of, but not on, a complex of moraines overlain by Mazama ash. Radiocarbon ages of 7670±130 14C yr BP (8415±110 cal yr) and 7045±65 14C yr BP (7890±90 cal yr) were obtained from charred wood below the Mazama ash and above till of the moraines, bracketing the age of the glacial advance between ˜7700 and 8400 14C yr BP (˜8400 and 9450 cal yr). Well-preserved Little Ice Age moraines occur proximal to the maximum Holocene positions. Assuming that precipitation regimes were similar, depression of former equilibrium line altitudes suggests that climate during the early Holocene event was at most ˜2°C cooler than present, and ˜0.5°C cooler than the Little Ice Age.

  8. A new method for the determination of Holocene palaeohydrology

    NASA Astrophysics Data System (ADS)

    Wade, A. J.; Smith, S. J.; Black, E. C. L.; Brayshaw, D. J.; Holmes, P. A. C.; El-Bastawesy, M.; Rambeau, C. M. C.; Mithen, S. J.

    2012-02-01

    SummaryThis paper describes a new method for the assessment of palaeohydrology through the Holocene. A palaeoclimate model was linked with a hydrological model, using a weather generator to correct bias in the rainfall estimates, to simulate the changes in the flood frequency and the groundwater response through the late Pleistocene and Holocene for the Wadi Faynan in southern Jordan, a site considered internationally important due to its rich archaeological heritage spanning the Pleistocene and Holocene. This is the first study to describe the hydrological functioning of the Wadi Faynan, a meso-scale (241 km 2) semi-arid catchment, setting this description within the framework of contemporary archaeological investigations. Historic meteorological records were collated and supplemented with new hydrological and water quality data. The modelled outcomes indicate that environmental changes, such as deforestation, had a major impact on the local water cycle and this amplified the effect of the prevailing climate on the flow regime. The results also show that increased rainfall alone does not necessarily imply better conditions for farming and highlight the importance of groundwater. The discussion focuses on the utility of the method and the importance of the local hydrology to the sustained settlement of the Wadi Faynan through pre-history and history.

  9. Late Weichselian and Holocene paleoceanography of Storfjordrenna, southern Svalbard

    NASA Astrophysics Data System (ADS)

    Łącka, M.; Zajączkowski, M.; Forwick, M.; Szczuciński, W.

    2014-08-01

    Multiproxy analyses (incl. benthic and planktonic foraminifera, δ18O and δ13C records, grain-size distribution, ice-rafted debris, XRF geochemistry and magnetic susceptibility) were performed on a 14C dated marine sediment core from Storfjordrenna, off southern Svalbard. The sediments in the core cover the termination of Bølling-Allerød, the Younger Dryas and the Holocene, and they reflect general changes in the hydrology/climate of the European Arctic after the last glaciation. Grounded ice of the last Svalbard- Barents Sea Ice Sheet retreated from the coring site ca. 13 850 cal yr BP. During the transition from the sub-glacial to glacimarine setting, Arctic Waters dominated the hydrography in Storfjordrenna. However, the waters were not uniformly cold and experienced several warmer spells. A progressive warming and marked change in the nature of hydrology occurred during the early Holocene. Relatively warm and saline Atlantic Water started to dominate the hydrography from approx. 9500 cal yr BP. Even though the climate in eastern Svalbard was milder at that time than at present (smaller glaciers), there were two slight coolings observed in the periods of 9000-8000 cal yr BP and 6000-5500 cal yr BP. A change of the Storfjordrenna hydrology occurred at the beginning of late Holocene synchronously with glacier growth on land and enhanced bottom current velocities. Although cooling was observed in the surface water, Atlantic Water remained present in the deeper part of water column of Storfjordrenna.

  10. Effects of Two Football Stud Types on Knee and Ankle Kinetics of Single-Leg Land-Cut and 180° Cut Movements on Infilled Synthetic Turf.

    PubMed

    Bennett, Hunter J; Brock, Elizabeth; Brosnan, James T; Sorochan, John C; Zhang, Songning

    2015-10-01

    Higher ACL injury rates have been recorded in cleats with higher torsional resistance in American football, which warrants better understanding of shoe/stud-dependent joint kinetics. The purpose of this study was to determine differences in knee and ankle kinetics during single-leg land cuts and 180° cuts on synthetic infilled turf while wearing 3 types of shoes. Fourteen recreational football players performed single-leg land cuts and 180° cuts in nonstudded running shoes (RS) and in football shoes with natural (NTS) and synthetic turf studs (STS). Knee and ankle kinetic variables were analyzed with a 3 × 2 (shoe × movement) repeated-measures ANOVA (P < .05). A significant shoe-by-movement interaction was found in loading response peak knee adduction moments, with NTS producing smaller moments compared with both STS and RS only in 180° cuts. Reduced peak negative plantar flexor powers were also found in NTS compared with STS. The single-leg land cut produced greater loading response and push-off peak knee extensor moments, as well as peak negative and positive extensor and plantar flexor powers, but smaller loading peak knee adduction moments and push-off peak ankle eversion moments than 180° cuts. Overall, the STS and 180° cuts resulted in greater frontal plane knee loading and should be monitored for possible increased ACL injury risks.

  11. The mechanics of American football cleats on natural grass and infill-type artificial playing surfaces with loads relevant to elite athletes.

    PubMed

    Kent, Richard; Forman, Jason L; Lessley, David; Crandall, Jeff

    2015-06-01

    This study quantified the mechanical interactions of 19 American football cleats with a natural grass and an infill-type artificial surface under loading conditions designed to represent play-relevant manoeuvres of elite athletes. Variation in peak forces and torques was observed across cleats when tested on natural grass (2.8-4.2 kN in translation, 120-174 Nm in rotation). A significant (p < 0.05) relationship was found between the peak force and torque on natural grass. Almost all of the cleats caused shear failure of the natural surface, which generated a divot following a test. This is a force-limiting cleat release mode. In contrast, all but one of the cleat types held fast in the artificial turf, resulting in force and torque limited by the prescribed input load from the test device (nom. 4.8 kN and 200 Nm). Only one cleat pattern, consisting of small deformable nubs, released on the artificial surface and generated force (3.9 kN) comparable to the range observed with natural grass. These findings (1) should inform the design of cleats intended for use on natural and artificial surfaces and (2) suggest a mechanical explanation for a higher lower-limb injury rate in elite athletes playing on artificial surfaces.

  12. Tectono-sedimentary evolution of southern part of Benue Trough: from an asymmetric basin in middle Albian to an infilled basin in mid-Cenomanian

    SciTech Connect

    Ojoh, K.A.; Popoff, M.

    1989-03-01

    Before the opening of the Equatorial domain of the South Atlantic, the initiation and installation of most intracontinental basins within Gondwanaland took place before the Albian in northeastern Brazil and west Africa. The first pronounced marine incursion in the southern part of the Benue Trough was in the middle Albian. Subsidence was localized in the deep asymmetrical middle Albian basin. The latter, combined with a lowstand marine ingression in the southern Benue Trough and the progressive rifting-drifting of Africa and South America, engendered an unstable, tectonically active, over-supplied basin characterized by megaslumps and turbidites. During the late Albian, differential subsidence installed a stable platform with organic-rich fossiliferous black shales and littoral deposits contemporaneous with a highstand of sea level and the interconnection of the Central and South Atlantic oceans in the proto Gulf of Guinea. Volcanosedimentary tendencies have been documented from the littoral deposits, and pyroclastics containing molluscan fragments in the southern Benue Trough have also been attributed to the upper Albian. The high rate of subsidence during the Albian became very slow in the Cenomanian. It corresponds to a period of eustatic fall of sea level during the early and middle Cenomanian with high clastic influx into the basin. The middle Cenomanian is characterized as the period of an infilled basin with subaerial-submarine erosional surface (unconformity type 2) in the southern Benue Trough. This may be attributed to the global character of the Cenomanian lowstand of sea level.

  13. Takarkori rock shelter (SW Libya): an archive of Holocene climate and environmental changes in the central Sahara

    NASA Astrophysics Data System (ADS)

    Cremaschi, Mauro; Zerboni, Andrea; Mercuri, Anna Maria; Olmi, Linda; Biagetti, Stefano; di Lernia, Savino

    2014-10-01

    Rock shelters in the central Saharan massifs preserve anthropogenic stratigraphic sequences that represent both a precious archive for the prehistory of the region and a powerful proxy data for Holocene palaeoenvironments. The geoarchaeological (micromorphology) and archaeobotanical (pollen analysis) approaches were integrated to investigate the anthropogenic sedimentary sequence preserved within the Takarkori rock shelter, a Holocene archaeological site located in the Libyan central Sahara (southern Tadrart Acacus massif). The site was occupied throughout the Early and Middle Holocene (African Humid Period) by groups of hunter-gatherers before and by pastoral communities later. The investigation on the inner part of the sequence allows to recognize the anthropogenic contribution to sedimentation process, and to reconstruct the major changes in the Holocene climate. At the bottom of the stratigraphic sequence, evidence for the earliest frequentation of the site by hunters and gatherers has been recognized; it is dated to c. 10,170 cal yr BP and is characterized by high availability of water, freshwater habitats and sparsely wooded savannah vegetation. A second Early Holocene occupation ended at c. 8180 cal yr BP; this phase is marked by increased aridity: sediments progressively richer in organics, testifying to a more intense occupation of the site, and pollen spectra indicating a decrease of grassland and the spreading of cattails, which followed a general lowering of lake level or widening of shallow-water marginal habitats near the site. After this period, a new occupational phase is dated between c. 8180 and 5610 cal yr BP; this period saw the beginning of the frequentation of pastoral groups and is marked by an important change in the forming processes of the sequence. Sediments and pollen spectra confirm a new increase in water availability, which led to a change in the landscape surrounding the Takarkori rock shelter with the spreading of water bodies. The

  14. Late Pleistocene and Holocene Fire History of the California Islands

    NASA Astrophysics Data System (ADS)

    Scott, A. C.; Hardiman, M.; Pinter, N.; Anderson, R.

    2013-12-01

    Charcoal has been recovered from a range of late Pleistocene and Holocene sites on Santa Cruz Island and Santa Rosa Island, both islands part of California's Northern Channel Islands, U.S.A. Sediments have been dated using radiocarbon measurements based on wood charcoal, fungal sclerotia, glassy carbon and fecal pellets and are given as calendar years BP. This charcoal has been used to interpret the fire history of the Islands. Charcoal assemblages from samples dating from 24,690 to 12,900 years are dominated by coniferous wood charcoal. Little angiosperm charcoal was recovered in any of the samples. Fungal sclerotia are frequent in a number of samples from a range of ages both on Santa Cruz and Santa Rosa. Fecal pellets are common in most samples and abundant in others. Some of the fecal pellets have hexagonal sides and are likely to represent termite frass. The sediments are fluvial in origin and the distribution of charcoal is irregular making interpretation of fire return intervals and fire frequency difficult. The charcoal indicates a significant record of fire before the earliest documented human arrival on the islands. Charcoal reflectance data shows the occurrence of predominantly low temperature charcoals suggesting common surface fires in the coniferous forest. Soledad Pond sediments from Santa Rosa Island (Anderson et al., 2010) dating from 11,800 cal years BP show a distinctively different vegetation dominated by angiosperms and showing a very different fire history. Pinus stands, coastal sage scrub dominated by Baccharis sp. and grassland replaced the conifer forest as the climate warmed. The early Holocene became increasingly drier, particularly after ca. 9150 cal yr BP. By ca. 6900 cal yr BP grasslands recovered. Introduction of non-native species by ranchers occurred subsequent to AD 1850. Charcoal influx is high early in the Soledad Pond record, but declines during the early Holocene when minimal biomass suggests extended drought. A general

  15. Lacustrine Records of Holocene Mountain Glacier Fluctuations from Western Greenland

    NASA Astrophysics Data System (ADS)

    Schweinsberg, A.; Briner, J. P.; Bennike, O.

