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Sample records for interglacial conditions polar

  1. Collapse of polar ice sheets during the stage 11 interglacial.

    PubMed

    Raymo, Maureen E; Mitrovica, Jerry X

    2012-03-22

    Contentious observations of Pleistocene shoreline features on the tectonically stable islands of Bermuda and the Bahamas have suggested that sea level about 400,000 years ago was more than 20 metres higher than it is today. Geochronologic and geomorphic evidence indicates that these features formed during interglacial marine isotope stage (MIS) 11, an unusually long interval of warmth during the ice age. Previous work has advanced two divergent hypotheses for these shoreline features: first, significant melting of the East Antarctic Ice Sheet, in addition to the collapse of the West Antarctic Ice Sheet and the Greenland Ice Sheet; or second, emplacement by a mega-tsunami during MIS 11 (ref. 4, 5). Here we show that the elevations of these features are corrected downwards by ∼10 metres when we account for post-glacial crustal subsidence of these sites over the course of the anomalously long interglacial. On the basis of this correction, we estimate that eustatic sea level rose to ∼6-13 m above the present-day value in the second half of MIS 11. This suggests that both the Greenland Ice Sheet and the West Antarctic Ice Sheet collapsed during the protracted warm period while changes in the volume of the East Antarctic Ice Sheet were relatively minor, thereby resolving the long-standing controversy over the stability of the East Antarctic Ice Sheet during MIS 11. PMID:22419155

  2. Interglacial Durations

    NASA Astrophysics Data System (ADS)

    Mangili, Clara; McManus, Jerry F.; Raynaud, Dominique

    2014-05-01

    In the context of future global warming induced by human activities, it is essential to assess the role of natural climatic variations. Precise knowledge of the duration of past interglacial periods is fundamental to the understanding of the potential future evolution of the Holocene. Past ice age cycles provide a natural laboratory for exploring the progression and duration of interglacial climate. Palaeorecords from ice, land and oceans extend over the last 800 ka, revealing eight glacial-interglacial cycles, with a range of insolation and greenhouse gas influences. The interglacials display a correspondingly large variety of intensity and duration, thus providing an opportunity for major insights into the mechanisms involved in the behaviour of interglacial climates. A comparison of the duration of these interglacials, however, is often difficult, as the definition of an interglacial depends on the archive that is considered. Therefore, to compare interglacial length and climate conditions from different archives, a consistent definition of interglacial conditions is required, ideally one that is not bound to the method nor to the archive under consideration. Here we present a method to identify interglacials and to calculate their length by mean of a simple statistical approach. We based our method on ~ 400 ka windows of time to determine mean climatic conditions while allowing for the possibility of long term evolution of the climatic baseline. For our study of interglacials of the past 800 ka, we used two windows that largely align with the pre- (800-430 ka ago) and post- (430-0 ka ago) mid-Brunhes event (MBE), although the resulting conclusions are not sensitive to this particular division. We applied this method to the last 800 ka of a few palaeoclimate records: the deuterium ice core (EDC) record as a climatic proxy, the benthic δ18O stack (LR04) as a proxy for sea level/ice volume, ice core (Vostok, EDC) atmospheric CO2 and additional records. Although

  3. An Interglacial Polar Bear and an Early Weichselian Glaciation at Poolepynten, Western Svalbard

    NASA Astrophysics Data System (ADS)

    Ingolfsson, O.; Alexanderson, H.

    2012-12-01

    Recent discovery of a subfossil polar bear (Ursus maritimus) jawbone in the Poolepynten coastal cliff sequence, western Svalbard (Ingolfsson & Wiig, 2009), and its implications for the natural history of the polar bear (Lindqvist et al. 2010; Miller et al. 2012), motivated an effort to better constrain the environmental history and age envelope of the Poolepynten sediment sequence, particularly the lithostratigraphy of the coastal cliffs with emphasis on re-dating the sequence using the optically stimulated luminescence (OSL) dating technique. We report a revised lithostratigraphy and nine new OSL ages. It is concluded that the Poolepynten sequence holds evidence of four regional glaciation events, recorded in the strata as erosional unconformities and/or glacial deposits followed by shallow-marine deposition signifying transgressions and subsequent glacio-isostatic rebound and regression. Our OSL ages refine previous age determinations (14C and IRSL) and support the interpretation that the subfossil polar bear jawbone is of last interglacial (Eemian) age (Alexanderson et al. in press). References: Alexanderson, H., Ingolfsson, O., Murray, A.S. & Dudek, J. in press. An Interglacial Polar Bear and an Early Weichselian Glaciation at Poolepynten, Western Svalbard. Boreas 00, 000-000. Ingolfsson, O. & Wiig, O. 2009. Late Pleistocene fossil find in Svalbard: the oldest remains of a polar bear (Ursus maritimus Phipps, 1744) ever discovered. Polar Research 28, 455-466. Lindqvist, C., Schuster, S. C., Sun, Y., Talbot, S. L., Qi, J., Ratan, A., Tomsho, L. P., Kasson, L., Zeyl, E., Aars, J., Miller, W., Ingólfsson, Ó., Bachmann, L. & Wiig, Ø. 2010. Complete mitochondrial genome of a Pleistocene jawbone unveils the origin of polar bear. Proceedings of the National Academy of Sciences 107, 5053-5057. Miller, W., Schuster, S. C., Welch, A. J., Ratan, A., Bedoya-Reina, O. C., Zhao, F., Kim, H. L., Burhans, R.C., Drautz, D.I., Wittekindt, N.E., Tomsho, L.P., Ibarra-Laclette, E

  4. Multi-proxy insights into last interglacial (MIS 5e) conditions in the southern Labrador Sea: Consistencies and inconsistencies

    NASA Astrophysics Data System (ADS)

    Van Nieuwenhove, Nicolas; Retailleau, Sophie; de Vernal, Anne; Hillaire-Marcel, Claude

    2013-04-01

    Last interglacial (Marine Isotopic Stage or MIS 5e) sediments from the Gloria Drift in the southernmost Labrador Sea (Core HU91-045-91; 53.33N 45.26W) were studied for their dinoflagellate cyst (dinocyst) content and their planktic foraminiferal assemblages and isotopic compositions. While both microfossil groups clearly reveal the occurrence of typical interglacial conditions in the area, they also reflect a slightly different evolution of the MIS 5e surface water conditions. The dinocyst assemblages are dominated by the cold-temperate species Nematosphaeropsis labyrinthus, with the secondary assemblages being composed by temperate oceanic Impagidinium species and the cosmopolitan species Operculodinium centrocarpum. The latter species shows a steady increase during the first half of MIS 5e, mirrored by a gradual decline of the polar planktic foraminifer Neogloboquadrina pachyderma (s). Still, reconstructed temperatures from the application of the modern analogue technique for this interval are fairly stable, albeit that those reconstructed from the dinocyst assemblages (~10 and 17 °C for winter and summer, respectively) exceed those reconstructed from the planktic foraminiferal assemblages (~5.5 and 9.5 °C) as well as modern values (~5.5 and 10.6 °C) by several degrees. This apparent inconsistency might be partly explained by distinct conditions within the respective water depth habitats of these micro-organisms, but other factors likely intervened, such as an offset in their respective seasonal production time and/or mixing of the fossil assemblages through advection from slightly distinct production areas. The early MIS 5e trend ended abruptly with a marked event characterized by a peak of Turborotalita quinqueloba, the quasi-disappearance of dinocysts, and a divergent shift of the stable oxygen isotope values in the polar and subpolar foraminifer species. This might hint towards a possible meltwater-related perturbation of the prevailing upper ocean

  5. Dust deposition in Antarctica in glacial and interglacial climate conditions: a modelling study

    NASA Astrophysics Data System (ADS)

    Sudarchikova, N.; Mikolajewicz, U.; Timmreck, C.; O'Donnell, D.; Schurgers, G.; Sein, D.; Zhang, K.

    2014-09-01

    The mineral dust cycle responds to climate variations and plays an important role in the climate system by affecting the radiative balance of the atmosphere and modifying biogeochemistry. Polar ice cores provide a unique information about deposition of aeolian dust particles transported over long distance. These cores are a paleoclimate proxy archive of climate variability thousands of years ago. The current study is a first attempt to simulate past interglacial dust cycles with a global aerosol-climate model ECHAM5-HAM. The results are used to explain the dust deposition changes in Antarctica in terms of quantitative contribution of different processes, such as emission, atmospheric transport and precipitation, which will help to interpret paleodata from Antarctic ice cores. The investigated periods include four interglacial time-slices such as the pre-industrial control (CTRL), mid-Holocene (6000 yr BP), last glacial inception (115 000 yr BP) and Eemian (126 000 yr BP). One glacial time interval, which is Last Glacial Maximum (LGM) (21 000 yr BP) was simulated as well as to be a reference test for the model. Results suggest an increase of mineral dust deposition globally, and in Antarctica, in the past interglacial periods relative to the pre-industrial CTRL simulation. Approximately two thirds of the increase in the mid-Holocene and Eemian is attributed to enhanced Southern Hemisphere dust emissions. Slightly strengthened transport efficiency causes the remaining one third of the increase in dust deposition. The moderate change of dust deposition in Antarctica in the last glacial inception period is caused by the slightly stronger poleward atmospheric transport efficiency compared to the pre-industrial. Maximum dust deposition in Antarctica was simulated for the glacial period. LGM dust deposition in Antarctica is substantially increased due to 2.6 times higher Southern Hemisphere dust emissions, two times stronger atmospheric transport towards Antarctica, and

  6. Modelling of mineral dust for interglacial and glacial climate conditions with a focus on Antarctica

    DOE PAGESBeta

    Sudarchikova, Natalia; Mikolajewicz, Uwe; Timmreck, C.; O'Donnell, D.; Schurgers, G.; Sein, Dmitry; Zhang, Kai

    2015-05-19

    The mineral dust cycle responds to climate variations and plays an important role in the climate system by affecting the radiative balance of the atmosphere and modifying biogeochemistry. Polar ice cores provide unique information about deposition of aeolian dust particles transported over long distances. These cores are a palaeoclimate proxy archive of climate variability thousands of years ago. The current study is a first attempt to simulate past interglacial dust cycles with a global aerosol–climate model ECHAM5-HAM. The results are used to explain the dust deposition changes in Antarctica in terms of quantitative contribution of different processes, such as emission,more » atmospheric transport and precipitation, which will help to interpret palaeodata from Antarctic ice cores. The investigated periods include four interglacial time slices: the pre-industrial control (CTRL), mid-Holocene (6000 yr BP; hereafter referred to as \\"6 kyr\\"), last glacial inception (115 000 yr BP; hereafter \\"115 kyr\\") and Eemian (126 000 yr BP; hereafter \\"126 kyr\\"). One glacial time interval, the Last Glacial Maximum (LGM) (21 000 yr BP; hereafter \\"21 kyr\\"), was simulated as well to be a reference test for the model. Results suggest an increase in mineral dust deposition globally, and in Antarctica, in the past interglacial periods relative to the pre-industrial CTRL simulation. Approximately two-thirds of the increase in the mid-Holocene and Eemian is attributed to enhanced Southern Hemisphere dust emissions. Slightly strengthened transport efficiency causes the remaining one-third of the increase in dust deposition. The moderate change in dust deposition in Antarctica in the last glacial inception period is caused by the slightly stronger poleward atmospheric transport efficiency compared to the pre-industrial. Maximum dust deposition in Antarctica was simulated for the glacial period. LGM dust deposition in Antarctica is substantially increased due to 2.6 times

  7. Modelling of mineral dust for interglacial and glacial climate conditions with a focus on Antarctica

    SciTech Connect

    Sudarchikova, Natalia; Mikolajewicz, Uwe; Timmreck, C.; O'Donnell, D.; Schurgers, G.; Sein, Dmitry; Zhang, Kai

    2015-05-19

    The mineral dust cycle responds to climate variations and plays an important role in the climate system by affecting the radiative balance of the atmosphere and modifying biogeochemistry. Polar ice cores provide unique information about deposition of aeolian dust particles transported over long distances. These cores are a palaeoclimate proxy archive of climate variability thousands of years ago. The current study is a first attempt to simulate past interglacial dust cycles with a global aerosol–climate model ECHAM5-HAM. The results are used to explain the dust deposition changes in Antarctica in terms of quantitative contribution of different processes, such as emission, atmospheric transport and precipitation, which will help to interpret palaeodata from Antarctic ice cores. The investigated periods include four interglacial time slices: the pre-industrial control (CTRL), mid-Holocene (6000 yr BP; hereafter referred to as \\"6 kyr\\"), last glacial inception (115 000 yr BP; hereafter \\"115 kyr\\") and Eemian (126 000 yr BP; hereafter \\"126 kyr\\"). One glacial time interval, the Last Glacial Maximum (LGM) (21 000 yr BP; hereafter \\"21 kyr\\"), was simulated as well to be a reference test for the model. Results suggest an increase in mineral dust deposition globally, and in Antarctica, in the past interglacial periods relative to the pre-industrial CTRL simulation. Approximately two-thirds of the increase in the mid-Holocene and Eemian is attributed to enhanced Southern Hemisphere dust emissions. Slightly strengthened transport efficiency causes the remaining one-third of the increase in dust deposition. The moderate change in dust deposition in Antarctica in the last glacial inception period is caused by the slightly stronger poleward atmospheric transport efficiency compared to the pre-industrial. Maximum dust deposition in Antarctica was simulated for the glacial period. LGM dust deposition in Antarctica is substantially increased due to 2.6 times higher

  8. Belgian speleothems from the Last Interglacial: insights in the onset of glacial conditions in north western Europe.

    NASA Astrophysics Data System (ADS)

    Vansteenberge, Stef; Verheyden, Sophie; Cheng, Hai; Edwards, Lawrence R.; Keppens, Eddy; Claeys, Philippe

    2015-04-01

    Currently, a dataset combining at least four speleothems from two different cave systems in southern Belgium (Han-sur-Lesse and Remouchamps) is being constructed to improve the understanding of the termination of the Eemian and the millennial to decadal variability of the Early Glacial times in north western Europe. Here, one of those speleothems is presented. The Han-stm-9 (or 'Triptyque') speleothem is a broken, 68 cm long and candle-shaped stalagmite from the Han-sur-Lesse cave system. The stalagmite was collected in summer 2013 within the southern part of the cave network and was dated between ~126 and ~99ka. Most likely, climate optimum conditions during the 130-125ka interval are linked to the growth of this and other speleothems from Belgian caves. This particular speleothem gained interest because of the partial conformity with the continental interglacial period in northern western Europe (130 - 118ka) and its dense calcite composition with visible layering, excluding post-depositional deformation. Furthermore, the stalagmite displays a complex growth history, with large variations in growth rates (ranging from and periods of ceased speleothem formation. Two hiatuses, with a distinct macroscopic expression, occur. The first one starts at 118.4ka and lasts until 113.0ka. A second hiatus is situated between ~108ka and 103.7ka. A trend in growth rate, consisting of slow growth gradually increasing towards very fast speleothem formation before both hiatuses, is observed. These intervals with very high growth rates, for instance around 118ka, enable high-resolution climate reconstructions via stable isotopes (δ18O and δ13C) and trace elements (Mg, Sr, Ba and P), down to centennial and decadal scale. The timing of the first hiatus corresponds with Greenland Stadial 26 and with the generally accepted termination of the Eemian in northern Europe at 119-118ka. Also, preliminary stable isotope studies have indicated a large detoriation of δ13C occurring right

  9. Late attainment of full Holocene interglacial conditions in the northern North Atlantic

    NASA Astrophysics Data System (ADS)

    de Vernal, Anne; Hillaire-Marcel, Claude; Van Nieuwenhove, Nicolas; Fréchette, Bianca; Gibb, Olivia; Ouellet-Bernier, Marie-Michèle

    2015-04-01

    The postglacial changes in sea surface conditions were reconstructed in more than 30 cores from the northern North Atlantic and subarctic seas based on the modern analogue technique applied to dinocyst assemblages. The reconstructed parameters include winter and summer sea-surface temperature (SST) and salinity (SSS) in addition to sea-ice cover, thus allowing assessment of surface density and seasonal contrast of climate. Results illustrate important changes in sea-surface conditions through the early to mid-Holocene transition. Despite differences in timing and amplitude, the overall data point to the persistence of strong east to west gradients and to a late attainment of "optimum" conditions. In the western part of the basin (northern Labrador Sea, Baffin Bay, eastern Greenland margins), a main change is marked by an increase in salinity and a decrease in the seasonal contrast of temperature from 7.5 ka BP. In several of the study cores, the isotopic composition (18O and 13C) of planktic foraminifers (N. pachyderma left-coiled) provides complementary information on subsurface conditions. By combining the information from dinocyst and isotope proxies, it was possible to calibrate potential density vs calcite-18O relationships, and therefore to calculate density gradients from surface to sub-surface water masses, along the pycnocline. Paleo-density gradients also illustrate east to west differences and reveal conditions unfavorable to vertical convection after 7.5 ka BP if not later in the Labrador Sea, and about 6.5 ka in the western Nordic Seas.

  10. Paired microfossil evidence for a delayed development of fully marine surface water conditions in the Nordic seas during the Last interglacial (MIS 5e)

    NASA Astrophysics Data System (ADS)

    van Nieuwenhove, N.; Bauch, H. A.; Kandiano, E. S.

    2010-12-01

    Dinoflagellate cyst (dinocyst) and foraminiferal records of sediment cores from The Vøring and Iceland Plateau and south of the Fram Strait were used to reconstruct the evolution of the surface circulation in the Nordic seas during the last interglacial (Marine Isotopic Stage or MIS 5e). The location of the cores, under the modern pathway of the warm Norwegian Atlantic Current (NwAC) and within the mixing zone of the NwAC and the cold East Greenland Current (EGC), allows to reconstruct the spreading of inflowing North Atlantic surface waters across the Nordic seas during the climate progression of MIS 5e. The microfossil records, supported by stable isotope and IRD data, reveal that during the first ~6000 years of MIS 5e a more pronounced stratification and seasonality existed in the eastern Nordic seas, presumably as a result of long-lasting deglacial effects. Thus, the northward heat flux was reduced during this time in this area. It was only during late MIS 5e, and when IRD-input into the eastern Nordic seas had come to a halt, that the northward flow of warm Atlantic water masses intensified so that interglacial conditions became also eminent in the surface waters south of the Fram Strait. Our data further suggest that the stronger NwAC of late MIS 5e entailed an intensification of the EGC. While this brought comparatively colder conditions towards the Iceland Plateau it was also the only time when proper, that is fully marine, warm interglacial surface conditions co-existed in the eastern Nordic seas.

  11. Last interglacial climates

    USGS Publications Warehouse

    Kukla, G.J.; Bender, M.L.; de Beaulieu, J. -L.; Bond, G.; Broecker, W.S.; Cleveringa, P.; Gavin, J.E.; Herbert, T.D.; Imbrie, J.; Jouzel, J.; Keigwin, L.D.; Knudsen, K.-L.; McManus, J.F.; Merkt, J.; Muhs, D.R.; Muller, H.; Poore, R.Z.; Porter, S.C.; Seret, G.; Shackleton, N.J.; Turner, C.; Tzedakis, P.C.; Winograd, I.J.

    2002-01-01

    The last interglacial, commonly understood as an interval with climate as warm or warmer than today, is represented by marine isotope stage (MIS) 5e, which is a proxy record of low global ice volume and high sea level. It is arbitrarily dated to begin at approximately 130,000 yr B.P. and end at 116,000 yr B.P. with the onset of the early glacial unit MIS 5d. The age of the stage is determined by correlation to uranium-thorium dates of raised coral reefs. The most detailed proxy record of interglacial climate is found in the Vostok ice core where the temperature reached current levels 132,000 yr ago and continued rising for another two millennia. Approximately 127,000 yr ago the Eemian mixed forests were established in Europe. They developed through a characteristic succession of tree species, probably surviving well into the early glacial stage in southern parts of Europe. After ca. 115,000 yr ago, open vegetation replaced forests in northwestern Europe and the proportion of conifers increased significantly farther south. Air temperature at Vostok dropped sharply. Pulses of cold water affected the northern North Atlantic already in late MIS 5e, but the central North Atlantic remained warm throughout most of MIS 5d. Model results show that the sea surface in the eastern tropical Pacific warmed when the ice grew and sea level dropped. The essentially interglacial conditions in southwestern Europe remained unaffected by ice buildup until late MIS 5d when the forests disappeared abruptly and cold water invaded the central North Atlantic ca. 107,000 yr ago. ?? 2002 University of Washington.

  12. Polarity in Conditionals and Conditional-Like Constructions

    ERIC Educational Resources Information Center

    Hsieh, I-Ta Chris

    2012-01-01

    This dissertation concerns the distribution of negative polarity items (henceforth, NPIs) in conditionals and conditional-like constructions. NPIs include words such as any and ever and idioms such as "give a damn" and "lift a finger"; these expressions have only a limited distribution. In this dissertation, the distribution of…

  13. Interglacial complex and solcomplex

    NASA Astrophysics Data System (ADS)

    Schirmer, Wolfgang

    2010-03-01

    All younger Pleistocene interglacials form interglacial complexes. The term interglacial complex is a short term for a tight complex of interglacials, interstadials and breviglacials, separating a complex of warm periods from the long glacial periods (euglacials). In the terrestric environment the interglacial complexes are represented by soil clusters (solcomplexes). Therein which occur interglacial and interstadial soils of different types in the loess environment separated by thin beds of loess or loess derivates (breviglacials). This article considers the mutilation and simulation of solcomplexes. Frequently, fossil solcomplexes present themselves as diminished to a few soils or to one single soil. This mutilation of solcomplexes can be due to soil convergence (soils of different warm periods — interglacials, interstadials — merge to form optically one soil), syn-solcomplex erosion or post-solcomplex erosion and sometimes to soil disguise. Conversely solcomplexes may be simulated by narrowing of soils which belong to different interglacial complexes and moreover by soil divergence (splitting of a soil of one single warm period by an interlayer of rock) or by reworked soil sediment.

  14. N2O and δ15N-N2O and δ18O-N2O from polar ice cores: interpretable data for interglacials

    NASA Astrophysics Data System (ADS)

    Bock, Michael; Schmitt, Jochen; Seth, Barbara; Beck, Jonas; Fischer, Hubertus

    2014-05-01

    Ice cores provide a wealth of information on climate change. For instance, the history of the atmospheric greenhouse gas N2O can be reconstructed using air entrapped in polar ice cores. N2O has several sources in both terrestrial and marine ecosystems, predominantly wetland soils and oxygen minimum zones in the ocean. N2O records generally follow the climatic changes during the glacial-interglacial cycles with higher N2O mixing ratios during warmer climate stages. However, the underlying processes driving these changes are difficult to identify from N2O mixing ratios alone. Additional information on the individual sources and sinks are provided by stable isotope measurements. The emission fluxes of the dominant N2O sources are ascribed to several pathways (nitrification, denitrification), with characteristic fractionation factors for the nitrogen and oxygen isotope signatures of the generated N2O (δ15N-N2O and δ18O-N2O). In the end, the individual proportions of pathways are responsible for distinct δ15N-N2O and δ18O-N2O for the average terrestrial and marine sources. Here, we present new ice core measurements of δ15N-N2O and δ18O-N2O covering the Holocene, MIS 5 and MIS 11. For the past 15 kyrs the δ15N-N2O record shows a continuous decrease starting at 15 kyrs to about 6 kyrs; during the past 6 kyrs δ15N-N2O remains rather constant. The resemblance with a recently published global reconstruction of bulk δ15N is remarkable (McLauchlan et al. 2013, Nature). Taken at face value this could mean that mainly the terrestrial source signature changed rather than a shift in the relative proportions of the terrestrial and marine source. The integrity of N2O ice core records relies on the assumption that the measurements truly represent the past atmosphere. However, comparative analyses of different ice cores from the same age intervals show offsets in the N2O mixing ratios among the records. One likely assumption is that higher mixing ratios are due to in

  15. Semi-open environmental conditions during phases of hominin occupation at the Eemian Interglacial basin site Neumark-Nord 2 and its wider environment

    NASA Astrophysics Data System (ADS)

    Pop, Eduard; Bakels, Corrie

    2015-06-01

    Neandertal occupation of Eemian environments in Europe is well attested by several archaeological sites dating to this interglacial period. Does this mean that Neandertals were living in closed forest environments? Due to the potential variability of Eemian environments in space and time, it is necessary to study environmental records that can be correlated with phases of hominin presence, as reflected in the archaeological record. Such a perspective can be obtained from the small basin locality Neumark-Nord 2, as it contains an extensive and detailed environmental record, as well as a large archaeological record consisting of several distinct find levels. Analysis shows that hominin presence is predominantly associated with semi-open environmental conditions. A review of the data from the neighbouring Neumark-Nord 1 basin shows that semi-open environments were also characterizing the wider environment during phases of hominin presence at both basin localities. Large herbivores attracted to the water in these basins may have played an important role in the vegetation openness, probably in conjunction with (local) climatic conditions. The relationship between hominin presence and semi-open environments is explained as Neandertals exploiting the large herbivores aggregating around these freshwater localities, while the more varied vegetation would also have provided them with edible plant foods. Other Eemian sites from freshwater contexts provide evidence for semi-open conditions as well.

  16. Characterization for imperfect polarizers under imperfect conditions.

    PubMed

    Nee, S M; Yoo, C; Cole, T; Burge, D

    1998-01-01

    The principles for measuring the extinction ratio and transmittance of a polarizer are formulated by use of the principal Mueller matrix, which includes both polarization and depolarization. The extinction ratio is about half of the depolarization, and the contrast is the inverse of the extinction ratio. Errors in the extinction ratio caused by partially polarized incident light and the misalignment of polarizers can be corrected by the devised zone average method and the null method. Used with a laser source, the null method can measure contrasts for very good polarizers. Correct algorithms are established to deduce the depolarization for three comparable polarizers calibrated mutually. These methods are tested with wire-grid polarizers used in the 3-5-microm wavelength region with a laser source and also a lamp source. The contrasts obtained from both methods agree. PMID:18268560

  17. Lunar Polar Environmental Testing: Regolith Simulant Conditioning

    NASA Technical Reports Server (NTRS)

    Kleinhenz, Julie Elise

    2014-01-01

    As ISRU system development approaches flight fidelity, there is a need to test hardware in relevant environments. Extensive laboratory and field testing have involved relevant soil (lunar regolith simulants), but the current design iterations necessitate relevant pressure and temperature conditions. Including significant quantities of lunar regolith simulant in a thermal vacuum chamber poses unique challenges. These include facility operational challenges (dust tolerant hardware) and difficulty maintaining a pre-prepared soil state during pump down (consolidation state, moisture retention).For ISRU purposes, the regolith at the lunar poles will be of most interest due to the elevated water content. To test at polar conditions, the regolith simulant must be doped with water to an appropriate percentage and then chilled to cryogenic temperatures while exposed to vacuum conditions. A 1m tall, 28cm diameter bin of simulant was developed for testing these simulant preparation and drilling operations. The bin itself was wrapped with liquid nitrogen cooling loops (100K) so that the simulant bed reached an average temperature of 140K at vacuum. Post-test sampling was used to determine desiccation of the bed due to vacuum exposure. Depth dependent moisture data is presented from frozen and thawed soil samples.Following simulant only evacuation tests, drill hardware was incorporated into the vacuum chamber to test auguring techniques in the frozen soil at thermal vacuum conditions. The focus of this testing was to produce cuttings piles for a newly developed spectrometer to evaluate. This instrument, which is part of the RESOLVE program science hardware, detects water signatures from surface regolith. The drill performance, behavior of simulant during drilling, and characteristics of the cuttings piles will be offered.

  18. A hypothesis linking sub-optimal seawater pCO2 conditions for cnidarian-Symbiodinium symbioses with the exceedence of the interglacial threshold (> 260 ppmv)

    NASA Astrophysics Data System (ADS)

    Wooldridge, S. A.

    2011-11-01

    Most scleractinian corals and many other cnidarians host intracellular photosynthetic dinoflagellate symbionts ("zooxanthellae"). The zooxanthellae contribute to host metabolism and skeletogenesis to such an extent that this symbiosis is well recognised for its contribution in creating the coral reef ecosystem. The stable functioning of cnidarian symbioses is however dependent upon the host's ability to maintain demographic control of its algal partner. In this review, I explain how the modern envelope of seawater conditions found within many coral reef ecosystems (characterised by elevated temperatures, rising pCO2, and enriched nutrient levels) are antagonistic toward the dominant host processes that restrict excessive symbiont proliferation. Moreover, I outline a new hypothesis and initial evidence base, which support the suggestion that the additional "excess" zooxanthellae fraction permitted by seawater pCO2 levels beyond 260 ppmv significantly increases the propensity for symbiosis breakdown ("bleaching") in response to temperature and irradiance extremes. The relevance of this biological threshold is discussed in terms of historical reef extinction events, glacial-interglacial climate cycles and the modern decline of coral reef ecosystems.

  19. A hypothesis linking sub-optimal seawater pCO2 conditions for cnidarian-Symbiodinium symbioses with the exceedence of the interglacial threshold (>260 ppmv)

    NASA Astrophysics Data System (ADS)

    Wooldridge, S. A.

    2012-05-01

    Most scleractinian corals and many other cnidarians host intracellular photosynthetic dinoflagellate symbionts ("zooxanthellae"). The zooxanthellae contribute to host metabolism and skeletogenesis to such an extent that this symbiosis is well recognised for its contribution in creating the coral reef ecosystem. The stable functioning of cnidarian symbioses is however dependent upon the host's ability to maintain demographic control of its algal partner. In this review, I explain how the modern envelope of seawater conditions found within many coral reef ecosystems (characterised by elevated temperatures, rising pCO2, and enriched nutrient levels) are antagonistic toward the dominant host processes that restrict excessive symbiont proliferation. Moreover, I outline a new hypothesis and initial evidence base, which support the suggestion that the additional "excess" zooxanthellae fraction permitted by seawater pCO2 levels beyond 260 ppmv significantly increases the propensity for symbiosis breakdown ("bleaching") in response to temperature and irradiance extremes. The relevance of this biological threshold is discussed in terms of historical reef extinction events, glacial-interglacial climate cycles and the modern decline of coral reef ecosystems.

  20. Response of Asian summer monsoon duration to orbital forcing under glacial and interglacial conditions: Implication for precipitation variability in geological records

    NASA Astrophysics Data System (ADS)

    Shi, Zhengguo

    2016-05-01

    The responses of Asian summer monsoon and associated precipitation to orbital forcing have been intensively explored during the past 30 years, but debate still exists regarding whether or not the Asian monsoon is controlled by northern or southern summer insolation on the precessional timescale. Various modeling studies have been conducted that support the potential roles played by the insolation in both hemispheres. Among these previous studies, however, the main emphasis has been on the Asian monsoon intensity, with the response of monsoon duration having received little consideration. In the present study, the response of the rainy season duration over different monsoon areas to orbital forcing and its contribution to total annual precipitation are evaluated using an atmospheric general circulation model. The results show that the durations of the rainy seasons, especially their withdrawal, in northern East Asia and the India-Bay of Bengal region, are sensitive to precession change under interglacial-like conditions. Compared to those during stronger boreal summer insolation, the Asian monsoon-associated rainy seasons at weaker insolation last longer, although the peak intensity is smaller. This longer duration of rainfall, which results from the change in land-ocean thermal contrast associated with atmospheric diabatic heating, can counterbalance the weakened intensity in certain places and induce an opposite response of total annual precipitation. However, the duration effect of Asian monsoon is limited under glacial-like conditions. Nevertheless, monsoon duration is a factor that can dominate the orbital-scale variability of Asian monsoon, alongside the intensity, and it should therefore receive greater attention when attempting to explain orbital-scale monsoon change.

  1. Can we predict the duration of an interglacial?

    NASA Astrophysics Data System (ADS)

    Tzedakis, P. C.; Wolff, E. W.; Skinner, L. C.; Brovkin, V.; Hodell, D. A.; McManus, J. F.; Raynaud, D.

    2012-04-01

    Differences in the duration of interglacials have long been apparent in palaeoclimate records of the Late and Middle Pleistocene. However, a systematic evaluation of such differences has been hampered by the lack of a metric that can be applied consistently through time and by difficulties in separating the local from the global component in various proxies. This, in turn, means that a theoretical framework with predictive power for interglacial duration has remained elusive. Here we propose that the interval between the terminal oscillation of the bipolar-seesaw and three thousand years (kyr) before its first major reactivation provides an estimate that approximates the length of the sea-level highstand, a measure of interglacial duration. We apply this concept to interglacials of the last 800 kyr by using a recently-constructed record of interhemispheric variability. The onset of interglacials occurs within 2 kyr of the peak in boreal summer insolation and is consistent with the canonical view of Milankovitch forcing dictating the broad timing of interglacials. Glacial inception always takes place when obliquity is decreasing and never after the obliquity minimum. The phasing of precession and obliquity appears to influence the persistence of interglacial conditions over one or two insolation peaks, leading to shorter (~13 kyr) and longer (~28 kyr) interglacials. Glacial inception occurs approximately 10 kyr after peak interglacial conditions in temperature and CO2, representing an interglacial "relaxation" time over which gradual cooling takes place. Second-order differences in duration may be a function of stochasticity in the climate system, or small variations in background climate state and the magnitude of feedbacks and mechanisms contributing to glacial iinception, and as such, difficult to predict. On the other hand, the broad duration of an interglacial may be determined by the phasing of astronomical parameters and the history of insolation, rather than

  2. Can we predict the duration of an interglacial?

    NASA Astrophysics Data System (ADS)

    Tzedakis, P. C.; Wolff, E. W.; Skinner, L. C.; Brovkin, V.; Hodell, D. A.; McManus, J. F.; Raynaud, D.

    2012-09-01

    Differences in the duration of interglacials have long been apparent in palaeoclimate records of the Late and Middle Pleistocene. However, a systematic evaluation of such differences has been hampered by the lack of a metric that can be applied consistently through time and by difficulties in separating the local from the global component in various proxies. This, in turn, means that a theoretical framework with predictive power for interglacial duration has remained elusive. Here we propose that the interval between the terminal oscillation of the bipolar seesaw and three thousand years (kyr) before its first major reactivation provides an estimate that approximates the length of the sea-level highstand, a measure of interglacial duration. We apply this concept to interglacials of the last 800 kyr by using a recently-constructed record of interhemispheric variability. The onset of interglacials occurs within 2 kyr of the boreal summer insolation maximum/precession minimum and is consistent with the canonical view of Milankovitch forcing pacing the broad timing of interglacials. Glacial inception always takes place when obliquity is decreasing and never after the obliquity minimum. The phasing of precession and obliquity appears to influence the persistence of interglacial conditions over one or two insolation peaks, leading to shorter (~ 13 kyr) and longer (~ 28 kyr) interglacials. Glacial inception occurs approximately 10 kyr after peak interglacial conditions in temperature and CO2, representing a characteristic timescale of interglacial decline. Second-order differences in duration may be a function of stochasticity in the climate system, or small variations in background climate state and the magnitude of feedbacks and mechanisms contributing to glacial inception, and as such, difficult to predict. On the other hand, the broad duration of an interglacial may be determined by the phasing of astronomical parameters and the history of insolation, rather than the

  3. Interglacials of the last 800,000 years

    NASA Astrophysics Data System (ADS)

    Past Interglacials Working Group Of Pages

    2016-03-01

    Interglacials, including the present (Holocene) period, are warm, low land ice extent (high sea level), end-members of glacial cycles. Based on a sea level definition, we identify eleven interglacials in the last 800,000 years, a result that is robust to alternative definitions. Data compilations suggest that despite spatial heterogeneity, Marine Isotope Stages (MIS) 5e (last interglacial) and 11c (~400 ka ago) were globally strong (warm), while MIS 13a (~500 ka ago) was cool at many locations. A step change in strength of interglacials at 450 ka is apparent only in atmospheric CO2 and in Antarctic and deep ocean temperature. The onset of an interglacial (glacial termination) seems to require a reducing precession parameter (increasing Northern Hemisphere summer insolation), but this condition alone is insufficient. Terminations involve rapid, nonlinear, reactions of ice volume, CO2, and temperature to external astronomical forcing. The precise timing of events may be modulated by millennial-scale climate change that can lead to a contrasting timing of maximum interglacial intensity in each hemisphere. A variety of temporal trends is observed, such that maxima in the main records are observed either early or late in different interglacials. The end of an interglacial (glacial inception) is a slower process involving a global sequence of changes. Interglacials have been typically 10-30 ka long. The combination of minimal reduction in northern summer insolation over the next few orbital cycles, owing to low eccentricity, and high atmospheric greenhouse gas concentrations implies that the next glacial inception is many tens of millennia in the future.

  4. Mars Express MARSIS Radar: A Prediction of the Effect of Overlying Ice on Detecting Polar Basal Lakes and Inter-Glacial Aquifers

    NASA Technical Reports Server (NTRS)

    Farrell, W. M.; Plaut, J. J.; Gurnett, D. A.; Picardi, G.

    2004-01-01

    The penetration of the MARSIS radar signal into the polar ice mass is modeled to determine the capability of the instrument to locate sub-glacial aquifers. As a ground penetrating radar, the orbiting MARSIS transmits a signal greater than 1 W between 1-5 MHz. In this work we will investigate the effect of ice conductive losses on the radar-detection of subsurface aquifers. Based on wave propagation analysis, it is found that for a bulk ice conductivity below 10-5 S/m, conductive losses in the medium are not significant. However, if the bulk ice conductivity is relatively large (greater than 10-5 S/m), the reflected signal from any deep aquifer will be absorbed as it propagates in the lossy ice medium limiting the probing depth.

  5. Ultracompact and broadband polarization beam splitter based on polarization-dependent critical guiding condition.

    PubMed

    Ying, Zhoufeng; Wang, Guanghui; Zhang, Xuping; Ho, Ho-pui; Huang, Ying

    2015-05-01

    An ultracompact and broadband polarization beam splitter (PBS) based on the polarization-dependent critical guiding condition of an asymmetrical directional coupler is proposed. The device consists of a pair of silicon waveguides with different height and width. Due to the different cutoff conditions for the TE and TM polarization modes, it is possible to have the TM mode guided in one waveguide while the TE mode is supported in both. Therefore, only the phase-matching condition for the cross-coupling of the TE mode needs to be considered. This approach not only simplifies the design procedures but also significantly improves device performance with smaller total length and larger bandwidth. Finally, regardless of the contribution of S-bend waveguides, our proposed PBS has a coupling region as short as 0.2 μm, which is the shortest reported until now. The simulation result shows that the extinction ratios for the TE and TM polarization are 13.5 and 16.6 dB at their respective output ports, and their insertion losses are 0.29 and 0.13 dB, respectively. Numerical simulations also show that the device offers a very large bandwidth (∼140  nm) with large extinction ratio (>10  dB) and low insertion loss (<1  dB). PMID:25927804

  6. Illumination Conditions of the Lunar Polar Regions Using LOLA Topography

    NASA Technical Reports Server (NTRS)

    Mazarico, E.; Neumann, G. A.; Smith, D. E.; Zuber, M. T.; Torrence, M. H.

    2011-01-01

    We use high-resolution altimetry data obtained by the Lunar Orbiter Laser Altimeter instrument onboard the Lunar Reconnaissance Orbiter to characterize present illumination conditions in the polar regions of the Moon. Compared to previous studies, both the spatial and temporal extent of the simulations are increased significantly, as well as the coverage (fill ratio) of the topographic maps used, thanks to the 28 Hz firing rate of the five-beam instrument. We determine the horizon elevation in a number of directions based on 240 m-resolution polar digital elevation models reaching down to 75 latitude. The illumination of both polar regions extending to 80 can be calculated for any geometry from those horizon longitudinal profiles. We validated our modeling with recent Lunar Reconnaissance Orbiter Wide-Angle Camera images. We assessed the extent of permanently shadowed regions (PSRs, defined as areas that never receive direct solar illumination), and obtained total areas generally larger than previous studies (12,866 and 16,055 km2, in the north and south respectively). We extended our direct illumination model to account for singly-scattered light, and found that every PSR does receive some amount of scattered light during the year. We conducted simulations over long periods (several 18.6-years lunar precession cycles) with a high temporal resolution (6 h), and identified the most illuminated locations in the vicinity of both poles. Because of the importance of those sites for exploration and engineering considerations, we characterized their illumination more precisely over the near future. Every year, a location near the Shackleton crater rim in the south polar region is sunlit continuously for 240 days, and its longest continuous period in total darkness is about 1.5 days. For some locations small height gains ( 10 m) can dramatically improve their average illumination and reduce the night duration, rendering some of those particularly attractive energy-wise as

  7. Plasma Conditions in Polar Plumes and Interplume Regions in Polar Coronal Holes

    NASA Astrophysics Data System (ADS)

    Cranmer, S. R.; Kohl, J. L.; Miralles, M.; Panasyuk, A. V.

    2001-05-01

    During times of low solar activity, large polar coronal holes are observed to contain bright raylike polar plumes that appear to follow open magnetic field lines. Plumes are believed to be flux tubes that are heated impulsively at their base, which leads to a higher density, a lower outflow speed, and a lower overall temperature in the extended corona, compared to the surrounding interplume regions. Despite years of white light and spectroscopic observations, though, the differences in mass, momentum, and energy flux in plumes and between plumes are not known precisely. This poster presents an updated survey of data from the Ultraviolet Coronagraph Spectrometer (UVCS), aboard SOHO, that attempts to sort out the local plume and interplume conditions. These results will be compared with previous analyses that characterized the ``mean'' plume/interplume coronal hole, averaged over many lines of sight through varying concentrations of plumes. Limits on the relative contributions of plumes and interplume regions to the high-speed solar wind will be determined, with emphasis on the proton outflow speed in the corona and at 1 AU. Implications for theoretical models of coronal heating and solar wind acceleration will be discussed. This work is supported by the National Aeronautics and Space Administration under grant NAG5-10093 to the Smithsonian Astrophysical Observatory, by Agenzia Spaziale Italiana, and by the Swiss contribution to the ESA PRODEX program.

  8. Pennsylvanian tropical rain forests responded to glacial-interglacial rhythms

    NASA Astrophysics Data System (ADS)

    Falcon-Lang, Howard J.

    2004-08-01

    Pennsylvanian tropical rain forests flourished during an icehouse climate mode. Although it is well established that Milankovitch-band glacial-interglacial rhythms caused marked synchronous changes in Pennsylvanian tropical climate and sea level, little is known of vegetation response to orbital forcing. This knowledge gap has now been addressed through sequence- stratigraphic analysis of megafloral and palynofloral assemblages within the Westphalian D Cantabrian Sydney Mines Formation of eastern Canada. This succession was deposited in a low- accommodation setting where sequences can be attributed confidently to glacio-eustasy. Results show that long-lived, low-diversity peat mires dominated by lycopsids were initiated during deglaciation events, but were mostly drowned by rising sea level at maximum interglacial conditions. Only upland coniferopsid forests survived flooding without significant disturbance. Mid- to late interglacial phases witnessed delta-plain progradation and establishment of high-diversity, mineral-substrate rain forests containing lycopsids, sphenopsids, pteridosperms, cordaites, and tree ferns. Renewed glaciation resulted in sea-level fall, paleovalley incision, and the onset of climatic aridity. Glacial vegetation was dominated by cordaites, pteridosperms, and tree ferns; hydrophilic lycopsids and sphenopsids survived in paleovalley refugia. Findings clearly demonstrate the dynamic nature of Pennsylvanian tropical ecosystems and are timely given current debates about the impact of Quaternary glacial-interglacial rhythms on the biogeography of tropical rain forest.

  9. Comparative carbon cycle dynamics of the present and last interglacial

    NASA Astrophysics Data System (ADS)

    Brovkin, Victor; Brücher, Tim; Kleinen, Thomas; Zaehle, Sönke; Joos, Fortunat; Roth, Raphael; Spahni, Renato; Schmitt, Jochen; Fischer, Hubertus; Leuenberger, Markus; Stone, Emma J.; Ridgwell, Andy; Chappellaz, Jérôme; Kehrwald, Natalie; Barbante, Carlo; Blunier, Thomas; Dahl Jensen, Dorthe

    2016-04-01

    Changes in temperature and carbon dioxide during glacial cycles recorded in Antarctic ice cores are tightly coupled. However, this relationship does not hold for interglacials. While climate cooled towards the end of both the last (Eemian) and present (Holocene) interglacials, CO2 remained stable during the Eemian while rising in the Holocene. We identify and review twelve biogeochemical mechanisms of terrestrial (vegetation dynamics and CO2 fertilization, land use, wildfire, accumulation of peat, changes in permafrost carbon, subaerial volcanic outgassing) and marine origin (changes in sea surface temperature, carbonate compensation to deglaciation and terrestrial biosphere regrowth, shallow-water carbonate sedimentation, changes in the soft tissue pump, and methane hydrates), which potentially may have contributed to the CO2 dynamics during interglacials but which remain not well quantified. We use three Earth System Models (ESMs) of intermediate complexity to compare effects of selected mechanisms on the interglacial CO2 and δ13CO2 changes, focusing on those with substantial potential impacts: namely carbonate sedimentation in shallow waters, peat growth, and (in the case of the Holocene) human land use. A set of specified carbon cycle forcings could qualitatively explain atmospheric CO2 dynamics from 8 ka BP to the pre-industrial. However, when applied to Eemian boundary conditions from 126 to 115 ka BP, the same set of forcings led to disagreement with the observed direction of CO2 changes after 122 ka BP. This failure to simulate late-Eemian CO2 dynamics could be a result of the imposed forcings such as prescribed CaCO3 accumulation and/or an incorrect response of simulated terrestrial carbon to the surface cooling at the end of the interglacial. These experiments also reveal that key natural processes of interglacial CO2 dynamics - shallow water CaCO3 accumulation, peat and permafrost carbon dynamics - are not well represented in the current ESMs. Global

  10. Warm climate isotopic simulations: what do we learn about interglacial signals in Greenland ice cores?

    NASA Astrophysics Data System (ADS)

    Sime, Louise C.; Risi, Camille; Tindall, Julia C.; Sjolte, Jesper; Wolff, Eric W.; Masson-Delmotte, Valérie; Capron, Emilie

    2013-05-01

    Measurements of Last Interglacial stable water isotopes in ice cores show that central Greenland δ18O increased by at least 3‰ compared to present day. Attempting to quantify the Greenland interglacial temperature change from these ice core measurements rests on our ability to interpret the stable water isotope content of Greenland snow. Current orbitally driven interglacial simulations do not show δ18O or temperature rises of the correct magnitude, leading to difficulty in using only these experiments to inform our understanding of higher interglacial δ18O. Here, analysis of greenhouse gas warmed simulations from two isotope-enabled general circulation models, in conjunction with a set of Last Interglacial sea surface observations, indicates a possible explanation for the interglacial δ18O rise. A reduction in the winter time sea ice concentration around the northern half of Greenland, together with an increase in sea surface temperatures over the same region, is found to be sufficient to drive a >3‰ interglacial enrichment in central Greenland snow. Warm climate δ18O and δD in precipitation falling on Greenland are shown to be strongly influenced by local sea surface condition changes: local sea surface warming and a shrunken sea ice extent increase the proportion of water vapour from local (isotopically enriched) sources, compared to that from distal (isotopically depleted) sources. Precipitation intermittency changes, under warmer conditions, leads to geographical variability in the δ18O against temperature gradients across Greenland. Little sea surface warming around the northern areas of Greenland leads to low δ18O against temperature gradients (0.1-0.3‰ per °C), whilst large sea surface warmings in these regions leads to higher gradients (0.3-0.7‰ per °C). These gradients imply a wide possible range of present day to interglacial temperature increases (4 to >10 °C). Thus, we find that uncertainty about local interglacial sea surface

  11. Application of Laser Induced Breakdown Spectroscopy under Polar Conditions

    NASA Astrophysics Data System (ADS)

    Clausen, J. L.; Hark, R.; Bol'shakov, A.; Plumer, J.

    2015-12-01

    Over the past decade our research team has evaluated the use of commercial-off-the-shelf laser-induced breakdown spectroscopy (LIBS) for chemical analysis of snow and ice samples under polar conditions. One avenue of research explored LIBS suitability as a detector of paleo-climate proxy indicators (Ca, K, Mg, and Na) in ice as it relates to atmospheric circulation. LIBS results revealed detection of peaks for C and N, consistent with the presence of organic material, as well as major ions (Ca, K, Mg, and Na) and trace metals (Al, Cu, Fe, Mn, Ti). The detection of Ca, K, Mg, and Na confirmed that LIBS has sufficient sensitivity to be used as a tool for characterization of paleo-climate proxy indicators in ice-core samples. Techniques were developed for direct analysis of ice as well as indirect measurements of ice via melting and filtering. Pitfalls and issues of direct ice analysis using several cooling techniques to maintain ice integrity will be discussed. In addition, a new technique, laser ablation molecular isotopic spectroscopy (LAMIS) was applied to detection of hydrogen and oxygen isotopes in ice as isotopic analysis of ice is the main tool in paleoclimatology and glaciology studies. Our results demonstrated that spectra of hydroxyl isotopologues 16OH, 18OH, and 16OD can be recorded with a compact spectrograph to determine hydrogen and oxygen isotopes simultaneously. Quantitative isotopic calibration for ice analysis can be accomplished using multivariate chemometric regression as previously realized for water vapor. Analysis with LIBS and LAMIS required no special sample preparation and was about ten times faster than analysis using ICP-MS. Combination of the two techniques in one portable instrument for in-field analysis appears possible and would eliminate the logistical and cost issues associated with ice core management.

  12. Last Interglacial climate variability recorded in sediments of Lake Ohrid (Albania/Macedonia)

    NASA Astrophysics Data System (ADS)

    Vogel, H.; Valsecchi, V.; Schouten, S.; Leng, M. J.; Wagner, B.; Sulpizio, R.; Zanchetta, G.; Lotter, A. F.

    2010-12-01

    Lake Ohrid, a transboundary lake shared by the former Yugoslav Republic of Macedonia and the Republic of Albania is with its likely Pliocene age considered to be the oldest existing lake in Europe. Since 2004 several sediment successions have been recovered from Lake Ohrid. The longest records cover the last glacial-interglacial cycle and reach back to MIS 6. Independent age control is given by radiocarbon dating and tephrochronology. These records allow insights on climatic and environmental evolution of the last interglacial in a region, which today is densely populated and highly vulnerable to climate change. We used a multiproxy approach to study climatic and environmental variability during the last interglacial. This approach combines novel molecular (TEX86, MBT/CBT) and established sedimentological, geochemical and paleoecological tools. These combined data imply that the last interglacial at Lake Ohrid was preceded by an interstadial period between c. 133 and 131 ka that was followed by a stadial centred at c. 130 ka and characterized by a marked vegetation shift to more steppic elements around the lake. Subsequently, temperatures rose steadily from c. 129 to 122 ka. From c. 122 ka temperatures declined gradually. A sudden drop in temperatures starting at about 116 ka probably marks the end of the last interglacial period at Lake Ohrid. A comparison of highest temperatures during the Holocene and the last interglacial points to 2-3 °C higher temperatures during the last interglacial. A temperature increase in the same order is predicted by climate models for this region implying that last interglacial climatic and environmental conditions as recorded in Lake Ohrids sediments could provide a relatively good analogue for the future. However, longer records from this area are needed to gain a better understanding of natural climate variability during interglacials with a different setting of orbital parameters. In order to recover longer records extending

  13. Glacial-to-interglacial Changes in NADW Fluxes?

    NASA Technical Reports Server (NTRS)

    Mix, A. C.; Fairbanks, R. G.

    1984-01-01

    Interglacial gradients in delta 13C between Atlantic and Pacific deep waters reflect differences between low-nutrient, 13C-enriched North Atlantic Deep Water (NADW) and high-nutrient, 13C-depleted Pacific Deep Water. Reduced Atlantic-Pacific delta 13C and cadmium gradients at the last glacial maximum have been used to suggest substantial replacement of NADW with nutrient-rich Antarctic Bottom Water (Boyle and Keigwin, 1982; Shackleton et al., 1983). We show that the Atlantic delta 13C signal is linked directly to North Atlantic polar-front migration, as reflected by planktonic foraminiferal faunas.

  14. Major cooling intersecting peak Eemian Interglacial warmth in northern Europe

    NASA Astrophysics Data System (ADS)

    Helmens, Karin F.; Salonen, J. Sakari; Plikk, Anna; Engels, Stefan; Väliranta, Minna; Kylander, Malin; Brendryen, Jo; Renssen, Hans

    2015-08-01

    The degree of climate instability on the continent during the warmer-than-present Eemian Interglacial (around ca. 123 kyr ago) remains unsolved. Recently published high-resolution proxy data from the North Atlantic Ocean suggest that the Eemian was punctuated by abrupt events with reductions in North Atlantic Deep Water formation accompanied by sea-surface temperature cooling. Here we present multi-proxy data at an unprecedented resolution that reveals a major cooling event intersecting peak Eemian warmth on the North European continent. Two independent temperature reconstructions based on terrestrial plants and chironomids indicate a summer cooling of the order of 2-4 °C. The cooling event started abruptly, had a step-wise recovery, and lasted 500-1000 yr. Our results demonstrate that the common view of relatively stable interglacial climate conditions on the continent should be revised, and that perturbations in the North Atlantic oceanic circulation under warmer-than-present interglacial conditions may also lead to abrupt and dramatic changes on the adjacent continent.

  15. Extended megadroughts in the southwestern United States during Pleistocene interglacials.

    PubMed

    Fawcett, Peter J; Werne, Josef P; Anderson, R Scott; Heikoop, Jeffrey M; Brown, Erik T; Berke, Melissa A; Smith, Susan J; Goff, Fraser; Donohoo-Hurley, Linda; Cisneros-Dozal, Luz M; Schouten, Stefan; Sinninghe Damsté, Jaap S; Huang, Yongsong; Toney, Jaime; Fessenden, Julianna; WoldeGabriel, Giday; Atudorei, Viorel; Geissman, John W; Allen, Craig D

    2011-02-24

    The potential for increased drought frequency and severity linked to anthropogenic climate change in the semi-arid regions of the southwestern United States (US) is a serious concern. Multi-year droughts during the instrumental period and decadal-length droughts of the past two millennia were shorter and climatically different from the future permanent, 'dust-bowl-like' megadrought conditions, lasting decades to a century, that are predicted as a consequence of warming. So far, it has been unclear whether or not such megadroughts occurred in the southwestern US, and, if so, with what regularity and intensity. Here we show that periods of aridity lasting centuries to millennia occurred in the southwestern US during mid-Pleistocene interglacials. Using molecular palaeotemperature proxies to reconstruct the mean annual temperature (MAT) in mid-Pleistocene lacustrine sediment from the Valles Caldera, New Mexico, we found that the driest conditions occurred during the warmest phases of interglacials, when the MAT was comparable to or higher than the modern MAT. A collapse of drought-tolerant C(4) plant communities during these warm, dry intervals indicates a significant reduction in summer precipitation, possibly in response to a poleward migration of the subtropical dry zone. Three MAT cycles ∼2 °C in amplitude occurred within Marine Isotope Stage (MIS) 11 and seem to correspond to the muted precessional cycles within this interglacial. In comparison with MIS 11, MIS 13 experienced higher precessional-cycle amplitudes, larger variations in MAT (4-6 °C) and a longer period of extended warmth, suggesting that local insolation variations were important to interglacial climatic variability in the southwestern US. Comparison of the early MIS 11 climate record with the Holocene record shows many similarities and implies that, in the absence of anthropogenic forcing, the region should be entering a cooler and wetter phase. PMID:21350483

  16. Extended megadroughts in the southwestern United States during Pleistocene interglacials

    USGS Publications Warehouse

    Fawcett, P.J.; Werne, J.P.; Anderson, R. Scott; Heikoop, J.M.; Brown, E.T.; Berke, M.A.; Smith, S.J.; Goff, F.; Donohoo-Hurley, L.; Cisneros-Dozal, L. M.; Schouten, S.; Damste, J.S.S.; Huang, Y.; Toney, J.; Fessenden, J.; Woldegabriel, G.; Atudorei, V.; Geissman, J.W.; Allen, C.D.

    2011-01-01

    The potential for increased drought frequency and severity linked to anthropogenic climate change in the semi-arid regions of the southwestern United States (US) is a serious concern. Multi-year droughts during the instrumental period and decadal-length droughts of the past two millennia were shorter and climatically different from the future permanent, dust-bowl-like-megadrought conditions, lasting decades to a century, that are predicted as a consequence of warming. So far, it has been unclear whether or not such megadroughts occurred in the southwestern US, and, if so, with what regularity and intensity. Here we show that periods of aridity lasting centuries to millennia occurred in the southwestern US during mid-Pleistocene interglacials. Using molecular palaeotemperature proxies to reconstruct the mean annual temperature (MAT) in mid-Pleistocene lacustrine sediment from the Valles Caldera, New Mexico, we found that the driest conditions occurred during the warmest phases of interglacials, when the MAT was comparable to or higher than the modern MAT. A collapse of drought-tolerant C 4 plant communities during these warm, dry intervals indicates a significant reduction in summer precipitation, possibly in response to a poleward migration of the subtropical dry zone. Three MAT cycles-1/42-C in amplitude occurred within Marine Isotope Stage (MIS) 11 and seem to correspond to the muted precessional cycles within this interglacial. In comparison with MIS 11, MIS 13 experienced higher precessional-cycle amplitudes, larger variations in MAT (4-6??C) and a longer period of extended warmth, suggesting that local insolation variations were important to interglacial climatic variability in the southwestern US. Comparison of the early MIS 11 climate record with the Holocene record shows many similarities and implies that, in the absence of anthropogenic forcing, the region should be entering a cooler and wetter phase. ?? 2011 Macmillan Publishers Limited. All rights

  17. Dependence of polar hole density on magnetic and solar conditions

    NASA Technical Reports Server (NTRS)

    Hoegy, W. R.; Grebowsky, J. M.

    1991-01-01

    Electron densities from the Langmuir probes on the Atmospheric Explorer C and Dynamics Explorer 2 are used for analyzing the behavior of the high-altitude night-side F region polar hole as a function of solar and magnetic activity and of universal time (UT). The polar region of invariant latitude from 70 deg to 80 deg and MLT from 22 to 03 hours is examined. The strongest dependencies are observed in F10.7 and UT; a strong hemispherical difference due to the offset of the magnetic poles from the earth's rotation axis is observed in the UT dependence of the ionization hole. A seasonal variation in the dependence of ion density on solar flux is indicated, and an overall asymmetry in the density level between hemispheres is revealed, with the winter-hole density about a factor of 10 greater in the north than in the south.

  18. Extra-long interglacial in Northern Hemisphere during MISs 15-13 arising from limited extent of Arctic ice sheets in glacial MIS 14.

    PubMed

    Hao, Qingzhen; Wang, Luo; Oldfield, Frank; Guo, Zhengtang

    2015-01-01

    Knowledge of the behavior of Northern Hemisphere (NH) ice sheets over the past million years is crucial for understanding the role of orbitally driven insolation changes on glacial/interglacial cycles. Here, based on the demonstrable link between changes in Chinese loess grain-size and NH ice-sheet extent, we use loess grain-size records to confirm that northern ice-sheets were restricted during marine oxygen isotope stage (MIS) 14. Thus, an unusually long NH interglacial climate of over 100 kyr persisted during MISs 15-13, much longer than expected from marine oxygen isotope records. Taking a global view of the paleoclimate records, MIS 14 inception seems to be a response to changes in Antarctic ice-sheets rather than to NH cooling. Orbital configuration in the two Polar regions shows that the onset of MIS 14 was forced by austral insolation changes, rather than by boreal summer insolation, as Milankovitch theory proposes. Our analysis of MIS 14 raises the possibility that southern insolation forcing may have played an important role in the inception of several other glacials. We suggest that the extra-long NH interglacial climate during MISs 15-13 provided favorable conditions for the second major dispersal episode of African hominins into Eurasia. PMID:26159304

  19. Extra-long interglacial in Northern Hemisphere during MISs 15-13 arising from limited extent of Arctic ice sheets in glacial MIS 14

    PubMed Central

    Hao, Qingzhen; Wang, Luo; Oldfield, Frank; Guo, Zhengtang

    2015-01-01

    Knowledge of the behavior of Northern Hemisphere (NH) ice sheets over the past million years is crucial for understanding the role of orbitally driven insolation changes on glacial/interglacial cycles. Here, based on the demonstrable link between changes in Chinese loess grain-size and NH ice-sheet extent, we use loess grain-size records to confirm that northern ice-sheets were restricted during marine oxygen isotope stage (MIS) 14. Thus, an unusually long NH interglacial climate of over 100 kyr persisted during MISs 15−13, much longer than expected from marine oxygen isotope records. Taking a global view of the paleoclimate records, MIS 14 inception seems to be a response to changes in Antarctic ice-sheets rather than to NH cooling. Orbital configuration in the two Polar regions shows that the onset of MIS 14 was forced by austral insolation changes, rather than by boreal summer insolation, as Milankovitch theory proposes. Our analysis of MIS 14 raises the possibility that southern insolation forcing may have played an important role in the inception of several other glacials. We suggest that the extra-long NH interglacial climate during MISs 15−13 provided favorable conditions for the second major dispersal episode of African hominins into Eurasia. PMID:26159304

  20. Length of the current interglacial period and interglacial intervals of the last million years

    NASA Astrophysics Data System (ADS)

    Dergachev, V. A.

    2015-12-01

    It was ascertained that the long-term cyclical oscillations of the global climate of the Earth between glacial and interglacial states for the last million years respond to cyclical oscillations of the orbital parameters of the Earth. Cold glacial states with a period of approximately 100 ka give way to shorter intervals of warming of around 10-12 ka long. The current interglacial period—the so-called Holocene—started on Earth roughly 10 ka ago. The length of the current interglacial period and the causes of the climate change over the last approximately 50 years arouse sharp debates connected with the growing anthropogenic emission of greenhouse gases. To estimate the length of the current interglacial period, interglacial intervals near ~400 (MIS-11) and ~800 (MIS-19) ka are analyzed as its probable analogs.

  1. Marine Isotope Stage 31 (1.07 Ma): An extreme interglacial in the Antarctic nearshore zone

    NASA Astrophysics Data System (ADS)

    Scherer, R.; Bohaty, S.; Harwood, D.; Roberts, A.; Taviani, M.

    2003-04-01

    significant is the near absence of sea-ice related diatoms. These and other observations indicate that surface waters were notably warmer than present, and that sea-ice was drastically reduced during this interglacial stage. Such conditions likely signify partial or complete retreat West Antarctic Ice Sheet and significant modification in bottom water production. Although MIS-31 has received little prior attention as a key climate event, there is sufficient evidence from both low and high latitude records to indicate significant ocean circulation and ice volume changes during that interglacial, including relatively warm sea surface temperatures and strong North Atlantic Deep Water production. MIS-31 plays an important role in the transition from 41 kyr to 100 kyr climate cycles, and calculated orbital northern hemisphere summer insolation values for MIS-31 are among the highest of the last 5 Ma. High latitude stratigraphic records such as CRP-1, Unit 3.1 contain critical evidence of past climate extremes. We contend that such events provide evidence of past polar amplification during warm interglacials. There is continuing need for new drilling efforts along the Antarctic continental margin to recover additional records of past climate change that, like CRP-1, Unit 3.1, are proximal to the ice sheet.

  2. (Model) Peatlands in late Quaternary interglacials

    NASA Astrophysics Data System (ADS)

    Kleinen, Thomas; Brovkin, Victor

    2016-04-01

    Peatlands have accumulated a substantial amount of carbon, roughly 600 PgC, during the Holocene. Prior to the Holocene, there is relatively little direct evidence of peatlands, though coal deposits bear witness to a long history of peat-forming ecosystems going back to the Carboniferous. We therefore need to rely on models to investigate peatlands in times prior to the Holocene. We have developed a dynamical model of wetland extent and peat accumulation, integrated in the coupled climate carbon cycle model of intermediate complexity CLIMBER2-LPJ, in order to mechanistically model interglacial carbon cycle dynamics. This model consists of the climate model of intermediate complexity CLIMBER2 and the dynamic global vegetation model LPJ, which we have extended with modules to determine peatland extent and carbon accumulation. The model compares reasonably well to Holocene peat data. We have used this model to investigate the dynamics of atmospheric CO2 in the Holocene and two other late Quaternary interglacials, namely the Eemian, which is interesting due to its warmth, and Marine Isotope Stage 11 (MIS11), which is the longest interglacial during the last 500ka. We will also present model results of peatland extent and carbon accumulation for these interglacials. We will discuss model shortcomings and knowledge gaps currently preventing an application of the model to full glacial-interglacial cycles.

  3. Unusual Polar Conditions in Solar Cycle 24 and Their Implications for Cycle 25

    NASA Astrophysics Data System (ADS)

    Gopalswamy, Nat; Yashiro, Seiji; Akiyama, Sachiko

    2016-05-01

    We report on the prolonged solar-maximum conditions until late 2015 at the north-polar region of the Sun indicated by the occurrence of high-latitude prominence eruptions (PEs) and microwave brightness temperature close to the quiet-Sun level. These two aspects of solar activity indicate that the polarity reversal was completed by mid-2014 in the south and late 2015 in the north. The microwave brightness in the south-polar region has increased to a level exceeding the level of the Cycle 23/24 minimum, but just started to increase in the north. The north–south asymmetry in the polarity reversal has switched from that in Cycle 23. These observations lead us to the hypothesis that the onset of Cycle 25 in the northern hemisphere is likely to be delayed with respect to that in the southern hemisphere. We find that the unusual condition in the north is a direct consequence of the arrival of poleward surges of opposite polarity from the active region belt. We also find that multiple rush-to-the-pole episodes were indicated by the PE locations that lined up at the boundary between opposite-polarity surges. The high-latitude PEs occurred in the boundary between the incumbent polar flux and the insurgent flux of opposite polarity.

  4. Structural Anisotropy in Polar Fluids Subjected to Periodic Boundary Conditions

    PubMed Central

    2011-01-01

    A heuristic model based on dielectric continuum theory for the long-range solvation free energy of a dipolar system possessing periodic boundary conditions (PBCs) is presented. The predictions of the model are compared to simulation results for Stockmayer fluids simulated using three different cell geometries. The boundary effects induced by the PBCs are shown to lead to anisotropies in the apparent dielectric constant and the long-range solvation free energy of as much as 50%. However, the sum of all of the anisotropic energy contributions yields a value that is very close to the isotropic one derived from dielectric continuum theory, leading to a total system energy close to the dielectric value. It is finally shown that the leading-order contribution to the energetic and structural anisotropy is significantly smaller in the noncubic simulation cell geometries compared to when using a cubic simulation cell. PMID:22303290

  5. Evidence from the Seychelles of Last Interglacial Sea Level Oscillations

    NASA Astrophysics Data System (ADS)

    Vyverberg, K.; Dutton, A.; Dechnik, B.; Webster, J.; Zwartz, D.

    2014-12-01

    Several studies indicate that sea level oscillated during Marine Isotope Stage (MIS) 5e, but the details of these scenarios, including the number of sea level oscillations, are still debated. We lack a detailed understanding of the sensitivity of the large polar ice sheets to changes in temperature that could result in eustatic sea level oscillations. Because the Seychelles are located far from the margins of the Last Glacial Maximum northern hemisphere ice sheets, they have not been subjected to glacial isostatic adjustment, and have been tectonically stable since the Last Interglacial period; therefore, they provide a robust record of eustatic sea level during MIS 5e. All of the outcrops we examined contain unconformities and/or sharp transitions between facies, though the nature of these boundaries varies between sites. In some outcrops we observed a hardground comprising fine-grained, mollusc-rich sediment layer between distinct generations of in situ coralgal framework. In one outcrop, this succession was observed twice, where two generations of reef growth were each capped by a strongly indurated fine-grained, mollusc-rich sediment layer. At the site with the greatest vertical extent of outcrop, there is a marked difference in the taxonomic composition of the coral community above and below an unconformable surface, but the indurated fine-grained, sediment layer observed elsewhere was absent. Most of the other outcrops we studied contained a common succession of facies from in situ reef units overlain by cemented coral rubble. In two dated outcrops, the age of corals above and below the rubble layer are the same age. The hardgrounds and rubble layers may represent ephemeral exposure of the reef units during two drops in sea level. The inference of multiple meter-scale oscillations during the MIS 5e highstand indicates a more dynamic cryosphere than the present interglacial, although the climatic threshold for more volatile polar ice sheets is not yet clear.

  6. Glacial legacies on interglacial vegetation at the Pliocene-Pleistocene transition in NE Asia.

    PubMed

    Herzschuh, Ulrike; Birks, H John B; Laepple, Thomas; Andreev, Andrei; Melles, Martin; Brigham-Grette, Julie

    2016-01-01

    Broad-scale climate control of vegetation is widely assumed. Vegetation-climate lags are generally thought to have lasted no more than a few centuries. Here our palaeoecological study challenges this concept over glacial-interglacial timescales. Through multivariate analyses of pollen assemblages from Lake El'gygytgyn, Russian Far East and other data we show that interglacial vegetation during the Plio-Pleistocene transition mainly reflects conditions of the preceding glacial instead of contemporary interglacial climate. Vegetation-climate disequilibrium may persist for several millennia, related to the combined effects of permafrost persistence, distant glacial refugia and fire. In contrast, no effects from the preceding interglacial on glacial vegetation are detected. We propose that disequilibrium was stronger during the Plio-Pleistocene transition than during the Mid-Pliocene Warm Period when, in addition to climate, herbivory was important. By analogy to the past, we suggest today's widespread larch ecosystem on permafrost is not in climate equilibrium. Vegetation-based reconstructions of interglacial climates used to assess atmospheric CO2-temperature relationships may thus yield misleading simulations of past global climate sensitivity. PMID:27338025

  7. Glacial legacies on interglacial vegetation at the Pliocene-Pleistocene transition in NE Asia

    NASA Astrophysics Data System (ADS)

    Herzschuh, Ulrike; Birks, H. John B.; Laepple, Thomas; Andreev, Andrei; Melles, Martin; Brigham-Grette, Julie

    2016-06-01

    Broad-scale climate control of vegetation is widely assumed. Vegetation-climate lags are generally thought to have lasted no more than a few centuries. Here our palaeoecological study challenges this concept over glacial-interglacial timescales. Through multivariate analyses of pollen assemblages from Lake El'gygytgyn, Russian Far East and other data we show that interglacial vegetation during the Plio-Pleistocene transition mainly reflects conditions of the preceding glacial instead of contemporary interglacial climate. Vegetation-climate disequilibrium may persist for several millennia, related to the combined effects of permafrost persistence, distant glacial refugia and fire. In contrast, no effects from the preceding interglacial on glacial vegetation are detected. We propose that disequilibrium was stronger during the Plio-Pleistocene transition than during the Mid-Pliocene Warm Period when, in addition to climate, herbivory was important. By analogy to the past, we suggest today's widespread larch ecosystem on permafrost is not in climate equilibrium. Vegetation-based reconstructions of interglacial climates used to assess atmospheric CO2-temperature relationships may thus yield misleading simulations of past global climate sensitivity.

  8. Glacial legacies on interglacial vegetation at the Pliocene-Pleistocene transition in NE Asia

    PubMed Central

    Herzschuh, Ulrike; Birks, H. John B.; Laepple, Thomas; Andreev, Andrei; Melles, Martin; Brigham-Grette, Julie

    2016-01-01

    Broad-scale climate control of vegetation is widely assumed. Vegetation-climate lags are generally thought to have lasted no more than a few centuries. Here our palaeoecological study challenges this concept over glacial–interglacial timescales. Through multivariate analyses of pollen assemblages from Lake El'gygytgyn, Russian Far East and other data we show that interglacial vegetation during the Plio-Pleistocene transition mainly reflects conditions of the preceding glacial instead of contemporary interglacial climate. Vegetation–climate disequilibrium may persist for several millennia, related to the combined effects of permafrost persistence, distant glacial refugia and fire. In contrast, no effects from the preceding interglacial on glacial vegetation are detected. We propose that disequilibrium was stronger during the Plio-Pleistocene transition than during the Mid-Pliocene Warm Period when, in addition to climate, herbivory was important. By analogy to the past, we suggest today's widespread larch ecosystem on permafrost is not in climate equilibrium. Vegetation-based reconstructions of interglacial climates used to assess atmospheric CO2–temperature relationships may thus yield misleading simulations of past global climate sensitivity. PMID:27338025

  9. Transient modulation during different polarity states of the heliosphere: Solar maximium condition

    NASA Astrophysics Data System (ADS)

    Badruddin, B.

    TRANSIENT MODULATION DURING DIFFERENT POLARITY STATES OF THE HELIOSPHERE: SOLAR MAXIMUM CONDITION Badruddin Department of Physics, Aligarh Muslim University, Aligarh-202002, India E-mail:badr_phys@rediffmail.com/Fax: +91-0571-701001 We have studied the short-term decreases in cosmic ray intensity due to transient events in the heliosphere related to mass ejections from the sun during solar maximum periods with different heliospheric magnetic field polarities. Pressure corrected hourly neutron monitor data have been used as a measure of cosmic ray intensity. Method of superposed epoch analysis has been applied. As the direction of the particle drift depends upon the polarity of the heliospheric magnetic field and sign of the particle charge, the average profile of the cosmic ray decreases, due to transient heliospheric events, is obtained separately during different polarity states of the heliosphere. Simultaneous analysis of solar wind parameters is also done. The results are compared with model predictions with/without particle drifts.

  10. Tropical Atlantic temperature seasonality at the end of the last interglacial

    NASA Astrophysics Data System (ADS)

    Felis, Thomas; Giry, Cyril; Scholz, Denis; Lohmann, Gerrit; Pfeiffer, Madlene; Pätzold, Jürgen; Kölling, Martin; Scheffers, Sander R.

    2015-04-01

    The end of the last interglacial period, ~118 kyr ago, was characterized by substantial ocean circulation and climate perturbations resulting from instabilities of polar ice sheets. It has been suggested that these perturbations at the end of the last interglacial are crucial for a better understanding of future climate change. The seasonal temperature changes of the tropical ocean, however, which play an important role in seasonal climate extremes such as hurricanes, floods and droughts at the present day, are not well known for this period that led into the last glacial. Here we present a monthly resolved snapshot of reconstructed sea surface temperature in the tropical North Atlantic Ocean for 117.7 ± 0.8 kyr ago, using coral Sr/Ca and δ18O records in a precisely 230Th/U dated shallow-water fossil coral recovered from the southern Caribbean (Bonaire). We find that temperature seasonality was similar to today, which is consistent with the orbital insolation forcing. Our coral records and simulations with a coupled atmosphere-ocean general circulation model (COSMOS) indicate an orbital control on temperature seasonality in the tropical North Atlantic at the end of the last interglacial, despite the large-scale perturbations of ocean circulation and climate during this period, and suggest that temperature seasonality of the tropical surface ocean is controlled mainly by orbital insolation changes during interglacials.

  11. Regional differences in interglacial climate expression: A revisit to MIS 5e

    NASA Astrophysics Data System (ADS)

    Bauch, H. A.

    2015-12-01

    Reconstructions of air and surface ocean temperatures of the Eemian interglacial (MIS5e) often infer higher values than those of the Holocene, with a recently estimated global sea level 6-9m meters above the present highstand. Many a study also have reported on Eemian climate instability with respect to both variability in temperatures and sea level. These variabilities are often explained by AMOC changes and by invoking massive bi-polar ice sheet losses. In spite of recent sea-level compilation studies on such fluctuations during the last interglacial using coral evidence, the questions remain how, where, and, notably, when could a rapid ice growth have occurred during the otherwise so warm but relatively short Eemian full-interglacial period? Ocean field data now indicate a relatively cool polar North Atlantic for a substantial part of the post-deglacial (T2) interval, whereas in the subpolar region ocean temperature peaked directly after T2 together with high insolation. Thus, based on circumstantial evidence significant glacier ice must have remained at sea-level along the polar periphery for rather long. In addition with other proxy data the overall sequence of events would therefore dictate a late global sea-level highstand during MIS5e.

  12. Novel robust skylight compass method based on full-sky polarization imaging under harsh conditions.

    PubMed

    Tang, Jun; Zhang, Nan; Li, Dalin; Wang, Fei; Zhang, Binzhen; Wang, Chenguang; Shen, Chong; Ren, Jianbin; Xue, Chenyang; Liu, Jun

    2016-07-11

    A novel method based on Pulse Coupled Neural Network(PCNN) algorithm for the highly accurate and robust compass information calculation from the polarized skylight imaging is proposed,which showed good accuracy and reliability especially under cloudy weather,surrounding shielding and moon light. The degree of polarization (DOP) combined with the angle of polarization (AOP), calculated from the full sky polarization image, were used for the compass information caculation. Due to the high sensitivity to the environments, DOP was used to judge the destruction of polarized information using the PCNN algorithm. Only areas with high accuracy of AOP were kept after the DOP PCNN filtering, thereby greatly increasing the compass accuracy and robustness. From the experimental results, it was shown that the compass accuracy was 0.1805° under clear weather. This method was also proven to be applicable under conditions of shielding by clouds, trees and buildings, with a compass accuracy better than 1°. With weak polarization information sources, such as moonlight, this method was shown experimentally to have an accuracy of 0.878°. PMID:27410853

  13. A tale of two polar bear populations: Ice habitat, harvest, and body condition

    USGS Publications Warehouse

    Rode, K.D.; Peacock, E.; Taylor, M.; Stirling, I.; Born, E.W.; Laidre, K.L.; Wiig, O.

    2012-01-01

    One of the primary mechanisms by which sea ice loss is expected to affect polar bears is via reduced body condition and growth resulting from reduced access to prey. To date, negative effects of sea ice loss have been documented for two of 19 recognized populations. Effects of sea ice loss on other polar bear populations that differ in harvest rate, population density, and/or feeding ecology have been assumed, but empirical support, especially quantitative data on population size, demography, and/or body condition spanning two or more decades, have been lacking. We examined trends in body condition metrics of captured bears and relationships with summertime ice concentration between 1977 and 2010 for the Baffin Bay (BB) and Davis Strait (DS) polar bear populations. Polar bears in these regions occupy areas with annual sea ice that has decreased markedly starting in the 1990s. Despite differences in harvest rate, population density, sea ice concentration, and prey base, polar bears in both populations exhibited positive relationships between body condition and summertime sea ice cover during the recent period of sea ice decline. Furthermore, females and cubs exhibited relationships with sea ice that were not apparent during the earlier period (1977-1990s) when sea ice loss did not occur. We suggest that declining body condition in BB may be a result of recent declines in sea ice habitat. In DS, high population density and/or sea ice loss, may be responsible for the declines in body condition. ?? 2011 The Society of Population Ecology and Springer.

  14. Increased land use by Chukchi Sea polar bears in relation to changing sea ice conditions

    USGS Publications Warehouse

    Rode, Karyn D.; Wilson, Ryan R.; Regehr, Eric V.; St. Martin, Michelle; Douglas, David; Olson, Jay

    2015-01-01

    Recent observations suggest that polar bears (Ursus maritimus) are increasingly using land habitats in some parts of their range, where they have minimal access to their preferred prey, likely in response to loss of their sea ice habitat associated with climatic warming. We used location data from female polar bears fit with satellite radio collars to compare land use patterns in the Chukchi Sea between two periods (1986–1995 and 2008–2013) when substantial summer sea-ice loss occurred. In both time periods, polar bears predominantly occupied sea-ice, although land was used during the summer sea-ice retreat and during the winter for maternal denning. However, the proportion of bears on land for > 7 days between August and October increased between the two periods from 20.0% to 38.9%, and the average duration on land increased by 30 days. The majority of bears that used land in the summer and for denning came to Wrangel and Herald Islands (Russia), highlighting the importance of these northernmost land habitats to Chukchi Sea polar bears. Where bears summered and denned, and how long they spent there, was related to the timing and duration of sea ice retreat. Our results are consistent with other studies supporting increased land use as a common response of polar bears to sea-ice loss. Implications of increased land use for Chukchi Sea polar bears are unclear, because a recent study observed no change in body condition or reproductive indices between the two periods considered here. This result suggests that the ecology of this region may provide a degree of resilience to sea ice loss. However, projections of continued sea ice loss suggest that polar bears in the Chukchi Sea and other parts of the Arctic may increasingly use land habitats in the future, which has the potential to increase nutritional stress and human-polar bear interactions.

