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Sample records for interglacial conditions polar

  1. Climatic bisection of the last interglacial warm period in the Polar North Atlantic

    NASA Astrophysics Data System (ADS)

    Bauch, Henning A.; Kandiano, Evguenia S.; Helmke, Jan; Andersen, Nils; Rosell-Mele, Antoni; Erlenkeuser, Helmut

    2011-07-01

    New multiproxy marine data of the Eemian interglacial (MIS5e) from the Norwegian Sea manifest a cold event with near-glacial surface ocean summer temperatures (3-4 °C). This mid-Eemian cooling divided the otherwise relatively warm interglacial climate and was associated with widespread expansions of winter sea-ice and polar water masses due to changes in atmospheric circulation and ocean stability. While the data also verify a late rather than early last interglacial warm peak, which is in general disharmony with northern hemisphere insolation maximum and the regional climatic progression of the early Holocene, the cold event itself was likely instrumental for delaying the last interglacial climate development in the Polar North when compared with regions farther south. Such a 'climatic decoupling' of the Polar region may bear profound implications for the employment of Eemian conditions to help evaluate the present and future state of the Arctic cryosphere during a warming interglacial.

  2. No evidence of polar warming during penultimate interglacial

    NASA Astrophysics Data System (ADS)

    Bhattacharya, Atreyee

    2012-07-01

    The Atlantic Meridional Overturning Circulation (AMOC), driven by temperature and salinity gradients, is an important component of the climate system; it transfers an enormous amount of heat via ocean currents and atmospheric circulation to high northern latitudes and hence has bearing on climate in the region. Freshening of the surface ocean could weaken AMOC. But during warm interglacial periods the effect of a fresh surface ocean on AMOC may be muted. In fact, climate models predict that heat transfer from the North Atlantic to the Arctic may increase over the 21st century. A series of interconnected processes in the North Atlantic, known as polar amplification, could cause the Arctic to warm up faster compared to the rest of the world. It could even lead to ice-free conditions in the Arctic.

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

    PubMed

    Raymo, Maureen E; Mitrovica, Jerry X

    2012-03-14

    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.

  4. 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

  5. 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

  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. Variations in glacial and interglacial marine conditions over the last two glacial cycles off northern Greenland

    NASA Astrophysics Data System (ADS)

    Löwemark, Ludvig; Chao, Weng-Si; Gyllencreutz, Richard; Hanebuth, Till J. J.; Chiu, Pin-Yao; Yang, Tien-Nan; Su, Chih-Chieh; Chuang, Chih-Kai; León Dominguez, Dora Carolina; Jakobsson, Martin

    2016-09-01

    Five sediment cores from the Lomonosov Ridge and the Morris Jesup Rise north of Greenland show the history of sea-ice coverage and primary productivity over the last two glacial cycles. Variations in Manganese content, benthic and planktonic foraminifera, bioturbation, and trace fossil diversity are interpreted to reflect differences in sea-ice cover and sediment depositional conditions between the identified interglacials. Marine Isotope Stage (MIS) 1 and MIS 2 are represented by thin (<<5 cm) sediment units while the preceding interglacial MIS 5 and glacial MIS 6 are characterized by thick (10-20 cm) deposits. Foraminiferal abundances and bioturbation suggest that MIS 1 was generally characterized by severe sea-ice conditions north of Greenland while MIS 5 appears to have been considerably warmer with more open water, higher primary productivity, and higher sedimentation rates. Strengthened flow of Atlantic water along the northern continental shelf of Greenland rather than development of local polynyas is here suggested as a likely cause for the relatively warmer marine conditions during MIS 5 compared to MIS 1. The cores also suggest distinct differences between the glacial intervals MIS 2 and MIS 6. While MIS 6 is distinguished by a relatively thick sediment unit poor in foraminifera and with low Mn values, MIS 2 is practically missing. We speculate that this could be the effect from a paleocrystic sea-ice cover north of Greenland during MIS 2 that prevented sediment delivery from sea ice and icebergs. In contrast, the thick sequence deposited during MIS 6 indicates a longer glacial period with dynamic intervals characterized by huge drifting icebergs delivering ice rafted debris (IRD). A drastic shift from thinner sedimentary cycles where interglacial sediment parameters indicate more severe sea-ice conditions gave way to larger amplitude cycles with more open water indicators was observed around the boundary between MIS 7/8. This shift is in agreement with a

  9. Tropical tales of polar ice: evidence of Last Interglacial polar ice sheet retreat recorded by fossil reefs of the granitic Seychelles islands

    NASA Astrophysics Data System (ADS)

    Dutton, Andrea; Webster, Jody M.; Zwartz, Dan; Lambeck, Kurt; Wohlfarth, Barbara

    2015-01-01

    In the search for a record of eustatic sea level change on glacial-interglacial timescales, the Seychelles ranks as one of the best places on the planet to study. Owing to its location with respect to the former margins of Northern Hemisphere ice sheets that wax and wane on orbital cycles, the local-or relative-sea level history is predicted to lie within a few meters of the globally averaged eustatic signal during the Last Interglacial period. We have surveyed and dated Last Interglacial fossil corals to ascertain peak sea level and hence infer maximum retreat of polar ice sheets during this time interval. We observe a pattern of gradually rising sea level in the Seychelles between ˜129 and 125 thousand years ago (ka), with peak eustatic sea level attained after 125 ka at 7.6 ± 1.7 m higher than present. After accounting for thermal expansion and loss of mountain glaciers, this sea-level budget would require ˜5-8 m of polar ice sheet contribution, relative to today's volume, of which only ˜2 m came from the Greenland ice sheet. This result clearly identifies the Antarctic ice sheet as a significant source of melt water, most likely derived from one of the unstable, marine-based sectors in the West and/or East Antarctic ice sheet. Furthermore, the establishment of a +5.9 ± 1.7 m eustatic sea level position by 128.6 ± 0.8 ka would require that partial AIS collapse was coincident with the onset of the sea level highstand.

  10. The Last Interglacial Labrador Sea: A Pervasive Millennial Oscillation In Surface Water Conditions Without Labrador Sea Water Formation

    NASA Astrophysics Data System (ADS)

    Hillaire-Marcel, C.; de Vernal, A.

    A multi-proxy approach was developed to document secular to millenial changes of potential density in surface, mesopelagic, and bottom waters of the Labrador Sea, thus allowing to reconstruct situations when winter convection with intermediate or deep water formation occurred in the basin. This approach relies on dinocyst-transfer functions providing estimates of sea-surface temperature and salinity that are used to calibrate past-relationships between oxygen 18 contents in calcite and potential density gradients. The oxygen isotope compositions of epipelagic (Globigerina bul- loides), deeper-dwelling (Neogloboquadrina pachyderma, left coiling), and benthic (Uvigerina peregrina and Cibicides wuellerstorfi) foraminifera, then allow to extrap- olate density gradients between the corresponding water layers. This approach has been tested in surface sediments in reference to modern hydrographic conditions at several sites from the NW North Atlantic, then used to reconstruct past conditions from high resolution studies of cores raised from the southern Greenland Rise (off Cape Farewell). Results indicate that the modern-like regime established during the early Holocene and full developed after 7 ka only. It is marked by weak density gradi- ents between the surface and intermediate water masses, allowing winter convection down to a lower pycnocline between intermediate and deep-water masses, thus the formation of intermediate Labrador Sea Water (LSW). Contrasting with the middle to late Holocene situation, since the last interglacial and throughout the last climatic cycle, a single and dense water mass seems to have occupied the water column below a generally low-density surface water layer, thus preventing deep convection. There- fore, the production of LSW seems to be feature specific to the present interglacial interval that could soon cease to exist, due to global warming, as suggested by recent ocean model experiments and by the fact that it never occurred during the

  11. 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.

  12. 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.

  13. 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…

  14. Low-δD hydration rinds in Yellowstone perlites record rapid syneruptive hydration during glacial and interglacial conditions

    USGS Publications Warehouse

    Bindeman, Ilya N.; Lowenstern, Jacob B.

    2016-01-01

    Hydration of silicic volcanic glass forms perlite, a dusky, porous form of altered glass characterized by abundant “onion-skin” fractures. The timing and temperature of perlite formation are enigmatic and could plausibly occur during eruption, during post-eruptive cooling, or much later at ambient temperatures. To learn more about the origin of natural perlite, and to fingerprint the hydration waters, we investigated perlitic glass from several synglacial and interglacial rhyolitic lavas and tuffs from the Yellowstone volcanic system. Perlitic cores are surrounded by a series of conchoidal cracks that separate 30- to 100-µm-thick slivers, likely formed in response to hydration-induced stress. H2O and D/H profiles confirm that most D/H exchange happens together with rapid H2O addition but some smoother D/H variations may suggest separate minor exchange by deuterium atom interdiffusion following hydration. The hydrated rinds (2–3 wt% H2O) transition rapidly (within 30 µm, or by 1 wt% H2O per 10 µm) to unhydrated glass cores. This is consistent with quenched “hydration fronts” where H2O diffusion coefficients are strongly dependent on H2O concentrations. The chemical, δ18O, and δD systematics of bulk glass records last equilibrium between ~110 and 60 °C without chemical exchange but with some δ18O exchange. Similarly, the δ18O of water extracted from glass by rapid heating suggests that water was added to the glass during cooling at <200 °C. Our observations support fast hydration at temperatures as low as 60 °C; prolonged exposure to high temperature of 175°–225° during water addition is less likely as the glass would lose alkalies and should alter to clays within days. A compilation of low-temperature hydration diffusion coefficients suggests ~2 orders of magnitude higher rates of diffusion at 60–110 °C temperatures, compared with values expected from extrapolation of high-temperature (>400 °C) experimental data. The thick

  15. 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

  16. Interglacial climates and the Atlantic meridional overturning circulation: is there an Arctic controversy?

    NASA Astrophysics Data System (ADS)

    Bauch, Henning A.

    2013-03-01

    Arctic palaeorecords are important to understand the "natural range" of forcing and feedback mechanisms within the context of past and present climate change in this temperature-sensitive region. A wide array of methods and archives now provide a robust understanding of the Holocene climate evolution. By comparison rather little is still known about older interglacials, and in particular, on the effects of the northward propagation of heat transfer via the Atlantic meridional ocean circulation (AMOC) into the Arctic. Terrestrial records from this area often indicate a warmer and moister climate during past interglacials than in the Holocene implying a more vigorous AMOC activity. This is in conflict with marine data. Although recognized as very prominent interglacials in Antarctic ice cores, cross-latitudinal surface ocean temperature reconstructions show that little of the surface ocean warmth still identified in the Northeast Atlantic during older interglacial peaks (e.g., MIS5e, 9, 11) was further conveyed into the polar latitudes, and that each interglacial developed its own specific palaeoclimate features. Interactive processes between water mass overturning and the hydrological system of the Arctic, and how both developed together out of a glacial period with its particular ice sheet configuration and relative sea-level history, determined the efficiency of an evolving interglacial AMOC. Because of that glacial terminations developed some very specific water mass characteristics, which also affected the climate evolution of the ensuing interglacial periods. Moreover, the observed contrasts in the Arctic-directed meridional ocean heat flux between past interglacials have implications for the palaeoclimatic evaluation of this polar region. Crucial environmental factors of the Arctic climate system, such as the highly dynamical interactions between deep water mass flow, surface ocean temperature/salinity, sea ice, and atmosphere, exert strong feedbacks on

  17. 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

  18. 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.

  19. 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.

  20. Interglacial Climate Variability in the Mid-Latitude North Atlantic

    NASA Astrophysics Data System (ADS)

    Chapman, M. R.; Farmer, E. J.

    2009-04-01

    /4 transition. The SST records spanning the MIS 5e interval and isotopic data from planktonic foraminifera, together with an extremely high resolution sediment greyscale record, indicate that the climate of the last interglacial was not stable. In this region of the North Atlantic, the interval corresponding to the MIS 5e plateau can be separated into three distinct periods. The initial period is one of maximum warmth represented by a dominance of Neogloboquadrina pachyderma (dextral-coiling). This is followed by a cooler period characterised by increases in sub-polar species such as Globigerina bulloides and a decrease in N. pachyderma (dextral). The most convincing evidence for this climatic deterioration is the presence of low but significant amounts of IRD and an increase in the polar species N. pachyderma (sinistral-coiling). Benthic carbon isotope values suggest that some of these events were accompanied by changes in NADW production. The final part of the MIS 5e plateau shows a recovery to warmer conditions and stronger NADW production before the transition and multi-event, stepped cooling into MIS 5d. Surface conditions through the remainder of MIS 5 were appreciably cooler than the last interglacial period. Climate records across the MIS 5/4 transition reveal two distinct, extreme shifts in climate, apparently corresponding to extreme stadial-interstadial fluctuations in the Greenland ice cores, with oceanic SST reconstructions being charcterised by unusual interstadial warmth. Stadial coolings are preceded by small peaks in IRD, coincident with a freshening of surface waters. This signal is also translated to the deeper ocean, where benthic carbon isotope reductions of around 0.75 per mil suggest a significant reorganisation of NADW production.

  1. 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.

  2. 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.

  3. 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.

  4. Mueller matrix retinal imager with optimized polarization conditions.

    PubMed

    Twietmeyer, K M; Chipman, R A; Elsner, A E; Zhao, Y; VanNasdale, D

    2008-12-22

    A new Mueller matrix polarimeter was used to image the retinas of normal subjects. Light from a linearly polarized 780 nm laser was passed through a system of variable retarders and scanned across the retina. Light returned from the eye passed through a second system of retarders and a polarizing beamsplitter to two confocal detection channels. Optimization of the polarimetric data reduction matrix was via a condition number metric. The accuracy and repeatability of polarization parameter measurements were within +/- 5%. The magnitudes and orientations of retardance and diattenuation, plus depolarization, were measured over 15 degrees of retina for 15 normal eyes. PMID:19104564

  5. Mueller matrix retinal imager with optimized polarization conditions

    PubMed Central

    Twietmeyer, K. M.; Chipman, R. A.; Elsner, A. E.; Zhao, Y.; VanNasdale, D.

    2010-01-01

    A new Mueller matrix polarimeter was used to image the retinas of normal subjects. Light from a linearly polarized 780 nm laser was passed through a system of variable retarders and scanned across the retina. Light returned from the eye passed through a second system of retarders and a polarizing beamsplitter to two confocal detection channels. Optimization of the polarimetric data reduction matrix was via a condition number metric. The accuracy and repeatability of polarization parameter measurements were within ± 5%. The magnitudes and orientations of retardance and diattenuation, plus depolarization, were measured over 15° of retina for 15 normal eyes. PMID:19104564

  6. 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.

  7. 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.

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

    SciTech Connect

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

    1991-04-01

    The dependence of electron density in the polar F region ionization hole on solar activity, universal time (UT), magnetic activity, season, and hemisphere is studied using data from the Langmuir probes on Atmosphere Explorer C and Dynamics Explorer 2. The AE-C data were obtained during solar minimum when the 3-month average 10.7-cm solar flux index varied from 70 to 140; the DE 2 data were obtained near solar maximum when 10.7-cm solar flux index varied from 120 to 220. The polar hole is a region on the nightside of the polar cap where reduced ionization exists because of the long transport time of ionization from the dayside across the polar cap. The behavior of this region as a function of 10.7-cm solar flux (F10.7), UT, and Kp is statistically modeled for equinox, summer, and winter conditions for each hemisphere separately. The strongest dependencies are observed in F10.7 and UT; the Kp dependence is weak because it poorly represents the complexities of convection across the polar cap. 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: there is a density minimum at about 20.3 hours UT in the south and at about 4.8 hours UT in the north; the minimum to maximum UT density variation is about a factor of 8.9 in the south and about a factor of 2.1 in the north. There is a seasonal variation in the dependence of ion density (N{sub i}) on solar flux (F10.7). Use of the relationship (N{sub i}{approximately}F10.7{sup D}) yields values of D of approximately unity (1.) in the summer polar hole and about 2.1 during equinox. There is an overall asymmetry in the density level between hemispheres; it was found that the winter hole density is about a factor of 10 greater in the north than in the south. The Utah State University time dependent ionosphere model gives similar UT behavior to that found in the AE-C and DE 2 data.

  9. 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

  10. Probabilistic assessment of sea level during the last interglacial stage.

    PubMed

    Kopp, Robert E; Simons, Frederik J; Mitrovica, Jerry X; Maloof, Adam C; Oppenheimer, Michael

    2009-12-17

    With polar temperatures approximately 3-5 degrees C warmer than today, the last interglacial stage (approximately 125 kyr ago) serves as a partial analogue for 1-2 degrees C global warming scenarios. Geological records from several sites indicate that local sea levels during the last interglacial were higher than today, but because local sea levels differ from global sea level, accurately reconstructing past global sea level requires an integrated analysis of globally distributed data sets. Here we present an extensive compilation of local sea level indicators and a statistical approach for estimating global sea level, local sea levels, ice sheet volumes and their associated uncertainties. We find a 95% probability that global sea level peaked at least 6.6 m higher than today during the last interglacial; it is likely (67% probability) to have exceeded 8.0 m but is unlikely (33% probability) to have exceeded 9.4 m. When global sea level was close to its current level (>or=-10 m), the millennial average rate of global sea level rise is very likely to have exceeded 5.6 m kyr(-1) but is unlikely to have exceeded 9.2 m kyr(-1). Our analysis extends previous last interglacial sea level studies by integrating literature observations within a probabilistic framework that accounts for the physics of sea level change. The results highlight the long-term vulnerability of ice sheets to even relatively low levels of sustained global warming.

  11. Pleistocene reduction of polar ice caps: Evidence from Cariaco Basin marine sediments

    NASA Astrophysics Data System (ADS)

    Poore, R. Z.; Dowsett, H. J.

    2001-01-01

    Sea level is projected to rise between 13 and 94 cm over the next 100 yr due to continued climate warming. The sea-level projections assume that polar ice sheets will remain stable or even increase on time scales of centuries, but controversial geologic evidence suggests that current polar ice sheets have been eliminated or greatly reduced during previous Pleistocene interglacials indicating that modern polar ice sheets have become unstable within the natural range of interglacial climates. Sea level may have been more than 20 m higher than today during a presumably very warm interglacial about 400 ka during marine isotope stage 11. Because of the implications for future sea level rise, additional study of the conflicting evidence for warmer conditions and higher sea level during marine isotope stage 11 is needed. Here we present microfossil and isotopic data from marine sediments of the Cariaco Basin supporting the interpretation that global sea level was 10 20 m higher than today during marine isotope stage 11. The increased sea level requires reduction in modern polar ice sheets and is consistent with the interpretation that the West Antarctic ice sheet and the Greenland ice sheet were absent or greatly reduced during marine isotope stage 11. Our results show a warm marine isotope stage 11 interglacial climate with sea level as high as or above modern sea level that lasted for 25 to 30 k.y. Variations in Earth's orbit around the sun (Milankovitch cycles) are considered to be a primary external force driving glacial-interglacial cycles. Current and marine isotope stage 11 Milankovitch forcing are very similar, suggesting that the present interglacial (Holocene) that began ca. 10 ka will continue for another 15 to 20 k.y. Therefore any anthropogenic climate warming will accelerate the natural process toward reduction in polar ice sheets. The potential for increased rates of sea level rise related to polar ice sheet decay should be considered as a potential natural

  12. Pleistocene reduction of polar ice caps: Evidence from Cariaco Basin marine sediments

    USGS Publications Warehouse

    Poore, R.Z.; Dowsett, H.J.

    2001-01-01

    Sea level is projected to rise between 13 and 94 cm over the next 100 yr due to continued climate warming. The sea-level projections assume that polar ice sheets will remain stable or even increase on time scales of centuries, but controversial geologic evidence suggests that current polar ice sheets have been eliminated or greatly reduced during previous Pleistocene interglacials indicating that modern polar ice sheets have become unstable within the natural range of interglacial climates. Sea level may have been more than 20 m higher than today during a presumably very warm interglacial about 400 ka during marine isotope stage 11. Because of the implications for future sea level rise, additional study of the conflicting evidence for warmer conditions and higher sea level during marine isotope stage 11 is needed. Here we present microfossil and isotopic data from marine sediments of the Cariaco Basin supporting the interpretation that global sea level was 10-20 m higher than today during marine isotope stage 11. The increased sea level requires reduction in modern polar ice sheets and is consistent with the interpretation that the West Antarctic ice sheet and the Greenland ice sheet were absent or greatly reduced during marine isotope stage 11. Our results show a warm marine isotope stage 11 interglacial climate with sea level as high as or above modern sea level that lasted for 25 to 30 k.y. Variations in Earth's orbit around the sun (Milankovitch cycles) are considered to be a primary external force driving glacial-interglacial cycles. Current and marine isotope stage 11 Milankovitch forcing are very similar, suggesting that the present interglacial (Holocene) that began ca. 10 ka will continue for another 15 to 20 k.y. Therefore any anthropogenic climate warming will accelerate the natural process toward reduction in polar ice sheets. The potential for increased rates of sea level rise related to polar ice sheet decay should be considered as a potential natural

  13. 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.

  14. 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.

  15. No response to linear polarization cues in operant conditioning experiments with zebra finches.

    PubMed

    Melgar, Julian; Lind, Olle; Muheim, Rachel

    2015-07-01

    Many animals can use the polarization of light in various behavioural contexts. Birds are well known to use information from the skylight polarization pattern for orientation and compass calibration. However, there are few controlled studies of polarization vision in birds, and the majority of them have not been successful in convincingly demonstrating polarization vision. We used a two-alternative forced choice conditioning approach to assess linear polarization vision in male zebra finches in the 'visible' spectral range (wavelengths >400 nm). The birds were trained to discriminate colour, brightness and polarization stimuli presented on either one of two LCD-screens. All birds were able to discriminate the colour and brightness stimuli, but they were unable to discriminate the polarization stimuli. Our results suggest that in the behavioural context studied here, zebra finches are not able to discriminate polarized light stimuli.

  16. 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

  17. 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.

  18. Integrating Antarctic Near Shore and Deep Sea Records of Warm Interglacials

    NASA Astrophysics Data System (ADS)

    Scherer, R. P.

    2005-12-01

    The best way to accurately interpret polar ice sheet history is to make every effort to recover and date continental margin deposits proximal to the ice sheets, and confidently correlate these records with deep-sea cores. Deep-sea oxygen isotope records provide the best available archive of global ice volume, but they say nothing directly about specific changes in ice sheet configuration. Although geologic records along the margins of polar landmasses are rare, and those that exist are highly incomplete, they record climatic events in the global end-member environment, demonstrating the sensitivity of the system to climate change. Pelagic waters impinge far south along the Victoria Land coastline of Antarctica in McMurdo Sound. Increasing the southward encroachment of warm waters during interglacials affects moisture flux, sub-ice shelf circulation, and sea ice conditions, as well as surface water temperatures. These factors affect, in complex ways, ice shelf stability and, ultimately, marine (West Antarctic) and continental (East Antarctic) ice sheet configurations. The CIROS-2 drill core includes precisely dated and unequivocal evidence of pelagic waters in the near shore zone during the mid Pliocene. Likewise, the Cape Roberts Project (CRP-1) recovered a 2m thick carbonate-rich unit, unequivocally dated as MIS-31 (1.07 Ma) that indicates significantly elevated surface water temperatures and minimal sea ice. The warmest part of MIS-31 coincides with a paleomagnetic reversal (the base of the Jaramillo at 1.072 Ma), which offers an unprecedented opportunity for precise correlation with deep-sea cores, and offers the possibility of precise interhemispheric comparison of high latitude surface ocean conditions. Other marine interglacial deposits, notably MIS-11 and MIS-5e, have been recognized on the Antarctic margin, but dating is often not as precise as we strive for. High quality Pliocene through Holocene core is anticipated from the McMurdo Ice Shelf site of the

  19. 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

  20. 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.

  1. 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

  2. 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.

  3. 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

  4. Negligible glacial-interglacial variation in continental chemical weathering rates.

    PubMed

    Foster, Gavin L; Vance, Derek

    2006-12-14

    Chemical weathering of the continents is central to the regulation of atmospheric carbon dioxide concentrations, and hence global climate. On million-year timescales silicate weathering leads to the draw-down of carbon dioxide, and on millennial timescales chemical weathering affects the calcium carbonate saturation state of the oceans and hence their uptake of carbon dioxide. However, variations in chemical weathering rates over glacial-interglacial cycles remain uncertain. During glacial periods, cold and dry conditions reduce the rate of chemical weathering, but intense physical weathering and the exposure of carbonates on continental shelves due to low sea levels may increase this rate. Here we present high-resolution records of the lead isotope composition of ferromanganese crusts from the North Atlantic Ocean that cover the past 550,000 years. Combining these records with a simple quantitative model of changes in the lead isotope composition of the deep North Atlantic Ocean in response to chemical weathering, we find that chemical weathering rates were two to three times lower in the glaciated interior of the North Atlantic Region during glacial periods than during the intervening interglacial periods. This decrease roughly balances the increase in chemical weathering caused by the exposure of continental shelves, indicating that chemical weathering rates remained relatively constant on glacial-interglacial timescales. On timescales of more than a million years, however, we suggest that enhanced weathering of silicate glacial sediments during interglacial periods results in a net draw-down of atmospheric carbon dioxide, creating a positive feedback on global climate that, once initiated, promotes cooling and further glaciation.

  5. 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.

  6. 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.

  7. (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.

  8. 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.

  9. 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.

  10. 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

  11. 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°.

  12. 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.

  13. 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.

  14. 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

  15. 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

  16. 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.

  17. 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

  18. 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.

  19. 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

  20. 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.

  1. 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.

  2. The timing and duration of the Last Interglacial Asian Monsoon

    NASA Astrophysics Data System (ADS)

    Yuan, D.; Cheng, H.; Edwards, R.; Kelly, M.; Qing, J.; Lin, Y.; Zhang, M.

    2002-12-01

    from this value. If D4 growth rate is linear over the transition, as implied by long term stable growth rates (from 144 to 124 ka), the transition takes less than 500 y, with most of it taking less than 200 y. The Dongge Last Interglacial also ends with an abrupt δ18O shift (about 4 per mil). The midpoint is at 119.6 +/-0.6 ka based on direct dating of D3. D4 gives an age indistinguishable from this value. Assuming linear growth, the main portion of the transition took less than 700 y. Combining the onset and end ages of the Dongge Last Interglacial, the duration is 9.7 +/-1.1 ka, from 129.3 +/-0.9 ka to 119.6 +/-0.6 ka, remarkably similar to some estimates of full Last Interglacial sea levels. The timing is broadly consistent with orbital forcing of the Monsoon, although the abrupt shifts require the involvement of other mechanisms (e.g. changes in circulation). Dongge Termination II lags Devils Hole Termination II, some fraction of sea level Termination II, and likely Vostok temperature, Vostok CO2, and eastern Pacific sea surface temperature. However, there is some evidence that it coincides within error with the final rise in sea level to full Last Interglacial elevations. It may well be that Monsoon Termination II is an orbitally-forced event at the end of a sequence of events not directly caused by orbital forcing. As such it may mark the inception of full interglacial conditions world-wide. Orbital forcing may be necessary for full interglacial conditions, but not for many of the shifts toward interglacial conditions observed to prior to Dongge Termination II.

