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Sample records for holocene infilling processes

  1. Linking Grain Size and Sedimentary Structure to Autogenic and Allogenic Processes Associated with Holocene Valley Infill and Evolution, Brazos River, TX

    NASA Astrophysics Data System (ADS)

    Moran, K. E.; Nittrouer, J.; Lorenzo-Trueba, J.; Anderson, J. B.

    2014-12-01

    The Brazos River exhibits extraordinarily well-constrained allogenic processes including sea level and climate change, and our understanding of these variables prime the Brazos River to be an excellent natural laboratory for the examination of fluvial morphodynamics under the influence of allogenic and autogenic processes. This research seeks to elucidate an understanding of autogenic and allogenic signatures on stratigraphy through morphodynamic modeling of aggradation and avulsions of the Brazos River in conjunction with climate and sea level changes throughout Holocene time. Backwater length scales are hypothesized to propel autogenic responses of the Brazos system by dictating the loci of aggradation, which back-step and fill the valley as sea level rises. The backwater length scale and sea level covary, thus inducing an intrinsic, but historically complex, relationship between autogenic and allogenic processes that is sought to be discerned using the morphodynamic model presented herein. We simulate Brazos fluvial evolution via changes in fluid flow, sediment transport, and bed topography under the influence of allogenic perturbations. The results are used to characterize and quantify the stratigraphic evolution of the Brazos incised valley fill and are readily comparable to numerous previous studies of the system. The infill model is informed by grain size data collected from modern deposits and by modern channel dimensions. This research attempts to link rising Holocene sea level with a backwater length scale which coincides with the extent of back-stepping aggradation within the Brazos incised valley. Modeling responses to perturbations of the Brazos fluvial system can be applied, more holistically, to predict future coastal dynamics and to inform interpretations of paleo-fluvial systems and hydrocarbon reservoirs.

  2. An abrupt backreef infilling in a Holocene reef, Paraoir, Northwestern Luzon, Philippines

    NASA Astrophysics Data System (ADS)

    Gong, Shou-Yeh; Wu, Tso-Ren; Siringan, Fernando P.; Lin, Ke; Shen, Chuan-Chou

    2013-03-01

    We describe a sudden backreef infilling at the west coast of Luzon, Philippines, which occurred after 324 ± 12 yr ago (year BP, before 1950 AD). Results of 30 230Th-dated fossil corals from the surface and 5 cores, 17-29.1 m in length, recovered from a Holocene reef at Paraoir show that the reef flat developed in two stages. The reef margin is dated at 10,256 ± 50 (2 σ) yr BP at 23.9 m below mean sea level (MSL) and about 6,654 ± 29 yr BP at 3.7 m below MSL with ages increasing with depth. The reef flat was formed with sediments of 818-324 yr BP old, which do not follow an age-depth correlation. The evidence suggests that a backreef moat remained empty throughout the buildup of the reef for about 6 kyr and was filled abruptly with a 26-m-thick succession of rubble and bioclastics by an extreme wave event (EWE) after 324 ± 12 yr BP. Field evidence, historical records, and tsunami simulation suggest the EWE sedimentation was likely caused by a single severe tropical cyclone, although the possibility of tsunami is not ruled out. The Paraoir reef flat was built up in a mode different from previously reported cases of Holocene reefs.

  3. 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 ...

  4. 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 ...

  5. 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

  6. Fast Formation of Conductive Material by Simultaneous Chemical Process for Infilling Through-Silicon Via

    NASA Astrophysics Data System (ADS)

    Kawakita, Jin; Chikyow, Toyohiro

    2012-06-01

    It is necessary to develop a fast and inexpensive fabrication process of vertical electric wiring by through-silicon via (TSV) technology for advanced three-dimensional semiconductor devices. In this research, a fast-forming conductive composite was successfully developed by simultaneous deposition of conductive organic polymer (polypyrrole) and metal (silver) from the liquid phase, accelerated by photoirradiation. The growth rate of the composite was 38 nm·s-1, which is more than 10 times higher than that of copper by conventional plating. The electric conductivity of the composite was 2.1×104 Ω-1·cm-1, which is on the same level as general metal conductors. In addition, the effects of reaction conditions on the growth rate and the conductivity of the composites were revealed. From these results, the infilling time of the TSV was expected to shorten from the present 2-10 h to 5-10 m.

  7. 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.

  8. 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

  9. Sediment infilling of Louisiana continental-shelf dredge pits: a record of sedimentary processes in the Northern Gulf of Mexico

    NASA Astrophysics Data System (ADS)

    O'Connor, M. C.; Bentley, S. J.; Xu, K.; Obelcz, J.; Li, C.; Miner, M. D.

    2016-02-01

    Many sand resources, including buried paleo river channels, have been used as dredge sites for coastal restoration; our knowledge of infill rates and dynamics with the seafloor are limited. Sediment cores were collected at continental-shelf sites of the Northern Gulf of Mexico to develop a better understanding of mud-capped dredge pit post-dredging evolution. The two pits studied were Sandy Point (SP) and Raccoon Island (RI) (both at shelf depths of 10m), which were dredged in 2012 and 2013 respectively; vibracores and multicores were collected in 2015 and analyzed for Beryllium-7. SP1, the northwestern site in the Sandy Point dredge pit, showed 26 cm of 7Be. In the Raccoon Island multicores, 7Be penetration depths varied from 36 cm in the center of the dredge pit (RI3) to all 50 cm of the northern-most site (RI1) core, indicating that 7Be occurred deeper than the 50 cm long multicore. Surface sediment samples from outside the pit contained no 7Be. Of note is the surprising rate of deposition within the pits as well as the source of the infill material. Sediments laden with 7Be must have been deposited within 1-3 half lives of 7Be ( 50-150 days) prior to sampling, indicating recent sedimentation rates greater than 26-50 cm/year. The nearest major sources of river sediment are: 12.5 km offshore from Grand Pass of the Mississippi River for SP; and 147 km from the Mississippi and 90 km from the Atchafalaya River for RI. Because rivers are a major source of 7Be in coastal marine sediments, 26-50 cm of 7Be activity indicates rapid and long-distance transport of sediment from a likely fluvial source and suggests that the pits are efficient sediment traps. An alternative hypothesis would be that marine sediment accumulated and efficiently scavenged 7Be from marine and atmospheric sources. Regardless of source, the dredge pits are accumulating a record of sediment that would not be recorded on the shelf otherwise, and collapses of pit walls cannot explain the whole

  10. Sea-level rise and anthropogenic activities recorded in the late Pleistocene/Holocene sedimentary infill of the Guadiana Estuary (SW Iberia)

    NASA Astrophysics Data System (ADS)

    Delgado, J.; Boski, T.; Nieto, J. M.; Pereira, L.; Moura, D.; Gomes, A.; Sousa, C.; García-Tenorio, R.

    2012-02-01

    This study reviews data on sea-level rise during the last 13000 yr cal. BP (13 kyr) as recorded in the estuarine sediments of the Guadiana River (SE Portugal, SW Spain). We combined new data from a 63 m-long borehole, drilled through the entire postglacial sedimentary sequence, with information on five previously studied cores. By integrating sedimentological, geochemical and palaeontological proxies, we were able to make a palaeoenvironmental reconstruction of the Guadiana terminal palaeovalley during the last 13 kyr and propose a curve of sea-level rise for the SW Iberian Atlantic margin. Our foraminifera-based palaeoecological reconstruction, anchored to a 14C age model, reveals rapid sea-level rise from 13 kyr, interrupted during the Younger Dryas and resuming ca 11.5 kyr. The pace of marine transgression slackened ca. 7.5 kyr and since then has progressed upwards at a rate of 1.2 mm yr-1. Holocene-Anthropocene sediments from two boreholes were also analysed to assess the timing, levels and sources of trace metals produced by acid mine drainage from the Iberian Pyrite Belt. Study of metal/aluminium ratios through the profiles allowed background metal concentrations to be estimated from lithostratigraphic units older than ca. 5 kyr (i.e. unaffected by anthropogenic activities). Human activities are especially evident from 4.5 kyr (the beginning of the Copper Age), with anthropogenic sources of metal fluxes prevailing over natural sources (especially Pb, Co, Ni, and Mn, and, to a lesser extent, Zn, Cu, and Ni). Mining activities became particularly intensive between the late Bronze Age and the Roman period (3-1.5 kyr), when the highest metal enrichment factors were recorded: EFPb ≈ 2, EFCd > 10, EFCr ≈ 2, EFCu ≈ 3, EFZn = 1.4.This study reveals the utility of postglacial sedimentary records for reconstructing historical changes in regional water-sediment quality and separating natural and anthropogenic sources of geochemical contaminants.

  11. 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

  12. 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

  13. 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

  14. 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

  15. 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.

  16. 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.

  17. 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...

  18. 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...

  19. 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

  20. Aeolian processes during the Holocene in Gannan Region, Eastern Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Yang, S.; Cheng, T.; Li, S.; Liang, M.

    2016-12-01

    Aeolian desertification occurring in the Tibetan Plateau has received attention recently for it has become a severe environmental problem by accelerating the grassland degradation and eco-environment damage. The Gannan Region is located in the northeastern Tibetan Plateau with a mean altitude of 3500m. It is highly sensitive to global environmental change and human disturbance. Serious soil erosion and desertification and extensive land degradation have caused heavy eco-environmental impacts. To investigate the evolution of the desertification in Holocene in the Plateau is of great importance for understanding the desertification trend under the global changes in the Tibetan Plateau. Loess and aeolian sands is a key geological archive related to desertification processes and the past environment changes. In this study a typical 8.5m-thick loess-sands profile named MQQ, was selected at the Maqu city. It is situated on the first terrace (T1) of the Yellow River. Detailed accelerator mass spectrometry (AMS) 14C dating of bulk organic matter content has shown the Aeolian sediments of the MQQ section occurring since the early Holocene. the mass-specific frequency-dependent magnetic susceptibility (χfd) and grainsize records show a clear upward increase in the contents of superparamagnetic grains and fine fractions in grain size, which indicates a gradual wetting trend during the Holocene.The sediment rates change from very high in the early Holocene to low values after 8.2 ka. The wetting process can be divided into three steps: 10.0-8.2 ka, 8.2-3.0 ka and 3.0-present. It indicates that the climate in the eastern Tibetan Plateau was dry during the early Holocene. After that the climate was getting wet gradually. The variations of the westerlies and the Asian monsoon may cause the environmental change in this region.

  1. 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

  2. Quantitative estimation of Holocene surface salinity variation in the Black Sea using dinoflagellate cyst process length

    NASA Astrophysics Data System (ADS)

    Mertens, Kenneth Neil; Bradley, Lee R.; Takano, Yoshihito; Mudie, Petra J.; Marret, Fabienne; Aksu, Ali E.; Hiscott, Richard N.; Verleye, Thomas J.; Mousing, Erik A.; Smyrnova, Ludmila L.; Bagheri, Siamak; Mansor, Mashhor; Pospelova, Vera; Matsuoka, Kazumi

    2012-04-01

    Reconstruction of salinity in the Holocene Black Sea has been an ongoing debate over the past four decades. Here we calibrate summer surface water salinity in the Black Sea, Sea of Azov and Caspian Sea with the process length of the dinoflagellate cyst Lingulodinium machaerophorum. We then apply this calibration to make a regional reconstruction of paleosalinity in the Black Sea, calculated by averaging out process length variation observed at four core sites from the Black Sea with high sedimentation rates and dated by multiple mollusk shell ages. Results show a very gradual change of salinity from ˜14 ± 0.91 psu around 9.9 cal ka BP to a minimum ˜12.3 ± 0.91 psu around 8.5 cal ka BP, reaching current salinities of ˜17.1 ± 0.91 psu around 4.1 cal ka BP. The resolution of our sampling is about 250 years, and it fails to reveal a catastrophic salinization event at ˜9.14 cal ka BP advocated by other researchers. The dinoflagellate cyst salinity-proxy does not record large Holocene salinity fluctuations, and after early Holocene freshening, it shows correspondence to the regional sea-level curve of Brückner et al. (2010) derived from Balabanov (2007).

  3. Mathematical and field analysis of longitudinal reservoir infill

    NASA Astrophysics Data System (ADS)

    Ke, W. T.; Capart, H.

    2016-12-01

    In reservoirs, severe problems are caused by infilled sediment deposits. In long term, the sediment accumulation reduces the capacity of reservoir storage and flood control benefits. In the short term, the sediment deposits influence the intakes of water-supply and hydroelectricity generation. For the management of reservoir, it is important to understand the deposition process and then to predict the sedimentation in reservoir. To investigate the behaviors of sediment deposits, we propose a one-dimensional simplified theory derived by the Exner equation to predict the longitudinal sedimentation distribution in idealized reservoirs. The theory models the reservoir infill geomorphic actions for three scenarios: delta progradation, near-dam bottom deposition, and final infill. These yield three kinds of self-similar analytical solutions for the reservoir bed profiles, under different boundary conditions. Three analytical solutions are composed by error function, complementary error function, and imaginary error function, respectively. The theory is also computed by finite volume method to test the analytical solutions. The theoretical and numerical predictions are in good agreement with one-dimensional small-scale laboratory experiment. As the theory is simple to apply with analytical solutions and numerical computation, we propose some applications to simulate the long-profile evolution of field reservoirs and focus on the infill sediment deposit volume resulting the uplift of near-dam bottom elevation. These field reservoirs introduced here are Wushe Reservoir, Tsengwen Reservoir, Mudan Reservoir in Taiwan, Lago Dos Bocas in Puerto Rico, and Sakuma Dam in Japan.

  4. Mississippi River delta plain, Louisiana coast, and inner shelf Holocene geologic framework, processes, and resources

    USGS Publications Warehouse

    Williams, S. Jeffress; Kulp, Mark; Penland, Shea; Kindinger, Jack L.; Flocks, James G.; Buster, Noreen A.; Holmes, Charles W.

    2009-01-01

    Extending nearly 400 km from Sabine Pass on the Texas-Louisiana border east to the Chandeleur Islands, the Louisiana coastal zone (Fig. 11.1) along the north-central Gulf of Mexico is the southern terminus of the largest drainage basin in North America (>3.3 million km2), which includes the Mississippi River delta plain where approximately 6.2 million kilograms per year of sediment is delivered to the Gulf of Mexico (Coleman 1988). The Mississippi River, active since at least Late Jurassic time (Mann and Thomas 1968), is the main distributary channel of this drainage system and during the Holocene has constructed one of the largest delta plains in the world, larger than 30,000 km2 (Coleman and Prior 1980; Coleman 1981; Coleman et al. 1998). The subsurface geology and geomorphology of the Louisiana coastal zone reffects a complex history of regional tectonic events and fluvial, deltaic, and marine sedimentary processes affected by large sea-level fluctuations. Despite the complex geology of the north-central Gulf basin, a long history of engineering studies and Scientific research investigations (see table 11.1) has led to substantial knowledge of the geologic framework and evolution of the delta plain region (see also Bird et al., chapter 1 in this volume). Mississippi River delta plain, Louisiana coast, and inner shelf Holocene geologic framework, processes, and resources. Available from: https://www.researchgate.net/publication/262802561_Mississippi_River_delta_plain_Louisiana_coast_and_inner_shelf_Holocene_geologic_framework_processes_and_resources [accessed Sep 13, 2017].

  5. 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

  6. Nonlinear pushover analysis of infilled concrete frames

    NASA Astrophysics Data System (ADS)

    Huang, Chao Hsun; Tuan, Yungting Alex; Hsu, Ruo Yun

    2006-12-01

    Six reinforced concrete frames with or without masonry infills were constructed and tested under horizontal cyclic loads. All six frames had identical details in which the transverse reinforcement in columns was provided by rectangular hoops that did not meet current ACI specifications for ductile frames. For comparison purposes, the columns in three of these frames were jacketed by carbon-fiber-reinforced-polymer (CFRP) sheets to avoid possible shear failure. A nonlinear pushover analysis, in which the force-deformation relationships of individual elements were developed based on ACI 318, FEMA 356, and Chen’s model, was carried out for these frames and compared to test results. Both the failure mechanisms and impact of infills on the behaviors of these frames were examined in the study. Conclusions from the present analysis provide structural engineers with valuable information for evaluation and design of infilled concrete frame building structures.

  7. Late Pleistocene - Holocene surface processes and landscape evolution in the central Swiss Alps

    NASA Astrophysics Data System (ADS)

    Boxleitner, Max; Musso, Alessandra; Waroszewski, Jarosław; Malkiewicz, Małgorzata; Maisch, Max; Dahms, Dennis; Brandová, Dagmar; Christl, Marcus; de Castro Portes, Raquel; Egli, Markus

    2017-10-01

    The European Alps are a geomorphologically active region and experience a number of gravity-driven hillslope processes. Soil and landscape formation in the Alps has consequently undergone several minor and major traceable changes of developmental trajectories during the Holocene. Soil development is hypothesised to be often non-linear with time and characterised by stages of progressive and regressive evolution caused by upbuilding (formation, profile deepening) and erosion (profile shallowing). Several cold and warm climate phases are identified during the Holocene but it is largely unknown which effects these might have had on slope processes. By using datable moraines (10Be) and mires (14C), we have constructed a temporal framework for these processes. Using the geochemical imprint of mires in the Alpine setting of the Göschener-valley of the Central Swiss Alps, we reconstructed general (mostly erosional) landscape processes for the last ca. 10 ka. As this is the type locality for the Göschener cold phase, we assumed that this phase (Göschener cold phase I and II 1.5 and 2.5 ka BP) should have left easily recognizable traits. After deglaciation (11-12 ka BP), soil evolution was progressive. Beginning around 8 ka BP, we detect a distinct increase in erosion here, together with a vegetation change (towards tundra vegetation) and the highest measured rates of carbon sequestration. Other phases of high geomorphic activity were recognised ca. 5-6 ka BP, 4 ka BP and, to a lesser extent, 1-3 ka ago. The cold phase at 5-6 ka BP corresponds to a less distinct change in vegetation and lessened erosion. Human impact is increasingly obvious since about 2.4 ka BP which overlaps with the Göschener cold phase. Nonetheless, erosion processes were not extraordinarily high during this period and a climate effect cannot be distinguished. We detect evidence of increasing human disturbance (regressive soil evolution) for about the last 1 ka. We also detect an increase in dust

  8. 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.

  9. 3. EAST SIDE. Infill under portico roof from downspout to ...

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

    3. EAST SIDE. Infill under portico roof from downspout to right not original. See HABS No. SC-483-4 for extent of original infill - Stephan Williams House, U.S. Route 176, Holly Hill, Orangeburg County, SC

  10. 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

  11. Holocene ecological change in relation to hydroclimate variability and post-landslide landscape processes in semi-arid watersheds, Lost River Range, Idaho, USA

    NASA Astrophysics Data System (ADS)

    Krueger, C. R.; Finney, B.; Shapley, M.

    2013-12-01

    Lake sediment cores were collected from two landslide formed lakes in the Lost River Range, central Idaho. Grouse Creek Lake (2 m deep) is in a basin that was formed when a drainage was impounded by a debris slide, likely more than 10,000 yr BP. Under present conditions Grouse Creek Lake is closed to surface water outflow. Since the deposition of the Mazama tephra (c.a., 7,550 yr BP) 2.5 m of sediment containing authigenic carbonate has accumulated in this lake. Modern lake water dD and d18O displays an evaporative signal indicating that oxygen isotopes from Grouse Creek Lake authigenic carbonates should record a signal that is sensitive to past changes in precipitation and evaporation. This core was sampled at 1 cm intervals and sieved at 20 um to remove detrital and biogenic carbonate in preparation for analysis of the fine-grained, authigenic carbonate fraction. The oxygen isotope signal recovered has a range of 5‰ over the length of the record, with several major fluctuations since the deposition of the Mazama tephra. While the d18O generally increases over this period indicating decreasing effective precipitation (P - E), we are modeling the affects of changes in lake hypsometry due to sediment infilling on the isotopic composition of lake water to quantify the hydroclimate signal in the isotopic data. Carlson Lake (10 m deep) formed in the source area of a middle Holocene mudflow. Modern lake water chemistry indicates that Carlson Lake is sensitive to evaporative processes, however sediments from Carlson Lake do not contain enough carbonate for oxygen isotope analysis. A multiproxy effort (C and N isotopes, biogenic silica) is underway to understand how the landscape around Carlson Lake responded to changes in hydroclimate (as determined by the record from Grouse Creek Lake) and post-landslide soil and geomorphic processes. These records are from a region with sparse long-term hydroclimate data, and ultimately will help improve our understanding of past

  12. Pre-transgression morphology and Holocene stratigraphy of the Delaware estuarine and Atlantic coasts

    SciTech Connect

    Chrzastowski, J.J.; Kraft, J.C.

    1985-01-01

    The Holocene stratigraphic sequences of the ocean and estuarine coasts of Delaware record the marine transgression and sedimentary infill of deeply incised valleys of the ancestral Delaware River and its tributaries. Suspended sediment of the Delaware estuary has played an important role in the antecedent valley infill. Fine-grained deposition marginal to the ocean coast occurs in lagoonal, tidal stream and marsh environments. The stratigraphy of the lagoonal and estuarine shore areas show that a 1-2 m depth ravinement process is operative in these low energy coastal environments producing an eroded surface which precedes and is stratigraphically separate from the deeper (10 m depth) Atlantic shoreface ravinement. As the transgression continues, preservation of the Holocene sedimentary sequences is dependent on rate of sea-level rise and depth of ravinement. Relief on the antecedent topography is equally important, with maximum preservation occurring in antecedent valleys. At interglacial peak sea levels, lithosomes of all the paralic environments (including barriers and spits) may be preserved in lateral and vertical relationships unmodified by the ravinement process.

  13. Feedback process responsible for the suppression of ENSO activity during the mid-Holocene

    NASA Astrophysics Data System (ADS)

    An, Soon-Il; Bong, Hayoung

    2017-04-01

    Using the output of 12 models from the Paleoclimate Modeling Intercomparison Project Phase 3, we investigate the feedback process responsible for changes in El Niño-Southern Oscillation activity during the mid-Holocene based on a linear stability index (Bjerknes stability index; BJ index) analysis. The multi-model ensemble mean (MME) variance of the Niño-3.4 index (sea surface temperature anomalies averaged over 5°S-5°N, 170°-120°W) simulated for 6000 years ago (6 kya) was 13% lower than that for the pre-industrial era (0 kya), while changes in the MME BJ index were negligible. This is due to a balance between enhanced damping by anomalous thermal advection by mean currents (MA) and enhanced positive thermocline feedback (TH). Seven of the models show that MME variance of the Niño-3.4 and BJ indexes for the 6 kya run is 21 and 70% lower, respectively, than the 0 kya run. However, two models show the opposite change. Interestingly, MA in both model groups increases, especially due to the mean meridional current associated with enhanced trade winds, indicating a robust mechanism. The opposite tendency between the two groups is mainly due to large TH in the second group 6 kya, as a result of enhanced air-sea coupling and strongly reduced ocean stratification due to subsurface warming, which led to increased sensitivity of the zonal thermocline contrast to surface zonal wind stress.

  14. 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.

  15. 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

  16. Infill drilling keys recent Midcontinent activity

    SciTech Connect

    Petzet, G.A.

    1987-06-08

    Increased density and other development drilling headed Midcontinent activity in 1987 and late 1986 as most operators shifted spending to prospects they expected to pay out at $15-17/bbl for oil and $1.50/Mcf for gas. Exploration took a back seat, but a few interesting discoveries turned up in Oklahoma and Kansas. As 1987 budgets became available, operators spudded key wildcats in Oklahoma and Iowa. Kansas approved blanket infill drilling in most of the 4,163 spacing units in Kansas Hugoton field at the rate of one fourth of each operator's locations per year. Most operators began drilling eligible locations during first quarter 1987. Oklahoma asked operators to comment on whether it should move toward infill drilling in Guymon-Hugoton Gas Area, the Oklahoma portion of Hugoton field.

  17. Infill development in an old field

    SciTech Connect

    New, K.T.C.; Slik, P.; Tan, B.C. )

    1988-01-01

    The Seria field, on the North Western coastline of Borneo, South East Asia, has been in production since 1930 and up to now some 34% of STOIIP has been produced by 760 wells. Ultimate Recovery, estimated from extrapolation of performance is 39% of STOIIP. This paper outlines the approach followed in planning of infill drilling and presents a recent experience for the Seria West (SW) block and three other blocks of field.

  18. 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

  19. Evolutionary process of saline-water intrusion in Holocene and Late Pleistocene groundwater in southern Laizhou Bay.

    PubMed

    Liu, Sen; Tang, Zhonghua; Gao, Maosheng; Hou, Guohua

    2017-12-31

    Saline water intrusion is one of the most serious groundwater problems in southern Laizhou Bay. In this study, formation of groundwater with different qualities and saline water intrusion were analyzed using hydrochemical and stable isotopic methods, and the Hydrochemical Facies Evolution Diagram (HFE-Diagram). The results demonstrate that the structure of the sedimentary layer in this area is the dominant controlling factor of groundwater distribution. From the south (land) to the north (sea), the hydrochemical distribution presents a regular changing pattern following the order: HCO3-Na·Mg and HCO3·Cl-Mg·Ca (fresh water), HCO3·Cl-Na·Mg (brackish water), Cl-Na·Mg (saline water), Cl-Na (saline water) and Cl·HCO3-Na (brackish water). Hydrochemical data show that saline water and brine are not the result of evaporation or the concentration of seawater. Brackish water and saline water with low mineralization in Holocene groundwater are formed by the mixing of fresh water and highly mineralized saline water, dissolution of evaporates by meteoric water, and water/salt interaction. And the saline water formed through dissolution of evaporates in Holocene and Late Pleistocene groundwater. Isotopic results reveal that the main recharge of saline water in Holocene groundwater and Late Pleistocene groundwater is a combination of the meteoric water and lateral recharge from rivers. Saline water intrusion was found to follow a wedge-shaped intrusion pattern. Significant variations in Cl(-) and Na(+)indicate saline intrusion in the southern area. The degree of saline water intrusion in Holocene groundwater was found to be more serious than that in Late Pleistocene groundwater. Hydrochemical data and HFE-Diagram show that there is an intrusion process in Holocene groundwater. In this process, it is accepted the fresh water recharge, such as meteoric water and lateral recharge from rivers. In Late Pleistocene groundwater, it presents a simple intrusion process from saline

  20. 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

  1. 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.

  2. 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.

  3. 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.

  4. Modelling of masonry infill walls participation in the seismic behaviour of RC buildings using OpenSees

    NASA Astrophysics Data System (ADS)

    Furtado, André; Rodrigues, Hugo; Arêde, António

    2015-06-01

    Recent earthquakes show that masonry infill walls should be taken into account during the design and assessment process of structures, since this type of non-structural elements increase the in-plane stiffness of the structure and consequently the natural period. An overview of the past researches conducted on the modelling of masonry infilled frame issues has been done, with discussion of past analytical investigations and different modelling approaches that many authors have proposed, including micro- and macro-modelling strategies. After this, the present work presents an improved numerical model, based on the Rodrigues et al. (J Earthq Eng 14:390-416, 2010) approach, for simulating the masonry infill walls behaviour in the computer program OpenSees. The main results of the in-plane calibration analyses obtained with one experimental test are presented and discussed. For last, two reinforced concrete regular buildings were studied and subjected to several ground motions, with and without infills' walls.

  5. Habitat, dispersal and propagule pressure control exotic plant infilling within an invaded range

    Treesearch

    Robert J. Warren; T. Ursell; A.D. Keiser; M.A. Bradford

    2013-01-01

    Deep in the heart of a longstanding invasion, an exotic grass is still invading. Range infilling potentially has the greatest impact on native communities and ecosystem processes, but receives much less attention than range expansion. ‘Snapshot’ studies of invasive plant dispersal, habitat and propagule limitations cannot determine whether a landscape is saturated or...

  6. Impact of active faulting on the post LGM infill of Le Bourget Lake (western Alps, France)

    NASA Astrophysics Data System (ADS)

    de La Taille, Camille; Jouanne, François; Crouzet, Christian; Beck, Christian; Jomard, Hervé; de Rycker, Koen; Van Daele, Maarten

    2015-11-01

    We have used high resolution seismic imaging to detect and characterize the recent deformation recorded by the Quaternary sediments of Le Bourget Lake. The last glacial episodes (MIS 6a and 2, i.e., Riss and Würm) scoured out an elongated over-deepened basin to more than 300 m below the present lake level and the basin accumulated 150 m of post-LGM to Holocene sediments. The well-stratified character of the infill is locally disturbed by tectonic deformations and gravity reworking. A northern fault zone, in continuation with the left-lateral strike-slip Culoz Fault, is imaged within the Holocene and Late Glacial accumulations. A southern fault zone is also detected, which can be related to the sub-lacustrine continuation of a much smaller fault affecting the Jura alpine foreland: the Col du Chat left lateral strike-slip fault. Different generations of fractures have been identified in the lake, allowing correlation and mapping. In pre-Quaternary substratum, the Culoz Fault has a N 160° orientation. Within the post-LGM sediments, fractures related to the Culoz Fault have an orientation between N135° and 95°. A Cloos model (1932) is thus proposed to explain the observed pattern of lacustrine deformations. The calculated horizontal slip rate for Culoz Fault during Holocene is about 1.3 mm·yr- 1, and for the Col du Chat Fault is around 0.6 mm·yr- 1.

  7. 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

  8. 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.

  9. The eruption, pyroclastic flow behaviour, and caldera in-filling processes of the extremely large volume (> 1290 km3), intra- to extra-caldera, Permian Ora (Ignimbrite) Formation, Southern Alps, Italy

    NASA Astrophysics Data System (ADS)

    Willcock, M. A. W.; Cas, R. A. F.; Giordano, G.; Morelli, C.

    2013-09-01

    The Permian Ora Formation (277-274 Ma) preserves the products of the Ora caldera 'super-eruption', Northern Italy. The stratigraphic architecture of the exceptionally well preserved intra-caldera succession provides evidence for caldera collapse at the onset of the eruption, a multiple discharge point, fissure eruption style, and progressive, incremental caldera in-filling by numerous pyroclastic flow pulses within the caldera. The ignimbrites of the Ora Formation are voluminous (> 1290 km3), crystal-rich (~ 25 to 55%), and ubiquitously welded. The Ora Formation has been divided into four members (a-d), which also define the principal eruption phases. The eruption proceeded in four main stages: (1) early caldera collapse and vent opening, producing locally distributed, basal co-ignimbrite lithic breccia (member a); (2) vent clearing, which produced the eutaxitic, lithic-rich ignimbrite and minor thin ground and ash-cloud surge deposits (member b); (3) waxing and steady eruption, which produced the dominant eutaxitic, coarse-crystal-rich ignimbrite, with local lithic-rich and fine-crystal-rich ignimbrite and minor surge deposits (member c); and (4) waning eruption, recorded by the eutaxitic, fine-crystal-rich ignimbrite, with local lithic-rich ignimbrite deposits (member d).

  10. 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

  11. 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

  12. Measuring the Air Quality and Transportation Impacts of Infill Development

    EPA Pesticide Factsheets

    This report summarizes three case studies. The analysis shows how standard forecasting tools can be modified to capture at least some of the transportation and air quality benefits of brownfield and infill development.

  13. 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

  14. 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.

  15. 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

  16. 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

  17. A Bayesian approach to flow record infilling and extension for reservoir design

    NASA Astrophysics Data System (ADS)

    Jones, D. A.; Sene, K. J.

    A Bayesian approach is described for dealing with the problem of infilling and generating stochastic flow sequences using rainfall data to guide the flow generation process, and including bounded (censored) observed flow and rainfall data to provide additional information. Solutions are obtained using a Gibbs sampling procedure. Particular problems discussed include developing new procedures for fitting transformations when bounded values are available, coping with additional information in the form of values, or bounds, for totals of flows across several sites, and developing relationships between annual flow and rainfall data. Examples are shown of both infilled values of unknown past river flows, with assessment of uncertainty, and realisations of flows representative of what might occur in the future. Several procedures for validating the model output are described and the central estimates of flows, taken as a surrogate for historical observed flows, are compared with long term regional flow and rainfall data.

  18. Controls of Holocene to contemporary sedimentary source-to-sink fluxes in valley-fjord systems in western Norway

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

    The presented research has been carried out since 2004 in two selected valley-fjord systems (Erdalen and Bødalen) in Nordfjord, western Norway. The focus of the work has been on Holocene to contemporary sedimentary fluxes and budgets, with particular interest in (i) Analyzing in which way glacial isostatic adjustment and surface denudational processes have been interacting over the Holocene, (ii) Analyzing how the inheritance of the landscape due to the influence of the Last Glacial Maximum (LGM) has affected surface process rates over time, (iii) Documenting changes in surface process rates over different timescales by combining knowledge on Holocene surface process rates with data on subrecent and contemporary surface process rates. Detailed and longer-term monitoring of relevant denudational surface processes in the Erdalen and Bødalen drainage basin systems has provided high-resolution data for analyzing and quantifying contemporary solute and sedimentary fluxes as well as sediment sources, denudation rates, and meteorological and topographical / landscape morphometric controls of denudational surface processes. Proglacial lakes are functioning as significant sediment traps (with trap efficiencies reaching up to 85%) within both drainage basins and the volume and composition of lake sediments have been studied by using echo-sounder, georadar and different sediment coring techniques. Investigations on volumes and architecture of storage elements (talus cones, valley infills, deltas at the outlets of Erdalen and Bødalen) using different geophysical methods like georadar and seismic refraction surveys have been carried out to get quantitative knowledge on Holocene process rates and sedimentary budgets. Detailed geomorphological mapping has been conducted and interpreted in combination with slope and valley morphometric analyses and digital elevation models and data. It is found that the U-shaped valley morphometry is the main control of the spatial organization

  19. Infilling and quality checking of discharge, precipitation and temperature data using a copula based approach

    NASA Astrophysics Data System (ADS)

    Anwar, Faizan; Bárdossy, András; Seidel, Jochen

    2017-04-01

    Estimating missing values in a time series of a hydrological variable is an everyday task for a hydrologist. Existing methods such as inverse distance weighting, multivariate regression, and kriging, though simple to apply, provide no indication of the quality of the estimated value and depend mainly on the values of neighboring stations at a given step in the time series. Copulas have the advantage of representing the pure dependence structure between two or more variables (given the relationship between them is monotonic). They rid us of questions such as transforming the data before use or calculating functions that model the relationship between the considered variables. A copula-based approach is suggested to infill discharge, precipitation, and temperature data. As a first step the normal copula is used, subsequently, the necessity to use non-normal / non-symmetrical dependence is investigated. Discharge and temperature are treated as regular continuous variables and can be used without processing for infilling and quality checking. Due to the mixed distribution of precipitation values, it has to be treated differently. This is done by assigning a discrete probability to the zeros and treating the rest as a continuous distribution. Building on the work of others, along with infilling, the normal copula is also utilized to identify values in a time series that might be erroneous. This is done by treating the available value as missing, infilling it using the normal copula and checking if it lies within a confidence band (5 to 95% in our case) of the obtained conditional distribution. Hydrological data from two catchments Upper Neckar River (Germany) and Santa River (Peru) are used to demonstrate the application for datasets with different data quality. The Python code used here is also made available on GitHub. The required input is the time series of a given variable at different stations.

  20. Neogene basin infilling from cosmogenic nuclides (10Be and 21Ne) in Atacama, Chile

    NASA Astrophysics Data System (ADS)

    Sanchez, Caroline; Regard, Vincent; Carretier, Sébastien; Riquelme, Rodrigo; Blard, Pierre-Henri; Campos, Eduardo; Brichau, Stéphanie; Lupker, Marteen; Hérail, Gérard

    2017-04-01

    In the hyperarid Atacama Desert, northern Chile, Neogene sediments host copper rich layers (exotic supergene mineralization). Current mines are excavated into relatively thin (<200-300 m) Neogene basins whose infilling chronology is poorly constrained. We took advantage of one of these mining pits, and sampled for 10Be and 21Ne cosmogenic nuclide dosing. These cosmogenic nuclides help constraining the infilling chronology. Indeed, basin sediments were deposited with a cosmogenic nuclide content acquired on hillslopes. Then within the basin, cosmogenic nuclide concentrations evolved through the competing production (quickly decreasing with depth) and disintegration (not for 21Ne). Sampling depths are at ˜100 m and at ˜50 m below the desert surface. First, 21Ne gives lower boundaries for upstream erosion rates or local sedimentation rate. These bounds are between 2 and 10 m/Ma, which is quite important for the area. The ratio between the two cosmogenic nuclides indicate a maximum burial age of 12 Ma (minimal erosion rate of 15 m/Ma) and is surprisingly similar from bottom to top, indicating a probable rapid infilling. We finally processed a Monte-Carlo inversion. This inversion helps taking into account the post-deposition muonic production of cosmogenic nuclides. Inversion results is dependent on the muonic production scheme. Interestingly, the similarity in concentrations from bottom to top pleads for quite low production at depth. Our data finally indicates a quick infilling between 12.5 and 10 Ma BP accounting for ˜100 m of deposition (minimum sedimentation rate of 40 m/Ma).

  1. 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.

  2. 3. SOUTH FRONT, INFILL SECTION, LOOKING NORTH; MAIN SECTION OF ...

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

    3. SOUTH FRONT, INFILL SECTION, LOOKING NORTH; MAIN SECTION OF 90 BROAD STREET VISIBLE AT LEFT SIDE OF PHOTOGRAPH, OLD JEWISH ORPHANAGE (HABS NO. SC-13-15) VISIBLE AT RIGHT SIDE OF PHOTOGRAPH - 90 Broad Street (Commercial Building), Charleston, Charleston County, SC

  3. Holocene ruptures along the North Anatolia Fault in the Marmara Sea, Turkey: Sedimentary processes, spatial extent and age

    NASA Astrophysics Data System (ADS)

    Braudy, N.; McHugh, C. M.; Cagatay, M.; Seeber, L.; Henry, P.; Geli, L.

