Sample records for yr cal bp

  1. Climate forcing due to the 8200 cal yr BP event observed at Early Neolithic sites in the eastern Mediterranean

    NASA Astrophysics Data System (ADS)

    Weninger, Bernhard; Alram-Stern, Eva; Bauer, Eva; Clare, Lee; Danzeglocke, Uwe; Jöris, Olaf; Kubatzki, Claudia; Rollefson, Gary; Todorova, Henrieta; van Andel, Tjeerd

    2006-11-01

    We explore the hypothesis that the abrupt drainage of Laurentide lakes and associated rapid switch of the North Atlantic thermohaline circulation 8200 yr ago had a catastrophic influence on Neolithic civilisation in large parts of southeastern Europe, Anatolia, Cyprus, and the Near East. The event at 8200 cal yr BP is observed in a large number of high-resolution climate proxies in the Northern Hemisphere, and in many cases corresponds to markedly cold and arid conditions. We identify the relevant archaeological levels of major Neolithic settlements in Central Anatolia, Cyprus, Greece and Bulgaria, and examine published stratigraphic, architectural, cultural and geoarchaeological studies for these sites. The specific archaeological events and processes we observe at a number of these sites during the study interval 8400-8000 cal yr BP lead us to refine some previously established Neolithisation models. The introduction of farming to South-East Europe occurs in all study regions (Thrace, Macedonia, Thessaly, Bulgaria) near 8200 cal yr BP. We observe major disruptions of Neolithic cultures in the Levant, North Syria, South-East Anatolia, Central Anatolia and Cyprus, at the same time. We conclude that the 8200 cal yr BP aridity event triggered the spread of early farmers, by different routes, out of West Asia and the Near East into Greece and Bulgaria.

  2. Sedimentary Evidence for a Rapid Sea Level Rise at 7,600 cal yr BP from North-Central Cuba

    NASA Astrophysics Data System (ADS)

    Peros, M. C.; Agosta G'meiner, A. M.; Collins, S.

    2016-12-01

    A lack of high-resolution relative sea level (RSL) proxy data has meant that the pattern of early Holocene RSL change in the Caribbean is poorly understood. A RSL curve published by Toscano and Macintyre (2003) using inter-tidal mangrove peats and submerged corals suggests RSL underwent a relatively fast and `smooth' curvilinear increase during the Holocene. However, others, such as Blanchon and Shaw (1995), suggest that RSL increased rapidly at around 7600 cal yr BP, in response to the final stages of the melting of the Laurentide Ice Sheet (melt water pulse 1C or catastrophic rise event 3). We investigated this question using multi-proxy data from a flooded sinkhole (Cenote Jennifer) on the north coast of central Cuba. Cenote Jennifer is located 7 m above mean sea level and 2 km from the Bahamas Channel and appears to have a high degree of connectivity with the ocean through a network of underground caverns. The water depth is 13 m and the bottommost 5 m is anoxic. A sediment core collected from Cenote Jennifer was studied using loss-on-ignition, pollen analysis, high-resolution XRF core-scanning, and grain size analysis. An age-depth model was generated for the core by AMS dating. The results show that the bottommost stratigraphic unit ( 9000 to 7600 cal yr BP) is a fine-grained carbonate-rich mud (i.e., marl). This unit abruptly transitions into finely laminated organic-rich sediment from 7600 cal yr BP to the present. The pollen analysis shows that the sinkhole supported a cattail (Typha) community until 7600 cal yr BP, indicating low water levels ( 1 m). At 7600 cal yr BP, the cattail community disappeared and the vegetation of the surrounding bedrock became dominated by a thorny coastal scrubland. In addition, a 3 cm thick fining-upward siliciclastic unit is present immediately above the marl-organic contact, suggesting: 1) a marine sediment source given the limestone-dominated nature of the region, and 2) the presence of a short-duration, high

  3. Dietary shift after 3600 cal yr BP and its influencing factors in northwestern China: Evidence from stable isotopes

    NASA Astrophysics Data System (ADS)

    Ma, Minmin; Dong, Guanghui; Jia, Xin; Wang, Hui; Cui, Yifu; Chen, Fahu

    2016-08-01

    Human diets rely on natural resource availability and can reflect social and cultural values. When environments, societies, and cultures change, diets may also shift. This study traced the extent of dietary change and the factors influencing such change. Through stable carbon and nitrogen isotopic analysis of late Neolithic and early Bronze Age human and animal bone collagen, we found that significant shifts in human diets were closely associated with intercontinental cultural exchanges in Eurasia and climate change in northwestern China. The isotopic evidence indicated that human diets mainly consisted of C4 foodstuffs (presumably millet and/or animals fed with C4 foods) around 4000 calibrated years before the present (cal yr BP), corresponding to the flourishing of millet agriculture in the context of the optimal climate conditions of the mid-Holocene. Subsequently, more C3 foods (probably wheat, barley, and animals fed with C3 foods) were added to human diets post-3600 cal yr BP when the climate became cooler and drier. Such dietary variation is also consistent with the increasing intensity of long-distance exchange after 4000 cal yr BP. While many factors can lead to human dietary shifts (e.g. climate change, population growth, cultural factors, and human migration), climate may have been a key factor in Gansu and Qinghai.

  4. Dietary shift after 3600 cal yr BP and its influencing factors in northwestern China: Evidence from stable isotopes

    NASA Astrophysics Data System (ADS)

    Ma, Minmin; Dong, Guanghui; Jia, Xin; Wang, Hui; Cui, Yifu; Chen, Fahu

    2017-04-01

    :Human diets rely on natural resource availability and can reflect social and cultural values. When environments, societies, and cultures change, diets may also shift. This study traced the extent of dietary change and the factors influencing such change. Through stable carbon and nitrogen isotopic analysis of late Neolithic and early Bronze Age human and animal bone collagen, we found that significant shifts in human diets were closely associated with intercontinental cultural exchanges in Eurasia and climate change in northwestern China. The isotopic evidence indicated that human diets mainly consisted of C4 foodstuffs (presumably millet and/or animals fed with C4 foods) around 4000 calibrated years before the present (cal yr BP), corresponding to the flourishing of millet agriculture in the context of the optimal climate conditions of the mid-Holocene. Subsequently, more C3 foods (probably wheat, barley, and animals fed with C3 foods) were added to human diets post-3600 cal yr BP when the climate became cooler and drier. Such dietary variation is also consistent with the increasing intensity of long-distance exchange after 4000 cal yr BP. While many factors can lead to human dietary shifts (e.g. climate change, population growth, cultural factors, and human migration), climate may have been a key factor in Gansu and Qinghai.

  5. The late Holocene dry period: multiproxy evidence for an extended drought between 2800 and 1850 cal yr BP across the central Great Basin, USA

    USGS Publications Warehouse

    Mensing, Scott A.; Sharpe, Saxon E.; Tunno, Irene; Sada, Don W.; Thomas, Jim M.; Starratt, Scott W.; Smith, Jeremy

    2013-01-01

    Evidence of a multi-centennial scale dry period between ∼2800 and 1850 cal yr BP is documented by pollen, mollusks, diatoms, and sediment in spring sediments from Stonehouse Meadow in Spring Valley, eastern central Nevada, U.S. We refer to this period as the Late Holocene Dry Period. Based on sediment recovered, Stonehouse Meadow was either absent or severely restricted in size at ∼8000 cal yr BP. Beginning ∼7500 cal yr BP, the meadow became established and persisted to ∼3000 cal yr BP when it began to dry. Comparison of the timing of this late Holocene drought record to multiple records extending from the eastern Sierra Nevada across the central Great Basin to the Great Salt Lake support the interpretation that this dry period was regional. The beginning and ending dates vary among sites, but all sites record multiple centuries of dry climate between 2500 and 1900 cal yr BP. This duration makes it the longest persistent dry period within the late Holocene. In contrast, sites in the northern Great Basin record either no clear evidence of drought, or have wetter than average climate during this period, suggesting that the northern boundary between wet and dry climates may have been between about 40° and 42° N latitude. This dry in the southwest and wet in the northwest precipitation pattern across the Great Basin is supported by large-scale spatial climate pattern hypotheses involving ENSO, PDO, AMO, and the position of the Aleutian Low and North Pacific High, particularly during winter.

  6. Lateglacial vegetation dynamics in the eastern Baltic region between 14,500 and 11,400 cal yr BP: A complete record since the Bølling (GI-1e) to the Holocene

    NASA Astrophysics Data System (ADS)

    Veski, Siim; Amon, Leeli; Heinsalu, Atko; Reitalu, Triin; Saarse, Leili; Stivrins, Normunds; Vassiljev, Jüri

    2012-04-01

    This paper discusses a complete record of vegetation history since the Bølling (GI-1e) warming (14,500 cal yr BP) up to the Holocene in Latvia. To date, this is the only complete record of such age in the eastern Baltic area and the northernmost area for which Bølling records are present. Combining pollen evidence, pollen accumulation rates (PAR) and plant macrofossil data, we assess the local and regional vegetation development, and we attempt to separate the true Lateglacial vegetation signal by removing the obviously redeposited thermophilous pollen; however, we remove not only their signal, we discuss the possibilities of separating the redeposition signal of the so-called "local Lateglacial trees", pine and birch, by looking at their corrosion and degradation. The results show that the Bølling warming in the eastern Baltic area was a treeless tundra community consisting of the shrubs Betula nana, Dryas octopetala and Salix polaris. The Older Dryas cold spell is clearly recognised as a decline in the total concentration of plant macrofossils and PARs at between 14,200 and 13,500 cal yr BP. At 13,460 cal yr BP, the B. nana macrofossils disappear, and tree birch (Betula sect. Albae) appears, marking the start of tree birch forest. The presence of pine forest is confirmed by a variety of macrofossils, including bark, wood, needles and seeds, since 13,400 cal yr BP, at the same time at which pine stomata are found. The first identified pine stomata finds are associated with a Pinus PAR over 3000 grains cm-2 yr-1 and pine macrofossil finds with a Pinus PAR over 4000 grains cm-2 yr-1. During the warmest period of the GI-1a (Allerød) at 13,000-12,700 cal yr BP, a pine forest with deciduous trees (birch -Betula pendula and aspen -Populus tremula) developed in the study area. The Younger Dryas (GS-1) cooling strongly affected the floral composition in eastern Latvia. The PAR of the tree taxa declined abruptly from a maximum value at 12,700 to below 1000 grains cm-2

  7. Woody vegetation, fuel and fire track the melting of the Scandinavian ice-sheet before 9500 cal yr BP

    NASA Astrophysics Data System (ADS)

    Carcaillet, Christopher; Hörnberg, Greger; Zackrisson, Olle

    2012-11-01

    New studies indicate the presence of early Holocene ice-free areas far north in Scandinavia. Post-glacial fire and vegetation were investigated based on sedimentary charcoal and pollen from two small lakes in northern Sweden. Accumulation of organic sediment started around 10,900 and 9200 cal yr BP, showing that both lake valleys were ice-free extremely early given their northerly location. Fire events started after 9600 cal yr BP and became less common around the '8.2-ka event'. Woody vegetation provided fuel that contributed to fires. The first vegetation in our pollen record consisted of Hippophae, Dryas, grasses and sedges. Subsequently broadleaved trees (Betula, Salix) increased in abundance and later Pinus, Alnus, ferns and Lycopodium characterized the vegetation. Pollen from Larix, Picea and Malus were also found. The change in vegetation composition was synchronous with the decrease in lake-water pH in the region, indicating ecosystem-scale processes; this occurred during a period of net global and regional warming. The changes in fire frequency and vegetation appear independent of regional trends in precipitation. The reconstructed fire history and vegetation support the scenario of early ice-free areas far north in Scandinavia during early Holocene warming, creating favorable conditions for woody plants and wildfires.

  8. Circum-Mediterranean fire activity and climate changes during the mid Holocene environmental transition (8500-2500 cal yr BP)

    NASA Astrophysics Data System (ADS)

    Vannière, Boris; Power, Mitch J.; Roberts, Neil; Tinner, Willy; Carrión, José; Magny, Michel; Bartlein, Patrick

    2010-05-01

    In this contribution I will present a synthesis of mid- to late-Holocene fire activity from the Mediterranean basin and explore the linkages among fire, climate variability and seasonality, and people through several climatic and ecological transitions. Regional fire histories were created from 36 radiocarbon-dated sedimentary charcoal records, available from the Global Charcoal Database. During the mid-Holocene "Thermal Maximum", charcoal records from the northern Mediterranean suggest the region was more fire prone while records from the southern Mediterranean indicate a decrease in fire activity associated with wetter-than-present summers. A North-South partition at 40-43°N is apparent in the central and western Mediterranean. In the context of orbitally-induced summer insolation decrease, South Mediterranean wet conditions could be linked to the Afro-Asian summer monsoon which weakened after ca. 8000-6000 cal yr BP. Relatively abrupt changes in fire regime observed at ca. 5500-5000 cal yr BP may be associated to a threshold in this weakening influence of the orbitally-driven Afro-Asian monsoon strength. Charcoal records of past fire activity appear sensitive to both orbitally-forced climate changes and shorter lived excursions which may be related to cold events apparent in the North Atlantic record of ice-rafted debris. These results contradict former notions of gradual aridification of the entire region due to climatic forcing and/or human activities. In contrast, they suggest: 1) Teleconnections between the Mediterranean area and other climatic regions, in particular the North Atlantic and the low-latitude monsoon areas, influenced past fire regimes; 2) Gradual forcing, such as changes in orbital parameters, may have triggered more abrupt shifts in fire regime, either directly or indirectly through these teleconnections.

  9. The application of Flow Cytometry to the study of ancient agriculture: Evidence for Mesolithic farming in Northern Britain 7200 Cal yr BP.

    NASA Astrophysics Data System (ADS)

    Jones, Richard; Tennant, Richard; Hatton, Jackie; Lee, Rob; Love, John

    2017-04-01

    The onset of agriculture in the UK, (the Mesolithic-Neolithic transition 6000 - 5500 Cal yr BP), has commonly been viewed as the end point of a cultural and technological wave that began in Eastern Europe on the Hungarian Plain 7500 Cal yr BP. This view is not without its critics, due in part to the uncertainty regarding the timing and rate of expansion and the difficulty in identifying the point at which agriculture first arrived in a particular location. Evidence for potential 'episodes' of Mesolithic agricultural activity in the UK has been identified in the UK pollen record, but this data is very tentative. Cereal pollen is typically present in very low concentrations (requiring very large, time consuming counts) and differentiating early cereal pollen from local grasses is very problematic, particularly in areas where the local grasses were domesticated. We present a multi-proxy record from Mere Tarn (54°8'12.09" N 3°7'24.28"W), 2km from the Morecambe Bay coast in South Cumbria, UK; a region with a long history of human occupation extending back into the Palaeolithic. A lacustrine core spanning the Mesolithic and Neolithic has been analysed using a combination of 'traditional' pollen analysis, Flow Cytometry and ancient DNA (aDNA). Flow Cytometry is employed to increase the concentration of cereal type grains in a sample, whilst also providing a more 'targeted' sample for aDNA analysis. The results so far provide clear evidence for an early phase of 'Mesolithic' agriculture in the catchment, spanning only two centuries ( 7300 to 7100 Cal yr BP). This phase is characterised by the occurrence of large cereal type grains (> 38µm), evidence for woodland clearance and the expansion of key anthropogenic indicators such as P. lanceolata. It occurred over 1600 years before the main transition into permanent and intensive agriculture in the catchment, at a time of significant changes in regional climate and sea-level. The results from Mere Tarn provide the earliest

  10. Ostracode-based reconstruction from 23,300 to about 20,250 cal yr BP of climate, and paleohydrology of a groundwater-fed pond near St. Louis, Missouri

    USGS Publications Warehouse

    Curry, B.; Delorme, D.

    2003-01-01

    The water chemistry of a groundwater-fed sinkhole-pond near St. Louis, Missouri, and its associated climate during the last glaciation are reconstructed by comparison with autecological data of modern ostracodes from about 5,500 sites in Canada. A 4.8-m succession of fossiliferous sediment yielded ostracode assemblages that collectively are generally found today in ponds in North America including the species Cyclocypris ampla, C. laevis, Cypridopsis vidua, Candona crogmaniana, C. distincta, and C. ohioensis. Fossils of Picea needles and the ostracode Cyclocypris sharpei imply that best analog sites for the succession are in central to south-central Canada. The pond formed 23,300 ?? 400 cal yr BP when a sinkhole became plugged by a clay bed about 1 m thick. By about 20,250 cal yr BP, the pond had desiccated and was buried by loess. The sediment accumulation rate was about 0.18 cm/yr, and each sample interval (6 cm) represents a time slice of ???33 years. Data from this record provides the first fairly high resolution proxy record of the glacial paleoclimate of the mid-latitude of North America. The analog data indicate the water in the hydrologically-open spring-fed pond was less than 1 m deep. The paleoclimatic reconstructions imply gradually drier conditions and uniform, cool temperatures. The shallow water depth indicates that the temperature reconstruction is robust with mean annual temperatures (MATs) that ranged between 0.8 and 3.9??C, and mean July temperatures that ranged from 16.8 and 18.1??C. Other estimated climatic parameters include mean annual precipitation (MAP; 430 to 840 mm/yr), and moisture balance (P-E; -111 to 298 mm/yr). Compared to values measured today at St. Louis, the MAP was about 400 mm less, MAT about 10??C cooler, and P-E, about the same. These values are consistent with other published reconstructions based on modern analog analysis of fossil beetles and pollen, and paleothermometry based on amino acid racemization. The total dissolved

  11. Potential climatic mechanisms associated with the mega drought at 4200 cal yr BP: linking proxy data with modern climate analogues

    NASA Astrophysics Data System (ADS)

    Carter, V.; Shinker, J. J.

    2017-12-01

    Roughly 4200 years ago, a 150-year long mega drought occurred in the central Rocky Mountains, as indicated by pollen evidence from lake sediments from Long Lake, south-eastern Wyoming. However, pollen evidence does not record the climate mechanisms that caused the drought; they only provide evidence that the drought occurred. A modern climate analogue technique using North American Regional Reanalysis data was applied to the sedimentary data in order to identify possible synoptic and dynamic patterns that may have caused the mega drought at 4200 cal yr BP. Our results suggest warm and dry conditions were a result of anomalously higher-than-normal geopotential heights that were centred over the Great Plains beginning in the spring and persisting through the fall. Drought conditions during the growing seasons was the result of the anomalous high-pressure ridge, which suppressed moisture transport via the low level jet from the Gulf of Mexico, as well as brought in dry continental air from in the interior region of North America. The conditions associated with modern analogues offer a potential climate mechanism that caused the mega drought 4200 years ago, and likely led to the changes in vegetation composition as evidenced by the pollen record from Long Lake, Wyoming.

  12. A 12,000-Yr Pollen Record off Cape Hatteras: Pollen Sources and Mechanisms of Pollen Dispersion

    NASA Technical Reports Server (NTRS)

    Naughton, F.; Keigwin, L.; Peteet, D.; Costas, S.; Desprat, S.; Oliveira, D.; de Vernal, A.; Voelker, A.; Abrantes, F.

    2015-01-01

    Integrating both marine and terrestrial signals from the same sediment core is one of the primary challenges for understanding the role of ocean-atmosphere coupling throughout past climate changes. It is therefore vital to understand how the pollen signal of a given marine record reflects the vegetation changes of the neighboring continent. The comparison between the pollen record of marine core JPC32 (KNR178JPC32) and available terrestrial pollen sequences from eastern North America over the last 12,170 years indicates that the pollen signature off Cape Hatteras gives an integrated image of the regional vegetation encompassing the Pee Dee river, Chesapeake and Delaware hydrographic basins and is reliable in reconstructing the past climate of the adjacent continent. Extremely high quantities of pollen grains included in the marine sediments off Cape Hatteras were transferred from the continent to the sea, at intervals 10,100-8800 cal yr BP, 8300-7500 cal yr BP, 5800- 4300 cal yr BP and 2100-730 cal yr BP, during storm events favored by episodes of rapid sea-level rise in the eastern coast of US. In contrast, pollen grains export was reduced during 12,170-10,150 cal yr BP and 4200- 2200 cal yr BP, during episodes of intense continental dryness and slow sea level rise episodes or lowstands in the eastern coast of US. The near absence of reworked pollen grains in core JPC32 contrasts with the high quantity of reworked material in nearby but deeper located marine sites, suggesting that the JPC32 recordwas not affected by the DeepWestern Boundary Current (DWBC) since the end of the Younger Dryas and should be considered a key site for studying past climate changes in the western North Atlantic.

  13. Centennial and millennial-scale hydroclimate changes in northwestern Patagonia since 16,000 yr BP

    NASA Astrophysics Data System (ADS)

    Moreno, Patricio I.; Videla, Javiera

    2016-10-01

    We examine hydroclimate changes at centennial/millennial timescales since 16,000 yr BP in northwestern Patagonia based on the pollen and charcoal record from Lago El Salto, a small closed-basin lake located in the Chilean Lake District (41°38‧48.02″S, 73° 5‧48.42″W). We observe cold/wet conditions between 14,500-16,000 yr BP, followed by further cooling with increased precipitation until 13,000 yr BP, enhanced precipitation seasonality and/or variability between 11,600-13,000 yr BP, and an extended warm-and-dry interval between 7600 and 11,300 yr BP with peak paleofire activity. Colder-and-wetter than present conditions and muted paleofire activity prevail between 5300 and 7600 yr BP, followed by alternating cold/wet and centennial-scale warm/dry phases starting at 5300 yr BP with three conspicuous megadroughts since 2500 yr BP. The most recent megadrought occurred during the Medieval Climate Anomaly. We identify a cold reversal that spans the Antarctic Cold Reversal (ACR) and the Younger Dryas (YD) chrons with stronger-than-present westerly influence during the former and enhanced variability during the latter. These results extend the northern limit of strong cooling and increase in precipitation during the ACR and the southern limit of influence of strong hydrologic variations during the YD in terrestrial environments, suggesting an overlap in the spheres of influence of processes originating from southern and northern polar latitudes. An extended warm southern westerly wind (SWW)-minimum interval is evident between 7600 and 11,300 yr BP, followed by a rapid shift to cool-moist conditions between 5300 and 7600 yr BP brought by a mid-Holocene SWW maximum. Since then we observe centennial-scale hydroclimate variability, which has driven biodiversity and fire-regime shifts of evergreen temperate rainforests.

  14. Sediment record of environmental change at Lake Lop Nur (Xinjiang, NW China) from 13.0 to 5.6 cal ka BP

    NASA Astrophysics Data System (ADS)

    Wang, Jingzhong; Jia, Hongjuan

    2017-09-01

    Lake Lop Nur is located in the eastern part of the Tarim Basin in Xinjiang, northwestern China. A 220-cm-long sediment core was collected from the center of the ear-shaped depression forming the basin and dated with AMS14C. Grain size, total organic matter (TOC), total nitrogen (TN), and TOC/TN (C/N) analyses were used to reconstruct climatic conditions from 13.0 to 5.6 cal ka BP. The results showed five main climatic stages. Zone I (13.0-11.3 cal ka BP) was a wet-dry environment, whereas Zone II (11.3-8.9 cal ka BP) consisted of a primarily wet environment. Zone III (8.9-7.7 cal ka BP) was subdivided into Zone IIIa (8.9-8.2 cal ka BP) that indicated lake constriction and dry climate, and Zone IIIb (8.2-7.7 cal ka BP) in which the proxies indicated wet conditions. In Zone IV (7.7-6.6 cal ka BP), the climate presented a bit wet conditions. In Zone V (6.6-5.6 cal ka BP), abundant glauberite is present in the sediment and silt dominates the lithology; these results indicate the lake shrank and the overall climate was dry. Abrupt environmental events were also identified, including six dry events at 11.0, 10.5, 9.3, 8.6, 8.2, and 7.6 cal ka BP and one flood event from 7.8 to 7.7 cal ka BP in the Early-Middle Holocene.

  15. High resolution stable isotopes and elemental analysis on benthic foraminifera: a 4000 yr BP record from the ria de Muros (NW Spain)

    NASA Astrophysics Data System (ADS)

    Pena, L. D.; Francés, G.; Diz, P.; Nombela, M. A.; Alejo, I.

    2003-04-01

    Carbon and oxygen stable isotopes and ICP-OES elemental ratio concentrations (Mg/Ca, Sr/Ca, Ba/Ca) from core EUGC-3B (42 45.10'N; 9 02.23'W, at 38 m.b.s.l. and 410 cm length) were measured over monospecific benthic foraminiferal samples (Nonion fabum) ranging over the last 4500 yr BP. From the oldest analysed sample (289 cm) to the core top, stable isotopes signal shows that the whole record can be separated into 4 intervals lasting each of them about 1000 yr. The lowermost interval (4300-3000 yr BP) is characterized by relatively stable delta 18O values (mean 1.77 per mil). Delta 13C is relatively low except for a maximum around 3300 cal BP (-1.50 per mil). An abrupt decrease down to the minimum value in delta 13C (-4.41 per mil) is accomplished in approximately 200 yr. Mg/Ca and Ba/Ca match perfectly this event, both of them showing the respective maxima values. Sr/Ca has a very similar behaviour to that of delta 13C but with smoother fluctuations. We attribute high values of delta 13C, Sr/Ca and Ba/Ca to periods of enhanced coastal productivity, probably due to reinforced upwelling events in the region. According to Mg/Ca signal this reinforcement took place during a relatively warmer period. The most remarkable feature during the two next periods (3000-1900 yr BP and 1900-1000 yr BP) consists of a stepwise increase of delta 13C values punctuated by a sharp decrease at the end of each interval. All the remaining proxies exhibit a nearly constant trend over these intervals. Each period can be interpreted as a weak enhance of marine productivity that the system does not hold up and finally aborts. The most recent interval represents the establishment of current conditions in the coastal system. The most conspicuous event from this interval consists of an abrupt decrease of the delta 18O that lasted for 300 yr. This event could be correlated with the well recognized warm climatic event known as the Medieval Warm Period. However the Mg/Ca ratio does not show high

  16. Evidence of a prolonged drought ca. 4200 yr BP correlated with prehistoric settlement abandonment from the Gueldaman GLD1 Cave, N-Algeria

    NASA Astrophysics Data System (ADS)

    Ruan, J.; Kherbouche, F.; Genty, D.; Blamart, D.; Cheng, H.; Dewilde, F.; Hachi, S.; Edwards, L. R.; Régnier, E.; Michelot, J.-L.

    2015-07-01

    Middle Holocene cultures have been widely studied round the E-Mediterranean basin in the last 30 years and past cultural activities have been commonly linked with regional climate changes. However, in many cases such linkage is equivocal, in part due to existing climatic evidence that has been derived from areas outside the distribution of ancient settlements, leading to uncertainty from complex spatial heterogeneity in both climate and demography. A few high-resolution well-dated paleoclimate records were recently established using speleothems in the Central and E-Mediterranean basin, however, the scarcity of such records in the western part of the Mediterranean prevents us from correlating past climate evolutions across the basin and deciphering climate-culture relation at fine time scales. Here we report the first decadal-resolved Mid-Holocene climate proxy records from the W-Mediterranean basin based on the stable carbon and oxygen isotopes analyses of two U/Th dated stalagmites from the Gueldaman GLD1 Cave in N-Algeria. Comparison of our records with those from Italy and Israel reveals synchronous (multi) centennial dry phases centered at ca. 5600, ca. 5200 and ca. 4200 yr BP across the Mediterranean basin. New calibrated radiocarbon dating constrains reasonably well the age of rich anthropogenic deposits (e.g., faunal remains, pottery, charcoal) excavated inside the cave, which allows the comparison between in situ evidence of human occupation and of climate change. This approach shows that the timing of a prolonged drought at ca. 4400-3800 yr BP blankets the onset of cave abandonment shortly after ca. 4403 cal yr BP, supporting the hypothesis that a climate anomaly may have played a role in this cultural disruption.

  17. Evidence of a prolonged drought ca. 4200 yr BP correlated with prehistoric settlement abandonment from the Gueldaman GLD1 Cave, Northern Algeria

    NASA Astrophysics Data System (ADS)

    Ruan, J.; Kherbouche, F.; Genty, D.; Blamart, D.; Cheng, H.; Dewilde, F.; Hachi, S.; Edwards, R. L.; Régnier, E.; Michelot, J.-L.

    2016-01-01

    Middle Holocene cultures have been widely studied around the Eastern-Mediterranean basin in the last 30 years and past cultural activities have been commonly linked with regional climate changes. However, in many cases such linkage is equivocal, in part due to existing climatic evidence that has been derived from areas outside the distribution of ancient settlements, leading to uncertainty from complex spatial heterogeneity in both climate and demography. A few high-resolution well-dated paleoclimate records were recently established using speleothems in the Central and Eastern-Mediterranean basin, however, the scarcity of such records in the western part of the Mediterranean prevents us from correlating past climate evolutions across the basin and deciphering climate-culture relation at fine timescales. Here we report the first decadal-resolved Mid-Holocene climate proxy records from the Western-Mediterranean basin based on the stable carbon and oxygen isotopes analyses of two U/Th dated stalagmites from the Gueldaman GLD1 Cave in Northern Algeria. Comparison of our records with those from Italy and Israel reveals synchronous (multi) centennial dry phases centered at ca. 5600, ca. 5200 and ca. 4200 yr BP across the Mediterranean basin. New calibrated radiocarbon dating constrains reasonably well the age of rich anthropogenic deposits (e.g., faunal remains, pottery, charcoal) excavated inside the cave, which allows the comparison between in situ evidence of human occupation and of climate change. This approach shows that the timing of a prolonged drought at ca. 4400-3800 yr BP blankets the onset of cave abandonment shortly after ca. 4403 cal yr BP, supporting the hypothesis that a climate anomaly may have played a role in this cultural disruption.

  18. Great earthquakes of variable magnitude at the Cascadia subduction zone

    USGS Publications Warehouse

    Nelson, A.R.; Kelsey, H.M.; Witter, R.C.

    2006-01-01

    Comparison of histories of great earthquakes and accompanying tsunamis at eight coastal sites suggests plate-boundary ruptures of varying length, implying great earthquakes of variable magnitude at the Cascadia subduction zone. Inference of rupture length relies on degree of overlap on radiocarbon age ranges for earthquakes and tsunamis, and relative amounts of coseismic subsidence and heights of tsunamis. Written records of a tsunami in Japan provide the most conclusive evidence for rupture of much of the plate boundary during the earthquake of 26 January 1700. Cascadia stratigraphic evidence dating from about 1600??cal yr B.P., similar to that for the 1700 earthquake, implies a similarly long rupture with substantial subsidence and a high tsunami. Correlations are consistent with other long ruptures about 1350??cal yr B.P., 2500??cal yr B.P., 3400??cal yr B.P., 3800??cal yr B.P., 4400??cal yr B.P., and 4900??cal yr B.P. A rupture about 700-1100??cal yr B.P. was limited to the northern and central parts of the subduction zone, and a northern rupture about 2900??cal yr B.P. may have been similarly limited. Times of probable short ruptures in southern Cascadia include about 1100??cal yr B.P., 1700??cal yr B.P., 3200??cal yr B.P., 4200??cal yr B.P., 4600??cal yr B.P., and 4700??cal yr B.P. Rupture patterns suggest that the plate boundary in northern Cascadia usually breaks in long ruptures during the greatest earthquakes. Ruptures in southernmost Cascadia vary in length and recurrence intervals more than ruptures in northern Cascadia.

  19. Precipitation variability in the winter rainfall zone of South Africa during the last 1400 yr linked to the austral westerlies

    NASA Astrophysics Data System (ADS)

    Stager, J. C.; Mayewski, P. A.; White, J.; Chase, B. M.; Neumann, F. H.; Meadows, M. E.; King, C. D.; Dixon, D. A.

    2012-05-01

    The austral westerlies strongly influence precipitation and ocean circulation in the southern temperate zone, with important consequences for cultures and ecosystems. Global climate models anticipate poleward retreat of the austral westerlies with future warming, but the available paleoclimate records that might test these models have been limited to South America and New Zealand, are not fully consistent with each other and may be complicated by influences from other climatic factors. Here we present the first high-resolution diatom and sedimentological records from the winter rainfall region of South Africa, representing precipitation in the equatorward margin of the westerly wind belt during the last 1400 yr. Inferred rainfall was relatively high ∼1400-1200 cal yr BP, decreased until ∼950 cal yr BP, and rose notably through the Little Ice Age with pulses centred on ∼600, 530, 470, 330, 200, 90, and 20 cal yr BP. Synchronous fluctuations in Antarctic ice core chemistry strongly suggest that these variations were linked to changes in the westerlies. Equatorward drift of the westerlies during the wet periods may have influenced Atlantic meridional overturning circulation by restricting marine flow around the tip of Africa. Apparent inconsistencies among some aspects of records from South America, New Zealand and South Africa warn against the simplistic application of single records to the Southern Hemisphere as a whole. Nonetheless, these findings in general do support model projections of increasing aridity in the austral winter rainfall zones with future warming.

  20. Pollen-based biomes for Beringia 18,000, 6000 and 0 14C yr BP

    USGS Publications Warehouse

    Edwards, M.E.; Anderson, P.M.; Brubaker, L.B.; Ager, T.A.; Andreev, A.A.; Bigelow, N.H.; Cwynar, L.C.; Eisner, Wendy R.; Harrison, S.P.; Hu, F.-S.; Jolly, D.; Lozhkin, A.V.; MacDonald, G.M.; Mock, Cary J.; Ritchie, J.C.; Sher, A.V.; Spear, R.W.; Williams, J.W.; Yu, G.

    2000-01-01

    The objective biomization method developed by Prentice et al. (1996) for Europe was extended using modern pollen samples from Beringia and then applied to fossil pollen data to reconstruct palaeovegetation patterns at 6000 and 18,000 14C yr BP. The predicted modern distribution of tundra, taiga and cool conifer forests in Alaska and north-western Canada generally corresponds well to actual vegetation patterns, although sites in regions characterized today by a mosaic of forest and tundra vegetation tend to be preferentially assigned to tundra. Siberian larch forests are delimited less well, probably due to the extreme under-representation of Larix in pollen spectra. The biome distribution across Beringia at 6000 14C yr BP was broadly similar to today, with little change in the northern forest limit, except for a possible northward-advance in the Mackenzie delta region. The western forest limit in Alaska was probably east of its modern position. At 18,000 14C yr BP the whole of Beringia was covered by tundra. However, the importance of the various plant functional types varied from site to site, supporting the idea that the vegetation cover was a mosaic of different tundra types.

  1. Influence of Monsoon variations on ecosystem changes on the Central Tibetan Plateau during the last 24 ka cal BP (Invited)

    NASA Astrophysics Data System (ADS)

    Kasper, T.; Haberzettl, T.; Zhu, L.; Maeusbacher, R.

    2013-12-01

    Lakes as archives of climate and environmental change are well known and well investigated all over the world, also in high mountain areas such as the Tibetan Plateau (TP) which is one of the most important key players in global climate circulation. Lake sediment records in this area, which were subject to lots of paleoenvironmental investigations, are mostly focused on the Holocene, often showing discontinuities due to desiccation or are located at the margin of the TP, such as Lake Qinghai. Here we present the first continuous lake sediment record from the southern central TP from Lake Nam Co, comprising ~24 ka cal BP, i.e., the LGM, the post-Glacial and the entire Holocene. The record reveals environmental changes with varying intensities. Extraordinary high sediment accumulation rates (SAR = 1.3 mm a-1) and quite large quantities of minerogenic input associated with the absence of ostracods during the LGM point to a small lake within a cold and dry environment. Around 19 ka cal BP reduced SAR (~0.3 mm a-1) and the occurrence of ostracods refer to a rising lake level in a moister environment. During the post-Glacial (~16 ka cal BP) changes in the geochemical composition of the sediments and a shift in the pollen composition suggests a change in summer precipitation and wind direction associated with a stronger Indian Ocean Summer Monsoon (IOSM). Major variations in the geochemical parameters between ~12.6 and ~11.6 ka cal BP may reflect the Younger Dryas climate oscillation of the Northern Hemisphere with cool and arid environmental conditions. The most striking hydrological variation within this record occurs at ~9.5 ka cal BP in the early Holocene. A rise in TOC points to enhanced bio-productivity within the lake and the catchment as well as to hampered decomposition of organic matter at the lake floor. Pollen composition refers to alpine meadow vegetation assemblages during this time. This may reflect moist and warm conditions probably associated with a

  2. A 3500 14C yr High-Resolution Record of Water-Level Changes in Lake Titicaca, Bolivia/Peru

    NASA Astrophysics Data System (ADS)

    Abbott, Mark B.; Binford, Michael W.; Brenner, Mark; Kelts, Kerry R.

    1997-03-01

    Sediment cores collected from the southern basin of Lake Titicaca (Bolivia/Peru) on a transect from 4.6 m above overflow level to 15.1 m below overflow level are used to identify a new century-scale chronology of Holocene lake-level variations. The results indicate that lithologic and geochemical analyses on a transect of cores can be used to identify and date century-scale lake-level changes. Detailed sedimentary analyses of subfacies and radiocarbon dating were conducted on four representative cores. A chronology based on 60 accelerator mass spectrometer radiocarbon measurements constrains the timing of water-level fluctuations. Two methods were used to estimate the 14C reservoir age. Both indicate that it has remained nearly constant at ˜250 14C yr during the late Holocene. Core studies based on lithology and geochemistry establish the timing and magnitude of five periods of low lake level, implying negative moisture balance for the northern Andean altiplano over the last 3500 cal yr. Between 3500 and 3350 cal yr B.P., a transition from massive, inorganic-clay facies to laminated organic-matter-rich silts in each of the four cores signals a water-level rise after a prolonged mid-Holocene dry phase. Evidence of other significant low lake levels occurs 2900-2800, 2400-2200, 2000-1700, and 900-500 cal yr B.P. Several of the low lake levels coincided with cultural changes in the region, including the collapse of the Tiwanaku civilization.

  3. Extension of the Southern Hemisphere Atmospheric Radiocarbon Curve, 2120-850 years BP: Results from Tasmanian Huon Pine

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Zimmerman, S R; P.Guilderson, T; Buckley, B M

    2010-02-12

    Decadal samples of dendrochronologically-dated pine (Lagorostrobos franklinii) from the Stanley River basin, Tasmania have been radiocarbon dated between 2120-850 yr BP. This data set overlaps and extends the current Southern Hemisphere record, which currently covers the period 110-995 yr BP. There is good agreement between the two records between 995-850 yr BP, between sample replicates and with consensus values for standards. As in the younger dataset, we find evidence for a distinct but variable offset between the southern hemisphere data and IntCal04; although this is likely due to real temporal variability in the interhemispheric offset, further work is planned tomore » rule out possible laboratory or sample preparation differences.« less

  4. Tundra Fires in the Noatak National Preserve, Northwestern Alaska, Since 6000 yr BP

    NASA Astrophysics Data System (ADS)

    Chipman, M. L.; Higuera, P. E.; Allen, J.; Rupp, S.; Hu, F. S.

    2008-12-01

    Over 1.7 million hectares of Alaskan tundra have burned over the past 50 years, including the record-setting Anaktuvuk River fire in 2007. Despite this evidence indicating the flammable nature of these ecosystems under warm and dry conditions, land managers and global change scientists lack critical information concerning long-term relationships among fire, climate and tundra vegetation. This knowledge gap limits the ability to assess the response of the tundra fire regime to ongoing and predicted climate warming and potential feedbacks with Earth systems. We utilize macroscopic charcoal from lake-sediment cores to characterize the frequency component of fire regimes in shrub-dominated and herb-dominated tundra ecosystems in northwestern Alaska over the past 6000 years. Here we present the first long-term records of tundra fire regimes from the Noatak National Preserve, a region encompassing some of the most flammable tundra in the state. Results from three lakes indicate that fire has been a consistent process in the region, with fire return intervals (FRIs) ranging from 70 to 800+ years since 6000 yr BP. FRIs were similar between herb- and shrub-dominated tundra sites before ~2000 yr BP, with a mean FRI of 167 yr (95% CI 145-195) Over the past ~2000 years, however, herb- dominated sites burned more frequently (mean FRI 112 yr [95% CI 80-151]) than shrub-dominated sites (mean FRI 247 yr [95% CI 141-377]). At millennial time scales, shifts in historic FRIs were likely related to regional climate changes and/or associated vegetation changes. These results provide a context for resource management and serve to refine the tundra component of an ecosystem model designed to aid land managers in assessing fuels and fire hazards in the context of climatic change.

  5. Rapid settlement of Majuro Atoll, central Pacific, following its emergence at 2000 years CalBP

    NASA Astrophysics Data System (ADS)

    Kayanne, Hajime; Yasukochi, Toru; Yamaguchi, Toru; Yamano, Hiroya; Yoneda, Minoru

    2011-10-01

    Atoll islands are areas of low, flat land, and the sustainability of habitable land in such environments is sensitive to even slight changes in sea level. The projected rise in sea level during this century may lead to the submergence of atoll islands and the widespread loss of habitable land. However, the actual time sequence of past sea level change, island emergence events, and human settlement of newly emerged islands remain poorly constrained. The results of geomorphological and archaeological surveys, combined with calibrated radiocarbon age dates, at Majuro Atoll, Marshall Islands, central Pacific, reveal that the emergence of the island, triggered by a fall in sea level, was quickly followed by human settlement. The elevation of the central body of the island exceeded high water level at 2000 years CalBP, and the complete formation of the island occurred within an interval of 100 years. The island was colonized by people shortly after emergence, at 2000 years CalBP, prior to the establishment of dense vegetation, and has been continuously settled since that time.

  6. Late Quaternary palaeoecological and palaeoclimatological reconstruction in the Gutaiului Mountains, northwest Romania

    NASA Astrophysics Data System (ADS)

    Feurdean, Angelica; Bennike, Ole

    2004-12-01

    Macrofossil, pollen, lithostratigraphy, mineral magnetic measurements (SIRM and magnetic susceptibility), loss-on-ignition, and AMS radiocarbon dating on sediments from two former crater lakes, situated at moderate altitudes in the Gutaiului Mountains of northwest Romania, allow reconstruction of Late Quaternary climate and environment. Shrubs and herbs with steppe and montane affinities along with stands of Betula and Pinus, colonised the surroundings of the sites prior to 14 700 cal. yr BP and the inferred climatic conditions were cold and dry. The gradual transition to open Pinus-Betula forests, slightly higher lake water temperatures, and higher lake productivity, indicate more stable environmental conditions between 14 700 and 14 100 cal. yr BP. This development was interrupted by cooler and drier climatic conditions between 14 100 and 13 800 cal. yr BP, as inferred from a reduction of open forests to patches, or stands, of Pinus, Betula, Larix, Salix and Populus. The expansion of a denser boreal forest, dominated by Picea, but including Pinus, Larix, Betula, Salix, and Ulmus started at 13 800 cal. yr BP, although the forest density seems to have been reduced between 13400 and 13200cal.yrBP. Air temperature and moisture availability gradually increased, but a change towards drier conditions is seen at 13400cal.yrBP. A distinct decrease in temperature and humidity between 12900 and 11500cal.yrBP led to a return of open vegetation, with patches of Betula, Larix, Salix, Pinus and Alnus and individuals of Picea. Macrofossils and pollen of aquatic plants indicate rising lake water temperatures and increased aquatic productivity already by ca. 11800cal.yrBP, 300 years earlier than documented by the terrestrial plant communities. At the onset of the Holocene, 11500cal.yrBP, forests dominated by Betula, Pinus and Larix expanded and were followed by dense Ulmus forests with Picea, Betula and Pinus at 11250cal.yrBP. Larix pollen was not found, but macrofossil evidence

  7. Funnel Beaker weather (6200-4900 cal BP) - reconstructed from the palaeolimnological record of synchronously deposited varves in northern Germany

    NASA Astrophysics Data System (ADS)

    Dreibrodt, Stefan; Zahrer, Jürgen; Brauer, Achim

    2013-04-01

    Depositional patterns of synchronously deposited varves of Lake Belauer See and Lake Poggensee (northern Germany) were studied on thin sections under the microscope comparatively. Events and trends that occurred synchronously in the lake systems were detected and interpret as limnologic responses to supra-regional extrinsic (climate) drivers. The different thresholds of the compared lake systems implied by different lake size were utilized to infer about weather conditions. For Lake Belauer See microfacies types of sub-recent varves were proved to reflect responses of certain meteorological conditions (e.g. severity of winters). A short weather anomaly at around 5950 cal BP was detected. Cold summers of about 40 successive years (probably with sudden frost events) lead to breaks of the thermal summer stratification and the associated carbonate precipitation. Instead renewed blooms of planctic diatoms occurred. The subsequent interval of the Funnel Beaker Culture seems to have experienced a period with favorable wea¬ther conditions, with warm summers and not extra-ordinary severe winters. Between ca. 5400 and 5340 cal BP an interval with pronounced warm winters is indicated. The favorable weather conditions termina¬ted abruptly at around 5275 cal BP when the weather (in particular summers) became colder. The comparison of the sediment sequences also provides evidence for the asynchronic onset of anthropogenic activity in the catchment areas of the lakes. A significant increase of minerogenic matter (quartz grains) indication soil erosion in the lake catchment started at ca. 3850 cal BC in Lake Poggensee, and at ca. 3500 cal BC in Lake Belau. Cycles of minerogenic input have been detected with duration of 20-25 years. Whether these cycles could represent slash and burn cycles has to be studied further.

  8. Relative sea-level data from southwest Scotland constrain meltwater-driven sea-level jumps prior to the 8.2 kyr BP event

    NASA Astrophysics Data System (ADS)

    Lawrence, Thomas; Long, Antony J.; Gehrels, W. Roland; Jackson, Luke P.; Smith, David E.

    2016-11-01

    The most significant climate cooling of the Holocene is centred on 8.2 kyr BP (the '8.2 event'). Its cause is widely attributed to an abrupt slowdown of the Atlantic Meridional Overturning Circulation (AMOC) associated with the sudden drainage of Laurentide proglacial Lakes Agassiz and Ojibway, but model simulations have difficulty reproducing the event with a single-pulse scenario of freshwater input. Several lines of evidence point to multiple episodes of freshwater release from the decaying Laurentide Ice Sheet (LIS) between ∼8900 and ∼8200 cal yr BP, yet the precise number, timing and magnitude of these events - critical constraints for AMOC simulations - are far from resolved. Here we present a high-resolution relative sea level (RSL) record for the period 8800 to 7800 cal yr BP developed from estuarine and salt-marsh deposits in SW Scotland. We find that RSL rose abruptly in three steps by 0.35 m, 0.7 m and 0.4 m (mean) at 8760-8640, 8595-8465, 8323-8218 cal yr BP respectively. The timing of these RSL steps correlate closely with short-lived events expressed in North Atlantic proxy climate and oceanographic records, providing evidence of at least three distinct episodes of enhanced meltwater discharge from the decaying LIS prior to the 8.2 event. Our observations can be used to test the fidelity of both climate and ice-sheet models in simulating abrupt change during the early Holocene.

  9. Precipitation variability in the winter rainfall zone of South Africa during the last 1400 yr linked to the austral westerlies

    NASA Astrophysics Data System (ADS)

    Stager, J. C.; Mayewski, P. A.; White, J.; Chase, B. M.; Neumann, F. H.; Meadows, M. E.; King, C. D.; Dixon, D. A.

    2011-12-01

    The austral westerlies strongly influence precipitation and ocean circulation in the southern temperate zone, with important consequences for cultures and ecosystems. Global climate models anticipate poleward contraction of the austral westerlies with future warming, but the available paleoclimate records that might test these models have been largely limited to South America, are not fully consistent with each other, and may be complicated by influences from other climatic factors. Here we present the first fine-interval diatom and sedimentological records from the winter rainfall region of South Africa, representing precipitation during the last 1400 yr. Inferred rainfall increased ~1400-1200 cal yr BP and most notably during the Little Ice Age with pulses centered on ~600, 530, 470, 330, 200, and 90 cal yr BP. Synchronous fluctuations in Antarctic ice core chemistry strongly suggest that these variations are linked to changes in the westerlies. Partial inconsistencies among South African and South American records warn against the simplistic application of local-scale histories to the Southern Hemisphere as a whole. Nonetheless, these findings in general do support model projections of increasing aridity in austral winter rainfall zones with future warming.

  10. Late Quaternary dynamics of forest vegetation on northern Vancouver Island, British Columbia, Canada

    NASA Astrophysics Data System (ADS)

    Lacourse, Terri

    2005-01-01

    Pollen analysis of radiocarbon-dated lake sediment from northern Vancouver Island, southwest British Columbia reveals regional changes in forest vegetation over the last 12,200 14C yr (14,900 cal yr). Between at least 12,200 and 11,700 14C yr BP (14,900-13,930 cal yr BP), open woodlands were dominated by Pinus contorta, Alnus crispa, and various ferns. As P. contorta decreased in abundance, Alnus rubra and more shade-tolerant conifers (i.e., Picea and Tsuga mertensiana) increased. Increases in T. mertensiana, P. contorta, and A. crispa pollen accumulation rates (PARs) between 10,600 and 10,400 14C yr BP (11,660-11,480 cal yr BP) reflect a cool and moist climate during the Younger Dryas chronozone. Orbitally induced warming around 10,000 14C yr BP (11,090 cal yr BP) allowed the northward extension of Pseudotsuga menziesii, although Picea, Tsuga heterophylla, and A. rubra dominated early Holocene forests. By 7500 14C yr BP (8215 cal yr BP), shade-tolerant T. heterophylla was the dominant forest tree. Cupressaceae ( Thuja plicata and Chamaecyparis nootkatensis) was present by 7500 14C yr BP but reached its maximum after 3500 14C yr BP (3600 cal yr BP), when a cooler and wetter regional climate facilitated the development of temperate rainforest. The highest rates of vegetation change are associated with Lateglacial climate change and species with rapid growth rates and short life spans.

  11. Impact of climate variability on terrestrial environment in Western Europe between 45 and 9 kyr cal. BP: vegetation dynamics recorded by the Bergsee Lake (Black Forest, Germany).

    NASA Astrophysics Data System (ADS)

    Duprat-Oualid, Fanny; Begeot, Carole; Rius, Damien; Millet, Laurent; Magny, Michel

    2016-04-01

    Between 9 and 45 kyr cal. BP, two great transitions lead the global climate system to evolve from the Last-Glacial period (115-14.7 kyr cal. BP), to two successive warmer periods, the Late-Glacial Interstadial (14.7-11.7 kyr cal. BP) and the Holocene (11.7-0 kyr cal. BP). δ18O variations recorded in Greenland ice cores (GRIP & NGRIP) revealed high frequency climate variability within the Last Glacial. These reference isotopic records highlighted a succession of centennial-to-millennial warm/cold events, the so-called Greenland Interstadials (GI) and Greenland Stadials (GS). The number continental records about the period 14.7-0 kyr cal. BP is substantial. This allowed to understand the vegetation dynamics in response to climate changes this period at the North-Atlantic scale. However, sequences covering the glacial period (beyond 20 kyr cal.BP) remain rare, because of hiatuses mostly due to local glaciers. Therefore, sedimentary continuous records of vegetation dynamics are still needed to better understand climate changes during the Last Glacial in Western Europe (Heiri et al. 2014). Here we present a new high-resolution pollen record from Lake Bergsee (47°34'20''N, 7°56'11''E, 382 m a.s.l). This lake is located south of Black Forest and north of the Alps, beyond the zone of glaciers maximal extension. Therefore it could have recorded the whole last climatic cycle, i.e. 120-0 kyr cal. BP. In 2013, a 29 m long core was extracted from the Bergsee. According to the depth-age model based on 14C AMS dating and the Laacher See Tephra (LST), the record spans continuously at least the last 45 kyrs. The first series of pollen analysis, focused on the 45-9 kyr cal. BP time window, allows us to reconstruct a precise, faithful and continuous vegetation history at the centennial scale. This high temporal resolution enabled to assess the response of vegetation to secular climate events (e.g. GI-4 = 200 yrs). First, our results show that vegetation responded to climate

  12. Chronostratigraphy in karst records from the Epipaleolithic to the Mid/Early Neolithic (c. 13.0-6.0 cal ka BP) in the Catalan Coastal Ranges of NE Iberia: environmental changes, sedimentary processes and human activity

    NASA Astrophysics Data System (ADS)

    Bergadà, M. Mercè; Cervelló, Josep M.; Edo, Manel; Cebrià, Artur; Oms, F. Xavier; Martínez, Pablo; Antolín, Ferran; Morales, Juan Ignacio; Pedro, Mireia

    2018-03-01

    The stratigraphic, sedimentary and palaeoenvironmental features reflected in cavities in the Catalan Coastal Ranges of NE Iberia (Can Sadurní and Guineu caves) characterize the periods of pronounced climatic and human complexity that occurred c. 13.0-6.0 cal ka BP. This includes the stages of the Younger Dryas and Mid/Early Holocene, the latter being one of the periods of so-called Rapid Climatic Changes (RCCs). These caves, like others in Mediterranean contexts, are the result of an old duct originating in the saturated zone of the karst system and open to the outside; recording a succession of different detrital and anthropic episodes of the Epipaleolithic, Mesolithic and Neolithic communities. From this study it can be seen that paleoclimatic events do not always present clear signals in the karst records, especially c. 12.7-7.4 cal ka BP, corresponding to the Epipaleolithic and Mesolithic. It is characterized by a stratigraphic discontinuity in which there are phases with predominantly detrital sedimentation alternating with hiatus intervals. Detrital sedimentation formed by fine material colluvium with gravitational movements or solifluction processes in fresh and humid conditions. It appears in the following chronological intervals: 12.7-12.2 cal ka BP, 11.5/11.1-10.7/10.4 cal ka BP and 8.2-8.0 cal ka BP (less humid). Hiatus phases are represented in the rest of the sequence up to c. 7.4 cal ka BP. From the sedimentary point of view these stages of hiatus are indicative of phases of stability or lack of episodes with seasonal contrasts; a fact that would cause interruptions to detrital deposition in the interior of the caves. In contrast, in the period c. 7.4 to 6.0 cal ka BP, attributed to the Middle and Early Neolithic, there is a certain stratigraphic continuity. From the sedimentary point of view it is distinguished by a variability of processes that responds to accumulative episodes of short duration characteristic of morphogenesis of the slopes in an

  13. The 3000-4000 cal. BP anthropogenic shift in fire regime in the French Pyrenees.

    NASA Astrophysics Data System (ADS)

    Rius, D.; Vannière, B.; Galop, D.; Richard, H.

    2009-04-01

    Fire is a key disturbing agent in a wide range of ecosystems: boreal biome (Pitkanen, 2000), Mediterranean area (Colombaroli et al., 2008) as well as temperate European mountain zones (Tinner et al., 1999). During the Holocene, climate may control fire regime by both ignition and fire spread-favouring conditions (i.e. composition, structure and moisture of biomass) whereas man may change charcoal accumulation patterns through type and intensity of agro-pastoral activities. In western and Mediterranean Europe, single sites charcoal analysis recorded the anthropogenic forcing over fire regime broadly between the mid and the late-Holocene. Turner et al (2008) showed that climate and fire had been disconnected since 1700 cal. BP in Turkey. In central Swiss, Mean Fire Interval decreased by two times 2000 years ago due to increasing human impact (Stahli et al., 2006). In Italy, climate and man have had a combined influence on fire-hazard since ca 4000 cal. BP (Vannière et al., 2008). In the Pyrenees Mountains, the linkage between agro-pastoral practices and fire could be dated back to ca 4000-3000 cal. BP with a clear succession of a clearance phase (high fire frequency) followed by a quite linear trend throughout Middle Ages and Modern times corresponding to a change in fire use (Vanniere et al., 2001; Galop et al., 2002, Rius et al., in press). The quantification of fire regimes parameters such as frequency with robust methodological tools (Inferred Fire Frequency, Mean Fire Interval) is needed to understand and characterise such shifts. Here we present two sequences from the Lourdes basin (col d'Ech peat bog) and from the occidental Pyrenees (Gabarn peat bog), which cover the last 9000 years with high temporal resolution. The main goals of this study were to (1) assess control factors of fire regime throughout the lateglacial and Holocene (climate and/or man) on the local scale, (2) evidence the local/regional significance of these control factors , (3) discuss the

  14. A new Late Weichselian and Holocene marine chronology for the western Svalbard slope 30,000-0 cal years BP

    NASA Astrophysics Data System (ADS)

    Jessen, Simon P.; Rasmussen, Tine L.; Nielsen, Tove; Solheim, Anders

    2010-05-01

    Data have been compiled from eleven sediment cores from 76° to 80°N on the western Svalbard slope. The cores are from water depths between 630 and 1880 m and show clear similarities in lithology and magnetic susceptibility. All cores penetrated into mass transported sediments from glacigenic debris flow events and turbidity flow events. The mass transport probably occurred when the ice reached the shelf edge. The deposits date between 24,080 ± 150 and 23,550 ± 185 calibrated (cal) years BP. The records also include laminated, fine grained sediments interpreted as deposits from sediment-laden meltwater plumes dated between 14,780 ± 220 and 14,300 ± 260 cal years BP. In Holocene sediments a diatom-rich fine grained layer dates 10,100 ± 150 to 9840 ± 200 cal years BP. The eleven cores have been stacked into one record with absolute age control from 35 AMS 14C dates. Together with oxygen isotope stratigraphy and contents of ice rafted detritus the stacked record provides a useful chronology tool for cores on the western Svalbard slope. Our study improves the age control of earlier well documented glacial events and shows that the maximum glacial state and the onset of the deglaciation both occurred 2500-3000 years earlier than previously reconstructed for the western Svalbard margin. The results indicate that during the last 30,000 years advance and retreat of the Svalbard-Barents Sea Ice Sheet was closely linked to the flow of Atlantic Water and Polar Water over the margin.

  15. Continuous lake-sediment records of glaciation in the Sierra Nevada between 52,600 and 12,500 14C yr B.P.

    USGS Publications Warehouse

    Benson, L.V.; May, Howard M.; Antweiler, Ronald C.; Brinton, T.I.; Kashgarian, Michaele; Smoot, J.P.; Lund, S.P.

    1998-01-01

    The chemistry of the carbonate-free clay-size fraction of Owens Lake sediments supports the use of total organic carbon and magnetic susceptibility as indicators of stadial-interstadial oscillations. Owens Lake records of total organic carbon, magnetic susceptibility, and chemical composition of the carbonate-free, clay-size fraction indicate that Tioga glaciation began ~24,500 and ended by ~13,600 14C yr B.P. Many of the components of glacial rock flour (e.g., TiO2, MnO, BaO) found in Owens Lake sediments achieved maximum values during the Tioga glaciation when valley glaciers reached their greatest extent. Total organic carbon and SiO2 (amorphous) concentrations reached minimum values during Tioga glaciation, resulting from decreases in productivity that accompanied the introduction of rock flour into the surface waters of Owens Lake. At least 20 stadial-interstadial oscillations occurred in the Sierra Nevada between 52,600 and 14,000 14C yr B.P. Total organic carbon data from a Pyramid Lake sediment core also indicate oscillations in glacier activity between >39,500 and ~13,600 14C yr B.P. Alpine glacier oscillations occurred on a frequency of ???1900 yr in both basins, suggesting that millennial-scale oscillations occurred in California and Nevada during most of the past 52,600 yr.

  16. Postglacial vegetation history of Mitkof Island, Alexander Archipelago, southeastern Alaska

    USGS Publications Warehouse

    Ager, T.A.; Carrara, P.E.; Smith, Jane L.; Anne, V.; Johnson, J.

    2010-01-01

    An AMS radiocarbon-dated pollen record from a peat deposit on Mitkof Island, southeastern Alaska provides a vegetation history spanning ∼12,900 cal yr BP to the present. Late Wisconsin glaciers covered the entire island; deglaciation occurred > 15,400 cal yr BP. The earliest known vegetation to develop on the island (∼12,900 cal yr BP) was pine woodland (Pinus contorta) with alder (Alnus), sedges (Cyperaceae) and ferns (Polypodiaceae type). By ∼12,240 cal yr BP, Sitka spruce (Picea sitchensis) began to colonize the island while pine woodland declined. By ∼11,200 cal yr BP, mountain hemlock (Tsuga mertensiana) began to spread across the island. Sitka spruce-mountain hemlock forests dominated the lowland landscapes of the island until ∼10,180 cal yr BP, when western hemlock (Tsuga heterophylla) began to colonize, and soon became the dominant tree species. Rising percentages of pine, sedge, and sphagnum after ∼7100 cal yr BP may reflect an expansion of peat bog habitats as regional climate began to shift to cooler, wetter conditions. A decline in alders at that time suggests that coastal forests had spread into the island's uplands, replacing large areas of alder thickets. Cedars (Chamaecyparis nootkatensis, Thuja plicata) appeared on Mitkof Island during the late Holocene.

  17. Postglacial vegetation history of Mitkof Island, Alexander Archipelago, southeastern Alaska

    NASA Astrophysics Data System (ADS)

    Ager, Thomas A.; Carrara, Paul E.; Smith, Jane L.; Anne, Victoria; Johnson, Joni

    2010-03-01

    An AMS radiocarbon-dated pollen record from a peat deposit on Mitkof Island, southeastern Alaska provides a vegetation history spanning ˜12,900 cal yr BP to the present. Late Wisconsin glaciers covered the entire island; deglaciation occurred > 15,400 cal yr BP. The earliest known vegetation to develop on the island (˜12,900 cal yr BP) was pine woodland ( Pinus contorta) with alder ( Alnus), sedges (Cyperaceae) and ferns (Polypodiaceae type). By ˜12,240 cal yr BP, Sitka spruce ( Picea sitchensis) began to colonize the island while pine woodland declined. By ˜11,200 cal yr BP, mountain hemlock ( Tsuga mertensiana) began to spread across the island. Sitka spruce-mountain hemlock forests dominated the lowland landscapes of the island until ˜10,180 cal yr BP, when western hemlock ( Tsuga heterophylla) began to colonize, and soon became the dominant tree species. Rising percentages of pine, sedge, and sphagnum after ˜7100 cal yr BP may reflect an expansion of peat bog habitats as regional climate began to shift to cooler, wetter conditions. A decline in alders at that time suggests that coastal forests had spread into the island's uplands, replacing large areas of alder thickets. Cedars ( Chamaecyparis nootkatensis, Thuja plicata) appeared on Mitkof Island during the late Holocene.

  18. Holocene multidecadal and multicentennial droughts affecting Northern California and Nevada

    USGS Publications Warehouse

    Benson, L.; Kashgarian, Michaele; Rye, R.; Lund, S.; Paillet, F.; Smoot, J.; Kester, C.; Mensing, S.; Meko, D.; Lindstrom, S.

    2002-01-01

    Continuous, high-resolution ??18O records from cored sediments of Pyramid Lake, Nevada, indicate that oscillations in the hydrologic balance occurred, on average, about every 150 years (yr) during the past 7630 calendar years (cal yr). The records are not stationary; during the past 2740 yr, drought durations ranged from 20 to 100 yr and intervals between droughts ranged from 80 to 230 yr. Comparison of tree-ring-based reconstructions of climate change for the past 1200 yr from the Sierra Nevada and the El alpais region of northwest New Mexico indicates that severe droughts associated with Anasazi withdrawal from Chaco Canyon at 820 cal yr BP (calendar years before present) and final abandonment of Chaco Canyon, Mesa Verde, and the Kayenta area at 650 cal yr BP may have impacted much of the western United States.During the middle Holocene (informally defined in this paper as extending from 8000 to 3000 cal yr BP), magnetic susceptibility values of sediments deposited in Pyramid Lake's deep basin were much larger than late-Holocene (3000-0 cal yr BP) values, indicating the presence of a shallow lake. In addition, the mean ?? 18O value of CaCO3 precipitated between 6500 and 3430 cal yr BP was 1.6??? less than the mean value of CaCO3 precipitated after 2740 cal yr BP. Numerical calculations indicate that the shift in the ??18O baseline probably resulted from a transition to a wetter (> 30%) and cooler (3-5??C) climate. The existence of a relatively dry and warm middle-Holocene climate in the Truckee River - Pyramid Lake system is generally consistent with archeological, sedimentological, chemical, physical, and biological records from various sites within the Great Basin of the western United States. Two high-resolution Holocene-climate records are now available from the Pyramid and Owens lake basins which suggest that the Holocene was characterized by five climatic intervals. TIC and ??18O records from Owens Lake indicate that the first interval in the early Holocene

  19. Holocene multidecadal and multicentennial droughts affecting Northern California and Nevada

    NASA Astrophysics Data System (ADS)

    Benson, Larry; Kashgarian, Michaele; Rye, Robert; Lund, Steve; Paillet, Fred; Smoot, Joseph; Kester, Cynthia; Mensing, Scott; Meko, Dave; Lindström, Susan

    2002-02-01

    Continuous, high-resolution δ18O records from cored sediments of Pyramid Lake, Nevada, indicate that oscillations in the hydrologic balance occurred, on average, about every 150 years (yr) during the past 7630 calendar years (cal yr). The records are not stationary; during the past 2740 yr, drought durations ranged from 20 to 100 yr and intervals between droughts ranged from 80 to 230 yr. Comparison of tree-ring-based reconstructions of climate change for the past 1200 yr from the Sierra Nevada and the El Malpais region of northwest New Mexico indicates that severe droughts associated with Anasazi withdrawal from Chaco Canyon at 820 cal yr BP (calendar years before present) and final abandonment of Chaco Canyon, Mesa Verde, and the Kayenta area at 650 cal yr BP may have impacted much of the western United States.During the middle Holocene (informally defined in this paper as extending from 8000 to 3000 cal yr BP), magnetic susceptibility values of sediments deposited in Pyramid Lake's deep basin were much larger than late-Holocene (3000-0 cal yr BP) values, indicating the presence of a shallow lake. In addition, the mean δ18O value of CaCO 3 precipitated between 6500 and 3430 cal yr BP was 1.6‰ less than the mean value of CaCO 3 precipitated after 2740 cal yr BP. Numerical calculations indicate that the shift in the δ18O baseline probably resulted from a transition to a wetter (>30%) and cooler (3-5°C) climate. The existence of a relatively dry and warm middle-Holocene climate in the Truckee River-Pyramid Lake system is generally consistent with archeological, sedimentological, chemical, physical, and biological records from various sites within the Great Basin of the western United States. Two high-resolution Holocene-climate records are now available from the Pyramid and Owens lake basins which suggest that the Holocene was characterized by five climatic intervals. TIC and δ18O records from Owens Lake indicate that the first interval in the early Holocene

  20. Pollen record of the mid- to late-Holocene centennial climate change on the East coast of South Korea and its influential factors

    NASA Astrophysics Data System (ADS)

    Song, Bing; Yi, Sangheon; Jia, Hongjuan; Nahm, Wook-Hyun; Kim, Jin-Cheul; Lim, Jaesoo; Lee, Jin-Young; Sha, Longbin; Mao, Limi; Yang, Zhongyong; Nakanishi, Toshimichi; Hong, Wan; Li, Zhen

    2018-01-01

    To understand historical climate change in western Pacific coastal areas, a sediment core (SOJ-2) from the stable sedimentary environment of the Songjiho Lagoon on the east coast of South Korea was obtained for centennial-resolution palynological analysis. The ages of the SOJ-2 core is well controlled by carbon 14 dating with high-resolution accelerator mass spectrometry (AMS), and the results indicated a general warm to cold climate trend from the mid-Holocene to the present, which can be divided into two different stages: a warmer stage between 6842 and 1297 cal yr BP and a colder stage from 1297 cal yr BP to the present, with fluctuations during these stages. The climate was wetter from 6842 to 6227 cal yr BP and 4520 to 1297 cal yr BP and was drier from 6227 to 4520 cal yr BP. The climate changed to cold and dry during the period from 1297-425 cal yr BP. The impact of human activity on the climate began at approximately 1297 cal yr BP and became pronounced starting in 425 cal yr BP. The general cooling trend may represent a response to decreasing solar insolation; however, the relative dryness or wetness of the climate may have been co-determined by westerlies and the East Asian summer monsoon (EASM). The climate had a teleconnection with the North Atlantic region, resulting from changes in solar activity. Nevertheless, EI Niño-Southern Oscillation (ENSO) activity played an important role in impacting the EASM changes in western Pacific coastal areas.

  1. Holocene seasonal variability inferred from multiple proxy records from Crevice Lake, Yellowstone National Park, USA

    USGS Publications Warehouse

    Whitlock, Cathy; Dean, Walter E.; Fritz, Sherilyn C.; Stevens, Lora R.; Stone, Jeffery R.; Power, Mitchell J.; Rosenbaum, Joseph R.; Pierce, Kenneth L.; Bracht-Flyr, Brandi B.

    2012-01-01

    A 9400-yr-old record from Crevice Lake, a semi-closed alkaline lake in northern Yellowstone National Park, was analyzed for pollen, charcoal, geochemistry, mineralogy, diatoms, and stable isotopes to develop a nuanced understanding of Holocene environmental history in a region of northern Rocky Mountains that receives both summer and winter precipitation. The limited surface area, conical bathymetry, and deep water (> 31 m) of Crevice Lake create oxygen-deficient conditions in the hypolimnion and preserve annually laminated sediment (varves) for much of the record. Pollen data indicate that the watershed supported a closed Pinus-dominated forest and low fire frequency prior to 8200 cal yr BP, followed by open parkland until 2600 cal yr BP, and open mixed-conifer forest thereafter. Fire activity shifted from infrequent stand-replacing fires initially to frequent surface fires in the middle Holocene and stand-replacing events in recent centuries. Low values of δ18O suggest high winter precipitation in the early Holocene, followed by steadily drier conditions after 8500 cal yr BP. Carbonate-rich sediments before 5000 cal yr BP imply warmer summer conditions than after 5000 cal yr BP. High values of molybdenum (Mo), uranium (U), and sulfur (S) indicate anoxic bottom-waters before 8000 cal yr BP, between 4400 and 3900 cal yr BP, and after 2400 cal yr BP. The diatom record indicates extensive water-column mixing in spring and early summer through much of the Holocene, but a period between 2200 and 800 cal yr BP had strong summer stratification, phosphate limitation, and oxygen-deficient bottom waters. Together, the proxy data suggest wet winters, protracted springs, and warm effectively wet summers in the early Holocene and less snowpack, cool springs, warm dry summers in the middle Holocene. In the late Holocene, the region and lake experienced extreme changes in winter, spring, and summer conditions, with particularly short springs and dry summers and winters during

  2. Continuous Lake-Sediment Records of Glaciation in the Sierra Nevada between 52,600 and 12,500 14C yr B.P

    NASA Astrophysics Data System (ADS)

    Benson, Larry V.; May, Howard M.; Antweiler, Ronald C.; Brinton, Terry I.; Kashgarian, Michaele; Smoot, Joseph P.; Lund, Steve P.

    1998-09-01

    The chemistry of the carbonate-free clay-size fraction of Owens Lake sediments supports the use of total organic carbon and magnetic susceptibility as indicators of stadial-interstadial oscillations. Owens Lake records of total organic carbon, magnetic susceptibility, and chemical composition of the carbonate-free, clay-size fraction indicate that Tioga glaciation began ˜24,500 and ended by ˜13,600 14C yr B.P. Many of the components of glacial rock flour (e.g., TiO 2, MnO, BaO) found in Owens Lake sediments achieved maximum values during the Tioga glaciation when valley glaciers reached their greatest extent. Total organic carbon and SiO 2(amorphous) concentrations reached minimum values during Tioga glaciation, resulting from decreases in productivity that accompanied the introduction of rock flour into the surface waters of Owens Lake. At least 20 stadial-interstadial oscillations occurred in the Sierra Nevada between 52,600 and 14,000 14C yr B.P. Total organic carbon data from a Pyramid Lake sediment core also indicate oscillations in glacier activity between >39,500 and ˜13,600 14C yr B.P. Alpine glacier oscillations occurred on a frequency of ≤1900 yr in both basins, suggesting that millennial-scale oscillations occurred in California and Nevada during most of the past 52,600 yr.

  3. Vegetation history along the eastern, desert escarpment of the Sierra San Pedro Mártir, Baja California, Mexico

    USGS Publications Warehouse

    Holmgren, Camille A.; Betancourt, Julio L.; Rylander, Kate A.

    2011-01-01

    Plant macrofossils from 38 packrat middens spanning the last ~ 33,000 cal yr BP record vegetation between ~ 650 and 900 m elevation along the eastern escarpment of the Sierra San Pedro Mártir, northern Baja California. The middens span most of the Holocene, with a gap between ~ 4600 and 1800 cal yr BP, but coverage in the Pleistocene is uneven with a larger hiatus between 23,100 and 14,400 cal yr BP. The midden flora is relatively stable from the Pleistocene to Holocene. Exceptions include Pinus californiarum, Juniperus californica and other chaparral elements that were most abundant > 23,100 cal yr BP and declined after 14,400 cal yr BP. Despite being near the chaparral/woodland-desertscrub ecotone during glacial times, the midden assemblages reflect none of the climatic reversals evident in the glacial or marine record, and this is corroborated by a nearby semi-continuous pollen stratigraphy from lake sediments. Regular appearance of C4 grasses and summer-flowering annuals since 13,600 cal yr BP indicates occurrence of summer rainfall equivalent to modern (JAS average of ~ 80–90 mm). This casts doubt on the claim, based on temperature proxies from marine sediments in the Guaymas Basin, that monsoonal development in the northern Gulf and Arizona was delayed until after 6200 cal yr BP.

  4. Late Holocene monsoon climate as evidenced by proxy records from a lacustrine sediment sequence in western Guangdong, South China

    NASA Astrophysics Data System (ADS)

    Zhong, Wei; Cao, jiayuan; Xue, Jibin; Ouyang, Jun; Tang, Xiaohong; Yin, Huanling; Liao, Congyun; Long, Kun

    2014-02-01

    The study of a 300-cm-thick exposed lacustrine sediment section in the Hedong village in Zhaoqing area which is located in sub-tropical west Guangdong Province in South China, demonstrates that the lacustrine sedimentary sequence possibly contains evidence for exploring variation of Asian monsoon climate. Multi-proxy records, including the humification intensity, total organic carbon, and grain size fractions, reveal a general trend towards dry and cold conditions in the late Holocene that this is because of a decrease in solar insolation on an orbital scale. Three intensified Asian summer monsoon (ASM) intervals (˜3300-3000 cal yr BP, ˜2600-1600 cal yr BP, and ˜900-600 cal yr BP), and three weakened ASM intervals (˜4000-3300 cal yr BP, ˜3000-2600 cal yr BP, and ˜1600-900 cal yr BP) are identified. Our humification record (HDcal) shows a good correlation on multi-centennial scale with the tree ring Δ14C record, a proxy of solar activity. A spectral analysis of HDcal reveals four significant cycles, i.e., ˜1250 yr, 300 yr, 110 yr, and 70 yr, and most of these cycles are related to the solar activity. Our findings indicate that solar output and oceanic-atmospheric circulation probably have influenced the late Holocene climate variability in the study region.

  5. Holocene vegetation change in the northern Peten and its implications for Maya prehistory

    NASA Astrophysics Data System (ADS)

    Wahl, David; Byrne, Roger; Schreiner, Thomas; Hansen, Richard

    2006-05-01

    An ˜8400 cal yr record of vegetation change from the northern Peten, Guatemala, provides new insights into the environmental history of the archaeological area known as the Mirador Basin. Pollen, loss on ignition, and magnetic susceptibility analyses indicate warm and humid conditions in the early to mid-Holocene. Evidence for a decrease in forest cover around 4600 cal yr B.P. coincides with the first appearance of Zea mays pollen, suggesting that human activity was responsible. The period between 3450 cal yr B.P. and 1000 cal yr B.P. is characterized by a further decline in forest pollen types, includes an abrupt increase in weedy taxa, and exhibits the highest magnetic susceptibility values since the early Holocene, all of which suggest further agricultural disturbance in the watershed. A brief drop in disturbance indicators around 1800 cal yr B.P. may represent the Preclassic abandonment of the area. Changing pollen frequencies around 1000 cal yr B.P. indicate a cessation of human disturbance, which represents the Late Classic collapse of the southern Maya lowlands.

  6. The abrupt climate change near 4,400 yr BP on the cultural transition in Yuchisi, China and its global linkage.

    PubMed

    Wang, Jianjun; Sun, Liguang; Chen, Liqi; Xu, Libin; Wang, Yuhong; Wang, Xinming

    2016-06-10

    Extreme climatic events have profound impacts on human society. Here we present the results of a study of organic biomarkers within a sedimentary section at the archaeological site of Yuchisi, eastern China, in order to reconstruct climatic variability during the Dawenkou (5,050-4,400 yr BP) and Longshan (4,400-4,000 yr BP) cultures. At ~4,400 yr BP, within the cultural transition horizon, abrupt changes in biomarkers, such as the fatty acid ratio C18:2/C18:0, 2C31/(C27 + C29), n-C18-ol and n-C30-ol, indicate the occurrence of local climate changes over the course of a few decades. These changes occurred during the transition from the Holocene warm period to a subsequent cold period which lasted for the following 600 years. This climatic shift has been recorded at numerous sites worldwide, and it is likely to have been the main cause of the widespread collapse of many isolated cultures at that time. The palaeoclimatic and archaeological data from the Yuchisi sediments may provide new insights into the relationship between climate change and prehistoric cultural transitions.

  7. The abrupt climate change near 4,400 yr BP on the cultural transition in Yuchisi, China and its global linkage

    PubMed Central

    Wang, Jianjun; Sun, Liguang; Chen, Liqi; Xu, Libin; Wang, Yuhong; Wang, Xinming

    2016-01-01

    Extreme climatic events have profound impacts on human society. Here we present the results of a study of organic biomarkers within a sedimentary section at the archaeological site of Yuchisi, eastern China, in order to reconstruct climatic variability during the Dawenkou (5,050–4,400 yr BP) and Longshan (4,400–4,000 yr BP) cultures. At ~4,400 yr BP, within the cultural transition horizon, abrupt changes in biomarkers, such as the fatty acid ratio C18:2/C18:0, 2C31/(C27 + C29), n-C18-ol and n-C30-ol, indicate the occurrence of local climate changes over the course of a few decades. These changes occurred during the transition from the Holocene warm period to a subsequent cold period which lasted for the following 600 years. This climatic shift has been recorded at numerous sites worldwide, and it is likely to have been the main cause of the widespread collapse of many isolated cultures at that time. The palaeoclimatic and archaeological data from the Yuchisi sediments may provide new insights into the relationship between climate change and prehistoric cultural transitions. PMID:27283832

  8. Holocene environmental changes in southern Kamchatka, Far Eastern Russia, inferred from a pollen and testate amoebae peat succession record

    NASA Astrophysics Data System (ADS)

    Klimaschewski, A.; Barnekow, L.; Bennett, K. D.; Andreev, A. A.; Andrén, E.; Bobrov, A. A.; Hammarlund, D.

    2015-11-01

    High resolution palaeoenvironmental records in Far-Eastern Russia are rare, and the Kamchatka Peninsula is among the least studied areas of the region. This paper describes a record spanning the last ca. 11,000 yr, obtained from a bog in the southern part of Kamchatka. The radiocarbon dated core was analysed for pollen, testate amoebae, charcoal and loss-on-ignition (LOI). The vegetation during the early Holocene was dominated by grasses (Poaceae), birch (Betula) and heath (Ericaceae p. p.). Around 10,300 cal yr BP there was a substantial change in the vegetation cover to shrub alder (Alnus viridis s.l.) stands with sedges and ferns (Polypodiophyta) as well as herbs such as meadow rue (Thalictrum) in the understory. In the surroundings of Utka peatlands started to form. The variations in the vegetation cover were most probably caused by climatic changes. At the beginning of sediment accumulation, before 10,300 cal yr BP, the composition of the vegetation points to cooler summers and/or decreased annual precipitation. Around 10,300 cal yr BP, changes in vegetation occurred due to rising temperatures and/or changed water regimes. Increased abundancies of dry indicating testate amoebae after 9100 cal yr BP point to intermediate to dry soil conditions. Between 8600 and 7700 cal yr BP tree alder (Alnus incana) was widely spread at the site which probably indicates optimal environmental conditions. The tephra layer at 381-384.5 cm (ca. 8500 cal yr BP) produces a strong impact on the testate amoebae assemblages. At 7700 cal yr BP there was a sudden drop of A. incana in the local vegetation. From this time on, A. incana and also A. viridis decrease continuously whereas Betula gradually increases. The upper part of the sequence (after 6300 cal yr BP) shows higher abundancies of meadowsweet (Filipendula) and sweet gale (Myrica) pollen. After 6300 cal yr BP, changes in testate amoebae demonstrate variable soil moisture conditions at the site. Between 3700 and 1800 cal yr BP

  9. Tsunami history of an Oregon coastal lake reveals a 4600 yr record of great earthquakes on the Cascadia subduction zone

    USGS Publications Warehouse

    Kelsey, H.M.; Nelson, A.R.; Hemphill-Haley, E.; Witter, R.C.

    2005-01-01

    Bradley Lake, on the southern Oregon coastal plain, records local tsunamis and seismic shaking on the Cascadia subduction zone over the last 7000 yr. Thirteen marine incursions delivered landward-thinning sheets of sand to the lake from nearshore, beach, and dune environments to the west. Following each incursion, a slug of marine water near the bottom of the freshwater lake instigated a few-year-to-several-decade period of a brackish (??? 4??? salinity) lake. Four additional disturbances without marine incursions destabilized sideslopes and bottom sediment, producing a suspension deposit that blanketed the lake bottom. Considering the magnitude and duration of the disturbances necessary to produce Bradley Lake's marine incursions, a local tsunami generated by a great earthquake on the Cascadia subduction zone is the only accountable mechanism. Extreme ocean levels must have been at least 5-8 m above sea level, and the cumulative duration of each marine incursion must have been at least 10 min. Disturbances without marine incursions require seismic shaking as well. Over the 4600 yr period when Bradley Lake was an optimum tsunami recorder, tsunamis from Cascadia plate-boundary earthquakes came in clusters. Between 4600 and 2800 cal yr B.P., tsunamis occurred at the average frequency of ??? 3-4 every 1000 yr. Then, starting ???2800 cal yr B.P., there was a 930-1260 yr interval with no tsunamis. That gap was followed by a ???1000 yr period with 4 tsunamis. In the last millennium, a 670-750 yr gap preceded the A.D. 1700 earthquake and tsunami. The A.D. 1700 earthquake may be the first of a new cluster of plate-boundary earthquakes and accompanying tsunamis. Local tsunamis entered Bradley Lake an average of every 390 yr, whereas the portion of the Cascadia plate boundary that underlies Bradley Lake ruptured in a great earthquake less frequently, about once every 500 yr. Therefore, the entire length of the subduction zone does not rupture in every earthquake, and Bradley

  10. Chronological reconstruction of eolianites and transversal mobile dunes of northwest coast of Ceará State - Brazil, in the last 3000 cal yrs BP

    NASA Astrophysics Data System (ADS)

    Castro, João Wagner Alencar; Malta, Julia Varella; Miguel, Lucas Lavo Antonio Jimo; Cabral, Caique Lima; Passemilio, Alvaro Balmant

    2017-10-01

    Dunefields are very common in the northern coastal zone of northeast Brazil. They have the potential to yield important information about paleoclimate, paleo-winds and regional winds and their response to sea-level fluctuations during the Holocene. We reconstructed the coastal dunes geochronological evolution of northwest Ceará State - Brazil, in the last 3000 cal yrs BP, using detailed analyses of lithostratigraphy, microfossil (foraminifera), wind regime, dune monitoring and 8 radiocarbon dates. The chronology was based on 14C dating in eolianites and monitoring transversal mobile dunes movement processes. Radiocarbon date results indicated that the dunes corresponding to eolianites revealed ages between 2760-2480 and 980-750 cal yrs BP, suggesting that the vast transversal mobile dunefields were formed after this period in similar condition to the current sea-level. We considered that the material transportation by the prevailing east winds towards the transversal dunes is estimated in the order of 11.0 m/year, thus the current aeolian system is less than 1000 yrs BP.

  11. Holocene vegetation and climate change recorded in alpine bog sediments from the Borreguiles de la Virgen, Sierra Nevada, southern Spain

    NASA Astrophysics Data System (ADS)

    Jiménez-Moreno, Gonzalo; Anderson, R. Scott

    2012-01-01

    High-resolution pollen and magnetic susceptibility (MS) analyses have been carried out on a sediment core taken from a high-elevation alpine bog area located in Sierra Nevada, southern Spain. The earliest part of the record, from 8200 to about 7000 cal yr BP, is characterized by the highest abundance of arboreal pollen and Pediastrum, indicating the warmest and wettest conditions in the area at that time. The pollen record shows a progressive aridification since 7000 cal yr BP that occurred in two steps, first shown by a decrease in Pinus, replaced by Poaceae from 7000 to 4600 cal yr BP and then by Cyperaceae, Artemisia and Amaranthaceae from 4600 to 1200 cal yr BP. Pediastrum also decreased progressively and totally disappeared at ca. 3000 yr ago. The progressive aridification is punctuated by periodically enhanced drought at ca. 6500, 5200 and 4000 cal yr BP that coincide in timing and duration with well-known dry events in the Mediterranean and other areas. Since 1200 cal yr BP, several changes are observed in the vegetation that probably indicate the high-impact of humans in the Sierra Nevada, with pasturing leading to nutrient enrichment and eutrophication of the bog, Pinus reforestation and Olea cultivation at lower elevations.

  12. Late Holocene vegetation and fire dynamics from a savanna-forest ecotone in Roraima state, northern Brazilian Amazon

    NASA Astrophysics Data System (ADS)

    da Silva Meneses, Maria Ecilene Nunes; da Costa, Marcondes Lima; Behling, Hermann

    2013-03-01

    Two sediment cores from Mauritia flexuosa palm swamps have been studied by pollen and charcoal analysis. The cores Fazenda Cigana (FC) and Terra Indígena Aningal (TIA) were taken from a savanna-forest ecotone area in the Roraima State, northern Brazilian Amazon. Based on 5 radiocarbon dates, these records allow the reconstruction of the vegetation fire and climate dynamics during the past 1550 years. At the FC site was recorded a higher proportion of forest cover, suggesting local wetter climatic conditions favorable for forest expansion, especially by gallery forests, between 1550 and 1400 cal yr BP. Stands of M. flexuosa started to establish on the site indicating sufficient soil moisture. From 1400 to 1050 cal yr BP, forest cover retreated while savanna, and the Mauritia palm swamp expanded considerably. The FC site was marked by savanna and Mauritia cover with a slight increase of forest between ca. 1050 and 900 cal yr BP. From 900 to 300 cal yr BP the savanna and palm swamp taxa became dominant and the forest area decreased. At the TIA site the savanna cover was dominant between 1200 and 1000 cal yr BP. From 1000 to 700 forest expanded while savanna and Mauritia palm swamp reduced. Between 700 and 300 cal yr BP savanna and Mauritia palm swamp increased and forest area decreased. The high amount of charred particles found in the sediments, indicate fires with a marked increase between 1400 to 1000 cal yr BP (FC site) and 700 to 300 cal yr BP (TIA site), and probably caused the retreat of forest cover during these two time intervals. The relatively lower fire activity after 300 cal yr BP until present-day favored the increase of forested area at both TIA and FC sites. The arrival of the European settler and the subsequent introduction of cattle, is suggested as the main reason for the decrease of fire in the study region. The results point the fire caused by indigenous people as the principal controlling factor for forest and savanna dynamics during the past

  13. Late Quaternary deglacial history of the Mérida Andes, Venezuela

    NASA Astrophysics Data System (ADS)

    Stansell, Nathan D.; Abbott, Mark B.; Polissar, Pratigya J.; Wolfe, Alexander P.; Bezada, Maximiliano; Rull, Valentí

    2005-10-01

    Radiocarbon-dated sediment cores from seven lakes and two bogs spanning the Cordillera de Mérida in the Venezuelan Andes were used to identify and date the regional history of late Pleistocene and Holocene glacial activity. Coring sites were selected at different elevations across a pronounced rain shadow from southeast (wet) to northwest (dry). Sediment lithostratigraphy and magnetic susceptibility, in conjunction with AMS radiocarbon dates on macrofossils and charcoal, were used to constrain deglaciation. The local expression of the Last Glacial Maximum occurred between 22 750 and 19 960 cal. yr BP. On the wetter southeastern side of the Cordillera de Mérida, glaciers had significantly retreated by 15 700 cal. yr BP, followed by several minor glacial advances and retreats between 14 850 and 13 830 cal. yr BP. At least one major glacial readvance occurred between 13 830 and 10 000 cal. yrBP in the wetter southeastern sector of the region. The drier northwest side of the Cordillera de Mérida records initial glacial retreat by 14240cal.yrBP. Multiple sites on both sides of the Mérida Andes record a further phase of extensive deglaciation approximately 10000cal.yrBP. However, the north-northwest facing Mucubají catchment remained partially glaciated until ca. 6000cal.yrBP. Deglacial ages from the Venezuelan Andes are consistently younger than those reported from the Southern Hemisphere Andes, suggesting an inter-hemispheric deglacial lag in the northern tropics of the order of two thousand years.

  14. Quartz grains reveal sedimentary palaeoenvironment and past storm events: A case study from eastern Baltic

    NASA Astrophysics Data System (ADS)

    Kalińska-Nartiša, Edyta; Stivrins, Normunds; Grudzinska, Ieva

    2018-01-01

    Sediment record collected from the coastal lake serves as a powerful tool for reconstructing changes in palaeoenvironment and understanding the potential signals of past storminess. In this study, we use several proxies from sediment of the Holocene Thermal Maximum at coastal Lake Lilaste, Latvia. We focus on surface texture of quartz grains from the mineral inorganic fraction as indicators of depositional environments. We then use this as a proxy for potential storm transport and combine with information on granulometry, diatom stratigraphy and chronology to answer the question whether flux of quartz grains in the lake originated from the sea or from the land. Analyses in a binocular and scanning electron microscope reveal that most of the investigated quartz grains originate from dwelling in the seawater and wave action in the nearshore zone. Grains representing very energetic subaqueous environment similar to storm events are also present. Terrestrial record is of minor significance and visible through occurrence of aeolian quartz grains. During drier and colder conditions, an influx of sand with aeolian imprint was delivered to the lake between 8500 and 7800 cal yr BP. Marine and terrestrial conditions alternated between 7800 and 6000 cal yr BP. Storm-induced grains were likely deposited three times: at 7300 cal yr BP, 6600-6400 cal yr BP, and 6200-6000 cal yr BP. Overall stable marine environmental conditions prevailed between 6000 and 4000 cal yr BP except of the last portion of terrestrial-induced sediment at 4100 cal yr BP.

  15. Vegetation, fire, climate and human disturbance history in the southwestern Mediterranean area during the late Holocene

    NASA Astrophysics Data System (ADS)

    Jiménez-Moreno, Gonzalo; García-Alix, Antonio; Hernández-Corbalán, María Dolores; Anderson, R. Scott; Delgado-Huertas, Antonio

    2013-03-01

    Detailed pollen, charcoal, isotope and magnetic susceptibility data from an alpine lake sediment core from Sierra Nevada, southern Spain record changes in vegetation, fire history and lake sedimentation since ca. 4100 cal yr BP. The proxies studied record an arid period from ca. 3800 to 3100 cal yr BP characterized by more xerophytic vegetation and lower lake levels. A humid period is recorded between ca. 3100 and 1850 cal yr BP, which occurred in two steps: (1) an increase in evergreen Quercus between 3100 and 2500 cal yr BP, indicating milder conditions than previously and (2) an increase in deciduous Quercus and higher lake levels, between ca. 2500 and 1850 cal yr BP, indicating a further increase in humidity and reduction in seasonal contrast. Humid maxima occurred during the Roman Humid Period, previously identified in other studies in the Mediterranean region. Intensified fire activity at this time could be related to an increase in fuel load and/or in human disturbance. An arid period subsequently occurred between 1850 and 650 cal yr BP, though a decrease in Quercus and an increase in xerophytes. The alternation of persistent North Atlantic Oscillation modes probably played an important role in controlling these humid-arid cycles.

  16. Climate change and human occupations in the Lake Daihai basin, north-central China over the last 4500 years: A geo-archeological perspective

    NASA Astrophysics Data System (ADS)

    Xu, Lichen; Liu, Yan; Sun, Qianli; Chen, Jing; Cheng, Peng; Chen, Zhongyuan

    2017-05-01

    High-resolution climate variations since the last 4500 years in the monsoonal-arid transition zone of north-central China were revealed through the integration of proxies from sediment cores in the Lake Daihai basin. Human occupations in the lake basin deduced from archeological findings and historical literatures were then incorporated into the climate sequence to demonstrate the patterns of human responses to the climate changes, and the recent anthropogenic effects. It indicated that: (1) Climate dominated human-environment adaptations prevailed prior to ∼2700 cal yr BP. An amicable climate setting before ∼4100 cal yr BP would facilitate the growth of the Laohushan Culture (LC) in the lake basin, while a pronounced deterioration of water thermal condition after that had led to human exodus and the collapse of the LC. The reduced human activity in the lake basin indicated at ∼3800-3500 cal yr BP and a subsequent cultural blank at ∼3500-2700 cal yr BP, were both in response to the climate and lake level fluctuations during ∼3800-2800 cal yr BP. (2) Transition to a positive human adaptation was seen at ∼2700-1100 cal yr BP, represented by the exploitation of arable land for cultivation and animal husbandry as the lake contracted. (3) An increasing human presence that affected environmental processes became more severe over the last ∼1100 cal yr BP. This was basically due to the ongoing lake shore reclamation for cropping, and more recently heavy metals emissions from fossil fuel combustion and local industries.

  17. The Primacy of Multidecadal to Centennial Variability Over Late Holocene Forced Change of the Asian Monsoon on the Southern Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Conroy, J. L.; Hudson, A. M.; Overpeck, J. T.; Liu, K. B.; Luo, W.; Cole, J. E.

    2016-12-01

    The nature of multidecadal to centennial variability of the Asian monsoon remains largely unknown. Here we use the sediment record from a closed-basin lake in southern Tibet, Ngamring Tso, to assess summer monsoon precipitation from 4100 cal yr BP to present. The first principal component of the Ngamring Tso grain size record correlates significantly with observed June-September precipitation. From CE 1940-2007, grain size decreased with increasing summer precipitation and increased with decreasing summer precipitation. Satellite images of Ngamring Tso suggest precipitation-induced changes in lake depth or area likely govern grain size variability. Prolonged periods of weak summer monsoon precipitation occurred from 2800-2600 cal yr BP, 2500-2300 cal yr BP, and 1600-400 cal yr BP. A trend toward increased summer precipitation began around 1000 cal yr BP, with above-average summer precipitation from 400 cal yr BP to present, peaking between 200-100 cal yr BP. Dry and wet periods are coincident with dry and wet periods in other south-central Tibetan lake sediment records and with regional proxies of the ISM and EASM, indicating south-central Tibet is influenced by both monsoon subsystems. 20th century precipitation variability in southern Tibet falls within the range of natural variability in the last 4100 years, and does not show a clear trend of increasing precipitation as projected by models. Instead, it appears that poorly understood internal modes of monsoon variability remained influential throughout the last 4100 years. Substantial multidecadal to centennial-scale variability will thus complicate our ability to project future anthropogenic changes in the region's monsoon precipitation.

  18. Holocene East Asian Monsoon Variability: Links to Solar and Tropical Pacific Forcing

    NASA Astrophysics Data System (ADS)

    Kandasamy, S.; Chen, C. A.; Lou, J.

    2006-12-01

    Sedimentary geochemical records from subalpine Retreat Lake, subtropical Taiwan, document the unstable East Asian Monsoon (EAM) climate for the last ~10250 calendar years before the present (cal yr B.P.). The proxy records demonstrate cool, glacial conditions with weak EAM between ~10250 and 8640 cal yr B.P., the strongest EAM during the "Holocene optimum" (8640-4500 cal yr B.P.) with an abrupt, decadal onset of postglacial EAM (8640-8600 cal yr B.P.), and relatively dry conditions since 4500 cal yr B.P. Although after 8600 cal yr B.P., EAM strength reduces gradually in response to the Northern Hemisphere summer insolation, heat and moisture transport and the development of late Holocene El-Niño-Southern Oscillation in the tropical Pacific appear to corroborate the periods of abrupt monsoon changes. Our proxy records reveal several weak monsoon intervals that correlate to low sea surface temperatures in the western tropical Pacific and cold events in the North Atlantic, suggesting a mechanistic link. Among those, four weak EAM events at 8170, 5400, 4500-2100 and 2000-1600 cal yr B.P. are in phase with the timings of low concentrations of atmospheric methane and periods of reduced North Atlantic Deep Water production as well as the `8.2 ka cold spell' and widespread event of low-latitude cultural collapse. Our EAM records exhibit strong correlations with high- and low-latitude climate and monsoon records; thus, provide robust evidences that the centennial-millennial scale monsoon variability during the Holocene are globally-mediated via sun- ocean-monsoon-North Atlantic linkages.

  19. Post-glacial flooding of the Bering Land Bridge dated to 11 cal ka BP based on new geophysical and sediment records

    NASA Astrophysics Data System (ADS)

    Jakobsson, Martin; Pearce, Christof; Cronin, Thomas M.; Backman, Jan; Anderson, Leif G.; Barrientos, Natalia; Björk, Göran; Coxall, Helen; de Boer, Agatha; Mayer, Larry A.; Mörth, Carl-Magnus; Nilsson, Johan; Rattray, Jayne E.; Stranne, Christian; Semiletov, Igor; O'Regan, Matt

    2017-08-01

    The Bering Strait connects the Arctic and Pacific oceans and separates the North American and Asian landmasses. The presently shallow ( ˜ 53 m) strait was exposed during the sea level lowstand of the last glacial period, which permitted human migration across a land bridge today referred to as the Bering Land Bridge. Proxy studies (stable isotope composition of foraminifera, whale migration into the Arctic Ocean, mollusc and insect fossils and paleobotanical data) have suggested a range of ages for the Bering Strait reopening, mainly falling within the Younger Dryas stadial (12.9-11.7 cal ka BP). Here we provide new information on the deglacial and post-glacial evolution of the Arctic-Pacific connection through the Bering Strait based on analyses of geological and geophysical data from Herald Canyon, located north of the Bering Strait on the Chukchi Sea shelf region in the western Arctic Ocean. Our results suggest an initial opening at about 11 cal ka BP in the earliest Holocene, which is later than in several previous studies. Our key evidence is based on a well-dated core from Herald Canyon, in which a shift from a near-shore environment to a Pacific-influenced open marine setting at around 11 cal ka BP is observed. The shift corresponds to meltwater pulse 1b (MWP1b) and is interpreted to signify relatively rapid breaching of the Bering Strait and the submergence of the large Bering Land Bridge. Although the precise rates of sea level rise cannot be quantified, our new results suggest that the late deglacial sea level rise was rapid and occurred after the end of the Younger Dryas stadial.

  20. Landscape transformations at the dawn of agriculture in southern Syria (10.7-9.9 ka cal. BP): Plant-specific responses to the impact of human activities and climate change

    NASA Astrophysics Data System (ADS)

    Arranz-Otaegui, Amaia; López-Sáez, José Antonio; Araus, José Luis; Portillo, Marta; Balbo, Andrea; Iriarte, Eneko; Gourichon, Lionel; Braemer, Frank; Zapata, Lydia; Ibáñez, Juan José

    2017-02-01

    In southwest Asia, the accelerated impact of human activities on the landscape has often been linked to the development of fully agricultural societies during the middle and late Pre-Pottery Neolithic B (PPNB) period (around 10.2-7.9 ka cal. BP). This work contributes to the debate on the environmental impact of the so-called Neolitisation process by identifying the climatic and anthropogenic factors that contributed to change local and regional vegetation at the time when domesticated plants appeared and developed in southern Syria (around 10.7-9.9 ka cal. BP). In this work a multidisciplinary analysis of plant microremains (pollen and phytoliths) and macroremains (wood charcoal) is carried out along with stable carbon isotope discrimination of wood charcoals in an early PPNB site (Tell Qarassa North, west of the Jabal al-Arab area). Prior to 10.5 ka cal. BP, the results indicate a dynamic equilibrium in the local and regional vegetation, which comprised woodland-steppe, Mediterranean evergreen oak-woodlands, wetland vegetation and coniferous forests. Around 10.5-9.9 ka cal. BP, the elements that regulated the vegetation system changed, resulting in reduced proportions of arboreal cover and the spread of cold-tolerant and wetlands species. Our data show that reinforcing interaction between the elements of the anthropogenic (e.g. herding, fire-related activities) and climatic systems (e.g. temperature, rainfall) contributed to the transformation of early Holocene vegetation during the emergence of fully agricultural societies in southern Syria.

  1. Timing of atmospheric precipitation in the Zagros Mountains inferred from a multi-proxy record from Lake Mirabad, Iran

    NASA Astrophysics Data System (ADS)

    Stevens, Lora R.; Ito, Emi; Schwalb, Antje; Wright, Herbert E.