    2014-12-01

    Recent studies have focused on documenting fluctuations of the Greenland Ice Sheet margin throughout the Holocene but few data exist that constrain past changes of local glaciers independent of the ice sheet. Our research combines proglacial lake sediment analysis with cosmogenic 10Be dating of Holocene moraines and radiocarbon dating of ice-cap-killed vegetation with an overall objective to use this multi-proxy approach to generate a detailed record of the coupled climate-glacier system through the Holocene. Here, we present lacustrine records of mountain glacier variability from continuous pro-glacial lake sediment sequences recovered from two glaciated catchments in northeastern Nuussuaq, western Greenland. We use radiocarbon-dated sediments from Sikuiui and Pauiaivik lakes to reconstruct the timing of advance and retreat of local glaciers. Sediments were characterized with magnetic susceptibility (MS), gamma density, Itrax XRF and visible reflectance spectroscopy at 0.2 cm intervals and sediment organic matter at 0.5 cm intervals. Basal radiocarbon ages provide minimum-age constraints on deglaciation from Sikuiui and Pauiaivik lakes of ~9.6 and 8.7 ka, respectively. Organic-rich gyttja from deglaciation until ~5.0 ka in Pauiaivik Lake suggests minimal glacial extent there while slightly elevated MS values from ~9.0 - 7.0 ka in Sikuiui Lake may reflect early Holocene glacial advances. Minerogenic sediment input gradually increases starting at ~5.0 ka in Pauiaivik Lake, which we interpret as the onset of Neoglaciation in the catchment. Furthermore, a distinct episode of enhanced glacial activity from ~4.0 - 2.2 ka in Sikuiui Lake may be correlative to a period of persistent snowline lowering evidenced by radiocarbon dates of ice-killed vegetation from nearby ice cap margins. Results from these lacustrine records and our ice-killed vegetation dataset suggest a middle Holocene onset of Neoglaciation ~5.0 - 4.0 ka in this region. We are supplementing these records

  16. Holocene glacier activity in the British Columbia Coast Mountains, Canada

    NASA Astrophysics Data System (ADS)

    Mood, Bryan J.; Smith, Dan J.

    2015-11-01

    The Coast Mountains flank the Pacific Ocean in western British Columbia, Canada. Subdivided into the southern Pacific Ranges, central Kitimat Ranges and northern Boundary Ranges, the majority of large glaciers and icefields are located in the Boundary and Pacific ranges. Prior descriptions of the Holocene glacial history of this region indicate the Holocene was characterized by repeated episodes of ice expansion and retreat. Recent site-specific investigations augment our understanding of the regional character and duration of these events. In this paper, previously reported and new radiocarbon evidence is integrated to provide an updated regional assessment. The earliest evidence of glacier expansion in the Coast Mountains comes from the Boundary Ranges at 8.9 and 7.8 ka and in the Pacific Ranges at 8.5-8.2 ka, with the latter advance corresponding to an interval of rapid, global climate deterioration. Although generally warm and dry climates from 7.3 to 5.3 ka likely limited the size of glaciers in the region, there is radiocarbon evidence for advances over the interval from 7.3 to 6.0 and at 5.4-5.3 ka in the Pacific Ranges. Following these advances, glaciers in the Pacific Ranges expanded down valley at 4.8-4.6, 4.4-4.0, 3.5-2.6, 1.4-1.2, and 0.8-0.4 ka, while glaciers in Boundary Ranges were advancing at 4.1-4.0, 3.7-3.4, 3.1-2.8, 2.3, 1.7-1.1, and 0.8-0.4 ka. After 0.4 ka, it appears that most glaciers in the Coast Mountains continued to expand to attain their maximum Holocene extents by the early 18th to late 19th centuries. This enhanced record of Holocene glacier activity highlights the temporal synchrony in the Coast Mountains. Individual expansion events in the mid-to late Holocene broadly correspond to intervals of regional glacier activity reported in the Canadian Rocky Mountains, in Alaska, and on high-elevation volcanic peaks in Washington State.

  17. A previously unrecognized path of early Holocene base flow and elevated discharge from Lake Minong to Lake Chippewa across eastern Upper Michigan

    USGS Publications Warehouse

    Loope, Walter L.; Jol, Harry M.; Fisher, Timothy G.; Blewett, William L.; Loope, Henry M.; Legg, Robert J.

    2014-01-01

    It has long been hypothesized that flux of fresh meltwater from glacial Lake Minong in North America's Superior Basin to the North Atlantic Ocean triggered rapid climatic shifts during the early Holocene. The spatial context of recent support for this idea demands a reevaluation of the exit point of meltwater from the Superior Basin. We used ground penetrating radar (GPR), foundation borings from six highway bridges, a GIS model of surface topography, geologic maps, U.S. Department of Agriculture–Natural Resources Conservation Service soils maps, and well logs to investigate the possible linkage of Lake Minong with Lake Chippewa in the Lake Michigan Basin across eastern Upper Michigan. GPR suggests that a connecting channel lies buried beneath the present interlake divide at Danaher. A single optical age hints that the channel aggraded to 225 m as elevated receipt of Lake Agassiz meltwater in the Superior Basin began to wane <10.6 ka. The large supply of sediment required to accommodate aggradation was immediately available at the channel's edge in the littoral shelves of abandoned Lake Algonquin and in distal parts of post-Algonquin fans. As discharge decreased further, the aggraded channel floor was quickly breached and interbasin flow to Lake Chippewa was restored. Basal radiocarbon ages on wood from small lakes along the discharge path and a GIS model of Minong's shoreline are consistent with another transgression of Minong after ca. 9.5 ka. At the peak of the latter transgression, the southeastern rim of the Superior Basin (Nadoway Drift Barrier) failed, ending Lake Minong. Upon Minong's final drop, aggradational sediments were deposited at Danaher, infilling the prior breach.

  18. Holocene climate variability, vegetation dynamics and fire regime in the central Pyrenees: the Basa de la Mora sequence (NE Spain)

    NASA Astrophysics Data System (ADS)

    Pérez-Sanz, A.; González-Sampériz, P.; Moreno, A.; Valero-Garcés, B.; Gil-Romera, G.; Rieradevall, M.; Tarrats, P.; Lasheras-Álvarez, L.; Morellón, M.; Belmonte, A.; Sancho, C.; Sevilla-Callejo, M.; Navas, A.

    2013-08-01

    High resolution multiproxy data (pollen, sedimentology, geochemistry, chironomids and charcoal) from the Basa de la Mora (BSM) lake sequence (42° 32' N, 0° 19' E, 1914 m a.s.l.) show marked climate variability in the central southern Pyrenees throughout the Holocene. A robust age model based on 15 AMS radiocarbon dates underpins the first precise reconstruction of rapid climate changes during the Holocene from this area. During the Early Holocene, increased winter snowpack and high snowmelt during summer, as a consequence of high seasonality, led to higher lake levels, a chironomid community dominated by non-lacustrine taxa (Orthocladiinae) related to higher inlet streams, and a forested landscape with intense run-off processes in the watershed. From 9.8 to 8.1 cal ka BP, climate instability is inferred from rapid and intense forest shifts and high fluctuation in surface run-off. Shifts among conifers and mesophytes reveal at least four short-lived dry events at 9.7, 9.3, 8.8 and 8.3 cal ka BP. Between 8.1 and 5.7 cal ka BP a stable climate with higher precipitation favoured highest lake levels and forest expansion, with spread of mesophytes, withdrawal of conifers and intensification of fires, coinciding with the Holocene Climate Optimum. At 5.7 cal ka BP a major change leading to drier conditions contributed to a regional decline in mesophytes, expansion of pines and junipers, and a significant lake level drop. Despite drier conditions, fire activity dropped as consequence of biomass reduction. Two arid intervals occurred between 2.9 and 2.4 cal ka BP and at 1.2-0.7 cal ka BP (800-1300 AD). The latter coincides with the Medieval Climate Anomaly and is one of the most arid phases of the Holocene in BSM sequence. Anthropogenic disturbances were small until 700 AD, when human pressure over landscape intensified, with Olea cultivation in the lowlands and significant deforestation in highlands. Colder and unfavourable weather conditions during the second part of the

  19. Postglacial development of the eastern Gulf of Finland: from Pleistocene glacial lake basins to Holocene lagoon systems

    NASA Astrophysics Data System (ADS)

    Ryabchuk, Daria; Sergeev, Alexander; Kotilainen, Aarno; Hyttinen, Outi; Grigoriev, Andrey; Gerasimov, Dmitry; Anisimov, Mikhail; Gusentsova, Tatiana; Zhamoida, Vladimir; Amantov, Aleksey; Budanov, Leonid

    2016-04-01

    Despite significant amount of data, there are still lots of debatable questions and unsolved problems concerning postglacial geological history of the Eastern Gulf of Finland, the Baltic Sea. Among these problems are: 1) locations of the end moraine and glacio-fluvial deposits; 2) time and genesis of the large accretion forms (spits, bars, dunes); 3) basinwide correlations of trangression/regression culminations with the other parts of the Baltic Sea basin; 4) study of salinity, timing, frequency and intensity of Holocene saline water inflows and their links of sedimentation processes associated with climate change. Aiming to receive new data about regional postglacial development, the GIS analyses of bottom relief and available geological and geophysical data was undertaken, the maps of preQuaternary relief, moraine and Late Pleistocene surfaces, glacial moraine and Holocene sediments thicknesses were compiled. High-resolution sediment proxy study of several cores, taken from eastern Gulf of Finland bottom, allows to study grain-size distribution and geochemical features of glacial lake and Holocene sediments, to reveal sedimentation rates and paleoenvironment features of postglacial basins. Interdisciplinary geoarcheological approaches offer new opportunities for studying the region's geological history and paleogeography. Based on proxy marine geological and coastal geoarcheological studies (e.g. off-shore acoustic survey, side-scan profiling and sediment sampling, on-shore ground-penetrating radar (GPR SIR 2000), leveling, drilling, grain-size analyses and radiocarbon dating and archeological research) detailed paleogeographical reconstruction for three micro-regions - Sestroretsky and Lahta Lowlands, Narva-Luga Klint Bay and Southern Ladoga - were compiled. As a result, new high resolution models of Holocene geological development of the Eastern Gulf of Finland were received. Model calibration and verification used results from proxy geoarcheological research

  20. Holocene fluctuations of Bregne ice cap, Scoresby Sund, eastern Greenland

    NASA Astrophysics Data System (ADS)

    Levy, L.; Kelly, M. A.; Lowell, T. V.; Hall, B. L.

    2011-12-01

    The Arctic cryosphere is responding rapidly to modern global warming. Documenting past changes in the Arctic cryosphere, particularly during times of warmer than present conditions such as the Holocene Thermal Maximum (HTM; 9,000-5,000 yr BP) provides an important background against which the present response and potential for future changes can be compared. Small ice caps located adjacent to the Greenland Ice Sheet respond sensitively to climate change and their past extents provide a proxy for the climatic conditions that have influenced the ice sheet margin. In order to document cryosphere and climatic changes during warmer conditions, we are constructing records of Holocene fluctuations of small ice caps in the Scoresby Sund region of eastern Greenland (71° N, 25.6° W). We use geomorphic mapping, lake sediment records, radiocarbon, and surface exposure (10Be) dating to reconstruct past ice extents. Lake sediment records are from both glacially fed (i.e., threshold) lakes and lakes with no glacial input during the time of interest (i.e., control). Here we present a record of the Holocene extents of Bregne ice cap, Milne Land, western Scoresby Sund, ~50 km southeast of Renland ice cap. Sediments from Two Move Lake (TML), a threshold lake, register the entire Holocene in a thickness of ~70 cm. Radiocarbon dates of lake sediments indicate that the onset of organic accumulation in the lake following the Last Glacial Maximum occurred 8,890±120 cal yr BP. The mid-Holocene is characterized by organic rich mud that is finely laminated in some sections. The onset of Neoglaciation (cooling after HTM) occurs at 2,810±50 cal yr BP and finely laminated sediments during Neoglaciation may register annual deposition. The sediment record from Last Chance Lake, a control lake located 0.5 km from TML, indicates that there has been no glacial input since deglaciation from the Last Glacial Maximum. Unweathered moraines occur <0.5 km from the modern ice cap margin, inboard from

  1. Holocene Scarp on the Sawtooth Normal Fault, Central Idaho

    NASA Astrophysics Data System (ADS)

    Thackray, G. D.; Rodgers, D. W.; Streutker, D. R.; Kemp, C. D.; Drabick, A. J.