  15. Increased Land Use by Chukchi Sea Polar Bears in Relation to Changing Sea Ice Conditions.

    PubMed

    Rode, Karyn D; Wilson, Ryan R; Regehr, Eric V; St Martin, Michelle; Douglas, David C; Olson, Jay

    2015-01-01

    Recent observations suggest that polar bears (Ursus maritimus) are increasingly using land habitats in some parts of their range, where they have minimal access to their preferred prey, likely in response to loss of their sea ice habitat associated with climatic warming. We used location data from female polar bears fit with satellite radio collars to compare land use patterns in the Chukchi Sea between two periods (1986-1995 and 2008-2013) when substantial summer sea-ice loss occurred. In both time periods, polar bears predominantly occupied sea-ice, although land was used during the summer sea-ice retreat and during the winter for maternal denning. However, the proportion of bears on land for > 7 days between August and October increased between the two periods from 20.0% to 38.9%, and the average duration on land increased by 30 days. The majority of bears that used land in the summer and for denning came to Wrangel and Herald Islands (Russia), highlighting the importance of these northernmost land habitats to Chukchi Sea polar bears. Where bears summered and denned, and how long they spent there, was related to the timing and duration of sea ice retreat. Our results are consistent with other studies supporting increased land use as a common response of polar bears to sea-ice loss. Implications of increased land use for Chukchi Sea polar bears are unclear, because a recent study observed no change in body condition or reproductive indices between the two periods considered here. This result suggests that the ecology of this region may provide a degree of resilience to sea ice loss. However, projections of continued sea ice loss suggest that polar bears in the Chukchi Sea and other parts of the Arctic may increasingly use land habitats in the future, which has the potential to increase nutritional stress and human-polar bear interactions. PMID:26580809

  16. Increased Land Use by Chukchi Sea Polar Bears in Relation to Changing Sea Ice Conditions

    PubMed Central

    Rode, Karyn D.; Wilson, Ryan R.; Regehr, Eric V.; St. Martin, Michelle; Douglas, David C.; Olson, Jay

    2015-01-01

    Recent observations suggest that polar bears (Ursus maritimus) are increasingly using land habitats in some parts of their range, where they have minimal access to their preferred prey, likely in response to loss of their sea ice habitat associated with climatic warming. We used location data from female polar bears fit with satellite radio collars to compare land use patterns in the Chukchi Sea between two periods (1986–1995 and 2008–2013) when substantial summer sea-ice loss occurred. In both time periods, polar bears predominantly occupied sea-ice, although land was used during the summer sea-ice retreat and during the winter for maternal denning. However, the proportion of bears on land for > 7 days between August and October increased between the two periods from 20.0% to 38.9%, and the average duration on land increased by 30 days. The majority of bears that used land in the summer and for denning came to Wrangel and Herald Islands (Russia), highlighting the importance of these northernmost land habitats to Chukchi Sea polar bears. Where bears summered and denned, and how long they spent there, was related to the timing and duration of sea ice retreat. Our results are consistent with other studies supporting increased land use as a common response of polar bears to sea-ice loss. Implications of increased land use for Chukchi Sea polar bears are unclear, because a recent study observed no change in body condition or reproductive indices between the two periods considered here. This result suggests that the ecology of this region may provide a degree of resilience to sea ice loss. However, projections of continued sea ice loss suggest that polar bears in the Chukchi Sea and other parts of the Arctic may increasingly use land habitats in the future, which has the potential to increase nutritional stress and human-polar bear interactions. PMID:26580809

  17. Auxin polar transport in arabidopsis under simulated microgravity conditions - relevance to growth and development

    NASA Astrophysics Data System (ADS)

    Miyamoto, K.; Oka, M.; Yamamoto, R.; Masuda, Y.; Hoson, T.; Kamisaka, S.; Ueda, J.

    1999-01-01

    Activity of auxin polar transport in inflorescence axes of Arabidopsis thaliana grown under simulated microgravity conditions was studied in relation to the growth and development. Seeds were germinated and allowed to grow on an agar medium in test tubes on a horizontal clinostat. Horizontal clinostat rotation substantially reduced the growth of inflorescence axes and the productivity of seeds of Arabidopsis thaliana (ecotypes Landsberg erecta and Columbia), although it little affected seed germination, development of rosette leaves and flowering. The activity of auxin polar transport in inflorescence axes decreased when Arabidopsis plants were grown on a horizontal clinostat from germination stage, being ca. 60% of 1 g control. On the other hand, the auxin polar transport in inflorescence axes of Arabidopsis grown in 1 g conditions was not affected when the segments were exposed to various gravistimuli, including 3-dimensional clinorotation, during transport experiments. Pin-formed mutant of Arabidopsis, having a unique structure of the inflorescence axis with no flower and extremely low levels of the activity of auxin polar transport in inflorescence axes and endogenous auxin, did not continue its vegetative growth under clinostat rotation. These facts suggest that the development of the system of auxin polar transport in Arabidopsis is affected by microgravity, resulting in the inhibition of growth and development, especially during reproductive growth.

  18. Polarity-consistent excitation amplitude imaging condition for elastic reverse time migration

    NASA Astrophysics Data System (ADS)

    Du, Qizhen; Zhang, Mingqiang; Gong, Xufei; Chen, Xiaoran

    2015-02-01

    Imaging conditions can not only affect the computational efficiency and storage cost of reverse time migration (RTM) but determine the quality of the final migrated images. This paper extends the idea of the well amplitude-preserved and highly-efficient excitation amplitude imaging condition from acoustic RTM to elastic RTM. For elastic RTM, the maximum amplitude of the separated P-wave and the corresponding image time of each grid point are saved during the forward modeling of the source wavefield and then PP and PS images are obtained by dividing the separated P- and S-waves of the backward-propagated receiver wavefield by the precomputed P-waves at each grid point that satisfies the image time. However, polarity reversals of the PS image will cause destructive interference when the stacked image is needed. In order to solve this problem, we propose the polarity-consistent excitation amplitude imaging condition by combining the excitation amplitude imaging condition with a shot-domain polarity reversal correction method. Then we provide the detailed realization process of this imaging condition in elastic RTM. By utilizing the relatively stable and well amplitude-preserved source-normalized cross-correlation imaging condition as a comparison, we testify to the feasibility and validity of the proposed imaging condition in the aspects of amplitude preservation property, imaging capability of complex structures, storage cost and computational efficiency. Considering the balance between the efficiency and image quality, the polarity-consistent excitation amplitude imaging condition can be a good choice for elastic RTM.

  19. Polarized single-mode condition for SOI rib waveguide with large cross section

    NASA Astrophysics Data System (ADS)

    Yuan, Dengpeng; Dong, Ying; Liu, Yujin; Li, Tianjian; Zhang, Xudong; Tan, Yushan

    2015-08-01

    In this paper the single mode condition of silicon-on-insulator (SOI) rib waveguide with large cross section is investigated based on the effective index method (EIM) by using numerical computation and analytical derivation with the consideration of the polarization effects. A polarized single-mode condition for SOI rib waveguide with large cross section is presented, the results from analytical derivation are highly concordant with that from numerical computation. For the vertical single-mode condition, the deviations between HE and EH modes correlate oppositely with the total rib height of rib waveguide, and the critical rib height ratio gradually approaches but never equals to 0.5 with the increase of the total rib height. There, HE mode and EH mode are commonly known as quasi-transverse-electric (TE) mode and quasi-transverse-magnetic (TM) mode respectively. The deviation of the critical rib width between HE and EH modes for the lateral single-mode condition is relatively small, which is a function of the rib height ratio but irrelevant to the total rib height for the specified index profile. The fact that the total rib height, index profile, and polarization of modes have effects on the single-mode condition of SOI rib waveguide with large cross section was demonstrated in this work, which was not discussed in the previous works. The results in this work can give guidance to design, simulation and fabrication of SOI rib waveguide with large cross section in practical applications.

  20. Cross-latitudinal climate teleconnections during the last interglacial

    NASA Astrophysics Data System (ADS)

    Bauch, H. A.; Kandiano, E.; Fahl, K.

    2014-12-01

    A series of climate interruptions have been noted around the last warm period (MIS5e). Some of these are particularly conspicuous and occurred during both the deglacial as well as the glacial onset. These events are often associated with iceberg/meltwater charges into the subpolar/polar North Atlantic. A new multiproxy analysis using planktic foraminiferal abundances and SSTs, abundances of alkenone compounds and alkenone SSTs, and stable O/C isotope measurements was performed for Site 975 (Balearic Basin; Western Mediterranean). Samples covered the time from late MIS 6 to early MIS 5d with emphasis on the climate progression of the last interglacial period. A number of abrupt climate changes related to alternating influence of northern nutrient rich and southern oligotrophic water masses was revealed. Among the climate fluctuations, North Atlantic events Heinrich 11 as well as cooling events C27 - C23 could all be identified. However, in comparison to the eastern North Atlantic mid-latitude region, at Site 975 events C27 and C26 seem to be significantly more pronounced. This fact, along with evidence of a two-phase climate optimum with the SST maximum reached during its later phase, implies close similarity in climate dynamics between the Western Mediterranean and the polar Nordic Seas. It is therefore proposed that the postglacial marine development in the Nordic Seas - for instance, due to presence of winter sea ice - had a strong impact on the western Mediterranean climate via meridional atmospheric circulation patterns and temperature gradients.

  1. Tropical Atlantic temperature seasonality at the end of the last interglacial.

    PubMed

    Felis, Thomas; Giry, Cyril; Scholz, Denis; Lohmann, Gerrit; Pfeiffer, Madlene; Pätzold, Jürgen; Kölling, Martin; Scheffers, Sander R

    2015-01-01

    The end of the last interglacial period, ~118 kyr ago, was characterized by substantial ocean circulation and climate perturbations resulting from instabilities of polar ice sheets. These perturbations are crucial for a better understanding of future climate change. The seasonal temperature changes of the tropical ocean, however, which play an important role in seasonal climate extremes such as hurricanes, floods and droughts at the present day, are not well known for this period that led into the last glacial. Here we present a monthly resolved snapshot of reconstructed sea surface temperature in the tropical North Atlantic Ocean for 117.7±0.8 kyr ago, using coral Sr/Ca and δ(18)O records. We find that temperature seasonality was similar to today, which is consistent with the orbital insolation forcing. Our coral and climate model results suggest that temperature seasonality of the tropical surface ocean is controlled mainly by orbital insolation changes during interglacials. PMID:25609544

  2. Tropical Atlantic temperature seasonality at the end of the last interglacial

    PubMed Central

    Felis, Thomas; Giry, Cyril; Scholz, Denis; Lohmann, Gerrit; Pfeiffer, Madlene; Pätzold, Jürgen; Kölling, Martin; Scheffers, Sander R.

    2015-01-01

    The end of the last interglacial period, ~118 kyr ago, was characterized by substantial ocean circulation and climate perturbations resulting from instabilities of polar ice sheets. These perturbations are crucial for a better understanding of future climate change. The seasonal temperature changes of the tropical ocean, however, which play an important role in seasonal climate extremes such as hurricanes, floods and droughts at the present day, are not well known for this period that led into the last glacial. Here we present a monthly resolved snapshot of reconstructed sea surface temperature in the tropical North Atlantic Ocean for 117.7±0.8 kyr ago, using coral Sr/Ca and δ18O records. We find that temperature seasonality was similar to today, which is consistent with the orbital insolation forcing. Our coral and climate model results suggest that temperature seasonality of the tropical surface ocean is controlled mainly by orbital insolation changes during interglacials. PMID:25609544

  3. Polar Bear Conservation Status in Relation to Projected Sea-ice Conditions

    NASA Astrophysics Data System (ADS)

    Regehr, E. V.

    2015-12-01

    The status of the world's 19 subpopulations of polar bears (Ursus maritimus) varies as a function of sea-ice conditions, ecology, management, and other factors. Previous methods to project the response of polar bears to loss of Arctic sea ice—the primary threat to the species—include expert opinion surveys, Bayesian Networks providing qualitative stressor assessments, and subpopulations-specific demographic analyses. Here, we evaluated the global conservation status of polar bears using a data-based sensitivity analysis. First, we estimated generation length for subpopulations with available data (n=11). Second, we developed standardized sea-ice metrics representing habitat availability. Third, we projected global population size under alternative assumptions for relationships between sea ice and subpopulation abundance. Estimated generation length (median = 11.4 years; 95%CI = 9.8 to 13.6) and sea-ice change (median = loss of 1.26 ice-covered days per year; 95%CI = 0.70 to 3.37) varied across subpopulations. Assuming a one-to-one proportional relationship between sea ice and abundance, the median percent change in global population size over three polar bear generations was -30% (95%CI = -35% to -25%). Assuming a linear relationship between sea ice and normalized estimates of subpopulation abundance, median percent change was -4% (95% CI = -62% to +50%) or -43% (95% CI = -76% to -20%), depending on how subpopulations were grouped and how inference was extended from relatively well-studied subpopulations (n=7) to those with little or no data. Our findings suggest the potential for large reductions in polar bear numbers over the next three polar bear generations if sea-ice loss due to climate change continues as forecasted.

  4. Phytoplankton communities of polar regions--Diversity depending on environmental conditions and chemical anthropopressure.

    PubMed

    Kosek, Klaudia; Polkowska, Żaneta; Żyszka, Beata; Lipok, Jacek

    2016-04-15

    The polar regions (Arctic and Antarctic) constitute up to 14% of the biosphere and offer some of the coldest and most arid Earth's environments. Nevertheless several oxygenic phototrophs including some higher plants, mosses, lichens, various algal groups and cyanobacteria, survive that harsh climate and create the base of the trophic relationships in fragile ecosystems of polar environments. Ecosystems in polar regions are characterized by low primary productivity and slow growth rates, therefore they are more vulnerable to disturbance, than those in temperate regions. From this reason, chemical contaminants influencing the growth of photoautotrophic producers might induce serious disorders in the integrity of polar ecosystems. However, for a long time these areas were believed to be free of chemical contamination, and relatively protected from widespread anthropogenic pressure, due their remoteness and extreme climate conditions. Nowadays, there is a growing amount of data that prove that xenobiotics are transported thousands of kilometers by the air and ocean currents and then they are deposed in colder regions and accumulate in many environments, including the habitats of marine and freshwater cyanobacteria. Cyanobacteria (blue green algae), as a natural part of phytoplankton assemblages, are globally distributed, but in high polar ecosystems they represent the dominant primary producers. These microorganisms are continuously exposed to various concentration levels of the compounds that are present in their habitats and act as nourishment or the factors influencing the growth and development of cyanobacteria in other way. The most common group of contaminants in Arctic and Antarctic are persistent organic pollutants (POPs), characterized by durability and resistance to degradation. It is important to determine their concentrations in all phytoplankton species cells and in their environment to get to know the possibility of contaminants to transfer to higher

  5. A GCM comparison of Pleistocene super-interglacial periods in relation to Lake El'gygytgyn, NE Arctic Russia

    NASA Astrophysics Data System (ADS)

    Coletti, A. J.; DeConto, R. M.; Brigham-Grette, J.; Melles, M.

    2015-07-01

    Until now, the lack of time-continuous, terrestrial paleoenvironmental data from the Pleistocene Arctic has made model simulations of past interglacials difficult to assess. Here, we compare climate simulations of four warm interglacials at Marine Isotope Stages (MISs) 1 (9 ka), 5e (127 ka), 11c (409 ka) and 31 (1072 ka) with new proxy climate data recovered from Lake El'gygytgyn, NE Russia. Climate reconstructions of the mean temperature of the warmest month (MTWM) indicate conditions up to 0.4, 2.1, 0.5 and 3.1 °C warmer than today during MIS 1, 5e, 11c and 31, respectively. While the climate model captures much of the observed warming during each interglacial, largely in response to boreal summer (JJA) orbital forcing, the extraordinary warmth of MIS 11c compared to the other interglacials in the Lake El'gygytgyn temperature proxy reconstructions remains difficult to explain. To deconvolve the contribution of multiple influences on interglacial warming at Lake El'gygytgyn, we isolated the influence of vegetation, sea ice and circum-Arctic land ice feedbacks on the modeled climate of the Beringian interior. Simulations accounting for climate-vegetation-land-surface feedbacks during all four interglacials show expanding boreal forest cover with increasing summer insolation intensity. A deglaciated Greenland is shown to have a minimal effect on northeast Asian temperature during the warmth of stages 11c and 31 (Melles et al., 2012). A prescribed enhancement of oceanic heat transport into the Arctic Ocean does have some effect on Lake El'gygytgyn's regional climate, but the exceptional warmth of MIS l1c remains enigmatic compared to the modest orbital and greenhouse gas forcing during that interglacial.

  6. High herbivore density associated with vegetation diversity in interglacial ecosystems

    PubMed Central

    Sandom, Christopher J.; Ejrnæs, Rasmus; Hansen, Morten D. D.; Svenning, Jens-Christian

    2014-01-01

    The impact of large herbivores on ecosystems before modern human activities is an open question in ecology and conservation. For Europe, the controversial wood–pasture hypothesis posits that grazing by wild large herbivores supported a dynamic mosaic of vegetation structures at the landscape scale under temperate conditions before agriculture. The contrasting position suggests that European temperate vegetation was primarily closed forest with relatively small open areas, at most impacted locally by large herbivores. Given the role of modern humans in the world-wide decimations of megafauna during the late Quaternary, to resolve this debate it is necessary to understand herbivore–vegetation interactions before these losses. Here, a synthetic analysis of beetle fossils from Great Britain shows that beetles associated with herbivore dung were better represented during the Last Interglacial (132,000–110,000 y B.P., before modern human arrival) than in the early Holocene (10,000–5,000 y B.P.). Furthermore, beetle assemblages indicate closed and partially closed forest in the early Holocene but a greater mixture of semiopen vegetation and forest in the Last Interglacial. Hence, abundant and diverse large herbivores appear to have been associated with high structural diversity of vegetation before the megafauna extinctions at the end of the Pleistocene. After these losses and in the presence of modern humans, large herbivores generally were less abundant, and closed woodland was more prevalent in the early Holocene. Our findings point to the importance of the formerly rich fauna of large herbivores in sustaining structurally diverse vegetation in the temperate forest biome and provide support for recent moves toward rewilding-based conservation management. PMID:24591633

  7. Interglacial geomorphic dynamics during the Quaternary: Does glacial erosion dominates interglacial adjustment?

    NASA Astrophysics Data System (ADS)

    Hoffmann, T.; Johnson, E. A.

    2012-04-01

    High mountains are generally sculptured by glacial erosion, which resulted in the formation of glacial cirques and U-shaped valleys with strongly over-steepened hillslopes and widespread glacial deposits. The abundance of glacial (erosion and depositional) landforms in high mountains has been attributed to very effective glacial erosion and sediment transfer. Furthermore, it has been argued that geomorphic activity remains increased after the retreat of valley glaciers at the transition between glacial and interglacial periods. Thus, geologists and geomorphologist generally tend to look at glaciers as geomorphic agents that strongly enhance erosion and sediment fluxes. An important aspect of glacial erosion is the affect of glacial erosion on the decoupling of headwater basins from main river systems. Strong glacial erosion results in flat valley bottoms and glacial over-deepenings, with reduced transport capacities of the interglacial rivers draining formerly glaciated headwaters. While this effect has been described earlier, quantitative estimates of the degree of decoupling of glacial headwaters are missing. In this paper, we will present evidences of decreased sediment yields in glacial headwaters, which results from the transition of glacial to peri-/paraglacial process regimes. These evidences are derived from geomorphomteric analysis, numerical sediment flux models and sediment budget approaches, which were conducted in the Kananaskis Valley (Canadian Rocky Mountains). Furthermore, we will compare the duration of glacial and interglacial periods during the Quaternary and the calculated interglacial erosion rates with glacial rates. We discuss the wider implications of the results with respect to the landform evolution of glaciated mountains during the Quaternary.

  8. Pre-glacial and interglacial pollen records over the last 3 Ma from northwest Canada: Why do Holocene forests differ from those of previous interglaciations?

    NASA Astrophysics Data System (ADS)

    Schweger, Charles; Froese, Duane; White, James M.; Westgate, John A.

    2011-08-01

    We synthesize pollen spectra from eleven dated stratigraphic sections from central and northern Yukon. Palaeomagnetic and tephra dating indicates the earliest assemblages, representing closed canopy Pinus and Picea forest, are middle-late Pliocene age. More open forest conditions, indicated by increased Poaceae and with evidence of permafrost, are dated at ca 3 Ma. While Pinus pollen is abundant at 3 Ma, it is reduced in records after 2.6 Ma, and subsequent Pleistocene interglacial forest records are repeatedly dominated by Picea, along with Alnus and small but significant amounts of Abies. Surface sample comparisons indicate that Abies was more widespread and abundant in past interglaciations than at present and that Middle-Pleistocene Picea- Abies forest grew in the northern Yukon Porcupine Basin, 500 km beyond modern Abies limits. In contrast, Pinus, which occurs today in southern and central Yukon, was not a significant component of these Pleistocene interglacial forests. Late-Holocene pollen assemblages with rare Abies and high Pinus are the most distinct in the past 2.6 Ma. Possible factors driving Holocene difference are paleoclimate, paludification, changes in megafaunal herbivory and an unusual fire regime. Anthropogenic burning is a factor unique to the Holocene, and if it is shown to be important in this case, it would challenge our notion of what constitutes boreal wilderness.

  9. Automorphosis and auxin polar transport of etiolated pea seedlings under microgravity conditions.

    PubMed

    Hoshino, Tomoki; Miyamoto, Kensuke; Ueda, Junichi

    2004-11-01

    On STS-95 space experiment, etiolated pea (Pisum sativum L. cv. Alaska) seedlings showed automorphosis and activities of auxin polar transport in epicotyls were substantially suppressed. These results together with the fact that inhibitors of auxin polar transport induced automorphosis-like growth and development strongly suggested that there are close relationships between automorphosis and auxin polar transport in etiolated pea seedlings. In order to know how gravistimuli control auxin polar transport at molecular levels, we isolated novel cDNAs of PsPIN2 and PsAUX1 encoding putative auxin efflux and influx carriers from etiolated pea seedlings. Significantly high levels in homology were found on nucleotide and deduced amino acid sequences among PsPIN2, PsPIN1 (accession no. AY222857) and AtPINs, and between PsAUX1 and AtAUX1. Exogenously applied auxin substantially enhanced the expression of PsAUX1 and PsPIN2 as well as PsPIN1. Simulated microgravity conditions on a 3-dimensional clinostat remarkably increased gene expression of PsPIN1 and PsAUX1 in the hook and the 1st internode of pea epicotyls, while the increase of expression of PsPIN2 in both organs was not so much. These results suggest that PsPINs and PsAUX1 are auxin-inducible genes, and the expression of PsPINs and PsAUX1 is under the control of gravistimulation. A possible role of these genes in regulating auxin transport relevant to automorphosis of etiolated pea seedlings is also discussed. PMID:15858337

  10. A Millennial-Scale Reduction in Ventilation of the Deep South Atlantic During the Last Interglacial Period

    NASA Astrophysics Data System (ADS)

    Hayes, C. T.; Martinez-Garcia, A.; Hasenfratz, A. P.; Jaccard, S.; Hodell, D. A.; Sigman, D. M.; Haug, G. H.; Anderson, R. F.

    2014-12-01

    During the last interglacial period, global temperatures were ~2°C warmer than present and sea level was 6-8 m higher. Southern Ocean sediments from ODP Site 1094 reveal a spike in authigenic uranium 127,000 years ago, within the last interglacial, reflecting decreased oxygenation of deep water by Antarctic Bottom Water (AABW). Increased deep storage of respired carbon due to this circulation event may explain an observed decline in atmospheric CO2 at this time. Unlike ice age reductions in AABW, the interglacial stagnation event appears decoupled from open ocean conditions and may have resulted from coastal freshening due to mass loss from the Antarctic ice sheet. AABW reduction coincided with increased North Atlantic Deep Water (NADW) formation, and the subsequent reinvigoration in AABW coincided with reduced NADW formation. Alternation of deep water formation between the Antarctic and the North Atlantic, believed to characterize ice ages, apparently also occurs in warm climates.

  11. Glacial-interglacial variability in diatom abundance and valve size: Implications for Southern Ocean paleoceanography

    NASA Astrophysics Data System (ADS)

    Nair, Abhilash; Mohan, Rahul; Manoj, M. C.; Thamban, Meloth

    2015-10-01

    Antarctic sea ice extent along with Southern Ocean biological productivity varied considerably during glacial-interglacial periods, and both are known to have played a considerable role in regulating atmospheric CO2 variations in the past. Here we present data on diatom absolute abundance (valves/g of sediment) and size over the past ~ 42 ka B.P. and how they link to glacial-interglacial changes in Antarctic sea ice extent, Southern Ocean frontal systems, and aeolian dust flux. Our records of sea ice and permanent open ocean zone diatom abundances suggest a shift in the Antarctic winter sea ice limit and Polar Front respectively up to the modern-day Polar Frontal Zone during marine isotopic stages (MIS) 2 and late MIS 3. In addition to glacial shifts in the Polar Front, diatom assemblages also recorded a plausible northward shifts in Polar Front during few intervals of MIS 1. Glacial periods north of the Polar Front in the Indian sector of the Southern Ocean were characterized by higher total diatom abundance, larger Fragilariopsis kerguelensis apical length, and Thalassiosira lentiginosa radius. This is probably a consequence of (1) a northward expansion of the opal belt, a region characterized by high production and export of biogenic silica; (2) an increase in terrigenous input, via erosion of Crozet Islands; and (3) the alleviation of iron deficit by high input of Fe-bearing dust. The larger and highly silicified diatoms such as F. kerguelensis and T. lentiginosa may have mainly contributed in transporting biogenic silica and organic carbon to the seabed for the last 42 ka, in the northern Polar Frontal Zone of the Indian sector of the Southern Ocean.

  12. Pleistocene glacial/interglacial contrasts in the Labrador Sea prior and after the Mid-Brunhes transition

    NASA Astrophysics Data System (ADS)

    Hillaire-Marcel, Claude; de Vernal, Anne; Teboulle, Oury; Aubry, Aurélie; Fréchette, Bianca

    2016-04-01

    Isotopic, microfaunal and palynological records from the northern (Eirik Ridge) and southern (Orphan Knoll) Labrador Sea -LS- (Eirik Ridge and Orphan Knoll) are used to document paleoceanographic conditions in the basin during a few interglacials from MIS 31, to MIS 5e, with some specific attention to MIS 13, 11 and 5e. Most features, particularly oxygen isotope records in planktics highlight a major difference between the pre Mid-Brunhes (MB) and post-MB intervals (i.e, before MIS 11 and from MIS 11 to MIS 1), with the exception of MIS 7 showing features resembling those of the pre-MB interglacials. In a similar fashion, glacials from MIS 12 and later differ significantly from earlier ones by their more pronounced 18O-enrichments in planktic foraminifers, thus possibly larger continental ice volume. Another feature of interest concerning glacials is found in the relative abundance of reworked palynomorphs, in the Northern Labrador Sea record, during pre-MB glacials (MIS 12 and earlier) and during a short mid-MIS 7 glacial excursion. These reworked microfossils suggest significant ice streaming over Paleozoic outcrops either along the western Scandinavian Ice Sheet margin and/or in the Fram Strait area. Within interglacials, MIS 13 records large amplitude coolings, the presence of continental ice over NE Canada indicated by sporadic detrital carbonate-rich IRD-pulses. Evidence for the persistence of a relatively large interglacial Greenland Ice Sheet is found for post MIS 11 interglacials only. Finally, density conditions in surface water (calculated using paleo-SSTs and paleo-SSs from dinocysts), suggest that if convection with production of Labrador Sea Water (LSW), as observed since ca 7 ka BP, was unlikely during most interglacials (and notably MIS 5e), but very likely during MIS 11, due to relatively high salinity conditions at surface. A conclusion from this overview of t mid- to late Pleistocene glacial vs interglacial stages is that glacials were pre-conditioning

  13. Problem of the length of the current interglacial

    NASA Astrophysics Data System (ADS)

    Dergachev, V. A.; Raspopov, O. M.

    2013-12-01

    The climate during the past hundreds of thousands of years has been characterized by a rather distinct periodicity of about 100000 yr with brief warming periods (interglacials) lasting approximately 10000-12000 yr. Today, mankind is living in an interglacial period that began about 11 ka ago. In light of the discussion about global warming observed in recent decades, which advocates of an anthropogenic impact associate with emission of greenhouse gases due to combustion of fossil fuel, the question arises concerning the duration of the current interglacial. The data available on climate change and solar radiation on a time scale of the last millions of years are critically analyzed in this article and the problem of the length of the current interglacial is discussed.

  14. Formation of polar ionospheric tongue of ionization during minor geomagnetic disturbed conditions

    NASA Astrophysics Data System (ADS)

    Liu, Jing; Nakamura, Takuji; Liu, Libo; Wang, Wenbin; Balan, Nanan; Nishiyama, Takanori; Hairston, Marc R.; Thomas, E. G.

    2015-08-01

    Previous investigations of ionospheric storm-enhanced density (SED) and tongue of ionization (TOI) focused mostly on the behavior of TOI during intense geomagnetic storms. Little attention has been paid to the spatial and temporal variations of TOI during weak to moderate geomagnetic disturbed conditions. In this paper we investigate the source and development of TOI during a moderate geomagnetic storm on 14 October 2012. Multi-instrumental observations including GPS total electron content (TEC), Defense Meteorological Satellite Program (DMSP) in situ measured total ion concentration and ion drift velocity, SuperDARN measured polar ion convection patterns, and electron density profiles from the Poker Flat Incoherent Scatter Radar (PFISR) have been utilized in the current analysis. GPS TEC maps show salient TOI structures persisting for about 5 h over high latitudes of North America on 14 October 2012 in the later recovery phase of the storm when the magnitudes of IMF By and Bz were less than 5 nT. The PFISR electron density profiles indicate that the extra ionization for TEC enhancements mainly occurred in the topside ionosphere with no obvious changes in the bottomside ionosphere and vertical plasma drifts. Additionally, there were no signatures of penetration electric fields in the equatorial electrojet data and upward ion drifts at high latitudes. At the same time, strong subauroral polarization streams with ion drift speeds exceeding 2.5 km/s carried sunward fluxes and migrated toward lower latitudes for about 5° based on the DMSP cross-track drift measurements. Based on those measurements, we postulate that the combined effects of initial build-up of ionization at midlatitudes through daytime production of ionization and equatorward (or less poleward than normal daytime) neutral wind reducing downward diffusion along the inclined filed lines, and an expanded polar ion convection pattern and its associated horizontal plasma transport are important in the

  15. Formation of Polar Ionospheric Tongue of Ionization during Minor Geomagnetic Disturbed Conditions

    NASA Astrophysics Data System (ADS)

    Liu, J.; Wang, W.; Burns, A. G.; Yue, X.; Zhang, S.; Zhang, Y.

    2015-12-01

    Previous investigations of ionospheric storm-enhanced density (SED) and tongue of ionization (TOI) focused mostly on the behavior of TOI during intense geomagnetic storms. Little attention has been paid to the spatial and temporal variations of TOI during weak to moderate geomagnetic disturbed conditions. we investigate the source and development of TOI during a moderate geomagnetic storm on 14 October 2012.Multi-instrumental observations including GPS total electron content (TEC), Defense Meteorological SatelliteProgram(DMSP) in situ measured total ion concentration and ion drift velocity, SuperDARN measured polar ionconvection patterns, and electron density profiles from the Poker Flat Incoherent Scatter Radar (PFISR) have been utilized in the current analysis. GPS TEC maps show salient TOI structures persisting for about 5 h over high latitudes of North America on 14 October 2012 in the later recovery phase of the storm when the magnitudes of IMF By and Bz were less than 5 nT. The PFISR electron density profiles indicate that the extra ionization for TEC enhancements mainly occurred in the topside ionosphere with no obvious changes in the bottom side ionosphere and vertical plasma drifts. Additionally, there were no signatures of penetration electric fields in the equatorial electrojet data and upward ion drifts at high latitudes. At the same time, strong subauroral polarization streams with ion drift speeds exceeding 2.5 km/s carried sunward fluxes and migrated toward lower latitudes for about 5° based on the DMSP cross-track driftmeasurements. Based on those measurements,we postulate that the combined effects of initial build-up of ionization at midlatitudes through daytime production of ionization and equatorward (or less poleward than normal daytime) neutral wind reducing downward diffusion along the inclined filed lines, and an expanded polar ion convection pattern and its associated horizontal plasma transport are important in the formation of the TOI.

  16. Similarities and dissimilarities between the last two deglaciations and interglaciations in the North Atlantic region

    NASA Astrophysics Data System (ADS)

    Grimalt, Joan O.; Martrat, Belen; Jimenez-Amat, Patricia; Zahn, Rainer

    2014-05-01

    Sea surface temperatures (SSTs) recorded by alkenones and oxygen isotopes in the Alboran basin (cores ODP976, ODP977 and MD95-2043) are used here to describe the present interglaciation (PIG, initiated at 11.7 ka BP), the last interglaciation (LIG, onset approximately at 129 ka) and respective deglaciations at an unprecedented fine time resolution. Similarities and dissimilarities of the recorded climate progression are reviewed in comparison with ice cores and stalagmites. During deglaciations (perihelion aligned with NH summer solstice) organic rich layers were deposited, which are useful as reference. The SST trend during the PIG involved changes of about 2ºC (from 20ºC to 18ºC) but the trend was steeper than during the LIG which involved up to 5ºC change from the early interglaciation (23ºC) to immediately before the glacial inception (18ºC). Cooling events were observed during the last deglaciation at 17 ka, 14.8 ka and 11.7 ka. They were reminiscent of cooling events during the penultimate deglaciation at 136 ka, 132 ka and 129 ka, respectively. The cold spells which coeval with the Heinrich events described in the North Atlantic were observed. They included strong multi-decadal scale oscillations that were not observed in previous studies at lower resolution. The interglacial conditions showed a long term trend towards colder SSTs that was interrupted by warm periods (ca. from 8.2 ka to 5.3 ka for the PIG and 125 ka to 121 ka for the LIG). These warm periods were exceptional, interglacial cooling is the rule. A cold spell at about 2.8 ka during the PIG, possibly mimicked during the LIG by a cold event at 118 ka that lasted and terminated the cooling trend and stabilised interglacial SST at around 18ºC. The inception within the LIG, barely evident at the beginning ca. 115 ka (perihelion aligned with NH winter solstice), culminated at 111 ka.

  17. Validation of adipose lipid content as a body condition index for polar bears

    USGS Publications Warehouse

    McKinney, Melissa A.; Atwood, Todd; Dietz, Rune; Sonne, Christian; Iverson, Sara J.; Peacock, Elizabeth

    2014-01-01

    Body condition is a key indicator of individual and population health. Yet, there is little consensus as to the most appropriate condition index (CI), and most of the currently used CIs have not been thoroughly validated and are logistically challenging. Adipose samples from large datasets of capture biopsied, remote biopsied, and harvested polar bears were used to validate adipose lipid content as a CI via tests of accuracy, precision, sensitivity, biopsy depth, and storage conditions and comparisons to established CIs, to measures of health and to demographic and ecological parameters. The lipid content analyses of even very small biopsy samples were highly accurate and precise, but results were influenced by tissue depth at which the sample was taken. Lipid content of capture biopsies and samples from harvested adult females was correlated with established CIs and/or conformed to expected biological variation and ecological changes. However, lipid content of remote biopsies was lower than capture biopsies and harvested samples, possibly due to lipid loss during dart retrieval. Lipid content CI is a biologically relevant, relatively inexpensive and rapidly assessed CI and can be determined routinely for individuals and populations in order to infer large-scale spatial and long-term temporal trends. As it is possible to collect samples during routine harvesting or remotely using biopsy darts, monitoring and assessment of body condition can be accomplished without capture and handling procedures or noninvasively, which are methods that are preferred by local communities. However, further work is needed to apply the method to remote biopsies.

  18. Late Pleistocene lithostratigraphy and sequences in the southwestern Mesopotamia (Argentina): Evidences of the last interglacial stage

    NASA Astrophysics Data System (ADS)

    Ernesto, Brunetto; Soledad, Ferrero Brenda; Ignacio, Noriega Jorge

    2015-03-01

    The aim of this paper is to show the stratigraphic record of the Late Pleistocene corresponding to the distal region of the Paraná River basin. It displays sedimentological, paleontological and geochronological evidences that characterise the last interglacial-glacial cycle. In particular, strong environmental records are shown for the Last Interglacial Stage (LIS). Salto Ander Egg Formation (SAEF) is defined as a new lithostratigraphic unit representative of the Late Pleistocene in southwestern Mesopotamia. This unit is formed of complex fluvial deposits, which contains a heterogeneous collection of sub-environments, of ages ranging from 120 to 60 ky BP. The clast-supported gravel facies containing sparse boulders indicate high flow during a humid climate. The large and middle-scale architectures of fluvial sedimentary bodies evidence the relationship between the sediment accommodation and the sea level oscillations. Three sub-sequences identified in the succession suggest a transgressive trend during the MIS5e, a highstand stage in MIS5c, and a minor transgressive cycle during MIS3. A Brazilian faunal association collected at the bottom of the sequence and sedimentological interpretations display wet and warm climatic conditions, typical of tropical or subtropical environments. Such environmental conditions are characteristic of the maximum of the last interglacial stage (MIS5e) and show a signal stronger than the signal of the current interglacial stage. All these data show a direct correlation between the increases of paleodischarges and the elevation of the sea level. The whole sequence is completed with transitional swampy deposits, accumulated probably during the MIS3/MIS2 transition, and the typical loess of the Tezanos Pinto Formation, mantled during the Last Maximum Glacial.

  19. The last interglacial-glacial period on spitsbergen, Svalbard

    NASA Astrophysics Data System (ADS)

    Mangerud, Jan; Svendsen, John Inge

    The glaciation history of Svalbard (78°N) and the NW Barents Sea is reconstructed for the last 130 ka, based on studies of sediments exposed in coastal cliffs at the head of Isfjorden. Four different till beds separated by marine sediments are recognized. The lowest marine formation, containing Mytilus edulis, reflects warmer conditions than at present, and is correlated with the last interglacial, the Eemian of Europe and Oxygen Isotope Substage 5e in the deep sea. The post-Eemian tills are inferred to represent major glaciations around 110 ka BP, 75-50 ka BP, and 25-10 ka BP. During the intervening intervals the glaciers on Svalbard were not significantly larger than at present and the NW Barents Sea was probably ice-free. The ice-free periods, named Phantomodden and Kapp Ekholm interstadials, lasted from about 110 to 75 and from 50 to 25 ka BP respectively. The marine fauna from both these interstadials indicate seasonally ice free conditions. The ages of the recorded glaciations coincide with, or are slightly younger than, periods with insolation minima, which at this latitude is determined by a low tilt of the Earth's axis. Thus we postulate that the Quaternary glaciations of Svalbard were driven by orbital variations with the 41 ka tilt period, in contrast to the lower-latitude glaciations of Scandinavia that were partly driven by the precession cycle with a periodicity of around 23 ka.

  20. Characteristics of energetic electron precipitation into the earth's polar atmosphere and geomagnetic conditions

    NASA Astrophysics Data System (ADS)

    Makhmutov, V. S.; Bazilevskaya, G. A.; Krainev, M. B.

    A number of energetic electron precipitation events (EPEs) were observed in the Earth's polar atmosphere (Murmansk region, geographical coordinates 68.57 N, 33.03 E and Mirny, Antarctica, 66.34 S, 92.55 E) during the long-term cosmic ray balloon experiment from 1957 up to now. During geomagnetic storms significant X-ray fluxes caused by precipitating electrons at the top of the atmosphere sometimes penetrated to the atmospheric depth of 60 gcm-2. We show that (1) there is a quasi-11-year cycle in EPE occurrence shifted with respect to solar activity cycle, and (2) the yearly rate of EPE occurrence has an ascending trend during the period 1965-1999. The EPE characteristics evaluated from the balloon experiment are compared with the available data on geomagnetic activity and the possible relations between the features of EPE events and geomagnetic conditions are discussed.

  1. Tropically-driven climate shifts in southwestern Europe during MIS 19, a low eccentricity interglacial

    NASA Astrophysics Data System (ADS)

    Sánchez Goñi, M. F.; Rodrigues, T.; Hodell, D. A.; Polanco-Martínez, J. M.; Alonso-García, M.; Hernández-Almeida, I.; Desprat, S.; Ferretti, P.

    2016-08-01

    The relative roles of high- versus low-latitude forcing of millennial-scale climate variability are still not well understood. Here we present terrestrial-marine climate profiles from the southwestern Iberian margin, a region particularly affected by precession, that show millennial climate oscillations related to a nonlinear response to the Earth's precession cycle during Marine Isotope Stage (MIS) 19. MIS 19 has been considered the best analogue to our present interglacial from an astronomical point of view due to the reduced eccentricity centred at 785 ka. In our records, seven millennial-scale forest contractions punctuated MIS 19 superimposed to two orbitally-driven Mediterranean forest expansions. In contrast to our present interglacial, we evidence for the first time low latitude-driven 5000-yr cycles of drying and cooling in the western Mediterranean region, along with warmth in the subtropical gyre related to the fourth harmonic of precession. These cycles indicate repeated intensification of North Atlantic meridional moisture transport that along with decrease in boreal summer insolation triggered ice growth and may have contributed to the glacial inception, at ∼774 ka. The freshwater fluxes during MIS 19ab amplified the cooling events in the North Atlantic promoting further cooling and leading to MIS 18 glaciation. The discrepancy between the dominant cyclicity observed during MIS 1, 2500-yr, and that of MIS 19, 5000-yr, challenges the similar duration of the Holocene and MIS 19c interglacials under natural boundary conditions.

  2. Cyclic 100-ka (glacial-interglacial) migration of subseafloor redox zonation on the Peruvian shelf

    PubMed Central

    Contreras, Sergio; Meister, Patrick; Liu, Bo; Prieto-Mollar, Xavier; Hinrichs, Kai-Uwe; Khalili, Arzhang; Ferdelman, Timothy G.; Kuypers, Marcel M. M.; Jørgensen, Bo Barker

    2013-01-01

    The coupling of subseafloor microbial life to oceanographic and atmospheric conditions is poorly understood. We examined diagenetic imprints and lipid biomarkers of past subseafloor microbial activity to evaluate its response to glacial-interglacial cycles in a sedimentary section drilled on the Peruvian shelf (Ocean Drilling Program Leg 201, Site 1229). Multiple and distinct layers of diagenetic barite and dolomite, i.e., minerals that typically form at the sulfate−methane transition (SMT), occur at much shallower burial depth than the present SMT around 30 meters below seafloor. These shallow layers co-occur with peaks of 13C-depleted archaeol, a molecular fossil of anaerobic methane-oxidizing Archaea. Present-day, non-steady state distributions of dissolved sulfate also suggest that the SMT is highly sensitive to variations in organic carbon flux to the surface shelf sediments that may lead to shoaling of the SMT. Reaction-transport modeling substantiates our hypothesis that shallow SMTs occur in response to cyclic sediment deposition with a high organic carbon flux during interglacials and a low organic carbon flux during glacial stages. Long diffusion distances expectedly dampen the response of deeply buried microbial communities to changes in sediment deposition and other oceanographic drivers over relatively short geological time scales, e.g., glacial-interglacial periods. However, our study demonstrates how dynamically sediment biogeochemistry of the Peru Margin has responded to glacial-interglacial change and how these changes are now preserved in the geological record. Such changes in subsurface biogeochemical zonation need to be taken into account to assess the role of the subseafloor biosphere in global element and redox cycling. PMID:24145422

  3. The strength and characteristics of interglacials in the late Quaternary

    NASA Astrophysics Data System (ADS)

    Lang, N.; Wolff, E. W.

    2009-04-01

    Analysis of the EPICA Dome C ice core has provided high resolution records of climate variability over the last 800ka and reveal, for example, variations in the duration, 'shape' and strength of interglacial and glacial periods during this time. This variability is also seen in other palaeoclimate records such as foraminiferal ^18O records; however no synthesis of available 800ka ice, marine and terrestrial records has yet been made to compare and contrast interglacial and glacial characteristics. Records of ^D, CO2, CH4, temperature and Ca flux from EDC, globally distributed high resolution benthic & planktonic ^18O records, loess records from the Chinese Loess Plateau, Lake Baikal biosilica and the Tenaghi Philippon pollen record have been selected for their length, resolution, continuity and spatial distribution. Marine records have been aligned with the LR04 stack using the graphic alignment program Match to enable comparison with ice core records on the EDC3 timescale, as the differences between these two age models have already been evaluated. Terrestrial records are evaluated on their existing published age models. Variations in age model construction, orbital tuning of age models and graphic alignment of the records mean it is not possible to address phasing (and duration) in this study. A suite of characteristics from these records, including average and peak values of interglacial and glacial intensity & termination magnitude, are being compared to discover what the similarities and differences can suggest about the character and mechanisms of long term climate change over the last 800ka. Termination magnitude is defined as simply the difference between peak (average) interglacial and glacial values. Rampfit was used to objectively estimate average glacial and interglacial values, and the beginning and end of the glacial-interglacial transition and uncertainties for these parameters. We are thus able to derive spatial patterns of the strength and

  4. The strength and characteristics of late Quaternary interglacials

    NASA Astrophysics Data System (ADS)

    Lang, Nicola; Wolff, Eric

    2010-05-01

    Analysis of the EPICA Dome C ice core has provided high resolution records of climate variability over the last 800ka and reveal, for example, variations in the duration, ‘shape' and strength of interglacial and glacial periods during this time. This variability is also seen in other palaeoclimate records such as foraminiferal δ18O records; however no synthesis of available 800ka ice, marine and terrestrial records has yet been made to compare and contrast interglacial and glacial characteristics. Records of δD, CO2, CH4, temperature and Ca flux from EDC, globally distributed high resolution benthic & planktonic δ18O records, loess records from the Chinese Loess Plateau, Lake Baikal biosilica and the Tenaghi Philippon pollen record have been selected for their length, resolution, continuity and spatial distribution. Marine records have been aligned with the LR04 stack using the graphic alignment program Match to enable comparison with ice core records on the EDC3 timescale, as the differences between these two age models have already been evaluated. Terrestrial records are evaluated on their existing published age models. Variations in age model construction, orbital tuning of age models and graphic alignment of the records mean it is not possible to address phasing (and duration) in this study. A suite of characteristics from these records, including average and peak values of interglacial and glacial intensity & termination magnitude, are being compared to discover what the similarities and differences can suggest about the character and mechanisms of long term climate change over the last 800ka. Termination magnitude is defined as simply the difference between peak (average) interglacial and glacial values. Rampfit was used to objectively estimate average glacial and interglacial values, and the beginning and end of the glacial-interglacial transition and uncertainties for these parameters. We are thus able to derive spatial patterns of the strength and

  5. Various environments of interglacials recorded by Pleistocene paleosoils in Hungary (Central Europe)

    NASA Astrophysics Data System (ADS)

    Varga, György; Kis, Éva

    2015-04-01

    Based on stable isotope analyses of worldwide reference curves from deep sea, ice core and speleothem records, it has long been apparent that duration, intensity and climatic conditions of different interglacial periods were significantly diverse. As a consequence of negligible fresh, detrital material admixture during interglacials, the soil formation intensity and maturity of various kinds of past soils have been holding vital information on the environmental conditions at the time the soils formed. This, in turn, means that several physical and chemical properties of soils allow us to reconstruct past climatic regimes. Loess-paleosol sequences in Hungary (Central Europe) provide insight into the cyclic nature of glacial-interglacial variations of the last 1 million years. The paleosoils have been recognized as the product of warmer and moister interglacials, when the (glacial) loess material was altered by chemical weathering and pedogenic processes. 12 pedogene units from MIS-19 to MIS-5 strata were analysed in the course of this study, with a special attention to MIS-11 and MIS-19 periods, because of these can be regarded as analogues of the Holocene interglacial (due to the similarities in obliquity and eccentricity). Grain size, geochemical and (clay)mineralogical studies were elaborated and were gathered from previously published papers to quantify past weathering intensity and paleoenvironmental conditions by geochemical climofunctions. The Upper and partly, the Middle Pleistocene loess deposits are intercalated by steppe, forest-steppe and brown forest soils, while the older pedogene horizons are different kinds; these are red, Mediterranean-type soils. The MIS-5 pedocomplex consist of three parts at several Hungarian sites, however the pedogene units cannot be correlated unequivocally with the three MIS-5 warmer substages, due to the scarce absolute age data. The MIS-7 and MIS-9 stages are represented by three forest steppe soils. The MIS-11 pedocomplex

  6. Validation of adipose lipid content as a body condition index for polar bears

    PubMed Central

    McKinney, Melissa A; Atwood, Todd; Dietz, Rune; Sonne, Christian; Iverson, Sara J; Peacock, Elizabeth

    2014-01-01

    Body condition is a key indicator of individual and population health. Yet, there is little consensus as to the most appropriate condition index (CI), and most of the currently used CIs have not been thoroughly validated and are logistically challenging. Adipose samples from large datasets of capture biopsied, remote biopsied, and harvested polar bears were used to validate adipose lipid content as a CI via tests of accuracy, precision, sensitivity, biopsy depth, and storage conditions and comparisons to established CIs, to measures of health and to demographic and ecological parameters. The lipid content analyses of even very small biopsy samples were highly accurate and precise, but results were influenced by tissue depth at which the sample was taken. Lipid content of capture biopsies and samples from harvested adult females was correlated with established CIs and/or conformed to expected biological variation and ecological changes. However, lipid content of remote biopsies was lower than capture biopsies and harvested samples, possibly due to lipid loss during dart retrieval. Lipid content CI is a biologically relevant, relatively inexpensive and rapidly assessed CI and can be determined routinely for individuals and populations in order to infer large-scale spatial and long-term temporal trends. As it is possible to collect samples during routine harvesting or remotely using biopsy darts, monitoring and assessment of body condition can be accomplished without capture and handling procedures or noninvasively, which are methods that are preferred by local communities. However, further work is needed to apply the method to remote biopsies. PMID:24634735

  7. Validation of adipose lipid content as a body condition index for polar bears.

    PubMed

    McKinney, Melissa A; Atwood, Todd; Dietz, Rune; Sonne, Christian; Iverson, Sara J; Peacock, Elizabeth

    2014-02-01

    Body condition is a key indicator of individual and population health. Yet, there is little consensus as to the most appropriate condition index (CI), and most of the currently used CIs have not been thoroughly validated and are logistically challenging. Adipose samples from large datasets of capture biopsied, remote biopsied, and harvested polar bears were used to validate adipose lipid content as a CI via tests of accuracy, precision, sensitivity, biopsy depth, and storage conditions and comparisons to established CIs, to measures of health and to demographic and ecological parameters. The lipid content analyses of even very small biopsy samples were highly accurate and precise, but results were influenced by tissue depth at which the sample was taken. Lipid content of capture biopsies and samples from harvested adult females was correlated with established CIs and/or conformed to expected biological variation and ecological changes. However, lipid content of remote biopsies was lower than capture biopsies and harvested samples, possibly due to lipid loss during dart retrieval. Lipid content CI is a biologically relevant, relatively inexpensive and rapidly assessed CI and can be determined routinely for individuals and populations in order to infer large-scale spatial and long-term temporal trends. As it is possible to collect samples during routine harvesting or remotely using biopsy darts, monitoring and assessment of body condition can be accomplished without capture and handling procedures or noninvasively, which are methods that are preferred by local communities. However, further work is needed to apply the method to remote biopsies. PMID:24634735

  8. Condition for Gaussian Schell-model beam to maintain the state of polarization on the propagation in free space.

    PubMed

    Zhao, Xinhui; Yao, Yong; Sun, Yunxu; Liu, Chao

    2009-09-28

    In the free space optical communication system with circle polarization shift keying (CPolSK) modulation, the changes of polarization state of light beam have significant influence on the system performance. Keeping the state of polarization (SOP) unchanged on propagation can reduce the bit error rate. Based on the unified theory of coherence and polarization, we derive the sufficient condition for Gaussian Schell-model (GSM) beam to keep the SOP unchanged. We found that when the three spectral correlation widths (delta(xx), delta(yy) and delta(xy)) equal to each other and sigma(x) = sigma(y), the GSM beam maintains the SOP on propagation. This conclusion can be helpful for the design of the transmitter in the CPolSK system. PMID:19907577

  9. The rich phase behavior of the thermopolarization of water: from a reversal in the polarization, to enhancement near criticality conditions.

    PubMed

    Iriarte-Carretero, Irene; Gonzalez, Miguel A; Armstrong, Jeff; Fernandez-Alonso, Felix; Bresme, Fernando

    2016-07-20

    We investigate using non-equilibrium molecular dynamics simulations the polarization of water induced by thermal gradients using the accurate TIP4P/2005 water model. The full dependence of the polarization covering a wide range of thermodynamic states, from near supercritical to ambient conditions, is reported. Our results show a strong dependence of the thermo-polarization field with the thermodynamic state. The field features a strong enhancement near the critical point, which can be rationalized in terms of the large increase and ultimately the divergence of the thermal expansion of the fluid at the critical temperature. We also show that the TIP4P/2005 model features a reversal in the sign of the thermal polarization at densities ∼1 g cm(-3). The latter result is consistent with the recent observation of this reversal phenomenon in SPC/E water and points the existence of this general physical phenomenon in water. PMID:27397622

  10. Sea surface temperature variability of the Peru-Chile Current during the previous ten interglacials

    NASA Astrophysics Data System (ADS)

    Caniupan, M.; Martinez-Mendez, G.; Lamy, F.; Hebbeln, D.; Mohtadi, M.; Pantoja, S.

    2014-12-01

    There are several interglacial periods during the Quaternary that were characterized by climates warmer than present and higher sea level and thus may serve as analogues for future global warming scenarios. These include Marine Isotope Stages (MIS) 5e, 9c and 11c. Little is known about past sea surface temperatures (SST) during these warm intervals in the Southern Hemisphere, particularly along the Peru-Chile Current (PCC) which plays a critical role in the Southern Hemisphere surface circulation as it connects the low and high latitudes by transporting sub-polar water masses and thus, a high-latitude climate signal towards the tropics. Here, we present new high-resolution alkenone-derived SST records from marine sediment cores located beneath the PCC. Core GeoB15016 was recovered from off northern Chile (27.5°S; 71.1°W) with the seafloor drill rig MARUM-MeBo. We analyzed the ca. 60 meters composite depth complemented by gravity core GeoB3375-1 (27.5°S; 71.3°W) for the upper part to generate a continuous record that extends back to 970 ka BP. Our record is the first continuous SST reconstruction from the Chilean margin extending back to MIS 25. SST varies between ~8°C and ~20°C over the past ~970 ka. Glacial-interglacial SST amplitudes are in the order of 6°C (see Groeneveld's et al. contribution for Mg/Ca-derived Glacial SST estimations). During MIS 5e, 7e, 9c and 11c, the record reaches SST maxima which are ca. 3ºC warmer than present annual mean SST in the area. Our results suggest a substantial warming of the PCC over past interglacials that may reflect reduced advection of subantarctic surface water from the south and/or enhanced tropical influence from the north.

  11. Halogen species record Antarctic sea ice extent over glacial-interglacial periods

    NASA Astrophysics Data System (ADS)

    Spolaor, A.; Vallelonga, P.; Plane, J. M. C.; Kehrwald, N.; Gabrieli, J.; Varin, C.; Turetta, C.; Cozzi, G.; Boutron, C.; Barbante, C.

    2013-02-01

    Sea ice is an integral part of the Earth's climate system because it affects planetary albedo, sea surface salinity, and the atmosphere-ocean exchange of reactive gases and aerosols. Bromine and iodine chemistry is active at polar sea ice margins with the occurrence of bromine explosions and the biological production of organo-iodine from sea ice algae. Satellite measurements demonstrate that concentrations of bromine oxide (BrO) and iodine oxide (IO) decrease over sea ice toward the Antarctic interior. Here we present speciation measurements of bromine and iodine in the TALDICE (TALos Dome Ice CorE) ice core (159°11' E, 72°49' S, 2315 m a.s.l.) spanning the last 215 ky. The Talos Dome ice core is located 250 km inland and is sensitive to marine air masses intruding onto the Antarctic Plateau. Talos Dome bromide (Br-) is positively correlated with temperature and negatively correlated with sodium (Na). Based on the Br-/Na seawater ratio, bromide is depleted in the ice during glacial periods and enriched during interglacial periods. Total iodine, consisting of iodide (I-) and iodate (IO3-), peaks during glacials with lower values during interglacial periods. Although IO3- is considered the most stable iodine species in the atmosphere it was only observed in the TALDICE record during glacial maxima. Sea ice dynamics are arguably the primary driver of halogen fluxes over glacial-interglacial timescales, by altering the distance between the sea ice edge and the Antarctic plateau and by altering the surface area of sea ice available to algal colonization. Based on our results we propose the use of both halogens for examining Antarctic variability of past sea ice extent.

  12. Halogen species record Antarctic sea ice extent over glacial-interglacial periods

    NASA Astrophysics Data System (ADS)

    Spolaor, A.; Vallelonga, P.; Plane, J. M. C.; Kehrwald, N.; Gabrieli, J.; Varin, C.; Turetta, C.; Cozzi, G.; Kumar, R.; Boutron, C.; Barbante, C.

    2013-07-01

    Sea ice is an integral part of the earth's climate system because it affects planetary albedo, sea-surface salinity, and the atmosphere-ocean exchange of reactive gases and aerosols. Bromine and iodine chemistry is active at polar sea ice margins with the occurrence of bromine explosions and the biological production of organoiodine from sea ice algae. Satellite measurements demonstrate that concentrations of bromine oxide (BrO) and iodine oxide (IO) decrease over sea ice toward the Antarctic interior. Here we present speciation measurements of bromine and iodine in the TALDICE (TALos Dome Ice CorE) ice core (159°11' E, 72°49' S; 2315 m a.s.l.) spanning the last 215 ky. The Talos Dome ice core is located 250 km inland and is sensitive to marine air masses intruding onto the Antarctic Plateau. Talos Dome bromide (Br-) is positively correlated with temperature and negatively correlated with sodium (Na). Based on the Br-/Na seawater ratio, bromide is depleted in the ice during glacial periods and enriched during interglacial periods. Total iodine, consisting of iodide (I-) and iodate (IO3-), peaks during glacials with lower values during interglacial periods. Although IO3- is considered the most stable iodine species in the atmosphere it was only observed in the TALDICE record during glacial maxima. Sea ice dynamics are arguably the primary driver of halogen fluxes over glacial-interglacial timescales, by altering the distance between the sea ice edge and the Antarctic plateau and by altering the surface area of sea ice available to algal colonization. Based on our results we propose the use of both halogens for examining Antarctic variability of past sea ice extent.

  13. The last interglacial in the Mediterranean as a model for the present interglacial

    NASA Astrophysics Data System (ADS)

    Zaso, C.; Goy, J. L.; Dabrio, C. J.; Bardaji, T.; Somoza, L.; Silva, P. G.

    1993-05-01

    Deposits of the Last Interglacial on the south and southeastern coasts of Spain are shallow marine and coastal sediments, with a warm fauna of Strombus bubonius. These units exhibit a diversity of morpho-sedimentary models controlled by the tectonic activity of the Mediterranean area, which is closely related to the approximation of Africa and Iberia during the Quaternary. There are three well-dated peaks of maximum sea level (T-I: isotopic substage 7a, T-II: isotopic substage 5e, T-III: isotopic substage 5c). A younger episode, T-IV, probably corresponds to the isotopic substage 5a. Episodes T-II, T-III and T-IV were laid down during Last Interglacial age. In addition, three Holocene peaks of maximum sea level: H 1 ca. 5100 yr B.P., H 2 ca. 3500 yr B.P. and H 3 ca. 2400 yr B.P. were found. The three main peaks of the Last Interglacial correspond to the morpho-sedimentary Tyrrhenian units T-II, T-III and T-IV, deposited during a time span of some 45,000 years. Several smaller oscillations can be distinguished within each of these units as subunits separated by erosional surfaces. At least three of such mapable subunits were distinguished within the peak T-II (5e); each lasted ca. 10,500 yr. As the positive oscillations of sea level (H 1, H 2, and H 3) recorded during the present Interglacial (Holocene) are much shorter, we infer that they are smaller-scale fluctuations (2500-1100 yr cycles) within the first oscillation (duration: ca. 10,500 yr) of the first Holocene peak of sea level which has not yet been completed. In addition to changes of sea level, the vertical and lateral arrangement of morpho-sedimentary units, which can be designated as the stratigraphic architecture, depends on tectonics and oceanography, including geoidal and steric changes and coastal dynamics. The coastal dynamics factor largely depends on the exchange of waters between the Atlantic and the Mediterranean. Maximum incursions of water coincides with warm periods (highstands) when the

  14. Speleothem records of western Mediterranean. Hydrological variability along the Last Interglacial Period and marine linkages

    NASA Astrophysics Data System (ADS)

    Torner, Judit; Cacho, Isabel; Moreno, Ana; Stoll, Heather; Belmonte, Anchel; Sierro, Francisco J.; Frigola, Jaime; Martrat, Belen; Fornós, Joan; Arnau Fernández, Pedro; Hellstrom, John; Cheng, Hai; Edwards, R. Lawrence

    2016-04-01

    This study aims to identify and characterize regional hydrological variability in the western Mediterranean region in base to different geochemical parameters (δ18O, δ13C, and Mg/Ca ratios). Speleothems have been recovered from several caves located in southern central Pyrenees one and the others form the Balearic Islands. Their chronologies have been constructed in base on U/Th absolute dating and indicate that the speleothem sequences cover the end of the last interglacial and the glacial inception. One of the most remarkable features of the records is the intense and abrupt shift toward more arid conditions that marks the end of the last interglacial (MIS 5e). Furthermore, our speleothem records also show relatively humid but highly variable hydrological conditions during the interstadial periods from MIS 5c to 5a. These speleothem records have been compared with new generated western Mediterranean marine records from the Balearic Sea (MD99-2343) and Alboran Sea (OPD-977). Marine records include (1) proxies of sea surface temperature and changes in evaporation-precipitation rates based on pair analysis of δ18O and the Mg/Ca ratios in planktonic foraminifera Globigerina bulloides; (2) proxies of deep-water currents associated with the Western Mediterranean Deep Water (WMDW) based on grain size analyses. The results reveal that arid conditions on land were coeval with cold sea surface sub-stages (MIS 5b and 5d), and also with increases in the intensity of the WMDW-related currents. By contrast, humid and hydrological unstable atmosphere conditions were synchronous with sea surface warm sub-stages, and lower WMDW-related currents intensities (MIS 5a, c and e). Consequently, our results highly evidence a strong atmospheric-oceanic coupling, involving parallel changes in both surface but also deep western Mediterranean Sea conditions during the last interglacial period and the glacial inception.

  15. Dependence of polarization mode dispersion of slotted core NZDF ribbon on cable design and environmental conditions

    NASA Astrophysics Data System (ADS)

    Karlik, Sait Eser; Yilmaz, Gunes

    2006-09-01

    Non-zero dispersion fiber (NZDF) ribbon cable has recently become a considerable alternative in long-haul high-speed network construction. Since long-distance high-bit rate transmission requires low polarization mode dispersion (PMD), it is very important to know the PMD performance of this type of optical fiber cables. In this paper, we report experimental analysis of effects of the cable design and environmental parameters, in particular ribbon thickness, positions of fibers in the ribbon, flexing and vibration, on PMD performances of several slotted-core fiber ribbon cables. Results show that ribbon thickness and positions of fibers in the ribbon alter the PMD values of NZDF ribbon cables. Also, 23% and 11% PMD variations have been determined in flexing and vibration experiments, respectively. Moreover, it has been observed that vibration amplitude has significant effects and vibration frequency has little effects (14% and 6% variations, respectively) on fiber PMD. Results are important for understanding effects of installation conditions and wind, especially for aerial fibers, on PMD values of cables.

  16. Corrosion of low-antimony lead-cadmium alloys in conditions of long-term polarization

    NASA Astrophysics Data System (ADS)

    Nuzhny, Alex

    Nowadays, lead-acid battery grids are manufactured mostly from low-antimony and lead-calcium alloys. A variable corrosion resistance of battery grids is caused by either battery operation conditions, purity of used alloy components, an alloy makeup, and the castings quality. Such compositions as usual lead-antimony alloy, low-antimony lead-arsenious alloy and lead-calcium alloy with moderate content of tin today may be regarded as the most studied ones. A significant share of published works has been devoted to low-antimony lead-tin alloys. In the present article, results of corrosion tests of the samples made with application of cadmium as the second component of low-antimony alloy, has been represented. Several samples were extra-alloyed by selenium and silver. Samples of lead-calcium and usual antimony alloys as well as pure lead samples were being tested simultaneously. Upon termination of polarization, weight of anodic films referred to a unit of the sample surface has been determined. Thus, the film covering lead-antimony alloy sample has the maximal weight, whereas the oxidation products on the pure lead surface have the lowest one. Among low-antimony alloys, the highest corrosion resistance has been found out with the samples alloyed by a low amount of silver. The microstructure of the castings surface has been analysed. Process of corrosion has been considered in connection with size of grains.

  17. Paleomonsoonal Precipitation and Hydroclimate Variability from Glacial to Interglacial Climates in the Southwest: The Stoneman Lake, Arizona Record

    NASA Astrophysics Data System (ADS)

    Garcia, D.; Fawcett, P. J.; Anderson, R. S.; Sharp, Z. D.

    2015-12-01

    Oxygen isotope values from diatom silica have been used to determine past hydrological conditions in a variety of settings including differentiating summer monsoonal paleoprecipitation from winter frontal paleoprecipitation in the American southwest. Lacustrine cores from the Valles Caldera, New Mexico, show a distinct change in silica oxygen isotope values from glacial to interglacial as a switch from a purely winter frontal precipitation during the glacial to a mix of winter frontal and summer monsoonal precipitation during the interglacial. A relatively large (ca. 20‰) and rapid increase in δ18O following the glacial termination implies an abrupt onset of the North American monsoon. We plan to elaborate on this research to see if this is true elsewhere in the southwest. Two lacustrine sediment cores (70 m deep and 30 m deep respectively) were recovered from Stoneman Lake, northern Arizona in October of 2014. With these cores we plan to determine regional hydroclimate variability between the Pleistocene-Holocene glacial transition ca. 14 ka. Oxygen isotope analysis from diatom silica will allow us to determine past sources of precipitation to the basin (Gulf of Mexico vs North Pacific), and paleoprecipitation variability. In conjunction with other proxies, we can determine if the onset of paleomonsoonal precipitation in central Arizona occurs immediately after the glacial termination as in NM, or if there is some component of monsoonal precipitation during the late glacial period. Diatom sampling was performed at approximately every 50 cm. To purify the diatoms, the samples are chemically and physically separated. The step wise fluorination and laser ablation technique are then applied to remove water & hydroxyl groups and to extract O2 & SiF4 respectively.If results from the Stoneman Lake core are similar to that of the Valles Caldera core, we should expect to see a nearly 20‰ increase in δ18Olake water. This would suggest a: 1) collapse of the summer

  18. Application of Polar Cap (PC) indices in analyses and forecasts of geophysical conditions

    NASA Astrophysics Data System (ADS)

    Stauning, Peter

    2016-07-01

    The Polar Cap (PC) indices could be considered to represent the input of power from the solar wind to the Earth's magnetosphere. The indices have been used to analyse interplanetary electric fields, effects of solar wind pressure pulses, cross polar cap voltages and polar cap diameter, ionospheric Joule heating, and other issues of polar cap dynamics. The PC indices have also been used to predict auroral electrojet intensities and global auroral power as well as ring current intensities. For specific space weather purposes the PC indices could be used to forecast substorm development and predict associated power line disturbances in the subauroral regions. The presentation shall outline the general background for applying the PC indices in analyses or forecasts of solar wind-magnetosphere-ionosphere interactions and provide illustrative examples of the use of the Polar Cap indices in specific cases

  19. Direct observations of the full Dungey convection cycle in the polar ionosphere for southward interplanetary magnetic field conditions

    NASA Astrophysics Data System (ADS)

    Zhang, Q.-H.; Lockwood, M.; Foster, J. C.; Zhang, S.-R.; Zhang, B.-C.; McCrea, I. W.; Moen, J.; Lester, M.; Ruohoniemi, J. M.

    2015-06-01

    Tracking the formation and full evolution of polar cap ionization patches in the polar ionosphere, we directly observe the full Dungey convection cycle for southward interplanetary magnetic field (IMF) conditions. This enables us to study how the Dungey cycle influences the patches' evolution. The patches were initially segmented from the dayside storm enhanced density plume at the equatorward edge of the cusp, by the expansion and contraction of the polar cap boundary due to pulsed dayside magnetopause reconnection, as indicated by in situ Time History of Events and Macroscale Interactions during Substorms (THEMIS) observations. Convection led to the patches entering the polar cap and being transported antisunward, while being continuously monitored by the globally distributed arrays of GPS receivers and Super Dual Auroral Radar Network radars. Changes in convection over time resulted in the patches following a range of trajectories, each of which differed somewhat from the classical twin-cell convection streamlines. Pulsed nightside reconnection, occurring as part of the magnetospheric substorm cycle, modulated the exit of the patches from the polar cap, as confirmed by coordinated observations of the magnetometer at Tromsø and European Incoherent Scatter Tromsø UHF radar. After exiting the polar cap, the patches broke up into a number of plasma blobs and returned sunward in the auroral return flow of the dawn and/or dusk convection cell. The full circulation time was about 3 h.

  20. Intra-interglacial climate variability: model simulations of Marine Isotope Stages 1, 5, 11, 13, and 15

    NASA Astrophysics Data System (ADS)

    Rachmayani, Rima; Prange, Matthias; Schulz, Michael

    2016-03-01

    Using the Community Climate System Model version 3 (CCSM3) including a dynamic global vegetation model, a set of 13 time slice experiments was carried out to study global climate variability between and within the Quaternary interglacials of Marine Isotope Stages (MISs) 1, 5, 11, 13, and 15. The selection of interglacial time slices was based on different aspects of inter- and intra-interglacial variability and associated astronomical forcing. The different effects of obliquity, precession, and greenhouse gas (GHG) forcing on global surface temperature and precipitation fields are illuminated. In most regions seasonal surface temperature anomalies can largely be explained by local insolation anomalies induced by the astronomical forcing. Climate feedbacks, however, may modify the surface temperature response in specific regions, most pronounced in the monsoon domains and the polar oceans. GHG forcing may also play an important role for seasonal temperature anomalies, especially at high latitudes and early Brunhes interglacials (MIS 13 and 15) when GHG concentrations were much lower than during the later interglacials. High- versus low-obliquity climates are generally characterized by strong warming over the Northern Hemisphere extratropics and slight cooling in the tropics during boreal summer. During boreal winter, a moderate cooling over large portions of the Northern Hemisphere continents and a strong warming at high southern latitudes is found. Beside the well-known role of precession, a significant role of obliquity in forcing the West African monsoon is identified. Other regional monsoon systems are less sensitive or not sensitive at all to obliquity variations during interglacials. Moreover, based on two specific time slices (394 and 615 ka), it is explicitly shown that the West African and Indian monsoon systems do not always vary in concert, challenging the concept of a global monsoon system on astronomical timescales. High obliquity can also explain

  1. A microwave satellite water vapour column retrieval for polar winter conditions

    NASA Astrophysics Data System (ADS)

    Perro, Christopher; Lesins, Glen; Duck, Thomas J.; Cadeddu, Maria

    2016-05-01

    A new microwave satellite water vapour retrieval for the polar winter atmosphere is presented. The retrieval builds on the work of Miao et al. (2001) and Melsheimer and Heygster (2008), employing auxiliary information for atmospheric conditions and numerical optimization. It was tested using simulated and actual measurements from the Microwave Humidity Sounder (MHS) satellite instruments. Ground truth was provided by the G-band vapour radiometer (GVR) at Barrow, Alaska. For water vapour columns less than 6 kg m-2, comparisons between the retrieval and GVR result in a root mean square (RMS) deviation of 0.39 kg m-2 and a systematic bias of 0.08 kg m-2. These results are compared with RMS deviations and biases at Barrow for the retrieval of Melsheimer and Heygster (2008), the AIRS and MIRS satellite data products, and the ERA-Interim, NCEP, JRA-55, and ASR reanalyses. When applied to MHS measurements, the new retrieval produces a smaller RMS deviation and bias than for the earlier retrieval and satellite data products. The RMS deviations for the new retrieval were comparable to those for the ERA-Interim, JRA-55, and ASR reanalyses; however, the MHS retrievals have much finer horizontal resolution (15 km at nadir) and reveal more structure. The new retrieval can be used to obtain pan-Arctic maps of water vapour columns of unprecedented quality. It may also be applied to measurements from the Special Sensor Microwave/Temperature 2 (SSM/T2), Advanced Microwave Sounding Unit B (AMSU-B), Special Sensor Microwave Imager/Sounder (SSMIS), Advanced Technology Microwave Sounder (ATMS), and Chinese MicroWave Humidity Sounder (MWHS) instruments.

  2. The last glacial-interglacial cycle in Lake Ohrid (Macedonia/Albania): testing diatom response to climate

    NASA Astrophysics Data System (ADS)

    Reed, J. M.; Cvetkoska, A.; Levkov, Z.; Vogel, H.; Wagner, B.

    2010-06-01

    Lake Ohrid is a site of global importance for palaeoclimate research. This study presents results of diatom analysis of a ca. 136 ka sequence, Co1202, from the northeast of the lake basin. It offers the opportunity to test diatom response across two glacial-interglacial transitions and within the Last Glacial, while setting up taxonomic protocols for future research. The results are outstanding in demonstrating the sensitivity of diatoms to climate change, providing proxy evidence for temperature change marked by glacial-interglacial shifts between the dominant planktonic taxa, Cyclotella fottii and C. ocellata, and exact correlation with geochemical proxies to mark the start of the Last Interglacial at ca. 130 ka. Importantly, diatoms show much stronger evidence in this site for warming during MIS3 than recorded in other productivity-related proxies, peaking at ca. 39 ka, prior to the extreme conditions of the Last Glacial maximum. In the light of the observed patterns, and from the results of analysis of early Holocene sediments from a second core, Lz1120, the lack of a response to Late Glacial and early Holocene warming from ca. 15-7.4 ka suggests the Co1202 sequence may be compromised during this phase. After ca. 7.4 ka, there is evidence for enhanced nutrient enrichment compared to the Last Interglacial, following by a post-Medieval cooling trend. Taxonomically, morphological variability in C. fottii shows no clear trends linked to climate, but an intriguing change in central area morphology occurs after ca. 48.7 ka, coincident with a tephra layer. In contrast, C. ocellata shows morphological variation in the number of ocelli between interglacials, suggesting climatically-forced variation or evolutionary selection pressure. The application of a simple dissolution index does not track preservation quality very effectively, underlining the importance of diatom concentration data in future studies.

  3. The last glacial-interglacial cycle in Lake Ohrid (Macedonia/Albania): testing diatom response to climate

    NASA Astrophysics Data System (ADS)

    Reed, J. M.; Cvetkoska, A.; Levkov, Z.; Vogel, H.; Wagner, B.

    2010-10-01

    Lake Ohrid is a site of global importance for palaeoclimate research. This study presents results of diatom analysis of a ca. 136 ka sequence, Co1202, from the northeast of the lake basin. It offers the opportunity to test diatom response across two glacial-interglacial transitions and within the Last Glacial, while setting up taxonomic protocols for future research. The results are outstanding in demonstrating the sensitivity of diatoms to climate change, providing proxy evidence for temperature change marked by glacial-interglacial shifts between the dominant planktonic taxa, Cyclotella fottii and C. ocellata, and exact correlation with geochemical proxies to mark the start of the Last Interglacial at ca. 130 ka. Importantly, diatoms show much stronger evidence in this site for warming during MIS3 than recorded in other productivity-related proxies, peaking at ca. 39 ka, prior to the extreme conditions of the Last Glacial maximum. In the light of the observed patterns, and from the results of analysis of early Holocene sediments from a second core, Lz1120, the lack of a response to Late Glacial and early Holocene warming from ca. 14.7-6.9 ka suggests the Co1202 sequence may be compromised during this phase. After ca. 7.4 ka, there is evidence for enhanced nutrient enrichment compared to the Last Interglacial, followed by a post-Medieval loss of diversity which is consistent with cooling, but not definitive. Taxonomically, morphological variability in C. fottii shows no clear trends linked to climate, but an intriguing change in central area morphology occurs after ca. 48.7 ka, coincident with a tephra layer. In contrast, C. ocellata shows morphological variation in the number of ocelli between interglacials, suggesting climatically-forced variation or evolutionary selection pressure. The application of a simple dissolution index does not track preservation quality very effectively, underlining the importance of diatom accumulation data in future studies.

  4. Cyclic climate fluctuations during the last interglacial in central Europe

    NASA Astrophysics Data System (ADS)

    Müller, Ulrich C.; Klotz, Stefan; Geyh, Mebus A.; Pross, Jörg; Bond, Gerard C.

    2005-06-01

    Differentiating natural climate change from anthropogenic forcing is a major challenge in the prediction of future climates. In this context, the investigation of interglacials provides valuable information on natural climate variability during periods that resemble the present. This paper shows that natural cyclic changes in winter climates affected central European environments during the last interglacial, i.e., the Eemian, 126 110 ka. As a result of the extraordinarily high counting sums performed at Eemian pollen samples, it was possible to reveal a robust presence absence pattern of the insect-pollinated, and therefore in the pollen rain underrepresented, taxon Hedera. This plant is known to require the influence of oceanic winter climates, i.e., moist and mild, in northwest and central Europe. By analogy with recent findings from the North Atlantic's Holocene interglacial, the trigger of the Eemian climate variability may have been changes in solar activity, possibly amplified by changes in North Atlantic ocean currents and/or in the North Atlantic Oscillation. Our findings suggest natural cyclic changes to be a persistent feature of interglacial climates.

  5. The last interglacial climate: comparing direct and indirect impacts of insolation changes

    NASA Astrophysics Data System (ADS)

    Pedersen, Rasmus A.; Langen, Peter L.; Vinther, Bo M.

    2016-07-01

    The last interglacial climate was influenced by substantial changes in the annual insolation cycle that led to a warmer climate state with pronounced high northern latitude warming. We analyze the impact of the insolation changes 125,000 years before present using an equilibrium snapshot simulation with the EC-Earth coupled climate model at high spatial resolution. Using additional atmosphere-only simulations, we separate the direct impact from the changed insolation from the secondary contribution from changed sea surface conditions. These simulations are forced with a combination of last interglacial sea surface temperatures and sea ice conditions and pre-industrial insolation, and vice versa. The coupled simulation yields an annual mean global warming of approximately 0.5 °C compared to pre-industrial conditions. While the warming over the continents follows the annual cycle of the insolation anomalies, two regions exhibit persistent responses throughout the year: The tropical region exhibits lower temperatures and stronger monsoonal systems, while the Arctic region shows a warming of more than 2 °C in all seasons. The hybrid simulations reveal that the changed sea surface conditions dominate the response at high northern latitudes, including the North Atlantic region and Europe, while the direct insolation impact is more dominant in the tropics.

  6. Sedimentary Record of the Last two Interglacials in the Terrestrial Canadian Arctic (Pingualuit Crater Lake, Nunavik)

    NASA Astrophysics Data System (ADS)

    St-Onge, G.; Guyard, H.; Pienitz, R.; Hausmann, S.; Francus, P.; Salonen, V.; Luoto, T.; Black, J.; Lamothe, M.; Zolitschka, B.; Larocque, I.