  3. A stagnation event in the deep South Atlantic during the last interglacial period.

    PubMed

    Hayes, Christopher T; Martínez-García, Alfredo; Hasenfratz, Adam P; Jaccard, Samuel L; Hodell, David A; Sigman, Daniel M; Haug, Gerald H; Anderson, Robert F

    2014-12-19

    During the last interglacial period, global temperatures were ~2°C warmer than at present and sea level was 6 to 8 meters higher. Southern Ocean sediments 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). 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. Thus, alternation of deep water formation between the Antarctic and the North Atlantic, believed to characterize ice ages, apparently also occurs in warm climates.

  4. Asymmetric simultaneous phase-inversion cross-polarization in solid-state MAS NMR: Relaxing selective polarization transfer condition between two dilute spins

    NASA Astrophysics Data System (ADS)

    Zhang, Zhengfeng; Fu, Riqiang; Li, Jianping; Yang, Jun

    2014-05-01

    Double cross polarization (DCP) has been widely used for heteronuclear polarization transfer between 13C and 15N in solid-state magic-angle spinning (MAS) NMR. However, DCP is such sensitive to experimental settings that small variations or deviations in RF fields would deteriorate its efficiency. Here, we report on asymmetric simultaneous phase-inversion cross polarization (referred as aSPICP) for selective polarization transfer between low-γ 13C and 15N spins. We have demonstrated through simulations and experiments using biological solids that the asymmetric duration in the simultaneous phase-inversion cross polarization scheme leads to efficient polarization transfer between 13C and 15N even with large chemical shift anisotropies in the presence of B1 field variations or mismatch of the Hartmann-Hahn conditions. This could be very useful in the aspect of long-duration experiments for membrane protein studies at high fields.

  5. Modeling the Seasonal South Polar Cap Sublimation Rates at Dust Storm Conditions

    NASA Technical Reports Server (NTRS)

    Bonev, B. P.; James, P. B.; Wolff, M. J.; Bjorkman, J. E.; Hansen, G. B.; Benson, J. L.

    2003-01-01

    Carbon dioxide is the principal component of the Martian atmosphere and its interaction with the polar caps forms the CO2 seasonal cycle on the planet. A significant fraction of the atmospheric constituent condenses on the surface during the polar winter and sublimes back during spring. The basic aspects of the CO2 cycle have been outlined by Leighton and Murray and a number of follow-up theoretical models ranging from energy balance to general circulation models have been used to study the physical processes involved in the cycle. This paper presents a modeling study on the seasonal south polar cap subliminiation rate under dust storm conditions. Mars Global Surveyor observations are also presented.

  6. Effect of Polarization on Airway Epithelial Conditioning of Monocyte-Derived Dendritic Cells.

    PubMed

    Papazian, Dick; Chhoden, Tashi; Arge, Maria; Vorup-Jensen, Thomas; Nielsen, Claus H; Lund, Kaare; Würtzen, Peter A; Hansen, Soren

    2015-09-01

    Airway epithelial cells (AECs) form polarized barriers that interact with inhaled allergens and are involved in immune homeostasis. We examined how monocyte-derived dendritic cells (MDDCs) are affected by contact with the airway epithelium. In traditional setups, bronchial epithelial cell lines were allowed to polarize on filter inserts, and MDDCs were allowed to adhere to the epithelial basal side. In an optimized setup, the cell application was reversed, and the culture conditions were modified to preserve cellular polarization and integrity. These two parameters were crucial for the MDDCs' immunoregulatory properties; thus, previous observations obtained using traditional setups should be considered with caution. Using the optimized setup, AEC conditioning of MDDCs led to increased expression of programmed death 1 ligand 1, immunoglobulin-like transcript 3, CD40, CD80, and CD23. This increased expression was accompanied by decreased secretion of monocyte chemotactic protein 1 and eotaxin and donor-variable effects on IL-12 and IL-10 secretion. Conditioning varied between maturation states and depended partly on direct contact between AECs and MDDCs. The setup allowed MDDCs on the basal side of the epithelium to sample allergens administered to the apical side. Allergen uptake depended on polarization and the nature of the allergen. AEC conditioning led to decreased birch allergen-specific proliferation of autologous T cells and a trend toward decreased secretion of the Th2-specific cytokines IL-5 and IL-13. In conclusion, we determined that AEC conditioning favoring cellular integrity leads to a tolerogenic MDDC phenotype, which is likely to be important in regulating immune responses against commonly inhaled allergens.

  7. Tropical Atlantic Temperature Seasonality at the End of the Last Interglacial

    NASA Astrophysics Data System (ADS)

    Felis, T.; Giry, C.; Scholz, D.; Lohmann, G.; Pfeiffer, M.; Pätzold, J.; Kölling, M.; Scheffers, S. R.

    2014-12-01

    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, which are partially comparable to those projected for 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 lead into the last glacial. Here we present a monthly resolved snapshot of reconstructed sea surface temperature variability in the tropical North Atlantic Ocean for 117.7 ± 0.8 kyr ago, using fossil coral (Diploria strigosa) Sr/Ca and δ18O records from Bonaire (Caribbean Netherlands). Our 20-year snapshot of reconstructed sea surface temperature variability for the end of the last interglacial is compared with Bonaire monthly coral Sr/Ca and δ18O records for snapshots since the mid-Holocene, comprising a total length of 295 years. We find that temperature seasonality in the southern Caribbean Sea at the end of the last interglacial was relatively stable and similar to today. 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 was a relatively stable feature of the ocean-atmosphere system at the end of the last interglacial.

  8. 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.

  9. 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

  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.

    2015-01-01

    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.

  11. 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.

  12. 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

  13. 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

  14. Cross-polarization microwave radar return at severe wind conditions: laboratory model and geophysical model function.

    NASA Astrophysics Data System (ADS)

    Troitskaya, Yuliya; Abramov, Victor; Ermoshkin, Alexey; Zuikova, Emma; Kazakov, Vassily; Sergeev, Daniil; Kandaurov, Alexandr

    2014-05-01

    Satellite remote sensing is one of the main techniques of monitoring severe weather conditions over the ocean. The principal difficulty of the existing algorithms of retrieving wind based on dependence of microwave backscattering cross-section on wind speed (Geophysical Model Function, GMF) is due to its saturation at winds exceeding 25 - 30 m/s. Recently analysis of dual- and quad-polarization C-band radar return measured from satellite Radarsat-2 suggested that the cross-polarized radar return has much higher sensitivity to the wind speed than co-polarized back scattering [1] and conserved sensitivity to wind speed at hurricane conditions [2]. Since complete collocation of these data was not possible and time difference in flight legs and SAR images acquisition was up to 3 hours, these two sets of data were compared in [2] only statistically. The main purpose of this paper is investigation of the functional dependence of cross-polarized radar cross-section on the wind speed in laboratory experiment. Since cross-polarized radar return is formed due to scattering at small-scale structures of the air-sea interface (short-crested waves, foam, sprays, etc), which are well reproduced in laboratory conditions, then the approach based on laboratory experiment on radar scattering of microwaves at the water surface under hurricane wind looks feasible. The experiments were performed in the Wind-wave flume located on top of the Large Thermostratified Tank of the Institute of Applied Physics, where the airflow was produced in the flume with the straight working part of 10 m and operating cross section 0.40?0.40 sq. m, the axis velocity can be varied from 5 to 25 m/s. Microwave measurements were carried out by a coherent Doppler X-band (3.2 cm) scatterometer with the consequent receive of linear polarizations. Experiments confirmed higher sensitivity to the wind speed of the cross-polarized radar return. Simultaneously parameters of the air flow in the turbulent boundary layer

  15. The Sea-Level Fingerprints of Ice-Sheet Collapse During Interglacial Periods (Invited)

    NASA Astrophysics Data System (ADS)

    Hay, C.; Mitrovica, J. X.; Gomez, N. A.; Creveling, J. R.; Austermann, J.; Kopp, R. E.

    2013-12-01

    Peak sea-level highstands during previous interglacials provide important insight into the stability of polar ice sheets in a warming world. In most previous analyses of such highstands, site-specific sea-level records are first corrected for the ongoing effects of glacial isostatic adjustment (GIA). The residual sea level is then interpreted as representing the net eustatic signal associated with any excess melting of the polar ice sheets relative to their present-day volumes. However, it is now well understood that the collapse of polar ice sheets produces a distinct geometry, or fingerprint, of sea-level change. These sea-level fingerprints must be accounted for in order to accurately estimate global eustatic sea level from site-specific (GIA-corrected) records. To investigate this issue, we compute fingerprints associated with the collapse of the Greenland Ice Sheet, West Antarctic Ice Sheet, and marine sectors of the East Antarctic Ice Sheet. We demonstrate that these fingerprints are, in contrast to those computed for modern melt scenarios, relatively insensitive to the detailed geometry of ice-sheet collapse. Moreover, using these fingerprints, we isolate regions that would have experienced greater-than-eustatic sea-level change regardless of the melt scenario. Finally, we use the fingerprints to demonstrate that some previous analyses of sea-level records from past interglacials may have overestimated peak eustatic sea level (and thus the net excess melting of polar ice sheets) by 1-2 m.

  16. 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

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

    PubMed

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

    2014-03-18

    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.

  18. 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

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

    PubMed

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

    2014-03-18

    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

  20. 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.

  1. How warm was Greenland during the last interglacial period?

    NASA Astrophysics Data System (ADS)

    Landais, Amaelle; Masson-Delmotte, Valérie; Capron, Emilie; Langenbroeck, Petra; Bakker, Pepijn; Stone, Emma; Fischer, Hubertus; Vinther, Bo; Dahl-Jensen, Dorthe

    2016-04-01

    The last interglacial period (LIG, ~129-116 thousand years ago) provides the most recent evidence for the response of Greenland and Antarctic ice sheets to polar warming above pre-industrial level, and a valuable test bed for ice sheet models. Key constraints on past changes in both ice sheet topography and surface temperature are derived from Greenland ice cores. The large warming estimated from the recent NEEM ice core drilled in northwest Greenland (8 ±4°C above pre-industrial) together with the evidence for limited local ice thinning have led to the "NEEM paradox", suggesting more stability of the ice sheet than simulated by ice flow models in response to such large warming. Here, we provide a new assessment of the LIG warming using ice core air isotopic composition (d15N) together with available relationships for Greenland between accumulation rate and temperature. The temperature at the upstream NEEM deposition site is estimated to be between -20°C to -24°C which is consistent with the 8±4°C warming relative to pre-industrial previously determined from water isotopic records measured on the NEEM ice, although we feel the lower end of this range to be more likely. Moreover, we show that under such warm temperature, melting of snow probably led to a significant firn shrinking by 15 m. We show that confirmation of this high temperature range for the LIG in Greenland is difficult to reconcile with climate modeling experiments

  2. Two middle Pleistocene glacial-interglacial cycles from the Valle Grande, Jemez Mountains, northern New Mexico

    USGS Publications Warehouse

    Fawcett, Peter J.; Heikoop, Jeff; Goff, Fraser; Anderson, R. Scott; Donohoo-Hurley, L.; Geissman, John William; WoldeGabriel, Giday; Allen, Craig D.; Johnson, Catrina M.; Smith, Susan J.; Fessenden-Rahn, Julianna

    2006-01-01

    A long-lived middle Pleistocene lake formed in the Valle Grande, a large moat valley of the Valles caldera in northern New Mexico, when a post-caldera eruption (South Mountain rhyolite) dammed the drainage out of the caldera. The deposits of this lake were cored in May 2004 (GLAD5 project, hole VC-3) and 81 m of mostly lacustrine silty mud were recovered. A tentative chronology has been established for VC-3 with a basal tephra Ar-Ar date of 552 +/- 3 ka, a correlation of major climatic changes in the core with other long Pleistocene records (deep sea oxygen isotope records and long Antarctic ice core records), and the recognition of two geomagnetic field polarity events in the core which can be correlated with globally recognized events. This record spans a critical interval of the middle Pleistocene from MIS 14 (552 ka) to MIS 10 (~360 ka), at which time the lacustrine sediments filled the available accommodation space in the caldera moat. Multiple analyses, including core sedimentology and stratigraphy, sediment density and rock magnetic properties, organic carbon content and carbon isotope ratios, C/N ratios, and pollen content reveal two glacial/interglacial cycles in the core (MIS 14 to MIS 10). This record includes glacial terminations V and VI and complete sections spanning interglacials MIS 13 and MIS 11. In the VC-3 record, both of these interglacials are relatively long compared with the intervening glacials (MIS 14 and MIS 12), and interglacial MIS 13 is significantly muted in amplitude compared with MIS 11. These features are similar to several other mid-Pleistocene records. The glacial terminations are quite abrupt in this record with notable changes in sedimentation, organic carbon content, C/N ratios and watershed vegetation type. Termination V is the largest climate change evident in this part of the middle Pleistocene. The glacial inceptions tend to be more gradual, on the order of a few thousand years.

  3. Interglacial Surface Ocean Temperatures Reveal Strong Ocean-Atmosphere Linkages Between the Subtropical and Subpolar Regions

    NASA Astrophysics Data System (ADS)

    Kandiano, E.; Bauch, H. A.; Fahl, K.; Helmke, J.; Roehl, U.

    2008-12-01

    Investigating ocean-atmospheric processes of past interglaciations may provide a better understanding of the climatic development of the present warm period. Here we present a detailed reconstruction of the meridional sea surface temperature (SST) across MIS 11 using three sites: ODP 958 (off NW Africa), ODP 975 (western Mediterranean Sea) and M23414 (subpolar NE Atlantic). Sea surface temperatures (SST) were derived from foraminiferal assemblages and alkenones, further supported by planktic and benthic O-isotope records as well as by iron content, the latter as indicator for Saharan dust export and continental dryness. On a large scale, reconstructed SSTs reveal a close synchronism of environmental changes between all three sites. It shows that, before full interglacial conditions became established, there was a long-lasting, glacial- interglacial transition with a total temperature increase of about 10°C in the subtropical as well as in the subpolar North Atlantic. After the main glacial-interglacial transition was over, SSTs continued to rise and reached their maximum during, what could be considered, the upper main phase of high sea-level stand in MIS 11. In the western Mediterranean SSTs show several cooling events with amplitudes of up to 4°C during the early full-interglacial warm period. Off NW Africa this phase is characterized by rather humid conditions, as inferred from strongly decreased values of iron in the sediments, and successive changes in the foraminiferal assemblages. We assume that these rather wet conditions at the lower latitudes were related to an intensification of the West African monsoon that increased summer moisture flux over Northwest Africa and runoff into the Mediterranean. At the same time increased abundance of subtropical, deep- dwelling foraminiferal species are found in the subpolar region implying a strong linkage between the subtropical atmospheric circulation regime over NW Africa and the northward propagation, of

  4. Constraining the Antarctic contribution to interglacial sea-level rise

    NASA Astrophysics Data System (ADS)

    Naish, T.; Mckay, R. M.; Barrett, P. J.; Levy, R. H.; Golledge, N. R.; Deconto, R. M.; Horgan, H. J.; Dunbar, G. B.

    2015-12-01

    Observations, models and paleoclimate reconstructions suggest that Antarctica's marine-based ice sheets behave in an unstable manner with episodes of rapid retreat in response to warming climate. Understanding the processes involved in this "marine ice sheet instability" is key for improving estimates of Antarctic ice sheet contribution to future sea-level rise. Another motivating factor is that far-field sea-level reconstructions and ice sheet models imply global mean sea level (GMSL) was up to 20m and 10m higher, respectively, compared with present day, during the interglacials of the warm Pliocene (~4-3Ma) and Late Pleistocene (at ~400ka and 125ka). This was when atmospheric CO2 was between 280 and 400ppm and global average surface temperatures were 1- 3°C warmer, suggesting polar ice sheets are highly sensitive to relatively modest increases in climate forcing. Such magnitudes of GMSL rise not only require near complete melt of the Greenland Ice Sheet and the West Antarctic Ice Sheet, but a substantial retreat of marine-based sectors of East Antarctic Ice Sheet. Recent geological drilling initiatives on the continental margin of Antarctica from both ship- (e.g. IODP; International Ocean Discovery Program) and ice-based (e.g. ANDRILL/Antarctic Geological Drilling) platforms have provided evidence supporting retreat of marine-based ice. However, without direct access through the ice sheet to archives preserved within sub-glacial sedimentary basins, the volume and extent of ice sheet retreat during past interglacials cannot be directly constrained. Sediment cores have been successfully recovered from beneath ice shelves by the ANDRILL Program and ice streams by the WISSARD (Whillans Ice Stream Sub-glacial Access Research Drilling) Project. Together with the potential of the new RAID (Rapid Access Ice Drill) initiative, these demonstrate the technological feasibility of accessing the subglacial bed and deeper sedimentary archives. In this talk I will outline the

  5. Vegetation and paleoclimate of the last interglacial period, central Alaska

    USGS Publications Warehouse

    Muhs, D.R.; Ager, T.A.; Beget, J.E.

    2001-01-01

    The last interglacial period is thought to be the last time global climate was significantly warmer than present. New stratigraphic studies at Eva Creek, near Fairbanks, Alaska indicate a complex last interglacial record wherein periods of loess deposition alternated with periods of soil formation. The Eva Forest Bed appears to have formed about the time of or after deposition of the Old Crow tephra (dated to ??? 160 to ??? 120 ka), and is therefore correlated with the last interglacial period. Pollen, macrofossils, and soils from the Eva Forest Bed indicate that boreal forest was the dominant vegetation and precipitation may have been greater than present around Fairbanks during the peak of the last interglacial period. A new compilation of last interglacial localities indicates that boreal forest was extensive over interior Alaska and Yukon Territory. Boreal forest also extended beyond its present range onto the Seward and Baldwin Peninsulas, and probably migrated to higher elevations, now occupied by tundra, in the interior. Comparison of last interglacial pollen and macrofossil data with atmospheric general circulation model results shows both agreement and disagreement. Model results of warmer-than-present summers are in agreement with fossil data. However, numerous localities with boreal forest records are in conflict with model reconstructions of an extensive cool steppe in interior Alaska and much of Yukon Territory during the last interglacial. ?? 2000 Elsevier Science Ltd.

  6. 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.

  7. 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

  8. Polar organic chemical integrative samplers for pesticides monitoring: impacts of field exposure conditions.

    PubMed

    Lissalde, Sophie; Mazzella, Nicolas; Mazellier, Patrick

    2014-08-01

    This study focuses on how Polar Organic Chemical Integrative Samplers (POCIS) work in real environmental conditions. A selection of 23 polar pesticides and 8 metabolites were investigated by exposure of triplicates of integrative samplers in two rivers in France for successive 14-day periods. The pesticides and metabolites were trapped not only in Oasis HLB sorbent but also in the polyethersulfone (PES) membrane of the POCIS. The distribution of pesticides depended on the molecular structure. The use of the Performance Reference Compound (PRC) is also discussed here. The impact of some environmental parameters and exposure setup on the transfer of pesticides in POCIS sorbent was studied: river flow rate, biofouling on membranes, sampler holding design and position in the stream. Results show a significant impact of river flow velocity on PRC desorption, especially for values higher than 4 cm·s(-1). Some fouling was observed on the PES membrane which could potentially have an impact on molecule accumulation in the POCIS. Finally, the positioning of the sampler in the river did not have significant effects on pesticide accumulation, when perpendicular exposures were used (sampler positioning in front of the water flow). The POCIS with PRC correction seems to be a suitable tool for estimating time-weighted average (TWA) concentrations, for all the molecules except for one of the nine pesticides analyzed in these two French rivers.

  9. 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.

  10. 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.

  11. 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.

  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. 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

  14. 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

  15. Geomagnetic Dipole Lows and Excursions of the last 800 ka : connection with Interglacials and/or low Obliquity Times?

    NASA Astrophysics Data System (ADS)

    Thouveny, N.

    2006-12-01

    Paleomagnetic directions, relative paleointensities (RPI) and authigenic 10Be/9Be ratio were measured along sedimentary clayey-carbonate sequences in high accumulation rate sites of the Portuguese margin (0-400 ka BP) and West-Equatorial Pacific (600-1300 ka BP. Series of high and low RPI features are placed on the chronological scale using C-14 ages, using correlations with of delta O-18 records with the Greenland ice cores and SPECMAP records, and using the ages of polarity reversals. During the time intervals of dramatically low RPI anomalous paleodirections document excursions or polarity reversals. Significant peaks of the authigenic 10Be/9Be ratio point in stratigraphic layers recording all low RPI phases. Plotted against RPI data the 10Be/9Be ratios statistically follow the expected power law (Elsasser et al. ,1958 and Lal, 1988), which strongly establishes the unique and direct link between the recorded cosmogenic enhancement and dipole moment loss, allowing us to univocally interpret our 10Be/9Be ratio and RPI records in terms of geomagnetic dipole moment lows and highs (DML and DMH) alternation. delta O-18 records of the same cores (e.g. Abreu et al. 2004), provide the frame to interpret dipole moment variations in a paleoclimatic context within strict stratigraphic terms. We note that most DML of the last 400 ka fall in the end of interglacial stages, while DMH are rather related with full glacials. We then confirm this coincidence, though whithout strict stratigraphic control, by comparing the SINT-800 curve (Guyodo and Valet, 1999) and the S. E. Pacific near Sea Floor mag. record (Gee et al., 2000), with the highest resolution 18O record yet available (Bassinot et al. 1994). Complex Wavelet analyses using modulus and phase reveal that the geomagnetic moment proxy records contain a maximum power for periods between 30 and 100 ka. DML do not occur in any fixed eccentricity context, but several DML fall at the time of obliquity minima. The comparison of

  16. 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.

  17. The role of mineral dust aerosols in polar amplification

    NASA Astrophysics Data System (ADS)

    Lambert, F.; Kug, J.; Park, R.; Jin, F.; Lee, J. H.

    2010-12-01

    During today’s global warming, as well as during glacial-interglacial changes, temperature increase is larger in polar areas than the global average, a phenomenon called “polar amplification”. Model studies suggest ice cap melting due to greenhouse gas induced temperature rise, and consequent decrease of albedo and enhanced oceanic and atmospheric heat transport, as the primary cause for this phenomenon in nowadays Arctic. However, the underlying causes for polar amplification on glacial-interglacial timescales are still unclear, especially in the Antarctic where sea ice coverage does not change as drastically as in the North. Recent results have shown that the temperature increase is not limited to the surface and that these changes can not be explained by snow and ice changes alone. Starting with dust flux measurements from ice cores in Greenland and Antarctica, we have estimated tropospheric concentrations using deposition velocities and vertical concentration profiles for Holocene and LGM conditions from the National Center for Atmospheric Research’s Community Climate System Model (CCSM3) and a 3-D global chemical transport model (GEOS-Chem). The radiative forcing due to mineral dust aerosols was then estimated using the GEOS-Chem model, based on the particle properties found in the ice. Preliminary results point towards positive forcing of dust because of the high albedo of the underlying ice sheets.

  18. 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

  19. How warm was Greenland during the last interglacial period?

    NASA Astrophysics Data System (ADS)

    Landais, Amaelle; Masson-Delmotte, Valérie; Capron, Emilie; Langebroek, Petra M.; Bakker, Pepijn; Stone, Emma J.; Merz, Niklaus; Raible, Christoph C.; Fischer, Hubertus; Orsi, Anaïs; Prié, Frédéric; Vinther, Bo; Dahl-Jensen, Dorthe

    2016-09-01

    The last interglacial period (LIG, ˜ 129-116 thousand years ago) provides the most recent case study of multimillennial polar warming above the preindustrial level and a response of the Greenland and Antarctic ice sheets to this warming, as well as a test bed for climate and ice sheet models. Past changes in Greenland ice sheet thickness and surface temperature during this period were recently derived from the North Greenland Eemian Ice Drilling (NEEM) ice core records, northwest Greenland. The NEEM paradox has emerged from an estimated large local warming above the preindustrial level (7.5 ± 1.8 °C at the deposition site 126 kyr ago without correction for any overall ice sheet altitude changes between the LIG and the preindustrial period) based on water isotopes, together with limited local ice thinning, suggesting more resilience of the real Greenland ice sheet than shown in some ice sheet models. Here, we provide an independent assessment of the average LIG Greenland surface warming using ice core air isotopic composition (δ15N) and relationships between accumulation rate and temperature. The LIG surface temperature at the upstream NEEM deposition site without ice sheet altitude correction is estimated to be warmer by +8.5 ± 2.5 °C compared to the preindustrial period. This temperature estimate is consistent with the 7.5 ± 1.8 °C warming initially determined from NEEM water isotopes but at the upper end of the preindustrial period to LIG temperature difference of +5.2 ± 2.3 °C obtained at the NGRIP (North Greenland Ice Core Project) site by the same method. Climate simulations performed with present-day ice sheet topography lead in general to a warming smaller than reconstructed, but sensitivity tests show that larger amplitudes (up to 5 °C) are produced in response to prescribed changes in sea ice extent and ice sheet topography.

  20. About past interglacials as analogues to the Holocene and Anthropocene

    NASA Astrophysics Data System (ADS)

    Berger, Andre; Yin, Qiuzhen

    2014-05-01

    To understand better our current interglacial and its future, we have investigated the response of the climate system to insolation and CO2 at the peaks of the interglacials over the past 800,000 years using both LOVECLIM and CCSM3. If we identify these peaks with NH summer at perihelion, MIS-1, MIS-11 and MIS-19 show a pretty similar latitudinal and seasonal distribution of the incoming solar radiation, which leads to similar climate response to insolation. However, differences exist. When compared to the average of the last 9 interglacials, a warming over the Southern Ocean in austral winter occurs during MIS-1 and MIS-19 due to the summer remnant effect of insolation. However, this does not happen in MIS-11 because the large global cooling during this season is dominating the remnant effect of the austral summer. This leads to MIS-11 being a cool insolation-induced interglacial and thus not as good an analogue of MIS-1 as MIS-19, at least as far as insolation is concerned. The CO2 equivalent concentration is practically the same for MIS-1 and MIS-19 but is larger for MIS-11. The lower CO2 during MIS-1 and MIS-19 cools the Earth, reinforcing the insolation-induced cooling during boreal summer and moderating the warming during boreal winter. The reverse happens for MIS-11 for which its higher CO2 allows it to be finally classified among the warm interglacials. The interglacials MIS-9 and MIS-5 are the warmest over the last 800 ka and, as such, are considered as analogues for our CO2-induced future warm interglacial. However, their astronomical forcings are largely different from MIS-1 and its future, leading to a completely different seasonal and regional climate response compared to the simulated future climate. The best analogue to MIS-1 depends therefore upon the criteria used to select such an analogue. The climate simulated with insolation when NH summer at perihelion will be compared to climate resulting from other insolation scenario. If we look for

  1. Are boundary conditions in surface productivity at the Southern Polar Front reflected in benthic activity?

    NASA Astrophysics Data System (ADS)

    Brandt, Angelika; Vanreusel, Ann; Bracher, Astrid; Jule Marie Hoppe, Clara; Lins, Lidia; Meyer-Löbbecke, Anna; Altenburg Soppa, Mariana; Würzberg, Laura

    2014-10-01

    In austral summer 2012, during the expedition ANT-XXVIII/3 on board RV Polarstern, two sites were sampled 1600 km apart in the South Polar Front area (52°S) at the boundary of different productivity regimes for meio- and macrobenthos using a multiple-corer and an epibenthic sledge, respectively. Patterns in density and abundance data were compared between different size classes of the benthos and interpreted in relation to surface primary productivity data and sediment oxygen consumption. We tested the hypothesis that long-term satellite-derived surface phytoplankton biomass, in situ real time biomass, and productivity measurements at the surface and throughout the euphotic zone are reflected in abyssal benthos densities, abundances and activity. Specifically, we investigated the effect of boundary conditions for lower and higher surface productivity. Surface and integrated to 100 m depth biomass and primary productivity measurements vary stations, with the lowest values at station 85 (0.083 mg Chl-a m-3 at surface, 9 mg Chl-a m-2 and 161 mg C m-2 d-1- integrated over the first 100 m depth), and the highest values at station 86 (2.231 mg Chl-a m-3 at surface, 180 mg Chl-a m-2 and 2587 mg C m-2 d-1 integrated over first 100 m depth). Total meiofaunal densities varied between 102 and 335 individuals/10 cm². Densities were the highest at station 86-30 (335 individuals) and lowest at station 81-13 (102 individuals). Total macrofaunal densities (individuals/1000 m²) varied between 26 individuals at station 81-17 and 194 individuals at station 86-24. However, three EBS hauls were taken at station 86 with a minimum of 80 and a maximum of 194 individuals. Sediment oxygen consumption did not vary significantly between stations from east to west. Bentho-pelagic coupling of meio- and macrobenthic communities could not be observed in the South Polar Front at the boundary conditions from low to high surface productivity between stations 81 and 86.

