Science.gov

Sample records for holocene lacustrine carbonate

  1. A lacustrine carbonate record of Holocene seasonality and climate

    USGS Publications Warehouse

    Wittkop, Chad A.; Teranes, Jane L.; Dean, Walter E.; Guilderson, Thomas P.

    2009-01-01

    Annually laminated (varved) Holocene sediments from Derby Lake, Michigan, display variations in endogenic calcite abundance reflecting a long-(millennial-scale) decrease in burial punctuated with frequent short- (decadal-scale) oscillations due to carbonate dissolution. Since 6000 cal yr B.P., sediment carbonate abundance has followed a decreasing trend while organic-carbon abundance has increased. The correlation between organic-carbon abundance and the sum of March-April-October-November insolation has an r2 value of 0.58. We interpret these trends to represent a precession-driven lengthening of the Holocene growing season that has reduced calcite burial by enhancing net annual organic-matter production and associated calcite dissolution. Correlations with regional paleoclimate records suggest that changes in temperature and moisture balance have impacted the distribution of short- oscillations in carbonate and organic-matter abundance superimposed on the precession-driven trends.

  2. Regional Atmospheric Circulation Change in the North Pacific During the Holocene Inferred from Lacustrine Carbonate Oxygen Isotopes, Yukon Territory, Canada

    NASA Astrophysics Data System (ADS)

    Anderson, L.; Abbott, M. B.; Finney, B. P.; Burns, S. J.

    2004-12-01

    Analyses of sediment cores from Jellybean Lake, a small, hydrologically-open groundwater-fed lake, provide a record of changes in North Pacific atmospheric circulation for the last 7500 years at twenty to thirty-year resolution. A regional isotope hydrology study in the southern Yukon indicates that the oxygen isotope composition of water from Jellybean Lake reflects the oxygen isotope composition of mean annual precipitation. Thus, the oxygen isotope history of Jellybean Lake inferred from sedimentary carbonate oxygen isotope ratios suggests multi-decadal shifts in the oxygen isotope composition of mean annual precipitation superimposed on century and millennial trends. Recent fluctuations of Jellybean oxygen isotopes correlate well with changes in the North Pacific Index, a measure of the intensity and position of the Aleutian Low. We propose that oxygen isotope variability of precipitation in the interior of the Yukon is related to the degree of fractionation during moisture transport from the Gulf of Alaska across the St Elias Mountains that is ultimately controlled by the position and strength of the Aleutian Low. Following this model, Aleutian Low intensity during the early to middle Holocene was relatively reduced and increasing intensity coincided with the initial onset of Neoglacial advances. Rapid shifts during the last two millennia corresponds with glacial activity, changes in North Pacific salmon abundance, and shifts in atmospheric circulation over the Beaufort Sea.

  3. Regional atmospheric circulation change in the North Pacific during the Holocene inferred from lacustrine carbonate oxygen isotopes, Yukon Territory, Canada

    NASA Astrophysics Data System (ADS)

    Anderson, Lesleigh; Abbott, Mark B.; Finney, Bruce P.; Burns, Stephen J.

    2005-07-01

    Analyses of sediment cores from Jellybean Lake, a small, evaporation-insensitive groundwater-fed lake, provide a record of changes in North Pacific atmospheric circulation for the last ˜7500 yr at 5- to 30-yr resolution. Isotope hydrology data from the southern Yukon indicate that the oxygen isotope composition of water from Jellybean Lake reflects the composition of mean-annual precipitation, δ 18O p. Recent changes in the δ 18O of Jellybean sedimentary calcite (δ 18O ca) correspond to changes in the North Pacific Index (NPI), a measure of the intensity and position of the Aleutian Low (AL) pressure system. This suggests that δ 18O p variability was related to the degree of fractionation during moisture transport from the Gulf of Alaska across the St. Elias Mountains and that Holocene shifts were controlled by the intensity and position of the AL. Following this model, between ˜7500 and 4500 cal yr B.P., long-term trends suggest a predominantly weaker and/or westward AL. Between ˜4500 and 3000 cal yr B.P. the AL shifted eastward or intensified before shifting westward or weakening between ˜3000 and 2000 cal yr B.P. Rapid shifts eastward and/or intensification occurred ˜1200 and 300 cal yr B.P. Holocene changes in North Pacific atmospheric circulation inferred from Jellybean Lake oxygen isotopes correspond with late Holocene glacial advances in the St. Elias Mountains, changes in North Pacific salmon abundance, and shifts in atmospheric circulation over the Beaufort Sea.

  4. Climate Change During the Late Glacial and Early Holocene From Lough Monreagh, Western Ireland: Evidence From Carbon and Oxygen Isotope Values of Lacustrine Marl

    NASA Astrophysics Data System (ADS)

    Manchester, C. W.; Patterson, W. P.

    2008-12-01

    Lake sediment is an archive of climate variability reconstructed using proxy data such as stable isotope values and trace element chemistry. These proxy data permit reconstruction of temperature, precipitation, and terrestrial vegetation variability through time. Stable oxygen isotope values conflate temperature and water oxygen isotope variability, while carbon isotope values of marl provide a record of variability in dissolved inorganic carbon (DIC). An 8.67m core, obtained from Lough Monreagh, Western Ireland, contains marl ranging in age from about 17,300-7,894 cal yr B.P. Marl was analyzed at 1mm resolution for stable oxygen and carbon isotope values. Variation in sedimentation rate results in samples that represent up to five years at minimum resolution and as little as four months at highest resolution. Oxygen isotope values decrease at 13,500 yr B.P. from -3.5 to -5 per mil VPDB inferring a decrease in temperature followed by a warming period consistent with previous interpretations of the Older Dryas. Another decrease in oxygen isotope values (-3.9 to -7.0 per mil VPDB) occurs from 12,800-11,500 yr B.P. indicating a significant decrease in temperature consistent with the Younger Dryas. Carbon isotope values increase between 17,200-14,000 yr B.P. from 3.6 to 6.0 per mil VPDB suggesting high productivity is forcing the carbon isotope values of DIC higher than bedrock values, contrary to ostracod population data that suggest low productivity. Carbon isotope values decrease between 12,800-11,500 from 4.0 to 3.0 per mil VPDB coincident with the Younger Dryas clay layer, a time where marl was not produced in the lake. A 6 per mil decrease in carbon isotope values between 11,262-10860 yr B.P. from 4 to -2 per mil VPDB indicates a significant increase in terrestrial vegetation. Sample to sample variability nearing the top of the core is higher due to increased sedimentation rate and concomitantly the sample resolution increases. This study represents the highest

  5. Sr Isotope Analysis of Lacustrine Fossils Reveals Paleohydrological Reorganisation in the Turkana Basin Through the Holocene.

    NASA Astrophysics Data System (ADS)

    Vonhof, H.; Lubbe, J. V. D.; Joordens, J. J.; Feibel, C. S.; Junginger, A.; Garcin, Y.; Krause-Nehring, J.; Beck, C.; Johnson, T. C.

    2015-12-01

    Lake Turkana in northern Kenya is one of the largest lakes in the East African Rift System (EARS) that experienced significant climate-driven lake level variation over the Holocene. Arguably the most important feature of Holocene climate change in the EARS is the termination of the African Humid Period (AHP), that caused a ~70 meter lake level drop in Lake Turkana. The precise hydrological response to the termination of the AHP is potentially complex, because Lake Turkana lies at the cross roads of two large atmospheric convection systems; the Intertropical Convergence Zone (ITCZ) and the Congo Air Boundary (CAB). Shifting of these atmospheric systems around the end of the AHP dramatically rearranged spatial rainfall patterns in the Turkana Basin catchment, causing changes in relative runoff contributions from the different sub-catchments in the Turkana Basin. We here present a Holocene Turkana lake water Sr-isotope reconstruction, based on the analysis of well-dated lacustrine ostracods and shells. This reconstruction reveals consistently high Sr isotope values for the early Holocene, followed by a remarkable drop of Sr isotope ratios around the AHP termination. We interpret this pattern to represent a westward shift in the location of the CAB, leading to the reduction and eventual shutdown of runoff contribution from the Chew Bahir Basin to the Turkana Basin at the end of the AHP. The record demonstrates the exceptional suitability of Sr isotope data for this type of paleohydrological reconstructions. This is mainly due to the chemically conservative Sr-isotope mass balance in EARS lake systems, which is insensitive to environmental change at seasonal timescales that so often overprints the longer term climate signal in stable (oxygen and carbon) isotope records of these lakes. Furthermore, when Sr-isotope signatures of the contributing sub-catchments are known, the observed Sr isotope trends can be interpreted in terms of spatial shifts in climate driven runoff

  6. A multi-proxy lacustrine record of Holocene climate change in SW Patagonia, Chile

    NASA Astrophysics Data System (ADS)

    LeRoy, S. L.; Mucciarone, D. A.; Dunbar, R. B.

    2014-12-01

    One of the largest uncertainties in the Holocene ocean-atmosphere carbon cycle is the role of the Southern Ocean (SO) and subpolar seas in controlling atmospheric CO2 levels. The strength and position of the westerly winds is thought to control rates of CO2 exchange as well as depth of ventilation. Secondarily, through their control on the large scale geostrophic circulation, the westerlies influence the position of major ocean frontal boundaries as well as stratification in the Southern Ocean - additional controls on SO carbon uptake. However, little is known about westerly wind variability over the Holocene. Southern Patagonia is an ideal locality for addressing this uncertainty, as it is the only major landmass that extends into the southern westerly wind field. In particular, lake and fjord environments hold potential for reconstructing precipitation, which is closely correlated with westerly wind strength in this region. Here we present a multi-proxy lacustrine sediment core record from Lago Sarmiento (51.06˚S, 72.91˚W), a large, closed-basin lake in southwest Chilean Patagonia. We observe highly variable C:N ratios between ~12,500 and ~6,000 14C yr BP, indicating recurrent transitions from grassland to forest. We measured a steady increase in the C:N ratio from ~6,000 14C yr BP to present, indicating a sustained shift from grassland to the modern Nothofagus forest and more humid conditions. We observe a general decreasing trend in bulk carbonate δ18O since ~4,000 14C yr BP, which we interpret as a progressive increase in westerly wind intensity and associated tendency towards positive water balance. Weight percent bulk carbonate varies greatly, with a strong decreasing trend in the early Holocene, followed by an increasing trend during the mid-Holocene, and a dip followed by a short rise in the late Holocene. Comparison with other records from southern Patagonia and Antarctica is improving our understanding of the forcing mechanisms driving changes in the

  7. Holocene fire history reconstruction using Tibetan lacustrine sediments

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  8. Lacustrine carbonates of the northern Great Plains of Canada

    NASA Astrophysics Data System (ADS)

    Last, Fawn M.; Last, William M.

    2012-11-01

    The northern Great Plains of western Canada, a vast region stretching from the Precambrian Shield east of Winnipeg, Manitoba, westward for some 1600 km to the foothills of the Rocky Mountains, contains literally millions of lakes and wetlands. Although often characterized as a saline, Na-SO4 system, in fact the wide range of water chemistries exhibited by the lakes results in an unusually large diversity of sediment composition. Despite a long history of limnogeological study, it is only recently that the spectrum of carbonate minerals and sedimentological processes in these lakes has been realized. About 30 species of carbonate minerals have been reported from the modern and Holocene sediment of about 50 basins in the region. The ubiquity of detrital calcite and dolomite is a legacy of the carbonate bedrock and carbonate-rich glacial sediments. Elevated salinities of the lakes, together with high alkalinities, productivity, and pH values, act in concert to create thermodynamically saturated or supersaturated conditions with respect to many carbonate minerals. The most common non-detrital components are Mg-calcite, aragonite and non-stoichiometric dolomite. Many of the basins whose brines have very high Mg/Ca ratios also contain hydromagnesite, magnesite, and nesquehonite. Although not common, sodium carbonates, including trona, natron and nahcolite, also occur in some of the hypersaline lakes. Because of their great range of formative conditions, carbonates have been the workhorse for much of the physical and geochemical paleolimnology in the Canadian Great Plains. However, the often-difficult task of distinguishing endogenic lacustrine carbonates from allogenic and authigenic minerals has limited the use of carbonate stratigraphy in the region. Despite this problem, the carbonates have been useful in deciphering (i) past changes in hydrology and drainage basin characteristics, (ii) lake level and water column stratification fluctuations, and (iii) water chemistry

  9. A Clumped Isotope Calibration for Lacustrine Carbonates

    NASA Astrophysics Data System (ADS)

    Mitsunaga, B. A.; Mering, J. A.; Petryshyn, V. A.; Dunbar, R. B.; Cohen, A. S.; Liu, X.; Kaufman, D. S.; Eagle, R.; Tripati, A.

    2014-12-01

    Our capacity to understand Earth's environmental history is highly dependent on the accuracy of past climate reconstructions. Unfortunately, many terrestrial proxies—tree rings, speleothems, leaf margin analyses, etc.—are influenced by the effects of both temperature and precipitation. Methods that can isolate the effects of temperature alone are needed, and clumped isotope thermometry has the potential to be a useful tool for determining terrestrial climates. Multiple studies have shown that the fraction of 13C—18O bonds in carbonates is inversely related to the temperature at which the rocks formed and may be a useful proxy for reconstructing temperatures on land. An in-depth survey of lacustrine carbonates, however, has not yet been published. Therefore we have been measuring the abundance of 13C18O16O in the CO2 produced by the dissolution of modern lake samples' carbonate minerals in phosphoric acid and comparing results to independently known estimates of lake water temperature and air temperature. Some of the sample types we have investigated include endogenic carbonates, freshwater gastropods, bivalves, microbialites, and ooids.

  10. Holocene environmental changes in northern Lebanon as inferred from a multiproxy study on lacustrine-palustrine sediment

    NASA Astrophysics Data System (ADS)

    Vidal, L.; Hage-Hassan, J.; Gasse, F. A.; Demory, F.; van Campo, E.; Develle, A.; Elias, A.

    2013-12-01

    The reconstruction of the Levantine post-glacial environmental evolution is essential to understand the interactions between variability of regional water cycle, dynamics of the global climate, and cultural evolution. Here, we present an Holocene record from the karstic Yammouneh basin (34.06N-34.09N; 36.0E-36.03E, 1360 m a.s.l.), located on the eastern flank of Mount Lebanon (northern Levant). Two new sedimentary profiles (from 1 gully and 1 trench) complement former data from 2 trenches and 1 core collected in different points of the basin (Daeron et al., 2007; Develle et al., 2009, 2010). A total of 42 AMS 14C dating (partly carbonized wood) provide a solid chronology from the YD to present. Holocene sediments (1.5 to 3.6 m thick) consist of pale lacustrine chalk interrupted by an ash layer and remarkable centimetric beds of ocher to dark brown silty clays used, in addition to 14C ages, as stratigraphical markers. Lacustrine biogenic remains are diversified and abundant (ostracods, gastropods, charophytes, chlorophyceae, plant debris...) all reflecting a freswater, generally shallow waterbody. We analysed the sediment mineralogy, TOM contents, magnetic properties (magnetic susceptibility and its frequency dependence), pollen and calcite oxygen isotope composition derived from ostracod shells. Results reveal the following main features : 1- intervals dominated by authigenic calcite suggest that the major water supply was the karstic springs, which still deliver Ca-rich water and low surface runoff; 2- the lake oxygen isotope composition has been impacted by the source isotope composition throughout the Holocene and by increased inland rainfall during the early Holocene; 3- a decideous oak forest, implying much more soil water availability than today, was developed around the lake from ca. 11.5 to 9.5 kyr (the very bad pollen preservation after 8.3 kyr reflects oxidation or frequent oscillations of the water level); 4- four paleosols evidenced from lithofacies and

  11. Lacustrine records of continental climate in northwest Greenland through the Holocene and Last Interglacial

    NASA Astrophysics Data System (ADS)

    McFarlin, J. M.; Axford, Y.; Osburn, M. R.; Lasher, G. E.; Francis, D. R.; Kelly, M. A.; Osterberg, E. C.

    2015-12-01

    Lake sediment records provide opportunities for high-resolution observations of paleoclimate that help to place modern climate change in geologic context. Here we present a terrestrial record of July air temperature for northwest Greenland (Nunatarssuaq, ~25 km east of the Thule Air Base) through the Holocene and a prior warm period, inferred from subfossil insect remains (Chironomidae) preserved in lacustrine sediments. In addition, we discuss ongoing work in characterizing the sources and isotopic composition of leaf waxes preserved in the same sediments. Multiple parallel sediment cores were collected in the summers of 2012 and 2014 from Wax Lips Lake (informal name), a non-glacial lake situated <2 km from the current margin of the Greenland Ice Sheet. Radiocarbon ages were obtained on aquatic mosses from intact laminae, and indicate that the record spans the Holocene, beginning at ~10.4 ka, as well as an interval beyond the range of 14C (>44 ka) and thus predates the Last Glacial Maximum (LGM). Our results demonstrate temperatures warmer than present through the early and mid Holocene followed by cooling in the late Holocene. Material that pre-dates the LGM contains insect assemblages indicating temperatures warmer than the warmest millennia of the Holocene. We interpret this material as most likely dating to the Last Interglacial Period (MIS 5). Along with assemblages of Chironomidae, we find subfossil Chaoboridae in one section of the pre-LGM sediments, suggesting exceptionally warm conditions based upon the distribution of modern-day Chaoborus. We find abundant n-alkanes and n-acids are preserved in the Holocene and pre-LGM sediments, allowing for complementary compound-specific δD analyses and identification of organic matter source in addition to chironomid derived temperature records.

  12. Holocene environmental changes in northern Lebanon as inferred from a multiproxy study on lacustrine-palustrine sediment

    NASA Astrophysics Data System (ADS)

    Vidal, Laurence; Jenna, Hage-Hassen; Demory, François; Develle, Anne-Lise; van Campo, Elise; Elias, Ata

    2016-04-01

    The reconstruction of the Levantine post-glacial environmental evolution is essential to understand the interactions between variability of regional water cycle, dynamics of the global climate, and cultural evolution. We present a paleolacustrine record from the karstic Yammouneh basin (34.06N-34.09N; 36.0E-36.03E, 1360 m a.s.l.), located on the eastern flank of Mount Lebanon (northern Levant). Holocene sediments (retrieved from gully and a trenbch) (1.5 to 3.6 m thick) consist of pale lacustrine chalk interrupted by an ash layer and remarkable centimetric beds of ocher to dark brown silty clays used, in addition to 14C ages, as stratigraphical markers. Lacustrine biogenic remains are diversified and abundant (ostracods, gastropods, charophytes, chlorophyceae, plant debris…) all reflecting a freswater, generally shallow waterbody. We analysed the sediment mineralogy and geochemistry, TOM contents, magnetic properties, pollen and calcite oxygen isotope composition derived from ostracod shells. These sequences are compared to former data from 2 trenches and 1 core collected in different points of the basin (Daeron et al., 2007; Develle et al., 2009, 2010). A total of 42 AMS 14C dating (partly carbonized wood) provide a solid chronology from the YD to present. Results reveal the following main features : 1- intervals dominated by authigenic calcite suggest that the major water supply was the karstic springs, which still deliver Ca-rich water and low surface runoff; 2- the lake oxygen isotope composition has been impacted by the source isotope composition throughout the Holocene and by increased inland rainfall during the early Holocene; 3- a decideous oak forest, implying much more soil water availability than today, was developed around the lake from ca. 11.5 to 9.5 kyr (the very bad pollen preservation after 8.3 kyr reflects oxidation or frequent oscillations of the water level); 4- four paleosols evidenced from lithofacies and magnetic properties are identified

  13. Holocene Environmental Change in the Skallingen Area, Eastern North Greenland, Based on a Lacustrine Record

    NASA Astrophysics Data System (ADS)

    Wagner, B.; Bennike, O.

    2014-12-01

    Although lakes are known to provide excellent high-resolution records of climate and environmental change over long periods, only few records exist from the high arctic regions. For example, only very few records exist from northernmost Greenland (> 80°N). Some of the existing records are chronologically poorly constrained or cover only the latest part of the Holocene. A new lacustrine record from a small lake (80°01'N, 22°39'W) in the Skallingen area in northeastern Greenland indicates that the region was deglaciated prior to 8000 cal. a BP. Deglaciation was probably triggered by high temperatures, but it took more than 1000 years for the lake and the catchment to stabilise. Chironomids were amongst the first invertebrates to colonize the lake. The fossil chironomid assemblage is fairly rich and comparable to other records from further south in Greenland. The pioneer vegetation in the area consisted of mosses and herbaceous plants. The only woody plants recorded comprise Salix arctica and Dryas integrifolia, which appear at around 7700 cal. a BP and 6700 cal. a BP, respectively. Maximum concentrations of chironomids, maximum occurrence of ephippia of the water flea Daphnia pulex, highest organic matter contents and lowest minerogenic input from c. 7700 to 4400 cal. a BP probably reflect the Holocene thermal maximum (HTM). A maximum of Salix arctica, which is considered a warmth-loving plant, indicates that the highest temperatures during the HTM are recorded around 7000 cal. a BP. However, the occurrence of several warmth-demanding species particularly in the early Holocene sediments indicates redeposition and implies that temperatures in the past, most likely during an interglacial period, were significantly higher than during the HTM. Comparisons with Holocene records from East and North Greenland show similar immigration histories and similar trends, with the Little Ice Age as the coldest period during the Holocene culminating about 150 year ago. Subsequent

  14. Holocene environment changes around the Sara Us River, northern China, revealed by optical dating of lacustrine-aeolian sediments

    NASA Astrophysics Data System (ADS)

    Zhao, Hui; Sheng, Yongwei; Li, Bo; Fan, Yuxin

    2016-04-01

    The Sara Us River is located along the boundary of the Mu Us Desert and the Chinese Loess Plateau in northern China. The river has cut down through Quaternary sediments creating 70-80 m deep valleys with thick lacustrine/aeolian sequences exposed. We applied optical stimulated luminescence on sediments from a Holocene section of aeolian sand/lacustrine deposits in the top of the river valley. The dating results show that a humid period existed from 7.1 to 2.0 ka ago as evidenced by two layers of peat and lacustrine sediments. However, compared to other published Holocene sections in the Sara Us River valleys close to the section under studying, the local environment experienced very complicated changes during the Holocene. All of the sections recorded a period with drought and/or cold before the Holocene at around 13 ka, and an episode of aridity after about 2 ka ago as evidenced by the layers of aeolian sand. However, the ages of the lacustrine and peat layers in these sections are substantially different. Geomorphological analysis by digital elevation models does not support the existence of a mega lake covering the study area at 2 ka. The intricate environmental changes may have been caused by the meandering of the Sara Us River. Environmental changes also strongly affected human migration in this area, which is documented by Chinese historical records.

  15. The Lower Murray River's Mannum Muds: A Holocene Age Lacustrine Deposit In A Bedrock Gorge

    NASA Astrophysics Data System (ADS)

    Hubble, T.; De Carli, E.; Clarke, S. L.; Penny, D.; Hamilton, R. J.; Petley, D. N.; Gadd, P.

    2014-12-01

    Middle to Late Holocene age, horizontally laminated clays and muds of lacustrine origin predominate the uppermost layers of the valley-fill sequence deposited in the lower Murray River's bedrock gorge upstream of the set of lakes which separate Australia's largest river system, The Murray-Darling, from its discharge point to the Southern Ocean. The top surface of the Coonambidgal Formation muds is developed at a constant elevation approximately coincident with the Holocene sea-level maximum and the mud deposit thins progressively in thickness upstream from ~30 m to ~10 m over a distance of 150 km due to a gradual, upstream rise in the elevation of the unit's base. Radiocarbon ages for wood and charcoal fragments recovered from two cores indicates the uppermost four to five metres of these muds were deposited after the mid-Holocene sea-level maximum, at below sea-level elevations indicating that the discharge of the Murray-Darling fluvial system was contained and effectively dammed by an obstruction developed downstream of Lake Alexandrina where the present-day river mouth is located. This feature is suspected to be the precursor of the present-day dune and beach-barrier system which occasionally blocks the river mouth and diverts fresh-water flow into the Coorong Wetlands. Muddy sediment from the entire Murray-Darling catchment was effectively trapped in the lower Murray Gorge palaeolake, herein named Lake Mannum, during the mid to late Holocene. High rates of sedimentation (one to two meters per thousand years) produced exquisitely fine-scaled (1 mm to 1 cm) laminations in the upper Coonambidgal Formation. This material has not been disturbed by bioturbation and presents a sediment record with the potential to yield a high-resolution record of the Murray-Darling catchment's discharge for much of the Holocene. The present-day lower Murray River channel currently presents a meandering but constant planform geometry upstream of Lake Alexandrina that developed as a

  16. Geochemical characteristics of Holocene laminated sapropel (unit II) and underlying lacustrine unit III in the Black Sea

    USGS Publications Warehouse

    Dean, Walter E.; Arthur, Michael A.

    2011-01-01

    eg 1 of the 1988 R/V Knorr expeditions to the Black Sea recovered 90 gravity and box cores. The longest recovery by gravity cores was about 3 meters, with an average of about 2.5 meters, recovering all of the Holocene and upper Pleistocene sections in the Black Sea. During the latest Pleistocene glaciation, sea level dropped below the 35-meters-deep Bosporus outlet sill of the Black Sea. Therefore throughout most of its history the Black Sea was a lake, and most of its sediments are lacustrine. The oldest sediments recovered (older than 8,000 calendar years) consist of massive to coarsely banded lacustrine calcareous clay designated as lithologic Unit III, generally containing less than 1 percent organic carbon (OC). The base of overlying Unit II marks the first incursion of Mediterranean seawater into the Black Sea, and the onset of bottom-water anoxia about 7,900 calendar years. Unit II contains as much as 15 percent OC in cores from the deepest part of the Black Sea (2,200 meters). The calcium carbonate (CaCO3) remains of the coccolith Emiliania huxleyi form the distinctive white laminae of overlying Unit I. The composition of Unit III and Unit II sediments are quite different, reflecting different terrigenous clastic sources and increased contributions from hydrogenous and biogenic components in anoxic Unit II sapropel. In Unit II, positive covariance between OC and three trace elements commonly concentrated in OC-rich sediments where sulfate reduction has occurred (molybdenum, nickel, and vanadium) and a nutrient (phosphorus) suggest a large marine source for these elements although nickel and vanadium also have a large terrigenous clastic source. The marine sources may be biogenic or hydrogenous. A large biogenic source is also suggested for copper and cobalt. Because abundant pyrite forms in the water column and sediments of the Black Sea, we expected to find a large hydrogenous iron component, but a strong covariance of iron with aluminum suggests that the

  17. Holocene glacier fluctuations inferred from lacustrine sediment, Emerald Lake, Kenai Peninsula, Alaska

    NASA Astrophysics Data System (ADS)

    LaBrecque, Taylor S.; Kaufman, Darrell S.

    2016-01-01

    Physical and biological characteristics of lacustrine sediment from Emerald Lake were used to reconstruct the Holocene glacier history of Grewingk Glacier, southern Alaska. Emerald Lake is an ice-marginal threshold lake, receiving glaciofluvial sediment when Grewingk Glacier overtops the topographic divide that separates it from the lake. Sub-bottom acoustical profiles were used to locate core sites to maximize both the length and resolution of the sedimentary sequence recovered in the 4-m-long cores. The age model for the composite sequence is based on 13 14C ages and a 210Pb profile. A sharp transition from the basal inorganic mud to organic-rich mud at 11.4 ± 0.2 ka marks the initial retreat of Grewingk Glacier below the divide of Emerald Lake. The overlaying organic-rich mud is interrupted by stony mud that records a re-advance between 10.7 ± 0.2 and 9.8 ± 0.2 ka. The glacier did not spill meltwater into the lake again until the Little Ice Age, consistent with previously documented Little Ice Ages advances on the Kenai Peninsula. The retreat of Grewingk Glacier at 11.4 ka took place as temperature increased following the Younger Dryas, and the subsequent re-advance corresponds with a climate reversal beginning around 11 ka across southern Alaska.

  18. Sulfidization of lacustrine glacial clay upon Holocene marine transgression (Arkona Basin, Baltic Sea)

    NASA Astrophysics Data System (ADS)

    Holmkvist, Lars; Kamyshny, Alexey; Brüchert, Volker; Ferdelman, Timothy G.; Jørgensen, Bo Barker

    2014-10-01

    Towards the end of the last deglaciation more than 13,500 years ago the southern Baltic Sea was a freshwater lake, the Baltic Ice Lake, for several thousand years during which iron-rich, organic-poor clay was deposited. The modern brackish-marine stage started about 8600 years ago with the deposition of organic-rich mud, which is today characterized by high rates of sulfate reduction and high concentrations of free sulfide. We studied the iron-sulfur diagenesis in gravity cores from the Arkona Basin, SW Baltic Sea, to track the progressing sulfidization front in the buried Ice Lake sediment. The geochemical zonation was unusual as the sulfate concentration dropped steeply by two thirds below which it increased again due to a deep sulfate reservoir. The reservoir had been established during the early Holocene marine period as sulfate and other seawater ions diffused down into the lake sediment for several thousand years. Sulfur isotope analyses confirmed its origin as seawater sulfate, while its oxygen isotope composition indicated a microbially catalyzed equilibration with ambient interstitial water, decoupled from net sulfate reduction. Today, hydrogen sulfide diffuses from the marine mud down into the lake sediment where a black band with high magnetic susceptibility and high iron monosulfide, greigite and elemental sulfur content shows progressing sulfidization of the large pool of solid-phase reactive iron. Dissolved iron from the deep Ice Lake sediment diffuses up to the sulfide front and provides a small supplement to the solid Fe(III) pool as a sulfide sink. Pyrite formation at the sulfidization front may involve surface-bound zero-valent sulfur while, above the front, polysulfides are in equilibrium with the system hydrogen sulfide - polysulfide - rhombic sulfur and may not be important for further pyrite formation. The Holocene iron-sulfur diagenesis observed in the Arkona Basin represents an important transitional state for post-glacial transgressions

  19. Vegetation and carbon cycle dynamics in Holocene

    NASA Astrophysics Data System (ADS)

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

    2009-04-01

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

  20. Holocene fluctuations of Quelccaya Ice Cap, Peru based on lacustrine and surficial geologic archives

    NASA Astrophysics Data System (ADS)

    Stroup, J. S.; Kelly, M. A.; Lowell, T. V.; Beal, S. A.; Smith, C. A.

    2013-12-01

    Peru's Quelccaya Ice Cap (QIC; 13.9°S, 70.8°W, ~5200-5670 m asl) is an important site for understanding tropical paleoclimate, mainly because of annually layered ice cores that provide an ~1800 year long record of tropical paleoclimatic conditions (e.g., Thompson et al., 2013). Here, we present a detailed record of QIC fluctuations using surficial deposits and lake sediments that extend back to late glacial time. We compare the late Holocene records of QIC 10Be-dated moraines and ice core data with lake sediments from a nearby glacially fed lake to establish the framework we use to interpret a Holocene long sediment record from a glacially fed lake. We also examine sediments from a nearby non-glacial lake to constrain non-glacial clastic input. We collected two ~5 m-long sediment cores, one from Laguna Challpacocha, which is currently fed by QIC meltwater, and one from the Laguna Yanacocha, which has not received QIC meltwater since ~12.3 ka. Changes in magnetic susceptibility, loss on ignition, bulk density and X-ray fluorescence chemistry combined with 14C and 210Pb chronologies provide information about sediment transported to the lakes. Retreat from the late Holocene extent defined by the 10Be-dated moraine record (~0.52 ka) is contemporaneous with a sharp transition from organic to clastic sedimentation in the Challpacocha core at ~ 0.52 ka. This implies that glacially-sourced clastic sedimentation, as tracked by loss on ignition, Ti counts and bulk density, increased during ice cap recession. Based on these same proxy data, we suggest the following Holocene history of QIC: QIC receded from the Challpacocha basin by ~10.6 ka. Increased clastic sedimentation at 8.2 - 4.1, 3.6 - 2.7 ka and from 0.55 ka - present are interpreted as times of ice cap recession. The increased clastic sedimentation at ~8.2 - 4.1 ka is consistent with surficial deposits near the present-day ice margin that indicate that at ~7.0 - 4.6 ka QIC was smaller than at present (Buffen et al

  1. High-resolution seismic stratigraphy of an Holocene lacustrine delta in western Lake Geneva (Switzerland)

    USGS Publications Warehouse

    Baster, I.; Girardclos, S.; Pugin, A.; Wildi, W.

    2003-01-01

    A high-resolution seismic survey was conducted in western Lake Geneva on a small delta formed by the Promenthouse, the Asse and the Boiron rivers. This dataset provides information on changes in the geometry and sedimentation patterns of this delta from Late-glacial to Present. The geometry of the deposits of the lacustrine delta has been mapped using 300-m spaced grid lines acquired with a 12 kHz Echosounder subbottom profiler. A complete three dimensional image of the sediment architecture was reconstructed through seismic stratigraphic analysis. Six different delta lobes have been recognized in the prodelta area. Depositional centers and lateral extension of the delta have changed through time, indicating migration and fluctuation of river input as well as changes in lake currents and wind regime from the time of glacier retreat to the Present. The delta slope is characterized by a high instability causing stumps developing and by the accumulation of biogenic gas that prevents seismic penetration.

  2. Diagenesis of Late Miocene micritic lacustrine carbonates, Madrid Basin, Spain

    NASA Astrophysics Data System (ADS)

    Wright, V. P.; Zarza, A. M. Alonso; Sanz, M. E.; Calvo, J. P.

    1997-12-01

    Mud-grade lacustrine limestones of Miocene age from the Madrid Basin, Spain, reveal varied and complex diagenetic histories. Microporous micrites occur as well as micrites with anhedral mosaics. The micrites have recrystallized from a metastable precursor, in part under sub-oxic meteoric diagenetic conditions probably before extensive karstification in the Pliocene. The absence of aragonite relics, their mainly micritic microfabric, low Sr content and covariant trend of Sr and Mg suggest that the micrites formed from mainly high-magnesian calcite muds. Lacustrine micrites can be compared to marine forms and criteria used to assess the composition of the marine precursor muds can be applied to lacustrine limestones to complement other techniques to identify original lake water compositions.

  3. Exploration models for Tertiary lacustrine carbonates, Liaodong Bay, People's Republic of China

    SciTech Connect

    Lomando, A.J. )

    1996-01-01

    Lacustrine carbonates are a significant reservoir target in the basins of eastern China. Difficulty in seismically imaging this play type generates the need for accurate exploration models to define geometries for lead and prospect identification. Rifted and karsted Cambro-Ordovician carbonates form the base of the section which is overlain by thick Tertiary lacustrine deposits. Two types of lacustrine carbonate plays have been identified. Carbonate alluvial fans developed from the erosion of Cambro-Ordovician dolomites and limestones in places along the flanks of tilted fault block ridges. During lake formation and expansion, these fans formed small shelves along the lake margins which became the sites of active carbonate production and winnowing. This play type forms discontinuous trends of lacustrine shoreline skeletal grainstones which mimic the underlying fan geometries. A second play type was identified in the JZ-20/JZ-9 trend. Stacked, shoaling upward cycles of skeletal grainstones occur on the gentle ramp sides of tilted fault blocks. In contrast, a different style of lake margin accumulation occurs on the bounding fault side of these blocks. Blocks with single major bounding faults have narrow shelves prohibiting accumulation of carbonate, whereas structures with sets of subsidiary faults form perched platforms ideal for the accumulation of thick lacustrine carbonate sections. Both of these play types have good modern analogues from the Great Salt Lake in Utah and the East African Rift System.

  4. Exploration models for Tertiary lacustrine carbonates, Liaodong Bay, People`s Republic of China

    SciTech Connect

    Lomando, A.J.

    1996-12-31

    Lacustrine carbonates are a significant reservoir target in the basins of eastern China. Difficulty in seismically imaging this play type generates the need for accurate exploration models to define geometries for lead and prospect identification. Rifted and karsted Cambro-Ordovician carbonates form the base of the section which is overlain by thick Tertiary lacustrine deposits. Two types of lacustrine carbonate plays have been identified. Carbonate alluvial fans developed from the erosion of Cambro-Ordovician dolomites and limestones in places along the flanks of tilted fault block ridges. During lake formation and expansion, these fans formed small shelves along the lake margins which became the sites of active carbonate production and winnowing. This play type forms discontinuous trends of lacustrine shoreline skeletal grainstones which mimic the underlying fan geometries. A second play type was identified in the JZ-20/JZ-9 trend. Stacked, shoaling upward cycles of skeletal grainstones occur on the gentle ramp sides of tilted fault blocks. In contrast, a different style of lake margin accumulation occurs on the bounding fault side of these blocks. Blocks with single major bounding faults have narrow shelves prohibiting accumulation of carbonate, whereas structures with sets of subsidiary faults form perched platforms ideal for the accumulation of thick lacustrine carbonate sections. Both of these play types have good modern analogues from the Great Salt Lake in Utah and the East African Rift System.

  5. Major hydrologic shifts in northwest Florida during the Holocene from a lacustrine sediment record

    NASA Astrophysics Data System (ADS)

    Rodysill, J. R.; Donnelly, J. P.

    2011-12-01

    Recent climate extremes have threatened water resource availability and destroyed homes and infrastructure along the heavily populated northern Gulf of Mexico coast. Water resources in Northwest Florida, in particular, suffer from declining aquifer levels and salt water intrusion despite the presence of extensive river and aquifer systems. Intensive water resource management has been necessary to meet water supply demands during recent droughts. Advanced preparedness for abrupt climate events requires the ability to anticipate when hydrologic extremes are likely to occur; however, the long-term history of hydrologic extremes is not well known, and the instrumental record is too short to resolve longer-term hydrologic variability. Reconstructing the pre-instrumental hydrologic history is essential to building our understanding of the timing of and the driving forces behind wet and dry extremes. Here we present a new record of paleohydrology in northwest Florida based upon variations in sediment lithology and geochemistry from Rattlesnake Lake. We see evidence for both brief and long-lived changes in the lake environment during the Holocene. We compare our record to published pollen-based reconstructions of paleohydrology to examine the spatial and temporal patterns of paleohydrologic extremes across the northern Gulf of Mexico region during the Holocene.

  6. 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.

  7. Holocene palaeoecology of the Golan Heights (Near East): investigation of lacustrine sediments from Birkat Ram crater lake

    NASA Astrophysics Data System (ADS)

    Schwab, Markus J.; Neumann, Frank; Litt, Thomas; Negendank, Jorg F. W.; Stein, Mordechai

    2004-09-01

    Lacustrine deposits of the crater lake Birkat Ram located in the northern Golan Heights have been used as a paleoecological archive. Preliminary sedimentological and palynological investigations based on a composite profile allow the reconstruction of the environmental history of the last 6500 years. Fluctuations of the pollen composition (trees and shrubs versus herbs, values of oak and olive tree) correspond to changes in different sediment parameters (total organic carbon, magnetic susceptibility) which can be interpreted as the effects of human impact on the geo-biosphere. Four phases with strong settlement activities can be identified for the Northern Golan Heights: (1) during the Chalcolithic period/Early Bronze Age, (2) during the Hellenistic-Roman-Byzantine periods, (3) during the Crusader period, and finally during modern time. These periods were interrupted by wooded regeneration phases with low anthropogenic activities.

  8. Impact of Holocene climate variability on lacustrine records and human settlements in South Greenland

    NASA Astrophysics Data System (ADS)

    Guillemot, T.; Bichet, V.; Simonneau, A.; Rius, D.; Massa, C.; Gauthier, E.; Richard, H.; Magny, M.

    2015-11-01

    Due to its sensitivity to climate changes, south Greenland is a particularly suitable area to study past global climate changes and their influence on locale Human settlements. A paleohydrological investigation was therefore carried out on two river-fed lakes: Lake Qallimiut and Little Kangerluluup, both located close to the Labrador Sea in the historic farming center of Greenland. Two sediment cores (QAL-2011 and LKG-2011), spanning the last four millennia, were retrieved and showed similar thin laminae, described by high magnetic susceptibility and density, high titanium and TOC / TN atomic ratio, and coarse grain size. They are also characterized either by inverse grading followed by normal grading or by normal grading only and a prevalence of red amorphous particles and lignocellulosic fragments, typical of flood deposits. Flood events showed similar trend in both records: they mainly occurred during cooler and wetter periods characterized by weaker Greenlandic paleo-temperatures, substantial glacier advances, and a high precipitation on the Greenlandic Ice Sheet and North Atlantic ice-rafting events. They can therefore be interpreted as a result of ice and snow-melting episodes. They occurred especially during rapid climate changes (RCC) such as the Middle to Late Holocene transition around 2250 BC, the Sub-boreal/Sub-atlantic transition around 700 BC and the Little Ice Age (LIA) between AD 1300 and AD 1900, separated by cycles of 1500 years and driven by solar forcing. These global RCC revealed by QAL-2011 and LKG-2011 flood events may have influenced Human settlements in south Greenland, especially the paleo-Eskimo cultures and the Norse settlement, and have been mainly responsible for their demise.

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

    SciTech Connect

    Kokorowski, H D; Anderson, P M; Sletten, R S; Lozhkin, A V; Brown, T A

    2008-05-20

    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 indicates 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.

  10. Improved Stratigraphic Interpretation of Dense Lacustrine Carbonates from Lake Bonneville, UT

    NASA Astrophysics Data System (ADS)

    Steponaitis, E.; McGee, D.; Quade, J.

    2014-12-01

    Recent work on the past hydroclimate of the Bonneville Basin has utilized dense, laminated carbonate deposits that formed beneath the surface of Lake Bonneville starting around 26 ka (McGee et al. 2012). These calcite and aragonite deposits form in calm, protected spaces that have been submerged by the lake, including hillside caves, cracks in bedrock, and interstitial spaces in tufa and abandoned beach gravel deposits. Dense lacustrine carbonates are very useful for paleoclimate studies because they can be used to develop continuous records of lake chemistry anchored by precise U-Th dates. However, many questions remain about the conditions in which these dense carbonates form: at what depth range do these carbonates form, and can basal and top ages help constrain the lake level curve? Do coeval carbonates formed at different depths in the lake preserve information about vertical gradients in lake water properties like δ18O and 87Sr/86Sr? To address these questions and others, this study examines a sequence of dense lacustrine carbonates deposited within bedrock, tufa, and abandoned shoreline gravels from Stansbury Island, UT. We use U-Th dating, local stratigraphic interpretations, and previously established lake level constraints to draw insights into the formation and context of these deposits. Improved understanding of dense lacustrine carbonates will facilitate more detailed and accurate interpretations of their stratigraphic significance, and ultimately, aid the development of improved paleoclimate records from Lake Bonneville and beyond. McGee, D., et al. 2012. Lacustrine Cave Carbonates : Novel Archives of Paleohydrologic Change in the Bonneville Basin (Utah , USA). Earth and Planetary Science Letters (351-352): 182-194.

  11. Diagenetic effects on magnetic minerals in a Holocene lacustrine sediment core from Huguangyan maar lake, southeast China

    NASA Astrophysics Data System (ADS)

    Wu, Xudong; Wang, Yong; Bian, Liu; Shen, Ji

    2016-06-01

    Post-depositional reductive diagenesis usually results in partial or entire cleansing of the pristine palaeomagnetic signal, therefore, its intensity is important to be assessed for sediments that are in the purpose of retrieving palaeomagnetic information. Grain size, rock magnetic and geochemical studies on the entire core, along with scanning electron microscope (SEM) observations and X-ray diffraction (XRD) analyses for representative samples were carried out on a Holocene sediment core retrieved from the deep water part of Huguangyan maar lake (HGY), southeast China. The pristine magnetic mineral assemblage of the studied core is domianted by superparamagnetic (SP) and stable single domain (SSD) titanomagnetite, and high coercivity minerals are not detectable. Based on down-core variations of the average grain size (MZ), total organic carbon (TOC), detrital elements (Al, Ti, Fe and Mn), and the concentration and mineralogy of magnetic minerals, the studied core could be divided into three subsections. The uppermost subsection is the least affected by diagenesis, with detrital titanomagnetite as the dominant magnetic mineral. This is owing to low TOC contents, but high detrital input generated by weak Asian summer monsoon intensity during the late Holocene. The intermediate subsection shows down-core progressively enhanced dissolution of detrital titanomagnetite, and concomitant formation of authigenic pyrite and siderite, which indicates down-core progressively enhanced diagenesis generated by down-core progressive increasing TOC content, but decreasing detrital input as the result of down-core progressively strengthened Asian summer monsoon intensity. The pristine magnetic mineral assemblage has been profoundly modified in the lowermost subsection. At certain positions of the lowermost subsection, detrital titanomagnetite has been even completely dissolved via diagenesis, giving place to authigenic pyrite and siderite. High TOC content, but low detrital input

  12. Clumped isotope calibration data for lacustrine carbonates: A progress report

    NASA Astrophysics Data System (ADS)

    Tripati, A.

    2015-12-01

    Our capacity to understand Earth's environmental history is highly dependent on the accuracy of reconstructions of past climates. Lake sediments provide important archives of terrestrial climate change, and represent an important tool for reconstructing paleohydrology, paleoclimate, paleoenvironment, and paleoaltimetry. Unfortunately, while multiple methods for constraining marine temperature exist, quantitative terrestrial proxies are scarcer - tree rings, speleothems, and leaf margin analyses have all been used with varying degrees of accuracy. Clumped isotope thermometry has the potential to be a useful instrument for determining terrestrial climates: multiple studies have shown the fraction of 13C—18O bonds in carbonates is inversely related to the temperature at which the rocks formed. We have been measuring the abundance of 13C18O16O in the CO2 produced by the dissolution of carbonate minerals in phosphoric acid in modern lake samples and comparing results to independently known estimates of lake water temperature. Here we discuss an extensive calibration dataset comprised of 132 analyses of 97 samples from 44 localities, including microbialites, tufas, and micrites endogenic carbonates, freshwater gastropods, bivalves, microbialites, and ooids.

  13. Applying magnetostratigraphy to lacustrine sediments to obtain a non-hard-water-effect affected pattern of late Holocene monsoon dynamics on the Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Haberzettl, T.; Kasper, T.; Su, Y.; Daut, G.; Frenzel, P.; Henderson, A.; Opitz, S.; Doberschütz, S.; Liebke, U.; Wang, J.; Zhu, L.; Mäusbacher, R.

    2011-12-01

    The Tibetan Plateau is commonly believed to react very inhomogeneous to monsoon variations. This is hitherto attributed to complex responses to environmental and atmospheric variations due to extreme differences in the mountain landscapes where minor differences in elevation can cause strong variation in microenvironments (Wischnewski et al. 2011). Another important role play differences in the source of the monsoon which potentially affect different regions of the Tibetan Plateau. However, it was possible to show a similar pattern of Indian Ocean Summer Monsoon strength, i.e., hydrological variations, in Nam Co (Co = lake) located on the central Tibetan Plateau and Hongyuan peat bog (Hong et al. 2003) situated on the north-eastern margin of the Plateau (Kasper et al. submitted). Peat dating at Hongyuan minimizes reservoir effect uncertainties since it is generally accepted that the dating of peat samples is hardly affected (Long et al., 2010). The chronology of Nam Co was supported by the comparison of paleosecular variations calculated from these sediments to geomagnetic field models (Kasper et al. submitted). This was necessary since almost all radiocarbon ages obtained from lacustrine sediments on the Tibetan Plateau are affected by a reservoir effect. In this study we present late Holocene paleosecular variations obtained from lacustrine sediments from Nam Co, Tangra Yumco, Donggi Cona, Peiku Co and Npen Co - all located on the Tibetan Plateau and considerably affected by a reservoir effect. We show the applicability of paleomagnetic investigations on sediments from these lakes and how these analyses can help to emerge the contemporaneousness of certain hydrological variations during this time. This is done by comparing and tuning for example inclination or declination to geomagnetic field models or interarchive comparison of the lakes mentioned above. Applying this approach for example to Nam Co and Tangra Yumco, a very similar progression of hydrological

  14. The middle Holocene climatic records from Arabia: Reassessing lacustrine environments, shift of ITCZ in Arabian Sea, and impacts of the southwest Indian and African monsoons

    NASA Astrophysics Data System (ADS)

    Enzel, Yehouda; Kushnir, Yochanan; Quade, Jay

    2015-06-01

    A dramatic increase in regional summer rainfall amount has been proposed for the Arabian Peninsula during the middle Holocene (ca. 9-5 ka BP) based on lacustrine sediments, inferred lake levels, speleothems, and pollen. This rainfall increase is considered primarily the result of an intensified Indian summer monsoon as part of the insolation-driven, northward shift of the boreal summer position of the Inter-Tropical Convergence Zone (ITCZ) to over the deserts of North Africa, Arabia, and northwest India. We examine the basis for the proposed drastic climate change in Arabia and the shifts in the summer monsoon rains, by reviewing paleohydrologic lacustrine records from Arabia. We evaluate and reinterpret individual lake-basin status regarding their lacustrine-like deposits, physiography, shorelines, fauna and flora, and conclude that these basins were not occupied by lakes, but by shallow marsh environments. Rainfall increase required to support such restricted wetlands is much smaller than needed to form and maintain highly evaporating lakes and we suggest that rainfall changes occurred primarily at the elevated edges of southwestern, southern, and southeastern Arabian Peninsula. These relatively small changes in rainfall amounts and local are also supported by pollen and speleothems from the region. The changes do not require a northward shift of the Northern Hemisphere summer ITCZ and intensification of the Indian monsoon rainfall. We propose that (a) latitudinal and slight inland expansion of the North African summer monsoon rains across the Red Sea, and (b) uplifted moist air of this monsoon to southwestern Arabia highlands, rather than rains associated with intensification of Indian summer monsoon, as proposed before, increased rains in that region; these African monsoon rains produced the modest paleo-wetlands in downstream hyperarid basins. Furthermore, we postulate that as in present-day, the ITCZ in the Indian Ocean remained at or near the equator all

  15. A Holocene lacustrine record of Lake Sonkul: hydro-climatic changes in central Asia and possible interactions between westerlies and Asian monsoon

    NASA Astrophysics Data System (ADS)

    Huang, X.; Oberhänsli, H.; Mathis, M.; Prasad, S.; von Suchodoletz, H.