    2006-11-01

    A sediment core 7.2 m long from Lake Mirabad, Iran, was examined for loss-on-ignition, mineralogy, oxygen-isotopic composition of authigenic calcite, and trace-element composition of ostracodes to complement earlier pollen and ostracode-assemblage studies. Pollen, ostracode-inferred lake level, and high Sr/Ca ratios indicate that the early Holocene (10000 to 6500 cal yr BP) was drier than the late Holocene. Low δ18O values during this interval are interpreted as resulting from winter-dominated precipitation, characteristic of a Mediterranean climate. Increasing δ18O values after 6500 cal yr BP signal a gradual increase in spring rains, which are present today. A severe 600-yr drought occurred at ca. 5500 cal yr BP, shortly after the transition from pistachio-almond to oak forest. During the late Holocene, two milder droughts occurred at about 1500 and 500 cal yr BP. Within the resolution of the record, no drought is evident during the collapse of the Akkadian empire (4200-3900 cal yr BP). Rather, a decrease in δ18O values to early-Holocene levels may indicate the return to a Mediterranean precipitation regime.

  2. Late Pleistocene to Holocene lake levels of Lake Warner, Oregon (USA) and their effect on archaeological site distribution patterns

    NASA Astrophysics Data System (ADS)

    Wriston, T.; Smith, G. M.

    2017-12-01

    Few chronological controls are available for the rise and fall of small pluvial lake systems in the Northwestern Great Basin. Within Warner Basin this control was necessary for interpretation of known archaeological sites and for predicting where evidence of its earliest inhabitants might be expected. We trenched along relic beach ridges of Lake Warner, surveyed a stratified sample of the area for archaeological sites, and excavated some sites and a nearby rockshelter. These efforts produced new ages that we used to construct a lake level curve for Lake Warner. We found that the lake filled the valley floor between ca. 30,000 cal yr BP and ca. 10,300 cal yr BP. In nearby basins, several oscillations are evident before ca. 21,100 cal yr BP, but a steep rise to the LGM maximum occurred between 21,000 and 20,000 cal yr BP. Lake Warner likely mirrored these changes, dropped to the valley floor ca. 18,340 cal yr BP, and then rose to its maximum highstand when its waters briefly reached 1454 m asl. After this highstand the lake receded to moderately high levels. Following ca. 14,385 cal yr BP, the lake oscillated between moderate to moderately-high levels through the Bolling-Allerod interstadials and into the Younger Dryas stadial. The basin's first occupants arrived along its shore around this time, while the lake still filled the valley floor. These earliest people carried either Western Stemmed or Clovis projectile points, both of which are found along the lake margin. The lake receded into the valley floor ca. 10,300 cal yr BP and dune development began, ringing wetlands and small lakes that persisted in the footprint of the once large lake. By the time Mazama tephra fell 7,600 cal yr BP it blanketed pre-existing dunes and marsh peats. Our Lake Warner lake level curve facilitates interdisciplinary testing and refinement of it and similar curves throughout the region while helping us understand the history of lake and the people who lived along its shores.

  3. Are signals of westerly wind strength and hydroclimate change during the late Holocene preserved in Antarctic peatbanks?

    NASA Astrophysics Data System (ADS)

    Stelling, J.; Yu, Z.; Beilman, D. W.; Loisel, J.

    2017-12-01

    Over the second half of the 20th century the western Antarctic Peninsula experienced a warmer and moister climate, possibly brought by the poleward expansion of the southern westerly wind belt. However, it is not well-known how terrestrial ecosystems on the peninsula have responded to circulation change over the last two millennia. Here we present a paleoecological and geochemical record derived from peatbank deposits on contrasting slopes on Litchfield Island (64°46'S; 64°06'W) to better understand ecosystem response over the late Holocene. Chronology of our three peat cores is constrained by 18 radiocarbon dates. The north-facing peatbank initiated 2700 calibrated years before present (cal yr BP) had a time-weighted accumulation rate of 0.3 mm yr-1 with the interval of lowest growth (<0.03 mm yr-1) from 1300 to 500 cal yr BP. However, the last 500 cal yr BP show increased accumulation rate (>0.6 mm yr-1). The other two peatbanks (southwest and west-facing) initiated after 500 cal yr BP with 1.5 mm yr-1 vertical accumulation rate. We suspect the delayed initiation in southwest or west-facing slopes was caused by cold/cool summer and likely persistent snow cover before 500 cal yr BP. Under the same regional climate, the cool summer, and perhaps more snow, on the north-facing slope causes the slow accumulation rate there at 1300-500 cal yr BP. Furthermore, the results show that carbon accumulation follows a similar pattern with an increased rate (greater than the time-weighted mean 20 g C m-2 yr-1), of up to 110 g C m-2 yr-1 at 1300 cal yr BP, and then decreased accumulation thereafter until 500 cal yr BP. Surprisingly, on peatbanks with different microclimates, there is a common pattern of large-scale species dominance shifts —from less than 10% to greater than >80%—between drier Polytrichum and wetter Chorisodontium. These dominance shifts indicate that despite differing accumulation histories, patterns of external influence can be detected. Warmer and

  4. Marine04 Marine radiocarbon age calibration, 26 ? 0 ka BP

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Hughen, K; Baille, M; Bard, E

    2004-11-01

    New radiocarbon calibration curves, IntCal04 and Marine04, have been constructed and internationally ratified to replace the terrestrial and marine components of IntCal98. The new calibration datasets extend an additional 2000 years, from 0-26 ka cal BP (Before Present, 0 cal BP = AD 1950), and provide much higher resolution, greater precision and more detailed structure than IntCal98. For the Marine04 curve, dendrochronologically dated tree-ring samples, converted with a box-diffusion model to marine mixed-layer ages, cover the period from 0-10.5 ka cal BP. Beyond 10.5 ka cal BP, high-resolution marine data become available from foraminifera in varved sediments and U/Th-dated corals.more » The marine records are corrected with site-specific {sup 14}C reservoir age information to provide a single global marine mixed-layer calibration from 10.5-26.0 ka cal BP. A substantial enhancement relative to IntCal98 is the introduction of a random walk model, which takes into account the uncertainty in both the calendar age and the radiocarbon age to calculate the underlying calibration curve. The marine datasets and calibration curve for marine samples from the surface mixed layer (Marine04) are discussed here. The tree-ring datasets, sources of uncertainty, and regional offsets are presented in detail in a companion paper by Reimer et al.« less

  5. Holocene environmental and climatic changes at Gorgo Basso, a coastal lake in southern Sicily, Italy

    NASA Astrophysics Data System (ADS)

    Tinner, Willy; van Leeuwen, Jacqueline F. N.; Colombaroli, Daniele; Vescovi, Elisa; van der Knaap, W. O.; Henne, Paul D.; Pasta, Salvatore; D'Angelo, Stefania; La Mantia, Tommaso

    2009-07-01

    We used a new sedimentary record to reconstruct the Holocene vegetation and fire history of Gorgo Basso, a coastal lake in south-western Sicily (Italy). Pollen and charcoal data suggest a fire-prone open grassland near the site until ca 10,000 cal yr BP (8050 cal BC), when Pistacia shrubland expanded and fire activity declined, probably in response to increased moisture availability. Evergreen Olea europaea woods expanded ca 8400 to decline abruptly at 8200 cal yr BP, when climatic conditions became drier at other sites in the Mediterranean region. Around 7000 cal yr BP evergreen broadleaved forests ( Quercus ilex, Quercus suber and O. europaea) expanded at the cost of open communities. The expansion of evergreen broadleaved forests was associated with a decline of fire and of local Neolithic ( Ficus carica-Cerealia based) agriculture that had initiated ca 500 years earlier. Vegetational, fire and land-use changes ca 7000 cal yr BP were probably caused by increased precipitation that resulted from (insolation-forced) weakening of the monsoon and Hadley circulation ca 8000-6000 cal yr BP. Low fire activity and dense coastal evergreen forests persisted until renewed human activity (probably Greek, respectively Roman colonists) disrupted the forest ca 2700 cal yr BP (750 BC) and 2100 cal yr BP (150 BC) to gain open land for agriculture. The intense use of fire for this purpose induced the expansion of open maquis, garrigue, and grassland-prairie environments (with an increasing abundance of the native palm Chamaerops humilis). Prehistoric land-use phases after the Bronze Age seem synchronous with those at other sites in southern and central Europe, possibly as a result of climatic forcing. Considering the response of vegetation to Holocene climatic variability as well as human impact we conclude that under (semi-)natural conditions evergreen broadleaved Q. ilex- O. europaea (s.l.) forests would still dominate near Gorgo Basso. However, forecasted climate change and

  6. Mineral magnetism and other characteristics of sediments from a sub-alpine lake (3080 m a.s.l.) in central east China and their implications on environmental changes for the last 5770 years

    NASA Astrophysics Data System (ADS)

    Wang, Hongya; Song, Yaqiong; Cheng, Ying; Luo, Yao; Zhang, Cai'na; Gao, Yishen; Qiu, An'an; Deng, Lei; Liu, Hongyan

    2016-10-01

    A sediment sequence (SQC07) was recovered from Sanqing Chi, a small sub-alpine lake (3080 m a.s.l.) on Taibai (3767 m a.s.l.), the highest mountain in east mainland China (east of 105°). The Mountain is also the highest part and central massif of the Qinling Mountain Range functioning as the boundary between the warm temperate climate zone to the north and sub-tropical climate zone to the south in east China. Soils and debris were also sampled from the catchment of Sanqing Chi. SQC07 was AMS 14C dated. Mineral magnetism was measured for the sediment sequence and catchment samples. Particle-size, TOC and TN analysis were undertaken on SQC07, while pollen analysis was made for the sediment sequence and surface-soil samples. With the mineral magnetism of the catchment materials, the magnetic and other characteristics of SQC07 indicate the environmental changes occurring on the high altitudes of Taibai Mountain during the past 5770 years. Environments were still moderately warm and wet over 5770-5100 cal. yr BP around this sub-alpine lake. Then cold and dry conditions persisted in the period of 5100-4000 cal. yr BP. Local environments began to ameliorate from 4000 cal. yr BP onwards and were thus generally warm and wet over 4000-1200 cal. yr BP. The warmth and wetness culminated in 1200-800 cal. yr BP. During the period of 800-400 cal. yr BP, cold and arid conditions again predominated. Environments have subsequently become warm and humid since ∼400 cal. yr BP. The overall trend of the changes is coincident with what have been identified at several other sites in east mainland China and Taiwan. Presumably, the deterioration over 5100-4000 cal. yr BP marks the termination of the Holocene optimum, corresponds to or encompasses Holocene event 3, while the deterioration occurring in 800-400 cal. yr BP may correspond to LIA cooling. However, they appear to have commenced earlier than the aforementioned sites at relatively low altitudes in east mainland China or even

  7. Vegetation and environmental responses to climate forcing during the Last Glacial Maximum and deglaciation in the East Carpathians: attenuated response to maximum cooling and increased biomass burning

    NASA Astrophysics Data System (ADS)

    Magyari, E. K.; Veres, D.; Wennrich, V.; Wagner, B.; Braun, M.; Jakab, G.; Karátson, D.; Pál, Z.; Ferenczy, Gy; St-Onge, G.; Rethemeyer, J.; Francois, J.-P.; von Reumont, F.; Schäbitz, F.

    2014-12-01

    The Carpathian Mountains were one of the main mountain reserves of the boreal and cool temperate flora during the Last Glacial Maximum (LGM) in East-Central Europe. Previous studies demonstrated Lateglacial vegetation dynamics in this area; however, our knowledge on the LGM vegetation composition is very limited due to the scarcity of suitable sedimentary archives. Here we present a new record of vegetation, fire and lacustrine sedimentation from the youngest volcanic crater of the Carpathians (Lake St Anne, Lacul Sfânta Ana, Szent-Anna-tó) to examine environmental change in this region during the LGM and the subsequent deglaciation. Our record indicates the persistence of boreal forest steppe vegetation (with Pinus, Betula, Salix, Populus and Picea) in the foreland and low mountain zone of the East Carpathians and Juniperus shrubland at higher elevation. We demonstrate attenuated response of the regional vegetation to maximum global cooling. Between ˜22,870 and 19,150 cal yr BP we find increased regional biomass burning that is antagonistic with the global trend. Increased regional fire activity suggests extreme continentality likely with relatively warm and dry summers. We also demonstrate xerophytic steppe expansion directly after the LGM, from ˜19,150 cal yr BP, and regional increase in boreal woodland cover with Pinus and Betula from 16,300 cal yr BP. Plant macrofossils indicate local (950 m a.s.l.) establishment of Betula nana and Betula pubescens at 15,150 cal yr BP, Pinus sylvestris at 14,700 cal yr BP and Larix decidua at 12,870 cal yr BP. Pollen data furthermore support population genetic inferences regarding the regional presence of some temperate deciduous trees during the LGM (Fagus sylvatica, Corylus avellana, Fraxinus excelsior). Our sedimentological data also demonstrate intensified aeolian dust accumulation between 26,000 and 20,000 cal yr BP.

  8. Climatic Oscillations 10,000-155,000 yr B.P. at Owens Lake, California Reflected in Glacial Rock Flour Abundance and Lake Salinity in Core OL-92

    NASA Astrophysics Data System (ADS)

    Bischoff, James L.; Menking, Kirsten M.; Fitts, Jeffrey P.; Fitzpatrick, John A.

    1997-11-01

    Chemical analyses of the acid-soluble and clay-size fractions of sediment samples (1500-yr resolution) reveal oscillations of lake salinity and of glacial advances in core OL-92 back to 155,000 yr B.P. Relatively saline conditions are indicated by the abundance of carbonate and smectite (both pedogenic and authigenic), reflected by Ca, Sr, and Mg in the acid-soluble suite, and by Cs 2O, excess MgO, and LOI (loss on ignition) in the clay-size fraction. Rock flour produced during glacial advances is represented by the abundance of detrital plagioclase and biotite in the clay-size fraction, the ratio of which remains essentially constant over the entire time span. These phases are quantitatively represented by Na 2O, TiO 2, Ba, and Mn in the clay fraction. The rock-flour record indicates two major ice-advances during the penultimate glacial cycle corresponding to marine isotope stage (MIS) 6, no major advances during the last interglaciation (entire MIS 5), and three major advances during the last glacial cycle (MIS 2, 3, and 4). The ages of the latter three correspond rather well to 36Cl dates reported for Sierra Nevada moraines. The onset of the last interglaciation is shown by abrupt increases in authigenic CaCO 3and an abrupt decrease in rock flour, at about 118,000 yr B.P. according to our time scale. In contrast, the boundary appears to be gradual in the δ 18O record in which the change from light to heavy values begins at about 140,000 yrs B.P. The exact position of the termination, therefore, may be proxy-dependent. Conditions of high carbonate and low rock flour prevailed during the entire period from 118,000 yr B.P. until the glacial advance at 53,000 yr B.P. signaled the end of this long interglaciation.

  9. Postglacial vegetation history of Orcas Island, northwestern Washington

    NASA Astrophysics Data System (ADS)

    Leopold, Estella B.; Dunwiddie, Peter W.; Whitlock, Cathy; Nickmann, Rudy; Watts, William A.

    2016-05-01

    The revegetation of islands following retreat of Pleistocene glaciers is of great biogeographical interest. The San Juan Islands, Washington, feature regionally distinctive xerophytic plant communities, yet their vegetation history, as it relates to past climate and sea level, is poorly known. We describe a 13,700-year-old pollen record from Killebrew Lake Fen and compare the vegetation reconstruction with others from the region. The data suggest that the narrow channels surrounding Orcas Island were not a barrier to early postglacial immigration of plants. Between 13,700 and 12,000 cal yr BP, Pinus, Tsuga, Picea, Alnus viridis, and possibly Juniperus maritima were present in a mosaic that supported Bison antiquus and Megalonyx. The rise of Alnus rubra-type pollen and Pteridium spores at ca. 12,000 cal yr BP suggests a warming trend and probably more fires. Temperate conifer taxa, including Cupressaceae, Pseudotsuga, Tsuga heterophylla, and Abies, increased after 11,000 cal yr BP and especially in the last 7000 cal yr BP. After 6000 cal yr BP, Pseudotsuga and Cupressaceae dominated the vegetation. The last 1500 yr were the wettest period of the record. Due to its rain shadow location, Orcas Island experienced drier conditions than on the mainland during most of the postglacial period.

  10. Depositional Architecture of Late Pleistocene-Holocene Coastal Alluvial-fan System in the Coastal Range, Taiwan

    NASA Astrophysics Data System (ADS)

    Chen, S. T.; Chen, W. S.

    2016-12-01

    Since late Pleistocene, the Coastal Range (Philippine Sea plate) collided and overridden on the Central Range (Eurasian Plate) along the Longitudinal Valley Fault. Therefore, the Coastal Range is exposed widely the late Pleistocene-Holocene marine and fluvial terraces caused by the tectonic uplift. Based on the estimation of paleosea-level elevations (Δh), depositional paleodepth, altitude distribution of Holocene deposits (D), altitude of outcrops (H), and 14C dating of marine deposits (t), the uplift rate (=(Δh+H +d-D)/t) is about 5-10 mm/yr in the southern Coastal Range. In this study, we suggest through field logging that the deposits can be divided into alluvial, foreshore (intertidal), shoreface, and offshore environments. In Dulan area in the southern Coastal Range, the uplift rate was 6-7 mm/yr during 16,380-10,000 cal yr BP and 3-4 mm/yr after 7,000 cal yr BP. Results from the Dulan Coastal alluvial-fan system can be divided into five depositional stages: (1) 16,380-14,300 cal yr BP: The rate of global sea level rise (SLR) has averaged about 6-7 mm/yr, similar to the tectonic uplift rate. In this stage, the bedrock was eroded and formed a wide wave-cut platform. (2) 14,300-10,000 cal yr BP: SLR of about 14 mm/yr that was faster than tectonic uplift rate of 6-7 mm/yr. As a result of transgression, the beach-lagoon deposits about 5 m thick were unconformably overlain on the wave-cut platform. (3) 10,000-8,200 cal yr BP: The ongoing sea level rise (SLR: 11 mm/yr), the lagoon deposits were overlain by an offshore slump deposits representing a gradual deepening of the depositional environment. (4) 8,200-7,930 cal yr BP (SLR: 6-7 mm/yr): The tectonic uplift rate may occur at similar SLR. The alluvial-fan deposits have prograded over the shallow marine deposits. (5) After 7,000 cal yr BP (SLR: 1-0 mm/yr): SLR was much slower than tectonic uplift rate of 3-4 mm/yr. Thus, Holocene marine terraces are extensively developed in the coastal region, showing that the

  11. Interplay between Amazonia Tropical Rain Forest Fires (Mesoscale distribution) and global carbon cycle

    NASA Astrophysics Data System (ADS)

    Cordeiro, R. C.; Turcq, B.; Sifeddine, A.

    2009-12-01

    Soil samples were collected at 9 different depths, from zero to 100 cm at six points distributed along a transect of 1700 m in upland and lowland areas of the Km 41 reserve near Manaus in Central Brazilian Amazonia, in order to compare the frequency, dimension and extension of past fires in different topographic environmental situations. The average charcoal mass distribution is higher in uplands than in lowlands. This distribution shows a gradient with a high correlation between the two topographic levels, demonstrating a characteristic depth distribution pattern. The highest charcoal concentrations were found at a depth of 20-50 cm in all the six profiles. These fires have affected the upland areas more severely than the lowlands, probably allowing the survival of the vegetation along the small streams.. Two periods of intense fire activity were identified through the distribution of the biomass of charcoal: from around 1320 cal yr BP (ca 1400 14C yr BP) to 1050 cal yr BP (ca 1100 14C yr BP), and between 610 cal yr BP (ca 600 14C yr BP) to 330 cal yr BP (ca 300 yr 14C yr BP). These forest fire phases were probably favored by dry climate which is recorded in other regions of Amazonia and South America by archaeological and palaeoecological data.. Observe that the data found in this article related to the disturbances of fire events in the Central Amazon region appear to be synchronous with events of disruption of populations and vegetation changes and background to the development of indigenous people. Thus it seems plausible that these disturbance phenomena may have an origin presumably climatic than anthropogenic. This possible relationship between climate and forest, ecosystems of high productivity and biomass, and humans should be look carefully in relation to the carbon cycle dynamics demonstrated by the air bubbles extracted of the ice core records.. Increase is observed in the CO2 concentration of the Taylor Dome record just after the increase in frequency

  12. Early atmospheric metal pollution provides evidence for Chalcolithic/Bronze Age mining and metallurgy in Southwestern Europe.

    PubMed

    Martínez Cortizas, Antonio; López-Merino, Lourdes; Bindler, Richard; Mighall, Tim; Kylander, Malin E

    2016-03-01

    Although archaeological research suggests that mining/metallurgy already started in the Chalcolithic (3rd millennium BC), the earliest atmospheric metal pollution in SW Europe has thus far been dated to ~3500-3200 cal.yr. BP in paleo-environmental archives. A low intensity, non-extensive mining/metallurgy and the lack of appropriately located archives may be responsible for this mismatch. We have analysed the older section (>2100 cal.yr. BP) of a peat record from La Molina (Asturias, Spain), a mire located in the proximity (35-100 km) of mines which were exploited in the Chalcolithic/Bronze Age, with the aim of assessing evidence of this early mining/metallurgy. Analyses included the determination of C as a proxy for organic matter content, lithogenic elements (Si, Al, Ti) as markers of mineral matter, and trace metals (Cr, Cu, Zn, Pb) and stable Pb isotopes as tracers of atmospheric metal pollution. From ~8000 to ~4980 cal.yr. BP the Pb composition is similar to that of the underlying sediments (Pb 15 ± 4 μg g(-1); (206)Pb/(207)Pb 1.204 ± 0.002). A sustained period of low (206)Pb/(207)Pb ratios occurred from ~4980 to ~2470 cal.yr. BP, which can be divided into four phases: Chalcolithic (~4980-3700 cal.yr. BP), (206)Pb/(207)Pb ratios decline to 1.175 and Pb/Al ratios increase; Early Bronze Age (~3700-3500 cal.yr. BP), (206)Pb/(207)Pb increase to 1.192 and metal/Al ratios remain stable; Late Bronze Age (~3500-2800 cal.yr. BP), (206)Pb/(207)Pb decline to their lowest values (1.167) while Pb/Al and Zn/Al increase; and Early Iron Age (~2800-2470 cal.yr. BP), (206)Pb/(207)Pb increase to 1.186, most metal/Al ratios decrease but Zn/Al shows a peak. At the beginning of the Late Iron Age, (206)Pb/(207)Pb ratios and metal enrichments show a rapid return to pre-anthropogenic values. These results provide evidence of regional/local atmospheric metal pollution triggered by the earliest phases of mining/metallurgy in the area, and reconcile paleo-environmental and

  13. Holocene environmental changes inferred from biological and sedimentological proxies in a high elevation Great Basin lake in the northern Ruby Mountains, Nevada, USA

    USGS Publications Warehouse

    Wahl, David B.; Starratt, Scott W.; Anderson, Lysanna; Kusler, Jennifer E.; Fuller, Christopher C.; Addison, Jason A.; Wan, Elmira

    2015-01-01

    Multi-proxy analyses were conducted on a sediment core from Favre Lake, a high elevation cirque lake in the northern Ruby Mountains, Nevada, and provide a ca. 7600 year record of local and regional environmental change. Data indicate that lake levels were lower from 7600-5750 cal yr BP, when local climate was warmer and/or drier than today. Effective moisture increased after 5750 cal yr BP and remained relatively wet, and possibly cooler, until ca. 3750 cal yr BP. Results indicate generally dry conditions but also enhanced climatic variability from 3750-1750 cal yr BP, after which effective moisture increased. The timing of major changes in the Favre Lake proxy data are roughly coeval and in phase with those recorded in several paleoclimate studies across the Great Basin, suggesting regional climatic controls on local conditions and similar responses at high and low altitudes.

  14. Biomes of western North America at 18,000, 6000 and 0 14C yr BP reconstructed from pollen and packrat midden data

    USGS Publications Warehouse

    Thompson, R.S.; Anderson, K.H.

    2000-01-01

    A new compilation of pollen and packrat midden data from western North America provides a refined reconstruction of the composition and distribution of biomes in western North America for today and for 6000 and 18,000 radiocarbon years before present (14C yr BP). Modern biomes in western North America are adequately portrayed by pollen assemblages from lakes and bogs. Forest biomes in western North America share many taxa in their pollen spectra and it can be difficult to discriminate among these biomes. Plant macrofossils from packrat middens provide reliable identification of modern biomes from arid and semiarid regions, and this may also be true in similar environments in other parts of the world. However, a weighting factor for trees and shrubs must be used to reliably reconstruct modern biomes from plant macrofossils. A new biome, open conifer woodland, which includes eurythermic conifers and steppe plants, was defined to categorize much of the current and past vegetation of the semiarid interior of western North America. At 6000 14C yr BP, the forest biomes of the coastal Pacific North-west and the desert biomes of the South-west were in near-modern positions. Biomes in the interior Pacific North-west differed from those of today in that taiga prevailed in modern cool/cold mixed forests. Steppe was present in areas occupied today by open conifer woodland in the northern Great Basin, while in the central and southern Rocky Mountains forests grew where steppe grows today. During the mid-Holocene, cool conifer forests were expanded in the Rocky Mountains (relative to today) but contracted in the Sierra Nevada. These differences from the forests of today imply different climatic histories in these two regions between 6000 14C yr BP and today. At 18,000 14C yr BP, deserts were absent from the South-west and the coverage of open conifer woodland was greatly expanded relative to today. Steppe and tundra were present in much of the region now covered by forests in

  15. Holocene relative sea-level change in Hiroshima Bay, Japan: A semi-quantitative reconstruction based on ostracodes

    USGS Publications Warehouse

    Yasuhara, Moriaki; Seto, Koji

    2006-01-01

    Holocene relative sea-level changes in Hiroshima Bay were reconstructed from fossil ostracodes from a core, using a semi-quantitative method. In Hiroshima Bay, relative sea level rose rapidly (about 25 m) between ca. 9000 cal yr BP and ca. 5800 cal yr BP, after which it gradually fell (about 5 m) to its present level. The peak in relative sea level occurred at ca. 5800 cal yr BP. The sea-level curve for Hiroshima Bay is similar to curves for tectonically stable areas of Japan (e.g., Osaka Bay). ?? by the Palaeontological Society of Japan.

  16. Paleoenvironmental dynamics in South Amazonia, Brazil, during the last 35,000 years inferred from pollen and geochemical records of Lago do Saci

    NASA Astrophysics Data System (ADS)

    Fontes, D.; Cordeiro, R. C.; Martins, G. S.; Behling, H.; Turcq, B.; Sifeddine, A.; Seoane, J. C. S.; Moreira, L. S.; Rodrigues, R. A.

    2017-10-01

    Paleoenvironmental changes for the last 35,000 years were reconstructed from palynological, sedimentological and organic geochemical evidence from a well-dated sediment core from Lago do Saci (South Amazonia). Dry climatic conditions occurred between 35,000 and 18,200 cal yr BP as recorded by high frequencies of open savanna taxa and low lake level indicated by Sagittaria and low Total Organic Carbon content. Cold temperatures are indicated by the presence of Podocarpus and Ilex. A sedimentation hiatus observed between 18,200 and 9200 cal yr BP was likely related to dry conditions. The beginning of the Holocene was marked by rainforest expansion and an increase in carbon content that represented high lake levels and warmer and wetter climate conditions. Between 7500 and 5000 cal yr BP, the expansion of open savanna, seasonal forest elements and abundant black carbon suggests a dry phase. After 5000 cal yr BP, rainforest expansion and higher lake levels indicate a return to wetter conditions. A reduction of flooding taxa (Celtis and Mauritia) between 1800 and 1300 cal yr BP, high lake level conditions and maintenance of a forest physiognomy, suggests a decrease of regional precipitation and subsequent reduction of the flooded areas in a still humid climate regime.

  17. Climatic Oscillations 10,000-155,000 yr B.P. at Owens Lake, California Reflected in Glacial Rock Flour Abundance and Lake Salinity in Core OL-92

    USGS Publications Warehouse

    Bischoff, J.L.; Menking, K.M.; Fitts, J.P.; Fitzpatrick, J.A.

    1997-01-01

    Chemical analyses of the acid-soluble and clay-size fractions of sediment samples (1500-yr resolution) reveal oscillations of lake salinity and of glacial advances in core OL-92 back to 155,000 yr B.P. Relatively saline conditions are indicated by the abundance of carbonate and smectite (both pedogenic and authigenic), reflected by Ca, Sr, and Mg in the acid-soluble suite, and by Cs2O, excess MgO, and LOI (loss on ignition) in the clay-size fraction. Rock flour produced during glacial advances is represented by the abundance of detrital plagioclase and biotite in the clay-size fraction, the ratio of which remains essentially constant over the entire time span. These phases are quantitatively represented by Na2O, TiO2, Ba, and Mn in the clay fraction. The rock-flour record indicates two major ice-advances during the penultimate glacial cycle corresponding to marine isotope stage (MIS) 6, no major advances during the last interglaciation (entire MIS 5), and three major advances during the last glacial cycle (MIS 2, 3, and 4). The ages of the latter three correspond rather well to 36Cl dates reported for Sierra Nevada moraines. The onset of the last interglaciation is shown by abrupt increases in authigenic CaCO3 and an abrupt decrease in rock flour, at about 118,000 yr B.P. according to our time scale. In contrast, the boundary appears to be gradual in the ??18O record in which the change from light to heavy values begins at about 140,000 yrs B.P. The exact position of the termination, therefore, may be proxy-dependent. Conditions of high carbonate and low rock flour prevailed during the entire period from 118,000 yr B.P. until the glacial advance at 53,000 yr B.P. signaled the end of this long interglaciation. ?? 1997 University of Washington.

  18. New stratigraphic constraints on Holocene glacier advances at Mt. Baker, Washington

    NASA Astrophysics Data System (ADS)

    Clark, D.; Ryane, C.; Tucker, D.; Davis, T.; Bowerman, N.; Osborn, G.; Clague, J.; Menounos, B.; Scott, K.; Guilderson, T.; Riedel, J.; Steig, E.

    2007-12-01

    New data from a lake sediment core and moraine exposures at Mt. Baker, WA, indicate that a purported early Holocene glacier advance occurred earlier, likely at the end of the Pleistocene. Previous workers used 14C ages associated with small cirque moraines on the SW flank of Mt. Baker, along with the apparent absence of a distinctive scoria (set SC; 8850 14C yr BP, ~9900 cal yr BP) from other moraines on Mt. Baker, as evidence for an advance at ~8400 14C yr BP (~9450 cal yr BP). Such an advance is important to test because it would contrast with glacial records throughout most of the rest of western North America. A 1.2-m sediment core collected from Pocket Lake, which is dammed by one of the previously dated cirque moraines, contains three tephras: Baker set BA (~5800 14C yr BP; 6600 cal yr BP), Mazama ash (6800 14C yr BP; 7600 cal yr BP), and a basal set of ash beds that are tentatively identified as Baker set SC. The lowest macrofossil in the core, ~2 cm above the top of the basal ash beds, yielded an age of 7640 ± 50 14C yr BP (~8400 cal yr BP), consistent with the tephra being SC. Initial geochemical analyses of the tephra also support this identification. These findings indicate that the previous age on the cirque moraine, from organics near the surface of the till, provides a minimum rather than a direct age for the advance that formed the moraine. A 14C age of 11,400 ± 110 14C yr BP (~13,300 cal yr BP) on bulk sediments below the basal ash is likely contaminated and therefore too old. Tephra overlying other ridges at Mt. Baker that were previously identified as post-SC, early-Holocene moraines has been identified as set SC. The ridges thus are actually pre-SC rather than post-SC in age; they may not be moraines in any event. Meanwhile, abundant 14C ages on tills below Deming Glacier indicate both Younger Dryas and Neoglacial advances, but no early Holocene advances. Together, these observations indicate that glaciers in the Mt. Baker area advanced during

  19. Ancient charcoal as a natural archive for paleofire regime and vegetation change in the Mayumbe, Democratic Republic of the Congo

    NASA Astrophysics Data System (ADS)

    Hubau, Wannes; Van den Bulcke, Jan; Kitin, Peter; Mees, Florias; Baert, Geert; Verschuren, Dirk; Nsenga, Laurent; Van Acker, Joris; Beeckman, Hans

    2013-09-01

    Charcoal was sampled in four soil profiles at the Mayumbe forest boundary (DRC). Five fire events were recorded and 44 charcoal types were identified. One stratified profile yielded charcoal assemblages around 530 cal yr BP and > 43.5 cal ka BP in age. The oldest assemblage precedes the period of recorded anthropogenic burning, illustrating occasional long-term absence of fire but also natural wildfire occurrences within tropical rainforest. No other charcoal assemblages older than 2500 cal yr BP were recorded, perhaps due to bioturbation and colluvial reworking. The recorded paleofires were possibly associated with short-lived climate anomalies. Progressively dry climatic conditions since ca. 4000 cal yr BP onward did not promote paleofire occurrence until increasing seasonality affected vegetation at the end of the third millennium BP, as illustrated by a fire occurring in mature rainforest that persisted until around 2050 cal yr BP. During a drought episode coinciding with the 'Medieval Climate Anomaly', mature rainforest was locally replaced by woodland savanna. Charcoal remains from pioneer forest indicate that fire hampered forest regeneration after climatic drought episodes. The presence of pottery shards and oil-palm endocarps associated with two relatively recent paleofires suggests that the effects of climate variability were amplified by human activities.

  20. Mid-Holocene palaeoflood events recorded at the Zhongqiao Neolithic cultural site in the Jianghan Plain, middle Yangtze River Valley, China

    NASA Astrophysics Data System (ADS)

    Wu, Li; Zhu, Cheng; Ma, Chunmei; Li, Feng; Meng, Huaping; Liu, Hui; Li, Linying; Wang, Xiaocui; Sun, Wei; Song, Yougui

    2017-10-01

    Palaeo-hydrological and archaeological investigations were carried out in the Jianghan Plain in the middle reaches of the Yangtze River. Based on a comparative analysis of modern flood sediments and multidisciplinary approaches such as AMS14C and archaeological dating, zircon micromorphology, grain size, magnetic susceptibility, and geochemistry, we identified palaeoflood sediments preserved at the Zhongqiao archaeological site. The results indicate that three palaeoflood events (i.e. 4800-4597, 4479-4367, and 4168-3850 cal. yr BP) occurred at the Zhongqiao Site. Comparisons of palaeoflood deposit layers at a number of Neolithic cultural sites show that two extraordinary palaeoflood events occurred in the Jianghan Plain during approximately 4900-4600 cal. yr BP (i.e.mid-late Qujialing cultural period) and 4100-3800 cal. yr BP (i.e. from late Shijiahe cultural period to the Xia Dynasty). Further analysis of the environmental context suggests that these flooding events might have been connected with great climate variability during approximately 5000-4500 cal. yr BP and at ca. 4000 cal. yr BP. These two palaeoflood events were closely related to the expansion of the Jianghan lakes driven by the climatic change, which in turn influenced the rise and fall of the Neolithic cultures in the middle reaches of the Yangtze River. Other evidence also suggests that the intensified discrepancy between social development and environmental change processes (especially the hydrological process) during the late Shijiahe cultural period might be the key factor causing the collapse of the Shijiahe Culture. The extraordinary floods related to the climatic anomaly at ca. 4000 cal. yr BP and political conflicts from internal or other cultural areas all accelerated the collapse of the Shijiahe Culture.

  1. Early to Middle Holocene sea level fluctuation, coastal progradation and the Neolithic occupation in the Yaojiang Valley of southern Hangzhou Bay, Eastern China

    NASA Astrophysics Data System (ADS)

    Liu, Yan; Sun, Qianli; Fan, Daidu; Dai, Bin; Ma, Fuwei; Xu, Lichen; Chen, Jing; Chen, Zhongyuan

    2018-06-01

    The Yaojiang Valley (YJV) of southern Hangzhou Bay was the birthplace of the well-known Hemudu Culture (HC), one of the representatives of Neolithic civilization in eastern China. To explore the magnitude of natural environmental effects on the HC trajectory, the palaeo-embayment setting of the YJV was studied in detail for the first time in terms of 3D Holocene strata supported by a series of new radiocarbon-dated cores. The results indicated that the local relative sea level rose rapidly during the Early Holocene in the YJV, reached its maximum flooding surface ca. 7900 cal yr BP, and then remained stable ca. 7900-7600 cal yr BP. Thereupon, an estuary stretching inland was first formed by marine transgression, and then, it was transformed to an alluvial-coastal plain by regressive progradation. The alluvial plain was initiated in the foothills and then spread towards the valley centre after sea level stabilization ca. 7600 cal yr BP. Accompanying these natural environmental changes, the earliest arrivals of foragers in the valley occurred no later than ca. 7000 cal yr BP. They engaged in rice farming and fostered the HC for approximately two millennia from ca. 7000-5000 cal yr BP as more lands developed from coastal progradation. The rise and development of the HC are closely associated with the sea level-induced landscape changes in the YJV in the Early-Middle Holocene, but the enigmatic exodus of the HC people after ca. 5000 cal yr BP is still contentious and possibly linked with the rapid waterlogging and deterioration of this setting in such a low-lying coastal plain as well as with associated social reasons.

  2. Late Quaternary palaeolakes, rivers, and wetlands on the Bolivian Altiplano and their palaeoclimatic implications

    NASA Astrophysics Data System (ADS)

    Rigsby, Catherine A.; Platt Bradbury, J.; Baker, Paul A.; Rollins, Stephanie M.; Warren, Michelle R.

    2005-10-01

    Drill cores of sediments from the Rio Desaguadero valley, Bolivia, provide new information about the climate of tropical South America over the past 50 000 years. The modern Rio Desaguadero is fed by Lake Titicaca overflow (and by local tributaries) in the wetter northern Altiplano and discharges into Lake Poopo in the more arid central Altiplano. During the late Quaternary the Rio Desaguadero valley was the site of several generations of palaeolakes and wetlands that formed during periods of increased precipitation and local runoff, augmented by increased overflow from Lake Titicaca. Sediments recovered by drilling in eight localities along the 390-km long valley of the Rio Desaguadero yield a regional history of lacustrine sedimentation and effective precipitation. Lacustrine strata in the drill cores record 12 distinct wet periods in the past 50 000 years. Four of these wet periods resulted in the formation of major palaeolakes in the Rio Desaguadero valley: during the last glacial maximum from before 20 000 to 16 000 cal. yr BP, during the late glacial from about 14 000 to 12 000 cal. yr BP, in the early Holocene from about 10 000 to 7900 cal. yr BP, and in the late Holocene from 4500 cal. yrBP to present. The period that appears to have been most arid was between 7900 and 4500cal.yrBP. The Altiplano wet periods were generally synchronous with North Atlantic cold events (respectively, the last glacial maximum, the Younger Dryas, the 8200cal.yrBP event, and the Neoglacial) implying a relationship between past precipitation variability in tropical South America and North Atlantic sea-surface temperature.

  3. Mid-Holocene hydrology change in the south Taihu area of the Yangtze delta plain, China, and its relationship to the development of Neolithic cultures

    NASA Astrophysics Data System (ADS)

    Chen, T.; Ryves, D.; Wang, Z.; Lewis, J.

    2017-12-01

    During the middle Holocene, the hydrological environments in the Taihu Plain, Yangtze Delta, China, varied tremendously under the influence of sea-level and climate change. Simultaneously, several Neolithic cultures, such as, the Majiabang, Songze, and Liangzhu culture, developed in this region. Basing on AMS14C dating, diatom identification, measurements of C-N elements and their stable isotopes of sediments from core DTX4 and DTX10, obtained in the East Tiaoxi Plain, south Taihu plain, we discussed the influence of hydrology changes on the development of Neolithic cultures. The results revealed that the East Tiaoxi River plain was in an estuary (the Palaeo-Taihu Estuary) condition at 7500 cal. yr BP, undergoing elevated in-fill in response to rapid sea-level rise. After 7500 cal. yr BP, low salinity conditions occurred, likely influenced by the Yangtze freshwater evidenced by constant occurrence of Aulacoseira granulata, which implied Yangtze runoff discharged along the channel of Palaeo-incised Taihu valley into the Hangzhou Bay during the middle Holocene. Sea-water penetration interrupted after 7000 cal. yr BP caused by an abrupt sea-level rise. During 6500-5600 cal. yr BP, sea-water retreated gradually, corresponding to the infilling of Palaeo-Taihu Estuary. Combing records from previously studied cores in the Taihu plain, stable freshwater condition (or dry land) established in most area of the Taihu plain after 5600 cal. yr BP due to the closure of the Palaeo-Taihu Estuary. We speculate that the low-salinity marsh started at about 7500-7000 cal. yr BP probably attracted the early Majiabang people to live around the Palaeo-Taihu Estuary. The sea water penetration between 7000-6500 cal. yr BP matches the left of the late Majiabang and the early-middle Songze people lived in the east of the Palaeo-Taihu Estuary, to the north and east of the Taihu Plain. The context of stable freshwater condition (or dry land) in the East Tiaoxi River plain promoted the

  4. Development of the mixed conifer forest in northern New Mexico and its relationship to Holocene environmental change

    NASA Astrophysics Data System (ADS)

    Anderson, R. Scott; Jass, Renata B.; Toney, Jaime L.; Allen, Craig D.; Cisneros-Dozal, Luz M.; Hess, Marcey; Heikoop, Jeff; Fessenden, Julianna

    2008-03-01

    Chihuahueños Bog (2925 m) in the Jemez Mountains of northern New Mexico contains one of the few records of late-glacial and postglacial development of the mixed conifer forest in southwestern North America. The Chihuahueños Bog record extends to over 15,000 cal yr BP. An Artemisia steppe, then an open Picea woodland grew around a small pond until ca. 11,700 cal yr BP when Pinus ponderosa became established. C/N ratios, δ13C and δ15N values indicate both terrestrial and aquatic organic matter was incorporated into the sediment. Higher percentages of aquatic algae and elevated C/N ratios indicate higher lake levels at the opening of the Holocene, but a wetland developed subsequently as climate warmed. From ca. 8500 to 6400 cal yr BP the pond desiccated in what must have been the driest period of the Holocene there. C/N ratios declined to their lowest Holocene levels, indicating intense decomposition in the sediment. Wetter conditions returned after 6400 cal yr BP, with conversion of the site to a sedge bog as groundwater levels rose. Higher charcoal influx rates after 6400 cal yr BP probably result from greater biomass production rates. Only minor shifts in the overstory species occurred during the Holocene, suggesting that mixed conifer forest dominated throughout the record.

  5. Development of the mixed conifer forest in northern New Mexico and its relationship to Holocene environmental change

    USGS Publications Warehouse

    Anderson, R. Scott; Jass, R.B.; Toney, J.L.; Allen, Craig D.; Cisneros-Dozal, L. M.; Hess, M.; Heikoop, Jeff; Fessenden, J.

    2008-01-01

    Chihuahueños Bog (2925 m) in the Jemez Mountains of northern New Mexico contains one of the few records of late-glacial and postglacial development of the mixed conifer forest in southwestern North America. The Chihuahueños Bog record extends to over 15,000 cal yr BP. AnArtemisiasteppe, then an openPiceawoodland grew around a small pond until ca. 11,700 cal yr BP whenPinus ponderosabecame established. C/N ratios,δ 13C andδ 15N values indicate both terrestrial and aquatic organic matter was incorporated into the sediment. Higher percentages of aquatic algae and elevated C/N ratios indicate higher lake levels at the opening of the Holocene, but a wetland developed subsequently as climate warmed. From ca. 8500 to 6400 cal yr BP the pond desiccated in what must have been the driest period of the Holocene there. C/N ratios declined to their lowest Holocene levels, indicating intense decomposition in the sediment. Wetter conditions returned after 6400 cal yr BP, with conversion of the site to a sedge bog as groundwater levels rose. Higher charcoal influx rates after 6400 cal yr BP probably result from greater biomass production rates. Only minor shifts in the overstory species occurred during the Holocene, suggesting that mixed conifer forest dominated throughout the record.

  6. Late Quaternary vegetation and climate history of a perennial river canyon in the Rīo Salado basin (22°S) of Northern Chile

    USGS Publications Warehouse

    Latorre, Claudio; Betancourt, Julio L.; Arroyo, Mary T.K.

    2006-01-01

    Plant macrofossils from 33 rodent middens sampled at three sites between 2910 and 3150 m elevation in the main canyon of the Rīo Salado, northern Chile, yield a unique record of vegetation and climate over the past 22,000 cal yr BP. Presence of low-elevation Prepuna taxa throughout the record suggests that mean annual temperature never cooled by more than 5°C and may have been near-modern at 16,270 cal yr BP. Displacements in the lower limits of Andean steppe and Puna taxa indicate that mean annual rainfall was twice modern at 17,520-16,270 cal yr BP. This pluvial event coincides with infilling of paleolake Tauca on the Bolivian Altiplano, increased ENSO activity inferred from a marine core near Lima, abrupt deglaciation in southern Chile, and Heinrich Event 1. Moderate to large increases in precipitation also occurred at 11,770-9550 (Central Atacama Pluvial Event), 7330-6720, 3490-2320 and at 800 cal yr BP. Desiccation occurred at 14,180, 8910-8640, and 4865 cal yr BP. Compared to other midden sites in the region, early Holocene desiccation seems to have happened progressively earlier farther south. Emerging trends from the cumulative midden record in the central Atacama agree at millennial timescales with improved paleolake chronologies for the Bolivian Altiplano, implying common forcing through changes in equatorial Pacific sea-surface temperature gradients.

  7. Late Quaternary paleoclimate of western Alaska inferred from fossil chironomids and its relation to vegetation histories

    USGS Publications Warehouse

    Kurek, Joshua; Cwynar, Les C.; Ager, Thomas A.; Abbott, Mark B.; Edwards, Mary E.

    2009-01-01

    Fossil Chironomidae assemblages (with a few Chaoboridae and Ceratopogonidae) from Zagoskin and Burial Lakes in western Alaska provide quantitative reconstructions of mean July air temperatures for periods of the late-middle Wisconsin (~39,000-34,000 cal yr B.P.) to the present. Inferred temperatures are compared with previously analyzed pollen data from each site summarized here by indirect ordination. Paleotemperature trends reveal substantial differences in the timing of climatic warming following the late Wisconsin at each site, although chronological uncertainty exists. Zagoskin Lake shows early warming beginning at about 21,000 cal yr B.P., whereas warming at Burial Lake begins ~4000 years later. Summer climates during the last glacial maximum (LGM) were on average ~3.5C° below the modern temperatures at each site. Major shifts in vegetation occurred from ~19,000 to 10,000 cal yr B.P. at Zagoskin Lake and from ~17,000 to 10,000 cal yr B.P. at Burial Lake. Vegetation shifts followed climatic warming, when temperatures neared modern values. Both sites provide evidence of an early postglacial thermal maximum at ~12,300 cal yr B.P. These chironomid records, combined with other insect-based climatic reconstructions from Beringia, indicate that during the LGM: (1) greater continentality likely influenced regions adjacent to the Bering Land Bridge and (2) summer climates were, at times, not dominated by severe cold.

  8. Geochronology and Geomorphology of the Pioneer Archaeological Site (10BT676), Upper Snake River Plain, Idaho

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Keene, Joshua L.

    2015-04-01

    The Pioneer site in southeastern Idaho, an open-air, stratified, multi-component archaeological locality on the upper Snake River Plain, provides an ideal situation for understanding the geomorphic history of the Big Lost River drainage system. We conducted a block excavation with the goal of understanding the geochronological context of both cultural and geomorphological components at the site. The results of this study show a sequence of five soil formation episodes forming three terraces beginning prior to 7200 cal yr BP and lasting until the historic period, preserving one cultural component dated to ~3800 cal yr BP and multiple components dating tomore » the last 800 cal yr BP. In addition, periods of deposition and stability at Pioneer indicate climate fluctuation during the middle Holocene (~7200-3800 cal yr BP), minimal deposition during the late Holocene, and a period of increased deposition potentially linked to the Little Ice Age. In addition, evidence for a high-energy erosion event dated to ~3800 cal yr BP suggest a catastrophic flood event during the middle Holocene that may correlate with volcanic activity at the Craters of the Moon lava fields to the northwest. This study provides a model for the study of alluvial terrace formations in arid environments and their potential to preserve stratified archaeological deposits.« less

  9. 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.

  10. A 3400 year paleolimnological record of prehispanic human–environment interactions in the Holmul region of the southern Maya lowlands

    USGS Publications Warehouse

    Wahl, David B.; Estrada-Belli, Francisco; Anderson, Lysanna

    2015-01-01

    The timing, magnitude and drivers of late Holocene environmental change in the Holmul region of the southern Maya lowlands are examined by combining paleoenvironmental and archeological data. Environmental proxy analyses on a ~ 3350 cal yr lacustrine sediment record include pollen, charcoal, loss on ignition, magnetic suscep- tibility, and elemental geochemistry. Archeological evidence is derived from extensive settlement surveys conducted near the study site. Results indicate nearby settlement and agricultural activity taking place in an environment characterized by open forest from around 3350 to 950 cal yr BP. The fire history shows a dramatic increase in burning during the Classic period, possibly reflecting changing agricultural strategies. A distinct band of carbonate deposited from 1270 to 1040 cal yr BP suggests decreased hydrologic input associated with drier conditions. Abrupt changes in proxy data around 940 cal yr BP indicate a cessation of human disturbance and local abandonment of the area.

  11. Late Quaternary stratigraphy and geochronology of the western Killpecker Dunes, Wyoming, USA

    USGS Publications Warehouse

    Mayer, J.H.; Mahan, S.A.

    2004-01-01

    New stratigraphic and geochronologic data from the Killpecker Dunes in southwestern Wyoming facilitate a more precise understanding of the dune field's history. Prior investigations suggested that evidence for late Pleistocene eolian activity in the dune field was lacking. However, luminescence ages from eolian sand of ???15,000 yr, as well as Folsom (12,950-11,950 cal yr B.P.) and Agate Basin (12,600-10,700 cal yr) artifacts overlying eolian sand, indicate the dune field existed at least during the latest Pleistocene, with initial eolian sedimentation probably occurring under a dry periglacial climate. The period between ???13,000 and 8900 cal yr B.P. was characterized by relatively slow eolian sedimentation concomitant with soil formation. Erosion occurred between ???8182 and 6600 cal yr B.P. on the upwind region of the dune field, followed by relative stability and soil formation between ???5900 and 2700 cal yr B.P. The first of at least two latest Holocene episodes of eolian sedimentation occurred between ???2000 and 1500 yr, followed by a brief (???500 yr) episode of soil formation; a second episode of sedimentation, occurring by at least ???700 yr, may coincide with a hypothesized Medieval warm period. Recent stabilization of the western Killpecker Dunes likely occurred during the Little Ice Age (???350-100 yr B.P.). The eolian chronology of the western Killpecker Dunes correlates reasonably well with those of other major dune fields in the Wyoming Basin, suggesting that dune field reactivation resulted primarily due to departures toward aridity during the late Quaternary. Similar to dune fields on the central Great Plains, dune fields in the Wyoming Basin have been active under a periglacial climate during the late Pleistocene, as well as under near-modern conditions during the latest Holocene. ?? 2003 University of Washington. All rights reserved.

  12. Paleoenvironmental and Paleoclimate Changes Since 21,000 Cal Years BP in the Northeastern part of Brazil Inferred From Sediment Records in Lagoa do Caco (Maranhao State, Brazil)

    NASA Astrophysics Data System (ADS)

    Sifeddine, A.; Meyers, P. A.; Gustavo, A.; Spadano Albuquerque, A. L.; Turcq, B.; Campbello Cordeiro, R.; Abrao, J. J.

    2004-12-01

    Two cores from Caco Lake, Maranhao State (North Brazil) record different histories of sediment accumulation on the margin and center of the lake that reflect changes in lake level. Seismic profiles, mineralogy and organic geochemical studies, backed by radiocarbon dating, reveal variable climatic and environmental conditions over the last 21 Cal Kyr BP. During the Last Glacial Maximum, regional climate was predominantly dry but was interrupted by short humid phases as reflected by a succession of very thin layers of sand and organic matter. The late glacial climate was relatively wet and included two rapid lake-level increases accompanied by forest expansion. The two wet phases were separated by a phase where the lake level remained stable and the forest changes were marked by the development of cool "Podocarpus" forest. These humid climate periods differed significantly from present warm tropical conditions.. The Holocene period is characterized by progressive increase of lake level, which reaches his maximum at around 7,000 Cal years BP. The period between 4,000 Cal years BP and the present shows high variability in lake level. Comparing with other South American and African records, we conclude that Late Glacial humid conditions were controlled by intensification of the ITCZ or shifts of its position, resulting in southeasterly trade wind variations and in interconnection between northern South America and the Atlantic tropical ocean-atmosphere system. The climatic variability during the Holocene is probably the result of sub-Milankovitch solar cycles and regional responses to these global forcings that are related to Atlantic and Pacific variability and their interconnections.

  13. A 2650-year-long record of environmental change from northern Yellowstone National Park based on a comparison of multiple proxy data

    USGS Publications Warehouse

    Whitlock, C.; Dean, W.; Rosenbaum, J.; Stevens, L.; Fritz, S.; Bracht, B.; Power, M.

    2008-01-01

    Geochemical, stable-isotope, pollen, charcoal, and diatom records were analyzed at high-resolution in cores obtained from Crevice Lake, a varved-sediment lake in northern Yellowstone National Park. The objective was to reconstruct the ecohydrologic, vegetation, and fire history of the watershed for the last 2650 years to better understand past climate variations at the forest-steppe transition. The data suggest a period of limited bottom-water anoxia, relatively wet winters, and cool springs and summers from 2650 to 2100 cal yr BP (700-150 BC). Dry warm conditions occurred between 2100 and 850-800 cal yr BP (150 BC and AD 1100-1150), when the lake was anoxic, winter precipitation was low, and summer stratification was protracted. The data are consistent with overall warmer/drier conditions during the Medieval Climate Anomaly, although they suggest a shift towards wetter winters within that period. The period from 850 to 800 cal yr BP (AD 1100-1150) to 250 cal yr BP (AD 1700) was characterized by greater water-column mixing and cooler spring/summer conditions than before. In addition, fire activity shifted towards infrequent large events and pollen production was low. From 250 to 150 cal yr BP (AD 1700-1800), winter precipitation was moderate compared to previous conditions, and the lake was again stratified, suggesting warm summers. Between 150 and 42 cal yr BP (AD 1800-1908), winter precipitation increased and spring and summer conditions became moderate. Metal pollution, probably from regional mining operations, is evident in the 1870s. Large fires occurred between ca. 1800-1880, but in general the forests were more closed than before. The Crevice Lake record suggests that the last 150 years of Yellowstone's environmental history were characterized by intermediate conditions when compared with the previous 2500 years. ?? 2007 Elsevier Ltd and INQUA.

  14. A 28,000 year history of vegetation and climate from Lower Red Rock Lake, Centennial Valley, Southwestern Montana, USA

    USGS Publications Warehouse

    Mumma, Stephanie Ann; Whitlock, Cathy; Pierce, Kenneth

    2012-01-01

    A sediment core extending to 28,000 cal yr BP from Lower Red Rock Lake in the Centennial Valley of southwestern Montana provides new information on the nature of full-glacial vegetation as well as a history of late-glacial and Holocene vegetation and climate in a poorly studied region. Prior to 17,000 cal yr BP, the eastern Centennial Valley was occupied by a large lake (Pleistocene Lake Centennial), and valley glaciers were present in adjacent mountain ranges. The lake lowered upon erosion of a newly formed western outlet in late-glacial time. High pollen percentages of Juniperus, Poaceae, Asteraceae, and other herbs as well as low pollen accumulation rates suggest sparse vegetation cover. Inferred cold dry conditions are consistent with a strengthened glacial anticyclone at this time. Between 17,000 and 10,500 cal yr BP, high Picea and Abies pollen percentages suggest a shift to subalpine parkland and warmer conditions than before. This is attributed to the northward shift of the jet stream and increasing summer insolation. From 10,500 to 7100 cal yr BP, pollen evidence of open dry forests suggests warm conditions, which were likely a response to increased summer insolation and a strengthened Pacific subtropical high-pressure system. From 7100 to 2400 cal yr BP, cooler moister conditions promoted closed forest and wetlands. Increases in Picea and Abies pollen percentages after 2400 cal yr BP suggest increasing effective moisture. The postglacial pattern of Pseudotsuga expansion indicates that it arrived later on the Atlantic side of the Continental Divide than on the Pacific side. The Divide may have been a physical barrier for refugial populations or it delimited different climate regions that influenced the timing of Pseudotsuga expansion.

  15. Are Avellino (4365 cal BP) and Pompeii twin plinian eruptions? Pre-eruptive constraints and degassing history

    NASA Astrophysics Data System (ADS)

    Boudon, Georges; Balcone-Boissard, Hélène; Villemant, Benoît.; Ucciani, Guillaume; Cioni, Raffaello

    2010-05-01

    Somma-Vesuvius activity started 35 ky ago and is characterized by numerous eruptions of variable composition and eruptive style, sometimes interrupted by long periods of unrest. The main explosive eruptions are represented by four plinian eruptions: Pomici di Base eruption (22 cal ky), Mercato (~8900 cal BP), Avellino (4365 cal BP) and Pompeii (79 AD). The 79 AD eruption embodies the most famous eruption since it's responsible of the destruction of Pompeii and Herculanum and it's the first described eruption. The Avellino eruption represents the last plinian event that preceded the Pompeii eruption. The eruptive sequence is similar to the 79 AD plinian eruption, with an opening phase preceding a main plinian fallout activity which ended by a phreatomagmatic phase. The fallout deposit displays a sharp colour contrast from white to grey pumice, corresponding to a magma composition evolution. We focus our study on the main fallout deposit that we sampled in detail in the Traianello quarry, 9 km North-North East of the crater, to investigate the degassing processes during the eruption, using volatile content and textural observations. Density and vesicularity measurements were obtained on a minimum of 100 pumice clasts sampled in 10 stratigraphic levels in the fallout deposit. On the basis of the density distribution, bulk geochemical data, point analytical measurements on glasses (melt inclusions and residual glass) and textural observations were obtained simultaneously on a minimum of 5 pumice clasts per eruptive unit. The glass composition, in particular the Na/K ratio, evolves from Na-rich phonolite for white pumices to a more K-rich phonolite for grey pumices. The pre-eruptive conditions are constrained by systematic Cl measurements in melt inclusions and matrix glass of pumice clasts. The entire magma was saturated relative to sub-critical fluids (a Cl-rich H2O vapour phase and a brine), with a Cl melt content buffered at ~6000 ppm, and a mean pre-eruptive H2O

  16. Holocene vegetation and fire regimes in subalpine and mixed conifer forests, southern Rocky Mountains, USA

    USGS Publications Warehouse

    Anderson, R. Scott; Allen, Craig D.; Toney, J.L.; Jass, R.B.; Bair, A.N.

    2008-01-01

    Our understanding of the present forest structure of western North America hinges on our ability to determine antecedent forest conditions. Sedimentary records from lakes and bogs in the southern Rocky Mountains of Colorado and New Mexico provide information on the relationships between climate and vegetation change, and fire history since deglaciation. We present a new pollen record from Hunters Lake (Colorado) as an example of a high-elevation vegetation history from the southern Rockies. We then present a series of six sedimentary records from ???2600 to 3500-m elevation, including sites presently at the alpine?subalpine boundary, within the Picea engelmannii?Abies lasiocarpa forest and within the mixed conifer forest, to determine the history of fire in high-elevation forests there. High Artemisia and low but increasing percentages of Picea and Pinus suggest vegetation prior to 13 500 calendar years before present (cal yr BP) was tundra or steppe, with open spruce woodland to ???11 900 cal yr BP. Subalpine forest (Picea engelmannii, Abies lasiocarpa) existed around the lake for the remainder of the Holocene. At lower elevations, Pinus ponderosa and/or contorta expanded 11 900 to 10 200 cal yr BP; mixed conifer forest expanded ???8600 to 4700 cal yr BP; and Pinus edulis expanded after ???4700 cal yr BP. Sediments from lake sites near the alpine?subalpine transition contained five times less charcoal than those entirely within subalpine forests, and 40 times less than bog sites within mixed conifer forest. Higher fire episode frequencies occurred between ???12 000 and 9000 cal yr BP (associated with the initiation or expansion of south-west monsoon and abundant lightning, and significant biomass during vegetation turnover) and at ???2000?1000 cal yr BP (related to periodic droughts during the long-term trend towards wetter conditions and greater biomass). Fire episode frequencies for subalpine?alpine transition and subalpine sites were on average 5 to 10 fire

  17. AMS radiocarbon dating and varve chronology of Lake Soppensee: 6000 to 12000 14C years BP

    NASA Astrophysics Data System (ADS)

    Hajdas, Irena; Ivy, Susan D.; Beer, Jürg; Bonani, Georges; Imboden, Dieter; Lotted, André F.; Sturm, Michael; Suter, Martin

    1993-12-01

    For the extension of the radiocarbon calibration curve beyond 10000 14C y BP, laminated sediment from Lake Soppensee (central Switzerland) was dated. The radiocarbon time scale was obtained using accelerator mass spectrometry (AMS) dating of terrestrial macrofossils selected from the Soppensee sediment. Because of an unlaminated sediment section during the Younger Dryas (10000 11000 14C y BP), the absolute time scale, based on counting annual layers (varves), had to be corrected for missing varves. The Soppensee radiocarbon-verve chronology covers the time period from 6000 to 12000 14C y BP on the radiocarbon time scale and 7000 to 13000 calendar y BP on the absolute time scale. The good agreement with the tree ring curve in the interval from 7000 to 11450 cal y BP (cal y indicates calendar year) proves the annual character of the laminations. The ash layer of the Vasset/Killian Tephra (Massif Central, France) is dated at 8230±140 14C y BP and 9407±44 cal y BP. The boundaries of the Younger Dryas biozone are placed at 10986±69 cal y BP (Younger Dryas/Preboreal) and 1212±86 cal y BP (Alleröd/Younger Dryas) on the absolute time scale. The absolute age of the Laacher See Tephra layer, dated with the radiocarbon method at 10 800 to 11200 14C y BP, is estimated at 12350 ± 135 cal y BP. The oldest radiocarbon age of 14190±120 14C y BP was obtained on macrofossils of pioneer vegetation which were found in the lowermost part of the sediment profile. For the late Glacial, the offset between the radiocarbon (10000 12000 14C y BP) and the absolute time scale (11400 13000 cal y BP) in the Soppensee chronology is not greater than 1000 years, which differs from the trend of the U/Th-radiocarbon curve derived from corals.

  18. 12,000-Years of fire regime drivers in the lowlands of Transylvania (Central-Eastern Europe): a data-model approach

    NASA Astrophysics Data System (ADS)

    Feurdean, A.; Liakka, J.; Vannière, B.; Marinova, E.; Hutchinson, S. M.; Mosburgger, V.; Hickler, T.

    2013-12-01

    The usefulness of sedimentary charcoal records to document centennial to millennial scale trends in aspects of fire regimes (frequency, severity) is widely acknowledged, yet the long-term variability in these regimes is poorly understood. Here, we use a high-resolution, multi-proxy analysis of a lacustrine sequence located in the lowlands of Transylvania (NW Romania), alongside global climate simulations in order to disentangle the drivers of fire regimes in this dry climatic region of Central-Eastern Europe. Periods of greater fire activity and frequency occurred between 10,700 and 7100 cal yr BP (mean Fire Interval = mFI 112 yr), and between 3300 and 700 cal yr BP (mFI 150 yr), whereas intervals of lower fire activity were recorded between 12,000 and 10,700 cal yr BP (mFI 217 yr), 7100 and 3300 cal yr BP (mFI 317 yr), and over last 700 years (no fire events detected). We found good correlations between simulated early summer (June, July) soil moisture content and near-surface air temperature with fire activity, particularly for the early to mid Holocene. A climate-fire relationship is further supported by local hydrological changes, i.e., lake level and runoff fluctuations. Fuel limitation, as a result of arid and strongly seasonal climatic conditions, led to low fire activity before 10,700 cal yr BP. However, fires were most frequent during climatically drier phases for the remaining, fuel-sufficient, part of the Holocene. Our results also suggest that the occurrence of more frequent fires in the early Holocene has kept woodlands open, promoted grassland abundance and sustained a more flammable ecosystem (mFI < 150 years) whereas the decline in fire risk under cooler and wetter climate conditions (mFI = 317 years) favoured woodland development. From 3300 cal yr BP, human impacts clearly were partly responsible for changes in fire activity, first increasing fire frequency and severity in periods with fire-favourable climatic conditions (halving the mFI from 300

  19. Late Quaternary paleoclimate of western Alaska inferred from fossil chironomids and its relation to vegetation histories

    NASA Astrophysics Data System (ADS)

    Kurek, Joshua; Cwynar, Les C.; Ager, Thomas A.; Abbott, Mark B.; Edwards, Mary E.

    2009-05-01

    Fossil Chironomidae assemblages (with a few Chaoboridae and Ceratopogonidae) from Zagoskin and Burial Lakes in western Alaska provide quantitative reconstructions of mean July air temperatures for periods of the late-middle Wisconsin (˜39,000-34,000 cal yr B.P.) to the present. Inferred temperatures are compared with previously analyzed pollen data from each site summarized here by indirect ordination. Paleotemperature trends reveal substantial differences in the timing of climatic warming following the late Wisconsin at each site, although chronological uncertainty exists. Zagoskin Lake shows early warming beginning at about 21,000 cal yr B.P., whereas warming at Burial Lake begins ˜4000 years later. Summer climates during the last glacial maximum (LGM) were on average ˜3.5 °C below the modern temperatures at each site. Major shifts in vegetation occurred from ˜19,000 to 10,000 cal yr B.P. at Zagoskin Lake and from ˜17,000 to 10,000 cal yr B.P. at Burial Lake. Vegetation shifts followed climatic warming, when temperatures neared modern values. Both sites provide evidence of an early postglacial thermal maximum at ˜12,300 cal yr B.P. These chironomid records, combined with other insect-based climatic reconstructions from Beringia, indicate that during the LGM: (1) greater continentality likely influenced regions adjacent to the Bering Land Bridge and (2) summer climates were, at times, not dominated by severe cold.

  20. Holocene vegetation, environment and anthropogenic influence in the Fuzhou Basin, southeast China

    NASA Astrophysics Data System (ADS)

    Yue, Yuanfu; Zheng, Zhuo; Rolett, Barry V.; Ma, Ting; Chen, Cong; Huang, Kangyou; Lin, Gongwu; Zhu, Guangqi; Cheddadi, Rachid

    2015-03-01

    A ∼40 m sediment core (FZ4) was collected from the Fuzhou Basin, near the lower reaches of the Min River, in Fujian Province on the southeast coast of China. The sediment and pollen record contributes to our understanding of Holocene paleogeography, including local changes in vegetation and climate in the context of Neolithic cultural developments. The sediment record reveals a fluvial environment in the Fuzhou Basin during the late Pleistocene, and it demonstrates that a change from fluvial to estuarine conditions at ∼9000 cal yr BP resulted from postglacial sea level rise. Evidence of abundant marine diatoms and tidal flat laminations observed in the FZ4 sediments, implies that the Fuzhou Basin was under marine influence between ∼9000 and ∼2000 cal yr BP. After 2000 cal yr BP, a rapid retreat in coastline associated with fluvial aggradation and coastal progradation produced more shallow water for wetlands and initiated formation of the floodplain landscape. The pollen record reveals the presence of a dense subtropical forest between ca. 9000 and 7000 cal yr BP, representing the Holocene thermal maximum, which is linked with rising sea level and marine transgression in the Fuzhou Basin. Between ca. 5500 and 2000 cal yr BP, the thermophilous forest dominated by Castanopsis retreated and coniferous forest expanded, reflecting moderate climatic cooling during this period. Timing of the high frequencies for Pinus and ferns correspond with the mid-late Holocene cooling trend recorded in local mountain peatland and coastal regions of the lower Yangtze and Hanjiang deltas. Anthropogenically induced land cover change was negligible prior to the Tanshishan cultural period, which marks the beginning of Neolithic era sedentary village life on the Fujian coast around 5500 BP. The pollen transition at ca. 3000-1500 cal yr BP, distinguished by rising frequencies of Poaceae and taxa (including Cyperaceae and Artemisia) closely associated with agricultural land cover

  1. The Bonneville Estates Rockshelter rodent fauna and changes in Late Pleistocene-Middle Holocene climates and biogeography in the Northern Bonneville Basin, USA

    NASA Astrophysics Data System (ADS)

    Schmitt, Dave N.; Lupo, Karen D.

    2012-07-01

    Excavations at Bonneville Estates Rockshelter, Nevada recovered rodent remains from stratified deposits spanning the past ca. 12,500 14C yr BP (14,800 cal yr BP). Specimens from horizons dating to the late Pleistocene and early Holocene include species adapted to montane and moist and cool habitats, including yellow-bellied marmot (Marmota flaviventris) and bushy-tailed woodrat (Neotoma cinerea). Shortly after 9000 14C BP (10,200 cal yr BP) these mammals became locally extinct, or nearly so, taxonomic diversity declined, and the region became dominated by desert woodrats (Neotoma lepida) and other species well-adapted to xeric, low-elevation settings. The timing and nature of changes in the Bonneville Estates rodent fauna are similar to records reported from nearby Homestead and Camels Back caves and provide corroborative data on terminal Pleistocene-early Holocene environments and mammalian responses to middle Holocene desertification. Moreover, the presence of northern pocket gopher (Thomomys talpoides) at Bonneville Estates adds to a sparse regional record for that species and, similar to Homestead Cave, it appears that the ca. 9500 14C yr BP (10,800 cal yr BP) replacement of the northern pocket gopher by Botta's pocket gopher in the Great Salt Lake Desert vicinity was also in response to climate change.

  2. Middle to Late Holocene Fluctuations of C3 and C4 Vegetation in a Northern New England Salt Marsh, Sprague Marsh, Phippsburg Maine

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Johnson, B J; Moore, K A; Lehmann, C

    2006-05-26

    A 3.1 meter sediment core was analyzed for stable carbon isotope composition of organic matter and higher plant leaf wax (HPLW) lipid biomarkers to determine Holocene shifts in C{sub 3} (higher high marsh) and C{sub 4} (low and/or high marsh) plant deposition at the Sprague River Salt Marsh, Phippsburg, Maine. The carbon isotope composition of the bulk sediment and the HPLW parallel each other throughout most of the core, suggesting that terrestrial plants are an important source of organic matter to the sediments, and diagenetic alteration of the bulk sediments is minimal. The current salt marsh began to form 2500more » cal yr BP. Low and/or high C{sub 4} marsh plants dominated deposition at 2000 cal yr BP, 700 cal yr BP, and for the last 200 cal yr BP. Expansion of higher high marsh C{sub 3} plants occurred at 1300 and 600 cal yr BP. These major vegetation shifts result from a combination of changes in relative sea-level rise and sediment accumulation rates. Average annual carbon sequestration rates for the last 2500 years approximate 40 g C yr{sup -1} m{sup -2}, and are in strong agreement with other values published for the Gulf of Maine. Given that Maine salt marshes cover an area of {approx}79 km{sup 2}, they represent an important component of the terrestrial carbon sink. More detailed isotopic and age records from a network of sediment cores at Sprague Marsh are needed to truly evaluate the long term changes in salt marsh plant communities and the impact of more recent human activity, including global warming, on salt marsh vegetation.« less

  3. Early-to-middle Holocene sea-level fluctuations, coastal progradation and the Neolithic occupations in Yaojiang valley of southern Hangzhou bay, eastern China

    NASA Astrophysics Data System (ADS)

    Liu, Y.; Sun, Q.; Fan, D.; Chen, Z.

    2017-12-01

    The formation of Holocene coast in eastern China provided material base for the development of Neolithic civilizations. The coastal Yaojiang valley of south Hangzhou bay was one of the examples where the well-known Neolithic Hemudu Culture (HC) of Eastern China initiated. Here, we studied the early-to-middle Holocene environment changes in relation to sea-level fluctuations on the basis of a serial of sediment cores based on a set of new Accelerator Mass Spectrometry radiocarbon (AMS 14C) chronology. The result indicated that relative sea-level rose rapidly in the Yaojiang valley at the early Holocene, reaching its maximum at ca. 8000-7800 cal yr BP and then decelerated at ca. 7800-7500 cal yr BP. The alluvial plain in Yaojiang valley began to form at the foothills first and then grew towards the valley center accompanying with the sea-level stabilization after ca. 7500 cal yr BP. This progressive progradation of alluvial plain would attract the early arrivals of foragers to dwell at the foothills to engaging in rice farming after ca.7000 cal yr BP and starting the epic Hemudu Culture. The HC people then move down to the valley center as more land became available thanks to sediment aggregation and progradation. The rise and development of HC were closely associated with the sea-level induced landscape changes in Yaojiang valley at the early-middle Holocene, and the unstable hydraulic condition in the valley after 5000 cal yr BP could be accountable for the cultural termination.

  4. Response of Everglades tree islands to environmental change

    USGS Publications Warehouse

    Willard, Debra A.; Bernhardt, Christopher E.; Holmes, Charles W.; Landacre, Bryan; Marot, Marci E.

    2006-01-01

    Tree islands are centers of biodiversity within the Florida Everglades, USA, but the factors controlling their distribution, formation, and development are poorly understood. We use pollen assemblages from tree islands throughout the greater Everglades ecosystem to reconstruct the timing of tree island formation, patterns of development, and response to specific climatic and environmental stressors. These data indicate that fixed (teardrop-shaped) and strand tree islands developed well before substantial human alteration of the system, with initial tree island vegetation in place between 3500 and 500 calibrated years before present (cal yr BP), depending on the location in the Everglades wetland. Tree island development appears to have been triggered by regional- to global-scale climatic events at 2800 cal yr BP, 1600–1500 cal yr BP, 1200–1000 cal yr BP (early Medieval Warm Period), and 500–200 cal yr BP (Little Ice Age). These periods correspond to drought intervals documented in Central and South America and periods of southward displacement of the Intertropical Convergence Zone. The records indicate a coherence of climate patterns in both subtropical North America and the Northern Hemisphere Neotropics. Water management practices of the 20th century altered plant communities and size of tree islands throughout the Everglades. Responses range from loss of tree islands due to artificially long hydroperiods and deep water to expansion of tree islands after flow reductions. These data provide evidence for the rapidity of tree island response to specific hydrologic change and facilitate prediction of the response to future changes associated with Everglades restoration plans.

  5. Combining charcoal sediment and molecular markers to infer a Holocene fire history in the Maya lowlands of Petén, Guatemala

    NASA Astrophysics Data System (ADS)

    Kirchgeorg, Torben; Schüpbach, Simon; Colombaroli, Daniele; Beffa, Giorgia; Radaelli, Marta; Kehrwald, Natalie; Barbante, Carlo

    2015-04-01

    Holocene vegetation changes in the Maya Lowlands during the Holocene are a result of changing climate conditions, solely anthropogenic activities, or interactions of both factors. As a consequence, it is difficult to assess how tropical ecosystems will cope with projected changes in precipitation and land-use intensification over the next decades. We investigated the role of fire during the Holocene by combining different proxies. We distinguished between three different morphotypes (grass, wood and leaves) in macroscopic charcoal. We also determined the molecular fire proxies levoglucosan, mannosan and galactosan. Combining these different fire proxies allows a more robust understanding of the complex history of fire regimes at different spatial scales during the Holocene. Comparing the two biomass burning proxies may help increase our understanding about advantages and limitations of molecular markers as proxies for past fire reconstruction in lake sediments. In order to infer changes in past biomass burning, we analysed a lake sediment core from Lake Petén Itzá, Guatemala (17°00'N, 89°50'W, 110 m above sea level), and compared our results with millennial-scale vegetation and climate change data available in this area. Some differences were observed between the two records and we assumed that while macroscopic charcoal represents a local fire signal, the molecular fire proxies records seem to be influenced by regional to supra-regional fire or low temperature fires. During the Holocene we detected three periods of high fire activity: 9500-6000 cal yr BP, 3800 cal yr BP and 2700 cal yr BP. We attributed the first maximum (9500-6000 cal yr BP) to only climate conditions, which corresponds with observations from previous studies in this region. The fast decrease in the relative abundance of woody charcoal to grass charcoal at the 3800 cal yr BP fire maximum may result from human activity, but we cannot exclude that this shift was related to climate conditions

  6. Prehistoric fires and the shaping of colonial transported landscapes in southern California: A paleoenvironmental study at Dune Pond, Santa Barbara County

    NASA Astrophysics Data System (ADS)

    Ejarque, Ana; Anderson, R. Scott; Simms, Alexander R.; Gentry, Beau J.

    2015-03-01

    Using a novel combination of paleoecologic proxies including pollen, non-pollen palynomorphs (NPPs), macroscopic charcoal, and Spheroidal Carbonaceous Particles (SCPs), 5000 years of landscape change, fire history and land-use have been reconstructed from Dune Pond, Santa Barbara County, California. The pond was sensitive to Holocene regional climatic variability, showing different phases of lower (4600-3700 cal yr BP, 2100-700 cal yr BP, historical period) and higher (3700-2100 cal yr BP, 700-150 cal yr BP) local moisture availability. During this period the landscape was dominated by a coastal mosaic vegetation including dune mats, coastal scrub and salt marshes on the dunes and backdunes, with chaparral and oak woodland growing in the valley plains and foothills. Fire was intimately linked with such dominating mosaic vegetation, and the combination of wet conditions and the presence of nearby human settlement were a trigger favoring coastal fires for at least two periods: from 3100 to 1500 cal yr BP and from 650 cal yr BP until the 18th century. In both cases fire was an important tool to keep an open coastal landscape attractive to hunting wildlife. Finally, matching this varied range of high-resolution paleoecological proxies with historical records we could characterize the development of colonial transported landscapes following the Euro-American settlement of Santa Barbara. The introduction of livestock grazing by Spanish colonists favored erosive processes and the introduction of fecal-borne parasites in freshwater bodies, negatively impacted salt and brackish coastal marshes, and promoted the invasion of alien grasses and ruderals. This agro-pastoral landscape was consolidated during the American period, with a greater role for cultivation, the development of industrial activities and increased population. Despite negative environmental consequences such as the loss of native habitats, exotic land-uses and plants introduced during the historical period

  7. Origin and dynamics of the northern South American coastal savanna belt during the Holocene - the role of climate, sea-level, fire and humans

    NASA Astrophysics Data System (ADS)

    Alizadeh, Kamaleddin; Cohen, Marcelo; Behling, Hermann

    2015-08-01

    Presence of a coastal savanna belt expanding from British Guiana to northeastern Brazil cannot be explained by present-day climate. Using pollen and charcoal analyses on an 11.6 k old sediment core from a coastal depression in the savanna belt near the mouth of the Amazon River we investigated the paleoenvironmental history to shed light on this question. Results indicate that small areas of savanna accompanied by a forest type composed primarily by the genus Micropholis (Sapotaceae) that has no modern analog existed at the beginning of the Holocene. After 11,200 cal yr BP, savanna accompanied by few trees replaced the forest. In depressions swamp forest developed and by ca 10,000 cal yr BP replaced by Mauritia swamps. Between 8500 and 5600 cal yr BP gallery forest (composed mainly of Euphorbiaceae) and swamp forest succeeded the treeless savanna. The modern vegetation with alternating gallery forest and savanna developed after 5600 cal yr BP. We suggest that the early Holocene no-analog forest is a relict of previously more extensive forest under cooler and moister Lateglacial conditions. The early Holocene savanna expansion indicates a drier phase probably related to the shift of the Intertropical Convergence Zone (ITCZ) towards its northernmost position. The mid-Holocene forest expansion is probably a result of the combined influence of equatorwards shift of ITCZ joining the South Atlantic Convergence Zone (SACZ). The ecosystem variability during the last 5600 cal yr BP, formed perhaps under influence of intensified ENSO condition. High charcoal concentrations, especially during the early Holocene, indicate that natural and/or anthropogenic fires may have maintained the savanna. However, our results propose that climate change is the main driving factor for the formation of the coastal savanna in this region. Our results also show that the early Holocene sea level rise established mangroves near the study site until 7500 cal yr BP and promoted swamp formation in

  8. Last glacial maximum and Holocene lake levels of Owens Lake, eastern California, USA

    USGS Publications Warehouse

    Bacon, S.N.; Burke, R.M.; Pezzopane, S.K.; Jayko, A.S.

    2006-01-01

    Stratigraphic investigations of fluvio-deltaic and lacustrine sediments exposed in stream cuts, quarry walls, and deep trenches east of the Sierra Nevada in Owens Valley near Lone Pine, California have enabled the reconstruction of pluvial Owens Lake level oscillations. Age control for these sediments is from 22 radiocarbon (14C) dates and the identification and stratigraphic correlation of a tephra, which when plotted as a function of age versus altitude, define numerous oscillations in the level of pluvial Owens Lake during the latest Pleistocene and early Holocene. We have constructed a lake-level altitude curve for the time interval ???27,000 cal yr BP to present that is based on the integration of this new stratigraphic analysis with published surface stratigraphic data and subsurface core data. Pluvial Owens Lake regressed from its latest Pleistocene highstands from ???27,000 to ???15,300 cal yr BP, as recorded by ???15 m of down cutting of the sill from the altitudes of ???1160 to 1145 m. By ???11,600 cal yr BP, the lake had dropped ???45 m from the 1145 m sill. This lowstand was followed by an early Holocene transgression that attained a highstand near 1135 m before dropping to 1120 m at 7860-7650 cal yr BP that had not been recognized in earlier studies. The lake then lowered another ???30 m to shallow and near desiccation levels between ???6850 and 4300 cal yr BP. Fluvial cut-and-fill relations north of Lone Pine and well-preserved shoreline features at ???1108 m indicate a minor lake-level rise after 4300 cal yr BP, followed by alkaline and shallow conditions during the latest Holocene. The new latest Quaternary lake-level record of pluvial Owens Lake offers insight to the hydrologic balance along the east side of the southern Sierra Nevada and will assist regional paleoclimatic models for the western Basin and Range. ?? 2005 Elsevier Ltd. All rights reserved.

  9. Subdivision of Glacial Deposits in Southeastern Peru Based on Pedogenic Development and Radiometric Ages

    NASA Astrophysics Data System (ADS)

    Goodman, Adam Y.; Rodbell, Donald T.; Seltzer, Geoffrey O.; Mark, Bryan G.

    2001-07-01

    The Cordillera Vilcanota and Quelccaya Ice Cap region of southern Peru (13°30‧-14°00‧S; 70°40‧-71°25‧W) contains a detailed record of late Quaternary glaciation in the tropical Andes. Quantification of soil development on 19 moraine crests and radiocarbon ages are used to reconstruct the glacial history. Secondary iron and clay increase linearly in Quelccaya soils and clay accumulates at a linear rate in Vilcanota soils, which may reflect the semicontinuous addition of eolian dust enriched in secondary iron to all soils. In contrast, logarithmic rates of iron buildup in soils in the Cordillera Vilcanota reflect chemical weathering; high concentrations of secondary iron in Vilcanota tills may mask the role of eolian input to these soils. Soil-age estimates from extrapolation of field and laboratory data suggest that the most extensive late Quaternary glaciation occurred >70,000 yr B.P. This provides one of the first semiquantitative age estimates for maximum ice extent in southern Peru and is supported by a minimum-limiting age of ∼41,520 14C yr B.P. A late glacial readvance culminated ∼16,650 cal yr B.P. in the Cordillera Vilcanota. Following rapid deglaciation of unknown extent, an advance of the Quelccaya Ice Cap occurred between ∼13,090 and 12,800 cal yr B.P., which coincides approximately with the onset of the Younger Dryas cooling in the North Atlantic region. Moraines deposited <394 cal yr B.P. in the Cordillera Vilcanota and <300 cal yr B.P. on the west side of the Quelccaya Ice Cap correlate with Little Ice Age moraines of other regions.

  10. Benthic foraminifera response to Holocene environmental changes in the ria de Muros (NW Spain)

    NASA Astrophysics Data System (ADS)

    Diz, P.; Francés, G.; Pena, L. D.; Nombela, M. A.; Alejo, I.

    2003-04-01

    Benthic foraminifera assemblages from the outer sector of the ría de Muros have been analyzed in order to obtain a detailed reconstruction of Holocene environmental evolution. The studied core (EUGC-3B: 42' 45.10'N; 9' 02.23'W, at 38 m.b.s.l. and 410 cm length) consists of muddy sand from the core bottom (8200 cal yr BP) to 200 cm (2700 cal yr BP) and mainly mud from 200 cm to the core top. Measurements of geochemical properties carried out by a XRF core scanner revealed different signatures in the two aforementioned intervals and an enhancing terrigenous influence during the last 2000 yr. The prevalence of Bulimina spp., Nonion fabum, Ammonia beccarii and Cibicides ungerianus along the whole core indicates high organic carbon concentration and/or low oxygenation levels into the sediment. Nevertheless, the percentage of these species shows noticeable changes, indicating the existence of five periods with different environmental conditions. The basal assemblage (8200-7500 cal yr BP) is dominated by epifaunal taxa and it can be interpreted as a low sea level assemblage. An increase of fresh water influence during the Holocene Climate Optimum (7500-5000 cal yr BP) is revealed by maxima percentages of A. beccarii. The oceanic influence increased during the Subboreal period (5000-2750 cal yr BP) leading to an active water interchange between the ría and the open ocean and a higher marine productivity. The oceanic influence is recorded by the increase of typical marine species as Elphidium advenum, Bulimina spp., N. fabum, and Nonionella turgida. The appearance of Rectuvigerina phlegeri at 4000 cal yr BP denotes full marine conditions. Environmental conditions similar to the current ones were achieved during the Subatlantic period (2750-Rec). In a first step an assemblage dominated by Bulimina spp. N. fabum, and C. ungerianus permit us to interpret a relatively stable period with episodic pulses of fluvial influence. Afterwards the appearance and the rapid increase of

  11. Volcanic influence of Mt. Fuji on the watershed of Lake Motosu and its impact on the lacustrine sedimentary record

    NASA Astrophysics Data System (ADS)

    Lamair, Laura; Hubert-Ferrari, Aurélia; Yamamoto, Shinya; El Ouahabi, Meriam; Vander Auwera, Jacqueline; Obrochta, Stephen; Boes, Evelien; Nakamura, Atsunori; Fujiwara, Osamu; Shishikura, Masanobu; Schmidt, Sabine; Siani, Giuseppe; Miyairi, Yosuke; Yokoyama, Yusuke; De Batist, Marc; Heyvaert, Vanessa M. A.; QuakeRecNankai Team

    2018-01-01

    Lacustrine sediments are particularly sensitive to modifications within the lake catchment. In a volcanic area, sedimentation rates are directly affected by the history of the volcano and its eruptions. Here, we investigate the impact of Mt. Fuji Volcano (Japan) on Lake Motosu and its watershed. The lacustrine infill is studied by combining seismic reflection profiles and sediment cores. We show evidence of changes in sedimentation patterns during the depositional history of Lake Motosu. The frequency of large mass-transport deposits recorded within the lake decreases over the Holocene. Before 8000 cal yr BP, large sublacustrine landslides and turbidites were filling the lacustrine depression. After 8000 cal yr BP, only one large sublacustrine landslide was recorded. The change in sedimentation pattern coincides with a change in sediment accumulation rate. Over the last 8000 cal yr BP, the sediment accumulation rate was not sufficient enough to produce large sublacustrine slope failures. Consequently, the frequency of large mass-transport deposits decreased and only turbidites resulting from surficial slope reworking occurred. These constitute the main sedimentary infill of the deep basin. We link the change in sediment accumulation rate with (i) climate and vegetation changes; and (ii) the Mt. Fuji eruptions which affected the Lake Motosu watershed by reducing its size and strongly modified its topography. Moreover, this study highlights that the deposition of turbidites in the deep basin of Lake Motosu is mainly controlled by the paleobathymetry of the lakefloor. Two large mass-transport deposits, occurring around 8000 cal yr BP and 2000 cal yr BP respectively, modified the paleobathymetry of the lakefloor and therefore changed the turbidite depositional pattern of Lake Motosu.

  12. An 11 000-year-long record of fire and vegetation history at Beaver Lake, Oregon, central Willamette Valley

    USGS Publications Warehouse

    Walsh, Megan K.; Pearl, Christopher A.; Whitlock, Cathy; Bartlein, Patrick J.; Worona, Marc A.

    2010-01-01

    High-resolution macroscopic charcoal and pollen analysis were used to reconstruct an 11??000-year-long record of fire and vegetation history from Beaver Lake, Oregon, the first complete Holocene paleoecological record from the floor of the Willamette Valley. In the early Holocene (ca 11??000-7500 calendar years before present [cal??yr??BP]), warmer, drier summers than at present led to the establishment of xeric woodland of Quercus, Corylus, and Pseudotsuga near the site. Disturbances (i.e., floods, fires) were common at this time and as a result Alnus rubra grew nearby. High fire frequency occurred in the early Holocene from ca 11??200-9300??cal??yr??BP. Riparian forest and wet prairie developed in the middle Holocene (ca 7500??cal??yr??BP), likely the result of a decrease in the frequency of flooding and a shift to effectively cooler, wetter conditions than before. The vegetation at Beaver Lake remained generally unchanged into the late Holocene (from 4000??cal??yr??BP to present), with the exception of land clearance associated with Euro-American settlement of the valley (ca 160??cal??yr BP). Middle-to-late Holocene increases in fire frequency, coupled with abrupt shifts in fire-episode magnitude and charcoal composition, likely indicate the influence anthropogenic burning near the site. The paleoecological record from Beaver Lake, and in particular the general increase in fire frequency over the last 8500??years, differs significantly from other low-elevation sites in the Pacific Northwest, which suggests that local controls (e.g., shifts in vegetation structure, intensification of human land-use), rather than regional climatic controls, more strongly influenced its environmental history. ?? 2010 Elsevier Ltd.

  13. Chironomid-based reconstructions of summer air temperature from lake deposits in Lyndon Stream, New Zealand spanning the MIS 3/2 transition

    NASA Astrophysics Data System (ADS)

    Woodward, C. A.; Shulmeister, J.

    2007-01-01

    We present chironomid-based temperature reconstructions from lake sediments deposited between ca 26,600 cal yr BP and 24,500 cal yr BP from Lyndon Stream, South Island, New Zealand. Summer (February mean) temperatures averaged 1 °C cooler, with a maximum inferred cooling of 3.7 °C. These estimates corroborate macrofossil and beetle-based temperature inferences from the same site and suggest climate amelioration (an interstadial) at this time. Other records from the New Zealand region also show a large degree of variability during the late Otiran glacial sequence (34,000-18,000 cal yr BP) including a phase of warming at the MIS 2/3 transition and a maximum cooling that did not occur until the global LGM (ca 20,000 cal yr BP). The very moderate cooling identified here at the MIS 2/3 transition confirms and enhances the long-standing discrepancy in New Zealand records between pollen and other proxies. Low abundances (<20%) of canopy tree pollen in records from late MIS 3 to the end of MIS 2 cannot be explained by the minor (<5 °C) cooling inferred from this and other studies unless other environmental parameters are considered. Further work is required to address this critical issue.

  14. Vegetation history of the English chalklands: a mid-Holocene pollen sequence from the Caburn, East Sussex

    NASA Astrophysics Data System (ADS)

    Waller, Martyn P.; Hamilton, Sue

    2000-03-01

    A pollen diagram has been produced from the base of the Caburn (East Sussex) that provides a temporally and spatially precise record of vegetation change on the English chalklands during the mid-Holocene (ca. 7100 to ca. 3800 cal. yr BP). During this period the slopes above the site appear to have been well-wooded, with vegetation analogous to modern Fraxinus-Acer-Mercurialis communities in which Tilia was also a prominent constituent. However, scrub and grassland taxa such as Juniperus communis, Cornus sanguinea and Plantago lanceolata are also regularly recorded along with, from ca. 6000 cal. yr BP onwards, species specific to Chalk grassland (e.g. Sanguisorba minor). This supports suggestions that elements of Chalk grassland persisted in lowland England through the Holocene. Such communities are most likely to have occupied the steepest slopes, although the processes that maintained them are unclear. Human interference with vegetation close to the site may have begun as early as ca. 6350 cal. yr BP and initially involved a woodland management practice such as coppicing. From the primary Ulmus decline (ca. 5700 cal. yr BP) onwards, phases of limited clearance accompanied by cereal cultivation occurred. Taxus baccata was an important component of the woodland which regenerated between these phases.

  15. Depositional evolution of the Lower Khuzestan plain (SW Iran) since the end of the Late Pleistocene

    NASA Astrophysics Data System (ADS)

    Bogemans, Frieda; Janssens, Rindert; Baeteman, Cecile

    2017-09-01

    A detailed sedimentological investigation of sixty-six cores supported by radiocarbon age determination enabled the reconstruction of the depositional environmental evolution since the end of the Late Pleistocene in the Iranian part of the Mesopotamian plain. Both fluvial and estuarine environments have been identified on the basis of the sediment characteristics and their between-core stratigraphic correlations. At the end of the Late Pleistocene the fluvial behaviour allowed only the deposition of sand. Prior to 12400-12040 yr cal BP the palaeohydraulics changed by which heterolithic fluvial facies were deposited. Shortly after 12400 - 12040 yr cal BP an erosional phase caused the incision of depressions most probably because of a climate change to further arid conditions. In the early Holocene, mud-dominated river systems filled the depressions; a situation that lasted at least until 7900 - 7700 yr cal BP. After this period tides invaded via the active channels in the downstream part of the area, which turned into an estuarine environment for a period of about 2000-2500 years. Tidal influence diminished and stopped around 5000 yr cal BP because of progradation. Fluvial processes dominated again the sedimentary environment in the study area, except at the southern margin of it where tides controlled, although very locally, the environment.

  16. Late Glacial and Early Holocene Climatic Changes Based on a Multiproxy Lacustrine Sediment Record from Northeast Siberia

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Kokorowski, H D; Anderson, P M; Sletten, R S

    Palynological (species assemblage, pollen accumulation rate), geochemical (carbon to nitrogen ratios, organic carbon and biogenic silica content), and sedimentological (particle size, magnetic susceptibility) data combined with improved chronology and greater sampling resolution from a new core from Elikchan 4 Lake provide a stronger basis for defining paleoenvironmental changes than was previously possible. Persistence of herb-dominated tundra, slow expansion of Betula and Alnus shrubs, and low percentages of organic carbon and biogenic silica suggest that the Late-Glacial transition (ca. 16,000-11,000 cal. yr BP) was a period of gradual rather than abrupt vegetation and climatic change. Consistency of all Late-Glacial data indicatesmore » no Younger Dryas climatic oscillation. A dramatic peak in pollen accumulation rates (ca. 11,000-9800 cal. yr BP) suggests a possible summer temperature optimum, but finer grain-sizes, low magnetic susceptibility, and greater organic carbon and biogenic silica, while showing significant warming at ca. 11,000 cal. yr BP, offer no evidence of a Holocene thermal maximum. When compared to trends in other paleo-records, the new Elikchan data underscore the apparent spatial complexity of climatic responses in Northeast Siberia to global forcings between ca. 16,000-9000 cal. yr BP.« less

  17. Holocene history of a lake filling and vegetation dynamics of the Serra Sul dos Carajás, southeast Amazonia.

    PubMed

    Guimarães, José T F; Sahoo, Prafulla K; Souza-Filho, Pedro W M; Figueiredo, Mariana M J Costa DE; Reis, Luiza S; Silva, Marcio S DA; Rodrigues, Tarcísio M

    2017-07-24

    Down-core changes in sedimentary facies, elemental geochemistry, pollen, spore, δ13C, δ15N and radiocarbon records from a filled lake, named R4, of the Serra Sul dos Carajás were used to study the relationship between the paleomorphological and paleoecological processes and their significance for Holocene paleoclimatology of the southeast Amazonia. The sediment deposition of the R4 lake started around 9500 cal yr BP. Increase of detrital components from 9500 to 7000 cal yr BP suggests high weathering of surrounding catchment rocks and soils, and deposition into the lake basin under mudflows. At that time, montane savanna and forest formation were already established suggesting predominance of wet climate. However, from 7000 to 3000 cal yr BP, a decline of detrital input occurred. Also, forest formation and pteridophytes were declined, while palms and macrophytes were remained relatively stable, indicating that water levels of the lake is likely dropped allowing the development of plants adapted to subaerial condition under drier climate conditions. After 3000 cal yr BP, eutrophication and low accommodation space lead to high lake productivity and the final stage of the lake filling respectively, and forest formation may has acquired its current structure, which suggests return of wetter climate conditions.

  18. A late Holocene paleoenvironmental reconstruction from Agua Caliente, southern Belize, linked to regional climate variability and cultural change at the Maya polity of Uxbenká

    NASA Astrophysics Data System (ADS)

    Walsh, Megan K.; Prufer, Keith M.; Culleton, Brendan J.; Kennett, Douglas J.

    2014-07-01

    We report high-resolution macroscopic charcoal, pollen and sedimentological data for Agua Caliente, a freshwater lagoon located in southern Belize, and infer a late Holocene record of human land-use/climate interactions for the nearby prehistoric Maya center of Uxbenká. Land-use activities spanning the initial clearance of forests for agriculture through the drought-linked Maya collapse and continuing into the historic recolonization of the region are all reflected in the record. Human land alteration in association with swidden agriculture is evident early in the record during the Middle Preclassic starting ca. 2600 cal yr BP. Fire slowly tapered off during the Late and Terminal Classic, consistent with the gradual political demise and depopulation of the Uxbenká polity sometime between ca. 1150 and 950 cal yr BP, during a period of multiple droughts evident in a nearby speleothem record. Fire activity was at its lowest during the Maya Postclassic ca. 950-430 cal yr BP, but rose consistent with increasing recolonization of the region between ca. 430 cal yr BP and present. These data suggest that this environmental record provides both a proxy for 2800 years of cultural change, including colonization, growth, decline, and reorganization of regional populations, and an independent confirmation of recent paleoclimate reconstructions from the same region.

  19. High-resolution paleoenvironmental records during the late Quaternary from the marginal seas of East Asia: the intrusion of open-ocean current

    NASA Astrophysics Data System (ADS)

    Kong, G. S.; Kim, S. P.; Choi, H. S.

    2012-04-01

    Four long mud-dominated sediment cores (35m-long YSDP 103, 32m-long SSDP 102, 72m-long SSDP103 and 52m-long SSDP 105) were recovered in the continental shelves of Korea and were examined through the analysis of AMS 14C dating, lithology, organic geochemistry and stable isotopes to reconstruct the paleoenvironmental histories during the late Quaternary. These drill cores acquired from the thick Holocene mud deposits allow us to obtain high-resolution paleoenvironmental records concerning the intrusion of open-ocean warm currents triggered by the last deglacial sea-level rise. Various organic geochemical results (TOC, C/N, C/S, HI, δ13Corg) of core YSDP 103, taken from the southeastern Yellow Sea, showed that terrigenous organic matters were significantly dominant in the southeastern Yellow Sea between 16,600 and 4,300 cal. yr BP probably due to the influence of freshwater derived from an adjacent river and then the dominance of organic matter origin changed to marine type affected by surface primary productivity after 4,300 cal. yr BP. These results may indicate that the marine environment of the southeastern Yellow Sea changed from brackish to a modern-type shelf environment since 4,300 cal. yr BP, implying the intrusion of the open-ocean current. The δ18O values of benthic foraminifer Cibicides lobatulus, however, showed that variation changed from high-amplitude to low-amplitude fluctuations at around 3,500 cal. yr. The time discrepancy of 800 years between organic geochemical proxies and stable isotope proxies is interpreted to reflect that a modern-type shelf environment was not fully developed in the southeastern Yellow Sea until 3,500 cal. yr BP, even though the open-ocean current (Yellow Sea Warm Current) began to flow into the Yellow Sea at 4,300 cal. Yr. BP. The results of core SSDP 102 collected in the Korean Strait reveal that the area experienced 4 stages of environmental change during the last 13,900 cal. yr BP. Occurrence of well-rounded, oxidized

  20. Environmental changes, forest history and human impact in the southern part of Valdai Hills (European Russia) during the last 7000 years

    NASA Astrophysics Data System (ADS)

    Novenko, Elena; Tsyganov, Andery; Pisarchuk, Natalia; Kozlov, Daniil

    2017-04-01

    Understanding the long-term ecological dynamics of swampy boreal forest is essential for assessment of the possible responses and feedbacks of forest ecosystems to climate change and natural disturbance. The multi-proxy record from the Central Forest State Natural Biosphere Reserve (CFSNBR), locate on the South of Valdai Hills, provides important new data on the forest history, human impact, paludification dynamics and environmental changes in the central part of the East European Plain during the Holocene. The results of peat humification, pollen, plant macrofossil, micro charcoal and testate amoeba analyses from forest pealand show that between 7000 and 4000 cal yr BP the southern part of Valdai Hills was occupied by broad-leaved forests. Spruce occurred in forest communities as small admixture and gradually increased its abundance. After 4000 cal yr BP spruce rapidly become the main forest forming species, however broad-leaved trees took place in plant cover. Despite significant climatic fluctuation, mixed broad-leaved-spruce forests persisted in vegetation until 900 cal yr BP and then were replaced by waterlogged herbal spruce forests. The extensive Sphagnum spruce forests are recent plant communities and were formed during the last 100 years that could be explain by changes in water balance of the territory due to both climate and anthropogenic factors. According to reconstruction of Mid- and Late Holocene climate changes, warm and relatively dry period of the Holocene Thermal Maximum (7000-5500 cal yr BP) was followed by climate cooling that included several relatively cold phases at about 5000, 3500, 2000, 1200 cal yr BP and warm intervals at about 2600, 1500 and 900 cal yr BP. The distinct cooling was reconstructed between 800 and 400 cal yr BP, apparently, correlated with the Little Ice Age. Climate dynamics appeared as significant changes of environmental conditions at local ecosystem. Warming phases are indicated by high peat humification and organic

  1. The anatomy of Last Glacial Maximum climate variations in south Westland, New Zealand, derived from pollen records

    NASA Astrophysics Data System (ADS)

    Vandergoes, Marcus J.; Newnham, Rewi M.; Denton, George H.; Blaauw, Maarten; Barrell, David J. A.

