Last Interglacial climate and sea-level evolution from a coupled ice sheet-climate model

NASA Astrophysics Data System (ADS)

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

2016-12-01

As the most recent warm period in Earth's history with a sea-level stand higher than present, the Last Interglacial (LIG, ˜ 130 to 115 kyr BP) is often considered a prime example to study the impact of a warmer climate on the two polar ice sheets remaining today. Here we simulate the Last Interglacial climate, ice sheet, and sea-level evolution with the Earth system model of intermediate complexity LOVECLIM v.1.3, which includes dynamic and fully coupled components representing the atmosphere, the ocean and sea ice, the terrestrial biosphere, and the Greenland and Antarctic ice sheets. In this setup, sea-level evolution and climate-ice sheet interactions are modelled in a consistent framework.Surface mass balance change governed by changes in surface meltwater runoff is the dominant forcing for the Greenland ice sheet, which shows a peak sea-level contribution of 1.4 m at 123 kyr BP in the reference experiment. Our results indicate that ice sheet-climate feedbacks play an important role to amplify climate and sea-level changes in the Northern Hemisphere. The sensitivity of the Greenland ice sheet to surface temperature changes considerably increases when interactive albedo changes are considered. Southern Hemisphere polar and sub-polar ocean warming is limited throughout the Last Interglacial, and surface and sub-shelf melting exerts only a minor control on the Antarctic sea-level contribution with a peak of 4.4 m at 125 kyr BP. Retreat of the Antarctic ice sheet at the onset of the LIG is mainly forced by rising sea level and to a lesser extent by reduced ice shelf viscosity as the surface temperature increases. Global sea level shows a peak of 5.3 m at 124.5 kyr BP, which includes a minor contribution of 0.35 m from oceanic thermal expansion. Neither the individual contributions nor the total modelled sea-level stand show fast multi-millennial timescale variations as indicated by some reconstructions.

(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.

Deglacial Meltwater Pulse Recorded in Last Interglacial Mollusk Shells from Bermuda

NASA Astrophysics Data System (ADS)

Winkelstern, I. Z.; Rowe, M. P.; Lohmann, K. C.; Defliese, W.; Petersen, S. V.; Brewer, A. W.

2016-12-01

Iceberg scours as far south as the Florida Strait and the presence of ice rafted debris in sediments from the Bermuda Rise indicate that during the last glacial phase icebergs traveled quite far south during episodes of excessive iceberg discharge from the Laurentide Ice Sheet (Heinrich Events). We present evidence that the effects of these events extended southward into the subtropics during the previous deglaciation (Termination-II), potentially aligned with Heinrich Event 11, and that meltwater reached Bermuda. Temperatures 10° C colder and seawater δ18O values 2 ‰ more negative than modern are derived from Last Interglacial Cittarium pica shells from Grape Bay, Bermuda using the clumped isotope paleothermometer. In contrast, Last Interglacial shells from Rocky Bay record temperatures only slightly colder and seawater δ18O values similar to modern, potentially representing more typical Last Interglacial conditions in Bermuda outside of a meltwater event. The cold ocean conditions observed illustrate extreme sensitivity of Bermudian climate to rapid climate and ocean circulation changes. They also provide further evidence for routine meltwater transport in the North Atlantic to near-equatorial latitudes during deglaciation.

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

Insights into Penultimate Interglacial-Glacial Climate Change on Vegetation History at Lake Van, Turkey

NASA Astrophysics Data System (ADS)

Pickarski, N.; Litt, T.

2017-12-01

A new detailed pollen and oxygen isotope record of the penultimate interglacial-glacial cycle (ca. 250-129 ka; MIS 7-6), has been generated from the sediment core at Lake Van, Turkey. The integration of all available proxies (pollen, microscopic charcoal, δ18Obulk, and XRF) shows three temperate intervals of high effective soil moisture availability. This is evidenced by the predominance of oak steppe-forested landscapes similar to the present interglacial vegetation in this sensitive semiarid region. The wettest/warmest stage, as indicated by highest temperate tree percentages, can be broadly correlated with MIS 7c, while the amplitude of the tree population maximum during the oldest penultimate interglacial (MIS 7e) appears to be reduced due to warm but drier climatic conditions. A detailed comparison of the penultimate interglacial complex (MIS 7) to the last interglacial (MIS 5e) and the current interglacial (MIS 1) provides a vivid illustration of possible differences in the successive climatic cycles. Intervening periods of treeless vegetation (MIS 7d, 7a) were predominated by steppe elements. The occurrence of Artemisia and Chenopodiaceae during MIS 7d indicates very dry and cold climatic conditions, while higher temperate tree percentages (mainly deciduous Quercus) points to relatively humid and mild conditions throughout MIS 7b. Despite the general dominance of dry and cold desert-steppe vegetation during the penultimate glacial (MIS 6), this period can be divided into two parts: an early stage (ca. 193-157 ka) with higher oscillations in tree percentages and a later stage (ca. 157-131 ka) with lower tree percentages and subdued oscillations. Furthermore, we are able to identify the MIS 6e event (ca. 179-159 ka), which reveals clear climate variability due to rapid alternation in the vegetation cover. In comparison with long European pollen archives, speleothem isotope records from the Near East, and global climate parameters, the new high

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.

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.

Polar oceans in a changing climate.

PubMed

Barnes, David K A; Tarling, Geraint A

2017-06-05

Most of Earth's surface is blue or white, but how much of each would depend on the time of observation. Our planet has been through phases of snowball (all frozen), greenhouse (all liquid seas) and icehouse (frozen and liquid). Even during current icehouse conditions, the extent of ice versus water has changed considerably between ice ages and interglacial periods. Water has been vital for life on Earth and has driven and been influenced by transitions between greenhouse and icehouse. However, neither the possession of water nor having liquid and frozen seas are unique to Earth (Figure 1). Frozen water oceans on the moons Enceladus and Europa (and possibly others) and the liquid and frozen hydrocarbon oceans on Titan probably represent the most likely areas to find extraterrestrial life. We know very little about life in Earth's polar oceans, yet they are the engine of the thermohaline 'conveyor-belt', driving global circulation of heat, oxygen, carbon and nutrients as well as setting sea level through change in ice-mass balance. In regions of polar seas, where surface water is particularly cold and dense, it sinks to generate a tropic-ward flow on the ocean floor of the Pacific, Atlantic and Indian Oceans. Cold water holds more gas, so this sinking water exports O 2 and nutrients, thereby supporting life in the deep sea, as well as soaking up CO 2 from the atmosphere. Water from mid-depths at lower latitudes flows in to replace the sinking polar surface water. This brings heat. The poles are cold because they receive the least energy from the sun, and this extreme light climate varies on many different time scales. To us, the current warm, interglacial conditions seem normal, yet such phases have represented only ∼10% of Homo sapiens' existence. Variations in Earth's orbit (so called 'Milankovitch cycles') have driven cyclical alternation of glaciations (ice ages) and warmer interglacials. Despite this, Earth's polar regions have been our planet's most

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, Craig 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 C4 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.

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.

Last interglacial temperature seasonality reconstructed from tropical Atlantic corals

NASA Astrophysics Data System (ADS)

Felis, T.; Brocas, W.; Obert, J. C.; Gierz, P.; Lohmann, G.; Scholz, D.; Kölling, M.; Pfeiffer, M.; Scheffers, S. R.

2016-12-01

Reconstructions of last interglacial ( 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. However, the seasonal temperature changes of the tropical ocean are not well known for the last interglacial period. Here we present well preserved fossil corals (Diploria strigosa) recovered from the southern Caribbean island of Bonaire. These corals have been precisely dated by the 230Th/U-method to between 130 and 118 ka ago. Annual banding of the coral skeleton enabled construction of time windows of monthly resolved Sr/Ca temperature proxy records. Our eight coral records of up to 37 years in length cover a total of 105 years within the last interglacial period. From these coral records, sea surface temperature (SST) seasonality 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 last interglacial (120 - 118 ka). However, within the mid-last interglacial, 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 (COSMOS) and are consistent with the evolving amplitude of orbitally induced changes in seasonality of insolation throughout the last interglacial, irrespective of wider climatic instabilities that characterised this period, e.g. at 118 ka ago. The climate model simulations suggest that the SST seasonality changes documented in our last interglacial 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-last interglacial is caused primarily by summer warming. Furthermore, a 124 ka old coral documents evidence of decadal SST variability in the tropical North Atlantic during the last interglacial, akin to that

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

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…

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

NASA Astrophysics Data System (ADS)

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

2015-04-01

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

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.

Diachronous high-latitude North Atlantic temperature evolution across the last interglaciation

NASA Astrophysics Data System (ADS)

Carlson, A. E.; He, F.; Clark, P. U.

2017-12-01

A direct response of Northern Hemisphere temperatures to last interglacial boreal summer insolation forcing and atmospheric carbon dioxide concentration would predict early interglacial warmth followed by a gradual cooling trend across the last interglaciation (128-116 ka). In contrast, some Labrador and Greenland-Iceland-Norwegian (GIN) sea surface temperature (SST) records show relatively cool early last-interglacial SSTs followed by warming in the latter part of the interglaciation. This phenomenon has sometimes been attributed to meltwater forcing from continued retreat of the Greenland ice sheet through the last interglaciation that suppressed North Atlantic overturning circulation, in agreement with proxy records. Here we investigate this observation with the first fully-coupled transient general circulation model simulation of the last interglacial period using CCSM3. Termination II deglacial meltwater forcing is stopped at 129 ka and the subsequent simulation is forced by changing orbital parameters and atmospheric greenhouse gases. We find that Labrador and GIN SSTs remain relatively cool followed by warming to peak interglacial temperatures after 124 ka. We show that this delayed warming is due to reduced convection in the GIN sea, despite a cessation of meltwater forcing at 129 ka, with convection onset at 124 ka and attendant sea-ice retreat in response to orbital- and greenhouse gas-forcing alone. Our results demonstrate that delayed high-latitude North Atlantic SST warming during the last interglaciation does not necessitate meltwater forcing from the Greenland ice sheet, rectifying the apparent disconnect between a small meltwater forcing (<2.5 m of sea-level rise over 8 ka, or <0.004 Sverdrups into the Labrador and GIN seas) and a relatively large North Atlantic overturning response.

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

How Are MIS-5e And MIS-11 Different From Other Interglacials And the Future?

NASA Astrophysics Data System (ADS)

Yin, Q.; Berger, A.

2017-12-01

MIS-5e and MIS-11 appear in many proxy records as the warmest interglacials of the last million years although their astronomical configurations are very different. To investigate how they are different from other interglacials and between themselves, the climate of nine interglacials of the past 800,000 years has been simulated using both snapshot and transient experiments. These simulations allow to investigate the relative contributions of insolation and CO2 to the intensity and duration of each interglacial as well as the differences and similarities between the interglacials. The transient simulations which cover a large range of precession, obliquity and eccentricity allow to investigate the response of different climate variables and different regions to the three astronomical parameters. My presentation will focus on the characteristics of the climate forcing and response of MIS-5e and MIS-11 in comparison with the other intergalcials. Their duration and intensity at global and regional scales will be shown and the causes will be discussed. Unique features in astronomical forcing as well as in regional climate response are found in MIS-5e and MIS-11, which might help to understand why they appear to be among the warmest interglacials. The model results also show that the warm interval of MIS-11 is the longest, confirming its long duration as found in many proxy records. The long duration of MIS-11 is related to a particular combination of eccentricity, obliquity and precession as well as to its long-lasting high CO2 concentration. The differences between the seasonal behaviour of the past interglacials highlight the importance of seasonal climate reconstruction and therefore the necessity to obtain seasonal proxies. The simulated climate of MIS-5e and MIS-11 will also be compared with the climate of today and of the future to investigate the differences and similarities between the past warm conditions and the projected future warming. Part of the results

Similarity of vegetation dynamics during interglacial periods

PubMed Central

Cheddadi, Rachid; de Beaulieu, Jacques-Louis; Jouzel, Jean; Andrieu-Ponel, Valérie; Laurent, Jeanne-Marine; Reille, Maurice; Raynaud, Dominique; Bar-Hen, Avner

2005-01-01

The Velay sequence (France) provides a unique, continuous, palynological record spanning the last four climatic cycles. A pollen-based reconstruction of temperature and precipitation displays marked climatic cycles. An analysis of the climate and vegetation changes during the interglacial periods reveals comparable features and identical major vegetation successions. Although Marine Isotope Stage (MIS) 11.3 and the Holocene had similar earth precessional variations, their correspondence in terms of vegetation dynamics is low. MIS 9.5, 7.5, and especially 5.5 display closer correlation to the Holocene than MIS 11.3. Ecological factors, such as the distribution and composition of glacial refugia or postglacial migration patterns, may explain these discrepancies. Comparison of ecosystem dynamics during the past five interglacials suggests that vegetation development in the current interglacial has no analogue from the past 500,000 years. PMID:16162676

Atlantic water heat transfer through the Arctic Gateway (Fram Strait) during the Last Interglacial

NASA Astrophysics Data System (ADS)

Zhuravleva, Anastasia; Bauch, Henning A.; Spielhagen, Robert F.

2017-10-01

The Last Interglacial in the Arctic region is often described as a time with warmer conditions and significantly less summer sea ice than today. The role of Atlantic water (AW) as the main oceanic heat flux agent into the Arctic Ocean remains, however, unclear. Using high-resolution stable isotope and faunal records from the only deep Arctic Gateway, the Fram Strait, we note for the upper water column a diminished influence of AW and generally colder-than-Holocene surface ocean conditions. After the main Saalian deglaciation had terminated, a first intensification of northward-advected AW happened ( 124 ka). However, an intermittent sea surface cooling, triggered by meltwater release at 122 ka, caused a regional delay in the further development towards peak interglacial conditions. Maximum AW heat advection occurred during late MIS 5e (118.5-116 ka) and interrupted a longer-term cooling trend at the sea surface that started from about 120 ka on. Such a late occurrence of the major AW-derived near-surface warming in the Fram Strait - this is in stark contrast to an early warm peak in the Holocene - compares well in time with upstream records from the Norwegian Sea, altogether implying a coherent development of south-to-north ocean heat transfer through the eastern Nordic Seas and into the high Arctic during the Last Interglacial.

Vegetation and climate variability during the Last Interglacial evidenced in the pollen record from Lake Baikal

NASA Astrophysics Data System (ADS)

Granoszewski, W.; Demske, D.; Nita, M.; Heumann, G.; Andreev, A. A.

2005-04-01

A pollen record from the core sediments collected in the northern part of Lake Baikal represents the latest stage of the Taz (Saale) Glaciation, Kazantsevo (Eemian) Interglacial (namely the Last Interglacial), and the earliest stage of the Zyryanka (Weichselian) Glaciation. According to the palaeomagnetic-based age model applied to the core, the Last Interglacial in the Lake Baikal record lasted about 10.6 ky from 128 to 117.4 ky BP, being more or less synchronous with the Marine Isotope Stage 5e. The reconstructed changes in the south Siberian vegetation and climate are summarised as follows: a major spread of shrub alder ( Alnus fruticosa) and shrub birches ( Betula sect. Nanae/ Fruticosae) in the study area was a characteristic feature during the late glacial phase of the Taz Glaciation. Boreal trees e.g. spruce ( Picea obovata) and birch ( Betula sect. Albae) started to play an important role in the regional vegetation with the onset of the interglacial conditions. Optimal conditions for Abies sibirica- P. obovata taiga development occurred ca. 126.3 ky BP. The maximum spread of birch forest-steppe communities took place at the low altitudes ca. 126.5-125.5 ky BP and Pinus sylvestris started to form forests in the northern Baikal area after ca. 124.4 ky BP. Re-expansion of the steppe communities, as well as shrubby alder and willow communities and the disappearance of forest vegetation occurred at about 117.4 ky BP, suggesting the end of the interglacial succession. The changes in the pollen assemblages recorded in the sediments from northern Baikal point to a certain instability of the interglacial climate. Three phases of climate deterioration have been distinguished: 126-125.5, 121.5-120, and 119.5-119 ky BP. The penultimate cooling signal may be correlated with the cool oscillation recorded in European pollen records. However, such far distant correlation requires more careful investigation.

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.

Arctic Ocean sea ice cover during the penultimate glacial and the last interglacial.

PubMed

Stein, Ruediger; Fahl, Kirsten; Gierz, Paul; Niessen, Frank; Lohmann, Gerrit

2017-08-29

Coinciding with global warming, Arctic sea ice has rapidly decreased during the last four decades and climate scenarios suggest that sea ice may completely disappear during summer within the next about 50-100 years. Here we produce Arctic sea ice biomarker proxy records for the penultimate glacial (Marine Isotope Stage 6) and the subsequent last interglacial (Marine Isotope Stage 5e). The latter is a time interval when the high latitudes were significantly warmer than today. We document that even under such warmer climate conditions, sea ice existed in the central Arctic Ocean during summer, whereas sea ice was significantly reduced along the Barents Sea continental margin influenced by Atlantic Water inflow. Our proxy reconstruction of the last interglacial sea ice cover is supported by climate simulations, although some proxy data/model inconsistencies still exist. During late Marine Isotope Stage 6, polynya-type conditions occurred off the major ice sheets along the northern Barents and East Siberian continental margins, contradicting a giant Marine Isotope Stage 6 ice shelf that covered the entire Arctic Ocean.Coinciding with global warming, Arctic sea ice has rapidly decreased during the last four decades. Here, using biomarker records, the authors show that permanent sea ice was still present in the central Arctic Ocean during the last interglacial, when high latitudes were warmer than present.

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.

New Constraints from the Seychelles on the Timing and Magnitude of Peak Global Mean Sea Level during the Last Interglacial

NASA Astrophysics Data System (ADS)

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

2016-12-01

Projecting the rate of future sea-level rise remains a primary challenge associated with continued climate change. However, uncertainties remain in our understanding of the rate of polar ice sheet retreat in warmer-than-present climates. To address this issue, we present a new sea level reconstruction from the tectonically stable granitic Seychelles based on Last Interglacial coral ages and elevations within their sedimentary and stratigraphic context, including estimates of paleo-water depth based on newly defined coralgal assemblages. The reef facies analyzed here has a narrow and shallow paleowater depth range (<2 m) providing increased control on the absolute position of sea level during this time period. Corrected for local glacial isostatic adjustment effects including the fingerprint associated with polar ice sheet mass loss, corals found in primary growth position within in situ coralgal reef framework confirm that global mean sea level (GMSL) was nearly 6 m above present early in the interglacial period. Each coral was dated in triplicate and screened for anomalous U-series geochemistry parameters. The combination of age-elevation data with the sedimentary micro and macro facies and stratigraphic analysis reveals a sea-level rise over 5-6 thousand years that is punctuated by repeated episodes of reef disturbance. These episodes are marked stratigraphically by coral rubble layers or extensive lateral encrustations of Millepora sp. that are infested with coral-dwelling barnacles. These disturbance layers may have been generated through internal reef processes and/or external agents, including coral disease, bleaching, predation, hurricanes, or sub-aerial exposure. In total, these new observations provide improved constraints on the timing, magnitude, and rates of sea-level rise during the Last Interglacial.

Alternative glacial-interglacial refugia demographic hypotheses tested on Cephalocereus columna-trajani (Cactaceae) in the intertropical Mexican drylands

PubMed Central

Cornejo-Romero, Amelia; Aguilar-Martínez, Gustavo F.; Medina-Sánchez, Javier; Rendón-Aguilar, Beatriz; Valverde, Pedro Luis; Zavala-Hurtado, Jose Alejandro; Serrato, Alejandra; Rivas-Arancibia, Sombra; Pérez-Hernández, Marco Aurelio; López-Ortega, Gerardo; Jiménez-Sierra, Cecilia

2017-01-01

, these results suggest that C. columna-trajani experienced an expansion following the warm conditions of interglacials, in accordance with the GRH. PMID:28426818

Alternative glacial-interglacial refugia demographic hypotheses tested on Cephalocereus columna-trajani (Cactaceae) in the intertropical Mexican drylands.

PubMed

Cornejo-Romero, Amelia; Vargas-Mendoza, Carlos Fabián; Aguilar-Martínez, Gustavo F; Medina-Sánchez, Javier; Rendón-Aguilar, Beatriz; Valverde, Pedro Luis; Zavala-Hurtado, Jose Alejandro; Serrato, Alejandra; Rivas-Arancibia, Sombra; Pérez-Hernández, Marco Aurelio; López-Ortega, Gerardo; Jiménez-Sierra, Cecilia

2017-01-01

, these results suggest that C. columna-trajani experienced an expansion following the warm conditions of interglacials, in accordance with the GRH.

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

Nonlinear climatic sensitivity to greenhouse gases over past 4 glacial/interglacial cycles.

PubMed

Lo, Li; Chang, Sheng-Pu; Wei, Kuo-Yen; Lee, Shih-Yu; Ou, Tsong-Hua; Chen, Yi-Chi; Chuang, Chih-Kai; Mii, Horng-Sheng; Burr, George S; Chen, Min-Te; Tung, Ying-Hung; Tsai, Meng-Chieh; Hodell, David A; Shen, Chuan-Chou

2017-07-04

The paleoclimatic sensitivity to atmospheric greenhouse gases (GHGs) has recently been suggested to be nonlinear, however a GHG threshold value associated with deglaciation remains uncertain. Here, we combine a new sea surface temperature record spanning the last 360,000 years from the southern Western Pacific Warm Pool with records from five previous studies in the equatorial Pacific to document the nonlinear relationship between climatic sensitivity and GHG levels over the past four glacial/interglacial cycles. The sensitivity of the responses to GHG concentrations rises dramatically by a factor of 2-4 at atmospheric CO 2 levels of >220 ppm. Our results suggest that the equatorial Pacific acts as a nonlinear amplifier that allows global climate to transition from deglacial to full interglacial conditions once atmospheric CO 2 levels reach threshold levels.

The PMIP4 contribution to CMIP6 - Part 2: Two interglacials, scientific objective and experimental design for Holocene and Last Interglacial simulations

NASA Astrophysics Data System (ADS)

Otto-Bliesner, Bette L.; Braconnot, Pascale; Harrison, Sandy P.; Lunt, Daniel J.; Abe-Ouchi, Ayako; Albani, Samuel; Bartlein, Patrick J.; Capron, Emilie; Carlson, Anders E.; Dutton, Andrea; Fischer, Hubertus; Goelzer, Heiko; Govin, Aline; Haywood, Alan; Joos, Fortunat; LeGrande, Allegra N.; Lipscomb, William H.; Lohmann, Gerrit; Mahowald, Natalie; Nehrbass-Ahles, Christoph; Pausata, Francesco S. R.; Peterschmitt, Jean-Yves; Phipps, Steven J.; Renssen, Hans; Zhang, Qiong

2017-11-01

Two interglacial epochs are included in the suite of Paleoclimate Modeling Intercomparison Project (PMIP4) simulations in the Coupled Model Intercomparison Project (CMIP6). The experimental protocols for simulations of the mid-Holocene (midHolocene, 6000 years before present) and the Last Interglacial (lig127k, 127 000 years before present) are described here. These equilibrium simulations are designed to examine the impact of changes in orbital forcing at times when atmospheric greenhouse gas levels were similar to those of the preindustrial period and the continental configurations were almost identical to modern ones. These simulations test our understanding of the interplay between radiative forcing and atmospheric circulation, and the connections among large-scale and regional climate changes giving rise to phenomena such as land-sea contrast and high-latitude amplification in temperature changes, and responses of the monsoons, as compared to today. They also provide an opportunity, through carefully designed additional sensitivity experiments, to quantify the strength of atmosphere, ocean, cryosphere, and land-surface feedbacks. Sensitivity experiments are proposed to investigate the role of freshwater forcing in triggering abrupt climate changes within interglacial epochs. These feedback experiments naturally lead to a focus on climate evolution during interglacial periods, which will be examined through transient experiments. Analyses of the sensitivity simulations will also focus on interactions between extratropical and tropical circulation, and the relationship between changes in mean climate state and climate variability on annual to multi-decadal timescales. The comparative abundance of paleoenvironmental data and of quantitative climate reconstructions for the Holocene and Last Interglacial make these two epochs ideal candidates for systematic evaluation of model performance, and such comparisons will shed new light on the importance of external

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.

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.

On the Formation of Meridional Overturning Circulation in the Pacific Ocean during the MIS31 Interglacial

NASA Astrophysics Data System (ADS)

Justino, F. J.; Lindemann, D.; Kucharski, F.

2016-02-01

Earth climate history has been punctuated by cold (glacial) and warm (inter-glacial) intervals associated with modification of the planetary orbit and subsequently changes in paleotopography.During the Pleistocene epoch, the time interval between 1.8 million and 11,700 before present, remarkable episodes of warmer climates such as the Marine IsotopeStage (MIS) 1, 5e, 11c, and 31 which occurred at 9, 127, 409, and 1080 ka, lead to changes in air temperature in the polar regions and substantial melting of polar glaciers. Based on first ever multi-millennium coupled climate simulations of the Marine Isotope Stage 31 (MIS31), long-term oceanic conditions characteristic of this interval have been analyzed. Modeling experiments forced by modified West Antarctic Ice Sheet (WAIS) topography and astronomical configuration, demonstrated that substantial increase in the thermohaline flow and its associated northward heat transport in both Atlantic and Pacific oceans are predicted to occur during the MIS31. In the Atlantic these changes are driven by enhanced oceanic heat loss and increased water density. In the Pacific, anomalous atmospheric circulation leads to an overall increase of the water mass transport in the subtropical gyre, and drastically modified subtropical cell.Additional aspects related to the formation of the Pacific ocean MOC will be presented. This study is sponsored by the Brazilian Antarctic Program Grant CNPq 407681/2013-2.

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

PubMed

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

2015-05-01

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

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.

Detection of a dynamic topography signal in last interglacial sea-level records

PubMed Central

Austermann, Jacqueline; Mitrovica, Jerry X.; Huybers, Peter; Rovere, Alessio

2017-01-01

Estimating minimum ice volume during the last interglacial based on local sea-level indicators requires that these indicators are corrected for processes that alter local sea level relative to the global average. Although glacial isostatic adjustment is generally accounted for, global scale dynamic changes in topography driven by convective mantle flow are generally not considered. We use numerical models of mantle flow to quantify vertical deflections caused by dynamic topography and compare predictions at passive margins to a globally distributed set of last interglacial sea-level markers. The deflections predicted as a result of dynamic topography are significantly correlated with marker elevations (>95% probability) and are consistent with construction and preservation attributes across marker types. We conclude that a dynamic topography signal is present in the elevation of last interglacial sea-level records and that the signal must be accounted for in any effort to determine peak global mean sea level during the last interglacial to within an accuracy of several meters. PMID:28695210

Glacimarine Sedimentary Processes and Facies on the Polar North Atlantic Margins

NASA Astrophysics Data System (ADS)

Dowdeswell, J. A.; Elverhfi, A.; Spielhagen, R.

Major contrasts in the glaciological, oceanic and atmospheric parameters affecting the Polar North Atlantic, both over space between its eastern and western margins, and through time from full glacial to interglacial conditions, have lead to the deposition of a wide variety of sedimentary facies in these ice-influenced seas. The dynamics of the glaciers and ice sheets on the hinterlands surrounding the Polar North Atlantic have exterted a major influence on the processes, rates and patterns of sedimentation on the continental margins of the Norwegian and Greenland seas over the Late Cenozoic. The western margin is influenced by the cold East Greenland Current and the Svalbard margin by the northernmost extent of the warm North Atlantic Drift and the passage of relatively warm cyclonic air masses. In the fjords of Spitsbergen and the northwestern Barents Sea, glacial meltwater is dominant in delivering sediments. In the fjords of East Greenland the large numbers of icebergs produced from fast-flowing outlets of the Greenland Ice Sheet play a more significant role in sedimentation. During full glacials, sediments are delivered to the shelf break from fast-flowing ice streams, which drain huge basins within the parent ice sheet. Large prograding fans located on the continental slope offshore of these ice streams are made up of stacked debris flows. Large-scale mass failures, turbidity currents, and gas-escape structures also rework debris in continental slope and shelf settings. Even during interglacials, both the margins and the deep ocean basins beyond them retain a glacimarine overprint derived from debris in far-travelled icebergs and sea ice. Under full glacial conditions, the glacier influence is correspondingly stronger, and this is reflected in the glacial and glacimarine facies deposited at these times.

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

Reassessing the penultimate interglacial analog for current climate change, evidence from Antarctic dust

NASA Astrophysics Data System (ADS)

Aarons, S. M.; Aciego, S.; McConnell, J.

2017-12-01

Dust emissions and transport are linked to spatial and temporal climate variability, with dust provenance providing clues to past climate and climate impacts. The penultimate interglacial period (MIS 5e) has been suggested as an analog to Holocene climate change. We present the first evaluation of the MIS 5e ice archive developed at Taylor Glacier, East Antarctica and provide a record of dust transported to Taylor Glacier during MIS 5e. Our record shows significant differences between MIS 5e, Holocene, and pre-industrial dust transported to East Antarctica. The MIS 5e dust is sourced from New Zealand and southern South America (SSA), while the Holocene dust is sourced from local Antarctic, SSA, and potentially Australian sources. This profound change in composition suggests a variation in atmospheric transport pathways and/or paleo-environmental conditions between the interglacial periods, and indicates that MIS 5e should be reassessed as an analog for climate change and associated impacts.

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

Vegetation responses to interglacial warming in the Arctic, examples from Lake El'gygytgyn, northeast Siberia

NASA Astrophysics Data System (ADS)

Lozhkin, A. V.; Anderson, P. M.

2013-01-01

Palynological data from Lake El'gygytgyn reveal responses of plant communities to a range of climatic conditions that can help assess the possible impact of global warming on arctoboreal ecosystems. Vegetation associated with climatic optima suggests two types of interglacial responses: one is dominated by deciduous taxa (the postglacial thermal maximum (PGTM) and marine isotope stage (MIS5)) and the second by evergreen conifers (MIS11, MIS31). The MIS11 forests show a similarity to Picea-Larix-Betula-Alnus forests of Siberia. While dark coniferous forest also characterizes MIS31, the pollen taxa show an affinity to the modern boreal forest of the lower Amur valley in the Russian Far East. Despite vegetation differences during the thermal maxima, all four glacial-interglacial transitions are alike, being dominated by deciduous woody taxa. Initially Betula shrub tundra established and was replaced by tundra with tree-sized shrubs (PGTM), Betula woodland (MIS5), or Betula-Larix (MIS11, MIS31) forest. The consistent occurrence of deciduous forest and/or high shrub tundra in all interglaciations as they approach or achieve maximum warmth underscores the significance of this biome for modeling efforts. The El'gygytgyn data also suggest the possible elimination or massive reduction of arctic plant communities under extreme warm-earth scenarios.

Glacial versus interglacial sedimentation rates and turbidite frequency in the Bahamas

NASA Astrophysics Data System (ADS)

Droxler, Andre W.; Schlager, Wolfgang

1985-11-01

The southern Tongue of the Ocean is a 1300-m-deep, flat-floored basin in the Bahamas that receives large amounts of sediment from the carbonate platforms surrounding it on three sides. We have examined five 8 13-m-long piston cores and determined bulk sedimentation rates, turbidite frequency, and turbidite accumulation rates for the past two glacial and interglacial periods. The mean of bulk sedimentation rates is four to six times higher in interglacial periods; average accumulation rates of recognizable turbidites are higher by a factor of 21 to 45, and interglacial turbidite frequency is higher by a factor of 6 to 14. Sediment composition indicates that increased interglacial rates are due to higher accumulation of platform-derived material. Additional data from other Bahamian basins as well as published material from the Caribbean strongly suggest that highstand shedding is a general trend in pure carbonate depositional systems. Carbonate platforms without a siliciclastic component export more material during highstands of sea level when the platform tops are flooded and produce sediment. The response of carbonate platforms to Quaternary sea-level cycles is opposed to that of siliciclastic ocean margins, where sediment is stored on the inner shelf during highstands and passed on to continental rises and abyssal plains during lowstands of sea level.

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

Genesis, evolution, and catastrophic burying of the Ryshkovo paleosol of the Mikulino Interglacial (MIS 5e)

NASA Astrophysics Data System (ADS)

Sycheva, S. A.; Sedov, S. N.; Bronnikova, M. A.; Targulian, V. O.; Solleiro-Rebolledo, E.

2017-09-01

The results of a hierarchical morphogenetic, physicochemical, and mineralogical study of the Ryshkovo full-profile texture-differentiated paleosol of the Mikulino Interglacial from the section at Aleksandrov quarry in Kursk oblast are discussed. The correlation analysis of the stratigraphy of this section with global geological records made it possible to determine the position of the Ryshkovo paleosol in the chronostratigraphic system of the Late Pleistocene and to attribute it to stage MIS 5e; the duration of pedogenesis for this paleosol was no more than 12-15 ka. The results of the study indicate that the Ryshkovo paleosol is close in its properties to the Holocene soddy-podzolic soils of the East European Plain. No direct evidences in favor of the former interpretation of this paleosol as a lessivated soil genetically close to Luvisols of nemoral broadleaved forest of Central Europe have been found. The difference between the paleosol of the Mikulino Interglacial and the modern soddy-podzolic soils is mainly related to the distribution of clay coatings. In the upper part of the illuvial horizon of Mikulino paleosol, clay coatings are few in number, and typical tongues of podzolized (albic) material are absent in the profile. At the same time, silty coatings (skeletans) are abundant even in the lower part of the illuvial horizon. In general, the Mikulino paleosol is characterized by a smaller diversity of clay pedofeatures. These differences might be related to less contrasting fluctuations of the environmental conditions in the second half of the Mikulino Interglacial, to the periodical renewal of the eluvial part of Mikulino paleosol by erosional and accumulative processes, and to the absence of anthropogenic impacts on the soil during the Mikulino Interglacial. The burying of the Ryshkovo paleosol took place due to the intense development of erosional processes induced by the contrasting climatic events at the end of the interglacial period accompanied by

Marine Isotope Stage 11 : The Role of Co2, Insolation and Antarctica Ice Sheet On This Interglacial

NASA Astrophysics Data System (ADS)

Raynaud, D.; Loutre, M. F.; Ritz, C.; Barnola, J.-M.; Berger, A.; Chappellaz, J.; Jouzel, J.; Lipenkov, V.; Petit, J.-R.; Vimeux, F.

The Marine Isotopic Stage 11 (MIS 11), around 400kyr BP ago, has been suggested as an analogue for a future climate under natural forcing because of the similar condi- tions of orbitally driven insolation during this interglacial period and the one covering the Holocene and the near future. There are many open questions about unusual MIS 11 climatic conditions (length of the interglacial, temperature, sea level, marine car- bonate system), as recorded in different marine and continental records. The Antarctic Vostok ice core provides the only atmospheric record extending back to MIS 11 and we use it to discuss the Antarctic temperature, the atmospheric CO2 concentration and the ice sheet stability in the central part of East Antarctica during this interglacial. The unique nature of the Vostok atmospheric record leads us to use the available Vos- tok data to drive climate and ice sheet models for MIS 11. A model of intermediate complexity (LLN-2D model) is used to investigate the sensitivity of the simulated MIS 11 deglaciation to the interplay between insolation and CO2. It is shown that the length of the simulated interglacial depends strongly on the phasing between these two climate forcings. We also investigate the response of the Antarctic Ice Sheet to changing climate through simulations performed with the LGGE 3-D ice sheet model. The results indicate that sea level stands during MIS 11 as high as 20 m. above present level, as suggested by different elevated marine terraces, cannot be explained, except by assuming that MIS 11 was very dry over Antarctica.

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.

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.

Synoptic conditions of fine-particle transport to the last interglacial Red Sea-Dead Sea from Nd-Sr compositions of sediment cores

NASA Astrophysics Data System (ADS)

Palchan, Daniel; Stein, Mordechai; Goldstein, Steven L.; Almogi-Labin, Ahuva; Tirosh, Ofir; Erel, Yigal

2018-01-01

The sediments deposited at the depocenter of the Dead Sea comprise high-resolution archive of hydrological changes in the lake's watershed and record the desert dust transport to the region. This paper reconstructs the dust transport to the region during the termination of glacial Marine Isotope Stage 6 (MIS 6; ∼135-129 ka) and the last interglacial peak period (MIS5e, ∼129-116 ka). We use chemical and Nd and Sr isotope compositions of fine detritus material recovered from sediment core drilled at the deepest floor of the Dead Sea. The data is integrated with data achieved from cores drilled at the floor of the Red Sea, thus, forming a Red Sea-Dead Sea transect extending from the desert belt to the Mediterranean climate zone. The Dead Sea accumulated flood sediments derived from three regional surface cover types: settled desert dust, mountain loess-soils and loess-soils filling valleys in the Dead Sea watershed termed here "Valley Loess". The Valley Loess shows a distinct 87Sr/86Sr ratio of 0.7081 ± 1, inherited from dissolved detrital calcites that originate from dried waterbodies in the Sahara and are transported with the dust to the entire transect. Our hydro-climate and synoptic conditions reconstruction illustrates the following history: During glacial period MIS6, Mediterranean cyclones governed the transport of Saharan dust and rains to the Dead Sea watershed, driving the development of both mountain soils and Valley Loess. Then, at Heinrich event 11, dry western winds blew Saharan dust over the entire Red Sea - Dead Sea transect marking latitudinal expansion of the desert belt. Later, when global sea-level rose, the Dead Sea watershed went through extreme aridity, the lake retreated, depositing salt and accumulating fine detritus of the Valley Loess. During peak interglacial MIS 5e, enhanced flooding activity flushed the mountain soils and fine detritus from all around the Dead Sea and Red Sea, marking a significant "contraction" of the desert belt

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

The sensitivity of the Greenland Ice Sheet to glacial-interglacial oceanic forcing

NASA Astrophysics Data System (ADS)

Tabone, Ilaria; Blasco, Javier; Robinson, Alexander; Alvarez-Solas, Jorge; Montoya, Marisa

2018-04-01

Observations suggest that during the last decades the Greenland Ice Sheet (GrIS) has experienced a gradually accelerating mass loss, in part due to the observed speed-up of several of Greenland's marine-terminating glaciers. Recent studies directly attribute this to warming North Atlantic temperatures, which have triggered melting of the outlet glaciers of the GrIS, grounding-line retreat and enhanced ice discharge into the ocean, contributing to an acceleration of sea-level rise. Reconstructions suggest that the influence of the ocean has been of primary importance in the past as well. This was the case not only in interglacial periods, when warmer climates led to a rapid retreat of the GrIS to land above sea level, but also in glacial periods, when the GrIS expanded as far as the continental shelf break and was thus more directly exposed to oceanic changes. However, the GrIS response to palaeo-oceanic variations has yet to be investigated in detail from a mechanistic modelling perspective. In this work, the evolution of the GrIS over the past two glacial cycles is studied using a three-dimensional hybrid ice-sheet-shelf model. We assess the effect of the variation of oceanic temperatures on the GrIS evolution on glacial-interglacial timescales through changes in submarine melting. The results show a very high sensitivity of the GrIS to changing oceanic conditions. Oceanic forcing is found to be a primary driver of GrIS expansion in glacial times and of retreat in interglacial periods. If switched off, palaeo-atmospheric variations alone are not able to yield a reliable glacial configuration of the GrIS. This work therefore suggests that considering the ocean as an active forcing should become standard practice in palaeo-ice-sheet modelling.

The Preboreal-like Asian monsoon climate in the early last interglacial period recorded from the Dark Cave, Southwest China

NASA Astrophysics Data System (ADS)

Jiang, Xiuyang; He, Yaoqi; Wang, Xiaoyan; Sun, Xiaoshuang; Hong, Hui; Liu, Juan; Yu, Tsai-Luen; Li, Zhizhong; Shen, Chuan-Chou

2017-08-01

Transitions of glacial-interglacial cycles are critical periods for Quaternary climate shifts. Here, we present new, decadal resolution Asian summer monsoon (ASM) record from three stalagmites obtained from the Dark Cave in southwestern China over 130-114 thousand years ago (ka, before CE 1950). Chronology was anchored by 28 230Th dates with typical uncertainties of ±0.3-1.0 kyr, allowing an assessment of timing and transition of climate changes during the onset and end of the last interglacial. An agreement between this new and previous stalagmite δ18O records supports that summer insolation predominates orbital-scale ASM evolution. A 2-3 kyr-long gradually increasing ASM period, analogous to the classical Preboreal episode in the early Holocene, follows the termination of a weak monsoon interval at 129.0 ± 0.8 ka. This finding suggests a strong influence of high-latitude ice-sheet dynamics on Asian monsoonal conditions during the early interglacial period. An abrupt end of the marine isotope stage 5e at 118.8 ± 0.6 ka was probably caused by the internal climate system threshold effects.

The History of Tree and Shrub Taxa on Bol’shoy Lyakhovsky Island (New Siberian Archipelago) since the Last Interglacial Uncovered by Sedimentary Ancient DNA and Pollen Data

PubMed Central

Raschke, Elena; Epp, Laura S.; Stoof-Leichsenring, Kathleen R.; Schwamborn, Georg; Herzschuh, Ulrike

2017-01-01

Ecosystem boundaries, such as the Arctic-Boreal treeline, are strongly coupled with climate and were spatially highly dynamic during past glacial-interglacial cycles. Only a few studies cover vegetation changes since the last interglacial, as most of the former landscapes are inundated and difficult to access. Using pollen analysis and sedimentary ancient DNA (sedaDNA) metabarcoding, we reveal vegetation changes on Bol’shoy Lyakhovsky Island since the last interglacial from permafrost sediments. Last interglacial samples depict high levels of floral diversity with the presence of trees (Larix, Picea, Populus) and shrubs (Alnus, Betula, Ribes, Cornus, Saliceae) on the currently treeless island. After the Last Glacial Maximum, Larix re-colonised the island but disappeared along with most shrub taxa. This was probably caused by Holocene sea-level rise, which led to increased oceanic conditions on the island. Additionally, we applied two newly developed larch-specific chloroplast markers to evaluate their potential for tracking past population dynamics from environmental samples. The novel markers were successfully re-sequenced and exhibited two variants of each marker in last interglacial samples. SedaDNA can track vegetation changes as well as genetic changes across geographic space through time and can improve our understanding of past processes that shape modern patterns. PMID:29027988

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

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.

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

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

USGS Publications Warehouse

Rode, Karyn D.; Peacock, Elizabeth; Taylor, Mitchell K.; Stirling, Ian; Born, Erik W.; Laidre, Kristin L.; Wiig, Øystein

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.

Glacial/interglacial wetland, biomass burning, and geologic methane emissions constrained by dual stable isotopic CH4 ice core records.