    2012-04-01

    As evidenced by a number of lake sediment records, the climate in central Asia has experienced a significant change from wet to dry during the Holocene. However, it is still highly debated on which component of atmospheric circulation, either mid-latitude westerlies or Asian monsoon, should be responsible for the climate change in central Asia. By a detailed investigation on a 133-cm length of paleolimnological record of Lake Sonkul in Kyrgyzstan and comparison with previously published records, we attempt to understand hydro-climatic changes in central Asia and discuss the possible interactions between westerlies and Asian monsoon. The age-depth model of this record was established based on six AMS 14C dates. We examined the geochemical and isotopic signatures of the record at a depth interval of 1 cm (equivalent to ~40 year), including total nitrogen (TN), total carbon (TC), total organic carbon (TOC), organic carbon isotopes as well as oxygen and carbon isotopes of bulk carbonates. To thoroughly understand and explain the above indicators, microfacies and X-ray diffraction analyses of selected samples and three thin sections were also conducted. As shown by the results, there were two significant changes of the lake environment centered at ~5, 300 cal yr BP and at ~3,400 cal yr BP. Accordingly, the lake hydrological history could be defined into three units. Unit III (133-88cm; 7, 600- 5, 300 cal yr BP) is characterized by rapid fluctuations in the lake level as indicated by pronounced changes in TN, TOC, CaCO3, carbon and oxygen isotopes of carbonates. In contrast, variations of these proxies in Unit II (88 - 44.5 cm; 5, 300 - 3, 400 cal yr BP) and Unit I (44.5 - 0 cm; 3, 400 -1, 900 cal yr BP) are less significant, suggesting relatively stable hydrological environment. We conclude that the hydrological changes of Lake Sonkul are generally consistent with the climate trend from wet to dry in central Asia during the early and mid Holocene. The changes are

  16. Holocene aeolian sedimentation and episodic mass-wasting events recorded in lacustrine sediments on Langøya in Vesterålen, northern Norway

    NASA Astrophysics Data System (ADS)

    Nielsen, Pål Ringkjøb; Dahl, Svein Olaf; Jansen, Henrik Løseth; Støren, Eivind N.

    2016-09-01

    In this study, the frequency of mass-wasting events and past storminess has been reconstructed throughout the Holocene (11,500 cal yr BP to present) from lacustrine sediments in lake Trehynnvatnet (33 m a.s.l.), which is located in a glacially carved valley at Nykvåg on the outmost coast of western Langøya, Vesterålen, northern Norway. Sediment cores (∼2-5 m long) have been examined by use of high-resolution magnetic susceptibility and XRF-scanning as well as grain size and loss-on-ignition analysis. In total 35 episodic event layers have been identified throughout the Holocene. The majority of these events are characterized as discrete coarse-grained sediment layers followed by normal grading, and are related to past mass-wasting activity within the catchment. Periods with high mass-wasting activity are dated to 11,000-10,500, 5500-4500, 4000-3500, 3000-2500, 2000-1000 and 500-0 cal yr BP. The continuous input of sand grains (>250 μm) has been systematically investigated throughout the sediment cores. The sand grains are related to catchment samples from the sandy beach deposits in Sandvikbukta c. 750 m away in SW direction, and are suggested to indicate (niveo-) aeolian influx to the lake. The content of sand grains varies greatly throughout the record, although there is a clear increase in influx of sand during the last 2800 years. Periods with high aeolian influx are proposed to indicate increased storminess, which occurred between 1600 and 1550 (350-400 CE), 1400-1300 (450-550 CE), 750-550 (1200-1400 CE) and 250-20 cal yr BP (1700-1930 CE), which to some degree coincides with periods of increased storminess and winter precipitation recorded in other studies around the North Eastern Atlantic region.

  17. Lacustrine evidence of Holocene environmental change from three Faroese lakes: a multiproxy XRF and stable isotope study

    NASA Astrophysics Data System (ADS)

    Olsen, Jesper; Björck, Svante; Leng, Melanie J.; Gudmundsdóttir, Esther Ruth; Odgaard, Bent V.; Lutz, Christina M.; Kendrick, Chris P.; Andersen, Thorbjørn J.; Seidenkrantz, Marit-Solveig

    2010-09-01

    The vegetation history of the Faroe Islands has been investigated in numerous studies all broadly showing that the early-Holocene vegetation of the islands largely consisted of fellfield with gravely and rocky soils formed under a continental climate which shifted to an oceanic climate around 10,000 cal yr BP when grasses, sedges and finally shrubs began to dominant the islands. Here we present data from three lake sediment cores and show a much more detailed history from geochemical and isotope data. These data show that the Faroe Islands were deglaciated by the end of Younger Dryas (11,700 - 10,300 cal yr BP), at this time relatively high sedimentation rates with high δ13C imply poor soil development. δ13C, Ti and χ data reveal a much more stable and warm mid-Holocene until 7410 cal yr BP characterised by increasing vegetation cover and build up of organic soils towards the Holocene thermal maximum around 7400 cal yr BP. The final meltdown of the Laurentide ice sheet around 7000 cal yr BP appears to have impacted both ocean and atmospheric circulation towards colder conditions on the Faroe Islands. This is inferred by enhanced weathering and increased deposition of surplus sulphur (sea spray) and erosion in the highland lakes from about 7400 cal yr BP. From 4190 cal yr BP further cooling is believed to have occurred as a consequence for increased soil erosion due to freeze/thaw sequences related to oceanic and atmospheric variability. This cooling trend appears to have advanced further from 3000 cal yr BP. A short period around 1800 cal yr BP appears as a short warm and wet phase in between a general cooling characterised by significant soil erosion lasting until 725 cal yr BP. Interestingly, increased soil erosion seems to have begun at 1360 cal yr BP, thus significantly before the arrival of the first settlers on the Faroe Island around 1150 cal yr BP, although additional erosion took place around 1200 cal yr BP possibly as a consequence of human activities

  18. Holocene lagoonal development in the isolated carbonate platforms off Belize

    NASA Astrophysics Data System (ADS)

    Gischler, Eberhard

    2003-06-01

    Thirty-one vibracores were taken in interior lagoons of Glovers Reef, Lighthouse Reef, and Turneffe Islands—three isolated carbonate platforms offshore Belize, Central America. Holocene facies successions overlying the Pleistocene limestone bedrock begin with soils, followed by mangrove peats, and marine carbonate sediments of lagoonal origin. The soils formed on top of subaerially exposed Pleistocene limestone before the Holocene transgression. Mangrove peats developed during initial flooding of the platforms (Glovers ca. 8.5 ky, Lighthouse ca. 7 ky, Turneffe ca. 6 ky BP). As water depths increased, reefs colonized platform margins, lagoonal circulation improved thereby promoting carbonate production. The basal lagoonal carbonate sediments are characterized by shell beds and/or Halimeda packstones-grainstones. Mollusk-dominated wackestones and packstones follow upsection in Glovers and Lighthouse Reefs. At present, open circulation prevails in Glovers and Lighthouse lagoons. In contrast, organic-rich Halimeda wackestones and packstones dominate the Turneffe Islands Holocene succession. The main lagoon area of Turneffe is enclosed by mangroves, and restricted circulation prevails. Factors that explain the differences in geomorphology, circulation, and facies are variations in depth of antecedent topography and degree of exposure to waves and currents. The thickness of Holocene lagoon sediments may exceed the maximum core length of 6 m in all atolls. Holocene sedimentation rates average 0.6 m/ky, with highest rates in Turneffe (0.82 m/ky), followed by Lighthouse (0.53 m/ky), and Glovers (0.46 m/ky). Like in many other isolated carbonate platforms and atolls, lagoon floor sedimentation did not keep pace with rising sea level, leading to unfilled accommodation space. At present, Glovers has an 18 m deep lagoon, while Lighthouse and the main Turneffe lagoon are 8 m deep. It is unlikely that the lagoons will be completely filled during the Holocene sea level highstand

  19. Lacustrine cave carbonates: Novel archives of paleohydrologic change in the Bonneville Basin (Utah, USA)

    NASA Astrophysics Data System (ADS)

    McGee, David; Quade, Jay; Edwards, R. Lawrence; Broecker, Wallace S.; Cheng, Hai; Reiners, Peter W.; Evenson, Nathan

    2012-10-01

    Records of past changes in lake levels and lake water isotopic composition in closed basins provide key insights into past variations in the hydrological cycle; however, these records are often limited by dating precision and temporal resolution. Here we present data from lacustrine cave carbonates, a previously unexplored class of carbonates that comprise a promising new archive of past hydrologic changes in the Bonneville Basin of the northeastern Great Basin (USA). These dense carbonates precipitated within caves, crevices, and other protected spaces flooded by Lake Bonneville during its highstand in the last glacial period. We report on deposits in Cathedral and Craners caves, located ˜50 km apart at similar elevations approximately 100 m above the modern Great Salt Lake and almost 200 m below Lake Bonneville's highstand shoreline. Carbonates from the two caves show similar chronologies, mineralogical transitions, isotopic compositions, and uranium concentrations. These findings suggest that lacustrine cave carbonates record changes in lake level and in the isotopic composition and chemistry of lake water. Importantly, the deposits can be precisely dated by U-Th methods, providing the first records of Lake Bonneville's water balance changes tied to precise U-Th ages. Close agreement between paired U-Th and calibrated 14C ages in the deposits suggests a minimal (<200 a) carbon reservoir effect in the lake and allows 14C dating to be used for age control in portions of the deposits less suitable for U-Th dating. We use ages for the onset and cessation of lacustrine cave carbonate deposition to offer new constraints on past changes in lake level and the carbonate saturation state of lake water. We also present precisely dated, high-resolution oxygen and uranium isotope records from the deposits. Within a first phase of deposition reflecting the lake's transgression between 26 and 18 ka, our isotopic data suggest a large influx of freshwater during Heinrich

  20. The Effect of Local Lacustrine Conditions on the Expression of Regional Holocene Climate in the Ruby Mountains, Nevada, USA

    NASA Astrophysics Data System (ADS)

    Starratt, S.; Kusler, J. E.; Addison, J. A.; Wahl, D.

    2013-12-01

    Climate of the north-central Great Basin currently exhibits a bimodal precipitation pattern, dominated by winter (NDJF) precipitation from the eastern Pacific Ocean, augmented by late spring (MJ) convectional precipitation. Reconstruction of past moisture variability has proven difficult due to limited paleoclimate records in this region and the effect of lake-specific and local watershed characteristics. In order to better understand the Holocene climate record a series of cores were collected in Favre Lake (2902 masl, 8 ha, 12 m deep) 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 ~7700 cal yr B.P. The pollen record is dominated by Pinus and Artemisia, followed by subordinate levels of Poaceae, Asteraceae, Amaranthaceae, and Sarcobatus. Small fragilarioid diatoms (Pseudostaurosira, Staurosira, and Staurosirella) comprise as much as 80% of the assemblage. The remainder of the assemblage is dominated by benthic taxa. Planktonic species account for about 10% of the assemblage. Biogenic silica values vary between 20 and 30 wt %. These proxies suggest that the lake was small between 7,700 and 5,500 cal yr BP; for most of the remainder of the record, the lake covered a shallow (~1 m deep) shelf, resulting in the dominance of small fragilarioid diatoms. Planktonic species increase in abundance in the last 200 years, indicating the establishment of modern conditions. In order to evaluate the role of local conditions on the climate record, surface sediments were collected from tarns in the northern Ruby Mountains (Lamoille Lake, 2976 masl, 6 ha; Upper Dollar Lake, 2942 masl, ~1 ha, 2 m deep; Lower Dollar Lake, 2937 masl, ~1 ha, 2 m deep; Liberty Lake, 3064 masl, 9 ha, 33 m deep; Castle Lake, 2980 masl, 6 ha, 4.6 m deep; Favre Lake), and East Humboldt Range (Angel Lake, 2553 masl, 5 ha, 9 m deep). Slope aspects above the lakes are north (Lamoille

  1. New insights into the Glacial to Holocene climatic evolution of Southern Patagonia from lacustrine lipid biomarker isotope records

    NASA Astrophysics Data System (ADS)

    Hockun, K.; Mollenhauer, G.; Sachse, D.; Schefuß, E.

    2015-12-01

    Southern Patagonia is a key region for paleoclimatic reconstructions in the Southern Hemisphere as it is the only landmass located in the Southern Hemisphere westerly wind (SHW) belt. Within the framework of the ICDP drilling campaign PASADO ("Potrok Aike Maar Lake Sediment Archive Drilling Project"), a high resolution sediment record was recovered from Laguna Potrok Aike (LPTA, 51°58´S, 70°23´W). In order to identify the sources of organic matter contributions to the sedimentary archive, we investigated long-chain n-alkanes as tracers for terrestrial and aquatic plants. We analysed n-alkane distributions and their compound-specific hydrogen (δD) and stable carbon (δ13C) isotopic composition in various sample types such as soils, dust, aquatic and terrestrial plants and lake surface sediments. Based on two different model approaches, one using the n-alkane distributions and the other the compound-specific isotope values, we traced the origin of mid- (n-C23) and long- (n-C29) chain n-alkanes into modern lake sediments. Both models yield similar results: around 70% of the n-C23 originates from aquatic plants and more than 80% of the n-C29 is delivered from dust and terrestrial plants to the sediment. These results provide the basis for a robust paleo-environmental reconstruction of the lipid biomarker isotope records from LPTA. Compound-specific δD and δ13C records for the last 55,000 years from the PASADO core are interpreted in the framework of these findings. Here, δD of the n-C23 alkane serves as proxy for lake water isotopic changes driven by the precipitation-evaporation balance, moisture sources and water column stratification. In contrast, we interpret changes in δD of the n-C29 alkane to reflect dust source area changes and therefore, the intensity of the SHW. A 50‰ shift in the δD record of the n-C23 alkane between 10.000 to 8.000 years age indicates a major hydrological change affecting the lake level while isotopic changes in the n-C29 alkane

  2. The lacustrine carbon cycle as illuminated by the waters and sediments of two hydrologically distinct headwater lakes in North-Central Minnesota, U.S.A

    USGS Publications Warehouse

    Dean, W.E.; Schwalb, A.

    2002-01-01

    concentrations of Fe and Mn do not build up in the hypolimnion. The concentration of CaCO3 is about 80 wt. % in lower Holocene sediments of both lakes. The lower Holocene sediments in both lakes also contain high concentrations of Fe and Mn, and the lower Holocene sediments of Shingobee are laminated. The waters of both lakes had identical values of ??13C and ??18O during the early Holocene, but the waters of Williams Lake "evolved" during the early Holocene, increasing about 10??? in both ??13C and ??18O. Deposits of lacustrine marl occur as much as seven meters above the present elevation of Williams Lake, the highest of the two lakes. Taken together, these observations suggest that the lakes were once connected to form a larger lake called Lake Willobee with a hypolimnion that was anoxic, at least seasonally.

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

    SciTech Connect

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

    1987-05-01

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

  4. Deciphering the Paleochemistry and Holocene Environmental Variability in Central New York: Different Perspectives from the Stable Carbon Isotopes of Organic Matter and Carbonates.

    NASA Astrophysics Data System (ADS)

    Finkelstein, D. B.; Colcord, D. E.; Curtin, T.

    2014-12-01

    This study investigates environmental variability recorded in lacustrine and wetland sediments of Seneca Lake. Sediments display a range of stable isotopic and elemental chemistries suggesting there are changes in lake level, climate, or both during the Holocene in central New York. A ~13.5 m sediment core collected from the Catharine Creek wetland located south of Watkins Glen, NY at the southern tip of Seneca Lake was analyzed for total nitrogen (% TN), total organic carbon (% TOC), C/N ratios, δ13C of bulk organic matter (δ13Corg) and δ13Ccc and δ18Occ of carbonate. There is little change in TOC with the exception of an organic-rich interval (~20% TOC) between 5.5 and 4.3 m. Between 13.5 and 6 m, the C/N ratios decrease gradually upcore, from ~40 to ~10 - 20 and is paralleled by an increase in δ13Corg values from ~ -27‰ to ~ -24‰. Between 6-5.5 m, δ13C becomes significantly more negative (~ -30‰). The δ13Corg increases (to -26‰) upcore from 5.5 to 2.4 m. High C/N values (ranging from 60 to 20) from 15.5 to 11.8 m are consistent with input of land plants. The C/N values from 11.8 to 2.6 m range from 10 - 20 and represents a mixed signal of both algal and land plant derived organic matter. Throughout the Holocene, there has been a steady shift from negative δ13Corg values to more positive values of organic matter, which is consistent with an increase in the abundance of C4 plants in the watershed. Shifts in C/N over the length of the core suggest changes in lake level. In contrast, carbonate isotopic values (δ13Ccc and δ18Occ) do not covary and trends are consistent with a fresh-water, over-filled lake. In most lacustrine carbonate studies, calculated paleo-water temperatures from δ18Occ are commonly used prima facie to reflect environmental variability and constrain temperatures. In this study, wide variations in the calculated paleo-water temperatures reflect multiple carbonate sources / fractionations invalidating their use as a first order

  5. A shift of thermokarst lakes from carbon sources to sinks during the Holocene epoch.

    PubMed

    Anthony, K M Walter; Zimov, S A; Grosse, G; Jones, M C; Anthony, P M; Chapin, F S; Finlay, J C; Mack, M C; Davydov, S; Frenzel, P; Frolking, S

    2014-07-24

    Thermokarst lakes formed across vast regions of Siberia and Alaska during the last deglaciation and are thought to be a net source of atmospheric methane and carbon dioxide during the Holocene epoch. However, the same thermokarst lakes can also sequester carbon, and it remains uncertain whether carbon uptake by thermokarst lakes can offset their greenhouse gas emissions. Here we use field observations of Siberian permafrost exposures, radiocarbon dating and spatial analyses to quantify Holocene carbon stocks and fluxes in lake sediments overlying thawed Pleistocene-aged permafrost. We find that carbon accumulation in deep thermokarst-lake sediments since the last deglaciation is about 1.6 times larger than the mass of Pleistocene-aged permafrost carbon released as greenhouse gases when the lakes first formed. Although methane and carbon dioxide emissions following thaw lead to immediate radiative warming, carbon uptake in peat-rich sediments occurs over millennial timescales. We assess thermokarst-lake carbon feedbacks to climate with an atmospheric perturbation model and find that thermokarst basins switched from a net radiative warming to a net cooling climate effect about 5,000 years ago. High rates of Holocene carbon accumulation in 20 lake sediments (47 ± 10 grams of carbon per square metre per year; mean ± standard error) were driven by thermokarst erosion and deposition of terrestrial organic matter, by nutrient release from thawing permafrost that stimulated lake productivity and by slow decomposition in cold, anoxic lake bottoms. When lakes eventually drained, permafrost formation rapidly sequestered sediment carbon. Our estimate of about 160 petagrams of Holocene organic carbon in deep lake basins of Siberia and Alaska increases the circumpolar peat carbon pool estimate for permafrost regions by over 50 per cent (ref. 6). The carbon in perennially frozen drained lake sediments may become vulnerable to mineralization as permafrost disappears

  6. A shift of thermokarst lakes from carbon sources to sinks during the Holocene epoch

    USGS Publications Warehouse

    Walter Anthony, K. M.; Zimov, S. A.; Grosse, G.; Jones, Miriam C.; Anthony, P.; Chapin, F. S., III; Finlay, J. C.; Mack, M. C.; Davydov, S.; Frenzel, P.F.; Frolking, S.

    2014-01-01

    Thermokarst lakes formed across vast regions of Siberia and Alaska during the last deglaciation and are thought to be a net source of atmospheric methane and carbon dioxide during the Holocene epoch1,2,3,4. However, the same thermokarst lakes can also sequester carbon5, and it remains uncertain whether carbon uptake by thermokarst lakes can offset their greenhouse gas emissions. Here we use field observations of Siberian permafrost exposures, radiocarbon dating and spatial analyses to quantify Holocene carbon stocks and fluxes in lake sediments overlying thawed Pleistocene-aged permafrost. We find that carbon accumulation in deep thermokarst-lake sediments since the last deglaciation is about 1.6 times larger than the mass of Pleistocene-aged permafrost carbon released as greenhouse gases when the lakes first formed. Although methane and carbon dioxide emissions following thaw lead to immediate radiative warming, carbon uptake in peat-rich sediments occurs over millennial timescales. We assess thermokarst-lake carbon feedbacks to climate with an atmospheric perturbation model and find that thermokarst basins switched from a net radiative warming to a net cooling climate effect about 5,000 years ago. High rates of Holocene carbon accumulation in 20 lake sediments (47±10 grams of carbon per square metre per year; mean±standard error) were driven by thermokarst erosion and deposition of terrestrial organic matter, by nutrient release from thawing permafrost that stimulated lake productivity and by slow decomposition in cold, anoxic lake bottoms. When lakes eventually drained, permafrost formation rapidly sequestered sediment carbon. Our estimate of about 160petagrams of Holocene organic carbon in deep lake basins of Siberia and Alaska increases the circumpolar peat carbon pool estimate for permafrost regions by over 50 per cent (ref. 6). The carbon in perennially frozen drained lake sediments may become vulnerable to mineralization as permafrost disappears7

  7. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  9. Holocene peatland shifts in vegetation, carbon, and climate at Imnavait, Alaska

    NASA Astrophysics Data System (ADS)

    Peteet, D. M.; Nichols, J. E.; Ouni, S.; Pavia, F.; Pearl, Y.

    2012-12-01

    The Imnavait Creek basin (68 40'N, 149 20'W; elevation 875-945 m) in the foothills of the Brooks Range, AK has been well studied in terms of modern vegetational communities, hydrology, and soils. But paleoclimate and paleovegetation reconstructions are limited. We retrieved a 2-m peatland core to examine the macrofossil/biomarker/carbon sequestration history throughout the Holocene and late-glacial. AMS 14C dates of the macrofossil remains will allow us to calculate carbon sequestration rates. The Holocene history (the top meter) records marked shifts in vascular plant as well as bryophyte history. A tri-partite sequence is apparent, with Andromeda/Sphagnum remains abundant in the early Holocene. The absence of bryophytes and the presence of Eriophorum and Carex achenes characterize the mid-Holocene. Andromeda and Betula nana with Sphagnum remains are abundant in the upper 30 cm of the core. Hydrogen isotope ratios of leaf wax alkanes record higher effective moisture in the early and late Holocene, suggesting more evaporative loss in the mid-Holocene which is characterized by Eriophorum. We compare our results with previously observed palynological shifts from lakes in the region and place this Arctic paleorecord in a larger perspective of peatland histories in a N-S transect covering nearly 10 degrees of latitude across Alaska. This tripartite pattern of effective moisture appears to be the same throughout the Alaskan transect, suggesting strong climatic control.

  10. A Holocene record of endogenic iron and manganese precipitation, isotopic composition of endogenic carbonate, and vegetation history in a lake-fen complex in northwestern Minnesota

    USGS Publications Warehouse

    Dean, Walter E.; Doner, Lisa A.

    2011-01-01

    Little Shingobee Lake and Fen are part of an extensive network of lakes and wetlands in the Shingobee River headwaters area of northwestern Minnesota. Prior to about 9800 radiocarbon years, most of the lakes in the Shingobee watershed area were interconnected to form glacial Lake Willobee. From 9800 to 7700 radiocarbon years, the level of Lake Willobee fell as a result of breaching of a dam, leaving small separated basins containing the existing lakes and wetlands. The dominant components in the sediments in a 9-meter core from Little Shingobee Lake (LSL-B), and lacustrine sediments under 3.3 meters of peat in a 17-meter core from Little Shingobee Fen (LSF-10) are detrital clastic material, endogenic CaCO3, and organic matter. The detrital fraction in the Holocene section in core LSL-B varies considerably from 7 weight percent to 82 weight percent and closely parallels the concentration of detrital quartz measured by X-ray diffraction. The CaCO3 concentration, which also varies considerably from 10 weight percent to 70 weight percent, is generally antithetic to the detrital concentration owing to the dilution of detrital material by CaCO3, particularly during the early to middle Holocene (about 9000-6500 calendar years). The organic-matter content varies from 5 weight percent to 25 weight percent and, together with CaCO3, serves to dilute the allogenic detrital fraction. In both cores almost all of the iron (Fe) and manganese (Mn) is in endogenic minerals, presumed to be oxyhydroxide minerals, that are important components throughout the core; little Fe and Mn are contributed by detrital aluminosilicate minerals. The endogenic Fe mineral, calculated as Fe(OH)3, forms a larger percentage of the sediment than endogenic organic material throughout most of the Holocene section in the LSL-B core and in the lacustrine sediments below the peat in the LSF-10 core. Biogenic silica as opal (biopal; diatom debris) was not measured, but the average calculated biopal is 5

  11. Constraining water balance in the Bonneville Basin during the last glacial period and deglaciation using 87Sr/86Sr and δ18O of lacustrine carbonates

    NASA Astrophysics Data System (ADS)

    Steponaitis, E.; McGee, D.; Quade, J.; Edwards, R.; Broecker, W. S.; Cheng, H.; Reiners, P. W.; Evenson, N. S.

    2012-12-01

    Geochemical records from closed basin lakes provide important constraints on past changes in regional precipitation - evaporation (P-E). This study refines our understanding of paleohydrology in the Bonneville Basin and explores the Basin's response to past abrupt changes, including Heinrich Event 2. We present Sr and O isotope records from lacustrine carbonates deposited in caves and other protected spaces during periods of higher lake levels (McGee et al., 2012). These records, anchored by precise U/Th and 14C dating, offer new insights into changes in lake level and water balance during the last glacial period and deglaciation. The Sr isotope composition of lake water is determined by the relative contributions of the two major fluvial inputs to the lake, the Bear River in the north and the Sevier River in the south, which have distinct 87Sr/86Sr ratios (Hart et al. 2004). Sr ratios of lake water, as recorded in lacustrine carbonates from different locations and elevations in the basin, offer insight into both lake mixing and changes in the position of the winter storm track, the primary source of precipitation to the Great Basin. High-resolution δ18O data from the carbonates trace changes in basin P-E and water column mixing. Trace element concentrations in the carbonates, especially those of Mg, Rb and Ba, are used to test interpretations of Sr and O isotope changes. Hart, W.S. et al., The 87Sr/86Sr ratios of lacustrine carbonates and lake-level history of the Bonneville paleolake system. GSA Bulletin 2004; 116: 1107-1119. McGee, D., et al. Lacustrine cave carbonates: Novel archives of paleohydrologic change in the Bonneville Basin (Utah, USA). EPSL 2012; In press.

  12. Holocene carbon dynamics and radiative forcing of three different types of peatlands in Finland

    NASA Astrophysics Data System (ADS)

    Mathijssen, Paul; Väliranta, Minna; Lohila, Annalea; Minkkinen, Kari; Tuittila, Eeva-Stiina; Tuovinen, Juha-Pekka; Korrensalo, Aino

    2016-04-01

    Peatlands contain approximately a third of all soil carbon globally and as they exchange carbon dioxide (CO2) and methane (CH4) copiously with the atmosphere, changes in peatland carbon budgets have a large impact on the global carbon balance and the concentration of greenhouse gasses in the atmosphere. There has been a growing interest in reconstructing and linking peatland carbon dynamics to past climate variations, because quantitative reconstructions can be used as a basis for future carbon balance predictions. In order to increase our understanding on peatland development and response patterns we quantitatively reconstructed Holocene carbon dynamics of three different peatlands in Finland: a subarctic fen, a boreal peatland complex and a boreal managed pine bog. Several cores from each peatland were investigated. The peatlands showed distinct successional pathways, which were sometimes triggered by fires. Successional stages were partly reflected in carbon accumulation patterns. Sometimes variations in carbon accumulation rates coincided with autogenic changes in peat type and vegetation, but accumulation rates were also related to the large-scale Holocene climate phases. However, Holocene climate changes as such did not seem to result in changes in the peat plant species composition. The mid-Holocene warm and dry climate conditions reduced the carbon accumulation in the subarctic fen and in the fen part of the boreal peatland complex, but when the peatland was in bog phase this effect was not visible. Some bog cores showed a clear increase in carbon accumulation after fen-bog transition, but the pattern was not unanimous. In addition to carbon accumulation, we estimated past CH4 emissions for each peatland respectively by applying different methods and by utilising the established current vegetation-CH4 emission relationship. The reconstructions showed that CH4 emissions always decreased during bog stages, but that the CH4 emissions played a major role in the

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    Inland waters act as an important control on the global carbon cycle. Deep tectonic lakes may provide a key link between short-term and long-term carbon cycles as buried carbon is essentially locked away from the atmosphere over geological timescales. Here we investigate Holocene carbon dynamics in one of the worlds most important lake ecosystems, Lake Baikal, Siberia. We test the hypothesis that multiple factors play a significant role in determining long-term carbon dynamics in central Asia, and that these factors change in importance over time. Carbon isotopes (δ13C), percentage total organic carbon (%TOC) were analysed during combustion in a Carlo Erba 1500 on-line to a VG Triple Trap and dual-inlet mass spectrometer. A multi-decadal organic geochemistry record (%TOC; δ13C, C/N ratios) was determined on Holocene sediments extracted from a slope terrace c. 600 m deep. Age-depth modelling on radiocarbon-dated pollen extracts was undertaken using 'Bacon', which takes into account variable sediment accumulation rates. Carbon mass accumulation rates (CMAR; g cm-2 yr-1) were estimated at a centennial scale resolution. δ13C values were routinely higher during cool glacial periods (-26 ‰) than during warmer climates (-28 ‰) linked to changes in carbon sources. Diatom productivity & boreal forest expansion were strongly associated with δ13C variability during the early Holocene, but after 8 kyr BP, no relationships are apparent. CMAR were highest during the early Holocene (11.7 - 8 kyr BP) although rates fluctuated considerably. Peak values of 12.5 g cm-2 yr-1 were observed at 10.35 kyr BP before a rapid decline to c. 5.2 g cm-2 yr-1 at 10.05 kyr BP. CMAR declined to lowest Holocene values of 3.5 g cm-2 yr-1 by 3.9 kyr BP at the same time as maximum δ13C values (-27.0 ‰), indicative of low palaeoproductivity. Our data show that measures of palaeoproductivity in Lake Baikal are complex, and during the early Holocene are strongly associated with allochthonous

  14. Mineral magnetism and geomagnetic secular variation of marine and lacustrine sediments from central Italy: timing and nature of local and regional Holocene environmental change

    NASA Astrophysics Data System (ADS)

    Rolph, Timothy C.; Vigliotti, Luigi; Oldfield, Frank

    2004-07-01

    Sediment core palaeomagnetic and mineral magnetic records from two crater lakes in central Italy and from the western margin of the Adriatic Sea have been used to evaluate local and regional responses to Holocene environmental change. In all cores, sediment magnetism reflects the interplay between catchment material and the in situ production of bacterial magnetite (magnetotactic bacteria). In the lakes, the earliest Holocene sediments record a waning catchment input that we attribute to rising lake levels and increased tree cover in the catchment. From ˜9000 to 5000 yr BP, both lakes become anoxic, a consequence of water-mass stratification driven by high lake levels. Bottom-water anoxia also developed in the Adriatic, with sapropel S1 produced between ˜9000 and 7000 yr BP. Subsequently, the lake and Adriatic mineral magnetic records show evidence for increased catchment delivery, consistent with pollen evidence for Bronze Age deforestation. In the lakes, this evidence is first recorded at ˜4300 yr BP and a number of distinct clearance events are recorded. In comparison, at Adriatic site RF93-30, lithogenic input increases abruptly at ˜3500 yr BP and is followed by a slowly changing record of waxing and waning sediment delivery. Inter-site comparisons of palaeomagnetic data point to a possible link between the magnitude of the bacterial magnetite component and the recorded magnetic inclination. The sites are at near identical latitudes and have similar sediment accumulation rates but the Adriatic sites have a core-average magnetic inclination that is some 10° steeper than the lake average values. We suggest that the large dipole moment of the magnetosome chains, which in life produce the passive alignment of the bacterium along the local geomagnetic field line, produce a more faithful (albeit smoothed) record of the geomagnetic field.

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  16. Late Holocene evolution of playa lakes in the central Ebro depression based on geophysical surveys and morpho-stratigraphic analysis of lacustrine terraces

    NASA Astrophysics Data System (ADS)

    Gutiérrez, F.; Valero-Garcés, B.; Desir, G.; González-Sampériz, P.; Gutiérrez, M.; Linares, R.; Zarroca, M.; Moreno, A.; Guerrero, J.; Roqué, C.; Arnold, L. J.; Demuro, M.

    2013-08-01

    The origin and morpho-stratigraphic evolution of the largest playa-lake system (La Playa-El Pueyo) in the Bujaraloz-Sástago endorheic area, located in the semiarid central sector of the Ebro Depression, are analysed. The enclosed depressions are developed on gypsiferous Tertiary bedrock and show a prevalent WNW-ESE orientation parallel to the direction of the prevalent strong local wind (Cierzo). Yardangs have been carved in bedrock and unconsolidated terrace deposits in the leeward sector of the largest lake basins. A sequence of three lacustrine terrace levels has been identified by detailed geomorphological mapping. The treads of the upper, middle and lower terrace levels are situated at + 9 m, + 6 m and + 0.5 m above the playa-lake floors, respectively. Seismic refraction and electrical resistivity profiles acquired in La Playa reveal a thin basin fill (~ 2 m) with a planar base. These data allow ruling out the genetic hypothesis for the depressions involving the collapse of large bedrock cavities and support a mixed genesis of combined widespread dissolution and subsidence by groundwater discharge and eolian deflation during dry periods. The 5 m thick deposit of the middle terrace was investigated in hand-dug and backhoe trenches. Six AMS radiocarbon ages from this terrace indicate an aggradation phase between 3.9 ka and ca. 2 ka. These numerical ages yield a maximum average aggradation rate of 2.6 mm/yr and a minimum excavation rate by wind deflation of 3 mm/yr subsequent to the accumulation of the middle terrace. The latter figure compares well with those calculated in several arid regions of the world using yardangs carved in palaeolake deposits. The aggradation phase between 4 and 2 ka is coherent with other Iberian and Mediterranean records showing relatively more humid conditions after 4 ka, including the Iron Ages and the Iberian-Roman Period.

  17. Ongoing Buildup of Refractory Organic Carbon in Boreal Soils During the Holocene

    NASA Astrophysics Data System (ADS)

    Smittenberg, R. H.; Eglinton, T. I.; Schouten, S.; Damsté, J. S. Sinninghe

    2006-11-01

    Radiocarbon ages of vascular plant wax derived n-alkanes preserved in well-dated Holocene sediments in an anoxic fjord (Saanich Inlet, Canada) were found to be not only substantially older than the depositional age but increasingly so during the Holocene. Assuming that n-alkanes serve as a proxy for recalcitrant terrigenous organic matter, this indicates that the accumulation of refractory organic carbon in soils that developed after the deglaciation of the American Pacific Northwest is ongoing and may still be far from equilibrium with mineralization and erosion rates.

  18. Carbonate replacement of lacustrine gypsum deposits in two Neogene continental basins, eastern Spain

    NASA Astrophysics Data System (ADS)

    Anadón, P.; Rosell, L.; Talbot, M. R.

    1992-07-01

    Bedded nonmarine gypsum deposits in the Miocene Teruel and Cabriel basins, eastern Spain, are partly replaced by carbonate. The Libros gypsum (Teruel Graben) is associated with fossiliferous carbonate wackestones and finely laminated, organic matter-rich mudstones which accumulated under anoxic conditions in a meromictic, permanent lake. The gypsum is locally pseudomorphed by aragonite or, less commonly, replaced by calcite. Low δ 13C values indicate that sulphate replacement resulted from bacterial sulphate reduction processes that were favoured by anacrobic conditions and abundant labile organic matter in the sediments. Petrographic evidence and oxygen isotopic composition suggest that gypsum replacement by aragonite occurred soon after deposition. A subsequent return to oxidising conditions caused some aragonite to be replaced by diagenetic gypsum. Native sulphur is associated with some of these secondary gypsum occurrences. The Los Ruices sulphate deposits (Cabriel Basin) contain beds of clastic and selenitic gypsum which are associated with limestones and red beds indicating accumulation in a shallow lake. Calcite is the principal replacement mineral. Bacterial sulphate reduction was insignificant in this basin because of a scarcity of organic matter. Stable isotope composition of diagenetic carbonate indicates that gypsum replacement occurred at shallow burial depths due to contact with dilute groundwaters of meteoric origin. Depositional environment evidently has a major influence upon the diagenetic history of primary sulphate deposits. The quantity of preserved organic matter degradable by sulphate-reducing bacteria is of particular importance and, along with groundwater composition, is the main factor controlling the mechanism of gypsum replacement by carbonate.

  19. Evaluation of clumped isotope paleotemperatures across carbon isotope excursions from lacustrine strata of the Aptian Xiagou Formation, China

    NASA Astrophysics Data System (ADS)

    Suarez, M. B.; Gonzalez, L. A.; Ludvigson, G. A.; You, H.

    2014-12-01

    Carbon cycle perturbations associated with Ocean Anoxic Event 1a have been implicated in global climate and environmental changes in the Early Aptian, in particular evidence for high sea surface temperatures (SST) and carbonate platform drowning. Records of environmental changes in the terrestrial realm remain sparse. This study provides additional data on clumped isotope derived temperatures (T(Δ47)) from lacustrine carbonates of the Xiagou Formation, Gansu Province, China. In addition, Vitrinite reflectance and the Rock-Eval parameter Tmax were used to evaluate the potential for 13C-18O bonds in the carbonates to have experienced reordering. Clumped isotope derived temperatures range from 28.8 °C to 45.9°C. Vitrinite reflectance values range from 0.67 to 0.72 and Tmax ranges from 429 °C to 443 °C. The warmest temperature, derived from a very fine-grained calcareous sandstone, is at the upper limit of known modern Earth surface temperatures, and prompts concern that the T(Δ47) may be shifted to warmer temperatures as a result of burial diagenesis. Vitrinite reflectance and Tmax values indicate the samples have reached early maturity for oil generation (oil window from 60 °C to 150°C), so may have reached the lower end of temperatures for bond reordering to have occurred (~100 °C for ~100 million years). Despite this, the T(Δ47) are consistent with summer temperatures in a warm Cretaceous. In addition, temperature variations are similar to TEX86 records, especially from SST of the tropical Pacific. Two temperature increases and decreases occur, with the first peak in temperature occurring at the negative carbon isotope excursion (C3) associated with the initiation of the Selli Event (OAE1a). This study provides evidence that climate variations occurring during the Selli Event were experienced in terrestrial environments, and provides maximum summer temperatures for this part of the Asian continent during the Cretaceous. While it was intended that thermal

  20. Did fires drive Holocene carbon sequestration in boreal ombrotrophic peatlands of eastern Canada?

    NASA Astrophysics Data System (ADS)

    van Bellen, Simon; Garneau, Michelle; Ali, Adam A.; Bergeron, Yves

    2012-07-01

    Wildfire is an important factor on carbon sequestration in the North American boreal biomes. Being globally important stocks of organic carbon, peatlands may be less sensitive to burning in comparison with upland forests, especially wet unforested ombrotrophic ecosystems as found in northeastern Canada. We aimed to determine if peatland fires have driven carbon accumulation patterns during the Holocene. To cover spatial variability, six cores from three peatlands in the Eastmain region of Quebec were analyzed for stratigraphic charcoal accumulation. Results show that regional Holocene peatland fire frequency was ~ 2.4 fires 1000 yr- 1, showing a gradually declining trend since 4000 cal yr BP, although inter- and intra-peatland variability was very high. Charcoal peak magnitudes, however, were significantly higher between 1400 and 400 cal yr BP, possibly reflecting higher charcoal production driven by differential climatic forcing aspects. Carbon accumulation rates generally declined towards the late-Holocene with minimum values of ~ 10 g m- 2 yr- 1 around 1500 cal yr BP. The absence of a clear correlation between peatland fire regimes and carbon accumulation indicates that fire regimes have not been a driving factor on carbon sequestration at the millennial time scale.

  1. Large Nankai Trough earthquake and tsunami found in lacustrine deposits through late Holocene-time along the western coast of Kii Peninsula, southwestern Japan

    NASA Astrophysics Data System (ADS)

    Okamura, M.; Matsuoka, H.; Tsuzuki, M.; Toraya, K.

    2015-12-01

    We continue paleo-seismic studies through Late Holocene-time in coastal marsh ponds along the Nankai Trough . These ponds which are co-seismic subsidence areas have continuous muddy sediment stratigraphy and sporadic tsunami induced coarse material. Well controlled age data has been collected from the core-sample that contains plant remains under anoxic sedimentary environment . Total 21 cores collected from two coastal ponds Ashihama-ike and Zasa-ike which locate behind beach-ridge along southeastern coast of Kii Peninsula under Tokai/Tonankai Earthquake assumption areas. Tsunami events are recognized after eighty AMS C-14 dating through recent (core top) to 7300 yBP interval. Among these interval, two remarkable events found in sediment, which are 2050yBP to 2300yBP (=2K event) and 1000yBP to 1100 yBP. 2k event consists thick sand, well rounded gravel in chaotic mud and wood fragment derived from forests surrounding lakes. Later event is correspond to the historical Ninna Nankai earthquake (AD887, 26 August under the old lunar calendar). Rather small events are occurred in 3500yBP and 1100yBP. These events are found from both of two ponds which has two kilometers in distance each other. Cores bottom are composed of 7400yBP huge-tsunami event caused simultaneously by the Kikai-caldera eruption (over 170 cubic km ejecta) is just covered with the Kikai-Akahoya (K-Ah) tephra. The 2K and volcanic tsunami events have also found widely, not only Kii Peninsula but southern Shikoku (Tokushima Pref. and Kochi Pref.) and Kyushu through the Nankai Trough.

  2. Sediment and particulate organic carbon fluxes in various lacustrine basins of tropical Africa and in the Gulf of Guinea

    NASA Astrophysics Data System (ADS)

    Giresse, P.; Makaya-Mvoubou

    2010-07-01

    This study presents a synthetic approach based on the combined use of sediment and C org accumulation rates of well studied lake systems and oceanic margins. Importance of latitude is expressed by the advected flux of terrestrial sediment and, especially, of particulate organic carbon. This most important factor varies throughout the Quaternary, particularly with the intensification of fluxes during Holocene. These changes are linked to the strengthening of monsoon circulation. In various lake systems from Cameroon (Barombi Mbo, Ossa, Assom and Bambili), Gabon (Kamalete) and Congo (Kitina and Sinnda), the global sedimentation and the C org accumulation were slow during dry period and increased during wet period. This relationship is verified to the scale of the Gabon and Congo oceanic margins where the accumulation rates increase during extent of ombrophilous forest. However, the greatest fluxes of organic carbon during wet periods would be balanced by higher concentrations values during the dry period resulting in a nearly homogenous carbon accumulation. These carbon concentrations are generally explained by the input of coarse debris by abrupt floods and by a less degraded organic matter as a result of the cooling of the climate. But, according to specific morphology features or vegetation cover, some lake systems exhibit distinct trends of the sedimentary and C org accumulation rates: (1) Highest accumulation rates coincided with a forest retreat when the slope is too steep (Kamalete in Gabon and Bosumtwi in Ghana) or when river flood overrun (Nguene in Gabon) (2) Increase of the accumulation rate are registered without change of the vegetal cover and express only rainfall growth (Bambili and Assom).

  3. Recent and Holocene climate change controls on vegetation and carbon accumulation in Alaskan coastal muskegs

    NASA Astrophysics Data System (ADS)

    Peteet, Dorothy M.; Nichols, Jonathan E.; Moy, Christopher M.; McGeachy, Alicia; Perez, Max

    2016-01-01

    Pollen, spore, macrofossil and carbon data from a peatland near Cordova, Alaska, reveal insights into the climate-vegetation-carbon interactions from the initiation of the Holocene, c. the last 11.5 ka, to the present (1 ka = 1000 calibrated years before present where 0 = 1950 CE). The Holocene period is characterized by early deposition of gyttja in a pond environment with aquatics such as Nuphar polysepalum and Potamogeton, and a significant regional presence of Alnus crispa subsp. sinuata. Carbon accumulation (50 g/m2/a) was high for a short interval in the early Holocene when Sphagnum peat accumulated, but was followed by a major decline to 13 g/m2/a from 7 to 3.7 ka when Cyperaceae and ericads such as Rhododendron (formerly Ledum) groenlandicum expanded. This shift to sedge growth is representative of many peatlands throughout the south-central region of Alaska, and indicates a drier, more evaporative environment with a large decline in carbon storage. The subsequent return to Sphagnum peat after 4 ka in the Neoglacial represents a widespread shift to moister, cooler conditions, which favored a resurgence of ericads, such as Andromeda polifolia, and increased carbon accumulation rate. The sustained Alnus expansion visible in the top 10 cm of the peat profile is correlative with glacial retreat and warming of the region in the last century, and suggests this colonization will continue as temperature increases and ice melts.

  4. The 87Sr/86Sr ratios of lacustrine carbonates and lake-level history of the Bonneville paleolake system

    USGS Publications Warehouse

    Hart, W.S.; Quade, Jay; Madsen, D.B.; Kaufman, D.S.; Oviatt, Charles G.

    2004-01-01

    Lakes in the Bonneville basin have fluctuated dramatically in response to changes in rainfall, temperature, and drainage diversion during the Quaternary. We analyzed tufas and shells from shorelines of known ages in order to develop a relation between 87Sr/86Sr ratio of carbonates and lake level, which then can be used as a basis for constraining lake level from similar analyses on carbonates in cores. Carbonates from the late Quaternary shorelines yield the following average 87Sr/86Sr ratios: 0.71173 for the Stansbury shoreline (22-20 14C ka; 1350 m), 0.71153 for the Bonneville shoreline (15.5-14.5 14C ka; 1550 m), 0.71175 for the Provo shoreline (14.4-14.0 14C ka; 1450 m), 0.71244 for the Gilbert shoreline (???10.3-10.9 14C ka; 1300 m), and 0.71469 for the modern Great Salt Lake (1280 m). These analyses show that the 87Sr/86Sr ratio of lacustrine carbonates changes substantially at low- to mid-lake levels but is invariant at mid- to high-lake levels. Sr-isotope mixing models of Great Salt Lake and the Bonneville paleolake system were constructed to explain these variations in 87Sr/86Sr ratios with change in lake level. Our model of the Bonneville system produced a 87Sr/86Sr ratio of 0.71193, very close to the observed ratios from high-shoreline tufa and shell. The model verifies that the integration of the southern Sevier and Beaver rivers with the Bear and others rivers in the north is responsible for the lower 87Sr/86Sr ratios in Lake Bonneville compared to the modern Great Salt Lake. We also modeled the 87Sr/86Sr ratio of Lake Bonneville with the upper Bear River diverted into the Snake River basin and obtained an 87Sr/86Sr ratio of 0.71414. Coincidentally, this ratio is close to the observed ratio for Great Salt Lake of 0.71469. This means that 87Sr/86Sr ratios of >0.714 for carbonate can be produced by climatically induced low-lake conditions or by diversion of the upper Bear River out of the Bonneville basin. This model result also demonstrates that the

  5. Sediment magnetism constraints on the age and paleoclimate implications of a Holocene lacustrine record from the headwater region of the Rio Claro, Elqui Valley, Regíon de Coquimbo, Chile

    NASA Astrophysics Data System (ADS)

    Tiner, R.; Negrini, R. M.; Antinao, J. L.; Maldonado, A.; Bobbitt, M.; Casas, K.; Kayser, M.

    2015-12-01

    Magnetostratigraphy and paleolimnological proxies are reported for a Holocene lake sediment record from the headwater region of the Rio Claro of the Elqui Valley in Northern Chile. Laguna Cerritos Blancos (LCB), the lake cored, is located at approximately 30° S latitude and 3844 m asl. This lake is fed by a stream that cut through a terminal moraine and is damned by an older moraine/rock glacier complex. This site sits at the boundary between important circulation features of the southern hemisphere, including the Southeast Pacific Subtropical Anticyclone and the Westerly winds. Any major movements of these circulation features should be reflected in the climate record of the study area (Garreaud, 2009). The Natural Remanent Magnetization (NRM) recorded in the sediments exhibits demagnetization behavior dominated by a single component of magnetization and shows a paleomagnetic secular variation (PSV) signal similar to that of a marine core (ODP Leg 202, Site 1233) from offshore Valparaíso (Lund et al., 2006) suggesting that the 1.5 m of lake record represents the past ~5,000 years. The continuous nature of the PSV record and a lack of sedimentary features, indicating a lack of unconformities, suggests that the current low lake levels are anomalous for the late Holocene. However, gradually decreasing clay percent up section shows a coarsening upward trend suggesting gradual shallowing of the lake over the past ~5,000 yrs. Over this time period LCB has been characterized by stable conditions and gradual shallowing with few disruptions to this trend. These initial paleoclimate hypotheses are currently being tested with the acquisition of additional paleoclimate proxies on these core sediments including C/N ratios, total inorganic carbon, palynology, and additional measurements of sediment magnetism.