    2010-12-01

    The North Anatolian fault (NAF), which extends east west for over 1600 km across Turkey, is one of the world's major continental transforms. Since 1939, a sequence of M>7 earthquakes ruptured progressively westward the entire NAF east of Marmara. The most recent and westernmost events in this sequence, the Mw7.4 Izmit and the Mw7.2 Duzce main shocks of 1999, ruptured about 160 km of the fault and were particularly destructive (~17,000 deaths). The only portion of the NAF that did not rupture in the last century is the segment beneath the Marmara Sea that is considered a seismic gap and presents high risk to Istanbul and surroundings. To decipher Holocene earthquake ruptures and the processes leading to their signature in the sedimentary record we applied submarine paleoseismology techniques to study a transect of three 10 m long cores recovered from the Central Basin. The sediments were analyzed with x-ray radiography, for grain size variability at cm-scale, geochemical elements at mm-scale and physical properties. These measurements were calibrated to a chronology developed from short-lived radioisotopes (137-Cs, 210-Pb) and radiocarbon. Turbidites were sampled from the deepest part of the Central Basin, from 1248 to 1262 m depth. As previously documented by McHugh et al (2006), these turbidites are characterized by multiple sand and coarse silt beds, each normally graded, and that together grade upwards into a non-stratified silt that also fines upwards. Elemental concentrations of Al and Si increase with the sand and coarser silt components indicative of an influx of terrigenous components. These complex turbidites-homogenites are as thick as 1 m and dominate the sedimentation in the basin (≈80%). The remainder includes 10 to 20 cm thick fining upwards silt deposits. We interpret these depositional events to represent large earthquakes, the ones including transport of sand are proximal, and the ones without the sand are distal. We measured concentrations of Ca

  4. 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.

  5. The bone degenerative processes in senile fishes from Holocene Brazilian shell mounds.

    PubMed

    Aguilera, O; Rocha, I; Lopes, M S; Lima, I; Lopes, R T; Machado, A S; Guimarães, R B; Crapez, M A C; Tenório, M C; Nepomuceno, A

    2017-07-14

    Zooarchaeological collections from shell mounds in Rio de Janeiro (2,470-4,632 cal BP) contain a high prevalence of swollen fish bones belonging to the Atlantic spadefish (Chaetodipterus faber), crevalle jack (Caranx hippos) and fat snook (Centropomus parallelus). Given the lack of knowledge of the bone degenerative process in senile fishes, this study analysed hyperostotic bone in zooarchaeological and modern specimens to obtain high-resolution morphology and microstructure reconstruction. We used microCT as well as X-ray diffraction to characterize the crystallographic changes associated with fish senility. Our results showed that trabecular microstructures in hyperostotic bones were consistent with estimated values of the per cent bone volume-to-total volume ratio (BV/TV) and were greater than 60% in cortical bone. Hyperostotic bones indicated a high radiograph density, and X-ray diffractograms showed a decrease in hydroxyapatite [Ca10 (PO4 )6 (OH)2 ] and calcite (CaCO3 ) neocrystallization. These crystalline and density changes revealed an advanced stage of fish senile and indicate the vulnerability of ageing fish populations. © 2017 John Wiley & Sons Ltd.

  6. 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.

  7. 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

  8. 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.

  9. 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.

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

    PubMed

    Liu, Yao; Gibbs, Markelle; Perkins, Craig L; Tolentino, Jason; Zarghami, Mohammad H; Bustamante, 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. (1) 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.

  11. Deciphering the geochemical and mineralogical changes of a Miocene sedimentary basin infill, Mendoza Province, Argentina

    NASA Astrophysics Data System (ADS)

    Hunger, Gabriel; Moscariello, Andrea; Ventra, Dario

    2017-04-01

    Sediments deposited in foreland basins are accurate recorders of processes acting at different temporal and spatial scales during orogenic uplift. The effects of allogenic forcing on foreland sedimentation are well known at basin-scale, but uncertainties remain in deciphering and interpreting them at higher resolution, and in differentiating them from the sedimentary changes due to autogenic processes. We present observations on the continental sedimentology and stratigraphy of the Central Argentinian Foreland. The majority of the basin infill is comprised by the Mariño Fm. and La Pilona Fm., which were deposited during the Miocene and cover almost 2000 m of stratigraphy. The large scale stratigraphy trend leads to interpret the entire alluvial system as a large fluvial fan that prograded over the proximal margin of the foreland basin. The basin infill records a continuous sediment supply from the rising Principal Cordillera and the first stages of the uplift of the Frontal Cordillera. The interaction of different allogenic forcing factors, but also autogenic processes, is recorded in the compositional changes of the sedimentary infill. This project aims to provide a detailed reconstruction of paleoenvironmental dynamics and unravel the relative roles of climate and tectonics, using a high-resolution, integrated compositional and sedimentological analysis of the Mariño Formation and the basal part of the La Pilona Formation. The followed approach embodies the use of automated QEMSCAN technology, geochemistry, heavy-minerals and radiogenic isotope analysis. Along 1500 m of stratigraphy we recognize compositional variations related to the evolution of the basin infill due to, at least, 5 phases of non-steady state conditions. Principal component analysis done with the major elements, main mineral phases and heavy minerals allow us to recognize the importance of the weathering and diagenesis in the total compositional variability. The A-CN-K ternary diagram displays

  12. 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

  13. Holocene and modern sediments in the Seine estuary (France): a synthesis

    NASA Astrophysics Data System (ADS)

    Lesueur, P.; Lesourd, S.; Lefebvre, D.; Garnaud, S.; Brun-Cottan, J. C.

    2003-02-01

    This synthesis of numerous studies on the Holocene and modern sediments in the macrotidal setting of the Seine estuary demonstrates their overall evolution. In common with a number of estuaries, the lower Seine was an incised valley during the Weichselian glacio-eustatic sea-level fall, and infilling occurred during the subsequent lowstand, the Holocene sea-level rise and the late Holocene stillstand. In the upper estuary, above the basal gravel bed, fluvial freshwater deposits filled the valley. Next, fine sand and silts invaded the estuary upstream to Rouen; the sequence ends in loam, resulting from an increase in the supply of sediment to the fluvial system. In the upper estuary, anthropogenic deepening of the modern channel results in erosion of the Holocene sediments; the only bedforms are thin and narrow sand sheets and some rare megaripples. In the lower estuary, above the Weichselian basal gravel, the Holocene wedge records the change from a transgressed fluvial setting (i.e. gravel beds) to an open estuarine environment (i.e. tidal delta). The modern Seine estuary has been progressively infilled by marine sands and silts. Now silts and clays supplied during high river flows accumulate at the outlet, and offshore sands and gravel of the eastern Bay of the Seine are temporarily covered with veneers of mud. These freshly deposited muds (i.e. mud patches) are periodically partly reworked by waves and strong tidal currents, but silting of the inner shelf is noticeable.

  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. Reinterpretation of the Quaternary sedimentary infill of the Ría de Vigo, NW Iberian Peninsula, as a compound incised valley

    NASA Astrophysics Data System (ADS)

    Martínez-Carreño, N.; García-Gil, S.

    2017-10-01

    Seismic data have been used to investigate the stratigraphy of the Galician rias for more than two decades. Here, we present a new interpretation of the sedimentary infill of an incised valley (Ría de Vigo, NW Iberian Peninsula), based on high-resolution seismic profiles, core sediment analysis, and radiocarbon 14C data. The new data indicate that the stratigraphic architecture of the Galician rias result from multiple incision/infill phases and, therefore, they are reclassified as compound rather than simple incised valleys. Seven seismic units were identified: one of Tertiary age (U1), four of Pleistocene age (U2-U5) which are interpreted as 4th-order sequences deposited between MIS 11 and MIS 2, and Late Pleistocene (U6) and Holocene (U7) units corresponding with post-glacial sedimentation. The sedimentary infill overlies a highly faulted irregular granitic and metamorphic basement; the inherited morphology is shown to be important for controlling the pathway and evolution of the fluvial network as well as preservation of the sedimentary deposits during several glacial/interglacial cycles. The presence of a rocky barrier at the mouth of the ria is a distinctive feature that conditions sedimentation and exchange of sediment between the ria and the adjacent shelf. For the first time, faults and tilted blocks affecting Late Pleistocene (MIS 3) deposits have been identified. The new data presented here provide the opportunity to reconstruct the evolution of the sedimentary infill of a ria, with especially high-resolution during the last post-glacial transgression.

  17. Evaluation of Channel Infill Processes in Relation to Forcing Data

    DTIC Science & Technology

    2016-05-01

    often more exposed either due to decreased land cover or the receding water levels and therefore more prone to erosion by wind or rain. Additionally...System (SJOFS) to show only the general progression of tides near Mayport. WIND -DRIVEN MECHANISMS: Winds are another important meteorological forcing...factor that influences flows in navigation channels both when considered in the context of strong tropical storms as well as the typical wind direction

  18. 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.

  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. Reassessing Catastrophic Infill of the Pokhara Valley, Nepal Himalaya

    NASA Astrophysics Data System (ADS)

    Schwanghart, Wolfgang; Bernhardt, Anne; Stolle, Amelie; Adhikari, Basantha; Korup, Oliver

    2014-05-01

    The Pokhara valley, home to Nepal's second largest city and a major tourist attraction (28°15'N, 83°58'E), is covered by 4-5 km3 and 50-100 m thick intramontane fan deposits that resulted from massive aggradation of the Seti Khola, a river draining the Annapurna Massif of the Greater Himalaya. Poorly sorted, gravelly fluvial facies intercalated with debris-flow and mud-flow facies known as the Pokhara Gravels attest to highly energetic transport conditions during one or several catastrophic flow events. In May 2012, a devastative flash flood/debris flow in the Seti Khola rekindled interest in the formation processes and timing of the Pokhara Gravels as they may provide constraints on the magnitudes and frequencies of similar past events. Interpretations of previous sedimentological work and radiocarbon dating (Yamanaka, 1982; Fort, 1987) culminated in the belief that the Pokhara Gravels were catastrophically emplaced only 500 to 1000 years ago, although the exact nature, timing, and triggers of the purported event(s) remain obscure. Specifically, it remains debated whether the Pokhara Gravels were deposited instantaneously, possibly within less than a year, or whether sedimentation was more protracted over perhaps decades to millennia. We present new geomorphological, sedimentological, geochemical, and radiocarbon data and re-assess a potential catastrophic infill of the Pokhara Valley during one or several high-magnitude events. Support for this scenario is given by laterally continuous long-runout (~40 km) debris-flow deposits topped by large (i.e. up to >11-m) boulders, a distinctly calcareous lithology diagnostic of a small Greater Himalayan source area tens of kilometres upstream, and by historical anecdotes of a large flood that destroyed an earlier settlement in the area. However, we show that dated outcrops of fine-grained sediments in tributaries blocked by the Pokhara Gravels yield asynchronous ages. Although our radiocarbon dates are consistent with

  1. Retrofit of hollow concrete masonry infilled steel frames using glass fiber reinforced plastic laminates

    NASA Astrophysics Data System (ADS)

    Hakam, Zeyad Hamed-Ramzy

    2000-11-01

    This study focuses on the retrofit of hollow concrete masonry infilled steel frames subjected to in-plane lateral loads using glass fiber reinforced plastic (GFRP) laminates that are epoxy-bonded to the exterior faces of the infill walls. An extensive experimental investigation using one-third scale modeling was conducted and consisted of two phases. In the first phase, 64 assemblages, half of which were retrofitted, were tested under various combined in-plane loading conditions similar to those which different regions of a typical infill wall are subjected to. In the second phase, one bare and four masonry-infilled steel frames representative of a typical single-story, single-bay panel were tested under diagonal loading to study the overall behavior and the infill-frame interaction. The relative infill-to-frame stiffness was varied as a test parameter by using two different steel frame sections. The laminates altered the failure modes of the masonry assemblages and reduced the variability and anisotropic nature of the masonry. For the prisms which failed due to shear and/or mortar joint slip, significant strength increases were observed. For those exhibiting compression failure modes, a marginal increase in strength resulted. Retrofitting the infilled frames resulted in an average increase in initial stiffness of two-fold compared to the unretrofitted infilled frames, and seemed independent of the relative infill-to-frame stiffness. However, the increase in the load-carrying capacity of the retrofitted frames compared to the unretrofitted counterparts was higher for those with the larger relative infill-to-frame stiffness parameter. Unlike the unretrofitted infill walls, the retrofitted panels demonstrated almost identical failure modes that were characterized as "strictly comer crushing" in the vicinity of the loaded comers whereas no signs of distress were evident throughout the remainder of the infill. The laminates also maintained the structural integrity of

  2. 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.

  3. 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.

  4. 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

  5. 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.

  6. 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.

  7. Models for Holocene valley-fill sequences from high-resolution seismic facies of Galveston Bay

    SciTech Connect

    Smyth, W.; Thomas, M.A.; Anderson, J.B.

    1988-01-01

    Reconstructions of the northern Gulf of Mexico shelf for the Holocene have relied on the dating of isolated bathymetric banks. These banks, which are interpreted as former shorelines, provide snapshots of the shelf during periods of relative sea level stillstand. A more complete sedimentary record of the Holocene transgression is likely preserved in the incised valley-fill sequences. The first step in deciphering the record of Holocene valley-fill sequences is development of high-resolution seismic facies models based on modern environments. The modern incised valley-estuarine system of Galveston Bay has been seismically surveyed. Important environments include bayhead delta (Trinity River delta), tidal inlet, flood tidal delta (Bolivar Roads), and estuarine sediments (central bay). Additionally, fluvial sediments partially infill the entrenched Trinity River valley. Seismic facies interpretation was corroborated by information obtained from sediment cores.

  8. 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.

  9. 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).

  10. Infill Optimization for Additive Manufacturing -- Approaching Bone-like Porous Structures.

    PubMed

    Wu, Jun; Aage, Niels; Westermann, Ruediger; Sigmund, Ole

    2017-01-23

    Porous structures such as trabecular bone are widely seen in nature. These structures are lightweight and exhibit strong mechanical properties. In this paper, we present a method to generate bone-like porous structures as lightweight infill for additive manufacturing. Our method builds upon and extends voxel-wise topology optimization. In particular, for the purpose of generating sparse yet stable structures distributed in the interior of a given shape, we propose upper bounds on the localized material volume in the proximity of each voxel in the design domain. We then aggregate the local per-voxel constraints by their p-norm into an equivalent global constraint, in order to facilitate an efficient optimization process. Implemented on a high-resolution topology optimization framework, our results demonstrate mechanically optimized, detailed porous structures which mimic those found in nature. We further show variants of the optimized structures subject to different design specifications, and we analyze the optimality and robustness of the obtained structures.

  11. From incision to infill: What a Late Quaternary valley system records?

    NASA Astrophysics Data System (ADS)

    Maselli, V.; Asioli, A.; Trincardi, F.; Ceregato, A.; Rizzetto, F.; Taviani, M.

    2014-12-01

    Erosional sequence boundaries and incised valleys buried in modern continental shelves represent the response of alluvial and coastal systems to Quaternary sea level oscillations. The study of the processes leading to valley incision reveals, at both regional and global scales, the influence of tectonics and eustatism on the evolution of fluvial landforms in coastal plains, while the sedimentary infill of the valley may represents one of the best archives to investigate past environmental changes. Although the time registered in the stratigraphic record represents only a small portion of the geological history, informations about the processes governing the evolution of past landscapes can be quantified by looking to erosional surfaces, where much of the time is condensed. The Manfredonia Incised Valley (southern Adriatic Sea), is a very interesting case of valley as it formed during a single episode of incision related to the last glacial sea level fall and was completely filled during the post-glacial sea level rise. The inverse-funnel shape of the incision, and its confinement toward the mid-inner shelf reveal the impact of the step-wise sea level fall on preexisting coastal morphologies, in particular during the MIS5-4 and MIS3-2 transitions. The 45 m thick sedimentary succession filling the valley recorded the post-glacial sea level rise, as revealed by the upward transition from fluvial to shallow-marine deposits, and the impact of base level and high-frequency climate change on river to coastal systems. The upper 15 m of infill, in particular, consist of multiple bayhead delta progradations occurred synchronously to the formation of sapropel S1, and represent the very-shallow water equivalent of the cm-thick sapropel layers accumulated offshore in the deeper southern Adriatic basin.

  12. Turbiditic minibasin infill patterns: Insights from a novel integrated modeling approach

    NASA Astrophysics Data System (ADS)

    Luthi, Stefan; Hodgson, David; Wang, Xiaoxi; Groenenberg, Remco

    2017-04-01

    The seafloor bathymetry of intraslope minibasins on continental margins is known to play a significant role in controlling turbidity current pathways and the resulting sediment distribution. To investigate the governing processes, we combine laboratory analogue modelling of intraslope minibasin formation with numerical flow simulations of multi-event turbidity currents, an approach that allows an improved understanding of evolving flow-bathymetry-deposit interactions and the resulting internal stacking patterns of the minibasin infills. The bathymetry includes a shelf-to-slope channel followed by an upper minibasin, which are separated by a confining ridge from two lower minibasins that compares well with analogous bathymetries reported from various natural settings. A series of 100 consecutive flows is here reported in detail. They are released into the top of the channel and upon reaching the upper minibasin they follow a series of stages from short initial ponding, filling-and-spilling and an extended transition to long retrogradational ponding. Upon reaching the upper minibasin floor the currents undergo a hydraulic jump, causing much sediment to be deposited in the central part of the minibasin and on the counterslope. This modifies the bathymetry such that during the fill-and-spill stage, flow stripping and grain size partitioning cause some finer sediment to be transported across the confining ridge into the lower minibasins. Throughout the basin infill process the deposits retrograde upstream accompanied by lateral switching into locally formed depressions in the upper minibasin. After the fill-and-spill stage, significant deposition occurs in the channel where cyclic steps with wavelengths of 1-2 km develop as a function of pulsating flow behaviour that switches repeatedly between sub- to supercritical flow conditions. These results are at variance with conventional schemes that emphasise sequential downstream minibasin filling through ponding dominated by

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

    NASA Astrophysics Data System (ADS)

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

    2004-08-01

    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.

  14. 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.

  15. 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

  16. 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

  17. Infilling of Pore Spaces in Mortar Using Electrically-Driven Solution Transport Systems

    NASA Astrophysics Data System (ADS)

    Morefield, Sean W.; Weiss, Charles A.; Malone, Philip G.; Hock, Vincent F.

    2010-05-01

    It has been widely established that all types of conventional concrete can be strengthened by reducing the porosity of the concrete matrix. Attempts to infill the pores by converting reactive phases such as calcium hydroxide into calcium carbonate have been partly successful, but the success of this approach has been limited by the amount of Ca(OH)2 produced in the hydration of the concrete and by the positions of the new crystalline phases that are formed. These limitations can be overcome by using a combination of electrophoresis to move particles into concrete pores and the use of ion transport to move new dissolved reactants into the concrete mass. Bench scale experiments have demonstrated that significant density and strength increases can be obtained by electrophoretically moving seed crystals of selected mineral phases such as calcite, aragonite, or vaterite into the larger pores in concrete and then using a low-voltage DC current to migrate in calcium and carbonate ions to grow the selected crystalline phases in masses sufficient to fill up both large and small pores. This can be done in such a way as to leave even the reactive phases such as Ca(OH)2 unaltered. The bulk pH of the concrete is not reduced in the mineralization process as it would be in simple carbonation. Pore in-filling using electrophoretic and electro-transport systems can potentially be of use in creating very high-density concrete for concrete pipes, and panels with lower porosity than can be obtained using carbonation or pressure infiltration.

  18. Graben infilling in Gulf of Suez and Red Sea

    SciTech Connect

    Burollet, P.F.

    1986-05-01

    During the last 4 years, the French research group Genegass has completed geological and geophysical studies in the Red Sea and the Gulf of Suez. Neogene infilling of the basin is related with basement quality and volume of clastic supply, and inherited structural features are important to the development of Miocene rifting. The Neogene series may be divided into four major groups (Listed A-D), each limited by unconformities that seem to reflect the major stages of rifting. (A) The lowermost formations begin with a conglomerate and are followed by a variegated unit of sand and clay. In the Gulf of Suez, especially on the eastern bank, these formations are marine. Along the Red Sea, tilted blocks may be capped by stromatolites, and the valleys between them are the site of shale and evaporite sedimentation (lower Miocene). (B) The main extension phase results in an invasion of marine shales. The lower zones contain coarse clastics, and the high zones contain reefs and bioclastic limestone (late Burdigalian to early Serravallian). (C) The middle to late Miocene corresponds to a regional basinward tilting. Stromatolites coat the slopes, and conglomerate fans are found in the lower zones. Evaporite sedimentation dominates; anhydrite is found on the borders, and in the basin, thick halite is overlain by a clastic series. Basement shoulders are uplifted. (D) During the Pliocene and Pleistocene, the central part of the graben showed an important subsidence, and salt tectonism was active with diapirs and collapses.

  19. 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

  20. 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

  1. Non-cohesive fine grained turbidity current flow processes: insights from Late Holocene sandy-silt and silty-sand turbidites

    NASA Astrophysics Data System (ADS)

    Strachan, Lorna; Bostock, Helen; Barnes, Philip; Neil, Helen

    2016-04-01

    Silt-rich turbidites are commonly interpreted as distal deposits associated with interlaminated clay and silt deposition of turbidity current tails and overspilling flows. Here multibeam bathymetric and shallow sediment core data from the intraslope Secretary, Looking Glass and George basins, offshore Fiordland, New Zealand are used to describe a suite of Late Holocene proximal sandy-silt and silty-sand turbidites that contain negligible clay and a wide variety of vertical grading patterns. The silt-sand sediment mixtures and diversity of preserved vertical grading patterns imply a range of non-cohesive turbidity current flow processes, and a wide variety of flow concentrations. For example, inversely graded turbidites and are interpreted to preserve evidence of deposition of traction carpets from high concentration silt-sand flows. The very fine and fine sand modal grain sizes of sandy-silt and silty-sand turbidites are significantly coarser than classical abyssal plain silt turbidites and generally coarser than overbank silt turbidites. While the low percentage of clays within sandy-silt and silty-sand turbidites represents a fundamental difference between these and other silt and mud turbidites we suggest these beds represent a previously poorly described suite of proximal deposits.

  2. City Green: Innovative Green Infrastructure Solutions for Downtowns and Infill Locations

    EPA Pesticide Factsheets

    City Green uses case studies to illustrate how green infrastructure techniques can be used in downtowns and infill locations, where space is limited, to protect water quality and bring other environmental and community benefits.

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

    PubMed

    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.

  4. Holocene palaeoDEMs for lowland coastal and delta plain landscape reconstructions

    NASA Astrophysics Data System (ADS)

    Cohen, Kim M.; Koster, Kay; Pierik, Harm-Jan; Van der Meulen, Bas; Hijma, Marc; Schokker, Jeroen; Stafleu, Jan

    2017-04-01

    Geological mapping of Holocene deposits of coastal plains, such as that of The Netherlands can reach high resolution (dense population, diverse applied usage) and good time control (14C dating, archaeology). The next step is then to create time sliced reconstructions for stages in the Holocene, peeling of the subrecent and exposing past relief situation. This includes winding back the history of sea-level rise and delta progradation etc. etc. So far, this has mainly be done as 2D series of landscape maps, or as sea-level curve age-depth plots. In the last decade, academic and applied projects at Utrecht University, TNO Geological Survey of The Netherlands and Deltares have developed palaeoDEMs for the Dutch low lands, that are a third main way of showing coastal plain evolution. Importantly, we produce two types of palaeoDEMs: (1) geological surface mapping using deposit contacts from borehole descriptions (and scripted 3D processing techniques - e.g. Van der Meulen et al. 2013) and (2) palaeogroundwater surfaces, using sea-level and inland water-level index-points (and 3D kriging interpolations - e.g. Koster et al. 2016). The applications for the combined palaeoDEMs range from relative sea-level rise mapping and assessment of variation in rate of GIA across the coastal plain, to quantification of soft soil deformation, to analysis of pre-embankment extreme flood levels. Koster, K., Stafleu, J., & Cohen, K.M. (2016). Generic 3D interpolation of Holocene base-level rise and provision of accommodation space, developed for the Netherlands coastal plain and infilled palaeovalleys. Basin Research. DOI 10.1111/bre.12202 Van der Meulen, M.J., Doornenbal, J.C., Gunnink, J.L., Stafleu, J., Schokker, J., Vernes, R.W., Van Geer, F.C., Van Gessel, S.F., Van Heteren, S., Van Leeuwen, R.J.W. & Bakker, M.A.J. (2013). 3D geology in a 2D country: perspectives for geological surveying in the Netherlands. Netherlands Journal of Geosciences, 92, 217-241. DOI 10.1017/S0016774600000184

  5. Constitutive Models for Nonlinear Finite Element Analysis of Masonry Prisms and Infill Walls

    DTIC Science & Technology

    2008-03-01

    based on a hyperbolic function proposed by Lotfi and Shing (1994), and is capable of modeling damage accumulation at mortar joints under increasing...loading and the effect that damage accumulation has on the modeling of the masonry infills. The re- view presented here discusses models that consider...nonlinear, plastic be- havior and damage effects resulting from masonry infill as an isotropic or orthotropic brittle or quasi-brittle material and/or

  6. 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.

  7. 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.

  8. 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.

  9. Response of the Selle River to climatic modifications during the Lateglacial and Early Holocene (Somme Basin-Northern France)

    NASA Astrophysics Data System (ADS)

    Antoine, Pierre; Munaut, André-Valentin; Limondin-Lozouet, Nicole; Ponel, Philippe; Dupéron, Jean; Dupéron, Monique

    2003-10-01

    Research on Lateglacial sequences from the Selle valley leads to an overview of its evolution in relation to climatic variations between the end of the Weichselian Upper Pleniglacial and the beginning of the Holocene. The first major modification of the fluvial morphology is dated at the Upper Pleniglacial/Lateglacial transition (13,000 14C-yr BP). At that time, the response to climatic improvement and environmental modifications is marked by downcutting and evolution from a braided river to a transitional river pattern (Bølling infilling in the newly created channels). After a short cold phase recorded in a thin calcareous bed at the top of the Bølling peat attributed to the Older Dryas (Dr. II), the Allerød is characterized by the deposition of organic overbank silts within a large single channel meandering system. In lower slope environments, this period is also marked by slow rates of colluvial accumulation and by the development of upbuilding soils (Allerød soil). On the other hand, the end of the Lateglacial, is characterised by the infilling of the whole valley by fine calcareous overbank silts during the Younger Dryas cold phase (overflow of a large single channel and lateral input of chalk mud). A second major downcutting phase occurs at the beginning of the Holocene at around 10,000 BP, in parallel with another rapid climatic improvement and the renewed spread of vegetation. From a general point of view, the evolution of fluvial environments in the Selle valley is comparable with many other river valleys in NW Europe, showing that fluvial systems react very quickly to climatic variations of short duration (1000 to 100 years). Finally, in the Upper Selle River, incision events occur clearly before the main modifications of the vegetal cover. They are most likely linked to a rapid shift in the balance between water discharge and sediment supply, caused by climate modifications (shift to more temperate and oceanic conditions), and the resulting

  10. Diatom-inferred hydrological changes and Holocene geomorphic transitioning of Africa's largest estuarine system, Lake St Lucia

    NASA Astrophysics Data System (ADS)

    Gomes, M.; Humphries, M. S.; Kirsten, K. L.; Green, A. N.; Finch, J. M.; de Lecea, A. M.

    2017-06-01

    The diverse lagoons and coastal lakes along the east coast of South Africa occupy incised valleys that were flooded during the rise and subsequent stabilisation of relative sea-level during the Holocene. Sedimentary deposits contained within these waterbodies provide an opportunity to investigate complex hydrological and sedimentological processes, and examine sea-level controls governing system geomorphic evolution. In this paper, we combine diatom and sulfur isotope analyses from two sediment cores extracted from the northern sub-basins of Lake St Lucia, a large shallow estuarine lake that is today largely isolated from direct ocean influence behind a Holocene-Pleistocene barrier complex. Analyses allow the reconstruction of hydrological changes associated with the geomorphic development of the system over the mid-to late Holocene. The sedimentary sequences indicate that St Lucia was a shallow, partially enclosed estuary/embayment dominated by strong tidal flows prior to ∼6200 cal. BP. Infilling was initiated when sea-level rise slowed and stabilised around present day levels, resulting in the accumulation of fine-grained sediment behind an emergent proto-barrier. Diatom assemblages, dominated by marine benthic and epiphytic species, reveal a system structured by marine water influx and characterised by marsh and tidal flat habitats until ∼4550 cal. BP. A shift in the biological community at ∼4550 cal. BP is linked to the development of a back-barrier water body that supported a brackish community. Marine planktonics and enrichments in δ34S suggest recurrent, large-scale barrier inundation events during this time, coincident with a mid-Holocene sea-level highstand. Periodic marine incursions associated with episodes of enhanced storminess and overwash remained prevalent until ∼1200 cal. BP, when further barrier construction ultimately isolated the northern basins from the ocean. This study provides the first reconstruction of the palaeohydrological

  11. Holocene sedimentation in Richardson Bay, California

    USGS Publications Warehouse

    Connor, Cathy L.

    1983-01-01

    Examination of foraminifers, diatoms, ostracodes, clay mineralogy, and sediment-size variation from 9 borehole sites along the salt-marsh margins of Richardson Bay reveals a record of gradual infilling of fine-grained estuarine sediments. Over the past 10,000 years this area was transformed from a V-shaped Pleistocene stream valley to a flat-floored arm of the San Francisco Bay estuary. A radiocarbon date obtained from a basal peat overlying nonmarine alluvial sand near the town of Mill Valley indicates that stable salt-marsh vegetation was present in the northwestern arm of Richardson Bay 4600?165 years ago and agrees within error limits with a Holocene sea-level curve developed by Atwater, Hedel, and Helley in 1977 for southern San Francisco Bay. The average sedimentation rate over the last 4600 years is estimated to be 0.2 cm/yr for the inner part of the bay. Comparison of early maps with updated versions as well as studies of marsh plant zonations in disturbed and nondisturbed areas shows that almost half of the marsh in Richardson Bay has been leveed or filled since 1899.

  12. 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.

  13. The Holocene temperature conundrum

    PubMed Central

    Liu, Zhengyu; Zhu, Jiang; Rosenthal, Yair; Zhang, Xu; Otto-Bliesner, Bette L.; Timmermann, Axel; Smith, Robin S.; Lohmann, Gerrit; Zheng, Weipeng; Elison Timm, Oliver

    2014-01-01

    A recent temperature reconstruction of global annual temperature shows Early Holocene warmth followed by a cooling trend through the Middle to Late Holocene [Marcott SA, et al., 2013, Science 339(6124):1198–1201]. This global cooling is puzzling because it is opposite from the expected and simulated global warming trend due to the retreating ice sheets and rising atmospheric greenhouse gases. Our critical reexamination of this contradiction between the reconstructed cooling and the simulated warming points to potentially significant biases in both the seasonality of the proxy reconstruction and the climate sensitivity of current climate models. PMID:25114253

  14. The Holocene temperature conundrum.

    PubMed

    Liu, Zhengyu; Zhu, Jiang; Rosenthal, Yair; Zhang, Xu; Otto-Bliesner, Bette L; Timmermann, Axel; Smith, Robin S; Lohmann, Gerrit; Zheng, Weipeng; Elison Timm, Oliver

    2014-08-26

    A recent temperature reconstruction of global annual temperature shows Early Holocene warmth followed by a cooling trend through the Middle to Late Holocene [Marcott SA, et al., 2013, Science 339(6124):1198-1201]. This global cooling is puzzling because it is opposite from the expected and simulated global warming trend due to the retreating ice sheets and rising atmospheric greenhouse gases. Our critical reexamination of this contradiction between the reconstructed cooling and the simulated warming points to potentially significant biases in both the seasonality of the proxy reconstruction and the climate sensitivity of current climate models.

  15. 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.

  16. 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.

  17. Effects of Cyclic Loading on the Shear Behaviour of Infilled Rock Joints Under Constant Normal Stiffness Conditions

    NASA Astrophysics Data System (ADS)

    Mirzaghorbanali, Ali; Nemcik, Jan; Aziz, Naj

    2014-07-01

    The variation of the shear strength of infilled rock joints under cyclic loading and constant normal stiffness conditions is studied. To simulate the joints, triangular asperities inclined at angles of 9.5° and 18.5° to the shear movement were cast using high-strength gypsum plaster and infilled with clayey sand. These joints were sheared cyclically under constant normal stiffness conditions. It was found that, for a particular normal stiffness, the shear strength is a function of the initial normal stress, initial asperity angle, joint surface friction angle, infill thickness, infill friction angle, loading direction and number of loading cycles. Based on the experimental results, a mathematical model is proposed to evaluate the shear strength of infilled rock joints in cyclic loading conditions. The proposed model takes into consideration different initial asperity angles, initial normal stresses and ratios of infill thickness to asperity height.

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

    SciTech Connect

    Fowler, Joele Johnston

    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.

  19. Dosimetric characterization of 3D printed bolus at different infill percentage for external photon beam radiotherapy.

    PubMed

    Ricotti, Rosalinda; Ciardo, Delia; Pansini, Floriana; Bazani, Alessia; Comi, Stefania; Spoto, Ruggero; Noris, Samuele; Cattani, Federica; Baroni, Guido; Orecchia, Roberto; Vavassori, Andrea; Alicja Jereczek-Fossa, Barbara

    2017-07-01

    3D printing is rapidly evolving and further assessment of materials and technique is required for clinical applications. We evaluated 3D printed boluses with acrylonitrile butadiene styrene (ABS) and polylactide (PLA) at different infill percentage. A low-cost 3D printer was used. The influence of the air inclusion within the 3D printed boluses was assessed thoroughly both with treatment planning system (TPS) and with physical measurements. For each bolus, two treatment plans were calculated with Monte Carlo algorithm, considering the computed tomography (CT) scan of the 3D printed bolus or modelling the 3D printed bolus as a virtual bolus structure with a homogeneous density. Depth dose measurements were performed with Gafchromic films. High infill percentage corresponds to high density and high homogeneity within bolus material. The approximation of the bolus in the TPS as a homogeneous material is satisfying for infill percentages greater than 20%. Measurements performed with PLA boluses are more comparable to the TPS calculated profiles. For boluses printed at 40% and 60% infill, the discrepancies between calculated and measured dose distribution are within 5%. 3D printing technology allows modulating the shift of the build-up region by tuning the infill percentage of the 3D printed bolus in order to improve superficial target coverage. Copyright © 2017 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

  20. 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

  1. Sequence of infilling events in Gale Crater, Mars: Results from morphology, stratigraphy, and mineralogy

    NASA Astrophysics Data System (ADS)

    Le Deit, Laetitia; Hauber, Ernst; Fueten, Frank; Pondrelli, Monica; Rossi, Angelo Pio; Jaumann, Ralf

    2013-12-01

    Crater is filled by sedimentary deposits including a mound of layered deposits, Aeolis Mons. Using orbital data, we mapped the crater infillings and measured their geometry to determine their origin. The sediment of Aeolis Mons is interpreted to be primarily air fall material such as dust, volcanic ash, fine-grained impact products, and possibly snow deposited by settling from the atmosphere, as well as wind-blown sands cemented in the crater center. Unconformity surfaces between the geological units are evidence for depositional hiatuses. Crater floor material deposited around Aeolis Mons and on the crater wall is interpreted to be alluvial and colluvial deposits. Morphologic evidence suggests that a shallow lake existed after the formation of the lowermost part of Aeolis Mons (the Small yardangs unit and the mass-wasting deposits). A suite of several features including patterned ground and possible rock glaciers are suggestive of periglacial processes with a permafrost environment after the first hundreds of thousands of years following its formation, dated to ~3.61 Ga, in the Late Noachian/Early Hesperian. Episodic melting of snow in the crater could have caused the formation of sulfates and clays in Aeolis Mons, the formation of rock glaciers and the incision of deep canyons and valleys along its flanks as well as on the crater wall and rim, and the formation of a lake in the deepest portions of Gale.

  2. 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

  3. The Mafic Holocene Sand Mountain-Nash Crater Chain, Oregon Cascade Range: Preliminary Insights Into Enigmatic Crustal Contamination Processes

    NASA Astrophysics Data System (ADS)

    Ramos, F. C.; Conrey, R. M.

    2003-12-01

    enigma presented by the compositional variation in these lavas may shed light on common assimilation processes, especially in the deep crust, which likely affect many mafic arc magmas.

  4. 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

  5. Hydroxypyrene in urine of football players after playing on artificial sports field with tire crumb infill.

    PubMed

    van Rooij, Joost G M; Jongeneelen, Frans J

    2010-01-01

    Artificial sports fields are increasingly being used for sports. Recycled rubber from automotive and truck scrap rubber tires are used as an infill material for football grounds. There are concerns that football players may be at risk due to exposure from released compounds from rubber infill. Compounds from crumb infill may be inhaled and dermal exposure may occur. A study was performed to assess the exposure of football players to polycyclic aromatic hydrocarbons due to sporting on synthetic ground with rubber crumb infill. In this study, football players were trained and had a match on the artificial turf pitch during 2.5 h. They had an intensive skin contact with rubber infill. All urine of seven nonsmoking football players was collected over a 3-day period, the day before sporting, the day of sporting and the day after sporting. Urine samples were analyzed for 1-hydroxypyrene. Confounding exposure from environmental sources and diet was controlled for. The individual increase of the amount of excretion over time was used as a measure to assess the uptake of PAH. It appeared that the baseline of excreted 1-hydroxypyrene in 4 of 7 volunteers was sufficient stable and that 1 volunteer out of 4 showed after the 2.5-h period of training and match on the playground an increase in hydroxypyrene in urine. However, concomitant dietary uptake of PAH by this volunteer was observed. This study provides evidence that uptake of PAH by football players active on artificial grounds with rubber crumb infill is minimal. If there is any exposure, than the uptake is very limited and within the range of uptake of PAH from environmental sources and/or diet.