PubMed

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

2017-07-18

Atmospheric methane (CH 4 ) records reconstructed from polar ice cores represent an integrated view on processes predominantly taking place in the terrestrial biogeosphere. Here, we present dual stable isotopic methane records [δ 13 CH 4 and δD(CH 4 )] from four Antarctic ice cores, which provide improved constraints on past changes in natural methane sources. Our isotope data show that tropical wetlands and seasonally inundated floodplains are most likely the controlling sources of atmospheric methane variations for the current and two older interglacials and their preceding glacial maxima. The changes in these sources are steered by variations in temperature, precipitation, and the water table as modulated by insolation, (local) sea level, and monsoon intensity. Based on our δD(CH 4 ) constraint, it seems that geologic emissions of methane may play a steady but only minor role in atmospheric CH 4 changes and that the glacial budget is not dominated by these sources. Superimposed on the glacial/interglacial variations is a marked difference in both isotope records, with systematically higher values during the last 25,000 y compared with older time periods. This shift cannot be explained by climatic changes. Rather, our isotopic methane budget points to a marked increase in fire activity, possibly caused by biome changes and accumulation of fuel related to the late Pleistocene megafauna extinction, which took place in the course of the last glacial.

Glacial/interglacial wetland, biomass burning, and geologic methane emissions constrained by dual stable isotopic CH4 ice core records

NASA Astrophysics Data System (ADS)

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

2017-07-01

Atmospheric methane (CH4) records reconstructed from polar ice cores represent an integrated view on processes predominantly taking place in the terrestrial biogeosphere. Here, we present dual stable isotopic methane records [δ13CH4 and δD(CH4)] from four Antarctic ice cores, which provide improved constraints on past changes in natural methane sources. Our isotope data show that tropical wetlands and seasonally inundated floodplains are most likely the controlling sources of atmospheric methane variations for the current and two older interglacials and their preceding glacial maxima. The changes in these sources are steered by variations in temperature, precipitation, and the water table as modulated by insolation, (local) sea level, and monsoon intensity. Based on our δD(CH4) constraint, it seems that geologic emissions of methane may play a steady but only minor role in atmospheric CH4 changes and that the glacial budget is not dominated by these sources. Superimposed on the glacial/interglacial variations is a marked difference in both isotope records, with systematically higher values during the last 25,000 y compared with older time periods. This shift cannot be explained by climatic changes. Rather, our isotopic methane budget points to a marked increase in fire activity, possibly caused by biome changes and accumulation of fuel related to the late Pleistocene megafauna extinction, which took place in the course of the last glacial.

Meteoric 10Be as a tracer of subglacial processes and interglacial surface exposure in Greenland

NASA Astrophysics Data System (ADS)

Graly, Joseph A.; Corbett, Lee B.; Bierman, Paul R.; Lini, Andrea; Neumann, Thomas A.

2018-07-01

In order to test whether sediment emerging from presently glaciated areas of Greenland was exposed near or at Earth's surface during previous interglacial periods, we measured the rare isotope 10Be contained in grain coatings of sediment collected at five ice marginal sites. Such grain coatings contain meteoric 10Be (10Bemet), which forms in the atmosphere and is deposited onto Earth's surface. Samples include sediment entrained in ice, glaciofluvial sediment collected at the ice margin, and subglacial sediment extracted during hot water drilling in the ablation zone. Due to burial by ice, contemporary subglacial sediment could only have acquired substantial 10Bemet concentrations during periods in the past when the Greenland Ice Sheet was less extensive than present. The highest measured 10Bemet concentrations are comparable to those found in well-developed, long-exposed soils, suggesting subglacial preservation and glacial transport of sediment exposed during preglacial or interglacial periods. Ice-bound sediment has significantly higher 10Bemet concentrations than glaciofluvial sediment, suggesting that glaciofluvial processes are sufficiently erosive to remove tracers of previous interglacial exposures. Northern Greenland sites where ice and sediment are supplied from the ice sheet's central main dome have significantly higher 10Bemet concentrations than sites in southern Greenland, indicating greater preglacial or interglacial landscape preservation in central Greenland than in the south. Because southern Greenland has more frequent and spatially extensive periods of glacial retreat but nevertheless has less evidence of past subaerial exposure, we suggest that 10Bemet measurements in glacial sediment are primarily controlled by erosional efficiency rather than interglacial exposure length.

Can energy fluxes be used to interpret glacial/interglacial precipitation changes in the tropics?

NASA Astrophysics Data System (ADS)

Roberts, W. H. G.; Valdes, P. J.; Singarayer, J. S.

2017-06-01

Recent theoretical advances in the relationship between heat transport and the position of the Intertropical Convergence Zone (ITCZ) present an elegant framework through which to interpret past changes in tropical precipitation patterns. Using a very large ensemble of climate model simulations, we investigate whether it is possible to use this framework to interpret changes in the position of the ITCZ in response to glacial and interglacial boundary conditions. We find that the centroid of tropical precipitation, which represents the evolution of precipitation in the whole tropics, is best correlated with heat transport changes. We find that the response of the annual mean ITCZ to glacial and interglacial boundary conditions is quite different to the response of the climatological annual cycle of the ITCZ to the seasonal cycle of insolation. We show that the reason for this is that while the Hadley Circulation plays a dominant role in transporting heat over the seasonal cycle, in the annual mean response to forcing, the Hadley Circulation is not dominant. When we look regionally, rather than at the zonal mean, we find that local precipitation is poorly related either to the zonal mean ITCZ or to meridional heat transport. We demonstrate that precipitation is spatially highly variable even when the zonal mean ITCZ is in the same location. This suggests only limited use for heat transport in explaining local precipitation records; thus, there is limited scope for using heat transport changes to explain individual paleoprecipitation records.

The Relationship between Climate and Iceland Scotland Overflow Water During Mid-Late Pleistocene Interglacials

NASA Astrophysics Data System (ADS)

Nuber, S.; Thornalley, D.; Forman, M.; Barker, S.; Oppo, D.

2016-12-01

Ocean circulation has been identified as an important climate feedback mechanism in a warming world. An area of particular importance in global ocean circulation is the high latitude North Atlantic and the Nordic Seas. Here, cooling of northward flowing warm surface water produces dense deep water which sinks to the ocean floor and returns southward as part of the Atlantic Meridional Overturning Circulation (AMOC). Density structures in the Nordic Seas can change as a response to enhanced freshwater input (e.g. from the melting Greenland Ice Sheet or a stronger hydrological cycle) which in turn may perturb the AMOC. It is therefore important that we develop our understanding of the relationship between climate and the return flow of dense water formed in the high latitude North Atlantic, focusing in particular on past warm climates that can act as partial analogues for future global warming scenarios. Previous work investigating the Holocene has revealed long-term trends in the strength of the dense overflow from the Nordic Seas into the North Atlantic via Iceland Scotland Overflow Water (ISOW). These changes have been related to variations in the freshwater budget and the water densities in the Nordic Seas (Thornalley et al., 2013). Across earlier interglacials, ISOW dynamics remain poorly constrained. To gain a more complete understanding of the coupling of climate and ISOW during past warm climates, we reconstructed ISOW flow speeds across an additional five Pleistocene interglacials, using the sortable silt proxy and a newly developed calibration curve. We find that there is large variability in inferred ISOW flow speeds between interglacials, as well as different temporal evolution of flow speed through the various interglacials. Our results suggest that preceded deglacial dynamics may be an important influence on the interglacial ISOW flow structure and highlight the tight coupling between climate and the ISOW.

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

NASA Technical Reports Server (NTRS)

Gopalswamy, Nat; Yashiro, Seiji; Akiyama, Sachiko

2016-01-01

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 northsouth 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.

Insights into North Atlantic deep water formation during the peak interglacial interval of Marine Isotope Stage 9 (MIS 9)

NASA Astrophysics Data System (ADS)

Mokeddem, Zohra; McManus, Jerry F.

2017-11-01

Foraminifera abundance and stable isotope records from ODP Site 984 (61.25°N, 24.04°W, 1648 m) in the North Atlantic are used to reconstruct surface circulation variations and the relative strength of the North Atlantic Deep Water (NADW) formation over the period spanning the peak warmth of Marine Interglacial Stage (MIS) 9e ( 324-336 ka). This interval includes the preceding deglaciation, Termination 4 (T4), and the subsequent glacial inception of MIS 9d. The records indicate a greatly reduced contribution of NADW during T4, as observed in more recent deglaciations. In contrast with the most recent deglaciation, the lack of a significant NADW signal extended from T4 well into the peak interglacial MIS 9e and persisted nearly until the transition to the subsequent glacial stage MIS 9d. Although NADW formation resumed during MIS 9e, only depths greater than 2000 m appear to have been ventilated. The poorly ventilated intermediate depth of Site 984 (<2000 m) may have resulted on one hand from a general reduction of deep water ventilation by NADW during the study interval or, on the other hand, from different pathways of the spread of newly formed NADW that bypassed the study location. The intermediate depths may have also been invaded by southern-sourced waters as the formation of intermediate depth NADW weakened. The absence of any significant NADW signal at the water depth of Site 984 during the climatic optimum contrasts sharply with subsequent interglacial peaks (MIS 5e and the Holocene). Despite the perturbed intermediate depth circulation, oceanic heat transport northeastward was not interrupted and may have contributed to the relatively mild interglacial conditions of MIS 9e.

Sedimentology, palaeoecology and geochronology of Last Interglacial deposits from Deeping St James, Lincolnshire, England

NASA Astrophysics Data System (ADS)

Keen, D. H.; Bateman, M. D.; Coope, G. R.; Field, M. H.; Langford, H. E.; Merry, J. S.; Mighall, T. M.

1999-08-01

Pollen, plant macrofossil, molluscan and coleopteran data from organic muds below the low terrace of the River Welland at Deeping St James, Lincolnshire indicate deposition in the mixed oak forest phase of a Late Pleistocene interglacial. Coleopteran and molluscan data suggest summer temperatures up to 4°C warmer than at present in eastern England, and plant macrofossil material suggests a climate more continental than that of Britain in the Holocene. No direct analogue of this biota, however, exists currently in Europe. Biostratigraphical indications from the pollen coleoptera and Mollusca suggest an age in the Ipswichian Interglacial. Thermoluminescence dates between 120 ka and 75 ka and amino-acid ratios with a mean of 0.11 show that deposition of the sediments took place during Oxygen Isotope Stage 5. This accurate dating of a partial Ipswichian succession allows discussion of the ages of a number of other interglacial sites in eastern England of assumed Ipswichian age.

Response of rainy season duration over Asian monsoon region to astronomical forcing under glacial and interglacial conditions

NASA Astrophysics Data System (ADS)

Shi, Z.

2017-12-01

The responses of Asian summer monsoon and associated precipitation to astronomical forcing have beenintensively explored during the past decades, but debate still exists regarding whether or not the Asianmonsoon is controlled by northern or southern summer insolation. Various modeling studies have been conducted that support the potential roles played by the insolation in bothhemispheres. Among these previous studies, however, the main emphasis has been on the Asianmonsoon intensity, with the response of monsoon duration having received little consideration. In thepresent study, the response of the rainy season duration over different monsoon areas to astronomical forcingand its contribution to total annual precipitation are evaluated using an atmospheric general circulationmodel. The results show that the durations of the rainy seasons, especially their withdrawal, in northernEast Asia and the India-Bay of Bengal region, are sensitive to precession change under interglacial-likeconditions. Compared to those during stronger boreal summer insolation, the Asian monsoon associatedrainy seasons at weaker insolation last longer, although the peak intensity is smaller. Thislonger duration of rainfall, which results from the change in land-ocean thermal contrast associated withatmospheric diabatic heating, can counterbalance the weakened intensity in certain places and induce anopposite response of total annual precipitation. However, the duration effect of Asian monsoon is limitedunder glacial-like conditions. Nevertheless, monsoon duration is a factor that can dominate the astronomical-scalevariability of Asian monsoon, alongside the intensity, and it should therefore receive greaterattention when attempting to explain astronomical-scale monsoon change.

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

Modelling silicon supply during the Last Interglacial (MIS 5e) at Lake Baikal

NASA Astrophysics Data System (ADS)

Panizzo, V. N.; Swann, G. E. A.; Mackay, A. W.; Pashley, V.; Horstwood, M. S. A.

2018-06-01

Limnological reconstructions of primary productivity have demonstrated its response over Quaternary timescales to drivers such as climate change, landscape evolution and lake ontogeny. In particular, sediments from Lake Baikal, Siberia, provide a valuable uninterrupted and continuous sequence of biogenic silica (BSi) records, which document orbital and sub-orbital frequencies of regional climate change. We here extend these records via the application of stable isotope analysis of silica in diatom opal (δ30Sidiatom) from sediments covering the Last Interglacial cycle (Marine Isotope Stage [MIS] 5e; c. 130 to 115 ka BP) as a means to test the hypothesis that it was more productive than the Holocene. δ30Sidiatom data for the Last Interglacial range between +1.29 and +1.78‰, with highest values between c. 127 to 124 ka BP (+1.57 to +1.78‰). Results show that diatom dissolved silicon (DSi) utilisation, was significantly higher (p = 0.001) during MIS 5e than the current interglacial, which reflects increased diatom productivity over this time (concomitant with high diatom biovolume accumulation rates [BVAR] and warmer pollen-inferred vegetation reconstructions). Diatom BVAR are used, in tandem with δ30Sidiatom data, to model DSi supply to Lake Baikal surface waters, which shows that highest delivery was between c. 123 to 120 ka BP (reaching peak supply at c. 120 ka BP). When constrained by sedimentary mineralogical archives of catchment weathering indices (e.g. the Hydrolysis Index), data highlight the small degree of weathering intensity and therefore representation that catchment-weathering DSi sources had, over the duration of MIS 5e. Changes to DSi supply are therefore attributed to variations in within-lake conditions (e.g. turbulent mixing) over the period, where periods of both high productivity and modelled-DSi supply (e.g. strong convective mixing) account for the decreasing trend in δ30Sidiatom compositions (after c. 124 ka BP).

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

NASA Astrophysics Data System (ADS)

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

2012-04-01

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

The Last Interglacial Climate Variability in Northern China

NASA Astrophysics Data System (ADS)

Li, X.; Lu, Y.; Sinha, A.; Ma, Z.; Tan, M.; Edwards, R.; Cheng, H.

2013-12-01

Speleothem oxygen isotope (δ18O) records can reconstruct high-resolution and absolutely dated climate history, in particular, the variability of monsoon precipitation that is associated with the changes in atmospheric circulation and, in turn, the δ18O of precipitation. In the East Asian monsoon domain, although speleothem records have been established in southeastern China over the last decade, including several records covering the last interglacial period (MIS 5e), similar records are virtually absent in northern China. This hampers our understanding of the mechanism of the East Asian monsoon changes, because the northern China δ18O record is, as recently shown by modeling work, more sensitive to changes in summer monsoon precipitation than that from southeastern China. Here we provide a high-resolution and absolutely dated speleothem δ18O record between ~129 and 119 ka BP from Kulishu cave, Beijing, northern China. It shows an abrupt onset of MIS 5e at 129.4×0.7 ka BP, similar within dating uncertainty to the Dongge, Hulu, and Sanbao records from southeastern China. However, the end of MIS 5e is rather gradual in comparison to the southern China counterparts. While overall MIS5e monsoon climate appears to be rather stable on orbital timescales, broadly following northern hemisphere summer insolation, millennial/centennial-scale events punctuate the Kulishu record. Spectral analysis reveals a significant quasi-1500 year periodicity, comparable to the Bond cycle, first observed in the North Atlantic during the Holocene, and more recently in interglacial East Asian monsoon cave records. As such, events with a ~1500 year pacing appear to be a persistent characteristic of the East Asian monsoon for good portions of the past two glacial-interglacial periods. Changes in solar output would be one possibility for the trigger; changes in ocean circulation with a ~1500-year time constant would be another. Comparison with Hulu(MSX, Cheng et al., 2006)-Dongge(D3, D4

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

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

The vegetation history of the last glacial-interglacial cycle in eastern New South Wales, Australia

NASA Astrophysics Data System (ADS)

Williams, N. J.; Harle, K. J.; Gale, S. J.; Heijnis, H.

2006-10-01

We present a reconstruction of the vegetation history of the last glacial-interglacial cycle (ca. 75 k cal. yr BP-present) at Redhead Lagoon, an enclosed lake basin in coastal, eastern New South Wales, Australia. The sequence of vegetation change at the site is broadly comparable with the pattern of climatically induced changes observed in many other pollen records in southeast Australia. Open woodland-herbland and woodland-forest communities correspond with glacial and interglacial periods respectively, with an additional change towards a more open understorey vegetation assemblage over the last 40 000 yr. The driest conditions appear to have occurred during the height of the last glacial (some time between 30 and 20 k cal. yr BP). This is consistent with other records from southeast Australia, and provides support for a poleward shift in the subtropical anticyclone belt and, less certainly, for the thesis that the Southern Hemisphere westerlies intensified during this period. In marked contrast to most sites in southeast Australia, Casuarinaceae dominates the pollen record through the height of the last glacial period and into the Holocene. The postglacial climatic amelioration is accompanied by the general reappearance of tree pollen in the record, by the disappearance of several open and disturbed environment indicator taxa, by increases in organic sediment deposition and pollen taxon diversity, and by higher water balances. While climate appears to have been the major control on patterns of vegetation change at this site throughout most of the last glacial-interglacial cycle, changes in depositional environment and hydrology have also played a role. Significantly, substantial increases in the rate and magnitude of many indicators of environmental disturbance since European settlement suggest that humans are now the most important mechanism for environmental change. Copyright

Glacial/interglacial wetland, biomass burning, and geologic methane emissions constrained by dual stable isotopic CH4 ice core records

PubMed Central

Beck, Jonas; Seth, Barbara; Chappellaz, Jérôme

2017-01-01

Atmospheric methane (CH4) records reconstructed from polar ice cores represent an integrated view on processes predominantly taking place in the terrestrial biogeosphere. Here, we present dual stable isotopic methane records [δ13CH4 and δD(CH4)] from four Antarctic ice cores, which provide improved constraints on past changes in natural methane sources. Our isotope data show that tropical wetlands and seasonally inundated floodplains are most likely the controlling sources of atmospheric methane variations for the current and two older interglacials and their preceding glacial maxima. The changes in these sources are steered by variations in temperature, precipitation, and the water table as modulated by insolation, (local) sea level, and monsoon intensity. Based on our δD(CH4) constraint, it seems that geologic emissions of methane may play a steady but only minor role in atmospheric CH4 changes and that the glacial budget is not dominated by these sources. Superimposed on the glacial/interglacial variations is a marked difference in both isotope records, with systematically higher values during the last 25,000 y compared with older time periods. This shift cannot be explained by climatic changes. Rather, our isotopic methane budget points to a marked increase in fire activity, possibly caused by biome changes and accumulation of fuel related to the late Pleistocene megafauna extinction, which took place in the course of the last glacial. PMID:28673973

Response of the carbon cycle in an intermediate complexity model to the different climate configurations of the last nine interglacials

NASA Astrophysics Data System (ADS)

Bouttes, Nathaelle; Swingedouw, Didier; Roche, Didier M.; Sanchez-Goni, Maria F.; Crosta, Xavier

2018-03-01

Atmospheric CO2 levels during interglacials prior to the Mid-Brunhes Event (MBE, ˜ 430 ka BP) were around 40 ppm lower than after the MBE. The reasons for this difference remain unclear. A recent hypothesis proposed that changes in oceanic circulation, in response to different external forcings before and after the MBE, might have increased the ocean carbon storage in pre-MBE interglacials, thus lowering atmospheric CO2. Nevertheless, no quantitative estimate of this hypothesis has been produced up to now. Here we use an intermediate complexity model including the carbon cycle to evaluate the response of the carbon reservoirs in the atmosphere, ocean and land in response to the changes of orbital forcings, ice sheet configurations and atmospheric CO2 concentrations over the last nine interglacials. We show that the ocean takes up more carbon during pre-MBE interglacials in agreement with data, but the impact on atmospheric CO2 is limited to a few parts per million. Terrestrial biosphere is simulated to be less developed in pre-MBE interglacials, which reduces the storage of carbon on land and increases atmospheric CO2. Accounting for different simulated ice sheet extents modifies the vegetation cover and temperature, and thus the carbon reservoir distribution. Overall, atmospheric CO2 levels are lower during these pre-MBE simulated interglacials including all these effects, but the magnitude is still far too small. These results suggest a possible misrepresentation of some key processes in the model, such as the magnitude of ocean circulation changes, or the lack of crucial mechanisms or internal feedbacks, such as those related to permafrost, to fully account for the lower atmospheric CO2 concentrations during pre-MBE interglacials.

Novel method in solving non-polarizing condition in frustrated total internal reflection layers

NASA Astrophysics Data System (ADS)

Shi, Jin Hui; Wang, Zheng Ping

2008-03-01

When used at oblique angles of incidence, the reflectance and transmittance of thin films exhibit strong polarization effects, particularly for the films inside a glass cube. However, the polarization effects are undesirable in many applications. Novel non-polarizing beam splitter designs are shown, non-polarizing beam splitters with unique optical thin films are achieved through combination of interference and frustrated total internal reflection, the non-polarizing condition expressions based on frustrated total internal reflection is derived, and applied examples of the non-polarizing beam splitters are also presented with the optimization technique and the results of Rp=(50+/-0.4)% and Rs=(50+/-0.4)% in the wavelength range of 500-600nm are obtained.

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

Sea ice variations in the central Okhotsk Sea during the last two glacial-interglacial cycles

NASA Astrophysics Data System (ADS)

Lo, L.; Cabedo-Sanz, P.; Lattaud, J.; Belt, S. T.; Schouten, S.; Huang, J. J.; Timmermann, A.; Zeeden, C.; Wei, K. Y.; Shen, C. C.; Hodell, D. A.; Elderfield, H.

2016-12-01

Sea ice system as one of the critical and sensitive climate components in the Earth's climate system has experienced dramatically declination for the past few decades. Little knowledge, however, about the sea ice variations in the past orbital timescales has been obtained by paleoclimatic studies due to the lack of reliable sea ice proxy and age model constrain in the high productivity subpolar to polar regions. Here we present continuous 180,000 years subarctic northwestern Pacific sea ice and surface temperature (SST) records in the center Okhotsk Sea, the southernmost of seasonal sea ice fomration region in the Northern Hemisphere by using by using novel organic and non-destructive geochemical proxies from Site MD01-2414 (53oN, 149oE, water depth 1123 m). High resolution X-ray fluoresces scanning biogenic/terrestrial (Ba/Ti) elemental ratio represent clear glacial-interglacial cycles. Organic geochemical proxies (IP25 and TEX86) derived sea ice and SST changes in the same time resolution reveal the seasonality in the center Okhotsk Sea. Sea ice shows strong 23-kyr precession cycle control with modulation of 100-kyr eccentricity cycle during the peak interglacial periods (Marine Isotope Stage 5e and Holocene). On the other hand, SST represent global background climate change of 100-kyr cycle with very strong obliquity changes. According to the timeseries analyses, we argue that the sea ice minimum in the center of Okhotsk Sea has mainly been controlled by the local autumn insolation. SST represent annual insolation increasing due to local summer insolation and the obliquity pacing. This study firstly demonstrated clear seasonality in the same site. Further study of the relationship between sea ice and seawater thermal hisotries on the orbital timescale in the subarctic Pacific is crucial in the understanding of past major climate event, e.g. Middle Pleistocene Transition and Middle Brunhes Event.

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.

Pennsylvanian - Early Cisuralian interglacial macrofloristic succession in Paraná Basin of the State of São Paulo

NASA Astrophysics Data System (ADS)

Bernardes-de-Oliveira, Mary Elizabeth Cerruti; Kavali, Pauline Sabina; Mune, Sandra Eiko; Shivanna, Mahesh; Souza, Paulo Alves de; Iannuzzi, Roberto; Jasper, André; Hoelzel, Amanda; Boardman, Daiana R.; Rohn, Rosemarie; Ricardi-Branco, Fresia

2016-12-01

One of the most completely preserved glacial sedimentary records from the Late Carboniferous to the Early Permian time corresponds to the Itararé Group, which presents a large outcropping thickness in the northeastern border of Paraná Basin, especially in the State of São Paulo. This unit corresponds to the base of the Gondwana I Supersequence and is composed of continental to marine glacial and interglacial deposits. Based on some macrofloristic, lithostratigraphic and palynostratigraphic data, a formal scheme of the macrofloral succession is herein proposed for this interval, comprising five associations in ascending stratigraphic order namely: (1) Dwykea-Sublagenicula-Calamospora Association (recorded in Campinas Municipality), composed of lycophyte megaspores (Sublagenicula, Trileites and Calamospora sp.) and some bryophytes (Dwykea), concerning to a coastal glacial or coastal interglacial environment; (2) Eusphenopteris-Nothorhacopteris-Botrychiopsis Association (registered in Itapeva and Buri municipalities), composed of Eusphenopteris, Nothorhacopteris, Botrychiopsis, Paracalamites spp. along with Sphenophyllum, Koretrophyllites, Noeggerathiopsis and rare Cordaicarpus and Samaropsis - concerning to an interglacial deltaic plain associated to coal forming swamps with cold temperate hydro-hygrophilous vegetation; (3) Paranocladus-Ginkgophyllum-Brasilodendron Association (registered in Monte Mor Municipality), composed of the first conifers of the Paraná Basin (Paranocladus, Paranospermum and few Buriadia-type), lycophytes (Brasilodendron, Bumbudendron), Ginkgophyllum, Noeggerathiopsis, Samaropsis and Cordaicarpus and rare Nothorhacopteris, Botrychiopsis, Koretrophyllites and Sphenophyllum, interpreted as interglacial deltaic flood plain; (4) Dwykea-Sublagenicula-Calamospora Recurrent Association (recorded in Salto Municipality), composed of bryophytes (Dwykea) and lycopod megaspores, very similar to the first association, related to a coastal glacial or

The End of the Penultimate Interglacial Recorded in Santa Barbara Basin, California

NASA Astrophysics Data System (ADS)

Cannariato, K. G.; Kennett, J. P.

2005-12-01

The marine sediments accumulating in the Santa Barbara Basin, located on the southern California margin, represent a remarkable climate archive. The high sediment accumulation rate, location at the intersection of the cool California Current and warm Countercurrent, and other factors affecting the basin have combined to make the paleoclimate records generated from these sediments highly resolved and very sensitive to global climate change. Because of the effort by Dr. James Kennett over a decade ago to persuade the Ocean Drilling Program to core the basin, the paleoceanographic community has been able to produce some of the most detailed records of Northern Hemisphere climate change over most of the last two glacial-interglacial cycles rivaling those of the Greenland ice cores. Here we present high-resolution planktic and benthic oxygen isotope records from that Santa Barbara Basin core, ODP Site 893, covering the penultimate interglacial and the beginning of the last glacial (MIS 5e to 5d transition). The results indicate that the California Current system exhibited millennial and centennial variability during the penultimate interglacial similar to the early-middle Holocene. The magnitude of this millennial variability increased dramatically and quickly during the transition from MIS 5e to 5d. These millennial-scale oscillations appear to be correlated to those recognized in the North Atlantic region. The implications of this variability will be discussed.

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

Modeling surface response of the Greenland Ice Sheet to interglacial climate

NASA Astrophysics Data System (ADS)

Rau, Dominik; Rogozhina, Irina

2013-04-01

We present a new parameterization of surface mass balance (SMB) of the Greenland Ice Sheet (GIS) under interglacial climate conditions validated against recent satellite observations on a regional scale. Based on detailed analysis of the modeled surface melting and refreezing rates, we conclude that the existing SMB parameterizations fail to capture either spatial pattern or amplitude of the observed surface response of the GIS. This is due to multiple simplifying assumptions adopted by the majority of modeling studies within the frame of the positive degree day method. Modeled spatial distribution of surface melting is found to be highly sensitive to a choice of daily temperature standard deviation (SD) and degree-day factors, which are generally assumed to have uniform distribution across the entire Greenland region. However, the use of uniform SD distribution and the range of commonly used SD values are absolutely unsupported by the ERA-40 and ERA-Interim climate data. In this region, SD distribution is highly inhomogeneous and characterized by low amplitudes during the summer months in the areas where most surface ice melting occurs. In addition, the use of identical degree day factors on both the eastern and western slopes of the GIS results in overestimation of surface runoff along the western coast of Greenland and significant underestimation along its eastern coast. Our approach is to make use of (i) spatially and seasonally variable SDs derived from ERA-40 and ERA-Interim time series, and (ii) spatially variable degree-day factors, measured across Greenland, Arctic Canada, Norway, Spitsbergen and Iceland. We demonstrate that the new approach is extremely efficient for modeling the evolution of the GIS during the observational period and the entire Holocene interglacial.

Hydrothermal deposition on the Juan de Fuca Ridge over multiple glacial-interglacial cycles

NASA Astrophysics Data System (ADS)

Costa, Kassandra M.; McManus, Jerry F.; Middleton, Jennifer L.; Langmuir, Charles H.; Huybers, Peter J.; Winckler, Gisela; Mukhopadhyay, Sujoy

2017-12-01

Hydrothermal systems play an important role in modern marine chemistry, but little is known about how they may have varied on 100,000 year timescales. Here we present high-resolution records of non-lithogenic metal fluxes within sediment cores covering the last 500,000 years of hydrothermal deposition on the flanks of the Juan de Fuca Ridge. Six adjacent, gridded cores were analyzed by x-ray fluorescence for Fe, Mn, and Cu concentrations, corrected for lithogenic inputs with Ti, and normalized to excess initial 230Th to generate non-lithogenic metal flux records that provide the longest orbitally resolved reconstructions of hydrothermal activity currently available. Fe fluxes vary with global sea level over the last two glacial cycles, suggesting higher hydrothermal deposition during interglacial periods. The observed negative relationship between Fe and Mn indicates variable sediment redox conditions and diagenetic remobilization of sedimentary Mn over time. Thus, Mn fluxes may not be a reliable indicator for hydrothermal activity in the Juan de Fuca Ridge sediment cores. Cu fluxes show substantial high-frequency variability that may be linked to changes in vent temperature related to increased magmatic production during glacial periods. Deglacial hydrothermal peaks on the Juan de Fuca Ridge are consistent with previously published records from the Mid-Atlantic Ridge and the East Pacific Rise. Moreover, on the Juan de Fuca Ridge, the deglacial peaks in hydrothermal activity are followed by relatively high hydrothermal fluxes throughout the ensuing interglacial periods relative to the previous glacial period.

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.

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

NASA Astrophysics Data System (ADS)

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

2014-12-01

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

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.

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.

Polar ice-sheet contributions to sea level during past warm periods

NASA Astrophysics Data System (ADS)

Dutton, A.

2015-12-01

Recent sea-level rise has been dominated by thermal expansion and glacier loss, but the contribution from mass loss from the Greenland and Antarctic ice sheets is expected to exceed other contributions under future sustained warming. Due to limitations of existing ice sheet models and the lack of relevant analogues in the historical record, projecting the timing and magnitude of polar ice sheet mass loss in the future remains challenging. One approach to improving our understanding of how polar ice-sheet retreat will unfold is to integrate observations and models of sea level, ice sheets, and climate during past intervals of warmth when the polar ice sheets contributed to higher sea levels. A recent review evaluated the evidence of polar ice sheet mass loss during several warm periods, including interglacials during the mid-Pliocene warm period, Marine Isotope Stage (MIS) 11, 5e (Last Interglacial), and 1 (Holocene). Sea-level benchmarks of ice-sheet retreat during the first of these three periods, when global mean climate was ~1 to 3 deg. C warmer than preindustrial, are useful for understanding the long-term potential for future sea-level rise. Despite existing uncertainties in these reconstructions, it is clear that our present climate is warming to a level associated with significant polar ice-sheet loss in the past, resulting in a conservative estimate for a global mean sea-level rise of 6 meters above present (or more). This presentation will focus on identifying the approaches that have yielded significant advances in terms of past sea level and ice sheet reconstruction as well as outstanding challenges. A key element of recent advances in sea-level reconstructions is the ability to recognize and quantify the imprint of geophysical processes, such as glacial isostatic adjustment (GIA) and dynamic topography, that lead to significant spatial variability in sea level reconstructions. Identifying specific ice-sheet sources that contributed to higher sea levels

Fossil Find on Svalbard Highlights the Natural History of the Polar Bear (Ursus maritimus)

NASA Astrophysics Data System (ADS)

Ingolfsson, O.; Wiig, O.

2007-12-01

During recent fieldwork on Svalbard a well preserved subfossil left ramus of a polar bear (Ursus maritimus) mandible was discovered. A 14C age determination shows that it is older than 45 ka (kilo-years), and an OSL (Optical Stimulated Luminescence) age determination together with the stratigraphic position of the bone suggests that it is of Eemian-Early Weichselian/Wisconsinan age, 150-80 ka old. This puts the find among the oldest fossil remains of a polar bear ever discovered. Osteological study of the mandible suggests that it comes from a fully grown female. The fossil record suggests that polar bears may have developed from brown bears during the early part of the last glacial cycle, some 100 ka ago. The present interglacial might be the first such that the species has to endure. This underlines the potential status of the polar bears as an endangered species if the current warming trend and diminishing of sea ice cover in the Arctic continues.

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

Angle of sky light polarization derived from digital images of the sky under various conditions.

PubMed

Zhang, Wenjing; Cao, Yu; Zhang, Xuanzhe; Yang, Yi; Ning, Yu

2017-01-20

Skylight polarization is used for navigation by some birds and insects. Skylight polarization also has potential for human navigation applications. Its advantages include relative immunity from interference and the absence of error accumulation over time. However, there are presently few examples of practical applications for polarization navigation technology. The main reason is its weak robustness during cloudy weather conditions. In this paper, the real-time measurement of the sky light polarization pattern across the sky has been achieved with a wide field of view camera. The images were processed under a new reference coordinate system to clearly display the symmetrical distribution of angle of polarization with respect to the solar meridian. A new algorithm for the extraction of the image axis of symmetry is proposed, in which the real-time azimuth angle between the camera and the solar meridian is accurately calculated. Our experimental results under different weather conditions show that polarization navigation has high accuracy, is strongly robust, and performs well during fog and haze, clouds, and strong sunlight.

Tridacna Derived ENSO Records From The Philippines During The Last Interglacial Show Similar ENSO Activity To The Present Day

NASA Astrophysics Data System (ADS)

Welsh, K.; Morgan, Z.; Suzuki, A.

2016-12-01

Although modeled predictions for the relative strength and frequency of ENSO under mean warming conditions suggest an increase in the number and strength of ENSO event, however there are limited seasonally resolved records of ENSO variability during previous warm periods for example the last interglacial to test these models as reliable archives such as corals are not generally well preserved over these time periods. Presented here are two multi decadal Tridacna gigas derived stable isotopic time series from a coral terrace on the island of Cebu in the Philippines that formed during MIS5e based upon geomorphology and open-system corrected U/Th dating of corals. The ENSO activity observed in these time well preserved records indicate a similar level of ENSO activity during the last interglacial period as the present day based upon comparisons with recent coral derived stable isotopic records. Though these are relatively short records they provide further windows into ENSO activity from this important time period and demonstrate this area may be provide more opportunities to gather these archives.

Exploring the Mass Balance and Sea Level Contribution of Global Glaciers During the Last Interglaciation and Mid-Holocene

NASA Astrophysics Data System (ADS)

Smith, S.; Ullman, D. J.; He, F.; Carlson, A. E.; Marzeion, B.; Maussion, F.

2017-12-01

Understanding the behavior of the world's glaciers during previous interglaciations is key to interpreting the sensitivity and behavior of the cryosphere under scenarios of future anthropogenic warming. Previous studies of the Last Interglaciation (LIG, 130 ka to 116 ka) indicate elevated global temperatures and higher sea levels than the Holocene, but most assessments of the impact on the cryosphere have focused on the mass balance and volume change of polar ice sheets. In assessing sea-level sources, most studies assume complete deglacation of global glaciers, but this has yet to be tested. In addition, the significant changes in orbital forcing during the LIG and the associated impacts on climate seasonality and variability may have led to unique glacier evolution.Here, we explore the effect of LIG climate on the global glacier budget. We employ the Open Global Glacier Model (OGGM), forced by simulated LIG equilibrium climate anomalies (127 ka) from the Community Climate System Model Version 3 (CCSM3). OGGM is a glacier mass balance and dynamics model, specifically designed to reconstruct global glacier volume change. Our simulations have been conducted in an equilibrium state to determine the effect of the prolonged climate forcing of the LIG. Due to unknown flow characteristics of glaciers during the LIG, we explore the parametric uncertainty in the mass balance and flow sensitivity parameters. As a point of comparison, we also conduct a series of simulations using forcing anomalies from the CCSM3 mid-Holocene (6 ka) experiment. Results from both experiments show that glacier mass balance is highly sensitive to these sensitivity parameters, pointing at the need for glacier margin calibration for OGGM in paleoclimate applications.

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

NASA Astrophysics Data System (ADS)

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

2012-04-01

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

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

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

Earth system model simulations show different feedback strengths of the terrestrial carbon cycle under glacial and interglacial conditions

NASA Astrophysics Data System (ADS)

Adloff, Markus; Reick, Christian H.; Claussen, Martin

2018-04-01

In simulations with the MPI Earth System Model, we study the feedback between the terrestrial carbon cycle and atmospheric CO2 concentrations under ice age and interglacial conditions. We find different sensitivities of terrestrial carbon storage to rising CO2 concentrations in the two settings. This result is obtained by comparing the transient response of the terrestrial carbon cycle to a fast and strong atmospheric CO2 concentration increase (roughly 900 ppm) in Coupled Climate Carbon Cycle Model Intercomparison Project (C4MIP)-type simulations starting from climates representing the Last Glacial Maximum (LGM) and pre-industrial times (PI). In this set-up we disentangle terrestrial contributions to the feedback from the carbon-concentration effect, acting biogeochemically via enhanced photosynthetic productivity when CO2 concentrations increase, and the carbon-climate effect, which affects the carbon cycle via greenhouse warming. We find that the carbon-concentration effect is larger under LGM than PI conditions because photosynthetic productivity is more sensitive when starting from the lower, glacial CO2 concentration and CO2 fertilization saturates later. This leads to a larger productivity increase in the LGM experiment. Concerning the carbon-climate effect, it is the PI experiment in which land carbon responds more sensitively to the warming under rising CO2 because at the already initially higher temperatures, tropical plant productivity deteriorates more strongly and extratropical carbon is respired more effectively. Consequently, land carbon losses increase faster in the PI than in the LGM case. Separating the carbon-climate and carbon-concentration effects, we find that they are almost additive for our model set-up; i.e. their synergy is small in the global sum of carbon changes. Together, the two effects result in an overall strength of the terrestrial carbon cycle feedback that is almost twice as large in the LGM experiment as in the PI experiment

Impact of glacial/interglacial sea level change on the ocean nitrogen cycle.

PubMed

Ren, Haojia; Sigman, Daniel M; Martínez-García, Alfredo; Anderson, Robert F; Chen, Min-Te; Ravelo, Ana Christina; Straub, Marietta; Wong, George T F; Haug, Gerald H

2017-08-15

The continental shelves are the most biologically dynamic regions of the ocean, and they are extensive worldwide, especially in the western North Pacific. Their area has varied dramatically over the glacial/interglacial cycles of the last million years, but the effects of this variation on ocean biological and chemical processes remain poorly understood. Conversion of nitrate to N 2 by denitrification in sediments accounts for half or more of the removal of biologically available nitrogen ("fixed N") from the ocean. The emergence of continental shelves during ice ages and their flooding during interglacials have been hypothesized to drive changes in sedimentary denitrification. Denitrification leads to the occurrence of phosphorus-bearing, N-depleted surface waters, which encourages N 2 fixation, the dominant N input to the ocean. An 860,000-y record of foraminifera shell-bound N isotopes from the South China Sea indicates that N 2 fixation covaried with sea level. The N 2 fixation changes are best explained as a response to changes in regional excess phosphorus supply due to sea level-driven variations in shallow sediment denitrification associated with the cyclic drowning and emergence of the continental shelves. This hypothesis is consistent with a glacial ocean that hosted globally lower rates of fixed N input and loss and a longer residence time for oceanic fixed N-a "sluggish" ocean N budget during ice ages. In addition, this work provides a clear sign of sea level-driven glacial/interglacial oscillations in biogeochemical fluxes at and near the ocean margins, with implications for coastal organisms and ecosystems.

Impact of glacial/interglacial sea level change on the ocean nitrogen cycle

NASA Astrophysics Data System (ADS)

Ren, Haojia; Sigman, Daniel M.; Martínez-García, Alfredo; Anderson, Robert F.; Chen, Min-Te; Ravelo, Ana Christina; Straub, Marietta; Wong, George T. F.; Haug, Gerald H.

2017-08-01

The continental shelves are the most biologically dynamic regions of the ocean, and they are extensive worldwide, especially in the western North Pacific. Their area has varied dramatically over the glacial/interglacial cycles of the last million years, but the effects of this variation on ocean biological and chemical processes remain poorly understood. Conversion of nitrate to N2 by denitrification in sediments accounts for half or more of the removal of biologically available nitrogen (“fixed N”) from the ocean. The emergence of continental shelves during ice ages and their flooding during interglacials have been hypothesized to drive changes in sedimentary denitrification. Denitrification leads to the occurrence of phosphorus-bearing, N-depleted surface waters, which encourages N2 fixation, the dominant N input to the ocean. An 860,000-y record of foraminifera shell-bound N isotopes from the South China Sea indicates that N2 fixation covaried with sea level. The N2 fixation changes are best explained as a response to changes in regional excess phosphorus supply due to sea level-driven variations in shallow sediment denitrification associated with the cyclic drowning and emergence of the continental shelves. This hypothesis is consistent with a glacial ocean that hosted globally lower rates of fixed N input and loss and a longer residence time for oceanic fixed N—a “sluggish” ocean N budget during ice ages. In addition, this work provides a clear sign of sea level-driven glacial/interglacial oscillations in biogeochemical fluxes at and near the ocean margins, with implications for coastal organisms and ecosystems.

Impact of glacial/interglacial sea level change on the ocean nitrogen cycle

PubMed Central

Ren, Haojia; Sigman, Daniel M.; Martínez-García, Alfredo; Anderson, Robert F.; Chen, Min-Te; Ravelo, Ana Christina; Straub, Marietta; Wong, George T. F.; Haug, Gerald H.

2017-01-01

The continental shelves are the most biologically dynamic regions of the ocean, and they are extensive worldwide, especially in the western North Pacific. Their area has varied dramatically over the glacial/interglacial cycles of the last million years, but the effects of this variation on ocean biological and chemical processes remain poorly understood. Conversion of nitrate to N2 by denitrification in sediments accounts for half or more of the removal of biologically available nitrogen (“fixed N”) from the ocean. The emergence of continental shelves during ice ages and their flooding during interglacials have been hypothesized to drive changes in sedimentary denitrification. Denitrification leads to the occurrence of phosphorus-bearing, N-depleted surface waters, which encourages N2 fixation, the dominant N input to the ocean. An 860,000-y record of foraminifera shell-bound N isotopes from the South China Sea indicates that N2 fixation covaried with sea level. The N2 fixation changes are best explained as a response to changes in regional excess phosphorus supply due to sea level-driven variations in shallow sediment denitrification associated with the cyclic drowning and emergence of the continental shelves. This hypothesis is consistent with a glacial ocean that hosted globally lower rates of fixed N input and loss and a longer residence time for oceanic fixed N—a “sluggish” ocean N budget during ice ages. In addition, this work provides a clear sign of sea level-driven glacial/interglacial oscillations in biogeochemical fluxes at and near the ocean margins, with implications for coastal organisms and ecosystems. PMID:28760968

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.