    2009-05-01

    The Pingualuit crater lake (Nunavik, Canada) resulted from a meteoritic impact that occurred ca. 1.4 million years ago. Due to its unique morphometry (depth and shape), the lake bottom may have escaped glacial erosion. Based on a punctual seismic profile acquired using a 12 kHz Knudsen echosounder and using both gravity and piston corers, we recovered the uppermost 8.5 m of sediments. High-resolution physical (CAT- Scan, Multi Sensor Core Logger, diffuse spectral reflectance), geochemical (ITRAX core scanner, carbon and nitrogen contents, δ13C of the organic matter) and magnetic (magnetic susceptibility, natural, anhysteretic, isothermal and saturation isothermal remanent magnetizations) analyses were performed. Two main lithofacies were clearly identified by the different measurements and likely represent successive interglacial/glacial cycles. Most of the sediment consists of light grey silts containing several angular rock fragments, that is characterized by very low organic carbon content, relatively high density and magnetic susceptibility values, suggesting a deposition during glacial conditions. Interbedded between this facies are at least two decimetre-thick, organic-rich and finely laminated intervals likely representing ice free periods. The presence of diatoms, chrysophytes and chironomid head capsules in smear and microscope slides from these two intervals supports this hypothesis. In addition, preliminary Infrared Stimulated Luminescence (IRSL) measurements indicate that the upper organic-rich layer has an age coeval with the last interglacial (Oxygen Isotope Stage 5), while the age of the lower organic-rich layer is consistent with an older interglacial, likely the Oxygen Isotope Stage 7. The sedimentary infill thus constitutes a unique long-term terrestrial record of environmental and climatic conditions in the Canadian Arctic. Furthermore, because these sediments escaped glacial erosion, it suggests the presence of a subglacial lake during the last

  7. Bipolar seesaw control on last interglacial sea level.

    PubMed

    Marino, G; Rohling, E J; Rodríguez-Sanz, L; Grant, K M; Heslop, D; Roberts, A P; Stanford, J D; Yu, J

    2015-06-11

    Our current understanding of ocean-atmosphere-cryosphere interactions at ice-age terminations relies largely on assessments of the most recent (last) glacial-interglacial transition, Termination I (T-I). But the extent to which T-I is representative of previous terminations remains unclear. Testing the consistency of termination processes requires comparison of time series of critical climate parameters with detailed absolute and relative age control. However, such age control has been lacking for even the penultimate glacial termination (T-II), which culminated in a sea-level highstand during the last interglacial period that was several metres above present. Here we show that Heinrich Stadial 11 (HS11), a prominent North Atlantic cold episode, occurred between 135 ± 1 and 130 ± 2 thousand years ago and was linked with rapid sea-level rise during T-II. Our conclusions are based on new and existing data for T-II and the last interglacial that we collate onto a single, radiometrically constrained chronology. The HS11 cold episode punctuated T-II and coincided directly with a major deglacial meltwater pulse, which predominantly entered the North Atlantic Ocean and accounted for about 70 per cent of the glacial-interglacial sea-level rise. We conclude that, possibly in response to stronger insolation and CO2 forcing earlier in T-II, the relationship between climate and ice-volume changes differed fundamentally from that of T-I. In T-I, the major sea-level rise clearly post-dates Heinrich Stadial 1. We also find that HS11 coincided with sustained Antarctic warming, probably through a bipolar seesaw temperature response, and propose that this heat gain at high southern latitudes promoted Antarctic ice-sheet melting that fuelled the last interglacial sea-level peak. PMID:26062511

  8. Vegetation and climate changes in western Amazonia during a previous Interglacial- Glacial transition

    NASA Astrophysics Data System (ADS)

    Cardenas, M. L.; Gosling, W. D.; Sherlock, S. C.; Poole, I.; Pennington, R. T.

    2009-12-01

    Amazonia is one of the most biodiverse areas of the world and its vegetation plays a crucial role in controlling the global climate through the regulation of the levels of atmospheric CO2. However, Amazonian ecosystems and their role in the climate system are threatened by ongoing the human impact (already estimated loss of 60% of the species in western Amazonia) and predicted climate change (+1.1-6.4oC by 2100). Unfortunately, there is absence of data relating to the ecological baseline function and response to global climate change of western Amazonian ecosystems in the absence of humans. To help anticipate the impact of future climate change predictions an improved understanding of the natural responses of tropical vegetation to known past climate change is required. Here we present the first study that shows the response of pristine tropical ecosystems in western Amazonia biodiversity hotspot to a major global climate change event (a Quaternary Interglacial-Glacial transition). Pleistocene lake/swamp sediments preserved at the Erazo study site (Lat. 00o 33’S, Long. 077o 52’W, 1927m alt.) today within tropical cloud forest vegetation provide a unique opportunity to examine the impact of past climate shifts. The sediment are >40,000 years old (radiocarbon infinite) and younger than 1 million years (presence of Alder biomarker) and consist of organic layers interbedded with volcanic ash (tephra). This study presents data from multiple proxies (fossil pollen, wood macrofossils and charcoal) to establish a comprehensive picture of regional and local vegetation change prior to human arrival. Our data show a change of vegetation from palm-dominated forest indicative of warm and wet conditions similar to the present at the base of this record, to a forest dominated by Podocarpus sp. suggesting cold and wet conditions at the top of the record. The transition between these two vegetation communities appears to be progressive with small sharp changes along the

  9. Migration of the Antarctic Polar Front through the mid-Pleistocene transition: evidence and climatic implications

    NASA Astrophysics Data System (ADS)

    Kemp, A. E. S.; Grigorov, I.; Pearce, R. B.; Naveira Garabato, A. C.

    2010-08-01

    The Antarctic Polar Front is an important biogeochemical divider in the Southern Ocean. Laminated diatom mat deposits record episodes of massive flux of the diatom Thalassiothrix antarctica beneath the Antarctic Polar Front and provide a marker for tracking the migration of the Front through time. Ocean Drilling Program Sites 1091, 1093 and 1094 are the only deep piston cored record hitherto sampled from the sediments of the circumpolar biogenic opal belt. Mapping of diatom mat deposits between these sites indicates a glacial-interglacial front migration of up to 6 degrees of latitude in the early/mid Pleistocene. The mid-Pleistocene transition marks a stepwise minimum 7° northward migration of the locus of the Polar Front sustained for about 450 kyr until an abrupt southward return to a locus similar to its modern position and further south than any mid-Pleistocene locus. This interval from a "900 ka event" that saw major cooling of the oceans and a δ 13C minimum through to the 424 ka Mid-Brunhes Event at Termination V is also seemingly characterised by 1) sustained decreased carbonate in the sub-tropical south Atlantic, 2) reduced strength of Antarctic deep meridional circulation, 3) lower interglacial temperatures and lower interglacial atmospheric CO 2 levels (by some 30 per mil) than those of the last 400 kyr, evidencing less complete deglaciation. This evidence is consistent with a prolonged period lasting 450 kyr of only partial ventilation of the deep ocean during interglacials and suggests that the mechanisms highlighted by recent hypotheses linking mid-latitude atmospheric conditions to the extent of deep ocean ventilation and carbon sequestration over glacial-interglacial cycles are likely in operation during the longer time scale characteristic of the mid-Pleistocene transition. The cooling that initiated the "900 ka event" may have been driven by minima in insolation amplitude related to eccentricity modulation of precession that also affected low

  10. Electric-field-dependent dynamic polarizability and state-insensitive conditions for optical trapping of diatomic polar molecules

    SciTech Connect

    Kotochigova, Svetlana; DeMille, David

    2010-12-15

    Selection of state-insensitive or 'magic' trapping conditions with ultracold atoms or molecules, where pairs of internal states experience identical trapping potentials, brings substantial benefits to precision measurements and quantum computing schemes. Working at such conditions could ensure that the detrimental effects of inevitable inhomogeneities across an ultracold sample are significantly reduced. However, this aspect of confinement remains unexplored for ultracold polar molecules. Here, we present means to control the ac Stark shift of rotational states of ultracold diatomic polar molecules, when subjected to both trapping laser light and an external electric field. We show that both the strength and relative orientation of the two fields influence the trapping potential. In particular, we predict 'magic electric field strengths' and a 'magic angle', where the Stark shift is independent of the dc external field for certain rotational states of the molecule.

  11. Future sea ice conditions in Western Hudson Bay and consequences for polar bears in the 21st century.

    PubMed

    Castro de la Guardia, Laura; Derocher, Andrew E; Myers, Paul G; Terwisscha van Scheltinga, Arjen D; Lunn, Nick J

    2013-09-01

    The primary habitat of polar bears is sea ice, but in Western Hudson Bay (WH), the seasonal ice cycle forces polar bears ashore each summer. Survival of bears on land in WH is correlated with breakup and the ice-free season length, and studies suggest that exceeding thresholds in these variables will lead to large declines in the WH population. To estimate when anthropogenic warming may have progressed sufficiently to threaten the persistence of polar bears in WH, we predict changes in the ice cycle and the sea ice concentration (SIC) in spring (the primary feeding period of polar bears) with a high-resolution sea ice-ocean model and warming forced with 21st century IPCC greenhouse gas (GHG) emission scenarios: B1 (low), A1B (medium), and A2 (high). We define critical years for polar bears based on proposed thresholds in breakup and ice-free season and we assess when ice-cycle conditions cross these thresholds. In the three scenarios, critical years occur more commonly after 2050. From 2001 to 2050, 2 critical years occur under B1 and A2, and 4 under A1B; from 2051 to 2100, 8 critical years occur under B1, 35 under A1B and 41 under A2. Spring SIC in WH is high (>90%) in all three scenarios between 2001 and 2050, but declines rapidly after 2050 in A1B and A2. From 2090 to 2100, the mean spring SIC is 84 (±7)% in B1, 56 (±26)% in A1B and 20 (±13)% in A2. Our predictions suggest that the habitat of polar bears in WH will deteriorate in the 21st century. Ice predictions in A1B and A2 suggest that the polar bear population may struggle to persist after ca. 2050. Predictions under B1 suggest that reducing GHG emissions could allow polar bears to persist in WH throughout the 21st century. PMID:23716301

  12. Solar Wind Influence on the Oxygen Content of Ion Outflow in the High Altitude Polar Cap During Solar Minimum Conditions

    NASA Technical Reports Server (NTRS)

    Elliott, Heather A.; Comfort, Richard H.; Craven, Paul D.; Chandler, Michael O.; Moore, Thomas E.

    2000-01-01

    We correlate solar wind and IMF properties with the properties of O(+) and H(+) in the polar cap in early 1996 during solar minimum conditions at altitudes between 5.5 and 8.9 Re geocentric using the Thermal Ion Dynamics Experiment (TIDE) on the POLAR satellite. Throughout the high altitude polar cap, we observe H(+) to be more abundant than O(+). H(+) is a significant fraction of both the ionosphere and the solar wind, and O(+) is not a significant species in the solar wind. O(+) is the major species in the ionosphere so the faction of O(+) present in the magnetosphere is commonly used as a measure of the ionospheric contribution to the magnetosphere. For these reasons, 0+ is of primary interest in this study. We observe O(+) to be most abundant at lower latitudes when the solar wind speed is low (and low Kp), and at higher solar wind speeds (and high Kp) O(+) is observed across most of the polar cap. We also find that O(+) density and parallel flux are well organized by solar wind dynamic pressure; they both increase with solar wind dynamic pressure. H(+) is not as highly correlated with solar wind and IMF parameters, but H(+) density and parallel flux have some negative correlation with IMF By, and some positive correlation with VswBIMF. In this solar minimum data set, H(+) is dominant so that contributions of this plasma to the plasma sheet would have a very low O(+) to H(+) ratio.

  13. Ages of fossil bones from British interglacial sites

    USGS Publications Warehouse

    Szabo, B. J.; Collins, D.

    1975-01-01

    THE time gap between the upper limit of radiocarbon dating (???60,000 yr BP) and the lower limit of dates generally obtainable using the K-Ar method (???250,000 yr BP) accounts for the scarcity of dates for the last two interglaciations (the Ipswichian and Hoxnian of Britain; the Eemian and Holsteinian of northern Europe). Accordingly, the ages of such important fossils as the Swanscombe and Steinheim skulls can only be guessed at. For that reason, the adaptation of a method that may date these interglacial periods is highly desirable. We discuss here the application of a uranium-series dating technique pertaining to that span of time. ?? 1975 Nature Publishing Group.

  14. Carrier accumulation near electrodes in ferroelectric films due to polarization boundary conditions

    SciTech Connect

    Misirlioglu, I. B. Yildiz, M.

    2014-07-14

    We study the effect of surface polarization on the distribution of free carriers in a wide bandgap semiconductor ferroelectric (FE) film using a thermodynamic approach. We show that free carriers, namely, holes and electrons from ionizable impurities or atomic vacancies can accumulate near the film-electrode interface, if FE polarization profile has a very steep change near the surface that is specified by the extrapolation length. Such an outcome is just the opposite of what happens in a Schottky junction in a partially or fully depleted film. This is also an entirely different effect than what has been often studied in similar structures, where the work function and screening length of the electrode metal determines the electronic character of the interface. Even for low-to-moderate densities of ionizable defects with states within the bandgap close to the band edges, high densities of carriers can localize close to the electrodes in a single domain state FE film when above a critical thickness. For very low densities of such ionizable defects, short extrapolation lengths cause electrical domain formation with minimal carrier accumulation because of the already weak depolarizing fields. This is also true for films below a critical thickness with low-to-moderate densities of ionizable impurities, i.e., electrical domains get stabilized regardless of defect density. The implications of our findings for polarization controlled Schottky to Ohmic-like transition of an interface and experimental results are discussed. It is also found that interfaces of an n-type FE heterostructure can behave like a p-type depending on the barrier heights and impurity density. We conclude that, for low-to-moderate ionizable impurity densities, it is the rate of change of polarization at the interface with position rather than solely its presence that leads to carrier accumulation and that both interfaces can become Ohmic-like with opposite signs of carriers.

  15. A White Nile megalake during the last interglacial period

    NASA Astrophysics Data System (ADS)

    Barrows, Timothy T.; Williams, Martin A. J.; Mills, Stephanie C.; Duller, Geoff A. T.; Fifield, L. Keith; Haberlah, David; Tims, Stephen G.; Williams, Frances M.

    2014-05-01

    The eastern Sahara Desert of Africa is one of the most climatically sensitive areas on Earth, varying from lake-studded savannah woodland to hyperarid desert over the course of a glacial-interglacial cycle. In currently semiarid Sudan there is widespread evidence that a very large freshwater lake once filled the White Nile River valley (Barrows et al., 2014). Here we present the first quantitative estimate for the dimensions of the lake and a direct age for the emplacement of its shoreline. Using a profile dating approach with the cosmogenic nuclide 10Be, we estimate an exposure age of 109 ± 8 ka for this megalake, indicating that it probably formed during the last interglacial period. This age is supported by optically stimulated luminescence dating of Blue Nile paleochannels associated with the lake. Using a high-resolution digital elevation model, we estimate that the lake was more than 45,000 km2 in area, making it comparable to the largest freshwater lakes on Earth today. We attribute the lake's existence to seasonal flood pulses as a result of local damming of the White Nile by a more southern position of the Blue Nile and greatly increased precipitation associated with an enhanced monsoon. References Barrows, T.T., Williams, M.A.J., Mills, S.C., Duller, G.A.T., Fifield, L.K., Haberlah, D., Tims, S.G., Williams, F.M., 2014. A White Nile megalake during the last interglacial period. Geology. 10.1130/g35238.1

  16. Dynamic simulation of stable water isotopes during the last interglacial

    NASA Astrophysics Data System (ADS)

    Gierz, P.; Lohmann, G.; Brocas, W.; Felis, T.

    2014-12-01

    Using the novel isotope module of the global fully coupled climate model COSMOS, we simulate the climate of the last interglacial for three time slices at 120, 125, and 130 kiloyears before present. The inclusion of stable water isotopes allows us to not only have a comprehensive picture of the climate state during a warm interglacial, but also allows for a direct comparison with climate proxy records. We compare our simulation with isotope data gathered from fossilized corals, which have an excellent temporal resolution and well constrained dating. A model data comparison allows us to see that there was an enhanced seasonality of both temperature and rainfall during the Eemian. While the data tends to produce a stronger winter cooling than the model, we suggest that this may be due to an incomplete climatology, as the measurements taken from the coral only encompasses a few decades. If the data happens to fall during an usually cool decade, the mismatch could be rectified. Alternatively, the data may include the cooling signal associated with centennial scale cold stadials during the Eemian. We test this by performing a freshwater perturbation experiment during the peak interglacial, which causes a pronounced cooling at the core site while the ocean circulation is depressed.

  17. Analysis of optimum conditions of depolarization imaging by polarization-sensitive optical coherence tomography in the human retina

    NASA Astrophysics Data System (ADS)

    Sugita, Mitsuro; Pircher, Michael; Zotter, Stefan; Baumann, Bernhard; Saito, Kenichi; Makihira, Tomoyuki; Tomatsu, Nobuhiro; Sato, Makoto; Hitzenberger, Christoph K.

    2015-01-01

    Measurement and imaging of depolarization by polarization-sensitive optical coherence tomography (PS-OCT) requires averaging of Stokes vector elements within two- or three-dimensional (3-D) evaluation windows to obtain the degree of polarization uniformity (DOPU). By use of a PS-OCT system with an integrated retinal tracker, we analyze optimum conditions for depolarization imaging, data processing, and segmentation of depolarizing tissue in the human retina. The trade-offs between figures of merit like DOPU imaging sensitivity, efficiency, and susceptibility are evaluated in terms of 3-D resolution. The results are used for a new, detailed interpretation of PS-OCT high-resolution images of the human retinal pigment epithelium and Bruch's membrane.

  18. Growth condition dependence of photoluminescence polarization in (100) GaAs/AlGaAs quantum wells at room temperature

    SciTech Connect

    Iba, Satoshi; Saito, Hidekazu; Yuasa, Shinji; Watanabe, Ken; Ohno, Yuzo

    2015-08-28

    We conducted systematic measurements on the carrier lifetime (τ{sub c}), spin relaxation time (τ{sub s}), and circular polarization of photoluminescence (P{sub circ}) in (100) GaAs/AlGaAs multiple quantum wells grown by molecular beam epitaxy (MBE). The τ{sub c} values are strongly affected by MBE growth conditions (0.4–9 ns), whereas the τ{sub s} are almost constant at about 0.13 ns. The result suggests that spin detection efficiency [τ{sub s}/(τ{sub c} + τ{sub s})], which is expected to be proportional to a steady-state P{sub circ}, is largely dependent on growth condition. We confirmed that the P{sub circ} has similar dependence on growth condition to those of τ{sub s}/(τ{sub c} + τ{sub s}) values. The study thus indicates that choosing the appropriate growth condition of the QW is indispensable for obtaining a high P{sub circ} from a spin-polarized light-emitting diode (spin-LED)

  19. Glacial-interglacial shifts in global and regional precipitation δ18O

    NASA Astrophysics Data System (ADS)

    Jasechko, S.; Lechler, A.; Pausata, F. S. R.; Fawcett, P. J.; Gleeson, T.; Cendón, D. I.; Galewsky, J.; LeGrande, A. N.; Risi, C.; Sharp, Z. D.; Welker, J. M.; Werner, M.; Yoshimura, K.

    2015-03-01

    Previous analyses of past climate changes have often been based on site-specific isotope records from speleothems, ice cores, sediments and groundwaters. However, in most studies these dispersed records have not been integrated and synthesized in a comprehensive manner to explore the spatial patterns of precipitation isotope changes from the last ice age to more recent times. Here we synthesize 88 globally-distributed groundwater, cave calcite, and ice core isotope records spanning the last ice age to the late-Holocene. Our data-driven review shows that reconstructed precipitation δ18O changes from the last ice age to the late-Holocene range from -7.1‰ (ice age δ18O < late-Holocene δ18O) to +1.8‰ (ice age δ18O > late-Holocene δ18O) with wide regional variability. The majority (75%) of reconstructions have lower ice age δ18O values than late-Holocene δ18O values. High-magnitude, negative glacial-interglacial precipitation δ18O shifts (ice age δ18O < late-Holocene δ18O by more than 3‰) are common at high latitudes, high altitudes and continental interiors. Conversely, lower-magnitude, positive glacial-interglacial precipitation δ18O shifts (ice age δ18O > late-Holocene δ18O by less than 2‰) are most common along subtropical coasts. Broad, global patterns of glacial-interglacial precipitation δ18O shifts are consistent with stronger-than-modern isotopic distillation of air masses during the last ice age, likely impacted by larger global temperature differences between the tropics and the poles. Further, to complement our synthesis of proxy-record precipitation δ18O, we compiled isotope enabled general circulation model simulations of recent and last glacial maximum climate states. Simulated precipitation δ18O from five general circulation models show better inter-model and model-observation agreement in the sign of δ18O changes from the last ice age to present day in temperate and polar regions than in the tropics. Further model precipitation

  20. Polarization electric field in subalfvenic plasma jet under condition of field- aligned currents generation

    NASA Astrophysics Data System (ADS)

    Sobyanin, D.; Gavrilov, B.; Podgorny, I.

    The subalfvenic magnetized plasma jet propagating across the geomagnetic field generates field-aligned currents in the ionospheric plasma. As a result the transverse polarization electric field Ep =-VxB/c in the jet should be reduced (plasma jet depolarization). These phenomena are investigated in the laboratory experiment. It was revealed that the depolarization is accompanied by the appearing of the electric field E along the plasma velocity vector. The value of E is comparable with theaa transverse electric field. It results in the plasma jet deflection. The possibility of manifestation of these effects in the NORTH STAR Russian-American active rocket experiment is discussed.

  1. Troposphere-Stratosphere Dynamic Coupling Under Strong and Weak Polar Vortex Conditions

    NASA Technical Reports Server (NTRS)

    Perlwitz, Judith; Graf, Hans-F.; Hansen, James E. (Technical Monitor)

    2001-01-01

    The relationship between Northern Hemisphere (NH) tropospheric and stratospheric wave-like anomalies of spherical zonal wave number (ZWN) 1 is studied by applying Canonical Correlation Analysis (CCA). A lag-correlation technique is used with 10-day lowpass filtered daily time series of 50- and 500-hPa geopotential heights. Generally stratospheric circulation is determined by ultralong tropospheric planetary waves. During winter seasons characterized either by any anomalously strong or weak polar winter vortex different propagation characteristics for waves of ZWN 1 are observed. The non-linear perspective of the results have implications for medium range weather forecast and climate sensitivity experiments.

  2. A Cross-Polarization Based Rotating-Frame Separated-Local-Field NMR Experiment Under Ultrafast MAS Conditions

    PubMed Central

    Zhang, Rongchun; Damron, Joshua; Vosegaard, Thomas

    2014-01-01

    Rotating-frame separated-local-field solid-state NMR experiments measure highly resolved heteronuclear dipolar couplings which, in turn, provide valuable interatomic distances for structural and dynamic studies of molecules in the solid-state. Though many different rotating-frame SLF sequences have been put forth, recent gains in ultrafast MAS technology have considerably simplified pulse sequence requirements due to the suppression of proton-proton dipolar interactions. In this study we revisit a simple two-dimensional 1H-13C dipolar coupling/chemical shift correlation experiment using 13C detected Cross-Polarization with a Variable Contact time (CPVC) and systematically study the conditions for its optimal performance at 60 kHz MAS. In addition, we demonstrate the feasibility of a proton-detected version of the CPVC experiment. The theoretical analysis of the CPVC pulse sequence under different Hartmann-Hahn matching conditions confirms that it performs optimally under the ZQ (w1H-w1C=±wr) condition for polarization transfer. The limits of the cross polarization process are explored and precisely defined as a function of offset and Hartmann-Hahn mismatch via spin dynamics simulation and experiments on a powder sample of uniformly 13C-labeled L-isoleucine. Our results show that the performance of the CPVC sequence and subsequent determination of 1H-13C dipolar couplings are insensitive to 1H/13C frequency offset frequency when high RF fields are used on both RF channels. Conversely, the CPVC sequence is quite sensitive to the Hartmann-Hahn mismatch, particularly for systems with weak heteronuclear dipolar couplings. We demonstrate the use of the CPVC based SLF experiment as a tool to identify different carbon groups, and hope to motivate the exploration of more sophisticated 1H detected avenues for ultrafast MAS. PMID:25486635

  3. Oceanographic Influences on the Style and Timing of Glacial-Interglacial Change in Western Beringia

    NASA Astrophysics Data System (ADS)

    Brigham-Grette, J.; Glushkova, O. Y.; Anderson, P.; Lozhkin, A.; Gualtieri, L.

    2004-12-01

    deposits (Gubik FM) dated to MIS stage 5a on the Alaskan North Slope, record both flooding of the Bering Strait and collapse of an ice sheet that likely accumulated since 5d over some part of the western Canadian Arctic. Flooding of the Bering Strait in MIS 5a, coupled with an insolation high, may have contributed to the collapse of Canadian and Eurasian ice sheets allowing the penetration of moisture across the continent and the expansion of valley glaciers in the Bering Straits region well beyond LGM limits. Increasing continentality, sea ice cover and the expansion of the Scandinavian/Eurasian ice sheet (Siegert et al., 2001) then limited available moisture supply across most of Beringia. During MIS stage 3 climate remained relatively harsh across much of Alaska, but parts of western Beringia experienced the temporary return of interglacial vegetation to near modern conditions coincident with insolation highs. LGM glaciation across most of Beringia was restricted to local mountain ranges and dominated by valley and cirque glaciers. A mosaic of dry habitats characterized by herb and forb-tundra dominated ice -free valleys and lowlands with some evidence for mesic conditions across parts of central Beringia. A rapid rise of sea level at the end of the LGM likely caused swift migration of the shoreline as summers warmed into the early Holocene and re-established modern vegetation.

  4. Effect of the surface condition of silicas with grafted monofunctional polyfluoroalkylsilanes on the adsorption of polar molecules

    NASA Astrophysics Data System (ADS)

    Roshchina, T. M.; Shoniya, N. K.; Tayakina, O. Ya.; Tkachenko, O. P.; Kustov, L. M.

    2013-08-01

    Lyophobized silicas containing relatively small numbers of grafted perfluorohexyl (1.1 nm-2) and perfluorobutyl (1.7 nm-2) groups are studied by means of gas chromatography, adsorption under static conditions, and IR spectroscopy. The results are compared to those obtained by us previously for a series of samples with dense polyfluoroalkyl monolayers (≥2.0 nm-2). Effects related to the influence of the grafting density and the size of fluorine-containing groups on the adsorption of polar compounds and the hydrophobicity of the surface are discussed.

  5. Application of novel polar representation method for monitoring minor engine condition variations

    NASA Astrophysics Data System (ADS)

    Charles, P.; Sinha, Jyoti K.; Gu, F.; Ball, A. D.

    2010-04-01

    In an earlier study, a Noval Polar Presentation (NPP) method has been suggested to detect the engine combustion-related faults for medium-speed diesel engines. The earlier proposed NPP method basically used the signature of the crankshaft torsional vibration to identify the faulty cylinder accurately. However, the detection of only a large fault like the cylinder misfiring for the 2 typical engines (16-cylinder and 20-cylinder engines) has been demonstrated in the earlier study. Now the usefulness of the NPP method in detection of even a very small level of the engine combustion fault like an earlier or later opening of the fuel injection valve by just a few degrees has been presented here.

  6. Glacial-interglacial changes in H218O, HDO and deuterium excess - results from the fully coupled ECHAM5/MPI-OM Earth system model

    NASA Astrophysics Data System (ADS)

    Werner, M.; Haese, B.; Xu, X.; Zhang, X.; Butzin, M.; Lohmann, G.

    2016-02-01

    In this study we present the first results of a new isotope-enabled general circulation model set-up. The model consists of the fully coupled ECHAM5/MPI-OM atmosphere-ocean model, enhanced by the JSBACH interactive land surface scheme and an explicit hydrological discharge scheme to close the global water budget. Stable water isotopes H218O and HDO have been incorporated into all relevant model components. Results of two equilibrium simulations under pre-industrial and Last Glacial Maximum conditions are analysed and compared to observational data and paleoclimate records for evaluating the model's performance in simulating spatial and temporal variations in the isotopic composition of the Earth's water cycle. For the pre-industrial climate, many aspects of the simulation results of meteoric waters are in good to very good agreement with both observations and earlier atmosphere-only simulations. The model is capable of adequately simulating the large spread in the isotopic composition of precipitation between low and high latitudes. A comparison to available ocean data also shows a good model-data agreement; however, a strong bias of overly depleted ocean surface waters is detected for the Arctic region. Simulation results under Last Glacial Maximum boundary conditions also fit to the wealth of available isotope records from polar ice cores, speleothems, as well as marine calcite data. Data-model evaluation of the isotopic composition in precipitation reveals a good match of the model results and indicates that the temporal glacial-interglacial isotope-temperature relation was substantially lower than the present spatial gradient for most mid- to high-latitudinal regions. As compared to older atmosphere-only simulations, a remarkable improvement is achieved for the modelling of the deuterium excess signal in Antarctic ice cores. Our simulation results indicate that cool sub-tropical and mid-latitudinal sea surface temperatures are key for this progress. A recently

  7. Geological "Ground Truth" of Sea-level Highstand Events During Warm Interglaciations (MIS 11 and 5e): Taking the Punch out of Proxy Precision

    NASA Astrophysics Data System (ADS)

    Hearty, P. J.

    2005-12-01

    High-resolution sea-level records for marine isotope stages (MIS) 11 and 5e from coastal outcrops in Bahamas, Bermuda, Hawaii, and Western Australia provide physical confirmation of extreme ice-melting events during Pleistocene interglacials. Field evidence indicates MIS 11 sea level rose in a series of oscillations to c. +20 m, while that of MIS 5e reached its maximum of +6-10 m. Because these were brief events (100s yrs), their true magnitude is generally muted or obscured in deep-sea oxygen isotope records; generally averaged over thousands of years by the combined effects of sampling, bioturbation, and sedimentation rates. Further unresolvable variables such as temperature and salinity further cloud the isotope proxy record. Thus, the tangible rock record is of greatest importance in understanding the nature of these extreme events. Geomorphology, sedimentary structures, taphonomy of and dating of organisms, and petrology provide ground truth at field sites. Sea-level highstands preserve terraces and benches by erosion and subsequent deposition of sub- and intertidal sediments. Fenestral porosity is a measure of intertidal wetting and drying of sand, while decimetre-scale, high-angle cross beds of poorly-sorted sand and gravel indicate shallow subtidal conditions. In situ coral heads describe similar subtidal conditions. Delicate, sometimes partially articulated skeletons of birds and reptiles in sea caves reveal a protected shoreline. An early generation of isopachous, fibrous cement verifies the presence of marine phreatic water over a sustained period of time. These features, often misinterpreted (McMurtry, 2004, AGU Fall Meeting, OS21E-06), categorically exclude emplacement by tsunami waves. Oceanic isotope records cannot produce an equivalent level of resolution of short, extreme events via (in terms of age, duration, rates of sea-level and ice-volume changes), thus shifting the `burden of proof' to proxy methods to identify such events. In our quest to

  8. Glacial-interglacial changes of H218O, HDO and deuterium excess - results from the fully coupled Earth System Model ECHAM5/MPI-OM

    NASA Astrophysics Data System (ADS)

    Werner, M.; Haese, B.; Xu, X.; Zhang, X.; Butzin, M.; Lohmann, G.

    2015-10-01

    In this study we present first results of a new isotope-enabled general circulation model setup. The model consists of a fully coupled atmosphere-ocean model ECHAM5/MPI-OM, enhanced by the interactive land surface scheme JSBACH and an explicit hydrological discharge scheme to close the global water budget. Stable water isotopes H218O and HDO have been incorporated into all relevant model components. Results of two equilibrium simulations under pre-industrial and last glacial maximum conditions are analysed and compared to observational data and paleoclimate records for evaluating the model's performance of simulating spatial and temporal variations in the isotopic composition of the Earth's water cycle. For the pre-industrial climate, many aspects of the simulation results of meteoric waters are in good to very good agreement with both observations and earlier atmosphere-only simulations. The model is capable of adequately simulating the large spread in the isotopic composition of precipitation between low and high latitudes. A comparison to available ocean data also shows a good model-data agreement, however a strong bias of too depleted ocean surface waters is detected for the Arctic region. Simulation results under last glacial maximum boundary conditions also fit to the wealth of available isotope records from polar ice cores, speleothems, as well as marine calcite data. Data-model evaluation of the isotopic composition in precipitation reveals a good match of the model results and indicates that the temporal glacial-interglacial isotope-temperature relation was substantially lower than the present spatial gradient for most mid- to high-latitudinal regions. As compared to older atmosphere-only simulations, a remarkable improvement is achieved for the modelling of the deuterium excess signal in Antarctic ice cores. Our simulation results indicate that cool sub-tropical and mid-latitudinal sea surface temperatures are key for this progress. A recently discussed

  9. A high-resolution mid-Pleistocene temperature record from Arctic Lake El'gygytgyn: a 50 kyr super interglacial from MIS 33 to MIS 31?

    NASA Astrophysics Data System (ADS)

    de Wet, Gregory A.; Castañeda, Isla S.; DeConto, Robert M.; Brigham-Grette, Julie

    2016-02-01

    Previous periods of extreme warmth in Earth's history are of great interest in light of current and predicted anthropogenic warming. Numerous so called "super interglacial" intervals, with summer temperatures significantly warmer than today, have been identified in the 3.6 million year (Ma) sediment record from Lake El'gygytgyn, northeast Russia. To date, however, a high-resolution paleotemperature reconstruction from any of these super interglacials is lacking. Here we present a paleotemperature reconstruction based on branched glycerol dialkyl glycerol tetraethers (brGDGTs) from Marine Isotope Stages (MIS) 35 to MIS 29, including super interglacial MIS 31. To investigate this period in detail, samples were analyzed with an unprecedented average sample resolution of 500 yrs from MIS 33 to MIS 30. Our results suggest the entire period currently defined as MIS 33-31 (∼1114-1062 kyr BP) was characterized by generally warm and highly variable conditions at the lake, at times out of phase with Northern Hemisphere summer insolation, and that cold "glacial" conditions during MIS 32 lasted only a few thousand years. Close similarities are seen with coeval records from high southern latitudes, supporting the suggestion that the interval from MIS 33 to MIS 31 was an exceptionally long interglacial (Teitler et al., 2015). Based on brGDGT temperatures from Lake El'gygytgyn (this study and unpublished results), warming in the western Arctic during MIS 31 was matched only by MIS 11 during the Pleistocene.

  10. Luminescence dating of interglacial coastal depositional systems: Recent developments and future avenues of research

    NASA Astrophysics Data System (ADS)

    Lamothe, Michel

    2016-08-01

    luminescence-dated coastal feature of all, as the chronology of the sea level markers is crucial to assess global eustatic sea level variations through the course of the last interglacial. Nevertheless, the observed abundance of young (100-120 ka) luminescence ages for presumed MIS5e sediments may underline methodological issues, and/or reflect the higher preservation potential of late regressive sequences. On the other hand, the occurrence of geographically distant reports of MIS5a high stand might reflect a true eustatic origin for this event. Age analysis supports the impression of general reliability of luminescence for the timing of former sea level high stands. There is a clear need to address issues in dose rate variability, in the phenomenology of fading in feldspar, and in the behaviour of luminescence growth with dose, both in laboratory and natural conditions. These could be addressed and properly evaluated by dating different minerals, as multiple or single grains, with consequent variable internal dose rates. More robust practices in the application of luminescence dating techniques could eventually constrain the age uncertainties to no better than 2-3%. Therefore, the strength of luminescence as a dating tool is more in terms of its extended age range and the ubiquity of datable material.

  11. Aboveground activity rhythm in Arctic black-capped marmot ( Marmota camtschatica bungei Katschenko 1901) under polar day conditions

    NASA Astrophysics Data System (ADS)

    Semenov, Youri; Ramousse, Raymond; Le Berre, Michel; Vassiliev, Vladimir; Solomonov, Nikita

    2001-04-01

    Daily aboveground activity of wild black-capped marmots of Yakutia ( Marmota camtschatica bungei) was recorded under 'polar day' conditions at 71°56' N and 127°19' E (north of the Polar Circle). From the beginning of May until the end of August, the sun was permanently above or close to the horizon. However under this condition of continuous lighting, the aboveground activity of these arctic hibernating mammals was periodic. Onset and end of activity showed marked changes throughout the seasons. Activity time increased strongly from hibernation emergence until the end of July and then decreased slowly until onset of hibernation. Below daily mean temperatures of 5 °C, activity started when the sun was 35° above the horizon, and ended when it dropped below 28°. When daily mean temperatures were above 5 °C, activity onset was synchronised with a solar altitude around 17-18° and activity ended at 10°. Activity onset was more precise relative to the solar altitude than the end of activity. This may be explained by late feeding bouts, following a midday thermal stress. In absence of rapid natural light-dark (LD) transitions that occur at civil twilight, our results suggest that the activity pattern of black-capped marmots may be synchronised by the light cycle through the solar altitude and ambient temperature.

  12. Coupled Warming and Drought in the American Southwest During Long mid-Pleistocene Interglacials (MIS 11 and 13)

    NASA Astrophysics Data System (ADS)

    Fawcett, P. J.; Werne, J.; Anderson, R.; Heikoop, J.; Brown, E.; Hurley, L.; Smith, S.; Berke, M.; Soltow, H.; Goff, F.; Geissman, J.; Woldegabriel, G.; Fessenden, J.; Cisneros-Dozal, M.; Allen, C. D.

    2008-12-01

    timescales, superimposed on future anthropogenic warming. Intervals of mudcrack facies representing significant drought conditions occur during or just after the warmest phases of the two interglacials. This past coupling between warm temperatures and extended drought in the SW as a natural feature of long interglacials is consistent with recent predictions of extended Dust-Bowl-like conditions in the SW as a response to global warming.

  13. Co-variation of nitrogen isotopes and redox states through glacial-interglacial cycles in the Black Sea

    NASA Astrophysics Data System (ADS)

    Quan, Tracy M.; Wright, James D.; Falkowski, Paul G.

    2013-07-01

    In all aquatic environments, nitrogen cycling within the water column is strongly influenced by oxygen. We hypothesize that the nitrogen isotopic composition (δ15N) of organic matter deposited in the sediments is a proxy for the redox state of the water column at the time of deposition. We tested the hypothesis by measuring the bulk sedimentary δ15N values in a drill core from the Black Sea, a basin that alternates between oxic, less saline conditions and anoxic, marine conditions on glacial-interglacial time scales. We reconstructed these changes in Black Sea redox conditions using sedimentary δ15N, total organic carbon (TOC), total nitrogen (TN), redox-sensitive metals, and micropaleontological data from a deep-sea core (DSDP Site 380). The sedimentary data reveal that during the transitions between oxic and anoxic conditions, δ15N values increased relative to the preceding and succeeding quasi-steady-state oxic and anoxic periods. The results indicate that the reciprocal transitional states from anoxic to oxic conditions were accompanied by intense denitrification; during the quasi-stable oxic and anoxic states (characterized by glacial fresh water and interglacial marine conditions) nitrification and complete nitrate utilization, respectively, dominate the nitrogen cycle. While other factors may influence the δ15N record, our results support the hypothesis that the variations in nitrogen isotopic composition of organic matter are strongly influenced by changes in redox state in the Black Sea subphotic zone on glacial-interglacial time scales, and can be explained by a relatively simple model describing the effects of oxygen on the microbial processes that drive the nitrogen cycle in marine ecosystems. Our model suggests that the nitrogen isotopic composition of marine sediments, on geological time scales, can be used to reconstruct the redox state of the overlying water column.

  14. Rocket observations of positive ions during polar mesosphere winter echo conditions at Andenes in January 2005; first analysis and interpretations

    NASA Astrophysics Data System (ADS)

    Brattli, A.; Rapp, M.; Singer, W.; Lattek, R.; Friedrich, M.; Havnes, O.; Blix, T. A.; Svenes, K. R.

    2005-08-01

    On Janurary 18, 2005, two instrumented miniaturised rocket payloads, each with a Positive Ion Probe (PIP) and a Faraday rotation/differential absorption experiment, were launched from Andøya Rocket Range (69°N). The instrumented payloads were launched into conditions with Polar Mesosphere Winter Echoes (PMWE) as part of a salvo of meteorological rockets measuring temperature and wind using falling spheres and chaff. Layers of PMWE were detected in the altitude range 55-77 km by the 53.5 MHz ALWIN radar. Fluctuations in the ion density, as measured in situ by the instrumented payloads, show that there was turbulence inside the PMWE layers, but not above/below and between. Data from the PIPs are analysed and related to the geophysical conditions, as observed with the ALWIN radar and meteorological rockets.

  15. Polar Vortex Conditions during the 1995-96 Artic Winter: Meteorology and MLS Ozone

    NASA Technical Reports Server (NTRS)

    Manney, G. L.; Santee, M. L.; Froidevaux, L.; Waters, J. W.; Zurek, R. W.

    1996-01-01

    The 1995-96 northern hemisphere (NH) 205 winter stratosphere was colder than in any of the previous 17 winters, with lower stratospheric temperatures continuously below the type 1 (primarily HN03) polar stratospheric cloud (PSC) threshold for over 2 1/2 months. Upper tropospheric ridges in late Feb and early Mar 1996 led to the lowest observed NH lower stratospheric temperatures, and the latest observed NH temperatures below the type 2 (water ice) PSC threshold. Consistent with the unusual cold and chemical processing on PSCS, Upper Atmosphere Research Satellite (UARS) MLS observed a greater decrease in lower stratospheric ozone (03) in 1995-96 than in any of the previous 4 NH winters. 03 decreased throughout the vortex over an altitude range nearly as large as that typical of the southern hemisphere (SH). The decrease between late Dec 1995 and early Mar 1996 was about 2/3 of that over the equivalent SH period. As in other NH winters, temperatures in 1996 rose above the PSC threshold before the spring equinox, ending chemical processing in the NH vortex much earlier than is usual in the SH. A downward trend in column 03 above 100 hPa during Jan and Feb 1996 appears to be related to the lower stratospheric 03 depletion.

  16. Predicting field-scale dispersion under realistic conditions with the polar Markovian velocity process model

    NASA Astrophysics Data System (ADS)

    Dünser, Simon; Meyer, Daniel W.

    2016-06-01

    In most groundwater aquifers, dispersion of tracers is dominated by flow-field inhomogeneities resulting from the underlying heterogeneous conductivity or transmissivity field. This effect is referred to as macrodispersion. Since in practice, besides a few point measurements the complete conductivity field is virtually never available, a probabilistic treatment is needed. To quantify the uncertainty in tracer concentrations from a given geostatistical model for the conductivity, Monte Carlo (MC) simulation is typically used. To avoid the excessive computational costs of MC, the polar Markovian velocity process (PMVP) model was recently introduced delivering predictions at about three orders of magnitude smaller computing times. In artificial test cases, the PMVP model has provided good results in comparison with MC. In this study, we further validate the model in a more challenging and realistic setup. The setup considered is derived from the well-known benchmark macrodispersion experiment (MADE), which is highly heterogeneous and non-stationary with a large number of unevenly scattered conductivity measurements. Validations were done against reference MC and good overall agreement was found. Moreover, simulations of a simplified setup with a single measurement were conducted in order to reassess the model's most fundamental assumptions and to provide guidance for model improvements.

  17. Driving Stresses in Mars Polar Ice Caps and Conditions for Ice Flow

    NASA Technical Reports Server (NTRS)

    Zwally, H. Jay; Saba, Jack L.

    1999-01-01

    Measurements of the topography of the North polar ice cap by the Mars Orbiter Laser Altimeter (MOLA) show that the ice cap is 2950 +/- 200 meters thick. The volume of the cap is about 1.2 x 10(exp 6) cu km covering an area of 1.04 x 10(exp 6) sq km, which is about 40 percent of the Greenland ice sheet in volume and 62 percent in area. The composition of the Northern cap was previously concluded to be predominately H2O, rather than CO2 ice, based on thermodynamic considerations of the insustainablity of CO2 during summer. Principal questions about the cap are: does the ice move and at what rate, is the cap currently growing or depleting in volume, and how and when was the cap formed? Recent research on terrestrial ice sheets indicates that rates of ice deformation at the low stress values characteristic of ice sheets are significantly higher than the rates given by the classic viscous-plastic flow laws commonly used.

  18. Dynamics of the Polar Cusps for Active Solar Wind Conditions: Large-scale Modeling

    NASA Astrophysics Data System (ADS)

    Berchem, J.; Richard, R. L.; Escoubet, C. P.; Taylor, M. G.; Laakso, H. E.; Masson, A.; Dandouras, I. S.; Reme, H.; Pitout, F.; Lucek, E. A.

    2010-12-01

    The energy-latitude dispersion of precipitating particles observed by spacecraft near the high-latitude dayside magnetosphere offers a unique opportunity to investigate the large-scale topology and dynamics of the polar cusps. In particular, consecutive crossings of the cusps made by the Cluster spacecraft in a string of pearl configuration are particularly well suited for investigating the temporal and spatial evolution of precipitating particles as solar wind discontinuities interact with the dayside magnetopause. We present the results of large-scale simulation studies based on Cluster observations of ion dispersions following rapid changes in the direction of the interplanetary magnetic field (IMF). First, we use three-dimensional magnetohydrodynamic (MHD) simulations to follow the evolution of the global topology of the magnetic field during the events. Subsequently, the time-dependent electric and magnetic fields predicted by the MHD simulations are utilized to compute the trajectories of large samples of solar wind ions launched upstream of the bow shock. We assess the results of the studies by comparing Cluster ion measurements with ion dispersions calculated from the simulations along the spacecraft trajectories and discuss the temporal evolution and spatial extent of precipitating particles in the context of the reconnection process at the dayside magnetopause.

  19. Orbital forcing of the marine isotope stage 9 interglacial.

    PubMed

    Stirling, C H; Esat, T M; Lambeck, K; McCulloch, M T; Blake, S G; Lee, D C; Halliday, A N

    2001-01-12

    Milankovitch orbital forcing theory has been used to assign time scales to many paleoclimate records. However, the validity of this theory remains uncertain, and independent sea-level chronologies used to test its applicability have been restricted largely to the past approximately 135,000 years. Here, we report U-series ages for coral reefs formed on Henderson Island during sea-level high-stands occurring at approximately 630,000 and approximately 330,000 years ago. These data are consistent with the hypothesis that interglacial climates are forced by Northern Hemisphere summer solar insolation centered at 65 degrees N latitude, as predicted by Milankovitch theory. PMID:11209076

  20. Comparing Terrestrial Organic Carbon Cycle Dynamics in Interglacial and Glacial Climates in the South American Tropics

    NASA Astrophysics Data System (ADS)

    Fornace, K. L.; Galy, V.; Hughen, K. A.

    2014-12-01

    The application of compound-specific radiocarbon dating to molecular biomarkers has allowed for tracking of specific organic carbon pools as they move through the environment, providing insight into complex processes within the global carbon cycle. Here we use this technique to investigate links between glacial-interglacial climate change and terrestrial organic carbon cycling in the catchments of Cariaco Basin and Lake Titicaca, two tropical South American sites with well-characterized climate histories since the last glacial period. By comparing radiocarbon ages of terrestrial biomarkers (leaf wax compounds) with deposition ages in late glacial and Holocene sediments, we are able to gauge the storage time of these compounds in the catchments in soils, floodplains, etc. before transport to marine or lacustrine sediments. We are also able to probe the effects of temperature and hydrologic change individually by taking advantage of opposite hydrologic trends at the two sites: while both were colder during the last glacial period, precipitation at Titicaca decreased from the last glacial period to the Holocene, but the late glacial was marked by drier conditions at Cariaco. Preliminary data from both sites show a wide range of apparent ages of long-chain n-fatty acids (within error of 0 to >10,000 years older than sediment), with the majority showing ages on the order of several millennia at time of deposition and age generally increasing with chain length. While late glacial leaf waxes appear to be older relative to sediment than those deposited in the Holocene at both sites, at Cariaco we find a ~2-3 times larger glacial-interglacial age difference than at Titicaca. We hypothesize that at Titicaca the competing influences of wetter and colder conditions during the last glacial period, which respectively tend to increase and decrease the rate of organic carbon turnover on land, served to minimize the contrast between glacial and interglacial leaf wax storage time

  1. Where clocks are redundant: weak circadian mechanisms in reindeer living under polar photic conditions

    NASA Astrophysics Data System (ADS)

    van Oort, Bob E. H.; Tyler, Nicholas J. C.; Gerkema, Menno P.; Folkow, Lars; Stokkan, Karl-Arne

    2007-03-01

    Biological rhythms are a result of interplay between endogenous clocks and the ambient light-dark (LD) cycle. Biological timing in resident polar organisms presents a conundrum because these experience distinct daily LD cycles for only a few weeks each year. We measured locomotor activity in reindeer, Rangifer tarandus platyrhynchus (SR, n = 5 and 6) and R. tarandus tarandus (NR, n = 6), ranging freely at 78 and 70°N, respectively, continuously throughout 1 year using data loggers. NR, but not SR, are gregarious which enabled us to examine the integrated effects of differences in social organisation and the photic environment at two different latitudes on the organisation of activity. In both sub-species, ultradian bouts of activity and inactivity alternated across the 24-h day throughout the year. This pattern was modified by the LD cycle in NR but barely at all in SR. Periodogram analysis revealed significant ultradian rhythmicity in both sub-species; the frequency of daily cycles of activity increased from three per day in winter to nearly five in summer. We conclude that this increase, and a concomitant increase in the level of daily activity, reflected the seasonal increase in the animals’ appetite and the quality of their forage. Secondly, the combination, most evident in SR, of a weak photic response, weak circadian mechanisms and a weak social synchronization reduces the constraints of biological timing in an environment which is effectively non-rhythmic most of the year and permits expression of the basic ultradian pattern of ruminant activity. Third, the weaker 24-h rhythmicity in SR compared to NR indicates a latitudinal decrease in circadian organization and photic responsiveness in Rangifer.

  2. Middle pleistocene interglacial sediments at Tye green, Stansted Airport, Essex, England

    NASA Astrophysics Data System (ADS)

    Boreham, S.; Field, M. H.; Gibbard, P. L.

    1999-05-01

    Interglacial lake deposits at Tye Green, Stansted, resting on unweathered till and overlain by a weathered diamicton are correlated with the temperate Hoxnian Stage. The sediments represent the infilling of an isolated kettle-hole type of lake basin formed at the end of the cold Anglian Stage. Through the temperate period this basin was infilled by inorganic and organic sediments that record the development and decline of deciduous forest. Later periglacial conditions are indicated by the final infilling of the basin by reworked till. The sedimentary sequence and vegetational development recorded in the sediments at Tye Green are compared with other Hoxnian sites in eastern England. Changes in deposition rates are interpreted as representing water-table fluctuations resulting from changes in precipitation. The deposits at Tye Green provide a useful stratigraphical marker in the glacial sequence of the district.

  3. Last Interglacial (MIS5e) hydrographic shifts linked to meltwater discharges from the East Greenland margin

    NASA Astrophysics Data System (ADS)

    Zhuravleva, Anastasia; Bauch, Henning A.; Van Nieuwenhove, Nicolas

    2016-04-01

    The East Greenland Current (EGC) plays a key role in transporting polar water from the Arctic to convectional sites of the Iceland and Labrador seas. Ongoing melting of the Greenland Ice Sheet (GIS) as well as the Arctic sea ice prompts freshening of the EGC and accumulation of low-density water in the subpolar North Atlantic, thus affecting the stabilities of water mass overturning and subsequent northward heat transfer. To assess natural eastern GIS dynamics and possible freshwater-induced regional oceanic reorganizations we analyzed several sediment sequences from the poorly investigated area along the eastern Greenland margin and the western Nordic Seas. Records span the last interglacial (LIG, MIS5e) cycle, including deglacial Termination 2 and the LIG climatic optimum. On a global scale, the latter is believed to have been warmer than present, with a higher sea level, and may, therefore, serve as a promising analogue for future hydrographic changes. Based on various proxy data (stable isotopes, planktic foraminiferal assemblages, ice-rafted debris) our reconstructions support the notion of a "two-step development" of Termination 2 which underwent severe surface freshening in the subpolar North Atlantic. This is shown in extremely light oxygen isotopic values registered all along the eastern Greenland margin during early MIS5e, which are indicative for pronounced eastern/central GIS retreat and a further propagation of the resulting meltwater southward via the EGC. In addition, we find compelling evidence for at least two separate meltwater episodes in proximity of the eastern GIS during early MIS5e. The climatic episode in between is correlated with an early LIG warm peak, which may be linked to enhanced presence of Atlantic water in the central Nordic Seas (Bauch et al., 2012) and further downstream along southern Greenland (Hillaire-Marcel et al., 1994, Irvali et al., 2012). Our data, therefore, reveal a complex and variable dynamic of the EGC during MIS5e

  4. Effects of Solar Wind Conditions on the Plasma Wake Within a Polar Crater: Preliminary Results

    NASA Technical Reports Server (NTRS)

    Zimmerman, M. I.; Farrell, W. M.; Stubbs, T. J.

    2011-01-01

    As the solar wind sweeps horizontally past a shadowed lunar crater it simultaneously diffuses toward the surface through an ambipolar process, forming a plasma wake (e.g., Figure 1). Importantly, the resulting electric field structure diverts solar wind protons toward the cold crater floor where they may represent a source of surficial hydrogen. We present a handful of two-dimensional kinetic simulations exploring the range of wake structures and surface particle fluxes possible under various background plasma conditions.

  5. Continued Melting of Greenland Ice-Sheet Regulated Northern Hemisphere Climate During the Last Interglacial

    NASA Astrophysics Data System (ADS)

    Govin, A.; Michel, E.; Marti, O.; Braconnot, P.; Jansen, E.; Labeyrie, L.; Landais, A.; Mosquet, E.; Risebrobakken, B.; Swingedouw, D.; Waelbroeck, C.

    2008-12-01

    The evolution of Northern Hemisphere climate during the Last Interglacial (LIG) (129--118 ka) is significant for the study of future climate changes as it may provide information on the climate system responses and feedbacks to radiative forcing (Jansen et al. 2007). We present here a comparison of foraminiferal records from high latitude deep-sea cores with model simulations over the LIG period. We compare high-resolution benthic oxygen and carbon isotope composition records, Sea Surface Temperature (SST) and Ice-Rafted Detritus (IRD) records from a Southern Ocean core with three North Atlantic cores at different water--depth, and one Norwegian Sea core. Our strategy is to correlate in details high latitude sea surface records from both hemispheres with corresponding ice isotopic records using atmospheric markers for the interhemispheric correlation (e.g. Blunier et al 1998; Landais et al 2003). We observe persistent iceberg melting at the beginning of the LIG which maintained relatively cold and fresh surface-water conditions in the North Atlantic and the Nordic Seas between 129 and 125 ka. Similarly, benthic δ13C data indicate different LIG deep-water ventilation patterns, with North Atlantic Deep Waters sinking shallower during the 129--125 ka interval than during the later climatic optimum. The establishment of peak interglacial conditions in the high northern latitudes and associated strengthening of North Atlantic thermohaline circulation were delayed in consequence. Simulations with the IPSL--CM4 ocean--atmosphere coupled model (Marti et al. 2005) suggest that our results are consistent with the impact of a continued melting of Greenland ice sheet on Northern Hemisphere climate, in response to a particularly high boreal summer insolation.

  6. Humid glacials, arid interglacials? Results from a multiproxy study of the loess-paleosol sequence Crvenka, Serbia

    NASA Astrophysics Data System (ADS)

    Zech, R.; Zech, M.; Markovic, S.; Huang, Y.

    2012-04-01

    The loess-paleosol sequences in the Carpathian Basin, southeast Europe, are up to tens of meters thick and provide valuable archives for paleoenvironmental and -climate change over several glacial-interglacial cycles. The Crvenka section spans the full last glacial cycle and is used in this multi-proxy study to reconstruct past climate conditions. Crvenka features the characteristic pattern in terms of grain size and weathering intensity, i.e. finer grain sizes and more intensive weathering in the paleosols compared to the glacial loess units. The analysis of plant-derived long-chain n-alkanes as molecular biomarkers for past vegetation indicates the presence of trees during glacials, which is consistent with other e.g. macrofossil findings and the notion that parts of southeast Europe served as tree-refugia. However, virtually tree-less grass steppes are reconstructed for the Eemian, the last interglacial. More humid conditions during glacials and more arid conditions during interglacials would be in good agreement with lake-level reconstructions from the Dead Sea, but they seem to be at odds with traditional interpretations of pollen and stable isotope records for the Mediterranean region. In order to further contribute to this issue, we performed compound-specific D/H analyses on the most abundant alkanes C29 and C31, which should mainly record past changes in the isotopic composition of precipitation. The absence of a clear signal towards more depleted values during glacials shows that the temperature-effect is not dominant and probably offset by a strong source-effect, namely the enrichment of the Mediterranean sea water during glacials. This very same source effect may generally need to be taken into account when interpreting terrestrial isotope records in the Mediterranean, which implies that more positive values during glacials may not necessarily indicate an amount-effect and more arid conditions.

  7. Persistent climatic and oceanographic oscillations in the subpolar North Atlantic during the MIS 6 glaciation and MIS 5 interglacial

    NASA Astrophysics Data System (ADS)

    Mokeddem, Zohra; McManus, Jerry F.

    2016-06-01

    Rapidly accumulating sediments from the Björn drift deposit south of Iceland are studied for comparison of glacial/interglacial climate changes related to millennial variability of the subpolar surface and deep ocean circulation in the North Atlantic. High-resolution faunal, isotopic, and sedimentary analyses reveal a strong multimillennial climatic variability interpreted as oscillations in heat transport westward south of Iceland during marine isotope stage 6 (MIS 6), possibly related to the strength of the subpolar gyre (SPG). The oscillations persisted from MIS 6 through the following interglacial (MIS 5), although with diminished magnitude, and were respectively characterized by repeated advances of the polar front south of Iceland during MIS 6 and southward migrations of the Arctic front due to cold surface outflow through the East Greenland and East Iceland Currents during MIS 5. Incursions of cold, fresh surface waters, and drifting ice affected the dynamics of the SPG, episodically causing it to weaken and contract to the northwest. During these intervals of diminished SPG, the northward transport of subtropical heat and salt was strengthened and preferentially conveyed to the northeast past Iceland, enhancing deep-water formation in the Nordic Seas. By contrast, when the SPG was strong, more subtropical water and its associated heat were entrained within the relatively warm Irminger Current flowing westward south of Iceland. These oceanographic oscillations were associated with repeated multimillennial cooling and warming episodes during the glacial stage MIS 6, equivalent to the Dansgaard-Oeschger cycles of the last glaciation.

  8. Tolerance to Excess-Boron Conditions Acquired by Stabilization of a BOR1 Variant with Weak Polarity in Arabidopsis

    PubMed Central

    Wakuta, Shinji; Fujikawa, Teppei; Naito, Satoshi; Takano, Junpei

    2016-01-01

    Boron (B) is a metalloid that is essential for plant growth but is toxic when present in excess. Arabidopsis BOR1 is a borate exporter, facilitating B translocation from root to shoot under limited-B conditions. BOR1 shows stele side polar localization in the plasma membrane of various root cells, presumably to support B translocation toward the stele. BOR1 is degraded under high-B supply through vacuolar sorting via ubiquitination at the K590 residue to prevent the accumulation of B to a toxic level in shoots. A previous study showed that overexpression of BOR1 under control of the cauliflower mosaic virus 35S RNA promoter improved the growth of Arabidopsis under limited-B conditions without affecting the growth under sufficient-to-excess-B conditions. In this study, we unexpectedly found that ubiquitous expression of a stabilized BOR1 variant improved tolerance to excess-B in Arabidopsis. We established transgenic plants expressing BOR1-GFP fused with hygromycin phosphotransferase (HPT) and BOR1(K590A)-GFP-HPT under control of the ubiquitin 10 promoter. BOR1-GFP-HPT and BOR1(K590A)-GFP-HPT were expressed in various cell types in leaves and roots and showed weak polar localization in root tip cells. BOR1-GFP-HPT, but not BOR1(K590A)-GFP-HPT, was degraded through an endocytic pathway under high-B conditions. Transgenic plants with the stabilized variant BOR1(K590A)-GFP-HPT showed improved root and shoot growth under excess-B conditions. The concentration of B was greater in the shoots of plants with BOR1(K590A)-GFP-HPT or BOR1-GFP-HPT than in those of untransformed wild-type plants. These results suggest that BOR1(K590A)-GFP-HPT confers tolerance to excess-B by excluding B from the cytosol of shoot cells. Results from this study indicate the potential for engineering the trafficking properties of a transporter to produce plants that are tolerant to mineral stress. PMID:26870730

  9. Geomagnetic polarity reversals, Earth's core evolution, and conditions for dynamo action in the cores of terrestrial exoplanets

    NASA Astrophysics Data System (ADS)

    Driscoll, Peter E.

    Planetary dynamos are responsible for the generation of large-scale magnetic fields and are ubiquitous in the solar system. Magnetic fields generated by dynamo action in a planetary core offer unique insight into the internal structure, composition, and energetics of the planet. This dissertation consists of two main parts, the first focuses on long period fluctuations in Earth's magnetic field and the second explores conditions for dynamo action in the cores of terrestrial exoplanets. The first part consists of three projects using first-principle numerical magnetohydrodynamic models of the geodynamo to investigate the relationship between two fundamental, but poorly understood, aspects of the geomagnetic field: magnetic polarity reversals and the influence of core evolution. The first project explores the dependence of various dynamo properties on the relative strengths of buoyancy and rotation, and identifies several dynamical regimes whose magnetic field fluctuations over time are consistent with the paleomagnetic field. We find that normal evolution of buoyancy production in the core and planetary rotation rate over 100 Myr produce a negligible change in dynamo polarity reversal rate and field intensity, implying that the observed fluctuations in the geomagnetic reversal rate requires either anomalous core evolution or a rough dynamo regime boundary. The second project models the long time-scale evolution of the Earth's core using time-dependent control parameters, which are constrained by the secular cooling of the core and tidal deceleration. We find that fluctuations in the geodynamo are closely coupled to the evolution of the core, which implies a connection between the long time-scale trends in the seafloor geomagnetic polarity reversal rate and the rate of core evolution over the last 100 Myr. In the third project we investigate the hypothesis that the long period (˜200 Myr) oscillation in paleomagnetic reversal frequency is controlled by the heat flow

  10. Methane excess production in oxygen-rich polar water and a model of cellular conditions for this paradox

    NASA Astrophysics Data System (ADS)

    Damm, E.; Thoms, S.; Beszczynska-Möller, A.; Nöthig, E. M.; Kattner, G.

    2015-09-01

    Summer sea ice cover in the Arctic Ocean has undergone a reduction in the last decade exposing the sea surface to unforeseen environmental changes. Melting sea ice increases water stratification and induces nutrient limitation, which is also known to play a crucial role in methane formation in oxygenated surface water. We report on an excess of methane in the marginal ice zone in the western Fram Strait. Our study is based on measurements of oxygen, methane, DMSP, nitrate and phosphate concentrations as well as on phytoplankton composition and light transmission, conducted along the 79°N oceanographic transect, in the western part of the Fram Strait and in Northeast Water Polynya region off Greenland. Between the eastern Fram Strait, where Atlantic water enters from the south and the western Fram Strait, where Polar water enters from the north, different nutrient limitations occurred and consequently different bloom conditions were established. Ongoing sea ice melting enhances the environmental differences between both water masses and initiates regenerated production in the western Fram Strait. We show that in this region methane is in situ produced while DMSP (dimethylsulfoniopropionate) released from sea ice may serve as a precursor for the methane formation. The methane production occured despite high oxygen concentrations in this water masses. As the metabolic activity (respiration) of unicellular organisms explains the presence of anaerobic conditions in the cellular environment we present a theoretical model which explains the maintenance of anaerobic conditions for methane formation inside bacterial cells, despite enhanced oxygen concentrations in the environment.

  11. A GCM comparison of Plio-Pleistocene interglacial-glacial periods in relation to Lake El'gygytgyn, NE Arctic Russia

    NASA Astrophysics Data System (ADS)

    Coletti, A. J.; DeConto, R. M.; Brigham-Grette, J.; Melles, M.

    2014-08-01

    Until now, the lack of time-continuous, terrestrial paleoenvironmental data from the Pleistocene Arctic has made model simulations of past interglacials difficult to assess. Here, we compare climate simulations of four warm interglacials at Marine Isotope Stage (MIS) 1 (9 ka), 5e (127 ka), 11c (409 ka), and 31 (1072 ka) with new proxy climate data recovered from Lake El'gygytgyn, NE Russia. Climate reconstructions of the Mean Temperature of the Warmest Month (MTWM) indicate conditions 2.1, 0.5 and 3.1 °C warmer than today during MIS 5e, 11c, and 31, respectively. While the climate model captures much of the observed warming during each interglacial, largely in response to boreal summer orbital forcing, the extraordinary warmth of MIS 11c relative to the other interglacials in the proxy records remain difficult to explain. To deconvolve the contribution of multiple influences on interglacial warming at Lake El'gygytgyn, we isolated the influence of vegetation, sea ice, and circum-Arctic land ice feedbacks on the climate of the Beringian interior. Simulations accounting for climate-vegetation-land surface feedbacks during all four interglacials show expanding boreal forest cover with increasing summer insolation intensity. A deglaciated Greenland is shown to have a minimal effect on Northeast Asian temperature during the warmth of stage 11c and 31 (Melles et al., 2012). A prescribed enhancement of oceanic heat transport into the Arctic ocean has some effect on Beringian climate, suggesting intrahemispheric coupling seen in comparisons between Lake El'gygytgyn and Antarctic sediment records might be related to linkages between Antarctic ice volume and ocean circulation. The exceptional warmth of MIS 11c remains enigmatic however, relative to the modest orbital and greenhouse gas forcing during that interglacial. Large Northern Hemisphere ice sheets during Plio-Pleistocene glaciation causes a substantial decrease in Mean Temperature of the Coldest Month (MTCM) and

  12. Key conditions for stable ion radiation pressure acceleration by circularly polarized laser pulses

    NASA Astrophysics Data System (ADS)

    Qiao, B.; Zepf, M.; Gibbon, P.; Borghesi, M.; Schreiber, J.; Geissler, M.

    2011-05-01

    Radiation pressure acceleration (RPA) theoretically may have great potential to revolutionize the study of laserdriven ion accelerators due to its high conversion efficiency and ability to produce high-quality monoenergetic ion beams. However, the instability issue of ion acceleration has been appeared to be a fundamental limitation of the RPA scheme. To solve this issue is very important to the experimental realization and exploitation of this new scheme. In our recent work, we have identified the key condition for efficient and stable ion RPA from thin foils by CP laser pulses, in particular, at currently available moderate laser intensities. That is, the ion beam should remain accompanied with enough co-moving electrons to preserve a local "bunching" electrostatic field during the acceleration. In the realistic LS RPA, the decompression of the co-moving electron layer leads to a change of local electrostatic field from a "bunching" to a "debunching" profile, resulting in premature termination of acceleration. One possible scheme to achieve stable RPA is using a multi-species foil. Two-dimensional PIC simulations show that 100 MeV/u monoenergetic C6+ and/or proton beams are produced by irradiation of a contaminated copper foil with CP lasers at intensities 5 × 1020W/cm2, achievable by current day lasers.

  13. Comparison of Interglacial fire dynamics in Southern Africa

    NASA Astrophysics Data System (ADS)

    Brücher, Tim; Daniau, Anne-Laure

    2016-04-01

    Responses of fire activity to a change in climate are still uncertain and biases exist by integrating this non-linear process into global modeling of the Earth system. Warming and regional drying can force fire activity in two opposite directions: an increase in fire in fuel supported ecosystems or a fire reduction in fuel-limited ecosystems. Therefore, climate variables alone can not be used to estimate the fire risk because vegetation variability is an important determinant of fire dynamics and responds itself to change in climate. Southern Africa (south of 20°S) paleofire history reconstruction obtained from the analysis of microcharcoal preserved in a deep-sea core located off Namibia reveals changes of fire activity on orbital timescales in the precession band. In particular, increase in fire is observed during glacial periods, and reduction of fire during interglacials such as the Eemian and the Holocene. The Holocene was characterized by even lower level of fire activity than Eemian. Those results suggest the alternance of grass-fueled fires during glacials driven by increase in moisture and the development of limited fueled ecosystems during interglacials characterized by dryness. Those results question the simulated increase in the fire risk probability projected for this region under a warming and drying climate obtained by Pechony and Schindell (2010). To explore the validity of the hypotheses we conducted a data-model comparison for both interglacials from 126.000 to 115.000 BP for the Eemian and from 8.000 to 2.000 BP for the Holocene. Data out of a transient, global modeling study with a Vegetation-Fire model of full complexity (JSBACH) is used, driven by a Climate model of intermediate complexity (CLIMBER). Climate data like precipitation and temperature as well as vegetation data like soil moisture, productivity (NPP) on plant functional type level are used to explain trends in fire activity. The comparison of trends in fire activity during the

  14. Debris flow sensitivity to glacial-interglacial climate change - supply vs transport

    NASA Astrophysics Data System (ADS)

    D'Arcy, Mitch; Roda Boluda, Duna C.; Whittaker, Alexander C.

    2016-04-01

    Numerical models suggest that small mountain catchment-alluvial fan systems might be sensitive to climate changes over glacial-interglacial cycles, and record these palaeoclimate signals in the sedimentology of their deposits. However, these models are still largely untested, and the propagation of climate signals through simple sediment routing systems remains contentious. Here, we present detailed sedimentological records from 8 debris flow fan systems in Owens Valley, California, that capture the past ~ 120 ka of deposition. We identify a strong and sustained relationship between deposit grain size and palaeoclimate records over a full glacial-interglacial cycle, with significantly coarser-grained deposits found in warm and dry periods. Our data show that these systems are highly sensitive to climate with a rapid response timescale of < 10ka, which we attribute to rapid transfer from source to sink. This sensitive record might be explained by changes in sediment supply and/or changes in sediment mobilisation, and we evaluate these mechanisms quantitatively. We find little evidence that changes in catchment hypsometry, weathering patterns, past glaciation or sediment production can explain the grain size changes we observe on the fans. However we do find that grain size has increased exponentially with rising temperatures, at a rate that matches the intensification of storms with warming. As these debris flows are triggered by surface runoff during intense storms, we interpret that enhanced runoff rates in warm and stormy conditions are responsible for entraining larger clasts during debris flow initiation. This implies that debris flow fans might record signals of past storm intensity. Our study utilises field sedimentology and focuses on short transport distances (~ 10 km) and climate changes over ~ 1-100 ka timespans, but could additionally have important implications for how eroding landscapes might respond to future warming scenarios. We address the

  15. Nucleation and growth of crystals under cirrus and polar stratospheric cloud conditions

    NASA Technical Reports Server (NTRS)

    Hallett, John; Queen, Brian; Teets, Edward; Fahey, James

    1995-01-01

    Laboratory studies examine phase changes of hygroscopic substances which occur as aerosol in stratosphere and troposphere (sodium chloride, ammonium sulfate, ammonium bisulfate, nitric acid, sulfuric acid), under controlled conditions, in samples volume 1 to 10(exp -4) ml. Crystallization of salts from supersaturated solutions is examined by slowly evaporating a solution drop on a substrate, under controlled relative humidity, until self nucleation occurs; controlled nucleation of ice in a mm capillary U-tube gives a measured ice crystallization velocity at known supercooling. Two states of crystallization occur for regions where hydrates exist. It is inferred that all of the materials readily exist as supersaturated/supercooled solutions; the degree of metastability appears to be slightly enhanced by inclusion of aircraft produced soot. The crystallization velocity is taken as a measure of viscosity. Results suggest an approach to a glass transition at high molality, supersaturation and/or supercooling within the range of atmospheric interest. It is hypothesized that surface reactions occur more readily on solidified particles - either crystalline or glass, whereas volume reactions are more important on droplets with sufficiently low viscosity and volume diffusivity. Implications are examined for optical properties of such particles in the atmosphere. In a separate experiment, crystal growth was examined in a modified thermal vapor diffusion chamber over the range of cirrus temperature (-30 to -70 C) and under controlled supersaturation and air pressure. The crystals grew at a velocity of 1-2 microns/s, thickness 60-70 micron, in the form of thin column crystals. Design criteria are given for a system to investigate particle growth down to -100 C, (PSC temperatures) where nitric acid particles can be grown under similar control and in the form of hydrate crystals.

  16. Milankovitch forcing of the last interglacial sea level.

    PubMed

    Crowley, T J; Kim, K Y

    1994-09-01

    During the last interglacial, sea level was as high as present, 4000 to 6000 years before peak Northern Hemisphere insolation receipt 126,000 years ago. The sea-level results are shown to be consistent with climate models, which simulate a 3 degrees to 4 degrees C July temperature increase from 140,000 to 130,000 years ago in high latitudes, with all Northern Hemisphere land areas being warmer than present by 130,000 years ago. The early warming occurs because obliquity peaked earlier than precession and because precession values were greater than present before peak precessional forcing occurred. These results indicate that a fuller understanding of the Milankovitch-climate connection requires consideration of fields other than just insolation forcing at 65 degrees N. PMID:17801535

  17. Milankovitch forcing of the last interglacial sea level

    SciTech Connect

    Crowley, T.J.; Kim, K.Y.

    1994-09-09

    During the last interglacial, sea level was as high as present, 4000 to 6000 years before peak Northern Hemisphere insolation receipt 126,000 years ago. The sea-level results are shown to be consistent with climate models, which simulate a 3{degrees} to 4{degrees}C July temperature increase from 140,000 to 130,000 years ago in high latitudes, with all Northern Hemisphere land areas being warmer than present by 130,000 years ago. The early warming occurs because obliquity peaked earlier than precession and because precession values were greater than present before peak precessional forcing occurred. These results indicate that a fuller understanding of the Milankovitch-climate connection requires consideration of fields other than just insolation forcing at 65{degrees}N. 16 refs., 4 figs.

  18. The Last Interglacial History of the Antarctic Ice sheet

    NASA Astrophysics Data System (ADS)

    Bradley, Sarah; Siddall, Mark; Milne, Glenn A.; Masson-Delmotte, Valerie; Wolff, Eric; Hindmarsh, Richard C. A.

    2014-05-01

    In this paper we present a summary of the work which was conducted as part of the 'PAST4FUTURE -WP4.1: Sea Level and Ice sheets' project. The overall aim of this study was to understand the response of the Antarctic Ice sheet (AIS) to climate forcing during the Last interglacial (LIG) and its contribution to the observed higher than present sea level during this period. The study involved the application and development of a novel technique which combined East Antarctic stable isotope ice core data with the output from a Glacial Isostatic Adjustment (GIA) model [Bradley et al., 2012]. We investigated if the stable isotope ice core data are sensitive to detecting isostatically driven changes in the surface elevation driven by changes in the ice-loading history of the AIS and if so, could we address some key questions relating to the LIG history of the AIS. Although it is believed that the West Antarctic Ice sheet (WAIS) reduced in size during the LIG compared to the Holocene, major uncertainties and unknowns remain unresolved: Did the WAIS collapse? What would the contribution of such a collapse be the higher than present LIG eustatic sea level (ESL)? We will show that a simulated collapse of the WAIS does not generate a significant elevation driven signal at the EAIS LIG ice core sites, and as such, these ice core records cannot be used to assess WAIS stability over this period. However, we will present 'treasure maps' [Bradley et al., 2012] to identify regions of the AIS where results from geological studies and/or new paleoclimate data may be sensitive to detecting a WAIS collapse. These maps can act as a useful tool for the wider science community/field scientists as a guide to highlight sites suitable to constrain the evolution of the WAIS during the LIG. Studies have proposed that the surface temperature across the East Antarctic Ice Sheet (EAIS) was significantly warmer, 2-5°C during the LIG compared to present [Lang and Wolff, 2011]. These higher

  19. Theoretical explanation of the polarization-converting system achieved by beam shaping and combination technique and its performance under high power conditions

    NASA Astrophysics Data System (ADS)

    Wang, Peng; Li, Xiao; Shang, YaPing; Xu, XiaoJun

    2015-10-01

    The fiber laser has very obvious advantages and broad applications in remote welding, 3D cutting and national defense compared with the traditional solid laser. But influenced by heat effect of gain medium, nonlinear effect, stress birefringence effect and other negative factors, it's very difficult to get high power linearly polarized laser just using a single laser. For these limitations a polarization-converting system is designed using beam shaping and combination technique which is able to transform naturally polarized laser to linearly polarized laser at real time to resolve difficulties of generating high-power linearly polarized laser from fiber lasers in this paper. The principle of the Gaussian beam changing into the hollow beam passing through two axicons and the combination of the Gaussian beam and the hollow beam is discussed. In the experimental verification the energy conversion efficiency reached 93.1% with a remarkable enhancement of the extinction ratio from 3% to 98% benefited from the high conversion efficiency of axicons and the system worked fine under high power conditions. The system also kept excellent far field divergence. The experiment phenomenon also agreed with the simulation quite well. The experiment proves that this polarization-converting system will not affect laser structure which controls easily and needs no feedback and controlling system with stable and reliable properties at the same time. It can absolutely be applied to the polarization-conversion of high power laser.

  20. Modes of interglacial sea-level change: evidence from a late Pleistocene highstand in the UK

    NASA Astrophysics Data System (ADS)

    Saher, Margot; Barlow, Natasha; Long, Antony; Gehrels, Roland; Sparkes, Amy; Riley, Rachel; Penkman, Kirsty

    2014-05-01

    Interglacial sea-level extremes provide a useful analogue for future sea-level behaviour. The Holocene has been characterized by an overall stable sea level, but earlier interglacials, especially the Last Interglacial, are reported to have experienced meter-scale fluctuations (e.g. Rohling et al. 2008). Whether interglacial sea-level maxima are reached gradually or in 'steps' has serious societal implications, as the latter mechanism is associated with much higher rates of sea-level rise. Furthermore, the fluctuating Red Sea model of Last Interglacial sea-level change (Rohling et al. 2008) now underpins the high-end sea-level scenario ("High ++") adopted by the UK Climate Impact Programme. To better constrain interglacial sea-level behaviour, the iGlass consortium, funded by the UK Natural Environment Research Council, aims to constrain interglacial sea-level fluctuations from a variety of archives, e.g. corals, speleothems, marine isotopes and estuarine sediments. In this paper we investigate estuarine sediments and apply microfossil analyses, used widely to constrain Holocene sea-level changes, to sediments from interglacial deposits recovered from the Nar Valley, Norfolk, United Kingdom. A coring transect, comprised of 8 cores in 6 locations, traces an interglacial transgressive sequence inland. The litho- and biostratigraphy (mainly foraminifera) record the nature of this transgression. Sediments are either MIS 9 or 11 in age and include freshwater peats and marine clays, buried by glacial sands and gravels. Previous palynological work (Ventris, 1996) has indicates the sediments represent the entire interglacial period. The top of the marine clays has been tracked laterally for ~15 km and was found to have (at least) a 18 m vertical range, up to ~18 m above present mean sea level. Foraminiferal assemblages are dominated by the shallow water dweller Ammonia spp, and suggest only one sequence of deepening and shallowing. We further constrain the chronology using

  1. Extreme Dead Sea drying event during the last interglacial from the ICDP Dead Sea Deep Drill Core

    NASA Astrophysics Data System (ADS)

    Goldstein, S.; Stein, M.; Ben-Avraham, Z.; Agnon, A.; Ariztegui, D.; Brauer, A.; Haug, G.; Ito, E.; Kitagawa, H.; Torfstein, A.; Yasuda, Y.