    2013-08-01

    We present pollen records from three sites in south Westland, New Zealand, that document past vegetation and inferred climate change between approximately 30,000 and 15,000 cal. yr BP. Detailed radiocarbon dating of the enclosing sediments at one of those sites, Galway tarn, provides a more robust chronology for the structure and timing of climate-induced vegetation change than has previously been possible in this region. The Kawakawa/Oruanui tephra, a key isochronous marker, affords a precise stratigraphic link across all three pollen records, while other tie points are provided by key pollen-stratigraphic changes which appear to be synchronous across all three sites. Collectively, the records show three episodes in which grassland, interpreted as indicating mostly cold subalpine to alpine conditions, was prevalent in lowland south Westland, separated by phases dominated by subalpine shrubs and montane-lowland trees, indicating milder interstadial conditions. Dating, expressed as a Bayesian-estimated single 'best' age followed in parentheses by younger/older bounds of the 95% confidence modelled age range, indicates that a cold stadial episode, whose onset was marked by replacement of woodland by grassland, occurred between 28,730 (29,390-28,500) and 25,470 (26,090-25,270) cal. yr BP (years before AD, 1950), prior to the deposition of the Kawakawa/Oruanui tephra. Milder interstadial conditions prevailed between 25,470 (26,090-25,270) and 24,400 (24,840-24,120) cal. yr BP and between 22,630 (22,930-22,340) and 21,980 (22,210-21,580) cal. yr BP, separated by a return to cold stadial conditions between 24,400 and 22,630 cal. yr BP. A final episode of grass-dominated vegetation, indicating cold stadial conditions, occurred from 21,980 (22,210-21,580) to 18,490 (18,670-17,950) cal. yr BP. The decline in grass pollen, indicating progressive climate amelioration, was well advanced by 17,370 (17,730-17,110) cal. yr BP, indicating that the onset of the termination in south

  2. Ostracods and sediment geochemistry as indicators of hydrologic and climatic variability in the central part of the Mexican Chihuahuan Desert over the last 27 ka cal BP

    NASA Astrophysics Data System (ADS)

    Chávez Lara, C. M.; Roy, P. D.; Lozano Santa Cruz, R.; López Balbiaux, N.

    2013-12-01

    The paleolake Santiaguillo (Durango State) is located in the central part of the Chihuahuan Desert (Mexico). The lacustrine basin covers an area of approximately 1,964 km2 and is surrounded by mountains up to ca. 2,700 masl. This basin was formed by tectonic processes and the basement is formed by volcanic felsic rocks of Tertiary age. Four sediment cores were obtained from central and western part of the basin to reconstruct hydrologic and climate variability during the late Pleistocene and Holocene. In this work, we present paleo-ecology of ostracods and sedimentary geochemistry from two sediment cores (300 cm and 200 cm long) collected from the western basin margin. The age model was constructed from 8 AMS radiocarbon dates and the longest profile represents the last 27 cal ka BP. The ostracode faunal content consists of 4 different species: Limnocythere bradburyi, Cadona patzcuaro, Cypridopsis vidua and Limnocythere ceriotuberosa (listed from highest to lowest abundance) and total abundance varies between 0 and 125 valves/g. Paleo-environmental conditions were reconstructed from the Total Organic Carbon (TOC), Total Inorganic Carbon (TIC), Carbon/Nitrogen ratios (C/N), Chemical Index of Alteration (CIA) and concentrations of Ti, Ca, Si and Al. The results were divided into two zones for interpretation. Zone 1 covers ca. 27-17 cal ka BP (300-191 cm) and is characterized by higher Ti concentrations and above average CIA values. This suggests greater interaction between water and sediment, lower evaporation and relatively higher lake level in the basin. During this interval of higher lakestand, the deposited organic matter was autochthonous (lacustrine origin) and ostracodes suggest presence of a warm and dilute water column (>13 °C and >100 ppm). Sediments of the last 17 cal ka BP (191-0 cm) (Zone 2) are characterized by below average water-sediment interaction, higher carbonate precipitation and deposition of allochthonous organic matter (terrestrial origin

  3. Holocene paleoclimate inferred from salinity histories of adjacent lakes in southwestern Sicily (Italy)

    USGS Publications Warehouse

    Curry, B Brandon; Henne, Paul; Mezquita-Joanes, Francesc; Marrone, Federico; Pieri, Valentina; La Mantia, Tommaso; Calo, Camilla; Tinner, Willy

    2016-01-01

    Marked uncertainties persist regarding the climatic evolution of the Mediterranean region during the Holocene. For instance, whether moisture availability gradually decreased, remained relatively constant, or increased during the last 7000 years remains a matter of debate. To assess Holocene limnology, hydrology and moisture dynamics, the coastal lakes Lago Preola and Gorgo Basso, located in southwestern Sicily, were investigated through several stratigraphic analyses of ostracodes, including multivariate analyses of assemblages, transfer functions of salinity, and biochemical analyses of valves (Sr/Ca, δ18O and δ13C). During the early Holocene, the Gorgo Basso and Lago Preola ostracode records are similar. After an initial period of moderate salinity (1690–6100 mg/l from ca. 10,000–8190 cal yr BP), syndepositional or diagenetic dissolution of ostracode valves suggests that salinity declined to <250 mg/L from ca. 8190 to 7000 cal yr BP at both sites. After ca. 6250 cal yr BP, the ostracode records are strikingly different. Lago Preola became much more saline, with paleosalinity values that ranged from 2270 to about 24,420 mg/L. We suggest that Lago Preola's change from a freshwater to mesosaline lake at about 6250 cal yr BP was related to sea level rise and resulting intrusion of seawater-influenced groundwater. In contrast, Gorgo Basso remained a freshwater lake. The salinity of Gorgo Basso declined somewhat after 6250 cal yr BP, in comparison to the early Holocene, ranging from about 550 to 1680 mg/L. Cypria ophtalmica, a species capable of rapid swimming and flourishing in waters with low dissolved oxygen levels, became dominant at approximately the time when Greek civilization took root in Sicily (2600 cal yr BP), and it completely dominates the record during Roman occupation (roughly 2100 to 1700 cal yr BP). These freshwater conditions at Gorgo Basso suggest high effective moisture when evergreen olive-oak forests collapsed in response

  4. Holocene paleoclimate inferred from salinity histories of adjacent lakes in southwestern Sicily (Italy)

    NASA Astrophysics Data System (ADS)

    Curry, Brandon; Henne, Paul D.; Mesquita-Joanes, Francesc; Marrone, Federico; Pieri, Valentina; La Mantia, Tommaso; Calò, Camilla; Tinner, Willy

    2016-10-01

    Marked uncertainties persist regarding the climatic evolution of the Mediterranean region during the Holocene. For instance, whether moisture availability gradually decreased, remained relatively constant, or increased during the last 7000 years remains a matter of debate. To assess Holocene limnology, hydrology and moisture dynamics, the coastal lakes Lago Preola and Gorgo Basso, located in southwestern Sicily, were investigated through several stratigraphic analyses of ostracodes, including multivariate analyses of assemblages, transfer functions of salinity, and biochemical analyses of valves (Sr/Ca, δ18O and δ13C). During the early Holocene, the Gorgo Basso and Lago Preola ostracode records are similar. After an initial period of moderate salinity (1690-6100 mg/l from ca. 10,000-8190 cal yr BP), syndepositional or diagenetic dissolution of ostracode valves suggests that salinity declined to <250 mg/L from ca. 8190 to 7000 cal yr BP at both sites. After ca. 6250 cal yr BP, the ostracode records are strikingly different. Lago Preola became much more saline, with paleosalinity values that ranged from 2270 to about 24,420 mg/L. We suggest that Lago Preola's change from a freshwater to mesosaline lake at about 6250 cal yr BP was related to sea level rise and resulting intrusion of seawater-influenced groundwater. In contrast, Gorgo Basso remained a freshwater lake. The salinity of Gorgo Basso declined somewhat after 6250 cal yr BP, in comparison to the early Holocene, ranging from about 550 to 1680 mg/L. Cypria ophtalmica, a species capable of rapid swimming and flourishing in waters with low dissolved oxygen levels, became dominant at approximately the time when Greek civilization took root in Sicily (2600 cal yr BP), and it completely dominates the record during Roman occupation (roughly 2100 to 1700 cal yr BP). These freshwater conditions at Gorgo Basso suggest high effective moisture when evergreen olive-oak forests collapsed in response to increased Greco

  5. Late Quaternary distal tephra-fall deposits in lacustrine sediments, Kenai Peninsula, Alaska

    USGS Publications Warehouse

    de Fontaine, C.S.; Kaufman, D.S.; Scott, Anderson R.; Werner, A.; Waythomas, C.F.; Brown, T.A.

    2007-01-01

    Tephra-fall deposits from Cook Inlet volcanoes were detected in sediment cores from Tustumena and Paradox Lakes, Kenai Peninsula, Alaska, using magnetic susceptibility and petrography. The ages of tephra layers were estimated using 21 14C ages on macrofossils. Tephras layers are typically fine, gray ash, 1-5??mm thick, and composed of varying proportions of glass shards, pumice, and glass-coated phenocrysts. Of the two lakes, Paradox Lake contained a higher frequency of tephra (0.8 tephra/100 yr; 109 over the 13,200-yr record). The unusually large number of tephra in this lake relative to others previously studied in the area is attributed to the lake's physiography, sedimentology, and limnology. The frequency of ash fall was not constant through the Holocene. In Paradox Lake, tephra layers are absent between ca. 800-2200, 3800-4800, and 9000-10,300??cal yr BP, despite continuously layered lacustrine sediment. In contrast, between 5000 and 9000??cal yr BP, an average of 1.7 tephra layers are present per 100 yr. The peak period of tephra fall (7000-9000??cal yr BP; 2.6 tephra/100 yr) in Paradox Lake is consistent with the increase in volcanism between 7000 and 9000 yr ago recorded in the Greenland ice cores. ?? 2007 Elsevier Inc. All rights reserved.

  6. Spatially-Explicit Holocene Drought Reconstructions in Amazonian Forests

    NASA Astrophysics Data System (ADS)

    McMichael, C.; Bush, M. B.

    2014-12-01

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

  7. Dynamics of floodplain lakes in the Upper Amazon Basin during the late Holocene

    NASA Astrophysics Data System (ADS)

    Quintana-Cobo, Isabel; Moreira-Turcq, Patricia; Cordeiro, Renato C.; Aniceto, Keila; Crave, Alain; Fraizy, Pascal; Moreira, Luciane S.; Duarte Contrera, Julia Maria de Aguiar; Turcq, Bruno

    2018-01-01

    To better understand the impact of channel migration processes and climate change on the depositional dynamics of floodplain lakes of the upper Amazon Basin during the late Holocene, we collected three sediment cores from floodplain lakes of the Ucayali River and one from the Marañón River. The cores were dated with 14C, radiographed and described. Bulk density, grain size analysis and total organic carbon (TOC) were determined. The results show that sedimentation in Ucayali floodplain lakes was marked by variations during the late Holocene, with periods of intense hydrodynamic energy and abrupt accumulations, a gap in the record between about 2870 and 690 cal yr BP, and periods of more lacustrine conditions. These changes in sedimentation were associated with variations in the river's influence related to changes in its meandering course (2870 cal yr BP) and a period of severe flooding between 3550 and 3000 cal yr BP. Lake Lagarto on the Marañón River floodplain exhibits a different sedimentary environment of low hydrodynamics with palm trees and macrophytes. Apparently, the lake has not experienced intense migration processes during the last 600 cal yr BP (base of the core). Nevertheless, the river sediment flux to the lake was important from 600 to 500 cal yr BP, although it decreased thereafter until the present. This decrease in the mineral accumulation rate indicates a decrease in river discharge since 500 cal yr BP, which coincides with precipitation records from the central Andes. In the upper part of the three Ucayali floodplain cores, a 30- to 250-cm-thick layer of reworked sediments has been deposited since 1950 AD (post-bomb). In Lake Carmen, this layer is associated with invasion of the lake by the levee of a migrating meander of the Ucayali. In Lakes Hubos and La Moringa, however, the river is still far away and the deposition must be interpreted as the result of extreme flooding. The beginning of the Ucayali meander migration is dated back to

  8. Diatom-inferred Holocene record of moisture variability in Lower Bear Lake, San Bernardino Mountains, California, USA

    NASA Astrophysics Data System (ADS)

    Starratt, S.; Kirby, M. E.

    2014-12-01

    Although Holocene diatom records from southern California lakes have been difficult to obtain, diatoms have been found in Lower Bear Lake (LBL) sediments, providing a 9200-year hydroclimatological record for the San Bernardino Mountains. Based on several physical and chemical properties as well as gastropod and ostracod assemblages. Kirby et al. (2012, QSR,46:57-65) inferred nine decadal to multi-centennial pluvial episodes (five major (PE-V to PE-I), four minor (PE-IIIa-c, PE-IIa) in sediment core BBLVC05-1 (34o15'20" N, 116o55'20" W; 4.5 m long). Here, we consider the implications of this new diatom data. The diatom record shows a gradual increase in salinity during the Holocene, corroborating the inference of decreasing lake size made by Kirby et al. (2012). The longest pluvial (PE-V; 9170?-8250 cal yr BP), is dominated by small fragilaroid taxa, indicating fresh, slightly alkaline waters. An increase in halophilic taxa at ~8700 cal yr BP suggests a several-decades-long drier interval within the pluvial. PE-IV (7000-6400 cal yr BP) is dominated by benthic taxa, including relatively high numbers of epiphytic taxa, indicating an increase in aquatic macrophytes. The abundance of Aulacoseira in PE-IV and PE-III (3350-3000 cal yr BP) suggests increased turbulence due to increased storminess. PE-III and PE-II (850-700 cal yr BP) contain greater abundances of benthic (epiphytic) and halophilic species, although the latter never dominate the assemblage. PE-I (500-476 cal yr BP) was not sampled. Aerophilic taxa comprise up to 3% of the assemblage during pluvial events suggesting increased erosion during those periods and the presence of symbiotic species throughout the record indicates nitrogen-depleted waters. The diatom data generally support the occurrence of multiple pluvials over the Holocene with the most sustained occurring in the early Holocene. Furthermore, the diatom data suggest LBL likely diminished in size through the Holocene becoming more saline in the

  9. Diverse rupture modes for surface-deforming upper plate earthquakes in the southern Puget Lowland of Washington State

    USGS Publications Warehouse

    Nelson, Alan R.; Personius, Stephen F.; Sherrod, Brian L.; Kelsey, Harvey M.; Johnson, Samuel Y.; Bradley, Lee-Ann; Wells, Ray E.

    2014-01-01

    Earthquake prehistory of the southern Puget Lowland, in the north-south compressive regime of the migrating Cascadia forearc, reflects diverse earthquake rupture modes with variable recurrence. Stratigraphy and Bayesian analyses of previously reported and new 14C ages in trenches and cores along backthrust scarps in the Seattle fault zone restrict a large earthquake to 1040–910 cal yr B.P. (2σ), an interval that includes the time of the M 7–7.5 Restoration Point earthquake. A newly identified surface-rupturing earthquake along the Waterman Point backthrust dates to 940–380 cal yr B.P., bringing the number of earthquakes in the Seattle fault zone in the past 3500 yr to 4 or 5. Whether scarps record earthquakes of moderate (M 5.5–6.0) or large (M 6.5–7.0) magnitude, backthrusts of the Seattle fault zone may slip during moderate to large earthquakes every few hundred years for periods of 1000–2000 yr, and then not slip for periods of at least several thousands of years. Four new fault scarp trenches in the Tacoma fault zone show evidence of late Holocene folding and faulting about the time of a large earthquake or earthquakes inferred from widespread coseismic subsidence ca. 1000 cal yr B.P.; 12 ages from 8 sites in the Tacoma fault zone limit the earthquakes to 1050–980 cal yr B.P. Evidence is too sparse to determine whether a large earthquake was closely predated or postdated by other earthquakes in the Tacoma basin, but the scarp of the Tacoma fault was formed by multiple earthquakes. In the northeast-striking Saddle Mountain deformation zone, along the western limit of the Seattle and Tacoma fault zones, analysis of previous ages limits earthquakes to 1200–310 cal yr B.P. The prehistory clarifies earthquake clustering in the central Puget Lowland, but cannot resolve potential structural links among the three Holocene fault zones.

  10. Holocene climatic variations in the Western Cordillera of Colombia: A multiproxy high-resolution record unravels the dual influence of ENSO and ITCZ

    NASA Astrophysics Data System (ADS)

    Muñoz, Paula; Gorin, Georges; Parra, Norberto; Velásquez, Cesar; Lemus, Diego; Monsalve-M., Carlos; Jojoa, Marcela

    2017-01-01

    The Páramo de Frontino (3460 m elevation) in Colombia is located approximately halfway between the Pacific and Atlantic oceans. It contains a 17 kyr long, stratigraphically continuous sedimentary sequence dated by 30 AMS 14C ages. Our study covers the last 11,500 cal yr and focuses on the biotic (pollen) and abiotic (microfluorescence-X or μXRF) components of this high mountain ecosystem. The pollen record provides a proxy for temperature and humidity with a resolution of 20-35 yr, and μXRF of Ti and Fe is a proxy for rainfall with a sub-annual (ca. 6-month) resolution. Temperature and humidity display rapid and significant changes over the Holocene. The rapid transition from a cold (mean annual temperature (MAT) 3.5 °C lower than today) and wet Younger Dryas to a warm and dry early Holocene is dated at 11,410 cal yr BP. During the Holocene, MAT varied from ca. 2.5 °C below to 3.5° above present-day temperature. Warm periods (11,410-10,700, 9700-6900, 4000-2400 cal yr BP) were separated by colder intervals. The last 2.4 kyr of the record is affected by human impact. The Holocene remained dry until 7500 cal yr BP. Then, precipitations increased to reach a maximum between 5000 and 4500 cal yr BP. A rapid decrease occurred until 3500 cal yr BP and the late Holocene was dry. Spectral analysis of μXRF data show rainfall cyclicity at millennial scale throughout the Holocene, and at centennial down to ENSO scale in more specific time intervals. The highest rainfall intervals correlate with the highest activity of ENSO. Variability in solar output is possibly the main cause for this millennial to decadal cyclicity. We interpret ENSO and ITCZ as the main climate change-driving mechanisms in Frontino. Comparison with high-resolution XRF data from the Caribbean Cariaco Basin (a proxy for rainfall in the coastal Venezuelian cordilleras) demonstrates that climate in Frontino was Pacific-driven (ENSO-dominated) during the YD and early Holocene, whereas it was Atlantic

  11. Postglacial diatom-climate responses in a small lake in the Pacific Northwest of North America

    NASA Astrophysics Data System (ADS)

    Egan, J.; Allott, T. E.; Fletcher, W.

    2017-12-01

    Understanding the variability of ocean-atmosphere interactions in the Pacific Northwest (PNW) of North America is essential for climate forecasting, particularly variations in the El Niño-Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO). Research suggests that global warming is increasing the frequency of extreme El Niño events, which can have global climatic impacts (e.g. disrupting global weather patterns, affecting ecosystems and agriculture and extreme weather events (flood, drought, bushfires)). A diatom record spanning 14,500 Cal yr BP from Moss Lake, Washington is used to assess Holocene climate change in the PNW including evidence for periodicities related to ocean-atmosphere interactions and/or variations in solar output, and is directly compared to the Moss Lake pollen record. Three climate phases were identified: 1) the Late Pleistocene (until 11,800 Cal yr BP), with a cold climate evidenced by the low abundance of diatoms; 2) the early to mid-Holocene (11,800 - 7500 Cal yr BP), with warm climate, longer growing seasons and shorter periods of ice cover, indicated by the increase of Cyclotella pseudostelligera and decrease of Fragilaria taxa; and 3) the mid-to-late Holocene from 7500 Cal yr BP onwards, with a cooler climate reflected by a decrease in Cyclotella pseudostelligera and an increase in Fragilaria taxa. These climate shifts correlate with the regional and local pollen record. Fluctuations in Cyclotella pseudostelligera and Aulacoseira taxa suggest climatic cycles of varying amplitude throughout. RedFit and Wavelet analyses revealed periodicities of approximately 2000, 1300, and 450 yrs. The 2000 yr cycle is attributed to solar variation; the Hallstatt Oscillation. The 1300 yr and 450 yr cycles are attributed to ENSO and PDO like cycles. The 1300 periodicity is evident throughout the Late Pleistocene and Holocene and reflects shifts from El Niño/positive PDO (weak wind intensity, warm temperature) to La Niña/Negative PDO

  12. Multistep food plant processing at Grotta Paglicci (Southern Italy) around 32,600 cal B.P.

    PubMed Central

    Mariotti Lippi, Marta; Foggi, Bruno; Aranguren, Biancamaria; Ronchitelli, Annamaria; Revedin, Anna

    2015-01-01

    Residue analyses on a grinding tool recovered at Grotta Paglicci sublayer 23A [32,614 ± 429 calibrated (cal) B.P.], Southern Italy, have demonstrated that early modern humans collected and processed various plants. The recording of starch grains attributable to Avena (oat) caryopses expands our information about the food plants used for producing flour in Europe during the Paleolithic and about the origins of a food tradition persisting up to the present in the Mediterranean basin. The quantitative distribution of the starch grains on the surface of the grinding stone furnished information about the tool handling, confirming its use as a pestle-grinder, as suggested by the wear-trace analysis. The particular state of preservation of the starch grains suggests the use of a thermal treatment before grinding, possibly to accelerate drying of the plants, making the following process easier and faster. The study clearly indicates that the exploitation of plant resources was very important for hunter–gatherer populations, to the point that the Early Gravettian inhabitants of Paglicci were able to process food plants and already possessed a wealth of knowledge that was to become widespread after the dawn of agriculture. PMID:26351674

  13. Multistep food plant processing at Grotta Paglicci (Southern Italy) around 32,600 cal B.P.

    PubMed

    Mariotti Lippi, Marta; Foggi, Bruno; Aranguren, Biancamaria; Ronchitelli, Annamaria; Revedin, Anna

    2015-09-29

    Residue analyses on a grinding tool recovered at Grotta Paglicci sublayer 23A [32,614 ± 429 calibrated (cal) B.P.], Southern Italy, have demonstrated that early modern humans collected and processed various plants. The recording of starch grains attributable to Avena (oat) caryopses expands our information about the food plants used for producing flour in Europe during the Paleolithic and about the origins of a food tradition persisting up to the present in the Mediterranean basin. The quantitative distribution of the starch grains on the surface of the grinding stone furnished information about the tool handling, confirming its use as a pestle-grinder, as suggested by the wear-trace analysis. The particular state of preservation of the starch grains suggests the use of a thermal treatment before grinding, possibly to accelerate drying of the plants, making the following process easier and faster. The study clearly indicates that the exploitation of plant resources was very important for hunter-gatherer populations, to the point that the Early Gravettian inhabitants of Paglicci were able to process food plants and already possessed a wealth of knowledge that was to become widespread after the dawn of agriculture.

  14. Paleoecology of a Northern Michigan Lake and the relationship among climate, vegetation, and Great Lakes water levels

    USGS Publications Warehouse

    Booth, R.K.; Jackson, S.T.; Thompson, T.A.

    2002-01-01

    We reconstructed Holocene water-level and vegetation dynamics based on pollen and plant macrofossils from a coastal lake in Upper Michigan. Our primary objective was to test the hypothesis that major fluctuations in Great Lakes water levels resulted in part from climatic changes. We also used our data to provide temporal constraints to the mid-Holocene dry period in Upper Michigan. From 9600 to 8600 cal yr B.P. a shallow, lacustrine environment characterized the Mud Lake basin. A Sphagnum-dominated wetland occupied the basin during the mid-Holocene dry period (???8600 to 6600 cal yr B.P.). The basin flooded at 6600 cal yr B.P. as a result of rising water levels associated with the onset of the Nipissing I phase of ancestral Lake Superior. This flooding event occured contemporaneously with a well-documented regional expansion of Tsuga. Betula pollen increased during the Nipissing II phase (4500 cal yr B.P.). Macrofossil evidence from Mud Lake suggests that Betula alleghaniensis expansion was primarily responsible for the rising Betula pollen percentages. Major regional and local vegetational changes were associated with all the major Holocene highstands of the western Great Lakes (Nipissing I, Nipissing II, and Algoma). Traditional interpretations of Great Lakes water-level history should be revised to include a major role of climate. ?? 2002 University of Washington.

  15. Evidence of a higher late-Holocene treeline along the Continental Divide in central Colorado

    USGS Publications Warehouse

    Carrara, Paul E.; McGeehin, John

    2015-01-01

    Using a combination of 23 radiocarbon ages and annual ring counts from 18 Rocky Mountain bristlecone pine (Pinus aristata) remnants above the local present-day limits, a period of higher treeline has been determined for two sites near the Continental Divide in central Colorado. The highest remnants were found about 30 m above live bristlecone pines of similar size. The majority of the remnants, consisting of standing snags, large logs, and smaller remains, are highly eroded, such that the innermost annual rings of all but one are missing. The radiocarbon ages obtained from the oldest wood recovered from each remnant indicate that the majority were established above the present-day limit of bristlecone pine from prior to 2700 cal. yr BP to no later than about 1200 cal. yr BP. These radiocarbon ages combined with the annual ring count from the corresponding remnant indicate that the majority of the sampled remnants grew above the present-day limit of bristlecone pine from sometime before 2700 cal. yr BP to about 800 cal. yr BP. Evidence of recent climatic warming is demonstrated at one of the sites by young bristlecone pine saplings growing next to the highest remnants; the saplings were established after AD 1965 and represent the highest advance of treeline in at least 1200 years.

  16. Seismic Triggers of Lacustrine Subaqueous Landslides in Lake Champlain, USA

    NASA Astrophysics Data System (ADS)

    Manley, P.; Manley, T.; Ghosh, S. J.; Rosales-Underbrink, P.; Silverhart, P.

    2017-12-01

    Lacustrine slumps and debris flows (landslides) have been identified in Lake Champlain via Multibeam and CHIRP (compressed high intensity radar pulse) seismic profile data. Numerous large landslides studied by Ghosh (2012), Rosales-Underbrink (2015), and Silverhart (2016) have shown that many of these landslides are coeval. All landslides failed on a specific interface between marine Champlain Sea and modern lacustrine Lake Champlain sediments. Utilizing radionuclide dating on sediment from the unfailed slopes or undisturbed sediment above failed deposits, sedimentation rates were determined and used to calculate the approximate failure ages for each of the landslides studied. The northernmost failure, south of the Bouquet River, occurred about 950-1200 cal yr BP and is the first mass wasting event of this age to be recorded on Lake Champlain. The remaining landslides failed about 4500-5200 cal yr BP and agree with nearby Western Quebec Seismic Zone (WQSZ) with clusters of terrestrial landslides occurring at 1000 and 5000 cal yr BP triggered by large earthquakes (Brooks, 2015) along the same interface. The 5000 cal yr BP event has been attributed to a M 6.4 or greater earthquake within the WQSZ. The coeval landslides observed in Lake Champlain were likely triggered by this same earthquake. Lake tsunami models show that these simultaneous landslide failures can generate surface waves wave that can impact the Lake Champlain shoreline within 3-10 minutes after the earthquake.

  17. A geochemical record of the link between chemical weathering and the East Asian summer monsoon during the late Holocene preserved in lacustrine sediments from Poyang Lake, central China

    NASA Astrophysics Data System (ADS)

    Huang, Chao; Wei, Gangjian; Li, Wuxian; Liu, Ying

    2018-04-01

    This paper presents relatively high-resolution geochemical records spanning the past 4000 cal yr BP obtained from the lacustrine sediments of Poyang Lake in central China. The variations in the intensity of the East Asian summer monsoon (EASM) are traced using the K/Na, Ti/Na, Al/K, kaolinite/illite and clay/feldspar ratios, together with the chemical index of alteration (CIA), as indicators of chemical weathering. During the last 4000 years, the proxy records of chemical weathering from Poyang Lake exhibit an overall enhanced trend, consistent with regional hydrological changes in previous independent records. Further comparisons and analyses demonstrate that regional moisture variations in central China is inversely correlated with the EASM intensity, with weak EASM generating high precipitation in central China. Our data reveal three intervals of dramatically dry climatic conditions (i.e., ca. 4000-3200 cal yr BP, ca. 2800-2400 cal yr BP, and ca. 500-200 cal yr BP). A period of weak chemical weathering, related to cold and dry climatic conditions, occurred during the Little Ice Age (LIA), whereas more intense chemical weathering, reflecting warm and humid climatic conditions, was recorded during the Medieval Warm Period (MWP). Besides, an intensification of chemical weathering in Poyang Lake during the late Holocene agrees well with strong ENSO activity, suggesting that moisture variations in central China may be predominantly driven by ENSO variability.

  18. Timing of the southward retreat of the ITCZ at the end of the Holocene Humid Period in Southern Arabia: Data-model comparison

    NASA Astrophysics Data System (ADS)

    Lézine, Anne-Marie; Ivory, Sarah J.; Braconnot, Pascale; Marti, Olivier

    2017-05-01

    New pollen data from Omani mangroves (Kwar-al-Jaramah [22.49° N - 59.76° E] and Filim [20.61° N - 58.17° E]), in addition to previously published paleohydrological records from Southern Arabia improve our understanding of the timing and amplitude of the southward retreat of the Indian monsoon influence in Southern Arabia along a north-south transect. Comparison with simulations performed with the IPSL climate model, considering both snapshot experiments and transient simulations from 6000 cal yr BP to the present, confirm the latitudinally time-transgressive nature of the humid-arid transition at the end of the Holocene Humid Period. This occurred in two steps, respectively dated at around 5000 and 2700 cal yr BP. At around 5000 cal yr BP, the southward ITCZ shift was orbitally-driven and led to the abrupt aridification at Kwar-al-Jaramah and the progressive increase of dryness at Filim as the mean position of the ITCZ was centered ca 22.30°N. At 2700 cal yr BP, aridity was fully in place over all of southern Arabia due to increased climate variability. More intense rainy events during the last millennium, however, may have contributed to the discrete hydrological improvement without any impact on the regional vegetation which has remained desert to the present day.

  19. Evidence for smaller extents of the northwestern Greenland Ice Sheet and North Ice Cap during the Holocene

    NASA Astrophysics Data System (ADS)

    Kelly, M. A.; Osterberg, E. C.; Axford, Y.; Bigl, M.; Birkel, S. D.; Corbett, L. B.; Roy, E. P.; Thompson, J. T.; Whitecloud, S.

    2013-12-01

    The Greenland Ice Sheet (GrIS) and local glaciers on Greenland are responding dynamically to warming temperatures with widespread retreat. GRACE satellite data (e.g., Kahn et al., 2010) and the Petermann Glacier calving events document the recent expansion of ice loss into northwestern Greenland. To improve the ability to estimate future ice loss in a warming climate, we are developing records of the response of the northwestern Greenlandic cryosphere to Holocene climatic conditions, with a focus on past warm periods. Our ongoing research includes analyses of glacial geology, sub-fossil vegetation, lake sediment cores, chironomid assemblages and ice cores combined with glaciological modeling. To constrain past ice extents that were as small as, or smaller than, at present, we recovered sub-fossil vegetation exposed at the receding margins of the GrIS and North Ice Cap (NIC) in the Nunatarssuaq region (~76.7°N, 67.4°W) and of the GrIS near Thule (~76.5°N, 68.7°W). We present vegetation types and radiocarbon ages of 30 plant samples collected in August 2012. In the Nunatarssuaq region, five ages of in situ (rooted) vegetation including Polytrichum moss, Saxifraga nathorstii and grasses located <5 m outboard of the GrIS margin are ~120-200 cal yr BP (range of medians of the 2-sigma calibrated age ranges). Nine ages of in situ Polytrichum, Saxifraga oppositafolia and grasses from ~1-5 m inboard of the NIC margin (excavated from beneath ice) range from ~50 to 310 cal yr BP. The growth of these plants occurred when the GrIS and NIC were at least as small as at present and their ages suggest that ice advances occurred in the last 50-120 yrs. In addition to the in situ samples, we collected plants from well-preserved ground material exposed along shear planes in the GrIS margins. In Nunatarssuaq, two Polytrichum mosses rooted in ground material and exposed along a shear plane in the GrIS margin date to 4680 and 4730 cal yr BP. Near Thule, three ages of Salix arctica

  20. Wood Usage and Fire Veneration in the Pamir, Xinjiang, 2500 yr BP.

    PubMed

    Shen, Hui; Wu, Xinhua; Tang, Zihua; Zhou, Xinying; Sun, Nan; Li, Xiaoqiang

    2015-01-01

    Located on the Pamir Plateau in Xinjiang Province, China, the Ji'erzankale Necropolis dates back to 2500 yr BP. Many materials that have been unearthed in this cemetery, including shoo konghou (musical instrument), bronze mirrors and glass beads, suggest cultural transference between East and West. Furthermore, small-sized and rounded fire altars made from sweet-scented Sabina were found for the first time and regarded as implements for fire veneration. We identified 70 wooden objects from 25 tombs within the Necropolis, and found that each object had been made from one of seven tree species. Analysis revealed that the inhabitants of the region mainly used the most widely available types of wood, namely Betula and Populus. People also specifically chose inflammable Populus wood to make hearth boards and hand drills (both are used for making fire by drilling), rigid Betula wood to craft wooden plates. Salix was used for fashioning wooden sticks, while sweet-scented Sabina was the preferred choice for making fire altars. Lonicera was selected for arrow shaft manufacture and Fraxinus syriaca, which has a beautiful grain, was chosen for making musical instruments. Conscious selection of different types of wood indicates that people of the Pamir Plateau were aware of the properties of various types of timbers, and were able to exploit these properties to the full. In turn, this demonstrates their wisdom and their ability to survive in, and adapt to, their local environment.

  1. Wood Usage and Fire Veneration in the Pamir, Xinjiang, 2500 yr BP

    PubMed Central

    Shen, Hui; Wu, Xinhua; Tang, Zihua; Zhou, Xinying; Sun, Nan; Li, Xiaoqiang

    2015-01-01

    Located on the Pamir Plateau in Xinjiang Province, China, the Ji’erzankale Necropolis dates back to 2500 yr BP. Many materials that have been unearthed in this cemetery, including shoo konghou (musical instrument), bronze mirrors and glass beads, suggest cultural transference between East and West. Furthermore, small-sized and rounded fire altars made from sweet-scented Sabina were found for the first time and regarded as implements for fire veneration. We identified 70 wooden objects from 25 tombs within the Necropolis, and found that each object had been made from one of seven tree species. Analysis revealed that the inhabitants of the region mainly used the most widely available types of wood, namely Betula and Populus. People also specifically chose inflammable Populus wood to make hearth boards and hand drills (both are used for making fire by drilling), rigid Betula wood to craft wooden plates. Salix was used for fashioning wooden sticks, while sweet-scented Sabina was the preferred choice for making fire altars. Lonicera was selected for arrow shaft manufacture and Fraxinus syriaca, which has a beautiful grain, was chosen for making musical instruments. Conscious selection of different types of wood indicates that people of the Pamir Plateau were aware of the properties of various types of timbers, and were able to exploit these properties to the full. In turn, this demonstrates their wisdom and their ability to survive in, and adapt to, their local environment. PMID:26308646

  2. Early Holocene vegetation - climate interactions in the central part of European Russia

    NASA Astrophysics Data System (ADS)

    Novenko, Elena; Olchev, Alexander

    2017-04-01

    The new Early Holocene vegetation and climate reconstruction (approximately 10100 -7800 cal. yr. BP) for the forest zone the central European Russia are based on pollen records from three key regions located in taiga, mixed coniferous-broadleaved and broadleaved forest zones. The climatic parameters (the mean annual temperature and precipitation) and total forest coverage during the early Holocene were reconstructed using the Best Modern Analogue technique. Information about moistening conditions was revealed from reconstructions of actual evapotranspiration (ET) and potential evaporation (PET). For calculation of the annual ET and PET rates of the forest landscapes a regression model was applied. The model is based on nonlinear approximations of annual values of ET and PET provided by the Levenberg-Marquardt method using the results of numerical simulations of ET and PET carried out by a Mixfor-SVAT model for the forests with different species compositions under various thermal and moistening conditions. Mixfor-SVAT is an one-dimensional model of the energy, H2O and CO2 exchange between vertically structured mono- and multi-specific forest stands and the atmosphere (Olchev et al., 2002). Obtained results showed that the considered period was characterized by relatively low air temperatures and high precipitation compared with modern conditions. Analysis of the long-term pattern of the mean annual temperature for all three regions reveal two synchronous significant cooling periods observed in 9100-9300 cal. yr. BP and 8100-8500 cal. yr. BP as well as rapid growth of the air temperature in 8100-7800 cal. yr. BP, when the annual temperatures increased by 3°C during about 300 years. The cooling phase of 8100-8500 cal. yr. BP could be corresponded to the distinct "8.2 ka event" widely recorded across Europe. Periods of climate warming are coincided with periods of precipitation rise whereas the cool phases are characterized by its decrease. The lowest ET and PET rates

  3. An 8700 year paleoclimate reconstruction from the southern Maya lowlands

    USGS Publications Warehouse

    Wahl, David B.; Byrne, Roger; Anderson, Lysanna

    2014-01-01

    Analysis of a sediment core from Lago Puerto Arturo, a closed basin lake in northern Peten, Guatemala, has provided an ∼8700 cal year record of climate change and human activity in the southern Maya lowlands. Stable isotope, magnetic susceptibility, and pollen analyses were used to reconstruct environmental change in the region. Results indicate a relatively wet early to middle Holocene followed by a drier late Holocene, which we interpret as reflecting long-term changes in insolation (precession). Higher frequency variability is more likely attributable to changes in ocean/atmosphere circulation in both the North Atlantic and the Pacific Oceans. Pollen and isotope data show that most of the period of prehispanic agricultural settlement, i.e. ∼5000–1000 cal yr BP, was characterized by drier conditions than previous or subsequent periods. The presence ofZea (corn) pollen through peak aridity during the Terminal Classic period (∼1250–1130 cal yr BP) suggests that drought may not have had as negative an impact as previously proposed. A dramatic negative shift in isotope values indicates an increase in precipitation after ∼950 cal yr BP (hereafter BP).

  4. Middle Holocene rapid environmental changes and human adaptation in Greece

    NASA Astrophysics Data System (ADS)

    Lespez, Laurent; Glais, Arthur; Lopez-Saez, José-Antonio; Le Drezen, Yann; Tsirtsoni, Zoï; Davidson, Robert; Biree, Laetitia; Malamidou, Dimitra

    2016-03-01

    Numerous researchers discuss of the collapse of civilizations in response to abrupt climate change in the Mediterranean region. The period between 6500 and 5000 cal yr BP is one of the least studied episodes of rapid climate change at the end of the Late Neolithic. This period is characterized by a dramatic decline in settlement and a cultural break in the Balkans. High-resolution paleoenvironmental proxy data obtained in the Lower Angitis Valley enables an examination of the societal responses to rapid climatic change in Greece. Development of a lasting fluvio-lacustrine environment followed by enhanced fluvial activity is evident from 6000 cal yr BP. Paleoecological data show a succession of dry events at 5800-5700, 5450 and 5000-4900 cal yr BP. These events correspond to incursion of cold air masses to the eastern Mediterranean, confirming the climatic instability of the middle Holocene climate transition. Two periods with farming and pastural activities (6300-5600 and 5100-4700 cal BP) are evident. The intervening period is marked by environmental changes, but the continuous occurrence of anthropogenic taxa suggests the persistence of human activities despite the absence of archaeological evidence. The environmental factors alone were not sufficient to trigger the observed societal changes.

  5. Relative Sea-Level Stability in Natuna Island, Indonesia, since 6400 yr BP

    NASA Astrophysics Data System (ADS)

    Wan, J. X. W.; Meltzner, A. J.; Switzer, A.; Horton, B.; Ke, L.; Wang, X.; Bradley, S.; Natawidjaja, D.; Suwargadi, B. W.

    2017-12-01

    In order to understand the regional variability of relative sea level (RSL) due to glacio-isostatic adjustment (GIA) and other natural influences, high-precision records of Holocene RSL on the Sunda Shelf are required. Accurate estimates of past RSL at a variety of locations allow us to validate geophysical and climate models, and provide context for understanding modern RSL change in the face of global climate change. For the aforementioned purposes, we surveyed and dated coral microatoll colonies, which are precise RSL proxy archives, from Natuna Island in Indonesia. Our analysis of 11 coral microatoll elevations from a total of four sites on Natuna Island is constrained in time by a minimum of one radiocarbon date and one U-Th age on each microatoll. The distribution of ages and elevations indicates that RSL was relatively stable from 6400 to 1400 yr BP at 0.3-0.6 m higher than present, before a more recent fall to current levels. The radiocarbon and U-Th ages are consistent with one another, with preliminary estimates of ΔR ≈ 0 for our entire data set. Our data are roughly compatible with predictions of a recently developed GIA model for the Southeast Asia region (Bradley et al., 2016, Quat. Sci. Rev.). This new dataset is part of larger project with more than 25 sites in Malaysia and Indonesia. Our new constraints on past RSL on the Sunda Shelf will allow for validation and calibration of GIA models in the tropics, where RSL data are presently insufficient.

  6. Tree and timberline shifts in the northern Romanian Carpathians during the Holocene and the responses to environmental changes

    NASA Astrophysics Data System (ADS)

    Feurdean, Angelica; Gałka, Mariusz; Tanţău, Ioan; Geantă, Anca; Hutchinson, Simon M.; Hickler, Thomas

    2016-02-01

    High altitude environments are experiencing more rapid changes in temperature than the global average with the risk of losing essential ecosystem services in mountain environments. The Carpathians Mountains are regarded as hosting Europe's most pristine mountain ecosystems, yet the paucity of past environmental records limits our understanding of their sensitivity to the various drivers of change. A multi-proxy palaeoecological approach (plant macro-remains, pollen, charcoal) applied to three Holocene sediment sequences (between 1540 and 1810 m a.s.l.) in the Rodna Mountains documents past treeline and timberline shifts in response to climate change and human impact to anticipate the likely future responses. Our results indicate that forest reacted sensitively to past climate conditions. The timberline had exceeded an elevation of 1540 m a.s.l. by 10,200 cal. yr BP, when summers were warmer than today. The treeline remained below 1810 m a.s.l. at this time and reached its maximum elevation after 8500 cal. yr BP, when winter temperatures became milder. Cool summer conditions probably caused a lowering of the timberline and an extension of the treeline ecotone from 4900 cal. yr BP, a process accentuated by human impact from the Bronze Age (3500 cal. yr BP) onwards. The anticipated upslope tree movements as a consequence ongoing global warming are not yet clearly visible in our records, but will more probably take place in abandoned agricultural areas and be counter-balanced by re-enforced anthropogenic pressure elsewhere. Pinus sylvestris was the dominant tree species in the timberline under a warm and dry climate, when fires were frequent, during the early Holocene (11,250-10,200 cal. yr BP), while Picea abies became dominant in the timberline and Pinus mugo in the treeline ecotone, respectively from 10,200 cal. yr BP to the present. Abies alba became a significant component of the timber over the last four millennia. The anticipated future warmer and moister

  7. Stable-Isotope Perspectives on Holocene Environmental Change at Archaeological Sites in the Middle Tanana Valley, Interior Alaska

    NASA Astrophysics Data System (ADS)

    Johnson, W. C.; Gaines, E. P.

    2010-12-01

    Summer of 2009, Colorado State University Center for Environmental Management of Military Lands conducted test excavations of 29 prehistoric archaeological sites situated on a loess-mantled morainal ridge complex within the Jarvis Creek valley of the Tanana River system at Fort Wainwright in Interior Alaska. Initial loess deposition on the moraines began about 13,000 cal yr BP, with subsequent long-term, nomadic occupation of the area occurring from 9,500 to 1,060 cal yr BP. An array of data were extracted from bulk-sediment samples and used to assess past environmental conditions. Parameters and approaches used to generate these data included stable carbon isotope ratios, magnetic susceptibility, biogenic opal analysis, detrital charcoal content, quantitative color (L*a*b), and particle-size distribution. Stable carbon isotope trends, in combination with the other environmental proxy data, document major environmental changes. Data from the glacial till-loess transition and lower silt mantle indicate that the area was cold and slightly mesic, and dominated by treeless C3-dominated grassland immediately after the terminal Pleistocene glacial retreat (~12,700 cal yr BP). A dearth of particulate charcoal and charred phytoliths from sediments of this period suggests a minor role for fire, e.g., only localized, small fires. Cold, treeless environmental conditions continued throughout the Early Holocene (~12,000-7,000 cal yr BP), though it was more mesic than earlier. Middle Holocene (~7000-5000 cal yr BP) data display a shift in C3 grass species (increased δ13C values), the appearance of a shrub component to the plant community, significant surface stability, and more widespread fire occurrence. Picea glauca (white spruce) and Alnus sp. (alder) appear in the later parts of the Middle Holocene, and charcoal concentration increases. The Late Holocene (since ~5,000 cal yr BP) witnessed a decline in P. glauca by about 50%, a tenfold increase in Alnus, and the appearance

  8. The ~ 2500 yr B.P. Chicoral non-cohesive debris flow from Cerro Machín Volcano, Colombia

    NASA Astrophysics Data System (ADS)

    Murcia, H. F.; Hurtado, B. O.; Cortés, G. P.; Macías, J. L.; Cepeda, H.

    2008-04-01

    Cerro Machín Volcano (CMV) is located in the central part of the Colombian Andes (2750 m asl), 150 km southwest of Bogotá. It is considered the most dangerous active volcano of Colombia. CMV has experienced at least six major explosive eruptions during the last 5000 years. These eruptions have emplaced many types of pyroclastic deposits with associated lahars that have traveled more than 100 km. One of these lahars is called Chicoral Debris Flow Deposit (DFD2). This deposit is exposed as discontinuous terraces (3-20 m thick) along the Coello and Magdalena rivers up to 109 km from the source. The DFD2 covers a minimum area of 62 km 2 and has a minimum volume of 0.57 km 3. It comprises two dacite-rich volcaniclastic units. Grain-size analysis reveals that the matrix content and sorting increase with distance while the average grain size decreases. The clay content of the DFD2 matrix is approximately 1%, thus categorizing it as a non-cohesive debris flow. Radiocarbon dates obtained from underlying and overlying paleosols yielded ages of 2505 + 65 and 1640 + 45 yr B.P., respectively. These dates suggest that DFD2 is related to the ~ 2600 yr B.P. El Guaico eruption of CMV. This eruption produced a block-and-ash flow that filled and blocked the Toche River up to 5 km from the volcano. Subsequent remobilization of this loose material by runoff water generated a massive debris flow that traveled 91 km along the Toche and Coello rivers and continued across the Espinal Alluvial Fan debouching into the Magdalena River where it continued another 18 km prior to its transformation into a sediment-laden flow. Because the last eruption of the volcano occurred ca. 900 years ago, no historic activity of CMV is known among inhabitants of the region. Hence the region has developed without awareness of volcanic hazards. Therefore an assessment of volcanic hazards is essential for understanding and evaluating the vulnerability and risk to which people are exposed in case of a future

  9. Summer moisture changes in the Lake Qinghai area on the northeastern Tibetan Plateau recorded from a meadow section over the past 8400 yrs

    NASA Astrophysics Data System (ADS)

    Li, Xiangzhong; Liu, Xiangjun; He, Yuxin; Liu, Weiguo; Zhou, Xin; Wang, Zheng

    2018-02-01

    Holocene climatic and environmental changes on the northeastern Tibetan Plateau (TP) have been widely discussed based on the climatic records from sedimentary cores. However, differences in the reconstructed climatic history from various studies in this region still exist, probably due to influence of climatic proxies from multiple factors and the chronological uncertainties in lacustrine sediments. Here we present records of terrestrial plant δ13C, soil color and total organic carbon content over the past 8400 years from a well-dated meadow section on the northeastern TP. The terrestrial plant δ13C value serves as a good summer precipitation/moisture indicator in the studied region. Soil color property and TOC content are also able to disentangle the moisture evolution history. All the data show much wet climates at 8400-7400 cal yr BP, dry climates at 7400-6000 cal yr BP and then wet conditions with fluctuation at 6000-3200 cal yr BP. Late Holocene moisture appears to be comparable with moist conditions from 6000 to 3200 cal yr BP. By further comparing the climatic variations in the Lake Qinghai area with records of the reconstructed summer temperature and the Asian Monsoon precipitation, we believe that the pattern of moisture/precipitation evolution in the Lake Qinghai area was not completely consistent with regions around Lake Qinghai, probably due to complicated interaction between the East Asian Summer Monsoon and the Indian Summer Monsoon.

  10. Late-glacial and Holocene records of fire and vegetation from Cradle Mountain National Park, Tasmania, Australia

    NASA Astrophysics Data System (ADS)

    Stahle, Laura N.; Chin, Hahjung; Haberle, Simon; Whitlock, Cathy

    2017-12-01

    Fire activity was reconstructed at five sites and vegetation history at three sites in northwest Tasmania, Australia in order to examine the climate and human drivers of environmental change in the region. Watershed-scale reconstructions of fire were compared to regional vegetation history. Fire activity was very low until ca. 12,000 cal yr BP. An early-Holocene fire maximum, ca. 11,800-9800 cal yr BP, occurred during the warmest interval of the Holocene as recorded by regional paleoclimate proxy records. This period of elevated burning was also coincident with an increase in arboreal sclerophyll plant taxa. A maximum in rainforest taxa occurred at ca. 8500-5800 cal yr BP concurrent with sharply diminished biomass burning compared with the early Holocene. The increase in rainforest taxa is attributed to elevated effective moisture during this period. Conditions were drier and variable in the late Holocene as compared with earlier periods. A rise in fire activity at ca. 4800-3200 cal yr BP was accompanied by an increase in sclerophyll taxa and decline of rainforest and subalpine taxa. Elevated palynological richness during the late Holocene co-occurred with high levels of charcoal suggesting that fires promoted high floristic diversity. At Cradle Mountain, there is no clear evidence that fire regimes or vegetation were extensively modified by humans prior to European settlement. Climate was the primary driver of fire activity over millennial timescales as explained by the close relationship between charcoal and climate proxy data.

  11. Vegetation stability in the Southeastern Brazilian coastal area from 5500 to 1400 14C yr BP deduced from charcoal analysis.

    PubMed

    Scheel-Ybert

    2000-06-01

    Charcoal analysis of six shell mounds showed that no major changes of the mainland vegetation ecosystem have taken place along the southeastern Brazilian coast (22 degrees 53'-22 degrees 57'S, 42 degrees 03'-42 degrees 33'W) from 5500 to 1400 14C yr BP. These shell mounds have been occupied by sedentary fisher-gatherer-hunters. Charcoal fragments retrieved from vertical profiles in the archaeological sites were examined; taxonomic determinations were based on a reference collection of charred woods and a program for computer-aided identification. Charcoal assemblages of all the studied sites present taxa from various restinga vegetation types, mangroves, xeromorphic coastal forest, and inland Atlantic Forest. The restinga ecosystem, characteristic of the Brazilian coast, is associated with sandy beach ridges; the restinga forest was much more abundant during the studied period than nowadays. The charcoal assemblages represent mainly the local vegetation; a regional reconstruction depends on the study of numerous sites. In the Cabo Frio region, open restinga taxa are more abundant in the Sambaqui do Forte, while forest elements are more important in the Sambaquis Salinas Peroano and Boca da Barra. The sites studied in the Arraial do Cabo (Sambaqui da Ponta da Cabeça) and in the Saquarema regions (Sambaquis da Pontinha and da Beirada) show that open restinga formations were locally predominant. A comparison of multivariate analysis applied to both charcoal assemblages and to phytosociological data of the extant vegetation showed a good correspondence between the charcoal spectra and the present vegetation. The high taxonomic diversity of archaeological charcoal samples and numerous fragments showing traces of decay before charring suggests that aleatory gathering of dead wood constituted the main source of firewood for fisher-gatherer-hunters populations. Condalia sp. was probably selected for cultural reasons.The only significant fluctuations on the charcoal

  12. Vibrio parahaemolyticus CalR down regulates the thermostable direct hemolysin (TDH) gene transcription and thereby inhibits hemolytic activity.

    PubMed

    Zhang, Yiquan; Zhang, Ying; Gao, He; Zhang, Lingyu; Yin, Zhe; Huang, Xinxiang; Zhou, Dongsheng; Yang, Huiying; Yang, Wenhui; Wang, Li

    2017-05-20

    TDH, encoded by tdh gene, is a major virulent determinant of V. parahaemolyticus that controls various biological activities, such as hemolytic activity, cytotoxicity, and enterotoxicity. The hemolytic activity on Wagatsuma agar ascribed to TDH is called Kanagawa phenomenon (KP). All KP positive strains contain tdh1 and tdh2 genes, but tdh2 is predominantly responsible for KP. CalR is a regulatory protein that was originally identified as a repressor of swarming motility and T3SS1 gene expression in V. parahaemolyticus. In the present study, the regulation of tdh2 by CalR was investigated using a set of experiments including qRT-PCR, primer extension, LacZ fusion, hemolytic phenotype, EMSA, and DNase I footprinting assays. The results showed that His-CalR protected a single region from 224bp to 318bp upstream of tdh2 against DNase I digestion, and a transcriptional start site located at 42bp upstream of tdh2 was detected and its transcribed activity was inhibited by CalR. Moreover, the KP test results showed that the hemolytic activity of V. parahaemolyticus is also under negative control of CalR. The data demonstrated that CalR is a repressor of the tdh2 transcription and thereby inhibits the hemolytic activity of V. parahaemolyticus. Copyright © 2017. Published by Elsevier B.V.

  13. Climate change in southern Illinois, USA, based on the age and δ13C of organic matter in cave sediments

    USGS Publications Warehouse

    Panno, Samuel V.; Curry, B. Brandon; Wang, Hongfang; Hackley, Keith C.; Liu, Chao-Li; Lundstrom, Craig; Zhou, Juanzuo

    2004-01-01

    Matrix-supported diamicton and uniform to laminated, silty, fine-grained sediment deposited from about 42,500 to 27,600 cal yr B.P. under slackwater conditions nearly filled two caves in southwestern Illinois. At some point, most of the sediment was flushed from the caves and from about 22,700 to 4000 cal yr B.P., floods deposited a drape of sandy and silty sediment on remnant slackwater successions, cobbly alluvium, and bedrock (especially from 7700 to 4000 cal yr B.P.). Clay mineral analyses of the slackwater cave sediment reveal a provenance of chiefly Petersburg Silt, a smectite- and illite-rich proglacial lacustrine unit present in the overlying Illinois Episode glacial succession. Today, remnants of the ancient subterranean slackwater deposits nearly fill several secondary passages and, in at least two locations, cover a cobble-mantled strath terrace 1.3 to 1.5 m above active stream channels. Slumping and sinkhole formation appear to have been important mechanisms for deposition of the ancient subterranean deposits. Slumping of these surficial deposits and associated vegetation can occur along the flanks of sinkholes (in addition to sinkhole formation) and enter caves; however, the finer organics, some of them comminuted during transport into the caves, become part of the cave alluvium. This finer organic fraction is the modern analog of the humified organic matter disseminated in slackwater sediment dated in this investigation by radiocarbon methods. Twenty-four 14C ages on humified organic matter provide chronologic control. The ??13C values of the organic matter reflect the proportion of C4-type to C3-type vegetation growing in and around swallets and sinkholes at the time of redeposition. Drought-tolerant C4-type vegetation was more prevalent relative to C3-type vegetation from 42,500 to 31,200 cal yr B.P. compared to conditions from 28,800 cal yr B.P. to the present. The ??13C values are consistent with the results from other investigations of

  14. Holocene vegetation and climatic variations in Central India: A study based on multiproxy evidences

    NASA Astrophysics Data System (ADS)

    Chauhan, M. S.; Sharma, Anupam; Phartiyal, Binita; Kumar, Kamlesh

    2013-11-01

    Palynology, texture, mineralogy, geochemistry, and magnetic susceptibility analysis of a 2 m deep sediment core from Padauna Swamp, southeastern Madhya Pradesh infers that between 8600 and 7500 cal yr BP a warm and relatively less-humid climate prevailed with open tree-savannahs dominated by grasses followed by sedges, Artemisia and members of Chenopodiaceae/Amaranthaceae with scanty trees viz., Schrebera, Aegle marmelos and Sterculia urens. This is well supported by lower organic to carbonate carbon ratio, coarser texture having relatively low CIA and magnetic susceptibility values and presence of some primary minerals. Between 7500 and 6250 cal yr BP the tree-savannahs were succeeded by open mixed deciduous forests with the invasion of a few more trees viz., Madhuca indica, Holoptelea, Emblica officinalis, Mitragyna parvifolia and members of Anacardiaceae in response to onset of a warm and humid climate. A considerable rise in organic carbon generated from the degradation of plentiful biomass along with increase in clay content with signs of kaolinite and increase in immobile over mobile elements with slightly higher CIA and magnetic susceptibility values also suggest climatic amelioration. The presence of ruderal plants such as Artemisia, Cannabis sativa and Cheno/Am further infers initiation of human activities in the region. Between 6250 and 2800 cal yr BP, the mixed deciduous forests became more diverse and dense, subduing grasses and other herbaceous elements. Sporadic incursion of Shorea robusta (Sal) in forest floristic was recorded around 5000 cal yr BP. The overall change in the vegetation mosaic reflects that a warm and more-humid climate prevailed in the region, probably on account of invigoration of southwest monsoon. This observation is further corroborated by other proxy data showing a spurt in organic/inorganic carbon ratio, increase in clay content with matured mineralogy, significantly higher CIA and magnetic susceptibility values. Since 2800 cal

  15. Climate Change in Lowland Central America During the Late Deglacial and Early Holocene

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Hillesheim, M B; Hodell, D A; Leyden, B W

    2005-02-08

    The transition from arid glacial to moist early Holocene conditions represented a profound change in northern lowland Neotropical climate. Here we report a detailed record of changes in moisture availability during the latter part of this transition ({approx}11,250 to 7,500 cal yr BP) inferred from sediment cores retrieved in Lake Peten Itza, northern Guatemala. Pollen assemblages demonstrate that a mesic forest had been largely established by {approx}11,250 cal yr BP, but sediment properties indicate that lake level was more than 35 m below modern stage. From 11,250 to 10,350 cal yr BP, during the Preboreal period, lithologic changes in sedimentsmore » from deep-water cores (>50 m below modern water level) indicate several wet-dry cycles that suggest distinct changes in effective moisture. Four dry events (designated PBE1-4) occurred at 11,200, 10,900, 10,700, and 10,400 cal yr BP and correlate with similar variability observed in the Cariaco Basin titanium record and glacial meltwater pulses into the Gulf of Mexico. After 10,350 cal yr BP, multiple sediment proxies suggest a shift to a more persistently moist early Holocene climate. Comparison of results from Lake Peten Itza with other records from the circum-Caribbean demonstrates a coherent climate response during the entire span of our record. Furthermore, lowland Neotropical climate during the late deglacial and early Holocene period appears to be tightly linked to climate change in the high-latitude North Atlantic. We speculate that the observed changes in lowland Neotropical precipitation were related to the intensity of the annual cycle and associated displacements in the mean latitudinal position of the Intertropical Convergence Zone and Azores-Bermuda high-pressure system. This mechanism operated on millennial-to-submillennial timescales and may have responded to changes in solar radiation, glacial meltwater, North Atlantic sea ice, and the Atlantic meridional overturning circulation (MOC).« less

  16. Sedimentary archives of fire, vegetation history, and human impacts during the late Holocene in the eastern lowland of Taiwan

    NASA Astrophysics Data System (ADS)

    Wang, Liang-Chi

    2017-04-01

    The Hualien Plain is one of the richest prehistoric sites in eastern Taiwan, and the reconstruction of late Holocene environment on the basis of the lacustrine sediments near Hualien Plain can benefit to the understandings of human-climate-environment interactions in past. The multi-decadal records of vegetation history, agriculture evidences and fire events in Liyu Lake of eastern Taiwan were reconstructed by using palynological and charcoal analysis of lake sediments. A 2.8 m sediment core covering a time period from 2,680 cal BP to the present was used to investigate the alterations in the landscape with respect to human activities and climate change. During 2680-2410 cal yr BP, frequent burning and high preservation of cultivated Poaceae pollen indicated the early cultivation during the late Neolithic period. There followed a warm climate during 2,410-1,510 cal yr BP, and the increase of lowland forest pollen showed a period of forest recovery as a consequence of reducing human activity. Following a phase of recolonization of prehistory human during 1510-560 cal yr BP, a slightly increasing trend of cultivated Poacease indicated the human activities, but the human population was low. The last 560 years record showed an intense trend of deforestation and cultivation which may correlate to a rapid increase in the human population in this area.

  17. Oscillations in the Indian summer monsoon during the Holocene inferred from a stable isotope record from pyrogenic carbon from Lake Chenghai, southwest China

    NASA Astrophysics Data System (ADS)

    Sun, Weiwei; Zhang, Enlou; Liu, Enfeng; Ji, Ming; Chen, Rong; Zhao, Cheng; Shen, Ji; Li, Yanling

    2017-02-01

    A robust, well-dated record of centennial-scale abrupt changes in the Asian summer monsoon is crucial for understanding the potential forcing factors and their environmental effects. In this study, we analyzed the stable carbon isotopes of pyrogenic carbon (δ13CPC) in a 556-cm long sediment core retrieved from Lake Chenghai in the Yunnan Plateau, China. The results provide a continuous 7660-year precipitation record of the Indian summer monsoon (ISM). They indicate that from ∼7600 cal yr BP precipitation in the Lake Chenghai catchment gradually increased until 5030 cal yr BP, and then subsequently decreased in the second half of the Holocene. In addition, at least six centennial-scale droughts occurred at about 7300, 6300, 5500, 3400, 2500 and 500 cal yr BP. Our findings suggest that ISM intensity is primary controlled by variations in solar irradiance on a centennial time scale. This external forcing may be amplified by North Atlantic cooling events and El Niño-Southern Oscillation activity in the eastern tropical Pacific, which shift the intertropical convergence zone further southwards.

  18. A multi proxy reconstruction of paleoproductivity of Cleland Lake British Columbia, Canada

    NASA Astrophysics Data System (ADS)

    Mihindukulasooriya, L. N.; Pompeani, D. P.; Ortiz, J. D.; Steinman, B. A.; Abbott, M. B.

    2013-12-01

    In small closed-basin lakes in semi arid regions, variations in precipitation/evaporation (P/E) balance affect the physical, biological, and chemical composition of the lake water and sediment. This study presents color reflectance, XRF derived elemental concentrations and δ18O values of carbonates (δ18Ocarb) in sediment cores from Cleland Lake, British Columbia to provide insight into paleolimnological variations during the past 7500 years. Principal Component (PC) 1 of the reflectance data, i.e, Illite+ sphalerite is used as a clay mineral proxy, and PC 4, diatoms+ cyanobacteria, is used as a paleoproductivity proxy. Lake paleoproductivity history is divided into three temporal periods, 400 to 2500 (denoted as P1), 2500 to 5000 (P2) and 5000 to 7500 (P3) calibrated years before present (Cal yr BP). Fe and Mn concentrations gradually increase during P3, reach high values during P2 and rapidly drop to the lowest values after 2600 Cal yr BP. Diatom abundances have a positive correlation with illite (r= 0.79, n=73 α=0.01) throughout the record. In contrast, negative correlations (table 1) exists between δ18Ocarb and diatom abundances during P2 and P3, indicating higher diatom abundance during wet periods. After 3000 cal yr BP, the correlation reverses (table 1), indicating low diatom abundance during wet periods. Variability in diatom abundances is greater than that of the δ18Ocarb values, indicating that factors other than the P/E balance affects phytoplankton abundance. P 1 is characterized by three periods (centered at 2500, 2100 and 1400 Cal yr BP) of predominantly low diatom abundance that occur simultaneously with low Mn and Cr concentrations. Low Mn and Cr levels may indicate intense reducing conditions, while the observed peaks in Ni and Cu concentration might indicate reducing conditions resulting from high rates of organic matter decomposition (Tribovillard et al., 2006). Contemporaneous with the abrupt δ18Ocarb depletion around 2600 Cal yr BP, trace

  19. Neoglacial fluctuations of Deming Glacier, Mt. Baker, Washington USA.

    NASA Astrophysics Data System (ADS)

    Osborn, G.; Menounos, B.; Scott, K.; Clague, J. J.; Tucker, D.; Riedel, J.; Davis, P.

    2007-12-01

    Deming Glacier flows from the upper west slopes of Mt. Baker, a stratovolcano in the Cascade Range of Washington, USA. The north and south lateral moraines of Deming Glacier are composed of at least four tills separated by layers of detrital wood and sheared stumps in growth position. The stratigraphy records fluctuations of the glacier during the Holocene. The outer ten rings of an in situ stump from the middle wood layer, which is about 40 m below the north lateral moraine crest and 1.2 km downvalley from the present glacier terminus, yielded an age of 1750 ± 50~~ 14C yr BP [1810-1550 cal yr BP]. The stump revealed at least 300 rings and thus records a period of landscape stability and relatively restricted glaciation for several hundred years prior to ca. 1750 14C yr BP . Samples from the lowest wood layer also have been submitted for radiocarbon dating. Outer rings of detrital wood samples collected from two wood mats exposed in the south lateral moraine, 2.3 km downvalley of the glacier terminus, returned radiocarbon ages of 1600 ± 30~~ 14C yr BP [1550- 1410 cal yr BP] and 430 ± 30~~ 14C yr BP [AD 1420-1620]. These data indicate that Deming Glacier advanced over a vegetated moraine sometime after 1810 cal yr BP to a position less extensive that it achieved at the peak of the Little Ice Age. The glacier then receded before it began its final and most extensive Holocene advance after AD 1420. The older advance is correlative with the 'First Millennium AD' advance, recently recognized throughout western North America. The younger advance coincides with an advance of Mt. Baker's Easton Glacier [AD 1430-1630], and advances of many alpine glaciers elsewhere in western North America. Our data suggest that glaciers on Mt. Baker fluctuated in a similar manner to alpine glaciers in the Coast Mountains of British Columbia and in other mountain ranges of northwest North America during Neoglaciation.

  20. Fire history and climate characteristics during the last millennium of the Great Hinggan Mountains at the monsoon margin in northeastern China

    NASA Astrophysics Data System (ADS)

    Gao, Chuanyu; He, Jiabao; Zhang, Yan; Cong, Jinxin; Han, Dongxue; Wang, Guoping

    2018-03-01

    The northeastern region of China, at the limit of the summer monsoon, is characterized by the presence of mountains that influenced by the Asian summer monsoon on one side and the westerlies on the other; however, few studies have compared the environmental characteristics on the two sides of these mountains. In this study, two peatland cores from the western and eastern sides of the Great Hinggan Mountains were investigated to better understand the climatic and environmental conditions and the measurements of black carbon (BC) and δ13C-BC were used to reconstruct the fire history and environmental characteristics during the last millennium. Our results showed that the variations in the δ13C-BC values are more sensitive to climate changes than the BC fluxes, and the climate forcing mechanisms differed between the two sides of the mountains. Lower δ13C-BC values around 500 cal yr BP on the western side of the mountains indicated climate conditions were wetter than that on the eastern side, and were influenced by low sea surface temperatures in the North Atlantic Ocean. The region east of the mountains was mainly influenced by the strong Asian summer monsoon, and the decreasing of δ13C-BC values indicated climate conditions became wetter from 250 cal yr BP to the present and were wetter than that on the western side after 150 cal yr BP. Moreover, when one of these two forcing factors weakened and the other strengthened (e.g. from 400 to 150 cal yr BP), climate conditions in these two sides were similar.

  1. Late Neolithic vegetation history at the pile-dwelling site of Palù di Livenza (northeastern Italy

    NASA Astrophysics Data System (ADS)

    Pini, Roberta

    2004-12-01

    The Late Neolithic pile-dwelling of Palù di Livenza yielded archaeological remains typical of the Square Mouth Pottery and Lagozza Cultures. A palynological investigation reveals important changes in the vegetation due to anthropogenic pressure. Between ca. 6590 and 5960 cal. yr BP, dense oak wood forests with deciduous Quercus, Fagus and Corylus extended around the mire, with no signs of human impact. The establishment of the pile-dwelling, dated to ca. 5960 cal. yr BP, led to a strong reduction of forests, reclamation of wetlands, and expansion of herbaceous communities, with cultivated species, infestant weeds, nitrophilous and ruderal herbs, pastures and meadows. According to AMS dates and previous archaeological chronologies, the pile-dwelling persisted for about 700 years (from ca. 5960 to 5260 cal. yr BP). The history of the pile-dwelling after ca. 5260 cal. yr BP cannot be reconstructed because of recent contamination of the top part of the section. Rarefaction analysis was applied to estimate changes of palynological richness through time: the highest E(Tn) (between 56 and 69 taxa) are contemporaneous with the local development of the pile-dwelling. The comparison of pollen data with archaeobotanical evidence indicates that Fragaria vesca, Malus sylvestris, Papaver somniferum and Physalis alkekengi were gathered at some distance from the site and that Linum usitatissimum is strongly under-represented in pollen samples. Crop cultivation can be estimated for a radius of several hundred metres around the mire. Palù di Livenza is significant in the context of Neolithic archaeobotany of northern Italy and neighbouring countries. Copyright

  2. A Detailed 31,000-Year Record of Climate and Vegetation Change, from the Isotope Geochemistry of Two New Zealand Speleothems

    NASA Astrophysics Data System (ADS)

    Hellstrom, John; McCulloch, Malcolm; Stone, John

    1998-09-01

    Uranium-series dating and stable isotope analyses of two speleothems from northwest Nelson, New Zealand, record changes in regional climate and local forest extent over the past 31,000 years. Oxygen isotope variation in these speleothems primarily represents changes in the meteoric waters falling above the caves, possibly responding to latitudinal changes in the position of the Subtropical Front in the Tasman Sea. Seven positive excursions can be identified in the oxygen isotope record, which coincide with periods of glacier advance, known to be sensitive to northward movement of the Subtropical Front. Four glacier advances occurred during oxygen isotope stage 2, with the most extreme glacial conditions centered on 19,000 cal yr B.P. 2An excursion in the oxygen isotope record from 13,800 to 11,700 cal yr B.P. provides support for a previously identified New Zealand glacier advance at the time of the Younger Dryas Stade, but suggests it began slightly before the Younger Dryas as recorded in Greenland ice cores. Carbon isotope variations in the speleothems record changes in forest productivity, closely matching existing paleovegetation records. On the basis of vegetation changes, stage 2 glacial climate conditions terminated abruptly in central New Zealand, from 15,700 to 14,200 cal yr B.P. Evidence of continuous speleothem growth at one site suggests that depression of the local treeline was limited to 600-700 m below its present altitude, throughout the last 31,000 years. All ages reported or cited in this paper are in calendar years before present, expressed as "cal yr B.P." With the exception of the U-series dates of Williams (1996), all ages cited for events in New Zealand were reported by the sources cited as radiocarbon ages. In this paper, these radiocarbon ages have been corrected to calendar years before present using the 1993 calibration data set of Stuiver and Reimer (1993), or, for ages of greater than 19,000 14C yr B.P., by the addition of 4000 yr, on

  3. 1400 yr multiproxy record of climate variability from the northern Gulf of Mexico

    USGS Publications Warehouse

    Richey, J.N.; Poore, R.Z.; Flower, B.P.; Quinn, T.M.

    2007-01-01

    A continuous decadal-scale resolution record of climate variability over the past 1400 yr in the northern Gulf of Mexico was constructed from a box core recovered in the Pigmy Basin, northern Gulf of Mexico. Proxies include paired analyses of Mg/Ca and δ18O in the white variety of the planktic foraminifer Globigerinoides ruber and relative abundance variations of G. sacculifer in the foraminifer assemblages. Two multi-decadal intervals of sustained high Mg/Ca indicate that Gulf of Mexico sea surface temperatures (SSTs) were as warm or warmer than near-modern conditions between 1000 and 1400 yr B.P. Foraminiferal Mg/Ca during the coolest interval of the Little Ice Age (ca. 250 yr B.P.) indicate that SST was 2–2.5 °C below modern SST. Four minima in the Mg/Ca record between 900 and 250 yr B.P. correspond with the Maunder, Spörer, Wolf, and Oort sunspot minima, suggesting a link between changes in solar insolation and SST variability in the Gulf of Mexico. An abrupt shift recorded in both δ18Ocalcite and relative abundance of G. sacculifer occurred ca. 600 yr B.P. The shift in the Pigmy Basin record corresponds with a shift in the sea-salt-sodium (ssNa) record from the Greenland Ice Sheet Project 2 ice core, linking changes in high-latitude atmospheric circulation with the subtropical Atlantic Ocean.

  4. Holocene climatic change, aeolian sedimentation and the nomadic Anthropocene in Eastern Tibet

    NASA Astrophysics Data System (ADS)

    Lehmkuhl, F.; Schlütz, F.

    2009-04-01

    Geomorphological and palynological studies from the Nianbaoyeze Shan in Eastern Tibet provides detailed information on the Holocene landscape and vegetation development of a mountain system located on the westernmost boundary of the modern forest belt. In addition, detailed sedimentological work was done on a section south of the Anyemachin Shan further west. Our study provides detailed information on the late glacial landscape and vegetation development of eastern Tibet. Based on a suite of geomorphological and palynological proxy data from the Nianbaoyeze Shan on the eastern margin of the Tibetan Plateau (33°N/101°E, 3300-4500 m asl) we reconstruct recent landscape dynamics as a function of climate change and the longevity of human influence. Study results constrain several major phases of aeolian sedimentation between 50 - 15 ka and various glacier advances during the Late Pleistocene, the Holocene and the Little Ice Age (LIA). Increased aeolian deposition was primarily associated with periods of more extensive glacial ice extent. Fluvial and alluvial sediment pulses also document an increase of erosion starting at about 4000 cal yr B.P. coinciding with cooling (Neoglacial) and a growing anthropo-zoogenic influence. Evidence for periglacial mass movements indicate that the late Holocene cooling started at around 2000 cal yr B.P. demonstrating increased surface activity under the combined effects of human influence and climate deterioration (LIA). In a section south of the Anyemachin about 150 km further west Holocene silt and paleosols development match to these results but showing higher Holocene aeolian activity. The Holocene vegetation history started with an open landscape dominated by pioneer shrubs along braided rivers (<10,600 - 9800 cal yr B.P.), followed by the spreading of conifers (Picea, Juniperus, Abies) and Betula-trees accompanied by a successive closing of the vegetation cover by Poaceae, Cyperaceae and herbs (9800 - 8300 cal yr B.P.). First

  5. Climate versus human-driven fire regimes in Mediterranean landscapes: the Holocene record of Lago dell’Accesa (Tuscany, Italy)

    NASA Astrophysics Data System (ADS)

    Vannière, B.; Colombaroli, D.; Chapron, E.; Leroux, A.; Tinner, W.; Magny, M.

    2008-06-01

    A high-resolution sedimentary charcoal record from Lago dell'Accesa in southern Tuscany reveals numerous changes in fire regime over the last 11.6 kyr cal. BP and provides one of the longest gap-free series from Italy and the Mediterranean region. Charcoal analyses are coupled with gamma density measurements, organic-content analyses, and pollen counts to provide data about sedimentation and vegetation history. A comparison between fire frequency and lake-level reconstructions from the same site is used to address the centennial variability of fire regimes and its linkage to hydrological processes. Our data reveal strong relationships among climate, fire, vegetation, and land-use and attest to the paramount importance of fire in Mediterranean ecosystems. The mean fire interval (MFI) for the entire Holocene was estimated to be 150 yr, with a minimum around 80 yr and a maximum around 450 yr. Between 11.6 and 3.6 kyr cal. BP, up to eight high-frequency fire phases lasting 300-500 yr generally occurred during shifts towards low lake-level stands (ca 11,300, 10,700, 9500, 8700, 7600, 6200, 5300, 3400, 1800 and 1350 cal. yr BP). Therefore, we assume that most of these shifts were triggered by drier climatic conditions and especially a dry summer season that promoted ignition and biomass burning. At the beginning of the Holocene, high climate seasonality favoured fire expansion in this region, as in many other ecosystems of the northern and southern hemispheres. Human impact affected fire regimes and especially fire frequencies since the Neolithic (ca 8000-4000 cal. yr BP). Burning as a consequence of anthropogenic activities became more frequent after the onset of the Bronze Age (ca 3800-3600 cal. yr BP) and appear to be synchronous with the development of settlements in the region, slash-and-burn agriculture, animal husbandry, and mineral exploitation. The anthropogenic phases with maximum fire activity corresponded to greater sensitivity of the vegetation and triggered

  6. Evidence for millennial-scale climate change during marine isotope stages 2 and 3 at Little Lake, Western Oregon, U.S.A.

    USGS Publications Warehouse

    Grigg, L.D.; Whitlock, C.; Dean, W.E.

    2001-01-01

    Pollen and geochemical data from Little Lake, western Oregon, suggest several patterns of millennial-scale environmental change during marine isotope stage (MIS) 2 (14,100-27,600 cal yr B.P.) and the latter part of MIS 3 (27,600-42,500 cal yr B.P.). During MIS 3, a series of transitions between warm- and cold-adapted taxa indicate that temperatures oscillated by ca. 2??-4??C every 1000-3000 yr. Highs and lows in summer insolation during MIS 3 are generally associated with the warmest and coldest intervals. Warm periods at Little Lake correlate with warm sea-surface temperatures in the Santa Barbara Basin. Changes in the strength of the subtropical high and the jet stream may account for synchronous changes at the two sites. During MIS 2, shifts between mesic and xeric subalpine forests suggest changes in precipitation every 1000-3000 yr. Increases in Tsuga heterophylla pollen at 25,000 and 22,000 cal yr B.P. imply brief warmings. Minimum summer insolation and maximum global ice-volumes during MIS 2 correspond to cold and dry conditions. Fluctuations in precipitation at Little Lake do not correlate with changes in the Santa Barbara Basin and may be explained by variations in the strength of the glacial anticyclone and the position of the jet stream. ?? 2001 University of Washington.

  7. Paleoenvironmental records of water level and climatic changes from the middle to late Holocene at a Lake Erie coastal wetland, Ontario, Canada

    NASA Astrophysics Data System (ADS)

    Finkelstein, Sarah A.; Davis, Anthony M.

    2006-01-01

    Pollen and diatom assemblages, and peat stratigraphies, from a coastal wetland on the northern shore of Lake Erie were used to analyze water level and climatic changes since the middle Holocene and their effects on wetland plant communities. Peat deposition began 4700 cal yr B.P. during the Nipissing II transgression, which was driven by isostatic rebound. At that time, a diatom-rich wild rice marsh existed at the site. Water level dropped at the end of the Nipissing rise at least 2 m within 200 yr, leading to the development of shallower-water plant communities and an environment too dry for most diatoms to persist. The sharp decline in water level was probably driven primarily by outlet incision, but climate likely played some role. The paleoecological records provide evidence for post-Nipissing century-scale transgressions occurring around 2300, 1160, 700 and 450 cal yr B.P. The chronology for these transgressions correlates with other studies from the region and implies climatic forcing. Peat inception in shallow sloughs across part of the study area around 700 cal yr B.P. coincides with the Little Ice Age. These records, considered alongside others from the region, suggest that the Little Ice Age may have resulted in a wetter climate across the eastern Great Lakes region.

  8. Four thousand years of environmental change and human activity in the Cochabamba Basin, Bolivia

    NASA Astrophysics Data System (ADS)

    Williams, Joseph J.; Gosling, William D.; Coe, Angela L.; Brooks, Stephen J.; Gulliver, Pauline

    The Cochabamba Basin (Bolivia) is on the ancient road network connecting Andean and lowland areas. Little is known about the longevity of this trade route or how people responded to past environmental changes. The eastern end of the Cochabamba valley system constricts at the Vacas Lake District, constraining the road network and providing an ideal location in which to examine past human-environmental interactions. Multi-proxy analysis of sediment from Lake Challacaba has allowed a c. 4000 year environmental history to be reconstructed. Fluctuations in drought tolerant pollen taxa and calcium carbonate indicate two periods of reduced moisture availability ( c. 4000-3370 and c. 2190-1020 cal yr BP) compared to adjacent wetter episodes ( c. 3370-2190 and c. 1020 cal yr BP-present). The moisture fluctuations broadly correlate to El Niño/Southern Oscillation variations reported elsewhere. High charcoal abundance from c. 4000 to 2000 yr ago indicates continuous use of the ancient road network. A decline in charcoal and an increase in dung fungus ( Sporormiella) c. 1340 -1210 cal yr BP, suggests that cultural changes were a major factor in shaping the modern landscape. Despite undisputable impacts of human populations on the Polylepis woodlands today, we see no evidence of woodland clearance in the Challacaba record.

  9. The development and adaption of early agriculture in Huanghe River Valley, China

    NASA Astrophysics Data System (ADS)

    Li, X.

    2017-12-01

    The expanding and developing of agriculture are the basic of population growth, the expansions of material cultures and civilization. The Huanghe River valley, as the origin center of millet agriculture, lies between the heartlands of wheat and rice, which gestates the flourishing Neolithic culture based on agriculture. Recent work using botanical remains has greatly expanded the knowledge concerning early agriculture. Here, we report the new progress on the development and adaption of early agriculture in Huanghe River valley and the surrounding areas. Based on the analysis of phytolith from 13 sites in middle reaches of Huanghe River and the survey of crop seeds from 5 sites in Guanzhong Basin, the rice have been cultivated around 7600 cal BP in semi-humid regions dominated by rain-fed agriculture. The mixed agriculture of common millet, foxtail millet, and rice continued to exist between 7600-3500 BP. In semi-arid region of Huanghe River valley, the agriculture was dominated by the production of common and foxtail millet and 3 major changes have taken place around 6500 BP, 5500 BP, and 4000 BP during Neolithic. The cultivating ratio of common and foxtail millet was adjusted by farmer for adapting the climate changes during Holocene. Approximately 5000 yr BP, the rain-fed agriculture continues to break geographical boundaries to expand to west and southwest from Huanghe River valley. Millet agriculture appeared in southern Ganshu and north eastern Tibetan Plateau. The common and foxtail millet spread to the arid-area of Hexi corridor, a major crossroad of the famous Silk Road, around 4500 yr BP. Wheat was added as a new crop to the existing millet based agricultural systems around 4100-4000 cal yr BP in Hexi corridor. Between 3800 and 3400 cal yr BP, the proportion of wheat and barley in agriculture was up to 90%,which have replaced the local millet and become the main crops. And now, some new evidences of wheat agriculture from NW Xijiang have been obtained and

  10. Reconstruction of Holocene environmental changes in Southern Kurils (North-Western Pacific) based on palaeolake sediment proxies from Shikotan Island

    NASA Astrophysics Data System (ADS)

    Nazarova, Larisa; Grebennikova, Tatiana A.; Razjigaeva, Nadezhda G.; Ganzey, Larisa A.; Belyanina, Nina I.; Arslanov, Khikmat A.; Kaistrenko, Victor M.; Gorbunov, Aleksey O.; Kharlamov, Andrey A.; Rudaya, Natalia; Palagushkina, Olga; Biskaborn, Boris K.; Diekmann, Bernhard

    2017-12-01

    We investigated a well-dated sediment section of a palaeolake situated in the coastal zone of Shikotan Island (Lesser Kurils) for organic sediment-geochemistry and biotic components (diatoms, chironomids, pollen) in order to provide a reconstruction of the palaeoenvironmental changes and palaeo-events (tsunamis, sea-level fluctuations and landslides) in Holocene. During the ca 8000 years of sedimentation the changes in organic sediment-geochemistry and in composition of the diatoms and chironomids as well as the shifts in composition of terrestrial vegetation suggest that the period until ca 5800 cal yr BP was characterized by a warm and humid climate (corresponds to middle Holocene optimum) with climate cooling thereafter. A warm period reconstructed from ca 900 to at least ca 580 cal yr BP corresponds to a transition to a Nara-Heian-Kamakura warm stage and can be correlated to a Medieval Warm Period. After 580 cal yr PB, the lake gradually dried out and climatic signals could not be obtained from the declining lacustrine biological communities, but the increasing role of spruce and disappearance of the oak from the vegetation give evidences of the climate cooling that can be correlated with the LIA. The marine regression stages at the investigated site are identified for ca 6200-5900 (at the end of the middle Holocene transgression), ca 5500-5100 (Middle Jomon regression or Kemigawa regression), and ca 1070-360 cal yr BP (at the end of Heian transgression). The lithological structure of sediments and the diatom compositions give evidences for the multiple tsunami events of different strengths in the Island. Most remarkable of them can be dated at around ca 7000, 6460, 5750, 4800, 950 cal yr BP. The new results help to understand the Holocene environmental history of the Southern Kurils as a part of the Kuril-Kamchatka and Aleutian Marginal Sea-Island Arc Systems in the North-Western Pacific region.

  11. Rich fen development in SE Poland and its response to climate changes and human impacts in the late Holocene

    NASA Astrophysics Data System (ADS)

    Gałka, Mariusz; Apolinarska, Karina; Aunina, Liene; Feurdean, Angelica; Hutchinson, Simon; Kołaczek, Piotr

    2016-04-01

    Rich fens are one of the most important wetland ecosystems due to their high species-richness and unique species composition. They are occupied by endangered, vulnerable and protected plants, such as Cladium mariscus and Schoenus ferrugineus. For this reason knowledge of the history of rich fens is important for the development of effective management strategies to protect or restore these widely threatened habitats. Our palaeoecological study reconstructs the development of Bagno Serebryskie rich fen (ca. 376 ha), a site with the largest population of Cladium mariscus in CE Europe, and its response to climate changes and human impacts during the last 3500 years. For this we analyse two peat profiles at this site, at a high resolution (1 and 2 cm) using multi-aspect palaeoecological analyses (plant macrofossils, pollen, molluscs, geochemistry, charcoal and AMS 14C radiocarbon) to assess the impact of climate changes, human activity, and fires on local vegetation. Local plant succession in our two coring points followed parallel trajectories; after a lake stage, ca. 1800 cal yr BP (core I) and 3300 cal yr BP (core II), fen species e.g. Menyanthes trifoliata, Mentha aquatic, Carex lasiocarpa appeared, followed at ca. 500 cal. yr BP by Cladium mariscus, which is currently the dominant plant species in the Bagno Serebryskie peatland. In one peat profile (core II) we found abundant macrocharcoal particles at 1050, 700, 400 cal yr BP and the present, but fires had no significant impact on the development of the mire. In the other peat profile (core I) we noted four stages (at 2300, 1350, 400, 100 cal yr BP) with an increasing diversity of mollusc species typical of overgrown, but permanent water bodies. Their increased abundance and diversity can be linked to a rise in mire water table at these times. Our studies indicate that rich fens can provide reliable sites for palaeoecological reconstruction of the late Holocene providing valuable information that can be applied

  12. Holocene temperature variations at a high-altitude site in the Eastern Alps: a chironomid record from Schwarzsee ob Sölden, Austria

    PubMed Central

    Ilyashuk, Elena A.; Koinig, Karin A.; Heiri, Oliver; Ilyashuk, Boris P.; Psenner, Roland

    2011-01-01

    Few well-dated, quantitative Holocene temperature reconstructions exist from high-altitude sites in the Central Eastern Alps. Here, we present a chironomid-based quantitative reconstruction of mean July air temperatures (TJuly) throughout the Holocene for a remote high-mountain lake, Schwarzsee ob Sölden, situated above the treeline at 2796 m a.s.l. in the Austrian Alps. Applying a chironomid-temperature inference model developed from lakes of the Alpine region to a high-resolution chironomid record from the lake provides evidence for early Holocene (ca 10000–8600 cal yr BP) TJuly of up to 8.5 °C, i.e. >4 °C above the modern (1977–2006) mean July temperature. The reconstruction reveals the so-called ‘8.2-ka cold event’ centered at ca 8250–8000 cal yr BP with temperatures ca 3 °C below the early-Holocene thermal maximum. Rather warm (ca 6 °C) and productive conditions prevailed during ca 7900–4500 cal yr BP. The chironomid record suggests a climate transition between ca 5200 and 4500 cal yr BP to cooler TJuly. A distinct cooling trend is evident from ca 4500 until ca 2500 cal yr BP. Thereafter, the study site experienced its coldest conditions (around 4 °C or less) throughout the rest of the Holocene, with the exception of the warming trend during the late 20th century. Beside other factors, the Northern Hemisphere summer insolation seems to be the major driving force for the long-term trends in TJuly at high altitudes in the Eastern Alps. Due to the extreme location of the lake and the limited temperature range represented by the applied calibration data set, the chironomid-based temperature reconstruction fails to track phases of the late-Holocene climatic history with TJuly cooler than 4 °C. Further chironomid-based palaeoclimate model and down-core studies are required to address this problem, provide more realistic TJuly estimates from undisturbed high-altitude lakes in the Alps, and extract a reliable regional

  13. Organic geochemical investigations of the Dali Lake sediments in northern China: Implications for environment and climate changes of the last deglaciation in the East Asian summer monsoon margin

    NASA Astrophysics Data System (ADS)

    Fan, Jiawei; Xiao, Jule; Wen, Ruilin; Zhang, Shengrui; Wang, Xu; Cui, Linlin; Yamagata, Hideki

    2017-06-01

    Millennial-scale environment and climate changes in the East Asian summer monsoon margin during the last deglaciation are reconstructed by systematic studies on the characteristic of sedimentary organic matter from Dali Lake in northern China. Concurrent increases in the TOC and TN concentrations indicate increases in terrestrial organic matter and nutrient inputs to the lake and a development of terrestrial vegetation and phytoplankton productivity related to increases in regional temperature and precipitation. C/N ratios reflect changes in the proportions of terrestrial and aquatic organic matter. Decreases in both δ13Corg and δ15N values indicate increases in the isotopically lighter, terrestrial carbon and nitrogen inputs to the lake, due to increases in surface runoffs; while a sharp decrease in the δ15N value implies a significant weakening in the biological activities of nitrifying and amonifying bacteria, due to abrupt decrease in the water temperature. The geochemical data indicate that regional temperature and precipitation exhibited increasing trends from 15,000 to 12,350 cal yr BP; temperature decreased abruptly at 12,350 cal yr BP and then maintained a low level from 12,350 to 11,400 cal yr BP, precipitation decreased to a relatively low level from 12,350 to 11,400 cal yr BP; and both temperature and precipitation returned to increase after 11,400 cal yr BP. The climate change in the Dali Lake region during the last deglaciation corresponds, within age uncertainties, to the Bølling-Allerød (BA) warm phase and Younger Dryas (YD) cold reversal occurring over northern high latitudes. However, the gradual and mild increasing trends of regional temperature and precipitation during the BA warm period contrasts with the general cooling trend in northern high latitude temperature, implying a dominant influence from increases in the Northern Hemisphere summer insolation; while the slight decreases in regional precipitation relative to the rapid and

  14. A High-Resolution Reconstruction of Late Holocene Environmental Change from Laguna Ek'Naab, Northern Holmul Region, Peten, Guatemala

    NASA Astrophysics Data System (ADS)

    Anderson, L.; Wahl, D.; Estrada-Belli, F.

    2015-12-01

    Widespread demographic shifts in the southern Maya lowlands at the end of the Classic period have been attributed to environmental change caused by human activity and/or climate variability. Fire was essential to landscape modification and was a primary agent of environmental change associated with prehispanic land use. While several studies have provided insight into the dynamic relationship between natural and anthropogenic drivers of change, defining the specific interplay between natural environmental change, human modification of the environment, and cultural response to changes remains a persistent challenge. Here we present the results of a multi-proxy study that reconstructs fire history, agricultural land use, and environmental change during and after Pre-Columbian Maya settlement. Results are interpreted in the context of settlement history as inferred from archaeological mapping around the study site. Our findings suggest landscape disturbance, as indicated by erosion, local burning, and nearby maize agriculture, was at its peak during the Early Classic period. This disturbance was likely due to large-scale settlement at the nearby site of Witzna'. All proxies indicate a slow decline in disturbance into the Late Classic period, beginning around 1300 cal yr BP. Cival and Chanchich, two proximal site centers to the south of Laguna Ek'Naab, supported their largest populations during the Late Preclassic and Late Classic, with little or no settlement during the Early Classic. The data from Laguna Ek'Naab suggests that Witzna' may have been an important center during the Early Classic. Whether the decreasing environmental degradation after 1240 cal yr BP is do to a decline in local population or changing land use strategies is not discernable based on the data thus far. However, the near complete absence of burning and continued decrease in erosion from 1240-1090 cal yr BP suggests little anthropogenic activity in the area. Burning resumes in the watershed

  15. An 11,000-year record of depositional environmental change based upon particulate organic matter and stable isotopes (C and N) in a lake sediment in southeastern Brazil

    NASA Astrophysics Data System (ADS)

    Lorente, Flávio Lima; Pessenda, Luiz Carlos Ruiz; Oboh-Ikuenobe, Francisca; Buso Junior, Antonio Alvaro; Rossetti, Dilce de Fátima; Giannini, Paulo César Fonseca; Cohen, Marcelo Cancela Lisboa; de Oliveira, Paulo Eduardo; Mayle, Francis Edward; Francisquini, Mariah Izar; França, Marlon Carlos; Bendassolli, José Albertino; Macario, Kita

    2018-07-01

    The aim of this paper is to reconstruct an 11,000-year history of depositional environmental change in southeastern Brazil, based upon the integration of particulate organic matter and stable isotope (C and N) data from a 136-cm sediment core from Lake Canto Grande. These proxies are used to explore the evolution of terrestrial and marine influence on the lake. Isotopic (δ13C: -27.87‰ to -31.9‰; δ15N: -0.07‰-4.9‰) and elemental (total organic carbon - TOC: 0.58%-37.19%; total nitrogen - TN: 0.08%-1.73%; C/N: 0.3 to 54.7) values recorded in Lake Canto Grande suggest that the sedimentary organic matter was derived from mostly C3 land plants and freshwater phytoplankton. Particulate organic matter and cluster analyses distinguished four associations characterized by the predominance of amorphous organic matter, followed by phytoclasts and palynomorphs. These results indicate two different phases of lake evolution. The first phase (136 - 65 cm; ∼10,943 cal yr. B.P. to ∼8529 cal yr. B.P.) is recorded by sand layers interbedded with mud, which contain amorphous organic matter (AOM, 45-59%) and phytoclasts (opaques - OP: 6-18%; non-opaques - NOP: 17-23%) which indicate a floodplain area. The second phase (65-0 cm; ∼8529 cal yr. B.P. to ∼662 cal yr. B.P.) comprises mud, AOM (68-86%) and palynomorphs (PAL, 8-16%) related to lake establishment comparable to modern conditions. Thus, characterizing particulate organic matter, in combination with stable isotopes, proved to be invaluable proxies for lacustrine paleoenvironmental change through the Holocene.

  16. Ice-borne prehistoric finds in the Swiss Alps reflect Holocene glacier fluctuations

    NASA Astrophysics Data System (ADS)

    Grosjean, Martin; Suter, Peter J.; Trachsel, Mathias; Wanner, Heinz

    2007-03-01

    During the hot summer of 2003, reduction of an ice field in the Swiss Alps (Schnidejoch) uncovered spectacular archaeological hunting gear, fur, leather and woollen clothing and tools from four distinct windows of time: Neolithic Age (4900 to 4450 cal. yr BP), early Bronze Age (4100-3650 cal. yr BP), Roman Age (1st-3rd century AD), and Medieval times (8-9th century AD and 14-15th century AD). Transalpine routes connecting northern Italy with the northern Alps during these slots is consistent with late Holocene maximum glacier retreat. The age cohorts of the artefacts are separated which is indicative of glacier advances when the route was difficult and not used for transit. The preservation of Neolithic leather indicates permanent ice cover at that site from ca. 4900 cal. yr BP until AD 2003, implying that the ice cover was smaller in 2003 than at any time during the last 5000 years. Current glacier retreat is unprecedented since at least that time. This is highly significant regarding the interpretation of the recent warming and the rapid loss of ice in the Alps. Copyright

  17. Lacustrine records of Holocene flood pulse dynamics in the Upper Paraguay River watershed (Pantanal wetlands, Brazil)

    USGS Publications Warehouse

    McGlue, Michael M.; Silva, Aquinaldo; Zani, Hiran; Corradini, Fabricio A.; Parolin, Mauro; Abel, Erin J.; Cohen, Andrew S.; Assine, Mario L.; Ellis, Geoffrey S.; Trees, Mark A.; Kuerten, Sidney; Gradella, Frederico dos Santos; Rasbold, Giliane Gessica

    2012-01-01

    The Pantanal is the world's largest tropical wetland and a biodiversity hotspot, yet its response to Quaternary environmental change is unclear. To address this problem, sediment cores from shallow lakes connected to the UpperParaguayRiver (PR) were analyzed and radiocarbon dated to track changes in sedimentary environments. Stratal relations, detrital particle size, multiple biogeochemical indicators, and sponge spicules suggest fluctuating lake-level lowstand conditions between ~ 11,000 and 5300 cal yr BP, punctuated by sporadic and in some cases erosive flood flows. A hiatus has been recorded from ~ 5300 to 2600 cal yr BP, spurred by confinement of the PR within its channel during an episode of profound regional drought. Sustained PR flooding caused a transgression after ~ 2600 cal yr BP, with lake-level highstand conditions appearing during the Little Ice Age. Holocene PR floodpulsedynamics are best explained by variability in effective precipitation, likely driven by insolation and tropical sea-surface temperature gradients. Our results provide novel support for hypotheses on: (1) stratigraphic discontinuity of floodplain sedimentary archives; (2) late Holocene methane flux from Southern Hemisphere wetlands; and (3) pre-colonial indigenous ceramics traditions in western Brazil.

  18. Development and application of a pollen-based paleohydrologic reconstruction from the lower Roanoke River Basin, North Carolina, USA

    USGS Publications Warehouse

    Willard, D.; Bernhardt, C.; Brown, R.; Landacre, B.; Townsend, P.

    2011-01-01

    We used pollen assemblages to reconstruct late-Holocene paleohydrologic patterns in floodplain deposits from the lower Roanoke River basin (North Carolina, southeastern USA). Using 120 surface samples from 38 transects, we documented statistical relationships between pollen assemblages, vegetation, and landforms. Backswamp pollen assemblages (long hydroperiods) are dominated by Nyssa (tupelo) and Taxodium (cypress) and have high pollen concentrations. Sediments from elevated levees and seasonally flooded forests (shorter hydroperiods) are characterized by dominant Pinus (pine) pollen, variable abundance of hardwood taxa, and low pollen concentrations. We apply the calibration data set to interpret past vegetation and paleohydrology. Pollen from a radiocarbon-dated sediment core collected in a tupelo-cypress backswamp indicates centennial-scale fluctuations in forest composition during the last 2400 years. Backswamp vegetation has occupied the site since land clearance began ~300 years ago. Recent dam emplacement affected sedimentation rates, but vegetation changes are small compared with those caused by pre-Colonial climate variability. The occurrence of wetter conditions from ~2200 to 1800 cal. yr BP, ~1100 to 750 cal. yr BP, and ~400 to 250 cal. yr BP may indicate changes in cyclonic circulation patterns related to shifts in the position of the Bermuda High and jet stream.

  19. The history of South American tropical precipitation for the past 25,000 years.

    PubMed

    Baker, P A; Seltzer, G O; Fritz, S C; Dunbar, R B; Grove, M J; Tapia, P M; Cross, S L; Rowe, H D; Broda, J P

    2001-01-26

    Long sediment cores recovered from the deep portions of Lake Titicaca are used to reconstruct the precipitation history of tropical South America for the past 25,000 years. Lake Titicaca was a deep, fresh, and continuously overflowing lake during the last glacial stage, from before 25,000 to 15,000 calibrated years before the present (cal yr B.P.), signifying that during the last glacial maximum (LGM), the Altiplano of Bolivia and Peru and much of the Amazon basin were wetter than today. The LGM in this part of the Andes is dated at 21,000 cal yr B.P., approximately coincident with the global LGM. Maximum aridity and lowest lake level occurred in the early and middle Holocene (8000 to 5500 cal yr B.P.) during a time of low summer insolation. Today, rising levels of Lake Titicaca and wet conditions in Amazonia are correlated with anomalously cold sea-surface temperatures in the northern equatorial Atlantic. Likewise, during the deglacial and Holocene periods, there were several millennial-scale wet phases on the Altiplano and in Amazonia that coincided with anomalously cold periods in the equatorial and high-latitude North Atlantic, such as the Younger Dryas.

  20. A 100 000-year record of annual and seasonal rainfall and temperature for northwestern Australia based on a pollen record obtained offshore

    NASA Astrophysics Data System (ADS)

    van der Kaars, Sander; de Deckker, Patrick; Gingele, Franz X.