    2006-12-01

    Analysis of LiDAR, air photo, and field data indicates the east-dipping, range-front normal fault of the Sawtooth Mountains has previously unrecognized Holocene offset. A fault scarp is most clearly represented in a bare- earth digital elevation model (DEM) derived from high-resolution LiDAR data. First and last pulse LiDAR data with an average post spacing of 0.5 m were used to compute both bare-earth elevation and local slope values. As the area is forested, vegetation removal was performed using an iterative interpolation method. Holocene fault offset likely extends along at least 23 km of the range front. In the vicinity of Redfish Lake, the scarp can be traced discontinuously for ca. 13 km (the length of LiDAR coverage) along the eastern range-front and cuts glacial, fluvial, and hillslope landforms of Late Pleistocene to Holocene age. Air photo analysis of the range-front north and south of the LiDAR coverage area yields strong evidence, such as topographic offsets, vegetation lineaments, and stream alignments, that late Pleistocene and Holocene faulting likely extends ca. 23 km along the range front, from Decker Creek to Stanley Lake. This zone of clearest postglacial offset corresponds with the highest range front topography in the Sawtooth Range. Weaker evidence suggests that postglacial faulting may extend as much as 10 km further NW of and 17 km further SE of that 23 km section. Scarp geometry and offset vary with location. The fault scarp generally strikes 025 deg. but changes to 040 deg. north of Goat Creek. A single, east-facing scarp is present in some places, such as at Bench Lakes, but more commonly en echelon scarps define a fault zone about 20 m wide. Scarp height, as measured from LiDAR data, ranges from 2.5 to 8 m (typically 3-5 m). Late Pleistocene glacial landforms are offset 4-8 m, while uncommon Holocene fluvial surfaces (e.g., at Fishhook Creek) are offset 2.5 to 3 m. These relationships potentially document two fault ruptures since

  2. Charcoal and the Record of Fire-related Sedimentation in Holocene Alluvial Sediments

    NASA Astrophysics Data System (ADS)

    Meyer, G. A.

    2006-12-01

    Over the last few decades, rising temperatures and ensuing severe wildfires in the western USA cordillera have provided the opportunity to examine processes and deposits of postfire sedimentation on alluvial fans and floodplains. Most events are generated by widespread surface runoff from intense convective-storm precipitation on severely burned slopes. Flow processes range from debris flow to sediment-charged water floods. Muddy debris flows best preserve coarse charcoal in fan deposits, whereas gravelly debris flows often comminute charcoal into fine particles. As charcoal remains suspended in high-energy hyperconcentrated and water floods, only their fine-grained deposits typically contain much charcoal. Charcoal is locally concentrated in low-energy fluvial deposits, but displays increasing evidence for reworking with distance from source. Charred vegetation and litter marking burned soil surfaces may be preserved under postfire fan and fluvial sediments. Modern deposits provide models for identification of Holocene fire-related sediments and estimates of paleofire severity. AMS 14C dating of discrete charcoal fragments allows sample selection to minimize errors of sample age > fire age. Fires are incompletely recorded in the event stratigraphy of one fan, but larger populations of 14C ages from numerous fans permit composite probability distributions that represent centennial- to millennial-scale changes in fire-related sedimentation across a study area. Records from Yellowstone and central Idaho indicate the large role of fire in episodic erosion across a range of conifer forests, most strongly during severe, multidecadal droughts in warmer periods (e.g. in Medieval time 900-1300 AD). In central Idaho, identification of charcoal macrofossils indicates broadly similar, aspect-controlled forest compositions over the last 3000 yr. Emerging data from the Sacramento Mountains, New Mexico, show rapid fan aggradation due to fire-related events in the warm middle

  3. Spatial and temporal variability of late Holocene sea-level changes in the North Atlantic (Invited)

    NASA Astrophysics Data System (ADS)

    Kemp, A.; Kopp, R. E.; Horton, B.; Cahill, N.

    2013-12-01

    Proxy sea-level reconstructions spanning the last ~2000 years capture multiple phases of climate and sea level behavior for model calibration, provide a pre-anthropogenic background against which to compare recent trends, and characterize patterns of natural spatial and temporal variability. In the western North Atlantic basin, salt-marsh sediment is an archive for reconstructing sea level with the decimeter and multi-decadal resolution necessary to characterize subtle changes. New and existing salt-marsh reconstructions from northern Florida, North Carolina, New Jersey, Connecticut, and Massachusetts provide a dataset for investigating spatial and temporal sea-level variability during the late Holocene. The reconstructions were developed using foraminifera, plants, and bulk sediment δ13C values as sea-level proxies. The age of sediment deposition was estimated from composite chronologies of radiocarbon and chronohorizons of regional pollution and land-use change that were combined in age depth models. We used a spatio-temporal Gaussian process model to identify and characterize persistent phases of sea level behavior during the late Holocene in the western North Atlantic Ocean. The results indicate an acceleration in global mean sea level from the early 19th century through the early 20th century. The rate of sea-level rise increased significantly in the late 19th century. The timing and magnitude of this rise varied among sites even after accounting for differences in glacio-isostatic adjustment. Sea level in North Carolina rose faster than in New Jersey sea-level during the Medieval Climate Optimum, while sea level in New Jersey rose faster during the Little Ice Age. Spatially variable sea-level rise on the Atlantic coast of North America can be caused by dynamic oceanographic processes and/or melting of the Greenland Ice Sheet. Our analysis suggests that plausible levels of meltwater input from Greenland would be inadequate to explain the reconstructed pattern

  4. Holocene sediment distribution on the inner continental shelf of northeastern South Carolina: implications for the regional sediment budget and long-term shoreline response

    USGS Publications Warehouse

    Denny, Jane F.; Schwab, William C.; Baldwin, Wayne E.; Barnhardt, Walter A.; Gayes, Paul T.; Morton, R.A.; Warner, John C.; Driscoll, Neal W.; Voulgaris, George

    2013-01-01

    High-resolution geophysical and sediment sampling surveys were conducted offshore of the Grand Strand, South Carolina to define the shallow geologic framework of the inner shelf. Results are used to identify and map Holocene sediment deposits, infer sediment transport pathways, and discuss implications for the regional coastal sediment budget. The thickest deposits of Holocene sediment observed on the inner shelf form shoal complexes composed of moderately sorted fine sand, which are primarily located offshore of modern tidal inlets. These shoal deposits contain ~67 M m3 of sediment, approximately 96% of Holocene sediment stored on the inner shelf. Due to the lack of any significant modern fluvial input of sand to the region, the Holocene deposits are likely derived from reworking of relict Pleistocene and older inner-shelf deposits during the Holocene marine transgression. The Holocene sediments are concentrated in the southern part of the study area, due to a combination of ancestral drainage patterns, a regional shift in sediment supply from the northeast to the southwest in the late Pleistocene, and proximity to modern inlet systems. Where sediment is limited, only small, low relief ridges have formed and Pleistocene and older deposits are exposed on the seafloor. The low-relief ridges are likely the result of a thin, mobile veneer of sediment being transported across an irregular, erosional surface formed during the last transgression. Sediment textural trends and seafloor morphology indicate a long-term net transport of sediment to the southwest. This is supported by oceanographic studies that suggest the long-term sediment transport direction is controlled by the frequency and intensity of storms that pass through the region, where low pressure systems yield net along-shore flow to the southwest and a weak onshore component. Current sediment budget estimates for the Grand Strand yield a deficit for the region. Volume calculations of Holocene deposits on the

  5. Late Holocene environmental change in the coastal southern Somalia inferred from Achatina and rhizoliths

    NASA Astrophysics Data System (ADS)

    Matteucci, R.; Belluomini, G.; Manfra, L.

    2007-10-01

    Surfaces of poorly cemented carbonate dunes of the coast of southern Somalia contain as exhumed bodies treelet rhizoliths and subfossil shells of the giant land snail Achatina. Present-day coastal dunes in southern Somalia are poorly vegetated and do not support living Achatinas. Thus, the presence of these subfossils provides evidence for a more humid period in the past: the subfossil giant land snails and the rhizoliths indicate a palaeoenvironment which was probably similar to the modern environment of the coastal belt of Kenya and of the southernmost corner of coastal Somalia, where living Achatinas are frequent and the forest-savannah mosaic vegetation type [Bonnefille, R., 1985. Evolution of the continental vegetation: the palaeobotanical record from East Africa. South African Journal of Science 81, 267-270] is widespread. According to radiometric ages of Achatina shells and geological observations, aridification process probably took place in the Late Holocene. Somali data are consistent with the known regional climatic trends.

  6. Mid-Holocene Climate and Culture Change in the Atacama Desert, Northern Chile

    NASA Astrophysics Data System (ADS)

    Grosjean, Martin; Núñez, Lautaro; Cartajena, Isabel; Messerli, Bruno

    1997-09-01

    Twenty archaeological campsites intercalated between more than 30 debris flows caused by heavy rainfall events between 6200 and 3100 14C yr B.P. have recently been discovered at Quebrada Puripica in the Atacama Desert of northern Chile. This record provides detailed information about extreme, short-lived climatic events during the hyperarid mid-Holocene period. For the first time, we found evidence of continuous human occupation in this area, filling the regional hiatus in the Atacama basin ("Silencio Arqueologico") between 8000 and 4800 14C yr B.P. The transformation of Early Archaic hunters into the complex Late Archaic cultural tradition was an adaptive process. During this time, the site was a local ecological refuge with abundant resources in a generally hostile environment.

  7. Sediment infill within rift basins: Facies distribution and effects of deformation: Examples from the Kenya and Tanganyika Rifts, East Africa

    SciTech Connect

    Tiercelin, J.J.; Lezzar, K.E. ); Richert, J.P. )

    1994-07-01

    Oil is known from lacustrine basins of the east African rift. The geology of such basins is complex and different depending on location in the eastern and western branches. The western branch has little volcanism, leading to long-lived basins, such as Lake Tanganyika, whereas a large quantity of volcanics results in the eastern branch characterized by ephemeral basins, as the Baringo-Bogoria basin in Kenya. The Baringo-Bogoria basin is a north-south half graben formed in the middle Pleistocene and presently occupied by the hypersaline Lake Bogoria and the freshwater Lake Baringo. Lake Bogoria is fed by hot springs and ephemeral streams controlled by grid faults bounding the basin to the west. The sedimentary fill is formed by cycles of organic oozes having a good petroleum potential and evaporites. On the other hand, and as a consequence of the grid faults, Lake Baringo is fed by permanent streams bringing into the basin large quantities of terrigenous sediments. Lake Tanganyika is a meromictic lake 1470 m deep and 700 km long, of middle Miocene age. It is subdivided into seven asymmetric half grabens separated by transverse ridges. The sedimentary fill is thick and formed by organic oozes having a very good petroleum potential. In contrast to Bogoria, the lateral distribution of organic matter is characterized by considerable heterogeneity due to the existence of structural blocks or to redepositional processes.

  8. New Whole-House Solutions Case Study: Affordable Cold Climate Infill Housing with Hybrid Insulation Approach, Wyandotte, Michigan

    SciTech Connect

    2013-11-01

    Even builders who are relatively new to energy-efficient construction can consistently reach a target whole house airtightness of 1.5 air changes per hour at 50 Pascals (ACH50) with high R-value enclosures that use a hybrid insulation approach. In 2010, the City of Wyandotte, Michigan, started construction to build affordable, energy-efficient homes on lots in existing neighborhoods. A goal was to engage local builders in energy-efficient construction and be able to deliver the new houses for less than $100/ft2. By the end of 2012, approximately 25 new houses were built by five local builders under this program. To help builders consistently achieve the airtightness target, a local architect worked with researchers from Building Science Corporation, a Building America team, to develop a technology specification with several key pieces. A high R-value wall and roof assembly made use of 2 ×6 advanced framing and a hybrid insulation approach that included insulating sheathing to control thermal bridging and closed cell spray polyurethane foam insulation (ccSPF) for its airtightness and vapor control benefits. This approach allows the air barrier to be completed and tested before any finishing work occurs, ensuring that problems are spotted and corrected early in the construction process.

  9. Paleoclimatic and Paleoceanographic Holocene Sedimentary Records in the Gulf of California - Eastern Pacific Ocean Interhemispheric Connections

    NASA Astrophysics Data System (ADS)

    Perez-Cruz, L.; Urrutia-Fucugauchi, J.

    2009-05-01

    Initial results of a study on the distribution, thickness and stratigraphy of the sedimentary sequences in the Gulf of California are presented. The Gulf is an elongated narrow young oceanic basin bordered by the Baja California peninsula and mainland Mexico. The Gulf extends over 1200 km across the Tropic of Cancer from the tropical to the temperate zones, surrounded by arid and semi-arid regions, including the Sonora-Mojave Desert. Paleoceanographic conditions are dominated by water exchange at the Gulf mouth and water masses changes along the Gulf. Tectonic basins reach down in excess of 3000 m depths and get shallower to the north. Here we focus on the Holocene sediment sequences in the southern sector, which contains several marginal and central anoxic basins that constitute rich archives of paleoclimatic and paleoenvironmental evolution for the past 3.6 Ma. In the mouth area, main sources of sediments are silicic volcanic and intrusive rocks in the Baja peninsula and mainland, including Los Cabos and Puerto Vallarta batholiths. Fine-grained eolian dusts, pluvial and biogenic sediments are present in the sediment cores in the Gulf basins such as La Paz, Alfonso, Carmen, Pescadero and Guaymas basins. Turbiditic currents and tephra deposits also occur in the cores. Paleoclimatic records show the influences of regional processes, including the ENSO and PDO signals marked by drought and increased precipitation phases. Relative distribution and thickness of sediments at the mouth of the Gulf correlate with bathymetry and location with respect to spreading center, transform faults and margins of the peninsula and mainland Mexico. Rock magnetic core scans and mineralogy at few locations are available, which allow inferences on sediment sources, transport and deposition processes, diagenesis, paleoceanographic and paleoclimatic evolution for the Holocene.