Modern and Interglacial Marine Ostracode Species Diversity Patterns off Eastern North America

NASA Astrophysics Data System (ADS)

Chiu, W. T. R.; Yasuhara, M.; Cronin, T. M.; Hunt, G.; Gemery, L.

2016-02-01

Latitudinal species diversity gradients (LSDGs) are a major feature of various marine groups. However, the detailed shape of LSDG in each marine taxonomic group and the causes of the diversity patterns, notably climatic factors, are still controversial due to limited sampling of many taxa in the world's oceans. We analyzed benthic podocopid ostracode faunal assemblages on the continental shelf regions from Arctic to tropical regions off eastern North America to determine biodiversity patterns and their relationships to oceanographic conditions (temperature, productivity, etc). Our database consists of 200 ostracode species from more than 100 bottom sediment samples. Preliminary results suggest that biodiversity, as measured using simple diversity (S), rarefaction, Shannon and α-Fisher indices, show strong latitudinal diversity gradients in which diversity is 2 to 3 times higher in tropical and subtropical regions that in northern high latitude areas. These modern ostracode diversity patterns will be compared with those from past interglacial periods of global warmth during the Pliocene and Pleistocene to assess the impact of warmer-than- present climate conditions on diversity.

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.

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

NASA Astrophysics Data System (ADS)

Hu, Xue-Feng; Du, Yan

2013-04-01

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

Polypedogenic case of loess overlying red clay as a response to the Last Glacial-Interglacial cycle in mid-subtropical Southeast China

NASA Astrophysics Data System (ADS)

Hu, Xue-Feng; Du, Yan; Liu, Xiang-Jun; Zhang, Gan-Lin; Jiang, Ying; Xue, Yong

2015-03-01

To study the paleoclimatic implications of the loess-like Yellow-brown Earth (YBE) overlying red clay (RC) along the Yangtze River, mid-subtropical Southeast China, four YBE-RC profiles in southern Anhui Province were investigated. Grain-size and geochemical characteristics indicated that the YBE is homologous to the aeolian Xiashu Loess; and the underlying RC, sub-divided into uniform RC (URC) and reticulate RC (RRC), is more intensively weathered but also exhibits aeolian dust characteristics. Optically stimulated luminescence (OSL) dating indicated that the YBE was formed during the Last Glacial, the RRC mainly during the Last Interglacial, and the URC during the transitional period between the YBE and RC. The YBE-RC transition reflects a significant paleoclimatic change in mid-subtropical China during the Last Glacial-Interglacial cycle. Sub-events of the Last Glacial, correlated with the marine isotopic stages (MIS) 2 and 3, can be identified within the YBE; however, those of the Last Interglacial, potential correlated with MIS 5a-5e, cannot be identified within the RRC possibly due to paleoclimatic overprinting. The rubification had been replaced by loess deposition along the Yangtze River since the early Last Glacial. With both highly weathered and aeolian-dust characteristics, the underlying RRC may indicate paleoclimatic instability given the multiple alternations between loess deposition and rubification of the Last Interglacial. The climatic change during the Last Glacial-Interglacial cycle significantly influenced the pedogenesis and made soil diversified in the study areas.

Sensitivity of the Greenland Ice Sheet to Interglacial Climate Forcing: MIS 5e Versus MIS 11

NASA Astrophysics Data System (ADS)

Rachmayani, Rima; Prange, Matthias; Lunt, Daniel J.; Stone, Emma J.; Schulz, Michael

2017-11-01

The Greenland Ice Sheet (GrIS) is thought to have contributed substantially to high global sea levels during the interglacials of Marine Isotope Stage (MIS) 5e and 11. Geological evidence suggests that the mass loss of the GrIS was greater during the peak interglacial of MIS 11 than MIS 5e, despite a weaker boreal summer insolation. We address this conundrum by using the three-dimensional thermomechanical ice sheet model Glimmer forced by Community Climate System Model version 3 output for MIS 5e and MIS 11 interglacial time slices. Our results suggest a stronger sensitivity of the GrIS to MIS 11 climate forcing than to MIS 5e forcing. Besides stronger greenhouse gas radiative forcing, the greater MIS 11 GrIS mass loss relative to MIS 5e is attributed to a larger oceanic heat transport toward high latitudes by a stronger Atlantic meridional overturning circulation. The vigorous MIS 11 ocean overturning, in turn, is related to a stronger wind-driven salt transport from low to high latitudes promoting North Atlantic Deep Water formation. The orbital insolation forcing, which causes the ocean current anomalies, is discussed.

Solving the riddle of interglacial temperatures over the last 1.5 million years with a future IPICS "Oldest Ice" ice core

NASA Astrophysics Data System (ADS)

Fischer, Hubertus

2014-05-01

The sequence of the last 8 glacial cycles is characterized by irregular 100,000 year cycles in temperature and sea level. In contrast, the time period between 1.5-1.2 million years ago is characterized by more regular cycles with an obliquity periodicity of 41,000 years. Based on a deconvolution of deep ocean temperature and ice volume contributions to benthic δ18O (Elderfield et al., Science, 2012), it is suggested that glacial sea level became progressively lower over the last 1.5 Myr, while glacial deep ocean temperatures were very similar. At the same time many interglacials prior to the Mid Brunhes event showed significantly cooler deep ocean temperatures than the Holocene, while at the same time interglacial ice volume remained essentially the same. In contrast, interglacial sea surface temperatures in the tropics changed little (Herbert et al., Science,2010) and proxy reconstructions of atmospheric CO2 using δ11B in planktic foraminifera (Hönisch et al., Science, 2009) suggest that prior to 900,000 yr before present interglacial CO2 levels did not differ substantially from those over the last 450,000 years. Accordingly, the conundrum arises how interglacials can differ in deep ocean temperature without any obvious change in ice volume or greenhouse gas forcing and what caused the change in cyclicity of glacial interglacial cycles over the Mid Pleistocene Transition. Probably the most important contribution to solve this riddle is the recovery of a 1.5 Myr old ice core from Antarctica, which among others would provide an unambiguous, high-resolution record of the greenhouse gas history over this time period. Accordingly, the international ice core community, as represented by the International Partnership for Ice Core Science (IPICS), has identified such an 'Oldest Ice' ice core as one of the most important scientific targets for the future (http://www.pages.unibe.ch/ipics/white-papers). However, finding stratigraphically undisturbed ice, which covers this

Climate Events and Cycles During the Last Glacial-Interglacial Transition

NASA Astrophysics Data System (ADS)

Lee, Eun Hee; Lee, Dae-Young; Park, Mi-Young

2017-09-01

During the last glacial-interglacial transition, there were multiple intense climatic events such as the Bølling-Allerød warming and Younger Dryas cooling. These events show abrupt and rapid climatic changes. In this study, the climate events and cycles during this interval are examined through wavelet analysis of Arctic and Antarctic ice-core 18O and tropical marine 14C records. The results show that periods of 1383-1402, 1029-1043, 726-736, 441-497 and 202-247 years are dominant in the Arctic region, whereas periods of 1480, 765, 518, 311, and 207 years are prominent in the Antarctic TALDICE. In addition, cycles of 1019, 515, and 209 years are distinct in the tropical region. Among these variations, the de Vries cycle of 202-209 years, correlated with variations in solar activity, was detected globally. In particular, this cycle shows a strong signal in the Antarctic between about 13,000 and 10,500 yr before present (BP). In contrast, the Eddy cycle of 1019-1043 years was prominent in Greenland and the tropical region, but was not detected in the Antarctic TALDICE records. Instead, these records showed that the Heinrich cycle of 1480 year was very strong and significant throughout the last glacial-interglacial interval.

Investigating Mercury's South Polar Deposits with High-Resolution Determination of Illumination Conditions

NASA Astrophysics Data System (ADS)

Shread, E. E.; Chabot, N. L.

2018-05-01

High-resolution images acquired by MESSENGER's Mercury Dual Imaging System were used to investigate the illumination conditions of Mercury's south polar deposits and to map the areas of permanent shadow in the region to compare with radar imaging.

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.

Giant Ferroelectric Polarization in Ultrathin Ferroelectrics via Boundary-Condition Engineering.

PubMed

Xie, Lin; Li, Linze; Heikes, Colin A; Zhang, Yi; Hong, Zijian; Gao, Peng; Nelson, Christopher T; Xue, Fei; Kioupakis, Emmanouil; Chen, Longqing; Schlom, Darrel G; Wang, Peng; Pan, Xiaoqing

2017-08-01

Tailoring and enhancing the functional properties of materials at reduced dimension is critical for continuous advancement of modern electronic devices. Here, the discovery of local surface induced giant spontaneous polarization in ultrathin BiFeO 3 ferroelectric films is reported. Using aberration-corrected scanning transmission electron microscopy, it is found that the spontaneous polarization in a 2 nm-thick ultrathin BiFeO 3 film is abnormally increased up to ≈90-100 µC cm -2 in the out-of-plane direction and a peculiar rumpled nanodomain structure with very large variation in c/a ratios, which is analogous to morphotropic phase boundaries (MPBs), is formed. By a combination of density functional theory and phase-field calculations, it is shown that it is the unique single atomic Bi 2 O 3 - x layer at the surface that leads to the enhanced polarization and appearance of the MPB-like nanodomain structure. This finding clearly demonstrates a novel route to the enhanced functional properties in the material system with reduced dimension via engineering the surface boundary conditions. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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.

Conditional Bounds on Polarization Transfer

NASA Astrophysics Data System (ADS)

Nielsen, N. C.; Sorensen, O. W.

The implications of constraints on unitary transformations of spin operators with respect to the accessible regions of Liouville space are analyzed. Specifically, the effects of spin-permutation symmetry on the unitary propagators are investigated. The influence of S2 and S3 propagator symmetry on two-dimensional bounds for F z = Σ Ni=1 I iz ↔ G z = Σ Mj=1 S jz polarization transfer in IS and I 2S spin- {1}/{2} systems is examined in detail. One result is that the maximum achievable F z ↔ G z polarization transfer is not reduced by permutation symmetry among the spins. For I 2S spin systems, S3 symmetry in the unitary propagator is shown to significantly reduce the accessible region in the 2D F z-S z Liouville subspace compared to the case restricted by unitarity alone. That result is compared with transformations under symmetric dipolar and scalar J coupling as well as shift and RF interactions. An important practical implication is that the refined spin thermodynamic theory of Levitt, Suter, and Ernst ( J. Chem. Phys.84, 4243, 1986) for cross polarization in solid-state NMR does not predict experimental outcomes incompatible with constraints of unitarity and spin-permutation symmetry.

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°.

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

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

Ice core evidence for extensive melting of the greenland ice sheet in the last interglacial.

PubMed

Koerner, R M

1989-05-26

Evidence from ice at the bottom of ice cores from the Canadian Arctic Islands and Camp Century and Dye-3 in Greenland suggests that the Greenland ice sheet melted extensively or completely during the last interglacial period more than 100 ka (thousand years ago), in contrast to earlier interpretations. The presence of dirt particles in the basal ice has previously been thought to indicate that the base of the ice sheets had melted and that the evidence for the time of original growth of these ice masses had been destroyed. However, the particles most likely blew onto the ice when the dimensions of the ice caps and ice sheets were much smaller. Ice texture, gas content, and other evidence also suggest that the basal ice at each drill site is superimposed ice, a type of ice typical of the early growth stages of an ice cap or ice sheet. If the present-day ice masses began their growth during the last interglacial, the ice sheet from the earlier (Illinoian) glacial period must have competely or largely melted during the early part of the same interglacial period. If such melting did occur, the 6-meter higher-than-present sea level during the Sangamon cannot be attributed to disintegration of the West Antarctic ice sheet, as has been suggested.

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

NASA Astrophysics Data System (ADS)

Kleinen, Thomas; Brovkin, Victor; Munhoven, Guy

2016-11-01

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

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

Loess deposits in Beijing and their paleoclimatic implications during the last interglacial-glacial cycle

NASA Astrophysics Data System (ADS)

Tian, Shengchen; Sun, Jimin; Gong, Zhijun

2017-12-01

Loess-paleosol sequences are important terrestrial paleoclimatic archives in the semi-arid region of north-central China. Compared with the numerous studies on the loess of the Chinese Loess Plateau, the eolian deposits, near Beijing, have not been well studied. A new loess section in the northeast suburb of Beijing provides an opportunity for reconstructing paleoenvironmental changes in this region. An optically stimulated luminescence (OSL) chronology yields ages of 145.1 to 20.5 ka, demonstrating that the loess deposits accumulated during the last interglacial-glacial cycle. High-resolution climatic proxies, including color-index, particle size and magnetic parameters, reveal orbital-scale climatic cycles, corresponding to marine oxygen isotope stages (MIS) 6 to MIS 2. In contrast to the loess deposits of the central Loess Plateau, loess near Beijing is a mixture of distal dust materials from gobi and sand deserts in the arid part of northwestern China and proximal, local alluvial sediments. Climatic change in Beijing during the last interglacial-glacial cycle was controlled primarily by the changing strength of the East Asian monsoon. Paleosols developed during the last interglacial complex (between 144.0 and 73.0 ka) and the interstadial of the last glaciation (between 44.6 and 36.2 ka), being associated with an enhanced summer monsoon in response to increased low-latitude insolation and a weakened Siberia High. Loess accumulation occurred during cold-dry stages of the last glaciation, in response to the intensified winter monsoon driven by the strengthened Siberia High and its longer residence time.

Penultimate Glacial-Interglacial Climate Variability in the Southern Great Plains of North America

NASA Astrophysics Data System (ADS)

Bartow-Gillies, E.; Maupin, C. R.; Roark, E. B.; Chou, Y. C.; White, K.; Kampen-Lewis, S. V.; Shen, C. C.

2017-12-01

Projections of changes in rainfall under future warming scenarios vary in their sign and intensity over the Southern Great Plains (SGP). A scarcity of local paleoclimate information before the Last Glacial Maximum (LGM) limits our understanding of regional climate responses to changes in mean state and forcing. Here, we present absolutely U/Th-dated oxygen and carbon isotope records from a calcite stalagmite near Georgetown, Texas (30°N, 98°W), spanning 98 to 209 kyr before present (kyr BP). SGP moisture is primarily sourced from the Gulf of Mexico, and precipitation exhibits clear seasonality, with a biannual rainy season divided into late boreal spring and fall. We interpret the oxygen isotopic composition of the stalagmite to reflect changes in rainwater δ18O composition, as well as cave temperature, through time. There are no clear kinetic isotope effects observed within the stalagmite. More negative (positive) δ18O values are a reflection of warmer and wetter (cooler and drier) conditions based on modern observations of rainwater δ18O at the study site. Variations in stalagmite δ13C may be driven by shifts in overlying vegetation type and changes in the rates of karst flow and prior calcite precipitation. The stalagmite records include Marine Isotope Stage (MIS) 5e, an interval where global temperatures may have been as much as 2°C warmer and sea level 4-6 m higher than present. Thus, our δ18O record provides context of unique importance for how SGP hydroclimate may respond to future warming. Prominent features in the δ18O record, including a warm and wet MIS 5e appear to be paced by precession, with the timing of δ18O minima (maxima) broadly consistent with that of maxima (minima) in monthly insolation at 30°N. The δ13C record exhibits a striking similarity to canonical, sawtooth records of glacial-interglacial variability, which suggests Great Plains vegetation communities may be sensitive to the status of Northern Hemisphere glaciation. Our SGP

The last interglacial in eastern Canada and the northwest North Atlantic : further evidence for warmer climate and ocean conditions than during the Holocene

NASA Astrophysics Data System (ADS)

de Vernal, A.; Fréchette, B.; Hillaire-Marcel, C.; van Nieuwenhove, N.; Retailleau, S.

2012-04-01

The climate conditions of the last interglacial (LI) in northeastern and southeastern Canada are documented from pollen data of Baffin Island and Cape Breton Island respectively. The LI pollen assemblages indicate very different vegetation than at present and a northern limit of the deciduous forest biome as far as 500 km north of its modern position. The application of the modern analogue technique also reveal warmer climate during the LI than at present, 4-5°C warmer on Baffin Island at ~67-70°N in the Canadian Arctic, and up to 7°C warmer on Cape Breton Island at ~45°N in the southeastern Canada. The contrast between LI and Holocene climates is also shown from marine data (dinocysts, foraminifers, oxygen and carbon isotopes) that document warmer than Holocene conditions in surface waters (up to 5.5°C in summer, notably off southwest Greenland) and very distinct distribution of intermediate to deep waters in northern and southern part of the Labrador Sea. An important zonal atmospheric circulation component at mid-latitudes of the North Atlantic is also evidenced from the pollen content of marine cores collected in central North Atlantic (IODP Site 1304), which strongly suggests an origin from southeastern Canada. Altogether the data demonstrate much warmer conditions along the eastern Canadian margins, from North to South. The mild conditions along the coastlines and the relatively warm waters off eastern Canada and southern Greenland suggest reduced Arctic outflow components through the East Greenland Current and Labrador Current. Comparisons with records from eastern North Atlantic lead us to conclude in a more zonal climate during the LI than the Holocene, especially the early Holocene that was marked by a particularly pronounced west to east gradient of temperatures. Hence, the thermal optimum of the LI and that of the Holocene provide two examples of very different climate and ocean circulation regimes in the circum-Atlantic region during the "warm

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).

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.

Glacial vs. Interglacial Period Contrasts in Midlatitude Fluvial Systems, with Examples from Western Europe and the Texas Coastal Plain

NASA Astrophysics Data System (ADS)

Blum, M.

2001-12-01

Mixed bedrock-alluvial valleys are the conveyor belts for sediment delivery to passive continental margins. Mapping, stratigraphic and sedimentologic investigations, and development of geochronological frameworks for large midlatitude rivers of this type, in Western Europe and the Texas Coastal Plain, provide for evaluation of fluvial responses to climate change over the last glacial-interglacial period, and the foundations for future quantitative evaluation of long profile evolution, changes through time in flood magnitude, and changes in storage and flux of sediments. This paper focuses on two issues. First, glacial vs. interglacial period fluvial systems are fundamentally different in terms of channel geometry, depositional style, and patterns of sediment storage. Glacial-period systems were dominated by coarse-grained channel belts (braided channels in Europe, large-wavelength meandering in Texas), and lacked fine-grained flood-plain deposits, whereas Holocene units, especially those of late Holocene age, contain appreciable thicknesses of flood-plain facies. Hence, extreme overbank flooding was not significant during the long glacial period, most flood events were contained within bankfull channel perimeters, and fine sediments were bypassed through the system to marine basins. By contrast, extreme overbank floods have been increasingly important during the relatively short Holocene, and a significant volume of fine sediment is sequestered in flood-plain settings. Second, glacial vs. interglacial systems exhibit different amplitudes and frequencies of fluvial adjustment to climate change. High-amplitude but low-frequency adjustments characterized the long glacial period, with 2-3 extended periods of lateral migration and sediment storage puncuated by episodes of valley incision. Low-amplitude but high-frequency adjustments have been more typical of the short Holocene, when there has been little net valley incision or net changes in sediment storage, but

Sub-Auroral Polarization Stream (SAPS) Events Under Non-storm Conditions

NASA Astrophysics Data System (ADS)

Sazykin, S. Y.; Coster, A. J.; Huba, J.; Spiro, R. W.; Baker, J. B.; Kunduri, B.; Ruohoniemi, J. M.; Erickson, P. J.; Wolf, R.

2017-12-01

The occurrence of Sub-Auroral Polarization Stream, or SAPS, structures, defined here as latitudinally narrow channels of enhanced westward plasma convection in the evening ionosphere equatorward of the auroral electron precipitation boundary, is most dramatic during geomagnetic storms. However, SAPS-like structures known as Polarization Jets or SAIDs (Sub-Auroral Ion Drift events) are also frequently observed during non-storm conditions, typically during periods of isolated substorm activity or during bursts of enhanced convection associated with southward IMF Bz component. This paper presents results from data analysis and numerical simulations of several SAPS/SAID events observed during non-storm conditions. We use convection velocity measurements from the mid-latitude chain of SuperDARN radars and cross-track drift meter data from DMSP spacecraft to identify SAPS/SAID and to characterize their structure and temporal evolution. DMSP topside ion density data and high-resolution ground-based GPS total electron content (TEC) maps are used to determine the ionospheric and plasmaspheric morphology of SAPS regions. DMSP electron precipitation data are used to determine auroral boundaries. We also present simulation results of the chosen event intervals obtained with the SAMI3-RCM ionosphere-magnetosphere coupled model. Observational results are analyzed to identify systematic differences between non-storm SAPS/SAID and the picture that has emerged based on previous storm time studies. Simulation results are used to provide physical interpretation of these differences.

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

Constraints on the thermosteric component of Last Interglacial sea level

NASA Astrophysics Data System (ADS)

Shackleton, S. A.; Severinghaus, J. P.; Petrenko, V. V.; Dyonisius, M.; Hmiel, B.

2016-12-01

With global temperatures 1 to 2°C above preindustrial, but sea level exceeding current levels by upwards of 8 meters, the Last Interglacial (LIG) period at 125 ka may provide valuable insight into Earth system constraints under future global warming. The relative contributions of thermal expansion and ice sheet loss to sea level rise over this period are of particular interest in seeking to improve sea level projections in the upcoming decades and beyond. Here we quantify this thermosteric component from a reconstruction of global ocean temperature over the LIG from atmospheric noble gases trapped in glacial ice. With no major sources or sinks outside of the ocean-atmosphere system, the relative changes in the atmospheric content of krypton, xenon, and nitrogen reflect changes in ocean gas storage. This storage is primarily governed by solubility and ocean temperature, making dKr/N2, dXe/N2­, and dXe/Kr unique tracers of globally integrated oceanic heat content. However, processes within the firn can fractionate these gases, and firn effects on these tracers must be removed to derive an ocean temperature. We present high precision measurements of these gas ratios along with isotopes of argon, krypton, and xenon in firn air withdrawn from the snowpack at Summit, Greenland. We use these isotopes to identify sources of fractionation within the firn and quantify their effects on the noble gas tracers, enabling a reconstruction of Last Interglacial ocean temperature.

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.

The Glacial-Interglacial summer monsoon recorded in southwest Sulawesi speleothems: Evidence for sea level thresholds driving tropical monsoon strength

NASA Astrophysics Data System (ADS)

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

2016-12-01

Southwest Sulawesi lies within the Indo-Pacific Warm Pool (IPWP), at the center of atmospheric convection for two of the largest circulation cells on the planet, the meridional Hadley Cell and zonal Indo-Pacific Walker Circulation. Due to the geographic coincidence of these circulation cells, southwest Sulawesi serves as a hotspot for changes in tropical Pacific climate variability and Australian-Indonesian summer monsoon (AISM) strength over glacial-interglacial (G-I) timescales. The work presented here spans 386 - 127 ky BP, including glacial terminations IV ( 340 ky BP) and both phases of TIII (TIII 248 ky BP and TIIIa 217 ky BP). This record, along with previous work from southwest Sulawesi spanning the last 40 kyr, reveals coherent climatic features over three complete G-I cycles. The multi-stalagmite Sulawesi speleothem δ18O record demonstrates that on G-I timescales, the strength of the AISM is most sensitive to changes in sea level and its impact on the regional distribution of land and shallow ocean. Stalagmite δ18O and trace element (Mg/Ca) data indicate a rapid increase in rainfall at glacial terminations and wet interglacials. TIV, TIII, TIIIa, and TI are each characterized by an abrupt 3‰ decrease in δ18O that coincides with sea level rise and flooding of the Sunda and Sahul shelves. Strong evidence for a sea level (flooding/exposure) threshold is found throughout the southwest Sulawesi record. This is most clearly demonstrated over the period 230 - 212 ky BP (MIS 7d-7c), when a sea level fall to only -80 to -60 m for 10 kyr results in a weakened AISM and glacial conditions, followed by a full termination. Taken together, both glaciations and glacial terminations imply a sea level threshold driving the AISM between two primary levels of intensity (`interglacial' & `glacial'). These massive, sea-level driven shifts in AISM strength are superimposed on precession-scale variability associated with boreal fall insolation at the equator, indicating

Lunar Polar Environmental Testing: Regolith Simulant Conditioning

NASA Technical Reports Server (NTRS)

Kleinhenz, Julie

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.

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

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.

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

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

Impact of paleoceanographic changes at glacial/interglacial transitions on benthic foraminiferal faunas of the eastern North Atlantic (IODP Expedition 339, Site U1385)

NASA Astrophysics Data System (ADS)

Grunert, Patrick; Hodell, David; Alvarez Zarikian, Carlos; Hernández-Molina, F. Javier; Stow, Dorrik A. V.

2014-05-01

Communities of deep-sea foraminifera are sensitive recorders of environmental conditions. Consequently, the actualistic interpretation of fossil foraminiferal assemblages has become a valuable tool for the reconstruction of paleoceanographic conditions at the sea-floor. For the present study, a quantitative data-set of benthic foraminifera >125μm from the eastern North Atlantic has been analysed to understand paleoceanographic changes (AMOC, ventilation, productivity) associated with glacial/interglacial transitions in more detail. The data-set consists of a series of samples from IODP Site U1385 spanning Terminations I, II and IV and several short-term (millennial-scale) climatic events including the Younger Dryas (YD), Heinrich (H) 1, and H 11. On the family and generic levels, a characteristic succession of foraminiferal assemblages can be recognized at all studied glacial/interglacial transitions: a glacial fauna with abundant occurrences of cassidulinids (Cassidulina, Globocassidulina); a fauna characterized by high abundances of buliminds (Bulimina, Globobulimina) and/or bolivinellids (Bolivinita) that is associated with H-events and the beginning of each termination; a fauna with high abundances of miliolids (mainly Pyrgo) and cibicidids at the end of the termination; an interglacial fauna composed of buliminds (Bulimina), gavellinellids (Gyroidinoides), and pseudoparrellids (Epistominella). For the glacial and interglacial endmembers, this succession indicates a moderately oxygenated environment at the seafloor with mesotrophic conditions due to moderate export productivity. For the early phase of the terminations as well as the short-term events, the dominance of infaunal taxa and high abundances of deep infaunal taxa indicate an environment with high export productivity that is mainly controlled by oxygen. Conversely, the absence of these taxa and the presence of miliolids suggests well-ventilated environments and decreasing export productivity during

Vegetation responses to interglacial warming in the Arctic: examples from Lake El'gygytgyn, Far East Russian Arctic

NASA Astrophysics Data System (ADS)

Lozhkin, A. V.; Anderson, P. M.

2013-06-01

Preliminary analyses of Lake El'gygytgyn sediment indicate a wide range of ecosystem responses to warmer than present climates. While palynological work describing all interglacial vegetation is ongoing, sufficient data exist to compare recent warm events (the postglacial thermal maximum, PGTM, and marine isotope stage, MIS5) with "super" interglaciations (MIS11, MIS31). Palynological assemblages associated with these climatic optima suggest two types of vegetation responses: one dominated by deciduous taxa (PGTM, MIS5) and the second by evergreen conifers (MIS11, MIS31). MIS11 forests show a similarity to modern Picea-Larix-Betula-Alnus forests of Siberia. While dark coniferous forest also characterizes MIS31, the pollen taxa show an affinity to the boreal forest of the lower Amur valley (southern Russian Far East). Despite vegetation differences during these thermal maxima, all glacial-interglacial transitions are alike, being dominated by deciduous woody taxa. Initially Betula shrub tundra established and was replaced by tundra with tree-sized shrubs (PGTM), Betula woodland (MIS5), or Betula-Larix (MIS11, MIS31) forest. The consistent occurrence of deciduous forest and/or high shrub tundra before the incidence of maximum warmth underscores the importance of this biome for modeling efforts. The El'gygytgyn data also suggest a possible elimination or massive reduction of Arctic plant communities under extreme warm-earth scenarios.

Sea-level history of past interglacial periods: New evidence from uranium-series dating of corals from Curaçao, Leeward Antilles islands

USGS Publications Warehouse

Muhs, Daniel R.; Pandolfi, John M.; Simmons, Kathleen R.; Schumann, R. Randall

2012-01-01

Curaçao has reef terraces with the potential to provide sea-level histories of interglacial periods. Ages of the Hato (upper) unit of the “Lower Terrace” indicate that this reef dates to the last interglacial period, Marine Isotope Stage (MIS) 5.5. On Curaçao, this high sea stand lasted at least 8000 yr (~ 126 to ~ 118 ka). Elevations and age of this reef show that late Quaternary uplift rates on Curaçao are low, 0.026–0.054 m/ka, consistent with its tectonic setting. Ages of ~ 200 ka for corals from the older Cortalein unit of the Lower Terrace correlate this reef to MIS 7, with paleo-sea level estimates ranging from − 3.3 m to + 2.3 m. The estimates are in agreement with those for MIS 7 made from other localities and indicate that the penultimate interglacial period was a time of significant warmth, on a par with the present interglacial period. The ~ 400 ka (MIS 11) Middle Terrace I on Curaçao, dated by others, may have formed from a paleo-sea level of + 8.3 to + 10.0 m, or (less likely) + 17 m to + 20 m. The lower estimates are conservative compared to previous studies, but still require major ice sheet loss from Greenland and Antarctica.

Vegetation responses to abrupt climatic changes during the Last Interglacial Complex (Marine Isotope Stage 5) at Tenaghi Philippon, NE Greece

NASA Astrophysics Data System (ADS)

Milner, A. M.; Roucoux, K. H.; Collier, R. E. L.; Müller, U. C.; Pross, J.; Tzedakis, P. C.

2016-12-01

The discovery that climate variability during the Last Glacial shifted rapidly between climate states has intensified efforts to understand the distribution, timing and impact of abrupt climate change under a wide range of boundary conditions. In contribution to this, we investigate the nature of abrupt environmental changes in terrestrial settings of the Mediterranean region during the Last Interglacial Complex (Marine Isotope Stage [MIS] 5) and explore the relationships of these changes to high-latitude climate events. We present a new, temporally highly resolved (mean: 170 years) pollen record for the Last Interglacial Complex from Tenaghi Philippon, north-east Greece. The new pollen record, which spans the interval from 130,000 to 65,000 years ago, forms part of an exceptionally long polleniferous sediment archive covering the last 1.35 million years. The pollen data reveal an interglacial followed by alternating forest and steppe phases representing the interstadials and stadials of the Early Glacial. Superimposed on these millennial-scale changes is evidence of persistent sub-millennial-scale variability. We identify ten high-amplitude abrupt events in the pollen record, characterised by rapid contractions of closed forest to open steppe environment and interpreted to indicate major changes in moisture availability and temperature. The contractions in forest cover on millennial timescales appear associated with cooling events in the Mediterranean Sea, North Atlantic and Greenland regions, linked to the Dansgaard-Oeschger (DO) cycles of the Early Glacial. On sub-millennial timescales, the pattern of changes in forest cover at Tenaghi Philippon display a structure similar to the pattern of short-lived precursor and rebound-type events detected in the Greenland ice-core record. Our findings indicate that persistent, high-amplitude environmental variability occurred throughout the Early Glacial, on both millennial and submillennial timescales. Furthermore, the

Quaternary history of sea ice and paleoclimate in the Amerasia Basin, Arctic Ocean, as recorded in the cyclical strata of Northwind Ridge

USGS Publications Warehouse

Phillips, R.L.; Grantz, A.

1997-01-01

productivity, and strong oxidization of the pelagic sediment. The lithostratigraphy of Northwind Ridge suggests that during at least late Pleistocene time, glacial conditions in the Arctic Ocean were initiated abruptly and continued unabated until terminated, also abruptly, by onset of the succeeding interglacial warming. Variations in abundance of glacial erratics within the interglacial units of the late Pleistocene indicate that during at least most interglacial episodes northern North America was glaciated, but with generally diminishing severity, until onset of the succeeding continental glaciation. Magnetostratigraphy suggests that the glacial-interglacial cycles on Northwind Ridge had an average periodicity of approximately 93.5 k.y. during the Brunhes normal and approximately 105 k.y. during the latter part of the Matuyama reverse polarity zone. These average periodicities are close to the 100 k.y. temperature cycles found in North Atlantic deep-water sediments of the Brunhes normal polarity chron, which have been ascribed to forcing by a Milankovitch eccentricity cycle. They are also close, however, to the average interval (101 k.y.) between the aperiodic glacial terminations in the 500 k.y. Pleistocene continental climate record from Devil's Hole, Nevada, which have been ascribed to nonlinear feedbacks within the Earth's atmosphere-ice sheet-ocean system.

Glacial-interglacial atmospheric CO2 change: a possible "standing volume" effect on deep-ocean carbon sequestration

NASA Astrophysics Data System (ADS)

Skinner, L. C.

2009-09-01

So far, the exploration of possible mechanisms for glacial atmospheric CO2 drawdown and marine carbon sequestration has tended to focus on dynamic or kinetic processes (i.e. variable mixing-, equilibration- or export rates). Here an attempt is made to underline instead the possible importance of changes in the standing volumes of intra-oceanic carbon reservoirs (i.e. different water-masses) in influencing the total marine carbon inventory. By way of illustration, a simple mechanism is proposed for enhancing the marine carbon inventory via an increase in the volume of relatively cold and carbon-enriched deep water, analogous to modern Lower Circumpolar Deep Water (LCDW), filling the ocean basins. A set of simple box-model experiments confirm the expectation that a deep sea dominated by an expanded LCDW-like watermass holds more CO2, without any pre-imposed changes in ocean overturning rate, biological export or ocean-atmosphere exchange. The magnitude of this "standing volume effect" (which operates by boosting the solubility- and biological pumps) might be as large as the contributions that have previously been attributed to carbonate compensation, terrestrial biosphere reduction or ocean fertilisation for example. By providing a means of not only enhancing but also driving changes in the efficiency of the biological- and solubility pumps, this standing volume mechanism may help to reduce the amount of glacial-interglacial CO2 change that remains to be explained by other mechanisms that are difficult to assess in the geological archive, such as reduced mass transport or mixing rates in particular. This in turn could help narrow the search for forcing conditions capable of pushing the global carbon cycle between glacial and interglacial modes.

Seasonally resolved climate variability during the last interglacial from southern Caribbean corals

NASA Astrophysics Data System (ADS)

Brocas, William; Felis, Thomas; Kölling, Martin; Scholz, Denis; Lohmann, Gerrit; Scheffers, Sanders

2013-04-01

A range of future climate scenarios have been predicted for a warmer Earth as a result of varying anthropogenic greenhouse emissions. The Last Interglacial period (~125,000 years ago, Marine Isotope Stage 5) offers a period in time which is estimated to have been in the range of 0.1 to > 2oC warmer than present (AD 1961-1990). Although this period is not considered completely analogous for future climate states, the mechanisms behind such changes have the potential to be well understood. Here we present the initial findings of a study which aims to augment current understanding by quantifying the climate dynamics of the tropical southern Caribbean using high resolution marine climate archives. In doing so, we highlight geochemical proxies obtained from aragonitic coral skeletons as a proxy for seasonality and interannual to decadal climate variability. Unique fossil coral material has been collected from an uplifted reef terrace on the island of Bonaire (Netherlands Antilles), which according to 230Th/U dating, was deposited during the Last Interglacial. The sampling technique employed here has been focused using C/T scanning and X-radiography which revealed annual density bands in 21 individual coral colonies. Due to a high average extension rate of greater than 6mm/year, monthly records are available which represent growth periods from 9 to 40 years and so cover various time windows across the Last Interglacial. We discuss the results from geochemical signals of Sr/Ca and oxygen isotope ratios (δ18O) which reflect, respectively, regional temperature and hydrological balance at the sea surface. The finding that Sr/Ca and δ18O cycles occur alongside visible annual density bands allows the quality of the fossil coral material to be considered high and reliable. To further supplement the interpretation of these records greyscale increment analysis, Mg/Ca and δ13C records are presented. The implications of these findings, when compared to Holocene records, identify

Quantifying the influence of the terrestrial biosphere on glacial-interglacial climate dynamics

NASA Astrophysics Data System (ADS)

Davies-Barnard, Taraka; Ridgwell, Andy; Singarayer, Joy; Valdes, Paul

2017-10-01

The terrestrial biosphere is thought to be a key component in the climatic variability seen in the palaeo-record. It has a direct impact on surface temperature through changes in surface albedo and evapotranspiration (so-called biogeophysical effects) and, in addition, has an important indirect effect through changes in vegetation and soil carbon storage (biogeochemical effects) and hence modulates the concentrations of greenhouse gases in the atmosphere. The biogeochemical and biogeophysical effects generally have opposite signs, meaning that the terrestrial biosphere could potentially have played only a very minor role in the dynamics of the glacial-interglacial cycles of the late Quaternary. Here we use a fully coupled dynamic atmosphere-ocean-vegetation general circulation model (GCM) to generate a set of 62 equilibrium simulations spanning the last 120 kyr. The analysis of these simulations elucidates the relative importance of the biogeophysical versus biogeochemical terrestrial biosphere interactions with climate. We find that the biogeophysical effects of vegetation account for up to an additional -0.91 °C global mean cooling, with regional cooling as large as -5 °C, but with considerable variability across the glacial-interglacial cycle. By comparison, while opposite in sign, our model estimates of the biogeochemical impacts are substantially smaller in magnitude. Offline simulations show a maximum of +0.33 °C warming due to an increase of 25 ppm above our (pre-industrial) baseline atmospheric CO2 mixing ratio. In contrast to shorter (century) timescale projections of future terrestrial biosphere response where direct and indirect responses may at times cancel out, we find that the biogeophysical effects consistently and strongly dominate the biogeochemical effect over the inter-glacial cycle. On average across the period, the terrestrial biosphere has a -0.26 °C effect on temperature, with -0.58 °C at the Last Glacial Maximum. Depending on

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

Decoupled evolution of temperature and precipitation in western Germany during the Last Interglacial reconstructed from a precisely dated speleothem

NASA Astrophysics Data System (ADS)

Scholz, Denis; Hoffmann, Dirk; Spötl, Christoph; Hopcroft, Peter; Mangini, Augusto; Richter, Detlef K.

2010-05-01

evolution of δ18O and δ13C, and thus temperature and precipitation, is opposite. Whereas the δ18O signal suggests the warmest temperatures around 125 ka followed by a gradual decrease, the δ13C signal indicates wetter conditions towards the end of the Last Interglacial. The decoupling of temperature and precipitation during this time period is also seen in a series of snapshot simulations performed using a fast coupled ocean-atmosphere general circulation model. This behaviour can be explained by the influence of varying solar insolation patterns (in response to changing orbital configuration) on atmospheric dynamics and the resulting influence on storm activity in the region. References Fairchild, I. J. and Treble, P. C., 2009. Trace elements in speleothems as recorders of environmental change. Quaternary Science Reviews 28, 449-468. Martrat, B., Grimalt, J. O., Shackleton, N. J., de Abreu, L., Hutterli, M. A., and Stocker, T. F., 2007. Four climate cycles of recurring deep and surface water destabilizations on the Iberian Margin. Science 317, 502-507. North Greenland Ice Core Project members, 2004. High-resolution record of Northern Hemisphere climate extending into the last interglacial period. Nature 431, 147-151.

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

Polarized skylight navigation.

PubMed

Hamaoui, Moshe

2017-01-20

Vehicle state estimation is an essential prerequisite for navigation. The present approach seeks to use skylight polarization to facilitate state estimation under autonomous unconstrained flight conditions. Atmospheric scattering polarizes incident sunlight such that solar position is mathematically encoded in the resulting skylight polarization pattern. Indeed, several species of insects are able to sense skylight polarization and are believed to navigate polarimetrically. Sun-finding methodologies for polarized skylight navigation (PSN) have been proposed in the literature but typically rely on calibration updates to account for changing atmospheric conditions and/or are limited to 2D operation. To address this technology gap, a gradient-based PSN solution is developed based upon the Rayleigh sky model. The solution is validated in simulation, and effects of measurement error and changing atmospheric conditions are investigated. Finally, an experimental effort is described wherein polarimetric imagery is collected, ground-truth is established through independent imager-attitude measurement, the gradient-based PSN solution is applied, and results are analyzed.

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

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

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

1994-10-07

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

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.

Human responses and non-responses to climatic variations during the last Glacial-Interglacial transition in the eastern Mediterranean

NASA Astrophysics Data System (ADS)

Roberts, Neil; Woodbridge, Jessie; Bevan, Andrew; Palmisano, Alessio; Shennan, Stephen; Asouti, Eleni

2018-03-01

We review and evaluate human adaptations during the last glacial-interglacial climatic transition in southwest Asia. Stable isotope data imply that climatic change was synchronous across the region within the limits of dating uncertainty. Changes in vegetation, as indicated from pollen and charcoal, mirror step-wise shifts between cold-dry and warm-wet climatic conditions, but with lag effects for woody vegetation in some upland and interior areas. Palaeoenvironmental data can be set against regional archaeological evidence for human occupancy and economy from the later Epipalaeolithic to the aceramic Neolithic. Demographic change is evaluated from summed radiocarbon date probability distributions, which indicating contrasting - and in some cases opposite - population trajectories in different regions. Abrupt warming transitions at ∼14.5 and 11.7 ka BP may have acted as pacemakers for rapid cultural change in some areas, notably at the start of the Natufian and Pre-Pottery Neolithic cultures. However temporal synchroneity does not mean that climatic changes had the same environmental or societal consequences in different regions. During cold-dry time intervals, regions such as the Levant acted as refugia for plant and animal resources and human population. In areas where socio-ecological continuity was maintained through periods of adverse climate (e.g. Younger Dryas) human communities were able to respond rapidly to subsequent climatic improvement. By contrast, in areas where there was a break in settlement at these times (e.g. central Anatolia), populations were slower to react to the new opportunities provided by the interglacial world.

Geochemical Identification in Sediment Provenance during Glacial/Interglacial Period: the Southern Drake Passage

NASA Astrophysics Data System (ADS)

Park, Y. K.; Jung, J.; Lee, J. I.; Yoo, K. C.; Kim, J. W.

2016-12-01

Clay mineralogy and crystal size distribution in marine sediment is used for the indication of a sediment provenance and climatic changes. Objective of this study is to trace the sediment provenances in the Southern Drake Passage with clay mineralogy, elemental composition and crystal size distributions (CSDs) of clay mineral. In the present study, X-Ray Diffractometer (XRD) measurements showed that smectite, illite and chlorite are dominant phases. The semi-quantitative analysis showed that the relatively proportion of smectite is 50 - 60% in interglacial stage, 30 - 39% in glacial stage. Comparing with REE data, sediments supply was influenced by Weddell sea current and Antarctic Circumpolar Current (ACC). Moreover, elemental composition and microscopic analysis of smectites were carried by Transmission Electron Microscopy (TEM) and energy dispersive spectroscopy (EDS). The composition of smectite clay minerals were plotted on the tertiary diagram indicating that Smectite in Drake Passage was transported from three provenances: South Shetland island, east and west side of Antarctic peninsula during glacial - interglacial period. The CSDs of smectite also indicate the various source of smectite. The variation in the values of α (mean thickness) and β2 (shape or uniformity of the distribution) of smectite grain size will be discussed in terms of the sediment provenance.