    2006-12-01

    Pollen recovered from core tops of deep-sea cores from offshore northwestern Western Australia were used to build climatic transfer functions applied to sediment samples from major rivers bordering the ocean in the same region and a deep-sea core offshore Northwest Cape. Results show for the last 100 000 years, with a gap in the record spanning the 64 000 to 46 000 years interval, that from about 100 000 to 82 000 yr BP, climatic conditions represented by rainfall, temperature and number of humid months, were significantly higher than today's values. For the entire record, the coldest period occurred about 43 000 to 39 000 yr BP but it was wetter than today, whereas the Last Glacial Maximum saw a significant reduction in summer rainfall, interpreted as a result of the absence of monsoonal activity in the region. The Holocene can be divided into two distinct phases: one peaking around 6000 cal. yr BP with highest rainfall and summer temperatures; the second one commencing at 5000 cal. yr BP and showing a progressive decrease in summer rainfall in contrast to an increase in winter rainfall, paralleled by a progressive decrease in temperatures. Copyright

  1. Hydroclimate variability in the low-elevation Atacama Desert over the last 2500 yr

    NASA Astrophysics Data System (ADS)

    Gayo, E. M.; Latorre, C.; Santoro, C. M.; Maldonado, A.; de Pol-Holz, R.

    2012-02-01

    Paleoclimate reconstructions reveal that Earth system has experienced sub-millennial scale climate changes over the past two millennia in response to internal/external forcing. Although sub-millennial hydroclimate fluctuations have been detected in the central Andes during this interval, the timing, magnitude, extent and direction of change of these events remain poorly defined. Here, we present a reconstruction of hydroclimate variations on the Pacific slope of the central Andes based on exceptionally well-preserved plant macrofossils and associated archaeological remains from a hyperarid drainage (Quebrada Maní, ∼21° S, 1000 m a.s.l.) in the Atacama Desert. During the late Holocene, riparian ecosystems and farming social groups flourished in the hyperarid Atacama core as surface water availability increased throughout this presently sterile landscape. Twenty-six radiocarbon dates indicate that these events occurred between 1050-680, 1615-1350 and 2500-2040 cal yr BP. Regional comparisons with rodent middens and other records suggest that these events were synchronous with pluvial stages detected at higher-elevations in the central Andes over the last 2500 yr. These hydroclimate changes also coincide with periods of pronounced SST gradients in the Tropical Pacific (La Niña-like mode), conditions that are conducive to significantly increased rainfall in the central Andean highlands and flood events in the low-elevation watersheds at inter-annual timescales. Our findings indicate that the positive anomalies in the hyperarid Atacama over the past 2500 yr represent a regional response of the central Andean climate system to changes in the global hydrological cycle at centennial timescales. Furthermore, our results provide support for the role of tropical Pacific sea surface temperature gradient changes as the primary mechanism responsible for climate fluctuations in the central Andes. Finally, our results constitute independent evidence for comprehending the

  2. Holocene Development of Subarctic Permafrost Peatlands in Finnmark, Northern Norway

    NASA Astrophysics Data System (ADS)

    Sannel, B.; Axelsson, P.; Kjellman, S.; Etzelmuller, B.; Westermann, S.

    2017-12-01

    Subarctic permafrost peatlands have acted as important carbon sinks throughout the Holocene. An improved knowledge of peat properties and sensitivity to past climate changes in these environments can help us better predict future responses under warmer climatic conditions, and associated permafrost carbon feedbacks. In this study analyses of plant macrofossils, bulk density, organic, carbon and nitrogen content, and AMS radiocarbon dating have been performed for four profiles collected from peat plateaus in Finnmark, northern Norway. Preliminary results suggest that peatland development started around 9800-9200 cal yr BP at the two continental sites, Suossjavri and Iskoras. Here, the long-term net carbon accumulation rates are around 12-17 gC m-2 yr-1, and the total carbon storage c. 113-156 kgC m-2. The other two sites, Lakselv and Karlebotn, are located in maritime settings close to the coast where there has been a time lag between deglaciation of the Fennoscandian Ice Sheet and emergence of land by isostatic uplift. At these sites peatland inception begun around 6200-5200 cal yr BP, and the carbon accumulation rates are c. 7-12 gC m-2 yr-1. Because of a shorter time period available for peat accumulation the carbon storage at these sites is lower, around 56-64 kgC m-2. All four peatlands developed as wet fens, and have remained permafrost-free throughout most of the Holocene. Permafrost aggradation, causing frost heave and a shift in the vegetation assemblage from wet fen to dry bog species, probably did not occur until during the onset of the Little Ice Age c. 1000-800 cal yr BP (at Iskoras and Karlebotn) or even later, around 100 cal yr BP (at Suossjavri and Lakselv). If the permafrost thaws in a future warmer climate, the carbon that has been stored in the frozen peat since the Little Ice Age can become available for decomposition and be emitted to the atmosphere either as carbon dioxide from expanding active layers or as methane from thermokarst lakes and

  3. 60,000 Year Climate and Vegetation History of Southeast Alaska

    NASA Astrophysics Data System (ADS)

    Wilcox, Paul S.

    Sedimentological and palynological analyses of lacustrine cores from Baker Island, located in Southeast Alaska's Alexander Archipelago, indicate that glaciers persisted on the island until 14,500 cal yr. BP. However, the appearance of tree pollen, including Pinus cf. contorta ssp. contorta (shore pine) and Tsuga mertensiana (mountain hemlock) immediately following deglaciation suggests that a forest refugium may have been present on ice-free portions of neighboring islands or the adjacent continental shelf. Sedimentological and palynological analyses indicate a variable climate during the Younger Dryas interval between 13,000 and 11,500 cal yr. BP, with a cold and dry onset followed by ameliorating conditions during the latter half of the interval. An eight cm-thick black tephra dated to 13,500 +/- 250 cal yr. BP is geochemically distinct from the Mt. Edgecumbe tephra and thus derived from a different volcano. Based on overall thickness, multiple normally graded beds, and grain size, I infer that the black tephra was emplaced by a large strombolian-style paroxysm. Because the dominant wind direction along this coast is from the west, the Addington Volcanic Field on the continental shelf, which would have been subaerially exposed during the eruption, is a potential source. The similarity in timing between this eruption and the Mt. Edgecumbe eruption suggests a shared trigger, possibly a response to unloading as the Cordilleran Ice Sheet retreated. To complement the Baker Island lacustrine record, a speleothem paleoclimate record based on delta13C and delta18O values spanning the interval from 60,000 yr. BP to 11,150 yr. BP was recovered from El Capitan Cave on neighboring Prince of Wales Island. More negative delta13 C values are attributed to predominance of angiosperms in the vegetation above the cave at 22,000 yr. BP and between 53,000 and 46,000 yr. BP while more positive delta13C values in speleothem EC-16-5-F indicate the presence of gymnosperms. These data

  4. Paleoclimate of the Neoglacial and Roman Warm Period Reconstructed from Oxygen Isotope Ratios of Limpet Shells (Patella vulgata), Northwest Scotland

    NASA Astrophysics Data System (ADS)

    Wang, T.; Surge, D. M.; Mithen, S.

    2010-12-01

    Paleoclimate reconstructions from different regions have reported abrupt climate change around 2800-2700 cal yr B.P. The timing of this abrupt climate change is close to the boundary between the Neoglacial (3300-2500 cal yr B.P.) and Roman Warm Period (2500-1600 cal yr B.P.). However, temporal and spatial variability observed in this climate change event raises controversies about the forcing factors driving it and why it has regional variability. Scotland lies in the North Atlantic Ocean, which responds sensitively to climate change. Therefore, even in the case of subtle climate change, the climate variability of Scotland should be able to capture such change. In this study, we expect that paleoclimate reconstructions of the Neoglacial and Roman Warm Period in Scotland will help improve our knowledge of abrupt climate change at 2800-2700 cal yr B.P. Archaeological shell deposits provide a rich source of climate proxy data preserved as oxygen isotope ratios in shell carbonate. Croig Cave on the Isle of Mull, Scotland, contains a nearly continuous accumulation of shells ranging from 800 BC-500 AD and possibly older. This range represents a broad chronology of human use from the late Bronze to Iron Ages and spans the Neoglacial through Roman Warm Period climate episodes. Here, we present seasonal temperature variability of the two climate episodes based on oxygen isotope ratios of ten limpet shells (Patella vulgata) from Croig Cave. Based on AMS dating (2 sigma calibration), the oldest shell was from 3480-3330 cal yr B.P. and the youngest shell was from 2060-1870 cal yr B.P. Our results indicated that estimated temperatures from the Neoglacial limpets average 6.44±0.56°C for coldest winters and 15.06±0.67°C for warmest summers. For the Roman Warm Period limpets, the average is 5.68±0.36°C for coldest winters and 14.14±0.81°C for warmest summers. We compared our estimated temperatures to the present sea surface temperature (SST) from 1961 to 1990 near our

  5. Radiocarbon ages of terrestrial gastropods extend duration of ice-free conditions at the Two Creeks forest bed, Wisconsin, USA

    USGS Publications Warehouse

    Rech, Jason A.; Nekola, Jeffrey C.; Pigati, Jeffrey S.

    2012-01-01

    Analysis of terrestrial gastropods that underlie the late Pleistocene Two Creeks forest bed (~ 13,800–13,500 cal yr BP) in eastern Wisconsin, USA provides evidence for a mixed tundra-taiga environment prior to formation of the taiga forest bed. Ten new AMS 14C analyses on terrestrial gastropod shells indicate the mixed tundra-taiga environment persisted from ~ 14,500 to 13,900 cal yr BP. The Twocreekan climatic substage, representing ice-free conditions on the shore of Lake Michigan, therefore began near the onset of peak warming conditions during the Bølling–Allerød interstadial and lasted ~ 1000 yr, nearly 600 yr longer than previously thought. These results provide important data for understanding the response of continental ice sheets to global climate forcing and demonstrate the potential of using terrestrial gastropod fossils for both environmental reconstruction and age control in late Quaternary sediments.

  6. Holocene geoarchaeology of the Sixteen Mile Beach barrier dunes in the Western Cape, South Africa

    NASA Astrophysics Data System (ADS)

    Compton, John S.; Franceschini, Giuliana

    2005-01-01

    Holocene evolution and human occupation of the Sixteen Mile Beach barrier dunes on the southwest coast of South Africa between Yzerfontein and Saldanha Bay are inferred from the radiocarbon ages of calcareous dune sand, limpet shell ( Patella spp.) manuports and gull-dropped white mussel shells ( Donax serra). A series of coast-parallel dunes have prograded seaward in response to an overall marine regression since the mid-Holocene with dated shell from relict foredunes indicating periods of shoreline progradation that correspond to drops in sea level at around 5900, 4500 and 2400 calibrated years before the present (cal yr B.P.). However, the active foredune, extensively covered by a layer of gull-dropped shell, has migrated 500 m inland by the recycling of eroded dune sand in response to an approximate 1 m sea level rise over the last 700 yr. Manuported limpet shells from relict blowouts on landward vegetated dunes indicate human occupation of coastal dune sites at 6200 and 6000 cal yr B.P. and help to fill the mid-Holocene gap in the regional archaeological record. Coastal midden shells associated with small hearth sites exposed in blowouts on the active foredune are contemporaneous (1600-500 cal yr B.P.) with large midden sites on the western margin of Langebaan Lagoon and suggest an increase in marine resource utilisation associated with the arrival of pastoralism in the Western Cape.

  7. Record of the North American southwest monsoon from Gulf of Mexico sediment cores

    USGS Publications Warehouse

    Poore, R.Z.; Pavich, M.J.; Grissino-Mayer, H. D.

    2005-01-01

    Summer monsoonal rains (the southwest monsoon) are an important source of moisture for parts of the southwestern United States and northern Mexico. Improved documentation of the variability in the southwest monsoon is needed because changes in the amount and seasonal distribution of precipitation in this semiarid region of North America influence overall water supply and fire severity. Comparison of abundance variations in the planktic foraminifer Globigerinoides sacculifer in marine cores from the western and northern Gulf of Mexico with terrestrial proxy records of precipitation (tree-ring width and packrat-midden occurrences) from the southwestern United States indicate that G. sacculifer abundance is a proxy for the southwest monsoon on millennial and submillennial time scales. The marine record confirms the presence of a severe multicentury drought centered ca. 1600 calendar (cal.) yr B.P. as well as several multidecadal droughts that have been identified in a long tree-ring record spanning the past 2000 cal. yr from westcentral New Mexico. The marine record further suggests that monsoon circulation, and thus summer rainfall, was enhanced in the middle Holocene (ca. 6500-4500 14C yr B.P.; ca. 6980-4710 cal. yr B.P.). The marine proxy provides the potential for constructing a highly resolved, well-dated, and continuous history of the southwest monsoon for the entire Holocene. ?? 2005 Geological Society of America.

  8. Influence of solar activity on the development of calcareous nannofossils from a Middle Holocene costal paleo-ria (SW Portugal)

    NASA Astrophysics Data System (ADS)

    Hernández, Armand; Cachão, Mário; Trigo, Ricardo M.; Conceição Freitas, M.

    2015-04-01

    A 27 m long core was recovered from a present day flat-floored small fluvial valley, tributary of the Mira River (SW Portugal) allowing to span almost the complete Holocene sedimentary sequence directly overlaying Paleozoic schists and greywackes. A high resolution study of its micropaleontological content (Alday et al. 2006) was performed and 5 sedimentary stages were established: i) a coccolith-barren lower fluvial stage; ii) a coccolith intermittent lower estuarine stage; iii) a coccolith rich marine (ria) stage; iv) a coccolith intermittent upper estuarine/lagoonal stage and v) a coccolith-barren upper fluvial stage. The usefulness of calcareous nannofossils as natural tracers of the marine sedimentation contributing with valuable information for environmental reconstructions has been thoroughly demonstrated. Here, we present a high-resolution paleoenvironmental reconstruction from the interpreted marine (ria) section of the core, between 8.8k and 4.8k cal yr BP using most abundant calcareous nannofossils. Factor Analysis retrieved two major factors from the coccolith assemblages. Factor 1 (24% var.) is related to oceanic affinity community (e.g. Gephyrocapsa muellerae, Syracosphaera pulchra and Umbilicosphaera sibogae) whereas Factor 2 (23% var.) is linked to coastal neritic taxa (e.g. Ascidian spicules, Gephyrocapsa oceanica, Coccolithus pelagicus braarudii, Heliscosphaera carteri and Braarudosphaera bigelowii). These scores showed the existence of two episodes (8.8k to 7.4k and 5.8k to 5.2k cal yr BP) of marine colonization inside the paleoecological succession of the Holocene paleo-ria (8.8k and 4.8k cal yr BP). In order to establish the relationship between the solar activity and calcareous nannofossils sedimentation, cyclicity on the studied time series was investigated by performing spectral analysis on Factor 1 (F1) and Factor 2 (F2) scores. F1 score periodogram discloses three significant periodicities (460, 350 and 236-yrs) whereas F2 score

  9. Late-Holocene vegetation and climate change in Jeju Island, Korea and its implications for ENSO influences

    NASA Astrophysics Data System (ADS)

    Park, Jungjae; Shin, Young Ho; Byrne, Roger

    2016-12-01

    Several recent studies suggest the hypothesis that the El Niño-Southern Oscillation (ENSO) is an important factor controlling the Holocene East Asian Monsoon (EAM). However, the mechanism underlying this influence remains unclear due to the lack of high-resolution paleoclimate records from the coast of East Asia. Here, we provide a new record of late Holocene climate change in coastal East Asia based on multi-proxy evidence (pollen, organic content, magnetic susceptibility, grain size) obtained from a sediment core from Jeju Island, South Korea. As Jeju Island is strongly influenced by the Kuroshio flow, our sediment proxy records contain ENSO signals from the tropical Pacific. The study area was affected by dry/cool conditions in the western tropical Pacific (WTP) between 4350 and 1920 cal yr BP when El Niños were frequent, and by rapid warming/wetting and forestation since 1920 cal yr BP when La Niñas were more common. Jeju Island was relatively dry/cool between 2100 and 1600, 1300-1200, 1100-1000, 800-650, and 300-50 cal yr BP, as opposed to the Galápagos Islands, which were relatively wet/warm, reflecting the ENSO-related negative correlation between eastern and western margins of Pacific. Wet conditions may have prevailed during the early Little Ice Age (LIA) (620-280 cal yr BP) despite consistent cooling. This period of high precipitation may have been associated with the increased landfall of typhoons and with warmer Kuroshio currents under La Niña-like conditions. According to our results, EAM on the East Asian coastal margin was predominantly driven by ENSO activity, rather than by the precession effect. Paleoclimatic data from Jeju Island, with its insular position and closeness to warm Kuroshio currents, provide clear evidence of these ENSO influences.

  10. Testate amoebae analysis in the peat deposits of the swamp Dolgon’koye in the south of Western Siberia and peatland paleohydrology for last 3100 years

    NASA Astrophysics Data System (ADS)

    Kurina, Irina V.; Blyakharchuk, Tatiana A.

    2018-03-01

    Our research is devoted to paleohydrological reconstruction in the swamp located in the river valley on the piedmont of the Altai Mountains in the south of Western Siberia. The reconstruction was carried out based on rhizopod analysis for the last 3100 cal yr. A large amount of different testate amoebae was found in the peat. Total 64 testate amoebae taxa were recorded in the peat core with the most abundant being: Trinema lineare, Centropyxis aculeata, C. aerophila, Euglypha rotunda, Cryptodifflugia sp. Decrease of surface wetness in the swamp are observed 2280, 2140, 1900–600 cal yr BP and increase – in 2700, 2500–1900, 230–215 cal yr BP. The results of our reconstruction of the swamp paleohydrology agrees well with the paleoclimatic data obtained earlier for the central area of the south of Western Siberia Plain. It indicates a high sensitivity of the swamp to climatic changes in the Holocene. The rhizopod analysis proved to be very effective when used for paleohydrology reconstruction in minerotrophic peat.

  11. Major hydrological regime change along the semiarid western coast of South America during the early Holocene

    NASA Astrophysics Data System (ADS)

    Ortega, Cristina; Vargas, Gabriel; Rutllant, José A.; Jackson, Donald; Méndez, César

    2012-11-01

    Water availability in the semiarid western coast of Chile (30-32°S) is conditioned by high interannual precipitation variability, reflecting the transition between arid subtropical and moist mid-latitude climates in the Southeastern Pacific Ocean. A paleoclimate reconstruction based on the latest Pleistocene-Holocene geological record from the Quebrada Santa Julia archeological site in Chile (31°50'S) and on modern meteorological mechanisms producing alluvial episodes in this region indicates a major change in the rainfall regime shortly after 8600 cal yr BP. This, together with other paleoclimate proxies along the west coast of South America (34°-14°S), suggests La Niña-like conditions 13,000-8600 cal yr BP. Based on sedimentological and geomorphologic evidence, we hypothesized that the absence of heavy rainfall events in northern Chile and the new hydrological regime that prevailed ca. 8600-5700 cal yr BP in north-central Chile resulted from an increase in the large-scale westerly flow over central Chile, as expected in near-neutral ENSO conditions. This atmospheric circulation anomaly is compatible with an equatorward shift of the influence of the Southeast Pacific Subtropical Anticyclone relative to the early Holocene, prior to the onset of modern ENSO variability.

  12. Assessing the effects of climate change and land use on northern Labrador forest stands based on paleoecological data

    NASA Astrophysics Data System (ADS)

    Lemus-Lauzon, Isabel; Bhiry, Najat; Woollett, James

    2016-11-01

    We reconstructed the late Holocene vegetation of the Nain region (northern Labrador, northeastern Canada) in order to assess the influence of climate and historic land use on past shifts in forest composition. Chronostratigraphy was used in combination with macrofossil and pollen data from monoliths sampled from four peatlands. Paleoecological reconstructions produced a vegetation history spanning 4900 years for the Nain region that is largely concordant with other studies in Labrador. An initial open forest tundra phase was followed by an increase in tree cover at around 2800 cal yr BP. Paludification began ∼200 cal yr BP. A decline in Picea and its subsequent disappearance from most of the sites occurred ∼170 cal yr BP (AD 1780) in a period of relatively mild conditions during the Little Ice Age. This event was followed by the establishment of Larix laricina in the region. Local anthropogenic factors are likely responsible for these later developments, as they were not observed in other regional studies. The period around AD 1780 corresponds to the establishment of the Moravian missionaries on the Labrador coast, which increased the need for fuel and lumber. We conclude that changes in land use are reflected in the patterns of vegetation and hydrological change at the study sites.

  13. Implications of S1 tephra findings in Dead Sea and Tayma palaeolake sediments for marine reservoir age estimation and palaeoclimate synchronisation

    NASA Astrophysics Data System (ADS)

    Neugebauer, Ina; Wulf, Sabine; Schwab, Markus J.; Serb, Johanna; Plessen, Birgit; Appelt, Oona; Brauer, Achim

    2017-08-01

    Here we report on the first findings of a cryptotephra in the Holocene lacustrine sediment records of the Dead Sea and Tayma palaeolake (NW Arabian Peninsula). The major element glass composition of this rhyolitic tephra is identical to the distal 'S1' tephra layer identified in the Yammoûneh palaeolake (Lebanon), in a marine sediment record from the SE Levantine basin and in the Sodmein Cave archaeological site in Egypt. The S1 tephra corresponds to the early Holocene 'Dikkartın' dome eruption of the Erciyes Dağ volcano in central Anatolia (Turkey) and has been dated in the marine record at 8830 ± 140 cal yr BP. We present new age estimates of the S1 tephra based on radiocarbon dating of terrestrial plant remains and pollen concentrates revealing ages of 8939 ± 83 cal yr BP in the Dead Sea sediments and 9041 ± 254 cal yr BP in Tayma. The precise date from the Dead Sea allows refining the early Holocene marine reservoir age in the SE Levantine Sea to ca. 320 ± 50 years. Synchronisation of marine and terrestrial palaeoclimate records in the eastern Mediterranean region using the S1 tephra further suggests a time-transgressive expansion of the early Holocene humid period.

  14. Climate change and human occupation in the Southern Arabian lowlands during the last deglaciation and the Holocene

    NASA Astrophysics Data System (ADS)

    Lézine, Anne-Marie; Robert, Christian; Cleuziou, Serge; Inizan, Marie-Louise; Braemer, Frank; Saliège, Jean-François; Sylvestre, Florence; Tiercelin, Jean-Jacques; Crassard, Rémy; Méry, Sophie; Charpentier, Vincent; Steimer-Herbet, Tara

    2010-07-01

    Paleohydrological and archaeological evidence from the Southern and South-Eastern Arabian Peninsula reveal strong relations between phases of human settlements and climate change linked to the Indian monsoon system. During the early to mid-Holocene, large fresh-water lakes extended in the lowland deserts of Ramlat as-Sab'atayn (Yemen) and Wahiba Sands (Oman), which were very similar to those occurring in the North, in the Rub' al-Khali (Saudi Arabia), at that time. Many archaeological sites, characterized by scattered stone artefacts, ostrich-eggshells and bones around hearths, are related to this lacustrine phase, which culminated around 10 000-8000 cal yr B.P. in the lowland deserts before the lakes progressively dried up. The last record of fresh-water bodies' extensions date back 7300 cal yr B.P. at Shabwa (Yemen) and 7500 cal yr B.P. at al-Haid (Oman). Then, fresh-water was probably available only from seasonal run-off from adjacent highlands, where paleolakes persisted into the late Holocene. Dry climate conditions in the inland desert of Yemen during the late Holocene coincide with a phase of intensive human inhabitation as testified by development of irrigation in the piedmontane areas, numerous necropolises of built collective burials and houses.

  15. A sedimentary-based history of hurricane strikes on the southern Caribbean coast of Nicaragua

    NASA Astrophysics Data System (ADS)

    McCloskey, Terrence Allen; Liu, Kam-biu

    2012-11-01

    Multi-millennial hurricane landfall records from the western North Atlantic indicate that landfall frequency has varied dramatically over time, punctuated by multi-centennial to millennial scale periods of hyperactivity. We extend the record geographically by presenting a paleostrike record inferred from a four-core transect from a marsh on the Caribbean coast of Nicaragua. Fossil pollen indicates that the site was a highly organic wetland from ~ 5400-4900 cal yr BP, at which time it became a shallow marine lagoon until ~ 2800 cal yr BP when it transitioned back into swamp/marsh, freshening over time, with the present fresh-to-brackish Typha marsh developing over the very recent past. Hurricane Joan, 1988, is recorded as a distinctive light-colored sand-silt-clay layer across the top of the transect, identifiable by abrupt shifts in color from the dark marsh deposits, increased grain size, and two upward-fining sequences, which are interpreted as representing the storm's traction and suspension loads. The six layers identified as hurricane-generated display temporal clustering, featuring a marked increase in landfall frequency ~ 800 cal yr BP. This pattern is anti-phase with the activity pattern previously identified from the northern Caribbean and the Atlantic coast of North America, thereby opposing the view that hyperactivity occurs simultaneously across the entire basin.

  16. Reconstruction of the long-term fire history of an old-growth deciduous forest in Southern Québec, Canada, from charred wood in mineral soils

    NASA Astrophysics Data System (ADS)

    Talon, Brigitte; Payette, Serge; Filion, Louise; Delwaide, Ann

    2005-07-01

    Charcoal particles are widespread in terrestrial and lake environments of the northern temperate and boreal biomes where they are used to reconstruct past fire events and regimes. In this study, we used botanically identified and radiocarbon-dated charcoal macrofossils in mineral soils as a paleoecological tool to reconstruct past fire activity at the stand scale. Charcoal macrofossils buried in podzolic soils by tree uprooting were analyzed to reconstruct the long-term fire history of an old-growth deciduous forest in southern Québec. Charcoal fragments were sampled from the uppermost mineral soil horizons and identified based on anatomical characters. Spruce ( Picea spp.) fragments dominated the charcoal assemblage, along with relatively abundant wood fragments of sugar maple ( Acer saccharum) and birch ( Betula spp.), and rare fragments of pine ( Pinus cf. strobus) and white cedar ( Thuja canadensis). AMS radiocarbon dates from 16 charcoal fragments indicated that forest fires were widespread during the early Holocene, whereas no fires were recorded from the mid-Holocene to present. The paucity of charcoal data during this period, however, does not preclude that a fire event of lower severity may have occurred. At least eight forest fires occurred at the study site between 10,400 and 6300 cal yr B.P., with a dominance of burned conifer trees between 10,400 and 9000 cal yr B.P. and burned conifer and deciduous trees between 9000 and 6300 cal yr B.P. Based on the charcoal record, the climate at the study site was relatively dry during the early Holocene, and more humid from 6300 cal yr B.P. to present. However, it is also possible that the predominance of conifer trees in the charcoal record between 10,400 and 6300 cal yr B.P. created propitious conditions for fire spreading. The charcoal record supports inferences based on pollen influx data (Labelle, C., Richard, P.J.H. 1981. Végétation tardiglaciaire et postglaciaire au sud-est du Parc des Laurentides, Qu

  17. Late-glacial and Holocene Vegetation and Climate Variability, Including Major Droughts, in the Sky Lakes Region of Southeastern New York State

    NASA Technical Reports Server (NTRS)

    Menking, Kirsten M.; Peteet, Dorothy M.; Anderson, Roger Y.

    2012-01-01

    Sediment cores from Lakes Minnewaska and Mohonk in the Shawangunk Mountains of southeastern New York were analyzed for pollen, plantmacrofossils, macroscopic charcoal, organic carbon content, carbon isotopic composition, carbon/nitrogen ratio, and lithologic changes to determine the vegetation and landscape history of the greater Catskill Mountain region since deglaciation. Pollen stratigraphy generally matches the New England pollen zones identified by Deevey (1939) and Davis (1969), with boreal genera (Picea, Abies) present during the late Pleistocene yielding to a mixed Pinus, Quercus and Tsuga forest in the early Holocene. Lake Minnewaska sediments record the Younger Dryas and possibly the 8.2 cal kyr BP climatic events in pollen and sediment chemistry along with an 1400 cal yr interval of wet conditions (increasing Tsuga and declining Quercus) centered about 6400 cal yr BP. BothMinnewaska andMohonk reveal a protracted drought interval in themiddle Holocene, 5700-4100 cal yr BP, during which Pinus rigida colonized the watershed, lake levels fell, and frequent fires led to enhanced hillslope erosion. Together, the records show at least three wet-dry cycles throughout the Holocene and both similarities and differences to climate records in New England and central New York. Drought intervals raise concerns for water resources in the New York City metropolitan area and may reflect a combination of enhanced La Niña, negative phase NAO, and positive phase PNA climatic patterns and/or northward shifts of storm tracks.

  18. Experimental petrology applied in deposits of the 550 yr b.p. eruption at El Chichon volcano, Chiapas.

    NASA Astrophysics Data System (ADS)

    Mora, J. C.

    2002-12-01

    The 550 years ago a plinian-type eruption took place at El Chich¢n volcano, this event produced a 1.5 km3 pumice fall deposit. Contrary to the 1982 eruption, this event occurred under open vent conditions similar to the present crater. Comparing the pre-eruptive conditions of these two events would shed new lights on the location of the magma chamber, and the magmatic evolution. In order to determine the pre-eruptive conditions (P and T) of the 550 yr BP magma, laboratory experiments were carried out under fixed pressure and temperature conditions at the University of Alaska at Fairbanks. For this purpose fresh samples of the pumice were crushed, pulverized and saturated with water. The sample was then placed into ~2mg experimental tube charges of Ag70Pd30 of 2mm diameter. Our results indicate that prior to the 550 plinian the magma has a temperature of 825-830°C. and at approximated pressure of 2500 bars. This pressure estimate differs from the 4000 bars estimated with the geobaromether of Al-hornblende. The water contents obtained in the experiments were oversaturated similar to the calculated with the plagioclase-melts equation (5.3-6.1 percent in vol.)

  19. Late Holocene swampy forest of Loango Bay (Congo). Sedimentary environments and organic matter deposition

    NASA Astrophysics Data System (ADS)

    Malounguila-Nganga, Dieudonné; Giresse, Pierre; Boussafir, Mohammed; Miyouna, Timothée

    2017-10-01

    This region, comprised between the Kouilou estuary and Pointe-Noire, is characterised by a very specific morphological setting. On the continental side, the coastal sector is dominated by cliffs of sand over 100 m high, referred to as the Série des Cirques, whereas, on the ocean side, very active erosion is presently taking place which has resulted in a retreat of the shoreline of more than 100 m over the last hundred years. New 14C datings and different analyses of organic matter and clay minerals (X-Ray data) were performed in order to reconstruct the geological and ecological evolution of the area during the Late Holocene and replace it in the palaeoclimatic scheme deduced from previous regional studies. From 7 to 6000 yr cal BP, the accumulation of important beach barriers by the oceanic drift allowed the definition of a narrow swamp depression several tens of kilometres long. A dense ombrophile and hydromorphic forest, in spite of being very close to the oceanic coast, remained sheltered from any brackish influence and fed accumulations of peat and organic muds. The emersive trend of 3000-2000 yr BP, i.e. the passage from a vast forest swamp with a water body several metres deep to a wet zone with some emersions, is expressed by a large colluvial accumulation. High primary production is not clearly attested in this wet area. High HI values would indicate rather long-lasting conservation in a swampy environment, the lowest values indicating alternating episodes of emersion and immersion. In such peatlands, OM preservation is favoured by an anoxic environment and rapid burial. The δ 13C values of older peats dated ca. 7000 yr cal BP are -28 to -26‰, typical of a C3 origin. Thus, the ca. -16‰ value indicates the greatest opening of the cover, suggesting a forest-savanna mosaic ca. 2500 yr cal BP. At Kivesso, several proxies suggest a wetter trend towards 500 yr cal BP. An ultimate drier trend is observed during the last two centuries, which has been

  20. Holocene Millennial Time Scale Hydrological Changes In Central-east Africa

    NASA Astrophysics Data System (ADS)

    Jolly, D.; Bonnefille, R.; Beaufort, L.

    The Holocene hydrological changes of a tropical swamp is reconstructed using a high resolution pollen record (ca 50 yrs) from the Kuruyange valley (Burundi, Africa, 3°35'S, 29°41'E), at 2000 m elevation. The sequence was dated by 10 radiocarbon dates, allowing reconstruction between ca 12 500 and 1000 cal yr B.P. In the Kuruyange swamp, peat accumulated rapidly at a sedimentation rate varying from 0.73 (prior to 6200 cal yr B.P.) to 1.51 mm/yr (during the late Holocene). A pollen index of water table, based on a ratio of aquatic versus non-aquatic plants has been used in order to test the hypothesis of hydrological constraints on the swampy ecosystem. Eight arid phases are evidenced by the index minima at 12 200, 11 200, 9900, 8600, 6500, 5000, 3400, 1600 cal yr B.P. The good agreement existing between this index and independent data such as (i) low-resolution East-African lake level reconstruct ions (Gillespie et al., 1983) and (ii) ?18O analyses from Arabian Sea (Sirocko et al., 1993) suggests the water table level responds to the monsoon dynamic. The Index varies periodically with a combination of 1/1515, 1/880 and 1/431 years-1 frequencies, revealed by time series analyses (Blackman-Tukey and Maximum Entropy). The extrapolation of the composite curve based on these 3 periodicities show that two major climatic events defined in the high latitudes between 1000 and 660 cal yr B.P. (Medieval Warm Period) and between 500 and 100 cal yr B.P. (Little Ice Age) are recorded in our data and show respectively high and low stands of the water table. Our results support some previous pollen-derived climate estimates in Ethiopia done by Bonnefille and Umer (1994). Moreover, the "1500 year" cycle registered in our data from the tropics, already evidenced in higher latitudes (Wijmstra et al., 1984; Bondet al., 1997; Schulz et al., 1999; Bond et al., 2001) support the hypothesis of strong teleconnections between tropical/subtropical and polar climates during the deglaciation

  1. Holocene glacier variability and Neoglacial hydroclimate at Ålfotbreen, western Norway

    NASA Astrophysics Data System (ADS)

    Gjerde, Marthe; Bakke, Jostein; Vasskog, Kristian; Nesje, Atle; Hormes, Anne

    2016-02-01

    Glaciers and small ice caps respond rapidly to climate perturbations (mainly winter precipitation, and summer temperature), and the mass-balance of glaciers located in western Norway is governed mainly by winter precipitation (Pw). Records of past Pw can offer important insight into long-term changes in atmospheric circulation, but few proxies are able to accurately capture winter climate variations in Scandinavia. Reconstructions of equilibrium-line-altitude (ELA) variations from glaciers that are sensitive to changes in Pw therefore provide a unique opportunity to quantify past winter climate in this region. Here we present a new, Holocene glacier activity reconstruction for the maritime ice cap Ålfotbreen in western Norway, based on investigations of distal glacier-fed lake sediments and modern mass balance measurements (1963-2010). Several lake sediment cores have been subject to a suite of laboratory analyses, including measurements of physical parameters such as dry bulk density (DBD) and loss-on-ignition (LOI), geochemistry (XRF), surface magnetic susceptibility (MS), and grain size distribution, to identify glacial sedimentation in the lake. Both radiocarbon (AMS 14C) and 210Pb dating were applied to establish age-depth relationships in the sediment cores. A novel approach was used to calibrate the sedimentary record against a simple ELA model, which allowed reconstruction of continuous ELA changes for Ålfotbreen during the Neoglacial (when Ålfotbreen was present, i.e. the last ∼1400 years). Furthermore, the resulting ELA variations were combined with an independent summer temperature record to calculate Neoglacial Pw using the 'Liestøl equation'. The resulting Pw record is of higher resolution than previous reconstructions from glaciers in Norway and shows the potential of glacier records to provide high-resolution data reflecting past variations in hydroclimate. Complete deglaciation of the Ålfotbreen occurred ∼9700 cal yr BP, and the ice cap was

  2. Arctic ground squirrels of the mammoth-steppe: paleoecology of Late Pleistocene middens (˜24 000 29 450 14C yr BP), Yukon Territory, Canada

    NASA Astrophysics Data System (ADS)

    Zazula, Grant D.; Froese, Duane G.; Elias, Scott A.; Kuzmina, Svetlana; Mathewes, Rolf W.

    2007-04-01

    This paper presents paleoecological analyses of 48 fossil arctic ground squirrel ( Spermophilus parryii) middens (nests and caches) recovered from ice-rich loess sediments in the Klondike region of west-central Yukon Territory. AMS radiocarbon dates and stratigraphic association of middens with Dawson tephra (˜25 300 14C yr BP), indicate these paleoecological data reflect the onset of glacial conditions of early Marine Isotope Stage (MIS) 2 and terminal MIS 3 (˜24 000-29 450 14C yr BP). Plant macrofossils include at least 60 plant taxa, including diverse graminoids ( Poa, Elymus trachycaulus, Kobresia myosuroides), steppe forbs ( Penstemon gormanii, Anemone patens var. multifida, Plantago cf. canescens), tundra forbs ( Draba spp., Bistorta vivipara), dwarf shrubs ( Salix cf. arctica, S. cf. polaris), sage ( Artemisia frigida) and rare trees ( Picea mariana). Many of these taxa identified in the middens represent the first recorded fossils for these plants in Eastern Beringia and add to our knowledge of the floristic composition of Pleistocene vegetation and biogeography in this region. Fossil beetles include typical members of the Eastern Beringian steppe-tundra fauna ( Lepidophorus lineaticollis and Connatichela artemisiae) and others suggesting predominantly dry, open habitats. Cache forage selection is suggested by some plant taxa which were particularly frequent and abundant in the middens ( Bistorta vivipara, Kobresia myosuroides, Ranunculus spp., Potentilla, Erysimum cf. cheiranthoides, Poa, Carex and Draba). Factors such as proximity of vegetation to burrows and abundance of fruits and seeds per plant were probably important in cache selection. Glacial conditions enabled arctic ground squirrels to form widespread and dense populations in regions such as the Klondike in which they are rare or absent at present. This fossil midden record supports previous hypotheses that suggest arctic ground squirrels evolved in and are well-adapted to the open, steppe

  3. High-resolution chronology for deglaciation of the Patagonian Ice Sheet at Lago Buenos Aires (46.5°S) revealed through varve chronology and Bayesian age modelling

    NASA Astrophysics Data System (ADS)

    Bendle, Jacob M.; Palmer, Adrian P.; Thorndycraft, Varyl R.; Matthews, Ian P.

    2017-12-01

    Glaciolacustrine varves offer the potential to construct continuous, annually-resolved chronologies for ice-sheet deglaciation, and improved understanding of glacier retreat dynamics. This paper investigates laminated glaciolacustrine sediments deposited around the waning margins of the Patagonian Ice Sheet, following the local Last Glacial Maximum (LGM). Detailed macro- and microfacies analyses confirm an annual (varve) structure within these sediments. The correlation of annual layers (varves) across five sites in eastern Lago Buenos Aires yields a 994 ± 36 varve-year (vyr) chronology and thickness record. The floating chronology has been anchored to the calendar-year timescale through identification of the Ho tephra (17,378 ± 118 cal a BP) in the varve sequences. Using a Bayesian age model to integrate the new varve chronology with published moraine ages, the onset of deglaciation at 46.5°S is dated to 18,086 ± 214 cal a BP. New age estimates for deglacial events are combined with high-resolution analysis of varve thickness trends, and new lithostratigraphic data on ice-margin position(s), to reconstruct ice-margin retreat rates for the earliest ca. 1000 years of ice-sheet demise. Glacier retreat rates were moderate (5.3-10.3 m yr-1) until 17,322 ± 115 cal a BP, but subsequently accelerated (15.4-18.0 m yr-1). Sustained influxes of ice-rafted debris (IRD) after 17,145 ± 122 cal a BP suggest retreat rates were enhanced by calving after ice contracted into deeper lake waters. Ice persisted in eastern Lago Buenos Aires until at least 16,934 ± 116 cal a BP, after which the glacier started to retreat towards the Patagonian mountains.

  4. Influence of system controls on the Late Quaternary geomorphic evolution of a rapidly-infilled incised-valley system: The lower Manawatu valley, North Island New Zealand

    NASA Astrophysics Data System (ADS)

    Clement, Alastair J. H.; Fuller, Ian C.

    2018-02-01

    The Manawatu incised-valley estuary was rapidly infilled between 12,000-4700 cal. yr BP. A combination of empirical measurements of sedimentation rates, a reconstruction of relative sea-level (RSL) change, and digital elevation models of key surfaces within the Holocene sedimentary fill of the valley were integrated to produce a numerical model to investigate the influence of the system controls of sea-level change, sediment flux, and accommodation space on the rapid infilling history of the palaeo-estuary. The numerical model indicates that sediment flux into the palaeo-estuary was greatest during the Holocene marine transgression between 12,000-8000 years BP. The average rate of sediment deposition in the estuary during this period was 1.0 M m3 yr- 1. This rapid rate of sedimentation was controlled by the rate of accommodation space creation, as regulated by the rate of sea-level rise and the antecedent configuration of the valley. By the time sea levels stabilised c. 7500 cal. yr BP, the palaeo-estuary had been substantively infilled. Limited accommodation space resulted in rapid infilling of the central basin, though sediment flux into the estuary between 7100 and 4500 cal. yr BP was at a lower rate of 234,000 m3 yr- 1. The limited accommodation space also influenced hydrodynamic conditions in the estuarine central basin, driving export of fine-grained sediment from the estuary. Once the accommodation space of the estuarine basin was infilled sediment bypassed the system, with a consequent reduction in the sedimentation rate in the valley. More accurate partitioning of the sources of sediment driving the infilling is necessary to quantify sediment bypassing. Post-depositional lowering of RSL index points from the valley is driven by neotectonics and sediment compaction.

  5. Pre-Clovis occupation 14,550 years ago at the Page-Ladson site, Florida, and the peopling of the Americas.

    PubMed

    Halligan, Jessi J; Waters, Michael R; Perrotti, Angelina; Owens, Ivy J; Feinberg, Joshua M; Bourne, Mark D; Fenerty, Brendan; Winsborough, Barbara; Carlson, David; Fisher, Daniel C; Stafford, Thomas W; Dunbar, James S

    2016-05-01

    Stone tools and mastodon bones occur in an undisturbed geological context at the Page-Ladson site, Florida. Seventy-one radiocarbon ages show that ~14,550 calendar years ago (cal yr B.P.), people butchered or scavenged a mastodon next to a pond in a bedrock sinkhole within the Aucilla River. This occupation surface was buried by ~4 m of sediment during the late Pleistocene marine transgression, which also left the site submerged. Sporormiella and other proxy evidence from the sediments indicate that hunter-gatherers along the Gulf Coastal Plain coexisted with and utilized megafauna for ~2000 years before these animals became extinct at ~12,600 cal yr B.P. Page-Ladson expands our understanding of the earliest colonizers of the Americas and human-megafauna interaction before extinction.

  6. High latitude Southern Hemisphere fire history during the mid-late Holocene (750- 6000 yr BP)

    USGS Publications Warehouse

    Battistel, Dario; Kehrwald, Natalie; Zennaro, Piero; Pellegrino, Giuseppe; Barbaro, Elena; Zangrando, Roberta; Pedeli, Xanthi X.; Varin, Cristiano; Spolaor, Andrea; Vallelonga, Paul T.; Gambaro, Andrea; Barbante, Carlo

    2018-01-01

    We determined the specific biomass burning biomarker levoglucosan in an ice core from the TALos Dome Ice CorE drilling project (TALDICE) during the mid- to late Holocene (6000–750 BP). The levoglucosan record is characterized by a long-term increase with higher rates starting at  ∼  4000 BP and peaks between 2500 and 1500 BP. The anomalous increase in levoglucosan centered at  ∼  2000 BP is consistent with other Antarctic biomass burning records. Multiple atmospheric phenomena affect the coastal Antarctic Talos Dome drilling site, where the Southern Annular Mode (SAM) is the most prominent as the Southern Annular Mode Index (SAMA) correlates with stable isotopes in precipitation throughout the most recent 1000 years of the ice core. If this connection remains throughout the mid- to late Holocene, then our results demonstrate that changes in biomass burning, rather than changes in atmospheric transport, are the major influence on the TALDICE levoglucosan record. Comparisons with charcoal syntheses help evaluate fire sources, showing a greater contribution from southern South American fires than from Australian biomass burning. The levoglucosan peak centered at  ∼  2000 BP occurs during a cool period throughout the Southern Hemisphere, yet during a time of increased fire activity in both northern and southern Patagonia. This peak in biomass burning is influenced by increased vegetation in southern South America from a preceding humid period, in which the vegetation desiccated during the following cool, dry period. The Talos Dome ice core record from 6000 to  ∼  750 BP currently does not provide clear evidence that the fire record may be strongly affected by anthropogenic activities during the mid- to late Holocene, although we cannot exclude at least a partial influence.

  7. The timing and nature of Late Quaternary vegetation changes in the northern Great Plains, USA and Canada: a re-assessment of the spruce phase

    NASA Astrophysics Data System (ADS)

    Yansa, Catherine H.

    2006-02-01

    This paper revises the chronology for the northward migration of Picea glauca (white spruce) across the northern Great Plains, following the recession of the Laurentide Ice Sheet, and reinterprets the species composition and structure of the late-glacial vegetation on the basis of pollen and plant-macrofossil analysis. The timing of spruce migration is based on 26 14C ages obtained from Picea macrofossils. The date for the appearance of white spruce in southern South Dakota, USA, remains unchanged, 12,600 14C yr BP (ca 15,000 cal yr BP), but its arrival in southern Saskatchewan, Canada, by 10,300 14C yr BP (ca 12,100 cal yr BP) is about 1500 years later than previously estimated based on an organic sediment date. Picea glauca thus migrated northwards at an average rate of 0.38 km/ 14C year (0.30 km/calendar year), significantly slower than the previously published rate of 2 km/ 14C year. White spruce trees probably inhabited lake shorelines, whereas prairie, parkland, and boreal plants occupied both lowlands and uplands, forming an open white spruce parkland. This interpretation differs from a previous reconstruction of a boreal-type spruce forest and thus offers another paleoclimatic interpretation. Precipitation was probably low and summer temperatures relatively mild, averaging about 19 °C.

  8. Bayesian chronological analyses consistent with synchronous age of 12,835-12,735 Cal B.P. for Younger Dryas boundary on four continents.

    PubMed

    Kennett, James P; Kennett, Douglas J; Culleton, Brendan J; Aura Tortosa, J Emili; Bischoff, James L; Bunch, Ted E; Daniel, I Randolph; Erlandson, Jon M; Ferraro, David; Firestone, Richard B; Goodyear, Albert C; Israde-Alcántara, Isabel; Johnson, John R; Jordá Pardo, Jesús F; Kimbel, David R; LeCompte, Malcolm A; Lopinot, Neal H; Mahaney, William C; Moore, Andrew M T; Moore, Christopher R; Ray, Jack H; Stafford, Thomas W; Tankersley, Kenneth Barnett; Wittke, James H; Wolbach, Wendy S; West, Allen

    2015-08-11

    The Younger Dryas impact hypothesis posits that a cosmic impact across much of the Northern Hemisphere deposited the Younger Dryas boundary (YDB) layer, containing peak abundances in a variable assemblage of proxies, including magnetic and glassy impact-related spherules, high-temperature minerals and melt glass, nanodiamonds, carbon spherules, aciniform carbon, platinum, and osmium. Bayesian chronological modeling was applied to 354 dates from 23 stratigraphic sections in 12 countries on four continents to establish a modeled YDB age range for this event of 12,835-12,735 Cal B.P. at 95% probability. This range overlaps that of a peak in extraterrestrial platinum in the Greenland Ice Sheet and of the earliest age of the Younger Dryas climate episode in six proxy records, suggesting a causal connection between the YDB impact event and the Younger Dryas. Two statistical tests indicate that both modeled and unmodeled ages in the 30 records are consistent with synchronous deposition of the YDB layer within the limits of dating uncertainty (∼ 100 y). The widespread distribution of the YDB layer suggests that it may serve as a datum layer.

  9. Bayesian chronological analyses consistent with synchronous age of 12,835-12,735 Cal B.P. for Younger Dryas boundary on four continents

    NASA Astrophysics Data System (ADS)

    Kennett, James P.; Kennett, Douglas J.; Culleton, Brendan J.; Emili Aura Tortosa, J.; Bischoff, James L.; Bunch, Ted E.; Daniel, I. Randolph, Jr.; Erlandson, Jon M.; Ferraro, David; Firestone, Richard B.; Goodyear, Albert C.; Israde-Alcántara, Isabel; Johnson, John R.; Jordá Pardo, Jesús F.; Kimbel, David R.; LeCompte, Malcolm A.; Lopinot, Neal H.; Mahaney, William C.; Moore, Andrew M. T.; Moore, Christopher R.; Ray, Jack H.; Stafford, Thomas W., Jr.; Barnett Tankersley, Kenneth; Wittke, James H.; Wolbach, Wendy S.; West, Allen

    2015-08-01

    The Younger Dryas impact hypothesis posits that a cosmic impact across much of the Northern Hemisphere deposited the Younger Dryas boundary (YDB) layer, containing peak abundances in a variable assemblage of proxies, including magnetic and glassy impact-related spherules, high-temperature minerals and melt glass, nanodiamonds, carbon spherules, aciniform carbon, platinum, and osmium. Bayesian chronological modeling was applied to 354 dates from 23 stratigraphic sections in 12 countries on four continents to establish a modeled YDB age range for this event of 12,835-12,735 Cal B.P. at 95% probability. This range overlaps that of a peak in extraterrestrial platinum in the Greenland Ice Sheet and of the earliest age of the Younger Dryas climate episode in six proxy records, suggesting a causal connection between the YDB impact event and the Younger Dryas. Two statistical tests indicate that both modeled and unmodeled ages in the 30 records are consistent with synchronous deposition of the YDB layer within the limits of dating uncertainty (∼100 y). The widespread distribution of the YDB layer suggests that it may serve as a datum layer.

  10. Four millennia of woodland structure and dynamics at the Arctic treeline of eastern Canada.

    PubMed

    Auger, Sarah; Payette, Serge

    2010-05-01

    Paleoecological analysis using complementary indicators of vegetation and soil can provide spatially explicit information on ecological processes influencing trajectories of long-term ecosystem change. Here we document the structure and dynamics of an old-growth woodland before and after its inception 1000 years ago. We infer vegetation and soil characteristics from size and age distributions of black spruce (Picea mariana (Mill.) B.S.P.), soil properties, plant fossils, and paleosols. Radiocarbon ages of charcoal on the ground and in the soil indicate that the fire return interval was approximately 300 years between 2750 and 1000 cal. yr BP. No fire evidence was found before and after this period despite the presence of spruce since 4200 cal. yr BP. The size structures of living and dead spruce suggest that the woodland is in equilibrium with present climate in absence of fire. Tree establishment and mortality occurred regularly since the last fire event around 950 cal. yr BP. Both layering and occasional seeding have contributed to stabilize the spatial distribution of spruce over the past 1000 years. Since initial afforestation, soil development has been homogenized by the changing spatial distribution of spruce following each fire. We conclude that the history of the woodland is characterized by vegetation shifts associated with fire and soil disturbances and by millennial-scale maintenance of the woodland's structure despite changing climatic conditions.

  11. Miscanti-1: Human occupation during the arid Mid-Holocene event in the high-altitude lakes of the Atacama Desert, South America

    NASA Astrophysics Data System (ADS)

    Núñez, Lautaro; Loyola, Rodrigo; Cartajena, Isabel; López, Patricio; Santander, Boris; Maldonado, Antonio; de Souza, Patricio; Carrasco, Carlos

    2018-02-01

    This paper presents an interdisciplinary study of the Miscanti-1 archaeological site, located in the Holocene terrace deposits accumulated on the eastern margin of Miscanti Lake (4120 m.a.s.l.), northern Chile (23.7° S, 67.7° W). The human response to environmental and climatic variability in the Mid-Holocene (9500-4500 cal yr BP) is discussed through the zooarchaeological, lithic and paleoenvironmental records. We propose that, due to the increased aridity of the period, Miscanti Lake became a brackish paleowetland that attracted discrete groups of hunter-gatherers from lower elevation Andean areas. In contrast with the high frequency of human occupations known for the humid Late Pleistocene and Early Holocene (12600-9500 yr cal BP), the Miscanti-1 site is one of the few occupations recorded in the Atacama Highlands during the Mid-Holocene period. Data analysis suggests logistic and short-term campsite use for hunting the wild camelids that were attracted by the wetlands and fresh water (8100-8300 yr cal BP). In contrast to previous proposals for this period, we propose that access to high altitude environments did not cease, but was made possible by a shift to highly scheduled mobility and a specialized bifacial technology. Finally, the temporal and spatial links of Miscanti-1 are discussed in a regional context.

  12. Magmatic controls on eruption dynamics of the 1950 yr B.P. eruption of San Antonio Volcano, Tacaná Volcanic Complex, Mexico-Guatemala

    NASA Astrophysics Data System (ADS)

    Mora, Juan Carlos; Gardner, James Edward; Macías, José Luis; Meriggi, Lorenzo; Santo, Alba Patrizia

    2013-07-01

    San Antonio Volcano, in the Tacaná Volcanic Complex, erupted ~ 1950 yr. B.P., with a Pelean type eruption that produced andesitic pyroclastic surges and block-and-ash flows destroying part of the volcano summit and producing a horse-shoe shaped crater open to the SW. Between 1950 and 800 yr B.P. the eruption continued with effusive andesites followed by a dacite lava flow and a summit dome, all from a single magma batch. All products consist of phenocrysts and microphenocrysts of zoned plagioclase, amphibole, pyroxene, magnetite ± ilmenite, set in partially crystallized groundmass of glass and microlites of the same mineral phases, except for the lack of amphibole. Included in the andesitic blocks of the block-and-ash flow deposit are basaltic andesite enclaves with elongated and ellipsoidal forms and chilled margins. The enclaves have intersertal textures with brown glass between microphenocrysts of plagioclase, hornblende, pyroxene, and olivine, and minor proportions of phenocrysts of plagioclase, hornblende, and pyroxene. A compositional range obtained of blocks and enclaves resulted from mixing between andesite (866 °C ± 22) and basaltic andesite (enclaves, 932 °C ± 22), which may have triggered the explosive Pelean eruption. Vestiges of that mixing are preserved as complex compositional zones in plagioclase and clinopyroxene-rich reaction rims in amphibole in the andesite. Whole-rock chemistry, geothermometry, experimental petrology and modeling results suggest that after the mixing event the eruption tapped hybrid andesitic magma (≤ 900 °C) and ended with effusive dacitic magma (~ 825 °C), all of which were stored at ~ 200 MPa water pressure. A complex open-system evolution that involved crustal end-members best explains the generation of effusive dacite from the hybrid andesite. Amphibole in the dacite is rimmed by reaction products of plagioclase, orthopyroxene, and Fe-Ti oxides produced by decompression during ascent. Amphibole in the andesite

  13. High-resolution Record of Holocene Climate, Vegetation, and Fire from a Raised Peat Bog, Prince Edward Island, Canadian Maritimes

    NASA Astrophysics Data System (ADS)

    Peros, M. C.; Chan, K.; Ponsford, L.; Carroll, J.; Magnan, G.

    2014-12-01

    Raised peat bogs receive all precipitation and nutrients from the atmosphere and are thus widely used archives for information on past environments and climates. In this paper we provide high-resolution multi-proxy data from a raised bog from northeastern Prince Edward Island, located in the Gulf of St. Lawrence, Canada. We studied testate amoeba (a proxy for water table depth), macrocharcoal (a proxy for local-scale fire), peat humification (a proxy for decomposition), plant macrofossils (indicative of local-scale vegetation), and organic matter content (yielding carbon accumulation rates) from a 5.5 m long core lifted from the center of Baltic Bog. Eleven AMS radiocarbon dates show that peat accumulation began before 9000 cal yr BP and continued almost uninterrupted until the present. The macrofossil data show that a transition from a sedge-dominated fen to a sphagnum-dominated bog occurred around 8000 cal yr BP, and sphagnum remained dominant in the bog throughout most of the Holocene. A testate amoeba-based reconstruction of water table depth indicates that conditions were drier during the early Holocene (~8000 to 5000 cal yr BP) and became gradually wetter into the late Holocene. In addition, a number of higher frequency shifts in precipitation are inferred throughout the Holocene on the basis of the testate amoeba and humification results. The macrocharcoal evidence indicates fire—probably in the surrounding forest—was relatively more common during the early Holocene, perhaps due to drier climate conditions. A large influx of charcoal at around 2000 cal yr BP suggests the presence of one or more major fires at this time, and a concurrent decrease in the rate of peat accumulation indicates the fire may have affected the bog itself. The data from Baltic Bog is broadly comparable to other proxy data (in particular pollen studies) from the Canadian Maritimes. This work is important because it: 1) helps us better understand the role of hydroclimatic

  14. Holocene and Last Interglacial climate of the Faroe Islands from sedimentary leaf wax hydrogen isotopes

    NASA Astrophysics Data System (ADS)

    Curtin, L.; D'Andrea, W. J.; de Wet, G.; Balascio, N.; Bradley, R. S.

    2017-12-01

    The climate of the North Atlantic region is extremely sensitive to changes in ocean and atmospheric circulation, and understanding past natural variability in North Atlantic climate provides important context for modern climate change. Here, we present Holocene and Eemian hydrogen isotope (δD) records from leaf waxes preserved in lacustrine sediments from the North Atlantic Faroe Islands and interpret them as a proxy for temperature and hydroclimate variability. In addition to helping to constrain the timing and amplitude of climate evolution during each of these interglacial periods, the data can be used to directly compare Eemian and Holocene climate using the same proxy from the same terrestrial location. Of the leaf waxes measured, the δD values of long-chain and mid-chain n-alkanes showed two different signals, which we interpret to represent leaf water δD values and lake water δD values, respectively. The δD values for long-chain and mid-chain fatty acids were most similar to the mid-chain n-alkanes, and likely represent a mixture of terrestrial and aquatic sources. Leaf wax-inferred δD values of precipitation during the early Holocene (10,000 to 8,000 cal yr BP) are 13‰ enriched compared to the remainder of the Holocene (after 8,000 cal yr BP), which show relatively stable values over time. Inferred lake water δD values decreased slowly over the late Holocene, suggesting a gradual transition to a wetter climate after 4,000 cal yr BP. At 2,000 cal yr BP there was a significant change in the distribution of leaf waxes that suggests a transition from shrubland to grassland, but which pre-dates the pollen evidence for this transition. The last interglacial period has been suggested as an analog for future climate conditions. We found that long-chain alkane δD values from the Eemian are most similar to the earliest Holocene, which corroborate previous pollen studies suggesting a warmer climate at the Faroe Islands during this period.

  15. Climatic and lacustrine morphometric controls of diatom paleoproductivity in a tropical Andean lake

    NASA Astrophysics Data System (ADS)

    Bao, R.; Hernández, A.; Sáez, A.; Giralt, S.; Prego, R.; Pueyo, J. J.; Moreno, A.; Valero-Garcés, B. L.

    2015-12-01

    The coupling of lake dynamics with catchment biogeochemistry is considered the key element controlling primary production in mountain lakes at time scales of a few decades to millennia, yet little is known on the impacts of the morphometry of lakes throughout their ontogeny. As Lake Chungará (Central Andean Altiplano, northern Chile) experienced long-term lake-level fluctuations that strongly modified its area:volume ratio, it is an ideal system for exploring the relative roles that long-term climatic shifts and lake morphometry play on biosiliceous lacustrine productivity. In this paper, we review previous data on the percent contents of total organic carbon, total inorganic carbon, total nitrogen, total biogenic silica, isotopic composition of organic matter, carbonates, and diatom frustules, as well as data on the abundance of the chlorophycean Botryococcus braunii in this lake for the period 12,400-1300 cal yr BP. We also include new data on organic carbon and biogenic silica mass accumulation rates and the diatom assemblage composition of an offshore core dated using 14C and U/Th. Biosiliceous productivity in Lake Chungará was influenced by shifts in allochthonous nutrient inputs related to variability in precipitation. Humid phases dated at approx. 12,400 to 10,000 and 9600 to 7400 cal yr BP coincide with periods of elevated productivity, whereas decreases in productivity were recorded during arid phases dated at approx. 10,000 to 9600 and 7400 to 3550 cal yr BP (Andean mid-Holocene Aridity Period). However, morphometry-related in-lake controls led to a lack of a linear response of productivity to precipitation variability. During the late Glacial to early Holocene, lowstands facilitated complete water column mixing, prompting episodic massive blooms of a large centric diatom, Cyclostephanos cf. andinus. Thus, moderate productivity could be maintained, regardless of aridity, by this phenomenon of morphometric eutrophy during the early history of the lake

  16. Postglacial history of alpine vegetation, fire, and climate from Laguna de Río Seco, Sierra Nevada, southern Spain

    NASA Astrophysics Data System (ADS)

    Anderson, R. S.; Jiménez-Moreno, G.; Carrión, J. S.; Pérez-Martínez, C.

    2011-06-01

    The Sierra Nevada of southern Spain is a landscape with a rich biological and cultural heritage. The range was extensively glaciated during the late Pleistocene. However, the postglacial paleoecologic history of the highest range in southern Europe is nearly completely unknown. Here we use sediments from a small lake above present treeline - Laguna de Río Seco at 3020 m elevation - in a paleoecological study documenting over 11,500 calendar years of vegetation, fire and climate change, addressing ecological and paleoclimatic issues unique to this area through comparison with regional paleoecological sequences. The early record is dominated by Pinus pollen, with Betula, deciduous Quercus, and grasses, with an understory of shrubs. It is unlikely that pine trees grew around the lake, and fire was relatively unimportant at this site during this period. Aquatic microfossils indicate that the wettest conditions and highest lake levels at Laguna de Río Seco occurred before 7800 cal yr BP. This is in contrast to lower elevation sites, where wettest conditions occurred after ca 7800. Greater differences in early Holocene seasonal insolation may have translated to greater snowpack and subsequently higher lake levels at higher elevations, but not necessarily at lower elevations, where higher evaporation rates prevailed. With declining seasonality after ca 8000 cal yr BP, but continuing summer precipitation, lake levels at the highest elevation site remained high, but lake levels at lower elevation sites increased as evaporation rates declined. Drier conditions commenced regionally after ca 5700 cal yr BP, shown at Laguna de Río Seco by declines in wetland pollen, and increases in high elevation steppe shrubs common today ( Juniperus, Artemisia, and others). The disappearance or decline of mesophytes, such as Betula from ca 4000 cal yr BP is part of a regional depletion in Mediterranean Spain and elsewhere in Europe from the mid to late Holocene. On the other hand

  17. Holocene Paleoenvironment of the North-central Great Basin: Preliminary Results from Favre Lake, Northern Ruby Mountains, Nevada

    NASA Astrophysics Data System (ADS)

    Starratt, S.; Wahl, D.; Wan, E.; Anderson, L.; Wanket, J.; Olson, H.; Lloyd-Davies, T.; Kusler, J.

    2009-12-01

    Little is known about Holocene climate variability in north-central Nevada. This study aims to assess changes in watershed vegetation, fire history, lake levels and limnological conditions in order to understand secular to millennial-scale changes in regional climate. Favre Lake (2,899 m a.s.l.; 12 m deep; 7.7 hectares) is a flow-through lake in the northern Ruby Mountains. The primary sources of influent, both of which appear to be intermittent, are Castle Lake (2,989 m a.s.l.) and Liberty Lake (3,077 m a.s.l.). The bedrock of the three lake basins is early Paleozoic marble and Mesozoic granite and metamorphic rocks. Bathymetric maps and temperature, pH, salinity, and conductivity profiles have been generated for Favre Lake. Surface samples and a series of cores were also collected using a modified Livingstone piston corer. The presence of the Mazama ash in the basal sediment (~4 m below the sediment/water interface) indicates the record extends to ~7,700 cal yr B.P. Magnetic susceptibility (MS) and loss-on-ignition data indicate that the sediments in the lowest part of the core contain primary and reworked Mazama ash. About 2,000 years ago CaCO3 increased from 2 to 3% of the inorganic sediment. The upper 25 cm of the core are marked by an increase in MS which may indicate increased erosion due to grazing. Between about 7,700 and 6,000 cal yr B.P. the diatom flora is dominated by a diverse assemblage of benthic species. The remainder of the core is dominated by Fragilaria, suggesting that lake level rose and flooded the shelf that surrounds the depocenter of the lake. This is supported by changes in the abundance of the aquatic fern Isoetes. Pinus and Artemisia dominate the pollen record, followed by subordinate levels of Poaceae, Asteraceae, Amaranthaceae, and Sarcobatus. The late early Holocene (7,700-6,000 cal yr B.P.) is dominated by Pinus which is present in reduced amounts during the middle Holocene (6,000-3,000 cal yr B.P.) and then returns to dominance in

  18. The Holocene history of the North American Monsoon: 'known knowns' and 'known unknowns' in understanding its spatial and temporal complexity

    USGS Publications Warehouse

    Metcalfe, Sarah E.; Barron, John A.; Davies, Sarah J.

    2015-01-01

    Evidence for climatic change across the North American Monsoon (NAM) and adjacent areas is reviewed, drawing on continental and marine records and the application of climate models. Patterns of change at 12,000, 9000, 6000 and 4000 cal yr BP are presented to capture the nature of change from the Younger Dryas (YD) and through the mid-Holocene. At the YD, conditions were cooler overall, wetter in the north and drier in the south, while moving into the Holocene wetter conditions became established in the south and then spread north as the NAM strengthened. Until c. 8000 cal yr BP, the Laurentide Ice Sheet influenced precipitation in the north by pushing the Bermuda High further south. The peak extent of the NAM seems to have occurred around 6000 cal yr BP. 4000 cal yr BP marks the start of important changes across the NAM region, with drying in the north and the establishment of the clear differences between the summer-rain dominated south and central areas and the north, where winter rain is more important. This differentiation between south and north is crucial to understanding many climate responses across the NAM. This increasing variability is coincident with the declining influence of orbital forcing. 4000 cal yr BP also marks the onset of significant anthropogenic activity in many areas. For the last 2000 years, the focus is on higher temporal resolution change, with strong variations across the region. The Medieval Climate Anomaly (MCA) is characterised by centennial scale ‘megadrought’ across the southwest USA, associated with cooler tropical Pacific SSTs and persistent La Niña type conditions. Proxy data from southern Mexico, Central America and the Caribbean reveal generally wetter conditions, whereas records from the highlands of central Mexico and much of the Yucatan are typified by long -term drought. The Little Ice Age (LIA), in the north, was characterised by cooler, wetter winter conditions that have been linked with increased

  19. Earliest domestication of common millet (Panicum miliaceum) in East Asia extended to 10,000 years ago

    PubMed Central

    Lu, Houyuan; Zhang, Jianping; Liu, Kam-biu; Wu, Naiqin; Li, Yumei; Zhou, Kunshu; Ye, Maolin; Zhang, Tianyu; Zhang, Haijiang; Yang, Xiaoyan; Shen, Licheng; Xu, Deke; Li, Quan

    2009-01-01

    The origin of millet from Neolithic China has generally been accepted, but it remains unknown whether common millet (Panicum miliaceum) or foxtail millet (Setaria italica) was the first species domesticated. Nor do we know the timing of their domestication and their routes of dispersal. Here, we report the discovery of husk phytoliths and biomolecular components identifiable solely as common millet from newly excavated storage pits at the Neolithic Cishan site, China, dated to between ca. 10,300 and ca. 8,700 calibrated years before present (cal yr BP). After ca. 8,700 cal yr BP, the grain crops began to contain a small quantity of foxtail millet. Our research reveals that the common millet was the earliest dry farming crop in East Asia, which is probably attributed to its excellent resistance to drought. PMID:19383791

  20. Pre-Clovis occupation 14,550 years ago at the Page-Ladson site, Florida, and the peopling of the Americas

    PubMed Central

    Halligan, Jessi J.; Waters, Michael R.; Perrotti, Angelina; Owens, Ivy J.; Feinberg, Joshua M.; Bourne, Mark D.; Fenerty, Brendan; Winsborough, Barbara; Carlson, David; Fisher, Daniel C.; Stafford, Thomas W.; Dunbar, James S.

    2016-01-01

    Stone tools and mastodon bones occur in an undisturbed geological context at the Page-Ladson site, Florida. Seventy-one radiocarbon ages show that ~14,550 calendar years ago (cal yr B.P.), people butchered or scavenged a mastodon next to a pond in a bedrock sinkhole within the Aucilla River. This occupation surface was buried by ~4 m of sediment during the late Pleistocene marine transgression, which also left the site submerged. Sporormiella and other proxy evidence from the sediments indicate that hunter-gatherers along the Gulf Coastal Plain coexisted with and utilized megafauna for ~2000 years before these animals became extinct at ~12,600 cal yr B.P. Page-Ladson expands our understanding of the earliest colonizers of the Americas and human-megafauna interaction before extinction. PMID:27386553

  1. Synchronous mid-Holocene climate deteriorations in circum-Mediterranean and their links with ancient civilizations: first speloethem and archeological evidences from N-Algeria

    NASA Astrophysics Data System (ADS)

    Ruan, Jiaoyang; Kherbouche, Farid; Genty, Dominique; Cheng, Hai; Dewilde, Fabien; Blamart, Dominique

    2015-04-01

    Over the last decades, ancient civilizations during the Holocene were heavily studied at many places around the Mediterranean region such as Libya and Italy, and changes in the past social activities were widely assumed to be linked to regional climate variability. However, in many cases the climatic records were apart from the archaeological sites and the archaeological chronologies were not well constrained, which makes these links uncertain. Here we present a 230Th-dated decadal resolution climate record for 6034-3185yr BP based on the δ18O and δ13C analyses of two overlapping stalagmites from Gueldaman GLD1 Cave (36°26'N, 4°34'E, 507 m asl), N-Algeria. Recent archaeological work in this cave brought first information about the Neolithisation process since ca 7000yr cal BP in the region where little was known before. Together with new charcoal 14C dates from the digging sections we test the link between past climate change and human activities in the cave. GLD1 stalagmite records reveal a dry event at ca 5700-5500yr BP and a drying trend toward extreme aridity, since ca 4700yr BP, peaking at ca 4200yr BP. These climatic deteriorations in N-Algeria, within dating errors, are synchronous with dry phases observed on speleothem records from central (Corchia Cave and Renella Cave, Italy) and eastern (Soreq Cave, Israel) Mediterranean. Specifically, climatic condition was harsher at ca 4200yr BP than at ca 5700-5500yr BP in central and W-Mediterranean; while it was harsher at ca 5700-5500yr BP in E-Mediterranean. The new 14C dates relatively well anchor the age of sediment layers with the richest anthropogenic deposits (i.e. charcoal, bone and Neolithic pottery) to ca 4900-4400yr cal BP, coinciding with the wettest period inferred from the stalagmite records. Shortly following this period, archaeological remains were becoming very rare in the sediments, which might be the consequence of establishing extremely arid phase at ca 4200yr BP. This suggests a possible

  2. Testing Younger Dryas ET Impact (YDB) Evidence at Hall’s Cave, Texas

    NASA Astrophysics Data System (ADS)

    Stafford, T. W.; Lundelius, E.; Kennett, J.; Kennett, D. J.; West, A.; Wolbach, W. S.

    2009-12-01

    Hall’s Cave, Kerrville County Texas, 167 km WSW of Austin, provides a unique opportunity for testing the presence of a chronostratigraphic datum (YDB layer) containing rare and exotic proxies, including nanodiamonds, aciniform soot, and magnetic spherules, the origins of which remain controversial, but possibly derive from a cosmic impact ~12,900 CAL BP. The karst-collapse cave in Cretaceous limestone on the Edwards Plateau contains ≥ 3.7 m of stratified clays grading to clayey silts recording continuous deposition from 16 ka RC yr to present. The cave’s small catchment area and mode of deposition were constant, and the stratigraphy is well dated based on 162 AMS 14C dates from individual vertebrate fossils, snails, charcoal, and sediment chemical fractions. The cave sequence contains an abundant small animal vertebrate fossil record, exhibiting biostratigraphic changes, and the timing of the late Pleistocene megafaunal extinction is consistent with that elsewhere in North America. At 151 cm below datum is the extremely sharp, smooth contact separating lower, dusky red (2.5YR3/2) clays below from overlying dark reddish brown (5YR3/3) clays (forming a 20-cm-thick dark layer) and dating to 13,000 CAL BP, at or close to the age of the YDB datum elsewhere. This appears to be the most distinctive lithologic change of the deglacial sequence. Sediments at or within 10 cm of this contact contain the local extinction of 4 species of bats, the local extinction of the prairie dog (Cynomys sp.) and perhaps other burrowing mammals in response to decrease in soil thickness, and the uppermost occurrence of 6 late Pleistocene megafaunal taxa that, although rare in the cave, do not extend younger than 12.9 ka. We collected and analyzed sediments at high resolution above and below the distinct lithologic contact at 151 cm. The red clays from 151 to 153 cm and immediately preceding the lithologic contact contain an abundance of nanodiamonds (5 different allotropes), aciniform

  3. Episodes of low dissolved oxygen indicated by ostracodes and sediment geochemistry at Crystal Lake, Illinois, USA

    USGS Publications Warehouse

    Curry, B. Brandon; Filippelli, G.M.

    2010-01-01

    Low dissolved oxygen during the summer and early fall controls profundal continental ostracode distribution in Crystal Lake (McHenry County), Illinois, favoring Cypria ophthalmica and Physocypria globula at water depths from 6 to 13 m. These species also thrived in the lake's profundal zone from 14,165 to 9600 calendar year before present (cal yr b.p.) during the late Boiling, Allerod, and Younger Dryas chronozones, and early Holocene. Characterized by sand, cemented tubules, large aquatic gastropod shells, and littoral ostracode valves, thin (1-6 cm) tempestite deposits punctuate thicker deposits of organic gyttja from 16,080 to 11,900 cal yr b.p. The succeeding 2300 yr (11,900-9600 cal yr b.p.) lack tempestites, and reconstructed water depths were at their maximum. Deposition of marl under relatively well-oxygenated conditions occurred during the remainder of the Holocene until the arrival of Europeans, when the lake returned to a pattern of seasonally low dissolved oxygen. Such conditions are also indicated in the lake sediment by the speciation of phosphorus, high concentrations of organic carbon, and abundant iron and manganese occluded to mineral grains. Initial low dissolved oxygen was probably caused by the delivery of dissolved P and Fe in shallow groundwater, the chemistry of which was influenced by Spodosol pedogenesis under a spruce forest. The triggering may have been regionally warm and wet conditions associated with retreat of the Lake Michigan lobe (south-central Laurentide Ice Sheet). ?? 2010, by the American Society of Limnology and Oceanography Inc.

  4. Potentials and problems of building detailed dust records using peat archives: An example from Store Mosse (the "Great Bog"), Sweden

    NASA Astrophysics Data System (ADS)

    Kylander, Malin E.; Martínez-Cortizas, Antonio; Bindler, Richard; Greenwood, Sarah L.; Mörth, Carl-Magnus; Rauch, Sebastien

    2016-10-01

    Mineral dust deposition is a process often overlooked in northern mid-latitudes, despite its potential effects on ecosystems. These areas are often peat-rich, providing ample material for the reconstruction of past changes in atmospheric deposition. The highly organic (up to 99% in some cases) matrix of atmospherically fed mires, however, makes studying the actual dust particles (grain size, mineralogy) challenging. Here we explore some of the potentials and problems of using geochemical data from conservative, lithogenic elements (Al, Ga, Rb, Sc, Y, Zr, Th, Ti and REE) to build detailed dust records by using an example from the 8900-yr peat sequence from Store Mosse (the ;Great Bog;), which is the largest mire complex in the boreo-nemoral region of southern Sweden. The four dust events recorded at this site were elementally distinct, suggesting different dominant mineral hosts. The oldest and longest event (6385-5300 cal yr BP) sees a clear signal of clay input but with increasing contributions of mica, feldspar and middle-REE-rich phosphate minerals over time. These clays are likely transported from a long-distance source (<100 km). While dust deposition was reduced during the second event (5300-4370 cal yr BP), this is the most distinct in terms of its source character with [Eu/Eu∗]UCC revealing the input of plagioclase feldspar from a local source, possibly active during this stormier period. The third (2380-2200 cal yr BP) and fourth (1275-1080 cal yr BP) events are much shorter in duration and the presence of clays and heavy minerals is inferred. Elemental mass accumulation rates reflect these changes in mineralogy where the relative importance of the four dust events varies by element. The broad changes in major mineral hosts, grain size, source location and approximated net dust deposition rates observed in the earlier dust events of longer duration agree well with paleoclimatic changes observed in northern Europe. The two most recent dust events are much

  5. Optically stimulated luminescence dating of late Holocene raised strandplain sequences adjacent to Lakes Michigan and Superior, Upper Peninsula, Michigan, USA

    USGS Publications Warehouse

    Argyilan, Erin P.; Forman, Steven L.; Johnston, John W.; Wilcox, Douglas A.

    2005-01-01

    This study evaluates the accuracy of optically stimulated luminescence to date well-preserved strandline sequences at Manistique/Thompson bay (Lake Michigan), and Tahquamenon and Grand Traverse Bays (Lake Superior) that span the past ∼4500 yr. The single aliquot regeneration (SAR) method is applied to produce absolute ages for littoral and eolian sediments. SAR ages are compared against AMS and conventional 14C ages on swale organics. Modern littoral and eolian sediments yield SAR ages 14C ages on swale organics. Significant variability in 14C ages >2000 cal yr B.P. complicates comparison to SAR ages at all sites. However, a SAR age of 4280 ± 390 yr (UIC913) on ridge77 at Tahquamenon Bay is consistent with regional regression from the high lake level of the Nipissing II phase ca. 4500 cal yr B.P. SAR ages indicate a decrease in ridge formation rate after ∼1500 yr ago, likely reflecting separation of Lake Superior from lakes Huron and Michigan. This study shows that SAR is a credible alternative to 14C methods for dating littoral and eolian landforms in Great Lakes and other coastal strandplains where 14C methods prove problematic.

  6. Historical anthropogenic contributions to mercury accumulation recorded by a peat core from Dajiuhu montane mire, central China.

    PubMed

    Li, Yuanping; Ma, Chunmei; Zhu, Cheng; Huang, Run; Zheng, Chaogui

    2016-09-01

    Mercury (Hg) accumulation records spanning the last 16,000 years before present (yr BP, relative to AD 1950) were derived from a peat core collected from Dajiuhu mire, central China. The natural Hg concentration and accumulation rate (free from anthropogenic influence) were 135.5 ± 53.9 ng g(-1) and 6.5 ± 4.5 μg m(-2) yr(-1), respectively. The increase in Hg flux that started from a core depth of 96.5 cm (3358 cal yr BP) is independent of soil erosion and organic matter content. We attribute this to an increase in atmospheric Hg deposition derived from regional anthropogenic activities. Anthropogenic Hg accumulation rates (Hg-ARA) in the pre-industrial period peaked during the Ming and the early Qing dynasties (582-100 cal yr BP), with Hg-ARA of 9.9-24.6 and 10.7-24.4 μg m(-2) yr(-1), respectively. In the industrial interval (post∼1850 AD), Hg-ARA increased progressively and reached 32.7 μg m(-2) yr(-1) at the top of the core. Our results indicate the existence of regional atmospheric Hg pollution spanning the past ∼3400 years, and place recent Hg enrichment in central China in a broader historical context. Copyright © 2016 Elsevier Ltd. All rights reserved.

  7. Extent, timing, and climatic significance of latest Pleistocene and Holocene glaciation in the Sierra Nevada, California

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Clark, Douglas Howe

    Despite more than a century of study, scant attention has been paid to the glacial record in the northern end of the Sierra Nevada, and to the smaller moraines deposited after the retreat of the Tioga (last glacial maximum) glaciers. Equilibrium-line altitude (ELA) estimates of the ice fields indicate that the Tioga ELA gradients there are consistent with similar estimates for the southern half of the range, and with an intensification of the modern temperature/precipitation pattern in the region. The Recess Peak advance has traditionally been considered to be mid-Neoglacial age, about 2--3,000 yr B.P., on the basis of relativemore » weathering estimates. Sediment cores of lakes dammed behind moraines correlative with Recess Peak in four widely spaced sites yields a series of high-resolution AMS radiocarbon dates which demonstrate that Recess Peak glaciers retreated before ~13,100 cal yr B.P.. This minimum limiting age indicates that the advance predates the North Atlantic Younger Dryas cooling. It also implies that there have been no advances larger than the Matthes in the roughly 12,000 year interval between it and the Recess Peak advance. This finding casts doubt on several recent studies that claim Younger Dryas glacier advances in western North America. The 13,100 cal yr B.P. date is also a minimum age for deglaciation of the sample sites used to calibrate the in situ production rates of cosmogenic 10Be and 26Al. The discrepancy between this age and the 11,000 cal yr B.P. exposure age assumed in the original calibration introduces a large (> 19%) potential error in late-Pleistocene exposure ages calculated using these production rates.« less

  8. Temporal and spatial climatic controls on Holocene fire-related erosion and sedimentation, Jemez Mountains, New Mexico

    NASA Astrophysics Data System (ADS)

    Fitch, Erin P.; Meyer, Grant A.

    2016-01-01

    In the Jemez Mountains, tree-ring data indicate that low-severity fires characterized the 400 yr before Euro-American settlement, and that subsequent fire suppression promoted denser forests, recent severe fires, and erosion. Over longer timescales, climate change may alter fire regimes; thus, we used fire-related alluvial deposits to assess the timing of moderate- to high-severity fires, their geomorphic impact, and relation to climate over the last 4000 yr. Fire-related sedimentation does not clearly follow millennial-scale climatic changes, but probability peaks commonly correspond with severe drought, e.g., within the interval 1700-1400 cal yr BP, and ca. 650 and ca. 410 cal yr BP. The latter episodes were preceded by prolonged wet intervals that could promote dense stands. Estimated recurrence intervals for fire-related sedimentation are 250-400 yr. Climatic differences with aspect influenced Holocene post-fire response: fire-related deposits constitute 77% of fan sediments from north-facing basins but only 39% of deposits from drier southerly aspects. With sparser vegetation and exposed bedrock, south aspects can generate runoff and sediment when unburned, whereas soil-mantled north aspects produce minor sediment unless severely burned. Recent channel incision appears unprecedented over the last 2300 yr, suggesting that fuel loading and extreme drought produced an anomalously severe burn in 2002.

  9. Climatic and anthropogenic forcing of prehistorical vegetation succession and fire dynamics in the Lago di Como area (N-Italy, Insubria)

    NASA Astrophysics Data System (ADS)

    Martinelli, Elisa; Michetti, Alessandro Maria; Colombaroli, Daniele; Mazzola, Eleonora; Motella De Carlo, Sila; Livio, Franz; Gilli, Adrian; Ferrario, Maria Francesca; Höbig, Nicole; Brunamonte, Fabio; Castelletti, Lanfredo; Tinner, Willy

    2017-04-01

    Combined pollen, charcoal and modeling evidence from the Insubria Region suggests that fire was a major driver of late Holocene vegetation change. However, the extent and timing of fire response dynamics are not clear yet. We use lacustrine sediments from Lago di Como (N-Italy, S-Alps) to assess if the reconstructed vegetation and fire dynamics were relevant at large scales and if they coincided in time with those observed at smaller sites. The lake, due to its size (142 km2) and economic potential, was very attractive for early land use and human presence in this area is well documented since ca. 10,000 yrs ago (Mesolithic). We used pollen, plant macrofossils and charcoal to reconstruct the vegetation composition and fire activity. During the Younger Dryas and the Early Holocene until ca. 8000 cal BP natural dynamics prevailed. Subsequently, land use and slash-and-burn activities increased at the Mesolithic-Neolithic transition and became widespread around ca. 6500 cal BP. Microscopic charcoal and numerical analyses demonstrate that anthropogenic fires had a determinant influence on long-term vegetation dynamics at regional scales in Insubria. Microscopic charcoal and pollen and spores indicative of land use show that human pressure intensified after ca. 5300 cal yr BP and even more since ca. 4300 cal yr BP. Our results suggest that important species which disappeared or were strongly reduced by land use and fire (e.g. Abies alba, Tilia, Ulmus) will potentially reestablish in the Lago di Como area and elsewhere in Insubria, if land abandonment initiated in the 1950s will continue.

  10. Millenial-scale climatic and vegetation changes in a northern Cerrado (Northeast, Brazil) since the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Ledru, Marie-Pierre; Ceccantini, Gregorio; Gouveia, Susy E. M.; López-Sáez, José Antonio; Pessenda, Luiz C. R.; Ribeiro, Adauto S.

    2006-05-01

    In the Southern Hemisphere, lacustrine sediments started to be deposited with the beginning of the deglaciation at ca 19,000 cal yr BP. At this time the region of Lake Caço was dominated by sparse and shrubby vegetation with dominance of steppic grasses in a poor sandy soil. The landscape did not present any ecological characteristics of a modern Cerrado. However single pollen grains of two Cerrado indicators, Byrsonima and Mimosa, suggest that some Cerrado species were able to survive under the prevailing arid climate, probably as small shrubs. After 15,500 cal yr BP, a sudden increase in the moisture rates is evidenced with the progressive expansion of rainforest showing successive dominance of various associations of taxa. The development of the forest stopped abruptly at the end of the Pleistocene between 12,800 and 11,000 cal yr BP, as attested by strong fires and the expansion of Poaceae. In the early Holocene an open landscape with a relatively high level of water in the lake preceded the progressive expansion of Cerrado species towards a denser forested landscape; fires are recorded from then on, resulting in the physiognomy of the Cerrado we know today. Late Pleistocene paleoenvironmental records from northern Brazil reflect the interplay between insolation forcing of two hemispheres with the local components represented by the interannual shift of the Inter Tropical Convergence Zone and the influence of seasonal equatorwards polar air incursions.

  11. Late Holocene expansion of Siberian dwarf pine (Pinus pumila) in Kamchatka in response to increased snow cover as inferred from lacustrine oxygen-isotope records

    NASA Astrophysics Data System (ADS)

    Hammarlund, Dan; Klimaschewski, Andrea; St. Amour, Natalie A.; Andrén, Elinor; Self, Angela E.; Solovieva, Nadia; Andreev, Andrei A.; Barnekow, Lena; Edwards, Thomas W. D.

    2015-11-01

    Holocene records of cellulose-inferred lake-water δ18O were produced from two lake-sediment sequences obtained in central and northern Kamchatka, Russian Far East. The sediment records share similar fluctuations in δ18O during the interval of ca. 5000-800 cal yr BP that correspond (inversely) with changes in K+ content of the GISP2 ice-core record from Greenland, a proxy for the relative strength of the Siberian High, suggesting control by climate-related variability in δ18O of regional precipitation. The dramatic expansion of Siberian dwarf pine (Pinus pumila) in northern and central Kamchatka between ca. 5000 and 4000 cal yr BP, as inferred from pollen records from the same and neighbouring sites, appears to have occurred at a time of progressively declining δ18O of precipitation. This development is interpreted as reflecting a regional cooling trend accompanied by increasing winter snowfall related to gradual intensification of the Siberian High from ca. 5000 to ca. 3000 cal yr BP. A thicker and more long-lasting snow cover can be assumed to have favoured P. pumila by providing a competitive advantage over other boreal and subalpine tree and shrub species in the region during the later part of the Holocene. These results, which are the first of their kind from Kamchatka, provide novel insight into the Holocene vegetational and climatic development in easternmost Asia, as well as long-term atmospheric circulation dynamics in Beringia.

  12. Climatic oscillations in central Italy during the Last Glacial-Holocene transition: the record from Lake Accesa

    NASA Astrophysics Data System (ADS)

    Magny, Michel; de Beaulieu, Jacques-Louis; Drescher-Schneider, Ruth; Vannière, Boris; Walter-Simonnet, Anne-Véronique; Millet, Laurent; Bossuet, Gilles; Peyron, Odile

    2006-05-01

    This paper presents an event stratigraphy based on data documenting the history of vegetation cover, lake-level changes and fire frequency, as well as volcanic eruptions, over the Last Glacial-early Holocene transition from a terrestrial sediment sequence recovered at Lake Accesa in Tuscany (north-central Italy). On the basis of an age-depth model inferred from 13 radiocarbon dates and six tephra horizons, the Oldest Dryas-Bølling warming event was dated to ca. 14 560 cal. yr BP and the Younger Dryas event to ca. 12 700-11 650 cal. yr BP. Four sub-millennial scale cooling phases were recognised from pollen data at ca. 14 300-14 200, 13 900-13 700, 13 400-13 100 and 11 350-11 150 cal.yrBP. The last three may be Mediterranean equivalents to the Older Dryas (GI-1d), Intra-Allerød (GI-1b) and Preboreal Oscillation (PBO) cooling events defined from the GRIP ice-core and indicate strong climatic linkages between the North Atlantic and Mediterranean areas during the last Termination. The first may correspond to Intra-Bølling cold oscillations registered by various palaeoclimatic records in the North Atlantic region. The lake-level record shows that the sub-millennial scale climatic oscillations which punctuated the last deglaciation were associated in central Italy with different successive patterns of hydrological changes from the Bølling warming to the 8.2ka cold reversal. Copyright

  13. Dynamics of marsh-mangrove ecotone since the mid-Holocene: A palynological study of mangrove encroachment and sea level rise in the Shark River Estuary, Florida

    PubMed Central

    Liu, Kam-biu

    2017-01-01

    Sea level rise and the associated inland shift of the marsh-mangrove ecotone in south Florida have raised many scientific and management concerns in recent years. Holocene paleoecological records can provide an important baseline to shed light on the long-term dynamics of vegetation changes across this ecotone in the past, which is needed to predict the future. In this study, we present palynological, X-ray fluorescence, and loss-on ignition data from four sedimentary cores recovered from a 20-km marine-to-freshwater transect along the Shark River Estuary, southwest Everglades, to document the patterns and processes of coastal vegetation changes in response to sea level rise since the mid-Holocene. Our record indicates that freshwater marsh progressively replaced marl prairies at the Shark River Estuary between 5700 and 4400 cal yr BP. As marine transgression continued, marine influence reached the threshold necessary for mangroves to establish at the current mouth of the Shark River Slough at 3800 cal yr BP. During the next 3000 years, although sea level rise in the Western North Atlantic slowed down to 0.4 mm/yr, a spatial and temporal gradient was evident as the marsh-mangrove ecotone shifted inland by 20 km from 3800 to 800 cal yr BP, accompanied by a gradual landward replacement of freshwater marsh by mangrove forest. If sea level continues to rise at 2.33 mm/yr in the 21st century in south Florida, it is possible that marine influence will reach the threshold for mangroves to establish in the central Everglades, and we could expect a much more aggressive mangrove encroachment toward the northern and interior parts of south Florida in the next few centuries. PMID:28282415

  14. Dynamics of marsh-mangrove ecotone since the mid-Holocene: A palynological study of mangrove encroachment and sea level rise in the Shark River Estuary, Florida.

    PubMed

    Yao, Qiang; Liu, Kam-Biu

    2017-01-01

    Sea level rise and the associated inland shift of the marsh-mangrove ecotone in south Florida have raised many scientific and management concerns in recent years. Holocene paleoecological records can provide an important baseline to shed light on the long-term dynamics of vegetation changes across this ecotone in the past, which is needed to predict the future. In this study, we present palynological, X-ray fluorescence, and loss-on ignition data from four sedimentary cores recovered from a 20-km marine-to-freshwater transect along the Shark River Estuary, southwest Everglades, to document the patterns and processes of coastal vegetation changes in response to sea level rise since the mid-Holocene. Our record indicates that freshwater marsh progressively replaced marl prairies at the Shark River Estuary between 5700 and 4400 cal yr BP. As marine transgression continued, marine influence reached the threshold necessary for mangroves to establish at the current mouth of the Shark River Slough at 3800 cal yr BP. During the next 3000 years, although sea level rise in the Western North Atlantic slowed down to 0.4 mm/yr, a spatial and temporal gradient was evident as the marsh-mangrove ecotone shifted inland by 20 km from 3800 to 800 cal yr BP, accompanied by a gradual landward replacement of freshwater marsh by mangrove forest. If sea level continues to rise at 2.33 mm/yr in the 21st century in south Florida, it is possible that marine influence will reach the threshold for mangroves to establish in the central Everglades, and we could expect a much more aggressive mangrove encroachment toward the northern and interior parts of south Florida in the next few centuries.

  15. Sedimentary evidence of landscape and climate history since the end of MIS 3 in the Krkonoše Mountains, Czech Republic

    NASA Astrophysics Data System (ADS)

    Engel, Zbyněk; Nývlt, Daniel; Křížek, Marek; Treml, Václav; Jankovská, Vlasta; Lisá, Lenka

    2010-04-01

    A sedimentary core recovered from the cirque basin of Labský důl valley (1039 m a.s.l.) in the Krkonoše Mountains reflects the environmental history for approximately the last 30,000 years. Analyses of magnetic susceptibility, carbon content, pollen assemblages and macrofossil data in a 15 m thick sediment sequence provide the first continuous record of Lateglacial and Holocene vegetation history in Sudetes region of the Czech Republic. The succession of sedimentary units in the lower part of the core suggests that the cirque was ice-free before the onset of the last glaciation at the beginning of marine isotope stage 2. Highly variable climate prevailed during this period with cold conditions culminating about 18 cal ka BP. Cold climates persisted until the Lateglacial period, evidenced by an identified warming and subsequent cooling event correlated with the Younger Dryas period. Sparse, treeless vegetation dominated in the catchment area at that time. The sequence of interrupted thinly laminated silts reflects the retreat and temporary readvance of a local glacier in the cirque during 12.5-10.8 cal ka BP. Subsequently, the alpine treeline ecotone gradually shifted above the cirque floor. Palaeoclimatic conditions in the early Holocene fluctuated strongly, whereas since 5.1 cal ka BP conditions have been more stable. Pollen-based climate reconstructions suggest significant cooling at around 9.8-9.3, 7.7-7.5 and 4.0-3.3 cal ka BP. Spruce forests have dominated the site since 5.0 cal ka BP when the vegetation became similar to the modern one. Two phases of increased sedimentation were identified within the Holocene culminating about 9.2-7.5 cal ka BP and 5.8-5.5 cal ka BP. Sediment yield was as high as 2.4 mm yr -1 during the period, reflecting environmental changes during the Atlantic/Sub-Boreal transition.

  16. Developmental evolution of flowering plant pollen tube cell walls: callose synthase (CalS) gene expression patterns

    PubMed Central

    2011-01-01

    Background A number of innovations underlie the origin of rapid reproductive cycles in angiosperms. A critical early step involved the modification of an ancestrally short and slow-growing pollen tube for faster and longer distance transport of sperm to egg. Associated with this shift are the predominantly callose (1,3-β-glucan) walls and septae (callose plugs) of angiosperm pollen tubes. Callose synthesis is mediated by callose synthase (CalS). Of 12 CalS gene family members in Arabidopsis, only one (CalS5) has been directly linked to pollen tube callose. CalS5 orthologues are present in several monocot and eudicot genomes, but little is known about the evolutionary origin of CalS5 or what its ancestral function may have been. Results We investigated expression of CalS in pollen and pollen tubes of selected non-flowering seed plants (gymnosperms) and angiosperms within lineages that diverged below the monocot/eudicot node. First, we determined the nearly full length coding sequence of a CalS5 orthologue from Cabomba caroliniana (CcCalS5) (Nymphaeales). Semi-quantitative RT-PCR demonstrated low CcCalS5 expression within several vegetative tissues, but strong expression in mature pollen. CalS transcripts were detected in pollen tubes of several species within Nymphaeales and Austrobaileyales, and comparative analyses with a phylogenetically diverse group of sequenced genomes indicated homology to CalS5. We also report in silico evidence of a putative CalS5 orthologue from Amborella. Among gymnosperms, CalS5 transcripts were recovered from germinating pollen of Gnetum and Ginkgo, but a novel CalS paralog was instead amplified from germinating pollen of Pinus taeda. Conclusion The finding that CalS5 is the predominant callose synthase in pollen tubes of both early-diverging and model system angiosperms is an indicator of the homology of their novel callosic pollen tube walls and callose plugs. The data suggest that CalS5 had transient expression and pollen

  17. Mass-movement and flood-induced deposits in Lake Ledro, southern Alps, Italy: implications for Holocene palaeohydrology and natural hazards

    NASA Astrophysics Data System (ADS)

    Simonneau, A.; Chapron, E.; Vannière, B.; Wirth, S. B.; Gilli, A.; Di Giovanni, C.; Anselmetti, F. S.; Desmet, M.; Magny, M.

    2013-03-01

    High-resolution seismic profiles and sediment cores from Lake Ledro combined with soil and riverbed samples from the lake's catchment area are used to assess the recurrence of natural hazards (earthquakes and flood events) in the southern Italian Alps during the Holocene. Two well-developed deltas and a flat central basin are identified on seismic profiles in Lake Ledro. Lake sediments have been finely laminated in the basin since 9000 cal. yr BP and frequently interrupted by two types of sedimentary events (SEs): light-coloured massive layers and dark-coloured graded beds. Optical analysis (quantitative organic petrography) of the organic matter present in soil, riverbed and lacustrine samples together with lake sediment bulk density and grain-size analysis illustrate that light-coloured layers consist of a mixture of lacustrine sediments and mainly contain algal particles similar to the ones observed in background sediments. Light-coloured layers thicker than 1.5 cm in the main basin of Lake Ledro are synchronous to numerous coeval mass-wasting deposits remoulding the slopes of the basin. They are interpreted as subaquatic mass-movements triggered by historical and pre-historical regional earthquakes dated to AD 2005, AD 1891, AD 1045 and 1260, 2545, 2595, 3350, 3815, 4740, 7190, 9185 and 11 495 cal. yr BP. Dark-coloured SEs develop high-amplitude reflections in front of the deltas and in the deep central basin. These beds are mainly made of terrestrial organic matter (soils and lignocellulosic debris) and are interpreted as resulting from intense hyperpycnal flood event. Mapping and quantifying the amount of soil material accumulated in the Holocene hyperpycnal flood deposits of the sequence allow estimating that the equivalent soil thickness eroded over the catchment area reached up to 5 mm during the largest Holocene flood events. Such significant soil erosion is interpreted as resulting from the combination of heavy rainfall and snowmelt. The recurrence of

  18. Multidisciplinary distinction of mass-movement and flood-induced deposits in lacustrine environments: implications for Holocene palaeohydrology and natural hazards (Lake Ledro, Southern Alps, Italy)

    NASA Astrophysics Data System (ADS)

    Simonneau, A.; Chapron, E.; Vannière, B.; Wirth, S. B.; Gilli, A.; Di Giovanni, C.; Anselmetti, F. S.; Desmet, M.; Magny, M.

    2012-08-01

    High-resolution seismic profiles and sediment cores from Lake Ledro combined with soil and river-bed samples from the lake's catchment area are used to assess the recurrence of natural hazards (earthquakes and flood events) in the southern Italian Alps during the Holocene. Two well-developed deltas and a flat central basin are identified on seismic profiles in Lake Ledro. Lake sediments are finely laminated in the basin since 9000 cal. yr BP and frequently interrupted by two types of sedimentary events: light-coloured massive layers and dark-coloured graded beds. Optical analysis (quantitative organic petrography) of the organic matter occurring in soils, river beds and lacustrine samples together with lake-sediment bulk density and grain-size analysis illustrate that light-coloured layers consist of a mixture of lacustrine sediments and mainly contain algal particles similar to the ones observed in background sediments. Light-coloured layers thicker than 1.5 cm in the main basin of Lake Ledro are dense and synchronous to numerous coeval mass-wasting deposits remoulding the slopes of the basin. They are interpreted as subaquatic mass movements triggered by historical and pre-historical regional earthquakes dated to 2005 AD, 1891 AD, 1045 AD and 1260, 2545, 2595, 3350, 3815, 4740, 7190, 9185 and 11495 cal. yr BP. Dark-coloured sedimentary event are dense and develop high-amplitude reflections in front of the deltas and in the deep central basin. These beds are mainly made of terrestrial organic matter (soils and ligno-cellulosic debris) and are interpreted as resulting from intense hyperpycnal flood events. Mapping and quantifying the amount of soil material accumulated in the Holocene hyperpycnal flood deposits of the sequence and applying the De Ploey erosion model allow estimating that the equivalent soil thickness eroded over the catchment area reached up to 4 mm during the largest Holocene flood events. Such significant soil erosion is interpreted as resulting

  19. Bayesian chronological analyses consistent with synchronous age of 12,835–12,735 Cal B.P. for Younger Dryas boundary on four continents

    PubMed Central

    Kennett, James P.; Kennett, Douglas J.; Culleton, Brendan J.; Aura Tortosa, J. Emili; Bischoff, James L.; Bunch, Ted E.; Daniel, I. Randolph; Erlandson, Jon M.; Ferraro, David; Firestone, Richard B.; Goodyear, Albert C.; Israde-Alcántara, Isabel; Johnson, John R.; Jordá Pardo, Jesús F.; Kimbel, David R.; LeCompte, Malcolm A.; Lopinot, Neal H.; Mahaney, William C.; Moore, Andrew M. T.; Moore, Christopher R.; Ray, Jack H.; Stafford, Thomas W.; Tankersley, Kenneth Barnett; Wittke, James H.; Wolbach, Wendy S.; West, Allen

    2015-01-01

    The Younger Dryas impact hypothesis posits that a cosmic impact across much of the Northern Hemisphere deposited the Younger Dryas boundary (YDB) layer, containing peak abundances in a variable assemblage of proxies, including magnetic and glassy impact-related spherules, high-temperature minerals and melt glass, nanodiamonds, carbon spherules, aciniform carbon, platinum, and osmium. Bayesian chronological modeling was applied to 354 dates from 23 stratigraphic sections in 12 countries on four continents to establish a modeled YDB age range for this event of 12,835–12,735 Cal B.P. at 95% probability. This range overlaps that of a peak in extraterrestrial platinum in the Greenland Ice Sheet and of the earliest age of the Younger Dryas climate episode in six proxy records, suggesting a causal connection between the YDB impact event and the Younger Dryas. Two statistical tests indicate that both modeled and unmodeled ages in the 30 records are consistent with synchronous deposition of the YDB layer within the limits of dating uncertainty (∼100 y). The widespread distribution of the YDB layer suggests that it may serve as a datum layer. PMID:26216981

  20. Mid- to late Holocene climate-driven regime shifts inferred from diatom, ostracod and stable isotope records from Lake Son Kol (Central Tian Shan, Kyrgyzstan)

    NASA Astrophysics Data System (ADS)

    Schwarz, Anja; Turner, Falko; Lauterbach, Stefan; Plessen, Birgit; Krahn, Kim J.; Glodniok, Sven; Mischke, Steffen; Stebich, Martina; Witt, Roman; Mingram, Jens; Schwalb, Antje

    2017-12-01

    Arid Central Asia represents a key region for understanding climate variability and interactions in the Northern Hemisphere. Patterns and mechanisms of Holocene climate change in arid Central Asia are, however, only partially understood. Multi-proxy data combining diatom, ostracod, sedimentological, geochemical and stable isotope analyses from a ca. 6000-year-old lake sediment core from Son Kol (Central Kyrgyzstan) show distinct and repeated changes in species assemblages. Diatom- and ostracod-inferred conductivity shifts between meso-euhaline and freshwater conditions suggest water balance and regime shifts. Organism-derived data are corroborated by stable isotope, mineralogical and geochemical records, underlining that Son Kol was affected by strong lake level fluctuations of several meters. The δ13Ccarb/δ18Ocarb correlation shows repeated switchovers from a closed to an open lake system. From 6000 to 3800 and 3250 to 1950 cal. yr BP, Son Kol was a closed basin lake with higher conductivities, increased nutrient availability and a water level located below the modern outflow. Son Kol became again a hydrologically open lake at 3800 and 1950 cal. yr BP. Comparisons to other local and regional paleoclimate records indicate that these regime shifts were largely controlled by changing intensity and position of the Westerlies and the Siberian Anticyclone that triggered changes in the amount of winter precipitation. A strong influence of the Westerlies ca. 5000-4400, 3800-3250 and since 1950 cal. yr BP enhanced the amount of precipitation during spring, autumn and winter, whereas cold and dry winters prevailed during phases with a strong Siberian Anticyclone and southward shifted Westerlies at ca. 6000-5000, 4400-3800 and 3250-1950 cal. yr BP. Similarities between variations in winter precipitation at Son Kol and records of the predominant NAO-mode further suggest a teleconnection between wet (dry) winter climate in Central Asia and a positive (negative) NAO

  1. Paleoenvironmental evolution of the coastal plain of Southern Brazil: palynological data from a Holocene core in Santa Catarina State.