  6. Similar glacial and Holocene deep water circulation inferred from southeast Pacific benthic foraminiferal carbon isotope composition

    NASA Astrophysics Data System (ADS)

    Matsumoto, Katsumi; Lynch-Stieglitz, Jean

    1999-04-01

    We present Holocene and last glacial maximum (LGM) oxygen and carbon isotope measurements on Planulina wuellerstorfi in six southeast Pacific cores. Sedimentation rates are low in this part of the ocean, and measurements were made on individual foraminiferal shells in order to identify the Holocene and glacial individuals on the basis of their extreme δ18O. The new δ13C data were combined with previous P. wuellerstorfi data for interpretation of global thermohaline circulation. Data from the Southern Ocean were examined closely for regional coherency and a few anomalous δ13C values suspected of having productivity overprint were removed. The resulting global δ13C distributions and gradients indicate that the deep water circulation was similar during the Holocene and LGM. This interpretation brings δ13C data to a better agreement with Cd/Ca data and marks a sharp contrast with a widely held view based on δ13C measurements that the glacial Southern Ocean was the terminus of the thermohaline circulation. The proposed presence of glacial North Atlantic Deep Water does not necessarily contradict the postulated presence of Glacial North Atlantic Intermediate Water.

  7. Reconstruction of Holocene carbon dynamics in a large boreal peatland complex, southern Finland

    NASA Astrophysics Data System (ADS)

    Mathijssen, Paul J. H.; Väliranta, Minna; Korrensalo, Aino; Alekseychik, Pavel; Vesala, Timo; Rinne, Janne; Tuittila, Eeva-Stiina

    2016-06-01

    Holocene peatland development and associated carbon (C) dynamics were reconstructed for a southern boreal Finnish peatland complex with fen and bog areas. In order to assess the role of local factors and long-term allogenic climate forcing in peatland development patterns, we studied a total of 18 peat cores and reconstructed vertical peat growth and lateral peat area expansion rates, the C accumulation rate (CAR), past vegetation composition and past methane (CH4) fluxes. We combined fossil plant data with measured contemporary CH4 flux - vegetation relationship data to reconstruct CH4 fluxes over time. When these reconstructions were added to the CAR estimations, a more complete picture of Holocene-scale C dynamics was achieved. Basal peat ages showed that expansion of the peat area was rapid between 11,000 and 8000 cal. BP, but decreased during the dry mid-Holocene and is probably currently limited by basal topography. A similar pattern was observed for peat growth and CAR in the fen core, whereas in the bog core CAR increased after ombrotrophication, i.e. after 4400 cal. BP. The effect of fire on vegetation and CAR was more conspicuous at the bog site than at the fen site. The CH4 flux reconstructions showed that during the Holocene CH4 emissions at the fen site decreased from 19 ± 15 to 16 ± 8 g CH4 m-2 yr-1 and at the bog site from 20 ± 15 to 14 ± 8 g CH4 m-2 yr-1. Our results suggest that a combination of changing climate, fire events and local conditions have modified the autogenic peatland development and C dynamics.

  8. Reconstruction of Holocene carbon dynamics in a large boreal peatland complex, southern Finland

    NASA Astrophysics Data System (ADS)

    Mathijssen, Paul J. H.; Väliranta, Minna; Korrensalo, Aino; Alekseychik, Pavel; Vesala, Timo; Rinne, Janne; Tuittila, Eeva-Stiina

    2016-06-01

    Holocene peatland development and associated carbon (C) dynamics were reconstructed for a southern boreal Finnish peatland complex with fen and bog areas. In order to assess the role of local factors and long-term allogenic climate forcing in peatland development patterns, we studied a total of 18 peat cores and reconstructed vertical peat growth and lateral peat area expansion rates, the C accumulation rate (CAR), past vegetation composition and past methane (CH4) fluxes. We combined fossil plant data with measured contemporary CH4 flux - vegetation relationship data to reconstruct CH4 fluxes over time. When these reconstructions were added to the CAR estimations, a more complete picture of Holocene-scale C dynamics was achieved. Basal peat ages showed that expansion of the peat area was rapid between 11,000 and 8000 cal. BP, but decreased during the dry mid-Holocene and is probably currently limited by basal topography. A similar pattern was observed for peat growth and CAR in the fen core, whereas in the bog core CAR increased after ombrotrophication, i.e. after 4400 cal. BP. The effect of fire on vegetation and CAR was more conspicuous at the bog site than at the fen site. The CH4 flux reconstructions showed that during the Holocene CH4 emissions at the fen site decreased from 19 ± 15 to 16 ± 8 g CH4 m-2 yr-1 and at the bog site from 20 ± 15 to 14 ± 8 g CH4 m-2 yr-1. Our results suggest that a combination of changing climate, fire events and local conditions have modified the autogenic peatland development and C dynamics.

  9. The relationship between carbonate facies, volcanic rocks and plant remains in a late Palaeozoic lacustrine system (San Ignacio Fm, Frontal Cordillera, San Juan province, Argentina)

    NASA Astrophysics Data System (ADS)

    Busquets, P.; Méndez-Bedia, I.; Gallastegui, G.; Colombo, F.; Cardó, R.; Limarino, O.; Heredia, N.; Césari, S. N.

    2013-07-01

    The San Ignacio Fm, a late Palaeozoic foreland basin succession that crops out in the Frontal Cordillera (Argentinean Andes), contains lacustrine microbial carbonates and volcanic rocks. Modification by extensive pedogenic processes contributed to the massive aspect of the calcareous beds. Most of the volcanic deposits in the San Ignacio Fm consist of pyroclastic rocks and resedimented volcaniclastic deposits. Less frequent lava flows produced during effusive eruptions led to the generation of tabular layers of fine-grained, greenish or grey andesites, trachytes and dacites. Pyroclastic flow deposits correspond mainly to welded ignimbrites made up of former glassy pyroclasts devitrified to microcrystalline groundmass, scarce crystals of euhedral plagioclase, quartz and K-feldspar, opaque minerals, aggregates of fine-grained phyllosilicates and fiammes defining a bedding-parallel foliation generated by welding or diagenetic compaction. Widespread silicified and silica-permineralized plant remains and carbonate mud clasts are found, usually embedded within the ignimbrites. The carbonate sequences are underlain and overlain by volcanic rocks. The carbonate sequence bottoms are mostly gradational, while their tops are usually sharp. The lower part of the carbonate sequences is made up of mud which appear progressively, filling interstices in the top of the underlying volcanic rocks. They gradually become more abundant until they form the whole of the rock fabric. Carbonate on volcanic sandstones and pyroclastic deposits occur, with the nucleation of micritic carbonate and associated production of pyrite. Cyanobacteria, which formed the locus of mineral precipitation, were related with this nucleation. The growth of some of the algal mounds was halted by the progressive accumulation of volcanic ash particles, but in most cases the upper boundary is sharp and suddenly truncated by pyroclastic flows or volcanic avalanches. These pyroclastic flows partially destroyed the

  10. Identification and carbon isotope composition of a novel branched GDGT isomer in lake sediments: Evidence for lacustrine branched GDGT production

    NASA Astrophysics Data System (ADS)

    Weber, Yuki; De Jonge, Cindy; Rijpstra, W. Irene C.; Hopmans, Ellen C.; Stadnitskaia, Alina; Schubert, Carsten J.; Lehmann, Moritz F.; Sinninghe Damsté, Jaap S.; Niemann, Helge

    2015-04-01

    Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are bacterial membrane lipids that occur ubiquitously in soils and lacustrine sediments and have great potential as proxy indicators for paleotemperature and pH reconstructions. Initially, brGDGTs in lakes were thought to originate from soils of the watershed. The composition of the lacustrine brGDGT pool, however, often differs substantially from that in catchment soils, complicating the application of the brGDGT paleothermometer to lake sediments. This suggests that terrigenous brGDGT signals in lacustrine sedimentary archives may be affected by aquatic in situ production. In sediments of a Swiss mountain lake, we detected a novel hexamethylated brGDGT, which elutes between the known 5- and 6-methyl brGDGT isomers during HPLC-MS analysis. This novel isomer accounted for 8.5% of the total brGDGTs. Most remarkably, this brGDGT was not detected in soils collected from the catchment of the lake, providing circumstantial evidence for an in situ brGDGT source in the lake's water column or sediments. Isolation of the compound by preparative HPLC and subsequent GC-MS analysis of the alkyl chains revealed that the novel brGDGT comprises two structural isomers. One possesses a 5,13,16- and a 6,13,16-trimethyloctacosanyl moiety and constitutes 84% of the new brGDGT; the second contains a 13,16-dimethyloctacosanyl and a 5,13,16,23-tetramethyloctacosanyl moiety. The δ13C values of both the alkyl chains derived from the novel brGDGT (-46‰) and all other major brGDGTs (-43‰ to -44‰) were significantly lower than those of brGDGT-derived alkanes in catchment soils (-27‰ to -28‰) further attesting to in situ production of brGDGTs in the studied lake.

  11. Holocene Carbon Accumulation Rates in the SPRUCE Bog Prior to Warming and Elevated CO2 Treatment

    NASA Astrophysics Data System (ADS)

    McFarlane, K. J.; Iversen, C. M.; Phillips, J. R.; Brice, D. J.; Hanson, P. J.

    2015-12-01

    In the Spruce and Peatland Responses Under Climatic and Environmental Change (SPRUCE) experiment warming and elevated CO2 treatments are being applied to an ombrotrophic spruce bog: the S1 Bog (S1) at Marcell Experimental Forest in northern Minnesota. To provide a historical context for recent and expected experimentally-induced changes in the bog's belowground carbon balance, we reconstructed historical carbon accumulation rates in peat using radiocarbon from 19 peat cores collected from randomly distributed SPRUCE plots. This unusually high number of cores allows us to assess spatial variability in age-depth profiles and accumulation rates across the SPRUCE study area within S1. This data, along with recent C flux measurements, show that the bog has been accumulating carbon for at least 12,0000 years and has continued to be a sink for atmospheric carbon of approximately 150 g C m-2 yr-1 in recent decades. Early Holocene accumulation rates are similar to those reported for other northern peatlands (approximately 25 g C m-2 yr-1), but apparent carbon accumulation decreased substantially around 3,000 years ago (to 5-15 g C m-2 yr-1) and stayed low until the last century. This decrease is considerably larger than that reported for other peatlands and is therefore unlikely to result only from cooling during the Holocene or bog succession. Although no charcoal has been found in peat at this site, evidence from a neighboring bog indicates a considerable amount of peat formed during this period was consumed by fire and it is possible that smoldering fires consumed peat, resulting in low apparent accumulation rates. Past droughts may have also contributed to observed trends by lowering the acrotelm/catotelm boundary, allowing for enhanced aerobic peat decomposition. This work provides important background information on spatial variability and carbon biogeochemistry that will aid in interpretation of climate change simulation experiments at S1.

  12. Neogene-holocene mixed carbonate-siliciclastic deposition in eastern Gulf of Mexico with earlier analogs

    SciTech Connect

    Doyle, L.J.; Locker, S.D.

    1988-01-01

    The Neogene to Holocene history of the eastern Gulf of Mexico reveals a complex interplay between carbonate and siliciclastic sedimentation that may help interpret and explain many ancient deposits. Well data from the Florida Panhandle have been correlated with over 1,900 mi of high-resolution seismic reflection profiles collected on a 2-mi grid as part of a major geophysical program sponsored by GECO Geophysical Company, Inc. Data show a shift from flat carbonate sequences to prograding sequences about a major Neogene unconformity. Below that unconformity, carbonate sedimentation was dominant; afterward sediments became progressively more siliciclastic, grading into the Apalachicola delta and a surficial quartz sand sheet. The quartz sand grades laterally into the west Florida carbonate margin, bounded on the east by fine quartz sand beaches and terrace deposits of the Florida peninsula and on the west by the massive siliciclastic Mississippi fan. Siliciclastic sediments must have advanced and retreated across the carbonate shelf with sea level rise and fall. DSDP Leg 9 cores and seismic profiles suggest that, periodically, portions of the west Florida and probably Yucatan margins have failed, injecting massive carbonate gravity deposits into the deep Gulf of Mexico. These deposits have become intercalated into the Mississippi fan. Examples of quartz sandfilled channels in carbonate rocks and carbonate gravity deposits within siliciclastic (e.g., south Pyrenean basin and some deposits of the Permian basin) are found in the ancient record where they provide excellent isochronous marker beds as well as good potential reservoirs for hydrocarbons.

  13. Late Holocene vegetation, climate, and land-use impacts on carbon dynamics in the Florida Everglades

    NASA Astrophysics Data System (ADS)

    Jones, Miriam C.; Bernhardt, Christopher E.; Willard, Debra A.

    2014-04-01

    Tropical and subtropical peatlands are considered a significant carbon sink. The Florida Everglades includes 6000-km2 of peat-accumulating wetland; however, detailed carbon dynamics from different environments within the Everglades have not been extensively studied or compared. Here we present carbon accumulation rates from 13 cores and 4 different environments, including sawgrass ridges and sloughs, tree islands, and marl prairies, whose hydroperiods and vegetation communities differ. We find that the lowest rates of C accumulation occur in sloughs in the southern Everglades. The highest rates are found where hydroperiods are generally shorter, including near-tails of tree islands and drier ridges. Long-term average rates of 100 to >200 g C m-2 yr-1 are as high, and in some cases, higher than rates recorded from the tropics and 10-20 times higher than boreal averages. C accumulation rates were impacted by both the Medieval Climate Anomaly and the Little Ice Age, but the largest impacts to C accumulation rates over the Holocene record have been the anthropogenic changes associated with expansion of agriculture and construction of canals and levees to control movement of surface water. Water management practices in the 20th century have altered the natural hydroperiods and fire regimes of the Everglades. The Florida Everglades as a whole has acted as a significant carbon sink over the mid- to late-Holocene, but reduction of the spatial extent of the original wetland area, as well as the alteration of natural hydrology in the late 19th and 20th centuries, have significantly reduced the carbon sink capacity of this subtropical wetland.

  14. Holocene reef associated carbonate sediments and their Pleistocene counterparts, Miyako Islands, Ryukyus, southwest of Japan

    SciTech Connect

    Tsuji, Y.; Yamamura, T.; Kodato, T.; Sunouchi, H.

    1988-01-01

    Holocene carbonate sedimentary facies distribution, from sea level to shelf slope about 1,000 m in depth, and its relationship to bathymeltry, off Miyako Island, Ryukyus, southwest of Japan were clarified by surveys with sidescan sonar, sparker, uniboom, sea-bottom camera, and sediment sampler. Six facies were recognized using the acoustic data, sample analytical data, and sea-bottom photographs. These are as follows: (A) Reef facies: made mainly of autochthonous hermatypic corals and encrusting algae, 0-60 m deep. (B) Inter-reef muddy facies: consists of very fine sand-size carbonate fraction and line mud, 20-60 m deep surrounded area be reefal relief and islands. (C) Inter-reef and near-reef sandy facies: characterized by tests of shallow benthic foraminifera Calcarina and Marginopora, and Halimeda fragments, 0-90 m deep. (D) Rhodolith and large foraminiferal gravelly shelf facies: contains pebble to cobble-size rhodolith and/and foraminifera Cycloclypeus and Operculina, 60-200 m deep. (E) Bryozoan sandy shelf facies: rich in byrozoan fragments, 80-200 m deep. (F) Shelf slope pelagic foraminiferal facies: dominated by pelagic foraminifera and pteropod molluscan tests, deeper than 200 m. Counterparts of these facies in emerged Pleistocene limestone sequences have been recognized in outcrops and core samples. The results of the marine survey on Holocene deposits made it easy to interpret the Pleistocene depositional environments and sea level changes.

  15. Holocene sediment dynamics on a cool-water carbonate shelf: Otway, southeastern Australia

    SciTech Connect

    Boreen, T.D.; James, N.P. )

    1993-07-01

    The Otway Shelf is covered by cool waters and veneered by bryozoan-dominated carbonate sediments. Radiocarbon dating and stratigraphy of shelf vibracores and slope gravity cores document late Pleistocene/Holocene deposition. Shelf sediments of the late Pleistocene high-stand are rare, either never having been deposited or having been removed during the following sea-level fall. During the subsequent lowstand the shelf was exposed, facies shifted basinward, and beach/dune complexes were constructed near the shelf edge. The deep shelf was characterized by nondeposition and hardground formation, and the shelf margin became locally erosional. Upper-slope bryozoan/sponge assemblages continued to grow actively, and lower-slope foraminifera and nannofossil ooze was increasingly enriched in hemipelagic terrigenous mud swept off the wide shelf. Coarse shelf debris and lowstand dune sands were erosively reworked and transported onto the upper slope and redistributed to deep-slope aprons during early transgression. The late Quaternary shelf record resembles that of flat-topped, warm-water platforms with Holocene sediment overlying Pleistocene/Tertiary limestone, but for different reasons. The slow growth potential, uniform profile of sediment production and distribution, and inability of constituent organisms to construct rigid frameworks favor maintenance of a shallow ramp profile and makes the cool-water carbonate system an excellent modern analog for interpretation of many ancient ramp successions.

  16. Drivers of Holocene peatland carbon accumulation across a climate gradient in northeastern North America

    NASA Astrophysics Data System (ADS)

    Charman, Dan J.; Amesbury, Matthew J.; Hinchliffe, William; Hughes, Paul D. M.; Mallon, Gunnar; Blake, William H.; Daley, Tim J.; Gallego-Sala, Angela V.; Mauquoy, Dmitri

    2015-08-01

    Peatlands are an important component of the Holocene global carbon (C) cycle and the rate of C sequestration and storage is driven by the balance between net primary productivity and decay. A number of studies now suggest that climate is a key driver of peatland C accumulation at large spatial scales and over long timescales, with warmer conditions associated with higher rates of C accumulation. However, other factors are also likely to play a significant role in determining local carbon accumulation rates and these may modify past, present and future peatland carbon sequestration. Here, we test the importance of climate as a driver of C accumulation, compared with hydrological change, fire, nitrogen content and vegetation type, from records of C accumulation at three sites in northeastern North America, across the N-S climate gradient of raised bog distribution. Radiocarbon age models, bulk density values and %C measurements from each site are used to construct C accumulation histories commencing between 11,200 and 8000 cal. years BP. The relationship between C accumulation and environmental variables (past water table depth, fire, peat forming vegetation and nitrogen content) is assessed with linear and multivariate regression analyses. Differences in long-term rates of carbon accumulation between sites support the contention that a warmer climate with longer growing seasons results in faster rates of long-term carbon accumulation. However, mid-late Holocene accumulation rates show divergent trends, decreasing in the north but rising in the south. We hypothesise that sites close to the moisture threshold for raised bog distribution increased their growth rate in response to a cooler climate with lower evapotranspiration in the late Holocene, but net primary productivity declined over the same period in northern areas causing a decrease in C accumulation. There was no clear relationship between C accumulation and hydrological change, vegetation, nitrogen content

  17. Stable carbon and nitrogen isotopes and amino acids in Holocene sediments of Lake Lonar, central India

    NASA Astrophysics Data System (ADS)

    Menzel, Philip; Gaye, Birgit; Wiesner, Martin; Basavaiah, Nathani; Prasad, Sushma; Stebich, Martina; Anoop, Ambili; Riedel, Nils

    2013-04-01

    Investigations on surface sediments and a sediment core from Lake Lonar in central India were carried out within the framework of the HIMPAC (Himalaya: Modern and Past Climate) programme. The aim was to understand recent productivity, sedimentation, and degradation processes and to reconstruct variations in Holocene lake conditions on the basis of biogeochemical analysis on a 10 m long sediment core retrieved from the centre of Lake Lonar. Located in India's core monsoon zone, Lake Lonar offers valuable information about the climate development of the whole region. The lake is situated at the floor of a meteorite impact structure on the Deccan plateau basalt. The modern lake is characterised by brackish water, high alkalinity, severe eutrophication, and bottom water anoxia. The lake is about 6 m deep and fed by rainfall during the SW monsoon season and three perennial streams. Since no out-flowing stream is present and no seepage loss occurs, the lake level is highly sensitive to the balance of precipitation and evaporation. Here we present C/N, carbon and nitrogen isotope, and amino acid data of bulk organic matter from modern lake and Holocene core sediments. Modern conditions are mainly related to human activity which started to have persistent influence on the biological and chemical lake properties at ~1200 cal a BP. The distribution of δ13C in the modern sediments is driven by the ratio between terrestrial and aquatic organic matter, while δ15N seems to be influenced by redox conditions at the sediment-water-interface with elevated values at shallow oxic stations. Differences in the amino acid assemblages of oxic and anoxic surface sediment samples were used to calculate an Ox/Anox ratio indicating the redox conditions during organic matter degradation. The onset of the monsoon reconstructed from the sediment core occurred at ca. 11450 cal a BP. The early Holocene core sediments are characterised by low sedimentation rate, low aquatic productivity, and

  18. Structure of the carbon isotope excursion in a high-resolution lacustrine Paleocene-Eocene Thermal Maximum record from central China

    NASA Astrophysics Data System (ADS)

    Chen, Zuoling; Wang, Xu; Hu, Jianfang; Yang, Shiling; Zhu, Min; Dong, Xinxin; Tang, Zihua; Peng, Ping'an; Ding, Zhongli

    2014-12-01

    The carbon isotope excursion (CIE) associated with the Paleocene-Eocene Thermal Maximum (PETM) has been recognized for the first time in the micritic carbonate, total organic carbon (TOC) and black carbon (BC) contained within the lacustrine sediments from the Nanyang Basin, central China. The remarkably large excursion (∼ - 6 ‰) in the δ13CTOC and δ13CBC values is possibly attributable to increased humidity and elevated pCO2 concentration. The ∼ - 4 ‰ CIE recorded in the δ13Ccalcite, reflecting the average isotope change of the watershed system, is consistent with that observed in planktonic foraminifera. This correspondence suggests that the true magnitude of the carbon isotope excursion in the ocean-atmosphere system is likely close to - 4 ‰. The ∼10 m excursion onset in our multi-proxy δ13C records demonstrates that the large input of 13C-depleted carbon into the ocean-atmosphere system was not geologically instantaneous. Despite difference and somewhat smoothness in detailed pattern of the CIE due to localized controls on different substrates, inorganic and organic δ13C data generally depict a gradual excursion onset at least over timescales of thousands of years. In addition, continental temperature reconstruction, based on the distribution of membrane lipids of bacteria, suggests a warming of ∼4 °C prior to the PETM and ∼7 °C increase in temperature during the PETM. The temperature data are overall similar in pattern and trend to the δ13C change across the PETM. These observations, combined with pre-CIE warming, are in line with the idea that 13C-depleted carbon release operated as a positive feedback to temperature, suggesting supply from one or more large organic carbon reservoirs on Earth's surface.

  19. Stable-Carbon Isotopes of U.S. Great Plains Soils and Climate Events during the Holocene.

    Technology Transfer Automated Retrieval System (TEKTRAN)

    A suite of 12 soil profiles from the U.S. Great Plains and western Corn Belt were sampled to a depth of 2 m and radiocarbon dating control was established to investigate possible changes in stable-carbon isotope composition of SOC over space and time associated with major Holocene climate events. T...

  20. Sedimentology and geomorphology of a relict lacustrine system in Tingri, Tibet, China

    NASA Astrophysics Data System (ADS)

    Chiu, H.; Switzer, A. D.; Aitchison, J.

    2010-12-01

    A patchy sequence of near horizontal sedimentary deposits composed of consolidated carbonate-rich laminated gravelly sand and silt are exposed on the hill slopes near Tingri, Tibet, China. They are classified as mid- to late-Pleistocene and Holocene lacustrine deposits in Chinese geological maps, but the style and nature of lacustrine deposition and the facies associations in the sequence have never been reported. This study presents a number of sections in the locality showing the varied sedimentology of the deposits. The deposits are interpreted as relict sandy or gravelly dune ridges and plains, salt pans, prograded deltas, and lacustrine sediments. Interpretation was primarily based on a comparison with modern inland lakes in the Tibetan Plateau as analogues of processes in arid mountain lake systems. Relict dune ridges appear on the margins of many Tibetan inland lakes where the highly erosive regime allowed an abundant supply of gravels and sand to deposit along lake shorelines. The strong winds in Tibet have also allowed high to medium energy shoreline systems to develop in exposed areas. The high gravel and carbonate content in the gravelly ridges provided ample resistance to erosion and they often remain a topographically pronounced feature after lake drainage. Salt pans and gravelly or sandy ridge fields are also left after lake regression along with rare lacustrine deltas represented by the lakeward prograding beds. Laminated shelly sand or silt preserved in pockets near the valley floor characterise deposition at deeper lacustrine regimes. At Tingri the exposures of the palaeoshoreline deposits can reach 20 m in thickness and are identified at an elevation ranging from 4286 to 4404 masl. Although patchy in occurrence the sequence suggests a relatively long lived relict lake system. The timing of lake phases is poorly constrained by optically stimulated luminescence mid-to-late Pleistocene and Holocene. A number of incised channels are observed in

  1. Holocene siliciclastic-carbonate facies mosaics, Northern Belize: Exploration analog to some midcontinent Pennsylvanian (Morrowan) reservoirs

    SciTech Connect

    Lowe, D.B.; Mazzullo, S.J.

    1995-09-01

    Midwinter Lagoon is a large, shallow coastal lagoon, bordered on its seaward side by a barrier, along the mainland coast of northern Belize. As much as 19 ft of Holocene sediments, deposited on karsted Tertiary limestones during the Flandrian transgression, consist of a complex mosaic of mixed siliciclastic and carbonate facies. Basal transgressive marine, intra-lagoonal facies are variously siliciclastic-rich carbonates to carbonate-rich siliciclastics, locally with layers of shoreline mangrove peat. These facies shallow-upward to either siliciclastic or carbonate-dominated sands or muds. Lagoonal facies were deposited within a broad topographic low, locally punctuated by bedrock highs, on the underlying limestone. The seaward edge of the barrier bar complex, which was deposited on a linear topographic high, consists mostly of quartz sands, whereas the lagoonal side is a mixture of quartzose and carbonate sediments (sands and muds). The barrier bar appears to have accreted southward in response to southerly longshore drift as a tidal inlet-spit complex; quartz sands are being transported into the lagoon from its seaward side. In terms of geometry, modern and buried, intra-lagoonal carbonate sands occur as lobes deposited proximal to extant and older tidal inlets. Either carbonate or siliciclastic sands variously occur as erratically distributed, anastomosing beach deposits around small mangrove islands and along the irregular mainland coast. In contrast, siliciclastic sands on the seaward side of the barrier define a narrow but areally persistent linear trend. Similar complex facies associations and geometries are typical of many Pennsylvanian (Morrowan) reservoirs in the midcontinent US.

  2. Carbon storage increases by major forest ecosystems in tropical South America since the Last Glacial Maximum and the early Holocene

    NASA Astrophysics Data System (ADS)

    Behling, Hermann

    2002-06-01

    To study the carbon storage increase of major forest ecosystems in tropical South America, such as Amazon rain forest, Atlantic rain forest, semideciduous forest, and Araucaria forest, the Last Glacial Maximum (LGM) and the early Holocene vegetation cover were reconstructed by pollen records. Marked forest expansion points to a significant total carbon storage increase by tropical forests in South America since the LGM and the early Holocene. The Amazon rain forest expansion, about 39% in area, had 28.3×10 9 tC (+20%), the highest carbon storage increase since the LGM. The expansion of the other much smaller forest areas also had a significant carbon storage increase since the LGM, the Atlantic rain forest with 4.9×10 9 tC (+55%), the semideciduous forest of eastern Brazil with 6.3×10 9 tC (+46%), the Araucaria forest with 3.4×10 9 tC (+108%). The estimated carbon storage increase of the four forest biomes since the early Holocene is also remarkable. The extensive deforestation in the last century strongly affected the carbon storage by tropical forests.

  3. Sobol' sensitivity analysis of the Holocene Peat Model: What drives carbon accumulation in peatlands?

    NASA Astrophysics Data System (ADS)

    Quillet, Anne; Garneau, Michelle; Frolking, Steve

    2013-03-01

    Understanding the development of northern peatlands and their carbon accumulation dynamics is crucial in order to confidently integrate northern peatlands into global carbon cycle models. To achieve this, northern peatland models are becoming increasingly complex and now include feedback processes between peat depth, decomposition, hydrology, and vegetation composition and productivity. Here we present results from a global sensitivity analysis performed to assess the behavior and parameter interaction of a peatland simulation model. A series of simulations of the Holocene Peat Model were performed with different parameter combinations in order to assess the role of parameter interactions on the simulated total carbon mass after 5000 years of peatland development. The impact of parameter uncertainty on the simulation results is highlighted, as is the importance of multiple parameter interactions. The model sensitivity indicates that peat physical properties play an important role in peat accumulation; these parameters are poorly constrained by observations and should be a focus of future research. Furthermore, the results show that autogenic processes are able to produce a wide range of peatland development behaviors independently of any external environmental changes.

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

    SciTech Connect

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

    1990-05-01

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

  5. Multicycle Holocene dolomite in cool-water carbonate sediments Lacepede Shelf, South Australia

    SciTech Connect

    Bone, Y. ); James, N.P. ); Kyser, T.K. )

    1991-03-01

    Modern carbonate sediments on the Lacepede Shelf contain up to 10% dolomite particles, as either single rhombs or clusters. The rhombs vary from sharply edged crystals and nonabraded to slightly worn to completely rounded rhombs. These groups probably represent different times of formation and transportation during Holocene glacioeustatic sea-level changes. The abraded aggregates that are loosely cemented by calcite occasionally have pristine rhombs attached. Color varies from transparent and colorless or light orange to dark red, without apparent pattern. Cathodoluminescence shows distinctive zoning, analogous to nearby mid-Cenozoic dolomites. Similarly the dolomite is Ca-rich (43 mole % Mg). It occurs within bryozoan-bivalve sediments that are a mixture of relict and modern bioclastic components, across the entire shelf, from siliciclastic sediments debouching from the Murray River to completely carbonate sediments at the shelf edge. Greatest concentrations are fund adjacent to seafloor highs, sites of abundant bryozoan, sponge, and coralline algae growth. Stable isotope values, however, are compatible with precipitation from seawater, similar to those of associated living brachiopods and Mg-rich bryozoans. Sr isotopes confirm the time of formation as modern, unlike the mid-Cenozoic time of formation for similar Tertiary dolomites. These multicycle rhombs and rhomb clusters may therefore be the nucleii for epitaxial precipitation of dolomite either on the modern sea floor or later during burial.

  6. Holocene Carbon Accumulation and Soil Properties in Northern Peatlands: A Circum-Arctic Synthesis (Invited)

    NASA Astrophysics Data System (ADS)

    Loisel, J.; Beilman, D.; Yu, Z.; Camill, P.

    2013-12-01

    Of all terrestrial ecosystems, peatlands are arguably the most efficient at sequestering carbon (C) over long time scales. However, ongoing and projected climate change could shift the balance between peat production and organic matter decomposition, potentially impacting the peatland C-sink capacity and modifying peat-C fluxes to the atmosphere. Yet, the sign and magnitude of the peatland carbon-climate feedback remain uncertain and difficult to assess because of (1) limited understanding of peatland responses to climate change, (2) data gaps and large uncertainties in regional peatland C stocks, and (3) non-linear peatland responses to external forcing. Here we present results from a comprehensive compilation of peat soil properties and Holocene C data for northern peatlands. Our compiled database consists of >250 peat cores from > 200 sites located north of 45N. This synthesis is novel in that our C accumulation estimates are based on directly measured bulk density and C content values. It also encompasses regions within which peat-C data have only recently become available, such as the West Siberia Lowlands, Hudson Bay Lowlands and Kamchatka. Our averaged bulk density value of 0.13 g cm-3 (n = 17,319) is about 16% higher than Gorham's (1991, Ecol. Appl.) widely used estimate of 0.112 g cm-3 for northern peatlands, and 30% larger than the generic value of 0.10 g cm-3 used in recent synthesis (Yu et al. 2009, AGU Monograph 184). When combined with our mean C content value of 48% (n = 2431), these differences in bulk density have important implications for estimating the total C stocks in northern peatlands. Soil organic carbon density (SOC) ranged from 12 to 334 kg C m-2, with a mean value of 102 kg C m-2. A regression model revealed a significant, positive correlation between peat depths and SOC (R2 = 0.675, p < 0.0001), such that higher SOC densities characterized deeper sites. Comparing these values with those published in soil-C surveys that only account for

  7. Factors Affecting 14C Ages of Lacustrine Carbonates: Timing and Duration of the Last Highstand Lake in the Lahontan Basin

    USGS Publications Warehouse

    Benson, L.

    1993-01-01

    Two processes contribute to inaccurate 14C age estimates of carbonates precipitated within the Lahontan basin, NevadaCalifornia: low initial 14C/C ratios in lake water (reservoir effect) and addition of modern carbon to calcium carbonate after its precipitation. The mast reliable set of 14C ages on carbonates from elevations > 1310 m in the Pyramid and Walker Lake subbasins indicate that lakes in all seven Lahontan subbasins coalesced ???14,200 14C yr B.P. forming Lake Lahontan. Lake Lahontan achieved its 1330-m highstand elevation by ???13,800 14 C yr B.P. and receded to 1310 m by ???13,700 14C yr B.P. Calculations, based on measured carbonate-accumulation rates, of the amount of time Lake Lahontan exceeded 1310 and 1330 m (500 and 50 yr) are consistent with this chronology. The timing of the Lake Lahontan highstand is of interest because of the linkage of highstand climates with proximity to the polar jet stream. The brevity of the Lahontan highstand is interpreted to indicate that the core of the southern branch of the polar jet stream remained only briefly over the Lahontan basin.

  8. Mid-Holocene paleoceanographic conditions in the Limfjord region from gastropod (Littorina littorea) oxygen and carbon isotopes

    NASA Astrophysics Data System (ADS)

    Burman, J.; Schmitz, B.

    2003-04-01

    Stable oxygen and carbon isotope intrashell transects of common intertidal gastropods Littorina littorea have been used to reconstruct environmental conditions in the Limfjord region during the mid-Holocene (late Atlantic time). The subfossil specimens studied are from the excavated Stone Age Kitchenmidden in Ertebølle, northern Denmark, dated between 5970±95 to 5070±90 B.P. In addition recent specimens were studied from different coastal localities within the Limfjord, along a salinity gradient from the west to east. These modern shells were used as control samples, in order to construct an oceanographic model for the Limfjord, in which the seasonal isotopic range from the Littorina subfossils could be interpreted. The coastal marine climate in the Ertebølle region during the mid-Holocene indicates summer-SST close to 22^oC and 4-5 ppm reduced salinity compared to fully marine conditions. The mid-Holocene central Limfjord can be described as a coastal area, which experienced similar salinity conditions (c. 30.5 PSU) that prevail in the western part (Odden area) today. In terms of summer-SST as compared with a 10-year average (1989-1998) for the Limfjord region, temperatures were 2-3^oC above recent climatic settings. These results point towards a mid-Holocene Limfjord in contact with the North Sea/Skagerrak with possibly more pronounced water exchange with the North Sea than today.

  9. Long-term stabilization of deep soil carbon by fire and burial during early Holocene climate change

    NASA Astrophysics Data System (ADS)

    Marin-Spiotta, Erika; Chaopricha, Nina T.; Plante, Alain F.; Diefendorf, Aaron F.; Mueller, Carsten W.; Grandy, A. Stuart; Mason, Joseph A.

    2014-06-01

    Buried soils contain large reservoirs of organic carbon at depths that are not typically included in regional and global soil carbon inventories. One such palaeosol, the Brady soil of southwestern Nebraska, USA, is buried under six metres of loess. The Brady soil developed at the land surface on the late-Pleistocene-aged Peoria Loess in a period of warmth and wetness during which dunefields and dust sources across the region were stabilized. Abrupt climate change in the early Holocene led to increased loess deposition that buried the soil. Here, we used spectroscopic and isotopic analyses to determine the composition and stability of organic carbon in the Brady soil. We identify high levels of black carbon, indicating extensive biomass burning. In addition, we found intact vascular plant lipids in soil organic matter with radiocarbon ages ranging from 10,500 to 12,400 cal yr BP, indicating decomposition was slowed by rapid burial at the start of the Holocene. We conclude that landscape disturbance caused by abrupt climate change, fire and the loss of vegetative cover contributed to deep carbon sequestration as the soil was quickly buried under accumulating loess. We suggest that terrestrial soil carbon storage in arid and semi-arid environments could undergo landscape-scale shifts in response to rising temperatures, increased fire activity or drought.

  10. Demise of reef-flat carbonate accumulation with late Holocene sea-level fall: Evidence from Molokai, Hawaii

    USGS Publications Warehouse

    Engels, M.S.; Fletcher, C.H.; Field, M.; Conger, C.L.; Bochicchio, C.

    2008-01-01

    Twelve cores from the protected reef-flat of Molokai revealed that carbonate sediment accumulation, ranging from 3 mm year-1 to less than 1 mm year-1, ended on average 2,500 years ago. Modern sediment is present as a mobile surface veneer but is not trapped within the reef framework. This finding is consistent with the arrest of deposition at the end of the mid-Holocene highstand, known locally as the "Kapapa Stand of the Sea," ???2 m above the present datum ca. 3,500 years ago in the main Hawaiian Islands. Subsequent erosion, non-deposition, and/or a lack of rigid binding were probable factors leading to the lack of reef-flat accumulation during the late Holocene sea-level fall. Given anticipated climate changes, increased sedimentation of reef-flat environments is to be expected as a consequence of higher sea level. ?? 2008 Springer-Verlag.

  11. Dating lacustrine episodes in the eastern Sahara by the epimerization of isoleucine in ostrich eggshells

    USGS Publications Warehouse

    Miller, G.H.; Wendorf, F.; Ernst, R.; Schild, R.; Close, A.E.; Friedman, I.; Schwarcz, H.P.

    1991-01-01

    The eggshell of the African ostrich, Struthio camelus, closely approximates a closed system for the retention of indigenous proteinaceous residues. Epimerization of the protein amino acid isoleucine follows linear first-order kinetics in laboratory simulations nearly to racemic equilibrium, and the variation in D/L ratio within a single fragment, or between fragments of the same age, is significantly less than in other carbonate systems. These observations suggest that the extent of isoleucine epimerization (aIle/Ile ratio) in ostrich eggshell offers the potential for high-resolution geochronology of Quaternary deposits. From the simulation experiments, and dated early Holocene samples for which we have in situ mean annual sediment temperature measurements, Arrhenius parameters have been calculated; the activation energy is 30.33 kcal mol-1, similar to that of other carbonate systems. We have measured the aIle/Ile ratio in ostrich eggshell associated with lacustrine episodes at Bir Tarfawi and Bir Sahara East, two depressions in what is currently the hyperarid eastern Sahara. The ratios can be used directly to indicate qualitatively the time represented by each series of lake sediment, and to correlate disjunct lacustrine deposits within and between the basins. Uranium-series disequilibrium dating of algal mats contained within some of the lake beds indicate that a major wet interval occurred about 130 ka ago. Using the U-series date for calibration, the amino acid ratios are used to date the most recent lacustrine interval to about 100 ka B.P., and two older intervals, one about 200 ?? 25 ka B.P., and an older interval that occurred prior to 250 ka ago. ?? 1991.

  12. Fine-tuning of age integrating magnetostratigraphy, radiocarbon dating, and carbonate cyclicity: Example of lacustrine sediments from Heqing basin (Yunnan, China) covering the past 1 Myr

    NASA Astrophysics Data System (ADS)

    Hu, Shouyun; Goddu, Srinivasa Rao; Appel, Erwin; Verosub, Ken

    2007-05-01

    High-resolution magnetostratigraphy, wavelength spectra of carbonate cyclicities, and AMS radiocarbon dating are integrated to establish an optimum age model for a 168 m long drill core of lacustrine sediments from Heqing basin, Yunnan Province, southwestern China. A 14C age of 51.62 +2.42/-1.85 kyr BP is obtained at a depth of 7.3 m. Remanent magnetization is carried by maghemite and partly in addition by magnetite, both showing the same direction. The polarity sequence clearly reveals the Brunhes/Matuyama (B/M) boundary at 141.5 m. Blake Event is found between 16.3 and 17.5 m, and the upper boundary of Jaramillo is indicated at 167.0 m. Carbonate content and magnetic susceptibility were used for spectral analysis. Fourier analysis was done on the depth section for sliding windows with different window lengths. The spectra within the range of window centers (30-140 m) show a dominant long wavelength, which changes from about 18.5 m in the lower part (>65 m depth) to about 14.5 m in the upper part (<65 m depth) of the core. It is assumed that the long wavelength peak represents the 95-kyr Milankovitch eccentricity cycle. The B/M boundary and Blake Event match very well with this model, but the age of Jaramillo is strongly underestimated. Fourier spectra of sliding windows slightly indicate a drop of the sedimentation rate at the lowermost part of the core. An optimum age model is calculated by cubic spline interpolation using tie points from 14C dating, magnetostratigraphy ('true' ages of Blake Event, B/M boundary, and Jaramillo), and wavelengths of carbonate (change in sedimentation rate at 65 m). Alternative depth-to-age transfer functions were tested, i.e. a wavelength age model (using sedimentation rates with 14C as a tie point), a cyclostratigraphic model (using bandpass-filtered carbonate data corresponding to 95 kyr eccentricity cycles) and correlation of carbonate variations to the marine oxygen isotope curve. However, none of the approaches lead to a

  13. Anthropogenic and geomorphic controls on peatland dynamics in contrasting floodplain environments during the Holocene and its impact on carbon storage

    NASA Astrophysics Data System (ADS)

    Verstraeten, Gert; Broothaerts, Nils; Notebaert, Bastiaan

    2016-04-01

    Peatlands are an important store of carbon in terrestrial environments, and scientific interest in peatlands has increased strongly in the light of the recent global climatic changes. Much attention has been paid to peatland dynamics in extensive arctic and boreal wetlands or to blanket peat in temperate regions. Nevertheless, long-term dynamics of peat in alluvial wetlands in temperate regions remains largely underresearched. In this study, data from three contrasting environments were used to provide more insights in the anthropogenic and geomorphic controls on peatland dynamics. The results show a high variability in alluvial peatland dynamics between the different study sites. In the central Belgian Loess Belt, alluvial peatlands developed during the early Holocene but gradually disappeared from the Mid-Holocene onwards due to the gradual intensification of agricultural activities in the catchment and consequent higher sedimentation rates in the floodplain system. The end of peat growth is shown to be diachronous at catchment scale, ranging between 6500 and 500 cal a BP. The disappearance of the alluvial peatlands has important implications since it potentially reduces the storage of locally produced C. Nevertheless, it was shown that this reduced production of local C but was outbalanced by the burial of hillslope derived C. Also within the sandy catchments of the Belgian Campine region alluvial peatlands initiated in the early Holocene but, here, they abruptly disappeared in the Mid-Holocene before the onset of intense agricultural activities in the catchment. This suggests that for the sandy regions, anthropogenic impact on peatland dynamics is less important compared to natural factors. For these regions, the disappearance of alluvial peatland formation resulted in a sharp decline in alluvial carbon storage as there is no compensation through hillslope derived C input. For the upper Dee catchment in NE Scotland, Holocene carbon floodplain storage varies

  14. Pseudospherulitic fibrous calcite from the Quaternary shallow lacustrine carbonates of the Farafra Oasis, Western Desert, Egypt: A primary precipitate with possible bacterial influence

    NASA Astrophysics Data System (ADS)

    Wanas, H. A.

    2012-04-01

    Pseudospherulitic fibrous calcite (PFC) has been found as a major constituent (85-90%) within thin massive limestone beds of the Quaternary mudflat-shallow lacustrine facies association (1.5-2 m thick) that forms part of combined facies associations of the Quaternary clastic-carbonate unit (25-30 m thick) at Bir-Karawein area in the Farafra Oasis, Western Desert, Egypt. The thin massive limestone beds (2-5 cm thick) are devoid of pedogenic features and marine fossils. They form a rhythmic cyclic succession with thin massive mudrocks (5-10 cm thick). The mudflat-shallow lacustrine facies association herein occurs within a depositional sequence of distal alluvial-floodplain (6-12 m thick) and palustrine (1.5-4.5 m thick) facies associations. The PFC is a composed of loosely packed rounded to sub-rounded single low-Mg-calcite crystals (150-250 μm-sized) with intracrystalline fibrous microfabric marked by fibers (150-250 μm long and 10-20 μm wide) radiating from the center of the individual crystals and displaying irregular internal growth with lobate pattern. The PFC crystals show non-planar to highly irregular intercrystalline boundaries. Under SEM, the individual crystal fibers group of PFC form ellipsoid to sub-globular bodies. Each PFC crystal exhibits successive zones of thick non-luminescence and thin brightly orange to dull luminescence. The matrix (10-15%) between the PFC crystals is mainly a honeycomb-like smectite. The PFC is postulated to be a primary precipitate. This concept is reached because the PFC: (i) does not display the criteria of typical Microcodium structures, root-calcification, speleothem structures, calcite spherulites of laminar calcretes, and calcitization of precursor dolomite or aragonite, (ii) possesses homogenous compositional and textural characteristics, and (iii) occurs within limestone beds that lie in between impermeable massive mudrock beds that dampen diagenesis. A role for possible bacterial contribution in crystallization of

  15. Carbon accumulation and sequestration of lakes in China during the Holocene.

    PubMed

    Wang, Mei; Chen, Huai; Yu, Zicheng; Wu, Jianghua; Zhu, Qiu'an; Peng, Changhui; Wang, Yanfen; Qin, Boqiang

    2015-12-01

    Understanding the responses of lake systems to past climate change and human activity is critical for assessing and predicting the fate of lake carbon (C) in the future. In this study, we synthesized records of the sediment accumulation from 82 lakes and of C sequestration from 58 lakes with direct organic C measurements throughout China. We also identified the controlling factors of the long-term sediment and C accumulation dynamics in these lakes during the past 12 ka (1 ka = 1000 cal yr BP). Our results indicated an overall increasing trend of sediment and C accumulation since 12 ka, with an accumulation peak in the last couple of millennia for lakes in China, corresponding to terrestrial organic matter input due to land-use change. The Holocene lake sediment accumulation rate (SAR) and C accumulation rate (CAR) averaged (mean ± SE) 0.47 ± 0.05 mm yr(-1) and 7.7 ± 1.4 g C m(-2)  yr(-1) in China, respectively, comparable to the previous estimates for boreal and temperate regions. The SAR for lakes in the East Plain of subtropical China (1.05 ± 0.28 mm yr(-1) ) was higher than those in other regions (P < 0.05). However, CAR did not vary significantly among regions. Overall, the variability and history of climate and anthropogenic interference regulated the temporal and spatial dynamics of sediment and C sequestration for lakes in China. We estimated the total amount of C burial in lakes of China as 8.0 ± 1.0 Pg C. This first estimation of total C storage and dynamics in lakes of China confirms the importance of lakes in land C budget in monsoon-influenced regions. PMID:26220607

  16. A 10,900 yr lacustrine record of hydroclimate variability inferred from stable isotope analysis of authigenic carbonate, west-central Newfoundland, Canada

    NASA Astrophysics Data System (ADS)

    Finkenbinder, M. S.; Pompeani, D. P.; Abbott, M. B.

    2013-12-01

    Lakes that precipitate carbonate minerals within the water column provide an important archive to investigate hydroclimate variability and the isotopic composition of paleo-precipitation. Terrestrial isotope records of δ18O and δ13C spanning the Holocene from sub-Arctic eastern Canada are rare, in contrast to the relatively numerous marine records available from the Labrador Sea and North Atlantic Ocean. In an effort to improve understanding of the spatial and temporal variability in terrestrial hydroclimate from Newfoundland, Canada during the Holocene, we utilized stable isotopes of oxygen preserved in authigenic calcite from sediment cores recovered from Cheeseman Lake (informal name; 49.351, -57.603; 180 m asl); a small (0.2 km2), surficially-open lake located near the coast of west-central Newfoundland. A composite 2.63 m core was recovered from 4.1 m water at Cheeseman Lake in August, 2012. Cores were analyzed for dry bulk density, loss-on-ignition analysis, powder X-ray diffraction, scanning electron microscopy, and carbonate stable isotopes of δ18O and δ13C. Age control is provided by 210Pb and 8 AMS 14C dates from terrestrial macrofossils and mollusk shells. Surface water samples from several regional lakes and rivers were also collected and analyzed for δ18O and δD to investigate the sensitivity of Cheeseman Lake to changes in hydroclimate variability. Instrumental weather data from a nearby weather station and monthly precipitation δ18O and δD data from a Canadian Network of Isotopes in Precipitation (CNIP) station at Bay d'Espoir (south-central Newfoundland) are used to investigate modern lake-catchment hydrologic and water isotope relationships. Preliminary results demonstrate that authigenic calcite is preserved continuously in Cheeseman Lake from 10,900 to 1,600 yr BP. Water stable isotope samples and the Bay d'Espoir CNIP data indicate that surface waters at Cheeseman Lake plot along the local meteoric water line, indicating a high degree of

  17. Response of the ocean, climate and terrestrial carbon cycle to Holocene freshwater discharge after 8 kyr BP

    NASA Astrophysics Data System (ADS)

    Wang, Yi; Mysak, Lawrence A.

    2005-08-01

    The ``green'' McGill Paleoclimate Model is run from 8 to 0 kyr BP under variable insolation (Milankovitch forcing), Taylor Dome CO2 (radiative forcing) and four prescribed meltwater scenarios (freshwater forcing) due to the retreat of the Laurentide Ice Sheet (LIS). For each scenario, we constrain the total volume of meltwater to be 1.62 × 1015 m3 (sea level-equivalent of 4.62 m), which is obtained from the work of Paterson (1972) and the reconstructed sea level increase between 8 and 6 kyr BP. During each freshwater perturbation, the simulated maximum Atlantic meridional overturning circulation (MOC) intensity is reduced, by amounts of up to 8 Sv. During the time of a weakened MOC, the sea surface temperature is reduced in the high-latitude North Atlantic and increased in the Southern Ocean. Our model results indicate that the freshwater impact on the Holocene climate and terrestrial carbon cycle is likely negligible after the 8.2-kyr cold event. Only a large freshwater perturbation (>0.1 Sv) has a significant impact on the Holocene climate and terrestrial carbon cycle; it results in an enhanced cooling of about 1°C in the Northern Hemisphere (NH) and notable drops in the global net primary productivity (2 PgC/yr) and total land carbon storage (40 PgC).