    2012-04-01

    The ICDP funded Dead Sea Deep Drilling Project (DSDDP) recovered the longest and most complete paleo-environmental record in the Middle East, drilling holes in a deep and a shallow site extending to ~450 meters. The Dead Sea expands during the glacials and contracts during interglacials, and the sediments are an archive of the evolving climatic conditions. During glacials the sediments comprise intervals of marl (aragonite, gypsum and detritus) and during interglacials they are salts and marls. We estimate that the deep site core spans ~200 kyr (to early MIS 7). A dramatic discovery is a ~40 cm interval of rounded pebbles at ~235 m below the lake floor, the only clean pebbly unit in the entire core. It appears to be a beach layer, near the deepest part of the Dead Sea, lying above ~35 meters of mainly salt. If it is a beach layer, it implies an almost complete dry-down of the paleo-Dead Sea. The pebble layer lies within the last interglacial interval. Our initial attempt to estimate the age of the possible dry down shows an intriguing correlation between the salt-mud stratigraphy of the Dead Sea core and the oxygen isotope record of Soreq Cave, whereby excursions to light oxygen in the speleothems correspond to periods of salt deposition. Through this comparison, we estimate that the dry down occurred during MIS 5e. The occurrence of ~35 meters of mainly salt along with the pebble layer demonstrates a severe dry interval during MIS 5. This observation has implications for the Middle East today, where the Dead Sea level is dropping as all the countries in the area use the runoff. GCM models indicate a more arid future in the region. The core shows that the runoff nearly stopped during a past warm period without human intervention.

  2. The role of mechanical pressure difference in the generation of membrane voltage under conditions of concentration polarization.

    PubMed

    Grzegorczyn, Sławomir; Ślęzak, Andrzej

    2016-06-01

    The mechanical pressure difference across the bacterial cellulose membrane located in a horizontal plane causes asymmetry of voltage measured between electrodes immersed in KCl solutions symmetrically on both sides of the membrane. For all measurements, KCl solution with lower concentration was above the membrane. In configuration of the analyzed membrane system, the concentration boundary layers (CBLs) are created only by molecular diffusion. The voltages measured in the membrane system in concentration polarization conditions were compared with suitable voltages obtained from the model of diffusion through CBLs and ion transport through the membrane. An increase of difference of mechanical pressure across the membrane directed as a difference of osmotic pressure always causes a decrease of voltage between the electrodes in the membrane system. In turn, for mechanical pressure difference across the membrane directed in an opposite direction to the difference of osmotic pressure, a peak in the voltage as a function of mechanical pressure difference is observed. An increase of osmotic pressure difference across the membrane at the initial moment causes an increase of the maximal value of the observed peak and a shift of this peak position in the direction of higher values of the mechanical pressure differences across the membrane. PMID:27060081

  3. Response of Phytoplankton Photophysiology to Varying Environmental Conditions in the Sub-Antarctic and Polar Frontal Zone

    PubMed Central

    Cheah, Wee; McMinn, Andrew; Griffiths, F. Brian; Westwood, Karen J.; Wright, Simon W.; Clementson, Lesley A.

    2013-01-01

    Climate-driven changes are expected to alter the hydrography of the Sub-Antarctic Zone (SAZ) and Polar Frontal Zone (PFZ) south of Australia, in which distinct regional environments are believed to be responsible for the differences in phytoplankton biomass in these regions. Here, we report how the dynamic influences of light, iron and temperature, which are responsible for the photophysiological differences between phytoplankton in the SAZ and PFZ, contribute to the biomass differences in these regions. High effective photochemical efficiency of photosystem II (/0.4), maximum photosynthesis rate (), light-saturation intensity (), maximum rate of photosynthetic electron transport (1/), and low photoprotective pigment concentrations observed in the SAZ correspond to high chlorophyll and iron concentrations. In contrast, phytoplankton in the PFZ exhibits low / ( 0.2) and high concentrations of photoprotective pigments under low light environment. Strong negative relationships between iron, temperature, and photoprotective pigments demonstrate that cells were producing more photoprotective pigments under low temperature and iron conditions, and are responsible for the low biomass and low productivity measured in the PFZ. As warming and enhanced iron input is expected in this region, this could probably increase phytoplankton photosynthesis in this region. However, complex interactions between the biogeochemical processes (e.g. stratification caused by warming could prevent mixing of nutrients), which control phytoplankton biomass and productivity, remain uncertain. PMID:23977242

  4. Oceanography in northwestern Europe during the last interglacial from intrashell δ 18O ranges in Littorina littorea gastropods

    NASA Astrophysics Data System (ADS)

    Burman, Johan; Påsse, Tore

    2008-07-01

    Coastal sea-surface temperature (SST) and sea-surface salinity (SSS), including seasonality, in northwest (NW) Europe during the early phase of the Eemian interglacial ca. 125 ka ago were reconstructed from Littorina littorea (common periwinkle) gastropods. The results were based on intra-annual δ 18O analyses in recent and fossil shells, mainly originating from the sea of Kattegat (Sweden) and the English Channel (United Kingdom), and confined to intertidal settings. The Eemian L. littorea shells indicated annual SSTs in the range 8-18°C for the English Channel and 8-26°C for Kattegat. All specimens from the Eemian sites experienced summer SSTs of ca. 1-3°C above recent conditions. The estimated winter SST in the English Channel during the Eemian was comparable to modern measurements of ca. 8°C. However, the Kattegat region displayed Eemian winter SST approximately 8°C warmer than today, and similar to conditions in the western English Channel. The recent-fossil isotope analogue approach indicated high SSS above 35 practical salinity units (psu) for a channel south of England in full contact with the North Atlantic Ocean during the last interglacial. In addition, the Kattegat shells indicated a SSS of ca. 29 psu, which points out a North Sea affinity for this region during the Eemian.

  5. Last interglacial plant macrofossils and climates from Ziegler Reservoir, Snowmass Village, Colorado, USA

    USGS Publications Warehouse

    Strickland, Laura E.; Baker, Richard G.; Thompson, Robert S.; Miller, Dane M.

    2014-01-01

    Ninety plant macrofossil taxa from the Ziegler Reservoir fossil site near Snowmass Village, Colorado, record environmental changes at high elevation (2705 m asl) in the Rocky Mountains during the Last Interglacial Period. Present-day vegetation is aspen forest (Populus tremuloides) intermixed with species of higher (Picea, Abies) and lower (Artemisia, Quercus) elevations. Stratigraphic units 4–13 contain montane forest taxa found near the site today and several species that today generally live at lower elevations within (Abies concolor, Lycopus americanus) and outside Colorado (Najas flexilis). These data suggest near-modern climatic conditions, with slightly warmer summer and winter temperatures. This montane forest period was succeeded by a shorter treeless interval (Unit 14) representing colder and/or drier conditions. In units 15–16, conifer trees reoccur but deciduous and herb taxa are lacking, suggesting a return to warmer conditions, although cooler than during the earlier forest period. Comparison of these inferred paleoclimatic changes with the site's geochronologic framework indicates that the lower interval of sustained warmth correlates with late MIS 6–early 5b (~ 138–94 ka), the cold interval with MIS 5b (~ 94–87 ka), and the uppermost cool assemblages with MIS 5a (~ 87–77 ka).

  6. Last interglacial plant macrofossils and climates from Ziegler Reservoir, Snowmass Village, Colorado, USA

    NASA Astrophysics Data System (ADS)

    Strickland, Laura E.; Baker, Richard G.; Thompson, Robert S.; Miller, Dane M.

    2014-11-01

    Ninety plant macrofossil taxa from the Ziegler Reservoir fossil site near Snowmass Village, Colorado, record environmental changes at high elevation (2705 m asl) in the Rocky Mountains during the Last Interglacial Period. Present-day vegetation is aspen forest (Populus tremuloides) intermixed with species of higher (Picea, Abies) and lower (Artemisia, Quercus) elevations. Stratigraphic units 4-13 contain montane forest taxa found near the site today and several species that today generally live at lower elevations within (Abies concolor, Lycopus americanus) and outside Colorado (Najas flexilis). These data suggest near-modern climatic conditions, with slightly warmer summer and winter temperatures. This montane forest period was succeeded by a shorter treeless interval (Unit 14) representing colder and/or drier conditions. In units 15-16, conifer trees reoccur but deciduous and herb taxa are lacking, suggesting a return to warmer conditions, although cooler than during the earlier forest period. Comparison of these inferred paleoclimatic changes with the site's geochronologic framework indicates that the lower interval of sustained warmth correlates with late MIS 6-early 5b (~ 138-94 ka), the cold interval with MIS 5b (~ 94-87 ka), and the uppermost cool assemblages with MIS 5a (~ 87-77 ka).

  7. Palaeoceanography & Palaeoclimate during the penultimate Glacial-Interglacial transition in the Black Sea - Termination II

    NASA Astrophysics Data System (ADS)

    Wegwerth, Antje; Dellwig, Olaf; Kaiser, Jérôme; Bard, Edouard; Ménot, Guillemette; Nowaczyk, Norbert; Plessen, Birgit; Schnetger, Bernhard; Shumilovskikh, Lyudmila; Arz, Helge

    2013-04-01

    The epicontinental Black Sea is very sensitive to environmental changes thus forming an ideal archive of regional climate change and teleconnective responses to the coupled North Atlantic ocean-atmosphere system. Here we focus on the climatic and hydrological evolution of the SE Black Sea during the glacial-interglacial transition of Termination II to the Eemian (~134-122 ka BP) by using different geochemical and sedimentological proxies. Long-term cold conditions during the ending penultimate glacial are provided by TEX86 derived summer sea-surface temperatures (SST) of around 9°C and are thus considerable lower than present values of about 23°C. Coastal ice formation during extreme winters accounted for huge discharge of ice rafted debris (IRD) until 130.5 ka BP. Milder more humid conditions during this period are indicated for instance by elevated Cr/Al values typical for an ultramafic Pontic Mountain source (Piper and Calvert, 2011) thereby suggesting an increased sediment load mainly from the east-Anatolian rivers Kizilirmak and Yesilirmak. The abrupt disappearance of IRD along with increasing δ18O, Mg/Ca, and Sr/Ca of benthic ostracods (Candona spp.) resulted from slightly rising temperatures (SST 11°C) until 128.8 ka BP. Thereafter, SST rapidly increased within less than 500 years to about 25°C revealing a dramatic change from glacial to interglacial conditions. First analyses of U/Ca-ratios of ostracods show sharply increasing values not before ~128.3 ka BP, synchronous to the appearance of larval Mytilus galloprovincialis shells, due to the Mediterranean transgression into the Black Sea. The simultaneous increase of TOC and Mo/Al of the bulk sediment indicates the development of oxygen-deficient bottom waters and Eemian sapropel formation favoured by the establishment of a halocline shortly after the Mediterranean-Black Sea reconnection. About 500 years after the temperature maximum, the continental environment responded to the warming by elevated

  8. Experimental Demonstration of the Formation of Liquid Brines under Martian Polar Conditions in the Michigan Mars Environmental Chamber

    NASA Astrophysics Data System (ADS)

    Fischer, Erik; Martinez, German; Elliott, Harvey; Borlina, Caue; Renno, Nilton

    2014-05-01

    Liquid water is one of the necessary ingredients for the development of life as we know it. The behavior of various liquid states of H2O such as liquid brine, undercooled liquid interfacial water, subsurface melt water and ground water [1] needs to be understood in order to address the potential habitability of Mars for microbes and future human exploration. It has been shown thermodynamically that liquid brines can exist under Martian polar conditions [2, 3]. We have developed the Michigan Mars Environmental Chamber (MMEC) to simulate the entire range of Martian surface and shallow subsurface conditions with respect to temperature, pressure, relative humidity, solar radiation and soil wetness at equatorial and polar latitudes. Our experiments in the MMEC show that deliquescence of NaClO4, Mg(ClO4)2 and Ca(ClO4)2 occurs diurnally under the environmental conditions of the Phoenix landing site when these salts get in contact with water ice. Since Phoenix detected these salts and water ice at the landing site, including frost formation, it is extremely likely that deliquescence occurs at the Phoenix landing site. By layering NaClO4, Mg(ClO4)2 or Ca(ClO4)2 on top of a pure water ice slab at 800 Pa and 190 K and raising the temperature stepwise across the eutectic temperature of the perchlorate salts, we observe distinct changes in the Raman spectra of the samples when deliquescence occurs. When crossing the eutectic temperatures of NaClO4 (236 K), Mg(ClO4)2 (205 K) and Ca(ClO4)2 (199 K) [4, 5], the perchlorate band of the Raman spectrum shows a clear shift from 953 cm-1 to 936 cm-1. Furthermore, the appearance of a broad O-H vibrational stretching spectrum between 3244 cm-1 and 3580 cm-1 is another indicator of deliquescence. This process of deliquescence occurs on the order of seconds when the perchlorate salt is in contact with water ice. On the contrary, when the perchlorate salt is only subjected to water vapor in the Martian atmosphere, deliquescence was not

  9. Multiproxy record of the last interglacial (MIS 5e) off central and northern California, U.S.A., from Ocean Drilling Program sites 1018 and 1020

    USGS Publications Warehouse

    Poore, Richard Z.; Dowsett, H.J.; Barron, J.A.; Heusser, L.; Ravelo, A.C.; Mix, A.

    2000-01-01

    Environmental and climatic conditions during the last interglacial (about 125,000 years ago) along the Central and Northern California coastal region are interpreted from study of marine cores recovered by the Ocean Drilling Program at sites 1018 and 1020. Marine microfossil and pollen assemblages, oxygen isotopes in benthic foraminifers, physical properties, and calcium carbonate contents of cored sediments are proxies indicating strong links between the marine and terrestrial environments during marine isotope stage 5 (MIS 5). At the beginning of the last interglacial (MIS 5e), reduction in global ice volume, increase in surface temperature, and warming of air temperature along the Central and Northern California coast were synchronous within the resolution of our sampling record.

  10. Soil profile of Yellow-brown Earth overlying Red Clay in southern Anhui Province: A pedogenic response to the Last Glacial - Interglacial cycle in mid-subtropical China

    NASA Astrophysics Data System (ADS)

    Hu, Xue-Feng; Du, Yan

    2013-04-01

    Soil profile of Yellow-brown Earth (YBE) overlying Red Clay (RC) is commonly seen along the Yangtze River in mid-subtropical China. To study its paleoclimatic implications, one YBE - RC profile in Langxi county, southern Anhui Province, were dated with the optically stimulated luminescence (OSL) method in detail. The results indicated that the dual - layered profile is actually a pedogenic response to a great climatic change during the Last Glacial - Last Interglacial cycle: The YBE is homogenous to the aeolian Xiashu Loess widely distributed along the Yangtze River and was dated from 12.2 ka to 57.1 ka; and the underlying RC approximately from 60 ka to 132.8 ka, which fully suggests that the YBE is really the Last Glacial loess, correlated with the Malan Loess in the Chinese Loess Plateau, Northwest China, and the RC was mainly formed during the Last Interglacial. Two sub-class events of the Last Glacial, the Last Glacial Maximum (LGM) and the Last Glacial Optimum (LGO), correlated with the marine oxygen isotopic stage (MIS) 2 and 3, can be separated and identified in the YBE. Likewise, the RC can be divided into the Uniform Red Clay (URC) and Reticulate Red Clay (RRC). The URC was formed during the transitional time from the Last Interglacial to the Last Glacial, and the RRC mainly during the Last Interglacial, MIS 5. The RC is highly weathered but still shows aeolian-dust characteristics. The duplicate information implies that the paleoclimate during the Last Interglacial is instable and might also oscillate between warm and cold, but sub-class paleoclimatic events, potential correlated with MIS 5 a - 5 e, cannot be identified in the RRC possibly due to the overlapped paleoclimatic information caused by highly chemical weathering. A great climatic transfer during the Last Glacial - Interglacial cycle left soil parent materials diversified in the study areas and hence caused the parallel distribution of different zonal soils in a small scale. Two surface soils

  11. South Carolina interglacial sites and stage 5 sea levels

    NASA Astrophysics Data System (ADS)

    Hollin, John T.; Hearty, Paul J.

    1990-01-01

    Amino acid and other studies have been made on the 30-km Pleistocene sections of the Intracoastal Waterway between Myrtle Beach and Little River, South Carolina. Our ratios differentiate the long-established Waccamaw (oldest), Canepatch, and Socastee formations. The ratios from the four laboratories that have worked in this area agree very well, and apparent conflicts with U-series dates may merely reflect an abundance of reworked corals. Our amino acid correlations with U-series coral dates in South Carolina, Bermuda, and the Mediterranean all argue that the classical Canepatch and its Horry Clay date from isotope stage 5e and not, as has been implied, from stage 7, 9, 11, or 13. Excavations and erosion have increased position-fixing problems along the Waterway, and "Canepatch" amino acid ratios and U-series dates (460,000 ± 100,000 yr B.P.) at "ICW5" may be from an older unit. The Canepatch shows the double marine transgression visible in many stage 5e deposits. Pollen shows that the second transgression occurred late in the interglaciation, and stratigraphic studies show that it reached 14 m. It therefore fits very well Antarctic ice-surge models of stage 5 sea level and climate. The Socastee adds to the evidence for one or more sea levels above 0 m late in stage 5.

  12. Contrasting scaling properties of interglacial and glacial climates

    NASA Astrophysics Data System (ADS)

    Shao, Zhi-Gang; Ditlevsen, Peter D.

    2016-03-01

    Understanding natural climate variability is essential for assessments of climate change. This is reflected in the scaling properties of climate records. The scaling exponents of the interglacial and the glacial climates are fundamentally different. The Holocene record is monofractal, with a scaling exponent H~0.7. On the contrary, the glacial record is multifractal, with a significantly higher scaling exponent H~1.2, indicating a longer persistence time and stronger nonlinearities in the glacial climate. The glacial climate is dominated by the strong multi-millennial Dansgaard-Oeschger (DO) events influencing the long-time correlation. However, by separately analysing the last glacial maximum lacking DO events, here we find the same scaling for that period as for the full glacial period. The unbroken scaling thus indicates that the DO events are part of the natural variability and not externally triggered. At glacial time scales, there is a scale break to a trivial scaling, contrasting the DO events from the similarly saw-tooth-shaped glacial cycles.

  13. Eemian interglacial reconstructed from a Greenland folded ice core.

    PubMed

    2013-01-24

    Efforts to extract a Greenland ice core with a complete record of the Eemian interglacial (130,000 to 115,000 years ago) have until now been unsuccessful. The response of the Greenland ice sheet to the warmer-than-present climate of the Eemian has thus remained unclear. Here we present the new North Greenland Eemian Ice Drilling ('NEEM') ice core and show only a modest ice-sheet response to the strong warming in the early Eemian. We reconstructed the Eemian record from folded ice using globally homogeneous parameters known from dated Greenland and Antarctic ice-core records. On the basis of water stable isotopes, NEEM surface temperatures after the onset of the Eemian (126,000 years ago) peaked at 8 ± 4 degrees Celsius above the mean of the past millennium, followed by a gradual cooling that was probably driven by the decreasing summer insolation. Between 128,000 and 122,000 years ago, the thickness of the northwest Greenland ice sheet decreased by 400 ± 250 metres, reaching surface elevations 122,000 years ago of 130 ± 300 metres lower than the present. Extensive surface melt occurred at the NEEM site during the Eemian, a phenomenon witnessed when melt layers formed again at NEEM during the exceptional heat of July 2012. With additional warming, surface melt might become more common in the future. PMID:23344358

  14. Greenland ice sheet melting during the last interglacial

    NASA Astrophysics Data System (ADS)

    Langebroek, Petra M.; Nisancioglu, Kerim H.

    2016-04-01

    During the last interglacial period (LIG) peak temperatures over Greenland were several degrees warmer than today. The Greenland ice sheet (GIS) retreated causing a global sea-level rise in the order of several meters. Large uncertainties still exist in the exact amount of melt and on the source location of this melt. Here we examine the GIS response to LIG temperature and precipitation patterns using the SICOPOLIS ice sheet model. The LIG climate was simulated by forcing the Norwegian Earth System Model (NorESM) with the appropriate greenhouse gases and orbital settings. The resulting LIG ice volume evolution strongly depends on the chosen value of uncertain model parameters for the ice sheet (e.g. basal sliding parameter, PDD factors, and atmospheric temperature lapse rate). We reduce the uncertainty by evaluating an ensemble of model results against present-day observations of ice sheet size, elevation and stability, together with paleo information from deep ice cores. We find a maximum GIS reduction equivalent to 0.8 to 2.2m of global sea-level rise. In this model set-up most of the melting occurs in southwestern Greenland.

  15. Contrasting scaling properties of interglacial and glacial climates

    PubMed Central

    Shao, Zhi-Gang; Ditlevsen, Peter D.

    2016-01-01

    Understanding natural climate variability is essential for assessments of climate change. This is reflected in the scaling properties of climate records. The scaling exponents of the interglacial and the glacial climates are fundamentally different. The Holocene record is monofractal, with a scaling exponent H∼0.7. On the contrary, the glacial record is multifractal, with a significantly higher scaling exponent H∼1.2, indicating a longer persistence time and stronger nonlinearities in the glacial climate. The glacial climate is dominated by the strong multi-millennial Dansgaard–Oeschger (DO) events influencing the long-time correlation. However, by separately analysing the last glacial maximum lacking DO events, here we find the same scaling for that period as for the full glacial period. The unbroken scaling thus indicates that the DO events are part of the natural variability and not externally triggered. At glacial time scales, there is a scale break to a trivial scaling, contrasting the DO events from the similarly saw-tooth-shaped glacial cycles. PMID:26980084

  16. Contrasting scaling properties of interglacial and glacial climates.

    PubMed

    Shao, Zhi-Gang; Ditlevsen, Peter D

    2016-01-01

    Understanding natural climate variability is essential for assessments of climate change. This is reflected in the scaling properties of climate records. The scaling exponents of the interglacial and the glacial climates are fundamentally different. The Holocene record is monofractal, with a scaling exponent H∼0.7. On the contrary, the glacial record is multifractal, with a significantly higher scaling exponent H∼1.2, indicating a longer persistence time and stronger nonlinearities in the glacial climate. The glacial climate is dominated by the strong multi-millennial Dansgaard-Oeschger (DO) events influencing the long-time correlation. However, by separately analysing the last glacial maximum lacking DO events, here we find the same scaling for that period as for the full glacial period. The unbroken scaling thus indicates that the DO events are part of the natural variability and not externally triggered. At glacial time scales, there is a scale break to a trivial scaling, contrasting the DO events from the similarly saw-tooth-shaped glacial cycles. PMID:26980084

  17. Denudation of the continental shelf between Britain and France at the glacial-interglacial timescale

    NASA Astrophysics Data System (ADS)

    Mellett, Claire L.; Hodgson, David M.; Plater, Andrew J.; Mauz, Barbara; Selby, Ian; Lang, Andreas

    2013-12-01

    The erosional morphology preserved at the sea bed in the eastern English Channel dominantly records denudation of the continental shelf by fluvial processes over multiple glacial-interglacial sea-level cycles rather than by catastrophic flooding through the Straits of Dover during the mid-Quaternary. Here, through the integration of multibeam bathymetry and shallow sub-bottom 2D seismic reflection profiles calibrated with vibrocore records, the first stratigraphic model of erosion and deposition on the eastern English Channel continental shelf is presented. Published Optical Stimulated Luminescence (OSL) and 14C ages were used to chronometrically constrain the stratigraphy and allow correlation of the continental shelf record with major climatic/sea-level periods. Five major erosion surfaces overlain by discrete sediment packages have been identified. The continental shelf in the eastern English Channel preserves a record of processes operating from Marine Isotope Stage (MIS) 6 to MIS 1. Planar and channelised erosion surfaces were formed by fluvial incision during lowstands or relative sea-level fall. The depth and lateral extent of incision was partly conditioned by underlying geology (rock type and tectonic structure), climatic conditions and changes in water and sediment discharge coupled to ice sheet dynamics and the drainage configuration of major rivers in Northwest Europe. Evidence for major erosion during or prior to MIS 6 is preserved. Fluvial sediments of MIS 2 age were identified within the Northern Palaeovalley, providing insights into the scale of erosion by normal fluvial regimes. Seismic and sedimentary facies indicate that deposition predominantly occurred during transgression when accommodation was created in palaeovalleys to allow discrete sediment bodies to form. Sediment reworking over multiple sea-level cycles (Saalian-Eemian-early Weichselian) by fluvial, coastal and marine processes created a multi-lateral, multi-storey succession of

  18. Denudation of the continental shelf between Britain and France at the glacial–interglacial timescale

    PubMed Central

    Mellett, Claire L.; Hodgson, David M.; Plater, Andrew J.; Mauz, Barbara; Selby, Ian; Lang, Andreas

    2013-01-01

    The erosional morphology preserved at the sea bed in the eastern English Channel dominantly records denudation of the continental shelf by fluvial processes over multiple glacial–interglacial sea-level cycles rather than by catastrophic flooding through the Straits of Dover during the mid-Quaternary. Here, through the integration of multibeam bathymetry and shallow sub-bottom 2D seismic reflection profiles calibrated with vibrocore records, the first stratigraphic model of erosion and deposition on the eastern English Channel continental shelf is presented. Published Optical Stimulated Luminescence (OSL) and 14C ages were used to chronometrically constrain the stratigraphy and allow correlation of the continental shelf record with major climatic/sea-level periods. Five major erosion surfaces overlain by discrete sediment packages have been identified. The continental shelf in the eastern English Channel preserves a record of processes operating from Marine Isotope Stage (MIS) 6 to MIS 1. Planar and channelised erosion surfaces were formed by fluvial incision during lowstands or relative sea-level fall. The depth and lateral extent of incision was partly conditioned by underlying geology (rock type and tectonic structure), climatic conditions and changes in water and sediment discharge coupled to ice sheet dynamics and the drainage configuration of major rivers in Northwest Europe. Evidence for major erosion during or prior to MIS 6 is preserved. Fluvial sediments of MIS 2 age were identified within the Northern Palaeovalley, providing insights into the scale of erosion by normal fluvial regimes. Seismic and sedimentary facies indicate that deposition predominantly occurred during transgression when accommodation was created in palaeovalleys to allow discrete sediment bodies to form. Sediment reworking over multiple sea-level cycles (Saalian–Eemian–early Weichselian) by fluvial, coastal and marine processes created a multi-lateral, multi-storey succession of

  19. Denudation of the continental shelf between Britain and France at the glacial-interglacial timescale.

    PubMed

    Mellett, Claire L; Hodgson, David M; Plater, Andrew J; Mauz, Barbara; Selby, Ian; Lang, Andreas

    2013-12-01

    The erosional morphology preserved at the sea bed in the eastern English Channel dominantly records denudation of the continental shelf by fluvial processes over multiple glacial-interglacial sea-level cycles rather than by catastrophic flooding through the Straits of Dover during the mid-Quaternary. Here, through the integration of multibeam bathymetry and shallow sub-bottom 2D seismic reflection profiles calibrated with vibrocore records, the first stratigraphic model of erosion and deposition on the eastern English Channel continental shelf is presented. Published Optical Stimulated Luminescence (OSL) and (14)C ages were used to chronometrically constrain the stratigraphy and allow correlation of the continental shelf record with major climatic/sea-level periods. Five major erosion surfaces overlain by discrete sediment packages have been identified. The continental shelf in the eastern English Channel preserves a record of processes operating from Marine Isotope Stage (MIS) 6 to MIS 1. Planar and channelised erosion surfaces were formed by fluvial incision during lowstands or relative sea-level fall. The depth and lateral extent of incision was partly conditioned by underlying geology (rock type and tectonic structure), climatic conditions and changes in water and sediment discharge coupled to ice sheet dynamics and the drainage configuration of major rivers in Northwest Europe. Evidence for major erosion during or prior to MIS 6 is preserved. Fluvial sediments of MIS 2 age were identified within the Northern Palaeovalley, providing insights into the scale of erosion by normal fluvial regimes. Seismic and sedimentary facies indicate that deposition predominantly occurred during transgression when accommodation was created in palaeovalleys to allow discrete sediment bodies to form. Sediment reworking over multiple sea-level cycles (Saalian-Eemian-early Weichselian) by fluvial, coastal and marine processes created a multi-lateral, multi-storey succession of

  20. Interglacial genetic diversification of Moussonia deppeana (Gesneriaceae), a hummingbird-pollinated, cloud forest shrub in northern Mesoamerica.

    PubMed

    Ornelas, Juan Francisco; González, Clementina

    2014-08-01

    Recent empirical work on cloud forest-adapted species supports the role of both old divergences across major geographical areas and more recent divergences attributed to Pleistocene climate changes. The shrub Moussonia deppeana is distributed in northern Mesoamerica, with geographically disjunct populations. Based on sampling throughout the species range and employing plastid and nuclear markers, we (i) test whether the fragmented distribution is correlated with main evolutionary lineages, (ii) reconstruct its phylogeographical history to infer the history of cloud forest in northern Mesoamerica and (iii) evaluate a set of refugia/vicariance scenarios for the region and demographic patterns of the populations whose ranges expanded and tracked cloud forest conditions during the Last Glacial Maximum. We found a deep evolutionary split in M. deppeana about 6-3 Ma, which could be consistent with a Pliocene divergence. Comparison of variation in plastid and nuclear markers revealed several lineages mostly congruent with their isolated geographical distribution and restricted gene flow among groups. Results of species distribution modelling and coalescent simulations fit a model of multiple refugia diverging during interglacial cycles. The demographic history of M. deppeana is not consistent with an expanding-contracting cloud forest archipelago model during the Last Glacial Maximum. Instead, our data suggest that populations persisted across the geographical range throughout the glacial cycles, and experienced isolation and divergence during interglacial periods. PMID:24954419

  1. How warm was the last interglacial? New model-data comparisons.

    PubMed

    Otto-Bliesner, Bette L; Rosenbloom, Nan; Stone, Emma J; McKay, Nicholas P; Lunt, Daniel J; Brady, Esther C; Overpeck, Jonathan T

    2013-10-28

    A Community Climate System Model, Version 3 (CCSM3) simulation for 125 ka during the Last Interglacial (LIG) is compared to two recent proxy reconstructions to evaluate surface temperature changes from modern times. The dominant forcing change from modern, the orbital forcing, modified the incoming solar insolation at the top of the atmosphere, resulting in large positive anomalies in boreal summer. Greenhouse gas concentrations are similar to those of the pre-industrial (PI) Holocene. CCSM3 simulates an enhanced seasonal cycle over the Northern Hemisphere continents with warming most developed during boreal summer. In addition, year-round warming over the North Atlantic is associated with a seasonal memory of sea ice retreat in CCSM3, which extends the effects of positive summer insolation anomalies on the high-latitude oceans to winter months. The simulated Arctic terrestrial annual warming, though, is much less than the observational evidence, suggesting either missing feedbacks in the simulation and/or interpretation of the proxies. Over Antarctica, CCSM3 cannot reproduce the large LIG warming recorded by the Antarctic ice cores, even with simulations designed to consider observed evidence of early LIG warmth in Southern Ocean and Antarctica records and the possible disintegration of the West Antarctic Ice Sheet. Comparisons with a HadCM3 simulation indicate that sea ice is important for understanding model polar responses. Overall, the models simulate little global annual surface temperature change, while the proxy reconstructions suggest a global annual warming at LIG (as compared to the PI Holocene) of approximately 1(°)C, though with possible spatial sampling biases. The CCSM3 SRES B1 (low scenario) future projections suggest high-latitude warmth similar to that reconstructed for the LIG may be exceeded before the end of this century. PMID:24043870

  2. Changes in southern hemispheric polar amplification over the past 5 million years revealed by climate modelling

    NASA Astrophysics Data System (ADS)

    Hoencamp, Jori; Stap, Lennert; Tuenter, Erik; Lourens, Luc; van de Wal, Roderik

    2016-04-01

    Knowledge on polar amplification is important to relate high latitude climate records to global mean temperature changes. Several studies have pointed out that the strength of polar amplification in the Northern Hemisphere varies considerably due to the presence of large ice sheets and more sea ice during colder climate conditions. As a result, the polar amplification in the Northern Hemisphere decreases for warmer climates. In this study, we address the fact that these changes in the Northern Hemisphere also affect the polar amplification in the Southern Hemisphere. We study the Southern and Northern Hemisphere amplification together over the past 5 million years with the CLIMBER-2 intermediate complexity model. Radiation, land ice extent and height, and greenhouse gases are prescribed as forcing. We find that in contrast to the reduction in polar amplification in the Northern Hemisphere, polar amplification in the Southern Hemisphere increases for warmer climates. The amplification decreases in the Northern Hemisphere from 2.7 during glacial conditions to 1.6 for a pre-industrial climate, which is line with other climate simulations. Over the same CO2 range the southern hemispheric polar amplification increases from 1 to 1.6. This is caused by the fact that the atmospheric transport needed to balance the radiation surplus in the equatorial region needs to be compensated by relatively stronger transport of energy in Southern direction while the transport in Northern direction reduces. This reduction in Northern direction is driven by less (land and sea) ice resulting in a smaller meridional gradient in Northern direction and hence a smaller atmospheric transport. As a consequence, the traditional scaled (with LGM temperature) Dome C record needs to be corrected with a maximum of 0.6 degrees half-way glacial and interglacial conditions, if it is to be interpreted as global mean temperature change indicator. While this changes the amplitude, the phasing of

  3. The Last Interglacial in the Levant: Perspective from the ICDP Dead Sea Deep Drill Core

    NASA Astrophysics Data System (ADS)

    Goldstein, S. L.; Torfstein, A.; Stein, M.; Kushnir, Y.; Enzel, Y.; Haug, G. H.

    2014-12-01

    Sediments recovered by the ICDP Dead Sea Deep Drilling Project provide a new perspective on the climate history of the Levant during the last interglacial period MIS5. They record the extreme impacts of an intense interglacial characterized by stronger insolation, warmer mean global temperatures, and higher sea-levels than the Holocene. Results show both extreme hyper-aridity during MIS5e, including an unprecedented drawdown of Dead Sea water levels, and the impacts of a strong precession-driven African monsoon responsible for a major sapropel event (S5) in the eastern Mediterranean. Hyper-arid conditions at the beginning of MIS5e prior to S5 (~132-128 ka) are evidenced by halite deposition, indicating declining Dead Sea lake levels. Surprisingly, the hyper-arid phase is interrupted during the MIS5e peak (~128-120 ka), coinciding with the S5 sapropel, which is characterized by a thick (23 m) section of silty detritus (without any halite) whose provenance indicates southern-sourced wetness in the watershed. Upon weakening of the S5 monsoon (~120-115 ka), the return of extreme aridity resulted in an unprecedented lake level drawdown, reflected by massive salt deposition, and followed by a sediment hiatus (~115-100 ka) indicating prolonged low lake level. The resumption of section follows classic Levant patterns with more wetness during cooler MIS5b and hyper-aridity during warmer MIS5a. The ICDP core provides the first evidence for a direct linkage between an intense precession-driven African monsoon and wetness at the high subtropical latitude (~30N) of the Dead Sea watershed. Combined with coeval deposition of Negev speleothems and travertines, and calcitification of Red Sea corals, the evidence indicates a wet climatic corridor that could facilitate homo sapiens migration out of Africa during the MIS5e peak. In addition, the MIS 5e hyper-arid intervals may provide an important cautionary analogue for the impact of future warming on regional water resources.

  4. Interglacial occurrence of cold-water corals off Cape Lookout (NW Atlantic): First evidence of the Gulf Stream influence

    NASA Astrophysics Data System (ADS)

    Matos, Lélia; Mienis, Furu; Wienberg, Claudia; Frank, Norbert; Kwiatkowski, Cornelia; Groeneveld, Jeroen; Thil, François; Abrantes, Fatima; Cunha, Marina R.; Hebbeln, Dierk

    2015-11-01

    Climatic and oceanographic changes, as occurring at a glacial-interglacial scale, may alter the environmental conditions needed for the development of prolific cold-water coral reefs and mounds. Studies constraining the temporal distribution of cold-water corals in the NE Atlantic suggested the cyclic changes of the Atlantic Meridional Overturning Circulation as the main driver for the development and dispersal of cold-water coral ecosystems. However, conclusions were hindered by lack of data from the NW Atlantic. Aiming to overcome this lack of data, the temporal occurrence of cold-water corals in the Cape Lookout area along the southeastern US margin was explored by U-series dating. Furthermore, the local influence of the regional water masses, namely the Gulf Stream, on cold-water coral proliferation and occurrence since the Last Glacial Maximum was examined. Results suggest that the occurrence of cold-water corals in the Cape Lookout area is restricted to interglacial periods, with corals being present during the last ~7 kyr and also during the Eemian (~125 ka). The reconstructed local environmental conditions suggest an offshore displacement of the Gulf Stream and increased influence from the Mid-Atlantic Bight shelf waters during the last glacial period. During the deglacial sea level rise, the Gulf Stream moved coastward providing present-day-like conditions to the surface waters. Nevertheless, present-day conditions at the ocean sea floor were not established before 7.5 cal ka BP once the ultimate demise of the Laurentide ice-sheet caused the final sea level rise and the displacement of the Gulf Stream to its present location. Occasional presence of the Gulf Stream over the site during the Mid- to Late Holocene coincides with enhanced bottom current strength and a slightly higher bottom water temperature, which are environmental conditions that are favorable for cold-water coral growth.

  5. Midge-Inferred Temperatures from Three Interglacial Periods in the Eastern Canadian Arctic

    NASA Astrophysics Data System (ADS)

    Axford, Y.; Briner, J. P.; Francis, D. R.; Baker, G.; Miller, G. H.

    2005-12-01

    Lake sediments recovered from a Canadian Arctic lake are providing a rare opportunity to reconstruct Holocene, last interglacial, and earlier temperature changes at centennial to decadal resolution. Lake CF8 (informal name) is a small (0.5 km2) lake situated on an inter-fjord lowland in northeastern Baffin Island at 70o N latitude. Sediment cores from Lake CF8 contain three organic lake sediment units, separated by non-lacustrine sands. Radiocarbon ages from the uppermost organic unit span the entire Holocene. The middle organic unit is beyond the limit of radiocarbon dating. Comparison with a similar lacustrine record from Fog Lake, Baffin Island, indicates that this middle unit most likely records the last interglacial (Eemian) period. The lowest organic unit was only partially recovered, but may record the late stages of the penultimate interglacial. Subfossil midges (Chironomidae) are abundant and well-preserved throughout the organic sediments, providing a quantitative means for temperature reconstruction. Midge-based temperature reconstructions indicate that summer temperatures at Lake CF8 surpassed modern values by 10 cal kyr BP. Summer temperatures during the first half of the Holocene were as much as 5oC warmer than present. Similarly, the early part of the last interglacial was several degrees warmer than the latter part of the period. The bottommost lake sediments we recovered, which were presumably deposited during the late stages of a prior interglacial period, record summer temperatures similar to those of the latter parts of the Holocene and last interglacial. The magnitude of early Holocene and last interglacial warmth at this high-latitude site lends support to concerns about Arctic amplification of future warming.

  6. Last interglacial temperature seasonality reconstructed from tropical Atlantic corals

    NASA Astrophysics Data System (ADS)

    Brocas, William M.; Felis, Thomas; Obert, J. Christina; Gierz, Paul; Lohmann, Gerrit; Scholz, Denis; Kölling, Martin; Scheffers, Sander R.

    2016-09-01

    Reconstructions of last interglacial (LIG, MIS 5e, ∼127-117 ka) climate offer insights into the natural response and variability of the climate system during a period partially analogous to future climate change scenarios. We present well preserved fossil corals (Diploria strigosa) recovered from the southern Caribbean island of Bonaire (Caribbean Netherlands). These have been precisely dated by the 230Th/U-method to between 130 and 120 ka ago. Annual banding of the coral skeleton enabled construction of time windows of monthly resolved strontium/calcium (Sr/Ca) temperature proxy records. In conjunction with a previously published 118 ka coral record, our eight records of up to 37 years in length, cover a total of 105 years within the LIG period. From these, sea surface temperature (SST) seasonality and variability in the tropical North Atlantic Ocean is reconstructed. We detect similar to modern SST seasonality of ∼2.9 °C during the early (130 ka) and the late LIG (120-118 ka). However, within the mid-LIG, a significantly higher than modern SST seasonality of 4.9 °C (at 126 ka) and 4.1 °C (at 124 ka) is observed. These findings are supported by climate model simulations and are consistent with the evolving amplitude of orbitally induced changes in seasonality of insolation throughout the LIG, irrespective of wider climatic instabilities that characterised this period. The climate model simulations suggest that the SST seasonality changes documented in our LIG coral Sr/Ca records are representative of larger regions within the tropical North Atlantic. These simulations also suggest that the reconstructed SST seasonality increase during the mid-LIG is caused primarily by summer warming. A 124 ka old coral documents, for the first time, evidence of decadal SST variability in the tropical North Atlantic during the LIG, akin to that observed in modern instrumental records.

  7. Stable Isotope Stratigraphy of a Late Last Interglacial Speleothem from Rana, Northern Norway

    NASA Astrophysics Data System (ADS)

    Linge, Henriette; Lauritzen, Stein-Erik; Lundberg, Joyce

    2001-09-01

    A stalagmite from Rana, northern Norway, dated by the TIMS uranium-series technique, yields records of stable oxygen and carbon isotopes covering the period from late marine oxygen isotope substages (MIS) 5e to 5a, that is, 123,350 to 73,300 yr ago. Rapid growth (∼46 μm/yr) between 123,350 and 119,500 yr ago reflects climatic conditions favorable for speleothem growth. This period is characterized by century- to millennial-scale oscillations in both stable isotope records, where both the absolute values and the isotope ranges are similar to Holocene and older samples from the region. From 119,500 to 107,700 yr ago, speleothem growth was slow (∼0.7 μm/yr), and between 107,700 and 73,300 yr ago growth is barely noticeable (0.07 μm/yr). During the period of slow growth the stable isotope records show an overall enrichment trend. The transition between rapid and slow growth rate occurring sometime between 119,500 and 107,700 yr ago is believed to reflect the termination of interglacial climate in this region. The absence of detritus and corrosion features in the slowly deposited calcite suggests that the valley outside the cave remained sufficiently ice free for speleothem growth to occur until at least 73,300 yr ago.

  8. Mechanisms behind primary production distribution during the last glacial-interglacial cycle

    NASA Astrophysics Data System (ADS)

    Le Mézo, Priscilla; Kageyama, Masa; Bopp, Laurent; Beaufort, Luc

    2015-04-01

    Reconstructions of past climates are possible through the analysis of organisms contained in marine and terrestrial sediments. Most of the paleorecords depend on biological processes, e.g. production of shells for coccolithophorids in the ocean, and these processes are sensitive to climate fluctuations from seasonal to orbital timescales. Consequently, depending on where and when the organisms that record climate conditions lived in the past, different factors may have influenced their abundance, their functioning, and thus it may bias interpretations of paleodata. In this context, it is necessary to evaluate the response of paleorecorders to climate variability at different timescales. In order to do so, we are using the coupled Earth System Model IPSLCM5A, which has a biogeochemical component PISCES that simulates primary production. We use 9 climate simulations of the IPSL-CM5A model, from -80kyr BP climate conditions to a preindustrial state. Thanks to different forcing conditions of these simulations we are able to disentangle the effects of precession changes from those of obliquity, sea level or gases concentrations. The objectives are to characterize the mechanisms behind the observed changes in primary production between the different time periods. The results of this modeling study will also be compared to reconstructed productions in the Indian, West and East Tropical Pacific Oceans obtained from core sediments with the method described in Beaufort et al. 1997. The early results on seasonal cycles show that, in the Indian Ocean, precession is not the main driver of changes in primary production. Indeed, we observe a grouping between simulations having the same sea level, which suggests that changes in primary production are more sensitive to parameters that define glacial-interglacial conditions such as ice sheets which affect oceanic circulation.

  9. Quantitative reconstruction of the last interglacial vegetation and climate based on the pollen record from Lake Baikal, Russia

    NASA Astrophysics Data System (ADS)

    Tarasov, P.; Granoszewski, W.; Bezrukova, E.; Brewer, S.; Nita, M.; Abzaeva, A.; Oberhänsli, H.

    2005-11-01

    Changes in mean temperature of the coldest ( T c) and warmest month ( T w), annual precipitation ( P ann) and moisture index (α) were reconstructed from a continuous pollen record from Lake Baikal, Russia. The pollen sequence CON01-603-2 (53°57'N, 108°54'E) was recovered from a 386 m water depth in the Continent Ridge and dated to ca. 130 114.8 ky BP. This time interval covers the complete last interglacial (LI), corresponding to MIS 5e. Results of pollen analysis and pollen-based quantitative biome reconstruction show pronounced changes in the regional vegetation throughout the record. Shrubby tundra covered the area at the beginning of MIS 5e (ca. 130 128 ky), consistent with the end of the Middle Pleistocene glaciation. The late glacial climate was characterised by low winter and summer temperatures ( T c ~ -38 to -35°C and T w~11 13°C) and low annual precipitation ( P ann~300 mm). However, the wide spread of tundra vegetation suggests rather moist environments associated with low temperatures and evaporation (reconstructed α~1). Tundra was replaced by boreal conifer forest (taiga) by ca. 128 ky BP, suggesting a transition to the interglacial. Taiga-dominant phase lasted until ca. 117.4 ky BP, e.g. about 10 ky. The most favourable climate conditions occurred during the first half of the LI. P ann reached 500 mm soon after 128 ky BP. However, temperature changed more gradually. Maximum values of T c ~ -20°C and T w~16 17°C are reconstructed from about 126 ky BP. Conditions became gradually colder after ca. 121 ky BP. T c dropped to ~ -27°C and T w to ~15°C by 119.5 ky BP. The reconstructed increase in continentality was accompanied by a decrease in P ann to ~400 420 mm. However, the climate was still humid enough (α~0.9) to support growth of boreal evergreen conifers. A sharp turn towards a dry climate is reconstructed after ca. 118 ky BP, causing retreat of forest and spread of cool grass-shrub communities. Cool steppe dominated the vegetation in the

  10. Impact of oceanic circulation changes on the CO2 concentration during past interglacials

    NASA Astrophysics Data System (ADS)

    Bouttes, Nathaelle; Swingedouw, Didier; Crosta, Xavier; Fernanda Sanchez Goñi, Maria; Roche, Didier

    2016-04-01

    Interglacials before the Mid-Bruhnes Event (around 430 kyrs BP) were characterized by colder temperature in Antarctica, lower sea level and lower atmospheric CO2 compared to the more recent interglacials. Recent climate simulations have shown that the climate of the interglacials before and after the MBE can only be reproduced when taking into account changes in orbital parameters and atmospheric CO2 concentrations (Yin and Berger, 2010; Yin and Berger, 2012). Indeed, interglacial atmospheric CO2 concentrations were ~250 ppm and ~280 ppm prior and after the MBE, respectively. Yet, the cause for this change in atmospheric CO2 remains mainly unknown. climate simulations suggest that oceanic circulation was different during the interglacials due to the different climate states (Yin, 2013). The changes of oceanic circulation could have modified the carbon cycle: a more sluggish circulation would lead to greater carbon sequestration in the deep ocean and, subsequently, a decrease of atmospheric CO2. However, the impact of oceanic circulation changes on the carbon cycle during the interglacials of the last 800 kyrs has never been tested in coupled carbon-climate models. Here, we evaluate the role of ocean circulation changes on the carbon cycle during interglacials by using the intermediate complexity model iLOVECLIM (Goosse et al., 2010 ; Bouttes et al., 2015). This model includes a carbon cycle module on land and in the ocean and simulates carbon isotopes. The interglacial simulations are forced with orbital parameters, ice sheets and CO2 concentrations from data reconstructions. The model computes carbon fluxes between the reservoirs and an atmospheric CO2 that is distinct from the one used as a forcing. We will present simulations from this climate model for different interglacial periods of the last 800 000 years and use model-data comparison to analyse and evaluate the changes in the carbon cycle, including CO2. References Bouttes, N. et al. (2015), Geosci. Model

  11. Seasonal and diurnal variation of geomagnetic activity: Russell-McPherron effect during different IMF polarity and/or extreme solar wind conditions

    NASA Astrophysics Data System (ADS)

    Zhao, H.; Zong, Q.-G.

    2012-11-01

    The Russell-McPherron (R-M) effect is one of the most prevailing hypotheses accounting for semiannual variation of geomagnetic activity. To validate the R-M effect and investigate the difference of geomagnetic activity variation under different interplanetary magnetic field (IMF) polarity and during extreme solar wind conditions (interplanetary shock), we have analyzed 42 years interplanetary magnetic field and geomagnetic indices data and 1270 SSC (storm sudden commencement) events from the year 1968 to 2010 by defining the R-M effect with positive/negative IMF polarity (IMF away/toward the Sun). The results obtained in this study have shown that the response of geomagnetic activity to the R-M effect with positive/negative IMF polarity are rather profound: the geomagnetic activity is much more intense around fall equinox when the direction of IMF is away the Sun, while much more intense around spring equinox when the direction of IMF is toward the Sun. The seasonal and diurnal variation of geomagnetic activity after SSCs can be attributed to both R-M effect and the equinoctial hypothesis; the R-M effect explains most part of variance of southward IMF, while the equinoctial hypothesis explains similar variance of ring current injection and geomagnetic indices as the R-M effect. However, the R-M effect with positive/negative IMF polarity explains the difference between SSCs with positive/negative IMF By accurately, while the equinoctial hypothesis cannot explain such difference at the spring and fall equinoxes. Thus, the R-M effect with positive/negative IMF polarity is more reasonable to explain seasonal and diurnal variation of geomagnetic activity under extreme solar wind conditions.

  12. Characterising the Last Interglacial: High-resolution palaeoclimatic records from the Mediterranean

    NASA Astrophysics Data System (ADS)

    Milner, Alice; Martrat, Belen; Skinner, Luke; Tzedakis, Polychronis; Grimalt, Joan

    2013-04-01

    Evidence of abrupt climate variability during the Last Interglacial (approximately equivalent to MIS 5e) and glacial inception is detected in a variety of palaeoarchives but the nature of the variability is not yet satisfactorily resolved, nor are the causes fully understood. To improve our understanding of the climatic forcing and response to abrupt variability, detailed palaeoclimate data from a range of sites are required. The sensitivity of the Mediterranean region to global climate change makes it an ideal location from which to investigate variability during interglacials on decadal to millennial- timescales. We present a high-resolution palaeoclimatic record from the Central Mediterranean Sea with an aim of better understanding interglacial climate evolution and variability in the Mediterranean and its links to high- and low-latitude climate systems. High-resolution alkenone- and faunal-based sea surface temperature and pollen data are presented for the mid-latitude ODP Site 963 in the Strait of Sicily. This coupled terrestrial-marine record allows in situ assessment of the leads and lags of climate change in the terrestrial and marine environments. The new data provide evidence for intra-interglacial variability both on land and in the ocean, with a similar level of climate variability to that seen in the North Atlantic marine and Greenland ice core records. Our results suggests a close relation between the high northern latitudes and the Mediterranean during the Last Interglacial.

  13. Arabidopsis response to low-phosphate conditions includes active changes in actin filaments and PIN2 polarization and is dependent on strigolactone signalling

    PubMed Central

    Kumar, Manoj; Pandya-Kumar, Nirali; Dam, Anandamoy; Haor, Hila; Mayzlish-Gati, Einav; Belausov, Eduard; Wininger, Smadar; Abu-Abied, Mohamad; McErlean, Christopher S. P.; Bromhead, Liam J.; Prandi, Cristina; Kapulnik, Yoram; Koltai, Hinanit

    2015-01-01

    Strigolactones (SLs) are plant hormones that regulate the plant response to phosphate (Pi) growth conditions. At least part of SL-signalling execution in roots involves MAX2-dependent effects on PIN2 polar localization in the plasma membrane (PM) and actin bundling and dynamics. We examined PIN2 expression, PIN2 PM localization, endosome trafficking, and actin bundling under low-Pi conditions: a MAX2-dependent reduction in PIN2 trafficking and polarization in the PM, reduced endosome trafficking, and increased actin-filament bundling were detected in root cells. The intracellular protein trafficking that is related to PIN proteins but unassociated with AUX1 PM localization was selectively inhibited. Exogenous supplementation of the synthetic SL GR24 to a SL-deficient mutant (max4) led to depletion of PIN2 from the PM under low-Pi conditions. Accordingly, roots of mutants in MAX2, MAX4, PIN2, TIR3, and ACTIN2 showed a reduced low-Pi response compared with the wild type, which could be restored by auxin (for all mutants) or GR24 (for all mutants except max2-1). Changes in PIN2 polarity, actin bundling, and vesicle trafficking may be involved in the response to low Pi in roots, dependent on SL/MAX2 signalling. PMID:25609825

  14. Integrative algorithm of determining ice conditions in Polar Regions by data of satellite microwave radiometry (VASIA2)

    NASA Astrophysics Data System (ADS)

    Tikhonov, V. V.; Repina, I. A.; Raev, M. D.; Sharkov, E. A.; Boyarskii, D. A.; Komarova, N. Yu.

    2015-12-01

    In this paper, a new algorithm for determining the concentration of the ice cover in Polar Regions by data of satellite microwave radiometry is considered. The technique of its construction is described in detail; it cardinally differs from the technique of creating present-day algorithms. The new algorithm demonstrates good results in determining the concentration of the ice cover in Polar Regions. The algorithm permits one not only to obtain maps of ice concentration, but also to determine areas of puddles covering the ice-cover surface in summer months. The algorithm is easy-to-use and requires no additional or fitting parameters. At the end of the work, advantages and disadvantages of the new algorithm are discussed.

  15. U-series evidence for two high Last Interglacial sea levels in southeastern Tunisia

    NASA Astrophysics Data System (ADS)

    Jedoui, Younes; Reyss, Jean-Louis; Kallel, Nejib; Montacer, Mabrouk; Ismaı̈l, Hedi Ben; Davaud, Eric

    2003-02-01

    Pleistocene raised marine deposits in southeastern Tunisia consist of a siliciclastic unit that culminates at +3 m asl, overlain by a carbonate-rich unit with Strombus bubonius that culminates at +5 m asl. 234U/ 238U ratios on fossil Ostraea shells from both units are compatible with a marine origin from the uranium incorporated into the shells and show narrowly clustered 230Th-ages, respectively, between 147 and 110 ka and 141 and 100 ka. The two units were therefore developed during Marine Isotopic Substage 5e (MISs 5e, Last Interglacial). Their heights are comparable to those of contemporaneous marine deposits found in many tectonically stable areas of the world such as in the Bahamas and in Bermuda and can therefore be used as indicators of eustatic changes during the Last Interglacial. It is argued that on the basis of this evidence, the Last Interglacial was characterised by two eustatic maxima.

  16. Interglacial hydroclimate in the tropical West Pacific through the Late Pleistocene.

    PubMed

    Meckler, A N; Clarkson, M O; Cobb, K M; Sodemann, H; Adkins, J F

    2012-06-01

    Records of atmospheric carbon dioxide concentration (P(CO(2))) and Antarctic temperature have revealed an intriguing change in the magnitude of interglacial warmth and P(CO(2)) at around 430,000 years ago (430 ka), but the global climate repercussions of this change remain elusive. Here, we present a stalagmite-based reconstruction of tropical West Pacific hydroclimate from 570 to 210 ka. The results suggest similar regional precipitation amounts across the four interglacials contained in the record, implying that tropical hydroclimate was insensitive to interglacial differences in P(CO(2)) and high-latitude temperature. In contrast, during glacial terminations, drying in the tropical West Pacific accompanied cooling events in northern high latitudes. Therefore, the tropical convective heat engine can either stabilize or amplify global climate change, depending on the nature of the climate forcing. PMID:22555435

  17. Antarctic last interglacial isotope peak in response to sea ice retreat not ice-sheet collapse.

    PubMed

    Holloway, Max D; Sime, Louise C; Singarayer, Joy S; Tindall, Julia C; Bunch, Pete; Valdes, Paul J

    2016-01-01

    Several studies have suggested that sea-level rise during the last interglacial implies retreat of the West Antarctic Ice Sheet (WAIS). The prevalent hypothesis is that the retreat coincided with the peak Antarctic temperature and stable water isotope values from 128,000 years ago (128 ka); very early in the last interglacial. Here, by analysing climate model simulations of last interglacial WAIS loss featuring water isotopes, we show instead that the isotopic response to WAIS loss is in opposition to the isotopic evidence at 128 ka. Instead, a reduction in winter sea ice area of 65±7% fully explains the 128 ka ice core evidence. Our finding of a marked retreat of the sea ice at 128 ka demonstrates the sensitivity of Antarctic sea ice extent to climate warming. PMID:27526639

  18. Antarctic last interglacial isotope peak in response to sea ice retreat not ice-sheet collapse

    PubMed Central

    Holloway, Max D.; Sime, Louise C.; Singarayer, Joy S.; Tindall, Julia C.; Bunch, Pete; Valdes, Paul J.

    2016-01-01

    Several studies have suggested that sea-level rise during the last interglacial implies retreat of the West Antarctic Ice Sheet (WAIS). The prevalent hypothesis is that the retreat coincided with the peak Antarctic temperature and stable water isotope values from 128,000 years ago (128 ka); very early in the last interglacial. Here, by analysing climate model simulations of last interglacial WAIS loss featuring water isotopes, we show instead that the isotopic response to WAIS loss is in opposition to the isotopic evidence at 128 ka. Instead, a reduction in winter sea ice area of 65±7% fully explains the 128 ka ice core evidence. Our finding of a marked retreat of the sea ice at 128 ka demonstrates the sensitivity of Antarctic sea ice extent to climate warming. PMID:27526639

  19. Thorium-230 ages of corals and duration of the last interglacial sea-level high stand on Oahu, Hawaii

    SciTech Connect

    Szabo, B.J.; Ludwig, K.R.; Muhs, D.R.; Simmons, K.R.

    1994-10-07

    Thorium-230 ages of emergent marine deposits on Oahu, Hawaii, have a uniform distribution of ages from {approximately}114,000 to {approximately}131,000 years, indicating a duration for the last interglacial sea-level high stand of {approximately}17,000 years, in contrast to a duration of {approximately}8000 years inferred from the orbitally tuned marine oxygen isotope record. Sea level on Oahu rose to {>=}1 to 2 meters higher than present by 131,000 years ago or {approximately}6000 years earlier than inferred from the marine record. Although the latter record suggests a shift back to glacial conditions beginning at {approximately}119,000 years ago, the Oahu coral ages indicate a near present sea level until {approximately}114,000 years ago.

  20. Glacial-interglacial organic carbon record from the Makassar Strait, Indonesia: Implications for regional changes in continental vegetation

    USGS Publications Warehouse

    Visser, K.; Thunell, R.; Goni, M.A.

    2004-01-01

    Recent studies convincingly show that climate in the Western Pacific Warm Pool and other equatorial/tropical regions was significantly colder (by ???3-4??C) during glacial periods, prompting a reexamination of the late Pleistocene paleoenvironments of these regions. This study examines changes in continental vegetation during the last two deglaciations (Terminations I and II) using a sediment core (MD9821-62) recovered from the Makassar Strait, Indonesia. Evidence based on the lignin phenol ratios suggests that vegetation on Borneo and other surrounding islands did not significantly change from tropical rainforest during the last two glacial periods relative to subsequent interglacial periods. This supports the hypothesis that the winter monsoon increased in strength during glacial periods, allowing Indonesia to maintain high rainfall despite the cooler conditions. ?? 2003 Elsevier Ltd. All rights reserved.

  1. 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

  2. Corals deep under the stream: how the Gulf Stream is driving the interglacial occurrence of cold-water corals off Cape Lookout, NC

    NASA Astrophysics Data System (ADS)

    Matos, L.; Mienis, F.; Frank, N.; Thil, F.; Wienberg, C.; Hebbeln, D.

    2012-12-01

    Late Quaternary climate variability has been frequently related to oceanographic forcing. In the North Atlantic, recent glacial-interglacial cycles and abrupt millennial-scale climate changes have been linked to reorganisations of the Meridional Overturning Circulation. Among others, aragonite-forming cold-water corals (CWC) have become important archives to unravel the water-mass history. While being accurately datable by means of mass spectrometric Uranium-series dating and given their intermediate depth distribution and specific ecological requirements, the CWC distribution through time can reveal important insights into the oceanographic conditions that favour coral growth (Frank et al., Geology, 2011). In the northeast Atlantic, climate driven variations in the strength and flow path of the Mediterranean Outflow Water, surface productivity and mid-depth temperature have been suggested to cause a south-north see-saw pattern in the CWC distribution on glacial-interglacial time scales: abundant coral growth occurred north of 50°N during interglacial periods (Marine Isotope Stages MIS1, 5 and 7); and south of 37°N during glacial periods (MIS2, 3, 4 and 6). Stepping forward on the development of basin-scale knowledge on the North Atlantic distribution of framework forming CWC species and its relation to water mass dynamics, we present 19 ages of the CWC Lophelia pertusa sampled from mound structures at 320-500m water depth off Cape Lookout (Blake Plateau) on the North Carolina margin (34°N). Coral (on-mound) and sediment (off-mound) samples were used to accurately reconstruct ages of fossil coral fragments and to determine the sedimentation history via AMS-14C dating of planktonic foraminifera. Our L. pertusa samples revealed interglacial ages from early Eemian and from Mid- to Late-Holocene (last and present interglacials, respectively), thus differing from the predominantly glacial temperate East Atlantic CWC developments. The temporal distribution of CWC off

  3. 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

  4. Triple water-isotopologue record from WAIS Divide, Antarctica: Controls on glacial-interglacial changes in 17Oexcess of precipitation

    NASA Astrophysics Data System (ADS)

    Schoenemann, Spruce W.; Steig, Eric J.; Ding, Qinghua; Markle, Bradley R.; Schauer, Andrew J.

    2014-07-01

    Measurements of the 17Oexcess of H2O were obtained from ice cores in West and East Antarctica. Combined with previously published results from East Antarctica, the new data provide the most complete spatial and temporal view of Antarctic 17Oexcess to date. There is a steep spatial gradient of 17Oexcess in present-day precipitation across Antarctica, with higher values in marine-influenced regions and lower values in the East Antarctic interior. There is also a spatial pattern to the change in 17Oexcess between the Last Glacial Maximum (LGM) and Holocene periods. At coastal locations, there is no significant change in 17Oexcess. At both the West Antarctic Ice Sheet Divide site and at Vostok, East Antarctica, the LGM to Early Holocene change in 17Oexcess is about 20 per meg. Atmospheric general circulation model (GCM) experiments show that both the observed spatial gradient of 17Oexcess in modern precipitation, and the spatial pattern of LGM to Early Holocene change, can be explained by kinetic isotope effects during snow formation under supersaturated conditions, requiring a high sensitivity of supersaturation to temperature. The results suggest that fractionation during snow formation is the primary control on 17Oexcess in Antarctic precipitation. Variations in moisture source relative humidity play a negligible role in determining the glacial-interglacial 17Oexcess changes observed in Antarctic ice cores. Additional GCM experiments show that sea ice expansion increases the area over which supersaturating conditions occur, amplifying the effect of colder temperatures. Temperature and sea ice changes alone are sufficient to explain the observed 17Oexcess glacial-interglacial changes across Antarctica.

  5. Glacial-interglacial Variations of Molybdenum Isotopes in the Peruvian Oxygen Minimum Zone

    NASA Astrophysics Data System (ADS)

    Siebert, C.; Frank, M.; Scholz, F.

    2015-12-01

    Mo isotopes have been widely used as a tool to constrain redox-conditions during major global events such as the oxygenation of the oceans in the Precambrian and Cretaceous Ocean Anoxic Events. In addition, Mo isotopes have considerable, yet underexplored potential to quantitatively track local redox-variation at high resolution on shorter timescales. Here we present data from piston core M77/2-024-5 that was retrieved in the Peruvian oxygen minimum zone in the context of Collaborative Research Centre (SFB) 754 of the Deutsche Forschungs Gemeinschaft (DFG). The age model for this core is well constrained and the core covers the last 140 ka with a hiatus between 20 and 50 ky BP. The oxygen minimum zone along the Peru continental margin is thought to have been better ventilated and therefore less pronounced during glacial periods compared to interglacials. Concentrations of redox-sensitive trace elements show high-amplitude changes and indicate periods of strongly sulphidic conditions with high Mo fixation rate and oxygenated periods with limited Mo fixation (Scholz et al 2014). Mo isotopes do not show straightforward correlations with elemental redox tracers and are only weakly correlated with Mo/U and total organic carbon (TOC). However, Mo isotopes become significantly heavier around the last glacial maximum (Δ98Mo of 0.4 permil). The observed signatures indicate that the Mo isotope composition is dominated by changes in the operating Mo delivery mechanism, i.e. particulate transport versus molecular diffusion. Our results suggest that Mo isotopes can track local redox variation therefore adding to our understanding of this complex indicator for marine environmental change. Scholz et al., (2014), Nature Geosciences, Vol. 7, Pages 433-437

  6. Plio-Pleistocene glacial-interglacial productivity changes in the eastern equatorial Pacific upwelling system

    NASA Astrophysics Data System (ADS)

    Jakob, Kim A.; Wilson, Paul A.; Bahr, André; Bolton, Clara T.; Pross, Jörg; Fiebig, Jens; Friedrich, Oliver

    2016-03-01

    The eastern equatorial Pacific Ocean (EEP) upwelling system supports >10% of the present-day global ocean primary production, making it an important component in Earth's atmospheric and marine carbon budget. Traditionally, it has been argued that since intensification of Northern Hemisphere glaciation (iNHG, ~2.7 Ma), changes in EEP productivity have predominantly depended on trade wind strength-controlled upwelling intensity. An alternative hypothesis suggests that EEP productivity is primarily controlled by nutrient supply from the high southern latitudes via mode waters. Here we present new high-resolution data for the latest Pliocene/early Pleistocene from Ocean Drilling Program Site 849, located within the equatorial divergence system in the heart of the EEP upwelling regime. We use carbon isotopes in benthic and planktic foraminiferal calcite and sand accumulation rates to investigate glacial-interglacial (G-IG) productivity fluctuations between 2.65 and 2.4 Ma (marine isotope stages (MIS) G1 to 94). This interval includes MIS 100, 98, and 96, three large-amplitude glacials (~1‰ in benthic δ18O) representing the culmination of iNHG. Our results suggest that latest Pliocene/early Pleistocene G-IG productivity changes in the EEP were strongly controlled by nutrient supply from Southern Ocean-sourced mode waters. Our records show a clear G-IG cyclicity from MIS 100 onward with productivity levels increasing from full glacial conditions and peaking at glacial terminations. We conclude that enhanced nutrient delivery from high southern latitudes during full glacial conditions together with superimposed intensified regional upwelling toward glacial terminations strongly regulated primary productivity rates in the EEP from MIS 100 onward.

  7. Multi-decadal-scale records of North Atlantic climate variability during the last and present interglacials and preceding glacial terminations.

    NASA Astrophysics Data System (ADS)

    Jimenez-Amat, Patricia; Zahn, Rainer

    2013-04-01

    High-resolution records of natural interglacial climate variability can provide knowledge if the currently ongoing climate change and variability are part of or are already beyond the natural state. Warmer-than-present climatic conditions, a reduced Greenland Ice Sheet and higher sea level are some of the features the Last Interglacial (LIG, MIS5e; 129-115 kyr) climate has in common with numerous model projections of our future climate (Otto-Bliesner et al., 2006; Koop et al., 2009). Establishing multi-decadal resolution records of past North Atlantic climate variability hence contributes to a better understanding of the ocean and climate sensitivity of the wider North Atlantic region. We present palaeoceanographic time series of surface ocean climatology from Ocean Drilling Program (ODP) Site 976 in the Alboran Sea, westernmost Mediterranean that span the LIG and Present Interglacial (PIG, Holocene, 11-0 kyr). The site receives North Atlantic climate signals through the atmosphere and with the advection of Atlantic inflow waters which in connection with the high rate of sediment deposition underscores the exceptional quality of the site to monitor North Atlantic climate variability at multi-decadal resolution (60-90 yrs). Sea surface temperature (SST) time series derived from Mg/Ca ratios and stable isotope records (δ18O, δ13C) of the planktonic foraminifera Globigerina bulloides are presented. Mg/Ca data display similar SST for the climatic optima PIG and LIG. The records compare well with speleothem and ice core palaeoclimatic profiles, confirming that Site 976 palaeo-profiles reflect climate of the North Atlantic region. The close link between SSTMg-Caand the LIG δ18O record from the Antro del Corchia speleothem in northern Italy highlights the strong connection between marine and terrestrial climatology during that time indicating a farfield contribution of atmospheric signals. Comparison with SST and benthic δ13C records at North Atlantic sites instructs

  8. Interglacial climate dynamics and advanced time series analysis

    NASA Astrophysics Data System (ADS)

    Mudelsee, Manfred; Bermejo, Miguel; Köhler, Peter; Lohmann, Gerrit

    2013-04-01

    Studying the climate dynamics of past interglacials (IGs) helps to better assess the anthropogenically influenced dynamics of the current IG, the Holocene. We select the IG portions from the EPICA Dome C ice core archive, which covers the past 800 ka, to apply methods of statistical time series analysis (Mudelsee 2010). The analysed variables are deuterium/H (indicating temperature) (Jouzel et al. 2007), greenhouse gases (Siegenthaler et al. 2005, Loulergue et al. 2008, L¨ü thi et al. 2008) and a model-co-derived climate radiative forcing (Köhler et al. 2010). We select additionally high-resolution sea-surface-temperature records from the marine sedimentary archive. The first statistical method, persistence time estimation (Mudelsee 2002) lets us infer the 'climate memory' property of IGs. Second, linear regression informs about long-term climate trends during IGs. Third, ramp function regression (Mudelsee 2000) is adapted to look on abrupt climate changes during IGs. We compare the Holocene with previous IGs in terms of these mathematical approaches, interprete results in a climate context, assess uncertainties and the requirements to data from old IGs for yielding results of 'acceptable' accuracy. This work receives financial support from the Deutsche Forschungsgemeinschaft (Project ClimSens within the DFG Research Priority Program INTERDYNAMIK) and the European Commission (Marie Curie Initial Training Network LINC, No. 289447, within the 7th Framework Programme). References Jouzel J, Masson-Delmotte V, Cattani O, Dreyfus G, Falourd S, Hoffmann G, Minster B, Nouet J, Barnola JM, Chappellaz J, Fischer H, Gallet JC, Johnsen S, Leuenberger M, Loulergue L, Luethi D, Oerter H, Parrenin F, Raisbeck G, Raynaud D, Schilt A, Schwander J, Selmo E, Souchez R, Spahni R, Stauffer B, Steffensen JP, Stenni B, Stocker TF, Tison JL, Werner M, Wolff EW (2007) Orbital and millennial Antarctic climate variability over the past 800,000 years. Science 317:793. Köhler P, Bintanja R

  9. Tooth enamel stable isotopes of Holocene and Pleistocene fossil fauna reveal glacial and interglacial paleoenvironments of hominins in Indonesia

    NASA Astrophysics Data System (ADS)

    Janssen, Renée; Joordens, Josephine C. A.; Koutamanis, Dafne S.; Puspaningrum, Mika R.; de Vos, John; van der Lubbe, Jeroen H. J. L.; Reijmer, John J. G.; Hampe, Oliver; Vonhof, Hubert B.

    2016-07-01

    The carbon (δ13C) and oxygen (δ18O) isotope compositions of fossilized animal tissues have become important proxies of paleodiet and paleoenvironment, but such stable isotope studies have not yet been extensively applied to the fossil assemblages of Sundaland (the biogeographical region comprising most of the Indonesian Archipelago). Here, we use the isotope composition of tooth enamel to investigate the diet and habitat of bovids, cervids, and suids from several Holocene and Pleistocene sites on Java and Sumatra. Our carbon isotope results indicate that individual sites are strongly dominated by either C3-browsers or C4-grazers. Herbivores from the Padang Highlands (Sumatra) and Hoekgrot (Java) cave faunas were mainly C3-browsers, while herbivores from Homo erectus-bearing sites Trinil and Sangiran (Java) utilized an almost exclusive C4 diet. The suids from all sites show a wide range of δ13C values, corroborating their omnivorous diet. For the dataset as a whole, oxygen and carbon isotope values are positively correlated. This suggests that isotopic enrichment of rainwater and vegetation δ18O values coincides with an increase of C4-grasslands. We interpret this pattern to mainly reflect the environmental contrast between glacial (drier, more C4) and interglacial (wetter, more C3) conditions. Intermediate herbivore δ13C values indicating mixed C3/C4 feeding is relatively rare, which we believe to reflect the abruptness of the transition between glacial and interglacial precipitation regimes in Sundaland. For seven Homo erectus bone samples we were not able distinguish between diagenetic overprint and original isotope values, underlining the need to apply this isotopic approach to Homo erectus tooth enamel instead of bone. Importantly, our present results on herbivore and omnivore faunas provide the isotopic framework that will allow interpretation of such Homo erectus enamel isotope data.

  10. Contrasting glacial/interglacial regimes in the western Arctic Ocean as exemplified by a sedimentary record from the Mendeleev Ridge

    USGS Publications Warehouse

    Polyak, L.; Curry, W.B.; Darby, D.A.; Bischof, J.; Cronin, T. M.

    2004-01-01

    Distinct cyclicity in lithology and microfaunal distribution in sediment cores from the Mendeleev Ridge in the western Arctic Ocean (water depths ca. 1. 5 km) reflects contrasting glacial/interglacial sedimentary patterns. We conclude that during major glaciations extremely thick pack ice or ice shelves covered the western Arctic Ocean and its circulation was restricted in comparison with interglacial, modern-type conditions. Glacier collapse events are marked in sediment cores by increased contents of ice-rafted debris, notably by spikes of detrital carbonates and iron oxide grains from the Canadian Arctic Archipelago. Composition of foraminiferal calcite ?? 18O and ??13C also shows strong cyclicity indicating changes in freshwater balance and/or ventilation rates of the Arctic Ocean. Light stable isotopic spikes characterize deglacial events such as the last deglaciation at ca. 12 14C kyr BP. The prolonged period with low ??18O and ??13C values and elevated contents of iron oxide grains from the Canadian Archipelago in the lower part of the Mendeleev Ridge record is interpreted to signify the pooling of freshwater in the Amerasia Basin, possibly in relation to an extended glaciation in arctic North America. Unique benthic foraminiferal events provide a means for an independent stratigraphic correlation of sedimentary records from the Mendeleev Ridge and other mid-depth locations throughout the Arctic Ocean such as the Northwind and Lomonosov Ridges. This correlation demonstrates the disparity of existing age models and underscores the need to establish a definitive chronostratigraphy for Arctic Ocean sediments. ?? 2003 Elsevier B.V. All rights reserved.

  11. A Longer-lasting and warmer interglacial episode during isotopic stage 11: Marine terrace evidence in tropical western Americas

    NASA Astrophysics Data System (ADS)

    Ortlieb, Luc; Guzmán, Nury; Marquardt, Carlos

    Coastal areas of Baja California, Peru and northern Chile, which experienced relatively high uplift rates during the last half-million years, show a particularly wide development of marine terrace remnants assigned to the MIS 11. Morphologic characteristics of this terrace along the tropical eastern Pacific coasts (30°N to 30°S) suggest that the MIS 11 lasted longer than the other interglacials (more than 40 ky?) and that sea-level reached a higher "eustatic" position than at present and during MIS 5. A precise determination of the paleo-sea level position at the maximum of the MIS 11 transgression is hindered by uncertainties on variations in rates of tectonic uplift motions, in the course of the last 400 ky. Paleontological and paleoecological particularities of MIS 11 coastal deposits in northern Chile provide relevant data regarding nearshore marine and climatic conditions. Warm water mollusks from the Panamic Province (living presently north of 6°S) are retrieved in some MIS 11 coastal deposits at 23°S latitude (Mejillones peninsula), while a few species currently living in north and central Peru are found in coeval deposits at 23-30°S latitudes. Extralimital faunal elements thus co-existed with cool-water species of the Peruvian Province, and formed typical "TAMAs" (Thermally Anomalous Molluscan Assemblages). During the MIS 11 interglacial, for thousands of years, warm water populations lived in protected lagoons and embayments, where the water was apparently heated all year long by significantly warmer air-temperature than nowadays. The replenishment of the lagoonal assemblages by extralimital Panamic elements most probably involved episodic larval transports from lower latitudes, that reflect persistently strong and frequent ENSO manifestations.

  12. 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.

  13. Dead Sea drawdown and monsoonal impacts in the Levant during the last interglacial

    NASA Astrophysics Data System (ADS)

    Torfstein, Adi; Goldstein, Steven L.; Kushnir, Yochanan; Enzel, Yehouda; Haug, Gerald; Stein, Mordechai

    2015-02-01

    Sediment cores recovered by the Dead Sea Deep Drilling Project (DSDDP) from the deepest basin of the hypersaline, terminal Dead Sea (lake floor at ∼725 m below mean sea level) reveal the detailed climate history of the lake's watershed during the last interglacial period (Marine Isotope Stage 5; MIS5). The results document both a more intense aridity during MIS5 than during the Holocene, and the moderating impacts derived from the intense MIS5e African Monsoon. Early MIS5e (∼133-128 ka) was dominated by hyperarid conditions in the Eastern Mediterranean-Levant, indicated by thick halite deposition triggered by a lake-level drop. Halite deposition was interrupted however, during the MIS5e peak (∼128-122 ka) by sequences of flood deposits, which are coeval with the timing of the intense precession-forced African monsoon that generated Mediterranean sapropel S5. A subsequent weakening of this humidity source triggered extreme aridity in the Dead Sea watershed and resulting in the biggest known lake level drawdown in its history, reflected by the deposition of thick salt layers, and a capping pebble layer corresponding to a hiatus at ∼116-110 ka. The DSDDP core provides the first evidence for a direct association of the African monsoon with mid subtropical latitude climate systems effecting the Dead Sea watershed. Combined with coeval deposition of Arabia and southern Negev speleothems, Arava travertines, and calcification of Red Sea corals, the evidence points to a climatically wet corridor that could have facilitated homo sapiens migration "out of Africa" during the MIS5e peak. The hyperaridity documented during MIS5e may provide an important analogue for future warming of arid regions of the Eastern Mediterranean-Levant.

  14. Large-amplitude, circularly polarized, compressive, obliquely propagating electromagnetic proton cyclotron waves throughout the Earth's magnetosheath: low plasma β conditions

    SciTech Connect

    Remya, B.; Reddy, R. V.; Lakhina, G. S.; Tsurutani, B. T.; Falkowski, B. J.; Echer, E.; Glassmeier, K.-H.

    2014-09-20

    During 1999 August 18, both Cassini and WIND were in the Earth's magnetosheath and detected transverse electromagnetic waves instead of the more typical mirror-mode emissions. The Cassini wave amplitudes were as large as ∼14 nT (peak to peak) in a ∼55 nT ambient magnetic field B {sub 0}. A new method of analysis is applied to study these waves. The general wave characteristics found were as follows. They were left-hand polarized and had frequencies in the spacecraft frame (f {sub scf}) below the proton cyclotron frequency (f{sub p} ). Waves that were either right-hand polarized or had f {sub scf} > f{sub p} are shown to be consistent with Doppler-shifted left-hand waves with frequencies in the plasma frame f{sub pf} < f{sub p} . Thus, almost all waves studied are consistent with their being electromagnetic proton cyclotron waves. Most of the waves (∼55%) were found to be propagating along B {sub 0} (θ{sub kB{sub 0}}<30{sup ∘}), as expected from theory. However, a significant fraction of the waves were found to be propagating oblique to B {sub 0}. These waves were also circularly polarized. This feature and the compressive ([B {sub max} – B {sub min}]/B {sub max}, where B {sub max} and B {sub min} are the maximum and minimum field magnitudes) nature (ranging from 0.27 to 1.0) of the waves are noted but not well understood at this time. The proton cyclotron waves were shown to be quasi-coherent, theoretically allowing for rapid pitch-angle transport of resonant protons. Because Cassini traversed the entire subsolar magnetosheath and WIND was in the dusk-side flank of the magnetosheath, it is surmised that the entire region was filled with these waves. In agreement with past theory, it was the exceptionally low plasma β (0.35) that led to the dominance of the proton cyclotron wave generation during this interval. A high-speed solar wind stream ((V{sub sw} ) = 598 km s{sup –1}) was the source of this low-β plasma.