  6. Sensitivity of Holocene atmospheric CO2 and the modern carbon budget to early human land use: analyses with a process-based model

    NASA Astrophysics Data System (ADS)

    Stocker, B. D.; Strassmann, K.; Joos, F.

    2011-01-01

    A Dynamic Global Vegetation model coupled to a simplified Earth system model is used to simulate the impact of anthropogenic land cover changes (ALCC) on Holocene atmospheric CO2 and the contemporary carbon cycle. The model results suggest that early agricultural activities cannot explain the mid to late Holocene CO2 rise of 20 ppm measured on ice cores and that proposed upward revisions of Holocene ALCC imply a smaller contemporary terrestrial carbon sink. A set of illustrative scenarios is applied to test the robustness of these conclusions and to address the large discrepancies between published ALCC reconstructions. Simulated changes in atmospheric CO2 due to ALCC are less than 1 ppm before 1000 AD and 30 ppm at 2004 AD when the HYDE 3.1 ALCC reconstruction is prescribed for the past 12 000 years. Cumulative emissions of 69 GtC at 1850 and 233 GtC at 2004 AD are comparable to earlier estimates. CO2 changes due to ALCC exceed the simulated natural interannual variability only after 1000 AD. To consider evidence that land area used per person was higher before than during early industrialisation, agricultural areas from HYDE 3.1 were increased by a factor of two prior to 1700 AD (scenario H2). For the H2 scenario, the contemporary terrestrial carbon sink required to close the atmospheric CO2 budget is reduced by 0.5 GtC yr-1. Simulated CO2 remains small even in scenarios where average land use per person is increased beyond the range of published estimates. Even extreme assumptions for preindustrial land conversion and high per-capita land use do not result in simulated CO2 emissions that are sufficient to explain the magnitude and the timing of the late Holocene CO2 increase.

  7. Sensitivity of Holocene atmospheric CO2 and the modern carbon budget to early human land use: analyses with a process-based model

    NASA Astrophysics Data System (ADS)

    Stocker, B.; Strassmann, K.; Joos, F.

    2010-02-01

    A Dynamic Global Vegetation model is used as part of a simplified Earth system model to simulate the impact of human land use on Holocene atmospheric CO2 and the contemporary carbon cycle. We show that suggested upward revisions of Holocene land use reconstructions imply a smaller contemporary terrestrial carbon sink and that early agricultural activities did only marginally contribute to the late Holocene CO2 rise of 20 ppm measured on ice cores. Scenarios are used to test the robustness of the results. Simulated changes in atmospheric CO2 due to land use are less than 1 ppm before 0 AD and 22 ppm by 2004 AD when prescribing the HYDE 3.1 land use reconstruction over the past 12 000 years. Cumulative emissions are with 50 GtC by 1850 and 177 GtC by 2004 AD comparable to earlier estimates. In scenario H2, agricultural area from HYDE 3.1 is scaled by a factor of two before 1700 AD, thereby taking into account evidence that land area used per person was higher before than during early industrialisation. Then, the contemporary terrestrial carbon sink, required to close the atmospheric CO2 budget, is reduced by 0.5 GtC yr-1. CO2 changes due to land use change exceed natural interannual variability only after 1000 AD and are less than 4 ppmv until 1850 AD. Simulated CO2 change remains small even in scenarios where average land use per person is unrealistically increased by a factor of 4 to 8 above published estimates. Our results falsify the hypothesis that humans are responsible for the late Holocene CO2 increase and that anthropogenic land use prevented a new ice age.

  8. 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.

  9. 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.

  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. Models for Holocene valley-fill sequences from high-resolution seismic facies of Galveston Bay

    SciTech Connect

    Smyth, W.; Thomas, M.A.; Anderson, J.B. )

    1988-02-01

    Reconstructions of the northern Gulf of Mexico shelf for the Holocene have relied on the dating of isolated bathymetric banks. These banks, which are interpreted as former shorelines, provide snapshots of the shelf during periods of relative sea level stillstand. A more complete sedimentary record of the Holocene transgression is likely preserved in the incised valley-fill sequences. The first step in deciphering the record of Holocene valley-fill sequences is development of high-resolution seismic facies models based on modern environments. The modern incised valley-estuarine system of Galveston Bay has been seismically surveyed. Important environments include bayhead delta (Trinity River delta), tidal inlet, flood tidal delta (Bolivar Roads), and estuarine sediments (central bay). Additionally, fluvial sediments partially infill the entrenched Trinity River valley. Seismic facies interpretation was corroborated by information obtained from sediment cores. The influence of the rate of relative sea level rise on incised valley-fill facies architecture is demonstrated in hypothetical sequence models which are applied to the interpretation of high-resolution surveys of Holocene shelf deposits.

  12. Late Holocene sedimentation in a high Arctic coastal setting: Simpson Lagoon and Colville Delta, Alaska

    NASA Astrophysics Data System (ADS)

    Hanna, Andrea J. M.; Allison, Mead A.; Bianchi, Thomas S.; Marcantonio, Franco; Goff, John A.

    2014-02-01

    Arctic coastal environments near major river outfalls, like Simpson Lagoon, Alaska and the adjacent Colville River Delta, potentially contain high-resolution sediment records useful in elucidating late Holocene Arctic sediment transport pathways and coupled terrestrial-ocean evidence of paleoclimate variability. This study utilizes a multi-tracer geochronology approach (137Cs, 239,240Pu, and 14C) tailored for high-latitude environments to determine the age models for cores collected from Simpson Lagoon, and to date seismic boundaries in shallow acoustic reflection data (CHIRP) to examine late Holocene infill patterns. Modern (~100 y) sediment accumulation rates range from <0.02 to 0.46±0.04 cm y-1, with a primary depocenter in western Simpson Lagoon adjacent to the Colville Delta and a secondary depocenter in eastern Simpson Lagoon. CHIRP reflectors, age-constrained by 14C analysis, reveal rapid late Holocene (0-3500 y BP) transgression consistent with high modern shoreline retreat rates. The western depocenter contains >5 m of late Holocene interbedded sediments, likely derived primarily from the Colville River, with onset of accumulation occurring prior to ~3500 y BP. A paleo-high in central Simpson Lagoon, separating the two depocenters, was subaerially exposed prior to ~600 y BP. The millimeters-per-year sedimentation rates across the lagoon, coupled with the undisturbed, interbedded sediment record, indicate that these settings hold great potential to develop new Arctic paleoenvironmental records.

  13. 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.

  14. 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

  15. 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.

  16. 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

  17. 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)

  18. 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).

  19. Socioeconomic Impact of Infill Drilling Recovery from Carbonate Reservoirs in the Permian Basin, West Texas

    DTIC Science & Technology

    1994-05-01

    revenues of infill drilling and the creation of jobs in the Permian basin communities, and ( 3 ) develops a correlation between the increased tax...1 3 viii Page CHAPTER IV THE AMOUNT OF REVENUE FROM OIL PRODUCTION...the Permian Basin ........................ 32 4.5 Percent of Federal Income Tax ............................................ 3 33 4.6 Rule of Thumb in

  20. Cryogenic processes and fire activity in a high Atlantic mountain area in NW Iberia (Picos de Europa) during the Mid-Late Holocene.

    PubMed

    Ruiz-Fernández, Jesús; Nieuwendam, Alexandre; Oliva, Marc; Lopes, Vera; Cruces, Anabela; Freitas, Maria Conceição; Janeiro, Ana I; López-Sáez, José Antonio

    2016-12-15

    Mid-Late Holocene environmental changes in the Cantabrian Mountains are a consequence of both climate variability and human activity. A 182cm-long sedimentary sequence was collected from Belbín depression, Western Massif of Picos de Europa (Cantabrian Mountains, NW Spain), in order to reconstruct Holocene environmental dynamics and the factors triggering landscape changes in the area. Using multi-proxy analysis of the uppermost 60cm of the sediments (texture, organic matter content, quartz grains microstructures, charcoal deposition) together with three (14)C AMS dates, a sequence of alternating warmer and colder phases has been inferred for the last ca. 6.7kycalBP. Warm stages are defined by low to moderate chemical weathering of the quartz grain particles with relative increases of the C/N ratio, while colder phases show a moderate to intense physical weathering of the quartz grains and lower C/N ratios. Warmer temperatures were recorded in Belbín area between: 6.7-5, 3.7-3, 2.6-1.1, 0.87-0.51 and since 0.01kycalBP. A colder regime occurred between 5-3.7, 3-2.6, 1.1-0.87 and 0.51 to 0.01kycalBP. The increasing organic matter content during the Late Holocene may be associated with increasing temperatures. The charcoal particles do not show a higher or lower concentration during prevailing colder or warmer conditions, and therefore may be linked to human-induced fire management of the landscape. The most intense period with fire activity occurred between 3.5 and 3kycalBP during the Bronze Age.

  1. Influences of Shear History and Infilling on the Mechanical Characteristics and Acoustic Emissions of Joints

    NASA Astrophysics Data System (ADS)

    Meng, Fanzhen; Zhou, Hui; Wang, Zaiquan; Zhang, Liming; Kong, Liang; Li, Shaojun; Zhang, Chuanqing

    2017-08-01

    Filled joints, which are characterized by high deformability and low shear strength, are among the most critical discontinuities in rock mass and may be sheared repeatedly when subject to cyclic loading. Shear tests were carried out on tension splitting joints, with soil and granular cement mortar particles used as infillings, and the effects of the shear history on the mechanical behavior and acoustic emission (AE) of clean and filled joints were studied. The maximum strength in the subsequent shears was approximately 60% of the peak strength of the first shear for a clean joint, and the friction angle degraded from 63° to 45° after the first shear. The maximum shear strength of the filled joints was lower than 35% of the peak strength of the clean joint under the same normal stress. The change in the shear strength of filled joints with the number of shearing cycles was closely related to the transformation of the shear medium. Rolling friction occurred and the shear strength was low for the granular particle-filled joint, but the strength was elevated when the particles were crushed and sliding friction occurred. The AEs were significantly reduced during the second shear for the clean joint, and the peak AEs were mainly obtained at or near the turning point of the shear stress curve for the filled joint. The AEs were the highest for the cement particle-filled joint and lowest for the dry soil-filled joint; when subjected to repeated shears, the AEs were more complex because of the continuous changes to the shear medium. The evolution of the AEs with the shear displacement can accurately reflect the shear failure mechanism during a single shear process.

  2. Modern and subrecent spatial distribution and characteristics of sediment infill controlled by internal depositional dynamics, Laguna Potrok Aike (southern Patagonia, Argentina)

    NASA Astrophysics Data System (ADS)

    Kastner, S.; Ohlendorf, C.; Haberzettl, T.; Lücke, A.; Maidana, N. I.; Mayr, C.; Schäbitz, F.; Zolitschka, B.

    2009-04-01

    45 m. Thus, samples of the surface sediments were taken from all 46 cores while sub-sampling of selected time intervals - AD 1960, 1800, 1610, 1500, 1380 - was only possible for up to 26 well correlated cores from the deep central basin. These time slices cover palaeoenvironmental distinctive intervals representing different hydrological settings (Haberzettl et al., 2005). Geochemical, sedimentological, palynological, diatomological, and stable isotope data were used to produce distribution maps for all these parameters and for every time slice by kriging methods. Results of the surficial sediments, i.e. representing the last 20 years of the record, confirm pronounced differences between the littoral cores and the lake's profundal cores separated from each other by steep slopes. Modern sedimentation patterns point to distinct internal depositional dynamics induced by the dominant westerly winds. At the eastern shore frequent erosion, resuspension and redistribution of littoral sediment is followed by transport to a profundal accumulation area. Hence, sedimentation within this terminal lake is not only influenced by lake level changes, episodic inflows and the surrounding geology but also by wind driven wave action and resulting internal currents. The subrecent spatial sediment distribution is evaluated and interpreted in the context of these modern processes. Changing wind patterns and varying lake levels are assumed to cause modifications of depositional dynamics and affect the varying palaeo-shoreline proximity to the analysed sediment cores during the selected late Holocene time sections. Comparable to modern patterns intensified sediment redistribution at the eastern shore is observed during the post-Little Ice Age (AD 1960) comprising a low lake level and strengthened winds. In contrast, Little Ice Age (AD 1800) conditions of a lake level high stand and less intense westerly winds result in a more homogeneous sediment distribution within the deep central basin

  3. 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.

  4. 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.

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

    PubMed Central

    Jones, Miriam C.; Yu, Zicheng

    2010-01-01

    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

  6. 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.

  7. The FP4026 Research Database on the fundamental period of RC infilled frame structures.

    PubMed

    Asteris, Panagiotis G

    2016-12-01

    The fundamental period of vibration appears to be one of the most critical parameters for the seismic design of buildings because it strongly affects the destructive impact of the seismic forces. In this article, important research data (entitled FP4026 Research Database (Fundamental Period-4026 cases of infilled frames) based on a detailed and in-depth analytical research on the fundamental period of reinforced concrete structures is presented. In particular, the values of the fundamental period which have been analytically determined are presented, taking into account the majority of the involved parameters. This database can be extremely valuable for the development of new code proposals for the estimation of the fundamental period of reinforced concrete structures fully or partially infilled with masonry walls.

  8. 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.

  9. Influence of Conowingo Reservoir Infill on Chesapeake Bay Deep Water Hypoxia

    NASA Astrophysics Data System (ADS)

    Linker, L. C.; Cerco, C. F.; Batiuk, R.

    2014-12-01

    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 the 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 dynamic equilibrium. The development of the Chesapeake TMDL in 2010 was with the hydrology of a 1991-2000 simulation period, and carried with this simulation period the implicit model calibration assumption, based on the 1991-2000 nutrient and sediment observations, of a Conowingo Reservoir that was still effectively trapping sediment. 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 attainment of living resource based water quality standards, the estimated nutrient and sediment loads from a simulated infill of the Conowingo Reservoir was determined. The influence on Chesapeake water quality by a large storm and scour event of January 1996 on the Susquehanna was estimated and the same storm and scour events were also evaluated in the more critical living resource periods of June and October. An analysis was also made on the estimated influence of more moderate but frequent high flow events. The infill of the Conowingo reservoir had estimated impairments of water quality at both the simulated high flow scour events and at the more frequent moderate storm flows. The estimated impairment was primarily on the deep water and deep channel dissolved oxygen because of increased scour and transport of dissolved particulate organic nutrients under conditions of Conowingo infill. Figure 1 describes the linked models used to assess the impact of Conowingo Reservoir infill on Chesapeake hypoxia.

  10. 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.

  11. 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.

  12. Evidence for millennial-scale climatic events in the sedimentary infilling of a macrotidal estuarine system, the Seine estuary (NW France)

    NASA Astrophysics Data System (ADS)

    Sorrel, Philippe; Tessier, Bernadette; Demory, François; Delsinne, Nicolas; Mouazé, Dominique

    2009-03-01

    High-resolution sedimentological and rock magnetic analyses from sediment cores collected in the Seine estuary record changes in coastal sedimentary dynamics linked to climatic variations during the late Holocene. Using AMS 14C and paleomagnetic data we present a first attempt in developing a reliable age model on macrotidal estuarine archives, with a decadal resolution. Correlations between sedimentary successions from the outer Seine estuary document the main sedimentary infilling phases of the system during the last 3000 years. Between 3000 and 1150 cal. BP sedimentary patterns reveal that sequence deposition and preservation are predominantly controlled by marine and tidal hydrodynamics while severe storm events are recorded at ca. 2700 and 1250 cal. BP in the outermost estuary. Conversely, the Medieval Warm Period (MWP; 900-1200 AD) is characterized by a drastic waning of the influence of marine hydrodynamics on sediment preservation. Pronounced episodes of Seine river floods indicate a much stronger impact of continental inputs on sedimentary patterns during this period. The onset of the Little Ice Age marks a diminishing influence of continental inputs while tidal and open marine hydrodynamics again exerted a primary control on the sedimentary evolution of the system during 1200-2003 AD. Coastal sedimentary dynamics as preserved within sedimentary successions appear to have been largely influenced by changes in storminess during the last 3000 years. We have matched the preservation of MWP Seine river floods, as revealed by sedimentological and rock magnetic proxy data, to a prolonged interval of weakened storminess in Normandy permitting the preservation of estuarine flood deposits within a context of reduced coastal erosion in northern Europe. The preservation of sedimentary successions in the Seine estuary is therefore maximal when climate conditions resembled those of the preferred low phase of the NAO on multidecadal timescales such as during 800-1200 AD

  13. Volcanic Infillings of Large Basins on Mercury as Indicators of Mantle Thermal State and Composition

    NASA Astrophysics Data System (ADS)

    Padovan, Sebastiano; Tosi, Nicola; Plesa, Ana-Catalina; Ruedas, Thomas

    2017-04-01

    The crust of Mercury is mostly the cumulative result of partial melting in the mantle associated with solid-state convection [1]. The details of how the surface composition represents the result of dynamical processes in the interior are difficult to elucidate. Explanations for the observed geochemically varied surface include a heterogeneous mantle, the effects of ancient giant impacts, an evolving mantle composition, or a combination of these processes [e.g., 2]. Here we explore the effects of large impacts on mantle dynamics and associated melt production. With the convection code GAIA we compute thermal evolution histories of Mercury compatible with the expected amount of heat producing elements in the mantle and with the crustal thickness inferred from gravity and topography data. We estimate the thermal anomalies in the mantle generated by large impacts using scaling laws [3]. Impactors have a velocity of 42 km/s and an impact angle of 45°, as appropriate for Mercury [4]. Their size is varied in order to produce basins with diameters in the range from 715 km (Rembrandt) to 1550 km (Caloris). Depending on the timing of the impact, the melt erupting in the basin interior is a combination of convective melt generated at depth and shallow melt resulting from shallow impact-induced convective currents. The volcanic infillings following an impact happening early in the evolution of the planet, when convection is still vigorous, are dominated by convective melt. Later in the evolution, the erupted melt shows the signature of the impact-induced shallow melt. We show that the properties of melt sheets within the young large basins Caloris and Rembrandt depend on the mantle thermal state and composition. In particular, we predict the source depth of the volcanic plains within large young basins to be different from the source depth of older surface units, a result that can help explaining the peculiar composition of the volcanic plains inside Caloris [2, 5]. [1] Tosi

  14. Comparative study on diagonal equivalent methods of masonry infill panel

    NASA Astrophysics Data System (ADS)

    Amalia, Aniendhita Rizki; Iranata, Data

    2017-06-01

    Infrastructure construction in earthquake prone area needs good design process, including modeling a structure in a correct way to reduce damages caused by an earthquake. Earthquakes cause many damages e.g. collapsed buildings that are dangerous. An incorrect modeling in design process certainly affects the structure's ability in responding to load, i.e. an earthquake load, and it needs to be paid attention to in order to reduce damages and fatalities. A correct modeling considers every aspect that affects the strength of a building, including stiffness of resisting lateral loads caused by an earthquake. Most of structural analyses still use open frame method that does not consider the effect of stiffness of masonry panel to the stiffness and strength of the whole structure. Effect of masonry panel is usually not included in design process, but the presence of this panel greatly affects behavior of the building in responding to an earthquake. In worst case scenario, it can even cause the building to collapse as what has been reported after great earthquakes worldwide. Modeling a structure with masonry panel as consideration can be performed by designing the panel as compression brace or shell element. In designing masonry panel as a compression brace, there are fourteen methods popular to be used by structure designers formulated by Saneinejad-Hobbs, Holmes, Stafford-Smith, Mainstones, Mainstones-Weeks, Bazan-Meli, Liauw Kwan, Paulay and Priestley, FEMA 356, Durani Luo, Hendry, Al-Chaar, Papia and Chen-Iranata. Every method has its own equation and parameters to use, therefore the model of every method was compared to results of experimental test to see which one gives closer values. Moreover, those methods also need to be compared to the open frame to see if they can result values within limits. Experimental test that was used in comparing all methods was taken from Mehrabi's research (Fig. 1), which was a prototype of a frame in a structure with 0.5 scale and the

  15. 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.

  16. Modeling the Sedimentary Infill of Lakes in the East African Rift: A Case Study of Multiple versus Single Rift Basin Segments

    NASA Astrophysics Data System (ADS)

    Zhang, C.; Scholz, C. A.

    2016-12-01

    The sedimentary basins in the East African Rift are considered excellent modern examples for investigating sedimentary infilling and evolution of extensional systems. Some lakes in the western branch of the rift have formed within single-segment systems, and include Lake Albert and Lake Edward. The largest and oldest lakes developed within multi-segment systems, and these include Lake Tanganyika and Lake Malawi. This research aims to explore processes of erosion and sedimentary infilling of the catchment area in single-segment rift (SSR) and multi-segment rift (MSR) systems. We consider different conditions of regional precipitation and evaporation, and assess the resulting facies architecture through forward modeling, using state-of-the-art commercial basin modeling software. Dionisos is a three-dimensional numerical stratigraphic forward modeling software program, which simulates basin-scale sediment transport based on empirical water- and gravity-driven diffusion equations. It was classically used to quantify the sedimentary architecture and basin infilling of both marine siliciclastic and carbonate environments. However, we apply this approach to continental rift basin environments. In this research, two scenarios are developed, one for a MSR and the other for a SSR. The modeled systems simulate the ratio of drainage area and lake surface area observed in modern Lake Tanganyika and Lake Albert, which are examples of MSRs and SSRs, respectively. The main parameters, such as maximum subsidence rate, water- and gravity-driven diffusion coefficients, rainfall, and evaporation, are approximated using these real-world examples. The results of 5 million year model runs with 50,000 year time steps show that MSRs are characterized by a deep water lake with relatively modest sediment accumulation, while the SSRs are characterized by a nearly overfilled lake with shallow water depths and thick sediment accumulation. The preliminary modeling results conform to the features

  17. Sedimentary archives of the French Atlantic coast (inner Bay of Vilaine, south Brittany): Depositional history and late Holocene climatic and environmental signals

    NASA Astrophysics Data System (ADS)

    Sorrel, Philippe; Tessier, Bernadette; Demory, François; Baltzer, Agnès; Bouaouina, Firas; Proust, Jean-Noël; Menier, David; Traini, Camille

    2010-06-01

    The late Holocene is of particular interest to our understanding of the evolution of coastal sedimentary systems because this period encompasses warmer and cooler periods, and rising sea level in northern Europe. Based on an approach combining AMS 14C, sedimentological and rock magnetic analyses on sediment cores complemented with seismic data collected in the macrotidal Bay of Vilaine (south Brittany), we document the depositional history of the inner bay coeval to the mid- to late-Holocene transgression in south Brittany. Correlation between sedimentary archives revealed the main sedimentary infilling phases during the last 6000 years. Four units (U1-U4) are recognized in the coastal sediment wedge of the system, corresponding to the stepwise marine invasion of the bay. We show that (1) marine inundation, due to the steep morphology of the bedrock, is diachronous between distal and proximal records. A time lag of ˜1000 years is inferred over a distance of less than 5 km; (2) in the outer areas, the sedimentation has been condensed since 3000 years; (3) proximal estuarine archives offer the best record of sedimentary processes covering the last 2000 years, including the Medieval Warm Period (MWP). Correlations in proximal records in the Bay of Vilaine assess the connection between coastal sedimentary dynamics, climatic conditions and anthropogenic activities during the MWP. We match the preservation of clay deposits to increased river-borne suspended matter transported to the estuary probably as a result of accelerated land-use development (higher soil erosion) in the catchment area between ca. 880 and 1050 AD. Because the preservation of estuarine sedimentary successions is favoured when coastal wave sediment reworking is minimal, it is proposed that the prevailing climatic regime in south Brittany during the MWP likely resembled to that of the preferred negative phase of the North Atlantic Oscillation (NAO). Our data are fairly consistent with other late

  18. Physics-Based Simulation and Experiment on Blast Protection of Infill Walls and Sandwich Composites Using New Generation of Nano Particle Reinforced Materials

    NASA Astrophysics Data System (ADS)

    Irshidat, Mohammad

    A critical issue for the development of nanotechnology is our ability to understand, model, and simulate the behavior of small structures and to make the connection between nano structure properties and their macroscopic functions. Material modeling and simulation helps to understand the process, to set the objectives that could guide laboratory efforts, and to control material structures, properties, and processes at physical implementation. These capabilities are vital to engineering design at the component and systems level. In this research, experimental-computational-analytical program was employed to investigate the performance of the new generation of polymeric nano-composite materials, like nano-particle reinforced elastomeric materials (NPREM), for the protection of masonry structures against blast loads. New design tools for using these kinds of materials to protect Infill Walls (e.g. masonry walls) against blast loading were established. These tools were also extended to cover other type of panels like sandwich composites. This investigation revealed that polymeric nano composite materials are strain rate sensitive and have large amount of voids distributed randomly inside the materials. Results from blast experiments showed increase in ultimate flexural resistance achieved by both unreinforced and nano reinforced polyurea retrofit systems applied to infill masonry walls. It was also observed that a thin elastomeric coating on the interior face of the walls could be effective at minimizing the fragmentation resulting from blast. More conclusions are provided with recommended future research.

  19. Terrestrial and Marine Organic Matter Accumulation in Hudson Bay: A High-Resolution Record of Climate/Watershed Processes over the Late Holocene

    NASA Astrophysics Data System (ADS)

    Alleau, Y.; Goni, M. A.; Kolcynski, L.; St-Onge, G.; Lajeunesse, P.; Haberzettl, T.

    2014-12-01

    A high-resolution record of organic matter accumulation in sediments from a combined gravity-piston core was collected from a site located at a water depth of 104 m inside Nastapoka Sound in the south-eastern region of Hudson Bay. The drainage basins in this region of Hudson Bay coincide roughly with the present-day tree line location and are within the forest-tundra transition zone. CAT- Scan and multi-sensor core logger data revealed relatively uniform sediments throughout the core. 14C-based geochronology indicates that the combined record extends to ~3200 cal BP and that accumulation rates were relatively constant (0.1-0.2 cm/y). Organic carbon, inorganic carbon and nitrogen contents display down-core variability consistent with changes in organic matter inputs but overall relatively stable depositional conditions over the last 3,000 years. Compositionally, we measured steady increases in the carbon:nitrogen ratios and lignin phenol content of sedimentary organic matter from 3200 cal BP to present consistent with enhanced inputs of vascular plant-derived organic matter. Lignin compositions (i.e. S/V and C/V phenol ratios) throughout the core are consistent with contributions from a mixture of conifer and angiosperm non-woody plant sources. Steady decreases in both S/V and C/V phenol ratios since 3200 cal BP to the present indicate enhanced contributions from conifer-dominated vegetation and are consistent with a steady expansion of boreal forests (white and black spruce) over shrub -dominated tundra (dwaf birch, willows, sedges) in this southern Arctic region over the late Holocene. No clear trends in the ratio of combustion products over lignin products are evident, suggesting a low fire frequency in the area during the covered time span of the record.

  20. The Holocene sedimentary history of the Kangerlussuaq Fjord-valley fill, West Greenland

    NASA Astrophysics Data System (ADS)

    Storms, Joep E. A.; de Winter, Ilja L.; Overeem, Irina; Drijkoningen, Guy G.; Lykke-Andersen, Holger

    2012-03-01

    West Greenland has been intensively studied to reconstruct and better understand past relative sea level changes and deglacial history. This study extends these efforts by linking sea level and deglacial history to the sedimentary infill successions of Kangerlussuaq Fjord and associated landward valleys. Based on published and new land- and sea-based geophysical data, radiocarbon dates and geological observations we have characterized the infill and reconstructed the sedimentation history during the Holocene. Based on a revised sea level curve and data presented in this paper we defined three depositional phases. Phase I (>7000 yr BP) is represented by dominant glaciomarine deposition associated with a tide-water glacier system. As the Greenland Ice Sheet (GIS) continued to retreat it became land based. During phase II (7000-1500 yr BP) two separate depocenters formed. Keglen delta depocenter arose from a temporary stabilization phase of the GIS and prograded rapidly over the glaciomarine deposits of Phase I. Further inland, proglacial lake formation and subsequent sedimentary infill associated with the ongoing GIS retreat is represents the second depocenter. The Watson River connected both depocenters by a flood plain which transferred sediment from the GIS to the Keglen delta. Ongoing sea level fall due to glacio-isostastic uplift combined with a gradually cooler and dryer climate resulted in terrace formation along the Watson River flood plain. Around 4000 yr BP, the GIS margin reached its most landward location and began to advance to its present location. The final phase (Phase III; <1500 yr BP) is represented by a stabilized GIS position and a relative sea level rise which led to aggrading conditions near the present-day delta plain of Watson River. Simultaneously, subaqueous channels were formed at the delta front by hyperpycnal flows associated with jökulhlaup events.

  1. 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

  2. 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.

  3. 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.

  4. 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.

  5. Dynamic out-of-plane and in-plane testing of full-scale hollow clay tile infilled frames. [Final report

    SciTech Connect

    Gambill, J.B.

    1994-12-31

    Many of the Y-12 Plant buildings are made of steel and concrete frames infilled with unreinforced clay tile walls; in many instances these infill walls comprise the major lateral load resisting capacity of the structures. A research program was begun to evaluate clay tile infill behavior. This test report describes testing done by USACERL as part of shake table testing; the tests were on a biaxial shock test machine.

  6. The evolution of the Rhone River in the Basses Terres basin during the Holocene (Alpine foothills, France)

    NASA Astrophysics Data System (ADS)

    Salvador, Pierre-Gil; Berger, Jean-François

    2014-01-01

    This paper concerns the evolution during the Holocene of the floodplain of the Rhone River in the Basses Terres basin, 70 km northeast of Lyon. Geomorphological mapping of a number of paleochannels has been carried out, using topographic maps, aerial photos, and landform surveys, and mechanical cores have been taken that enable the reconstruction of several stratigraphies in cross section. The chronology of fluvial deposits relies mainly on the radiocarbon dating of organic materials collected from the abandoned fluvial fills. Paleochannel infillings were also used to record fluvial style changes and floodplain aggradation rates. The main results show that the region has a mountainous piedmont plain controlled by local factors (inherited from glacial times) that have led to the atypical predominance of a meandering river pattern controlling the evolution of the floodplain in the Basses Terres area during the Holocene. A major avulsion of the Rhone, when it switched to its present-day northern course around 2700-2600 cal. BP, strongly influenced the evolution of the Holocene floodplain, causing a sharp decrease in the aggradation of the abandoned section. In addition, four major occurrences of strong and increased sediment discharge took place around 10,000-7500, 3000-2700, 2400/1500-1000, and 230-50 cal. BP. Two of these (ca. 3000-2700 and 230-50 cal. BP) are correlated to a braided pattern and represent temporary fluvial metamorphoses of the Rhone. The infilling rates of several paleochannels also reveal periods of strong sediment deposition around 5500-5250, 3500-3200, 1400-1200, and 600-400 cal. BP, consistent with previous regional paleohydrological phases as well as new ones. These phases are synchronous with the hydrosedimentary variations identified on a regional scale in the Rhone catchment area and the northern Alps.

  7. Application of integrated reservoir management and reservoir characterization to optimize infill drilling

    SciTech Connect

    1997-04-01

    This project has used a multi-disciplinary approach employing geology, geophysics, and engineering to conduct advanced reservoir characterization and management activities to design and implement an optimized infill drilling program at the North Robertson (Clearfork) Unit in Gaines County, Texas. The activities during the first Budget Period consisted of developing an integrated reservoir description from geological, engineering, and geostatistical studies, and using this description for reservoir flow simulation. Specific reservoir management activities were identified and tested. The geologically targeted infill drilling program currently being implemented is a result of this work. A significant contribution of this project is to demonstrate the use of cost-effective reservoir characterization and management tools that will be helpful to both independent and major operators for the optimal development of heterogeneous, low permeability shallow-shelf carbonate (SSC) reservoirs. The techniques that are outlined for the formulation of an integrated reservoir description apply to all oil and gas reservoirs, but are specifically tailored for use in the heterogeneous, low permeability carbonate reservoirs of West Texas.

  8. 3D-printed applicators for high dose rate brachytherapy: Dosimetric assessment at different infill percentage.

    PubMed

    Ricotti, Rosalinda; Vavassori, Andrea; Bazani, Alessia; Ciardo, Delia; Pansini, Floriana; Spoto, Ruggero; Sammarco, Vittorio; Cattani, Federica; Baroni, Guido; Orecchia, Roberto; Jereczek-Fossa, Barbara Alicja

    2016-12-01

    Dosimetric assessment of high dose rate (HDR) brachytherapy applicators, printed in 3D with acrylonitrile butadiene styrene (ABS) at different infill percentage. A low-cost, desktop, 3D printer (Hamlet 3DX100, Hamlet, Dublin, IE) was used for manufacturing simple HDR applicators, reproducing typical geometries in brachytherapy: cylindrical (common in vaginal treatment) and flat configurations (generally used to treat superficial lesions). Printer accuracy was investigated through physical measurements. The dosimetric consequences of varying the applicator's density by tuning the printing infill percentage were analysed experimentally by measuring depth dose profiles and superficial dose distribution with Gafchromic EBT3 films (International Specialty Products, Wayne, NJ). Dose distributions were compared to those obtained with a commercial superficial applicator. Measured printing accuracy was within 0.5mm. Dose attenuation was not sensitive to the density of the material. Surface dose distribution comparison of the 3D printed flat applicators with respect to the commercial superficial applicator showed an overall passing rate greater than 94% for gamma analysis with 3% dose difference criteria, 3mm distance-to-agreement criteria and 10% dose threshold. Low-cost 3D printers are a promising solution for the customization of the HDR brachytherapy applicators. However, further assessment of 3D printing techniques and regulatory materials approval are required for clinical application. Copyright © 2016 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

  9. Evaluation of long-term trends in extreme precipitation: Implications of in-filled historical data use for analysis

    NASA Astrophysics Data System (ADS)

    Teegavarapu, Ramesh S. V.; Nayak, Anurag

    2017-07-01

    This study focuses on the assessment of biases from infilling missing precipitation data on the detection of long-term change using parametric and non-parametric statistical techniques. Long-term historical precipitation data available for almost 100 years at 53 rain gages in south Florida, USA, with gages having varying lengths of missing data are used for the study. Precipitation data with gaps and time series with spatial interpolated data are analyzed. Chronologically complete datasets are often used in climate variability studies by analyzing data in multiple temporal windows. The temporal windows selected in this work coincide with Atlantic multi-decadal oscillation (AMO) cool and warm phases that strongly influence precipitation extremes and characteristics in the study region. Selection of these windows has helped in evaluating the extremes derived based on infilled and unfilled data. The frequency of occurrence of precipitation extremes over a pre-specified threshold is also analyzed. Results indicate that infilled precipitation data introduce large biases in the statistical trends and over and under-estimate low and high extremes respectively. Evaluation of three extreme precipitation indices (i.e. Rx1day, R25mm and R50mm) indicates that bias increases with increase in amount of missing data. Nonparametric hypothesis tests indicate that statistical distributions of data of infilled and unfilled data are different when the data infilled is more than 5% of the entire data. Infilled data also introduced high variability in precipitation extremes in AMO cool and warm phases along with the changes in the frequency of occurrence of extreme events over a threshold.

  10. Sedimentary infilling of bedrock-controlled palaeo-embayments off Cape Trafalgar, Strait of Gibraltar (Gulf of Cadiz)

    NASA Astrophysics Data System (ADS)

    de Castro, Sandra; Lobo, Francisco J.

    2017-05-01

    This study investigates two bedrock-controlled palaeo-coastal embayments on the Barbate Platform off Cape Trafalgar near the Strait of Gibraltar (Gulf of Cadiz shelf, SW Iberian Peninsula), aiming to reveal their infilling dynamics and the influence of rocky outcrops on shallow-water hydrodynamics and sediment transport. The approach relies on detailed multibeam bathymetric data, high-resolution seismic profiles and tidal current simulations. Elongated rocky outcrops formed a palaeo-coast when sea level was approximately 35 to 20 m below that of the present day, and bound a relatively flat area. However, the seismic profiles enabled to distinguish two main troughs (A and B) that were infilled following a distinctive evolution during the last transgression. Five seismic units were identified (I to V, from base to top). Deposit A is composed of seismic units II to V and is interpreted as a marine embayment infill, here termed the Barbate palaeo-embayment (BPE). Deposit B is composed of seismic units I to IV and is interpreted as a palaeo-valley infill, here termed the Barbate palaeo-valley (BPV). The complex internal stratigraphic architecture depicts an overall evolution from tidal/fluvial deposits to shallow-water marine deposits. Most significant is the occurrence of coupled tidal flats/estuarine sand bars constituting the infilling of the BPE; this suggests the persistence of a high-energy current in a shallow, confined embayment, which was amplified by the rocky outcrop constrictions and possibly facilitated by the episodic movement of a normal fault. In contrast to this active setting, the nearby straight and narrow BPV was subjected to lower-energy infilling dynamics during its initial flooding phases. There, tidal activity was possibly reduced by the straight morphology of the valley and the occurrence of a topographic constriction (i.e. the Barbate Passage) at the mouth of the valley.