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

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.

Last interglacial semi-desert expansions in southern Africa

NASA Astrophysics Data System (ADS)

Urrego, D. H.; Sanchez Goni, M.; Lechevrel, S.; Daniau, A.

2013-05-01

While our understanding of the effects of orbital-scale variability on the vegetation has grown during the past decades, empirical data from some climatically important periods and regions are still lacking. Scarce data exist for instance for deep-time glacial-interglacial cycles that could provide suitable analogs for current climate change. Recent global-scale syntheses of vegetation responses to rapid events during the last glacial have been useful, however, these global compilations clearly show that some regions, namely the southern tropics and subtropics, remain understudied. We use pollen analysis of marine sediments from core MD96-2098 to produce a paleoenvironmental record from southern Africa spanning MIS 6 to 3. Our interpretations are supported by an analysis of present-day pollen-vegetation-climate relationships for the region. We applied canonical correspondence analysis (CCA) and detrended correspondence analysis (DCA) on pollen spectra from terrestrial surface samples to investigate these relationships and to identify pollen taxa that are suitable bioclimatic indicators for the different South African biomes. Semi-desert vegetation dominated southern Africa during the MIS 5 interglacial. Expansion of the semi-desert biome into the Namib desert likely resulted from the reduction of the Benguela upwelling and a relative decrease in aridity. In its eastern boundary, the semi-desert likely expanded at the expense of grasslands as a result of increased subtropical high pressure and reduced summer precipitation. Semi-desert expansion in its southern boundary probably resulted from reduced influence of the southern westerlies and decreased winter precipitation. This atmospheric configuration was probably exacerbated during the three warm substages of MIS 5. During glacial isotopic stages MIS 6, 4 and 3 grasslands gained area over the semi-desert as summer precipitation increased. The area occupied by Fynbos vegetation was particularly large at the

Contrasting Responses of the Humboldt Current Ecosystem between the Holocene and MIS5e Interglacials Revealed from Multiple Sediment Records

NASA Astrophysics Data System (ADS)

Salvatteci, R.; Schneider, R. R.; Blanz, T.; Martinez, P.; Crosta, X.

2016-12-01

The Humboldt Current Ecosystem (HCE) off Peru yields about 10% of the global fish catch, producing more fish per unit area than any other region in the world. The high productivity is maintained by the upwelling of cold, nutrient-rich water from the oxygen minimum zone (OMZ), driven by strong trade winds. However, the potential impacts of climate change on upwelling dynamics and oceanographic conditions in the near future are uncertain, threatening local and global economies. Here, we unravel the response of the HCE to contrasting climatic conditions during the last two interglacials (i.e. Holocene and MIS5e) providing an independent insight about the relation between climatic factors and upwelling and productivity dynamics. For this purpose, we used multiple cores to reconstruct past changes in OMZ and upwelling intensity, productivity and fish biomass variability. Chronologies for the Holocene were obtained by multiple 14C ages and laminae correlations among cores, while for the MIS5e they were mainly done by correlation of prominent features in several proxies with other published records. We used a multiproxy approach including alkenones to reconstruct sea surface temperatures, δ15N as a proxy for water column denitrification, redox sensitive metals as proxies for sediment redox conditions, and diatom and fish debris assemblages to reconstruct ecological changes. The results show a very different response of the HCE to climate conditions during the last 2 interglacials, likely driven by changes in Tropical Pacific dynamics. During the Holocene we find that 1) the Late Holocene exhibits higher multi-centennial scale variability compared to the Early Holocene, 2) increased upwelling and a weak OMZ during the mid-Holocene, and 3) long term increase in productivity (diatoms and fishes) from the Early to the Late Holocene. During the MIS5e we find an 1) intense OMZ, 2) strong water column stratification, 3) high siliceous biomass, and 4) low fish biomass compared

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.

New data on the natural environment of the Middle and Late Neopleistocene interglacial periods in the east of the European Subarctic Region of Russia

NASA Astrophysics Data System (ADS)

Andreicheva, L. N.; Marchenko-Vagapova, T. I.

2017-11-01

The data obtained from investigation of the Middle and Late Neopleistocene lake sediments in the European Subarctic Region of Russia are reported. Chirva, Rodionovo (Scklov), Sula (Mikulino), and Byzovaya (Leningrad) sediments were subject to palynological analysis and investigation of particle size distribution and mineral composition. The spore-pollen spectra of the Chirva sediments demonstrate two climatic optima: the lower optimum is dominated by the pollen of Pinus sylvestris and broad-leaved species (up to 10%); the upper optimum is dominated by Picea sp. and Pinus sylvestris, while the pollen of Picea sect. Omorica and broad-leaved species are sporadic. The Rodionovo flora is characterized by a more xerophilous composition relative to the Chirva flora and a higher pollen content of pine, birch, wormseed plants, and wormwood. The climatic optimum of the Sula interglacial is distinguished by boreal vegetation, including spruce, birch, and birch-spruce forests with sparse broad-leaved species. The Byzovaya interstadial is marked by seven stages of changes in the vegetation: from tundra and forest-tundra communities to taiga forests with some broad-leaved species. The natural climatic sedimentation conditions in the Middle and Late Neopleistocene interglacial periods are reconstructed. The mineral composition of sediments was largely formed owing to underlying deposits.

Investigating Mercury's South Polar Deposits: Arecibo Radar Observations and High-Resolution Determination of Illumination Conditions

NASA Astrophysics Data System (ADS)

Chabot, Nancy L.; Shread, Evangela E.; Harmon, John K.

2018-02-01

There is strong evidence that Mercury's polar deposits are water ice hosted in permanently shadowed regions. In this study, we present new Arecibo radar observations of Mercury's south pole, which reveal numerous radar-bright deposits and substantially increase the radar imaging coverage. We also use images from MESSENGER's full mission to determine the illumination conditions of Mercury's south polar region at the same spatial resolution as the north polar region, enabling comparisons between the two poles. The area of radar-bright deposits in Mercury's south is roughly double that found in the north, consistent with the larger permanently shadowed area in the older, cratered terrain at the south relative to the younger smooth plains at the north. Radar-bright features are strongly associated with regions of permanent shadow at both poles, consistent with water ice being the dominant component of the deposits. However, both of Mercury's polar regions show that roughly 50% of permanently shadowed regions lack radar-bright deposits, despite some of these locations having thermal environments that are conducive to the presence of water ice. The observed uneven distribution of water ice among Mercury's polar cold traps may suggest that the source of Mercury's water ice was not a steady, regular process but rather that the source was an episodic event, such as a recent, large impact on the innermost planet.

Stalagmite geochemistry and the timing of the last interglacial-glacial transition in Central Europe (NE Hungary)

NASA Astrophysics Data System (ADS)

Siklosy, Z.; Demeny, A.; Pilet, S.; Leel-Ossy, Sz.; Lin, K.; Shen, C.-C.

2009-04-01

Speleothems can provide accurate chronologies for reconstructions of climate change by combination of U/Th dating and climate-related geochemical compositions. Geochemical studies of speleothems from Central Europe are mostly based on stable C and O isotope analyses, thus, complex geochemical studies combining isotope and trace element measurements are needed for more reliable climate models for this transitional area between oceanic and continental regions. We present stable H-C-O isotope and trace element records obtained on speleothems covering the Last Interglacial (MIS 5e) and the transition to MIS 5d. A stalagmite from Baradla Cave grew from 127.5 to 110 ka. Accelerated growth rates have been detected by U/Th age data in the 127 to 126 ka and 119 to 117 ka parts. Trace element compositions and 230Th/232Th ratios suggest changes in the hydrological regime, whereby early calcite precipitates formed in fissures during the dry and cold glacial period were dissolved by the starting flux of infiltrating meteoric water (producing elevated dissolved ion concentration but low detrital Th component), then the increasing amount of dripwater during the interglacial period resulted in trace element dilution. Temperature and precipitation amount variations are also reflected by the stable isotope compositions. Oxygen isotope composition shows a continuous increase from 127.5 ka until about 118 ka most probably related to temperature rise, whereas C isotope values are shifted in negative direction suggesting increasing humidity in accordance with trace element contents. The presumably warmest period at ca. 118 ka is associated with rather arid climate as indicated by peak d18O values coinciding with the highest dD values of fluid inclusion water. This is followed by a pronounced negative shift in both O and H isotope values, similarly to recent Alpine studies (Meyer et al., 2008), most probably related to cooling. Hydrogen isotope compositions of fluid inclusion water

New sea-level data of the MIS 5e interglacial of Mallorca Island, Spain

NASA Astrophysics Data System (ADS)

Lorscheid, Thomas; Stocchi, Paolo; de Boer, Bas; Mann, Thomas; Westphal, Hildegard; Rovere, Alessio

2015-04-01

The island of Mallorca (Balearic Islands, Spain) is one of the key locations in the Western Mediterranean for the study of Last Interglacial sea levels. Although MIS 5e deposits and landforms have been investigated by several authors since Cuerda (1979), most former studies concentrate on few outcrops. Although description of fossils, facies and age attribution for these outcrops are known in detail, these sites have never been the object of differential GPS measurements and glacial isostatic adjustment effects have never been taken into consideration. In this study, we present the results of fieldwork at several outcrops around the Island of Mallorca. We measured the elevation of deposits and landforms associated with the Last Interglacial with a high-precision GPS-system, and we calculated for each the reference water level and indicative range using modern analogs along the same shorelines. Moreover, we took samples of some outcrops for radiometric dating. The outcrops consist mainly of beach deposits at 1-3 m apsl and one elevated deposit in the Southeast of the island at 8 m apsl. We use an earth-ice coupled GIA-model for the Mediterranean to compare the elevation of our deposits to expected GIA signal in this region and discuss our results in terms of tectonics and eustasy.

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.

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

NASA Astrophysics Data System (ADS)

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

2017-12-01

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

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

NASA Astrophysics Data System (ADS)

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

2014-12-01

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

Using a Glacial Isostatic Adjustment model to investigate the contribution of the Antarctic and Greenland Ice sheet to the Last Interglacial Sea Level.

NASA Astrophysics Data System (ADS)

Bradley, Sarah; Hindmarsh, Richard C. A.

2014-05-01

Eustatic Sea Level during the Last interglacial (LIG) is likely to have been 4- 6 m higher than present day, with the observed relative sea level (RSL) at numerous far-field sites even higher [Dutton and Lambeck, 2012]. It has been suggested to generate this higher than present day sea level requires a retreat of both the Antarctic (AIS) and Greenland (GIS) Ice sheets beyond the present day extent, but the exact contribution of these two global ice sheets has yet to be resolved. By combing a Glacial Isostatic Adjustment (GIA) model with a suite of LIG ice-loading histories we will address a number of outstanding issues (i) What was the contribution of the AIS and GIS to ESL, (ii) Was the AIS or the GIS smaller during the LIG than the present interglacial? (iii) Can we generate the observed higher LIG RSL at a range of far-field sites? The suite of AIS and GIS ice-loading histories is constrained using the most recent near-field evidence, LIG stable isotope ice core data [Dahl-Jensen et al., 2013; Masson-Delmotte et al., 2011] and the output from ice sheet and climate models [Helsen et al., 2013; Pollard and DeConto, 2009; Stone et al., 2013]. Comparing the predicted RSL to a recent database of observed LIG far-field sea level [Dutton and Lambeck, 2012] allows for an assessment of the plausibility of the suite of ice loading histories. With this study, we aim to provide insight into the LIG history of the AIS and GIS. Dahl-Jensen, D., et al. (2013), Eemian interglacial reconstructed from a Greenland folded ice core, Nature, 493(7433), 489-494. Dutton, A., and K. Lambeck (2012), Ice Volume and Sea Level During the Last Interglacial, Science, 337(6091), 216-219. Helsen, M. M., W. J. van de Berg, R. S. W. van de Wal, M. R. van den Broeke, and J. Oerlemans (2013), Coupled regional climate-ice-sheet simulation shows limited Greenland ice loss during the Eemian, Clim Past, 9(4), 1773-1788. Masson-Delmotte, V., et al. (2011), A comparison of the present and last

Optical dating of eolian deposits since the last interglacial along the northern margin of the Chinese Loess Plateau

NASA Astrophysics Data System (ADS)

Lü, Tongyan; Sun, Jimin; Gong, Zhijun

2018-04-01

Understanding the chronology of eolian sand-loess-paleosol sequences along the northern margin of the Chinese Loess Plateau (CLP) is crucial for comprehending climate change and the advance and retreat of the adjacent Mu Us desert. In this study, a sand-loess-soil sequence from the northern margin of the CLP was studied by applying the single aliquot regenerative (SAR) protocol to quartz grains, and the multi-elevated-temperature post-IR IRSL (MET-pIRIR) protocol to K-feldspar grains. For equivalent dose (De) determination, 63-90 μm quartz and K-feldspar grains were used. Our results indicate that the MET-pIRIR ages of K-feldspar grains in this sequence range from 94.4 ± 7.0 ka to 148.3 ± 13.3 ka for the last interglacial paleosol (S1); for the upper part of the section, quartz-based SAR-OSL dating was used, yielding ages spanning from 5.8 ± 0.4 ka to 35.9 ± 4.1 ka. After cross-checking these results with previously-reported isochron OSL and TL ages, the reliability of the MET-pIRIR protocol when applied to the last interglacial paleosol was confirmed. Based on a new OSL chronology of the Shimao profile, the studied eolian deposits can be broadly correlated with the last glacial-interglacial cycle, but their dating also points to sedimentary hiatuses occurring at 94.4 ka, 35.9 ka and 5.8 ka, due most probably to strong wind erosion caused by intensified cold-dry winter monsoonal circulations during the last glacial maxima.

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

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 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.

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

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

NASA Astrophysics Data System (ADS)

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

2010-05-01

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

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

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

Interglacial Extension of the Boreal Forest Limit in the Noatak Valley, Northwest Alaska: Evidence from an Exhumed River-Cut Bluff and Debris Apron

USGS Publications Warehouse

Edwards, M.E.; Hamilton, T.D.; Elias, S.A.; Bigelow, N.H.; Krumhardt, A.P.

2003-01-01

Numerous exposures of Pleistocene sediments occur in the Noatak basin, which extends for 130 km along the Noatak River in northwestern Alaska. Nk-37, an extensive bluff exposure near the west end of the basin, contains a record of at least three glacial advances separated by interglacial and interstadial deposits. An ancient river-cut bluff and associated debris apron is exposed in profile through the central part of Nk-37. The debris apron contains a rich biotic record and represents part of an interglaciation that is probably assignable to marine-isotope stage 5. Pollen spectra from the lower part of the debris apron closely resemble modern samples taken from the Noatak floodplain in spruce gallery forest, and macrofossils of spruce are also present at this level. Fossil bark beetles and carpenter ants occur higher in the debris apron. Mutual Climatic Range (MCR) estimates from the fossil beetles suggest temperatures similar to or warmer than today. Together, these fossils indicate the presence of an interglacial spruce forest in the western part of the Noatak Basin, which lies about 80 km upstream of the modern limit of spruce forest.

Evidence for the timing and duration of the last interglacial period from high-precision uranium-series ages of corals on tectonically stable coastlines

USGS Publications Warehouse

Muhs, D.R.

2002-01-01

The last interglacial period has a timing and duration that can be estimated from U-series dating of emergent, coral-bearing deposits on tectonically stable coastlines. High-precision dating from Bermuda, the Bahamas, Hawaii, and Australia suggests that the last interglacial period had a sea level at least as high as present from ???128,000 to 116,000 yr B.P. Sea level reached a near-present level more quickly after the close of the penultimate glacial period than at the close of the last glacial period and the duration of high sea level is longer than that implied by the deep-sea record. ?? 2002 University of Washington.

Implications of the circumpolar genetic structure of polar bears for their conservation in a rapidly warming Arctic.

PubMed

Peacock, Elizabeth; Sonsthagen, Sarah A; Obbard, Martyn E; Boltunov, Andrei; Regehr, Eric V; Ovsyanikov, Nikita; Aars, Jon; Atkinson, Stephen N; Sage, George K; Hope, Andrew G; Zeyl, Eve; Bachmann, Lutz; Ehrich, Dorothee; Scribner, Kim T; Amstrup, Steven C; Belikov, Stanislav; Born, Erik W; Derocher, Andrew E; Stirling, Ian; Taylor, Mitchell K; Wiig, Øystein; Paetkau, David; Talbot, Sandra L

2015-01-01

We provide an expansive analysis of polar bear (Ursus maritimus) circumpolar genetic variation during the last two decades of decline in their sea-ice habitat. We sought to evaluate whether their genetic diversity and structure have changed over this period of habitat decline, how their current genetic patterns compare with past patterns, and how genetic demography changed with ancient fluctuations in climate. Characterizing their circumpolar genetic structure using microsatellite data, we defined four clusters that largely correspond to current ecological and oceanographic factors: Eastern Polar Basin, Western Polar Basin, Canadian Archipelago and Southern Canada. We document evidence for recent (ca. last 1-3 generations) directional gene flow from Southern Canada and the Eastern Polar Basin towards the Canadian Archipelago, an area hypothesized to be a future refugium for polar bears as climate-induced habitat decline continues. Our data provide empirical evidence in support of this hypothesis. The direction of current gene flow differs from earlier patterns of gene flow in the Holocene. From analyses of mitochondrial DNA, the Canadian Archipelago cluster and the Barents Sea subpopulation within the Eastern Polar Basin cluster did not show signals of population expansion, suggesting these areas may have served also as past interglacial refugia. Mismatch analyses of mitochondrial DNA data from polar and the paraphyletic brown bear (U. arctos) uncovered offset signals in timing of population expansion between the two species, that are attributed to differential demographic responses to past climate cycling. Mitogenomic structure of polar bears was shallow and developed recently, in contrast to the multiple clades of brown bears. We found no genetic signatures of recent hybridization between the species in our large, circumpolar sample, suggesting that recently observed hybrids represent localized events. Documenting changes in subpopulation connectivity will allow

Implications of the Circumpolar Genetic Structure of Polar Bears for Their Conservation in a Rapidly Warming Arctic

PubMed Central

Peacock, Elizabeth; Sonsthagen, Sarah A.; Obbard, Martyn E.; Boltunov, Andrei; Regehr, Eric V.; Ovsyanikov, Nikita; Aars, Jon; Atkinson, Stephen N.; Sage, George K.; Hope, Andrew G.; Zeyl, Eve; Bachmann, Lutz; Ehrich, Dorothee; Scribner, Kim T.; Amstrup, Steven C.; Belikov, Stanislav; Born, Erik W.; Derocher, Andrew E.; Stirling, Ian; Taylor, Mitchell K.; Wiig, Øystein; Paetkau, David; Talbot, Sandra L.

2015-01-01

We provide an expansive analysis of polar bear (Ursus maritimus) circumpolar genetic variation during the last two decades of decline in their sea-ice habitat. We sought to evaluate whether their genetic diversity and structure have changed over this period of habitat decline, how their current genetic patterns compare with past patterns, and how genetic demography changed with ancient fluctuations in climate. Characterizing their circumpolar genetic structure using microsatellite data, we defined four clusters that largely correspond to current ecological and oceanographic factors: Eastern Polar Basin, Western Polar Basin, Canadian Archipelago and Southern Canada. We document evidence for recent (ca. last 1–3 generations) directional gene flow from Southern Canada and the Eastern Polar Basin towards the Canadian Archipelago, an area hypothesized to be a future refugium for polar bears as climate-induced habitat decline continues. Our data provide empirical evidence in support of this hypothesis. The direction of current gene flow differs from earlier patterns of gene flow in the Holocene. From analyses of mitochondrial DNA, the Canadian Archipelago cluster and the Barents Sea subpopulation within the Eastern Polar Basin cluster did not show signals of population expansion, suggesting these areas may have served also as past interglacial refugia. Mismatch analyses of mitochondrial DNA data from polar and the paraphyletic brown bear (U. arctos) uncovered offset signals in timing of population expansion between the two species, that are attributed to differential demographic responses to past climate cycling. Mitogenomic structure of polar bears was shallow and developed recently, in contrast to the multiple clades of brown bears. We found no genetic signatures of recent hybridization between the species in our large, circumpolar sample, suggesting that recently observed hybrids represent localized events. Documenting changes in subpopulation connectivity will

Implications of the circumpolar genetic structure of polar bears for their conservation in a rapidly warming Arctic

USGS Publications Warehouse

Peacock, Elizabeth; Sonsthagen, Sarah A.; Obbard, Martyn E.; Boltunov, Andrei N.; Regehr, Eric V.; Ovsyanikov, Nikita; Aars, Jon; Atkinson, Stephen N.; Sage, George K.; Hope, Andrew G.; Zeyl, Eve; Bachmann, Lutz; Ehrich, Dorothee; Scribner, Kim T.; Amstrup, Steven C.; Belikov, Stanislav; Born, Erik W.; Derocher, Andrew E.; Stirling, Ian; Taylor, Mitchell K.; Wiig, Øystein; Paetkau, David; Talbot, Sandra L.

2015-01-01

We provide an expansive analysis of polar bear (Ursus maritimus) circumpolar genetic variation during the last two decades of decline in their sea-ice habitat. We sought to evaluate whether their genetic diversity and structure have changed over this period of habitat decline, how their current genetic patterns compare with past patterns, and how genetic demography changed with ancient fluctuations in climate. Characterizing their circumpolar genetic structure using microsatellite data, we defined four clusters that largely correspond to current ecological and oceanographic factors: Eastern Polar Basin, Western Polar Basin, Canadian Archipelago and Southern Canada. We document evidence for recent (ca. last 1–3 generations) directional gene flow from Southern Canada and the Eastern Polar Basin towards the Canadian Archipelago, an area hypothesized to be a future refugium for polar bears as climate-induced habitat decline continues. Our data provide empirical evidence in support of this hypothesis. The direction of current gene flow differs from earlier patterns of gene flow in the Holocene. From analyses of mitochondrial DNA, the Canadian Archipelago cluster and the Barents Sea subpopulation within the Eastern Polar Basin cluster did not show signals of population expansion, suggesting these areas may have served also as past interglacial refugia. Mismatch analyses of mitochondrial DNA data from polar and the paraphyletic brown bear (U. arctos) uncovered offset signals in timing of population expansion between the two species, that are attributed to differential demographic responses to past climate cycling. Mitogenomic structure of polar bears was shallow and developed recently, in contrast to the multiple clades of brown bears. We found no genetic signatures of recent hybridization between the species in our large, circumpolar sample, suggesting that recently observed hybrids represent localized events. Documenting changes in subpopulation connectivity will

Investigation on principle of polarization-difference imaging in turbid conditions

NASA Astrophysics Data System (ADS)

Ren, Wei; Guan, Jinge

2018-04-01

We investigate the principle of polarization-difference imaging (PDI) of objects in optically scattering environments. The work is performed by both Marius's law and Mueller-Stokes formalism, and is further demonstrated by simulation. The results show that the object image is obtained based on the difference in polarization direction between the scatter noise and the target signal, and imaging performance is closely related to the choice of polarization analyzer axis. In addition, this study illustrates the potential of Stoke vector for promoting application of PDI system in the real world scene.

Response of the Indian Creek alluvial fan, Nevada, to glacial-interglacial climate change

NASA Astrophysics Data System (ADS)

D'Arcy, Mitch; Roda-Boluda, Duna; Whittaker, Alexander; Brooke, Sam

2017-04-01

Alluvial fans have been shown to record signals of glacial-interglacial climate changes. Specifically, it has been suggested that their down-system grain size fining patterns may record changes in sediment flux. However, very few field studies have tested this because they require (i) robust fan chronologies, (ii) constraints on basin subsidence and 3D fan geometry, and (iii) a suitable model for inverting grain size fining for sediment flux. Here, we present a case study from the fluvially-dominated Indian Creek fan system in Fish Lake Valley, Nevada, which satisfies these criteria. We measure grain size fining patterns on a surface dating to the mid-glacial period ˜71 kyr ago, and a surface dating to the Holocene, which between them represent an overall warming (˜3 ˚ C) and drying (˜30%) of the regional climate. We use constraints on basin subsidence and a self-similar model of grain size fining to reconstruct sediment fluxes to the alluvial fan during the time periods captured by the two surfaces. Our results indicate a decline in sediment flux of ˜38% between the deposition of the ˜71 kyr and Holocene surfaces, implying significant sensitivity to climatic forcing over time periods of >10 kyr. This could represent a decrease in catchment erosion rates and/or a decrease in sediment export as the climate dried. Our results offer quantitative new constraints on how simple landscapes react to known glacial-interglacial climate shifts.

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

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

NASA Astrophysics Data System (ADS)

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 1H-13C dipolar coupling/chemical shift correlation experiment using 13C detected cross-polarization with a variable contact time (CPVC) and systematically study the conditions for its optimal performance at 60 kHz MAS. In addition, we demonstrate the feasibility of a proton-detected version of the CPVC experiment. The theoretical analysis of the CPVC pulse sequence under different Hartmann-Hahn matching conditions confirms that it performs optimally under the ZQ (w1H - w1C = ±wr) condition for polarization transfer. The limits of the cross polarization process are explored and precisely defined as a function of offset and Hartmann-Hahn mismatch via spin dynamics simulation and experiments on a powder sample of uniformly 13C-labeled L-isoleucine. Our results show that the performance of the CPVC sequence and subsequent determination of 1H-13C dipolar couplings are insensitive to 1H/13C frequency offset frequency when high RF fields are used on both RF channels. Conversely, the CPVC sequence is quite sensitive to the Hartmann-Hahn mismatch, particularly for systems with weak heteronuclear dipolar couplings. We demonstrate the use of the CPVC based SLF experiment as a tool to identify different carbon groups, and hope to motivate the exploration of more sophisticated 1H detected avenues for ultrafast MAS.

Glacial-interglacial cycles in detrital sediment supply to the Amundsen Sea: Implications for West Antarctic Ice Sheet dynamics during the Late Pleistocene

NASA Astrophysics Data System (ADS)

Simoes Pereira, P.; van de Flierdt, T.; Hillenbrand, C. D.; Hemming, S. R.; Kuhn, G.

2017-12-01

The West Antarctic Ice Sheet (WAIS) plays a key role in the global climate system and its collapse could contribute up to 4.3 m of sea-level rise. Mass loss of this marine-based ice sheet is largely caused by ocean-driven melting of ice shelves. This is confimed by modern observational data which show significant glacier thinning and retreat of grounding lines, particularly in the Amundsen Sea area. We here apply an integrated approach to determine provenance of marine sediments, which enables us to trace erosion of different bedrock lithologies, ultimately tied to the location of the eroding ice through time. We present provenance analysis on detrital Holocene seafloor sediments from the Amundsen Sea Embayment as well as from two marine cores PS58/254 (69°19´S, 108°27´W) and PC493 (71°09´S, 119°57´W), located on the continental rise of the Amundsen Sea and covering glacial-interglacial cycles of the past 800 kyrs. We use strontium (Sr) and neodymium (Nd) isotopic compositions of fine terrigenous grains (<63μm), and 40Ar/39Ar ages on ice-rafted (>150μm) hornblende and biotite grains. Our Holocene mapping results reveal drainage pathways with distinct signatures in the eastern and western Amundsen Sea Embayment. The western embayment records a homogenous provenance signature, pointing to a local source area in the hinterland, while the eastern embayment shows a range of compositions indicating erosion of the eastern coastal margin and a distinct, but unexposed source lithology under Pine Island Glacier and/or its drainage basin. Systematic isotope variations are detected between glacial and interglacial stages in both downcore records. Core PS58/254 exhibits a radiogenic fingerprint throughout the Late Pleistocene and systematic glacial-interglacial fluctuations in the order of three ɛNd units. They correlate with physical properties of the sediments (i.e. magnetic susceptibility) and trend towards lower values during interglacials, notably during Marine

Increasing nest predation will be insufficient to maintain polar bear body condition in the face of sea ice loss.

PubMed

Dey, Cody J; Richardson, Evan; McGeachy, David; Iverson, Samuel A; Gilchrist, Hugh G; Semeniuk, Christina A D

2017-05-01

Climate change can influence interspecific interactions by differentially affecting species-specific phenology. In seasonal ice environments, there is evidence that polar bear predation of Arctic bird eggs is increasing because of earlier sea ice breakup, which forces polar bears into nearshore terrestrial environments where Arctic birds are nesting. Because polar bears can consume a large number of nests before becoming satiated, and because they can swim between island colonies, they could have dramatic influences on seabird and sea duck reproductive success. However, it is unclear whether nest foraging can provide an energetic benefit to polar bear populations, especially given the capacity of bird populations to redistribute in response to increasing predation pressure. In this study, we develop a spatially explicit agent-based model of the predator-prey relationship between polar bears and common eiders, a common and culturally important bird species for northern peoples. Our model is composed of two types of agents (polar bear agents and common eider hen agents) whose movements and decision heuristics are based on species-specific bioenergetic and behavioral ecological principles, and are influenced by historical and extrapolated sea ice conditions. Our model reproduces empirical findings that polar bear predation of bird nests is increasing and predicts an accelerating relationship between advancing ice breakup dates and the number of nests depredated. Despite increases in nest predation, our model predicts that polar bear body condition during the ice-free period will continue to decline. Finally, our model predicts that common eider nests will become more dispersed and will move closer to the mainland in response to increasing predation, possibly increasing their exposure to land-based predators and influencing the livelihood of local people that collect eider eggs and down. These results show that predator-prey interactions can have nonlinear responses to

Timing of insolation forcing, CO2 and sea level changes around the current and last four interglacial periods

NASA Astrophysics Data System (ADS)

Kawamura, K.; Aoki, S.; Nakazawa, T.; Abe-Ouchi, A.; Saito, F.

2013-12-01

Investigation of the roles of different forcings (e.g. orbital variations and greenhouse gases) on climate and sea level requires a paleoclimate chronology with high accuracy. Such a chronology for the past 360 ky was constructed through orbital tuning of O2/N2 ratio of trapped air in the Dome Fuji and Vostok ice cores with local summer insolation (Kawamura et al., 2007). We extend the O2/N2 chronology back to ~500 kyr by analyzing the second Dome Fuji ice core, and find the duration of 11 ka, 5 ka, 9 ka, and 20 ka for MIS 5e, 7e, 9e and 11c interglacial periods in Antarctica, with similar variations in atmospheric CO2. The termination timings are consistent with the rising phase of Northern Hemisphere summer insolation. Marine sediment cores from northern North Atlantic contain millennial-scale signatures in various proxy records (e.g. SST, IRD), including abrupt climatic shifts and bipolar seesaw. Based on the bipolar correlation of millennial-scale events, it is possible to transfer our accurate chronology to marine cores from the North Atlantic. As a first attempt, we correlate the planktonic δ18O and IRD records from the marine core ODP 980 with the ice-core δ18O and CH4 around MIS 11. We find that the durations of interglacial plateaus of planktonic δ18O (proxy for sea surface environments) and benthic δ18O (proxy for ice volume and deep-sea temperature) for MIS 11c are 20 and 15 ka, respectively, which are significantly shorter than originally suggested. These durations are similar to that of Antarctic climate and atmospheric CO2. However, the onsets of interglacial levels in ODP980 for MIS 11 are significantly later than those in Antarctic δ18O and atmospheric CO2 (by as much as ~10 ka), suggesting very long duration (more than one precession cycle) for the complete deglaciation and northern high-latitude warming for Termination V. Atmospheric CO2 may have been the critical forcing for this termination. The long duration of Termination V is consistent

Polarization of perceived Procedural Justice.

PubMed

Flint, Douglas H; Hernandez-Marrero, Pablo; Wielemaker, Martin

2006-02-01

This study examined polarization of perceptions of Procedural Justice. Two polarization mechanisms are examined, Persuasive Arguments and Social Comparisons. Participants were students enrolled in a first-year introductory business class. There were 216 participants in the Persuasive Arguments study, 429 in the Social Comparisons study. The average age of all participants was 22.3 yr. (SD = 2.1); 56% were women. Fields of study represented were business, engineering, information technology, and sports. Analysis showed under conditions of low Procedural Justice, polarization effects were only found with the Persuasive Arguments mechanism. Under conditions of high Procedural Justice, polarization effects were only found with Social Comparisons. Implications for group polarization and Procedural Justice theories are considered.

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

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

Iba, Satoshi; Saito, Hidekazu; Yuasa, Shinji

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{submore » 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)« less

Contrasting scaling properties of interglacial and glacial climates

NASA Astrophysics Data System (ADS)

Ditlevsen, Peter; Shao, Zhi-Gang

2017-04-01

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. Ref: Zhi-Gang Shao and Peter Ditlevsen, Nature Comm. 7, 10951, 2016

The Impact of the AMOC Resumption in the Western South Atlantic Thermocline at the Onset of the Last Interglacial

NASA Astrophysics Data System (ADS)

Santos, Thiago P.; Lessa, Douglas O.; Venancio, Igor M.; Chiessi, Cristiano M.; Mulitza, Stefan; Kuhnert, Henning; Albuquerque, Ana Luiza S.

2017-11-01

After glacial terminations, large amounts of heat and salt were transferred from low to high latitudes, which is a crucial phenomenon for the reestablishment of the Atlantic Meridional Overturning Circulation (AMOC). However, how different glacial terminations evolved in the (sub)tropics is still poorly documented. Here we use foraminifera oxygen (δ18O) and carbon (δ13C) stable isotopes to show that the North Atlantic heat piracy, following the AMOC resumption at the early Last Interglacial, affected the thermocline δ18O levels of the subtropical western South Atlantic. Because of the cooling imposed by this process, glacial δ18O persisted in the thermocline for 7 kyr after the onset of the Last Interglacial, dampening the effect of sea level rise usually imprinted on foraminifera δ18O during terminations. Faunal composition and δ13C also suggest the existence of a colder and thicker South Atlantic Central Water coeval with the AMOC recovery. This process apparently did not occur during the last deglaciation.

Investigating Mercury’s South Polar Deposits: Arecibo Radar Observations and High-resolution Determination of Illumination Conditions

PubMed Central

Chabot, Nancy L.; Shread, Evangela E.; Harmon, John K.

2018-01-01

There is strong evidence that Mercury’s polar deposits are water ice hosted in permanently shadowed regions. In this study, we present new Arecibo radar observations of Mercury’s south pole, which reveal numerous radar-bright deposits and substantially increase the radar imaging coverage. We also use images from MESSENGER’s full mission to determine the illumination conditions of Mercury’s south polar region at the same spatial resolution as the north polar region, enabling comparisons between the two poles. The area of radar-bright deposits in Mercury’s south is roughly double that found in the north, consistent with the larger permanently shadowed area in the older, cratered terrain at the south relative to the younger smooth plains at the north. Radar-bright features are strongly associated with regions of permanent shadow at both poles, consistent with water ice being the dominant component of the deposits. However, both of Mercury’s polar regions show that roughly 50% of permanently shadowed regions lack radar-bright deposits, despite some of these locations having thermal environments that are conducive to the presence of water ice. The observed uneven distribution of water ice among Mercury’s polar cold traps may suggest that the source of Mercury’s water ice was not a steady, regular process but rather that the source was an episodic event, such as a recent, large impact on the innermost planet. PMID:29552436

Palynology of the Last Interglacial Complex at Lake Ohrid: palaeoenvironmental and palaeoclimatic inferences

NASA Astrophysics Data System (ADS)

Sinopoli, Gaia; Masi, Alessia; Regattieri, Eleonora; Wagner, Bernd; Francke, Alexander; Peyron, Odile; Sadori, Laura

2018-01-01

In this article, we present new, high-resolution, pollen results obtained from the DEEP site sequence recovered from Lake Ohrid (Albania/FYROM) for the Last Interglacial Complex (LIC), corresponding to Marine Isotope Stage 5 (MIS 5) of the marine isotope stratigraphy. LIC covers the period between 130 and 70 ka and includes the Eemian (Last Interglacial, LI) and the succession of stadial and interstadial phases of the Early Last Glacial. During the LIC, the pollen record shows an alternation of periods characterized by forest and open vegetation, clearly resembling the well-known vegetational succession of other European records. Our results reveal three key phases for the LI: a first period (128-125 ka) with a rapid increase in temperature and precipitation, a central phase (125-118.5 ka) characterized by a slight cooling, and a late phase (118.5-112 ka), with a decline both in temperatures and precipitation. Besides the LI, we identify four more forested periods dominated by mesophilous trees and intercalated by colder and drier steppe phases, during which, however, most arboreal taxa never disappear. During the Early Last Glacial we also identify several abrupt events that can be correlated to the succession of cold events recorded in the Greenland ice core records, associated to a weakening of the North Atlantic Meridional Overturning Circulation. The new high-resolution record indicates that Lake Ohrid is an important site to understand the response of vegetation to fluctuations in regional moisture availability and temperature changes, and thus provides new evidence for the connection between the Mediterranean Region and Northern Hemisphere climate oscillations.

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.

Using Polar Coronal Hole Area Measurements to Determine the Solar Polar Magnetic Field Reversal in Solar Cycle 24

NASA Technical Reports Server (NTRS)

Karna, N.; Webber, S.A. Hess; Pesnell, W.D.

2014-01-01

An analysis of solar polar coronal hole (PCH) areas since the launch of the Solar Dynamics Observatory (SDO) shows how the polar regions have evolved during Solar Cycle 24. We present PCH areas from mid-2010 through 2013 using data from the Atmospheric Imager Assembly (AIA) and Helioseismic and Magnetic Imager (HMI) instruments onboard SDO. Our analysis shows that both the northern and southern PCH areas have decreased significantly in size since 2010. Linear fits to the areas derived from the magnetic-field properties indicate that, although the northern hemisphere went through polar-field reversal and reached solar-maximum conditions in mid-2012, the southern hemisphere had not reached solar-maximum conditions in the polar regions by the end of 2013. Our results show that solar-maximum conditions in each hemisphere, as measured by the area of the polar coronal holes and polar magnetic field, will be offset in time.

Fibrinogen adsorption onto 316L stainless steel under polarized conditions.

PubMed

Gettens, Robert T T; Gilbert, Jeremy L

2008-04-01

Adsorption of the plasma protein fibrinogen onto electrically polarized 316L stainless steel was observed and quantified using both in situ and ex situ atomic force microscopy (AFM) techniques. Significant differences in fibrinogen adsorption were observed across voltages. Ex situ studies showed significantly lower area coverage (theta) and height of adsorbed Fb on cathodically polarized surfaces when compared to anodically polarized surfaces. Conformational differences in the protein may explain the distinctions in Fb surface area coverage (theta) and height between the anodic and cathodic cases. In situ studies showed significantly slower kinetics of Fb adsorption onto surfaces below -100 mV (vs. Ag/AgCl) compared to surfaces polarized above -100 mV. Electrochemical current density data showed large charge transfer processes (approximately 1 x 10(-5) to 1 x 10(-4) A/cm(2)) taking place on the 316L SS surfaces at voltages below -100 mV (vs. Ag/AgCl). These relatively large current densities point to flux of ionic species away from the surface as a major source of the reduction in adsorption kinetics rather than just hydrophilic or electrostatic effects. Copyright 2007 Wiley Periodicals, Inc.

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.

Central Tropical Pacific Variability And ENSO Response To Changing Climate Boundary Conditions: Evidence From Individual Line Island Foraminifera

NASA Astrophysics Data System (ADS)

Rustic, G. T.; Polissar, P. J.; Ravelo, A. C.; White, S. M.

2017-12-01

The El Niño Southern Oscillation (ENSO) plays a dominant role in Earth's climate variability. Paleoceanographic evidence suggests that ENSO has changed in the past, and these changes have been linked to large-scale climatic shifts. While a close relationship between ENSO evolution and climate boundary conditions has been predicted, testing these predictions remains challenging. These climate boundary conditions, including insolation, the mean surface temperature gradient of the tropical Pacific, global ice volume, and tropical thermocline depth, often co-vary and may work together to suppress or enhance the ocean-atmosphere feedbacks that drive ENSO variability. Furthermore, suitable paleo-archives spanning multiple climate states are sparse. We have aimed to test ENSO response to changing climate boundary conditions by generating new reconstructions of mixed-layer variability from sedimentary archives spanning the last three glacial-interglacial cycles from the Central Tropical Pacific Line Islands, where El Niño is strongly expressed. We analyzed Mg/Ca ratios from individual foraminifera to reconstruct mixed-layer variability at discrete time intervals representing combinations of climatic boundary conditions from the middle Holocene to Marine Isotope Stage (MIS) 8. We observe changes in the mixed-layer temperature variability during MIS 5 and during the previous interglacial (MIS 7) showing significant reductions in ENSO amplitude. Differences in variability during glacial and interglacial intervals are also observed. Additionally, we reconstructed mixed-layer and thermocline conditions using multi-species Mg/Ca and stable isotope measurements to more fully characterize the state of the Central Tropical Pacific during these intervals. These reconstructions provide us with a unique view of Central Tropical Pacific variability and water-column structure at discrete intervals under varying boundary climate conditions with which to assess factors that shape ENSO

Simulating climate and stable water isotopes during the Last Interglacial using a coupled climate-isotope model

NASA Astrophysics Data System (ADS)

Gierz, Paul; Werner, Martin; Lohmann, Gerrit

2017-09-01

Understanding the dynamics of warm climate states has gained increasing importance in the face of anthropogenic climate change, and while it is possible to simulate warm interglacial climates, these simulated results cannot be evaluated without the aid of geochemical proxies. One such proxy is δ18O, which allows for inference about both a climate state's hydrology and temperature. We utilize a stable water isotope equipped climate model to simulate three stages during the Last Interglacial (LIG), corresponding to 130, 125, and 120 kyr before present, using forcings for orbital configuration as well as greenhouse gases. We discover heterogeneous responses in the mean δ18O signal to the climate forcing, with large areas of depletion in the LIG δ18O signal over the tropical Atlantic, the Sahel, and the Indian subcontinent, and with enrichment over the Pacific and Arctic Oceans. While we find that the climatology mean relationship between δ18O and temperature remains stable during the LIG, we also discover that this relationship is not spatially consistent. Our results suggest that great care must be taken when comparing δ18O records of different paleoclimate archives with the results of climate models as both the qualitative and quantitative interpretation of δ18O variations as a proxy for past temperature changes may be problematic due to the complexity of the signals.

A continuous record of glacial-interglacial cycles spanning more than 500 kyr from Lake Junín, Perú

NASA Astrophysics Data System (ADS)

Rodbell, D. T.; Abbott, M. B.; McGee, D.; Chen, C. Y.; Stoner, J. S.; Hatfield, R. G.; Tapia, P. M.; Bush, M. B.; Weidhaas, N.; Woods, A.; Valero-Garces, B. L.; Lehmann, S. B.; Bustamante, M. G.; Larsen, D. J.