  15. Increased seasonality in Middle East temperatures during the last interglacial period.

    PubMed

    Felis, Thomas; Lohmann, Gerrit; Kuhnert, Henning; Lorenz, Stephan J; Scholz, Denis; Pätzold, Jürgen; Al-Rousan, Saber A; Al-Moghrabi, Salim M

    2004-05-13

    The last interglacial period (about 125,000 years ago) is thought to have been at least as warm as the present climate. Owing to changes in the Earth's orbit around the Sun, it is thought that insolation in the Northern Hemisphere varied more strongly than today on seasonal timescales, which would have led to corresponding changes in the seasonal temperature cycle. Here we present seasonally resolved proxy records using corals from the northernmost Red Sea, which record climate during the last interglacial period, the late Holocene epoch and the present. We find an increased seasonality in the temperature recorded in the last interglacial coral. Today, climate in the northern Red Sea is sensitive to the North Atlantic Oscillation, a climate oscillation that strongly influences winter temperatures and precipitation in the North Atlantic region. From our coral records and simulations with a coupled atmosphere-ocean circulation model, we conclude that a tendency towards the high-index state of the North Atlantic Oscillation during the last interglacial period, which is consistent with European proxy records, contributed to the larger amplitude of the seasonal cycle in the Middle East. PMID:15141207

  16. Color characteristics of Chinese loess and its paleoclimatic significance during the last glacial-interglacial cycle

    NASA Astrophysics Data System (ADS)

    Wang, Qiansuo; Song, Yougui; Zhao, Zhijun; Li, Jijun

    2016-02-01

    The soil color is widely used in paleoclimate and paleoenvironment reconstructions in the Chinese Loess Plateau. To better understand the color spatial changes during the glacial-interglacial cycle, the soil color lightness (L*), characteristic spectra, magnetic susceptibilities and mean grain sizes of three loess-paleosol sequences were compared. Results showed that high L* and low hematite to goethite ratios (Hm/Gt) appeared in loess units, and low L* and high Hm/Gt ratios accompanied paleosol layers, indicating glacial-interglacial hydrothermal oscillation. L* in the Yulin section was higher than in the Chaona and Lihuacun sections, indicating that different precipitations have great effect on L*. Furthermore, Hm/Gt, magnetic susceptibility (χlf), and mean grain size are correlated closely with L*. L* and Hm/Gt not only document climatic variations in the glacial-interglacial cycle vis-à-vis loess-paleosol sequences, but also can identify Heinrich cold events and millennial scale Dansgaard-Oeschger (D-O) warm events. It suggests that soil color responds sensitively to global climate change driven by ice volumes. L* and Hm/Gt curves exhibit higher frequencies and larger amplitudes than magnetic susceptibility (χlf) curves, indicating that L* and Hm/Gt can be regarded as sensitive and reliable proxies for characterizing high-resolution climate change during the last glacial-interglacial cycle.

  17. Polar Vortex Conditions During the 1995-96 Arctic Winter: MLS CL0 and HNO(sub 3)

    NASA Technical Reports Server (NTRS)

    Santee, M. L.; Manney, G. L.; Read, W. G.; Froidevaux, L.; Waters, J. W.

    1996-01-01

    Microwave Limb Sounder (MLS) measurements of lower stratospheric CLO and HNO(sub 3) during the 1995-96 Arctic winter are presented. The 1995-96 Arctic winter was both colder and more persistently cold than usual, leading to an enhancement in lower stratospheric CLO of greater magnitude, vertical extent, and duration than has been previously observed in the Arctic. Vortex concentrations of HNO(sub 3) in mid-December were large due to diabetic decent. Trajectory calculations indicate that localized severe depletions of gas-phase HNO(sub 3) in mid-February and early March did not arise from intrainment of midlatitude air into the vortex and were therefore probably related to polar stratospheric cloud (PSC) formation.

  18. Temperature trends during the Present and Last Interglacial periods - a multi-model-data comparison

    NASA Astrophysics Data System (ADS)

    Bakker, P.; Masson-Delmotte, V.; Martrat, B.; Charbit, S.; Renssen, H.; Gröger, M.; Krebs-Kanzow, U.; Lohmann, G.; Lunt, D. J.; Pfeiffer, M.; Phipps, S. J.; Prange, M.; Ritz, S. P.; Schulz, M.; Stenni, B.; Stone, E. J.; Varma, V.

    2014-09-01

    Though primarily driven by insolation changes associated with well-known variations in Earth's astronomical parameters, the response of the climate system during interglacials includes a diversity of feedbacks involving the atmosphere, ocean, sea ice, vegetation and land ice. A thorough multi-model-data comparison is essential to assess the ability of climate models to resolve interglacial temperature trends and to help in understanding the recorded climatic signal and the underlying climate dynamics. We present the first multi-model-data comparison of transient millennial-scale temperature changes through two intervals of the Present Interglacial (PIG; 8-1.2 ka) and the Last Interglacial (LIG; 123-116.2 ka) periods. We include temperature trends simulated by 9 different climate models, alkenone-based temperature reconstructions from 117 globally distributed locations (about 45% of them within the LIG) and 12 ice-core-based temperature trends from Greenland and Antarctica (50% of them within the LIG). The definitions of these specific interglacial intervals enable a consistent inter-comparison of the two intervals because both are characterised by minor changes in atmospheric greenhouse gas concentrations and more importantly by insolation trends that show clear similarities. Our analysis shows that in general the reconstructed PIG and LIG Northern Hemisphere mid-to-high latitude cooling compares well with multi-model, mean-temperature trends for the warmest months and that these cooling trends reflect a linear response to the warmest-month insolation decrease over the interglacial intervals. The most notable exception is the strong LIG cooling trend reconstructed from Greenland ice cores that is not simulated by any of the models. A striking model-data mismatch is found for both the PIG and the LIG over large parts of the mid-to-high latitudes of the Southern Hemisphere where the data depicts negative temperature trends that are not in agreement with near zero

  19. The last interglacial (Eemian) climate simulated by LOVECLIM and CCSM3

    NASA Astrophysics Data System (ADS)

    Nikolova, I.; Yin, Q.; Berger, A.; Singh, U. K.; Karami, M. P.

    2012-10-01

    This paper presents a detailed analysis of the climate of the last interglacial simulated by two climate models of different complexities, LOVECLIM and CCSM3. The simulated surface temperature, hydrological cycle, vegetation and ENSO variability during the last interglacial are analyzed through the comparison with the simulated Pre-Industrial (PI) climate. In both models, the last interglacial period is characterized by a significant warming (cooling) over almost all the continents during boreal summer (winter) leading to a largely increased (reduced) seasonal contrast in the northern (southern) hemisphere. This is mainly due to the much higher (lower) insolation received by the whole Earth in boreal summer (winter) during this interglacial. The arctic is warmer than PI through the whole year, resulting from its much higher summer insolation and its remnant effect in the following fall-winter through the interactions between atmosphere, ocean and sea ice. In the tropical Pacific, the change in the SST annual cycle is suggested to be related to a minor shift towards an El Nino, slightly stronger for MIS-5 than for PI. Intensified African monsoon and vegetation feedback are responsible for the cooling during summer in North Africa and Arabian Peninsula. Over India precipitation maximum is found further west, while in Africa the precipitation maximum migrates further north. Trees and grassland expand north in Sahel/Sahara. A mix of forest and grassland occupies continents and expand deep in the high northern latitudes. Desert areas reduce significantly in Northern Hemisphere, but increase in North Australia. The simulated large-scale climate change during the last interglacial compares reasonably well with proxy data, giving credit to both models and reconstructions. However, discrepancies exist at some regional scales between the two models, indicating the necessity of more in depth analysis of the models and comparisons with proxy data.

  20. Phosphorus burial in the ocean over glacial-interglacial time scales

    NASA Astrophysics Data System (ADS)

    Tamburini, F.; Föllmi, K. B.

    2008-12-01

    The role of nutrients and their impact on primary productivity and the fluctuations in atmospheric CO2 over glacial-interglacial periods are intensely debated. One of the cornerstones is the role of phosphorus (P; in the form of phosphate). Suggestions as to the importance of P evolved from an earlier proposal that P actively participated in changing productivity rates and therefore climate change, to the most recent one that changes in the glacial ocean inventory of phosphorus were small and not influential if compared to other macronutrients, such as nitrogen. Using new data coming from a selection of ODP sites, we illustrate oceanic P sedimentary phases distribution and reactive P burial fluxes, and we show how P burial fluxes changed over the last glacial-interglacial period. Concentrations of reactive P are generally lower during glacial times, while mass accumulation rates (MAR) show higher variability. On a global scale, glacial burial fluxes of reactive P are lower than those during interglacial periods by 7-10%, because lack of burial of reactive P on the glacial reduced shelf was apparently not compensated by burial in other regions of the ocean. Using the calculated changes in P burial, we try to infer their possible impact on the phosphate inventory in the world oceans. Using a simple mathematical approach, we find that these changes alone could have increased the phosphate inventory of glacial ocean waters by 20-40% compared to interglacial stages. Variations in the C/P reactive ratios and in the P sedimentary phases distribution at the investigated sites seem to indicate that at the onset of interglacial stages, shallower sites experienced an increase in reactive P concentrations. This seems to point to P-richer waters at glacial terminations, supporting the shelf-nutrient hypothesis and giving phosphorus a role as a potential player in climate change.

  1. Phosphorus burial in the ocean over glacial-interglacial time scales

    NASA Astrophysics Data System (ADS)

    Tamburini, F.; Föllmi, K. B.

    2009-04-01

    The role of nutrients, such as phosphorus (P), and their impact on primary productivity and the fluctuations in atmospheric CO2 over glacial-interglacial periods are intensely debated. Suggestions as to the importance of P evolved from an earlier proposal that P actively participated in changing productivity rates and therefore climate change, to most recent ones that changes in the glacial ocean inventory of phosphorus were important but not influential if compared to other macronutrients, such as nitrate. Using new data coming from a selection of ODP sites, we analyzed the distribution of oceanic P sedimentary phases and calculate reactive P burial fluxes, and we show how P burial fluxes changed over the last glacial-interglacial period at these sites. Concentrations of reactive P are generally lower during glacial times, while mass accumulation rates (MAR) of reactive P show higher variability. If we extrapolate for the analyzed sites, we may assume that in general glacial burial fluxes of reactive P are lower than those during interglacial periods by about 8%, because the lack of burial of reactive P on the glacial shelf reduced in size, was apparently not compensated by burial in other regions of the ocean. Using the calculated changes in P burial, we evaluate their possible impact on the phosphate inventory in the world oceans. Using a simple mathematical approach, we find that these changes alone could have increased the phosphate inventory of glacial ocean waters by 17-40% compared to interglacial stages. Variations in the distribution of sedimentary P phases at the investigated sites seem to indicate that at the onset of interglacial stages, shallower sites experienced an increase in reactive P concentrations, which seems to point to P-richer waters at glacial terminations. All these findings would support the Shelf-Nutrient Hypothesis, which assumes that during glacial low stands nutrients are transferred from shallow sites to deep sea with possible

  2. Interglacial Greenland aerosol deposition: comparison of continuous high resolution chemical ice core records from the Eemian and Holocene

    NASA Astrophysics Data System (ADS)

    Gfeller, Gideon; Bigler, Matthias; Schüpbach, Simon; Mini, Olivia; Leuenberger, Daiana; Fischer, Hubertus

    2014-05-01

    Earth's climate system has been oscillating over the last million years between cold glacials and warm interglacials, leaving the imprints of their climate states in form of isotopes variations and chemical impurities in polar ice caps. In the course of the North Greenland Eemian Ice Drilling (NEEM) project, the NEEM ice core has been entirely analysed in very high depth resolution with a Continuous Flow Analysis (CFA) system for the concentrations of chemical aerosol tracers in the ice. Only in the brittle ice zone (600-1100 m depth equivalent to the time interval 3000-8000 years before present) most of the ice had to be discarded due to multifractured core material. Based on the unique reconstructed age scale to unfold the stratigraphically disturbed part from about 2200 m depth downwards (NEEM community members, Nature, 2013), we are able to present the first Greenland chemistry record over the entire last interglacial, the so called Eemian period (about 128'000 to 115'000 years ago). As the Eemian is believed to have been 4 to 8 degrees C warmer than the modern climate, it can be used as an analogue for our present warming climate and, thus, contributes to a better understanding of processes causing natural variations. By means of the chemistry records we are able to assess the natural variability of Greenland Eemian climate and gain insight in its biogeochemical state. Here, short-term variability as well as long term trends of soluble chemical impurities in the Eemian are investigated and compared with those in the Holocene. Changes of organic processes in soils and biomass burning for example are assessed through soluble ammonium and nitrate concentrations. In comparison to the Holocene, ammonium concentrations were about 25% higher during the Eemian. Nitrate, on the other hand, shows about 25% lower concentrations. Sodium concentrations, reflecting changes in sea salt aerosol, are about 35% lower during the Eemian than during the Holocene. Calcium

  3. MIS 5e sea level: up to what point can we use literature reviews to answer the most pressing questions on the Last Interglacial ice sheets?

    NASA Astrophysics Data System (ADS)

    Rovere, A.; Raymo, M. E.

    2014-12-01

    During MIS 5e (between ~128 and 116 kyr BP) greenhouse gas concentrations were comparable to pre-industrial levels, summer insolation was higher by ~10% at high latitudes and polar temperatures in both hemispheres were about 3-5 °C warmer than today. Sea level (SL) at this time has been a subject of numerous studies (and some debate) with ~1000 sites with MIS 5e sea level markers recognized worldwide. Recently, Kopp et al. (Nature, 2009) and Dutton & Lambeck (Science, 2012) analyzed worldwide datasets of sea level markers pertaining to the last interglacial. After accounting for GIA, they reached similar conclusions that eustatic (i.e., globally averaged) sea level (ESL) was between +5 and +9.4 m above modern during MIS 5e. Furthermore, Kopp et al. (Nature, 2009; GJI, 2013) suggest that sea level was not uniform during the LIG, but instead underwent at least two rapid oscillations including a rapid late 5e rise first proposed by Hearty et al. (QSR, 2007) and later by O'Leary et al. (Nat. Geo., 2013). Investigating the temporal and geographic variability of MIS 5e sea level opens new lines of research, in particular the possibility to fingerprint (Hay et al., QSR, 2014) the source of the proposed rapid ice sheet collapse near the end of the Last Interglacial. In this presentation we ask: can we use a database of published sea level estimates for this purpose? To answer this question, we built a relative sea level (RSL) database using RSLcalc 2.0; this is a relational database specifically designed to review relative sea level data points while keeping all the relevant information contained in the original publications. RSlcalc allows to estimate the measurement error (on the actual elevation of the SL feature), the error on the indicative range (the elevation range occupied by a sea level indicator) as well as the reference water level (the relationship between the marker and the former sea level). We show that the majority of published data have an accuracy of few

  4. The impact of precession changes on the Arctic climate during the last interglacial glacial transition

    NASA Astrophysics Data System (ADS)

    Khodri, Myriam; Cane, Mark A.; Kukla, George; Gavin, Joyce; Braconnot, Pascale

    2005-07-01

    Three sensitivity experiments using an Ocean Atmosphere General Circulation Model (OAGCM) are conducted to simulate the climate impact of precession. The relative contributions of components of the hydrological cycle including the albedo of Arctic sea ice, advection of atmospheric water vapor and sea surface temperature to the summer Arctic melt process are evaluated. Timing of the perihelion is varied in each experiment with meteorological spring (SP), winter (WP) and autumn (AP) perihelion corresponding to conditions at 110, 115 and 120 ky BP, respectively. Obliquity is unchanged at the 115 ky level which is lower than today. The experiments are assessed relative to the present day control, which has been shown to simulate current conditions based on observations. In the SP experiment, top of the atmosphere (TOA) insolation is weaker than today between the summer solstice and autumnal equinox. In the AP case representing the interglacial, it is less intense between vernal equinox and summer solstice but stronger during the remainder of the year. Although the incident solar radiation is reduced in summer in the SP experiment, increased melting of snow is found primarily as a result of feedbacks from the delayed seasonal cycle of hydrologic components. This is in contrast to both the WP and AP cases in which the perennial snow cover is simulated. At the time of the last glacial inception, 115 ky BP, the WP experiment shows lower insolation to the high northern latitudes in late spring and summer mainly as a result of lower obliquity than today. Dynamical ocean-atmosphere interactions in response to precession maintain the reduced sea ice melting in late spring, strengthen the annual equator-to-pole sea surface temperature (SST) gradient and increase atmospheric moisture convergence in glaciation-sensitive regions. In both the WP and AP experiments seasonal sea ice melting is weakened resulting in pronounced outgoing radiative flux at the locations of expanded sea

  5. Modelling the thermosteric contribution to global and regional sea-level rise during the last interglacial

    NASA Astrophysics Data System (ADS)

    Singarayer, Joy; Stone, Emma; Whipple, Matthew; Lunt, Dan; Bouttes, Nathaelle; Gregory, Jonathan

    2014-05-01

    Global sea level during the last interglacial is likely to have been between 5.5 and 9m above present (Dutton and Lambeck, 2012). Recent calculations, taking into account latest NEEM ice core information, suggest that Greenland would probably not have contributed more than 2.2m to this (Stone et al, 2013), implying a considerable contribution from Antarctica. Previous studies have suggested a significant loss from the West Antarctic ice-sheet (e.g. Holden et al, 2010), which could be initiated following a collapse of the Atlantic Meridional Overturning Circulation (AMOC) and resultant warming in the Southern Ocean. Here, model simulations with FAMOUS and HadCM3 have been performed of the last interglacial under various scenarios of reduced Greenland and Antarctic ice-sheet configurations, and with and without collapsed AMOC. Thermal expansion and changes in regional density structure (resulting from ocean circulation changes) can also influence sea level, in addition to ice mass effects discussed thus far. The HadCM3 and FAMOUS simulations will be used to estimate the contribution to global and regional sea level change in interglacials from the latter two factors using a similar methodology to the IPCC TAR/AR4 estimations of future sea level rise (Gregory and Lowe, 2000). The HadCM3 and FAMOUS both have a rigid lid in their ocean model, and consequently a fixed ocean volume. Thermal expansion can, however, be calculated as a volume change from in-situ density (a prognostic variable from the model). Relative sea surface topography will then be estimated from surface pressure gradients and changes in atmospheric pressure. Dutton A., and Lambeck K., 2013. Ice Volume and Sea Level During the Last Interglacial. Science, 337, 216-219 Gregory J.M. and Lowe J.A., 2000. Predictions of global and regional sea-level using AOGCMs with and without flux adjustment. GRL, 27, 3069-3072 Holden P. et al., 2010. Interhemispheric coupling, the West Antarctic Ice Sheet and warm

  6. The Influence of Glacial-Interglacial Cycles on the Erosion of Orogens

    NASA Astrophysics Data System (ADS)

    Yanites, Brian; Ehlers, Todd

    2010-05-01

    The evolution of mountain topography and sediment flux to adjacent basins is dictated by variations in the rates of rock-uplift, climate, lithology, and vegetation. Currently, many mountainous settings are in a state of a ‘glacial hangover' whereby Quaternary glaciation has dramatically altered catchment morphology and produced non-equilibrium conditions with respect to the environmental conditions preceding this major climatic transition. In this study, we investigate transients in mountain erosion and morphology due to glacial-interglacial cycles imposed on landscapes previously dominated by fluvial and hillslope processes. In our approach, we use a surface process model to produce an equilibrium fluvial landscape for rock uplift rates between 0.25-1.0 mm/yr. The landscapes are then subjected to repeated glacial cycles of different periodicity and intensity. Variations in predicted glacial basal sliding velocity, erosion, topography and sediment flux are tracked. Results indicate that glacial processes increase rates of valley bottom erosion by one to two orders of magnitude higher than fluvial processes, a result consistent with low-temperature thermochronological data from a number of glaciated catchments worldwide. Increased rates of hillslope and ridgetop erosion occur in response to increased glacial erosion and lag behind the onset of glaciation, thereby producing a complicated history of local relief. The timescale of this lag can vary by orders of magnitude and depends on model parametrization. We also find that two broad effects compete to control the evolution of sediment leaving such an orogen: 1) the topographic disequilibrium with glacial processes acts to initially increase sediment production, but as the topography readjusts, the disequilibrium wanes; 2) the initial geometry of the drainage basin is inefficient at providing ice to the sliding portions of the glaciers, thus impeding erosion early on, but as the topography becomes more

  7. Simulating the last glacial-interglacial transition with a coupled atmosphere-ocean-ice sheet model

    NASA Astrophysics Data System (ADS)

    Mikolajewicz, Uwe; Ziemen, Florian

    2015-04-01

    One of the major challenges in climate modeling is the simulation of glacial-interglacial transitions. A few models of intermediate complexity have been successful in simulating the last termination. Complex atmosphere-ocean general circulation models have been shown to be able to yield realistic climate changes with prescribed ice sheets. Here we presents results from a first attempt to simulate a substantial part of the last glacial cycle with an AOGCM coupled interactively with a state-of-the-art ice sheet model. The ECHAM5/MPIOM AOGCM has been interactively coupled to the dynamical ice sheet model PISM. The latter is run for most of the northern hemisphere with a horizontal resolution of 20 km. An earlier version of this model ( Ziemen et al. 2014) has been applied to a steady state simulation of the last glacial maximum (LGM). The model was integrated from the late Glacial into the Holocene using insolation and greenhouse gas concentrations as transient forcing. Land sea mask and ocean topography are fixed at LGM conditions, river routing and surface elevation for the atmospheric model component are calculated interactively depending on the simulated ice sheets. To make these long simulations feasible, the atmosphere is accelerated by a factor of 10 relative to the other model components using a periodically-synchronous coupling technique. A mini-ensemble with different initial conditions has been run. In all simulation the northern hemispheric deglaciation starts between 18 and 17 kyr BP, consistent with the onset of global warming. The model produces Heinrich event like variability as part of its internal variability. These rapid ice discharge events have a strong impact on the North Atlantic meridional overturning circulation (NAMOC). During the peak deglaciation the NAMOC is collapsed (with a few short interruptions) for several thousand years, which is longer than the estimates from reconstructions. This seems to be an artifact due to keeping ocean

  8. Warm Greenland during the last interglacial: the role of sea ice

    NASA Astrophysics Data System (ADS)

    Merz, Niklaus; Born, Andreas; Raible, Christoph C.; Stocker, Thomas F.

    2016-04-01

    The last interglacial, the Eemian, is characterized by warmer than present conditions in the high latitudes and is therefore often considered as a possible analogue for the climate in the near future. Simulations of Eemian surface air temperatures (SAT) in the Northern Hemisphere (NH), however, show large variations between different climate models and it has been hypothesized that this model spread relates to diverse representations of the Eemian sea ice cover. Here we use version 3 and 4 of the Community Climate System Model (CCSM3 and CCSM4), to highlight the crucial role of sea ice and sea surface temperatures during the Eemian, in particular for SAT in the North Atlantic sector and in Greenland. A substantial reduction in NH sea ice results in an amplified atmospheric warming and, thus, a better agreement with Eemian proxy records. Sensitivity experiments with idealized lower boundary conditions reveal that warming over Greenland is mostly due to a sea ice retreat in the Nordic Seas. In contrast, sea ice changes in the Labrador Sea have a limited local impact. Changes in sea ice in either region are transferred to the overlying atmosphere through anomalous surface energy fluxes. The large-scale warming simulated for the sea ice retreat in the Nordic Seas further relates to anomalous heat advection. Diabatic processes play a secondary role, yet distinct changes in the hydrological cycle are possible. Our results imply that temperature and accumulation records from Greenland ice cores are sensitive to sea ice changes in the Nordic Seas but insensitive to sea ice changes in the Labrador Sea. Moreover, our simulations suggest that the uncertainty in the Eemian sea ice cover accounts for 1.6°C of the Eemian warming at the NEEM ice core site. The estimated Eemian warming of 5°C above present-day based on the NEEM δ15N record can be reconstructed by the CCSM4 model for the scenario that a sea ice retreat in the Nordic Seas coincided with a reduced Greenland ice

  9. Uranium-series ages of corals, sea level history, and palaeozoogeography, Canary Islands, Spain: an exploratory study for two Quaternary interglacial periods

    USGS Publications Warehouse

    Muhs, Daniel R.; Meco, Joaquín; Simmons, Kathleen R.

    2014-01-01

    .5 interglacials, decreased insolation may have resulted in southward migration of the ITCZ, strengthened trade winds, and re-establishment of upwelling. Such conditions may have brought about not only local extinction of the Senegalese fauna, but allowed southward migration of the cooler-water Mediterranean fauna to the Canary Islands in the later parts of interglacials, a complex palaeoclimate record that is mirrored in the deep-sea core record.

  10. Glacial- interglacial temperature change based on 13C18O carbonate bond with in fish bone otoliths from Red Sea sediments

    NASA Astrophysics Data System (ADS)

    Ghosh, P.; Eiler, J.; Feeney, R.

    2006-12-01

    Determining the past record of temperature and salinity of ocean surface waters is essential for understanding past changes in climate, such as those which occur across glacial-interglacial transitions. As a useful proxy, the clumped isotope of CO2 in carbonate (13C18O16O or ?47) from inorganic precipitation experiment has been shown to reflect surface temperature with high degree of confidence (Ghosh et al., 2006). The last glacial cycle was characterized by climate fluctuations, but the extent of any associated changes in global sea level (or, equivalently, ice volume) remains elusive. High stands of sea level can be reconstructed from dated fossil and isotopic analyses of foraminifera and terapods, and these data are complemented by a compilation of global sea-level estimates based on deep-sea oxygen isotope ratios. Salinity derived from the records of oxygen isotopes ratios, however, contains uncertainties due to lack of information about the sea surface temperature change. Here we used combination of clumped isotopes technique and oxygen isotope measurement from fish otoliths (Myctophiformes; lanternfishes) extracted from two piston cores (Ku et al., 1969) (CH-154 and CH-153) to understand the temperature evolution and salinity variation of Red Sea water (300-800m) during the last 70 k.y. We analyzed well preserved unaltered otoliths from 7 different stratigraphic horizons from sediment core CH-154. Our preliminary observation suggests ~20 degree Celsius differences in sea water temperatures between glacial and interglacial time. We showed that the region has experienced fluctuation in climatic and tectonic processes during glacial interglacial time and the otoliths developed within the fishes captured the information about temperature change and salinity variation. Our results indicate a drop in temperature and restricted exchange of water with the open ocean during glaciations. The Red Sea environment was also highly saline even during the interglacial event

  11. First fossil evidence of an ``interglacial refugium'' in the Pyrenean region

    NASA Astrophysics Data System (ADS)

    López-García, Juan Manuel; Blain, Hugues-Alexandre; Allué, Ethel; Bañuls, Sandra; Bargalló, Amelia; Martín, Patricia; Morales, Juan Ignacio; Pedro, Mireia; Rodríguez, Anna; Solé, Alex; Oms, F. Xavier

    2010-08-01

    A refugium is generally understood as an area where temperate species survive cold periods, such as the Iberian, Italian, or Balkan Peninsulas in Europe. Strictly speaking, this definition refers to what is known as a glacial refugium. However, there are various types of lesser-known refugia such as the interglacial refugium, which denotes a mountainous region at low latitudes, such as the Pyrenees, where species adapted to the cold survive during interstadial periods. The small-vertebrate association from the sequence of Cova Colomera, which is located on the southern face of the Pyrenees and contains the final cold spell of the Late Pleistocene and the beginnings of the temperate period in which we currently find ourselves (the Holocene), could constitute the first fossil evidence of such an interglacial refugium, thus providing new paleoecological data on the phenomenon.

  12. Degradation and Local Survival of Permafrost Through the Last Interglaciation in Interior Alaska and Yukon Territory

    NASA Astrophysics Data System (ADS)

    Reyes, A. V.; Froese, D. G.; Jensen, B. J.

    2006-12-01

    Permafrost in northern North America is warming, and recent modeling efforts have predicted the widespread disappearance of permafrost through much of the northern hemisphere over the next century. However, little is known of the impacts of past sustained warm intervals on permafrost dynamics, antiquity, and distribution due to difficulties in establishing reliable chronologies. Permafrost thus remains the last element of the Arctic cryosphere for which there is poor understanding of its adaptability to past warmer-than-present climate. Here we present observations from three sites in the region of interior Alaska and Yukon Territory that remained ice-free during Plio-Pleistocene glaciations, which collectively demonstrate the variable nature of the response of permafrost to warming during the last interglaciation. Chronology for all sites is based on identification of Old Crow tephra (OCt; 140±10 ka) by glass major element composition. Throughout the study region, OCt is consistently associated with organic-rich sediments that represent the last interglaciation on the basis of pollen, insect, and macrofossil assemblages. At the Palisades site on the Yukon River, 250 km west of Fairbanks, OCt is 1.5-3.5 m below thick (>1m) organic-rich silts and peats that are locally rich in beaver-chewed wood and large wood stumps, some of which are in growth position. In contrast, placer mining at Thistle Creek in central Yukon Territory exposes a dramatic thaw unconformity that is presumably related to local, but incomplete, permafrost degradation during the last interglaciation. In upslope positions at Thistle Creek, OCt is incorporated into a steeply dipping, 30 cm thick, organic-rich silt horizon that truncates at least one intact, relict ice wedge. The steeply dipping organic- rich horizon grades downslope into organic-rich silt with dense accumulations of wood fragments, including tree stems up to 2 m long. Evidence for similar permafrost degradation during the last

  13. Terrigenous Fe input and biogenic sedimentation in the glacial and interglacial equatorial Pacific Ocean

    SciTech Connect

    Murray, R.W.; Leinen, M.; Knowlton, C.W.

    1995-12-01

    This study was performed to determine the relationship of particulate iron from land erosion to the accumulation of biogenic matter in the equatorial Pacific Ocean. Sediment cores representing the last six glacial-interglacial cycles and previously published mineralogic records were used as data input. Total iron, terrigenous, and biogenic components were determined for three sediment cores. The study determined that there is no relationship between terrigenous iron input and sedimentary carbon sequestering. This is based on chemical, spectral, and stratigraphic anlyses which showed: (1) no consistent pattern of terrigenous input during glacial or interglacial periods, (2) a close relationshipe between the accumulation of particulate iron and the accumulation of terrigenous matter, (3) no coherent spectral correlations between glacial periodicity and iron input, (4) an inverse correlation of iron input and calcium carbonate, and (5) no spectral or linear relationship between iron accumulation and calcium carbonate, organic carbon, or opal. 55 refs., 6 figs., 3 tabs.

  14. Estimating pesticide sampling rates by the polar organic chemical integrative sampler (POCIS) in the presence of natural organic matter and varying hydrodynamic conditions

    USGS Publications Warehouse

    Charlestra, Lucner; Amirbahman, Aria; Courtemanch, David L.; Alvarez, David A.; Patterson, Howard

    2012-01-01

    The polar organic chemical integrative sampler (POCIS) was calibrated to monitor pesticides in water under controlled laboratory conditions. The effect of natural organic matter (NOM) on the sampling rates (Rs) was evaluated in microcosms containing -1 of total organic carbon (TOC). The effect of hydrodynamics was studied by comparing Rs values measured in stirred (SBE) and quiescent (QBE) batch experiments and a flow-through system (FTS). The level of NOM in the water used in these experiments had no effect on the magnitude of the pesticide sampling rates (p > 0.05). However, flow velocity and turbulence significantly increased the sampling rates of the pesticides in the FTS and SBE compared to the QBE (p < 0.001). The calibration data generated can be used to derive pesticide concentrations in water from POCIS deployed in stagnant and turbulent environmental systems without correction for NOM.

  15. Cryogenian Interglacial Litho- and C Isotope Chemo-stratigraphy of the Amadeus Basin, Central Australia

    NASA Astrophysics Data System (ADS)

    Verdel, C.; Campbell, M.; Phelps, B.

    2015-12-01

    The Cryogenian stratigraphy of the Amadeus Basin in central Australia consists of the Areyonga, Aralka, and Olympic Formations. Both the Areyonga and Olympic Fms. include glacial deposits overlain by cap carbonates, observations that have prompted correlation of these formations with the global Sturtian and Marinoan glaciations, respectively. In this study we focus on the interglacial stratigraphic unit (Aralka Fm.), which is subdivided into the lower Ringwood Mbr. and the upper Limbla Mbr. C isotope values from carbonates within the Limbla Mbr. are particularly large (up to +10 per mil), suggesting that it correlates with the global "Keele Peak" anomaly. The underlying Ringwood Mbr. (the base of which comprises the Sturtian cap carbonate of the Amadeus Basin) varies from thin or non-existent in the northwestern part of the basin to hundreds of meters thick in eastern parts. C isotope values from Ringwood Mbr. carbonates are roughly -5 per mil at its base and rise rapidly up-section. A mid-interglacial negative C isotope excursion to values of approximately -5 per mil in the Ringwood Mbr. may correlate with the Tayshir anomaly of the Mongolian Neoproterozoic succession. Interglacial carbonates of the Aralka Fm. therefore have C isotope compositions that span at least 15 per mil and include both positive and negative isotopic excursions that seem to be globally correlative. Furthermore, detailed field observations from the Ringwood Mbr. suggest that it can be subdivided into three submembers, each of which is marked by stromatolitic intervals. Shallowing-upward parasequences in the Ringwood Mbr., as well as a major change in lithology from siltstones and microbialites of the Ringwood Mbr. to dominantly coarse-grained, cross-stratified sandstones of the Limbla Mbr., suggest that the interglacial strata of the Amadeus Basin were deposited during a period of significant and repeated changes in relative sealevel.

  16. A simple metabolic model of glacial-interglacial energy supply to the upper ocean

    NASA Astrophysics Data System (ADS)

    Pelegrí, J. L.; Olivella, R.; García-Olivares, A.

    2011-03-01

    We use a simple two-state two-box ocean to simulate the CO2 signal during the last four glacial-interglacial transitions in the earth system. The model is inspired by the similarity in spatial organization and temporal transition patterns between the earth and other complex systems, such as mammals. The comparison identifies the earth's metabolic rate with net autotrophic primary production in the upper ocean, sustained through new inorganic carbon and nutrients advected from the deep ocean and organic matter remineralized within the upper ocean. We view the glacial-interglacial transition as a switch of the upper ocean from a basal to an enhanced metabolic state, with energy supply initially relying on the remineralization of the local organic sources and the eventual steady state resulting from the increased advective supply of inorganic deep sources. During the interglacial-glacial transition the opposite occurs, with an initial excess of advective supply and primary production that allows the replenishment of the upper-ocean organic storages. We set the relative change in energy supply from the CO2 signal and use genetic algorithms to explore the sensitivity of the model output to both the basal recirculation rate and the intensity-timing of the maximum recirculation rate. The model is capable of reproducing quite well the long-term oscillations, as shown by correlations with observations typically about 0.8. The dominant time scale for each cycle ranges between about 40 and 45 kyr, close to the 41 kyr average obliquity astronomical period, and the deep-ocean recirculation rate increases between one and two orders of magnitude from glacial to interglacial periods.

  17. Were the MIS 11 and MIS 5e warmer and/or wetter than the Holocene? Test comparison of Interglacial intensities using stable isotope data from Northern France tufa deposits.

    NASA Astrophysics Data System (ADS)

    Dabkowski, J.; Limondin-Lozouet, N.; Antoine, P.; Marca-Bell, A.; Andrews, J.

    2012-04-01

    Many recent palaeoclimatic studies have focused on MIS 5 (Eemian) and 11 as they are supposed to be the best analogues for our modern interglacial. As they are characteristic of temperate periods and result of calcite precipitation from meteogene water, tufas are key-deposits for palaeoclimatic reconstructions of these interglacials. Calcite oxygen and carbon stable isotopes (δ18O and δ13C) are known since the 80s to be important palaeoclimatic proxies for the Holocene and we recently have shown their suitability in Pleistocene tufas. At decadal-scale sampling resolution, δ18O of tufa records variations in δ18O of regional rainfall, and in this way reflects source or amount effects (particularly continentality), and temperature depending on locality. δ13C of tufa indicates moisture availability (linked to biomass type/abundance) and rainfall intensity. Using our new results from the tufa of Saint-Germain-le-Vasson (Normandy) dated to the first half of the Holocene, and those from Caours (Somme) and La-Celle-sur-Seine (Seine-et-Marne) respectively assigned to MIS 5e and MIS 11, we investigate similarities or differences between these Pleistocene interglacials and the modern one. Comparison between the sites is relevant as these tufas developed in a similar geological area (the Paris Basin) and are nowadays in the same humid and temperate climatic area. The Caours tufa presents carbon and oxygen isotopic compositions similar to the Saint-Germain sequence. Comparable temperature and humidity conditions are thus recorded during the Eemian and the Holocene. However, δ13C for the MIS 5e optimum are more negative than those for the Atlantic optimum (Holocene), which may indicate wetter conditions. In La Celle, slightly warmer conditions appear to be recorded for MIS 11 compared to the Holocene by higher δ18O values than in Saint-Germain. Moreover, two very humid episodes are observed in the La Celle δ13C profile whereas such wet conditions are not observed during

  18. Localizing the Holy Grail: Glacial/interglacial variations in atmospheric CO2 and oceanic deepwater production

    NASA Astrophysics Data System (ADS)

    Zeebe, R. E.

    2003-04-01

    The 'Holy Grail' of glacial/interglacial CO_2 research is to identify the major driver for variations in atmospheric CO_2 on this time scale. A simple mechanism has hitherto remained elusive. I use an entirely new approach to the problem, namely a global vertical advection-diffusion balance of tracers in the ocean which shows that the ocean's deepwater production (DWP) is the sought-after physical mechanism. The model adequately reproduces modern pCO_2 and vertical profiles of temperature, ΣCO_2, Alkalinity, PO_4, and O_2 in the ocean. Based on recently advanced compelling evidence for reduced glacial DWP, the model will then be shown to explain the glacial pCO_2 of 200~μatm. over a full glacial/interglacial transition (20~ky), model results excellently reproduce the observed temporal evolution of atmospheric CO_2 and deep ocean CaCO_3 saturation. The mechanism also explains the remarkable correlation between Antarctic temperature and CO_2 as recorded in ice cores. The ocean's deepwater production rate is hence identified as the dominant driver of glacial/interglacial CO_2 variations through its effect on the vertical distribution of heat and elements in the sea, initially set into motion in the Southern Hemisphere.

  19. Fire in Ice: Glacial-Interglacial biomass burning in the NEEM ice core

    NASA Astrophysics Data System (ADS)

    Zennaro, Piero; Kehrwald, Natalie; Zangrando, Roberta; Gambaro, Andrea; Barbante, Carlo

    2014-05-01

    Earth is an intrinsically flammable planet. Fire is a key Earth system process with a crucial role in biogeochemical cycles, affecting carbon cycle mechanisms, land-surface properties, atmospheric chemistry, aerosols and human activities. However, human activities may have also altered biomass burning for thousands of years, thus influencing the climate system. We analyse the specific marker levoglucosan to reconstruct past fire events in ice cores. Levoglucosan (1,6-anhydro-β-D-glucopyranose) is an organic compound that can be only released during the pyrolysis of cellulose at temperatures > 300°C. Levoglucosan is a major fire product in the fine fraction of woody vegetation combustion, can be transported over regional to global distances, and is deposited on the Greenland ice sheet. The NEEM, Greenland ice core (77 27'N, 51 3'W, 2454 masl) documents past fire activity changes from the present back to the penultimate interglacial, the Eemian. Here we present a fire activity reconstruction from both North American and Eurasian sources over the last 120,000 yrs based on levoglucosan signatures in the NEEM ice core. Biomass burning significantly increased over the boreal Northern Hemisphere since the last glacial, resulting in a maximum between 1.5 and 3.5 kyr BP yet decreasing from ~2 kyr BP until the present. Major climate parameters alone cannot explain the observed trend and thus it is not possible to rule out the hypothesis of early anthropogenic influences on fire activity. Over millennial timescales, temperature influences Arctic ice sheet extension and vegetation distribution at Northern Hemisphere high latitudes and may have altered the distance between NEEM and available fuel loads. During the last Glacial, the combination of dry and cold climate conditions, together with low boreal insolation and decreased atmospheric carbon dioxide levels may have also limited the production of available biomass. Diminished boreal forest extension and the southward

  20. Are Physical Properties Able to Differentiate Glacial and Interglacial Coral Identity?

    NASA Astrophysics Data System (ADS)

    Lado-Insua, T.; Moran, K.; Anderson, L.; Webster, J. M.; Morgan, S.; Fehr, A.; Lofi, J.; Lukies, V.; Loggia, D.; Iodp Expedition 325 Scientists

    2010-12-01

    The Integrated Ocean Drilling Program Expedition 325 to the Great Barrier Reef provides new information on past sea-level changes and better understanding of mechanisms driving glacial-interglacial cycles. Coral samples recovered during this expedition provide a deeper understanding of coral reef responses to environmental stresses. Inter- and intra-specific differences, growth rates, coral health, symbiotic algae and environmental conditions are all potential causes of differences in the density of coral skeletons and their distribution. Past changes in sea level and temperature can be related not only to isotope ratios but also to the presence of different communities of corals. Density changes in the coral composition can be detected using physical properties such as an increase in the calcium carbonate of a sample. De’ath et al. (2009) reported severe and sudden recent declines in calcification in Porites spp. corals in the Great Barrier Reef in the present that have not been observed over at least the last 400 years, and they attributed the decrease in calcification to changes in sea level, sea surface temperature (SST) and saturation of aragonite in the water column, all of which can limit the capacity of the corals to precipitate calcium carbonate. Variation in Sr/Ca can be related to SST, but different strains of symbiotic algae in the corals’ tissues can also be an important factor affecting skeletal Sr/Ca ratios. Such changes have never been tracked during previous glaciations, but the samples from Expedition 325 give the opportunity to explore their values during and since the last glacial maximum. Physical properties such as gamma ray density, electrical resistivity, and acoustic p-wave velocity can be related to characteristics of the marine sediments that, in turn, are indicative of the depositional environments. We performed a multivariate analysis that relates physical characteristics measured with a multi-sensor core logger (MSCL) and downhole

  1. Debris flow grain size scales with sea surface temperature over glacial-interglacial timescales

    NASA Astrophysics Data System (ADS)

    D'Arcy, Mitch; Roda Boluda, Duna C.; Whittaker, Alexander C.; Araújo, João Paulo C.

    2015-04-01

    Debris flows are common erosional processes responsible for a large volume of sediment transfer across a range of landscapes from arid settings to the tropics. They are also significant natural hazards in populated areas. However, we lack a clear set of debris flow transport laws, meaning that: (i) debris flows remain largely neglected by landscape evolution models; (ii) we do not understand the sensitivity of debris flow systems to past or future climate changes; and (iii) it remains unclear how to interpret debris flow stratigraphy and sedimentology, for example whether their deposits record information about past tectonics or palaeoclimate. Here, we take a grain size approach to characterising debris flow deposits from 35 well-dated alluvial fan surfaces in Owens Valley, California. We show that the average grain sizes of these granitic debris flow sediments precisely scales with sea surface temperature throughout the entire last glacial-interglacial cycle, increasing by ~ 7 % per 1 ° C of climate warming. We compare these data with similar debris flow systems in the Mediterranean (southern Italy) and the tropics (Rio de Janeiro, Brazil), and find equivalent signals over a total temperature range of ~ 14 ° C. In each area, debris flows are largely governed by rainfall intensity during triggering storms, which is known to increase exponentially with temperature. Therefore, we suggest that these debris flow systems are transporting predictably coarser-grained sediment in warmer, stormier conditions. This implies that debris flow sedimentology is governed by discharge thresholds and may be a sensitive proxy for past changes in rainfall intensity. Our findings show that debris flows are sensitive to climate changes over short timescales (≤ 104 years) and therefore highlight the importance of integrating hillslope processes into landscape evolution models, as well as providing new observational constraints to guide this. Finally, we comment on what grain size

  2. Glacial-interglacial variability of the Greenland Ice Sheet in the Pliocene

    NASA Astrophysics Data System (ADS)

    Koenig, S. J.; Deconto, R.; Pollard, D.

    2010-12-01

    Significant built-up of ice caps on Greenland is believed to have begun in the Pliocene (5.33 - 2.58 Ma). The ice sheet has likely been highly dynamic, and paced by Milankovitch orbital cycles, variations in atmospheric carbon dioxide concentrations (pCO2 [ppmv]) and internal forcings, and feedbacks related to both local energy balance and far-field influences. The likely locations, extents and volumes of continental ice on Greenland during the Pliocene remain largely unconstrained. Feedback mechanisms involving coupling between ice sheets and sea ice have been proposed to have a significant impact on the Pleistocene climate-cryospheric system and the pacing of glacial-interglacial cycles. Here, we show the results of a sensitivity study exploring (i) the sensitivity of Northern Hemisphere sea ice to forcing and (ii) the impact of sea ice on northern-hemispheric climatic and cryospheric evolution through the Plio-Pleistocene. We investigate the threshold for the growth and decay of the Greenland Ice Sheet and the ice sheet's impact on sea ice extent and thickness with a coupled GCM-ice sheet model using combining sets of orbital parameters, and pCO2 levels. Additionally, we test the dynamic response of vegetation and assess the vegetation feedback under the prescribed orbits and pCO2. The paleoclimate simulations use both modern and ice-free isostatically equilibrated Greenland topography with modern (control) and cold and warm boreal summer orbits, and a range of pCO2 levels chosen to broadly represent both warm Pliocene and cold Pleistocene conditions. Model simulations are compared with available sea surface temperature and other proxy data on and around Greenland. We find that Pliocene Greenland (at elevated CO2 levels) is highly sensitive to orbital forcing. Sea ice-albedo feedback has important effects on the hydrological cycle and largely governs insulation receipts at the surface. Sea ice cover modifies moisture availability by controlling the air

  3. Initiation age and incision rates of inner gorges: Do they record multiple glacial-interglacial cycles?

    NASA Astrophysics Data System (ADS)

    Delunel, Romain; Casagrande, Jan; Schlunegger, Fritz; Akçar, Naki; Kubik, Peter W.

    2015-04-01

    Inner gorges represent some of the most conspicuous landforms in the European Alps. They form narrow and deep active-channel incisions that link hanging tributaries with trunk valleys in glacially-conditioned environments. Despite abundant research carried out on these objects, both their origin and evolution have remained unclear. In particular, the age of initiation, the rate of incision, and the respective contribution of fluvial and subglacial processes in the evolution of inner gorges have still been a matter of scientific debate. Indeed, answering these questions has been complicated by the lack of appropriate quantitative methods and/or suitable sampling strategies for studying inner gorges. Here, we report 10Be concentrations measured in alluvial sediments that have been collected along the main stream of a ~20-km2-catchment in the Swiss foreland (Central European Alps). This catchment hosts a ca. 100-m-deep and 2-km-long inner gorge that has been cut mainly in glacial till. Catchment wide denudation rates inferred from 10Be analyses (n = 15) vary from ~120 to 650 mm/ka and show a general downstream increasing trend. Additional field observations and GIS analyses reveal that the denudation rates within the catchment increase from the headwaters, characterized by relict glacial/periglacial landscapes, to the downstream end of the basin where the inner gorge has been formed. Using a 10Be-based sediment budget approach and the delineation of topographic domains from a 2-m-resolution LIDAR, we provide an estimate of erosion rates within the gorge that are higher than 2.5 m/ka and can reach up to ~ 7 m/ka. Combining these estimated erosion rates with the reconstruction of eroded volumes within the gorge, we obtain a rough initiation age in the early Holocene, in general agreement with previous studies reporting a postglacial origin for the inner gorges. Our results therefore appear contradictory with recent findings arguing for a gradual formation of inner

  4. On the glacial and interglacial thermohaline circulation and the associated transports of heat and freshwater

    NASA Astrophysics Data System (ADS)

    Ballarotta, M.; Falahat, S.; Brodeau, L.; Döös, K.

    2014-11-01

    The thermohaline circulation (THC) and the oceanic heat and freshwater transports are essential for understanding the global climate system. Streamfunctions are widely used in oceanography to represent the THC and estimate the transport of heat and freshwater. In the present study, the regional and global changes of the THC, the transports of heat and freshwater and the timescale of the circulation between the Last Glacial Maximum (LGM, ≈ 21 kyr ago) and the present-day climate are explored using an Ocean General Circulation Model and streamfunctions projected in various coordinate systems. We found that the LGM tropical circulation is about 10% stronger than under modern conditions due to stronger wind stress. Consequently, the maximum tropical transport of heat is about 20% larger during the LGM. In the North Atlantic basin, the large sea-ice extent during the LGM constrains the Gulf Stream to propagate in a more zonal direction, reducing the transport of heat towards high latitudes by almost 50% and reorganising the freshwater transport. The strength of the Atlantic Meridional Overturning Circulation depends strongly on the coordinate system. It varies between 9 and 16 Sv during the LGM, and between 12 to 19 Sv for the present day. Similar to paleo-proxy reconstructions, a large intrusion of saline Antarctic Bottom Water takes place into the Northern Hemisphere basins and squeezes most of the Conveyor Belt circulation into a shallower part of the ocean. These different haline regimes between the glacial and interglacial period are illustrated by the streamfunctions in latitude-salinity coordinates and thermohaline coordinates. From these diagnostics, we found that the LGM Conveyor Belt circulation is driven by an enhanced salinity contrast between the Atlantic and the Pacific basin. The LGM abyssal circulation lifts and makes the Conveyor Belt cell deviate from the abyssal region, resulting in a ventilated upper layer above a deep stagnant layer, and an

  5. The last interglacial climate in EC-Earth - comparing the direct and indirect impacts of the insolation changes

    NASA Astrophysics Data System (ADS)

    Anker Pedersen, Rasmus; Langen, Peter Lang; Vinther, Bo

    2016-04-01

    The last interglacial warm climate state was influenced by substantial changes in the annual insolation cycle. The impact of the insolation changes has been investigated using a time-slice simulation with the EC-Earth earth system model. The model climate was forced with the insolation and atmospheric greenhouse gas concentrations from 125,000 years before present, and the resulting quasi-equilibrium state has been analyzed and compared to a pre-industrial climate state. The simulations indicate an annual mean global warming of approximately 1 K. The tropical region exhibits lower temperatures and stronger monsoonal systems, while the Arctic region shows a warming of about 3 K throughout the year. Arctic sea ice changes appear to be an important driver of warming, especially in relation to a northward shift of the ice edge in the North Atlantic region. Proxy data from ice and ocean sediment cores indicate substantial warming in parts of the North Atlantic region that could be related to similar sea ice changes. The relative importance of the sea ice and sea surface temperature changes and the direct contribution from the insolation is further investigated using a series of experiments in an atmosphere-only version of the model. Based on the results from the coupled model, we assess the relative contributions using hybrid simulations of the atmospheric response to a combination of last interglacial sea surface temperatures and sea ice conditions and pre-industrial insolation, and vice versa. Special attention is given to the simulated response over the Greenland ice sheet and the potential implications for proxy data from ice cores. Both temperature and precipitation changes could impact the ice core records, and the seasonal and spatial changes over Greenland are analyzed in detail. At the NEEM ice core location, a general warming tendency is accompanied by an increase of summer snowfall that contributes to a further increase of the precipitation

  6. Open oceanic productivity changes at mid-latitudes during interglacials and its relation to the Atlantic Meridional Overturning Circulation

    NASA Astrophysics Data System (ADS)

    Nave, Silvia; Lebreiro, S.; Kissel, C.; Guihou, A.; Figueiredo, M. O.; Silva, T. P.; Michel, E.; Cortijo, E.; Labeyrie, L.; Voelker, A.

    2010-05-01

    Variations in the interactions between marine ecosystems, thermohaline circulation, external forcing and atmospheric greenhouse gases concentrations are not yet fully represented in detailed models of the glacial-interglacial transitions. Most of the research on past productivity changes has been focused so far on high-productivity areas such as upwelling areas (i.e. equatorial or coastal upwelling areas) even though those regions appraise only a little part of the ocean. Accordingly, the importance of oceanic productivity changes over glacial/interglacial cycles should be better known, as it may also play an important role on the loss of photosynthetically generated carbon as a central mechanism in the global carbon cycle. Its understanding will help quantifying the parameters needed to run comprehensive climate models, and subsequently help to better predict climate change for the near future. A high-resolution study of oceanic productivity, bottom water flow speed, surface and deep-water mass, bottom water ventilation, and terrestrial input changes during two interglacials (Holocene and Marine Isotope Stage [MIS] 5), at an open ocean site approximately 300 km west off Portugal [IMAGES core MD01-2446: 39°03'N, 12°37'W, 3547 m water depth] was conducted within the AMOCINT project (ESF-EUROCORES programme, 06-EuroMARC-FP-008). Even though siliceous productivity is expectedly low for oceanic regions, it shows a robust and consistent pattern with increased values during cold phases of MIS 5, and during the glacial stages 4 and 6 suggesting higher nutrient availability, during these periods. The same pattern is observed for MIS2 and the last deglaciation. The opal record is fully supported by the organic carbon content and to the estimated productivity using foraminifera based FA20 and SIMMAX.28 transfer functions for a near location. The benthic δ13C record suggests less North Atlantic Deep Water (NADW) coincident with periods of higher productivity. The grain

  7. Exceedingly Low Freezing Rates of Aqueous Hno3 and Hno3/h2so4 Droplets Under Polar Stratospheric Conditions

    NASA Astrophysics Data System (ADS)

    Knopf, D. A.; Koop, T.; Luo, B.; Weers, U. G.; Peter, T.

    In the Arctic winter 1999/2000 large particles containing nitric acid were observed during in situ field measurements. These large particles are important for the deni- trification of the Arctic stratosphere. It has been proposed that such particles form by homogeneous nucleation of nitric acid hydrates from liquid stratospheric aerosol droplets. Homogeneous nucleation rates of NAT (Nitric Acid Trihydrate) and NAD (Nitric Acid Dihydrate) have been determined in laboratory experiments for binary HNO3/H2O solutions only at supersaturations much larger than observed in the stratosphere. Therefore, an extrapolation of such laboratory data is required for the modelling of stratospheric particle formation and subsequent denitrification. We will present new laboratory data of homogeneous nucleation rates of NAT and NAD from droplets consisting of both binary HNO3/H2O as well as ternary HNO3/H2O/H2SO4 solutions. Optical microscopy has been used to deduce the droplet freezing tempera- tures. The nature of the crystallized solids was identified by Raman spectroscopy. The freezing data have been analyzed within the framework of classical nucleation theory. Our results are consistent with previously published laboratory aerosol data. However, for stratospheric conditions, we infer homogeneous nucleation rates to be lower by orders of magnitude than the extrapolation currently in use. We conclude that homo- geneous nucleation of NAT and NAD is not sufficient to explain the observed number concentrations of large nitric acid containing particles in the stratosphere.

  8. Sea level rise from the Greenland Ice Sheet during the Eemian interglacial: Review of previous work with focus on the surface mass balance

    NASA Astrophysics Data System (ADS)

    Plach, Andreas; Hestnes Nisancioglu, Kerim

    2016-04-01

    The contribution from the Greenland Ice Sheet (GIS) to the global sea level rise during the Eemian interglacial (about 125,000 year ago) was the focus of many studies in the past. A main reason for the interest in this period is the considerable warmer climate during the Eemian which is often seen as an equivalent for possible future climate conditions. Simulated sea level rise during the Eemian can therefore be used to better understand a possible future sea level rise. The most recent assessment report of the Intergovernmental Panel on Climate Change (IPCC AR5) gives an overview of several studies and discusses the possible implications for a future sea level rise. The report also reveals the big differences between these studies in terms of simulated GIS extent and corresponding sea level rise. The present study gives a more exhaustive review of previous work discussing sea level rise from the GIS during the Eemian interglacial. The smallest extents of the GIS simulated by various authors are shown and summarized. A focus is thereby given to the methods used to calculate the surface mass balance. A hypothesis of the present work is that the varying results of the previous studies can largely be explained due to the various methods used to calculate the surface mass balance. In addition, as a first step for future work, the surface mass balance of the GIS for a proxy-data derived forcing ("index method") and a direct forcing with a General Circulation Model (GCM) are shown and discussed.

  9. Possible Evidence of Multiple Sea Level Oscillations in the Seychelles During the Last Interglacial

    NASA Astrophysics Data System (ADS)

    Dutton, A. L.; Vyverberg, K.; Webster, J.; Dechnik, B.; Zwartz, D.; Lambeck, K.

    2013-12-01

    In search of a eustatic sea level signal on glacial-interglacial timescales, the Seychelles ranks as one of the best places on the planet to study. Owing to its far-field location with respect to the former margins of Northern Hemisphere ice sheets, glacio-hydro-isostatic models predict that relative sea level in the Seychelles should lie within a few meters of the globally averaged eustatic signal during interglacial periods. We have surveyed and dated fossil coral reefs from the last interglacial period to determine the magnitude of peak sea level and to assess sedimentologic evidence of potential sea level oscillations. Numerous outcrops we studied in detail exhibit a stratigraphic sequence comprised of in situ coralgal framework at the base, capped by thick coralline algae crusts, and overlain by coral rubble deposits. We also observed a succession of three stacked coralgal reefs within a single outcrop, separated by hardgrounds that have been bored by molluscs. In general, the succession within each reef unit consists of interlayered corals and crusts of coralline algae-vermetid gastropods-encrusting foraminifera. The lower two reef units are capped by a well-cemented 5 to 10 cm thick carbonate mud layer that is heavily bored by molluscs. These two surfaces may represent exposure surfaces during brief sea level oscillations, where sea level fell and exposed the top of the reef sequence, which was subsequently bored when sea level rose again and reef growth resumed. The elevations of the corals in each reef unit provide minimum elevations of sea level during each of the three pulses of sea level highstands during the last interglacial period. Significantly, since many of these corals are capped by thick coralline algae layers that contain vermetid gastropods and encrusting foraminifera that are indicative of the intertidal zone, there is strong evidence that these corals grew in extremely shallow water, providing a robust indication of sea level position. These

  10. Patterns of glacial-interglacial vegetation and climate variability in eastern South Africa

    NASA Astrophysics Data System (ADS)

    Dupont, Lydie; Caley, Thibaut; Malaizé, Bruno; Giraudeau, Jacques

    2010-05-01

    Vegetation is an integrated part of the earth system and our understanding needs records of its glacial-interglacial variability. Although the data coverage for South Africa is slightly better than for some other parts of Africa, there are only very few records that allow us a glimpse of the vegetation history and development through one or more late Quaternary climate cycles. The existing evidence is fragmentary and in some cases contradictory. Marine sediments can offer here continuous sequences that cover large periods of time and provide a record of a signal that integrates rather large continental regions. Core MD96-2048 has been cored off the Limpopo River mouth at 26°10'S 34°01'E in 660 m water depth. This area is under the double influence of continental discharge and Agulhas current water advection. The sedimentation is slow and continuous. The upper 5 meter (down till 250 ka) have been analysed for pollen and spores at millennial resolution. The terrestrial pollen assemblages indicate that during interglacials the vegetation of eastern South Africa and southern Mozambique largely consisted of evergreen and deciduous forests with an increase of dry deciduous forest and open woodland during interglacial optima. During glacials open mountainous shrubland extended. The pattern strongly suggests a shifting of altitudinal vegetation belts in the mountains primarily depending on temperature, although the decline of forested areas during glacial times might also be the effect of low atmospheric carbon dioxide concentrations. This pattern in eastern South Africa differs from that suggested for western South Africa, where extension of the winter rain climate seems likely, and corroborates findings of increased C4 vegetation during the Glacial of eastern South Africa. The spread of dry deciduous forest and open woodland suggests a hot and dry climate during interglacial optima. The vegetation and climate of eastern South Africa seems to follow a mid to high

  11. Similarities and dissimilarities between the last two deglaciations and interglaciations in the North Atlantic region

    NASA Astrophysics Data System (ADS)

    Martrat, Belen; Jimenez-Amat, Patricia; Zahn, Rainer; Grimalt, Joan O.

    2014-09-01

    Sea surface temperatures (SSTs) recorded by alkenones and oxygen isotopes in the Alboran basin are used here to describe, at an unprecedented fine temporal resolution, the present interglaciation (PIG, initiated at 11.7 ka BP), the last interglaciation (LIG, onset approximately at 129 ka) and respective deglaciations. Similarities and dissimilarities in the progression of these periods are reviewed in comparison with ice cores and stalagmites. Cold spells coeval with the Heinrich events (H) described in the North Atlantic include multi-decadal scale oscillations not previously obvious (up to 4 °C in less than eight centuries within the stadials associated with H1 and H11, ca 133 ka and 17 ka respectively). These abrupt oscillations precede the accumulation of organic rich layers deposited when perihelion moves from alignment with NH spring equinox to the summer solstice, a reference for deglaciations. Events observed during the last deglaciation at 17 ka, 14.8 ka and 11.7 ka are reminiscent of events occurred during the penultimate deglaciation at ca 136 ka, 132 ka and 129 ka, respectively. The SST trend during the PIG is no more than 2 °C (from 20 °C to 18 °C; up to -0.2 °C/ka). The trend is steeper during the LIG, i.e. up to a 5 °C change from the early interglaciation to immediately before the glacial inception (from 23 °C to 18 °C; up to -0.4 °C/ka). Events are superimposed upon a long term trend towards colder SSTs, beginning with SST maxima followed by temperate periods until perihelion aligned with the NH autumn equinox (before ca 5.3 ka for the PIG and 121 ka for the LIG). A cold spell of around eight centuries at 2.8 ka during the PIG was possibly mimicked during the LIG at ca 118 ka by a SST fall of around 1 °C in a millennium. These events led interglacial SST to stabilise at around 18 °C. The glacial inception, barely evident at the beginning ca 115 ka (North Atlantic event C25, after perihelion passage in the NH winter solstice), culminated

  12. The last interglacial (Eemian) climate simulated by LOVECLIM and CCSM3

    NASA Astrophysics Data System (ADS)

    Nikolova, I.; Yin, Q.; Berger, A.; Singh, U. K.; Karami, M. P.

    2013-08-01

    This paper presents a detailed analysis of the climate of the last interglacial simulated by two climate models of different complexities, CCSM3 (Community Climate System Model 3) and LOVECLIM (LOch-Vecode-Ecbilt-CLio-agIsm Model). The simulated surface temperature, hydrological cycle, vegetation and ENSO variability during the last interglacial are analyzed through the comparison with the simulated pre-industrial (PI) climate. In both models, the last interglacial period is characterized by a significant warming (cooling) over almost all the continents during boreal summer (winter) leading to a largely increased (reduced) seasonal contrast in the Northern (Southern) Hemisphere. This is mainly due to the much higher (lower) insolation received by the whole Earth in boreal summer (winter) during this interglacial. The Arctic is warmer than PI through the whole year, resulting from its much higher summer insolation, its remnant effect in the following fall-winter through the interactions between atmosphere, ocean and sea ice and feedbacks from sea ice and snow cover. Discrepancies exist in the sea-ice formation zones between the two models. Cooling is simulated by CCSM3 in the Greenland and Norwegian seas and near the shelves of Antarctica during DJF but not in LOVECLIM as a result of excessive sea-ice formation. Intensified African monsoon is responsible for the cooling during summer in northern Africa and on the Arabian Peninsula. Over India, the precipitation maximum is found further west, while in Africa the precipitation maximum migrates further north. Trees and grassland expand north in Sahel/Sahara, more clearly seen in LOVECLIM than in CCSM3 results. A mix of forest and grassland occupies continents and expands deep into the high northern latitudes. Desert areas reduce significantly in the Northern Hemisphere, but increase in northern Australia. The interannual SST variability of the tropical Pacific (El-Niño Southern Oscillation) of the last interglacial

  13. Short-term climate changes in the Holsteinian Interglacial - EGU2012-132

    NASA Astrophysics Data System (ADS)

    Nitychoruk, J.; Bińka, K.; Ruppert, H.; Tudryn, A.

    2012-04-01

    Oxygen and carbon stable isotopes from fossil lake sediments of the Holsteinian age (eastern Poland) give evidence for the abrupt climate shifts in this interglacial that coincide with the changes in vegetation inferred from palaeobotanical data. Especially changes of the stable isotope ratios as well as decrease in the carbonate content in the deposits and increase in silicate redeposited from the area around the lake are synchronous with the short-term climatic deteriorations within the interglacial pollen flora. Two distinct climate shifts are recorded in the Holsteinian. The first one is marked by the very characteristic pine-birch cold phase after the yew (Taxus) domination that is reported from numerous pollen diagrams from Central Europe. This distinct cooling resembles a phenomenon known as 8.2 ka event in the Holocene, when waters of the Agassiz Lake in North America drained into the Atlantic Ocean (Koutsodendris et al. 2010). Enormous volumes of freshwater from melting of the Laurentian ice-sheet caused disturbances in the Gulf Stream and as a result some decrease in regional temperatures. The second distinct cooling of a lower rank took place within the younger part of the climatic optimum of the Holsteinian. It is relatively less known, because most often pollen records lack sufficient temporal resolution needed to identify this event. A well documented cooling in the Holsteinian deposits from Dethlingen, northern Germany (Koutsodendris et al. 2010) and from the Ossówka, eastern Poland (Nitychoruk et al. 2005) are exceptional. In the sequence from Dethlingen, a distinct increase in the percentage of pioneer trees is accompanied by a lower content of temperate taxa. At Ossówka, the shift of climate is noted as the rise of ratio of oxygen and carbon isotopes. According to Nitychoruk (2000) the cold event is coincident with volcanic eruptions evidenced by volcanic ash found in the lake deposits at that time. Literature Koutsodendris, A., Müller, U

  14. The Physics of Polarization

    NASA Astrophysics Data System (ADS)

    Degl'Innocenti, Egidio Landi

    2015-10-01

    The introductory lecture that has been delivered at this Symposium is a condensed version of an extended course held by the author at the XII Canary Island Winter School from November 13 to November 21, 2000. The full series of lectures can be found in Landi Degl'Innocenti (2002). The original reference is organized in 20 Sections that are here itemized: 1. Introduction, 2. Description of polarized radiation, 3. Polarization and optical devices: Jones calculus and Muller matrices, 4. The Fresnel equations, 5. Dichroism and anomalous dispersion, 6. Polarization in everyday life, 7. Polarization due to radiating charges, 8. The linear antenna, 9. Thomson scattering, 10. Rayleigh scattering, 11. A digression on Mie scattering, 12. Bremsstrahlung radiation, 13. Cyclotron radiation, 14. Synchrotron radiation, 15. Polarization in spectral lines, 16. Density matrix and atomic polarization, 17. Radiative transfer and statistical equilibrium equations, 18. The amplification condition in polarized radiative transfer, and 19. Coupling radiative transfer and statistical equilibrium equations.

  15. P-polarized reflectance spectroscopy: A high sensitive real-time monitoring technique to study surface kinetics under steady state epitaxial deposition conditions

    NASA Technical Reports Server (NTRS)

    Dietz, Nikolaus; Bachmann, Klaus J.

    1995-01-01

    This paper describes the results of real-time optical monitoring of epitaxial growth processes by p-polarized reflectance spectroscopy (PRS) using a single wavelength application under pulsed chemical beam epitaxy (PCBE) condition. The high surface sensitivity of PRS allows the monitoring of submonolayer precursors coverage on the surface as shown for GaP homoepitaxy and GaP on Si heteroepitaxy as examples. In the case of heteroepitaxy, the growth rate and optical properties are revealed by PRS using interference oscillations as they occur during growth. Super-imposed on these interference oscillations, the PRS signal exhibits a fine structure caused by the periodic alteration of the surface chemistry by the pulsed supply of chemical precursors. This fine structure is modeled under conditions where the surface chemistry cycles between phosphorus supersaturated and phosphorus depleted surfaces. The mathematical model describes the fine structure using a surface layer that increases during the tertiarybutyl phosphine (TBP) supply and decreases during and after the triethylgallium (TEG) pulse, which increases the growing GaP film thickness. The imaginary part of the dielectric function of the surface layer is revealed from the turning points in the fine structure, where the optical response to the first precursor pulse in the cycle sequence changes sign. The amplitude of the fine structure is determined by the surface layer thickness and the complex dielectric functions for the surface layer with the underlying bulk film. Surface kinetic data can be obtained by analyzing the rise and decay transients of the fine structure.

  16. The Last Interglacial-Glacial cycle (MIS 5-2) re-examined based on long proxy records from central and northern Europe

    NASA Astrophysics Data System (ADS)

    Helmens, Karin F.

    2014-02-01

    Current multi-proxy studies on a long sediment sequence preserved at Sokli (N Finland), i.e. in the central area of Fennoscandian glaciations, are drastically changing classic ideas of glaciations, vegetation and climate in northern Europe during the Late Pleistocene. The sediments in the Sokli basin have escaped major glacial erosion due to non-typical bedrock conditions. In this review, the Sokli record is compared in great detail with other long proxy records from central, temperate and northern, boreal Europe. These comprise the classic records of La Grande Pile (E France) and Oerel (N Germany) and more recently obtained records from Horoszki Duże (E Poland) and Lake Yamozero (NW Russia). The focus of the review is on pollen, lithology and macrofossil- and insect-based temperature inferences. The long records are further compared with recent proxy data from nearby terrestrial sites as well as with the rapidly accumulating high-resolution proxy data from the ocean realm. The comparison allows a re-examination of the environmental history and climate evolution of the Last Interglacial-Glacial (LI-G) cycle (MIS 5-2). It shows that environmental and climate conditions during MIS 5 (ca 130-70 ka BP) were distinctly different from those during MIS 4-2 (ca 70-15 ka BP). MIS 5 is characterized by three long forested intervals (broadly corresponding to MIS 5e, 5c, 5a), both in temperate and northern boreal Europe. These mild periods were interrupted by two short, relatively cold and dry intervals (MIS 5d and 5b) with mountain-centered glaciation in Fennoscandia. Millennial scale climate events were superimposed upon these longer lasting climate fluctuations. The time interval encompassing MIS 4-2 shows open vegetation. It is characterized by two glacial maxima (MIS 4 and 2) with sub-continental scale glaciation over northern Europe and dry conditions in strongly continental eastern European settings. High amplitude climate oscillations of millennial duration

  17. Sea level changes during the last and present interglacials in Sal Island (Cape Verde archipelago)

    NASA Astrophysics Data System (ADS)

    Zazo, C.; Goy, J. L.; Hillaire-Marcel, C.; Dabrio, C. J.; González-Delgado, J. A.; Cabero, A.; Bardají, T.; Ghaleb, B.; Soler, V.

    2010-07-01

    Last interglacial and Holocene deposits are particularly well developed in the southern parts of Sal Island (Cape Verde Archipelago). They primarily consist of low-elevation (≤ 2 m above sea level [a.s.l.]) marine deposits made of a basal conglomerate embedded in carbonate mud, passing upwards to calcarenites. All deposits contain an abundant fauna with corals, algae and molluscs with Strombus latus Gmelin and accompanying warm water species of the "Senegalese" fauna. Small scale geomorphological mapping with detailed morphosedimentary analysis revealed lateral facies changes and imbricate (offlapping) structures that suggest small-scale oscillations of paleo-sealevels during high sea stand intervals. U-series measurements (in coral fragments) allowed unequivocal identification of Marine Isotope Substage (MIS) 5.5 units, but were not precise enough to date the sea level oscillations of the interval. However, geomorphological data and sedimentary facies analysis suggest a double sea level highstand during the peak of the last interglacial. MIS 5.5 age deposits occur at Sal and the Canary Islands at low topographic elevations, between 1 and 2 masl. However, these values are lower than the elevations measured for the correlative terraces outcropping at the western tropical Atlantic islands, widely considered to be tectonically stable. Combining the results in this paper with earlier investigations of the "Senegalese" fauna distribution as far north as the Mediterranean basin, it is suggested that the last-interglacial oceanic temperatures in this basin, as well as the temperatures in other islands of the Eastern Atlantic and the coasts of Morocco, were warmer than modern temperatures.

  18. The Antarctic Ice Sheet during the last Interglaciation: Insights from my Thesis

    NASA Astrophysics Data System (ADS)

    Whipple, Matthew; Lunt, Dan; Singarayer, Joy; Bradley, Sarah; Milne, Glenn; Wolff, Eric; Siddall, Mark

    2015-04-01

    The last interglaciation represents a period of warmer climates and higher sea levels, and a useful analogue to future climate. While many studies have focussed on the response of the Greenland Ice sheet, far less is known about the response of the Antarctic ice sheet. Here, I present the summarised results of my PhD thesis "Constraints on the minimum extent of the Antarctic ice sheet during the last interglaciation". Firstly, I cover the timings of interglaciation in Antarctica, and their differences with respect to the Northern Hemisphere timings, based on paleo sea level indicators, and oceanic temperature records. I move on to cover climate forcings, and how they influence the ice sheet, relative to present, and early Holocene. Secondly, I present thesis results, from looking at ice core stable water isotopes. These are compared with Isostatic and Climatic modelling results, for various different Ice sheet scenarios, as to the resulting Climate, from changes in Elevation, Temperature, Precipitation, and Sublimation, all contributing to the recorded stable water isotope record. Thirdly, I move on to looking at the mid-field relative sea level records, from Australia and Argentina. Using isostatic modelling, these are used to assess the relative contribution of the Eastern and Western Antarctic Ice sheets. Although data uncertainties result in us being to identify the contribution from West Antarctica. Overall, using model-data comparison, we find a lack of evidence for a substantial retreat of the Wilkes Subglacial basin. No data location is close enough to determine the existence of the marine based West Antarctic Ice sheet. Model uncertainty is unable to constrain evidence of variations in ice thickness in East Antarctica.

  19. Glacial-interglacial variation in denudation rates from interior Texas, USA, established with cosmogenic nuclides

    NASA Astrophysics Data System (ADS)

    Hidy, Alan J.; Gosse, John C.; Blum, Michael D.; Gibling, Martin R.

    2014-03-01

    The Brazos, Colorado, and Trinity rivers of Texas drain a tectonically quiescent, non-glaciated, and low-relief landscape inland from the Gulf of Mexico, where long-term [103-105 a] changes in denudation rates are probably driven largely by climate change. Here, we use cosmogenic 10Be to obtain spatially averaged denudation rates for these river catchments, primarily from terrace deposits associated with glacial or interglacial intervals over the past half million years. The denudation rates are ∼30-35% higher during interglacial periods than during glacial periods, and correlate broadly with temperature. The results are consistent with predictions from the BQART sediment flux model, and support the hypothesis that increased weathering rates associated with warmer climates will accelerate landscape erosion. Furthermore, by analyzing 26Al/10Be in these deposits, we can estimate the bed load sourced from up-catchment surfaces. The stored coastal plain fraction varies from ∼10% to 30%, and is greater during times of relatively lower sea level. The results indicate that although sediment flux is moderated by coastal-plain storage, increased up-catchment flux during warmer interglacial periods outpaces evacuation of stored sediment during glacial periods, resulting in a net increase in sediment flux to the ocean during warm intervals. If this temperature-sediment flux relationship is valid beyond the Plio-Pleistocene transition, then global sediment flux to the ocean from passive, non-glaciated, and low-relief landscapes would have been greater during the Pliocene than in the cooler Quaternary.

  20. The Glacial-Interglacial Monsoon Recorded by Speleothems from Sulawesi, Indonesia

    NASA Astrophysics Data System (ADS)

    Kimbrough, A. K.; Gagan, M. K.; Dunbar, G. B.; Krause, C.; Hantoro, W. S.; Cheng, H.; Edwards, R. L.; Shen, C. C.; Sun, H.; Cai, B.; Hellstrom, J. C.; Rifai, H.

    2015-12-01

    The Indo-Pacific Warm Pool is a primary source of heat and moisture to the global atmosphere and a key player in tropical and global climate variability. There is mounting evidence that atmospheric convection and oceanic processes in the tropics can modulate global climate on orbital and sub-orbital timescales. Glacial-interglacial cycles represent the largest natural climate changes over the last 800 kyr with each cycle terminated by rapid global warming and sea level rise. Our understanding of the role and response of tropical atmospheric convection during these periods of dramatic warming is limited. We present the first speleothem paleomonsoon record for southwest Sulawesi (5ºS, 119ºE), spanning two glacial-interglacial cycles, including glacial termination IV (~340 kyr BP) and both phases of termination III (~248 and ~220 kyr BP). This unique record is constructed from multiple stalagmites from two separate caves and is based on a multi-proxy approach (δ18O, δ13C, Mg/Ca, Sr/Ca) that provides insight into the mechanisms controlling Australian-Indonesian summer monsoon variability. Speleothem δ18O and trace element data indicate a rapid increase in rainfall at glacial terminations and wet interglacials. Terminations IV, III, and I are each characterized by an abrupt 3‰ decrease in δ18O. Variability in δ18O leading-in to glacial terminations is also similar, and corresponds to October insolation. Prior to deglaciation, there is a distinct shift to higher δ18O that is synchronized with weak monsoon intervals in Chinese speleothem records. The remarkably consistent pattern among terminations implies that the response of tropical convection to changing background climates is well regulated. Furthermore, we find that speleothem δ13C leads δ18O by ~5 kyr during glacial terminations. The early decrease in speleothem δ13C may reflect the response of tropical vegetation to rising atmospheric CO2 and temperature, rather than regional changes in rainfall.

  1. Glacial-interglacial variability in ocean oxygen and phosphorus in a global biogeochemical model

    NASA Astrophysics Data System (ADS)

    Palastanga, V.; Slomp, C. P.; Heinze, C.

    2013-02-01

    Increased transfer of particulate matter from continental shelves to the open ocean during glacials may have had a major impact on the biogeochemistry of the ocean. Here, we assess the response of the coupled oceanic cycles of oxygen, carbon, phosphorus, and iron to the input of particulate organic carbon and reactive phosphorus from shelves. We use a biogeochemical ocean model and specifically focus on the Last Glacial Maximum (LGM). When compared to an interglacial reference run, our glacial scenario with shelf input shows major increases in ocean productivity and phosphorus burial, while mean deep-water oxygen concentrations decline. There is a downward expansion of the oxygen minimum zones (OMZs) in the Atlantic and Indian Ocean, while the extension of the OMZ in the Pacific is slightly reduced. Oxygen concentrations below 2000 m also decline but bottom waters do not become anoxic. The model simulations show when shelf input of particulate organic matter and particulate reactive P is considered, low oxygen areas in the glacial ocean expand, but concentrations are not low enough to generate wide scale changes in sediment biogeochemistry and sedimentary phosphorus recycling. Increased reactive phosphorus burial in the open ocean during the LGM in the model is related to dust input, notably over the southwest Atlantic and northwest Pacific, whereas input of material from shelves explains higher burial fluxes in continental slope and rise regions. Our model results are in qualitative agreement with available data and reproduce the strong spatial differences in the response of phosphorus burial to glacial-interglacial change. Our model results also highlight the need for additional sediment core records from all ocean basins to allow further insight into changes in phosphorus, carbon and oxygen dynamics in the ocean on glacial-interglacial timescales.

  2. Modeling of Two-Plasmon-Decay Experiments at Polar-Direct-Drive Ignition-Relevant Plasma Conditions at the National Ignition Facility

    NASA Astrophysics Data System (ADS)

    Solodov, A. A.; Rosenberg, M. J.; Myatt, J. F.; Epstein, R.; Regan, S. P.; Seka, W.; Shaw, J. G.; Hohenberger, M.; Moody, J. D.; Ralph, J. E.; Turnbull, D. P.

