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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. 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

  3. 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.

  4. 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.

  5. 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

  6. 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

  7. 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.

  8. 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

  9. Late Holocene Lacustrine Records of Climate and Vegetation Change From Southernmost South America

    NASA Astrophysics Data System (ADS)

    Moy, C. M.; Dunbar, R. B.; Francois, J.; Moreno, P. I.; Villa Martínez, R.

    2006-12-01

    The westerly wind field is one of the most prominent atmospheric circulation features in the Southern Hemisphere and has a major impact on the climate of southern South America as well as Southern Ocean hydrography. Southernmost South America is well-located to investigate past changes in the westerly winds because regional precipitation variability is controlled by the location and intensity of the wind field and it is the only landmass to extend within the core of the westerlies. Here we present late Holocene lacustrine records of climate change related to the westerlies from southern Patagonia, Chile. We focus on Lago Guanaco, a small hydrologically closed-basin lake in Southern Patagonia, and use stable isotope and pollen data from this site and three additional lakes in order to reconstruct changes in moisture balance related to the westerlies. Lago Guanaco (51°S, 72°W) is located close to the Nothofagus forest-Patagonian Steppe transition in the eastern region of Parque Nacional Torres del Paine. The location and composition of this important biological discontinuity is highly sensitive to the W-E precipitation gradient throughout Patagonia. The 4.75 m sediment core we obtained from the center of the lake has high concentrations of organic mater in addition to ostracodes and bivalves, which are relatively rare in Chilean Patagonia. Eleven AMS radiocarbon dates on organic and carbonate fractions indicate that the record spans the last ~14,400 cal yr BP and modern dates from core tops suggest little influence by old carbon sources. Changes in moisture balance and forest density/proximity are reflected in downcore variations in δ18Obivalve and δ18Oostracode, the Nothofagus/Poaceae paleovegetation index, and the C/N ratio of bulk decalcified organic matter. Combined, these variables document changes in the isotopic composition of the lake water, which largely reflect the isotopic composition of precipitation and the influence of evaporation, as well as shifts

  10. 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

  11. 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.

  12. Late Holocene Lacustrine Records of Climate and Vegetation Change From Southern Patagonia, Chile

    NASA Astrophysics Data System (ADS)

    Moy, C. M.; Francois, J.; Moreno, P.; Villa Martinez, R.; Dunbar, R. B.

    2004-12-01

    The westerly wind field is one of the most prominent atmospheric circulation features in the Southern Hemisphere, having a major impact on the climate of Chile and hydrographic conditions in the Southern Ocean. The latitudinal position and strength of the westerlies directly influences the amount and isotopic composition of precipitation that falls in southern Chile. Although instrumental records provide information on how the westerlies have varied over the recent past there is still an incomplete understanding of how the strength and latitudinal position of the southern westerlies have changed during the Holocene and how the wind field has varied at millennial to sub-decadal timescales. In this study we relate changes in the westerly winds to changes in water balance as recorded in closed-basin lakes. Sediment cores were obtained from Laguna Guanacos in Parque Nacional Torres del Paine (51° S, 72° W) during the austral summer of 2004 and sampled at 1-2cm intervals for pollen, charcoal, and stable isotope analysis. Laguna Guanacos is a small closed-basin lake situated in the core of westerly wind belt and is therefore sensitive to fluctuations in the strength and position of the westerlies. The sediment cores obtained from the lake reveal high concentrations of organic mater ( ˜20%) and biogenic carbonate, which is rare in Chilean Patagonia. AMS radiocarbon dates on the organic and carbonate fractions indicate that the record spans the last ˜14,000 calendar years and modern dates from core tops suggest little influence by old or dead carbon sources. Pollen analysis on the late Holocene portion of the record reveals a significant expansion of the Nothofagus forest since ˜3500 cal yr BP, suggesting an overall increase in precipitation during this interval. Millennial- and centennial-scale fluctuations in bulk carbonate content and forest and steppe pollen are superimposed upon this pattern, providing a view of a highly dynamic westerly wind regime and forest

  13. The Holocene history of Oro Lake, one of the western Canada's longest continuous lacustrine records

    NASA Astrophysics Data System (ADS)

    Last, William M.; Vance, Robert E.

    2002-04-01

    Over the past decade, there have been significant advances in our understanding of the Holocene history of the Great Plains region of western Canada. However, despite this increased interest, paleolimnological research is limited by a paucity of study sites with relatively long, uninterrupted stratigraphic sequences. To date, only three Canadian Great Plains lakes have provided complete, uninterrupted sequences spanning the past 10,000 years. Oro Lake is one of these. Oro Lake is small, perennial, and saline. It occupies a topographically closed basin on the Missouri Coteau in southern Saskatchewan, Canada. Its 10,000-year stratigraphic sequence consists mainly of well-bedded, calcareous, and gypsiferous clayey silts. A short-lived early Holocene freshwater siliciclastic-dominated lake occupied the newly formed basin immediately after deglaciation. At ˜9300 BP, limnological conditions changed dramatically and abruptly. Since then, alkaline, high-salinity brines with high Mg/Ca ratios have prevailed. Stable meromictic conditions existed from about 9300 to ˜7400 BP, with maximum salinities (>75 ppt) occurring at 8300 BP. About 7400 years ago, gradually increasing aridity during the mid-Holocene resulted in increased eolian sedimentation, reorganization of the groundwater influx, and occasional breakdown of meromixis. About 4000 BP, the lake returned to a mainly stratified water column with subaqueous soluble salts being precipitated from the monimolimnion, and aragonite and Mg-carbonates being generated from the mixolimnion. During the most recent 1000 years, periodic hypersaline conditions became more common, coincident with decreased concentrations of Ca 2+ and complimentary increased proportions of Mg 2+ and Na + ions.

  14. Sulfur Geochemistry of a Lacustrine Record from Taiwan Reveals Enhanced Marine Aerosol Input during the Early Holocene.

    PubMed

    Ding, Xiaodong; Li, Dawei; Zheng, Liwei; Bao, Hongyan; Chen, Huei-Fen; Kao, Shuh-Ji

    2016-12-12

    Lacustrine record of marine aerosol input has rarely been documented. Here, we present the sulfur geochemistry during the last deglaciation and early Holocene of a sediment core retrieved from the Dongyuan Lake in southern Taiwan. An unusually high sulfur peak accompanying pyrite presence is observed at 10.5 ka BP. Such high sulfur content in lacustrine record is unusual. The δ(34)S of sulfur varied from +9.5 to + 17.1‰ with two significant positive shifts at 10.5 and 9.4 ka BP. The sources of sulfur and potential processes involving the sulfur isotope variation including bacterial sulfate reduction, volcanic emissions, in-catchment sulfide oxidation and marine aerosol input are discussed. Enhanced marine aerosol input is the most likely explanation for such sulfur peaks and δ(34)S shifts. The positive δ(34)S shifts appeared concurrently with the maximum landslide events over Taiwan resulted from enhanced typhoon activities. The synchronicity among records suggests that increased typhoon activities promoted sea spray, and consequently enhanced the marine aerosol input with (34)S-enriched sulfate. Our sulfur geochemistry data revealed sea spray history and marine influence onto terrestrial environment at coastal regions. Wider coverage of spatial-temporal lacustrine sulfur geochemistry record is needed to validate the applicability of sulfur proxy in paleoenvironmental research.

  15. Sulfur Geochemistry of a Lacustrine Record from Taiwan Reveals Enhanced Marine Aerosol Input during the Early Holocene

    PubMed Central

    Ding, Xiaodong; Li, Dawei; Zheng, Liwei; Bao, Hongyan; Chen, Huei-Fen; Kao, Shuh-Ji

    2016-01-01

    Lacustrine record of marine aerosol input has rarely been documented. Here, we present the sulfur geochemistry during the last deglaciation and early Holocene of a sediment core retrieved from the Dongyuan Lake in southern Taiwan. An unusually high sulfur peak accompanying pyrite presence is observed at 10.5 ka BP. Such high sulfur content in lacustrine record is unusual. The δ34S of sulfur varied from +9.5 to + 17.1‰ with two significant positive shifts at 10.5 and 9.4 ka BP. The sources of sulfur and potential processes involving the sulfur isotope variation including bacterial sulfate reduction, volcanic emissions, in-catchment sulfide oxidation and marine aerosol input are discussed. Enhanced marine aerosol input is the most likely explanation for such sulfur peaks and δ34S shifts. The positive δ34S shifts appeared concurrently with the maximum landslide events over Taiwan resulted from enhanced typhoon activities. The synchronicity among records suggests that increased typhoon activities promoted sea spray, and consequently enhanced the marine aerosol input with 34S-enriched sulfate. Our sulfur geochemistry data revealed sea spray history and marine influence onto terrestrial environment at coastal regions. Wider coverage of spatial-temporal lacustrine sulfur geochemistry record is needed to validate the applicability of sulfur proxy in paleoenvironmental research. PMID:27941864

  16. Sulfur Geochemistry of a Lacustrine Record from Taiwan Reveals Enhanced Marine Aerosol Input during the Early Holocene

    NASA Astrophysics Data System (ADS)

    Ding, Xiaodong; Li, Dawei; Zheng, Liwei; Bao, Hongyan; Chen, Huei-Fen; Kao, Shuh-Ji

    2016-12-01

    Lacustrine record of marine aerosol input has rarely been documented. Here, we present the sulfur geochemistry during the last deglaciation and early Holocene of a sediment core retrieved from the Dongyuan Lake in southern Taiwan. An unusually high sulfur peak accompanying pyrite presence is observed at 10.5 ka BP. Such high sulfur content in lacustrine record is unusual. The δ34S of sulfur varied from +9.5 to + 17.1‰ with two significant positive shifts at 10.5 and 9.4 ka BP. The sources of sulfur and potential processes involving the sulfur isotope variation including bacterial sulfate reduction, volcanic emissions, in-catchment sulfide oxidation and marine aerosol input are discussed. Enhanced marine aerosol input is the most likely explanation for such sulfur peaks and δ34S shifts. The positive δ34S shifts appeared concurrently with the maximum landslide events over Taiwan resulted from enhanced typhoon activities. The synchronicity among records suggests that increased typhoon activities promoted sea spray, and consequently enhanced the marine aerosol input with 34S-enriched sulfate. Our sulfur geochemistry data revealed sea spray history and marine influence onto terrestrial environment at coastal regions. Wider coverage of spatial-temporal lacustrine sulfur geochemistry record is needed to validate the applicability of sulfur proxy in paleoenvironmental research.

  17. Lacustrine sediments and Holocene climates in the southern Sahara: the example of paleolakes in the Grand Erg of Bilma (Zoo Baba and Dibella, eastern Niger)

    NASA Astrophysics Data System (ADS)

    Grunert, J.; Baumhauer, R.; Völkel, J.

    Two endoreic depressions of the central Erg of Bilma/eastern Republic of Niger are described here. Special interest is given to widespread lacustrine sediments (diatomites) in the depressions, indicating paleolakes with an extension of some 10 km 2. The minimum depth of the lakes has been found to be 25 m (Zoo Baba) and 36 m (Dibella). At Dibella there is evidence of two lacustrine phases of Early Holocene (9785-7890 years B.P.) and of Mid-Holocene age (about 6500 years B.P.). At Zoo Baba only one lacustrine phase of Mid-Holocene age (about 6000-5370 years B.P.) can be proven for Zoo Baba. The difference between the Early- and Mid-Holocene diatomites Di I and Di II is based not only on radiocarbon data but also on geomorphological characteristics. Despite the small distance of only 70 km between the two depressions, the reconstruction of pluvial water chemistry particularly by analyzing the diatoms shows great differences. The Mid-Holocene Zoo Baba lake was a freshwater lake; the Early- and Mid-Holocene Dibella lakes obviously contained brackish water with great fluctuations of salinity. An explanation may be given by the varying groundwater influence during the pluvial periods. It is supposed that Zoo Baba has been touched by the large Kaouar/Bilma aquifer while Dibella has been influenced by a smaller local aquifer. Any groundwater supply from Paleo-Chad can be excluded. Both the rising of groundwater table and of lake levels must have been induced by a largely increased annual precipitation rate (today 20-40 mm only), combined with a very effective reduction in evaporation rate. Based on lacrustine sediments, paleosoils and geomorphological features (fossil landslides of Zoo Baba), the Early Holocene annual precipitation rate is estimated at least at 300-400 mm, the Mid-Holocene rate at 200-300 mm. The special character of precipitations cannot be reconstructed.

  18. 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.

  19. 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.

  20. 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.

  1. Late Holocene lacustrine chronology and archaeology of ancient Lake Cahuilla, California

    NASA Astrophysics Data System (ADS)

    Waters, Michael R.

    1983-05-01

    Freshwater lakes existed intermittently in the Salton Trough of southern California during the late Holocene. The lakes formed north of the subaerial Colorado River Delta whenever the Colorado River flowed west into the trough instead of south to the Gulf of California. Water filled the trough to a maximum altitude of 12 m. Stratigraphy, radiocarbon dates, and supplementary evidence document four lacustral intervals of Lake Cahuilla between A.D. 700 and 1580. Archaeological sites are associated with the 12-m shoreline and their occupation correlates with these lacustral intervals.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

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

    NASA Astrophysics Data System (ADS)

    Bertrand, S.; Fagel, N.

    2003-04-01

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

  7. 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.

  8. 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.

  9. 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

    2016-09-01

    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 observations and X-ray diffraction 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 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 generated from

  10. Integrative analysis of a lacustrine carbonate reservoir, Kambala field, Cabinda, Angola

    SciTech Connect

    Lomando, A.J.; Griscom, M. )

    1993-09-01

    The presalt lacustrine rift basins of west Africa are the continued focus of exploration and development in this prolific petroleum province. Kambala field produces from the Barremian-Aptian lacustrine carbonates of the TOCA Formation. Source rocks are the rich lacustrine shales of the Bucomazi Formation. TOCA carbonates were deposited along major shorelines and around islands in large lake systems. Reservoir studies provide the necessary models and analogs to guide exploration and evaluation efforts. The TOCA reservoirs in Kambala field have been subdivided into two units. The lower TOCA is characterized by limestones and cherty dolomites, which range texturally from high-energy ooid and oncoid grainstones and packstones to lower energy ostracod wackestones and marls. The upper and lower TOCA are separated by a unit of middle Bucomazi shale. The upper TOCA is composed of thin beds of low-energy facies and thick porous carbonate units, which are pervasively dolomitized. Kambala field sits over a northwest-southeast-trending basement high. The field is bounded by intense faulting on the west and dips gently to the northeast. The faults on the eastern side are more widely spaced and have less throw than the ones on the west. Seismic amplitude maps on the upper TOCA show markedly higher amplitudes on the western and southern edges of the field. The high seismic amplitudes and intense faulting generally correlate with the zone of porous dolomite.

  11. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2012-08-01

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

  13. Mass-transfer in solution: on the context and cause of spherulitic lacustrine carbonate deposits

    NASA Astrophysics Data System (ADS)

    Rogerson, Michael; Mercedes-Martin, Ramon; Brasier, Alex; Vonhof, Hubert; Prior, Tim; Fellows, Simon; Reijmer, John; Pedley, Martyn; McGill, Rona

    2016-04-01

    Understanding how laterally extensive spherulitic carbonate deposits originated in the 'Pre-Salt' Aptian volcanic-influenced lacustrine basins of Brazil and Angola is challenging, especially as few good analog systems are known to compare the Pre-Salt to. Here, we report a particularly good analog system in the Carboniferous of the Scotland (the East Kirkton Limestone), and examine the geochemical and sedimentological context in which spherular radial calcite has developed. Using empirical and theoretical approaches, we analyse the link between metal mobilization from sub-surface volcaniclastic rocks, and the potential precipitation of carbonates, Mg-Si minerals and chalcedony in a lacustrine spherulitic carbonate setting. This suite of minerals at the surface can be explained by CO2 ingassing to a springwater derived from reaction of alkali igneous rocks in the subsurface with meteoric groundwater. This forms a 'source-to-sink' system occurring entirely in solution in the subsurface, but demonstrably capable of forming significant depositional units at the surface. We hypothesise that analogous processes occurring on a larger scale are implicated in the development of the 'Pre-Salt' spherulitic carbonate deposits.

  14. Unusual Holocene and late Pleistocene carbonate sedimentation in Bear Lake, Utah and Idaho, USA

    USGS Publications Warehouse

    Dean, W.; Rosenbaum, J.; Skipp, G.; Colman, S.; Forester, R.; Liu, A.; Simmons, K.; Bischoff, J.

    2006-01-01

    Bear Lake (Utah-Idaho, USA) has been producing large quantities of carbonate minerals of varying mineralogy for the past 17,000 years. The history of sedimentation in Bear Lake is documented through the study of isotopic ratios of oxygen, carbon, and strontium, percent organic carbon, percent CaCO3, X-ray diffraction mineralogy, HCl-leach inorganic geochemistry, and magnetic properties on samples from three piston cores. Historically, the Bear River, the main source of water for Great Salt Lake, did not enter Bear Lake until it was artificially diverted into the lake at the beginning of the 20th century. However, during the last glacial interval, the Bear River did enter Bear Lake depositing red, calcareous, silty clay. About 18,000 years ago, the Bear River became disconnected from Bear Lake. A combination of warmer water, increased evaporation, and increased organic productivity triggered the precipitation of calcium carbonate, first as calcite. As the salinity of the lake increased due to evaporation, aragonite began to precipitate about 11,000 years ago. Aragonite is the dominant mineral that accumulated in bottom sediments of the lake during the Holocene, comprising an average of about 70 wt.% of the sediments. Aragonite formation in a large, cold, oligotrophic, high latitude lake is highly unusual. Lacustrine aragonite usually is found in small, saline lakes in which the salinity varies considerably over time. However, Bear Lake contains endemic ostracodes and fish, which indicate that the chemistry of the lake has remained fairly constant for a long time. Stable isotope data from Holocene aragonite show that the salinity of Bear Lake increased throughout the Holocene, but never reached highly evolved values of ??18O in spite of an evaporation-dominated water balance. Bear Lake hydrology combined with evaporation created an unusual situation that produced large amounts of aragonite, but no evaporite minerals.

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  16. 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

  17. 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.

  18. Holocene biomass burning and global dynamics of the carbon cycle.

    PubMed

    Carcaillet, C; Almquist, H; Asnong, H; Bradshaw, R H W; Carrión, J S; Gaillard, M J; Gajewski, K; Haas, J N; Haberle, S G; Hadorn, P; Müller, S D; Richard, P J H; Richoz, I; Rösch, M; Sánchez Goñi, M F; von Stedingk, H; Stevenson, A C; Talon, B; Tardy, C; Tinner, W; Tryterud, E; Wick, L; Willis, K J

    2002-12-01

    Fire regimes have changed during the Holocene due to changes in climate, vegetation, and in human practices. Here, we hypothesise that changes in fire regime may have affected the global CO2 concentration in the atmosphere through the Holocene. Our data are based on quantitative reconstructions of biomass burning deduced from stratified charcoal records from Europe, and South-, Central- and North America, and Oceania to test the fire-carbon release hypothesis. In Europe the significant increase of fire activity is dated approximately 6000 cal. yr ago. In north-eastern North America burning activity was greatest before 7500 years ago, very low between 7500-3000 years, and has been increasing since 3000 years ago. In tropical America, the pattern is more complex and apparently latitudinally zonal. Maximum burning occurred in the southern Amazon basin and in Central America during the middle Holocene, and during the last 2000 years in the northern Amazon basin. In Oceania, biomass burning has decreased since a maximum 5000 years ago. Biomass burning has broadly increased in the Northern and Southern hemispheres throughout the second half of the Holocene associated with changes in climate and human practices. Global fire indices parallel the increase of atmospheric CO2 concentration recorded in Antarctic ice cores. Future issues on carbon dynamics relatively to biomass burning are discussed to improve the quantitative reconstructions.

  19. 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

  20. 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.

  1. Antarctic black carbon tracks Southern Hemisphere climate throughout the Holocene

    NASA Astrophysics Data System (ADS)

    Arienzo, M. M.; McConnell, J.

    2015-12-01

    Biomass-burning and fossil-fuel combustion emit black carbon (BC) aerosols which impact climate directly by changing Earth's radiation budget and indirectly by changing cloud formation and reducing albedo when deposited on bright surfaces such as snow and ice. BC aerosols have been shown to be the second most important anthropogenic climate-forcing agent today, after carbon dioxide. However, on longer timescales, knowledge of natural variations in BC emissions and climate drivers of regional-scale biomass burning is limited. Here we present the first high-resolution 14,000-year record of BC aerosol deposition in Antarctica. The two ice cores analyzed were the West Antarctic Ice Sheet Divide (WD) core from 14,000 years before 1950 (yr BP) to 2,475 yr BP and the East Antarctic B40 core from 2,485 yr BP to present. BC and a wide range of trace elements were analyzed via a continuous melter system allowing for sub-annual resolution in both cores. For BC concentration determinations, a Single Particle Soot Photometer (SP2; Droplet Measurement Technologies) was used. BC fluxes in the WD and B40 Holocene composite more than doubled from <25 μg m-2 yr-1 at the end of the last glacial termination (14 kyr BP) to >50 μg m-2 yr-1 in the mid-Holocene (~7.5 kyr BP), and then declined to <20 μg m-2 yr-1 in the late Holocene, with lowest BC fluxes observed during the Little Ice Age. We compare Antarctic BC fluxes to low-latitude paleoclimate proxies to investigate a potential link between low latitude climate, biomass burning and BC emissions.

  2. 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.

  3. 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

  4. 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

  5. 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.; 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

  6. 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

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

    PubMed

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

    2017-05-01

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

  8. 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.

  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. 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

  12. 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.

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

    PubMed

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

    2009-09-24

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

  14. 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.

  15. 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

  16. 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

  17. Holocene ochreous lacustrine sediments within the Famatina Belt, NW Argentina: A natural case for fossil damming of an acid drainage system

    NASA Astrophysics Data System (ADS)

    Maza, Santiago N.; Collo, Gilda; Astini, Ricardo A.; Nieto, Fernando; Nieto, José Miguel

    2014-07-01

    A 44 m-thick lacustrine succession of silty-clay banded ochres and subordinated sandstones, and conglomerates (known as the Corral Amarillo Formation) is superbly exposed within the Famatina Belt (Central Andes of Argentina) after deep entrenchment by the present-day Amarillo river due to strong recent uplifting and consequent relative drop in base level. The unusual ochreous-rich succession was produced by natural damming (3.48-3.54 14C kyr BP) of an acid drainage system linked to the alteration cap of polymetallic deposits. Facies of silty-clay ochre (wet season) and banded ochre (dry season) from the paleolacustrine setting are composed of jarosite + goethite and goethite respectively. Geochemically, these layers record high concentrations of Fe2O3 (25-55 wt. %) and trace elements (Cu, Zn, Co, As, and Mo with mean concentrations of 2759; 2467; 109; 375 and 116 ppm, respectively). Their origin is inferred from a comparative analysis with the present-day Amarillo river, which has a pH of ˜3, (SO4)2- concentrations of ˜5000 mg/l, and jarosite as the dominant phase, in the upper catchments. Waters downstream have pH values of 3-4.5, (SO4)2- concentrations of ˜3000-480 mg/l, and schwertmannite as the dominant phase. Thus goethite in the paleolake facies is likely related to schwertmannite transformation by an aging process, whereas jarosite is probably transported from the river but could also be associated with post-depositional formation regulated by variations in grain size and the pore fluid chemistry. The Corral Amarillo Formation offers a Natural model, which may be employed to infer the effect on nature of acid drainage of mineralized areas.

  18. 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.

  19. An integrated archeomagnetic and C14 study on pre-Columbian potsherds and associated charcoals intercalated between Holocene lacustrine sediments in Western Mexico: Geomagnetic implications

    NASA Astrophysics Data System (ADS)

    Aguilar Reyes, B.; Goguitchaichvili, A.; Morales, J.; GarduñO, V. H.; Pineda, M.; Carvallo, C.; Moran, Tomas GonzáLez; Israde, Isabel; Rathert, Manuel Calvo

    2013-06-01

    The firm relationship between archeomagnetic samples and their absolute ages, which is usually determined or estimated using a variety of methods (archaeological context, thermoluminiscense, C14, etc.), is crucial in any archaeomagnetic investigation. In this paper, we report 18 successful (from 65 analyzed) archaeointensity determinations of high technical quality performed on specimens obtained from three fragments of pre-Columbian potsherds. These are unambiguously correlated with charcoal samples, as they were found together in three thin lacustrine sedimentary layers in western Mexico. Moreover, new radiometric results were obtained in this study from all charcoal samples (beta analytic) yielding ages of 1490 ± 40, 1510 ± 40, and 1580 ± 40 BP. In addition, detailed magnetic measurements were carried out on all studied ceramic fragments. These rock magnetic experiments, which included low field susceptibility versus temperature, hysteresis, and first-order reversal curve measurements, indicate that the main magnetic carrier is Ti-poor titanomagnetite. The average archeointensity values per ceramic fragments obtained in this study are very similar in all three cases: 35.2 ± 1.3 μT (N = 5), 36.8 ± 1.6 μT (N = 6), and 37.2 ± 3.4 μT (N = 7). This corresponds to an average intensity of 36.4 ± 1.1 μT and a virtual axial dipole moment value of 8.1 ± 0.2 × 1022 Am2, which is slightly lower than the present field strength, corresponding at an age interval between 640 and 430 A.D. Although we detected some relationship between the Earth's magnetic field intensity and multidecadal climatic events, such observations can only be considered tentative at this stage.

  20. 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.

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

    SciTech Connect

    Tsuji, Yoshihiro; Tsuneo Yamamura; Toshio Kodato; Hisao Sunouchi; Tomoya Yuki

    1988-02-01

    Holocene carbonate sedimentary facies distribution, from sea level to shelf slope about 1,000 m in depth, and its relationship to bathymetry, off Miyako Island, Ryukyus, southwest of Japan were clarified by surveys with sidescan sonar, sparker, uniboom, sea-bottom camera, and sediment sampler.

  2. Lagoa Feia Formation (Lower Cretaceous), Campos basin, offshore Brazil - Rift-Valley-Stage Lacustrine carbonate reservoirs

    SciTech Connect

    Bertani, R.; Petrobras, T.; Carozzi, A.V.

    1985-02-01

    The Lagoa Feia Formation, buried in excess of 3000 m, is the exploration frontier of the prolific Campos basin. It contains the source beds of all the basin's oil in addition to having its own potential carbonate reservoirs. The faulted margins of the basin fed a system of alluvial fans, sand flats, and mud flats. Alternating dry and rainy period regulated the size and nature of contemporaneous basinal alkaline lakes. Dry periods corresponded to contracted playa lakes with ostracod carbonates and euxinic shales; rainy periods corresponded to expanded pluvial lakes with pelecypod banks. Subaqueous intrusions of basaltic magma generated hyaloclastites with kerolitic ooids and hyalotuffs. Petrographic analysis reveals 5 diagenetic stages: (1) syndepositional alteration of lithoclasts to trioctahedral smectites; (2) early dolomitization, early silicification, and cementation by bladed-rim calcite and zeolites; (3) freshwater-vadose dissolution of bioclasts and lithoclasts, freshwater-phreatic sparite cementation, and neomorphism; (4) mixed saline-freshwater silicification; and (5) burial with compaction, late dolomitization, and partial conversion of smectites to illite. Pelecypod limestones with primary interparticle, secondary intraparticle, moldic, and moldic-enlarged porosities are the potential reservoirs. Ideal conditions for porosity generation and preservation were subaerial exposure followed by rapid lake expansion and burial.

  3. 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.

  4. Holocene carbonate record of Lake Kivu reflects the history of hydrothermal activity.

    PubMed

    Votava, Jillian E; Johnson, Thomas C; Hecky, Robert E

    2017-01-10

    The sediment record of Lake Kivu reveals a complex volcanogenic and climatic Holocene history. Investigation of the inorganic carbonate record dates the onset of carbonate deposition in the mid-Holocene in Kivu's deep northern and eastern basins and identifies conditions enabling deposition. The magnitude and timing of carbonate-rich sedimentation is not so much controlled by climate but, instead, linked strongly to hydrothermal activity in the basin. Sublacustrine springs supply the vast majority of the calcium and carbonate ions required for supersaturation with respect to aragonite. This major hydrothermal activity that permanently stratifies Lake Kivu today was initiated ∼3,100 y before present (3.1 ka), when carbonate-rich sediments first appeared in the Holocene record. Aragonite is the dominant CaCO3 mineral present in the lake deposits. Both δ(13)C and δ(18)O of the aragonite are enriched above the expected kinetic fractionation of meteoric waters, suggesting a volcanogenic influence on the formation waters. Repeated major fluctuations in the carbonate record after 3.1 ka therefore most likely reflect the historical variation in hydrothermal inputs.

  5. Holocene carbonate record of Lake Kivu reflects the history of hydrothermal activity

    NASA Astrophysics Data System (ADS)

    Votava, Jillian E.; Johnson, Thomas C.; Hecky, Robert E.

    2017-01-01

    The sediment record of Lake Kivu reveals a complex volcanogenic and climatic Holocene history. Investigation of the inorganic carbonate record dates the onset of carbonate deposition in the mid-Holocene in Kivu’s deep northern and eastern basins and identifies conditions enabling deposition. The magnitude and timing of carbonate-rich sedimentation is not so much controlled by climate but, instead, linked strongly to hydrothermal activity in the basin. Sublacustrine springs supply the vast majority of the calcium and carbonate ions required for supersaturation with respect to aragonite. This major hydrothermal activity that permanently stratifies Lake Kivu today was initiated ˜3,100 y before present (3.1 ka), when carbonate-rich sediments first appeared in the Holocene record. Aragonite is the dominant CaCO3 mineral present in the lake deposits. Both δ13C and δ18O of the aragonite are enriched above the expected kinetic fractionation of meteoric waters, suggesting a volcanogenic influence on the formation waters. Repeated major fluctuations in the carbonate record after 3.1 ka therefore most likely reflect the historical variation in hydrothermal inputs.

  6. Atmospheric CO2 and carbon cycle during the late Holocene

    NASA Astrophysics Data System (ADS)

    Ahn, J.; Brook, E.; Marcott, S. A.

    2015-12-01

    Atmospheric CO2 records during the late Holocene are of great interest because climate boundary conditions for the time interval are similar to those of present and near future. Here we show CO2 records from West Antarctic Ice Sheet (WAIS) Divide ice core that cover the last 2500 years with 10- to 20-year resolutions. The records reveal pre-industrial CO2 variability of ~ 6 ppm on multi-centennial to millennial timescales. We found that the millennial variability is positively correlated with westerly wind stress in the Southern Ocean and the high northern hemispheric climate.

  7. Coccolith-Carbonate Sedimentation in the Northern North Atlantic : an Holocene Perspective

    NASA Astrophysics Data System (ADS)

    Giraudeau, J.; Garcia, J.; Dylmer, C. V.; Husum, K.; Werner, K.; Spielhagen, R. F.; Müller, J.; Moros, M.; Risebrobakken, B.

    2011-12-01

    High concentrations of carbonate in surface sediments of the Nordic Seas are generally related to warm Atlantic Water (AW) inflow. This relationship was recently used to infer the Holocene dynamics of Atlantic-derived water off North-West Iceland (Giraudeau et al, 2010; QSR vol. 29) following suggestions that carbonate production in the vicinity of Denmark Strait is tightly linked with inputs of warm, nutrient-rich Irminger Current waters. The present study aims at testing this assumption in the two main passageways of AW to the Arctic Ocean: Fram Strait and the Barents Sea, with a focus on a high resolution Holocene sediment record collected off western Svalbard. Our datasets on extant coccolithophores, as well as estimates of coccolith-carbonate contents within the studied marine cores suggest that sedimentation of calcium carbonate in the northernmost North Atlantic essentially reflects production rates of coccolithophores, and that sedimentation of their fossil remains is driving to a high extent the Holocene variations in net CaCO3 accumulation in Fram Strait and the SW Barents Sea. Our coccolith-based proxy records are indicative of a complex regional dynamics of Holocene surface water changes in these two regions. With the exception of a ca. 2 000 years delayed recovery of surface AW influence to the SW Barents Sea in the early Holocene, both regions experienced the same history of surface water temperature changes until ca. 3 000 cal.yrs BP. A Holocene sea-surface thermal optimum is clearly recognized in both regions during the 8 000 to 7 000 cal. yrs BP interval, followed by a large scale surface cooling triggered by reduced poleward inflow of AW across the Iceland-Scotland Ridge. A decoupling in the pattern of coccolith-carbonate sedimentation between Fram Strait and the SW Barents Sea characterizes the late Holocene. While near continuous surface water warming impacted the southern Barents Sea throughout the last 3 000 years, the eastern Fram Strait was

  8. 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

  9. 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.

  10. Carbon sequestration in Southeast Asian tropical peatlands over the Holocene period: large-scale hydrological controls

    NASA Astrophysics Data System (ADS)

    Dommain, R.; Couwenberg, J.; Cobb, A.; Gandois, L.; Kai, F.; Su'ut, N.; Abu Salim, K.; Harvey, C. F.; Glaser, P. H.; Joosten, H.

    2012-12-01

    Tropical peatlands are recognized as a significant sink of carbon dioxide and an important source of methane. Low latitude peatlands contain an estimated pool of 90 Pg C, of which ca. 70 Pg C is stored in Southeast Asian peatlands. However, the Holocene development of this carbon reservoir is poorly established. Here we provide a synthesis of carbon uptake rates by tropical peatlands in Southeast Asia across millennial timescales for the past 11,000 years. Our reconstruction of the carbon accumulation history for Borneo, Sumatra and Peninsular Malaysia is based on a synthesis of radiocarbon dated peat profiles, modeling of peatland extent, and a new carbon accumulation record from Brunei (NW-Borneo). During the early Holocene the first peatlands formed in southern Borneo under the influence of a strong monsoon and rapid rise in sea-level. The carbon accumulation rate (CAR) in these peatlands was on average 60 g C m-2 yr-1 at this time. Peatlands started to spread across the coastal lowlands of Borneo, Sumatra and Peninsular Malaysia after 8000 cal BP only when the rate of rising sea-level decreased. The major phase of coastal peatland initiation lasted from 7000 to 4000 cal BP. This period was marked by a Holocene precipitation maximum, suppressed El Niño activity, and the Holocene maximum in sea-level on the Sunda Shelf. The mean CAR of coastal peatlands at this time was 80 g C m-2 yr-1, with a Holocene peak of ~100 g C m-2 yr-1 from 4900 to 4500 cal BP. Significantly, atmospheric CO2 concentrations measured in the Taylor Dome Antarctic ice core indicate a plateau during this period of otherwise rising CO2 concentrations. During the Late Holocene CAR declined both in coastal peatlands (ca. 70 g C m-2 yr-1) and in southern Borneo (ca. 20 g C m-2 yr-1) in response to falling sea-levels and increased El Niño frequency and intensity. In fact, several peatlands in southern Borneo have stopped accumulating peat-carbon under higher El Niño activity. These results

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

    NASA Astrophysics Data System (ADS)

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

    2011-08-01

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

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

    NASA Astrophysics Data System (ADS)

    Kleinen, Thomas; Brovkin, Victor; Munhoven, Guy

    2016-11-01

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

  13. 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

  14. 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.

  15. 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.

  16. Carbonate-evaporite cycles in the Miocene to Holocene of Abu Dhabi, United Arab Emirates

    SciTech Connect

    Whittle, G.L.; Alsharhan, A.S.; Takezaki, H.

    1995-08-01

    The coastal sabkhas of the United Arab Emirates provide a Holocene analog for the study of evaporite formation. Carbonate-evaporite sequences are common throughout geologic history and, in the Arabian Gulf region in particular, create the reservoir-seal relationship of some of the most prolific hydrocarbon reservoirs in the world. Detailed core description, thin section study and geochemical analysis of Miocene to Holocene cores from the sabkha of Abu Dhabi have been performed in order to characterize modern sabkha diagenetic patterns. Two primary lithologies, dolomite and anhydrite were identified and subdivided into lithofacies. Based on these lithofacies, deposition is interpreted to have occurred in shallow open marine, lagoonal, tidal channel, tidal/algal flats and supratidal sabkha settings. The primary diagenetic effects are dolomitization, anhydritc formation and leaching. As anhydrite precipitated (in the form of gypsum), the Mg:Ca ratio increased to the point where rapid dolomitization of original limestone occurred. Leaching was pervasive, as subaerial exposure led to the formation of moldic porosity in dolomitized packstones and grainstones. Dolomitic cements in these pores, and leached zones in some of these crystals suggests that leaching continued after dolomitization. By comparing the Holocene sabkha sediments to ancient ones, insight may be gained into the extent of dolomilization both with depth and distance for in the high water mark, the zonation of the stratigraphy from upper supratidal to shallow shelf, the preservation potential of algal mats after burial, the compaction effects after shallow burial, and other diagenetic alterations.

  17. 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.

  18. Alaskan transect links Holocene carbon shifts to peatland paleoecology and paleoclimate

    NASA Astrophysics Data System (ADS)

    Peteet, D. M.; Nichols, J. E.; Andreev, A.; McGeachy, A.; Perez, M.

    2011-12-01

    Arctic and subarctic peatlands are highly sensitive to climate shifts, and greenhouse warming is greatest at high latitudes. As high latitudes warm and peatlands provide positive and negative feedbacks in carbon sequestration, the paleo-perspective becomes critical in assessing future peatland stocks. We target a north-south (temperature) and east-west (moisture) transect of Alaskan peatlands using pollen and spores, plant macrofossils, charcoal, stable isotopes, and C/N coupled with carbon to explore the relationship of climate and vegetation shifts to carbon storage through time. Since deglaciation, peatlands have developed in a variety of maritime and continental subarctic and arctic environments with vegetation ranging from fens to bogs. Factors affecting the net carbon storage (productivity and decomposition) include the vegetation type, precipitation, temperature, bryophyte component, seasonality, snow history, fire history, and permafrost. New paleoecological records from three Holocene peatlands, each spanning at least 9000 years, include a continental boreal forest site, Goldmine Bog, Fairbanks, (65°N, 147°W), and maritime sites including Phalarope Bog, Kodiak (57°N, 154°W), and Bear Bog, Cordova (60°N, 145°W). Major shifts in moisture and temperature are evident throughout the Holocene from our multiproxy investigations of each site. Our data address several questions about subarctic/arctic carbon storage and climate, such as whether bogs or fens sequester more carbon, as this topic is intensely debated in the current literature. We also compare shifts in inferred moisture and temperature with carbon storage at each site, and with other coastal and interior sites for a fuller understanding of changes in the climate of this important region.

  19. Carbon accumulation rates and the origin of the Holocene sapropel in the Black Sea

    NASA Astrophysics Data System (ADS)

    Calvert, S. E.; Vogel, J. S.; Southon, J. R.

    1987-10-01

    A detailed radiocarbon chronology obtained by accelerator mass spectrometry together with organic carbon and carbonate measurements on two Black Sea cores has been used to compare and contrast the burial fluxes of organic carbon in the Holocene sapropel and the modern sediment. At both deep-water and eastern-slope sites, the sapropel is separated from the modern facies by a variable thickness of compositionally homogeneous sediment with low levels of organic carbon and anomalously old radiocarbon ages. This homogeneous unit probably represents deposition by slumping or mudflow. The age limits of the sapropel are 1600 6600 B.P. at the deep-water site and 4000 6000 B.P. (radiocarbon years before 1950 A.D.) at the shallow-water site. The carbon accumulation rate in the deep-water sapropel is higher than that in the modern deep-water facies by a factor of 2 and is approximately the same as that in the modern sediment in shallow water. The revised chronology of sapropel formation and the differences in the carbon accumulation rates probably indicate that the sapropel was formed by increased production during the transition from the premodern lake to the modern marine phases of the Black Sea. This conclusion is consistent with the clear marine carbon-isotope signal in the organic matter in the sapropel in both cores (results to be reported elsewhere), in contrast to the mixed source of carbon in the other facies.

  20. 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.

  1. 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.

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

    USGS Publications Warehouse

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

    2014-01-01

    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.

  3. 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.

  4. 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.

  5. Holocene coastal carbonates and evaporites of the southern Arabian Gulf and their ancient analogues

    NASA Astrophysics Data System (ADS)

    Alsharhan, A. S.; Kendall, C. G. St. C.