2017-12-01

Lake Junín (11.0°S, 76.2°W) is a shallow (zmax 12 m), intermontane, high-elevation (4080 masl) lake in the inner-tropics of the Southern Hemisphere that spans 300 km2. It is dammed by coalescing alluvial fans that are >250 ka that emanate from glacial valleys. Lake Junín has not been overrun by glacial ice in several hundred thousand years and is ideally located to receive glacigenic sediment. The Junín basin is underlain by carbonate rocks that have provided a source of Ca and HCO3 ions; precipitation of CaCO3 in the western margin of the lake during the present interglacial period has occurred at 1mm yr-1. An airgun seismic survey revealed a strong reflector at 105 meters depth, which marks the base of the lacustrine section. Drilling focused on three sites. Site 1, located near the depocenter and most distal to glacial sources, yielded a composite sediment thickness of 95m; Site 2, proximal to glacial outwash fans, yielded a composite thickness of 28 m; Site 3, located at an intermediate distance yielded a sediment thickness of 55m. The stratigraphy of Site 1 is marked by 8 glacial/interglacial cycles; the latter are characterized by low bulk density and magnetic susceptibility (MS) and high CaCO3. These units are intercalated with glacigenic sediment that has high density and MS, and low CaCO3. The age model for Site 1 is based on AMS radiocarbon dates on terrestrial macrofossils and dozens of U/Th ages on authigenic CaCO3. Strong and protracted interglacial periods appear to be associated with intervals of reduced variability of solar insolation in the Southern Hemisphere tropics. During these intervals there is strong covariation (r2>0.9) between the δ13C and δ18O of authigenic calcium carbonate, and δ18O values are relatively enriched (-12 to -2‰); examples include interglacial periods correlative with marine isotope stages (MIS) 1, 13, and 15. The magnitude of tropical glaciation appears to have been greater during glacial cycles prior to the LGM

Precession-paced thermocline water temperature changes in response to upwelling conditions off southern Sumatra over the past 300,000 years

NASA Astrophysics Data System (ADS)

Wang, Xingxing; Jian, Zhimin; Lückge, Andreas; Wang, Yue; Dang, Haowen; Mohtadi, Mahyar

2018-07-01

Modern variations of sea surface temperature (SST) and thermocline water temperature (TWT) off southern Sumatra are responding to local upwelling conditions which are controlled by the Australian-Indonesian winter monsoon. The relationships between SST, TWT and upwelling during the past glacial-interglacial cycles are less clearly understood. In this study, SST and TWT variabilities over the past 300 kyr are reconstructed by using foraminiferal Mg/Ca-paleothermometry in sediment core SO139-74 KL off southern Sumatra (6°32.6‧S, 103°50‧E; 1690 m water depth). Whereas SST shows a clear glacial-interglacial cycle, TWT displays a predominant cycle at the precession band. Generally, the TWT record varies with total organic carbon content, revealing that similar to today, TWT and upwelling intensity off southern Sumatra vary in concert during the past 300 kyr. The lack of glacial-interglacial variability in the TWT suggests a limited role of glacial boundary conditions, such as changing sea level and ice volume, on the upwelling intensity in this region. The vertical gradients of upper water δ18O and temperature at this site also reveal precessional cyclicity. Our model simulation of air-sea interaction further supports the low TWTs during periods of enhanced upwelling and precession minimum.

Distinct water activation on polar/non-polar facets of ZnO nanoparticles

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

Zhang, He; Sun, Junming; Liu, Changjun

2015-11-01

ZnO nanoparticles with differing dominant facets were prepared and characterized by a complimentary of techniques such as X-ray diffraction, electron microscopy, temperature programmed desorption of H2O, and Fourier transform infrared spectroscopy analysis of adsorbed D2O. For the first time, water interaction/activation is compared on ZnO polar and non-polar facets. We report that non-polar facets exhibit high activity in water activation, which favors reactions such as ketonization and steam reforming in which dissociated water is involved. The distinct water dissociation on ZnO non-polar facets could be related to its facile formation of oxygen vacancies under realistic reaction conditions.

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. © 2013 John Wiley & Sons Ltd.

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.

Geometrical dart infrared polarization signatures

NASA Astrophysics Data System (ADS)

Lewis, Gareth D.; Jordan, David L.

1996-06-01

The 8 - 12 micrometer polarization signatures of diffuse and specular aluminum geometrical darts were analyzed outdoors using a polarization sensitive thermal imager. Results of the degree and plane of polarization are presented for different thermal imager gain bands and weather conditions during a two week period. The 0 degree, 45 degree, 90 degree and 135 degree polarizer orientations were thermally calibrated and the S1 and S2 Stokes parameters shown as radiometric temperature differences. The effect on the polarization signatures of range is considered for these targets at 100 m and 370 m. A comparison of the degree of polarization to changes in the emission/reflection balance and to variations in the dart's complex refractive index is made.

The Physics of Polarization

NASA Astrophysics Data System (ADS)

Landi Degl'Innocenti, Egidio

2015-10-01

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

Unexpected weak seasonal climate in the western Mediterranean region during MIS 31, a high-insolation forced interglacial

NASA Astrophysics Data System (ADS)

Oliveira, Dulce; Sánchez Goñi, Maria Fernanda; Naughton, Filipa; Polanco-Martínez, J. M.; Jimenez-Espejo, Francisco J.; Grimalt, Joan O.; Martrat, Belen; Voelker, Antje H. L.; Trigo, Ricardo; Hodell, David; Abrantes, Fátima; Desprat, Stéphanie

2017-04-01

Marine Isotope Stage 31 (MIS 31) is an important analogue for ongoing and projected global warming, yet key questions remain about the regional signature of its extreme orbital forcing and intra-interglacial variability. Based on a new direct land-sea comparison in SW Iberian margin IODP Site U1385 we examine the climatic variability between 1100 and 1050 ka including the ;super interglacial; MIS 31, a period dominated by the 41-ky obliquity periodicity. Pollen and biomarker analyses at centennial-scale-resolution provide new insights into the regional vegetation, precipitation regime and atmospheric and oceanic temperature variability on orbital and suborbital timescales. Our study reveals that atmospheric and SST warmth during MIS 31 was not exceptional in this region highly sensitive to precession. Unexpectedly, this warm stage stands out as a prolonged interval of a temperate and humid climate regime with reduced seasonality, despite the high insolation (precession minima values) forcing. We find that the dominant forcing on the long-term temperate forest development was obliquity, which may have induced a decrease in summer dryness and associated reduction in seasonal precipitation contrast. Moreover, this study provides the first evidence for persistent atmospheric millennial-scale variability during this interval with multiple forest decline events reflecting repeated cooling and drying episodes in SW Iberia. Our direct land-sea comparison shows that the expression of the suborbital cooling events on SW Iberian ecosystems is modulated by the predominance of high or low-latitude forcing depending on the glacial/interglacial baseline climate states. Severe dryness and air-sea cooling is detected under the larger ice volume during glacial MIS 32 and MIS 30. The extreme episodes, which in their climatic imprint are similar to the Heinrich events, are likely related to northern latitude ice-sheet instability and a disruption of the Atlantic Meridional Overturning

Reconstruction of the North Atlantic end-member of the Atlantic Meridional Overturning Circulation over glacial-interglacial cycles

NASA Astrophysics Data System (ADS)

Kim, J.; Seguí, M. J.; Knudson, K. P.; Yehudai, M.; Goldstein, S. L.; Pena, L. D.; Basak, C.; Ferretti, P.

2017-12-01

North Atlantic Deep Water (NADW) represents the major water mass that drives the Atlantic Meridional Ocean Circulation (AMOC), which undergoes substantial reorganization with changing climate. In order to understand its impact on ocean circulation and climate through time, it is necessary to constrain its composition. We report Nd isotope ratios of Fe-Mn oxide encrusted foraminifera and fish debris from DSDP Site 607 (41.00N 32.96W, 3427m), in the present-day core of NADW, and ODP 1063 (33.68N 57.62W, 4585m), on the deep abyssal plain at the interface between NADW and Antarctic Bottom Water. We provide a new North Atlantic paleocirculation record covering 2 Ma. At Site 607 interglacial ɛNd-values are consistently similar to present-day NADW (ɛNd -13.5), with median ɛNd-values of -14.3 in the Early Pleistocene and -13.8 in the Late Pleistocene. Glacial ɛNd-values are higher by 1 ɛNd-unit in the Early Pleistocene, and 1.5-2 ɛNd-units in the Late Pleistocene. Site 1063 shows much greater variability, with ɛNd ranging from -10 to -26. We interpret the North Atlantic AMOC source as represented by the Site 607 interglacial ɛNd-values, which has remained nearly stable throughout the entire period. The higher glacial ɛNd-values reflect incursions of some southern-sourced waters to Site 607, which is supported by coeval shifts to lower benthic foraminiferal d13C. In contrast, the Site 1063 ɛNd-values do not appear to reflect the AMOC end-member, and likely reflects local effects from a bottom source. A period of greatly disrupted ocean circulation marks 950-850 Ma, which may have been triggered by enhanced ice growth in the Northern Hemisphere that began around 1.2 Ma, as suggested by possible input events of Nd from the surrounding cratons into the North Atlantic observed in Site 607. Interglacial AMOC only recovers to the previously observed vigor over 200 ka following the disruption, whereas further intensified SSW incursion into the deep North Atlantic come to

Search for Polarization Effects in the Antiproton Production Process

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

Grzonka, D.; Kilian, K.; Ritman, J.

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.

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

NASA Astrophysics Data System (ADS)

Bindeman, Ilya N.; Lowenstern, Jacob B.

2016-11-01

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 hydration rinds in perlites

The Polar Ionosphere and Interplanetary Field.

DTIC Science & Technology

1987-08-01

model for investigating time dependent behavior of the Polar F-region ionosphere in response to varying interplanetary magnetic field (IMF...conditions. The model has been used to illustrate ionospheric behavior during geomagnetic storms conditions. Future model applications may include...magnetosphere model for investigating time dependent behavior of the polar F-region ionosphere in response to varying interplanetary magnetic field

Mineralogical evidence of reduced East Asian summer monsoon rainfall on the Chinese loess plateau during the early Pleistocene interglacials

NASA Astrophysics Data System (ADS)

Meng, Xianqiang; Liu, Lianwen; Wang, Xingchen T.; Balsam, William; Chen, Jun; Ji, Junfeng

2018-03-01

The East Asian summer monsoon (EASM) is an important component of the global climate system. A better understanding of EASM rainfall variability in the past can help constrain climate models and better predict the response of EASM to ongoing global warming. The warm early Pleistocene, a potential analog of future climate, is an important period to study EASM dynamics. However, existing monsoon proxies for reconstruction of EASM rainfall during the early Pleistocene fail to disentangle monsoon rainfall changes from temperature variations, complicating the comparison of these monsoon records with climate models. Here, we present three 2.6 million-year-long EASM rainfall records from the Chinese Loess Plateau (CLP) based on carbonate dissolution, a novel proxy for rainfall intensity. These records show that the interglacial rainfall on the CLP was lower during the early Pleistocene and then gradually increased with global cooling during the middle and late Pleistocene. These results are contrary to previous suggestions that a warmer climate leads to higher monsoon rainfall on tectonic timescales. We propose that the lower interglacial EASM rainfall during the early Pleistocene was caused by reduced sea surface temperature gradients across the equatorial Pacific, providing a testable hypothesis for climate models.

A regional tephrostratigraphic framework for central and southern European climate archives during the Last Glacial to Interglacial transition: comparisons north and south of the Alps

NASA Astrophysics Data System (ADS)

Lane, C. S.; Blockley, S. P. E.; Lotter, A. F.; Finsinger, W.; Filippi, M. L.; Matthews, I. P.

2012-03-01

This paper summarises the results of tephrochronological investigations into a suite of central and southern European records, which include: Rotmeer, southern Germany; Soppensee and Rotsee, central Swiss Plateau; Lago di Lavarone and Lago Piccolo di Avigliana, Italian southern Alpine foreland. These sites provide records of palaeoenvironmental changes for the Last Glacial to Interglacial Transition (LGIT) at the boundary between North Atlantic and Mediterranean climatic influences. Chemical characterisation of glass shards in volcanic ash layers indicates that multiple volcanic sources have contributed to the central European tephra record. Amongst other volcanic markers, the Laacher See Tephra, originating from the Eifel region of Germany c. 12.9 ± 0.1 ka, and the Vedde Ash from Iceland c. 12.1 ± 0.1 ka, are found co-located within the sediments of Rotmeer, Soppensee, Rotsee and Lago Piccolo di Avigliana. These key horizons, which bracket the onset of the Younger Dryas stadial, provide precise calendrically-dated tie points around which a detailed picture of the timing of local and regional environmental transitions can be constructed. Using the co-located tephra layers the re-colonisation of Northern Italian catchment areas by Quercus is shown to occur just prior to the deposition of the Laacher See Tephra layer, whereas to the North of the Alps Quercus and other thermophilous trees do not reappear until several centuries after the deposition of the Vedde Ash. Furthermore, the discovery of the Vedde Ash in Lago Piccolo di Avigliana and Lago di Lavarone is indicative of atmospheric transport of polar air into southern Europe during the Younger Dryas stadial, matching evidence proposed for such transport of polar air during the Last Glacial Maximum (LGM).

A Si nanocube array polarizer

NASA Astrophysics Data System (ADS)

Chen, Linghua; Jiang, Yingjie; Xing, Li; Yao, Jun

2017-10-01

We have proposed a full dielectric (silicon) nanocube array polarizer based on a silicon dioxide substrate. Each polarization unit column includes a plurality of equal spaced polarization units. By optimizing the length, the width, the height of the polarization units and the center distance of adjacent polarization unit (x direction and y direction), an extinction ratio (ER) of higher than 25dB was obtained theoretically when the incident light wavelength is 1550nm. while for applications of most polarization optical elements, ER above 10dB is enough. With this condition, the polarizer we designed can work in a wide wavelength range from 1509.31nm to 1611.51nm. Compared with the previous polarizer, we have introduced a polarizer which is a full dielectric device, which solves the problems of low efficiency caused by Ohmic loss and weak coupling. Furthermore, compared with the existing optical polarizers, our polarizer has the advantages of thin thickness, small size, light weight, and low processing difficulty, which is in line with the future development trend of optical elements.

Linear and non-linear responses of vegetation and soils to glacial-interglacial climate change in a Mediterranean refuge.

PubMed

Holtvoeth, Jens; Vogel, Hendrik; Valsecchi, Verushka; Lindhorst, Katja; Schouten, Stefan; Wagner, Bernd; Wolff, George A

2017-08-14

The impact of past global climate change on local terrestrial ecosystems and their vegetation and soil organic matter (OM) pools is often non-linear and poorly constrained. To address this, we investigated the response of a temperate habitat influenced by global climate change in a key glacial refuge, Lake Ohrid (Albania, Macedonia). We applied independent geochemical and palynological proxies to a sedimentary archive from the lake over the penultimate glacial-interglacial transition (MIS 6-5) and the following interglacial (MIS 5e-c), targeting lake surface temperature as an indicator of regional climatic development and the supply of pollen and biomarkers from the vegetation and soil OM pools to determine local habitat response. Climate fluctuations strongly influenced the ecosystem, however, lake level controls the extent of terrace surfaces between the shoreline and mountain slopes and hence local vegetation, soil development and OM export to the lake sediments. There were two phases of transgressional soil erosion from terrace surfaces during lake-level rise in the MIS 6-5 transition that led to habitat loss for the locally dominant pine vegetation as the terraces drowned. Our observations confirm that catchment morphology plays a key role in providing refuges with low groundwater depth and stable soils during variable climate.

Photoelectrons in the Quiet Polar Wind

NASA Technical Reports Server (NTRS)

Glocer, A.; Khazanov, G.; Liemohn, M.

2017-01-01

This study presents a newly coupled model capable of treating the superthermal electron population in the global polar wind solution. The model combines the hydrodynamic Polar Wind Outflow Model (PWOM) with the kinetic SuperThermal Electron Transport (STET) code. The resulting PWOM-STET coupled model is described and then used to investigate the role of photoelectrons in the polar wind. We present polar wind results along single stationary field lines under dayside and nightside conditions, as well as the global solution reconstructed from nearly 1000 moving field lines. The model results show significant day-night asymmetries in the polar wind solution owing to the higher ionization and photoelectron fluxes on the dayside compared to the nightside. Field line motion is found to modify this dependence and create global structure by transporting field lines through different conditions of illumination and through the localized effects of Joule heating.

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

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.

Polarization rotation in meteor burst communication systems

NASA Astrophysics Data System (ADS)

Cannon, P. S.

1986-06-01

Theoretical modeling of several meteor burst communication (MBC) paths indicates that polarization rotation losses are significant for a linearly polarized system operating near 40 MHz. Losses for a hybrid system with physical installation problems, consisting of linearly polarized transmitting and circularly polarized receiving antennas, were found to be less. Both ionospheric Faraday rotation polarization changes, and underdense meteor trail scattering wave polarization rotation, are considered. These losses are found to cause a 15-70 percent data throughput reduction of the value predicted for the situation without polarization rotation, in the two 40-MHz linearly polarized links considered for noon summer solstice conditions during high solar sunspot number periods. Qualitative experimental confirmation is provided through a cross polarization approach.

Polarization effects in recoil-induced resonances

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

Lazebnyi, D. B., E-mail: becks.ddf@gmail.com; Brazhnikov, D. V.; Taichenachev, A. V.

2017-01-15

The effect of the field polarization on the amplitude of recoil-induced resonances (RIRs) is considered for laser-cooled free atoms and for atoms in a working magneto-optical trap (MOT). For all closed dipole transitions, explicit analytical expressions are obtained for the polarization dependence of the resonance amplitudes within a perturbation theory. Optimal polarization conditions are found for the observation of resonances.

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

Cross-Polarization Optical Coherence Tomography with Active Maintenance of the Circular Polarization of a Sounding Wave in a Common Path System

NASA Astrophysics Data System (ADS)

Gelikonov, V. M.; Romashov, V. N.; Shabanov, D. V.; Ksenofontov, S. Yu.; Terpelov, D. A.; Shilyagin, P. A.; Gelikonov, G. V.; Vitkin, I. A.

2018-05-01

We consider a cross-polarization optical coherence tomography system with a common path for the sounding and reference waves and active maintenance of the circular polarization of a sounding wave. The system is based on the formation of birefringent characteristics of the total optical path, which are equivalent to a quarter-wave plate with a 45° orientation of its optical axes with respect to the linearly polarized reference wave. Conditions under which any light-polarization state can be obtained using a two-element phase controller are obtained. The dependence of the local cross-scattering coefficient of light in a model medium and biological tissue on the sounding-wave polarization state is demonstrated. The necessity of active maintenance of the circular polarization of a sounding wave in this common path system (including a flexible probe) is shown to realize uniform optimal conditions for cross-polarization studies of biological tissue.

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.

Glacial-interglacial vegetation dynamics in South Eastern Africa coupled to sea surface temperature variations in the Western Indian Ocean

NASA Astrophysics Data System (ADS)

Dupont, L. M.; Caley, T.; Kim, J.-H.; Castañeda, I.; Malaizé, B.; Giraudeau, J.

2011-11-01

Glacial-interglacial fluctuations in the vegetation of South Africa might elucidate the climate system at the edge of the tropics between the Indian and Atlantic Oceans. However, vegetation records covering a full glacial cycle have only been published from the eastern South Atlantic. We present a pollen record of the marine core MD96-2048 retrieved by the Marion Dufresne from the Indian Ocean ∼120 km south of the Limpopo River mouth. The sedimentation at the site is slow and continuous. The upper 6 m (spanning the past 342 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. During glacials open mountainous scrubland dominated. Montane forest with Podocarpus extended during humid periods was favoured by strong local insolation. Correlation with the sea surface temperature record of the same core indicates that the extension of mountainous scrubland primarily depends on sea surface temperatures of the Agulhas Current. Our record corroborates terrestrial evidence of the extension of open mountainous scrubland (including fynbos-like species of the high-altitude Grassland biome) for the last glacial as well as for other glacial periods of the past 300 Ka.

Resonant Polarization Spectroscopy for Hot X-ray Plasmas

DOE PAGES

Chen, Guo -Xin

2016-04-28

X-ray line polarization spectroscopy is a method of choice for probing hot plasma conditions. The precise roles of resonant structures in this method have not been realized and fully understood. With a sophisticated relativistic close coupling Dirac R-matrix calculation of polarized radiation of the quadrupole magnetic M2 line at 2.717 Å in Ba 46+, we revealed the nature of resonant structures in x-ray line polarization spectroscopy. We found that signatures with a heavy resonance forest imprinting on polarization may be used for a sensitive new spectroscopic method. The resonant polarization spectrum was used to determine or constrain the directional beammore » electron distribution of the laboratory Ba plasma. Lastly, our results provide a start of resonant polarization spectroscopy as a method for diagnostics of laboratory, fusion and astrophysical plasma source conditions.« less

Polarization behaviour of polyvinylidenefluoride-polysulfone (PVDF: PSF) blends under high field and high temperature condition

NASA Astrophysics Data System (ADS)

Shrivas, Sandhya; Patel, Swarnim; Dubey, R. K.; Keller, J. M.

2018-05-01

Thermally stimulated discharge currents of PVDF: PSF blend samples in ratio 80:20 and 95:05 prepared by the solution cast technique have been studied as a function of polarizing field and polarizing temperature, the temperature corresponding to a peak in TSDC is found to be independent of polarizing field but dependent on the polarizing temperature.

Eemian and Holocene interglacial climate in northwest Greenland inferred from insect assemblages, lipid δ2H, and chitin δ18O preserved in lake sediments

NASA Astrophysics Data System (ADS)

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

2016-12-01

We present a millennial-scale reconstruction of Holocene and Last Interglacial (Eemian) climate in northwest Greenland, inferred from insect assemblages (chironomid-inferred temperatures, CITs) and compound-specific organic isotopes (sedimentary lipid δ2H and chitin δ18O). Sediment cores collected from `Wax Lips Lake' (informal name), a non-glacial lake situated <2 km from the present margin of the Greenland Ice Sheet, yield radiocarbon ages that indicate preservation of Holocene lake sediments as well as an underlying unit of interglacial lake sediments that predate the Last Glacial Maximum (LGM). Terrestrial archives of continuous interglacial climate that predate the LGM and capture peak Last Interglacial (LIG) warmth are rare in Greenland and across the glaciated Arctic. Our quantitative estimates of LIG temperatures are derived from CITs and supported by enrichment in stable isotopes of precipitation (in both lipid δ2H and chitin δ18O) and the presence of the warm-dwelling insect Chaoboridae. Our record agrees with estimates of the peak LIG temperature anomaly (relative to the last millennium) from ice cores at NEEM (+8±4°C; Dahl-Jensen et al. 2013), also in northern Greenland. Peak LIG temperatures at both sites exceeded those of the Holocene. We pair an independent temperature proxy with proxies recording the stable isotopic composition of precipitation and lake water at this high-latitude site to provide insight on how hydroclimate changed over Arctic Greenland during two different warm periods - the Holocene Thermal Maximum and the LIG. We find general agreement amongst recorders of lake water isotopic composition, including δ18O of chitin from chironomid head capsules and δ2H of aquatic lipids. We infer the isotopic composition of precipitation from δ2H of long-chain n-alkanes from terrestrial plants. The δ2H of long-chain n-alkanes are internally consistent and deviate from lake water during prolonged periods of warmth, indicating changes in

Polarizing the Nazarov cyclization: efficient catalysis under mild conditions.

PubMed

He, Wei; Sun, Xiufeng; Frontier, Alison J

2003-11-26

Substituted divinyl ketones were studied in the Nazarov cyclization. alpha-Carbomethoxy divinyl ketones underwent efficient Nazarov cyclization with catalytic copper triflate (2 mol %) to give a single cyclopentenone regio- and stereoisomer. The efficiency of the cyclizations correlated with the ability of the substituents to favorably polarize the pi-system of the cationic intermediate.

Antarctic climate and ice-sheet configuration during the early Pliocene interglacial at 4.23 Ma

NASA Astrophysics Data System (ADS)

Golledge, Nicholas R.; Thomas, Zoë A.; Levy, Richard H.; Gasson, Edward G. W.; Naish, Timothy R.; McKay, Robert M.; Kowalewski, Douglas E.; Fogwill, Christopher J.

2017-07-01

The geometry of Antarctic ice sheets during warm periods of the geological past is difficult to determine from geological evidence, but is important to know because such reconstructions enable a more complete understanding of how the ice-sheet system responds to changes in climate. Here we investigate how Antarctica evolved under orbital and greenhouse gas conditions representative of an interglacial in the early Pliocene at 4.23 Ma, when Southern Hemisphere insolation reached a maximum. Using offline-coupled climate and ice-sheet models, together with a new synthesis of high-latitude palaeoenvironmental proxy data to define a likely climate envelope, we simulate a range of ice-sheet geometries and calculate their likely contribution to sea level. In addition, we use these simulations to investigate the processes by which the West and East Antarctic ice sheets respond to environmental forcings and the timescales over which these behaviours manifest. We conclude that the Antarctic ice sheet contributed 8.6 ± 2.8 m to global sea level at this time, under an atmospheric CO2 concentration identical to present (400 ppm). Warmer-than-present ocean temperatures led to the collapse of West Antarctica over centuries, whereas higher air temperatures initiated surface melting in parts of East Antarctica that over one to two millennia led to lowering of the ice-sheet surface, flotation of grounded margins in some areas, and retreat of the ice sheet into the Wilkes Subglacial Basin. The results show that regional variations in climate, ice-sheet geometry, and topography produce long-term sea-level contributions that are non-linear with respect to the applied forcings, and which under certain conditions exhibit threshold behaviour associated with behavioural tipping points.

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. Copyright © 2014 Elsevier B.V. All rights reserved.

Growth, Uplift and Truncation of Indo-Burman Anticlines Paced By Glacial-Interglacial Sea Level Change

NASA Astrophysics Data System (ADS)

Gale, J.; Steckler, M. S.; Sousa, D.; Seeber, L.; Goodbred, S. L., Jr.; Ferguson, E. K.

2014-12-01

The Ganges-Brahmaputra Delta abuts the Indo-Burman Arc on the east. Subduction of the thick delta strata has generated a large subaerial accretionary prism, up to 250 km wide, with multiple ranges of anticlines composed of the folded and faulted delta sediments. As the wedge has grown, the exposed anticlines have become subject to erosion by the rivers draining the Himalaya, a local Indo-Burman drainage network, and coastal processes. Multiple lines of geophysical, geologic, and geomorphologic evidence indicate anticline truncation as a result of interaction with the rivers of the delta and sea level. Seismic lines, geologic mapping, and geomorphology reveal truncated anticlines with angular unconformities that have been arched due to continued growth of the anticline. Buried, truncated anticlines have been identified by seismic lines, tube well logs, and resistivity measurements. The truncation of these anticlines also appears to provide a pathway for high-As Holocene groundwater into the generally low-As Pleistocene groundwater. Overall, the distribution of anticline erosion and elevation in the fold belt appears to be consistent with glacial-interglacial changes in river behavior in the delta. The anticline crests are eroded during sea level highstands as rivers and the coastline sweep across the region, and excavated by local drainage during lowstands. With continued growth, the anticlines are uplifted above the delta and "survive" as topographic features. As a result, the maximum elevations of the anticlines are clustered in a pattern suggesting continued growth since their last glacial highstand truncation. An uplift rate is calculated from this paced truncation and growth that is consistent with other measurements of Indo-Burman wedge advance. This rate, combined with the proposed method of truncation, give further evidence of dynamic fluvial changes in the delta between glacial and interglacial times.

Experimental testing of scattering polarization models

NASA Astrophysics Data System (ADS)

Li, Wenxian; Casini, Roberto; Tomczyk, Steven; Landi Degl'Innocenti, Egidio; Marsell, Brandan

2018-06-01

We realized a laboratory experiment to study the polarization of the Na I doublet at 589.3 nm, in the presence of a magnetic field. The purpose of the experiment is to test the theory of scattering polarization for illumination conditions typical of astrophysical plasmas. This work was stimulated by solar observations of the Na I doublet that have proven particularly challenging to reproduce with current models of polarized line formation, even casting doubts on our very understanding of the physics of scattering polarization on the Sun. The experiment has confirmed the fundamental correctness of the current theory, and demonstrated that the "enigmatic'' polarization of those observations is exclusively of solar origin.

Oligocene sea water temperatures offshore Wilkes Land (Antarctica) indicate warm and stable glacial-interglacial variation and show no 'late Oligocene warming'

NASA Astrophysics Data System (ADS)

Hartman, Julian; Bijl, Peter; Peterse, Francien; Schouten, Stefan; Salabarnada, Ariadna; Bohaty, Steven; Escutia, Carlota; Brinkhuis, Henk; Sangiorgi, Francesca

2017-04-01

At present, warming of the waters below the Antarctic ice shelves is a major contributor to the instability of the Antarctic cryosphere. In order to get insight into future melt behavior of the Antarctic ice sheet, it is important to look at past warm periods that can serve as an analogue for the future. The Oligocene ( 34-23 Ma) is a period within the range of CO2 concentrations predicted by the latest IPCC report for the coming century and is characterized by a very dynamic Antarctic ice sheet, as suggested by benthic δ18O records from ice-distal sites. We suspect that, like today, environmental changes in the Southern Ocean are in part responsible for this dynamicity. To gain more insight into this, we have reconstructed sea water temperatures (SWT) based on Thaumarchaeotal lipids (TEX86) for the Oligocene record obtained from the ice-proximal Site U1356 (Integrated Ocean Drilling Program), offshore Wilkes Land. Part of our record shows a strong coupling between the lithology and SWT, which we attribute to glacial-interglacial variation. Our data shows that both glacial and interglacial temperatures are relatively warm throughout the Oligocene: 14°C and 18°C respectively, which is consistent with previously published estimates based on UK'37 and clumped isotopes for the early Oligocene. Our SST records show only a minor decline between 30 and 24 Ma, and thus show no evidence for a 'late Oligocene warming' as was suggested based on benthic δ18O records from low latitudes. Instead, the discrepancy between our SST trend and the δ18O trend suggests that the late-Oligocene benthic δ18O decrease is likely related to a decline in ice volume. After 24 Ma, however, glacial-interglacial temperature variation appears to increase. In particular, some large temperature drops occur, one of which can be related to the Mi-1 event and a major expansion of the Antarctic ice sheet.

Eye contrast polarity is critical for face recognition by infants.

PubMed

Otsuka, Yumiko; Motoyoshi, Isamu; Hill, Harold C; Kobayashi, Megumi; Kanazawa, So; Yamaguchi, Masami K

2013-07-01

Just as faces share the same basic arrangement of features, with two eyes above a nose above a mouth, human eyes all share the same basic contrast polarity relations, with a sclera lighter than an iris and a pupil, and this is unique among primates. The current study examined whether this bright-dark relationship of sclera to iris plays a critical role in face recognition from early in development. Specifically, we tested face discrimination in 7- and 8-month-old infants while independently manipulating the contrast polarity of the eye region and of the rest of the face. This gave four face contrast polarity conditions: fully positive condition, fully negative condition, positive face with negated eyes ("negative eyes") condition, and negated face with positive eyes ("positive eyes") condition. In a familiarization and novelty preference procedure, we found that 7- and 8-month-olds could discriminate between faces only when the contrast polarity of the eyes was preserved (positive) and that this did not depend on the contrast polarity of the rest of the face. This demonstrates the critical role of eye contrast polarity for face recognition in 7- and 8-month-olds and is consistent with previous findings for adults. Copyright © 2013 Elsevier Inc. All rights reserved.

Polarization-induced hole doping in N-polar III-nitride LED grown by metalorganic chemical vapor deposition

NASA Astrophysics Data System (ADS)

Yan, Long; Zhang, Yuantao; Han, Xu; Deng, Gaoqiang; Li, Pengchong; Yu, Ye; Chen, Liang; Li, Xiaohang; Song, Junfeng

2018-04-01

Polarization-induced doping has been shown to be effective for wide-bandgap III-nitrides. In this work, we demonstrated a significantly enhanced hole concentration via linearly grading an N-polar AlxGa1-xN (x = 0-0.3) layer grown by metal-organic chemical vapor deposition. The hole concentration increased by ˜17 times compared to that of N-polar p-GaN at 300 K. The fitting results of temperature-dependent hole concentration indicated that the holes in the graded p-AlGaN layer comprised both polarization-induced and thermally activated ones. By optimizing the growth conditions, the hole concentration was further increased to 9.0 × 1017 cm-3 in the graded AlGaN layer. The N-polar blue-violet light-emitting device with the graded p-AlGaN shows stronger electroluminescence than the one with the conventional p-GaN. The study indicates the potential of the polarization doping technique in high-performance N-polar light-emitting devices.

An invisible medium for circularly polarized electromagnetic waves.

PubMed

Tamayama, Y; Nakanishi, T; Sugiyama, K; Kitano, M

2008-12-08

We study the no reflection condition for a planar boundary between vacuum and an isotropic chiral medium. In general chiral media, elliptically polarized waves incident at a particular angle satisfy the no reflection condition. When the wave impedance and wavenumber of the chiral medium are equal to the corresponding parameters of vacuum, one of the circularly polarized waves is transmitted to the medium without reflection or refraction for all angles of incidence. We propose a circular polarizing beam splitter as a simple application of the no reflection effect. (c) 2008 Optical Society of America

Projected polar bear sea ice habitat in the Canadian Arctic Archipelago.

PubMed

Hamilton, Stephen G; Castro de la Guardia, Laura; Derocher, Andrew E; Sahanatien, Vicki; Tremblay, Bruno; Huard, David

2014-01-01

Sea ice across the Arctic is declining and altering physical characteristics of marine ecosystems. Polar bears (Ursus maritimus) have been identified as vulnerable to changes in sea ice conditions. We use sea ice projections for the Canadian Arctic Archipelago from 2006 - 2100 to gain insight into the conservation challenges for polar bears with respect to habitat loss using metrics developed from polar bear energetics modeling. Shifts away from multiyear ice to annual ice cover throughout the region, as well as lengthening ice-free periods, may become critical for polar bears before the end of the 21st century with projected warming. Each polar bear population in the Archipelago may undergo 2-5 months of ice-free conditions, where no such conditions exist presently. We identify spatially and temporally explicit ice-free periods that extend beyond what polar bears require for nutritional and reproductive demands. Under business-as-usual climate projections, polar bears may face starvation and reproductive failure across the entire Archipelago by the year 2100.

Vegetation Response to Upper Pliocene Glacial/Interglacial Cyclicity in the Central Mediterranean

NASA Astrophysics Data System (ADS)

Combourieu-Nebout, Nathalie

1993-09-01

New detailed pollen analysis of the lower part of the Upper Pliocene Semaforo section (Crotone, Italy) documents cyclic behavior of vegetation at the beginning of the Northern Hemisphere glaciations. The competition between four vegetation units (subtropical humid forest, deciduous temperate forest, altitudinal coniferous forest, and open xeric assemblage) probably reflects modifications of vegetation belts at this montane site. Several increases in herbaceous open vegetation regularly alternate with subtropical humid forest, which expresses rapid climatic oscillations. The complete temporal succession—deciduous forest (rich in Quercus), followed by subtropical humid forest (Taxodiaceae and Cathaya), then altitudinal coniferous forest ( Tsuga, Cedrus, Abies, and Picea), and finally herbaceous open vegetation (Graminae, Compositae, and Artemisia )—displays the climatic evolution from warm and humid interglaciation to cold and dry glaciation. It also suggests an independent variation of temperature and humidity, the two main climatic parameters. The vegetation history of southern Calabria recorded in the Semaforo section have been correlated with the ∂ 18O signal established in the Atlantic Ocean.

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

USGS Publications Warehouse

McKinney, Melissa A.; Atwood, Todd C.; 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.

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

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.

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.

Completed Beltrami-Michell Formulation in Polar Coordinates

NASA Technical Reports Server (NTRS)

Patnaik, Surya N.; Hopkins, Dale A.

2005-01-01

A set of conditions had not been formulated on the boundary of an elastic continuum since the time of Saint-Venant. This limitation prevented the formulation of a direct stress calculation method in elasticity for a continuum with a displacement boundary condition. The missed condition, referred to as the boundary compatibility condition, is now formulated in polar coordinates. The augmentation of the new condition completes the Beltrami-Michell formulation in polar coordinates. The completed formulation that includes equilibrium equations and a compatibility condition in the field as well as the traction and boundary compatibility condition is derived from the stationary condition of the variational functional of the integrated force method. The new method is illustrated by solving an example of a mixed boundary value problem for mechanical as well as thermal loads.

Size and shape stasis in late Pleistocene mammals and birds from Rancho La Brea during the Last Glacial-Interglacial cycle

NASA Astrophysics Data System (ADS)

Prothero, Donald R.; Syverson, Valerie J.; Raymond, Kristina R.; Madan, Meena; Molina, Sarah; Fragomeni, Ashley; DeSantis, Sylvana; Sutyagina, Anastasiya; Gage, Gina L.

2012-11-01

Conventional neo-Darwinian theory views organisms as infinitely sensitive and responsive to their environments, and considers them able to readily change size or shape when they adapt to selective pressures. Yet since 1863 it has been well known that Pleistocene animals and plants do not show much morphological change or speciation in response to the glacial-interglacial climate cycles. We tested this hypothesis with all of the common birds (condors, golden and bald eagles, turkeys, caracaras) and mammals (dire wolves, saber-toothed cats, giant lions, horses, camels, bison, and ground sloths) from Rancho La Brea tar pits in Los Angeles, California, which preserves large samples of many bones from many well-dated pits spanning the 35,000 years of the Last Glacial-Interglacial cycle. Pollen evidence showed the climate changed from chaparral/oaks 35,000 years ago to snowy piñon-juniper forests at the peak glacial 20,000 years ago, then back to the modern chaparral since the glacial-interglacial transition. Based on Bergmann's rule, we would expect peak glacial specimens to have larger body sizes, and based on Allen's rule, peak glacial samples should have shorter and more robust limbs. Yet statistical analysis (ANOVA for parametric samples; Kruskal-Wallis test for non-parametric samples) showed that none of the Pleistocene pit samples is statistically distinct from the rest, indicating complete stasis from 35 ka to 9 ka. The sole exception was the Pit 13 sample of dire wolves (16 ka), which was significantly smaller than the rest, but this did not occur in response to climate change. We also performed a time series analysis of the pit samples. None showed directional change; all were either static or showed a random walk. Thus, the data show that birds and mammals at Rancho La Brea show complete stasis and were unresponsive to the major climate change that occurred at 20 ka, consistent with other studies of Pleistocene animals and plants. Most explanations for such

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

Eemian interglacial reconstructed from a Greenland folded ice core.

PubMed

2013-01-24

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

Climate, atmosphere, and volatile inventory evolution: Polar processes, climate records, volatile inventories

NASA Technical Reports Server (NTRS)

Pollack, J. B.

1988-01-01

Climate change on Mars was driven by long term changes in the solar luminosity, variations in the partitioning of volatiles between the atmosphere and near-surface reservoirs, and astronomical variations in axial and orbital properties. There are important parallels between these drives for Mars and comparable ones for Earth. In the early history of the solar system, the Sun's luminosity was 25 to 30 percent lower than its current value. It is suggested that an early benign climate on Earth was due to the presence of much more carbon dioxide in its atmosphere at these early times than currently resides there. Such a partitioning of carbon dioxide, at the expense of the carbonate rock reservoir, may have resulted from a more vigorous tectonic and volcanic style at early times. Such a line of reasoning may imply that much more carbon dioxide was present in the Martian atmosphere during the planet's early history than resides there today. It is now widely recognized that astronomical variations of the Earth's axial and orbital characteristics have played a dominant role in causing the succession of glacial and interglacial periods characterizing the last several million years. The magnitude of the axial and eccentricity variations are much larger for Mars than for Earth. Such changes on Mars could result in sizeable variations in atmospheric pressure, dust storm activity, and the stability of perennial carbon dioxide and water ice polar caps. These quasi-periodic climate changes occur on periods of 100,000 to 1,000,000 years and may be recorded in the sedimentary layers of the polar layered terrain.

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.

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

NASA Astrophysics Data System (ADS)

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

2015-10-01

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

Fractal model of polarization switching kinetics in ferroelectrics under nonequilibrium conditions of electron irradiation

NASA Astrophysics Data System (ADS)

Maslovskaya, A. G.; Barabash, T. K.

2018-03-01

The paper presents the results of the fractal and multifractal analysis of polarization switching current in ferroelectrics under electron irradiation, which allows statistical memory effects to be estimated at dynamics of domain structure. The mathematical model of formation of electron beam-induced polarization current in ferroelectrics was suggested taking into account the fractal nature of domain structure dynamics. In order to realize the model the computational scheme was constructed using the numerical solution approximation of fractional differential equation. Evidences of electron beam-induced polarization switching process in ferroelectrics were specified at a variation of control model parameters.

Effects of wildfire smoke on atmospheric polarization

NASA Astrophysics Data System (ADS)

Shaw, Joseph A.; Pust, Nathan J.; Forbes, Elizabeth

2014-05-01

A continuously operating all-sky polarization imager recorded the skylight polarization pattern as conditions transitioned from clear and clean to extremely smoky. This transition included a period when a local wildfire plume filled part of the sky with smoke, creating a highly asymmetric distribution of aerosols. Multiple scattering in the smoke plume strongly reduced the degree of polarization in the smoky region of the sky. Once the smoke plume spread out to cover the entire local sky, the degree of polarization was strongly reduced everywhere. However, this example differed from previously observed smoke events because, even though the usual skylight polarization pattern generally persisted throughout the event, this time the smoke-covered sky exhibited a spatially asymmetric profile along the band of maximum polarization. This pattern of reduced polarization toward the horizon is hypothesized to be a result of an optically thick but physically thin smoke layer. The skylight polarization observations are supplemented with optical depth measurements and aerosol size distribution retrievals from a solar radiometer.

Celestial polarization patterns sufficient for Viking navigation with the naked eye: detectability of Haidinger's brushes on the sky versus meteorological conditions

NASA Astrophysics Data System (ADS)

Horváth, Gábor; Takács, Péter; Kretzer, Balázs; Szilasi, Szilvia; Száz, Dénes; Farkas, Alexandra; Barta, András

2017-02-01

If a human looks at the clear blue sky from which light with high enough degree of polarization d originates, an 8-shaped bowtie-like figure, the yellow Haidinger's brush can be perceived, the long axis of which points towards the sun. A band of high d arcs across the sky at 90° from the sun. A person can pick two points on that band, observe the yellow brushes and triangulate the position of the sun based on the orientation of the two observed brushes. This method has been suggested to have been used on the open sea by Viking navigators to determine the position of the invisible sun occluded by cloud or fog. Furthermore, Haidinger's brushes can also be used to locate the sun when it is below the horizon or occluded by objects on the horizon. To determine the position of the sun using the celestial polarization pattern, the d of the portion of the sky used must be greater than the viewer's degree of polarization threshold d* for perception of Haidinger's brushes. We studied under which sky conditions the prerequisite d > d* is satisfied. Using full-sky imaging polarimetry, we measured the d-pattern of skylight in the blue (450 nm) spectral range for 1296 different meteorological conditions with different solar elevation angles θ and per cent cloud cover ρ. From the measured d-patterns of a given sky we determined the proportion P of the sky for which d > d*. We obtained that P is the largest at low solar elevations θ ≈ 0° and under totally or nearly clear skies with cloud coverage ρ = 0%, when the sun's position is already easily determined. If the sun is below the horizon (-5° ≤ θ < 0°) during twilight, P = 76.17 ± 4.18% for dmin∗=23 % under clear sky conditions. Consequently, the sky-polarimetric Viking navigation based on Haidinger's brushes is most useful after sunset and prior to sunrise, when the sun is not visible and large sky regions are bright, clear and polarized enough for perception of Haidinger's brushes.