    2015-11-01

    The two-plasmon-decay (TPD) instability can be detrimental for direct-drive inertial confinement fusion because of target preheat by high-energy electrons generated by TPD. The radiation-hydrodynamic code DRACO has been used to design planar target experiments that generate plasma and interaction conditions relevant to ignition polar-direct-drive (PDD) designs. The use of planar targets allows TPD to be decoupled from cross-beam energy transfer, which reduces the laser absorption in current National Ignition Facility (NIF) PDD implosion experiments. The laser-plasma interaction code LPSE has been used to investigate TPD using the predicted plasma profiles and laser irradiation geometry in three dimensions. The energetic electrons generated by LPSE are propagated into the planar target using the Monte Carlo transport code EGSnrc. This enables a direct comparison between the simulated and experimentally observed Mo Kα fluorescence and hard x-ray bremsstrahlung. The plasma profiles have been post-processed for stimulated Raman and Brillouin backscatter gains. Comparisons of these results with recent experiments at the NIF and the implications for ignition-scale PDD experiments will be presented. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

  3. Depth-resolved simplified characterization of collagen depletion in dermis with polarization sensitive optical coherence tomography applicable to non-laboratory conditions

    NASA Astrophysics Data System (ADS)

    Tougbaev, Vitali; Eom, Tae Joong; Shin, Woojin; Lee, Yeung Lak; Yu, Bong-Ahn; Kee, Chul-Sik; Ko, Do-Kyeong; Lee, Jongmin

    2007-07-01

    A further insight into the prior concept of polarization sensitive optical coherence tomography system intended for non-laboratory conditions is brought forward and an experimental proof-of-concept is presented. A phenomenological model is adopted from the theory of light depolarization in crystalline polymers and modified to yield a simplified algorithm for mapping depolarization ratio in dermis. The algorithm could distinguish between dermal layers with depleted collagen content and normal dermis of normal perilesional skin. Dermis is simulated by bireringent lamellae of collagen arranged chaotically in multiple layers parallel to the skin surface. Both the design concept and the model imply the sub-millimeter tumor thickness as a proofed prognostic factor and an important criterion for complementary functional diagnostics of skin cancers at their early phase of vertical growth. Choice of the model is inspired by similarity of structural and optical properties between liquid-crystal collagen fibers in dermis and birefringent crystalline lamellae in polymer materials. The numerical computation based on the model allowing for real characteristics of dermis gives plausible interpreting of depolarization peculiarities caused by collagen depletion. Feasibility is discussed of exploiting fiber optic analogs of achromatic retarders. Fabrication of the fiber retarders is shown to be realistic by making use of the photonics technology possessed by the authors.

  4. Conditions for efficient and stable ion acceleration by moderate circularly polarized laser pulses at intensities of 10{sup 20} W/cm{sup 2}

    SciTech Connect

    Qiao, B.; Zepf, M.; Borghesi, M.; Dromey, B.; Kar, S.; Geissler, M.; Gibbon, P.; Schreiber, J.

    2011-04-15

    Conditions for efficient and stable ion radiation pressure acceleration (RPA) from thin foils by circularly polarized laser pulses at moderate intensities are theoretically and numerically investigated. It is found that the unavoidable decompression of the co-moving electron layer in Light-Sail RPA leads to a change of the local electrostatic field from a ''bunching'' to a ''debunching'' profile, ultimately resulting in premature termination of ion acceleration. One way to overcome this instability is the use of a multispecies foil where the high-Z ions act as a sacrificial species to supply excess co-moving electrons for preserving stable acceleration of the lower-Z ion species. It is shown by 2D particle-in-cell simulations that 100 MeV/u monoenergetic C{sup 6+} ion beams are produced by irradiation of a Cu-C-mixed foil with laser pulses at intensities 5 x 10{sup 20} W/cm{sup 2}, which can be easily achieved by current day lasers.

  5. Foraminiferal calcification response to glacial-interglacial changes in atmospheric CO2.

    PubMed

    Barker, Stephen; Elderfield, Henry

    2002-08-01

    A record of foraminiferal shell weight across glacial-interglacial Termination I shows a response related to seawater carbonate ion concentration and allows reconstruction of a record of carbon dioxide in surface seawater that matches the atmospheric record. The results support suggestions that higher atmospheric carbon dioxide directly affects marine calcification, an effect that may be of global importance to past and future changes in atmospheric CO2. The process provides negative feedback to the influence of marine calcification on atmospheric carbon dioxide and is of practical importance to the application of paleoceanographic proxies. PMID:12161653

  6. The Mid-Holocene and Last Interglacial Experiments in PMIP4/CMIP6

    NASA Astrophysics Data System (ADS)

    Otto-Bliesner, Bette L.; Braconnot, Pascale; Abe-Ouchi, Ayako

    2016-04-01

    Understanding the forcings and feedbacks that produced interglacial warmth and the outcomes from it can help us better project the future climate of our planet. CMIP6 will include two interglacial experiments to explore the responses of the models to the forcing by orbital variations: the Mid-Holocene (MH 6000 years ago [6 ka]) and Last Interglacial (LIG 127,000 years ago [127 ka]). The dominant orbital forcing changes from modern modified the incoming solar insolation at the top of the atmosphere, resulting in large positive anomalies in summer in the Northern Hemisphere. Greenhouse gas concentrations were close to those of the pre-industrial. This pair of simulations will allow an assessment of the scaling and thresholds of the Earth system to the magnitude of the solar insolation changes (larger seasonal anomalies at 127 ka than 6 ka). High latitude feedbacks from sea-ice, water vapor and clouds will be a focus, and the implications for the stability of the Greenland and West Antarctic (WAIS) ice sheets. This output will be used by the ice sheet modeling community, with an intercomparison being coordinated as a joint activity of PMIP4 and ISMIP6 for CMIP6. As well, these experiments will explore the relative changes of the low-latitude hydrological cycle and monsoons. The MH and LIG are the most suitable of the warm interglacials for a CMIP6 assessment because of the wealth of data including: ice cores providing measurements of well-mixed greenhouse gases, aerosols including dust and sea salt, and stable water isotopes as a proxy for temperature, as well as for Greenland, ice sheet elevation and extent; marine records for ocean temperatures and geotracers that can be interpreted in terms of water masses and overturning strength; speleothems that provide indication of monsoon strength; fossil corals and sediments for interannual to multi-decadal variability; and terrestrial records that indicate temperature, vegetation, lake level, and hydroclimate changes. As

  7. Heinrich-like events in the Southeast Pacific: Abrupt climate change during the last interglacial

    NASA Astrophysics Data System (ADS)

    Jacobel, A. W.; Mokeddem, Z.; McManus, J. F.

    2010-12-01

    Many previous studies of orbital and sub-orbital scale climate changes in the marine record during the last glacial-interglacial transition have focused on evidence from the Northern Hemisphere. While solar insolation at 65°N evidently plays a primary role in pacing orbital changes, determining the mechanism(s) transferring climatic changes around the globe at orbital and sub-orbital time scales also requires records from the mid and high southern latitudes (Pahnke et al., 2003). Here we present such a record from ODP Leg 202, Site 1234 located 65 km off the Chilean margin (36°13.153'S, 73°40.902'W). With a high sedimentation rate of ~80 cm/kyr, the core site represents an opportunity to examine Marine Isotope Stage 5 (MIS 5), the last interglacial, in high resolution. Using quantifications of ice rafted debris (IRD), foraminiferal abundances, N. pachyderma (sinistral) abundance and oxygen isotopes from planktonic and benthic foraminifera, the present study provides an 80 kyr record of climate change. We resolved MIS 5 in sufficient detail to observe the MIS 5/6 boundary, sub-stages MIS 5a through MIS 5e, and millennial-scale variability during the transition from the last interglacial into the last glacial era. Comparison of our records of MIS 5 with records from the North Atlantic (Oppo et al., 2001) demonstrates that orbital-scale warming in the two hemispheres appears to be approximately synchronous, though from our data it is not possible to infer a precise phase relationship in order to constrain a synchronization mechanism. At shorter time scales, a comparison of our records during the last interglacial with records from the North Atlantic (McManus et al., 1998) shows that episodes of ice rafting at our site, associated with changes in foraminiferal abundances and oxygen isotope content, are similar to, and correlated with, evidence of small-scale Heinrich events in the North Atlantic. This suggests that the expansion and retreat of Andean glaciers, as

  8. Glacial-interglacial variations in coupled thermocline ventilation and sedimentary iron delivery to the Peru upwelling system

    NASA Astrophysics Data System (ADS)

    Scholz, F.; McManus, J.; Mix, A. C.; Hensen, C.; Schneider, R. R.

    2013-12-01

    Primary productivity in the Humboldt Current system off Peru is limited by the supply of bioavailable iron (Fe) from reducing seafloor sediments. Previous studies have demonstrated that bottom water redox conditions exert first-order control on the Fe efflux from continental margin sediments. Fluctuations in thermocline ventilation therefore have the potential to modulate ocean fertility by altering the net efflux of Fe from the seafloor on a variety of timescales. We present a 140 ka record of high-resolution XRD core scanning, reactive Fe, redox sensitive trace metal and nitrogen isotope data for a sediment core from the present-day oxygen minimum zone off Peru. Coarser grain size as well as decreased δ15N values (≥3 ‰) and increased uranium to molybdenum ratios (≤1.6 μg g-1/μg g-1) indicate enhanced thermocline ventilation compared to the present-day (δ15 ≈ 6 ‰, U/Mo ≈ 0.2 μg g-1/μg g-1) during the LGM, MIS4, MIS5b, MIS5d and MIS6. Sediments that were deposited during these intervals are depleted in reactive Fe suggesting that the redox regime prevailing during cooler intervals fostered seafloor Fe release. The relative accumulation rate of uranium and molybdenum indicates that shifts in the Fe mobilization efficiency were related to a transition from sulfate- to Fe-reducing conditions in the sediment pore water. We suggest that lower concentrations of pore water sulfide close to the sediment surface facilitated dissolved Fe loss across the benthic boundary by decreasing Fe fixation as Fe sulfide. Our data suggest that a redox-shift toward more reducing conditions in oxygen minimum zones may not enhance but rather decrease the sedimentary Fe efflux. We will discuss implications of these findings for nitrate utilization and productivity in the ocean at glacial-interglacial transitions and in response to future de-oxygenation.

  9. Oceanographic dynamics and the end of the last interglacial in the subpolar North Atlantic.

    PubMed

    Mokeddem, Zohra; McManus, Jerry F; Oppo, Delia W

    2014-08-01

    The last interglacial interval was terminated by the inception of a long, progressive glaciation that is attributed to astronomically influenced changes in the seasonal distribution of sunlight over the earth. However, the feedbacks, internal dynamics, and global teleconnections associated with declining northern summer insolation remain incompletely understood. Here we show that a crucial early step in glacial inception involves the weakening of the subpolar gyre (SPG) circulation of the North Atlantic Ocean. Detailed new records of microfossil foraminifera abundance and stable isotope ratios in deep sea sediments from Ocean Drilling Program site 984 south of Iceland reveal repeated, progressive cold water-mass expansions into subpolar latitudes during the last peak interglacial interval, marine isotope substage 5e. These movements are expressed as a sequence of progressively extensive southward advances and subsequent retreats of a hydrographic boundary that may have been analogous to the modern Arctic front, and associated with rapid changes in the strength of the SPG. This persistent millennial-scale oceanographic oscillation accompanied a long-term cooling trend at a time of slowly declining northern summer insolation, providing an early link in the propagation of those insolation changes globally, and resulting in a rapid transition from extensive regional warmth to the dramatic instability of the subsequent ∼ 100 ka. PMID:25049405

  10. Reconstructing Variations of Global Sea-Surface Temperature during the Last Interglaciation

    NASA Astrophysics Data System (ADS)

    Hoffman, J. S.; Clark, P. U.; He, F.; Parnell, A. C.

    2015-12-01

    The last interglaciation (LIG; ~130-116 ka) was the most recent period in Earth history with higher-than-present global sea level (≥6 m) under similar-to-preindustrial concentrations of atmospheric CO2, suggesting additional feedbacks related to albedo, insolation, and ocean circulation in generating the apparent climatic differences between the LIG and present Holocene. However, our understanding of how much warmer the LIG sea surface was relative to the present interglaciation remains uncertain, with current estimates suggesting from 0°C to 2°C warmer than late-20thcentury average global temperatures. Moreover, the timing, spatial expression, and amplitude of regional and global sea surface temperature variability related to other climate forcing during the LIG are poorly constrained, largely due to uncertainties in age control and proxy temperature reconstructions. An accurate characterization of global and regional temperature change during the LIG can serve as a benchmark for paleoclimate modeling intercomparison projects and help improve understanding of sea-level sensitivity to temperature change. We will present a global compilation (~100 published records) of sea surface temperature (SST) and other climate reconstructions spanning the LIG. Using a Monte Carlo-enabled cross-correlation maximization algorithm to climatostratigraphically align proxy records and then account for both the resulting chronologic and proxy calibration uncertainties with Bayesian statistical inference, our results quantify the spatial timing, amplitude, and uncertainty in estimates of global and regional sea surface temperature change during the LIG and its relation to potential forcings.

  11. Saharan dust deposition in the Carpathian Basin and its possible effects on interglacial soil formation

    NASA Astrophysics Data System (ADS)

    Varga, György; Cserháti, Csaba; Kovács, János; Szalai, Zoltán

    2016-09-01

    Several hundred tons of windblown dust material are lifted into the atmosphere and are transported every year from Saharan dust source areas towards Europe having an important climatic and other environmental effect also on distant areas. According to the systematic observations of modern Saharan dust events, it can be stated that dust deflated from North African source areas is a significant constituent of the atmosphere of the Carpathian Basin and Saharan dust deposition events are identifiable several times in a year. Dust episodes are connected to distinct meteorological situations, which are also the determining factors of the different kinds of depositional mechanisms. By using the adjusted values of dust deposition simulations of numerical models, the annual Saharan dust flux can be set into the range of 3.2-5.4 g/m2/y. Based on the results of past mass accumulation rates calculated from stratigraphic and sedimentary data of loess-paleosol sequences, the relative contribution of Saharan dust to interglacial paleosol material was quantified. According to these calculations, North African exotic dust material can represent 20-30% of clay and fine silt-sized soil components of interglacial paleosols in the Carpathian Basin. The syngenetic contribution of external aeolian dust material is capable to modify physicochemical properties of soils and hereby the paleoclimatic interpretation of these pedogene stratigraphic units.

  12. Oceanographic dynamics and the end of the last interglacial in the subpolar North Atlantic

    PubMed Central

    Mokeddem, Zohra; McManus, Jerry F.; Oppo, Delia W.

    2014-01-01

    The last interglacial interval was terminated by the inception of a long, progressive glaciation that is attributed to astronomically influenced changes in the seasonal distribution of sunlight over the earth. However, the feedbacks, internal dynamics, and global teleconnections associated with declining northern summer insolation remain incompletely understood. Here we show that a crucial early step in glacial inception involves the weakening of the subpolar gyre (SPG) circulation of the North Atlantic Ocean. Detailed new records of microfossil foraminifera abundance and stable isotope ratios in deep sea sediments from Ocean Drilling Program site 984 south of Iceland reveal repeated, progressive cold water-mass expansions into subpolar latitudes during the last peak interglacial interval, marine isotope substage 5e. These movements are expressed as a sequence of progressively extensive southward advances and subsequent retreats of a hydrographic boundary that may have been analogous to the modern Arctic front, and associated with rapid changes in the strength of the SPG. This persistent millennial-scale oceanographic oscillation accompanied a long-term cooling trend at a time of slowly declining northern summer insolation, providing an early link in the propagation of those insolation changes globally, and resulting in a rapid transition from extensive regional warmth to the dramatic instability of the subsequent ∼100 ka. PMID:25049405

  13. Estimating the sea-level highstand during the Last Interglacial: a probabilistic massive ensemble approach

    NASA Astrophysics Data System (ADS)

    Düsterhus, André; Tamisiea, Mark E.; Jevrejeva, Svetlana

    2016-05-01

    Essential to understanding sea-level change and its causes during the last interglacial is the quantification of uncertainties. In order to estimate the uncertainties, we develop a statistical framework for the comparison of paleao-climatic sea-level index points and GIA model predictions. For the investigation of uncertainties, as well as to generate better model predictions, we implement a massive ensemble approach by applying a data assimilation scheme based on particle filter methods. The different runs are distinguished through varying ice sheet reconstructions based on oxygen-isotope curves and different parameter selections within the GIA model. This framework has several advantages over earlier work, such as the ability to examine either the contribution of individual observations to the results or the probability of specific input parameters. This exploration of input parameters and data leads to a larger range of estimates than previously published work. We illustrate how the assumptions that enter into the statistical analysis, such as the existence of outliers in the observational database or the initial ice volume history, can introduce large variations to the estimate of the maximum highstand. Thus, caution is required to avoid over-interpreting results. We conclude that there are reasonable doubts whether the datasets previously used in statistical analyses are able to tightly constrain the value of maximum highstand during the last interglacial (LIG).

  14. Increased aridity in southwestern Africa during the warmest periods of the last interglacial

    NASA Astrophysics Data System (ADS)

    Urrego, D. H.; Sánchez Goñi, M. F.; Daniau, A.-L.; Lechevrel, S.; Hanquiez, V.

    2015-10-01

    Terrestrial and marine climatic tracers from marine core MD96-2098 were used to reconstruct glacial-interglacial climate variability in southwestern Africa between 194 and 24 thousand years before present. The pollen record documented three pronounced expansions of Nama-karoo and fine-leaved savanna during the last interglacial (Marine Isotopic Stage 5 - MIS 5). These Nama-karoo and fine-leaved savanna expansions were linked to increased aridity during the three warmest substadials of MIS 5. Enhanced aridity potentially resulted from a combination of reduced Benguela Upwelling, expanded subtropical high-pressure cells, and reduced austral-summer precipitation due to a northward shift of the Intertropical Convergence Zone. Decreased austral-winter precipitation was likely linked to a southern displacement of the westerlies. In contrast, during glacial isotopic stages MIS 6, 4 and 3, fynbos expanded at the expense of Nama-karoo and fine-leaved savanna indicating a relative increase in precipitation probably concentrated during the austral winter months. Our record also suggested that warm-cold or cold-warm transitions between isotopic stages and substages were punctuated by short increases in humidity. Increased aridity during MIS 5e, 5c and 5a warm substages coincided with minima in both precessional index and global ice volume. On the other hand, austral-winter precipitation increases were associated with precession maxima at the time of well-developed Northern Hemisphere ice caps.

  15. Characteristics of volume polarization holography with linear polarization light

    NASA Astrophysics Data System (ADS)

    Zang, Jinliang; Wu, An'an; Liu, Ying; Wang, Jue; Lin, Xiao; Tan, Xiaodi; Shimura, Tsutomu; Kuroda, Kazuo

    2015-10-01

    Volume polarization holographic recording in phenanthrenequinone-doped poly(methyl methacrylate) (PQ-PMMA) photopolymer with linear polarized light is obtained. The characteristics of the volume polarization hologram are experimentally investigated. It is found that beyond the paraxial approximation the polarization states of the holographic reconstruction light are generally different from the signal light. Based on vector wave theoretical analyses and material properties, the special exposure condition for correctly holographic reconstruction is obtained and experimentally demonstrated.

  16. The last interglacial period on the Pacific Coast of North America: Timing and paleoclimate

    USGS Publications Warehouse

    Muhs, D.R.; Simmons, K.R.; Kennedy, G.L.; Rockwell, T.K.

    2002-01-01

    New, high-precision U-series ages of solitary corals (Balanophyllia elegans) coupled with molluscan faunal data from marine terraces on the Pacific Coast of North America yield information about the timing and warmth of the last interglacial sea-level highstand. Balanophyllia elegans takes up U in isotopic equilibrium with seawater during growth and shortly after death. Corals from the second terrace on San Clemente Island (offshore southern California), the third terrace on Punta Banda (on the Pacific Coast of northern Baja California), and the Discovery Point Formation on Isla de Guadalupe (in the Pacific Ocean offshore Baja California) date to the peak of the last interglacial period and have U-series ages ranging from ca. 123 to 114 ka. The first terrace on Punta Banda has corals with ages ranging from ca. 83 to 80 ka, which corresponds to a sea-level highstand formed in the late last interglacial period. U-series analyses of corals from the Cayucos terrace (central California) and the Nestor terrace at Point Loma (southern California) show that these fossils have evidence of open-system history, similar to what has been reported by other workers for the same localities. Nevertheless, a model of continuous, secondary U and Th uptake shows that two ages of corals are likely present at these localities, representing the ca. 105 and ca. 120 ka sea-level highstands reported elsewhere. U-series ages of last interglacial corals from the Pacific Coast overlap with, but are on average younger than the ages of corals from Barbados, the Bahamas, and Hawaii. This age difference is explained by the nature of the geomorphic response to sea-level change: fringing or barrier reefs on low-latitude coastlines have an accretionary growth style that keeps pace with rising sea level, whether on a tectonically rising or stable coastline. In contrast, midlatitude, high-energy coastlines are sites of platform cutting during the early part of a sea-level high stand and terrace

  17. Expression of PIN and AUX1 genes encoding putative carrier proteins for auxin polar transport in etiolated pea epicotyls [correction of epicotyles] under simulated microgravity conditions on a three-dimensional clinostat.

    PubMed

    Hoshino, Tomoki; Hitotsubashi, Reiko; Miyamoto, Kensuke; Tanimoto, Eiichi; Ueda, Junichi

    2003-10-01

    Etiolated pea (Pisum sativum L. cv. Alaska) seedlings grown under simulated microgravity conditions on a 3-dimensional clinostat showed automorphosis-like growth and development similar to that observed in true microgravity conditions in space. Application of inhibitors of auxin polar transport phenocopied automorphosis-like growth on 1 g conditions, suggesting that automorophosis is closely related to auxin polar transport. Strenuous efforts to know the relationships between automorphosis and auxin polar transport in pea seedlings at molecular bases resulted in successful identification of PsPIN2 and PsAUX1 encoding putative auxin efflux and influx carrier protein, respectively. Significantly high levels in homology were found on nucleotide and deduced amino acid sequences among PsPIN2, PsPIN1 and AtPINs, and between PsAUX1 and AtAUX1. Expression of PsPIN1 and PsAUX1 genes in etiolated pea seedlings grown on the clinostat were substantially affected, but that of PsPIN2 was not. Roles of these genes in auxin polar transport and automorphosis of etiolated pea seedlings are also described. PMID:14676360

  18. Near-field sea-level variability in northwest Europe and ice sheet stability during the last interglacial

    NASA Astrophysics Data System (ADS)

    Long, A. J.; Barlow, N. L. M.; Busschers, F. S.; Cohen, K. M.; Gehrels, W. R.; Wake, L. M.

    2015-10-01

    Global sea level during the Last Interglacial (LIG, Marine Isotope Sub-stage 5e) peaked between c. 5.5 and 9 m above present, implying significant melt from Greenland and Antarctica. Relative sea level (RSL) observations from several far- and intermediate-field sites suggest abrupt fluctuations or jumps in RSL during the LIG highstand that require one or more episodes of ice-sheet collapse and regrowth. Such events should be manifest as unique sea-level fingerprints, recorded in far-, intermediate- and near-field sites depending on the source(s) of ice-mass change involved. To date, though, no coherent evidence of such fluctuations has been reported from near-field RSL studies in northwest Europe. This is an important problem because RSL fluctuations during the LIG are portrayed as warning signs for how polar ice sheets may behave in a future, warmer than present, world. Here we review the evidence for RSL change during the LIG using stratigraphic data from the best resolved highstand records that exist in the near-field of northwest Europe, from a range of settings that include lagoonal, shallow marine, tidal flat, salt marsh and brackish-water fluviatile environments. Consideration of previously published stratigraphic records from two sites in the Eemian coastal-marine embayment that existed in the central Netherlands, yields no clear indications for abrupt RSL change during the attainment of the near-field highstand. Nor do we find any such indications common to other records from countries bordering the North Sea, the Baltic Sea and the White Sea. Two modelling experiments that explore the global signal of hypothetical sea-level oscillations caused by partial collapse and regrowth of either the Greenland or Antarctic LIG ice-sheet, show that the North Sea region is relatively insensitive to mass changes sourced from Greenland but should clearly register events with an Antarctic origin, especially those that occur late in the LIG. The lack of evidence for

  19. Sediment core fossils in ancient Lake Ohrid: testing for faunal change since the Last Interglacial

    NASA Astrophysics Data System (ADS)

    Albrecht, C.; Vogel, H.; Hauffe, T.; Wilke, T.

    2010-11-01

    Ancient Lake Ohrid is probably of early Pleistocene or Pliocene origin and amongst the few lakes in the world harbouring an outstanding degree of endemic biodiversity. Although there is a long history of evolutionary research in Lake Ohrid, particularly on molluscs, a mollusc fossil record has been missing up to date. For the first time, gastropod and bivalve fossils are reported from the basal, calcareous part of a 2.6 m long sediment succession (core Co1200) from the north-eastern part of Lake Ohrid. Electron spin resonance (ESR) dating of mollusc shells from the same stratigraphic level yielded an age of 130 ± 28 ka. Lithofacies III sediments, i.e. a stratigraphic subdivision comprising the basal succession of core Co1200 between 181.5-263 cm, appeared solid, greyish-white, and consisted almost entirely of silt-sized endogenic calcite (CaCO3>70%) and intact and broken mollusc shells. Here we compare the faunal composition of the thanatocoenosis with recent mollusc associations in Lake Ohrid. A total of 13 mollusc species (9 gastropod and 4 bivalve species) could be identified within Lithofacies III sediments. The value of sediment core fossils for reconstructing palaeoenvironmental settings was evaluated and the agreement between sediment and palaeontological proxies was tested. The study also aims at investigating major faunal changes since the Last Interglacial and searching for signs of extinction events. The combined findings of the ecological study and the sediment characteristics suggest deposition in a shallow water environment during the Last Interglacial. The fossil fauna exclusively included species also found in the present fauna, i.e. no extinction events are evident for this site since the Last Interglacial. The thanatocoenosis showed the highest similarity with recent Intermediate Layer (5-25 m water depth) mollusc assemblages. The demonstrated existence of a mollusc fossil record in Lake Ohrid sediment cores also has great significance for future

  20. Arctic Interglacial Warmth - can Beringian paleoclimate records inform us concerning the transition we are now in?

    NASA Astrophysics Data System (ADS)

    Brigham-Grette, J.

    2011-12-01

    Contemporary change cannot be evaluated without the perspective of past rates of change in concert with a complete evaluation of associated feedbacks and forcings. Paleoclimate studies offer the only valid context for evaluating trajectories and dynamics in the climate system especially in a warming world driven by anthropogenic CO2. "If it happened before it could happen again" and it is with this adage that most of the paleoclimate community is now screaming déjà vu. The present rate of global scale warming is unprecedented within the resolution of paleorecords. High resolution terrestrial studies (lakes, tree rings and ice cores) of the last 2 ka across the Arctic clearly show that the wholesale warming of the past few decades is unprecedented and likely forced by increases in green house gas emissions. Emerging evidence of earlier warm periods over the past few million years inform us about the sensitivity of the arctic system to change, particularly the rates and magnitudes of warmth that directly impact the seasonal extent and existence of sea ice, the melt of glacial systems and changes in sea level. While there is some consensus about the rapid response of the sea-ice albedo feedback processes, it still remains difficult to model. Large changes in seasonal ice across the Arctic have been documented for parts of the early Holocene due to insolation forcing and sea ice was arguably less extensive during MIS 5e (125ka), and several other interglacials. Along with less sea ice there are data to suggest large northward range extensions of marine flora and fauna that likely accompanied changes in water mass structure. Sustained warmth during the Pliocene (especially 3.0 to 3.6 Ma) suggests several intervals when summer sea ice was absent and even the presence of winter sea ice is debated. While different research groups have each produced a variety estimates for pCO2 in mid Pliocene ranging from 280 ppm to 400 ppm, most agree that pCO2 may have been like today

  1. Vegetation and climate of the southern Levant during the last Interglacial

    NASA Astrophysics Data System (ADS)

    Chen, Chunzhu; Litt, Thomas

    2015-04-01

    Sediments in the Dead Sea basin are outstanding archives for understanding the paleoenvironment of the southern Levant because of their locations at the boundary between the Mediterranean and Arabian-Sahara climate zones. During the past decades, extensive investigations have demonstrated high lake levels during the last Glacial but low lake levels during the present and last Interglacial. However, palynological results from Lake Kinneret and Birkat Ram suggested a dry last Glacial and wet Holocene (Schiebel, 2013; Chen and Miebach, unpublished). Studies on Lake Samra (last interglacial precursor of the modern Dead Sea) became a focus after deep drilling cores were retrieved in 2011. Core 5017-1A encompasses the most complete Samra profile in the region, which exhibits thick halite layers indicating extremely low lake levels (Neugebauer et al., 2014). As interpreted based on lithological and hydrological results, the marine isotope stage (MIS) 5e was the most arid period (work in progress). In this case, pollen analysis would provide independent evidence of the regional climate changes. Our preliminary result shows that late MIS 6 was characterized by an expansion of goosefoot (Chenopodiaceae)-dominated desert/semi-desert. During the MIS 6/5 transition, an abrupt increase of grasses and a corresponding decline of goosefoot suggest the occurrence of a more humid grass steppe, whereas the woodlands were still open. The MIS 5e has witnessed higher woodland density and moisture availability provided high values of Mediterranean woodland components (mainly olives and deciduous oaks). From MIS 5d to 5a, a drying trend was recorded from the contraction of the Mediterranean biome and the expansion of steppe/semi-steppe. As a key time interval of our study, MIS 5e comprised a typical vegetation succession process that is also prevalent in other Mediterranean pollen records. Therefore, in biostratigraphical terms, high abundances of woody taxa marks the MIS 5e, although the

  2. Evolution of Temperature and Carbon Storage Within the Deep Southeast Atlantic Ocean Across the Last Glacial/Interglacial Cycle Inferred from a Highly-Resolved Sedimentary Depth Transect

    NASA Astrophysics Data System (ADS)

    Foreman, A. D.; Charles, C. D.; Rae, J. W. B.; Adkins, J. F.; Slowey, N. C.

    2015-12-01

    Many models show that the relative intensity of stratification is a primary variable governing the sequestration and release of carbon from the ocean over ice ages. The wide-scale observations necessary to test these model-derived hypotheses are not yet sufficient, but sedimentary depth transects represent a promising approach for making progress. Here we present paired stable isotopic (d18O, d13C) and trace metal data (Mg/Ca, B/Ca) from benthic foraminifera collected from a highly vertically-resolved depth transect from the mid-depth and deep SE Atlantic. These observations, which cover Marine Isotope Stages 5e, 5d, 5a, 4, and the Last Glacial Maximum, document the evolution of glacial conditions from the previous interglacial, and provide detailed observations regarding the magnitude and timing of changes in temperature and salinity within the deep ocean at key time points over the last glacial/interglacial cycle. Furthermore, the comparison between purely 'physical' tracers (i.e. Mg/Ca, d18O) and tracers sensitive to the carbon cycle (i.e. d13C and B/Ca) provides critical insight into the relationship between deep/mid-depth stratification and global carbon dynamics. Notably among our observations, the paired stable isotope and trace metal results strongly suggest that much of the ice-age cooling of deep South Atlantic occurred at the MIS 5e/5d transition, while the onset of salinity stratification in the mid-depth South Atlantic occurred at the MIS 5/4 transition.

  3. On the glacial and inter-glacial thermohaline circulation and the associated transports of heat and freshwater

    NASA Astrophysics Data System (ADS)

    Ballarotta, M.; Falahat, S.; Brodeau, L.; Döös, K.

    2014-03-01

    The change of the thermohaline circulation (THC) between the Last Glacial Maximum (LGM, ≈ 21 kyr ago) and the present day climate are explored using an Ocean General Circulation Model and stream functions projected in various coordinates. Compared to the present day period, the LGM circulation is reorganised in the Atlantic Ocean, in the Southern Ocean and particularly in the abyssal ocean, mainly due to the different haline stratification. Due to stronger wind stress, the LGM tropical circulation is more vigorous than under modern conditions. Consequently, the maximum tropical transport of heat is slightly larger during the LGM. In the North Atlantic basin, the large sea-ice extent during the LGM constrains the Gulf Stream to propagate in a more zonal direction, reducing the transport of heat towards high latitudes and reorganising the freshwater transport. The LGM circulation is represented as a large intrusion of saline Antarctic Bottom Water into the Northern Hemisphere basins. As a result, the North Atlantic Deep Water is shallower in the LGM simulation. The stream functions in latitude-salinity coordinates and thermohaline coordinates point out the different haline regimes between the glacial and interglacial period, as well as a LGM Conveyor Belt circulation largely driven by enhanced salinity contrast between the Atlantic and the Pacific basin. The thermohaline structure in the LGM simulation is the result of an abyssal circulation that lifts and deviates the Conveyor Belt cell from the area of maximum volumetric distribution, resulting in a ventilated upper layer above a deep stagnant layer, and an Atlantic circulation more isolated from the Pacific. An estimation of the turnover times reveal a deep circulation almost sluggish during the LGM, and a Conveyor Belt cell more vigorous due to the combination of stronger wind stress and shortened circulation route.

  4. Concerning KAr dating of a basalt flow from the Tahoe-Tioga interglaciation, Sawmill Canyon, southeastern Sierra Nevada, California

    USGS Publications Warehouse

    Dalrymple, G.B.; Burke, R.M.; Birkeland, P.W.

    1982-01-01

    New KAr ages for a basalt flow interbedded with Tahoe and Tioga tills in Sawmill Canyon, southeastern Sierra Nevada, slightly refine previously published ages for the flow and provide an estimate of 53,000 ?? 44,000 yr for the Tahoe-Tioga interglaciation. ?? 1982.

  5. Timing and warmth of the Last Interglacial period: new U-series evidence from Hawaii and Bermuda and a new fossil compilation for North America

    NASA Astrophysics Data System (ADS)

    Muhs, Daniel R.; Simmons, Kathleen R.; Steinke, Bree

    2002-07-01

    The timing and duration of the Last Interglacial period have been controversial, with some studies suggesting a relatively short duration that is orbitally forced and others suggesting a long duration that is at most only partly related to orbital forcing. New, high-precison thermal ionization mass spectrometric (TIMS) U-series ages of Last Interglacial corals from Hawaii and Bermuda test these competing hypotheses. Waimanalo Formation corals from slowly uplifting Oahu, Hawaii range in age from ˜134 to ˜113 ka, with most ages between ˜125 and ˜115 ka. Combined with published U-series ages from nearby Lanai, the data suggest a long Last Interglacial period that may have occurred from ˜136 to at least 115 ka. The results indicate that orbital forcing may not have been the only control on ice sheet growth and decay, because sea level would have been high at times of relatively low Northern Hemisphere summer insolation. On tectonically stable Bermuda, deposits from the ˜200 ka (penultimate interglacial period), ˜120 ka (peak Last Interglacial period) and ˜80 ka (late Last Interglacial period) high sea stands have been newly dated. Fossil corals on Bermuda are derived from patch reefs that likely were "catch-up" responses to sea level rise. It is expected that U-series ages of Last-Interglacial corals on Bermuda should overlap with, but not be as old as the range of corals on Oahu. Last-Interglacial corals on Bermuda give a range of ˜125-113 ka, which supports this hypothesis. A large number of emergent marine deposits on Hawaii, Bermuda and along coastal North America have now been dated to the Last Interglacial period. Both Oahu and Bermuda have marine invertebrate faunas with a number of extralimital southern species of mollusks, suggesting warmer-than-present waters during the Last Interglacial period. Warmer waters are also suggested for Last-Interglacial localities around most of North America, from Florida to Canada and Greenland and Baja California to

  6. Timing and warmth of the Last Interglacial period: New U-series evidence from Hawaii and Bermuda and a new fossil compilation for North America

    USGS Publications Warehouse

    Muhs, D.R.; Simmons, K.R.; Steinke, B.

    2002-01-01

    The timing and duration of the Last Interglacial period have been controversial, with some studies suggesting a relatively short duration that is orbitally forced and others suggesting a long duration that is at most only partly related to orbital forcing. New, high-precison thermal ionization mass spectrometric (TIMS) U-series ages of Last Interglacial corals from Hawaii and Bermuda test these competing hypotheses. Waimanalo Formation corals from slowly uplifting Oahu, Hawaii range in age from ???134 to ???113 ka, with most ages between ???125 and ???115 ka. Combined with published U-series ages from nearby Lanai, the data suggest a long Last Interglacial period that may have occurred from ???136 to at least 115 ka. The results indicate that orbital forcing may not have been the only control on ice sheet growth and decay, because sea level would have been high at times of relatively low Northern Hemisphere summer insolation. On tectonically stable Bermuda, deposits from the ???200 ka (penultimate interglacial period), ???120 ka (peak Last Interglacial period) and ???80 ka (late Last Interglacial period) high sea stands have been newly dated. Fossil corals on Bermuda are derived from patch reefs that likely were "catch-up" responses to sea level rise. It is expected that U-series ages of Last-Interglacial corals on Bermuda should overlap with, but not be as old as the range of corals on Oahu. Last-Interglacial corals on Bermuda give a range of ???125-113 ka, which supports this hypothesis. A large number of emergent marine deposits on Hawaii, Bermuda and along coastal North America have now been dated to the Last Interglacial period. Both Oahu and Bermuda have marine invertebrate faunas with a number of extralimital southern species of mollusks, suggesting warmer-than-present waters during the Last Interglacial period. Warmer waters are also suggested for Last-Interglacial localities around most of North America, from Florida to Canada and Greenland and Baja

  7. European warming linked to Greenland melting during the Last Interglacial North Atlantic climate optimum

    NASA Astrophysics Data System (ADS)

    Sanchez Goni, M.; Michel, E.; Desprat, S.; Carlson, A. E.; Naughton, F.; Fletcher, W. J.; Rossignol, L.

    2010-12-01

    Recent models and data synthesis suggest that the Last Interglacial North Atlantic warm optimum, ~130 ±2 ka, corresponded with a sea level stand of 4-9 m higher than that of the present-day implying that a substantial part of the Greenland Ice Sheet (GIS) melted at that time. This makes this interglacial a good analogue for understanding the impact of the ongoing global warming and GIS melting on the Atlantic Meridional Overturning Circulation (AMOC) and adjacent landmasses. Here we provide new insights on the impact of insolation and AMOC changes on western European ecosystems and climate and their regional transmission during an episode of GIS melting that can be considered somehow similar to that predicted for 2100 C.E. from IPCC projections. We have revisited three pollen-rich western European margin sequences distributed from 37 to 45°N, MD04-2845, MD95-2042 and MD99-2331, which span all of MIS 5 and are directly affected by the descending branch of the North Atlantic Drift. The analysis of these sequences allows us to directly correlate marine tracers of AMOC variability and changes in ice volume, sea surface temperature (SST), iceberg discharges and pollen-derived European vegetation and climate. The comparison of these observations with those inferred from other locations in the North Atlantic region directly affected by the AMOC and records from the Eirik Drift off southern Greenland document the response of North Atlantic climate to GIS melting during the Last Interglacial. Large and rapid increase in the Western European forest cover and mid-latitude North Atlantic SST at the beginning of MIS 5e benthic isotopic plateau following the YD-like event coincide with strong GIS melting. Despite continued GIS melting during this interval, AMOC strength gradually increases. The dramatic expansion of western European forest could be the result of both AMOC and insolation increase. Subsequently sustained warm SSTs and strong AMOC do not preclude the long term

  8. Timing of the Last-Interglacial High Sea Level on the Seychelles Islands, Indian Ocean

    NASA Astrophysics Data System (ADS)

    Israelson, Carsten; Wohlfarth, Barbara

    1999-05-01

    Corals from the Seychelles Islands, Indian Ocean, occur mainly as small coralline algae-vermetid remnants found in cavities adhering to the rock surface, and they rarely attain more than 2 m2in area. Samples ofGoniastreaandPoritesfrom elevations between 1.7 and 6 m above present mean sea level were dated by TIMS238U-234U-230Th techniques. The ages from well-preserved corals lie between 131,000 and 122,000 yr B.P., in agreement with most other observations of the last-interglacial sea level. Field evidence and dating from high marine limestones from two sections at La Digue Island indicate a period of coral buildup until 131,000 yr B.P., followed by a drop in sea level between 131,000 and 122,000 yr B.P.

  9. Glacial/interglacial size variation in fossil spotted hyenas ( Crocuta crocuta) from Britain

    NASA Astrophysics Data System (ADS)

    Klein, Richard G.; Scott, Katharine

    1989-07-01

    The lower carnassial lengths of spotted hyenas ( Crocuta crocuta) in 12 late Pleistocene samples from Britain indicate that, on average, local hyenas of the last (Devensian) glaciation were significantly larger than their last-interglaciation (Ipswichian) counterparts. Together with the tendency for spotted hyena carnassial length to increase with latitude in present-day Africa, this suggests that spotted hyena body size is inversely related to temperature, as predicted by Bergmann's rule. The implication is that spotted hyena carnassial length can be used as an independent gauge of Pleistocene temperature variation, though the combined African and British data imply that the relationship between carnassial length and temperature is curvilinear, such that as temperature declines, equal amounts of further decline produce progressively smaller increases in average carnassial length.

  10. Pacific deep circulation: A velocity increase at the end of the interglacial stage 5?

    NASA Astrophysics Data System (ADS)

    Mangini, A.; Dominik, J.; Müller, P. J.; Stoffers, P.

    1982-12-01

    Re-evaluation of 230Th and 231Pa data on 16 sediment cores recovered in the equatorial North Pacific, between the Clarion-Clipperton Fracture Zone and in the Aitutaki Passage, suggests that a major event modifying the sedimentary regime occurred about 70,000 y B.P. The change is recorded in 12 cores either as the onset of sediment accumulation following a period of sediment erosion or as a remarkable increase in the accumulation rate resulting from enhanced accumulation of redistributed sediment in abyssal plains. Both the onset of sediment accumulation and the enhanced accumulation of redistributed sediment could be attributed to bottom water velocities similar to present ones. Erosion, by contrast, is related to a period of maximum bottom water flow at the boundary of interglacial stage 5 and glacial stage 4.

  11. Ocean biology could control atmospheric δ13C during glacial-interglacial cycle

    NASA Astrophysics Data System (ADS)

    Brovkin, Victor; Hofmann, Matthias; Bendtsen, Jørgen; Ganopolski, Andrey

    2002-05-01

    Estimates of changes in the global carbon budget are often based on the assumption that the terrestrial biosphere controls the isotopic composition of atmospheric CO2 since terrestrial plants discriminate against the 13C isotope during photosynthesis. However, this method disregards the influence of 13C fractionation by the marine biota. Here an interpretation of the glacial-interglacial shifts in the atmospheric CO2 concentration and δ13CO2 measured in the Taylor Dome ice core [Smith et al., 1999] is given by accounting for possible changes in the ocean biology based on sensitivity simulations undertaken with the intermediate complexity model CLIMBER-2. With a combined scenario of enhanced biological and solubility pumps, the model simulates glacial atmospheric CO2 and δ13CO2 similar to those inferred from the ice core. The simulations reveal that a strengthening of the oceanic biological carbon pump considerably affects the atmospheric δ13CO2.

  12. Polarization developments

    SciTech Connect

    Prescott, C.Y.

    1993-07-01

    Recent developments in laser-driven photoemission sources of polarized electrons have made prospects for highly polarized electron beams in a future linear collider very promising. This talk discusses the experiences with the SLC polarized electron source, the recent progress with research into gallium arsenide and strained gallium arsenide as a photocathode material, and the suitability of these cathode materials for a future linear collider based on the parameters of the several linear collider designs that exist.

  13. High-precision U-series dating of Last Interglacial events by mass spectrometry: Houtman Abrolhos Islands, western Australia

    NASA Astrophysics Data System (ADS)

    Zhu, Z. R.; Wyrwoll, K.-H.; Collins, L. B.; Chen, J. H.; Wasserburg, G. J.; Eisenhauer, A.

    1993-07-01

    The Houtman Abrolhos Islands, situated at the western passive margin of the Australian continent, consist of a series of shelf-edge coral reefs. The central platforms of the reefs are Late Pleistocene in age and are generally some 3-5 m above present sea level. The uppermost part of the Last Interglacial reefs normally has an upward-shallowing sequence, consisting of coral framestone, coralline algal bindstone and skeletal grainstone to rudstone. This sequence represents deposition in water depths of less than 2 m, and provides a good indicator of sea level. High-precision mass-spectrometric dates of corals from the Abrolhos reefs, including dates obtained from drill cores, arological, isotopic and stratigraphic criteria are established for the selection of suitable samples for dating and for assessing the reliability of dates. Using the screened dates and the stratigraphic evidence, the timing and character of the sea level variations of the Last Interglacial in the Abrolhos region are examined. The data show that sea level of the Last Interglacial in the Abrolhos was 4 m below its present height by ca. 134 ka BP and probably reached about 2 m above present height at ca. 133 ka BP. The exact time at which sea level reached its peak (6 m above present sea level) cannot be determined from our data. But it is clear that the sea level high stand of the Last Interglacial lasted until ca. 116 ka BP and that for much of the Last Interglacial sea level at the Abrolhos was at a height of about 4 m above its present level.

  14. What caused the glacial/interglacial atmospheric pCO2 cycles?

    NASA Astrophysics Data System (ADS)

    Archer, David; Winguth, Arne; Lea, David; Mahowald, Natalie

    2000-05-01

    Fifteen years after the discovery of major glacial/interglacial cycles in the CO2 concentration of the atmosphere, it seems that all of the simple mechanisms for lowering pCO2 have been eliminated. We use a model of ocean and sediment geochemistry, which includes new developments of iron limitation of biological production at the sea surface and anoxic diagenesis and its effect on CaCO3 preservation in the sediments, to evaluate the current proposals for explaining the glacial/interglacial pCO2 cycles within the context of the ocean carbon cycle. After equilibration with CaCO3 the model is unable to generate glacial pCO2 by increasing ocean NO3- but predicts that a doubling of ocean H4SiO4 might suffice. However, the model is unable to generate a doubling of ocean H4SiO4 by any reasonable changes in SiO2 weathering or production. Our conclusions force us to challenge one or more of the assumptions at the foundations of chemical oceanography. We can abandon the stability of the "Redfield ratio" of nitrogen to phosphorus in living marine phytoplankton and the ultimate limitation of marine photosynthesis by phosphorus. We can challenge the idea that the pH of the deep ocean is held relatively invariant by equilibrium with CaCO3. A third possibility, which challenges physical oceanographers, is that diapycnal mixing in ocean circulation models exceeds the rate of mixing in the real ocean, diminishing the model pCO2 sensitivity to biological carbon uptake.

  15. Reconstructing the last interglacial at Summit, Greenland: Insights from GISP2.

    PubMed

    Yau, Audrey M; Bender, Michael L; Robinson, Alexander; Brook, Edward J

    2016-08-30

    The Eemian (last interglacial, 130-115 ka) was likely the warmest of all interglacials of the last 800 ka, with summer Arctic temperatures 3-5 °C above present. Here, we present improved Eemian climate records from central Greenland, reconstructed from the base of the Greenland Ice Sheet Project 2 (GISP2) ice core. Our record comes from clean, stratigraphically disturbed, and isotopically warm ice from 2,750 to 3,040 m depth. The age of this ice is constrained by measuring CH4 and δ(18)O of O2, and comparing with the historical record of these properties from the North Greenland Ice Core Project (NGRIP) and North Greenland Eemian Ice Drilling (NEEM) ice cores. The δ(18)Oice, δ(15)N of N2, and total air content for samples dating discontinuously from 128 to 115 ka indicate a warming of ∼6 °C between 127-121 ka, and a similar elevation history between GISP2 and NEEM. The reconstructed climate and elevation histories are compared with an ensemble of coupled climate-ice-sheet model simulations of the Greenland ice sheet. Those most consistent with the reconstructed temperatures indicate that the Greenland ice sheet contributed 5.1 m (4.1-6.2 m, 95% credible interval) to global eustatic sea level toward the end of the Eemian. Greenland likely did not contribute to anomalously high sea levels at ∼127 ka, or to a rapid jump in sea level at ∼120 ka. However, several unexplained discrepancies remain between the inferred and simulated histories of temperature and accumulation rate at GISP2 and NEEM, as well as between the climatic reconstructions themselves. PMID:27528680

  16. Neuronal polarization.

    PubMed

    Takano, Tetsuya; Xu, Chundi; Funahashi, Yasuhiro; Namba, Takashi; Kaibuchi, Kozo

    2015-06-15

    Neurons are highly polarized cells with structurally and functionally distinct processes called axons and dendrites. This polarization underlies the directional flow of information in the central nervous system, so the establishment and maintenance of neuronal polarization is crucial for correct development and function. Great progress in our understanding of how neurons establish their polarity has been made through the use of cultured hippocampal neurons, while recent technological advances have enabled in vivo analysis of axon specification and elongation. This short review and accompanying poster highlight recent advances in this fascinating field, with an emphasis on the signaling mechanisms underlying axon and dendrite specification in vitro and in vivo. PMID:26081570

  17. Polarization Aberrations

    NASA Technical Reports Server (NTRS)

    Mcguire, James P., Jr.; Chipman, Russell A.

    1990-01-01

    The analysis of the polarization characteristics displayed by optical systems can be divided into two categories: geometrical and physical. Geometrical analysis calculates the change in polarization of a wavefront between pupils in an optical instrument. Physical analysis propagates the polarized fields wherever the geometrical analysis is not valid, i.e., near the edges of stops, near images, in anisotropic media, etc. Polarization aberration theory provides a starting point for geometrical design and facilitates subsequent optimization. The polarization aberrations described arise from differences in the transmitted (or reflected) amplitudes and phases at interfaces. The polarization aberration matrix (PAM) is calculated for isotropic rotationally symmetric systems through fourth order and includes the interface phase, amplitude, linear diattenuation, and linear retardance aberrations. The exponential form of Jones matrices used are discussed. The PAM in Jones matrix is introduced. The exact calculation of polarization aberrations through polarization ray tracing is described. The report is divided into three sections: I. Rotationally Symmetric Optical Systems; II. Tilted and Decentered Optical Systems; and Polarization Analysis of LIDARs.

  18. Stress and stress relaxation behaviors of multi-layered polarizer structures under a reliability test condition characterized by use of a bending beam technique

    NASA Astrophysics Data System (ADS)

    Lin, Taiy-In; Hsieh, Chih-Yung; Li, I.-Yin; Leu, Jihperng

    2015-04-01

    The bending curvature, stresses, and stress relaxation of various multi-layered structures with different adhesive layers pertaining to the polarizer in a thin-film transistor liquid-crystal display (TFT-LCD) have been successfully characterized by using bending beam technique under reliability test. To be more specific, three different types of pressure-sensitive adhesive (hard-, middle-, and soft-type) and various poly(vinyl alcohol) (PVA) stretched directions are devised to examine to key stress contributors and correlations with light leakage. The shrinkage stress in stretched PVA film and stress relaxation ability of pressure-sensitive adhesives (PSA) layers are found to be the key factors determining the stress distribution and out-of-plane displacement of a polarizer stack. For hard-type PSA, its polarizer stack generates the highest bending curvature with maximum out-of-plane displacement but minimum in-plane displacement, leading to anisotropic stress distribution with high stress around the edges. On the other hand, polarizer stack with soft-type PSA yields the maximum in-plane displacement but the minimum out-of-plane displacement, resulting in isotropic stress distribution.

  19. Polar Bear

    USGS Publications Warehouse

    Amstrup, S.D.; DeMaster

    1988-01-01

    Polar bears are long-lived, late-maturing carnivores that have relatively low rates of reproduction and natural mortality. Their populations are susceptible to disturbance from human activities, such as the exploration and development of mineral resources or hunting. Polar bear populations have been an important renewable resource available to coastal communities throughout the Arctic for thousands of years.

  20. Polarized rainbow.

    PubMed

    Können, G P; de Boer, J H

    1979-06-15

    The Airy theory of the rainbow is extended to polarized light. For both polarization directions a simple analytic expression is obtained for the intensity distribution as a function of the scattering angle in terms of the Airy function and its derivative. This approach is valid at least down to droplet diameters of 0.3 mm in visible light. The degree of polarization of the rainbow is less than expected from geometrical optics; it increases with droplet size. For a droplet diameter >1 mm the locations of the supernumerary rainbows are equal for both polarization directions, but for a diameter <1 mm the supernumerary rainbows of the weaker polarization component are located between those in the strong component. PMID:20212586

  1. Polarization contrast vision

    NASA Astrophysics Data System (ADS)

    Pugh, Edward N.

    1990-05-01

    An attempt is made to establish the possibility that the geometry of certain classes of vertebrate photoreceptors results in a birefringence that allows the animals to utilize the state of polarization of light striking their retinas as a meaningful stimulus parameter. Simulate the photoreceptors as dielectric waveguides using a simple physical model, and augment this theoretical work with empirical measurements of the light guiding properties of photoreceptors in isolated pieces of retina from a green sunfish (Lepomis cyanellus). With a classical conditioning paradigm, this fish's sensitivity to light is modulated by the orientation of the plane of polarization of linearly polarized light. This functional dependence was predicted by a hypothetical antagonistic mechanism between twin cones of two orientations in the animal's retinal mosaic. Further study is planned for the nature of the stimulus to which the fish is sensitive by creating a camera that will generate images based purely upon the contrast between orthogonal polarizations at each point in space.

  2. Solar Wind Influence on the Oxygen Content of Ion Outflow in the High-Altitude Polar Cap During Solar Minimum Conditions

    NASA Technical Reports Server (NTRS)

    Elliott, H. A.; Comfort, R. H.; Craven, P. D.; Chandler, M. O.; Moore, T. E.

    2001-01-01

    We correlate solar wind and interplanetary magnetic field (IMF) properties with the properties of O(+) and H(+) during early 1996 (solar minimum) at altitudes between 5.5 and 8.9 R(sub E) geocentric using the Thermal Ion Dynamics Experiment (TIDE) on the Polar satellite. Throughout the high-altitude polar cap we observe H(+) to be more abundant than O(+). O(+) is found to be more abundant at lower latitudes when the solar wind speed is low (and Kp is low), while at higher solar wind speeds (and high Kp), O(+) is observed across most of the polar cap. The O(+) density and parallel flux are well organized by solar wind dynamic pressure, both increasing with solar wind dynamic pressure. Both the O(+) density and parallel flux have positive correlations with both V(sub SW)B(sub IMF) and E(sub SW). No correlation is found between O(+) density and IMF Bz, although a nonlinear relationship with IMF By is observed, possibly due to a strong linear correlation with the dynamic pressure. H(+) is not as highly correlated with solar wind and IMF parameters, although H(+) density and parallel flux are negatively correlated with IMF By and positively correlated with both V(sub SW)B(sub IMF) and E(sub SW). In this solar minimum data set, H(+) is dominant, so that contributions of this plasma to the plasma sheet would have very low O(+) to H(+) ratios.

  3. INFLUENCE OF THE POLAR CAP CURRENT ON PULSAR POLARIZATION

    SciTech Connect

    Kumar, D.; Gangadhara, R. T. E-mail: ganga@iiap.res.in

    2012-07-20

    We have developed a model for the polarization of curvature radiation by taking into account the polar-cap-current-induced perturbation on the dipolar magnetic field. We present the effects of the polar cap current on the pulsar radio emission in an artificial case when the rotation effects, such as aberration and retardation, are absent. Our model indicates that the intensity components and the polarization angle inflection point can be shifted to either the leading or the trailing side depending upon the prevailing conditions in the viewing geometry, the non-uniformity in source distribution (modulation), and the polar-cap-current-induced perturbation. Also, we find evidence for the origin of symmetric-type circular polarization in addition to the antisymmetric type. Our model predicts a stronger trailing component compared to that on the leading side of a given cone under some specific conditions.

  4. Polar Glaciology

    NASA Technical Reports Server (NTRS)

    Robin, G. D.

    1984-01-01

    Two fields of research on polar ice sheets are likely to be of dominant interest during the 1990s. These are: the role of polar ice sheets in the hydrological cycle ocean-atmosphere-ice sheets-oceans, especially in relation to climate change; and the study and interpretation of material in deep ice cores to provide improved knowledge of past climates and of the varying levels of atmospheric constituents such as CO2, NOx, SO2, aerosols, etc., over the past 200,000 years. Both topics require a better knowledge of ice dynamics. Many of the studies that should be undertaken in polar regions by Earth Observing System require similar instruments and techniques to those used elsewhere over oceans and inland surfaces. However to study polar regions two special requirements need to be met: Earth Observing System satellite(s) need to be in a sufficiently high inclination orbit to cover most of the polar regions. Instruments must also be adapted, often by relatively limited changes, to give satisfactory data over polar ice. The observational requirements for polar ice sheets in the 1990s are summarized.

  5. Late glacial and interglacial sea ice variability in the Arctic Ocean: new insights from proxy and numerical modelling data

    NASA Astrophysics Data System (ADS)

    Müller, Juliane; Wagner, Axel; Stärz, Michael; Stein, Ruediger

    2013-04-01

    The importance of Arctic Ocean sea ice coverage for global climate (change) is widely acknowledged. Due to its high albedo and its capacity to insulate the sea surface from the atmosphere the ice directly impacts on the oceanic and atmospheric heat and moisture balance and thus affects large-scale circulation patterns. At the same time, sea ice displays a sensitive responder to changes in 1) orbital forcing (i.e. insolation), 2) large-scale wind patterns (governing ice drift) and 3) ocean temperature (e.g. due to fluctuations in the Atlantic water advection). Among climate proxies preserved within marine sediments the IP25 sea ice biomarker and the novel PIP25 index derived therefrom seem to be most promising means for sea ice reconstructions in the Arctic (Belt et al., 2007; Müller et al., 2011). The identification of this molecule in marine sediment cores thus enables the assessment of spatial and temporal variations in sea ice coverage through time. Among numerical climate models the high-resolution regional ocean-sea ice model NAOSIM repeatedly has been applied for palaeo sea ice modelling studies (e.g. Stärz et al., 2012). Here we present and discuss biomarker-based sea ice reconstructions with an unusual high temporal resolution covering the past glacial, deglacial and the Holocene climate history of eastern Fram Strait. These proxy results are complemented by model data obtained from NAOSIM. The documentation of changing sea ice conditions that accompanied the transition from the last glacial to interglacial climate mode contributes to the understanding of oceanic and atmospheric driving and feedback mechanisms associated with this large-scale climate shift. Furthermore, the continuous biomarker records from Fram Strait enable the assessment of how fast sea surface conditions (i.e. sea ice cover) responded to climate perturbations. Events of abruptly retreating or advancing sea ice cover as well as long-term trends are observable. Comparison of these proxy

  6. Diatom and Geochemical Constraints on Pliocene Sea Surface Conditions on the Wilkes Land Margin, East Antarctica

    NASA Astrophysics Data System (ADS)

    Riesselman, C. R.; Taylor-Silva, B.

    2015-12-01

    The mid-Pliocene is the most recent interval in Earth's history to sustain global temperatures within the range of warming predicted for the 21st century, providing an appealing analog with which to examine the changes we might encounter in the coming century. Diatom-based Southern Ocean sea surface and sea ice reconstructions by the USGS Pliocene Research Interpretations and Synoptic Mapping (PRISM) Group suggest an average +2° summer SST anomaly during the 3.3-3.0 Ma interval relative to modern. Here, we present a reconstruction of Pliocene sea surface conditions from a marine sediment core collected at IODP Site U1361, on the continental rise of the Wilkes Land margin. U1361 biogenic silica concentrations document the alternation of diatom-rich and diatom-poor lithologies; we interpret 8 diatom-rich mudstones within this sequence to record interglacial conditions between 3.8 and 2.8 Ma, across the transition from obliquity control to precession control on East Antarctic ice volumes. This progression also preserves 3 packages of interglacial sediments within the 3.3-3.0 PRISM interval, providing an opportunity for direct comparison to proximal PRISM site Eltanin 50-28. Diatom assemblages in both cores are characterized by Fragilariopsis barronii and Rouxia antarctica, extinct species with an inferred ecological preference for waters south of the polar front. However F. weaveri, an extinct diatom with inferred preference for more northerly waters and moderate abundance in E50-28, has not been identified at U1361. This may indicate that the polar frontal zone migrated across E50-28 (62° 54'S) but remained north of U1361 (64° 25'S) during the mid-Pliocene. This interpretation is bolstered by the low abundance of extant polar front species (e.g., Thalassiosira oliverana, T. lentiginosa) at U1361; these diatoms dominate the E50-28 assemblage. In contrast, the U1361 assemblage includes a number of extant sea ice indicators (F. sublinearis, F. curta, Chaetoceros

  7. Rapid East Asian Monsoon change during the Last Interglacial in the Bohai Sea Coastal Zone, China

    NASA Astrophysics Data System (ADS)

    Du, S.; Li, B.; Chen, M.; Zhang, D.; Xiang, R.; Niu, D.

    2013-12-01

    The Bohai Sea coastal zone of China faces the Pacific Ocean to the east and the Eurasian continent to the west, hence, this region is influenced by both the ocean and continental landmasses. The Bohai Sea coastal zone has significant monsoon climate characteristics and a strong sensitivity to climate change. The Miaodao stratigraphical section (MDS) contains historical information about climate features in the region, especially the high-frequency variations during the last interglacial, sea level changes, and the evolution of the East Asian monsoon. By analyzing the ages of different sedimentary facies in combination with proxy paleoclimatic indices (i.e., grain <63 μm fraction, average grain size (Mz), clay + silt/sand content (SC/D), magnetic susceptibility, and the ratios of Na2O/Al2O3 and (Al2O3+TOFe)/SiO2, in the fifth segments of the MDS from the last-interglacial (MDS5), we conclude that subsections 5a, 5c, and 5e were controlled by summer monsoons, whereas subsections 5b and 5d were formed when winter monsoons prevailed. These results were similar to oxygen isotope analyses from previous studies including the Spectral Mapping Project (SPECMAP) and the North Greenland Ice Core Project (NorthGRIP). Five and a half comparable oscillations in proxy indices that were dated to ca. 116.1, 118.3, 121.2, 122.7, 125.9, and 128.7 ka occurred within the MDS 5e subsection when winter monsoon winds strengthened. This millennial-scale climate variability during the Eemian period may have reached up to ten and a half oscillations with a quasi-periodicity of approximately a 1,470 year cycle during the late glacial period. This rapid period of climate change has been recorded in northern and central Europe, central Asia, as well as in East Asia. The climate forming mechanism was probably initiated by changes in solar activity, and driven by the East Asian monsoon and sea level oscillations. Comparison of Miaodao section records with other paleoclimatic records during the

  8. Polarizing cues.

    PubMed

    Nicholson, Stephen P

    2012-01-01

    People categorize themselves and others, creating ingroup and outgroup distinctions. In American politics, parties constitute the in- and outgroups, and party leaders hold sway in articulating party positions. A party leader's endorsement of a policy can be persuasive, inducing co-partisans to take the same position. In contrast, a party leader's endorsement may polarize opinion, inducing out-party identifiers to take a contrary position. Using survey experiments from the 2008 presidential election, I examine whether in- and out-party candidate cues—John McCain and Barack Obama—affected partisan opinion. The results indicate that in-party leader cues do not persuade but that out-party leader cues polarize. This finding holds in an experiment featuring President Bush in which his endorsement did not persuade Republicans but it polarized Democrats. Lastly, I compare the effect of party leader cues to party label cues. The results suggest that politicians, not parties, function as polarizing cues. PMID:22400143

  9. Polar motion

    NASA Technical Reports Server (NTRS)

    Kolenkiewicz, R.

    1973-01-01

    Tracking of the Beacon Explorer-C satellite by a precision laser system was used to measure the polar motion and solid earth tide. The tidal perturbation of satellite latitude is plotted as variation in maximum latitude in seconds of arc on earth's surface as a function of the date, and polar motion is shown by plotting the variation in latitude of the laser in seconds of arc along the earth's surface as a function of date

  10. Leeward vs windward effects on glacial/interglacial periplatform aragonite cycles off Pedro Bank and Jamaica (northern Nicaragua rise)

    SciTech Connect

    Glaser, K.S.; Droxler, A.W.; Haddad, G.A. )

    1990-05-01

    Fine (< 62 {mu}m) aragonite content in periplatform sediment from the northern (leeward) and southern (windward) slopes of Pedro Bank shows late Quaternary climate-induced cyclic downcore variations. Intervals characterized by high aragonite content correspond to interglacial stages. The aragonite cycles are clearly developed despite significant windward/leeward differences in sediment sources and composition, pelagic productivity( ), and current regime. Interglacial sedimentation rates on the leeward slope (LS) are nearly twice as high as those on the windward slope (WS), and twice as high as LS glacial sedimentation rates. Carbonate values (75-85%) in sediments deposited on the northern slope of Pedro Bank are higher than those (50-70%) on its southern slope. On both slopes, high carbonate values correspond to interglacial intervals. The lowest carbonate values occur during glacial intervals on the southern slope and are explained by an increase of siliciclastic input from Jamaica during sea level lowstands. This siliciclastic increase could compensate for the drop of bank-derived fine aragonite, and thus, could explain the constant glacial/interglacial sedimentation rates found on the southern slope. In addition, high pteropod abundance during glacial stages along the southern slope may also indicate higher glacial pelagic productivity. Winnowing effects are rather conspicuous in one core from the northern slope within Walton basin (600 m water depth) during glacial intervals, when values of the coarse (> 62 {mu}m) fraction are the highest (the opposite is observed in the other cores). In this relatively shallow core, partial cementation during glacial intervals is also observed.

  11. Rapid sea-level rise and reef back-stepping at the close of the last interglacial highstand.

    PubMed

    Blanchon, Paul; Eisenhauer, Anton; Fietzke, Jan; Liebetrau, Volker

    2009-04-16

    Widespread evidence of a +4-6-m sea-level highstand during the last interglacial period (Marine Isotope Stage 5e) has led to warnings that modern ice sheets will deteriorate owing to global warming and initiate a rise of similar magnitude by ad 2100 (ref. 1). The rate of this projected rise is based on ice-sheet melting simulations and downplays discoveries of more rapid ice loss. Knowing the rate at which sea level reached its highstand during the last interglacial period is fundamental in assessing if such rapid ice-loss processes could lead to future catastrophic sea-level rise. The best direct record of sea level during this highstand comes from well-dated fossil reefs in stable areas. However, this record lacks both reef-crest development up to the full highstand elevation, as inferred from widespread intertidal indicators at +6 m, and a detailed chronology, owing to the difficulty of replicating U-series ages on submillennial timescales. Here we present a complete reef-crest sequence for the last interglacial highstand and its U-series chronology from the stable northeast Yucatán peninsula, Mexico. We find that reef development during the highstand was punctuated by reef-crest demise at +3 m and back-stepping to +6 m. The abrupt demise of the lower-reef crest, but continuous accretion between the lower-lagoonal unit and the upper-reef crest, allows us to infer that this back-stepping occurred on an ecological timescale and was triggered by a 2-3-m jump in sea level. Using strictly reliable (230)Th ages of corals from the upper-reef crest, and improved stratigraphic screening of coral ages from other stable sites, we constrain this jump to have occurred approximately 121 kyr ago and conclude that it supports an episode of ice-sheet instability during the terminal phase of the last interglacial period. PMID:19370032

  12. Simulated Trends in African Glacial and Interglacial Vegetation: Implications for Late-Pleistocene Hominid-Plant Interactions

    NASA Astrophysics Data System (ADS)

    Cowling, S. A.; Cox, P. M.; Jones, C. D.; Maslin, M. A.; Spall, S. A.

    2004-12-01

    Most theories of human evolution in south, central and eastern Africa are predicated on the assumption that savannas and grasslands almost exclusively dominated Pleistocene (glacial) landscapes. It was our aim to evaluate this assumption using a state-of-the-art fully-coupled earth system model (HadCM3LC), which we used to predict potential palaeovegetation following representative glacial and interglacial climate-forcing. Our glacial simulations indicate that tropical broadleaf forest was not severely displaced by grassland expanding into central Africa, although the outer extent of closed forest decreases, particularly in the north. Our vegetation-climate simulations also indicate that the extent of closed tropical forest during typical interglacials is not represented by today's observed vegetation distributions. Simulated interglacial climate results in expansion of tropical forest from coast-to-coast across much of central Africa. Our modelling experiments have implications for interpreting biogeography and phylogenies of various African plant and animal species, including the evolution of our own species, Homo sapiens sapiens.

  13. Influence of former glaciations on interglacial landscape evolution: A case study from the LGM nunatak Hörnli, Eastern Switzerland

    NASA Astrophysics Data System (ADS)

    Buechi, M. W.; Kober, F.; Ivy-Ochs, S.; Kubik, P.

    2012-04-01

    We assess the effect of glaciations on the subsequent interglacial landscape evolution. The Hörnli-area in eastern Switzerland that, in its central parts, was a nunatak during the last glacial maximum (LGM) is an ideal field location to investigate the hypothesized inheritance effects. The proximity of catchments covering the entire range from formerly fully glaciated to not-glaciated, periglacial allows to exclude most other modifying controls on landscape evolution (especially climate, lithology and tectonics). 30 catchments have been studied combining field investigations, GIS-based landscape analysis of a high resolution DEM and catchment-wide denudation rates based on terrestrial cosmogenic 10Be concentration in fluvial quartz sand. Landforms and digitally derived geomorphometrics allow the definition of two distinctly different landscape characters: Rugged, high-relief catchments dominated by fluvial and mass-wasting processes comprising high drainage densities are observed in areas outside the LGM extent. A smooth, low-relief landscape with soil-mantled slopes and low drainage densities is observed in the formerly glaciated areas mainly as the result of glacier erosion, deposition and proglacial lake formation during glacier retreat. This gentle landscape character is contrasted by up to 2.5 km long and 100 m deep incised stream reaches towards the main trunk stream (Thur river). The catchment-wide denudation rates in formerly not-glaciated catchments are around 300 mm/ky, correlated with mean basin slope and in good agreement with results from similar studies in the Northern Alpine foreland (e.g. Wittmann et al., 2007; Norton et al., 2008). In contrast, in the formerly glaciated catchments the average denudation rates measured cluster around 30 mm/ky and are not correlated to any standard morphometric parameter. This finding is surprising as the occurrence of incised gorges is an indicator for strongly transient conditions, i.e. adjustment to base

  14. Polar motion as boundary condition in an adaptive Kalman filter approach for the determination of period and damping of the Chandler oscillation

    NASA Astrophysics Data System (ADS)

    Seitz, F.; Kirschner, S.; Neubersch, D.

    2012-12-01

    Earth rotation has been monitored using space geodetic techniques since many decades. The geophysical interpretation of observed time series of Earth rotation parameters (ERP) polar motion and length-of-day is commonly based on numerical models that describe and balance variations of angular momentum in various subsystems of the Earth. Naturally, models are dependent on geometrical, rheological and physical parameters. Many of these are weakly determined from other models or observations. In our study we present an adaptive Kalman filter approach for the improvement of parameters of the dynamic Earth system model DyMEG which acts as a simulator of ERP. In particular we focus on the improvement of the pole tide Love number k2. In the frame of a sensitivity analysis k2 has been identified as one of the most crucial parameters of DyMEG since it directly influences the modeled Chandler oscillation. At the same time k2 is one of the most uncertain parameters in the model. Our simulations with DyMEG cover a period of 60 years after which a steady state of k2 is reached. The estimate for k2, accounting for the anelastic response of the Earth's mantle and the ocean, is 0.3531 + 0.0030i. We demonstrate that the application of the improved parameter k2 in DyMEG leads to significantly better results for polar motion than the original value taken from the Conventions of the International Earth Rotation and Reference Systems Service (IERS).

  15. Ocean temperature thresholds for Last Interglacial West Antarctic Ice Sheet collapse

    NASA Astrophysics Data System (ADS)

    Sutter, Johannes; Gierz, Paul; Grosfeld, Klaus; Thoma, Malte; Lohmann, Gerrit

    2016-03-01

    The West Antarctic Ice Sheet (WAIS) is considered the major contributor to global sea level rise in the Last Interglacial (LIG) and potentially in the future. Exposed fossil reef terraces suggest sea levels in excess of 7 m in the last warm era, of which probably not much more than 2 m are considered to originate from melting of the Greenland Ice Sheet. We simulate the evolution of the Antarctic Ice Sheet during the LIG with a 3-D thermomechanical ice sheet model forced by an atmosphere-ocean general circulation model (AOGCM). Our results show that high LIG sea levels cannot be reproduced with the atmosphere-ocean forcing delivered by current AOGCMs. However, when taking reconstructed Southern Ocean temperature anomalies of several degrees, sensitivity studies indicate a Southern Ocean temperature anomaly threshold for total WAIS collapse of 2-3°C, accounting for a sea level rise of 3-4 m during the LIG. Potential future Antarctic Ice Sheet dynamics range from a moderate retreat to a complete collapse, depending on rate and amplitude of warming.

  16. Glacial-interglacial changes in central tropical Pacific surface seawater property gradients

    NASA Astrophysics Data System (ADS)

    Lynch-Stieglitz, Jean; Polissar, Pratigya J.; Jacobel, Allison W.; Hovan, Steven A.; Pockalny, Robert A.; Lyle, Mitchell; Murray, Richard W.; Ravelo, A. Christina; Bova, Samantha C.; Dunlea, Ann G.; Ford, Heather L.; Hertzberg, Jennifer E.; Wertman, Christina A.; Maloney, Ashley E.; Shackford, Julia K.; Wejnert, Katherine; Xie, Ruifang C.

    2015-05-01

    Much uncertainty exists about the state of the oceanic and atmospheric circulation in the tropical Pacific over the last glacial cycle. Studies have been hampered by the fact that sediment cores suitable for study were concentrated in the western and eastern parts of the tropical Pacific, with little information from the central tropical Pacific. Here we present information from a suite of sediment cores collected from the Line Islands Ridge in the central tropical Pacific, which show sedimentation rates and stratigraphies suitable for paleoceanographic investigations. Based on the radiocarbon and oxygen isotope measurements on the planktonic foraminifera Globigerinoides ruber, we construct preliminary age models for selected cores and show that the gradient in the oxygen isotope ratio of G. ruber between the equator and 8°N is enhanced during glacial stages relative to interglacial stages. This stronger gradient could reflect enhanced equatorial cooling (perhaps reflecting a stronger Walker circulation) or an enhanced salinity gradient (perhaps reflecting increased rainfall in the central tropical Pacific).

  17. Modelling the Isotopic Response to Antarctic Ice Sheet Change During the Last Interglacial

    NASA Astrophysics Data System (ADS)

    Holloway, Max; Sime, Louise; Singarayer, Joy; Tindall, Julia; Valdes, Paul

    2015-04-01

    Ice sheet changes can exert major control over spatial water isotope variations in Antarctic surface snow. Consequently a significant mass loss or gain of the West Antarctic Ice Sheet (WAIS) would be expected to cause changes in the water isotope record across Antarctic ice core sites. Analysis of sea level indicators for the last interglacial (LIG), around 125 to 128 ka, suggest a global sea level peak 6 to 9 m higher than present. Recent NEEM Greenland ice core results imply that Greenland likely provided a modest ~2m contribution towards this global sea level rise. This implies that a WAIS contribution is necessary to explain the LIG sea level maxima. In addition, Antarctic ice core records suggest that Antarctic air temperatures during the LIG were up to 6°C warmer than present. Climate models have been unable to recreate such warmth when only orbital and greenhouse gas forcing are considered. Thus changes to the Antarctic ice sheet and ocean circulation may be required to reconcile model simulations with ice core data. Here we model the isotopic response to differing WAIS deglaciation scenarios, freshwater hosing, and sea ice configurations using a fully coupled General Circulation Model (GCM) to help interpret Antarctic ice core records over the LIG. This approach can help isolate the contribution of individual processes and feedbacks to final isotopic signals recorded in Antarctic ice cores.

  18. Glacial-interglacial Changes in Ocean Carbon Chemistry constrained by Boron Isotopes, Trace Elements, and Modelling

    NASA Astrophysics Data System (ADS)

    Rae, J. W. B.; Adkins, J. F.; Foreman, A. D.; Charles, C.

    2014-12-01

    Deep ocean carbon storage and release is commonly invoked to explain glacial-interglacial CO2 cycles, but records of the carbonate chemistry of the glacial ocean have, until recently, been scarce. Here we present new boron isotope (δ11B) and trace metal data from benthic foraminifera from a suite of 15 cores from the South Atlantic from depths ranging from 1500 to 4000 m. These records show distinct changes in the water column depth structure of these tracers between the last glacial maximum (LGM) and late Holocene. Comparison of these paired trace element and isotope ratios reveals new insights to the shared and individual controls on tracers including Li/Ca, Sr/Ca, U/Ca, Mg/Li and δ11B. We further examine these data using a recently developed tracer fields modelling approach (Lund et al. 2011). This has previously been applied to δ18O data to investigate changes in circulation at the LGM. Here we extend this method to non-conservative isotopic and trace elemental tracers, allowing us to constrain the roles of circulation, the biological pump of organic carbon and CaCO3, and carbonate compensation, in setting deep ocean carbon storage at the LGM. Lund, D. C., J. F. Adkins, and R. Ferrari (2011), Abyssal Atlantic circulation during the Last Glacial Maximum: Constraining the ratio between transport and vertical mixing, Paleoceanography, 26, PA1213, doi:10.1029/2010PA001938.

  19. Glacial/interglacial ice-stream stability in the Weddell Sea embayment, Antarctica

    NASA Astrophysics Data System (ADS)

    Hein, Andrew S.; Fogwill, Christopher J.; Sugden, David E.; Xu, Sheng

    2011-07-01

    The resilience of the Antarctic Ice Sheet and its effect on global sea level depends on the dynamics of ice streams. Antarctic ice streams are known to be responsive to changes at the ocean interface and, as expected, most have thinned in response to ocean warming and sea-level rise since the Last Glacial Maximum (LGM). Here we provide direct and unexpected evidence that points toward the glacial/interglacial stability of the Slessor and Recovery glaciers, ice streams of the East Antarctic Ice Sheet (EAIS) which merge with the West Antarctic Ice Sheet (WAIS) to form the Filchner Ice Shelf in the Weddell Sea embayment. Cosmogenic-nuclide measurements in the Shackleton Range suggest that the Slessor and Recovery ice streams were not significantly thicker than today during the LGM. We hypothesise that the glaciers did not thicken because the grounding line was not able to migrate seaward beyond the deep Thiel/Crary Trough beneath the Filchner Ice Shelf immediately offshore. This discovery reveals how a topographic threshold can affect the dynamics of ice streams. It also reduces uncertainties on the thickness, extent and volume of the Antarctic Ice Sheet in a large but unknown sector of the Antarctic Ice Sheet; it constrains the potential sea-level rise from Antarctica; it helps explain observed anomalies in glacio-isostatic adjustment; above all it suggests that the behaviour of the Atlantic-facing Weddell Sea sector of the WAIS contrasts with that of the Pacific-facing Ross and Amundsen Sea sectors.

  20. Subsurface geology of Kansai International Airport: sequence related to global glacial - interglacial cycles and island tectonics

    NASA Astrophysics Data System (ADS)

    Takemura, K.; Kitada, N.; Furudoi, T.; Nakaseko, K.

    2007-12-01

    Tectonic sedimentary basins aligned in the central part of Japan during Quaternary . Thick sediments deposited in these basins provide useful records of climatic changes and tectonics throughout Quaternary. The Osaka sedimentary basin including Osaka Bay and area of Kansai International Airport is one of them. The Quaternary Osaka sedimentary basin has developed at an eastern contractional bend of a major transcurrent fault system named the Median Tectonic Line, which divides the southwest Japan arc. The thickness of Pliocene - Pleistocene sediments reaches to ca 3500m at the deepest part. These sequences are called the Osaka Group and are distributed in the Osaka Bay and exposed in the surrounding mountain areas. The Osaka Group is characterized by alternating sequences of marine and nonmarine strata. The subsurface sediments of Kansai International Airport (KIA) is composed mainly of Pliocene - Pleistocene sediments, which is characterized by alternating sequences of marine and nonmarine strata related to glacial - interglacial cycles. . The stratigraphy at KIA was established by micropaleontological, tephrochronological and magnetostratigraphical method. The sedimentary sequence at KIX is divided into two main units (Kukojima and Sennanoki Formations in ascending order) with the uncomformity within two units. Although thick marine clay units are mainly of the subsurface sequence, characteristics of coarser sediment units have an important role of moving of water during construction of the reclaimed land.

  1. Sea-level highstands during the Last interglacial (MIS 5e) in Mallorca

    NASA Astrophysics Data System (ADS)

    Lorscheid, T.; Stocchi, P.; Rovere, A.; Gómez-Pujol, L.; Mann, T.; Fornos, J. J.

    2015-12-01

    Last Intergalcial in the island of Mallorca (NW Mediterranean) have been the subject of research since the early 60's (Butzer & Cuerda 1960). Despite both the location and stratigraphy of MIS 5e outcrops in the island are well known, the elevation of relative sea level (RSL) markers around the island has never been measured with high-accuracy topographic techniques (e.g. DGPS) and the interpretation of the paleo RSL has never been carried out using standardized definition of the indicative meaning of each RSL marker. In this study we present the results of two field trips aimed at measuring last interglacial deposits in Mallorca with high-accuracy GPS and at establishing, surveying modern shorelines as analogs, indicative ranges and reference water level values for RSL markers across the island. Using an earth-ice coupled GIA-model we performed several model-runs for investigating isostatic adjustment since MIS 5e in the island. These results are compared with the elevation of our deposits in the field and discussed in terms of tectonics and eustasy.