  18. Shoreline and Lacustrine Records of Late Quaternary Climate Change in the Chihuahuan Desert, Mexico

    NASA Astrophysics Data System (ADS)

    Castiglia, P. J.; Fawcett, P. J.

    2001-12-01

    Spatial and temporal patterns of Quaternary moisture and temperature variability in northern Mexico are difficult to reconstruct given the paucity of continuous, long-term Quaternary climate records from the region. Preliminary shoreline age dates and a pair of lacustrine sediment cores from Laguna Fresnal in northern Chihuahua, Mexico, record climate-driven variations in both lake level and sedimentologic input. Reeves (1969) first described Laguna Fresnal as part of Pluvial Lake Palomas, a Pleistocene lake composed of 3 interconnected sub-basins: Laguna Guzman, Santa Maria, and Fresnal. Six AMS 14C age dates from previously unrecognized lake fauna on a beach ridge complex indicate a number of Holocene lakes as well. These preserved shorelines increase in age with distance and elevation from the playa surface and include early Holocene (8456\\pm97 14C yrs BP; 1225 m asl), middle Holocene (6180\\pm53, 6401\\pm58, and 6721\\pm68 14C yrs BP; 1200 m asl), and Little Ice Age (435\\pm39 14C yrs BP; 1175 m asl) lake stands. These ages correlate with beach ridge chronologies throughout the western US and northern Mexico. However, during the middle Holocene Laguna Fresnal exhibits a pronounced high stand while other records show a prolonged dry episode. Two 17 m-long cores from the basin center provide a continuous record of sedimentation during the late Quaternary. Several abrupt changes in lake level are indicated by mud cracks preserved as sharp, light gray lineations (487-548 cm and 975-1130 cm), sharply overlain by finely laminated silt and clay. Drying episodes are preserved in the basal section of the cores as several 0.5-2 cm-thick gypsum horizons, overlain by 3-5 cm-thick, carbon-poor (0.02-0.05% TOC), light gray silt. Five distinct zones of coupled, alternating relatively high and low average magnetic susceptibility (MS) and bulk density further reveals changes in lacustrine sedimentation. Peaks in MS generally correlate with peaks in bulk density, with the

  19. Holocene Charcoal Deposition From Brazilian Forest Fires

    NASA Astrophysics Data System (ADS)

    Turcq, B.; Cordeiro, R. C.; Albuquerque, A. S.; Simoes, F. L.; Sifeddine, A.

    2004-12-01

    Determination of charcoal accumulation rate in lacustrine sediments allows to reconstruct the fire history of the region surrounding the lake. Our studies have been achieved in three Amazonian sites and one site in Atlantic rainforest. Charcoal fragments are identified and counted under a microscope. Typical size of these charcoals is around ten micrometers and they probably have been subject to eolian transport. The highest charcoal accumulation rates were obtained in sediments from Middle Holocene in Carajás region, eastern Amazonia. These rates are on the same order than the present day charcoal accumulation rate in Alta Floresta, a region of Amazonia which is being submited to intense slash and burn. The lowest values were found in Lagoa da Pata in Sao Gabriel da Cachoeira, a very humid area in western Amazon. We observed from the D. Helvécio record, in the Atlantic rainforest, fire occurrences from 8,400 to 6,400 cal years BP. For Carajás lake, surrounded by tropical rain forest, we had identified fires during the period between 8,000 and 5,300 cal years BP. Finally, the lake Caracarana, which is surrounded by grass savanna, showed a record of main fire occurrence phase at 9,750 cal yrs BP and a second phase marked by charcoal peaks at 7,680, 6,990 and 6,460 cal yrs BP. The synchronism of the fire occurrence periods in different Brazilian regions is related to the Middle Holocene dry climate phase provoked by the low summer insolation. Differences in the accumulation rates can be attributed to differences in biomass availability and fire return time. The carbon released in the atmosphere by this fires must have contributed to the observed increase of CO2, poorer in 13C, during the middle Holocene.

  20. High-resolution records of Bonneville Basin paleohydrology offer new insights into changing atmospheric circulation patterns over North America from 26 ka through the Holocene

    NASA Astrophysics Data System (ADS)

    Steponaitis, E.; McGee, D.; Quade, J.; Andrews, A.; Edwards, R.; Hsieh, Y.; Broecker, W. S.; Cheng, H.

    2013-12-01

    The tremendous lateral extent of the Bonneville Basin, which covers much of western Utah, makes paleoclimate records from this region highly sensitive to global-scale changes in atmospheric circulation and hydrology. New paleoclimate records from speleothems and lacustrine carbonates offer insight into the hydrology the Bonneville Basin spanning from 26 ka through the Holocene. Anchored by high-precision U-Th dates, Sr records from crystalline lacustrine carbonates from throughout the basin provide a mechanism for constraining zonal variations in precipitation over time. To accomplish this, we exploit spatial variations in the 87Sr/86Sr ratios of fluvial inputs to Lake Bonneville (Hart et al. 2004). Paired with stable isotope records, these Sr records give a spatially detailed view of the response of Great Basin to global climate change, and by extension, insight into atmospheric circulation patterns over North America during abrupt climate changes. Stable isotope and trace metal records from Lehman Cave speleothems provide a high-resolution extension of these Great Basin hydrological records into the Holocene. Here we provide an overview of these unique paired records, focusing particular attention on the region's response to the Younger Dryas and Heinrich events 1 and 2. Hart, W.S. et al., The 87Sr/86Sr ratios of lacustrine carbonates and lake-level history of the Bonneville paleolake system. GSA Bulletin. 2004; 116: 1107-1119.

  1. Calcium-magnesium carbonate solid solutions from Holocene conglomerate cements and travertines in the Coast Range of California

    USGS Publications Warehouse

    Barnes, I.; O'Neil, J.R.

    1971-01-01

    Two calcium-magnesium carbonate solid solutions form Holocene travertines and conglomerate cements in fresh water stream channels of the Coast Range of California. Calcite does not yield the {015} diffraction maximum. The {006} diffraction maximum is lacking over most of the range of composition of calcite. Calcite has compositions from CaCO3 to Ca0.5Mg0.5CO3. Dolomite yields both the {006} and {015} diffraction maxima over its entire composition range, Ca0.6Mg0.4CO3 to Ca0.5Mg0.5CO3. The Ca-Mg carbonates form in isotopic equilibrium and thermodynamic disequilibrium from dispersion of Ca2+-rich water into CO32--rich water within the alluvium. The stable isotope data suggest that all the Mg-rich carbonates are primary precipitates and not a result of Mg-substitution in precursor CaCO3. There is a correlation between ??C13 and Mg content of the carbonates which predicts a 5%. fractionation of C13 between dolomite and calcite at sedimentary temperatures. C14 is incorporated in Ca-Mg carbonates forming from C13-poor meteoric waters and C13-rich waters from Cretaceous sediments. C14 ages of the Ca-Mg carbonates are apparent, and cannot be corrected to absolute values. Solution rates of calcite decrease with increasing MgCO3 content; dolomite dissolves slower than any calcite. ?? 1971.

  2. Ideas and perspectives: why Holocene thermokarst sediments of the Yedoma region do not increase the northern peatland carbon pool

    NASA Astrophysics Data System (ADS)

    Hugelius, G.; Kuhry, P.; Tarnocai, C.

    2015-11-01

    Permafrost deposits in the Beringian Yedoma region store large amounts of organic carbon (OC). Walter Anthony et al. (2014) describe a previously unrecognized pool of 159 Pg OC accumulated in Holocene thermokarst sediments deposited in Yedoma region alases (thermokarst depressions). They claim that these alas sediments increase the previously recognized circumpolar permafrost peat OC pool by 50 %. It is stated that previous integrated studies of the permafrost OC pool have failed to account for these deposits because the Northern Circumpolar Soil Carbon Database (NCSCD) is biased towards non-alas field sites and that the soil maps used in the NCSCD underestimate coverage of organic permafrost soils. Here we evaluate these statements against a brief literature review, existing datasets on Yedoma region soil OC storage and independent field-based and geospatial datasets of peat soil distribution in the Siberian Yedoma region. Our findings are summarised in three main points. Firstly, the sediments described by Walter Anthony et al. are primarily mineral lake sediments and do not match widely used international scientific definitions of peat or organic soils. They can therefore not be considered an addition to the circumpolar peat carbon pool. Secondly, independent field data and geospatial analyses show that the Siberian Yedoma regions is dominated by mineral soils, not peatlands. Thus, there is no evidence to suggest any systematic bias in the NCSCD field data or maps. Thirdly, there is spatial overlap between these Holocene thermokarst sediments and previous estimates of permafrost soil and sediment OC stocks. These carbon stocks were already accounted for by previous studies and cannot be added to the permafrost OC count. We suggest that statements made in Walter Anthony et al. (2014) resulted from misunderstandings caused by conflicting definitions and terminologies across different geoscientific disciplines. A careful cross-disciplinary review of terminologies

  3. Assessing influences on speleothem dead carbon variability over the Holocene: Implications for speleothem-based radiocarbon calibration

    NASA Astrophysics Data System (ADS)

    Noronha, Alexandra L.; Johnson, Kathleen R.; Hu, Chaoyong; Ruan, Jiaoyang; Southon, John R.; Ferguson, Julie E.

    2014-05-01

    Recently, it has been shown that U-Th dated speleothems may provide a valuable archive of atmospheric radiocarbon (14C), but the reliability of these records is dependent upon the stability of the dead carbon proportion (DCP) derived from the soil and bedrock. In order to assess climatic influences on speleothem DCP, we have investigated DCP variability over the Holocene interval where atmospheric 14C is well known based on dendrochronologically dated tree rings by conducting 14C measurements on a U-Th dated stalagmite (HS4) from Heshang Cave, Hubei Province, China (30°27‧N, 110°25‧E; 294 m) spanning 0.5-9.6 ka. We investigated climatic controls on DCP, and found that DCP in HS4 has an average value over the Holocene of 10.3±1.5%, with an average age offset from atmospheric radiocarbon of 875±130 years, and displays a response to both precipitation increases and decreases. HS4 DCP increases during the wetter mid-Holocene interval (˜5.5-7.1 ka), likely reflecting a shift to more closed-system dissolution in response to increased soil moisture. DCP decreases during the 8.2 ka event, a time period of dry conditions at Heshang Cave, though the lower amplitude of this shift indicates that DCP may be less sensitive to dry events. Speleothems are potentially valuable archives of atmospheric radiocarbon, especially in older portions of the 14C calibration curve where knowledge of atmospheric 14C is limited, however minor climatic influences on DCP could introduce uncertainties of several hundred years to calibrated ages.

  4. Late Holocene Climate Variability and Land-use change impacts on fire disturbance and carbon dynamics in the Florida Everglades

    NASA Astrophysics Data System (ADS)

    Jones, M.; Bernhardt, C. E.; Willard, D. A.

    2012-12-01

    Wetlands are an important component in the global carbon cycle because their waterlogged soils promote soil carbon storage as well as methane emissions. It has been established that boreal peatlands occupy only 3% of the terrestrial Earth's surface, but they store one-third to half of the global soil carbon, which has accumulated slowly as peat over thousands of years. However, the role of low latitude peat-accumulating wetlands in the global carbon cycle has not been thoroughly characterized. The Florida Everglades represent one of the major low-latitude peat accumulating systems. The Everglades occupy roughly 6,000 km2 in southern Florida, and consist of a matrix of tree islands, mangrove swamps, cypress domes, marl prairies, sawgrass marshes, sawgrass ridges, and sloughs. Peat has accumulated in much of the Everglades since inception ~7ka, and hydrologic fluctuations related to global- to regional- scale changes in sea level and climate have influenced vegetation patterns. Land-use change since the late 19th century, primarily through the installation of canals and levees and other water-control structures, has altered the hydrology and impacted distribution of native plant communities as well as the occurrence of wildfires. To determine differences in carbon stocks among the dominant ecosystem types and to examine how natural climate variability and land-use change impacts carbon dynamics and the occurrence of wildfires in these systems, we analyzed the carbon accumulation rates from 13 peat cores in four vegetation communities from the Florida Everglades. Although drainage has resulted in the subsidence and oxidation of Everglades peat in many locations, recently collected cores show distinct patterns in carbon storage related to habitat and both natural and anthropogenic changes in hydrology and vegetation community. To further evaluate shifts in wildfire regimes over the late Holocene, we analyzed charcoal records from 10 cores in four vegetation communities

  5. Telling time in shallow water carbonates - from the Cambrian of Morocco to the Holocene of the Bahamas

    NASA Astrophysics Data System (ADS)

    Maloof, A. C.; Bowring, S. A.; Fike, D. A.; Grotzinger, J. P.

    2008-12-01

    Virtually all pre-Mesozoic records of changing ocean-atmosphere chemistry and temperature are derived from chemical sediments deposited on continental shelves. Paired isotope studies of these carbonate rocks have placed the evolution of life in the context of a variable and, at times, non-uniformitarian carbon-sulfur cycle. Furthermore, paired δ13C and 87Sr/86Sr have allowed for global correlation of these stratigraphic successions and have built a framework for studying the history of global change. However, in the absence of quantitative constraints on the rate and duration of geochemical variability, paired stable isotope data tell us little about the processes most important to the variable carbon-sulfur cycle and the co-evolution of life and the surface environment. We discuss two methods of telling time in shelfal carbonate successions. First, we illustrate the use of interbedded volcanic ashes in determining the rate of isotopic change during the Cambrian radiation of animals in Morocco. Next, we present a study of Holocene stratigraphy in the Bahamas that sheds light on the characteristic timescales for the dominant processes controlling carbonate production on continental shelves, and discuss the promise and risk of determining an absolute timescale in the absence of geochronology.

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

    NASA Astrophysics Data System (ADS)

    Gasse, Françoise

    2002-03-01

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

  7. 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

  8. Holocene Palaeoenvironment on Kamchatka

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  9. Holocene freshwater carbonate structures in the hyper-arid Gebel Uweinat region of the Sahara Desert (Southwestern Egypt)

    NASA Astrophysics Data System (ADS)

    Marinova, Margarita M.; Meckler, A. Nele; McKay, Christopher P.

    2014-01-01

    The eastern part of the Sahara is at present the driest region of the desert. Yet the extensive animal rock art in the area, presumed to depict real activities in the lives of the painters, suggests that environmental conditions were significantly different when the rock art was produced. Here we report on exploration of the area, which led to the discovery of morphologically-distinct carbonate structures that line the walls of two valleys in Gebel Uweinat, and were likely formed in standing water. The carbonate structures comprise what appear to be shoreline carbonate formations, and date back to 8100 and 9400 years BP. The chemical and morphological similarity of these formations to carbonate structures from modern lakes suggests that these lakes contained fresh, standing water suitable for human and animal use. However, the significant quartz content suggests that windblown sand was pervasive, and thus the vegetation cover may have been sparse. This discovery supports the possibility of grasslands in the area, which may have been able to support human habitation, and adds to the evidence for a wetter climate in the area in the early Holocene.

  10. The influence of Holocene climate and catchment ontogeny on organic carbon cycling in low-Arctic lakes of SW Greenland

    NASA Astrophysics Data System (ADS)

    Leng, Melanie; Anderson, N. John

    2014-05-01

    Arctic soils represent a major store of organic carbon which is now under threat from regional warming. While much of the carbon is mineralized and released directly to the atmosphere as CO2, some is moved laterally as dissolved and particulate organic C into streams and lakes where it fuels microbial processes and is degassed, some however is buried in lake sediments, where it is effectively removed from the terrestrial C cycle. It is possible to consider how catchment-lake C interactions have varied under natural climate variability and soil/vegetation development by using lake sediment records. Here we present Holocene organic C concentration and isotope data (TOC, C/N, δ13C) from a series of small lakes along Kangerlussuaq (coast to ice cap margin), southwest Greenland, a transect that covers a natural climate gradient and range of limnological conditions. Most Arctic lakes, including those in coastal west Greenland are considered to be net heterotrophic (ecosystem respiration is greater than primary production), i.e. they are net CO2 sources. However, there is evidence that some of the inland Kangerlussuaq lakes are autotrophic. The coastal lakes formed c. 11 cal. ka BP following initial retreat of the ice sheet margin while the inland lakes formed between 8-7 ka BP after its rapid retreat eastwards. The sediment C isotope data suggest a complex Holocene history of interactions between the lakes and their catchments, reflecting glacial retreat, soil and vegetation development and climate-driven hydrological change that had a strong influence on transfer of terrestrially-derived carbon from land to water. At the coast, after 8.5 cal. ka BP, soil development and associated vegetation processes began to exert a strong control on terrestrial-aquatic C-cycling. This is not seen in the inland lakes until ca. 5 ka BP with the maximum extent of dwarf shrub tundra. Some of the lakes respond to Neoglacial cooling from around 5-4 cal. ka BP, when there was a change in

  11. Carbon isotopes in charcoal and soils in studies of paleovegetation and climate changes during the late Pleistocene and the Holocene in the southeast and centerwest regions of Brazil

    NASA Astrophysics Data System (ADS)

    Gouveia, S. E. M.; Pessenda, L. C. R.; Aravena, R.; Boulet, R.; Scheel-Ybert, R.; Bendassoli, J. A.; Ribeiro, A. S.; Freitas, H. A.

    2002-06-01

    This paper attempts to reconstruct vegetation changes and to infer climate changes during the late Pleistocene and the Holocene in the southeast (Botucatu, Anhembi and Jaguariúna, São Paulo State) and centerwest of Brazil (Pontes e Lacerda, Mato Grosso State). The research approach included the use of carbon isotopes ( 13C and 14C) in soil organic matter (SOM) and the evaluation of charcoal distribution and its identification at the species level. Soils sampled in this study were located under natural vegetation, along the slopes of small hills. Charcoal was found predominantly between 150 and 50-cm depth, indicating a period of greater frequency of fires in the study areas, between 6000 and 3000 years BP. For the Botucatu, Anhembi and Pontes e Lacerda sites, the δ13C profiles suggest the predominance of C 3 plants during the entire Holocene. The 13C patterns obtained at the Jaguariúna site that show a more significant presence of C 4 plants compared to the other regions, suggest that this region has been drier than the others during the Holocene. These patterns also indicate the presence of a drier climate compared with present-day conditions at the Jaguariúna region during late Pleistocene until the middle Holocene. This study shows the complexity of vegetation dynamics in the southeast of Brazil during the Holocene. It also shows that the analyses of multiple soil cores representative of the main vegetation communities are necessary for paleovegetation studies.

  12. Eastern Mediterranean hydroclimate over the late glacial and Holocene, reconstructed from the sediments of Nar lake, central Turkey, using stable isotopes and carbonate mineralogy

    NASA Astrophysics Data System (ADS)

    Dean, Jonathan R.; Jones, Matthew D.; Leng, Melanie J.; Noble, Stephen R.; Metcalfe, Sarah E.; Sloane, Hilary J.; Sahy, Diana; Eastwood, Warren J.; Roberts, C. Neil

    2015-09-01

    There is a lack of high-resolution records of hydroclimate variability in the Eastern Mediterranean from the late glacial and early Holocene. More knowledge of the speed of climate shifts and the degree to which they were synchronous with changes in the North Atlantic or elsewhere is required to understand better the controls on Eastern Mediterranean climate. Using endogenic carbonate from a sediment sequence from Nar Gölü, a maar lake in central Turkey, dated by varve counting and uranium-thorium methods, we present high-resolution (˜25 years) oxygen (δ18O) and carbon isotope records, supported by carbonate mineralogy data, spanning the late glacial and Holocene. δ18Ocarbonate at Nar Gölü has been shown previously to be a strong proxy for regional water balance. After a dry period (i.e. evaporation far exceeding precipitation) in the Younger Dryas, the data show a transition into the relatively wetter early Holocene. In the early Holocene there are two drier periods that appear to peak at ˜9.3 ka and ˜8.2 ka, coincident with cooling 'events' seen in North Atlantic records. After this, and as seen in other records from the Eastern Mediterranean, there is a millennial-scale drying trend through the Mid Holocene Transition. The relatively dry late Holocene is punctuated by centennial-scale drought intervals, at the times of 4.2 ka 'event' and Late Bronze Age societal 'collapse'. Overall, we show that central Turkey is drier when the North Atlantic is cooler, throughout this record and at multiple timescales, thought to be due to a weakening of the westerly storm track resulting from reduced cyclogenesis in the North Atlantic. However, some features, such as the Mid Holocene Transition and the fact the early Holocene dry episodes at Nar Gölü are of a longer duration than the more discrete 'events' seen in North Atlantic records, imply there are additional controls on Eastern Mediterranean hydroclimate.

  13. Changes in Terrestrial Organic Carbon Delivery to the Colville River Delta and Adjacent Simpson's Lagoon Over the Late Holocene

    NASA Astrophysics Data System (ADS)

    Schreiner, K. M.; Bianchi, T. S.; Allison, M. A.; Miller, A. J.; Marcantonio, F.

    2012-04-01

    The Colville River in Alaska is the largest river in North America that drains only continuously permafrosted tundra, and as such provides a unique signal of historical changes in one of the world's most vulnerable areas to climate changes. Additionally, the Colville flows into Simpson's Lagoon, a shallow area of the Alaskan Beaufort coast protected by a barrier island chain, lessening the impacts of Arctic storms and ice grounding on sediment mixing. Cores collected from the Colville river delta in August of 2010 were found to be composed of muddy, organic-rich, well-laminated sediments. The 2.5 to 3 meter length of each core spans about one to two thousand years of Holocene history, including the entire Anthropocene and much of the late Holocene. Three cores were sampled for this data set, arranged latitudinally from the mouth of the Colville River east into Simpson's Lagoon. Samples were taken every 2 cm for the entire length of all cores. Bulk analyses including percent organic carbon, percent nitrogen, and stable carbon isotopic analysis were performed, and compound specific analyses including lignin-phenol and algal pigment analyses were performed. These analyses showed significant changes in carbon storage over the past one to two thousand years. There were also significant spatial differences in organic carbon inputs across the ~20km distance between the Colville mouth and the easternmost core. Lignin-phenol concentrations in surface sediments nearest to the river mouth correlated positively with reconstructed Alaskan North Slope temperatures, suggesting more terrestrial organic matter was delivered during higher temperature regimes. Molar C:N ratios and plant pigments correlated negatively and positively, respectively, with reconstructed Alaskan North Slope moisture regime, indicating greater algal inputs during wetter time periods. These data may in part be consistent with observed woody shrub encroachment and increasing expanse of permafrost lakes on the

  14. Lateglacial and Holocene climatic changes in south-eastern Patagonia inferred from carbonate isotope records of Laguna Potrok Aike (Argentina)

    NASA Astrophysics Data System (ADS)

    Oehlerich, M.; Mayr, C.; Gussone, N.; Hahn, A.; Hölzl, S.; Lücke, A.; Ohlendorf, C.; Rummel, S.; Teichert, B. M. A.; Zolitschka, B.

    2015-04-01

    First results of strontium, calcium, carbon and oxygen isotope analyses of bulk carbonates from a 106 m long sediment record of Laguna Potrok Aike, located in southern Patagonia are presented. Morphological and isotopic investigations of μm-sized carbonate crystals in the sediment reveal an endogenic origin for the entire Holocene. During this time period the calcium carbonate record of Laguna Potrok Aike turned out to be most likely ikaite-derived. As ikaite precipitation in nature has only been observed in a narrow temperature window between 0 and 7 °C, the respective carbonate oxygen isotope ratios serve as a proxy of hydrological variations rather than of palaeotemperatures. We suggest that oxygen isotope ratios are sensitive to changes of the lake water balance induced by intensity variations of the Southern Hemisphere Westerlies and discuss the role of this wind belt as a driver for climate change in southern South America. In combination with other proxy records the evolution of westerly wind intensities is reconstructed. Our data suggest that weak SHW prevailed during the Lateglacial and the early Holocene, interrupted by an interval with strengthened Westerlies between 13.4 and 11.3 ka cal BP. Wind strength increased at 9.2 ka cal BP and significantly intensified until 7.0 ka cal BP. Subsequently, the wind intensity diminished and stabilised to conditions similar to present day after a period of reduced evaporation during the "Little Ice Age". Strontium isotopes (87Sr/86Sr ratio) were identified as a potential lake-level indicator and point to a lowering from overflow conditions during the Glacial (∼17 ka cal BP) to lowest lake levels around 8 ka cal BP. Thereafter the strontium isotope curve resembles the lake-level curve which is stepwise rising until the "Little Ice Age". The variability of the Ca isotope composition of the sediment reflects changes in the Ca budget of the lake, indicating higher degrees of Ca utilisation during the period with

  15. Investigation of Long-Term Drought in Mesoamerica Using Lacustrine Proxy Records, Instrumental Data, and Model Output

    NASA Astrophysics Data System (ADS)

    Bhattacharya, T.; Byrne, R.; Chiang, J. C. H.

    2014-12-01

    Paleoclimate research in Mesoamerica suggests that multidecadal droughts in the late Holocene were a factor in the demise of many pre-Columbian sites. However, our understanding of the spatial patterns of these droughts, and the causal mechanisms underlying them, remains poor. Our research is motivated by two main questions: First, we ask whether there is evidence that late Holocene droughts in Mesoamerica were spatially coherent across broad spatial scales. Second, we ask what mechanisms may be responsible for the patterns of paleoclimate change observed in proxy records. To address our first question, we present a record of late Holocene paleoclimatic change from the maar lake Aljojuca, in the eastern Trans-Mexican Volcanic Belt. A chronology established via radiocarbon dating shows that the core spans 6,200 cal. years B.P. We use geochemical proxies, in particular oxygen isotopes from authigenic carbonates, to reconstruct changes in lake level. We also draw on previously published lacustrine paleoclimatic records from across Mesoamerica. Using resampling techniques, we evaluate the impact of age uncertainty on estimates of the timing of late Holocene droughts over the past 2000 years. Our initial results suggest evidence of coherent drought in proxy records from the Yucatan Peninsula to highland Mexico between 1300 and 1000 cal yr. B.P., although there are subsequent intervals when proxy records show diverging trends. To address our second question, we use multivariate statistical techniques to explore coupled patterns of variability between Mesoamerican rainfall and remote sea surface temperatures in instrumental data and climate model control simulations (i.e. CCSM4.0's pre-industrial control simulation). Initial results suggest that low-frequency changes in rainfall may be forced by changes in SSTs in the Pacific or Atlantic basins that alter patterns of moisture transport.

  16. Analysis and Characterization of Organic Carbon in Early Holocene Wetland Paleosols using Ramped Pyrolysis 14C and Biomarkers

    NASA Astrophysics Data System (ADS)

    Vetter, L.; Schreiner, K. M.; Fernandez, A.; Rosenheim, B. E.; Tornqvist, T. E.

    2014-12-01

    Radiocarbon analyses are a key tool for quantifying the dynamics of carbon cycling and storage in both modern soils and Quaternary paleosols. Frequently, bulk 14C dates of paleosol organic carbon provide ages older than the time of soil burial, and 14C dates of geochemical fractions such as alkali and acid extracts (operationally defined as humic acids) can provide anomalously old ages when compared to coeval plant macrofossil dates. Ramped pyrolysis radiocarbon analysis of sedimentary organic material has been employed as a tool for investigating 14C age spectra in sediments with multiple organic carbon sources. Here we combine ramped pyrolysis 14C analysis and biomarker analysis (lignin-phenols and other cupric oxide products) to provide information on the source and diagenetic state of the paleosol organic carbon. We apply these techniques to immature early Holocene brackish wetland entisols from three sediment cores in southeastern Louisiana, along with overlying basal peats. Surprisingly, we find narrow 14C age spectra across all thermal aliquots from both paleosols and peats. The weighted bulk 14C ages from paleosols and overlying peats are within analytical error, and are comparable to independently analyzed 14C AMS dates from charcoal fragments and other plant macrofossils from each peat bed. Our results suggest high turnover rates of carbon in soils relative to input of exogenous carbon sources. These data raise broader questions about processes within the active soil and during pedogenesis and burial of paleosols that can effectively homogenize radiocarbon content in soils across the thermochemical spectrum. The concurrence of paleosol and peat 14C ages also suggests that, in the absence of peats with identifiable plant macrofossils, ramped pyrolysis 14C analyses of paleosols may be used to provide ages for sea-level indicators.

  17. Ideas and perspectives: Holocene thermokarst sediments of the Yedoma permafrost region do not increase the northern peatland carbon pool

    NASA Astrophysics Data System (ADS)

    Hugelius, Gustaf; Kuhry, Peter; Tarnocai, Charles

    2016-04-01

    Permafrost deposits in the Beringian Yedoma region store large amounts of organic carbon (OC). Walter Anthony et al. (2014) describe a previously unrecognized pool of 159 Pg OC accumulated in Holocene thermokarst sediments deposited in Yedoma region alases (thermokarst depressions). They claim that these alas sediments increase the previously recognized circumpolar permafrost peat OC pool by 50 %. It is stated that previous integrated studies of the permafrost OC pool have failed to account for these deposits because the Northern Circumpolar Soil Carbon Database (NCSCD) is biased towards non-alas field sites and that the soil maps used in the NCSCD underestimate coverage of organic permafrost soils. Here we evaluate these statements against a brief literature review, existing data sets on Yedoma region soil OC storage and independent field-based and geospatial data sets of peat soil distribution in the Siberian Yedoma region. Our findings are summarized in three main points. Firstly, the sediments described by Walter Anthony et al. (2014) are primarily mineral lake sediments and do not match widely used international scientific definitions of peat or organic soils. They can therefore not be considered an addition to the circumpolar peat carbon pool. We also emphasize that a clear distinction between mineral and organic soil types is important since they show very different vulnerability trajectories under climate change. Secondly, independent field data and geospatial analyses show that the Siberian Yedoma region is dominated by mineral soils, not peatlands. Thus, there is no evidence to suggest any systematic bias in the NCSCD field data or maps. Thirdly, there is spatial overlap between these Holocene thermokarst sediments and previous estimates of permafrost soil and sediment OC stocks. These carbon stocks were already accounted for by previous studies and they do not significantly increase the known circumpolar OC pool. We suggest that these inaccurate

  18. Marine record of Holocene climate, ocean, and cryosphere interactions: Herbert Sound, James Ross Island, Antarctica

    NASA Astrophysics Data System (ADS)

    Minzoni, Rebecca Totten; Anderson, John B.; Fernandez, Rodrigo; Wellner, Julia Smith

    2015-12-01

    The sediment record offshore James Ross Island, northeast Antarctic Peninsula presents an unparalleled opportunity to directly compare marine and terrestrial climate records spanning the Holocene in maritime Antarctica. An 11 m drill core was collected between Herbert Sound and Croft Bay as part of the SHALDRIL NBP-0502 initiative and produced the southernmost sediment record from the eastern side of the AP. Thirty-eight radiocarbon ages are used to construct an age model of centennial-scale resolution. Multi-proxy records, including magnetic susceptibility, pebble content, particle size, total organic carbon, and diatom assemblages, were interrogated in the context of nearby Holocene-age ice core, lake, and drift records from James Ross Island. Differences in the timing and expression of Holocene events reflect marine controls on tidewater glaciers, such as water mass configurations and sea ice. Glacial behavior mimics ice core paleotemperatures during the Holocene, with the exception of distinct ocean warming events. Herbert Sound was fully occupied by grounded ice during the Last Glacial Maximum, and experienced rapid lift-off, followed by a floating ice phase. The canopy of floating ice receded by 10 ± 2.4 cal kyr BP, presumably in response to Early Holocene warming. Herbert Sound and Croft Bay fully deglaciated by 7.2 cal kyr BP, when the Mid Holocene Hypsithermal commenced and the sound became open and productive. An extreme peak in productivity ˜6.1 cal kyr BP indicates an oceanic warming event that is not reflected in atmospheric temperature or lacustrine sediment records. Increase in sea ice cover and ice rafting mark the onset of the Neoglacial ˜2.5 cal kyr BP, when pronounced atmospheric cooling is documented in the James Ross Island ice core. Our comparison facilitates more holistic understanding of atmosphere-ocean-cryosphere interactions that may aid predictions of glacial response to future warming and sea-level scenarios.

  19. Stable carbon isotope values document how a Late Holocene expansion in grasslands impacted vertebrates in northwestern Madagascar

    NASA Astrophysics Data System (ADS)

    Crowley, B. E.; Samonds, K.

    2012-12-01

    Madagascar is home to some of the world's most distinctive plants and animals. Unfortunately, forest loss and habitat degradation has had a dramatic impact on both floral and faunal communities. Here we use carbon isotope values in radiocarbon-dated bones to examine how the vertebrate community at Anjohibe Cave, northwestern Madagascar, responded to a Late Holocene increase in C4 grass abundance. Our data demonstrate that major changes in the vegetation and animal community are recent phenomena at Anjohibe. Extinct lemurs and hippopotamuses were present until ca. 1500 years ago. These taxa relied exclusively on C3 resources. Locally extirpated fauna were present until 300 years ago. The majority of these species also relied on C3 resources. Their presence strongly suggests that the region surrounding the cave was more wooded than it is now, possibly as recently as 300 years ago. All introduced individuals are modern. Rats (Rattus sp.), shrews (Suncus murinus), and the giant frog Hoplobatrachus cf. tigrinus, have remarkably high carbon isotope values, implicating substantial ingestion of C4 foods. It is possible that grass abundance has increased dramatically in the past 100 years. Alternatively, opportunistically granivorous rats and shrews may selectively consume seeds from C4 grasses. In agreement with previous studies, stable isotope data reveal details of vegetation and faunal turnover in Northwestern Madagascar. Grasses have increased, forest dwelling species have vanished, and introduced taxa are exploiting a novel niche.

  20. Developing inorganic carbon-based radiocarbon chronologies for Holocene lake sediments in arid NW China

    NASA Astrophysics Data System (ADS)

    Zhang, Jiawu; Ma, Xueyang; Qiang, Mingrui; Huang, Xiaozhong; Li, Shuang; Guo, Xiaoyan; Henderson, Andrew C. G.; Holmes, Jonathan A.; Chen, Fahu

    2016-07-01

    Inorganic carbonates are often used to establish radiocarbon (14C) chronologies for lake sediments when terrestrial plant remains (TPR) are rare or when bulk organic matter is insufficient for dating, a problem that is common for many lakes in arid regions. However, the reservoir effect (RE), as well as old carbon contributed from the lakes catchment make it difficult to establish reliable chronologies. Here we present a systematic study of inorganic 14C ages of two lake-sediment sequences, one from a small-enclosed saline lake - Lake Gahai in Qaidam Basin, and the other from a large freshwater lake - Lake Bosten in Xinjiang. Modern dissolved inorganic carbon (DIC) of the lakes, paleo-lake sediments exposed in the catchment, and mollusk shells in core sediments from Lake Gahai were dated to assess the RE and the contribution of pre-aged carbon to the old ages in the cores. We propose a statistical regression to assess more than one RE for the 14C carbonate ages within our sedimentary sequences. Old radiocarbon ages contributed by detrital carbonates were assessed by comparing the ages of mollusk shells with those of carbonates at the same sediment depths. We established the RE of the authigenic component and assessed detrital old carbon contributions to our two sites, and this was used to correct the 14C ages. Based on this approach, we developed age models for both cores, and tested them using 210Pb ages in both cores and TPR-based 14C-ages recovered from Lake Bosten. We further tested our age models by comparing carbonate-based oxygen isotope (δ18O) records from both lakes to an independently-dated regional speleothem δ18O record. Our results suggest if sedimentary sequences are densely dated and the RE and the contribution of old carbon from detrital carbonates can be ascertained, robust chronological frameworks based on carbonate-based 14C determinations can be established.

  1. Peatland Carbon Dynamics on the North Slope of Alaska During the Holocene: The Role of Climate, Sea Ice, and Buried Peat

    NASA Astrophysics Data System (ADS)

    Yu, Zicheng; Massa, Charly; Cleary, Kathleen; Jones, Benjamin; Grosse, Guido

    2014-05-01

    Our recent and ongoing data syntheses indicate that peatlands accumulated more carbon (C) during past warm climate intervals in the circum-Arctic region, including Alaska. In particular, peak C accumulations have been observed during the Holocene Thermal Maximum (HTM) in the early Holocene when summer insolation was higher. However, we do not know the regional patterns and impacts of sea-ice change on Holocene peat C accumulation, especially around the Arctic Ocean where increased vegetation productivity has already been linked to sea ice declines in recent decades. Here we review Holocene peatland and tundra C accumulation records on the North Slope, along with our preliminary results, to investigate spatiotemporal pattern of C accumulation and the possible role of sea-ice change. As in many other northern high-latitude regions, most peatlands on the North Slope initiated in the early Holocene. Several discontinuous and low-resolution peat accumulation records from the region appear to show high accumulation rates or high C content in the early Holocene. In addition, we note that many peatlands that existed during the earlier Holocene on the North Slope have disappeared and are presently covered by mineral soils under tundra or eolian sandy deposits, indicating that current peatland extent is only a fraction of early Holocene extent. In contrast to highest C accumulation rates in the early Holocene, our preliminary results from a 70-cm-long peat core (lat. 70.71 N; long. 153.87 W) from northwest Teshekpuk Lake, near the Teshekpuk Lake Observatory on the Arctic Coastal Plain, about 10 km from the Arctic Ocean, shows a very different pattern. The highest C accumulation of 12.7 gC/m2/yr is observed after 2.9 ka, much higher than the rate of 3.8 gC/m2/yr at 8.1-2.9 ka. Furthermore, the period with high C rates after 2.9 ka at this site was dominated by well-preserved peat mosses (Sphagnum) and with abundant leaf fragments, likely from dwarf birch (Betula nana). This

  2. Lacustrine Environments and Landing Sites

    NASA Astrophysics Data System (ADS)

    Ori, G. G.; Marinangeli, L.

    1999-01-01

    The most promising sites for landing exploration on Mars are lacustrine deposits because on Earth these environments bear a wealth of life varying form benthic to plantonic organisms. Based on the state-of-the-art geology, several areas are thought to be covered by standing bodies of water and, among them, the ones contained in impact craters are the most recognisable. Craters provide a pre-formed basin with well defined rims and the body of water inside could form more evident morphological features than in lakes with broader and less defined margins. The undoubt identification of lacustrine environments will rise from the availability of mineralogical data and high resolution imaging from the future missions. However, the current data of MGS mission do provide enough compelling evidence strongly suggesting the presence of these bodies of water. Lacustrine deposits are quite good landing sites even in term of safety. Usually the floor is remarkably flat and, apart from coarse-grained basin margins, the sediment of the lake bottom is fine-grained. Moreover, the possible rough topography of the substratum can be buried by the lacustrine sedimentation that tends to smooth rough surfaces and relief.

  3. The impact of land use on carbon and climate in the preindustrial Holocene: What have we learned and what are the priorities for future research?

    NASA Astrophysics Data System (ADS)

    Ellis, E. C.; Kaplan, J. O.

    2015-12-01

    Did humans affect global climate over the before the Industrial Era? While this question is hotly debated, the co-evolution of humans and the natural environment over the last 11,700 years had an undisputed role in influencing the development and present state of terrestrial ecosystems. Yet we still have a very incomplete picture of human-environment interactions over the Holocene. In order to address this lack of understanding, both bottom-up and top-down approaches have been used to reconstruct past human impact on the global carbon cycle and climate. Top-down approaches rely on the analysis of the concentrations and isotopic signature of trace gases trapped in polar ice to identify human contributions to atmospheric composition. Bottom-up approaches combine historical and archaeological data to reconstruct land use, and using these reconstructions drive earth system models that simulate carbon cycling and climate. Recently a number of studies, both top-down and bottom-up, have shed new light on the role of land use influencing the carbon cycle and climate over the preindustrial Holocene. Ice core studies generally suggested that late Holocene CO2 was driven by natural fluctuations in climate and ocean circulation. The evidence from bottom-up studies is more nuanced. Most scenarios of Holocene anthropogenic land cover change (ALCC) tend to agree in the net magnitude of deforestation at AD 1850. But ALCC scenarios vary widely in the timing of deforestation over the course of the preindustrial Holocene. These differences lead to multiple plausible explanations to the atmospheric composition record, including scenarios that allow for a substantial amount of anthropogenic deforestation in preindustrial time. Uncertainty in our understanding of preindustrial ALCC also leads to large differences in the estimated importance of land use on climate earlier in the Holocene. For example, modelling experiments performed for Europe representing conditions at the peak of the

  4. The origin of meter-scale upward-shallowing parasequences in carbonate stratigraphy: Comparing the Holocene of northwest Andros Island, Bahamas to the Paleozoic and Precambrian (Invited)

    NASA Astrophysics Data System (ADS)

    Maloof, A. C.; Grotzinger, J. P.

    2013-12-01

    We present a field study of Holocene peritidal carbonate accumulation at Triple Goose Creek, northwest Andros Island, Bahamas. Our aim is to understand the possible origin of the meter-scale upward-shallowing parasequences that frequently dominate stratigraphic records of ancient carbonate platforms. We determine the relative importance of channel migration and sea level change in controlling parasequence architecture by integrating surface lithofacies maps and differential GPS topographic surveys with 187 sediment cores that each span the entire Holocene stratigraphy. We show that channels have migrated at rates of 0-6 cm per year. Visibly very different lithofacies are sensitive to elevation changes as small as 5 cm, and are responding to both internal (sediment supply) and external (sea level rise) controls. Therefore, although the location of channels is responsible for the modern mosaic of lithofacies, these lithofacies and the channels that control them have not migrated substantially during the 1200 years of sediment accumulation at Triple Goose Creek. We discuss the evolution of the Holocene upward-shallowing parasequence at Triple Goose Creek, and compare it to pre-Cenozoic icehouse and greenhouse examples.

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

    NASA Astrophysics Data System (ADS)

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

    2008-12-01

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

  6. Carbon storage and late Holocene chronostratigraphy of a Mississippi River deltaic marsh, St. Bernard Parish, Louisiana

    USGS Publications Warehouse

    Markewich, H. W., (Edited By)

    1998-01-01

    Today, the causes, results, and time scale(s) of climate change, past and potential, are the focus of much research, news coverage, and pundit speculation. Many of the US government scientific agencies have some funds earmarked for research into past and (or) future climate change (National Science and Technology Council, 1997). The Mississippi Basin Carbon Project (MBCP) is part of the U.S. Geological Survey (USGS) effort in global change research . The project is motivated by the need to increase our understanding of the role of terrestrial carbon in the global carbon cycle, particularly in the temperate latitudes of North America. The global land area between 30 O and 60 O N is thought to be a large sink for atmospheric CO2 (IPCC, 1996). The identity of this sink is unknown, but is in part the soil and sediment that makes up the upper several meters of the Earth's surface. The MBCP focuses on the Mississippi River basin, the third largest river system in the world (fig. 1), that drains an area of 3.3 x 10 6 km 2 (1.27 x 10 6 mi 2 ). The Mississippi River basin includes more than 40 percent of the land surface, and is the home of more than one-third of the population, of the conterminous United States. Because climate, vegetation, and land use vary greatly within the Mississippi River basin, the primary terrestrial sinks for carbon need to be identified and quantified for representative parts of the basin. The primary goal of the MBCP is to quantify the interactive effects of land-use, erosion, sedimentation, and soil development on carbon storage and nutrient cycles within the Mississippi River basin. The project includes spatial analysis of a wide variety of geographic data, estimation of whole-basin and sub-basin carbon and sediment budgets, development and implementation of terrestrial carbon-cycle models, and site-specific field studies of relevant processes. Areas can be studied and compared, and estimates can be made for whole-basin carbon storage and flux.

  7. A Holocene record of climate-driven shifts in coastal carbon sequestration

    USGS Publications Warehouse

    Mitra, Siddhartha; Zimmerman, A.R.; Hunsinger, G.B.; Willard, D.; Dunn, J.C.

    2009-01-01

    A sediment core collected in the mesohaline portion of Chesapeake Bay was found to contain periods of increased delivery of refractory black carbon (BC) and polycyclic aromatic hydrocarbons (PAHs). The BC was most likely produced by biomass combustion during four centennialscale dry periods as indicated by the Palmer Drought Severity Index (PDSI), beginning in the late Medieval Warm Period of 1100 CE. In contrast, wetter periods were associated with increased non-BC organic matter influx into the bay, likely due to greater runoff and associated nutrient delivery. In addition, an overall increase in both BC and non-BC organic matter deposition during the past millennium may reflect a shift in climate regime. The finding that carbon sequestration in the coastal zone responds to climate fluctuations at both centennial and millennial scales through fire occurrence and nutrient delivery has implications for past and future climate predictions. Drought-induced fires may lead, on longer timescales, to greater carbon sequestration and, therefore, represent a negative climate feedback. Copyright 2009 by the American Geophysical Union.

  8. Evaluating Carbon Isotope Signature of Bulk Organic Matter and Plant Wax Derived n-alkanes from Lacustrine Sediments as Climate Proxies along the Western Side of the Andes

    NASA Astrophysics Data System (ADS)

    Contreras, S.; Werne, J. P.; Araneda, A.; Conejero, C. A.

    2015-12-01

    Sedimentary carbon isotope values (δ13C) of bulk organic matter and long chain (C25 to C35) n-alkanes are among the most long-lived and widely utilized proxies of organic matter and vegetation source. The carbon distribution (e.g. average carbon chain length, ACL) and isotope signature from long chain n-alkanes had been intensively used on paleoclimate studies because they are less influenced by diagenesis, differential preservation of compound classes, and changes in the sources of organic matter than bulk δ13C values. Recently, studies of modern plant n-alkanes have challenged the use of carbon distribution and carbon isotope signature from sedimentary n-alkanes as reliable indicators of vegetation and climate change. The climate in central-south western South America (SA) is projected to become significantly warmer and drier over the next several decades to centuries in response to anthropogenically driven warming. Paleolimnological studies along western SA are critical to obtain more realistic and reliable regional reconstructions of past climate and environments, including vegetation and water budget variability. Here we discuss bulk δ13C, distribution and δ13C in long chain n-alkanes from a suite of ~40 lake surface sediment (core-top) samples spanning the transition from a Mediterranean climate with a patchwork of cultivated vegetation, pastureland, conifers in central Chile to a rainy temperate climate dominated by broadleaf deciduous and evergreen forest. Data are compared to the latitudinal and orographic climatic trends of the Andes based on the climatology (e.g. precipitation and temperature) of the locations of all lakes involved in this study, using monthly gridded reanalysis products of the Climate Forecast System Reanalysis (CFSR), based on the NCEP global forecast model and meteorological stations available in the region, from January 1979 to December 2010 with a 0.5° horizontal resolution.

  9. Spatial variability of tephra and carbon accumulation in a Holocene peatland

    NASA Astrophysics Data System (ADS)

    Watson, E. J.; Swindles, G. T.; Lawson, I. T.; Savov, I. P.

    2015-09-01

    Microscopic tephra layers ('cryptotephras') represent important age-equivalent stratigraphic markers utilised in many palaeoenvironmental reconstructions. When used in conjunction with proximal records of volcanic activity they can also provide information about volcanic ash cloud fallout and frequency. However, the spatial distributions of tephra layers can be discontinuous even within the same region. Understanding the deposition and post-depositional redistribution of tephra is vital if we are to use cryptotephras as records of ash cloud occurrence and chronostratigraphic markers. The discrete nature of tephra layers also allows for detailed study into processes of deposition and reworking which affect many palaeoenvironmental proxy records. We undertook a multi-core study in order to examine the historical tephrostratigraphy of a raised peatland in Northern Ireland. Three tephra layers originating from Iceland (Hekla 1947, Hekla 1845 and Hekla 1510) are present in 14 of the 15 cores analysed. This suggests that in areas not influenced by snowfall or anthropogenic disturbance at the time of tephra delivery, the presence or absence of a tephra layer is generally consistent across a peatland of this type. However, tephra shard counts (per unit area) vary by an order of magnitude between cores. These intra-site differences may confound the interpretation of shard counts from single cores as records of regional ash cloud mass/density. Bootstrap resampling analysis suggests that total shard counts from multiple cores are required in order to make a reliable estimate of median shard counts for a site. The presence of three historical tephras in 14 cores enables a spatio-temporal analysis of the long-term apparent rate of carbon accumulation (LARCA) in the peatland. Substantial spatial and temporal variations in LARCA are identified over the last ∼450 years. This high variability needs to be taken into account when designing studies of peatland carbon accumulation.

  10. Geochemical anomalies in carbonate lacustrine sediments as seasonal and centennial environmental proxy for continental climate conditions in South Siberia during the last 2450 yrs.

    NASA Astrophysics Data System (ADS)

    Kalugin, I.; Darin, A.; Tretyakov, G.; Rogozin, D.; Khromykh, S.; Kholodova, L.; Maksimova, N.