Celestial polarization patterns sufficient for Viking navigation with the naked eye: detectability of Haidinger's brushes on the sky versus meteorological conditions

PubMed Central

Takács, Péter; Kretzer, Balázs; Szilasi, Szilvia; Száz, Dénes; Farkas, Alexandra; Barta, András

2017-01-01

If a human looks at the clear blue sky from which light with high enough degree of polarization d originates, an 8-shaped bowtie-like figure, the yellow Haidinger's brush can be perceived, the long axis of which points towards the sun. A band of high d arcs across the sky at 90° from the sun. A person can pick two points on that band, observe the yellow brushes and triangulate the position of the sun based on the orientation of the two observed brushes. This method has been suggested to have been used on the open sea by Viking navigators to determine the position of the invisible sun occluded by cloud or fog. Furthermore, Haidinger's brushes can also be used to locate the sun when it is below the horizon or occluded by objects on the horizon. To determine the position of the sun using the celestial polarization pattern, the d of the portion of the sky used must be greater than the viewer's degree of polarization threshold d* for perception of Haidinger's brushes. We studied under which sky conditions the prerequisite d > d* is satisfied. Using full-sky imaging polarimetry, we measured the d-pattern of skylight in the blue (450 nm) spectral range for 1296 different meteorological conditions with different solar elevation angles θ and per cent cloud cover ρ. From the measured d-patterns of a given sky we determined the proportion P of the sky for which d > d*. We obtained that P is the largest at low solar elevations θ ≈ 0° and under totally or nearly clear skies with cloud coverage ρ = 0%, when the sun's position is already easily determined. If the sun is below the horizon (−5° ≤ θ < 0°) during twilight, P = 76.17 ± 4.18% for dmin∗=23% under clear sky conditions. Consequently, the sky-polarimetric Viking navigation based on Haidinger's brushes is most useful after sunset and prior to sunrise, when the sun is not visible and large sky regions are bright, clear and polarized enough for perception of Haidinger

Celestial polarization patterns sufficient for Viking navigation with the naked eye: detectability of Haidinger's brushes on the sky versus meteorological conditions.

PubMed

Horváth, Gábor; Takács, Péter; Kretzer, Balázs; Szilasi, Szilvia; Száz, Dénes; Farkas, Alexandra; Barta, András

2017-02-01

If a human looks at the clear blue sky from which light with high enough degree of polarization d originates, an 8-shaped bowtie-like figure, the yellow Haidinger's brush can be perceived, the long axis of which points towards the sun. A band of high d arcs across the sky at 90° from the sun. A person can pick two points on that band, observe the yellow brushes and triangulate the position of the sun based on the orientation of the two observed brushes. This method has been suggested to have been used on the open sea by Viking navigators to determine the position of the invisible sun occluded by cloud or fog. Furthermore, Haidinger's brushes can also be used to locate the sun when it is below the horizon or occluded by objects on the horizon. To determine the position of the sun using the celestial polarization pattern, the d of the portion of the sky used must be greater than the viewer's degree of polarization threshold d * for perception of Haidinger's brushes. We studied under which sky conditions the prerequisite d  >  d * is satisfied. Using full-sky imaging polarimetry, we measured the d -pattern of skylight in the blue (450 nm) spectral range for 1296 different meteorological conditions with different solar elevation angles θ and per cent cloud cover ρ . From the measured d -patterns of a given sky we determined the proportion P of the sky for which d  >  d *. We obtained that P is the largest at low solar elevations θ  ≈ 0° and under totally or nearly clear skies with cloud coverage ρ  = 0%, when the sun's position is already easily determined. If the sun is below the horizon (-5° ≤  θ  < 0°) during twilight, P  = 76.17 ± 4.18% for [Formula: see text] under clear sky conditions. Consequently, the sky-polarimetric Viking navigation based on Haidinger's brushes is most useful after sunset and prior to sunrise, when the sun is not visible and large sky regions are bright, clear and polarized enough for

Do embryonic polar bodies commit suicide?

PubMed

Fabian, Dušan; Čikoš, Štefan; Rehák, Pavol; Koppel, Juraj

2014-02-01

The extrusion and elimination of unnecessary gametic/embryonic material is one of the key events that determines the success of further development in all living organisms. Oocytes produce the first polar body to fulfill the maturation process just before ovulation, and release the second polar body immediately after fertilization. The aim of this study was to compile a physiological overview of elimination of polar bodies during early preimplantation development in mice. Our results show that three-quarters of the first polar bodies were lost even at the zygotic stage; the 4-cell stage embryos contained only one (second) polar body, and the elimination of second polar bodies proceeded continuously during later development. Both first and second polar bodies showed several typical features of apoptosis: phosphatidylserine redistribution (observed for the first time in the first polar body), specific DNA degradation, condensed nuclear morphology, and inability to exclude cationic dye from the nucleus during the terminal stage of the apoptotic process. Caspase-3 activity was recorded only in the second polar body. From the morphological point of view, mouse polar bodies acted very similarly to damaged embryonic cells which have lost contact with their neighboring blastomeres. In conclusion, polar bodies possess all the molecular equipment necessary for triggering and executing an active suicide process. Furthermore, similarly as in dying embryonic cells, stressing external conditions (culture in vitro) might accelerate and increase the incidence of apoptotic elimination of the polar bodies in embryos.

Spontaneous growth of polarizing refractory metal ‘nano-fins’

NASA Astrophysics Data System (ADS)

Tai, M. C.; Gentle, A. R.; Arnold, M. D.; Cortie, M. B.

2018-03-01

Traditional polymer polarizers degrade in harsh environments and at high temperatures, reducing the polarization effect. In contrast, polarizers produced with refractory metals have vastly improved thermal stability and resistance to harsh environments but are expensive to fabricate. Here we demonstrate prototype refractory metal wire grid polarizers produced by co-sputtering molybdenum and aluminum under specific conditions. Removal of the aluminum through selective dissolution enables the nanostructure array to transmit light. The polarization spans 500-1100 nm and the extinction ratio significantly increases to >100. Possessing broadband polarization and sufficient extinction ratios, the new polarizing film has potential applications in coatings for sunglasses, windows, pyrometers, scientific instruments, and LCD panels.

Effects of translational and rotational motions and display polarity on visual performance.

PubMed

Feng, Wen-Yang; Tseng, Feng-Yi; Chao, Chin-Jung; Lin, Chiuhsiang Joe

2008-10-01

This study investigated effects of both translational and rotational motion and display polarity on a visual identification task. Three different motion types--heave, roll, and pitch--were compared with the static (no motion) condition. The visual task was presented on two display polarities, black-on-white and white-on-black. The experiment was a 4 (motion conditions) x 2 (display polarities) within-subjects design with eight subjects (six men and two women; M age = 25.6 yr., SD = 3.2). The dependent variables used to assess the performance on the visual task were accuracy and reaction time. Motion environments, especially the roll condition, had statistically significant effects on the decrement of accuracy and reaction time. The display polarity was significant only in the static condition.

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.

Superstorms at the end of the Last Interglacial (MIS 5e)? Modeling paleo waves and the transport of giant boulders.

NASA Astrophysics Data System (ADS)

Rovere, Alessio; Harris, Daniel; Casella, Elisa; Lorscheid, Thomas; Stocchi, Paolo; Nandasena, Napayalage; Sandstrom, Michael; D'Andrea, William; Dyer, Blake; Raymo, Maureen

2017-04-01

We present the results of high-resolution field surveys and wave models along the cliffs of the northern part of the Island of Eleuthera, Bahamas. Previous studies have proposed that cliff top mega-boulders were emplaced at the end of the Last Interglacial (MIS 5e, 128-116 ka) by giant swells caused by super-storms that find no counterpart in the Holocene (including historical times). Our results suggest that these boulders could have instead been transported from the cliff face to the top of the cliff by a storm analogous to the 1991 'Perfect Storm', if sea level during MIS 5e sea was more than 4 meters higher than today. We remark that the data-model approach used here is essential to interpreting the geologic evidence of extreme storms during past warm periods, which in turn, is an important tool for predicting the intensity of extreme storm events in future climates. Our results indicate that even without an increase in storm intensity, cliffs and hard coastal barriers might be subject to significant increases wave-generated stresses under conditions of sea levels modestly higher than present.

Validity of the Polar V800 monitor for measuring heart rate variability in mountain running route conditions.

PubMed

Caminal, Pere; Sola, Fuensanta; Gomis, Pedro; Guasch, Eduard; Perera, Alexandre; Soriano, Núria; Mont, Lluis

2018-03-01

This study was conducted to test, in mountain running route conditions, the accuracy of the Polar V800™ monitor as a suitable device for monitoring the heart rate variability (HRV) of runners. Eighteen healthy subjects ran a route that included a range of running slopes such as those encountered in trail and ultra-trail races. The comparative study of a V800 and a Holter SEER 12 ECG Recorder™ included the analysis of RR time series and short-term HRV analysis. A correction algorithm was designed to obtain the corrected Polar RR intervals. Six 5-min segments related to different running slopes were considered for each subject. The correlation between corrected V800 RR intervals and Holter RR intervals was very high (r = 0.99, p < 0.001), and the bias was less than 1 ms. The limits of agreement (LoA) obtained for SDNN and RMSSD were (- 0.25 to 0.32 ms) and (- 0.90 to 1.08 ms), respectively. The effect size (ES) obtained in the time domain HRV parameters was considered small (ES < 0.2). Frequency domain HRV parameters did not differ (p > 0.05) and were well correlated (r ≥ 0.96, p < 0.001). Narrow limits of agreement, high correlations and small effect size suggest that the Polar V800 is a valid tool for the analysis of heart rate variability in athletes while running high endurance events such as marathon, trail, and ultra-trail races.

Cyclonic Vortices in Polar Airmasses

NASA Astrophysics Data System (ADS)

Businger, Steven

Cyclonic vortices in polar airmasses are investigated to determine their storm-scale and mesoscale structures and the nature of the environments conducive to their formation. Case studies of polar low outbreaks show that the environments conducive to the development of strong polar lows include deep outflow of arctic air over open water and a broad closed-low aloft. Once favorable environmental conditions for the formation of polar lows have developed, several storms may form in close proximity to each other during a relatively short time interval. Furthermore, these conditions may persist for several days. To develope a climatology of the synoptic environments conducive to the formation of polar lows, NMC gridded data were composited. The results reveal the presence of significant negative anomalies in the temperature and height fields at the 500 mb level on the days when mature polar lows were present, indicating the presence of strong positive vorticity and low static stability over the area. Aircraft observations made during the 1984 FOX field study indicate that convection in an incipient comma cloud was organized into distinct rainbands ((TURN)50 km wavelength), with tops extending to the tropopause. Equivalent -potential vorticity, computed from cross sections of the dropwindsonde data, showed that the region in which the convective activity was embedded was unstable to moist -symmetric overturnings. As the comma cloud approached a pre-existing polar front, a wave cyclone rapidly developed on the front. Surface data showed unexpectedly strong winds and heavy rain squalls when the comma cloud passed Juneau. Comprehensive data sets were collected in two comma cloud systems during CYCLES. Rainbands, with a wavelength of (TURN)50 km, were present in both comma-cloud systems. Precipitation cores, produced by embedded convection within the rainbands contained updraft speeds of (TURN)1-2 m s('-1) and relatively high liquid water counts; they retained their

Liquid-crystal-based switchable polarizers for sensor protection

NASA Astrophysics Data System (ADS)

Wu, Chiung-Sheng; Wu, Shin-Tson

1995-11-01

Linear polarizers are generally employed in conjunction with advanced liquid-crystal filters for the protection of human eyes and optical sensors. For detection sensitivity under a no-threat condition to be maximized, the polarizer should remain in a clear state with a minimum insertion loss. When threats are present, it should be quickly switched to function as a linear polarizer with a high extinction ratio. Two types of switchable polarizer for sensor protection are demonstrated. The polarization conversion type exhibits a high optical efficiency in its clear state, a high extinction ratio in the linear polarizer state, and a fast switching speed, except that its field of view is limited to approximately +/-10 deg In contrast, an improved switchable dichroic polarizer functions effectively over a much wider field of view. However, its extinction ratio and optical efficiency in its clear state are lower than those of the polarization conversion type.

Liquid-crystal-based switchable polarizers for sensor protection.

PubMed

Wu, C S; Wu, S T

1995-11-01

Linear polarizers are generally employed in conjunction with advanced liquid-crystal filters for the protection of human eyes and optical sensors. For detection sensitivity under a no-threat condition to be maximized, the polarizer should remain in a clear state with a minimum insertion loss. When threats are present, it should be quickly switched to function as a linear polarizer with a high extinction ratio. Two types of switchable polarizer for sensor protection are demonstrated. The polarization conversion type exhibits a high optical efficiency in its clear state, a high extinction ratio in the linear polarizer state, and a fast switching speed, except that its field of view is limited to approximately ±10°. In contrast, an improved switchable dichroic polarizer functions effectively over a much wider field of view. However, its extinction ratio and optical efficiency in its clear state are lower than those of the polarization conversion type.

Stable isotope compositions 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; Siklósy, Zoltán; Lin, Ke; Hu, Hsun-Ming; Shen, Chuan-Chou; Vennemann, Torsten W.; Haszpra, László

2017-04-01

Studies on the last interglacial (LIG) can provide information on how our environment behaved in a period of slightly higher global temperatures at about 125 ± 4 ka, even if it is not the best analogue for the Holocene. The available LIG climate proxy records are usually better preserved and can be studied at a higher resolution than those of the preceding interglacials, allowing detailed comparisons. This paper presents complex stable hydrogen, carbon and oxygen isotope records obtained for carbonate (δ13C and δ18Ocarb) and fluid inclusion hosted water (δD and δ18Ow) of a stalagmite from the Baradla Cave system in Central Europe that covers most of the LIG, as proven by U-Th dates. Comparing its 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 following the general paleotemperature pattern from the climate optimum (high δD values up to -64‰ around 120 ka) to the subsequent cooling starting at about 119 ka (low δD values down to -90‰ at about 109 ka), a period between 126.5 and 123 ka with low δD values (down to -81‰) is detected in the BAR-II stalagmite. Although the isotope shifts are muted in the C-O isotope data of carbonate due to competitive fractionation processes, the δ13C data show a positive relationship with the δD pattern, indicating humidity - and possibly temperature - variations. The periods with low δD values fit well to temperature and humidity changes inferred from proxy records from western Europe to the eastern Mediterranean. Spatial distributions of these variables

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

NASA Astrophysics Data System (ADS)

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

2015-02-01

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

Model-based analysis supports interglacial refugia over long-dispersal events in the diversification of two South American cactus species

PubMed Central

Perez, M F; Bonatelli, I A S; Moraes, E M; Carstens, B C

2016-01-01

Pilosocereus machrisii and P. aurisetus are cactus species within the P. aurisetus complex, a group of eight cacti that are restricted to rocky habitats within the Neotropical savannas of eastern South America. Previous studies have suggested that diversification within this complex was driven by distributional fragmentation, isolation leading to allopatric differentiation, and secondary contact among divergent lineages. These events have been associated with Quaternary climatic cycles, leading to the hypothesis that the xerophytic vegetation patches which presently harbor these populations operate as refugia during the current interglacial. However, owing to limitations of the standard phylogeographic approaches used in these studies, this hypothesis was not explicitly tested. Here we use Approximate Bayesian Computation to refine the previous inferences and test the role of different events in the diversification of two species within P. aurisetus group. We used molecular data from chloroplast DNA and simple sequence repeats loci of P. machrisii and P. aurisetus, the two species with broadest distribution in the complex, in order to test if the diversification in each species was driven mostly by vicariance or by long-dispersal events. We found that both species were affected primarily by vicariance, with a refuge model as the most likely scenario for P. aurisetus and a soft vicariance scenario most probable for P. machrisii. These results emphasize the importance of distributional fragmentation in these species, and add support to the hypothesis of long-term isolation in interglacial refugia previously proposed for the P. aurisetus species complex diversification. PMID:27071846

The Polar Night Nitric Oxide Experiment

NASA Image and Video Library

2017-12-08

The Polar Night Nitric Oxide or PolarNOx experiment from Virginia Tech is launched aboard a NASA Black Brant IX sounding rocket at 8:45 a.m. EST, Jan. 27, from the Poker Flat Research Range in Alaska. PolarNOx is measuring nitric oxide in the polar night sky. Nitric oxide in the polar night sky is created by auroras. Under appropriate conditions it can be transported to the stratosphere where it may destroy ozone resulting in possible changes in stratospheric temperature and wind and may even impact the circulation at Earth’s surface. Credit: NASA/Wallops/Jamie Adkins NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Magnetic Field Fluctuations in the High Ionosphere at Polar Latitudes: Impact of the IMF Conditions

NASA Astrophysics Data System (ADS)

De Michelis, P.; Consolini, G.; Tozzi, R.

2016-12-01

The characterization of ionospheric turbulence plays an important role for all those communication systems affected by the ionospheric medium. For instance, independently of geomagnetic latitude, ionospheric turbulence represents a considerable issue for all Global Navigation Satellite Systems (GNSS). Swarm constellation measurements of the Earth's magnetic field allow a precise characterization of ionospheric turbulence. This is possible using a range of indices derived from the analysis of the scaling properties of the geomagnetic field. In particular, by the scaling properties of the 1st order structure function, a scale index can be obtained, with a consequent characterization of the degree of persistence of the fluctuations and of their spectral properties. The knowledge of this index provides a global characterization of the nature and level of ionospheric turbulence on a local scale, which can be displayed along a single satellite orbit or through maps over the region of interest. The present work focuses on the analysis of the scaling properties of the 1st order structure function of magnetic field fluctuations measured by Swarm constellation at polar latitudes in the Northern Hemisphere. They are studied according to different interplanetary magnetic field conditions and Earth's seasons to characterize the possible drivers of magnetic field variability. The obtained results are discussed in the framework of Sun-Earth relationship and ionospheric polar convection. This work is supported by the Italian National Program for Antarctic Research (PNRA) Research Project 2013/AC3.08

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.

Polar Flagellar Motility of the Vibrionaceae

PubMed Central

McCarter, Linda L.

2001-01-01

Polar flagella of Vibrio species can rotate at speeds as high as 100,000 rpm and effectively propel the bacteria in liquid as fast as 60 μm/s. The sodium motive force powers rotation of the filament, which acts as a propeller. The filament is complex, composed of multiple subunits, and sheathed by an extension of the cell outer membrane. The regulatory circuitry controlling expression of the polar flagellar genes of members of the Vibrionaceae is different from the peritrichous system of enteric bacteria or the polar system of Caulobacter crescentus. The scheme of gene control is also pertinent to other members of the gamma purple bacteria, in particular to Pseudomonas species. This review uses the framework of the polar flagellar system of Vibrio parahaemolyticus to provide a synthesis of what is known about polar motility systems of the Vibrionaceae. In addition to its propulsive role, the single polar flagellum of V. parahaemolyticus is believed to act as a tactile sensor controlling surface-induced gene expression. Under conditions that impede rotation of the polar flagellum, an alternate, lateral flagellar motility system is induced that enables movement through viscous environments and over surfaces. Although the dual flagellar systems possess no shared structural components and although distinct type III secretion systems direct the simultaneous placement and assembly of polar and lateral organelles, movement is coordinated by shared chemotaxis machinery. PMID:11528005

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.

TIMS U-series dating and stable isotopes of the last interglacial event in Papua New Guinea

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

Stein, M.; Wasserburg, G.J.; Chen, J.H.

1993-06-01

The extensive flight of uplifted reef terraces which occurs along the Vitiaz strait on the northern flank of the Huon Peninsula in PNG (Papua New Guinea) contains a particularly good record of sea level changes in the last 250 ky. The Huon terraces were the target of an international expedition which took place in July--August 1988. In particular, the authors searched for suitable samples for U-series dating in a reef complex designated as VII, which is correlated with the last interglacial episode and high sea level stand. This complex is composed of a barrier reef (VIIb), a lagoon, and amore » fringing reef (VIIa). Twelve corals from these terraces and two corals from the older reef complex VIII were selected for analysis. The petrography, oxygen and carbon isotope compositions, and magnesium and strontium concentrations were determined along with the concentrations and isotopic compositions of uranium and thorium. The simplest model for sea level height for terrace VII is a continuous rise between 134 and 118 ky. Alternatively, there may have been two periods of rapid sea level rise. In contrast, in the Bahamas, there is evidence that sea level remained rather constant over the time interval 132 to 120 ky. The absence of ages between 132 and 120 ky in PNG could be the result of changes in the local tectonic uplift rates during that time, or erosion that disrupted the continuous record. In any event, the authors find no basis for accepting a single brief time for the age of the last interglacial and applying this age as a precise chronometer for worldwide correlation, or as a test of climatic models. The older ages reported here precede the Milankovitch solar insolation peak at 128 ky, and the younger ages are [approximately]10 ky after this peak. If the present high-precision data are correct, then it will be necessary to reassess the validity of the Milankovitch theory of climatic changes. 76 refs., 6 figs., 6 tabs.« less

Polarization properties of long-lived stimulated photon echo

NASA Astrophysics Data System (ADS)

Reshetov, V. A.; Popov, E. N.

2015-01-01

The polarization properties of the long-lived stimulated photon echo formed on the transition ja → jb with the atomic levels degenerate in the projections of the angular momenta are studied theoretically. The two particular transitions ja = 1 → jb = 0 and ja = 1 → jb = 1 with degenerate ground state ja = 1 are discussed. For the transitions ja = 1 → jb = 1 the polarizations and areas of the first (‘write’) and the third (‘read’) excitation pulses are found when the echo polarization faithfully reproduces the arbitrary polarization of the weak (single-photon) second (‘information’) pulse, so that this echo scheme may implement the quantum memory for a single-photon polarization qubit, while for the transitions ja = 1 → jb = 0 it is shown, that the echo polarization differs from that of the second pulse at any conditions.

Sediment Production and Storage Through a Glacial-Interglacial Cycle on a Cool-Temperate Glaciated Margin

NASA Astrophysics Data System (ADS)

Powell, R. D.

2001-12-01

The southern Alaska margin has high coastal mountains, which coupled with temperate glaciation, result in extremely high modern erosion rates (e.g. Jaeger et al., 2001), possibly exceeding rates of orogenic uplift (Meigs and Sauber, 2000). Where measured, modern sediment yields are among the highest of any basin worldwide (Hallet et al., 1996; Elverhoi et al., 1998; Jaeger et al., 1998). In Muir Inlet, Glacier Bay, sediment yields from slowly retreating glaciers decrease logarithmically with decreasing drainage basin area (Powell, 1991), a trend also reflected in regional data synthesized in Hallet et al. (1996). Alley (1997) then hypothesized that if erosion increases with basin area then where two tributaries join, deeper erosion would ensue, which is consistent with linear erosional troughs and hanging valleys. The idea is also consistent with the general downglacier increase in water flux at the glacier bed. However over longer periods, data from seismic profiles of the Gulf of Alaska shelf, show sediment yields are nearly the same through a glacial-interglacial cycle; regional data from other glaciated basins appear to confirm that trend (Elverhoi et al., 1998). If yields are continuously high from bedrock erosion, then why are mountains not eroded to base level because erosion rates are higher than isostatic uplift? Why are trends in yields apparently different during recent retreats with decreasing basin sizes than during longer term glacial cycles? Answers to these questions may be numerous and compound; however, one possibility will be evaluated. We know there is significant modern bedrock erosion occurring during glacial retreat and that also appears to have been the case during advance. Native stories describing the last (Little Ice Age) advance in Glacier Bay describe a large amount of sediment being produced (Powell et al., 1995) indicating that significant erosion was occurring. Fjord-wall stratigraphy shows that sediment had infilled much of the Bay

Martian polar expeditions: problems and solutions.

PubMed

Cockell, C S

2001-12-01

The Martian polar ice caps are regions of substantial scientific interest, being the most dynamic regions of Mars. They are volatile sinks and thus closely linked to Martian climatic conditions. Because of their scale and the precedent set by the past history of polar exploration on Earth, it is likely that an age of polar exploration will emerge on the surface of Mars after the establishment of a capable support structure at lower latitudes. Expeditions might be launched either from a lower latitude base camp or from a human-tended polar base. Based on previously presented expeditionary routes to the Martian poles, in this paper a "spiral in-spiral out" unsupported transpolar assault on the Martian north geographical pole is used as a Reference expedition to propose new types of equipment for the human polar exploration of Mars. Martian polar "ball" tents and "hover" modifications to the Nansen sledge for sledging on CO2-containing water ice substrates under low atmospheric pressures are suggested as elements for the success of these endeavours. Other challenges faced by these expeditions are quantitatively and qualitatively addressed. c 2001 Elsevier Science Ltd. All rights reserved.

Trapped particles in the polar wind

NASA Astrophysics Data System (ADS)

Demars, H. G.; Barakat, A. R.; Schunk, R. W.

1998-01-01

The flow of plasma along open field lines at high latitudes is highly variable and depends both on conditions in the underlying ionosphere and thermosphere and on the transport of particles and energy from the magnetosphere. Past attempts to model this time variability have, for the most part, examined the response of the plasma on a stationary field line to certain prespecified boundary conditions and heat sources. While such prespecified conditions may bear some resemblance to what occurs naturally, they are artificial and cannot be expected to yield a truly quantitative understanding of the various physical processes that interact to produce the dynamic polar wind. The present study is one in a series of studies that attempts to eliminate this artificiality by coupling the mathematical description of the polar wind to a three-dimensional time-dependent model of the high-latitude ionosphere. In this study, an individual flux tube of plasma is followed as it moves under the influence of combined corotation and convection electric fields. Boundary conditions at the lower end of the flux tube are obtained from the ionosphere model, which takes into account all significant particle species, chemical reactions, and heat sources that contribute to the state of the ionosphere. A multi-ion macroscopic particle-in-cell code is used to model the plasma in the flux tube. A description of the behavior of H+ and O+ for the altitude range from 2000 km to about 8 Earth radii is obtained as the flux tube moves along the trajectory, which traverses regions of the subauroral ionosphere, dayside and nightside ovals, and polar cap. The goal of the study is to determine the extent to which ion trapping can occur in the polar wind and the effects that collisions, wave-particle interactions, centrifugal acceleration, and varying ionospheric conditions have on the trapped ions. The main conclusion of the study is that O+ trapping is important and it acts to increase the O+ density at

Many-body kinetics of dynamic nuclear polarization by the cross effect

NASA Astrophysics Data System (ADS)

Karabanov, A.; Wiśniewski, D.; Raimondi, F.; Lesanovsky, I.; Köckenberger, W.

2018-03-01

Dynamic nuclear polarization (DNP) is an out-of-equilibrium method for generating nonthermal spin polarization which provides large signal enhancements in modern diagnostic methods based on nuclear magnetic resonance. A particular instance is cross-effect DNP, which involves the interaction of two coupled electrons with the nuclear spin ensemble. Here we develop a theory for this important DNP mechanism and show that the nonequilibrium nuclear polarization buildup is effectively driven by three-body incoherent Markovian dissipative processes involving simultaneous state changes of two electrons and one nucleus. We identify different parameter regimes for effective polarization transfer and discuss under which conditions the polarization dynamics can be simulated by classical kinetic Monte Carlo methods. Our theoretical approach allows simulations of the polarization dynamics on an individual spin level for ensembles consisting of hundreds of nuclear spins. The insight obtained by these simulations can be used to find optimal experimental conditions for cross-effect DNP and to design tailored radical systems that provide optimal DNP efficiency.

Neogene ice sheet, paleoclimatic and geological history of the McMurdo Sound region, Victoria Land Basin, Antarctica: overview of ANDRILL's first two drilling projects

NASA Astrophysics Data System (ADS)

Powell, R.; Naish, T.; Harwood, D.; Florindo, F.; Levy, R.; Teams, M. S.

2008-12-01

The ANtarctic geological DRILLing Program (ANDRILL), an international collaboration within IPY, has recovered 2 cores: from under the Ross Ice Shelf (McMurdo Ice Shelf Project (MIS) - AND-1B), and from the land-fast sea-ice of McMurdo Sound (Southern McMurdo Sound Project (SMS) - AND-2A). Drill cores reached respective total depths of 1285mbsf in c. 850m of water (MIS) and 1138.54mbsf in c. 380m of water (SMS). Repetitive facies successions in AND-1B core imply at least 60 fluctuations, of probable Milankovitch- duration, between subglacial, ice proximal and ice distal open marine environments. These are grouped into 3 types of facies cycles corresponding to glacial-interglacial variability during climatically distinct periods of Late Neogene: (1) cold-polar climate and ice (late Miocene and Pleistocene); (2) relatively warmer climate, polythermal ice and interglacials dominated by pelagic diatomite (Pliocene); (3) warmer climate, polythermal ice with interglacials dominated by hemipelagites (early late Miocene). A c. 80m-thick interval of diatomite of mid to late Pliocene age shows no apparent glacial cyclicity and represents an extended period of ice-free conditions indicating reduced or absent WAIS. Late Pliocene glacial-interglacial cycles characterized by abrupt alternations between subglacial/ice-proximal facies and open marine diatomite units imply significant WAIS dynamism, and contribution to global ice volume changes coeval with the initiation of Northern Hemisphere glaciations. A c. 4m-thick interval of diatomaceous mudstone in the mid-Pleistocene also represents warm-interglacial ice-free conditions. Intriguingly, glacial deposits interrupted by periodic, small- scale grounding-line retreats dominate the last 1m.y. Inter-hemispheric ice sheet coupling was probably controlled by Northern Hemispheric insolation and consequent glacial eustasy to account for much of the orbital-scale WAIS variability since 2.5Ma. A further expansion of WAIS occurred across

Adaptive polarization image fusion based on regional energy dynamic weighted average

NASA Astrophysics Data System (ADS)

Zhao, Yong-Qiang; Pan, Quan; Zhang, Hong-Cai

2005-11-01

According to the principle of polarization imaging and the relation between Stokes parameters and the degree of linear polarization, there are much redundant and complementary information in polarized images. Since man-made objects and natural objects can be easily distinguished in images of degree of linear polarization and images of Stokes parameters contain rich detailed information of the scene, the clutters in the images can be removed efficiently while the detailed information can be maintained by combining these images. An algorithm of adaptive polarization image fusion based on regional energy dynamic weighted average is proposed in this paper to combine these images. Through an experiment and simulations, most clutters are removed by this algorithm. The fusion method is used for different light conditions in simulation, and the influence of lighting conditions on the fusion results is analyzed.

Polarization and Dielectric Study of Methylammonium Lead Iodide Thin Film to Reveal its Nonferroelectric Nature under Solar Cell Operating Conditions

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

Hoque, Md Nadim Ferdous; Yang, Mengjin; Li, Zhen

2016-07-08

Researchers have debated whether methylammonium lead iodide (MAPbI3), with a perovskite crystal structure, is ferroelectric and therefore contributes to the current--voltage hysteresis commonly observed in hybrid perovskite solar cells (PSCs). We thoroughly investigated temperature-dependent polarization, dielectric, and impedance spectroscopies, and we found no evidence of ferroelectric effect in a MAPbI3 thin film at normal operating conditions. Therefore, the effect does not contribute to the hysteresis in PSCs, whereas the large component of ionic migration observed may play a critical role. Our temperature-based polarization and dielectric studies find that MAPbI3 exhibits different electrical behaviors below and above ca. 45 degrees C,more » suggesting a phase transition around this temperature. In particular, we report the activation energies of ionic migration for the two phases and temperature-dependent permittivity of MAPbI3. This study contributes to the understanding of the material properties and device performance of hybrid perovskites.« less

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.

Polarized radiance distribution measurement of skylight. II. Experiment and data.

PubMed

Liu, Y; Voss, K

1997-11-20

Measurements of the skylight polarized radiance distribution were performed at different measurement sites, atmospheric conditions, and three wavelengths with our newly developed Polarization Radiance Distribution Camera System (RADS-IIP), an analyzer-type Stokes polarimeter. Three Stokes parameters of skylight (I, Q, U), the degree of polarization, and the plane of polarization are presented in image format. The Arago point and neutral lines have been observed with RADS-IIP. Qualitatively, the dependence of the intensity and polarization data on wavelength, solar zenith angle, and surface albedo is in agreement with the results from computations based on a plane-parallel Rayleigh atmospheric model.

A NOTE ON THE RELATIVE PHOTOSENSORY EFFECT OF POLARIZED LIGHT

PubMed Central

Crozier, W. J.; Mangelsdorf, A. F.

1924-01-01

Experiments were made to compare the stimulating effectiveness of vertically and horizontally polarized lights and non-polarized lights of equal intensity upon phototropic movements of the beetle Tetraopes tetraopthalmus; and to compare the effectiveness of two light beams polarized at right angles to one another upon phototropic orientation of the land isopod Cylisticus convexus. Tetraopes is positively, and Cylisticus, negatively phototropic. Tests were also made of the intensities of horizontally and of vertically polarized light required to inhibit stereotropism in larvæ of Tenebrio. Under the conditions of the tests, no certain qualitative effect connected with polarization could be detected. PMID:19872110

Neural mechanisms in insect navigation: polarization compass and odometer.

PubMed

Labhart, Thomas; Meyer, Eric P

2002-12-01

Insect navigation relies on path integration, a procedure by which information about compass bearings pursued and distances travelled are combined to calculate position. Three neural levels of the polarization compass, which uses the polarization of skylight as a reference, have been analyzed in orthopteran insects. A group of dorsally directed, highly specialized ommatidia serve as polarization sensors. Polarization-opponent neurons in the optic lobe condition the polarization signal by removing unreliable and irrelevant components of the celestial stimulus. Neurons found in the central complex of the brain possibly represent elements of the compass output. The odometer for measuring travelling distances in honeybees relies on optic flow experienced during flight, whereas desert ants most probably use proprioreceptive cues.

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.

Evaluating climate controls on isotopic shifts in high-altitude forests during the Last Interglacial

NASA Astrophysics Data System (ADS)

Insel, N.; Berkelhammer, M. B.; Sturm, C.; Karimova, G.

2016-12-01

Forests play a significant role in the global carbon cycle, and influence climate through their effect on albedo and latent heat flux. Predicting the response of these ecosystems to climate change is complicated by competing influences between rising CO2, warming, and shifts in hydrology such as timing, rate, and type of precipitation. A key to detection and prediction of future regional and global changes of modern ecosystems lies in understanding the causes and characteristics of historical variations at the ecosystem level. The Last Interglacial (LIG: 130 to 116 ka) is the most recent period in Earth's history when growing season temperature exceeded those of today. In this study, we are using isotope-enabled regional climate model (REMOiso) simulations under LIG (115ka, 125 ka and 135 ka) and modern forcings to evaluate climate controls on boreal forest in the western US. In particular, we investigate (1) changes in moisture sources and moisture transport, (2) changes in the annual and seasonal extent and duration of precipitation, and (3) temperature variations to explore how ecosystem carbon and water fluxes change under coupled temperature and precipitation variability. Eemian wood samples from the Rocky Mountains in Colorado show a progressive increase in the 18O seasonal cycle that may be related to trees utilizing isotopically enriched monsoonal moisture. However, Eemian climate simulations (125ka) incorporate orbital forcings that result in stronger seasonal changes in temperature, precipitation, and snow cover in comparison to today, while annual anomalies are small. The seasonal shift in climate affects the water availability and the length of growing season for Eemian plants. Model results indicate only a very slight increase in monsoonal moisture transport from the south, resulting in slightly wetter conditions in western Colorado, but slightly drier conditions in the eastern part. Preliminary results suggest that changes in the North American

Is Polar Bear Hair Fiber Optic?

NASA Astrophysics Data System (ADS)

Koon, Daniel W.

1998-05-01

New direct measurement of high optical attenuation rates in polar bear hairs 2 8 dB mm in the visible and reanalysis of the data of Tributsch et al . Sol. Energy Mater. 21, 219 (1990) seem to rule out the UV waveguiding proposed by Grojean et al . Appl. Opt. 19, 339 (1980) . The case against fiber-optic polar bear hairs is summarized, and four conditions are given that any variation of the model of Grojean et al . would have to satisfy.

Analysis of the infrared detection system operating range based on polarization degree

NASA Astrophysics Data System (ADS)

Jiang, Kai; Liu, Wen; Liu, Kai; Duan, Jing; Yan, Pei-pei; Shan, Qiu-sha

2018-02-01

Infrared polarization detection technology has unique advantages in the field of target detection and identification because of using the polarization information of radiation. The mechanism of infrared polarization is introduced. Comparing with traditional infrared detection distance model, infrared detection operating range and Signal to Noise Ratio (SNR) model is built according to the polarization degree and noise. The influence of polarization degree on the SNR of infrared system is analyzed. At last, the basic condition of polarization detection SNR better than traditional infrared detection SNR is obtained.

Microwave frequency effect in the formation of Au nanocolloids in polar and non-polar solvents

NASA Astrophysics Data System (ADS)

Horikoshi, Satoshi; Abe, Hideki; Sumi, Takuya; Torigoe, Kanjiro; Sakai, Hideki; Serpone, Nick; Abe, Masahiko

2011-04-01

Given earlier observations that microwave frequencies can have a substantial effect on the photoactivity of a well-known photocatalyst (TiO2), in the synthesis of 3,6-diphenyl-4-n-butylpyridazine through a Diels-Alder process, and in the one-pot solvent-free synthesis of a room-temperature ionic liquid, we proceeded to examine the frequency effects of the 5.8 and 2.45 GHz microwave (MW) radiation in the synthesis of gold nanoparticles in non-polar media, such as oleylamine, which have a low dielectric constant (ε'), and we further examine differences in shape and size under otherwise identical temperature conditions when the synthesis of the gold nanoparticles was carried out in an ethylene glycol polar medium in the presence of polyvinylpyrrolidone. Whereas a change in microwave frequency from 2.45 to 5.8 GHz at equal microwave power levels led to the synthesis of gold nanoparticles in the non-polar media, a change in the microwave frequency had no effect on the size and shape of the gold nanoparticles synthesized in polar media for identical microwave power levels.

Microwave frequency effect in the formation of Au nanocolloids in polar and non-polar solvents.

PubMed

Horikoshi, Satoshi; Abe, Hideki; Sumi, Takuya; Torigoe, Kanjiro; Sakai, Hideki; Serpone, Nick; Abe, Masahiko

2011-04-01

Given earlier observations that microwave frequencies can have a substantial effect on the photoactivity of a well-known photocatalyst (TiO(2)), in the synthesis of 3,6-diphenyl-4-n-butylpyridazine through a Diels-Alder process, and in the one-pot solvent-free synthesis of a room-temperature ionic liquid, we proceeded to examine the frequency effects of the 5.8 and 2.45 GHz microwave (MW) radiation in the synthesis of gold nanoparticles in non-polar media, such as oleylamine, which have a low dielectric constant (ε'), and we further examine differences in shape and size under otherwise identical temperature conditions when the synthesis of the gold nanoparticles was carried out in an ethylene glycol polar medium in the presence of polyvinylpyrrolidone. Whereas a change in microwave frequency from 2.45 to 5.8 GHz at equal microwave power levels led to the synthesis of gold nanoparticles in the non-polar media, a change in the microwave frequency had no effect on the size and shape of the gold nanoparticles synthesized in polar media for identical microwave power levels.

Blend lines in the polarized spectrum of the Sun

NASA Astrophysics Data System (ADS)

Sowmya, K.; Nagendra, K. N.; Sampoorna, M.

2012-07-01

Blend lines form an integral part of the theoretical analysis and modelling of the polarized spectrum of the Sun. Their interaction with other spectral lines needs to be explored and understood before we can properly use the main spectral lines to diagnose the Sun. They are known to cause a decrease in the polarization in the wings of the main line on which they superpose, or in the polarization of the continuum, when they are assumed to be formed either under the local thermodynamic equilibrium (LTE) conditions or when their intrinsic polarizability factor is zero. In this paper, we describe the theoretical framework to include the blend lines formed under non-LTE conditions, in the radiative transfer equation, and the numerical techniques to solve it. The properties of a blend line having an intrinsic polarization of its own and its interaction with the main line are discussed. The results of our analysis show that the influence of the blend lines on the main spectral lines, though small in the present context, is important and needs to be considered when interpreting the polarized spectral lines in the second solar spectrum.

An analytical model for the celestial distribution of polarized light, accounting for polarization singularities, wavelength and atmospheric turbidity

NASA Astrophysics Data System (ADS)

Wang, Xin; Gao, Jun; Fan, Zhiguo; Roberts, Nicholas W.

2016-06-01

We present a computationally inexpensive analytical model for simulating celestial polarization patterns in variable conditions. We combine both the singularity theory of Berry et al (2004 New J. Phys. 6 162) and the intensity model of Perez et al (1993 Sol. Energy 50 235-245) such that our single model describes three key sets of data: (1) the overhead distribution of the degree of polarization as well as the existence of neutral points in the sky; (2) the change in sky polarization as a function of the turbidity of the atmosphere; and (3) sky polarization patterns as a function of wavelength, calculated in this work from the ultra-violet to the near infra-red. To verify the performance of our model we generate accurate reference data using a numerical radiative transfer model and statistical comparisons between these two methods demonstrate no significant difference in almost all situations. The development of our analytical model provides a novel method for efficiently calculating the overhead skylight polarization pattern. This provides a new tool of particular relevance for our understanding of animals that use the celestial polarization pattern as a source of visual information.

A dual polarized antenna system using a meanderline polarizer

NASA Technical Reports Server (NTRS)

Burger, H. A.

1978-01-01

Certain applications of synthetic aperture radars require transmitting on one linear polarization and receiving on two orthogonal linear polarizations for adequate characterization of the surface. To meet the current need at minimum cost, it was desirable to use two identical horizontally polarized shaped beam antennas and to change the polarization of one of them by a polarization conversion plate. The plate was realized as a four-layer meanderline polarizer designed to convert horizontal polarization to vertical.

Comparative analysis of electric field influence on the quantum wells with different boundary conditions.: I. Energy spectrum, quantum information entropy and polarization.