    2003-06-01

    The Holocene sediments of the coast of the United Arab Emirates in the southeastern Arabian Gulf are frequently cited in the literature as type examples for analogous assemblages of carbonates, evaporites and siliciclastics throughout the geologic record. This paper is intended as a convenient single source for the description of sediments of this region, providing information on how to reach the classic localities and some of the analogs. The Holocene sediments of the region accumulate over an area that is 500 km long and up to 60 km wide. The sediments collecting offshore are predominantly pelecypod sands mixed with lime and argillaceous mud, with these latter fine sediments increasing as the water deepens. The pelecypod-rich sediments also collect east of Abu Dhabi Island both in the deeper tidal channels between the barrier island lagoons and in deeper portions of the protected lagoons. West of Abu Dhabi Island the shallow water margin is the site of coral reefs and coralgal sands, whereas to the east oolites accumulate on the tidal deltas of channels located between barrier islands. Grapestones accumulate to the lee of the reefs and the oolite shoals where cementation becomes more common. They are particularly common on the less protected shallow water margins of the lagoons west of Abu Dhabi Island. Pelleted lime muds accumulate in the lagoons in the lee of the barrier islands of the eastern Abu Dhabi. Lining the inner shores of the protected lagoons of Abu Dhabi and on other islands to the west are cyano-bacterial mats and mangrove swamps. Landward of these, a prograding north facing shoreline is formed by supratidal salt flats (sabkhas), in which evaporite minerals are accumulating. This paper describes the localities associated with (1) the mangrove swamps of the west side of the Al Dhabaiya peninsula; (2) the indurated cemented carbonate crusts, cyanobacterial flats and sabkha evaporites on the shore of the Khor al Bazam south of Qanatir Island; (3) the

  6. 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

  7. 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...

  8. 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.

  9. Carbon storage and potential methane production in the Hudson Bay Lowlands since mid-Holocene peat initiation.

    PubMed

    Packalen, Maara S; Finkelstein, Sarah A; McLaughlin, James W

    2014-06-11

    Peatlands have influenced Holocene carbon (C) cycling by storing atmospheric C and releasing methane (CH4). Yet, our understanding of contributions from the world's second largest peatland, the Hudson Bay Lowlands (HBL), Canada, to peat-climate-C-dynamics is constrained by the paucity of dated peat records and regional C-data. Here we examine HBL peatland development in relation to Holocene C-dynamics. We show that peat initiation in the HBL is tightly coupled with glacial isostatic adjustment (GIA) through most of the record, and occurred within suitable climatic conditions for peatland development. HBL peatlands initiated most intensively in the mid-Holocene, when GIA was most rapid and climate was cooler and drier. As the peat mass developed, we estimate that the HBL potentially released 1-7 Tg CH4 per year during the late Holocene. Our results indicate that the HBL currently stores a C-pool of ~30 Pg C and provide support for a peatland-derived CH4 contribution to the late Holocene atmosphere.

  10. Short organic carbon turnover time and narrow 14C age spectra in early Holocene wetland paleosols

    NASA Astrophysics Data System (ADS)

    Vetter, Lael; Rosenheim, Brad E.; Fernandez, Alvaro; Törnqvist, Torbjörn E.

    2017-01-01

    Paleosols contain information about the rates of soil organic carbon turnover when the soil was actively forming. However, this temporal information is often difficult to interpret without tight stratigraphic control on the age of the paleosol. Here we apply ramped pyrolysis/oxidation (Ramped PyrOx) 14C analyses to evaluate age spectra of transgressive early Holocene paleosols from the Mississippi Delta in southeastern Louisiana, USA. We find 14C age spectra from soil organic matter (SOM) in both paleosols and overlying basal peats that represent variability in age that is close to, or only slightly greater than, analytical uncertainty of 14C measurements, despite different sources of carbon with likely disparate ages. Such age spectra have not previously been observed in the sedimentary record. Here they indicate vigorous soil carbon turnover prior to burial, which homogenized 14C ages within SOM across the entire thermochemical spectrum. The weighted bulk 14C ages from Ramped PyrOx of paleosols and overlying peats are identical within analytical and process-associated uncertainty, and corroborate 14C ages from charcoal fragments and plant macrofossils from the overlying peat. The youngest ages from Ramped PyrOx age spectra may also potentially be applied as chronometers for stratigraphic burial ages. Our results suggest rapid turnover (≪300 years) of carbon in these soils relative to input of allochthonous carbon, indicating that the 14C age of different soil components is decoupled from thermochemical stability and instead reflects vigorous turnover processes. The concurrence of paleosol and peat 14C ages also suggests that pedogenic processes were linked with the development of coastal marshes, and that the priming effect potentially masked the signal of allochthonous carbon inputs during sea level rise.

  11. 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.

  12. 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.

  13. 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.

  14. Natural variability in ocean carbon chemistry on the California margin during the Holocene

    NASA Astrophysics Data System (ADS)

    Chrystal, A. E.; Paytan, A.

    2011-12-01

    Limited information is available to understand the potential magnitude and consequences of ocean acidification in temperate coastal environments. Some regions, such as the California margin, are influenced both by terrestrial runoff and by a strong upwelling system, which brings nutrient-rich, but corrosive, low-pH and low [CO_{3}^{2-}] water to the surface. Coastal upwelling areas may therefore be particularly sensitive to additional carbon input due to anthropogenic carbon emissions. Regions with strong coastal upwelling are among the most biologically productive marine sites in the world and are fundamental to the integrity of oceanic food webs and economic fisheries. Thus, it is important that we understand how anthropogenic acidification will affect these coastal ecosystems. A critical step in understanding the influence of reduced pH and [CO_{3}^{2-}] on coastal environments is to quantify the natural variability in ocean pH over long timescales (thousands of years) and to constrain the components that impact carbon chemistry in coastal systems; these include terrestrial freshwater input, upwelling, circulation changes, productivity, and anthropogenic CO_{2} flux. We propose to create a baseline against which to compare anthropogenic change via an integrative study of these variables over the past 10,000 years (Holocene). As a preliminary step, we will measure Mg/Ca, B/Ca and U/Ca in benthic foraminifera from the Santa Monica Basin (ODP 1015) and compare these with existing radio-carbon measurements and high-resolution δ^{18}O and δ^{13}C records from the same site to evaluate pH changes in the context of variability in salinity, upwelling and circulation changes.

  15. 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

  16. Aridification of the Indian Subcontinent during the Holocene: Implications for Landscape Evolution, Sedimentation, Carbon Cycle, and Human Civilizations

    DTIC Science & Technology

    2012-06-01

    whole or in part is permitted for any purpose of the United States Government. This thesis should be cited as: Camilo Ponton, 2012. Holocene...K. Fournillier, E. L. Leithold, and L. B. Childress. 2010. Resolving organic carbon of differing diagenetic/catagenetic states in riverine and...Proceedings of the National Academy of Sciences of the United States of America 107 (15):6748-6752. Chao, W. C. 2000. Multiple quasi equilibria of the

  17. 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.

  18. 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

  19. 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

  20. 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.

  1. Lacustrine varve formation through time

    USGS Publications Warehouse

    Anderson, R.Y.; Dean, W.E.

    1988-01-01

    Studies using sediment traps in lakes reveal that the seasonal flux of sediment regulates both the composition and timing of deposition of materials that reach the bottoms of lakes. If the bottom waters of a lake are partly or totally anoxic, the seasonally deposited materials are preserved as annual groupings of laminae (varves). Common components that form individual laminae consist of allochthonous clastic material derived from the drainage basin, precipitated carbonate minerals, diatom frustules, iron-rich and manganese-rich flocs, autochthonous organic detritus, and autochthonous and allochthonous materials resuspended from the bottom. The "style" of varving has changed over geologic time, reflecting changes in biologic evolution and types of materials available. Precipitated iron-rich laminations were common in the middle Precambrian. Graded sets of clastic organic laminations persisted through the Precambrian, prior to the evolution of bioturbating benthic organisms. Glaciolacustrine varves appear to have retained their distinctive character through time. Carbonate-rich varves occurred sporadically in the Precambrian and Phanerozoic. With the exception of diatoms, major components of modern lacustrine varves were present through the Paleozoic and Mesozoic, and yet varves are rare in strata of these ages, and may have accumulated in marine to brackish-water environments. Diatoms were introduced into lacustrine systems in Early Tertiary time and are common components of varves from then on. Diatom laminae, combined with a greater chance for geologic preservation of younger lake deposits, have increased the number of geologically young occurrences of varved sediments. However, seasonal associations of modern varve components, and the processes they represent, are present in ancient deposits and provide clues to the interpretation of ancient environments. ?? 1988.

  2. Organic Carbon Transport through Holocene and Pleistocene Sediment from Southeast Asia: Implications for Arsenic Mobilization

    NASA Astrophysics Data System (ADS)

    Stanimirova, R.; Mailloux, B. J.; Sun, J.; Bostick, B. C.; Mulvihill, C.; van Geen, A.; Mihajlov, I.; Magyar, J. S.; Ahmed, K.; Choudhury, I.; Stute, M.

    2013-12-01

    The oxidation of organic carbon coupled to the reduction of Fe (hydr)oxides is causing the mobilization of arsenic from sediment to groundwater in Southeast Asia and has resulted in a public health crisis. Recent results indicate that advected organic carbon could be a primary source of the reactive OC to the subsurface. Little is known about OC transport through aquifer sediments and its impact on aquifer geochemistry. The goal of this work was to perform column experiments using intact sediments from Holocene and Pleistocene drinking water aquifers of Southeast Asia in which unreactive OC, Eliot soil Humic Acid (ESHA), was flushed through the column and effluent geochemistry was monitored. In field-run columns flushed with anaerobic site groundwater and no ESHA, As, Fe, and Mn aqueous concentrations remained constant or decreased with flushing, indicating that redox reactions were not occurring within the columns and these elements appear to just be slowly mobilized and flushed from the sediment. In anaerobic laboratory run columns with ESHA a large range of redox responses occurred. In site F sediment complete breakthrough of ESHA occurred within 5 PV and Mn reduction occurred during the injection of ESHA, but no response of Fe and As occurred, indicating flushing of these elements. In site K sediment, complete breakthrough of ESHA occurred in 20 PV and redox reactions occurred with increases in concentration of As, Fe, and Mn, indicating that the in situ microbial population was stimulated. In Cambodian Pleistocene sediment ESHA breakthrough occurred with bromide breakthrough and no redox reactions were observed and only flushing occurred. Fluorescence analysis indicates that the ESHA mobilized in situ sediment OC during initial breakthrough in each column. These results indicate that OC can be transported through Bangladesh sediments, but that more interactions between ESHA and the sediment result in more redox reactions and As mobilization and it is this

  3. 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.

  4. 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

  5. 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.

  6. Holocene Age Methane and Carbon Dioxide Dominate Northern Alaska Thaw Lake Emissions

    NASA Astrophysics Data System (ADS)

    Elder, C.; Townsend-Small, A.; Hinkel, K. M.; Xu, X.; Czimczik, C. I.

    2015-12-01

    Lakes expanding into ice-rich permafrost can rapidly re-introduce large quantities of ancient organic carbon (C) to the atmosphere as carbon dioxide (CO2) or the more powerful greenhouse gas methane (CH4). Quantifying the sources of greenhouse gas emissions from arctic lakes will reduce large uncertainties in the magnitude and timing of the C-climate feedback from the Arctic, and thus trajectories of climate change. This work provides the first regional assessment of integrated whole-lake radiocarbon (14C) ages of dissolved CH4 and CO2 as a proxy for C emission sources in northern Alaska. We collected water samples from below ice along two 170 km north-south transects on the Arctic Coastal Plain (ACP) of Alaska in April 2012 and 2013. These lakes represent a network monitored by the US-NSF funded project, Circum-Arctic Lakes Observation Network (CALON), http://www.arcticlakes.org/. Dissolved CH4 and CO2 were extracted and analyzed for their 14C content. The presence of winter ice on the surface of lakes obstructs the emission of CH4 and CO2 originating from the perennially thawed sub-lake sediments. The trapped gases are forced to mix, thus measured 14C ages are integrated signatures representing the whole-lake emissions. Dissolved CH4 and CO2 ages do not correlate with latitude, yet seem to be driven by surficial geology. Of nearly 150 14C measurements, below-ice dissolved CH4 is the oldest (around 2145 ± 15 14C YBP) in a lake residing on "peaty, sandy lowland" on the northern ACP near the town of Barrow. Modern CH4 and CO2 dominate emissions from "eolian sandy lowlands" in the interior of the ACP. Across all lakes, dissolved CH4 (avg. 836 14C YBP) is older than dissolved CO2 (avg. 480 14C YBP) by a regional average of ca. 360 14C YBP. Results from this study indicate that decomposing Holocene-age organic material is the primary source of CH4 and CO2 emissions from the Alaskan ACP. This baseline dataset provides the foundation for future regional lake monitoring

  7. Quantification of Aridity Changes During the Late Holocene From the Carbon Isotope Composition of Fossil Charcoal

    NASA Astrophysics Data System (ADS)

    Voltas, J.; Ferrio, P.; Espinar, C.

    2006-12-01

    Climate dynamics during the Holocene can be characterized by a variety of proxies that provide information at a different scale and accuracy. In seasonally dry climates, the carbon isotope composition of tree-rings has been related to variables such as rainfall or evaporative demand. Extensive tree-ring records, however, are not always available owing to factors such as human-induced deforestation or harsh conditions for most long-lived trees to thrive. An illustrative example concerns the Mediterranean region. In this work, we aim to show that the original climate signal of wood δ13C is preserved in fossil charcoal (recovered from archaeological sites), and thus can be used to quantify past changes in water availability. We present two case studies on climate reconstruction at the temporal and spatial dimensions from Eastern Spain. We first describe, for a restricted area, the evolution of aridity during the last 4000 years using charcoals ranging from the Bronze Age (ca. 2100 BCE) to the Modern Age (XVIII ca. CE) (1). Further, we characterize, for a larger region, the transition between Bronze and Iron Ages, the so called Cold Iron Age Epoch (ca. 700-500 BCE), using remains from a set of contemporary sites (2). Climatic inferences were obtained after calibration of quantitative models predicting rainfall from wood δ13C. For case (1), charcoals of Mediterranean trees (Aleppo pine, several oaks, mastic) were analysed for δ13C. We found similar trends for the time course of changes in this parameter regardless of the species. Estimated rainfall in the past was 25% to 40% higher than present, with phases of greater water availability (1500-900 BCE; 300 BCE-300 CE) alternating with drier periods (900-300 BCE; 900-1100 CE). For case (2), we combined data from Aleppo pine and Holm oak, which exhibit differential responses to changes in climate seasonality, to provide information on intra-annual rainfall dynamics. The divergence in δ13C between pines and oaks can be

  8. 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.

  9. 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.

  10. 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

  11. Holocene Vegetation and Climate Shifts from Sutherland Fen, Black Rock Forest, New York - Plant Macrofossils, Charcoal, and Carbon

    NASA Astrophysics Data System (ADS)

    Peteet, D. M.; Guilderson, T.

    2008-12-01

    Sutherland Fen formed about 12,600 C-14 years ago (15,000 calendar years), the same time as adjacent Sutherland Pond and regional deglaciation. High-resolution (2 cm) analysis of the 3.2 m fen core indicates three major macrofossils zones indicative of climate shifts. These climate shifts were defined over fifty years ago through pollen stratigraphy of the regional northeastern US, but macrofossils provide new details concerning hydrological and ecological shifts. The lowest (SUB-1) dated to the late-glacial, is indicative of a shallow pond characterized by Najas, Nuphar, and Potamogeton seeds and containing Salix (willow) buds, a Rubus (berry) seed, and Picea glauca (white spruce) needles and sterigmata from the surrounding upland. Sedimention rates are highest in this boreal environmental zone. The overlying zone (SUB-2) beginning at 11,500 years ago (Holocene) indicates a continuing pond environment with aquatics such as Najas, Nuphar, and Brasenia, but Picea disappears and Pinus strobus (white pine) dominates the lower section of the zone. A warmer, drier climate produces sustained charcoal in the record at the Holocene boundary. Pinus strobus needles and seeds subsequently disappear and are replaced from 9000 to 7500 years ago by Pinus rigida (pitch pine), Betula populifolia/papyrifera (grey/paper birch), and emergent wetland plants such as Decodon, Cladium, and Cephalanthus, as well as Dulichium, Eleocharis, and Carex, suggesting a shallowing pond and a drier climate. Chara oospores indicate probably groundwater influx into the fen. About 4000 years ago, charcoal again is present. In the subsequent late Holocene a more acidic, moist, fen environment is characterized by Sphagnum, Rubus, Hypericum, Viola, Chamaedaphne, and Carex, though Brasenia and Potamogeton (pond indicators) are occasionally present. The continued presence of Sphagnum led to high carbon accumulation because of less decomposition. This increase in Sphagnum in recent millennia with aquatics

  12. 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

  13. 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

  14. 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.

  15. Holocene Millennial-scale Surface and Bottom Water Variability, Feni Drift, NE Atlantic Ocean: Carbonate Record and Bottom Current Strength

    NASA Astrophysics Data System (ADS)

    Richter, T. O.; Lassen, S. J.; de Stigter, H. C.; van Weering, T. C. E.; de Haas, H.

    North Atlantic sediment drifts provide expanded sedimentary records, which can be directly linked to bottom current activity. At Feni Drift (core ENAM9606, 56N 14W, 2543 m water depth), Ca count rates obtained by non-destructive XRF logging with the CORTEX corescanner trace biogenic calcium carbonate, whereas grainsize data (terrigenous sortable silt mean size) indicate bottom current variability. Both records show cyclic fluctuations throughout the entire Holocene with generally sharper min- ima and broader, more variable maxima. Spectral analysis reveals dominant peaks at 1/1,500a, with additional frequencies at 1/830a and 1/500a. A comparison of the Ca record with residual 14C data suggests that part of its variability might be related to solar forcing. The amplitude of 1.5ky cycles increases in the upper Holocene, and the sortable silt record implies a general slight decrease in bottom current speed and especially more pronounced minima. This broadly coincides with the onset of Neoglaciation, characterized by renewed glacier advances in the northern hemisphere and slight climatic deterioration.

  16. 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.

  17. 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.

  18. 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

  19. 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

  20. Combining Carbon Accumulation and Hydroclimatic Variations Throughout the Holocene: Can we Detect a Climate Signal from Northeastern Canadian Boreal Peatlands ?

    NASA Astrophysics Data System (ADS)

    Garneau, M.; van Bellen, S.; Magnan, G.; Lamarre, A.; Thibault, A.

    2013-12-01

    In northeastern Canada, data on peatland development, carbon accumulation and hydroclimatic variations show changes throughout the Holocene period. Regional comparisons following south-north gradients from both western and eastern parts of the Québec province are used to evaluate the long-term processes influencing the peatlands carbon dynamics in this region of Canada. Seven different ecoclimatic subregions of the boreal biome distributed along two main geographic gradients (continental and maritime) have been characterized in terms of carbon accumulation and hydroclimatic variations. Results show an important maritime influence in terms of temperature (in particular through sea ice cover duration), relative humidity and wind exposure on peatland dynamics. In all regions, except in depressed areas, forests have first colonized the land following ice retreat and withdrawal of the marine waters. Peat accumulation has been initiated by paludification from 5500 cal BP mainly. Results show variations in the timing of trophic status transitions but there is a relative synchronic decrease in peat C accumulation in all regions from the Neoglacial cooling period. Cooler climatic conditions seem responsible for a decrease in biomass productivity and a rise in bog surface wetness due to lower evapotranspiration. Changes in hydroclimatic conditions may also have favored the development or expansion of pools and flarks at the peatland surfaces. These allogenic conditions also mediated by internal (autogenic) processes have been important factors controlling the long-term carbon dynamics of the studied peatlands. Impacts on carbon dioxide uptake and methane emissions through time require further considerations to evaluate the response of these systems to climate change.

  1. Weathering, mineralogical evolution and soil organic matter along a Holocene soil toposequence developed on carbonate-rich materials

    NASA Astrophysics Data System (ADS)

    Egli, Markus; Merkli, Christian; Sartori, Giacomo; Mirabella, Aldo; Plötze, Michael

    2008-05-01

    A toposequence of Holocene soils located between 1100-2400 m asl in the Italian Alps served as the basis for the following analyses: the weathering of limestone and dolomite, the calculation of mass balances, understanding the formation of pedogenic Fe and Al, the determination of soil mineral and clay mineral reactions and transformation and the measurement of accumulation and stabilisation mechanisms of soil organic matter. Leaching of carbonates is most intense at the lower elevations, although calcite and dolomite have a higher solubility at low temperatures. The pCO 2 in the soil is higher at lower elevations and weathering is driven mainly by carbonic acids. At higher elevations, organic acids appear to determine the mineral transformations and weathering reactions to a greater extent. This suggests that two very different weathering regimes (carbonic and organic acid weathering) exist along the toposequence. The transformation of mica into vermiculite is the main process in both the clay and fine-earth fraction. Weathering of silicate minerals started even before the carbonates had been completely removed from the soils. The transformation mechanisms of silicate minerals in the A and O horizon at higher elevations was at least as intensive as that at the climatically warmer sites. The neoformation of pedogenetic clays at climatically cooler sites was slightly greater than that at the warmer sites. However, the formation rate of secondary Fe and Al phases was more pronounced at lower elevation, which means that this process seemed to be driven dominantly by carbonic acid (weathering of primary minerals). Soil organic matter (SOM) abundance in the mineral soil is nearly 15 kg/m 2 at all sites and, surprisingly, no climate-driven effect could be detected. In general, the preservation and stabilisation of SOM was due to poorly crystalline Al and Fe phases and vermiculite, regardless of some variations in the composition of the parent material (varying calcite

  2. 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.

  3. 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.

  4. 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.

  5. Carbon Storage, Leaf Wax Abundances, D/H ratios, and Moss Diversity Linked to Increased Moisture in Early Holocene Arctic Alaska Records

    NASA Astrophysics Data System (ADS)

    Peteet, D. M.; Nichols, J. E.; Fedio, C.; Gemma, M.; Mann, D. H.

    2013-12-01

    Lake of the Pleistocene (LOP) is a drained lake basin with a lithostratigraphic sequence ranging from 50,000 to 5000 yr BP (Mann et al., 2002). Previous sedimentological and palynological investigations documented the shifts in moisture ranging from the dry, cold conditions during the glacial maximum; to warm, moist conditions between 15,000 and 12,800 cal yr BP; to maximal moisture during the early Holocene. Our analysis of the carbon accumulation rate and plant macrofossils in the lake sediments, primarily composed of bryophyte remains, indicate an increase in carbon accumulation rate from the Pleistocene to the Holocene, with a maximum in carbon accumulation rate between 10-9000 cal years ago. Enriched D/H ratios of terrestrial plant biomarkers during this interval indicate warm, moist conditions in the early Holocene. Distributions of leaf wax alkanes indicate reduced input by shallow water macrophytes during this period, supporting the interpretation of increased lake level. Our dates support regional and global assessments that have shown maximal C storage in wetlands and shallow lakes throughout the Arctic in a warm, wetter climate.

  6. 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

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

    NASA Astrophysics Data System (ADS)

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

    2011-01-01

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

  8. [Carbon accumulation in soils of forest and bog ecosystems of southern Valdai in the Holocene].

    PubMed

    Minaeva, T Iu; Trofimov, S Ia; Chichagova, O A; Dorofeeva, E I; Sirin, A A; Glushkov, I V; Mikhaĭlov, I D; Kromer, B

    2008-01-01

    Carbon stocks and accumulation rates in humus and peat horizons of the contiguous soil series of forest and bog ecosystems have been studied in the Central Forest State Biosphere Reserve (CFSBR, Tver region). Upland soil types (soddy podzolic, brown, and white podzolic) have been compared to waterlogged (peaty gley podzolic and peaty gley) and bog soils differing in trophic status, including those of raised, transitional, and lowland bogs. The results show that carbon stocks in mineral soils are many times smaller than in waterlogged soils and an order of magnitude smaller than in bog soils. Mineral and bog soils are characterized by similar rates of carbon accumulation averaged over the entire period of their existence. The highest rate of carbon accumulation has been noted for the soils of waterlogged habitats, although this process may be periodically disturbed by fires and other stress influences.

  9. Numerical Ages of Holocene Tributary Debris Fans Inferred from Dissolution Pitting on Carbonate Boulders in the Grand Canyon of Arizona

    NASA Astrophysics Data System (ADS)

    Hereford, Richard; Thompson, Kathryn S.; Burke, Kelly J.

    1998-09-01

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

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

    USGS Publications Warehouse

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

    1998-01-01

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

  11. Allogenic and Autogenic Controls on Carbon Uptake and Release since Mid-Holocene Peat Initiation in the Hudson Bay Lowlands, Canada

    NASA Astrophysics Data System (ADS)

    Packalen, M.; Finkelstein, S. A.; McLaughlin, J.

    2014-12-01

    Current interglacial development of a nearly continuous peat cover in the Hudson Bay Lowlands, Canada has resulted in a globally significant carbon (C) reservoir. Yet, the fate of peatland C stores and related climate system feedbacks remain uncertain under scenarios of a changing climate and enhanced anthropogenic pressure. Here, we examine peatland development in the HBL in relation to Holocene C-dynamics, together with records of paleo- and modern climate, glacial isostatic adjustment (GIA) and paleoenvironmental change. We report that the timing of peat initiation is tightly coupled with GIA in the HBL, while peatland age, trophic status, and paleoclimate contribute to explaining some of the temporal variation in C accumulation rates (CARs). Our results show that CARs are greatest from younger, minerotrophic peatlands and in association with warmer Holocene climates. Peat initiation rates and CARs in the HBL were greatest during the mid-Holocene; however, model evidence indicates that two-thirds of the HBL C pool is stored in peat of late Holocene age, owing to long-term peatland expansion and development. Since mid-Holocene peat initiation, the HBL has been a net C-sink and currently stores ~ 30 Pg C, with spatial climate patterns accounting for up to half of the C-mass distribution. Yet, the HBL has also been a modest C-source since peat initiation, with 85% of the losses occurring during the late Holocene. Our results indicate that the HBL may have been a potential terrestrial source of 1 - 7 Tg CH4 y-1 to the late Holocene atmosphere, due to the decay of previously accrued peat, under wetter conditions than present, and from a landscape occupied by an abundance of minerotrophic peatlands. While the peatlands of the HBL may continue to function as a globally significant C reservoir, conservative climate scenarios predict a warmer and wetter HBL in the next century that may lie outside the range of past climate variability. Disproportionate hydroclimatic

  12. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

    Mixed carbonate-siliciclastic lagoons of barrier reefs provide great potential as sedimentary archives focusing on paleoenvironmental and paleoclimatic changes as well as on event deposition. Sediment sources include lagoonal carbonate production, the marginal reef and the volcanic hinterland. Mixed carbonate-siliciclastic continent-attached coastal lagoons have been intensively studied, however, their isolated oceanic counterparts have been widely disregarded. Here, we present a new model of Holocene sediment dynamics in the barrier-reef lagoon of Bora Bora based on sedimentological, paleontological, geochronological and geochemical data. The lagoonal succession started with a Pleistocene soil representing the Lowstand Systems Tract. As the rising Holocene sea inundated the carbonate platform, peat accumulated locally 10,650-9400 years BP. Mixed carbonate-siliciclastic sedimentation started ca. 8700-5500 years BP and represents the Transgressive Systems Tract. During that time, sediments were characterized by relatively coarse grain size and contained high amounts of terrestrial material from the volcanic hinterland as well as carbonate sediments mainly produced within the lagoon. Siliciclastic content decreases throughout the Holocene. After the rising sea had reached its modern level, sand aprons formed between reef crest and lagoon creating transport pathways for reef-derived material leading to carbonate-dominated sedimentation ca. 6000-3000 years BP during the Highstand Systems Tract. However, mainly fine material was transported and accumulated in the lagoon while coarser grains were retained on the prograding sand apron. From ca. 4500-500 years BP, significant variations in grain-size, total organic carbon as indicator for primary productivity, Ca and Cl element intensities as qualitative indicators for carbonate availability and lagoonal salinity are seen. Such patterns could indicate event (re-)deposition and correlate with contemporaneous event deposits

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

    USGS Publications Warehouse

    Markewich, H. W.

    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.

  15. 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.

  16. 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.

  17. A High-Resolution Carbonate Record from Holocene IMAGES core MD992286, Skagerrak

    NASA Astrophysics Data System (ADS)

    Gyllencreutz, R.

    2003-04-01

    Marine sediments in the 32.4 m long piston core MD99-2286, provides a continuous and detailed palaeoceanographic and palaeoenvironmenatal record of the last 12 000 years in the Skagerrak. The investigated area is characterised by high sedimentation rates and intense water mass mixing, as a branch of the North Atlantic Current turns anti-clockwise, slows down and becomes mixed with other waters to form the Norwegian Coastal Current. Present-day SSTs in Skagerrak are strongly linked to the NAO-index. Carbonate content in core MD99-2286 was measured using coulometry with 5-cm resolution. The carbonate record shows a steep rise from 9 to 15 % carbonate from 10 ka to 8 ka, and then a gradual decreasing trend down to about 12 % around 4 500 cal y BP. The timing of the peak at 8 ka coincides with the opening of the English Channel. The most likely processes controlling carbonate content in the Skagerrak sediments are redeposition of older carbonate particles (mainly controlled by the Jutland Current) and primary productivity competing with dilution by terrigenous material. The carbonate record from MD99-2286 correlates with a palaeotemperature reconstruction based on oxygen isotopes from a speleothem in northern Norway. The correlation is positive in the interval 9 ka to about 5 ka, and negative from 5 ka to present. The timing of the shift in correlation matches the establishment of the modern circulation pattern, which is marked by a hydrographic shift at 5.5 ka, interpreted from grain size and biostratigraphical data in a core from Skagen. This shift is manifested by an increase in the Jutland Current and stronger inflow of saline North Sea water to Skagerrak and Kattegat. The CALYPSO-corer used for core MD99-2286 is believed to disturb the topmost sediments in cores. Therefore, a 2.5 m long gravity core, Sk000209-2, was retrieved from a nearby location in order to get full recovery of the surface sediments. Age control in core MD99-2286 is obtained from 20 AMS C-14

  18. 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

  19. Diffuse Spectral Reflectance Records from the Northeast Pacific Oxygen Minimum Zone: Evidence for Rapid Shifts in Carbonate and Organic Carbon throughout the Holocene

    NASA Astrophysics Data System (ADS)

    Delvisico, J. G.; OConnell, S.; Ortiz, J. D.

    2002-05-01

    Sediment cores collected within the Oxygen Minimum Zone (O2 < 5 μ m/kg; 400-1300 m depth) from off the coast of Baja California at 25oN during a 1999 R/V Melville cruise present the most southerly evidence of centennial to decadal scale climate instability yet observed on the open Northeast Pacific margin. The development of high resolution proxies through statistical analysis of extensive Diffuse Spectral Reflectance (DSR) data sets provides the framework for gauging rapid shifts in carbonate and organic carbon within the spatial/temporal bounds of the Oxygen Minimum Zone from the last deglaciation to the Holocene (15 to 0 Ka). These shifts are potentially controlled by changes in local primary production or sub-surface water mass ventilation, however the relative importance of each process over this time scale is not well understood. This study focuses on five 10 to 14 m piston cores (MV 01 PC12-16) collected within the Soledad Basin, desirable for its high sedimentation rates (100-120cm/kyr) and its 200 m sill depth. We maintain the hypothesis that variations in carbonate and organic carbon seen through the Diffuse Spectral Reflectance (DSR) will preferentially show the effects of local production on the spatial/temporal extent of the Oxygen Minimum Zone due to the circulation restrictions imposed on the basin by its shallow sill depth. The summer's work involved compiling a composite proxy record of variations in organic carbon through R-mode factor analysis of the Diffuse Spectral Reflectance signal, which was then further constrained through coulometry to provide confidence points for reflectance-derived proxy values. Through the compilation of the five piston core records, a continuous, high frequency climatic proxy record of changes in productivity was constructed over the past 15 Ka. Organic carbon shifts within the Soledad record also contain a periodicity within the time scale bounds of the present day Pacific Decadal Oscillation (20-50 year quasi

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

    PubMed

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

    2007-08-01

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

  1. 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.

  2. Miocene lacustrine algal reefs—southwestern Snake River Plain, Idaho

    NASA Astrophysics Data System (ADS)

    Straccia, Frances G.; Wilkinson, Bruce H.; Smith, Gerald R.

    1990-04-01

    The Hot Spring limestone is a shallow-water algal carbonate within a late Tertiary transgressive lacustrine sequence exposed in the southwestern Snake River Plain. This 5 m thick lensoid sequence crops out over an 80 km 2 area that closely approximates original areal extent of nearshore carbonate accumulation. Reefal bodies consist of closely packed algal cylinders, several decimeters in height, each of which includes a dense laminated carbonate wall surrounding porous digitate carbonate that radiates outward and upward from one or more hollow tubes. These coalesce upsection into separate vertical columns several meters in diameter. Moderately well-sorted terrigenous and molluscan debris deposited between columns during growth indicates these structures were resistant to wave erosion and, therefore, were true reefs. Thick rings of littoral carbonate surrounding the upper walls of each column record the final stages of reef development. Structural attributes exhibited by these Miocene carbonate bodies are also common to a number of Tertiary and Quaternary algal buildups reported from other lacustrine settings. Although features within the Hot Spring limestone are complex in gross morphology and structural detail, both columnar reefs and algal cylinders display little variation in size, shape, or internal structure between areas of varying water depth and wave energy, thus reflecting the importance of biological processes as well as physical processes during reef development.

  3. 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.

  4. 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

  5. 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.

  6. 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.

  7. 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

  8. 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

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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

  14. 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.

  15. 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.

  16. 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.

  17. Lower Cretaceous lacustrine deposits and paleosol development

    SciTech Connect

    Mantzios, C.; Vondra, C.F.

    1987-05-01

    The Little Sheep Mudstone Member of the Lower Cretaceous Cloverly Formation in the Big Horn basin, Wyoming, is predominantly a montmorillonite-rich lacustrine deposit. It is informally subdivided into lower and upper units. The lower unit is a playa-lake deposit rich in bentonite derived from the alteration of volcanic ash which had its origin to the west. Horizons of silcretes and septarian nodules are common. The latter show irregular lenticular cracks and are filled with coarse calcite and barite crystals. They formed by desiccation of a clay-gel during dry periods. Silcretes are diagenetic products that formed due to the lowering of silica solubility along with decreasing of the pH value. Desiccation cracks on the playa surface were filled with chalcedony which later underwent replacement by calcite. The upper unit is a perennial saline lake deposit similar to that accumulating in Lake Magadi of the Eastern Rift Valley, Kenya, Chert nodules covered with calcium carbonate form stratigraphically persistent horizons. This chert is the product of the magadiite-kenyaite-chert transformation of Hay. Lenticular devitrified tuffs occurring at various stratigraphic positions up to 3 m thick were deposited in depressions or swales. Locally the tuffs show evidence of mass movement. Pedogenic features in both units indicate paleosol development. Tree trunks, plant roots, burrows, clay-rich zones, and organic-rich A and more iron-rich B master horizons are recognized. These paleosols resemble modern-day Vertisols. The lower unit is not as extensive areally as the upper unit which is present throughout the Big Horn basin, indicating that extensive lakes occurred during the Early Cretaceous in the Sevier foreland basin.

  18. 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

  19. 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

  20. 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

  1. 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

  2. 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

  3. Response of vegetation and carbon accumulation to changes in precipitation and water table depths in two bogs during the Holocene: a modelling exercise

    NASA Astrophysics Data System (ADS)

    Quillet, A.; Garneau, M.; van Bellen, S.; Frolking, S. E.; Tuittila, E.

    2013-12-01

    To assess the influence of hydrological changes on northern peatland ecosystems, we analysed the response of the Holocene Peat Model (HPM, Frolking et al. 2010), designed to simulate peatland development at millennial timescale, to two hydrological settings, based on precipitation and water table depths reconstructions. The studied sites are two open ombrotrophic peatlands located in the James Bay Lowlands in Northeastern Canada. For both sites, two simulations were realised: one based on a precipitation reconstruction from pollen data, used as input in the model, and a second using a water table depth reconstruction derived from testate amoebae to apply a water table forcing on the model. Simulated variations in carbon accumulation rates (CAR) and vegetation composition were analysed against the palaeoecological datasets. Results in CAR in both sites and hydrological settings showed periods of net carbon loss, which coincided with fluctuations in observed CAR, though they cannot be traced in palaeoecological datasets. The comparison between plant macrofossils records and simulated vegetation distributions highlighted differences between precipitation and water table depth driven simulations that can be used to distinguish the origin of vegetation shifts. The methodology used could thus be useful in paleoecological studies when two or more proxies are available.

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

    NASA Astrophysics Data System (ADS)

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

    2017-02-01

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

  5. Holocene ice-wedge polygon development in northern Yukon permafrost peatlands (Canada)

    NASA Astrophysics Data System (ADS)

    Fritz, Michael; Wolter, Juliane; Rudaya, Natalia; Palagushkina, Olga; Nazarova, Larisa; Obu, Jaroslav; Rethemeyer, Janet; Lantuit, Hugues; Wetterich, Sebastian

    2016-09-01

    Ice-wedge polygon (IWP) peatlands in the Arctic and Subarctic are extremely vulnerable to climatic and environmental change. We present the results of a multidisciplinary paleoenvironmental study on IWPs in the northern Yukon, Canada. High-resolution laboratory analyses were carried out on a permafrost core and the overlying seasonally thawed (active) layer, from an IWP located in a drained lake basin on Herschel Island. In relation to 14 Accelerator Mass Spectrometry (AMS) radiocarbon dates spanning the last 5000 years, we report sedimentary data including grain size distribution and biogeochemical parameters (organic carbon, nitrogen, C/N ratio, δ13C), stable water isotopes (δ18O, δD), as well as fossil pollen, plant macrofossil and diatom assemblages. Three sediment units (SUs) correspond to the main stages of deposition (1) in a thermokarst lake (SU1: 4950 to 3950 cal yrs BP), (2) during transition from lacustrine to palustrine conditions after lake drainage (SU2: 3950 to 3120 cal yrs BP), and (3) in palustrine conditions of the IWP field that developed after drainage (SU3: 3120 cal yrs BP to 2012 CE). The lacustrine phase (pre 3950 cal yrs BP) is characterized by planktonic-benthic and pioneer diatom species indicating circumneutral waters, and very few plant macrofossils. The pollen record has captured a regional signal of relatively stable vegetation composition and climate for the lacustrine stage of the record until 3950 cal yrs BP. Palustrine conditions with benthic and acidophilic diatom species characterize the peaty shallow-water environments of the low-centered IWP. The transition from lacustrine to palustrine conditions was accompanied by acidification and rapid revegetation of the lake bottom within about 100 years. Since the palustrine phase we consider the pollen record as a local vegetation proxy dominated by the plant communities growing in the IWP. Ice-wedge cracking in water-saturated sediments started immediately after lake drainage at

  6. Impacts of shore expansion and catchment characteristics on lacustrine thermokarst records in permafrost lowlands, Alaska Arctic Coastal Plain

    USGS Publications Warehouse

    Lenz, Josefine; Jones, Benjamin M.; Wetterich, Sebastian; Tjallingii, Rik; Fritz, Michael; Arp, Christopher D.; Rudaya, Natalia; Grosse, Guido

    2016-01-01

    Arctic lowland landscapes have been modified by thermokarst lake processes throughout the Holocene. Thermokarst lakes form as a result of ice-rich permafrost degradation, and they may expand over time through thermal and mechanical shoreline erosion. We studied proximal and distal sedimentary records from a thermokarst lake located on the Arctic Coastal Plain of northern Alaska to reconstruct the impact of catchment dynamics and morphology on the lacustrine depositional environment and to quantify carbon accumulation in thermokarst lake sediments. Short cores were collected for analysis of pollen, sedimentological, and geochemical proxies. Radiocarbon and 210Pb/137Cs dating, as well as extrapolation of measured historic lake expansion rates, were applied to estimate a minimum lake age of ~1400 calendar years BP. The pollen record is in agreement with the young lake age as it does not include evidence of the “alder high” that occurred in the region ~4000 cal yr BP. The lake most likely initiated from a remnant pond in a drained thermokarst lake basin (DTLB) and deepened rapidly as evidenced by accumulation of laminated sediments. Increasing oxygenation of the water column as shown by higher Fe/Ti and Fe/S ratios in the sediment indicate shifts in ice regime with increasing water depth. More recently, the sediment source changed as the thermokarst lake expanded through lateral permafrost degradation, alternating from redeposited DTLB sediments, to increased amounts of sediment from eroding, older upland deposits, followed by a more balanced combination of both DTLB and upland sources. The characterizing shifts in sediment sources and depositional regimes in expanding thermokarst lakes were, therefore, archived in the thermokarst lake sedimentary record. This study also highlights the potential for Arctic lakes to recycle old carbon from thawing permafrost and thermokarst processes.