  2. The Eemian Climate Controversy in the Polar North

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

    The cold polar North plays a central role in the global climate system through its influence on ocean-atmosphere heat balance and circulation. Still, understanding naturally and/or anthropogenically forced variability of Arctic change remains somewhat elusive due to the relative shortness of available time series records. Thus, paleoclimate archives, which contain past environmental information similar to the present warm period, comprise a useful target for further studies. Paleoclimate records of the last interglacial (Eemian) are often used to test various physical aspects of a warm climate. On a global scale, the Eemian is generally regarded a time with higher temperatures and sea-level than the Holocene. But little data exist so far from the Arctic Ocean proper and its bounding margins that would allow for a profound statement on how the high-northern latitudes responded to a warmer-than-present interglacial climate. In these northern regions, there are conflicting interpretations on the basis of different data sets. For instance, deep-sea marine records from the Nordic seas clearly indicate much cooler-than-early-Holocene surface ocean conditions throughout the Eemian, whereas coastal records from raised shallow marine sediments may support an opposite view. New marine data from the central and eastern Nordic seas now describe a very different picture on the history of the northbound flow of warm Atlantic waters. Accordingly, the Eemian climate of that region developed rather differently from the Holocene, with noticeable strong variabilties during Termination 2 but also during the ensuing peak interglacial phase. The cause for all this may be various. But, processes connected with the huge Fennoscandian Saalian ice sheet on land, its particular deglacial melting history, as well as the spatial distribution of water masses and seasonal sea ice during the ensuing peak interglacial times were largely involved. Our results provide more insight into the temporal

  3. A comparison of the present and last interglacial periods in six Antarctic ice cores

    NASA Astrophysics Data System (ADS)

    Masson-Delmotte, V.; Buiron, D.; Ekaykin, A.; Frezzotti, M.; Gallée, H.; Jouzel, J.; Krinner, G.; Landais, A.; Motoyama, H.; Oerter, H.; Pol, K.; Pollard, D.; Ritz, C.; Schlosser, E.; Sime, L. C.; Sodemann, H.; Stenni, B.; Uemura, R.; Vimeux, F.

    2010-10-01

    We compare the present and last interglacial periods as recorded in Antarctic water stable isotope records now available at various temporal resolutions from six East Antarctic ice cores: Vostok, Taylor Dome, EPICA Dome C (EDC), EPICA Dronning Maud Land (EDML), Dome Fuji and the recent TALDICE ice core from Talos Dome. We first review the different modern site characteristics in terms of ice flow, meteorological conditions, precipitation intermittency and moisture origin, as depicted by meteorological data, atmospheric reanalyses and Lagrangian moisture source diagnostics. These different factors can indeed alter the relationships between temperature and water stable isotopes. Using five records with sufficient resolution on the EDC3 age scale, common features are quantified through principal component analyses. Consistent with instrumental records and atmospheric model results, the ice core data depict rather coherent and homogenous patterns in East Antarctica during the last two interglacials. Across the East Antarctic plateau, regional differences, with respect to the common East Antarctic signal, appear to have similar patterns during the current and last interglacials. We identify two abrupt shifts in isotopic records during glacial inception at TALDICE and EDML, likely caused by regional sea ice expansion. These regional differences are discussed in terms of moisture origin and in terms of past changes in local elevation histories which are compared to ice sheet model results. Our results suggest that, for coastal sites, elevation changes may contribute significantly to inter-site differences. These elevation changes may be underestimated by current ice sheet models.

  4. A comparison of the present and last interglacial periods in six Antarctic ice cores

    NASA Astrophysics Data System (ADS)

    Masson-Delmotte, V.; Buiron, D.; Ekaykin, A.; Frezzotti, M.; Gallée, H.; Jouzel, J.; Krinner, G.; Landais, A.; Motoyama, H.; Oerter, H.; Pol, K.; Pollard, D.; Ritz, C.; Schlosser, E.; Sime, L. C.; Sodemann, H.; Stenni, B.; Uemura, R.; Vimeux, F.

    2011-04-01

    We compare the present and last interglacial periods as recorded in Antarctic water stable isotope records now available at various temporal resolutions from six East Antarctic ice cores: Vostok, Taylor Dome, EPICA Dome C (EDC), EPICA Dronning Maud Land (EDML), Dome Fuji and the recent TALDICE ice core from Talos Dome. We first review the different modern site characteristics in terms of ice flow, meteorological conditions, precipitation intermittency and moisture origin, as depicted by meteorological data, atmospheric reanalyses and Lagrangian moisture source diagnostics. These different factors can indeed alter the relationships between temperature and water stable isotopes. Using five records with sufficient resolution on the EDC3 age scale, common features are quantified through principal component analyses. Consistent with instrumental records and atmospheric model results, the ice core data depict rather coherent and homogenous patterns in East Antarctica during the last two interglacials. Across the East Antarctic plateau, regional differences, with respect to the common East Antarctic signal, appear to have similar patterns during the current and last interglacials. We identify two abrupt shifts in isotopic records during the glacial inception at TALDICE and EDML, likely caused by regional sea ice expansion. These regional differences are discussed in terms of moisture origin and in terms of past changes in local elevation histories, which are compared to ice sheet model results. Our results suggest that elevation changes may contribute significantly to inter-site differences. These elevation changes may be underestimated by current ice sheet models.

  5. Impact of meltwater on high-latitude early Last Interglacial climate

    NASA Astrophysics Data System (ADS)

    Stone, Emma J.; Capron, Emilie; Lunt, Daniel J.; Payne, Antony J.; Singarayer, Joy S.; Valdes, Paul J.; Wolff, Eric W.

    2016-09-01

    Recent data compilations of the early Last Interglacial period have indicated a bipolar temperature response at 130 ka, with colder-than-present temperatures in the North Atlantic and warmer-than-present temperatures in the Southern Ocean and over Antarctica. However, climate model simulations of this period have been unable to reproduce this response, when only orbital and greenhouse gas forcings are considered in a climate model framework. Using a full-complexity general circulation model we perform climate model simulations representative of 130 ka conditions which include a magnitude of freshwater forcing derived from data at this time. We show that this meltwater from the remnant Northern Hemisphere ice sheets during the glacial-interglacial transition produces a modelled climate response similar to the observed colder-than-present temperatures in the North Atlantic at 130 ka and also results in warmer-than-present temperatures in the Southern Ocean via the bipolar seesaw mechanism. Further simulations in which the West Antarctic Ice Sheet is also removed lead to warming in East Antarctica and the Southern Ocean but do not appreciably improve the model-data comparison. This integrated model-data approach provides evidence that Northern Hemisphere freshwater forcing is an important player in the evolution of early Last Interglacial climate.

  6. 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.

  7. 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

  8. 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

  9. Was the Asian monsoon climate stable or not during the last interglacial?

    NASA Astrophysics Data System (ADS)

    Cai, Y.; An, Z.; Qin, S.; Cheng, H.; Edwards, R.; Zhang, H.

    2012-12-01

    The climate during the last interglacial was stable or not is still an open question. Here, we present an absolute-dated δ18O record during the Marin Isotope Stage 5e (Emian in Europe) from Xiaotian Cave, southeast of Chinese Loess Plateau, a region sensitive to the East Asia monsoon changes. This speleothem calcite δ18O record shows substantial centennial time-scales changes with large amplitude of ~3‰ during the last interglacial. These changes are similar to the variations found in the δ18O record from Tianmen Cave, south central Tibetan, another region sensitive to the Indian summer monsoon changes. This similarity indicates that there were significant changes occurred in the Asian summer monsoon circulations and confirms the instability of Asian summer monsoon climate during the last interglacial. Our record also indicates that the speleothem calcite δ18O values increased abruptly around 122ka BP, which is consistent with the previously reported δ18O records from Dongge, Sanbao and Tianmen caves within the quoted dating errors, demonstrating the abrupt weakening of Asian summer monsoon at the transition from MIS 5e to MIS 5d. This abrupt change of Asian summer monsoon could correlate with the temperature records from North Atlantic region. It is most likely that the decreased thermohaline circulation resulted in the cooling of the high north latitude regions and then weakened the Asian summer monsoon. In addition, the general trend of the speleothem calcite δ18O records during the last interglacial was not following the insolation changes, which is different from the scenery during the Holocene. This discrepancy may be caused by the different seasonality of insolation in the northern hemisphere and also the different lower boundary conditions, such as the ice sheet size and distribution and ocean circulations etc.

  10. 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

  11. Glacial-Interglacial Climate Changes Recorded by Debris Flow Grain Size, Eastern Sierra Nevada, California

    NASA Astrophysics Data System (ADS)

    D'Arcy, M. K.; Whittaker, A. C.; Roda Boluda, D. C.

    2015-12-01

    Uncertainties remain about the sensitivity of eroding landscapes to climate changes over a range of frequencies and amplitudes. Numerical models suggest that simple catchment-fan systems should be responsive to glacial-interglacial climate cycles, recording them in both sediment flux and the grain size distribution of their deposits. However these models are largely untested and the propagation of climatic signals through simple sediment routing systems remains contentious. Here, we present detailed sedimentological data from 8 debris flow fans in Owens Valley, eastern California. These fans have an exceptionally well-constrained depositional record spanning the last 120 ka, which we use to examine how sediment export has varied as a function of high-amplitude climate changes. We find a strong and sustained relationship between debris flow grain size and paleoclimate proxies over an entire glacial-interglacial cycle, with significantly coarser-grained deposits correlated with warm and dry conditions. Our data suggest these systems are highly reactive to climate forcing, with a short response timescale of <10 ka and no evidence of signal buffering, which we interpret to be driven by rapid sediment transfer from source to sink. We demonstrate that debris flow grain size follows an exponential relationship with temperature, coarsening at a rate of ~10 % per °C. Using this observation, and a known relationship between temperature and storm intensity, we propose that the climate signal recorded in these fan deposits captures changing storm intensity during the last glacial-interglacial cycle. This study offers a direct test of existing models of catchment-fan systems, confirming that glacial-interglacial climate changes can be clearly expressed in their grain size records. Our results also suggest that these debris flow deposits contain a high-resolution, testable record of past storm intensity, and that storminess is the primary control on their sedimentological

  12. 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.

  13. 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

  14. 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

  15. 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.

  16. The last interglaciation in Alaska: Stratigraphy and paleoecology of potential sites

    USGS Publications Warehouse

    Hamilton, T.D.; Brigham-Grette, J.

    1991-01-01

    At least 20 localities in Alaska contain deposits that may provide information on the last interglaciation (Oxygen-Isotope Substage 5e). These widely dispersed localities include river bluffs, coastal bluffs and terraces, elevated marine shorelines, lake basins, and artificial excavations. Most of the inferred interglacial deposits contain macrofossils or pollen that are older than the range of radiocarbon dating and commonly indicate climate as warm as or warmer than the present. At a few localities, evidence for deep thaw of permafrost also indicates a warm paleoclimate. At eight localities, the Old Crow tephra occurs at or below organic deposits that may represent Substage 5e. The tephra occurs beneath conspicuous organic deposits at Fairbanks, the Yukon Palisades, and Holitna lowland, and directly above a peat bed at Hogatza Mine. At Birch Creek, Halfway House, Ky-11, and Imuruk Lake, the tephra occurs within a paleosol or organic deposit, but other organic horizons that more likely indicate interglacial conditions occur at higher stratigraphic levels. The varied stratigraphic relations of the Old Crow tephra suggest that it may have been deposited close to the boundary between Isotope Substages 6 and 5, which is dated at about 130 ka in the marine record and between 132 and 140 ka on land. These age relations suggests that the tephra may have been deposited about 135 ?? 5 ka, validating the recent fission-track age determination of 140 ?? 10 ka for this deposit. Six coastal localities contain deposits of probable interglacial age, and these commonly are associated with evidence for eustatic sea levels higher than those of the present. Beach and sublittoral sediments of the Pelukian transgression occur up to 12 m asl along the northwest coast of Alaska, and are correlative with barrier island and lagoonal sediments on the Alaskan Arctic Coastal Plain. Both sets of deposits commonly contain extralimital mollusks and microfauna that indicate marine water slightly

  17. 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.

  18. Duration and structure of the past four interglaciations

    USGS Publications Warehouse

    Winograd, I.J.; Landwehr, J.M.; Ludwig, K. R.; Coplen, T.B.; Riggs, A.C.

    1997-01-01

    Reanalysis and additional dating of the Devils Hole ??18O paleotemperature record confirm that the last interglaciation in the Great Basin (the continental analog of marine isotopic substage 5e) lasted ???22,000 yr, consistent with the Vostok paleotemperature record which suggests a duration of ???19,000 yr for this event in Antarctica. The three preceding interglaciations in the Devils Hole record (analogs of marine isotopic substages 7e, 9c, and 11c) range from 20,000 to 26,000 yr in duration. A ???20,000-yr duration for the last interglaciation is consistent with TIMS uranium-series dated sea-level high stands. Thus, the widely held view that interglaciations were of 11,000-to 13,000-yr duration and constituted only about 10% of mid-to-late Pleistocene climatic cycles needs reexamination. The warmest portion of each interglaciation in the Devils Hole time series is marked by a ??18O plateau, signifying apparent climatic stability for periods of 10,000-to 15,000-yr duration. ?? 1997 University of Washington.

  19. 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.

  20. 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.

  1. 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

  2. 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.

  3. 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.

  4. Ice volume and sea level during the last interglacial.

    PubMed

    Dutton, A; Lambeck, K

    2012-07-13

    During the last interglacial period, ~125,000 years ago, sea level was at least several meters higher than at present, with substantial variability observed for peak sea level at geographically diverse sites. Speculation that the West Antarctic ice sheet collapsed during the last interglacial period has drawn particular interest to understanding climate and ice-sheet dynamics during this time interval. We provide an internally consistent database of coral U-Th ages to assess last interglacial sea-level observations in the context of isostatic modeling and stratigraphic evidence. These data indicate that global (eustatic) sea level peaked 5.5 to 9 meters above present sea level, requiring smaller ice sheets in both Greenland and Antarctica relative to today and indicating strong sea-level sensitivity to small changes in radiative forcing.

  5. 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

  6. 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

  7. Spectral induced polarization of the three-phase system CO2 - brine - sand under reservoir conditions

    NASA Astrophysics Data System (ADS)

    Börner, Jana H.; Herdegen, Volker; Repke, Jens-Uwe; Spitzer, Klaus

    2016-10-01

    The spectral complex conductivity of a water-bearing sand during interaction with carbon dioxide (CO2) is influenced by multiple, simultaneous processes. These processes include partial saturation due to the replacement of conductive pore water with CO2 and chemical interaction of the reactive CO2 with the bulk fluid and the grain-water interface. We present a laboratory study on the spectral induced polarization (SIP) of water-bearing sands during exposure to and flow-through by CO2. Conductivity spectra were measured successfully at pressures up to 30 MPa and 80°C during active flow and at steady-state conditions concentrating on the frequency range between 0.0014 and 100 Hz. The frequency range between 0.1 and 100 Hz turned out to be most indicative for potential monitoring applications. The presented data show that the impact of CO2 on the electrolytic conductivity may be covered by a model for pore-water conductivity, which depends on salinity, pressure and temperature and has been derived from earlier investigations of the pore-water phase. The new data covering the three-phase system CO2-brine-sand further show that chemical interaction causes a reduction of surface conductivity by almost 20 per cent, which could be related to the low pH-value in the acidic environment due to CO2 dissolution and the dissociation of carbonic acid. The quantification of the total CO2 effect may be used as a correction during monitoring of a sequestration in terms of saturation. We show that this leads to a correct reconstruction of fluid saturation from electrical measurements. In addition, an indicator for changes of the inner surface area, which is related to mineral dissolution or precipitation processes, can be computed from the imaginary part of conductivity. The low frequency range between 0.0014 and 0.1 Hz shows additional characteristics, which deviate from the behaviour at higher frequencies. A Debye decomposition approach is applied to isolate the feature dominating

  8. 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.

  9. Genetic consequences of interglacial isolation in a steppe bird.

    PubMed

    Garcia, J T; Mañosa, S; Morales, M B; Ponjoan, A; García de la Morena, E L; Bota, G; Bretagnolle, V; Dávila, J A

    2011-12-01

    In response to climate changes that have occurred during Pleistocene glacial cycles, taxa associated to steppe vegetation might have followed a pattern of historical evolution in which isolation and fragmentation of populations occurred during the short interglacials and expansion events occurred during the long glacial periods, in contrast to the pattern described for temperate species. Here, we use molecular genetic data to evaluate this idea in a steppe bird with Palaearctic distribution, the little bustard (Tetrax tetrax). Overall, extremely low genetic diversity and differentiation was observed among eight little bustard populations distributed in Spain and France. Mismatch distribution analyses showed that most little bustard populations expanded during cooling periods previous to, and just after, the last interglacial period (127,000-111,000 years before present), when steppe habitats were widespread across Europe. Coalescent-based methods suggested that glacial expansions have resulted in substantial admixture in Western Europe due to the existence of different interglacial refugia. Our results are consistent with a model of evolution and genetic consequences of Pleistocene cycles with low between-population genetic differentiation as a result of short-term isolation periods during interglacials and long-term exchange during glacial periods. PMID:21835255

  10. 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

  11. 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.

  12. 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.

  13. EPICA Dome C record of glacial and interglacial intensities

    NASA Astrophysics Data System (ADS)

    Masson-Delmotte, V.; Stenni, B.; Pol, K.; Braconnot, P.; Cattani, O.; Falourd, S.; Kageyama, M.; Jouzel, J.; Landais, A.; Minster, B.; Barnola, J. M.; Chappellaz, J.; Krinner, G.; Johnsen, S.; Röthlisberger, R.; Hansen, J.; Mikolajewicz, U.; Otto-Bliesner, B.

    2010-01-01

    Climate models show strong links between Antarctic and global temperature both in future and in glacial climate simulations. Past Antarctic temperatures can be estimated from measurements of water stable isotopes along the EPICA Dome C ice core over the past 800 000 years. Here we focus on the reliability of the relative intensities of glacial and interglacial periods derived from the stable isotope profile. The consistency between stable isotope-derived temperature and other environmental and climatic proxies measured along the EDC ice core is analysed at the orbital scale and compared with estimates of global ice volume. MIS 2, 12 and 16 appear as the strongest glacial maxima, while MIS 5.5 and 11 appear as the warmest interglacial maxima. The links between EDC temperature, global temperature, local and global radiative forcings are analysed. We show: (i) a strong but changing link between EDC temperature and greenhouse gas global radiative forcing in the first and second part of the record; (ii) a large residual signature of obliquity in EDC temperature with a 5 ky lag; (iii) the exceptional character of temperature variations within interglacial periods. Focusing on MIS 5.5, the warmest interglacial of EDC record, we show that orbitally forced coupled climate models only simulate a precession-induced shift of the Antarctic seasonal cycle of temperature. While they do capture annually persistent Greenland warmth, models fail to capture the warming indicated by Antarctic ice core δD. We suggest that the model-data mismatch may result from the lack of feedbacks between ice sheets and climate including both local Antarctic effects due to changes in ice sheet topography and global effects due to meltwater-thermohaline circulation interplays. An MIS 5.5 sensitivity study conducted with interactive Greenland melt indeed induces a slight Antarctic warming. We suggest that interglacial EDC optima are caused by transient heat transport redistribution comparable with

  14. 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

  15. A warm interglacial episode during oxygen isotope stage 11 in northern Chile

    NASA Astrophysics Data System (ADS)

    Ortlieb, Luc; Diaz, Amanda; Guzman, Nury

    Combined paleontological, morphostratigraphic and geochronologic data from emerged Middle Pleistocene coastal deposits in Mejillones Peninsula (23°S), northern Chile, strongly suggest that climatic conditions were particularly warm during the particularly warm during the Oxygen Isotope Stage 11 high seastand episode. An anomalous warm-water molluscan assemblage from localities assigned to that interglaciation included several extralimital species, presently living only north of 6°S (or 14°S), that were not present in the area during subsequent Middle and Late Pleistocene, or Holocene, interglacial episodes. Only two of these extralimital species may be found nowadays at the 23°S latitude, in a protected locality, immediately after the occurrence of strong El Niño events. Many of the species of the thermally anomalous molluscan assemblage (TAMA) are the same as those which lived in a closed shallow lagoon near Santa, north-central Peru (9°S) during a brief mid-Holocene episode. The new findings thus indicate that lagoonal and protected embayments were significantly warmer than the open marine environment ca. 400 ka. Actually, the co-occurrence of cool water fauna in exposed sectors of the coastline at that time suggests that the coastal upwelling activity and the Humboldt Current effects were not strongly reduced. The warm-water conditions prevailing in lagoons and protected bays during the Mid-Brunhes episode may reflect particularly warm air temperatures and distinct ocean-atmosphere relationships than those prevalent nowadays. These data support the hypothesis that the Oxygen Isotope Stage 11 was the warmest interglaciation, at least in the southern hemisphere.

  16. 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.

  17. 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

  18. 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.

  19. Ion and neutral polar winds for northward interplanetary magnetic field conditions

    NASA Astrophysics Data System (ADS)

    Gardner, Larry C.; Schunk, Robert W.

    2006-08-01

    The coupling of the ionosphere/magnetosphere system at high-latitudes is dependent in part upon the transport of neutral atoms from the ionosphere to the magnetosphere, and visa versa. The neutral atoms that flow between the ionosphere and the magnetosphere are neutral stream atoms that are produced in charge exchange reactions between the ions in the polar wind and the background thermal and geocoronal atoms. The characteristics of these neutral stream particles are highly dependent upon the ions in the polar cap. The ions are convected across the polar cap due to convection electric fields, and thus the neutral stream particles are also indirectly affected by the convection electric fields due to charge exchange. The horizontal flow of neutral stream particles, therefore, shows a general anti-sunward motion during periods of southward interplanetary magnetic field (IMF), and a general sunward flow across the magnetic pole during times of northward IMF. The vertical fluxes of these neutral stream particles depend upon several processes, including the heat input due to precipitating electrons, the vertical velocity of the ions involved in the charge exchange reactions that produce the neutral stream particles, and the time history of neutral stream particles in the high-latitude region.

  20. Records of glacial-interglacial variability during the Pliocene: IODP Expedition 318 - Site U1361

    NASA Astrophysics Data System (ADS)

    Gonzalez, J. J.; Escutia, C.; Espejo, F. J.; Williams, T.; McKay, R. M.; Passhier, S.; van de Flierdt, T.; Tauxe, L.; Brinkhuis, H.

    2012-04-01

    One of the aims of IODP Expedition 318 drilling on the East Antarctic Wilkes Land margin was to obtain the record of Antarctic climate and cryosphere variability during the past warm climates of the early-middle Pliocene. A complete Pliocene section was recovered from Site U1361, located on the continental rise eastern levee of the Jussieu Channel. We present the results from a continous high-resolution geochemical study (X-Ray Fluorescence (XRF) scanner and discrete XRF analysis) conducted on sediments from Site U1361. These records are compared with shipboard physical properties data measured on the core, clay mineralogy analyses and with a post-cruise revised sedimentary facies model. Age constrains for the studied sediments are provided by the age-depth model constructed shipboard and refined post-cruise, which indicated the studies sediments to be comprised between 5.18 and 2.46 Ma. The downcore variations of these multiple proxies is interpreted to result from changes in primary biogenic productivity, terrigenous supply, and sedimentary processes that allow us to reconstruct changes in paleoceanographic and paleoenvironmental conditions associated with glacial-interglacial cyclicity. In this sense it is remarkable the Ba/Al and Ca variations, associated to the diatomaceous-rich silty-clay facies, suggesting high-productivity during interglacial periods at our site. In addition to the glacial/interglacial cyclic variability, we also discuss a marked change in the compositional and physical properties variability patterns within the section that we interpret to correspond with the start of the Pliocene cooling trend in this margin. This contribution results from work funded by: the Integrated Ocean Drilling Program, CTM2009-08467-E (Spanish Ministry of Science and Education and FEDER funds); and the Spanish Ministry of Science and Innovation project CAGES (CTM2011-24079).

  1. Interglacial analogues of the Holocene and its natural near future

    NASA Astrophysics Data System (ADS)

    Yin, Qiuzhen; Berger, André

    2015-07-01

    In an attempt to find potential interglacial analogues of our present interglacial and its natural future, five interglacials (MIS-1, 5, 9, 11 and 19) are studied in terms of their astronomical characteristics, greenhouse gases concentration and climate simulated using both snapshot and transient experiments. Transient simulations covering a full range of obliquity, precession and eccentricity allow to develop an OPE index to estimate the climate sensitivity to astronomical forcing. They also show that obliquity and precession have different weight on the annual mean temperature and precipitation of different latitudinal zones, leading to varying phasing of these climate variables between different latitudes. However, the variations in boreal summer temperature of different latitudes (except the Southern Ocean) are in phase and are dominated by precession. All the interglacials are shown to be warmer than the natural climate of the present day and of the next centuries during boreal summer and for the annual mean temperature with varying duration and intensity. Such warming is mainly caused by changes in insolation, unlike the present global warming which mainly results from anthropogenic CO2 increase. The exceptionally long duration of MIS-11 is confirmed by our simulations, and it is demonstrated to be related to the long-lasting low eccentricity and high CO2 concentration and to the anti-phase relationship between obliquity maximum and precession minimum during MIS-11. As far as the variations of annual and seasonal temperatures are concerned, both snapshot and transient simulations show that MIS-19 is the best analogue of the present interglacial. MIS-11 is also a decent analogue when the impact of insolation alone is considered, but it is warmer than MIS-1 when the impact of CO2 is additionally included. Due to the large amplitude in the variations of insolation, MIS-5 and MIS-9 can hardly be considered as an analogue of the natural present-day climate and of

  2. 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)

  3. 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.

  4. 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.