  10. ‘Cape capture’: Geologic data and modeling results suggest the Holocene loss of a Carolina Cape

    USGS Publications Warehouse

    Thieler, E. Robert; Ashton, Andrew D.

    2011-01-01

    For more than a century, the origin and evolution of the set of cuspate forelands known as the Carolina Capes—Hatteras, Lookout, Fear, and Romain—off the eastern coast of the United States have been discussed and debated. The consensus conceptual model is not only that these capes existed through much or all of the Holocene transgression, but also that their number has not changed. Here we describe bathymetric, lithologic, seismic, and chronologic data that suggest another cape may have existed between Capes Hatteras and Lookout during the early to middle Holocene. This cape likely formed at the distal end of the Neuse-Tar-Pamlico fluvial system during the early Holocene transgression, when this portion of the shelf was flooded ca. 9 cal (calibrated) kyr B.P., and was probably abandoned by ca. 4 cal kyr B.P., when the shoreline attained its present general configuration. Previously proposed mechanisms for cape formation suggest that the large-scale, rhythmic pattern of the Carolina Capes arose from a hydrodynamic template or the preexisting geologic framework. Numerical modeling, however, suggests that the number and spacing of capes can be dynamic, and that a coast can self-organize in response to a high-angle-wave instability in shoreline shape. In shoreline evolution model simulations, smaller cuspate forelands are subsumed by larger neighbors over millennial time scales through a process of ‘cape capture.’ The suggested former cape in Raleigh Bay represents the first interpreted geological evidence of dynamic abandonment suggested by the self-organization hypothesis. Cape capture may be a widespread process in coastal environments with large-scale rhythmic shoreline features; its preservation in the sedimentary record will vary according to geologic setting, physical processes, and sea-level history.

  11. In-filled reservoirs serving as sediment archives to analyse soil organic carbon erosion - Taking a closer look at the Karoo rangelands

    NASA Astrophysics Data System (ADS)

    Krenz, Juliane; Greenwood, Philip; Kuhn, Brigitte; Heckrath, Goswin; Foster, Ian; Boardman, John; Meadows, Michael; Kuhn, Nikolaus

    2016-04-01

    The semi-arid rangelands of the Great Karoo region in South Africa, which are nowadays characterized by badlands on the foot slopes of upland areas and complex gully systems in valley bottoms, have experienced a number of environmental changes. With the settlement of European farmers in the late 18th century agricultural activities increased, leading to overgrazing which probably acted as a trigger to land degradation. As a consequence of higher water demands and shifting rainfall patterns, many dams and small reservoirs have been constructed to provide drinking water for cattle or to facilitate irrigation during dry periods. Most of these dams are now filled with sediment and many have become breached, revealing sediment archives that can be used to analyse land use changes as well as carbon erosion and deposition during the last ca. 100 years. In this ongoing project, a combination of analytical methods that include drone imagery, landscape mapping, erosion modelling and sediment analysis have been employed to trace back the sediment origin and redistribution within the catchment, setting a special focus on the carbon history. Sediment deposits from a silted-up reservoir were analysed for varying physicochemical parameters, in order to analyse erosional and depositional patterns. A sharp decrease in total carbon content with decreasing depth suggests that land degradation during and after the post-European settlement most likely triggered erosion of the relatively fertile surface soils which presumably in-filled the reservoirs. It is assumed that the carbon-rich bottom layers of the dam deposits originate from these eroded surface soils. A combination of erosion modelling and sediment analysis will be used to determine the source areas of the depositional material and might clarify the question if land degradation in the Karoo has resulted in its return from being a net sink of carbon into a net source of carbon.

  12. Late Glacial and Holocene Flow Dynamics of the Denmark Strait Overflow Water

    NASA Astrophysics Data System (ADS)

    Williams, M.; Schmidt, D. N.; Andersen, M. B.; Barker, S.; McCave, I. N. N.

    2014-12-01

    The overflow of dense water from the Nordic Seas to the North Atlantic across the Greenland-Scotland Ridge forms a major component of the deep branch of the Atlantic Meridional Overturning Circulation and influences the climate system in Northwest Europe. Research has focused on deep convection of the Iceland Scotland Overflow Water (ISOW) and its links to climate variability in the North Atlantic. Our understanding of the history of the Denmark Strait Overflow Water (DSOW) is significantly less constrained and yet it accounts for half of the total overflow production today. We focus on the Eirik Drift south of Greenland in the vicinity of the DSOW. Down-core 230Thxs derived sediment focusing factors (Ψ) and measurements of the mean size of sortable silt reveal winnowed sediments during the Last Glacial Maximum and Heinrich 1 suggesting an influx of vigorous southern sourced waters and restricted DSOW production. Reduced overflow may be due to glacial isostatic processes which shoaled the Denmark Strait sill combined with a southward shift of deep convection sites in response to enhanced ice cover in the Nordic Seas. Intensification of the DSOW is evident between 9 and 13ka BP indicating initial deepening of the Denmark Strait sill and northward migration of the locus of deep water production. Ψ values for the Holocene suggest an active DSOW with a shift in the flow regime at 6.8 ka BP indicated by a reduction and subsequent stabilization of mean size sortable silt during the mid-late Holocene. This is corroborated by other studies showing a reorganization of the deep water after 7ka. An establishment of the Labrador Sea Water at intermediate depths altered the density structure of the deep western boundary current and weakened the ISOW. Changes in deep water circulation occur as North Atlantic climate entered Neoglacial cooling determined by Mg/Ca derived sea surface temperatures and abundances of the polar planktic foraminifera species N. pachyderma. They

  13. An updated database of Holocene relative sea level changes along the Mediterranean coasts

    NASA Astrophysics Data System (ADS)

    Vacchi, Matteo; Rovere, Alessio

    2014-05-01

    Present-day sea level variations in the Mediterranean depend on various factors, including recent climatic forcing, tectonic activity, anthropogenic effects, and glacio-isostatic adjustment (GIA). Mediterranean coasts offer an exceptional opportunity to investigate the various mechanisms that contribute to sea level variations on different time-scales. In fact, geological, geomorphological and archaeological indicators can be coupled with the available instrumental observations. Several areas of the Mediterranean basin are affected by a significant tectonic activity contributing to a widespread coastal instability. The northern Mediterranean coasts are, potentially, the most affected by the process of isostatic adjustment due to the proximity to the former Alpine and Fennoscandian ice sheets. However, GIA-related deformation of the whole Mediterranean basin is mainly driven by water-loading, which contributes to a significant and widespread subsidence whose extension and strength, in turn, directly depend on ice sheet chronology and Earth viscosity. In the Mediterranean, different kinds of RSL markers have been used to reconstruct RSLs: biological, sedimentary, geomorphological and archaeological. The production of such great amount of literature, which is still rapidly growing in number, has led to the obvious consequence of fragmented information, only occasionally reviewed in some localities, but never collected into an organic database to be analysed at the scale of the Mediterranean basin. We aim to create a database of Holocene (last 10 ka) geological data across the Mediterranean basin. This represents a tool of fundamental importance for understanding and tuning GIA models and to assess sea level rise hazards, which are particularly magnified in low-lying or subsiding coastal areas. Here we present the first results of this study carried out both in tectonically active areas (Aegean Sea, Greece) and stable ones (Southern France and Corsica, NE Spanish coast

  14. Holocene Deglaciation of the Scandinavian Ice Sheet: Preliminary 10Be Ages

    NASA Astrophysics Data System (ADS)

    Cuzzone, J. K.; Clark, P. U.; Marcott, S. A.; Lunkka, J.; Wohlfarth, B.; Caffee, M. W.; Carlson, A. E.

    2013-12-01

    The response of ice sheets to a warming climate is not well understood. Because we are limited in our understanding of present dynamics, reconstructing the deglaciation of former ice sheets allows for a better understanding of how past ice sheets responded to a warming climate along with their contribution to sea-level rise. These reconstructions also serve as critical constraints for ice sheet modeling efforts. Here, we present a suite of new 10Be ages from erratic boulders along three transects spanning southern to northern Sweden and Finland, that improve our understanding of the deglaciation of the Scandinavian Ice Sheet (SIS) beginning ~ 11.7ka through its final demise during the early Holocene. Dates from southern Finland, beginning at the Salpausselka Younger Dryas moraine (11.5 × 0.7 ka, n=4), inland southern Finland near Jyvaskyla (11.5 × 0.5ka, n=2), and coastal Finland (~60km from Gulf of Bothnia) near Vimpeli (11.5 × 0.4ka, n=4) indicate a rapid retreat following the Younger Dryas for Southern Finland (~500km within uncertainty of ages). Preliminary dates also exist for Northern Finland, near Inari (10.8 × 0.5ka, n=4) and near Oulu (10.5 × 0.6 ka, n = 4) suggesting a later retreat in the north. Dates from southern Sweden, near Skovde (12.73 × 0.8ka, n=4) to Mora (10.41 × 0.6ka, n=5) suggest a slower retreat (over ~400km). Lastly, dates in Northwestern Sweden suggest a final termination of the SIS around 9.4 × 0.7ka (n = 3). Additional ages are now being processed at PRIME Lab, Purdue University, which will further strengthen our understanding of SIS retreat from all sampled sites. These new data will help to constrain the Holocene deglaciation of the SIS and its associated retreat rates, and establish the SIS contribution to Holocene sea level rise, which will improve our understanding of ice-sheet response to a warming climate.

  15. Late Pleistocene and Holocene sedimentation on the George V Continental Shelf, East Antarctica

    NASA Astrophysics Data System (ADS)

    Presti, Massimo; De Santis, Laura; Busetti, Martina; Harris, Peter T.

    2003-05-01

    Climatically controlled glaciological and oceanographic environmental changes off the George V Coast during the Late Pleistocene and Holocene have been reconstructed from changes in sedimentation processes. The evolution of a sediment drift deposit (Mertz Drift) located in the deep trough on the shelf has been assessed using a sedimentological approach. Up to 5.5 m long cores have been collected. Four Late Pleistocene to Holocene sediment units have been distinguished on the basis of their physical properties, grain-size distributions, geochemical characteristics and ages. The basal Unit 1 is a grey, sandy clayey diamicton (27-37 wt% sand) deposited before 14,000 14C yr before present ( 14C yr BP). Unit 1 represents a Late Pleistocene, sub-ice shelf water-lain till, overlain by a thin current-winnowed sandy sub-unit. Unit 2 is a massive siliceous sandy mud (11-30 wt% sand), rich in ice-rafted debris, deposited between about 14,000 and 5000 14C yr BP. It likely represents an open-marine setting, proximal to a retreating ice-front, where strong bottom currents were frequent. The overlying Unit 3 is a laminated siliceous mud and diatomaceous ooze, with less terrigenous material (4-5 wt% average sand), deposited between 5000 and 3000 14C yr BP. The low wet bulk density values (<2 g/cm 3) and mass-specific magnetic susceptibility values (<25×10 -8 m 3/kg) of sediments of Unit 3 are a consequence of the high content of biogenic material (C org content >1 wt%; biogenic opal averaging 55 wt%). Unit 3 is probably related to a phase of increased sediment accumulation on the drift site and low bottom current activity on the shelf, with a stratified upper water column that could have lead to an enhanced primary productivity. Occurrence of crossed lamination indicates episodes of slightly enhanced bottom currents, probably with velocities up to 3-5 cm/s. The top Unit 4 is a bioturbated siliceous sandy mud, on average 50 cm thick, deposited under an energetic bottom current

  16. Perchlorate in pleistocene and holocene groundwater in North-Central New Mexico

    USGS Publications Warehouse

    Plummer, L.N.; Böhlke, J.K.; Doughten, M.W.