  7. 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.

  8. Holocene aridification of India

    USGS Publications Warehouse

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

    2012-01-01

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

  9. Turbidite systems of lacustrine rift basins: Examples from the Lake Kivu and Lake Albert rifts, East Africa

    NASA Astrophysics Data System (ADS)

    Zhang, Xuewei; Scholz, Christopher A.

    2015-07-01

    The Holocene turbidite systems of Lake Kivu and the Pliocene turbidite systems of Lake Albert in the East African Rift were examined using high-resolution 2-D and 3-D seismic reflection data and sediment core information. Based on investigations of seismic facies and lithofacies, several key turbidity-flow depositional elements were observed, including channels, overbank levees with sediment waves, and depositional lobes. Analyses of the sources of the recent and ancient turbidite systems in these two extensional basins suggest that flood-induced hyperpycnal flows are important triggers of turbidity currents in lacustrine rift basins. From source to sink, sediment dispersal, facies distribution, and depositional thickness of the turbidite systems are strongly influenced by rift topography. The Lake Kivu and Lake Albert rifts serve as excellent analogues for understanding the sedimentary patterns of lacustrine turbidites in extensional basins.

  10. 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.

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

    USGS Publications Warehouse

    Anderson, Lysanna; Wahl, David B.

    2016-01-01

    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.

  12. 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

  13. The impact of high tephra loading on late-Holocene carbon accumulation and vegetation succession in peatland communities

    NASA Astrophysics Data System (ADS)

    Hughes, P. D. M.; Mallon, G.; Brown, A.; Essex, H. J.; Stanford, J. D.; Hotes, S.

    2013-05-01

    Peatlands are major terrestrial stores of carbon (C) of importance to the global climate system. Recent studies have made progress in understanding the climatic controls on the C cycle; however, important interactions between volcanic deposition and peatland C stores remain to be addressed. This study uses a 3000-year peatland record from northern Japan to examine the interactions between carbon accumulation, vegetation community succession and volcanic ash deposition. Plant macrofossil and testate amoebae records are presented alongside records of total organic carbon, nitrogen and phosphorous. Age-depth models are developed using a Bayesian approach, with seven AMS radiocarbon dates and two identified historical tephras from Baitoushan (AD 969 (981 cal. BP)), and Hokkaido-Komagatake (AD 1640 (310 cal. BP)) volcanoes. Results show that moderate to high tephra loading can shift peatland plant communities from Sphagnum to monocotyledon domination. This vegetation change is associated with increased peat humification and reduced carbon accumulation. Where tephra deposition and reworking has occurred, the apparent rate of carbon accumulation can be halved while high tephra loading of the mire surface is sustained. Sphagnum species vary in their tolerance to tephra deposition. After each ash fall Sphagnum magellanicum disappeared from the plant macrofossil record, whereas Sphagnum papillosum showed apparent continuity of development through the 1856 (94 cal. BP) Ko-c1 tephra. High rates of carbon accumulation (peaking at >100 g m-2 yr-1), 2-3 times faster than the average for northern peatlands, were recorded in the Sphagnum communities that established after the cessation of tephra deposition and reworking from the AD 969 Baitoushan ash fall (B-Tm tephra). This peak in C accumulation was coincident with a radical shift in mire nutrient cycling most probably caused by the interaction of S. magellanicum with leachates from the underlying tephras. The phase of high C

  14. 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

  15. 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

  16. Extensive Holocene tropical peat and carbon accumulation within a subsiding intraforeland basin (Pastaza fan and Ucamara floodbasin), Peruvian Amazonia

    NASA Astrophysics Data System (ADS)

    Lähteenoja, Outi; Räsänen, Matti; Rojas Reátegui, Yully; Del Castillo, Dennis; Oinonen, Markku

    2010-05-01

    Several studies discuss the role of the Amazon Basin in the global carbon cycle, but the existence of extensive tropical peat deposits in lowland Amazonia has been suggested only recently. These up to 5.9 m thick peat deposits documented from a floodplain environment in Western Amazonia have accumulated at high rates (0.94-4.88 mm per year) acting as a strong carbon sink (Lähteenoja et al. 2009). The tectonic environment of Western Amazonia is a foreland belt formed during the uplift of the Andes Mountains as a result of shallow subduction and compressive foreland shortening (Räsänen et al. 1987, Dumont 1996). These foreland basins are characterized by high subsidence rates, up to 4-11 km of sediment deposits as well as river aggradation and avulsions (Räsänen et al. 1987). We studied peat and carbon accumulation in the Pastaza-Marañón intraforeland basin, which consists of the volcanogenic Pastaza alluvial fan and the Ucamara meandering river floodbasin. Together, they form the largest modern tropical system of fluvial aggradation, whose potential to accumulate peat is considerable. In 13 wetland sites detected in Landsat TM satellite images, we measured peat thickness along a transect and collected peat samples for determination of total organic content, carbon content, dry bulk density, AMS radiocarbon age and peat and carbon accumulation rates. According to the results, the Pastaza fan and the Ucamara floodbasin harbor thick peatlands, whose existence has not been previously discussed. All the study sites had either a continuous peat deposit over clastic sediments or a complex stratigraphy of successive layers of clastic sediments, clayey peat and pure peat. Thickness of these heterogeneous deposits varied from 0.20 to 7.5 m. Bulk density, total organic content and carbon content varied from 0.01 to 0.26 g/cm3, from 37 to 99 %, and from 19 to 59 %, respectively. The complex stratigraphies (encountered especially in the Ucamara floodbasin) are obviously

  17. Evolution of the siliciclastic-carbonate shelf system of the northern Kenyan coastal belt in response to Late Pleistocene-Holocene relative sea level changes

    NASA Astrophysics Data System (ADS)

    Accordi, Giovanni; Carbone, Federico

    2016-11-01

    A classification of depositional environments of the Lamu Archipelago is proposed based on a sedimentary facies analysis of unconsolidated and hard bottoms of the study area. The genesis of the siliciclastic-carbonate depositional pattern, typical of this East African region, is closely related both to the presence of a quartz-dominate Pleistocene riverine net-flooded during the Holocene sea level rise-and to the coeval development on the shallow shelf of a coral ecosystem producing vast skeletal sediments. The present facies pattern originates from the variable contribution in time and space of three sediment types: skeletal carbonate, quartz and palimpsest debris. The facies analysis allowed to distinguish 10 depositional facies and to differentiate them into three main types of substratum: soft bottom, reefal hard bottom and non-reefal hard bottom. These three types define both the loose facies typical of the channelized coastal belt and several facies of the shallow shelf. In the first, the amounts and textures of the stored sediment are strictly related to three major geomorphic types of substratum: sheltered mangal flat, shallow channel and deep channel. In the second and the third, a wide range of textures is related to coastal flats, benches, islets and emerging rocks. This modern facies pattern is implemented through a series of evolutionary phases: i-during the Last Interglacial Period, since isotope substage 5b, the shallow shelf-above -20 m-is permanently exposed for about 80 ka, with erosion, karstification and cuts of river channels through the shelf; ii-after the Last Glacial Maximum, when the sea level fell to about 110-115 m b.p.s.l. (below present sea level) at 18-17 ka BP, the sea level rose at -20 m for about 9 ka, flooding the shallow shelf area and gradually drowning the riverine net; iii-the maximum flooding of the coastal belt was reached at about 4.5 ka BP, when a gradual moisture reduction caused a decrease of siliciclastic sediment supply

  18. Remote Sensing and GIS Based Quantification of Thermokarst in North Siberian Yedoma Deposits and Implications for Holocene Landscape and Carbon Dynamics

    NASA Astrophysics Data System (ADS)

    Grosse, G.; Schirrmeister, L.; Romanovsky, V. E.

    2007-12-01

    Ice Complex deposits, also known as yedoma, are widely distributed in the North Siberian coastal lowlands. These Late Pleistocene terrestrial accumulations of up to several tens of meters in thickness are characterised by fine to medium grained clastic sediments, a very high ground ice content up to 90 vol-%, and mean total organic carbon (TOC) contents of 2-4%. Ground ice content includes large ice wedges and segregated ground ice in the form of small ice lenses and ice bands. Degradation of the Ice Complex in the form of thermokarst and thermo-erosion during the course of the Holocene produced massive landscape changes degenerating the existing accumulation plains to a complex system of thermokarst basins, lakes, and thermo-erosive valleys. Thermokarst triggered several feedback mechanisms that involve hydrology, vegetation and energy and matter fluxes. Thermokarst was a major agent in the partial transformation of the stored TOC into greenhouse gases. To evaluate the past and possible future impacts of thermokarst and related environmental feedbacks, the assessment of the current distribution and characteristics of Ice Complex deposits and thermokarst features is an important task. Field data, remote sensing, and terrain modelling within a geographical information system (GIS) are used to characterize Ice Complex deposits and thermokarst for a variety of sites in the Laptev Sea region, North Siberia. Field data consists of Ice Complex distribution, thickness, ice content, and TOC. Remote sensing was applied for the mapping of Ice Complex extent and distribution of thermokarst surface features in this area. Terrain modelling was used to quantify the volume of Ice Complex deposits based on digital elevation models, stratigraphical information, and satellite image mapping. Subsequently, terrain modelling was also applied to characterize thermokarst in this area. An assessment of the original, eroded, and remaining volume for the Ice Complex in the study area is

  19. 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

  20. 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.

  1. 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.

  2. Regional paleohydrologic and paleoclimatic settings of wetland/lacustrine depositional systems in the Morrison Formation (Upper Jurassic), Western Interior, USA

    USGS Publications Warehouse

    Dunagan, S.P.; Turner, C.E.

    2004-01-01

    During deposition of the Upper Jurassic Morrison Formation, water that originated as precipitation in uplands to the west of the Western Interior depositional basin infiltrated regional aquifers that underlay the basin. This regional groundwater system delivered water into the otherwise dry continental interior basin where it discharged to form two major wetland/lacustrine successions. A freshwater carbonate wetland/lacustrine succession formed in the distal reaches of the basin, where regional groundwater discharged into the Denver-Julesburg Basin, which was a smaller structural basin within the more extensive Western Interior depositional basin. An alkaline-saline wetland/lacustrine complex (Lake T'oo'dichi') formed farther upstream, where shallower aquifers discharged into the San Juan/Paradox Basin, which was another small structural basin in the Western Interior depositional basin. These were both wetlands in the sense that groundwater was the major source of water. Input from surface and meteoric water was limited. In both basins, lacustrine conditions developed during episodes of increased input of surface water. Inclusion of wetlands in our interpretation of what had previously been considered largely lacustrine systems has important implications for paleohydrology and paleoclimatology. The distal carbonate wetland/lacustrine deposits are well developed in the Morrison Formation of east-central Colorado, occupying a stratigraphic interval that is equivalent to the "lower" Morrison but extends into the "upper" Morrison Formation. Sedimentologic, paleontologic, and isotopic evidence indicate that regional groundwater discharge maintained shallow, hydrologically open, well oxygenated, perennial carbonate wetlands and lakes despite the semi-arid climate. Wetland deposits include charophyte-rich wackestone and green mudstone. Lacustrine episodes, in which surface water input was significant, were times of carbonate and siliciclastic deposition in scarce deltaic

  3. 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

  4. 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.

  5. Lacustrine lignin biomarker record reveals a severe drought during the late Younger Dryas in southern Taiwan

    NASA Astrophysics Data System (ADS)

    Ding, Xiaodong; Bao, Hongyan; Zheng, Liwei; Li, Dawei; Kao, Shuh-Ji

    2017-03-01

    The Younger Dryas (YD) event, which punctuated the last glacial-Holocene transition period and had a profound impact on global climate, is the most well studied millennial-scale climate event although the triggering mechanism remains debate. Weakened Asian summer monsoon during the YD is recorded in oxygen isotopes of stalagmite from Mainland China. However, lacustrine climate record of the YD event has not been reported from the subtropical land-ocean boundary of the Asian continent near the Pacific warm pool. We provide a lignin biomarker record covering the last deglaciation and early Holocene (17-9 ka BP) from the Dongyuan Lake, southern Taiwan, located at the frontal zone of typhoon invasion. The lignin phenol ratio S/V shows that the vegetation in the catchments had shifted from gymnosperm dominant to angiosperm dominant plants since 12.2 ka BP. Significantly decreased lignin concentrations (TLP and λ8) and elevated lignin degradation parameters ((Ad/Al)v, P/(V + S), DHBA/V) in combination with other organic proxies (TOC, δ13Corg) during the late YD suggest a severe drought had occurred in southern Taiwan during this specific period. Changes in the lignin proxies from the Dongyuan Lake lagged the climate changes registered in stalagmite records by around 500-800 years, suggesting a slow response of vegetation and soil processes to rapid climate changes.

  6. 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

  7. The Cup of Tea - Drift Sediment Analogy: The Example of a Southern Patagonian Lacustrine Basin

    NASA Astrophysics Data System (ADS)

    Gilli, A.; Anselmetti, F. S.; Ariztegui, D.; McKenzie, J. A.; Markgraf, V.

    2001-12-01

    The tools to probe both modern and ancient lake deposits were perfected to a large degree during the 1970's when Kerry Kelts coined the concept of Limnogeology. Lakes could then be used as small, well-defined laboratories for ocean processes and marine techniques adapted to limnic settings. We present here a further application of a lake as a geological laboratory by comparing the sediment transport and drift deposition in a closed lacustrine basin as an analogue to marine settings. An ongoing study in Lago Cardiel, a 20 km diameter closed-basin in southern Patagonia (Argentina), is providing a wealth of limnogeological data that will help to clarify some fundamental questions concerning timing and extend of global paleoclimatic change. A dense grid of seismic lines with both a 3.5 kHz single-channel and a stronger boomer source has provided excellent seismic penetration with up to 10 cm vertical resolution. The quasi 3D mapping of six major acoustic packages resulted in detailed contour and thickness maps for each identified sequence. Combined with piston core analyses and AMS radiocarbon dating these data allowed a continuous lake level reconstruction since and beyond the last glacial maximum. Low lake levels are identified prior to 11.2 kyr and a prominent desiccation ca. 21 kyr. The Pleistocene/Holocene transition is characterized by a large lake level rise of at least 80 m higher than modern level. The transgression and the time there after are characterized by an almost uniform sediment distribution with a weak focusing towards the center of the basin. A dramatic change in depositional pattern characterizes the Mid- and Late-Holocene. A thick dome-shaped sediment package was deposited just north of the center of the basin during the last 5'000 years, with an average sedimentation rate of 6 m per 1000 years. Striking similarities can be observed among these lacustrine sediment geometries and marine drift settings such as the Straits of Florida or the Marion

  8. 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.

  9. 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

  10. 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.

  11. Trace fossil analysis of lacustrine facies and basins

    USGS Publications Warehouse

    Buatois, L.A.; Mangano, M.G.

    1998-01-01

    Two ichnofacies are typical of lacustrine depositional systems. The Scoyenia ichnofacies characterizes transitional terrestrial/nonmarine aquatic substrates, periodically inundated or desiccated, and therefore is commonly present in lake margin facies. The Mermia ichnofacies is associated with well oxygenated, permanent subaqueous, fine-grained substrates of hydrologically open, perennial lakes. Bathymetric zonations within the Mermia ichnofacies are complicated by the wide variability of lacustrine systems. Detected proximal-distal trends are useful within particular lake basins, but commonly difficult to extrapolate to other lakes. Other potential ichnofacies include the typically marine Skolithos ichnofacies for high-energy zones of lakes and substrate-controlled, still unnamed ichnofacies, associated to lake margin deposits. Trace fossils are useful for sedimentologic analysis of event beds. Lacustrine turbidites are characterized by low-diversity suites, reflecting colonization by opportunistic organisms after the turbidite event. Underflow current beds record animal activity contemporaneous with nearly continuous sedimentation. Ichnologic studies may also help to distinguish between marine and lacustrine turbidites. Deep-marine turbidites host the Nereites ichnofacies that consists of high diversity of ornate grazing traces and graphoglyptids, recording highly specialized feeding strategies developed to solve the problem of the scarcity of food in the deep sea. Deep lacustrine environments contain the Mermia ichnofacies, which is dominated by unspecialized grazing and feeding traces probably related to the abundance and accessibility of food in lacustrine systems. The lower diversity of lacustrine ichnofaunas in comparison with deep-sea assemblages more likely reflects lower species diversity as a consequence of less stable conditions. Increase of depth and extent of bioturbation through geologic time produced a clear signature in the ichnofabric record of

  12. 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.

  13. 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.

    PubMed

    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.

  14. 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.

  15. Glacial-Holocene paleoceanography of the western equatorial Pacific: Carbonate dissolution and sea surface temperatures in the south China and Sulu Seas

    SciTech Connect

    Miao, Qingmin; Thunell, R.C. . Dept. of Geological Sciences)

    1992-01-01

    Six sediments cores from the South China Sea (SCS) and four from the Sulu Sea (SS) have been used in a detailed study of sea surface temperature changes in these two basins during the last 25,000 year. Sea surface temperature (SST) estimates were derived using a planktonic foraminiferal transfer function (FP-12E). The water depths for the cores range 500 m to more than 4,000 m. The time series (SST) records indicate that winter and summer temperatures during the Holocene were approximately 27 C and 29.5 C, respectively, for both the (SC) and (SS). During the last glacial maximum, summer sea surface temperatures were approximately 28.5 C in the (SCS) and 29 C in the (SS), and thus very similar to the Holocene. In contrast, glacial winter (SST) are estimated at 21 C for the (SCS) and 24 C for the (SS). This decrease in glacial winter (SST) results in a much larger seasonality during the last glacial compared to the Holocene. Variation in intensity of the monsoon system and surface water exchange rates between basins are the major factors controlling glacial-interglacial SST fluctuations in the (SC) and (SS). The primary factor influencing the accuracy of the SST estimates is the quality of preservation of planktonic foraminiferal assemblages. Results show that increasing levels of dissolution result in systematically cooler SST estimates. This is due to the fact that warm water foraminifera tend to be more solution susceptible and as dissolution progresses the assemblage becomes enriched in the more resistant, cool water taxa. Since dissolution is more intense during interglacials than glacials in the Pacific, dissolution tends to reduce the amplitude of the true glacial-interglacial temperature difference.

  16. 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

  17. 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.

  18. 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

  19. The Holocene temperature conundrum.

    PubMed

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

    2014-08-26

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

  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. 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.

  2. 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

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

    PubMed

    Jones, Miriam C; Yu, Zicheng

    2010-04-20

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

  4. 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.

  5. 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.

  6. 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.

  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. Holocene paleoclimatic variation in the Schirmacher Oasis, East Antarctica: A mineral magnetic approach

    NASA Astrophysics Data System (ADS)

    Phartiyal, Binita

    2014-12-01

    An analysis of remanent magnetism and radiocarbon ages in the dry lacustrine/sediment fills of the Schirmacher Oasis (SO) in East Antarctica was conducted to reconstruct past climatic condition. The statistically run mineral magnetic data on paleontological statistics software package (multivariate cluster analysis) placed on accelerator mass spectrometer radiocarbon chronology of the three sediment sections, trace 6 phases of climatic fluctuation between 13 and 3 ka, (Phases 1, 3 and 5 represent cold periods while Phases 2, 4, and 6 represent warm periods). One short warm period (Phase 2, ca. 12.5 ka) occurred in the late Pleistocene, and two marked warm periods (Phase 4, 11-8.7 ka; Phase 6, 4.4-3 ka) occurred in the Holocene. High magnetic susceptibility (χ), saturation isothermal remanent magnetism (SIRM), and soft isothermal remanent magnetism (soft IRM) values correspond to colder periods and low values reflect comparatively warmer lacustrine phases. Holocene Optima (Phase 4) and Mid Holocene Hypsithermal (Phase 6) are distinguished by decreased values of concentrations dependent parameters. Remanence is preserved in the low-coercive minerals. Heavy metals in the sediments include, Fe, Rb, Zn, Mo, Co, Pb, Mn, Cu, and As in order of decreasing abundance.

  9. 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.

  10. 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

  11. Microorganisms and typical organic matter responsible for lacustrine "black bloom".

    PubMed

    Feng, Ziyan; Fan, Chengxin; Huang, Weiyi; Ding, Shiming

    2014-02-01

    Identifying the causation of the black substance in lacustrine "black bloom" is of great significance for forecasting and preventing black bloom in many waters of the world. In this research, an array of black bloom was simulated in a laboratory to investigate how microorganisms and organic matter affect black bloom. Sulphate-reducing bacteria (SRB) are the main biological factor, and protein is the key organic factor contributing to lacustrine black bloom. The black colour of black bloom is strongly associated with a relatively high SRB population density. Hydrogen sulphide concentration can serve as a predictor of black bloom.

  12. Holocene palaeoenvironmental changes in the central Sahara (NE-Niger)

    NASA Astrophysics Data System (ADS)

    Brauneck, J.; Baumhauer, R.

    2009-04-01

    cannot be determined precisely but can be narrowed to a period around 6 ka BP. The results obtained from the core are compared with those from terrestrial and lacustrine sediments from outside the depression, situated a few hundred kilometres further to the north. Within the plateau landscape of Djado, Mangueni and Tchigai, two depressions and a valley containing lacustrine deposits, were investigated for palaeoenvironmental reconstruction. Depending on modifying local factors, these sediment archives were of shorter existence than the lake, but reveal additional information about the landscape dynamics from Early to Mid Holocene. These supplementary study sites are required to validate the information obtained from the coring, as it showed no noticeable signs of climatic alterations until Mid Holocene. Nevertheless, the supplementary sediment archives evidence the previous onset of aeolian activity and simultaneous presence of alternating amounts of precipitation and therefore indicate major variations in the timing and extent of lacustrine and aeolian periods. The Early Holocene can generally be considered a period of wetter conditions, although the different study sites showed major variations in the timing and extent of lacustrine and aeolian periods, depending on modifying local factors. Evidently, a transitional time has existed between 7 to 5 ka BP where alternating climatic influences prevailed. In a landscape of limited palaeoenvironmental archives, where solitary under favourable conditions information has been conserved, only the investigation of several dissimilar spots within a designated study area has the potential to provide a complete picture of landscape succession. Therefore, the objective of further environmental reconstruction is to provide not only a multi-proxy but also a multi-habitat approach.

  13. 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.

  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. 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

  16. The First Dated Eemian Lacustrine Deposit in Romania

    NASA Astrophysics Data System (ADS)

    Petroniu Onac, Bogdan; Björkman, Leif; Björck, Svante; Clichici, Octavian; Tamas, Tudor; Peate, David; Wohlfarth, Barbara

    2001-07-01

    A complex interglacial sequence of lacustrine sediments has been found near the village of Turbuta in NW Romania. Mollusk, plant macrofossil, and pollen analyses reflect climatic and environmental changes around the last interglacial climatic optimum. U-Th TIMS dating of snails strongly indicates an Eemian age of the organic sediments.

  17. Did Iceland's icecaps disappear in the Warm Early Holocene?

    NASA Astrophysics Data System (ADS)

    Geirsdottir, A.; Miller, G. H.; Black, J.; Thordarson, T.

    2002-12-01

    We address the magnitude of Holocene climate change in the North Atlantic region, especially the warmth of the early Holocene, by reconstructing changes in Langjokull, one of the four largest icecaps on Iceland today. Outlet glaciers from Langjokull drained into Hvitarvatn, a large (12 x 3 km; 70 m deep) lake until AD 1945, and continue to dominate sedimentation in the lake at present. If the icecap disappeared in the early Holocene, sedimentation would have been slow and dominated by fluvially transported sediment. When glacial erosion occurs in the catchment, sedimentation rates increase and grain size decreases. When outlet glaciers calve directly into the lake, ice-rafted detritus (IRD) occurs. Because Iceland's climate, and therefore glacier mass balance, is highly sensitive to ocean/atmosphere changes in the North Atlantic, the status of Iceland's glaciers provides a sensitive monitor of North Atlantic climate change throughout the Holocene. Seismic reflection data divide the history of sedimentation into five well-defined episodes: The basin is floored by an acoustically chaotic seismic unit with an undulating upper contact (till). Ponded on the basal seismic unit is a seismic facies 10 to >30 m thick showing prograding reflection characteristics with common hard reflectors indicating deltaic deposition (deglaciation). Unit 3 is a 3-to-5-m-thick, acoustically transparent, suggesting lacustrine sedimentation without episodes of rapid sedimentation. The upper two seismic units are characterized by closely spaced strong horizontal seismic reflectors indicative of glacier-dominated sedimentation (Neoglaciation). To evaluate the long-term status of Langj”kull we cored on a bedrock high, where sedimentation is dominated by suspension settling. We sampled 13 m of sediment in two 5.4 m cores, reaching most of the way through seismic unit 3. Seismic Units 1 and 2 (upper10 m) are laminated, with the laminations increasing in definition and thickness towards the

  18. 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.

  19. Holocene paleoenvironments of Northeast Iowa

    USGS Publications Warehouse

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

    1996-01-01

    present, but mosses of forest habitats completely disappear when prairie became dominant. A few deciduousforest taxa return during the late-Holocene, when oak savanna prevailed. The C-O isotopic record from stalagmite "s" in Coldwater Cave indicates a relatively stable environment from ??? 8000 to 5100 yr BP, when the 813C values indicate a change in vegetation dominated by C3 (predominantly forest) to C4 (predominantly prairie) plants. About 4900 yr BP, the rise in 18O values indicates a temperature increase of ??? 1.5??C. The fact that the vegetational change suggested by the ??13C values preceded the temperature increase suggests that fire may have been an important factor in converting forest to prairie. Abundant charred seeds and other plant material at Roberts Creek 4830 yr BP support this hypothesis. The 18O values remain constant from ???5100 to ???3000 yr BP. but the ??13C values gradually rise, indicating that soil formed under forest takes at least 2000 yr for its carbon to reach equilibrium after replacement by prairie vegetation. The return of oak to form savanna is reflected in the gradual decline of ??13C values in the last 3000 yr BP: O isotopic values drop sharply by ??? 1??C ??? 2800 yr BP and then were relatively stable. In contrast to the vegetational and isotopic records, the insect assemblages suggest little change in the local environments throughout most of the Holocene. All of the beetle taxa presently occur in eastern Iowa. The relative stability through the Holocene indicates that both open grassland and riparian woodland elements were present throughout. Settlement, land clearing, and land cultivation by EuroAmericans in the region caused rapid erosion of the upland landscape, the deposition of 1-2 m of sediment across the floodplain, a replacement of the native vegetation with ruderal species, a decimation of the native insect fauna, and a degradation of water quality in the stream. These changes in the landscape, vegetation, and insect faunas

  20. 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

  1. 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

  2. The significance of dropstones in a tropical lacustrine setting, eastern Cameros Basin (Late Jurassic-Early Cretaceous, Spain)

    NASA Astrophysics Data System (ADS)

    Doublet, Stéfan; Garcia, Jean-Pierre

    2004-01-01

    Outsized clasts (mainly white quartzite pebbles) are found in carbonate deposits of the Enciso Group exposed on the northern border of the Cameros rift basin (Late Jurassic-Early Cretaceous, northern Spain). In the Arnedillo section, all the stones are enclosed in micrite, which was assumed deposited in littoral to open lacustrine environments, with minor inputs of deltaic sandstones. The clasts are found in fine-grained lacustrine sediments either as isolated stones or as loosely packed elongated clusters occasionally associated with quartz sands and gravels. The mean size of the clasts is 40 mm (range: 3-100 mm); they are polished, well-rounded, and lack any faceting or striae. Lithology suggests that the clasts were potentially supplied by three stratigraphic formations cropping out in the catchment area of the Cameros lake. The occurrence of outsized stones within featureless micrite indicative of low-energy conditions involves a hydrodynamic paradox which can only be resolved by their vertical or oblique emplacement in the host sediment as dropstones. The lack of mass-flow deposits in the Enciso Group precludes gravitational processes and suggests deposition from a rafting agent. Icebergs and stone-swallowing animals are the main transport agents identified in continental settings. Here, stone swallowing is rejected as the transport mechanism because the stones are loosely packed and are never associated with skeletal remains. Ice rafting is also rejected because of the low density of clusters, and the absence of faceting and striations which characterize glacial sediments. Furthermore, the sub-tropical position of Iberia, the absence of surrounding high relief, and global climatic models for the Aptian corroborate the absence of a glaciolacustrine environment. Consequently, we propose wood rafting as an alternative depositional mechanism for dropstones in non-glacial lacustrine environments. Although no direct evidence has yet been found (i.e. stones enclosed

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

    USGS Publications Warehouse

    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

  5. 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.

  6. Deposition times in the northeastern United States during the Holocene: establishing valid priors for Bayesian age models

    NASA Astrophysics Data System (ADS)

    Goring, S.; Williams, J. W.; Blois, J. L.; Jackson, S. T.; Paciorek, C. J.; Booth, R. K.; Marlon, J. R.; Blaauw, M.; Christen, J. A.

    2012-08-01

    Age-depth relationships in sedimentary archives such as lakes, wetlands and bogs are non-linear with irregular probability distributions associated with calibrated radiocarbon dates. Bayesian approaches are thus well-suited to understanding relationships between age and depth for use in paleoecological studies. Bayesian models for the accumulation of sediment and organic matter within basins combine dated material from one or more records with prior information about the behavior of deposition times (yr/cm) based on expert knowledge. Well-informed priors are essential to good modeling of the age-depth relationship, but are particularly important in cases where data may be sparse (e.g., few radiocarbon dates), or unclear (e.g., age-reversals, coincident dates, age offsets, outliers and dates within a radiocarbon plateau). Here we assessed Holocene deposition times using 204 age-depth models obtained from the Neotoma Paleoecology Database (www.neotomadb.org) for both lacustrine and palustrine environments across the northeastern United States. These age-depth models were augmented using biostratigraphic events identifiable within pollen records from the northeastern United States during the Holocene and late-Pleistocene. Deposition times are significantly related to depositional environment (palustrine and lacustrine), sediment age, and sediment depth. Spatial variables had non-significant relationships with deposition time when site effects were considered. The best-fit model was a generalized additive mixed model that relates deposition time to age, stratified by depositional environment with site as a random factor. The best-fit model accounts for 63.3% of the total deviance in deposition times. The strongly increasing accumulation rates of the last 500-1000 years indicate that gamma distributions describing lacustrine deposition times (α = 1.08, β = 18.28) and palustrine deposition times (α = 1.23, β = 22.32) for the entire Holocene may be insufficient for

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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

  12. Late Pleistocene and Holocene sedimentation, organic-carbon delivery, and paleoclimatic inferences on the continental slope of the northern Pandora Trough, Gulf of Papua

    NASA Astrophysics Data System (ADS)

    Febo, Lawrence A.; Bentley, Samuel J.; Wrenn, John H.; Droxler, André W.; Dickens, Gerald R.; Peterson, Larry C.; Opdyke, Bradley N.

    2008-03-01

    We investigated sediment and organic-carbon accumulation rates in two jumbo piston cores (MV-54, MV-51) retrieved from the midslope of the northeastern Pandora Trough in the Gulf of Papua, Papua New Guinea. Our data provide a first assessment of mass fluxes over the past ˜33,000 14C years B.P. and variations in organic-carbon sources. Core sediments were analyzed using a suite of physical properties, organic geochemistry, and micropaleontological measurements. MV-54 and MV-51 show two periods of rapid sediment accumulation. The first interval is from ˜15,000 to 20,400 Cal. years B.P. (MV-51: ˜1.09 m ka-1 and ˜81.2 g cm-2 ka-1) and the second occurs at >32,000 14C years B.P. (˜2.70 m ka-1 and ˜244 g cm-2 ka-1). Extremely high accumulation rates (˜3.96 m ka-1; ˜428 g cm-2 ka-1) characterize 15,800-17,700 Cal. years B.P. in MV-54 and likely correspond to early transgression when rivers delivered sediments much closer to the shelf edge. A benthic foraminiferal assemblage in MV-51 from ˜18,400 to 20,400 Cal. years B.P. indicates a seasonally variable flux of organic carbon, possibly resulting from enhanced contrast between monsoon seasons. The oldest sediments, >32,000 14C years B.P., contain TOC fluxes >200 g cm2 ka-1, with >50% of it derived from C3 vascular plant matter. Magnetic susceptibility values are 2 to 3 times higher and benthic foraminiferal accumulation rates are 6 times higher during this interval than at any younger time, indicating a greater influence of detrital minerals and labile organic carbon. The MS data suggest more direct dispersal pathways from central and eastern PNG Rivers to the core site.

  13. 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

  14. 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

  15. 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

  16. 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

  17. Late Quaternary lacustrine paleoenvironments in the Cuenca de México

    NASA Astrophysics Data System (ADS)

    Bradbury, J. P.

    A late Quaternary paleolimnological history from the Mexican highlands has been obtained by diatom analysis of short cores and stratigraphic sections of lake and marsh sediments from the Cuenca de México, the large, endorheic, graben basin that holds Mexico City. The records, dated by radiocarbon and tephrochronologic methods, extend back to about 30 ka BP and document the presence of extensive, saline lakes in the basin until 25 ka BP. Thereafter, lake levels fell and marginal sites became shallow and fresh under the influence of surficial drainage and (especially) spring discharge. A shallow, saline lake existed 18 ka BP in Texcoco, the central and lowest basin in the system, reflecting moderately increased effective moisture at that time. By 16 ka BP, Lake Texcoco had become so shallow that diatoms were no longer preserved. However, marginal sites nourished by spring flow recorded changes in the local hydrologic balance resulting from increased infiltration at higher elevations. These changes appear to coincide with glacial advances between about 14 and 10 ka BP on the volcanic mountains surrounding the basin. Dry climates with reduced infiltration characterized the early Holocene, but by 5 ka BP a modest increase in precipitation established the modern climatic regime. These lacustrine records offer important insights for evaluating the paleoenvironmental history of the Cuenca de México based on other evidence. They confirm glaciological, stratigraphic and palynologic data that suggest dry climates and the absence of large pluvial lakes in the Cuenca de México during and after the full glacial, but document climates of significantly increased precipitation at least 10 ka prior to 18 ka BP.

  18. 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

  19. Holocene monsoon variability inferred from Targo Xian peat bog in the Tangra Yumco basin, central Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Henkel, Karoline; Haberzettl, Torsten; Miehe, Sabine; Frenzel, Peter; Daut, Gerhard; Dietze, Elisabeth; Kasper, Thomas; Ahlborn, Marieke; Mäusbacher, Roland

    2013-04-01

    The Tibetan Plateau is the greatest plateau on Earth with an average altitude of 4,500 m asl. Due to its high elevation, large area and significant role in the formation of the Asian Monsoon Systems (e.g., Indian Ocean and East-Asian Summer Monsoon) it is considered to react very sensitive to climate variations. The numerous lake systems on the Tibetan Plateau represent excellent archives reflecting variations in the strength of the monsoon system in terms of hydrological changes expressed in lake level fluctuations. For example, terraces and lacustrine deposits around the saline lake Tangra Yumco indicate lake level highstands up to ~215 m higher than the present lake level. To study Holocene lake level variations we investigated a 3.6 m long sediment core recovered from a peat bog (near the Targo Xian settlement, 30°46'N, 86°40'E) on a recessional lake level terrace ~150 m above the present shoreline of Tangra Yumco. In particular, our analyses of sedimentological (grain size), geochemical (CNS and ICP-OES) and mineralogical (XRD) data allow a detailed and high-resolution interpretation of the hydrological conditions during the Holocene. The existence of two carbonate layers in the Targo Xian record, separated by a sand layer and intercalated in peat sequences at the bottom and top of the core, provide evidence for two stable lake stages at the coring position. Peat at the bottom of the core, which is radiocarbon-dated to 11,130 +130/-345 cal BP, indicates wetland conditions similar to the Recent situation (Miehe et al., submitted). After a transition zone, a layer of pure aragonitic lake marl gives evidence for a lake stage. During this stage, high values of the total inorganic carbon (TIC) and Ca/Ti ratios as well as low C/N ratios point to a stable lake due to wet climatic conditions. This carbonate layer can be correlated with a 2-3 m thick carbonate layer found in outcrops around the present lake Tangra Yumco presenting a high lake level until approx. 2

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

    SciTech Connect

    Foley, J.A.

    1994-12-01

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

  1. 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

  2. Lacustrine evidence of anti-phase distribution of moisture in Southern South America during the Neoglacial period (Invited)

    NASA Astrophysics Data System (ADS)

    Piovano, E.; Ariztegui, D.; Sylvestre, F.; Córdoba, F.

    2009-12-01

    An increasing number of lacustrine records is now available for southern South America east of the Andes. As a result a network of well-studied sites is emerging allowing to track hydrological changes throughout time at a regional scale. New limnogeological results spanning the Holocene across the subtropical Pampean plains of Southern South America are compared with lacustrine records covering both Andean and extra Andean sectors of eastern Patagonia. The development of contrasting hydrological patterns can be observed between the Pampas (Laguna Mar Chiquita, 30°S; Laguna Melincué, 34°S; Lagunas Encadenadas del Oeste de Buenos Aires, 37°S) and eastern Patagonia (Lago Frías, 41°S; Lago Cardiel, 49°S; and Laguna Potrok Aike, 52°S) at both sides of the South American Arid Diagonal (AD) during prevailing warm or cold climatic phases, respectively. Paleohydrological reconstructions suggest wet conditions in regions located west and south of the AD, like Patagonia or even the Central Andes, during cold climatic phases such as those occurred during neoglaciations including the Little Ice Age (LIA). These phases are characterized by a dominant Pacific source of moisture. Conversely, dry conditions can be proposed for the same climatic interval across the subtropical low-lands east of the AD. These areas are mostly under the influence of an Atlantic summer rain regime. Conversely, extensive dryness across Patagonia and wet conditions in the Pampas can be inferred during warm climatic phases such as the Medieval Climatic Anomaly or the last part of the 20th century. This new paleohydrological data from Patagonia and the Pampean plains further indicate that the development of this anti-phase hydrological pattern was active only after the middle Holocene. Thus, it appears as contemporaneous to an intensification of the Southern Westerlies in concert with a weakened Monsoonal circulation. The anti-phasing cold/wet vs. cold/dry hydrological conditions at different

  3. Major and trace elements documented paleoenvironmental and provenance signatures as inferred from the lacustrine sequence of Orog Nuur, southern Mongolia

    NASA Astrophysics Data System (ADS)

    Yu, Kaifeng; Lehmkuhl, Frank; Diekmann, Bernhard; Nottebaum, Veit; Stauch, Georg

    2016-04-01

    In arid realm, due to scarce of continuous terrestrial archives, lacustrine sequences were more often employed as the paleoenvironmental repository. However, there exist numerous spatial and temporal heterogeneities concerning existing studied sites. In the Gobi Desert of southern Mongolia, only two records i.e., Bayan Tohomin Nuur and Ulaan Nuur, were previously reported, neither of them, however, provided records older than ~15 ka. A record that spans longer time period is therefore indispensable to better understand the thermal and hydrologic pattern and their driving mechanisms. Among the suite of the multidisciplinary studies on lacustrine archive, geochemistry appears most likely the promising tool to decipher the interplay between the environmental change, source lithotype and sediment bulk-composition. Considering the late Quaternary lacustrine sediments, the bulk-geochemistry may be controlled by source terranes, authigenic or allothigenic input, which can be altered by the past environment conditions. Knowledge of the bulk-geochemistry downcore variance along with the field investigation and carefully examined geologic mapping will thereby allow us to gain a better understanding of the climate-induced provenance changes throughout the deposition process. On the other hand, surveys considering the bulk-geochemistry and corresponding environmental interpretations in the pelagic realm have been systematically conducted and reviewed, while their counterpart explanations in the lacustrine sediments still need more investigations. Two parallel cores (ONW I, 6.00 m; ONW II, 13.36 m) was retrieved from Orog Nuur, Gobi Desert of southern Mongolia. A suite of high resolution element abundances were examined based on core ONW II in an attempt to gain a better understanding of the paleoenvironment and provenance history of the catchment system over the last ~50 ka. Due to the predominant clay or silty-clay fractions in the lacustrine sediments, Al and Si display

  4. Carbon isotopes in peat, DOC, CO{sub 2}, and CH{sub 4} in a Holocene peatland on Dartmoor, southwest England

    SciTech Connect

    Charman, D.J.; Aravena, R.; Bryant, C.L.; Harkness, D.D.