  5. Conditional knockout of polarity complex (atypical) PKCι reveals an anti-inflammatory function mediated by NF-κB

    PubMed Central

    Forteza, Radia; Figueroa, Yolanda; Mashukova, Anastasia; Dulam, Vipin; Salas, Pedro J.

    2016-01-01

    The conserved proteins of the polarity complex made up of atypical PKC (aPKC, isoforms ι and ζ), Par6, and Par3 determine asymmetry in several cell types, from Caenorhabditis elegans oocytes to vertebrate epithelia and neurons. We previously showed that aPKC is down-regulated in intestinal epithelia under inflammatory stimulation. Further, expression of constitutively active PKCι decreases NF-κB activity in an epithelial cell line, the opposite of the effect reported in other cells. Here we tested the hypothesis that aPKC has a dual function in epithelia, inhibiting the NF-κB pathway in addition to having a role in apicobasal polarity. We achieved full aPKC down-regulation in small intestine villi and colon surface epithelium using a conditional epithelium-specific knockout mouse. The results show that aPKC is dispensable for polarity after cell differentiation, except for known targets, including ROCK and ezrin, claudin-4 expression, and barrier permeability. The aPKC defect resulted in increased NF-κB activity, which could be rescued by IKK and ROCK inhibitors. It also increased expression of proinflammatory cytokines. In contrast, expression of anti-inflammatory IL-10 decreased. We conclude that epithelial aPKC acts upstream of multiple mechanisms that participate in the inflammatory response in the intestine, including, but not restricted to, NF-κB. PMID:27226486

  6. A cross-polarization based rotating-frame separated-local-field NMR experiment under ultrafast MAS conditions.

    PubMed

    Zhang, Rongchun; Damron, Joshua; Vosegaard, Thomas; Ramamoorthy, Ayyalusamy

    2015-01-01

    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 advances 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 (1)H-(13)C dipolar coupling/chemical shift correlation experiment using (13)C 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 (13)C-labeled L-isoleucine. Our results show that the performance of the CPVC sequence and subsequent determination of (1)H-(13)C dipolar couplings are insensitive to (1)H/(13)C 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 (1)H detected avenues for ultrafast MAS.

  7. 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

  8. 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.

  9. Changes in ocean denitrification during Late Carboniferous glacial-interglacial cycles

    NASA Astrophysics Data System (ADS)

    Algeo, Thomas; Rowe, Harry; Hower, James C.; Schwark, Lorenz; Herrmann, Achim; Heckel, Phil

    2008-10-01

    Denitrification (the process by which nitrate and nitrite are reduced to nitrogen gas) in the oxygen-minimum zones of modern oceans is an important part of the global nitrogen cycle. Variations in rates of denitrification over Quaternary glacial-interglacial timescales may have affected global climate. Evidence of denitrification has been reported from some older marine systems, but it is unclear whether denitrification rates varied during pre-Quaternary glacial cycles. Here we present ratios of organic carbon to nitrogen and nitrogen isotope data from the Upper Carboniferous black shales of the North American mid-continent. In these cyclic deposits, we find evidence of variations in the intensity of denitrification in the eastern tropical Panthalassic Ocean associated with glacially driven sea-level changes. Sedimentary δ15N increases during the interval of rapid sea-level rise in each cycle, indicative of intensified denitrification, before returning to background levels as sea level stabilized during the interglacial phase. Nearly identical patterns of denitrification have been observed in the eastern tropical Pacific during the Quaternary period. We therefore conclude that ice ages have produced similar oceanographic conditions and nitrogen cycle dynamics in these regions over the past 300million years.

  10. Enhanced Southern Westerly Activity During the Last Glacial Interglacial Transition in SW Patagonia

    NASA Astrophysics Data System (ADS)

    Moreno, P. I.; Villa-Martinez, R. P.; Cardenas, M. L.; Moy, C. M.

    2008-12-01

    Much of the ongoing controversy regarding synchrony or bipolar asynchrony has centered on the timing and structure of temperature changes during the Last Glacial Interglacial Transition (LGIT) in the southern mid- latitudes, in particular the Patagonian region (40°-56°S) of South America. South America is the only continuous continental landmass in the Southern Hemisphere that intersects the entire westerly wind belt and lies in the critical climatic interface between mid- to high latitudes. The region between 50°- 55°S is of particular interest considering its proximity to the polar front and the southern margin of the westerly winds, and the possibility of monitoring paleoclimate changes at or near this important oceanic- atmospheric boundary. Present and past climate studies, including modeling simulations, have emphasized that interactions between changes in the Antarctic Circumpolar Current, the southern westerly winds, sea ice, and the polar front are important drivers for deep ocean circulation changes, variations in atmospheric CO2, and equator-to-pole temperature and pressure gradients. Yet, the behavior of the westerly winds and the adjacent Southern Ocean during the LGIT is still poorly understood despite their fundamental influence on modern hemispheric and global climate. In this study we compare sediment cores from small closed-basin lakes and a bog from the Ultima Esperanza area of SW Patagonia (52°S), an area affected solely by the southern westerlies. Lake sediment cores from three lakes show lacustrine sedimentation over the last 17,000 years. In contrast, the Dumestre bog shows subaerial peat deposition since 15 ka interrupted by a prominent lacustrine phase dated between 14.5-11.5 ka. During this interval palynological records indicate the preponderance of cold-resistant herbs, along with aquatic taxa, followed by a rapid expansion of Nothofagus woodlands/forests, a lake regressive phase in Dumestre, and disappearance of laminated calcite

  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. 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.

  13. 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.

  14. Enhanced diagnostic of skin conditions by polarized laser speckles: phantom studies and computer modeling

    NASA Astrophysics Data System (ADS)

    Tchvialeva, Lioudmila; Lee, Tim K.; Markhvida, Igor; Zeng, Haishan; Doronin, Alexander; Meglinski, Igor

    2014-03-01

    The incidence of the skin melanoma, the most commonly fatal form of skin cancer, is increasing faster than any other potentially preventable cancer. Clinical practice is currently hampered by the lack of the ability to rapidly screen the functional and morphological properties of tissues. In our previous study we show that the quantification of scattered laser light polarization provides a useful metrics for diagnostics of the malignant melanoma. In this study we exploit whether the image speckle could improve skin cancer diagnostic in comparison with the previously used free-space speckle. The study includes skin phantom measurements and computer modeling. To characterize the depolarization of light we measure the spatial distribution of speckle patterns and analyse their depolarization ratio taken into account radial symmetry. We examine the dependences of depolarization ratio vs. roughness for phantoms which optical properties are of the order of skin lesions. We demonstrate that the variation in bulk optical properties initiates the assessable changes in the depolarization ratio. We show that image speckle differentiates phantoms significantly better than free-space speckle. The results of experimental measurements are compared with the results of Monte Carlo simulation.

  15. 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.

  16. 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.

  17. Mitochondrial DNA analysis and numerical chromosome condition in human oocytes and polar bodies.

    PubMed

    Gianaroli, Luca; Luiselli, Donata; Crivello, Anna Maria; Lang, Martin; Ferraretti, Anna Pia; De Fanti, Sara; Magli, M Cristina; Romeo, Giovanni

    2015-01-01

    To investigate the mitochondrial DNA (mtDNA) segregation in human oocytes, the level of heteroplasmy in the three products of meioses, polar bodies (PBs) and corresponding oocytes, was assessed by studying the hypervariable region I (HVRI) of the D-loop region. The DNA from 122 PBs and 51 oocytes from 16 patients was amplified by whole genome amplification (WGA). An aliquot of the WGA product was used to assess aneuploidy, and another aliquot to study mtDNA. The HVRI was amplified and sequenced with an efficiency of 75.4 and 63%, respectively, in PBs, and of 100% in oocytes. The comparison with the mtDNA sequences from blood of the individual donors showed full correspondence of polymorphisms with the matching oocytes, whilst in PBs the degree of concordance dropped to 89.6%. Haplogroups were inferred for all 16 patients. Of the 89 diagnosed PBs from the 13 patients belonging to macrohaplogroup R, 23 were euploid and 66 aneuploid. The incidence of total anomalies was significantly lower in haplogroup H (6.5%) when compared with haplogroups J and T (17.6 and 13.4% respectively; P < 0.001). In haplogroup J, hypoaneuploidy occurred more frequently than hyperaneuploidy. In the three patients belonging to haplogroup N*, 81% of PBs were aneuploid with similar rates of chromosome hypoaneuploidy and hyperaneuploidy. The presence of mtDNA base changes confined to PBs could reflect a selection mechanism against severe mtDNA mutations, while permitting a high evolution rate that could result in bioenergetic diversity. The different susceptibility to aneuploidy by some haplogroups strongly supports this hypothesis. PMID:25301778

  18. 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

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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

  5. 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

  6. 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.

  7. 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

  8. Ice Core Measurements and GCM Simulation of the Spatial Distribution and Glacial-Interglacial Change of 17O-excess in Antarctica

    NASA Astrophysics Data System (ADS)

    Schoenemann, S.; Ding, Q.; Steig, E.; Schauer, A.

    2012-04-01

    Stable isotope ratios of water in polar precipitation, as measured in ice cores, have been fundamental to the quantification of past climate variability and change. Recent development of techniques to measure the 17O/16O ratio precisely has allowed 17Oexcess to be added to the ice-core isotope toolbox. The combination of δ17O with the conventional measurements of δ18O and δD - giving the parameter 17Oexcess - provides valuable new information on the evaporative conditions of the oceanic moisture sources for Antarctic precipitation. We measured δ17O and δ18O from a number of Antarctic ice cores (West Antarctic Ice Sheet Divide, Siple Dome, Taylor Dome), and determined 17Oexcesson modern, Holocene, and glacial timescales. These results, combined with the work of Landais et al. [2008] and Winkler et al. [2011] at Talos Dome, Dome C, and Vostok, provide the most complete spatial and temporal view of Antarctic 17Oexcess to date. We have added 17Oexcess to the independent isotope modules of two atmospheric general circulation models (CCSM CAM3 and ECHAM4.6). Both models are capable of qualitatively reproducing the observed spatial distribution of modern 17Oexcess in Antarctic precipitation, although our current implementation of CAM3 currently overestimates the average value of 17Oexcess. Simulation of glacial-interglacial changes in ECHAM4.6 also realistically captures the differences in magnitude of the glacial/interglacial changes in 17Oexcess between different ice core sites, with the details dependent on the magnitude of sea ice changes and to a lesser degree the chosen supersaturation parameter. Both models show strong gradients in 17Oexcess at the ocean-sea ice boundary, associated with the strong gradient in near surface water vapor concentration (i.e., the normalized relative humidity). Our results suggest that the low 17Oexcess values found at Talos Dome and Siple Dome reflect their proximity to local moisture sources (e.g. from sea ice leads and polynyas

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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

  15. 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

  16. 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

  17. Coupled ice sheet-climate interactions during the Last Interglacial simulated with LOVECLIM

    NASA Astrophysics Data System (ADS)

    Goelzer, H.; Huybrechts, P.; Loutre, M.; Fichefet, T.

    2013-12-01

    The Last Interglacial warm period (LIG, ~130 to 115 kyr BP) represents a real-world test case for the stability of the Greenland and Antarctic ice sheets, both thought to have lost considerable amounts of ice compared to their present-day configuration. We use the Earth system model of intermediate complexity LOVECLIM version 1.3 to perform transient simulations over the LIG forced with changes in orbital parameters and greenhouse gases. The model includes thermomechanically coupled models of the Greenland and Antarctic ice sheets, which are interactively coupled with the atmosphere and ocean components. We present modeling results with focus on the evolution of the polar ice sheets and their sea-level contribution, ice-climate interactions and inter-hemispheric coupling. LOVECLIM simulates annual mean temperature and summer temperature anomalies over central Greenland relative to the present day that peak at 5.5 °C and 10.7 °C, respectively. The Greenland ice sheet sea-level contribution peaks at between 1.0 and 2.6 m mainly caused by increased summer temperatures. While changes in surface melting have a negligible effect for the evolution of the Antarctic ice sheet during the LIG, a peak sea-level contribution of 2.1 m is governed by West Antarctic grounding-line retreat. For both ice sheets interactive ice-climate coupling is crucial to produce a temperature evolution over the ice sheets better in line with ice core records.

  18. A last interglacial fauna from the Eastern Sahara

    NASA Astrophysics Data System (ADS)

    Kowalski, Kazimierz; Neer, Wim van; Bocheński, Zygmunt; Młynarski, Marian; Rzebik-Kowalska, Barbara; Szyndlar, Zbigniew; Gautier, Achilles; Schild, Romuald; Close, Angela E.; Wendorf, Fred

    1989-11-01

    Recent work on the middle Paleolithic at Bir Tarfawi, in the hyperarid Eastern Sahara (<1 mm of rain per annum), has yielded a rich faunal assemblage, including several thousand remains of fish, amphibians, reptiles, birds, and small mammals. They are derived from the sediments of two consecutive lakes dated by several techniques to about 135,000 yr B.P. Fifty-nine taxa have been identified and indicate that at times during the Last Interglaciation the area received at least 500 mm of rainfall as a result of the northward shift of the monsoon belt, and that, on several occasions, there may have been water connections between Bir Tarfawi and unidentified but permanent bodies of water elsewhere.

  19. 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

  20. 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

  1. 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

  2. Project CELIA: Climate and environment of the last interglacial (Isotope Stage 5) in arctic and subarctic North America

    SciTech Connect

    Brigham-Grette, J.

    1992-03-01

    Stage 5e of the marine oxygen isotope record is the last time when world ice volume was lower, sea level was higher, and world climate warmer than during any part of the Holocene. To develop more accurate proxy data for natural climate change during the last interglacial, a multidisciplinary group of scientists working as regional teams has developed Project CELIA to generate and synthesize knowledge for this period from high latitude terrestrial and nearshore marine environments. The authors have cited 13 terrestrial sequences distributed across the Arctic and Subarctic for detailed study based upon well-exposed stratigraphy, abundance of organic remains, and geochronological potential. In addition, information from select marine cores bearing terrestrial pollen and ice cores from Devon and Agassiz Ice Caps will also be incorporated. These data will highlight regional changes in vegetation patterns, tree line position, permafrost distribution, and sea ice conditions from which ocean/atmospheric changes can be inferred. This information will be of value for testing hypotheses generated by GCMs and other simulations of interglacial conditions, refining such models and providing insight to future environments resulting from global warming. CELIA will be carried out over the next 5 years and will be directed by an international board of experts under the auspices of the University of Alberta's Canadian Circumpolar Institute.

  3. 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.

  4. 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).

  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. 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

  7. 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

  8. 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.

  9. Identification of last interglacial deposits in eastern Beringia: a cautionary note from the Palisades, interior Alaska

    USGS Publications Warehouse

    Reyes, Alberto V.; Zazula, Grant D.; Kuzmina, Svetlana; Ager, Thomas A.; Froese, Duane G.

    2011-01-01

    Last interglacial sediments in unglaciated Alaska and Yukon (eastern Beringia) are commonly identified by palaeoecological indicators and stratigraphic position ~2-5m above the regionally prominent Old Crow tephra (124 + or - 10ka). We demonstrate that this approach can yield erroneous age assignments using data from a new exposure at the Palisades, a site in interior Alaska with numerous exposures of last interglacial sediments. Tephrochronology, stratigraphy, plant macrofossils, pollen and fossil insects from a prominent wood-rich organic silt unit are all consistent with a last interglacial age assignment. However, six 14C dates on plant and insect macrofossils from the organic silt range from non-finite to 4.0 14C ka BP, indicating that the organic silt instead represents a Holocene deposit with a mixed-age assemblage of organic material. In contrast, wood samples from presumed last interglacial organic-rich sediments elsewhere at the Palisades, in a similar stratigraphic position with respect to Old Crow tephra, yield non-finite 14C ages. Given that local permafrost thaw since the last interglaciation may facilitate reworking of older sediments into new stratigraphic positions, minimum constraining ages based on 14C dating or other methods should supplement age assignments for last interglacial sediments in eastern Beringia that are based on palaeoecology and stratigraphic association with Old Crow tephra.

  10. 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.

  11. 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

  12. 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

  13. 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.

  14. Seasonality in the Arabian Sea over glacial-interglacial cycles

    NASA Astrophysics Data System (ADS)

    de Nooijer, L. J.; Tjallingii, R.; Brummer, G. J.; Reichart, G. J.

    2012-04-01

    The Indian monsoon system controls seasonal precipitation alterations over the Indian continent and upwelling of nutrient-rich waters to the surface in the northern Arabian Sea. Functioning and strength of this weather system due to climate change is one of the important issues in predicting the effects of global warming on the region's economy, agriculture and social welfare. The strength of the Indian monsoon system through time can be studied by changes in seawater temperature and chemistry from single-specimen analysis of planktic foraminiferal calcite. Temperature reconstructions based on many single specimens allow reconstruction of past seasonal sea water temperatures ranges and thus seasonal temperature variability. . Here we present seawater reconstructions based on single-specimen Mg/Ca of the surface dweller Globigerinoides ruber and the deeper-living G. dutertrei of two sediment cores of the western equatorial Indian Ocean off Tanzania and the northern Arabian Sea. From both cores, specimens are analyzed for calcitic Mg/Ca using laser ablation-ICP-MS of time-intervals representing the Holocene optimum, Last Glacial Maximum, Marine Isotope Stage 4, MIS 5 and MIS6. The resulting temperature ranges allow reconstruction of variability in the strength of the Indian Monsoon as well as cross-equatorial heat transport during glacials and interglacials.

  15. Involvement of Protein Kinase C in the Suppression of Apoptosis and in Polarity Establishment in Aspergillus nidulans under Conditions of Heat Stress

    PubMed Central

    Katayama, Takuya; Uchida, Hirotaka; Ohta, Akinori; Horiuchi, Hiroyuki

    2012-01-01

    The pkcA gene, which encodes a protein kinase C (PKC) in the filamentous fungus Aspergillus nidulans, is essential for its viability. However, little is known about its functions. To address this issue, we constructed and characterized temperature-sensitive mutants of pkcA. The conidia of these mutants swelled slightly and exhibited apoptotic phenotypes at 42°C. The apoptotic phenotypes were suppressed by an osmotic stabilizer. Under these conditions, the conidia swelled extensively and did not form germ tubes. Moreover, polarized distribution of F-actin was not observed. We then utilized deletion mutants of bckA, an ortholog of Saccharomyces cerevisiae bck1 that encodes a mitogen-activated protein (MAP) kinase kinase kinase and functions downstream of PKC in the cell wall integrity pathway. These mutants exhibited apoptotic phenotypes at 42°C, but they did not show defects in polarity establishment under osmotically stabilized conditions. These results suggest that PkcA plays multiple roles during germination under conditions of heat stress. The first of these roles is the suppression of apoptosis induction, while the other involves polarity establishment. The former depends on the MAP kinase cascade, whereas the latter does not. In addition, repolarization, which was observed after depolarization in the wild-type strain and the bckA deletion mutant under conditions of heat stress, was not observed in the pkcA-ts mutant. This suggests that PkcA also plays role in polarity establishment during hyphal growth independent of the MAP kinase cascade under these conditions. PMID:23209763

  16. 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

  17. 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

  18. 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

  19. Greenland during the last interglacial: the relative importance of insolation and oceanic changes

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

    Insolation changes during the Eemian (the last interglacial period, 129 000-116 000 years before present) resulted in warmer than present conditions in the Arctic region. The NEEM ice core record suggests warming of 8 ± 4 K in northwestern Greenland based on stable water isotopes. Here we use general circulation model experiments to investigate the causes of the Eemian warming in Greenland. Simulations of the atmospheric response to combinations of Eemian insolation and preindustrial oceanic conditions and vice versa are used to disentangle the impacts of the insolation change and the related changes in sea surface temperatures and sea ice conditions. The changed oceanic conditions cause warming throughout the year, prolonging the impact of the summertime insolation increase. Consequently, the oceanic conditions cause an annual mean warming of 2 K at the NEEM site, whereas the insolation alone causes an insignificant change. Taking the precipitation changes into account, however, the insolation and oceanic changes cause more comparable increases in the precipitation-weighted temperature, implying that both contributions are important for the ice core record at the NEEM site. The simulated Eemian precipitation-weighted warming of 2.4 K at the NEEM site is low compared to the ice core reconstruction, partially due to missing feedbacks related to ice sheet changes and an extensive sea ice cover. Surface mass balance calculations with an energy balance model further indicate that the combination of temperature and precipitation anomalies leads to potential mass loss in the north and southwestern parts of the ice sheet. The oceanic conditions favor increased accumulation in the southeast, while the insolation appears to be the dominant cause of the expected ice sheet reduction. Consequently, the Eemian is not a suitable analogue for future ice sheet changes.

  20. Research of beam conditioning technologies using continuous phase plate, Multi-FM smoothing by spectral dispersion and polarization smoothing

    NASA Astrophysics Data System (ADS)

    Zhang, Rui; Jia, Huaiting; Tian, Xiaocheng; Yuan, Haoyu; Zhu, Na; Su, Jingqin; Hu, Dongxia; Zhu, Qihua; Zheng, Wanguo

    2016-10-01

    In the research of inertial confinement fusion, laser plasma interaction (LPI) is becoming a key problem that affects ignition. Here, multi-frequency modulation (Multi-FM) smoothing by spectral dispersion (SSD), continuous phase plate (CPP) and polarization smoothing (PS) were experimentally studied and implemented on the SG-III laser facility. After using these techniques, the far field distribution of SG-Ⅲ laser facility can be adjusted, controlled and repeated accurately. The output spectrums of the cascade phase modulators used for Multi-FM SSD were stable and the FM-to-AM effect can be restrained. Experiments on SG-III laser facility indicate that when the number of color cycles adopts 1, imposing SSD with 3.3 times diffraction limit (TDL) did not lead to pinhole closure in the spatial filters of preamplifier and main amplifiers with 30-TDL pinhole size. The nonuniformity of the focal spots using Multi-FM SSD, CPP and PS drops to 0.18, comparing to 0.26 with CPP+SSD, 0.57 with CPP+PS and 0.84 with only CPP and wedged lens. Polarization smoothing using flat birefringent plate in the convergent beam of final optics assembly (FOA) was studied. The PS plates were manufactured and equipped on SG-III laser facility for LPI research. Combined beam smoothing and polarization manipulation were also studied to solve the LPI problem. Results indicate that through adjusting dispersion directions of SSD beams in a quad, two dimensional SSD can be obtained. Using polarization control plate (PCP), polarization on the near field and far field can be manipulated, providing new method to solve LPI problem in indirect drive laser fusion.

  1. Growth and development, and auxin polar transport in higher plants under microgravity conditions in space: BRIC-AUX on STS-95 space experiment.

    PubMed

    Ueda, J; Miyamoto, K; Yuda, T; Hoshino, T; Fujii, S; Mukai, C; Kamigaichi, S; Aizawa, S; Yoshizaki, I; Shimazu, T; Fukui, K

    1999-12-01

    The principal objectives of the space experiment, BRIC-AUX on STS 95, were the integrated analysis of the growth and development of etiolated pea and maize seedlings in space and a study of the effects of microgravity conditions in space on auxin polar transport in these segments. Microgravity significantly affected the growth and development of etiolated pea and maize seedlings. Epicotyls of etiolated pea seedlings were the most oriented toward about 40 to 60 degrees from the vertical. Mesocotyls of etiolated maize seedlings were curved at random during space flight but coleoptiles were almost straight. Finally the growth inhibition of these seedlings in space was also observed. Roots of some pea seedlings grew toward to the aerial space of Plant Growth Chamber. Extensibilities of cell walls of the third internode of etiolated pea epicotyls and the top region of etiolated maize coleoptiles, which were germinated and grown under microgravity conditions in space, were significantly low as compared with those grown on the ground of the earth. Activities of auxin polar transport in the second internode segments of etiolated pea seedlings and coleoptile segments of etiolated maize seedlings were significantly inhibited and promoted, respectively, under microgravity conditions in space. These results strongly suggest that auxin polar transport as well as the growth and development of plants is controlled under gravity on the earth.

  2. 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.

  3. 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.

  4. Riparian landscapes and human habitat preferences during the Hoxnian (MIS 11) Interglacial

    NASA Astrophysics Data System (ADS)

    Ashton, Nick; Lewis, Simon G.; Parfitt, Simon; White, Mark

    2006-07-01

    The archaeological, environmental and geological data from Hoxnian Interglacial (Marine Isotope Stage (MIS) 11) sites from Britain are examined to elucidate the type of habitats that humans preferred during this temperate episode. The conclusion is that humans avoided lacustrine situations, but did make use of the full range of resources that fluvial environments provide. This model is strengthened by the examination of other non-archaeological Hoxnian sites. The problem of archaeological visibility in lacustrine sediment sequences is also discussed and methods of identifying other evidence of human presence are suggested that may offset the deficiencies in the lithic record. These include presence of cut-marked bone, micro-debitage and possibly charcoal in fine-grained sediments deposited in distal settings. The reasons for human selection of fluvial situations are discussed. It is concluded that these environments provide a greater diversity of animal, plant and lithic resources, but also are major route-ways through the landscape. Patterns of human site use are identified, which seem to be triggered by local changes in hydrology and drainage, themselves possibly caused by regional changes in climate. Finally, Lower Palaeolithic sites on the interfluves are discussed. Although they lack environmental or dating evidence, it is tentatively suggested that they were used during cooler episodes, when more open conditions prevailed. Copyright

  5. 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

  6. 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

  7. Late Quaternary Variations of Atmospheric Nitrous Oxide Reconstructed from Polar Ice Cores

    NASA Astrophysics Data System (ADS)

    Schilt, A.; Baumgartner, M.; Blunier, T.; Schwander, J.; Spahni, R.; Fischer, H.; Stocker, T. F.

    2009-12-01

    Air extracted from polar ice cores offers the unique possibility to reconstruct the past composition of Earth’s atmosphere, and thus to study natural changes in biogeochemical cycles. Here, we present records of the greenhouse gas nitrous oxide (N2O) measured along the EPICA Dome C, EPICA Dronning Maud Land, Talos Dome and NGRIP ice cores. These records allow for the reconstruction of the N2O concentration during the interglacials of the last 800,000 years, while for most glacial time intervals an atmospheric record is missing due to insitu production of N2O in the ice. N2O which has both terrestrial and marine sources, varies in concert with Antarctic temperature during all interglacials back to Marine Isotope Stage 19. However, in contrast to carbon dioxide (CO2) and methane (CH4), N2O does not show lower concentrations in response to the lower temperature recorded for the interglacials between 800,000 and 440,000 years before present compared to the interglacials of the last 440,000 years. Also, N2O remains substantially longer at interglacial levels than CH4 at the end of most interglacials. On millennial time scales, N2O shows variations in concert with CH4 throughout the last 800,000 years. We suggest that these millennial-scale variations have been driven by a similar mechanism as the Dansgaard/Oeschger events known from the last glacial. We further establish a N2O composite record which covers, without gaps, more than one glacial-interglacial cycle, i.e. it reaches back to the beginning of the penultimate interglacial (Marine Isotope Stage 5.5) about 140,000 years ago. This composite record reveals substantial N2O variations in response to all Dansgaard/Oeschger events of the last glacial, and a N2O concentration of about 200 parts per billion by volume during the Last Glacial Maximum.

  8. Multilocus phylogeography of the European ground squirrel: cryptic interglacial refugia of continental climate in Europe.