    2006-01-01

    Groundwater from remote parts of the Middle Rio Grande Basin in north-central New Mexico has perchlorate (ClO4-) concentrations of 0.12-1.8 ??g/L Because the water samples are mostly preanthropogenic in age (0-28 000 years) and there are no industrial sources in the study area, a natural source of the ClO4- is likely. Most of the samples have Br-, Cl-, and SO42- concentrations that are similar to those of modern bulk atmospheric deposition with evapotranspiration (ET) factors of about 7-40. Most of the ET values for Pleistocene recharge were nearly twice that for Holocene recharge. The NO3-/Cl- and ClO4-/Cl- ratios are more variable than those of Br -/Cl- or SO42-/Cl-. Samples thought to have recharged under the most arid conditions in the Holocene have relatively high NO3-/Cl- ratios and low ??15N values (+1 per mil (???)) similar to those of modern bulk atmospheric N deposition. The ??18O values of the NO 3- (-4 to 0 ???) indicate that atmospheric N0 3- was not transmitted directly to the groundwater but may have been cycled in the soils before infiltrating. Samples with nearly atmospheric NO3-/Cl- ratios have relatively high ClO4- concentrations (1.0-1.8 ??g/L) with a nearly constant ClO4-/Cl- mole ratio of (1.4 ?? 0.1) ?? 10-4, which would be consistent with an average ClO 4- concentration of 0.093 ?? 0.005 ??g/L in bulk atmospheric deposition during the late Holocene in north-central NM. Samples thought to have recharged underwetter conditions have higher ??15N values (+3 to +8 ???), lower N03-/Cl- ratios, and lower ClO4-/Cl- ratios than the ones most likely to preserve an atmospheric signal. Processes in the soils that may have depleted atmospherically derived NO3- also may have depleted ClO4- to varying degrees prior to recharge. If these interpretations are correct, then ClO4- concentrations of atmospheric origin as high as 4 ??g/L are possible in preanthropogenic groundwater in parts of the Southwest where ET approaches a factor of 40. Higher ClO4

  17. Foraminiferal stable isotope constraints on salinity changes in the deglacial and early Holocene Baltic Sea region

    NASA Astrophysics Data System (ADS)

    Quintana Krupinski, Nadine; Filipsson, Helena; Bokhari-Friberg, Yasmin; Knudsen, Karen-Luise; Mackensen, Andreas; Groeneveld, Jeroen; Austin, William

    2015-04-01

    The northern European Baltic Sea shows evidence of strong coupling with North Atlantic climate over recent glacial-interglacial cycles, but existing climate proxy evidence from regional sediment records suggest that the coupling may occur through non-linear processes. High-resolution regional climate records in Europe and from the Baltic Sea are critical for evaluating this coupling and the regional sensitivity to North Atlantic and global climate signals. However, evaluating the drivers and mechanisms of proposed links between the North Atlantic and Baltic Sea climate has often been hampered by a lack of long, continuous, high-resolution climate records from this area. New high-resolution sediment cores collected by IODP/ECORD Expedition 347 (Baltic Sea Paleoenvironment) allow such records to be generated, including foraminiferal geochemistry records of Baltic Sea hydrographic conditions during the most recent deglaciation and early Holocene (~19-7 cal. ka). The dramatic changes in salinity, sea level, circulation, temperature, and oxygenation during this period, e.g. through massive meltwater release from proglacial lakes and the early Holocene inundation of the Baltic by seawater highlight these non-linear links between the Baltic and North Atlantic. This work uses benthic foraminiferal stable isotope records (δ18O and δ13C) from sites in the western Baltic (M0059, Lillebælt, early Holocene marine stage (Littorina Sea)) and Kattegat (M0060, Anholt, deglaciation) to constrain salinity changes during these intervals. Because of the dramatic changes in salinity this region experiences today and during the study periods, oxygen isotope records (δ18O) here primarily reflect a signal of changing salinity, with a reduced temperature effect. Early δ18O results from the western Baltic (M0059) show a trend of declining δ18O/salinity during the first several kyr of the Littorina Sea stage, in agreement with previous work indicating declining salinity due to gradual

  18. Large variations in the Holocene marine radiocarbon reservoir effect reflect ocean circulation and climatic changes

    NASA Astrophysics Data System (ADS)

    Hua, Quan; Webb, Gregory E.; Zhao, Jian-xin; Nothdurft, Luke D.; Lybolt, Matthew; Price, Gilbert J.; Opdyke, Bradley N.

    2015-07-01

    Accurate radiocarbon dating of marine samples requires knowledge of the marine radiocarbon reservoir effect. This effect for a particular site/region is generally assumed constant through time when calibrating marine 14C ages. However, recent studies have shown large temporal variations of several hundred to a couple of thousand years in this effect for a number of regions during the late Quaternary and Holocene. Here we report marine radiocarbon reservoir correction (ΔR) for Heron Reef and Moreton Bay in southwestern (SW) Pacific for the last 8 ka derived from 14C analysis of 230Th-dated corals. Most of our ΔR for the last ∼5.4 ka agree well with their modern value, but large ΔR variability of ∼410 yr (from trough to peak) with possible decadal/centennial fluctuations is evident for the period ∼5.4-8 ka. The latter time interval also has significant variations with similar features in previously published ΔR values for other sites in the Pacific, including southern Peru-northern Chile in southeastern (SE) Pacific, the South China Sea, Vanuatu and Papua New Guinea, with the largest magnitude of ∼920 yr from SE Pacific. The mechanisms for these large ΔR variations across the Pacific during the mid-Holocene are complex processes involving (1) changes in the quantity and 14C content of upwelled waters in tropical east Pacific (TEP) (frequency and intensity of ocean upwelling in the TEP, and contribution of Subantarctic Mode Water to the upwelled waters, which is influenced by the intensity and position of southern westerly winds), and (2) variations in ocean circulation associated with climate change (La Niña/El Niño conditions, intensity of easterly trade winds, positions of the Intertropical Convergence Zone and the South Pacific Convergence Zone), which control the spreading of the older upwelled surface waters in the TEP to the western sites. Our results imply the need for employing temporal changes in ΔR values, instead of constant (modern) values

  19. Late Pleistocene and Holocene Fire History of the Swiftcurrent Lake basin, eastern Glacier National Park, Montana

    NASA Astrophysics Data System (ADS)

    Kutvirt, J. C.; MacGregor, K. R.; Riihimaki, C. A.; Myrbo, A.

    2010-12-01

    High altitude alpine landscapes of the northern U.S. Rocky Mountains are geomorphically dynamic and sensitive to climate change. Understanding the timing and magnitude of past changes in temperature, aridity, and other factors such as seasonality and storminess are key in constraining natural climate variability in these sensitive environments. Fire frequency can provide strong insight into past climate regimes, with increased periodicity and/or intensity of fires reflecting episodes of warming and/or aridity. Lacustrine climate records in the Rockies are most abundant either further south of northern Montana at lower elevations, or in the Canadian Rockies further north. Here we examine a ˜12,900 year long lake sediment record from the northeastern basin of Swiftcurrent Lake in eastern Glacier National Park, MT to document fire frequency as a proxy for aridity in the region. Swiftcurrent Lake is fed mainly by melt from Grinnell Glacier, and thus reflects glacial, geomorphic, and climatic processes throughout the Holocene. Existing data, such as mineralogy, percent organic carbon, C/N, and grain size will be paired with the fire frequency record over the Holocene and latest Pleistocene to develop a comprehensive environmental history of the Swiftcurrent Lake Basin and greater Grinnell Glacier Valley. A clear understanding of fire history in the basin is important for future fire management decisions in Glacier National Park. Charcoal particles were tallied at contiguous 0.5 cm intervals over the first half meter of the core, and at 1 cm intervals over the remaining ~6.0 m, then converted to charcoal abundance and accumulation rates. Based age controls from radiocarbon analyses and ash fingerprinting the sampling interval represents between 5 and 20 years. A core collected in July 2010 will be analyzed for lead-210, providing additional age control for the past few centuries. Preliminary results show low charcoal counts overall with some clear peaks. High charcoal

  20. Spline analysis of Holocene sediment magnetic records: Uncertainty estimates for field modeling

    NASA Astrophysics Data System (ADS)

    Panovska, S.; Finlay, C. C.; Donadini, F.; Hirt, A. M.

    2012-02-01

    Sediment and archeomagnetic data spanning the Holocene enable us to reconstruct the evolution of the geomagnetic field on time scales of centuries to millennia. In global field modeling the reliability of data is taken into account by weighting according to uncertainty estimates. Uncertainties in sediment magnetic records arise from (1) imperfections in the paleomagnetic recording processes, (2) coring and (sub) sampling methods, (3) adopted averaging procedures, and (4) uncertainties in the age-depth models. We take a step toward improved uncertainty estimates by performing a comprehensive statistical analysis of the available global database of Holocene magnetic records. Smoothing spline models that capture the robust aspects of individual records are derived. This involves a cross-validation approach, based on an absolute deviation measure of misfit, to determine the smoothing parameter for each spline model, together with the use of a minimum smoothing time derived from the sedimentation rate and assumed lock-in depth. Departures from the spline models provide information concerning the random variability in each record. Temporal resolution analysis reveals that 50% of the records have smoothing times between 80 and 250 years. We also perform comparisons among the sediment magnetic records and archeomagnetic data, as well as with predictions from the global historical and archeomagnetic field models. Combining these approaches, we arrive at individual uncertainty estimates for each sediment record. These range from 2.5° to 11.2° (median: 5.9°; interquartile range: 5.4° to 7.2°) for inclination, 4.1° to 46.9° (median: 13.4°; interquartile range: 11.4° to 18.9°) for relative declination, and 0.59 to 1.32 (median: 0.93; interquartile range: 0.86 to 1.01) for standardized relative paleointensity. These values suggest that uncertainties may have been underestimated in previous studies. No compelling evidence for systematic inclination shallowing is

  1. Late-Glacial to early Holocene basin development of annually laminated Lake Tiefer See

    NASA Astrophysics Data System (ADS)

    Theuerkauf, Martin; Lorenz, Sebastian; Schult, Manuela; Lampe, Reinhard; Dräger, Nadine; Wulf, Sabine; Brauer, Achim

    2014-05-01

    Lake Tiefer See (N 53.59°, E 12.53°) is one of the rare lakes with a long sequence of annually laminated Holocene sediments in northern Central Europe. The lake is thus of great potential for past climate, vegetation and human land use studies. It furthermore provides a valuable link between laminated lakes in more oceanic climates of the Eifel region and NW Germany and laminated lakes in the more continental climate of Poland. The sediments of Lake Tiefer See are not uniform but show repeated changes in varve composition and include several non-varved sequences. Interpreting these changes requires a sound understanding of the deposition processes in the lake and the development of the lake basin itself. While modern sediment deposition is studied in an extensive monitoring program, we explore lake basin development using numerous cores from the lake margins down to the bottom of the lake. The lake is exceptionally deep (62 m) with steep slopes and may thus be susceptible to sediment re-deposition and focusing. Most marginal cores, which reach down to 10 m water depth, show a prominent basal peat layer. This peat layer indicates that basin development started by paludification of an originally flat surface following dead-ice melting. However, even in neighboring cores the timing of the onset of peat formation appears to differ substantially. While in some cores, the prominent Laacher See Tephra (12.880 cal. BP) is found at the bottom of the peat layer, it is found well above the peat basis in other cores. Dead-ice melting may thus initially have produced a pattern of shallow depressions with ongoing peat formation within a still terrestrial surface. The formation of the deep lake is than indicated by an abrupt shift to calcareous gyttjas, which show an initially increased silicate content. The lake obviously only developed long after first peat deposition, possibly in the early Holocene. Further dates to verify this hypothesis are expected. In several marginal

  2. Perchlorate in pleistocene and holocene groundwater in north-central New Mexico.

    PubMed

    Plummer, L Niel; Böhlke, John Karl; Doughten, Michael W

    2006-03-15

    Groundwater from remote parts of the Middle Rio Grande Basin in north-central New Mexico has perchlorate (ClO4-) concentrations of 0.12-1.8 micro/L. Because the water samples are mostly preanthropogenic in age (0-28000 years) and there are no industrial sources in the study area, a natural source of the ClO4- is likely. Most of the samples have Br-, Cl-, and SO4(2-) concentrations that are similar to those of modern bulk atmospheric deposition with evapotranspiration (ET) factors of about 7-40. Most of the ET values for Pleistocene recharge were nearly twice that for Holocene recharge. The N03-/Cl- and CIO-/Cl-ratios are more variable than those of Br-/Cl- or S04(2-)/Cl-. Samples thought to have recharged under the most arid conditions in the Holocene have relatively high N03-/Cl- ratios and low delta 15N values (+1 per mil (% per thousand)) similar to those of modern bulk atmospheric N deposition. The delta 18O values of the N03- (-4 to 0% per thousand) indicate that atmospheric N03- was not transmitted directly to the groundwater but may have been cycled in the soils before infiltrating. Samples with nearly atmospheric N03-/CI- ratios have relatively high Cl04- concentrations (1.0-1.8 ug/L) with a nearly constant Cl04-/CI- mole ratio of (1.4 +/- 0.1) x 10(-4), which would be consistent with an average Cl04-concentration of 0.093 0.005 ,ug/L in bulk atmospheric deposition during the late Holocene in north-central NM. Samples thought to have recharged under wetter conditions have higher delta 15N values (+3 to +8 % per thousando), lower NO3-/Cl- ratios, and lower ClO4-/Cl- ratios than the ones most likely to preserve an atmospheric signal. Processes in the soils that may have depleted atmospherically derived NO3-also may have depleted ClO4- to varying degrees prior to recharge. If these interpretations are correct, then ClO4- concentrations of atmospheric origin as high as 4 microg/L are possible in preanthropogenic groundwater in parts of the Southwest where ET