  2. Estimating the sea level highstand during the last interglacial: a probabilistic massive ensemble approach

    NASA Astrophysics Data System (ADS)

    Düsterhus, André; Tamisiea, Mark E.; Jevrejeva, Svetlana

    2016-08-01

    Essential to understanding sea level change and its causes during the last interglacial (LIG) is the quantification of uncertainties. In order to estimate the uncertainties, we develop a statistical framework for the comparison of palaeoclimatic sea level index points and GIA model predictions. For the investigation of uncertainties, as well as to generate better model predictions, we implement a massive ensemble approach by applying a data assimilation scheme based on particle filter methods. The different runs are distinguished through varying ice sheet reconstructions based on oxygen-isotope curves and different parameter selections within the GIA model. This framework has several advantages over earlier work, such as the ability to examine either the contribution of individual observations to the results or the probability of specific input parameters. This exploration of input parameters and data leads to a larger range of estimates than previously published work. We illustrate how the assumptions that enter into the statistical analysis, such as the existence of outliers in the observational database or the initial ice volume history, can introduce large variations to the estimate of the maximum highstand. Thus, caution is required to avoid overinterpreting results. We conclude that there are reasonable doubts whether the data sets previously used in statistical analyses are able to tightly constrain the value of maximum highstand during the LIG.

  3. Pumice in the interglacial Whidbey Formation at Blowers Bluff, central Whidbey Island, WA, USA

    USGS Publications Warehouse

    Dethier, D.P.; Dragovich, J.D.; Sarna-Wojcicki, A. M.; Fleck, R.J.

    2008-01-01

    A new 40Ar/39Ar age of 128??9 ka and chemical analyses of pumice layers from interglacial alluvium at Blowers Bluff, Whidbey Island, WA, show that the deposits are part of the Whidbey Formation, a widespread, mainly subsurface unit. Glass chemistry of the dated dacitic pumice does not match any analyzed northern Cascade source, but upper Pleistocene dacites from Glacier Peak and early Pleistocene silicic rocks from the Kulshan caldera are chemically similar. The chemistry of pumiceous dacite in younger units, including the latest Pleistocene Partridge Gravel, is similar to that of the dated material. The deep troughs of the modern northern Puget lowland must have been filled during deposition of the Whidbey Formation, allowing volcanic-rich sediment to reach what is now Whidbey Island. Topographic analysis of LIDAR images demonstrates that extensive erosion occurred during latest Pleistocene ice retreat. The Partridge Gravel likely records subglacial fluvial erosion along an ice tunnel and ice-marginal deposition into adjacent marine waters. Pumice in the Partridge Gravel probably was reworked from stratigraphically and topographically lower deposits, including those at Blowers Bluff. ?? 2007 Elsevier Ltd and INQUA.

  4. Precise timing of the last interglacial period from mass spectrometric determination of thorium-230 in corals

    SciTech Connect

    Edwards, R.L.; Chen, J.H.; Ku, T.L.; Wasserburg, G.J.

    1987-06-19

    The development of mass spectrometric techniques for determination of STTh abundance has made it possible to reduce analytical errors in STYU-STUU-STTh dating of corals even with very small samples. Samples of 6 x 10Y atoms of STTh can be measured to an accuracy of +/- 3% (2sigma) and 3 x 10 atoms of STTh can be measured to an accuracy of +/- 0.2%. The time range over which useful age data on corals can be obtained now ranges from about 50 to about 500,000 years. For young corals, this approach may be preferable to UC dating. The precision should make it possible to critically test the Milankovitch hypothesis concerning Pleistocene climate fluctuations. Analyses of a number of corals that grew during the last interglacial period yield ages of 122,000 to 130,000 years. The ages coincide with, or slightly postdate, the summer solar insolation high at 65N latitude which occurred 128,000 years ago. This supports the idea that changes in Pleistocene climate can be the result of variations in the distribution of solar insolation caused by changes in the geometry of the earth's orbit and rotation axis.

  5. Precise timing of the last interglacial period from mass spectrometric determination of thorium-230 in corals

    NASA Technical Reports Server (NTRS)

    Chen, J. H.; Wasserburg, G. J.; Ku, T.-L.; Edwards, R. Lawrence

    1987-01-01

    The development of mass spectrometric techniques for determination of Th-230 abundance has made it possible to reduce analytical errors in (U-238)-(U-234)-(Th-230) dating of corals even with very small samples. Samples of 6 x 10 to the 8th atoms of Th-230 can be measured to an accuracy of + or - 3 percent (2sigma), and 3 x 10 to the 10th atoms of Th-230 can be measured to an accuracy of + or - 0.2 percent. The time range over which useful age data on corals can be obtained now ranges from about 50 to about 500,000 years. For young corals, this approach may be preferable to C-14 dating. The precision with which the age of a coral can now be determined should make it possible to critically test the Milankovitch hypothesis concerning Pleistocene climate fluctuations. Analyses of a number of corals that grew during the last interglacial period yield ages of 122,000 to 130,000 years. The ages coincide with, or slightly post-date, the summer solar insolation high at 65 deg N latitude which occurred 128,000 years ago. This supports the idea that changes in Pleistocene climate can be the result of variations in the distribution of solar insolation caused by changes in the geometry of the earth's orbit and rotation axis.

  6. The last glacial-interglacial transition and dinoflagellate cysts in the western Mediterranean Sea

    NASA Astrophysics Data System (ADS)

    Rouis-Zargouni, Imene; Turon, Jean-Louis; Londeix, Laurent; Kallel, Néjib; Essallami, Latifa

    2012-02-01

    Using the analysis of dinoflagellate cysts in three deep-sea sediments cores situated in the Sicilian-Tunisian Strait, in the Gulf of Lions and in the Alboran Sea, we reconstruct the paleoenvironmental changes that took place during the last glacial-interglacial transition in the western Mediterranean Sea. The development of the warm microflora Impagidinium aculeatum and especially Spiniferites mirabilis appears to be an important proxy for recognizing warm periods as the Bölling/Alleröd and the Early Holocene. Bitectatodinium tepikiense, Spiniferites elongatus and Nematosphaeropsis labyrinthus mark the end of the Heinrich event 1 and the Younger Dryas. This cold microfloral association confirms the drastic climate changes in the western Mediterranean Sea synchronous to the dry and cold climate which occurred in the South European margin. The dinocyst N. labyrinthus shows high percentages in all studied regions during the Younger Dryas. Its distribution reveals a significant increase from the South to the North of this basin during this cold brief event. Thus, we note that this species can be considered as a new eco-stratigraphical tracer of the Younger Dryas in the western Mediterranean Sea.

  7. Sea surface temperature and salinity patterns in the northern North Atlantic and the Arctic during interglacial MIS 11c: Implications for oceanic circulation reconstruction

    NASA Astrophysics Data System (ADS)

    Kandiano, E.; van der Meer, M.; Schouten, S.; Fahl, K.; Polyak, L. V.; Cronin, T. M.; Bauch, H. A.; Sinninghe Damste, J. S.

    2013-12-01

    Sea surface temperature (SST) patterns in the northern North Atlantic, the Nordic seas, and the western Arctic Ocean (AO) were reconstructed across the MIS 11c interglacial, a potential future climate analogue, using planktic foraminiferal abundances, alkenone-based Uk'37 and glycerol dialkyl glycerol tetraether (GDGT)-based TEX86 analyses. Foraminiferal SST reconstructions were supported by foraminiferal counts of small-sized fractions and rare foraminiferal species, stable oxygen isotope measurements on benthic and planktic foraminifers, and ice rafted debris records. Additionally, the hydrogen isotopic (δD) compositions of long chain alkenones were determined to assess variations in paleo sea surface salinity in the North Atlantic. In the North Atlantic our newly produced TEX86 -based SSTs range between 14 and 19 °C in agreement with summer foraminiferal SST (13 and 18 °C) and alkenone SSTs (13 and 16 °C). However, the former showed higher fluctuations than SSTs based on foraminiferal abundances. In concordance with δ18O records TEX86 SSTs demonstrate notable variability in the middle of MIS 11c, between 400 and 410 ka, which is consistent with the intra-MIS 11c cold event in the Arctic indicated by planktic foraminifers. This pattern implies that the interglacial MIC 11c climate was probably not as stable as it widely believed. The preliminary alkenone δD data show that during MIS 11c salinity values in the North Atlantic were similar to Holocene values. Foraminiferal SST records imply that during MIS 11c at least parts of the AO experienced unusually warm and probably ice free conditions, whereas the Nordic seas remained rather cold, especially during the early phase of this period, as it is inferred from foraminiferal and alkenone SSTs. At the same time all our SST records show that the North Atlantic was 1-2°C warmer than present during MIS 11c. This pattern suggests that during MIS 11c the North Atlantic Current was deflected to the west, which

  8. Variability of surface water dynamics during eccentricity minima interglacials of the last 1 Myr in the North Atlantic

    NASA Astrophysics Data System (ADS)

    Palumbo, Eliana; Emanuele, Dario; Ferretti, Patrizia; Flores, José-Abel; Perugia, Carmen; Petrillo, Zaccaria; Ornella Amore, Filomena

    2014-05-01

    Eccentricity minima occurred only three times during the last 1 Myr in correspondence of Marine Isotope Stages (MIS) 1 (last 11 ka), 11 (425-360 ka) and 19 (791-763 ka). All these stages are characterised by similar orbital configurations and the Pleistocene eccentricity minima interglacials are considered, by several authors, as possible analogues for the Holocene and its future evolution. Surface water dynamics were reconstructed through quantitative analyses performed on coccolithophore assemblages in two key-sites of the North Atlantic: MD03-2699 core, retrieved off Iberian Margin (IM), and IODP Site U1313, located in the upper western flank of the Mid-Atlantic Ridge. Nowadays, IODP Site U1313 is under the influence of a northern ramification of the Gulf Stream, the North Atlantic Current (NAC). This current forms a transitional zone between the productive cold polar system and the oligotrophic warm subtropical system. In addition, the NAC represents the northern boundary of the Portugal Current (PC) system which influences the modern surface oceanography off the IM at MD03-2699 site. Coccolithophore data were carried out by sediments of MD03-2699 core for MIS 11 and MIS 1(Amore et al., 2012; Palumbo et al., 2013a,b) and by IODP Site U1313 for MIS 19 (Emanuele, 2013). The mean sampling resolution for MIS 1 is 140 yrs, for MIS 11 about 400 yrs and for MIS 19 about 220 yrs. The high samples resolution allowed reconstructing long term changes at orbital timescale as well as rapid changes at millennial scale. Data from coccolithophore assemblages were compared with available proxy for the studied cores such as alkenones, lithics, oxygen and carbon isotopes. Coccolithophores belong to phytoplankton group and they are widely used as proxy of surface water dynamics thanks to their attitude to record the smallest paleoclimatic changes and because they directly depend on sea surface temperature and salinity, sunlight and availability of nutrients. Through the use of

  9. Enhanced transcytosis of R5-tropic human immunodeficiency virus across tight monolayer of polarized human endometrial cells under pro-inflammatory conditions.

    PubMed

    Carreno, Marie-Paule; Krieff, Corrine; Irinopoulou, Theano; Kazatchkine, Michel D; Belec, Laurent

    2002-12-21

    Most cases of human immunodeficiency virus (HIV) infection worldwide occur following sexual contact, implying that the virus may breach the protective epithelial barrier lining the genital tract. HIV infection is known to preferentially occur when the genital epithelial integrity is altered, particularly when epithelial micro-ulcerations occur during heterosexual intercourse or ulcerations appear, due to sexually transmitted infections or else in the context of ectopy of the endocervical mucosa, which may leave the genital tissue. We report that R5-tropic infectious HIV-1 isolates are capable of in vitro transcytosis through a tight and polarized monolayer of human endometrial HEC-1 cells. Transcytosis of HIV particles was increased 2-fold within a pro-inflammatory micro-environment. Our findings suggest that transcytosis may be a relevant mechanism for the passage of virus through the genital mucosa in vivo, particularly when inflammatory cells and mediators are present in the vicinity of the mucosal surface. PMID:12633571

  10. Glacial-Interglacial, Orbital and Millennial-Scale Climate Variability for the Last Glacial Cycle at Shackleton Site U1385 based on Dinoflagellate Cysts

    NASA Astrophysics Data System (ADS)

    Datema, M.

    2015-12-01

    The Shackleton Site (IODP Expedition 339 Site U1385), located off the West-Portuguese Margin, preserves a continuous high-fidelity record of millennial-scale climate variability for the last several glacial cycles (~1.4 Myr) that can be correlated precisely to patterns observed in polar ice cores. In addition, rapid delivery of terrestrial material to the deep-sea environment allows the correlation of these marine records to European terrestrial climate records. This unique marine-ice-terrestrial linkage makes the Shackleton Site the ideal reference section for studying Quaternary abrupt climate change. The main objective of studying Site U1385 is to establish a marine reference section of Pleistocene climate change. We generated (sub)millennial-scale (~600 year interval) dinoflagellate cyst (dinocyst) assemblage records from Shackleton Site U1385 (IODP Expedition 339) to reconstruct sea surface temperature (SST) and productivity/upwelling over the last 152 kyrs. In addition, our approach allows for detailed land-sea correlations, because we also counted assemblages of pollen and spores from higher plants. Dinocyst SST and upwelling proxies, as well as warm/cold pollen proxies from Site U1385 show glacial-interglacial, orbital and stadial-interstadial climate variability and correlate very well to Uk'37, planktic foraminifer δ18O and Ca/Ti proxies of previously drilled Shackleton Sites and Greenland Ice Core δ18O. The palynological proxies capture (almost) all Dansgaard-Oeschger events of the last glacial cycle, also before ~70 ka, where millennial-scale variability is overprinted by precession. We compare the performance and results of the palynology of Site U1385 to proxies of previously drilled Shackleton Sites and conclude that palynology strengthens the potential of this site to form a multi-proxy reference section for millennial scale climate variability across the Pleistocene-Holocene. Finally, we will present a long-term paleoceanographic perspective down

  11. Periodic isolation of the southern coastal plain of South Africa and the evolution of modern humans over late Quaternary glacial to interglacial cycles

    NASA Astrophysics Data System (ADS)

    Compton, J. S.

    2012-04-01

    Humans evolved in Africa, but where in Africa and by what mechanisms remain unclear. The evolution of modern humans over the last million years is associated with the onset of major global climate fluctuations, glacial to interglacial cycles, related to the build up and melting of large ice sheets in the Northern Hemisphere. During interglacial periods, such as today, warm and wet climates favored human expansion but during cold and dry glacial periods conditions were harsh and habitats fragmented. These large climate fluctuations periodically expanded and contracted African ecosystems and led to human migrations to more hospitable glacial refugia. Periodic isolation of relatively small numbers of humans may have allowed for their rapid evolutionary divergence from the rest of Africa. During climate transitions these divergent groups may have then dispersed and interbred with other groups (hybridization). Two areas at the opposite ends of Africa stand out as regions that were periodically isolated from the rest of Africa: North Africa (the Maghreb) and the southern coastal plain (SCP) of South Africa. The Maghreb is isolated by the Sahara Desert which periodically greens and is reconnected to the rest of Africa during the transition from glacial to interglacial periods. The SCP of South Africa is isolated from the rest of Africa by the rugged mountains of the Cape Fold Belt associated with inedible vegetation and dry climates to the north. The SCP is periodically opened when sea level falls by up to 130 m during glacial maxima to expose the present day submerged inner continental shelf. A five-fold expansion of the SCP receiving more rainfall in glacial periods may have served as a refuge to humans and large migratory herds. The expansive glacial SCP habitat abruptly contracts, by as much as one-third in 300 yr, during the rapid rise in sea level associated with glacial terminations. Rapid flooding may have increased population density and competition on the SCP to

  12. Genera variation of tropical mid-upper montane rainforest inferred from a marine pollen record in southern Philippines during the glacial-interglacial cycle

    NASA Astrophysics Data System (ADS)

    Bian, Y.

    2015-12-01

    Tropical vegetation is the most outstanding and obvious feature of South-East Asia, and it is expected to provide valuable information for the palaeoclmatic conditions. Pollen records from the tropical West Pacific indicate that the tropical vegetation is much sensitive to the environment and climate change, and their good correspondence with palaeocliamte change in glacial/interglacial timescales. It is shown that the range of the tropical montane rainforest was affected by the temperature change during the glacial cycle. But, from some marine core, the genera variation of tropical mid-upper montane pollen record is also distinct during the glacial cycle. In this study, examination of the pollen content of marine core MD06-3075 taken from Davao Gulf in the Southern Philippines reveals a ~116,000 year record of tropical vegetation change as well as the influence of the environment and climate variability on the ecosystem of the tropical area. Chronology was determined by 16 AMS 14C dates and a detailed oxygen isotope record. A high representation of pollen from tropical upper montane rainforest (mainly Podocarpus) (40-60%) during the last glacial period indicates that this forest type extended to lower attitudes. And the genera variations of the tropical mid-upper montane rainforest exist between the Phyllocladus and Podocarpus with the environment and climate changing. The pollen content of Phyllocladus is much high in marine isotope stage (MIS) 5, but Podocarpus is much higher in the glacial period. During the onset of MIS 5a and 5c, the percentage of Phyllocladus pollen declines dramatically. Vegetation investigation in Mindanao, shows that Podocarpus exists in altitude ranging from 1,200-1,700 m, and Phyllocladus appear in altitude range from 1700-2100 m, but is more abundant above the 2,400 m. Thus, Phyllocladus might be more sensitive to the temperature change. Then, in this study, the pollen content of is much high during the interglacial period

  13. Climatic control of sediment transport from the Himalayas to the proximal NE Bengal Fan during the last glacial-interglacial cycle

    NASA Astrophysics Data System (ADS)

    Joussain, Ronan; Colin, Christophe; Liu, Zhifei; Meynadier, Laure; Fournier, Léa; Fauquembergue, Kelly; Zaragosi, Sébastien; Schmidt, Frédéric; Rojas, Virginia; Bassinot, Franck

    2016-09-01

    Clay mineralogy, siliciclastic grain-size, major elements, 87Sr/86Sr, and εNd analyses of deep-sea sediments cored in the north-eastern Bay of Bengal are used to reconstruct evolution of detrital sources and sediment transport to the proximal part of the Bengal deep-sea fan during the last climatic cycle. εNd values (-13.3 to -9.7) and 87Sr/86Sr ratios (0.721-0.733) indicate a mixture of sediments originating from the Ganges-Brahmaputra rivers and the Indo-Burman ranges. Interglacial Marine Isotopic Stages (MIS) 5 and 1 are associated with a higher contribution of sediments from the Ganges-Brahmaputra river system than is the case for glacial MIS 6, 4, 3, and 2. Siliciclasitic grain-size combined with Si/Al and Si/Fe ratios indicate coarser glacial sediments with numerous turbidite layers. Glacial turbidite layers display similar clay mineralogical compositions to hemipelagic sediments. Only few of turbidite layers (MIS 6, 4, and 2) are slightly unradiogenic (εNd -13.3), suggesting a higher contribution of Ganges-Brahmaputra river sediments. Independently of changes in the sedimentary sources, the smectite/(illite + chlorite) ratio of cores located on the NE Bengal Fan indicates higher inputs of primary minerals (illite and chlorite) from the highlands of the river basins (relief) during glacial MIS 6, 4, 3, and 2 and an increased contribution of pedogenic minerals (smectite and kaolinite) during interglacial MIS 5 and 1. Maximum smectite/(illite + chlorite) ratios during the warm sub-stages of MIS 5 suggest an intensification of summer monsoon rainfall associated with higher rates of physical erosion of the Indo-Gangetic flood-plain and/or dominant summer hydrological conditions transporting a higher proportion of sediments deriving from the Ganges-Brahmaputra rivers to the NE Bengal Fan. In addition, a higher production of smectite in soils of the Indo-Gangetic flood-plain during periods of intensification of monsoon rainfall cannot be excluded.

  14. Polar Stratigraphy

    NASA Technical Reports Server (NTRS)

    1999-01-01

    These three images were taken on three different orbits over the north polar cap in April 1999. Each shows a different part of the same ice-free trough. The left and right images are separated by a distance of more than 100 kilometers (62 miles). Note the similar layers in each image.

  15. Political polarization

    PubMed Central

    Dixit, Avinash K.; Weibull, Jörgen W.

    2007-01-01

    Failures of government policies often provoke opposite reactions from citizens; some call for a reversal of the policy, whereas others favor its continuation in stronger form. We offer an explanation of such polarization, based on a natural bimodality of preferences in political and economic contexts and consistent with Bayesian rationality. PMID:17452633

  16. Sea-level history of the past two interglacial periods: new evidence from U-series dating of reef corals from south Florida

    NASA Astrophysics Data System (ADS)

    Muhs, Daniel R.; Simmons, Kathleen R.; Schumann, R. Randall; Halley, Robert B.

    2011-03-01

    As a future warm-climate analog, much attention has been directed to studies of the Last Interglacial period or marine isotope substage (MIS) 5.5, which occurred ˜120,000 years ago. Nevertheless, there are still uncertainties with respect to its duration, warmth and magnitude of sea-level rise. Here we present new data from tectonically stable peninsular Florida and the Florida Keys that provide estimates of the timing and magnitude of sea-level rise during the Last Interglacial period. The Last Interglacial high sea stand in south Florida is recorded by the Key Largo Limestone, a fossil reef complex, and the Miami Limestone, an oolitic marine sediment. Thirty-five new, high-precision, uranium-series ages of fossil corals from the Key Largo Limestone indicate that sea level was significantly above present for at least 9000 years during the Last Interglacial period, and possibly longer. Ooids from the Miami Limestone show open-system histories with respect to U-series dating, but show a clear linear trend toward an age of ˜120 ka, correlating this unit with the Last Interglacial corals of the Key Largo Limestone. Older fossil reefs at three localities in the Florida Keys have ages of ˜200 ka and probably correlate to MIS 7. These reefs imply sea level near or slightly above present during the penultimate interglacial period. Elevation measurements of both the Key Largo Limestone and the Miami Limestone indicate that local (relative) sea level was at least 6.6 m, and possibly as much as 8.3 m higher than present during the Last Interglacial period.

  17. Sea-level history of the past two interglacial periods: New evidence from U-series dating of reef corals from south Florida

    USGS Publications Warehouse

    Muhs, D.R.; Simmons, K.R.; Schumann, R.R.; Halley, R.B.

    2011-01-01

    As a future warm-climate analog, much attention has been directed to studies of the Last Interglacial period or marine isotope substage (MIS) 5.5, which occurred ???120,000 years ago. Nevertheless, there are still uncertainties with respect to its duration, warmth and magnitude of sea-level rise. Here we present new data from tectonically stable peninsular Florida and the Florida Keys that provide estimates of the timing and magnitude of sea-level rise during the Last Interglacial period. The Last Interglacial high sea stand in south Florida is recorded by the Key Largo Limestone, a fossil reef complex, and the Miami Limestone, an oolitic marine sediment. Thirty-five new, high-precision, uranium-series ages of fossil corals from the Key Largo Limestone indicate that sea level was significantly above present for at least 9000 years during the Last Interglacial period, and possibly longer. Ooids from the Miami Limestone show open-system histories with respect to U-series dating, but show a clear linear trend toward an age of ???120 ka, correlating this unit with the Last Interglacial corals of the Key Largo Limestone. Older fossil reefs at three localities in the Florida Keys have ages of ???200 ka and probably correlate to MIS 7. These reefs imply sea level near or slightly above present during the penultimate interglacial period. Elevation measurements of both the Key Largo Limestone and the Miami Limestone indicate that local (relative) sea level was at least 6.6 m, and possibly as much as 8.3 m higher than present during the Last Interglacial period. ?? 2010.

  18. Quercus suber range dynamics by ecological niche modelling: from the Last Interglacial to present time

    NASA Astrophysics Data System (ADS)

    Vessella, Federico; Simeone, Marco Cosimo; Schirone, Bartolomeo

    2015-07-01

    Ecological Niche Modelling (ENM) is widely used to depict species potential occurrence according to environmental variables under different climatic scenarios. We tested the ENM approach to infer past range dynamics of cork oak, a keystone species of the Mediterranean Biome, from 130 ka to the present time. Hindcasting implications would deal with a better species risk assessment and conservation management for the future. We modelled present and past occurrence of cork oak using seven ENM algorithms, starting from 63,733 spatially unique presence points at 30 arc-second resolution. Fourteen environmental variables were used and four time slices were considered (Last Interglacial, Last Glacial Maximum, mid-Holocene and present time). A threshold-independent evaluation of the goodness-of-fit of the models was evaluated by means of ROC curve and fossil or historical evidences were used to validate the results. Four weighted average maps depicted the dynamics of area suitability for cork oak in the last 130 ka. The derived species autoecology allowed its long-term occurrence in the Mediterranean without striking range reduction or shifting. Fossil and historical post-processing validation support the modelled past spatial extension and a neglected species presence at Levantine until the recent time. Despite the severe climatic oscillation since the Last Glacial Maximum, cork oak potential distribution area experienced limited range changes, confirming its strong link with the Mediterranean Basin. The ecological amplitude of Quercus suber could be therefore adopted as a reference to trace the Mediterranean bioclimate area. A better knowledge of the past events of Mediterranean vegetation, a wider range of study species and environmental determinants are essential to inform us about its current state, its sensitivity to human impact and the potential responses to future changes.

  19. Relative sea-level fall since the last interglacial stage: Are coasts uplifting worldwide?

    NASA Astrophysics Data System (ADS)

    Pedoja, Kevin; Husson, Laurent; Regard, Vincent; Cobbold, Peter Robert; Ostanciaux, Emilie; Johnson, Markes E.; Kershaw, Stephen; Saillard, Marianne; Martinod, Joseph; Furgerot, Lucille; Weill, Pierre; Delcaillau, Bernard

    2011-09-01

    The growing interest in quantification of vertical ground motion stems from the need to understand in detail how the Earth's crust behaves, for both scientific and social reasons. However, only recently has the refinement of dating techniques made possible the use of paleoshorelines as reliable tools for tectonic studies. Although there are many local studies of Quaternary vertical motions of coastlines, we know of no comprehensive worldwide synthesis. Here we provide a compilation of 890 records of paleoshoreline sequences, with particular emphasis on the last interglacial stage (Marine Isotopic Stage [MIS] 5e, ~ 122 ka). The quality of dating MIS 5e makes it a reliable marker to evaluate vertical ground motion rates during the late Quaternary on a global scale. The results show that most coastal segments have risen relative to sea-level with a mean uplift rate higher than 0.2 mm/yr, i.e. more than four times faster than the estimated eustatic drop in sea level. The results also reveal that the uplift rate is faster on average for active margins than for passive margins. Neither dynamic topography nor glacio-hydro-isostasy may explain sustained uplift of all continental margins, as revealed by the wide distribution of uplifted sequences of paleoshorelines. Instead, we suggest that only plate-tectonic processes reconcile all observations of Quaternary coastal uplift. We propose that long-term continental accretion has led to compression of continental plates and uplift of their margins. Therefore this study concludes that plate-tectonics processes impact all margins and emphasizes the fact that the notion of a stable platform is unrealistic. These results therefore seriously challenge the evaluation of past sea levels from the fossil shoreline record.

  20. Continental shelf landscapes of the southeastern United States since the last interglacial

    NASA Astrophysics Data System (ADS)

    Harris, M. Scott; Sautter, Leslie Reynolds; Johnson, Kacey L.; Luciano, Katherine E.; Sedberry, George R.; Wright, Eric E.; Siuda, Amy N. S.

    2013-12-01

    The wide, sediment-starved continental shelf and modern coastal areas of the southeastern United States retain well-preserved but scattered remnants of a submerged paleolandscape. This paper presents a conceptual model of stratigraphic deposition and landscape formation since the last interglacial on the continental shelf of South Carolina, with portions of North Carolina, Georgia, and Florida (USA). Data for this study include multibeam bathymetry surveys, sidescan sonar mosaics, high-resolution subbottom profiles, and ground-truth surveys from - 250 m to the modern tidewater region. Four bathymetric zones are recognized with eleven landforms and landform indicators. The described zones range in depths from the modern shoreline, across the shelf, and over the shelf edge to - 250 m MSL. Relative sea level curves are presented for the area and discussed in conjunction with cultural and climatic events. The potential for preservation of Paleoamerican sites is high at the shelf edge between - 130 m and - 45 m, with Archaic and later occupations likely in depths of less than - 25 m. Prominent vantage points for Paleoamericans (> 11 kya) would have existed at the shelf edge, and tidewater resources would have been available nearby for a period of almost 6 ka. Rapid transgression rates (> 60 km/ka) after the sea level rose over the shelf edge make preservation of tidewater sites less likely on the outer and middle shelf. Searches for the earliest Paleoamericans should focus on promontories at the edge of the shelf and along future discoveries of paleoincisions on the shelf. Mapping and delineating this paleolandscape and associated unconsolidated sedimentary deposits interspersed with rocky plains and ledges will continue to be a priority to marine archeologists, coastal managers, fishery scientists, and marine spatial planners over the next several decades.

  1. Quantifying rates of coastal subsidence since the last interglacial and the role of sediment loading

    NASA Astrophysics Data System (ADS)

    Simms, Alexander R.; Anderson, John B.; DeWitt, Regina; Lambeck, Kurt; Purcell, Anthony

    2013-12-01

    The rate of sea-level rise is expected to increase over the next century. In many areas, increasing rates of sea-level rise are exacerbated by subsidence. In order to develop proper mitigation strategies for coastal change, better estimates for the rates of subsidence are needed. In this study we outline a strategy for calculating long-term subsidence rates for coastlines based on the differential elevations of modern shorelines and their last interglacial (LIG) equivalent geomorphic features. We apply this strategy to the LIG shoreline of the USA Texas coast. We first obtained optically stimulated luminescence ages of features long conjectured to be LIG, but, until now have remained undated. We use a digital elevation model to calculate the difference in elevations between the modern and MIS5e shorelines. This difference is corrected for glacial-hydro-isostatic adjustments to the Texas coast over the last 120 ky. Our analysis shows spatial variability in the rate of subsidence that increases seaward and at locations closer to the Brazos/Colorado delta. The lowest rates of subsidence were 0.03 mm/yr at the most inland site. The highest rates were 0.09 mm/yr near the modern Brazos/Colorado Delta. The spatial pattern of subsidence suggests that most of the long-term vertical motion along the Texas coast is due to sediment loading. The rates of subsidence along the portions of the Texas coast are equal to, and in some places greater than, glacial-isostatic adjustments (GIA), thus highlighting the importance of other vertical motions such as sediment loading when using sea-level data to constrain GIA models even in the absence of active tectonics. In addition, these rates are two orders of magnitude less than modern rates of relative sea-level rise recorded at tide gauges along the Texas coast, highlighting the importance of Holocene compaction and fluid withdrawal in accelerating rates of subsidence along the Texas coast.

  2. Polar low dynamics

    SciTech Connect

    Montgomery, M.T.; Farrell, B.F. )

    1992-12-15

    Polar lows are intense subsynoptic-scale cyclones that form over high-latitude oceans in association with deep cumulus convection and strong ambient baroclinicity. Recent observations indicate that polar lows are generally initiated by a nonaxisymmetric interaction between a surface disturbance and an upper-level mobile trough. Extant theories of polar low formation preclude study of such a process since they either constrain their models to be axisymmetric, or do not explicitly account for his transient interaction. In this work the physics of interacting upper- and lower-level potential vorticity structures is studied as an initial-value problem using a three-dimensional nonlinear geostrophic momentum model that incorporates moist processes and includes strong baroclinic dynamics. Model results illustrate the rapid formation of an intense small-scale cyclone whose structure is consistent with observations of mature polar lows. A conceptual model of polar low development is proposed. In the first stage of development, called induced self-development, a mobile upper trough initiates a rapid low-level spinup due to the enhanced omega response in a conditionally neutral baroclinic atmosphere. A secondary development follows, called diabatic destabilization, that is associated with the production of low-level potential vorticity by diabatic processes. Diabatic destabilization represents a simple mechanism for maintaining the intensity of polar lows until they reach land. In exceptional instances of negligible upper-level forcing, the latter may also describe the gradual intensification of small-scale cyclones in regions of sustained neutrality and surface baroclinicity. Ideas regarding polar low equilibration and prospects for a unified theory of arctic and midlatitude cyclones are discussed. 75 refs., 4 figs., 1 tab.

  3. Initiation and development of the Laurentide and Cordilleran Ice Sheets following the last interglaciation

    USGS Publications Warehouse

    Clark, P.U.; Clague, J.J.; Curry, B. Brandon; Dreimanis, A.; Hicock, S.R.; Miller, G.H.; Berger, G.W.; Eyles, N.; Lamothe, M.; Miller, B.B.; Mott, R.J.; Oldale, R.N.; Stea, R.R.; Szabo, J.P.; Thorleifson, L.H.; Vincent, J.-S.

    1993-01-01

    Fossil records from sites overridden by or adjacent to the Laurentide Ice Sheet indicate that the climate of the last interglaciation (Oxygen-Isotope Substage 5e, ca. 130-116 ka) was warmer than today. Following the last interglaciation, the Laurentide Ice Sheet first developed during Stage 5 over Keewatin, Quebec and Baffin Island. Along its northern margin, the ice sheet reached its maximum extent of the last glaciation during Stage 5. The ice sheet advanced across Baffin Island onto the continental shelf early during Stage 5 (5d?), whereas the advance into the western Canadian Arctic occurred late during Stage 5 (5b?). The ice sheet also may have advanced into the St Lawrence Lowland during Substage 5b, although this event may be younger (Stage 4). The Hudson Bay lowland became ice-free during Substage 5a. Retreat of the ice sheet on Baffin Island occurred during late Stage 5, probably Substage 5a. The exact timing of retreat from the western Canadian Arctic is unknown, but it occurred before 48 ka. The southern sector, including the St Lawrence Lowland, was ice-free during late Stage 5. The Hudson Bay lowland may have remained ice free through Stage 4 and much of Stage 3. Because of conflicting chronologies, however, it is more likely that this area was glaciated throughout Stage 3 and perhaps Stage 4. Nevertheless, the data demonstrate that the lowland was ice-free during part of the last glaciation. An independent ice cap developed over the Appalachian Uplands and advanced across Nova Scotia during Stage 4, perhaps as far as the edge of the continental shelf. The ice cap remained active over Nova Scotia as a setellite to the Laurentide Ice Sheet throughout the remainder of the last glaciation. The ice sheet advanced into the St Lawrence Lowland during Stage 4 and subsequently overwhelmed the local ice cap in the Appalachian Uplands, advancing perhaps into northern New England, but not farther south. The Lowland remained covered by the ice sheet until late

  4. Palaeoclimatic significance of co-occurring wind- and water-induced sedimentary structures in the last-interglacial coastal deposits from Bermuda and the Bahamas

    NASA Astrophysics Data System (ADS)

    Kindler, P.; Strasser, A.

    2000-03-01

    The late Pleistocene stratigraphic record from the Bahamas and Bermuda archipelagoes includes peculiar V-shaped coastal ridges and wedges of seaward-dipping planar beds showing fenestral porosity up to 40 m above present sea level. Judging from this porosity, these landforms were till now interpreted as resulting from the action of giant waves during a period of climatic instability at the end of the last interglacial period. The occurrence of widespread mm-thick laminae of aeolian origin (subcritically climbing translatent stratification) throughout these deposits does not agree with this hypothesis. It rather suggests that the V-shaped ridges and seaward-dipping beds represent fossil parabolic and climbing aeolian dunes, respectively. The occurrence of fenestrae high above the intertidal zone could be related to both wave splashing and rainfall action. Parabolic dunes are restricted to the NW Bahamas. They were probably formed during a time interval (ca. 500-5000 yr), when regional climatic conditions were dryer than today, and characterized by persistently blowing NE trade winds.

  5. Evaluation of chromatographic conditions in reversed phase liquid chromatography-mass spectrometry systems for fingerprinting of polar and amphiphilic plant metabolites.

    PubMed

    Nielsen, Nikoline J; Tomasi, Giorgio; Christensen, Jan H

    2016-08-01

    Metabolic fingerprinting is a relatively young scientific discipline requiring robust, yet flexible and fit-for-purpose analytical methods. Here, we introduce a simple approach to select reversed phase LC systems with electrospray MS detection for fingerprinting of polar and amphiphilic plant metabolites. The approach does not rely on isotopic labeling or biological origin of sample constituent and can also be used for non-biological matrices (e.g., oil or sewage sludge) or for other optimization purposes (e.g., mass spectrometric source parameterization). The LC systems varied in column chemistry and temperature, mobile phase pH/additive, gradient steepness/eluotropic strength, and electrospray mode of operation. The systems were evaluated based on the number of features detected using the matchedFilter algorithm from XCMS and the repeatability of this detection across analytical replicates. For negative ion mode detection, the best performances were obtained with an HSS T3 column operated at low pH, which produced a 3-fold increase in the number of reliable features extracted compared with the worst system. The best system for positive ion mode (i.e., the BEH C18 column operated at intermediate pH) only produced a 50 % increase in the number of reliable features. The data also indicate that baseline removal is unavoidable for reliable intensity estimations using peak areas, and that peak heights may be a more robust measure of intensity when baselines cannot be completely removed or in case of coelution, fronting or tailing. PMID:27344456

  6. Polarization of Starlight

    NASA Astrophysics Data System (ADS)

    Whittet, D. C. B.

    The polarization of starlight is universally attributed to directional extinction arising when dust grains along the line of sight are aligned in the presence of a magnetic field. This phenomenon provides a powerful tool for studying the optical properties of the dust (size, shape, refractive index) and for charting the galactic magnetic field. Current observational constraints at all wavelengths are consistent with a picture in which only the larger grains in the size range responsible for extinction are efficient polarizers. Small grains are much less well aligned and/or more isotropic in shape than large grains. The polarizing grains include silicates, but it is not clear whether they contain appreciable quantities of carbon. The degree of alignment is highly sensitive to ambient physical conditions as well as to particle size. The polarization efficiency per unit extinction declines with increasing density within dark clouds, hindering attempts to map the intracloud magnetic field. However, spectropolarimetric studies of interstellar ice absorption features seen in deeply embedded YSOs indicate that mantled grains within dense molecular clouds can be surprisingly efficient polarizers, suggesting that a qualitatively different alignment mechanism is operating compared with diffuse regions of the ISM. This talk will present a brief overview of key observations and their interpretation, highlight areas of uncertainty, and suggest avenues of future research. The physics of grain alignment is reviewed elsewhere in this meeting (see paper by Roberge).

  7. Cell polarity

    PubMed Central

    Romereim, Sarah M

    2011-01-01

    Despite extensive genetic analysis of the dynamic multi-phase process that transforms a small population of lateral plate mesoderm into the mature limb skeleton, the mechanisms by which signaling pathways regulate cellular behaviors to generate morphogenetic forces are not known. Recently, a series of papers have offered the intriguing possibility that regulated cell polarity fine-tunes the morphogenetic process via orienting cell axes, division planes and cell movements. Wnt5a-mediated non-canonical signaling, which may include planar cell polarity, has emerged as a common thread in the otherwise distinct signaling networks that regulate morphogenesis in each phase of limb development. These findings position the limb as a key model to elucidate how global tissue patterning pathways direct local differences in cell behavior that, in turn, generate growth and form. PMID:22064549

  8. Polypedogenic case of loess overlying red clay as a response to the Last Glacial-Interglacial cycle in mid-subtropical Southeast China

    NASA Astrophysics Data System (ADS)

    Hu, Xue-Feng; Du, Yan; Liu, Xiang-Jun; Zhang, Gan-Lin; Jiang, Ying; Xue, Yong

    2015-03-01

    To study the paleoclimatic implications of the loess-like Yellow-brown Earth (YBE) overlying red clay (RC) along the Yangtze River, mid-subtropical Southeast China, four YBE-RC profiles in southern Anhui Province were investigated. Grain-size and geochemical characteristics indicated that the YBE is homologous to the aeolian Xiashu Loess; and the underlying RC, sub-divided into uniform RC (URC) and reticulate RC (RRC), is more intensively weathered but also exhibits aeolian dust characteristics. Optically stimulated luminescence (OSL) dating indicated that the YBE was formed during the Last Glacial, the RRC mainly during the Last Interglacial, and the URC during the transitional period between the YBE and RC. The YBE-RC transition reflects a significant paleoclimatic change in mid-subtropical China during the Last Glacial-Interglacial cycle. Sub-events of the Last Glacial, correlated with the marine isotopic stages (MIS) 2 and 3, can be identified within the YBE; however, those of the Last Interglacial, potential correlated with MIS 5a-5e, cannot be identified within the RRC possibly due to paleoclimatic overprinting. The rubification had been replaced by loess deposition along the Yangtze River since the early Last Glacial. With both highly weathered and aeolian-dust characteristics, the underlying RRC may indicate paleoclimatic instability given the multiple alternations between loess deposition and rubification of the Last Interglacial. The climatic change during the Last Glacial-Interglacial cycle significantly influenced the pedogenesis and made soil diversified in the study areas.

  9. Interglacial refugia preserved high genetic diversity of the Chinese mole shrew in the mountains of southwest China.

    PubMed

    He, K; Hu, N-Q; Chen, X; Li, J-T; Jiang, X-L

    2016-01-01

    The mountains of southwest China (MSC) harbor extremely high species diversity; however, the mechanism behind this diversity is unknown. We investigated to what degree the topography and climate change shaped the genetic diversity and diversification in these mountains, and we also sought to identify the locations of microrefugia areas in these mountains. For these purposes, we sampled extensively to estimate the intraspecific phylogenetic pattern of the Chinese mole shrew (Anourosorex squamipes) in southwest China throughout its range of distribution. Two mitochondrial genes, namely, cytochrome b (CYT B) and NADH dehydrogenase subunit 2 (ND2), from 383 archived specimens from 43 localities were determined for phylogeographic and demographic analyses. We used the continuous-diffusion phylogeographic model, extensive Bayesian skyline plot species distribution modeling (SDM) and approximate Bayesian computation (ABC) to explore the changes in population size and distribution through time of the species. Two phylogenetic clades were identified, and significantly higher genetic diversity was preserved in the southern subregion of the mountains. The results of the SDM, continuous-diffusion phylogeographic model, extensive Bayesian skyline plot and ABC analyses were congruent and supported that the Last Interglacial Maximum (LIG) was an unfavorable period for the mole shrews because of a high degree of seasonality; A. squamipes survived in isolated interglacial refugia mainly located in the southern subregion during the LIG and rapidly expanded during the last glacial period. These results furnished the first evidence for major Pleistocene interglacial refugia and a latitudinal effect in southwest China, and the results shedding light on the higher level of species richness in the southern subregion. PMID:26286667

  10. High interglacial diatom paleoproductivity in the westernmost Indo-Pacific Warm Pool during the past 130,000 years

    NASA Astrophysics Data System (ADS)

    Romero, Oscar E.; Mohtadi, Mahyar; Helmke, Peer; Hebbeln, Dierk

    2012-09-01

    A wealth of sedimentary records aimed at reconstructing late Quaternary changes in productivity and temperature have been devoted to understanding linkages between the Indo-Pacific Warm Pool (IPWP) and other distant oceanic areas. Most of these reconstructions are based, however, on biogeochemical and sedimentological proxies, with comparatively less attention devoted to microfossils. A high-resolution (<1 ka) study of diatom concentrations and the community at site GeoB10038-4, recovered off southern Sumatra (ca. 6°S, 103°E), closely tracks the variations of diatom concentrations in the westernmost IPWP during the last glacial-interglacial cycle. The diatom record provides evidence that diatom paleoproductivity was highest during interglacials, primarily due to the input of lithogenics and nutrients following the rise in sea level after full glacials. In addition, the co-variation of total diatom concentration and Northern Hemisphere forcing for Marine Isotope Stage 5 suggests a direct response of diatom productivity and upwelling intensity to boreal summer insolation. Temporal shifts of the diverse diatom community at site GeoB10038-4 correspond well with the present-day seasonal monsoon pattern and the strengthening and weakening phases of upwelling along the southern coast of Sumatra. Resting spores ofChaetoceros, typical of nutrient-rich waters, were dominant during periods of highest diatom paleoproductivity and responded to the strengthening of the SE monsoon, while diatoms of oligotrophic to mesotrophic waters characterized intermonsoon periods. The close correspondence between the dominance of upwelling diatoms and the boreal summer insolation resembles the present-day dynamics of diatom production. The observed interglacial highs and glacial lows of diatom productivity at site GeoB10038-4 is a unique pattern in the late Quaternary tropics.

  11. Regional differences in the δO2/N2 records from East Antarctica over the last interglacial

    NASA Astrophysics Data System (ADS)

    Bazin, L.; Landais, A.; Masson-Delmotte, V.; Kageyama, M.; Paillard, D.; Bopp, L.; Ritz, C.; Leuenberger, M.

    2013-12-01

    Ice cores are the only climate archives offering samples of past atmosphere. The air is trapped at around 100 m under the surface, where the snow is compacted into ice. During this process, multiple influences may modify the air composition as the quantity of insolation received at the surface impacts snow metamorphism and hence air trapping conditions at the basis of the firn (top ~100m of the ice sheet). Analyses of trapped air in ice cores thus give us information on both local and global scales. In this study, we focus on temporal variations of elemental and isotopic composition of oxygen from East Antarctic ice cores. On the one hand, the δ18Oatm, uniformly distributed in the atmosphere, is known to be related to the hydrological cycle and the vegetation cover (Landais et al., 2010), and can be linked to the precession variations. The δO2/N2, on the other hand, appears to be influenced by the local insolation, probably because of modification of the snow structure affecting pore close-off. These two quantities have largely been used as orbital tuning tools for dating purposes in several ice cores from Antarctica (Bender 2002, Suwa et Bender 2008, Kawamura et al., 2007, Dreyfus et al., 2007,Landais et al., 2012, Bazin et al., 2013). Still, gaps in our understanding of the exact mechanisms explaining the δ18Oatm and δO2/N2 variations lead to quite large uncertainties when using these proxies as tie-points for dating purposes. In this study, we use several ice core records in low accumulation rate sites of East Antarctica to decipher global and local effects on the δO2/N2 records. First, we present a compilation of δO2/N2 measurements of the Dome F, Vostok and Dome C ice cores over the last interglacial period. While Dome F and Vostok data were corrected for gas loss during several years of storage at -25°C, new measurements of the air isotopic composition on the Dome C ice core were performed on well-conserved ice (-50°C). Different δO2/N2 mean levels

  12. Polar Textures

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site] Context image for PIA03646 Polar Textures

    This VIS image shows part of the south polar region. The ejecta from the relatively young crater covers the rougher textured polar surface.

    Image information: VIS instrument. Latitude 81S, Longitude 54.5E. 17 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  13. Deep into an interglacial: A compound-specific biomarker study of Marine Isotope Stage 11 (Tenaghi Philippon, Greece)

    NASA Astrophysics Data System (ADS)

    Ardenghi, N.; Niedermeyer, E. M.; Kahmen, A.; Pross, J.; Mulch, A.

    2015-12-01

    Marine Isotope Stage (MIS) 11 is a mid-Pleistocene interglacial, characterized by a minimum in orbital eccentricity, and therefore often studied as a climate analogue for the Holocene (MIS 1). However, a slightly different phasing of obliquity and precession between these two interglacials sparks strong interrogatives about the MIS 1-11 alignment and its meaningfulness for Holocene predictions.MIS 11c represents an unusually long warm subphase immediately after the "Mid-Brunhes Event" (≈430 ka bp), which marks the passage from the 40 ka (obliquity-) to the 100 ka (eccentricity-driven) world. The following subphases MIS 11b and MIS 11a, represent a series of cold-warm oscillations, terminated by the glacial inception of MIS10. Our aim is to describe atmospheric circulation patterns and their changes through glacial and interglacial transitions while tracking the evolution of the respective terrestrial temperatures and levels of biomass burning.We worked on a peat core from Tenaghi Philippon, an intramontane peat deposit in Eastern Macedonia (Greece); its position at the convergence zone of Atlantic, monsoonal and Siberian-influenced climates makes it an excellent archive to study climate change during MIS11 in the Eastern Mediterranean. We show the stable hydrogen isotopic composition of higher plant waxes (δD) as proxy for changes in atmospheric circulation and related shifts of moisture source, together with changes in air temperature based on GDGTs (Glycerol Dialkyl Glycerol Tetraethers) analysis. In addition, we studied the chain-length distribution of higher plant-wax n-alkanes to derive the "aquatic index" (Paq), a measure of wetland aggradation. Paq varies between 0.2 and 0.9, indicating pronounced shifts of the water table throughout the record, and neatly traces Termination V (the warming leading to MIS11), MIS11c as well as the inception of MIS10.Levoglucosan in turn, a marker for biomass burning, shows a strong glacial-interglacial dichotomy with low

  14. Last interglacial sea-surface temperature estimates from the California margin; improvements to the modern analog technique

    USGS Publications Warehouse

    Dowsett, Harry J.; Poore, Richard Z.

    1999-01-01

    Total faunal analyses of planktic foraminifer assemblages are used to derive sea surface temperature estimates for the last interglacial from Ocean Drilling Program Sites 1018 and 1020 off northern and central California. Foraminifer assemblage data were transformed to sea-surface temperature (SST) estimates by using the modern analog technique (MAT). In order to improve our ability to estimate SST in this area, the coretop calibration data base used in the MAT was augmented by 13 new age-validated coretop assemblages from the U.S. Pacific Margin.

  15. Polar low monitoring

    NASA Astrophysics Data System (ADS)

    Bobylev, Leonid; Zabolotskikh, Elizaveta; Mitnik, Leonid

    2010-05-01

    passive microwave data make it possible to retrieve several important atmospheric and oceanic parameters inside the polar lows, such as sea surface wind speed, water vapour content in the atmosphere, total liquid water content in the clouds and others, providing not only qualitative image of a vortex, but also quantitative information about these severe events, constituting a promising tool for their study and monitoring. An approach for detection and tracking of polar lows is developed utilizing the data from two sensors: SSM/I onboard DMSP and Advanced Microwave Scanning Radiometer - Earth Observing System (AMSR-E) onboard Aqua satellite. This approach consists of two stages. At the first stage total atmospheric water vapor fields are retrieved from SSM/I and AMSRE-E measurement data using precise Arctic polar algorithms, developed at NIERSC. These algorithms are applicable over open water. They have high retrieval accuracies under a wide range of environmental conditions. Algorithms are based on numerical simulation of brightness temperatures and their inversion by means of Neural Networks. At the second stage the vortex structures are detected in these fields, polar lows are identified and tracked and some of their parameters are calculated. A few case studies are comprehensively conducted based on SSM/I and AMSRE-E measurements and using other satellite data including visible, infrared and SAR images, QuickScat Scatterometer wind fields, surface analysis maps and re-analysis data, which demonstrated the advantages of satellite passive microwave data usage in the polar low studies.

  16. From the Last Interglacial to the Anthropocene: Modelling a Complete Glacial Cycle (PalMod)

    NASA Astrophysics Data System (ADS)

    Brücher, Tim; Latif, Mojib; Claussen, Martin; Schulz, Michael

    2016-04-01

    We will give a short overview of the national climate modelling initiative (PalMod - Paleo Modelling, www.palmod.de) on the understanding of the climate system dynamics and its variability during the last glacial cycle. PalMod is funded by the German Federal Ministry of Education and Research (BMBF) and its specific topics are: (i) to identify and quantify the relative contributions of the fundamental processes which determined the Earth's climate trajectory and variability during the last glacial cycle, (ii) to simulate with comprehensive Earth System Models (ESMs) the climate from the peak of the last interglacial - the Eemian warm period - up to the present, including the changes in the spectrum of variability, and (iii) to assess possible future climate trajectories beyond this century during the next millennia with sophisticated ESMs tested in such a way. The research is intended to be conducted over a period of 10 years, but with shorter funding cycles. The envisioned approach is innovative in three respects. First, the consortium aims at simulating a full glacial cycle in transient mode and with comprehensive ESMs which allow full interactions between the physical and biogeochemical components of the Earth system, including ice sheets. Second, we shall address climate variability during the last glacial cycle on a large range of time scales, from interannual to multi-millennial, and attempt to quantify the relative contributions of external forcing and processes internal to the Earth system to climate variability at different time scales. Third, in order to achieve a higher level of understanding of natural climate variability at time scales of millennia, its governing processes and implications for the future climate, we bring together three different research communities: the Earth system modeling community, the proxy data community and the computational science community. The consortium consists of 18 partners including all major modelling centers within

  17. A cool eastern Pacific Ocean at the close of the Last Interglacial complex

    USGS Publications Warehouse

    Muhs, D.R.; Simmons, K.R.; Kennedy, G.L.; Ludwig, K. R.; Groves, L.T.

    2006-01-01

    New high-precision thermal ionization mass-spectrometric (TIMS) U-series ages of solitary corals (Balanophyllia elegans) from several marine terrace localities along the California and southern Oregon coasts date to the ???80,000 yr BP high stand of sea, correlative with marine isotope substage 5a, late in the last interglacial complex. Ages of multiple corals from localities north of Point An??o Nuevo (central California) and San Nicolas Island (southern California) suggest that this high sea stand could have lasted at least 8000 yr, from ???84,000 to ???76,000 yr BP. These ages overlap with those from marine deposits on tectonically stable Bermuda and tectonically emergent Barbados. Higher-elevation terraces at two California localities, in the Palos Verdes Hills and on San Nicolas Island, have corals with ages that range mostly from ???121,000 to ???116,000 yr BP, correlative with marine isotope substage 5e. These ages are similar to those reported for other terraces in southern California but are younger than some ages reported from Hawaii, Barbados and the Bahamas. Marine terrace faunas are excellent proxies for nearshore marine paleotemperatures during past high sea stands. Terraces on the Palos Verdes Hills and San Nicolas Island dated to the ???120,000 yr BP high sea stand have dominantly zoogeographically "neutral" species in exposed coastal localities, indicating nearshore waters similar to those of today. In contrast, ???80,000 yr BP, exposed coastal localities typically have molluscan faunas characterized by numerous extralimital northern species and a lack of extralimital southern species. These fossil assemblages are indicative of nearshore water temperatures that were cooler than modern temperatures at ???80,000 yr BP. Waters at least as warm as today's at ???120,000 yr BP and cooler than present at ???80,000 yr BP are in excellent agreement with marine alkenone records and coastal vegetation records derived from pollen data, from both southern and

  18. The interglacial-glacial cycle and geochemical evolution of Canadian and Fennoscandian Shield groundwaters

    NASA Astrophysics Data System (ADS)

    Stotler, R. L.; Frape, S. K.; Ruskeeniemi, T.; Pitkänen, P.; Blowes, D. W.

    2012-01-01

    Results from cryogenic column experiments are compared with the geochemical data collected in the Canadian and Fennoscandian Shields over the past 25 years to investigate the relative influence of the glacial-interglacial cycle; specifically, the impact of continental glaciers, permafrost, and methane hydrate, on the evolution of groundwater from crystalline shield environments. Several different geochemical indicators of freezing processes (either glacial or permafrost-related) were utilized: comparisons of Na/Cl and Br/Cl ratios, δ 18O and δ 2H values, and δ 18O values and Cl - concentration. During freezing, fluids with different dominant cations follow distinctly different linear trends when Na/Cl and Br/Cl ratios are compared. Significantly, none of the freezing trends follows the trend hypothesized by Herut et al. (1990) for the evolution of seawater chemistry during freezing. Intrusion of glacial meltwater and in situ freezing (i.e., permafrost formation) result in a similar end-member when comparing δ 18O values and Cl - concentration. The geochemical influence of a freezing process on fresh, brackish, and some saline fluids was identified at some, but not all Canadian Shield sites, regardless of site location with respect to modern-day permafrost. Appreciably, physical and geochemical data do not support the formation of brines through any freezing process in the Canadian and Fennoscandian Shields, as hypothesized by Starinsky and Katz (2003). Rather, on all diagnostic freezing plots, brines are an end-member, indicating a different evolutionary pathway. Significant depletions in 18O with respect to modern precipitation, an indication of either glacial meltwater or a freezing process, were identified at depths of up to 1 km at some sites in the Canadian Shield, and to shallower depths in the Fennoscandian Shield. The potential of this fluid to reach such depths could be attributable to artificial gradients and mixing, glacial recharge, permafrost or

  19. The Last Interglacial sea level change: new evidence from the Abrolhos islands, West Australia

    NASA Astrophysics Data System (ADS)

    Eisenhauer, A.; Zhu, Z. R.; Collins, L. B.; Wyrwoll, K. H.; Eichstätter, R.

    U-series ages measured by thermal ionisation mass spectrometry (TIMS) are reported for a Last Interglacial (LI) fossil coral core from the Turtle Bay, Houtman Abrolhos islands, western Australia. The core is 33.4m long the top of which is approximately 5ma.p.s.l. (above present sea level). From the 232Th concentrations and the reliability of the U-series ages, two sections in the core can be distinguished. Calculated U/Th ages in core sectionI (3.3ma.p.s.l to 11mb.p.s.l) vary between 124+/-1.7kaBP (3.3ma.p.s.l.) and 132.5+/-1.8ka (4mb.p.s.l., i.e. below present sea level), and those of sectionII (11-23mb.p.s.l.) between 140+/-3 and 214+/-5kaBP, respectively. The ages of core sectionI are in almost perfect chronological order, whereas for sectionII no clear age-depth relationship of the samples can be recognised. Further assessments based on the ∂234U(T) criteria reveal that none of the samples of core sectionII give reliable ages, whereas for core sectionI several samples can be considered to be moderately reliable within 2ka. The data of the Turtle Bay core complement and extend our previous work from the Houtman Abrolhos showing that the sea level reached a height of approximately 4mb.p.s.l at approximately 134kaBP and a sea level highstand of at least 3.3ma.p.s.l. at approximately 124kaBP. Sea level dropped below its present position at approximately 116kaBP. Although the new data are in general accord with the Milankovitch theory of climate change, a detailed comparison reveals considerable differences between the Holocenand LI sea level rise as monitored relative to the Houtman Abrolhos islands. These observation apparently add further evidence to the growing set of data that the LI sea level rise started earlier than recognised by SPECMAP chronology. A reconciliation of these contradictionary observations following the line of arguments presented by Crowley (1994) are discussed with respect to the Milankovitch theory.

  20. Midlatitude cooling caused by geomagnetic field minimum during polarity reversal.

    PubMed

    Kitaba, Ikuko; Hyodo, Masayuki; Katoh, Shigehiro; Dettman, David L; Sato, Hiroshi

    2013-01-22

    The climatic effects of cloud formation induced by galactic cosmic rays (CRs) has recently become a topic of much discussion. The CR-cloud connection suggests that variations in geomagnetic field intensity could change climate through modulation of CR flux. This hypothesis, however, is not well-tested using robust geological evidence. Here we present paleoclimate and paleoenvironment records of five interglacial periods that include two geomagnetic polarity reversals. Marine oxygen isotope stages 19 and 31 contain both anomalous cooling intervals during the sea-level highstands and the Matuyama-Brunhes and Lower Jaramillo reversals, respectively. This contrasts strongly with the typical interglacial climate that has the temperature maximum at the sea-level peak. The cooling occurred when the field intensity dropped to <40% of its present value, for which we estimate >40% increase in CR flux. The climate warmed rapidly when field intensity recovered. We suggest that geomagnetic field intensity can influence global climate through the modulation of CR flux. PMID:23297205

  1. Midlatitude cooling caused by geomagnetic field minimum during polarity reversal

    PubMed Central

    Kitaba, Ikuko; Hyodo, Masayuki; Katoh, Shigehiro; Dettman, David L.; Sato, Hiroshi

    2013-01-01

    The climatic effects of cloud formation induced by galactic cosmic rays (CRs) has recently become a topic of much discussion. The CR–cloud connection suggests that variations in geomagnetic field intensity could change climate through modulation of CR flux. This hypothesis, however, is not well-tested using robust geological evidence. Here we present paleoclimate and paleoenvironment records of five interglacial periods that include two geomagnetic polarity reversals. Marine oxygen isotope stages 19 and 31 contain both anomalous cooling intervals during the sea-level highstands and the Matuyama–Brunhes and Lower Jaramillo reversals, respectively. This contrasts strongly with the typical interglacial climate that has the temperature maximum at the sea-level peak. The cooling occurred when the field intensity dropped to <40% of its present value, for which we estimate >40% increase in CR flux. The climate warmed rapidly when field intensity recovered. We suggest that geomagnetic field intensity can influence global climate through the modulation of CR flux. PMID:23297205

  2. Recent and past Saharan dust deposition in the Carpathian Basin and its possible effects on interglacial soil formation

    NASA Astrophysics Data System (ADS)

    Varga, György

    2016-04-01

    Several hundred tons of windblown dust material are transported every year from Saharan dust source areas into direction of Europe, modifying important climatic and other environmental processes of distant areas. North African aerosols have been also identified several times a year in the Carpathian Basin, where under the influence of certain synoptic meteorological conditions Saharan dust accumulation can clearly be observed. Previous satellite based studies were suitable to estimate the frequency and magnitude of Saharan dust episodes in the investigation area, however, the assessment of North African dust deposition can be done with model simulations. In this study, calculations were made by using the data of BSC-DREAM8b (Barcelona Supercomputing Center's Dust REgional Atmospheric Model) v1.0 and v2.0 database. Simulation results of the BSC-DREAM8b v1.0 are available from 1 January 2000 to 31 December 2012, while the results of the updated v2.0 calculations are ready for the period between 1 January 2006 and 31 December 2014. BSC DREAM8b v1.0 model simulations for the period between 2000 and 2012 provided an annual mean of 0.0285 g/m2/y dry and 0.034 g/m2/y wet deposition values in the Carpathian Basin, which is equivalent to a total of 0.0636 g/m2/y. The updated v2.0 version for the period of 2006-2014 gave significantly larger values: 0.133 g/m2/y dry; 0.085 g/m2/y wet and 0.219 g/m2/y total annual dust deposition. By comparing the results of the overlapping period between 2006 and 2012 of the v1.0 and v2.0 simulations, the updated depositional scheme of the newer version provided ˜3.7-fold values in case of dry deposition and ˜1.9-fold increase in results of the wet deposition. Information available from individual events showed that the simulated wet and dry dust deposition rates are significantly underestimated. This is also suggested by previous model calculations which reported values between 5 and 10 g/m2/y for modern dust flux in the investigated area

  3. Polar Landforms

    NASA Technical Reports Server (NTRS)

    2005-01-01

    10 August 2005 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows eroded remnants of carbon dioxide ice in the south polar residual cap of Mars. The scarps that outline each small mesa have retreated about 3 meters (10 feet) per Mars year since MGS began orbiting the red planet in 1997.

    Location near: 87.0oS, 31.9oW Image width: width: 3 km (1.9 mi) Illumination from: upper left Season: Southern Spring

  4. Millennial-scale Climate Variability During the Last Interglacial Recorded in Two Speleothems from Eastern North America

    NASA Astrophysics Data System (ADS)

    Gao, Y.; Rowe, H. D.; Rao, Z.; Buckles, J. A.; Wang, X.; Cheng, H.; Edwards, R. L.

    2014-12-01

    Two speleothems from eastern North America grew throughout the warmest part of the Last Interglacial (128 -120 ka BP). High-resolution stable isotope δ18O and δ13C records are constrained by 20 230Th age dates. The high-resolution speleothem records from Morril's Cave (aka Worley's Cave) in the eastern North America region demonstrate millennial-scale climate variability. ''Warmer-wetter'' periods are interspersed with ''cooler-drier'' periods at millennial-scale based on shifts of stable isotope values. Between 123.8 to 123.6 BP, both δ18O and δ13C values dropped more than 2‰ in the TNMOR1-12 speleothem record. The abrupt negative excursions of δ18O and δ13C values indicate the transition from the "coolest-driest" to the "warmest-wettest" in the middle of MIS 5e. Overall, the isotope record is anti-phasing with a stalagmite record from southwestern France (BDinf), which may indicate that orbitally driven western Europe and eastern North America anti-phasing precipitation occurred during the warmest period of the Last Interglacial.

  5. Optical polarizer material

    DOEpatents

    Ebbers, Christopher A.

    1999-01-01

    Several crystals have been identified which can be grown using standard single crystals growth techniques and which have a high birefringence. The identified crystals include Li.sub.2 CO.sub.3, LiNaCO.sub.3, LiKCO.sub.3, LiRbCO.sub.3 and LiCsCO.sub.3. The condition of high birefringence leads to their application as optical polarizer materials. In one embodiment of the invention, the crystal has the chemical formula LiK.sub.(1-w-x-y) Na.sub.(1-w-x-z) Rb.sub.(1-w-y-z) Cs.sub.(1-x-y-z) CO.sub.3, where w+x+y+z=1. In another embodiment, the crystalline material may be selected from a an alkali metal carbonate and a double salt of alkali metal carbonates, where the polarizer has a Wollaston configuration, a Glan-Thompson configuration or a Glan-Taylor configuration. A method of making an LiNaCO.sub.3 optical polarizer is described. A similar method is shown for making an LiKCO.sub.3 optical polarizer.

  6. Optical polarizer material

    DOEpatents

    Ebbers, C.A.

    1999-08-31

    Several crystals have been identified which can be grown using standard single crystals growth techniques and which have a high birefringence. The identified crystals include Li.sub.2 CO.sub.3, LiNaCO.sub.3, LiKCO.sub.3, LiRbCO.sub.3 and LiCsCO.sub.3. The condition of high birefringence leads to their application as optical polarizer materials. In one embodiment of the invention, the crystal has the chemical formula LiK.sub.(1-w-x-y) Na.sub.(1-w-x-z) Rb.sub.(1-w-y-z) Cs.sub.(1-x-y-z) CO.sub.3, where w+x+y+z=1. In another embodiment, the crystalline material may be selected from a an alkali metal carbonate and a double salt of alkali metal carbonates, where the polarizer has a Wollaston configuration, a Glan-Thompson configuration or a Glan-Taylor configuration. A method of making an LiNaCO.sub.3 optical polarizer is described. A similar method is shown for making an LiKCO.sub.3 optical polarizer.

  7. Search for Polarization Effects in the Antiproton Production Process

    DOE PAGESBeta

    Grzonka, D.; Kilian, K.; Ritman, J.; Sefzick, T.; Oelert, W.; Diermaier, M.; Widmann, E.; Zmeskal, J.; Głowacz, B.; Moskal, P.; et al

    2015-01-01

    For the production of a polarized antiproton beam, various methods have been suggested including the possibility that antiprotons may be produced polarized which will be checked experimentally. The polarization of antiprotons produced under typical conditions for antiproton beam preparation will be measured at the CERN/PS. If the production process creates some polarization, a polarized antiproton beam could be prepared by a rather simple modification of the antiproton beam facility. The detection setup and the expected experimental conditions are described.

  8. The Last Interglacial recorded in a Remouchamps cave speleothem (Belgium) -Information on seasonal changes and on the chronology of first climate deteriorations.

    NASA Astrophysics Data System (ADS)

    Verheyden, Sophie; Genty, Dominique; Blamart, Dominique; Cheng, Hai; Hodel, Florent; Vansteenberghe, Stef; McGavick, Matthew L.; Gillikin, David P.; Quinif, Yves

    2015-04-01

    A ~3m long stalagmite from the Remouchamps and ~15cm long stalagmite from the Han-sur-Lesse caves (Belgium) grew from ~124 to 100ka with growth rates going from 0.8mm/century to 30mm/century. Stable isotope (d18O and d13C) and growth-rate analyses suggest a rather stable climate from 122.0 to 115.8 ka. A clear climate deterioration is observed at ~115.8 ka and lasts until 111.2ka (±0.5ka, 2s), which corresponds well with Greenland Stadial 26. Several short-term but clear changes are observed in the stable isotopic composition at ~121.5, 119.5, 118.4, 117.6 (±0.5ka, 2s)) and are interpreted as climatic events of ~several hundred years long. They correspond with changes in stalagmite diameter and growth rate. Depending on the combination of changes in the d18O, d13C, growth rate and stalagmite diameter, the events are interpreted as corresponding to changes in rainfall amount or temperature. The RSM17 stalagmite exhibits visible seasonal layering during the entire 120-115ka period on which changes in Mg, Sr, Ba en P have been observed. This well pronounced lamination, likely annual as suggested by the U-Th data, demonstrates a strong seasonal character of the climate and/or vegetation activity during this period. We compare these MIS5 seasonality to the present day calcite layering observed in the cave. Both stalagmites, with a growth-rate increase after 125ka globally corresponding to the so-called Eemian optimum, seem to start later than other southern stalagmites from France, Italy or Spain. This observation raises the question of a possible late onset of interglacial conditions in north-west Europe and a progressive S-N advance of warmer conditions between 130 and 125ka through Western Europe.

  9. Stalagmite geochemistry and the timing of the last interglacial-glacial transition in Central Europe (NE Hungary)

    NASA Astrophysics Data System (ADS)

    Siklosy, Z.; Demeny, A.; Pilet, S.; Leel-Ossy, Sz.; Lin, K.; Shen, C.-C.

    2009-04-01

    Speleothems can provide accurate chronologies for reconstructions of climate change by combination of U/Th dating and climate-related geochemical compositions. Geochemical studies of speleothems from Central Europe are mostly based on stable C and O isotope analyses, thus, complex geochemical studies combining isotope and trace element measurements are needed for more reliable climate models for this transitional area between oceanic and continental regions. We present stable H-C-O isotope and trace element records obtained on speleothems covering the Last Interglacial (MIS 5e) and the transition to MIS 5d. A stalagmite from Baradla Cave grew from 127.5 to 110 ka. Accelerated growth rates have been detected by U/Th age data in the 127 to 126 ka and 119 to 117 ka parts. Trace element compositions and 230Th/232Th ratios suggest changes in the hydrological regime, whereby early calcite precipitates formed in fissures during the dry and cold glacial period were dissolved by the starting flux of infiltrating meteoric water (producing elevated dissolved ion concentration but low detrital Th component), then the increasing amount of dripwater during the interglacial period resulted in trace element dilution. Temperature and precipitation amount variations are also reflected by the stable isotope compositions. Oxygen isotope composition shows a continuous increase from 127.5 ka until about 118 ka most probably related to temperature rise, whereas C isotope values are shifted in negative direction suggesting increasing humidity in accordance with trace element contents. The presumably warmest period at ca. 118 ka is associated with rather arid climate as indicated by peak d18O values coinciding with the highest dD values of fluid inclusion water. This is followed by a pronounced negative shift in both O and H isotope values, similarly to recent Alpine studies (Meyer et al., 2008), most probably related to cooling. Hydrogen isotope compositions of fluid inclusion water

  10. Polar ozone

    NASA Technical Reports Server (NTRS)

    Solomon, S.; Grose, W. L.; Jones, R. L.; Mccormick, M. P.; Molina, Mario J.; Oneill, A.; Poole, L. R.; Shine, K. P.; Plumb, R. A.; Pope, V.

    1990-01-01

    The observation and interpretation of a large, unexpected ozone depletion over Antarctica has changed the international scientific view of stratospheric chemistry. The observations which show the veracity, seasonal nature, and vertical structure of the Antarctic ozone hole are presented. Evidence for Arctic and midlatitude ozone loss is also discussed. The chemical theory for Antarctic ozone depletion centers around the occurrence of polar stratospheric clouds (PSCs) in Antarctic winter and spring; the climatology and radiative properties of these clouds are presented. Lab studies of the physical properties of PSCs and the chemical processes that subsequently influence ozone depletion are discussed. Observations and interpretation of the chemical composition of the Antarctic stratosphere are described. It is shown that the observed, greatly enhanced abundances of chlorine monoxide in the lower stratosphere are sufficient to explain much if not all of the ozone decrease. The dynamic meteorology of both polar regions is given, interannual and interhemispheric variations in dynamical processes are outlined, and their likely roles in ozone loss are discussed.

  11. Polar Markings

    NASA Technical Reports Server (NTRS)

    2006-01-01

    [figure removed for brevity, see original site] Context image for PIA02155 Polar Markings

    These bright and dark markings occurred near the end of summer in the south polar region. The dark material is likely dust that has been freed of frost cover.

    Image information: VIS instrument. Latitude -76.3N, Longitude 84.9E. 17 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  12. Polar Layers

    NASA Technical Reports Server (NTRS)

    2006-01-01

    [figure removed for brevity, see original site] Context image for PIA02153 Polar Layers

    This image of the south polar region shows layered material. It is not known if the layers are formed yearly or if they form over the period of 10s to 100s of years or more.

    Image information: VIS instrument. Latitude -80.3N, Longitude 296.2E. 17 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  13. Polar Ridges

    NASA Technical Reports Server (NTRS)

    2006-01-01

    [figure removed for brevity, see original site] Context image for PIA03662 Polar Ridges

    This ridge system is located in the south polar region.

    Image information: VIS instrument. Latitude -81.7N, Longitude 296.5E. 17 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  14. Polar Textures

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site] Context image for PIA03638 Polar Textures

    This image illustrates the variety of textures that appear in the south polar region during late summer.

    Image information: VIS instrument. Latitude 80.5S, Longitude 57.9E. 17 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  15. Polar Terrains

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site] Context image for PIA03577 Polar Terrains

    The region surrounding the South Polar Cap contains many different terrain types. This image shows both etched terrain and a region of 'mounds'.

    Image information: VIS instrument. Latitude 75S, Longitude 286.5E. 17 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  16. Thermal and dynamical perturbations in the winter polar mesosphere-lower thermosphere region associated with sudden stratospheric warmings under conditions of low solar activity

    NASA Astrophysics Data System (ADS)

    Lukianova, Renata; Kozlovsky, Alexander; Shalimov, Sergey; Ulich, Thomas; Lester, Mark

    2015-06-01

    The upper mesospheric neutral winds and temperatures have been derived from continuous meteor radar (MR) measurements over Sodankyla, Finland, in 2008-2014. Under conditions of low solar activity pronounced sudden mesospheric coolings linked to the major stratospheric warming (SSW) in 2009 and a medium SSW in 2010 are observed while there is no observed thermal signature of the major SSW in 2013 occurred during the solar maximum. Mesosphere-ionosphere anomalies observed simultaneously by the MR, the Aura satellite, and the rapid-run ionosonde during a period of major SSW include the following features. The mesospheric temperature minimum occurs 1 day ahead of the stratospheric maximum, and the mesospheric cooling is almost of the same value as the stratospheric warming (~50 K), the former decay faster than the latter. In the course of SSW, a strong mesospheric wind shear of ~70 m/s/km occurs. The wind turns clockwise (anticlockwise) from north-eastward (south-eastward) to south-westward (north-westward) above (below) 90 km. As the mesospheric temperature reaches its minimum, the gravity waves (GW) in the ionosphere with periods of 10-60 min decay abruptly while the GWs with longer periods are not affected. The effect is explained by selective filtering and/or increased turbulence near the mesopause.

  17. The physics of polarization

    NASA Astrophysics Data System (ADS)

    Landi Degl'Innocenti, Egidio

    ). Finally, the third part (Sects. 15-19) is devoted to give a sketch of the theory of the generation and transfer of polarized radiation in spectral lines. After a general introduction to the argument (Sect. 15), the concepts of density-matrix and of atomic polarization are illustrated in Sect. 16. In Sect. 17, a parallelism is established, within the framework of the theory of stellar atmospheres, between the usual formalism, which neglects polarization phenomena, and the more involved formalism needed for the interpretation of spectro-polarimetric observations. Some consequences of the radiative transfer equations for polarized radiation, pointing to the importance of dichroism phenomena in establishing the amplification condition via stimulated emission, are discussed in Sect. 18. The last section (Sect. 19) is devoted to introduce the problem of finding a self-consistent solution of the radiative transfer equations for polarized radiation and of the statistical equilibrium equations for the density matrix (non-LTE of the 2nd kind).

  18. New ice core records on the glacial/interglacial change in atmospheric δ13CO2

    NASA Astrophysics Data System (ADS)

    Fischer, H.; Schmitt, J.; Schneider, R.; Elsig, J.; Lourantou, A.; Leuenberger, M.; Stocker, T. F.; Koehler, P.; Lavric, J.; Raynaud, D. P.; Chappellaz, J. A.

    2010-12-01

    The reconstruction of δ13CO2 using Antarctic ice cores promises a deeper understanding on the causes of past atmospheric CO2 changes. Previous measurements on the Taylor Dome ice core over the last 30,000 years (Smith et al., 1999) indicated marine processes to be dominating the significant δ13CO2 changes over the transition, whereas glacial δ13CO2 was only slightly depleted relative to the Holocene (Leuenberger et al., 1992; Smith et al., 1999). However, significant uncertainty and the low temporal resolution of the Taylor Dome δ13CO2 data prevented a more detailed interpretation. Recently, substantial improvements have been made in the analysis and the resolution of ice core δ13CO2 records (Elsig et al., 2009; Lourantou et al., 2010). With these and new measurements presented here, three independent δ13CO2 data sets over the last glacial/interglacial transition have now been derived from the two EPICA and the Talos Dome ice cores. Two of the methods use traditional dry extraction techniques with a reproducibility of 0.07-0.1‰. The third method uses a novel sublimation technique with a reproducibility of 0.05‰. Here we compare the data sets, their analytical setups and discuss their joint information as well as their differences. The three records provide a more detailed picture on the temporal evolution of δ13CO2 and confirm two pronounced isotope minima between 18-12,000 years BP in parallel to the two major phases of CO2 increase (Lourantou et al., 2010; Smith et al., 1999) as also reflected in marine sediments (Marchitto et al., 2007; Skinner et al., 2010). Accordingly, a release of old carbon from the deep ocean is most likely responsible for a large part of the long-term increase in atmospheric CO2 in this time interval. However, the fast CO2 jumps at a round 12,000 and 14,000 years BP may be partly of terrestrial origin (Elsig, 2009; Köhler et al., 2010b). The new sublimation data set provides also unambiguous δ13CO2 data for clathrate ice in

  19. Polar Barchans

    NASA Technical Reports Server (NTRS)

    2004-01-01

    20 July 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows dark, barchan sand dunes of the north polar region of Mars. Barchan dunes are simple, rounded forms with two horns that extend downwind. Inequalities in local wind patterns may result in one horn being extended farther than the other, as is the case for several dunes in this image. The image also shows several barchans may merge to form a long dune ridge. The horns and attendant slip faces on these dunes indicate wind transport of sand from the upper left toward the lower right. The image is located near 77.6oN, 103.6oW. The picture covers an area about 3 km (1.9 mi) wide; sunlight illuminates the scene from the lower left.

  20. Polar Polygons

    NASA Technical Reports Server (NTRS)

    2004-01-01

    26 December 2003 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) picture displays polygons outlined by cracks in the martian south polar region. This southern summer view was acquired in October 2003 and is located near 86.9oS, 170.6oW. Polygons similar in size and shape to these are common in the arctic and antarctic regions of Earth. On Earth, they indicate the presence (or the past presence) of ground ice and the freeze-thaw cycles that accompany this ice. On Mars, whether ground ice was responsible for these landforms is uncertain, but their presence is suggestive that ground ice may exist or may once have existed in this region. The picture covers an area 3 km (1.9 mi) wide. Sunlight illuminates the scene from the upper left.

  1. Titan's Polar Atmosphere

    NASA Astrophysics Data System (ADS)

    Flasar, F. M.; Achterberg, R. K.; Schinder, P. J.

    2015-12-01

    its formation. A key question is whether the more compact polar vortex and colder temperatures seen in the south will evolve to the conditions observed in the north in midwinter, or whether the poles behave asymmetrically. Observations from the remainder of the Cassini Mission can elucidate this.

  2. Glacial-interglacial cycles of erosion and sediment transport along the western North American margin constrained by reconciling geologic and climate model data sets

    NASA Astrophysics Data System (ADS)

    Vanlaningham, S.; Pisias, N. G.; Duncan, R. A.; Hostetler, S. W.; Wilson, K. L.