    PubMed

    Říčanová, Štěpánka; Koshev, Yordan; Říčan, Oldřich; Ćosić, Nada; Ćirović, Duško; Sedláček, František; Bryja, Josef

    2013-08-01

    The theory of classical and cryptic Pleistocene refugia is based mainly on historical changes in temperature, and the refugia are usually defined within a latitudinal gradient. However, the gradient of oceanic-continental climate (i.e. longitudinal) was also significantly variable during glacial cycles with important biotic consequences. Range-wide phylogeography of the European ground squirrel (EGS) was used to interpret the evolutionary and palaeogeographical history of the species in Europe and to shed light on its glacial-interglacial dynamic. The EGS is a steppe-inhabiting species and the westernmost member of the genus in the Palaearctic region. We have analysed 915 specimens throughout the present natural range by employing mitochondrial DNA sequences (cytochrome b gene) and 12 nuclear microsatellite markers. The reconstructed phylogeography divides the species into two main geographical groups, with deep substructuring within both groups. Bulgaria is the centre of the ancestral area, and it also has the highest genetic diversity within the species. The northernmost group of the EGS survived in the southern part of Pannonia throughout several glacial-interglacial cycles. Animals from this population probably repeatedly colonized areas further to the north and west during the glacial periods, while in the interglacial periods, the EGS distribution contracted back to this Pannonian refugium. The EGS thus represents a species with a glacial expansion/interglacial contraction palaeogeographical dynamics, and the Pannonian and southeastern Balkanian steppes are supported as cryptic refugia of continental climate during Pleistocene interglacials.

  9. A terrestrial record from Iles Kerguelen: Reconstructing climate history in the sub-Antarctic Indian Ocean during the last glacial-interglacial transition

    NASA Astrophysics Data System (ADS)

    Van der Putten, Nathalie; Verbruggen, Cyriel; Björck, Svante; Michel, Elisabeth; Disnar, Jean-Robert; Chapron, Emmanuel; de Beaulieu, Jacques-Louis

    2014-05-01

    The Southern Ocean is characterised by (i) the Antarctic Circumpolar Current (ACC), flowing from west to east around the Antarctic continent and connecting the Atlantic, Indian and Pacific Ocean basins and (ii) several oceanic fronts such as the Polar Front (PF). Storm tracks, often with high wind speeds, prevail at these latitudes as they are strongly influenced by the Southern Hemisphere Westerlies (SHW). Information on past climate change at the mid- and high southern latitudes (40°-70°S), especially from a terrestrial point of view, is still sparse in comparison with the same latitudes in the Northern Hemisphere. Fortunately, dispersed and remote islands and island groups occur in the Southern Ocean. Changes in zonal circulation - i.e. the strength and position of the SHW - result in significant imprints in this region and it is therefore imperative to map, in time and space, the strength and latitudinal shifts of this zonal circulation. Latitudinal shifts of the ACC and PF during periods of climate change must have influenced climate conditions on, at least, some of these islands, offering the possibility to reconstruct changes of the oceanic frontal systems in the Southern Ocean. Here we present preliminary results from a chronologically well constrained terrestrial record sampled on Iles Kerguelen (49°S - 69°E, South Indian Ocean), situated in the core of the SHW and at the PF. We focus on the last glacial-interglacial transition, a period characterised by a return to cold conditions, after an initial post-LGM warming. The Estacade sequence presented here is analysed with multi-proxy approach (peat stratigraphy, pollen, plant macrofossils, magnetic susceptibility, biogenic silica and Rock Eval). The onset of peat growth at the Estacade site c. 16.3 kyr BP coincides with the post-LGM warming in Antarctica, which already started 18 kyr BP (EPICA Dome C ice core). At c. 14 kyr BP, so c.500 years later as the onset of the ACR, a sudden change to more humid

  10. Sub-seasonally resolved coral records of northern Red Sea - eastern Mediterranean climate during the Holocene and the last interglacial

    NASA Astrophysics Data System (ADS)

    Felis, T.; Rimbu, N.; Al-Rousan, S.; Kuhnert, H.; Lohmann, G.; Kölling, M.; Pätzold, J.

    2012-04-01

    The northern Red Sea represents a unique location where ocean currents transport warm tropical waters northward, enabling coral reef growth at unusually high latitudes of up to 29 °N. Moreover, one of the world's northernmost complexes of uplifted Pleistocene reef terraces can be found here at Aqaba (Jordan). We present sub-seasonally resolved reconstructions of surface ocean conditions in the northern Red Sea derived from annually banded Porites corals. The Sr/Ca and δ18O variations in the aragonitic skeletons of our modern and fossil coral colonies provide proxy records of temperature, salinity and hydrologic balance at the sea surface during the last centuries and during time windows (40 to 100 years length) of the Holocene and the last interglacial period. Previous work has shown that seasonality and interannual to decadal climate variability in the northern Red Sea as documented in our coral records is strongly coupled to climate variations in the eastern Mediterranean, Middle East and Europe, reflecting the prominent role of atmospheric teleconnections of the Arctic Oscillation (AO)/North Atlantic Oscillation (NAO) in controlling regional climate on these timescales. New coral Sr/Ca data, in combination with δ18O, reveal an abrupt regime shift toward fresher surface ocean conditions in northern Red Sea surface waters at the end of the Little Ice Age. Possible mechanisms include a re-organization of the Northern Hemisphere atmospheric circulation. Sr/Ca records from a large number of fossil corals indicate a trend of decreasing temperature seasonality over the last 6000 years toward present-day. Such a trend is expected in the higher latitudes of the Northern Hemisphere from insolation changes on orbital timescales. Coral δ18O and Sr/Ca records suggest an increased seasonality in the hydrologic balance during time intervals around 4400, 4600 and 6000 years ago, which could result from both enhanced winter evaporation or increased summer precipitation

  11. 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

  12. 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.

  13. 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

  14. 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.

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

    USGS Publications Warehouse

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

    1994-01-01

    Thorium-230 ages of emergent marine deposits on Oahu, Hawaii, have a uniform distribution of ages from ~114,000 to ~131,000 years, indicating a duration for the last interglacial sea-level high stand of ~17,000 years, in contrast to a duration of ~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 ~6000 years earlier than inferred from the marine record. Although the latter record suggests a shift back to glacial conditions beginning at ~119,000 years ago, the Oahu coral ages indicate a near present sea level until ~114,000 years ago.

  16. 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.

  17. Permafrost response to last interglacial warming: field evidence from non-glaciated Yukon and Alaska

    NASA Astrophysics Data System (ADS)

    Reyes, Alberto V.; Froese, Duane G.; Jensen, Britta J. L.

    2010-11-01

    We present stratigraphic observations from three sites in eastern Beringia - Ch'ijee's Bluff in northern Yukon and nearby exposures on the Old Crow River, the Palisades on the Yukon River in Alaska, and placer mining exposures at Thistle Creek in west-central Yukon - which provide insight into the response of permafrost to regional warming during the last interglaciation. Chronology is based on the presence of Old Crow tephra, an important regional stratigraphic marker that dates to late Marine Isotope Stage 6, supplemented by paleoecology and non-finite 14C ages on wood-rich organic silts. Old Crow tephra overlies several relict ice wedges at the Palisades and Thistle Creek, indicating that permafrost at these sites did not thaw completely during the last interglaciation. Prominent deposits of last interglacial wood-rich organic silt are present at multiple sites in eastern Beringia, and probably represent accumulations of reworked forest vegetation due to thaw slumping or deposition into thermokarst ponds or depressions. Consistent stratigraphic relations between these deposits, Old Crow tephra, and ice wedge pseudomorphs at our three study sites, and at least six other sites in eastern Beringia, suggest that thaw of shallow permafrost was widespread during the last interglaciation. Limited stratigraphic evidence suggests that thaw was probably on the order of meters, rather than 10s of meters. The ubiquity of shallow permafrost degradation during the last interglaciation suggests that current ground warming may foreshadow widespread near-surface thaw under even modest future warming scenarios. However, the persistence of relict pre-last interglacial ice wedges highlights the potential for the regional antiquity of discontinuous permafrost, and provides compelling field evidence for the long-term resilience of deep permafrost during sustained periods of warmer-than-present climate.

  18. 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

  19. 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

  20. 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.

  1. Total synthesis of cephalosporolide E via a tandem radical/polar crossover reaction. The use of the radical cations under nonoxidative conditions in total synthesis.

    PubMed

    Cortezano-Arellano, Omar; Quintero, Leticia; Sartillo-Piscil, Fernando

    2015-03-01

    The present work reports the first example of the use of the chemistry of radical cations under nonoxidative conditions in total synthesis. Using a late-stage tandem radical/polar crossover reaction, a highly stereoselective total synthesis of cephalosporolide E (which is typically obtained admixed with cephalosporolide F) was accomplished. The reaction of a phthalimido derivative with triphenyltin radical in refluxing toluene engenders a contact ion-pair (radical cation) that leads, in the first instance, to the cephalosporolide F, which is transformed into the cephalosporolide E via a stereocontrolled spiroketal isomerization promoted by the diphenylphosphate acid that is formed during the tandem transformation.

  2. 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.

  3. Nitrogen Cycling in the Black Sea on Glacial-Interglacial Time Scales

    NASA Astrophysics Data System (ADS)

    Quan, T. M.; Wright, J. D.; Falkowski, P. G.

    2010-12-01

    On geological time scales, the nitrogen cycle consists of three main processes: nitrogen fixation, nitrification, and denitrification/anammox, all of which are affected by the amount of oxygen present in the water column. The balance between nitrogen fixation and denitrification/anammox controls the pool of fixed inorganic nitrogen, and can be traced using nitrogen isotopes. We have previously proposed a conceptual model that relates sedimentary δ15N to deep water oxygen concentrations using a simple, non-linear curve. Provided that the sediment record is well-preserved, the nitrogen isotopic profile at a given location reflects history of the relative contributions of nitrogen fixation to denitrifiation and thus the past redox environment. Our goal was to test this model using deep sea sediments from the Black Sea, which alternates from an anoxic, stratified, marine water body during interglacial periods to a less saline, oxygenated lake during glacial events. We find that the measured δ15N profile in general corresponds to the changes in redox state as determined by trace metal concentrations and micropaleontology. Higher δ15N values occur during suboxic transitional periods, with lower δ15N values appearing under anoxic and oxic conditions, supporting our hypothesis that the nitrogen cycle is regulated by oxygen concentration. We also identify some intervals where the correlation between redox proxies appears to fail. While the lack of ancillary data from the paleo-Black Sea makes interpretation difficult, we believe analysis of these intervals may provide more information about Black Sea paleoenvironmental and paleoredox conditions.

  4. 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

  5. Apical-basal membrane polarity of membrane phosphatases in isolated capillary endothelium: alteration in ultrastructural localisation under culture conditions.

    PubMed Central

    Roberts, R L; Sandra, A

    1993-01-01

    Capillaries from freshly isolated rat epididymal fat were subjected to protocols that allowed ultrastructural localisation of alkaline phosphatase and 5'-nucleotidase. Alkaline phosphatase was almost entirely restricted to the capillary luminal membrane and vesicles associated with this membrane. 5'-nucleotidase was localised on the basal or abluminal membrane and associated vesicles. Arterioles and occasional venules were also present in the cell isolates, and arteriole localisation of 5'-nucleotidase was identical to that in capillaries. In venules, 5'-nucleotidase often failed to exhibit a polarised distribution and was present on both membrane domains. In confluent cultured endothelial cells, 5'-nucleotidase was not expressed in a predominantly polarised arrangement. Alkaline phosphatase was found on apical surfaces and regions of lateral cell contact. The results of these studies show that capillary endothelial cells exhibit enzyme polarity of their surface membranes which is subject to change on introduction of the cells to tissue culture. Images Fig. 1 Fig. 2 Fig. 3 Fig. 4 Fig. 5 PMID:8226289

  6. Changes on a glacial-interglacial timescale in the oceanic inventory of phosphorus and its relation to climate change

    NASA Astrophysics Data System (ADS)

    Tamburini, F.; Föllmi, K. B.

    2003-12-01

    Phosphorus (P) is an important nutrient, which, along with other macro- and micronutrients, limits productivity in oceans. On a glacial-interglacial timescale, potential variations in the oceanic inventory of P, which are invoked by changes in the continental weathering regime, may have an impact on global primary production, on CO2 drawdown from the atmosphere, and on climate. It is crucial, therefore, to constrain P inventory changes throughout glacial and interglacial periods. We present new data that illustrate how P is distributed in marine sediments and how its inventory changed during the last 150,000 years. We have applied the SEDEX techinique (Ruttenberg, 1992) on sediments from eight different Ocean Drilling Program (ODP) Sites (Northeastern Atlantic; Peru margin; Oman margin; Japan Sea; Ontong Java plateau; North Atlantic; South China Sea). Authigenic and Fe-bound minerals, and organic material represent the principal sinks of reactive P in oceanic sediments. Regardless of the environmental setting and type of sediment, P phases have been detected at all sites. Moreover, average reactive P concentrations are in the same range of values, between 0.3 and 0.6 mg/g. Only concentrations at the Oman and the Peru margin sites fall outside this interval, showing concentrations characteristic of phosphogenesis. Average concentrations calculated over glacial and interglacial periods do not show any significant difference. Changes in P distribution and concentrations in the sediments, and mass accumulation rates seem closely linked to local climatic and oceanographic conditions, but still reflect global processes (i.e., oceanic circulation and climate). On a global average, P accumulation rates in the sediments increased during the last glacial, suggesting a positive relationship between cold climate, increased physical weathering and P sink in the ocean sediments. Reactive P inventory variations seem paced by the precessional cycle (23 kyr), pointing at the

  7. The Role of the Eastern Equatorial Pacific in Carbon Sequestration and Ventilation over the Last Glacial-Interglacial Transition

    NASA Astrophysics Data System (ADS)

    Umling, N. E.; Thunell, R.

    2015-12-01

    The last glacial-interglacial transition is punctuated by brief periods of rapid return to glacial-like conditions followed by abrupt warmings. Ice core records reveal episodes of rapid increases in CO2 and synchronous decreases in Δ14C that co-occur with these abrupt warmings (Hughen et al., 2000; Fairbanks et al., 2005). As the largest mobile carbon reservoir, the deep oceans have been implicated as the most likely source of this 14C-deplete CO2. Records of benthic radiocarbon offsets from the atmosphere provide evidence of intermediate depth ventilation of a 14C-deplete reservoir during deglaciation. However, modeling studies focusing on ocean circulation changes alone are unable to replicate the full-observed glacial-interglacial CO2 change. Changes in the biological pump could provide an additional mechanism contributing to the glacial drawdown and deglacial release of CO2. The Eastern Equatorial Pacific (EEP) is currently responsible for ~10% of global ocean primary productivity and is strongly connected to the Southern Ocean (Pennington et al., 2006) making it ideally suited for studying past changes in the biological pump. This study uses a multi-proxy approach to investigate the role of carbonate compensation and export productivity over the last 26,000yrs. Intermediate to deep-water transects of B/Ca, Cd/Ca, and U/Ca for the benthic foraminifera Cibicidoides wuelerstorfi were developed from 7 EEP cores (1620-3200m water-depth) extending from 8.2°N to 2.3°S in the Panama Basin. The fraction of calcite dissolved was estimated for high-resolution core TR163-23 (2,730m; 0.41°N, 92.16°W) using the G. menardii fractionation index (MFI) (Mekik et al., 2002). A record of benthic foraminiferal radiocarbon offsets from the atmosphere was also developed for TR163-23 providing a larger picture of the relative role of both ventilation and the biological pump in changing atmospheric CO2 concentrations over the last glacial-interglacial transition.

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  12. 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.

  13. 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

  14. Hybrid polarity SAR architecture

    NASA Astrophysics Data System (ADS)

    Raney, R. Keith

    2009-05-01

    A space-based synthetic aperture radar (SAR) designed to provide quantitative information on a global scale implies severe requirements to maximize coverage and to sustain reliable operational calibration. These requirements are best served by the hybrid-polarity architecture, in which the radar transmits in circular polarization, and receives on two orthogonal linear polarizations, coherently, retaining their relative phase. This paper summarizes key attributes of hybrid-polarity dual- and quadrature-polarized SARs, reviews the associated advantages, formalizes conditions under which the signal-to-noise ratio is conserved, and describes the evolution of this architecture from first principles.

  15. 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.

  16. 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

  17. 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

  18. 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

  19. 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

  20. 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.

  1. The Marine Isotope Stage 19 in the mid-latitude North Atlantic Ocean: astronomical signature and intra-interglacial variability

    NASA Astrophysics Data System (ADS)

    Ferretti, Patrizia; Crowhurst, Simon J.; Naafs, B. David A.; Barbante, Carlo

    2015-01-01

    Since the seminal work by Hays et al. (1976), a plethora of studies has demonstrated a correlation between orbital variations and climatic change. However, information on how changes in orbital boundary conditions affected the frequency and amplitude of millennial-scale climate variability is still fragmentary. The Marine Isotope Stage (MIS) 19, an interglacial centred at around 785 ka, provides an opportunity to pursue this question and test the hypothesis that the long-term processes set up the boundary conditions within which the short-term processes operate. Similarly to the current interglacial, MIS 19 is characterised by a minimum of the 400-kyr eccentricity cycle, subdued amplitude of precessional changes, and small amplitude variations in insolation. Here we examine the record of climatic conditions during MIS 19 using high-resolution stable isotope records from benthic and planktonic foraminifera from a sedimentary sequence in the North Atlantic (Integrated Ocean Drilling Program Expedition 306, Site U1313) in order to assess the stability and duration of this interglacial, and evaluate the climate system's response in the millennial band to known orbitally induced insolation changes. Benthic and planktonic foraminiferal δ18O values indicate relatively stable conditions during the peak warmth of MIS 19, but sea-surface and deep-water reconstructions start diverging during the transition towards the glacial MIS 18, when large, cold excursions disrupt the surface waters whereas low amplitude millennial scale fluctuations persist in the deep waters as recorded by the oxygen isotope signal. The glacial inception occurred at ˜779 ka, in agreement with an increased abundance of tetra-unsaturated alkenones, reflecting the influence of icebergs and associated meltwater pulses and high-latitude waters at the study site. After having combined the new results with previous data from the same site, and using a variety of time series analysis techniques, we evaluate

  2. Dinocysts as tracers of sea-surface conditions and sea-ice cover in polar and subpolar environments

    NASA Astrophysics Data System (ADS)

    de Vernal, Anne; Rochon, André

    2011-05-01

    Dinoflagellates are unicellular protists that produce a cyst (dinocyst) as part of their life cycle. The cyst wall of many species is composed of highly resistant organic matter. Dinocysts are thus routinely recovered in marine sediments and occur in high number along the continental margins of the world oceans notably in high latitude environments. They are widely used as proxy indicators of marine conditions and provide valuable information on the natural variability of climate, which in turn helps understanding and assessing the potential threat posed by the actual global warming. Here we present a brief outline of their biology, ecology and distribution in Arctic and subarctic areas. We also provide a few examples of paleoenvironmental reconstructions and briefly discuss on the significance of these results.

  3. Glacial-interglacial variations of microbial communities in permafrost and lake deposits in the Siberian Arctic

    NASA Astrophysics Data System (ADS)

    Mangelsdorf, Kai; Bischoff, Juliane; Gattinger, Andreas; Wagner, Dirk

    2013-04-01

    The Artic regions are expected to be very sensitive to the currently observed climate change. When permafrost is thawing, the stored carbon becomes available again for microbial degradation, forming a potential source for the generation of carbon dioxide and methane with their positive feedback effect on the climate warming. For the prediction of future climate evolution it is, therefore, important to improve our knowledge about the microbial-driven greenhouse gas dynamics in the Siberian Arctic and their response to glacial-interglacial changes in the past. Sample material was drilled on Kurungnahk Island (Russian-German LENA expedition) located in the southern part of the Lena delta and in lake El'gygytgyn (ICDP-project) in the eastern part of Siberia. The Kurungnahk samples comprise Late Pleistocene to Holocene deposits, whereas the lake El'gygytgyn samples cover Middle to Late Pleistocene sediments. Samples were investigated applying a combined biogeochemical and microbiological approach. The methane profile of the Kurungnahk core reveals highest methane contents in the warm and wet Holocene and Late Pleistocene (LP) deposits and correlates largly to the organic carbon (TOC) contents. Archaeol concentrations, being a biomarker for past methanogenic archaea, are also high during the warm and wet Holocene and LP intervals and low during the cold and dry LP periods. This indicates that part of the methane might be produced and trapped in the past. However, biomarkers for living microorganisms (bacteria and archaea) and microbial activity measurements of methanogens point, especially, for the Holocene to a viable archaeal community, indicating a possible in-situ methane production. Furthermore, warm/wet-cold/dry climate cycles are recorded in the archaeal diversity as revealed by genetic fingerprint analysis. Although the overlying lake water buffers the temperature effect on the lake sediments, which never became permafrost, the bacterial and archaeal biomarker

  4. 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

  5. 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

  6. 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

  7. Water uptake on polar stationary phases under conditions for hydrophilic interaction chromatography and its relation to solute retention.

    PubMed

    Dinh, Ngoc Phuoc; Jonsson, Tobias; Irgum, Knut

    2013-12-13

    Since water associated with the stationary phase surface appears to be the essence of the retention mechanism in hydrophilic interaction chromatography (HILIC), we developed a method to characterize the water-absorbing capabilities of twelve different HILIC stationary phases. Adsorption isotherms for non-modified and monomerically functionalized silica phases adhered to a pattern of monolayer formation followed by multilayer adsorption, whereas water uptake on polymerically functionalized silica stationary phases showed the characteristics of formation and swelling of hydrogels. Water accumulation was affected by adding ammonium acetate as buffer electrolyte and by replacing 5% of the acetonitrile with tertiary solvents capable of hydrogen bonding such as methanol or tetrahydrofuran. The relationship between water uptake and retention mechanism was investigated by studying the correlations between retention factors of neutral analytes and the phase ratios of HILIC columns, calculated either from the surface area (adsorption) or the volume of the water layer enriched from the acetonitrile/water eluent (partitioning). These studies made it evident that adsorption and partitioning actually coexist as retention promoters for neutral solutes in the water concentration regime normally encountered in HILIC. Which factors that dominates is dependent on the nature of the solute, the stationary phase, and the eluting conditions. PMID:24200388

  8. 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.

  9. 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

  10. Direct terrestrial–marine correlation demonstrates surprisingly late onset of the last interglacial in central Europe

    PubMed Central

    Sier, Mark J.; Roebroeks, Wil; Bakels, Corrie C.; Dekkers, Mark J.; Brühl, Enrico; De Loecker, Dimitri; Gaudzinski-Windheuser, Sabine; Hesse, Norbert; Jagich, Adam; Kindler, Lutz; Kuijper, Wim J.; Laurat, Thomas; Mücher, Herman J.; Penkman, Kirsty E.H.; Richter, Daniel; van Hinsbergen, Douwe J.J.

    2011-01-01

    An interdisciplinary study of a small sedimentary basin at Neumark Nord 2 (NN2), Germany, has yielded a high-resolution record of the palaeomagnetic Blake Event, which we are able to place at the early part of the last interglacial pollen sequence documented from the same section. We use this data to calculate the duration of this stratigraphically important event at 3400 ± 350 yr. More importantly, the Neumark Nord 2 data enables precise terrestrial–marine correlation for the Eemian stage in central Europe. This shows a remarkably large time lag of ca. 5000 yr between the MIS 5e ‘peak’ in the marine record and the start of the last interglacial in this region. PMID:26523075

  11. 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.

  12. Trace fossils of talitrid sandhoppers in interglacial littoral calcareous sandstones, Cornwall, U.K.

    NASA Astrophysics Data System (ADS)

    Scourse, James

    Small (<6cm) isolated cylindrical shafts observed in carbonate-cemented current-bedded interglacial littoral sands ('sandrock') in Cornwall have previously been interpreted as intrasedimentary stalactites. An alternative explanation as trace fossils of the ichnogenus Skolithos is proposed. Probable attribution to talitrid Amphipoda (sandhoppers), in particular Talitrus saltator (Montagu), is supported by the similarity of the features to the modern burrows of this organism, the facies-dependence of the features, and by independent evidence on the backshore-frontal dune environment of deposition. The ecological requirements of T. saltator support the interpretation of the raised beaches as interglacial in status based on thermoluminescence (TL) dating and aminostratigraphy, and conflict with a recent suggestion that they may be of cold stage origin.

  13. 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.

  14. 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.

  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. 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

  17. 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

  18. 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

  19. 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

  20. 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

  1. 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

  2. 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

  3. 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

  4. 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.

  5. 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

  6. Marine Isotope Stage 11: Palaeoclimates, palaeoenvironments and its role as an analogue for the current interglacial

    NASA Astrophysics Data System (ADS)

    Candy, Ian; Schreve, Danielle C.; Sherriff, Jennifer; Tye, Gareth J.

    2014-01-01

    Interglacials of the Quaternary Period are currently the focus of a great deal of attention within the scientific community. This is primarily because they play a vital role in distinguishing between "natural" and "human" climate change in the current interglacial and in understanding how the Holocene would evolve in the absence of anthropogenic greenhouse warming. In this respect, Marine Isotope Stage 11 (MIS 11, ca 410,000 yr BP) is one of the key interglacial stages of the past 450,000 yr. The pattern of insolation variability that occurs during MIS 11 matches that which occurs in the Holocene more closely than in any other warm stage of the past half a million years. In addition there is now an extensive range of evidence for MIS 11 palaeoclimates and palaeoenvironments from marine, ice core, lacustrine and terrestrial sequences. The aim of this paper is to provide a comprehensive review of the current state of our understanding of MIS 11. This is the first paper to provide a detailed review of MIS 11 that incorporates the wide range of marine, ice core, long lacustrine and terrestrial records that have been generated over the last ten years since the last major overview. Crucially, it is the first review of MIS 11 that incorporates a detailed synthesis of the high-resolution terrestrial sequences of western and central Europe. This paper, therefore, provides a holistic integration of a diverse range of proxies and archives to provide a detailed understanding of the expression of MIS 11 in the Earth system. In particular the review focuses on: (1) the climatic background of MIS 11, (2) the robustness of the identification of MIS 11 in a diverse range of sequences, (3) the climatic structure of MIS 11, (4) the magnitude of warmth that occurred in this warm stage, (5) MIS 11 sea level magnitude and variability, (6) the duration of MIS 11, (7) evidence for abrupt climatic events within the interglacial of MIS 11 and (8) precipitation patterns and trends during

  7. 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

  8. The Response of Northern Hemisphere Extratropical Climate and Vegetation to Orbitally Induced Changes in Insolation during the Last Interglaciation

    NASA Astrophysics Data System (ADS)

    Harrison, Sandy P.; Kutzbach, John E.; Prentice, I. Colin; Behling, Pat J.; Sykes, Martin T.