  11. Holocene peatland initiation in the Greater Everglades

    NASA Astrophysics Data System (ADS)

    Dekker, Stefan; de Boer, Hugo; Dermody, Brian; Wagner-Cremer, Friederike; Wassen, Martin; Eppinga, Maarten

    2015-04-01

    The mechanisms involved in the initiation and development of the Greater Everglades peatland ecosystems in South Florida (USA) remain a topic of discussion. In this study, we present an overview of basal ages of peat deposits in South Florida, which shows two major episodes of peatland initiation between 7.0-4.5 kyr and 3.5-2.0 kyr. Our analysis of regional climate proxy datasets led to three alternative hypotheses that may explain the timing and duration of these two peatland initiation episodes: (1) decreased drainage due to relative sea level (RSL) rise during the Holocene (2) gradual increase in precipitation throughout the Holocene, and (3) a combination of increasing precipitation, rising RSL and oscillations in the climate system. We test whether these three hypotheses can explain the pattern of initiation and development of the Greater Everglades peatlands using models that simulate the non-linear processes involved in peat production and decomposition in combination with the local drainage conditions of Southern Florida. The model results suggest that RSL-rise alone cannot predict the onset of peat initiation in the Greater Everglades using our model setup. The model also implies that the climate was wet enough for peat development also during the early Holocene. The first two hypothesized mechanisms in combination with climate oscillations may explain the onset of peat accumulation at 8.2 kyr BP. The two-phased character of peat land initiation may be explained by the spatial distribution of local drainage conditions. As peatland development is highly non-linear, our model uncovers a mechanistic way how peats can suddenly shift from a dry high equilibrium to a wet low equilibrium resulting in lake formation as observed in paleo-ecological studies in the Greater Everglades.

  12. Holocene peatland initiation in the Greater Everglades

    NASA Astrophysics Data System (ADS)

    Dekker, Stefan C.; de Boer, Hugo J.; Dermody, Brian J.; Wagner-Cremer, Friederike; Wassen, Martin J.; Eppinga, Maarten B.

    2015-02-01

    The mechanisms involved in the initiation and development of the Greater Everglades peatland ecosystems remain a topic of discussion. In this study, we first present an overview of basal ages of peat deposits in South Florida, which shows two major episodes of peatland initiation between 7.0-4.5 kyr and 3.5-2.0 kyr. Our analysis of regional climate proxy data sets led to three alternative hypotheses that may explain the timing and duration of these two peatland initiation episodes: (1) decreased drainage due to relative sea level (RSL) rise during the Holocene, (2) gradual increase in precipitation throughout the Holocene, and (3) a combination of increasing precipitation, rising RSL, and oscillations in the climate system. We test whether these three hypotheses can explain the pattern of initiation and development of the Greater Everglades peatlands using models that simulate the nonlinear processes involved in peat production and decomposition. The model results suggest that RSL rise could explain the onset of peatland initiation and imply that the climate was wet enough for peat development also during the early Holocene. The first two hypothesized mechanisms in combination with climate oscillations may explain the onset of peat accumulation at 8.2 kyr B.P. The two-phased character of peatland initiation maybe explained by the spatial distribution of local drainage conditions. As peatland development is highly nonlinear, our model uncovers a mechanistic way how peats can suddenly shift from a dry high equilibrium to a wet low equilibrium resulting in lake formation as observed in paleoecological studies in the Greater Everglades.

  13. 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

  14. Pliocene to recent infilling and subsidence of intraslope basins offshore Louisiana

    SciTech Connect

    Pratson, L.F.; Ryan, W.B.F.

    1994-10-01

    Intraslope basins on the lower eastern Louisiana continental slope are modern analogs of large oil- and gas-charged basins infilled on the upper Louisiana slope and buried landward beneath the shelf. High-resolution, gridded multibeam bathymetry and single-channel seismic reflection profiles are used to (1) characterize the morphology and shallow stratigraphy of 46 intraslope basins within the outer slope region; and (2) look for surficial evidence among the basins of slope channelways that fed sediment flows to the Mississippi Fan during the Pliocene-Pleistocene. Computer algorithms, traditionally employed for automatically mapping river networks in gridded land topography, are used to extract morphologic measurements of the intraslope basins from the gridded bathymetry. The basins are found to average approximately 15 km in length, 10 km in width, and 200 m in depth and occur over a map area of about 50 km{sup 2}. These dimensions, however, can range over an order of magnitude.

  15. 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.

  16. 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

    2016-01-08

    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.

  17. 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.

  18. Holocene intramontane lake development: A new model in the Jáchal River Valley, Andean Precordillera, San Juan, Argentina

    NASA Astrophysics Data System (ADS)

    Colombo, Ferran; Busquets, Pere; Sole de Porta, Nuria; Limarino, Carlos Oscar; Heredia, Nemesio; Rodriguez-Fernandez, Luis Roberto; Alvarez-Marron, Joaquina

    2009-10-01

    The Jáchal River Valley displays a number of significant Holocene sedimentary accumulations made up of fine-grained materials. These deposits are interpreted as the sedimentary infill of shallow temporary lakes that were generated by slow growing episodes of alluvial fans that obstructed the Jáchal River Valley. The association of fossil remains through the Holocene sedimentary sequence suggests that the accumulation of lacustrine sediments was affected by climate variations. The predominant aridity was punctuated by very few humid episodes characterised by fresh-water gastropoda and the intercalations of muddy sediments. The high proportion of charcoal particles in some samples indicates periodic forest fires. Abundant non-pollen forest remains suggest that an open zone dominated by several types of grasses underwent a dry season during part of the year. The palynomorph associations found in the Jáchal River Valley Holocene lacustrine sediments suggest that the humid conditions were less intense than those in the San Juan River Valley located more than one hundred kilometres southwards. Our study suggests that lake formation could have been controlled by climate oscillation probably related to the ENSO variation at 30° south latitude.

  19. 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.

  20. The rate of infill and colonization by invertebrates of borrow pits in the Wash (S.E. England)

    NASA Astrophysics Data System (ADS)

    McGrorty, S.; Reading, C. J.

    1984-09-01

    The outer borrow pit had a volume of 458 000 m3 when excavated and was further increased (by 22 500 m3) by the erosion of a lagoon, but was completely infilled in 3·5 years. The rate of sedimentation in the outer borrow pit, though declining with time, was considerably greater than previously recorded rates for intertidal banks and probably accounted for the paucity of fauna in the pit until completely infilled. Poorly sorted, unconsolidated, anaerobic, clay and silt sediments initially accumulated in the outer pit with up to 5 cm liquid mud at the surface, but after 2 years the predominant fraction was fine sand. Only Nepthys hombergii became established in the outer borrow pit before the pit was completely infilled, when the other pre-excavation, dominant species returned. The expectation that Capitella capitata and oligochaete species (opportunistic, 'pollution indicator' species) would be the first colonizers was not realized, though the oligochaete, Tubificoides benedeni was the most abundant species in the more consolidated, sandier sediments in the inner borrow pit 4 years after its excavation. The density of invertebrates in the inner pit was greater than the surrounding mud flats and was a focus for birds feeding in the area. The outer borrow pit after complete infill also had higher desities of bird food species than before excavation but was rarely visited by birds.

  1. Holocene climate of New England

    NASA Astrophysics Data System (ADS)

    Davis, Margaret B.; Spear, Ray W.; Shane, Linda C. K.

    1980-09-01

    Stratigraphic studies of pollen and macrofossils from six sites at different elevations in the White Mountains of New Hampshire demonstrate changes in the distributions of four coniferous tree species during the Holocene. Two species presently confined to low elevations extended farther up the mountain slopes during the early Holocene: white pine grew 350 m above its present limit beginning 9000 yr B.P., while hemlock grew 300-400 m above its present limit soon after the species immigrated to the region 7000 yr. B.P. Hemlock disappeared from the highest sites about 5000 yr B.P., but both species persisted at sites 50-350 m above their present limits until the Little Ice Age began a few centuries ago. The history of the two main high-elevation conifers is more difficult to interpret. Spruce and fir first occur near their present upper limits 9000 or 10,000 yr B.P. Fir persisted in abundance at elevations similar to those where it occurs today throughout the Holocene, while spruce became infrequent at all elevations from the beginning of the Holocene until 2000 yr B.P. These facts suggest a more complex series of changes than a mere upward shift of the modern environmental gradient. Nevertheless, we conclude that the minimum climatic change which would explain the upward extensions of hemlock and white pine is a rise in temperature, perhaps as much as 2°C. The interval of maximum warmth started 9000 yr B.P. and lasted at least until 5000 yr B.P., correlative with the Prairie Period in Minnesota.

  2. Holocene fire occurrence and alluvial responses at the leading edge of pinyon–juniper migration in the Northern Great Basin, USA

    USGS Publications Warehouse

    Weppner, Kerrie N.; Pierce, Jennifer L.; Betancourt, Julio L.

    2013-01-01

    Fire and vegetation records at the City of Rocks National Reserve (CIRO), south-central Idaho, display the interaction of changing climate, fire and vegetation along the migrating front of single-leaf pinyon (Pinus monophylla) and Utah juniper (Juniperus osteosperma). Radiocarbon dating of alluvial charcoal reconstructed local fire occurrence and geomorphic response, and fossil woodrat (Neotoma) middens revealed pinyon and juniper arrivals. Fire peaks occurred ~ 10,700–9500, 7200–6700, 2400–2000, 850–700, and 550–400 cal yr BP, whereas ~ 9500–7200, 6700–4700 and ~ 1500–1000 cal yr BP are fire-free. Wetter climates and denser vegetation fueled episodic fires and debris flows during the early and late Holocene, whereas drier climates and reduced vegetation caused frequent sheetflooding during the mid-Holocene. Increased fires during the wetter and more variable late Holocene suggest variable climate and adequate fuels augment fires at CIRO. Utah juniper and single-leaf pinyon colonized CIRO by 3800 and 2800 cal yr BP, respectively, though pinyon did not expand broadly until ~ 700 cal yr BP. Increased fire-related deposition coincided with regional droughts and pinyon infilling ~ 850–700 and 550–400 cal yr BP. Early and late Holocene vegetation change probably played a major role in accelerated fire activity, which may be sustained into the future due to pinyon–juniper densification and cheatgrass invasion.

  3. Holocene fire occurrence and alluvial responses at the leading edge of pinyon-juniper migration in the Northern Great Basin, USA

    NASA Astrophysics Data System (ADS)

    Weppner, Kerrie N.; Pierce, Jennifer L.; Betancourt, Julio L.

    2013-09-01

    Fire and vegetation records at the City of Rocks National Reserve (CIRO), south-central Idaho, display the interaction of changing climate, fire and vegetation along the migrating front of single-leaf pinyon (Pinus monophylla) and Utah juniper (Juniperus osteosperma). Radiocarbon dating of alluvial charcoal reconstructed local fire occurrence and geomorphic response, and fossil woodrat (Neotoma) middens revealed pinyon and juniper arrivals. Fire peaks occurred ~ 10,700-9500, 7200-6700, 2400-2000, 850-700, and 550-400 cal yr BP, whereas ~ 9500-7200, 6700-4700 and ~ 1500-1000 cal yr BP are fire-free. Wetter climates and denser vegetation fueled episodic fires and debris flows during the early and late Holocene, whereas drier climates and reduced vegetation caused frequent sheetflooding during the mid-Holocene. Increased fires during the wetter and more variable late Holocene suggest variable climate and adequate fuels augment fires at CIRO. Utah juniper and single-leaf pinyon colonized CIRO by 3800 and 2800 cal yr BP, respectively, though pinyon did not expand broadly until ~ 700 cal yr BP. Increased fire-related deposition coincided with regional droughts and pinyon infilling ~ 850-700 and 550-400 cal yr BP. Early and late Holocene vegetation change probably played a major role in accelerated fire activity, which may be sustained into the future due to pinyon-juniper densification and cheatgrass invasion.

  4. 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.

  5. Past Holocene detritism quantification and modeling from lacustrine archives in order to deconvoluate human-climate interactions on natural ecosystem over long time-scale

    NASA Astrophysics Data System (ADS)

    Simonneau, Anaëlle; Chapron, Emmanuel; Di Giovanni, Christian; Galop, Didier; Darboux, Frédéric

    2014-05-01

    Water budget is one of the main challenges to paleoclimate researchers in relation to present-day global warming and its consequences for human societies. Associated soil degradation and erosion are thereby becoming a major concern in many parts of the world and more particularly in the Alps. Moreover, humans are considered as geomorphologic agents since few thousand years and it is now recognized that such an impact on natural ecosystem profoundly modified soils properties as well as aquatic ecosystems dynamics over long-term periods. The quantification of such inference over long time-scale is therefore essential to establish new policies to reduce mechanic soil erosion, which is one of the dominant processes in Europe, and anticipate the potential consequences of future climate change on hydric erosion. The mechanical erosion of continental surfaces results from climatic forcing, but can be amplified by the anthropogenic one. We therefore suggest that quantifying and modelling soil erosion processes within comparable Holocene lacustrine archives, allows to estimate and date which and when past human activities have had an impact on soil fluxes over the last 10000 years. Based on the present-day geomorphology of the surrounding watershed and the evolution of the vegetation cover during the Holocene, we develop an interdisciplinary approach combining quantitative organic petrography (i.e. optical characterization and quantification of soil particles within lake sediments) with high-resolution seismic profiling, age-depth models on lacustrine sediment cores and soil erosional susceptibility modeling, in order to estimate the annual volume of soil eroded over the last 10000 years, and in fine to quantify the volume of human-induced soil erosion during the Holocene period. This method is applied to close but contrasted mountainous lacustrine environments from the western French Alps: lakes Blanc Huez and Paladru, sensitive to same climatic influences but where past

  6. 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.

  7. A `Pole To Pole' Holocene Sea-Level Database

    NASA Astrophysics Data System (ADS)

    Horton, B.; Vacchi, M.; Shaw, T.; Ashe, E.; Engelhart, S. E.; Khan, N.; Kopp, R. E.

    2016-12-01

    Holocene relative sea-level (RSL) records exhibit spatial and temporal variability that arises from the complex pattern of interactions among eustatic (land ice volume and thermal expansion), isostatic (glacio and hydro), tectonic (neotectonic deformation) and local (tidal range change and sediment compaction) components. Each of these components have different response timescales varying relative importance during the Holocene and among regions. We have compiled a Holocene RSL database of 3000 validated sea-level index points from Greenland, North American Atlantic coast, Caribbean, South American Atlantic coast and Antarctica. The databases were constructed from previously published results that were collated in a formalized and consistent methodology to facilitate the development and comparison of regional RSL records. The RSL records are mostly derived from sea-level indicators from intertidal environments. The database also includes information relevant to sediment compaction, and modelling of both modern-day and paleotidal ranges. We assess rates of RSL change by fitting the RSL records with noisy-input Gaussian process models. Holocene RSL records from near-field regions (e.g., Antarctica, Greenland and Canada) reveal a complex pattern of RSL fall from a maximum marine limit due to the net effect of eustatic sea-level rise and glacio-isostatic uplift with rates of RSL fall as great as 69 m/ka. Intermediate field regions (e.g., U.S. mid-Atlantic coast, St. Croix) display variable rates of RSL rise from the cumulative effect of eustatic and isostatic factors. Fast rates of RSL rise (up to 10 m/ka) are found in the early Holocene in regions near the center of forebulge collapse. Far-field RSL records (South America) exhibit a mid-Holocene highstand, the timing and magnitude of which varies between 8 and 4 ka and <1 and 6 m, respectively. By comparing these records across a pole to pole database that spans a range of `fingerprints' from land-based ice sheets, we

  8. 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

  9. 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

  10. Drivers of Holocene sea-level change in the Caribbean

    NASA Astrophysics Data System (ADS)

    Khan, Nicole S.; Ashe, Erica; Horton, Benjamin P.; Dutton, Andrea; Kopp, Robert E.; Brocard, Gilles; Engelhart, Simon E.; Hill, David F.; Peltier, W. R.; Vane, Christopher H.; Scatena, Fred N.

    2017-01-01

    We present a Holocene relative sea-level (RSL) database for the Caribbean region (5°N to 25°N and 55°W to 90°W) that consists of 499 sea-level index points and 238 limiting dates. The database was compiled from multiple sea-level indicators (mangrove peat, microbial mats, beach rock and acroporid and massive corals). We subdivided the database into 20 regions to investigate the influence of tectonics and glacial isostatic adjustment on RSL. We account for the local-scale processes of sediment compaction and tidal range change using the stratigraphic position (overburden thickness) of index points and paleotidal modeling, respectively. We use a spatio-temporal empirical hierarchical model to estimate RSL position and its rates of change in the Caribbean over 1-ka time slices. Because of meltwater input, the rates of RSL change were highest during the early Holocene, with a maximum of 10.9 ± 0.6 m/ka in Suriname and Guyana and minimum of 7.4 ± 0.7 m/ka in south Florida from 12 to 8 ka. Following complete deglaciation of the Laurentide Ice Sheet (LIS) by ∼7 ka, mid-to late-Holocene rates slowed to < 2.4 ± 0.4 m/ka. The hierarchical model constrains the spatial extent of the mid-Holocene highstand. RSL did not exceed the present height during the Holocene, except on the northern coast of South America, where in Suriname and Guyana, RSL attained a height higher than present by 6.6 ka (82% probability). The highstand reached a maximum elevation of +1.0 ± 1.1 m between 5.3 and 5.2 ka. Regions with a highstand were located furthest away from the former LIS, where the effects from ocean syphoning and hydro-isostasy outweigh the influence of subsidence from forebulge collapse.

  11. Drivers of Holocene sea-level change in the Caribbean

    USGS Publications Warehouse

    Khan, Nicole; Ashe, Erica; Horton, Benjamin P.; Dutton, Andrea; Kopp, Robert E.; Brocard, Gilles; Engelhart, Simon E.; Hill, David F.; Peltier, W.R.; Vane, Christopher H.; Scatena, Fred N.

    2017-01-01

    We present a Holocene relative sea-level (RSL) database for the Caribbean region (5°N to 25°N and 55°W to 90°W) that consists of 499 sea-level index points and 238 limiting dates. The database was compiled from multiple sea-level indicators (mangrove peat, microbial mats, beach rock and acroporid and massive corals). We subdivided the database into 20 regions to investigate the influence of tectonics and glacial isostatic adjustment on RSL. We account for the local-scale processes of sediment compaction and tidal range change using the stratigraphic position (overburden thickness) of index points and paleotidal modeling, respectively. We use a spatio-temporal empirical hierarchical model to estimate RSL position and its rates of change in the Caribbean over 1-ka time slices. Because of meltwater input, the rates of RSL change were highest during the early Holocene, with a maximum of 10.9 ± 0.6 m/ka in Suriname and Guyana and minimum of 7.4 ± 0.7 m/ka in south Florida from 12 to 8 ka. Following complete deglaciation of the Laurentide Ice Sheet (LIS) by ∼7 ka, mid-to late-Holocene rates slowed to < 2.4 ± 0.4 m/ka. The hierarchical model constrains the spatial extent of the mid-Holocene highstand. RSL did not exceed the present height during the Holocene, except on the northern coast of South America, where in Suriname and Guyana, RSL attained a height higher than present by 6.6 ka (82% probability). The highstand reached a maximum elevation of +1.0 ± 1.1 m between 5.3 and 5.2 ka. Regions with a highstand were located furthest away from the former LIS, where the effects from ocean syphoning and hydro-isostasy outweigh the influence of subsidence from forebulge collapse.

  12. Response of Red Sea circulation to Holocene insolation forcing

    NASA Astrophysics Data System (ADS)

    Trommer, G.; Siccha, M.; Schulz, H.; Hemleben, Ch.; Rohling, E. J.; van der Meer, M. T. J.; Schouten, S.; Kucera, M.

    2009-04-01

    The Red Sea is a marginal, oligotrophic basin of the Indian Ocean located at the interface between two climate systems: the Indian Monsoon and the Mediterranean climate. Whereas on glacial-interglacial timescales, the oceanography of the Red Sea is determined by eustatic sea level changes, at times of relatively stable sea level, the oceanography of the basin is controlled by these climate systems via processes like evaporation and precipitation. Since planktonic foraminifera in the Red Sea are sensitive to the supply of nutrients in waters from the Indian Ocean, we tried to uncover fluctuations of the monsoonal and mediterranean climate systems throughout the Holocene by investigating foraminiferal faunal assemblages in two cores of the Red Sea. In order to unravel changes in past circulation patterns, foraminifer assemblage counts were supplemented by stable isotopic measurements and organic geochemical proxies. An age model of the records based on ten AMS 14-C dates indicates a close coupling of the circulation pattern with Holocene insolation change. We find in the early Holocene indications for extended and weak summer circulation conditions, which can be explained by a strong summer Monsoon. These conditions disappear in phase with the decreasing summer insolation in the early Holocene. In the Mid to Late-Holocene (3.5-2 cal. Ka BP) we observe a distinct event characterised by a change towards a foraminiferal fauna which indicates increased productivity in the Red Sea and a more pronounced winter circulation. This circulation shift towards a stronger winter surface water inflow from the Gulf of Aden into the Red Sea is consistent with increased aridity in the region causing increasing winter evaporation and deep water formation in the northern Red Sea. It is only after this arid period, that the present-day circulation pattern in the Red Sea developed.

  13. 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.

  14. Holocene transgression of the Taipei Basin, northern Taiwan

    NASA Astrophysics Data System (ADS)

    Su, P.-J.; Teng, L. S.

    2012-04-01

    The Taipei Basin, a Late Quaternary rift basin in the collapsing northern Taiwan mountain belt, is situated 10 km away from the ocean and has only passage connected to the Taiwan Strait through the Dan-Shui river. Though the present Dan-Shui river is microtidal with a maximum tidal range around 2 meters, borehole facies characteristics show that the Taipei Basin was mainly occupied by tide-dominated environments during the Holocene transgression. Based on the facies analysis of sediment cores from 5 boreholes aligned in a NW-SE dip section provided by the Central Geological Survey, the Upper Pleistocene and Holocene deposits of the Taipei Basin can be divided into 5 facies associations, namely fluvial channel, floodplain, tidal-fluvial plain, bayhead delta and estuarine central basin, in which fluvial deposits dominate in the Pleistocene. Vivianite shows up widely in floodplain facies as an indication of fresh water and tranquil environments. About 9ka, the Holocene transgression caused the northwestern part of the basin to become a tide-dominated estuarine central basin, and the marginal area of the estuarine central basin forming bayhead deltas. Sporadic occurrences of shell fragments (especially Placuna sp.) and foraminifera (mostly Ammonia sp. and Elphidium sp.) in the estuarine deposits vindicate a brackish-water environment, in which heterolithic beddings and rhythmic sand-clay laminations indicative of tidal influence can be observed. Above the maximum flooding surface dated around 8ka, the depositional environments gradually returned into river dominated from inland out to the sea until the present. These sedimentary features show that wave influence was inhibited in the Taipei Basin during the early Holocene transgression so that tidal processes dominated in the basin sedimentation and built a well developed estuarine central basin and marginal bayhead deltas. Such a dramatic change in depositional environments in the late Holocene remains an intriguing

  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. 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.

  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. Holocene eruptive activity of El Chichon volcano, Chiapas, Mexico

    NASA Astrophysics Data System (ADS)

    Tilling, R. I.; Rubin, M.; Sigurdsson, H.; Carey, S.; Duffield, W. A.; Rose, W. I.

    1984-05-01

    Geologic and radiometric-age data indicate that El Chichon 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 domegrowth processes, were apparently separated by intervals of approximately 350 to 650 years. Some of El Chichon's eruptions may correlate with unusual atmospheric phenomena around A.D. 1300 and possibly A.D. 623.

  19. Holocene eruptive activity of El Chichon volcano, Chiapas, Mexico

    NASA Technical Reports Server (NTRS)

    Tilling, R. I.; Rubin, M.; Sigurdsson, H.; Carey, S.; Duffield, W. A.; Rose, W. I.

    1984-01-01

    Geologic and radiometric-age data indicate that El Chichon 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 domegrowth processes, were apparently separated by intervals of approximately 350 to 650 years. Some of El Chichon's eruptions may correlate with unusual atmospheric phenomena around A.D. 1300 and possibly A.D. 623.

  20. Concrete Infill Monitoring in Concrete-Filled FRP Tubes Using a PZT-Based Ultrasonic Time-of-Flight Method.

    PubMed

    Luo, Mingzhang; Li, Weijie; Hei, Chuang; Song, Gangbing

    2016-12-07

    Concrete-filled fiber-reinforced polymer tubes (CFFTs) have attracted interest for their structural applications in corrosive environments. However, a weak interfacial strength between the fiber-reinforced polymer (FRP) tube and the concrete infill may develop due to concrete shrinkage and inadequate concrete compaction during concrete casting, which will destroy the confinement effect and thereby reduce the load bearing capacity of a CFFT. In this paper, the lead zirconate titanate (PZT)-based ultrasonic time-of-flight (TOF) method was adopted to assess the concrete infill condition of CFFTs. The basic idea of this method is that the velocity of the ultrasonic wave propagation in the FRP material is about half of that in concrete material. Any voids or debonding created along the interface between the FRP tube and the concrete will delay the arrival time between the pairs of PZT transducers. A comparison of the arrival times of the PZT pairs between the intact and the defected CFFT was made to assess the severity of the voids or the debonding. The feasibility of the methodology was analyzed using a finite-difference time-domain-based numerical simulation. Experiments were setup to validate the numerical results, which showed good agreement with the numerical findings. The results showed that the ultrasonic time-of-flight method is able to detect the concrete infill condition of CFFTs.

  1. Concrete Infill Monitoring in Concrete-Filled FRP Tubes Using a PZT-Based Ultrasonic Time-of-Flight Method

    PubMed Central

    Luo, Mingzhang; Li, Weijie; Hei, Chuang; Song, Gangbing

    2016-01-01

    Concrete-filled fiber-reinforced polymer tubes (CFFTs) have attracted interest for their structural applications in corrosive environments. However, a weak interfacial strength between the fiber-reinforced polymer (FRP) tube and the concrete infill may develop due to concrete shrinkage and inadequate concrete compaction during concrete casting, which will destroy the confinement effect and thereby reduce the load bearing capacity of a CFFT. In this paper, the lead zirconate titanate (PZT)-based ultrasonic time-of-flight (TOF) method was adopted to assess the concrete infill condition of CFFTs. The basic idea of this method is that the velocity of the ultrasonic wave propagation in the FRP material is about half of that in concrete material. Any voids or debonding created along the interface between the FRP tube and the concrete will delay the arrival time between the pairs of PZT transducers. A comparison of the arrival times of the PZT pairs between the intact and the defected CFFT was made to assess the severity of the voids or the debonding. The feasibility of the methodology was analyzed using a finite-difference time-domain-based numerical simulation. Experiments were setup to validate the numerical results, which showed good agreement with the numerical findings. The results showed that the ultrasonic time-of-flight method is able to detect the concrete infill condition of CFFTs. PMID:27941617

  2. 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.

  3. The influences of the AMO and NAO on the sedimentary infill in an Azores Archipelago lake since ca. 1350 CE

    NASA Astrophysics Data System (ADS)

    Hernández, Armand; Sáez, Alberto; Bao, Roberto; Raposeiro, Pedro M.; Trigo, Ricardo M.; Doolittle, Sara; Masqué, Pere; Rull, Valentí; Gonçalves, Vítor; Vázquez-Loureiro, David; Rubio-Inglés, María J.; Sánchez-López, Guiomar; Giralt, Santiago

    2017-07-01

    The location of the Azores Archipelago in the North Atlantic makes this group of islands an excellent setting to study the long-term behavior of large oceanic and atmospheric climate dynamic patterns, such as the Atlantic Multidecadal Oscillation (AMO) and the North Atlantic Oscillation (NAO). Here, we present the impacts of these patterns on Lake Empadadas (Azores Archipelago) from the Medieval Climate Anomaly (MCA) - Little Ice Age (LIA) transition to the present based on sedimentological, geochemical and biological characterizations of the sedimentary record. Multivariate analyses of a number of proxies including X-ray fluorescence (XRF), X-ray diffraction (XRD), total organic and inorganic carbon (TOC and TIC) and diatom life forms abundance reveal that the sedimentary infill evolution has been controlled by (i) fluctuations in the lake level and (ii) variations in organic matter accumulation. Both processes are governed by climate variability and modulated by anthropogenic activities associated with changes on the lake catchment. Changes in these two sedimentary processes have been used to infer five stages: (i) the MCA-LIA transition (ca. 1350-1450 CE) was characterized by a predominantly positive AMO phase, which led to intermediate lake levels and high organic matter concentration; (ii) the first half of the LIA (ca. 1450-1600 CE) was characterized by predominant lowstand conditions and intermediate organic matter deposition mainly related to negative AMO phases; (iii) the second half of the LIA (ca. 1600-1850 CE) was characterized by negative AMO and NAO phases, implying intermediate lake levels and high organic matter deposition; (iv) the Industrial era (ca. 1850-1980 CE) was characterized by the lowest lake level and organic matter accumulation associated with negative AMO phases; and (v) the period spanning between 1980 CE and the present reveals the highest lake levels and low organic matter deposition, being associated with very positive AMO

  4. The sensitivity of the terrestrial biosphere to climatic change: A simulation of the middle Holocene

    SciTech Connect

    Foley, J.A.

    1994-12-01

    A process-based ecosystem model, DEMETER, is used to simulate the sensitivity of the terrestrial biosphere to changes in climate. In this study, DEMETER is applied to the two following climatic regimes: (1) the modern observed climate and (2) a simulated mid-Holocene climate (6000 years before present). The mid-Holocene climate is simulated using the GENESIS global climate model, where shifts in the Earth`s orbital parameters result in warmer northern continents and enhanced monsoons in Asia, North Africa, and North America. DEMETER simulates large differences between modern and mid-Holocene vegetation cover: (1) mid-Holocene boreal forests extend farther poleward than present in much of Europe, Asia, and North America, and (2) mid-Holocene North African grasslands extend substantially farther north than present. The simulated patterns of mid-Holocene vegetation are consistent with many features of the paleobotanical record. Simulated mid-Holocene global net primary productivity is approximately 3% larger than present, largely due to the increase of boreal forest and tropical grasslands relative to tundra and desert. Global vegetation carbon is higher at 6 kyr B.P. compared to present by roughly the same amount (4%). Mid-Holocene global litter carbon is larger than present by 10%, while global soil carbon is approximately 1% less. Despite the regional changes in productivity and carbon storage the simulated total carbon storage potential of the terrestrial biosphere (not including changes in peat) does not change significantly between the two simulations. 53 refs., 12 figs., 4 tabs.

  5. 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.

  6. Off-river waterbodies on tidal rivers: Human impact on rates of infilling and the accumulation of pollutants

    NASA Astrophysics Data System (ADS)

    Woodruff, Jonathan D.; Martini, Anna P.; Elzidani, Emhmed Z. H.; Naughton, Thomas J.; Kekacs, Daniel J.; MacDonald, Daniel G.

    2013-02-01

    Cut-off meanders, backwater ponds, and blocked valley coves are all common features along the tidal reaches of lowland rivers. While significant progress has been made to understand sediment dynamics in similar off-river environments above the head of tides, less is known about the processes driving transport and sedimentation within these systems when tidally influenced. To provide insight we combine sedimentological observations with flux analyses for a series of tidal off-river waterbodies along the Lower Connecticut River spanning the river's entire 100 km tidal reach. Sedimentation rates exhibit a clear seaward increase with growing tidal influence, and are an order of magnitude higher than accumulation rates obtained previously from neighboring marsh and subtidal environments. A simplified mass balance can relate time-series measurements of water level and suspended sediment concentration to observed trends in sedimentation, and support flood-dominated asymmetry in tidal sediment flux (i.e. tidal pumping) as the primary mechanism for enhanced trapping. Relatively steady rates of deposition are observed in off-river waterbodies over the last century, with little evidence of deposition dominated by extreme events. Suspended sediment concentrations rise significantly in the main tidal river with increasing river discharge, while tidal range is damped with rising freshwater flow. The net result is an optimal freshwater discharge for maximizing the tidal pumping of sediment from the main river into tidal off-river waterbodies, with more routine discharge events largely responsible for driving long-term trends in deposition. A sudden shift in lithology towards more inorganic, fluvial derived sediment is commonly observed towards the end of the 19th century, along with over an order of magnitude increase in the rate of deposition. The timing of the onset of rapid infilling occurs contemporaneous with the documented creation and/or deepening of tidal tie

  7. 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.

  8. 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.

  9. 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

  10. 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.

  11. 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.

  12. Faunal histories from Holocene ancient DNA.

    PubMed

    de Bruyn, Mark; Hoelzel, A Rus; Carvalho, Gary R; Hofreiter, Michael

    2011-08-01

    Recent studies using ancient DNA have been instrumental in advancing understanding of the impact of Holocene climate change on biodiversity. Ancient DNA has been used to track demography, migration and diversity, and is providing new insights into the long-term dynamics of species and population distributions. The Holocene is key to understanding how the past has impacted on the present, as it bridges the gap between contemporary phylogeographic studies and those with inference on Pleistocene patterns, based on ancient DNA studies. Here, we examine the major patterns of Holocene faunal population dynamics and connectivity; highlighting the dynamic nature of species and population responses to Holocene climatic change, thereby providing an 'analogue' for understanding potential impacts of future change.

  13. 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.

  14. Atmospheric methane control mechanisms during the early Holocene

    NASA Astrophysics Data System (ADS)

    Yang, Ji-Woong; Ahn, Jinho; Brook, Edward J.; Ryu, Yeongjun

    2017-09-01

    Understanding processes controlling the atmospheric methane (CH4) mixing ratio is crucial to predict and mitigate future climate changes in this gas. Despite recent detailed studies of the last ˜ 1000 to 2000 years, the mechanisms that control atmospheric CH4 still remain unclear, partly because the late Holocene CH4 budget may be comprised of both natural and anthropogenic emissions. In contrast, the early Holocene was a period when human influence was substantially smaller, allowing us to elucidate more clearly the natural controls under interglacial conditions more clearly. Here we present new high-resolution CH4 records from Siple Dome, Antarctica, covering from 11.6 to 7.7 thousands of years before 1950 AD (ka). We observe four local CH4 minima on a roughly 1000-year spacing, which correspond to cool periods in Greenland. We hypothesize that the cooling in Greenland forced the Intertropical Convergence Zone (ITCZ) to migrate southward, reducing rainfall in northern tropical wetlands. The inter-polar difference (IPD) of CH4 shows a gradual increase from the onset of the Holocene to ˜ 9.5 ka, which implies growth of boreal source strength following the climate warming in the northern extratropics during that period.

  15. Inception of a global atlas of Holocene sea levels

    NASA Astrophysics Data System (ADS)

    Khan, Nicole; Rovere, Alessio; Engelhart, Simon; Horton, Benjamin

    2017-04-01

    Determining the rates, mechanisms and geographic variability of sea-level change is a priority science question for the next decade of ocean research. To address these research priorities, the HOLocene SEA-level variability (HOLSEA) working group is developing the first standardized global synthesis of Holocene relative sea-level data to: (1) estimate the magnitudes and rates of global mean sea-level change during the Holocene; and (2) identify trends in spatial variability and decipher the processes responsible for geographic differences in relative sea-level change. Here we present the preliminary efforts of the working group to compile the database, which includes sea-level index points and limiting data from a range of different indicators across seven continents from the Last Glacial Maximum to present. We follow a standard protocol that incorporates full consideration of vertical and temporal uncertainty for each sea-level index point, including uncertainties associated with the relationship of each indicator to past sea-level and the methods used to date each indicator. We describe the composition of the global database, identify gaps in data availability, and highlight our effort to create an online platform to access the data. These data will be made available in a special issue of Quaternary Science Reviews and archived on NOAA's National Centers for Environmental Information (NCEI) in early 2018. We also invite researchers who collect or model Holocene sea-level data to participate. Long-term, this effort will enhance predictions of 21st century sea-level rise, and provide a vital contribution to the assessment of natural hazards with respect to sea-level rise and coastal response.

  16. 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.

  17. 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.

  18. Fluvial system evolution and environmental changes during the Holocene in the Mue valley (Western France)

    NASA Astrophysics Data System (ADS)

    Lespez, Laurent; Clet-Pellerin, Martine; Limondin-Lozouet, Nicole; Pastre, Jean-François; Fontugne, Michel; Marcigny, Cyril

    2008-06-01

    Geomorphological and palaeoenvironmental research on Holocene sedimentation in the Mue valley provides evidence for fluvial system changes related to climate and human activities in Normandy, a poorly studied area of the Paris basin. The 24-km long valley bottom has been investigated through a systematic survey. It shows an original longitudinal sedimentary pattern in relation with valley morphology and local geological controls. Minerogenic, tufaceous and peaty deposits provide opportunities for multi-proxy analyses and radiocarbon dating control. Sedimentation began around 9500 14C BP with silt deposition in a meandering system. The Boreal and the Lower Atlantic periods (8500-6000 14C BP) were mainly characterized by unlithified calcareous tufa. Locally, these deposits are very thick (7 to 13 m). The tufa formed barrages across the valley bottom, providing an autogenic control on upstream sedimentation. During the Upper Atlantic period (6000-4700 14C BP), the valley experienced a decrease in calcareous sedimentation and the development of organic deposits. At the beginning of the Subboreal (4700-3500 14C BP), peat deposits expanded, especially behind the tufa barrages. The valley bottom was characterized by large marshy areas whereas the regional vegetation was progressively modified by human activities. At the end of the Subboreal (3300-3000 14C BP) the infilling of the valley by calcareous silt was caused by an increase of river activity related to climatic and land use changes. From the Iron Age and Gallo-Roman periods (2800-1700 14C BP), the valley bottom was filled by silty overbank deposits related to an increase of soil erosion. The slopes and river system were once again coupled and the fluvial system functioned as a continuum from upstream to downstream. The alluvial record of the Mue valley reflects a broad regional pattern of environmental changes but presents particular features, which highlight the need of longitudinal studies to take into account

  19. 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.

  20. A Comparison of 20th Century and Holocene Historical Lake Areas and Implications for Reconstruction of Holocene Moisture Balance.

    NASA Astrophysics Data System (ADS)

    Plank, C. P.; Ferreira, M.; Shuman, B.; Ito, E.