  3. Late Holocene paleoclimate records from Lakes Sibaya and Verlorenvlei, South Africa.

    NASA Astrophysics Data System (ADS)

    Stager, J. Curt; Neumann, Frank; Chase, Brian M.; Meadows, Michael E.; Fitzpatrick, Jason; Hazzard, Matt; King, Christiaan; Madson, Jerome; White, Jay

    2010-05-01

    Detailed, continuous paleoclimatic records of the late Holocene are relatively uncommon in the southern hemisphere, and the environmental interpretations of some important southern records remain unresolved. Such issues have hindered the understanding of continental and hemispheric-scale climatic processes, including the roles of solar variability, ENSO, and latitudinal positions of key weather systems, in the long-term evolution of tropical climates. Sediment cores from two widely separated lakes on the South African coast now shed additional light on precipitation variability in the region as well as on the interpretation of existing records from other sites that are located farther inland. Lake Sibaya, in the northeastern sector, receives most of its rain during austral summers and can be influenced by latitudinal shifts in the position of the ITCZ; its climatic history may therefore be informative for the understanding of unusual precipitation patterns during the late Holocene that have been reported from equatorial East Africa. Verlorenvlei, in the southwestern sector, receives most of its rain during austral winters and is well situated to register latitudinal shifts in the positions of mid-latitude westerly storm tracks which, in turn, are sensitive to atmospheric and marine conditions around Antarctica. Comparing sedimentary records from these two sites can therefore be helpful in testing the hypothesis that synchronous changes in low- and mid-latitude weather systems have occurred during the late Holocene, presumably in response to solar variability or other disruptions of large-scale air and ocean circulation patterns. In this presentation, diatom, pollen, and sedimentological data from Sibaya and Verlorenvlei are used to address the nature and origins of climatic changes in tropical and southernmost Africa during the last 1500 years. In addition, because the variability of lacustrine conditions at these two sites appears to be primarily the result of

  4. Late-Glacial to Holocene Hydroclimatic Change in the Mojave Desert: Silver Lake, CA

    NASA Astrophysics Data System (ADS)

    Kirby, M. E.; Knell, E. J.; Anderson, W. T., Jr.; Lachniet, M. S.; Eeg, H.; Lucero, R.; Murrieta, R.; Arevalo, A.; Silveira, E.; Hiner, C.; Palermo, J. A.

    2014-12-01

    Silver Lake is the modern terminal playa of the Mojave River. As a result, it is well located to record both influences from the winter precipitation dominated San Bernardino Mountains - the source of the Mojave River - as well as the late-summer to early-fall North American monsoon. Here, we present various physical and geochemical data from a new 8.2 m sediment core taken from Silver Lake, CA that spans modern through 14.8 kcal yrs BP. Age control is based on six bulk organic C radiocarbon dates processed with Bacon v2.2 to generate an age model. Texturally, the core varies between a silty clay and a silty sand, often with abrupt sedimentological transitions. Our working hypothesis states that high percent clay values indicate persistent standing water wherein the deposition, accumulation, and preservation of fine grain sediment exceeds some undefined thickness that inhibits deflation during succeeding desiccation events or ephemeral lake environments. Based on this clay - lake status hypothesis, the sediment core is divided into five lake status intervals. Clay values are highest between 14.4 - 13.5 kcal yrs BP, coeval to Lake Mojave II. Clay values decrease abruptly at 13.5 kcal yrs BP (encapsulating the Younger Dryas) indicating a return to an ephemeral lake. At 11.3 kcal yrs BP, clay values rise abruptly indicating a return to a perennial lake; this early Holocene pluvial ended abruptly at 7.8 kcal yrs BP. From 7.8 - 4.2 kcal yrs BP, clay is low, but variable and mudcracks are common. At 4.2 kcal yrs BP, clay values increase but only moderately indicating a return to more frequent sustained perennial lakes. The early Holocene pluvial is likely a result of higher summer insolation, which generated a more intense and spatially expansive North American monsoon. Coupled with lower winter insolation and thus more winter storms across the region, Silver Lake flourished. A comparison to stable carbon isotope data from Leviathan Cave (NV), support our interpretation

  5. Perchlorate in pleistocene and holocene groundwater in north-central New Mexico.

    PubMed

    Plummer, L Niel; Böhlke, John Karl; Doughten, Michael W

    2006-03-15

    Groundwater from remote parts of the Middle Rio Grande Basin in north-central New Mexico has perchlorate (ClO4-) concentrations of 0.12-1.8 micro/L. Because the water samples are mostly preanthropogenic in age (0-28000 years) and there are no industrial sources in the study area, a natural source of the ClO4- is likely. Most of the samples have Br-, Cl-, and SO4(2-) concentrations that are similar to those of modern bulk atmospheric deposition with evapotranspiration (ET) factors of about 7-40. Most of the ET values for Pleistocene recharge were nearly twice that for Holocene recharge. The N03-/Cl- and CIO-/Cl-ratios are more variable than those of Br-/Cl- or S04(2-)/Cl-. Samples thought to have recharged under the most arid conditions in the Holocene have relatively high N03-/Cl- ratios and low delta 15N values (+1 per mil (% per thousand)) similar to those of modern bulk atmospheric N deposition. The delta 18O values of the N03- (-4 to 0% per thousand) indicate that atmospheric N03- was not transmitted directly to the groundwater but may have been cycled in the soils before infiltrating. Samples with nearly atmospheric N03-/CI- ratios have relatively high Cl04- concentrations (1.0-1.8 ug/L) with a nearly constant Cl04-/CI- mole ratio of (1.4 +/- 0.1) x 10(-4), which would be consistent with an average Cl04-concentration of 0.093 0.005 ,ug/L in bulk atmospheric deposition during the late Holocene in north-central NM. Samples thought to have recharged under wetter conditions have higher delta 15N values (+3 to +8 % per thousando), lower NO3-/Cl- ratios, and lower ClO4-/Cl- ratios than the ones most likely to preserve an atmospheric signal. Processes in the soils that may have depleted atmospherically derived NO3-also may have depleted ClO4- to varying degrees prior to recharge. If these interpretations are correct, then ClO4- concentrations of atmospheric origin as high as 4 microg/L are possible in preanthropogenic groundwater in parts of the Southwest where ET

  6. Linking Holocene sedimentary and water column records from Fiordland, New Zealand to westerly wind variability

    NASA Astrophysics Data System (ADS)

    Hinojosa, J.; Moy, C. M.; Wilson, G. S.; Stirling, C.

    2012-12-01

    The strength and latitudinal position of the Southern Hemisphere westerly winds play a fundamental role in the global carbon cycle by regulating Southern Ocean CO2 flux. Modeling studies predict that when the winds are centered over the Antarctic Circumpolar Current, carbon-rich deepwater is upwelled, enhancing CO2 outgassing to the atmosphere. When the winds shift north, atmospheric CO2 is entrained in downwelling intermediate waters, causing uptake processes to dominate. Resolving past westerly wind variability is crucial for evaluating the how the winds influence the the Southern Ocean CO2 sink along geologic timescales, yet broadly distributed paleoclimate records currently limit our ability to do so. We have begun a research program that aims to develop high-resolution records of the westerly winds throughout the Holocene using sediment cores from Fiordland, New Zealand. Fiordland is one of two regions globally that intersects the northern reach of the modern wind field maximum and there is a strong relationship between the strength of the overlying winds and the amount of precipitation falling at interannual timescales. The New Zealand fjords offer high sedimentation rate (>1mm/yr) in sub-oxic to anoxic basins that can yield high-resolution sediment records of climate, environmental, and hydrographic change. In April 2012, we collected seismic data, surface sediment, water column samples, and multiple piston cores from Doutbful Sound, Dagg Sound, Dusky Sound, and Preservation Inlet with the University of Otago research vessel Polaris II. We characterized the physical oceanography of the fjords with multiple CTD casts and measured dissolved oxygen concentrations to determine the extent of anoxia within selected sub-basins. We also characterized the relative input of marine and terrestrial sources using carbon and nitrogen concentration and isotope variations and macrofossil identification. From this preliminary work, and our understanding of regional climate

  7. Holocene Evolution of Incised Coastal Channels on the Isle of Wight, UK: Interpretation via Numerical Simulation.

    NASA Astrophysics Data System (ADS)

    Leyland, J.; Darby, S. E.

    2006-12-01

    Holocene coastal processes, as well as providing the long-term context necessary to manage Chine habitats appropriately. In particular a critical threshold drainage area is defined that provides knickpoint recession rates that are sufficient to generate self- sustaining Chines in relation to cliff recession rates.

  8. Holocene changes in eastern equatorial Atlantic salinity as estimated by water isotopologues

    NASA Astrophysics Data System (ADS)

    Leduc, Guillaume; Sachs, Julian P.; Kawka, Orest E.; Schneider, Ralph R.

    2013-01-01

    The isotopic composition of surface seawater is widely used to infer past changes in sea surface salinity using paired foraminiferal Mg/Ca and δ18O from marine sediments. At low latitudes, paleosalinity reconstructions using this method have largely been used to document changes in the hydrological cycle. This method usually assumes that the modern seawater δ18O (δ18Osw)/salinity relationship remained constant through time. Modelling studies have shown that such assumptions may not be valid because large-scale atmospheric circulation patterns linked to global climate changes can alter the seawater δ18Osw/salinity relationship locally. Such processes have not been evidenced by paleo-data so far because there is presently no way to reconstruct past changes in the seawater δ18Osw/salinity relationship. We have addressed this issue by applying a multi-proxy salinity reconstruction from a marine sediment core collected in the Gulf of Guinea. We measured hydrogen isotopes in C37:2 alkenones (δDa) to estimate changes in seawater δD. We find a smooth, long-term increase of ˜10‰ in δDa between 10 and 3 kyr BP, followed by a rapid decrease of ˜10‰ in δDa between 3 kyr BP and core top to values slightly lighter than during the early Holocene. Those features are inconsistent with published salinity estimations based on δ18Osw and foraminiferal Ba/Ca, as well as nearby continental rainfall history derived from pollen analysis. We combined δDa and δ18Osw values to reconstruct a Holocene record of salinity and compared it to a Ba/Ca-derived salinity record from the same sedimentary sequence. This combined method provides salinity trends that are in better agreement with both the Ba/Ca-derived salinity and the regional precipitation changes as inferred from pollen records. Our results illustrate that changes in atmospheric circulation can trigger changes in precipitation isotopes in a counter-intuitive manner that ultimately impacts surface salinity estimates

  9. North Atlantic forcing of moisture delivery to Europe throughout the Holocene.

    PubMed

    Smith, Andrew C; Wynn, Peter M; Barker, Philip A; Leng, Melanie J; Noble, Stephen R; Tych, Wlodek

    2016-01-01

    Century-to-millennial scale fluctuations in precipitation and temperature are an established feature of European Holocene climates. Changes in moisture delivery are driven by complex interactions between ocean moisture sources and atmospheric circulation modes, making it difficult to resolve the drivers behind millennial scale variability in European precipitation. Here, we present two overlapping decadal resolution speleothem oxygen isotope (δ(18)O) records from a cave on the Atlantic coastline of northern Iberia, covering the period 12.1-0 ka. Speleothem δ(18)O reveals nine quasi-cyclical events of relatively wet-to-dry climatic conditions during the Holocene. Dynamic Harmonic Regression modelling indicates that changes in precipitation occurred with a ~1500 year frequency during the late Holocene and at a shorter length during the early Holocene. The timing of these cycles coincides with changes in North Atlantic Ocean conditions, indicating a connectivity between ocean conditions and Holocene moisture delivery. Early Holocene climate is potentially dominated by freshwater outburst events, whilst ~1500 year cycles in the late Holocene are more likely driven by changes internal to the ocean system. This is the first continental record of its type that clearly demonstrates millennial scale connectivity between the pulse of the ocean and precipitation over Europe through the entirety of the Holocene. PMID:27109216