    1995-03-01

    The last interglaciation (substage 5e) provides an opportunity to examine the effects of extreme orbital changes on regional climates. We have made two atmospheric general circulation model experiments: P+T+ approximated the northern hemisphere seasonality maximum near the beginning of 5e; P-T- approximated the minimum near the end of 5e. Simulated regional climate changes have been translated into biome changes using a physiologically based model of global vegetation types. Major climatic and vegetational changes were simulated for the northern hemisphere extratropics, due to radiational effects that were both amplified and modified by atmospheric circulation changes and sea-ice feedback. P+T+ showed mid-continental summers up to 8°C warmer than present. Mid-latitude winters were 2-4°C cooler than present but in the Arctic, summer warmth reduced sea-ice extent and thickness, producing winters 2-8°C warmer than present. The tundra and taiga biomes were displaced poleward, while warm-summer steppes expanded in the mid latitudes due to drought. P-T- showed summers up to 5°C cooler than present, especially in mid latitudes. Sea ice and snowpack were thicker and lasted longer; polar desert, tundra, and taiga biomes were displaced equatorward, while cool-summer steppes and semideserts expanded due to the cooling. A slight winter warming in mid latitudes, however, caused warm-temperate evergreen forests and scrub to expand poleward. Such qualitative contrasts in the direction of climate and vegetation change during 5e should be identifiable in the paleorecord.

  9. 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.

  10. Radiative Transfer Modeling of Radio-Band Linear Polarization Observations as a Probe of the Physical Conditions in the Jets of γ-Ray Flaring Blazars

    NASA Astrophysics Data System (ADS)

    Aller, Margo; Hughes, Philip; Aller, Hugh; Hovatta, Talvikki; Ramakrishnan, Venkatessh

    2016-09-01

    Since the mid-1980s the shock-in-jet model has been the preferred paradigm to explain radio-band flaring in blazar jets. We describe our radiative transfer model incorporating relativistically-propagating shocks, and illustrate how the 4.8, 8, and 14.5 GHz linear polarization and total flux density data from the University of Michigan monitoring program, in combination with the model, constrain jet flow conditions and shock attributes. Results from strong Fermi-era flares in 4 blazars with widely-ranging properties are presented. Additionally, to investigate jet evolution on decadal time scales we analyze 3 outbursts in OT 081 spanning nearly 3 decades and find intrinsic changes attributable to flow changes at a common spatial location, or, alternatively, to a change in the jet segment viewed. The model's success in reproducing these data supports a scenario in which relativistic shocks compress a plasma with an embedded passive, initially-turbulent magnetic field, with additional ordered magnetic field components, one of which may be helical.

  11. 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.

  12. 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

  13. 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.

  14. Analyzing Glacial-Interglacial Ocean Biogeochemical States in the MPI-Earth System Model

    NASA Astrophysics Data System (ADS)

    Heinze, M.; Ilyina, T.

    2015-12-01

    There is still little consensus about the mechanisms causing the glacial - interglacial variationsin atmospheric CO2 concentrations of around 100 ppm. Some of those mechanisms aredriven by alterations in ocean biogeochemical cycles. Hence, it is crucial to understand oceanbiogeochemistry dynamics during glacial-interglacial transitions. Within the German nationalclimate modeling initiative PalMod, aiming at simulating a full glacial cycle (135k - today) intransient mode with a state-of-the-art Earth System Model (ESM), we address the oceanbiogeochemistry cycles using a comprehensive modeling approach. In order to set up themodel we start with ocean only simulations, which are based on the 3-D ocean generalcirculation model MPIOM coupled to the ocean biogeochemistry model HAMOCC.Atmospheric forcing data is derived from a fully coupled LGM simulation including theatmosphere general circulation model ECHAM6. This setup provides us a sophisticatedrepresentation of the ocean biogeochemistry during the LGM without using any kind of datarestoring,to be consistent with the biological, chemical and physical dynamics of the model.We analyze alterations in ocean biogeochemistry during the LGM in comparison to a preindustrialcontrol climate. We discuss and quantify the changes in ocean biogeochemicalcycles between these two states, as well as possible implications for carbon transfer due tochanges in ocean dynamics. In the next steps we will use the ocean biogeochemistry model aspart of the fully coupled MPI-ESM. Our results aim at improving the understanding of glacial- interglacial changes in atmospheric CO2, especially in terms of marine carbon sequestrationand release. The presented work contributes to developing comprehensive ESMs, which arecapable of simulating the climate evolution and the variability during the last glacial cycle.

  15. 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.

  16. 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.

  17. 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.

  18. Using isostatic scenarios to assess coherence between continuous and instantaneous sea level indicators through the last interglacial

    NASA Astrophysics Data System (ADS)

    Williams, Felicity; Tamisiea, Mark E.; Rohling, Eelco J.; Hibbert, Fiona; Zhao, Cheng

    2014-05-01

    As a given volume of ice melt will not have a uniform impact on sea level, glacial isostatic adjustment is an essential tool for reconciling sea level indicators taken from multiple locations across the globe. We generate four ice loading histories based on the continuous ice volume record of de Boer, the δ18O stack of Lisiecki and Raymo, the composite relative sea level record of Waelbroeck, and our Red Sea relative sea level curve. Using these ice histories we model relative sea level curves for locations where fossil coral sea level indicators have been published and compiled into a standardised database. Although we apply screening criteria to the coral datapoints, preferentially focusing on those samples that are less likely to have undergone diagenic alteration, the fit between the sea level curves and the coral indicators is unsatisfactory. The relative sea level curves do not replicate the duration and amplitude of maximum sea level that is found in the coral record during MIS5e. We therefore explore three isostatic scenarios, whereby ice volume is reduced over the interglacial, the duration of the interglacial is extended, and the duration of the preceding glacial is extended in order to constrain possible explanations for the variations between the different records. We find that the continuous records require either a longer interglacial period or a combination of longer interglacial duration and less interglacial ice volume in order to more closely replicate the coral record.

  19. 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

  20. 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.

  1. 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

  2. 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.

  3. 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.

  4. POLARIZED PROTON COLLISIONS AT RHIC.

    SciTech Connect

    BAI, M.; AHRENS, L.; ALEKSEEV, I.G.; ALESSI, J.; ET AL.

    2005-05-16

    The Relativistic Heavy Ion Collider provides not only collisions of ions but also collisions of polarized protons. In a circular accelerator, the polarization of polarized proton beam can be partially or fully lost when a spin depolarizing resonance is encountered. To preserve the beam polarization during acceleration, two full Siberian snakes were employed in RHIC. In 2002, polarized proton beams were first accelerated to 100 GeV and collided in RHIC. Beams were brought into collisions with longitudinal polarization at the experiments STAR and PHENIX by using spin rotators. Optimizing polarization transmission efficiency and improving luminosity performance are significant challenges. Currently, the luminosity lifetime in RHIC is limited by the beam-beam effect. The current state of RHIC polarized proton program, including its dedicated physics run in 2005 and efforts to optimize luminosity production in beam-beam limited conditions are reported.

  5. 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

  6. Coastal deformation between the Versilia and the Garigliano plains (Italy) since the last interglacial stage

    NASA Astrophysics Data System (ADS)

    Nisi, Marco F.; Antonioli, Fabrizio; Pra, Giuseppe Dai; Leoni, Gabriele; Silenzi, Sergio

    2003-12-01

    The opening of the north-central Tyrrhenian Sea is the result of the Cretaceous-Paleogene alpine collision, which triggered a series of regional uplift, subsidence and transcurrent tectonic mechanisms along the coastal Tyrrhenian sectors of peninsular Italy. These tectonic processes, in conjunction with the effects of glacio- and hydro-isostasy during the Quaternary, produced substantial crustal responses that, in some cases, reached metres in extent. In the study of coastal neotectonics, geomorphological markers of the last interglacial maximum, corresponding to marine isotope stage 5.5, are generally used to quantify the magnitude of the vertical crustal displacements that have occurred since 125 kyr. Through altimetrical, palaeoenvironmental and chronological reinterpretation of the most significant works published since 1913, combined with an additional set of data reported here, a detailed reconstruction of the shoreline displacements evident along 500 km of coast between northern Tuscany and southern Latium is presented. The reconstruction was carried out by quantifying the vertical movement since the last interglacial period and by identifying the tectonic behaviour of different coastal sectors. This has been done by carefully choosing the eustatic marker, among those available at each study site, in order to minimize the margin of error associated with the measurements. Copyright

  7. 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.

  8. 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.

  9. Intra-interglacial climate variability from Marine Isotope Stage 15 to the Holocene

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

    Using the Community Climate System Model version 3 (CCSM3) including a dynamic global vegetation model a set of 13 interglacial time slice experiments was carried out to study global climate variability between and within the Quaternary interglaciations of Marine Isotope Stages (MIS) 1, 5, 11, 13, and 15. The different effects of obliquity, precession and greenhouse gas forcing on global surface temperature and precipitation fields are illuminated. Several similarities with previous idealized orbital-forcing experiments can be identified. In particular, a significant role of meridional insolation-gradient forcing by obliquity variations in forcing the West African monsoon is found. The sensitivity of the West African monsoon to this obliquity forcing, however, depends on the climatic precession. According to the CCSM3 results, the Indian monsoon is less sensitive to direct obliquity-induced insolation forcing, consistent with the interpretation of proxy records from the Arabian Sea. Moreover, the model results suggest that the two monsoon systems do not always vary in concert, challenging the concept of a global monsoon system at orbital timescales. High obliquity can also explain relatively warm Northern Hemisphere high-latitude summer temperatures despite maximum precession around 495 kyr BP (MIS 13) probably preventing a glacial inception at that time.

  10. 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

  11. U-Series dates for stalagmitic flowstone E (Riss/Würm interglaciation) at Grotte du Lazaret, Nice, France

    USGS Publications Warehouse

    Falgueres, Christophe; de Lumley, Henry; Bischoff, James L.

    1992-01-01

    Several samples of stalagmitic flowstone (Ensemble E) at Grotte du Lazaret (Nice, France) were dated by U-series isotopes. The results show that this speleothem began to grow about 130,000 yr B.P. and continued to about 70,000 yr B.P., coinciding almost exactly with the last interglaciation (isotope stage 5). Even though Ensemble E is not in direct stratigraphic relation with the cave deposits, this study shows that the Acheulian artifacts industry and fauna within Lazaret are older than the Riss/Wurm interglaciation.

  12. 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

  13. The Glacial-Interglacial Deuterium Excess Signal in the Illimani ice Core (Bolivia) Reveals Long Term and Abrupt Climate Changes

    NASA Astrophysics Data System (ADS)

    Vimeux, F.; Ramirez, E.; Sylvestre, F.; Hoffmann, G.

    2006-12-01

    The Illimani ice core, located on the Bolivian Cordillera Real (16S, 67W, 6350m) and covering approximately the last 18,000 years, has provided a wealth of paleoclimate information relative to the Andean and Amazonian regions. Specifically, isotopic composition of the ice has documented well known past climate changes (the Last Glacial Maximum, the Younger Dryas period, the Holocene Optimum and the last thousand years) that might be interpreted in terms of changes in precipitation over Amazonia. Here, we present new isotopic measurements from this ice core: deuterium excess at a 1cm- depth resolution (i.e around 30-year resolution) from the bottom of the core to around 5,000 years BP present. Deuterium excess (d= delta D-8*deltaO18) is a measure of the degree to which phase change occurs away from the thermodynamic equilibrium along air masses trajectory and therefore changes with the meteorological conditions (relative humidity, surface temperature and wind) during non-total evaporation (from the ocean surface, stagnant waters as lakes, rivers or flooded soil, droplets, or canopy-intercepted water) and with the supersaturation during condensation to ice. It thus might be sensitive to climate changes 1- impacting humidity and saturation conditions of the atmosphere and 2- changing the relative moisture sources contribution of Andean precipitation (recycling versus advective moisture). Based on a calibration combining isotopic composition of modern precipitation and modeling works, we discuss the significant glacial-interglacial deuterium excess change of about 3 permil as well as the very abrupt changes (between 4 and 12 per mil) occuring during well known lacustrine Tauca phase.

  14. Vegetation dynamics during the Last Interglacial-Glacial cycle in the Arno coastal plain (Tuscany, western Italy): location of a new tree refuge

    NASA Astrophysics Data System (ADS)

    Lucchi, M. Ricci

    2008-12-01

    Pollen analysis of the pre-Last Glacial Maximum succession of a 105 m-long continuous core from Tirrenia (Tuscany) provides evidence for the existence of an area of relatively high ecological stability where the effects of climate change were mitigated. The chronological framework of the vegetation record, spanning the Last Interglacial-Glacial cycle, was established by (i) AMS 14C dating, (ii) correlation with well-dated pollen sequences, and (iii) local stratigraphical constraints. A high lithological and sedimentological variability, with facies associations changing from fluvial to alluvial and coastal plain, enhances the palaeoenvironmental control on pollen distribution, thus helping to discriminate the impact of local factors on vegetation history. The most remarkable evidence, however, is represented by the continuous record of temperate trees throughout the whole glacial period, which provides useful indications on the location and nature of cold stage refugia. Most of the vegetation changes recorded in the core can be compared to the vegetation history of the Last Interglacial-Glacial cycle from southern Europe as a whole. In addition, local geographic and environmental features account for a more complex and varied floristic composition. Only the last phase of the Penultimate Glacial (MIS6), which was characterized by the diffusion of an arid steppe tundra, is recorded at the base of the core. The subsequent Last Interglacial (MIS5e) interval shows a poor and scattered pollen content due to the instability of the sedimentary environment. Nevertheless, it provides evidence of both global and local controls on vegetation dynamics, as indicated by the initial expansion of thermophilous forests and the remarkably late diffusion of conifers ( Pinus-Abies-Picea forests), respectively. Similarly, the transition to the Last Glacial (MIS5b and 5a in the core) is characterized by a reduced vegetation response to the typical stadial/interstadial climate variability

  15. Hybrid-Polarity SAR Architecture

    NASA Astrophysics Data System (ADS)

    Raney, R. K.; Freeman, A.

    2009-04-01

    A space-based synthetic aperture radar (SAR) designed to provide quantitative information on a global scale implies severe requirements to maximize coverage and to sustain reliable operational calibration. These requirements are best served by the hybrid-polarity architecture, in which the radar transmits in circular polarization, and receives on two orthogonal linear polarizations, coherently, retaining their relative phase. This paper reviews those advantages,summarizes key attributes of hybrid-polarity dual- and quadrature-polarized SARs including conditions under which the signal-to-noise ratio is conserved, and describes the evolution of this architecture from first principles.

  16. Polar Bear

    USGS Publications Warehouse

    Amstrup, S.D.; ,; Lentfer, J.W.

    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.

  17. 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

  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. 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

  20. 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

  1. 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.

  2. Interglacial/glacial changes in coccolith-rich deposition in the SW Pacific Ocean: An analogue for a warmer world?

    NASA Astrophysics Data System (ADS)

    Duncan, Bella; Carter, Lionel; Dunbar, Gavin; Bostock, Helen; Neil, Helen; Scott, George; Hayward, Bruce W.; Sabaa, Ashwaq

    2016-09-01

    Satellite observations of middle to high latitudes show that modern ocean warming is accompanied by increased frequency and poleward expansion of coccolithophore blooms. However, the outcomes of such events and their causal processes are unclear. In this study, marine sediment cores are used to investigate past coccolithophore production north and south of the Subtropical Front. Calcareous pelagites from subtropical waters off northernmost New Zealand (site P71) and from subantarctic waters on Campbell Plateau (Ocean Drilling Program [ODP] site 1120C) record marked changes in pelagite deposition. At both locations, foraminiferal-rich sediments dominate glacial periods whereas coccolith-rich sediments characterise specific interglacial periods. Sediment grain size has been used to determine relative abundances of coccoliths and foraminifers. Results show coccoliths prevailed around certain Marine Isotope Stage (MIS) transitions, at MIS 7b/a and MIS 2/1 at P71, and at MIS 6/5e at ODP 1120C. Palaeo-environmental proxies suggest that coccolithophore production and deposition at P71 reflect enhanced nutrient availability associated with intense winter mixing in the subtropical Tasman Sea. An increased inflow of that warm, micronutrient-bearing subtropical water in concert with upper ocean thermal stratification in late spring/summer, led to peak phytoplankton production. At ODP 1120C during MIS 6/5e, an increased inflow of subtropical water, warm sea surface temperatures and a thermally stratified upper ocean also favoured coccolithophore production. These palaeo-environmental reconstructions together with model simulations suggest that (i) future subtropical coccolithophore production at P71 is unlikely to reach abundances recorded during MIS 7b/a but (ii) future subantarctic production is likely to dominate sedimentation over Campbell Plateau as modern conditions trend towards those prevalent during MIS 5e.

  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. Glacial-interglacial dynamics of Antarctic firn columns: comparison between simulations and ice core air-?15N measurements

    NASA Astrophysics Data System (ADS)

    Capron, E.; Landais, A.; Buiron, D.; Cauquoin, A.; Chappellaz, J. A.; Debret, M.; Jouzel, J.; Leuenberger, M.; Martinerie, P.; Masson-Delmotte, V.; Mulvaney, R.; Parrenin, F.; Prié, F.

    2013-12-01

    Correct estimation of the firn lock-in depth is essential for correctly linking gas and ice chronologies in ice core studies. Here, two approaches to constrain the firn depth evolution in Antarctica are presented over the last deglaciation: outputs of a firn densification model, and measurements of δ15N of N2 in air trapped in ice core, assuming that δ15N is only affected by gravitational fractionation in the firn column. Since the firn densification process is largely governed by surface temperature and accumulation rate, we have investigated four ice cores drilled in coastal (Berkner Island, BI, and James Ross Island, JRI) and semi-coastal (TALDICE and EPICA Dronning Maud Land, EDML) Antarctic regions. Combined with available ice core air- δ15N measurements from the EPICA Dome C (EDC) site, the studied regions encompass a large range of surface accumulation rates and temperature conditions. Our δ15N profiles reveal a heterogeneous response of the firn structure to glacial-interglacial climatic changes. While firn densification simulations correctly predict TALDICE δ15N variations, they systematically fail to capture the large millennial-scale δ15N variations measured at BI and the δ15N glacial levels measured at JRI and EDML - a mismatch previously reported for central East Antarctic ice cores. New constraints of the EDML gas-ice depth offset during the Laschamp event (41 ka) and the last deglaciation do not favour the hypothesis of a large convective zone within the firn as the explanation of the glacial firn model- δ15N data mismatch for this site. While we could not conduct an in-depth study of the influence of impurities in snow for firnification from the existing datasets, our detailed comparison between the δ15N profiles and firn model simulations under different temperature and accumulation rate scenarios suggests that the role of accumulation rate may have been underestimated in the current description of firnification models.

  5. Glacial-interglacial dynamics of Antarctic firn columns: comparison between simulations and ice core air-δ15N measurements

    NASA Astrophysics Data System (ADS)

    Capron, E.; Landais, A.; Buiron, D.; Cauquoin, A.; Chappellaz, J.; Debret, M.; Jouzel, J.; Leuenberger, M.; Martinerie, P.; Masson-Delmotte, V.; Mulvaney, R.; Parrenin, F.; Prié, F.

    2013-05-01

    Correct estimation of the firn lock-in depth is essential for correctly linking gas and ice chronologies in ice core studies. Here, two approaches to constrain the firn depth evolution in Antarctica are presented over the last deglaciation: outputs of a firn densification model, and measurements of δ15N of N2 in air trapped in ice core, assuming that δ15N is only affected by gravitational fractionation in the firn column. Since the firn densification process is largely governed by surface temperature and accumulation rate, we have investigated four ice cores drilled in coastal (Berkner Island, BI, and James Ross Island, JRI) and semi-coastal (TALDICE and EPICA Dronning Maud Land, EDML) Antarctic regions. Combined with available ice core air-δ15N measurements from the EPICA Dome C (EDC) site, the studied regions encompass a large range of surface accumulation rates and temperature conditions. Our δ15N profiles reveal a heterogeneous response of the firn structure to glacial-interglacial climatic changes. While firn densification simulations correctly predict TALDICE δ15N variations, they systematically fail to capture the large millennial-scale δ15N variations measured at BI and the δ15N glacial levels measured at JRI and EDML - a mismatch previously reported for central East Antarctic ice cores. New constraints of the EDML gas-ice depth offset during the Laschamp event (~41 ka) and the last deglaciation do not favour the hypothesis of a large convective zone within the firn as the explanation of the glacial firn model-δ15N data mismatch for this site. While we could not conduct an in-depth study of the influence of impurities in snow for firnification from the existing datasets, our detailed comparison between the δ15N profiles and firn model simulations under different temperature and accumulation rate scenarios suggests that the role of accumulation rate may have been underestimated in the current description of firnification models.

  6. 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.

  7. 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

  8. 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.

  9. 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

  10. A High Resolution Record of Ocean Circulation since the last Interglacial from Nd isotopes

    NASA Astrophysics Data System (ADS)

    Goldstein, S. L.; Piotrowski, A. M.; Hemming, S. R.; Fairbanks, R. G.; Zylberberg, D. R.

    2004-12-01

    The variability of the global conveyor through ice ages has been a matter of dispute due to different indications from different paleocirculation proxies. Nd isotopes in marine precipitates conservatively reflect water mass mixing along their transport paths, and are changed only by addition of a new component of Nd. We present the first high resolution Nd isotope record of paleocirculation between MIS 1 and 5c from Cape Basin cores RC11-83 and TNO57-21. The record indicates a strong conveyer during warm northern hemisphere interglacial and interstadial intervals, and a weaker one during glacials and stadial intervals. The pattern of changes varies with Greenland paleotemperature. A first quantification attempt indicates that NADW export during the LGM was half the magnitude of the early Holocene. The strengthening through Termination 1 covaries with Greenland temperature and North Atlantic sea ice coverage. It markedly weakens between the Bolling and Younger Dryas. The weakening during the MIS 5a/4 transition is sharp, occurring within 1 ka. Throughout MIS 3 short-term maxima are associated with prominent interstadials in Greenland ice records (8, 12, 14, 17). Local minima at ~40 and ~62 ka may be associated with Heinrich events 4 and 6. During the ice age initiation and termination, global carbon budget shifts preceded circulation changes, and these were preceded by ice sheet growth during the initiation. There is no apparent lead-lag during interstadial warmings. The observations allow for ocean circulation to be a trigger of major climate change during abrupt events that are not driven by orbital forcing. At major glacial-interglacial boundaries, the global carbon budget and thermohaline ocean circulation both respond to the climate changes that forced the growth and decline of continental ice sheets. Overall the data show that Nd isotope ratios can be a powerful tool to trace paleocirculation history.

  11. Numerical model of the geothermal regime on the Beaufort Shelf, arctic Canada since the Last Interglacial

    NASA Astrophysics Data System (ADS)

    Taylor, Alan E.; Dallimore, S. R.; Hill, P. R.; Issler, D. R.; Blasco, S.; Wright, F.

    2013-12-01

    finite element geothermal model is developed for the outer Mackenzie Delta-Beaufort Sea shelf to predict permafrost evolution since the Last Interglacial ~130-116 kaBP(cal). The purpose is to reconcile sparse observations of the depth and extent of ice-bonded permafrost with sediment properties and the paleoenvironment. Sea level curves determine, as a function of time, areas of the shelf that were subaerially exposed, promoting permafrost aggradation, and areas that were submerged, promoting permafrost degradation. Assuming as a model starting point that a paleoclimate similar to today persisted through the Last Interglacial, permafrost subsequently aggrades in depth and advances seaward from the present shoreline to the shelf/slope bathymetric break by the Last Glacial Maximum (LGM) ~26 kaBP(cal). Modeled permafrost exhibits reduced growth in depth and seaward progression that correlate with early and middle Wisconsin stillstands in sea level. Following the LGM and rise in sea level, offshore permafrost degrades and permafrost base rises ~100 m to its present depth of ~600 m. The offshore limit of modeled ice-bonded permafrost lies at the ~95 m isobath, within 1 km of the bathymetric shelf/slope break. The model replicates features of offshore permafrost body observed seismically and demonstrates that warm outflow from the Mackenzie River depresses the upper surface of offshore permafrost by tens of meters to the 20 m isobath. Although Pleistocene permafrost predated the Wisconsinan, the model demonstrates that the paleoenvironment of the last 125,000 years is sufficient to develop the depth, seaward extent, and principal features of the permafrost body.

  12. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

    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 δ18O 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 δ18Oice, δ15N 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.

  14. 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

  15. Quelccaya Ice Cap extents during the last glacial-interglacial transition: evidence for rapid climate changes in the southern tropics during Younger Dryas time

    NASA Astrophysics Data System (ADS)

    Kelly, M. A.; Lowell, T. V.; Applegate, P. J.; Smith, C.; Phillips, F. M.; Hudson, A. M.

    2011-12-01

    Paleoglacial data from the Peruvian Andes shed light on the mechanisms which influenced rapid climate changes during late glacial time. Here, we present a radiocarbon-based chronology of Quelccaya Ice Cap (QIC) fluctuations during the last glacial-interglacial transition that registers paleoclimatic conditions at high altitude (~5000 m asl) in the southern tropics (~14°S, 70°W). Subsequent to the last glacial maximum, major recession of QIC was underway by ~17.2 ka. The timing of this recession is prior to the warming registered by Greenland ice cores, but similar to the timing of mountain glacier recession in both Northern and Southern hemispheres, likely influenced by rising atmospheric CO2 concentrations. At ~12.6 ka, QIC underwent the most significant readvance during the last glacial-interglacial transition, reaching a position ~4-5 km from the modern ice cap margin and depositing a prominent set of moraines that is nearly continuous on the western side of the ice cap. Recession from this rapid readvance was underway by ~12.3 ka, and QIC was within its Little Ice Age extent (~1-2 km from the modern ice margin) by ~11.2 ka. The readvance of QIC occurred early in the Younger Dryas cold interval (12.9-11.7 ka) and ice cap recession was underway while Greenland ice cores registered continuously cold conditions. Whereas QIC receded by at least 3-4 km between 12.3 and 11.2 ka, paleo-lake levels and other indicators of moisture on the Bolivian Altiplano, document wet conditions in the southern tropics until the end of the Younger Dryas. Thus, we suggest that QIC recession at ~12.3 ka was associated with warming in the tropics that occurred during middle Younger Dryas time. Warming at this time is also registered by climate proxy records from the Cariaco Basion, in the northern tropical Atlantic region, and in the eastern tropical Pacific Ocean. Recent modeling studies suggest that a southerly position of the Intertropical Convergence Zone (ITCZ) associated with

  16. 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.

  17. A Remarkably High-Speed Solution-Phase Combinatorial Synthesis of 2-Substituted-Amino-4-Aryl Thiazoles in Polar Solvents in the Absence of a Catalyst under Ambient Conditions and Study of Their Antimicrobial Activities

    PubMed Central

    Dighe, Satish N.; Chaskar, Pratip K.; Jain, Kishor S.; Phoujdar, Manisha S.; Srinivasan, Kumar V.