    1999-06-01

    Carbon gases with younger {sup 14}C ages than those of the surrounding peat have been reported from continental boreal peatlands, a fact which suggests that significant movement of CO{sub 2}, CH{sub 4}, or DOC (dissolved organic carbon) and export of C via subsurface processes are not accounted for in most estimates of contributions to the C cycle. This paper tests the hypothesis that similar processes can occur in oceanic ombrotrophic mires where water and gas movement is theoretically minimal. Measurements of {sup 14}C and {delta}{sup 13}C in CO{sub 2}, CH{sub 4}, and DOC, and of tritium, are reported from depths to 250 cm at Tor Royal, a raised mire in southwest England. Radiocarbon ages of gases are 1,460 to 500 yr younger than those of peat from the same depths, and CO{sub 2} is consistently younger than CH{sub 4}. DOC is 1,260 to 830 yr younger than the peat, and significant amounts of tritium were found at all depths. Gas ages are mostly intermediate between the age of the peat and that of the DOC, which suggests that C is principally transported as DOC. However, some gases are younger than their associated DOC, which implies that movement of dissolved gases may also take place. {delta}{sup 13}C values in gases suggest that CO{sub 2} reduction is the major pathway for CH{sub 4} production. Transport of C in deep peats is likely to be a significant component in the overall C budget of ombrotrophic oceanic peatlands, and C export via discharge to ground or surface waters may be an important mechanism for gaseous C emissions.

  5. Late Cenozoic geology and lacustrine history of Searles Valley, Inyo and San Bernardino Counties, California

    USGS Publications Warehouse

    Smith, George I.

    2009-01-01

    Canyon Formation and deposits mapped as older gravel and older tufa are extensively exposed over much of the basin floor. The older gravel unit and the gravel facies of the Christmas Canyon Formation are boulder alluvial gravels; parts of these units are probably correlative. The lacustrine facies of the Christmas Canyon Formation includes the Lava Creek ash, which is dated at 0.64 Ma; the older tufa deposits may be equivalent in age to those sediments. Most of this study concerns sediments of the newly described Searles Lake Formation, whose deposition spanned the period between about 150 ka and 2 ka. Most of this formation is lacustrine in origin, but it includes interbedded alluvium. To extract as much geologic detail as possible, criteria were developed that permitted (1) intrabasin correlation of some thin outcrop units representative of only a few thousand years (or less), (2) identification of unconformities produced by subaerial erosion, (3) identification of unconformities produced by sublacustrine erosion, and (4) correlation of outcrop units with subsurface units. The Searles Lake Formation is divided into seven main units, many of which are subdivided on the five larger scale geologic maps. Units A (oldest), B, C, and D are dominantly lacustrine in origin. The Pleistocene-Holocene boundary is placed at the top of unit C. In areas that were a kilometer or more from shore at the time of deposition, deposits of units A,B, and C consist of fine, highly calcareous sand, silt, or clay; nearer to shore they consist of well-sorted coarse sand and gravel. Unit A has been locally subdivided into as many as four subunits, unit B into six subunits, and unit C into six subunits. The finer facies of units A, B, and C contain such high percentages of Caco3 that they are best described as marl. Sediments of unit C, and to a lesser extent those of unit B, are laminated with light- to white-colored layers of aragonite, calcite, or dolomite(?) that may repre

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

    USGS Publications Warehouse

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

    1997-01-01

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

  7. Microbially Induced Reductive Dissolution of Trace Element-Rich Lacustrine Iron-Oxides

    NASA Astrophysics Data System (ADS)

    Crowe, S. A.; Kulczykci, E.; O'Neill, A. H.; Roberts, J. A.; Fowle, D. A.

    2004-12-01

    Iron (oxy)hydroxides are ubiquitous components of surfacial materials and are often the dominant redox buffering solid phases in soils and sediments. As a result, the geochemical behavior of these minerals has a profound influence on the global biogeochemical cycling of trace elements, including heavy metals and arsenic (As), in addition to nutrients such as, sulfur (S), carbon (C), nitrogen (N), and phosphorus (P). Understanding the behavior of trace elements and nutrients during biological and abiotic processes that effect iron (Fe) mineral phase transformations is paramount for predicting their distribution, mobility, and bioavailability in the environment. To evaluate the impact of dissimilatory Fe-reduction (DIR) on trace element mobility we have conducted batch incubations of Fe-rich lateritic lacustrine sediments. In contrast to mid-latitude lakes where Fe (oxy)hydroxides constitute only a small fraction of the total sediment, tropical lake sediments have been known to comprise up to 40-60 wt. % Fe-oxides. Under suboxic and nonsulphidogenic conditions it is likely that DIR plays a prominent role in early diagenesis and therefore may exert control on the fate and distribution of many trace elements in this environment (e.g. Crowe et al. 2004). In batch incubations conducted in a minimal media of similar composition to typical freshwater the lacustrine Fe-oxides were reductively dissolved at a rate very similar to pure synthetic goethite of similar surface area (measured by N2-BET). This is in contrast to the slower rates previously observed for trace element substituted Fe-oxides. These slower rates have been attributed to surface passivation by secondary Al and Cr mineral precipitation. We propose that these passivation effects may be offset in minimal media incubations by enhanced microbial metabolism due the presence of nutrients (P, Co and other metals) in the lacustrine Fe-oxides. These nutrients became available with progressive reduction as the

  8. Discovery of silicified lacustrine micro-fossils and stromatolites: Triassic-Jurassic Fundy Group, Nova Scotia

    SciTech Connect

    Cameron, B.

    1985-01-01

    A unique assemblage of silicified invertebrate and algal fresh-water lake fossils has been discovered in the Scots Bay Formation at the top of the Triassic-Jurassic Fundy Group of the Fundy Basin in Nova Scotia. This is important because the basins of the eastern North American Triassic-Jurassic rift system have not yielded many invertebrate and algal fossils. These new finds will contribute significantly to evolutionary, paleoecological and biostratigraphic studies of fresh-water Mesozoic deposits. Silicified fossils have been extracted from chert-bearing, mixed carbonate and siliciclastic lithologies. They include ostracodes, gastropods, rare bivalves, charaphytes (algae), stromatolites, and chert nodules cored with well-preserved woody tissues of tree trunks. Possible algal filaments occur in the silicified stromatolites. This association of charaphytes, ostracodes, microscopic gastropods and stromatolites is found in carbonate lakes today. The Scots Bay Formation is probably a near-shore carbonate facies of the more widespread silicilastic lacustrine McCoy Brook Formation. The gastropods and ostracodes, studied by SEM, indicate a Jurassic age for the Scots bay Formation, confirming speculations based on other data.

  9. Thermal and spectral characterization of anaerobic thermal behavior patterns in a lacustrine sediment core.

    PubMed

    Guo, Fei; Mu, Yunsong; Chen, Cheng; Liao, Haiqing; Bai, Yingchen

    2016-10-01

    The thermal evolution of sedimentary organic matter is a significant mechanism in continental oil and gas formation. This study presents a new method to estimate vertical thermal evolution trends in a lake sediment core. Twenty sediment samples from a 60-cm core recovered from Lake Bosten were heated to 600 °C at a rate of 10 °C min(-1) under a N2 atmosphere. The sediments were characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), and then, the samples were analyzed with total organic carbon (TOC) analyses, X-ray diffraction, and (137)Cs isotopic dating techniques. Two main anaerobic thermal degradation processes were observed in the thermograms. The pyrolysis results showed variations with sediment age, with labile carbon (237.2 ± 42.98 °C) manifesting different thermogram patterns than recalcitrant carbon (498.35 ± 30.09 °C). There was a significant linear correlation between sample weight loss and TOC (r = 0.972, p < 0.001), as well as between the DSC and TGA peaks (r = 0.963, p < 0.001). As a conclusion, the thermal stability of both labile organic carbon and recalcitrant organic carbon in lacustrine sediment core increased gradually with age. These results confirm that advanced thermal techniques (DSC and TGA) operated in inert gas are potential quantitative methods to characterize the anaerobic thermal behavior of sediment organic carbon.

  10. Evolution of a coquina barrier in Shark Bay, Australia by GPR imaging: Architecture of a Holocene reservoir analog

    NASA Astrophysics Data System (ADS)

    Jahnert, Ricardo; de Paula, Osni; Collins, Lindsay; Strobach, Elmar; Pevzner, Roman

    2012-12-01

    The Holocene hypersaline carbonate system in Shark Bay, Australia is represented by microbial deposits (stromatolites and thrombolites) and a supratidal coquina beach ridge system which overlies the Pleistocene Bibra Formation and is prograding seaward, since 4500 years ago, over supratidal-intertidal microbial deposits as a consequence of Late Holocene sea level fall, and the high volume of bivalve shells available. The extent, internal architecture and ridge constructional types of coquina deposits in this World Heritage area have not been previously investigated in detail by cores tied with geophysical images. Here we document external and internal architecture of the Holocene coquina system in southeast Hamelin Pool showing three depositional units which comprise the ridge system construction: (1) tabular layers complex, (2) convex-up ridges and (3) washover deposits. Bivalve skeletons represent almost the total amount of bioclasts with symmetrical semi-circular formats and valve sizes 5-9 mm. Based on Ground Penetrating Radar (GPR) images the number of prograding layers present in each transect line varies from 252 to 433, which when compared with the measured 14C ages, shows lateral growth of the system at average rates from 10 years per layer on proximal older sequences to 30 years per layer in the younger and thicker packages which display more gentle inclination and sub-horizontal arrangement. Divergent orientation of tabular layers relates to changes in energy of currents and waves and involves time gaps and erosion. After earliest crest construction the system experienced a decrease in sea level (3600-3000 14C years BP) that left behind a sequence of parallel tabular layers with dip angles (> 10° to < 20°) which accreted seaward as the first major prograding event. The accretionary tabular layers progressively lost height till near 3000 years BP, representing continuous relative SL and storm energy fall, when the first major swale was constructed

  11. 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

  12. Diatom Records of Holocene Environmental and Climatic Change in Southeastern British Columbia

    NASA Astrophysics Data System (ADS)

    Westover, K. S.; Gavin, D. G.; Fritz, S. C.; Hu, F.; Roschen, L. A.

    2004-12-01

    The sediments of three lakes, spanning a latitudinal gradient and situated within the Interior Cedar-Hemlock biogeoclimatic zone of southeast British Columbia, have been analyzed for independent records of Holocene climate and vegetation history in order to evaluate the role of climate as a control on range expansion of western hemlock and western redcedar. Holocene climate reconstructions are based on multiple proxies, including the diatom and biogenic silica stratigraphies presented here. To our knowledge, these sites provide the first continuous Holocene paleoecological and paleoclimatic records from the region between the Interior Plateau and the Rocky Mountains. Stratigraphic variability in the diatom sedimentary records reflects lake response to changes in water balance, catchment development, and atmospheric inputs of silica (i.e. volcanic ash). At Eleanor Lake, the diatom record shows significant assemblage shifts at ˜7500, 6300, and 3700 cal yr BP. Increased abundance of planktonic and tychoplanktonic diatoms and an increase in the abundance of chrysophyte cysts relative to diatoms at 6300 cal yr BP is consistent with an increase in effective moisture at this time. At Mirror Lake, in the south, an assemblage dominated by small benthic species is replaced by a predominantly planktonic assemblage at 6900 cal yr BP, suggesting an earlier increase in lake level. After 6000 cal yr BP, planktonic diatoms further increase in dominance. These dates are consistent with reconstructions of Holocene climate in south-central British Columbia, which suggest a shift to moister conditions ca. 7000 to 6000 cal yr BP. The pollen record indicates the expansion of western hemlock and western redcedar near Mirror Lake at 3550 cal yr BP and 3250 cal yr BP respectively. At Eleanor Lake, hemlock expansion is dated at 4350 cal yr BP. The data indicate a difference of 1950 to > 3000 years between the lacustrine record of increased effective moisture and the vegetation response and

  13. Using Macroscopic Charcoal to Reconstruct the Holocene Fire Activity of the Willamette Valley, Oregon and Washington

    NASA Astrophysics Data System (ADS)

    Walsh, M. K.; Whitlock, C.; Bartlein, P. J.; Pearl, C. A.

    2006-12-01

    High-resolution macroscopic charcoal analysis of two lacustrine records has revealed the Holocene fire activity of the Willamette Valley, located between the Coast and Cascade ranges of southwestern Washington and northwestern Oregon. The Willamette Valley experienced major environmental and cultural changes during the Holocene, however, its long-term fire history is poorly known. Of particular interest are shifts in fire activity that occurred in response to (1) millennial- and centennial-scale climate and vegetation changes (e.g., the Early Holocene warm period, the Little Ice Age) and (2) major shifts in human activity and population size (e.g., Native American population decline, Euro-American settlement). Macroscopic charcoal analysis of contiguous core samples was used to reconstruct fire activity at each site. Charcoal source (i.e., herbaceous or woody) was also determined based on particle morphology. Charcoal influx was decomposed into a peak component (which indicates fire episodes) and a background component (which indicates changes in burnable biomass). Charcoal records from Battle Ground Lake and Beaver Lake reveal major shifts in fire activity that are consistent with known changes in regional climate on orbital time scales. The Battle Ground Lake charcoal data, for example, show a general increase in fire frequency from the beginning of the Holocene to a maximum of ~18 fire episodes/1000 years at 6500 cal yr BP, associated with the early Holocene insolation maximum and its influence on summer drought, followed by a decrease to ~5 fire episodes/1000 years at present. Similar trends are indicated by the Beaver Lake charcoal data. Both records also indicate shifts in fire activity that suggest the possibility of anthropogenic burning, but at different times at each site. Additional records are being analyzed to examine the spatial and temporal patterns of fire activity across the Willamette Valley as a whole.

  14. Multiescalar studies of fracturing mechanisms in fluvial-lacustrine basins

    NASA Astrophysics Data System (ADS)

    Carreon-Freyre, D.; Cerca, M.; Hidalgo, C.; Hernandez-Marin, M.

    2007-05-01

    Fracturing of clayey fluvial and lacustrine deposits has become a major problem in several cities of central Mexico. The available data reveals the coexistence of several factors determining fracturing at different scales. As main factors we analyze the variation in compressibility of sediments causing differential deformation and withdrawal of groundwater causing a drop in pore pressure. Compressibility depends on consolidation, a term that in soil mechanics refers to the expulsion of interstitial water, and provokes volume decrease and land subsidence. Although major volume decrease occurs in the vertical scale, consolidation of silty clayey materials generates also horizontal tensile stresses. Considering that this factor can be determining to the generation of fractures, the deformational conditions of clayey, silty and sandy sequences is analyzed integrating their stratigraphy and mechanical characteristics. A particular emphasis is made in the mineralogical heterogeneity of the clay fraction that can be related to compressibility variations and can generate micro-fracturing by differential deformation. As study case we analyze the mechanical and geological properties of two sedimentary sequences with contrasting hydraulic and mechanical behavior. Our results show that the paleoenvironmental history of sediments can be used to determine a specific type of fracturing. Thus, the fracturing in fluvial lacustrine deposits is not a random phenomenon but is highly dependent of the geological properties of materials.

  15. Paleoweathering and paleoenvironmental change recorded in lacustrine sediments of the early to middle Eocene in Fushun Basin, Northeast China

    NASA Astrophysics Data System (ADS)

    Chen, Zuoling; Ding, Zhongli; Tang, Zihua; Yang, Shiling; Wang, Xu; Cui, Linlin

    2017-01-01

    Deciphering the long-term interaction among continental silicate weathering, global climate, and atmospheric CO2 concentrations is helpful in understanding the mechanisms of the Cenozoic climate change and accessing the future climatic and environmental response to anthropogenic carbon emissions. The Eocene, which is characterized by the Early Eocene Climatic Optimum (EECO) and the following global cooling, represents an ideal test case. Here we generate geochemical data of the Eocene lacustrine sediments from the Fushun Basin, northeast China, to explore the regional climatic response to the global climate change. The chemical index of alteration (CIA) and plagioclase index of alteration (PIA) consistently show a gradual, long-term decrease, indicating a climatic transition from warm and humid to relatively cold and arid during the Eocene in the Fushun Basin. This climatic trend is broadly coincident with the global cooling and decreasing CO2 concentration, implying that the regional climate is closely correlated with the global climate change over geological time scales. Additionally, the extreme silicate weathering and high lake productivity as reflected by relatively positive δ13C values of lacustrine organic matter are associated with the EECO. This consistency may demonstrate that enhanced continental weathering and lake productivity had served as effective sinks to lower atmospheric CO2 across the EECO. Collectively, our new geochemical data add supporting evidence for a long-term, close coupling among continental silicate weathering, climate, and global carbon cycle during the Eocene.

  16. Characteristics of kerogens from Recent marine and lacustrine sediments: GC/MS analysis of alkaline permanganate oxidation products

    NASA Astrophysics Data System (ADS)

    Ishiwatari, Ryoshi; Morinaga, Shigeo; Yamamoto, Shuichi; Machihara, Tsutomu

    Extensive studies have been carried out by many workers on sedimentary kerogens. However little is known of the details of the chemical structure of kerogens and of the relation between immature and mature kerogens on a molecular basis. The present authors have been studying young kerogens (kerogens in young sediments). This study aimed to determine the structural pecularities of young kerogens from marine and lacustrine sediments. Kerogen samples were isolated from marine (Tanner Basin, offshore California) and freshwater lake (Lake Haruna, Japan) sediments. The kerogens belong to Type II or III. These kerogens were oxidized by alkaline permanganate and analyzed for their degradation products by GC/MS. The major degradation products are aliphatic normal α,ω-dicarboxylic acids with carbon numbers of 4-14; aliphatic normal monocarboxylic acids with carbon numbers of 8-26, and benzene mono-, di- and tetracarboxylic acids. A marked difference between kerogens from two environments was observed in the distribution of aliphatic dicarboxylic acids: C 4-C 10 acids are higher for marine kerogens than for lacustrine kerogens. This difference is probably due to the difference in the fatty acid composition of precursory materials (e.g. phytoplankton). These results indicate that the molecular structure of kerogens reflects generally the molecular composition of precursory materials, and consequently the present alkaline KMnO 4 oxidation method is useful for subtyping of kerogens.

  17. Tracking Holocene glacial and high-altitude alpine environments fluctuations from minerogenic and organic markers in proglacial lake sediments (Lake Blanc Huez, Western French Alps)

    NASA Astrophysics Data System (ADS)

    Simonneau, Anaëlle; Chapron, Emmanuel; Garçon, Marion; Winiarski, Thierry; Graz, Yann; Chauvel, Catherine; Debret, Maxime; Motelica-Heino, Mickaël; Desmet, Marc; Di Giovanni, Christian

    2014-04-01

    Holocene palaeoenvironmental evolution and glacial fluctuations at high-altitude in the western French Alps are reconstructed based on a multiproxy approach within Lake Blanc Huez (2550 m a.s.l.) drainage basin. The combination of seismic profiling (3.5 kHz), piston coring and radiocarbon dating in proglacial lacustrine sediments together with a detailed organic analysis of autochthonous and allochthonous supply allows documenting the evolution of glacier activity during the Holocene. Over the last 9700 years, the Holocene lake record has a bimodal pattern whose transition is progressive and occurring between 5400 and 4700 cal BP. During the Early Holocene, the organic lacustrine facies reflects reduced glacial activity in the catchment. This major glacial retreat seems to result from solar forcing and high summer insolation. After 5400 cal BP, lacustrine sedimentation is marked by the gradual increase both of minerogenic supply and soil erosion, suggesting a progressive transition to wetter climatic conditions. This climate change is synchronous both from the gradual decrease of summer insolation and the gradual reorganization of oceanic and atmospheric circulations, characterizing the beginning of the Neoglacial period. Both colder temperature and humid climate induced significant glacier advance, since 4700 cal BP. Over this global trend, three periods are particularly associated with higher runoff processes and higher soil erosion interpreted as wetter time intervals resulting from enhanced northern Westerlies regimes across the North Atlantic and Western Europe. They are dated from 8700 to 7000, 4700 to 2500 and 1200 to 200 cal BP. These wetter phases drastically contrast with periods of reduced glacial activities dated from the Early Bronze Age (ca 3870-3770 cal BP), the Iron Age (ca 2220-2150 cal BP), the Roman period (ca AD115-330) and the Medieval Warm Period (ca AD760-1160). In addition, these dryer periods are associated with mining activities at high-altitude.

  18. Holocene environmental change in Kamchatka: A synopsis

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

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

  19. Multiproxy paleolimnological evidence of Holocene temperature and precipitation variability from the Eastern Cordillera, Colombia

    NASA Astrophysics Data System (ADS)

    Bixler, C. W.; Shanahan, T. M.

    2011-12-01

    The late Holocene was characterized by a number of significant, widespread multi-century climate anomalies, the most prominent and well documented of which are the Little Ice Age and the Medieval Warm Period. Existing paleoclimate reconstructions from South and Central America provide evidence for anomalous climate conditions during these time periods but the spatial and temporal resolution of existing records is limited and quantitative data on the magnitudes of these events is lacking. These limitations make it difficult to fully evaluate the causes and large scale impacts of these apparently global events. Here, we present new high-resolution multiproxy lacustrine records of late Holocene climate change in the Eastern Cordillera of Colombia over the last 2 millennia by combining high-resolution core scanning approaches with molecular and stable isotope analysis of lipid biomarkers. Preliminary paleoclimate reconstructions from these archives suggest that the northern tropics of South America strongly reflect global century-scale climate variability over this time period, with significant hydrologic and temperature anomalies that are broadly synchronous with events in the high latitudes of the northern hemisphere. The magnitude and widespread nature of late Holocene century-scale droughts in this region likely had significant ecological and societal impacts in the Eastern Cordillera.

  20. Carbon and nitrogen isotope composition of core catcher samples from the ICDP deep drilling at Laguna Potrok Aike (Patagonia, Argentina)

    NASA Astrophysics Data System (ADS)

    Luecke, Andreas; Wissel, Holger; Mayr*, Christoph; Oehlerich, Markus; Ohlendorf, Christian; Zolitschka, Bernd; Pasado Science Team

    2010-05-01

    Glacial (up to 22.0 per mil) are only sporadically reached down core. Compared to this, separated moss debris is remarkably 13C depleted with a minimum at 31.5 per mil. The nitrogen isotope ratios of glacial Laguna Potrok Aike sediments are lower (2.5 per mil) than those of the younger part of the record. The core catcher samples indicate several oscillations between 0.5 and 3.5 per mil. Data suggest a correlation between nitrogen isotopes and C/N ratios, but no linear relation between carbon isotopes and carbon content and an only weak relationship between carbon and nitrogen isotopes. Increasing nitrogen isotope values from 8000 cm downwards could probably be related to changed environmental conditions of Marine Isotope Stage 3 (MIS 3) compared to Marine Isotope Stage 2 (MIS 2). This will be further evaluated with higher resolution from the composite profile including a detailed study of discrete plant debris layers. References Haberzettl, T. et al. (2007). Lateglacial and Holocene wet-dry cycles in southern Patagonia: chronology, sedimentology and geochemistry of a lacustrine record from Laguna Potrok Aike, Argentina. The Holocene, 17: 297-310. Mayr, C. et al. (2009). Isotopic and geochemical fingerprints of environmental changes during the last 16,000 years on lacustrine organic matter from Laguna Potrok Aike (southern Patagonia, Argentina). Journal of Paleolimnology, 42: 81-102.

  1. The HOLOANTAR project: Holocene environmental change in the Maritime Antarctic. Interactions between permafrost and the lacustrine environment

    NASA Astrophysics Data System (ADS)

    Oliva, Marc; Vieira, Gonçalo; Mora, Carla; Trindade, Alexandre; Agrela, Joao; Batista, Vanessa; Correia, António; Schaefer, Carlos; Simas, Felipe; Ramos, Miguel; De Pablo, Miguel Angel; Toro, Manuel; Antoniades, Dermot; Galan, Luis; Giralt, Santiago; Granados, Ignacio; Pla, Sergi; Serrano, Enrique

    2013-04-01

    The objective of this abstract is to present the HOLOANTAR project, a multidisciplinary research funded by the Portuguese Government. The project integrates 16 researchers from different international institutions (Portugal, Spain, Brazil and Uruguay).. The main purpose of HOLOANTAR is to infer the palaeoenvironmental evolution and associated climate variability occurred over the last millennia in ice-free areas of the Maritime Antarctica based on the study of lake sediments. The South Shetland Islands (SSI) are located in the northwestern tip of the Antarctic Peninsula, one of the Earth's regions that have experienced a stronger warming signal during the second half of the 20th century. In the ice-free areas of this archipelago the terrestrial ecosystem is supported by permafrost, though its reaction to climate change is still poorly known. However, in the recent years a very important effort took place to monitor the thermal state and characteristics of permafrost in order to study its response to the recent warming trend. Many international teams are involved on several of these long-term monitoring projects, but HOLOANTAR, in addition, pretends to offer a new integrated approach aiming to bridge the gap between contemporary and past changes in permafrost environments. HOLOANTAR project is based on two main hypotheses: a) A multi-proxy analysis of lake sediments will allow reconstructing the palaeoecological evolution in the Maritime Antarctic and the role played in it by permafrost and active layer dynamics, b) The detection of activity rates, spatial patterns and geographical controls of contemporary key-geomorphic processes and permafrost distribution, will allow defining their limiting climatic conditions that will be used to interpret the sedimentary record. This approach is innovative since it will focus on both present and past geomorphodynamics as keys for understanding the landscape evolution. In Byers Peninsula (Livingston), the largest ice-free area in the South Shetland Islands, where the environment is dominated by permafrost and active layer dynamics, climate variability should have induced modifications on the erosion rates at the slopes, mass movements, active layer thickness, biological activity, etc. In a context of fast rate of current change in mean annual air temperatures, it is possible that by studying similar features at different altitudes, different movement rates and an altitudinal/climatic boundary for their activity may be found, thus providing important applications for the palaeoenvironmental reconstruction. We will approach the two leading hypothesis in Byers environment by executing five main tasks: geomorphological mapping, geomorphological monitoring and permafrost distribution, sedimentological field work, laboratory analyses and palaeoenvironmental reconstruction. During the first field work campaign that took place in November-December 2012, up to four lakes were sampled. Future studies of these sediments will allow reconstructing the environment in Byers since the deglaciation of westernmost part of Livingston island.

  2. Holocene Enviromental Changes in AN Amazonian Floodplain Lake

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  3. High Molybdenum availability for evolution in a Mesoproterozoic lacustrine environment.

    PubMed

    Parnell, John; Spinks, Samuel; Andrews, Steven; Thayalan, Wanethon; Bowden, Stephen

    2015-05-19

    Trace metal data for Proterozoic marine euxinic sediments imply that the expansion of nitrogen-fixing cyanobacteria and diversification of eukaryotes were delayed while the availability of bioessential metals such as molybdenum in the ocean was limited. However, there is increasing recognition that the Mesoproterozoic evolution of nitrogen fixation and eukaryotic life may have been promoted in marginal marine and terrestrial environments, including lakes, rather than in the deep ocean. Molybdenum availability is critical to life in lakes, just as it is in the oceans. It is, therefore, important to assess molybdenum availability to the lacustrine environment in the Mesoproterozoic. Here we show that the flux of molybdenum to a Mesoproterozoic lake was 1 to 2 orders of magnitude greater than typical fluxes in the modern and ancient marine environment. Thus, there was no barrier to availability to prevent evolution in the terrestrial environment, in contrast to the nutrient-limited Mesoproterozoic oceans.

  4. High Molybdenum availability for evolution in a Mesoproterozoic lacustrine environment

    NASA Astrophysics Data System (ADS)

    Parnell, John; Spinks, Samuel; Andrews, Steven; Thayalan, Wanethon; Bowden, Stephen

    2015-05-01

    Trace metal data for Proterozoic marine euxinic sediments imply that the expansion of nitrogen-fixing cyanobacteria and diversification of eukaryotes were delayed while the availability of bioessential metals such as molybdenum in the ocean was limited. However, there is increasing recognition that the Mesoproterozoic evolution of nitrogen fixation and eukaryotic life may have been promoted in marginal marine and terrestrial environments, including lakes, rather than in the deep ocean. Molybdenum availability is critical to life in lakes, just as it is in the oceans. It is, therefore, important to assess molybdenum availability to the lacustrine environment in the Mesoproterozoic. Here we show that the flux of molybdenum to a Mesoproterozoic lake was 1 to 2 orders of magnitude greater than typical fluxes in the modern and ancient marine environment. Thus, there was no barrier to availability to prevent evolution in the terrestrial environment, in contrast to the nutrient-limited Mesoproterozoic oceans.

  5. Age and paleoenvironmental reconstruction of partially remagnetized lacustrine sedimentary rocks (Oligocene Aktoprak basin, central Anatolia, Turkey)

    NASA Astrophysics Data System (ADS)

    Meijers, Maud J. M.; Strauss, Becky E.; Özkaptan, Murat; Feinberg, Joshua M.; Mulch, Andreas; Whitney, Donna L.; Kaymakçı, Nuretdin

    2016-03-01

    The age and paleoenvironmental record of lacustrine deposits in the Aktoprak basin of south-central Turkey provides information about the evolution of topography, including the timing of development of an orographic rain shadow caused by uplift of the mountain ranges fringing the Central Anatolian Plateau. New magnetostratigraphy-based age estimates, in combination with existing biostratigraphic ages, suggest that the partially remagnetized Kurtulmuş Tepe section of the basin is Chattian (Upper Oligocene). The mean carbon and oxygen stable isotope ratios (δ18O= 24.6 ± 2.0 ‰, δ13C= -4.9 ± 1.1‰) are largely constant through the section and indicative of a subtropical, open freshwater lake. These isotopic values are also similar to those of the Chattian Mut basin to the south, on the Mediterranean side of the modern orographic barrier (Tauride Mountains), and indicate absence of an orographic barrier during Late Oligocene basin deposition. Post-depositional partial remagnetization occurred after tilting of the basin sequence and was mineralogically controlled, affecting grey, carbonate-rich rocks (average %CaCO3= 82), whereas interlayered pink carbonate-poor rocks (average %CaCO3= 38) carry a primary, pretilt magnetization. The pink rocks are rich in clay minerals that may have reduced the permeability of these rocks that carry a primary magnetization, concentrating basinal fluid flow in the carbonate-rich grey layers and leading to the removal and reprecipitation of magnetic minerals. The normal and reverse polarities recorded by the remagnetized rocks suggest that remagnetization occurred over a protracted period of time.

  6. A Deglacial and Holocene Record of Climate Variability in South-Central Alaska from Stable Oxygen Isotopes and Plant Macrofossils in Peat

    NASA Technical Reports Server (NTRS)

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

    2014-01-01

    We used stable oxygen isotopes derived from bulk peat (delta-O-18(sub TOM) in conjunction with plant macrofossils and previously published carbon accumulation records, in a approximately14,500 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 delta-O-18(sub TOM) 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 delta-O-18(sub TOM) values) during the Bolling-Allerod, 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 delta-O-18 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 delta-O-18(sub TOM) 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 delta-O-18(sub TOM) values in peat can be applied

  7. Lacustrine Mineral Deposits and their Geologic Context at Bradbury Crater on Mars

    NASA Astrophysics Data System (ADS)

    Tirsch, Daniela; Erkeling, Gino; Bishop, Janice L.; Tornabene, Livio L.; Hiesinger, Harald; Jaumann, Ralf

    2016-04-01

    The 60-km Bradbury Crater (85.8° E; 2.7° N) is located at the Libya Montes region at the southern rim of the Isidis impact basin on Mars. This area is predominantly characterized by Noachian-aged highland massifs that were heavily modified by fluvial, lacustrine, aeolian, volcanic, and impact processes occurring in multiple recurring events. Bradbury Crater stands out for its abundance of fluvial and lacustrine landforms, which reflect a varied history of aqueous-related geological processes. A 2.8 by 5 km-sized fan-shaped deposit has been interpreted to have played a significant role in the hydrologic evolution of landforms at Bradbury Crater. This deposit is partly composed of Al-rich phyllosilicates, indicating aqueous alteration processes. The current work is directed towards shedding light on the origin and timing of these aqueous alteration processes. HRSC digital terrain models give conclusive insight into the stratigraphic relationships of those sediments to each other. Geological analyses have been performed on the basis of HRSC, CTX and HiRISE image data in combination with HRSC and HiRISE digital elevation models. Mineral detection has been performed by spectral analyses of targeted CRISM images. Fe/Mg-smectites are detected along the walls of the ancient Libya Montes bedrocks and could be a result of Isidis impact-related hydrothermal alteration. Carbonates intermixed with Fe/Mg-smectites occur at the base of the bedrock unit. Carbonate formation may have been driven by the interaction of hydrous CO2rich fluids with olivine at the paleolake site. An Al-smectite, consistent with beidellite, is exposed within several layers of the deltaic deposit. Because beidellite forms at elevated temperatures, its presence might either result from alteration in a warm paleolake at this site or it could be an allochtonous sediment deposited here subsequently. Since the strongest beidellite signatures are detected within the foreset and the bottomset layer of the

  8. Organic sedimentation in modern lacustrine systems: A case study from Lake Malawi, East Africa

    USGS Publications Warehouse

    Ellis, Geoffrey S.; Barry J. Katz,; Christopher A. Scholz,; Peter K. Swart,

    2015-01-01

    This study examines the relationship between depositional environment and sedimentary organic geochemistry in Lake Malawi, East Africa, and evaluates the relative significance of the various processes that control sedimentary organic matter (OM) in lacustrine systems. Total organic carbon (TOC) concentrations in recent sediments from Lake Malawi range from 0.01 to 8.80 wt% and average 2.83 wt% for surface sediments and 2.35 wt% for shallow core sediments. Hydrogen index (HI) values as determined by Rock-Eval pyrolysis range from 0 to 756 mg HC g−1 TOC and average 205 mg HC g−1 TOC for surface sediments and 228 mg HC g−1 TOC for shallow core samples. On average, variations in primary productivity throughout the lake may account for ~33% of the TOC content in Lake Malawi sediments (as much as 1 wt% TOC), and have little or no impact on sedimentary HI values. Similarly, ~33% to 66% of the variation in TOC content in Lake Malawi sediments appears to be controlled by anoxic preservation of OM (~1–2 wt% TOC), although some component of the water depth–TOC relationship may be due to physical sediment transport processes. Furthermore, anoxic preservation has a minimal effect on HI values in Lake Malawi sediments. Dilution of OM by inorganic sediment may account for ~16% of variability in TOC content in Lake Malawi sediments (~0.5 wt% TOC). The effect of inputs of terrestrial sediment on the organic character of surface sediments in these lakes is highly variable, and appears to be more closely related to the local depositional environment than the regional flux of terrestrial OM. Total nitrogen and TOC content in surface sediments collected throughout the lake are found to be highly correlated (r2 = 0.95), indicating a well-homogenized source of OM to the lake bottom. The recurring suspension and deposition of terrestrial sediment may account for significant amounts of OM deposited in offshore regions of the lake. This process effectively separates denser

  9. Holocene Lakes from Ramlat as-Sab'atayn (Yemen) Illustrate the Impact of Monsoon Activity in Southern Arabia*1

    NASA Astrophysics Data System (ADS)

    Lézine, Anne-Marie; Saliège, Jean-François; Robert, Christian; Wertz, Frédéric; Inizan, Marie-Louise

    1998-11-01

    Paleoecology and paleohydrology of the Ramlat as-Sab'atayn (Southern Arabia) are reconstructed from a comparative study including sedimentology, mineralogy, stable isotope ratios of carbonates, and palynology of lacustrine sediments recovered from the al-Hawa depression. The section dates from 8700 to 7200 yr B.P. and records an early phase of flooding followed by distinct lacustrine development from 7800 to 7200 yr B.P., coeval with maximum activity of the Indian monsoon. Comparison of the pollen record with modern pollen deposition suggests that regional vegetation was then already of desert type and was related to strong seasonal trade winds.

  10. The chemistry of playa-lake-sediments as a tool for the reconstruction of Holocene environmental conditions - a case study from the central Ebro basin

    NASA Astrophysics Data System (ADS)

    Schütt, Brigitta

    The focus of the presented study is the reconstruction of the Holocene limnic and drainage basin conditions of the Laguna de Jabonera, a today playa-lake-system in the Desierto de Calanda, central Ebro Basin, using the inorganic characters of the lacustrine sediments. Mineralogical fabric helped to reconstruct the overall geomorphic processes and gives clues to the synsedimentary limnic environment (paleosalinity). The chemical composition of the lacustrine sediments largely reflects the mineralogical composition, but the higher resolution of the geochemical data compared to the mineralogical data enables to stratigraphically split the extracted core profile into three stratigraphic units. Supplementally, it is demonstrated that Statistics between chemical compounds point to the synsedimentary intensity of weathering and soil forming processes. As for the lacustrine sediments investigated there are no data yet available a preliminary chronological framework is derived by comparison with results from neighbouring areas. Based on this the hypothesis is put forward that during the socalled Little Ice Age subhumid to dry-subhumid environmental conditions occurred. Also possibly during the late Subboreal distinct wetter environmental conditions than today prevailed. Additionally, it is demonstrated that in the most recent past human impact is causing increased erosion rates and, thus, increased deposition of detritals in the most recent lacustrine sediments.

  11. Glacial history of the Polar Urals inferred from terrestrial and lacustrine data

    NASA Astrophysics Data System (ADS)

    Svendsen, J. I.; Astakhov, V. I.; Bakke, J.; Gyllencreutz, R.; Henriksen, M.; Karlsen, L.; Lohne, Ø.; Mangerud, J.; Nazarov, D.

    2009-04-01

    A lake coring campaign in the Polar Urals is carried out within the framework of the Russian-Norwegian IPY-project "The Ice Age Development and Human Settlement in Northern Eurasia" (ICEHUS). The purpose is to improve the description and understanding of the Late Quaternary glacial and climate changes in this part of the Russian Arctic. Sediment cores are being obtained from selected mountain lakes that according to our hypothesis were not reached by local glaciers during the Last Glacial Maximum (LGM) some 25-20,000 years ago. The results are compared with other terrestrial data used to constrain the timing and extent of the former glaciers. This includes moraines, ice-dammed lakes, outwash sediments and other observations. The chronology is based on radiocarbon dating, cosmogenic isotope dating of erratics, and a large number of optically stimulated luminescence (OSL) dating of sediments. Judged from geomorphologic as well as stratigraphic observations it seems clear that the last major glaciation that affected the northern part of the Ural Mountains was a shelf-centred ice sheet that inundated the mountain valleys during the Early Weichselian. The OSL-dates of this event cluster around 75-80 ka. Following this glaciations the local glaciers appears to have been rather small and there is nothing to suggest that extensive valley glaciers existed, not even during the LGM. Coring results from the eastern foothills of the Polar Urals indicate that this area was affected by a major ice sheet advance during the Early Weichselian, but that the final deglaciation took place more than 70,000 yrs ago. This summer we will equip another field expedition aiming at retrieving long sediment cores from a 140 m deep lake (Bol. Schuchye) in the central part of the Polar Urals. Seismic profiles show that this basin contains more than a hundred meters of soft lacustrine sediments above bedrock. Radiocarbon dates from a short core that was collected in 2007 indicate that the upper 3

  12. Charophytes as lacustrine biomarkers during the quaternary in North Africa

    NASA Astrophysics Data System (ADS)

    Soulié-Märsche, I.

    The use of charophytes as biomarkers is discussed with emphasis on the differences in study methods for cosmopolitan and ecotype species. A first extensive inventory of Quaternary deposits of charophytes in Africa north of the equator comprising 18 sites from Senegal to the Sudan is drawn up with data on spatial and temporal distribution. The existence of relatively deep cold lakes in the Holocene is shown by the frequent presence of specimens of cold flora no longer present in Africa today. All the original data show the complementary nature of the study of fossil Charophyta for the multidisciplinary reconstitution of palaeoenvironments.