    2012-04-01

    Sedimentation history of saline lakes efficiently reflects environmental change in catchment area especially for wet-arid conditions. Different sediment carbonates allows quantitative assessment of physicochemical conditions and bioproduction. Shira lake in South Siberia is a good representative object for detail weather-climate modeling due to it`s local hydroclimatic information and annually laminated bottom sediments. Thermodynamic estimation of rock-water multisystem in conformity with local conditions and source matter gives grounds for interpretation of measured geochemical parameters in sediments as environmental indicators like temperature, salinity, pH etc. At the same time using a modern scanning X-ray fluorescence technique for sub-millimeter microstratigraphic study of varves results quantitative environmental reconstruction year by year. Meromictic Shira Lake is closed shallow (25 m) basin 9,4x5,3 km2 of brackish water (total salinity up to 19 g/l) inflowed by small Son river. Continental climate provides mean July temperature 18o and January -20oC. A long-term waterbody stratification with intra-annual chemocline depth 11-16,2 m is observed as well as level oscillations up to 7 m Sediment has thin laminated structure, where black clay-carbonate organic bearing layers are coupled with white organic free ones. Thickness of rhythms varied from 2 mm in the uppermost 20 cm of core to 0.4 mm close to the bottom. Clastic components quartz, feldspar, micas, chlorite are distributed under dust and flood events but not regularly. Visible 6 light intervals depleted of organics are revealed along the core. They have 45-120 mm in thickness and are repeated every 200-250 mm. Dark and light sediments are different in water content as well as rock-forming element composition. LOI<500oC is rather lower in light components, that confirms lack organic matter. Correspondingly, calcite (18-30%) and monohydrocalcite (13-14%) predominate in black muds coloured by organics

  11. A Holocene climate record from palaeolakes in NW India

    NASA Astrophysics Data System (ADS)

    Dixit, Y.; Hodell, D. A.; Petrie, C.

    2011-12-01

    The plains of NW India encompasses arid, semi-arid to sub-humid zones and archaeological research indicate this region was intensively settled by the Indus Valley Civilization. The precise climatological and environmental history of this region during the Holocene period remain largely unknown. We present high-resolution isotope proxy records of local palaeoclimate change from lacustrine deposits in two different climatic zones from west to east; Palaeo-lake Riwasa in the semi-arid and paleo-lake Kotla Dahar in the sub-humid region in Haryana plains, India. The oxygen isotope record from palaeolake Riwasa indicates the inception of wet climate conditions and establishment of a deep, permanent lake in the basin at ~8870 14C yr BP, coinciding approximately with the early Holocene maximum in the Indian monsoon. A major desiccation event occurs after ~7000 14C yr BP. Our results from palaeolake Riwasa indicate that the permanent deep-water lake and major desiccation event in semi-arid region pre-dated the urban phase of the Indus Civilization. Palaeolake Kotla Dahar is located further east than Riwasa in the sub-humid zone, and receives 500-700mm rainfall. Calcium carbonate percent of bulk sediments from Kotla Dahar increases down section to a maximum of 72%, indicating the presence of a deep carbonate marl lake. Oxygen isotopes are currently being measured on gastropod and ostracod shells and radiocarbon dates are being obtained from this section. We speculate that the oxygen isotope record from Kotla Dahar may provide critical climate data for the period between 5000-3500 BP, the period of Harappan Urbanism. Our study of palaeo-lakes Riwasa and Kotla Dahar constitute the first oxygen isotope records from the plains of NW India to interpret the palaeoclimate history of this region.

  12. High-resolution leaf wax carbon and hydrogen isotopic record of the late Holocene paleoclimate in arid Central Asia

    NASA Astrophysics Data System (ADS)

    Aichner, B.; Feakins, S. J.; Lee, J. E.; Herzschuh, U.; Liu, X.

    2015-04-01

    Central Asia is located at the confluence of large-scale atmospheric circulation systems. It is thus likely to be highly susceptible to changes in the dynamics of those systems; however, little is still known about the regional paleoclimate history. Here we present carbon and hydrogen isotopic compositions of n-alkanoic acids from a late Holocene sediment core from Lake Karakuli (eastern Pamir, Xinjiang Province, China). Instrumental evidence and isotope-enabled climate model experiments with the Laboratoire de Météorologie Dynamique Zoom model version 4 (LMDZ4) demonstrate that δ D values of precipitation in the region are influenced by both temperature and precipitation amount. We find that these parameters are inversely correlated on an annual scale, i.e., the climate has varied between relatively cool and wet and more warm and dry over the last 50 years. Since the isotopic signals of these changes are in the same direction and therefore additive, isotopes in precipitation are sensitive recorders of climatic changes in the region. Additionally, we infer that plants use year-round precipitation (including snowmelt), and thus leaf wax δ D values must also respond to shifts in the proportion of moisture derived from westerly storms during late winter and early spring. Downcore results give evidence for a gradual shift to cooler and wetter climates between 3.5 and 2.5 cal kyr BP, interrupted by a warm and dry episode between 3.0 and 2.7 kyr BP. Further cool and wet episodes occur between 1.9 and 1.5 and between 0.6 and 0.1 kyr BP, the latter coeval with the Little Ice Age. Warm and dry episodes from 2.5 to 1.9 and 1.5 to 0.6 kyr BP coincide with the Roman Warm Period and Medieval Climate Anomaly, respectively. Finally, we find a drying tend in recent decades. Regional comparisons lead us to infer that the strength and position of the westerlies, and wider northern hemispheric climate dynamics, control climatic shifts in arid Central Asia, leading to complex

  13. Facies analyses of cold-water spring-fed fluvial carbonates: Implications for a terrestrial Holocene (?) record of wet events in Southern California

    NASA Astrophysics Data System (ADS)

    Ibarra, Y.; Corsetti, F. A.; Feakins, S. J.

    2012-12-01

    was active. The presence of groundwater-fed carbonate deposits in this region constitute a unique opportunity to compare/compliment a record of terrestrial wet events to proximal high-resolution records of Holocene climate from the sediments of Zaca Lake located about 2km away and the diverse assemblage of Holocene climate records from the Santa Barbara Basin located about 50km to the south.

  14. Unusual carbon and oxygen isotropic ratios of ostracodal calcite from last interglacial (Sangamon episode) lacustrine sediment in Raymond Basin, Illinois, USA

    USGS Publications Warehouse

    Curry, B. Brandon; Anderson, T.F.; Lohmann, K.C.

    1997-01-01

    The stable isotopic records of ostracode valves deposited during the last interglaciation in Raymond Basin, Illinois, have ??13C and ??18O values as high as +16.5??? and +9.2??? respectively, the highest values yet reported from continental ostracodal calcite. Located in south-central Illinois, Raymond, Pittsburgh, Bald Knob, and Hopwood Farm basins collectively have yielded important long pollen and ostracode records that date from about 130 000 years ago to the present. Although fossils from the present-day interglaciation are not well preserved, these records constitute the only described, conformable, fossiliferous successions of this age from the interior of glaciated North America. The high ??13C values from Raymond Basin are attributed to the residual effects of methane loss either by ebullition or by emission through the stems of senescent emergent aquatic vegetation. A mass balance model suggests that an increase in ??13C of dissolved inorganic carbon on the order of +15??? is possible within a few hours given modest rates of methanogenesis of about 0.02 mol m-2 d-1. The ??13C records from other studies of ostracode valves have values approaching, but not exceeding about +14??? suggesting a limiting value to ???13C enrichment due to simultaneous inputs and outputs of dissolved inorganic carbon. Values of ??18O in ostracodal calcite are quite variable (-4 to +9???) in sediment from the late Sangamon subepisode. A model of isotopic enrichment in a desiccating water body implies that a reduction in reservoir volume of 20% could produce this range of isotopic values. High humidity and evaporation probably account for most of the ??18O variability.

  15. Organic Carbon Delivery to a High Arctic Watershed over the Late Holocene: Insights from Plant Biomarkers and Compound Specific δ13C and Δ14C Measurements

    NASA Astrophysics Data System (ADS)

    Schreiner, K. M.; Bianchi, T. S.; Eglinton, T. I.; Allison, M. A.

    2012-12-01

    The Colville River in Alaska is the largest river in North America which has a drainage basin that is exclusively underlain by permafrost, and as such provides a unique signal of historical changes in one of the world's most vulnerable areas to climate changes. Additionally, the Colville flows into Simpson's Lagoon, an area of the Alaskan Beaufort coast protected by a barrier island chain, lessening the impacts of Arctic storms and ice grounding on sediment mixing. Cores collected from the Colville river delta in August of 2010 were found to be composed of muddy, organic-rich, well-laminated sediments. The 2.5 to 3 meter length of each core spans about one to two thousand years of Holocene history, including the entire Anthropocene and much of the late Holocene. Two cores were sampled for this data set - one from close to the river mouth, and one from farther east in Simpson's Lagoon. Samples were taken every 2 cm for the entire length of both cores. In order to determine how the amount of terrestrial organic matter input changed over the Holocene, bulk analyses including percent organic carbon, percent nitrogen, and stable carbon isotopic analysis were performed, and biomarkers including lignin-phenols and fatty acids were measured. It was shown that lignin-phenol input is positively correlated with Alaskan North Slope temperature reconstructions. To determine whether the source of this increased terrestrial organic matter input was from fresh vegetation (for example, shrub encroachment onto tundra areas) or aged soil organic matter (potentially due to permafrost thawing and breakdown), selected samples were analyzed for compound-specific δ13C and Δ14C of fatty acids and lignin-phenols. These analyses show significant changes in carbon storage and in terrestrial carbon delivery to the Lagoon over time. These results represent the first fine-scale organic biomarker study in a high Arctic North American Lagoon, and have many implications for the future of carbon

  16. Reconstruction of Holocene southern African continental climate using biomarkers from salt pan sediments

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

    The climate system of southern Africa is strongly influenced by large scale atmospheric and marine circulation processes and, therefore, very sensitive to global climate change. Recent publications provided evidence for strong spatial and temporal climate variability in southern Africa over the Holocene. It is of major importance to understand the mechanisms driving the southern African climate system in order to estimate regional implications of current global change. However, proxy datasets from continental geoarchives especially of the semi-arid western Kalahari region are still scarce. A main problem is the absence of conventional continental climatic archives, due to the lack of lacustrine systems. In this study we are exploring the utility of sediments from western Kalahari salt pans, i.e. local depressions which are flooded temporarily during rainfall events. Besides the analyses of basic geochemical bulk parameters including TOC, δ13Corg, TIC, δ13Ccarb, δ18Ocarb, TN, δ15N, the paleo-climatic approach focuses on reconstruction of local vegetation assemblages to identify changes in the ecosystem. This is pursued using plant biomarkers, particularly leaf wax n-alkanes and n-alcohols and their stable carbon and hydrogen isotopic signatures. Preliminary results show prominent shifts in n-alkane distribution and δ13C values of the C33 homologue during late Pleistocene and early Holocene. These shifts correlate to changes of the TOC content. Our data indicate changes in carbon sources which possibly reflect major environmental changes.

  17. Concordance of Oxygen Isotope Palaeotemperature Proxies Using Fossil Phosphate and Carbonate: Implications for Tracking Palaeoclimate Change in Eocene-Oligocene Fluvio-lacustrine Sediments.

    NASA Astrophysics Data System (ADS)

    Grimes, S.; Mattey, D. P.; Hooker, J.; Collinson, M.

    2001-12-01

    An understanding of palaeoclimates is critical to interpretation of earth history and biotic response to global climate change. A proxy for meteoric water \\delta18O values is the oxygen isotope composition of mammalian phosphate in tooth enamel. Combining the \\delta18O of meteoric water with the \\delta18O of a carbonate, or phosphate organism precipitated from it then allows the calculation of palaeotemperatures. Using a single palaeoproxy through a large succession of terrestrial deposits is difficult, but not impossible, due to species extinction and changing depositional conditions affecting preservation. Ideally one would like to use different palaeoproxies at different horizons. However, before this can be done all the palaeoproxies must be employed at a single horizon to see if they produce similar temperatures. This has not been done before, most likely due to insufficient biodiversity at a single horizon. Such a rich horizon exists in the Osborne Member of the Hampshire Basin Solent Group, UK. Here we present palaeotemperatures calculated using 4 different freshwater palaeoproxies. Phosphate analyses (Thalerimys fordi and Isoptychus tooth enamel and gar scale) were conducted using a direct laser-fluorination method (Lindars et al. 2001, GCA 65:2535-2548). Carbonate analyses were conducted on a Micromass Isoprime multiflow mass-spec. The local water \\delta18O value (-1.25 +/- 1.68\\permil n = 62) was calculated using corrected Thalerimys fordi and Isoptychus tooth enamel results (See abstract by Lindars et al.). The group, common name and object, plus the \\delta18O results, reference, equation and calculated palaeotemperatures are given below. Gastropod, pond snail, shell. \\delta18OCarbonate = -1.71 +/- 1.25\\permil n = 50. (Chaix et al. 1982, Arch. de Sci. 35:3-22) Temperature = 19.43 - 4.00(\\delta18OCarbonate - \\delta18O{Local water}) = 21 +/- 2° C (2σ standard error (stde)). Fish, gar, scale. δ 18OPhosphate = + 19.71 +/- 0.64‰ n = 20

  18. Late Holocene climate and land-use impacts on ecology and carbon cycling in Atlantic coastal plain tidal freshwater wetlands

    NASA Astrophysics Data System (ADS)

    Jones, M.; Bernhardt, C. E.

    2013-12-01

    Tidal freshwater wetlands are vulnerable to degradation from changing climate, land-use practices, and sea level. Their position between fully tidal and fully non-tidal ecosystems and sensitivity to minor fluctuations in salinity makes them ideal candidates to record the effects of climate and sea-level variability. These wetlands also act as a substantial carbon (C) sink, and paleoclimate studies provide important evidence not only on the long-term impact of perturbations on their ecological structure and function, but also on their ability to store C. Here we examine the late Holocene impacts of climate, land-use change, and sea level rise on four tidal freshwater wetlands in the Waccamaw River and Turkey Creek, South Carolina. A transect of four sites that range from an almost completely fresh forested swamp at the most upstream site to a higher salinity oligohaline marsh downstream. The two intermediate sites are forested swamps at different stages of degradation. We analyzed pollen assemblages, plant macrofossils, and carbon accumulation rates from sediment cores spanning the last ~1500-2000 years. Overall, higher rates of C accumulation are associated with woody swamp peat than with herbaceous peat, as determined from peat macrofossils and pollen assemblages. All sites show decreased C accumulation rates with the onset of the Medieval Climate Anomaly (MCA), which remained low through the Little Ice Age (LIA) (~1500 to 150 cal yr BP). These changes are accompanied by a switch from woody swamp peat to a graminoid-dominated peat lithology in the two uppermost forested swamp locations, as well as in the oligohaline marsh located farthest south along the transect. The switch from swamp to the modern oligohaline marsh during the MCA suggests that both sea level and land-use change permanently transformed the wetland. Rice cultivation beginning ~300 cal yr BP may be responsible for an apparent hiatus in several of the cores and may explain a Poaceae spike in the

  19. Late Holocene Environmental Reconstruction and Flood Records of Lake Bafa, Western Turkey

    NASA Astrophysics Data System (ADS)

    Yalamaz, Burak; Bulkan, Özlem; Namık Çaǧatay, M.; Acar, Dursun

    2016-04-01

    Lake Bafa is a significant inland lake located in the Büyük Menderes River Basin near the Aegean Sea in the horst and graben system of western Turkey. Lake Bafa was part of the ancient Gulf of Latmos that was gradually filled by the prograding sediments of Büyük Menderes River during the Holocene transgression, and resulted in the creation of the Lake in the southern part. The lake is presently located 15 km from the shoreline, 2 m above sea level. It has a maximum depth of 21 m and surface area of 60 km2. We used multi-proxy analyses of a 4.17 m-long core extending back to ca. 2300 years from the central depo centre of the lake. The objectives are to reconstruct the environmental evolution of the Lake Bafa as it changed from a marginal marine to a lacustrine environment, and to investigate the flood records during the past 2300 yrs. The core is composed of three units: an uppermost lacustrine unit, a unit representing marine to lacustrine conditions and a lowermost marine unit. The uppermost lacustrine unit is 1 m-thick, homogenous clayey silt mud layer with relatively high total organic carbon (TOC= 2.5 - 4.5 %), high total inorganic carbon (TIC = 1.8 -4.5 %) and low detrital input (Si, K, Zr, Ti). According to AMS radiocarbon dating, it was deposited over the last 600 yrs under brackish lacustrine conditions. The underlying unit is 2 m-thick, and consists of banded mud layers with relatively low TOC (1.2-4 %) and TIC (1.2-3.5) contents and high detrital input. Its fossil content, with scarce Cardium sp. and Ammonia sp., indicates that it was deposited under brackish water conditions and represents a transition from marine to lacustrine environments. The unit was deposited between ca. 600 and 1750 yrs BP, and includes frequent flood units ranging up to 10 cm-thick fine sand- to clay-bearing coarse silt. The lowermost unit is characterized by relatively high TOC (2-5.5 %), TIC (1.5-3.5 %) contents and high detrital input. With its abundant Cardium sp. and

  20. Nanometer-Scale Pore Characteristics of Lacustrine Shale, Songliao Basin, NE China

    PubMed Central

    Wang, Min; Yang, Jinxiu; Wang, Zhiwei; Lu, Shuangfang

    2015-01-01

    In shale, liquid hydrocarbons are accumulated mainly in nanometer-scale pores or fractures, so the pore types and PSDs (pore size distributions) play a major role in the shale oil occurrence (free or absorbed state), amount of oil, and flow features. The pore types and PSDs of marine shale have been well studied; however, research on lacustrine shale is rare, especially for shale in the oil generation window, although lacustrine shale is deposited widely around the world. To investigate the relationship between nanometer-scale pores and oil occurrence in the lacustrine shale, 10 lacustrine shale core samples from Songliao Basin, NE China were analyzed. Analyses of these samples included geochemical measurements, SEM (scanning electron microscope) observations, low pressure CO2 and N2 adsorption, and high-pressure mercury injection experiments. Analysis results indicate that: (1) Pore types in the lacustrine shale include inter-matrix pores, intergranular pores, organic matter pores, and dissolution pores, and these pores are dominated by mesopores and micropores; (2) There is no apparent correlation between pore volumes and clay content, however, a weak negative correlation is present between total pore volume and carbonate content; (3) Pores in lacustrine shale are well developed when the organic matter maturity (Ro) is >1.0% and the pore volume is positively correlated with the TOC (total organic carbon) content. The statistical results suggest that oil in lacustrine shale mainly occurs in pores with diameters larger than 40 nm. However, more research is needed to determine whether this minimum pore diameter for oil occurrence in lacustrine shale is widely applicable. PMID:26285123

  1. Nanometer-Scale Pore Characteristics of Lacustrine Shale, Songliao Basin, NE China.

    PubMed

    Wang, Min; Yang, Jinxiu; Wang, Zhiwei; Lu, Shuangfang

    2015-01-01

    In shale, liquid hydrocarbons are accumulated mainly in nanometer-scale pores or fractures, so the pore types and PSDs (pore size distributions) play a major role in the shale oil occurrence (free or absorbed state), amount of oil, and flow features. The pore types and PSDs of marine shale have been well studied; however, research on lacustrine shale is rare, especially for shale in the oil generation window, although lacustrine shale is deposited widely around the world. To investigate the relationship between nanometer-scale pores and oil occurrence in the lacustrine shale, 10 lacustrine shale core samples from Songliao Basin, NE China were analyzed. Analyses of these samples included geochemical measurements, SEM (scanning electron microscope) observations, low pressure CO2 and N2 adsorption, and high-pressure mercury injection experiments. Analysis results indicate that: (1) Pore types in the lacustrine shale include inter-matrix pores, intergranular pores, organic matter pores, and dissolution pores, and these pores are dominated by mesopores and micropores; (2) There is no apparent correlation between pore volumes and clay content, however, a weak negative correlation is present between total pore volume and carbonate content; (3) Pores in lacustrine shale are well developed when the organic matter maturity (Ro) is >1.0% and the pore volume is positively correlated with the TOC (total organic carbon) content. The statistical results suggest that oil in lacustrine shale mainly occurs in pores with diameters larger than 40 nm. However, more research is needed to determine whether this minimum pore diameter for oil occurrence in lacustrine shale is widely applicable. PMID:26285123

  2. Evolution of fluvio-lacustrine systems in the Cretaceous Gyeongsang Basin, Korea

    NASA Astrophysics Data System (ADS)

    Lee, Yong Il; Lim, Hyoun Soo

    2016-04-01

    The Cretaceous Gyeongsang Basin in southeastern Korea is a nonmarine sedimentary basin formed in an active continental margin caused by the subduction of the Paleo-Pacific (Izanagi) Plate beneath the East Asian continent. The basin fill of the Cretaceous Gyeongsang Basin, Korea comprises mainly fluvial to lacustrine deposits with minor alluvial-fan deposits. It is subdivided into three groups: from the base up the Sindong, Hayang, and Yucheon groups. The fluvio-lacustrine system of the Sindong and Hayang groups in the Gyeongsang Basin is characterized by the cyclic deposition of fluvial deposit below and lacustrine deposit above. The Sindong Group is consisted of the alluvial fan-fluvial Nakdong and Hasandong formations and lacustrine Jinju Formation, and the Hayang Group is consisted of the fluvial Chilgok, Silla, and Haman formations and lacustrine Jindong Formation. The fluvio-lacustrine system of the Sindong Group is represented by the development of meandering to braided streams and lacustrine deltas, whereas that of the Hayang Group is represented by a wide sandflat to mudflat setting which was contiguous to a shallow lake. In general, the floodplain deposits of both groups are composed of red beds. The Sindong Group floodplain deposits contain coal layers in the lower part and well-developed paleosols including abundant pedogenic carbonates in the middle to upper parts, whereas the Hayang Group floodplain deposits contain sparse pedogenic carbonates. Such difference in the fluvio-lacustrine systems during the evolution of the Gyeognsang Basin can be accounted for by the changing climatic conditions, with increasing aridity through time. The possible cause of increasing aridity seems to be related to the development of topographically high arc platform during the Hayang Group deposition.

  3. Chapter D: With or Without Salt-a Comparison of Marine and Continental-Lacustrine Diatomite Deposits

    USGS Publications Warehouse

    Moyle, Phillip R.; Dolley, Thomas P.

    2003-01-01

    Diatoms in sedimentary deposits of marine and continental, especially lacustrine, origin have similar nutrient (for example, phosphate, nitrate, and silica) and light requirements; however, their geologic ranges and physiographic environments vary. Marine diatoms range in age from Early Cretaceous to Holocene, and continental diatoms range in age from Eocene to Holocene; however, most commercial diatomites, both marine and lacustrine, were deposited during the Miocene. Marine deposits of commercial value generally accumulated along continental margins with submerged coastal basins and shelves where wind-driven boundary currents provided the nutrient-rich upwelling conditions capable of supporting a productive diatom habitat. Commercial freshwater diatomite deposits occur in volcanic terrains associated with events that formed sediment-starved drainage basins, such as the Basin and Range Province, particularly in Nevada. Marine habitats generally are characterized by stable conditions of temperature, salinity, pH, nutrients, and water currents, in contrast to lacustrine habitats, which are characterized by wide variations in these conditions. Marine deposits generally are of higher quality and contain larger resources, owing to their greater areal extent and thickness, whereas most of the world's known diatomites are of lacustrine origin. Both types of deposit are commonly mined by open-pit methods and subjected to processing designed to remove organic matter, CO2, pore water, and inorganic contaminants in order to produce purified products. The highest quality diatomites, predominantly from marine sources, are used in filtration, although both types of deposit produce filter grades, and additional end uses include fillers, additives, absorbents, and abrasives.

  4. Sedimentologic and biostratigraphic implications for early Eocene lacustrine systems, eastern Great Basin, Nevada

    SciTech Connect

    Dubiel, R.F.; Potter, C.J.; Snee, L.W. ); Good, S.C. )

    1993-04-01

    A multidisciplinary study integrating sedimentology, molluscan paleontology and paleoecology, structural and geologic mapping, and [sup 40]Ar/[sup 39]Ar dating of volcanic flows indicates the White Sage Formation north of the Deep Creek Range on the NV-UT border was deposited during the early Eocene in marginal-lacustrine, lacustrine, freshwater-marsh, and minor terrestrial settings. Sedimentary facies include wave-reworked, locally derived Paleozoic carbonate-clast basal conglomerates in contact with bedrock; carbonate tufa mounds; organic-rich mudstones; and laminated to medium-bedded carbonates. The wave-reworked conglomerate implies a broad lake with considerable fetch to generate large waves, but one with only small drainage basins with sharp relief to supply the locally-derived clasts. There is a striking lack of any fluvial, deltaic, or alluvial-fan deposits that would indicate development of substantial drainage areas. The large tufa mounds indicate a high-wave-energy shoaling environment with stable substrate and topography. The profusion of lacustrine carbonates indicates dominantly chemical- or biochemical-induced deposition in a carbonate-saturated lake. The aquatic molluscan fauna indicates shallow, quiet lacustrine conditions with emergent vegetation. The limpets inhabited areas of rooted aquatic vegetation, and the terrestrial gastropods indicate marshes adjacent to the lacustrine system. The molluscan assemblage constrains the age of the White Sage as early Eocene, indicating a lacustrine system equivalent to the Sheep Pass Formation and to outcrops near Illipah, NV that have similar facies and molluscan faunas and that also lack significant fluvial, deltaic, or alluvial fan deposits. The data are consistent with a model wherein the White Sage, Sheep Pass, and Illipah carbonates were deposited in a large lake superimposed on preexisting topography with low relief and little or no syndepositional extension.

  5. Reservoir characterization of lacustrine sediments from the Late Triassic, Beryl Field, UK North Sea

    SciTech Connect

    Bond, J.; Welton, J.E.

    1996-12-31

    Located on the western flank of the Viking Graben, the Beryl Field has been producing from the Late Triassic Lewis reservoir since first oil in 1976. The Beryl A Triassic contains an estimated STOIIP of 256 mmstb, with a cumulative production of 31 mmstb (8/95) (12% recovery). Low recovery to date, coupled with high remaining reserves potential, necessitated a new simulation model and optimized development program for the Lewis reservoir. This paper summarizes the revised reservoir description of the Beryl A Triassic, a complex lacustrine and fluvial system, and its integration with the reservoir simulation. The Triassic reservoir is subdivided into four zones: Lewis Units I, II, III and IV. Six lithofacies associations are identified in core: offshore lacustrine, lacustrine sandflat, marginal lacustrine, floodplain, sheetflood/overbank, and fluvial. Detailed petrological studies were conducted which confirmed that both depositional and diagenetic processes influenced reservoir properties and quality. Optimal reservoir quality is preserved in fluvial and lacustrine sandflat deposits. Argillaceous floodplain and lacustrine facies are non-reservoir and form barriers to vertical fluid migration. Calcrete lags (concentrated at the base of fluvial channels) and carbonate paleosols form baffles to flow. Fieldwide correlation of core and log facies resulted in the identification of 27 genetic flow-units. This geologically-based layering scheme was integrated with production data to generate the framework for vertical zonation for the new reservoir simulation. The simulation studies produced as accelerated development program for the Beryl A Triassic. Reserves have increased as result of optimizing secondary recovery.

  6. Reservoir characterization of lacustrine sediments from the Late Triassic, Beryl Field, UK North Sea

    SciTech Connect

    Bond, J. ); Welton, J.E. )

    1996-01-01

    Located on the western flank of the Viking Graben, the Beryl Field has been producing from the Late Triassic Lewis reservoir since first oil in 1976. The Beryl A Triassic contains an estimated STOIIP of 256 mmstb, with a cumulative production of 31 mmstb (8/95) (12% recovery). Low recovery to date, coupled with high remaining reserves potential, necessitated a new simulation model and optimized development program for the Lewis reservoir. This paper summarizes the revised reservoir description of the Beryl A Triassic, a complex lacustrine and fluvial system, and its integration with the reservoir simulation. The Triassic reservoir is subdivided into four zones: Lewis Units I, II, III and IV. Six lithofacies associations are identified in core: offshore lacustrine, lacustrine sandflat, marginal lacustrine, floodplain, sheetflood/overbank, and fluvial. Detailed petrological studies were conducted which confirmed that both depositional and diagenetic processes influenced reservoir properties and quality. Optimal reservoir quality is preserved in fluvial and lacustrine sandflat deposits. Argillaceous floodplain and lacustrine facies are non-reservoir and form barriers to vertical fluid migration. Calcrete lags (concentrated at the base of fluvial channels) and carbonate paleosols form baffles to flow. Fieldwide correlation of core and log facies resulted in the identification of 27 genetic flow-units. This geologically-based layering scheme was integrated with production data to generate the framework for vertical zonation for the new reservoir simulation. The simulation studies produced as accelerated development program for the Beryl A Triassic. Reserves have increased as result of optimizing secondary recovery.

  7. Modern and late Holocene dolomite formation: Manito Lake, Saskatchewan, Canada

    NASA Astrophysics Data System (ADS)

    Last, Fawn M.; Last, William M.; Halden, Norman M.

    2012-12-01

    Major advances have occurred in our understanding of modern dolomite formation and penecontemporaneous dolomitization over the past several decades. Manito Lake, located in west-central Saskatchewan, Canada, is a large (65 km2), deep (zmax: 22 m) perennial saline (~ 45 ppt TDS) lake in which modern and late Holocene dolomite coexists with other endogenic and authigenic carbonate precipitates, including aragonite, monohydrocalcite, calcite, and Mg-calcite. Like many other lacustrine dolomites, Manito Lake dolomite is microcrystalline (less than 1 μm to 5 μm), Ca-rich and poor to moderately ordered. It occurs as relatively pure hardgrounds and as a component of nearshore microbialites. It also forms isopachous cements in consolidated siliciclastic shoreline sediments. Manito Lake dolomite is most likely forming by mainly biomediated precipitation at or near the sediment-water interface (i) in pore spaces of coarse siliciclastic sediments (i.e., beachrock), (ii) as fine laminae associated with microbialites, and (iii) as a major component of mudstone hardgrounds and pavements.

  8. Glacial inception during the late Holocene without carbon emissions from early agriculture: lessons from the stage-19 glacial inception

    NASA Astrophysics Data System (ADS)

    He, F.; Vavrus, S. J.; Kutzbach, J. E.; Ruddiman, W. F.; Tzedakis, P. C.

    2013-12-01

    Decreases in orbitally-forced summer insolation along with downward trends in greenhouse gases (GHG) have been precursors to incipient glaciation in the past. In the last several thousand years of the current interglacial, while summer insolation has decreased, there was a reversal of the downward trends in CH4 and CO2 concentration within the Holocene around 5,000 and 7,000 years ago. While the cause of this reversal remains unresolved, a leading hypothesis is Ruddiman's Early Anthropogenic Hypothesis that early agriculture, starting several thousand years ago, caused emissions of GHG large enough to reverse natural downward trends in CO2 and CH4 and kept Earth's climate anomalously warm, with the corollary that this may have prevented incipient glaciation during the late Holocene. Here we use the 1-degree, fully coupled Community Climate System Model version 4 (CCSM4) with climate forcings (orbital parameters and GHG) of a previous glacial inception to investigate whether glacial inception should have occurred prior to the industrial revolution if the concentrations of CH4 and CO2 had followed their natural downward trends throughout the Holocene. Tzedakis et al. [2012] show that for the previous eight interglacials, Stage 11 and Stage 19 are the best analogs of the Holocene because of their low eccentricities, and Stage 19 is a better analog than Stage 11 for the Holocene due to the in-phase relationship between obliquity and precession. Furthermore, their study suggests that 777 ka BP (777,000 years before present) is the timing of glacial inception for Stage 19, based on the occurrence of the earliest bipolar seesaw event associated with glacial melting. Not only do the orbital parameters at 777 ka BP resemble pre-industrial conditions, but the concentrations of CO2 at that time were essentially the same as their expected 'natural' pre-industrial values in the absence of anthropogenic greenhouse emissions. Our multi-millennial coupled CCSM4 simulations show

  9. Holocene and late glacial palaeoceanography and palaeolimnology of the Black Sea: Changing sediment provenance and basin hydrography over the past 20,000 years

    NASA Astrophysics Data System (ADS)

    Piper, D. Z.; Calvert, S. E.

    2011-10-01

    The elemental geochemistry of Late Pleistocene and Holocene sediments of the Black Sea, recovered in box cores from the basin margins and a 5-m gravity core from the central abyssal region of the basin, identifies two terrigenous sediment sources over the last 20 kyrs. One source region includes Anatolia and the southern Caucasus; the second region is the area drained by rivers entering the Black Sea from Eastern Europe. Alkali metal:Al and heavy:light rare-earth element ratios reveal that the relative contribution of the two sources shifted abruptly every few thousand years during the late glacial and early Holocene lacustrine phase of the basin. The shifts in source were coeval with changes in the lake level as determined from the distribution of quartz and the heavy mineral-hosted trace elements Ti and Zr. The geochemistry of the abyssal sediments further recorded a sequence of changes to the geochemistry of the water column following the lacustrine phase, when high salinity Mediterranean water entered the basin beginning 9.3 kyrs BP. Bottom water that had been oxic throughout the lake phase became anoxic at approximately 8.4 kyrs BP, as recorded by the accumulation from the water column of several redox-sensitive trace metals (Mo, Re, U). The accumulation of organic carbon and several trace nutrients (Cd, Cu, Ni, Zn) increased sharply ca. 0.4 kyrs later, at 8.0 kyrs BP, reflecting an increase of primary productivity. Its increase was coeval with a shift in the dinoflagellate ecology from stenohaline to euryhaline assemblages. During this profound environmental change from the lacustrine to the marine phase, the accumulation rate of the lithogenous sediment fraction decreased as much as 10-fold in response to the rise of the water level in the basin from a low stand ca. 9.3 ka to its current level.

  10. Holocene and late glacial palaeoceanography and palaeolimnology of the Black Sea: Changing sediment provenance and basin hydrography over the past 20,000years

    USGS Publications Warehouse

    Piper, D.Z.; Calvert, S.E.

    2011-01-01

    The elemental geochemistry of Late Pleistocene and Holocene sediments of the Black Sea, recovered in box cores from the basin margins and a 5-m gravity core from the central abyssal region of the basin, identifies two terrigenous sediment sources over the last 20. kyrs. One source region includes Anatolia and the southern Caucasus; the second region is the area drained by rivers entering the Black Sea from Eastern Europe. Alkali metal:Al and heavy:light rare-earth element ratios reveal that the relative contribution of the two sources shifted abruptly every few thousand years during the late glacial and early Holocene lacustrine phase of the basin. The shifts in source were coeval with changes in the lake level as determined from the distribution of quartz and the heavy mineral-hosted trace elements Ti and Zr. The geochemistry of the abyssal sediments further recorded a sequence of changes to the geochemistry of the water column following the lacustrine phase, when high salinity Mediterranean water entered the basin beginning 9.3. kyrs BP. Bottom water that had been oxic throughout the lake phase became anoxic at approximately 8.4. kyrs BP, as recorded by the accumulation from the water column of several redox-sensitive trace metals (Mo, Re, U). The accumulation of organic carbon and several trace nutrients (Cd, Cu, Ni, Zn) increased sharply ca. 0.4. kyrs later, at 8.0. kyrs BP, reflecting an increase of primary productivity. Its increase was coeval with a shift in the dinoflagellate ecology from stenohaline to euryhaline assemblages. During this profound environmental change from the lacustrine to the marine phase, the accumulation rate of the lithogenous sediment fraction decreased as much as 10-fold in response to the rise of the water level in the basin from a low stand ca. 9.3. ka to its current level. ?? 2011.

  11. A Multiproxy Reconstruction of Holocene Southern Westerlies from the Auckland Islands

    NASA Astrophysics Data System (ADS)

    Nichols, J. E.; Moy, C. M.; Peteet, D. M.; Weiss, A.; Curtin, L. G.

    2015-12-01

    The strength and position of the Southern Hemisphere Westerly Wind belt plays an important role in our understanding of the global carbon cycle and glacial-interglacial climate change. We present a paleoclimate record that is primarily influenced by the strength and latitudinal position of the Southern Hemisphere Westerly Winds from a late Holocene lake sediment core and a peat core that spans the last 13,000 years, both obtained from New Zealand's subantarctic Auckland Islands (50°S, 166°E). Several proxy indicators contribute to our reconstruction. Hydrogen isotope ratios of specific organic molecules allow us to reconstruct the hydrogen isotope ratios of precipitation. Using macrofossil counts and the abundances of leaf wax biomarkers, we are able to estimate the moisture balance at our sites. Model simulations of the Westerlies and the rate and isotope ratios of precipitation allow us to interpret our proxy data as changes in the strength and position of the Westerly Winds. In our lacustrine sediment, we found that the Westerlies have been shifting southward since the Little Ice Age, consistent with modern observations of a southward shift. In the peatland sediment, we found a multi-millennial northward shift in the Westerlies during the middle Holocene. We will present further ongoing work that strengthens the chronology of Auckland Islands environmental change and integrates these results with vegetation shifts identified in pollen and macrofossil data.

  12. Holocene Lake Records on Kamchatka

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  13. Inferences on Late Holocene climate from stable carbon and oxygen isotope ratio variability in soil and land snail shells from archaeological site 41KM69 in Texas, USA

    NASA Astrophysics Data System (ADS)

    Paul, D.; Mauldin, R.; Munoz, C. M.

    2011-12-01

    Well-preserved land snail shell excavate from archaeological site 41KM69 in Texas, USA, span the past 2200 years and provide an opportunity to explore the paleoclimate implications of isotopic variability in archaeological shell carbonates, bulk soil carbonates and soil organic matter. Terrestrial snail shells belonging to three genera (Polygyra, Rabdotus, and Helicina) were hand-picked from the 120 cm thick soil profile, for stable isotopic analyses. A wood charcoal radiocarbon date constrains samples below 100 cm depth in our soil profile to be ~2200 14C yr BP. Isotopic composition of modern adult snail specimens (n=24) and plants (n=18), collected from the study area, were determined for comparison with the archaeological data sets. All isotopic analyses were performed at the University of Texas at San Antonio using a Thermo Finnigan Gasbench II and a Costech Elemental Analyzer (EA) attached online to a DeltaPlus XP Stable Isotope Ratio Mass Spectrometer in continuous flow mode. Carbon isotopic compositions of both modern (-12.72 to -5.49%) and archaeological (-5.34 to -8.99%) adult snail shell carbonates suggest significant (> 60%) input of C3 plants into the diet of the snails over the past 2200 yrs. Oxygen isotopic compositions of archaeological and modern shells vary from -2.21% to -0.71% and -2.88 to +0.99%), respectively. This suggests that isotopic composition of environmental water (mainly rainwater) available at the time of shell growth was similar to that of the present day. A linearly decreasing trend in δ13C of soil organic matter from -22.83% at 2200 14C yr BP to -25.61% for modern samples imply progressively increasing abundance of C3 plants up to the present day. This implies a progressively wetter climate, or decreasing summer rainfall and less severe water stress conditions, in agreement with other studies on Holocene climate change in the southern Great Plains of USA. The studies, in general, document warm/arid conditions at ~ 2000 BP and

  14. Holocene late Pleistocene non-tropical carbonate sediments and tectonic history of the western rift basin margin of the southern Gulf of California

    NASA Astrophysics Data System (ADS)

    Halfar, Jochen; Godinez-Orta, Lucio; Goodfriend, Glenn A.; Mucciarone, David A.; Ingle, James C.; Holden, Peter

    2001-10-01

    Using high-resolution seismic reflection profiling and dating of (1) shallow marine vibracores and (2) sediments collected from uplifted marine terraces we reconstruct the tectonic history and sediment accumulation patterns of Holocene to late Pleistocene warm-temperate to subtropical carbonates in the southern Gulf of California, Mexico. The study was conducted in the vicinity of La Paz where carbonates form along the fault bounded narrow western shelf of the tectonically active Gulf of California rift basin. The non-tropical nature of the setting is responsible for (1) poor cementation of the bioclastic carbonates, and (2) a composition which is dominated by rhodoliths (coralline red algae), corals and mollusks. Unrimmed carbonate flats forming in small pocket bays and a rhodolith bioherm, which has a surface area of more than 20 km 2 and is up to 16 m thick, constitute the major carbonate factories. Holocene carbonate accumulation rates were deduced from seismic and core data and are highest on the rhodolith bioherm (260 cm/ka) and in subtidal zones of pocket bays (210 cm/ka), and lowest on the inner and middle shelf (100 cm/ka). Taken together, rates of carbonate accumulation are intermediate in magnitude between higher rates recorded in fully tropical carbonate settings and lower rates typical of cool-water carbonates. Seismic reflection profiles demonstrate that Isla Espiritu Santo in the center of the study area is a west dipping fault block, which is tectonically influenced by two distinct faults, the La Paz and Espiritu Santo faults. The latter fault accommodates at least 700 m of east-side down normal offset, and forms a steep eastern escarpment leading into the La Paz slope basin. Some of the sediments produced in the shallow carbonate factories of the narrow La Paz shelf are transported across this escarpment and are redeposited in the slope basin at a water depth of 750 m. Uranium-series dates of marine terraces exposed on Isla Espiritu Santo indicate

  15. Late Holocene stable carbon and nitrogen isotopic variation of bulk organic matter deposited in Blackwood Sinkhole, Abaco, The Bahamas

    NASA Astrophysics Data System (ADS)

    Tamalavage, A.; van Hengstum, P. J.; Louchouarn, P.; Fall, P. L.; Donnelly, J. P.

    2015-12-01

    In the modern climate of the Bahamas, a latitudinal precipitation gradient only allows Pine (Pinus caribaea var. bahamensis) dominated forests to exist on the more mesic (humid) northern islands (Abaco, Andros, New Providence, Grand Bahamas). Previous research suggests that the northern Bahamas underwent dramatic environmental changes in the late Holocene (e.g., waves of human arrival, shifts in terrestrial vegetation and animal extinctions). However, disentangling the timing and relative forcing (climatic vs. anthropogenic) of these changes has proven challenging without high-resolution terrestrial climate records. Recently, a late Holocene decadal to multi-decadal laminated sedimentary record was recovered from Blackwood Sinkhole, on Abaco Island. The bottom of the sinkhole is characterized by anoxic, saline groundwater, while the upper, brackish meteoric lens provides a habitat to fish, algae and other organisms. Here, we present δ13Corg and δ15Norg values of bulk organic matter (OM) taken every cm of the 110 cm core to help elucidate changes in the chemical composition of the source of OM reaching the anoxic sediments of the sinkhole. δ13Corg values change at 812 Cal yrs BP (2s: 931-681 Cal yrs BP, 31.7 cm depth) from -30.5 ± 1.6‰ in the lower 80 cm of the core to -27.6 ± 1.2‰ in the upper 30 cm. There is a synchronous change from more enriched δ15N values, 3.7 ± 1.1‰, in the lower portion of the core, to lower δ15N values (1.9 ± .5‰), in the upper portion of the core. A pollen-based reconstruction of terrestrial vegetation from the same core indicates that these isotopic shifts are concomitant with a shift from a dominance of Arecaceae (Palms) and tropical dry hardwoods below 30 cm, to Pinus and Conocarpus predominance above 30 cm. These results indicate that the source of sedimentary OM deposited into the sinkhole changed coherently with regional landscape change. Biomarker analyses will be used to further identify the role of autochthonous

  16. Formation of lacustrine plains in west-central Alaska as a result of permafrost degradation and aggradation

    NASA Astrophysics Data System (ADS)

    Kanevskiy, M. Z.; Jorgenson, M. T.; Shur, Y.; O'Donnell, J.; Harden, J. W.; Fortier, D.

    2012-12-01

    Perennially frozen lacustrine sediments containing a large amount of ground ice comprise a significant part of the upper permafrost of the lowlands of west-central Alaska, including Koyukuk Flats and Innoko Flats. Study sites are located in the discontinuous permafrost zone, where permafrost was encountered mainly within uplifted peat plateaus. The upper part of studied sections is formed by frozen peat up to 3 m thick underlain by lacustrine silt, which is mostly ice-rich. Cryogenic structure of lacustrine sediments at different sites has common features: (1) prevalence of layered, braided, and reticulate cryostructures; (2) high variability in the ice content of sediments; (3) high density and low water content of soil aggregates separated by ice lenses. Volume of visible ice in silt reaches at places 40% and more. The thickness of ice lenses generally varies from 1 to 5 cm and occasionally reaches 10 cm. Remnants of peat plateaus are surrounded by unfrozen bogs and fens, formed as a result of thawing and settling of ice-rich lacustrine silt. Modern thermokarst scars initially form at places where ice-rich silt is not protected by a thick layer of organic material. Further development of thermokarst bogs includes lateral enlargement of thaw bulbs and collapsing of the margins of peat plateaus. Lacustrine silt within taliks is covered by woody peat accumulated under forests during the stage of permafrost plateau formation and then by aquatic sphagnum peat accumulated in taliks after collapse. We relate the formation of ice-rich lacustrine sediments to development of lake thermokarst, which affected ice-rich silty yedoma deposits during the transition from Pleistocene to Holocene. Terrain development in lacustrine lowlands of west-central Alaska includes five stages related to permafrost aggradation and degradation from the late Pleistocene to the present time: 1) formation of the ice-rich syngenetic permafrost (yedoma) during the late Pleistocene; 2) yedoma

  17. Holocene monsoon variability inferred from palaeolake sediments in NW India.

    NASA Astrophysics Data System (ADS)

    Dixit, Y.; Hodell, D. A.; Petrie, C. A.

    2012-04-01

    The plains of NW India encompasses arid, semi-arid to sub-humid zones and are characterized by numerous palaeolakes and playas. The sedimentary records from these water bodies provide a rich source of paleoclimatic information. We present a high-resolution, Holocene monsoon-variation record inferred from three palaeolakes lying across the precipitation gradient in NW India; palaeolake Karsandi in arid Rajasthan and palaeolake Riwasa, palaeolake Kotla Dahar in semi-arid and sub-humid regions, respectively, in Haryana plains. Laminated and massive gypsum deposits characterize Palaeolake Karsandi in the arid region. Oxygen isotopes are being measured on the gastropod shells and gypsum hydration of water (Hodell et al 2011) for a continuous isotopic record from Rajasthan. The oxygen isotope record from palaeolake Riwasa in the semi-arid region indicates the inception of a wet period at 9700-9500 cal yr (BP) with the establishment of a deep, permanent lake coinciding with the early Holocene maximum in the Indian monsoon. The deep, permanent-lake phase ended with a desiccation event at approximately 8200 BP coinciding with the '8.2kyr' weakening of the monsoon. In contrast, palaeolake Kotla Dahar, lying further east of Riwasa in the sub-humid region, receives 500-700mm annual rainfall. At Kotla Dahar, bulk CaCO3 (%), gastropod abundance and isotope data indicate that the deep lacustrine sequence ends at c.185 cm. Extrapolating from the AMS radio-carbon dated sediments at 135cm (4870-4650 BP) and 230cm (2000-1870 BP), places the 185 cm horizon at c.3970-3720 BP. Our results so far indicate that the Riwasa paleolake lying west of Kotla Dahar dries earlier than Kotla Dahar during the mid-Holocene. The precise date of the transition from a deep-lake water phase to an ephemeral lake in Kotla Dahar is pending, but the projected date suggests that the event coincides with the decline of the urban phase of the Indus Civilization at c. 3900 BP. These three lakes lying across

  18. Cryogenic Structure of Perennially Frozen Lacustrine Sediments

    NASA Astrophysics Data System (ADS)

    Kanevskiy, M.; Shur, Y.; Jorgenson, T.

    2007-12-01

    The existing data on cryogenic structure of lacustrine sediments in various permafrost regions of Eurasia and North America show that these sediments can vary from ice-poor to extremely ice-rich. Complicated cryogenic structure of lacustrine sediments can indicate the conditions of freezing; its study helps to reconstruct the history of permafrost development. There are four mechanisms of lacustrine sediments freezing and formation of their cryogenic structure: 1) epigenetic; 2) syngenetic; 3) para-syngenetic; 4) quasi-syngenetic. Para-syngenetic type of freezing is the most widespread for the lacustrine sediments accumulating in the taliks surrounded by permafrost. The freezing of such sediments goes in various directions (from the surface, from the bottom, from the sides). The ice layers and lenses in para-syngenetic sediments are usually inclined, and the ice content is relatively small in the central parts of the lens-like geological bodies of lacustrine origin. Ice content increases towards top, bottom, and marginal parts of these geological bodies. Such distribution of the ice content is connected with water migration to the multidirectional fronts of freezing. Our study includes the data from several field sites located in Russia and Alaska. One of the most interesting sections was studied in the Kular mining region, Northern Yakutia, where the big lens of lacustrine silts, whose thickness reaches 18-20 m, was observed. This lens was enclosed in the ice-rich syngenetic Late Pleistocene "Yedoma" sediments containing huge ice wedges. The cryogenic structure of the most part of the observed geological body is typical for para-syngenetic sediments. Gravimetric moisture content of lacustrine silts varies in wide range: from 35% up to 130%. At the upper part of the section the ice lenses up to 10-15 cm thick were observed. Ice wedge pseudomorphs were found at the boundary between lacustrine sediments and underlying alluvial gravels. Para-syngenetic part of this

  19. Accurate lacustrine and wetland sediment accumulation rates determined from 14c activity of bulk sediment fractions

    Technology Transfer Automated Retrieval System (TEKTRAN)

    In the absence of identifiable macrofossils in lacustrine sediments, 14C dating must rely on pollen or bulk sediment fractions. Bulk sediment fractions are not generally preferred because they contain an unknown mixture of organic material of variable age, they may contain dead carbon such as ligni...

  20. Holocene aridification of India

    NASA Astrophysics Data System (ADS)

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

    2012-02-01

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

  1. An analysis of open-basin lake deposits on Mars: Evidence for the nature of associated lacustrine deposits and post-lacustrine modification processes

    NASA Astrophysics Data System (ADS)

    Goudge, Timothy A.; Head, James W.; Mustard, John F.; Fassett, Caleb I.