    2009-12-01

    This study aims to determine whether observed shifts in sediment source (indicated by bulk sediment 40Ar-39Ar and Nd isotopic tracers) at a northeast Pacific core site are in response to variations in river basin erosion or transport pathways of terrigenous sediment once it reaches the ocean. We synthesize geologic and climate model data sets to evaluate whether climate model (REGCM2) outputs of precipitation-evaporation (P-E) can be linked to observed changes in erosion and landscape evolution along the western North American margin (core site EW9504-17PC, offshore southern Oregon) over the last glacial-interglacial cycle. This site is ideally located to test this new approach as it captures the combined sediment fluxes from coastal N. California/S. Oregon and the interior Cascade Volcanic Ranges, which have drastically different 40Ar-39Ar bedrock ages (130-147 Ma versus 10-30 Ma, respectively) and different climate responses occurring on glacial-interglacial timescales. We perturb a watershed-scale model of bedrock 40Ar-39Ar ages by the P-E changes to reproduce the total range of variability observed in downcore, bulk sediment 40Ar-39Ar ages and Nd isotopic values at the core site. We find that climate model percent changes in P-E values cannot reproduce the total range of variability seen in the provenance record before 22 ka without invoking drastic reductions in Klamath Mountain and Eel River sediment sources. A relatively unconstrained variable in the source area at this time is the presence of a large pluvial lake, Lake Modoc. It is possible that discharges from it could carry large volumes of young, Cascade Mountain-derived sediments offshore. Alternatively, an offshore switch in ocean current direction or reduction (relative to present-day) could explain the downcore sedimentological changes, as material discharged from the Eel River (the largest sediment source south of the core site) would not be carried north. To reproduce the observed downcore shift in

  3. Sediment core fossils in ancient Lake Ohrid: testing for faunal change in molluscs since the Last Interglacial period

    NASA Astrophysics Data System (ADS)

    Albrecht, C.; Vogel, H.; Hauffe, T.; Wilke, T.

    2010-05-01

    Ancient Lake Ohrid is probably of early Pleistocene or Pliocene origin and amongst the few lakes in the world harboring an outstanding degree of endemic biodiversity. Although there is a long history of evolutionary research in Lake Ohrid, particularly on molluscs, a mollusc fossil record has been missing up to date. For the first time, gastropod and bivalve fossils are reported from the basal, calcareous part of a 2.6 m long sediment succession (core Co1200) from the north-eastern part of Lake Ohrid. Electron spin resonance (ESR) dating of mollusc shells from the same stratigraphic level yielded an age of 130±28 ka. Lithofacies III sediments, i.e. a subdivision of the stratigraphic unit comprising the basal succession of core Co1200 between 181.5-263 cm appeared solid, grayish-white, and consisted almost entirely of silt-sized endogenic calcite (CaCO3>70%) and intact and broken mollusc shells. Here we compare the faunal composition of the thanatocoenosis with recent mollusc associations in Lake Ohrid. A total of 13 mollusc species (9 gastropod and 4 bivalve species) could be identified within Lithofacies III sediments. The value of sediment core fossils for reconstructing palaeoenvironmental settings was evaluated. The agreement between sediment and palaeontological proxies was tested. The combined findings of the ecological study and the sediment characteristics suggest deposition in a shallow water environment during the Last Interglacial period. We tested for major faunal changes since the Last Interglacial period and searched for signs of extinction events. The fossil fauna exclusively included species also found in the present fauna, i.e. no extinction events are evident for this site since the Last Interglacial. The thanatocoenosis showed the highest similarity with recent Intermediate Layer (5-25 m) mollusc assemblages. The demonstrated existence of a mollusc fossil record in Lake Ohrid sediment cores also has great significance for future deep drilling

  4. Potential of Lake Ohrid for long palaeoclimatic and palaeoenvironemental records: The last glacial-interglacial cycle (140 ka)

    NASA Astrophysics Data System (ADS)

    Belmecheri, S.; von Grafenstein, U.; Namiotko, T.; Robert, C. M.; Andersen, N.; Danielopol, D. L.; Caron, B.; Bordon, A.; Regnier, D.; Mazaud, A.; Sulpizio, R.; Zanchetta, G.; Grenier, C.; Tiercelin, J.; Fouache, E.; Lézine, A.

    2009-12-01

    Lake Ohrid (Albania, Macedonia) is probably the oldest and one of the deepest lakes in Europe. It potentially provides a continuous palaeoenvironmental record over the entire Quaternary. In 2004, a 10-m-long sediment record (JO2004-1) was recovered from the south-western part of the lake from a depth of 100 m (40°55.000 N, 20°40.297 E). The record is a composite of two series of consecutive 3-m-long sections taken from two sites within 5 m lateral distance using a modified Streif-Livingston piston corer (UWITEC, Austria). On the basis of seven AMS radiocarbon dating, five tephras layers and derived accumulation rate model, the Ohrid sequence extends back to 140 ka. It covers the last glacial-interglacial cycle with nearly continuous sedimentation (0.075 mm/yr, on average), except for a major hiatus (at 532.4 cm) of roughly 12,000 years between 102.75 and 89.90 ka. We evaluate the potential of using the oxygen and carbon isotope signature of the calcite of the benthic ostracod valves deposited in Lake Ohrid sediments as a palaeoclimate proxy. Twelve ostracod species, which are all endemic to Lake Ohrid, were preserved only during the interglacial phases. Their absence during full glacial periods is most likely due to calcium carbonate under-saturation of the lake water, when permafrost prohibited infiltration of atmospheric water into the limestone complexes in the lake drainage basin. For periods with ostracod preservation, the oxygen isotope signature of ostracod calcite is a reliable measure of the oxygen isotope composition of past lake water. However, the climatic interpretation of this record is strongly biased by water balance variations and by varying contribution of different vapour sources. The carbon isotope record of ostracods responds more consistently to climatic changes, and is a potentially quantifiable proxy for vegetation cover and soil build-up. Ostracod preservation and oxygen and carbon isotopes both record a succession of glacial-interglacial

  5. Eastern Mediterranean sea levels through the last interglacial from a coastal-marine sequence in northern Israel

    NASA Astrophysics Data System (ADS)

    Sivan, D.; Sisma-Ventura, G.; Greenbaum, N.; Bialik, O. M.; Williams, F. H.; Tamisiea, M. E.; Rohling, E. J.; Frumkin, A.; Avnaim-Katav, S.; Shtienberg, G.; Stein, M.

    2016-08-01

    A last interglacial (Marine Isotope Stage, MIS5e) marine-coastal sequence has been identified along the Galilee coast of Israel, with the type section located at Rosh Hanikra (RH). The microtidal regime and tectonic stability, along with the detailed stratigraphy of the RH shore, make the study region ideally suited for determining relative sea level (RSL) through the MIS5e interval in the eastern Mediterranean. The sequence contains fossilized microtidal subunits at a few meters above the current sea level. Unfortunately, all fossils were found to be altered, so that U-Th datings cannot be considered to represent initial deposition. We contend that U-Th dating of Strombus bubonius shells (recrystallized to calcite) suffices to indicate a lower limit of ∼110 ± 8 ka for the time sea level dropped below the RH sedimentary sequence. The RH-section comprises three main subunits of a previously determined member (the Yasaf Member): (a) a gravelly unit containing the diagnostic gastropod Strombus bubonius Lamarck (Persististrombus latus), which was deposited in the intertidal to super-tidal stormy zone; (b) Vermetidae reef domes indicating a shallow-water depositional environment; and (c) coarse to medium-sized, bioclastic sandstone, probably deposited in the shallow sub-tidal zone. The sequence overlies three abrasion platforms that are cut by tidal channels at elevations of +0.8 m, +2.6 m and +3.4 m, and which are filled with MIS5e sediments. We present a detailed study of the sequence, with emphasis on stratigraphic, sedimentological, and palaeontological characteristics that indicate sea-level changes. Although without precise absolute dating, the stratigraphic sequence of RH through MIS5e allows us to identify a time-series of RSL positions, using the elevations of three stratigraphic subunits. Reconstructed RSL values range from +1.0 m to +7 m (with uncertainly < 1 m), and most fall within a narrow range of +1.0 to +3.3 m. Toward the end of MIS5e, RSL exceeded

  6. Cross-polarization for dissolution dynamic nuclear polarization.

    PubMed

    Batel, Michael; Däpp, Alexander; Hunkeler, Andreas; Meier, Beat H; Kozerke, Sebastian; Ernst, Matthias

    2014-10-21

    Dynamic nuclear polarization (DNP) in combination with subsequent dissolution of the sample allows the detection of low-γ nuclei in the solution state with a signal gain of up to tens of thousand times compared to experiments starting from Boltzmann conditions. The long polarization build-up times of typically more than one hour are a drawback of this technique. The combination of dissolution DNP with cross-polarization (CP) in the solid state was shown to have the potential to overcome this disadvantage. In this article we discuss the cross-polarization step under dissolution DNP conditions in more detail. We show that adiabatic half-passage pulses allow us to enhance the CP efficiency in power-limited DNP probes. As a low-power alternative to Hartmann-Hahn CP we also demonstrate the applicability of frequency-swept de- and re-magnetization pulses for polarization transfer via dipolar order. We investigate the implications and restrictions of the common solid-state DNP mechanisms to the DNP-CP technique and apply a spin-thermodynamic model based on the thermal-mixing mechanism. The model allows us to investigate the dynamics of the polarization levels in a system with two nuclear Zeeman reservoirs and explains the enhanced DNP efficiency upon solvent deuteration within a spin-thermodynamic picture. PMID:25182534

  7. Lithologic expressions of glacial/interglacial and millennial-scale variability in the Pacific sub-Arctic record during the Pleistocene (Bering Sea, IODP Exp. 323)

    NASA Astrophysics Data System (ADS)

    Drake, M.; Aiello, I. W.

    2012-12-01

    Diatom-rich, Pleistocene sediments collected in the Bering Sea during IODP Exp. 323 in the Bering Slope (Sites U1339 and U1344) and at the Bowers Ridge (Site U1340) show prominent variability of physical properties (e.g. bulk density), lithology and in the preservation of diatom valves. Using the shipboard physical property data in combination with newly generated smear slide counts and laser particle size (LPS) analyses we were able to quantify the sedimentary components for statistical analysis. Our data confirm that bulk density is negatively correlated with mean grain size (~30%) and abundance of diatoms (~40%) while it positively correlates with clay size particles (~20%) and silt-size siliciclastic particles (~20%). However, clay size particles and silt-size siliciclastic show no significant correlation, suggesting independent sources. We also found that diatom valve integrity is correlated with the abundance of diatoms (~40%) suggesting that diatom preservation increases with increasing opal fluxes. Finally, we found a surprisingly low correlation (only ~30%) between abundance of clay minerals (from smear slide counts) and percent clay-sized particles (LPS); SEM analysis supports the interpretation that a significant portion of clay-sized particles could derive from the dissolution/fragmentation of diatom biosilica. In conclusion, more than 40% of lithologic variability in the Bering Sea sediments reflects changes in the abundance of diatoms and siliciclastic particles: glacial/stadial (interglacial/interstadial) conditions were characterized by lower (higher) primary productivity, higher (lower) terrigenous input, and diatom valve dissolution and formation of clay-size biosilica particles (higher diatom valve preservation). Our approach offers new insights on the links between changes in sedimentation and oceanography at different scales of climate variability in the Bering Sea and potentially in other similar high latitude basins.

  8. Cova del Rinoceront (Castelldefels, Barcelona): a terrestrial record for the Last Interglacial period (MIS 5) in the Mediterranean coast of the Iberian Peninsula

    NASA Astrophysics Data System (ADS)

    Daura, J.; Sanz, M.; Julià, R.; García-Fernández, D.; Fornós, J. J.; Vaquero, M.; Allué, E.; López-García, J. M.; Blain, H. A.; Ortiz, J. E.; Torres, T.; Albert, R. M.; Rodríguez-Cintas, À.; Sánchez-Marco, A.; Cerdeño, E.; Skinner, A. R.; Asmeron, Y.; Polyak, V. J.; Garcés, M.; Arnold, L. J.; Demuro, M.; Pike, A. W. G.; Euba, I.; Rodríguez, R. F.; Yagüe, A. S.; Villaescusa, L.; Gómez, S.; Rubio, A.; Pedro, M.; Fullola, J. M.; Zilhão, J.

    2015-04-01

    The Cova del Rinoceront, a site in NE Iberia, contains a thick sedimentary fill preserving a faunal archive from the penultimate glacial and the the last interglacial periods. Layers I to III have been dated to between 74 and 147 ka, coinciding with MIS 5a to 5e, a period poorly represented in the Mediterranean terrestrial record. The results from Cova del Rinoceront are of broader interest for the reconstruction of ecological dynamics during warm stages and the understanding of the evolution and geographical variation of several taxa. The palaeoecological evidence suggests a landscape dominated by mixed wooded vegetation with mild climatic conditions, slightly more humid than today. Several vertebrate taxa, including Haploidoceros mediterraneus, Stephanorhinus hundsheimensis and Glis glis, are documented for the first time in the early Upper Pleistocene of Europe, showing that these species persisted across the region for longer than previously thought. In addition, the recovery of a small lithic assemblage indicates human presence in the surroundings of the site. The 11 m-thick stratigraphic section also provides an ideal setting in which to compare several geochronological methods. U-Th dating of the flowstones that cap the deposit, of speleothems formed along the cave walls, and of speleothems buried by the deposit at different elevations provides minimum and maximum ages of 74 and 175 ka, respectively, for the accumulation. The ages obtained by luminescence, electron spin resonance (ESR), amino acid racemisation (AAR), palaeomagnetism and U-series dating of bone are in good agreement with each other and are stratigraphically consistent. This well-dated faunal succession presents a unique opportunity to assess changes in the Pleistocene fauna of the Mediterranean coast over an interval of more than 100 ka.

  9. Phylogenetic assemblage structure of North American trees is more strongly shaped by glacial-interglacial climate variability in gymnosperms than in angiosperms.

    PubMed

    Ma, Ziyu; Sandel, Brody; Svenning, Jens-Christian

    2016-05-01

    How fast does biodiversity respond to climate change? The relationship of past and current climate with phylogenetic assemblage structure helps us to understand this question. Studies of angiosperm tree diversity in North America have already suggested effects of current water-energy balance and tropical niche conservatism. However, the role of glacial-interglacial climate variability remains to be determined, and little is known about any of these relationships for gymnosperms. Moreover, phylogenetic endemism, the concentration of unique lineages in restricted ranges, may also be related to glacial-interglacial climate variability and needs more attention. We used a refined phylogeny of both angiosperms and gymnosperms to map phylogenetic diversity, clustering and endemism of North American trees in 100-km grid cells, and climate change velocity since Last Glacial Maximum together with postglacial accessibility to recolonization to quantify glacial-interglacial climate variability. We found: (1) Current climate is the dominant factor explaining the overall patterns, with more clustered angiosperm assemblages toward lower temperature, consistent with tropical niche conservatism. (2) Long-term climate stability is associated with higher angiosperm endemism, while higher postglacial accessibility is linked to to more phylogenetic clustering and endemism in gymnosperms. (3) Factors linked to glacial-interglacial climate change have stronger effects on gymnosperms than on angiosperms. These results suggest that paleoclimate legacies supplement current climate in shaping phylogenetic patterns in North American trees, and especially so for gymnosperms. PMID:27252830

  10. A Tale of Two Interglacials: A Stalagmite Stable Isotope Record of Climate inYucatán, Mexico Since 128,000 YBP

    NASA Astrophysics Data System (ADS)

    Frappier, A. E.; Brenner, L. D.

    2010-12-01

    Earth’s glacial climate has been punctuated with warm interglacial periods lasting ~10,000 years. Current anthropogenic greenhouse gas forcing is pushing climate towards a state that deviates from established Quaternary patterns. In predicting future rapid climate changes, two key analogs are the end of the last glacial, Termination 1 at ~14,000 years ago, and the Eemian, the penultimate interglacial ~130-114,000 years ago. Speleothems or cave formations record changes in the isotopic composition of rainwater infiltrating the cave during paleoclimate shifts. Stalagmite YAX-2 was deposited in Yucatán, Mexico within a -40m deep cave lacking natural entrances from ~128,000 years ago to the most recent millennium, therefore including both analogs. U/Th dating shows that YAX-2 grew most rapidly during interglacials. We present the YAX-2 record of stable carbon and oxygen isotope values as indicators of environmental change in Yucatán, Mexico and compare our results to published research on abrupt tropical climate change and interglacial climate dynamics.

  11. Sea-level history of past interglacial periods from uranium-series dating of corals, Curaçao, Leeward Antilles islands

    NASA Astrophysics Data System (ADS)

    Muhs, Daniel R.; Pandolfi, John M.; Simmons, Kathleen R.; Schumann, R. Randall

    2012-09-01

    Curaçao has reef terraces with the potential to provide sea-level histories of interglacial periods. Ages of the Hato (upper) unit of the "Lower Terrace" indicate that this reef dates to the last interglacial period, Marine Isotope Stage (MIS) 5.5. On Curaçao, this high sea stand lasted at least 8000 yr (~ 126 to ~ 118 ka). Elevations and age of this reef show that late Quaternary uplift rates on Curaçao are low, 0.026-0.054 m/ka, consistent with its tectonic setting. Ages of ~ 200 ka for corals from the older Cortalein unit of the Lower Terrace correlate this reef to MIS 7, with paleo-sea level estimates ranging from - 3.3 m to + 2.3 m. The estimates are in agreement with those for MIS 7 made from other localities and indicate that the penultimate interglacial period was a time of significant warmth, on a par with the present interglacial period. The ~ 400 ka (MIS 11) Middle Terrace I on Curaçao, dated by others, may have formed from a paleo-sea level of + 8.3 to + 10.0 m, or (less likely) + 17 m to + 20 m. The lower estimates are conservative compared to previous studies, but still require major ice sheet loss from Greenland and Antarctica.

  12. The relative importance of methane sources and sinks over the Last Interglacial period and into the last glaciation

    NASA Astrophysics Data System (ADS)

    Quiquet, A.; Archibald, A. T.; Friend, A. D.; Chappellaz, J.; Levine, J. G.; Stone, E. J.; Telford, P. J.; Pyle, J. A.

    2015-03-01

    All recent climatic projections for the next century suggest that we are heading towards a warmer climate than today (Intergovernmental Panel on Climate Change; Fifth Assessment Report), driven by increasing atmospheric burdens of anthropogenic greenhouse gases. In particular, the volume mixing ratio of methane, the second-most important anthropogenic greenhouse gas, has increased by a factor of ˜2.5 from the beginning of the European Industrial Revolution. Due to their complex responses to climatic factors, understanding of the dynamics of future global methane emissions and sinks is crucial for the next generation of climate projections. Of relevance to this problem, the Earth likely experienced warmer average temperatures than today during the Last Interglacial (LIG) period (130-115 kaBP). Interestingly, ice cores do not indicate a different methane mixing ratio from the Pre-Industrial Holocene (PIH), in other words the current interglacial period prior to anthropogenic influence. This is surprising as warmer temperatures might be expected to increase methane emissions. The present study aims to improve our understanding of the changes in the global methane budget through quantifying the relative importance of sources and sinks of methane during the last full glacial-interglacial cycle. A fairly limited number of studies have investigated this cycle at the millenium time scale with most of them examining the doubling in CH4 from the Last Glacial Maximum (LGM) to the PIH. Though it is still a matter of debate, a general consensus suggests a predominant role to the change in methane emissions from wetlands and only a limited change in the oxidising capacity of the atmosphere. In the present study we provide an estimate of the relative importance of sources and sinks during the LIG period, using a complex climate-chemistry model to quantify the sinks, and a methane emissions model included in a global land surface model, for the sources. We are not aware of any

  13. Trends in stomatal density and 13C/12C ratios of Pinus flexilis needles during last glacial-interglacial cycle

    USGS Publications Warehouse

    Van De Water, Peter K.; Leavitt, Steven W.; Betancourt, J.L.

    1994-01-01

    Measurements of stomatal density and ?? 13C of limber pine (Pinus flexilis) needles (leaves) preserved in pack rat middens from the Great Basin reveal shifts in plant physiology and leaf morphology during the last 30,000 years. Sites were selected so as to offset glacial to Holocene climatic differences and thus to isolate the effects of changing atmospheric CO2 levels. Stomatal density decreased ~17 percent and ?? 13C decreased ~1.5 per mil during deglaciation from 15,000 to 12,000 years ago, concomitant with a 30 percent increase in atmospheric CO2. Water-use efficiency increased ~15 percent during deglaciation, if temperature and humidity were held constant and the proxy values for CO2 and ?? 13C of past atmospheres are accurate. The ??13C variations may help constrain hypotheses about the redistribution of carbon between the atmosphere and biosphere during the last glacial-interglacial cycle.

  14. High-precision U-series dating of corals from Western Australia and implications for the timing and duration of the Last Interglacial

    NASA Astrophysics Data System (ADS)

    Stirling, C. H.; Esat, T. M.; McCulloch, M. T.; Lambeck, K.

    1995-10-01

    U-series ages using methods of thermal ionisation mass spectrometry (TIMS) are reported for Last Interglacial fossil reefs along the stable coastal margin of Western Australia. Thorium isotope ratios were measured with superior precision using methods of charge collection. High levels of precision in the measurement of both uranium and thorium isotopes has reduced the age uncertainty due to analytical errors, excluding the uncertainty in the decay constants, by a factor of four over the precisions reported by many earlier TIMS workers. Uncertainties in δ234U(T), determined from both 230Th/ 238U and 234U/ 238U, are also significantly smaller than previously reported, allowing samples which have undergone diagenetic exchange of uranium and thorium to be more easily identified. Strict criteria were adopted to screen the new Western Australian data. Reliable ages range from 127 to 122 ka. Published TIMS observations from other localities have been assessed using the same strict criteria. When these are combined with glacio-hydro isostatic sea-level models they indicate that the Last Interglacial period occurred from at least 130 to 117 ka. However, these age constraints are largely determined from single data points and need to be verified with additional ages before considering them to be robust estimates for the timing of onset and termination of the Last Interglacial. Globally, the main episode of reef growth appears to be confined to a narrow interval occurring from 127 to 122 ka, in direct agreement with the narrow range in ages obtained from the Western Australian sites. This may indicate that the Last Interglacial was of short duration, extending from 127 to 122 ka only. Alternatively, this interval may reflect a major reef-building event in the middle of a longer duration (130-117 ka) interglacial interval.

  15. TIMS U-series dating and stable isotopes of the last interglacial event in Papua New Guinea

    SciTech Connect

    Stein, M.; Wasserburg, G.J.; Chen, J.H. ); Aharon, P. ); Zhu, Z.R.; Chappell, J. ); Bloom, A. )

    1993-06-01

    The extensive flight of uplifted reef terraces which occurs along the Vitiaz strait on the northern flank of the Huon Peninsula in PNG (Papua New Guinea) contains a particularly good record of sea level changes in the last 250 ky. The Huon terraces were the target of an international expedition which took place in July--August 1988. In particular, the authors searched for suitable samples for U-series dating in a reef complex designated as VII, which is correlated with the last interglacial episode and high sea level stand. This complex is composed of a barrier reef (VIIb), a lagoon, and a fringing reef (VIIa). Twelve corals from these terraces and two corals from the older reef complex VIII were selected for analysis. The petrography, oxygen and carbon isotope compositions, and magnesium and strontium concentrations were determined along with the concentrations and isotopic compositions of uranium and thorium. The simplest model for sea level height for terrace VII is a continuous rise between 134 and 118 ky. Alternatively, there may have been two periods of rapid sea level rise. In contrast, in the Bahamas, there is evidence that sea level remained rather constant over the time interval 132 to 120 ky. The absence of ages between 132 and 120 ky in PNG could be the result of changes in the local tectonic uplift rates during that time, or erosion that disrupted the continuous record. In any event, the authors find no basis for accepting a single brief time for the age of the last interglacial and applying this age as a precise chronometer for worldwide correlation, or as a test of climatic models. The older ages reported here precede the Milankovitch solar insolation peak at 128 ky, and the younger ages are [approximately]10 ky after this peak. If the present high-precision data are correct, then it will be necessary to reassess the validity of the Milankovitch theory of climatic changes. 76 refs., 6 figs., 6 tabs.

  16. Glacial/Interglacial changes of southwest Pacific intermediate- and deep-water circulation over the last 350,000 years

    NASA Astrophysics Data System (ADS)

    Ronge, Thomas; Tiedemann, Ralf; Prange, Matthias; Merkel, Ute; Kuhn, Gerhard; Lamy, Frank

    2015-04-01

    On glacial/interglacial timescales, Southern Ocean air-sea gas exchange is considered to be an important factor, driving the variability of atmospheric CO2 concentrations. To understand the role of oceanic variability in the global carbon cycle, it is necessary to reconstruct changes in deep- and intermediate-water circulation and chemistry of Southern Ocean water masses. In this context, our study aims on the reconstruction of glacial/interglacial changes in the vertical expansion of southwest Pacific Antarctic Intermediate Water. For our study, we compared isotope records (δ13C and δ18O) measured on the epibenthic foraminifera Cibicidoides wuellerstorfi from the Antarctic Intermediate Water and the Upper Circumpolar Deep Water (943 - 2066 m water depth) off New Zealand. We used two sediment cores from the Tasman Sea (MD06-2990 and MD06-2986), retrieved during R/V Marion Dufresne cruise MD152, and three sediment cores from the Bounty Trough east of New Zealand (MD97-2120, SO 213-82-1 and SO 213-84-1). Comparing these records, we can monitor changes in southwest Pacific water mass circulation over the past 350,000 years. Over this time period, we record a significant shoaling of the boundary between Antarctic Intermediate Water and Upper Circumpolar Deep Water during all glacial stages. We propose that freshwater input by melting sea ice into the glacial intermediate-water increased the buoyancy difference to underlying deep-waters, thus hampering the downward expansion of southwest Pacific Antarctic Intermediate Water during glacials. This interpretation is consistent with our modeling results, based on the Community Climate System model version 3, which also indicate a shoaling of glacial intermediate waters due to the input of meltwater. The glacial upward displacement of the water mass boundary significantly increased the vertical extent of circumpolar deep-waters, consequently extending the volume of the proposed glacial deep-water carbon pool.

  17. Glacial-interglacial temperature change in the tropical West Pacific: A comparison of stalagmite-based paleo-thermometers

    NASA Astrophysics Data System (ADS)

    Meckler, A. Nele; Affolter, Stéphane; Dublyansky, Yuri V.; Krüger, Yves; Vogel, Nadia; Bernasconi, Stefano M.; Frenz, Martin; Kipfer, Rolf; Leuenberger, Markus; Spötl, Christoph; Carolin, Stacy; Cobb, Kim M.; Moerman, Jessica; Adkins, Jess F.; Fleitmann, Dominik

    2015-11-01

    In the tropics, geochemical records from stalagmites have so far mainly been used to qualitatively reconstruct changes in precipitation, but several new methods to reconstruct past temperatures from stalagmite material have emerged recently: i) liquid-vapor homogenization of fluid inclusion water ii) noble gas concentrations in fluid inclusion water, iii) the partitioning of oxygen isotopes between fluid inclusion water and calcite, and iv) the abundance of the 13C18O16O ('clumped') isotopologue in calcite. We present, for the first time, a direct comparison of these four paleo-thermometers by applying them to a fossil stalagmite covering nearly two glacial-interglacial cycles (Marine Isotope Stages (MIS) 12-9) and to two modern stalagmites, all from northern Borneo. The temperature estimates from the different methods agree in most cases within errors for both the old and recent samples; reconstructed formation temperatures of the recent samples match within 2-sigma errors with measured cave temperatures. However, slight but systematic deviations are observed between noble gas and liquid-vapor homogenization temperatures. Whereas the temperature sensitivity of fluid inclusion δ18O and clumped isotopes is currently debated, we find that the calibration of Tremaine et al. (2011) for fluid inclusion δ18O and a synthetic calcite-based clumped isotope calibration (Ziegler et al., in prep.) yield temperature estimates consistent with the other methods. All methods (with the potential exception of clumped isotopes) show excellent agreement on the amplitude of glacial-interglacial temperature change, indicating temperature shifts of 4-5 °C. This amplitude is similar to the amplitude of Mg/Ca-based regional sea surface temperature records, when correcting for sea level driven changes in cave elevation. Our reconstruction of tropical temperature evolution over the time period from 440 to 320 thousand years ago (ka) adds support to the view that climate sensitivity to

  18. Li/Ca in multiple species of benthic and planktonic foraminifera: thermocline, latitudinal, and glacial-interglacial variation 1

    NASA Astrophysics Data System (ADS)

    Hall, Jenney M.; Chan, L.-H.

    2004-02-01

    Li/Ca ratios were measured in planktonic and benthic foraminifera from a variety of hydrographic settings to investigate the factors influencing lithium incorporation into foraminiferal tests including temperature, dissolution, pressure, and interspecies differences. Down-core measurements of planktonic ( Orbulina universa, Globigerinoides ruber, and Globigerinoides sacculifer) and benthic foraminifera (calcitic Cibicides wuellerstorfi and aragonitic Hoeglandina elegans) show a systematic variation in Li/Ca with δ 18O through the last glacial-interglacial transition. All species examined exhibit an increase in Li/Ca between 14 to 50% from the Holocene to the last glacial maximum. Li/Ca generally increases with decreasing temperature as seen in a latitudinal transect of planktonic O. universa and down-slope benthic species along the Bahama Bank margins. Postdepositional dissolution possibly causes a decrease in planktonic foraminiferal Li/Ca along the Sierra Leone Rise, and increased water depth causes a decrease in benthic foraminiferal Li/Ca in the deep Caribbean. However, none of these effects are sufficient to account for the observed glacial-interglacial changes. Physiological factors such as calcification rate may affect the Li/Ca content of foraminiferal calcite. The calcification rate in turn may be a function of carbonate ion concentration of ambient ocean water. This work shows that incorporation of lithium by foraminifera appears to be influenced by factors other than seawater composition and does not appear to be dominated by changes in temperature, dissolution, or pressure. We hypothesize that the consistent increase in foraminiferal Li/Ca during the last glacial maximum may be linked to changes in seawater carbonate ion concentration. Important parameters to be tested include calcification rate and foraminiferal test size and weight. If foraminiferal Li/Ca is dominantly controlled by calcification rate as a function of seawater carbonate ion

  19. North Polar Cap

    NASA Technical Reports Server (NTRS)

    2004-01-01

    [figure removed for brevity, see original site]

    This week we will be looking at five examples of laminar wind flow on the north polar cap. On Earth, gravity-driven south polar cap winds are termed 'catabatic' winds. Catabatic winds begin over the smooth expanse of the cap interior due to temperature differences between the atmosphere and the surface. Once begun, the winds sweep outward along the surface of the polar cap toward the sea. As the polar surface slopes down toward sealevel, the wind speeds increase. Catabatic wind speeds in the Antartic can reach several hundreds of miles per hour.

    In the images of the Martian north polar cap we can see these same type of winds. Notice the streamers of dust moving downslope over the darker trough sides, these streamers show the laminar flow regime coming off the cap. Within the trough we see turbulent clouds of dust, kicked up at the trough base as the winds slow down and enter a chaotic flow regime.

    The horizontal lines in these images are due to framelet overlap and lighting conditions over the bright polar cap.

    Image information: VIS instrument. Latitude 86.5, Longitude 64.5 East (295.5 West). 40 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation

  20. North Polar Cap

    NASA Technical Reports Server (NTRS)

    2004-01-01

    [figure removed for brevity, see original site]

    This week we will be looking at five examples of laminar wind flow on the north polar cap. On Earth, gravity-driven south polar cap winds are termed 'catabatic' winds. Catabatic winds begin over the smooth expanse of the cap interior due to temperature differences between the atmosphere and the surface. Once begun, the winds sweep outward along the surface of the polar cap toward the sea. As the polar surface slopes down toward sealevel, the wind speeds increase. Catabatic wind speeds in the Antartic can reach several hundreds of miles per hour.

    In the images of the Martian north polar cap we can see these same type of winds. Notice the streamers of dust moving downslope over the darker trough sides, these streamers show the laminar flow regime coming off the cap. Within the trough we see turbulent clouds of dust, kicked up at the trough base as the winds slow down and enter a chaotic flow regime.

    The horizontal lines in these images are due to framelet overlap and lighting conditions over the bright polar cap.

    Image information:VIS instrument. Latitude 86.5, longitude 57.4 East (302.6 West). 40 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is

  1. North Polar Cap

    NASA Technical Reports Server (NTRS)

    2004-01-01

    [figure removed for brevity, see original site]

    This week we will be looking at five examples of laminar wind flow on the north polar cap. On Earth, gravity-driven south polar cap winds are termed 'catabatic' winds. Catabatic winds begin over the smooth expanse of the cap interior due to temperature differences between the atmosphere and the surface. Once begun, the winds sweep outward along the surface of the polar cap toward the sea. As the polar surface slopes down toward sealevel, the wind speeds increase. Catabatic wind speeds in the Antartic can reach several hundreds of miles per hour.

    In the images of the Martian north polar cap we can see these same type of winds. Notice the streamers of dust moving downslope over the darker trough sides, these streamers show the laminar flow regime coming off the cap. Within the trough we see turbulent clouds of dust, kicked up at the trough base as the winds slow down and enter a chaotic flow regime.

    The horizontal lines in these images are due to framelet overlap and lighting conditions over the bright polar cap.

    Image information: VIS instrument. Latitude 84.3, Longitude 314.4 East (45.6 West). 40 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation

  2. North Polar Cap

    NASA Technical Reports Server (NTRS)

    2004-01-01

    [figure removed for brevity, see original site]

    This week we will be looking at five examples of laminar wind flow on the north polar cap. On Earth, gravity-driven south polar cap winds are termed 'catabatic' winds. Catabatic winds begin over the smooth expanse of the cap interior due to temperature differences between the atmosphere and the surface. Once begun, the winds sweep outward along the surface of the polar cap toward the sea. As the polar surface slopes down toward sealevel, the wind speeds increase. Catabatic wind speeds in the Antartic can reach several hundreds of miles per hour.

    In the images of the Martian north polar cap we can see these same type of winds. Notice the streamers of dust moving downslope over the darker trough sides, these streamers show the laminar flow regime coming off the cap. Within the trough we see turbulent clouds of dust, kicked up at the trough base as the winds slow down and enter a chaotic flow regime.

    The horizontal lines in these images are due to framelet overlap and lighting conditions over the bright polar cap.

    Image information: VIS instrument. Latitude 84.2, Longitude 57.4 East (302.6 West). 40 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation

  3. Polarized internal target apparatus

    DOEpatents

    Holt, R.J.

    1984-10-10

    A polarized internal target apparatus with a polarized gas target of improved polarization and density (achieved by mixing target gas atoms with a small amount of alkali metal gas atoms, and passing a high intensity polarized light source into the mixture to cause the alkali metal gas atoms to become polarized which interact in spin exchange collisions with target gas atoms yielding polarized target gas atoms) is described.

  4. Polarized internal target apparatus

    DOEpatents

    Holt, Roy J.

    1986-01-01

    A polarized internal target apparatus with a polarized gas target of improved polarization and density achieved by mixing target gas atoms with a small amount of alkali metal gas atoms, and passing a high intensity polarized light source into the mixture to cause the alkali metal gas atoms to become polarized which interact in spin exchange collisions with target gas atoms yielding polarized target gas atoms.

  5. Polar Attraction.

    ERIC Educational Resources Information Center

    Hoff, David J.

    2001-01-01

    Describes the experiences of a high school science teacher who joined a 5-week National Science Foundation research excursion to Antarctica that involved him as a participating researcher. The paper explains challenges that he encountered related to the physical environment, working conditions, and relationships with his colleagues. (SM)

  6. Polar Color

    NASA Technical Reports Server (NTRS)

    2004-01-01

    [figure removed for brevity, see original site]

    Released 3 May 2004 This nighttime visible color image was collected on January 1, 2003 during the Northern Summer season near the North Polar Troughs.

    This daytime visible color image was collected on September 4, 2002 during the Northern Spring season in Vastitas Borealis. The THEMIS VIS camera is capable of capturing color images of the martian surface using its five different color filters. In this mode of operation, the spatial resolution and coverage of the image must be reduced to accommodate the additional data volume produced from the use of multiple filters. To make a color image, three of the five filter images (each in grayscale) are selected. Each is contrast enhanced and then converted to a red, green, or blue intensity image. These three images are then combined to produce a full color, single image. Because the THEMIS color filters don't span the full range of colors seen by the human eye, a color THEMIS image does not represent true color. Also, because each single-filter image is contrast enhanced before inclusion in the three-color image, the apparent color variation of the scene is exaggerated. Nevertheless, the color variation that does appear is representative of some change in color, however subtle, in the actual scene. Note that the long edges of THEMIS color images typically contain color artifacts that do not represent surface variation.

    Image information: VIS instrument. Latitude 79, Longitude 346 East (14 West). 19 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with

  7. Penta prism laser polarizer.

    PubMed

    Lotem, H; Rabinovitch, K

    1993-04-20

    A novel type of laser prism polarizer is proposed. The polarizer is characterized by a high transmission efficiency, a high optical damage threshold, and a high extinction ratio. The polarizer is shaped like a regular penta prism and, thus, it is a constant deviation angle device. Polarization effects occur upon the two internal cascade reflections in the prism. Anisotropic and Isotropic types of the polarizer are discussed. The isotropic polarizer is a prism made of a high refractive-index glass coated by multilayer polarization-type dielectric coatings. Efficient s-state polarization is obtained because of p-state leakage upon the two internal cascade reflections. The anisotropic polarizer is made of a birefringent crystal in which angular polarization splitting is obtained by the bireflectance (double-reflection) effect. Fanning of a laser beam into up to eight polarized beams is possible in a prism made of a biaxial crystal. PMID:20820335

  8. Full Stokes polarization imaging camera

    NASA Astrophysics Data System (ADS)

    Vedel, M.; Breugnot, S.; Lechocinski, N.

    2011-10-01

    Objective and background: We present a new version of Bossa Nova Technologies' passive polarization imaging camera. The previous version was performing live measurement of the Linear Stokes parameters (S0, S1, S2), and its derivatives. This new version presented in this paper performs live measurement of Full Stokes parameters, i.e. including the fourth parameter S3 related to the amount of circular polarization. Dedicated software was developed to provide live images of any Stokes related parameters such as the Degree Of Linear Polarization (DOLP), the Degree Of Circular Polarization (DOCP), the Angle Of Polarization (AOP). Results: We first we give a brief description of the camera and its technology. It is a Division Of Time Polarimeter using a custom ferroelectric liquid crystal cell. A description of the method used to calculate Data Reduction Matrix (DRM)5,9 linking intensity measurements and the Stokes parameters is given. The calibration was developed in order to maximize the condition number of the DRM. It also allows very efficient post processing of the images acquired. Complete evaluation of the precision of standard polarization parameters is described. We further present the standard features of the dedicated software that was developed to operate the camera. It provides live images of the Stokes vector components and the usual associated parameters. Finally some tests already conducted are presented. It includes indoor laboratory and outdoor measurements. This new camera will be a useful tool for many applications such as biomedical, remote sensing, metrology, material studies, and others.

  9. Conditional unitary transformation on biphotons

    SciTech Connect

    Brida, G.; Genovese, M.; Gramegna, M.; Chekhova, M.V.; Krivitsky, L.A.; Kulik, S.P.

    2004-09-01

    A conditional unitary transformation (90 deg. polarization rotation) is performed at single-photon level. The transformation is realized by rotating polarization for one of the photons of a polarization-entangled biphoton state (signal photon) by means of a Pockel cell triggered by the detection of the other (idler) photon after polarization selection. As a result, the state of the signal photon is losslessly changed from being completely unpolarized to being partially polarized, so that the final polarization degree is given by the idler detector quantum efficiency. This experiment can be used for developing a different method of absolute quantum efficiency calibration.

  10. Polarized Light in Astronomy.

    ERIC Educational Resources Information Center

    King, D. J.

    1983-01-01

    The application of very sensitive electronic detecting devices during the last decade has revolutionized and revitalized the study of polarization in celestial objects. The nature of polarization, how polaroids work, interstellar polarization, dichroic filters, polarization by scattering, and modern polarimetry are among the topics discussed. (JN)

  11. Linearly polarized fiber amplifier

    DOEpatents

    Kliner, Dahv A.; Koplow, Jeffery P.

    2004-11-30

    Optically pumped rare-earth-doped polarizing fibers exhibit significantly higher gain for one linear polarization state than for the orthogonal state. Such a fiber can be used to construct a single-polarization fiber laser, amplifier, or amplified-spontaneous-emission (ASE) source without the need for additional optical components to obtain stable, linearly polarized operation.

  12. Controlled switching of ultrafast circular polarization oscillations in spin-polarized vertical-cavity surface-emitting lasers

    SciTech Connect

    Höpfner, Henning Lindemann, Markus; Gerhardt, Nils C.; Hofmann, Martin R.

    2014-01-13

    We demonstrate a scheme for controlled switching of polarization oscillations in spin-polarized vertical-cavity surface-emitting lasers (spin-VCSEL). Under hybrid electrical and optical pumping conditions, our VCSEL devices show polarization oscillations with frequencies far above the VCSEL's electrical modulation bandwidth. Using multiple optical pulses, we are able to excite and amplify these polarization oscillations. When specific phase and amplitude conditions for the optical excitation pulses are met, destructive interference leads to switch-off of the polarization oscillation, enabling the generation of controlled short polarization bursts.

  13. Nondiffracting transversally polarized beam.

    PubMed

    Yuan, G H; Wei, S B; Yuan, X-C

    2011-09-01

    Generation of a nondiffracting transversally polarized beam by means of transmitting an azimuthally polarized beam through a multibelt spiral phase hologram and then highly focusing by a high-NA lens is presented. A relatively long depth of focus (∼4.84λ) of the electric field with only radial and azimuthal components is achieved. The polarization of the wavefront near the focal plane is analyzed in detail by calculating the Stokes polarization parameters. It is found that the polarization is spatially varying and entirely transversally polarized, and the polarization singularity disappears at the beam center, which makes the central bright channel possible. PMID:21886250

  14. Stable isotope compositions of carbonate and inclusion-hosted water of speleothems from the last interglacial - spatial patterns of climate fluctuations in Europe

    NASA Astrophysics Data System (ADS)

    Demény, Attila; Kern, Zoltán; Czuppon, György; Németh, Alexandra; Leél-Őssy, Szabolcs; Shen, Chuan-Chou; Vennemann, Torsten

    2016-04-01

    Studies on the last interglacial (LIG) can provide information on how our environment behaved in a period of slightly higher global temperatures at about 120 ka compared to the current climate conditions. This paper presents complex stable H-C-O isotope records obtained for carbonate and fluid inclusion hosted water of U-Th dated stalagmites from the Baradla Cave system in Central Europe. Comparing C and O isotope data with records reported for other speleothem (cave-hosted carbonate) deposits from Europe revealed the complex behavior of these climate proxies, with a concerted relative increase in 18O of carbonates from 128 to 120 ka and synchronized shifts in the opposite direction after 119 ka. The hydrogen isotope analyses of inclusion-hosted water extracted from the BAR-II stalagmite also correspond to the regional climate proxy records, with meaningful deviations from global temperature trends. Beside the well known 120 ka climate optimum and the subsequent cooling starting at about 118 ka, the δD values show a negative peak at about 124-125 ka that does not appear in the C-O isotope data. This negative peak fits well to temperature and humidity changes inferred from proxy records from the northern Atlantic to the eastern Mediterranean. Spatial distributions of these variables show, that while the northern Atlantic ocean experienced a cold phase (possibly also dry in NW Europe), the Mediterranean region was characterized by warm, humid conditions and enhanced seasonality, most probably related to a freshwater flux to the North Atlantic and consequent large-scale heat and moisture transport changes affecting the Mediterranean. The combined interpretation of H-C-O isotope data revealed that the Alpine and Mediterranean regions behaved differently again during Greenland Stadial 26 (GS26, ~119 to 115.5 ka). While the Alpine records fluctuated in close agreement with the Central Greenland ice core δ18O data, the BAR-II stalagmite and southern European records

  15. 230Th/U dating of Last Interglacial brain corals from Bonaire (southern Caribbean) using bulk and theca wall material

    NASA Astrophysics Data System (ADS)

    Obert, J. Christina; Scholz, Denis; Felis, Thomas; Brocas, William M.; Jochum, Klaus P.; Andreae, Meinrat O.

    2016-04-01

    We compared the suitability of two skeletal materials of the Atlantic brain coral Diploria strigosa for 230Th/U-dating: the commonly used bulk material comprising all skeletal elements and the denser theca wall material. Eight fossil corals of presumably Last Interglacial age from Bonaire, southern Caribbean Sea, were investigated, and several sub-samples were dated from each coral. For four corals, both the ages and the activity ratios of the bulk material and theca wall agree within uncertainty. Three corals show significantly older ages for their bulk material than for their theca wall material as well as substantially elevated 232Th content and (230Th/238U) ratios. The bulk material samples of another coral show younger ages and lower (230Th/238U) ratios than the corresponding theca wall samples. This coral also contains a considerable amount of 232Th. The application of the available open-system models developed to account for post-depositional diagenetic effects in corals shows that none of the models can successfully be applied to the Bonaire corals. The most likely explanation for this observation is that the assumptions of the models are not fulfilled by our data set. Comparison of the theca wall and bulk material data enables us to obtain information about the open-system processes that affected the corals. The corals showing apparently older ages for their bulk material were probably affected by contamination with a secondary (detrital) phase. The most likely source of the detrital material is carbonate sand. The higher (230Th/232Th) ratio of this material implies that detrital contamination would have a much stronger impact on the ages than a contaminant with a bulk Earth (230Th/232Th) ratio and that the threshold for the commonly applied 232Th reliability criterion would be much lower than the generally used value of 1 ng g-1. The coral showing apparently younger ages for its bulk material was probably influenced by more than one diagenetic process. A

  16. Crossed elliptical polarization undulator

    SciTech Connect

    Sasaki, Shigemi

    1997-05-01

    The first switching of polarization direction is possible by installing two identical helical undulators in series in a same straight section in a storage ring. By setting each undulator in a circular polarization mode in opposite handedness, one can obtain linearly polarized radiation with any required polarization direction depending on the modulator setting between two undulators. This scheme can be used without any major degradation of polarization degree in any low energy low emittance storage ring.

  17. Polarization-balanced beamsplitter

    DOEpatents

    Decker, D.E.

    1998-02-17

    A beamsplitter assembly is disclosed that includes several beamsplitter cubes arranged to define a plurality of polarization-balanced light paths. Each polarization-balanced light path contains one or more balanced pairs of light paths, where each balanced pair of light paths includes either two transmission light paths with orthogonal polarization effects or two reflection light paths with orthogonal polarization effects. The orthogonal pairing of said transmission and reflection light paths cancels polarization effects otherwise caused by beamsplitting. 10 figs.

  18. Polarization-balanced beamsplitter

    DOEpatents

    Decker, Derek E.

    1998-01-01

    A beamsplitter assembly that includes several beamsplitter cubes arranged to define a plurality of polarization-balanced light paths. Each polarization-balanced light path contains one or more balanced pairs of light paths, where each balanced pair of light paths includes either two transmission light paths with orthogonal polarization effects or two reflection light paths with orthogonal polarization effects. The orthogonal pairing of said transmission and reflection light paths cancels polarization effects otherwise caused by beamsplitting.

  19. Polarized light transmission characteristics in smoke indoor test scheme

    NASA Astrophysics Data System (ADS)

    Liu, Boyu; Fu, Qiang; Duan, Jing

    2014-11-01

    the polarized light is used in polarization imaging and detection in complex environment, turbid atmosphere under the harsh conditions. Polarized light in the transmission process is affected by smoke composition, the uneven distribution of concentration, particle shape,particle refractive index and other aspects of the causes of polarized light transmission, and the degree of polarization and polarization parameters change. The polarized light research is single on theory study, the experiment equipment simulating environment is not conducive to the transmission characteristics of quantitative study of polarized light in smoke environment. This paper from the research and simulation of smoke device, the device uesd the temperature and humidity adjusting device to control the generation of water mist, to simulate the natural environment in the haze environment, and use of particle size instrument and concentration detection device real-time monitoring test . Polarized light transmission characteristics in the test program and its influencing factors, which can provide reference of polarized light for the transmission characteristics.

  20. Neutron polarizers based on polarized ^3He

    NASA Astrophysics Data System (ADS)

    Gentile, T. R.; Jones, G. L.; Thompson, A. K.; Fei, X.; Keith, C. D.; Rich, D.; Snow, W. M.; Penttila, S.

    1997-10-01

    Research is underway at NIST, Indiana Univ., and LANL to develop neutron polarizers and analyzers based on polarized ^3He. Such devices, which rely on the strong spin dependence of the neutron capture cross section by polarized ^3He, have applications in weak interaction physics and materials science. In addition, the technology for polarized ^3He production is directly applicable to polarized gas MRI of lungs, and polarized targets. Our program, which includes both the spin-exchange and metastability-exchange optical pumping methods, will be reviewed. Spin-exchange has been used to analyze a polarized cold neutron beam at NIST, and also for lung imaging in collaboration with the Univ. of Pennsylvania. In the metastable method, the ^3He is polarized at low pressure, and must be substantially compressed. A piston compressor has been designed for this goal at Indiana Univ. and is under construction. At NIST we have compressed polarized gas using an apparatus that is based on a modified commercial diaphragm pump.

  1. Evidence for the timing and duration of the last interglacial period from high-precision uranium-series ages of corals on tectonically stable coastlines

    USGS Publications Warehouse

    Muhs, D.R.

    2002-01-01

    The last interglacial period has a timing and duration that can be estimated from U-series dating of emergent, coral-bearing deposits on tectonically stable coastlines. High-precision dating from Bermuda, the Bahamas, Hawaii, and Australia suggests that the last interglacial period had a sea level at least as high as present from ???128,000 to 116,000 yr B.P. Sea level reached a near-present level more quickly after the close of the penultimate glacial period than at the close of the last glacial period and the duration of high sea level is longer than that implied by the deep-sea record. ?? 2002 University of Washington.

  2. Brewster Angle Polarizing Beamsplitter Laser Damage Competition: P polarization

    NASA Astrophysics Data System (ADS)

    Stolz, Christopher J.; Runkel, Jeff

    2012-11-01

    Brewster angle plate polarizing beamsplitters play a critical role in splitting and combining beams within high power laser systems. A laser damage competition of polarizer beamsplitter coatings creates the opportunity to survey the current laser resistance these coatings within private industry, governmental institutions, and universities by a direct comparison of samples tested under identical conditions. The requirements of the coatings are a minimum transmission of 95% at "P" polarization and minimum reflection of 99% at "S" polarization at 1064 nm and 56.4 degrees angle of incidence. The choice of coating materials, design, and deposition method were left to the participant. Laser damage testing was performed according to the ISO 11254 standard utilizing a 1064 nm wavelength laser with a 10 ns pulse length operating at a repetition rate of 20 Hz. A double blind test assured sample and submitter anonymity so only a summary of the results are presented. In addition to the laser resistance results, details of cleaning methods, deposition processes, coating materials and layer count, and spectral results are also shared. Because of the large number of samples that were submitted, damage testing was conducted at "P" polarization only with "S" polarization damage testing reserved for next year on these submitted samples. Also the samples were only tested in the forward propagating direction; specifically samples were irradiated from air as the incident medium, through the thin film, and then through the substrate. In summary, a 6:1 difference existed for "P" polarization damage fluences amongst all of the competitors with the dominate variables that impacted the laser resistance being the deposition materials, deposition process, and cleaning method.

  3. The timing of sea level highstands over the last 600,000 years, with a special focus on the Last Interglacial

    NASA Astrophysics Data System (ADS)

    Thompson, William G.; O'Leary, Michael

    2010-05-01

    U-series dating of reef-building coral sea level indicators has been used to support the idea that the timing of the Penultimate Deglaciation (Termination II) and the Last Interglacial sea level highstand is anomalous with respect to northern hemisphere forcing and that Milankovitch-based orbital tuning is not a universally applicable dating approach. However, U-series coral ages are subject to artifacts caused by open-system processes affecting the isotopes used for dating. New high-precision U-Th ages from Western Australia clearly demonstrate that these corals are significantly impacted by such age artifacts and that current screening criteria are not adequate to reject these spurious ages. As a result, Western Australian coral ages are biased by artifacts that make the Last Interglacial appear older and longer than it truly was. Exploiting recent technical advances in mass spectrometry, we reduce the age error associated with isotope ratio measurements to approximately 100 years for Last Interglacial corals. At these levels of analytical precision, it is clear that the understanding of open-system effects is by far the most significant obstacle to be overcome in reconstructing an accurate history of sea level for the Last Interglacial. We suggest a simple and effective approach for quantifying and reducing the age errors associated with open-system effects by measuring discrete sub-samples of individual corals. A compilation of the currently available U-series coral data for the last 600,000 years strongly supports the traditional Milankovitch view of a northern hemisphere ice-sheet control and the utility of orbital tuning techniques.

  4. δ18O of mollusc shell carbonate as a proxy for summer river water temperature: Reconstructing British interglacial climates over the past 800,000 years

    NASA Astrophysics Data System (ADS)

    Candy, Ian; Waghorn, Ruth

    2010-05-01

    A range of carbonates exist in terrestrial and freshwater environments that may act as the basis for palaeo-temperature estimation. In many regions, such as Europe, the potential of using freshwater molluscs as a basis for reconstructing Quaternary environments is highly desirable because; 1) they are abundant in a wide range of deposits (interglacial, interstadial and stadial), and 2) isotopic analysis may allow climates to be reconstructed from a small number of individuals rather than extensive assemblages. Work in southern England in monitored river systems has shown that the shells of modern molluscs (Valavata piscinalis, Bithynia tentaculata) form in isotopic equilibrium with river waters during the summer months. This is true for both large river systems such as the Thames and smaller tributary systems and suggests that this proxy could allow the reconstruction of past summer temperatures. The potential of this technique for reconstructing relative temperatures is investigated by studying fossil shell assemblages from 6 of the last 8 interglacials over the last 800,000 years. Analysed samples all come from riverine deposits in southern and eastern England and are chosen from deposits which have known quantified estimates of summer temperatures from a number of biological proxies (beetles, plant macrofossils, vertebrates). There is a general consistency of 18O values from shell assemblages from all the interglacial sites, however, a large deviation from modern shell 18O values is found within assemblages from interglacial deposits which record summer temperatures that are significantly higher (3-6oC warmer) than temperatures in southern day England. The technique, therefore, allows a potential method of identifying periods of enhanced warmth in the Quaternary record. The relationship between shell 18O and water temperature is discussed and methods of quantification are proposed.

  5. Interglacial Extension of the Boreal Forest Limit in the Noatak Valley, Northwest Alaska: Evidence from an Exhumed River-Cut Bluff and Debris Apron

    USGS Publications Warehouse

    Edwards, M.E.; Hamilton, T.D.; Elias, S.A.; Bigelow, N.H.; Krumhardt, A.P.

    2003-01-01

    Numerous exposures of Pleistocene sediments occur in the Noatak basin, which extends for 130 km along the Noatak River in northwestern Alaska. Nk-37, an extensive bluff exposure near the west end of the basin, contains a record of at least three glacial advances separated by interglacial and interstadial deposits. An ancient river-cut bluff and associated debris apron is exposed in profile through the central part of Nk-37. The debris apron contains a rich biotic record and represents part of an interglaciation that is probably assignable to marine-isotope stage 5. Pollen spectra from the lower part of the debris apron closely resemble modern samples taken from the Noatak floodplain in spruce gallery forest, and macrofossils of spruce are also present at this level. Fossil bark beetles and carpenter ants occur higher in the debris apron. Mutual Climatic Range (MCR) estimates from the fossil beetles suggest temperatures similar to or warmer than today. Together, these fossils indicate the presence of an interglacial spruce forest in the western part of the Noatak Basin, which lies about 80 km upstream of the modern limit of spruce forest.

  6. Creation of polar cap patches

    NASA Astrophysics Data System (ADS)

    Hosokawa, K.; Taguchi, S.; Ogawa, Y.

    2014-12-01

    Polar cap patches, which are islands of enhanced plasma density drifting anti-sunward, are one of the outstanding phenomena in the polar cap F region ionosphere. In the last decade, data from all-sky airglow imagers have been extensively used for better understanding the propagation of patches in the central polar cap region. But still, it has been rather difficult to capture the birth of patches in their generation region near the dayside cusp, because, in most places, the dayside part of the polar cap ionosphere is sunlit even in winter. In Longyearbyen (78.1N, 15.5E), Norway, however, optical observations are possible near the dayside cusp region in a limited period around the winter solstice. This enables us to directly image how polar cap patches are born in the cusp. In this paper, we present a few intervals of daytime optical observations, during which polar cap patches were generated within the field-of-view of an all-sky imager in Longyearbyen. During all the intervals studied here, we identified several signatures of poleward moving auroral forms (PMAF) in the equatorward half of the field-of-view, which are known as ionospheric manifestations of dayside reconnection. Interestingly, patches were directly produced from such poleward moving auroral signatures and propagated poleward along the anti-sunward convection near the cusp. In the literature, Lorentzen et al. (2012) first reported such a direct production of patches from PMAFs. During the current observations, however, we succeeded in tracking the propagation of patches until they reached the poleward edge of the field-of-view of the imager. This confirms that the faint airglow structures produced from PMAFs were actually transported for a long distance towards the central polar cap area; thus, polar cap patches were produced. From this set of observations, we suggest that polar cap patches during moderately disturbed conditions (i.e, non-storm time conditions) can be directly produced by the

  7. Age and origin of ice-rich Yedoma silts at Duvanny Yar, northeast Siberia: a record of Beringian environmental change since the last interglacial

    NASA Astrophysics Data System (ADS)

    Murton, J.; Edwards, M. E.; Murton, D.; Bateman, M.; Haile, J.

    2010-12-01

    dust deposits and palaeosols. U-series dating of wood contained within thaw-lake deposits at the base of the sequence provides an age from the Last Interglacial. Overall, dating of the yedoma sequence constrains interpretation of ancient soil DNA contained within the silts and provides a basis for reconstructing LGM palaeo-wind conditions associated with the Siberian high-pressure cell.

  8. Mississippi freshwater discharge and terrigenous sediment supply into the northern Gulf of Mexico and Loop Current dynamics over glacial/interglacial changes

    NASA Astrophysics Data System (ADS)

    Nuernberg, D.; Kujau, A.; Rieken, S.; Bahr, A.; Karas, C.; Ziegler, M.

    2011-12-01

    We here present (isotope)geochemical and sedimentological data from marine sediment cores from the northern Gulf of Mexico to approximate the temporally and spatially varying terrigenous sediment contribution via the Mississippi River and the related spread of freshwater over the last glacial-interglacial cycles, with specific focus on the last ca. 42.000 years. Our study is based on cores from the DeSoto Canyon (MD02-2576 and 2575), from ~90 km southeast off the Mississippi River delta (M78-181), and from southwest of the delta (IODP 1319A). The geochemical signature of the eastern cores closely matches that of the Mississippi catchment area rather than those of the Alabama and Mobile River catchments. In particular, the siliciclastic major element potassium (K), estimated from calibrated XRF core scanning, serves as a suitable proxy for Mississippi River sediment discharge, becoming less concentrated with distance from the delta. The K variability suggests enhanced glacial phase terrigenous influx triggered by strengthened fluvial runoff and changing fluvial and ice sheet dynamics. Mississippi River influx was at a maximum during glacial MIS 2/3, late MIS 8 and MIS 10, reflected by sedimentation rates being 4 to 5 times higher than in the Holocene. Late glacial to deglacial fluvial sediment supply, however, decreased abruptly at ca. 20 ka at our easternmost core location (MD02-2576), and ca. 2 kyr later at our core location closest to the Mississippi Delta, implying a gradual westward shift of the Mississippi outflow. Due to synchronous changes in sea-surface temperatures, we hypothesize an increasing impact of the northward extending Loop Current on the Mississippi outflow pattern. Combined stable oxygen isotope and element ratios from shallow and deep-dwelling as well as benthic foraminifers allow to approximate paleosalinity, and hence to follow the dispersal of freshwater across the Gulf of Mexico. According to our data, Mississippi freshwater discharge

  9. Astronomically forced variations in western African rainfall (21°N-20°S) during the Last Interglacial period

    NASA Astrophysics Data System (ADS)

    Govin, Aline; Varma, Vidya; Prange, Matthias

    2014-03-01

    This study documents the long-term evolution of western African precipitation during the Last Interglacial (LIG). We compare geochemical records obtained on nine sediment cores from the western African margin to a transient simulation (130-115 ka) performed with an ocean-atmosphere general circulation model and insolation as sole forcing. Good agreement between proxy records and model outputs indicates that long-term changes in western African precipitation largely responded to insolation variations during most of the LIG. After an early LIG dry phase (related to high-latitude iceberg melting or dating uncertainties), boreal summer insolation controlled the intensification of the North African monsoon between 127 and 122 ka, perhaps facilitating human migrations out of Africa. Equatorial African rainfall slightly increased throughout the LIG in response to increasing annual insolation. East-west contrasting rainfall evolutions at 10-20°S illustrate the complex southern African response, in contrast to more direct responses of North and equatorial western Africa, to insolation forcing.

  10. The impact of climate change on large mammal distribution and extinction: Evidence from the last glacial/interglacial transition

    NASA Astrophysics Data System (ADS)

    Lister, Adrian M.; Stuart, Anthony J.

    2008-09-01

    The last major global revolution of climate was the transition from the last glacial stage to the present interglacial, ca. 25-10 ka. Vegetational belts and mammalian communities underwent major reorganisation. New radiocarbon data show that the complex series of climatic changes affected the ranges of mammalian species dramatically, but in differing ways related to the ecologies of individual species. For species that ultimately went extinct, the reduction in range was a prolonged and geographically complex process taking thousands or tens of thousands of years. Recent genetic studies using ancient DNA show that this process was often accompanied by loss of genetic variation and, presumably, adaptive flexibility. Even so, some species survived for thousands of years in small, terminal refugia before finally becoming extinct - a pattern akin to the 'extinction lag' or 'extinction debt' posited for endangered modern taxa. Whether refugial species can survive to re-expand into new areas, especially in anthropogenically disturbed environments, is determined by a complex of factors and is not inevitable.

  11. The impact of glacial/interglacial climate changes on fluvial and mass-wasting processes in the Taiwan's mountains

    NASA Astrophysics Data System (ADS)

    Li, W. L.; Hsieh, M. L.; Tsui, H. K.; Hsiao, Y. T.

    2014-12-01

    The Taiwan orogenic belt, located in Southeastern Asia, is under monsoon climate, frequently attacked by tropical typhoons, and characterized by rapid tectonic uplift with high seismicity. Researchers have been linking the Taiwan's landscapes to active tectonic uplift. In this study, we show the significance of glacial/interglacial climate changes in shaping the landscapes. We focus on the mountain areas that have never been glaciated. Based on >400 radiocarbon dates (70 of which >12 ka), we find that both the slope and fluvial activities were generally low during the glacial time. Still, extensive alluviation had occurred at certain time periods, forming large debris slopes or alluvial fans (typically along mountain fronts), and causing significant aggradation along some major rivers. In contrast, with numerous landslides and debris flows, river incision has dominated during the postglacial time. Episodic river aggradation with alluvial-terrace development (typically at tributary mouths) also occurred during this time period, but was less extensive than previously. Some huge postglacial alluvial terraces have been proved sourced from the colluviums deposited in the glacial time. We attribute the low landscape activities of the glacial period to the dryness during the period. However, even in this time rare but severe rainfall events must have occurred to trigger some extensive alluviation. In contrast, the increase in both rainfall and typhoon frequency during the postglacial time drastically increased the slope instability and sediment yield. The great stream power, along with the sufficient coarse debris acting as erosion tools, ensured the rapid river incision during this time.

  12. New evidence for two highstands of the sea during the last interglacial, oxygen isotope substage 5e

    NASA Astrophysics Data System (ADS)

    Sherman, C. E.; Glenn, C. R.; Jones, A. T.; Burnett, W. C.; Schwarcz, H. P.

    1993-12-01

    Sedimentologic, stratigraphic, and geochronologic analyses of a previously undescribed carbonate section on Oahu, Hawaii, provide new evidence for two distinct sea-level highstands on Oahu during the last interglacial period (oxygen isotope substage 5e). Whereas electron-spin-resonance and uranium-series ages (122 ±8 ka to 152 ±25 ka, and 115 ±10 ka to 160 ±15 ka, respectively) of in situ corals place the age of the deposits within substage 5e, it is the unique sequence of strata found in these exposures that reveals the two transgressions. A highstand lagoonal deposit of coral-algal bafflestone is overlain by large seaward-dipping slabs of beach-rock. The beachrock, deposited during a mid-5e regression, is in turn overlain by a second highstand lagoonal deposit. This sequence was deposited in a broad, shallow, back-reef embayment that was very sensitive to fluctuations in sea level. Elsewhere, along much of the shoreline of Oahu, an in situ coral-algal framestone (Waimanalo Formation), representing the initial 5e highstand, is erosionally truncated on its upper surface. This erosional unconformity represents the mid-5e lowstand and separates the framestone from overlying, seaward-dipping, planar-bedded grainstone and rudstone (Leahi Formation) that accumulated during the second 5e highstand.

  13. Macrophage polarization in pathology.

    PubMed

    Sica, Antonio; Erreni, Marco; Allavena, Paola; Porta, Chiara

    2015-11-01

    Macrophages are cells of the innate immunity constituting the mononuclear phagocyte system and endowed with remarkable different roles essential for defense mechanisms, development of tissues, and homeostasis. They derive from hematopoietic precursors and since the early steps of fetal life populate peripheral tissues, a process continuing throughout adult life. Although present essentially in every organ/tissue, macrophages are more abundant in the gastro-intestinal tract, liver, spleen, upper airways, and brain. They have phagocytic and bactericidal activity and produce inflammatory cytokines that are important to drive adaptive immune responses. Macrophage functions are settled in response to microenvironmental signals, which drive the acquisition of polarized programs, whose extremes are simplified in the M1 and M2 dichotomy. Functional skewing of monocyte/macrophage polarization occurs in physiological conditions (e.g., ontogenesis and pregnancy), as well as in pathology (allergic and chronic inflammation, tissue repair, infection, and cancer) and is now considered a key determinant of disease development and/or regression. Here, we will review evidence supporting a dynamic skewing of macrophage functions in disease, which may provide a basis for macrophage-centered therapeutic strategies. PMID:26210152

  14. Constraints on Mueller matrices of polarization optics

    NASA Technical Reports Server (NTRS)

    Kostinski, Alexander B.; Givens, Clark R.; Kwiatkowski, John M.

    1993-01-01

    The issue of physical realizability constraints on depolarizing scattering or imaging systems is addressed. In particular, the overpolarization problem, i.e., the problem of ensuring that the output degree of polarization is always smaller than (or equal to) unity, is discussed in detail. A set of necessary conditions for the elements of a Mueller matrix is derived. These conditions can be used to test the accuracy of polarimetric measurements and computations. Several recent experimental examples from polarization optics and radar are discussed.

  15. Cross polarization in beam waveguide-fed Cassegrain reflector antennas

    NASA Astrophysics Data System (ADS)

    Houshmand, Bijan

    1991-02-01

    The sensitivity of the cross-polarization level to a deviation from the geometrical condition derived by Mizusawa and Kitsuregawa (1973) for different geometrical configurations is studied. This condition restricts the number of possible beam waveguide configurations for beam waveguide-fed Cassegrain reflector (BFCR) antennas. For a symmetrical feed, this condition results in a symmetrical aperture distribution with no cross-polarized component. By examining a number of beam waveguide configurations satisfying the condition, it was observed that for linearly polarized feed, the cross-polarization level is very sensitive to a deviation from this condition. For circularly polarized feed, deviation from this condition does not increase the cross-polarization level; however, it results in the squinting of the beam for BFCRs.

  16. Contrasted ocean conditions in the northwest North Atlantic during marine isotope stages (MIS) 11, 5e and 1

    NASA Astrophysics Data System (ADS)

    de Vernal, Anne; Fréchette, Bianca; Hillaire-Marcel, Claude

    2014-05-01

    Cores raised during the IODP Expedition 303 in the north Atlantic were analysed to document paleoceanographical conditions during recent interglacials (cf. Hillaire-Marcel et al., Marine Geol. 2011). Two key sites illustrate conditions in the inner vs outer Labrador Sea, respectively at the southwest Greenland margin (Eirik Ridge Site 1305; 57° N-48° W) and the southern Labrador rise (Orphan Knoll Site 1302/1303; 50° N-45° W). Special attention was paid to marine isotope stages (MIS) 11 (ca. 424-324 ka), 5e (ca. 128-117 ka) and the Holocene (last 11,000 years). The microfossil content of sediments (dinocyst notably) and the isotopic composition of foraminifers indicate significant differences in the conditions that prevailed during these 3 interglacial stages. Optimal conditions with regard to sea-surface temperatures (SSTs) prevailed during MIS 5e (anomalies of about + 5° C) at both sites. However, occurrence of ice rafted debris (IRD) and variations in salinity suggest meltwater discharge along the Greenland and Labrador margins during the last interglacial. On the contrary, during MIS 11, SSTs were similar to modern off Greenland or slightly lower at Orphan Knoll, but salinity was higher at both sites and IRD close to nil, whereas both sites are presently under iceberg routes. Stable oxygen isotope values in the mesopelagic Neogloboquadrina pachyderma left coiled (Npl), are generally not unlike values observed during MIS 9 or 7, i.e., slightly higher than those which characterized MIS 5e and the present interglacial, particularly in the outer Labrador Sea. This points to either a higher salinity and or a lower temperature in the subsurface water layer occupied by Npl. Low IRD, high salinity together with relatively high 18O values in foraminifers suggest limited influence of meltwater from ice cap and sea ice during MIS 11, especially the first part of the interglacial.

  17. Interferometric polarization control

    NASA Technical Reports Server (NTRS)

    Wollack, Edward J. (Inventor); Moseley, Samuel H. (Inventor); Novak, Giles A. (Inventor); Chuss, David T. (Inventor)

    2009-01-01

    A signal conditioning module provides a polarimeter capability in a photometric system. The module may include multiple variable delay polarization modulators. Each modulator may include an input port, and a first arm formed to include a first reflector and first rooftop mirror arranged in opposed relationship. The first reflector may direct an input radiation signal to the first rooftop mirror. Each modulator also may include an output port and a second arm formed to include a second reflector and second rooftop mirror arranged in opposed relationship. The second reflector can guide a signal from the second rooftop mirror towards the output port to provide an output radiation signal. A beamsplitting grid may be placed between the first reflector and the first rooftop mirror, and also between the second reflector and the second rooftop mirror. A translation apparatus can provide adjustment relative to optical path length vis-a-vis the first arm, the second arm and the grid.

  18. Interferometric Polarization Control

    NASA Technical Reports Server (NTRS)

    Chuss, David T. (Inventor); Wollack, Edward J. (Inventor); Moseley, Samuel H. (Inventor); Novak, Giles A. (Inventor)

    2008-01-01

    A signal conditioning module provides a polarimeter capability in a photometric system. The module may include multiple variable delay polarization modulators. Each modulator may include an input port, and a first arm formed to include a first reflector and first rooftop mirror arranged in opposed relationship. The first reflector may direct an input radiation signal to the first rooftop mirror. Each modulator also may include an output port and a second arm formed to include a second reflector and second rooftop mirror arranged in opposed relationship. The second reflector can guide a signal from the second rooftop mirror towards the output port to provide an output radiation signal. A beamsplitting grid may be placed between the first reflector and the first rooftop mirror, and also between the second reflector and the second rooftop mirror. A translation apparatus can provide adjustment relative to optical path length vis-a-vis the first arm, the second arm and the grid.

  19. Polarized Light Corridor Demonstrations.

    ERIC Educational Resources Information Center

    Davies, G. R.

    1990-01-01

    Eleven demonstrations of light polarization are presented. Each includes a brief description of the apparatus and the effect demonstrated. Illustrated are strain patterns, reflection, scattering, the Faraday Effect, interference, double refraction, the polarizing microscope, and optical activity. (CW)

  20. Polarization at SLAC

    SciTech Connect

    Woods, M.

    1995-01-01

    A highly polarized electron beam is a key feature. for the Current physics program at SLAC. An electron beam polarization of 80% can now be routinely achieved for typically 5000 hours of machine operation per year. Two main Physics programs utilize the polarized beam. Fixed target experiments in End Station A study the collision of polarized electrons with polarized nuclear targets to elucidate the spin structure of the nucleon and to provide an important test of QCD. Using the SLAC Linear Collider, collisions of polarized electrons with unpolarized positrons allow precise measurements of parity violation in the Z-fermion couplings and provide a very precise measurement of tile weak mixing angle. This paper discusses polarized beam operation at SLAC, and gives an overview of the polarized physics program.

  1. A Translational Polarization Rotator

    NASA Technical Reports Server (NTRS)

    Chuss, David T.; Wollack, Edward J.; Pisano, Giampaolo; Ackiss, Sheridan; U-Yen, Kongpop; Ng, Ming wah

    2012-01-01

    We explore a free-space polarization modulator in which a variable phase introduction between right- and left-handed circular polarization components is used to rotate the linear polarization of the outgoing beam relative to that of the incoming beam. In this device, the polarization states are separated by a circular polarizer that consists of a quarter-wave plate in combination with a wire grid. A movable mirror is positioned behind and parallel to the circular polarizer. As the polarizer-mirror distance is separated, an incident liear polarization will be rotated through an angle that is proportional to the introduced phase delay. We demonstrate a prototype device that modulates Stokes Q and U over a 20% bandwidth.

  2. Structure of polarization-resolved conoscopic patterns of planar oriented liquid crystal cells

    SciTech Connect

    Kiselev, A. D. Vovk, R. G.

    2010-05-15

    The geometry of distributions of the polarization of light in conoscopic patterns of planar oriented nematic and cholesteric liquid crystal (LC) cells is described in terms of the polarization singularities including C-points (points of circular polarization) and L lines (lines of linear polarization). Conditions for the formation of polarization singularities (C-points) in an ensemble of conoscopic patterns parametrized by the polarization azimuth and ellipticity of the incident light wave have been studied. A characteristic feature of these conditions is selectivity with respect to the polarization parameters of the incident light wave. The polarization azimuth and ellipticity are determining parameters for nematic and cholesteric LC cells, respectively.

  3. Polar Ozone Workshop. Abstracts

    NASA Technical Reports Server (NTRS)

    Aikin, Arthur C.

    1988-01-01

    Results of the proceedings of the Polar Ozone Workshop held in Snowmass, CO, on May 9 to 13, 1988 are given. Topics covered include ozone depletion, ozonometry, polar meteorology, polar stratospheric clouds, remote sensing of trace gases, atmospheric chemistry and dynamical simulations.

  4. Hybrid polarization control

    NASA Astrophysics Data System (ADS)

    Gray, George R.; Ibragimov, Edem; Sluz, Joseph; Sova, Raymond

    2005-05-01

    We demonstrate a novel method of polarization control that combines rotatable waveplates (angle control) and variable retarders (retardance control). Such a "hybrid" polarization controller performs far better than conventional controllers, allowing nearly perfect arbitrary-to-arbitrary polarization transformations. We show theoretically that the two control parameters augment one another because they tend to result in orthogonal movements on the Poincaré sphere.

  5. Graphing Polar Curves

    ERIC Educational Resources Information Center

    Lawes, Jonathan F.

    2013-01-01

    Graphing polar curves typically involves a combination of three traditional techniques, all of which can be time-consuming and tedious. However, an alternative method--graphing the polar function on a rectangular plane--simplifies graphing, increases student understanding of the polar coordinate system, and reinforces graphing techniques learned…

  6. Playing with Polarizers.

    ERIC Educational Resources Information Center

    Hecht, Jeff

    1991-01-01

    Discussed is how polarized sunglasses block glare, help spot subtle differences in surfaces, and give a clearer view under water. Information on unpolarized and polarized light is provided. The reasons causing glare to occur and how polarizers decrease glare are discussed. (KR)

  7. Polarity at Many Levels

    ERIC Educational Resources Information Center

    Flannery, Maura C.

    2004-01-01

    An attempt is made to find how polarity arises and is maintained, which is a central issue in development. It is a fundamental attribute of living things and cellular polarity is also important in the development of multicellular organisms and controversial new work indicates that polarization in mammals may occur much earlier than previously…

  8. Physics with Polarized Nuclei.

    ERIC Educational Resources Information Center

    Thompson, William J.; Clegg, Thomas B.

    1979-01-01

    Discusses recent advances in polarization techniques, specifically those dealing with polarization of atomic nuclei, and how polarized beams and targets are produced. These techniques have greatly increased the scope of possible studies, and provided the tools for testing fundamental symmetries and the spin dependence of nuclear forces. (GA)

  9. Bumblebees Learn Polarization Patterns

    PubMed Central

    Foster, James J.; Sharkey, Camilla R.; Gaworska, Alicia V.A.; Roberts, Nicholas W.; Whitney, Heather M.; Partridge, Julian C.

    2014-01-01

    Summary Foraging insect pollinators such as bees must find and identify flowers in a complex visual environment. Bees use skylight polarization patterns for navigation [1–3], a capacity mediated by the polarization-sensitive dorsal rim area (DRA) of their eye [4, 5]. While other insects use polarization sensitivity to identify appropriate habitats [6], oviposition sites, and food sources [7], to date no nonnavigational functions of polarization vision have been identified in bees. Here we investigated the ability of bumblebees (Bombus terrestris) to learn polarization patterns on artificial “flowers” in order to obtain a food reward. We show that foraging bumblebees can learn to discriminate between two differently polarized targets, but only when the target artificial “flower” is viewed from below. A context for these results is provided by polarization imaging of bee-pollinated flowers, revealing the potential for polarization patterns in real flowers. Bees may therefore have the ability to use polarization vision, possibly mediated by their polarization-sensitive DRA, both for navigation and to learn polarization patterns on flowers, the latter being the first nonnavigational function for bee polarization vision to be identified. PMID:24909321

  10. Polarization feedback laser stabilization

    DOEpatents

    Esherick, Peter; Owyoung, Adelbert

    1988-01-01

    A system for locking two Nd:YAG laser oscillators includes an optical path for feeding the output of one laser into the other with different polarizations. Elliptical polarization is incorporated into the optical path so that the change in polarization that occurs when the frequencies coincide may be detected to provide a feedback signal to control one laser relative to the other.

  11. Calculation of polarization effects

    SciTech Connect

    Chao, A.W.

    1983-09-01

    Basically there are two areas of accelerator applications that involve beam polarization. One is the acceleration of a polarized beam (most likely a proton beam) in a synchrotron. Another concerns polarized beams in an electron storage ring. In both areas, numerical techniques have been very useful.

  12. Fiber based generation of azimuthally polarized light

    NASA Astrophysics Data System (ADS)

    Jocher, Christoph; Jauregui, Cesar; Voigtländer, Christian; Stutzki, Fabian; Nolte, Stefan; Limpert, Jens; Tünnermann, Andreas

    2012-02-01

    We report on a novel approach for the generation of radially and azimuthally polarized light employing a fiber mode filter. The mode filter consists of a Fiber Bragg Grating written in a strongly guiding fiber with lifted modal degeneracy. These kinds of fibers guide radially and azimuthally polarized modes with non-degenerated, i.e. distinct, effective refractive indexes. The Fiber Bragg Grating reflects light only if the Bragg condition is fulfilled. In case of strongly guiding fibers the radially and azimuthally polarized modes are guided with different effective refractive indices and, consequently, the Bragg condition is fulfilled at different wavelengths. If the reflection bandwidth of the Fiber Bragg Grating is narrow enough, the radially and azimuthally polarized modes are spectrally separated. Thus, with such a mode filter it is possible to filter the radially or azimuthally polarized mode. This filter is suitable for its integration in a resonator for stable, compact a