    2011-01-01

    Remarkably high-speed synthesis of 2-substituted amino-4-aryl thiazoles in polar solvents with a minimum threshold polarity index of 4.8 was found to proceed to completion in just 30–40 sec. affording excellent yields of thiazoles under ambient temperature conditions without the use of any additional catalyst. The purification-free procedure afforded libraries based around a known pharmacophore, namely, substituted arylthiazoles and generated samples of high purity. In terms of combinatorial synthesis in a single solution phase, our protocol is significantly better than those hitherto reported and is amenable for HTS. The in vitro biological tests of some thiazoles showed good activity towards gram-positive bacteria, gram-negative bacteria and fungi comparable with the standard drugs, nitrofurantoin and griseofulvin, for their antibacterial and antifungal activities, respectively. PMID:24052822

  18. Polarization Considerations

    NASA Technical Reports Server (NTRS)

    Waluschka, Eugene

    1998-01-01

    As light passes through a optical system the reflections and refractions will in general change the polarization state of the light. If we assume that all of the materials in the thin film coatings and substrate are isotropic and homogeneous then calculating the amount of "instrumental" polarization is a relatively straight forward task. In the following sections we will present a of the steps required to perform a 'polarization ray trace' calculation for a single ray and monochromatic and hence polarized light. The thin film portion of the calculation is also shown. The reason for explicitly showing the thin film equations is that there are sign conventions imposed on the boundary value equations by the orientation and handedness of the various coordinate frames which are attached to the geometric rays. The attenuation of light through a optical system, is relatively simple, and requires at the very least a lens (average) reflectivity or transmissivity. Determining the polarization sensitivity of a optical system is still relatively straight forward requiring at least a knowledge of the behavior of the "s" and "p" components at each interface for the chief ray. Determining the thin film induced aberrations of a optical system are somewhat more demanding. Questions about the arithmetic sign of the phase factors and how this relates to the overall "OPD" of a ray are ubiquitous. Many rays are required to construct a wavefront. Thin film codes which modify the OPD's of rays are a requirement for this last mentioned computation. This requires a consistent scheme of coordinate frames and sign conventions and is probably the most demanding task of a polarization ray trace. Only the electric field will used in the discussion. This is not a restriction as the Stokes parameters are functions of the electric field. The following does not attempt to explain, but only to present all of the required concepts and formulas.

  19. 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).

  20. 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

  1. Geochemical and Sedimentological Proxies for the Extent of the Greenland Ice Sheet During the Penultimate Interglacial

    NASA Astrophysics Data System (ADS)

    Colville, E. J.; Carlson, A. E.; Beard, B. L.; Stoner, J.; Hillaire-Marcel, C.

    2008-12-01

    The greatest uncertainty for future sea level rise is the contribution from the Greenland Ice Sheet (GIS) due to limited understanding of GIS sensitivity to a warming climate. To better understand GIS climate sensitivity, we present new geochemical (Pb-Sr-Nd isotopes) and sedimentological data (% silt) from sediment core MD99-2227 (58°12.64'N, 48°22.38'W, 3460 m of water depth) located on the Eirik Drift. Prior work indicates that this site records the sedimentological record of GIS deglaciation. With our new data, we provide constraints on the aerial extent of the southern GIS during the last (TI, 21-7 ka) and penultimate (TII, 135-117 ka) deglaciations and subsequent interglacials. The % silt record suggests a significantly longer period of terrestrial sediment input during TII than TI (18 kyr vs. 5 kyr) in agreement with prior Ti, Fe and magnetic records. During TII, the radiogenic isotope records indicate that the earlier part of this sediment input (135-125 ka) has an ɛNd signature consistent with an Archean province (ɛNd ~- 20) that is likely derived from the southern Greenland Archean block (~64 °N), whereas sediment from 125-117 ka have ɛNd values of -15. The Sr-Nd-Pb isotope signature of sediment from 125- 117 ka are consistent with a sediment source of Proterozoic or younger affinity. This period of terrestrial sediment flux corresponds with the +6 m sea level high stand suggesting that the greatest GIS retreat occurred between 125-117 ka. If this younger sediment was derived from the Proterozoic Central Nagssugtoqidian Orogenic Belt (~67.5 °N), then the sediment data are consistent with ice sheet models that suggest a 3.5-4.5 m sea level contribution from the GIS to the +6 m sea level high stand. This sustained freshwater flux may have reduced the surface density of the Labrador Sea, explaining the lack of Labrador Sea deepwater formation during this interglacial. Further Pb-Sr-Nd-isotope analyses of the silt fraction of suspended load sediment

  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. Biostratigraphical distinction of interglacial coleopteran assemblages from southern Britain attributed to Oxygen Isotope Stages 5e and 7*1

    NASA Astrophysics Data System (ADS)

    Coope, G. R.

    2001-10-01

    Beetle assemblages are described from 14 interglacial sites in southern England, all of which post-date the Hoxnian Interglacial (in the broad sense) and which can safely be attributed to Oxygen Isotope Stages 5e and 7. The beetle faunas from these interglacial deposits are large and complex and together include at least 387 named species many of which are no longer found living in the British Isles. Almost all of the latter have modern geographical distributions exclusively to the south of Britain and some are predominantly Mediterranean. A few have their nearest relatives living today in North Africa or as far away as northern India. Some of these temperate beetle assemblages are remarkably similar to one another especially in their inclusion of diagnostic exotic species. Others, though indicative of a temperate climate, exhibit consistent differences so that the 14 assemblages clearly divide themselves into two groups; Group (a) and Group (b), based on differences in their species composition and abundance. Group (a) beetle faunas, from seven sites, may be termed "classic" Ipswichian (Eemian) since they closely resemble the assemblage from the type site at Bobbitshole near Ipswich and have unimpeachable stratigraphical contexts. All of these faunas can with confidence be attributed to an early phase of Oxygen Isotope Sub-Stage 5e. Group (b) beetle faunas, also from seven sites, are very different in their specific composition and are more of a puzzle because they include some fossil assemblages from deposits that have, in the past, been attributed to the latter part of the Ipswichian Interglacial and others that are undoubtedly from stratigraphical deposits that are earlier than the Ipswichian and which have been correlated with Oxygen Isotope Stage 7. It is with the deposits yielding Group (b) faunas that the greatest controversy arises. On-line appendix available at http://www.elsevier.com/locate/quascirev

  4. 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.

  5. Abrupt Sea Surface Temperature changes during The Last Glacial-Interglacial Transition in the Iberian margin: Sea Level implications

    NASA Astrophysics Data System (ADS)

    Rodrigues, Teresa; Grimalt, Joan; Abrantes, Fatima; Naughton, Filipa; Flores, José-Abel

    2010-05-01

    Uk'37-SST and organic terrestrial biomarkers were used to reconstruct Sea surface temperature (SST) and continental input in a shallow core (D13882) from the Tagus mud patch (Iberian margin) during last glacial and interglacial transition (LGIT). In the western Iberian margin the Heinrich 1 (H1) and the Younger Dryas (YD) represent two extreme episodes of cold sea surface temperature conditions mediated by a marine warm phase that coincides with the Bolling-Allerod event (B-A) in the neighbor continent. Following the YD event, an abrupt sea surface warming marks the beginning of the Holocene in this region. However, SST values and amplitude of variation recorded in core D13882 differ from deep sea core MD03- 2699 and other available palaeoclimate sequences from this region. While the SST values from most deep sea cores reflect the latitudinal gradient detected on the Iberian Peninsula during H1 and B-A, the shallow core (D13882) SSTs are colder than the ones recorded in the deep sea. This suggests that a supplementary input of cold freshwater coming from the continent reached shallow areas. This hypothesis is supported by the high terrigenous biomarkers and total organic carbon content as well as by the dominance of tetra alkenone in the Tagus mud patch. Furthermore, the comparison of all western Iberia SST records suggest that the SST increase during the B-A event started 1,000 yr before the meltwater pulse 1A (mwp-1A) and attained maximum values during or slightly after this sea level rise episode. Conversely, the sharp SST increase in the Iberian margin during the YD/Holocene transition, is synchronous with the meltwater pulse 1B (mwp-1B). The decrease of continental input in the Tagus mud patch confirms a sea level rise in the region. Thus, the synchronism between the maximum warming in the mid-latitudes of the western Iberian margin, in the adjacent landmasses and temperature in Greenland suggest that the mwp-1B, could have been initiated in the Northern

  6. Glacial-interglacial dynamics of Antarctic firn columns: comparison between simulations and ice core air-δ15N measurements

    NASA Astrophysics Data System (ADS)

    Capron, E.; Landais, A.; Buiron, D.; Cauquoin, A.; Chappellaz, J.; Debret, M.; Jouzel, J.; Leuenberger, M.; Martinerie, P.; Masson-Delmotte, V.; Mulvaney, R.; Parrenin, F.; Prié, F.

    2012-12-01

    Correct estimate of the firn lock-in depth is essential for correctly linking gas and ice chronologies in ice cores studies. Here, two approaches to constrain the firn depth evolution in Antarctica are presented over the last deglaciation: output of a firn densification model and measurements of δ15N of N2 in air trapped in ice core. Since the firn densification process is largely governed by surface temperature and accumulation rate, we have investigated four ice cores drilled in coastal (Berkner Island, BI, and James Ross Island, JRI) and semi coastal (TALDICE and EPICA Dronning Maud Land, EDML) Antarctic regions. Combined with available δ15N measurements performed from the EPICA Dome C (EDC) site, the studied regions encompass a large range of surface accumulation rate and temperature conditions. While firn densification simulations are able to correctly represent most of the δ15N trends over the last deglaciation measured in the EDC, BI, TALDICE and EDML ice cores, they systematically fail to capture BI and EDML δ15N glacial levels, a mismatch previously seen for Central East Antarctic ice cores. Using empirical constraints of the EDML gas-ice depth offset during the Laschamp event (~ 41 ka), we can rule out the existence of a large convective zone as the explanation of the glacial firn model-δ15N data mismatch for this site. The good match between modelled and measured δ15N at TALDICE as well as the lack of any clear correlation between insoluble dust concentration in snow and δ15N records in the different ice cores suggest that past changes in loads of impurities are not the only main driver of glacial-interglacial changes in firn lock-in depth. We conclude that firn densification dynamics may instead be driven mostly by accumulation rate changes. The mismatch between modelled and measured δ15N may be due to inaccurate reconstruction of past accumulation rate or underestimated influence of accumulation rate in firnification models.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. Imprints of AMOC Perturbation in the Intermediate water of Equatorial Atlantic during the Last Interglacial Improved

    NASA Astrophysics Data System (ADS)

    Weldeab, S.

    2014-12-01

    Understanding of the last interglacial (LIG) is critical for the assessment of long-term impact of global warming on the Atlantic meridional overturning circulation (AMOC) and climate. Relative to the Millennium, air temperature over Greenland and eustatic sea-level during the LIG was higher by 8±4˚C and 4-8 m, with a considerable oscillation in the rate of meltwater input (NEEM Community rembers, Nature, v.493, p.489; Kopp et al., Nature, v. 462, p. 863) . The impact of millennial-scale LIG meltwater input on the AMOC and global climate is, however, less understood. Here we present a highly resolved, benthic foraminiferal multi-proxy record from the eastern equatorial Atlantic. The record shows that the LIG was punctuated by at least two episodes of reduced AMOC whose impact on the global climate varied considerably. While the event between 126,000 and 123,800 years ago lacks imprints on available global climate records, the AMOC perturbation between 129,000 and 128,000 years ago provides a causative link to a rapid increase of atmospheric CO2, peak air warming over Antarctica, and a slow down of the rate of global monsoon intensification. We suggest that the rate of meltwater input into the North Atlantic and the size of remanent Greenland ice sheet was critical in determining the degree of AMOC reduction and its effect on the interhemispheric climate.

  13. Iron speciation in aerosol dust influences iron bioavailability over glacial-interglacial timescales

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

    Iron deposition influences primary production and oceanic sequestration of atmospheric carbon dioxide (CO2). Iron has two oxidation states, Fe(II) and Fe(III), with Fe(II) being more soluble and available for oceanic phytoplankton uptake. The past proportions of soluble iron in aerosol dust remain unknown. Here we present iron speciation (Fe2+ and Fe3+) in the Antarctic Talos Dome ice core over millennial time scales. We demonstrate that iron speciation over the last 55 kyr is linked to increasing quantities of fine dust (FD) (0.7-5 µm) and intensified long-range dust transport. We propose that Fe(II) and Fe2+ production is principally enhanced in FD by photoreduction, although pH and organic complexation may also contribute to the speciation dynamics. During the Last Glacial Maximum, Fe2+ concentrations in dust increased by up to seven times more than interglacial levels, while Fe3+ only doubled. Cold and dusty climatic periods may increase the percentage of biologically available Fe(II) and Fe2+ deposited in the nutrient-limited Southern Ocean, allowing greater phytoplankton uptake and perhaps increased CO2 drawdown.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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

  1. 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

  2. Polar Diving

    NASA Technical Reports Server (NTRS)

    2006-01-01

    3 July 2006 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows layers exposed by erosion in a trough within the north polar residual cap of Mars, diving beneath a younger covering of polar materials. The layers have, since the Mariner 9 mission in 1972, been interpreted to be composed of a combination of dust and ice in unknown proportions. In this scene, a layer of solid carbon dioxide, which was deposited during the previous autumn and winter, blankets the trough as well as the adjacent terrain. Throughout northern spring, the carbon dioxide will be removed; by summer, the layers will be frost-free.

    Location near: 81.4oN, 352.2oW Image width: 3 km (1.9 mi) Illumination from: lower left Season: Northern Spring

  3. Polar Summer

    NASA Technical Reports Server (NTRS)

    2005-01-01

    30 December 2005 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows eroding mesas of frozen carbon dioxide in the martian south polar residual cap. During the summer season, the scarps that bound each pit and mesa in the south polar region become dark as carbon dioxide sublimes away. The darkening might result from the roughening of the surfaces from which ice is subliming, or from the concentration of trace amounts of dust on these slopes, or both.

    Location near: 84.7oS, 48.2oW Image width: 3 km (1.9 mi) Illumination from: upper left Season: Southern Summer

  4. 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

  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.

  6. Long-term erosion and interglacial period exposure in Western Greenland from meteoric 10Be in ice-bound sediment

    NASA Astrophysics Data System (ADS)

    Graly, J. A.; Corbett, L.; Bierman, P. R.; Neumann, T.; Rood, D. H.; Finkel, R. C.

    2010-12-01

    To examine the history of surface exposure and erosion in areas of Western Greenland presently covered by ice, we measured the concentration of meteoric 10Be in ice-bound fine sediment at three locations: Kangerlussuaq (67.1°N), Ilulissat (69.4°N), and Upernavik (72.5°N). Meteoric 10Be concentrations at Ilulissat and Upernavik range from 2×106 to 2×108 atoms/g and are statistically indistinguishable from each other. Meteoric 10Be concentrations at Kangerlussuaq range from 2×106 to 5×107 atoms/g and are significantly lower than the values found at the northern two sites. Through comparison to typical meteoric 10Be distribution in soils, source soil ages can be estimated at each of these locations. These estimates suggest on the order of 105 years of exposure at the northern sites and on the order of 104 years of exposure at Kangerlussuaq. Because meteoric 10Be is lost from the soil system both by erosion and isotope decay, these exposure ages represent a minimum length of cumulative interglacial exposure. This exposure signal likely developed over several Late Pliocene and Pleistocene interglacial periods and prior to the onset of Northern hemisphere glaciation, ~2.7 Ma before present. To further constrain the glacial history of Western Greenland implied from the meteoric 10Be data, we constructed forward models of interglacial period exposure and glacial period erosion. The high levels of meteoric 10Be at Upernavik and Ilulissat imply erosion rates below 5 m/My and some preservation of pre-glacial regolith. The lower levels of meteoric 10Be at Kangerlussuaq can be explained with erosion rates as high as 20 m/My. Because of the substantial debris fluxes in modern Kangerlussuaq glaciers [Knight, et al., 2002], erosion rates greater than 10 m/My are likely. Meteoric 10Be inventories at Kangerlussuaq under 10-20 m/My of long-term erosion imply substantial interglacial exposure and the slow evacuation of sediment by glacial transport. These results suggest that

  7. 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

  8. 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.

  9. Retention prediction of highly polar ionizable solutes under gradient conditions on a mixed-mode reversed-phase and weak anion-exchange stationary phase.

    PubMed

    Balkatzopoulou, P; Fasoula, S; Gika, H; Nikitas, P; Pappa-Louisi, A

    2015-05-29

    In the present work the retention of three highly polar and ionizable solutes - uric acid, nicotinic acid and ascorbic acid - was investigated on a mixed-mode reversed-phase and weak anion-exchange (RP/WAX) stationary phase in buffered aqueous acetonitrile (ACN) mobile phases. A U-shaped retention behavior was observed for all solutes with respect to the eluent organic modifier content studied in a range of 5-95% (v/v). This retention behavior clearly demonstrates the presence of a HILIC-type retention mechanism at ACN-rich hydro-organic eluents and an RP-like retention at aqueous-rich hydro-organic eluents. Hence, this column should be promising for application under both RP and HILIC gradient elution modes. For this reason, a series of programmed elution runs were carried out with increasing (RP) and decreasing (HILIC) organic solvent concentration in the mobile phase. This dual gradient process was successfully modeled by two retention models exhibiting a quadratic or a cubic dependence of the logarithm of the solute retention factor (lnk) upon the organic modifier volume fraction (φ). It was found that both models produced by gradient retention data allow the prediction of solute retention times for both types of programmed elution on the mixed-mode column. Four, in the case of the quadratic model, or five, in the case of the cubic model, initial HILIC- and RP-type gradient runs gave satisfactory retention predictions of any similar kind elution program, even with different flow rate, with an overall error of only 2.5 or 1.7%, respectively.

  10. 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

  11. 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.

  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. 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

  14. Polar Layers

    NASA Technical Reports Server (NTRS)

    2005-01-01

    12 August 2005 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a slope upon which are exposed some of the layered materials that underlie the south polar cap of Mars. The layers are generally considered to be sediments--perhaps dust--that may have been cemented by water ice.

    Location near: 84.1oS, 343.9oW Image width: width: 3 km (1.9 mi) Illumination from: upper left Season: Southern Spring

  15. Influence of ice sheet topography on Greenland precipitation during the Eemian interglacial

    NASA Astrophysics Data System (ADS)

    Merz, N.; Gfeller, G.; Born, A.; Raible, C. C.; Stocker, T. F.; Fischer, H.

    2014-09-01

    Greenland precipitation and its relationship to the synoptic forcing has been studied for the last interglacial period (i.e., the Eemian) using a set of global climate simulations. We distinguish between precipitation changes due to the Eemian orbital forcing and responses to modifications in the Greenland ice sheet (GrIS) topography. Precipitation changes caused by orbital forcing alone are of moderate amplitude and are largely determined by large-scale changes in moisture availability. In contrast, changes in GrIS topography lead to distinct precipitation anomalies over Greenland, while the effect on far-field regions is negligible. The analysis of the simulations reveals the control of the GrIS topography on where moist air masses are orographically lifted and cause substantial precipitation. However, the general moisture availability and the moisture transport associated with typical weather situations remain unchanged in all simulations. A focal point of the study is precipitation at pNEEM, i.e., the suggested deposition site of Eemian ice archived in the North Greenland Eemian ice drilling project (NEEM) ice core. Eemian orbital forcing leads to an increase in summer precipitation at pNEEM, whereas changes in the GrIS topography can result in either increased or decreased precipitation. Transport routes prior to precipitation events at pNEEM show that moisture is predominantly advected from westerly to southerly directions as the GrIS acts as an impassable barrier for easterly moisture transport. One scenario of Eemian melting of northeastern Greenland, however, allows moist air masses from the Norwegian Sea to arrive at pNEEM. Consequently, this GrIS topography would result in transport-related changes of Eemian wet-deposited aerosol records.

  16. 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.

  17. 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.

  18. Glacial-Interglacial and Holocene N2O Stable Isotope Changes Constrain Terrestrial N Cycling

    NASA Astrophysics Data System (ADS)

    Schmitt, J.; Spahni, R.; Bock, M.; Seth, B.; Stocker, B. D.; Ri, X.; Schilt, A.; Brook, E.; Otto-Bliesner, B. L.; Liu, Z.; Prentice, I. C.; Fischer, H.; Joos, F.

    2015-12-01

    The land biosphere contributes most to the natural source of the long-lived greenhouse gas nitrous oxide (N2O), with N2O emissions being dependent on the turnover rate of both the terrestrial nitrogen (N) and carbon (C) cycle. The C:N stoichiometry of vegetation and soil organic matter links the cycles intimately. Sustained plant productivity increase must be supported by biological N fixation. Intensified N cycling in turn enhances N loss and thereby N2O emissions. The temporal and spatial dynamics of terrestrial N and C cycles and related terrestrial N2O emissions are poorly constrained over the glacial-interglacial transition and the Holocene. Here we reconstruct increased terrestrial N2O emissions since the Last Glacial Maximum based on N2O concentration and isotope measurements on several ice cores and show that this N2O increase can be explained by N cycle modelling - provided N fixation is allowed to respond dynamically to increasing N demand and turnover. The Ice core reconstructions suggest a deglacial increase of 1.1 ± 0.4 Tg N/yr in terrestrial and 0.6 ± 0.4 Tg/yr in oceanic N2O emissions, but relatively constant terrestrial emissions over the Holocene. Transient simulations with a Dynamic Global Vegetation Model are shown to represent the climate and CO2 induced changes in terrestrial N2O emission, and suggest a deglacial increase in biological N fixation by 20%, independently of its absolute magnitude. Deciphering the response of biological N fixation during climatic changes is an important factor for our understanding of plant growth and the land carbon sink, alongside anthropogenic greenhouse gas emissions.

  19. 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.

  20. 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.

  1. 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

  2. The PVDF (polarized polyvinylidene fluoride polymer film) piezoelectric polymer shock-stress sensor: Signal conditioning and analysis for field test application

    SciTech Connect

    Reed, R.P.; Greenwoll, J.I.

    1989-05-01

    The PVDF shock sensor is a piezoelectric polymer transducing element that converts stress to charge. This unusually versatile sensor allows accurate measurement of stress pulses of durations up to milliseconds with resolution of nanoseconds over a range of a few bars to at least 0.5 Mbar. Its measurement characteristics depend significantly on stress waveform and circuitry. Field test applications require special consideration of signal conditioning, system characterization, and data analysis. This report describes some unfamiliar characteristics of the PVDF sensor and a field-validated hybrid (complementary hardware and software) approach to the general measurement problem as encountered under field test conditions. Discussed are the use of the sensor, for estimation of signal voltage, through characterization and correction for system properties, design, and realization of special filters, to reduction of observed voltage to the stress experienced by the sensor. 9 refs., 10 figs., 1 tab.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  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 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.

  12. Past seismic activity in Eastern Anatolia recorded over several glacial/interglacial cycles in the sediments of Lake Van

    NASA Astrophysics Data System (ADS)

    Stockhecke, M.; Anselmetti, F.; Sturm, M.

    2012-12-01

    Lake sediments document besides paleoenvironmental and paleoclimate conditions also paleoseismic activity through various forms of deformation structures. These are especially visible in finely-laminated sediments. Being situated in a tectonically active region, the partly annually-laminated sedimentary sequence of the terminal Lake Van, recovered in 2010 under the context of the ICDP Paleovan project, shows dozens of earthquake-triggered microdeformations that document past seismic events of the last half a million years. Lithological and multiproxy analysis revealed that the Lake Van's depositional conditions varied in correspondence to Milankovitch and sub-Milankovitch cycles. Glacial/stadial and interglacial/interstadial conditions were recorded continuously over the last half a million years excluding two discontinuities, which indicate major hydrological and geomorphological changes in Lake Van's early history. Two sites were drilled 10 km apart: A primary drill site, situated on a ridge, covers the entire lake history since its initial transgression in the middle Pleistocene; A secondary drill site, located in a more shallow northern basin, covers the past 90'000 years. Multiple coring at both drill sites allows to establish two almost complete 220 m and 145 m long composite sections, respectively. Observing deformation structures in multiple parallel cores at each site is used as a criteria to distinguish 'true' paleoseismic deformation structures from potential drilling artifacts. Deformation structures consist of i) silt-filled vertical fractures, ii) microfaults with displacements at cm-scale, iii) microfolds, iv) liquefaction structures (mushroom, pseudonodules), iv) disturbed varve laminations and v) mixed layers. While the ridge site records the paleoseismic events as microdeformations, the northern basinal site rather records seismic events through the deposition of seismo-turbidites. In some cases, individual earthquake events can even be identified

  13. Search for Polarization Effects in the Antiproton Production Process

    SciTech Connect

    Grzonka, D.; Kilian, K.; Ritman, J.; Sefzick, T.; Oelert, W.; Diermaier, M.; Widmann, E.; Zmeskal, J.; Głowacz, B.; Moskal, P.; Zieliński, M.; Wolke, M.; Nadel-Turonski, P.; Carmignotto, M.; Horn, T.; Mkrtchyan, H.; Asaturyan, A.; Mkrtchyan, A.; Tadevosyan, V.; Zhamkochyan, S.; Malbrunot-Ettenauer, S.; Eyrich, W.; Hauenstein, F.; Zink, A.

    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.

  14. 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

  15. 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

  16. The last Glacial-Interglacial transition in Patagonia, Argentina: the stable isotope record of bulk sedimentary organic matter from Laguna Potrok Aike

    NASA Astrophysics Data System (ADS)

    PASADO Science Team Zhu, Jiayun; Lücke, Andreas; Wissel, Holger; Müller, Daniela; Mayr, Christoph; Ohlendorf, Christian; Zolitschka, Bernd

    2013-07-01

    An investigation of stable isotope (δ13CTOC and δ15NTN) and elemental parameters (TOC, TN contents and TOC/TN ratios) of bulk organic matter (<200 μm) from sediment cores recovered from the Patagonian lake Laguna Potrok Aike (Argentina) in the framework of the ICDP deep drilling project PASADO provided insights into past changes in lake primary productivity and environmental conditions in South Patagonia throughout the last Glacial-Interglacial transition. Stratigraphically constrained cluster analyses of all proxy parameters suggest four main phases. From ca 26,100 to 17,300 cal. years BP, lacustrine phytoplankton was presumably the predominant organic matter source in an aquatic environment with low primary productivity rates. At around 17,300 cal. years BP, abrupt and distinct shifts of isotopic and elemental values indicate that the lacustrine system underwent a rapid reorganization. Lake primary productivity (phytoplankton and aquatic macrophytes) shows higher levels albeit with large variations during most of the deglaciation until 13,000 cal. years BP. The main causes for this development can be seen in improved growing conditions for primary producers because of deglacial warming in combination with expedient availability of nutrients and likely calm wind conditions. After 13,000 cal. years BP, decreased δ13CTOC values, TOC, TN contents and TOC/TN ratios indicate that the lake approached a new state with reduced primary productivity probably induced by unfavourable growing conditions for primary producers like strengthened winds and reduced nutrient availability. The steady increase in δ15NTN values presumably suggests limitation of nitrate supply for growth of primary producers resulting from a nutrient shortage after the preceding phase with high productivity. Nitrate limitation and consequent decreased lacustrine primary productivity continued into the early Holocene (10,970-8400 cal. years BP) as reflected by isotopic and elemental values.

  17. 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.