    PubMed

    Kuhn, Lidia A; Souza, Paulo A; Cancelli, Rodrigo R; Silva, Wagner G; Macedo, Renato B

    2017-01-01

    This paper presents a paleoenvironmental reconstruction from palynological analyses of a sedimentary core of Holocene age, drilled at municipality of Garopaba (Santa Catarina), Southern Brazil. A total of 46 samples was collected for palynological analyses in the 450 cm-long core PCSC-3, as also three samples for radiocarbon dating and granulometric analyses. The palynological content includes 84 taxa related to pollen grains of angiosperms (38) and gimnosperm (3), spores of pteridophyta (16) and bryophyta (2), spores of fungi (8), algae (3), acritarchs (3), dinoflagellate cysts (2) and microforaminiferal linings (1). Three specimens of acritarchs are described and illustrated in detail. Three palynological phases were defined based on changes in assemblages: Phase I, Phase II and Phase III. The Phase I is characterized as a lagoonal paleoenvironment with marine influence from the beginning of the sedimentation (5390 cal yr BP), based on occurrences of acritarchs, dinoflagellate cysts and microforaminiferal linings. The Phase II (3032 yr BP until 858 cal yr BP) also is characterized by a lagoonal paleoenvironment, however, presented decrease in percentage of marine elements and increase in freshwater algae record, suggesting less marine influence in the lagoonal body. In Phase III (last 856 years), underwater sedimentation prevailed, under swamp-like conditions.

  2. Uplift and subsidence reveal a nonpersistent megathrust rupture boundary (Sitkinak Island, Alaska)

    USGS Publications Warehouse

    Briggs, Richard W.; Engelhart, Simon E.; Nelson, Alan R.; Dura, Tina; Kemp, Andrew C.; Haeussler, Peter J.; Corbett, D. Reide; Angster, Stephen J.; Bradley, Lee-Ann

    2014-01-01

    We report stratigraphic evidence of land-level change and tsunami inundation along the Alaska-Aleutian megathrust during prehistoric and historical earthquakes west of Kodiak Island. On Sitkinak Island, cores and tidal outcrops fringing a lagoon reveal five sharp lithologic contacts that record coseismic land-level change. Radiocarbon dates, 137Cs profiles, CT scans, and microfossil assemblages are consistent with rapid uplift ca. 290-0, 520-300, and 1050-790 cal yr BP, and subsidence in AD 1964 and ca. 640-510 cal yr BP. Radiocarbon, 137Cs, and 210Pb ages bracketing a sand bed traced 1.5 km inland and evidence for sudden uplift are consistent with Russian accounts of an earthquake and tsunami in AD 1788. The mixed uplift and subsidence record suggests that Sitkinak Island sits above a non-persistent boundary near the southwestern limit of the AD 1964 Mw 9.2 megathrust rupture.

  3. Selective transport of palynomorphs in marine turbiditic deposits: An example from the Ascension-Monterey Canyon system offshore central California

    USGS Publications Warehouse

    McGann, Mary

    2017-01-01

    The pollen assemblage of a deep-sea core (15G) collected at lower bathyal depths (3491 m) on a levee of Monterey Canyon off central California was investigated to gain insights into the delivery processes of terrigenous material to submarine fans and the effect this transport has on the palynological record. Thirty-two samples were obtained down the length of the core, 19 from hemipelagic and mixed mud deposits considered to be the background record, and 13 others from displaced flow deposits. The pollen record obtained from the background samples documents variations in the terrestrial flora as it adapted to changing climatic conditions over the last 19,000 cal yrs BP. A Q-mode cluster analysis defined three pollen zones: a Glacial Pollen Zone (ca. 20,000–17,000 cal yr BP), an overlying Transitional Pollen Zone (ca. 17,000–11,500 cal yr BP), and an Interglacial Pollen Zone (ca. 11,500 cal yr BP to present). Another Q-mode cluster analysis, of both the background mud and flow deposits, also defined these three pollen zones, but four of the 13 turbiditic deposits were assigned to pollen zones older than expected by their stratigraphic position. This was due to these samples containing statistically significant fewer palynomorphs than the background muds as well as being enriched (∼10–35% in some cases) in hydraulically-efficient Pinus pollen. A selective bias in the pollen assemblage, such as demonstrated here, may result in incorrect interpretations (e.g., climatic shifts or environmental perturbations) based on the floral record, indicating turbiditic deposits should be avoided in marine palynological studies. Particularly in the case of fine-grained flow deposits that may not be visually distinct, granulometry and grain size frequency distribution curves may not be enough to identify these biased deposits. Determining the relative abundance and source of displaced shallow-water benthic foraminifera entrained in these sediments serves as an excellent

  4. Effects of late Holocene climate variability and anthropogenic stressors on the vegetation of the Maya highlands

    NASA Astrophysics Data System (ADS)

    Franco-Gaviria, F.; Correa-Metrio, A.; Cordero-Oviedo, C.; López-Pérez, M.; Cárdenes-Sandí, G. M.; Romero, F. M.

    2018-06-01

    Climate variability and human activities have shaped the vegetation communities of the Maya region of southern Mexico and Central America on centennial to millennial timescales. Most research efforts in the region have focused on the lowlands, with relatively little known about the environmental history of the regional highlands. Here we present data from two sediment sequences collected from lakes in the highlands of Chiapas, Mexico. Our aim was to disentangle the relative contributions of climate and human activities in the development of regional vegetation during the late Holocene. The records reveal a long-term trend towards drier conditions with superimposed centennial-scale droughts. A declining moisture trend from 3400 to 1500 cal yr BP is consistent with previously reported southward displacement of the Intertropical Convergence Zone, whereas periodic droughts were probably a consequence of drivers such as El Niño. These conditions, together with dense human occupation, converted the vegetation from forest to more open systems. According to the paleoecological records, cultural abandonment of the area occurred ca. 1500 cal yr BP, favoring forest recovery that was somewhat limited by low moisture availability. About 600 cal yr BP, wetter conditions promoted the establishment of modern montane cloud forests, which consist of a diverse mixture of temperate and tropical elements. The vegetation types that occupied the study area during the last few millennia have remained within the envelope defined by the modern vegetation mosaic. This finding highlights the importance of microhabitats in the maintenance biodiversity through time, even under scenarios of high climate variability and anthropogenic pressure.

  5. A 75 ka Stalagmite Paleoclimate Record from Northern Venezuela

    NASA Astrophysics Data System (ADS)

    Retrum, J. B.; Gonzalez, L. A.; Edwards, R.; Tincher, S. M.; Cheng, H.; Urbani, F.

    2011-12-01

    A stalagmite collected from Cueva Zarraga in the northern Venezuelan Andes was analyzed to determine local paleoclimatic history and help examine climate change in the Caribbean. Ages were determined by U/Th disequilibrium and the stalagmite shows a nearly complete record for ~ 75 ka. Two significant periods of non-deposition have been identified. The first period ranges between the Last Glacial Maximum at 19,820 ± 149 cal yr BP and a brief resumption of stalagmite growth at 15,409 ± 747 cal yr BP, likely representing the Bølling-Allerød interstadial. After the brief period of deposition, growth does not resume unil the Holocene at 10,408 ± 78 cal yr BP. Carbon and oxygen isotopes show a major depletion shift from the last glacial period to the Holocene, suggesting warmer and wetter conditions during the Holocene. The oxygen isotope depletion shift is also seen in the Cariaco Basin foraminifera record off the northern coast of Venezuela. While tempting to attribute δ13C depletion to decrease of the C4 plant contribution, there is no evidence that the area experience major vegetation changes. We attribute the δ13C depletion to enhanced recycling of soil CO2 resulting from canopy effects. Today, Cueva Zarraga is at the northern extent of the Inter-Tropical Convergence Zone (ITCZ). The cooler and drier conditions of the last glacial period suggest a southern displacement of the ITCZ. The close proximity of Cueva Zarraga to Cariaco Basin may allow for a high resolution tropical terrestrial and oceanic climatic response comparison.

  6. Methane turnover and environmental change from Holocene biomarker records in a thermokarst lake in Arctic Alaska

    USGS Publications Warehouse

    Elvert, Marcus; Pohlman, John; Becker, Kevin W.; Gaglioti, Benjamin V.; Hinrichs, Kai-Uwe; Wooller, Matthew J.

    2016-01-01

    Arctic lakes and wetlands contribute a substantial amount of methane to the contemporary atmosphere, yet profound knowledge gaps remain regarding the intensity and climatic control of past methane emissions from this source. In this study, we reconstruct methane turnover and environmental conditions, including estimates of mean annual and summer temperature, from a thermokarst lake (Lake Qalluuraq) on the Arctic Coastal Plain of northern Alaska for the Holocene by using source-specific lipid biomarkers preserved in a radiocarbon-dated sediment core. Our results document a more prominent role for methane in the carbon cycle when the lake basin was an emergent fen habitat between ~12,300 and ~10,000 cal yr BP, a time period closely coinciding with the Holocene Thermal Maximum (HTM) in North Alaska. Enhanced methane turnover was stimulated by relatively warm temperatures, increased moisture, nutrient supply, and primary productivity. After ~10,000 cal yr BP, a thermokarst lake with abundant submerged mosses evolved, and through the mid-Holocene temperatures were approximately 3°C cooler. Under these conditions, organic matter decomposition was attenuated, which facilitated the accumulation of submerged mosses within a shallower Lake Qalluuraq. Reduced methane assimilation into biomass during the mid-Holocene suggests that thermokarst lakes are carbon sinks during cold periods. In the late-Holocene from ~2700 cal yr BP to the most recent time, however, temperatures and carbon deposition rose and methane oxidation intensified, indicating that more rapid organic matter decomposition and enhanced methane production could amplify climate feedback via potential methane emissions in the future.

  7. Late Holocene climate change in the western Mediterranean: centennial-scale vegetation and North Atlantic Oscillation variability

    NASA Astrophysics Data System (ADS)

    Ramos Román, M. J.; Jimenez-Moreno, G.; Anderson, R. S.; García-Alix, A.; Toney, J. L.; Jiménez-Espejo, F. J. J.; Carrión, J. S.

    2015-12-01

    Sediments from alpine peat bogs and lakes from the Sierra Nevada in southeastern Spain (western Mediterranean area) have been very informative in terms of how vegetation and wetland environments were impacted by past climate change. Recently, many studies try to find out the relationship between solar activity, atmosphere and ocean dynamics and changes in the terrestrial environments. The Mediterranean is a very sensitive area with respect to atmospheric dynamics due to (1) its location, right in the boundary between subtropical and temperate climate systems and (2) the North Atlantic Oscillation (NAO) is one of the main mechanism that influence present climate in this area. Here we present a multi-proxy high-resolution study from Borreguil de la Caldera (BdlC), a peat bog that records the last ca. 4500 cal yr BP of vegetation, fire, human impact and climate history from the Sierra Nevada. The pollen, charcoal and non-pollen palynomorphs (NPPs) reconstruction in the BdlC-01 record evidence relative humidity changes in the last millennia interrupting the late Holocene aridification trend. This study shows a relative arid period between ca. 4000 and 3100 cal yr BP; the Iberian Roman humid period (ca. 2600 to 1600 cal yr BP); a relative arid period during the Dark Ages (from ca. AD 500 to AD 900) and Medieval Climate Anomaly (from ca. AD 900 to ca. AD 1300) and predominantly wetter conditions corresponding with The Little Ice Age period (from ca. AD 1300 to AD 1850). This climate variability could be explained by centennial scale changes in the NAO and solar activity.

  8. Late Holocene vegetation and climate change on the southeastern Tibetan Plateau: Implications for the Indian Summer Monsoon and links to the Indian Ocean Dipole

    NASA Astrophysics Data System (ADS)

    Li, Kai; Liu, Xingqi; Wang, Yongbo; Herzschuh, Ulrike; Ni, Jian; Liao, Mengna; Xiao, Xiayun

    2017-12-01

    The Indian Summer Monsoon (ISM) is one of the most important climate systems, whose variability and driving mechanisms are of broad interest for academic and societal communities. Here, we present a well-dated high-resolution pollen analysis from a 4.82-m long sediment core taken from Basomtso, in the southeastern Tibetan Plateau (TP), which depicts the regional climate changes of the past millennium. Our results show that subalpine coniferous forest was dominant around Basomtso from ca. 867 to ca. 750 cal. yr BP, indicating a warm and semi-humid climate. The timberline in the study area significantly decreased from ca. 750 to ca. 100 cal. yr BP, and a cold climate, corresponding to the Little Ice Age (LIA) prevailed. Since ca. 100 cal. yr BP, the vegetation type changed to forest-meadow with rising temperatures and moisture. Ordination analysis reveals that the migration of vegetation was dominated by regional temperatures and then by moisture. Further comparisons between the Basomtso pollen record and the regional temperature reconstructions underscore the relevance of the Basomtso record from the southeastern TP for regional and global climatologies. Our pollen based moisture reconstruction demonstrates the strong multicentennial-scale link to ISM variability, providing solid evidence for the increase of monsoonal strengths over the past four centuries. Spectral analysis indicates the potential influence of solar forcing. However, a closer relationship has been observed between multicentennial ISM variations and Indian Ocean sea surface temperature anomalies (SSTs), suggesting that the variations in monsoonal precipitation over the southeastern TP are probably driven by the Indian Ocean Dipole on the multicentennial scale.

  9. Environmental Change recorded in Lacustrine Sediments from Tangra Yumco, Tibetan Plateau, at 16.5 ka cal BP and during the Younger Dryas Chronozone

    NASA Astrophysics Data System (ADS)

    Henkel, K.; Ahlborn, M.; Haberzettl, T.; Kasper, T.; Daut, G.; Ju, J.; Ma, Q.; Wang, J.; Zhu, L.; Maeusbacher, R.

    2013-12-01

    In the purpose of understanding the recent climate change on the Tibetan Plateau (TP) and beyond and to allow predictions for future climate scenarios it is imperative to investigate past climate changes. The numerous lake systems on the TP serve as ideal archives for past hydrological changes, which are assumed to be caused by variations in strength and extent of monsoonal air masses. By now, the spatial and temporal monsoonal evolution on the TP is intensively discussed. With the focus on a W-E lake transect on the southern TP we investigate lakes with a multi-dating and multi-proxy analyses approach, which has already been successfully carried out on Nam Co, the easternmost lake of the transect. In this study, we present results from a ~11.5 m long lacustrine sediment record from the terminal lake Tangra Yumco (4,540 m a.s.l., 31°13'N, 86°43'E), representing the center of the transect. Tangra Yumco is the deepest lake recorded on the TP so far. Via a hydro-acoustic survey observed submerged beach berms (45 m below recent lake level) and exposed lake level terraces up to ~205 m above lake level indicate large lake level fluctuations in the past. The record consists of an interbedding of fine grained silty sediments with a lamination of different thicknesses (sub-mm to cm) and partly intercalated blackish sandy layers. Homogeneous areas, which occur especially in the upper two thirds of the profile, represent turbidite deposits. Until now, color- and greyscale-, magnetic susceptibility- and XRF-scanning were applied. For age control 22 14C AMS-radiocarbon measurements were carried out on bulk organic matter. To determine a possible carbon reservoir effect, additional surface sediment samples were measured as well as one modern aquatic plant. The results indicate a reservoir effect of ~2,120 +110/-90 years. Assuming a constant reservoir effect, the base of the record reveals a corrected radiocarbon age of 17,270 +325/-310 cal BP. The sediment accumulation rate is

  10. A robust, multisite Holocene history of drift ice off northern Iceland: Implications for North Atlantic climate

    USGS Publications Warehouse

    Andrews, John T.; Darby, D.; Eberle, D.; Jennings, A.E.; Moros, M.; Ogilvie, A.

    2009-01-01

    An important indicator of Holocene climate change is provided by evidence for variations in the extent of drift ice. A proxy for drift ice in Iceland waters is provided by the presence of quartz. Quantitative x-ray diffraction analysis of the < 2 mm sediment fraction was undertaken on 16 cores from around Iceland. The quartz weight (wt.)% estimates from each core were integrated into 250-yr intervals between ????'0.05 and 11.7 cal. ka BP. Median quartz wt.% varied between 0.2 and 3.4 and maximum values ranged between 2.8 and 11.8 wt.%. High values were attained in the early Holocene and minimum values were reached 6 - 7 cal. ka BP. Quartz wt.% then rose steadily during the late Holocene. Our data exhibit no correlation with counts on haematite-stained quartz (HSQ) grains from VM129-191 west of Ireland casting doubt on the ice-transport origin. A pilot study on the provenance of Fe oxide grains in two cores that cover the last 1.3 and 6.1 cal. ka BP indicated a large fraction of the grains between 1 and 6 cal. ka BP were from either Icelandic or presently unsampled sources. However, there was a dramatic increase in Canadian and Russian sources from the Arctic Ocean ???1 cal. ka BP. These data may indicate the beginning of an Arctic Oscillation-like climate mode. ?? 2009 SAGE Publications.

  11. A Latest Glacial and Holocene Record From Medicine Lake, Siskiyou County, California: Preliminary Diatom, Pollen, and Sediment Data

    NASA Astrophysics Data System (ADS)

    Starratt, S. W.; Barron, J. A.; Kneeshaw, T.; Phillips, L.; Lowenstern, J.; Wanket, J. A.

    2002-12-01

    Medicine Lake is a small (165 ha), relatively shallow (average 7.3 m), medium- altitude (2,036 m) lake located within the summit caldera of Medicine Lake volcano, a dormant Quaternary shield volcano located in the southern Cascade Range. During September 1999 and 2000, high-resolution bathymetry, seismic-reflection profiles, and sediment cores were collected from the lake. Twenty six samples from core B100NC-1 (water depth 12.6 m; length 226 cm) were analyzed for physical properties, sediment grain size, diatoms, pollen, and total organic carbon (TOC). Using both 14C (AMS) dating and tephrochronology, the sediments at the bottom of the core are estimated to be 11,000 cal yr B.P., thus yielding an estimated average sedimentation rate of about 21 cm/1,000 yr. The lowermost part of the core (226 cm - ~200 cm) records the transition from glacial to interglacial conditions. During the period from about 11,000-7,200 cal yr B.P., lake level fluctuated between deeper oligotrophic conditions with a diatom flora dominated by Cyclotella spp. and shallower intervals with a diverse benthic flora. The relative low abundance (10-15%) of Abies (fir) pollen and relative high abundance (30-40%) of Artemesia (sagebrush) pollen in this interval suggest drier than present-day conditions. The lowest part of this interval (226 cm - 210 cm) is almost devoid of Cyclotella and may represent an ice-covered lake in which only a small benthic flora could exist around the margins of the lake where light penetration was the greatest. The sediments in this interval are relatively low in TOC and are dominated by glacial flour. From about 7,200 cal yr B.P. to the present, conditions have fluctuated between higher lake levels (three intervals) that are dominated by Cyclotella with a reduced number and diversity of benthic taxa, and lower lake levels (two intervals) during which the abundances of Cyclotella decrease to less than 10%. Relative values of Abies and Pinus (pine) pollen are higher during

  12. Holocene disturbance dynamics from a pine-dominated forest in central British Columbia, Canada

    NASA Astrophysics Data System (ADS)

    Brown, K. J.; Hebda, N.; Condor, N.; Hebda, R.; Hawkes, B.

    2013-12-01

    A lake sediment record was retrieved from the Sub-Boreal Pine-Spruce biogeoclimatic zone on the Chilcotin Plateau in central British Columbia, Canada. The record is being analyzed for charcoal, pollen, and magnetic susceptibility, as well as insect and mollusc content. The oldest radiocarbon age is 9.2 cal BP, illustrating that the record spans most of the Holocene. Regarding fire disturbance, charcoal fragments are persistent throughout the core, revealing that fire disturbance has characterized the site for millennia. In total, 74 fire events were recognized. During the warm dry early Holocene, fire frequency was 12-15 fires 2000 yr-1 and peak magnitudes were low, possibly in response to a more open landscape. A change in fire regime occurred at ca. 5000 cal BP, as fire frequency increased, peaking at ca. 20 fires 2000 yr-1 by 3000 cal BP. Peak magnitude likewise increased notably, possibly in response to the development of denser forest cover. On-going analysis of pollen will better constrain the vegetation history in this poorly sampled region. In contrast to charcoal, which was pervasive, Dendroctonus ponderosae (mountain pine beetle) remains were absent in both modern and paleo samples. Given that several insect outbreaks have occurred in the region in the last 100 years, the scarcity of remains is likely related to taphonomic issues.

  13. Land-Sea Sedimentary Facies Transition at the Mouth of a Small Mountain River on the West Coast of Taiwan Since 50,000 yr BP

    NASA Astrophysics Data System (ADS)

    Yang, R.; Liu, J. T.; Fan, D.; Burr, G.; Lin, H. L.; Chen, T.

    2016-02-01

    Taiwan is located in the collision zone of two tectonic plates, and receives impacts from the monsoons and typhoons. They contribute to the high sediment load delivered to the sea by small mountainous rivers on this island. The disproportionally large sediment load and the rising sea level constitute a favorable receiving-basin condition for the formation of river deltas. In this study, FATES-HYPERS team drilled two bore-holes on both sides of the Zhuoshui River mouth in central Taiwan. The length of each core was 104m (JRD-S) and 98m (JRD-N). Through AMS 14C dating from over 70 samples in each core a reliable age model was established to reconstruct the paleoenvironment of at the Zhuoshui River mouth during late Quaternary. These transitions indicate that the paleo-river mouth began to develop a transgressive-estuarine system at 10,000 yr BP, when the paleo-river mouth was inundated by the rising sea. The sediments that were come from Zhuoshui River accumulated slower than the sea-level rise. This resulted in gradually deeper environment. The evidence of maximum flooding surface (MFS) suggests transgression progressed until 5700 yr BP. Combined with findings from previous studies the position of MFS display a shallowing trend from the south to north. This implies that the deposition rate in the north was higher than that in the south. Therefore it is reasonable to assume that the paleo-river mouth was located north to the present position. After the sea level became stable, because of large terrestrial sediments discharge the paleo-river mouth was soon switched from a transgressive system to an aggradational delta system. The Zhuoshui River delta, unlike many well-known river delta systems, is limited by the depth of the Taiwan Strait. Shallow water depth and energetic hydrodynamics result in the non-deposition of muddy sediments near the river mouth. This caused the absence of thick muddy prodelta deposits in the upper part of the JRD cores. This caused the

  14. Striking similarities in temporal changes to spring sea ice occurrence across the central Canadian Arctic Archipelago over the last 7000 years

    NASA Astrophysics Data System (ADS)

    Belt, Simon T.; Vare, Lindsay L.; Massé, Guillaume; Manners, Hayley R.; Price, John C.; MacLachlan, Suzanne E.; Andrews, John T.; Schmidt, Sabine

    2010-12-01

    A 7000 year spring sea ice record for Victoria Strait (ARC-4) and Dease Strait (ARC-5) in the Canadian Arctic Archipelago (CAA) has been determined by quantification of the sea ice diatom-derived biomarker IP 25 in two marine sediment piston cores obtained in 2005. The chronologies of the ARC-4 and ARC-5 cores were determined using a combination of 14C AMS dates obtained from macrobenthic fossils and magnetic susceptibility measurements. The ages of the tops of the piston cores were estimated by matching chemical and physical parameters with those obtained from corresponding box cores. These analyses revealed that, while the top of the ARC-4 piston core was estimated to be essentially modern (ca. 60 cal yr BP), a few hundred years of sediment appeared to be absent from the ARC-5 piston core. Downcore changes to IP 25 fluxes for both cores were interpreted in terms of variations in spring sea ice occurrence, and correlations between the individual IP 25 flux profiles for Victoria Strait, Dease Strait and Barrow Strait (reported previously) were shown to be statistically significant at both 50 and 100-year resolutions. The IP 25 data indicate lower spring sea ice occurrences during the early part of the record (ca. 7.0-3.0 cal kyr BP) and for parts of the late Holocene (ca. 1.5-0.8 cal kyr BP), especially for the two lower latitude study locations. In contrast, higher spring sea ice occurrences existed during ca. 3.0-1.5 cal kyr BP and after ca. 800 cal yr BP. The observation of, consecutively, lower and higher spring sea ice occurrence during two periods of the late Holocene, coincides broadly with the Medieval Warm Period and Little Ice Age epochs, respectively. The IP 25 data are complemented by particle size and mineralogical data, although these may alternatively reflect changes in sea level at the study sites. The IP 25 data are also compared to previous proxy-based determinations of palaeo sea ice and palaeoclimate for the CAA, including those based on bowhead

  15. Ecotone shift and major droughts during the mid-late Holocene in the central Tibetan Plateau.

    PubMed

    Shen, Caiming; Liu, Kam-Biu; Morrill, Carrie; Overpeck, Jonathan T; Peng, Jinlan; Tang, Lingyu

    2008-04-01

    A well-dated pollen record from a large lake located on the meadow-steppe ecotone provides a history of ecotone shift in response to monsoonal climate changes over the last 6000 years in the central Tibetan Plateau. The pollen record indicates that the ecotone shifted eastward during 6000-4900, 4400-3900, and 2800-1600 cal. yr BP when steppes occupied this region, whereas it shifted westward during the other intervals when the steppes were replaced by meadows. The quantitative reconstruction of paleoclimate derived from the pollen record shows that monsoon precipitation fluctuated around the present level over the last 6000 years in the central Tibetan Plateau. Three major drought episodes of 5600-4900, 4400-3900, and 2800-2400 cal. yr BP are detected by pollen signals and lake sediments. Comparison of our record with other climatic proxy data from the Tibetan Plateau and other monsoonal regions shows that these episodes are three major centennial-scale monsoon weakening events.

  16. Stable isotope and 14C study of biogenic calcrete in a termite mound, Western Cape, South Africa, and its palaeoenvironmental significance

    NASA Astrophysics Data System (ADS)

    Potts, Alastair J.; Midgley, Jeremy J.; Harris, Chris

    2009-09-01

    Late Quaternary terrestrial climate records from the semi-arid zone of the Western Cape of South Africa are rare. However, palaeoenvironmental information may be inferred from ancient termite mounds of the region. Calcrete lenses in these mounds have δ 13C and δ 18O values that show systematic changes with radiocarbon dates, which range from 33,629-36,709 to 21,676-23,256 cal yr BP. These dates confirm that these heuweltjies had been present in the landscape since the last glacial period. The decrease in δ 13C and δ 18O from 33,629-36,709 to 21,676-23,256 cal yr BP indicates that climate information is recorded by the calcretes. It is suggested that a progressive decline in air temperature and an increase in moisture availability, and a decline in abundance of C 4 or CAM plants, occurred in the region during the time heuweltjie calcite precipitated.

  17. Human-ecosystem interactions in relation to Holocene environmental change in Port Joli Harbour, southwestern Nova Scotia, Canada

    NASA Astrophysics Data System (ADS)

    Neil, Karen; Gajewski, Konrad; Betts, Matthew

    2014-03-01

    A high-resolution pollen record from Path Lake in Port Joli Harbour, Nova Scotia, Canada, provides a paleo-ecological perspective on Holocene climate and vegetation variability within the context of local archaeological research. Pollen assemblages in the early Holocene reflect a post-glacial forest dominated by Pinus, Tsuga, Betula and Quercus. During this time, a lower frequency of radiocarbon dated cultural material suggests lower human settlement intensity. Shallow water aquatic (Isoetes) and wetland (Alnus, Sphagnum) taxa increased after 3400 cal yr BP in response to a transition towards wetter climatic conditions. Culturally significant periods, where settlement intensity increased in the Maritimes and Maine, coincide with maximum values of reconstructed total annual precipitation, suggesting that environmental conditions may have influenced prehistoric human activity. European settlement, after 350 cal yr BP, was marked by a rise in Ambrosia. The impact of anthropogenic fire disturbances on the landscape was evidenced by peak charcoal accumulations after European settlement.

  18. Holocene depositional environments and surface-level changes at Lake Fryxell, Antarctica

    USGS Publications Warehouse

    Whittaker, T.E.; Hall, B.L.; Hendy, C.H.; Spaulding, S.A.

    2008-01-01

    We report on Holocene surface-level variations of Lake Fryxell, Antarctica, as determined from multi-proxy analyses of 18 sediment cores. During this time accumulating sediments were predominantly aeolian sand with algal and carbonate laminae. Based on stratigraphy, mineralogy and diatom assemblages we suggest some carbonate laminae were deposited when lake level dropped, leading to concentration and subsequent precipitation of salts. Although lake level appears to have remained relatively stable throughout the Holocene, minor (<4.5 m below present) lowstands occurred at approximately 6400, 4700, 3800 and ??? 1600 cal. yr BP. The stability of Lake Fryxell during the Holocene contrasts with large-scale variability at other Dry Valleys lakes (eg, Lake Vanda) and with suggestions from chemical diffusion models of a near-desiccation at ???1200 cal. yr BP. The reason for the comparative stability of Lake Fryxell is uncertain, but may be the result of basin morphology and the number, aspect and proximity of meltwater sources. ?? 2008 SAGE Publications.

  19. Climate variability in the past ∼19,000 yr in NE Tibetan Plateau inferred from biomarker and stable isotope records of Lake Donggi Cona

    NASA Astrophysics Data System (ADS)

    Saini, Jeetendra; Günther, Franziska; Aichner, Bernhard; Mischke, Steffen; Herzschuh, Ulrike; Zhang, Chengjun; Mäusbacher, Roland; Gleixner, Gerd

    2017-02-01

    We investigated 4.84-m-long sediment record spanning over the Late Glacial and Holocene from Lake Donggi Cona to be able to reconstruct circulation pattern on the Tibetan Plateau (TP). Presently, Lake Donggi Cona is located at the boundaries of Westerlies and Asian monsoon circulations in the northeastern TP. However, the exact timing and stimulating mechanisms for climatic changes and monsoon shifts in this region are still debated. We used a 19-ka-long stable isotope record of sedimentary n-alkanes to address this discrepancy by providing insights into paleohydrological conditions. The δD of nC23 is influenced by lake water evaporation; the δD values of sedimentary nC29 are mainly controlled by moisture source and temperature changes. Long-chain n-alkanes dominate over the core whereas three mean clusters (i.e. microbial, aquatic and terrestrial) can be inferred. Multi-proxies suggest five major episodes in the history of Lake Donggi Cona. The Lake Donggi Cona record indicates that the Late Glacial (18.4-14.8 cal ka BP) was dominated by low productivity of mainly microbial and aquatic organisms. Relatively low δD values suggest low temperatures and moist conditions eventually caused by stronger Westerlies, winter monsoon and melt-water influence. Likely, the shift (∼17.9 cal ka BP) from microbial to enhanced aquatic input suggests either a change from deep to shallow water lake or a break in local stratification. Between 14.8 and 13.0 cal ka BP, variable climatic conditions prevailed. Although the Westerlies weekend, the increase in temperature enhanced the permafrost and snow melting (displayed by a high sedimentary accumulation rate). Higher δD values indicate increasingly arid conditions with higher temperatures which eventually lead to high evaporative conditions and lowest lake levels. Low vegetation cover and high erosion rates led to high sediment accumulation resulting in stratification followed by anoxia in the terminal lake. From 13.0 to 9.2 cal

  20. Late Holocene anthropogenic and climatic influences on the regional vegetation of Mexico's Cuenca Oriental

    NASA Astrophysics Data System (ADS)

    Bhattacharya, Tripti; Byrne, Roger

    2016-03-01

    Scholars continue to debate the relative magnitude of pre- and post-Conquest anthropogenic landscape transformation in many regions of Mesoamerica. These debates have important implications for our understanding of the role of anthropogenic practices in the development, or at times degradation, of regional environments. Paleoecological records that provide long-term perspectives on climate change and human land-use patterns are critical to addressing these uncertainties. However, many regions of Mexico including the Cuenca Oriental, a semi-arid basin in the rain shadow of the Sierra Madre Oriental, remain poorly studied. We present a new paleoecological record from sediment cores recovered from Lake Aljojuca, located in the southern part of the basin. Stable isotope analyses of authigenic carbonates provide an independent record of past climate, while pollen and microscopic charcoal provide insights into past vegetation and fire history. The Aljojuca record is one of the only well-dated multi-proxy paleolimnological records from the Cuenca Oriental, and is one of few charcoal studies from highland Mexico. Zea mays pollen and increased fire activity at 2700 calendar years before present (cal yr. BP) suggest Formative period human settlement around the lake. Between 1700 and 800 cal yr BP, a drying climate combined with human uses of fire likely resulted in increases in the extent of xeric scrub vegetation. The Aljojuca record also documents important landscape changes during the historic period ( 430 cal yr. BP-present) likely related to the introduction of invasive species and agricultural intensification. The Aljojuca record provides a unique perspective on human-environment relationships and highlights differences between landscape transformations in the pre- and post-Conquest periods.

  1. Numerical ages of Holocene tributary debris fans inferred from dissolution pitting on carbonate boulders in the Grand Canyon of Arizona

    USGS Publications Warehouse

    Hereford, R.; Thompson, K.S.; Burke, K.J.

    1998-01-01

    Carbonate boulders transported down steep tributary channels by debris flow came to rest on Holocene debris fans beside the Colorado River in Grand Canyon National Park. Weakly acidic rainfall and the metabolic activity of blue-green algae have produced roughly hemispheric dissolution pits as much as 2-cm deep on the initially smooth surfaces of the boulders. The average depth of dissolution pits increases with relative age of fan surfaces. The deepening rate averages 2.4 mm/1000 yr (standard error = 0.2 mm/1000 yr), as calculated from several radiometrically dated surfaces and an archeological structure. This linear rate, which appears constant over at least the past 3000 yr, is consistent with field relations limiting the maximum age of the fans and with the physical chemistry of limestone dissolution. Dissolution-pit measurements (n = 6973) were made on 617 boulders on 71 fan surfaces at the 26 largest debris fans in Grand Canyon. Among these fan surfaces, the average pit depth ranges from 1.2 to 17.4 mm, and the resulting pit dissolution ages range from 500 to 7300 cal yr B.P. Most (75%) surfaces are younger than 3000 yr, probably because of removal of older debris fans by the Colorado River. Many of the ages are close to 800, 1600, 2300, 3100, or 4300 cal yr B.P. If not the result of differential preservation of fan surfaces, this clustering implies periods of heightened debris-flow activity and increased precipitation.

  2. Mid-late Holocene climate and vegetation in northeastern part of the Altai Mountains recorded in Lake Teletskoye

    NASA Astrophysics Data System (ADS)

    Rudaya, Natalia; Nazarova, Larisa; Novenko, Elena; Babich, Valery; Kalugin, Ivan; Daryin, Andrei

    2015-04-01

    We report the first high-resolution (with intervals ca. 20-50 years) late-Holocene (4200 yr BP) pollen record from Lake Teletskoye, Altai Mountains, obtained from the underwater Ridge of Sofia Lepneva in 2006 (core Tel 2006). The study presents (i) the results of palynological analysis of Tel 2006; (ii) the results of spectral analysis of natural cycles based on the periodical fluctuation of taiga-biome curve; and (iii) quantitative reconstructions of the late-Holocene regional vegetation, woody coverage and climate in northern part of the Altai Mountains in order to define place of Northeast Altai on the map of the late-Holocene Central Asian environmental history. Late Holocene vegetation of the northeastern part of Altai recorded in Tel 2006 core is characterized by spread of dark-coniferous forest with structure similar to modern. Dominant trees, Siberian pine (Pinus sibirica) and Siberian fir (Abies sibirica), are the most ecological sensitive taxa between Siberian conifers (Shumilova, 1962), that as a whole suggests mild and humid climatic conditions during last 4200 years. However, changes of pollen taxa percentages and results of numerical analysis reveal pronounced fluctuation of climate and vegetation. Relatively cool and dry stage occurred prior to ca. 3500 cal yr BP. Open vegetation was widespread in the region with maximum deforestation and minimal July temperatures between 3800-3500 cal yr BP. Steppe-like communities with Artemisia, Chenopodiaceae and Cyperaceae could grow on the open sites around Lake Teletskoye. Reconstructed woody coverage is very low and varies between 29-35%. After ca. 3500 cal yr BP the area of dark-coniferous mountain taiga has significantly enlarged with maximums of woody coverages and taiga biome scores between ca. 2470-1040 cal yr BP. In the period of ~3500-2500 cal yr BP the averages July temperatures increased more than 1 0C. Climate became warmer and wetter. During last millennium (after 1040 cal yr BP) average July

  3. Vegetation and Water Level Changes for the Northeast U.S. During the "8.2 ka Event"

    NASA Astrophysics Data System (ADS)

    Newby, P. E.; Donnelly, J. P.; Shuman, B.; MacDonald, D.

    2006-12-01

    Cool conditions, known as the "8.2 ka event", occurred between 8400 and 7900 cal yr B.P. in Greenland, Europe and elsewhere in the North Atlantic. The impact of this brief cool interval on local forests is recorded in radiocarbon-dated, high-resolution pollen stratigraphies for New Long Pond (41^{0}50'N, 70^{0}42'W) and Davis Pond (42^{0}30'N, 73^{0}19'W), Massachusetts. The vegetation response to the event is recorded differently for regions with contrasting soil types. At New Long Pond, the sandy outwash derived soils are associated with changes in jack/red, white and pitch pine populations, whereas the dominant changes in vegetation for the clay-rich, proglacial lake derived soils around Davis Pond are among oak, hemlock, and beech. At both sites, pollen evidence for the "8.2 ka event" may be easily overlooked within the more dominant regional pattern for the Northeast, which shows a shift from dry to moist conditions in conjunction with changes from predominantly white pine to oak with more mesic plant taxa between 9000 and 8000 cal yr B.P. At New Long Pond, the "8.2 ka event" is brief, preceded by a low-stand in water-level during the early Holocene and dominated by white pine pollen. After 9000 cal yr B.P., pitch pine with beech, maple, hop/hornbeam, elm and ash pollen indicate a mixed mesophytic forest. A radiocarbon-dated decrease in loss-on-ignition values at 8400 cal yr B.P., likely related to a drawdown in lake level, distinguishes the "8.2 event" and helps highlight subtle shifts in vegetation that favor colder and drier conditions than before the event. Following this brief episode, the pollen data indicate a return to warm and moist conditions until about 5600 years ago. At Davis Pond, increased oak and decreased hemlock pollen abundances, followed by an increase in beech pollen abundance is evident and show what may be the dominant regional pollen signature for the "8.2 ka event" in the Northest. This pattern is also recorded at nearby Berry and

  4. Origin and paleoclimatic significance of late Quaternary loess in Nebraska: Evidence from stratigraphy, chronology, sedimentology, and geochemistry

    USGS Publications Warehouse

    Muhs, Daniel R.; Bettis, E. Arthur; Aleinikoff, John N.; McGeehin, John P.; Beann, Jossh; Skipp, Gary; Marshall, Brian D.; Roberts, Helen M.; Johnson, William C.; Benton, Rachel

    2008-01-01

    Loess is one of the most extensive surficial geologic deposits in midcontinental North America, particularly in the central Great Plains region of Nebraska. Last-glacial-age loess (Peoria Loess) reaches its greatest known thickness in the world in this area. New stratigraphic, geochronologic, mineralogic, and geochemical data yield information about the age and provenance of Peoria Loess, as well as evaluation of recent climate models. Sixteen new radiocarbon ages and recently acquired optically stimulated luminescence ages indicate that Peoria Loess deposition in Nebraska occurred between ca. 25,000 cal yr B.P. and ca. 13,000 cal yr B.P. After ca. 13,000 cal yr B.P. a period of pedogenesis began, represented by the dark, prominent Brady Soil. At some localities, further loess deposition was minimal. At other localities, sometime after ca. 11,000 cal yr B.P., there were additional episodes of loess deposition (Bignell Loess) intermittently throughout the Holocene. The spatial variability of particle size abundances in Peoria Loess shows a northwest-to-southeast fining in Nebraska, consistent with maps of previous workers that show a northwest-to-southeast thinning of loess. These observations indicate that paleowinds that deposited the loess were from the west or northwest and that the source or sources of Peoria Loess lay to the west or northwest. New mineralogical and geochemical data indicate that the most important sources of loess were likely Tertiary siltstones of the White River and Arikaree Groups, silt facies of Pliocene eolian sediments, and small contributions from Pierre Shale. It is likely that fine-grained silts were transported episodically through the Nebraska Sand Hills from Tertiary and Cretaceous bedrock sources to the north, in agreement with a model presented recently. The identification of Tertiary siltstones and silts as the primary sources of loess is consistent with isotopic data presented in a companion paper. Contributions of glaciogenic

  5. Holocene climate aridification trend and human impact interrupted by millennial- and centennial-scale climate fluctuations from a new sedimentary record from Padul (Sierra Nevada, southern Iberian Peninsula)

    NASA Astrophysics Data System (ADS)

    Ramos-Román, María J.; Jiménez-Moreno, Gonzalo; Camuera, Jon; García-Alix, Antonio; Anderson, R. Scott; Jiménez-Espejo, Francisco J.; Carrión, José S.

    2018-01-01

    Holocene centennial-scale paleoenvironmental variability has been described in a multiproxy analysis (i.e., lithology, geochemistry, macrofossil, and microfossil analyses) of a paleoecological record from the Padul Basin in Sierra Nevada, southern Iberian Peninsula. This sequence covers a relevant time interval hitherto unreported in the studies of the Padul sedimentary sequence. The ˜ 4700-year record has preserved proxies of climate variability, with vegetation, lake levels, and sedimentological change during the Holocene in one of the most unique and southernmost wetlands in Europe. The progressive middle and late Holocene trend toward arid conditions identified by numerous authors in the western Mediterranean region, mostly related to a decrease in summer insolation, is also documented in this record; here it is also superimposed by centennial-scale variability in humidity. In turn, this record shows centennial-scale climate oscillations in temperature that correlate with well-known climatic events during the late Holocene in the western Mediterranean region, synchronous with variability in solar and atmospheric dynamics. The multiproxy Padul record first shows a transition from a relatively humid middle Holocene in the western Mediterranean region to more aridity from ˜ 4700 to ˜ 2800 cal yr BP. A relatively warm and humid period occurred between ˜ 2600 and ˜ 1600 cal yr BP, coinciding with persistent negative North Atlantic Oscillation (NAO) conditions and the historic Iberian-Roman Humid Period. Enhanced arid conditions, co-occurring with overall positive NAO conditions and increasing solar activity, are observed between ˜ 1550 and ˜ 450 cal yr BP (˜ 400 to ˜ 1400 CE) and colder and warmer conditions occurred during the Dark Ages and Medieval Climate Anomaly (MCA), respectively. Slightly wetter conditions took place during the end of the MCA and the first part of the Little Ice Age, which could be related to a change towards negative NAO conditions

  6. A ~20,000 year history of glacial variability in the tropical Andes recorded in lake sediments from the Cordillera Blanca, Peru

    NASA Astrophysics Data System (ADS)

    Stansell, N.; Rodbell, D. T.; Moy, C. M.

    2010-12-01

    Pro-glacial lake sediments from the Cordillera Blanca, Peru contain continuous records of climate variability spanning the Last Glacial Maximum to present day. Here we present results from two alpine lake basins in the Queshgue Valley (9.8°S, 77.3°W) that contain high-resolution records of clastic sediment deposition for the last ~20,000 years. Radiocarbon-dated sediment cores were scanned at 0.5 to 1.0 cm resolution using a profiling x-ray fluorescence scanner for major and minor element distributions. In addition, we measured down-core variations in magnetic susceptibility, organic carbon, biogenic silica and calcium carbonate. Samples of bedrock and sediments from glacial moraines in the Queshgue watershed were analyzed using an ICP-MS in order to fingerprint and trace the source of glacial sediments deposited in the lakes. The bedrock is dominated by a combination of granodiorite with high Sr concentrations and meta-sedimentary rocks with high Zr values. Because the glacial sediments proximal to the modern glacier terminus are composed mostly of the granodiorite end-member, we interpret changes in Sr and clastic sediment concentrations in the lake sediment profiles as proxies for past glacial variability. Preliminary results indicate that glaciers retreated soon after ~14,500 cal yr BP and remained less extensive during the remaining late Glacial Stage and early Holocene. Gradually increasing clastic sediments through the middle and late Holocene indicate that glaciers became progressively larger, or more erosive towards present day. However, this overall Holocene trend of increasing glacier extent was interrupted by multiple periods of centennial- to millennial-scale ice margin retreat. For example, relative peaks in clastic sediments occurred from ~14,500 to 6000, 5600 to 5000, 4600 to 4200, 3600 to 3200, 2800 to 2700, 2400 to 2200, 1750 to 1550, 1100 to 900 cal yr BP, and during the Little Ice Age (~700 to 50 cal yr BP), while periods of low clastic

  7. Late-glacial and early Holocene changes in vegetation and lake-level at Hauterive/Rouges-Terres, Lake Neuchâtel (Switzerland)

    NASA Astrophysics Data System (ADS)

    Magny, Michel; Thew, Nigel; Hadorn, Philippe

    2003-01-01

    Palynological and sedimentological analyses of a sedimentary sequence sampled at Hauterive/Rouges-Terres, Lake Neuchâtel (Switzerland) provide documentation of changes in vegetation and lake-level during the Bølling, Younger Dryas and Preboreal pollen zones, and have allowed a comparison with sequences covering the same period from other sites located in the western part of the Swiss Plateau. The Juniperus-Hippophaë zone (regional pollen assemblage zone (RPAZ) CHb-2, first part of the Bølling, ca. 14 650-14 450 cal. yr BP) was characterised by a generally low lake-level. A weak rise occurred during this zone. The Juniperus-Hippophaë to Betula zone transition coincided with a lake-level lowering, interrupted by a short-lived but marked phase of higher lake-level recorded at the neighbouring site of Hauterive-Champréveyres, but not present at Hauterive/Rouges-Terres owing to an erosion surface. Shortly after the beginning of the Betula zone (RPAZ CHb-3, second part of the Bølling, ca 14 450-14 000 cal. yr BP), a marked rise in lake-level occurred. It was composed of two successive periods of higher level, coinciding with high values of Betula, separated by a short episode of relatively lower lake-level associated with raised values in Artemisia and other non-arboreal pollen. The last part of RPAZ CHb-3 saw a fall in lake-level. The lower lake-levels during RPAZ CHb-2 to early RPAZ CHb-3 can be correlated with the abrupt warming at the beginning of the Greenland Interstadial (GI) 1e thermal maximum. The successive episodes of higher lake-level punctuating the GI 1e might be linked to the so-called Intra-Bølling Cold Oscillations identified from several palaeoclimatic records in the North Atlantic area, and also documented in oxygen-isotope data sets from Swiss Plateau lakes. The Hauterive/Rouges-Terres lake-level record provides evidence for marked climatic drying through the second part of the Younger Dryas event (GS1), during the GS1-Preboreal (RPAZ CHb-4b-4

  8. Associated terrestrial and marine fossils in the late-glacial Presumpscot Formation, southern Maine, USA, and the marine reservoir effect on radiocarbon ages

    NASA Astrophysics Data System (ADS)

    Thompson, Woodrow B.; Griggs, Carol B.; Miller, Norton G.; Nelson, Robert E.; Weddle, Thomas K.; Kilian, Taylor M.

    2011-05-01

    Excavations in the late-glacial Presumpscot Formation at Portland, Maine, uncovered tree remains and other terrestrial organics associated with marine invertebrate shells in a landslide deposit. Buds of Populus balsamifera (balsam poplar) occurred with twigs of Picea glauca (white spruce) in the Presumpscot clay. Tree rings in Picea logs indicate that the trees all died during winter dormancy in the same year. Ring widths show patterns of variation indicating responses to environmental changes. Fossil mosses and insects represent a variety of species and wet to dry microsites. The late-glacial environment at the site was similar to that of today's Maine coast. Radiocarbon ages of 14 tree samples are 11,907 ± 31 to 11,650 ± 50 14C yr BP. Wiggle matching of dated tree-ring segments to radiocarbon calibration data sets dates the landslide occurrence at ca. 13,520 + 95/-20 cal yr BP. Ages of shells juxtaposed with the logs are 12,850 ± 65 14C yr BP ( Mytilus edulis) and 12,800 ± 55 14C yr BP ( Balanus sp.), indicating a marine reservoir age of about 1000 yr. Using this value to correct previously published radiocarbon ages reduces the discrepancy between the Maine deglaciation chronology and the varve-based chronology elsewhere in New England.

  9. 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

  10. A 13000-year, high-resolution multi-proxy record of climate variability with episodes of enhanced atmospheric dust in Western Asia: Evidence from Neor peat complex in NW Iran

    NASA Astrophysics Data System (ADS)

    Sharifi, O.; Pourmand, A.; Canuel, E. A.; Peterson, L. C.

    2011-12-01

    The regional climate over West Asia, extending between Iran and the Arabian Peninsula to the eastern Mediterranean Sea, is governed by interactions between three major synoptic systems; mid-latitude Westerlies, the Siberian Anticyclone and the Indian Ocean Summer Monsoon. In recent years, a number of paleoclimate studies have drawn potential links between episodes of abrupt climate change during the Holocene, and the rise and fall of human civilizations across the "Fertile Crescent" of West Asia. High-resolution archives of climate variability from this region, however, are scarce, and at times contradicting. For example, while pollen and planktonic data from lakes in Turkey and Iran suggest that dry, continental conditions prevailed during the early-middle Holocene, oxygen isotope records indicate that relatively wet conditions dominated during this interval over West Asia. We present interannual to decadal multi-proxy records of climate variability from a peat complex in NW Iran to reconstruct changes in moisture and atmospheric dust content during the last 13000 years. Radiocarbon dating on 20 samples from a 775-cm peat core show a nearly constant rate of accumulation (1.7 mm yr-1, R2=0.99) since 13356 ± 116 cal yr B.P. Down-core X-ray fluorescence measurements of conservative lithogenic elements (e.g., Al, Zr, Ti) as well as redox-sensitive elements (e.g., Fe, K, Rb, Zn, Cu, and Co) at 2 mm intervals reveal several periods of elevated dust input to this region since the early Holocene. Down-core variations of total organic carbon and total nitrogen co-vary closely and are inversely correlated with conservative lithogenic elements (Al, Si, Ti), indicating a potential link between climate change and accumulation of organic carbon in the Neor peat mire. Major episodes of enhanced dust deposition (13000-12000, 11700-11200, 9200-8800, 7000-6000, 4200-3200, 2800-2200 and 1500-600 cal yr B.P) are in good agreement with other proxy records that document more arid

  11. Blood pressure (BP) assessment-from BP level to BP variability.

    PubMed

    Feber, Janusz; Litwin, Mieczyslaw

    2016-07-01

    The assessment of blood pressure (BP) can be challenging in children, especially in very young individuals, due to their variable body size and lack of cooperation. In the absence of data relating BP with cardiovascular outcomes in children, there is a need to convert absolute BP values (in mmHg) into age-, gender- and height appropriate BP percentiles or Z-scores in order to compare a patient's BP with the BP of healthy children of the same age, but also of children of different ages. Traditionally, the interpretation of BP has been based mainly on the assessment of the BP level obtained by office, home or 24-h BP monitoring. Recent studies suggest that it is not only BP level (i.e. average BP) but also BP variability that is clinically important for the development of target organ damage, including the progression of chronic kidney disease. In this review we describe current methods to evaluate of BP level, outline available methods for BP variability assessment and discuss the clinical consequences of BP variability, including its potential role in the management of hypertension.

  12. Morus planting and silk production in Oxus civilization (2000 BC), Transoxiana

    NASA Astrophysics Data System (ADS)

    Zhou, X.; Li, X.; Wang, J.

    2017-12-01

    Silk is the most important luxury in ancient trade, which promoted communications between east and west civilizations that facilitated the development of them. Currently, probably more than 99% of the silk in commerce in the world today comes from a single species called the silkworm or mulberry silk moth, Bombyx mori (L.), of the family Bombycidae. At present, a list of occurrences of unearthed early silk thread, textile and terracotta figures of China suggests that wild silk has been widely used for weave in Yangtze river and Yellow River basin at least 5000 cal yr BP. On the other hand, the earliest silk fabric out China is from the earliest civilization Harappa site (4500-4000 cal a BP) that confirmed the early use of wild silkworms in South Asia.. In addition, in the Egyptian Deir al Medina relics site, the unearthed silk also as old as nearly 3000 cal a BP, and a serials of pre-han silk also unearthed 3000-2500 cal a BP in Europe. But, the appearance of these out-China silk is usually considered to be the result of the early trade or wild silkmoth products. Here we present a synthesis study of chronology, entomology, protein group, the paleoethnobotany form three Bronze Age site (Sapalli, Jarzgudan, Molleli) concerning on the paleo environment, agriculture gardening, and the possible mulberry silkworm utilization in Bronze Age Tensoxiana 4000 cal a BP. Together with archaeobotany and chronology data from Xinjiang, Hexi corridor and the Loess Plateau in China, we analysis the status of the mulberry silk factory in Bronze Age in Transoxiana and it possible connection to ancient China.

  13. The Glacial and Relative Sea Level History of Southern Banks Island, NT, Canada

    NASA Astrophysics Data System (ADS)

    Vaughan, Jessica Megan

    The mapping and dating of surficial glacial landforms and sediments across southern Banks Island document glaciation by the northwest Laurentide Ice Sheet (LIS) during the last glacial maximum. Geomorphic landforms confirm the operation of an ice stream at least 1000 m thick in Amundsen Gulf that was coalescent with thin, cold-based ice crossing the island's interior, both advancing offshore onto the polar continental shelf. Raised marine shorelines across western and southern Banks Island are barren, recording early withdrawal of the Amundsen Gulf Ice Stream prior to the resubmergence of Bering Strait and the re-entry of Pacific molluscs ~13,750 cal yr BP. This withdrawal resulted in a loss of ~60,000 km2 of ice --triggering drawdown from the primary northwest LIS divide and instigating changes in subsequent ice flow. The Jesse moraine belt on eastern Banks Island records a lateglacial stillstand and/or readvance of Laurentide ice in Prince of Wales Strait (13,750 -- 12,750 cal yr BP). Fossiliferous raised marine sediments that onlap the Jesse moraine belt constrain final deglaciation to ~12,600 cal yr BP, a minimum age for the breakup of the Amundsen Gulf Ice Stream. The investigation of a 30 m thick and 6 km wide stratigraphic sequence at Worth Point, southwest Banks Island, identifies an advance of the ancestral LIS during the Mid-Pleistocene (sensu lato), substantially diversifying the glacial record on Banks Island. Glacial ice emplaced during this advance has persisted through at least two glacial-interglacial cycles, demonstrating the resilience of circumpolar permafrost. Pervasive deformation of the stratigraphic sequence also records a detailed history of glaciotectonism in proglacial and subglacial settings that can result from interactions between cold-based ice and permafrost terrain. This newly recognized history rejects the long-established paleoenvironmental model of Worth Point that assumed a simple 'layer-cake' stratigraphy.

  14. An 8700 Year Record of Holocene Climate Variability from the Yucatan Peninsula

    NASA Astrophysics Data System (ADS)

    Wahl, D.; Byrne, R.; Anderson, L.

    2013-12-01

    Our understanding of Holocene climate change in the Maya lowlands of Central America has improved significantly during the last several decades thanks to the development of proxy climate records from lake cores and speleothems. One important finding is that longer-term climate changes (i.e., millennial scale) were driven primarily by precessional forcing; less clear, however, are the causes of abrupt shifts and higher frequency (centennial to decadal) change recognized in many Holocene climate reconstructions. The mechanisms driving climate change on these time scales have been difficult to identify in the region, in part because the Yucatan peninsula is influenced by climatic conditions linked to both the tropical Atlantic and Pacific oceans. Additional complications arise from the development of dense human populations following the initial introduction of agriculture ~5000 cal yr BP, which had significant impact on the environment as a whole. Here we present the results of analyses (stable isotope, pollen, magnetic susceptibility, and physical properties) of a 7.25 m sediment core from Lago Puerto Arturo, a closed basin lake in the northern Peten, Guatemala. An age-depth model, based on 6 AMS radiocarbon determinations and created using CLAM, indicates the record extends to 8700 cal yr BP. Proxy data suggest that, similar to other low latitude sites, millennial scale climate at Lago Puerto Arturo was driven by changes in insolation. Higher frequency variability is associated with El Niño/Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO) dynamics, reflecting latitudinal shifts in the Intertropical Convergence Zone in both the tropical North Atlantic and North Pacific. Solar forcing may also play a role in short-term climate change. The pollen and isotope records show that the entire period of prehispanic settlement and agricultural activity, i.e. ~5000-1000 cal yr B.P., was characterized by relatively dry conditions compared to before or after.

  15. Broadleaf deciduous forest counterbalanced the direct effect of climate on Holocene fire regime in hemiboreal/boreal region (NE Europe)

    NASA Astrophysics Data System (ADS)

    Feurdean, Angelica; Veski, Siim; Florescu, Gabriela; Vannière, Boris; Pfeiffer, Mirjam; O'Hara, Robert B.; Stivrins, Normunds; Amon, Leeli; Heinsalu, Atko; Vassiljev, Jüri; Hickler, Thomas

    2017-08-01

    Disturbances by fire are essential for the functioning of boreal/hemiboreal forests, but knowledge of long-term fire regime dynamics is limited. We analysed macrocharcoal morphologies and pollen of a sediment record from Lake Lielais Svētiņu (eastern Latvia), and in conjunction with fire traits analysis present the first record of Holocene variability in fire regime, fuel sources and fire types in boreal forests of the Baltic region. We found a phase of moderate to high fire activity during the cool and moist early (mean fire return interval; mFRI of ∼280 years; 11,700-7500 cal yr BP) and the late (mFRI of ∼190 years; 4500-0 cal yr BP) Holocene and low fire activity (mFRI of ∼630 years) during the Holocene Thermal Optimum (7500-4500 cal yr BP). Charcoal morphotypes and the pollen record show the predominance of frequent surface fires, occasionally transitioning to the crown during Pinus sylvestris-Betula boreal forests and less frequent surface fires during the dominance of temperate deciduous forests. In contrast to the prevailing opinion that fires in boreal forests are mostly low to moderate severity surface fires, we found evidence for common occurrence of stand-replacing crown fires in Picea abies canopy. Our results highlight that charcoal morphotypes analysis allows for distinguishing the fuel types and surface from crown fires, therefore significantly advancing our interpretation of fire regime. Future warmer temperatures and increase in the frequency of dry spells and abundant biomass accumulation can enhance the fire risk on the one hand, but will probably promote the expansion of broadleaf deciduous forests to higher latitudes, on the other hand. By highlighting the capability of broadleaf deciduous forests to act as fire-suppressing landscape elements, our results suggest that fire activity may not increase in the Baltic area under future climate change.

  16. Late Holocene Permafrost Aggradation in the Western Kenai Lowlands, Alaska: Implications for Climate Reconstruction and Carbon Cycling.

    NASA Astrophysics Data System (ADS)

    Hoefke, K.; Jones, M.; Jones, B. M.

    2017-12-01

    Rapid permafrost thaw is occurring throughout the permafrost zone, particularly at the southern margins, where mean annual air temperatures are above 0°C. As the Kenai lowlands experience ecosystem shifts due to human disturbance and climate change, understanding permafrost history is of particular interest given the direct impacts on hydrology, vegetation, and carbon cycling. Across the northern high latitudes, permafrost peatlands within the sporadic and isolated permafrost zone store 95 Pg of C and permafrost formation processes (i.e., syngenetic versus epigenetic) are thought to influence the degree of carbon loss following thaw. This study uses plant macrofossils and radiocarbon dating to determine the timing of permafrost aggradation of a recently-thawed (since 1950 CE) peatland located directly adjacent to a 5-meter thick permafrost plateau landform in the Kenai Peninsula lowlands in south-central Alaska. The coring site was selected using remote sensing imagery to identify areas where permafrost plateaus have been thawing since 1950 CE. Preliminary results show dominance of brown moss (Paludella squarrosa, Drepanocladus spp., Tomenthypnum nitens) and sedge (Carex spp.) from peat inception 11,700 cal yr BP to 3,000 cal yr BP indicative of a permafrost-free rich fen. A transition to silvic peat (Betula nana, Vaccinium oxycoccus, Ledum groenlandicum, ericaceous shrub macrofossils) 3,000 cal yr BP (indicates that permafrost aggradation coincided with neoglacial cooling. Since permafrost aggraded 9000 years after peat accumulation began and permafrost deepened to 5 m into unfrozen peat, this suggests mean annual air temperatures decreased significantly below 0ºC for several millennia in the late Holocene on the Kenai lowlands. This study will also examine impacts of permafrost aggradation and degradation on rates of carbon accumulation and loss.

  17. Late Glacial and Holocene Climate Change in the subantarctic Auckland Islands

    NASA Astrophysics Data System (ADS)

    Gilmer, G.; Moy, C. M.; Vandergoes, M.; Gadd, P.; Riesselman, C. R.; Jacobsen, G. E.; Wilson, G. S.; Visinand, C.

    2017-12-01

    Situated within the core of the Southern Hemisphere westerly winds, and between the subtropical and subantarctic fronts, the New Zealand subantarctic islands are uniquely positioned to evaluate past ocean and atmospheric change in the middle to high southern latitudes. We collected a series of sediment cores from Auckland Island fjords to produce a high-resolution record of climate change following the Last Glacial Maximum. Physical property and organic geochemical data, Itrax XRF, and visual core descriptions indicate the cores capture several phases of sedimentation. From these studies, we identify four primary sedimentary facies: 1) a deglacial facies exhibiting mm-scale laminae defined by magnetic susceptibility and density contrasts and high counts of elements associated with terrigenous sources; 2) a lacustrine facies defined by very low density, high organic carbon concentrations and low counts of lithophilic elements; 3) a marine transgression facies with moderate density, moderate bioturbation and alternating marine and lacustrine sedimentary components; 4) a marine facies that contains biogenic carbonate. Radiocarbon results indicate deglacial sedimentation was underway in the basin by approximately 19,000 cal yr BP. Lacustrine deposition in ice-free conditions began around 15,600 cal yr BP and continued until marine transgression at approximately 9,500 cal yr BP. During the early Holocene between 11 and 9.5 ka, we observe elevated n-alkane δD values and an overall increase in redox-sensitive elements that signal a combination of warmer atmospheric temperatures and reduced westerly wind strength that drives fjord stratification. Poleward-shifted westerlies south of the Auckland Islands could accommodate these results, but there are few records to corroborate this interpretation. We will discuss these results within the context of developing New Zealand and subantarctic paleoclimate records in order to provide a more comprehensive record of past change.

  18. Climate variability and fire effects on quaking aspen in the central Rocky Mountains, USA

    Treesearch

    Vachel A. Carter; Andrea Brunelle; Thomas A. Minckley; John D. Shaw; R. Justin DeRose; Simon Brewer

    2017-01-01

    Our understanding of how climate and fire have impacted quaking aspen (Populus tremuloides Michx.) communities prior to the 20th century is fairly limited. This study analysed the period between 4500 and 2000 cal. yr BP to assess the pre-historic role of climate and fire on an aspen community during an aspen-dominated period.

  19. A 27cal ka biomarker-based record of ecosystem changes from lacustrine sediments of the Chihuahua Desert of Mexico

    NASA Astrophysics Data System (ADS)

    Chávez-Lara, C. M.; Holtvoeth, J.; Roy, P. D.; Pancost, R. D.

    2018-07-01

    Hydroclimate variation of the northwest Mexico during the late Pleistocene and Holocene is an active area of debate, with uncertainty in the nature and sources of precipitation. Previous research has inferred the influences of winter storms, summer monsoonal rain and autumn tropical cyclones. The impacts on regional and local ecosystems, however, are not well constrained. Here, we investigate the response of lacustrine and terrestrial habitats of the Santiaguillo Basin in the Chihuahua Desert (Mexico) to hydrological changes occurring since the late last glacial. Biomarkers from the sediments reflect variable input of organic matter (OM) from algal and bacterial biomass, aquatic microfauna and surrounding vegetation, revealing distinct stages of ecosystem adaption over the last 27 cal ka. Based on previously published and new data, we show that a perennial productive lake was present during the late glacial and it persisted until 17.5 cal ka BP. Coinciding with Heinrich event 1, OM supply from deteriorating wetland soils may have been caused by early dry conditions. Further phases of increasing aridity and a shrinking water body drove changing OM quality and biomarker composition during the early and mid-Holocene. A pronounced shift in biomarker distributions at 4 cal ka BP suggests that the supply of plant litter from resinous trees and grasses increased, likely reflecting the establishment of modern vegetation. Our results illustrate the potential of biomarker applications in the area, adding to the evidence of hydroclimate variability and enabling reconstructions of local ecosystem dynamics.

  20. Limit on slip rate and timing of recent seismic ground-ruptures on the Jinghong fault, SE of the eastern Himalayan syntaxis

    NASA Astrophysics Data System (ADS)

    Shi, Xuhua; Weldon, Ray; Liu-Zeng, Jing; Wang, Yu; Weldon, Elise; Sieh, Kerry; Li, Zhigang; Zhang, Jinyu; Yao, Wenqian; Li, Zhanfei

    2018-06-01

    Quantifying slip rates and earthquake occurrence of active faults on the Shan Plateau, southeast of the eastern Himalayan syntaxis, is critical to assessing the seismic hazard and understanding the kinematics and geodynamics of this region. Most previous estimates of slip rates are averaged over either many millions of years using offset geological markers or decades using GPS. Well-constrained millennial slip rates of these faults remain sparse and constraints on recurrence rates of damaging earthquakes exist only for a few faults. Here we investigate the millennial slip rate and timing of recent earthquakes on the Jinghong fault, one of the geomorphically most significant sinistral-slip faults on the central Shan Plateau. We map and reconstruct fault offset (18 ± 5 m) of alluvial fan features at Manpa on the central Jinghong fault, using a 0.1 m-resolution digital surface model obtained from an unmanned aerial vehicle survey. We establish a slip rate, ≤2.5 ± 0.7 mm/yr over the past 7000 years, using pit-exposed stratigraphy. This millennial slip rate is consistent with rates averaged over both decadal and million-year timescales. Excavations at three sites near the town of Gelanghe on the northeastern Jinghong fault demonstrate 1) that the last seismic ground-rupture occurred between 482 and 889 cal yr BP, most likely in the narrower window 824-767 cal yr BP, if the lack of large earthquakes in the historical earthquake record is reliable, and 2) that multiple fault ruptures have occurred since 3618 cal yr BP. Combining this finding with a lack of large earthquakes in the 800-year-long Chinese historic record in this region, we suggest an average recurrence interval of seismic ground-ruptures on the order of 1000 years. This recurrence interval is consistent with the slip rate of the Jinghong fault and the size and earthquake frequency on other sinistral faults on the Shan Plateau.

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

    NASA Astrophysics Data System (ADS)

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

    2013-02-01

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

  2. Late Holocene climate variability from Lake Pupuke maar, Auckland, New Zealand

    NASA Astrophysics Data System (ADS)

    Striewski, B.; Shulmeister, J.; Augustinus, P. C.; Soderholm, J.

    2013-10-01

    Spectral analyses of quasi-annual organo-diatomaceous laminae couplets in an Auckland maar lake indicate brief (sub-decadal scale) episodes with strong spectral power and long periods of weak to no spectral power between c. 1700 to c. 550 cal. yr BP. Laminae couplet thickness appears to be a function of changes in wind flow over the basin, with enhanced wind flow deepening the mixing zone and providing additional nutrients for laminae formation. Aeolian dust from Australia amplifies the wind signal. Spectral signals in the high power episodes are focused in <4 years and 6-8 years windows. These are consistent with El Niño-Southern Oscillation (ENSO) periodicity. This climate system is known to play a major role in the modern Auckland climate whereby strongly negative (positive) ENSO are associated with enhanced (diminished) SW airflow over Auckland. ENSO events interact in the modern climate and the spectral results indicate that this is the case when spectral power is strong in the laminae. These results highlight strong but intermittent ENSO activity between 600 and 1400 cal. yr BP.

  3. Limiting age for the Provo shoreline of Lake Bonneville

    USGS Publications Warehouse

    Miller, David; Wahl, David B.; McGeehin, John; Rosario, Jose J.; Oviatt, Charles G.; Anderson, Lysanna; Presnetsova, Liubov S.

    2015-01-01

    Pluvial Lake Bonneville features a prominent shoreline at the Provo level, which has been interpreted as having formed during a period of threshold-stabilized overflow. The timing of Provo shoreline development is important for paleoclimate interpretations and for inferences on geomorphic process rates. Estimates for the timing of the shoreline formation, based on radiocarbon measurements from gastropod shells, are from approximately 18 to 15 cal ka. One key radiocarbon age on plant fragments from Swan Lake, which formed in the threshold spillway after overflow ceased, has been taken as a young limiting age. The conventional age of 12090 ± 300 14C when calibrated at 2σ has large uncertainty (13375–15103 cal BP). We report six new AMS radiocarbon ages recovered from new Swan Lake sediment cores. A twig near the base of lacustrine muds was dated at 11,615 ± 40 14C yr (13,350 to 13,560 cal BP). Age determinations on roots in that interval and deeper in the core are somewhat younger. These ages limit the last overflow of the Provo stand to earlier than ∼13.5 cal ka BP, consistent with the younger bound of the imprecise age reported by Bright. If conservative interpretations of sedimentation rates for the thick well-sorted sand interval below the lacustrine muds are correct and landscape change that resulted in damming of Swan Lake is accounted for, cessation of flow probably occurred before ∼14.5 cal ka BP.

  4. CalSimHydro Tool - A Web-based interactive tool for the CalSim 3.0 Hydrology Prepropessor

    NASA Astrophysics Data System (ADS)

    Li, P.; Stough, T.; Vu, Q.; Granger, S. L.; Jones, D. J.; Ferreira, I.; Chen, Z.

    2011-12-01

    CalSimHydro, the CalSim 3.0 Hydrology Preprocessor, is an application designed to automate the various steps in the computation of hydrologic inputs for CalSim 3.0, a water resources planning model developed jointly by California State Department of Water Resources and United States Bureau of Reclamation, Mid-Pacific Region. CalSimHydro consists of a five-step FORTRAN based program that runs the individual models in succession passing information from one model to the next and aggregating data as required by each model. The final product of CalSimHydro is an updated CalSim 3.0 state variable (SV) DSS input file. CalSimHydro consists of (1) a Rainfall-Runoff Model to compute monthly infiltration, (2) a Soil moisture and demand calculator (IDC) that estimates surface runoff, deep percolation, and water demands for natural vegetation cover and various crops other than rice, (3) a Rice Water Use Model to compute the water demands, deep percolation, irrigation return flow, and runoff from precipitation for the rice fields, (4) a Refuge Water Use Model that simulates the ponding operations for managed wetlands, and (5) a Data Aggregation and Transfer Module to aggregate the outputs from the above modules and transfer them to the CalSim SV input file. In this presentation, we describe a web-based user interface for CalSimHydro using Google Earth Plug-In. The CalSimHydro tool allows users to - interact with geo-referenced layers of the Water Budget Areas (WBA) and Demand Units (DU) displayed over the Sacramento Valley, - view the input parameters of the hydrology preprocessor for a selected WBA or DU in a time series plot or a tabular form, - edit the values of the input parameters in the table or by downloading a spreadsheet of the selected parameter in a selected time range, - run the CalSimHydro modules in the backend server and notify the user when the job is done, - visualize the model output and compare it with a base run result, - download the output SV file to be

  5. Dating the period when intensive anthropogenic activity began to influence the Sanjiang Plain, Northeast China.

    PubMed

    Cong, Jinxin; Gao, Chuanyu; Zhang, Yan; Zhang, Shaoqing; He, Jiabao; Wang, Guoping

    2016-02-24

    Dating the start of intensive anthropogenic influence on ecosystems is important for identifying the conditions necessary for ecosystem recovery. However, few studies have focused on determining when anthropogenic influences on wetland began through sedimentary archives. To fill this critical gap in our knowledge, combustion sources and emission intensities, reconstructed via black carbon (BC) and polycyclic aromatic hydrocarbons (PAHs) were analyzed in two wetlands in the Sanjiang Plain in Northeast China. (14)C provided age control for the sedimentary records. By combining previous sedimentary and archaeological studies, we attempt to date the beginning of intensive anthropogenic influences on the Sanjiang Plain. Our results showed that BC deposition fluxes increased from 0.02 to 0.7 g C/m(2).yr during the last 10,000 years. An upward trend was apparent during the last 500 years. Before 1200 cal yr BP, human activities were minor, such that the wetland ecosystem in the Sanjiang Plain before this period may represent the reference conditions that for the recovery of these wetlands. As the human population increased after 1200 cal yr BP, combustion sources changed and residential areas became a major source of BC and PAHs. In this way, the wetland ecosystem gradually became more heavily influenced by human activities.

  6. Dating the period when intensive anthropogenic activity began to influence the Sanjiang Plain, Northeast China

    NASA Astrophysics Data System (ADS)

    Cong, Jinxin; Gao, Chuanyu; Zhang, Yan; Zhang, Shaoqing; He, Jiabao; Wang, Guoping

    2016-02-01

    Dating the start of intensive anthropogenic influence on ecosystems is important for identifying the conditions necessary for ecosystem recovery. However, few studies have focused on determining when anthropogenic influences on wetland began through sedimentary archives. To fill this critical gap in our knowledge, combustion sources and emission intensities, reconstructed via black carbon (BC) and polycyclic aromatic hydrocarbons (PAHs) were analyzed in two wetlands in the Sanjiang Plain in Northeast China. 14C provided age control for the sedimentary records. By combining previous sedimentary and archaeological studies, we attempt to date the beginning of intensive anthropogenic influences on the Sanjiang Plain. Our results showed that BC deposition fluxes increased from 0.02 to 0.7 g C/m2.yr during the last 10,000 years. An upward trend was apparent during the last 500 years. Before 1200 cal yr BP, human activities were minor, such that the wetland ecosystem in the Sanjiang Plain before this period may represent the reference conditions that for the recovery of these wetlands. As the human population increased after 1200 cal yr BP, combustion sources changed and residential areas became a major source of BC and PAHs. In this way, the wetland ecosystem gradually became more heavily influenced by human activities.

  7. Dating the period when intensive anthropogenic activity began to influence the Sanjiang Plain, Northeast China

    PubMed Central

    Cong, Jinxin; Gao, Chuanyu; Zhang, Yan; Zhang, Shaoqing; He, Jiabao; Wang, Guoping

    2016-01-01

    Dating the start of intensive anthropogenic influence on ecosystems is important for identifying the conditions necessary for ecosystem recovery. However, few studies have focused on determining when anthropogenic influences on wetland began through sedimentary archives. To fill this critical gap in our knowledge, combustion sources and emission intensities, reconstructed via black carbon (BC) and polycyclic aromatic hydrocarbons (PAHs) were analyzed in two wetlands in the Sanjiang Plain in Northeast China. 14C provided age control for the sedimentary records. By combining previous sedimentary and archaeological studies, we attempt to date the beginning of intensive anthropogenic influences on the Sanjiang Plain. Our results showed that BC deposition fluxes increased from 0.02 to 0.7 g C/m2.yr during the last 10,000 years. An upward trend was apparent during the last 500 years. Before 1200 cal yr BP, human activities were minor, such that the wetland ecosystem in the Sanjiang Plain before this period may represent the reference conditions that for the recovery of these wetlands. As the human population increased after 1200 cal yr BP, combustion sources changed and residential areas became a major source of BC and PAHs. In this way, the wetland ecosystem gradually became more heavily influenced by human activities. PMID:26907560

  8. Influence of Land Development on Holocene Porites Coral Calcification at Nagura Bay, Ishigaki Island, Japan

    PubMed Central

    Sowa, Kohki; Watanabe, Tsuyoshi; Kan, Hironobu; Yamano, Hiroya

    2014-01-01

    To evaluate the relationships between coral calcification, thermal stress, and sedimentation and eutrophication linked to human impact (hereafter referred to as “land development”) by river discharge, we analyzed growth characteristics in the context of a paleoenvironment that was reconstructed from geochemical signals in modern and fossil (1.2 cal kyr BP and 3.5 cal kyr BP, respectively) massive Porites corals from Nagura Bay (“Nagura”) and from modern Porites corals from the estuary of the Todoroki River, Shiraho Reef (“Todoroki”). Both sites are on Ishigaki Island, Japan, and Nagura is located approximately 12 km west of Todoroki. At Nagura, the individual corals provide time windows of 13 (modern), 10 (1.2 cal kyr BP), and 38 yr in length (3.5 cal kyr BP). Here, we present the coral annual calcification for Nagura and Todoroki, and (bi) monthly resolved records of Sr/Ca (a proxy of sea surface temperature (SST)) and Ba/Ca (a proxy of sedimentation and nutrients related to land development) for Nagura. At Nagura, the winter SST was cooler by 2.8°C in the 1.2 cal kyr BP, and the annual and winter SSTs in the 3.5 cal kyr BP were cooler by 2.6°C and 4.6°C, respectively. The annual periodicity of Ba/Ca in modern coral is linked to river discharge and is associated with land development including sugar cane cultivation. Modern coral calcification also has declined with SST warming and increasing Ba/Ca peaks in winter. However, calcification of fossil corals does not appear to have been influenced by variations in Sr/Ca and Ba/Ca. Modern coral growth characteristics at Nagura and Todoroki indicate that coral growth is both spatially and temporally influenced by river discharge and land development. At Nagura, our findings suggest that land development induces negative thermal sensitivity for calcification in winter due to sugar cane harvest, which is a specifically modern phenomenon. PMID:24586393

  9. Holocene climate variability in the western Mediterranean through a multiproxy analysis from Padul peat bog (Sierra Nevada, Spain)

    NASA Astrophysics Data System (ADS)

    Ramos-Román, María J.; Jiménez-Moreno, Gonzalo; Camuera, Jon; García-Alix, Antonio; Anderson, R. Scott; Jiménez-Espejo, Francisco J.; Sachse, Dirk

    2017-04-01

    The Iberian Peninsula, located in the Mediterranean area, is an interesting location for paleoclimate studies due to its geographic situation between arid and humid climates. Sediments from peat bogs and lakes from Sierra Nevada, in southeastern Iberian Peninsula, have been very informative in terms of how vegetation and wetland environments were impacted by Holocene climate change. These studies are essential if we want to understand the past climate change in the area, which is the key to identify the possible environmental response of the Sierra Nevada ecosystems to future climate scenarios. Padul basin, located in the southwest of the Sierra Nevada mountain range, contains a ca. 100 m-thick peat bog sedimentary sequence that was deposited during the past 1 Ma making this area interesting for paleoenvironmental and paleoclimatic reconstructions. A new 43 m-long sedimentary record has recently been retrieved from the Padul peat bog. In this study we have developed a multiproxy analysis of the Holocene part of the Padul-15-05 core including pollen analysis, XRF-core scanner, magnetic susceptibility and organic geochemistry, supported by an age control based on AMS radiocarbon dates, providing with information about vegetation and climate variability during the past 9.9 cal ka BP. This multiproxy reconstruction of the Padul-15-05 evidences the Mediterranean as a sensitive area with respect to global-scale climate system, showing relevant climate episodes such as the ca. 8, 7.5, 6.5 and 5.5 cal ka BP events during the early and middle Holocene. The trend to aridification to the late Holocene is interrupted by more arid and humid periods as the Iberian Roman Humid Period (from ca. 3 to 1.6 cal ka BP), the Dark Ages (from ca. 1.5 to 1.1 cal ka BP), the Medieval Climate Anomaly (from ca. 1.1 to 1.3 cal ka BP) and the Little Ice Age period (from ca. 500 to 100 cal yr BP).

  10. Timing of late Holocene surface rupture of the Wairau Fault, Marlborough, New Zealand

    USGS Publications Warehouse

    Zachariasen, J.; Berryman, K.; Langridge, Rob; Prentice, C.; Rymer, M.; Stirling, M.; Villamor, P.

    2006-01-01

    Three trenches excavated across the central portion of the right-lateral strike-slip Wairau Fault in South Island, New Zealand, exposed a complex set of fault strands that have displaced a sequence of late Holocene alluvial and colluvial deposits. Abundant charcoal fragments provide age control for various stratigraphic horizons dating back to c. 5610 yr ago. Faulting relations from the Wadsworth trench show that the most recent surface rupture event occurred at least 1290 yr and at most 2740 yr ago. Drowned trees in landslide-dammed Lake Chalice, in combination with charcoal from the base of an unfaulted colluvial wedge at Wadsworth trench, suggest a narrower time bracket for this event of 1811-2301 cal. yr BP. The penultimate faulting event occurred between c. 2370 and 3380 yr, and possibly near 2680 ?? 60 cal. yr BP, when data from both the Wadsworth and Dillon trenches are combined. Two older events have been recognised from Dillon trench but remain poorly dated. A probable elapsed time of at least 1811 yr since the last surface rupture, and an average slip rate estimate for the Wairau Fault of 3-5 mm/yr, suggests that at least 5.4 m and up to 11.5 m of elastic shear strain has accumulated since the last rupture. This is near to or greater than the single-event displacement estimates of 5-7 m. The average recurrence interval for surface rupture of the fault determined from the trench data is 1150-1400 yr. Although the uncertainties in the timing of faulting events and variability in inter-event times remain high, the time elapsed since the last event is in the order of 1-2 times the average recurrence interval, implying that the Wairau Fault is near the end of its interseismic period. ?? The Royal Society of New Zealand 2006.

  11. Climate and tectonic variability during Late Quaternary in western fringe of Tibetan Plateau: case study from Trans-Himalayan ranges of Ladakh, NW India

    NASA Astrophysics Data System (ADS)

    Phartiyal, B.

    2016-12-01

    The climate system plays an important role in the geomorphological dynamics of a region. The cold, arid, high altitude, tectonically active areas of Ladakh (India) in Trans Himalaya, western Tibetan Plateau is none exception. Noticeable change in the landscape with a shift from fluvial to lacustrine regime at 10000 yrs BP forming big open valley lakes occupying the present day river valleys is attributed to the early Holocene northward advancement of the mean latitudinal position of the summer ITCZ causing wetter conditions in this dry area. The glaciers of the Ladakh range are almost depleted and the northern range glaciers show andrastic retreat in the Quaternary time. Lakes were studied using multi-proxies, to record centennial and decadal scale climatic variability. Spatial and temporal setting of Spituk palaeolake (12600-240 cal yrs BP) along Indus River, was analyzed using multi proxies. The lake that extended for 40-50 km covering an area of 106 km2, was formed after Older Dryas as a result of river blockage by precipitation induced debris flow and seismicity. Two lake phases between 12600-9000 and 5500-3200 cal yrs BP show stable lake conditions and have synchronous relationship between high variation in monsoon intensity, high δ18O values in the Guliya core, rise in temperature and high solar insolation. High magnetic susceptibility and clay content along with diversified diatom and other freshwater algae and land derived organic matter are indicative of fresh water supply leading to high lake level from 4700 yr BP onwards in the present pro-glacial lakes studied. The multi-proxy data provides evidence of much higher and stable lake level during 3700 yr BP and 3000 yr BP onwards due to high water supply in these lake. It is in contrast to the records of weak ISM conditions and low lake level in rest of the part of Indian peninsula during the period. The study also suggests strong western disturbance activity during 4800-3000 yr BP leading to high lake

  12. An 11 000-year-long record of fire and vegetation history at Beaver Lake, Oregon, central Willamette Valley

    Treesearch

    Megan K. Walsh; Christopher A. Pearl; Cathy Whitlock; Patrick J. Bartlein; Marc A. Worona

    2010-01-01

    High-resolution macroscopic charcoal and pollen analysis were used to reconstruct an 11 000-year-long record of fire and vegetation history from Beaver Lake, Oregon, the first complete Holocene paleoecological record from the floor of the Willamette Valley. In the early Holocene (ca 11 000-7500 calendar years before present [cal yr BP]), warmer, drier summers than at...

  13. Effects of Plinian Eruptions of Somma-vesuvius On People, Animals, Structures and Objects: Inferences From Avellino (3760 Yr B.p.) and Pompei (79 A.d.) Events.

    NASA Astrophysics Data System (ADS)

    Mastrolorenzo, G.; Petrone, P. P.; Geraci, G.; Guarino, F.; Incoronato, A.

    An interdisciplinary approach to the archaeological sites affected by Avellino (3750 yr. B.P.) and Pompei (79 A.D.) plinian eruptions of Somma-Vesuvius provides new data relative to the depositional mechanisms. Large scale stratigraphy and local evi- dences provide new informations about the physical conditions at the emplacement of PDCs and their effects on structures, people and environment. Field evidences indicate that fine grained pyroclastic deposits related to the column collapses propagate up to a distance of about 15 km from the crater and emplaced with conspicuous thickness. In both Avellino and Pompei eruptions, direct evidences from archaeological sites in- dicate that the emplacement in intermediate and distal areas was relatively quite (low mechanical energy). The recognition of thin, continuous, fine grained surge deposits up to a distance of ca. 15 km from the crater suggests that turbulence was important and the PDCs advanced as a relatively thick dilute current, very poorly controlled by the topography. Furthermore, due to the very small sizes, the particles were always transported in suspension, even at very low current velocity, thus avoiding vertical grading to occur. However, due to the very high depositional mass rate, the emplace- ment was very rapid causing buildings and hut, objects, animals and people to be engulfed within the ash deposits thus preserving their original position, as seen at Herculaneum, Oplontis, Pompeii (79 AD) and Nola (3760 bp). The skeletons of hu- man as well animal victims show high temperature effects. In particular, microscopic bones texture of the victims in the sites affected by the 79 A.D are consistent with very high temperatures, which are anomalous in pyroclastic surge clouds.

  14. Lake Sediment Records as an Indicator of Holocene Fluctuations of Quelccaya Ice Cap, Peru and Regional Climate

    NASA Astrophysics Data System (ADS)

    Stroup, J. S.; Kelly, M. A.; Lowell, T. V.; Beal, S. A.; Smith, C. A.; Baranes, H. E.

    2012-12-01

    The past fluctuations of Quelccaya Ice Cap, (QIC; 13°S, 70°W, 5200 m asl) located in the southeastern Peruvian Andes, provide a record of tropical climate since the last glacial-interglacial transition. A detailed surficial geomorphic record of past glacial extents developed over the last several decades (e.g. Mercer and Palacios 1977; Buffen et al. 2009; Kelly et al. 2012 accepted) demonstrates that QIC is a dynamic glacial system. These records show that the ice cap was larger than present and retreating by ~11,500 yr BP, and smaller than present between ~7,000 and ~4,600 yr BP. The most recent advance occurred during the late Holocene (Little Ice Age;LIA), dated with 10Be surface exposure ages (510±90 yrs (n = 8)) (Stroup et al. in prep.). This overrode earlier deposits obscuring a complete Holocene record; we aim to address the gaps in glacial chronology using the sedimentary record archived in lakes. We retrieved two sets cores (8 and 5 m-long) from Laguna Challpacocha (13.91°S, 70.86°W, 5040 m asl), a lake that currently receives meltwater from QIC. Four radiocarbon ages from the cores suggest a continuous record dating to at least ~10,500 cal. yr BP. Variations in magnetic susceptibility, percent organic and inorganic carbon, bulk density, grayscale and X-ray fluorescence chemistry indicate changes in the amount of clastic sediment deposition. We interpret clastic sediments to have been deposited from ice cap meltwater, thus indicating more extensive ice. Clastic sediments compose the top of the core from 4 to 30 cm depth, below there is a sharp transition to organic sediments radiocarbon dated to (500±30 and 550±20 cal. yr BP). The radiocarbon ages are similar to the 10Be dated (LIA) glacial position. At least three other clastic units exist in the core; dating to ~2600-4300, ~4800-7300 and older then ~10,500 cal. yr BP based on a linear age model with four radiocarbon dates. We obtained two, ~4 m long, cores from Laguna Yanacocha (13.95°S,70.87

  15. Great Basin Archaeology During the Middle Holocene: a Reflection of Environmental Change

    NASA Astrophysics Data System (ADS)

    Wriston, T.

    2008-12-01

    Varying types of proxy data in the Great Basin of the western United States suggest that the environment changed dramatically during the mid-Holocene. Lake, marsh, and spring systems dried; and dune fields, first established at the end of the Pleistocene, where again activated as sediments were swept from drying basin lowlands. Plant communities reorganized and migrated along elevation gradients to adapt to these changing conditions, and animal populations followed. However, recent data suggests that conditions during the middle Holocene were variable. Minimally, three distinct periods can be recognized, herein named: the Initial Middle Holocene (ca. 8000 to 5800 cal yr BP), the Middle Holocene Gap (ca. 5800 to 5200 cal yr BP), and the Terminal Middle Holocene (ca. 5200 to 4000 cal yr BP). Depending on location and the type of proxy data studied, these periods can vary in their character and timing, but their sequence is increasingly recognized in records of both regional and global-scale. The Initial Middle Holocene is the driest and most volatile of the three periods, with a shift from winter-to summer-dominated precipitation, often delivered by torrential storms. Conversely, the Middle Holocene Gap is a relatively mesic interval with increased winter precipitation and cooler temperatures. A shift towards drier conditions is again evidenced during the Terminal Middle Holocene; however, conditions are never again as dry or as volatile as during the Initial Middle Holocene. The archaeological signature of the Great Basin during the middle Holocene reflects adaptation to this changing environment. During the Initial Middle Holocene, archaeological sites are relatively scarce, and when present, are near water sources substantial enough to persist through the intense drought. The uplands became a focus of sustained seasonal use for the first time as increasingly diverse resources and environments are routinely exploited. It follows that milling gear is a regular and

  16. A Reconstruction of Humidity Changes for the Last 8000 Years, Yukon Territory, Canada

    NASA Astrophysics Data System (ADS)

    Anderson, L.; Abbott, M. B.; Burns, S. J.; Bruce, F. P.

    2002-12-01

    Oxygen isotope data from authigenic carbonate in the sediments from two geographically proximal lakes are used to calculate changes in humidity. Jellybean Lake (60.351 °N, 134.805 °W) is hydrologically open with modern lake water δ18O similar to rivers, spring water and precipitation (-21 per mil) in the region. Sediment-core carbonate values range from -19 to -21 per mil. Marcella Lake (60.074 °N, 133.898 °W) is hydrologically closed, such that most all of the outflow is via evaporation. Modern lake water in Marcella is -8 per mil and sediment-core carbonate values range from -8.5 to -12 per mil. Because Marcella Lake has been hydrologically closed throughout the Holocene, sediment-core δ18O values are primarily controlled by changes in regional humidity, which will govern evaporation rates. However, changes in the δ18O values of input waters, either because of changes in ambient temperature or moisture source regions, or both, may also be responsible. The latter factors can be accounted for by the changes in the δ18O of hydrologically open Jellybean Lake because the lake water is isotopically equivalent to meteoric precipitation. The 1-cm sampling interval used is equivalent to 20 years time. Chronologies for both lakes are constrained by 210Pb, the depth of the White River Ash and radiocarbon ages from terrestrial macrofossils. We calculate the isotopic enrichment in Marcella Lake due to evaporation by correcting the δ18O data with Jellybean Lake δ18O data. Changes in humidity were determined using a model of a terminal lake at hydrological and isotopic steady state. The δ18O of the uppermost sediments generate humidity values between 63 and 65%, which are consistent with the average humidity in Teslin, YT of 64.9%. During the last 2000 years, high values of 70% between ~2000 and 1200 cal yr B.P., are followed by a dry cycle between 1200 and 800 cal yr B.P. Intermediate values between 65 and 68% occurred between 800 and 300 cal yr B.P. At 290 cal yr B.P

  17. Terrestrial biomarker records in Seomjin Estuary in the South Sea of Korea: Implication for terrestrial flux and environmental changes

    NASA Astrophysics Data System (ADS)

    kim, Songyi; hyun, Sangmin; Kim, Wonnyon; Hyeong, Kiseong

    2016-04-01

    High-resolution records of terrestrial biomarkers, n-alkane compounds, were investigated in two gravity cores (SJP-2 and SJP-4) to evaluate variations in terrestrial organic matter influx. Based on 14C dating, sediments in both cores were deposited during the mid-Holocene; the ages of the bottom sediments of SJP-2 and SJP-4 reached 5,500 Cal yr BP and 5,000 Cal yr BP, respectively. High concentrations of total n-alkanes (nC25-35) in the two cores showed an increasing tendency from 4,500 yr to ca. 2,000 yr. The composition changed at the boundary of 2,500 yr in both cores, suggesting a variation in terrestrial biomarker influx at this time. Several indices including average chain length (ACL), carbon preference index (ICP), and paleo-vegetation index (Paq) showed coincident variations in both cores; ACL exhibited a narrow range of variations with a slight shift at 2,500 yr, CPI showed a decreasing tendency from 4,000 yr to 2,500 yr, and Paq increased during these intervals. Furthermore, the ratios of C23/C31 and C25/C31, indicate a relative abundance of epicuticular wax from vascular plants with coincident variations in both cores, and this also marched well with Paq. CPI excursions suggested that the total n-alkane proxy of the two cores might not only be linked to local climatic variability but also to local oceanographic conditions due to the different sedimentation rates. Variations in paleovegetation and paleoclimate around the study area might be strongly associated with the influx of terrestrial organic compounds derived from vascular plants. Additional 14C dating and isotope study of individual n-alkane biomarkers will provide detailed information on paleoclimatic and paleovegetation changes.

  18. Youngest radiocarbon age for Jefferson's ground sloth, Megalonyx jeffersonii (Xenarthra, Megalonychidae)

    NASA Astrophysics Data System (ADS)

    Gregory McDonald, H.; Stafford, Thomas W.; Gnidovec, Dale M.

    2015-03-01

    A partial skeleton of the extinct ground sloth, Megalonyx jeffersonii, recovered from a farm near Millersburg, Ohio in 1890, was radiocarbon dated for the first time. The ungual dated is part of a skeleton mounted for exhibit at the Orton Geological Museum at Ohio State University and was the first mounted skeleton of this animal. From its initial discovery the bones were treated with multiple organic compounds that had the potential to compromise the radiocarbon age and the specimen required special treatments in order to obtain a valid radiocarbon age. The 14C measurement on the ungual from this skeleton (11,235 ± 40 14C yr BP = 13,180-13,034 cal yr BP) is the youngest 14C age presently determined for M. jeffersonii.

  19. CalNex Observational Data

    EPA Pesticide Factsheets

    Observations made during the 2010 CalNex measurement campaign. This dataset is associated with the following publication:Woody , M., K. Baker , P. Hayes, J. Jimenez, B. Koo, and H. Pye. Understanding sources of organic aerosol during CalNex-2010 using the CMAQ-VBS. Atmospheric Chemistry and Physics. Copernicus Publications, Katlenburg-Lindau, GERMANY, 16: 4081-4100, (2016).

  20. Human (Clovis)-gomphothere (Cuvieronius sp.) association ∼ 13,390 calibrated yBP in Sonora, Mexico.

    PubMed

    Sanchez, Guadalupe; Holliday, Vance T; Gaines, Edmund P; Arroyo-Cabrales, Joaquín; Martínez-Tagüeña, Natalia; Kowler, Andrew; Lange, Todd; Hodgins, Gregory W L; Mentzer, Susan M; Sanchez-Morales, Ismael

    2014-07-29

    The earliest known foragers to populate most of North America south of the glaciers [∼ 11,500 to ≥ ∼ 10,800 (14)C yBP; ∼ 13,300 to ∼ 12,800 calibrated (Cal) years] made distinctive "Clovis" artifacts. They are stereotypically characterized as hunters of Pleistocene megamammals (mostly mammoth) who entered the continent via Beringia and an ice-free corridor in Canada. The origins of Clovis technology are unclear, however, with no obvious evidence of a predecessor to the north. Here we present evidence for Clovis hunting and habitation ∼ 11,550 yBP (∼ 13,390 Cal years) at "El Fin del Mundo," an archaeological site in Sonora, northwestern Mexico. The site also includes the first evidence to our knowledge for gomphothere (Cuvieronius sp.) as Clovis prey, otherwise unknown in the North American archaeological record and terminal Pleistocene paleontological record. These data (i) broaden the age and geographic range for Clovis, establishing El Fin del Mundo as one of the oldest and southernmost in situ Clovis sites, supporting the hypothesis that Clovis had its origins well south of the gateways into the continent, and (ii) expand the make-up of the North American megafauna community just before extinction.

  1. Human (Clovis)-gomphothere (Cuvieronius sp.) association ∼13,390 calibrated yBP in Sonora, Mexico

    NASA Astrophysics Data System (ADS)

    Sanchez, Guadalupe; Holliday, Vance T.; Gaines, Edmund P.; Arroyo-Cabrales, Joaquín; Martínez-Tagüeña, Natalia; Kowler, Andrew; Lange, Todd; Hodgins, Gregory W. L.; Mentzer, Susan M.; Sanchez-Morales, Ismael

    2014-07-01

    The earliest known foragers to populate most of North America south of the glaciers [∼11,500 to ≥ ∼10,800 14C yBP; ∼13,300 to ∼12,800 calibrated (Cal) years] made distinctive "Clovis" artifacts. They are stereotypically characterized as hunters of Pleistocene megamammals (mostly mammoth) who entered the continent via Beringia and an ice-free corridor in Canada. The origins of Clovis technology are unclear, however, with no obvious evidence of a predecessor to the north. Here we present evidence for Clovis hunting and habitation ∼11,550 yBP (∼13,390 Cal years) at "El Fin del Mundo," an archaeological site in Sonora, northwestern Mexico. The site also includes the first evidence to our knowledge for gomphothere (Cuvieronius sp.) as Clovis prey, otherwise unknown in the North American archaeological record and terminal Pleistocene paleontological record. These data (i) broaden the age and geographic range for Clovis, establishing El Fin del Mundo as one of the oldest and southernmost in situ Clovis sites, supporting the hypothesis that Clovis had its origins well south of the gateways into the continent, and (ii) expand the make-up of the North American megafauna community just before extinction.

  2. Stratigraphic reconstruction of two debris avalanche deposits at Colima Volcano (Mexico): Insights into pre-failure conditions and climate influence

    NASA Astrophysics Data System (ADS)

    Roverato, M.; Capra, L.; Sulpizio, R.; Norini, G.