  13. Global Change in the Holocene

    NASA Astrophysics Data System (ADS)

    Alverson, Keith

    2004-05-01

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

  14. Late Holocene stratigraphy of the Tetimpa archaeological sites, northeast flank of Popocatepetl volcano, central Mexico

    USGS Publications Warehouse

    Panfil, M.S.; Gardner, T.W.; Hirth, K.G.

    1999-01-01

    Late Holocene (240 km2 on the east side of the volcano with >25 cm of tephra. Lavas from eruptive sequence I dammed drainage in the lowland area near the town of San Nicolas and caused local upstream deposition of as much as 30 m of lacustrine silts, clays, and sands. These lacustrine deposits record an eruptive hiatus for the Tetimpa area of about 750 14C yr: between ca. 2100 and ca. 1350 yr B.P., no major tephras were deposited in the Tetimpa area. In upland areas, this time period is represented by an unconformity and by Entisols formed in the top of pumice deposits and lavas from eruptive sequence I. Artifacts, agricultural furrows, and dwellings record human reoccupation of this surface. At the end of this hiatus, several lahars were deposited above the lacustrine sequence and locally above the Entisol in upland positions adjacent to streams. Between ca. 1350 and ca. 1200 yr B.P., tephras from eruptive sequence II buried these paleosols, occupation sites, lacustrine sediments, and lahars. Andesitic (~62% SiO2) pumice lapilli deposits in the Tetimpa area record three pumice-fall eruptions directed northeast and east of the crater. The first and smallest of these (maximum Tetimpa area thickness = 12 cm; >52 km2 covered by >25 cm) took place at ca. 1350 yr B.P. and was accompanied by pyroclastic surge events preserved in the Tetimpa area by charcoal, sand waves, and cross-stratified sand-sized tephra. At ca. 1200 yr B.P., the products of two Plinian-style events and additional pyroclastic surges reached the Tetimpa area. The largest of these tephra-fall events covered the Tetimpa area with 0.5-1 m of tephra and blanketed an area of >230 km2 with a thickness of >25 cm. The Tetimpa record confirms two of the four periods of explosive volcanism recognized by studies conducted around Popocatepetl in the past 30 yr. Eruptive sequence I corresponds to the explosive period between 2100 and 2500 yr B.P., and eruptive sequence II corresponds to the period between 900 and

  15. Stratified tephra records from lake sediment archives: Holocene eruptions of the Virunga Volcanic Province, East African Rift

    NASA Astrophysics Data System (ADS)

    Lane, Christine; Scholz, Christopher; Poppe, Sam; Schmid, Martin; Ross, Kelly Ann

    2016-04-01

    Lake sediments preserve rare stratified records of explosive volcanism, often with accompanying chronological controls or climatostratigraphic detail. In proximal areas where outcrop stratigraphies are complex, exposures isolated and sediments frequently eroded, the lacustrine archive provides a means to check the order of events and identify additional eruptions not preserved on land. The visible volcanic ash (tephra) record within lake sediments may be limited by eruption volume, distance from source and high sedimentation rates. A more complete eruption history can be detected through the study of non-visible tephra layers. Such "cryptotephra" records may be revealed through non-destructive core-scanning methods, such as XRF-scanning or magnetic susceptibility measurements, or by more thorough laboratory processes and microscopic analysis. Compositional analysis of tephra glass shards using WDS-EPMA and LA-ICP-MS provide a means to provenance eruptions, to cross-correlate between multiple sediment cores, and to establish connections between the lacustrine record and proximal outcrops. Here we present the results of such a "tephrostratigraphic" approach applied to the Holocene volcanic record of the Virunga Volcanic Province (VVP). More than 10 explosive volcanic eruptions, attributed to multiple volcanic centres, are evidenced over the last 12,000 years. This unique insight into the frequency of explosive eruptions from the VVP, demonstrates the potential of visible and cryptotephra investigations in lacustrine sediment archives as a means of studying past, present and future volcanic hazards.

  16. An abrupt centennial-scale drought event and mid-holocene climate change patterns in monsoon marginal zones of East Asia.

    PubMed

    Li, Yu; Wang, Nai'ang; Zhang, Chengqi

    2014-01-01

    The mid-latitudes of East Asia are characterized by the interaction between the Asian summer monsoon and the westerly winds. Understanding long-term climate change in the marginal regions of the Asian monsoon is critical for understanding the millennial-scale interactions between the Asian monsoon and the westerly winds. Abrupt climate events are always associated with changes in large-scale circulation patterns; therefore, investigations into abrupt climate changes provide clues for responses of circulation patterns to extreme climate events. In this paper, we examined the time scale and mid-Holocene climatic background of an abrupt dry mid-Holocene event in the Shiyang River drainage basin in the northwest margin of the Asian monsoon. Mid-Holocene lacustrine records were collected from the middle reaches and the terminal lake of the basin. Using radiocarbon and OSL ages, a centennial-scale drought event, which is characterized by a sand layer in lacustrine sediments both from the middle and lower reaches of the basin, was absolutely dated between 8.0-7.0 cal kyr BP. Grain size data suggest an abrupt decline in lake level and a dry environment in the middle reaches of the basin during the dry interval. Previous studies have shown mid-Holocene drought events in other places of monsoon marginal zones; however, their chronologies are not strong enough to study the mechanism. According to the absolutely dated records, we proposed a new hypothesis that the mid-Holocene dry interval can be related to the weakening Asian summer monsoon and the relatively arid environment in arid Central Asia. Furthermore, abrupt dry climatic events are directly linked to the basin-wide effective moisture change in semi-arid and arid regions. Effective moisture is affected by basin-wide precipitation, evapotranspiration, lake surface evaporation and other geographical settings. As a result, the time scales of the dry interval could vary according to locations due to different geographical

  17. Transformation of marine sediment to paddy soil: Primary marine, lacustrine, and land plant lipids

    NASA Astrophysics Data System (ADS)

    Mueller-Niggemann, Cornelia; Cao, Zhihong; Schwark, Lorenz

    2010-05-01

    More than fifty percent of the world's population feeds on rice. The continuous population increase and urban sprawl leads to an ever-increasing demand for new rice cultivation area, in particular China. For centuries suitable coastal areas in China have been exploited for land reclamation, i.e. conversion of coastal marine and lacustrine marshlands into rice paddy fields. Flooded rice paddies are considered one of the major biogenic sources of methane into the atmospheric. Methane is thought to be about 30 times more efficient as greenhouse gas, when compared to carbon dioxide. Overall, rice fields are assumed to contribute app. 10-25% to global CH4 production. It is thus paramount importance to study the effects of increasing rice cultivation and land reclamation in China. For global carbon cycle investigation, it is crucial whether paddy soils, due to their large extent and higher carbon turnover, serve as carbon (CO2) sinks or sources. Here we present results from a chronosequence study of paddy soils with different and well known starting dates of cultivation, in the Zhejiang province (Yangtze River delta) by land reclamation through the building of protective dikes over the past 2000 years. Two end members of natural sediments subjected to land reclamation, a marine tidal mudflat in the Yangtze delta and a coastal lake, represent the substrate on which the paddy soil evolution started. Dike systems were constructed 2000, 1000, 700, 300, 100, and 50 years before present. We are thus able to follow the evolution of rice paddy soils developed on marine sediments using eight well defined tie-points. This chronosequence is then used for assessing the relative proportion of primary marine or lacustrine organic matter preserved in present day soils and to identify the amount and composition of organic matter added since cultivation started. Paddy soil management introduces rice plants debris and exudates as well as rice-associated microbial biomass (covered in a

  18. Prokaryotic diversity in sediments beneath two polar glaciers with contrasting organic carbon substrates.

    PubMed

    Stibal, Marek; Hasan, Fariha; Wadham, Jemma L; Sharp, Martin J; Anesio, Alexandre M

    2012-03-01

    Microbial ecosystems beneath glaciers and ice sheets are thought to play an active role in regional and global carbon cycling. Subglacial sediments are assumed to be largely anoxic, and thus various pathways of organic carbon metabolism may occur here. We examine the abundance and diversity of prokaryotes in sediment beneath two glaciers (Lower Wright Glacier in Antarctica and Russell Glacier in Greenland) with different glaciation histories and thus with different organic carbon substrates. The total microbial abundance in the Lower Wright Glacier sediment, originating from young lacustrine sediment, was an order of magnitude higher (~8 × 10(6) cells per gram of wet sediment) than in Russell Glacier sediment (~9 × 10(5) cells g(-1)) that is of Holocene-aged soil origin. 4% of the microbes from the Russell Glacier sediment and 0.04-0.35% from Lower Wright Glacier were culturable at 10°C. The Lower Wright Glacier subglacial community was dominated by Proteobacteria, followed by Firmicutes. The Russell Glacier library was much less diverse and also dominated by Proteobacteria. Low numbers and diversity of both Euryarchaeota and Crenarchaeota were found in both sediments. The identified clones were related to bacteria with both aerobic and anaerobic metabolisms, indicating the presence of both oxic and anoxic conditions in the sediments.

  19. Across an early Holocene humid phase in western Sahara:Pollen and isotope stratigraphy

    NASA Astrophysics Data System (ADS)

    Lézine, Anne-Marie; Casanova, Joël; Hillaire-Marcel, Claude

    1990-03-01

    Paleohydrology and paleoecology of the region around the Chemchane sabkha (Mauritania) are reconstructed from the comparative analyses of mineralogy, stable isotope ratios of bulk carbonates, and palynology from sediment cores. The age of the section is from ca. 13.5 ka to the middle Holocene. Maximum lake expansion between about 8.3 and 6.5 ka is recorded in a girdle of stromatolite carbonates. These document a lower-salinity lake concomitant with a general establishment of Sahel-Sudan vegetation. The Chemchane area is the northernmost (lat 21°N) occurrence of humid- phase elements that are related to maximum intensity of monsoon activity during the early Holocene.

  20. Hydroecology of Amazonian lacustrine Arcellinida (testate amoebae): A case study from Lake Quistococha, Peru.

    PubMed

    Patterson, R Timothy; Huckerby, Gail; Kelly, Thomas J; Swindles, Graeme T; Nasser, Nawaf A

    2015-10-01

    Organic rich sediments were obtained from seven core tops taken in Lake Quistococha, near the city of Iquitos in the Peruvian Amazon. Subsamples from 0 to 4cm depth in each core were analyzed under dissecting light microscopy to carry out the first investigation of Arcellinida (testate lobose amoebae) from a lacustrine environment in this ecologically important region. The fauna was characterized by a low diversity, low abundance community dominated by centropyxids. This fauna is similar to 'stressed' assemblages reported from temperate latitudes, except that test concentrations were two orders of magnitude lower than typical in temperate lakes. Principle arcellinidan stressors in Lake Quistococha likely include the low pH 4 conditions in the lake, and a general lack of suitable minerogenic material to construct tests in the organic rich lake substrate. The low pH conditions are the result of runoff and seepage of water high in dissolved organic carbon from the adjacent similarly low pH 4 terrestrial peatland. The dearth of minerogenic material is the result of the lake being isolated from riverine input for the past ∼2000 years, even during flooding events. Other limiting factors contributing to depressed arcellinidan populations may include nutrient supply, predation pressure, competition, and post-mortem taphonomic factors.

  1. The Anthropocene is functionally and stratigraphically distinct from the Holocene.

    PubMed

    Waters, Colin N; Zalasiewicz, Jan; Summerhayes, Colin; Barnosky, Anthony D; Poirier, Clément; Gałuszka, Agnieszka; Cearreta, Alejandro; Edgeworth, Matt; Ellis, Erle C; Ellis, Michael; Jeandel, Catherine; Leinfelder, Reinhold; McNeill, J R; Richter, Daniel deB; Steffen, Will; Syvitski, James; Vidas, Davor; Wagreich, Michael; Williams, Mark; Zhisheng, An; Grinevald, Jacques; Odada, Eric; Oreskes, Naomi; Wolfe, Alexander P

    2016-01-08

    Human activity is leaving a pervasive and persistent signature on Earth. Vigorous debate continues about whether this warrants recognition as a new geologic time unit known as the Anthropocene. We review anthropogenic markers of functional changes in the Earth system through the stratigraphic record. The appearance of manufactured materials in sediments, including aluminum, plastics, and concrete, coincides with global spikes in fallout radionuclides and particulates from fossil fuel combustion. Carbon, nitrogen, and phosphorus cycles have been substantially modified over the past century. Rates of sea-level rise and the extent of human perturbation of the climate system exceed Late Holocene changes. Biotic changes include species invasions worldwide and accelerating rates of extinction. These combined signals render the Anthropocene stratigraphically distinct from the Holocene and earlier epochs.

  2. Alluvial-fan and lacustrine fan-delta sedimentation in west-central California during the Middle Tertiary transition from subduction to transform tectonics

    SciTech Connect

    Cole, R.B. . Dept. of Geological Science); Stanley, R.G. )

    1992-01-01

    The Plush Ranch (PR) Formation was deposited in one of several sedimentary basins in west-central California. The PR consists of more than 1,800 m of nonmarine sedimentary rocks and interbedded basaltic volcanic rocks that together record a complicated history of synsedimentary faulting, volcanism, and deposition in alluvial-fan, fan-delta, and lacustrine depositional settings. The sedimentological analysis indicates that both the northern and southern margins of the PR basin apparently were controlled ENE-trending normal faults, but that the two margins are characterized from each other by distinctive depositional facies, provenance, and sediment transport directions. The northern basin margin is recorded by sandstone-dominated braidplain deposits, with interbedded lenses of boulder-rich breccia derived by landsliding from a nearby granitic provenance. The southern basin margin is represented by matrix- and clast-supported boulder- to pebble-conglomerate with interbedded trough-crossbedded sandstones; these represent debris-flow and stream-flow alluvial-fan deposits. The alluvial-fan deposits grade northward into lacustrine fan-delta facies and provide an excellent detailed record of interfingering between alluvial-fan and lacustrine fan-delta deposits on a bed-by-bed scale. Basalt are interbedded with turbidite sandstones and evaporite/carbonate-rich intervals, but not with alluvial-fan deposits. The analysis of the sedimentary record of the PR Formation permits documentation of detailed facies relations that are useful in understanding alluvial-fan and fan-delta transitions in fault-bounded lacustrine basins. In addition, results support the conclusion of earlier workers that the Big Pine fault was a down-to-the-north, normal-slip fault along the southern margin of the PR basin during late Oligocene-early Miocene time, and then became a predominantly left-slip fault during the Quaternary.

  3. Paleo-environmental controls on cold seep carbonate authigenesis in the Sea of Marmara

    NASA Astrophysics Data System (ADS)

    Crémière, Antoine; Bayon, Germain; Ponzevera, Emmanuel; Pierre, Catherine

    2013-08-01

    The factors controlling fluid emission dynamics at ocean margins are poorly understood. In particular, there are significant uncertainties on how fluid seepage at cold seeps may have responded to abrupt environmental changes in the geological past. This study reports on a detailed geochemical investigation of seafloor carbonate crusts sampled at cold seeps along the submerged part of the North Anatolian Fault system in the Sea of Marmara - an inland sea, which has experienced major paleo-environmental changes over the last deglaciation period. We also analyzed a series of authigenic carbonate concretions recovered from two sediment cores at the Western-High ridge, an active fluid venting area. The ages of seafloor carbonate crusts derived from isochron U-Th dating cover the last 7 kyr, suggesting that fluid activity along the fault system remained continuous over that time interval. In the sediment cores, carbonate concretions are concentrated at the lacustrine-to-marine transition, which corresponds to the period when Mediterranean waters flowed into the Marmara Basin about 12-14 kyr ago. U-Th isotopic data indicate that most of these concretions formed later during the Holocene, around 9-10 kyr ago, a period coinciding with an important anoxic event that led to the deposition of a sapropel layer in the Sea of Marmara. Based upon these results, we suggest that the absence of carbonate concretions in the lacustrine sediment unit indicates that dissolved sulfate concentrations in the Marmara lake pore waters during glacial time were too low to promote significant anaerobic methane oxidation, thereby preventing sedimentary carbonate authigenesis. In contrast, the progressive inflow of Mediterranean waters into the glacial Marmara lake after 15 ka provided a source of dissolved sulfate that allowed anaerobic oxidation of methane to proceed within the anoxic sediment. Importantly, the synchronism between the main phase of authigenic carbonate precipitation at the

  4. Local and regional oscillations of carbon and oxygen isotopes in terestrial carbonates

    NASA Astrophysics Data System (ADS)

    Skipitytė, Raminta; Stančikaitė, Miglė

    2014-05-01

    separate local, regional and even global environment condition impact to isotopic values in the past. 1. Hammarlund, Dan, et al. "Climate and environment during the Younger Dryas (GS-1) as reflected by composite stable isotope records of lacustrine carbonates at Torreberga, southern Sweden." Journal of Quaternary Science 14.1 (1999): 17-28. 2. Makhnach, N., et al. "Stable oxygen and carbon isotopes in Late Glacial-Holocene freshwater carbonates from Belarus and their palaeoclimatic implications." Palaeogeography, Palaeoclimatology, Palaeoecology 209.1 (2004): 73-101.

  5. Holocene climate of New England

    NASA Astrophysics Data System (ADS)

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

    1980-09-01

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

  6. Early Carboniferous (Visean) lacustrine oil shale in Canadian Arctic archipelago

    SciTech Connect

    Davies, G.R.; Nassichuk, W.W.

    1988-01-01

    The Lower Carboniferous (Visean) Emma Fiord Formation in the Canadian Arctic Archipelago is an oil shale of lacustrine origin composed of black carbonaceous shale, siltstone, and marlstone with interbedded sandstone, conglomerate, and oolitic and algal limestones. At Kleybolte Peninsula on Ellesmere Island, the Emma Fiord Formation was deposited on the tectonically active northwestern rim of the Sverdrup basin; it is now thermally overmature and well beyond the dry gas zone of organic maturation (vitrinite reflectance approx. = 5.0). In contrast, the Emma Fiord sequence on Grinnell Peninsula, Devon Island, near the southern edge of the Sverdrup basin, is immature to marginally mature (vitrinite reflectance = 0.26-0.44) and is composed predominantly of liptinite-rich oil shale. These kerogen-rich rocks contain a high volume of microcrystalline calcite and compositionally are marlstones. The Emma Fiord oil shales were deposited in lakes formed immediately prior to or possibly synchronous with the initiation of rifting in the Sverdrup basin. Syntectonic red-bed conglomerates derived from uplifted horst blocks directly overlie the Emma Fiord rocks. A few beds of conglomerate and sandstone in the upper part of the Emma Fiord Formation possibly record the onset of faulting. The formation closely resembles contemporaneous sequences in northern Alaska, Yukon Territory, Greenland, and Spitsbergen. Clearly, similar tectonic and paleoclimatic factors influenced sedimentation over this area in the Early Carboniferous, with the Sverdrup basin locations lying within 10/sup 0/-15/sup 0/ of the paleoequator. 11 figures, 2 tables.

  7. Ecological state of the Romanian Black Sea littoral lacustrine ecosystems

    NASA Astrophysics Data System (ADS)

    Gomoiu, M.-T.

    2009-04-01

    The author uses the results of his own researches as well as data from specialty literature to assess the ecological state of some typical lacustrine ecosystems considered, about 50 years ago, of major importance by their functions, services and researches, for the human populations in the settlements nearby. Based on this assessment the author recommends a few criteria which can be taken into account when programs of integrated management of these coastal ecosystems are initiated. The paper focuses on the study cases regarding the following major ecosystems: 1. Razelm-Sinoie Lagoon Complex - tightly linked to the Danube River and Delta systems, 2. Taşaul Lake - interfered in the last two decades by a branch of the DanubeRiver - Black Sea Canal and 3. Techirghiol Lake - for a long time under the sea level, a hyperhaline lake with therapeutic, sapropelic mud, disturbed by huge quantities of freshwaters infiltrated from the irrigation system. At present, the state of the lacustrine ecosystems at the Romanian Black Sea Coast can be characterized, mainly, by the following aspects: · Increase in the quantities of nutrients and chemical toxicants; · Rise in the level and frequency of eutrophication and pollution phenomena; · Drastic reduction of specific diversity; · Simplification of communities' structure - biocoenosis homogeneity; · Decrease in numerical abundance and biomass of benthic populations and consequently, low biofilter power by the decrease of the filter-feeder populations; · Worsening of the qualitative and the quantitative state of the biological benthic resources; · Thriving opportunistic forms (e.g. the worms causing sediment bioturbation); · Invasion by some exotic species, with harmful, unexpected consequences; · All populations undergo quantitative fluctuations; · Decrease in the fish population and in the use values of lacustrine assets, with strong impact on the welfare of the human society. Almost all pressure forms associated with the

  8. Small-scale lacustrine drifts in Lake Champlain, Vermont

    USGS Publications Warehouse

    Manley, Patricia L.; Manley, T.O.; Hayo, Kathryn; Cronin, Thomas

    2012-01-01

    High resolution CHIRP (Compressed High Intensity Radar Pulse) seismic profiles reveal the presence of two lacustrine sediment drifts located in Lake Champlain's Juniper Deep. Both drifts are positive features composed of highly laminated sediments. Drift B sits on a basement high while Drift A is built on a trough-filling acoustically-transparent sediment unit inferred to be a mass-transport event. These drifts are oriented approximately north–south and are parallel to a steep ridge along the eastern shore of the basin. Drift A, located at the bottom of a structural trough, is classified as a confined, elongate drift that transitions northward to become a system of upslope asymmetric mudwaves. Drift B is perched atop a structural high to the west of Drift A and is classified as a detached elongate drift. Bottom current depositional control was investigated using Acoustic Doppler Current Profilers (ADCPs) located across Drift A. Sediment cores were taken at the crest and at the edges of the Drift A and were dated. Drift source, deposition, and evolution show that these drifts are formed by a water column shear with the highest deposition occurring along its crest and western flank and began developing circa 8700–8800 year BP.

  9. Origin of lacustrine rocks of Wilkins Peak Member, Wyoming

    SciTech Connect

    Sullivan, R.

    1985-06-01

    Wilkins Peak Member of the Green River Formation, with its interbeds of trona, oil shale, and dolomitic mudstone, contrasts markedly with the predominantly oilshale and calcitic mudstone sequences of the remainder of the succession. Much discussion has centered on the origin of these lacustrine rocks. A perennial meromictic (stratified) lake model has been replaced in recent years by a playa-lake model. The subsurface stratigraphy, however, was not well known when the models were developed. Paleogeographic reconstruction indicates that the region was subjected to variations in hydrographic conditions mainly in response to climatic fluctuations. During humid subtropical periods, widespread during the deposition of the Tipton Shale Member and Laney Member, the lakes were predominantly open meromictic systems with rivers entering the basin from the north. These environmental conditions were modified during deposition of the Wilkins Peak Member as the climate became more arid, and along the southern margin of the basin, shallow, saline-alkaline playa lakes formed in response to these changes. The widespread occurrence in the subsurface of fluvial clastic sequences of the Wasatch Formation associated with the Wilkins Peak Member would indicate that the playa lakes were frequently flooded and freshened by southern drainage systems. Therefore, the lakes were continuously undergoing modifications under the influence of climatic and possibly tectonic processes.

  10. Holocene estuarine sediments as a source of arsenic in Pleistocene groundwater in suburbs of Hanoi, Vietnam

    NASA Astrophysics Data System (ADS)

    Kuroda, Keisuke; Hayashi, Takeshi; Funabiki, Ayako; Do, An Thuan; Canh, Vu Duc; Nga, Tran Thi Viet; Takizawa, Satoshi

    2017-01-01

    Groundwater pollution by arsenic is a major health threat in suburban areas of Hanoi, Vietnam. The present study evaluates the effect of the sedimentary environments of the Pleistocene and Holocene deposits, and the recharge systems, on the groundwater arsenic pollution in Hanoi suburbs distant from the Red River. At two study sites (Linh Dam and Tai Mo communes), undisturbed soil cores identified a Pleistocene confined aquifer (PCA) and Holocene unconfined aquifer (HUA) as major aquifers, and Holocene estuarine and deltaic sediments as an aquitard layer between the two aquifers. The Holocene estuarine sediments (approximately 25-40 m depth, 9.6-4.8 cal ka uc(BP)) contained notably high concentrations of arsenic and organic matter, both likely to have been accumulated by mangroves during the Holocene sea-level highstand. The pore waters in these particular sediments exhibited elevated levels of arsenic and dissolved organic carbon. Arsenic in groundwater was higher in the PCA (25-94 μg/L) than in the HUA (5.2-42 μg/L), in both the monitoring wells and neighboring household tubewells. Elevated arsenic concentration in the PCA groundwater was likely due to vertical infiltration through the arsenic-rich and organic-matter-rich overlying Holocene estuarine sediments, caused by massive groundwater abstraction from the PCA. Countermeasures to prevent arsenic pollution of the PCA groundwater may include seeking alternative water resources, reducing water consumption, and/or appropriate choice of aquifers for groundwater supply.

  11. Holocene paleoenvironmental change in southeastern Africa (Makwe Rockshelter, Zambia): Implications for the spread of pastoralism

    NASA Astrophysics Data System (ADS)

    Robinson, Joshua R.; Rowan, John

    2017-01-01

    The paleoenvironmental conditions surrounding the origins of pastoralism and the movement of herders from eastern to southern Africa sometime between ∼4000 and 2000 ybp have been much debated. We lack, however, detailed paleoenvironmental data from sites sampling the hunter-to-herder transition in southeastern Africa, the likely corridor from eastern to southern Africa for early pastoralists. Here we report on new paleoenvironmental data from a site in the under-sampled area of eastern Zambia, Makwe Rockshelter, which has two aggregates of archaeological horizons representing the mid-Holocene (∼5700-5000 ybp) and the late Holocene (∼1600-800 ybp). The mid-Holocene sediments at Makwe document a foraging society, whereas the late Holocene sediments include both wild game and domestic livestock. Using stable carbon isotopes (δ13C) of herbivore enamel (n = 107), we show that the shift from mid-Holocene to late Holocene paleoenvironments was characterized by an increase in C4 vegetation. These data are complemented by paleoenvironmental records from Lake Malawi that show that C4 vegetation peaked after ∼2000 ybp and was coincident with the onset of cooler, more arid climates. This combined paleoenvironmental record has implications for the spread of pastoralism across southeastern Africa between ∼3000 and 2000 ybp and potential 'animal disease barriers' these early herders may have faced.

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

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

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

  13. Mono- and bicyclic squalene derivatives as potential proxies for anaerobic photosynthesis in lacustrine sulfur-rich sediments

    NASA Astrophysics Data System (ADS)

    Behrens, Anke; Schaeffer, Philippe; Bernasconi, Stefano; Albrecht, Pierre

    2000-10-01

    Two novel triterpenoid biomarkers have been isolated from a recent anoxic sulfur-rich sediment (Lake Cadagno, Switzerland) and identified by NMR as 11,15-dihydro-Δ 13,10(14)-cyclosqualene 1 and bis-(6,11-cyclofarnesa-2,7(14)-diene) 2. Both compounds have a novel hydrocarbon skeleton not known thus far in living organisms and formed by cyclization of squalene, likely through an enzymatic process. Regarding their origin, the 13C-depleted values of their stable carbon isotopic composition suggest a derivation either from purple sulfur photosynthetic bacteria or from anaerobic heterotrophic organisms feeding on the 13C-depleted biomass fixed by photosynthetic bacteria. Therefore, these novel triterpenoids may represent potential proxies for photic zone anoxia in lacustrine settings.

  14. Lacustrine sequence stratigraphy and computer modeling of the Erlian fault basin, North China

    SciTech Connect

    Lin Changsong; Li Sitian; Ren Jianye; Zhang Yanmei )

    1996-01-01

    Erlian fault basin, a major oil prospecting and producing area in North China, comprises about 40 grabens and half grabens. The basin was formed by extension from Jurassic to Early Cretaceous and filled with more than 3000m thick of clastic lacustrine deposits. Based on the integrated analysis of seismic profiles, logging and cores, 5 sequence sets and 12 sequences, bounded by discontinuous, have been identified. Three types of lacustrine sequences have been identified: (1) deep lacustrine basin sequences, mainly consisting of sublacustrine fan and fan delta systems; (2) shallow lacustrine basin sequences, predominately composed of fan delta and braided delta systems and (3) shallow lacustrine and fluvial basin sequences. The sequence architecture and the basin filling evolution were controlled by the basin structural framework and lacustrine level changes. The computer modeling study by using the backstripping and forward modeling technique has shown that the major unconformities confining the sequences may be generated by the variation in tectonic subsidence rate caused by episodic lithospheric stretching. The model have also be used to predict the sequence architecture and the facies distribution in the basin.

  15. Lacustrine sequence stratigraphy and computer modeling of the Erlian fault basin, North China

    SciTech Connect

    Lin Changsong; Li Sitian; Ren Jianye; Zhang Yanmei

    1996-12-31

    Erlian fault basin, a major oil prospecting and producing area in North China, comprises about 40 grabens and half grabens. The basin was formed by extension from Jurassic to Early Cretaceous and filled with more than 3000m thick of clastic lacustrine deposits. Based on the integrated analysis of seismic profiles, logging and cores, 5 sequence sets and 12 sequences, bounded by discontinuous, have been identified. Three types of lacustrine sequences have been identified: (1) deep lacustrine basin sequences, mainly consisting of sublacustrine fan and fan delta systems; (2) shallow lacustrine basin sequences, predominately composed of fan delta and braided delta systems and (3) shallow lacustrine and fluvial basin sequences. The sequence architecture and the basin filling evolution were controlled by the basin structural framework and lacustrine level changes. The computer modeling study by using the backstripping and forward modeling technique has shown that the major unconformities confining the sequences may be generated by the variation in tectonic subsidence rate caused by episodic lithospheric stretching. The model have also be used to predict the sequence architecture and the facies distribution in the basin.

  16. Climatic change evidence and lacustrine waves from maar lakes, Germany

    SciTech Connect

    Zolitschka, B.

    1992-01-01

    Annually laminated, non-glacial lake sediments from Lake Holzmaar (Eifel, western Germany) were investigated using large {open_quotes}Merkt{close_quotes} thin sections. The absolute age of varve intervals with variations in thickness and composition were correlated to climatic changes recorded by glacier fluctuations in the Alps. Back to 8800 years VT (vuarve time = varve years before 1950) glacier advances coincide with sedimentation rate minima; prior to 8800 years VT they coincide with sedimentation rate maxima. The early and middle Holocene sediments suggest a periodicity of about 1000 years for cold/warm cycles. A sequence of 512 varve-thickness measurements was subjected to spectral analysis. These provide apparent evidence for a 11-year sun-spot cycle. 30 refs., 3 fig.

  17. A high resolution history of the El Niño - Southern Oscillation and of the solar activity during the Late Glacial - Early Holocene in the subtropical Andean region.

    NASA Astrophysics Data System (ADS)

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

    2009-04-01

    High-resolution laminated lacustrine sediments are excellent archives of the past hydrological changes and they provide valuable insights about the climatic processes that trigger these changes. The paleoclimatic records located in the Southern Hemisphere are fundamental for understanding the evolution of the El Niño - Southern Oscillation (ENSO) since this climatic phenomena is the main cause of droughts and floods in many areas of South America and other regions of the world, like Spain and Egypt. Available regional paleoclimate reconstructions show that modern climatic patterns in South America were established during the Late Holocene. The laminated sediments of Lago Chungará (18° 15' S - 69° 10' W, 4520 m a.s.l., Chilean altiplano) have allowed us to characterize the evolution of this climatic phenomena for the transition Late Glacial - Early Holocene (12,300 - 9,500 calendar years BP) as well as its relationship with other climate forcings, namely the solar activity. The studied sediments correspond to the lowermost 2.4 m of 8 m long Kullemberg cores recovered from this lake. These sediments are mainly made up of greenish and whitish laminae and thin layers constituted by diatomaceous oozes with carbonates and organic matter, arranged in rhythms and cycles. X-ray fluorescence (XRF) (Al, Si, S, K, Ca, Ti, Mn, Fe, Rb, Sr, Zn, Sb and Ba) analyses, total organic carbon (TOC), total carbon (TC), x-ray diffraction (XRD), biogenic silica, stable isotopes (delta18O and delta13C) on carbonates and on diatoms (delta18O) and magnetic susceptibility were determined in order to characterize the sediments of Lago Chungará. Previous statistical studies (cluster and Principal Component Analyses (PCA)) were used to disentangle the paleoclimatic signal from the other ones (volcanic and tectonic). The chronological model framework was built using 6 radiocarbon dates, allowing us to establish that laminated couplets were deposited on a pluriannual basis. These couplets are

  18. Constructing an Alpine Fault Paleoseismicity Record from Slumped Lacustrine Deposits in the Cascade River Valley, South Westland, New Zealand

    NASA Astrophysics Data System (ADS)

    Coffey, G.; Moy, C. M.; Toy, V. G.; Ohneiser, C.; Howarth, J. D.

    2014-12-01

    The Alpine Fault is a major structure in New Zealand capable of producing earthquakes of magnitude 7 or greater, which delineates the boundary between the Australian and Pacific plates. Paleoseismic records of these earthquakes indicate recurrence intervals of 300 - 400 years over the last 1,300 years. However, there are no pre-Holocene records. Documenting the late Pleistocene record of magnitude, timing, and frequency of earthquakes would significantly reduce uncertainty in hazard analyses. The tectonically complex Cascade River Valley follows the Southern Alpine Fault, where the fault dominantly accommodates strike-slip motion. Two ~7m outcrops of proglacial lacustrine silt are exposed along the river in which, deformed rhythmites bounded by planar laminated rhythmites have been identified. These exhibit a variety of fold geometries in outcrop and x-ray computed tomography (CT) scans, all of which show some degree of asymmetry. Initial radiocarbon ages of 14,400 and 13,300 14C yr BP have been obtained from terrestrial plant material isolated from samples near the base of one outcrop. Given the age range and laminae density, these dates suggest that the rhythmites are varves, but additional radiocarbon dates and CT-scans will be used to confirm this. The deformed horizons are interpreted to be seismites formed by slumping. Earthquake shaking triggers an increase in pore fluid pressure, which destabilises the sublacustrine slope causing failure and the release of silt into the sedimentary system. As silt is transported by downslope shear it is deformed in distinct layers. Displacement of volumes of silt also causes the formation of seiche waves that apply shear stress to lake floor sediments causing further deformation. Deviations in magnetic susceptibility and the declination of magnetic remanence observed underneath and within deformed horizons are interpreted to be a response of earthquake shaking. Data from these different proxies will be presented and

  19. The multiproxy analysis of a lacustrine-palustrine sediment core from Lebanon reveals four climate cycles

    NASA Astrophysics Data System (ADS)

    Gasse, F. A.; van Campo, E.; Demory, F.; Develle, A.; Tachikawa, K.; Buchet, N.; Sonzogni, C.; Thouveny, N.; Bard, E. G.; Vidal, L.

    2013-12-01

    The study of a sediment core retrieved from the small Yammouneh basin (34.06°N-34.09°N, 36.0°E-36.03°E, 1360 m a.s.l.), Lebanon, provides for the first time a nearly continuous record spanning approximately 360 ka in northern Levant. The basin, located on the eastern flank of Mount Lebanon, is mainly supplied by karstic springs which discharge snowmelt water infiltrated through the western highlands. Part of its water inputs is lost by seepage through its faulted bottom. The core, 73 m long, consists of four whitish carbonated intervals rich in lacustrine organism remains, interrupting a thick accumulation of colored silty clays almost devoid of shells but for ostracods. We analyzed sediment features (mineralogical and elemental composition, light microscopy and SEM observations, grain size), magnetic properties, pollen and calcite oxygen isotopes (δc) derived from ostracod shell composition. The chronological framework is based on 14C ages of wood fragments, U/Th dating, and a high resolution reconstruction of relative paleointensity variations correlated with regional (Portuguese margin) and global (Sint-800) master curves down to about 360 ka. Although the chronology still needs improvement, the 3 upper carbonated intervals undoubtedly fit Interglacials MIS 1, MIS 5.5 and MIS 7, respectively. The deepest one (49-60 m) is assigned to MIS 9 by its proxy analogies with dated Interglacials. The sequence covers a large part of MIS 10. Relationships between individual indicators are explored, in addition to visual comparisons of individual records, from the multiproxy matrix after resampling at a common depth scale of 25 cm. We compute simple linear coefficients between 20 variables, perform Principal Component Analyses based on all variables, on terrestrial pollen biomes, on all sedimentological proxies, and cross-correlations between them and δc. During Interglacial maxima, high local and regional efficient moisture is evidenced by dense arboreal vegetation of

  20. Characterizing Lacustrine Sediment that Records the Matuyama/Brunhes Polarity Transition at Bishop, California

    NASA Astrophysics Data System (ADS)

    Liddicoat, Joseph; Bergeron, Jennifer; Mailloux, Brian; Kenna, Timothy

    2013-04-01

    We are doing a study of the physical and chemical properties of exposed lacustrine sediment deposited in Pleistocene Owens Lake near Bishop, CA (37.3˚ N, 241.5˚ E) that was used in an investigation of the Matuyama/Brunhes (M/B) polarity transition (Liddicoat, 1993). The study complements one of similar lacustrine sediment that records the Mono Lake Excursion in the Mono Basin, CA (38.0˚ N, 240.8˚ E) where field strength (Coe and Liddicoat, 1994) and percentage of inorganic carbon seem to be contributing factors on the ability of magnetic grains to accurately record field direction when the field is changing rapidly. For instance, there is an inverse relationship between the percentage of total inorganic carbon (TIC) and the mobility of magnetic grains that preserve the remanence - the greater the percentage of TIC, the less likely grains become realigned when the field directions change (Spokowski et al., 2011). At Bishop, as in the Mono Basin, the sediment is unweathered fine- to medium-grain sand, silt, and volcanic ash from a nearby granitic (Sierra Nevada) and volcanic provenance (Lajoie, 1968), and the dominant magnetic mineral is magnetite (Liddicoat and Coe, 1979; Liddicoat, 1993). The Bishop Ash, dated by K/Ar at about 0.68 m.y. (Dalrymple et al., 1965), is in conformable contact with the lake sediments, which are exposed in the former bank of the Owens River. At Bishop we are using samples that record reverse (Matuyama), transitional, and normal (Brunhes) polarity that were demagnetized in an alternating field. The percentage of grains with a diameter less than 63 micrometers is about 40 percent in the reversely magnetized sediment and about 65 percent in the sediment that records transitional or normal polarity. These percentages differ somewhat from those in the Mono Basin where the percentage is about 80. The percentage of total organic carbon (TOC) does not exceed about 3 percent in the Owens Lake sediment and it is slightly less in the Mono Basin

  1. Synchronous climate-driven regime shifts at the onset of the Holocene inferred from diatom records in lakes of the Greater Yellowstone region

    NASA Astrophysics Data System (ADS)

    Lu, Y.; Stone, J.; Fritz, S. C.

    2013-12-01

    Diatom records covering the late-glacial and early Holocene periods were recovered from three lakes in different areas of Yellowstone National Park to investigate the impacts of large-scale climatic change on aquatic ecosystem evolution following deglaciation. All lakes show synchronous diatom community shifts from the dominance of tychoplanktic Fragilaria species to benthic species in the interval of 11,300-11500 cal yr BP, indicating a regional decrease in effective moisture. The synchroneity of changes in diatom community structure suggests the influence of overlying large-scale climatic change on lacustrine ecosystems. A major shift in the same interval also is evident in other proxy records, such as pollen and charcoal, throughout the Yellowstone region at the late-glacial/early-Holocene transition. This suggests that the summer insolation maximum induced a widespread and rapid reorganization of ecosystem structure and function.

  2. Late Pleistocene and Holocene paleolimnology of two mountain lakes in western Tasmania.

    USGS Publications Warehouse

    Platt, Bradbury J.