  10. North Atlantic forcing of moisture delivery to Europe throughout the Holocene

    PubMed Central

    Smith, Andrew C.; Wynn, Peter M.; Barker, Philip A.; Leng, Melanie J.; Noble, Stephen R.; Tych, Wlodek

    2016-01-01

    Century-to-millennial scale fluctuations in precipitation and temperature are an established feature of European Holocene climates. Changes in moisture delivery are driven by complex interactions between ocean moisture sources and atmospheric circulation modes, making it difficult to resolve the drivers behind millennial scale variability in European precipitation. Here, we present two overlapping decadal resolution speleothem oxygen isotope (δ18O) records from a cave on the Atlantic coastline of northern Iberia, covering the period 12.1–0 ka. Speleothem δ18O reveals nine quasi-cyclical events of relatively wet-to-dry climatic conditions during the Holocene. Dynamic Harmonic Regression modelling indicates that changes in precipitation occurred with a ~1500 year frequency during the late Holocene and at a shorter length during the early Holocene. The timing of these cycles coincides with changes in North Atlantic Ocean conditions, indicating a connectivity between ocean conditions and Holocene moisture delivery. Early Holocene climate is potentially dominated by freshwater outburst events, whilst ~1500 year cycles in the late Holocene are more likely driven by changes internal to the ocean system. This is the first continental record of its type that clearly demonstrates millennial scale connectivity between the pulse of the ocean and precipitation over Europe through the entirety of the Holocene. PMID:27109216

  11. Holocene faulting in the western Basin and Range, California

    SciTech Connect

    Bryant, W.A. . Div. of Mines and Geology)

    1993-04-01

    Principal late Quaternary faults in the Basin and Range Geomorphic Province of eastern and northeastern California were evaluated for evidence of Holocene surface fault rupture as part of DMG's Fault Evaluation and Zoning Project. Those faults considered to have been active in Holocene time were zoned for special studies in order to mitigate surface fault rupture hazard as authorized by the Alquist-Priolo Special Studies Zones Act of 1972. Thirty-seven faults or fault zones were evaluated from the southern Sierra Nevada east to Death Valley and north to Surprise Valley. About 70% of these faults have evidence of Holocene displacement. Slip-rates for 20 faults have been determined by others or were estimated during this study. It is difficult to categorize slip-rates in this region because fault zones often are characterized by a complex history of both right-lateral strike-slip (rlss) and normal dip-slip displacement include the Death Valley, Deep Springs, Genoa, Hilton Creek, Honey Lake, Owens Valley, and Panamint Valley faults. All but 2 of these faults (Deep Springs and Genoa) have correspondingly high slip-rates [>=] 2mm/yr. The Death Valley, Honey Lake, Owens Valley, and Panamint Valley faults are characterized primarily by rlss displacement; the other 3 faults have predominantly normal displacement. Most of the faults considered to have primarily vertical displacement are characterized by maximum vertical slip-rates less than 1mm/yr. Range-front faults with maximum vertical slip-rates [>=]1mm/yr include the Genoa, Hilton Creek, Mono Lake, Round Valley, Surprise Valley, and White Mountains faults.

  12. Holocene Deep Ocean Variability Detected with Individual Benthic Foraminifera

    NASA Astrophysics Data System (ADS)

    Bova, S. C.; Herbert, T.; Fox-Kemper, B.

    2015-12-01

    Historical observations of deep ocean temperatures (>700 m water depth) show apparently unprecedented rates of warming over the past half century that parallel observed surface warming, on the order of 0.1°C/decade (Purkey and Johnson 2010). Most water masses below 700 m depth, however, have not been at the sea surface where they exchange heat and carbon with the atmosphere since well before industrialization (Gebbie and Huybers 2012). How then has the heat content of isolated deep water masses responded to climate change over the last century? In models, wave mechanisms propagate thermocline anomalies quickly (Masuda et al. 2010), but these dynamics are not fully understood. We therefore turn to the sedimentary record to constrain the bounds of earlier variability from Holocene anomalies. The oxygen isotopic composition (δ18O) of individual benthic foraminifera provide approximately month-long snapshots of the temperature and salinity of ambient deep water during calcification. We exploit the short lifespan of these organisms to reconstruct variability in δ18Oshell, and thus the variability in deep water temperature and salinity, during five 200-yr Holocene intervals at 1000 m water depth in the Eastern Equatorial Pacific (EEP). Modern variability in benthic foraminifer δ18O was too weak to detect but variability at 1000 m water depth in the EEP exceeded our detection limit during two Holocene intervals at high confidence (p<0.01), with δ18O anomalies up to ~0.6 ± 0.15‰ that persist for a month or longer. Although the source of these anomalies remains speculative, rapid communication between the surface and deep ocean that operates on human timescales, faster than previously recognized, or intrinsic variability that has not been active during the history of ocean observations are potential explanations. Further work combining models and high-resolution proxy data is needed to identify the mechanism and global extent of this type of subsurface variability

  13. The Holocene Geoarchaeology of the Desert Nile in Northern Sudan

    NASA Astrophysics Data System (ADS)

    Woodward, Jamie; Macklin, Mark; Spencer, Neal; Welsby, Derek; Dalton, Matthew; Hay, Sophie; Hardy, Andrew

    2016-04-01

    Invited Paper Forty years ago Colin Renfrew declared that "every archaeological problem starts as a problem in geoarchaeology" (Renfrew, 1976 p. 2). With this assertion in mind, this paper draws upon the findings from field research in two sectors of the Nile Valley of Northern Sudan dedicated to the exploration of human-environment interactions during the middle and late Holocene. This part of the Nile corridor contains a rich cultural record and an exceptionally well preserved Holocene fluvial archive. A distinctive feature of these records is the variety of evidence for interaction between desert and river over a range of spatial and temporal scales. This interaction presented both challenges and opportunities for its ancient inhabitants. This paper will present evidence for large-scale landscape changes driven by shifts in global climate. It will also show how we have integrated the archaeological and geological records in the Northern Dongola Reach and at Amara West - where long-term field projects led by archaeologists from the British Museum have recognised the importance of a sustained commitment to interdisciplinary research to achieve a fully integrated geoarchaeological approach across a range of scales. The former project is a large-scale landscape survey with multiple sites across an 80 km reach of the Nile whilst the latter has a strong focus on a single New Kingdom town site and changes in its environmental setting. By combining multiple archaeological and geological datasets - and pioneering the use of OSL dating and strontium isotope analysis in the Desert Nile - we have developed a new understanding of human responses to Holocene climate and landscape change in this region. Renfrew, C. (1976) Archaeology and the earth sciences. In: D.A. Davidson and M.I. Shackley (eds) Geoarchaeology: Earth Science and the Past, Duckworth, London, 1-5.

  14. Late Weichselian and Holocene palaeoceanography of Storfjordrenna, southern Svalbard

    NASA Astrophysics Data System (ADS)

    Łącka, M.; Zajączkowski, M.; Forwick, M.; Szczuciński, W.

    2015-03-01

    Multiproxy analyses (including benthic and planktonic foraminifera, δ18O and δ13C records, grain-size distribution, ice-rafted debris, XRF geochemistry and magnetic susceptibility) were performed on a 14C-dated marine sediment core from Storfjordrenna, located off of southern Svalbard. The sediments in the core cover the termination of Bølling-Allerød, the Younger Dryas and the Holocene and reflect general changes in the oceanography/climate of the European Arctic after the last glaciation. Grounded ice of the last Svalbard-Barents Sea Ice Sheet retreated from the coring site ca. 13 950 cal yr BP. During the transition from the subglacial to glaciomarine setting, Arctic Waters dominated the hydrography in Storfjordrenna. However, the waters were not uniformly cold and experienced several warmer spells. A progressive warming and marked change in the nature of the hydrology occurred during the early Holocene. Relatively warm and saline Atlantic Water began to dominate the hydrography starting from approximately 9600 cal yr BP. Although the climate in eastern Svalbard was milder at that time than at present (smaller glaciers), two periods of slight cooling were observed in 9000-8000 and 6000-5500 cal yr BP. A change in the Storfjordrenna oceanography occurred at the beginning of the late Holocene (i.e. 3600 cal yr BP) synchronously with glacier growth on land and enhanced bottom current velocities. Although cooling was observed in the Surface Water, Atlantic Water remained present in the deeper portion of the water column of Storfjordrenna.

  15. Antarctic black carbon tracks Southern Hemisphere climate throughout the Holocene

    NASA Astrophysics Data System (ADS)

    Arienzo, M. M.; McConnell, J.

    2015-12-01

    Biomass-burning and fossil-fuel combustion emit black carbon (BC) aerosols which impact climate directly by changing Earth's radiation budget and indirectly by changing cloud formation and reducing albedo when deposited on bright surfaces such as snow and ice. BC aerosols have been shown to be the second most important anthropogenic climate-forcing agent today, after carbon dioxide. However, on longer timescales, knowledge of natural variations in BC emissions and climate drivers of regional-scale biomass burning is limited. Here we present the first high-resolution 14,000-year record of BC aerosol deposition in Antarctica. The two ice cores analyzed were the West Antarctic Ice Sheet Divide (WD) core from 14,000 years before 1950 (yr BP) to 2,475 yr BP and the East Antarctic B40 core from 2,485 yr BP to present. BC and a wide range of trace elements were analyzed via a continuous melter system allowing for sub-annual resolution in both cores. For BC concentration determinations, a Single Particle Soot Photometer (SP2; Droplet Measurement Technologies) was used. BC fluxes in the WD and B40 Holocene composite more than doubled from <25 μg m-2 yr-1 at the end of the last glacial termination (14 kyr BP) to >50 μg m-2 yr-1 in the mid-Holocene (~7.5 kyr BP), and then declined to <20 μg m-2 yr-1 in the late Holocene, with lowest BC fluxes observed during the Little Ice Age. We compare Antarctic BC fluxes to low-latitude paleoclimate proxies to investigate a potential link between low latitude climate, biomass burning and BC emissions.

  16. Holocene Vegetation and Climate History of the Northern Bighorn Basin, Southern Montana

    NASA Astrophysics Data System (ADS)

    Lyford, Mark E.; Betancourt, Julio L.; Jackson, Stephen T.

    2002-09-01

    Records of Holocene vegetation and climate change at low elevations (<2000 m) are rare in the central Rocky Mountain region. We developed a record of Holocene vegetation and climate change from 55 14C-dated woodrat middens at two low-elevation sites (1275 to 1590 m), currently vegetated by Juniperus osteosperma woodlands, in the northern Bighorn Basin. Macrofossil and pollen analyses show that the early Holocene was cooler than today, with warming and drying in the middle Holocene. During the Holocene, boreal ( Juniperus communis, J. horizontalis) and montane species ( J. scopulorum) were replaced by a Great Basin species ( J. osteosperma). J. osteosperma colonized the east side of the Pryor Mountains 4700 14C yr B.P. Downward movement of lower treeline indicates wetter conditions between 4400 and 2700 14C yr B.P. Increased aridity after 2700 14C yr B.P. initiated expansion of J. osteosperma from the east to west side of the Pryor Mountains.

  17. Holocene variations in peatland methane cycling associated with the Asian summer monsoon system

    PubMed Central

    Zheng, Yanhong; Singarayer, Joy S.; Cheng, Peng; Yu, Xuefeng; Liu, Zhao; Valdes, Paul J.; Pancost, Richard D.

    2014-01-01

    Atmospheric methane concentrations decreased during the early to middle Holocene; however, the governing mechanisms remain controversial. Although it has been suggested that the mid-Holocene minimum methane emissions are associated with hydrological change, direct evidence is lacking. Here we report a new independent approach, linking hydrological change in peat sediments from the Tibetan Plateau to changes in archaeal diether concentrations and diploptene δ13C values as tracers for methanogenesis and methanotrophy, respectively. A minimum in inferred methanogenesis occurred during the mid-Holocene, which, locally, corresponds with the driest conditions of the Holocene, reflecting a minimum in Asian monsoon precipitation. The close coupling between precipitation and methanogenesis is validated by climate simulations, which also suggest a regionally widespread impact. Importantly, the minimum in methanogenesis is associated with a maximum in methanotrophy. Therefore, methane emissions in the Tibetan Plateau region were apparently lower during the mid-Holocene and partially controlled by interactions of large-scale atmospheric circulation. PMID:25135106

  18. Decadal-scale Holocene climate variability in the Nordic seas

    NASA Astrophysics Data System (ADS)

    Koc, N.; Andersen, C.; Andrews, J.; Jennings, A.