    2011-10-01

    Throughout its history, Colima Volcano has experienced numerous partial edifice collapses with associated emplacement of debris avalanche deposits of contrasting volume, morphology and texture. A detailed stratigraphic study in the south-eastern sector of the volcano allowed the recognition of two debris avalanche deposits, named San Marcos (> 28,000 cal yr BP, V = ~ 1.3 km 3) and Tonila (15,000-16,000 cal yr BP, V = ~ 1 km 3 ). This work sheds light on the pre-failure conditions of the volcano based primarily on a detailed textural study of debris avalanche deposits and their associated pyroclastic and volcaniclastic successions. Furthermore, we show how the climate at the time of the Tonila collapse influenced the failure mechanisms. The > 28,000 cal yr BP San Marcos collapse was promoted by edifice steep flanks and ongoing tectonic and volcanotectonic deformation, and was followed by a magmatic eruption that emplaced pyroclastic flow deposits. In contrast, the Tonila failure occurred just after the Last Glacial Maximum (22,000-18,000 cal BP) and, in addition to the typical debris avalanche textural characteristics (angular to sub-angular clasts, coarse matrix, jigsaw fit) it shows a hybrid facies characterized by debris avalanche blocks embedded in a finer, homogenous and partially cemented matrix, a texture more characteristic of debris flow deposits. The Tonila debris avalanche is directly overlain by a 7-m thick hydromagmatic pyroclastic succession. Massive debris flow deposits, often more than 10 m thick and containing large amounts of tree trunk logs, represent the top unit in the succession. Fluvial deposits also occur throughout all successions; these represent periods of highly localized stream reworking. All these lines of evidence point to the presence of water in the edifice prior to the Tonila failure, suggesting it may have been a weakening factor. The Tonila failure appears to represent an anomalous event related to the particular climatic

  3. ZeroCal: Automatic MAC Protocol Calibration

    NASA Astrophysics Data System (ADS)

    Meier, Andreas; Woehrle, Matthias; Zimmerling, Marco; Thiele, Lothar

    Sensor network MAC protocols are typically configured for an intended deployment scenario once and for all at compile time. This approach, however, leads to suboptimal performance if the network conditions deviate from the expectations. We present ZeroCal, a distributed algorithm that allows nodes to dynamically adapt to variations in traffic volume. Using ZeroCal, each node autonomously configures its MAC protocol at runtime, thereby trying to reduce the maximum energy consumption among all nodes. While the algorithm is readily usable for any asynchronous low-power listening or low-power probing protocol, we validate and demonstrate the effectiveness of ZeroCal on X-MAC. Extensive testbed experiments and simulations indicate that ZeroCal quickly adapts to traffic variations. We further show that ZeroCal extends network lifetime by 50% compared to an optimal configuration with identical and static MAC parameters at all nodes.

  4. Stable isotopes, Sr/Ca, and Mg/Ca in biogenic carbonates from Petaluma Marsh, northern California, USA

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Ingram, B.L.; Deckker, P. de; Chivas, A.R.

    1998-10-01

    Stable isotope ({sup 18}O/{sup 16}O and {sup 13}C/{sup 12}C) and minor-element compositions (Sr/Ca and Mg/Ca ratios) of ostracodes and gastropods separated from marsh sediments from San Francisco Bay, Northern California, were used to reconstruct paleoenvironmental changes in Petaluma March over the past 700 yr. The value of {delta}{sup 18}O in the marsh carbonates reflects changes in freshwater inflow, evaporation, and temperature. Mg/Ca and Sr/Ca in ostracode calcite reflect changes in both freshwater inflow and temperature, although primarily reflect temperature changes in the salinity range of about 10--35{per_thousand}. Ostracode {delta}{sup 18}O values show a gradual increase by 5{per_thousand} between 500 yrmore » BP and the present, probably reflecting rising sea level and increased evaporation in the marsh. Superimposed on this trend are higher frequency Mg/Ca and {delta}{sup 18}O variations (3--4{per_thousand}), probably reflecting changes in freshwater inflow and evaporation. A period of low Mg/Ca occurred between about 100--300 cal yr BP, suggesting wetter and cooler conditions during the Little Ice Age. Higher Mg/Ca ratios occurred 600--700 cal yr BP, indicating drier and warmer conditions during the end of the Medieval Warm Period. Both ostracode and gastropod {delta}{sup 13}C values decrease up-core, reflecting decomposition of marsh vegetation, which changes from C{sub 4} ({delta}{sup 13}C {approximately} {minus}12{per_thousand}) to CAM ({delta}{sup 13}C = {minus}26{per_thousand})-type vegetation over time.« less

  5. Revision of Ernst Antevs' New England Varve Chronology: A Record of Meltwater Production and Southeastern LIS Recession: 18.2-12.5 kyr BP (Invited)

    NASA Astrophysics Data System (ADS)

    Ridge, J. C.

    2013-12-01

    New varve cores and 54 radiocarbon ages, have allowed the correction, closure of a gap, calibration, and expansion of Ernst Antevs' (1922) New England Varve Chronology from sediments of glacial Lake Hitchcock and it's successors in the Connecticut Valley of western New England (northeastern U.S.A.). The continuous 5659-yr chronology (18.2-12.5 kyr BP) has been renumbered as the North American Varve Chronology. Glacial varve thickness (18.2-13.7 kyr BP) documents abrupt changes in meltwater production related to varying ablation rate (summer climate) that is linked to ice sheet recession rates and advances, i.e. cold intervals are times of thin varves and slower ice recession or glacial readvances. To take advantage of the varve-climate relationship it is necessary to identify non-climatic events that can cause varve thickness to change. This includes sudden changes in lake level and flood events triggered by the abrupt drainage of tributary glacial lakes. A chronology of ice recession for intervals terminated by four stillstands and readvances of 1-2 century durations have been determined for the Connecticut Valley (from S to N): 50-100 m/yr in northern Connecticut to southern Massachusetts; Chicopee Readvance; 30-40 m/yr in central Mass.; Hatfield event; 80-90 m/yr from northern Mass. to central New Hampshire; North Charlestown end moraines; 300 m/yr to northern N.H.; Littleton Readvance; >300 m/yr to Quebec. Meltwater produced by ice recession of 300 m/yr modeled as a receding 1-bar ice sheet profile (from 100 km up ice near ELA to margin, valley width of 80 km, glacier flow rate of 200 m/yr at ELA) would be a minimum glacial meltwater discharge in the Connecticut Valley of ~90 x 109 m3/yr. This is ~10X the modern Conn. River discharge at Walpole, NH compressed almost entirely to the melt season. Non-glacial varves deposited after ice receded from the basin (13.7-12.5 kyr BP) also document climate change as a result of varve thickness varying with changes in

  6. An Early Holocene Record of Cimex (Hemiptera: Cimicidae) From Western North America.

    PubMed

    Adams, Martin E; Jenkins, Dennis L

    2017-07-01

    The subfossil remains of 14 cimicids (Hemiptera: Cimicidae) were recovered during archaeological investigations of the Paisley Five Mile Point Cave site (35LK3400), an exceptionally well-dated (n = 229 radiocarbon dates) late Pleistocene-early Holocene rock shelter site in south-central Oregon. Nine of the specimens have been assigned to three modern species of Nearctic Cimicidae-Cimex antennatus Usinger & Ueshima, Cimex latipennis Usinger & Ueshima, and Cimex pilosellus (Horváth)-whereas the remaining five individuals were too fragmentary to positively identify. The chronology of the insect assemblage puts one specimen at circa 5,100 calibrated years before present (cal. yr BP), and the remaining 13 range in age from 9,400 to almost 11,000 cal. yr BP. Although fossil and subfossil cimicid remains have been recovered at other archaeological sites, the fossil record for bed bugs is largely undocumented. The Paisley Caves specimens thus far represent the oldest remains of the genus in probable contact with humans on record. © The Authors 2017. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

  7. Patterns of human occupation during the early Holocene in the Central Ebro Basin (NE Spain) in response to the 8.2 ka climatic event

    NASA Astrophysics Data System (ADS)

    González-Sampériz, P.; Utrilla, P.; Mazo, C.; Valero-Garcés, B.; Sopena, MC.; Morellón, M.; Sebastián, M.; Moreno, A.; Martínez-Bea, M.

    2009-03-01

    The Central Ebro River Basin (NE Spain) is the most northern area of truly semi-arid Mediterranean climate in Europe and prehistoric human occupation there has been strongly influenced by this extreme environmental condition. Modern climate conditions single out this region due to the harsh environment, characterised by the highest absolute summer temperatures of the Ebro River Basin. The Bajo Aragón region (SE Ebro River Basin) was intensively populated during the Early Holocene (9400-8200 cal yr BP) but the settlements were abandoned abruptly at around 8200 cal yr BP. We propose that this "archaeological silence" was caused by the regional impact of the global abrupt 8.2 ka cold event. Available regional paleoclimate archives demonstrate the existence of an aridity crisis then that interrupted the humid Early Holocene. That environmental crisis would have forced hunter-gatherer groups from the Bajo Aragón to migrate to regions with more favourable conditions (i.e. more humid mountainous areas) and only return in the Neolithic. Coherently, archaeological sites persist during this crisis in the nearby Iberian Range (Maestrazgo) and the North Ebro River area (Pre-Pyrenean mountains and along the northwestern Ebro Basin).

  8. Human (Clovis)–gomphothere (Cuvieronius sp.) association ∼13,390 calibrated yBP in Sonora, Mexico

    PubMed Central

    Sanchez, Guadalupe; Holliday, Vance T.; Gaines, Edmund P.; Arroyo-Cabrales, Joaquín; Martínez-Tagüeña, Natalia; Kowler, Andrew; Lange, Todd; Hodgins, Gregory W. L.; Mentzer, Susan M.; Sanchez-Morales, Ismael

    2014-01-01

    The earliest known foragers to populate most of North America south of the glaciers [∼11,500 to ≥ ∼10,800 14C yBP; ∼13,300 to ∼12,800 calibrated (Cal) years] made distinctive “Clovis” artifacts. They are stereotypically characterized as hunters of Pleistocene megamammals (mostly mammoth) who entered the continent via Beringia and an ice-free corridor in Canada. The origins of Clovis technology are unclear, however, with no obvious evidence of a predecessor to the north. Here we present evidence for Clovis hunting and habitation ∼11,550 yBP (∼13,390 Cal years) at “El Fin del Mundo,” an archaeological site in Sonora, northwestern Mexico. The site also includes the first evidence to our knowledge for gomphothere (Cuvieronius sp.) as Clovis prey, otherwise unknown in the North American archaeological record and terminal Pleistocene paleontological record. These data (i) broaden the age and geographic range for Clovis, establishing El Fin del Mundo as one of the oldest and southernmost in situ Clovis sites, supporting the hypothesis that Clovis had its origins well south of the gateways into the continent, and (ii) expand the make-up of the North American megafauna community just before extinction. PMID:25024193

  9. Fond Memories of Cal Council

    ERIC Educational Resources Information Center

    Minnis, Douglas L.

    2015-01-01

    This article describes the author's personal involvement in the California Council for the Education of Teachers (Cal Council), beginning in 1960 and spanning four decades, which involved associations with key people in California teacher education and credentialing. The Cal Council was organized for leaders in teacher education from the…

  10. Rock-magnetic proxies of wind intensity and dust since 51,200 cal BP from lacustrine sediments of Laguna Potrok Aike, southeastern Patagonia

    NASA Astrophysics Data System (ADS)

    Lisé-Pronovost, Agathe; St-Onge, Guillaume; Gogorza, Claudia; Haberzettl, Torsten; Jouve, Guillaume; Francus, Pierre; Ohlendorf, Christian; Gebhardt, Catalina; Zolitschka, Bernd

    2015-02-01

    The sedimentary archive from Laguna Potrok Aike is the only continuous record reaching back to the last Glacial period in continental southeastern Patagonia. Located in the path of the Southern Hemisphere westerly winds and in the source region of dust deposited in Antarctica during Glacial periods, southern Patagonia is a vantage point to reconstruct past changes in aeolian activity. Here we use high-resolution rock-magnetic and physical grain size data from site 2 of the International Continental scientific Drilling Program (ICDP) Potrok Aike maar lake Sediment Archive Drilling prOject (PASADO) in order to develop magnetic proxies of dust and wind intensity at 52°S since 51,200 cal BP. Rock-magnetic analysis indicates the magnetic mineral assemblage is dominated by detrital magnetite. Based on the estimated flux of magnetite to the lake and comparison with distal dust records from the Southern Ocean and Antarctica, kLF is interpreted as a dust indicator in the dust source of southern Patagonia at the millennial time scale, when ferrimagnetic grain size and coercivity influence are minimal. Comparison to physical grain-size data indicates that the median destructive field of isothermal remanent magnetization (MDFIRM) mostly reflects medium to coarse magnetite bearing silts typically transported by winds for short-term suspension. Comparison with wind-intensity proxies from the Southern Hemisphere during the last Glacial period and with regional records from Patagonia since the last deglaciation including marine, lacustrine and peat bog sediments as well as speleothems reveals similar variability with MDFIRM up to the centennial time scale. MDFIRM is interpreted as a wind-intensity proxy independent of moisture changes for southeastern Patagonia, with stronger winds capable of transporting coarser magnetite bearing silts to the lake.

  11. A New Appraisal of Northern Peatlands and Global Atmospheric Methane Over the Holocene

    NASA Astrophysics Data System (ADS)

    MacDonald, G. M.; Holmquist, J. R.; Kremenetski, K.; Loisel, J.

    2015-12-01

    Use of large databases of peat cores to examine linkages between northern peatlands and atmospheric CH4 over the Holocene has been prone to uncertainties regarding 1. comparability of radiocarbon techniques and material dated, 2. appropriate summed probability distributions, 3. spatial representativeness of the sites, particularly in capturing sites south of the subarctic, 4. potential impacts of local lateral peatland expansion versus continental-scale peatland initiation, particularly in the late Holocene, and 5. impacts of changes in the proportion of high methane-producing fens vs Sphagnum bogs. We present a comparison of radiocarbon measurements from conventional counts, atomic mass spectrometry and differing peat materials to demonstrate a general compatibility of the various types of dates. We compare and apply several summed probability distribution methods to minimize any statistical bias in our analysis. We then present our analysis of a new data set of 7571 peatland cores from 4420 sites that extend into the temperate zone. Of these, 3732 cores inform on lateral expansion and 329 dates constrain the timing of fen-bog transition. Based on these data in original and gridded form we show that widespread peat initiation commenced at 16 kcal yr BP and reached a maximum rate at 11-8 kcal yr BP. Most sites began as fens, and peak transition to bogs occurred between 5 and 3 kcal yr BP, with a 1000 year lag between Eurasia and North America. There is no global late Holocene increase in lateral expansion. Based on modeled northern peatland area and ratio of fen/bog sites, CH4 production from northern peatlands increased rapidly from 11 to 9 cal yr BP, followed by slower increase until reaching a maximum at 5 kcal yr BP at 25 Tg per yr. From 4 kcal yr BP to Present, bogs become a dominant feature in the northern peatland landscape and CH4 production decreased to reach modern-day levels at about 20 Tg per yr. Northern peatlands have been a key infleunce on global

  12. Eastern Andean environmental and climate synthesis for the last 2000 years BP from terrestrial pollen and charcoal records of Patagonia

    NASA Astrophysics Data System (ADS)

    Sottile, G. D.; Echeverria, M. E.; Mancini, M. V.; Bianchi, M. M.; Marcos, M. A.; Bamonte, F. P.

    2015-06-01

    The Southern Hemisphere Westerly Winds (SWW) constitute an important zonal circulation system that dominates the dynamics of Southern Hemisphere mid-latitude climate. Little is known about climatic changes in the Southern South America in comparison to the Northern Hemisphere due to the low density of proxy records, and adequate chronology and sampling resolution to address environmental changes of the last 2000 years. Since 2009, new pollen and charcoal records from bog and lakes in northern and southern Patagonia at the east side of the Andes have been published with an adequate calibration of pollen assemblages related to modern vegetation and ecological behaviour. In this work we improve the chronological control of some eastern Andean previously published sequences and integrate pollen and charcoal dataset available east of the Andes to interpret possible environmental and SWW variability at centennial time scales. Through the analysis of modern and past hydric balance dynamics we compare these scenarios with other western Andean SWW sensitive proxy records for the last 2000 years. Due to the distinct precipitation regimes that exist between Northern (40-45° S) and Southern Patagonia (48-52° S) pollen sites locations, shifts on latitudinal and strength of the SWW results in large changes on hydric availability on forest and steppe communities. Therefore, we can interpret fossil pollen dataset as changes on paleohydric balance at every single site by the construction of paleohydric indices and comparison to charcoal records during the last 2000 cal yrs BP. Our composite pollen-based Northern and Southern Patagonia indices can be interpreted as changes in latitudinal variation and intensity of the SWW respectively. Dataset integration suggest poleward SWW between 2000 and 750 cal yrs BP and northward-weaker SWW during the Little Ice Age (750-200 cal yrs BP). These SWW variations are synchronous to Patagonian fire activity major shifts. We found an in phase

  13. Holocene tectonics and fault reactivation in the foothills of the north Cascade Mountains, Washington

    USGS Publications Warehouse

    Sherrod, Brian L.; Barnett, Elizabeth; Schermer, Elizabeth; Kelsey, Harvey M.; Hughes, Jonathan; Foit, Franklin F.; Weaver, Craig S.; Haugerud, Ralph; Hyatt, Tim

    2013-01-01

    We use LiDAR imagery to identify two fault scarps on latest Pleistocene glacial outwash deposits along the North Fork Nooksack River in Whatcom County, Washington (United States). Mapping and paleoseismic investigation of these previously unknown scarps provide constraints on the earthquake history and seismic hazard in the northern Puget Lowland. The Kendall scarp lies along the mapped trace of the Boulder Creek fault, a south-dipping Tertiary normal fault, and the Canyon Creek scarp lies in close proximity to the south-dipping Canyon Creek fault and the south-dipping Glacier Extensional fault. Both scarps are south-side-up, opposite the sense of displacement observed on the nearby bedrock faults. Trenches excavated across these scarps exposed folded and faulted late Quaternary glacial outwash, locally dated between ca. 12 and 13 ka, and Holocene buried soils and scarp colluvium. Reverse and oblique faulting of the soils and colluvial deposits indicates at least two late Holocene earthquakes, while folding of the glacial outwash prior to formation of the post-glacial soil suggests an earlier Holocene earthquake. Abrupt changes in bed thickness across faults in the Canyon Creek excavation suggest a lateral component of slip. Sediments in a wetland adjacent to the Kendall scarp record three pond-forming episodes during the Holocene—we infer that surface ruptures on the Boulder Creek fault during past earthquakes temporarily blocked the stream channel and created an ephemeral lake. The Boulder Creek and Canyon Creek faults formed in the early to mid-Tertiary as normal faults and likely lay dormant until reactivated as reverse faults in a new stress regime. The most recent earthquakes—each likely Mw > 6.3 and dating to ca. 8050–7250 calendar years B.P. (cal yr B.P.), 3190–2980 cal. yr B.P., and 910–740 cal. yr B.P.—demonstrate that reverse faulting in the northern Puget Lowland poses a hazard to urban areas between Seattle (Washington) and Vancouver

  14. Reconstructing water level in Hoyo Negro, Quintana Roo, Mexico, implications for early Paleoamerican and faunal access

    NASA Astrophysics Data System (ADS)

    Collins, S. V.; Reinhardt, E. G.; Rissolo, D.; Chatters, J. C.; Nava Blank, A.; Luna Erreguerena, P.

    2015-09-01

    The skeletal remains of a Paleoamerican (Naia; HN5/48) and extinct megafauna were found at -40 to -43 mbsl in a submerged dissolution chamber named Hoyo Negro (HN) in the Sac Actun Cave System, Yucatan Peninsula, Mexico. The human remains were dated to between 12 and 13 Ka, making these remains the oldest securely dated in the Yucatan. Twelve sediment cores were used to reconstruct the Holocene flooding history of the now phreatic cave passages and cenotes (Ich Balam, Oasis) that connect to HN. Four facies were found: 1. bat guano and Seed (SF), 2. lime Mud (MF), 3. Calcite Rafts (CRF) and 4. Organic Matter/Calcite Rafts (OM/CRF) which were defined by their lithologic characteristics and ostracod, foraminifera and testate amoebae content. Basal radiocarbon ages (AMS) of aquatic sediments (SF) combined with cave bottom and ceiling height profiles determined the history of flooding in HN and when access was restricted for human and animal entry. Our results show that the bottom of HN was flooded at least by 9850 cal yr BP but likely earlier. We also found, that the pit became inaccessible for human and animal entry at ≈8100 cal yr BP, when water reaching the cave ceiling effectively prevented entry. Water level continued to rise between ≈6000 and 8100 cal yr BP, filling the cave passages and entry points to HN (Cenotes Ich Balam and Oasis). Analysis of cave facies revealed that both Holocene sea-level rise and cave ceiling height determined the configuration of airways and the deposition of floating and bat derived OM (guano and seeds). Calcite rafts, which form on the water surface, are also dependent on the presence of airways but can also form in isolated air domes in the cave ceiling that affect their loci of deposition on the cave bottom. These results indicated that aquatic cave sedimentation is transient in time and space, necessitating extraction of multiple cores to determine a limit after which flooding occurred.

  15. Age and whole rock glass compositions of proximal pyroclastics from the major explosive eruptions of Somma-Vesuvius: A review as a tool for distal tephrostratigraphy

    NASA Astrophysics Data System (ADS)

    Santacroce, Roberto; Cioni, Raffaello; Marianelli, Paola; Sbrana, Alessandro; Sulpizio, Roberto; Zanchetta, Giovanni; Donahue, Douglas J.; Joron, Jean Louis

    2008-10-01

    A review of compositional data of the major explosive eruptions of Vesuvius is presented, comparing compositions (major elements) of whole rock with glass shards from the proximal deposits, hopefully useful for long-distance correlation. A critical review of published and new geochronological data is also provided. All available 14C ages are calibrated to give calendar ages useful for the reconstruction of the volcanological evolution of the volcanic complex. The pyroclastic deposits of the four major Plinian eruptions (22,000 yr cal BP "Pomici di Base", 8900 yr cal BP "Mercato Pumice", 4300 yr cal BP "Avellino Pumice", and A.D. 79 "Pompeii Pumice") are widely dispersed and allow a four-folded, Plinian to Plinian, stratigraphic division: 1. B-M (between Pomici di Base and Mercato); 2. M-A (between Mercato and Avellino); 3. A-P (between Avellino and Pompeii); 4. P-XX (from the Pompeii Pumice to the last erupted products of the XXth century). Within each interval, the age, lithologic and compositional features of pyroclastic deposits of major eruptions, potentially useful for tephrostratigraphic purposes on distal areas, are briefly discussed. The Vesuvius rocks are mostly high Potassic products, widely variable in terms of their silica saturation. They form three groups, different for both composition and age: 1. slightly undersaturated, older than Mercato eruption; 2. mildly undersaturated, from Mercato to Pompeii eruptions; 3. highly undersaturated, younger than Pompeii eruption. For whole rock analyses, the peculiar variations in contents of some major and trace elements as well as different trends in element/element ratios, allow a clear, unequivocal, easy diagnosis of the group they belong. Glass analyses show large compositional overlap between different groups, but selected element vs. element plots are distinctive for the three groups. The comparative analysis of glass and whole rock major element compositions provides reliable geochemical criteria helping

  16. Holocene palaeohydrological history of the Tǎul Muced peat bog (Northern Carpathians, Romania) based on testate amoebae (Protozoa) and plant macrofossils

    NASA Astrophysics Data System (ADS)

    Cosmin Diaconu, Andrei; Feurdean, Angelica; Lamentowicz, Mariusz; Gałka, Mariusz; Tanţǎu, Ioan

    2016-04-01

    Knowledge of past local vs. regional hydro-climate variability is a priority in climate research. This is because ecosystems and human depend on local climatic conditions and the magnitude of these climate changes is more variable at local and regional rather than at global scales. Ombrotrophic bogs are highly suitable for hydro-climate reconstructions as they are entirely dependent on the water from precipitation. We used stratigraphy, radiocarbon dating, testate amoebae (TA) and plant macrofossils on a peat profile from an ombrotrophic bog (Tǎul Muced) located in the Biosphere Reserve of the Rodna National Park Romania. We performed quantitative reconstruction of the depth to water table (DWT) and pH over the last 8000 years in a continental area of CE Europe. We identified six main stages in the development of the bog based on changes in TA assemblages in time. Wet conditions and pH between 2 and 4.5 were recorded between 4600-2750 and 1300-400 cal. yr BP, by the occurrence of Archerella flavum, Amphitrema wrightianum and Hyalosphenia papilio. This was associated to a local vegetation primarily composed of Sphagnum magellanicum and S. angustifolium. Dry stages and pH of 2.5 to 5 were inferred between 7550-4600, 2750-1300 and -50 cal. yr BP, by the dominance of Nebela militaris, Difflugia pulex and Phryganella acropodia. These overall dry conditions were also connected with increased abundance of Eriophorum vaginatum. The period between 400 and -50 cal. yr BP was characterized by a rapid shift from dry to wet conditions on the surface of the bog. Vegetation shifted from Sphagnum magellanicum to Sphagnum russowii dominated community. Our reconstruction remains in relatively good agreement with other palaeohydrological records from Central Eastern Europe. However, it shows contrasting conditions to others particularly with records from NW Europe. The valuable information regarding bog hydrology offered by our record puts an accent on the need of more regional TA

  17. Development and carbon sequestration of tropical peat domes in south-east Asia: links to post-glacial sea-level changes and Holocene climate variability

    NASA Astrophysics Data System (ADS)

    Dommain, René; Couwenberg, John; Joosten, Hans

    2011-04-01

    Tropical peatlands of SE-Asia represent a significant terrestrial carbon reservoir of an estimated 65 Gt C. In this paper we present a comprehensive data synthesis of radiocarbon dated peat profiles and 31 basal dates of ombrogenous peat domes from the lowlands of Peninsular Malaysia, Sumatra and Borneo and integrate our peatland data with records of past sea-level and climate change in the region. Based on their developmental features three peat dome regions were distinguished: inland Central Kalimantan (Borneo), Kutai basin (Borneo) and coastal areas across the entire region. With the onset of the Holocene the first peat domes developed in Central Kalimantan as a response to rapid post-glacial sea-level rise over the Sunda Shelf and intensification of the Asian monsoon. Peat accumulation rates in Central Kalimantan strongly declined after 8500 cal BP in close relation to the lowering rate of the sea-level rise and possibly influenced by the regional impact of the 8.2 ka event. Peat growth in Central Kalimantan apparently ceased during the Late Holocene in association with amplified El Niño activity as exemplified by several truncated peat profiles. Peat domes from the Kutai basin are all younger than ˜8300 cal BP. Peat formation and rates of peat accumulation were driven by accretion rates of the Mahakam River and seemingly independent of climate. Most coastal peat domes, the largest expanse of SE-Asian peatlands, initiated between 7000 and 4000 cal BP as a consequence of a Holocene maximum in regional rainfall and the stabilisation and subsequent regression of the sea-level. These boundary conditions induced the highest rates of peat accumulation of coastal peat domes. The Late Holocene sea-level regression led to extensive new land availability that allowed for continued coastal peat dome formation until the present. The time weighted mean Holocene peat accumulation rate is 0.54 mm yr -1 for Central Kalimantan, 1.89 mm yr -1 for Kutai and 1.77 mm yr -1 for

  18. The role of sediment compaction and groundwater withdrawal in local sea-level rise, Sandy Hook, New Jersey, USA

    NASA Astrophysics Data System (ADS)

    Johnson, Christopher S.; Miller, Kenneth G.; Browning, James V.; Kopp, Robert E.; Khan, Nicole S.; Fan, Ying; Stanford, Scott D.; Horton, Benjamin P.

    2018-02-01

    The rate of relative sea-level (RSL) rise at Sandy Hook, NJ (4.0 ± 0.5 mm/yr) was higher than The Battery, NY (3.0 ± 0.3 mm/yr) from 1900 to 2012 despite being separated by just 26 km. The difference cannot be explained by differential glacial isostatic adjustment (GIA; 1.4 ± 0.4 and 1.3 ± 0.4 mm/yr RSL rise, respectively) alone. We estimate the contribution of sediment compaction to subsidence at Sandy Hook using high-resolution grain size, percent organic matter, and porosity data from three upper Quaternary (≤13,350 cal yr) cores. The organic matter content (<2%) is too low to contribute to local subsidence. However, numerical modeling of the grain size-depth-age-porosity relationship indicates that compaction of deglacial silts likely reduced the column thickness by 10-20% over the past 13,350 cal yrs. While compaction rates were high immediately after the main silt deposition (13,350-13,150 cal yrs BP), rates decreased exponentially after deposition to an average 20th century rate of 0.16 mm/yr (90% Confidence Interval (C.I.), 0.06-0.32 mm/yr). The remaining ∼0.7 mm/yr (90% C.I. 0.3-1.2 mm/yr) difference in subsidence between Sandy Hook and The Battery is likely due to anthropogenic groundwater withdrawal. Historical data from Fort Hancock wells (2 km to the southeast of the Sandy Hook tide gauge) and previous regional work show that local and regional water extraction lowered the water levels in the aquifers underlying Sandy Hook. We suggest that the modern order of contribution to subsidence (highest to lowest) appears to be GIA, local/regional groundwater extraction, and compaction of thick Quaternary silts.

  19. 78 FR 60270 - BP America Inc., BP Corporation North America Inc., BP America Production Company, and BP Energy...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-10-01

    ... DEPARTMENT OF ENERGY Federal Energy Regulatory Commission [Docket No. IN13-15-000] BP America Inc., BP Corporation North America Inc., BP America Production Company, and BP Energy Company; Notice of Designation of Commission Staff as Non-Decisional With respect to an order issued by the Commission on August...

  20. Stable isotopes, Sr/Ca, and Mg/Ca in biogenic carbonates from Petaluma Marsh, northern California, USA

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Ingram, B.L.; De Deckker, P.; Chivas, A.R.

    2004-10-19

    Stable isotope ({sup 18}O/{sup 16}O and {sup 13}C/{sup 12}C) and minor-element compositions (Sr/Ca and Mg/Ca ratios) of ostracodes and gastropods separated from marsh sediments from San Francisco Bay, Northern California, were used to reconstruct paleoenvironmental changes in Petaluma Marsh over the past 700 yr. The value of {delta}{sup 18}O in the marsh carbonates reflects changes in freshwater inflow, evaporation, and temperature. Mg/Ca and Sr/Ca in ostracode calcite reflect changes in both freshwater inflow and temperature, although primarily reflect temperature changes in the salinity range of about 10-35 {per_thousand}. Ostracode {delta}{sup 18}O values show a gradual increase by 5 {per_thousand} betweenmore » 500 yr BR and the present, probably reflecting rising sea level and increased evaporation in the marsh. Superimposed on this trend are higher frequency Mg/Ca and {delta}{sup 18}O variations (3-4 {per_thousand}), probably reflecting changes in freshwater inflow and evaporation. A period of low Mg/Ca occurred between about 100-300 cal yr BP, suggesting wetter and cooler conditions during the Little Ice Age. Higher Mg/Ca ratios occurred 600-700 cal yr BP, indicating drier and warmer conditions during the end of the Medieval Warm Period. Both ostracode and gastropod {delta}{sup 13}C values decrease up-core, reflecting decomposition of marsh vegetation, which changes from C{sub 4} ({delta}{sup 13}C {approx} -12{per_thousand}) to CAM ({delta}{sup 13}C = -26 {per_thousand})-type vegetation over time.« less

  1. Late-Wisconsinan submarine moraines along the north shore of the Estuary and Gulf of St. Lawrence (Eastern Canada)

    NASA Astrophysics Data System (ADS)

    Lajeunesse, Patrick; St-Onge, Guillaume

    2013-04-01

    A series of ice-contact submarine fans and morainal banks along the Québec North-Shore of the Estuary and Gulf of St. Lawrence (Eastern Canada), between the Manicouagan River delta and the Mingan Islands, have been revealed with great detail by recent multibeam echosounder and high-resolution subbottom profiler surveys. These grounding-line landforms are observed between 65 and 190 m water depths and were constructed as the marine-based margin of the Laurentide Ice Sheet (LIS) stabilized or readvanced. Radiocarbon ages obtained from shells sampled in sediment cores collected in glaciomarine deposits 6 km south of a grounding line in the Sept-Iles area indicate a stabilisation that took place around 11 000 14C yr BP (12.5 ka cal BP with a ΔR=120 ± 40 yr). In the Mingan Islands area, organic matter collected in distal deposits of an ice-contact fan is dated at 10 800 14C yr BP (11.6 ka cal BP). The position of the Sept-Iles and Mingan deposits, 20 km south of the ~9.7-9.5 14C kyr BP North-Shore Moraine, suggests that these ice marginal landforms were constructed during the Younger Dryas (YD) cold episode and that they might be the eastward submarine extent of the early YD St. Narcisse morainic system. Superimposed till sheets and morainal banks observed within grounding line deposits indicate that this stability phase was interrupted by local readvances that were marked in some cases by ice streaming. Segments of this morainic system are also visible along the shoreline in some sectors, where they have been generally washed out of fine fragments by waves. Another series of ice-contact deposits and landforms of similar nature observed farther offshore and at greater depths (100-190 m) were formed during a previous phase of stabilisation of the LIS margin. This older morainic system was probably deposited immediately after the opening of the Estuary and Gulf of the St. Lawrence.

  2. Cal OES Internet Home Cal OES Home

    Science.gov Websites

    Sign In You may be trying to access this site from a secured browser on the server. Please enable scripts and reload this page. Turn on more accessible mode Turn off more accessible mode Skip Ribbon Commands Skip to main content Turn off Animations Turn on Animations image of CA.gov logo image of Cal OES

  3. Sedimentology and chronology of the advance and retreat of the last British-Irish Ice Sheet on the continental shelf west of Ireland

    NASA Astrophysics Data System (ADS)

    Peters, Jared L.; Benetti, Sara; Dunlop, Paul; Ó Cofaigh, Colm; Moreton, Steven G.; Wheeler, Andrew J.; Clark, Christopher D.

    2016-05-01

    The last British-Irish Ice Sheet (BIIS) had extensive marine-terminating margins and was drained by multiple large ice streams and is thus a useful analogue for marine-based areas of modern ice sheets. However, despite recent advances from investigating the offshore record of the BIIS, the dynamic history of its marine margins, which would have been sensitive to external forcing(s), remain inadequately understood. This study is the first reconstruction of the retreat dynamics and chronology of the western, marine-terminating, margin of the last (Late Midlandian) BIIS. Analyses of shelf geomorphology and core sedimentology and chronology enable a reconstruction of the Late Midlandian history of the BIIS west of Ireland, from initial advance to final retreat onshore. Five AMS radiocarbon dates from marine cores constrain the timing of retreat and associated readvances during deglaciation. The BIIS advanced without streaming or surging, depositing a bed of highly consolidated subglacial traction till, and reached to within ∼20 km of the shelf break by ∼24,000 Cal BP. Ice margin retreat was likely preceded by thinning, grounding zone retreat and ice shelf formation on the outer shelf by ∼22,000 Cal BP. This ice shelf persisted for ≤2500 years, while retreating at a minimum rate of ∼24 m/yr and buttressing a >150-km long, 20-km wide, bathymetrically-controlled grounding zone. A large (∼150 km long), arcuate, flat-topped grounding-zone wedge, termed here the Galway Lobe Grounding-Zone Wedge (GLGZW), was deposited below this ice shelf and records a significant stillstand in BIIS retreat. Geomorphic relationships indicate that the BIIS experienced continued thinning during its retreat across the shelf, which led to increased topographic influence on its flow dynamics following ice shelf break up and grounding zone retreat past the GLGZW. At this stage of retreat the western BIIS was comprised of several discrete, asynchronous lobes that underwent several

  4. Mitotic protein kinase CDK1 phosphorylation of mRNA translation regulator 4E-BP1 Ser83 may contribute to cell transformation

    DOE PAGES

    Velasquez, Celestino; Cheng, Erdong; Shuda, Masahiro; ...

    2016-07-11

    mTOR-directed 4E-BP1 phosphorylation promotes cap-dependent translation and tumorigen-esis. During mitosis, CDK1 substitutes for mTOR and fully phosphorylates 4E-BP1 at canoni-cal as well a non-canonical S83 site resulting in a mitosis-specific hyperphosphorylated δ isoform. Colocalization studies with a phospho-S83 specific antibody indicate that 4E-BP1 S83 phosphorylation accumulates at centrosomes during prophase, peaks at metaphase, and decreases through telophase. While S83 phosphorylation of 4E-BP1 does not affect in vitro cap-dependent translation, nor eIF4G/4E-BP1 cap-binding, expression of an alanine substitution mutant 4E-BP1.S83A partially reverses rodent cell transformation induced by Merkel cell polyomavirus (MCV) small T (sT) antigen viral oncoprotein. In contrast to inhibitorymore » mTOR 4E-BP1 phosphorylation, these findings suggest that mitotic CDK1-directed phosphorylation of δ-4E-BP1 may yield a gain-of-function, distinct from translation regulation, that may be important in tumorigenesis and mitotic centrosome function.« less

  5. A CAL-Based Undergraduate Genetics Course.

    ERIC Educational Resources Information Center

    Garbutt, K.; And Others

    1979-01-01

    Describes a second-year undergraduate practical course in quantitative genetics and biometrics, based upon computer-assisted learning (CAL); and discusses the educational benefits of the course, some problems encountered, and some implications of the extensive use of CAL. (Author/CMV)

  6. Multistage 8.2 kyr event revealed through high-resolution XRF core scanning of Cuban sinkhole sediments

    NASA Astrophysics Data System (ADS)

    Peros, Matthew; Collins, Shawn; G'Meiner, Anna Agosta; Reinhardt, Eduard; Pupo, Felipe Matos

    2017-07-01

    We use sediments from a flooded sinkhole (Cenote Jennifer) in northern Cuba to provide new, well-dated, high-resolution evidence for the 8.2 kyr event. From 7600 to 8700 cal yr B.P. the sinkhole contained shallow, low-salinity water, which supported a marsh dominated by cattail and grass. Peaks in Cl and Br—occurring at 8150, 8200, and 8250 cal yr B.P.—are attributable to increased evaporation due to regional drying associated with the 8.2 kyr event. The three peaks in these elements also closely correspond to the greyscale record from the Cariaco Basin, indicative of increased upwelling in the southern Caribbean Sea at this time, supporting the notion of a multistage 8.2 kyr event. Our work provides new data that help to clarify the initiation, behavior, and impacts of the 8.2 kyr event in the northern tropics.

  7. Paleoseismic evidence for late Holocene tectonic deformation along the Saddle mountain fault zone, Southeastern Olympic Peninsula, Washington

    USGS Publications Warehouse

    Barnett, Elizabeth; Sherrod, Brian; Hughes, Jonathan F.; Kelsey, Harvey M.; Czajkowski, Jessica L.; Walsh, Timothy J.; Contreras, Trevor A.; Schermer, Elizabeth R.; Carson, Robert J.

    2015-01-01

    Trench and wetland coring studies show that northeast‐striking strands of the Saddle Mountain fault zone ruptured the ground about 1000 years ago, generating prominent scarps. Three conspicuous subparallel fault scarps can be traced for 15 km on Light Detection and Ranging (LiDAR) imagery, traversing the foothills of the southeast Olympic Mountains: the Saddle Mountain east fault, the Saddle Mountain west fault, and the newly identified Sund Creek fault. Uplift of the Saddle Mountain east fault scarp impounded stream flow, forming Price Lake and submerging an existing forest, thereby leaving drowned stumps still rooted in place. Stratigraphy mapped in two trenches, one across the Saddle Mountain east fault and the other across the Sund Creek fault, records one and two earthquakes, respectively, as faulting juxtaposed Miocene‐age bedrock against glacial and postglacial deposits. Although the stratigraphy demonstrates that reverse motion generated the scarps, slip indicators measured on fault surfaces suggest a component of left‐lateral slip. From trench exposures, we estimate the postglacial slip rate to be 0.2  mm/yr and between 0.7 and 3.2  mm/yr during the past 3000 years. Integrating radiocarbon data from this study with earlier Saddle Mountain fault studies into an OxCal Bayesian statistical chronology model constrains the most recent paleoearthquake age of rupture across all three Saddle Mountain faults to 1170–970 calibrated years (cal B.P.), which overlaps with the nearby Mw 7.5 1050–1020 cal B.P. Seattle fault earthquake. An earlier earthquake recorded in the Sund Creek trench exposure, dates to around 3500 cal B.P. The geometry of the Saddle Mountain faults and their near‐synchronous rupture to nearby faults 1000 years ago suggest that the Saddle Mountain fault zone forms a western boundary fault along which the fore‐arc blocks migrate northward in response to margin‐parallel shortening across the Puget Lowland.

  8. Wisconsin Glaciation of the Sierra Nevada (79,000-15,000 yr B.P.) as Recorded by Rock Flour in Sediments of Owens Lake, California

    NASA Astrophysics Data System (ADS)

    Bischoff, James L.; Cummins, Kathleen

    2001-01-01

    Chemical analyses of the clay-sized fractions of 564 continuous sediment samples (200-yr resolution) from composite core OL90/92 allow quantification of an abundance of glacial rock flour. Rock flour produced during glacier advances is represented by clay-sized plagioclase, K-feldspar, and biotite in homogeneous internal composition. The abundance of rock flour is deemed proportional to the intensity of glacies advances. Age control for the composite section is provided by combining previously published radiocarbon dates on organics, U/Th dates on ostracode shells, and U/Th dates on saline minerals from nearby Searles Lake correlated to OL92 by pollen. The rock flour record displays three levels of variability: (1) a dominant one of about 20,000 yr related to summer insolation and precipitation; (2) an intermediate one of 3000-5000 yr, perhaps related to North Atlantic Heinrich events; and (3) a minor one of 1000-2000 yr, perhaps related to North Atlantic thermohaline-driven air-temperature variation.

  9. Wisconsin Glaciation of the Sierra Nevada (79,000-15,000 yr B.P.) as recorded by rock flour in sediments of Owens Lake, California

    USGS Publications Warehouse

    Bischoff, J.L.; Cummins, K.

    2001-01-01

    Chemical analyses of the clay-sized fractions of 564 continuous sediment samples (200-yr resolution) from composite core OL90/92 allow quantification of an abundance of glacial rock flour. Rock flour produced during glacier advances is represented by clay-sized plagioclase, K-feldspar, and biotite in homogeneous internal composition. The abundance of rock flour is deemed proportional to the intensity of glacies advances. Age control for the composite section is provided by combining previously published radiocarbon dates on organics, U/Th dates on ostracode shells, and U/Th dates on saline minerals from nearby Searles Lake correlated to OL92 by pollen. The rock flour record displays three levels of variability: (1) a dominant one of about 20,000 yr related to summer insolation and precipitation; (2) an intermediate one of 3000-5000 yr, perhaps related to North Atlantic Heinrich events; and (3) a minor one of 1000-2000 yr, perhaps related to North Atlantic thermohaline-driven air-temperature variation. ?? 2001 University of Washington.

  10. Crustal uplifting rate associated with late-Holocene glacial-isostatic rebound at Skallen and Skarvsnes, Lützow-Holm Bay, East Antarctica: evidence of a synchrony in sedimentary and biological facies on geological setting

    NASA Astrophysics Data System (ADS)

    Takano, Y.; Yokoyama, Y.; Tyler, J. J.; Kojima, H.; Fukui, M.; Sato, T.; Ogawa, N. O.; Suzuki, N.; Kitazato, H.; Ohkouchi, N.

    2010-06-01

    We determined the mean crustal uplifting rate during the late Holocene along the Soya Coast, Lützow-Holm Bay, East Antarctica, by dating a marine-lacustrine transition recorded in lake sediments. We focused on temporal variations in the chemical composition of sediments recovered from Lake Skallen Oike at Skallen and Lake Oyako at Skarvsnes. Both sets of lake sediments record environmental changes associated with a transition from marine to lacustrine (fresh water) settings, as indicated by analyses of sedimentary facies for carbon and nitrogen contents, nitrogen isotopic compositions (15N/14N), and major element concentrations. Changes in the dominant primary producers during the marine-lacustrine transition were also clearly revealed by biogenic Opal-A, diatom assemblages, and gradient gel electrophoresis (DGGE) with 16S rRNA gene analysis. Geochronology based on radiocarbon dating of acid-insoluble organic carbon suggested that the environmental transition from saline to fresh water occurred at 2940±100 cal yr BP at L. Skallen and 1060±90 cal yr BP at L. Oyako. Based on these data and a linear approximation model, we estimated a mean crustal uplifting rate of 3.6 mm yr-1 for the period since the marine-lacustrine transition via brackish condition; this uplift is attributed to glacial-isostatic rebound along the Soya Coast. The geological setting was the primary factor in controlling the emergence event and the occurrence of simultaneous changes in sedimentary and biological facies along the zone of crustal uplift.

  11. El Niño Variability in the Coastal Desert of Southern Peru during the Mid-Holocene

    NASA Astrophysics Data System (ADS)

    Fontugne, Michel; Usselmann, Pierre; Lavallée, Danièle; Julien, Michèle; Hatté, Christine

    1999-09-01

    Fourteen organic-rich sedimentary layers in the deposits at Quebrada de los Burros, in coastal southern Peru (Tacna department), lie between two debris-flow units, interpreted to result from El Niño events, at 8980 cal yr B.P. and after 3380 cal yr B.P., respectively. The accumulation of the fine-grained and low-energy sediments of this deposit during the mid-Holocene is incompatible with the occurrence of El Niño events in this region, as these would produce catastrophic flood deposits. The occurrence of organic-rich sediments and evidence of an enhancement of upwelling strength at this time imply the existence of a permanent water supply resulting from an increased condensation of fog at mid-altitudes. These results suggest a lower intensity and, perhaps, a lower frequency of occurrence of the El Niño phenomenon during the mid-Holocene. It is precisely during this period that the most important human settlements are found at this site, probably indicating the presence of reliable supply of fresh water. The chronologies for wetlands in the central south altiplano are out of phase with those indicating increased soil moisture episodes on the coast, implying a long-term difference in climate between these two regions.

  12. Late Holocene environmental reconstruction using cave sediments from Belize

    NASA Astrophysics Data System (ADS)

    Polk, Jason S.; van Beynen, Philip E.; Reeder, Philip P.

    2007-07-01

    Cave sediments collected from Reflection Cave on the Vaca Plateau, Belize show variations in the δ13C values of their fulvic acids (FAs), which indicate periods of vegetation change caused by climatic and Maya influences during the late Holocene. The δ13C values range from - 27.11‰ to - 21.52‰, a shift of ˜ 5.59‰, which suggests fluctuating contributions of C 3 and C 4 plants throughout the last 2.5 ka, with C 4 plant input reflecting periods of Maya agriculture. Maya activity in the study area occurred at different intensities from ˜ 2600 cal yr BP until ˜ 1500 cal yr BP, after which agricultural practices waned as the Maya depopulated the area. These changes in plant assemblages were in response to changes in available water resources, with increased aridity leading to the eventual abandonment of agricultural areas. The Ix Chel archaeological site, located in the study area, is a highland site that would have been among the first agricultural settlements to be affected during periods of aridity. During these periods, minimal water resources would have been available in this highly karstified, well-drained area, and supplemental groundwater extraction would have been difficult due to the extreme depth of the water table.

  13. Contrasting pollen histories of MIS 5e and the Holocene from Lake Titicaca (Bolivia/Peru)

    NASA Astrophysics Data System (ADS)

    Hanselman, Jennifer A.; Gosling, William D.; Paduano, Gina M.; Bush, Mark B.

    2005-10-01

    Two long sediment records (cores LTO1-2B and LT01-3B) from Lake Titicaca, Bolivia/Peru, are compared with a previously analysed Holocene record from this lake (core NE98-1PC). The Holocene records of LT01-2B and NE98-1PC are similar. There are striking differences, however, between the MIS 5e sections of the long cores and the Holocene records. In these records, temperature is probably the dominant parameter that determines the total fossil pollen concentration and is used to time the onset and termination of deglaciation. In contrast, the relative and absolute abundance of specific taxa (e.g. Polylepis/Acaena, Chenopodiaceae) are indicators of relative moisture availability. Although the Holocene contains a period of aridity between ca. 8000 cal. yr BP and 4300 cal. yr BP, it is a minor event compared with the more extreme aridity of MIS 5e. Core LT01-3B showed similar trends during MIS 5e when compared to LT01-2B, as did NE98-1PC when comparing Holocene records. MIS 5e and the Holocene are markedly different interglacials, depicted by shifts in pollen concentration and taxa representation over time.

  14. Holocene history and environmental reconstruction of a Hercynian mire and surrounding mountain landscape based on multiple proxies

    NASA Astrophysics Data System (ADS)

    Dudová, Lydie; Hájková, Petra; Opravilová, Věra; Hájek, Michal

    2014-07-01

    We discovered the first peat section covering the entire Holocene in the Hrubý Jeseník Mountains, representing an island of unique alpine vegetation whose history may display transitional features between the Hercynian and Carpathian regions. We analysed pollen, plant macrofossils (more abundant in bottom layers), testate amoebae (more abundant in upper layers), peat stratigraphy and chemistry. We found that the landscape development indeed differed from other Hercynian mountains located westward. This is represented by Pinus cembra and Larix during the Pleistocene/Holocene transition, the early expansion of spruce around 10,450 cal yr BP, and survival of Larix during the climatic optimum. The early Holocene climatic fluctuations are traced in our profile by species compositions of both the mire and surrounding forests. The mire started to develop as a calcium-rich percolation fen with some species recently considered to be postglacial relicts (Meesia triquetra, Betula nana), shifted into ombrotrophy around 7450 cal yr BP by autogenic succession and changed into a pauperised, nutrient-enriched spruce woodland due to modern forestry activities. We therefore concluded that its recent vegetation is not a product of natural processes. From a methodological viewpoint we demonstrated how using multiple biotic proxies and extensive training sets in transfer functions may overcome taphonomic problems.

  15. Holocene behavior of the Brigham City segment: implications for forecasting the next large-magnitude earthquake on the Wasatch fault zone, Utah

    USGS Publications Warehouse

    Personius, Stephen F.; DuRoss, Christopher B.; Crone, Anthony J.

    2012-01-01

    The Brigham City segment (BCS), the northernmost Holocene‐active segment of the Wasatch fault zone (WFZ), is considered a likely location for the next big earthquake in northern Utah. We refine the timing of the last four surface‐rupturing (~Mw 7) earthquakes at several sites near Brigham City (BE1, 2430±250; BE2, 3490±180; BE3, 4510±530; and BE4, 5610±650 cal yr B.P.) and calculate mean recurrence intervals (1060–1500  yr) that are greatly exceeded by the elapsed time (~2500  yr) since the most recent surface‐rupturing earthquake (MRE). An additional rupture observed at the Pearsons Canyon site (PC1, 1240±50 cal yr B.P.) near the southern segment boundary is probably spillover rupture from a large earthquake on the adjacent Weber segment. Our seismic moment calculations show that the PC1 rupture reduced accumulated moment on the BCS about 22%, a value that may have been enough to postpone the next large earthquake. However, our calculations suggest that the segment currently has accumulated more than twice the moment accumulated in the three previous earthquake cycles, so we suspect that additional interactions with the adjacent Weber segment contributed to the long elapse time since the MRE on the BCS. Our moment calculations indicate that the next earthquake is not only overdue, but could be larger than the previous four earthquakes. Displacement data show higher rates of latest Quaternary slip (~1.3  mm/yr) along the southern two‐thirds of the segment. The northern third likely has experienced fewer or smaller ruptures, which suggests to us that most earthquakes initiate at the southern segment boundary.

  16. Vegetation of Eurasia from the last glacial maximum to present: Key biogeographic patterns

    NASA Astrophysics Data System (ADS)

    Binney, Heather; Edwards, Mary; Macias-Fauria, Marc; Lozhkin, Anatoly; Anderson, Patricia; Kaplan, Jed O.; Andreev, Andrei; Bezrukova, Elena; Blyakharchuk, Tatiana; Jankovska, Vlasta; Khazina, Irina; Krivonogov, Sergey; Kremenetski, Konstantin; Nield, Jo; Novenko, Elena; Ryabogina, Natalya; Solovieva, Nadia; Willis, Kathy; Zernitskaya, Valentina

    2017-02-01

    Continental-scale estimates of vegetation cover, including land-surface properties and biogeographic trends, reflect the response of plant species to climate change over the past millennia. These estimates can help assess the effectiveness of simulations of climate change using forward and inverse modelling approaches. With the advent of transient and contiguous time-slice palaeoclimate simulations, vegetation datasets with similar temporal qualities are desirable. We collated fossil pollen records for the period 21,000-0 cal yr BP (kyr cal BP; calibrated ages) for Europe and Asia north of 40°N, using extant databases and new data; we filtered records for adequate dating and sorted the nomenclature to conform to a consistent yet extensive taxon list. From this database we extracted pollen spectra representing 1000-year time-slices from 21 kyr cal BP to present and used the biomization approach to define the most likely vegetation biome represented. Biomes were mapped for the 22 time slices, and key plant functional types (PFTs, the constituents of the biomes) were tracked though time. An error matrix and index of topographic complexity clearly showed that the accuracy of pollen-based biome assignments (when compared with modern vegetation) was negatively correlated with topographic complexity, but modern vegetation was nevertheless effectively mapped by the pollen, despite moderate levels of misclassification for most biomes. The pattern at 21 ka is of herb-dominated biomes across the whole region. From the onset of deglaciation (17-18 kyr cal BP), some sites in Europe record forest biomes, particularly the south, and the proportion of forest biomes gradually increases with time through 14 kyr cal BP. During the same period, forest biomes and steppe or tundra biomes are intermixed across the central Asian mountains, and forest biomes occur in coastal Pacific areas. These forest biome occurrences, plus a record of dated plant macrofossils, indicate that some tree

  17. The PlusCal Algorithm Language

    NASA Astrophysics Data System (ADS)

    Lamport, Leslie

    Algorithms are different from programs and should not be described with programming languages. The only simple alternative to programming languages has been pseudo-code. PlusCal is an algorithm language that can be used right now to replace pseudo-code, for both sequential and concurrent algorithms. It is based on the TLA + specification language, and a PlusCal algorithm is automatically translated to a TLA + specification that can be checked with the TLC model checker and reasoned about formally.

  18. Late Neolithic Mondsee Culture in Austria: living on lakes and living with flood risk?

    NASA Astrophysics Data System (ADS)

    Swierczynski, T.; Lauterbach, S.; Dulski, P.; Brauer, A.

    2013-07-01

    Neolithic and Bronze Age lake dwellings in the European Alps became recently protected under the UNESCO World Heritage. However, only little is known about the cultural history of the related pre-historic communities, their adaptation strategies to environmental changes and particularly about the almost synchronous decline of many of these settlements around the transition from the Late Neolithic to the Early Bronze Age. For example, there is an ongoing debate whether the abandonment of Late Neolithic lake dwellings at Lake Mondsee (Upper Austria) was caused by unfavourable climate conditions or a single catastrophic event. Within the varved sediments of Lake Mondsee, we investigated the occurrence of intercalated detrital layers from major floods and debris flows to unravel extreme surface runoff recurrence during the Neolithic settlement period. A combination of detailed sediment microfacies analysis and μXRF element scanning allows distinguishing debris flow and flood deposits. A total of 60 flood and 12 debris flow event layers was detected between 7000 and 4000 varve years (vyr) BP. Compared to the centennial- to millennial-scale average, a period of increased runoff event frequency can be identified between 5900 and 4450 vyr BP. Enhanced flood frequency is accompanied by predominantly siliciclastic sediment supply between ca. 5500 and 5000 vyr BP and enhanced dolomitic sediment supply between 4900 and 4500 vyr BP. A change in the location and the construction technique of the Neolithic lake dwellings at Lake Mondsee can be observed during the period of higher flood frequency. While lake dwellings of the first settlement period (ca. 5800-5250 cal. yr BP) were constructed directly on the wetlands, later constructions (ca. 5400-4700 cal. yr BP) were built on piles upon the water, possibly indicating an adaptation to either increased flood risk or a general increase of the lake level. However, our results also indicate that other than climatic factors (e

  19. Impact of managed MediCal on California family practice programs.

    PubMed

    Zweifler, J A

    2001-05-01

    An important source of patients for California's family practice program is MediCal. During the past 5 years, MediCal has established a variety of capitated managed care plans. To assess the impact of California's managed MediCal program on the state's 38 family practice training programs. A cross-sectional, retrospective descriptive survey. A 3-page, 11-question survey was developed by family practice residency directors and staff from the California Academy of Family Physicians, San Francisco. The 38 family practice programs in existence in California in September 1997 were stratified by type of managed MediCal in their county and by type of sponsoring institution--university, county, community based, staff-model health maintenance organization, or managed care system. Of the 38 family practice programs, 27 responded; 19 of 27 programs participated in managed MediCal. The total number of family health center patients, and the percentage of MediCal patients (48%-60%) at family practice programs was similar when stratified by programs with and without managed MediCal and by type of sponsorship. Most programs reported that they were able to compete effectively, although most also reported increased administrative, nursing, and front office costs. Managed MediCal patients were directly assigned to residents in only 3 of 19 programs. The introduction of managed MediCal has not adversely affected the number of patients cared for in California's family practice programs. Continued vigilance regarding California family practice programs' involvement in managed MediCal, including collection of accurate data on the number of MediCal patients and the financial and educational implications for California's family practice programs, is warranted.

  20. 9000 years of salmon fishing on the Columbia River, North America

    USGS Publications Warehouse

    Butler, V.L.; O'Connor, J. E.

    2004-01-01

    A large assemblage of salmon bones excavated 50 yr ago from an ???10,000-yr-old archaeological site near The Dalles, Oregon, USA, has been the primary evidence that early native people along the Columbia River subsisted on salmon. Recent debate about the human role in creating the deposit prompted excavation of additional deposits and analysis of archaeologic, geologic, and hydrologic conditions at the site. Results indicate an anthropogenic source for most of the salmonid remains, which have associated radiocarbon dates indicating that the site was occupied as long ago as 9300 cal yr B.P. The abundance of salmon bone indicates that salmon was a major food item and suggests that migratory salmonids had well-established spawning populations in some parts of the Columbia Basin by 9300-8200 yr ago. ?? 2004 University of Washington. All rights reserved.

  1. δ13Catm and [CO2] measurements in Antarctic ice cores, 160 kyrBP - present

    NASA Astrophysics Data System (ADS)

    Eggleston, Sarah; Schmitt, Jochen; Schneider, Robert; Joos, Fortunat; Fischer, Hubertus

    2014-05-01

    Measurements from Antarctic ice cores allow us to reconstruct atmospheric concentrations of climatically important gases including CO2 over the past 800 kyr. Such measurements show that [CO2] has varied in parallel with Antarctic temperatures on glacial-interglacial timescales. Knowledge of the variations of the stable carbon isotope of CO2, δ13Catm, can help us better understand the processes involved in these fluctuations. Here, we present a first complete δ13Catmrecord extending from 160 kyrBP to the present accompanied by δ15N2 measurements during Marine Isotope Stage 3 (MIS 3, 57 - 29 kyrBP). The present record, measured primarily on ice from the EPICA Dome C and Talos Dome ice cores, has an average resolution of 500 yr, focused mainly on the Last Glacial Maximum and termination (180 yr; Schmitt et al., 2012), MIS 3 (660 yr), and Termination II through MIS 5.4 (590 yr; Schneider et al., 2013). Throughout the record, δ13Catm varies between approximately -6.8 and -6.4‰Following a period of relatively constant δ13Catm at the end of MIS 6 (around -6.8), the boundaries of MIS 5 correspond roughly with the beginning and end of a gradual enrichment in this isotope. In comparison, the more recent record depicts three more abrupt excursions to lighter values around 63 - 59, 46, and 17 kyrBP, in each case followed by a slower return (0.4o over the course of 5 - 15 kyr) to more enriched isotopic values. These coincide with Heinrich events 6, 5, and 1, respectively. No direct correlation is observed between the concentration and carbon isotope of CO2 over the last 160 kyr. The data indicate rather that numerous processes, such as uptake and release of atmospheric CO2 by the ocean and land biosphere, perhaps influenced by regions of growing permafrost during MIS 3 and 4, acting on a variety of timescales must be considered in explaining the evolution of δ13Catm on glacial-interglacial timescales. References: Schmitt, J. et al. Science 336, 711-714 (2012) Schneider

  2. The paleoecology, peat chemistry and carbon storage of a discontinuous permafrost peatland

    NASA Astrophysics Data System (ADS)

    Talbot, Julie; Pelletier, Nicolas; Olefeldt, David; Turetsky, Merritt; Blodau, Christian; Sonnentag, Oliver; Quinton, William

    2017-04-01

    Permafrost in peatlands strongly influences ecosystem biogeochemical functioning, vegetation composition and hydrological functions. Permafrost peatlands of northwestern Canada store large amounts of carbon but the peatlands located at the southern margin of the permafrost zone are thawing rapidly. This thaw triggers changes in vegetation, hydrology and peat characteristics, and may affect carbon stocks. We present data from a permafrost plateau to thermokarst bog chronosequence located in the southern portion of the Scotty Creek watershed near Fort Simpson, Northwest Territories, Canada. We assessed changes in plant communities, hydrology, biogeochemistry and permafrost status over 9000 years of peatland development using plant macrofossil, testate amoeba and peat chemical characteristics. Peat accumulation started after the infilling of a lake 8500 cal. yr BP. Minerotrophic peat prevailed at the site until permafrost formed around 5000 cal. yr BP. Permafrost apparently formed three times, although there is spatial variability in the permafrost aggradation - degradation cycles. Permafrost thawed 550 cal. yr BP in the center of the thermokarst bog. Ombrotrophic peat is a fairly recent feature of the peat profiles, only appearing after the most recent permafrost thaw event. Both allogenic (temperature/precipitation/snow cover changes and wildfire) and autogenic (peat accumulation, Sphagnum growth) processes likely influenced permafrost aggradation and thaw. While apparent carbon accumulation rates were lower during present and past permafrost periods than during non-permafrost periods, long term carbon accumulation remained similar between cores with different permafrost period lengths. Deep peat was more decomposed in the thermokarst bog peat profile than in the permafrost plateau profile, highlighting the importance of considering potential deep peat carbon losses to project the fate of thawing permafrost peat carbon stores. Average long-term carbon accumulation

  3. Pollen, People and Place: Multidisciplinary Perspectives on Ecosystem change at Amboseli, Kenya

    NASA Astrophysics Data System (ADS)

    Githumbi, Esther N.; Kariuki, Rebecca; Shoemaker, Anna; Courtney-Mustaphi, Colin J.; Chuhilla, Maxmillian; Richer, Suzi; Lane, Paul; Marchant, Rob

    2017-12-01

    This study presents a multidisciplinary perspective for understanding environmental change and emerging socio-ecological interactions across the Amboseli region of southwestern Kenya. We focus on late Holocene (<5000 cal yr. BP) changes and continuities reconstructed from sedimentary, archaeological, historical records and socio-ecological models. We utilize multi-disciplinary approaches to understand environmental-ecosystem-social interactions over the longue durée and use this to simulate different land use scenarios supporting conservation and sustainable livelihoods using a socio-ecological model. Today the semi-arid Amboseli landscape supports a large livestock and wildlife population, sustained by a wide variety of plants and extensive rangelands regulated by seasonal rainfall and human activity. Our data provide insight into how large-scale and long-term interactions of climate, people, livestock, wildlife and external connections have shaped the ecosystems across the Amboseli landscape. Environmental conditions were dry between 5000–2000 cal yr. BP, followed by two wet periods at 2100–1500 and 1400–800 cal yr. BP with short dry periods; the most recent centuries were characterised by variable climate with alternative dry and wet phases with high spatial heterogeneity. Most evident in palaeo and historical records is the changing woody to grass cover ratio, driven by changes in climate and fire regimes entwined with fluctuating elephant, cattle and wild ungulate populations moderated by human activity, including elephant ivory trade intensification. Archaeological perspectives on the occupation of different groups (hunter-gatherers, pastoralists and farmers) in Amboseli region and the relationships between them are discussed. An overview of the known history of humans and elephants, expanding networks of trade, and the arrival and integration of metallurgy, livestock and domesticated crops in the wider region is provided. In recent decades, increased

  4. Pollen, People and Place: Multidisciplinary Perspectives on Ecosystem change at Amboseli, Kenya

    NASA Astrophysics Data System (ADS)

    Githumbi, Esther N.; Kariuki, Rebecca; Shoemaker, Anna; Courtney-Mustaphi, Colin J.; Chuhilla, Maxmillian; Richer, Suzi; Lane, Paul; Marchant, Rob

    2018-01-01

    This study presents a multidisciplinary perspective for understanding environmental change and emerging socio-ecological interactions across the Amboseli region of southwestern Kenya. We focus on late Holocene (<5000 cal yr. BP) changes and continuities reconstructed from sedimentary, archaeological, historical records and socio-ecological models. We utilize multi-disciplinary approaches to understand environmental-ecosystem-social interactions over the longue durée and use this to simulate different land use scenarios supporting conservation and sustainable livelihoods using a socio-ecological model. Today the semi-arid Amboseli landscape supports a large livestock and wildlife population, sustained by a wide variety of plants and extensive rangelands regulated by seasonal rainfall and human activity. Our data provide insight into how large-scale and long-term interactions of climate, people, livestock, wildlife and external connections have shaped the ecosystems across the Amboseli landscape. Environmental conditions were dry between 5000–2000 cal yr. BP, followed by two wet periods at 2100–1500 and 1400–800 cal yr. BP with short dry periods; the most recent centuries were characterised by variable climate with alternative dry and wet phases with high spatial heterogeneity. Most evident in palaeo and historical records is the changing woody to grass cover ratio, driven by changes in climate and fire regimes entwined with fluctuating elephant, cattle and wild ungulate populations moderated by human activity, including elephant ivory trade intensification. Archaeological perspectives on the occupation of different groups (hunter-gatherers, pastoralists and farmers) in Amboseli region and the relationships between them are discussed. An overview of the known history of humans and elephants, expanding networks of trade, and the arrival and integration of metallurgy, livestock and domesticated crops in the wider region is provided. In recent decades, increased

  5. Late Quaternary landscape development at the margin of the Pomeranian phase (MIS 2) near Lake Wygonin (Northern Poland)

    NASA Astrophysics Data System (ADS)

    Hirsch, Florian; Schneider, Anna; Nicolay, Alexander; Błaszkiewicz, Mirosław; Kordowski, Jarosław; Noryskiewicz, Agnieszka M.; Tyszkowski, Sebastian; Raab, Alexandra; Raab, Thomas

    2015-04-01

    In Central Europe, Late Quaternary landscapes experienced multiple phases of geomorphologic activity. In this study,we used a combined geomorphological, pedological, sedimentological and palynological approach to characterize landscape development after the Last Glacial Maximum (LGM) near Lake Wygonin in Northern Poland. The pedostratigraphical findings from soil pits and drillings were extrapolated using ground-penetrating radar (GPR) and electric resistivity tomography (ERT). During the Pomeranian phase, glacial and fluvioglacial processes dominated the landscape near Lake Wygonin. At the end of the glacial period, periglacial processes became relevant and caused the formation of ventifacts and coversands containing coated sand grains. At approximately 15,290-14,800 cal yr BP, a small pond formed in a kettle hole (profile BWI2). The lacustrine sediments lack eolian sand components and therefore indicate the decline of eolian processes during that time. The increase of Juniperus and rock-rose (Helianthemum) in the pollen diagram is a prominent marker of the Younger Dryas. At the end of the Younger Dryas, a partial reshaping of the landscape is indicated by abundant charcoal fragments in disturbed lake sediments. No geomorphologic activity since the beginning of the Holocene is documented in the terrestrial and wetland archives. The anthropogenic impact is reflected in the pollen diagram by the occurrence of rye pollen grains (Cerealia type, Secale cereale) and translocated soil sediments dated to 1560-1410 cal yr BP, proving agricultural use of the immediate vicinity. With the onset of land use, gully incision and the accumulation of colluvial fans reshaped the landscape locally. Since 540-460 cal yr BP, further gully incision in the steep forest tracks has been associated with the intensification of forestry. Outside of the gully catchments, the weakly podzolized Rubic Brunic Arenosols show no features of Holocene soil erosion. Reprinted from CATENA, Volume 124

  6. The Efficiency of Delone Coverings of the Canonical Tilings cal T}(*(A_4)) -> T^*(A4) and cal T}(*(D_6)) -> T^*(D6)

    NASA Astrophysics Data System (ADS)

    Papadopolos, Zorka; Kasner, Gerald

    This chapter is devoted to the coverings of the two quasiperiodic canonical tilings cal T}(*(A_4)) -> T^*(A4) and cal T}(*(D_6)) equiv {cal T}(*(2F)) -> T^*(D6) T^*(2F), obtained by projection from the root lattices A4 and D6, respectively. In the first major part of this chapter, in Sect. 5.2, we shall introduce a Delone covering cal C}(s_{{cal) T}(*(A_4)}) -> C^sT^*(A4) of the 2-dimensional decagonal tiling cal T}(*(A_4)) -> T^*(A4). In the second major part of this chapter, Sect. 5.3, we summarize the results related to the Delone covering of the icosahedral tiling cal T}(*(D_6)) -> T^*(D6), cal C}_{{cal T}(*(D_6)}) -> CT^*(D6) and determine the zero-, single-, and double- deckings and the resulting thickness of the covering. In the conclusions section, we give some suggestions as to how the definition of the Delone covering might be changed in order to reach some real (full) covering of the icosahedral tiling cal T}(*(D_6)) -> T^*(D6). In Section 5.2 the definition of the Delone covering is also changed in order to avoid an unnecessary large thickness of the covering.

  7. Fixed Combination Aerosol Foam Calcipotriene 0.005% (Cal) Plus Betamethasone Dipropionate 0.064% (BD) is More Efficacious than Cal or BD Aerosol Foam Alone for Psoriasis Vulgaris

    PubMed Central

    Tyring, Stephen; Bukhalo, Michael; Alonso-Llamazares, Javier; Olesen, Martin; Lowson, David; Yamauchi, Paul

    2016-01-01

    Objective: To evaluate the efficacy of fixed combination aerosol foam calcipotriene 0.005% (Cal) plus betamethasone dipropionate 0.064% (BD). Design: Patients were randomized (100:101:101) to receive Cal/BD foam, Cal foam, or BD foam once daily for four weeks. Setting: Twenty-eight United States centers. Participants: 302 patients (≥18 years) with Psoriasis vulgaris (plaque Psoriasis; ≥mild disease severity by physicians global assessment). Measurements: Treatment success of the body (“clear”/”almost clear” from baseline moderate/severe disease; “clear” from baseline mild disease). Involved scalp treatment success was an additional endpoint. Results: Most patients (76%) had moderate Psoriasis of the body (66% for scalp). At Week 4, 45 percent of Cal/BD foam patients achieved treatment success, significantly more than Cal foam (14.9%; OR 4.34 [95%CI 2.16,8.72] P<0.001) or BD foam (30.7%; 1.81 [1.00,3.26] P=0.047). Fifty-three percent of Cal/BD foam patients achieved treatment success of the scalp, significantly greater than Cal foam (35.6%; 1.91 [1.09,3.35] P=0.021), but not BD foam (47.5%; 1.24 [0.71,2.16] P=0.45). Mean modified Psoriasis area and severity index (population baseline 7.6) improved in all groups, with statistically significant differences in Week 4 Cal/BD foam score (2.37) versus Cal foam (4.39; mean difference -2.03 [-2.63][-1.43] P<0.001) and BD foam (3.37; -1.19 [-1.80][-0.59] P<0.001). Four (Cal/BD), 10 (Cal), and 8 (BD) adverse drug reactions were reported. Conclusion: Cal/BD foam was significantly more effective than Cal foam and BD foam in providing treatment success at Week 4 and effective on involved scalp. Trial registration: NCT01536938. PMID:27313822

  8. Late Holocene Lacustrine Records of Climate and Vegetation Change From Southernmost South America

    NASA Astrophysics Data System (ADS)

    Moy, C. M.; Dunbar, R. B.; Francois, J.; Moreno, P. I.; Villa Martínez, R.

    2006-12-01

    The westerly wind field is one of the most prominent atmospheric circulation features in the Southern Hemisphere and has a major impact on the climate of southern South America as well as Southern Ocean hydrography. Southernmost South America is well-located to investigate past changes in the westerly winds because regional precipitation variability is controlled by the location and intensity of the wind field and it is the only landmass to extend within the core of the westerlies. Here we present late Holocene lacustrine records of climate change related to the westerlies from southern Patagonia, Chile. We focus on Lago Guanaco, a small hydrologically closed-basin lake in Southern Patagonia, and use stable isotope and pollen data from this site and three additional lakes in order to reconstruct changes in moisture balance related to the westerlies. Lago Guanaco (51°S, 72°W) is located close to the Nothofagus forest-Patagonian Steppe transition in the eastern region of Parque Nacional Torres del Paine. The location and composition of this important biological discontinuity is highly sensitive to the W-E precipitation gradient throughout Patagonia. The 4.75 m sediment core we obtained from the center of the lake has high concentrations of organic mater in addition to ostracodes and bivalves, which are relatively rare in Chilean Patagonia. Eleven AMS radiocarbon dates on organic and carbonate fractions indicate that the record spans the last ~14,400 cal yr BP and modern dates from core tops suggest little influence by old carbon sources. Changes in moisture balance and forest density/proximity are reflected in downcore variations in δ18Obivalve and δ18Oostracode, the Nothofagus/Poaceae paleovegetation index, and the C/N ratio of bulk decalcified organic matter. Combined, these variables document changes in the isotopic composition of the lake water, which largely reflect the isotopic composition of precipitation and the influence of evaporation, as well as shifts

  9. Eruption dynamics and explosive-effusive transitions during the 1400 cal BP eruption of Opala volcano, Kamchatka, Russia

    NASA Astrophysics Data System (ADS)

    Andrews, Benjamin J.; Dufek, Josef; Ponomareva, Vera

    2018-05-01

    Deposits and pumice from the 1400 cal BP eruption of Opala volcano record activity that occurred at the explosive-effusive transition, resulting in intermittent, or stop-start, behavior, where explosive activity resumed following a pause. The eruption deposited distinctive, biotite-bearing rhyolite tephra across much of Kamchatka, and its stratigraphy consists of a lithic-rich pumice fall, overlain by pumice falls and pyroclastic density deposits, with the proportion of the latter increasing with height. This sequence repeats such that the middle of the total deposit is marked by a lithic-rich fall with abundant obsidian clasts. Notably, the eruptive pumice are poorly vesiculated, with vesicle textures that record fragmentation of a partially collapsed magmatic foam. The eruption vent, Baranii Amphitheater is filled with obsidian lavas of the same composition as the rhyolite tephra. Based upon the stratigraphic and compositional relations, we divide the eruption into four phases. Phase I initiated with eruption of a lithic-rich pumice fall, followed by eruption of Plinian falls and pyroclastic density currents. During Phase II, the eruption paused for at least 5-6 h; in this time, microlites nucleated and began to grow in the magma. Phase III essentially repeated the Phase I sequence. Obsidian lavas were emplaced during Phase IV. The pumice textures suggest that the magma ascended very near the threshold decompression rate for the transition between explosive (fast) and effusive (slow) behavior. The pause during Phase II likely occurred as decompression slowed enough for the magma to develop sufficient permeability for gas to escape resulting in collapse of the magmatic foam, stopping the eruption and temporarily sealing the conduit. After about 5-6 h, eruption resumed with, once again, magma decompressing very near the explosive-effusive transition. Phase III ended when the decompression rate slowed and lava dome emplacement began. Distributions of pumice and

  10. Cal-Adapt: California's Climate Data Resource and Interactive Toolkit

    NASA Astrophysics Data System (ADS)

    Thomas, N.; Mukhtyar, S.; Wilhelm, S.; Galey, B.; Lehmer, E.

    2016-12-01

    Cal-Adapt is a web-based application that provides an interactive toolkit and information clearinghouse to help agencies, communities, local planners, resource managers, and the public understand climate change risks and impacts at the local level. The website offers interactive, visually compelling, and useful data visualization tools that show how climate change might affect California using downscaled continental climate data. Cal-Adapt is supporting California's Fourth Climate Change Assessment through providing access to the wealth of modeled and observed data and adaption-related information produced by California's scientific community. The site has been developed by UC Berkeley's Geospatial Innovation Facility (GIF) in collaboration with the California Energy Commission's (CEC) Research Program. The Cal-Adapt website allows decision makers, scientists and residents of California to turn research results and climate projections into effective adaptation decisions and policies. Since its release to the public in June 2011, Cal-Adapt has been visited by more than 94,000 unique visitors from over 180 countries, all 50 U.S. states, and 689 California localities. We will present several key visualizations that have been employed by Cal-Adapt's users to support their efforts to understand local impacts of climate change, indicate the breadth of data available, and delineate specific use cases. Recently, CEC and GIF have been developing and releasing Cal-Adapt 2.0, which includes updates and enhancements that are increasing its ease of use, information value, visualization tools, and data accessibility. We showcase how Cal-Adapt is evolving in response to feedback from a variety of sources to present finer-resolution downscaled data, and offer an open API that allows other organization to access Cal-Adapt climate data and build domain specific visualization and planning tools. Through a combination of locally relevant information, visualization tools, and access to

  11. Inferences about winter temperatures and summer rains from the late Quaternary record of C4 perennial grasses and C3 desert shrubs in the northern Chihuahuan Desert

    USGS Publications Warehouse

    Holmgren, Camille A.; Norris, Jodi; Betancourt, Julio L.

    2007-01-01

    Late Quaternary histories of two North American desert biomes—C4 grasslands and C3 shrublands—are poorly known despite their sensitivity and potential value in reconstructing summer rains and winter temperatures. Plant macrofossil assemblages from packrat midden series in the northern Chihuahuan Desert show that C4 grasses and annuals typical of desert grassland persisted near their present northern limits throughout the last glacial-interglacial cycle. By contrast, key C3 desert shrubs appeared somewhat abruptly after 5000cal.yrBP. Bioclimatic envelopes for select C4 and C3 species are mapped to interpret the glacial-interglacial persistence of desert grassland and the mid-to-late Holocene expansion of desert shrublands. The envelopes suggest relatively warm Pleistocene temperatures with moist summers allowed for persistence of C4 grasses, whereas winters were probably too cold (or too wet) for C3 desert shrubs. Contrary to climate model results, core processes associated with the North American Monsoon and moisture transport to the northern Chihuahuan Desert remained intact throughout the last glacial-interglacial cycle. Mid-latitude effects, however, truncated midsummer (July-August) moisture transport north of 35° N. The sudden expansion of desert shrublands after 5000cal.yrBP may be a threshold response to warmer winters associated with increasing boreal winter insolation, and enhanced El Niño-Southern Oscillation variability.

  12. A chironomid-based record of temperature variability during the past 4000 years in northern China and its possible societal implications

    NASA Astrophysics Data System (ADS)

    Wang, Haipeng; Chen, Jianhui; Zhang, Shengda; Zhang, David D.; Wang, Zongli; Xu, Qinghai; Chen, Shengqian; Wang, Shijin; Kang, Shichang; Chen, Fahu

    2018-03-01

    Long-term, high-resolution temperature records which combine an unambiguous proxy and precise dating are rare in China. In addition, the societal implications of past temperature change on a regional scale have not been sufficiently assessed. Here, based on the modern relationship between chironomids and temperature, we use fossil chironomid assemblages in a precisely dated sediment core from Gonghai Lake to explore temperature variability during the past 4000 years in northern China. Subsequently, we address the possible regional societal implications of temperature change through a statistical analysis of the occurrence of wars. Our results show the following. (1) The mean annual temperature (TANN) was relatively high during 4000-2700 cal yr BP, decreased gradually during 2700-1270 cal yr BP and then fluctuated during the last 1270 years. (2) A cold event in the Period of Disunity, the Sui-Tang Warm Period (STWP), the Medieval Warm Period (MWP) and the Little Ice Age (LIA) can all be recognized in the paleotemperature record, as well as in many other temperature reconstructions in China. This suggests that our chironomid-inferred temperature record for the Gonghai Lake region is representative. (3) Local wars in Shanxi Province, documented in the historical literature during the past 2700 years, are statistically significantly correlated with changes in temperature, and the relationship is a good example of the potential societal implications of temperature change on a regional scale.

  13. Multi-Decadal to Millennial Scale Holocene Hydrologic Variation in the Southern Hemisphere Tropics of South America

    NASA Astrophysics Data System (ADS)

    Ekdahl, E. J.; Fritz, S. C.; Baker, P. A.; Burns, S. J.; Coley, K.; Rigsby, C. A.

    2005-12-01

    Numerous sites in the Northern Hemisphere show multi-decadal to millennial scale climate variation during the Holocene, many of which have been correlated with changes in atmospheric radiocarbon production or with changes in North Atlantic oceanic circulation. The manifestation of such climate variability in the hydrology of the Southern Hemisphere tropics of South America is unclear, because of the limited number of records at suitably high resolution. In the Lake Titicaca drainage basin of Bolivia and Peru, high-resolution lacustrine records reveal the overall pattern of Holocene lake-level change, the influence of precessional forcing of the South American Summer Monsoon, and the effects of high-frequency climate variability in records of lake productivity and lake ecology. Precessional forcing of regional precipitation is evident in the Lake Titicaca basin as a massive (ca. 85 m) mid-Holocene decline in lake level beginning about 7800 cal yr BP and a subsequent rise in lake level after 4000 cal yr BP. Here we show that multi-decadal to millennial-scale climate variability, superimposed upon the envelope of change at orbital time scales, is similar in timing and pattern to the ice-rafted debris record of Holocene Bond events in the North Atlantic. A high-resolution carbon isotopic record from Lake Titicaca that spans the entire Holocene suggests that cold intervals of Holocene Bond events are periods of increased precipitation, thus indicating an anti-phasing of precipitation variation on the Altiplano relative to the Northern Hemisphere tropics. A similar pattern of variation is also evident in high-resolution (2-30 yr spacing) diatom and geochemical records that span the last 7000 yr from two smaller lakes, Lagos Umayo and Lagunillas, in the Lake Titicaca drainage basin.

  14. A chronology for late prehistoric Madagascar.

    PubMed

    Burney, David A; Burney, Lida Pigott; Godfrey, Laurie R; Jungers, William L; Goodman, Steven M; Wright, Henry T; Jull, A J Timothy

    2004-01-01

    A database has been assembled with 278 age determinations for Madagascar. Materials 14C dated include pretreated sediments and plant macrofossils from cores and excavations throughout the island, and bones, teeth, or eggshells of most of the extinct megafaunal taxa, including the giant lemurs, hippopotami, and ratites. Additional measurements come from uranium-series dates on speleothems and thermoluminescence dating of pottery. Changes documented include late Pleistocene climatic events and, in the late Holocene, the apparently human-caused transformation of the environment. Multiple lines of evidence point to the earliest human presence at ca. 2300 14C yr BP (350 cal yr BC). A decline in megafauna, inferred from a drastic decrease in spores of the coprophilous fungus Sporormiella spp. in sediments at 1720+/-40 14C yr BP (230-410 cal yr AD), is followed by large increases in charcoal particles in sediment cores, beginning in the SW part of the island, and spreading to other coasts and the interior over the next millennium. The record of human occupation is initially sparse, but shows large human populations throughout the island by the beginning of the Second Millennium AD. Dating of the "subfossil" megafauna, including pygmy hippos, elephant birds, giant tortoises, and large lemurs, demonstrates that most if not all the extinct taxa were still present on the island when humans arrived. Many taxa overlapped chronologically with humans for a millennium or more. The extinct lemurs Hadropithecus stenognathus, Pachylemur insignis, Mesopropithecus pithecoides, and Daubentonia robusta, and the elephant birds Aepyornis spp. and Mullerornis spp., were still present near the end of the First Millennium AD. Palaeopropithecus ingens, Megaladapis edwardsi, and Archaeolemur sp. (cf. edwardsi) may have survived until the middle of the Second Millennium A.D. One specimen of Hippopotamus of unknown provenance dates to the period of European colonization.

  15. CubiCal: Suite for fast radio interferometric calibration

    NASA Astrophysics Data System (ADS)

    Kenyon, J. S.; Smirnov, O. M.; Grobler, T. L.; Perkins, S. J.

    2018-05-01

    CubiCal implements several accelerated gain solvers which exploit complex optimization for fast radio interferometric gain calibration. The code can be used for both direction-independent and direction-dependent self-calibration. CubiCal is implemented in Python and Cython, and multiprocessing is fully supported.

  16. Holocene Fluctuations of North Ice Cap, a Proxy for Climate Conditions along the Northwestern Margin of the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Kelly, M. A.; Osterberg, E. C.; Lasher, G. E.; Farnsworth, L. B.; Howley, J. A.; Axford, Y.; Zimmerman, S. R. H.

    2015-12-01

    North Ice Cap (~76.9°N, 68°W, summit elevation 1322 m asl), a small, independent ice cap in northwestern Greenland, is located within ~25 km of the Greenland Ice Sheet margin and Harald Molkte Bræ outlet glacier. We present geochronological, geomorphic and sedimentological data constraining the Holocene extents of North Ice Cap and suggest that its past fluctuations can be used as a proxy for climate conditions along the northwestern margin of the Greenland Ice Sheet. Prior work by Goldthwait (1960) used glacial geomorphology and radiocarbon ages of subfossil plants emerging along shear planes in the ice cap margin to suggest that that North Ice Cap was not present during the early Holocene and nucleated in the middle to late Holocene time, with the onset of colder conditions. Subfossil plants emerging at shear planes in the North Ice Cap margin yield radiocarbon ages of ~4.8-5.9 cal kyr BP (Goldthwait, 1960) and ~AD 1000-1350 (950-600 cal yr BP), indicating times when the ice cap was smaller than at present. In situ subfossil plants exposed by recent ice cap retreat date to ~AD 1500-1840 (450-110 cal yr BP) and indicate small fluctuations of the ice cap margin. 10Be ages of an unweathered, lichen-free drift <100 m from the present North Ice Cap margin range from ~500 to 8000 yrs ago. We suggest that the drift was deposited during the last ~500 yrs and that the older 10Be ages are influenced by 10Be inherited from a prior period of exposure. We also infer ice cap fluctuations using geochemical data from a Holocene-long sediment core from Deltasø, a downstream lake that currently receives meltwater from North Ice Cap. The recent recession of the North Ice Cap margin influenced a catastrophic drainage of a large proglacial lake, Søndre Snesø, that our field team documented in August 2012. To our knowledge, this is the first significant lowering of Søndre Snesø in historical time.

  17. Late Holocene slip rate and ages of prehistoric earthquakes along the Maacama Fault near Willits, Mendocino County, northern California

    USGS Publications Warehouse

    Prentice, Carol S.; Larsen, Martin C.; Kelsey, Harvey M.; Zachariasen, Judith

    2014-01-01

    The Maacama fault is the northward continuation of the Hayward–Rodgers Creek fault system and creeps at a rate of 5.7±0.1  mm/yr (averaged over the last 20 years) in Willits, California. Our paleoseismic studies at Haehl Creek suggest that the Maacama fault has produced infrequent large earthquakes in addition to creep. Fault terminations observed in several excavations provide evidence that a prehistoric surface‐rupturing earthquake occurred between 1060 and 1180 calibrated years (cal) B.P. at the Haehl Creek site. A folding event, which we attribute to a more recent large earthquake, occurred between 790 and 1060 cal B.P. In the last 560–690 years, a buried channel deposit has been offset 4.6±0.2  m, giving an average slip rate of 6.4–8.6  mm/yr, which is higher than the creep rate over the last 20 years. The difference between this slip rate and the creep rate suggests that coseismic slip up to 1.7 m could have occurred after the formation of the channel deposit and could be due to a paleoearthquake known from paleoseismic studies in the Ukiah Valley, about 25 km to the southeast. Therefore, we infer that at least two, and possibly three, large earthquakes have occurred at the Haehl Creek site since 1180 cal B.P. (770 C.E.), consistent with earlier studies suggesting infrequent, large earthquakes on the Maacama fault. The short‐term geodetic slip rate across the Maacama fault zone is approximately twice the slip rate that we have documented at the Haehl Creek site, which is averaged over the last approximately 600 years. If the geodetic rate represents the long‐term slip accumulation across the fault zone, then we infer that, in the last ∼1200 years, additional earthquakes may have occurred either on the Haehl Creek segment of the Maacama fault or on other active faults within the Maacama fault zone at this latitude.

  18. Engineering Students' Use of Computer Assisted Learning (CAL)

    ERIC Educational Resources Information Center

    Huczynski, Andrzej; Johnston, Scott Paul

    2005-01-01

    This study examines the use of Computer Assisted Learning (CAL) by undergraduate engineering students studying a business and management course. Discussing both the relationship between management and engineering and CAL applied to engineering education, this study is based on a survey of 82 undergraduates and adopts a quantitative research…

  19. Fire and vegetation history on Santa Rosa Island, Channel Islands, and long-term environmental change in southern California

    USGS Publications Warehouse

    Starratt, Scott W.; Pinter, N.; Anderson, Robert S.; Jass, R.B.

    2009-01-01

    The long-term history of vegetation and fire was investigated at two locations – Soledad Pond (275 m; from ca. 12 000 cal. a BP) and Abalone Rocks Marsh (0 m; from ca. 7000 cal. a BP) – on Santa Rosa Island, situated off the coast of southern California. A coastal conifer forest covered highlands of Santa Rosa during the last glacial, but by ca. 11 800 cal. a BP Pinus stands, coastal sage scrub and grassland replaced the forest as the climate warmed. The early Holocene became increasingly drier, particularly after ca. 9150 cal. a BP, as the pond dried frequently, and coastal sage scrub covered the nearby hillslopes. By ca. 6900 cal. a BP grasslands recovered at both sites. Pollen of wetland plants became prominent at Soledad Pond after ca. 4500 cal. a BP, and at Abalone Rocks Marsh after ca. 3465 cal. a BP. Diatoms suggest freshening of the Abalone Rocks Marsh somewhat later, probably by additional runoff from the highlands. Introduction of non-native species by ranchers occurred subsequent to AD 1850. Charcoal influx is high early in the record, but declines during the early Holocene when minimal biomass suggests extended drought. A general increase occurs after ca. 7000 cal. a BP, and especially after ca. 4500 cal. a BP. The Holocene pattern closely resembles population levels constructed from the archaeological record, and suggests a potential influence by humans on the fire regime of the islands, particularly during the late Holocene.

  20. Stone Age settlement and Holocene water level changes of the Baltic Sea in the Torvajoe Basin area, Narva-Luga Klint Bay, NE Estonia

    NASA Astrophysics Data System (ADS)

    Raig, Hanna; Rosentau, Alar; Muru, Merle; Risberg, Jan

    2014-05-01

    The Tõrvajõe basin is located in NE Estonia in the southern part of the Narva-Luga Klint Bay, that is characterized by slow post-glacial isostatic uplift (about 0-1mm/yr) and slowly undulating low topography. Post-glacial changes of the water-level of the Baltic Sea have at times flooded the area, and at times, it has emerged as terrestrial land. In addition to a complex geological development, the surroundings of the Tõrvajõe basin are interesting from the archaeological point of view because of abundant archaeological findings in the area, of which the oldest (c 8.1 cal ka BP) from the Mesolithic period and the majority, indicating very intense habitation (c 7.1-5.5 cal ka BP), from the Neolithic period. Development of the Tőrvajőe basin area during the period of Stone Age settlement (c 8.1-5.5 cal. ka BP) is studied with multiple geological and archaeological proxies. Sediments are described by lithostratigraphical methods, loss-on-ignition. AMS radiocarbon dates are used to date events and create an age-depth model. Environment is described by pollen analyses and water environment by siliceous microfossil analyses. Palaeogeographical reconstructions for time slices of interest are created to illustrate Stone Age settlement pattern and changes of the coastline and landscape over time. The aim of this interdisciplinary study is to investigate and associate palaeoenvironmental conditions and water-level changes with Stone Age settlement pattern in the Tőrvajőe area. Results show four developmental stages in the post-glacial history of the basin: Ancylus Lake lagoon, mire, lagoon during the Litorina Sea and mire. During the Ancylus Lake transgression at about 10.8-10.2 cal. ka BP a spit started to form north of the basin and a lagoon evolved behind it. Following the Ancylus Lake regression river activity and formation of palaeosoil and fen peat took place. Due to the Litorina Sea transgression, that was initially slower but accelerated around 7.8-7.6 cal ka

  1. Late Glacial-Holocene Pollen-Based Vegetation History from Pass Lake, Prince of Wales Island, Southeastern Alaska

    USGS Publications Warehouse

    Ager, Thomas A.; Rosenbaum, Joseph G.

    2009-01-01

    A radiocarbon-dated history of vegetation development since late Wisconsin deglaciation has been reconstructed from pollen evidence preserved in a sediment core from Pass Lake on Prince of Wales Island, southeastern Alaska. The shallow lake is in the south-central part of the island and occupies a low pass that was filled by glacial ice of local origin during the late Wisconsin glaciation. The oldest pollen assemblages indicate that pine woodland (Pinus contorta) had developed in the area by ~13,715 cal yr B.P. An abrupt decline in the pine population, coinciding with expansion of alder (Alnus) and ferns (mostly Polypodiaceae) began ~12,875 yr B.P., and may have been a response to colder, drier climates during the Younger Dryas climatic interval. Mountain hemlock (Tsuga mertensiana) began to colonize central Prince of Wales Island by ~11,920 yr B.P. and was soon followed by Sitka spruce (Picea sitchensis). Pollen of western hemlock (Tsuga heterophylla) began to appear in Pass Lake sediments soon after 11,200 yr B.P. The abundance of western hemlock pollen in the Pass Lake core during most of the Holocene appears to be the result of wind transport from trees growing at lower altitudes on the island. The late Holocene pollen record from Pass Lake is incomplete because of one or more unconformities, but the available record suggests that a vegetation change occurred during the late Holocene. Increases in pollen percentages of pine, cedar (probably yellow cedar, Chamaecyparis nootkatensis), and heaths (Ericales) suggest an expansion of muskeg vegetation occurred in the area during the late Holocene. This vegetation change may be related to the onset of cooler, wetter climates that began as early as ~3,774 yr B.P. in the region. This vegetation history provides the first radiocarbon-dated Late Glacial-Holocene terrestrial paleoecological framework for Prince of Wales Island. An analysis of magnetic properties of core sediments from Pass Lake suggests that unconformities

  2. Identification of contrasting seasonal sea ice conditions during the Younger Dryas

    NASA Astrophysics Data System (ADS)

    Cabedo-Sanz, P.; Belt, S. T.; Knies, J.

    2012-12-01

    The presence of the sea ice diatom biomarker IP25 in Arctic marine sediments has been used in previous studies as a proxy for past spring sea ice occurrence and as an indicator of wider palaeoenvironmental conditions for different regions of the Arctic over various timescales [e.g. 1, 2]. The current study focuses on high-resolution palaeo sea ice reconstructions for northern Norway during the last ca. 15 cal. kyr BP. Within this study, particular emphasis has been placed on the identification of the sea ice conditions during the Younger Dryas and the application of different biomarker-based proxies to both identify and quantify seasonal sea ice conditions. Firstly, the appearance of the specific sea ice diatom proxy IP25 at ca. 12.9 cal. kyr BP in a marine sediment core (JM99-1200) obtained from Andfjorden has provided an unambiguous but qualitative measure of seasonal sea ice and thus the onset of the Younger Dryas stadial. The near continuous occurrence of IP25 for the next ca. 1400 yr demonstrates seasonal sea ice during this interval, although variable abundances suggest that the recurrent conditions in the early-mid Younger Dryas (ca. 12.9 - 11.9 cal. kyr BP) changed significantly from stable to highly variable sea ice conditions at ca. 11.9 cal. kyr BP and this instability in sea ice prevailed for the subsequent ca. 400 yr. At ca. 11.5 cal. kyr BP, IP25 disappeared from the record indicating ice-free conditions that signified the beginning of the Holocene. Similarly, a high resolution record from the Kveithola Through, western Barents Sea, showed clearly higher IP25 concentrations during the Younger Dryas stadial compared to the Holocene. For both marine records, the IP25 concentrations were also combined with those of the open water phytoplankton biomarker brassicasterol to generate PBIP25 data from which more quantitative measurements of sea ice were determined. The contrasting seasonal sea ice conditions during the Younger Dryas were further verified

  3. Timing and east-west correlation of south Swedish ice marginal lines during the Late Weichselian

    NASA Astrophysics Data System (ADS)

    Lundqvist, Jan; Wohlfarth, Barbara

    2000-01-01

    The retreat of the Late Weichselian ice sheet over the southern part of Sweden is marked along the southwest coast by distinct marginal moraine ridges. Their timing can directly and indirectly be assessed based on a number of radiocarbon dates and pollen stratigraphic investigations on lake sediment sequences adjacent to the ice marginal lines. Along the southeastern side of the peninsula, the ice recession has been reconstructed based on a combination of clay-varve chronology, pollen and radiocarbon stratigraphy. A morphological correlation of ice marginal lines between the west and east coast is problematic since the distinct west-coast moraines cannot be followed through the central part of the peninsula towards the east coast. This paper is an attempt to reconstruct an age-equivalent west-east extension of the ice-recession lines on the basis of existing data sets. For our correlation we use calibrated radiocarbon ages for ice marginal deposits on the west coast and compare these with a partly radiocarbon-dated clay-varve chronology on the east coast. We conclude that the two oldest moraines on the west coast formed at ˜18,000-16,000 and ˜15,400-14,500 cal yr BP, respectively. During the following rapid deglaciation, which may have coincided with the beginning of the Bølling pollen zone, large parts of southernmost Sweden became ice free, except for higher elevated areas, where stagnant ice remained for another 400-500 yr. A best guess is that the formation of the next younger ice marginal lines may have occurred at ˜14,400-14,200, ˜14,200 and ˜13,400 cal yr BP and during the Younger Dryas cold event.

  4. Holocene lahars and their byproducts along the historical path of the White River between Mount Rainier and Seattle: Geological Society of America Field Trip

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Brown, T A; Zehfuss, P H; Atwater, B F

    2003-10-16

    Clay-poor lahars of late Holocene age from Mount Rainier change down the White River drainage into lahar-derived fluvial and deltaic deposits that filled an arm of Puget Sound between the sites of Auburn and Seattle, 110-150 km downvalley from the volcano's summit. Lahars in the debris-flow phase left cobbly and bouldery deposits on the walls of valleys within 70 km of the summit. At distances of 80-110 km, transitional (hyperconcentrated) flows deposited pebbles and sand that coat terraces in a gorge incised into glacial drift and the mid-Holocene Osceola Mudflow. On the broad, level floor of the Kent valley atmore » 110-130 km, lahars in the runout or streamflow phase deposited mostly sand-size particles that locally include the trunks of trees probably entrained by the flows. Beyond 130 km, in the Duwamish valley of Tukwila and Seattle, laminated andesitic sand derived from Mount Rainier built a delta northward across the Seattle fault. This distal facies, warped during an earthquake in A.D. 900-930, rests on estuarine mud at depths as great as 20 m. The deltaic filling occurred in episodes that appear to overlap in time with the lahars. As judged from radiocarbon ages of twigs and logs, at least three episodes of distal deposition postdate the Osceola Mudflow. One of these episodes occurred about 2200-2800 cal yr B.P., and two others occurred 1700-1000 cal yr B.P. The most recent episode ended by about the time of the earthquake of A.D. 900-930. The delta's northward march to Seattle averaged between 6 and 14 m/yr in the late Holocene.« less

  5. A comparison of the Greenland ice-core and IntCal timescales through the Laschamp geomagnetic excursion, utilising new 14C data from Tenaghi Philippon, Greece

    NASA Astrophysics Data System (ADS)

    Staff, Richard; Hardiman, Mark; Bronk Ramsey, Christopher; Hare, Vincent; Koutsodendris, Andreas; Pross, Jörg

    2017-04-01

    Cosmogenic radionuclides, such as 10Be and 14C, share a common production signal, with their formation in the Earth's upper atmosphere modulated by changes to the geomagnetic field, as well as variations in the intensity of the solar wind. Here, we present 54 14C measurements from a terrestrial fen peat core extracted from the site of Tenaghi Philippon, NE Greece, contiguously spanning the time period between 48,000 and 39,000 cal. BP. Utilising the most pronounced cosmogenic production peak of the last 100,000 years - that associated with the Laschamp geomagnetic excursion circa 41,000 years ago - we exploit this common production signal, comparing Greenland 10Be with our Tenaghi Philippon 14C record, thereby providing a means to assess the concordance between the radiocarbon (IntCal) and Greenland ice-core (GICC05) timescales themselves for this, the oldest portion of the radiocarbon technique.

  6. Faunal turnover in the Azraq Basin, eastern Jordan 28,000 to 9000 cal yr BP, signalling climate change and human impact

    NASA Astrophysics Data System (ADS)

    Martin, Louise; Edwards, Yvonne H.; Roe, Joe; Garrard, Andrew

    2016-09-01

    Recent zooarchaeological analyses of game exploitation in the Epipalaeolithic of the Southern Levant identify a decline in large game in the Natufian, with corresponding increase in small prey, interpreted as hunting pressure driven by population expansion. To date, studies focus on the Mediterranean zone. This paper adopts similar approaches to examine Epipalaeolithic to Neolithic faunal data from 16 sites in the steppic Jordanian Azraq Basin. Results here reveal very different trends. Large game, mainly equids, fluctuate throughout the Epipalaeolithic, due to climatic conditions and available water/vegetation. Cattle thrive in the Azraq oasis, showing no decline in the Late Epipalaeolithic. Gazelle exploitation is predominant and sustainable throughout the Epipalaeolithic, even at Kharaneh IV and Wadi Jilat 6 'megasites'. However, PPNB assemblages from the limestone steppe show intensive game exploitation resulting from longer-stay settlement. The focused gazelle-hunting camp at Dhuweila in the basalt desert also shows pressure from indiscriminate culling impacting herd demography, interpreted as providing meat for onwards exchange. Human impacts on steppe fauna appear both local and in many cases short-term, unlike the large-game suppression reported from west of the Rift Valley. Resource pressures and game over-kill, whether population-driven or otherwise, are not currently apparent east of the Jordan River.