    1986-01-01

    The analysis of diatoms from two lake-sediment cores from southwestern Tasmania that span the Pleistocene-Holocene boundary provides insight about paleolimnological and paleoclimatic change in this region. Both Lake Vera and Eagle Tarn have lacustrine records that begin about 12 000 yr ago. Both lakes have had similar limnological histories. Each appears to have been larger and more alkaline 12 000 yr ago and both became shallower through time. Fossil diatom assemblages about 11 000 yr old indicate shallow- water environments that fluctuated in pH, and between dilute and possibly slightly saline hydrochemical conditions. Beginning 11 500 yr ago, limnological conditions of shallow, dilute water of neutral pH prevailed, indicating reduction of moisture stress. A subsequent transition to diatom assemblages indicative of acidic conditions about 10 000 yr ago parallels the establishment of rain-forest vegetation and essentially modern climatic conditions with excess precipitation over evaporation. Changes at these separate and distinctive sites suggests a regional paleoclimatic cause rather than local environmental effects. Latest Pleistocene climates were apparently more continental and drier than Holocene climates in southwestern Tasmania.-from Author

  3. Holocene fire dynamics in Fennoscandia

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  4. A Holocene speleothem record from Morocco, NW Africa

    NASA Astrophysics Data System (ADS)

    Wassenburg, Jasper; Fietzke, Jan; Richter, Detlev; Immenhauser, Adrian

    2010-05-01

    A well dated Holocene speleothem (stalagmite) from the Middle Atlas Mountains in Morocco has been investigated for its continental climate record. The aim is to compile an improved understanding of the climatically complex triple point of the North Atlantic, Mediterranean and Saharan / Monsoonal climate realms in NW Africa. At present, only few studies concerning continental climate reconstructions from NW Africa have been published (Lamb et al. 1995, Cheddadi et al. 1998, Genty et al. 2006). Given the significance of this region, this lack of data forms a strong motivation for additional, well dated climate records. The speleothem (GP2) was sampled in the 'Grotte de Piste' (ca 800 m above sea level), mean annual precipitation is about 930 mm (mainly falling in the winter season) and the mean annual temperature is about 13° C. GP2 is 60 cm tall and grew - based on U/Th MC-ICP-MS data - continuously between 11.5 kyr BP (early Holocene) and 2.9 kyr BP (late Holocene). X-Ray Diffraction data indicate a mainly aragonitic mineralogy. 'Hendy tests' suggest that CaCO3 precipitation was close to isotopic equilibrium with respect to oxygen isotopes, however kinetic effects might have influenced carbon isotopes. Carbon and oxygen isotope data have been measured along a transect with increments of approximately 1 mm representing a resolution of about 15 yrs. Highly covariant oscillations in δ13C and δ18O with an average cyclicity of about 410 yrs. are observed. These oscillations coincide with macroscopically visible high density and low density layers, possibly reflecting a higher or lower amount of inclusions and perhaps higher and lower growth rates. Geochemical analysis of speloan aragonite is accompanied by cave monitoring that has started in November 2009. Parameters quantified include: drip water parameters, cave air humidity, pCO2 and cave air temperature. Precipitation experiments using watch glasses will also be performed. References Cheddadi, R., Lamb, H. F

  5. Holocene paleoenviroments of northwest Iowa

    SciTech Connect

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

    1996-05-01

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

  6. Intertidal stromatolites in a fringing Holocene reef complex, Bahamas

    NASA Astrophysics Data System (ADS)

    Reid, R. Pamela; Browne, Kathleen M.

    1991-01-01

    Intertidal stromatolites are major components of a fringing Holocene reef complex at Stocking Island, Exuma Cays, Bahamas. Trapping and binding of fine-grained carbonate sand by microorganisms, primarily filamentous cyanobacteria and diatoms, and differential lithification of sediment have produced layered structures with up to 0.5 m of relief. Formation of these stromatolites in an environment of normal marine salinity is attributed to reduced competition from crustose red algae, availability of a stable substrate, and rapid cementation. Destruction of lamination in Stocking Island stromatolites by molluscs, sponges, and worms suggests that boring invertebrates play a key role in stromatolite preservation.

  7. Biomarker analysis of Upper Permian lacustrine oil shales, Junggar basin, NW China

    SciTech Connect

    Carroll, A. )

    1990-05-01

    Upper Permian lacustrine oil shales containing up to 34% TOC (total organic carbon) underlie approximately 50,000 km{sup 2} of the Junggar basin in western China, and appear to be the principal source of oils in the giant Karamay field in the northwestern Junggar and in several recent discoveries in other areas of the basin. The siliceous oil shales were deposited in a sediment-starved foreland basin during a period of predominantly humid climate. Previous biomarker studies of crude oils from Karamay field have documented an abundance of {beta}-carotane (which in some cases dominates the aliphatic hydrocarbon distribution) and gammacerane, suggesting a source bed deposited under hypersaline conditions. However, relatively complete outcrop exposures of finely laminated oil shales in the southern Junggar conspicuously lack evaporites, extensive dessication horizons, or other sedimentological evidence of playa lake environments. Indeed, the aliphatic hydrocarbon distribution in bitumen extracts from southern Junggar oil shales appear characteristic of freshwater to brakish water deposition of organic matter in an anoxic lake. Normal alkanes show a slight odd-over-even preference with relatively low levels of the C{sub 22}, n-alkane, pristane/phytane ratios close to unity, low {beta}-carotane and gammacerane levels, and the absence of C{sub 34}-C{sub 35} hopanes. This apparent difference in source bed depositional environments may be due to tectonic partitioning between separate depocenters of the Late Permian Junggar basin. Alternatively, hypersaline oil shale facies may be limited to deeper basinal areas, whereas upslope southern Junggar sediments record highstands in lake level or influx of fresh water from the adjacent drainage areas.

  8. Correcting distorted paleosecular variation in late glacial lacustrine clay

    NASA Astrophysics Data System (ADS)

    Borradaile, G. J.; Almqvist, B. S.

    2008-01-01

    An undisturbed, horizontal chronostratigraphic marker horizon of laminated red glacio-lacustrine clay crops out over ˜25,000 km 2 in northern Ontario, Canada. The primary, clastic hematite laminae possess two stable vector components of magnetization. We sampled a 1.6 m vertical section at overlapping 2 cm intervals in cubic specimens (8 cm 3, n = 106), precisely oriented in geographic coordinates which permitted measurement of inclination and declination. Alternating field demagnetization (12-17 steps per specimen) isolated a characteristic (ChRM), primary component (coercivity ≥40 mT) approximately 30° shallower than the mean geomagnetic field inclination at this latitude, with distorted paleosecular secular variation (PSV). A lower coercivity overprint (20-40 mT) is 6° shallower than the present geomagnetic field and similarly inclined to the depositional-remanence deflection when the clay was re-sedimented in the laboratory. We believe this angle to be representative of the inclination of the deflected primary remanence inclination during deposition, caused by the magnetic anisotropy of the clay. Using this as a proxy for the initial inclination, the ChRM (hard-component) inclinations were restored to their original values assuming vertical compaction, which averages to 51%. The restored inclinations are compatible with site-latitude and the restored secular-variation loops centre reasonably on the geographic North Pole. The structural correction based on homogeneous vertical shortening over-simplifies the reality of heterogeneous particulate flow in which grain rotations depend on shape, size and packing and effectively combines influences of compaction and depositional settlement. Nevertheless, this correction makes the PSV data more useful and interpretable in terms of paleopole migration. The more logical correction technique using anisotropy of anhysteretic remanence (AARM; Jackson, M.J., Banerjee, S.K., Marvin, J.A., Lu, R., Gruber, W., 1991

  9. Downscaling precipitation in the Sahara-Sahelian region during the Holocene in order to decipher the paleo-variations of Lake Chad

    NASA Astrophysics Data System (ADS)

    Contoux, Camille; Bondeau, Alberte; Barrier, Nicolas; Sylvestre, Florence

    2016-04-01

    In order to understand the paleo-variability of Saharo-Sahelian paleoprecipitation, which is recorded in the sediments of Lake Chad situated in central Sahel, we use a modelling chain going from global climate to basin-scale hydrological model. Namely, climate model outputs for the Holocene, starting with the mid-Holocene (6ka) available from the IPSL-CM5 global climate model are statistically downscaled with the General Additive Model approach (Levavasseur et al., 2011), then used to feed the LPJmL model (Bondeau et al., 2007) which calculates the equilibrium vegetation and runoff. Climate and runoff are then given to the dynamic routing scheme HYDRA (Coe et al., 2000) in order to calculate the paleo river network and paleo extent of Lake Chad. The results at each step are compared with reconstructions derived from continental proxies on the regional scale in order to assess the robustness of the results. For the mid-Holocene, the downscaled precipitation matches very well precipitation estimations derived from lacustrine pollen data. For the historical period, the LPJmL simulated runoff averaged over the Chad basin depicts the same trend than observations of Lake Chad water level, but the absolute water level is overestimated in HYDRA, which can be attributed to humid biases both in LPJmL and HYDRA. Finally, we will investigate the relative changes in river network and Lake Chad extent between the present and the mid-Holocene.

  10. Holocene Temperature Reconstructions from Arctic Lakes based on Alkenone Paleothermometry and Non-Destructive Scanning Techniques

    NASA Astrophysics Data System (ADS)

    D'Andrea, W. J.; Balascio, N. L.; Bradley, R. S.; Bakke, J.; Gjerde, M.; Kaufman, D. S.; Briner, J. P.; von Gunten, L.

    2014-12-01

    Generating continuous, accurate and quantitative Holocene temperature estimates from the Arctic is an ongoing challenge. In many Arctic regions, tree ring-based approaches cannot be used and lake sediments provide the most valuable repositories for extracting paleotemperature information. Advances in lacustrine alkenone paleothermometry now allow for quantitative reconstruction of lake-water temperature based on the UK37 values of sedimentary alkenones. In addition, a recent study demonstrated the efficacy of non-destructive scanning reflectance spectroscopy in the visible range (VIS-RS) for high-resolution quantitative temperature reconstruction from arctic lake sediments1. In this presentation, I will report a new UK37-based temperature reconstruction and a scanning VIS-RS record (using the RABD660;670 index as a measure of sedimentary chlorin content) from Kulusuk Lake in southeastern Greenland (65.6°N, 37.1°W). The UK37 record reveals a ~3°C increase in summer lake water temperatures between ~10ka and ~7ka followed by sustained warmth until ~4ka and a gradual (~3°C) cooling until ~400 yr BP. The strong correlation between UK37 and RABD660;670 measured in the same sediment core provides further evidence that in arctic lakes where temperature regulates primary productivity, and thereby sedimentary chlorin content, these proxies can be combined to develop high-resolution quantitative temperature records. The Holocene temperature history of Kulusuk Lake determined using this approach corresponds to changes in the size of the glaciers adjacent to the lake, as inferred from sediment minerogenic properties measured with scanning XRF. Glaciers retreated during early Holocene warming, likely disappeared during the period of mid-Holocene warmth, and advanced after 4ka. I will also discuss new UK37 and RABD660;670 reconstructions from northwestern Svalbard and the central Brooks Range of Alaska within the framework of published regional temperature reconstructions and

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

    USGS Publications Warehouse

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

    2006-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Li, Yu; Morrill, Carrie

    2015-09-01

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

  13. The variability of the North Atlantic Oscillation throughout the Holocene

    NASA Astrophysics Data System (ADS)

    Wassenburg, Jasper; Dietrich, Stephan; Fietzke, Jan; Fohlmeister, Jens; Wei, Wei; Jochum, Klaus Peter; Scholz, Denis; Richter, Detlev; Sabaoui, Abdellah; Lohmann, Gerrit; Andreae, Meinrat; Immenhauser, Adrian

    2013-04-01

    The North Atlantic Oscillation (NAO) has a major impact on Northern Hemisphere winter climate. Trouet et al. (2009) reconstructed the NAO for the last millennium based on a Moroccan tree ring PDSI (Palmer Drought Severity Index) reconstruction and a Scottish speleothem record. More recently, Olsen et al. (2012) extended the NAO record back to 5.2 ka BP based on a lake record from West Greenland. It is, however, well known that the NAO exhibits non-stationary behavior and the use of a single location for a NAO reconstruction may not capture the complete variability. In addition, the imprint of the NAO on European rainfall patterns in the Early and Mid Holocene on (multi-) centennial timescales is still largely unknown. This is related to difficulties in establishing robust correlations between different proxy records and the fact that proxies may not only reflect winter conditions (i.e., the season when the NAO has the largest influence). Here we present a precisely dated, high resolution speleothem δ18O record from NW Morocco covering the complete Early and Mid Holocene. Carbon and oxygen isotopes were measured at a resolution of 15 years. A multi-proxy approach provides solid evidence that speleothem δ18O values reflect changes in past rainfall intensity. The Moroccan record shows a significant correlation with a speleothem rainfall record from western Germany, which covers the entire Holocene (Fohlmeister et al., 2012). The combination with the extended speleothem record from Scotland, speleothem records from north Italy and the NAO reconstruction from West Greenland (Olsen et al., 2012) allows us to study the variability of the NAO during the entire Holocene. The relation between West German and Northwest Moroccan rainfall has not been stationary, which is evident from the changing signs of correlation. The Early Holocene is characterized by a positive correlation, which changes between 9 and 8 ka BP into a negative correlation. Simulations with the state

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

    USGS Publications Warehouse

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

    2005-01-01

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

  15. The Holocene Paleolimnology of Lake Superior

    NASA Astrophysics Data System (ADS)

    Hyodo, A.; Longstaffe, F. J.

    2010-12-01

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

  16. Postglacial intra-lacustrine divergence of Icelandic threespine stickleback morphs in three neovolcanic lakes.

    PubMed

    Olafsdóttir, G A; Snorrason, S S; Ritchie, M G

    2007-09-01

    The geographical context of divergence and local adaptation of lacustrine fish is controversial. Despite recent theoretical support for sympatric and parapatric divergence, empirical studies providing unequivocal support for this remain scant. An important component of such a case would be where multiple lakes have different morphs and a range of markers, both mitochondrial and nuclear, show monophyly within lakes. Here we describe such a situation for threespine sticklebacks in three lakes in Iceland. By analysing the variation at nuclear and mitochondrial markers in several freshwater and marine populations as well as three pairs of intra-lacustrine morphs we infer their phylogenetic relationships and colonization pattern. There were high levels of microsatellite variation in all populations and no evidence was found for either repeated colonization of marine fish or colonization from distinct glacial refugia. Intra-lacustrine threespine stickleback morphs in all three lakes show significant genetic divergence probably indicating restricted gene flow.

  17. A temperature reversal within the rapid Younger Dryas-Holocene warming in the North Atlantic?

    NASA Astrophysics Data System (ADS)

    Vincent, Jessie H.; Cwynar, Les C.

    2016-12-01

    The onset of the Holocene has been generally considered rapid and uninterrupted in the circum-Atlantic region. Loss-on-ignition (LOI - an index of organic carbon) profiles from 18 lateglacial-aged lakes in Nova Scotia, Canada, together with chironomid-inferred temperature reconstructions at 5 sites, demonstrate that the rapid warming from the Younger Dryas (GS-1) to the Holocene was interrupted by a cooling of 1.6-6.4 °C in summer surface lake water temperature. The resulting inflection or reversal on the rising temperature curve has also been identified at 35 sites outside Nova Scotia from terrestrial and marine settings, indicating that this cool step is a robust feature throughout the North Atlantic and is likely the result of major oceanic and atmospheric reorganization of the Holocene climate system.

  18. Late Pleistocene-early Holocene karst features, Laguna Madre, south Texas: A record of climate change

    SciTech Connect

    Prouty, J.S.

    1996-09-01

    A Pleistocene coquina bordering Laguna Madre, south Texas, contains well-developed late Pleistocene-early Holocene karst features (solution pipes and caliche crusts) unknown elsewhere from coastal Texas. The coquina accumulated in a localized zone of converging longshore Gulf currents along a Gulf beach. The crusts yield {sup 14}C dates of 16,660 to 7630 B.P., with dates of individual crust horizons becoming younger upwards. The karst features provide evidence of regional late Pleistocene-early Holocene climate changes. Following the latest Wisconsinan lowstand 18,000 B.P. the regional climate was more humid and promoted karst weathering. Partial dissolution and reprecipitation of the coquina formed initial caliche crust horizons; the crust later thickened through accretion of additional carbonate laminae. With the commencement of the Holocene approximately 11,000 B.P. the regional climate became more arid. This inhibited karstification of the coquina, and caliche crust formation finally ceased about 7000 B.P.

  19. Sand-flat/playa mud-flat-lacustrine cycles in Fundy rift basin (Triassic-Jurassic), Nova Scotia: implications for climatic and tectonic controls

    SciTech Connect

    Mertz, K.A. Jr.; Hubert, J.F.

    1989-03-01

    Blomidon Formation red beds comprise over 200 m-scale cycles of (1) sand-flat sandstone (distal alluvial-fan deposits) and (2) playa sandy mudstone and/or lacustrine claystones. Rift basin subsidence and local sagging along the Glooscap fault system generated sand-flat/playa mud-flat cycles by shifting loci of active fan sedimentation toward and away from the playa surface as fan lobes migrated toward topographic lows. Episodes of intense aridity are recorded in the sand-flat and playa mud-flat deposits where amalgamated sheetflood packages are characterized by pervasive evaporite mineralization (principally gypsum) controlled by subsurface evolution of a Ca-SO/sub 4/-Na-Cl brine. Aridity is further evidenced by significant disruption of sedimentary fabrics beneath evaporite crusts, deep mud cracks, eolian sandstone layers and patches, and precipitation of authigenic calcium and magnesium-rich illite/smectite and analcime. Carbon isotopic data from early formed, low-magnesium calcite cements (pre-gypsum) reflect slightly to moderately elevated subsurface salinities that accompanied initial brine evolution. During relatively wetter periods, lacustrine platy claystones accumulated in shallow, oxidizing lakes that lapped onto the sand flats. Claystone units lack evaporite minerals and textures, and many units are partially burrowed. Carbon isotopic data from calcite cements are consistently lighter than sand-flat/playa mud-flat calcites and were in equilibrium with relatively fresh subsurface pore waters.

  20. European vegetation evolution during the Holocene simulated by Planet Simulator and CARAIB

    NASA Astrophysics Data System (ADS)

    Haberkorn, Kerstin; Fraedrich, Klaus; Henrot, Alexandra-Jane; François, Louis; Warnant, Pierre; Dury, Marie; Favre, Eric; Munhoven, Guy

    2010-05-01

    A transient Holocene simulation is carried out with an Earth system model of intermediate complexity (Planet Simulator). The spectral model is based on the moist primitive equations conserving momentum, mass, energy and moisture. For this study, the Planet Simulator is used in T21/5L-resolution and coupled to the LSG (large-scale geostrophic)-ocean model with orbital and CO2-forcing. The evolution of the European vegetation over the Holocene in response to the climate change is investigated using the dynamic vegetation model CARAIB (CARbon Assimilation in the Biosphere). Time slice simulations from 10 ky BP until the preindustrial period are carried out at high resolution using a specific European vegetation classification including 26 BAGs (Bioclimatic Affinity Groups; Laurent et al., J. Veg. Sci., 15, 739-746, 2004.). The results of the diagnosed vegetation distribution during the Holocene reflect the development of warmer and moister conditions at the Middle Holocene (around 6 ky BP). Broad-leaved deciduous trees expand in several parts of Western and Central Europe at the expense of needle-leaved evergreen trees, which prevail at the beginning of the Holocene.

  1. Holocene reservoir age corrections for the Norwegian Sea based on cold-water corals

    NASA Astrophysics Data System (ADS)

    Andersson Dahl, Carin; Linge, Henriette; Ascough, Philippa; Fietske, Jan; Telford, Richard

    2010-05-01

    There is an offset in 14C age in organisms that lived contemporaneously in the atmosphere relative to those that lived in other carbon reservoirs, such as the ocean. Information about this offset, or reservoir age, R(t), is needed to accurately calibrate marine 14C dates. Although the reservoir age of the ocean is not constant, difficulties in reconstruction the temporal changes in R(t) through time often result in the use of a constant reservoir age correction based on the pre-industrial estimate. This makes detailed comparisons between different archives difficult. Holocene cold-water corals are abundant on the Norwegian shelf and can be dated independently using two different radiometric dating method. The reservoir age correction (?R) of surface ocean waters in the eastern Norwegian Sea was determined for two Holocene periods (9763-9262 and 3097-365 cal. BP) using paired U/Th and AMS 14C dating of nineteen samples of the cold-water coral Lophelia pertusa. Assessment of Holocene ?R values show that early Holocene ?R values are higher compared to the late Holocene. In addition, there also appears to be a trend of increasing ?R values for the past 3000 years BP in the eastern Norwegian Sea. Comparisons to ?R values from the British Isles point towards that there is a latitudinal dependence in ?R in the North Atlantic realm.

  2. Late Pleistocene and Holocene Fire History of the California Islands

    NASA Astrophysics Data System (ADS)

    Scott, A. C.; Hardiman, M.; Pinter, N.; Anderson, R.

    2013-12-01

    Charcoal has been recovered from a range of late Pleistocene and Holocene sites on Santa Cruz Island and Santa Rosa Island, both islands part of California's Northern Channel Islands, U.S.A. Sediments have been dated using radiocarbon measurements based on wood charcoal, fungal sclerotia, glassy carbon and fecal pellets and are given as calendar years BP. This charcoal has been used to interpret the fire history of the Islands. Charcoal assemblages from samples dating from 24,690 to 12,900 years are dominated by coniferous wood charcoal. Little angiosperm charcoal was recovered in any of the samples. Fungal sclerotia are frequent in a number of samples from a range of ages both on Santa Cruz and Santa Rosa. Fecal pellets are common in most samples and abundant in others. Some of the fecal pellets have hexagonal sides and are likely to represent termite frass. The sediments are fluvial in origin and the distribution of charcoal is irregular making interpretation of fire return intervals and fire frequency difficult. The charcoal indicates a significant record of fire before the earliest documented human arrival on the islands. Charcoal reflectance data shows the occurrence of predominantly low temperature charcoals suggesting common surface fires in the coniferous forest. Soledad Pond sediments from Santa Rosa Island (Anderson et al., 2010) dating from 11,800 cal years BP show a distinctively different vegetation dominated by angiosperms and showing a very different fire history. Pinus stands, coastal sage scrub dominated by Baccharis sp. and grassland replaced the conifer forest as the climate warmed. The early Holocene became increasingly drier, particularly after ca. 9150 cal yr BP. By ca. 6900 cal yr BP grasslands recovered. Introduction of non-native species by ranchers occurred subsequent to AD 1850. Charcoal influx is high early in the Soledad Pond record, but declines during the early Holocene when minimal biomass suggests extended drought. A general

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

    SciTech Connect

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

    1992-03-01

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

  4. Mid-Eocene alluvial-lacustrine succession at Gebel El-Goza El-Hamra (Shabrawet area, NE Eastern Desert, Egypt): Facies analysis, sequence stratigraphy and paleoclimatic implications

    NASA Astrophysics Data System (ADS)

    Wanas, H. A.; Sallam, E.; Zobaa, M. K.; Li, X.

    2015-11-01

    This study aims to provide the depositional facies, sequence stratigraphic and paleoclimatic characteristics of the Mid-Eocene (Bartonian) continental succession exposed at Gebel El-Goza El-Hamra (Shabrawet Area, NE Eastern Desert, Egypt). The studied succession consists of siliciclastic rocks followed upward by carbonate rocks. Detailed field observation and petrographic investigation indicate accumulation in floodplain-dominated alluvial and shallow lacustrine systems. The floodplain-dominated alluvial facies (45 m thick) is composed mainly of carbonate nodules-bearing, mottled mudrock with subordinate sandstone and conglomerate beds. The conglomerate and pebbly sandstone bodies interpreted as ephemeral braided channel deposits. The massive, laminated, planner cross-bedded, fine- to medium-grained sandstone bodies interlayered within mudstone reflect sheet flood deposits. The mudrocks associated with paleosols represent distal floodplain deposits. The shallow lacustrine facies (15 m thick) is made up of an alternation of marlstone, micritic limestone, dolostone and mudrock beds with charophytes and small gastropods. Both the alluvial and lacustrine facies show evidence of macro-and micro-pedogenic features. Pollen assemblages, stable δ18O and δ13C isotopes, and paleopedogenic features reflect prevalence of arid to semi-arid climatic conditions during the Bartonian. The sequence stratigraphic framework shows an overall fining-upward depositional sequence, consisting of Low- and High-accommodation Systems Tracts (LAST, HAST), and is bounded by two sequence boundaries (SB-1, SB-2). Conglomerate and pebbly sandstone deposits (braided channel and sheet flood deposits) of the lower part of the alluvial facies reflect a LAST. Mudrock and silty claystone facies (distal floodplain deposits) of the upper part of alluvial facies and its overlying lacustrine facies correspond to a HAST. The LAST, HAST and SB were formed during different accommodation-to-sediment supply (A

  5. Stratigraphy and Facies Analysis of a 122 M Long Lacustrine Sequence from Chalco Lake, Central Mexico

    NASA Astrophysics Data System (ADS)

    Herrera, D. A.; Ortega, B.; Caballero, M.; Lozano, S.; Pi, T.; Brown, E. T.

    2010-12-01

    Chalco lake is located SE of the outskirts of Mexico City, at the central part of the Trans Mexican Volcanic Belt. Previous studies show the importance of this lacustrine sequence as an archive of paleoenvironmental and paleoclimatic changes. A set of five cores up to 122 m depth were drilled in the basin, in order to analyze the sedimentary record and to extent the previous knowledge of past environmental changes in central Mexico. As an initial step, in this work we present the identification and classification of sedimentary facies. Preliminary paleomagnetism analyses recognize the possible record of the Blake Event (ca. 120 kyr BP), and suggest that the sequence might span the last 240 kyr. In this case, variations in sedimentary facies could reflect the conditions of the MIS 1-7. The facies are mostly diatom ooze, carbonate mud, organic rich silt and volcaniclastic, both massive and laminated, and massive dark gray to reddish brown silt. From 1 to 8 m depth dominates the organic rich silt facies, which correlates with the MIS 1. Intercalations of reddish brown and grayish brown silt facies, between 8 to 60 m depth, indicate changes occurred during MIS 2 to 5d. Between 60-75 m depth the sequence is characterized by dark grayish silty clay facies, which possibly coincide with the MIS 5e. At 79 m depth (ca. 130 kyr BP) we found struvite (MgNH4PO4.6H2O), which may be related to dry conditions. The laminated diatom ooze facies dominates between 90 to 122 m depth and indicates rhythmic changes in the sediment deposition of the basin. The volcaniclastic facies is represented by lapilli and ash deposits in more than 100 individual tephra layers of both mafic and felsic composition. Some of them correspond to main volcanic eruptions, as the Upper Toluca Pumice (13,500 cal yr BP), from the Nevado de Toluca volcano and the Pómez con Andesita (17,700 cal yr BP) from the Popocatépetl volcano. The carbonate mud facies is composed of calcite and siderite, with frequent

  6. The Holocene Isolation of Dalma Island

    NASA Astrophysics Data System (ADS)

    Lokier, Stephen

    2010-05-01

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

  7. Distribution of calcium carbonate in desert soils: A model

    SciTech Connect

    Mayer, L.; McFadden, L.D.; Harden, J.W.

    1988-04-01

    A model that describes the distribution of calcium carbonate in desert soils as a function of dust flux, time, climate, and other soil-forming factors shows which factors most strongly influence the accumulation of carbonate and can be used to evaluate carbonate-based soil age estimates or paleoclimatic reconstructions. Models for late Holocene soils have produced carbonate distributions that are very similar to those of well-dated soils in New Mexico and southern California. These results suggest that (1) present climate is a fair representation of late Holocene climate, (2) carbonate dust flux can be approximated by its Holocene rate, and (3) changes in climate and/or dust flux at the end of the Pleistocene effected profound and complex changes in soil carbonate distributions. Both higher carbonate dust flux and greater effective precipitation are required during the latest Pleistocene-early Holocene to explain carbonate distributions in latest Pleistocene soils. 21 refs., 4 figs., 1 tab.

  8. Multiple thermal maxima during the Holocene

    SciTech Connect

    Davis, O.K.

    1984-08-10

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

  9. Faunal histories from Holocene ancient DNA.

    PubMed

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

    2011-08-01

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

  10. Dust fluxes and iron fertilization in Holocene and Last Glacial Maximum climates

    NASA Astrophysics Data System (ADS)

    Lambert, Fabrice; Tagliabue, Alessandro; Shaffer, Gary; Lamy, Frank; Winckler, Gisela; Farias, Laura; Gallardo, Laura; De Pol-Holz, Ricardo

    2015-07-01

    Mineral dust aerosols play a major role in present and past climates. To date, we rely on climate models for estimates of dust fluxes to calculate the impact of airborne micronutrients on biogeochemical cycles. Here we provide a new global dust flux data set for Holocene and Last Glacial Maximum (LGM) conditions based on observational data. A comparison with dust flux simulations highlights regional differences between observations and models. By forcing a biogeochemical model with our new data set and using this model's results to guide a millennial-scale Earth System Model simulation, we calculate the impact of enhanced glacial oceanic iron deposition on the LGM-Holocene carbon cycle. On centennial timescales, the higher LGM dust deposition results in a weak reduction of <10 ppm in atmospheric CO2 due to enhanced efficiency of the biological pump. This is followed by a further ~10 ppm reduction over millennial timescales due to greater carbon burial and carbonate compensation.

  11. Holocene flood stack from three Eifel maar lakes

    NASA Astrophysics Data System (ADS)

    Brunck, Heiko; Sirocko, Frank

    2015-04-01

    Lacustrine sediments are very sensitive to natural and anthropogenically enviromental changes. Thus, lake sediments are excellent climate archives and can be used for reconstructions of past precipitation and flood events. However, we extend our flood record for MIS 2/3 to the entire Holocene up to recent years to get a complete flood stack for the last 60 000 years. The present study reconstructs paleo floods from event layers in the sediment, of Schalkenmehren Maar (SM3), Ulmen Maar (UM1) and Holzmaar (HM1) combined with recent gauge time-series. All three maar lakes has an inflow by a local stream. Accordingly the sedimentation rate is directly linked to runoff activity and the bioturbation was low so that event layers become visible, but varves are only preserved in lake Holzmaar. The maar sites are situated in the Eifel near to the town of Daun and were drilled in the ELSA (Eifel Laminated Sediment archive) project. The Eifel area is well suited to approximate Central European weather, because modern water level gauge data from Eifel rivers correlate with respective data from the Rhine (Wernli and Pfahl, 2009). Combined sedimentological, paleobotanical and geochemical data received from SM3, UM1 and HM1 builds the foundation of the 14C based chronology. The synchronisation of the record is controlled by tephra time markers and pollen. Both are used to align the main cores of the ELSA project and construct an integrated age model for the last 220 000 years [b2k] (Förster and Sirocko, 2014). For the extension of our MIS 2/3 flood stack we used the Laacher See Tephra (10 900 BC) as marker for the correlation with the Holocene cores. To study the flood events in detail, 10 cm long thin sections were used to distinguish flood layers from distal turbidites. Turbidites have a continuous grain size gradation; the grains size profile of flood events is in contrast characterized by several grain size maxima over the entire layer thickness. A flood event over several

  12. Middle Holocene thermal maximum in eastern Beringia

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  13. Re–Os geochronology of the lacustrine Green River Formation: Insights into direct depositional dating of lacustrine successions, Re–Os systematics and paleocontinental weathering

    USGS Publications Warehouse

    Cumming, Vivien M.; Selby, David; Lillis, Paul G.

    2012-01-01

    Lacustrine sedimentary successions provide exceptionally high-resolution records of continental geological processes, responding to tectonic, climatic and magmatic influences. These successions are therefore essential for correlating geological and climatic phenomena across continents and furthermore the globe. Producing accurate geochronological frameworks within lacustrine strata is challenging because the stratigraphy is often bereft of biostratigraphy and directly dateable tuff horizons. The rhenium–osmium (Re–Os) geochronometer is a well-established tool for determining precise and accurate depositional ages of marine organic-rich rocks. Lake systems with stratified water columns are predisposed to the preservation of organic-rich rocks and thus should permit direct Re–Os geochronology of lacustrine strata. We present Re–Os systematics from one of the world's best documented lacustrine systems, the Eocene Green River Formation, providing accurate Re–Os depositional dates that are supported by Ar–Ar and U–Pb ages of intercalated tuff horizons. Precision of the Green River Formation Re–Os dates is controlled by the variation in initial 187Os/188Os and the range of 187Re/188Os ratios, as also documented in marine systems. Controls on uptake and fractionation of Re and Os are considered to relate mainly to depositional setting and the type of organic matter deposited, with the need to further understand the chelating precursors of Re and Os in organic matter highlighted. In addition to geochronology, the Re–Os data records the 187Os/188Os composition of lake water (1.41–1.54) at the time of deposition, giving an insight into continental runoff derived from weathering of the geological hinterland of the Green River Formation. Such insights enable us to evaluate fluctuations in continental climatic, tectonic and magmatic processes and provide the ability for chemostratigraphic correlation combined with direct depositional dates. Furthermore

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

    USGS Publications Warehouse

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

    2012-01-01

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

  15. Chronology of Holocene sediments from the archaeological Salawusu site in the Mu Us Desert in China and its palaeoenvironmental implications

    NASA Astrophysics Data System (ADS)

    Liu, Kai; Lai, Zhong Ping

    2012-02-01

    The archaeological Salawusu site is located at the southeast margin of the Mu Us Desert, and in the northern marginal area of the East Asian Monsoon. Therefore, its environment is sensitive to the changes of the East Asian Monsoon. At the palaeolithic Salawusu site, most of the previous studies are concerned with the age of the palaeoanthropic fossils (ages ranging from 30 to 120 ka) and the climate change in the last glaciation period, while studies on the chronology and climate change since the Late Glacial are very limited. In the current study, eight luminescence samples were collected from Dishaogouwan (DSG) section and dated using quartz optically stimulated luminescence (OSL). Radiocarbon samples were also collected, and the past environmental changes since the Late Glacial have been reconstructed based on stratigraphical and chronological data. The results show that: (1) the AMS age of modern weed living under water is about 1550 ± 35 a, which is the current reservoir effect age, and after reservoir effect subtraction the radiocarbon age of the shells is in agreement with the OSL age, while the radiocarbon age of the bulk sample is younger; (2) aeolian sand mobilization occurred in the studied region before ˜12 ka; (3) within the Holocene, the wettest climate occurred during the onset of the Holocene when an extensive palaolake existed in the study area, marked by the development of lacustrine sediments at around ˜12 ka; (4) after ˜12 ka, the climate showed a trend of increasing aridity, which led to a continuous shrinkage of the palaolake, and its ultimate desiccation between 1.8 and 1.0 ka evidenced by the shift from lacustrine sediments to peat, and finally to palaeosol; (5) the dating results also show an enormous incision of about 60 m in about 1.75 ka by the Salawusu River.

  16. Mineral Trends in Early Hesperian Lacustrine Mudstone at Gale Crater, Mars

    NASA Technical Reports Server (NTRS)

    Rampe, E. B.; Ming, D. W.; Grotzinger, J. P.; Morris, R. V.; Blake, D. F.; Vaniman, D. T.; Bristow, T. F.; Morrison, S. M.; Yen, A. S.; Chipera, S. J.; Downs, R. T.; Achilles, C. N.; Hazen, R. M.; Peretyazhko, T. S.; Sutter, B.; Treiman, A. H.; Craig, P. I.; Farmer, J. D.; Des Marais, D. J.; Fairen, A. G.

    2017-01-01

    The Mars Science Laboratory Curiosity rover landed in Gale crater in August 2012 to study the layered sediments of lower Aeolis Mons (i.e., Mount Sharp), which have signatures of phyllosilicates, hydrated sulfates, and iron oxides in orbital visible/near-infrared observations. The observed mineralogy within the stratigraphy, from phyllosilicates in lower units to sulfates in higher units, suggests an evolution in the environments in which these secondary phases formed. Curiosity is currently investigating the sedimentary structures, geochemistry, and mineralogy of the Murray formation, the lowest exposed unit of Mount Sharp. The Murray formation is dominated by laminated lacustrine mudstone and is approx.200 m thick. Curiosity previously investigated lacustrine mudstone early in the mission at Yellowknife Bay, which represents the lowest studied stratigraphic unit. Here, we present the minerals identified in lacus-trine mudstone from Yellowknife Bay and the Murray formation. We discuss trends in mineralogy within the stratigraphy and the implications for ancient lacustrine environments, diagenesis, and sediment sources.

  17. Harmotome in a basaltic, volcaniclastic sandstone from a lacustrine deposit near Kirkland Junction, Yavapai County, Arizona.

    USGS Publications Warehouse

    Sheppard, R.A.; Gude, A.J.

    1983-01-01

    Harmotome, a Ba-rich zeolite, is reported in a lacustrine sandstone dominated by basaltic fragments now mainly altered to smectite and iron oxides. Harmotome forms 4-5% of the rock and occurs as an authigenic layer of stubby prismatic crystals typically 2-7 mu m long, lining voids in the sandstone.-D.F.B.

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

    USGS Publications Warehouse

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

    2016-01-01

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

  19. Late Pleistocene to Holocene paleoceanographic and paleo-climatic changes in Gulf of Gemlik, Sea of Marmara, Turkey

    NASA Astrophysics Data System (ADS)

    Filikci, Betül; Kadir Eriş, K.; Namık Çaǧatay, M.; Gasperini, Luca; Sabuncu, Asen; Acar, Dursun; Yalamaz, Burak

    2016-04-01

    Gulf of Gemlik is an east-west oriented marine inlet with a maximum depth of 113 m in the south-eastern part of the Sea of Marmara. It is located on the middle branch of the North Anatolian Fault Zone. While the Gulf of Gemlik is separated from the SoM by a bedrock sill at -50 m, there were presumably several disconnections during the Late Pleistocene to Holocene, but the timing of the youngest connection around the onset of the Holocene is still controversial. Here, we attempt to elucidate the paleoceanographic and paleoenvironmental changes during the late glacial-Holocene using the multi-proxy analysis of a core extending back to 13 ka BP. The multi-proxy data include physical and geochemical properties together with AMS 14C ages. The core sediments covering the time period of the last 13 ka BP consists of two main lithostratigraphic units. The lower Unit L2 represents the lacustrine phase of the gulf prior to 10.6 ka BP, while the upper Unit L1 is an overlying transgressive mud drape deposited during the main part of the Holocene. Unit L2 deposited prior 10.6 ka BP represents Bølling-Allerød and Younger Dryas climatic periods, when prograding shelf edge sediments were deposited in the form of well sorted medium sands with brackish water bivalve shells (Dreissenapolymorpha). At the beginning of the Holocene, the rising sea level in the Sea of Marmara breached the -50 m sill at 10.6 ka BP, and therefore the Gulf of Gemlik was converted into a marine realm. Soon after, the water stratifications allowed to the formation of the previously studied two sapropels in the gulf, as shown by increased TOC contents. μ-XRF Ca/Ti and Sr/Ca profiles of Unit L1 provide evidence of rapid climatic changes at 8.2 ka BP and 4.2 ka BP, representing cold and dry short climatic periods which are well correlated with previous marine and lake studies in İznik Lake south of the Sea of Marmara. Keywords: Gemlik Gulf, core, paleoclimate, Late Pleistocene to Holocene

  20. Are watershed and lacustrine controls on planktonic N2 fixation hierarchically structured?

    PubMed

    Scott, J Thad; Doyle, Robert D; Prochnow, Shane J; White, Joseph D

    2008-04-01

    N2 fixation can be an important source of N to limnetic ecosystems and can influence the structure of phytoplankton communities. However, watershed-scale conditions that favor N2 fixation in lakes and reservoirs have not been well studied. We measured N2 fixation and lacustrine variables monthly over a 19-month period in Waco Reservoir, Texas, USA, and linked these data with nutrient-loading estimates from a physically based watershed model. Readily available topographic, soil, land cover, effluent discharge, and climate data were used in the Soil and Water Assessment Tool (SWAT) to derive watershed nutrient-loading estimates. Categorical and regression tree (CART) analysis revealed that lacustrine and watershed correlates of N2 fixation were hierarchically structured. Lacustrine conditions showed greater predictive capability temporally. For instance, low NO3(-) concentration (<25 microg N/L) and high water temperatures (>27 degrees C) in the reservoir were correlated with the initiation of N2 fixation seasonally. When lacustrine conditions were favorable for N2 fixation, watershed conditions appeared to influence spatial patterns of N2 fixation within the reservoir. For example, spatially explicit patterns of N2 fixation were correlated with the ratio of N:P in nutrient loadings and the N loading rate, which were driven by anthropogenic activity in the watershed and periods of low stream flow, respectively. Although N2 fixation contributed <5% of the annual N load to the reservoir, 37% of the N load was derived from atmospheric N2 fixation during summertime when stream flow in the watershed was low. This study provides evidence that watershed anthropogenic activity can exert control on planktonic N2 fixation, but that temporality is controlled by lacustrine conditions. Furthermore, this study also supports suggestions that reduced inflows may increase the propensity of N2-fixing cyanobacterial blooms in receiving waters of anthropogenically modified landscapes.