    2005-12-01

    Low lake stands during the Holocene document a period of drier than modern conditions in the upper Midwest after 8000 cal yr B.P. Here, we seek to compare the magnitudes and spatial extent of these mid-Holocene water-level changes with the changes that occurred during the 1930s Dust Bowl drought. The comparison allows us to consider the potential range of hydrologic conditions in the mid-continent, and to detect similarities or differences between the two periods as a way to learn more about the climatic controls on the mid-Holocene moisture-balance. (How good an analog is the 1930s drought for the mid-Holocene aridity?) Each lake record, however, is unique and comparisons among lakes have been hindered by local hydrologic influences and sedimentary processes. We therefore test the simple methodological assumption that the stratigraphic records of small lakes may be used in concert to produce valid and meaningful maps of Holocene moisture balance. First we confirm that broad regional trends in lake area reflect long-term moisture balance patterns by studying the 1930s aerial photography. Second, we confirm that regionally coherent patterns of sedimentary change related to past water levels can be detected for the mid-Holocene via GPR profiles. Changes in open water surface area in response to the 1930's drought are quantified and mapped for over 300 small (1km sq. or less) lakes of northern and central Minnesota in order to determine if small basins responded to drought with explainable regional coherency. A map of percent area change (between AD 1930 and 2003) reveals that coherent trends in surface area response reflect the gradient of moisture balance change over the same period. We found a trend in percent surface area change from east to west with western lakes completely drying out (>100% change), a wider variability of responses in central Minnesota, and eastern lakes undergoing almost no change (<10%). GPR profiles were collected on two east-west transects

  1. 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

  2. Electrochemical Infilling of CuInSe2 within TiO2 Nanotube Layers and Subsequent Photoelectrochemical Studies

    PubMed Central

    Das, Sayantan; Sopha, Hanna; Krbal, Milos; Zazpe, Raul; Podzemna, Veronika; Prikryl, Jan

    2017-01-01

    Abstract Anodic self‐organized TiO2 nanotube layers (with different aspect ratios) were electrochemically infilled with CuInSe2 nanocrystals with the aim to prepare heterostructures with a photoelectrochemical response in the visible light. The resulting heterostructure assembly was confirmed by field‐emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and X‐ray diffraction (XRD). High incident photon‐to‐electron conversion efficiency values exceeding 55% were obtained in the visible‐light region. The resulting heterostructures show promise as a candidate for solid‐state solar cells. PMID:28392991

  3. 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

  4. 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

  5. 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.

  6. Major Reorganization of the North Atlantic Oscillation during early Holocene deglaciation

    NASA Astrophysics Data System (ADS)

    Dietrich, S.; Wassenburg, J. A.; Lohmann, G.; Fietzke, J.; Fohlmeister, J.; Jochum, K. P.; Scholz, D.; Richter, D.; Abdellah, S.; Spoetl, C.; Andreae, M. O.; Immenhauser, A.

    2016-12-01

    Recent observations show that the Greenland Ice Sheet (GIS) melts. However, the climatic consequences and in particular its effect on the North Atlantic Oscillation (NAO) remains unclear. The Early Holocene is characterized by deglaciation processes, e.g. the remnant Laurentide Ice Sheet (LIS) and its melting and might provide an analogue to the melting of the GIS today. This study integrates new proxy climate data from a NW Moroccan (a key NAO region) speleothem that covers the Early to Late Holocene and results from the state-of-the-art earth-system-model COSMOS to study the variability of the NAO and its forcing mechanisms through the Holocene. Nowadays, the NAO leads to a negative correlation between precipitation in NW Morocco and W Germany. Based on a comparison of the Moroccan and a German proxy record, a positive correlation is observed during the Early Holocene. This correlation shift is examined by climate simulations of the Early (9 ka BP, including LIS and its melting), mid (6 ka BP) and Late Holocene (pre-industrial conditions). The influence of the LIS and its melt water contribution lead to a strong non-linear cooling of surface air temperatures during deglaciation. This synergetic influence of the LIS strengthens the melting effect on ocean circulation during the Early Holocene, which affects the Atlantic Meridional Overturning Circulation and sea-surface temperatures, which in turn may affect sea-level pressure and, eventually, the AO/NAO. Our climate simulations suggest that this reflects a major atmospheric and oceanic reorganization in response to changes in ice-sheet configuration and deglacial melt-water flux. In summary, synergetic effects of deglaciation explain the in-phase rainfall relationship between Morocco and Germany during the Early Holocene that does not account for recent climate conditions.

  7. Holocene glacial fluctuations in southern South America

    NASA Astrophysics Data System (ADS)

    Reynhout, S.; Sagredo, E. A.; Kaplan, M. R.; Aravena, J. C.; Martini, M. A.; Strelin, J. A.; Schaefer, J. M.

    2016-12-01

    Understanding the timing and magnitude of former glacier fluctuations is critical to decipher long-term climatic trends and to unravel both natural cycles and human impact on the current glacial behavior. Despite more than seven decades of research efforts, a unifying model of Holocene glacial fluctuations in Southern South America remains elusive. Here, we present the state-of-the-art regarding the timing of Holocene glacial fluctuation in southern Patagonia-Tierra del Fuego, with a focus on a new generation of high-resolution radiocarbon and 10Be surface exposure dating chronologies. Recently acquired evidence suggest that after receding from advanced Late Glacial positions, Patagonian glaciers were for the most part close to, or even behind, present ice margins during the Early Holocene. On the other hand, emerging chronologies indicate that in some areas there were extensive expansions (century scale?) that punctuated the warm interval. Subsequently, we have evidence of multiple millennial timescale glacial advances starting in the middle Holocene. Several glacial maxima are defined by moraines and other landforms from 7000 years ago to the 19th century, with a gap sometime between 4,500 and 2,500 years ago. The last set of advances began around 800-600 years ago. Although glacial activity is documented in Patagonia at the same time as the European Little Ice Age, the extent of these glacial events are less prominent than those of the mid-Holocene. The causes that may explain these glacial fluctuations remain elusive. Finally, we discuss ongoing efforts to better define the timing and extent of Holocene glaciations in southern South America, and to establish the basis to test competing hypothesis of regional Holocene climate variability.

  8. 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

  9. Challenges of Holocene sea-level reconstructions in area of low uplift rate

    NASA Astrophysics Data System (ADS)

    Grudzinska, Ieva; Vassiljev, Jüri; Stivrins, Normunds

    2017-04-01

    Isolated coastal water bodies provide an excellent sedimentary archive of the evolutionary stages of the coastal regions. It is relatively easy to determine lake isolation threshold, time and contact, where marine and brackish diatoms are replaced by halophilous and subsequently by freshwater diatoms, in areas with high land uplift rates and hard bedrock. Whereas, in areas where the land uplift rate is near zero and sedimentary cover of sand, silt and/or clay exists, determination of the lake isolation threshold and time is a rather complicated task. Such an area is the coast of the Gulf of Riga, where the apparent land uplift is about 1 mm yr-1 in the northern part and near zero in the southern part of the area. The aim of the study is to improve the understanding of the nature and extent of the Holocene sea level changes in the eastern Baltic Sea region, in the area with low land uplift rate. This study marks the first attempt to reconstruct sea level changes for a wide variety of settings based on high-resolution bio-, litho-, and chronostratigraphical evidence from sediment records of isolation basins in Latvia. In total, eight lakes were studied in order to revise the relative sea level (RSL) changes at the southern coast of the Gulf of Riga based on new litho- and biostratigraphical data and radiocarbon datings. The palaeogeographical reconstruction was challenging because we had to take into account that the process of isolation was influenced by various factors, such as gradual eustatic sea level (ESL) rise, river delta infilling by sediments and long-shore sediment transport. The water level in the Baltic Sea basin until 8,500 cal BP was influenced primarily by deglaciation dynamics, whereas in the last 8,500 years, the main factor was complicated interplay between the ESL rise and the land uplift rate. According to diatom composition and radiocarbon dates, the Litorina Sea transgression was a long-lasting event (ca. 2,200 years) in the southern part of

  10. Holocene Enviromental Changes in AN Amazonian Floodplain Lake

    NASA Astrophysics Data System (ADS)

    Moreira, L.; Moreira-Turcq, P. F.; Turcq, B.; Cordeiro, R. C.

    2011-12-01

    The floodplains lakes are built due to the fluctuations in the level of the rivers, which causes the formation of bars and accumulation of sediment carried by the rivers and its tributaries. Thus, significant quantities of organic matter can accumulate within these lakes that might represent important carbon sinks. The organic sedimentation process in the floodplains remains unknown as well as very little is known about past conditions in the Amazonian floodplains. Because these gaps, the aim of this work is to provide, through sedimentological, mineralogical and organic geochemical analysis of a 124-cm long core collected in Lago Comprido (eastern Amazonia), evidences of paleoenviromental changes during the Holocene. The core COM1 was analysed using radiocarbon dates, organic carbon concentration, C/N ratio, delta 13C and diatoms. The core points out different sedimentary environments that occurs in the last 9900 years cal BP. The record is divided into three phases: - phase III (124-94 cm, 9900 to 3200 cal years BP): this interval is characterized by delta 13C values typical of graminea, suggesting dry conditions with longer low water levels of the Amazon River. Supporting evidence for driest conditions during this period comes from low organic carbon values due to oxidation and absence of diatoms in the sediment. The carbon flux was very low, reaching an average of 0.9 g C/m2/year. - phase II (93-46 cm, 3200 to 940 years cal BP): increasing lake level beginning in this phase. The delta 13C values ranged between -25% and -29%, which are thought to represent terrestrial plants. This may indicate the presence of a flooded vegetation in this site. The freshwater planktonic diatoms Aulacoseira sp start to increase in this phase, additional evidence that the period of the annual high water stands was probably longer than before. Carbon flux increases, reaching an average of 5 g C/m2/year. - phase I (45-0cm, < 940 years cal BP): the delta 13C values and CN ratios did

  11. 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

  12. Early Holocene Great Salt Lake

    USGS Publications Warehouse

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

    2015-01-01

    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.

  13. Mineralogical assemblages, geochemistry and fossil associations of Pleistocene-Holocene complex siliciclastic deposits from the Southwestern Doñana National Park (SW Spain): A palaeoenvironmental approach

    NASA Astrophysics Data System (ADS)

    Pozo, Manuel; Ruiz, Francisco; Carretero, María Isabel; Vidal, Joaquín Rodríguez; Cáceres, Luís Miguel; Abad, Manuel; González-Regalado, María Luz

    2010-03-01

    On the basis of mineralogy, chemical and palaeontological data collected in a long core (93 m) three associations of facies are distinguished in the Late Pleistocene-Late Holocene evolution of the sedimentary infilling in nowadays Doñana National Park. From the lower, middle and upper associations of facies three sedimentological phases have been established. In the oldest phase (> 44 kyr BP), this area was occupied by supratidal, freshwater marshes located close to a brackish lagoon and inundated suddenly by brackish-marine inputs. The following phase (44-7 kyr BP) is characterized by the transition from supratidal to intertidal conditions, with the alternation of freshwater or brackish marshes situated very close or in the margin of the former lagoon and submitted to episodes of desiccation or tidal inundation. The last phase (7-3.0 cal kyr BP) comprised: a) a marine inundation during the maximum of the Flandrian transgression (˜ 7-6.5 cal kyr BP); and b) the progressive infilling of a brackish lagoon with marine connection and permanent fresh water inputs (6.5-3.5 cal kyr BP), partially enclosed by the Doñana spit. The phyllosilicate-rich, clayey-silty sequence of this latter infilling is interrupted by tsunami-like deposits at 4.2-3.6 cal kyr BP and 3.6-3.0 cal kyr BP. These high-energy events are characterized by textural (bimodal grain-size distribution, sorting decrease), mineralogical (crystallochemical changes in illites, increasing dolomite content) and geochemical changes (Ti anomaly), besides a sudden introduction of marine bivalves and microfauna and a strong decrease or the almost disappearance of the brackish ostracode assemblage. Ages of these deposits coincide with those indicated for other tsunamigenic layers detected in the southwestern Spanish coasts and some deep cores collected near the African-European plate boundary.

  14. Application of integrated reservoir management and reservoir characterization to optimize infill drilling. Annual report, June 13, 1994--June 12, 1995

    SciTech Connect

    Pande, P.K.

    1996-11-01

    This project has used a multi-disciplinary approach employing geology, geophysics, and engineering to conduct advanced reservoir characterization and management activities to design and implement an optimized infill drilling program at the North Robertson (Clearfork) Unit in Gaines County, Texas. The activities during the first Budget Period have consisted of developing an integrated reservoir description from geological, engineering, and geostatistical studies, and using this description for reservoir flow simulation. Specific reservoir management activities are being identified and tested. The geologically targeted infill drilling program will be implemented using the results of this work. A significant contribution of this project is to demonstrate the use of cost-effective reservoir characterization and management tools that will be helpful to both independent and major operators for the optimal development of heterogeneous, low permeability shallow-shelf carbonate (SSC) reservoirs. The techniques that are outlined for the formulation of an integrated reservoir description apply to all oil and gas reservoirs, but are specifically tailored for use in the heterogeneous, low permeability carbonate reservoirs of West Texas.

  15. Prediction of the Peak Shear Strength of Sandstone and Mudstone Joints Infilled with High Water-Cement Ratio Grouts

    NASA Astrophysics Data System (ADS)

    Ma, Hao; Liu, Quansheng

    2017-08-01

    There are very few studies on the peak shear strength of cement-infilled joints, despite it being a key parameter in the grouting technique. To quantify this strength, the average elastic modulus of hardened cement pastes with a high water-cement ratio (w/c) has been determined by using a homogenization method, in which the bleeding ratio is includes. Based on a scanning electron microscope analysis of the micromorphology of the rock joint surface and study of the interfacial transition zone, the mechanisms of the microscopic bond shear failure at the interfaces between the cement pastes and rocks have been deduced, in which the effect of the macroscopic roughness has not been taken into consideration. Based on the JRC-JCS model of unfilled joints, which takes the macroscopic roughness into consideration, together with the microscopic bond shear model, a model has been developed that can predict the peak shear strength of cement-infilled joints of sandstone and mudstone. The predictions have been verified by experimental results. The results show that if the w/ c is too low, then the grouting can weaken the rock mass. If the w/ c is appropriate, then the increase to the peak shear strength can be determined by the model.

  16. Large-scale bedforms as indicators of mutually evasive sand transport and the sequential infilling of wide-mouthed estuaries

    NASA Astrophysics Data System (ADS)

    Harris, Peter T.

    1988-06-01

    Large-scale bedforms (2-10 m in vertical and 10 2-10 3 m in horizontal dimensions) found in wide-mouthed estuaries are described. Different bedform types occur depending upon the local availability of sand. With an increasing sand supply, sand ribbons grade into elongate trains of sand waves and then form sandwave fields. Inshore, headland-associated sand banks are formed which multiply into en-echelon sand banks. Based upon a review of data on directions of sand transport from the Bristol Channel and Thames Estuary, U.K., and from Moreton Bay, Australia, charts of ebb- and flood-dominant transport zones are constructed for lower estuarine environments which have undergone different degrees of infilling. Linear sand banks are seen to delimit partially the boundaries between opposing sand transport zones. Transport paths demonstrate how sediments derived from outside of the estuary are dispersed through ebb and flood transport zones, to supply other areas of net deposition. A comparison between different estuaries reveals that variations in the compexity of ebb- and flood-dominant transport zones and the morphologies of large-scale bedforms are coupled with apparent changes in the relative amounts of sand available to each system. A model for the sequential infilling of estuaries and the evolution of large-scale bedforms is presented and applied to the interpretation of present day examples. Vertical sequences predicted to be generated by such bedform evolution are described and discussed, in terms of their preservation in the geological record.

  17. 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.

  18. The Deepest Lunar SPA Basin and its Unusual Infilling: Constraints Imposed by Angular Momentum Considerations

    NASA Astrophysics Data System (ADS)

    Kochemasov, G. G.

    1999-01-01

    Successful applications of planetary wave tectonics for predicting the shapes of small celestial bodies (asteroids, satellites), Phobos' rippling, the dumbbell shape of martian spheres, and fractionated martian crust, allow us to extend this method to lunar tectonics and related it to the chemistry of the enigmatic South Pole Aitken Basin. The accepted origin by many (but not all) planetologists is an impact hypothesis of the SPA basin; we alternatively, consider it as a part of a global lunar sectoral structure centered in the Mare Orientale. Sectoral structures of celestial bodies are a result of interference of standing inertia-gravity waves proceeding in four directions (ortho- and diagonal). These warping planetary waves arise in them as a result of their movements in elliptical orbits with periodically changing curvatures and cosmic accelerations. Fundamental waves of long 2-pi-R (R = body radius) produce tectonic dichotomy; waves of long pi-R (the first obertone) produce sectoring; and smaller waves length of which is proportional to orbital periods produce tectonic granulation. Segments, sectors, and granulas. of differing radius-vectors (risen + and fallen - tectonic domains) tend to equalize their angular momenta by density of infilling matter. That is why oceanic and mare basins normally are filled with denser material (basalts) than lighter highlands. On Earth one observes six antipodal centers of pi-R-structures (three pairs: (1) Equatorial Atlantic; (2) New Guinea; (3) The Pamirs-Hindukush; (4) Easter Island; (5) Bering Strait; and (6) Bouvet Island.) that regularly converge by common algorithm fallen normally oceanic and risen normally continental blocks. Around the Pamirs-Hindukush center, for example, are placed two differently risen sectors (African + +, Asian +) separated by 2 differently subsided ones (Eurasian -, Indoceanic - -). The six centers form vertices of an octahedron inscribed in the terrestrial sphere. The first antipodal pair lies in

  19. Holocene thinning of the Greenland ice sheet.

    PubMed

    Vinther, B M; Buchardt, S L; Clausen, H B; Dahl-Jensen, D; Johnsen, S J; Fisher, D A; Koerner, R M; Raynaud, D; Lipenkov, V; Andersen, K K; Blunier, T; Rasmussen, S O; Steffensen, J P; Svensson, A M

    2009-09-17

    On entering an era of global warming, the stability of the Greenland ice sheet (GIS) is an important concern, especially in the light of new evidence of rapidly changing flow and melt conditions at the GIS margins. Studying the response of the GIS to past climatic change may help to advance our understanding of GIS dynamics. The previous interpretation of evidence from stable isotopes (delta(18)O) in water from GIS ice cores was that Holocene climate variability on the GIS differed spatially and that a consistent Holocene climate optimum-the unusually warm period from about 9,000 to 6,000 years ago found in many northern-latitude palaeoclimate records-did not exist. Here we extract both the Greenland Holocene temperature history and the evolution of GIS surface elevation at four GIS locations. We achieve this by comparing delta(18)O from GIS ice cores with delta(18)O from ice cores from small marginal icecaps. Contrary to the earlier interpretation of delta(18)O evidence from ice cores, our new temperature history reveals a pronounced Holocene climatic optimum in Greenland coinciding with maximum thinning near the GIS margins. Our delta(18)O-based results are corroborated by the air content of ice cores, a proxy for surface elevation. State-of-the-art ice sheet models are generally found to be underestimating the extent and changes in GIS elevation and area; our findings may help to improve the ability of models to reproduce the GIS response to Holocene climate.

  20. 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.

  1. 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.

  2. Data-infilling in daily mean river flow records: first results using a visual analytics tool (gapIT)

    NASA Astrophysics Data System (ADS)

    Giustarini, Laura; Parisot, Olivier; Ghoniem, Mohammad; Trebs, Ivonne; Médoc, Nicolas; Faber, Olivier; Hostache, Renaud; Matgen, Patrick; Otjacques, Benoît

    2015-04-01

    Missing data in river flow records represent a loss of information and a serious drawback in water management. An incomplete time series prevents the computation of hydrological statistics and indicators. Also, records with data gaps are not suitable as input or validation data for hydrological or hydrodynamic modelling. In this work we present a visual analytics tool (gapIT), which supports experts to find the most adequate data-infilling technique for daily mean river flow records. The tool performs an automated calculation of river flow estimates using different data-infilling techniques. Donor station(s) are automatically selected based on Dynamic Time Warping, geographical proximity and upstream/downstream relationships. For each gap the tool computes several flow estimates through various data-infilling techniques, including interpolation, multiple regression, regression trees and neural networks. The visual application provides the possibility for the user to select different donor station(s) w.r.t. those automatically selected. The gapIT software was applied to 24 daily time series of river discharge recorded in Luxembourg over the period 01/01/2007 - 31/12/2013. The method was validated by randomly creating artificial gaps of different lengths and positions along the entire records. Using the RMSE and the Nash-Sutcliffe (NS) coefficient as performance measures, the method is evaluated based on a comparison with the actual measured discharge values. The application of the gapIT software to artificial gaps led to satisfactory results in terms of performance indicators (NS>0.8 for more than half of the artificial gaps). A case-by-case analysis revealed that the limited number of reconstructed record gaps characterized by a high RMSE values (NS>0.8) were caused by the temporary unavailability of the most appropriate donor station. On the other hand, some of the gaps characterized by a high accuracy of the reconstructed record were filled by using the data from

  3. 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.

  4. 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.

  5. Application of integrated reservoir management and reservoir characterization to optimize infill drilling. Quarterly technical progress report, September 13--December 12, 1996

    SciTech Connect

    1996-12-12

    Eighteen 10-acre infill wells have been drilled and completed as part of the Field Demonstration phase of the project at the North Robertson (Clearfork) Unit (NRU). The fourteen producing wells are pumped-off and producing at stable rates. The four injection wells are completed and have been on injection for three to four weeks. Current Unit production is approximately 3,400 STBO/D, of which approximately 900 STBO/D is being produced from the 10-acre infill wells. A change in the Statement of Work has been approved so that additional 10-acre infill wells can be drilled and/or 20-acre producing wells can be converted to injection during the next quarter as budget constraints and rig availability allow. Technical progress is described for the quarter in many related areas: implementation of the field demonstration; reservoir characterization; reservoir management activities and performance analysis; reservoir simulation; and technology transfer.

  6. 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.

  7. Holocene hillslope development in glacially formed valley systems in Nordfjord, western Norway

    NASA Astrophysics Data System (ADS)

    Laute, Katja; Beylich, Achim A.

    2013-04-01

    Large areas of the Norwegian fjord landscapes are covered by hillslopes that reflect the influence of glacial inheritance from the Last Glacial Maximum (LGM). The focus of this paper is two-fold: (1) analyze the spatio-temporal variability of relevant denudational slope processes and process intensities over the Holocene; and (2) detect Holocene modification of the glacial valley morphometry. Research was performed on hillslope systems within two steep, parabolic-shaped and glacier-fed tributary valleys, Erdalen and Bødalen located on the western side of the Jostedalsbreen ice cap in western Norway. Orthophoto delineation, high resolution mapping (TLS), detailed geomorphological information and spatial data analysis were combined with dating techniques and geophysical investigations. Calculated Holocene rockwall retreat rates at selected slope test sites range from 0.38 to 0.67 mm yr- 1, with a mean value of 0.53 mm yr- 1. Slightly higher values were found in Erdalen, with a mean rockwall retreat rate of 0.57 mm yr- 1 compared to 0.50 mm yr- 1 in Bødalen. Valley-wide Holocene rockwall retreat rates of 0.38-0.50 mm yr- 1 are consistent with other estimates of Holocene rockwall retreat rates in cold mountain environments. It is shown that the glacial inheritance of topography is the most important factor controlling valley development since the LGM and that sediment storage capacity is primarily conditioned by valley morphometry. Compared to contemporary rates, the results indicate enhanced denudation activity and intensity immediately following deglaciation and during the 'Little Ice Age'. The overall tendency of landscape development is postglacial widening of the parabolic-shaped valley morphometry through rockwall retreat with associated debris accumulation beneath rockwalls. As a result, the glacially sculpted topography has not yet adapted to denudational processes acting under Holocene environmental conditions.

  8. A Holocene East Asian winter monsoon record at the southern edge of the Gobi Desert and its comparison with a transient simulation

    NASA Astrophysics Data System (ADS)

    Li, Yu; Morrill, Carrie

    2015-09-01

    The East Asian winter monsoon (EAWM) exhibits significant variability on intraseasonal, interannual, and interdecadal time scales and the variability can be extended to Holocene centennial and millennial scales. Previous Holocene EAWM proxy data records, which were mostly located in Central, Eastern and Southern China, did not show a consistent Holocene EAWM history. Therefore, it is difficult to provide insights into mechanisms of the long-term winter monsoon variability on the basis of the records. Eolian sediments at the southern edge of the Gobi Desert, Western China, are sensitive to the EAWM changes and less affected by the East Asian summer monsoon due to an obstruction of the Qinghai-Tibet Plateau. This paper presents a comparison between a well-dated Holocene EAWM record and coupled climate model simulations, so as to explore physical processes and influencing factors of the Holocene EAWM. Sediment samples from two Holocene eolian sedimentary sections [Huangyanghe (a) and Huangyanghe (b)] were acquired at the southern edge of the Gobi Desert. Chronologies were established based on twenty bulk organic matter AMS 14C ages and five pollen concentrates AMS 14C ages. Proxy data, including grain-size, total organic carbon, magnetic susceptibility and carbonate content were obtained from the two eolian sections. The grain-size standard deviation model was applied to determine components sensitive to variability of the Holocene EAWM. After a comparison of environmentally-sensitive grain-size components and proxy data, the 20-200 μm component at the Huangyanghe (a) and the 20-159 μm component at the Huangyanghe (b) section were selected as indicators of the Holocene EAWM, which show a strong early Holocene winter monsoon and a decline of the winter monsoon since the mid-Holocene. We also present equilibrium and transient simulations of the climate evolution for the Holocene using a state-of-art coupled climate model: the Community Climate System Model version 3

  9. Tropical ocean-atmospheric forcing of Late Glacial and Holocene glacier fluctuations in the Cordillera Blanca, Peru

    NASA Astrophysics Data System (ADS)

    Stansell, Nathan D.; Licciardi, Joseph M.; Rodbell, Donald T.; Mark, Bryan G.

    2017-05-01

    Evaluating the timing and style of past glacier fluctuations in the tropical Andes is important for our scientific understanding of global environmental change. Terrestrial cosmogenic nuclide ages on moraine boulders combined with 14C-dated clastic sediment records from alpine lakes document glacial variability in the Cordillera Blanca of Peru during the last 16 ka. Late Glacial ice extents culminated at the start of the Antarctic Cold Reversal and began retracting prior to the Younger Dryas. Multiple moraine crests dating to the early Holocene mark brief readvances or stillstands that punctuated overall retreat of the Queshque Valley glacier terminus during this interval. Glaciers were less extensive during the middle Holocene before readvancing during the latest Holocene. These records suggest that tropical Atlantic and Pacific ocean-atmospheric processes exerted temporally variable forcing of Late Glacial and Holocene glacial changes in the Peruvian Andes.

  10. 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

  11. Holocene estuary development in the Algarve Region (Southern Portugal)

    NASA Astrophysics Data System (ADS)

    Schneider, Heike; Höfer, Dana; Trog, Carmen; Hempel, Rita; Daut, Gerhard; Mäusbacher, Roland

    2010-05-01

    Former coastal estuaries in the Algarve region of South Portugal are used for reconstruction coastal evolution since first marine transgression processes at about 8.000 years before. The sediments of these archives allow high resolution analyses of geochemical and palynological signals. Drillings in different lagoons of the Algarve region contain the sequences from the fluvial sediments during the early Holocene, marine transgression facies during the middle Holocene and the marine/fluvial sediment deposits until present. The results of the sedimentological, geochemical and palynological analyses show that each estuary developed differently, depending on the morphology of the paleovalley, environmental conditions and especially the influence of the sea and the formation of barrier systems. The estuaries were flooded between 7500 and 5500 cal a BP by sea level rise and were almost completely filled by sediment by the beginning of the Roman occupation (226 y BC / 2176 cal a BP). A clear change in sedimentological processes is evident in the estuaries between 5500 and 3000 cal a BP and is interpreted as a result of high energy events such as storms or tsunamis (Schneider et al. 2009, Hilbich et al. 2008 ). Palynological as well as archaeological investigations show distinct anthropogenic influences since 3500 cal. BP by increasing values in maquies, cereals and open land communities. References Hilbich, C., Mügler, I., Daut, G., Frenzel, P., van der Borg, K., Mäusbacher, R. (2008): Reconstruction of the depositional history of the former coastal lagoon of Vilamoura (Algarve, Portugal): A sedimentological, microfaunal and geophysical approach.- Journal of Coastal Research 24(2B), 83-91. Schneider, H., Höfer, D., Trog, C., Busch, S., Schneider, M., Baade, J., Daut, G. & R. Mäusbacher (2009): Holocene estuary development in the Algarve Region (Southern Portugal) - A reconstruction of sedimentological and ecological evolution. - Quaternary International (In Press

  12. 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.

  13. 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

  14. Holocene development of Amazonia's oldest peatland

    NASA Astrophysics Data System (ADS)

    Swindles, Graeme T.; Morris, Paul J.; Whitney, Bronwen; Galka, Mariusz; Galloway, Jennifer M.; Gallego-Sala, Angela; Macumber, Andrew L.; Mullan, Donal; Smith, Mark W.; Amesbury, Matt; Roland, Thomas; Sanei, Hameed; Patterson, R. Timothy; Parry, Lauren; Charman, Dan J.; Lopez, Omar R.; Valderamma, Elvis; Watson, Elizabeth J.; Lähteenoja, Outi; Baird, Andy J.

    2017-04-01

    Peatlands represent some of the most carbon-dense ecosystems of Amazonia. However, little is known about the mechanisms of Amazonian peatland development and their ecohydrological dynamics over time. We present a comprehensive multiproxy dataset from Aucayacu peat dome, the oldest peatland yet discovered in Amazonia (peat initiation occurred between 8.9 and 5.8 ka cal. BP). Our dataset includes analyses of peat physical properties, carbon and nitrogen, humification, organic matter characteristics, macrofossils, pollen, charcoal and testate amoebae. Sedimentological techniques were applied to minerogenic deposits underneath the peatland to understand the nature of the floodplain environment before peat initiation. A transfer function was used to reconstruct past hydrological conditions from subfossil testate amoeba assemblages and carbon accumulation (CA) rates were determined from bulk density and percentage carbon data. A robust chronology was achieved using 210Pb and 14C (14 radiocarbon dates on a 3-m core) determinations, modelled using a Bayesian approach. We used the datasets to investigate the long-term ecohydrological development and controls on carbon accumulation in an Amazonian peat dome. The peatland developed in three distinct stages; (i) abandoned river channel with standing open water and aquatic plants; (ii) inundated forest swamp; and (iii) ombrotrophic bog ( 3.9 ka cal. BP). Local burning occurred twice during the peatland's development as evidenced by macroscopic charcoal but appears to have become more pronounced in the last 100 years. We present a conceptual model of the role of autogenic and allogenic (climate, floodplain) processes on the long-term development of the peatland and the marked variations in carbon accumulation rates over the Holocene. Amazonian peatlands are important carbon stores and ecosystems, and represent important archives of past climatic and ecological information. They should form key foci for conservation efforts.

  15. 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

  16. Paleolandscape Reconstruction of Holocene Fluvial Drainage, Narragansett Bay, Rhode Island.

    NASA Astrophysics Data System (ADS)

    Hearn, C. K.

    2016-12-01

    The Narragansett Bay System (NBS) located in eastern Rhode Island, United States, formed as a drowned river valley that began its most recent inundation at approximately the start of the Holocene Era. The earliest regional evidence for human occupation predates the inundation of the NBS, which would have existed as a network of streams and lakes. An abundance of artifacts recovered from the shoreline of the modern NBS provide a record of continuous habitation throughout the Holocene. A paleolandscape reconstruction of the lower NBS is in development to aid in assessing the archaeological sensitivity of the region regarding ancient Native American sites of cultural significance that are now submerged. The degree of potential preservation for such sites is closely linked to the extent of sediment removal during inundation, which is a function of the wave energy and rate of shoreface advancement. Accurate reconstructions of the paleolandscape are then critical for archaeological assessments. The West Passage (WP) of the NBS, the likely location for an early-Holocene freshwater lake, is bounded to the south by a large sill, which may have forced the basin to drain to the North before joining the East Passage drainage. The advancing shore may likewise have followed this northern route and gradually flooded the WP while maintaining a low-energy wave environment favorable to preservation until late in the inundation process. Dense sub-bottom sonar profiles were analyzed in the WP of the NBS in an attempt to locate paleochannels and test the theory of a northern fluvial drainage pathway prior to inundation. Evidence for the presence or absence of paleochannels through the sill would significantly affect the archaeological preservation potential for the WP. These results will be incorporated with a reconstruction for the entire lower bay and outer coastal shelf as part of large-scale novel effort to merge modern scientific investigations with Native American historical

  17. 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

  18. Holocene carbon dynamics at the forest-steppe ecotone of southern Siberia.

    PubMed

    Mackay, Anson William; Seddon, Alistair W R; Leng, Melanie J; Heumann, Georg; Morley, David W; Piotrowska, Natalia; Rioual, Patrick; Roberts, Sarah; Swann, George E A

    2017-05-01

    The forest-steppe ecotone in southern Siberia is highly sensitive to climate change; global warming is expected to push the ecotone northwards, at the same time resulting in degradation of the underlying permafrost. To gain a deeper understanding of long-term forest-steppe carbon dynamics, we use a highly resolved, multiproxy, palaeolimnological approach, based on sediment records from Lake Baikal. We reconstruct proxies that are relevant to understanding carbon dynamics including carbon mass accumulation rates (CMAR; g C m(-2)  yr(-1) ) and isotope composition of organic matter (δ(13) CTOC ). Forest-steppe dynamics were reconstructed using pollen, and diatom records provided measures of primary production from near- and off-shore communities. We used a generalized additive model (GAM) to identify significant change points in temporal series, and by applying generalized linear least-squares regression modelling to components of the multiproxy data, we address (1) What factors influence carbon dynamics during early Holocene warming and late Holocene cooling? (2) How did carbon dynamics respond to abrupt sub-Milankovitch scale events? and (3) What is the Holocene carbon storage budget for Lake Baikal. CMAR values range between 2.8 and 12.5 g C m(-2)  yr(-1) . Peak burial rates (and greatest variability) occurred during the early Holocene, associated with melting permafrost and retreating glaciers, while lowest burial rates occurred during the neoglacial. Significant shifts in carbon dynamics at 10.3, 4.1 and 2.8 kyr bp provide compelling evidence for the sensitivity of the region to sub-Milankovitch drivers of climate change. We estimate that 1.03 Pg C was buried in Lake Baikal sediments during the Holocene, almost one-quarter of which was buried during the early Holocene alone. Combined, our results highlight the importance of understanding the close linkages between carbon cycling and hydrological processes, not just temperatures, in southern Siberian

  19. Late Glacial And Holocene Glacier Fluctuations In Lyngen, Troms, Northern Norway

    NASA Astrophysics Data System (ADS)

    Bakke, J.; Dahl, S. O.; Nesje, A.

    The area north of the Kjosen fjord on the Lyngen Peninsula is mapped focused on glacial geomorphological features, and 13 cirque glaciers and their catchments are in- vestigated in detail. The four lakes Aspevatnet (Holocene glacier fluctuations), Barhei- vatnet (bio-proxy lake), Elvejordsvatnet (Holocene glacier fluctuations) and Trollvat- net (early deglaciation, Holocene slope processes) are investigated and bathymetric maps produced. Based on the laboratory analyses it is possible to reconstruct detailed Holocene glacier fluctuations on glaciers with aspects both to the east and west on the Lyngen Peninsula. From lake Aspevatn at the western side, it seems possible to reconstruct at least 14 local glacial events during the last c. 10 200 cal. yr BP (basin isolated from the sea). Some major glacial events are recorded during the Preboreal, while the glaciers seem to have advanced due to an increase in winter precipitation (as snow) during the Holocene climatic temperature optimum. The final neo-glaciation(s) started c. 3800 cal. yr BP with a marked maximum in the late 18-century. The reconstructed TPW- ELAs for the Aspevatn catchment are situated at altitudes of 790 to 1200 m. By using radiocarbon dated shorelines as age control, it is possible to date reconstructed val- ley glaciers with fossil ice-cored moraines in front, existing from c. 16000 to 11500 cal. yr BP (termination of the Younger Dryas). These glaciers are reconstructed with TPW-ELAs situated between 130 and 650 m when adjusted for land uplift. As these glaciers most likely existed in a cold and dry climate regime, they are suggested to have been polythermal (subpolar). The results show that there is a great potential for reconstructing the complete glacial history of the northern Lyngen Peninsula from the early deglaciation after the LGM to at present. This is so far the northernmost complete Holocene glacier record in Scandinavia.

  20. 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.

  1. Evolution of Holocene tidal systems along the Dutch coast: effects of rivers, coastal boundary conditions, eco-engineering species, inherited relief and human interference

    NASA Astrophysics Data System (ADS)

    Haas, T. D.; Pierik, H. J.; van der Spek, A.; Cohen, K.; van Maanen, B.; Kleinhans, M. G.