    2003-04-01

    Sea-surface temperatures (SST) at decadal resolution have been reconstructed from core MD 95-2011, core MD 99-2269 and core BS88-6-5A based on diatom transfer functions. Core MD 95-2011 is located on the Vöring Plateau (66^o58.18N; 07^o38.36E, 1050 m water depth) along the main axis of the northward flowing warm Atlantic water. It is, therefore, in an ideal position to monitor changes in the northward heat flux to northwestern Europe. Core MD 99-2269 is located in the deep Hunafloi trough, off N Iceland (66^o37.53N; 20^o51.16W, 365 m water depth). Today the core lies under the influence of the Irminger current, but it also may be influenced by the cold East Greenland current (EGC) as the Polar front migrates eastward. Core BS88-6-5A is located on the East Greenland shelf (67^o07.54N; 30^o54.26W, 707 m water depth) and is influenced by the EGC. The cores has been dated by AMS C-14 and Pb 210 isotope profiles. SST variations are estimated by means of 3 different diatom transfer function methods. Results indicate a division of the Holocene into three periods and a climate development in step with the decreasing Northern Hemisphere insolation. However, regional differences between the surface currents occur regarding both timing and magnitude of changes. Superimposed on the general Holocene cooling trend there is a high frequency SST variability, which is in the order of 1--1.5 degrees C for the Vöring Plateau and the East Greenland shelf, and 2.5--3 degrees C for the North Iceland shelf. There is clear evidence for late Holocene climatic events such as the "Little Ice Age" and the "Medieval Warm Period". Timing of late Holocene climatic events at the eastern versus western Nordic Seas will be discussed.

  19. Holocene dynamics of North Atlantic Deep Water Masses

    NASA Astrophysics Data System (ADS)

    Hoogakker, B.; Chapman, M.; McCave, I. N.; Hillaire-Marcel, C.

    2012-12-01

    The Atlantic Meridional Overturning Circulation (AMOC) is a key component in latitudinal heat and salt transport, comprising northward flow of salty warm near-surface waters in the North Atlantic Current, and its compensating cool return flow at depth. During the early Holocene high summer insolation and strong inflow of North Atlantic surface waters into the Nordic Seas and the Arctic Ocean may have contributed to increased deep-water formation. To assess the effect of increased deep-water formation in the Nordic Seas and the Arctic Ocean on AMOC we reconstructed and assessed bottom flow vigour (using the mean grain size of the sortable silt) and hydrographic properties (using benthic foraminiferal isotopes) at key locations in the deep North Atlantic. The core sites of MD99-2251 and ODP 980 are currently influenced by North East Atlantic Deep Water (NEADW-origin Iceland Scotland Overflow Water), whilst that of MD95-2024 is under the influence of North West Atlantic Bottom Water (NWABW-currently densest North Atlantic Deep Water mass, origin Denmark Strait Overflow). When exiting the Labrador Sea, NEADW and NWABW mix to make up Lower North Atlantic Deep Water. Our results show that NEADW at Gardar Drift in the northeast Atlantic was considerably enhanced and denser (comparable to NWABW) during the early Holocene, until ~6.5 ka. The density increase is attributed to NEADW mainly consisting of Iceland Scotland Overflow Water, lacking significant contributions of Labrador Sea Water or Lower Deep Water (LDW-origin Antarctic Bottom Water) that it contains at present. This implies there was no density gradient between these two deep-water masses during the early Holocene, contrary to today. A subsequent weakening of NEADW accompanied with a reduction in its density after 6.5 ka allowed a shoaling of LDW and deeper eastward advection of Labrador Sea Water into the northeast Atlantic basin. The density gradient observed between current NEADW and NWABW might have been

  20. Holocene aeolian sediments on the NE Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Stauch, G.; Lehmkuhl, F.; Hilgers, A.; Zhao, H.

    2012-04-01

    The semiarid climate of the northeastern Tibetan Plateau supports the formation of different types of aeolian sediments and landforms during the Holocene. Aeolians silts and sands in the catchment of the Donggi Cona in an elevation above 4000m to 4800 m asl reflect variable climate conditions during that time as well as different sediment sources. Based on 51 OSL datings and catchment wide geomorphological mapping a complex pattern of long and short distance sediment transport has been reconstructed. Only few aeolian archives are preserved from the late Pleistocene in this mountain environment indicating cold and dry climate conditions which prevented a continuous accumulation. During the early Holocene a phase of increased aeolian sedimentation of sand at the slopes of the mountains has been reconstructed. The sand originated from a large alluvial fan which was highly active during the Pleistocene. In addition, a thin loess cover is preserved at a few sites in the neighboring mountains ranges. The sedimentation of the loess started around 2000 years later than the sedimentation of the sand at the foot slope. Both archives are related to an increase in precipitation at the northern margin of the Tibetan Plateau which was related to a strengthening of the Asian Monsoon during that time. The wetter climate conditions favored the development of a vegetation cover which leads to the trapping and fixation of the aeolian sediments. However, with a further strengthening of the Monsoon systems these archives subsequently eroded due to higher run off and accumulated as colluvial and fluvial deposits in the basins. These phase lasted until 6 ka. A second aeolian period started at around 3 ka with the formation new dunes in the basins. This period can be associated with dry and cold climate of the late Holocene supporting the reactivation of the sand in the area. This might be further enhanced by an increased human impact by grazing during the late Holocene and resulting

  1. Holocene alluvial fills in the South Loup Valley, Nebraska

    NASA Astrophysics Data System (ADS)

    May, David W.

    1989-07-01

    Four Holocene alluvial fills are present in Nebraska's South Loup River valley. Fill IV, the oldest and thickest, was deposited between 10,200 and 4800 14C yr B.P.; Fill III has an age of about 3000 14C yr B.P.; Fill II is younger than 2100 and older than 900 14C yr B.P.; and Fill I is younger than 900 14C yr B.P. Regional contemporaneity of valley alluviation in the eastcentral Great Plains suggests that climate has controlled long-term sediment storage in the South Loup River valley.

  2. Holocene glaciation of the central Sierra Nevada, California

    NASA Astrophysics Data System (ADS)

    Bowerman, Nicole D.; Clark, Douglas H.

    2011-05-01

    Sediment cores from two bedrock-dammed lakes in North Fork Big Pine Creek, Sierra Nevada, California, preserve the most detailed and complete record of Holocene glaciation yet recovered in the region. The lakes are fed by outwash from the Palisade Glacier, the largest (˜1.3 km 2) and presumably longest-lived glacier in the range, and capture essentially all of the rock flour it produces. Distinct late-Holocene (Matthes) and late-Pleistocene (Recess Peak) moraines lie between the modern glacier and the lakes. The lakes have therefore received continuous sedimentation from the basin since the retreat of the Tioga glacier (Last Glacial Maximum) and capture rock flour related to all post-LGM advances. A total of eight long cores (up to 5.5 m sediment depth) and one short surface sediment short core preserve a coherent record of fluctuating rock flour flux to the lakes through the Holocene. Age constraints on rock flour spikes in First and Second lakes based on 31 14C-dated macrofossils indicate Holocene glaciation began ˜3200 cal yr B P, followed by a possible glacier maximum at ˜2800 cal yr B P and four distinct glacier maxima at ˜2200, ˜1600, ˜700 and ˜250-170 cal yr. B.P., the most recent maximum being the largest. Reconstruction of the equilibrium-line altitudes (ELA) associated with each distinct advance recorded in the moraines (Recess Peak, Matthes, and modern) indicates ELA depressions (relative to modern) of ˜250 m and 90 m for Recess Peak and Matthes advances, respectively. These differences represent decreases in summer temperatures of 1.7-2.8 °C (Recess Peak) and 0.2-2° (Matthes), and increases in winter precipitation of 22-34 cm snow water equivalent (s.w.e.) (Recess Peak) and 3-26 cm s.w.e. (Matthes) compared to modern conditions. Although small, these changes are significant and similar to those noted in the Cascade Range to the north, and represent a significant departure from historical climate trends in the region.

  3. Holocene Paleoecology of the Western Tenere Desert, Niger, Africa

    NASA Astrophysics Data System (ADS)

    Sereno, P. C.; Caran, S. C.; Housh, T. B.

    2007-12-01

    Multiple paleontological, sedimentological, and isotopic/ionic geochemical indicators permit reconstruction of the Holocene ecology of the western Tenere Desert (southern Sahara hyper-desert). Modern precipitation is highly erratic, averaging 25 mm yearly, and vegetative cover is negligible. From the early to middle Holocene, however, grassland-shrublands and seasonal to permanent lakes and wetlands predominated, supporting diverse limnic, riparian, and upland communities. Annual precipitation probably was comparable to that of the modern southern Sahel, exceeding 350 mm. Coarse-grained sediment washed into the large lacustrine basin from exposures of metamorphic, plutonic, and volcanic rocks in the nearby Air Massif highland. Lake margins fluctuated in response to runoff and limited ground-water discharge. The water was non-saline and there is no evidence of evaporite deposition. Aquatic and riparian macrophytes thrived, as did an extensive lacustrine-palustrine macrofauna. A Sahelian flora of mixed grasses, thorn shrubs, and perhaps some larger woodland species occupied the contiguous uplands, supporting resident and migratory mammalian and avian faunas. Lake levels were high until 6300 to 5200 BP, possibly as late as 4800 BP locally. Deflation of lacustrine deposits during a subsequent dry period provided finer-grained eolian sediment accreting as proximal dunes. The composition of mineral sediment within the middle to late Holocene dunes is different from, but clearly a subset of the lacustrine deposits. Organic matter reworked from the lake sediment was deposited in the dunes and oxidized in situ, generating CO2 that dissolved in soil moisture, producing bicarbonate. The bicarbonate reacted with calcium from weathered minerals, producing calcic cementation about 5100 BP. The resulting petrocalcic horizon was later exposed, weathered, and colonized by sparse terrestrial vegetation for one or more brief periods. A late phase of pedogenesis concurrent with or

  4. Appalachian Piedmont landscapes from the Permian to the Holocene

    USGS Publications Warehouse

    Cleaves, E.T.

    1989-01-01

    Between the Potomac and Susquehanna Rivers and from the Blue Ridge to the Fall Zone, landscapes of the Piedmont are illustrated for times in the Holocene, Late Wisconsin, Early Miocene, Early Cretaceous, Late Triassic, and Permian. Landscape evolution took place in tectonic settings marked by major plate collisions (Permian), arching and rifting (Late Triassic) and development of the Atlantic passive margin by sea floor spreading (Early Cretaceous). Erosion proceeded concurrently with tectonic uplift and continued after cessation of major tectonic activity. Atlantic Outer Continental Shelf sediments record three major erosional periods: (1) Late Triassic-Early Jurassic; (2) Late Jurassic-Early Cretaceous; and (3) Middle Miocene-Holocene. The Middle Miocene-Holocene pulse is related to neotectonic activity and major climatic fluctuations. In the Piedmont upland the Holocene landscape is interpreted as an upland surface of low relief undergoing dissection. Major rivers and streams are incised into a landscape on which the landforms show a delicate adjustment to rock lithologies. The Fall Zone has apparently evolved from a combination of warping, faulting, and differential erosion since Late Miocene. The periglacial environment of the Late Wisconsin (and earlier glacial epochs) resulted in increased physical erosion and reduced chemical weathering. Even with lowered saprolitization rates, geochemical modeling suggests that 80 m or more of saprolite may have formed since Late Miocene. This volume of saprolite suggests major erosion of upland surfaces and seemingly contradicts available field evidence. Greatly subdued relief characterized the Early Miocene time, near the end of a prolonged interval of tropical morphogenesis. The ancestral Susquehanna and Potomac Rivers occupied approximately their present locations. In Early Cretaceous time local relief may have been as much as 900 m, and a major axial river draining both the Piedmont and Appalachians flowed southeast

  5. The Holocene separation of Jersey from France: the microfossil evidence

    NASA Astrophysics Data System (ADS)

    Consolaro, Chiara; Hart, Malcolm; Chambers, Paul; Evans, Graham; Nichols, Ralph; Smart, Christopher; Whittaker, John

    2014-05-01

    More than fifty marine boreholes have been drilled into the sea bed between France and the east coast of Jersey and these are being used to plan the route of a new electricity cable. The cores provide a comprehensive coverage of an Holocene sedimentary succession and core OVC-18 is being used as a reference because it contains a near-complete record of the transition from a terrestrial environment, with peats and plant beds, to inter-tidal mud flats and, eventually, marine sediments with abundant marine fossils and highly significant occurrences of the calcareous red alga known as maërl. This core, therefore, contains a near-complete record of mid-late Holocene sea level rise through to the invasion of the slipper limpet Crepidula in 1962. Almost all of the samples contain well-preserved assemblages of foraminifera and ostracods that allow the