  7. Nine thousand years of upper montane soil/vegetation dynamics from the summit of Caratuva Peak, Southern Brazil

    NASA Astrophysics Data System (ADS)

    Scheer, Maurício B.; Pereira, Nuno Veríssimo; Behling, Hermann; Curcio, Gustavo R.; Roderjan, Carlos V.

    2014-12-01

    Biodiversity loss, climate change, and increased freshwater consumption are some of the main environmental problems on Earth. Mountain ecosystems can reduce these threats by providing several positive influences, such as the maintenance of biodiversity, water regulation, and carbon storage, amongst others. The knowledge of the history of these environments and their response to climate change is very important for management, conservation, and environmental monitoring programs. The genesis of the soil organic matter of the current upper montane vegetation remains unclear and seems to be quite variable depending on location. Some upper montane sites in the very extensive coastal Sea Mountain Range present considerable organic matter from the late Pleistocene and other from only the Holocene. Our study was carried out on three soil profiles (two cores in grassland and one in forest) on the Caratuva Peak of the Serra do Ibitiraquire (a sub-range of Sea Mountain Range - Serra do Mar) in Southern Brazil. The δ13C isotopic analyses of organic matter in soil horizons were conducted to detect whether C3 or C4 plants dominated the past communities. Complementarily, we performed a pollen analysis and 14C dating of the humin fraction to obtain the age of the studied horizons. Except for a short and probably drier period (between 6000 and 4500 cal yr BP), C3 plants, including ombrophilous grasses and trees, have dominated the highlands of the Caratuva Peak (Pico Caratuva), as well as the other uppermost summits of the Serra do Ibitiraquire, since around 9000 cal yr BP. The Caratuva region represents a landscape of high altitude grasslands (campos de altitude altomontanos or campos altomontanos) and upper montane rain/cloud forests with soils that most likely contain some organic matter from the late Pleistocene, as has been reported in Southern and Southeastern Brazil for other sites. However, our results indicate that the studied deposits (near the summit) are from the early

  8. Holocene Beaver Effects on Small Streams in Yellowstone and Implications for Stream Restoration

    NASA Astrophysics Data System (ADS)

    Persico, L. P.; Meyer, G.

    2005-12-01

    It has been asserted that beaver ( Castor canadensis) damming has sustained long-term aggradation and exerted a dominant control on the morphology of small streams over much of North America. However, data on the temporal and spatial dimensions of beaver influence are extremely limited. Using beaver pond deposits and berms (abandoned dams), we document geomorphic effects of beavers on first- to fourth-order streams in semiarid-subhumid northern Yellowstone National Park, USA. Beavers were ubiquitous in the early 20th century, but are currently rare. Some formerly dammed streams have become ephemeral in recent droughts, suggesting that climate may be a significant factor controlling beaver occupation. Radiocarbon dating of wood preserved in pond deposits and berms shows notable periods of beaver activity 3655-3855, 1555-955, and 455-150 cal yr BP, but a distinct lack of activity 950-700 cal yr BP during the Medieval Climatic Anomaly, a time of severe multidecadal droughts in Yellowstone and the western USA. The spatial scale over which beavers incurred significant aggradation is controlled largely by geomorphic settings conducive to damming. Low-gradient (0.07 to 0.001) reaches with contributing areas of 4 to 70 km2 are typical for dam sites. Reaches with downstream valley constrictions are most susceptible to aggradation. Only a small fraction of the total stream length in the study area has experienced significant aggradation attributable to beaver damming, as shown by accumulations of sand and finer sediment of up to 3 m, thicker than typical overbank sediments. These sediments locally contain evidence of ponding in laminations, gleying, and high organic content. Many reaches show no evidence of any net aggradation since deglaciation. Many beaver-aggraded reaches are now incised, typically 1.5-2 m and up to 3 m. Some reaches have early Holocene (ca. 10150-8000 cal yr BP) terraces with treads ~2 m above current bankfull level, underlain by both gravelly and fine

  9. A late Holocene pollen record from proglacial Oblong Tarn, Mount Kenya.

    PubMed

    Courtney Mustaphi, Colin J; Gajewski, Konrad; Marchant, Rob; Rosqvist, Gunhild

    2017-01-01

    High-elevation ecosystems, such as those on Mount Kenya are undergoing significant changes, with accelerated glacial ice losses over the twentieth century creating new space for alpine plants to establish. These ecosystems respond rapidly to climatic variability and within decades of glacial retreat, Afroalpine pioneering taxa stabilize barren land and facilitate soil development, promoting complex patches of alpine vegetation. Periglacial lake sediment records can be used to examine centennial and millennial scale variations in alpine and montane vegetation compositions. Here we present a 5300-year composite pollen record from an alpine tarn (4370 m asl) in the Hausberg Valley of Mount Kenya. Overall, the record shows little apparent variation in the pollen assemblage through time with abundant montane forest taxa derived and transported from mid elevations, notably high abundances of aerophilous Podocarpus pollen. Afroalpine taxa included Alchemilla, Helichrysum and Dendrosenecio-type, reflecting local vegetation cover. Pollen from the ericaceous zone was present throughout the record and Poaceae percentages were high, similar to other high elevation pollen records from eastern Africa. The Oblong Tarn record pollen assemblage composition and abundances of Podocarpus and Poaceae since the late Holocene (~4000 cal yr BP-present) are similar to pollen records from mid-to-high elevation sites of nearby high mountains such as Mount Elgon and Kilimanjaro. These results suggest a significant amount of uphill pollen transport with only minor apparent variation in local taxa. Slight decreasing trends in alpine and ericaceous taxonomic groups show a long-term response to global late Holocene cooling and a step decrease in rate of change estimated from the pollen assemblages at 3100 cal yr BP in response to regional hydroclimatic variability. Changes in the principal component axis scores of the pollen assemblage were coherent with an independent mid-elevation temperature

  10. A late Holocene pollen record from proglacial Oblong Tarn, Mount Kenya

    PubMed Central

    Gajewski, Konrad; Marchant, Rob; Rosqvist, Gunhild

    2017-01-01

    High-elevation ecosystems, such as those on Mount Kenya are undergoing significant changes, with accelerated glacial ice losses over the twentieth century creating new space for alpine plants to establish. These ecosystems respond rapidly to climatic variability and within decades of glacial retreat, Afroalpine pioneering taxa stabilize barren land and facilitate soil development, promoting complex patches of alpine vegetation. Periglacial lake sediment records can be used to examine centennial and millennial scale variations in alpine and montane vegetation compositions. Here we present a 5300-year composite pollen record from an alpine tarn (4370 m asl) in the Hausberg Valley of Mount Kenya. Overall, the record shows little apparent variation in the pollen assemblage through time with abundant montane forest taxa derived and transported from mid elevations, notably high abundances of aerophilous Podocarpus pollen. Afroalpine taxa included Alchemilla, Helichrysum and Dendrosenecio-type, reflecting local vegetation cover. Pollen from the ericaceous zone was present throughout the record and Poaceae percentages were high, similar to other high elevation pollen records from eastern Africa. The Oblong Tarn record pollen assemblage composition and abundances of Podocarpus and Poaceae since the late Holocene (~4000 cal yr BP-present) are similar to pollen records from mid-to-high elevation sites of nearby high mountains such as Mount Elgon and Kilimanjaro. These results suggest a significant amount of uphill pollen transport with only minor apparent variation in local taxa. Slight decreasing trends in alpine and ericaceous taxonomic groups show a long-term response to global late Holocene cooling and a step decrease in rate of change estimated from the pollen assemblages at 3100 cal yr BP in response to regional hydroclimatic variability. Changes in the principal component axis scores of the pollen assemblage were coherent with an independent mid-elevation temperature

  11. Magma degassing and eruption dynamics of the Avellino pumice Plinian eruption of Somma-Vesuvius (Italy). Comparison with the Pompeii eruption

    NASA Astrophysics Data System (ADS)

    Balcone-Boissard, H.; Boudon, G.; Ucciani, G.; Villemant, B.; Cioni, R.; Civetta, L.; Orsi, G.

    2012-05-01

    The eruptive history of Mt. Somma-Vesuvius is characterised by large explosive events: Pomici di Base eruption (22,030 ± 175 yr cal BP), Mercato (8890 ± 90 yr cal BP), Avellino (3945 ± 10 yr cal BP) and Pompeii (79 AD). Pre-eruptive conditions and sin-eruptive degassing processes of the Avellino eruption, the highest-magnitude Plinian event, have been investigated, using volatile contents (F, Cl, H2O) in melt inclusions and residual glass, and textural characteristics of pumice clasts of the 9 fallout layers sampled in detail in a representative sequence. The sequence displays an up-section sharp colour change from white to grey, corresponding to variations in both magma composition and textural characteristics. The pre-eruptive conditions have been constrained by systematic measurements of Cl content in both melt inclusions and matrix glass of pumice clasts. The pumice glass composition varies from Na-rich phonolite (white pumice) to K-rich phonolite (grey pumice). The measured Cl values constantly cluster at 5200 ± 400 ppm (buffer value), whatever the composition of the melt, suggesting that the entire magma body was saturated with sub-critical fluids. This Cl saturation constrains the pre-eruptive pressures and maximum H2O contents at 200 ± 10 MPa and 6.3 ± 0.2 wt.% H2O for the white pumice melt and 195 ± 15 MPa and 5.2 ± 0.2 wt.% H2O for the grey pumice melt. The fluid phase, mainly composed of a H2O-rich vapour phase and brine, probably accumulated at the top of the reservoir and generated an overpressure able to trigger the onset of the eruption. Magma degassing was rather homogeneous for the white and grey eruptive units, mostly occurring through closed-system processes, leading to a typical Plinian eruptive style. A steady-state withdrawal of an H2O-saturated magma may explain the establishment of a sustained Plinian column. Variation from white to grey pumice is accompanied by decrease of mean vesicularity and increase of mean microcrystallinity

  12. Lake Level Variation in Small Lakes: Not a Clear Picture

    NASA Astrophysics Data System (ADS)

    Starratt, S.

    2017-12-01

    Lake level is a useful tool for identifying regional changes in precipitation and evaporation. Due to the volume of water in large lakes, they may only record large-scale changes in water balance, while smaller lakes may record more subtle variations. However, the record of water level in small lakes is affected by a number of factors including elevation, bathymetry, nutrient load, and aquatic macrophyte abundance. The latest Quaternary diatom records from three small lakes with areas of <10 ha (Hobart Lake, OR, 1458 masl; Swamp Lake, CA, 1554 masl; Favre Lake, NV, 2899 masl) and a larger lake (Medicine Lake, CA, 2036 masl, 154 ha) were compared in this study. All the lakes have a deep central basin (>10 m) surrounded by a shallow (1-2 m) shelf. Changes in the abundance of diatoms representing different life habits (benthic, tychoplanktic, planktic) were used to identify lake level variation. Benthic taxa dominate the assemblage when only the central basin is occupied. As the shallow shelf is flooded, the abundance of tychoplanktic taxa increases. Planktic taxa increase with the establishment of stratification. Favre Lake presents the clearest indication of initial lake level rise (7600-5750 cal yr BP) and intermittent flooding of the shelf for the remainder of the record. Stratification appears to become established only in the last few hundred years. Higher nutrient levels in the early part of the Hobart Lake record lead to a nearly monotypic planktic assemblage which is replaced by a tychoplanktic-dominated assemblage as the lake floods the shelf at about 3500 cal yr BP. The last 500 years is dominated by benthic taxa associated with aquatic macrophytes. The consistent presence of planktic taxa in the Swamp Lake record suggests that the lake was stratified during most of its history, although slight variations in the relative abundances of planktic and tychoplanktic groups occur. The Medicine Lake record shows a gradual increase in planktic species between 11

  13. A 6900-year history of landscape modification by humans in lowland Amazonia

    NASA Astrophysics Data System (ADS)

    Bush, M. B.; Correa-Metrio, A.; McMichael, C. H.; Sully, S.; Shadik, C. R.; Valencia, B. G.; Guilderson, T.; Steinitz-Kannan, M.; Overpeck, J. T.

    2016-06-01

    A sedimentary record from the Peruvian Amazon provided evidence of climate and vegetation change for the last 6900 years. Piston cores collected from the center of Lake Sauce, a 20 m deep lake at 600 m elevation, were 19.7 m in length. The fossil pollen record showed a continuously forested catchment within the period of the record, although substantial changes in forest composition were apparent. Fossil charcoal, found throughout the record, was probably associated with humans setting fires. Two fires, at c. 6700 cal BP and 4270 cal BP, appear to have been stand-replacing events possibly associated with megadroughts. The fire event at 4270 cal BP followed a drought that caused lowered lake levels for several centuries. The successional trajectories of forest recovery following these large fires were prolonged by smaller fire events. Fossil pollen of Zea mays (cultivated maize) provided evidence of agricultural activity at the site since c. 6320 cal BP. About 5150 years ago, the lake deepened and started to deposit laminated sediments. Maize agriculture reached a peak of intensity between c. 3380 and 700 cal BP. Fossil diatom data provided a proxy for lake nutrient status and productivity, both of which peaked during the period of maize cultivation. A marked change in land use was evident after c. 700 cal BP when maize agriculture was apparently abandoned at this site. Iriartea, a hyperdominant of riparian settings in western Amazonia, increased in abundance within the last 1100 years, but declined markedly at c. 1070 cal BP and again between c. 80 and -10 cal BP.

  14. 21,000 years of Ethiopian African monsoon variability recorded in sediments of the western Nile deep-sea fan: impact of the Nile freshwater inflow for the Mediterranean thermo-haline circulation

    NASA Astrophysics Data System (ADS)

    Revel, Marie; Colin, Christophe; Bernasconi, Stephano; Combourieu-Nebout, Nathalie; Ducassou, Emmanuelle; Rolland, Yann; Bosch, Delphine

    2014-05-01

    The Nile delta sedimentation constitutes a continuous high resolution (1.6 mm/year) record of Ethiopian African monsoon regime intensity. Multiproxy analyses performed on core MS27PT recovered in hemipelagic Nile sediment margin (<90 km outward of the Rosetta mouth of the Nile) allow the quantification of the Saharan aeolian dust and the Blue/White Nile River suspended matter frequency fluctuations during the last 21 cal. ka BP. The radiogenic Sr and Nd isotopes, clay mineralogy, bulk elemental composition and palynological analyses reveal large changes in source components, oscillating between a dominant aeolian Saharan contribution during the LGM and the Late Holocene (~4 to 2 cal. ka BP), a dominant Blue/Atbara Nile River contribution during the early Holocene (15 to 8.4 cal. ka BP) and a probable White Nile River contribution during the Middle Holocene (8.4 to 4 cal. ka BP). The following main features are highlighted: 1. The rapid shift from the LGM arid conditions to the African Humid Period (AHP) started at about 15 cal. ka BP. AHP extends until 8.4 cal. ka BP, and we suggest that the Ethiopian African Monsoon maximum between 12 and 8 cal. ka BP is responsible for a larger Blue/Atbara Nile sediment load and freshwater input into the Eastern Mediterranean Sea. 2. The transition between the AHP and the arid Late Holocene is gradual and occurs in two main phases between 8.4 and 6.5 cal. ka BP and 6.5 to 3.2 cal. ka BP. We suggest that the main rain belt shifted southward from 8.4 to ~4 cal. ka BP and was responsible for progressively reduced sediment load and freshwater input into the eastern Mediterranean Sea. 3. The aridification along the Nile catchments occurred from ~4 to 2 cal. ka BP. A dry period, which culminates at 3.2 cal. ka BP, and seems to coincide with a re-establishment of increased oceanic primary productivity in the western Mediterranean Sea. We postulate that the decrease in thermo-haline water Mediterranean circulation could be part of a

  15. Holocene paleoceanography of Bigo Bay, west Antarctic Peninsula: Connections between surface water productivity and nutrient utilization and its implication for surface-deep water mass exchange

    NASA Astrophysics Data System (ADS)

    Kim, Sunghan; Yoo, Kyu-Cheul; Lee, Jae Il; Khim, Boo-Keun; Bak, Young-Suk; Lee, Min Kyung; Lee, Jongmin; Domack, Eugene W.; Christ, Andrew J.; Yoon, Ho Il

    2018-07-01

    Paleoceanographic changes in response to Holocene climate variability in Bigo Bay, west Antarctic Peninsula (WAP) were reconstructed through geochemical, isotopic, sedimentological, and microfossil analysis. Core WAP13-GC47 is composed of 4 lithologic units. Unit 4 was deposited under ice shelf settings. Unit 3 represents the mid-Holocene open marine conditions. Unit 2 indicates lateral sediment transport by a glacier advance during the Neoglacial period. The chronological contrast between the timing of open marine conditions at core WAP13-GC47 (ca. 7060 cal. yr BP at 540 cm) and the ages of calcareous shell fragments (ca. 8500 cal. yr BP) in Unit 2b suggests sediment reworking during the Neoglacial period. Unit 1 was deposited during the Medieval Warm Period (MWP) and the Little Ice Age (LIA). Surface water productivity, represented by biogenic opal and total organic carbon (TOC) concentrations, increased and bulk δ15N (nitrate utilization) decreased during the warmer early to middle Holocene and the MWP. In contrast, surface water productivity decreased with increased bulk δ15N during the colder Neoglacial period and LIA in Bigo Bay. The nitrate utilization was enhanced during cold periods in association with strong surface water stratification resulting from increased sea ice meltwater discharge or proximity to an ice shelf calving front in Bigo Bay. Reduced nitrate utilization during warm periods is related to weak stratification induced by less sea ice meltwater input and stronger Circumpolar Deep Water influence.

  16. Radiocarbon dating of large termite mounds of the miombo woodland of Katanga, DR Congo

    NASA Astrophysics Data System (ADS)

    Erens, Hans; Boudin, Mathieu; Mees, Florias; Dumon, Mathijs; Mujinya, Basile; Van Strydonck, Mark; Baert, Geert; Boeckx, Pascal; Van Ranst, Eric

    2015-04-01

    The miombo woodlands of South Katanga (D.R. Congo) are characterized by a high spatial density of large conic termite mounds built by Macrotermes falciger (3 to 5 ha-1, ~5 m high, ~15 m in diameter). The time it takes for these mounds to attain this size is still largely unknown. In this study, the age of four of these mounds is determined by 14C-dating the acid-insoluble organic carbon fraction of samples taken along the central vertical axis of two active and two abandoned mounds. The age sequence in the active mounds is erratic, but the results for the abandoned mounds show a logical increase of 14C-age with depth. The ages measured at 50 cm above ground level were 2335 - 2119 cal yr BP for the large abandoned mound (630 cm high), and 796 - 684 cal yr BP for the small abandoned mound (320 cm high). Cold-water-extractable organic carbon (CWEOC) measurements combined with spectroscopic analysis revealed that the lower parts of the active mounds may have been contaminated with recent carbon that leached from the active nest. Nonetheless, this method appears to provide reliable age estimates of large, abandoned termite mounds, which are older than previously estimated. Furthermore, historical mound growth rates seem to correspond to past temperature changes, suggesting a relation between past environmental conditions and mound occupancy. Keywords : 14C, water-extractable carbon, low-temperature combustion

  17. Lake sediment-based Late Holocene glacier reconstruction reveals medieval retreat and two-phase Little Ice Age on subantarctic South Georgia

    NASA Astrophysics Data System (ADS)

    van der Bilt, W. G. M.; Bakke, J.; Werner, J.; Paasche, O.; Rosqvist, G. N.; Vatle, S. S.

    2016-12-01

    Southern Ocean climate is rapidly changing. Yet beyond the instrumental period (± 100 years), our comprehension of climate variability in the region is restricted by a lack of high-resolution paleoclimate records. Alpine glaciers, ubiquitous on Southern Ocean islands, may provide such data as they rapidly respond to climate shifts, recording attendant changes in extent by variations in glacial erosion. Rock flour, the fine-grained fraction of this process, is suspended in meltwater streams and transfers this signal to the sediments of downstream lakes, continuously recording glacier history. Here, we use this relationship and present the first reconstruction of the Late Holocene (1250 cal. yr BP - present) glacier history of the Southern Ocean island of South Georgia, using sediments from the glacier-fed Middle Hamberg lake. Variations are resolved on multi-centennial scales due to robust chronological control. To fingerprint a glacial erosion signal, we employed a set of routinely used physical, geochemical and magnetic parameters. Using Titanium counts, validated against changes in sediment density and grain size distribution, we continuously reconstruct glacier variations over the past millennium. Refining local moraine evidence and supporting evidence from other Southern Hemisphere sites, this study shows a progressive diminishing of consecutive Late Holocene advances. These include a two-stage Little Ice Age, in agreement with other Southern Hemisphere glacier evidence. The presented record furthermore captures an unreported retreat phase behind present limits around 500 cal. yr BP.

  18. Periodic input of dust over the Eastern Carpathians during the Holocene linked with Saharan desertification and human impact

    NASA Astrophysics Data System (ADS)

    Longman, Jack; Veres, Daniel; Ersek, Vasile; Salzmann, Ulrich; Hubay, Katalin; Bormann, Marc; Wennrich, Volker; Schäbitz, Frank

    2017-07-01

    Reconstructions of dust flux have been used to produce valuable global records of changes in atmospheric circulation and aridity. These studies have highlighted the importance of atmospheric dust in marine and terrestrial biogeochemistry and nutrient cycling. By investigating a 10 800-year-long paleoclimate archive from the Eastern Carpathians (Romania) we present the first peat record of changing dust deposition over the Holocene for the Carpathian-Balkan region. Using qualitative (X-ray fluorescence (XRF) core scanning) and quantitative inductively coupled plasma optical emission spectrometer(ICP-OES) measurements of lithogenic (K, Si, Ti) elements, we identify 10 periods of major dust deposition between 9500-9200, 8400-8100, 7720-7250, 6350-5950, 5450-5050, 4130-3770, 3450-2850, 2000-1450, 800-620, and 60 cal yr BP to present. In addition, we used testate amoeba assemblages preserved within the peat to infer local palaeohydroclimatic conditions. Our record highlights several discrepancies between eastern and western European dust depositional records and the impact of highly complex hydrological regimes in the Carpathian region. Since 6100 cal yr BP, we find that the geochemical indicators of dust flux have become uncoupled from the local hydrology. This coincides with the appearance of millennial-scale cycles in the dust input and changes in geochemical composition of dust. We suggest that this is indicative of a shift in dust provenance from local-regional (likely loess-related) to distal (Saharan) sources, which coincide with the end of the African Humid Period and the onset of Saharan desertification.

  19. Solar CalPoly

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Stannard, Sandra

    The target budget of INhouse was about $650,000 for all materials and student expenses of the Solar Decathlon competition. In order to reach our goal, Cal Poly students and faculty worked with the College of Architecture and Environmental Design’s External Relations office to actively fundraise for INhouse. Students connected with Cal Poly alumni through phone calls, postal mail, email, and live presentations to reach as many alumni in the state of California as possible. Before construction begun, students and faculty met on a weekly basis to determine what brands of materials for the home to use and who would bemore » responsible for reaching out to the company to seek a donation. Our College of Architecture and Environmental Design’s administration was essential in helping us fundraise. For some time, the college was hoping to depend on about half of our fundraising expenses to be covered through the sale of INhouse. However, plans to sell the home fell through during the design development phase; the college turned to the sale of a different asset in to help us meet our goal. If we were to do this project again, completing the design concept and securing a future location of our home sooner would have enhanced our fundraising activities.« less

  20. Vegetation and Climate Changes in Patagonia (46°S) during the Last 20 kyr cal. BP from South East Pacific MD 07 3088 Core

    NASA Astrophysics Data System (ADS)

    Montade, V.; Combourieu Nebout, N.; Siani, G.; Michel, E.; Kissel, C.; Carel, M.; Mulsow, S.

    2010-12-01

    The Chilean Patagonia (41°S to 56°S) crossed by the Andes from north to south represents a critical topographic constraint on atmospheric and oceanic systems, and the only continental landmass intercepting the entire Southern Westerlies Wind (SHW) belt in southern hemisphere. Therefore, the southern Chile is a key-area to study the paleoclimate changes and, to understand the synoptic scale ocean-atmospheric circulation systems of the mid to high southern latitudes. However, several questions remain partly unsolved: Is there abrupt reversal event during the Last Glacial-Interglacial transition (LGIT)? Is there a shift or an intensification of the SHW? When begin the Holocene onset? What are the inter or intra hemispheric climatic links? In this aim, we present here a detailed pollen record from the deep-sea core MD 07 3088 (46°04’S; 76°05’W, 1536 m) near Taitao peninsula, taken during the “Pachiderme” cruise (MD 159) within the IMAGES (International MArine Global changES) program (Kissel et al., 2007). The age model (Siani et al., in press) is based upon stable oxygen isotopes of planktonic foraminifera G. bulloïdes coupled to ten AMS 14C measurements performed on planktonic foraminifera and four tephrochronological markers attributed to the Hudson volcano (Haberle and Lumley, 1998). The pollen record expresses vegetation changes and thus climate variations during the last 20 kyr cal. BP. Several vegetation phases are observed during the LGIT and the Holocene onset: Before 18 kyr, the low diversity and pollen influx show the reduced vegetation due to the Patagonian Ice Cap extension and cold temperature. From 17.5 to 14.5 kyr, the diversity and pollen influx increase mark the vegetation development linked to the ice cap melting and temperature increase. From 14.5 to 12 kyr, the Astelia development illustrates the Magellanic Moorland extension and humid conditions linked to the SHW. Later 11.5 kyr, the forest diversification expresses the Holocene onset

  1. The Return of Two-Class Medicine—III Effects of Medi-Cal Reform

    PubMed Central

    Waitzkin, Howard

    1985-01-01

    California's drastic Medi-Cal reforms have created great difficulties in health care for the poor. Patients' clinical problems seldom are apparent in descriptions of changes in public insurance programs. Rapidly escalating costs of Medi-Cal led to irresistible pressures for reform, especially from the business community. The new Medi-Cal regulations provide for prospective contracts with hospitals for inpatient services, the transfer of “Medically Indigent Adults” to the responsibility of county governments and various other straightforward funding cutbacks. Confusion, disruption of services and adverse health outcomes have accompanied the Medi-Cal reforms. PMID:3892917

  2. A 40,000-year woodrat-midden record of vegetational and biogeographical dynamics in north-eastern Utah

    USGS Publications Warehouse

    Jackson, Stephen T.; Betancourt, Julio L.; Lyford, Mark E.; Gray, Stephen T.; Rylander, Kate Aasen

    2005-01-01

    Aim A conspicuous climatic and biogeographical transition occurs at 40-45° N in western North America. This pivot point marks a north–south opposition of wet and dry conditions at interannual and decadal time-scales, as well as the northern and southern limits of many dominant western plant species. Palaeoecologists have yet to focus on past climatic and biotic shifts along this transition, in part because it requires comparisons across dissimilar records [i.e. pollen from lacustrine sediments to the north and plant macrofossils from woodrat (Neotoma) middens to the south]. To overcome these limitations, we are extending the woodrat-midden record northward into the lowlands of the central Rocky Mountains.Location Woodrat middens were collected from crevices and rock shelters on south-facing slopes of Dutch John Mountain (2000-2200 m, 40°57′ N, 109°25′ W), situated on the eastern flanks of the Uinta Mountains in north-eastern Utah. The site is near the regional limits for Pinus ponderosa, P. edulis, P. contorta, Cercocarpus ledifolius var. intricatus, Abies concolor, Ephedra viridis and other important western species.Methods We analysed pollen and plant macrofossils from the 40,000-year midden sequence. The middens represent brief, depositional episodes (mostly years to decades). Four middens represent the early to full-glacial period (40,000–18,000 cal-yr bp), eight middens are from the late-glacial/early Holocene transition (13,500–9000 cal yr bp), and 33 middens span the mid-to-late Holocene (last 7500 years). Temporal density of our Holocene middens (one every c. 210 years) is comparable with typical Holocene pollen sequences from lake sediments.Results Early to full-glacial assemblages are characterized by low diversity and occurrence of montane conifers (Picea pungens, Pseudotsuga menziesii, P. flexilis, Juniperus communis) absent from the site today. Diversity increases in the late-glacial samples with the addition of J. scopulorum, J

  3. Holocene reef accretion: southwest Molokai, Hawaii, U.S.A.

    USGS Publications Warehouse

    Engels, Mary S.; Fletcher, Charles H.; Field, Michael E.; Storlazzi, Curt D.; Grossman, Eric E.; Rooney, John J.B.; Conger, Christopher L.; Glenn, Craig

    2004-01-01

    Two reef systems off south Molokai, Hale O Lono and Hikauhi (separated by only 10 km), show strong and fundamental differences in modern ecosystem structure and Holocene accretion history that reflect the influence of wave-induced near-bed shear stresses on reef development in Hawaii. Both sites are exposed to similar impacts from south, Kona, and trade-wind swell. However, the Hale O Lono site is exposed to north swell and the Hikuahi site is not. As a result, the reef at Hale O Lono records no late Holocene net accretion while the reef at Hikauhi records consistent and robust accretion over late Holocene time. Analysis and dating of 24 cores from Hale O Lono and Hikauhi reveal the presence of five major lithofacies that reflect paleo-environmental conditions. In order of decreasing depositional energy they are: (1) coral-algal bindstone; (2) mixed skeletal rudstone; (3) massive coral framestone; (4) unconsolidated floatstone; and (5) branching coral framestone-bafflestone. At Hale O Lono, 10 cores document a backstepping reef ranging from ∼ 8,100 cal yr BP (offshore) to ∼ 4,800 cal yr BP (nearshore). A depauperate community of modern coral diminishes shoreward and seaward of ∼ 15 m depth due to wave energy, disrupted recruitment activities, and physical abrasion. Evidence suggests a change from conditions conducive to accretion during the early Holocene to conditions detrimental to accretion in the late Holocene. Reef structure at Hikauhi, reconstructed from 14 cores, reveals a thick, rapidly accreting and young reef (maximum age ∼ 900 cal yr BP). Living coral cover on this reef increases seaward with distance from the reef crest but terminates at a depth of ∼ 20 m where the reef ends in a large sand field. The primary limitation on vertical reef growth is accommodation space under wave base, not recruitment activities or energy conditions. Interpretations of cored lithofacies suggest that modern reef growth on the southwest corner of Molokai, and by

  4. Evidence for latest Pleistocene to Holocene uplift at the southern margin of the Central Anatolian Plateau (CAP), southern Turkey

    NASA Astrophysics Data System (ADS)

    Cosentino, Domenico; Öǧretmen, Nazik; Cipollari, Paola; Gliozzi, Elsa; Radeff, Giuditta; Yıldırım, Cengiz; Baykara, Oruc M.; Shen, Chuan-Chou

    2016-04-01

    Along the Mediterranean coastal area of southern Anatolia, markers of ancient sea-level have been reported west of Alanya and east of the Göksu delta. In both areas, bioconstructed fossil rims, consisting mainly of calcareous algae, are situated 0.5 m above the live counterpart. The fossil rim to the west of Alanya has been dated between 2690 to 1545 yrs BP, evidencing late Holocene rock uplift at the CAP southern margin. More recently, based on beachrocks along the coastal area from Incekum to the south of Adana, authors showed that the shoreline was raised around 0.5 m after 19 BC-200 AD. Based on new field observations along the coast between Aydı ncı k and Ayaş (Mersin, southern Turkey), together with AMS 14C dating and high-resolution U-Th chronology, a more complex uplift history can be suggested. Along the coast of Yeşilovacı k, we observed up to seven uplifted marine notches, from 0.5 m to 6.10 m above sea level. Some of them show relationships with a travertine crust that yielded U-Th ages of 2727 ± 1559 years and 5236 ± 2255 years. In the same area, a calcareous algae fossil trottoir related to a marine notch 5.40 m above sea level yielded an AMS 14C 2σ age of 32700 to 31645 years cal BP. Considering that the global ocean was 60 m below the present sea level at 32 ka, the Yeşilovacı k coastal area has been uplifted at 2 mm/yr. Moving to the east, in a small embayment at Eǧribük, two distinct well cemented beach deposits containing Murex brandaris, Cerithium vulgatum, and Columbella rustica have been uplifted at 0.3 m and 0.7 m above the present sea level. Although it is difficult to reconstruct the paleodepth of those beach deposits, AMS 14C 2σ ages of 5575 to 5445 years cal BP and 2130 to 1965 years cal BP show late Holocene uplift. In the Narlı kuyu area, up to seven different uplifted markers of sea level were observed between 0.8 and 7.2 m above the present sea level. In addition, near Ayaş new insights for late Holocene uplift are

  5. Patterns of volcanism, weathering, and climate history from high-resolution geochemistry of the BINGO core, Mono Lake, California, USA

    NASA Astrophysics Data System (ADS)

    Zimmerman, S. R.; Starratt, S.; Hemming, S. R.

    2012-12-01

    years before present (cal yr BP) higher in the core, and significant disruption of the fine layers, this interval likely indicates a relatively deep lake persisting into the early Holocene, after the initial dramatic regression from late Pleistocene levels. The finely laminated olive-green silt of the period ~10,700 to ~7500 cal yr BP is very homogenous chemically, probably indicating a stable, stratified lake and a relatively wet climate. This section merits mm-scale scanning and petrographic examination in the future. The upper boundary of the laminated section shows rising Ca/K and decreasing Ti and Si/K, marking the appearance of authigenic carbonate layers. After ~7500 cal yr BP, the sediment in BINGO becomes highly variable, with increased occurrence of tephra layers and carbonate, indicating a lower and more variable lake level. A short interval of olive-green, laminated fine sand/silt just above a radiocarbon date of 3870 ± 360 cal yr BP may record the Dechambeau Ranch highstand of Stine (1990; PPP v. 78 pp 333-381), and is marked by a distinct low in Ca/K, lasting ~1000 years. The low terminates in a dramatic rise in Ca/K to some of the highest levels in the core, suggesting a period of ~1000 years of extremely dry climate, dwarfing all of the variability in Ca/K, and likely lake level, over the last 2000 years.

  6. Mid- to Late Holocene Climate Shift in the Southern Gulf of California and Tropical Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Perez-Cruz, L. L.; Fucugauchi, J. U.; Velasco, V.; Rodriguez, A.; Choumiline, K.

    2014-12-01

    A multiproxy record has been acquired from a gravity core (DIPAL-I K47) taken in La Paz Basin, an area which is situated in the southwestern sector of the Gulf of California at the junction to the Tropical Pacific Ocean. The high-resolution data sets, from XRF, TOC, magnetic susceptibility and hysteresis measurements, were used to track climatic changes in the tropical climate system at sub-centennial time scales over the past 7.3 cal kyr BP. The paleoprecipitation record shows variation trends, with a shift during the mid- to late Holocene, characterized by changes from high to low humidity. Pluvial, biogenic and eolian input, marked by variations in Ti, Si, Fe, K, Ca, Zr/Ti, Ca/Ti and magnetic susceptibility, shows trend changes between 7-5 cal kyr, 5-4.5 cal kyr, 4.5-3.5 cal kyr and 2.15-1.4 kyr. Drought events are recognized from 3.7 to 3.4, 2.8 to 1.8 cal kyr BP, and between 1.4 and 1.2 cal kyr BP. The southern Gulf is well suited for documenting the climatic and precipitation changes in the tropical Pacific Ocean associated with ITCZ latitudinal migration, PDO, ENSO events and the North American monsoon. Analysis of sourcing, transport and deposition of sediments is used for reconstructing the changing ocean-atmosphere circulation patterns, particularly sensitive to paleoprecipitation. The Bay receives sediments mainly from the surrounding volcanic ranges of the peninsular Baja California. There are no rivers in the peninsula and sediments are related to pluvial input trough ephemeral creeks along the steep cliff ranges and narrow shelf. Biogenic sediments are associated with productivity and oceanographic conditions through upwellings and mesoscale gyres. Eolian sediments are transported into the basin from the peninsula and continent, including transport of fine dust from the northern desert of Sonora-Mojave and arid terrains in the peninsula. It is important to highlight that a common 1800 yr solar variation spectral periodicity has been captured

  7. USS Cal Builders, Inc. Information Sheet

    EPA Pesticide Factsheets

    USS Cal Builders, Inc. (the Company) is located in Stanton, California. The settlement involves renovation activities conducted at property constructed prior to 1978, located in San Francisco, California.

  8. The vegetation history of the last glacial-interglacial cycle in eastern New South Wales, Australia

    NASA Astrophysics Data System (ADS)

    Williams, N. J.; Harle, K. J.; Gale, S. J.; Heijnis, H.

    2006-10-01

    We present a reconstruction of the vegetation history of the last glacial-interglacial cycle (ca. 75 k cal. yr BP-present) at Redhead Lagoon, an enclosed lake basin in coastal, eastern New South Wales, Australia. The sequence of vegetation change at the site is broadly comparable with the pattern of climatically induced changes observed in many other pollen records in southeast Australia. Open woodland-herbland and woodland-forest communities correspond with glacial and interglacial periods respectively, with an additional change towards a more open understorey vegetation assemblage over the last 40 000 yr. The driest conditions appear to have occurred during the height of the last glacial (some time between 30 and 20 k cal. yr BP). This is consistent with other records from southeast Australia, and provides support for a poleward shift in the subtropical anticyclone belt and, less certainly, for the thesis that the Southern Hemisphere westerlies intensified during this period. In marked contrast to most sites in southeast Australia, Casuarinaceae dominates the pollen record through the height of the last glacial period and into the Holocene. The postglacial climatic amelioration is accompanied by the general reappearance of tree pollen in the record, by the disappearance of several open and disturbed environment indicator taxa, by increases in organic sediment deposition and pollen taxon diversity, and by higher water balances. While climate appears to have been the major control on patterns of vegetation change at this site throughout most of the last glacial-interglacial cycle, changes in depositional environment and hydrology have also played a role. Significantly, substantial increases in the rate and magnitude of many indicators of environmental disturbance since European settlement suggest that humans are now the most important mechanism for environmental change. Copyright

  9. Were they all giants? Perspectives on late Holocene plate-boundary earthquakes at the northern end of the Cascadia subduction zone

    NASA Astrophysics Data System (ADS)

    Hutchinson, Ian; Clague, John

    2017-08-01

    The relative magnitude of plate-boundary earthquakes at the northern end of the Cascadia subduction zone was assessed from the temporal concordance between the ages of coseismically buried late Holocene soils in southwest Washington, their counterparts in central and southern Cascadia, offshore turbidites, and paleoseismic deposits on the west coast of Vancouver Island. Only three of the seven buried soils in southwest Washington that can be reliably traced as buried soils or paleotsunami deposits in the coastal lowlands of south-central and southern Cascadia have well-dated counterparts in northern Cascadia. The three wide-ranging events date from Cascadia earthquakes Y (∼250 cal BP), U (∼1260 cal BP), and N (∼2520 cal BP). All three likely ruptured the entire plate margin, and therefore potentially qualify as ;giants; (Mw ≥ 9). Deposits that may derive from tsunamis generated by earthquakes S (∼1570 cal BP), L (∼2870 cal BP) and J (∼3360 cal BP) can also be found in northern Cascadia, but the ages of these deposits are not yet well-enough constrained to determine whether they are coeval with their southern counterparts. Earthquake W (∼850 cal BP), appears to be present in the northern Cascadia paleoseismic record, but yields considerably older ages than in central Cascadia, and may be missing from southernmost Cascadia. The onshore record of an offshore turbidite (T2) displays a similar spatio-temporal pattern to that of earthquake W.

  10. CAMPARE and Cal-Bridge: Two Institutional Networks Increasing Diversity in Astronomy

    NASA Astrophysics Data System (ADS)

    Rudolph, Alexander L.; Smecker-Hane, Tammy A.

    2017-01-01

    We describe two programs, CAMPARE and Cal-Bridge, with the common mission of increasing participation of groups traditionally underrepresented in astronomy, through summer research opportunities, in the case of CAMPARE, scholarships in the case of Cal-Bridge, and significant mentoring in both programs, creating a national impact on their numbers successfully pursuing a PhD in the field.In 7 years, the CAMPARE program has sent 80 students, >80% from underrepresented groups, to conduct summer research at one of 14 major research institutions throughout the country. The graduation rate among CAMPARE scholars is 98%, and of the CAMPARE scholars who have graduated with a Bachelor’s degree, more than 60% have completed or are pursuing graduate education in astronomy or a related field, at institutions including UCLA, UC Riverside, UC Irvine, UC Santa Barbara, USC, Stanford, Univ. of Arizona, Univ. of Washington, and the Fisk-Vanderbilt Master’s-to-PhD program.Now entering its third year, the Cal-Bridge program is a CSU-UC Bridge program comprised of over 75 physics and astronomy faculty from 5 University of California (UC), 9 California State University (CSU), and 14 California Community College (CCC) campuses in Southern California. In the first three years, 22 Cal-Bridge Scholars have been selected, including 11 Hispanic, 3 African-American and 8 female students, 5 of whom are from URM groups. Nineteen (19) of the 22 Cal-Bridge Scholars are first-generation college students. The entire first cohort of 4 Cal-Bridge scholars was accepted to one or more PhD programs in astronomy or physics, including UC Irvine, UC Santa Cruz, UC Davis, Michigan State, and Georgia State Universities. The second cohort of 8 Cal-Bridge scholars is applying to graduate schools this fall.Cal-Bridge provides much deeper mentoring and professional development experiences over the last two years of undergraduate and first year of graduate school to students from this diverse network of higher

  11. Reconstructing Holocene seasonal hydrographic variability in the eastern North Atlantic using bivalve shells from St Kilda, Scotland

    NASA Astrophysics Data System (ADS)

    Alexandroff, Stella; Scourse, James; Butler, Paul; Schöne, Bernd; Reimer, Paula

    2017-04-01

    Bivalve shells like Arctica islandica and Glycymeris glycymeris can be used as highly resolved archives of past marine climate and long-term biomonitors. The annual growth patterns of the shell reflect the environment the animals live in and by cross-matching these growth patterns it is possible to construct multi-centennial, annually resolved chronologies that form a temporal template for isotope sampling. The aim of this study is to detect a signal of Atlantic hydrographic variability in Scottish Shelf Seas that is as far as possible uncontaminated by other influences. In May 2014, we collected dead valves and young live specimens of G. glycymeris from St Kilda, Outer Hebrides, Scotland, and in April 2016, live specimens of A. islandica were collected at the same location. This area is of particular interest as it is close to the Scottish shelf margin, has negligible freshwater input, and is thought to represent open-ocean North Atlantic signals well. We here present two floating chronologies, each spanning >180 years, built from dead-collected G. glycymeris shells from St Kilda. All the shells in these chronologies were assigned radiocarbon ages between 3700-3300 cal yr BP. By combining the radiocarbon dates and the chronological data derived from cross-matching annual bands in the shells, one of the floating chronologies could be further constrained to 3750-3500 cal yr BP (95% range). Sub-annual δ18O data from the floating chronologies and from the modern specimens show a strong seasonal signal and multi-year trends. We calibrate the δ18O results from the modern specimens with instrumental data, which enables us (subject to the assumption that there has been no change in δ18Owater) to compare mean and seasonal seawater temperatures between the present day and the fourth millennium BP.

  12. Biomization and quantitative climate reconstruction techniques in northwestern Mexico—With an application to four Holocene pollen sequences

    NASA Astrophysics Data System (ADS)

    Ortega-Rosas, C. I.; Guiot, J.; Peñalba, M. C.; Ortiz-Acosta, M. E.

    2008-04-01

    6 ka. Climate Dynamics 12, 185-194), we modified the pollen-PFT and PFT-biomes assignation of Thompson and Anderson (Thompson, R.S., Anderson, K.H., 2000. Biomes of western North America at 18,000; 6000 and 0 14C yr BP reconstructed from pollen and packrat midden data. Journal of Biogeography 27, 555-584) for a better representation of the modern vegetation of NW Mexico. The biome reconstruction method was validated with the modern pollen sites and applied to the fossil sites. Our results show that, during the early Holocene, a cool conifer forest extended at least down to 1700 m, while today this biome is present above 2000 m in the Chihuahua state. The Younger Dryas event was recorded in one site with cold and dry conditions. The reconstructed annual temperature for this period was 3°-6 °C colder than today, and annual precipitation was 250 mm lower than at present (900 mm/yr). The middle Holocene after 9200 cal yr BP was marked by a warming trend, reaching temperatures 2 °C warmer than today at 7000 cal yr BP, and by the installation of a warm mixed forest, the present day biome, at 1700 m elevation, while at higher elevations (1900 m) the cool conifer forest was still present. Summer precipitation was 200 mm/yr above the early Holocene values, suggesting that monsoon-like conditions strengthened since 9200 cal yr BP at this region. During the last 4000 yr, the same warm mixed forest was reconstructed below 1700 m and a conifer forest above 1700 m. A great variability of vegetation and climate patterns was recorded for the last 3000 yr particularly at high elevation sites, where warming and cooling trends would be coeval of the Medieval warm period and Little Ice Age, likely related to ENSO variability.

  13. PAS-cal: a Generic Recombinant Peptide Calibration Standard for Mass Spectrometry

    NASA Astrophysics Data System (ADS)

    Breibeck, Joscha; Serafin, Adam; Reichert, Andreas; Maier, Stefan; Küster, Bernhard; Skerra, Arne

    2014-08-01

    We describe the design, preparation, and mass-spectrometric characterization of a new recombinant peptide calibration standard with uniform biophysical and ionization characteristics for mass spectrometry. "PAS-cal" is an artificial polypeptide concatamer of peptide cassettes with varying lengths, each composed of the three small, chemically stable amino acids Pro, Ala, and Ser, which are interspersed by Arg residues to allow site-specific cleavage with trypsin. PAS-cal is expressed at high yields in Escherichia coli as a Small Ubiquitin-like MOdifier (SUMO) fusion protein, which is easily purified and allows isolation of the PAS-cal moiety after SUMO protease cleavage. Upon subsequent in situ treatment with trypsin, the PAS-cal polypeptide yields a set of four defined homogeneous peptides in the range from 2 to 8 kDa with equal mass spacing. ESI-MS analysis revealed a conveniently interpretable raw spectrum, which after deconvolution resulted in a very simple pattern of four peaks with similar ionization signals. MALDI-MS analysis of a PAS-cal peptide mixture comprising both the intact polypeptide and its tryptic fragments revealed not only the four standard peptides but also the singly and doubly charged states of the intact concatamer as well as di- and trimeric adduct ion species between the peptides, thus augmenting the observable m/z range. The advantageous properties of PAS-cal are most likely a result of the strongly hydrophilic and conformationally disordered PEG-like properties of the PAS sequences. Therefore, PAS-cal offers an inexpensive and versatile recombinant peptide calibration standard for mass spectrometry in protein/peptide bioanalytics and proteomics research, the composition of which may be further adapted to fit individual needs.

  14. Antiquity of coca-leaf chewing in the south central Andes: a 3,000 year archaeological record of coca-leaf chewing from northern Chile.

    PubMed

    Rivera, Mario A; Aufderheide, Arthur C; Cartmell, Larry W; Torres, Constantino M; Langsjoen, Odin

    2005-12-01

    Carbon-14 (14C) dating from mummies of the Alto Ramirez culture confirms that coca leaf chewing was an incipient practice among members of a population that peopled the valleys and coastal areas of Northern Chile by 3,000 years before the present (yr.B.P.). Out of eleven bodies from the burial site of Pisagua-7 (PSG-7, S 19 degrees 35', W 70 degrees 13') that were analyzed, two samples tested positive. Mummy 725-A C2 (dated 3,090 to 2,850 two sigma calibrated 14C years before the present) was shown to have a cocaine value of 13.3 nanograms/10 milligrams of sample (ng/10mg), and mummy 741 (2,890 to 2,760 two sigma cal yr B.P.), a 5.6 ng/10mg value.

  15. TopBP1 functions with 53BP1 in the G1 DNA damage checkpoint

    PubMed Central

    Cescutti, Rachele; Negrini, Simona; Kohzaki, Masaoki; Halazonetis, Thanos D

    2010-01-01

    TopBP1 is a checkpoint protein that colocalizes with ATR at sites of DNA replication stress. In this study, we show that TopBP1 also colocalizes with 53BP1 at sites of DNA double-strand breaks (DSBs), but only in the G1-phase of the cell cycle. Recruitment of TopBP1 to sites of DNA replication stress was dependent on BRCT domains 1–2 and 7–8, whereas recruitment to sites of DNA DSBs was dependent on BRCT domains 1–2 and 4–5. The BRCT domains 4–5 interacted with 53BP1 and recruitment of TopBP1 to sites of DNA DSBs in G1 was dependent on 53BP1. As TopBP1 contains a domain important for ATR activation, we examined whether it contributes to the G1 cell cycle checkpoint. By monitoring the entry of irradiated G1 cells into S-phase, we observed a checkpoint defect after siRNA-mediated depletion of TopBP1, 53BP1 or ATM. Thus, TopBP1 may mediate the checkpoint function of 53BP1 in G1. PMID:20871591

  16. TopBP1 functions with 53BP1 in the G1 DNA damage checkpoint.

    PubMed

    Cescutti, Rachele; Negrini, Simona; Kohzaki, Masaoki; Halazonetis, Thanos D

    2010-11-03

    TopBP1 is a checkpoint protein that colocalizes with ATR at sites of DNA replication stress. In this study, we show that TopBP1 also colocalizes with 53BP1 at sites of DNA double-strand breaks (DSBs), but only in the G1-phase of the cell cycle. Recruitment of TopBP1 to sites of DNA replication stress was dependent on BRCT domains 1-2 and 7-8, whereas recruitment to sites of DNA DSBs was dependent on BRCT domains 1-2 and 4-5. The BRCT domains 4-5 interacted with 53BP1 and recruitment of TopBP1 to sites of DNA DSBs in G1 was dependent on 53BP1. As TopBP1 contains a domain important for ATR activation, we examined whether it contributes to the G1 cell cycle checkpoint. By monitoring the entry of irradiated G1 cells into S-phase, we observed a checkpoint defect after siRNA-mediated depletion of TopBP1, 53BP1 or ATM. Thus, TopBP1 may mediate the checkpoint function of 53BP1 in G1.

  17. OSD CALS Architecture Master Plan Study. Concept Paper. Security. Volume 38

    DOT National Transportation Integrated Search

    1989-07-01

    Developing and executing a well-thought-out security policy is critical to the success of CALS. Without appropriate security measures, the integration of technology, organizations, functions, and data envisioned as Phase II CALS can not occur. Theref...

  18. Holocene fire activity and vegetation response in South-Eastern Iberia

    NASA Astrophysics Data System (ADS)

    Gil-Romera, Graciela; Carrión, José S.; Pausas, Juli G.; Sevilla-Callejo, Miguel; Lamb, Henry F.; Fernández, Santiago; Burjachs, Francesc

    2010-05-01

    Since fire has been recognized as an essential disturbance in Mediterranean landscapes, the study of long-term fire ecology has developed rapidly. We have reconstructed a sequence of vegetation dynamics and fire changes across south-eastern Iberia by coupling records of climate, fire, vegetation and human activities. We calculated fire activity anomalies (FAAs) in relation to 3 ka cal BP for 10-8 ka cal BP, 6 ka cal BP, 4 ka cal BP and the present. For most of the Early to the Mid-Holocene uneven, but low fire events were the main vegetation driver at high altitudes where broadleaved and coniferous trees presented a highly dynamic post-fire response. At mid-altitudes in the mainland Segura Mountains, fire activity remained relatively stable, at similar levels to recent times. We hypothesize that coastal areas, both mountains and lowlands, were more fire-prone landscapes as biomass was more likely to have accumulated than in the inland regions, triggering regular fire events. The wet and warm phase towards the Mid-Holocene (between ca 8 and 6 ka cal BP) affected the whole region and promoted the spread of mesophytic forest co-existing with Pinus, as FAAs appear strongly negative at 6 ka cal BP, with a less important role of fire. Mid and Late Holocene landscapes were shaped by an increasing aridity trend and the rise of human occupation, especially in the coastal mountains where forest disappeared from ca 2 ka cal BP. Mediterranean-type vegetation (evergreen oaks and Pinus pinaster- halepensis types) showed the fastest post-fire vegetation dynamics over time.

  19. An Interaction of Screen Colour and Lesson Task in CAL

    ERIC Educational Resources Information Center

    Clariana, Roy B.

    2004-01-01

    Colour is a common feature in computer-aided learning (CAL), though the instructional effects of screen colour are not well understood. This investigation considers the effects of different CAL study tasks with feedback on posttest performance and on posttest memory of the lesson colour scheme. Graduate students (n=68) completed a computer-based…

  20. CALS Infrastructure Analysis. Draft. Volume 21

    DOT National Transportation Integrated Search

    1990-03-01

    This executive overview to the DoD CALS Infrastructure Analysis Report summarizes the Components' current effort to modernize the DoD technical data infrastructure. This infrastructure includes all existing and planned capabilities to acquire, manage...

  1. Views of a Cal/OSHA Inspector.

    PubMed

    Oudiz, Jack

    2009-01-01

    Retiring CAL/OSHA Industrial Hygienist and Senior Safety Engineer Jack Oudiz offers his thoughts in the nature of a voluntary "exit interview" on his years working for the agency and its performance in its mission.

  2. Gran Sabana fires (SE Venezuela): a paleoecological perspective

    NASA Astrophysics Data System (ADS)

    Montoya, Encarni; Rull, Valentí

    2011-11-01

    Fires are among the most important risks for tropical ecosystems in a future climatic change scenario. Recently, paleoecological research has been addressed to discern the role played by fire in neotropical landscapes. However, given the magnitude of the Neotropics, many studies are relegated to infer just local trends. Here we present the compilation of the paleo-fire records developed until now in the southern Gran Sabana (SE Venezuela) with the aim to describe the fire history as well as to infer the possible forcing factors implied. In this sense, southern Gran Sabana has been under fire perturbation since the Lateglacial, with the concomitant effects upon vegetation, and persisted during the Holocene. Around 2000 cal yr BP onwards, the fire activity highly increased promoting the expansion of pre-existing savannas, the decrease of forests and the appearance and establishment of Mauritia palm swamps. The continuous fire incidence registered for several thousands of years has likely promoted the supremacy of treeless savannas upon other vegetation types and the degradation to secondary landscapes. Based on the available evidence, the anthropogenic nature of this high fire activity has been postulated. If so, it could be hypothesized that the timing arrival of Pemón, the present-day indigenous culture in the Gran Sabana, would be ca 2000 cal yr BP onwards, rather than the last centuries, as it has been formerly assumed. The implications of these ancient practices in the area are also discussed for present Gran Sabana landscapes sustainability and future conservation strategies.

  3. Patterns and processes of Late Quaternary environmental change in a montane region of southwestern Europe

    NASA Astrophysics Data System (ADS)

    Carrión, José S.

    2002-10-01

    This paper examines the Late Quaternary (c. 20,300-<505 cal yr BP) environmental history of Siles, a lake situated at 1320 m in the Segura mountains of southern Spain, with the goal of establishing the mechanisms exerting control on vegetation change. Palaeoecological indicators include pollen, microcharcoal, spores of terrestrial plants, fungi, and non-siliceous algae, and other microfossils. The Siles sequence is shown to be sensitive to climatic change, although the control exerted by climate on vegetation is ultimately shaped by disturbances and species interactions, determining the occurrence of century-scale lags and threshold responses. Biotically induced changes of vegetation are also shown at the intrazonal level of variation. The new sequence is placed in the context of two previous records to postulate a picture of Holocene environmental change for the Segura region. The existence of mid-elevation glacial refugia for a number of temperate and Mediterranean trees is shown. A mid-Holocene phase (c. 7500-5200 cal yr BP) emerges regionally as the time of maximum forest development and highest lake levels. The early Holocene occurs as a generally dry, pyrophytic period of pine forests, with grassland scrub in high altitudes, and the late Holocene as a period of protracted vegetation sensitivity, with return to development of pine forests, spread of xerophytic communities, and increased fire activity, under the context of dry spells, localized anthropogenic disturbance, and shallowing and desiccation of lakes. Several events described here correlate with established times of abrupt transitions in the climates of northern Europe, the Mediterranean basin, north Africa, and the Sahel.

  4. Climate and vegetation change during the Holocene in southern Iberia

    NASA Astrophysics Data System (ADS)

    Jimenez-Moreno, G.; Anderson, R. S.; Ramos Román, M. J.; García-Alix, A.; Jiménez-Espejo, F. J. J.; Hernández-Corbalán, M. D.; Toney, J. L.; Mesa-Fernández, J. M.; Camuera-Bidaurreta, J.; Carrión, J. S.

    2015-12-01

    Detailed pollen analysis has been carried out on several sediment cores taken from high-elevation alpine lakes and bog areas located in Sierra Nevada and coastal and offshore environments from southern Spain. The earliest part of the record, from 8200 to about 7000 cal yr BP, is characterized by the highest abundance of arboreal pollen and Pediastrum, indicating the warmest and wettest conditions in the area at that time. The pollen records show a progressive aridification trend since 7000 cal yr BP through a decrease in forest species and the increase in xerophytes. The progressive aridification is punctuated by millennial-scale periodically enhanced droughts that coincide in timing and duration with well-known arid events in the Mediterranean and other areas. A relatively humid period occurred during the Roman Humid Period. The Medieval Climate Anomaly (900-1300 AD) was characterized by a wet phase at first, coinciding with a solar minimum, and a later arid phase, coinciding with the Medieval solar Maximum and a positive NAO. The Little Ice Age (1300-1850 AD) was markedly wetter than earlier, as shown by the increase in tree pollen, coinciding with a phase of negative NAO and the Maunder solar minimum. This study shows that vegetation and climate in Western Mediterranean are modulated by solar and atmospheric factors. Several vegetation changes are observed in the last centuries, which probably indicate the high-impact of humans in the Sierra Nevada, with pasturing leading to nutrient enrichment and eutrophication of the wetlands, Olea cultivation at lower elevations and Pinus reforestation.

  5. An eLIMA model for the 67 s X-ray periodicity in CAL 83

    NASA Astrophysics Data System (ADS)

    Odendaal, A.; Meintjes, P. J.

    2017-05-01

    Supersoft X-ray sources (SSSs) are characterized by their low effective temperatures and high X-ray luminosities. The soft X-ray emission can be explained by hydrogen nuclear burning on the surface of a white dwarf (WD) accreting at an extremely high rate. A peculiar ˜67 s periodicity (P67) was previously discovered in the XMM-Newton light curves of the SSS CAL 83. P67 was detected in X-ray light curves spanning ˜9 yr, but exhibits variability of several seconds on time-scales as short as a few hours, and its properties are remarkably similar to those of dwarf nova oscillations (DNOs). DNOs are short time-scale modulations (≲1 min) often observed in dwarf novae during outburst. DNOs are explained by the well-established low-inertia magnetic accretor (LIMA) model. In this paper, we show that P67 and its associated period variability can be satisfactorily explained by an application of the LIMA model to the more 'extreme' environment in an SSS (eLIMA), contrary to another recent study attempting to explain P67 and its associated variability in terms of non-radial g-mode oscillations in the extended envelope of the rapidly accreting WD in CAL 83. In the eLIMA model, P67 originates in an equatorial belt in the WD envelope at the boundary with the inner accretion disc, with the belt weakly coupled to the WD core by an ˜105 G magnetic field. New optical light curves obtained with the Sutherland High-speed Optical Camera are also presented, exhibiting quasi-periodic modulations on time-scales of ˜1000 s, compatible with the eLIMA framework.

  6. The Influence of Wildfire on Long-Term Erosion: Insights from the Jemez Mountains, NM and the Western USA

    NASA Astrophysics Data System (ADS)

    Fitch, E. P.; Meyer, G. A.

    2017-12-01

    A major influence of wildfire on long-term erosion in the western USA is strongly suggested by extreme postfire debris flows and floods, where fire severity has increased in recent decades due to climate change and land use. Roughly 30% of the ponderosa-mixed conifer forests of the Jemez Mountains has burned in the last 20 yr, much at high severity, whereas tree-ring data indicate mostly lower-severity burns from 1600-1900 CE, before fire suppression and grazing. Fire-related alluvial deposits proximal to hillslopes reflect mostly small to moderate erosional events over the last 4000 yr, compared to thick, bouldery debris-flow deposits from recent severe fires; some modern postfire debris flows appear truly extreme in comparison to Holocene deposits. Recognizable fire-related deposits make up 77% of fans from moist north aspects, as relatively dense vegetation and thick soil yield minor surface runoff unless severely burned. Only 39% of fan sediments from drier south aspects are fire-related, however, as sparser vegetation and exposed bedrock can produce runoff and sediment when unburned. Peaks in fire-related sedimentation at 1800, 650, 410, and 300 cal yr BP coincide with severe droughts, often preceded by wetter decades that could suppress fire activity and promote denser stands. Although the Medieval Climatic Anomaly (MCA, 1050-700 cal yr BP) was marked by generally warmer temperatures and multidecadal episodes of widespread, severe drought in the western USA, fire-related sedimentation was relatively minor in the Jemez Mountains. In contrast, dense subalpine forests of Yellowstone and central Idaho burned less frequently and more severely in the late Holocene, and produced major debris flows in the MCA. Fire accounts for only 30-50% of Holocene fan deposition in these areas, as steep unburned basins also produce large debris flows in extreme storms. The relative importance of fire in erosion depends on topography, bedrock, soil cover, and forest composition

  7. Identification and synchronization of the common cosmic-ray signal in the IntCal13 14C calibration and the Greenland ice-core 10Be records

    NASA Astrophysics Data System (ADS)

    Muscheler, Raimund; Adolphi, Florian; Bronk Ramsey, Christopher; Rasmussen, Sune; Hughen, Konrad; Cooper, Alan; Turney, Chris

    2017-04-01

    The production rates of cosmogenic radionuclides (such as 10Be and 14C) are modulated by the solar and geomagnetic shielding of galactic cosmic rays. In addition, 14C and 10Be are influenced by the carbon cycle and the atmospheric transport and deposition, respectively. Isolating and identifying the common production signal allows us to synchronize ice core 10Be and tree ring 14C records during the Holocene (Adolphi and Muscheler, 2016), thereby connecting ice core climate records with 14C-dated records. Extending this comparison further back in time is challenging due to deteriorating quality of the 14C calibration record, IntCal13, (Reimer et al., 2013) and possible unidentified climate influences on the ice-core 10Be records. Nevertheless, by focusing on the most prominent production-rate features this comparison can be extended far back into the last glacial where, for example, the linkage of tree-ring based Kauri 14C data and the Greenland ice-core time scale (GICC05) suggested unresolved data and/or time scale differences around the period of the Laschamp geomagnetic field minimum at about 42000 yrs BP (Muscheler et al., 2014). Here we show that the data underlying the IntCal13 14C record and the ice-core 10Be records exhibit common variability that allows us to tentatively link the ice core GICC05 time scale to the radiocarbon time scale for almost the complete radiocarbon dating range. The observed time scale differences could be related to uncertainties in both the U/Th-based dating of the IntCal13 calibration data set and the GICC05 time scale, and we show that the two can be reconciled within the uncertainties of the ice-core layer counting. This direct comparison between IntCal13 and 10Be also suggests that the 14C differences shown in (Muscheler et al., 2014) around the Laschamp geomagnetic field minimum can be reduced by moderate adjustments to the GICC05 time scale. References: Adolphi, F., and Muscheler, R., 2016, Synchronizing the Greenland ice

  8. Measurements of Gases and Aerosols during 2010Cal-Mex

    NASA Astrophysics Data System (ADS)

    Zheng, J.; Zhang, R.; Molina, L.

    2012-04-01

    The major goal of the collaborative Cal-Mex 2010 research project is to assess the sources and processing of emissions along the California-Mexico border region and their effects on regional air quality and climate in order to provide scientific information to decision makers of both nations when addressing these two inter-related issues. During the Cal-Mex 2010 field study, the TAMU teams have collected extensive data sets from Tijuana/San Diego border, including volatile organic compounds (VOCs), gaseous sulfuric acid (H2SO4) and a suite set of physical and chemical parameters of aerosols. This comprehensive data set requires additional effort to process and analyze the measurements of gases and aerosols during Cal-Mex 2010. In this talk, preliminary data analysis of gases and aerosols will be presented, including VOCs and particle mixing states, morphology, and effective densities.

  9. Cal-Bridge and CAMPARE: Engaging Underrepresented Students in Physics and Astronomy

    NASA Astrophysics Data System (ADS)

    Rudolph, Alexander L.; Cal-Bridge and CAMPARE Teams

    2018-01-01

    We describe two programs, Cal-Bridge and CAMPARE, with the common mission of increasing participation of groups traditionally underrepresented in astronomy, through summer research opportunities, in the case of CAMPARE, scholarships in the case of Cal-Bridge, and significant mentoring in both programs, creating a national impact on their numbers successfully pursuing a PhD in the field.In 8 years, the CAMPARE program has sent 112 students, >80% from underrepresented groups, to conduct summer research at one of 14 major research institutions throughout the country. Of the CAMPARE scholars who have graduated with a Bachelor’s degree, almost two-thirds (65%) have completed or are pursuing graduate education in physics, astronomy, or a related field, at institutions including UCLA, UC Riverside, UC Irvine, UC Santa Barbara, USC, Stanford, Univ. of Arizona, Univ. of Washington, Univ. of Rochester, Michigan State Univ., Georgia Tech, Georgia State Univ., Kent State, Indiana Univ., Univ. of Oregon, Syracuse Univ., Montana State Univ., and the Fisk-Vanderbilt Master’s-to-PhD program.Now entering its fourth year, the Cal-Bridge program is a CSU-UC Bridge program comprised of >140 physics and astronomy faculty from 9 University of California (UC), 15 California State University (CSU), and 30 California Community College (CCC) campuses throughout California. In the first four years, 34 Cal-Bridge Scholars have been selected, including 22 Hispanic, 3 African-American and 13 women students, 10 of whom are from URM groups. Thirty (30) of the 34 Cal-Bridge Scholars are first generation college students. In the last two years, 11 of 13 Cal-Bridge Scholars have begun PhD programs in physics or astronomy at top PhD programs nationally. Three (3) of these 11 scholars have won NSF Graduate Research Fellowships; one more received an Honorable Mention. The next cohort applies this fall.Cal-Bridge provides much deeper mentoring and professional development experiences over the last

  10. A late Pleistocene human presence at Huaca Prieta, Peru, and early Pacific Coastal adaptations

    NASA Astrophysics Data System (ADS)

    Dillehay, Tom D.; Bonavia, Duccio; Goodbred, Steve L.; Pino, Mario; Vásquez, Victor; Tham, Teresa Rosales

    2012-05-01

    Archaeological excavations in deep pre-mound levels at Huaca Prieta in northern Peru have yielded new evidence of late Pleistocene cultural deposits that shed insights into the early human occupation of the Pacific coast of South America. Radiocarbon dates place this occupation between ~ 14,200 and 13,300 cal yr BP. The cultural evidence shares certain basic technological and subsistence traits, including maritime resources and simple flake tools, with previously discovered late Pleistocene sites along the Pacific coast of Peru and Chile. The results help to expand our knowledge of early maritime societies and human adaption to changing coastal environments.

  11. Postglacial viability and colonization in North America’s ice-free corridor

    NASA Astrophysics Data System (ADS)

    Pedersen, Mikkel W.; Ruter, Anthony; Schweger, Charles; Friebe, Harvey; Staff, Richard A.; Kjeldsen, Kristian K.; Mendoza, Marie L. Z.; Beaudoin, Alwynne B.; Zutter, Cynthia; Larsen, Nicolaj K.; Potter, Ben A.; Nielsen, Rasmus; Rainville, Rebecca A.; Orlando, Ludovic; Meltzer, David J.; Kjær, Kurt H.; Willerslev, Eske

    2016-09-01

    During the Last Glacial Maximum, continental ice sheets isolated Beringia (northeast Siberia and northwest North America) from unglaciated North America. By around 15 to 14 thousand calibrated radiocarbon years before present (cal. kyr BP), glacial retreat opened an approximately 1,500-km-long corridor between the ice sheets. It remains unclear when plants and animals colonized this corridor and it became biologically viable for human migration. We obtained radiocarbon dates, pollen, macrofossils and metagenomic DNA from lake sediment cores in a bottleneck portion of the corridor. We find evidence of steppe vegetation, bison and mammoth by approximately 12.6 cal. kyr BP, followed by open forest, with evidence of moose and elk at about 11.5 cal. kyr BP, and boreal forest approximately 10 cal. kyr BP. Our findings reveal that the first Americans, whether Clovis or earlier groups in unglaciated North America before 12.6 cal. kyr BP, are unlikely to have travelled by this route into the Americas. However, later groups may have used this north-south passageway.

  12. Postglacial viability and colonization in North America's ice-free corridor.

    PubMed

    Pedersen, Mikkel W; Ruter, Anthony; Schweger, Charles; Friebe, Harvey; Staff, Richard A; Kjeldsen, Kristian K; Mendoza, Marie L Z; Beaudoin, Alwynne B; Zutter, Cynthia; Larsen, Nicolaj K; Potter, Ben A; Nielsen, Rasmus; Rainville, Rebecca A; Orlando, Ludovic; Meltzer, David J; Kjær, Kurt H; Willerslev, Eske

    2016-09-01

    During the Last Glacial Maximum, continental ice sheets isolated Beringia (northeast Siberia and northwest North America) from unglaciated North America. By around 15 to 14 thousand calibrated radiocarbon years before present (cal. kyr bp), glacial retreat opened an approximately 1,500-km-long corridor between the ice sheets. It remains unclear when plants and animals colonized this corridor and it became biologically viable for human migration. We obtained radiocarbon dates, pollen, macrofossils and metagenomic DNA from lake sediment cores in a bottleneck portion of the corridor. We find evidence of steppe vegetation, bison and mammoth by approximately 12.6 cal. kyr bp, followed by open forest, with evidence of moose and elk at about 11.5 cal. kyr bp, and boreal forest approximately 10 cal. kyr bp. Our findings reveal that the first Americans, whether Clovis or earlier groups in unglaciated North America before 12.6 cal. kyr bp, are unlikely to have travelled by this route into the Americas. However, later groups may have used this north-south passageway.

  13. Improved marine reservoir age estimation and palaeoclimate synchronisation of the early Holocene Levantine/NW-Arabian region based on identification of the S1 tephra in Dead Sea and Tayma palaeolake sediments

    NASA Astrophysics Data System (ADS)

    Neugebauer, Ina; Wulf, Sabine; Schwab, Markus J.; Serb, Johanna; Plessen, Birgit; Appelt, Oona; Brauer, Achim

    2017-04-01

    Due to a lack of tephras identified in marine and terrestrial palaeoclimate records from the Levantine-Arabian area, this region is still not sufficiently connected to the eastern Mediterranean tephrostratigraphical lattice. Here we report on the first finding of cryptotephra in the Holocene lacustrine sediment records of the Dead Sea and the Tayma palaeolake (NW Arabian Peninsula). The major elemental chemistry of the rhyolitic glass shards proves this tephra identical to the distal 'S1 tephra' identified in the Yammoûneh palaeolake, Lebanon (Develle et al, 2009), in a marine sediment record from the SE Levantine basin (Hamann et al., 2010) and in the Sodmein Cave archaeological site in Egypt (Barton et al., 2015). The 'S1 tephra', most likely corresponding to the early Holocene 'Dikkartın' dome eruption of the Erciyes Daǧ volcano in central Anatolia, Turkey, has been dated in the marine record at 8830 ± 140 cal yr BP. We present new age estimates of the 'S1 tephra' based on radiocarbon dating of terrestrial plant remains (Migowski et al., 2004) and pollen concentrates (Dinies et al., 2015), which reveal modelled ages of 8939 ± 83 cal yr BP in the Dead Sea sediments and 9041 ± 254 cal yr BP in Tayma. This allows the estimation of an early Holocene marine reservoir age of ca. 320 years in the SE Levantine Sea. The timing of the volcanic eruption during the early Holocene humid period, which led to the formation of sapropel S1 in the Mediterranean Sea, and the identification of the 'S1 tephra' more than 1200 km to the south are crucial for the synchronisation of marine and terrestrial palaeoclimate records in the eastern Mediterranean region. References: Barton et al., 2015. The role of cryptotephra in refining the chronology of Late Pleistocene human evolution and cultural change in North Africa. Quaternary Sci. Rev. 118, 151-169. Develle et al., 2009. Early Holocene volcanic ash fallout in the Yammoûneh lacustrine basin (Lebanon): Tephrochronological

  14. The drainage of the Baltic Ice Lake and a new Scandinavian reference 10Be production rate

    NASA Astrophysics Data System (ADS)

    Stroeven, Arjen P.; Heyman, Jakob; Fabel, Derek; Björck, Svante; Caffee, Marc W.; Fredin, Ola; Harbor, Jonathan M.

    2015-04-01

    An important constraint on the reliability of cosmogenic nuclide exposure dating is the derivation of tightly controlled production rates. We present a new dataset for 10Be production rate calibration from Mount Billingen, southern Sweden, the site of the final drainage of the Baltic Ice Lake, an event dated to 11,620 ± 100 cal yr BP. Nine samples of flood-scoured bedrock surfaces and depositional boulders and cobbles unambiguously connected to the drainage event yield a reference 10Be production rate of 4.09 ± 0.22 atoms g-1 yr-1 for the CRONUS Lm scaling and 3.93 ± 0.21 atoms g-1 yr-1 for the LSD general spallation scaling. We also recalibrate the reference 10Be production rates for four sites in Norway and combine these with the Billingen results to derive a tightly clustered Scandinavian reference 10Be production rate of 4.12 ± 0.10 (4.12 ± 0.25 for altitude scaling) atoms g-1 yr-1 for the Lm scaling scheme and 3.96 ± 0.10 (3.96 ± 0.24 for altitude scaling) atoms g-1 yr-1 for the LSD scaling scheme.

  15. Palaeoenvironmental implications of a Holocene sequence of lacustrine-peat sediments from the desert-loess transitional zone in Northern China

    NASA Astrophysics Data System (ADS)

    Jia, Feifei; Lu, Ruijie; Liu, Xiaokang; Zhao, Chao; Lv, Zhiqiang; Gao, Shangyu

    2018-05-01

    A high-resolution lacustrine-peat record from the desert-loess transitional zone in Northern China was obtained to reconstruct Holocene environmental change in the region. AMS 14C dates are used to provide a chronology. The results indicate that the site was a desert environment before 12.2 cal kyr BP, and was then occupied by a paleolake which started to shrink, with a wetland occurring from 6.2 to 3.0 cal kyr BP. Subsequently, the site became a seasonally water-filled depression. Based on the lithology and measurements of grain size and total organic carbon content, the climate changed from arid to humid at 12.2 cal kyr BP, and became more humid after 8.3 cal kyr BP. From 6.2 to 3.0 cal kyr BP, precipitation decreased but the climate remained at an optimum. After 3.0 cal kyr BP, the climate was dry overall but with several humid intervals. A comparison of paleoclimatic records from lacustrine and aeolian deposits from the region reveals a discrepancy about the nature of the early Holocene climate, and we conclude that this is because lacustrine sediments responded more sensitively to precipitation than aeolian deposits when the temperature was low. The environmental evolution of the region was synchronous with changes in the Asian summer monsoon (ASM), but temperature also played a key role in the early Holocene.

  16. Stable isotope ratios in swale sequences of Lake Superior as indicators of climate and lake level fluctuations during the Late Holocene

    USGS Publications Warehouse

    Sharma, Shruti; Mora, G.; Johnston, J.W.; Thompson, T.A.

    2005-01-01

    Beach ridges along the coastline of Lake Superior provide a long-term and detailed record of lake level fluctuations for the past 4000 cal BP. Although climate change has been invoked to explain these fluctuations, its role is still in debate. Here, we reconstruct water balance by employing peat samples collected from swale deposits present between beach ridge sequences at two locations along the coastline of Lake Superior. Carbon isotope ratios for Sphagnum remains from these peat deposits are used as a proxy for water balance because the presence or absence of water films on Sphagnum controls the overall isotope discrimination effects. Consequently, increased average water content in Sphagnum produces elevated ??13C values. Two maxima of Sphagnum ??13C values interpreted to reflect wetter conditions prevailed from 3400 to 2400 cal BP and from about 1900 to 1400 cal BP. There are two relatively short drier periods as inferred from low Sphagnum ??13C values: one is centered at about 2300 cal BP, and one begins at 1400 cal BP. A good covariance was found between Sphagnum ??13C values and reconstructed lake-levels for Lake Michigan in which elevated carbon isotope values correlate well with higher lake levels. Based on this covariance, we conclude that climate exerts a strong influence on lake levels in Lake Superior for the past 4000 cal BP. ?? 2005 Elsevier Ltd. All rights reserved.

  17. Estimated contributions of primary and secondary organic aerosol from fossil fuel combustion during the CalNex and Cal-Mex campaigns

    NASA Astrophysics Data System (ADS)

    Guzman-Morales, J.; Frossard, A. A.; Corrigan, A. L.; Russell, L. M.; Liu, S.; Takahama, S.; Taylor, J. W.; Allan, J.; Coe, H.; Zhao, Y.; Goldstein, A. H.

    2014-05-01

    Observations during CalNex and Cal-Mex field campaigns at Bakersfield, Pasadena, Tijuana, and on board the R/V Atlantis show a substantial contribution of fossil fuel emissions to the ambient particle organic mass (OM). At least two fossil fuel combustion (FFC) factors with a range of contributions of oxidized organic functional groups were identified at each site and accounted for 60-88% of the total OM. Additional marine, vegetative detritus, and biomass burning or biogenic sources contribute up to 40% of the OM. Comparison of the FTIR spectra of four different unburned fossil fuels (gasoline, diesel, motor oil, and ship diesel) with PMF factors from ambient samples shows absorbance peaks from the fuels are retained in organic aerosols, with the spectra of all of the FFC factors containing at least three of the four characteristic alkane peaks observed in fuel standards at 2954, 2923, 2869 and 2855 cm-1. Based on this spectral similarity, we estimate the primary OM from FFC sources for each site to be 16-20%, with secondary FFC OM accounting for an additional 42-62%. Two other methods for estimating primary OM that use carbon monoxide (CO) and elemental carbon (EC) as tracers of primary organic mass were investigated, but both approaches were problematic for the CalNex and Cal-Mex urban sites because they were influenced by multiple emission sources that had site-specific and variable initial ratios to OM. For example, using the ΔPOM/ΔCO ratio of 0.0094 μg ppb V-1 proposed by other studies produces unrealistically high estimates of primary FFC OM of 55-100%.

  18. THE RELATIONSHIP BETWEEN MOTOR COMPETENCE AND PHYSICAL FITNESS IS WEAKER IN THE 15-16 YR. ADOLESCENT AGE GROUP THAN IN YOUNGER AGE GROUPS (4-5 YR. AND 11-12 YR.).

    PubMed

    Haga, Monika; Gísladóttír, Thórdís; Sigmundsson, Hermundur

    2015-12-01

    Developing motor competence and physical fitness can affect the maintenance of a sufficient level of physical activity in children and adolescents. This study assesses the relationship between motor competence and physical fitness from childhood through early adolescence. A cross-sectional sample of 194 participants from 4 to 16 years old were divided into three groups; 4-6 yr. (n=42, M age=5.2, SD 0.6), 11-12 yr. (n=58, M age=12.4, SD=0.3), and 15-16 yr. (n=94, M age=15.9, SD=0.4). To assess motor competence, each child completed the Movement Assessment Battery for Children (MABC). To measure physical fitness, three tasks (strength, speed, and endurance) were selected from the Test of Physical Fitness (TPF). To analyze the significance of the difference between the correlation coefficient in the three age groups (samples) (4-6, 11-12, and 15-16 yr.), Fischer r-to-z transformation was used. The correlation (Pearson's) between motor competence and physical fitness in the age groups was statistically higher for the youngest age groups (4-6 and 11-12 yr.) and the adolescent group (age 15-16). The differences between the two youngest age groups were not statistically significant. The results demonstrate that the correlation between motor competence and physical fitness decreases with age.

  19. Cal-Bridge and CAMPARE: Engaging Underrepresented Students in Physics and Astronomy

    NASA Astrophysics Data System (ADS)

    Rudolph, Alexander L.; Smecker-Hane, Tammy A.; Cal-Bridge Team; CAMPARE Team

    2018-06-01

    We describe two programs, Cal-Bridge and CAMPARE, with the common mission of increasing participation of groups traditionally underrepresented in astronomy, through summer research opportunities, in the case of CAMPARE, scholarships in the case of Cal-Bridge, and significant mentoring in both programs, creating a national impact on their numbers successfully pursuing a PhD in the field. In 9 years, the CAMPARE program has sent 150 students, >80% from underrepresented groups, to conduct summer research at one of 14 major research institutions throughout the country. Of the CAMPARE scholars who have graduated with a Bachelor’s degree, almost two-thirds (65%) have completed or are pursuing graduate education in physics, astronomy, or a related field, at institutions including UCLA, UC Riverside, UC Irvine, UC Santa Barbara, USC, Stanford, Univ. of Arizona, Univ. of Washington, Univ. of Rochester, Michigan State Univ., Georgia Tech, Georgia State Univ., Kent State, Indiana Univ., Univ. of Oregon, Syracuse Univ., Montana State Univ., and the Fisk- Vanderbilt Master’s-to-PhD program. Now in its fourth year, the Cal-Bridge program is a CSU-UC Bridge program comprised of physics and astronomy faculty from 9 University of California (UC), 15 California State University (CSU), and more than 30 California Community College (CCC) campuses throughout California. In the first four years, 34 Cal-Bridge Scholars have been selected, including 22 Hispanic, 3 African-American and 13 women students, 10 of whom are from URM groups. Thirty (30) of the 34 Cal-Bridge Scholars are first generation college students. In the last three years, 17 of 21 Cal-Bridge Scholars have begun or been accepted PhD programs in physics or astronomy at top PhD programs nationally. Three (3) of these scholars have won NSF Graduate Research Fellowships; one more received an Honorable Mention. Once selected, Cal-Bridge Scholars benefit from substantial financial support, intensive, joint mentoring by CSU

  20. The Late-Glacial and Holocene Marboré Lake sequence (2612 m a.s.l., Central Pyrenees, Spain): Testing high altitude sites sensitivity to millennial scale vegetation and climate variability

    NASA Astrophysics Data System (ADS)

    Leunda, Maria; González-Sampériz, Penélope; Gil-Romera, Graciela; Aranbarri, Josu; Moreno, Ana; Oliva-Urcia, Belén; Sevilla-Callejo, Miguel; Valero-Garcés, Blas

    2017-10-01

    This paper presents the environmental, climate and vegetation changes reconstructed for the last 14.6 kyr cal BP from the Marboré Lake sedimentary sequence, the highest altitude record (2612 m a.s.l.) in the Pyrenees studied up to date. We investigate the sensitivity of this high altitude site to vegetational and climate dynamics and altitudinal shifts during the Holocene by comparing palynological spectra of the fossil sequence and pollen rain content from current moss pollsters. We hypothesize that the input of sediments in lakes at such altitude is strongly controlled by ice phenology (ice-free summer months) and that during cold periods Pollen Accumulation Rate (PAR) and Pollen Concentration (PC) reflect changes in ice-cover and thus is linked to temperature changes. Low sedimentation rates and low PC and PAR occurred during colder periods as the Younger Dryas (GS-1) and the Holocene onset (12.6-10.2 kyr cal BP), suggesting that the lake-surface remained ice-covered for most of the year during these periods. Warmer conditions are not evident until 10.2 kyr cal BP, when an abrupt increase in sedimentation rate, PC and PAR occur, pointing to a delayed onset of the Holocene temperature increase at high altitude. Well-developed pinewoods and deciduous forest dominated the mid montane belt since 9.3 kyr cal BP until mid-Holocene (5.2 kyr cal BP). A downwards shift in the deciduous forest occurred after 5.2 kyr cal BP, in agreement with the aridity trend observed at a regional and Mediterranean context. The increase of herbaceous taxa during the late-Holocene (3.5 kyr cal BP-present) reflects a general trend to reduced montane forest, as anthropogenic disturbances were not evident until 1.3 kyr cal BP when Olea proportions from lowland areas and other anthropogenic indicators clearly expand. Our study demonstrates the need to perform local experimental approaches to check the effect of ice phenology on high altitude lakes sensitivity to vegetation changes to obtain

  1. Pollen-inferred quantitative reconstructions of Holocene land-cover in NW Europe for the evaluation of past climate-vegetation feedbacks - methods and first maps of the cover of plant functional types at 6000, 3000, 600, 200 and 0 BP.

    NASA Astrophysics Data System (ADS)

    Trondman, Anna-Kari; Gaillard, Marie-José; Sugita, Shinya; Mazier, Florence; Fyfe, Ralph; Nielsen, Anne-Birgitte; Leydet, Michelle; Members, Landclim

    2010-05-01

    ) number of pollen taxa, 3) PPEs dataset, and 4) number of dates per record used to establish the chronology (≥3 or ≥5) was tested (see Mazier et al. CL 1.21). Following the results of these tests, the first maps are based on REVEALS runs using pollen records from both lakes and bogs with ≥3 dates, 24 taxa (entomophilous taxa excluded), and the mean of all PPEs available in the study area. The maps are produced for 10 PFTs (LPJ-GUESS) and 3 PFTs (RCA3) at a spatial resolution of 1o x 1o for five selected time windows of the Holocene with contrasting human-induced land-cover (0-100 cal BP, 100-350 cal BP, 350-700 cal BP, 2700-3200 cal BP and 5700-6200 cal BP). The maps of PFTs show significant changes in the degree of human-induced vegetation openness through the Holocene over most of the study area. There are large discrepancies between these first quantitative land-cover maps and earlier maps based on pollen data and other methods such as biomization and the modern analogue approach. * The following LANDCLIM members are acknowledged for providing pollen records and for help with pollen databases: Teija Alenius (Espoo), Heather Almquist-Jacobson (Montana, USA), Lena Barnekow and Thomas Persson (Lund), Jonas Bergman (Stockholm), Anne Bjune and John Birks (Bergen), Thomas Giesecke (Göttingen), Rixt de Jong (Bern), Mihkel Kangur and Tiiuu Koff (Tallinn), Malgorzata Latalowa (Gdansk), Ann-Marie Robertsson (Stockholm), Ulf Segerström and Henrik von Stedingk (Umeå), Heikki Seppä (Helsinki). Sugita, S. 2007. The Holocene, 17, 229-241.

  2. Major storm periods and climate forcing in the Western Mediterranean during the Late Holocene

    NASA Astrophysics Data System (ADS)

    Degeai, Jean-Philippe; Devillers, Benoît; Dezileau, Laurent; Oueslati, Hamza; Bony, Guénaëlle

    2015-12-01

    Big storm events represent a major risk for populations and infrastructures settled on coastal lowlands. In the Western Mediterranean, where human societies colonized and occupied the coastal areas since the Ancient times, the variability of storm activity for the past three millennia was investigated with a multi-proxy sedimentological and geochemical study from a lagoonal sequence. Mappings of the geochemistry and magnetic susceptibility of detrital sources in the watershed of the lagoon and from the coastal barriers were undertaken in order to track the terrestrial or coastal/marine origin of sediments deposited into the lagoon. The multi-proxy analysis shows that coarser material, low magnetic susceptibility, and high strontium content characterize the sedimentological signature of the paleostorm levels identified in the lagoonal sequence. A comparison with North Atlantic and Western Mediterranean paleoclimate proxies shows that the phases of high storm activity occurred during cold periods, suggesting a climatically-controlled mechanism for the occurrence of these storm periods. Besides, an in-phase storm activity pattern is found between the Western Mediterranean and Northern Europe. Spectral analyses performed on the Sr content revealed a new 270-year solar-driven pattern of storm cyclicity. For the last 3000 years, this 270-year cycle defines a succession of ten major storm periods (SP) with a mean duration of 96 ± 54 yr. Periods of higher storm activity are recorded from >680 to 560 cal yr BC (SP10, end of the Iron Age Cold Period), from 140 to 820 cal yr AD (SP7 to SP5) with a climax of storminess between 400 and 800 cal yr AD (Dark Ages Cold Period), and from 1230 to >1800 cal yr AD (SP3 to SP1, Little Ice Age). Periods of low storm activity occurred from 560 cal yr BC to 140 cal yr AD (SP9 and SP8, Roman Warm Period) and from 820 to 1230 cal yr AD (SP4, Medieval Warm Period).

  3. OSD CALS Architecture Master Plan Study. Concept Paper. Configuration Management. Volume 28

    DOT National Transportation Integrated Search

    1989-10-01

    The mission of CALS is to enhance operational readiness of DoD weapon systems through application of information technology to the management of technical information. CALS will automate the current paper-intensive processes involved in weapon system...

  4. David Georgi's Cal Council Presidency

    ERIC Educational Resources Information Center

    Georgi, David

    2015-01-01

    When the author was asked to write a mini-memoir about his time as Cal Council president, his first thought was "Now, when exactly was that?" He says that pretty much summarizes the quality of his memory these days. The author's first contact with the California Council on the Education of Teachers was back in the 1970s when the…

  5. Antimony in recent, ombrotrophic peat from Switzerland and Scotland: Comparison with natural background values (5,320 to 8,020 14C yr BP) and implications for the global atmospheric Sb cycle

    NASA Astrophysics Data System (ADS)

    Shotyk, William; Krachler, Michael; Chen, Bin

    2004-03-01

    The lowest concentrations, atmospheric fluxes, and enrichments of Sb in a Swiss bog were found in peat samples dating from 8,020 to 5,320 14C yr BP when Sb inputs were proportional to those of Sc and effectively controlled by deposition of soil dust. For comparison with these ancient samples, modern peat samples from five rural areas of Switzerland and two remote areas of Scotland and Shetland are highly contaminated with Sb, with enrichments of the order of 30 to 80 times. "Lithogenic" Sb concentrations calculated using the Sc concentrations and background Sb/Sc ratio are dwarfed at all sites by "anthropogenic" Sb. The chronology and intensity of the Sb enrichments are in many ways similar to those of Pb which indicates that (1) Sb, like Pb, is well preserved in ombrotrophic peat and (2) the extent of human impacts on the geochemical cycle of Sb is comparable to that of Pb. The similar distribution of Sb and Pb can be explained in terms of their chemical and mineralogical associations, with most lead minerals being rich in Sb. Assuming that the "background" Sb flux (0.35 μg/m2/yr) from the Swiss bog is representative of preanthropogenic deposition rates worldwide, the global flux of natural Sb is estimated at 154 T/a. Using the natural Pb flux published by [1987] of 2600 T/a and the "background" Pb/Sb ratio (29) of the preanthropogenic peat samples, the global flux of natural Sb is estimated at 90 T/a. Either way, these values (90 to 154 T/a) are considerably lower than the current estimate of natural Sb to the global atmosphere (2400 T/a) published by [2001]. Assuming that the current estimate of anthropogenic Sb to the global atmosphere (1600 T/a) is correct [, 2001], the ratio of anthropogenic to natural Sb emissions is on the order of 10 to 18. Taken together, the data from modern and ancient peat samples suggests that the impact of human activities on the global geochemical cycle of Sb may have been underestimated by an order of magnitude. Like Pb, Sb has no

  6. 78 FR 1264 - CalAmp Wireless Networks Corporation, Waseca, MN; Notice of Negative Determination Regarding...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-01-08

    ... DEPARTMENT OF LABOR Employment and Training Administration [TA-W-81,646] CalAmp Wireless Networks...; CalAmp Wireless Networks Corporation, Waseca, Minnesota; expires on December 2, 2013). Conclusion Due to the eligibility of workers and former workers of CalAmp Wireless Networks Corporation, Waseca...

  7. GPR identification of an early monument at Los Morteros in the Peruvian coastal desert

    NASA Astrophysics Data System (ADS)

    Sandweiss, Daniel H.; Kelley, Alice R.; Belknap, Daniel F.; Kelley, Joseph T.; Rademaker, Kurt; Reid, David A.

    2010-05-01

    Los Morteros (8˚39'54″S, 78˚42 '00″W) is located in coastal, northern Peru, one of the six original centers of world civilization. The site consists of a large, sand-covered, isolated prominence situated on a Mid-Holocene shoreline, ˜ 5 km from the present coast. Preceramic archaeological deposits (4040 ± 75 to 4656 ± 60 14C yr BP or ˜ 3600-5500 cal yr BP) cap this feature, which has been identified by prior researchers as a sand-draped, bedrock-cored landform or a relict dune deposit. Because neither explanation is geomorphologically probable, we used ground-penetrating radar (GPR) and high-resolution mapping to assess the mound's interior structure. Our results indicate an anthropogenic origin for Los Morteros, potentially placing it among the earliest monumental structures in prehistoric South America. The extremely arid setting raises new questions about the purpose and the logistics of early mound construction in this region. This work demonstrates the value of an integrated Quaternary sciences approach to assess long-term landscape change and to understand the interaction between humans and the environment.

  8. Stratigraphy and chronology of offshore to nearshore deposits associated with the Provo shoreline, Pleistocene Lake Bonneville, Utah

    USGS Publications Warehouse

    Godsey, Holly S.; Oviatt, Charles G.; Miller, David M.; Chan, Marjorie A.

    2011-01-01

    Stratigraphic descriptions and radiocarbon data from eleven field locations are presented in this paper to establish a chronostratigraphic framework for offshore to nearshore deposits of Lake Bonneville. Based on key marker beds and geomorphic position, the deposits are interpreted to have accumulated during the period from the late transgressive phase, through the overflowing phase, into the regressive phase of the lake. Radiocarbon ages of sediments associated with the Provo shoreline indicate that Lake Bonneville dropped rapidly from the Provo shoreline at about 12,600 14C yr BP (15,000 cal yr B.P.). The presence of one or more sand beds in the upper part of the Provo-aged marl indicates rapid lowering of lake level or storm events at the end of the Provo episode. An accurate understanding of the timing and nature of Lake Bonneville's climate-driven regression from the Provo shoreline is critical to correlations with records of regional and hemispheric climate change. The rapid descent of the lake from the Provo shoreline correlates with the decline of Lakes Lahontan and Estancia, and with the onset of the BØlling–AllerØd warming event.

  9. Stratigraphy and chronology of offshore to nearshore deposits associated with the Provo shoreline, Pleistocene Lake Bonneville, Utah

    USGS Publications Warehouse

    Godsey, H.S.; Oviatt, Charles G.; Miller, D.M.; Chan, M.A.

    2011-01-01

    Stratigraphic descriptions and radiocarbon data from eleven field locations are presented in this paper to establish a chronostratigraphic framework for offshore to nearshore deposits of Lake Bonneville. Based on key marker beds and geomorphic position, the deposits are interpreted to have accumulated during the period from the late transgressive phase, through the overflowing phase, into the regressive phase of the lake. Radiocarbon ages of sediments associated with the Provo shoreline indicate that Lake Bonneville dropped rapidly from the Provo shoreline at about 12,600 14C yr BP (15,000 cal yr B.P.). The presence of one or more sand beds in the upper part of the Provo-aged marl indicates rapid lowering of lake level or storm events at the end of the Provo episode. An accurate understanding of the timing and nature of Lake Bonneville's climate-driven regression from the Provo shoreline is critical to correlations with records of regional and hemispheric climate change. The rapid descent of the lake from the Provo shoreline correlates with the decline of Lakes Lahontan and Estancia, and with the onset of the B??lling-Aller??d warming event. ?? 2011 Elsevier B.V.

  10. Environmental change and seasonal behavior of mastodons in the Great Lakes region inferred from stable isotope analysis

    NASA Astrophysics Data System (ADS)

    Metcalfe, Jessica Z.; Longstaffe, Fred J.

    2014-09-01

    We investigate seasonal variations in the diet and drinking water of four Great Lakes mastodon (Mammut americanum) specimens using stable isotope analysis of serially sampled inner-enamel bioapatite structural carbonate (δ13Csc, δ18Osc), and previously published bulk analyses. Isotopic analyses and thin section measurements showed that mastodon tooth enamel extension rates (~ 12-4 mm/yr, decreasing toward the cervix) were lower than those of mammoths or modern elephants. Mastodons had distinct and highly regular seasonal variations in δ13Csc and δ18Osc, which we interpret in the context of local glacial history and vegetation changes. Seasonal variations in δ18O were large but variations in δ13C were small, and may have been obscured if coarser sampling methods than our inner-enamel sampling approach were used. Thus, our approach may be particularly useful for understanding relatively small seasonal changes in δ13C within C3 environments. The seasonal patterns, though not entirely conclusive, suggest that the Ontario mastodons did not migrate over very long distances. Rather, the climate and seasonal dietary patterns of mastodons within the region changed over time, from ~ 12,400 to 10,400 14C yr BP (~ 15,000 - 12,000 cal yr BP). Insights gained using these methods can contribute to a better understanding of megafaunal extinctions and Paleoamerican lifeways.

  11. Holocene variations in mineral and grain-size composition along the East Greenland glaciated margin (ca 67°–70°N): local versus long-distance sediment transport

    USGS Publications Warehouse

    Andrews, John T.; Jennings, Anne E.; Coleman, George C.; Eberl, Dennis D.

    2010-01-01

    Quantitative X-Ray Diffraction (qXRD) analysis of the <2 mm sediment fraction from surface (sea floor) samples, and marine sediment cores that span the last 10-12 cal ka BP, are used to describe spatial and temporal variations in non-clay mineral compositions for an area between Kangerlussuaq Trough and Scoresby Sund (???67??-70??N), East Greenland. Bedrock consists primarily of an early Tertiary alkaline complex with high weight% of pyroxene and plagioclase. Farther inland and to the north, the bedrock is dominantly felsic with a high fraction of quartz and potassium feldspars. Principal Component (PC) analysis of the non-clay sediment compositions indicates the importance of quartz and pyroxene as compositional end members, with an abrupt shift from quartz and k-feldspar dominated sediments north of Scoresby Sund to sediments rich in pyroxene and plagioclase feldspars offshore from the early Tertiary basaltic outcrop. Coarse (<2 mm or <1 mm) ice-rafted sediments are largely absent from the trough sediments between ???8 and 5 cal ka BP, but then increase in the last 4 cal ka BP. Compositional unmixing of the sediments in Grivel Basin and Kangerlussuaq Trough indicate the dominance of local over long distance sediment sources, with pulses of sediment from tidewater glaciers in Kangerlussuaq and Nansen fjords reaching the inner shelf during the Neoglaciation. The change in IRD is more dramatic in the sediment grain-size proxies than in the quartz wt%. Forty to seventy percent of the variance in the quartz records from either side of Denmark Strait is explained by low frequency trends, but the data from the Grivel Basin, East Greenland, are distinctly different, with an approximate 2500 yr periodicity. ?? 2010 Elsevier Ltd.

  12. Data Management Standards in Computer-aided Acquisition and Logistic Support (CALS)

    NASA Technical Reports Server (NTRS)

    Jefferson, David K.

    1990-01-01

    Viewgraphs and discussion on data management standards in computer-aided acquisition and logistic support (CALS) are presented. CALS is intended to reduce cost, increase quality, and improve timeliness of weapon system acquisition and support by greatly improving the flow of technical information. The phase 2 standards, industrial environment, are discussed. The information resource dictionary system (IRDS) is described.

  13. Decadally resolved Lateglacial radiocarbon evidence from New Zealand kauri

    NASA Astrophysics Data System (ADS)

    Hogg, Alan; Southon, John; Turney, Chris; Palmer, Jonathan; Bronk Ramsey, Christopher; Fenwick, Pavla; Boswijk, Gretel; Büntgen, Ulf; Friedrich, Michael; Helle, Gerhard; Hughen, Konrad; Jones, Richard; Kromer, Bernd; Noronha, Alexandra; Reinig, Frederick; Reynard, Linda; Staff, Richard; Wacker, Lukas

    2017-04-01

    The Last Glacial-Interglacial Transition (LGIT; 15,000 - 11,000 cal BP) was characterised by complex spatiotemporal patterns of climate change, with numerous studies requiring accurate chronological control to decipher leads from lags in global palaeoclimatic, -environmental and archaeological records. However, close scrutiny of the few available tree-ring chronologies and radiocarbon-dated sequences composing the IntCal13 radiocarbon (14C) calibration curve, indicates significant weakness in 14C calibration across key periods of the LGIT. Here, we present a decadally-resolved atmospheric 14C record derived from New Zealand kauri spanning Greenland Stadial 1 (GS-1; 12,900 - 11,650 cal BP). Two floating kauri 14C time series, curve-matched to IntCal13, serve as a radiocarbon backbone through GS-1. Floating Northern Hemisphere (NH) 14C datasets are matched against the new kauri data, forming a robust NH 14C time series to 14,200 cal BP. Our results show that IntCal13 is questionable from 12,200 - 11,900 cal BP and the 10,400 BP 14C plateau is approximately five decades too short. By precisely aligning Southern and Northern Hemisphere tree-ring 14C records with marine 14C sequences, we document two relatively short periods of North Atlantic Meridional Overturning Circulation (AMOC) collapse during GS-1. Hence, sustained North Atlantic cooling across GS-1 was not driven by a prolonged AMOC reduction but was probably due to an equatorward migration of the Polar Front.