  1. 20 Myr of eccentricity paced lacustrine cycles in the Cenozoic Ebro Basin

    NASA Astrophysics Data System (ADS)

    Valero, Luis; Garcés, Miguel; Cabrera, Lluís; Costa, Elisenda; Sáez, Alberto

    2014-12-01

    Long-period orbital forcing is a crucial component of the major global climate shifts during the Cenozoic as revealed in marine pelagic records. A complementary regional perspective of climate change can be assessed from internally drained lake basins, which are directly affected by insolation and precipitation balance. The Ebro Basin in northeastern Iberia embraces a 20 Myr long continuous sedimentary record where recurrent expansions and retractions of the central lacustrine system suggest periodic shifts of water balance due to orbital oscillations. In order to test climatic (orbital) forcing a key-piece of the basin, the Los Monegros lacustrine system, has been analyzed in detail. The cyclostratigraphic analysis points to orbital eccentricity as pacemaker of short to long-term lacustrine sequences, and reveals a correlation of maxima of the 100-kyr, 400-kyr and 2.4-Myr eccentricity cycles with periods of lake expansion. A magnetostratigraphy-based chronostratigraphy of the complete continental record allows further assessing long-period orbital forcing at basin scale, a view that challenges alternate scenarios where the stratigraphic architecture in foreland systems is preferably associated to tectonic processes. We conclude that while the location of lacustrine depocenters reacted to the long-term tectonic-driven accommodation changes, shorter wavelenght oscillations of lake environments, still million-year scale, claims for a dominance of orbital forcing. We suggest a decoupling between (tectonic) supply-driven clastic sequences fed from basin margins and (climatic) base level-driven lacustrine sequences in active settings with medium to large sediment transfer systems.

  2. Late Pleistocene and Holocene palaeoenvironments in and around the middle Caspian basin as reconstructed from a deep-sea core

    NASA Astrophysics Data System (ADS)

    Leroy, Suzanne A. G.; López-Merino, Lourdes; Tudryn, Alina; Chalié, Françoise; Gasse, Françoise

    2014-10-01

    Late Pleistocene and/or Holocene high-resolution palynological studies are available for the south basin of the Caspian Sea (CS), the world's largest lake. However, the north and middle basins have not been the object of high-resolution palynological reconstructions. This new study presents the pollen, spores and dinoflagellate cysts records obtained from a 10 m-long sediment core recovered in the middle basin, which currently has brackish waters and is surrounded by arid and semi-arid vegetation. An age-depth model built based on six radiocarbon dates on ostracod shells indicates that the sequence spans the period from 14.47 to 2.43 cal. ka BP. The present palaeoenvironmental study focuses on the top 666 cm, or from 12.44 to 2.43 cal. ka BP. At the vegetation level, the Younger Dryas is characterised by an open landscape dominated by desert vegetation composed by Amaranthaceae with shrubs and salt-tolerant plants. However, although the Early Holocene is also characterised by desert vegetation, it is enriched in various shrubs such as Ephedra and Calligonum, but tree expansion is not important at the Holocene onset. After a major shift at 8.19 cal. ka BP, the Middle Holocene displays now both the character of desert and of steppe, although some trees such as Quercus and Corylus slightly spread. The Late Holocene records steppe vegetation as dominant, with more tree diversity. Regarding the lacustrine signal, the dinocyst assemblage record fluctuates between slightly brackish conditions highlighted by Pyxidinopsis psilata and Spiniferites cruciformis, and more brackish ones - similar to the present day - with the dominance of Impagidinium caspienense. The Late Pleistocene is characterised by low salinities, related to the Khvalynian highstand. From 11.56 cal. ka BP, slightly more saline waters are reconstructed with an increase of I. caspienense for a period of 1000 years, which could be attributed to the Mangyshlak lowstand. From 10.55 cal. ka BP, low salinity

  3. Glacial to Holocene climate changes in Easter Island (SE Pacific, 27

    NASA Astrophysics Data System (ADS)

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

    2009-04-01

    Sedimentary architecture and paleoclimate for the last 34 000 cal years BP and human activity during the last 850 years have been reconstructed from the Raraku Lake sediments in Easter Island (SE Pacific, 27°S) using a high-resolution multiproxy study of 8 cores, 36 AMS radiocarbon dates and correlation with previous core studies. The Last Glacial period was characterized by cold and relatively humid conditions between 34 to 28 cal kyr BP. High lake levels and clastic input dominated sedimentation in Raraku Lake and a relatively open forest developed at that time. Between 28 and 17.3 cal kyr BP, including LGM period, colder conditions contributed to a reduction of the tree coverage in the island. The end of Glacial Period occurred at 17.3 cal kyr BP and was characterized by a sharp decrease in lake level conducive to the development of major floods due to the erosion of littoral sediments. The Deglaciation Period (Termination 1) occurred between 17.3 and 12.5 cal kyr BP, characterized by an increase in lake productivity, a decrease in the terrigenous input and a rapid lake level recovery inaugurating a period of intermediate lake levels. During this period, the dominance of algal lamination is interpreted as a warmer climate. The timing and duration of this warming trend in Easter Island broadly agrees with other mid- and low latitude circum South Pacific terrestrial records. The early Holocene was characterized by low lake levels. The lake level dropped during the early Holocene (ca. 9.5 cal kyr BP) and peatbog and shallow lake conditions dominated till mid Holocene, partially caused by the colmatation of the lacustrine basin. During the mid Holocene an intense drought occurred that led to a persistent low water table period, subaerial exposure and erosion of some of the sediments, generating a sedimentary gap in the Raraku sequence, from 4.2 to 0.8 cal kyr BP. The palm deforestation of the Easter Island, attributed to the human colonization at about 850 cal yr

  4. Process interpretation of laminated lacustrine sediments from the valley of the river Alf, Quaternary West Eifel Volcanic Field, Germany

    NASA Astrophysics Data System (ADS)

    Eichhorn, Luise; Pirrung, Michael; Zolitschka, Bernd; Büchel, Georg

    2016-04-01

    High-resolution annually laminated sediment archives from lakes Holzmaar and Meerfelder Maar located in the Quaternary West Eifel Volcanic Field are in the focus of many investigations (e.g. Brauer et al. 2001, Zolitschka 1991). These publications are related to predominantly biogenic varves covering the last ca. 14 ka years, i.e. the Lateglacial and the Holocene. In our study, laminated sediments consisting of clay-silt couplets are presented from paleolake Alf. This paleolake formed in a valley dammed by volcanic products, and covers the Pleniglacial between 31 and 24 ka BP (Pirrung et al. 2007). The focus of our study is the characterization of the structure of clay-silt couplets and the determination of their origin. The applied granulometry revealed mean grain sizes of 10 μm for the light laminae (colors refer to core scan photo) and 14 μm for the dark laminae (both middle silt). X-ray diffraction confirms identical mineral phases for light and dark laminae, with light laminae being clay-enriched containing a higher amount of sericite and chlorite while dark laminae are enriched in quartz. X-ray fluorescence and detrital microfacies analysis on thin sections indicate that calcite dominates in the dark laminae. Microscopically, three different types of silt layers are present. Type I are laminae with homogeneous sublayers, Type II are graded laminae and Type III are laminae with graded sublayers. Processes causing the formation of these silt lamination types can be attributed to repeatedly occurring snow melting, permafrost thawing or rain events linked with sediment delivery from the catchment into the lake. The amount of precipitation and melt water, sediment discharge and density stratification lead to gravity suspension fall out, partial erosion of previously deposited unconsolidated sediments and resuspension in the lake. Brauer, A., et al. (2001). Lateglacial varve chronology and biostratigraphy of lakes Holzmaar and Meerfelder Maar, Germany. Boreas 30

  5. Holocene precipitation seasonality captured by a dual hydrogen and oxygen isotope approach at Steel Lake, Minnesota

    NASA Astrophysics Data System (ADS)

    Henderson, Anna K.; Nelson, David M.; Hu, Feng Sheng; Huang, Yongsong; Shuman, Bryan N.; Williams, John W.

    2010-12-01

    Middle-Holocene (8 to 4 ka BP) warmth and aridity are well recorded in sediment archives from midcontinental North America. However, neither the climatic driver nor the seasonal character of precipitation during this period is well understood because of the limitations of available proxy indicators. For example, an important challenge is to distinguish among the interacting effects of evaporation, temperature, or precipitation seasonality in existing δ 18O records from the region. Here we combine hydrogen isotopes of palmitic acid and oxygen isotopes of carbonate to derive lake-water isotopic values during the Holocene at Steel Lake in north-central Minnesota. In combination, these data enable us to separate variations in evaporation from variations in the isotopic composition of input-waters to lake. Variations in evaporation are used as a proxy for aridity and lake-water input isotopic values are used as a proxy for the isotopic values of meteoric precipitation. Our results suggest that lake-water input isotopic values were more negative during the middle Holocene than at present. To test whether these more negative values are related to temperature or precipitation seasonality, we compare pollen-inferred temperatures and the expected isotopic value of precipitation resulting from these temperatures to the reconstructed precipitation isotopic values. Results suggest that middle Holocene warmth and aridity were associated with increased evaporation rates and decreased summer precipitation. These inferences are consistent with climate simulations that highlight the role of seasonal insolation and sea surface temperatures in driving variations in precipitation seasonality during the Holocene. Results also suggest that changes in Holocene precipitation seasonality may have influenced the expansion of the prairie-forest border in Minnesota as well as regional variations in grassland community composition. This study demonstrates the efficacy of the dual hydrogen and

  6. Tropical Peat and Peatland Development in the Floodplains of the Greater Pamba Basin, South-Western India during the Holocene

    PubMed Central

    Padmalal, Damodaran; Limaye, Ruta B.; S., Vishnu Mohan; Jennerjahn, Tim; Gamre, Pradeep G.

    2016-01-01

    Holocene sequences in the humid tropical region of Kerala, South-western (SW) India have preserved abundance of organic—rich sediments in the form of peat and its rapid development in a narrow time frame towards Middle Holocene has been found to be significant. The sub—coastal areas and flood plains of the Greater Pamba Basin have provided palaeorecords of peat indicating that the deposits are essentially formed within freshwater. The combination of factors like stabilized sea level and its subsequent fall since the Middle Holocene, topographic relief and climatic conditions led to rapid peat accumulation across the coastal lowlands. The high rainfall and massive floods coupled with a rising sea level must have inundated > 75% of the coastal plain land converting it into a veritable lagoon—lake system that eventually led to abrupt termination of the forest ecosystem and also converted the floodplains into peatland where accumulation of peat almost to 2.0–3.0 m thickness in coastal lowlands and river basins during the shorter interval in the Middle Holocene. Vast areas of the coastal plains of Kerala have been converted into carbon rich peatland during the Middle Holocene and transforming the entire coastal stretch and associated landforms as one of the relatively youngest peatlands in the extreme southern tip of India. Unlike the uninterrupted formation of peatlands of considerable extent during the Holocene in Southeast Asia, the south Peninsular Indian region has restricted and short intervals of peatlands in the floodplains and coastal lowlands. Such a scenario is attributed to the topographic relief of the terrain and the prevailing hydrological regimes and environmental conditions as a consequence of monsoon variability since Middle Holocene in SW India. Considering the tropical coastal lowlands and associated peatlands are excellent repositories of carbon, they are very important for regional carbon cycling and habitat diversity. The alarming rate of

  7. Tropical Peat and Peatland Development in the Floodplains of the Greater Pamba Basin, South-Western India during the Holocene.

    PubMed

    Kumaran, Navnith K P; Padmalal, Damodaran; Limaye, Ruta B; S, Vishnu Mohan; Jennerjahn, Tim; Gamre, Pradeep G

    2016-01-01

    Holocene sequences in the humid tropical region of Kerala, South-western (SW) India have preserved abundance of organic-rich sediments in the form of peat and its rapid development in a narrow time frame towards Middle Holocene has been found to be significant. The sub-coastal areas and flood plains of the Greater Pamba Basin have provided palaeorecords of peat indicating that the deposits are essentially formed within freshwater. The combination of factors like stabilized sea level and its subsequent fall since the Middle Holocene, topographic relief and climatic conditions led to rapid peat accumulation across the coastal lowlands. The high rainfall and massive floods coupled with a rising sea level must have inundated > 75% of the coastal plain land converting it into a veritable lagoon-lake system that eventually led to abrupt termination of the forest ecosystem and also converted the floodplains into peatland where accumulation of peat almost to 2.0-3.0 m thickness in coastal lowlands and river basins during the shorter interval in the Middle Holocene. Vast areas of the coastal plains of Kerala have been converted into carbon rich peatland during the Middle Holocene and transforming the entire coastal stretch and associated landforms as one of the relatively youngest peatlands in the extreme southern tip of India. Unlike the uninterrupted formation of peatlands of considerable extent during the Holocene in Southeast Asia, the south Peninsular Indian region has restricted and short intervals of peatlands in the floodplains and coastal lowlands. Such a scenario is attributed to the topographic relief of the terrain and the prevailing hydrological regimes and environmental conditions as a consequence of monsoon variability since Middle Holocene in SW India. Considering the tropical coastal lowlands and associated peatlands are excellent repositories of carbon, they are very important for regional carbon cycling and habitat diversity. The alarming rate of land

  8. Insect-Based Holocene (and Last Interglacial?) Paleothermometry from the E and NW Greenland Ice Sheet Margins: A Fly's-Eye View of Warmth on Greenland

    NASA Astrophysics Data System (ADS)

    Axford, Y.; Bigl, M.; Carrio, C.; Corbett, L. B.; Francis, D. R.; Hall, B. L.; Kelly, M. A.; Levy, L.; Lowell, T. V.; Osterberg, E. C.; Richter, N.; Roy, E.; Schellinger, G. C.

    2011-12-01

    Here we present new paleotemperature reconstructions based upon insect (Chironomidae) assemblages and other proxies from lake sediment cores recovered in east Greenland at ~71° N near Scoresby Sund and in northwest Greenland at ~77° N near Thule/Qaanaaq. In east Greenland, Last Chance Lake (informal name) is a small, non-glacial lake situated ~90 km east of the Greenland Ice Sheet margin. The lake preserves a sedimentary record of the entire Holocene (Levy et al. 2013). Chironomids from Last Chance Lake record cold summer temperatures (and establishment of a cold-climate fauna including abundant Oliveridia and Pseudodiamesa) during the late Holocene, preceded by summer temperatures estimated to have been 3 to 6°C warmer during the first half of the Holocene (when summer insolation forcing was greater than today). In northwest Greenland, Delta Sø and Wax Lips Lake (informal name) both preserve Holocene sediments. Here we discuss the late Holocene chironomid record from Delta Sø, whereas from Wax Lips Lake (a small, non-glacial lake situated ~2 km west of the ice sheet margin) we present a longer sedimentary and biostratigraphic record. The deeper portions of cores from Wax Lips Lake yield pre-Holocene and nonfinite radiocarbon ages, suggesting that this lake preserves sediments predating the Last Glacial Maximum. Abundant chironomids in the pre-glacial sediments appear to record interglacial conditions, and we infer that these sediments may date to the Last Interglacial (Eemian). The preservation of in situ Last Interglacial lacustrine sediments so close to the modern ice sheet margin suggests a minimally erosive glacierization style throughout the last glacial period, like that inferred for other Arctic locales such as on Baffin Island (Briner et al. 2007), ~750 km southwest of our study site. Our study sites are situated nearby key ice core sites (including NEEM, Camp Century, Agassiz and Renland) and very close to the ice sheet margin. These chironomid

  9. Insect-Based Holocene (and Last Interglacial?) Paleothermometry from the E and NW Greenland Ice Sheet Margins: A Fly's-Eye View of Warmth on Greenland

    NASA Astrophysics Data System (ADS)

    Axford, Y.; Bigl, M.; Carrio, C.; Corbett, L. B.; Francis, D. R.; Hall, B. L.; Kelly, M. A.; Levy, L.; Lowell, T. V.; Osterberg, E. C.; Richter, N.; Roy, E.; Schellinger, G. C.

    2013-12-01

    Here we present new paleotemperature reconstructions based upon insect (Chironomidae) assemblages and other proxies from lake sediment cores recovered in east Greenland at ~71° N near Scoresby Sund and in northwest Greenland at ~77° N near Thule/Qaanaaq. In east Greenland, Last Chance Lake (informal name) is a small, non-glacial lake situated ~90 km east of the Greenland Ice Sheet margin. The lake preserves a sedimentary record of the entire Holocene (Levy et al. 2013). Chironomids from Last Chance Lake record cold summer temperatures (and establishment of a cold-climate fauna including abundant Oliveridia and Pseudodiamesa) during the late Holocene, preceded by summer temperatures estimated to have been 3 to 6°C warmer during the first half of the Holocene (when summer insolation forcing was greater than today). In northwest Greenland, Delta Sø and Wax Lips Lake (informal name) both preserve Holocene sediments. Here we discuss the late Holocene chironomid record from Delta Sø, whereas from Wax Lips Lake (a small, non-glacial lake situated ~2 km west of the ice sheet margin) we present a longer sedimentary and biostratigraphic record. The deeper portions of cores from Wax Lips Lake yield pre-Holocene and nonfinite radiocarbon ages, suggesting that this lake preserves sediments predating the Last Glacial Maximum. Abundant chironomids in the pre-glacial sediments appear to record interglacial conditions, and we infer that these sediments may date to the Last Interglacial (Eemian). The preservation of in situ Last Interglacial lacustrine sediments so close to the modern ice sheet margin suggests a minimally erosive glacierization style throughout the last glacial period, like that inferred for other Arctic locales such as on Baffin Island (Briner et al. 2007), ~750 km southwest of our study site. Our study sites are situated nearby key ice core sites (including NEEM, Camp Century, Agassiz and Renland) and very close to the ice sheet margin. These chironomid

  10. A Holocene Sediment Record From Lake Elsinore, Southern California: Evidence for Relative Lake Level Change and the Onset of ENSO.

    NASA Astrophysics Data System (ADS)

    Kirby, M. E.; Lund, S. P.; Poulsen, C. J.

    2003-12-01

    There are very few complete terrestrial, Holocene paleoclimate records from coastal southwestern North America. Lake Elsinore, located 120km southeast of Los Angeles, represents one of the only natural, non-playa lakes in the region. Furthermore, it is well documented that coastal southwestern North America is highly sensitive to changes in atmospheric circulation and its affect on regional hydrodynamics. As shown by Kirby et al. (in press), modern lake levels at Lake Elsinore respond directly to total annual precipitation, particularly winter season amounts. The lake is also located along the eastern Pacific Ocean where changes in ocean circulation and its thermal structure modulate the overlying atmosphere, and thus the adjacent continental climate. Here, we present two 7 meter sediment core records from Lake Elsinore spanning the entire Holocene. Although the cores are from the lake's littoral zone, they show surprisingly complete records with very little lithologic evidence for major hiatuses. A combination of sedimentological analyses (e.g., mass magnetic susceptibility (CHI); total percent carbonate; total organic matter) and lithologic descriptions provide insight to lake dynamics over the Holocene. Using the historical calibration between magnetic susceptibility and relative lake level (i.e., high lake levels = high CHI values and vice versa) from Kirby et al. (in press), we developed a first-order estimate of Holocene relative lake levels for Lake Elsinore. The historic calibration is extrapolated through the sediment record based on the assumption that, like today, first order lake level change is directly related to precipitation amount. Both total percent carbonate and total organic matter support our historical calibration between CHI and lake level. Our data suggest a relative increase in lake levels during the mid-Holocene (ca. 8,000 cal yr BP) and through to the present day. From this observation, we hypothesize that regional hydrology as linked to

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

    NASA Astrophysics Data System (ADS)

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

    2008-12-01

    multi-proxy study of selected cores retrieved from the deepest part of the lacustrine basin allows characterizing the Holocene sedimentary record. Detailed petrophysical, sedimentological and geochemical studies of a complete laminated sequence reveal fluctuations in major and trace elements, as well as total organic matter content and palynological data suggesting an apparent cyclicity. These results provide a unique dataset that can be compared with other marine and continental archives to improve our understanding of the forcing mechanisms behind climate change and to validate the outcome of existing ocean and atmospheric climatic models for the Southern Hemisphere.

  12. Holocene and recent sediment accumulation rates in southern Lake Michigan

    USGS Publications Warehouse

    Colman, Steven M.; King, J.W.; Jones, Glenn A.; Reynolds, R.L.; Bothner, Michael H.

    2000-01-01

    Rates of sediment accumulation in Lake Michigan are a key component of its geologic history and provide important data related to societal concerns such as shoreline erosion and the fate of anthropogenic pollutants. Previous attempts to reconstruct Holocene rates of sediment accumulation in Lake Michigan, as well as in the other Laurentian Great Lakes, have been bedeviled by the effect of refractory terrestrial material on radiocarbon ages from total organic carbon samples of lake sediments. AMS radiocarbon ages on small samples of biogenic carbonate (ostracodes and mollusks) in Lake Michigan provide accurate Holocene ages. The present bicarbonate reservoir effect is estimated from shells of mollusks collected live before atmospheric nuclear testing to be 250 yr. From paired samples of biogenic carbonate and terrestrial macrofossils, the past reservoir effect is thought to be less than 500 yr. The radiocarbon ages indicate a distinct decrease in sediment accumulation rates throughout the southern basin of Lake Michigan at about 5 ka, about the time when lake level stabilized at the Nipissing level after rising rapidly for several thousand years. Average rates of sediment accumulation for the historic period (the last 150 yr) can be estimated from radioisotopes (210Pb and 137Cs), pollen stratigraphy, and changes in sediment properties associated with human activity. Multiple methods are necessary because at any given site, problems arise in the assumptions or applicability of one or more methods. In general, the mass accumulation calculations suggest that sediments were deposited 4 to 11 times faster in the historic period than before human settlement. The character of the sediment did not change in a dramatic way, but sediment magnetic properties suggest shifts in the sources of sediment. The data suggest that some of the changes in sources and (or) character of the sediment occurred just before human settlement and were probably related to climatic changes

  13. Holocene Climatic Variability in the Indian Monsoon Domain

    NASA Astrophysics Data System (ADS)

    Mishra, Praveen Kumar; Anoop, Ambili; Menzel, Philip; Gaye, Birgit; Basavaiah, Nathani; Jehangir, Arshid; Prasad, Sushma

    2013-04-01

    The available data on Holocene climate variability from Asia indicates spatio-temporal changes in the precipitation over this vast region. Detailed information on the timing, duration, regionality, and causes of these fluctuations is not well understood, especially over the Indian subcontinent. My work focuses on long core sediments from lake Tso Moriri (78°14'-78°25'N and 32°40'-33°02'E; altitude: 4500 m) situated in climatically sensitive zone of NW Himalayas affected by both mid-latitude westerlies and Indian summer monsoon. Two cores ca.7 m were retrieved from the lake at different water depths (ca. 40m and 105m) in July 2011. Investigations reveal marked changes in grain size, lamination quality, mineralogy, organic and carbonate content suggesting changes in lake level, direction of inflow, and biological productivity that in turn are influenced by regional climate. As the lake lies in a tectonically active region, I have also undertaken detailed geomorphometric (knick-point, Hack index), and drainage pattern analysis of the major inflowing streams to decipher the active tectonics in the region. Sharp changes in river course and slope gradient indicates the presence of an active N-S trending fault in western flank of the lake. The data from lake Tso Moriri will be compared with other high-resolution records from lake Lonar and stalagmites in NE India to reconstruct the forcing mechanism of Holocene climatic variability.

  14. Contribution of bacterial cells to lacustrine organic matter based on amino sugars and D-amino acids

    NASA Astrophysics Data System (ADS)

    Carstens, Dörte; Köllner, Krista E.; Bürgmann, Helmut; Wehrli, Bernhard; Schubert, Carsten J.

    2012-07-01

    Amino sugars (ASs), D-amino acids (D-AAs), and bacterial cell counts were measured in two Swiss lakes to study the contribution of bacterial cells to organic matter (OM) and the fate of ASs and bacterial amino biomarkers during OM degradation. Concentrations of individual ASs (glucosamine, galactosamine, muramic acid, and mannosamine) in the particulate and total OM pools were analyzed in water-column profiles of Lake Brienz (oligotrophic and oxic throughout the entire water column) and Lake Zug (eutrophic, stratified, and permanently anoxic below 170 m) in spring and in fall. Generally, carbon-normalized AS concentrations decreased with water depth, indicating the preferential decomposition of ASs. For Lake Brienz the relative loss of particulate ASs was higher than in Lake Zug, suggesting enhanced AS turnover in an oligotrophic environment. AS ratio changes in the water column revealed a replacement of plankton biomass with OM from heterotrophic microorganisms with increasing water depth. Similar to the ASs, highest carbon normalized D-AA concentrations were found in the upper water column with decreasing concentrations with depth and an increase close to the sediments. In Lake Zug, an increase in the percentage of D-AAs also showed the involvement of bacteria in OM degradation. Estimations of OM derived from bacterial cells using cell counts and the bacterial biomarkers muramic acid and D-AAs gave similar results. For Lake Brienz 0.2-14% of the organic carbon pool originated from bacterial cells, compared to only 0.1-5% in Lake Zug. Based on our estimates, muramic acid appeared primarily associated with bacterial biomass and not with refractory bacterial necromass. Our study underscores that bacteria are not only important drivers of OM degradation in lacustrine systems, they also represent a significant source of OM themselves, especially in oligotrophic lakes.

  15. Tracking Nile Delta vulnerability to Holocene change.

    PubMed

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

    2013-01-01

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

  16. Holocene thinning of the Greenland ice sheet.

    PubMed

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

    2009-09-17

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

  17. Early Holocene Change in Atmospheric Circulation in the North-Central USA

    NASA Astrophysics Data System (ADS)

    Dean, W. E.

    2005-12-01

    beginning of the altithermal or prairie period in Minnesota. Substantial changes in salinity also occurred at many lacustrine sites in the Northern Great Plains around 8.2 cal. ka so that such changes are not unique to Elk Lake, and thus the driver of these changes must be regional or global in extent. Bear Lake, Utah and Idaho, is a mesosaline-alkaline lake that historically was bipassed by the Bear River to the east of the lake. However, during the last glacial interval the lake and river were connected until about 16 cal. ka. As the salinity of the lake increased without Bear River influx, carbonate began to precipitate, first as calcite and then as aragonite, the dominant carbonate mineral deposited during most of the Holocene. C- O- and Sr-isotope data indicate that at about 9.5 cal ka the lake abruptly freshened suggesting that Bear River was again reconnected to the lake. The cause of the reconnection of Bear River with Bear Lake may have been tectonic, geomorphic, or climatic. However, the dominance of a boreal ostracode assemblage prior to 8.2 cal ka in Elk Lake, indicating that the polar front was far south of its present position, may have permitted the temporary establishment of a polar low over Utah, Idaho, and Wyoming in winter, increasing the snow pack in the Uinta Mountains and the Bear River Range to the west of the lake thereby increasing the surface- and ground-water flow to the lake. By 8.5 cal ka the salinity of the lake had decreased sufficiently to trigger another pulse of calcite precipitation that lasted about 1000 years. At 8.2 cal ka, when the Elk Lake ostracode record indicates that the polar front had retreated to the north, the Bear River was disconnected from the lake, and by 7.5 cal ka aragonite was again forming.

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

    PubMed Central

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

    2014-01-01

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

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

    PubMed

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

    2014-01-01

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

  20. BIOGEOCHEMICAL CONTROLS ON REACTION OF SEDIMENTARY ORGANIC MATTER AND AQUEOUS SULFIDES IN HOLOCENE SEDIMENTS OF MUD LAKE FLORIDA

    EPA Science Inventory

    The distribution and quantity of organic sulfur and iron sulfur species were determined in the
    Holocene sediments from Mud Lake, Florida. The sediments of this shallow, sinkhole lake are characterized by high sulfur and organic carbon contents as well as active sulfate reducti...

  1. Exploring the Stable Isotope Record of Lake Carpenter: A Lacustrine Sequence in the Aptian-Albian Cretaceous Cedar Mountain Formation, Utah, USA

    NASA Astrophysics Data System (ADS)

    Montgomery, E.; Al-Suwaidi, A. H.; Suarez, M. B.; Kirkland, J. I.; Suarez, C. A.

    2014-12-01

    The Cedar Mountain Formation (CMF) represents the earliest deposition of terrestrial Cretaceous strata in the USA, recording significant changes in biota and climate. Understanding these transitions requires improved time constraints and high-resolution proxy records. Here we present new δ13C (organic carbon & carbonate) chemostratigraphic record of a lacustrine sequence in a locality named "Lake Carpenter", near Moab, Utah. Lake Carpenter (LC) comprises interbedded limestone and mudstone units of the Ruby Ranch Member of the CMF. Results of the chemostratigraphy are constrained by detrital zircons from the section allowing correlation of the chemostratigraphy to the carbon isotope segments C9 to C11 (Bralower et al., 1999) spanning the Late Aptian to Early Albian, and supported by previous litho- and chemostratigraphic work in the CMF. δ13Corg values show a pronounced negative stepped excursion, of -6‰ with values reaching -32.3 ‰ occurring in conjunction with an increase in TOC. This negative excursion is followed by a positive recovery, with values of ~-25‰ and relatively low TOC. δ13Ccarb records positive values, up to +8‰, in the lowermost part of the section (< ~7m) followed by a decrease to ~-7 ‰. δ18Ocarb over this interval records values between -2 and -4‰ followed by a decrease to ~-7‰. The lowermost portion of the LC section is indicative of relatively deep lacustrine environment in which organic carbon burial influenced the δ13C of dissolved inorganic carbon (DIC) in the lake. This lower δ13C of DIC may be due to increased upwelling and/or turnover and recycling of organic carbon in the lake. Variability of δ13Ccarb and δ18Ocarb values may reflect changes in water supply to the lake, or climatic variability resulting in the lake drying out. δ13Corg values may be affected by local lake dynamics, including variations in organic carbon storage and changes in algal productivity, perhaps also indicative of changes in nutrient

  2. Lacustrine turbidites in the Green River Formation, northwestern Colorado

    NASA Astrophysics Data System (ADS)

    Dyni, John R.; Hawkins, James E.

    1981-05-01

    A preliminary study of drill cores of blebby and streaked oil shale from the Green River Formation (Eocene) in the deep northern part of the Piceance Creek Basin, Colorado, shows sedimentary structures that suggest deposition by turbidity currents. This type of oil shale composes about one-half of the oil-shale deposits at the saline depocenter of Eocene Lake Uinta where it is interbedded with the well-known laminated type of oil shale described previously in the literature. Episodic and rapid deposition by lake-bottom currents of large amounts of carbonate-silicate sediments that formed high-grade oil shale is a new concept for the origin of a major part of the Green River oil-shale deposits. In contrast, the laminated oil shale, as previously described, accumulated very slowly as thin varves in a chemically stratified lake under stagnant conditions.

  3. Climate and lake-level history of the northern Altiplano, Bolivia, as recorded in Holocene sediments of the Rio Desaguadero

    SciTech Connect

    Baucom, P.C.; Rigsby, C.A.

    1999-05-01

    Strata exposed in terraces and modern cutbanks along the Rio Desaguadero contain a variety of lithofacies that were deposited in four distinct facies associations. These facies associations document a history of aggradation and downcutting that is linked to Holocene climate change on the Altiplano. Braided-stream, meandering-stream, deltaic and shoreline, and lacustrine sediments preserved in multi-level terraces in the northern Rio Desaguadero valley record two high-water intervals: one between 4,500 and 3,900 yr BP and another between 2,000 and 2,200 yr BP. These wet periods were interrupted by three periods of fluvial downcutting, centered at approximately 4,000 yr BP, 3,600 yr BP, and after 2,000 yr BP. Braided-river sediments preserved in a single terrace level in the southern Rio Desaguadero valley record a history of nearly continuous fluvial sedimentation from at least 7,000 yr BP until approximately 3,200 yr BP that was followed by a single episode (post-3,210 yr BP) of down-cutting and lateral migration. The deposition and subsequent fluvial downcutting of the northern strata was controlled by changes in effective moisture that can be correlated to Holocene water-level fluctuations of Lake Titicaca. The deposition and dissection of braided-stream sediments to the south are more likely controlled by a combination of base-level change and sediment input from the Rio Mauri.

  4. Terminal Pleistocene/Early Holocene Environmental Change at the Sunshine Locality, North-Central Nevada, U.S.A.

    NASA Astrophysics Data System (ADS)

    Huckleberry, Gary; Beck, Charlotte; Jones, George T.; Holmes, Amy; Cannon, Michael; Livingston, Stephanie; Broughton, Jack M.

    2001-05-01

    Sedimentological, faunal, and archaeological investigations at the Sunshine Locality, Long Valley, Nevada reveal a history of human adaptation and environmental change at the last glacial-interglacial transition in North America's north-central Great Basin. The locality contains a suite of lacustrine, alluvial, and eolian deposits associated with fluvially reworked faunal remains and Paleoindian artifacts. Radiocarbon-dated stratigraphy indicates a history of receding pluvial lake levels followed by alluvial downcutting and subsequent valley filling with marsh-like conditions at the end of the Pleistocene. A period of alluvial deposition and shallow water tables (9,800 to 11,000 14C yr B.P.) correlates to the Younger Dryas. Subsequent drier conditions and reduced surface runoff mark the early Holocene; sand dunes replace wetlands by 8,000 14C yr B.P. The stratigraphy at Sunshine is similar to sites located 400 km south and supports regional climatic synchroneity in the central and southern Great Basin during the terminal Pleistocene/early Holocene. Given regional climate change and recurrent geomorphic settings comparable to Sunshine, we believe that there is a high potential for buried Paleoindian features in primary association with extinct fauna elsewhere in the region yet to be discovered due to limited stratigraphic exposure and consequent low visibility.

  5. The Arctic Mountain Glacier, Austre Okstindbreen in Northern Norway, survived the 'Holocene Thermal Optimum

    NASA Astrophysics Data System (ADS)

    Bakke, Jostein; Paasche, Øyvind; Olaf Dahl, Svein

    2010-05-01

    Arctic glaciers are currently undergoing major changes, but accurate knowledge about how they have varied continuously during the Holocene (<11 700 years) is still scarce. Here we present a new glacier record from Austre Okstindbreen in Nordland, northern Norway. This continuous reconstruction is based on a number of short and long cores collected from several downstream basins, which have been analyzed by a suit of methods including geochemical elements (XRF), rock magnetic properties, dry bulk density (DBD) and Loss-on-ignition (LOI). Lake sediment distribution was surveyed and mapped by the use of ground penetrating radar (GPR), securing optimal coring sites. Independently lichen-dated marginal moraines and historical information from old photographs and maps have ensured that the moraine sequence can be closely linked to the lake sediment chronology. This new glacier reconstruction reveals that Austre Okstindbreen is the first known glacier in Scandinavia to have survived the "Holocene Thermal Optimum". It also brackets the four largest glacier advances to c 7000, 1300, 800 and 250 b2k. In contrast to most glaciers in Scandinavia, the largest glacier advance was not associated with the "Little Ice Age", but rather to an earlier period centred at 1300 b2k. Both the moraine chronology and the lacustrine records document this foremost Neoglacial advance. Compared to other glacier reconstructions from the Northern Hemisphere we identify near-synchronous glacier advances occurring roughly at 4ka, 1.3ka and during the "Little Ice Age". These shared advances across the Northern Hemisphere suggest that these centennial-scale events are a shared feature regardless of the large geographical distances separating them. Some of the events are not synchronous between the different records, which are probably due to lack of precise dating as well as the potential influence of local climatic conditions.

  6. A complete record of Holocene glacier variability at Austre Okstindbreen, northern Norway: an integrated approach

    NASA Astrophysics Data System (ADS)

    Bakke, Jostein; Dahl, Svein Olaf; Paasche, Øyvind; Riis Simonsen, Joachim; Kvisvik, Bjørn; Bakke, Kristina; Nesje, Atle

    2010-05-01

    Arctic glaciers are currently undergoing major changes, but accurate knowledge about how they varied during the entire Holocene is still scarce. Here we present a new complete glacier record from Austre Okstindbreen in Nordland, northern Norway. This reconstruction is based on a number of short and long cores retrieved from several downstream basins, which have been analyzed by a suite of methods including geochemical elements (XRF), rock magnetic properties, dry bulk density (DBD) and Loss-on-ignition (LOI). Lake sediment distribution was surveyed and mapped prior to coring by the use of ground penetrating radar (GPR). Independently lichen-dated marginal moraines and historical information about the glacier frontal positions from old photographs and maps have made it possible to link the moraine sequence to the 210Pb dated lake sediment chronology. This integrated approach reveals that Austre Okstindbreen is the first known glacier in Scandinavia to possibly have survived the "Holocene Thermal Optimum". It also brackets the four largest glacier advances to c 7400-7000, 1400-1200, 900-700 and 300-150 years before AD 2000 (b2k). In contrast to most reconstructed glaciers in Scandinavia, the largest glacier advance was not associated with the "Little Ice Age", but rather to an earlier period centred at 1300 b2k. Both the moraine chronology and the lacustrine records document this Neoglacial advance. Compared to other glacier reconstructions from the Northern Hemisphere, we identify near-synchronous glacier advances occurring roughly at 4000 b2k; 2700 b2k; 1300 b2k and during the "Little Ice Age". These correlative advances across the Northern Hemisphere suggest that these observed centennial-scale events are a shared feature regardless of the large geographical distances separating them. Some minor discrepancies between different geographical areas may be caused by lack of precise dating, but local climatic conditions may play a role as well.

  7. Megalake Chad impact on climate and vegetation during the late Pliocene and the mid-Holocene

    NASA Astrophysics Data System (ADS)

    Contoux, C.; Jost, A.; Ramstein, G.; Sepulchre, P.; Krinner, G.; Schuster, M.

    2013-07-01

    Given the growing evidence for megalakes in the geological record, assessing their impact on climate and vegetation is important for the validation of palaeoclimate simulations and therefore the accuracy of model-data comparison in lacustrine environments. Megalake Chad (MLC) occurrences are documented not only for the mid-Holocene but also for the Mio-Pliocene (Schuster et al., 2009). At this time, the surface covered by water would have reached up to ~350 000 km2 (Ghienne et al., 2002; Schuster et al., 2005; Leblanc et al., 2006), making it an important evaporation source, possibly modifying climate and vegetation in the Chad Basin. We investigated the impact of such a giant continental water area in two different climatic backgrounds within the Paleoclimate Model Intercomparison Project phase 3 (PMIP3): the late Pliocene (3.3 to 3 Ma, i.e. the mid-Piacenzian warm period) and the mid-Holocene (6 kyr BP). In all simulations including MLC, precipitation is drastically reduced above the lake surface because deep convection is inhibited by overlying colder air. Meanwhile, convective activity is enhanced around MLC because of the wind increase generated by the flat surface of the megalake, transporting colder and moister air towards the eastern shore of the lake. The effect of MLC on precipitation and temperature is not sufficient to widely impact vegetation patterns. Nevertheless, tropical savanna is present in the Chad Basin in all climatic configurations, even without MLC presence, showing that the climate itself is the driver of favourable environments for sustainable hominid habitats.

  8. Improving late Holocene radiocarbon-based chronologies by matching paleomagnetic secular variations to geomagnetic field models - Examples from Nam Co (Tibet) and Lake Kalimpaa (Sulawesi)

    NASA Astrophysics Data System (ADS)

    Haberzettl, T.; Kasper, T.; St-Onge, G.; Behling, H.; Daut, G.; Doberschütz, S.; Kirleis, W.; Mäusbacher, R.; Nowaczyk, N.