    2012-05-01

    A large number of candidate open-basin lakes (low-lying regions with both inlet valleys and an outlet valley) have been identified and mapped on Mars and are fed by valley network systems that were active near the Noachian-Hesperian boundary. The nature of processes that modified the open-basin lake interiors subsequent to lacustrine activity, and how frequently sedimentary deposits related to lacustrine activity remain exposed, has not been extensively examined. An analysis of 226 open-basin lakes was undertaken to identify evidence for: (1) exposed deposits of possible lacustrine origin and (2) post-lacustrine-activity processes that may have modified or resurfaced open-basin lakes. Spectroscopic data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument were analyzed over identified exposed open-basin lake deposits to assess the mineralogy of these deposits. Particular attention was paid to the possible detection of any component of aqueous alteration minerals (e.g. phyllosilicates, hydrated silica, zeolites) or evaporites (e.g. carbonates, sulfates, chlorides) associated with these exposed deposits. The aim of this paper is to act as a broad survey and cataloguing of the types of lacustrine and post-lacustrine deposits that are present within these 226 paleolake basins. Results of the morphologic classification indicate that 79 open-basin lakes (˜35% of the population) contain exposed deposits of possible lacustrine origin, identified on the basis of fan/delta deposits, layered deposits and/or exposed floor material of apparent lacustrine origin. Additionally, all 226 open-basin lakes examined appear to have been at least partially resurfaced subsequent to their formation by several processes, including volcanism, glacial and periglacial activity, impact cratering and aeolian activity. Results from the analysis of CRISM data show that only 10 (˜29% of the 34 deposits with CRISM coverage) of the exposed open-basin lake deposits

  2. Two Holocene paleofire records from Peten, Guatemala: Implications for natural fire regime and prehispanic Maya land use

    NASA Astrophysics Data System (ADS)

    Anderson, Lysanna; Wahl, David

    2016-03-01

    Although fire was arguably the primary tool used by the Maya to alter the landscape and extract resources, little attention has been paid to biomass burning in paleoenvironmental reconstructions from the Maya lowlands. Here we report two new well-dated, high-resolution records of biomass burning based on analysis of macroscopic fossil charcoal recovered from lacustrine sediment cores. The records extend from the early Holocene, through the full arc of Maya prehistory, the Colonial, and post-Colonial periods (~ 9000 cal yr BP to the present). (Hereafter BP) The study sites, Lago Paixban and Lago Puerto Arturo, are located in northern Peten, Guatemala. Results provide the first quantitative analysis from the region demonstrating that frequent fires have occurred in the closed canopy forests since at least the early Holocene (~ 9000 BP), prior to occupation by sedentary agriculturalists. Following the arrival of agriculture around 4600 BP, the system transitioned from climate controlled to anthropogenic control. During the Maya period, changes in fire regime are muted and do not appear to be driven by changes in climate conditions. Low charcoal influx and fire frequency in the Earliest Preclassic period suggest that land use strategies may have included intensive agriculture much earlier than previously thought. Preliminary results showing concentrations of soot/black-carbon during the middle and late Preclassic periods are lower than modern background values, providing intriguing implications regarding the efficiency of Maya fuel consumption.

  3. Investigation of the Origins of Modern Firmgrounds in Walker Lake, Nevada: Implications for Lacustrine Climate Records and Hardgrounds in the Rock Record

    NASA Astrophysics Data System (ADS)

    Beckerman, L. G.; Lau, K. V.; Stewart, L. C.; Loyd, S. J.; Ibarra, Y.; Corsetti, F. A.; Stevenson, B. S.; Stamps, B. W.; Spear, J. R.

    2014-12-01

    Walker Lake, Nevada, contains locally abundant Pleistocene and Holocene carbonate structures, including tufas, stromatolites, and lithified carbonate hardgrounds. Hardgrounds are classically interpreted as forming via geobiological processes in shallow sediments. To better understand the origins of ancient hardgrounds, we investigated modern firmgrounds which we hypothesized to be incipient hardgrounds. The studied firmgrounds were brown, 1-2 cm thick with a mm-scale white or brown crust, cohesive enough to retain sharp erosional features, and were located on the western shoreline where alluvial fans enter the lake. We analyzed the elemental composition of the lakewater and porewaters in order to model mineral saturation states under lake conditions. In addition, we analyzed 16S rRNA gene diversity of the firmgrounds, porewater of adjacent sediments, and lakewater to investigate potential biological involvement. This, combined with SEM imaging, XRD analyses, and EDS analyses indicate that the firmgrounds are likely dominated by clays and granitic minerals rather than carbonate like the ancient hardgrounds. We suggest that Walker Lake firmgrounds are formed by weathering of unstable granitic minerals with no clear biological influence, likely resulting from physio-chemical processes related to groundwater-lake water mixing. Such firmgrounds may undergo subsequent replacement by calcium carbonate to form hardgrounds, resulting in carbonates with δ13C and δ18O compositions that do not reflect the lake water in which they formed. Given the apparent influence of groundwater on their formation, our work suggests that caution should be used when interpreting lacustrine hardground isotopic records as indicators of lakewater chemistry and climate.

  4. From Pleniglacial to Holocene: a 14C chronostratigraphy of environmental changes in the Konya Plain, Turkey

    NASA Astrophysics Data System (ADS)

    Fontugne, M.; Kuzucuoǧlu, C.; Karabiyikoǧlu, M.; Hatté, C.; Pastre, J.-F.

    1999-04-01

    In the endoreic, semi-arid Konya basin on the central Anatolian plateaux, long-term hydrological evolution has left various landforms and lacustrine deposits reflecting the regional climatic evolution, as well as human influence on the local environments. This paper presents results from a cooperative programme grouping several institutes from Turkey and France, on lacustrine, marshy and aeolian sediment sequences of Upper Pleistocene and Holocene age. The detailed study of environmental evolution is based on the reconstruction as well as on the characterization of the extension and contraction phases of wetlands occupying the lowest parts of the Konya plain. A soil and a marsh layer are 14C dated ca. 28,000-25,000 yr BP. Three phases of Pleniglacial (from ca. 22,000 to 17,000 yr BP) high lake levels are distinguished. Complementary OSL dates on aeolian dunes confirm the occurrence of two drought periods: the first occurs around the start of the Late Glacial, the second after the Mid-Holocene climatic optimum, the latter being 'in phase' with a similar drought in other Eastern Mediterranean regions. After 17,000 yr BP, no lacustrine phase reached as high a level as the Pleniglacial lake. During the Late Glacial, a shallow freshwater lacustrine phase is identified from >12,500 to 11,000 yr BP. The Late Glacial to Holocene transition corresponds to a general absence of deposits and dateable material, thus suggesting a period of drought, to which no aeolian features have so far been related. The Holocene environmental evolution shows a period of marsh and shallow lake extansion from 6000 to 5500 yr BP; this wetter period is interrupted by the second drought (ca. 5500 yrs BP) as indicated by aeolian dune activity. During the Late Holocene, a renewal of marshes, as well as soil development on slopes, can be interpreted either as climatic changes or as impacts of human use of water and soil resources during prehistoric and historic times.

  5. Lake level and watershed vegetation changes from C and N isotopic analysis of lacustrine organic matter: Implications for late Quaternary hydroclimate variability in Interior Alaska

    NASA Astrophysics Data System (ADS)

    Brady, S.; Finney, B. P.

    2012-12-01

    Understanding climate controls over lake level and watershed vegetation changes throughout the Holocene is important to determine how future hydroclimates will affect freshwater and terrestrial systems. This study seeks to provide a detailed record of late Quaternary climate variability for interior Alaska by quantifying lake level and vegetation changes via C and N isotopic compositions of lacustrine organic matter. C and N stable isotopes are important paleoclimate proxies from lake sediments that identify general plant types growing in and around lakes at the time of deposition. At Little Harding Lake (N 64.409207, W 146.902278), low lake levels are inferred around 12,285 cal yr BP, a time when sediment organic matter is characterized by enriched δ13C and low C/N ratios, carbonate deposition occurred, and herb vegetation dominated the landscape. Concentration dependent mixing models suggest that terrestrial organic matter contributed 51% to lake sediments during this time. An intensified Aleutian Low during the latter half of the Younger Dryas may have created cold, dry conditions in the Alaskan interior. Lake level fluctuated and began to rise after 11,400 cal yr BP as moisture delivery increased to the Alaskan interior and birch expanded in the region. Rising lake level and C3 plant expansion are documented by depleted δ13C, higher C/N ratios, and a 30% increase in terrestrial organic matter contribution to Little Harding Lake. Further increases in lake level until 8,400 cal yr BP correlate with expansion of poplar, spruce and alder and higher organic matter accumulation rates. C3 tree expansion and increasing lake levels into the middle Holocene may be attributed to greater summer precipitation in the interior as the result of an increased East Asian trough to the west accompanied by ridging over Alaska. Comparisons with other regional records will be assessed to determine likely patterns of past atmospheric circulation that may explain late Quaternary lake

  6. Carbon and Nitrogen Isotope Variation in Peat Bogs in the Midwestern US: Implications for Holocene Climate Reconstruction

    NASA Astrophysics Data System (ADS)

    Wong, D.; Paytan, A.; Jackson, S.

    2008-12-01

    A peat core, from near the center of Minden Bog in Michigan, representing about 3500 years of accumulation was previously analyzed for plant macrofossils, colorimetric humification, and testate amoebae to yield three independent climate proxies (Booth and Jackson, 2003). The plant macrofossil data show the site to be sensitive to bog water table fluctuations. The data suggest that this may be related to regional climatic changes. We analyzed the carbon and nitrogen isotopes, as well as the carbon-nitrogen ratios in the bulk peat samples to determine if fluctuations of these records correspond to climate events as seen in the plant microfossil and amoebae records. The degree to which peat-based carbon and nitrogen isotope records reflect changes in the relative distribution of vegetation and, in turn, reflect temperature changes in effective precipitation (precipitation minus evapotranspiration) will be assessed. Peat carbon and nitrogen isotope records will be compared with existing proxy climate records and with a temperature reconstruction based on testate amoebae in bogs. We expect that climate-related changes, in the relative abundance of vegetation remains accumulating in the peat bogs, will be recorded in the organic matter in forms of carbon and nitrogen isotopes.

  7. Towards a Circum-Antarctic Holocene Paleointensity Record

    NASA Astrophysics Data System (ADS)

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

    2005-12-01

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

  8. Multiproxy Holocene paleoclimate records from the southern Peruvian Andes - what new can we learn from the stable carbon isotope composition of high altitude organic matter deposits?

    NASA Astrophysics Data System (ADS)

    Skrzypek, Grzegorz; Engel, Zbyněk

    2015-04-01

    Interpretation of the Central Andean paleoclimate over the last millennia still represents a research challenge demanding deeper studies [1,2]. Several high-resolution paleoclimate proxies for the last 10,000 years have been developed for the northern hemisphere. However, similar proxies are very limited for South America, particularly for high altitudes where, for example, tree-ring chronologies are not available and instrumental records are very limited. Consequently, our knowledge of high altitude climate changes in arid regions of the Peruvian Andes mainly relies on ice-core and lake deposit studies. In our study, we used a new alternative proxy for interpretation of palaeoclimate conditions based on a peat core taken from the Carhuasanta Valley at the foot of Nevado Mismi in the southern Peruvian Andes (15° 30'S, 71° 43'W, 4809m a.s.l.). The stable carbon isotope composition (δ13C) of Distichia peat reflects mainly the relative variation of the mean air temperature during subsequent growing seasons [3], and allows reconstructions of palaeotemperature changes. In contrast, peat organic carbon concentration (C % wt) records mainly wetness in the valley, directly corresponding to the changes in runoff in the upper part of the catchment. The most prominent climate changes recorded in the peat over last 4ka occurred between 3040 and 2750 cal. yrs BP. The initial warming turned to a very rapid cooling to temperatures at least 2° C lower than the mean for the Late Holocene. Initially drier conditions within this event turned to a short wet phase after 2780 cal. yrs BP, when the temperature increased again. This event coincides with significant changes in peat and ice core records in the Central Andes that match the timing of the global climate event around 2.8 cal. ka BP. Climatic conditions in the study area became relatively dry and stable after the event for about 800 years. Highly variable temperatures and humidity prevailed during the last 2000 years, when

  9. Martian lake basins and lacustrine plains

    NASA Astrophysics Data System (ADS)

    de Hon, R. A.

    1992-02-01

    A classification of Martian lake basins based on the location of the basin in respect to water sources is proposed. The classes are type 1: valley-head basins; type 2: intravalley basins; type 3: valley-terminal basins; and type 4: isolated basins. Martian lakes are ephemeral features. Many craters and irregular depressions impounded water only until the basins filled and overflowed. Water escaping by spillover rapidly cut crevasses in the downstream side of basins and drained the ponds. Clastic lacustrine sediments collected in the lakes as flowing water lost velocity and turbulence. Evaporitic deposits may be significant in those basins that were not rapidly drained. Sediments deposited in lake basins form smooth, featureless plains. Lacustrine plains are potentially candidate sites for Mars landings and for the search for evidence of ancient life.

  10. Through Layers of Mud and Time: Lacustrine Archives of Quaternary Climate Variation (Hans Oeschger Medal Lecture)

    NASA Astrophysics Data System (ADS)

    Fritz, Sherilyn Claire

    2014-05-01

    Lake sediments record climate dynamics and ecosystem response at resolutions ranging from sub-annual to millions of years, dependent upon on the age and depositional characteristics of the basin. Thus, they provide a rich archive for elucidating environmental dynamics at a range of temporal scales. In this lecture, I will discuss a selection of examples from lacustrine sequences in the Americas that provide insight into the magnitude, duration, forcing, and impacts of Quaternary climate variability. The first set of examples deals with hydroclimate variation during the Holocene in the North American continental interior. In agricultural regions, lake studies documented intervals of drought that were more persistent than any in recorded history, now referred to as "megadroughts". Subsequent tree-ring compilations have shown that these megadroughts were widespread throughout western NA during the last 1000 years. In the central Great Plains during Medieval times (~900-1300 CE), moisture deficits persisted for multiple decades and were sufficient to drop the water table, kill off native grassland vegetation, and mobilize sand dunes, as demonstrated by coupled lacustrine and geomorphic records. A network of late-Holocene lacustrine records spanning the Great Plains and northern Rocky Mountain regions shows that major climate excursions were synchronous across the northern tier of the continental interior, reflecting large-scale atmospheric dynamics driven by temperature variation in the Pacific and Atlantic Oceans. Lake records also have been instrumental in documenting tropical moisture variation associated with fluctuations in the South American Summer Monsoon (SASM). High lake levels and wet periods in the tropical Andes are correlated with cold intervals in the North Atlantic region at multiple temporal scales, from orbital to millennial to centennial, reflecting intensification of the SASM. Large changes in moisture availability (P-E) occurred on ~100 ka

  11. Modern lacustrine stromatolites, Walker Lake, Nevada

    NASA Astrophysics Data System (ADS)

    Osborne, Robert H.; Licari, Gerald R.; Link, Martin H.

    1982-05-01

    The Walker River drainage basin occupies about 10,000 km 2 in western Nevada and parts of California and is essentially a closed hydrologic system which drains from the crest of the Sierra Nevada in California and terminates in Walker Lake, Nevada. Walker Lake trends north and is about 27.4 km long and 8 km wide with water depths exceeding 30.5 m. The lake is situated in an asymmetric basin with steep alluvial fans flanking the western shoreline (Wassuk Range) and more gentle but areally more extensive alluvial fans flanking the eastern shoreline (Gillis Range). Exposed lake terraces and the present shoreline of Walker Lake record a sequence of Pleistocene and Holocene stromatolitic and tufaceous carbonate deposits. Small generalized and columnar stromatolites, frequently encrusted on exposed coarse-grained clasts or bedrock, are present along parts of the nearshore margin of Walker Lake and at elevated lake stands. Columnar stromatolites as much as 4 cm high are subcylindrical to club shaped discrete, and laterally linked at the base with local branching. These digitate stromatolites start as wavy, generalized stromatolites which are vertically transitional to small, laterally linked cabbage heads with laminae which thicken over the crests. Although algal structures are not well preserved in the older stromatolites, recent precipitation of low magnesium calcite occurs as smooth encrustations and as tiny mounds which are consistently associated with a diverse, seasonally variable, green and blue-green algal community including Cladophora glomerata, Ulothrix (cf. aequalis), Gongrosira, Schizothrix, Amphithrix janthina, Calothrix, Homeothrix, Spirulina, Anabaena, Lyngbya, and Entophysalis. Cladophora glomerata and a species of Ulothrix, which are the two most abundant algae within the Walker Lake stromatolite community, are known to condition semi-alkaline lake water by the removal of CO 2 from bicarbonate during photosynthesis. Such conditioning results in the

  12. Holocene Paleoecology of the Western Tenere Desert, Niger, Africa

    NASA Astrophysics Data System (ADS)

    Sereno, P. C.; Caran, S. C.; Housh, T. B.

    2007-12-01

    Multiple paleontological, sedimentological, and isotopic/ionic geochemical indicators permit reconstruction of the Holocene ecology of the western Tenere Desert (southern Sahara hyper-desert). Modern precipitation is highly erratic, averaging 25 mm yearly, and vegetative cover is negligible. From the early to middle Holocene, however, grassland-shrublands and seasonal to permanent lakes and wetlands predominated, supporting diverse limnic, riparian, and upland communities. Annual precipitation probably was comparable to that of the modern southern Sahel, exceeding 350 mm. Coarse-grained sediment washed into the large lacustrine basin from exposures of metamorphic, plutonic, and volcanic rocks in the nearby Air Massif highland. Lake margins fluctuated in response to runoff and limited ground-water discharge. The water was non-saline and there is no evidence of evaporite deposition. Aquatic and riparian macrophytes thrived, as did an extensive lacustrine-palustrine macrofauna. A Sahelian flora of mixed grasses, thorn shrubs, and perhaps some larger woodland species occupied the contiguous uplands, supporting resident and migratory mammalian and avian faunas. Lake levels were high until 6300 to 5200 BP, possibly as late as 4800 BP locally. Deflation of lacustrine deposits during a subsequent dry period provided finer-grained eolian sediment accreting as proximal dunes. The composition of mineral sediment within the middle to late Holocene dunes is different from, but clearly a subset of the lacustrine deposits. Organic matter reworked from the lake sediment was deposited in the dunes and oxidized in situ, generating CO2 that dissolved in soil moisture, producing bicarbonate. The bicarbonate reacted with calcium from weathered minerals, producing calcic cementation about 5100 BP. The resulting petrocalcic horizon was later exposed, weathered, and colonized by sparse terrestrial vegetation for one or more brief periods. A late phase of pedogenesis concurrent with or

  13. Oil source rocks in lacustrine sequences from Tertiary grabens, western Mediterranean rift system, northeast Spain

    SciTech Connect

    Anadon, P.; Cawley, S.J.; Julia, R.

    1988-08-01

    Lacustrine sequences, 100-250 m thick, containing oil-prone, organic-rich mudstones (ORM) are exposed in five Tertiary basins in northeastern Spain. They were deposited in small lacustrine basins (up to 50 km/sup 2/) that developed in grabens of the western Mediterranean rift system. ORMs from the Rubielos basin comprise laminated gray mudstones with interbedded rhythmite intervals (up to 2.5 m thick) formed by couplets of organic- and carbonate-rich laminae (< 1 mm thick). In marginal zones, ORMs (up to 10 m thick) alternate with lean, bioturbated green marls (up to 5 m thick). ORMs (Rock-Eval yields /approximately/ 40 kg/MT, HI /approximately/ 850 mg HC/g TOC) had a dominant waxy terrestrial plant input, with significant and variable algal/bacterial input. ORMs in these basins are immature for petroleum generation. Larger lacustrine basins similar to those described above, in more appropriate burial/thermal situations, can be envisioned as zones of potential interest for lacustrine oil exploration in the western Mediterranean.

  14. Holocene precipitation in the subtropical Pacific inferred from the carbon isotope composition of Melaleuca quinquenervia (The Broad-leaved Paper Bark tree) leaves

    NASA Astrophysics Data System (ADS)

    Tibby, John; Barr, Cameron; Henderson, Andrew; Leng, Melanie; Marshall, Jon; McGregor, Glenn

    2013-04-01

    Holocene records of the amounts of subtropical precipitation are rare, particularly in the Southern Hemisphere. Yet such information is vital for a comprehensive understanding of global climate system dynamics. We present a precipitation record inferred from the δ13C composition of Melaleuca quinquenervia leaves retrieved from the Holocene sediments of Swallow Lagoon, North Stradbroke Island, in the subtropics of Australia. The modern relationship between rainfall and δ13C was quantified using a collection of monthly leaf falls between 1992 and 2003 and climate data. We then used the calibration to reconstruct precipitation variability from 7500 to 600 cal. yr BP. Dry phases at Swallow Lagoon in the early to mid Holocene are correlated with cooling in the North Atlantic Ocean (i.e. "Bond" events). This relationship breaks down after ~3500 cal. yr BP. From 3500 cal. yr BP there is increased aridity (and variability) associated with the mid- to late Holocene establishment of modern El Niño Southern Oscillation conditions. Overall, these data show linkages between precipitation in the low latitudes of the Southern Hemisphere and Northern Hemisphere cooling events, with a shift to internal forcing of subtropical climate via the Pacific Ocean in the late Holocene.

  15. Early Holocene basinal sediments of the Dakhleh Oasis region, south central Egypt

    NASA Astrophysics Data System (ADS)

    Brookes, Ian A.

    1989-09-01

    Twenty samples of artifactual ostrich eggshell and hearth charcoal, firmly to loosely associated with basinal lacustrine, playa, and sand sheet sediments in the Dakhleh Oasis region of south-central Egypt, yield radiocarbon ages between ca. 8800 and ca. 4700 yr B.P. The sediments record variable sedimentary responses to an early Holocene pluvial interval in this virtually rainless region. Differences of hydrogeology and morphometry among and within basin types complicate paleoclimatic interpretation.

  16. Holocene glaciation and climate evolution of Baffin Island, Arctic Canada

    NASA Astrophysics Data System (ADS)

    Miller, Gifford H.; Wolfe, Alexander P.; Briner, Jason P.; Sauer, Peter E.; Nesje, Atle

    2005-08-01

    Lake sediment cores and cosmogenic exposure (CE) dates constrain the pattern of deglaciation and evolution of climate across Baffin Island since the last glacial maximum (LGM). CE dating of erratics demonstrates that the northeastern coastal lowlands became ice-free ca.14 ka as the Laurentide Ice Sheet (LIS) receded from its LGM margin on the continental shelf. Coastal lakes in southeastern Baffin Island started to accumulate sediment at this time, whereas initial lacustrine sedimentation was delayed by two millennia in the north. Reduced organic matter in lake sediment deposited during the Younger Dryas chron, and the lack of a glacial readvance at that time suggest cold summers and reduced snowfall. Ice retreated rapidly after 11 ka but was interrupted by a widespread readvance of both the LIS and local mountain glaciers ˜9.6 ka (Cockburn Substage). A second readvance occurred just before 8 ka during a period of unusually cold summers, corresponding to the 8.2 ka cold event in the Greenland Ice Sheet. Most local glaciers were behind their present margins before 7 ka, and in some instances much earlier, although the Foxe Dome of the LIS continued to slowly retract toward the present day Barnes Ice Cap throughout the Holocene. Pollen in lake sediments is rare and dominated by exotic sources prior to 12 ka. Subsequently, grass tundra became established, followed by modern tundra vegetation ca. 8 ka, with subtle changes in pollen assemblages in the late Holocene. Lake primary productivity peaked in the early Holocene, before terrestrial vegetation or marine surface waters reached their apparent thermal maxima. Lacustrine, marine, and glacial proxies all reflect significant late Holocene cooling. The onset of Neoglaciation is well dated in lacustrine records at ca. 6 ka, with intensification after 2.5 ka. The expansion of local glaciers during the Little Ice Age represents the most extensive advance since 7 ka. We suggest that the replacement of Atlantic surface

  17. Glacial-marine and glacial-lacustrine sedimentation in Sebago Lake, Maine: Locating the marine limit

    SciTech Connect

    Johnston, R.A.; Kelley, J.T. ); Belknap, D. . Dept. of Geological Sciences)

    1993-03-01

    The marine limit in Maine marks a sea-level highstand at approximately 13 ka. It was inferred to cross Sebago Lake near Frye Island by Thompson and Borns (1985) on the Surficial Geological Map of Maine, dividing the lake into a northern glacial-lacustrine basin and a southern glacial-marine basin. This study examined the accuracy of the mapped marine limit in the lake and the nature of glacial-lacustrine and glacial-marine facies in Maine. Recognition of the marine limit is usually based on mapped shorelines, glacial-marine deltas, and contacts with glacial-marine sediments. This study, in Maine's second largest lake, collected 100 kilometers of side-scan sonar images, 100 kilometers of seismic reflection profiles, and one core. Side-scan sonar records show coarse sand and gravel and extensive boulder fields at an inferred grounding-line position near Frye Island, where the marine limit was drawn. ORE Geopulse seismic reflection profiles reveal a basal draping unit similar to glacial-marine units identified offshore. Later channels cut more than 30 m into the basal stratified unit. In addition, till and a possible glacial-tectonic grounding-line feature were identified. Slumps and possible spring disruptions are found in several locations. The top unit is an onlapping ponded Holocene lacustrine unit. Total sediment is much thicker in the southern basin; the northern basin, >97 m deep, north of the marine limit appears to have been occupied by an ice block. Retrieved sediments include 12 meters of rhythmites. Microfossil identifications and dating will resolve the environments and time of deposition in this core.

  18. Late Pleistocene and Holocene Fire History of the Swiftcurrent Lake basin, eastern Glacier National Park, Montana

    NASA Astrophysics Data System (ADS)

    Kutvirt, J. C.; MacGregor, K. R.; Riihimaki, C. A.; Myrbo, A.

    2010-12-01

    High altitude alpine landscapes of the northern U.S. Rocky Mountains are geomorphically dynamic and sensitive to climate change. Understanding the timing and magnitude of past changes in temperature, aridity, and other factors such as seasonality and storminess are key in constraining natural climate variability in these sensitive environments. Fire frequency can provide strong insight into past climate regimes, with increased periodicity and/or intensity of fires reflecting episodes of warming and/or aridity. Lacustrine climate records in the Rockies are most abundant either further south of northern Montana at lower elevations, or in the Canadian Rockies further north. Here we examine a ˜12,900 year long lake sediment record from the northeastern basin of Swiftcurrent Lake in eastern Glacier National Park, MT to document fire frequency as a proxy for aridity in the region. Swiftcurrent Lake is fed mainly by melt from Grinnell Glacier, and thus reflects glacial, geomorphic, and climatic processes throughout the Holocene. Existing data, such as mineralogy, percent organic carbon, C/N, and grain size will be paired with the fire frequency record over the Holocene and latest Pleistocene to develop a comprehensive environmental history of the Swiftcurrent Lake Basin and greater Grinnell Glacier Valley. A clear understanding of fire history in the basin is important for future fire management decisions in Glacier National Park. Charcoal particles were tallied at contiguous 0.5 cm intervals over the first half meter of the core, and at 1 cm intervals over the remaining ~6.0 m, then converted to charcoal abundance and accumulation rates. Based age controls from radiocarbon analyses and ash fingerprinting the sampling interval represents between 5 and 20 years. A core collected in July 2010 will be analyzed for lead-210, providing additional age control for the past few centuries. Preliminary results show low charcoal counts overall with some clear peaks. High charcoal

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

    USGS Publications Warehouse

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

    2001-01-01

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

  20. A Late Glacial Environmental Reconstruction performed on Lacustrine Sediments from the Southern Tibetan Plateau identifies regional Monsoon Variations

    NASA Astrophysics Data System (ADS)

    Henkel, K.; Ahlborn, M.; Haberzettl, T.; Alivernini, M.; Kasper, T.; Thiele, A.; St-Onge, G.; Daut, G.; Frenzel, P.; Gleixner, G.; Wang, J.; Zhu, L.; Maeusbacher, R.

    2014-12-01

    The Tibetan Plateau (TP) is very sensitive to climate variations and is therefore an ideal study site to investigate past climate changes. Influenced by the Asian Monsoon system, the numerous lake systems on the TP serve as valuable archives for past hydrological changes, which are assumed to be caused by variations in strength and extent of the monsoonal impact. The lacustrine record from the terminal lake Tangra Yumco (4540 m a.s.l., 31°13'N, 86°43'E) consists of an interbedding of fine-grained silty sediments with laminations of different thicknesses (sub-mm to cm) and partly intercalated blackish sandy layers. Thin section analysis in the laminated areas reveals cyclic laminations composed of a carbonate and a detrital layer. Homogenous intervals represent turbidite deposits which are further detected based on lithology, radiography as well as changes in the water content, grain size, Ti-values (XRF) and in the paleomagnetic parameter median destructive field. The chronology is based on 27 AMS-radiocarbon ages on bulk organic matter and one piece of wood, which is of terrestrial origin. To determine a possible carbon reservoir effect, additional surface sediment samples and one modern aquatic plant were measured. The calculated reservoir effect of 2,120 +110/-90 years is assumed to be constant over the time and thus the base of the record reveals a corrected radiocarbon age of 17,270 +325/-310 cal BP. Additionally, investigations on paleomagnetic secular variations were carried out, showing that since 15,900 cal BP the record preserved a well-defined magnetization recording a genuine paleomagnetic signal. Regarding the geochemical (organic and inorganic), sedimentological, mineralogical and micropaleontological analyses, a low lake level with a high terrestrial input is observed for the Late Glacial. At 15.6 ka cal BP, a change in the sediment accumulation rate, increased allochthoneous input and changing ostracod fauna point to an increasing lake level. In

  1. A Laminated Carbonate Record of Late Holocene Mid-Continental Hydroclimate: Geochemical and Sedimentological Results from Martin Lake, LaGrange County, Indiana

    NASA Astrophysics Data System (ADS)

    Stamps, L. G.; Bird, B. W.; Gilhooly, W., III

    2014-12-01

    Paleoclimate records from the mid-continental United States that span the Holocene with sub-decadal resolution are rare. This is especially true for geochemical records that capture the isotopic composition of precipitation or local precipitation/evaporation balances. As a result, many questions remain about the hydrologic expression of abrupt climate events in this region that today is one of the world's largest agricultural centers. Here, we present sedimentological, geochemical, and chronological data spanning the last 3,000 years from a set of sediment cores from Martin Lake in northeastern Indiana. Today, this kettle lake is hydrologically open with persistent water column stratification and bottom water anoxia. Radiometric dating shows that the lake formed at approximately 16,000 cal yr BP and continuously accumulated sediment thereafter. We focus here on developing a stable isotope record of the late Holocene at decadal resolution to provide a detailed view of precipitation isotopic variability during this time. The Midwest has been influenced by changes in atmospheric circulation patterns throughout the late Holocene, leading to climate events like the Little Ice Age and Medieval Climate Anomaly, which significantly changed temperature and precipitation regimes. The isotopic composition of precipitation in the Midwest has been shown to be heavily influenced by the source of atmospheric moisture as mediated by the Pacific North American mode of atmospheric variability that in turn affects the position of the Polar Front Jetstream. Using high-resolution stable isotope measurements and ultimately climate modeling, we seek to reconstruct the isotopic expression of late Holocene climate events in the mid continental United States and assess the possible relationship with these dominant modes of atmospheric variability. Future work includes extending this reconstruction through the Holocene and increasing the temporal resolution of the data.

  2. Near-infrared spectroscopy of lacustrine sediments in the Great Salt Lake Desert: An analog study for Martian paleolake basins

    NASA Astrophysics Data System (ADS)

    Lynch, Kennda L.; Horgan, Briony H.; Munakata-Marr, Junko; Hanley, Jennifer; Schneider, Robin J.; Rey, Kevin A.; Spear, John R.; Jackson, W. Andrew; Ritter, Scott M.

    2015-03-01

    The identification and characterization of aqueous minerals within ancient lacustrine environments on Mars are a high priority for determining the past habitability of the red planet. Terrestrial analog studies are useful both for understanding the mineralogy of lacustrine sediments, how the mineralogy varies with location in a lacustrine environment, and for validating the use of certain techniques such as visible-near-infrared (VNIR) spectroscopy. In this study, sediments from the Pilot Valley paleolake basin of the Great Salt Lake desert were characterized using VNIR as an analog for Martian paleolake basins. The spectra and subsequent interpretations were then compared to mineralogical characterization by ground truth methods, including X-ray diffraction, automated scanning electron microscopy, and several geochemical analysis techniques. In general, there is good agreement between VNIR and ground truth methods on the major classes of minerals present in the lake sediments and VNIR spectra can also easily discriminate between clay-dominated and salt-dominated lacustrine terrains within the paleolake basin. However, detection of more detailed mineralogy is difficult with VNIR spectra alone as some minerals can dominate the spectra even at very low abundances. At this site, the VNIR spectra are dominated by absorption bands that are most consistent with gypsum and smectites, though the ground truth methods reveal more diverse mineral assemblages that include a variety of sulfates, primary and secondary phyllosilicates, carbonates, and chlorides. This study provides insight into the limitations regarding the use of VNIR in characterizing complex mineral assemblages inherent in lacustrine settings.

  3. Paleoclimate cycles and tectonic controls on fluvial, lacustrine, and eolian strata in upper Triassic Chinle Formation, San Juan basin

    SciTech Connect

    Dubiel, R.F. )

    1989-09-01

    Sedimentologic study of the Upper Triassic Chinle Formation in the San Juan basin (SJB) indicates that Late Triassic paleoclimate and tectonic movements influenced the distribution of continental lithofacies. The Shinarump, Monitor Butte, and Petrified Forest Members in the lower part of the Chinle consist of complexly interfingered fluvial, floodplain, marsh, and lacustrine rocks; the Owl Rock and Rock Point Members in the upper part consists of lacustrine-basin and eolian sandsheet strata. Facies analysis, vertebrate and invertebrate paleontology, and paleoclimate models demonstrate that the Late Triassic was dominated by tropical monsoonal circulation, which provided abundant precipitation interspersed with seasonally dry periods. Owl Rock lacustrine strata comprise laminated limestones that reflect seasonal monsoonal precipitation and larger scale, interbedded carbonates and fine-grained clastics that represent longer term, alternating wet and dry climatic cycles. Overlying Rock Point eolian sand-sheet and dune deposits indicate persistent alternating but drier climatic cyclicity. Within the Chinle, upward succession of lacustrine, alternating lacustrine/eolian sand-sheet, and eolian sand-sheet/dune deposits reflects an overall decrease in precipitation due to the northward migration of Pangaea out of low latitudes dominated by monsoonal circulation.

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

    NASA Astrophysics Data System (ADS)

    Aqrawi, Adnan A. M.

    2001-02-01

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

  5. Giant lacustrine pockmarks with subaqueous groundwater discharge and subsurface sediment mobilization

    NASA Astrophysics Data System (ADS)

    Reusch, Anna; Loher, Markus; Bouffard, Damien; Moernaut, Jasper; Hellmich, Franziska; Anselmetti, Flavio S.; Bernasconi, Stefano M.; Hilbe, Michael; Kopf, Achim; Lilley, Marvin D.; Meinecke, Gerrit; Strasser, Michael

    2015-05-01

    Subsurface fluid flow in oceans and lakes affects bathymetric morphology, sediment distribution, and water composition. We present newly discovered giant lacustrine pockmarks in Lake Neuchâtel (up to 160 m diameter and 30 m deep) that rank among the largest known pockmarks in lakes. Our multidisciplinary study reveals ~60 m of suspended sediment inside a pockmark. The sediment suspension is 2.6° warmer and isotopically lighter in δ18OH2O by 1.5‰ than the ambient lake water, documenting currently active fluid flow by karstic groundwater discharge from the Jura Mountain front into the Swiss Plateau hydrological system. Strikingly, the levees of the pockmarks comprise subsurface sediment mobilization deposits representing episodic phases of sediment expulsion during the past. They strongly resemble subsurface fluid flow features in the marine realm. Comparable processes are expected to also be relevant for other carbonate-dominated mountain front ranges, where karstic groundwater discharges into lacustrine or marine settings.

  6. Asynchronous evolution of the isotopic composition and amount of precipitation in north China during the Holocene revealed by a record of compound-specific carbon and hydrogen isotopes of long-chain n-alkanes from an alpine lake

    NASA Astrophysics Data System (ADS)

    Rao, Zhiguo; Jia, Guodong; Li, Yunxia; Chen, Jianhui; Xu, Qinghai; Chen, Fahu

    2016-07-01

    Both the timing of the maximum East Asian summer monsoon (EASM) intensity in monsoonal China and the environmental significance of the Chinese stalagmite oxygen isotopic record (δ18O) have been debated. Here, we present a ca. 120-year-resolution compound-specific carbon (δ13C) and hydrogen (δD) isotopes of terrestrial long-chain n-alkanes extracted from a well-dated sediment core from an alpine lake in north China. Our δ13C data, together with previously reported pollen data from a parallel core, demonstrate a humid mid-Holocene from ca. 8-5 ka BP. Assuming that the climatic humidity of north China is an indicator of the EASM intensity, then the maximum EASM intensity occurred in the mid-Holocene. Our δD data reveal a similar long-term trend to the δ18O record from nearby Lianhua Cave, indicating that the synchronous δD and δ18O records faithfully record the δD and δ18O of precipitation, respectively. The most negative δD and δ18O values occur in the early-mid Holocene, from ca. 11-5 ka BP. This contrast in the timing of isotopic variations demonstrates a complex relationship between the isotopic composition of precipitation and precipitation amount, or EASM intensity. Further comparisons indicate a possible linkage between the precipitation amount in north China and the west-east thermal gradient in the equatorial Pacific. In addition, the temperature of the moisture source area may play an important role in determining the isotopic composition of precipitation in monsoonal China.

  7. Diagenetic history of fluvial and lacustrine sandstones of the Hartford Basin (Triassic Jurassic), Newark Supergroup, USA

    NASA Astrophysics Data System (ADS)

    Wolela, A. M.; Gierlowski-Kordesch, E. H.

    2007-04-01

    The early introduction of clays into continental sandstones has been attributed to mechanical infiltration by percolation of clay-rich surface waters into grain framework or cutans formed from pedogenic processes. The discovery of pedogenic mud aggregates as traction-load mud in ancient fluvial deposits suggests that permeability and porosity of terrigenous sandstones can be influenced at deposition and control early diagenetic patterns. This study compares diagenesis in fluvial (subaerially exposed) sandstones with lacustrine (subaqueous) sandstones in a Triassic-Jurassic continental rift basin (Hartford Basin, Newark Supergroup). Diversity of diagenetic minerals and sequence of diagenetic alteration can be directly related to depositional environment. The fluvial sandstones in the New Haven Arkose, East Berlin Formation, and Shuttle Meadow Formation of the Hartford Basin are dominated by concretionary calcite and early calcite cement, infiltrated clays (illite-smectite), pedogenic mud aggregates (smectite and illite-smectite), grain coating clays (illite/hematite, illite-chlorite/hematite), quartz overgrowths, late stage carbonate cements (calcite, ferroan calcite), pore-filling clays (illite, kaolinite with minor amounts of smectite, smectite-chlorite, illite-smectite) and hematite. However, pedogenic processes in these fluvial sandstones retarded the development of quartz and feldspar overgrowths, and carbonate authigenesis, as well as the quality of diagenetically enhanced porosity. Dark gray-black lacustrine (subaqueous) sandstones and mudrocks in the East Berlin and Shuttle Meadow Formations are dominated by pyrite, concretionary dolomite and early dolomite cement, radial grain coating clays (smectite-chlorite, illite-smectite), late stage carbonate cements (dolomite, ferroan dolomite, ankerite), albite and pore-filling clays (smectite-chlorite, illite-smectite, illite-chlorite). Clay minerals exist as detrital, mechanically infiltrated, and neoformed clay

  8. Century-scale shifts in early holocene atmospheric CO2 concentration

    PubMed

    Wagner; Bohncke; Dilcher; Kurschner; van Geel B; Visscher

    1999-06-18

    The inverse relation between atmospheric carbon dioxide concentration and stomatal frequency in tree leaves provides an accurate method for detecting and quantifying century-scale carbon dioxide fluctuations. Stomatal frequency signatures of fossil birch leaves reflect an abrupt carbon dioxide increase at the beginning of the Holocene. A succeeding carbon dioxide decline matches the Preboreal Oscillation, a 150-year cooling pulse that occurred about 300 years after the onset of the Holocene. In contrast to conventional ice core estimates of 270 to 280 parts per million by volume (ppmv), the stomatal frequency signal suggests that early Holocene carbon dioxide concentrations were well above 300 ppmv. PMID:10373111

  9. Late Holocene Climate Change Inferred From Varved Proglacial Lake Sediments on Northeastern Baffin Island, Arctic Canada

    NASA Astrophysics Data System (ADS)

    Thomas, E. K.; Briner, J. P.; Axford, Y.

    2007-12-01

    The Arctic has a disproportionately large response to changes in radiative forcing of climate, and glaciers and arctic lacustrine ecosystems respond sensitively to these changes. Lacustrine ecosystems throughout the Arctic are undergoing rapid regime shifts, including dramatically increased primary productivity and changing aquatic floral and faunal assemblages. Our work on organic lake sediments from northeast Baffin Island shows a large increase in primary productivity, changes in insect (Chironomidae) assemblages including the disappearance of cold stenotherms, and a rise in chironomid-inferred summer water temperatures of at least 1.5°C over the past 50 years, reaching temperatures that were unprecedented in the past 5000 years. Here, we pursue the use of varve thickness, an abiotic temperature proxy, to expand our understanding of late Holocene temperature changes on northeast Baffin Island. We obtained a 14C- and 239+240Pu-dated surface core/percussion core pair from a proglacial lake. Together these cores span > 8000 years and the sediments are varved, as verified by the 239+240Pu analysis, for at least the past 700 years. Magnetic susceptibility was high during the early Holocene, decreased to near-zero values during the mid-Holocene and increased during the past 2500 years to reach the highest values seen in the record around 1000 years ago. Loss-on- ignition had an opposite trend, with the highest values in the mid-Holocene. Sedimentation rate was constant during most of the Holocene (0.03 cm yr -1) and increased during the past 1000 years to 0.05 cm yr -1. These parameters indicate that following the absence of an active glacier during the middle Holocene, glacier activity initiated ~2500 years ago and reached peak activity over the last 1000 years. Our ongoing work to obtain a varve-thickness record for at least the last 700 years, and its calibration to a nearby weather station, will be presented.

  10. An in lake comparison of the branched GDGT lacustrine paleothermometer with other temperature proxies

    NASA Astrophysics Data System (ADS)

    Loomis, S. E.; Russell, J. M.; Sinninghe Damste, J. S.

    2011-12-01

    Quantitative paleoclimate reconstructions are essential for testing the efficacy of climate models, yet there are very few proxies that can reconstruct temperature over much of the terrestrial landscape. A novel group of bacterial membrane lipids known as branched glycerol dialkyl glycerol tetraethers (GDGTs) have strong potential to be used as a paleotemperature proxy given their ubiquity in peats, soils, lacustrine sediments, and near shore ocean sediments. There are nine known branched GDGTs, and the degree of methylation and cyclisation of these compounds has been shown to relate to the mean annual air temperature (MAAT) of their environment. Several different calibrations have been put forth relating branched GDGT distribution to MAAT, but up to now, there has been limited success applying these calibrations lake cores to reconstruct paleotemperatures. We have now developed a branched GDGT temperature calibration based upon 109 lake surface sediments in tropical Africa. Here we test the applicability of branched GDGT lacustrine paleothermometer on three different tropical lakes, including Lake Tanganyika, Lake Malawi, and Lake Peten Itza. These lakes were chosen because they have paleotemperature reconstructions derived from proxies independent of branched GDGTs, including TEX86, fossil pollen (Tanganyika and Malawi) and biogenic carbonate isotopes (Peten Itza) to reconstruct past lake water temperatures, allowing us to directly compare our reconstructions to those derived from other proxies. We apply both published and unpublished calibrations to our lake core data in an attempt to deduce the most accurate calibrations to reconstruct temperatures from lacustrine sediments.

  11. Sterols of a contemporary lacustrine sediment. [in English postglacial lake

    NASA Technical Reports Server (NTRS)

    Gaskell, S. J.; Eglinton, G.

    1976-01-01

    Results are reported for detailed sterol analyses of several depths (corresponding to between zero and about 150 yr in age) in a contemporary lacustrine sediment from a freshwater lake of postglacial origin in England. Delta 5-, delta 22-, and delta 5,22-sterols are identified along with 5 alpha- and 5 beta-stanols as well as a C26 stanol with a C7 side chain. Solvent extraction yields carbon number distributions for the 5 alpha- and 5 beta-stanol sediment constituents that parallel the corresponding delta 5-sterol distributions. The amounts of 5 alpha-stanols are found to exceed those of 5 beta-stanols in the sediment, and variations in the ratio of 5 alpha- to 5 beta-stanol between sediment samples from similar depths are shown to suggest an inhomogeneity of the sediment. It is found that the sterol composition of sediment cores varies markedly with depth, reflecting both the effects of a sterol hydrogenation process and a changing input to the sediment. It is concluded that C29 sterols, of probable higher-plant origin, predominate at lower sediment depths while C27 sterols, possibly derived from autochthonous sources, are more abundant in the surface sediment.

  12. Physicochemical, mineralogical, and geochemical characteristics of lacustrine sediments of the Konya Basin, Turkey, and their significance in relation to climatic change

    NASA Astrophysics Data System (ADS)

    Inoue, K.; Saito, M.; Naruse, T.

    1998-06-01

    Physicochemical, mineralogical, and geochemical characteristics of 279 highly calcareous lacustrine sediment samples obtained from a 30 m drilling core in the western part of the Great Konya Basin, Turkey were studied. The sediments have a predominance of silt and clay fractions with a median diameter of 3-5 μm. Vertical changes of the amounts of water soluble components, gypsum, carbonates, and non-salt minerals such as quartz, feldspars, and layer silicates in the sediments suggest that there were climatic changes in the Konya Basin. The dominant clay mineral is smectite followed by kaolinite, illite, and palygorskite. The oxygen isotopic ( δ18O) ratios of six quartz samples from the Konya sediments, a terra rossa soil beside Lake Beyşehir gölü and paleosols at the foot of Mt. Erciyes Daǧ ranged from +18.1 to +20.6‰. The dominant clay minerals and δ18O ratios suggest that part of quartz and coexisting layer silicates is of long-range transported and/or local aeolian dust origin from arid and semi-arid regions such as North Africa, Israel, and the surroundings. The relatively high deposition rate might be due to aeolian dust input and/or the sediment input introduced by the rivers such as the Çarşamba river from the Toros (Taurus) mountains. The vertical distributions of electro-conductivity, amounts of water soluble and non-salt components, and the gypsum content of the sediments suggest that gypsum-rich layers were formed under shallow, saline waters, possibly associated with warm to hot and dry environments such as the Last Interglacial epoch and the Early Holocene. The sediments characterized by relatively high amounts of non-salt sediments, in which gypsum did not accumulate, could be deeper water phases formed under the cold and/or wet environments such as the Glacial epochs.

  13. An isotopic study of a fluvial-lacustrine sequence: The Plio-Pleistocene koobi fora sequence, East Africa

    USGS Publications Warehouse

    Cerling, T.E.; Bowman, J.R.; O'Neil, J.R.

    1988-01-01

    Stable isotopic analyses of Plio-Pleistocene and modern sediments in the fluvial-lacustrine system occupying the Turkana Basin, East Africa provide constraints on the paleoenvironmental and diagenetic histories of the Pliocene through the Recent sediments in the basin. The ??13C values for carbonates in lacustrine sediments range from -15 to +22??? relative to PDB, depending on the varying proportions of CO2 from the atmospheric reservoir and from various metabolic sources. The ??18O values of carbonates in lacustrine sediments indicate that the isotopic composition of paleolake water varied by over 10??? from the Pliocene to the present. The ??13C values for pedogenic carbonates record paleoccologic variations and suggest that C4 plants did not become well established in the preserved depositional parts of the basin until about 1.8 myr ago. The ??18O values pedogenic carbonates suggest a range of over 10??? for the isotopic composition of soil water during this interval. They also suggest a period of major climatic instability from about 3.4 to 3.1 myr and at about 1.8 myr. Together, the ??13C and ??18O values of pedogenic carbonates indicate that the present conditions are as arid and hot as any that had prevailed during deposition of these Plio-Pleistocene sediments. ?? 1988.

  14. Episodic drought during mid-Holocene warm period revealed by speleothem carbon and oxygen isotopes and UV fluorescence in southern Appalachians, USA

    NASA Astrophysics Data System (ADS)

    Li, Z.; Cheng, H.; Driese, S. G.