    2016-12-01

    Estuaries and tidal basins are partly enclosed coastal bodies of water with a free connection to the open sea at their tidal inlet and with no to marginal riverine input (tidal basins) or substantial riverine input (estuaries). Their tidal inlets can only remain open over Holocene timescales when (1) the formation of accommodation space exceeds infilling or (2) the inlet system is in dynamic equilibrium (sediment input equals output). Physical and numerical modelling suggest that estuaries and tidal basins develop toward a dynamic equilibrium under constant boundary conditions and remain open over long timescales, whereas many natural estuaries and tidal basins have filled up and were closed off or became deltas during the Holocene. This raises the question if and how tidal inlets can remain open over long timescales? And what is the effect of river inflow and sediment supply thereon? Here we compare the Holocene evolution of tidal systems along the Dutch coast to empirically identify the most important factors that control their long-term evolution. Along the coast of the Netherlands estuaries and tidal basins were formed during the middle Holocene driven by rapid relative sea-level rise and during the late Holocene driven by natural and human-induced subsidence in coastal plain peatlands. During the Holocene tidal inlets connected to rivers (estuaries) were able to persist and attain dynamic equilibrium while tidal basins without or with a very marginal riverine inflow were unstable and closed off under abundant sediment supply. There are many examples of long-lived tidal inlets that rapidly closed off after upstream river avulsion leading to a decrease and finally loss of riverine input. Long-term net import of sediment from the sea into Dutch tidal basins is favoured by strong, flood-dominated, tidal asymmetry along the Dutch coast, the shallow sand-rich floor of the North Sea and the abundance of mud in the coastal area supplied by the Rhine and Meuse rivers

  2. 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.

  3. 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

  4. The Holocene Isolation of Dalma Island

    NASA Astrophysics Data System (ADS)

    Lokier, Stephen

    2010-05-01

    extremely unlikely that the modern day bathymetry of the Gulf is exactly the same as that seen at the time of transgression. During transgression, marine waters would first have flooded areas to the north and east of Dalma Island thereby removing the source of much of the wind-blown sediment that contributed to the Gulf floor dune system. This resulted in deflation to the depth of the water table as sediment continued to be transported south-eastward. Flooding resulted in carbonate sedimentation becoming the dominant depositional process on the floor of the Gulf. Warm shallow water carbonate factories produce sediments at a rate far exceeding all but the most catastrophic rates of relative sea level rise. The sediment tail extending to the south of Dalma is formed of carbonate sediments up to 30 m thick and, as such, represents a considerable shallowing in the bathymetry to the south and south east of the island. Both of these factors would have resulted in a considerable reduction in water depths since flooding occurred. It is, therefore, very likely that the pre-flood topography/bathymetry around Dalma was much lower than that seen on bathymetric maps today. In this case isolation of the island would have occurred much sooner. Secondly, the above flooding history assumes that there has been little subsidence or uplift since the last glacial maximum. The combined effects of the glacio-eustatic and hydro-isostatic components would result in isostatic perturbations over the Gulf region throughout the initial phase of flooding (Late Pleistocene). However, it is widely inferred that, with the exception of the northern side of the Strait of Hormuz, there was no significant Holocene tectonic subsidence in the region of the Gulf.

  5. 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

  6. Diatom-inferred salinity and carbonate oxygen isotopes in Holocene waterbodies of the western Sahara and Sahel (Africa)

    NASA Astrophysics Data System (ADS)

    Gasse, Françoise

    2002-03-01

    Thirteen Holocene palaeolakes in the western Sahara and Sahel have provided diatom records, with carbonate oxygen isotope profiles available from eight of them. Most of these palaeolakes were groundwater-fed. Lake water chemistry is reconstructed using diatom transfer functions. Lake water salinity and 18O records are assembled with some isotopic and chemical groundwater data to better understand the response of the hydrological systems to climate changes over the past 15,000 yr. Data are in general agreement with climate simulations using coupled atmosphere-ocean-vegetation models which show a mid-Holocene wetting over the whole of northwest Africa, and a rapid drying by 6-4 ka. The lake record also shows that at many sites the major lake infilling lags the end of the Younger Dryas by 1-2 ka. Regional differences also appear in the timing of the lake hydrological optimum: ca. 10.5-8.5 and 7.5-4.5 ka in the northern Sahara, 10-8.5 ka in the Aı̈r-Ténéré, 10-5.7 or 4.5 in the Sahel, and 7.5 ka in Lake Chad. The whole of the Holocene is punctuated by short-term drying events. Changes in water isotopic composition through time are partly explained by changes in rainfall amount and air humidity. During the wet Holocene period however, the very low δ values in the southern Sahara also imply changes in the moisture transport pattern or rainfall mechanisms. Data suggest an apparent decrease in 18O content of precipitation along the monsoon flow, in contrast with modern patterns. Changes in water availability and quality have driven population migrations in and out of the Sahara-Sahel, but relationships between climate and cultures are complex. Short-term dry events might have driven inventive adaptations. In the Sahara, drying at 5-4.5 ka coincides with both the collapse of the classical Neolithic civilization and the settlement of new cultures.

  7. 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

  8. 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

  9. Disturbance Frequency Changes in Western North and South America During the Holocene

    NASA Astrophysics Data System (ADS)

    Whitlock, C.; Bartlein, P.; Bianchi, M. M.; Briles, C.; Brunelle, A.; Long, C.; Markgraf, V.; Marlon, J.; Meeker, C.; Power, M.; Walsh, M.

    2003-12-01

    Fire is the dominant form of natural disturbance in temperate forested ecosystems, and as such, it serves as a process that links climate change to biosphere response. High-resolution charcoal records from the western temperate forests of North and South America provide an opportunity to compare current and recent (pre-settlement) changes in disturbance frequency with those during the Holocene. Charcoal data describe past fire activity under different climate and vegetation settings and offer information on changing levels of biomass as well as variations in fire frequency. An assessment of North American sites indicates gradually increasing levels of charcoal from the late-glacial to 2 ka, which is consistent with increasing fuel production during the Holocene. Fire-frequency data from both hemispheres indicate that the spatial heterogeneity evident in modern fire regimes has existed throughout the Holocene despite changes in the large-scale controls of climate. The heterogeneity is a result of spatial variations in the seasonal distribution of precipitation and their influence on fire climate and weather. Summer-dry areas (i.e., low summer:annual precipitation) registered higher-than-present fire activity in the early Holocene from ca. 13 to 7 ka. In North America, fire activity was apparently controlled by the early-Holocene strengthening of the northeast Pacific subtropical high during the summer insolation maximum. In Patagonia, high fire activity may have caused by the carry-over effects of low winter soil moisture during the winter insolation maximum. A decline in fire activity in summer-dry regions in the late Holocene suggests seasonally wetter conditions as a result of the onset of ENSO, less seasonality in precipitation, and/or the development of more closed forests. Summer-wet regions show the influence of stronger monsoonal circulation in the early Holocene, which caused a reduction in fire activity. In these regions, the late Holocene featured

  10. Holocene Climate Change in Arctic Canada and Greenland

    NASA Astrophysics Data System (ADS)

    Briner, J. P.; McKay, N.; Axford, Y.; Bennike, O.; Bradley, R. S.; de Vernal, A.; Fisher, D. A.; Francus, P.; Fréchette, B.; Gajewski, K. J.; Jennings, A. E.; Kaufman, D. S.; Miller, G. H.; Rouston, C.; Wagner, B.

    2015-12-01

    We summarize the spatial and temporal pattern of climate change through the Holocene in Arctic Canada and Greenland. Our synthesis includes 47 records from a recent database of highly resolved, quantitative Holocene climate records from the Arctic (Sundqvist et al., 2014). We plot the temperature histories represented by the records in the database and compare them with paleoclimate information based on 53 additional records. Combined, the records include a variety of climate proxy types that range from ice (ice cores), land (lake and peat sequences) and marine (ocean sediment cores and coastal sediments) environments. 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 records). 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.

  11. Late glacial and holocene landscapes of central Beringia

    NASA Astrophysics Data System (ADS)

    Lozhkin, Anatoly V.; Anderson, Patricia; Eisner, Wendy R.; Solomatkina, Tatiana B.

    2011-11-01

    New palynological and sedimentological data from St. Lawrence Island present a rare view into late-glacial and Holocene environments of the central Bering Land Bridge. The late glaciation was a time of dynamic landscape changes in south-central Beringia, with active thermokarst processes, including the formation and drainage of thaw lakes. The presence of such a wet, unstable substrate, if widespread, probably would have had an adverse impact on food sources and mobility for many of the large mammal populations. The establishment of Betula shrub tundra on the island suggests late-glacial summers that were warmer than present, consistent with regional paleoclimatic interpretations. However, the increasing proximity to the Bering Sea, as postglacial sea levels rose, modified the intensity of warming and prevented the establishment of deciduous forest as found in other areas of Beringia at this time. The mid- to late Holocene is marked by more stable land surfaces and development of Sphagnum and Cyperaceae peat deposits. The accumulation of organic deposits, decline of shrub Betula, and decrease in thermokarst disturbance suggest that conditions were cooler than the previous. A recent decline in peat accumulation at the study sites may relate to local geomorphology, but similar decreases have been noted for other arctic regions.

  12. 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.

  13. 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

  14. 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.

  15. Morphodynamics of Holocene salt marshes: a review sketch from the Atlantic and Southern North Sea coasts of Europe

    NASA Astrophysics Data System (ADS)

    Allen, J. R. L.

    2000-07-01

    permeable sediment, and there is little or no tidal inundation, organogenic marshes in Northwest Europe typically lack surface channels for internal drainage. The stratigraphic sequences accumulated during the Holocene beneath coastal marshes and high tidal flats typically present an alternation on a vertical scale of decimetres to metres of silts (mineralogenic marshes, high intertidal mudflats) and peats (organogenic highest intertidal-supratidal marshes). Coastal barriers and some channels are represented by local accumulations of sand and/or gravel. The silts and peats form couplets which are generally considered to be related to fluctuations of sea-level about the general upward trend. Field investigations and modelling show that, in areas where marshes are mature, the upward change from an organogenic to a sequence of mineralogenic marshes (transgressive overlaps) is accompanied by the initiation and invasive development of a branching network of tidal creeks. These decay and infill during the reversal of the environmental sequence and the approach, expressed as a series of regressive overlaps, of the next set of peat-forming conditions. The operation of the continuous, progressive, irreversible and asymptotic process of sediment autocompaction exerts a major, secondary control on depositional regimes and marsh behaviour. A variety of local responses are consequently possible in an extensive marsh, even though the marsh may be everywhere in dynamic equilibrium with environmental factors. Autocompaction also strongly shapes the character of Holocene coastal sequences as now perceived, introducing significant stratigraphic distortions and displacements which, for the time being, limit the accuracy of sea-level curves and rates of sea-level change based on dated intercalated peats. Prehistoric humans benefitted from the resources of coastal salt marshes, especially at the times when peat marshes begin to be transgressed. Peat domes not yet fully collapsed may have

  16. 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 ...

  17. 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 ...

  18. 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

  19. 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

  20. 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

    2016-02-05

    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. Copyright © 2016, American Association for the Advancement of Science.

  1. 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.

  2. 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).

  3. 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.

  4. The Holocene History of Placentia Bay, Newfoundland

    NASA Astrophysics Data System (ADS)

    Sheldon, Christina; Seidenkrantz, Marit-Solveig; Reynisson, Njáll; Juncker Hansen, Mette; Zilmer Christensen, Eva; Kuijpers, Antoon

    2013-04-01

    Marine sediments analyzed from cores taken in Placentia Bay, Newfoundland, located in the Labrador Sea, captured oceanographic and climatic changes from the end of the Younger Dryas through the Holocene. Placentia Bay is an ideal site to capture changes in both the south-flowing Labrador Current and the north-flowing Gulf Stream, currents which are closely tied to the strength of the North Atlantic sub-polar gyre and the North Atlantic Oscillation. Changes in the atmospheric and oceanographic circulation patterns in the North Atlantic after the last glacial period are inferred from faunal assemblages, mineralogy and dinoflagellate analyses. During the 2007 Akademik Ioffe cruise, three cores were taken from Placentia Bay: AI07-14G, representing the time period 12.7 to 9.8 cal kyr BP, AI07-10G, covering the period ca. 10.4 cal kya BP to the present, and AI07-12G, representing the last 5.7 cal kya. These cores have been analyzed using several climate proxies, including benthic foraminifera, diatoms, IP25, dinoflagellate cysts and XRF. Together, these cores provide high-resolution records of the changes in climatic conditions over the last ca. 13,000 years in the southern Labrador Sea. After the Younger Dryas ended, the beginning of the warmer early Holocene was recorded by an increase in productivity-linked foraminiferal and diatom assemblages, as well as a drop in the presence of the sea-ice indicator IP25 in core 14G (Pearce et al., 2012). Variability in atmospheric circulation during the Holocene was analyzed in core 12G and used to reconstruct changes in the mode of the North Atlantic Oscillation during the late Holocene by analysis of exotic pollen grains. Sea-surface conditions during the late Holocene in Placentia Bay reflect a decrease in the strength of the Labrador Current, based on warmer sea-surface temperatures and a simultaneous decline in Arctic water export, from ~4000 cal years to ~3000 cal years BP, which falls into the overall large-scale trend of

  5. 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

  6. 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.

  7. 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.

  8. 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.

  9. Palaeohydrological controls on sedimentary organic matter on Amazon floodplain lakes during the Holocene

    NASA Astrophysics Data System (ADS)

    Moreira, L. S.; Moreira-Turcq, P. F.; Cordeiro, R. C.; Turcq, B.

    2014-12-01

    A synthesis of the impacts of the Amazon River hydrological changes on the sedimentation process of organic matter (OM) in three different floodplain lakes (Santa Ninha, Maracá, and Comprido lakes) is presented in this study. Today the Santa Ninha and Maracá lakes are directly and permanently connected with the main channel of the Amazon River, in contrast to Comprido Lake, which is indirectly and periodically influenced by the Amazon River due to its high distance from the main channel. All the sedimentary lake records showed a reduced river inflow due to dry climatic conditions during the Early and Middle Holocene followed by a humid Late Holocene with an increased fluvial input. In Santa Ninha and Maraca Lakes the reduced river inflow period was characterized by sediments with a low abundance of smectite (on average ~20 wt. %), a clay mineral mainly transported by the fluvial system, high total organic carbon (TOC) contents and a predominant C3 vegetation input evidenced by the C/N ratio and d13C. During the Late Holocene, a higher smectite abundance (on average ~43 wt. %) and a low TOC content (on average ~1.4 wt. %) pointed to dilution with the riverine lithogenic matter. In this period a enhanced aquatic primary productivity was evidenced by the increased d13C values and by a C/N typical of algae, suggesting an increased lake water level. In Comprido Lake, a sedimentation gap occurred during the Early and Middle Holocene. The humid Late Holocene, after 3,000 cal years BP, was characterized by high TOC values (on average ~9 wt. %) and increasing abundance of planktonic species, like Aulacoseira sp., which reflects the expansion of water bodies. The predominance of C3-vegetation and low smectite content suggest that in Comprido Lake the soil OM input from the local catchment area was predominant during the humid Late Holocene due to its high distance from the Amazon River main stem. Consequently, our study shows that the sedimentation processes of OM in

  10. 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.

  11. 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

  12. 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).

  13. Geometry and evolution of Holocene transgressive and regressive barriers on the semi-arid coast of NE Brazil

    NASA Astrophysics Data System (ADS)

    Henrique de Oliveira Caldas, Luciano; Gomes de Oliveira, Josibel; Eugênio de Medeiros, Walter; Stattegger, Karl; Vital, Helenice

    2006-11-01

    An integrated study based on ground penetrating radar (GPR) profiles, vibracore descriptions, water-well logs, and radiocarbon dating in a coastal deposit located in the northern region of Rio Grande do Norte State, northeastern Brazil, allowed us to identify Holocene transgressive and regressive barriers. The construction process for the studied coastal barrier is different from that proposed for the Holocene coastal plains along the eastern Brazilian coast, where the hydraulic barrier set up by large rivers for sediments transported by longshore currents has caused a strongly positive longshore sediment imbalance. In the study area, interpretation of the GPR images, within the constraints of vibracores data, allowed us to interpret five radar facies and four radar boundary sequences for these coastal deposits, which were built up during the Holocene coastal evolution of the region. As a result, the geometry of the coastal barrier was reconstructed. Based on barrier geometry, sediment ages, stratigraphic records, and sedimentation patterns, we propose a barrier evolutionary model for the Holocene for the study region. During the Holocene highstand, a transgressive barrier was deposited and a lagoon extended landward. During the sea-level fall soon after the Holocene highstand, the deposition of a regressive barrier (forced regression) started. This deposition was induced by the coastal geometry and high amounts of eolian sediments supplied by east-northeast winds. Also during this period of sea-level fall, the beach face became wider, and thus more subjected to wind action, facilitating the deposition of the first eolian deposits. These sediments were transported to the nearly formed embayment, providing a surplus for the construction of the regressive barrier. During the regressive phase, tidal channels closed and the lagoon became isolated from the open sea. The geometry of both the regressive and transgressive barriers as well as the stratigraphic relation

  14. 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.

  15. 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

  16. MOMBE selective infill growth of InP:Si and InGaAs:Si and large area MOMBE regrowth

    NASA Astrophysics Data System (ADS)

    Schelhase, S.; Böttcher, J.; Gibis, R.; Künzel, H.; Paraskevopoulos, A.

    1996-07-01

    MOMBE selective infill growth (SIG) of silicon-doped InP and InGaAs was investigated by variation of the principal growth parameters, i.e. temperature, {V}/{III}- ratio and rate. Excellent surface morphology in conjunction with perfect selectivity and defect-free vertical interfaces between the grown layer and the etched substrate sidewall was achieved by an appropriate optimization of the selective growth conditions for InP as well as, for the first time, InGaAs. In the case of SIG of InP, smooth growth boundaries were obtained in the [01¯1] direction, whereas in the [01¯1¯] direction minor growth perturbations occur, which are related to a strong orientation dependent diffusion behavior of the growth species on the growth front. In the case of SIG of InGaAs, slight perturbations accompanied by facet formation at the edges of the selectively grown windows were observed. In the perspective of device application, homogeneous large area MOMBE InGaAs regrowth of the embedded structures was successfully achieved.

  17. Equivalent Strut Method for the Modelling of Masonry Infill Walls in the Nonlinear Static Analysis of Buildings

    NASA Astrophysics Data System (ADS)

    Adukadukam, A.; Sengupta, A. K.

    2013-05-01

    In the seismic analysis of a framed building with masonry infill walls, it is necessary to model the effect of the walls on the lateral stiffness, strength and ductility of the building. The equivalent strut method is convenient for modelling the walls in a large building. However, an appropriate axial load versus deformation relationship for the strut is required in a nonlinear static method of seismic analysis, such as the pushover analysis. The present study proposes a nonlinear axial hinge property for the strut, with suitable performance levels. First, the equivalent strut method and the suitability of two approaches available in the literature for modelling the properties of the struts, are briefly discussed. Next, the nonlinear axial load versus deformation relationship is developed based on experimental data compiled from the literature. The parabolic-plastic relationship is idealized as a tri-linear axial hinge property, so that it can be incorporated in commercial software for undertaking pushover analysis. Next, the use of the hinge property is demonstrated in the pushover analyses of two framed reinforced concrete buildings. The pushover curves based on the proposed hinge property shows improved modelling of the inelastic drifts of the buildings. Although the modelling of a wall using a single strut has limitations, the proposed methodology is practical for a pushover analysis of a building.

  18. 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

  19. 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.

  20. 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.

  1. 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.

  2. 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

  3. 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.

  4. 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.

  5. 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

  6. 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.

  7. Holocene deglaciation of Byers Peninsula (Livingston Island, Maritime Antarctica) inferred from lake records

    NASA Astrophysics Data System (ADS)

    Oliva, Marc; Antoniades, Dermot; Giralt, Santiago; Granados, Ignacio; Toro, Manuel; Pla-Rabes, Sergi; Vieira, Gonçalo

    2014-05-01

    The South Shetland Islands are located in the northwestern tip of the Antarctic Peninsula. This area has been one of the regions in Earth where the climate warming recorded during the second half of the XXI century has been more significant (+2.5 ºC). However, a slight decrease in the rate of warming has been observed during the last decade. The HOLOANTAR project aims to provide accurate data on the Holocene climate conditions in this region in order to better frame this warming trend within the natural climate variability in the region. Our research is focused on the westernmost part of Livingston Island, Byers Peninsula, the largest ice-free area in the South Shetland Islands where tens of lakes and ponds are distributed. During the field work campaign in November-December'12 we collected the complete sedimentary sequence of four lakes distributed along a transect following the deglaciation of the peninsula: Chester, Escondido, Cerro Negro and Domo lakes. Geochemical, biological and geochronological studies are being undertaken on several of these cores. The ongoing analisys of their properties are providing insights about the Holocene palaeoenvironments and palaeoclimate conditions in Byers. In this communication we introduce the chronological framework for the Holocene deglaciation process in Byers Peninsula based on OSL, C14, Pb210 and Cs137 datings, as well as on tephrochronological data. According to these data, the deglaciation in Byers Peninsula started during the Early to Mid Holocene and continued through the Late Holocene, when the lakes distributed along the present-day moraines were formed.

  8. 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.

  9. 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.

  10. Interaction of (3)H(+) (as HTO) and (36)Cl(-) (as Na(36)Cl) with crushed granite and corresponding fracture infill material investigated in column experiments.

    PubMed

    Štamberg, K; Palágyi, Š; Videnská, K; Havlová, V

    The transport of (3)H(+) (as HTO) and (36)Cl(-) (as Na(36)Cl) was investigated in the dynamic system, i.e., in the columns filled with crushed pure granite and fracture infill of various grain sizes. The aim of column experiments was to determine important transport parameter, such as the retardation, respectively distribution coefficients, Peclet numbers and hydrodynamic dispersion coefficients. Furthermore, the research was focused to quantification of the effect of grain size on migration of studied radionuclides. The experimental breakthrough curves were fitted by a model based on the erfc-function, assuming a linear reversible equilibrium sorption/desorption isotherm, and the above mentioned transport parameters were determined. The results showed that influence of grain size on sorption of (3)H(+) and (36)Cl(-) was negligible. Retardation and distribution coefficients of both tracers converged to one and zero, respectively, in case of all fractions of crushed granite and infill material. Generally, the presumed ion exclusion of (36)Cl in anionic form was proved under given conditions, only very weak one seems to exist in a case of infill material. In principal, both radionuclides behaved as non-sorbing, conservative tracers. On the other hand, the influence of grain size on Peclet numbers value and on dispersion coefficient was observed for both crystalline materials, namely in agreement with theoretical suppositions that the values of Peclet numbers decrease with increasing grain size and values of dispersion coefficient increase.

  11. 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

  12. 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

  13. Quantitative estimates of Mid- to late Holocene Climate Variability in northeastern Siberia inferred from chironomids in lake sediments

    NASA Astrophysics Data System (ADS)

    Nazarova, Larisa; Diekmann, Bernhard; Pestrjakova, Ludmila; Herzschuh, Ulrike; Subetto, Dmitry

    2010-05-01

    faunistic changes take place after 4500 yBP. Temperature reconstruction has shown that around 4500 ka BP air temperature went down up to 2oC below modern temperature. These observations confirm end of Holocene climate optimum at this time. The lake status record reveals a long-term trend towards lake-level lowering in the course of climate deterioration after 4.2 cal. ka BP and reduced evaporation as well as progressive sediment infill. This long-term trend is overprinted by short-term fluctuations at centennial time scales with high lake levels and decreased biological productivity during cool climate spells with reduced evaporation, as also observed in modern thermokarst lakes of Central Yakutia.

  14. Holocene environmental changes from Dicksonfjorden sediments of western Spitsbergen, Svalbard

    NASA Astrophysics Data System (ADS)

    Joo, Young Ji; Nam, Seung-Il; Son, Yeong Ju; Forwick, Matthias

    2017-04-01

    The last deglaciation of the Svalbard-Barents ice sheet, initiated since 13000 yrs BP, and subsequent warming through the Holocene prompted dramatic climate changes in the Svalbard fjords. Consequently, significant changes are expected in processes that determine the nature of sediments delivered (often en masse) to the steep fjords system, including sediment weathering, primary production in fjords and terrestrial realms, and the main domain of sediment transport (i.e. a shift from ice-rafting to glaciofluvial). This study investigates paleoenvironmental changes in the western Svalbard region using the Holocene glaciomarine sediments from Dicksonfjorden of the west Spitsbergen. We examine geochemical composition of organic (carbon and nitrogen stable isotopes) and inorganic (major and trace elements concentrations) components of core sediments from the inner part of Dicksonfjorden, where sediments are mainly derived from the late Paleozoic mixed siliciclastic-carbonate sedimentary sequences distributed on the western Spitsbergen. Based on our preliminary result, carbon isotope data exhibits an overall 2 ‰ positive shift since the last deglaciation, suggesting a major change in the nature of organic matter. We posit that a shift of the major source of organic matter from terrestrial plant to aquatic algae. The rising temperature likely promoted chemical weathering and thus enhanced nutrient supply for algal growth, since the early Holocene climate optimum. It is corroborated by the organic C/N ratio showing an antithetic relationship with the 13Corg result. Principal component analysis is applied to major and trace element data, obtained by X-ray fluorescence (XRF) core scanning measurements, in order to uncover main controls on inorganic geochemistry of sediments. The result indicates that there are at least two periods marked with major changes in the inorganic sediment geochemistry, one in 13000 yrs BP and the other one in 5000 yrs BP. We will further test

  15. 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

  16. Holocene surface ocean temperatures in the Labrador Sea

    NASA Astrophysics Data System (ADS)

    Schneider, R. R.; Blanz, T.

    2016-12-01

    The Labrador Sea is a marginal sea in subpolar regions considered important for North Atlantic overturning circulation. It is surrounded by large land masses partly covered by glaciers and continental ice sheets that have and will strongly influence the freshwater/saltwater balance at the surface and thus, next to cooling and freezing processes in winter, control the formation of deep water masses that have strong impact on the deep Western Atlantic return flow in the North Atlantic thermohaline circulation. Reconstructions of centennial to millenial scale climate variability during the Holocene have also documented this complex interaction between inflow of relatively warm surface waters south of Greenland, mixing with meltwater intrusions from land, ice-berg calving and seasonal sea-ice coverage, leading to pronounced changes in the Labrador Current that fuels its surface and deeper water masses into the North Atlantic current systems. However, linking modern observations and historical times series with past records on Labrador Sea climate variability has been hampered by the lack of robust quantitative paleothermometers. Therefore, after re-calibrating the ketone unsaturation index of C37 long-chain hydrocarbon molecules in the temperature range between 0 and 10° C by comparing index values from recent surface sediments with ambient temperatures and salinities from the Greenland and Labrador Margins, we generated Holocene time series of surface temperatures and meltwater events. While sea surface temperatures in the eastern Labrador Sea, Westgreenland Current, have varied between 2 and 10°C, with higher meltwater intrusions leading to cooling in fjords, first results from the western Labrador Sea, Labrador Current, point to on average much colder surface temperatures between -1 and 5° C for the Labrador Basin outflow. This general E-W temperature difference in surface waters manifests the occurence of the modern surface temperature gradient, and thus a

  17. Modelled interglacial carbon cycle dynamics during the Holocene, the Eemian and Marine Isotope Stage (MIS) 11

    NASA Astrophysics Data System (ADS)

    Kleinen, Thomas; Brovkin, Victor; Munhoven, Guy

    2016-11-01

    Trends in the atmospheric concentration of CO2 during three recent interglacials - the Holocene, the Eemian and Marine Isotope Stage (MIS) 11 - are investigated using an earth system model of intermediate complexity, which we extended with process-based modules to consider two slow carbon cycle processes - peat accumulation and shallow-water CaCO3 sedimentation (coral reef formation). For all three interglacials, model simulations considering peat accumulation and shallow-water CaCO3 sedimentation substantially improve the agreement between model results and ice core CO2 reconstructions in comparison to a carbon cycle set-up neglecting these processes. This enables us to model the trends in atmospheric CO2, with modelled trends similar to the ice core data, forcing the model only with orbital and sea level changes. During the Holocene, anthropogenic CO2 emissions are required to match the observed rise in atmospheric CO2 after 3 ka BP but are not relevant before this time. Our model experiments show a considerable improvement in the modelled CO2 trends by the inclusion of the slow carbon cycle processes, allowing us to explain the CO2 evolution during the Holocene and two recent interglacials consistently using an identical model set-up.

  18. 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

  19. 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.

  20. Holocene environmental change in Kamchatka: A synopsis

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

    We present a synthesis of the results of a multiproxy, multisite, palaeoecological study of Holocene environmental change in Kamchatka, Far East Russia, details of which are presented elsewhere in the volume. We summarise the results of the analyses of pollen, diatom, chironomid, and testate amoebae assemblages, together with stable isotopes of oxygen and carbon, and sediment characteristics from the sediments of five lakes and a peat succession on a latitudinal gradient of the Kamchatka Peninsula, to infer environmental change and establish the major climate forcers and climatic teleconnections. There are synchronous shifts in the assemblage composition of most of the biota and across most sites at 6.5-6.2 ka BP, 5.2 ka BP, 4.0 ka BP, and 3.5 ka BP, suggesting a response to strong regional climate forcing at these times. These dates correspond to the warmest part of the Holocene Thermal Maximum (HTM) (6.5-6.2 ka BP), the beginning of the Neoglacial cooling (5.2 ka BP), the coolest and wettest part of the Neoglacial (4.0 ka BP), and a switch to warmer and drier conditions at 3.5 ka BP. Our results provide evidence for the penetration and domination of different air masses at different periods during the Holocene. Cool and dry periods in winter (e.g., at 6.0 ka BP) were driven by a relatively weak pressure gradient between the Siberian High and the Aleutian Low, whereas cool, wet periods in winter (e.g., the Neoglacial and during the LIA) developed when these two systems increased in strength. Warm, dry, continental periods in summer (e.g., at 2.5 ka BP) were driven by a weakening of the Siberian High. We find that the timing of the HTM in Kamchatka is later than in the Eurasian arctic but similar to northern Europe and the sub-arctic part of eastern Siberia. This progressive onset of the HTM was due to the effects of postglacial ice-sheet decay that modulated the routes of westerly storm tracks in Eurasia. A major ecosystem driver was the Siberian dwarf pine Pinus

  1. 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

  2. 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.

  3. A thousand bites - Insect introductions and late Holocene environments

    NASA Astrophysics Data System (ADS)

    Panagiotakopulu, Eva; Buckland, Paul C.

    2017-01-01

    The impact of insect species directly associated with man-made habitats and human dispersal has been, and remains globally significant. Their early expansion from their original niches into Europe is intrinsically related to discussions of climate change, origins of domesticated plants and animals, the spread of agriculture and infectious diseases. The Holocene fossil records of the dispersal of three storage pest species, Sitophilus granarius, Oryzaephilus surinamensis, and Tribolium castaneum, the housefly, Musca domestica, and the human flea, Pulex irritans from 221 sites have been mapped ranging from the Near East to Europe and from the Neolithic to the post medieval period. The importance of human induced change as a driver for the spread of synanthropic faunas and the potential for the spread of disease during this process are discussed. The results show links between mobility of farming groups and distribution of synanthropic insect species and produce a roadmap for the different cultural periods of the Late Holocene based on dispersal of these synanthropic insects. During the Neolithic, the first wave of insect introductions shows the northern European frontiers of storage of cereals, introduction of domestic animals and pastoralism and exchange. Pest introductions, linked with the itinerary of the Roman army, reached the most northerly parts of the Empire. During the medieval period, the insect records indicate further expansion and changes which parallel the spread of epidemic diseases like Plague. Understanding the timing and the rates of change of synanthropic insects provides key information about the development of the homogenised and highly anthropogenic environments in which we live today.

  4. 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.

  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. Central Greenland Holocene Deuterium Excess Variability

    NASA Astrophysics Data System (ADS)

    Masson-Delmotte, V.; Jouzel, J.; Falourd, S.; Cattani, O.; Dahl-Jensen, D.; Johnsen, S.; Sveinbjornsdottir, A. E.; White, J. W. C.

    Water stable isotopes (oxygen 18 and deuterium) have been measured along the Holocene part of two deep ice cores from central Greenland, GRIP and North GRIP. Theoretical studies have shown that the second-order isotopic parameter, the deu- terium excess (d=dD-8d18O), is an indicator of climatic changes at the oceanic mois- ture source reflecting at least partly changes in sea-surface-temperature. The two deu- terium excess records from GRIP and North GRIP show a long term increasing trend already observed in Antarctic deep ice cores and related to changes in the Earth's obliquity during the Holocene : an decreased obliquity is associated with a larger low to high latitude annual mean insolation gradient, warmer tropics, colder poles, and a more intense atmospheric transport from the tropics to the poles, resulting in a higher moisture source temperature and higher deuterium excess values. Superimposed onto this long term trend, central Greenland deuterium excess records also exhibit small abrupt events (8.2 ka BP and 4.5 ka BP) and a high frequency variability.

  7. Sea level changes in the holocene

    NASA Astrophysics Data System (ADS)

    Kidson, C.

    Over the last 30 years the emphasis in studies of the recovery from low last glaciation sea levels has changed significantly. The search for a eustatic sea level curve having global relevance has ended. Studies into the rheology of the earth's crust, and recognition that the geoid has not remained stable over time, have resulted in the recognition that there must have been regional differences in eustatic response to deglaciation. As a part of this re-appraisal there has been a growing appreciation that crustal isostatic response to the removal of the weight of ice sheets has been accompanied by a consequential hydro-isostatic response, particularly in the areas of the shelf seas. In the later part of the post-war period attention has additionally been focussed on the much greater potential for error over the whole field of palaeoenvironmental reconstruction in the Holocene, including not only errors in dating, but also a large number of possible sources of errors in heighting. As a result of this, an increasing number of scientists are withholding judgement on the nature of sea level rise and, more particularly, on the problem of higher than present late Holocene eustatic sea levels. The problems outstanding in the early 1960s have not yet been resolved but the bases of uncertainty have changed.

  8. 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

  9. Geologic records of Pleistocene, Holocene and Anthropocene beach profiles?

    NASA Astrophysics Data System (ADS)

    Dougherty, Amy; Choi, Jeong-Heon; Dosseto, Anthony

    2017-04-01

    The Anthropocene Working Group recently concluded that we have entered a new Epoch; starting during the last century when carbon dioxide, temperatures, and sea level all exceeding previous Holocene measurements. Climate change models predict a 1m rise in sea-level by 2100 coupled with increased storm intensity. Determining how vulnerable coasts will respond to global warming in the future, requires past records of sea-level and storm impacts to be deciphered. Paying specific attention to any changes prior to, and since, the onset of the Industrial Revolution. Coastal change over centennial time-scales has long fallen within a knowledge gap that exists between our understanding of shoreline behaviour measured over decades and that inferred from the landscape over millennia. Insight on shoreline behaviour across spatial and temporal scales is gained using computers to integrate models of short-term morphodynamics along beaches with longer-term coastal landscape evolution models. However, limitations exist as process-based engineering models depend on wave climate and beach profile data that is restricted to regional/historical records, while large-scale coastal behaviour models are based on general chronostratographic data from topographic profiles, interpolated cores, and isochrons extrapolated from deep radiocarbon ages. Here we demonstrate a unique methodology combining state-of-the-art geophysics, luminescence, and remote sensing techniques on prograded barriers to extract comprehensive chronostratigraphic records. Ground Penetrating Radar (GPR) data document beach and dune stratigraphy at decimetre resolution. Optically Stimulated Luminescence (OSL) directly date the formation of paleo-beachfaces and dunes. Light Detection and Ranging (LiDAR) image the lateral extent of strandplain ridge morphology. The resulting record of paleo-beach profiles spanning from the present-day beach through Holocene and Pleistocene barriers, enables our in-depth understanding of

  10. Implications of (reworked) aeolian sediments and paleosols for Holocene environmental change in Western Mongolia

    NASA Astrophysics Data System (ADS)

    Klinge, Michael; Lehmkuhl, Frank; Schulte, Philipp; Hülle, Daniela; Nottebaum, Veit

    2017-09-01

    In the semi-arid to semi-humid regions of western Mongolia four different geomorphological aeolian and fluvial archives were investigated in order to gain environmental information of landscape evolution during the late glacial and the Holocene. These archives, which contain aeolian deposits, fluvial sediments, and paleosols, are situated upon glacial moraines, fluvial terraces, floodplains, or mountain slopes. While radiometric dating provides information about the age of the sediment and paleosols, grain size and element distribution provide information about the sediment source and soil development. Extensive aeolian sediment transport occurred from 17 to 10 ka during the late glacial when climate was cold and dry. Since that period the developing steppe and alpine meadow vegetation served as a dust trap. During the warm and wet early to mid-Holocene sediment transport was reduced under a dense vegetation cover. All paleosols of the investigated archives show late Holocene ages which point to an environmental turning point around 3 ka. Since then, the Neoglacial period started with cooler climate conditions and periglacial processes intensified again. Recognizable glacier advances occurred during the Little Ice Age several centuries ago. Since then, global climate change leads to warmer and more arid conditions. During the late Holocene, a new period of strong geomorphological activity started and huge quantities of aeolian, colluvial and fluvial sediment accumulated. These intensified soil relocation processes cannot be explained exclusively by climate change because there are no explicit indications found in the palynological and lacustrine records of Mongolia. This discrepancy suggests that the additional factor of human impact has to be considered, which amplified the climate signal on the landscape. Simultaneously, when the enhanced geomorphological processes occurred, the prehistoric people changed from hunting and gathering to livestock husbandry. A first

  11. Reconstruction of Holocene short-term thermokarst dynamics in Central Yakutia

    NASA Astrophysics Data System (ADS)

    Ulrich, M.; Rudaya, N.; Wetterich, S.; Schmidt, J.; Frolova, L.; Strauss, J.; Zielhofer, C.; Fedorov, A. N.