  18. 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

  19. 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

  20. Tephrochronological dating of varved interglacial lake deposits from Piànico-Sèllere (Southern Alps, Italy) to around 400 ka

    NASA Astrophysics Data System (ADS)

    Brauer, Achim; Wulf, Sabine; Mangili, Clara; Moscariello, Andrea

    2007-01-01

    The sediment record from the Piànico palaeolake in the southern Alps is continuously varved, spans more than 15 500 years, and represents a key archive for interglacial climate variability at seasonal resolution. The stratigraphic position of the Piànico Interglacial has been controversial in the past. The identification of two volcanic ash layers and their microscopic analysis provides distinct marker layers for tephrochronological dating of these interglacial deposits. In addition to micro-facies analyses reconstructing depositional processes of both tephra layers within the lake environment, their mineralogical and geochemical composition has been determined through major-element electron probe micro-analysis on glass shards. Comparison with published tephra data traced the volcanic source regions of the Piànico tephras to the Campanian volcanic complex of Roccamonfina (Italy) and probably the Puy de Sancy volcano in the French Massif Central. Available dating of near-vent deposits from the Roccamonfina volcano provides a robust tephrochronological anchor point at around 400 ka for the Piànico Interglacial. These deposits correlate with marine oxygen isotope stage (MIS) 11 and thus are younger than Early to Middle Pleistocene previously suggested by K/Ar dating and older than the last interglacial as inferred from macrofloral remains and the geological setting. Copyright

  1. Polar Layers

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site] Context image for PIA03581 Polar Layers

    This image shows just one example of the bright and dark markings that appear during summer time. The marks are related to the polar layers. If you happen to see a wild-eyed guy sticking his tongue out at you, you'll know why this image qualifies for the old 'art' category of THEMIS releases.

    Image information: VIS instrument. Latitude 80.6S, Longitude 34.1E. 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.

  2. IRSL dating of Middle Pleistocene interglacial sediments from southern Quebec (Canada) using multiple and single grain aliquots

    USGS Publications Warehouse

    Balescu, S.; Lamothe, M.; Auclair, M.; Shilts, W.W.

    2001-01-01

    The IRSL dating of Middle Pleistocene interglacial fluvial sediments from Southern Quebec, correlated with oxygen isotopic stage 7, yields optical dates much younger than the expected geological age. Single grain IRSL measurements on alkali-feldspars, following the fadia protocol developed by Lamothe and Auclair (Earth and Planetary Science Letters, 171, 319-323, 1999), suggest that anomalous fading is the most probable cause for this severe age underestimation. The IRSL dates corrected for this anomalous fading are in better agreement with the expected ages. ?? 2000 Elsevier Science Ltd.

  3. 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

  4. 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.

  5. 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.

  6. 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

  7. Tracing Glacial-Interglacial Thermohaline Circulation with Nd isotopes: Progress and Precautions

    NASA Astrophysics Data System (ADS)

    Goldstein, S. L.; Hemming, S. R.; Piotrowski, A. M.; Rutberg, R. L.

    2002-12-01

    The variability of thermohaline circulation through glacial cycles is still an open issue because conventional paleoceanographic proxies disagree. Nd isotopes are potentially an effective tracer of ocean circulation because the end-member water masses are very different, with the Pacific having much higher values than the North Atlantic. Moreover, depth profiles show that Nd isotope ratios follow water masses. Nd is sequestered from deep water by Fe-Mn oxide precipitation, leaving a record that is extractable from deep sea cores. Unlike light stable isotopes or trace element ratios, Nd isotope ratios are not fractionated by biological processes. Over the few last years the Lamont group has focussed on testing the Nd isotope proxy through comparison of surface sediments and deep water, and examining variations through the last glacial period in deep sea cores with known chronologies. Samples that fail to give marine Sr isotope ratios are rejected. Finding samples that pass the Sr test is a challenge in some regions (for example, the Circum-Antarctic and North Atlantic). Experience shows that if a sample fails the Sr isotope test, then the entire core is likely to fail. Successful cores strongly indicate major changes in the export of NADW to the Southern Ocean over since the last interglacial on both long and millennial time-scales. The current data set can be summarized as follows. (1) Holocene coretop samples reflect present-day bottom water. (2) The conveyor was weak during MIS 2 and 4, and stronger during MIS 3. (3) Data from different depths in the Atlantic are not consistent with a shallowing of NADW and a constant flux during the LGM, but rather indicate weakening of the conveyor. (4) During Termination I, NADW export began to strengthen prior to the Bolling warming, and shows a general strengthening through the transition but a significant weakening during the Younger Dryas. (5) Dansgaard-Oeschger warmings during MIS 3 are accompanied by a strengthened

  8. 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.

  9. A terrestrial U/Th-dated stable isotope record of the Penultimate Interglacial

    NASA Astrophysics Data System (ADS)

    Spötl, Christoph; Scholz, Denis; Mangini, Augusto

    2008-12-01

    Here we present the first U-series dated stable oxygen isotope record in continental Europe that covers the entire tripartite Penultimate Interglacial, i.e. Marine Isotope Stages 7.5 to 7.1. This record was obtained from a U-rich stalagmite from Spannagel Cave in the Austrian Alps which is largely devoid of kinetic isotope fractionation effects which comprised previously studied flowstone from this site. Composed of dense, columnar calcite this speleothem apparently grew without significant interruption for ca. 50 ka, albeit at a very slow rate. The age model was established based on 23 individual U/Th TIMS dates using a combination of a Bayesian approach, which includes additional information using stratigraphic constraints, and the mixed-effect regression model. The resulting record shows three prominent maxima in δ 18O (MIS 7.5, 7.3 and 7.1) separated by a long earlier and a shorter later cold period (MIS 7.4 and 7.2, respectively). The mid points of the transitions into the three warm phases occurred at 240 ± 3, 215 ± 2 and 200 ± 3 ka and the MIS 7/6 transition was dated to 190 ± 3 ka. The timing of these climate transitions is supported by other samples from the same cave and agrees within analytical uncertainties with U/Th-dated evidence from corals, marine aragonitic sediments and submerged stalagmites, as well as with orbitally tuned deep-sea records. Good agreement was also found with new speleothem data from China as far as MIS 7.1 and 7.5 are concerned, whereas MIS 7.3 apparently started earlier and MIS 7.2 lasted longer than in the Alps. Comparing the European speleothem data with Antarctic ice cores reveals obvious differences in age (the latter suggesting an earlier start and a generally shorter duration of the three warm episodes). In essence, this study underscores the great potential of speleothems as accurate and precise chronometers of Pleistocene climate change and emphasizes the need for similar studies in other continents (including

  10. 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

  11. 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

  12. 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

  13. Chronology and dynamics of the Amundsen Gulf Ice Stream in Arctic Canada during the last glacial-interglacial transition

    NASA Astrophysics Data System (ADS)

    Lakeman, T. R.; MacLean, B.; Blasco, S.; Bennett, R.; Hughes Clarke, J. E.

    2012-04-01

    influence of the Mackenzie and other fluvial sediment discharge on the seabed over the last 13,000 cal yr BP. The deglacial history of Amundsen Gulf under ameliorating climate conditions of the last ~19,000 cal yr BP provides important constraints on the variables that occasioned the demise of the northwest Laurentide Ice Sheet, such as sea level change, paleoclimate, and regional ice sheet dynamics. Understanding the complex interplay among these variables during the last deglaciation will bear on current model projections of the dynamics of the Greenland and Antarctic ice sheets. In addition, quantifying past iceberg fluxes to the Arctic Ocean has implications for assessing the origin of deep ice scours in the Arctic Ocean Basin and the nature of rapid climate changes at the last glacial-interglacial transition.

  14. 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

  15. Cilia organize ependymal planar polarity

    PubMed Central

    Mirzadeh, Zaman; Han, Young-Goo; Soriano-Navarro, Mario; García-Verdugo, Jose Manuel; Alvarez-Buylla, Arturo

    2010-01-01

    Multi-ciliated epithelial cells, called ependymal cells, line the ventricles in the adult brain. Most ependymal cells are born prenatally and are derived from radial glia. Ependymal cells have a remarkable planar polarization that determines orientation of ciliary beating and propulsion of cerebrospinal fluid (CSF). Disruption of ependymal ciliary beating, by injury or disease, results in aberrant CSF circulation and hydrocephalus, a common disorder of the central nervous system. Very little is known about the mechanisms guiding ependymal planar polarity and whether this organization is acquired during ependymal cell development or is already present in radial glia. Here we show that basal bodies in ependymal cells in the lateral ventricle walls of adult mice are polarized in two ways: i) rotational; angle of individual basal bodies with respect to their long axis and ii) translational; the position of basal bodies on the apical surface of the cell. Conditional ablation of motile cilia disrupted rotational orientation, but translational polarity was largely preserved. In contrast, translational polarity was dramatically affected when radial glial primary cilia were ablated earlier in development. Remarkably, radial glia in the embryo have a translational polarity that predicts the orientation of mature ependymal cells. These results suggest that ependymal planar cell polarity is a multi-step process initially organized by primary cilia in radial glia and then refined by motile cilia in ependymal cells. PMID:20164345

  16. Impact of ice sheet meltwater fluxes on the climate evolution at the onset of the Last Interglacial

    NASA Astrophysics Data System (ADS)

    Goelzer, Heiko; Huybrechts, Philippe; Loutre, Marie-France; Fichefet, Thierry

    2016-08-01

    Large climate perturbations occurred during the transition between the penultimate glacial period and the Last Interglacial (Termination II), when the ice sheets retreated from their glacial configuration. Here we investigate the impact of ice sheet changes and associated freshwater fluxes on the climate evolution at the onset of the Last Interglacial. The period from 135 to 120 kyr BP is simulated with the Earth system model of intermediate complexity LOVECLIM v.1.3 with prescribed evolution of the Antarctic ice sheet, the Greenland ice sheet, and the other Northern Hemisphere ice sheets. Variations in meltwater fluxes from the Northern Hemisphere ice sheets lead to North Atlantic temperature changes and modifications of the strength of the Atlantic meridional overturning circulation. By means of the interhemispheric see-saw effect, variations in the Atlantic meridional overturning circulation also give rise to temperature changes in the Southern Hemisphere, which are additionally modulated by the direct impact of Antarctic meltwater fluxes into the Southern Ocean. Freshwater fluxes from the melting Antarctic ice sheet lead to a millennial timescale oceanic cold event in the Southern Ocean with expanded sea ice as evidenced in some ocean sediment cores, which may be used to constrain the timing of ice sheet retreat.

  17. 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.

  18. Correlation and interpretation of paleosols and loess across European Russia and Asia over the last interglacial-glacial cycle

    NASA Astrophysics Data System (ADS)

    Rutter, Nathaniel W.; Rokosh, Dean; Evans, Michael E.; Little, Edward C.; Chlachula, Jiri; Velichko, Andrei

    2003-07-01

    Loess-paleosol sequences of the last interglacial-glacial cycle are correlated from European Russia to central Siberia and the Chinese Loess Plateau. During cold periods represented by marine oxygen isotope stages (OIS) 2 and 4, loess deposition dominated in the Russian Plain and the Loess Plateau. In central Siberia, loess deposition took place also, but five to seven thin, weakly developed paleosols are identified in both stages. OIS 3, in the Chinese Loess Plateau near Yangchang, consists of a loess bed that is flanked by two weakly developed paleosols. At Kurtak, Siberia, OIS 3 is represented by two distinct, stacked paleosols with no loess bed separating the paleosols. In the Russian Plain, OIS 3 consists of a single, possibly welded paleosol, representing upper and lower stage-3 climates. Brunisols and Chernozems dominate the profiles in China and Siberia, whereas Regosols, Luvisols, and Chernozems are evident in the northern and southern Russian Plain, respectively. OIS 5 is represented in China and the Russian Plain by pedo complexes in a series of welded soils, whereas in contrast, the Kurtak site consists of six paleosols with interbedded loess. The paleosols consist largely of Brunisols and Chernozems. Although the three areas examined have different climates, geographical settings, and loess source areas, they all had similar climate changes during the last interglacial-glacial cycle.

  19. Interglacial microrefugia and diversification of a cactus species complex: phylogeography and palaeodistributional reconstructions for Pilosocereus aurisetus and allies.

    PubMed

    Bonatelli, Isabel A S; Perez, Manolo F; Peterson, A Townsend; Taylor, Nigel P; Zappi, Daniela C; Machado, Marlon C; Koch, Ingrid; Pires, Adriana H C; Moraes, Evandro M

    2014-06-01

    The role of Pleistocene climate changes in promoting evolutionary diversification in global biota is well documented, but the great majority of data regarding this subject come from North America and Europe, which were greatly affected by glaciation. The effects of Pleistocene changes on cold- and/or dry-adapted species in tropical areas where glaciers were not present remain sparsely investigated. Many such species are restricted to small areas surrounded by unfavourable habitats, which may represent potential interglacial microrefugia. Here, we analysed the phylogeographic structure and diversification history of seven cactus species in the Pilosocereus aurisetus complex that are restricted to rocky areas with high diversity and endemism within the Neotropical savannas of eastern South America. We combined palaeodistributional estimates with standard phylogeographic approaches based on two chloroplast DNA regions (trnT-trnL and trnS-trnG), exon 1 of the nuclear gene PhyC and 10 nuclear microsatellite loci. Our analyses revealed a phylogeographic history marked by multiple levels of distributional fragmentation, isolation leading to allopatric differentiation and secondary contact among divergent lineages within the complex. Diversification and demographic events appear to have been affected by the Quaternary climatic cycles as a result of isolation in multiple patches of xerophytic vegetation. These small patches presently harbouring P. aurisetus populations seem to operate as microrefugia, both at present and during Pleistocene interglacial periods; the role of such microrefugia should be explored and analysed in greater detail.

  20. A 3D-RISM-SCF method with dual solvent boxes for a highly polarized system: application to 1,6-anhydrosugar formation reaction of phenyl α- and β-D-glucosides under basic conditions.

    PubMed

    Aono, Shinji; Hosoya, Takashi; Sakaki, Shigeyoshi

    2013-05-01

    One of the difficulties in application of the usual reference interaction site model self-consistent field (RISM-SCF) method to a highly polarized and bulky system arises from the approximate evaluation of electrostatic potential (ESP) with pure point charges. To improve this ESP evaluation, the ESP near a solute is directly calculated with a solute electronic wavefunction, that distant from a solute is approximately calculated with solute point charges, and they are connected with a switching function. To evaluate the fine solvation structure near the solute by incorporating the long-range solute-solvent Coulombic interaction with low computational cost, we introduced the dual solvent box protocol; one small box with the fine spacing is employed for the first and the second solvation shells and the other large box with the normal spacing is employed for long-range solute-solvent interaction. The levoglucosan formation from phenyl α- and β-d-glucosides under basic conditions is successfully inspected by this 3D-RISM-SCF method at the MP2 and SCS-MP2 levels, though the 1D-RISM-SCF could not be applied to this reaction due to the presence of highly polarized and bulky species. This 3D-RISM-SCF calculation reproduces the experimentally reported higher reactivity of the β-anomer. The 3D-RISM-SCF-calculated activation free energy for the β-anomer is closer to the experimental value than the PCM-calculated one. Interestingly, the solvation effect increases the difference in reactivity between these two anomers. The reason is successfully elucidated with 3D-RISM-SCF-calculated microscopic solvation structure and decomposition analysis of solute-solvent interaction.

  1. 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.

  2. 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.

  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. Neuronal polarization in the developing cerebral cortex.

    PubMed

    Sakakibara, Akira; Hatanaka, Yumiko

    2015-01-01

    Cortical neurons consist of excitatory projection neurons and inhibitory GABAergic interneurons, whose connections construct highly organized neuronal circuits that control higher order information processing. Recent progress in live imaging has allowed us to examine how these neurons differentiate during development in vivo or in in vivo-like conditions. These analyses have revealed how the initial steps of polarization, in which neurons establish an axon, occur. Interestingly, both excitatory and inhibitory cortical neurons establish neuronal polarity de novo by undergoing a multipolar stage reminiscent of the manner in which polarity formation occurs in hippocampal neurons in dissociated culture. In this review, we focus on polarity formation in cortical neurons and describe their typical morphology and dynamic behavior during the polarization period. We also discuss cellular and molecular mechanisms underlying polarization, with reference to polarity formation in dissociated hippocampal neurons in vitro.

  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. 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

  7. 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

  8. Polar convection patterns under quiet conditions

    NASA Astrophysics Data System (ADS)

    Barbosa, D. D.

    1985-10-01

    Convection electric field patterns at high latitudes appropriate to periods of low geomagnetic activity are presented. The postulate that the global Joule dissipation rate is a minimum is employed to derive characteristic field distributions for the situation when ring current ohmic losses are negligible and the auroral oval enhancement of height-integrated Hall conductivity is small. The fast Fourier transform is introduced to compute Fourier coefficients of discrete field-aligned current data, and the method is shown to be quite useful in this context as a least squares fitting routine. The model calculations demonstrate the approach of the high-latitude ionosphere toward the perfect shielding configuration predicted by the theory for quiet times.

  9. 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

  10. 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

  11. Glacial-interglacial continental temperature variability in the Beringian Arctic: the MBT/CBT record of Lake El'gygytgyn

    NASA Astrophysics Data System (ADS)

    Castaneda, I. S.; Finkelstein, D. B.; Phu, V.; Brigham-Grette, J.; Wilkie, K. M.; D'anjou, R. M.; Wei, J. H.; Urann, B. M.

    2012-12-01

    In 2009, deep drilling at El'gygytgyn Crater Lake (Far East Russian Arctic) recovered sediments covering the past 3.6 Ma. These sediments provide the first terrestrial Arctic paleoclimate record spanning the Pliocene-Pleistocene from the largest and oldest unglaciated Arctic lake basin. Lake El'gygytgyn sediments thus offer a unique opportunity to examine high-latitude climate variability beyond the 100 Ka interval captured by Greenland ice core records. In this study we utilize an organic geochemical paleothermometer, the MBT/CBT Index based on branched glycerol dialkyl glycerol tetraethers (GDGTs; Weijers et al., 2007), to examine continental temperature variability during several key time intervals of interest. In particular, we focus on Marine Isotope Stages (MIS) 1-6, MIS 9-11, MIS 31 and during the earliest formation of lacustrine sediments in the impact basin in the middle Pliocene. Previous work on Lake El'gygytgyn sediments has identified MIS 11c and MIS 31 as "super" interglacials, which were characterized by significantly warmer temperatures than at present largely based on pollen spectra and modern analog analysis (Melles et al., 2012). Our results show that relative changes in MBT/CBT-derived temperatures display similar overall patterns of glacial-interglacial climate variability noted in temperature reconstructions from Lake El'gygytgyn (Melles et al., 2012) as well as Greenland ice core records, North Atlantic sea surface temperature records (e.g. Lawrence et al., 2010), and the global benthic δ18O stack (Lisiecki and Raymo, 2005). We demonstrate that MBT/CBT is a sensitive proxy for recording temperature variability at Lake El'gygytgyn. Interestingly, while pronounced warming is noted during interglacials, a number of abrupt and short-lived temperature reversals are also observed within these intervals, such as during MIS 5a and MIS 5e. Overall, we find that MBT/CBT temperatures closely track changes in local summer insolation at 67°N, in

  12. 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.

  13. 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.

  14. Linearly polarized fiber amplifier

    SciTech Connect

    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.

  15. 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.

  16. 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.

  17. 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

  18. A Detailed Record of Changing Surface Water Conditions From Sediments Deposited During Marine Isotope Stage 11, ODP Site 980, Northeast Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    Arvin, T. A.; Cullen, J. L.; Oppo, D. W.; McManus, J. F.

    2004-05-01

    Many recent paleoceanographic studies have focused on using high sedimentation rate deep-sea sediment sections that have produced records of abrupt climate variability operating at sub-orbital time scales. This is particularly true in the North Atlantic where proxies of changing surface water conditions from high quality sediment records have repeatedly demonstrated that millennial-scale climate change has been the rule rather than the exception over the past 500 kyr, during both glacial and interglacial intervals. Abrupt climate change during warm interglacials is an area of special interest as it may relate more directly to an understanding of recent and future climate change. With this in mind we have focused our efforts on documenting millennial-scale climate change from sediments deposited at ODP Site 980, northeast Atlantic Ocean during Marine Isotope Stage (MIS) 11. We have used unsplit, whole sample >150 micron size fractions from over 200 sediment samples to record changes in the number lithic grains per gram sediment to measure changes in the input of Ice-Rafted Debris (IRD). We then compare our new IRD record to previously generated records of changing surface water conditions during MIS11: variations in oxygen isotopic composition of the surface dwelling planktic foraminifer species N. pachyderma, right coiling and changes in the relative abundance of the polar species N. pachyderma, left coiling. Our MIS11 results are then compared to compatible records from MIS5e and the Holocene. Our detailed IRD record from around 418 kya to 382 kya reveals a remarkable lack of even trace amounts IRD input into sediments at ODP Site 980. IRD concentration abruptly drops and remains 0 to trace amounts per gram as soon as benthic delta O-18 values fall to and remain at < 3.5 per mil at the onset of MIS11. Only three very small amplitude IRD events are observed over the entire 35 kyr interval. The earliest 8 kyr of MIS11 is completely devoid of any IRD, despite the

  19. 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

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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

  5. 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.

  6. Interglacial responses of the southern Greenland ice sheet over the last 430,000 years determined using particle-size specific magnetic and isotopic tracers

    NASA Astrophysics Data System (ADS)

    Hatfield, Robert G.; Reyes, Alberto V.; Stoner, Joseph S.; Carlson, Anders E.; Beard, Brian L.; Winsor, Kelsey; Welke, Bethany

    2016-11-01

    The past behavior of the Greenland ice sheet can provide important insight into climatic thresholds that may initiate and drive major ice-sheet retreat. Particle-size-specific magnetic and Sr-Nd-Pb isotope records from Eirik Ridge sediments south of Greenland track southern Greenland ice sheet (sGIS) erosional signatures over the past ∼430 ka by discriminating changes in sediment source and transport over the Eirik Ridge. Ground-truthed magnetic and isotopic compositions of subglacial silt from south Greenland's Precambrian bedrock terranes constrain independent magnetic and isotopic estimates of Eirik Ridge silt provenance, which in turn indicate that the southern Greenland ice sheet (sGIS) retreated within its present margin during three of the four previous interglaciations over the past ∼430 ka. Retreat of the sGIS was extensive during the Marine Isotope Stage (MIS) 5e, 9, and 11 interglaciations, continuing unabated despite declining insolation during MIS 5e and 9, with near complete deglaciation in MIS 11. Retreat of the sGIS during MIS 7 was minimal, notwithstanding strong insolation forcing, while Holocene retreat slowed shortly after peak insolation. The reconstruction of sGIS retreat during the last five deglacial and interglacial periods suggests that a threshold for extensive sGIS retreat exists between the insolation and CO2 states of the Holocene and the MIS 5e and 9 interglaciations, with CO2 exerting a stronger control on sGIS retreat than insolation. Our results also suggest that the extent and stability of the sGIS in the Holocene is anomalous in the context of late-Quaternary interglaciations.

  7. 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.

  8. 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.

  9. Effects of climate change on polar bears.

    PubMed

    Wiig, Øystein; Aars, Jon; Born, Erik W

    2008-01-01

    In this article, we review the effects on polar bears of global warming that have already been observed, and try to evaluate what may happen to the polar bears in the future. Many researchers have predicted a wide range of impacts of climate change on polar bear demography and conditions. A predicted major reduction in sea ice habitat will reduce the availability of ice associated seals, the main prey of polar bears, and a loss and fragmentation of polar bear habitat will ultimately lead to large future reductions in most subpopulations. It is likely that polar bears will be lost from many areas where they are common today and also that the total population will change into a few more distinctly isolated populations.

  10. 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.

  11. Polarized Electron Source Developments

    SciTech Connect

    Charles K. Sinclair

    1990-02-23

    Presently, only two methods of producing beams of polarized electrons for injection into linear accelerators are in use. Each of these methods uses optical pumping by circularly polarized light to produce electron polarization. In one case, electron polarization is established in metastable helium atoms, while in the other case, the polarized electrons are produced in the conduction band of appropriate semiconductors. The polarized electrons are liberated from the helium metastable by chemi-ionization, and from the semiconductors by lowering the work function at the surface of the material. Developments with each of these sources since the 1988 Spin Physics Conference are reviewed, and the prospects for further improvements discussed.

  12. The period from the Last Interglacial to the Last Glacial Maximum (MIS 5 - 2) in different archives of southern Italy

    NASA Astrophysics Data System (ADS)

    Sauer, Daniela; Wagner, Stephen; Al-Sharif, Riyad; Brückner, Helmut; Scarciglia, Fabio; Mastronuzzi, Giuseppe; Stahr, Karl

    2010-05-01

    Sediment cores from S Italy provide excellent archives of Late Pleistocene climate and vegetation changes, particularly from the Lago Grande di Monticchio (Allen et al., 2000; Brauer et al., 2007), the crater lakes of the central West coast of Italy, Valle di Castiglione, Lagaccione, Lago di Vico, Stracciacappa (Follieri et al., 1998) and the marine core GNS84-C106 in the Gulf of Salerno (Di Donato et al., 2008). These records show that woody Mediterranean vegetation covered the region during most of the Last Interglacial (from 129-127 ka BP until 115-116 ka BP). In the last phase of the interglacial (from 115-116 ka BP until about 110 ka BP), the forest composition changed, showing an increase in Abies and Alnus and a decrease in Mediterranean taxa. The interglacial was terminated by the Melisey I Stadial, during which grasses and Betula predominated. Forests spread again during St. Germain I, but they consisted mainly of Fagus, Abies and various deciduous trees. A steppe phase (Melisey II) followed, in which Chenopodiaceae prevailed, before St. Germain II set in, with forests dominated by Abies, Ulmus and Carpinus. From the end of St. Germain II until the Lateglacial, steppe, composed of Artemisia, Gramineae and Chenopodiaceae, predominated, with week expansions of trees (mainly Pinus and Juniperus) during several periods. What information can be obtained from terrestrial geo-archives for the same region and time? Sea level highstands, corresponding to interglacial and interstadial periods, created marine terraces along the coasts of S Italy. We are currently carrying out a geomorphological, sedimentological and pedological study on a flight of 11 uplifted marine terraces in the central Gulf of Taranto, the lowermost of them falling into the time span of interest. The terraces generally comprise a gravel body, deposited in a littoral environment, covered by a layer of fine sediments of varying thickness. The latter were deposited when the terrace was still close

  13. 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.

  14. 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.

  15. 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)

  16. 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.

  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. 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

  19. 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…

  20. 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…

  1. 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.

  2. 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

  3. 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.

  4. 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.

  5. 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

  6. No change in the neodymium isotope composition of deep water exported from the North Atlantic on glacial-interglacial timescales

    NASA Astrophysics Data System (ADS)

    Vance, D.; Foster, G.

    2005-12-01

    Ocean circulation controls climate in two key ways: it transports heat and it determines the rate at which the carbon-laden deep ocean equilibrates with the atmosphere. In the Atlantic the meridional overturning circulation is a particularly important mechanism for the inter-hemispheric transport of heat. Recent studies1 have used neodymium (Nd) isotopes in the Southern Ocean to confirm a weakening of southward deep water export from the North Atlantic, and by implication a diminution in northward heat transport at the surface, during glacial periods. The timing of the Nd shift also suggests that such weakening post-dates both ice-sheet growth and major re-organisation of carbon reservoirs at glaical-interglacial boundaries. The use of Nd isotopes in the Southern Ocean to track changes in deep water export from the North Atlantic requires a knowledge of the secular evolution in the North Atlantic source itself. Here we report results of un-precedently high resolution (20 kyr) Nd isotope analyses of Fe-Mn crusts, obtained by laser ablation MC-ICPMS. T