  14. Marine reservoir effect on the Southeastern coast of Brazil: results from the Tarioba shellmound paired samples.

    PubMed

    Macario, K D; Souza, R C C L; Aguilera, O A; Carvalho, C; Oliveira, F M; Alves, E Q; Chanca, I S; Silva, E P; Douka, K; Decco, J; Trindade, D C; Marques, A N; Anjos, R M; Pamplona, F C

    2015-05-01

    On the Southeastern coast of Brazil the presence of many archaeological shellmounds offers a great potential for studying the radiocarbon marine reservoir effect (MRE). However, very few such studies are available for this region. These archaeological settlements, mostly dating from 5 to 2 kyr cal BP, include both terrestrial and marine remains in good stratigraphic context and secure association, enabling the comparison of different carbon reservoirs. In a previous study the chronology of the Sambaqui da Tarioba, located in Rio de Janeiro state, Brazil, was established based on marine mollusc shells and charcoal samples from hearths, from several layers in two excavated sectors. We now compare the different materials with the aim of studying the MRE in this region. Calibration was performed with Oxford software OxCal v4.2.3 using the marine curve Marine13 with an undetermined offset to account for local corrections for shell samples, and the atmospheric curve SHCal13 for charcoal samples. The distribution of results considering a phase model indicates a ΔR value of -127 ± 67 (14)C yr in the 1 sigma range and the multi-paired approach leads to a mean value of -110 ± 94 (14)C yr. Copyright © 2015 Elsevier Ltd. All rights reserved.

  15. Remapping of the stripe rust resistance gene Yr10 in common wheat.

    PubMed

    Yuan, Cuiling; Wu, Jingzheng; Yan, Baiqiang; Hao, Qunqun; Zhang, Chaozhong; Lyu, Bo; Ni, Fei; Caplan, Allan; Wu, Jiajie; Fu, Daolin

    2018-06-01

    Yr10 is an important gene to control wheat stripe rust, and the search for Yr10 needs to be continued. Wheat stripe rust or yellow rust is a devastating fungal disease caused by Puccinia striiformis f. sp. tritici (Pst). Host disease resistance offers a primary source for controlling wheat stripe rust. The stripe rust resistance gene Yr10 confers the race-specific resistance to most tested Pst races in China including CYR29. Early studies proposed that Yr10 was a nucleotide-binding site, leucine-rich repeat gene archived as GenBank accession AF149112 (hereafter designated the Yr10 candidate gene or Yr10 CG ). In this study, we revealed that 15 Chinese wheat cultivars positive for Yr10 CG are susceptible to CYR29. We then expressed the Yr10 CG cDNA in the common wheat 'Bobwhite'. The Yr10 CG -cDNA positive transgenic plants were also susceptible to CYR29. Thus, it is highly unlikely that Yr10 CG corresponds to the Yr10 resistance gene. Using the Yr10 donor 'Moro' and the Pst-susceptible wheat 'Huixianhong', we generated two F 3 populations that displayed a single Mendelian segregation on the Yr10 gene, and used them to remap the Yr10 gene. Six markers were placed in the Yr10 region, with the Yr10 CG gene now mapping about 1.2-cM proximal to the Yr10 locus and the Xsdauw79 marker is completely linked to the Yr10 locus. Apparently, the Yr10 gene has not yet been identified. Fine mapping and positional cloning of Yr10 is important for gene pyramiding for stripe rust resistance in wheat.

  16. Navy/Marine Corps Manager’s Desktop Guide for CALS Implementation. 2nd Edition

    DTIC Science & Technology

    1993-06-30

    significant process and productivity that CALS initiatives are providing within the Navy infrastructure. CALS programs are on-line and working in today’s Navy...era of declining budgets, CALS is most important in enhancing logistic support productivity to maintain operations and improve readiness. Our...is to be accomplished through the general adoption of a set of procedures and staridards for the production , access, management, maintenance, and

  17. Revised paleoenvironmental analysis of the Holocene portion of the Barbados sea-level record: Cobbler's Reef revisited

    NASA Astrophysics Data System (ADS)

    Toscano, Marguerite A.

    2016-06-01

    Sample elevations corrected for tectonic uplift and assessed relative to local modeled sea levels provide a new perspective on paleoenvironmental history at Cobbler's Reef, Barbados. Previously, 14C-dated surface samples of fragmented Acropora palmata plotted above paleo sea level based on their present (uplifted) elevations, suggesting supratidal rubble deposited during a period of extreme storms (4500-3000 cal BP), precipitating reef demise. At several sites, however, A. palmata persisted, existing until ~370 cal BP. Uplift-corrected A. palmata sample elevations lie below the western Atlantic sea-level curve, and ~2 m below ICE-6G-modeled paleo sea level, under slow rates of sea-level rise, negating the possibility that Cobbler's Reef is a supratidal storm ridge. Most sites show limited age ranges from corals likely damaged/killed on the reef crest, not the mixed ages of rubble ridges, strongly suggesting the reef framework died off in stages over 6500 yr. Reef crest death assemblages invoke multiple paleohistoric causes, from ubiquitous hurricanes to anthropogenic impacts. Comparison of death assemblage ages to dated regional paleotempestological sequences, proxy-based paleotemperatures, recorded hurricanes, tsunamis, European settlement, deforestation, and resulting turbidity, reveals many possible factors inimical to the survival of A. palmata along Cobbler's Reef.

  18. Perennial stream discharge in the hyperarid Atacama Desert of northern Chile during the latest Pleistocene

    PubMed Central

    Nester, Peter L.; Gayó, Eugenia; Latorre, Claudio; Jordan, Teresa E.; Blanco, Nicolás

    2007-01-01

    A large fraction of the vital groundwater in the Atacama Desert of northern Chile is likely composed of “fossil” or “ancient” reserves that receive little or no recharge in today's hyperarid climate. Here, we present evidence for latest Pleistocene perennial streamflow in canyons from the hyperarid core of the Atacama Desert in northern Chile. Fluvial terraces in the Pampa del Tamarugal (PdT) basin (21°S) contain widespread fossil wood, in situ roots, and well preserved leaf litter deposits indicative of perennial surface flow currently absent in these channels. Nineteen radiocarbon dates on these deposits from four separate drainages within this endorheic basin indicate ages from 16,380 to 13,740 cal yr BP, synchronous with paleolake Tauca on the Bolivian Altiplano and other regional evidence for wetter conditions during the latest Pleistocene. Groundwater-fed riparian ecosystems and associated fluvial deposits abound today in the absence of direct rainfall in northern Atacama canyons with perennial discharge. Our relict riparian ecosystems from the PdT basin are indicative of conditions similar to these northern canyons. Given that discharge was higher than present during this time, we propose that these deposits represent the most important groundwater recharge events of the last 18,000 years. A lesser recharge event occurred during the Holocene, when phreatophytic trees also grew in these drainages between 1,070 and 700 cal yr BP, during the Medieval Climatic Anomaly. Taken together, our evidence lends further support for gradient changes in the equatorial Pacific as a major driver of hydrologic change in the Atacama on both centennial and millennial time scales. PMID:18056645

  19. Quantitative mineralogy of surface sediments of the Iceland shelf, and application to down-core studies of holocene ice-rafted sediments

    USGS Publications Warehouse

    Andrews, John T.; Eberl, D.D.

    2007-01-01

    Quantitative X-ray diffraction analyses on the < 2 mm sediment fraction from the Iceland shelves are reported for subglacial diamictons, seafloor surface sediments, and the last 2000 cal yr BP from two cores. The overall goal of the paper is to characterize the spatial variability of the mineralogy of the present-day surface sediments (18 non-clay minerals and 7 clay minerals), compare that with largely in situ erosional products typified by the composition of subglacial diamictons, and finally examine the late Holocene temporal variability in mineral composition using multi-mineral compositions. The subglacial diamictons are dominated in the non-clay-mineral fraction by the plagioclase feldspars and pyroxene with 36.7 ?? 6.1 and 17.9 ?? 3.5 wt % respectively, with smectites being the dominant clay minerals. The surface seafloor sediments have similar compositions although there are substantial amounts of calcite, plus there is a distinct band of sites from NW to N-central Iceland that contain 1-6 wt% of quartz. This latter distribution mimics the modern and historic pattern of drift ice in Iceland waters. Principal component analysis of the transformed wt% (log-ratio) non-clay minerals is used to compare the subglacial, surface, and down-core mineral compositions. Fifty-eight percent of the variance is explained by the first two axes, with dolomite, microcline, and quartz being important "foreign" species. These analyses indicate that today the NW-N-central Iceland shelf is affected by the import of exotic minerals, which are transported and released from drift ice. The down-core mineralogy indicates that this is a process that has varied over the last 2000 cal yr BP. Copyright ?? 2007, SEPM (Society for Sedimentary Geology).

  20. Computer-aided acquisition and logistics support (CALS): Concept of Operations for Depot Maintenance

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Bourgeois, N.C.; Greer, D.K.

    1993-04-01

    This CALS Concept of Operations for Depot Maintenance provides the foundation strategy and the near term tactical plan for CALS implementation in the depot maintenance environment. The user requirements enumerated and the overarching architecture outlined serve as the primary framework for implementation planning. The seamless integration of depot maintenance business processes and supporting information systems with the emerging global CALS environment will be critical to the efficient realization of depot user's information requirements, and as, such will be a fundamental theme in depot implementations.

  1. Stratigraphic and microfossil evidence for a 4500-year history of Cascadia subduction zone earthquakes and tsunamis at Yaquina River estuary, Oregon, USA

    USGS Publications Warehouse

    Graehl, Nicholas A; Kelsey, Harvey M.; Witter, Robert C.; Hemphill-Haley, Eileen; Engelhart, Simon E.

    2015-01-01

    The Sallys Bend swamp and marsh area on the central Oregon coast onshore of the Cascadia subduction zone contains a sequence of buried coastal wetland soils that extends back ∼4500 yr B.P. The upper 10 of the 12 soils are represented in multiple cores. Each soil is abruptly overlain by a sandy deposit and then, in most cases, by greater than 10 cm of mud. For eight of the 10 buried soils, times of soil burial are constrained through radiocarbon ages on fine, delicate detritus from the top of the buried soil; for two of the buried soils, diatom and foraminifera data constrain paleoenvironment at the time of soil burial.We infer that each buried soil represents a Cascadia subduction zone earthquake because the soils are laterally extensive and abruptly overlain by sandy deposits and mud. Preservation of coseismically buried soils occurred from 4500 yr ago until ∼500–600 yr ago, after which preservation was compromised by cessation of gradual relative sea-level rise, which in turn precluded drowning of marsh soils during instances of coseismic subsidence. Based on grain-size and microfossil data, sandy deposits overlying buried soils accumulated immediately after a subduction zone earthquake, during tsunami incursion into Sallys Bend. The possibility that the sandy deposits were sourced directly from landslides triggered upstream in the Yaquina River basin by seismic shaking was discounted based on sedimentologic, microfossil, and depositional site characteristics of the sandy deposits, which were inconsistent with a fluvial origin. Biostratigraphic analyses of sediment above two buried soils—in the case of two earthquakes, one occurring shortly after 1541–1708 cal. yr B.P. and the other occurring shortly after 3227–3444 cal. yr B.P.—provide estimates that coseismic subsidence was a minimum of 0.4 m. The average recurrence interval of subduction zone earthquakes is 420–580 yr, based on an ∼3750–4050-yr-long record and seven to nine interearthquake

  2. Holocene Summer Monsoon Variability- Evidence from Marine Sediment of western Continental Shelf of Sri Lanka

    NASA Astrophysics Data System (ADS)

    Ranasinghage, P. N.; Ratnayake, K. M.; Dassanayake, D. M. K. K.; Mohtadi, M.; Hewawasam, T.; Jinadasa, S. U. P.; Jayawardena, S.; Siriwardana, S.

    2016-12-01

    Understanding long term variability of Indian monsoon system is essential for better climate forecasting which is a prerequisite for agricultural development and disaster management. Yet, it has been a least attended scientific question in Sri Lanka Therefore, this study was carried out to understand the monsoonal variability during the Holocene using multiple proxies on a sediment core, representing unmixed summer monsoonal record. A 390 cm long piston core was obtained from the continental shelf off Negombo by National Aquatic Resources Research and Development Agency , was used for this study. This site mainly receives sediment from rivers fed by summer monsoon. Colour reflectance and chemical composition of the sediments, and δ18O and δ13C of Globigerinoides ruber foraminifera, extracted from the sediments were measured at 0.1-2.0 cm resolutions. Principal component analysis of chemical compositional data and colour reflectance data was performed to extract important components that represent climate variability. Benthic and planktonic foraminifera species that indicate upwelling were counted at 2 cm resolution. Radiocarbon dating was carried out using intact micro-shells. Results indicate that upwelling proxies (δ13C, foraminiferal proxies, and colour reflectance-Chlorophyll) and δ18O, which indicates evaporation-precipitation (E-P), increased during 8000-10000 cal yrs BP, 2000-4000 cal yrs BP and again after 1000 cal yrs BP. This increase in upwelling and E-P indicates strengthening of summer monsoon during these periods. However, terrestrial proxies, (XRF-PC1-Terrestrial, Ti, and DSR-PC3-iron oxides)indicate decrease in terrestrial influx which represents rainfall, from 6000-1000 cal yrs BP followed by an increase after 1000 cal yrs BP. Gradual decrease in precipitation has been observed locally as well as regionally after around 6000 cal yrs BP followed by an increase after 1000 cal yrs BP. The contrast behavior of strengthening monsoonal winds and

  3. Holocene environmental change along the southern Cape coast of South Africa - Insights from the Eilandvlei sediment record spanning the last 8.9 kyr

    NASA Astrophysics Data System (ADS)

    Wündsch, Michael; Haberzettl, Torsten; Cawthra, Hayley C.; Kirsten, Kelly L.; Quick, Lynne J.; Zabel, Matthias; Frenzel, Peter; Hahn, Annette; Baade, Jussi; Daut, Gerhard; Kasper, Thomas; Meadows, Michael E.; Mäusbacher, Roland

    2018-04-01

    This study investigates Holocene sediments from Eilandvlei, a coastal lake located within the Wilderness embayment at the southern Cape coast of South Africa. The evolution of the present estuarine/coastal lake system is reconstructed based on seismic data as well as a multi-proxy approach on a 30.5 m sediment core spanning the last 8.9 kyr. Geochemical (Ca, TOC/S, Br/TOC) and micropalaeontological data (diatoms, foraminifera) reflect changes in the degree of marine influence at the core site. The embayment likely developed via distinct phases of connectivity to the Indian Ocean caused by sea level changes and dune progradation. Marine conditions prevailed at the core site from 8900 to 4700 cal BP. The rapid sea level rise during the early Holocene caused the inundation of a palaeovalley that most likely had formed at lower sea levels during the Pleistocene. Towards the mid-Holocene the sea level exceeded its present height around 7500 cal BP creating a marine embayment. At 4700 cal BP, the embayment became distinctly more disconnected from the ocean turning into a lagoon system that persisted until 1200 cal BP. Subsequently, the marine influence further decreased and the present estuarine/coastal lake system was established. Grain size and geochemical data (Fe, Si/Al, chemical index of alteration (CIA)) further reflect changes in the deposition of terrigenous sediments at the core site. While the sedimentation of fine-grained (<16 μm), iron-rich and highly weathered material is linked to periods of increased river discharge and rainfall, high amounts of deposited quartz (31-250 μm, high Si/Al) point to relatively dry and/or windy conditions during which increased aeolian transport of dune sands occurred. The proxies indicate reduced river discharge and hence possibly drier climatic conditions than today from 8900 to 7900 cal BP and 6400 to 3000 cal BP. In contrast, the periods between 7900-6400 cal BP and 3000 cal BP-present were likely characterized by high

  4. CAMPARE and Cal-Bridge: Two Institutional Networks Increasing Diversity in Astronomy

    NASA Astrophysics Data System (ADS)

    Rudolph, Alexander L.; Impey, Chris David; Smecker-Hane, Tammy A.

    2016-01-01

    We describe two programs, CAMPARE and Cal-Bridge, with the common mission of increasing participation of groups traditionally underrepresented in astronomy, through summer research opportunities, in the case of CAMPARE, scholarships in the case of Cal-Bridge, and significant mentoring in both programs, leading to an increase in their numbers successfully pursuing a PhD in the field.In 6 years, the CAMPARE program has sent 62 students, >85% from underrepresented groups, to conduct summer research at one of twelve major research institutions in California, Arizona, and Wyoming. The graduation rate among CAMPARE scholars is 97%, and of the 37 CAMPARE scholars who have graduated with a Bachelor's degree, almost 60% (21) have completed or are pursuing graduate education in astronomy or a related field, at institutions including UCLA, USC, UC Riverside, Stanford, Univ. of Rochester, Georgia Tech, Kent State, Indiana Univ., Univ. of Oregon, Syracuse, and the Fisk-Vanderbilt Master's-to-PhD program. The Cal-Bridge program is a CSU-UC Bridge program comprised of faculty form 5 University of California (UC), 8 California State University (CSU), and 8 California Community College (CCC) campuses in Southern California. Cal-Bridge provides much deeper mentoring and professional development experiences over the last two years of undergraduate and first year of graduate school to students from this diverse network of higher education institutions. Cal-Bridge Scholars benefit from financial support, intensive, joint mentoring by CSU and UC faculty, professional development workshops, and exposure to research opportunities at the participating UC campuses.

  5. Polymer-Based Black Phosphorus (bP) Hybrid Materials by in Situ Radical Polymerization: An Effective Tool To Exfoliate bP and Stabilize bP Nanoflakes

    PubMed Central

    2018-01-01

    Black phosphorus (bP) has been recently investigated for next generation nanoelectronic multifunctional devices. However, the intrinsic instability of exfoliated bP (the bP nanoflakes) toward both moisture and air has so far overshadowed its practical implementation. In order to contribute to fill this gap, we report here the preparation of new hybrid polymer-based materials where bP nanoflakes (bPn) exhibit a significantly improved stability. The new materials have been prepared by different synthetic paths including: (i) the mixing of conventionally liquid-phase exfoliated bP (in dimethyl sulfoxide, DMSO) with poly(methyl methacrylate) (PMMA) solution; (ii) the direct exfoliation of bP in a polymeric solution; (iii) the in situ radical polymerization after exfoliating bP in the liquid monomer (methyl methacrylate, MMA). This last methodology concerns the preparation of stable suspensions of bPn–MMA by sonication-assisted liquid-phase exfoliation (LPE) of bP in the presence of MMA followed by radical polymerization. The hybrids characteristics have been compared in order to evaluate the bP dispersion and the effectiveness of the bPn interfacial interactions with polymer chains aimed at their long-term environmental stabilization. The passivation of the bPn is particularly effective when the hybrid material is prepared by in situ polymerization. By using this synthetic methodology, the nanoflakes, even if with a gradient of dispersion (size of aggregates), preserve their chemical structure from oxidation (as proved by both Raman and 31P-solid state NMR studies) and are particularly stable to air and UV light exposure. The feasibility of this approach, capable of efficiently exfoliating bP while protecting the bPn, has been then verified by using different vinyl monomers (styrene and N-vinylpyrrolidone), thus obtaining hybrids where the nanoflakes are embedded in polymer matrices with a variety of intriguing thermal, mechanical, and solubility characteristics.

  6. CALS Baseline Architecture Analysis of Weapons System. Technical Information: Army, Draft. Volume 8

    DOT National Transportation Integrated Search

    1989-09-01

    This effort was performed to provide a common framework for analysis and planning of CALS initiatives across the military services, leading eventually to the development of a common DoD-wide architecture for CALS. This study addresses Army technical ...

  7. CalWater 2015 — Atmospheric Rivers and Aerosol Impacts on Precipitation

    NASA Astrophysics Data System (ADS)

    Spackman, J. R.; Ralph, F. M.; Prather, K. A.; Cayan, D.; DeMott, P. J.; Dettinger, M. D.; Doyle, J. D.; Fairall, C. W.; Leung, L. R.; Rosenfeld, D.; Rutledge, S. A.; Waliser, D. E.; White, A. B.

    2015-12-01

    The CalWater 2015 field experiment was conducted between January and March and consisted of more than fifty science flights, a major research cruise, and continuous ground-based observations coordinated to study phenomena driving the incidence of extreme precipitation events and the variability of water supply along the West Coast of the United States. CalWater 2015 examined key processes linked to (1) atmospheric rivers (ARs) in delivering much of the precipitation associated with major winter storms, and (2) aerosols, originating from local sources as well as from remote continents, within and between storms and their modulating effects on precipitation on the U.S. West Coast. As part of a large interagency field effort including NOAA, DOE, NASA, NSF, and the Naval Research Laboratory, four research aircraft from three government agencies were deployed in coordination with the oceangoing NOAA Ronald H. Brown and were equipped with meteorological and chemical observing systems in near-shore regions of California and the eastern Pacific. At the same time, ground-based measurements from NOAA's HydroMeteorological Testbed (HMT) network on the U.S. West Coast and a major NSF-supported observing site for aerosols and microphysics at Bodega Bay, California provided continuous near surface-level meteorological and chemical observations, respectively, during CalWater 2015. The DOE-sponsored ARM Cloud Aerosol and Precipitation Experiment (ACAPEX) was executed in close coordination with NOAA and NASA facilities and deployed airborne and ship-based observing systems. This presentation summarizes the objectives, implementation strategy, data acquisitions, and some preliminary results from CalWater 2015 addressing science gaps associated with (1) the evolution and structure of ARs including cloud and precipitation processes and air-sea interaction, and (2) aerosol interaction with ARs and the impact on precipitation, including locally-generated aerosol effects on orographic

  8. The X-ray eclipse of the LMC binary CAL 87

    NASA Technical Reports Server (NTRS)

    Schmidtke, P. C.; Mcgrath, T. K.; Cowley, A. P.; Frattare, L. M.

    1993-01-01

    ROSAT-PSPC observations of the LMC eclipsing binary CAL 87 show a short-duration, shallow X-ray eclipse which coincides in phase with the primary optical minimum. Characteristics of the eclipse suggest the X-ray emitting region is only partially occulted. Similarities with the eclipse of the accretion-disk corona in X 1822-37 are discussed. However, no temperature variation through eclipse is found for CAL 87. A revised orbital period, combining published data and recent optical photometry, is given.

  9. New tree-ring evidence for the Late Glacial period from the northern pre-Alps in eastern Switzerland

    NASA Astrophysics Data System (ADS)

    Reinig, Frederick; Nievergelt, Daniel; Esper, Jan; Friedrich, Michael; Helle, Gerhard; Hellmann, Lena; Kromer, Bernd; Morganti, Sandro; Pauly, Maren; Sookdeo, Adam; Tegel, Willy; Treydte, Kerstin; Verstege, Anne; Wacker, Lukas; Büntgen, Ulf

    2018-04-01

    The rate and magnitude of temperature variability at the transition from the Last Glacial Maximum into the early Holocene represents a natural analog to current and predicted climate change. A limited number of high-resolution proxy archives, however, challenges our understanding of environmental conditions during this period. Here, we present combined dendrochronological and radiocarbon evidence from 253 newly discovered subfossil pine stumps from Zurich, Switzerland. The individual trees reveal ages of 41-506 years and were growing between the Allerød and Preboreal (∼13‧900-11‧300 cal BP). Together with previously collected pines from this region, this world's best preserved Late Glacial forest substantially improves the earliest part of the absolutely dated European tree-ring width chronology between 11‧300 and 11‧900 cal BP. Radiocarbon measurements from 65 Zurich pines between ∼12‧320 and 13‧950 cal BP provide a perspective to prolong the continuous European tree-ring record by another ∼2000 years into the Late Glacial era. These data will also be relevant for pinpointing the Laacher See volcanic eruption (∼12‧900 cal BP) and two major Alpine earthquakes (∼13‧770 and ∼11‧600 cal BP). In summary, this study emphasizes the importance of dating precision and multi-proxy comparison to disentangle environmental signals from methodological noise, particularly during periods of high climate variability but low data availability, such as the Younger Dryas cold spell (∼11‧700 and 12‧900 cal BP).

  10. Human occupation and environmental change in Holocene from a case of XDW2 relic site in the Tibetan Plateau at above 4000 meters above sea level.

    NASA Astrophysics Data System (ADS)

    Hou, G.; Li, F.; Zhu, Y.

    2017-12-01

    XDW2 is an important microlithic cultural relics with continuous stratum that is located in the the Tibetan plateau at above 4,000 masl, wich is a window of revealing the evolution of early human activities and the response and adaptation to extreme environmental in the principal part of Tibetan plateau. So it has important research significance. The analysis on human activity indicator(stoneware, potsherds) and environmental indicators(magnetic susceptibility, color, granularity and pollen) showed: the winter wind and dust storm intensity is weak in this area during 7.0-6 cal. Ka BP, pedogenesis is strong, the climate is humid, environment is suitable relatively, when is Holocene Megathermal; the active phase of microlithic human activities occurred during 7.2-6 cal. ka BP, and quickly weakened after 6 cal. ka BP. The number of stone tools reveal that human activities are concentrated before and after 7-6.2 cal. ka BP, charcoal fragmental concentration indicates that microlithic human activity reached the peak at around 6.7 cal. ka BP. Thus relatively suitable environment during Holocene Megathermal is the important motivating factor of active hunter-gatherer activities in the principal part of Tibetan plateau. After 6 cal. ka BP, summer monsoon weakened rapidly, agricultural growers in the Loess Plateau began to expand towards the plateau, under the effect of environmental degradation and new technologies, microlithic hunter-gatherers in the principal part of plateau moved towards the river valley at low altitude, and learnt settlement and plantation, microlithic activity in the main plateau began to decline.

  11. Long-term man-environment interactions in the Bolivian Amazon: 8000 years of vegetation dynamics

    NASA Astrophysics Data System (ADS)

    Brugger, Sandra O.; Gobet, Erika; van Leeuwen, Jacqueline F. N.; Ledru, Marie-Pierre; Colombaroli, Daniele; van der Knaap, W. O.; Lombardo, Umberto; Escobar-Torrez, Katerine; Finsinger, Walter; Rodrigues, Leonor; Giesche, Alena; Zarate, Modesto; Veit, Heinz; Tinner, Willy

    2016-01-01

    Only few studies documenting the vegetation history of the Llanos de Moxos, one of the largest seasonally flooded wetland areas in South America, are available and little is known about the environmental impact of pre-Columbian settlements. We use radiocarbon-dated terrestrial plant macrofossils to establish a sound chronology and palynological analyses to reconstruct the vegetation and fire history of the Lago Rogaguado area. The sedimentary pollen and spore record suggests that wetland and wooded savannah (Cerrado) environments occurred around the lake between 8100 and 5800 cal BP. Fire activity was high during this period and was probably connected to the dry Cerrado environments. The pollen evidence suggests early plant cultivation (Zea mays, Annonaceae and Cucurbitaceae) from 6500 cal BP onwards, which is significantly earlier than hitherto assumed for Amazonia. Gallery forests expanded after 5800 cal BP, when fire activity strongly declined. Forest expansion intensified around 2800 cal BP and continued until 2000 cal BP, when forest cover reached its maximum and fire activity its minimum. The late-Holocene forest expansion to the south and the decrease of fire activity may have resulted from a climatic shift to moister conditions (possibly a shorter dry season). New crops (e.g. Avena-type) or adventive plants (e.g. Rumex acetosella-type) document the impact of European economies after ca. 500 cal BP. Land use intensity remained rather stable over the most recent centuries, arguing against a collapse of settlements in response to the arrival of Europeans, as reconstructed from other Amazonian pollen records.

  12. Paleoenvironmental changes during the past 2000 years, evidence from Kongsfjorden, Svalbard

    NASA Astrophysics Data System (ADS)

    Jernas, P.; Kristensen, D.; Koc, N.; Skirbekk, K.

    2009-04-01

    of fine grained sediment and decrease in ice rafting indicating less influence from glaciers. The foraminiferal species composition show decreasing content of agglutinated foraminifera down core caused by their low preservation potential. For this core site it confirms the importance of calcareous foraminifera as a fossil record tool. The two dominant species in the core are Elphidium excavatum and Nonionellina labradorica. During the last 2000 years the percentage of E. excavatum shows a general tendency to decrease while N. labradorica increases toward present. Elphidium excavatum is typical for arctic glaciomarine environments close to glaciers and ice caps, indicating harsh conditions (cold bottom waters temperatures, lower salinity) and probably extensive ice cover. Nonionellina labradorica indicates the vicinity of oceanographic fronts and high productivity. Another species Islandiella spp., often associated with increased productivity and presence of the sea ice edge, shows significant increase in percentage from 1000 to 800 cal yr BP. From 600 to 400 cal yr BP Bucella spp. start to decline suggesting increased sea ice cover and diminished influence of the Coastal Current on the inner shelf of Svalbard.

  13. Drivers of Change in a 7300-Year Holocene Diatom Record from the Hemi-Boreal Region of Ontario, Canada

    PubMed Central

    Beck, Kristen K.; Medeiros, Andrew S.

    2016-01-01

    A Holocene lake sediment record spanning the past 7300 years from Wishart Lake in the Turkey Lakes Watershed in the Hemi-Boreal of central Ontario, Canada, was used to evaluate the potential drivers of long-term change in diatom assemblages at this site. An analysis of diatom assemblages found that benthic and epiphytic taxa dominated the mid-Holocene (7300–4000 cal yr BP), indicating shallow, oligotrophic, circum-neutral conditions, with macrophytes present. A significant shift in diatom assemblages towards more planktonic species (mainly Cyclotella sensu lato, but also several species of Aulacoseira, and Tabellaria flocculosa) occurred ~4000 cal yr BP. This change likely reflects an increase in lake level, coincident with the onset of a more strongly positive moisture balance following the drier climates of the middle Holocene, established by numerous regional paleoclimate records. Pollen-inferred regional changes in vegetation around 4000 yrs BP, including an increase in Betula and other mesic taxa, may have also promoted changes in diatom assemblages through watershed processes mediated by the chemistry of runoff. A more recent significant change in limnological conditions is marked by further increases in Cyclotella sensu lato beginning in the late 19th century, synchronous with the Ambrosia pollen rise and increases in sediment bulk density, signaling regional and local land clearance at the time of Euro-Canadian settlement (1880 AD). In contrast to the mid-Holocene increase in planktonic diatoms, the modern increase in Cyclotella sensu lato likely indicates a response to land use and vegetation change, and erosion from the watershed, rather than a further increase in water level. The results from Wishart Lake illustrate the close connection between paleoclimate change, regional vegetation, watershed processes, and diatom assemblages and also provides insight into the controls on abundance of Cyclotella sensu lato, a diatom taxonomic group which has shown

  14. Holocene Climate Change in Sub-Alpine Southwestern Alberta: Evidence from Oxygen and Carbon Isotope values of Hogarth Lake Marl.

    NASA Astrophysics Data System (ADS)

    Matkowski, D.; Patterson, W. P.; Timsic, S.

    2017-12-01

    A 3.6-meter lake sediment core was recovered from Upper Hogarth Lake, providing proxy evidence for climate variability over the last 11,500 years. The core was sampled at millimeter scale for high-resolution oxygen and carbon isotope values. Large variations (up to 6‰) in the carbon isotope values are attributed to the increasingly dominant role of terrestrial-sourced organic matter over bedrock-sourced DIC during initial lake formation and subsequent changes in regional humidity. Variations (up to 4‰) in oxygen isotope values of the marl are interpreted as representing changes in meteoric water source and regional temperature. The hydrologically-open, fresh-water lake is hosted in Devonian-Carboniferous carbonates, recharged via groundwater, surface flow and precipitation. Marl sediment is generated by the green algae Chara sp., with marl deposition beginning approximately 11,500 cal yBP. Our age model was constructed using tephrochronology and radiocarbon dating of 8 terrestrial plant samples, then calibrated using the University of Minnesota's "Bacon" software. The presence of an ash layer in the core was associated with the Mazama ash layer dated 7,627 ±150 yBP, and was used to support the 14C age model. Sediment deposition is characterized by 3 stages: from the recent, dating back to 11,500 cal yBP, the core is marl dominated, comprising 70% of the 3.6m core. Prior to marl deposition there is a 500-year depositional period of carbonate and allochthonous clastic material. Below 2.65 meters, the sediment consists of fine sand and mud; sourced from the weathering of surrounding bedrock. Isotope data are characterized by 5 distinct periods. 7,800 cal yBP to the end Younger Dryas ( 11,500 cal yBP) exhibits irregular, and generally decreasing, δ13C and δ18O values, with a positive excursion in δ18O values occurring around 9,000 cal yBP. Climate was stable, cool and dry from 5,000-7,000 cal yBP, evidenced by relatively invariant δ13C and δ18O values. The

  15. Temporal and Spatial Variability in Relative Sea Level from Narragansett Bay, Rhode Island (USA)

    NASA Astrophysics Data System (ADS)

    Halavik, B. T.; Engelhart, S. E.

    2017-12-01

    Geological reconstructions of past relative sea level (RSL) provide observations to compare to instrumental measurements of land-level changes (e.g., GPS) and to provide constraints on Glacial Isostatic Adjustment (GIA) models. Given the importance of the east coast of the United States to our understanding of GIA (due to its proximity and orientation to the collapsing forebulge of the Laurentide ice sheet), we set out to reconstruct the first compaction-free late Holocene RSL record for Rhode Island, USA. We sought to quantify and compare RSL changes at multiple sites within Rhode Island's Narragansett Bay. Previous work suggests Narragansett Bay may span a gradient in GIA. The small tidal range (0.9-1.4m) in Narragansett Bay permits the development of high-resolution sea-level index points that have the potential to identify small differences in RSL between sites. To address our research goals we collected a south to north transect of salt marsh basal peats from four Rhode Island salt marshes at Fox Hill, Nag Creek, Touisset, and Osamequin. We reconstructed paleomarsh elevations utilizing a multi-proxy approach using salt-marsh foraminifera and bulk sediment δ13C. Sample age was determined using accelerated mass spectrometry (AMS) radiocarbon of identifiable in-situ plant macrofossils. Basal peats in Rhode Island typically form within the tidal frame as indicated by foraminifera within close proximity (<5cm) to the underlying glacial deposits. Our current database of RSL consists of 30 new sea-level index points that document changes in RSL since 3200 cal yrs BP. At our southerly Fox Hill site, 12 sea-level index points demonstrate that RSL rose from -3.87 ± 0.24 m at 3,140 ± 69 cal yrs BP. Conversely, at the northerly Touisset site, six sea-level index points demonstrate that salt marshes developed later in this region with RSL rising from -1.65 ± 0.22 m at 1,246 ± 56 cal yrs BP. An additional 12 sea-level index points have been reconstructed from Osamequin

  16. Holocene rainfall runoff in the central Ethiopian highlands and evolution of the River Nile drainage system as revealed from a sediment record from Lake Dendi

    NASA Astrophysics Data System (ADS)

    Wagner, Bernd; Wennrich, Volker; Viehberg, Finn; Junginger, Annett; Kolvenbach, Anne; Rethemeyer, Janet; Schaebitz, Frank; Schmiedl, Gerhard

    2018-04-01

    A 12 m long sediment sequence was recovered from the eastern Dendi Crater lake, located on the central Ethiopian Plateau and in the region of the Blue Nile headwaters. 24 AMS radiocarbon dates from bulk organic carbon samples indicate that the sediment sequence spans the last ca. 12 cal kyr BP. Sedimentological and geochemical data from the sediment sequence that were combined with initial diatom information show only moderate change in precipitation and catchment runoff during that period, probably due to the elevated location of the study region in the Ethiopian highlands. Less humid conditions prevailed during the Younger Dryas (YD). After the return to full humid conditions of the African Humid Period (AHP), a 2 m thick tephra layer, probably originating from an eruption of the Wenchi crater 12 km to the west of the lake, was deposited at 10.2 cal kyr BP. Subsequently, single thin horizons of high clastic matter imply that short spells of dry conditions and significantly increased rainfall, respectively, superimpose the generally humid conditions. The end of the AHP is rather gradual and precedes relatively stable and less humid conditions around 3.9 cal kyr BP. Subsequently, slightly increasing catchment runoff led to sediment redeposition, increasing nutrient supply, and highest trophic states in the lake until 1.5 cal kyr BP. A highly variable increase in clastic matter indicates fluctuating and increasing catchment runoff over the last 1500 years. The data from Lake Dendi show, in concert with other records from the Nile catchment and the Eastern Mediterranean Sea (EMS), that the Blue Nile discharge was relatively high between ca. 10.0 and 8.7 cal kyr BP. Subsequent aridification peaked with some regional differences between ca. 4.0 and 2.6 cal kyr BP. Higher discharge in the Blue Nile hydraulic regime after 2.6 cal kyr BP is probably triggered by more local increase in rainfall, which is tentatively caused by a change in the influence of the Indian Ocean

  17. Changes of environments and human activity at the Sannai-Maruyama ruins in Japan during the mid-Holocene Hypsithermal climatic interval

    NASA Astrophysics Data System (ADS)

    Kawahata, Hodaka; Yamamoto, Hisashi; Ohkushi, Ken'ichi; Yokoyama, Yusuke; Kimoto, Katsunori; Ohshima, Hideki; Matsuzaki, Hiroyuki

    2009-05-01

    Sannai-Maruyama is one of the most famous and best-researched mid-Holocene (mid-Jomon) archaeological sites in Japan, because of a large community of people for a long period. Archaeological studies have shown that the Jomon people inhabi1ted the Sannai-Maruyama site from 5.9 to 4.2 ± 0.1 cal kyr BP However, a continuous record of the terrestrial and marine environments around the site has not been available. Core KT05-7 PC-02, was recovered from Mutsu Bay, only 20 km from the site, for the reconstruction of high-resolution time series of environmental records, including sea surface temperature (SST). C 37 alkenone SSTs showed clear fluctuations, with four periods of high (8.4-7.9, 7.0-5.9, 5.1-4.1, and 2.3-1.4 cal kyr BP) and four of low (-8.4, 7.9-7.0, 5.9-5.1, and 4.1-2.3 cal kyr BP) SST. Thus, each SST cycle lasted 1.0-2.0 kyr, and the amplitude of fluctuation was about 1.5-2.0 °C. Total organic carbon (TOC) and C 37 alkenone contents, and the TOC/total nitrogen ratio indicate that marine biogenic production was low before 7.0 cal kyr BP, but was clearly increased between 5.9 and 4.0 cal kyr BP, because of stronger vertical mixing. During the period when the community at the site prospered (between 5.9 and 4.2 ± 0.1 cal kyr BP), the terrestrial climate was relatively warm. The high relative abundance of pollen of both Castanea and Quercus subgen. Cyclobalanopsis supports the interpretation that the local climate was optimal for human habitation. Between 5.9 and 5.1 cal kyr BP, in spite of warm terrestrial climates, the C 37 alkenone SST was low; this apparent discrepancy may be attributed to the water column structure in the Tsugaru Strait, which differed from the modern condition. The evidence suggests that at about 5.9 cal kyr B.P, high productivity of marine resources such as fish and shellfish and a warm terrestrial climate led to the establishment of a human community at the Sannai-Maruyama site. Then, at about 4.1 ± 0.1 cal kyr BP, abrupt marine and

  18. High-precision chronology for Central American maize diversification from El Gigante rockshelter, Honduras.

    PubMed

    Kennett, Douglas J; Thakar, Heather B; VanDerwarker, Amber M; Webster, David L; Culleton, Brendan J; Harper, Thomas K; Kistler, Logan; Scheffler, Timothy E; Hirth, Kenneth

    2017-08-22

    The first steps toward maize ( Zea mays subspecies mays ) domestication occurred in the Balsas region of Mexico by ∼9,000 calendar years B.P. (cal B.P.), but it remains unclear when maize was productive enough to be a staple grain in the Americas. Molecular and microbotanical data provide a partial picture of the timing and nature of morphological change, with genetic data indicating that alleles for some domestication traits were not yet fixed by 5,300 cal B.P. in the highlands of Mexico. Here, we report 88 radiocarbon dates on the botanical remains from El Gigante rockshelter (Honduras) to establish a Bayesian chronology over the past ∼11,000 y spanning the transition to maize-based food production. Botanical remains are remarkably well preserved and include over 10,000 maize macrofossils. We directly dated 37 maize cobs to establish the appearance and local change of maize at the site. Cobs are common in deposits dating between 4,340 and 4,020 cal B.P., and again between 2,350 and 980 cal B.P. The earliest cobs appear robustly domesticated, having 10-14 rows, suggesting strong selection for increased yield. The later cobs are comparable to these earliest ones, but show clear emergence of diverse traits, including increased cob width, rachis segment length, and cupule width. Our results indicate that domesticated landraces of maize productive enough to be a staple grain existed in Central America by 4,300 cal B.P.

  19. High-precision chronology for Central American maize diversification from El Gigante rockshelter, Honduras

    PubMed Central

    Kennett, Douglas J.; Thakar, Heather B.; VanDerwarker, Amber M.; Webster, David L.; Culleton, Brendan J.; Harper, Thomas K.; Kistler, Logan; Scheffler, Timothy E.; Hirth, Kenneth

    2017-01-01

    The first steps toward maize (Zea mays subspecies mays) domestication occurred in the Balsas region of Mexico by ∼9,000 calendar years B.P. (cal B.P.), but it remains unclear when maize was productive enough to be a staple grain in the Americas. Molecular and microbotanical data provide a partial picture of the timing and nature of morphological change, with genetic data indicating that alleles for some domestication traits were not yet fixed by 5,300 cal B.P. in the highlands of Mexico. Here, we report 88 radiocarbon dates on the botanical remains from El Gigante rockshelter (Honduras) to establish a Bayesian chronology over the past ∼11,000 y spanning the transition to maize-based food production. Botanical remains are remarkably well preserved and include over 10,000 maize macrofossils. We directly dated 37 maize cobs to establish the appearance and local change of maize at the site. Cobs are common in deposits dating between 4,340 and 4,020 cal B.P., and again between 2,350 and 980 cal B.P. The earliest cobs appear robustly domesticated, having 10–14 rows, suggesting strong selection for increased yield. The later cobs are comparable to these earliest ones, but show clear emergence of diverse traits, including increased cob width, rachis segment length, and cupule width. Our results indicate that domesticated landraces of maize productive enough to be a staple grain existed in Central America by 4,300 cal B.P. PMID:28784803

  20. CubiCal - Fast radio interferometric calibration suite exploiting complex optimisation

    NASA Astrophysics Data System (ADS)

    Kenyon, J. S.; Smirnov, O. M.; Grobler, T. L.; Perkins, S. J.

    2018-05-01

    It has recently been shown that radio interferometric gain calibration can be expressed succinctly in the language of complex optimisation. In addition to providing an elegant framework for further development, it exposes properties of the calibration problem which can be exploited to accelerate traditional non-linear least squares solvers such as Gauss-Newton and Levenberg-Marquardt. We extend existing derivations to chains of Jones terms: products of several gains which model different aberrant effects. In doing so, we find that the useful properties found in the single term case still hold. We also develop several specialised solvers which deal with complex gains parameterised by real values. The newly developed solvers have been implemented in a Python package called CubiCal, which uses a combination of Cython, multiprocessing and shared memory to leverage the power of modern hardware. We apply CubiCal to both simulated and real data, and perform both direction-independent and direction-dependent self-calibration. Finally, we present the results of some rudimentary profiling to show that CubiCal is competitive with respect to existing calibration tools such as MeqTrees.

  1. TheraCal LC: From Biochemical and Bioactive Properties to Clinical Applications

    PubMed Central

    Rabi, Tarek

    2018-01-01

    Background Direct pulp capping is a popular treatment modality among dentists. TheraCal LC is a calcium silicate-based material that is designed as a direct/indirect pulp capping material. The material might be very attractive for clinicians because of its ease of handling. Unlike other calcium silicate-based materials, TheraCal LC is resin-based and does not require any conditioning of the dentine surface. The material can be bonded with different types of adhesives directly after application. There has been considerable research performed on this material since its launching; however, there are no review articles that collates information and data obtained from these studies. This review discusses the various characteristics of the material with the aim of establishing a better understanding for its clinical use. Methods A search was conducted using search engines (PubMed and Cochrane databases) in addition to reference mining of the articles that was used to locate other papers. The process of searching for the relevant studies was performed using the keywords pulp protection, pulp capping, TheraCal, and calcium silicates. Only articles in English published in peer-reviewed journals were included in the review. Conclusion This review underlines the fact that further in vitro and in vivo studies are required before TheraCal LC can be used as a direct pulp capping material. PMID:29785184

  2. Inferring LGM sedimentary and climatic changes in the southern Eastern Alps foreland through the analysis of a 14C ages database (Brenta megafan, Italy)

    NASA Astrophysics Data System (ADS)

    Rossato, Sandro; Mozzi, Paolo

    2016-09-01

    The analysis of a database of radiocarbon ages is proposed as a tool for investigating major glaciofluvial systems of the Last Glacial Maximum (LGM) in the Alpine foreland, and their relations with glacier dynamics and climatic fluctuations. Our research concerns the Brenta megafan (NE Italy), where 110 radiocarbon dates integrate a robust regional stratigraphic and palaeoclimatic framework. Age-depth models allowed us to calculate sedimentation rates, while the time distribution of peat layers, which recurrently formed in this region during the LGM, were estimated through meta-analysis. The reliability of statistical results was carefully evaluated using Pearson and Spearman coefficients. Sedimentation rates in the Brenta megafan markedly fluctuated during LGM: ≈1.8 m/ka between 40 and 26.7 ka cal BP; ≈3 m/ka between 26.7 and 23.8 ka cal BP and ≈1.4 m/ka from 23.8 to 17.5 ka cal BP, when the distributary system deactivated due to fan-head trenching. This is evidence that sediment input and routing in the glaciofluvial distributary system was particularly efficient during the central part of LGM, when glaciers were stable at their outermost position. Meta-analysis indicates an increase in peat formation in correspondence with global (Heinrich Event 3 and/or the Greenland Interstadial 5.1 and 4 for the 30.5, 29.6 and 28.8 ka cal BP peaks) and regional (23.5 ka cal BP) wet events. Other peaks at 22.2, 21.8, 20.2 and 19 ka cal BP correlate with fluctuations of south-eastern Alpine glaciers. Significant peat formation continued until ≈18 ka cal BP, when the last peak occurred. A marked decrease in peat formation is recorded concomitantly with the onset of Heinrich Event 2 (i.e. the 26 ka cal BP trough). The good correspondence of sedimentary events in the Brenta glaciofluvial system with the dynamics of glaciers and glaciofluvial and lacustrine systems in the southern Eastern Alps suggests a common climatic forcing on the whole region during the LGM. Peat layer

  3. Late glacial to Holocene water level and climate changes in the Gulf of Gemlik, Sea of Marmara: evidence from multi-proxy data

    NASA Astrophysics Data System (ADS)

    Filikci, Betül; Eriş, Kürşad Kadir; Çağatay, Namık; Sabuncu, Asen; Polonia, Alina

    2017-10-01

    Multi-proxy analyses of new piston core M13-08 together with seismic data from the Gulf of Gemlik provide a detailed record of paleoceanographic and paleoclimatic changes with special emphasis on the timing of the connections between the Sea of Marmara (SoM) and the Gulf of Gemlik during the late Pleistocene to Holocene. The deposition of a subaqueous delta sourced from the Armutlu River to the north is attributed to the lowstand lake level at -60 m in the gulf prior to 13.5 cal ka BP. On the basis of the seismic data, it is argued that the higher lake level (-60 m) in the gulf compared to the SoM level (-85 m) attests to its disconnection from the SoM during the late glacial period. Ponto-Caspian assemblages in the lacustrine sedimentary unit covering the time period between 13.5 and 12 cal ka BP represent a relict that was introduced into the gulf by a Black Sea outflow during the marine isotope stage 3 interstadial. Contrary to the findings of previous studies, the data suggest that such an outflow into the Gulf of Gemlik during the late glacial period could have occurred only if the SoM lake level (-85 m) was shallower than the sill depth (-55 m) of the gulf in the west. A robust age model of the core indicates the connection of the gulf with the marine SoM at 12 cal ka BP, consistent with the sill depth (-55 m) of the gulf on the global sea level curve. Strong evidence of a marine incursion into the gulf is well documented by the μ-XRF Sr/Ca data. The available profiles of elemental ratios in core M13-08, together with the age-depth model, imply that a warm and wet climate prevailed in the gulf during the early Holocene (12-10.1 cal ka BP), whereas the longest drought occurred during the middle Holocene (8.2-5.4 cal ka BP). The base of the main Holocene sapropel in the gulf is dated at 10.1 cal ka BP, i.e., 500 years younger than its equivalent in the SoM. The late Holocene is earmarked by warm and wet climate periods (5.0-4.2 and 4.2-2.7 cal ka BP) with some

  4. Usefulness of Enzyme-linked Immunosorbent Assay Using Recombinant BP180 and BP230 for Serodiagnosis and Monitoring Disease Activity of Bullous Pemphigoid

    PubMed Central

    Lee, Eui Hyung; Kim, Yeon Hee; Kim, Sinyoung; Kim, Song-ee

    2012-01-01

    Background Bullous pemphigoid (BP) is an autoimmune subepidermal bullous disease associated with autoantibodies against BP180 and BP230. Enzyme-linked immunosorbent assay (ELISA) is a sensitive tool for the detection of immunoglobulin G (IgG) anti-BP180 and anti-BP230 autoantibodies. Objective The aim of this study was to evaluate the usefulness of ELISA for diagnosing and monitoring the disease activity of BP. Methods We evaluated serum IgG levels of anti-BP180 and anti-BP230 autoantibodies in 47 BP patients, 16 epidermolysis bullosa aquisita patients, and 15 healthy volunteers using ELISA. Through retrospective review of the medical records, the clinical characteristics of BP including disease activity, duration, pruritus severity and peripheral blood eosinophil counts were assessed. Results The sensitivity of BP180 ELISA was 97.9%, BP230 ELISA 72.3%, and a combination of the two was 100%. The specificity of BP180 ELISA was 90.3%, BP230 ELISA 100%, and a combination of the two was 90.3%. BP180 ELISA scores showed strong associations with disease activity, pruritus severity, peripheral blood eosinophil counts, and disease duration, whereas BP230 ELISA scores did not. Conclusion BP180 and BP230 ELISAs are highly sensitive methods for the diagnosis of BP, and BP180 ELISA, in particular, is a sensitive tool for monitoring the disease activity of BP. PMID:22363155

  5. Navy CALS Vision. Draft 2.0. Volume 25

    DOT National Transportation Integrated Search

    1990-10-01

    Computer-aided Acquisition and Logistic Support (CALS) is a joint initiative between industry and the Department of Defense (DoD) that is targeted at: (1) Improving designs for weapon systems; (2) Reducing both acquisition and logistic support costs ...

  6. Medi-Cal Hospital Contracting—Did It Achieve Its Legislative Objectives?

    PubMed Central

    Brown, E. Richard; Price, Walter T.; Cousineau, Michael R.

    1985-01-01

    The 1982 Medi-Cal reforms and reductions established selective contracting with hospitals for inpatient care of Medi-Cal beneficiaries. The legislation established a special negotiator and criteria to be used in selecting contract hospitals. We report the findings of a study that analyzed the characteristics of contract and noncontract hospitals in Los Angeles County to assess how well these criteria were reflected in the outcome of the contracting process. We examine issues of beneficiary access to general inpatient care and to specialized services, the efficiency of contract hospitals compared with noncontract ones and quality-related issues. PMID:3898595

  7. A CHRONOLOGICAL FRAMEWORK FOR THE HOLOCENE VEGETATIONAL HISTORY OF CENTRAL MINNESOTA: THE STEEL LAKE POLLEN RECORD

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Wright, H E; Stefanova, I; Tian, J

    Paleorecords from Minnesota and adjacent areas have often been used to evaluate large-scale climatic processes in the mid-continent of North America. However, most of these records are compromised by chronological flaws, making problematic any comparisons with climatic interpretations based on other records (e.g., GISP2 in Greenland). We report here a high-resolution pollen record with a secure chronology constrained by 26 {sup 14}C dates on terrestrial macrofossils from Steel Lake, central Minnesota. About 11,200 years ago (calibrated yr BP) the late-glacial Picea forest near Steel Lake was succeeded abruptly by Pinus banksiana and/or resinosa. The Pinus forest began to open 9.4more » ka cal BP with the expansion of prairie taxa, and a pine parkland or savanna prevailed until about 8 ka cal BP, when Quercus replaced Pinus to become the dominant tree in the prairie areas for 4500 years. The close chronological control permits the correlation of key vegetational changes with those at other reliably dated sites in the eastern Dakotas and in Minnesota, suggesting that the abrupt decline of the spruce forest was time-transgressive from southwest to northeast during 2000 years, and that the development of prairie was time-transgressive in the same direction over 2600 years. Correlation of key pollen horizons at Steel Lake with those in the high-resolution pollen profiles of Elk Lake, ca. 50 km northwest of Steel Lake, suggests that the well-known Elk Lake varve chronology for the early Holocene is about 1000 years too young.« less

  8. The reconstruction of late Holocene depth-to-water-table based on testate amoebae in an eastern Australian mire

    NASA Astrophysics Data System (ADS)

    Zheng, X.; Money, S.; Hope, G.

    2017-12-01

    There are relatively few quantitative palaeo-hydrological records available in eastern Australia, and those that are available, for example from dendroclimatology and the reconstruction of lake level, are often relatively short or have a relatively coarse temporal resolution (e.g. Wilkins et al. 2013; Palmer et al. 2015). Testate amoebae, a widely used hydrological proxy in the Northern Hemisphere, were used here to reconstruct depth to water table (DWT) at Snowy Flat, which is a Sphagnum-Richea-Empodismahigh altitude (1618 m asl) shrub bog in the Australian Capital Territory, Australia. Testate amoebae were quantified in a Snowy Flat core representing 4,200 cal Y BP and the community composition was used to reconstruct DWT based on our recently established transfer functions. Results from three different types of transfer functions (Fig. 1) consistently show there was a decreasing DWT (wetter) period centred on about 3350 cal Y BP, a trend towards increased dryness from about 3300 to 2200 cal Y BP and a distinctly drier period 850 to 700 cal Y BP which was immediately followed by a wetter period from 700 to 500 cal Y BP. We discuss these episodes and trends in relation to the drivers of climatic variability in this region and in particular, by comparing our results with other south-eastern Australia records, comment on the history of the southern annular mode.

  9. 7300 years of vegetation history and climate for NW Malta: a Holocene perspective

    NASA Astrophysics Data System (ADS)

    Gambin, B.; Andrieu-Ponel, V.; Médail, F.; Marriner, N.; Peyron, O.; Montade, V.; Gambin, T.; Morhange, C.; Belkacem, D.; Djamali, M.

    2015-09-01

    This paper investigates the Holocene vegetation dynamics for Burmarrad in north-west Malta and provides a pollen-based quantitative palaeoclimatic reconstruction for this centrally located Mediterranean archipelago. The pollen record from this site provides new insight into the vegetation changes from 7280 to 1730 cal BP which correspond well with other regional records. The climate reconstruction for the area also provides strong correlation with southern (below 40° N) Mediterranean sites. Our interpretation suggests an initially open landscape during the early Neolithic, surrounding a large palaeobay, developing into a dense Pistacia scrubland ca. 6700 cal BP. From about 4450 cal BP the landscape once again becomes open, coinciding with the start of the Bronze Age on the archipelago. This period is concurrent with increased climatic instability (between 4500 and 3700 cal BP) which is followed by a gradual decrease in summer moisture availability in the late Holocene. During the early Roman occupation period (1972 to 1730 cal BP) the landscape remains generally open with a moderate increase in Olea. This increase, corresponds to archaeological evidence for olive oil production in the area, along with increases in cultivated crop taxa and associated ruderal species, as well as a rise in fire events. The Maltese archipelago provides important insight into vegetation, human impacts and climatic changes in an island context during the Holocene.

  10. 7300 years of vegetation history and climate for NW Malta: a Holocene perspective

    NASA Astrophysics Data System (ADS)

    Gambin, B.; Andrieu-Ponel, V.; Médail, F.; Marriner, N.; Peyron, O.; Montade, V.; Gambin, T.; Morhange, C.; Belkacem, D.; Djamali, M.

    2016-02-01

    This paper investigates the Holocene vegetation dynamics for Burmarrad in Northwest Malta and provides a pollen-based quantitative palaeoclimatic reconstruction for this centrally located Mediterranean archipelago. The pollen record from this site provides new insight into the vegetation changes from 7280 to 1730 cal BP which correspond well with other regional records. The climate reconstruction for the area also provides strong correlation with southern (below 40° N) Mediterranean sites. Our interpretation suggests an initially open landscape during the early Neolithic, surrounding a large palaeobay, developing into a dense Pistacia scrubland ca. 6700 cal BP. From about 4450 cal BP the landscape once again becomes open, coinciding with the start of the Bronze Age on the archipelago. This period is concurrent with increased climatic instability (between 4500 and 3700 cal BP) which is followed by a gradual decrease in summer moisture availability in the late Holocene. During the early Roman occupation period (1972-1730 cal BP) the landscape remains generally open with a moderate increase in Olea. This increase corresponds to archaeological evidence for olive oil production in the area, along with increases in cultivated crop taxa and associated ruderal species, as well as a rise in fire events. The Maltese archipelago provides important insight into vegetation, human impacts, and climatic changes in an island context during the Holocene.

  11. An improved understanding of the Alaska coastal current: The application of a bivalve growth-temperature model to reconstruct freshwater-influenced paleoenvironments

    USGS Publications Warehouse

    Hallmann, N.; Schone, B.R.; Irvine, G.V.; Burchell, M.; Cokelet, E.D.; Hilton, M.R.

    2011-01-01

    Shells of intertidal bivalve mollusks contain sub-seasonally to interannually resolved records of temperature and salinity variations in coastal settings. Such data are essential to understand changing land-sea interactions through time, specifically atmospheric (precipitation rate, glacial meltwater, river discharge) and oceanographic circulation patterns; however, independent temperature and salinity proxies are currently not available. We established a model for reconstructing daily water temperatures with an average standard error of ???1.3 ??C based on variations in the width of lunar daily growth increments of Saxidomus gigantea from southwestern Alaska, United States. Temperature explains 70% of the variability in shell growth. When used in conjunction with stable oxygen isotope data, this approach can also be used to identify changes in past seawater salinity. This study provides a better understanding of the hydrological changes related to the Alaska Coastal Current (ACC). In combination with ??18Oshell values, increment-derived temperatures were used to estimate salinity changes with an average error of 1.4 ?? 1.1 PSU. Our model was calibrated and tested with modern shells and then applied to archaeological specimens. As derived from the model, the time interval of 988-1447 cal yr BP was characterized by ???1-2 ??C colder and much drier (2-5 PSU) summers. During that time, the ACC was likely flowing much more slowly than at present. In contrast, between 599-1014 cal yr BP, the Aleutian low may have been stronger, which resulted in a 3 ??C temperature decrease during summers and 1-2 PSU fresher conditions than today; the ACC was probably flowing more quickly at that time. The shell growth-temperature model can be used to estimate seasonal to interannual salinity and temperature changes in freshwater-influenced environments through time. ?? 2011 SEPM (Society for Sedimentary Geology).

  12. Chronology and ancient feeding ecology of two upper Pleistocene megamammals from the Brazilian Intertropical Region

    NASA Astrophysics Data System (ADS)

    de Melo França, Lucas; Trindade Dantas, Mário André; Bocchiglieri, Adriana; Cherckinsky, Alexander; de Souza Ribeiro, Adauto; Bocherens, Hervé

    2014-09-01

    In Brazilian Intertropical Region (BIR) fossil remains of the giant ground sloth Eremotherium laurillardi (Lund, 1842) and of the proboscidean Notiomastodon platensis (Ameghino, 1888) are the most abundant among megaherbivores. However, the paleoecology of both species needs to be better understood to enlighten why these species disappear in the end of the Pleistocene, an issue that is still debated. During the last decades, the carbon and oxygen stable isotopes have been increasingly being used to obtain paleoecological information about extinct animals, although this information is in most cases dissociated from chronological data. Thus, the main objective of this study is to contribute to the knowledge about feeding ecology and chronology of E. laurillardi and N. platensis within BIR. For each fossil sample we performed stable isotopes analyses (δ13C/δ18O) and radiocarbon dating (14C with AMS). The results showed that N. platensis occurred between 12,125 and 19,594 cal yr BP and exhibited a grazer diet (δ13C = -1.1‰-1.3‰), while E. laurillardi lived between 11,084 and 27,690 cal yr BP, with a mixed feeder diet (C3/C4 plants; values ratio δ13C = -7.7‰ to -3.3‰). The δ18O values of N. platensis ranged between 2.20‰ and 3.60‰, while the values of E. laurillardi ranged between -3.10‰ and -1.10‰. Neither species did exhibit differences in its diet through time, which suggests that the vegetational composition of this locality did not vary in the late Pleistocene. Both species were living in an open environment, rich in herbaceous plants (C4 plants) and with tree and shrub with disjoint distribution, maybe similar to some parts of recent Caatinga, where they have partitioned the spatial and feeding niches.

  13. Geomorphology and failure history of the earthquake-induced Farmington Siding landslide complex, Davis County, Utah

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Lowe, M.; Harty, K.M.

    1993-04-01

    The Farmington Siding landslide complex covers an area of 19.5 km[sup 2] in central Davis County. First identified and mapped in the 1970s, the feature was classified by previous researchers as a liquefaction-induced lateral spread based on surface geomorphology and exposures on the landslide complex. This was the first landslide in Utah to be attributed to earthquake-induced liquefaction. Geomorphic and geologic evidence indicate that the Farmington Sliding landslide complex likely consists of liquefaction-induced landslides that failed by means of both flow failure and lateral spreading. The landslide complex is located in an area underlain primarily by fine-grained deposits of Pleistocenemore » Lake Bonneville and Holocene Great Salt Lake. Geomorphic features of the landslide complex include main and minor scarps, hummocks, closed depressions, and transverse lineaments. The main scarp consists mostly of a series of arcuate scallops near the left flank of the landslide, but it is a relatively linear, single scarp near the right flank of the landslide. Hummocks and closed depressions are most common near the head region of the landslide complex. Failure of the Farmington Sliding landslide complex has occurred at least twice. The older, distal portion of the landslide complex is cut by the Gilbert shoreline of the Bonneville lake cycle, indicating that landsliding occurred more than 10,000 years ago. In the younger portion of the landslide complex, landsliding has disrupted the Gilbert shoreline. Radiocarbon age estimates from trenches on a hummock near the main scarp of the younger landslide indicate that slope failure occurred sometime between about 2,730 [+-] 370 cal. yr B.P. and 4,530 [+-] 300 cal. yr B.P., possibly during the penultimate or antepenultimate surface-faulting earthquake on the Weber segment of the Wasatch fault zone.« less

  14. Searching for a paleotsunami record in the Hawaiian Islands

    NASA Astrophysics Data System (ADS)

    La Selle, S.; Richmond, B. M.; Arcos, M. E. M.; Jaffe, B. E.; Lunghino, B.; Kane, H. H.; Bishop, J. M.; Habel, S. L.

    2016-12-01

    Historical records of tsunamis over the last 200 years in the state of Hawai'i demonstrate that earthquakes in subduction zones around the Pacific (Aleutian, Kuril-Kamchatka, Chile, Japan, and Alaska) can cause significant tsunami inundation on multiple Hawaiian islands. Deposits found along these subduction zones provide evidence for older tsunamis, but it is unclear if any of these prehistoric far-field events have impacted the Hawaiian islands because no study has successfully correlated Hawaiian paleotsunami deposits between sites or islands. We cored coastal marshlands on Óahu, Maui, and Kauái searching for tsunami deposits in order to determine the viability of extending the record of tsunami inundation in the state of Hawai'i. Sites were selected based on historical tsunami runup, numerical inundation modeling results, the presence of a coastal marsh in close proximity to a sandy shoreline, the extent of undisturbed wetlands, and the breadth of prior geological investigations. Several possible tsunami deposits were identified on the north and northeast shores of Kauái and Óahu as marine sand layers within marsh peat or mud. At some sites, the presence of deposits from the 1946 and 1957 Aleutian tsunamis aided identification of the deeper candidate tsunami deposits. Radiocarbon ages of the deeper sand layers suggest deposition around 800-600 cal yr B.P., which may coincide with a tsunami deposit in the eastern Aleutians that was deposited 660-560 cal yr B.P. (Witter et al., 2016). Further dating and analyses of the deposits is needed to determine whether or not deposition was synchronous on O'ahu and Kaua'i and to determine from sedimentological and micropaleontological characteristics that a tsunami formed the deposits.

  15. Post-glacial dispersal patterns of Northern pike inferred from an 8800 year old pike (Esox cf. lucius) skull from interior Alaska

    NASA Astrophysics Data System (ADS)

    Wooller, Matthew J.; Gaglioti, Benjamin; Fulton, Tara L.; Lopez, Andres; Shapiro, Beth

    2015-07-01

    The biogeography of freshwater fish species during and after late-Pleistocene glaciations relate to how these species are genetically organized today, and the management of these often disjunct populations. Debate exists concerning the biogeography and routes of dispersal for Northern pike (Esox lucius) after the last glaciation. A hypothesis to account for the relatively low modern genetic diversity for E. lucius is post-glacial radiation from refugia, including lakes from within the un-glaciated portions of eastern Beringia. We report the remains of a Northern pike (E. cf. lucius) skull, including bones, teeth, bone collagen and ancient DNA. The remains were preserved at a depth of between 440 and 446 cm in a 670 cm long core of sediment from Quartz Lake, which initiated at ˜11,200 cal yr BP in interior Alaska. A calibrated accelerator mass spectrometer (AMS) radiocarbon age of the collagen extracted from the preserved bones indicated that the organism was dated to 8820 cal yr BP and is bracketed by AMS values from analyses of terrestrial plant macrofossils, avoiding any potential aquatic reservoir effect that could have influenced the radiocarbon age of the bones. Scanning electron microscope images of the specimen show the hinged tooth anatomy typically of E. lucius. Molar C:N (3.5, 1σ = 0.1) value of the collagen from the specimen indicated well-preserved collagen and its mean stable nitrogen isotope value is consistent with the known predatory feeding ecology of E. lucius. Ancient DNA in the bones showed that the specimen was identical to modern E. lucius. Our record of E. lucius from interior Alaska is consistent with a biogeographic scenario involving rapid dispersal of this species from glacial refugia in the northern hemisphere after the last glaciation.

  16. Southern Hemisphere anticyclonic circulation drives oceanic and climatic conditions in late Holocene southernmost Africa

    NASA Astrophysics Data System (ADS)

    Hahn, Annette; Schefuß, Enno; Andò, Sergio; Cawthra, Hayley C.; Frenzel, Peter; Kugel, Martin; Meschner, Stephanie; Mollenhauer, Gesine; Zabel, Matthias

    2017-06-01

    Due to the high sensitivity of southern Africa to climate change, a reliable understanding of its hydrological system is crucial. Recent studies of the regional climatic system have revealed a highly complex interplay of forcing factors on precipitation regimes. This includes the influence of the tropical easterlies, the strength of the southern hemispheric westerlies as well as sea surface temperatures along the coast of the subcontinent. However, very few marine records have been available in order to study the coupling of marine and atmospheric circulation systems. Here we present results from a marine sediment core, recovered in shallow waters off the Gouritz River mouth on the south coast of South Africa. Core GeoB18308-1 allows a closer view of the last ˜ 4 kyr. Climate sensitive organic proxies, like the distribution and isotopic composition of plant-wax lipids as well as indicators for sea surface temperatures and soil input, give information on oceanographic and hydrologic changes during the recorded time period. Moreover, the micropaleontology, mineralogical and elemental composition of the sediments reflect the variability of the terrigenous input to the core site. The combination of down-core sediment signatures and a catchment-wide provenance study indicate that the Little Ice Age ( ˜ 300-650 cal yr BP) was characterized by climatic conditions favorable to torrential flood events. The Medieval Climate Anomaly ( ˜ 950-650 cal yr BP) is expressed by lower sea surface temperatures in the Mossel Bay area and humid conditions in the Gouritz River catchment. These new results suggest that the coincidence of humid conditions and cooler sea surface temperatures along the south coast of South Africa resulted from a strengthened and more southerly anticyclonic circulation. Most probably, the transport of moisture from the Indian Ocean by strong subtropical easterlies was coupled with Agulhas Bank upwelling pulses, which were initiated by an increase in

  17. CTN summary of DSREDS, EDCARS, EDMICS CALS readiness testing. [Computer-aided Acquisition and Logistic Support (CALS) CALS Test Network (CTN), Digital Storage Retrieval Eng. Data System (DSREDS), Eng. Data Computer Assisted Retrieval System (EDCARS), Eng. Data Management Information and Control System (EDMICS)

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Mitschkowetz, N.; Vickers, D.L.

    This report provides a summary of the Computer-aided Acquisition and Logistic Support (CALS) Test Network (CTN) Laboratory Acceptance Test (LAT) and User Application Test (UAT) activities undertaken to evaluate the CALS capabilities being implemented as part of the Department of Defense (DOD) engineering repositories. Although the individual testing activities provided detailed reports for each repository, a synthesis of the results, conclusions, and recommendations is offered to provide a more concise presentation of the issues and the strategies, as viewed from the CTN perspective.

  18. Chemical complexity and source of the White River Ash, Alaska and Yukon

    USGS Publications Warehouse

    Preece, S.J.; McGimsey, Robert G.; Westgate, J.A.; Pearce, N.J.G.; Hartmann, W.K.; Perkins, W.T.

    2014-01-01

    The White River Ash, a prominent stratigraphic marker bed in Alaska (USA) and Yukon (Canada), consists of multiple compositional units belonging to two geochemical groups. The compositional units are characterized using multiple criteria, with combined glass and ilmenite compositions being the best discriminators. Two compositional units compose the northern group (WRA-Na and WRA-Nb), and two units are present in the eastern group (WRA-Ea and the younger, WRA-Eb). In the proximal area, the ca. 1900 yr B.P. (Lerbekmo et al., 1975) WRA-Na displays reverse zoning in the glass phase and systematic changes in ilmenite composition and estimated oxygen fugacity from the base to the top of the unit. The eruption probably tapped different magma batches or bodies within the magma reservoir with limited mixing or mingling between them. The 1147 cal yr B.P. (calibrated years, approximately equivalent to calendric years) (Clague et al., 1995) WRA-Ea eruption is only weakly zoned, but pumices with different glass compositions are present, along with gray and white intermingled glass in individual pumice clasts, indicating the presence of multiple magmatic bodies or layers. All White River Ash products are high-silica adakites and are sourced from the Mount Churchill magmatic system.

  19. Climatic and palaeoecological changes during the mid- to Late Holocene transition in eastern China: high-resolution pollen and non-pollen palynomorph analysis at Pingwang, Yangtze coastal lowlands

    NASA Astrophysics Data System (ADS)

    Innes, James B.; Zong, Yongqiang; Wang, Zhanghua; Chen, Zhongyuan

    2014-09-01

    The transition to the Late Holocene/Neoglacial occurred as a worldwide process of climatic deterioration from the optimum thermal conditions of the mid-Holocene, culminating in an abrupt decline around 4200 cal yr ago, in a period of severe climatic deterioration that lasted for two or three centuries. This sudden climatic event has been recorded in many proxy data archives from around the world, and its effects were manifest in different ways depending on the reaction of regional weather systems and conditions, but often as greatly increased aridity and/or cold temperatures. It has been regarded as causing or contributing to the sudden collapse of several well-established human societies at that time, including advanced agricultural Late Neolithic cultures in eastern China. We have used high-resolution pollen and non-pollen palynomorph analysis to examine the nature of this climatic transition through its impacts on the vegetation and hydrology at Pingwang, a site in the Yangtze coastal lowlands which has no evidence of complicating environmental influences such as sea-level rise or significant human land-use activity, factors previously suggested as alternative reasons for changes in forest composition. Our results show two phases of forest alteration, one gradual from about 5500 cal BP and one sudden at about 4200 cal BP., in which the frequencies of subtropical forest elements fall and are replaced by those of conifers and cold-tolerant trees. Total arboreal pollen frequencies do not decline and the proportion of temperate forest trees, tolerant of a wide range of temperatures, remains unchanged throughout, both ruling out human land clearance as a cause of the change in forest composition. As these dates accord very well with the known timings of climate deterioration established from other proxy archives in the region, we conclude that climate was the main driver of vegetation change in eastern China at the mid- to Late Holocene transition. Our hydrological

  20. Radiocarbon analysis of halophilic microbial lipids from an Australian salt lake

    NASA Astrophysics Data System (ADS)

    Bray, P. Sargent; Jones, Claudia M.; Fallon, Stewart J.; Brocks, Jochen J.; George, Simon C.

    2012-01-01

    Assigning accurate dates to hypersaline sediments opens important terrestrial records of local and regional paleoecologies and paleoclimatology. However, as of yet no conventional method of dating hypersaline systems has been widely adopted. Biomarker, mineralogical, and radiocarbon analyses of sediments and organic extracts from a shallow (13 cm) core from a hypersaline playa, Lake Tyrrell, southeastern Australia, produce a coherent age-depth curve beginning with modern microbial mats and extending to ~ 7500 cal yr BP. These analyses are furthermore used to identify and constrain the timing of the most recent change in hydrological regime at Lake Tyrrell, a shift from a clay deposit to the precipitation of evaporitic sands occurring at some time between ~ 4500 and 7000 yr. These analyses show the potential for widespread dating of hypersaline systems integrating the biomarker approach, reinforce the value of the radiocarbon content of biomarkers in understanding the flow of carbon in modern ecologies, and validate the temporal dimension of data provided by biomarkers when dating late Quaternary sediments.

  1. A Simple Acronym for Doing Calculus: CAL

    ERIC Educational Resources Information Center

    Hathaway, Richard J.

    2008-01-01

    An acronym is presented that provides students a potentially useful, unifying view of the major topics covered in an elementary calculus sequence. The acronym (CAL) is based on viewing the calculus procedure for solving a calculus problem P* in three steps: (1) recognizing that the problem cannot be solved using simple (non-calculus) techniques;…

  2. Evaluation of CalMHSA Student Mental Health Online Resources

    PubMed Central

    Sontag-Padilla, Lisa; Kase, Courtney Ann; Woodbridge, Michelle W.; Stein, Bradley D.

    2016-01-01

    Abstract Analysis of visitors to CalMHSA-funded student mental health websites shows that visitors at educational institutions comprised the largest audience segment and promotional campaigns likely increased traffic. PMID:28083438

  3. Spatial Databases for CalVO Volcanoes: Current Status and Future Directions

    NASA Astrophysics Data System (ADS)

    Ramsey, D. W.

    2013-12-01

    The U.S. Geological Survey (USGS) California Volcano Observatory (CalVO) aims to advance scientific understanding of volcanic processes and to lessen harmful impacts of volcanic activity in California and Nevada. Within CalVO's area of responsibility, ten volcanoes or volcanic centers have been identified by a national volcanic threat assessment in support of developing the U.S. National Volcano Early Warning System (NVEWS) as posing moderate, high, or very high threats to surrounding communities based on their recent eruptive histories and their proximity to vulnerable people, property, and infrastructure. To better understand the extent of potential hazards at these and other volcanoes and volcanic centers, the USGS Volcano Science Center (VSC) is continually compiling spatial databases of volcano information, including: geologic mapping, hazards assessment maps, locations of geochemical and geochronological samples, and the distribution of volcanic vents. This digital mapping effort has been ongoing for over 15 years and early databases are being converted to match recent datasets compiled with new data models designed for use in: 1) generating hazard zones, 2) evaluating risk to population and infrastructure, 3) numerical hazard modeling, and 4) display and query on the CalVO as well as other VSC and USGS websites. In these capacities, spatial databases of CalVO volcanoes and their derivative map products provide an integrated and readily accessible framework of VSC hazards science to colleagues, emergency managers, and the general public.

  4. M2 .50-cal. Multishot Capabilities at the US Army Research Laboratory

    DTIC Science & Technology

    2015-09-01

    a platform was designed to simulate the 2-round burst of the M2 .50-caliber Browning machine gun (BMG). The 2-round-burst cyclic rate was achieved...ARL-TN-0694 ● SEP 2015 US Army Research Laboratory M2 .50-cal. Multishot Capabilities at the US Army Research Laboratory by...longer needed. Do not return it to the originator. ARL-TN-0694 ● SEP 2015 US Army Research Laboratory M2 .50-cal. Multishot

  5. Holocene evolution of the Liaohe Delta, a tide-dominated delta formed by multiple rivers in Northeast China

    NASA Astrophysics Data System (ADS)

    He, Lei; Xue, Chunting; Ye, Siyuan; Laws, Edward Allen; Yuan, Hongming; Yang, Shixiong; Du, Xiaolei

    2018-02-01

    The Liaohe Delta in Northeast China is one of the ecologically important estuarine deltas in China. It has been formed via the accumulation of sediment discharged by four rivers in the Liaohe Plain that enter Liaodong Bay. Twenty-seven 30-40 m long cores recovered from the Liaohe Plain and Liaodong Bay were analyzed for sedimentary characteristics, grain size, foraminifera species, and ages determined by accelerator mass spectrometry (AMS) 14C to document the stratigraphical sequence and the spatio-temporal evolution of the Liaohe Delta. Our results revealed that the sedimentary environments have evolved from fluvial, tidal flat/estuarine, to neritic and finally to a deltaic environment since the Late Pleistocene. The Holocene transgression arrived at the present coastline at ∼8500 cal a BP and flooded the maximum area of land at ∼7000 cal a BP. A deltaic environment prevailed in this area after 7000 cal a BP. Bounded by the modern Liaohe River mouth, the present deltaic sedimentary system can be divided into the eastern and western components. The rate of seaward progradation of the eastern paleocoastline was estimated to be ∼8.6 m/a since 7000 cal a BP; the eastern cores in the present coastline began receiving the deltaic sediments at ∼5000 cal a BP. The rate of seaward progradation of the western paleocoastline was estimated to be only ∼2.8 m/a since 7000 cal a BP. The coastline on the western side began accumulating deltaic sediments about 2000 years later than the eastern coastline. Depocenter shifting was hypothesized to be the reason for the spatial differences in the sedimentary processes. However, the change of sediment fluxes of the western rivers due to climate changes and ancient human impacts might be the reason for the differences of the temporal evolution of the eastern and western sedimentary systems in the Liaohe Delta.

  6. A multi-proxy approach to understanding complex responses of salt-lake catchments to climate variability and human pressure: A Late Quaternary case study from south-eastern, Spain

    NASA Astrophysics Data System (ADS)

    Jones, Samantha Elsie; Burjachs, Francesc; Ferrer-García, Carlos; Giralt, Santiago; Schulte, Lothar; Fernández-López de Pablo, Javier

    2018-03-01

    This article focuses on a former salt lake in the upper Vinalopó Valley in south-eastern Spain. The study spans the Late Pleistocene through to the Late Holocene, although with particular focus on the period between 11 ka cal BP and 3000 ka cal BP (which spans the Mesolithic and part of the Bronze Age). High resolution multi-proxy analysis (including pollen, non pollen palynomorphs, grain size, X-ray fluorescence and X-ray diffraction) was undertaken on the lake sediments. The results show strong sensitivity to both long term and small changes in the evaporation/precipitation ratio, affecting the surrounding vegetation composition, lake-biota and sediment geochemistry. To summarise the key findings the main general trends identified include: 1) Hyper-saline conditions and low lake levels at the end of the Late Glacial 2) Increasing wetness and temperatures which witnessed an expansion of mesophilic woodland taxa, lake infilling and the establishment of a more perennial lake system at the onset of the Holocene 3) An increase in solar insolation after 9 ka cal BP which saw the re-establishment of pine forests 4) A continued trend towards increasing dryness (climatic optimum) at 7 ka cal BP but with continued freshwater input 5) An increase in sclerophyllous open woody vegetation (anthropogenic?), and increasing wetness (climatic?) is represented in the lake record between 5.9 and 3 ka cal BP 6) The Holocene was also punctuated by several aridity pulses, the most prominent corresponding to the 8.2 ka cal BP event. These events, despite a paucity of well dated archaeological sites in the surrounding area, likely altered the carrying capacity of this area both regionally and locally, particularly during the Mesolithic-Neolithic transition, in terms of fresh water supply for human/animal consumption, wild plant food reserves and suitable land for crop growth.

  7. High-resolution fluvial records of Holocene environmental changes in the Sahel: the Yamé River at Ounjougou (Mali, West Africa)

    NASA Astrophysics Data System (ADS)

    Lespez, L.; Le Drezen, Y.; Garnier, A.; Rasse, M.; Eichhorn, B.; Ozainne, S.; Ballouche, A.; Neumann, K.; Huysecom, E.

    2011-03-01

    The Yamé river, in the Bandiagara Plateau, Dogon Country, Mali, is characterised by extensive alluvial sedimentary records, particularly in the 1 km long Ounjougou reach where Holocene floodplain pockets are inset in the Pleistocene formations. These alluvial records have been investigated via geomorphologic fieldwork and sedimentologic and micromorphologic analyses and are supported by 79 radiocarbon dates. The alluvial deposits of the valley floor correspond to a vertical accretion of 3-10 m. The reconstruction of fluvial style changes provides evidence of four main aggradation periods. From 11,500 to 8760 cal. BP, the alluvial architecture and grain-size parameters indicate a wandering river. This period included phases of pulsed high-energy floods and avulsion related to a northward shift of the summer monsoon to around 14°N after 11,500 cal. BP. From 7800 to 5300 cal. BP, a swampy floodplain environment with standing water pools within a Sudanian savanna/woodland mosaic corresponds to the culmination of the Holocene humid period. From 3800 cal. BP onwards, rhythmic sedimentation attests to an increase in the duration and/or intensity of the dry season, giving a precise date for the local termination of the Holocene Optimum period. During the last two millennia and for the first time during the Holocene, the alluvial formations are progressively restricted whereas the colluvial deposits increase, indicating strong soil erosion and redeposition within the watershed related to an increase in human impact. Four major periods are characterised by incision (I1: ante 11,500, I2: 8760-7800; I3: 6790-6500 cal. BP; I4; 2400-1700 cal. BP) pointing to dramatic changes in fluvial style. They result from high-energy flood flows during dry spells and confirm the capacity of the floodplain pocket in the upstream reach of the Sahelian belt to record rapid Holocene climatic change.

  8. Local Spatial Heterogeneity of Holocene Carbon Accumulation throughout the Peat Profile of an Ombrotrophic Northern Minnesota Bog

    DOE PAGES

    McFarlane, Karis J.; Hanson, Paul J.; Iversen, Colleen M.; ...

    2018-05-30

    Here, we evaluated the spatial heterogeneity of historical carbon accumulation rates in a forested, ombrotrophic bog in Minnesota to aid understanding of responses to an ongoing decade-long warming manipulation. Eighteen peat cores indicated that the bog has been accumulating carbon for over 11,000 years, to yield 176±40 kg C m –2 to 225±58 cm of peat depth. Estimated peat basal ages ranged from 5100 to 11,100 cal BP. The long-term apparent rate of carbon accumulation over the entire peat profile was 22±2 kg C m –2yr –1. Plot location within the study area did not affect carbon accumulation rates, butmore » estimated basal ages were younger in profiles from plots closer to the bog lagg and farther from the bog outlet. In addition, carbon accumulation varied considerably over time. Early Holocene net carbon accumulation rates were 30±6 g C m –2yr –1. Around 3300 calendar BP, net carbon accumulation rates dropped to 15±8 g C m –2yr –1until the last century when net accumulation rates increased again to 74±57 g C m –2yr –1. During this period of low accumulation, regional droughts may have lowered the water table, allowing for enhanced aerobic decomposition and making the bog more susceptible to fire. These results suggest that experimental warming treatments, as well as a future warmer climate may reduce net carbon accumulation in peat in this and other southern boreal peatlands. Furthermore, our we caution against historical interpretations extrapolated from one or a few peat cores.« less

  9. Local Spatial Heterogeneity of Holocene Carbon Accumulation throughout the Peat Profile of an Ombrotrophic Northern Minnesota Bog

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    McFarlane, Karis J.; Hanson, Paul J.; Iversen, Colleen M.

    Here, we evaluated the spatial heterogeneity of historical carbon accumulation rates in a forested, ombrotrophic bog in Minnesota to aid understanding of responses to an ongoing decade-long warming manipulation. Eighteen peat cores indicated that the bog has been accumulating carbon for over 11,000 years, to yield 176±40 kg C m –2 to 225±58 cm of peat depth. Estimated peat basal ages ranged from 5100 to 11,100 cal BP. The long-term apparent rate of carbon accumulation over the entire peat profile was 22±2 kg C m –2yr –1. Plot location within the study area did not affect carbon accumulation rates, butmore » estimated basal ages were younger in profiles from plots closer to the bog lagg and farther from the bog outlet. In addition, carbon accumulation varied considerably over time. Early Holocene net carbon accumulation rates were 30±6 g C m –2yr –1. Around 3300 calendar BP, net carbon accumulation rates dropped to 15±8 g C m –2yr –1until the last century when net accumulation rates increased again to 74±57 g C m –2yr –1. During this period of low accumulation, regional droughts may have lowered the water table, allowing for enhanced aerobic decomposition and making the bog more susceptible to fire. These results suggest that experimental warming treatments, as well as a future warmer climate may reduce net carbon accumulation in peat in this and other southern boreal peatlands. Furthermore, our we caution against historical interpretations extrapolated from one or a few peat cores.« less

  10. CAMPARE and Cal-Bridge: Two Institutional Networks Increasing Diversity in Astronomy

    NASA Astrophysics Data System (ADS)

    Rudolph, Alexander L.; Impey, Chris David; Phillips, Cynthia B.; Povich, Matthew S.; Prather, Edward E.; Smecker-Hane, Tammy A.

    2015-01-01

    We describe two programs, CAMPARE and Cal-Bridge, with the common mission of increasing participation of groups traditionally underrepresented in astronomy, particularly underrepresented minorities and women, through summer research opportunities, in the case of CAMPARE, scholarships in the case of Cal-Bridge, and significant mentoring in both programs, leading to an increase in their numbers successfully pursuing a PhD in the field.CAMPARE is an innovative REU-like summer research program, currently in its sixth year, comprising a network of comprehensive universities and community colleges in Southern California and Arizona (most of which are minority serving institutions), and ten major research institutions (University of Arizona Steward Observatory, the SETI Institute, JPL, Caltech, and the five Southern California UC campuses, UCLA, UCI, UCSD, UCR, and UCSB).In its first five summers, CAMPARE sent a total of 49 students from 10 different CSU and community college campuses to 5 research sites of the program. Of these 49 participants, 25 are women and 24 are men; 22 are Hispanic, 4 are African American, and 1 is Native American, including 6 female Hispanic and 2 female African-American participants. Twenty-one (21) CAMPARE participants have graduated from college, and more than half (11) have attended or are attending a graduate program, including 8 enrolled in PhD or Master's-to-PhD programs. Over twenty CAMPARE students have presented at the AAS and other national meetings.The Cal-Bridge program is a diverse network of higher education institutions in Southern California, including 5 UC campuses, 8 CSU campuses, and 7 community colleges dedicated to the goal of increasing the number of underrepresented minority and female students attending graduate school in astronomy or related fields. We have recently selected our inaugural group of five 2014 Cal-Bridge Scholars, including four women (two Hispanic and one part Native American), and one Hispanic man

  11. CAMPARE and Cal-Bridge: Two Institutional Networks Increasing Diversity in Astronomy

    NASA Astrophysics Data System (ADS)

    Rudolph, Alexander L.; Impey, Chris David; Phillips, Cynthia B.; Povich, Matthew S.; Prather, Edward E.; Smecker-Hane, Tammy A.

    2015-01-01

    We describe two programs, CAMPARE and Cal-Bridge, with the common mission of increasing participation of groups traditionally underrepresented in astronomy, particularly underrepresented minorities and women, through summer research opportunities, in the case of CAMPARE, scholarships in the case of Cal-Bridge, and significant mentoring in both programs, leading to an increase in their numbers successfully pursuing a PhD in the field.CAMPARE is an innovative REU-like summer research program, currently in its sixth year, comprising a network of comprehensive universities and community colleges in Southern California and Arizona (most of which are minority serving institutions), and ten major research institutions (University of Arizona Steward Observatory, the SETI Institute, JPL, Caltech, and the five Southern California UC campuses, UCLA, UCI, UCSD, UCR, and UCSB).In its first five summers, CAMPARE sent a total of 49 students from 10 different CSU and community college campuses to 5 research sites of the program. Of these 49 participants, 25 are women and 24 are men; 22 are Hispanic, 4 are African American, and 1 is Native American, including 6 female Hispanic and 2 female African-American participants. Twenty-one (21) CAMPARE participants have graduated from college, and more than half (11) have attended or are attending a graduate program, including 8 enrolled in PhD or Master's-to-PhD programs. Over twenty CAMPARE students have presented at the AAS and other national meetings.The Cal-Bridge program is a diverse network of higher education institutions in Southern California, including 5 UC campuses, 8 CSU campuses, and 7 community colleges dedicated to the goal of increasing the number of underrepresented minority and female students attending graduate school in astronomy or related fields. We have recently selected our inaugural group of five 2014 Cal-Bridge Scholars, including four women (two Hispanic and one part Native American), and one Hispanic man

  12. BP pledges to cut emissions

    NASA Astrophysics Data System (ADS)

    Showstack, Randy

    British Petroleum (BP), one of the world's biggest oil companies that could become even bigger if a merger with Amoco is approved, announced on September 18 that it will cut its emissions of greenhouse gases by 10% from a 1990 baseline of 40 million tons of carbon dioxide between now and the year 2010.The target, which is double the amount of emissions reductions that industrialized nations agreed to under the Kyoto protocol on climate change, will now stand next to BP's financial targets, said John Browne, group chief executive of BP.

  13. Holocene glaciation of the central Sierra Nevada, California

    NASA Astrophysics Data System (ADS)

    Bowerman, Nicole D.; Clark, Douglas H.

    2011-05-01

    Sediment cores from two bedrock-dammed lakes in North Fork Big Pine Creek, Sierra Nevada, California, preserve the most detailed and complete record of Holocene glaciation yet recovered in the region. The lakes are fed by outwash from the Palisade Glacier, the largest (˜1.3 km 2) and presumably longest-lived glacier in the range, and capture essentially all of the rock flour it produces. Distinct late-Holocene (Matthes) and late-Pleistocene (Recess Peak) moraines lie between the modern glacier and the lakes. The lakes have therefore received continuous sedimentation from the basin since the retreat of the Tioga glacier (Last Glacial Maximum) and capture rock flour related to all post-LGM advances. A total of eight long cores (up to 5.5 m sediment depth) and one short surface sediment short core preserve a coherent record of fluctuating rock flour flux to the lakes through the Holocene. Age constraints on rock flour spikes in First and Second lakes based on 31 14C-dated macrofossils indicate Holocene glaciation began ˜3200 cal yr B P, followed by a possible glacier maximum at ˜2800 cal yr B P and four distinct glacier maxima at ˜2200, ˜1600, ˜700 and ˜250-170 cal yr. B.P., the most recent maximum being the largest. Reconstruction of the equilibrium-line altitudes (ELA) associated with each distinct advance recorded in the moraines (Recess Peak, Matthes, and modern) indicates ELA depressions (relative to modern) of ˜250 m and 90 m for Recess Peak and Matthes advances, respectively. These differences represent decreases in summer temperatures of 1.7-2.8 °C (Recess Peak) and 0.2-2° (Matthes), and increases in winter precipitation of 22-34 cm snow water equivalent (s.w.e.) (Recess Peak) and 3-26 cm s.w.e. (Matthes) compared to modern conditions. Although small, these changes are significant and similar to those noted in the Cascade Range to the north, and represent a significant departure from historical climate trends in the region.

  14. Strong Altitudinal Control on Local Glacier's Response to Holocene Climate Change in Southwest Greenland

    NASA Astrophysics Data System (ADS)

    Larsen, N. K.; Levy, L.; Strunk, A.; Bjork, A. A.; Olsen, J.; Jeppesen, E.; Lauridsen, T.; Davidson, T. A.

    2017-12-01

    The sensitivity of glaciers and ice caps (GICs) in Greenland to prolonged warm periods is poorly constrained and geological records documenting the long-term glacial history are needed to put recent observations into a broader perspective. Here we report the results from three proglacial lakes where fluctuations in local glaciers located at different altitudes in Kobbefjord, southwest Greenland have been recorded. Our results show that the lakes received meltwater from the initial deglaciation of the area 9.2 cal. ka BP until 8.7-7.9 cal. ka BP when the meltwater input ceased as the glaciers most likely disappeared. Regrowth of glaciers began again at 5.5 cal. ka BP at 1,370 m a.s.l., 3.6 cal. ka at 1,170 m a.s.l., and 1.6 cal. ka BP at 1,000 m a.s.l., clearly reflecting strong altitudinal control of the GIC response to Neoglacial cooling. Our results highlight that GICs in Kobbefjord, southwest Greenland are primarily influenced by changes in summer air temperatures and winter precipitation and that they are facing a rapid decay that most likely will result in their disappearance within the next centuries as a consequence of global warming.

  15. Paleoseismic investigations at the Cal thrust fault, Mendoza, Argentina

    NASA Astrophysics Data System (ADS)

    Salomon, Eric; Schmidt, Silke; Hetzel, Ralf; Mingorance, Francisco

    2010-05-01

    Along the active mountain front of the Andean Precordillera between 30°S and 34°S in western Argentina several earthquakes occurred in recent times, including a 7.0 Ms event in 1861 which destroyed the city of Mendoza and killed two thirds of its population. The 1861 event and two other earthquakes (Ms = 5.7 in 1929 and Ms = 5.6 in 1967) were generated on the Cal thrust fault, which extends over a distance of 31 km north-south and runs straight through the center of Mendoza. In the city, which has now more than 1 million inhabitants, the fault forms a 3-m-high fault scarp. Although the Cal thrust fault poses a serious seismic hazard, the paleoseismologic history of this fault and its long-term slip rate remains largely unknown (Mingorance, 2006). We present the first results of an ongoing paleoseismologic study of the Cal thrust at a site located 5 km north of Mendoza. Here, the fault offsets Late Holocene alluvial fan sediments by 2.5 m vertically and exhibits a well developed fault scarp. A 15-m-long and 2-3-m-deep trench across the scarp reveals three east-vergent folds that we interpret to have formed during three earthquakes. Successive retrodeformation of the two youngest folds suggests that the most recent event (presumably the 1861 earthquake) caused ~1.1 m of vertical offset and ~1.8 m of horizontal shortening. For the penultimate event we obtain a vertical offset of ~0.7 m and a horizontal shortening of ~1.9 m. A vertical displacement of ~0.7 m observed on a steeply west-dipping fault may be associated with an older event. The cumulative vertical offset of 2.5 m for the three inferred events is in excellent agreement with the height of the scarp. Based on the retrodeformation of the trench deposits the fault plane dips ~25° to the west. In the deepest part of the trench evidence for even older seismic events is preserved beneath an angular unconformity that was formed during a period of erosion and pre-dates the present-day scarp. Dating of samples to

  16. CalTOX (registered trademark), A multimedia total exposure model spreadsheet user's guide. Version 4.0(Beta)

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    McKone, T.E.; Enoch, K.G.

    2002-08-01

    CalTOX has been developed as a set of spreadsheet models and spreadsheet data sets to assist in assessing human exposures from continuous releases to multiple environmental media, i.e. air, soil, and water. It has also been used for waste classification and for setting soil clean-up levels at uncontrolled hazardous wastes sites. The modeling components of CalTOX include a multimedia transport and transformation model, multi-pathway exposure scenario models, and add-ins to quantify and evaluate uncertainty and variability. All parameter values used as inputs to CalTOX are distributions, described in terms of mean values and a coefficient of variation, rather than asmore » point estimates or plausible upper values such as most other models employ. This probabilistic approach allows both sensitivity and uncertainty analyses to be directly incorporated into the model operation. This manual provides CalTOX users with a brief overview of the CalTOX spreadsheet model and provides instructions for using the spreadsheet to make deterministic and probabilistic calculations of source-dose-risk relationships.« less

  17. Delayed deglaciation or extreme Arctic conditions 21-16 cal. kyr at southeastern Laurentide Ice Sheet margin?

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Peteet, D. M.; Beh, M.; Orr, C.

    The conventionally accepted ages of the Last Glacial Maximum (LGM) retreat of the southeastern Laurentide Ice Sheet (LIS) are 26–21 cal. kyr (derived from bulk-sediment radiocarbon ages) and 28–23 cal. kyr (varve estimates). By utilizing accelerator mass spectrometry (AMS) 14C dating of earliest macrofossils in 13 lake/bog inorganic clays, we find that vegetation first appeared on the landscape at 16–15 cal. kyr, suggesting ice had not retreated until that time. The gap between previous age estimates and ours is significant and has large implications for our understanding of ocean-atmosphere linkages. Older ages imply extreme Arctic conditions for 9–5 cal kyr;more » a landscape with no ice, yet no deposition in lakes. Also, our new AMS chronology of LIS retreat is consistent with marine evidence of deglaciation from the N. Atlantic, showing significant freshwater input and sea level rise only after 19 cal kyr with a cold meltwater lid, perhaps delaying ice melt.« less

  18. Delayed deglaciation or extreme Arctic conditions 21-16 cal. kyr at southeastern Laurentide Ice Sheet margin?

    DOE PAGES

    Peteet, D. M.; Beh, M.; Orr, C.; ...

    2012-06-15

    The conventionally accepted ages of the Last Glacial Maximum (LGM) retreat of the southeastern Laurentide Ice Sheet (LIS) are 26–21 cal. kyr (derived from bulk-sediment radiocarbon ages) and 28–23 cal. kyr (varve estimates). By utilizing accelerator mass spectrometry (AMS) 14C dating of earliest macrofossils in 13 lake/bog inorganic clays, we find that vegetation first appeared on the landscape at 16–15 cal. kyr, suggesting ice had not retreated until that time. The gap between previous age estimates and ours is significant and has large implications for our understanding of ocean-atmosphere linkages. Older ages imply extreme Arctic conditions for 9–5 cal kyr;more » a landscape with no ice, yet no deposition in lakes. Also, our new AMS chronology of LIS retreat is consistent with marine evidence of deglaciation from the N. Atlantic, showing significant freshwater input and sea level rise only after 19 cal kyr with a cold meltwater lid, perhaps delaying ice melt.« less

  19. The Effect of the Younger Dryas on Paleoindian Occupations in Eastern North America Evidence from Artifactual, Pollen, and Radiocarbon Records

    NASA Astrophysics Data System (ADS)

    Anderson, D. G.; Meeks, S. C.; Miller, D. S.; Yerka, S. J.; Gillam, J. C.; Goodyear, A. C.; Johanson, E. N.; West, A.

    2008-12-01

    centuries of the Younger Dryas are decidedly uncommon in the Southeast and over the larger region. In a sample of 218 dates from the Southeast and adjoining areas, only seven fall between 10,900 and 10,570 14C yr BP or between ca. 12,850 and 12,600 cal yr BP, and all of these are at the recent end of this range, between 10,570 and 10,710 14C yr BP. In the Southeast, at least, there appears to be a ca. 250-300 year 'gap' in the distribution of radiocarbon dates, with few reported from ca. 12,900-12,600 cal yr BP. Finally, analyses of fossil pollen records from the southeastern United States, although admittedly few in number, indicate that major vegetational shifts, both abrupt and characterized by oscillations, were occurring across the region during the Pleistocene/Holocene transition and that these shifts appear to be synchronic or quasi-synchronic with the Younger Dryas. The results suggests that the earliest inhabitants in the southeastern United States were faced with an environment that was anything but stable.

  20. The influence of changes in soil moisture in association with geomorphic change on the formation of a subalpine coniferous forest on Mt. Akita-Komagatake, northern Japan

    NASA Astrophysics Data System (ADS)

    Konno, A.

    2015-12-01

    The coniferous forest (largely composed of Abies mariesii) is presently the typical vegetation of the subalpine zone in Japan. Pollen analysis revealed that few A. mariesii were present during the last glacial period, and the species began to expand to the subalpine zone during the Holocene (Morita, 1992). However, on Mt. Akita-Komagatake in northern Japan, the expected predominance of A. mariesii is not extensively observed, and the predominant vegetation is instead the dwarf bamboo (Sasa kurilensis). It is unknown why the area under coniferous forest is small in this region. Therefore, I examined this issue from the perspectives of (1) distribution of vegetation, (2) geomorphology, (3) soil moisture, and (4) vegetation history. (1) Precise digital elevation model data and photographic interpretation showed that this coniferous forest was densely distributed in a flat segment considered to be formed by a landslide; (2) this landslide is thought to have occurred up to 3,699 ± 26 yr BP because a boring-core specimen from the landslide included the AK-3 tephra layer (2,300-2,800 yr BP: Wachi et al, 1997) and the radiocarbon date of the lowermost humic soil layer was 3,699 ± 26 yr BP; (3) the soil in the forest area had higher volumetric water content than that in the non-forest area; and (4) phytolith analysis revealed that the main species in the study site was initially dwarf bamboo, but coniferous forest replaced it after the Towada-a tephra (1035 cal. BP, Machida and Arai, 1992) layer fell. These results suggest that soil water conditions changed because of the formation of the flat segment by the landslide, and the coniferous forest was consequently established. However, the landslide only indirectly affected the formation of the coniferous forest, because the forest developed over several thousand years after the landslide occurred. In other words, more direct reasons for the establishment of the coniferous forest may involve changes in soil moisture. This