    2016-12-01

    The aim of this study was to reconstruct Holocene thermokarst and alas evolution, their influencing factors and environmental conditions in Central Yakutia. Sediment cores were drilled down to 3-4 m depth and sampled from a large alas basin on the eastside of the Lena River valley; the alas Khara Bulgunnyakh (61.835215°N/130.647431°E). A multiproxy approach was applied to analyze the sedimentological and biogeochemical characteristics. One core drilled in a small pingo was additionally investigated for micropalaeontological proxies (pollen, ostracods, ephippia, diatoms) to determine Holocene environmental and thermokarst lake history and its contribution to alas evolution. Organic material and bulk sediment for selected samples were dated with the AMS method to determine 14C ages for thermokarst deposits and age-depth modeling was done for the pingo core. Our results point to small-scale varying depositional environments and predominantly lateral expansion in the edge region of rapidly growing small thermokarst lakes and basins by thermo-erosional processes during the Holocene. Their coalescence results finally in the development of the Khara Bulgunnyakh alas, which today cover an area of about 1.5 km². Clear evidence for long-lasting and stable lacustrine conditions was not obtained. The results of the 14C dating confirm an extensive deposition of reworked late Pleistocene sediments in peripheral basin zones during thermokarst lake extension, while the basin center is characterized by autochthonous thaw subsidence of Yedoma permafrost. Lacustrine fossil data of the KB7 core confirm lake presence between 6550 and 6350 cal yr BP that rapidly emerged and disappeared during the Holocene climatic optimum. The presented study emphasize that alas and thermokarst lake evolution in the Central Yakutia were limited to short-term phases of forcing climatic conditions that lead to very active thermokarst processes and rapid but locally variable landscape modification

  12. Constructing a High-Resolution Holocene Interpolar Methane Gradient

    NASA Astrophysics Data System (ADS)

    Sowers, Todd; Vladimirova, Diana; Blunier, Thomas

    2017-04-01

    The concentration of methane (CH4) in the northern hemisphere is elevated relative to the southern hemisphere primarily because of enhanced northern hemisphere CH4 emissions. During the preAnthropogenic era (prior to 1600AD) the interpolar CH4 gradient (IPG) is effectively dictated by the ratio of tropical to Pan Arctic CH4 emissions. IPG records from ice cores in Greenland and Antarctica therefore provide fundamental information for assessing the latitudinal distribution of CH4 emissions and their relation to global climate change. We recently constructed a high-resolution (100yr) record of IPG changes throughout the Holocene using the ReCAP (E. Greenland) and WAIS (W. Antarctica) ice cores. Contemporaneous samples from both cores were analyzed on the same day to minimize analytical uncertainties associated with IPG reconstructions. CH4 results from the WAIS core were indistinguishable from previous results suggesting our analytical scheme was intact (± 3ppb). Our reconstructed IPG showed early Holocene IPG values of ˜65ppb declining throughout the Holocene to values approximating ˜45 ppb during the latest portion of the Holocene (preAnthropogenic). Our results are consistent with the idea that early Holocene peatland development in the PanArctic regions followed glacier retreat near the end of the last glacial termination. These newly formed PanArctic peatlands contributed an additional 20Tg of CH4/yr during the Early Holocene relative to the late Holocene.

  13. A catastrophic holocene event in the lake bottom sediments of the Kola region (northeastern Fennoscandian shield)

    NASA Astrophysics Data System (ADS)

    Nikolaeva, S. B.; Lavrova, N. B.; Denisov, D. B.

    2017-03-01

    Horizons with seismogenic sediments are revealed in the bottom sediments of the lake basins in the southwestern Kola Peninsula. In the borehole cores, they are represented by material that sharply differs from the overlying and underlying sediments: fragments of gyttia, siltstone, wood, sand, and peat that are embedded in the sapropelic matrix and look like breccia. These sediments reflect a strong catastrophic event from the Holocene that occurred 6000-5400 14C yr BP. The seismic events that happened in the middle Holocene in the northeastern Fennoscandian shield indicate a significant role of the tectonic component in the damping process of relaxation of the Earth's crust in the unloading of the recent glacier cover.

  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. Variable Holocene deformation above a shallow subduction zone extremely close to the trench

    NASA Astrophysics Data System (ADS)

    Thirumalai, Kaustubh; Taylor, Frederick W.; Shen, Chuan-Chou; Lavier, Luc L.; Frohlich, Cliff; Wallace, Laura M.; Wu, Chung-Che; Sun, Hailong; Papabatu, Alison K.

    2015-06-01

    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.

  16. Variable Holocene deformation above a shallow subduction zone extremely close to the trench.

    PubMed

    Thirumalai, Kaustubh; Taylor, Frederick W; Shen, Chuan-Chou; Lavier, Luc L; Frohlich, Cliff; Wallace, Laura M; Wu, Chung-Che; Sun, Hailong; Papabatu, Alison K

    2015-06-30

    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 (230)Th 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.

  17. 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.

  18. 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

  19. 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.

  20. Role of wild plant foods among late Holocene hunter-gatherers from Central and North Patagonia (South America): an approach from dental evidence.

    PubMed

    Bernal, Valeria; Novellino, Paula; Gonzalez, Paula N; Perez, S Ivan

    2007-08-01

    This study evaluates the role of plant foods in the subsistence of hunter-gatherers that inhabited the Central East, Northwest, and Northeast Patagonia (Argentina) during the late Holocene (ca. 3,000-500 years BP). The goal of the present study is to assess the temporal variation of dental caries ratio and wear rate in skeletal samples to ascertain if the biological information supports the dietary shift toward greater consumption of wild plant foods around 1,500 years BP, suggested by other types of evidence. The authors registered caries, antemortem and postmortem tooth loss, and tooth wear from eight samples belonging to hunter-gatherers from Patagonia for which chronological sequences from early late Holocene (ca. 3,000-1,500 years BP) up to final late Holocene (ca. 1,500-500 years BP) are available. The results indicate that caries percentages in Patagonian samples fall within the range established for hunter-gatherers but there are significant geographical differences. In addition, caries ratio does not change significantly through time, so the amount of carbohydrates consumed seems to have remained fairly constant since 3,000 years BP. In contrast, there is a marked temporal trend toward the reduction of wear rates in the three areas, suggesting a faster rate in early late Holocene than in final late Holocene. These results would reflect a change to less hard and/or abrasive diets in the final late Holocene, probably owing to differences in food processing methods employed.

  1. 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

  2. Mid- to late-Holocene environmental evolution of the Loire estuary as observed from sedimentary characteristics and benthic foraminiferal assemblages

    NASA Astrophysics Data System (ADS)

    Durand, M.; Mojtahid, M.; Maillet, G. M.; Proust, J.-N.; Lehay, D.; Ehrhold, A.; Barré, A.; Howa, H.

    2016-12-01

    We used sedimentological and foraminiferal characteristics of four sedimentary cores, supported by paleogeographical and historical data, to reconstruct the depositional history of the inner Loire estuary (Near Saint-Nazaire, France) and the response of benthic foraminifera to the mid- to late-Holocene marine flooding of the incised valley. These were further used to evaluate the consequent changes in estuarine morphological and hydro-sedimentary patterns during this time period. Our results described significant changes in hydro-sedimentary dynamics over the past 6 kyrs BP. At our location, these changes expressed the combined influence of marine (e.g., tide, storm waves) and fluvial dynamics (e.g., floods), which are linked, on a broader scale, to sea-level variations and the regional climate regime. Three main periods stand out: (1) from 6.0 to 2.5 kyrs BP, when the sea-level rise slowed down, a large brackish bay extended over and around the study area. The fine-grained tidal rythmites recorded north of the Bilho bank (the main tidal bar located in our study area) indicated a calm depositional environment, protected from the main riverine influence. The presence of thick flood deposits from 5.4 to 4.0 kyrs BP near the Bilho bank indicates further the dominance of humid conditions. (2) From 2.5 kyrs BP to 1850 CE (pre-industrial state), sea-level stabilized at its present value, and the pre-existing bay was progressively infilled. North of the Bilho bank, near a major mudflat (Méan), the generally homogenous sedimentation composed of silty muds rich in organic matter indicated a sheltered environment; the main water flow channel being located south of the Bilho bank. Within this overall homogenous sedimentation, foraminiferal assemblages described rather accurately the progressive infilling of the valley (indicated by a decrease in the proportions of outer estuarine species), accompanied with the channelization of the main entering marine currents (tide, storm

  3. Search for continuous paleoclimatic record in Holocene lacustrine sediments from Lake District, Chile (40°S)

    NASA Astrophysics Data System (ADS)

    Bertrand, S.; Fagel, N.

    2003-04-01

    Our aim is to reconstruct a continuous Holocene climatic evolution related to ENSO variability in southern Chile. We focus on the sedimentary infilling of two glacial lakes from the Lake District Area (38-40°S). The preliminar sedimentological analysis must allow to define the key-site and the best palaeoclimatic proxies. This area, at the foothill of the Cordillera de Los Andes, has been affected by an intense Quaternary volcanic activity and by several historical earthquakes (e.g., Valdivia 1960). After preliminary seismic investigation, four cores were recovered in two lakes selected at the two ends of a N-S transect. (1) Icalma lake (12 km2, 38°S) is located in the Cordillera de Los Andes at an elevation of 1150m and results of the infilling of a glacial umbilic. The two 8m sediment cores consist of an alternation of laminated silts and volcanic layers. The sedimentary record is strongly disturbed by numerous seismic or volcanic events. The cumulated volcanogenic-derived material represents up to 50 % of the core length. In particular, the cores record at -4.50m a pumice layer widespread in the watershed and dated at 2900 yr BP. One core contains pluricentrimetric layers of wood accumulation. They could be due to earthquake impact on the vegetational cover in the watershed. An ubiquitous 6cm-thick slump described at -40 cm may be related with the 1960 Valdivia earthquake. (2) On Puyehue lake (164 km2, 40°S, elevation 185 m), two cores (7 and 11m) have been collected in both underflow and interflow sites. The interflow site (PUII) shows a very well laminated sediment, with only small disturbances due to volcanic and seismic activities. This core will be the key-site for the paleoclimatic study. The second core (PUI) is very rich in organic matter. The sediment is strongly destratified by numerous gas bubbles (methane). These characteristics are due to the dense vegetational cover in the watershed and to the core location near the delta of the main river. This

  4. Architectural variability of confined turbidite sheet-sands: facies, geometry and infill of associated elementary channels. Examples from the Trois Evêchés Basin, Annot Sandstone Formation, SE France

    NASA Astrophysics Data System (ADS)

    Etienne, S.; Mulder, T.; Pace, A.; Bez, M.; Desaubliaux, G.

    2012-04-01

    The worldwide known Annot Sandstone Formation has been considered as a reference of confined siliciclastic turbidite system. This formation crops out in SE France and represents the Upper Eocene to Lower Oligocene gravitary infill of complex foreland basins, developed in front of the Alpine thrusts. This system can be assimilated as a sand-rich turbidite ramp, sourced by multiple fan deltas leading to topographically complex sub-basins. Highly bypassing channelized systems dominate in the most proximal and most confined areas. They distally evolve to relatively less confined areas, in which sedimentary bodies appear to be more continuous and homogenous on a regional scale. These last architectural elements, defined as sheet-sands or depositional lobes, have been the focus of this study in poorly documented areas. From an important dataset made of very high resolution outcrop correlations (gathered mainly in the Trois Evêchés and Lauzanier sub-basins), we have quantified the complex distribution of sedimentary facies and structures, grain-size and key surfaces in sand-rich sheets. This was done to understand their variability from depositional event to architectural element scales and to better characterize dimensions and characteristics of their components. Six main types of architectural elements were defined, composed of both channelized and unchannelized elements. Channelized units show a high variability in terms of facies, geometry and patterns of infill that are related to multiple erosional and depositional processes, which will be discussed. We notably relate some evidences of sinuous channels, represented by lateral accretion deposits in the channel complex axis and by low angle cross-bedded facies. We interpret this particular facies as the result of flow deconfinement and overbanks above channel margins. The stratigraphic analysis of elementary objects allows us to propose a genetic model and a spatial distribution model of sheet-sand architectural

  5. 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.

  6. 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.

  7. Holocene paleotemperature signals based on polar firn water isotope diffusion studies from two Greenland ice cores.

    NASA Astrophysics Data System (ADS)

    Gkinis, Vasileios; Terkelsen Holme, Christian; Møllesøe Vinther, Bo

    2017-04-01

    Polar ice cores provide a wealth of paleoclimatic information that is characterised by high temporal resolution and continuity, with water isotopic ratios of polar precipitation (δ18O, δD) being one of the most prominent proxies for past temperatures. In particular, ice cores from Greenland, record the series of abrupt stadial - interstadial transitions during the last Glacial, pinpointing in time, abrupt temperature transitions adjoined by similar accumulation trends. While the signal to noise ratio of the isotopic signal clearly allows the observation of sizable climate changes during the Glacial, the situation differs considerably when one looks into the Holocene. With the exception of the 8.2ky event, the signal to noise ratio of δ18O over the Holocene is extremely low, suggesting negligible temperature changes during this period. This is contrary to signals obtained by other proxies from marine and terrestrial records from high latitudes. In this study we bypass the discussion that deals with the various processes that can negatively affect paleotemperature reconstructions based on the δ18O proxy from ice cores. Based on two ultra-high resolution and high precision isotopic records covering the last 20,000 years from the NorthGRIP and NEEM ice cores we make use of the available spectral information to infer polar firn paleotemperatures using a coupled densification - firn water isotope diffusion model. The processes involved in the densification of firn and the diffusion of water isotopes that takes place after deposition and until the pore close-off are temperature-dependent and do not present the limitations of the normal δ18O thermometer. We show here how this approach reveals significant temperature changes over the Holocene. We compare the signals of the two records and pay particular attention to the indications of a mid-Holocene climatic shift towards colder temperatures that is apparent in both temperature reconstructions.

  8. 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.

  9. 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

  10. Stature in Holocene foragers of North India.

    PubMed

    Lukacs, John R; Pal, J N; Nelson, Greg C

    2014-03-01

    The Ganga Plain of North India provides an archaeological and skeletal record of semi-nomadic Holocene foragers in association with an aceramic Mesolithic culture. Prior estimates of stature for Mesolithic Lake Cultures (MLC) used inappropriate equations from an American White reference group and need revision. Attention is given to intralimb body proportions and geo-climatic provenance of MLC series in considering the most suitable reference population. Regression equations from ancient Egyptians are used in reconstructing stature for MLC skeletal series from Damdama (DDM), Mahadaha (MDH), and Sarai Nahar Rai (SNR). Mean stature is estimated at between 174 (MDH) and 178 cm (DDM and SNR) for males, and between 163 cm (MDH) and 179 cm (SNR) for females. Stature estimates based on ancient Egyptian equations are significantly shorter (from 3.5 to 7.1 cm shorter in males; from 3.2 to 7.5 cm shorter in females) than estimates using the American White reference group. Revised stature estimates from tibia length and from femur + tibia more accurately estimate MLC stature for two reasons: a) these elements are highly correlated with stature and have lower standard estimates of error, and b) uncertainty regarding methods of measuring tibia length is avoided. When compared with Holocene samples of native Americans and Mesolithic Europeans, MLC series from North India are tall. This aspect of their biological variation confirms earlier assessments and results from the synergistic influence of balanced nutrition from broad-spectrum foraging, body-proportions adapted to a seasonally hot and arid climate, and the functional demands of a mobile, semi-nomadic life-style.

  11. Controls on fire activity over the Holocene

    NASA Astrophysics Data System (ADS)

    Kloster, S.; Brücher, T.; Brovkin, V.; Wilkenskjeld, S.

    2014-11-01

    Changes in fire activity over the last 8000 years are simulated with a global fire model driven by changes in climate and vegetation cover. The changes were separated into those caused through variations in fuel availability, fuel moisture or wind speed which react differently to changes in climate. Disentangling these controlling factors helps to understand the overall climate control on fire activity over the Holocene. Globally the burned area is simulated to increase by 2.5% between 8000 and 200 cal yr BP with larger regional changes compensating on a global scale. Despite the absence of anthropogenic fire ignitions, the simulated trends in fire activity agree reasonably well with continental scale reconstructions from charcoal records, with the exception of Europe. For some regions the change in fire activity is predominantly controlled through changes in fuel availability (Australia-Monsoon, American Tropics/Subtropics). For other regions changes in fuel moisture are more important for the overall trend in fire activity (North America, Sub-Saharan Africa, Europe, Asia-Monsoon). In Sub-Saharan Africa, for example, changes in fuel moisture alone lead to an increase in fire activity between 8000 and 200 cal yr BP, while changes in fuel availability lead to a decrease. Overall, the fuel moisture control is dominating the simulated fire activity for Sub-Saharan Africa. The simulations clearly demonstrate that both changes in fuel availability and changes in fuel moisture are important drivers for the fire activity over the Holocene. Fuel availability and fuel moisture do, however, have different climate controls. As such observed changes in fire activity can not be related to single climate parameters such as precipitation or temperature alone. Fire models, as applied in this study, in combination with observational records can help to understand the climate control on fire activity, which is essential to project future fire activity.

  12. Controls on fire activity over the Holocene

    NASA Astrophysics Data System (ADS)

    Kloster, S.; Brucher, T.; Brovkin, V.; Wilkenskjeld, S.

    2015-05-01

    Changes in fire activity over the last 8000 years are simulated with a global fire model driven by changes in climate and vegetation cover. The changes were separated into those caused through variations in fuel availability, fuel moisture or wind speed, which react differently to changes in climate. Disentangling these controlling factors helps in understanding the overall climate control on fire activity over the Holocene. Globally the burned area is simulated to increase by 2.5% between 8000 and 200 cal yr BP, with larger regional changes compensating nearly evening out on a global scale. Despite the absence of anthropogenic fire ignitions, the simulated trends in fire activity agree reasonably well with continental-scale reconstructions from charcoal records, with the exception of Europe. For some regions the change in fire activity is predominantly controlled through changes in fuel availability (Australia monsoon, Central America tropics/subtropics). For other regions changes in fuel moisture are more important for the overall trend in fire activity (North America, Sub-Saharan Africa, Europe, Asia monsoon). In Sub-Saharan Africa, for example, changes in fuel moisture alone lead to an increase in fire activity between 8000 and 200 cal yr BP, while changes in fuel availability lead to a decrease. Overall, the fuel moisture control is dominating the simulated fire activity for Sub-Saharan Africa. The simulations clearly demonstrate that both changes in fuel availability and changes in fuel moisture are important drivers for the fire activity over the Holocene. Fuel availability and fuel moisture do, however, have different climate controls. As such, observed changes in fire activity cannot be related to single climate parameters such as precipitation or temperature alone. Fire models, as applied in this study, in combination with observational records can help in understanding the climate control on fire activity, which is essential to project future fire

  13. 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

  14. The Pleistocene-Holocene Unconformity in California Prehistory

    NASA Astrophysics Data System (ADS)

    Jones, T. L.

    2007-05-01

    The earliest archaeological record from California shows a dramatic unconformity or cultural hiatus between the terminal Pleistocene and the early Holocene. Clovis-like fluted projectile points which mark initial human colonization ca. 13,300-12,900 cal BP, are relatively common and have been found throughout the state, but almost exclusively as isolates. Early Holocene sites are abundant as well, particularly on the coast where at least 23 deposits show occupation as old as ca. 10,000-9000-cal BP. Only one of these, Daisy Cave, extends back into the terminal Pleistocene, but the remainder mark occupations that began only at the onset of the Holocene. There are almost no archaeological sites in California that date between 12,900 and 10,300 cal BP or that exhibit superimposed terminal Pleistocene and early Holocene components. This pattern is consistent with a significant disruptive event during the Younger-Dryas.

  15. A Holocene pollen and diatom record from Vanderlin Island, Gulf of Carpentaria, lowland tropical Australia

    NASA Astrophysics Data System (ADS)

    Prebble, Matiu; Sim, Robin; Finn, Jan; Fink, David

    2005-11-01

    Sedimentary, palynological and diatom data from a dunefield lake deposit in the interior of Vanderlin Island in the Gulf of Carpentaria are presented. Prior to the formation of present perennial lake conditions, the intensified Australian monsoon associated with the early Holocene marine transgression allowed Cyperaceae sedges to colonise the alluvial margins of an expansive salt flat surrounded by an open Eucalyptus woodland. As sea level stabilised between 7500 and 4500 cal yr B.P. coastal dunes ceased to develop allowing dense Melaleuca forest to establish in a Restionaceae swamp. Dune-sand input into the swamp was diminished further as the increasingly dense vegetation prevented fluvial and aeolian transported sand arriving from coastal sources. This same process impounded the drainage basin allowing a perennial lake to form between 5500 and 4000 cal yr B.P. Myriophyllum and other aquatic taxa colonised the lake periphery under the most extensive woodland recorded for the Holocene. The palynological data support an effective precipitation model proposed for northern Australia that suggests more variable conditions in the late Holocene. A more precise measure of effective precipitation change is provided by diatom-based inferences that indicate few changes in lake hydrology. Such interpretations are explained in terms of palynological sensitivity to adjustments in local fire regimes where regional precipitation change may only be recorded indirectly through fire promoting mechanisms, including intensified ENSO periodicity and human impact.

  16. Human Responses to Middle Holocene (Altithermal) Climates on the North American Great Plains

    NASA Astrophysics Data System (ADS)

    Meltzer, David J.

    1999-11-01

    The climate of the Great Plains during the middle Holocene varied considerably, but overall it was marked by a north-south gradient of increasingly warmer and drier conditions, with a reduction in effective moisture, surface water, and resource abundance, and an increase in resource patchiness, sediment weathering, erosion, and aeolian activity. Pronounced drought conditions were most evident on the Southern High Plains. Understanding the human responses to middle Holocene climates is complicated by a lack of archaeological data, which is partly a result of geomorphic processes that removed or deeply buried sites of this age, and by the varying adaptive responses of hunter-gatherers during this period. On the Southern High Plains, where drought was most severe, surface and groundwater sources dried and bison populations were diminished, prompting substantial adaptive changes, including local abandonment, well-digging to tap underground water, and a widening of the diet breadth to incorporate higher-cost, lower-return seed and plant resources. Sites of this age on the Central and Northern Plains also show a possible increase in diet breadth (with the incorporation of plant foods in the diet), and perhaps changes in settlement mobility (including possible shift into higher elevation areas, or mapping-on to extant rivers and springs). But linking those changes to middle Holocene drought is less straightforward.

  17. 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.

  18. 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.

  19. Late Holocene peatland carbon dynamics inferred from Teringi Bog in southern Estonia

    NASA Astrophysics Data System (ADS)

    Hill, Kristyn; Stansell, Nathan; Klein, Eric; Borges, Alberto

    2015-04-01

    Radiocarbon dated peat cores collected along a transect from Teringi Bog, an ombotrophic peatland, record changes in carbon accumulation rates during the late Holocene in response to shifting climatic conditions. Stable oxygen isotope records from nearby lakes indicate that periods of wetter conditions during the Holocene occurred at times when carbon accumulation rates were higher at Teringi. This suggests that shifting water table conditions drove much of the observed changes in carbon dynamics. Modern surface process observations indicate that carbon accumulation rates are indeed more variable at locations where the height of the water table is highly sensitive to rainfall amounts. In addition, carbon isotopes measured on water samples indicate that there is a close relationship between δ13C values and methane concentrations, suggesting that methanogenesis is strongly biomediated, and likewise varies as a function of the regional hydrology. Regardless, all of the cores collected indicate that there was a trend toward higher carbon accumulation rates from ~4.2 to 3.5 ka when precipitation amounts were higher, followed by lower values under drier conditions until ~2.8 ka. There was then a trend toward higher carbon accumulation rates through the remaining late Holocene. These observations further highlight the importance of high latitude peatland in global carbon dynamics as both a potential sink and source of CO2 and CH4.

  20. 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.

  1. Organic sources and carbon sequestration in Holocene shelf sediments from the western Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Faux, Jessica F.; Belicka, Laura L.; Rodger Harvey, H.

    2011-08-01

    To quantify changes in organic carbon inputs and preservation, sediments from the Northern Chukchi Sea spanning the last 9000 years of the Holocene period were collected during the HOTRAX expedition and analyzed. The multi-proxy approach included molecular organic markers, bulk carbon and isotope measurements plus more recent approaches to terrestrial carbon estimation (the BIT index of Branched and Isoprenoid Tetraethers). The upper 1100 cm of the core, corresponding to the last 7.4 ka, showed a relatively stable total organic carbon content of 1.13-1.38% which decreased below 1100 cm to 0.6%. C:N ratios ranged from 8.4 to 10.83 over the Holocene time period examined. The distribution of n-alcohols and n-alkanes revealed major contributions from long-chain n-alcohols and n-alkanes while minimal contributions were seen from short-chain n-alkanes. The majority of the total fatty acids was comprised of saturated and monounsaturated fatty acids with short-chain and long-chain saturated fatty acids present in similar concentrations throughout most of the core and monounsaturated fatty acids decreasing down-core. Total sterol concentrations showed considerable inputs from marine sterols, C 28Δ 5,22, C 28Δ 5,24(28) and dinosterol, as well as C 29Δ 5, typically considered a terrestrial marker. The BIT indices for core sediments ranged from 0.021 to 0.216 with minor changes seen in older sequences. Overall, organic biomarkers indicate marine sources as the more dominant input of organic matter with lower but continual contributions from terrestrial sources at this location during the Holocene. The remarkable consistency among multiple molecular organic markers of both marine and terrestrial origin over the Holocene period encompassed by the core suggests that sinking material or surface sediments were heavily influenced by bottom currents or other mixing processes prior to their deposition.

  2. Holocene Mass Transport Deposits in Western Norwegian fjords and lakes revealing prehistoric earthquake history of Scandinavia

    NASA Astrophysics Data System (ADS)

    Bellwald, B.; Hjelstuen, B. O.; Sejrup, H. P.; Kuvås, J.; Stokowy, T.

    2016-12-01

    The sensitivity of fjord sediments to seismic shaking makes fjord systems appropriate study sites when extending regional earthquake catalogs back in time and when estimating recurrence rates of prehistoric earthquakes in intraplate settings. In this study we compiled evidence of 140 postglacial mass movement events and their associated mass transport deposits (MTDs) from previously analyzed and new sediment cores and high-resolution seismic profiles from 22 fjord systems and six lakes in Western Norway. Evaluation of trigger mechanisms make us infer that most of these mass movement events were initiated by regional earthquakes, and that both climate-related processes and tsunamis most likely can be excluded as trigger mechanism for most of the events. A total of 33 individual earthquakes has been identified, which most likely outbalance the historically recorded events in magnitude, thus indicating magnitudes >6. Frequency plots of MTDs suggest high seismic activity in the early Holocene (11000-9700 cal. yrs BP), followed by seismic quiescence in the mid-Holocene before a seismic reactivation took place at 4000 cal. yrs BP. Coevally-triggered MTDs at 8100 cal. yrs BP are identified in all the archives, and are correlating with the age of the offshore Storegga slide. We estimate earthquake recurrence rates of 1/80 years directly after the last deglaciation of Western Norway (12800-11600 ca. yrs BP), 1/200 years for the early Holocene and 1/300 years for the last 4000 years. Our compilation suggests that the mid-Holocene is characterized by low seismic activity, suggesting recurrence rates of 1/1300 years. Comparisons of the Western Norwegian dataset with paleoseimologic studies of other previously glaciated intraplate settings indicate that both Scandinavia and the Alps show similar trends as Western Norway, whereas Eastern Canada is not correlating with the paleoseismologic trend of this study, which could be explained by different deglaciation histories.

  3. Holocene winter climate variability in Central and Eastern Europe.

    PubMed

    Perșoiu, Aurel; Onac, Bogdan P; Wynn, Jonathan G; Blaauw, Maarten; Ionita, Monica; Hansson, Margareta

    2017-04-26

    Among abundant reconstructions of Holocene climate in Europe, only a handful has addressed winter conditions, and most of these are restricted in length and/or resolution. Here we present a record of late autumn through early winter air temperature and moisture source changes in East-Central Europe for the Holocene, based on stable isotopic analysis of an ice core recovered from a cave in the Romanian Carpathian Mountains. During the past 10,000 years, reconstructed temperature changes followed insolation, with a minimum in the early Holocene, followed by gradual and continuous increase towards the mid-to-late-Holocene peak (between 4-2 kcal BP), and finally by a decrease after 0.8 kcal BP towards a minimum during the Little Ice Age (AD 1300-1850). Reconstructed early Holocene atmospheric circulation patterns were similar to those characteristics of the negative phase of the North Atlantic Oscillation (NAO), while in the late Holocene they resembled those prevailing in the positive NAO phase. The transition between the two regimes occurred abruptly at around 4.7 kcal BP. Remarkably, the widespread cooling at 8.2 kcal BP is not seen very well as a temperature change, but as a shift in moisture source, suggesting weaker westerlies and increased Mediterranean cyclones penetrating northward at this time.

  4. Large Holocene lakes and climate change in the Chihuahuan Desert

    NASA Astrophysics Data System (ADS)

    Castiglia, Peter J.; Fawcett, Peter J.

    2006-02-01

    Lake-level variations preserved as beach ridges in the Laguna El Fresnal and Laguna Santa María subbasins, northern Mexico, record millennially spaced episodes of increased precipitation during the Holocene epoch. We find that the early, middle, and late Holocene were punctuated by periods wet enough to establish large pluvial lakes in currently dry basins in the Chihuahuan Desert; the largest dated pluvial lake covered ˜5650 km2 during the early Holocene. Constructional beach ridges in these subbasins are 221 ± 33 14C yr B.P. (Little Ice Age equivalent), 3815 ± 52 to 4251 ± 59 14C yr B.P. (early Neoglacial), 6110 ± 80 to 6721 ± 68 14C yr B.P. (mid-Holocene), and 8269 ± 64 to 8456 ± 97 14C yr B.P. (early Holocene), dates that correlate with other millennially spaced wet or cold events in the Northern Hemisphere. We attribute these wet episodes to increased precipitation, cooler temperatures, and reduced evaporation following southward shifts in winter storm tracks, which are related to long-term El Niño Southern Oscillation variability during the Holocene.

  5. 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.

  6. 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.

  7. Estimating environmental value losses from earth materials excavation and infilling for large-scale airport construction: a case of Dalian Offshore Airport, Dalian, China.

    PubMed

    Yan, Hua-Kun; Wang, Nuo; Wu, Nuan; Song, Nan-Qi; Zhu, Dao-Li

    2017-07-21

    Large-scale airport construction removes large quantities of earth materials, resulting in serious environmental pollution and ecosystem damage. However, studies of environmental concerns caused by the materials used in airport construction are still preliminary, and those case studies on the impacts of large-scale offshore airport development are very limited. China's Dalian Offshore Airport is considered here to study the environmental value loss from 240 million m(3) of materials excavations and 21 km(2) of artificial island infillings. The findings show that the calculated annual environmental value loss for the development of the Dalian Offshore Airport is approximately US$7.75 million, including US$1.81 million and US$1.47 million of direct economic loss of timber resources and marine biology resources, respectively, and US$1.53 million and US$2.79 million value losses of forest and marine ecosystem services damaged caused by materials excavation and infilling, respectively. The conclusions of this study provide an important foundation to quantitatively analyse the environmental impact of the Dalian Offshore Airport's development and can be used as a reference for similar engineering and environment impact assessment programs.

  8. Changes in mid to late Holocene monsoon strength in eastern Mexico inferred from high-resolution maar lake sediments

    NASA Astrophysics Data System (ADS)

    Bhattacharya, T.; Byrne, R.; Wogau, K.; Bohnel, H.

    2013-12-01

    Understanding the Holocene variation in central Mexico's summer precipitation can help identify the processes responsible for climatic change and clarify the role of climate in Mesoamerican cultural change. We present proxy results from Aljojuca, a maar lake in the Oriental-Serdan Basin in Mexico's Trans-Mexican Volcanic Belt. The 12 m sediment core from Aljojuca features a laminated, high-resolution proxy archive. A chronology established via radiocarbon dating shows a basal date of 6,200 cal. years B.P. We use fluctuations in pollen, elemental geochemistry, and the stable isotope ratios of authigenic carbonates to reconstruct the timing and duration of mid to late Holocene droughts in central Mexico. We compare these results with geochemical analyses of maar wall rocks and palynological analyses of modern moss polsters to strengthen our interpretations of proxy results. We interpret periods of aridity as periods of reduced summer precipitation and therefore decreased summer monsoon strength. Our results reveal evidence of a gradual decrease in monsoon strength from the mid to late Holocene. We also identify a multi-century dry period between 1,150 and 800 cal yr. BP, coinciding with the abandonment of the nearby fortified city of Cantona. Spatiotemporal analysis of this and other paleoclimatic records reveals region-wide evidence of this ';Terminal Classic' drought, although its timing is spatially heterogeneous. Our results represent one of the only high-resolution mid-Holocene records from the eastern Trans-Mexican Volcanic Belt.

  9. 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.

  10. Geomorphological processes in a semiarid badland area using new technologies: TLS, terrestrial and aerial SfM photogrammetry

    NASA Astrophysics Data System (ADS)

    Ferrer, Victor; Errea, Paz; Alonso, Esteban; Gómez-Gutiérrez, Álvaro; Nadal-Romero, Estela

    2017-04-01

    We used three different methods Terrestrial Laser Scanner (TLS), terrestrial Structure from Motion photogrammetry (SfM) and aerial SfM photogrammetry with an Unmanned Aerial Vehicle (UAV) to analyse geomorphological processes in a semiarid badland landscape. Los Aguarales badlands, located in the Ebro Depression (Spain), occur in the Holocene sediment accumulated in a wide valley infilled with silt and clay. The morphology of Los Aguarales badlands is complex, making the geomorphological interpretation a difficult task. Los Aguarales badlands are characterized by the sequence of incision and piping processes developing an abrupt and complex landscape. Three different representative and small study sites were selected to carry out a detailed analysis of the geomorphological processes. Moreover, the capability of the three methods to produce high resolution point clouds was evaluated. The obtained topographical changes were very low during the first 6 months (March-October 2016). Measured topographical changes, with TLS and terrestrial SfM, were very low, and these values fall within the range of the acquisition error of the devices used (2-6 cm). The preliminary results indicated the possibilities of a multiscale approach using new technologies to study geomorphological and erosion processes, although long-term studies will be necessary to obtain erosion rates in this semiarid badland area. Acknowledgement This research was supported by ESPAS and eTERA 3D projects (CGL2015- 65569-R and CGL2014-54822-R, funded by the MINECO-FEDER). Estela Nadal-Romero is the recipient of a Ramón y Cajal postdoctoral contract (Spanish Ministry of Economy and Competitiveness).

  11. Chronicles from the End of the Word: the Holocene climate variability in Tierra del Fuego

    NASA Astrophysics Data System (ADS)

    Waldmann, N.; Ariztegui, D.; Anselmetti, F.; Austin, J.; Moy, C.; Borromei, A.; Coronato, A.; Recasens, C.; Dunbar, R.; Martinez, M.; Olivera, D.

    2008-12-01

    Latest advances in the chronology and environmental importance of Antarctic paleoclimate records point towards a larger heterogeneity than previously thought. Thus, realistic inter-hemispheric correlations rely in the development of a tight array of well constrained records with a dense latitudinal coverage. Climatic records from southernmost Patagonia are hence critical corner-stones to link these Antarctic paleoclimatic archives with their South American counterparts. At 55° S on the Island of Tierra del Fuego, Lago Fagnano is located in one of the most substantially and extensively glaciated regions of southernmost South America during the Late Pleistocene. This elongated lake is the largest (~110 km long) and southernmost non-ice covered water body in the world. Existing on-shore geomorphological reconstructions combined with new lacustrine subsurface data, allowed us to better constrain the magnitude and chronology of the Fagnano glacier fluctuations since the LGM. The former Fagnano glacier flowed eastwards from the Darwin Cordillera fed by more than 50 tributary glaciers. The glacier spread over the low ranges and lowlands through three different lobes and was drained by four main outwash basins directly into the Atlantic Ocean. During the maximum ice-expansion, the ice-covered area was ca. 4000 km2 with a maximum length of ca. 132 km. A set of submerged frontal moraines covered by lacustrine infilling identified in the seismic survey suggests occasional eastward re-advances of the paleo-glacier within the overall westward deglaciation pattern. These re-advances may correspond to cold events such as the Antarctic Cold Reversal (ACR), the Huelmo- Mascardi Cold Event (HMCE) and/or the Younger Dryas Chronozone (YDC). The ongoing development of a robust age model blended with a multi-proxy dataset will potentially clarify remaining controversial issues dealing with the geographical extension and chronology of these cold episodes during the last deglaciation. A

  12. 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

  13. 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

  14. Late Holocene Andesitic Eruptions at Mount Rainier

    NASA Astrophysics Data System (ADS)

    Sisson, T. W.; Vallance, J. W.