    2010-12-01

    Precise age control is a prerequisite for reliable paleoenvironmental reconstruction. Almost all Holocene chronologies of lacustrine sequences are based on radiocarbon dating. Most reliable ages are obtained from fragile terrestrial vegetation remnants (e.g., leaves) as these neither yield a reservoir or hard water effect nor are reworked as they would be destroyed during this process. However, in many records no terrestrial plant remains or macro remains in general are found in the sediments. In this case the only option to establish a radiocarbon based chronology is to date bulk sediment. This sediment sometimes contains reworked material or, in hard water lakes, aquatic organic remains which contain old carbon - both resulting in older ages. Here we present two records dated by bulk material showing these inconveniences. Nam Co is a hard water lake on the Tibetan Plateau (30.5°N, 91°E). Previous studies from various sites in this lake revealed different hard water effects. A radiocarbon date of bulk sediment from the top of a gravity core yielded an age of 1420 ±40 BP for the sediment/water interface. In order to test if this value can be constantly extrapolated back in time we established a reservoir corrected chronology with this value. Subsequently, we compared inclination and declination data to the CALS3k.3 and the CALS7k geomagnetic field models which currently provide the best representation of the late Holocene geomagnetic field. This showed excellent accordance for the period covered by the gravity core, i.e., ~4000 cal BP. Lake Kalimpaa (1.3°S, 120.3°E) is located on the island of Sulawesi, Indonesia. Radiocarbon-dated bulk samples also showed inconsistencies. Most likely not only the autochthonous carbon fraction was dated but also some allochthonous organic matter was incorporated into the samples. If this is the case, all ages are tentatively too old. Following a conservative approach, in order to minimize this error, only the youngest dates

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

    NASA Astrophysics Data System (ADS)

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

    2004-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  12. Holocene climate variability in the North-Western Mediterranean Sea (Gulf of Lions)

    NASA Astrophysics Data System (ADS)

    Jalali, B.; Sicre, M.-A.; Bassetti, M.-A.; Kallel, N.

    2016-01-01

    Sea surface temperatures (SSTs) and land-derived input time series were generated from the Gulf of Lions inner-shelf sediments (NW Mediterranean Sea) using alkenones and high-molecular-weight odd-carbon numbered n-alkanes (TERR-alkanes), respectively. The SST record depicts three main phases: a warm Early Holocene ( ˜ 18 ± 0.4 °C) followed by a cooling of ˜ 3 °C between 7000 and 1000 BP, and rapid warming from ˜ 1850 AD onwards. Several superimposed multi-decadal to centennial-scale cold events of ˜ 1 °C amplitude were also identified. TERR-alkanes were quantified in the same sedimentary horizons to identify periods of high Rhone River discharge and compare them with regional flood reconstructions. Concentrations show a broad increase from the Early Holocene towards the present with a pronounced minimum around 2500 BP and large fluctuations during the Late Holocene. Comparison with Holocene flood activity reconstructions across the Alps region suggests that sediments of the inner shelf originate mainly from the Upper Rhone River catchment basin and that they are primarily delivered during positive North Atlantic Oscillation (NAO).

  13. Holocene climate variability in the North-Western Mediterranean Sea (Gulf of Lions)

    NASA Astrophysics Data System (ADS)

    Jalali, B.; Sicre, M.-A.; Bassetti, M.-A.; Kallel, N.

    2015-07-01

    Sea surface temperatures (SSTs) and land-derived input time series were generated from the Gulf of Lions inner-shelf sediments (NW Mediterranean Sea) using alkenones and high-molecular-weight odd-carbon numbered n-alkanes (TERR-alkanes), respectively. The SST record depicts three main phases: a warm Early Holocene (∼ 18 ± 0.4 °C) followed by a cooling of ∼ 3 °C (from 7000 to 1000 BP) and rapid warming from ∼ 1850 AD onwards. Several superimposed multi-decadal cooling events of ∼ 1 °C amplitude were also identified. TERR-alkanes were also quantified to identify periods of high river discharge in relation with flood events of the Rhone River and precipitations. Their concentrations show a broad increase from the early Holocene towards present with a pronounced minimum around 2500 BP and large fluctuations during the second part of the Holocene. Comparison with Holocene flood activity reconstructions across the Alps region suggests that sediments of the inner shelf originate mainly from the Upper Rhone River catchment basin and that they are primarily delivered during positive NAO.

  14. Spawning migration of lacustrine-adfluvial bull trout in a natural area

    USGS Publications Warehouse

    Brenkman, Samuel J.; Larson, Gary L.; Gresswell, Robert E.

    2001-01-01

    We investigated the spawning migration of lacustrine-adfluvial bull trout Salvelinus confluentus in the North Fork Skokomish River in Olympic National Park (Washington State) during 1996. Day-snorkeling and electrofishing were conducted to determine timing and duration of the migration and the distribution and abundance of bull trout. The primary spawning migration began in early October and was waning by December. Bull trout migrated 6 km or less up the river from Lake Cushman. Increased river discharge and decreased water temperature appeared to be the primary environmental variables corresponding to the initiation of the migration. Mean length of migratory bull trout increased from June to December. Comparisons with other lacustrine-adfluvial bull trout populations in Oregon, Montana, Idaho, and British Columbia suggested that these populations exhibit specific migratory strategies related to local environmental conditions.

  15. Taphonomic analysis in lacustrine environments: Two different contexts for Triassic lake paleofloras from Western Gondwana (Argentina)

    NASA Astrophysics Data System (ADS)

    Mancuso, Adriana Cecilia

    2009-12-01

    During the earliest Triassic several rift basins developed along the western margin of Gondwana associated with the pre-breakup of Pangea. They were filled by exclusively non-marine sediments including alluvial, fluvial, and lacustrine deposits. In the Ischigualasto-Villa Unión Basin, the lacustrine-deltaic succession is placed in the Los Rastros Formation and consists of several coarsening-upward cycles of black shale, siltstone, and sandstone. The paleontologic content of the succession includes abundant floral remains (related to the Dicroidium-type flora), invertebrates (conchostracans, insects), and vertebrates (fishes, a temnospondyl amphibian, ichnites). At the Cerro Puntudo area in the Cuyana Basin, the lacustrine succession forms the upper part of the Cerro Puntudo Formation and consists of limestone, stromatolitic limestone, mudstone, sandstone, and tuff. The paleontologic content includes scarce floral remains and rhizoliths; invertebrates are represented exclusively by traces (associated with ichnofacies of Skolithos and Scoyenia), and vertebrates by a fragment of the pelvic girdle of a basal arcosaur. The taphonomic analysis performed in the two Triassic lacustrine successions allows recognition of two different taphonomic histories for the plant remains. The Los Rastros lake preserved both autochthonous (originated in the littoral zone) and allochthonous (originated in the upstream fluvial system) elements. The offshore lacustrine area was dominated by autochthonous well-preserved elements and allochthonous plant debris and wood, which formed time-averaged accumulations. The delta deposits are characterized by allochthonous elements with varied preservational conditions, usually showing evidence of mechanical degradation and accumulation within a short time. Autochthonous and allochthonous material were preserved in the Los Rastros Lake by means of anoxic conditions in the offshore lacustrine area and high sedimentation rates in the delta. In

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

    NASA Astrophysics Data System (ADS)

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

    2010-05-01

    Yakutia (Russia, northeastern part of Eurasia) represents one of Earths most extreme climatic settings in the world with deep-reaching frozen ground and a semiarid continental climate with highest seasonal temperature contrasts in the northern hemisphere. The amplitude of temperature variations around the year sometimes exceeds 100oC. There are few examples of quantitative palaeoecological studies in Siberia and these data have to be tested by quantitative studies from other sites in this region, inferred from different proxies and using regional calibration datasets and temperature models that are still lacking. Chironomid midges (Insecta, Diptera, Chironomidae) have been widely used to reconstruct past climate variability in many areas of Western Europe and North America. A chironomid-mean July air temperature inference model has been developed, based on a modern calibration set of 200 lakes sampled along a transect from 110° to 159° E and 61° to73° N in northern Russia. The inference model was applied to sediment cores from 2 lakes in the Central Yakutia in order to reconstruct past July air temperatures. The lacustrine records span mid- to late Holocene. The downcore variability in the chironomid assemblages and the composition of organic matter give evidence of climate-driven and interrelated changes in biological productivity, lacustrine trophic states, and lake-level fluctuations. Three phases of the climate development in Central Yakutia can be derived from the geochemical composition of the lake cores and according to the inferred from chironomid assemblages mean July air ToC. Content of organic matters reached maximal values in the period between 7000-4500 yBP. Sedimentation rate is especially high, numerous molluscs shells are found in sediments. All this along with the reconstructed air temperature confirmed that Mid Holocene optimum in Central Yakutia took place in this period with the maximal temperatures up to 4oC above present day ToC. Strong

  17. Uranium and diagenesis in evaporitic lacustrine mudstone of the Oligocene White River Group, Dawes County, Nebraska

    SciTech Connect

    Dickinson, K.A.

    1991-01-01

    In this paper the uranium mineralization and diagenesis of an evaporitic lacustrine mudstone and related fluvial and colluvial facies in the White River Group in Dawes county, Nebraska, are described. Diagenetic minerals and textures are identified using a variety of petrologic methods, including x-ray diffraction, thin-section study, and scanning electron micrography. R-mode factor analysis was performed on a data base containing chemical and mineralogical data. Uranium distribution in the depositional and diagenetic environments is also analyzed.

  18. Ground Penetrating Radar (GPR) Signatures of Lacustrine Soils in Volcanic Basins of Mexico

    NASA Astrophysics Data System (ADS)

    Carreon-Freyre, D.; Oleschko, K.; Cerca, M.

    2002-12-01

    Ground Penetrating Radar (GPR) profiles have been collected in volcanic and lacustrine basins of Mexico in order to obtain radar signatures and correlate electromagnetic wave propagation with their near-surface stratigraphy. Study sites included Pleistocene to Recent lacustrine sequences in Chalco and Texcoco, near Mexico City, and a Pliocene to Quaternary fluvio-lacustrine sequence in the Queretaro Valley, 250 Km to the northwest. All the sequences present alterning layers of soils, fluvio-lacustrine sediments, pyroclastic and volcanic rocks. GPR method is used because of the sensitivity of the propagation of electromagnetic waves to the granulometric variations and water content of sediments (water molecules polarization). Profiles were carried out with a Zond 12c GPR (Radar Systems Inc.), using four main prospecting frequencies: 2000, 900, 300 and 100 MHz. The purpose of using these frequencies is to evaluate different ranges of depths of investigation and resolution for each site and to relate attenuation and variations in amplitude with impedances and reflection coefficients for stratigraphic associations such as clay-sand, silt-clay and pyroclastics-silt. The analysis of multiple sets of profiles in the studied areas and their correlation with the observed near-surface stratigraphy permits the identification of radar signatures for each depositional condition. GPR characterization also allowed to associate radar signatures with the evolution of fracturing within the sequence. In particular, the Chalco and Queretaro sites are affected by fracturing, an increasing problem in several urbanized areas of Mexico and the world. This phenomenon is generally associated to ground-water withdrawal but its geometry is related closely to the regional structural pattern. Another factor that influences the propagation and morphology of near-surface fracturing in volcanic valleys is their highly heterogeneous stratigraphy. Therefore, the propagation of electromagnetic waves

  19. Fluvial and Lacustrine Processes in Meridiani Planum and the Origin of the Hematite by Aqueous Alteration

    NASA Technical Reports Server (NTRS)

    Newsom, H. E.; Barber, C. A.; Schelble, R. T.; Hare, T. M.; Feldman, W. C.; Sutherland, V.; Livingston, A.; Lewis, K.

    2003-01-01

    The prime MER landing site in Meridiani Planum is located on layered materials, including hematite, whose origin as lacustrine or aeolian sediments, or volcanic materials is uncertain. Our detailed mapping of the region provides important constraints on the history of the region. Our mapping of the location of fluvial and lacustrine land forms in the region relative to the layered deposits provides new evidence of a long history of erosion and deposition as has long been noted . In addition, our detailed mapping of the southern boundary of the hematite deposit strongly supports an association between longlived fluvial channels and lacustrine basins and the strongest hematite signatures. This evidence supports an origin of the hematite deposits by interaction with water under ambient conditions in contrast to suggestions of hydrothermal processes due to volcanic or impact crater processes. An important part of the story is the evidence for the localization of the layered deposits due to topographic control induce by the presence of a large early basin we have identified that extends to the north-east of the landing site. Distribution of current channel networks, drainages,

  20. Volcanogenic Fluvial-Lacustrine Environments in Iceland and Their Utility for Identifying Past Habitability on Mars

    PubMed Central

    Cousins, Claire

    2015-01-01

    The search for once-habitable locations on Mars is increasingly focused on environments dominated by fluvial and lacustrine processes, such as those investigated by the Mars Science Laboratory Curiosity rover. The availability of liquid water coupled with the potential longevity of such systems renders these localities prime targets for the future exploration of Martian biosignatures. Fluvial-lacustrine environments associated with basaltic volcanism are highly relevant to Mars, but their terrestrial counterparts have been largely overlooked as a field analogue. Such environments are common in Iceland, where basaltic volcanism interacts with glacial ice and surface snow to produce large volumes of meltwater within an otherwise cold and dry environment. This meltwater can be stored to create subglacial, englacial, and proglacial lakes, or be released as catastrophic floods and proglacial fluvial systems. Sedimentary deposits produced by the resulting fluvial-lacustrine activity are extensive, with lithologies dominated by basaltic minerals, low-temperature alteration assemblages (e.g., smectite clays, calcite), and amorphous, poorly crystalline phases (basaltic glass, palagonite, nanophase iron oxides). This paper reviews examples of these environments, including their sedimentary deposits and microbiology, within the context of utilising these localities for future Mars analogue studies and instrument testing. PMID:25692905

  1. Seismic facies analysis of lacustrine system: Paleocene upper Fort Union Formation, Wind River basin, Wyoming

    SciTech Connect

    Liro, L.M.; Pardus, Y.C.

    1989-03-01

    The authors interpreted seismic reflection data, supported by well control, to reconstruct the stratigraphic development of Paleocene Lake Waltman in the Wind River basin of Wyoming. After dividing the upper Fort Union into eight seismic sequences, the authors mapped seismic attributes (amplitude, continuity, and frequency) within each sequence. Interpretation of the variation in seismic attributes allowed them to detail delta development and encroachment into Lake Waltman during deposition of the upper Fort Union Formation. These deltas are interpreted as high-energy, well-differentiated lobate forms with distinct clinoform morphology on seismic data. Prograding delta-front facies are easily identified on seismic data as higher amplitude, continuous events within the clinoforms. Seismic data clearly demonstrate the time-Transgressive nature of this facies. Downdip of these clinoforms, homogeneous shales, as evidenced by low-amplitude, generally continuous seismic events, accumulated in an interpreted quiet, areally extensive lacustrine setting. Seismic definition of the lateral extent of this lacustrine facies is excellent, allowing them to effectively delineate changes in the lake morphology during deposition of the upper Fort Union Formation. Encasing the upper Fort Union lacustrine deposits are fluvial-alluvial deposits, interpreted from discontinuous, variable-amplitude seismic facies. The authors highlight the correlation of seismic facies data and interpretation to well log data in the Frenchie Draw field to emphasize the accuracy of depositional environment prediction from seismic data.

  2. Lacustrine mollusc radiations in the Malawi Basin: experiments in a natural laboratory for evolution

    NASA Astrophysics Data System (ADS)

    Van Damme, D.; Gautier, A.

    2012-12-01

    In Terminal Pliocene-Early Pleistocene times, part of the Malawi Basin was occupied by palaeo-lake Chiwondo. Molluscan biostratigraphy situates this freshwater lake either in the East African wet phase between 2.7-2.4 Ma or that of 2.0-1.8 Ma. In-lake divergent evolution remained restricted to a few molluscan taxa and was very modest. The lacustrine Chiwondo fauna went extinct at the beginning of the Pleistocene. The Modern Lake Malawi malacofauna is poor and descends from ubiquistic South-East African taxa and some Malawi Basin endemics that invaded the present lake after the Late Pleistocene mega-droughts. The Pleistocene aridity crises caused dramatic changes, affecting the malacofauna of all East African lakes. All lacustrine endemic faunas that had evolved in the Pliocene rift lakes, such as palaeo-lake Chiwondo, became extinct. In Lake Tanganyika, the freshwater ecosystem did not crash as in other lakes, but the environmental changes were sufficiently important to trigger a vast radiation. All African endemic lacustrine molluscan clades that are the result of in-lake divergence are hence geologically young, including the vast Lavigeria clade in Lake Tanganyika (ca. 43 species).

  3. Lacustrine mollusc radiations in the Lake Malawi Basin: experiments in a natural laboratory for evolution

    NASA Astrophysics Data System (ADS)

    Van Damme, D.; Gautier, A.

    2013-09-01

    In terminal Pliocene-early Pleistocene times, part of the Malawi Basin was occupied by paleo-lake Chiwondo. Molluscan biostratigraphy situates this freshwater lake either in the East African wet phase between 2.7-2.4 Ma or that of 2.0-1.8 Ma. In-lake divergent evolution remained restricted to a few molluscan taxa and was very modest. The lacustrine Chiwondo fauna went extinct at the beginning of the Pleistocene. The modern Lake Malawi malacofauna is depauperate and descends from ubiquistic southeast African taxa and some Malawi basin endemics that invaded the present lake after the Late Pleistocene mega-droughts. The Pleistocene aridity crises caused dramatic changes, affecting the malacofauna of all East African lakes. All lacustrine endemic faunas that had evolved in the Pliocene rift lakes, such as paleo-lake Chiwondo, became extinct. In Lake Tanganyika, the freshwater ecosystem did not crash as in other lakes, but the environmental changes were sufficiently important to trigger a vast radiation. All African endemic lacustrine molluscan clades that are the result of in-lake divergence are hence geologically young, including the vast Lavigeria clade in Lake Tanganyika (ca. 43 species).

  4. Volcanogenic fluvial-lacustrine environments in iceland and their utility for identifying past habitability on Mars.

    PubMed

    Cousins, Claire

    2015-02-16

    The search for once-habitable locations on Mars is increasingly focused on environments dominated by fluvial and lacustrine processes, such as those investigated by the Mars Science Laboratory Curiosity rover. The availability of liquid water coupled with the potential longevity of such systems renders these localities prime targets for the future exploration of Martian biosignatures. Fluvial-lacustrine environments associated with basaltic volcanism are highly relevant to Mars, but their terrestrial counterparts have been largely overlooked as a field analogue. Such environments are common in Iceland, where basaltic volcanism interacts with glacial ice and surface snow to produce large volumes of meltwater within an otherwise cold and dry environment. This meltwater can be stored to create subglacial, englacial, and proglacial lakes, or be released as catastrophic floods and proglacial fluvial systems. Sedimentary deposits produced by the resulting fluvial-lacustrine activity are extensive, with lithologies dominated by basaltic minerals, low-temperature alteration assemblages (e.g., smectite clays, calcite), and amorphous, poorly crystalline phases (basaltic glass, palagonite, nanophase iron oxides). This paper reviews examples of these environments, including their sedimentary deposits and microbiology, within the context of utilising these localities for future Mars analogue studies and instrument testing.

  5. Petrographic and geochemical evidence for the formation of primary, bacterially induced lacustrine dolomite: La Roda 'white earth' (Pliocene, Central Spain)

    USGS Publications Warehouse

    Garcia, Del; Cura, M.A.; Calvo, J.P.; Ordonez, S.; Jones, B.F.; Canaveras, J.C.

    2001-01-01

    Upper Pliocene dolomites ('white earth') from La Roda, Spain, offer a good opportunity to evaluate the process of dolomite formation in lakes. The relatively young nature of the deposits could allow a link between dolomites precipitated in modern lake systems and those present in older lacustrine formations. The La Roda Mg-carbonates (dolomite unit) occur as a 3??5- to 4-m- thick package of poorly indurated, white, massive dolomite beds with interbedded thin deposits of porous carbonate displaying root and desiccation traces as well as local lenticular gypsum moulds. The massive dolomite beds consist mainly of loosely packed 1- to 2-??m-sized aggregates of dolomite crystals exhibiting poorly developed faces, which usually results in a subrounded morphology of the crystals. Minute rhombs of dolomite are sparse within the aggregates. Both knobbly textures and clumps of spherical bodies covering the crystal surfaces indicate that bacteria were involved in the formation of the dolomites. In addition, aggregates of euhedral dolomite crystals are usually present in some more clayey (sepiolite) interbeds. The thin porous carbonate (mostly dolomite) beds exhibit both euhedral and subrounded, bacterially induced dolomite crystals. The carbonate is mainly Ca-dolomite (51-54 mol% CaCO3), showing a low degree of ordering (degree of ordering ranges from 0??27 to 0??48). Calcite is present as a subordinate mineral in some samples. Sr, Mn and Fe contents show very low correlation coefficients with Mg/Ca ratios, whereas SiO2 and K contents are highly correlated. ??18O- and ??13C-values in dolomites range from -3??07??? to 5??40??? PDB (mean = 0??06, ?? = 1??75) and from -6??34??? to -0??39??? PDB (mean = -3??55, ?? = 1??33) respectively. Samples containing significant amounts of both dolomite and calcite do not in general show significant enrichment or depletion in 18O and 13C between the two minerals. The correlation coefficient between ??18O and ??13C for dolomite is extremely

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  7. Submarine lithification of Holocene reef hardground: north Jamaica

    SciTech Connect

    Mitchell, J.T.

    1987-05-01

    Submarine cementation and organic binding of skeletal reef debris have brought about the formation of an extensive carbonate hardground, which is exposed on the submerged seaward slope of the reefcrest at Discovery Bay, Jamaica. The hardground, dated as Holocene by carbon-14, is comprised of the fragmented and bioeroded remnants of a diverse coral-algal community. Mg-calcite and aragonite, the dominant cements, are common in a variety of growth forms and occupy intraskeletal and interparticle voids. In order of decreasing abundance, Mg-calcite cements exhibit the following growth forms: (1) cryptocrystalline (micritic); (2) submicrocrystalline rhombic; (3) microcrystalline, stubby-to-acicular isopachous; and (4) microcrystalline blocky mosaic. Mg-calcite peloids, spherical bodies 20-60 ..mu..m in diameter, are ubiquitous as geopedal pore-fill. Aragonite cement is most common as acicular needles 50-100 ..mu..m long which grow as syntaxial fringes on skeletal substrates. Less common aragonite cement forms are microcrystalline blocky mosaic cements and radial fibrous aggregates. Adjacent pore spaces generally exhibit different cement fabrics, indicating that pores have unique microenvironments. Electron microprobe analysis revealed dolomite dispersed in the peloidal pore-fill of a coral fragment sampled from 5 cm beneath the hardground surface. /sup 14/C dating, field relationships, isotopic and trace element analysis suggest that trace quantities of Holocene dolomite are forming in the shallow, subtidal reef environment. The formation of the extensive coral pavement is a consequence of the interplay between the destructive forces of catastrophic storm events and bioerosion on one hand and the constructive effects of submarine cementation and organic binding on the other hand.

  8. Holocene climate variability, vegetation dynamics and fire regime in the central Pyrenees: the Basa de la Mora sequence (NE Spain)

    NASA Astrophysics Data System (ADS)

    Pérez-Sanz, A.; González-Sampériz, P.; Moreno, A.; Valero-Garcés, B.; Gil-Romera, G.; Rieradevall, M.; Tarrats, P.; Lasheras-Álvarez, L.; Morellón, M.; Belmonte, A.; Sancho, C.; Sevilla-Callejo, M.; Navas, A.

    2013-08-01

    High resolution multiproxy data (pollen, sedimentology, geochemistry, chironomids and charcoal) from the Basa de la Mora (BSM) lake sequence (42° 32' N, 0° 19' E, 1914 m a.s.l.) show marked climate variability in the central southern Pyrenees throughout the Holocene. A robust age model based on 15 AMS radiocarbon dates underpins the first precise reconstruction of rapid climate changes during the Holocene from this area. During the Early Holocene, increased winter snowpack and high snowmelt during summer, as a consequence of high seasonality, led to higher lake levels, a chironomid community dominated by non-lacustrine taxa (Orthocladiinae) related to higher inlet streams, and a forested landscape with intense run-off processes in the watershed. From 9.8 to 8.1 cal ka BP, climate instability is inferred from rapid and intense forest shifts and high fluctuation in surface run-off. Shifts among conifers and mesophytes reveal at least four short-lived dry events at 9.7, 9.3, 8.8 and 8.3 cal ka BP. Between 8.1 and 5.7 cal ka BP a stable climate with higher precipitation favoured highest lake levels and forest expansion, with spread of mesophytes, withdrawal of conifers and intensification of fires, coinciding with the Holocene Climate Optimum. At 5.7 cal ka BP a major change leading to drier conditions contributed to a regional decline in mesophytes, expansion of pines and junipers, and a significant lake level drop. Despite drier conditions, fire activity dropped as consequence of biomass reduction. Two arid intervals occurred between 2.9 and 2.4 cal ka BP and at 1.2-0.7 cal ka BP (800-1300 AD). The latter coincides with the Medieval Climate Anomaly and is one of the most arid phases of the Holocene in BSM sequence. Anthropogenic disturbances were small until 700 AD, when human pressure over landscape intensified, with Olea cultivation in the lowlands and significant deforestation in highlands. Colder and unfavourable weather conditions during the second part of the

  9. The Holocene deglaciation of the Byers Peninsula (Livingston Island, Antarctica) based on the dating of lake sedimentary records

    NASA Astrophysics Data System (ADS)

    Oliva, M.; Antoniades, D.; Giralt, S.; Granados, I.; Pla-Rabes, S.; Toro, M.; Liu, E. J.; Sanjurjo, J.; Vieira, G.

    2016-05-01

    The process of deglaciation in the Antarctic Peninsula region has large implications for the geomorphological and ecological dynamics of the ice-free environments. However, uncertainties still remain regarding the age of deglaciation in many coastal environments, as is the case in the South Shetland Islands. This study focuses on the Byers Peninsula, the largest ice-free area in this archipelago and the one with greatest biodiversity in Antarctica. A complete lacustrine sedimentary sequence was collected from five lakes distributed along a transect from the western coast to the Rotch Dome glacier front: Limnopolar, Chester, Escondido, Cerro Negro and Domo lakes. A multiple dating approach based on 14C, thermoluminescence and tephrochronology was applied to the cores in order to infer the Holocene environmental history and identify the deglaciation chronology in the Byers Peninsula. The onset of the deglaciation started during the Early Holocene in the western fringe of the Byers Peninsula according to the basal dating of Limnopolar Lake (ca. 8.3 cal. ky BP). Glacial retreat gradually exposed the highest parts of the Cerro Negro nunatak in the SE corner of Byers, where Cerro Negro Lake is located; this lake was glacier-free since at least 7.5 ky. During the Mid-Holocene the retreat of the Rotch Dome glacier cleared the central part of the Byers plateau of ice, and Escondido and Chester lakes formed at 6 cal. ky BP and 5.9 ky, respectively. The dating of the basal sediments of Domo Lake suggests that the deglaciation of the current ice-free easternmost part of the Byers Peninsula occurred before 1.8 cal. ky BP.

  10. Climatic fluctuations during the Holocene based on eastern Mediterranean continental shelf sediment cores

    NASA Astrophysics Data System (ADS)

    Mor-Federman, Tsofit; Bookman, Revital; Almogi-Labin, Ahuva; Herut, Barak

    2013-04-01

    Sediments deposited on the south eastern Mediterranean continental shelf are sensitive recorders of climatic and oceanographic variability affected by the north Atlantic and indirectly by monsoonal systems. In order to reconstruct the influence of these climatic systems two cores were taken off shore the southern and central Israeli coast at water depths of ~35 m. The sediments were characterized by majors and traces elements, and the sediment provenance was determined using 87Sr/86Sr ratios. Detrital input from the Nile and local environment was studied using grain size distribution and sedimentation rates. Water column productivity was inferred by TOC and δ13Corg. The cores, dated to 7,630 and 8,440 14C years BP, show two distinct sedimentation regimes. The early Holocene is characterized by high sedimentation rates (190-140 cm/ka) that decrease in the last 5,500 years (50-60 cm/ka) in both north and central cores. Coarse grain size is dominant in the early Holocene, with a decreasing trend in the northern core. This distribution is probably connected to eustatic sea level rise and recycling of coarse sediments from the flooded shallow Nile cone. In the late Holocene, as sea level stabilized, grain size is finer in the south; while to the north, cycles of ~1,500 years in coarse grain size characterize the period. Carbonate and organic carbon further present the change along the period. Decrease in carbonate content and increase in δ13Corg during the late Holocene indicate decrease in water column productivity. In contradiction, organic carbon is relatively high in the late Holocene. This is explained by the coarse sediment texture in the early Holocene leading to better oxidation of buried organic matter. Strontium isotopes show changes in sediment provenance. In the early Holocene high 87Sr/86Sr values of ~0.71 reflect a dominant signature of the White Nile and the Yellow Nile and in part the local streams. During the last 5,500 years lower values of ~0

  11. Sporadic Groundwater Upwelling in Deep Martian Craters: Evidence for Lacustrine Clays and Carbonates

    NASA Technical Reports Server (NTRS)

    Michalski, J. R.; Rogers, A. D.; Wright, S. P.; Niles, P.; Cuadros, J.

    2012-01-01

    While the surface of Mars may have had an active hydrosphere early in its history [1], it is likely that this water retreated to the subsurface early on due to loss of the magnetic field and early atmosphere [2]. This likely resulted in the formation of two distinct aqueous regimes for Mars from the Late Noachian onward: one dominated by redistribution of surface ice and occasional melting of snow/ice [3], and one dominated by groundwater activity [4]. The excavation of alteration minerals from deep in the crust by impact craters points to an active, ancient, deep hydrothermal system [5]. Putative sapping features [6] may occur where the groundwater breached the surface. Upwelling groundwater may also have played a critical role in the formation of massive, layered, cemented sediments in Sinus Meridiani [7,8], in the Valles Marineris [9], and possibly in Gale Crater [10], where the Curiosity Rover will land later this year. Understanding the past distribution, geochemistry, and significance of groundwater on Mars is critical to untangling the origins of deep alteration minerals, Hesperian sulfate deposits, and crater fill deposits at Gale Crater or in other locations.

  12. Vegetation, climate and environment variability at Spicer Pond, Indiana, during the Holocene

    NASA Astrophysics Data System (ADS)

    Wang, Y.; Gill, J. L.; Alhambra, D.; Hernandez, S.; Kohrs, K.; Marsicek, J.; Williams, J. W.

    2012-12-01

    Many paleoclimate studies have shown that the midcontinent of North America experienced a warmer and drier-than-present climate during the early and middle Holocene and relatively humid climate during the late Holocene with several megadroughts. In response to this climate variability, Holocene vegetation changes in the Great Lake forests are broadly composed of two shifts: the moving northward and retreating of ecotone between mixed forest and deciduous forest - mainly composed of Quercus and Pinus, and the east-western gradient in prairie composition developed between 7,000 and 5,000 years BP. Superimposed on these ecotonal shifts are the range shifts of individual taxa and episodic declines in abundance of individual tree taxa, which appear to be linked to hydroclimatic variability (e.g. Fagus decline centering around 1,000 years B.P., Booth and Jackson, 2003). Most Holocene paleoecological research has been carried out in the northern Great Lakes states (MI, MN, WI) and the Holocene climate and vegetation dynamics in the south-central Great Lakes (IN, OH) remains relatively unknown. This study focuses on climate and vegetation changes during the Holocene at Spicer Pond in Indiana (41°44'52" N, 86°31'19" W, 237 m elevation), which is a kettle lake located in New Carlisle, north of Indiana, near the southeastern edge of Michigan. This study reports loss-on-ignition, pollen, and charcoal analyses to reconstruct the vegetation, climate and environment at Spicer Pond. Loss-on-ignition data indicate seven shifts of sharp increase of mineral and decrease of organic carbon that separately happened at about 300 years B.P., 1,800 years B.P., 2,800 years B.P., 5,000 years B.P., 6,700 years B.P., 8,000 years B.P. and 11,000 years B.P. during the Holocene. The most recent LOI peak is believed to be linked to changes sedimentation rates caused by Euroamerican land use. The cause of these Holocene peaks in mineral content at Spicer Pond is not yet known, and we have several

  13. A Holocene paleosecular variation from 14C-dated volcanic rocks in Western North America

    USGS Publications Warehouse

    Hagstrum, J.T.; Champion, D.E.

    2002-01-01

    A paleosecular variation (PSV) curve for western North America is presented on the basis of 94 virtual geomagnetic poles (VGPs) from dated volcanic rocks sampled at 446 sites. Approximately 60% of the paleomagnetic database has been previously published. A curve defined by "spherical smoothed splines" is fitted to the VGPs, ranked by the quality of the age determinations, where the data density is highest between 3690 and -30 years before present (B.P.) (A.D. 1950), between 7800 and 7050 years B.P., and between 14,060 and 12,700 years B.P. The younger segments of the curve derived from volcanic rocks are similar but less complex than other high-resolution PSV curves derived from lacustrine sediments, particularly the record at Fish Lake, Oregon. The PSV record from lava flows (PSVL), however, is perhaps more reliable in its general shape and chronology because of the higher fidelity of volcanic rocks as magnetic field recorders and because of the greater density of 14C dates. The new PSVL record provides a partial Holocene master curve for western North America and will be of particular value in dating geological and archeological materials using paleomagnetic directions.

  14. Holocene climate change in Arctic Canada and Greenland

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

  15. Missing-Presumed Eroded: Holocene Sedimentation Patterns in Seneca Lake, NY

    NASA Astrophysics Data System (ADS)

    Loddengaard, K.; Curtin, T. M.

    2006-12-01

    The Finger Lakes of New York underwent a significant change in climate during the transition from the Hypsithermal to the Neoglacial at ~5 ka. To determine the effects of changes in climate on sedimentation patterns in the northern region of Seneca Lake, NY, we analyzed three cores that were collected along a shallow to deep water transect. Analyses of magnetic susceptibility, organic matter and carbonate content, fossil content, and grain size at a 1-cm interval were used to correlate cores, identify periods of erosion or non- deposition and assess the relative truncation of the Holocene sediment record. The stratigraphy and sedimentology of the cores indicate the lake contains a spatially and temporally discontinuous sediment record. Preliminary results indicate that the early to mid-Holocene sediment record was preferentially eroded in the deepwater cores, between 20 and 50 m water depth. At the deepwater sites, there is a gap in the sediment record that spans between ~12 and ~5 ka. Conversely, the late Holocene record is more complete in the deepwater cores than in the shallow water cores (12-20 m water depth). This data suggests a significant change on the controls and location of erosion and deposition in the lake during the Holocene. We hypothesize that the early to mid-Holocene sediment may have been eroded by strong internal seiches during stormy conditions that were initiated by cooler temperatures and a change in the position of the jet stream during the Hypsithermal-Neoglacial transition. Erosion occurred primarily in shallow water sites (<~30 m) during the Neoglacial, perhaps as a result of a change in the number and frequency of storms or strength of the internal seiche.

  16. Holocene sea level variations on the basis of integration of independent data sets

    SciTech Connect

    Sahagian, D.; Berkman, P. . Dept. of Geological Sciences and Byrd Polar Research Center)

    1992-01-01

    Variations in sea level through earth history have occurred at a wide variety of time scales. Sea level researchers have attacked the problem of measuring these sea level changes through a variety of approaches, each relevant only to the time scale in question, and usually only relevant to the specific locality from which a specific type of data are derived. There is a plethora of different data types that can and have been used (locally) for the measurement of Holocene sea level variations. The problem of merging different data sets for the purpose of constructing a global eustatic sea level curve for the Holocene has not previously been adequately addressed. The authors direct the efforts to that end. Numerous studies have been published regarding Holocene sea level changes. These have involved exposed fossil reef elevations, elevation of tidal deltas, elevation of depth of intertidal peat deposits, caves, tree rings, ice cores, moraines, eolian dune ridges, marine-cut terrace elevations, marine carbonate species, tide gauges, and lake level variations. Each of these data sets is based on particular set of assumptions, and is valid for a specific set of environments. In order to obtain the most accurate possible sea level curve for the Holocene, these data sets must be merged so that local and other influences can be filtered out of each data set. Since each data set involves very different measurements, each is scaled in order to define the sensitivity of the proxy measurement parameter to sea level, including error bounds. This effectively determines the temporal and spatial resolution of each data set. The level of independence of data sets is also quantified, in order to rule out the possibility of a common non-eustatic factor affecting more than one variety of data. The Holocene sea level curve is considered to be independent of other factors affecting the proxy data, and is taken to represent the relation between global ocean water and basin volumes.

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

    NASA Astrophysics Data System (ADS)

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

    2013-03-01

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

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

    SciTech Connect

    Lighty, R.G.

    1983-03-01

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

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

    USGS Publications Warehouse

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

    2008-01-01

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

  20. Holocene surface faulting along the west flank of the Santa Rosa Range (Nevada-Oregon) and the possible northern extension of the Central Nevada Seismic Belt

    SciTech Connect

    Michetti, A.M. Univ. of Nevada, Reno, NV . Center for Neotectonic Studies); Wesnousky, S.G. . Center for Neotectonic Studies)

    1993-04-01

    The 130 km long Santa Rose Range fault system extends northward from a point about 70 km north of the 1915 Pleasant Valley earthquake fault ruptures to Blue Mountain Pass, Oregon. The authors have examined 1:12,000 low-sun-angle aerial photographs and conducted surveys of scarp morphology to investigate the neotectonic evolution and paleoseismicity of this possible northern extension of the Central Nevada Seismic Belt. Two adjoining segments of the fault zone are separated by a right step in the range-front and apparent absence of Holocene scarps. Each segment records evidence of a Holocene faulting event. The southern 31 km segment between Frey Ranch and the Willow Creek fan shows both small scarps (< 1 m) which cut Lahontan shorelines in the fluvio-lacustrine sediments of the Quinn River Valley and larger scarps which oversteepen the base of the adjacent range-front to slopes of 20[degree] to 24[degree]. The northern 42 km segment between Flat Creek and Oregon Canyon Creek shows a recent offset which rejuvenates older (pre-Lahontan) fault scarps and also cuts Holocene terraces along the base of the piedmont pediment. Based on preliminary morphometric data, the maximum vertical displacement (3--4 m) and age of the faulting (early Holocene) are similar in both segments but it is not known whether both segments ruptured contemporaneously. Except for the lack of large historical surface faulting the main neotectonic and geomorphic features of the Santa Rose Range fault zone are similar to that of the Dixie Valley and Pleasant Valley regions of the Central Nevada Seismic Belt. Hence, the occurrence of a large earthquake rupture along this range-front in the near future should not be viewed as a surprise.

  1. Holocene Climate Change in Arctic Canada and Greenland

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    We summarize the spatial and temporal pattern of climate change through the Holocene in Arctic Canada and Greenland. Our synthesis includes 47 records from a recent database of highly resolved, quantitative Holocene climate records from the Arctic (Sundqvist et al., 2014). We plot the temperature histories represented by the records in the database and compare them with paleoclimate information based on 53 additional records. Combined, the records include a variety of climate proxy types that range from ice (ice cores), land (lake and peat sequences) and marine (ocean sediment cores and coastal sediments) environments. The temperature-sensitive records indicate more consistent and earlier Holocene warmth in the north and east, and a more diffuse and later Holocene thermal maximum in the south and west. Principal components analysis reveals two dominant Holocene trends, one with early Holocene warmth followed by cooling in the middle Holocene, the other with a broader period of warmth in the middle Holocene followed by cooling in the late Holocene. The temperature decrease from the warmest to the coolest portions of the Holocene is 3.0±1.0°C on average (n=11 records). The Greenland Ice Sheet retracted to its minimum extent between 5 and 3 ka, consistent with many sites from around Greenland depicting a switch from warm to cool conditions around that time. The spatial pattern of temperature change through the Holocene was likely driven by the decrease in northern latitude summer insolation through the Holocene, the varied influence of waning ice sheets in the early Holocene, and the variable influx of Atlantic Water into the study region.

  2. Holocene stages of tufa deposition/erosion in Ethiopia: the role of climate fluctuations and human impact

    NASA Astrophysics Data System (ADS)

    Dramis, Francesco; Fubelli, Giandomenico

    2014-05-01

    The geomorphological-stratigraphic study of the backfill deposits of two tufa dams, May Makden and Tsabati Mariam, supported by 14C dates, has provided a detailed description of