    2012-12-01

    The geographical characteristics of the expression (onset, duration, frequency, and amplitude) and environmental impacts of the Holocene megadrought is poorly understood in the southeastern (SE) US, particularly in the inland, southern Appalachian region. Evidence indicates that drought conditions prevailed in the southwestern and mid-continent regions during the mid-Holocene, but the US eastern seaboard may have had increased precipitation. Here, we present a 15 ka speleothem isotope record from Raccoon Mountain Cave (RMC) in the southern Appalachians, showing episodic droughts during the mid-Holocene warm period. The speleothem (RM0710-2), collected from a constant, slow drip-rate site at the lower end of the cave passage, was constrained geochronologically by 11 U/Th dates. To determine the suitability of fossil speleothems as paleoclimate records in RMC, multiple cave materials were examined, including stalagmite, stalactite, cave water (pond and dripping water), limestone, cave soil, flowstone, cave surface soil, pond deposit, and soda straw. Stable isotope analysis of modern speleothems and cave drip water spatially collected from RMC revealed that the fossil speleothem δ13C and δ18O values record moisture conditions, with less negative isotope values corresponding to drier or higher evapo-transpiration conditions.Three major drought periods were identified: 7400~6890 yr BP, 5950~5340 yr BP, and 4870~4050 yr BP. A weak drought interval occurred during a major wet period (6890~5950 yr BP), between 6640~6280 yr BP. These drought intervals were bounded by three prominent wet periods centered at 6710 yr BP, 5970 yr BP, and 5210 yr BP. A profound, long-term wet period (~13,000~7,520 yr BP) started at the beginning of the Younger Dryas event that was characterized as a hiatus owing to speleothem submergence during high groundwater level. The major wet period between 6890 yr BP and 5950 yr BP characterized by more negative δ13C values covarying with more negative

  15. Exploring Spatiotemporal Patterns of Holocene Carbon Dynamics in Northern Peatlands by Incorporating Bayesian Age-Depth Modeling into Monte-Carlo EOF Analysis

    NASA Astrophysics Data System (ADS)

    Massa, Charly; Yu, Zicheng; Blaauw, Maarten; Loisel, Julie

    2014-05-01

    EOF (Empirical Orthogonal Functions) analysis is a common tool for exploring the spatiotemporal modes of instrumental climate data. Although rarely applied to paleo proxy records, the EOF method is an efficient tool for the detection and analysis of broad-scale patterns of centennial to millennial-scale climate variability. But most paleoclimate records are not annually resolved and have inherent chronological uncertainties that may be problematic using ordinary EOF. Anchukaitis et al. (2012) provided a major step forward in paleo proxy data analysis by adapting EOF to time-uncertain paleoclimate proxy records (Monte-Carlo EOF). However, additional problems may arise for analyzing flux-based paleo parameters, such as peat C accumulation rates, which are strongly dependent to age-depth modeling, that is, small uncertainties in ages may lead to large differences in accumulation rates. Here we present a new approach that combines Bayesian age modeling and Monte-Carlo EOF to analyze flux-based paleo-datasets by thoroughly addressing both chronological and flux measurement uncertainties. This approach, implemented as a suit of linked R functions, overcomes a number of technical challenges, such as the effective handling of large datasets, the reduction of computational requirements for calculating hundreds of thousands of iterations, standardization issues, and EOF computation of gappy data. As a case study we explored the recently published Holocene circum-Arctic peatland database with >100 sites (Loisel et al. in press) to investigate the spatiotemporal patterns and climate controls of peat C accumulation. The approach can be used for other flux-based proxies, such as charcoal influx, erosion rates or atmospheric depositions. Our preliminary results reveal different temporal patterns of C accumulation in major peatland regions, as controlled by various regional climate histories and other bioclimatic factors. For instance, peatlands in continental vs. oceanic settings

  16. The Holocene temperature conundrum

    PubMed Central

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

    2014-01-01

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

  17. Exceptionally well-preserved giant spermatozoa in male and female specimens of an ostracod Cypria ophtalmica (Crustacea: Ostracoda) from Late Glacial lacustrine sediments of Southern Carpathians, Romania

    NASA Astrophysics Data System (ADS)

    Iepure, Sanda; Namiotko, Tadeusz; Valdecasas, Antonio G.; Magyari, Enikö K.

    2012-07-01

    Exceptionally well-preserved giant spermatozoa observed between abundant decalcified carapace valves of ostracods (Crustacea: Ostracoda) were found in Late Glacial to Holocene (14,400 to 10,000 cal years bp) lacustrine sediments in the southern Romanian Carpathians. Analysis by scanning electron microscopy and laser scanning confocal microscopy revealed good preservation of the appendages enabling specific identification as Cypria ophtalmica (Candonidae) and indication of the presence of both female and male specimens based on the sexual dimorphism of the second antenna. This record represents the oldest and richest direct evidence of virtually morphologically unaltered animal spermatozoa preserved in females after mating.

  18. Phosphorus in lacustrine groundwater discharge drives eutrophication

    NASA Astrophysics Data System (ADS)

    Meinikmann, Karin; Hupfer, Michael; Lewandowski, Jörg

    2016-04-01

    Lake eutrophication has long been mainly associated with phosphorus (P) inputs from overland flow. Our work gives evidence that also groundwater can carry significant loads of dissolved P. We quantified P loads from groundwater to Lake Arendsee using near-shore measurements of P concentrations at a high spatial resolution and volume fluxes of lacustrine groundwater discharge (LGD) derived from a previous study. Results show that LGD accounts for more than 50% of the overall external P load, thus fueling the eutrophication of the lake. Several different approaches of groundwater sampling (groundwater observation wells, temporary piezometers, and domestic wells) reveal a broad spatial heterogeneity of P concentrations in the subsurface catchment of the lake. The highest P concentrations (above 4 mg/L) were found below a settled area along the southern lake shore. Contrary to expectations, other parameters (dissolved iron, ammonium, etc.) were not correlated with P, indicating that natural processes are superimposed by heavy contaminations. Both the intensity of the contamination and its proximity to the lake inhibit nutrient retention within vadose zone and aquifer and allow significant P loads to be discharged into the lake.

  19. Determining earthquake recurrence intervals from deformational structures in young lacustrine sediments

    USGS Publications Warehouse

    Sims, J.D.

    1975-01-01

    Examination of the silty sediments in the lower Van Normal reservoir after the 1971 San Fernando, California earthquake revealed three zones of deformational structures in the 1-m-thick sequence of sediments exposed over about 2 km2 of the reservoir bottom. These zones are correlated with moderate earthquakes that shook the San Fernando area in 1930, 1952, and 1971. The success of this study, coupled with the experimental formation of deformational structures similar to those of the Van Norman reservoir, led to a search for similar structures in Pleistocene and Holocene lakes and lake sediments in other seismically active areas. Thus, studies have been started in Pleistocene and Holocene silty and sandy lake sediments in the Imperial Valley, southeastern California; Clear Lake, in northern California; and the Puget Sound area of Washington. The Imperial Valley study has yielded spectacular results: five zones of structures in the upper 10 m of Late Holocene sediments near Brawley have been correlated over an area of approximately 100 km2, using natural outcrops. These structures are similar to those of the Van Norman reservoir and are interpreted to represent at least five moderate to large earthquakes that affected the southern Imperial Valley area during Late Holocene time. The Clear Lake study has provided ambiguous results with respect to determination of earthquake recurrence intervals because the cores studied are in clayey rich in organic material sediments that have low liquefaction potential. A study of Late Pleistocene varved glacio-lacustrine sediments has been started in the Puget Sound area of Washington, and thirteen sites have been examined. One has yielded 18.75 m of sediments that contains 1,804 varves and fourteen deformed zones interpreted as being caused by earthquake, because they are identical to structures formed experimentally by simulated seismic shaking. Correlation of deformational structures with seismic events is based on: 1. (1

  20. Geomorphology and OSL Ages of late-Holocene Baymouth Barriers in Door Peninsula, Wisconsin, USA

    NASA Astrophysics Data System (ADS)

    Gamboa, L.; Rawling, J., 3rd; Hanson, P. R.

    2012-12-01

    This study focuses on eolian and lacustrine sediments in two baymouth barrier systems found along Lake Michigan's western shoreline. We used optically stimulated luminescence (OSL) dating to constrain when lacustrine sediments were deposited and overlying dunes were activated at field sites at both Kangaroo and Clark Lakes. We sampled sediments from lacustrine and eolian deposits for particle size analysis and OSL dating using bucket augers and a vibracoring device. Lacustrine and eolian sediments were differentiated through particle size analysis and mineralogical observations. Our results show that the eolian sediment contains little to no locally derived dolomitic sand, and is consistently finer, more Quartz rich, and better sorted compared to the underlying lacustrine sediment. The elevations of the lacustrine sediment found within the two baymouth barriers range from 179-184 meters above mean sea level (mamsl). These deposits are found above the current Lake Michigan level which has historically fluctuated at ~ 177 mamsl, but at a similar elevation to littoral sediments deposited during the Nipissing lake level high which lie at ~ 184 mamsl. Our OSL ages from these lacustrine sediments also closely overlap with the Nipissing event, which occurred between ~ 5.5 to 4.5 ka in the Lake Michigan basin. The dunes found on these barriers also correspond to lake level fluctuations in the late Holocene. Ages from dunes at the Clark Lake site, including small parabolics ranging from 3-7 m in height and large complex parabolic dunes ranging from 18-24 m in relief, span the late Holocene with an apparent peak in activity around the Nipissing lake level high. At the Kangaroo Lake barrier two distinct dune ridges are separated by ~0.4 km. The dune ridge close to Lake Michigan has dunes with ~ 6 meters of relief and the ridge close to Kangaroo Lake has dunes with 15-24 meters of relief. OSL ages taken from the crests of the larger dunes at Kangaroo Lake correspond to the

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

    PubMed Central

    Jones, Miriam C.; Yu, Zicheng

    2010-01-01

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

  2. Late cenozoic lacustrine and climatic environments at Tule Lake, northern Great Basin, USA

    SciTech Connect

    Bradbury, J.P.

    1992-01-01

    Cores of lake sediment to a depth of 334 m in the town of Tulelake, northern California, document the late Cenozic paleolimnologic and paleoclimatic history of the northwestern Great Basin. Lacustrine diatoms are abundant throughout the record documenting a nearly continuous paleolimnologic history of the Tule Lake basin. Except for a drier (and cooler?) interval recorded by Fragilaria species about 2.4 Ma, the Pliocene is characterized by a dominance of planktonic Aulacoseira solida implying a warm monomictic lake under a climatic regime of low seasonality. Much of the Pleistocene is dominated by Stephanodiscus and Fragilaria species suggesting a cooler, drier, and highly variable climate. Benthic diatoms typical of alkaline-enriched saline waters commonly appear after 1.0 Ma, and tephrochronology indicates slow deposition and possible hiatuses between about 0.6 and 0.2 Ma. The chronology of even-numbered oxygen isotope stages approximately matches fluctuations in the abundance of Fragilaria since 800 ka indicating that glacial periods were drier environments at Tule Lake. Glacial and interglacial environments since 150 ka were distinct from, and more variable than, those occurring earlier. The last full glacial period was very dry, but shortly Tule Lake became a deep, cool lacustrine system indicating a substantial increase in precipitation. Aulacoseira ambigua characterized the latest glacial and Holocene record of Tule Lake, indicating that warmer and wetter climates began about 15 ka. Diatom concentration fluctuates at 41000 year intervals between 3.0 and 2.5 Ma and at approximately 100000 year intervals after 1.0 Ma. In the late Pliocene and early Pleistocene, Aulacoseira solida percentages wax and wane in an approximately 400000 year cycle. The possible response of Tule Lake diatom communities to orbitally-induced insolation cycles underscores the importance of this record for the study of late Cenozoic paleoclimate change. 41 refs., 8 figs.

  3. Microbiological Comparisons within and across Contiguous Lacustrine, Paleosol, and Fluvial Subsurface Sediments

    PubMed Central

    Kieft, T. L.; Fredrickson, J. K.; McKinley, J. P.; Bjornstad, B. N.; Rawson, S. A.; Phelps, T. J.; Brockman, F. J.; Pfiffner, S. M.

    1995-01-01

    Twenty-six subsurface samples were collected from a borehole at depths of 173.3 to 196.8 m in the saturated zone at the Hanford Site in south-central Washington State. The sampling was performed throughout strata that included fine-grained lacustrine (lake) sediments, a paleosol (buried soil) sequence, and coarse-grained fluvial (river) sediments. A subcoring method and tracers were used to minimize and quantify contamination to obtain samples that were representative of subsurface strata. Sediment samples were tested for total organic carbon, inorganic carbon, total microorganisms by direct microscopic counts, culturable aerobic heterotrophs by plate counts, culturable anaerobes by most-probable-number enumeration, basal respiration rates, and mineralization of (sup14)C-labeled glucose and acetate. Total direct microscopic counts of microorganisms were low, ranging from below detection to 1.9 x 10(sup5) cells g (dry weight)(sup-1). Culturable aerobes and anaerobes were below minimum levels of detection in most samples. Direct microscopic counts, basal respiration rates, and (sup14)C-glucose mineralization were all positively correlated with total organic carbon and were highest in the lacustrine sediments. In contrast to previous subsurface studies, these saturated-zone samples did not have higher microbial abundance and activities than unsaturated sediments sampled from the same borehole, the fine-textured lacustrine sediment had higher microbial numbers and activities than the coarse-textured fluvial sands, and the paleosol samples did not have higher biomass and activities relative to the other sediments. The results of this study expand the subsurface microbiology database to include information from an environment very different from those previously studied. PMID:16534940

  4. Holocene Biomass Burning, Environmental Change, and Human Land Use in the Southern Maya Lowlands

    NASA Astrophysics Data System (ADS)

    Anderson, L.; Wahl, D.

    2013-12-01

    For several decades scholars have studied the dynamic relationship between the prehispanic Maya and their environment in order to test hypotheses that environmental change played a role in the abandonment of the Maya lowlands. Fire was inherent in Maya land use practices, arguably the primary tool used to alter the landscape and extract resources. Opening of forest for agriculture, building, and extraction/production of construction material necessitated burning. The extensive production of lime plaster for architectural and domestic use demanded harvesting and burning of vast quantities of green wood. While we understand the fundamental role of fire in Maya land use, there are very few records of prehispanic biomass burning from the Maya lowlands. Consequently, only a limited understanding exists of both natural fire regimes and patterns of anthropogenic burning in the tropical dry forests of Central America. Here we report two new well-dated, high-resolution records of biomass burning based on analysis of fossil charcoal recovered from lacustrine sediment cores, extending from the early Holocene to the present. The study sites, Lagos Paixban and Puerto Arturo are located in the southern Maya lowlands in modern northern Peten, Guatemala. Macroscopic charcoal data are presented along with previously published proxy data from the sites, and interpreted in the context of existing regional and local paleoenvironmental and archeological records. Results show that frequent fires occurred in the closed canopy forests of the region since at least the early mid-Holocene (~9000 BP), prior to occupation by sedentary agriculturalists. Following the arrival of sedentary agriculture at around 4600 BP, the system transitioned from climate controlled to anthropogenic control. During the Maya period, changes in fire regime are muted and do not appear to be driven by changes in climate conditions. Low charcoal influx and fire frequency in the Preclassic period suggest that land use

  5. High Holocene lake levels in eastern Patagonia (Argentina) as a result of persistent Atlantic rainfall (Invited)

    NASA Astrophysics Data System (ADS)

    Ariztegui, D.; Compagnucci, R.; Agosta, E. A.

    2013-12-01

    Today's precipitation in central Patagonia, Argentina, mostly follows the intensity of the Westerlies. However, the extraordinary persistence of daily easterly winds can trigger episodes of intense rainfall reflected as water level variations in Lago Cardiel, a closed lacustrine basin located at 49°S. Meteorological data from 11-20 March 2002 at nearby Gobernador Gregores station recorded a heavy rain spell of 50mm accounting for 30% of the mean annual rainfall (167mm/year). The synoptic situation during this interval shows rainfall produced by wet air mass advection from the Atlantic. The weather surface maps for these days display a cyclone incoming at 45°S to the west of western Patagonia together with a concomitant anticyclone to the southwest, while a cyclogenesis initiates in eastern Patagonia. This pressure dipole produced east-north-eastern winds at the lake latitude and a generalized drop in the Westerlies intensity almost across the entire Patagonia. This is shown in distant stations such as Bariloche(41.9°S) and Rio Gallegos (51.4°S) in northwestern and southeastern Patagonia, respectively, as well as in Chilean stations such as Balmaceda (45.9°S) and Chile Chico (46.9°S). Similar pressure anomalies along with changes in wind intensity and direction have been previously simulated for the Austral winter (JJA) during the middle Holocene (7.0 to 4.5 kcal yrs BP). Thus, weaker Westerlies along with a higher frequency of the dipole-type atmospheric circulation than at present increased the described easterly winds-triggered rainfall. This inference agrees with high lake levels in the Lago Cardiel record along with more negative - Atlantic type - oxygen isotopic composition of authigenic carbonates. An increase in the frequency of this climatic configuration during longer time intervals could further explain the extreme lake highstands reconstructed for the early Holocene, and the contemporaneous negative isotopic signature of the carbonates. It could

  6. Geochemistry and diagenesis of Miocene lacustrine siliceous sedimentary and pyroclastic rocks, Mytilinii basin, Samos Island, Greece

    USGS Publications Warehouse

    Stamatakis, M.G.; Hein, J.R.; Magganas, A.C.

    1989-01-01

    A Late Miocene non-marine stratigraphic sequence composed of limestone, opal-CT-bearing limestone, porcelanite, marlstone, diatomaceous marlstone, dolomite, and tuffite crops out on eastern Samos Island. This lacustrine sequence is subdivided into the Hora Beds and the underlying Pythagorion Formation. The Hora Beds is overlain by the clastic Mytilinii series which contains Turolian (Late Miocene) mammalian fossils. The lacustrine sequence contains volcanic glass and the silica polymorphs opal-A, opal-CT, and quartz. Volcanic glass predominantly occurs in tuffaceous rocks from the lower and upper parts of the lacustrine sequence. Opal-A (diatom frustules) is confined to layers in the upper part of the Hora Beds. Beds rich in opal-CT underlie those containing opal-A. The occurrence of opal-CT is extensive, encompassing the lower Hora Beds and the sedimentary rocks and tuffs of the Pythagorion Formation. A transition zone between the opal-A and opal-CT zones is identified by X-ray diffraction patterns that are intermediate between those of opal-CT and opal-A, perhaps due to a mixture of the two polymorphs. Diagenesis was not advanced enough for opal-CT to transform to quartz or for volcanic glass to transform to opal-C. Based on geochemical and mineralogical data, we suggest that the rate of diagenetic transformation of opal-A to opal-CT was mainly controlled by the chemistry of pore fluids. Pore fluids were characterized by high salinity, moderately high alkalinity, and high magnesium ion activity. These pore fluid characteristics are indicated by the presence of evaporitic salts (halite, sylvite, niter), high boron content in biogenic silica, and by dolomite in both the opal-A and opal-CT-bearing beds. The absence of authigenic K-feldspar, borosilicates, and zeolites also support these pore fluid characteristics. Additional factors that influenced the rate of silica diagenesis were host rock lithology and the relatively high heat flow in the Aegean region from

  7. A deglacial and Holocene record of climate variability in south-central Alaska from stable oxygen isotopes and plant macrofossils in peat

    USGS Publications Warehouse

    Jones, Miriam C.; Wooller, Matthew J.; Peteet, Dorothy M.

    2014-01-01

    We used stable oxygen isotopes derived from bulk peat (δ18OTOM), in conjunction with plant macrofossils and previously published carbon accumulation records, in a ∼14,500 cal yr BP peat core (HT Fen) from the Kenai lowlands in south-central Alaska to reconstruct the climate history of the area. We find that patterns are broadly consistent with those from lacustrine records across the region, and agree with the interpretation that major shifts in δ18OTOM values indicate changes in strength and position of the Aleutian Low (AL), a semi-permanent low-pressure cell that delivers winter moisture to the region. We find decreased strength or a more westerly position of the AL (relatively higher δ18OTOM values) during the Bølling-Allerød, Holocene Thermal Maximum (HTM), and late Holocene, which also correspond to warmer climate regimes. These intervals coincide with greater peat preservation and enhanced carbon (C) accumulation rates at the HT Fen and with peatland expansion across Alaska. The HTM in particular may have experienced greater summer precipitation as a result of an enhanced Pacific subtropical high, a pattern consistent with modern δ18O values for summer precipitation. The combined warm summer temperatures and greater summer precipitation helped promote the observed rapid peat accumulation. A strengthened AL (relatively lower δ18OTOM values) is most evident during the Younger Dryas, Neoglaciation, and the Little Ice Age, consistent with lower peat preservation and C accumulation at the HT Fen, suggesting less precipitation reaches the leeward side of the Kenai Mountains during periods of enhanced AL strength. The peatlands on the Kenai Peninsula thrive when the AL is weak and the contribution of summer precipitation is higher, highlighting the importance of precipitation seasonality in promoting peat accumulation. This study demonstrates that δ18OTOM values in peat can be applied toward understand large-scale shifts in atmospheric circulation

  8. Geologic characteristics of hydrocarbon-bearing marine, transitional and lacustrine shales in China

    NASA Astrophysics Data System (ADS)

    Jiang, Shu; Xu, Zhengyu; Feng, Youliang; Zhang, Jinchuan; Cai, Dongsheng; Chen, Lei; Wu, Yue; Zhou, Dongsheng; Bao, Shujing; Long, Shengxiang

    2016-01-01

    Organic-rich shales spanning in age from Pre-Cambrian to Quaternary were widely deposited in China. This paper elaborates the geology and unique characteristics of emerging and potential hydrocarbon-bearing shales in China. The Pre-Cambrian Sinian Doushantuo to Silurian black marine shales in the intra-shelf low to slope environments were accumulated in South China and Tarim Platform in Northwest China. These marine shales with maturity (Ro) of 1.3-5% are in dry gas window. During Carboniferous to Permian, the shales associated with coal and sandstones were mainly deposited in coastal swamp transitional setting in north China, NE China, NW China and Yangtze platform in South China. These transitional shales are generally clay rich and are potential gas-bearing reservoirs. Since Middle Permian, the lacustrine shales with total carbon content (TOC) up to 30% and Ro mainly in oil window are widely distributed in all the producing basins in China. The lacustrine shales usually have more clay mineral content than marine shales and are characterized by rapid facies change and are interbedded with carbonates and sandstone. The high quality shale reservoir with high TOC, hydrocarbon content and brittle minerals content is usually located at transgressive systems tract (TST) to early highstand systems tract (EHST) interval deposited in anoxic depositional setting. Recent commercial shale gas production from the Silurian Longmaxi marine shale in the southeastern Sichuan Basin, preliminary tight oil production associated with lacustrine hydrocarbon-bearing shale intervals and hydrocarbon shows from many other shales have proven the hydrocarbon-bearing shales in China are emerging and potential shale gas and tight (shale) oil plays. Tectonic movements could have breached the early hydrocarbon accumulation in shales and tectonically stable areas are suggested to be favorable prospects for China shale plays exploration and production.

  9. Estimation of the tectonic slip-rate from Quaternary lacustrine facies within the intraplate Albacete province (SE of Spain)

    USGS Publications Warehouse

    Rodriguez-Pascua, M. A.; Bischoff, J.; Garduno-Monroy, Victor H.; Pérez-López, R.; Giner-Robles, J.L.; Israde-Alcántara, I.; Calvo, J.P.; Williams, Ross W.

    2009-01-01

    The Quaternary lacustrine basin of Cordovilla (CB) represents one of the most active tectonic areas of the Prebetic Zone (Albacete, SE of Spain). The Quaternary sedimentary deposits of this basin are mainly endoreic lacustrine carbonate and alluvial deposits, developed in a semi-arid climate (Pleistocene-present). The basin is a NW-SE-elongated graben bounded by a major right-lateral oblique-fault, the Pozohondo Fault. This fault trends NW-SE, with an approximate trace of 55 km, and is composed of various segments which are identified by fault scarps. In order to establish the slip-rate of the most active segment of the Pozohondo Fault, called the Cordovilla segment, we carried out a detailed study of the affected Quaternary lacustrine deposits. We found that the lacustrine facies could be related to episodic moderate paleoearthquakes. The slip-rate is calculated to be 0.05 and 0.09 mm/yr, using radiometric dating for the vertical offsets of the lacustrine facies. A trenching study at the northern part of the Cordovilla segment revealed two events caused by paleoearthquakes, with the most recent expressed as an oblique-fault off-setting a poorly-developed soil. The magnitude of the last event was greater than 6, using various empirical relationships for the fault displacement and the surface-length rupture. We estimate episodic activity across the Cordovilla segment, to be characterized by moderate-sized paleoearthquakes (M6), which is in agreement with the tectonic context of an intraplate zone of the Iberian plate. ?? 2009 Elsevier B.V.

  10. Estimation of the tectonic slip-rate from Quaternary lacustrine facies within the intraplate Albacete province (SE of Spain)

    NASA Astrophysics Data System (ADS)

    Rodríguez-Pascua, M. A.; Bischoff, J.; Garduño-Monroy, V. H.; Pérez-López, R.; Giner-Robles, J. L.; Israde-Alcántara, I.; Calvo, J. P.; Williams, R. W.

    2009-12-01

    The Quaternary lacustrine basin of Cordovilla (CB) represents one of the most active tectonic areas of the Prebetic Zone (Albacete, SE of Spain). The Quaternary sedimentary deposits of this basin are mainly endoreic lacustrine carbonate and alluvial deposits, developed in a semi-arid climate (Pleistocene-present). The basin is a NW-SE-elongated graben bounded by a major right-lateral oblique-fault, the Pozohondo Fault. This fault trends NW-SE, with an approximate trace of 55 km, and is composed of various segments which are identified by fault scarps. In order to establish the slip-rate of the most active segment of the Pozohondo Fault, called the Cordovilla segment, we carried out a detailed study of the affected Quaternary lacustrine deposits. We found that the lacustrine facies could be related to episodic moderate paleoearthquakes. The slip-rate is calculated to be 0.05 and 0.09 mm/yr, using radiometric dating for the vertical offsets of the lacustrine facies. A trenching study at the northern part of the Cordovilla segment revealed two events caused by paleoearthquakes, with the most recent expressed as an oblique-fault off-setting a poorly-developed soil. The magnitude of the last event was greater than 6, using various empirical relationships for the fault displacement and the surface-length rupture. We estimate episodic activity across the Cordovilla segment, to be characterized by moderate-sized paleoearthquakes (M6), which is in agreement with the tectonic context of an intraplate zone of the Iberian plate.

  11. Palaeogeographic, palaeoclimatic, palaeohydrological and chemical/biochemical controls on accumulation of late Eocene coastal lacustrine-palustrine limestones, Southern England

    NASA Astrophysics Data System (ADS)

    Armenteros, Ildefonso; Edwards, Nicholas

    2012-12-01

    relatively heavy tendency within published spectra for Tertiary lacustrine carbonates. The δ18O isotope results agree with published subtropical surface-water palaeotemperatures for this succession. The total characteristics of the Member therefore suggest a shallow-lacustrine to palustrine depositional environment. Pedogenic overprinting and mechanical reworking displayed by the limestones are attributable to seasonal fluctuations of water level during lake highstands, but in this marine-influenced setting, major long-term lake lowstands, resulting in deep erosion and palaeokarsting of the limestones, may be attributable to falls in relative sea-level. The biocalcilutites and humic muds accumulated during the ensuing lake transgressions.

  12. A high-resolution speleothem record of western equatorial Pacific rainfall: Implications for Holocene ENSO evolution

    NASA Astrophysics Data System (ADS)

    Chen, Sang; Hoffmann, Sharon S.; Lund, David C.; Cobb, Kim M.; Emile-Geay, Julien; Adkins, Jess F.

    2016-05-01

    The El Niño-Southern Oscillation (ENSO) is the primary driver of interannual climate variability in the tropics and subtropics. Despite substantial progress in understanding ocean-atmosphere feedbacks that drive ENSO today, relatively little is known about its behavior on centennial and longer timescales. Paleoclimate records from lakes, corals, molluscs and deep-sea sediments generally suggest that ENSO variability was weaker during the mid-Holocene (4-6 kyr BP) than the late Holocene (0-4 kyr BP). However, discrepancies amongst the records preclude a clear timeline of Holocene ENSO evolution and therefore the attribution of ENSO variability to specific climate forcing mechanisms. Here we present δ18 O results from a U-Th dated speleothem in Malaysian Borneo sampled at sub-annual resolution. The δ18 O of Borneo rainfall is a robust proxy of regional convective intensity and precipitation amount, both of which are directly influenced by ENSO activity. Our estimates of stalagmite δ18 O variance at ENSO periods (2-7 yr) show a significant reduction in interannual variability during the mid-Holocene (3240-3380 and 5160-5230 yr BP) relative to both the late Holocene (2390-2590 yr BP) and early Holocene (6590-6730 yr BP). The Borneo results are therefore inconsistent with lacustrine records of ENSO from the eastern equatorial Pacific that show little or no ENSO variance during the early Holocene. Instead, our results support coral, mollusc and foraminiferal records from the central and eastern equatorial Pacific that show a mid-Holocene minimum in ENSO variance. Reduced mid-Holocene interannual δ18 O variability in Borneo coincides with an overall minimum in mean δ18 O from 3.5 to 5.5 kyr BP. Persistent warm pool convection would tend to enhance the Walker circulation during the mid-Holocene, which likely contributed to reduced ENSO variance during this period. This finding implies that both convective intensity and interannual variability in Borneo are driven by

  13. Multi-proxy record of Holocene glacial history of the Spearhead and Fitzsimmons ranges, southern Coast Mountains, British Columbia

    NASA Astrophysics Data System (ADS)

    Osborn, Gerald; Menounos, Brian; Koch, Johannes; Clague, John J.; Vallis, Vanessa

    2007-02-01

    Evidence from glacier forefields and lakes is used to reconstruct Holocene glacier fluctuations in the Spearhead and Fitzsimmons ranges in southwest British Columbia. Radiocarbon ages on detrital wood and trees killed by advancing ice and changes in sediment delivery to downstream proglacial lakes indicate that glaciers expanded from minimum extents in the early Holocene to their maximum extents about two to three centuries ago during the Little Ice Age. The data indicate that glaciers advanced 8630-8020, 6950-6750, 3580-2990, and probably 4530-4090 cal yr BP, and repeatedly during the past millennium. Little Ice Age moraines dated using dendrochronology and lichenometry date to early in the 18th century and in the 1830s and 1890s. Limitations inherent in lacustrine and terrestrial-based methods of documenting Holocene glacier fluctuations are minimized by using the two records together.

  14. Holocene n-Fatty Acid Δd Records from Lake Hurleg, Northeastern Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    He, Y.; Zhao, C.; Liu, Z.; Wang, H.; Liu, W.; Yu, Z.

    2014-12-01

    The interpretation of δD records from the Tibetan Plateau region remains challenging due to multiple climatic factors influencing on the precipitation isotopic values. Here we study the mechanism of δD variation in this region, by reconstructing the past 10.5 ka n-fatty acid (FA) δD records from sediment core taken in Lake Hurleg on the northeastern Tibetan Plateau and comparing them to the previously presented temperature and moisture data from the same core. Comparison of both C16 and C26 n-FA δD with the average carbon length of n-FA suggests that n-FA δD variability was independent of the n-FA distribution. For δD in the C26 n-FA, it serves as an indicator of hydrogen isotopic signals in terrestrial water. During the Holocene, the heavier C26 n-FA δD values corresponded to millennial cold and wet conditions as inferred by the temperature and salinity records. Thus the terrestrial water δD value changes might be caused by factors other than temperature and moisture, such as the vegetation type and the glacial melt water input. As for the C16 n-FA, although it contains both terrestrial and aquatic source, it mainly mimics the lacustrine water isotopic signal. Therefore, the difference between C16 and C26 n-FA δD can be interpreted as the fractionation between terrestrial and aquatic water induced by evaporation on lake surface. Based on the δD records together with temperature and moisture records, we suggest in millennial timescale, not only stronger precipitation but also less evaporation occurred during the cold periods in the Lake Hurleg region.

  15. Early- to mid-Holocene vegetation development in northern Iceland: project outline and preliminary results

    NASA Astrophysics Data System (ADS)

    Eddudóttir, S.; Erlendsson, E.; Gísladóttir, G.

    2013-12-01

    Iceland is a key site for the study of Holocene vegetation and climate variations due to its location in the North Atlantic. The aim of the project is to reconstruct the history of Holocene vegetation development in Austur-Húnavatnssýsla, northern Iceland. Using pollen and macrofossils, patterns of vegetation change in three locations will be reconstructed, forming a transect from coastal extremes to the highland margin. The palynological and macrofossil data will be combined with a robust regional chronology, constructed by combining tephra layers with radiocarbon-dated macrofossils. Available data covering the vegetation history of Iceland are scarce. This study will improve the understanding of how environmental factors have driven vegetation development during the Holocene. Pollen analysis has been carried out on a section of a lacustrine core from the first study site of this project, a lowland site in Svínadalur valley. The analysed section of the core covers the period from Younger Dryas to the mid-Holocene. The results show a transition from pioneering vegetation during the cold period of Younger Dryas to the birch forests of the Holocene Thermal Maximum. An initial expansion of birch and gradual closing of vegetation cover was halted during early-Holocene, probably due to a period of cooling climate. An age model for the core has yet to be constructed, however this change in vegetation may be the result of cooling during the 8.2 ka event that has previously been recorded in proxies from Icelandic lakes. This cooling event has however not been seen in Icelandic terrestrial biotic palaeorecords before. The impact of this event seen in the Svínadalur core may underscore a vulnerability of the early-Holocene terrestrial ecosystem to climatic fluctuations. The study is funded by the Eimskip University fund, University of Iceland Research Fund and Landsvirkjun's Energy Research Fund, the study is also supported by the INTIMATE EU COST action in the form of a

  16. Lithology of lacustrine deposits in the Colca Valley

    NASA Astrophysics Data System (ADS)

    Kukulak, Józef; Paulo, Andrzej; Kalicki, Tomasz

    2016-08-01

    Remnant lacustrine sediments of three major lakes are preserved in the Rio Colca Valley in the Western Cordillera of the Central Andes, SW Peru. The older lake extended between Pinchollo and Coporaque until 0.61 Ma, while two Late Pleistocene lakes lied upstream of Chivay. The river cut through the sediments to a depth of approximately 300 m between Chivay and Pinchollo, over a distance of 30 km and formed several terraces in the lacustrine deposits. The highest outcrops of lacustrine sediments lie now at elevations of 3500-3600 m. Three types of lacustrine deposits are present. Spatially dominant are regularly layered and laminated fine-grained sediments (silt, sand, and locally diatomaceous ooze). The second type are coarse gravels and sands accumulated in deltas, and the third - colluvial material. The lacustrine sediments are weakly cemented. Petrographic and mineralogical analysis of the fine-grained varieties showed that their material came from many sources. Its major part came from the lake catchment and was supplied by the river, like gravels and coarse sands. Similar in origin are dark-gray fine sands derived from local regolith. White silts and fine sands are of volcanic origin (tuffites), probably derived from nearby volcanic pyroclastic covers of the Barroso and Tacaza groups. Additional pyroclastic material was supplied by volcanic ash falling out directly to the lake. Activity of nearby stratovolcanoes (eg. Hualca Hualca, Sabancaya, Ampato, Huarancante) and dwarf volcanoes of the Andahua Group during the existence of the lake is confirmed by intercalations of pumice, coarse volcanic debris and lava in the lacustrine sediments. The existence of the lakes between Pinchollo and Chivay can be related to the period of the Latest Pliocene - Late Pleistocene.

  17. Fluvial to Lacustrine Facies Transitions in Gale Crater, Mars

    NASA Technical Reports Server (NTRS)

    Sumner, Dawn Y.; Williams, Rebecca M. E.; Schieber, Juergen; Palucis, Marisa C.; Oehler, Dorothy Z.; Mangold, Nicolas; Kah, Linda C.; Gupta, Sanjeev; Grotzinger, John P.; Grant, John A., III; Edgar, Lauren A.; Dietrich, William E.

    2015-01-01

    NASA's Curiosity rover has documented predominantly fluvial sedimentary rocks along its path from the landing site to the toe of the Peace Vallis alluvial fan (0.5 km to the east) and then along its 8 km traverse across Aeolis Palus to the base of Aeolis Mons (Mount Sharp). Lacustrine facies have been identified at the toe of the Peace Vallis fan and in the lowermost geological unit exposed on Aeolis Mons. These two depositional systems provide end members for martian fluvial/alluvial-lacustrine facies models. The Peace Vallis system consisted of an 80 square kilometers alluvial fan with decimeter-thick, laterally continuous fluvial sandstones with few sedimentary structures. The thin lacustrine unit associated with the fan is interpreted as deposited in a small lake associated with fan runoff. In contrast, fluvial facies exposed over most of Curiosity's traverse to Aeolis Mons consist of sandstones with common dune-scale cross stratification (including trough cross stratification), interbedded conglomerates, and rare paleochannels. Along the southwest portion of the traverse, sandstone facies include south-dipping meter-scale clinoforms that are interbedded with finer-grained mudstone facies, interpreted as lacustrine. Sedimentary structures in these deposits are consistent with deltaic deposits. Deltaic deposition is also suggested by the scale of fluvial to lacustrine facies transitions, which occur over greater than 100 m laterally and greater than 10 m vertically. The large scale of the transitions and the predicted thickness of lacustrine deposits based on orbital mapping require deposition in a substantial river-lake system over an extended interval of time. Thus, the lowermost, and oldest, sedimentary rocks in Gale Crater suggest the presence of substantial fluvial flow into a long-lived lake. In contrast, the Peace Vallis alluvial fan onlaps these older deposits and overlies a major unconformity. It is one of the youngest deposits in the crater, and

  18. 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.

  19. Holocene climate change in Newfoundland reconstructed using oxygen isotope analysis of lake sediment cores

    NASA Astrophysics Data System (ADS)

    Finkenbinder, Matthew S.; Abbott, Mark B.; Steinman, Byron A.

    2016-08-01

    Carbonate minerals that precipitate from open-basin lakes can provide archives of past variations in the oxygen isotopic composition of precipitation (δ18Oppt). Holocene δ18Oppt records from the circum- North Atlantic region exhibit large fluctuations during times of rapid ice sheet deglaciation, followed by more stable conditions when interglacial boundary conditions were achieved. However, the timing, magnitude, and climatic controls on century to millennial-scale variations in δ18Oppt in northeastern North America are unclear principally because of a dearth of paleo-proxy data. Here we present a lacustrine sediment oxygen isotope (δ18O) record spanning 10,200 to 1200 calendar years before present (cal yr BP) from Cheeseman Lake, a small, alkaline, hydrologically open lake basin located in west-central Newfoundland, Canada. Stable isotope data from regional lakes, rivers, and precipitation indicate that Cheeseman Lake water δ18O values are consistent with the isotopic composition of inflowing meteoric water. In light of the open-basin hydrology and relatively short water residence time of the lake, we interpret down-core variations in calcite oxygen isotope (δ18Ocal) values to primarily reflect changes in δ18Oppt and atmospheric temperature, although other factors such as changes in the seasonality of precipitation may be a minor influence. We conducted a series of climate sensitivity simulations with a lake hydrologic and isotope mass balance model to investigate theoretical lake water δ18O responses to climate change. Results from these experiments suggest that Cheeseman Lake δ18O values are primarily controlled by temperature and to a much lesser extent, the seasonality of precipitation. Increasing and more positive δ18Ocal values between 10,200 and 8000 cal yr BP are interpreted to reflect the waning influence of the Laurentide Ice Sheet on atmospheric circulation, warming temperatures, and rapidly changing surface ocean δ18O from the input of

  20. Primary carbonates and Ca-chloride brines as monitors of a paleo-hydrological regime in the Dead Sea basin

    NASA Astrophysics Data System (ADS)

    Waldmann, Nicolas; Starinsky, Abraham; Stein, Mordechai

    2007-09-01

    Lakes Samra, Lisan and the Dead Sea occupied the Dead Sea basin during the Last Interglacial (˜140-75 ka BP), last glacial (˜70-14 ka BP) and Holocene periods, respectively. The age of Lake Lisan and Samra was determined by U-Th dating of primary aragonites comprising parts of the lacustrine sedimentary sequences. The lakes have periodically deposited sequences of layered calcitic marls (Lake Samra) or laminated primary aragonite (Lake Lisan). The deposition of aragonite as the primary carbonate phase reflects the contribution of the incoming freshwater (loaded with bi-carbonate) and high Mg-, Ca-chloride brine that originated from the subsurface vicinity of the Dead Sea basin. Deposition of calcitic marls suggests a minor effect of the brines. The Ca-chloride subsurface brine has been migrating in and out of the wall rocks of the Dead Sea basin, reflecting the regional hydrological conditions. During most of the last glacial period and during the late Holocene, sufficient precipitation above the Judea Mountains pushed the subsurface Ca-chloride brines into the lakes causing the deposition of aragonite. During the Last Interglacial period the rain that precipitated above the Judea Mountains was insufficient to induce brine flow toward Lake Samra. It appears that sporadic floods provided calcium, bicarbonate and detritus to produce the Samra calcitic marls. Travertines deposited at the Samra-Lisan boundary indicate the early stage in the resumption of groundwater (springs) activity that led to the resurgence of Ca-chloride brine and rise of Lake Lisan. Similar variations in the regional rain precipitation and hydrological activity probably characterized the long-term geochemical evolution of Pleistocene lacustrine water-bodies in the Dead Sea basin, enabling the use of the carbonates as paleo-hydrological monitors.

  1. The Birougou Mountains: Forested throughout the Holocene

    NASA Astrophysics Data System (ADS)

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

    2009-04-01

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

  2. Ecosystemic Postglacial Succession of Nettilling Lake (Baffin Island, Canada) Inferred by Oxygen Isotope Composition of Lacustrine Diatoms

    NASA Astrophysics Data System (ADS)

    Narancic, B.; Chapligin, B.; Meyer, H.; Pienitz, R.

    2014-12-01

    In 2012, a 82 cm long sediment core (Ni2B) was drilled at Nettilling Lake. We use a multi-proxy paleolimnological approach to study the sedimentary records preserved in Nettilling Lake (Baffin Island, Canada) in order to reconstruct the postglacial environmental history of the lake watershed. 31 samples of biogenic silica were purified, their contamination assessed and corrected for and subsequently analysed for the oxygen isotope composition (δ18Odiatom). Additionally, the diatom assemblage from 35 samples was quantified under the light microscope with x 1000 magnification. Our chronology extends to ~ BC 1200 yrs based on radiometric dating 210Pd and 14C from bulk sediment. Downcore variations in δ18Odiatom values show a marine-lacustrine transition. The samples from the marine-brackish zone show a higher isotopic composition (27.5‰, 58.5cm depth, ²middle Holocene²) than the samples from the lacustrine section (21.7‰, 1.5cm, 2002 AD). The transition zone can be distinguished by values between these extremes, too (23.4‰, 33cm, ~1240 BC). This likely reflects changes in the water source, from more isotopically enriched marine water in the past to more depleted and cold lacustrine water. The diatom assemblage reflects the same transition. The marine-brackish zone contains polyhalobous-mesohalobous benthic species (e.g. Trachyneis aspera, Gomphonemopsis aestuarii, G. pseudexigua,Cocconeis scutellum) which have a salinity preference between 35‰ to 5‰, indicating a shallow, littoral environment. The transition zone is characterized by a sharp rise of alkaliphilous freshwater benthic taxa (e.g. Staurosirelle pinnata, Staurosira construens, Staurosira brevistriata). The diatom flora of the upper zone is characterized by halophobous planktonic and benthic species (e.g. Cylotella rossii, Cyclotella pseudostelligera, Tabelaria floculosa, Encyonema silesiacum, Nitzschia perminuta). The δ18Odiatom and the diatom assemblage record from Nettilling Lake register

  3. Unravelling the chronology and evolution of the Pleistocene-Holocene basin in the hanging-wall of the 2009 L'Aquila earthquake fault by multidisciplinary approach (paleomagnetism, palaeontology, geochemistry and radiometric dating) on a 150 m deep hole

    NASA Astrophysics Data System (ADS)

    Mochales, T.; Porreca, M.; Smedile, A.; Buratti, N.; Macri', P.; Di Chiara, A.; Sagnotti, L.; Speranza, F.; Amoroso, S.; Nicolosi, I.; D'ajello Caracciolo, F.; Carluccio, R.; Di Giulio, G.; Vassallo, M.; Villani, F.; Civico, R.

    2013-12-01

    The Mw=6.1 L'Aquila earthquake struck the central Apennines (Italy), on April 6th, 2009. INSAR data showed that the maximum subsidence of ca. 15 cm was located in the continental Aterno Basin, partly controlled by the Paganica extensional fault, yielding the L'Aquila earthquake. Preliminary geological and geophysical surveys have been performed in the depocenter of the Aterno Basin to figure out the underground configuration and determine the best location for a deep hole. The drilling was performed in May-June 2013, recovering 151 m of continental Holocene and Pleistocene sediments. The upper sandy-silty sequence (41 m), interbedded with gravels, is interpreted as fluvial-alluvial origin. The lower clayey-silty sequence, interpreted as lacustrine sediments, continues downward until the bottom (disrupted by 30 m of gravels). The continuous sediment record of the hole is being processed along three stages: i) Description consists of the elaboration of stratigraphical logs, color description and photographic record of the core. The second stage consists of sampling for the different analyses. ii) Continuous samples (U-Channel) were collected from the undisturbed centre of the core for paleomagnetic measurements. Additional samples were collected in the clayey-silty fraction (10 to 25 cm spacing) for calcimetry, geochemical, palynological and ostracoda fauna analysis. Finally, individual levels rich in organic matter and charcoal were sampled for radiometric datings. Iii) The measurements include magnetic susceptibility, paleomagnetic and rock magnetic properties, content of calcium carbonate and 16/18 oxygen ratio, crumble and classification of fossils for pollens and ostracods analyses. Paleomagnetic analyses will hopefully allow us to obtain experimental constraints for dating the Holocene-Pleistocene sediments of the Aterno Basin. The presence of Carbon-14 in organic materials can yield absolute dating. Palynology, oxygen ratio and calcium carbonate content will

  4. Climate variability during the Holocene inferred from northeastern Iberian speleothems

    NASA Astrophysics Data System (ADS)

    Moreno, A.; Bartolomé, M.; Sancho, C.; Belmonte, Á.; Stoll, H.; Cacho, I.; Edwards, R. L.; Hellstrom, J.

    2012-04-01

    Although the general climate trends during the Holocene in the Iberian Peninsula have been well described after the study of marine and lacustrine records, many questions regarding the timing of some of the events together with the characterization of the higher-frequency climate variability are still poorly understood. New speleothem records from several caves in northeastern Iberia provide data to explore Holocene climate changes. The selected caves are located in a latitudinal transect from the Pyrenees to the Iberian Range and placed at different altitude. Two of them, 5 de Agosto and Pot au Feu, belong to the same karstic complex in Cotiella massif (Central Pyrenees, 1600 m asl). Seso Cave, also in the Central Pyrenees but at 781 m of altitude, and Molinos cave, a cavity very rich in speleothems located at 1040 m in the Iberian Range, complete the transect. Although in all the caves precipitation coming from Atlantic fronts dominates over the year, a significant Mediterranean influence, specially in summer months, is identified after rainfall monitoring. Speleothem formation during the Holocene occurred at a very low pace in 5 de Agosto cave (80yrs/mm) and increased dramatically at low-altitude caves and during particular periods proved to be wetter (eg. Early Holocene in Molinos cave, less than 10yr/mm). In Seso and Pot au Feu caves, up to seven studied speleothems only grew during short climatic events such as the Iron Cold Period (3000-2500 cal yr BP) or the Little Ice Age (1300-1850 yr AD) that, although cold, were particularly humid periods in northeastern Spain. First stable isotope results highlight the importance of comparing speleothems with similar growing rates and from the same cave to extract climate information and discard other influences. From the integration of four stalagmites from Molinos cave covering since the Holocene onset to 2000 cal yrs BP, the Early Holocene (11.7-8.5 ka BP) with d13C values between -11 and - 9‰ appears as the

  5. Paleoclimatic Comparisons Between Three Late Quaternary Amazonian Lacustrine Records

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    glacial maximum period. In this period was followed by an abrupt decrease of the moisture attested by decreasing values of TOC in all records. The second phase, between 25,000 and 16,000 cal yr BP is characterized by the lowest productivity indicators in Lagoa da Pata reaching the minimum at 21,950/17,800 cal yr BP as indicated by the lowest total organic carbon accumulation rate. The lowest value of TOC in Carajás was observed in these phase and high values of black carbon in Saci Lake. A third phase, from approximately 16,000 cal yr BP to the present an increase in lacustrine productivity attested by an increase total organic carbon accumulation rate probably corresponds to a lake level rise owing to a wetter, near-modern climate in Carajás and Lagoa da Pata records. In Saci Lake was observed a hiatus between 16,000 cal yr BP and 9,000 cal yr BP and after the highest values of paleoprodutivity indicators was observed.

  6. Holocene and latest Pleistocene climate and glacier fluctuations in Iceland

    NASA Astrophysics Data System (ADS)

    Geirsdóttir, Áslaug; Miller, Gifford H.; Axford, Yarrow; Ólafsdóttir, Sædís

    2009-10-01

    Multiproxy climate records from Iceland document complex changes in terrestrial climate and glacier fluctuations through the Holocene, revealing some coherent patterns of change as well as significant spatial variability. Most studies on the Last Glacial Maximum and subsequent deglaciation reveal a dynamic Iceland Ice Sheet (IIS) that responded abruptly to changes in ocean currents and sea level. The IIS broke up catastrophically around 15 ka as the Polar Front migrated northward and sea level rose. Indications of regional advance or halt of the glaciers are seen in late Alleröd/early Younger Dryas time and again in PreBoreal time. Due to the apparent rise of relative sea level in Iceland during this time, most sites contain evidence for fluctuating, tidewater glacier termini occupying paleo fjords and bays. The time between the end of the Younger Dryas and the Preboreal was characterized by repeated jökulhlaups that eroded glacial deposits. By 10.3 ka, the main ice sheet was in rapid retreat across the highlands of Iceland. The Holocene thermal maximum (HTM) was reached after 8 ka with land temperatures estimated to be 3 °C higher than the 1961-1990 reference, and net precipitation similar to modern. Such temperatures imply largely ice-free conditions across Iceland in the early to mid-Holocene. Several marine and lacustrine sediment climate proxies record substantial summer temperature depression between 8.5 and 8 ka, but no moraines have been detected from that time. Termination of the HTM and onset of Neoglacial cooling took place sometime after 6 ka with increased glacier activity between 4.5 and 4.0 ka, intensifying between 3.0 and 2.5 ka. Although a distinct warming during the Medieval Warm Period is not dramatically apparent in Icelandic records, the interval from ca AD 0 to 1200 is commonly characterized by relative stability with slow rates of change. The literature most commonly describes Little Ice Age moraines (ca AD 1250-1900) as representing the

  7. Lacustrine wetland in an agricultural catchment: nitrogen removal and related biogeochemical processes

    NASA Astrophysics Data System (ADS)

    Balestrini, R.; Arese, C.; Delconte, C.