    2005-12-01

    Holocene Mt. Rainier erupted much more frequently than is recorded by its 11 pumiceous tephras. In the 2.6-2.2 ka Summerland eruptive period, 6 groups of thin (1-5 mm) Sparsely Vesicular Glassy (SVG) ashes were deposited (S1-S6), followed by the 0.3 km3 C-tephra. Two groups of andesitic lava flows and one andesitic block-and-ash flow (2.45 ka) also erupted in the Summerland period (ice conceals any other products). Based on glass composition the pyroclastic flow correlates with S4 ashes that also contain pumiceous grains and rare pumice lapilli. The first of the lava groups, exposed in windows through the Emmons and Winthrop glaciers, is Sr-rich for Mt. Rainier eruptives and correlates with S5 & S6 ashes based on similar high-Sr plagioclase. The ensuing C-tephra formed by plinian eruption of mixed and mingled magma comprising 4 juvenile components: mixed porphyritic andesite pumice, crystal-poor andesite scoria, vesicular high-Sr dacite blebs in pumice and scoria, and poorly inflated crystal-rich high-Sr dacite. High-Sr components were probably entrained conduit linings and segregations from the preceding high-Sr eruptions. The youngest lava group, exposed at the summit, is normal-Sr andesite lacking mixing textures of the C-tephra, and represents eruption of another small batch of andesitic magma perhaps just after the C event. SVG ash grains have blocky-to-fluidal shapes, are rich in plagioclase microlites, and their glasses are high-SiO2 (66-78%) and low-Al2O3 (15-11%). Melting experiments yield apparent equilibration pressures <50MPa for SVG liquids. SVG ashes likely result from shallow hydromagmatic explosions as largely degassed magmas transited the upper-edifice hydrothermal system during effusive eruptions. Rare pumice lapilli codeposited with S1, S2, and S4 ashes have microlite-free dacitic glasses, one with nonreacted hbl phenocrysts. These pumice formed from magmas that ascended rapidly from reservoir depths, synchronous with or closely between effusive

  15. 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

  16. Bacterial diversity and distribution in the holocene sediments of a northern temperate lake.

    PubMed

    Nelson, David M; Ohene-Adjei, Samuel; Hu, Feng Sheng; Cann, Isaac K O; Mackie, Roderick I

    2007-08-01

    Sediments contain an abundance of microorganisms. However, the diversity and distribution of microorganisms associated with sediments are poorly understood, particularly in lacustrine environments. We used banding patterns from denaturing gradient gel electrophoresis (DGGE) and 16S rDNA sequences to assess the structure of bacterial communities in the Holocene sediments of a meromictic lake in Minnesota. Cluster analysis of the DGGE banding patterns indicates that the early- and middle-Holocene samples group separately from the late-Holocene samples. About 79% of the recovered bacterial sequences cluster with the alpha-, beta-, delta-, epsilon-, and gamma- Proteobacteriaceae and Firmicutes. The remaining approximately 21% lack cultured representatives. The taxonomic lineages of bacteria differ statistically among the early-, middle-, and late-Holocene samples, although the difference is smallest between early- and middle-Holocene samples. Early- and middle-Holocene samples are dominated by epsilon-Proteobacteriaceae, and late-Holocene samples are dominated by sequences from uncultured subphyla. We only recovered delta-Proteobacteriaceae in late-Holocene sediments and alpha- and gamma- Proteobacteriaceae in late- and middle-Holocene sediments. Diversity estimates derived from early-, middle-, and late-Holocene clone libraries indicate that the youngest (late-Holocene) samples had significantly greater bacterial diversity than the oldest (early-Holocene) samples, and the middle-Holocene samples contained intermediate levels of diversity. The observed patterns of diversity may be caused by increased bacterial niche-partitioning in younger sediments that contain a greater abundance of labile organic matter than older sediments.

  17. 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.

  18. 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

  19. 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

  20. 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

  1. Late Holocene rainforest disturbance in French Guiana.

    PubMed

    Ledru, M -P.

    2001-06-01

    Palm swamp forest sediments collected in French Guiana provide new data about late Holocene rainforest. Two cores were collected in 'Les Nouragues' ecological station (4 degrees 05'N, 52 degrees 40'W). The lithology shows two different types of sediment, organic peat in the upper part and oxidized clay with low organic content and lacking pollen in the lower part, both separated by a gravel horizon. Radiocarbon dates show that this gravel horizon could have been deposited between 4500 and 3000yrBP. Pollen analysis carried out on the organic sediments record rainforest disturbances between ca 1520-1380 and 1060-860cal yrBP suggested by the presence of the pioneer tree species Cecropia together with other shade intolerant genera. Cecropia is recorded for a period that lasts between 660 and 320 years. This abnormal duration for presence of a pioneer species in rainforest is explained by brief and repeated changes in the composition of the canopy asssociated to perturbations of the palm swamp.

  2. 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.

  3. 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.

  4. Persistence of ENSO-Like Climate Variability Throughout the Holocene

    NASA Astrophysics Data System (ADS)

    Asmerom, Y.; Polyak, V. J.; Rasmussen, J. B.; Burns, S. J.; Lachniet, M. S.

    2005-12-01

    The El Niño Southern Oscillation (ENSO) is a Pacific climate phenomenon with global climate teleconnections. Many aspects of the modern ENSO regime are unknown, and its persistence and modalities in the past are even less known. In continents, the main difficulty has been finding ENSO-sensitive proxies with near-annual resolution that are datable by isotopic techniques. Speleothems from ENSO-influenced regions, such as the Southwestern USA (SW), offer new opportunities. In the SW, El Niño years are typically wetter and La Niña years drier than normal. ENSO teleconnections with precipitation are especially strong when the SOI and NINO3 are out-of-phase during negative phases of the Pacific Decadal Oscillation (PDO) (1). Data from uranium-series dated late Holocene speleothems from southern New Mexico and an early Holocene-Pleistocene speleothem from the Grand Canyon (Arizona) are used to investigate ENSO variability during the Pleistocene-early Holocene as compared to the Late Holocene. It has been previously suggested that frequency and magnitude of ENSO has changed since the early Holocene (e.g. 2). Our data consist of growth thickness variations of annual bands for the late Holocene and gray scale and stable isotopic data for the early Holocene and the Pleistocene-Holocene transition. Previously we had demonstrated that growth thickness in our annually-banded speleothems is related to precipitation (3). Gray scale in our Grand Canyon speleothem is well-correlated with δ18O isotopic values (R = -0.63). Dark bands, which we interpret to represent arid years, correlate with high δ18O values. Multiple-taper spectral (MTM) and wavelet analyses of the late Holocene data show statistically significant (above 90% confidence) peaks at interannual (2-6 yr) timescales in addition to decadal and centennial frequencies throughout the record, which we suggest represent PDO and solar modulators. The prominent interannual frequencies in our datalikely reflect the

  5. 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.

  6. Evaluation of Holocene pollen records from the Romanian Plain.

    PubMed

    Tomescu

    2000-05-01

    This study is a critical review of pollen analyses carried out on Holocene sequences from 15 sites in and near the Romanian Plain. Three sites come from natural sediments, 10 sites are from anthropogenic deposits and two are from both anthropogenic and natural settings. The general reconstruction is of a steppe-forest-steppe vegetation through the Holocene. The nature of the deposits, however, casts doubts on this reconstruction. Deposits of archaeological sites generally yield pollen spectra that are influenced by human activities and thus unsuitable for vegetation reconstructions. Loess deposits are also unfavorable for pollen preservation because of high pH and porosity. Consequently, pollen spectra from loess deposits are strongly biased by selective pollen destruction. Research and experiments carried out by several authors suggest that spectra dominated by Asteraceae, Poaceae, Chenopodiaceae or Pinus pollen in soils and loess are a result of selective pollen destruction, especially if low pollen concentrations, progressive pollen deterioration or high frequencies of deteriorated or unidentifiable pollen are evidenced. The fact that pollen records from the Romanian Plain come from loess, alkaline peat or archaeological sites reduces their reliability for reconstructions of vegetation. The vegetation history of similar regions in Hungary, Bulgaria and Turkey suggests that early Holocene steppe vegetation was gradually replaced by forest or forest-steppe vegetation in the late Holocene. Records from lake sediments are required to find out whether the Holocene vegetation history of the Romanian Plain was similar.

  7. Seawater isotope constraints on tropical hydrology during the Holocene

    NASA Astrophysics Data System (ADS)

    Oppo, Delia W.; Schmidt, Gavin A.; LeGrande, Allegra N.

    2007-07-01

    Paleoceanographic data from the low latitude Pacific Ocean provides evidence of changes in the freshwater budget and redistribution of freshwater within the basin during the Holocene. Reconstructed Holocene seawater δ 18O changes compare favorably to differences predicted between climate simulations for the middle Holocene (MH) and for the pre-Industrial late Holocene (LH). The model simulations demonstrate that changes in the tropical hydrologic cycle affect the relationship between δ 18Osw and surface salinity, and allow, for the first time, quantitative estimates of western Pacific salinity change during the Holocene. The simulations suggest that during the MH, the mean salinity of the Pacific was higher because less water vapor was transported from the Atlantic Ocean and more was transported to the Indian Ocean. The salinity of the western Pacific was enhanced further due both to the greater advection of salt to the region by ocean currents and to an increase in continental precipitation at the expense of maritime precipitation, the latter a consequence of the stronger Asian summer monsoon.

  8. 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.

  9. 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.

  10. '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.

  11. 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.

  12. Holocene changes in eastern equatorial Atlantic salinity as estimated by water isotopologues

    NASA Astrophysics Data System (ADS)

    Leduc, G.; Sachs, J. P.; Kawka, O.; Schneider, R. R.

    2011-12-01

    last 7 ka (Vincens et al., 2010). Regardless of the uncertainties associated with the influence of salinity on lipid δD values and/or long-term changes in tropical Africa deuterium excess in rainfall, salinity estimates derived from combining δ18Osw and alkenone δD suggest that the decreases seen in both oxygen and hydrogen stable isotope ratios in our marine sediment core are not due to increased precipitation from the surrounding continent during the late Holocene. Those isotopic trends have striking counterparts in late Holocene δ18O trends observed in most of Chinese speleothem records (Dykoski et al., 2003; Wang et al., 2005), suggesting that they are due to fractionation processes affecting water vapour in monsoon regions over the last 2 millennia. We suggest that future efforts should be devoted to identifying the factors likely involved in shaping long-term isotopic trends recorded in precipitation records from monsoon regions. Dykoski, C.A., et al., 2005. Earth Planet. Sci. Lett. 233, 71-86. LeGrande, A.N. and Schmidt, G.A., 2011. Paleoceanography, doi :1029/2010PA002043, in press. Rohling, E.J., 2007. Paleoceanography 22, PA3215, doi:10.1029/2007PA001437. Vincens, A., et al., 2010. Clim. Past 6, 281-294. Wang, Y.J., et al., 2005. Science 308, 854-857. Weldeab, S., et al., 2007. Science 316, 1303-1307.

  13. 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.

  14. Submarine cementation patterns of Holocene reefs provide models for porosity development in ancient reef reservoirs

    SciTech Connect

    Lighty, R.G.

    1983-03-01

    An understanding of processes of formation and postdepositional alteration of Holocene carbonate buildups can aid the explorationist in locating and predicting reservoir facies in subsurface analogs. In the subsurface, ancient shelf-edge reefs may contain primary porosity that has escaped shallow subsurface cementation. This preserved primary porosity is commonly enhanced later by carbonate dissolution associated with widespread subsurface fluid migration and/or dissolution fronts along permeable stylolite zones. Therefore, given a burial history of continued subsidence, knowledge of early submarine cementation patterns is important for understanding reef facies distribution of late subsurface diagenesis.

  15. 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.

    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.

  16. Analysis of a Large Rock Slope Failure on the East Wall of the LAB Chrysotile Mine in Canada: Back Analysis, Impact of Water Infilling and Mining Activity

    NASA Astrophysics Data System (ADS)

    Grenon, Martin; Caudal, Philippe; Amoushahi, Sina; Turmel, Dominique; Locat, Jacques

    2017-02-01

    A major mining slope failure occurred in July 2012 on the East wall of the LAB Chrysotile mine in Canada. The major consequence of this failure was the loss of the local highway (Road 112), the main commercial link between the region and the Northeast USA. LiDAR scanning and subsequent analyses were performed and enabled quantifying the geometry and kinematics of the failure area. Using this information, this paper presents the back analysis of the July 2012 failure. The analyses are performed using deterministic and probabilistic limit equilibrium analysis and finite-element shear strength reduction analysis modelling. The impact of pit water infilling on the slope stability is investigated. The impact of the mining activity in 2011 in the lower part of the slope is also investigated through a parametric analysis.

  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. Upper Ocean Variability in the Indo-Pacific Warm Pool during the Late Holocene, Early Holocene and Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Xu, J.; Kuhnt, W.; Holbourn, A. E.; Andersen, N.

    2009-12-01

    We analyzed oxygen isotopes and Mg/Ca ratios in the surface dwelling planktonic foraminifer Globigerinoides ruber (white s.s.) and the thermocline dweller Pulleniatina obliquiloculata to improve understanding of upper ocean spatial variability in the Indo-Pacific Warm Pool (IPWP). We focused on three critical time intervals: the Last Glacial Maximum (LGM; 18-21.5 ka), the early Holocene (8-9 ka) and the late Holocene (0-2 ka). Our records from twenty-four stations in the South China Sea, Timor Sea, Indonesian seas and western Pacific indicate overall dry and cool conditions in the IPWP during the LGM with a low thermal gradient between surface and thermocline waters. Warm surface waters (>28 Celsius degree) spread over the entire region during the early Holocene, indicating substantial expansion of the IPWP. However in the eastern Indian Ocean (Timor Sea), the thermocline gradually shoaled from the LGM to early Holocene, reflecting intensification of the subsurface Indonesian Throughflow. Increased precipitation over the South China Sea appears related to an intensified summer monsoon and northward displacement of the Intertropical Convergence Zone. Increased freshwater export from the South China Sea through the Java Sea also contributed to a change in the vertical structure of the Indonesian Throughflow from surface- to thermocline-dominated flow and a freshening of Timor Sea waters during the early Holocene.

  20. 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

  1. 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

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

    PubMed

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

    2013-09-03

    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.

  3. 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.

  4. 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.

  5. 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.

  6. 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

  7. Historical Land Cover Change during the Holocene: An Application of the UVic ESCM

    NASA Astrophysics Data System (ADS)

    Simmons, C. T.; Mysak, L. A.; Matthews, D.

    2013-12-01

    The University of Victoria Earth System Climate Model v. 2.9 (UVic ESCM) is used in this study to examine the role of anthropogenic land cover change (ALCC) in the Holocene carbon cycle. Three ALCC scenarios were developed by scaling data from Hyde 3.1 (Klein Goldewijk et al 2011). Additionally, we introduced a new parameterization of soil management and erosion associated with increased tillage and agricultural intensity into the model. The transient simulations, covering the period from 6000 B.C. to 2000 A.D., indicate that even very high anthropogenic land use fractions during the Neolithic and Bronze ages led to a small (3-5 ppm) contribution to atmospheric CO2 concentrations by 1 A.D., with a larger 10 ppm atmospheric CO2 increase obtained in the ALCC scenarios by the beginning of the Industrial Era. While only able to explain a small fraction of the pre-industrial CO2 trend, these figures are higher than in some previous studies. In addition, certain ALCC scenarios with lower per-capita land use in the mid-to-late Holocene had greater sedimentation than a simulation without ALCC, implying that more moderate deforestation scenarios may stimulate a decrease in ocean alkalinity rather than the expected increase. In addition, our results with the original Hyde 3.1 database suggest that lower per-capita land use could stimulate greater deep water formation in the North Atlantic and a relatively large (+0.10°C) increase in global temperatures by 1 A.D. This process reduced oceanic uptake of atmospheric CO2 in our simulations. Overall, however, all simulations indicate that a decrease in ocean alkalinity from other processes would be necessary to reduce the oceanic sink for the ALCC release and to promote an increase in atmospheric CO2 during the mid-to-late Holocene.

  8. 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

  9. Holocene Sea-Level Database For The Caribbean Region

    NASA Astrophysics Data System (ADS)

    Khan, N. S.; Horton, B.; Engelhart, S. E.; Peltier, W. R.; Scatena, F. N.; Vane, C. H.; Liu, S.

    2013-12-01

    Holocene relative sea-level (RSL) records from far-field locations are important for understanding the driving mechanisms controlling the nature and timing of the mid-late Holocene reduction in global meltwaters and providing background rates of late Holocene RSL change with which to compare the magnitude of 20th century RSL rise. The Caribbean region has traditionally been considered far-field (i.e., with negligible glacio-isostatic adjustment (GIA) influence), although recent investigations indicate otherwise. Here, we consider the spatial variability in glacio-isostatic, tectonic and local contributions on RSL records from the circum-Caribbean region to infer a Holocene eustatic sea-level signal. We have constructed a database of quality-controlled, spatially comprehensive, Holocene RSL observations for the circum-Caribbean region. The database contains over 500 index points, which locate the position of RSL in time and space. The database incorporates sea-level observations from a latitudinal range of 5°N to 25°N and longitudinal range of 55°W to 90°W. We include sea-level observations from 11 ka BP to present, although the majority of the index points in the database are younger than 8 ka BP. The database is sub-divided into 13 regions based on the distance from the former Laurentide Ice Sheet and regional tectonic setting. The index points were primarily derived from mangrove peat deposits, which in the Caribbean form in the upper half of the tidal range, and corals (predominantly Acropora palmata), the growth of which is constrained to the upper 5 m of water depth. The index points are classified on the basis of their susceptibility to compaction (e.g., intercalated, basal). The influence of temporal changes in tidal range on index points is also considered. The sea-level reconstructions demonstrate that RSL did not exceed the present height (0 m) during the Holocene in the majority of locations, except at sites in Suriname/Guayana and possibly Trinidad

  10. Holocene climate variability and oceanographic changes off western South Africa

    NASA Astrophysics Data System (ADS)

    Zhao, Xueqin; Dupont, Lydie; E Meadows, Michael; Schefuß, Enno; Bouimetarhan, Ilham; Wefer, Gerold

    2017-04-01

    South Africa is located at a critical transition zone between subtropical and warm-temperate climate zones influenced by the Indian and Atlantic oceans. Presently, the seasonal changes of atmospheric and oceanic systems induce a pronounced rainfall seasonality comprised of two different rainfall zones over South Africa. How did this seasonality develop during the Holocene? To obtain a better understanding of how South African climates have evolved during the Holocene, we conduct a comprehensive spatial-temporal approach including pollen and dinoflagellate cyst records from marine sediment samples retrieved from the Namaqualand mudbelt, a Holocene terrigenous mud deposit on the shelf of western South Africa. The representation of different vegetation communities in western South Africa is assessed through pollen analysis of surface sediments. This approach allows for climate reconstructions of the summer rainfall zone (SRZ) using Group 1 (Poaceae, Cyperaceae, Phragmites-type and Typha) and winter rainfall zone (WRZ) using Group 2 (Restionaceae, Ericaceae, Anthospermum, Stoebe/Elytropappus-type, Cliffortia, Passerina, Artemisia-type and Pentzia-type) from a single marine archive. The fossil pollen data from gravity core GeoB8331-4 indicate contrasting climate patterns in the SRZ and WRZ especially during the early and middle Holocene. The rainfall amount in the SRZ is dominated by insolation forcing, while in the WRZ it is mainly attributed to the latitudinal position of the southern westerlies. Dinoflagellate cyst data show significantly different oceanographic conditions associated with climate changes on land. High percentages of autotrophic taxa like Operculodinium centrocarpum and Spiniferites spp. indicate warm and stratified conditions during the early Holocene, suggesting reduced upwelling. In contrast, the middle Holocene is characterized by a strong increase in heterotrophic taxa in particular Lejeunecysta paratenella and Echinidinium spp., indicating cool

  11. 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.

  12. Zoonotic parasites associated with felines from the Patagonian Holocene.

    PubMed

    Fugassa, Martín Horacio; Beltrame, María Ornela; Bayer, María S; Sardella, Norma Haydée

    2009-12-01

    Feline coprolites were examined for parasites with the aim of studying ancient infections that occurred in the Patagonian region during the Holocene period. Eggs compatible to Trichuris sp., Calodium sp., Eucoleus sp., Nematodirus sp., Oesophagostomum sp. (Nematoda), Monoecocestus sp. (Cestoda) and Eimeria macusaniensis (Coccidia) were recovered from faecal samples. The results obtained from the analysis provide evidence of consumption by felids of the viscera of both rodents and camelids. This knowledge allows for improved explanations as to the distribution of parasitism and its significance to the health of humans and animals inhabiting the area under study during the Middle Holocene.

  13. Holocene Millennial-Scale Climate Variability in Western North America

    NASA Astrophysics Data System (ADS)

    Fawcett, P. J.; Castiglia, P. J.; Meyer, G. A.; Armour, J.

    2002-12-01

    We compare several high-resolution paleoclimatic records from western North America that indicate near-synchronous millennial-scale climate variability through much of the Holocene. A Holocene pluvial lake system in northern Chihuahua, Mexico alternates between lake highstands representing cooler and wetter conditions and dry playa conditions representing warmer, drier climates. Alpine lakes and bogs from the Sangre de Cristo Mountains of northern New Mexico record a series of glacial and periglacial events (colder, effectively wetter climates) that alternate with warmer, drier climates over the late Pleistocene and the Holocene. Forest fire-related sedimentation and alluvial activity from northeast Yellowstone National Park also shows a clear response to millennial-scale climate change during the Holocene. Pulses of fire-related debris flow activity occur during warmer, drier periods that are more prone to droughts. These alternate with cooler, effectively wetter conditions that produce more river discharge and form broad flood plains later preserved as terraces. Pluvial lake highstands in northern Mexico are centered at the following calendar ages: 230 yr B.P., 4.2 ka, 7.4 ka, and 9.3 ka. The northern New Mexico chronology shows cold, effectively wetter climates at the following calendar age midpoints: 200 yr B.P., 3.0 ka, 3.9 ka and 5.7 ka. The Yellowstone chronology shows cold, effectively wetter climates during the following age ranges: 300 to 600 yr B.P., 1.4 to 1.6 ka, 2.8 to 3.1 ka, 3.9 to 4.3 ka, and 5.5 to 6.0 ka. In the Rocky Mountain records, the millennial-scale events are more prominent during the late Holocene Neoglacial interval than during the early to middle Holocene. These climate events in western North America reflect widespread temperature anomalies and to a lesser extent, precipitation anomalies. The cold phases of these events correlate with a North Atlantic record of ice-rafting and cool events (Bond et al., 2001) and suggest that

  14. Holocene sand shoals offshore of Mississippi River delta plain, Louisiana

    SciTech Connect

    Penland, S.; McBride, R.A. ); Suter, J.R. ); Williams, S.J. ); Kindinger, J.L. ); Boyd, R. )

    1989-09-01

    Offshore of the Mississippi River delta plain lies a series of Holocene sand shoals marking the position of ancient submerged shorelines. These ancient shorelines represent stillstand positions during which the Holocene transgression drove sea level across the former lowstand subaerial erosion surface of the Mississippi River delta plain. Short periods of rapid sea level rise led to the transgressive submergence of these sandy shorelines. Two shoreline trends can be recognized at the {minus}10-m and {minus}20-m isobaths on the continental shelf.

  15. The Holocene perspective of Northern Hemisphere temperature evolution

    NASA Astrophysics Data System (ADS)

    Lohmann, G.; Laepple, T.

    2009-04-01

    The average surface air temperature of the globe has increased by about 0.5°C since the middle of the nineteenth century. Regarding the climate changes observed during the 20th century, it is of particular importance to identify and quantify the environmental changes to put the recent warming in relationship with the natural climate variations at different timescales. Considering the relatively short period of the available instrumental data, the use of paleoclimate records in combination with model simulations proves to be very useful for the estimation of past climate variability. Here we analyse the Holocene temperature evolution of the past 6000 years as well as the recent and projected future climate evolution. For our analysis, we use the output of an ensemble of general circulation models for the mid-Holocene (PMIP II project) and for recent and projected future (CMIP 3 project), complemented by transient simulations over the mid-to-late Holocene. The model data are also compared to observations and proxy data. The general structure of the Northern Hemisphere appears to have a "Hockey Stick" shape: The Northern Hemisphere cooling during the mid-to-late Holocene (neoglaciation) has been partly compensated during the past century. The reason for the Holocene trend lies in the astronomical forcing in conjunction with climate feedbacks whereas the recent and projected future warming trend can be attributed to anthropogenic influence on greenhouse gas concentrations in the atmosphere plus climate feedbacks. It is important to detect regional differences: At low latitudes and over large parts of the open ocean, the present climate is already warmer than that of the mid-Holocene during boreal summer, whereas at mid and high latitudes (especially over land and parts of the Arctic Ocean) the mid-Holocene values will be reached within the next 20-80 years. Seasonality and regional circulation and temperature anomalies are discussed. It is argued that the Holocene

  16. 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

  17. 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

  18. 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

  19. 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

  20. 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

  1. A Holocene sea-level database for Southeast Asia

    NASA Astrophysics Data System (ADS)

    Bender, Maren; Mann, Thomas; Stocchi, Paolo; Switzer, Adam; Horton, Benjamin P.; Lukman, Muhammad; Jompa, Jamaluddin; Rovere, Alessio

    2017-04-01

    The study of former relative sea-level (RSL) changes is essential to disentangle changes in sea level due to vertical land motion (e.g. tectonics, Glacial Isostatic Adjustment - GIA) and eustatic (e.g. ice equivalent sea level) causes. To study RSL changes at a regional scale it is essential that databases of sea-level indicators are produced following standardized protocols (Hijma et al., 2015). This has been already done in several regions (e.g. the US Atlantic coast, the Caribbean, or the Mediterranean (Engelhart and Horton, 2012) A database has been compiled for Southeast Asia but was limited in geographical extent and didn't include the influence of local process such as tidal range changes and compaction. Southeast Asia is highly vulnerable to relative sea level changes, as it is characterized by low-lying, densely populated islands and subsiding deltas. We present a database of Holocene sea-level histories in Southeast Asia and part of the Indo-Pacific from published and unpublished data, which has been evaluated and using a standardized protocol. We analyzed 526 sea level index points, defining their locations the height of former sea level and the age with their associated uncertainty. Radiocarbon ages were re-calibrated using Calib 7.0.0 / 7.1 (Stuiver et al., 2017) and the calibration curves Intcal13 or Marine13. In our database, we also indicated possible tectonic vertical land motion, and we present the results of GIA modelling for different areas in SE Asia. We also show regions of South East Asia and parts of the Indo-Pacific where there is an absence of data and where the collection of new RSL data is mostly needed.

  2. 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.

  3. Conceptual framework for assessing the response of delta channel networks to Holocene sea level rise

    NASA Astrophysics Data System (ADS)

    Jerolmack, Douglas J.

    2009-08-01

    Recent research has identified two fundamental unit processes that build delta distributary channels. The first is mouth-bar deposition at the shoreline and subsequent channel bifurcation, which is driven by progradation of the shoreline; the second is avulsion to a new channel, a result of aggradation of the delta topset. The former creates relatively small, branching networks such as Wax Lake Delta; the latter generates relatively few, long distributaries such as the Mississippi and Atchafalaya channels on the Mississippi Delta. The relative rate of progradation to aggradation, and hence the creation of accommodation space, emerges as a controlling parameter on channel network form. Field and experimental research has identified sea level as the dominant control on Holocene delta growth worldwide, and has empirically linked channel network changes to changes in the rate of sea level rise. Here I outline a simple modeling framework for distributary network evolution, and use this to explore large-scale changes in Holocene channel pattern that have been observed in deltas such as the Rhine-Meuse and Mississippi. Rapid early- to mid-Holocene sea level rise forced many deltas into an aggradational mode, where I hypothesize that avulsion and the generation of large-scale branches should dominate. Slowing of sea level rise in the last ˜6000 yr allowed partitioning of sediment into progradation, facilitating the growth of smaller-scale distributary trees at the shorelines of some deltas, and a reduction in the number of large-scale branches. Significant antecedent topography modulates delta response; the filling of large incised valleys, for example, caused many deltas to bypass the aggradational phase. Human effects on deltas can be cast in terms of geologic controls affecting accommodation: constriction of channels forces rapid local progradation and mouth-bar bifurcation, while accelerated sea level rise increases aggradation and induces more frequent channel

  4. Assessing Holocene water level changes of Lake Turkana, Kenya with potential linkages to monsoon variability

    NASA Astrophysics Data System (ADS)

    Bloszies, C.; Forman, S. L.; Wright, D. K.

    2012-12-01

    This study focuses on better defining water level variability in the past 10 ka for Lake Turkana, Kenya. The water level of Lake Turkana was approximately 90m higher than today ca. 8 ka years ago, and in the past century lake levels have varied by up to 15 m. Lake level is especially sensitive to shifts in water balance with changes in regional rainfall linked to the relative strength of the Indian Ocean Monsoon. Variations in monsoonal precipitation in Kenya may be controlled by distinct modes of the Indian Ocean Dipole, with one mode associated with increased sea surface temperatures and concomitant heavy rainfall in the Turkana basin, and the other mode resulting in low precipitation. Well preserved beach ridges up to 90 m above present water level occur around the lake representing a record of varying elevations of lake level still-stands during the Holocene. Along this prograded strand plain there is evidence of a shift in human subsistence from fishing villages to pastoral encampments, possibly associated with pronounced mid-Holocene drying and a precipitous (>30 m) fall in lake level ca. between 7 and 5 ka. However, a recent GPS campaign of beach ridges on the east and west sides of the lake reveal variability in highstand beach ridge elevations, implying deferential tectonic deformation across the basin and possible crustal warping due to hydroisostatic processes. Radiocarbon dating of aquatic shells will resolve the ages of beach ridges and these ages will be tested by direct dating of littoral quartz grains by OSL. Stratigraphic exposures of this littoral system reveal new evidence for lake still-stands, transgressions and regressions. Ultimately, the data will constrain a basin hydrologic model to assess the catchment changes and evaporative conditions required to yield the tens of meters of lake level change in the Holocene and provide new insights into the magnitude and linkage to monsoon variability.

  5. A paleo-perspective on ocean heat content: Lessons from the Holocene and Common Era

    NASA Astrophysics Data System (ADS)

    Rosenthal, Yair; Kalansky, Julie; Morley, Audrey; Linsley, Braddock

    2017-01-01

    The ocean constitutes the largest heat reservoir in the Earth's energy budget and thus exerts a major influence on its climate. Instrumental observations show an increase in ocean heat content (OHC) associated with the increase in greenhouse emissions. Here we review proxy records of intermediate water temperatures from sediment cores and corals in the equatorial Pacific and northeastern Atlantic Oceans, spanning 10,000 years beyond the instrumental record. These records suggests that intermediate waters were 1.5-2 °C warmer during the Holocene Thermal Maximum than in the last century. Intermediate water masses cooled by 0.9 °C from the Medieval Climate Anomaly to the Little Ice Age. These changes are significantly larger than the temperature anomalies documented in the instrumental record. The implied large perturbations in OHC and Earth's energy budget are at odds with very small radiative forcing anomalies throughout the Holocene and Common Era. We suggest that even very small radiative perturbations can change the latitudinal temperature gradient and strongly affect prevailing atmospheric wind systems and hence air-sea heat exchange. These dynamic processes provide an efficient mechanism to amplify small changes in insolation into relatively large changes in OHC. Over long time periods the ocean's interior acts like a capacitor and builds up large (positive and negative) heat anomalies that can mitigate or amplify small radiative perturbations as seen in the Holocene trend and Common Era anomalies, respectively. Evidently the ocean's interior is more sensitive to small external forcings than the global surface ocean because of the high sensitivity of heat exchange in the high-latitudes to climate variations.

  6. 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.

  7. Climate controls on the Holocene development of a subarctic lake in northern Fennoscandia

    NASA Astrophysics Data System (ADS)

    Rantala, Marttiina V.; Luoto, Tomi P.; Weckström, Jan; Perga, Marie-Elodie; Rautio, Milla; Nevalainen, Liisa

    2015-10-01

    Climate exerts strong control over the functioning of northern freshwater ecosystems, yet their resilience and responses to climate forcing may vary. We examined postglacial development patterns in subarctic Lake Várddoaijávri to discern the impact of direct climate controls, catchment influence, and ontogenic processes on the ecological functioning of the lake over the Holocene. Subfossil diatom assemblages together with the elemental and stable isotopic (δ13C, δ15N) composition of sediment organic matter were used to examine climate-induced changes in the structure of the phototrophic community and transport of terrestrial organic matter from the catchment. Stable isotopic composition (δ13C, δ15N) of subfossil Cladocera (Crustacea) was further used to assess how the changes were reflected higher up the food web. The diatom assemblages and sediment geochemistry closely mirrored the established climate patterns of the Holocene, confirming the strong climate coupling evidenced by earlier studies from lakes across the circumpolar Arctic. Our record indicates overarching influence of moisture fluctuations, superimposing the impact of light limitation by terrestrial organic carbon and temperature-driven alterations to lake physical regimes, which have been emphasized by recent research. The millennial changes in humidity were reflected as shifting dominance between planktonic and benthic diatom life forms, related to changes in the depth of the water column, vertical mixing patterns, and underwater light conditions. Despite the marked regime shifts at the base of the food web, zooplankton carbon utilization was little changed over the Holocene, likely attributable to selective feeding strategies. Overall, our results propose that the projected increases in precipitation in high-latitude regions may have marked impact on the structure and functioning of aquatic communities in shallow subarctic lakes.

  8. 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.

  9. Biomass Stability during the Holocene in the Upper Midwest

    NASA Astrophysics Data System (ADS)

    Raiho, A.; McLachlan, J. S.; Paciorek, C. J.

    2016-12-01

    Paleoecological records have shown dramatic vegetation fluctuations in the Upper Midwest in response to changing climate over the Holocene. Such vegetation shifts have implications for the terrestrial carbon budget, but empirical reconstructions of the biomass consequences of vegetation shifts have not been previously developed. Here, we describe a new statistical model estimating changes in Midwestern biomass over the Holocene. We asked whether biomass was stable in the face of Holocene climate changes. There has been increasing evidence that climate-vegetation feedbacks make open forests unstable, and it has also been suggested that the stability of closed forests might be sensitive to changes in precipitation. Our statistical model estimates aboveground biomass based on fossil pollen data from 41 sites across the Upper Midwest. Biomass estimates in the model are calibrated against a Bayesian estimate of vegetation and biomass at time of settlement ( 1850) derived from Public Land Survey data. Leave one out cross validation of our model reproduced the observed biomass with high precision (R^2 = .713). Predictions back through the Holocene occurred at sites with good radiocarbon control spanning vegetation types. We define ecosystem stability as the relative change in biomass and calculate full posterior distributions of ecosystem stability based on 100 year estimates of aboveground biomass for the last 10,000 years. We found that over the last 10,000 years in the Upper Midwest that ecosystem stability is similar across ecosystems.

  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. Volcanic influence on centennial to millennial Holocene Greenland temperature change.

    PubMed

    Kobashi, Takuro; Menviel, Laurie; Jeltsch-Thömmes, Aurich; Vinther, Bo M; Box, Jason E; Muscheler, Raimund; Nakaegawa, Toshiyuki; Pfister, Patrik L; Döring, Michael; Leuenberger, Markus; Wanner, Heinz; Ohmura, Atsumu

    2017-05-03

    Solar variability has been hypothesized to be a major driver of North Atlantic millennial-scale climate variations through the Holocene along with orbitally induced insolation change. However, another important climate driver, volcanic forcing has generally been underestimated prior to the past 2,500 years partly owing to the lack of proper proxy temperature records. Here, we reconstruct seasonally unbiased and physically constrained Greenland Summit temperatures over the Holocene using argon and nitrogen isotopes within trapped air in a Greenland ice core (GISP2). We show that a series of volcanic eruptions through the Holocene played an important role in driving centennial to millennial-scale temperature changes in Greenland. The reconstructed Greenland temperature exhibits significant millennial correlations with K(+) and Na(+) ions in the GISP2 ice core (proxies for atmospheric circulation patterns), and δ(18)O of Oman and Chinese Dongge cave stalagmites (proxies for monsoon activity), indicating that the reconstructed temperature contains hemispheric signals. Climate model simulations forced with the volcanic forcing further suggest that a series of large volcanic eruptions induced hemispheric-wide centennial to millennial-scale variability through ocean/sea-ice feedbacks. Therefore, we conclude that volcanic activity played a critical role in driving centennial to millennial-scale Holocene temperature variability in Greenland and likely beyond.

  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. Mid-Holocene regional reorganization of climate variability

    NASA Astrophysics Data System (ADS)

    Wirtz, K. W.; Bernhardt, K.; Lohmann, G.; Lemmen, C.

    2009-04-01

    We integrate 130 globally distributed proxy time series to refine the understanding of climate variability during the Holocene. Cyclic anomalies and temporal trends in periodicity from the Lower to the Upper Holocene are extracted by combining Lomb-Scargle Fourier-transformed spectra with bootstrapping. Results were cross-checked by counting events in the time series. Main outcomes are: First, the propensity of the climate system to fluctuations is a region specific property. Many records of adjacent sites reveal a similar change in variability although they belong to different proxy types (e.g., δ18O, lithic composition). Secondly, at most sites, irreversible change occured in the Mid- Holocene. We suggest that altered ocean circulation together with slightly modified coupling intensity between regional climate subsystems around the 5.5 kyr BP event (termination of the African Humid Period) were responsible for the shift. Fluctuations especially intensified along a pan- American corridor. This may have led to an unequal crisis probability for early human civilizations in the Old and New World. Our study did not produce evidence for millennial scale cyclicity in some solar activity proxies for the Upper Holocene, nor for a privileged role of the prominent 250, 550, 900 and 1450 yr cycles. This lack of global periodicities corroborates the regional character of climate variability.

  14. Mid-Holocene regional reorganization of climate variability

    NASA Astrophysics Data System (ADS)

    Wirtz, K. W.; Bernhardt, K.; Lohmann, G.; Lemmen, C.

    2009-01-01

    We integrate 130 globally distributed proxy time series to refine the understanding of climate variability during the Holocene. Cyclic anomalies and temporal trends in periodicity from the Lower to the Upper Holocene are extracted by combining Lomb-Scargle Fourier-transformed spectra with bootstrapping. Results were cross-checked by counting events in the time series. Main outcomes are: First, the propensity of the climate system to fluctuations is a region specific property. Many records of adjacent sites reveal a similar change in variability although they belong to different proxy types (e.g., δ18O, lithic composition). Secondly, at most sites, irreversible change occured in the Mid-Holocene. We suggest that altered ocean circulation together with slightly modified coupling intensity between regional climate subsystems around the 5.5 kyr BP event (termination of the African Humid Period) were responsible for the shift. Fluctuations especially intensified along a pan-American corridor. This may have led to an unequal crisis probability for early human civilizations in the Old and New World. Our study did not produce evidence for millennial scale cyclicity in some solar activity proxies for the Upper Holocene, nor for a privileged role of the prominent 250, 550, 900 and 1450 yr cycles. This lack of global periodicities corroborates the regional character of climate variability.

  15. 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 speleo