PubMed

Olendski, Oleg

2015-04-01

Analytical solutions of the Schrödinger equation for the one-dimensional quantum well with all possible permutations of the Dirichlet and Neumann boundary conditions (BCs) in perpendicular to the interfaces uniform electric field [Formula: see text] are used for the comparative investigation of their interaction and its influence on the properties of the system. Limiting cases of the weak and strong voltages allow an easy mathematical treatment and its clear physical explanation; in particular, for the small [Formula: see text], the perturbation theory derives for all geometries a linear dependence of the polarization on the field with the BC-dependent proportionality coefficient being positive (negative) for the ground (excited) states. Simple two-level approximation elementary explains the negative polarizations as a result of the field-induced destructive interference of the unperturbed modes and shows that in this case the admixture of only the neighboring states plays a dominant role. Different magnitudes of the polarization for different BCs in this regime are explained physically and confirmed numerically. Hellmann-Feynman theorem reveals a fundamental relation between the polarization and the speed of the energy change with the field. It is proved that zero-voltage position entropies [Formula: see text] are BC independent and for all states but the ground Neumann level (which has [Formula: see text]) are equal to [Formula: see text] while the momentum entropies [Formula: see text] depend on the edge requirements and the level. Varying electric field changes position and momentum entropies in the opposite directions such that the entropic uncertainty relation is satisfied. Other physical quantities such as the BC-dependent zero-energy and zero-polarization fields are also studied both numerically and analytically. Applications to different branches of physics, such as ocean fluid dynamics and atmospheric and metallic waveguide electrodynamics, are discussed.

Automation of Mode Locking in a Nonlinear Polarization Rotation Fiber Laser through Output Polarization Measurements.

PubMed

Olivier, Michel; Gagnon, Marc-Daniel; Habel, Joé

2016-02-28

When a laser is mode-locked, it emits a train of ultra-short pulses at a repetition rate determined by the laser cavity length. This article outlines a new and inexpensive procedure to force mode locking in a pre-adjusted nonlinear polarization rotation fiber laser. This procedure is based on the detection of a sudden change in the output polarization state when mode locking occurs. This change is used to command the alignment of the intra-cavity polarization controller in order to find mode-locking conditions. More specifically, the value of the first Stokes parameter varies when the angle of the polarization controller is swept and, moreover, it undergoes an abrupt variation when the laser enters the mode-locked state. Monitoring this abrupt variation provides a practical easy-to-detect signal that can be used to command the alignment of the polarization controller and drive the laser towards mode locking. This monitoring is achieved by feeding a small portion of the signal to a polarization analyzer measuring the first Stokes parameter. A sudden change in the read out of this parameter from the analyzer will occur when the laser enters the mode-locked state. At this moment, the required angle of the polarization controller is kept fixed. The alignment is completed. This procedure provides an alternate way to existing automating procedures that use equipment such as an optical spectrum analyzer, an RF spectrum analyzer, a photodiode connected to an electronic pulse-counter or a nonlinear detecting scheme based on two-photon absorption or second harmonic generation. It is suitable for lasers mode locked by nonlinear polarization rotation. It is relatively easy to implement, it requires inexpensive means, especially at a wavelength of 1550 nm, and it lowers the production and operation costs incurred in comparison to the above-mentioned techniques.

Automation of Mode Locking in a Nonlinear Polarization Rotation Fiber Laser through Output Polarization Measurements

PubMed Central

Olivier, Michel; Gagnon, Marc-Daniel; Habel, Joé

2016-01-01

When a laser is mode-locked, it emits a train of ultra-short pulses at a repetition rate determined by the laser cavity length. This article outlines a new and inexpensive procedure to force mode locking in a pre-adjusted nonlinear polarization rotation fiber laser. This procedure is based on the detection of a sudden change in the output polarization state when mode locking occurs. This change is used to command the alignment of the intra-cavity polarization controller in order to find mode-locking conditions. More specifically, the value of the first Stokes parameter varies when the angle of the polarization controller is swept and, moreover, it undergoes an abrupt variation when the laser enters the mode-locked state. Monitoring this abrupt variation provides a practical easy-to-detect signal that can be used to command the alignment of the polarization controller and drive the laser towards mode locking. This monitoring is achieved by feeding a small portion of the signal to a polarization analyzer measuring the first Stokes parameter. A sudden change in the read out of this parameter from the analyzer will occur when the laser enters the mode-locked state. At this moment, the required angle of the polarization controller is kept fixed. The alignment is completed. This procedure provides an alternate way to existing automating procedures that use equipment such as an optical spectrum analyzer, an RF spectrum analyzer, a photodiode connected to an electronic pulse-counter or a nonlinear detecting scheme based on two-photon absorption or second harmonic generation. It is suitable for lasers mode locked by nonlinear polarization rotation. It is relatively easy to implement, it requires inexpensive means, especially at a wavelength of 1550 nm, and it lowers the production and operation costs incurred in comparison to the above-mentioned techniques. PMID:26967924

Three-dimensional polarization algebra for all polarization sensitive optical systems.

PubMed

Li, Yahong; Fu, Yuegang; Liu, Zhiying; Zhou, Jianhong; Bryanston-Cross, P J; Li, Yan; He, Wenjun

2018-05-28

Using three-dimensional (3D) coherency vector (9 × 1), we develop a new 3D polarization algebra to calculate the polarization properties of all polarization sensitive optical systems, especially when the incident optical field is partially polarized or un-polarized. The polarization properties of a high numerical aperture (NA) microscope objective (NA = 1.25 immersed in oil) are analyzed based on the proposed 3D polarization algebra. Correspondingly, the polarization simulation of this high NA optical system is performed by the commercial software VirtualLAB Fusion. By comparing the theoretical calculations with polarization simulations, a perfect matching relation is obtained, which demonstrates that this 3D polarization algebra is valid to quantify the 3D polarization properties for all polarization sensitive optical systems.

Direct-current polarization characteristics of various AlGaAs laser diodes

NASA Technical Reports Server (NTRS)

Fuhr, P. L.

1984-01-01

Polarization characteristics of AlGaAs laser diodes having various device geometries have been measured. Measurements were performed with the laser diodes operating under dc conditions. Results show that laser diodes having different device geometries have optical outputs that exhibit varying degrees of polarization purity. Implications of this result, with respect to incoherent polarization-beam combining, are addressed.

Critical evaluation of climate syntheses to benchmark CMIP6/PMIP4 127 ka Last Interglacial simulations in the high-latitude regions

NASA Astrophysics Data System (ADS)

Capron, E.; Govin, A.; Feng, R.; Otto-Bliesner, B. L.; Wolff, E. W.

2017-07-01

The Last Interglacial (LIG, ∼129-116 thousand years ago, ka) represents an excellent case study to investigate the response of sensitive components of the Earth System and mechanisms of high-latitude amplification to a climate warmer than present-day. The Paleoclimate Model Intercomparison Project (Phase 4, hereafter referred as PMIP4) and the Coupled Model Intercomparison Project (Phase 6, hereafter referred as CMIP6) are coordinating the design of (1) a LIG Tier 1 equilibrium simulation to simulate the climate response at 127 ka, a time interval associated with a strong orbital forcing and greenhouse gas concentrations close to preindustrial levels and (2) associated Tier 2 sensitivity experiments to examine the role of the ocean, vegetation and dust feedbacks in modulating the response to this orbital forcing. Evaluating the capability of the CMIP6/PMIP4 models to reproduce the 127 ka polar and sub-polar climate will require appropriate data-based benchmarks which are currently missing. Based on a recent data synthesis that offers the first spatio-temporal representation of high-latitude (i.e. poleward of 40°N and 40°S) surface temperature evolution during the LIG, we produce a new 126-128 ka time slab, hereafter named 127 ka time slice. This 127 ka time slice represents surface temperature anomalies relative to preindustrial and is associated with quantitative estimates of the uncertainties related to relative dating and surface temperature reconstruction methods. It illustrates warmer-than-preindustrial conditions in the high-latitude regions of both hemispheres. In particular, summer sea surface temperatures (SST) in the North Atlantic region were on average 1.1 °C (with a standard error of the mean of 0.7 °C) warmer relative to preindustrial and 1.8 °C (with a standard error of the mean of 0.8 °C) in the Southern Ocean. In Antarctica, average 127 ka annual surface air temperature was 2.2 °C (with a standard error of the mean of 1.4 °C) warmer

Polarization locked vector solitons and axis instability in optical fiber.

PubMed

Cundiff, Steven T.; Collings, Brandon C.; Bergman, Keren

2000-09-01

We experimentally observe polarization-locked vector solitons in optical fiber. Polarization locked-vector solitons use nonlinearity to preserve their polarization state despite the presence of birefringence. To achieve conditions where the delicate balance between nonlinearity and birefringence can survive, we studied the polarization evolution of the pulses circulating in a laser constructed entirely of optical fiber. We observe two distinct states with fixed polarization. This first state occurs for very small values birefringence and is elliptically polarized. We measure the relative phase between orthogonal components along the two principal axes to be +/-pi/2. The relative amplitude varies linearly with the magnitude of the birefringence. This state is a polarization locked vector soliton. The second, linearly polarized, state occurs for larger values of birefringence. The second state is due to the fast axis instability. We provide complete characterization of these states, and present a physical explanation of both of these states and the stability of the polarization locked vector solitons. (c) 2000 American Institute of Physics.

Polarization locked vector solitons and axis instability in optical fiber

NASA Astrophysics Data System (ADS)

Cundiff, Steven T.; Collings, Brandon C.; Bergman, Keren

2000-09-01

We experimentally observe polarization-locked vector solitons in optical fiber. Polarization locked-vector solitons use nonlinearity to preserve their polarization state despite the presence of birefringence. To achieve conditions where the delicate balance between nonlinearity and birefringence can survive, we studied the polarization evolution of the pulses circulating in a laser constructed entirely of optical fiber. We observe two distinct states with fixed polarization. This first state occurs for very small values birefringence and is elliptically polarized. We measure the relative phase between orthogonal components along the two principal axes to be ±π/2. The relative amplitude varies linearly with the magnitude of the birefringence. This state is a polarization locked vector soliton. The second, linearly polarized, state occurs for larger values of birefringence. The second state is due to the fast axis instability. We provide complete characterization of these states, and present a physical explanation of both of these states and the stability of the polarization locked vector solitons.

Numerical modeling of polar mesocyclones generation mechanisms

NASA Astrophysics Data System (ADS)

Sergeev, Dennis; Stepanenko, Victor

2013-04-01

Polar mesocyclones, commonly referred to as polar lows, remain of great interest due to their complicated dynamics. These mesoscale vortices are small short-living objects that are formed over the observation-sparse high-latitude oceans, and therefore, their evolution can hardly be observed and predicted numerically. The origin of polar mesoscale cyclones is still a matter of uncertainty, though the recent numerical investigations [3] have exposed a strong dependence of the polar mesocyclone development upon the magnitude of baroclinicity. Nevertheless, most of the previous studies focused on the individual polar low (the so-called case studies), with too many factors affecting it simultaneously. None of the earlier studies suggested a clear picture of polar mesocyclone generation within an idealized experiment, where it is possible to look deeper into each single physical process. The present paper concentrates on the initial triggering mechanism of the polar mesocyclone. As it is reported by many researchers, some mesocyclones are formed by the surface forcing, namely the uneven distribution of heat fluxes. That feature is common on the ice boundaries [2], where intense air stream flows from the cold ice surface to the warm sea surface. Hence, the resulting conditions are shallow baroclinicity and strong surface heat fluxes, which provide an arising polar mesocyclone with potential energy source converting it to the kinetic energy of the vortex. It is shown in this paper that different surface characteristics, including thermal parameters and, for example, the shape of an ice edge, determine an initial phase of a polar low life cycle. Moreover, it is shown what initial atmospheric state is most preferable for the formation of a new polar mesocyclone or in maintaining and reinforcing the existing one. The study is based on idealized high-resolution (~2 km) numerical experiment in which baroclinicity, stratification, initial wind profile and disturbance, surface

Quaternary geology of the Duck Hawk Bluffs, southwest Banks Island, Arctic Canada: a re-investigation of a critical terrestrial type locality for glacial and interglacial events bordering the Arctic Ocean

NASA Astrophysics Data System (ADS)

Evans, David J. A.; England, John H.; La Farge, Catherine; Coulthard, Roy D.; Lakeman, Thomas R.; Vaughan, Jessica M.

2014-05-01

Duck Hawk Bluffs, southwest Banks Island, is a primary section (8 km long and 60 m high) in the western Canadian Arctic Archipelago exposing a long record of Quaternary sedimentation adjacent to the Arctic Ocean. A reinvestigation of Duck Hawk Bluffs demonstrates that it is a previously unrecognized thrust-block moraine emplaced from the northeast by Laurentide ice. Previous stratigraphic models of Duck Hawk Bluffs reported a basal unit of preglacial fluvial sand and gravel (Beaufort Fm, forested Arctic), overlain by a succession of three glaciations and at least two interglacials. Our observations dismiss the occurrence of preglacial sediments and amalgamate the entire record into three glacial intervals and one prominent interglacial. The first glacigenic sedimentation is recorded by an ice-contact sandur containing redeposited allochthonous organics previously assigned to the Beaufort Fm. This is overlain by fine-grained sediments with ice wedge pseudomorphs and well-preserved bryophyte assemblages corresponding to an interglacial environment similar to modern. The second glacial interval is recorded by ice-proximal mass flows and marine rhythmites that were glacitectonized when Laurentide ice overrode the site from Amundsen Gulf to the south. Sediments of this interval have been reported to be magnetically reversed (>780 ka). The third interval of glacigenic sedimentation includes glacifluvial sand and gravel recording the arrival of Laurentide ice that overrode the site from the northeast (island interior) depositing a glacitectonite and constructing the thrust block moraine that comprises Duck Hawk Bluffs. Sediments of this interval have been reported to be magnetically normal (<780 ka). The glacitectonite contains a highly deformed melange of pre-existing sediments that were previously assigned to several formally named, marine and interglacial deposits resting in an undeformed sequence. In contrast, the tectonism associated with the thrust block moraine

Luminance and chromatic contributions to a hyperacuity task: isolation by contrast polarity and target separation

PubMed Central

Sun, Hao; Cooper, Bonnie; Lee, Barry B.

2012-01-01

Vernier thresholds are known to be elevated when a target pair has opposite contrast polarity. Polarity reversal is used to assess the role of luminance and chromatic pathways in hyperacuity performance. Psychophysical hyperacuity thresholds were measured for pairs of gratings of various combinations of luminance (Lum) and chromatic (Chr) contrast polarities, at different ratios of luminance to chromatic contrast. With two red-green gratings of matched luminance and chromatic polarity (+Lum+Chr), there was an elevation of threshold at isoluminance. When both luminance and chromatic polarity were mismatched (−Lum−Chr), thresholds were substantially elevated under all conditions. With the same luminance contrast polarity and opposite chromatic polarity (+Lum−Chr) thresholds were only elevated close to isoluminance; in the reverse condition (−Lum+Chr), thresholds were elevated as in the −Lum−Chr condition except close to equiluminance. Similar data were obtained for gratings isolating the short-wavelength cone mechanism. Further psychophysical measurements assessed the role of target separation with matched or mismatched contrast polarity; similar results were found for luminance and chromatic gratings. Comparison physiological data were collected from parafoveal ganglion cells of the macaque retina. Positional precision of ganglion cell signals was assessed under conditions related to the psychophysical measurements. On the basis of these combined observations, it is argued that both magnocellular, parvocellular, and koniocellular pathways have access to cortical positional mechanisms associated with vernier acuity. PMID:22306680

Different polarization dynamic states in a vector Yb-doped fiber laser.

PubMed

Li, Xingliang; Zhang, Shumin; Han, Huiyun; Han, Mengmeng; Zhang, Huaxing; Zhao, Luming; Wen, Fang; Yang, Zhenjun

2015-04-20

Different polarization dynamic states in an unidirectional, vector, Yb-doped fiber ring laser have been observed. A rich variety of dynamic states, including group velocity locked polarization domains and their splitting into regularly distributed multiple domains, polarization locked square pulses and their harmonic mode locking counterparts, and dissipative soliton resonances have all been observed with different operating parameters. We have also shown experimentally details of the conditions under which polarization-domain-wall dark pulses and bright square pulses form.

Developing and testing multimedia educational tools to teach Polar Sciences in the Italian school

NASA Astrophysics Data System (ADS)

Macario, Maddalena; Cattadori, Matteo; Bianchi, Cristiana; Zattin, Massimiliano; Talarico, Franco Maria

2013-04-01

In the last few years science education moved forward rapidly by connecting the expertise and enthusiasm of polar educators worldwide. The interest in Polar Sciences determined the creation of a global professional network for those that educate in, for, and about the Polar Regions. In Italy, this cooperation is well represented by APECS-Italy, the Italian section of the Association of Polar Early Career Scientists (APECS) that is composed by young researchers and teachers of the Italian School. The Polar Regions represent one of the best natural environments where students can investigate directly on global changes. In this sense, the working group UNICAMearth of the Geology Division of School of Science and Technology, University of Camerino (Italy), promotes the arrangement of instructional resources based on real data coming from the research world. Our project aims to develop innovative teaching resources and practices designed to bring the importance of the Polar Regions closer to home. Consequently, Polar Sciences could become a focus point in the new national school curricula, where Earth Sciences have to be thought and learnt in an integrated way together with other sciences. In particular, M. Macario is producing a teaching tool package, starting from a case study, which includes a dozen of full lesson plans based on multimedia tools (images, smart board lessons and videos of lab experiments) as well as on hands-on activities about polar issues and phenomena. Among the resources the teaching tool package is referring to, there is also an App for tablet named CLAST (CLimate in Antartica from Sediments and Tectonics). This App has been designed by a team made up of polar scientists belonging to the University of Siena and University of Padova, two science teachers of the Museo delle Scienze (MUSE) of Trento other than M. Macario. CLAST has been funded by two Research Projects, CLITEITAM ("CLImate-TEctonics Interactions along the TransAntarctic Mountains

Global Geospace Science/Polar Plasma Laboratory: POLAR

NASA Technical Reports Server (NTRS)

1996-01-01

The Global Geospace Science (GGS) Project is discussed as part of the International Solar-Terrestrial Physics (ISTP) Science Initiative. The objectives of Polar Plasma Laboratory (POLAR), one of the two spacecraft to be used by the Project to fill critical gaps in the scientific understanding of solar and plasma physics, are outlined. POLAR Laboratory is described, along with POLAR instrumentation, support subsystems, and orbits. Launch vehicle and injection into orbit are also addressed.

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

When measured spin polarization is not spin polarization

NASA Astrophysics Data System (ADS)

Dowben, P. A.; Wu, Ning; Binek, Christian

2011-05-01

Spin polarization is an unusually ambiguous scientific idiom and, as such, is rarely well defined. A given experimental methodology may allow one to quantify a spin polarization but only in its particular context. As one might expect, these ambiguities sometimes give rise to inappropriate interpretations when comparing the spin polarizations determined through different methods. The spin polarization of CrO2 and Cr2O3 illustrate some of the complications which hinders comparisons of spin polarization values.

Photometry of Polar-Ring Galaxies

NASA Astrophysics Data System (ADS)

Godínez-Martínez, A.; Watson, A. M.; Matthews, L. D.; Sparke, L. S.

2007-10-01

We have obtained photometry in B and R for seven confirmed or probable polar-ring galaxies from the Polar-Ring Catalog of Whitmore et al. (1990). The rings show a range of colors from B - R ≈ 0.6 to B - R ≈ 1.7. The bluest rings have bright H II regions, which are direct evidence for recent star formation. The minimum age of the reddest ring, that in PRC B-20, is somewhat uncertain because of a lack of knowledge of the internal reddening and metallicity, but appears to be at least 1.2 Gyr. As such, this ring is likely to be stable for at least several rotation periods. This ring is an excellent candidate for future studies that might better determine if it is truly old.

Late Pliocene cooling, sea ice and the establishment of a Ross Sea polynya: Geochemical and diatom assemblage constraints from McMurdo Sound, Antarctica

NASA Astrophysics Data System (ADS)

Riesselman, C.; Dunbar, R. B.; Sjunneskog, C. M.; Mucciarone, D. A.; Winter, D.; Olney, M.; Tuzzi, E.; McKay, R. M.; Scherer, R. P.

2010-12-01

.2 Ma, δ13C and δ15N vary in phase, the amplitude of δ13C fluctuations increases progressively up section, and peak interglacial δ15N trends toward more positive values, reflecting increasing variability in surface-water stratification within individual glacial minima. During the peaks of Late Pliocene glacial minima, negative δ13C values likely indicate enhanced wind mixing and summer polynya formation over AND-1B, while more positive values during the start and end of glacial minima indicate increased stratification due to sea ice melt or reduced wind stress. In sequence, these units offer a unique perspective on the changing character of the interglacial environment in the Ross Embayment spanning the transition from the mid-Pliocene climatic optimum into modern cold-polar conditions.

Impaired hair follicle morphogenesis and polarized keratinocyte movement upon conditional inactivation of integrin-linked kinase in the epidermis.

PubMed

Nakrieko, Kerry-Ann; Welch, Ian; Dupuis, Holly; Bryce, Dawn; Pajak, Agnieszka; St Arnaud, René; Dedhar, Shoukat; D'Souza, Sudhir J A; Dagnino, Lina

2008-04-01

Integrin-linked kinase (ILK) is key for cell survival, migration, and adhesion, but little is known about its role in epidermal development and homeostasis in vivo. We generated mice with conditional inactivation of the Ilk gene in squamous epithelia. These mice die perinatally and exhibit skin blistering and severe defects in hair follicle morphogenesis, including greatly reduced follicle numbers, failure to progress beyond very early developmental stages, and pronounced defects in follicular keratinocyte proliferation. ILK-deficient epidermis shows abnormalities in adhesion to the basement membrane and in differentiation. ILK-deficient cultured keratinocytes fail to attach and spread efficiently and exhibit multiple abnormalities in actin cytoskeletal organization. Ilk gene inactivation in cultured keratinocytes causes impaired ability to form stable lamellipodia, to directionally migrate, and to polarize. These defects are accompanied by abnormal distribution of active Cdc42 to cell protrusions, as well as reduced activation of Rac1 upon induction of cell migration in scraped keratinocyte monolayers. Significantly, alterations in cell spreading and forward movement in single cells can be rescued by expression of constitutively active Rac1 or RhoG. Our studies underscore a central and distinct role for ILK in hair follicle development and in polarized cell movements, two key aspects of epithelial morphogenesis and function.

Impaired Hair Follicle Morphogenesis and Polarized Keratinocyte Movement upon Conditional Inactivation of Integrin-linked Kinase in the Epidermis

PubMed Central

Nakrieko, Kerry-Ann; Welch, Ian; Dupuis, Holly; Bryce, Dawn; Pajak, Agnieszka; St. Arnaud, René; Dedhar, Shoukat

2008-01-01

Integrin-linked kinase (ILK) is key for cell survival, migration, and adhesion, but little is known about its role in epidermal development and homeostasis in vivo. We generated mice with conditional inactivation of the Ilk gene in squamous epithelia. These mice die perinatally and exhibit skin blistering and severe defects in hair follicle morphogenesis, including greatly reduced follicle numbers, failure to progress beyond very early developmental stages, and pronounced defects in follicular keratinocyte proliferation. ILK-deficient epidermis shows abnormalities in adhesion to the basement membrane and in differentiation. ILK-deficient cultured keratinocytes fail to attach and spread efficiently and exhibit multiple abnormalities in actin cytoskeletal organization. Ilk gene inactivation in cultured keratinocytes causes impaired ability to form stable lamellipodia, to directionally migrate, and to polarize. These defects are accompanied by abnormal distribution of active Cdc42 to cell protrusions, as well as reduced activation of Rac1 upon induction of cell migration in scraped keratinocyte monolayers. Significantly, alterations in cell spreading and forward movement in single cells can be rescued by expression of constitutively active Rac1 or RhoG. Our studies underscore a central and distinct role for ILK in hair follicle development and in polarized cell movements, two key aspects of epithelial morphogenesis and function. PMID:18234842

Conversion of polar and non-polar algae oil lipids to fatty acid methyl esters with solid acid catalysts--A model compound study.

PubMed

Asikainen, Martta; Munter, Tony; Linnekoski, Juha

2015-09-01

Bio-based fuels are becoming more and more important due to the depleting fossil resources. The production of biodiesel from algae oil is challenging compared to terrestrial vegetable oils, as algae oil consists of polar fatty acids, such as phospholipids and glycolipids, as well as non-polar triglycerides and free fatty acids common in vegetable oils. It is shown that a single sulphonated solid acid catalyst can perform the esterification and transesterification reactions of both polar and non-polar lipids. In mild reaction conditions (60-70 °C) Nafion NR50 catalyst produces methyl palmitate (FAME) from the palmitic acid derivatives of di-, and tri-glyceride, free fatty acid, and phospholipid with over 80% yields, with the glycolipid derivative giving nearly 40% yields of FAME. These results demonstrate how the polar and non-polar lipid derivatives of algal oil can be utilised as feedstocks for biodiesel production with a single catalyst in one reaction step. Copyright © 2015 Elsevier Ltd. All rights reserved.

Design of a TW-SLIM Module for Dual Polarity Confinement, Transport, and Reactions

NASA Astrophysics Data System (ADS)

Garimella, Sandilya V. B.; Webb, Ian K.; Prabhakaran, Aneesh; Attah, Isaac K.; Ibrahim, Yehia M.; Smith, Richard D.

2017-07-01

Here we describe instrumental approaches for performing dual polarity ion confinement, transport, ion mobility separations, and reactions in structures for lossless ion manipulations (SLIM). Previous means of ion confinement in SLIM, based upon rf-generated pseudopotentials and DC fields for lateral confinement, cannot trap ions of opposite polarity simultaneously. Here we explore alternative approaches to provide simultaneous lateral confinement of both ion polarities. Traveling wave ion mobility (IM) separations experienced in such SLIM cause ions of both polarities to migrate in the same directions and exhibit similar separations. The ion motion (and relative motion of the two polarities) under both surfing and IM separation conditions are discussed. In surfing conditions the two polarities are transported losslessly and non-reactively in their respective potential minima (higher absolute voltage regions confine negative polarities, and lower absolute potential regions are populated by positive polarities). In separation mode, where ions roll over an overtaking traveling wave, the two polarities can interact during the rollovers. Strategies to minimize overlap of the two ion populations to prevent reactive losses during separations are presented. A theoretical treatment of the time scales over which two populations (injected into a DC field-free region of the dual polarity SLIM device) interact is considered, and SLIM designs for allowing ion/ion interactions and other manipulations with dual polarities at 4 Torr are presented.

Camera characterization for all-sky polarization measurements during the 2017 solar eclipse

NASA Astrophysics Data System (ADS)

Hashimoto, Taiga; Dahl, Laura M.; Laurie, Seth A.; Shaw, Joseph A.

2017-08-01

A solar eclipse provides a rare opportunity to observe skylight polarization during conditions that are fundamentally different than what we see every day. On 21 August 2017 we will measure the skylight polarization during a total solar eclipse in Rexburg, Idaho, USA. Previous research has shown that during totality the sky polarization pattern is altered significantly to become nominally symmetric about the zenith. However, there are still questions remaining about the details of how surface reflectance near the eclipse observation site and optical properties of aerosols in the atmosphere influence the totality sky polarization pattern. We will study how skylight polarization in a solar eclipse changes through each phase and how surface and atmospheric features affect the measured polarization signatures. To accomplish this, fully characterizing the cameras and fisheye lenses is critical. This paper reports measurements that include finding the camera sensitivity and its relationship to the required short exposure times, measuring the camera's spectral response function, mapping the angles of each camera pixel with the fisheye lens, and taking test measurements during daytime and twilight conditions. The daytime polarimetric images were compared to images from an existing all-sky polarization imager and a polarimetric radiative transfer model.

How clear-sky polarization varies with wavelength in the visible-NIR

NASA Astrophysics Data System (ADS)

Pust, Nathan J.; Shaw, Joseph A.

2013-10-01

Because of the increasing variety of applications for polarization imaging and sensing, there is a growing need for information about polarization phenomenology in the natural environment, including the spectral distribution of polarization in the atmosphere. A computer model that has been validated in comparisons with measurements from our all-sky polarization imager has been used here to simulate the spectrum of clear-sky polarization at a many locations around the world, with a wide variety of underlying surface-reflectance and aerosol conditions. This study of the skylight polarization spectral variability shows that there is no simple spectrum that can be assumed or predicted without knowledge of the atmospheric aerosol properties and underlying surface reflectance.

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.

The physics of polarization

NASA Astrophysics Data System (ADS)

Landi Degl'Innocenti, Egidio

). Finally, the third part (Sects. 15-19) is devoted to give a sketch of the theory of the generation and transfer of polarized radiation in spectral lines. After a general introduction to the argument (Sect. 15), the concepts of density-matrix and of atomic polarization are illustrated in Sect. 16. In Sect. 17, a parallelism is established, within the framework of the theory of stellar atmospheres, between the usual formalism, which neglects polarization phenomena, and the more involved formalism needed for the interpretation of spectro-polarimetric observations. Some consequences of the radiative transfer equations for polarized radiation, pointing to the importance of dichroism phenomena in establishing the amplification condition via stimulated emission, are discussed in Sect. 18. The last section (Sect. 19) is devoted to introduce the problem of finding a self-consistent solution of the radiative transfer equations for polarized radiation and of the statistical equilibrium equations for the density matrix (non-LTE of the 2nd kind).

Luminance and chromatic contributions to a hyperacuity task: isolation by contrast polarity and target separation.

PubMed

Sun, Hao; Cooper, Bonnie; Lee, Barry B

2012-03-01

Vernier thresholds are known to be elevated when a target pair has opposite contrast polarity. Polarity reversal is used to assess the role of luminance and chromatic pathways in hyperacuity performance. Psychophysical hyperacuity thresholds were measured for pairs of gratings of various combinations of luminance (Lum) and chromatic (Chr) contrast polarities, at different ratios of luminance to chromatic contrast. With two red-green gratings of matched luminance and chromatic polarity (+Lum+Chr), there was an elevation of threshold at isoluminance. When both luminance and chromatic polarity were mismatched (-Lum-Chr), thresholds were substantially elevated under all conditions. With the same luminance contrast polarity and opposite chromatic polarity (+Lum-Chr) thresholds were only elevated close to isoluminance; in the reverse condition (-Lum+Chr), thresholds were elevated as in the -Lum-Chr condition except close to equiluminance. Similar data were obtained for gratings isolating the short-wavelength cone mechanism. Further psychophysical measurements assessed the role of target separation with matched or mismatched contrast polarity; similar results were found for luminance and chromatic gratings. Comparison physiological data were collected from parafoveal ganglion cells of the macaque retina. Positional precision of ganglion cell signals was assessed under conditions related to the psychophysical measurements. On the basis of these combined observations, it is argued that both magnocellular, parvocellular, and koniocellular pathways have access to cortical positional mechanisms associated with vernier acuity. Copyright © 2012 Elsevier Ltd. All rights reserved.

Generation of tunable radially polarized array beams by controllable coherence

NASA Astrophysics Data System (ADS)

Wang, Jing; Zhang, Jipeng; Zhu, Shijun; Li, Zhenhua

2017-05-01

In this paper, a new method for converting a single radial polarization beam into an arbitrary radially polarized array (RPA) beam such as a radial or rectangular symmetry array in the focal plane by modulating a periodic correlation structure is introduced. The realizability conditions for such source and the beam condition for radiation generated by such source are derived. It is illustrated that both the amplitude and the polarization are controllable by means of initial correlation structure and coherence parameter. Furthermore, by designing the source correlation structure, a tunable NUST-shaped RPA beam is demonstrated, which can find widespread applications in micro-nano engineering. Such a method for generation of arbitrary vector array beams is useful in beam shaping and optical tweezers.

Glacial/interglacial changes of Southern Hemisphere wind circulation from the geochemistry of South American dust

NASA Astrophysics Data System (ADS)

Gili, Stefania; Gaiero, Diego M.; Goldstein, Steven L.; Chemale, Farid; Jweda, Jason; Kaplan, Michael R.; Becchio, Raúl A.; Koester, Edinei

2017-07-01

The latitudinal displacement of the southern westerlies and associated climate systems is a key parameter for understanding the variations of Southern Hemisphere atmospheric circulation during the Late Quaternary Period. To increase understanding of past atmospheric circulation and of the paleo-environmental conditions associated with continental dust sources, we dig deeper into dust provenance in paleo-archives of the Southern Hemisphere. We present here a Sr-Nd isotopic and rare earth element study of surface sediments collected along a ∼4000 km latitudinal band from arid and semi-arid terrains in southern South America. Findings from terrains that served as paleo-dust suppliers are compared with modern dust collected from monitoring stations along the same latitudinal band, which affords a test on how actual present-day aeolian compositions compare to those of the past potential source areas. Moreover, the comparison between past and present-day datasets is useful for understanding present-day atmospheric circulation. Armed with a new comprehensive dataset, we revise previous interpretations of the provenance of dust trapped in the Antarctic ice and sediments deposited in the South Atlantic sector of the Southern Ocean. These comparisons support multiple source regions in southern South America that changed with climates. The findings reveal that, although Patagonia plays an important role in contributing dust to the higher latitudes, central Western Argentina and (to a lesser extent) the southern Puna region also emerge as potentially important dust sources during glacial times. The southern Altiplano appears to be a major contributor during interglacial periods as well. We rely in part on an understanding of modern wind-dust activities to conclude that the possible presence of southern South America source regions - other than Patagonia - in East Antarctic ice is consistent with an overall equatorward displacement during glacial times of both the mid

Doxycycline Inhibits Polarization of Macrophages to the Proangiogenic M2-type and Subsequent Neovascularization*

PubMed Central

He, Lizhi; Marneros, Alexander G.

2014-01-01

Macrophages occur along a continuum of functional states between M1-type polarized macrophages with antiangiogenic and antitumor activity and M2-type polarized macrophages, which have been implicated to promote angiogenesis and tumor growth. Proangiogenic M2-type macrophages promote various pathologic conditions, including choroidal neovascularization in models of neovascular age-related macular degeneration, or certain cancers, such as glioblastoma multiforme. Thus, a potential novel therapeutic approach to target pathological angiogenesis in these conditions would be to inhibit the polarization of macrophages toward the proangiogenic M2-type. However, no pharmacological inhibitors of M2-type macrophage polarization have been identified yet. Here we performed an unbiased pharmacological and small chemical screen to identify drugs that inhibit proangiogenic M2-type macrophage polarization and block pathologic macrophage-driven neovascularization. We identified the well tolerated and commonly used antibiotic doxycycline as a potent inhibitor of M2-type polarization of macrophages. Doxycycline inhibited, in a dose-dependent manner, M2-type polarization of human and bone marrow-derived mouse macrophages without affecting cell viability. Furthermore, doxycycline inhibited M2-type macrophage polarization and subsequent neovascularization in vivo in a laser injury model of choroidal neovascularization. Thus, doxycycline could be used to enhance current antiangiogenic treatment approaches in various conditions that are promoted by proangiogenic M2-type macrophages, including neovascular age-related macular degeneration and certain cancers. PMID:24505138

Gene transcription in polar bears (Ursus maritimus) from disparate populations

USGS Publications Warehouse

Bowen, Lizabeth; Miles, A. Keith; Waters, Shannon C.; Meyerson, Randi; Rode, Karyn D.; Atwood, Todd C.

2015-01-01

Polar bears in the Beaufort (SB) and Chukchi (CS) Seas experience different environments due primarily to a longer history of sea ice loss in the Beaufort Sea. Ecological differences have been identified as a possible reason for the generally poorer body condition and reproduction of Beaufort polar bears compared to those from the Chukchi, but the influence of exposure to other stressors remains unknown. We use molecular technology, quantitative PCR, to identify gene transcription differences among polar bears from the Beaufort and Chukchi Seas as well as captive healthy polar bears. We identified significant transcriptional differences among a priori groups (i.e., captive bears, SB 2012, SB 2013, CS 2013) for ten of the 14 genes of interest (i.e., CaM, HSP70, CCR3, TGFβ, COX2, THRα, T-bet, Gata3, CD69, and IL17); transcription levels of DRβ, IL1β, AHR, and Mx1 did not differ among groups. Multivariate analysis also demonstrated separation among the groups of polar bears. Specifically, we detected transcript profiles consistent with immune function impairment in polar bears from the Beaufort Sea, when compared with Chukchi and captive polar bears. Although there is no strong indication of differential exposure to contaminants or pathogens between CS and SB bears, there are clearly differences in important transcriptional responses between populations. Further investigation is warranted to refine interpretation of potential effects of described stress-related conditions for the SB population.

Development of high-polarization Fe/Ge neutron polarizing supermirror: Possibility of fine-tuning of scattering length density in ion beam sputtering

NASA Astrophysics Data System (ADS)

Maruyama, R.; Yamazaki, D.; Akutsu, K.; Hanashima, T.; Miyata, N.; Aoki, H.; Takeda, M.; Soyama, K.

2018-04-01

The multilayer structure of Fe/Si and Fe/Ge systems fabricated by ion beam sputtering (IBS) was investigated using X-ray and polarized neutron reflectivity measurements and scanning transmission electron microscopy with energy-dispersive X-ray analysis. The obtained result revealed that the incorporation of sputtering gas particles (Ar) in the Ge layer gives rise to a marked reduction in the neutron scattering length density (SLD) and contributes to the SLD contrast between the Fe and Ge layers almost vanishing for spin-down neutrons. Bundesmann et al. (2015) have shown that the implantation of primary Ar ions backscattered at the target is responsible for the incorporation of Ar particles and that the fraction increases with increasing ion incidence angle and increasing polar emission angle. This leads to a possibility of fine-tuning of the SLD for the IBS, which is required to realize a high polarization efficiency of a neutron polarizing supermirror. Fe/Ge polarizing supermirror with m = 5 fabricated under the same condition showed a spin-up reflectivity of 0.70 at the critical momentum transfer. The polarization was higher than 0.985 for the qz range where the correction for the polarization inefficiencies of the beamline works properly. The result of the polarized neutron reflectivity measurement suggests that the "magnetically-dead" layers formed at both sides of the Fe layer, together with the SLD contrast, play a critical role in determining the polarization performance of a polarizing supermirror.

Provenance Changes Over Glacial-Interglacial Timescales Recorded in Japan Sea Sediments (IODP Site U1430)

NASA Astrophysics Data System (ADS)

Kinsley, C. W.; McGee, D.; Anderson, C. H.; Murray, R. W.; Tada, R.; Alvarez Zarikian, C. A.

2017-12-01

Recent work has shown a mechanistic relationship between the Westerly Jet (WJ) and East Asian Monsoon (EAM) precipitation, as migration of the WJ to the northern edge of the Tibetan Plateau during spring and early summer appears to be essential for driving convective rainfall over eastern China. Chiang et al. (2015) has proposed the "Jet Transition Hypothesis" wherein it is put forward that changes to the seasonal meridional position of the WJ relative to the Tibetan Plateau drives rainfall climate changes over East Asia on paleoclimate timescales. This hypothesis would predict that in extreme scenarios such as cold phases of Dansgaard-Oeschger (D-O) stadials and during periods of low Northern Hemisphere summer insolation that the Jet would not move north of the Tibetan Plateau, keeping East Asia in prolonged spring conditions. Conversely, during periods of high Northern Hemisphere summer insolation it would be predicted that the Jet would move more quickly north of the Tibetan Plateau and remain there longer, keeping East Asia in prolonged summer conditions. Westerly Jet behavior can be reconstructed using sediments from the Japan Sea, as the WJ path and intensity determines dust emissions and transport paths from Chinese and Mongolian dust source areas, which is the primary source of terrigenous material to the Japan Sea. Radiogenic isotopes of Pb, Nd and Sr can be been applied to fingerprint the dust sources from Asia, and measurements of these isotopes downcore in the Japan Sea will allow reconstruction of the changing dust source area and thus behavior of the WJ. By coupling dust reconstructions lending insight to the behavior of the Westerly Jet with complementary records reflecting EAM intensity and precipitation distribution, the mean state and variability of the WJ and its coupling with the EAM can be examined. This study will measure a suite of samples for Pb, Nd and Sr isotopes from IODP Site U1430 over glacial-interglacial timescales, allowing detailed

Polar Rain Gradients and Field-Aligned Polar Cap Potentials

NASA Technical Reports Server (NTRS)

Fairfield, D. H.; Wing, S.; Newell, P. T.; Ruohoniemi, J. M.; Gosling, J. T.; Skoug, R. M.

2008-01-01

ACE SWEPAM measurements of solar wind field-aligned electrons have been compared with simultaneous measurements of polar rain electrons precipitating over the polar cap and detected by DMSP spacecraft. Such comparisons allow investigation of cross-polar-cap gradients in the intensity of otherwise-steady polar rain. The generally good agreement of the distribution functions, f, from the two data sources confirms that direct entry of solar electrons along open field lines is indeed the cause of polar rain. The agreement between the data sets is typically best on the side of the polar cap with most intense polar rain but the DMSP f's in less intense regions can be brought into agreement with ACE measurements by shifting all energies by a fixed amounts that range from tens to several hundred eV. In most cases these shifts are positive which implies that field-aligned potentials of these amounts exist on polar cap field lines which tend to retard the entry of electrons and produce the observed gradients. These retarding potentials undoubtedly appear in order to prevent the entry of low-energy electrons and maintain charge quasi-neutrality that would otherwise be violated since most tailward flowing magnetosheath ions are unable to follow polar rain electrons down to the polar cap. In more limited regions near the boundary of the polar cap there is sometimes evidence for field-aligned potentials of the opposite sign that accelerate polar rain electrons. A solar electron burst is also studied and it is concluded that electrons from such bursts can enter the magnetotail and precipitate in the same manner as polar rain.

Polarization-sensitive electro-optic detection of terahertz wave using three different types of crystal symmetry: Toward broadband polarization spectroscopy

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

Oguchi, Kenichi; Iwasaki, Hotsumi; Okano, Makoto

2016-01-04

We investigated polarization-sensitive electro-optic (EO) detection of terahertz (THz) waves by using two uniaxial crystals: a c-cut gallium selenide and a c-cut lithium niobate crystals. We formulated a general frequency-domain description of EO detection by in-plane isotropic EO crystals, which holds regardless of the frequency. Based on this description, the polarization of THz waves can be derived by analyzing EO sampling signals measured with two orthogonal configurations of the in-plane isotropic EO crystals as well as typical (111) zinc-blende EO crystals. In addition, we experimentally demonstrated that the frequency-dependent polarization of THz waves can be reproducibly retrieved using three EOmore » crystals with different crystal symmetries and with different phase matching conditions. Our description provides essential information for practical polarization sensing in the THz frequency range as well as in the mid-infrared range.« less

North Polar Cap

NASA Technical Reports Server (NTRS)

2004-01-01

[figure removed for brevity, see original site]

This week we will be looking at five examples of laminar wind flow on the north polar cap. On Earth, gravity-driven south polar cap winds are termed 'catabatic' winds. Catabatic winds begin over the smooth expanse of the cap interior due to temperature differences between the atmosphere and the surface. Once begun, the winds sweep outward along the surface of the polar cap toward the sea. As the polar surface slopes down toward sealevel, the wind speeds increase. Catabatic wind speeds in the Antartic can reach several hundreds of miles per hour.

In the images of the Martian north polar cap we can see these same type of winds. Notice the streamers of dust moving downslope over the darker trough sides, these streamers show the laminar flow regime coming off the cap. Within the trough we see turbulent clouds of dust, kicked up at the trough base as the winds slow down and enter a chaotic flow regime.

The horizontal lines in these images are due to framelet overlap and lighting conditions over the bright polar cap.