    2007-09-01

    The role of specific catchment areas, such as the soil-river or lake interfaces, in removing or buffering the flux of N from terrestrial to aquatic ecosystems is globally recognized but the extreme variability of microbiological and hydrological processes make it difficult to predict the extent to which different wetlands function as buffer systems. In this paper we evaluate the degree to which biogeochemical processes in a lacustrine wetland are responsible for the nitrate removal from ground waters feeding Candia Lake (Northern Italy). A transect of 18 piezometers was installed perpendicular to the shoreline, in a sub-unit formed by 80 m of poplar plantation, close to a crop field and 30 m of reed swamp. The chemical analysis revealed a drastic NO3-N ground water depletion from the crop field to the lake, with concentrations decreasing from 15-18 mg N/l to the detection limit within the reeds. Patterns of Cl, SO4, O2, NO2-N, HCO3 and DOC suggest that the metabolic activity of bacterial communities, based on the differential use of electron donors and acceptors in redox reactions is the key function of this system. The significant inverse relationship found between NO3-N and HCO3 is a valuable indicator of the denitrification activity. The pluviometric regime, the temperature, the organic carbon availability and the hydrogeomorphic properties are the main environmental factors affecting the N transformations in the studied lacustrine ecosystem.

  8. Lacustrine wetland in an agricultural catchment: nitrogen removal and related biogeochemical processes

    NASA Astrophysics Data System (ADS)

    Balestrini, R.; Arese, C.; Delconte, C.

    2008-03-01

    The role of specific catchment areas, such as the soil-river or lake interfaces, in removing or buffering the flux of N from terrestrial to aquatic ecosystems is globally recognized but the extreme variability of microbiological and hydrological processes make it difficult to predict the extent to which different wetlands function as buffer systems. In this paper we evaluate the degree to which biogeochemical processes in a lacustrine wetland are responsible for the nitrate removal from ground waters feeding Candia Lake (Northern Italy). A transect of 18 piezometers was installed perpendicular to the shoreline, in a sub-unit formed by 80 m of poplar plantation, close to a crop field and 30 m of reed swamp. The chemical analysis revealed a drastic NO3--N ground water depletion from the crop field to the lake, with concentrations decreasing from 15-18 mg N/l to the detection limit within the reeds. Patterns of Cl-, SO42-, O2, NO2--N, HCO3- and DOC suggest that the metabolic activity of bacterial communities, based on the differential use of electron donors and acceptors in redox reactions is the key function of this system. The significant inverse relationship found between NO3--N and HCO3- is a valuable indicator of the denitrification activity. The pluviometric regime, the temperature, the organic carbon availability and the hydrogeomorphic properties are the main environmental factors affecting the N transformations in the studied lacustrine ecosystem.

  9. Diatoms as Proxies for a Fluctuating Holocene Ice Cap Margin in Hvitarvatn, Iceland

    NASA Astrophysics Data System (ADS)

    Black, J. L.; Miller, G. H.; Geirsdottir, A.

    2006-12-01

    Hvitarvatn is a glacier-dominated lake located on the eastern margin of Langjokull, Iceland's second largest ice cap. Hvitarvatn is ideally positioned to provide a continuous record of Holocene climate change as 1) glacial erosion and soft bedrock result in high lacustrine sedimentation rates, 2) diagnostic tephras of known age aid the geochronology, and 3) a relatively flat ice-cap profile responds sensitively to small climate-driven changes in the equilibrium line altitude (ELA). The erosive power of Langjokull and the efficient delivery system of these glacial sediments into Hvitarvatn are the dominant factors affecting both the nutrient and light availability in the lake. Any perturbations to the lake system, such as large fluctuations of the ice cap margin, result in a swift response in the diatom community due to the rapid growth and immigration rates of diatoms. The Holocene diatom assemblages preserved in Hvitarvatn sediments are a key proxy for recording Iceland's sensitivity to changes in North Atlantic circulation and addressing whether Iceland's large ice caps disappeared in the early Holocene, and if they did, when they re-grew. The presence of the Saksunarvatn tephra in the Hvitarvatn sediments indicates the lake was deglaciated by 10,300 yr BP. The Holocene Thermal Maximum (HTM) is represented in the lake sediments by an abundant, diverse benthic diatom population that dominated Hvitarvatn between 6000-9000 yr BP. A resurgence of ice cap activity around 6000 yr BP is reflected by a shift to a planktonic diatom assemblage composed mostly of Aulacoseira subarctica. Langjokull grew to its largest Holocene extent during the LIA and reached its maximum between 150-300 yr BP. Diatom assemblages during the LIA are largely composed of Aulacoseira islandica and Aulacoseira subarctica, reflecting extremely low light and turbid water conditions.The diatom assemblages in Hvitarvatn indicate very large environmental changes occurred during the Holocene in Iceland.

  10. Proglacial lake sediments, cosmogenic ages and stable isotopes reveal Holocene climate changes in the Peruvian Andes

    NASA Astrophysics Data System (ADS)

    Stansell, N.; Rodbell, D. T.; Licciardi, J. M.; Abbott, M. B.; Mark, B. G.; Schweinsberg, A.

    2013-12-01

    Sediment records from lakes and cosmogenic ages on moraine boulders in central Peru document the waxing and waning of alpine glaciers since the end of the late glacial stage. These records from the southern tropical Andes tentatively suggest that a brief re-advance occurred during the early Holocene, even though conditions overall were relatively warm and dry from ~12 to 8 ka. The middle Holocene (between 8 and 4 ka) was marked by a shift to cooler, and possibly wetter conditions in certain regions, leading to glacial advances. Although there were multiple periods of brief ice advances that punctuated the overall late Holocene trend, glaciers in multiple valleys generally retreated from ~4.0 ka through the Medieval Climate Anomaly (1.0 to 0.7 ka). This late Holocene pattern of ice retreat occurred during a period when lake level studies, and both lacustrine and speleothem stable isotopic records indicate wetter conditions, suggesting that higher temperatures contributed to the pattern of ice retreat. Following this period of glacial retreat, multiple proxy records suggest that the start of the Little Ice Age (~0.6 to 0.1 ka) was a colder and wetter time throughout much of the tropical Andes. While there is emerging evidence that the strength of the South American Summer Monsoon increased through the Holocene, these shifting precipitation patterns do not fully explain the record of glaciation in Peru. It is likely that sea surface temperature distributions in the tropical Pacific Ocean also affected atmospheric temperature, precipitation and circulation patterns over the Andes. The combined influences of both Atlantic and Pacific ocean and atmospheric influences thus contributed to the observed pattern of glacial variability during the Holocene.

  11. Late Cenozoic lacustrine and climatic environments at Tule Lake, northern Great Basin, USA

    NASA Astrophysics Data System (ADS)

    Platt Bradbury, J.

    1992-01-01

    Cores of lake sediment to a depth of 334 m in the town of Tulelake, Siskiyou County, northern California, document the late Cenozoic paleolimnologic and paleoclimatic history of the northwestern edge of the Great Basin. The cores have been dated by radiometric, tephrochronologic and paleomagnetic analyses. Lacustrine diatoms are abundant throughout the record and document a nearly continuous paleolimnologic history of the Tule Lake basin for the last 3 Myr. During most of this time, this basin (Tule Lake) was a relatively deep, extensive lake. Except for a drier (and cooler?) interval recorded by Fragilaria species about 2.4 Ma, the Pliocene is characterized by a dominance of planktonic Aulacoseira solida implying a warm monomictic lake under a climatic regime of low seasonality. Much of the Pleistocene is dominated by Stephanodiscus and Fragilaria species suggesting a cooler, often drier, and highly variable climate. Benthic diatoms typical of alkaline-enriched saline waters commonly appear after 1.0 Ma, and tephrochronology indicates slow deposition and possible hiatuses between about 0.6 and 0.2 Ma. The chronology of even-numbered oxygen isotope stages approximately matches fluctuations in the abundance of Fragilaria since 800 ka indicating that glacial periods were expressed as drier environments at Tule Lake. Glacial and interglacial environments since 150 ka were distinct from, and more variable than, those occurring earlier. The last full glacial period was very dry, but shortly thereafter Tule Lake became a deep, cool lacustrine system indicating a substantial increase in precipitation. Aulacoseira ambigua characterized the latest glacial and Holocene record of Tule Lake. Its distribution indicates that warmer and wetter climates began about 15 ka in this part of the Great Basin. Diatom concentration fluctuates at 41 000 year intervals between 3.0 and 2.5 Ma and at approximately 100 000 year intervals after 1.0 Ma. In the late Pliocene and early Pleistocene

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

    NASA Astrophysics Data System (ADS)

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

    2009-10-01

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

  13. A 15,400-year record of climate variation from a subalpine lacustrine sedimentary sequence in the western Nanling Mountains in South China

    NASA Astrophysics Data System (ADS)

    Zhong, Wei; Cao, Jiayuan; Xue, Jibin; Ouyang, Jun

    2015-09-01

    Multi-proxy records of a subalpine lacustrine sequence in Daping Swamp in the western Nanling Mountains provide evidence for exploring climate variability in the past 15,400 yr. Two dry and cool (15,400-14,500 and 13,000-11,000 cal yr BP) and one humid and warm interval (14,500-13,200 cal yr BP), which we correlate to Heinrich Event 1, the Younger Dryas and the Bølling-Allerød event respectively, are revealed. The early Holocene climate (11,000-8000 cal yr BP) was characterized by less humid and warm conditions, suggesting a weaker Asian summer monsoon (ASM) intensity. Our findings indicate that the Holocene optimum occurred between 8000 and 4500 cal yr BP, and the most intensified ASM appears from 8000 to 7000 cal yr BP. After 4500 cal yr BP, climate shifted to relatively cool and dry conditions. We speculate that five short dry and cool events centered at ~ 11,000, 9000, 8400, 6000, and 3500 cal yr BP were linked to the Holocene ice-rafting events detected in the North Atlantic. Migration of the ITCZ, and the oceanic-atmospheric circulations, particularly SST changes in the tropical Pacific may play a pivotal role in climate variation of the study region.

  14. Organic matter accumulation in a thick, lacustrine, Lower Cretaceous sedimentary sequence in Gabon: Facies and maturity variations

    SciTech Connect

    Ralf, L.; Wilkes, H.

    1995-08-01

    A total of about forty core samples representing an almost two kilometer thick, lacustrine sedimentary sequence of Neocomian age in the south Gabon basin was analysed for its hydrocarbon generation potential, maturity and further organic matter characteristics. Organic carbon concentrations are variable and not particularly high (0.4-5%), but the organic matter is hydrogen-rich. This hydrogen-richness finds its expression in high hydrogen indices (about 600 to 700 mg hc/g TOC) which decrease with increasing maturation. According to pyrolysis experiments, hydrocarbon generation from the immature sediments is predicted to begin only at temperatures greater than 100{degrees}C and reaches a maximum only at temperatures greater than 150{degrees}C, because the organic material possesses a very high thermal stability. Such a high thermal stability was already established for lacustrine organic matter from some other deposits (e.g. Green River oil shales) and is certainly an important factor for the evaluation of hydrocarbon potentials in lacustrine basins. The maturity of the organic matter changes from immature to mature with increasing depth. Peak oil generation stage was almost reached by the deepest samples as indicated by a variety of optical and geochemical parameters. Generated petroleum should be wax-rich and rather poor in gas, except if oil to gas cracking occurs within the source rocks. With respect to molecular geochemistry, several interesting pecularities were found. As an example, variable distributions of several unknown tetracyclic terpanes (molecular formula C{sub 24}H{sub 42}) were detected in the samples of lower maturity. Two series of terpane pseudohomologues occur in the more mature samples, one of which is assumed to consist of diahopanes, the other yet remaining unknown. These compounds seem to be widely distributed in lacustrine sediments of higher maturity, thus possibly representing maturity and/or facies indicators.

  15. The Impact of Elevated Temperatures on Continental Carbon Cycling in the Paleogene

    NASA Astrophysics Data System (ADS)

    Pancost, R. D.; Handley, L.; Taylor, K. W.; Collinson, M. E.; Weijers, J.; Talbot, H. M.; Hollis, C. J.; Grogan, D. S.; Whiteside, J. H.

    2010-12-01

    Recent climate and biogeochemical modelling suggests that methane flux from wetlands and soils was greater during past greenhouse climates, due to a combination of higher continental temperatures, an enhanced hydrological cycle, and elevated primary production. Here, we examine continental environments in the Paleogene using a range of biomarker proxies (complemented by palaeobotanical approaches), including air temperatures derived from the distribution of soil bacterial glycerol dialkyl glycerol tetraethers (the MBT/CBT proxy), as well as evidence from wetland and lacustrine settings for enhanced methane cycling. Previously published and new MBT/CBT records parallel sea surface temperature records, suggesting elevated continental temperatures during the Eocene even at mid- to high latitudes (New Zealand, 20-28°C; the Arctic, 17°C; across the Sierra Nevada, 15-25°C; and SE England, 20-30°C). Such temperatures are broadly consistent with paleobotanical records and would have directly led to increased methane production via the metabolic impact of temperature on rates of methanogenesis. To test this, we have determined the distributions and carbon isotopic compositions of archaeal ether lipids and bacterial hopanoids in thermally immature Eocene lignites. In particular, the Cobham lignite, deposited in SE England and spanning the PETM, is characterised by markedly higher concentrations of both methanogen and methanotroph biomarkers compared to modern and Holocene temperate peats. Elevated temperatures, by fostering either stratification and/or decreased oxygen solubility, could have also led to enhanced methane production in Paleogene lakes. Both the Messel Shale (Germany) and Green River Formation, specifically the Parachute Creek oil shale horizons (Utah and Wyoming), are characterised by strongly reducing conditions (including euxinic conditions in the latter), as well as abundant methanogen and methanotroph biomarkers. Such results confirm model predictions

  16. A Habitable Fluvio-Lacustrine Environment at Yellowknife Bay, Gale Crater, Mars

    NASA Technical Reports Server (NTRS)

    Grotzinger, J. P.; Sumner, D. Y.; Kah, L. C.; Stack, K.; Gupta, S.; Edgar, L.; Rubin, D.; Lewis, K.; Schieber, J.; Mangold, N.; Milliken, R.; Conrad, P. G.; DesMarais, D.; Farmer, J.; Siebach, K.; Calef, F., III; Hurowitz, J.; McLennan, S. M.; Ming, D.; Vaniman, D.; Crisp, J.; Vasavada, A.; Edgett, K. S.; Malin, M.; Blake, D.; Gellert, R.; Mahaffy, P.; Wiens, R. C.; Maurice, S.; Grant, J. A.; Wilson, S.; Anderson, R. C.; Beegle, L.; Arvidson, R.; Hallet, B.; Bristow, T. F.; Eigenbrode, J.; Meyer, M.

    2013-01-01

    The Curiosity rover discovered fine-grained sedimentary rocks, which are inferred to represent an ancient lake and preserve evidence of an environment that would have been suited to support a martian biosphere founded on chemolithoautotrophy. This aqueous environment was characterized by neutral pH, low salinity, and variable redox states of both iron and sulfur species. Carbon, hydrogen, oxygen, sulfur, nitrogen, and phosphorus were measured directly as key biogenic elements; by inference, phosphorus is assumed to have been available. The environment probably had a minimum duration of hundreds to tens of thousands of years. These results highlight the biological viability of fluvial-lacustrine environments in the post-Noachian history of Mars.

  17. A Habitable Fluvio-Lacustrine Environment at Yellowknife Bay, Gale Crater, Mars

    NASA Astrophysics Data System (ADS)

    Grotzinger, J. P.; Sumner, D. Y.; Kah, L. C.; Stack, K.; Gupta, S.; Edgar, L.; Rubin, D.; Lewis, K.; Schieber, J.; Mangold, N.; Milliken, R.; Conrad, P. G.; DesMarais, D.; Farmer, J.; Siebach, K.; Calef, F.; Hurowitz, J.; McLennan, S. M.; Ming, D.; Vaniman, D.; Crisp, J.; Vasavada, A.; Edgett, K. S.; Malin, M.; Blake, D.; Gellert, R.; Mahaffy, P.; Wiens, R. C.; Maurice, S.; Grant, J. A.; Wilson, S.; Anderson, R. C.; Beegle, L.; Arvidson, R.; Hallet, B.; Sletten, R. S.; Rice, M.; Bell, J.; Griffes, J.; Ehlmann, B.; Anderson, R. B.; Bristow, T. F.; Dietrich, W. E.; Dromart, G.; Eigenbrode, J.; Fraeman, A.; Hardgrove, C.; Herkenhoff, K.; Jandura, L.; Kocurek, G.; Lee, S.; Leshin, L. A.; Leveille, R.; Limonadi, D.; Maki, J.; McCloskey, S.; Meyer, M.; Minitti, M.; Newsom, H.; Oehler, D.; Okon, A.; Palucis, M.; Parker, T.; Rowland, S.; Schmidt, M.; Squyres, S.; Steele, A.; Stolper, E.; Summons, R.; Treiman, A.; Williams, R.; Yingst, A.; MSL Science Team; Kemppinen, Osku; Bridges, Nathan; Johnson, Jeffrey R.; Cremers, David; Godber, Austin; Wadhwa, Meenakshi; Wellington, Danika; McEwan, Ian; Newman, Claire; Richardson, Mark; Charpentier, Antoine; Peret, Laurent; King, Penelope; Blank, Jennifer; Weigle, Gerald; Li, Shuai; Robertson, Kevin; Sun, Vivian; Baker, Michael; Edwards, Christopher; Farley, Kenneth; Miller, Hayden; Newcombe, Megan; Pilorget, Cedric; Brunet, Claude; Hipkin, Victoria; Léveillé, Richard; Marchand, Geneviève; Sánchez, Pablo Sobrón; Favot, Laurent; Cody, George; Flückiger, Lorenzo; Lees, David; Nefian, Ara; Martin, Mildred; Gailhanou, Marc; Westall, Frances; Israël, Guy; Agard, Christophe; Baroukh, Julien; Donny, Christophe; Gaboriaud, Alain; Guillemot, Philippe; Lafaille, Vivian; Lorigny, Eric; Paillet, Alexis; Pérez, René; Saccoccio, Muriel; Yana, Charles; Armiens-Aparicio, Carlos; Rodríguez, Javier Caride; Blázquez, Isaías Carrasco; Gómez, Felipe Gómez; Gómez-Elvira, Javier; Hettrich, Sebastian; Malvitte, Alain Lepinette; Jiménez, Mercedes Marín; Martínez-Frías, Jesús; Martín-Soler, Javier; Martín-Torres, F. Javier; Jurado, Antonio Molina; Mora-Sotomayor, Luis; Caro, Guillermo Muñoz; López, Sara Navarro; Peinado-González, Verónica; Pla-García, Jorge; Manfredi, José Antonio Rodriguez; Romeral-Planelló, Julio José; Fuentes, Sara Alejandra Sans; Martinez, Eduardo Sebastian; Redondo, Josefina Torres; Urqui-O'Callaghan, Roser; Mier, María-Paz Zorzano; Chipera, Steve; Lacour, Jean-Luc; Mauchien, Patrick; Sirven, Jean-Baptiste; Manning, Heidi; Fairén, Alberto; Hayes, Alexander; Joseph, Jonathan; Sullivan, Robert; Thomas, Peter; Dupont, Audrey; Lundberg, Angela; Melikechi, Noureddine; Mezzacappa, Alissa; DeMarines, Julia; Grinspoon, David; Reitz, Günther; Prats, Benito; Atlaskin, Evgeny; Genzer, Maria; Harri, Ari-Matti; Haukka, Harri; Kahanpää, Henrik; Kauhanen, Janne; Paton, Mark; Polkko, Jouni; Schmidt, Walter; Siili, Tero; Fabre, Cécile; Wray, James; Wilhelm, Mary Beth; Poitrasson, Franck; Patel, Kiran; Gorevan, Stephen; Indyk, Stephen; Paulsen, Gale; Bish, David; Gondet, Brigitte; Langevin, Yves; Geffroy, Claude; Baratoux, David; Berger, Gilles; Cros, Alain; d'Uston, Claude; Forni, Olivier; Gasnault, Olivier; Lasue, Jérémie; Lee, Qiu-Mei; Meslin, Pierre-Yves; Pallier, Etienne; Parot, Yann; Pinet, Patrick; Schröder, Susanne; Toplis, Mike; Lewin, Éric; Brunner, Will; Heydari, Ezat; Achilles, Cherie; Sutter, Brad; Cabane, Michel; Coscia, David; Szopa, Cyril; Robert, François; Sautter, Violaine; Le Mouélic, Stéphane; Nachon, Marion; Buch, Arnaud; Stalport, Fabien; Coll, Patrice; François, Pascaline; Raulin, François; Teinturier, Samuel; Cameron, James; Clegg, Sam; Cousin, Agnès; DeLapp, Dorothea; Dingler, Robert; Jackson, Ryan Steele; Johnstone, Stephen; Lanza, Nina; Little, Cynthia; Nelson, Tony; Williams, Richard B.; Jones, Andrea; Kirkland, Laurel; Baker, Burt; Cantor, Bruce; Caplinger, Michael; Davis, Scott; Duston, Brian; Fay, Donald; Harker, David; Herrera, Paul; Jensen, Elsa; Kennedy, Megan R.; Krezoski, Gillian; Krysak, Daniel; Lipkaman, Leslie; McCartney, Elaina; McNair, Sean; Nixon, Brian; Posiolova, Liliya; Ravine, Michael; Salamon, Andrew; Saper, Lee; Stoiber, Kevin; Supulver, Kimberley; Van Beek, Jason; Van Beek, Tessa; Zimdar, Robert; French, Katherine Louise; Iagnemma, Karl; Miller, Kristen; Goesmann, Fred; Goetz, Walter; Hviid, Stubbe; Johnson, Micah; Lefavor, Matthew; Lyness, Eric; Breves, Elly; Dyar, M. Darby; Fassett, Caleb; Edwards, Laurence; Haberle, Robert; Hoehler, Tori; Hollingsworth, Jeff; Kahre, Melinda; Keely, Leslie; McKay, Christopher; Bleacher, Lora; Brinckerhoff, William; Choi, David; Dworkin, Jason P.; Floyd, Melissa; Freissinet, Caroline; Garvin, James; Glavin, Daniel; Harpold, Daniel; Martin, David K.; McAdam, Amy; Pavlov, Alexander; Raaen, Eric; Smith, Michael D.; Stern, Jennifer; Tan, Florence; Trainer, Melissa; Posner, Arik; Voytek, Mary; Aubrey, Andrew; Behar, Alberto; Blaney, Diana; Brinza, David; Christensen, Lance; DeFlores, Lauren; Feldman, Jason; Feldman, Sabrina; Flesch, Gregory; Jun, Insoo; Keymeulen, Didier; Mischna, Michael; Morookian, John Michael; Pavri, Betina; Schoppers, Marcel; Sengstacken, Aaron; Simmonds, John J.; Spanovich, Nicole; Juarez, Manuel de la Torre; Webster, Christopher R.; Yen, Albert; Archer, Paul Douglas; Cucinotta, Francis; Jones, John H.; Morris, Richard V.; Niles, Paul; Rampe, Elizabeth; Nolan, Thomas; Fisk, Martin; Radziemski, Leon; Barraclough, Bruce; Bender, Steve; Berman, Daniel; Dobrea, Eldar Noe; Tokar, Robert; Cleghorn, Timothy; Huntress, Wesley; Manhès, Gérard; Hudgins, Judy; Olson, Timothy; Stewart, Noel; Sarrazin, Philippe; Vicenzi, Edward; Bullock, Mark; Ehresmann, Bent; Hamilton, Victoria; Hassler, Donald; Peterson, Joseph; Rafkin, Scot; Zeitlin, Cary; Fedosov, Fedor; Golovin, Dmitry; Karpushkina, Natalya; Kozyrev, Alexander; Litvak, Maxim; Malakhov, Alexey; Mitrofanov, Igor; Mokrousov, Maxim; Nikiforov, Sergey; Prokhorov, Vasily; Sanin, Anton; Tretyakov, Vladislav; Varenikov, Alexey; Vostrukhin, Andrey; Kuzmin, Ruslan; Clark, Benton; Wolff, Michael; Botta, Oliver; Drake, Darrell; Bean, Keri; Lemmon, Mark; Schwenzer, Susanne P.; Lee, Ella Mae; Sucharski, Robert; Hernández, Miguel Ángel de Pablo; Ávalos, Juan José Blanco; Ramos, Miguel; Kim, Myung-Hee; Malespin, Charles; Plante, Ianik; Muller, Jan-Peter; Navarro-González, Rafael; Ewing, Ryan; Boynton, William; Downs, Robert; Fitzgibbon, Mike; Harshman, Karl; Morrison, Shaunna; Kortmann, Onno; Williams, Amy; Lugmair, Günter; Wilson, Michael A.; Jakosky, Bruce; Balic-Zunic, Tonci; Frydenvang, Jens; Jensen, Jaqueline Kløvgaard; Kinch, Kjartan; Koefoed, Asmus; Madsen, Morten Bo; Stipp, Susan Louise Svane; Boyd, Nick; Campbell, John L.; Perrett, Glynis; Pradler, Irina; VanBommel, Scott; Jacob, Samantha; Owen, Tobias; Savijärvi, Hannu; Boehm, Eckart; Böttcher, Stephan; Burmeister, Sönke; Guo, Jingnan; Köhler, Jan; García, César Martín; Mueller-Mellin, Reinhold; Wimmer-Schweingruber, Robert; Bridges, John C.; McConnochie, Timothy; Benna, Mehdi; Franz, Heather; Bower, Hannah; Brunner, Anna; Blau, Hannah; Boucher, Thomas; Carmosino, Marco; Atreya, Sushil; Elliott, Harvey; Halleaux, Douglas; Rennó, Nilton; Wong, Michael; Pepin, Robert; Elliott, Beverley; Spray, John; Thompson, Lucy; Gordon, Suzanne; Ollila, Ann; Williams, Joshua; Vasconcelos, Paulo; Bentz, Jennifer; Nealson, Kenneth; Popa, Radu; Moersch, Jeffrey; Tate, Christopher; Day, Mackenzie; Francis, Raymond; McCullough, Emily; Cloutis, Ed; ten Kate, Inge Loes; Scholes, Daniel; Slavney, Susan; Stein, Thomas; Ward, Jennifer; Berger, Jeffrey; Moores, John E.

    2014-01-01

    The Curiosity rover discovered fine-grained sedimentary rocks, which are inferred to represent an ancient lake and preserve evidence of an environment that would have been suited to support a martian biosphere founded on chemolithoautotrophy. This aqueous environment was characterized by neutral pH, low salinity, and variable redox states of both iron and sulfur species. Carbon, hydrogen, oxygen, sulfur, nitrogen, and phosphorus were measured directly as key biogenic elements; by inference, phosphorus is assumed to have been available. The environment probably had a minimum duration of hundreds to tens of thousands of years. These results highlight the biological viability of fluvial-lacustrine environments in the post-Noachian history of Mars.

  18. A habitable fluvio-lacustrine environment at Yellowknife Bay, Gale crater, Mars.

    PubMed

    Grotzinger, J P; Sumner, D Y; Kah, L C; Stack, K; Gupta, S; Edgar, L; Rubin, D; Lewis, K; Schieber, J; Mangold, N; Milliken, R; Conrad, P G; DesMarais, D; Farmer, J; Siebach, K; Calef, F; Hurowitz, J; McLennan, S M; Ming, D; Vaniman, D; Crisp, J; Vasavada, A; Edgett, K S; Malin, M; Blake, D; Gellert, R; Mahaffy, P; Wiens, R C; Maurice, S; Grant, J A; Wilson, S; Anderson, R C; Beegle, L; Arvidson, R; Hallet, B; Sletten, R S; Rice, M; Bell, J; Griffes, J; Ehlmann, B; Anderson, R B; Bristow, T F; Dietrich, W E; Dromart, G; Eigenbrode, J; Fraeman, A; Hardgrove, C; Herkenhoff, K; Jandura, L; Kocurek, G; Lee, S; Leshin, L A; Leveille, R; Limonadi, D; Maki, J; McCloskey, S; Meyer, M; Minitti, M; Newsom, H; Oehler, D; Okon, A; Palucis, M; Parker, T; Rowland, S; Schmidt, M; Squyres, S; Steele, A; Stolper, E; Summons, R; Treiman, A; Williams, R; Yingst, A

    2014-01-24

    The Curiosity rover discovered fine-grained sedimentary rocks, which are inferred to represent an ancient lake and preserve evidence of an environment that would have been suited to support a martian biosphere founded on chemolithoautotrophy. This aqueous environment was characterized by neutral pH, low salinity, and variable redox states of both iron and sulfur species. Carbon, hydrogen, oxygen, sulfur, nitrogen, and phosphorus were measured directly as key biogenic elements; by inference, phosphorus is assumed to have been available. The environment probably had a minimum duration of hundreds to tens of thousands of years. These results highlight the biological viability of fluvial-lacustrine environments in the post-Noachian history of Mars. PMID:24324272

  19. A Lacustrine Record of Postglacial Dust Deposition from the Uinta Mountains, Utah, USA

    NASA Astrophysics Data System (ADS)

    Munroe, Jeffrey

    2015-04-01

    Samplers deployed in 2011 reveal a modern dust flux to the alpine zone (>3000 m asl) of the Uinta Mountains (Utah, USA) of ~4 gm/m2/yr. A notably uniform layer of silt, ~20 cm thick, in soil profiles from throughout the alpine zone, along with the presence in soils and modern dust of minerals not found in the bedrock, indicates that dust deposition has been an important long-term process in this environment. To evaluate how dust flux and properties have changed over the postglacial period a 190 cm-long lacustrine sediment core was analyzed. The core was collected with a percussion corer from a small lake (8 ha) at an elevation of 3043 m asl in 10.6 m of water. Six AMS 14C analyses on conifer needles, wood fragments, and bulk sediment support a depth-age model extending back to 12.7 ka BP. Loose near-surface sediment was not recovered, so the top of the core is truncated at 1.36 ka BP. Geochemical composition was evaluated at 2-cm intervals using ICP-AES after fluxing of ignited samples with LiBO2. The abundance of rare earth elements was determined for a subset of 16 samples using ICP-MS. Mineralogy was investigated at 2-cm intervals using XRD. Grain size distribution, organic matter content, and C:N ratio were determined at 1-cm intervals using laser scattering, loss-on-ignition, and an elemental analyzer, respectively. Results indicate that the flux and properties of dust arriving in the Uinta Mountains have varied over time, with the most significant variations occurring between 6.5 and 4.5 ka BP. During that time ratios of Zr/Al, Ti/Al and (Ca+Mg)/Fe rise to record-high values, and the abundance of Illite+Chlorite increases relative to feldspar. Prominent shifts occur in the abundances of some trace elements, such as Sc, along with changes in median grain size. The ratio La/Lu, as well as the magnitude of the Eu anomaly, also change. Collectively these fluctuations are consistent with a greater flux of dust to the Uinta Mountains, as well as a possible change

  20. Geophysical imaging of the lacustrine sediments deposited in the La Calderilla Volcanic Caldera (Gran Canaria Island, Spain) for paleoclimate research

    NASA Astrophysics Data System (ADS)

    Himi, Mahjoub; Rodríguez-González, Alejandro; Criado, Constantino; Tapias, Josefina C.; Ravazzi, Cesare; Pérez-Torrado, Francisco; Casas, Albert

    2016-04-01

    The discovery of well-preserved maar structures is important not only for studying the eruptive activity and formation of volcanoes, but also for paleoclimate research, since laminated maar lake sediments may contain very detailed archives of climate and environmental history. Maars are a singular type of volcanic structure generated by explosive phreatomagmatic eruptions as a result of interaction between rising magma and groundwater. This kind of structures are characterised by circular craters, often filled with water and/or lacustrine sediments and surrounded by a ring of pyroclastic deposits.Recently a borehole was drilled at the bottom of La Calderilla volcanic complex which penetrated about 8.7 m in its sedimentary sequence and paleobotanical study has supplied the first evidence of paleoenvironmental evolution during the Holocene on the Gran Canaria Island. This survey, however, did not penetrate into the substrate because the total thickness of the sedimentary fill was unknown. Since the age of formation of La Calderilla volcanic complex based on K/Ar dating is about 85,000 years (Upper Pleistocene), the possibility of its sedimentary fill extends beyond of the Holocene is extremely attractive, since, for example, there are few paleoenvironmental data regarding how much the last glaciation that affected the Canary Islands. In these circumstances, the knowledge of the total thickness of the lacustrine sediments is crucial to design a deeper borehole in the next future. Therefore, the subsurface characterisation provided by geophysics is essential for determining thickness and geometry of the sedimentary filling. Multielectrode ERT method was used to obtain five 2-D resistivity cross-sections into La Calderilla volcanic caldera. An Iris Syscal Pro resistivity system with 48 electrodes connected to a 94 m long cable (2m electrode spacing) in Wenner-Schlumberger configuration for an investigation depth of about 20 m. Data quality (q <2 %).was assessed by

  1. Plant Wax Biomarkers in Fluvial-Lacustrine Sediments from the Omo-Turkana and Awash Basins in Eastern Africa

    NASA Astrophysics Data System (ADS)

    Uno, K. T.; Polissar, P. J.; Bonnefille, R.; Brown, F.; Feibel, C. S.; Kahle, E.; Levin, N.; Lepre, C. J.; deMenocal, P. B.

    2013-12-01

    Stable isotope analysis of terrestrial plant biomarkers has emerged over the past decade as a powerful tool for reconstructing vegetation and hydroclimate from lacustrine and marine sediments in eastern Africa. Presently, no comprehensive biomarker records exist from late Miocene to late Pleistocene terrestrial sediments in eastern Africa. Fluvial-lacustrine deposits in the Omo-Turkana and Awash Basins located in Kenya and Ethiopia host a diverse faunal record that is rich in hominin taxa. Biomarker records from these deposits could provide continuous, high-resolution terrestrial paleoclimate records that would enable direct comparison of climate and biotic change through time, fill gaps in the discontinuous isotopic record from paleosol carbonates, and compliment existing biomarkers records from marine sediments. The heterogeneity of fluvial-lacustrine deposits compared to marine and continuous lacustrine deposits requires rigorous assessment of biomarker preservation and abundance prior to isotopic analysis. We analyzed fluvio-lacustrine sediments from the Sagantole, Hadar, and Busidima Fms. in the Awash Basin and the Shungura and Nachukui Fms. in the Omo-Turkana Basin to assess the feasibility of generating continuous isotopic records of vegetation and hydroclimate from these basins. We measured the distribution, abundance, and where possible, preliminary δD and δ13C values of n-alkanes and n-alkanoic acids extracted from sediments. The carbon preference index (CPI) serves as an indicator for biomarker preservation. The CPI for long-chain n-alkane and n-alkanoic acids is generally >2, suggesting suitable biomarker preservation in most cases. Abundances vary significantly in both n-alkanes and n-alkanoic acids, with higher concentrations in lacustrine versus fluvial samples. About two-thirds of the samples have concentrations sufficient for δD analysis given sample size (<200 g) and current analytical requirements, whereas δ13C analysis is feasible for a

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

    USGS Publications Warehouse

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

    1997-01-01

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

  3. Microsedimentological investigations in lacustrine sediments from a maar lake: implications for palaeoenvironmental reconstructions

    NASA Astrophysics Data System (ADS)

    Jouve, Guillaume; Francus, Pierre; De Coninck, Arnaud; Bouchard, Frédéric

    2013-04-01

    Twenty two thin sections from Laguna Potrok Aike (Santa Cruz province, Patagonia, Argentina) sediments were analyzed in high resolution using μ-XRF, SEM-EDS and grain size determination using image analysis, focusing on an interval spanning the last Glacial interval. The aim of this work was to improve our understanding and identification of all sedimentary facies and their geochemical signature in order to strengthen the paleoenvironmental reconstruction made from this record. High Ca, Ca/Ti and Ca/Si values are revealing coarse sediments during the Last Glacial. Previous studies showed that these ratios were also related to (1) the occurrence of a calcitic lorica green algae Phacotus lenticularis during the Late Glacial and (2) autochthonous calcite precipitations during the Holocene. Potassium revealed clays or turbidites. High Fe content pointed to high (1) clay, or (2) silt, or (3) vivianite content, or (4) to low micropumices content. Peaks of Fe/Ti were rather related to (1) high clay content (2) high micropumices content and (3) sand events. Concomitant Fe, Mn, Mn/Ti and Fe/Ti peaks revealed (1) dissolution of volcanic rocks, (2) vivianite concretions, (3) redox mobilization in sediments, or (4) redeposited layers. Finally, Si and Ti revealed sand and silt respectively, but only if sediments are not rich in micropumices. Consequently, identical geochemical signatures are indicative of many different sedimentary facies in this sedimentary sequence, so that the use of proxies for the whole sedimentary sequence is virtually impossible. This work cautions against the use of many μ-XRF proxies for an entire long lacustrine sedimentary sequence, and obviously warns about their use from one site to another.

  4. Impacts of flamingos on saline lake margin and shallow lacustrine sediments in the Kenya Rift Valley

    NASA Astrophysics Data System (ADS)

    Scott, Jennifer J.; Renaut, Robin W.; Owen, R. Bernhart

    2012-11-01

    Studies of modern, Holocene, and Pleistocene sediments around saline to hypersaline, alkaline Lake Bogoria and Lake Magadi show that evidence of flamingo activity in marginal areas of these lakes is nearly ubiquitous. Flamingos produce discrete structures such as webbed footprints (~ 9 cm long, ~ 11 cm wide) and nest mounds (~ 30 cm wide, ~ 20 cm high), and they also extensively rework sediments in delta front, delta plain, and shoreline areas. Large (~ 0.5-2 cm in diameter), pinched, 'bubble pores' and ped-like mud clumps are formed by the trampling and churning of wet clay-rich sediments in these settings. Flamingo nest mounds, although superficially similar to some thrombolite mounds, are typically internally structureless, unless formed on pre-existing sediments that preserve internal structures. The flamingo mounds consist of a dense, packed oval-shaped core, a surrounding 'body' of packed sediment, and an external layer with a ped-like texture of clumped mud. The nests may contain open holes from roots or feather shafts incorporated into the nest, and (or) burrows produced once the nests are abandoned. In areas with high densities of flamingos, lake margin sediments may be preferentially compacted, particularly at breeding sites, and become resistant to subaerial erosion and the effects of transgressive ravinement on time scales ranging from seasons to tens of thousands of years. The relatively well-compacted nest mounds and associated sediments also contribute to the stability of delta distributary channels during regressive-transgressive cycles, and can lead to the minor channelization of unconfined flows where currents are diverted around nest mounds. Pleistocene exhumed surfaces of relatively well-indurated lake margin sediments at Lake Bogoria and Lake Magadi that are interpreted as combined regressive and transgressive surfaces (flooding surface/sequence boundary) preserve evidence of flamingo activities, and are overlain by younger, porous lacustrine

  5. Reconstruction of Holocene Climate Variability within the Central Mediterranean Using Lake Sediments from the Akrotiri Peninsula, Crete

    NASA Astrophysics Data System (ADS)

    Magill, C. R.; Rosenmeier, M. F.; Cavallari, B. J.; Curtis, J. H.; Weiss, H.

    2005-12-01

    Middle and late Holocene geochemical records from the Limnes depression, a small sinkhole located within the Akrotiri Peninsula, Crete, document centennial and millennial-scale climate variability within the central Mediterranean region. The oldest sediments of the basin consist largely of fibrous plant macrofossils and organic matter and likely indicate lake filling and expansion of wetland vegetation beginning ~5700 radiocarbon years before present (14C-yrs B.P.) (4550 B.C.). The basal peat layers grade into predominantly open water and less shallow lacustrine deposits by 4500 14C-yrs B.P (3200 B.C.). Continuous open water sedimentation within the Limnes core is interrupted by a number of distinct lag deposits and peaty deposits centered at 3700, 1600, and 350 14C-yrs B.P (2100 B.C., 500 A.D., and 1500 A.D.) indicating periods of significantly lowered lake level or perhaps lake desiccation. These ages coincide roughly with oxygen isotope (δ18O) minima measured in biogenic carbonates (ostracod shells) and support the inference for low lake stage. Trace element (Ca, Mg, and Sr) concentrations in ostracod shells from the Limnes core parallel the oxygen isotope record, suggesting that the data reflect basin hydrology rather than changes in the isotopic composition of rainfall. Furthermore, covariance in both δ18O and Mg concentrations eliminate temperature as a control on the oxygen isotope record. Sediments from the basin also contain aragonite remains of the green alga Chara and isotope analysis of the calcite may record additional paleoenvironmental information. The paleoclimate history inferred from the Limnes record correlates temporally (albeit tenuously) to previous paleoenvironmental data that document abrupt onset of arid conditions in the eastern Mediterranean and western Asia ca. 2200 B.C. Moreover, stratigraphic and geochemical evidence of low lake level (drying) within the Limnes basin at 2100 B.C. may correspond to the termination of the Early Minoan

  6. Reconstructing Past Vegetation Types During the Late Holocene Using Stable Carbon Isotopes of Leporids from Archaeological Sites in the American Southwest

    NASA Astrophysics Data System (ADS)

    Mauldin, R. P.; Munoz, C.; Kemp, L.; Hard, R.

    2012-12-01

    Stable carbon isotopes (δ13C) from bone collagen in leporids provide high-resolution vegetation reconstruction. Leporids [e.g., cottontails (Sylvilagus sp.), jackrabbits (Lepus sp.)] die young (ca. 2 years) and use small home ranges (< 1 km2). They consume a variety of vegetation, including plants that use both C3 and C4/CAM photosynthetic pathways. Leporids appear to focus on new growth as it becomes available throughout the year, perhaps as a function of water content. Their diet, and their bone collagen, provides a high-resolution view of the carbon isotopic values present in their local plant community. Here we provide an example of the use of leporid bone collagen for reconstruction of past vegetation types using data from several archaeological sites as well as modern collections. All samples are from a basin and range setting within the Chihuahuan Desert in far west Texas and southern New Mexico, USA. The sites span a period back to roughly 1350 BP. Isotopic patterns in leporid collagen show clear evidence of change in vegetation from around 775 BP to the modern period, with a dramatic shift of 4.2‰ in median δ13C values over this period in jackrabbit collagen and a 7.3‰ decrease in median carbon isotopic values in cottontail rabbits. These data suggest a significant increase in C3 plants in leporid diet, and by extension a relative increase in these plant types in the local environment sampled by leporids. This shift is consistent with historic accounts of more C3 mesquite, possibly because of historic land use and ranching practices in the 1800s. However, while this shift may have been accelerated by historic land use changes, our data suggest that the vegetation shift began several hundred years earlier during the prehistoric period. The prehistoric collagen isotopic record also shows increased sample variability through time in both species, suggesting that year-to-year variability in vegetation may have increased late in that sequence. Our results

  7. Palynology, sedimentology and palaeoecology of the late Holocene Dead Sea

    NASA Astrophysics Data System (ADS)

    Neumann, Frank Harald; Kagan, Elisa J.; Schwab, Markus J.; Stein, Mordechai

    2007-06-01

    Palynological and sedimentological studies were performed at two Holocene profiles in erosion gullies (Ze'elim and Ein Feshkha) which dissect the retreating western shore of the Dead Sea. The aim of the project was to analyse possible links between climate, lithology, and vegetation development. The section in Ze'elim shows both lacustrine and fluvial sediments, whereas sedimentation at Ein Feshkha is predominantly lacustrine. The Ze'elim profile, previously used for paleo-lake reconstruction provides an opportunity to compare climate triggered lake levels as paleo-hydrological indicators and vegetation history by use of palynology. The vegetation development in Ze'elim and Ein Feshkha is influenced by both climate and human impact. The pollen record of Ze'elim begins in the Pottery Neolithic, the section of Ein Feshkha in the Late Bronze Age, both records end in the Middle Ages. The Ze'elim section is characterized by sedimentary hiati between the beginning of the Chalcolithic Period until the Middle Bronze Age and within the Late Bronze Age. Settlement periods during the Middle Bronze Age, Iron Age and Hellenistic-Roman-Byzantine Period are indicated by high values of anthropogenic indicators and/or Mediterranean trees. Collapses of agriculture, which can be related to climate effects, are evident during the Late Bronze Age, during the Iron Age and at the end of the Byzantine Period when the lake level curve indicates arid conditions. A comparison of the two pollen records, from different environments, illustrates a more prominent influence of Mediterranean vegetation and cultivated plants in the pollen diagram of Ein Feshkha. The southern Dead Sea region (at the desert fringe) is more vulnerable to regional climate change.

  8. Stratigraphic variations of lacustrine sediment gravity flow deposits and their recurrence intervals in the Middle Pleistocene Miyajima Formation, northeastern Japan: an implication for paleoenvironmental analysis

    NASA Astrophysics Data System (ADS)

    Sasaki, Hana; Onishi, Yuri; Ishihara, Yoshiro

    2016-04-01

    Lacustrine sediment gravity flow deposits have been proposed as archives for flood and earthquake events. Holocene lacustrine deposits are especially valuable because they can be correlated with historical records and other detailed paleoenvironmental indices. When sediment gravity flow deposits are intercalated in varved deposits, they can potentially be used for high resolution reconstruction of recurrence intervals of events in addition to environmental changes. The Shiobara Group in the Shiobara Basin, Tochigi Prefecture, northeastern Japan, consists of the upper Miyajima Formation and the lower Kamishiobara Formation. The Miyajima Formation includes varved deposits distributed at the center of the basin. These units are interpreted as lake floor deposits of the Paleo-Shiobara Caldera Lake. The varved deposits of the Miyajima Formation consist of cyclic repetitions of light-colored seasonal sub-layers mainly composed of diatoms (Stephanodiscus niagarae) and dark-colored seasonal sub-layers mainly composed of river inflow deposits. For this study, we measured lacustrine deposits of the Miyajima Formation and analyzed stratigraphic variation of varved deposits. Stratigraphic units of approximately 4 m in total thickness were studied, which included 416 events of sediment -gravity flow deposition over ca. 700 years. Sedimentary facies of the lacustrine sediment gravity flow deposits: The sediment gravity flow deposits can be classified by their erosional and internal features: whether they have an erosional base, whether they are graded, and whether they have rip-up clasts. Because high density currents were suggested from above features, most of the deposits are interpreted as the result of hyperpycnal flow. Also, the features suggest that the sediment gravity flow deposits originated from rivers around the lake. Stratigraphic variation of varved deposits: Average thicknesses of varves decrease from the lower and middle portions of the section to the upper part

  9. Temporal relationship between Holocene human occupation and vegetation change along the northwestern margin of the Central African rainforest

    NASA Astrophysics Data System (ADS)

    Lézine, Anne-Marie; Holl, Augustin F.-C.; Lebamba, Judicaël; Vincens, Annie; Assi-Khaudjis, Chimène; Février, Louis; Sultan, Émmanuelle

    2013-07-01

    This paper discusses the relationship between patterns of human settlements and environmental change during the Holocene along the northwestern margins of the equatorial rain forest of central Africa. Palaeoenvironmental data from high-resolution sediment cores from lacustrine deposits, plant macro-remains from forest soils, and archaeological data are harnessed to discuss the differential impact of climate and/or humans on the central African rain forest. It is shown that climate change impacted the rain forest well before the widespread expansion of human settlements all over the study area.

  10. Regional Variations in Middle Holocene Precipitation Across the Western United States

    NASA Astrophysics Data System (ADS)

    Starratt, S.

    2015-12-01

    Holocene climate patterns across the western US are controlled by complex ocean/atmosphere dynamics including (i)strength and position of the Aleutian Low and North Pacific High pressure systems which determine the magnitude, duration, and position of winter storm systems, and (ii) the North American Monsoon which is driven by Northern Hemisphere summer warming. On annual-to-decadal time scales, ENSO- and PDO-controlled precipitation variability is expressed as a north-south dipole in the western US, with a transition zone that separates a wet Pacific Northwest and a dry Southwest. Most lacustrine paleoclimate records suggest that water levels were lower across the western US, due to warmer, drier conditions during the middle Holocene. Lake levels rose with increased precipitation and decreased evaporation in the late Holocene. The magnitude of the lake level changes and the timing of these transitions vary with latitude and local conditions such as proximity to the coast and elevation. Favre Lake (2899 masl), located in the Ruby Mountains of northeastern Nevada filled gradually between 7625 and 5600 cal yr BP, after which lake level remained relatively stable for the remainder of the Holocene. Medicine Lake (2033 masl),lying within the caldera of Medicine Lake Volcano (northeastern California) filled to a maximum level between 11,400 and 6000 cal yr BP and then fluctuated by several meters during the remainder of the Holocene. The lowest elevation lake, Swamp Lake (1545 masl), exhibited the strongest record of changes in seasonality over the Holocene, beginning with a transition to warmer conditions ~10,800 cal yr BP, maximum drying between 7400-5500 cal yr BP, followed by a gradual increase in moisture for the remainder of the middle Holocene succeeded by a major shift to wetter conditions at about 3100 cal yr BP. Lower Bear Lake (2065 masl) in the San Bernardino Mountains east of Los Angeles is most strongly influenced by marine conditions. The overall Holocene