Image information: VIS instrument. Latitude 86.5, Longitude 64.5 East (295.5 West). 40 meter/pixel resolution.

Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation

North Polar Cap

NASA Technical Reports Server (NTRS)

2004-01-01

[figure removed for brevity, see original site]

This week we will be looking at five examples of laminar wind flow on the north polar cap. On Earth, gravity-driven south polar cap winds are termed 'catabatic' winds. Catabatic winds begin over the smooth expanse of the cap interior due to temperature differences between the atmosphere and the surface. Once begun, the winds sweep outward along the surface of the polar cap toward the sea. As the polar surface slopes down toward sealevel, the wind speeds increase. Catabatic wind speeds in the Antartic can reach several hundreds of miles per hour.

In the images of the Martian north polar cap we can see these same type of winds. Notice the streamers of dust moving downslope over the darker trough sides, these streamers show the laminar flow regime coming off the cap. Within the trough we see turbulent clouds of dust, kicked up at the trough base as the winds slow down and enter a chaotic flow regime.

The horizontal lines in these images are due to framelet overlap and lighting conditions over the bright polar cap.

Image information:VIS instrument. Latitude 86.5, longitude 57.4 East (302.6 West). 40 meter/pixel resolution.

Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is

North Polar Cap

NASA Technical Reports Server (NTRS)

2004-01-01

[figure removed for brevity, see original site]

This week we will be looking at five examples of laminar wind flow on the north polar cap. On Earth, gravity-driven south polar cap winds are termed 'catabatic' winds. Catabatic winds begin over the smooth expanse of the cap interior due to temperature differences between the atmosphere and the surface. Once begun, the winds sweep outward along the surface of the polar cap toward the sea. As the polar surface slopes down toward sealevel, the wind speeds increase. Catabatic wind speeds in the Antartic can reach several hundreds of miles per hour.

In the images of the Martian north polar cap we can see these same type of winds. Notice the streamers of dust moving downslope over the darker trough sides, these streamers show the laminar flow regime coming off the cap. Within the trough we see turbulent clouds of dust, kicked up at the trough base as the winds slow down and enter a chaotic flow regime.

The horizontal lines in these images are due to framelet overlap and lighting conditions over the bright polar cap.

Image information: VIS instrument. Latitude 84.3, Longitude 314.4 East (45.6 West). 40 meter/pixel resolution.

Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation

North Polar Cap

NASA Technical Reports Server (NTRS)

2004-01-01

[figure removed for brevity, see original site]

This week we will be looking at five examples of laminar wind flow on the north polar cap. On Earth, gravity-driven south polar cap winds are termed 'catabatic' winds. Catabatic winds begin over the smooth expanse of the cap interior due to temperature differences between the atmosphere and the surface. Once begun, the winds sweep outward along the surface of the polar cap toward the sea. As the polar surface slopes down toward sealevel, the wind speeds increase. Catabatic wind speeds in the Antartic can reach several hundreds of miles per hour.

In the images of the Martian north polar cap we can see these same type of winds. Notice the streamers of dust moving downslope over the darker trough sides, these streamers show the laminar flow regime coming off the cap. Within the trough we see turbulent clouds of dust, kicked up at the trough base as the winds slow down and enter a chaotic flow regime.

The horizontal lines in these images are due to framelet overlap and lighting conditions over the bright polar cap.

Image information: VIS instrument. Latitude 84.2, Longitude 57.4 East (302.6 West). 40 meter/pixel resolution.

Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation

Sensitivity enhancement by multiple-contact cross-polarization under magic-angle spinning

NASA Astrophysics Data System (ADS)

Raya, J.; Hirschinger, J.

2017-08-01

Multiple-contact cross-polarization (MC-CP) is applied to powder samples of ferrocene and L-alanine under magic-angle spinning (MAS) conditions. The method is described analytically through the density matrix formalism. The combination of a two-step memory function approach and the Anderson-Weiss approximation is found to be particularly useful to derive approximate analytical solutions for single-contact Hartmann-Hahn CP (HHCP) and MC-CP dynamics under MAS. We show that the MC-CP sequence requiring no pulse-shape optimization yields higher polarizations at short contact times than optimized adiabatic passage through the HH condition CP (APHH-CP) when the MAS frequency is comparable to the heteronuclear dipolar coupling, i.e., when APHH-CP through a single sideband matching condition is impossible or difficult to perform. It is also shown that the MC-CP sideband HH conditions are generally much broader than for single-contact HHCP and that efficient polarization transfer at the centerband HH condition can be reintroduced by rotor-asynchronous multiple equilibrations-re-equilibrations with the proton spin bath. Boundary conditions for the successful use of the MC-CP experiment when relying on spin-lattice relaxation for repolarization are also examined.

Comparative Habitable Planet Signatures in Polarized Light

NASA Astrophysics Data System (ADS)

Bott, K.; Bailey, J.; Meadows, V.; Kedziora-Chudczer, L.; Cotton, D.; Crisp, D.

2017-11-01

VSTAR polarized light models of terrestrial worlds are compared for varying cloud, atmospheric, and surface conditions. Archetypal "Earth-like" planets are compared and the observability of their combined polarimetric effects assessed.

Small Mammals as Indicators of Climate, Biodiversity, and Ecosystem Change

USGS Publications Warehouse

Hope, Andrew G.; Waltari, Eric; Morse, Nathan R.; Flamme, M.J.; Cook, Joseph A.; Talbot, Sandra L.

2017-01-01

Climate is a driving evolutionary force for biodiversity in high-latitude Alaska. This region is complex and dynamic with high annual variation in temperature and light. Through deeper time, Alaska has experienced major climate extremes over much longer periodicity. For example, the Quaternary Period (the last ~2.5 million years), commonly known as the Ice Age, was punctuated by more than 20 major glacial-interglacial cycles. During glacial phases, water was locked up in ice sheets that covered much of North America, and the resulting lower sea levels exposed a land connection between Alaska and Siberia, a combined region known as Beringia (Figure 1). This isthmus provided vast expanses of land for species to inhabit, provided they could withstand potentially harsh polar conditions. Each extended glacial phase periodically transitioned into a shorter interglacial warm phase. These climate reversals melted continental ice sheets to expose corridors for reinvasion of terrestrial species, particularly those associated with forested habitats further south. Those species that survived at northern latitudes through repeated glacial-interglacial cycles formed the Arctic tundra communities that persist today. At present, Alaska supports diverse communities associated with both tundra and forests (Figure 2). These communities often interact with one another across latitudinal and elevational gradients, with tundra species generally found further north or higher in elevation. Alaska’s climate is continuing to change today, strongly influencing local environments and the distribution and dynamics of wildlife species.

Giant boulders and Last Interglacial storm intensity in the North Atlantic

NASA Astrophysics Data System (ADS)

Rovere, Alessio; Casella, Elisa; Harris, Daniel L.; Lorscheid, Thomas; Nandasena, Napayalage A. K.; Dyer, Blake; Sandstrom, Michael R.; Stocchi, Paolo; D'Andrea, William J.; Raymo, Maureen E.

2017-11-01

As global climate warms and sea level rises, coastal areas will be subject to more frequent extreme flooding and hurricanes. Geologic evidence for extreme coastal storms during past warm periods has the potential to provide fundamental insights into their future intensity. Recent studies argue that during the Last Interglacial (MIS 5e, ˜128–116 ka) tropical and extratropical North Atlantic cyclones may have been more intense than at present, and may have produced waves larger than those observed historically. Such strong swells are inferred to have created a number of geologic features that can be observed today along the coastlines of Bermuda and the Bahamas. In this paper, we investigate the most iconic among these features: massive boulders atop a cliff in North Eleuthera, Bahamas. We combine geologic field surveys, wave models, and boulder transport equations to test the hypothesis that such boulders must have been emplaced by storms of greater-than-historical intensity. By contrast, our results suggest that with the higher relative sea level (RSL) estimated for the Bahamas during MIS 5e, boulders of this size could have been transported by waves generated by storms of historical intensity. Thus, while the megaboulders of Eleuthera cannot be used as geologic proof for past “superstorms,” they do show that with rising sea levels, cliffs and coastal barriers will be subject to significantly greater erosional energy, even without changes in storm intensity.

Giant boulders and Last Interglacial storm intensity in the North Atlantic.

PubMed

Rovere, Alessio; Casella, Elisa; Harris, Daniel L; Lorscheid, Thomas; Nandasena, Napayalage A K; Dyer, Blake; Sandstrom, Michael R; Stocchi, Paolo; D'Andrea, William J; Raymo, Maureen E

2017-11-14

As global climate warms and sea level rises, coastal areas will be subject to more frequent extreme flooding and hurricanes. Geologic evidence for extreme coastal storms during past warm periods has the potential to provide fundamental insights into their future intensity. Recent studies argue that during the Last Interglacial (MIS 5e, ∼128-116 ka) tropical and extratropical North Atlantic cyclones may have been more intense than at present, and may have produced waves larger than those observed historically. Such strong swells are inferred to have created a number of geologic features that can be observed today along the coastlines of Bermuda and the Bahamas. In this paper, we investigate the most iconic among these features: massive boulders atop a cliff in North Eleuthera, Bahamas. We combine geologic field surveys, wave models, and boulder transport equations to test the hypothesis that such boulders must have been emplaced by storms of greater-than-historical intensity. By contrast, our results suggest that with the higher relative sea level (RSL) estimated for the Bahamas during MIS 5e, boulders of this size could have been transported by waves generated by storms of historical intensity. Thus, while the megaboulders of Eleuthera cannot be used as geologic proof for past "superstorms," they do show that with rising sea levels, cliffs and coastal barriers will be subject to significantly greater erosional energy, even without changes in storm intensity.

Giant boulders and Last Interglacial storm intensity in the North Atlantic

PubMed Central

Casella, Elisa; Harris, Daniel L.; Lorscheid, Thomas; Nandasena, Napayalage A. K.; Dyer, Blake; Sandstrom, Michael R.; Stocchi, Paolo; D’Andrea, William J.; Raymo, Maureen E.

2017-01-01

As global climate warms and sea level rises, coastal areas will be subject to more frequent extreme flooding and hurricanes. Geologic evidence for extreme coastal storms during past warm periods has the potential to provide fundamental insights into their future intensity. Recent studies argue that during the Last Interglacial (MIS 5e, ∼128–116 ka) tropical and extratropical North Atlantic cyclones may have been more intense than at present, and may have produced waves larger than those observed historically. Such strong swells are inferred to have created a number of geologic features that can be observed today along the coastlines of Bermuda and the Bahamas. In this paper, we investigate the most iconic among these features: massive boulders atop a cliff in North Eleuthera, Bahamas. We combine geologic field surveys, wave models, and boulder transport equations to test the hypothesis that such boulders must have been emplaced by storms of greater-than-historical intensity. By contrast, our results suggest that with the higher relative sea level (RSL) estimated for the Bahamas during MIS 5e, boulders of this size could have been transported by waves generated by storms of historical intensity. Thus, while the megaboulders of Eleuthera cannot be used as geologic proof for past “superstorms,” they do show that with rising sea levels, cliffs and coastal barriers will be subject to significantly greater erosional energy, even without changes in storm intensity. PMID:29087331

Navigation by light polarization in clear and turbid waters

PubMed Central

Lerner, Amit; Sabbah, Shai; Erlick, Carynelisa; Shashar, Nadav

2011-01-01

Certain terrestrial animals use sky polarization for navigation. Certain aquatic species have also been shown to orient according to a polarization stimulus, but the correlation between underwater polarization and Sun position and hence the ability to use underwater polarization as a compass for navigation is still under debate. To examine this issue, we use theoretical equations for per cent polarization and electric vector (e-vector) orientation that account for the position of the Sun, refraction at the air–water interface and Rayleigh single scattering. The polarization patterns predicted by these theoretical equations are compared with measurements conducted in clear and semi-turbid coastal sea waters at 2 m and 5 m depth over sea floors of 6 m and 28 m depth. We find that the per cent polarization is correlated with the Sun's elevation only in clear waters. We furthermore find that the maximum value of the e-vector orientation angle equals the angle of refraction only in clear waters, in the horizontal viewing direction, over the deeper sea floor. We conclude that navigation by use of underwater polarization is possible under restricted conditions, i.e. in clear waters, primarily near the horizontal viewing direction, and in locations where the sea floor has limited effects on the light's polarization. PMID:21282170

Partial polarizer filter

NASA Technical Reports Server (NTRS)

Title, A. M. (Inventor)

1978-01-01

A birefringent filter module comprises, in seriatum. (1) an entrance polarizer, (2) a first birefringent crystal responsive to optical energy exiting the entrance polarizer, (3) a partial polarizer responsive to optical energy exiting the first polarizer, (4) a second birefringent crystal responsive to optical energy exiting the partial polarizer, and (5) an exit polarizer. The first and second birefringent crystals have fast axes disposed + or -45 deg from the high transmitivity direction of the partial polarizer. Preferably, the second crystal has a length 1/2 that of the first crystal and the high transmitivity direction of the partial polarizer is nine times as great as the low transmitivity direction. To provide tuning, the polarizations of the energy entering the first crystal and leaving the second crystal are varied by either rotating the entrance and exit polarizers, or by sandwiching the entrance and exit polarizers between pairs of half wave plates that are rotated relative to the polarizers. A plurality of the filter modules may be cascaded.

Stimulated electromagnetic emission polarization under different polarizations of pump waves

NASA Astrophysics Data System (ADS)

Tereshchenko, E. D.; Yurik, R. Y.; Baddeley, L.

2015-03-01

The results of investigations into the stimulated electromagnetic emission (SEE) polarization under different modes of the pump wave polarization are presented. The present results were obtained in November 2012 during a heating campaign utilizing the SPEAR (Space Plasma Exploration by Active Radar) heating facility, transmitting in both O- and X-mode polarization, and a PGI (Polar Geophysical Institute) radio interferometer capable of recording the polarization of the received radiation. The polarization ellipse parameters of the SEE DM (downshifted maximum) components were determined under both O-mode and X-mode polarization of the pump waves. The polarization direction of the SEE DM component was preserved under different polarizations of the pump waves. Different polarizations of the pump waves have a different SEE generation efficiency. The intensity of the DM component is observed to be greater during O-mode pumping. In addition, the numbers of observed SEE features are also greater during O-mode pumping.

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

USGS Publications Warehouse

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

1997-01-01

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

Polarization-Insensitive Tunable Optical Filters based on Liquid Crystal Polarization Gratings

NASA Astrophysics Data System (ADS)

Nicolescu, Elena

Tunable optical filters are widely used for a variety of applications including spectroscopy, optical communication networks, remote sensing, and biomedical imaging and diagnostics. All of these application areas can greatly benefit from improvements in the key characteristics of the tunable optical filters embedded in them. Some of these key parameters include peak transmittance, bandwidth, tuning range, and transition width. In recent years research efforts have also focused on miniaturizing tunable optical filters into physically small packages for compact portable spectroscopy and hyperspectral imaging applications such as real-time medical diagnostics and defense applications. However, it is important that miniaturization not have a detrimental effect on filter performance. The overarching theme of this dissertation is to explore novel configurations of Polarization Gratings (PGs) as simple, low-cost, polarization-insensitive alternatives to conventional optical filtering technologies for applications including hyperspectral imaging and telecommunications. We approach this goal from several directions with a combination of theory and experimental demonstration leading to, in our opinion, a significant contribution to the field. We present three classes of tunable optical filters, the first of which is an angle-filtering scheme where the stop-band wavelengths are redirected off axis and the passband is transmitted on-axis. This is achieved using a stacked configuration of polarization gratings of various thicknesses. To improve this class of filter, we also introduce a novel optical element, the Bilayer Polarization Grating, exhibiting unique optical properties and demonstrating complex anchoring conditions with high quality. The second class of optical filter is analogous to a Lyot filter, utilizing stacks of static or tunable waveplates sandwiched with polarizing elements. However, we introduce a new configuration using PGs and static waveplates to replace

NEW Planetarium Programs for Polar Informal Science Education

NASA Astrophysics Data System (ADS)

Sumners, C.; Schloss, A. L.; Reiff, P.

2007-12-01

The modern planetarium is an immersive full-dome theater that can take audiences to Polar Regions in the past, present, or future and can simulate dynamic polar events. With the goal of public engagement and education, we are producing two programs: Night of the Titanic and Ice Worlds. Night of the Titanic uses a famous tragedy to uncover the science that could have saved the ship and the changing conditions in the North Atlantic over the last century. This program also fosters discussion about how humans evaluate data and make critical decisions related to the changing condition of polar ice. Ice Worlds uses comparative planetology themes to present Earth in the context of all ice worlds in the solar system, thus providing a broader perspective for analysis of changes in Earth's Polar Regions. Both programs rely on themes of high public interest to drive attendance and engagement. Both programs are being developed for the large dome theater or planetarium market and for portable Discovery Domes, which can reach urban and rural audiences throughout the world. This paper focuses on techniques for presentation of rigorous science content in a context that will engage the general public as well as school groups over a wide age range.

Polar Rain Gradients and Field-Aligned Polar Cap Potentials

NASA Technical Reports Server (NTRS)

Fairfield, D. H.; Wing, S.; Newell, P. T.; Ruohoniemi, J. M.; Gosling, J. T.; Skoug, R. M.

2008-01-01

ACE SWEPAM measurements of solar wind field-aligned electrons have been compared with simultaneous measurements of polar rain electrons precipitating over the polar cap and detected by DMSP spacecraft. Such comparisons allow investigation of cross-polarcap gradients in the intensity of otherwise-steady polar rain. The generally good agreement of the distribution functions, f, from the two data sources confirms that direct entry of solar electrons along open field lines is indeed the cause of polar rain. The agreement between the data sets is typically best on the side of the polar cap with most intense polar rain but the DMSP f's in less intense regions can be brought into agreement with ACE measurements by shifting all energies by a fixed amounts that range from tens to several hundred eV. In most cases these shifts are positive which implies that field-aligned potentials of these amounts exist on polar cap field lines which tend to retard the entry of electrons and produce the observed gradients. These retarding potentials undoubtedly appear in order to prevent the entry of low-energy electrons and maintain charge quasi-neutrality that would otherwise be violated since most tailward flowing magnetosheath ions are unable to follow polar rain electrons down to the polar cap. In more limited regions near the boundary of the polar cap there is sometimes evidence for field-aligned potentials of the opposite sign that accelerate polar rain electrons. A solar electron burst is also studied and it is concluded that electrons from such bursts can enter the magnetotail and precipitate in the same manner as polar rain.

Polarization spectroscopy of atomic erbium in a hollow cathode lamp

NASA Astrophysics Data System (ADS)

Ang'ong'a, Jackson; Gadway, Bryce

2018-02-01

In this work we perform polarization spectroscopy of erbium atoms in a hollow cathode lamp (HCL). We review the theory behind Doppler-free polarization spectroscopy, theoretically model the expected erbium polarization spectra, and compare the numerically calculated spectra to our experimental data. We further analyze the dependence of the measured spectra on the HCL current and the peak intensities of our pump and probe lasers to determine conditions. Applications include wavelength stabilization of diode laser radiation to the 400.91 nm erbium transition.

Underwater linear polarization: physical limitations to biological functions

PubMed Central

Shashar, Nadav; Johnsen, Sönke; Lerner, Amit; Sabbah, Shai; Chiao, Chuan-Chin; Mäthger, Lydia M.; Hanlon, Roger T.

2011-01-01

Polarization sensitivity is documented in a range of marine animals. The variety of tasks for which animals can use this sensitivity, and the range over which they do so, are confined by the visual systems of these animals and by the propagation of the polarization information in the aquatic environment. We examine the environmental physical constraints in an attempt to reveal the depth, range and other limitations to the use of polarization sensitivity by marine animals. In clear oceanic waters, navigation that is based on the polarization pattern of the sky appears to be limited to shallow waters, while solar-based navigation is possible down to 200–400 m. When combined with intensity difference, polarization sensitivity allows an increase in target detection range by 70–80% with an upper limit of 15 m for large-eyed animals. This distance will be significantly smaller for small animals, such as plankton, and in turbid waters. Polarization-contrast detection, which is relevant to object detection and communication, is strongly affected by water conditions and in clear waters its range limit may reach 15 m as well. We show that polarization sensitivity may also serve for target distance estimation, when examining point source bioluminescent objects in the photic mesopelagic depth range. PMID:21282168

Update of the Polar SWIFT model for polar stratospheric ozone loss (Polar SWIFT version 2)

NASA Astrophysics Data System (ADS)

Wohltmann, Ingo; Lehmann, Ralph; Rex, Markus

2017-07-01

The Polar SWIFT model is a fast scheme for calculating the chemistry of stratospheric ozone depletion in polar winter. It is intended for use in global climate models (GCMs) and Earth system models (ESMs) to enable the simulation of mutual interactions between the ozone layer and climate. To date, climate models often use prescribed ozone fields, since a full stratospheric chemistry scheme is computationally very expensive. Polar SWIFT is based on a set of coupled differential equations, which simulate the polar vortex-averaged mixing ratios of the key species involved in polar ozone depletion on a given vertical level. These species are O3, chemically active chlorine (ClOx), HCl, ClONO2 and HNO3. The only external input parameters that drive the model are the fraction of the polar vortex in sunlight and the fraction of the polar vortex below the temperatures necessary for the formation of polar stratospheric clouds. Here, we present an update of the Polar SWIFT model introducing several improvements over the original model formulation. In particular, the model is now trained on vortex-averaged reaction rates of the ATLAS Chemistry and Transport Model, which enables a detailed look at individual processes and an independent validation of the different parameterizations contained in the differential equations. The training of the original Polar SWIFT model was based on fitting complete model runs to satellite observations and did not allow for this. A revised formulation of the system of differential equations is developed, which closely fits vortex-averaged reaction rates from ATLAS that represent the main chemical processes influencing ozone. In addition, a parameterization for the HNO3 change by denitrification is included. The rates of change of the concentrations of the chemical species of the Polar SWIFT model are purely chemical rates of change in the new version, whereas in the original Polar SWIFT model, they included a transport effect caused by the

Capillarity ion concentration polarization as spontaneous desalting mechanism.

PubMed

Park, Sungmin; Jung, Yeonsu; Son, Seok Young; Cho, Inhee; Cho, Youngrok; Lee, Hyomin; Kim, Ho-Young; Kim, Sung Jae

2016-04-01

To overcome a world-wide water shortage problem, numerous desalination methods have been developed with state-of-the-art power efficiency. Here we propose a spontaneous desalting mechanism referred to as the capillarity ion concentration polarization. An ion-depletion zone is spontaneously formed near a nanoporous material by the permselective ion transportation driven by the capillarity of the material, in contrast to electrokinetic ion concentration polarization which achieves the same ion-depletion zone by an external d.c. bias. This capillarity ion concentration polarization device is shown to be capable of desalting an ambient electrolyte more than 90% without any external electrical power sources. Theoretical analysis for both static and transient conditions are conducted to characterize this phenomenon. These results indicate that the capillarity ion concentration polarization system can offer unique and economical approaches for a power-free water purification system.

Predicting solvation free energies and thermodynamics in polar solvents and mixtures using a solvation-layer interface condition

PubMed Central

Goossens, Spencer; Mehdizadeh Rahimi, Ali

2017-01-01

We demonstrate that with two small modifications, the popular dielectric continuum model is capable of predicting, with high accuracy, ion solvation thermodynamics (Gibbs free energies, entropies, and heat capacities) in numerous polar solvents. We are also able to predict ion solvation free energies in water–co-solvent mixtures over available concentration series. The first modification to the classical dielectric Poisson model is a perturbation of the macroscopic dielectric-flux interface condition at the solute–solvent interface: we add a nonlinear function of the local electric field, giving what we have called a solvation-layer interface condition (SLIC). The second modification is including the microscopic interface potential (static potential) in our model. We show that the resulting model exhibits high accuracy without the need for fitting solute atom radii in a state-dependent fashion. Compared to experimental results in nine water–co-solvent mixtures, SLIC predicts transfer free energies to within 2.5 kJ/mol. The co-solvents include both protic and aprotic species, as well as biologically relevant denaturants such as urea and dimethylformamide. Furthermore, our results indicate that the interface potential is essential to reproduce entropies and heat capacities. These and previous tests of the SLIC model indicate that it is a promising dielectric continuum model for accurate predictions in a wide range of conditions.

Predicting solvation free energies and thermodynamics in polar solvents and mixtures using a solvation-layer interface condition

NASA Astrophysics Data System (ADS)

Molavi Tabrizi, Amirhossein; Goossens, Spencer; Mehdizadeh Rahimi, Ali; Knepley, Matthew; Bardhan, Jaydeep P.

2017-03-01

We demonstrate that with two small modifications, the popular dielectric continuum model is capable of predicting, with high accuracy, ion solvation thermodynamics (Gibbs free energies, entropies, and heat capacities) in numerous polar solvents. We are also able to predict ion solvation free energies in water-co-solvent mixtures over available concentration series. The first modification to the classical dielectric Poisson model is a perturbation of the macroscopic dielectric-flux interface condition at the solute-solvent interface: we add a nonlinear function of the local electric field, giving what we have called a solvation-layer interface condition (SLIC). The second modification is including the microscopic interface potential (static potential) in our model. We show that the resulting model exhibits high accuracy without the need for fitting solute atom radii in a state-dependent fashion. Compared to experimental results in nine water-co-solvent mixtures, SLIC predicts transfer free energies to within 2.5 kJ/mol. The co-solvents include both protic and aprotic species, as well as biologically relevant denaturants such as urea and dimethylformamide. Furthermore, our results indicate that the interface potential is essential to reproduce entropies and heat capacities. These and previous tests of the SLIC model indicate that it is a promising dielectric continuum model for accurate predictions in a wide range of conditions.

Metasurface polarization splitter

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

Slovick, Brian A.; Zhou, You; Yu, Zhi Gang

Polarization beam splitters, devices that separate the two orthogonal polarizations of light into different propagation directions, are among the most ubiquitous optical elements. However, traditionally polarization splitters rely on bulky optical materials, while emerging optoelectronic and photonic circuits require compact, chip-scale polarization splitters. Here, we show that a rectangular lattice of cylindrical silicon Mie resonators functions as a polarization splitter, efficiently reflecting one polarization while transmitting the other. We show that the polarization splitting arises from the anisotropic permittivity and permeability of the metasurface due to the twofold rotational symmetry of the rectangular unit cell. Lastly, the high polarization efficiency,more » low loss and low profile make these metasurface polarization splitters ideally suited for monolithic integration with optoelectronic and photonic circuits.« less

Metasurface polarization splitter

DOE PAGES

Slovick, Brian A.; Zhou, You; Yu, Zhi Gang; ...

2017-02-20

Polarization beam splitters, devices that separate the two orthogonal polarizations of light into different propagation directions, are among the most ubiquitous optical elements. However, traditionally polarization splitters rely on bulky optical materials, while emerging optoelectronic and photonic circuits require compact, chip-scale polarization splitters. Here, we show that a rectangular lattice of cylindrical silicon Mie resonators functions as a polarization splitter, efficiently reflecting one polarization while transmitting the other. We show that the polarization splitting arises from the anisotropic permittivity and permeability of the metasurface due to the twofold rotational symmetry of the rectangular unit cell. Lastly, the high polarization efficiency,more » low loss and low profile make these metasurface polarization splitters ideally suited for monolithic integration with optoelectronic and photonic circuits.« less

Measured Polarized Spectral Responsivity of JPSS J1 VIIRS Using the NIST T-SIRCUS

NASA Technical Reports Server (NTRS)

McIntire, Jeff; Young, James B.; Moyer, David; Waluschka, Eugene; Xiong, Xiaoxiong

2015-01-01

Recent pre-launch measurements performed on the Joint Polar Satellite System (JPSS) J1 Visible Infrared Imaging Radiometer Suite (VIIRS) using the National Institute of Standards and Technology (NIST) Traveling Spectral Irradiance and Radiance Responsivity Calibrations Using Uniform Sources (T-SIRCUS) monochromatic source have provided wavelength dependent polarization sensitivity for select spectral bands and viewing conditions. Measurements were made at a number of input linear polarization states (twelve in total) and initially at thirteen wavelengths across the bandpass (later expanded to seventeen for some cases). Using the source radiance information collected by an external monitor, a spectral responsivity function was constructed for each input linear polarization state. Additionally, an unpolarized spectral responsivity function was derived from these polarized measurements. An investigation of how the centroid, bandwidth, and detector responsivity vary with polarization state was weighted by two model input spectra to simulate both ground measurements as well as expected on-orbit conditions. These measurements will enhance our understanding of VIIRS polarization sensitivity, improve the design for future flight models, and provide valuable data to enhance product quality in the post-launch phase.

Cloud-top height retrieval from polarizing remote sensor POLDER

NASA Astrophysics Data System (ADS)

He, Xianqiang; Pan, Delu; Yan, Bai; Mao, Zhihua

2006-10-01

A new cloud-top height retrieval method is proposed by using polarizing remote sensing. In cloudy conditions, it shows that, in purple and blue bands, linear polarizing radiance at the top-of-atmosphere (TOA) is mainly contributed by Rayleigh scattering of the atmosphere's molecules above cloud, and the contribution by cloud reflection and aerosol scattering can be neglected. With such characteristics, the basis principle and method of cloud-top height retrieval using polarizing remote sensing are presented in detail, and tested by the polarizing remote sensing data of POLDER. The satellite-derived cloud-top height product can not only show the distribution of global cloud-top height, but also obtain the cloud-top height distribution of moderate-scale meteorological phenomena like hurricanes and typhoons. This new method is promising to become the operational algorithm for cloud-top height retrieval for POLDER and the future polarizing remote sensing satellites.

Specular, diffuse and polarized imagery of an oat canopy

NASA Technical Reports Server (NTRS)

Vanderbilt, Vern C.; De Venecia, Kurt J.

1988-01-01

Light, polarized by specular reflection, has been found to be an important part of the light scattered by several measured plant canopies. The authors investigate for one canopy the relative importance of specularly reflected sunlight, specularly reflected light from other sources including skylight, and diffusely upwelling light. Polarization images are used to gain increased understanding of the radiation transfer process in a plant canopy. Analysis of the results suggests that properly analyzed polarized remotely sensed data, acquired under specific atmospheric conditions by a specially designed sensor, potentially provide measures of physiological and morphological states of plants in a canopy.

The copepod Calanus spp. (Calanidae) is repelled by polarized light.

PubMed

Lerner, Amit; Browman, Howard I

2016-10-20

Both attraction and repulsion from linearly polarized light have been observed in zooplankton. A dichotomous choice experiment, consisting of plankton light traps deployed in natural waters at a depth of 30 m that projected either polarized or unpolarized light of the same intensity, was used to test the hypothesis that the North Atlantic copepod, Calanus spp., is linearly polarotactic. In addition, the transparency of these copepods, as they might be seen by polarization insensitive vs. sensitive visual systems, was measured. Calanus spp. exhibited negative polarotaxis with a preference ratio of 1.9:1. Their transparency decreased from 80% to 20% to 30% in the unpolarized, partially polarized, and electric (e-) vector orientation domains respectively - that is, these copepods would appear opaque and conspicuous to a polarization-sensitive viewer looking at them under conditions rich in polarized light. Since the only difference between the two plankton traps was the polarization cue, we conclude that Calanus spp. are polarization sensitive and exhibit negative polarotaxis at low light intensities (albeit well within the sensitivity range reported for copepods). We hypothesize that Calanus spp. can use polarization vision to reduce their risk of predation by polarization-sensitive predators and suggest that this be tested in future experiments.

The copepod Calanus spp. (Calanidae) is repelled by polarized light

NASA Astrophysics Data System (ADS)

Lerner, Amit; Browman, Howard I.

2016-10-01

Both attraction and repulsion from linearly polarized light have been observed in zooplankton. A dichotomous choice experiment, consisting of plankton light traps deployed in natural waters at a depth of 30 m that projected either polarized or unpolarized light of the same intensity, was used to test the hypothesis that the North Atlantic copepod, Calanus spp., is linearly polarotactic. In addition, the transparency of these copepods, as they might be seen by polarization insensitive vs. sensitive visual systems, was measured. Calanus spp. exhibited negative polarotaxis with a preference ratio of 1.9:1. Their transparency decreased from 80% to 20% to 30% in the unpolarized, partially polarized, and electric (e-) vector orientation domains respectively - that is, these copepods would appear opaque and conspicuous to a polarization-sensitive viewer looking at them under conditions rich in polarized light. Since the only difference between the two plankton traps was the polarization cue, we conclude that Calanus spp. are polarization sensitive and exhibit negative polarotaxis at low light intensities (albeit well within the sensitivity range reported for copepods). We hypothesize that Calanus spp. can use polarization vision to reduce their risk of predation by polarization-sensitive predators and suggest that this be tested in future experiments.

A microwave satellite water vapour column retrieval for polar winter conditions

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

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

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 aremore » 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.« less

Sea level and ground water table depth (WTD): A biogeochemical pacemaker for glacial-interglacial cycling

NASA Astrophysics Data System (ADS)

Cowling, S. A.

2016-11-01

The role that changes in sea level have on potential carbon-climate feedbacks are discussed as a potential contributing mechanism for terminating glacial periods. Focus will be on coastal wetlands because these systems can be substantially altered by changing sea level and ground water table depth (WTD); in addition to being important moderators of the exchange of nutrients and energy between terrestrial and marine ecosystems. A hypothesis is outlined that describes how the release of carbon from formerly anaerobic wetland soils and sediments can influence climate when sea levels begin to decline. As ground WTD deepens and eventually recedes from the surface, coastal wetland basins may become isolated from their belowground source of water. With their primary source of base flow removed, coastal wetlands likely dried up, promoting decomposition of the carbon compounds buried in their sediments. Depending on the timing of basin isolation and the timing of decomposition, glacial sea level lows could have triggered a relatively large positive carbon feedback on climate warming, just at the time when a new interglacial period is about to begin.

Metasurface polarization splitter

PubMed Central

Slovick, Brian A.; Zhou, You; Yu, Zhi Gang; Kravchenko, Ivan I.; Briggs, Dayrl P.; Moitra, Parikshit; Krishnamurthy, Srini

2017-01-01

Polarization beam splitters, devices that separate the two orthogonal polarizations of light into different propagation directions, are among the most ubiquitous optical elements. However, traditionally polarization splitters rely on bulky optical materials, while emerging optoelectronic and photonic circuits require compact, chip-scale polarization splitters. Here, we show that a rectangular lattice of cylindrical silicon Mie resonators functions as a polarization splitter, efficiently reflecting one polarization while transmitting the other. We show that the polarization splitting arises from the anisotropic permittivity and permeability of the metasurface due to the twofold rotational symmetry of the rectangular unit cell. The high polarization efficiency, low loss and low profile make these metasurface polarization splitters ideally suited for monolithic integration with optoelectronic and photonic circuits. This article is part of the themed issue ‘New horizons for nanophotonics’. PMID:28220002

Polarization splitter and polarization rotator designs based on transformation optics.

PubMed

Kwon, Do-Hoon; Werner, Douglas H

2008-11-10

The transformation optics technique is employed in this paper to design two optical devices - a two-dimensional polarization splitter and a three-dimensional polarization rotator for propagating beams. The polarization splitter translates the TM- and the TE-polarized components of an incident beam in opposite directions (i.e., shifted up or shifted down). The polarization rotator rotates the polarization state of an incoming beam by an arbitrary angle. Both optical devices are reflectionless at the entry and exit interfaces. Design details and full-wave simulation results are provided.

Polarization Of Light In The Natural Environment

NASA Astrophysics Data System (ADS)

Coulson, Kinsell L.

1990-01-01

This paper provides a characterization of the fields of light polarization with which the optical designer or user of optical devices in the natural environment must be concerned. After a brief historical outline of the principal developments in polarization theory and observations during the last two centuries, the main emphasis is on the two primary processes responsible for the polarization of light in nature--scattering of light by particles of the atmosphere and reflection from soils, vegetation, snow, and water at the earth's surface. Finally, a seven minute film on polarization effects which can be seen in everyday surroundings will be shown. Scattering by atmospheric particles is responsible for high values of polarization in various atmospheric conditions and at certain scattering geometries. Such scattering particles include molecules of the atmospheric gases, aerosols of dust, haze, and air pollution, water droplets of fog and clouds, and the ice crystals of cirrus. It is seen that development of the theory of scattering by such particles has outstripped the measurements necessary for validation of the theory, a fact which points up the importance of symposia such as the present one. The reverse is true, however, for the polarizing properties of natural surfaces. Only in the case of still water is the theory of reflection adequate to characterize in a quantitative fashion the polarizing effects produced by the reflection of light from such natural surfaces. Polarization of light by reflection from vegetation is of prime importance in a remote sensing context, but much further work is needed to characterize vegetative reflectance for the purpose. The short film on polarization effects provides a good visualization technique and training aid for students interested in the field.

Polarity Control and Growth of Lateral Polarity Structures in AlN

DTIC Science & Technology

2013-05-10

domains. Transmission electron microscopy shows mixed edge-screw type dislocations with polarity-dependent dislocation bending. Raman 1. REPORT DATE (DD-MM...polarity-dependent dislocation bending. Raman spectroscopy reveals compressively strained Al-polar and relaxed N-polar domains. The near band edge...dislocation bending. Raman spectroscopy reveals compressively strained Al-polar and relaxed N-polar domains. The near band edge luminescence consists of

Sensitivity enhancement by multiple-contact cross-polarization under magic-angle spinning.

PubMed

Raya, J; Hirschinger, J

2017-08-01

Multiple-contact cross-polarization (MC-CP) is applied to powder samples of ferrocene and l-alanine under magic-angle spinning (MAS) conditions. The method is described analytically through the density matrix formalism. The combination of a two-step memory function approach and the Anderson-Weiss approximation is found to be particularly useful to derive approximate analytical solutions for single-contact Hartmann-Hahn CP (HHCP) and MC-CP dynamics under MAS. We show that the MC-CP sequence requiring no pulse-shape optimization yields higher polarizations at short contact times than optimized adiabatic passage through the HH condition CP (APHH-CP) when the MAS frequency is comparable to the heteronuclear dipolar coupling, i.e., when APHH-CP through a single sideband matching condition is impossible or difficult to perform. It is also shown that the MC-CP sideband HH conditions are generally much broader than for single-contact HHCP and that efficient polarization transfer at the centerband HH condition can be reintroduced by rotor-asynchronous multiple equilibrations-re-equilibrations with the proton spin bath. Boundary conditions for the successful use of the MC-CP experiment when relying on spin-lattice relaxation for repolarization are also examined. Copyright © 2017 Elsevier Inc. All rights reserved.

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.

Toward a Last Interglacial Compilation Using a Tephra-based Chronology: a Future Reference For Model-data Comparison

NASA Astrophysics Data System (ADS)

Bazin, L.; Govin, A.; Capron, E.; Nomade, S.; Lemieux-Dudon, B.; Landais, A.

2017-12-01

The Last Interglacial (LIG, 129-116 ka) is a key period to decipher the interactions between the different components of the climate system under warmer-than-preindustrial conditions. Modelling the LIG climate is now part of the CMIP6/PMIP4 targeted simulations. As a result, recent efforts have been made to propose surface temperature compilations focusing on the spatio-temporal evolution of the LIG climate, and not only on its peak warmth as previously proposed. However, the major limitation of these compilations remains in the climatic alignment of records (e.g. temperature, foraminiferal δ18O) that is performed to define the sites' chronologies. Such methods prevent the proper discussion of phase relationship between the different sites. Thanks to recent developments of the Bayesian Datice dating tool, we are now able to build coherent multi-archive chronologies with a proper propagation of the associated uncertainties. We make the best use of common tephra layers identified in well-dated continental archives and marine sediment cores of the Mediterranean region to propose a coherent chronological framework for the LIG independent of any climatic assumption. We then extend this precise chronological context to the North Atlantic as a first step toward a global coherent compilation of surface temperature and stable isotope records. Based on this synthesis, we propose guidelines for the interpretation of different proxies measured from different archives that will be compared with climate model parameters. Finally, we present time-slices (e.g. 127 ka) of the preliminary regional synthesis of temperature reconstructions and stable isotopes to serve as reference for future model-data comparison of the up-coming CMIP6/PMIP4 LIG simulations.

Linear Polarization Measurements of Chromospheric Emission Lines

NASA Technical Reports Server (NTRS)

Sheeley, N. R., Jr.; Keller, C. U.

2003-01-01

We have used the Zurich Imaging Stokes Polarimeter (ZIMPOL I) with the McMath-Pierce 1.5 m main telescope on Kitt Peak to obtain linear polarization measurements of the off-limb chromosphere with a sensitivity better than 1 x 10(exp -5). We found that the off-disk observations require a combination of good seeing (to show the emission lines) and a clean heliostat (to avoid contamination by scattered light from the Sun's disk). When these conditions were met, we obtained the following principal results: 1. Sometimes self-reversed emission lines of neutral and singly ionized metals showed linear polarization caused by the transverse Zeeman effect or by instrumental cross talk from the longitudinal Zeeman effect in chromospheric magnetic fields. Otherwise, these lines tended to depolarize the scattered continuum radiation by amounts that ranged up to 0.2%. 2. Lines previously known to show scattering polarization just inside the limb (such as the Na I lambda5889 D2 and the He I lambda5876 D3 lines) showed even more polarization above the Sun's limb, with values approaching 0.7%. 3. The O I triplet at lambda7772, lambda7774, and lambda7775 showed a range of polarizations. The lambda7775 line, whose maximum intrinsic polarizability, P(sub max), is less than 1%, revealed mainly Zeeman contributions from chromospheric magnetic fields. However, the more sensitive lambda7772 (P(sub max) = 19%) and lambda7774 (P(sub max) = 29%) lines had relatively strong scattering polarizations of approximately 0.3% in addition to their Zeeman polarizations. At times of good seeing, the polarization spectra resolve into fine structures that seem to be chromospheric spicules.

New observations and a photographic atlas of polar-ring galaxies

NASA Technical Reports Server (NTRS)

Whitmore, Bradley C.; Lucas, Ray A.; Mcelroy, Douglas B.; Steiman-Cameron, Thomas Y.; Sackett, Penny D.

1990-01-01

A photographic atlas of polar-ring galaxies and related objects is presented. The atlas includes kinematically confirmed polar-ring galaxies (category A), good candidates based on their morphological appearance (category B), possible candidates (category C), and possibly related objects (category D). New photometric and kinematic observations are reported for several galaxies in the catalog, including observations that show that UGC 7576 and UGC 9796 ( = II ZW 73) are S0 galaxies with polar rings. Roughly 0.5 percent of all nearby S0 galaxies appear to have polar rings. When corrected for various selection effects (e.g., nonoptimal viewing orientation, possible dimming, or limited lifetime of the ring) the percentage increases to about 5 percent of S0 galaxies which have, or have had a polar ring.

Study on the measurement system of the target polarization characteristics and test

NASA Astrophysics Data System (ADS)

Fu, Qiang; Zhu, Yong; Zhang, Su; Duan, Jin; Yang, Di; Zhan, Juntong; Wang, Xiaoman; Jiang, Hui-Lin

2015-10-01

The polarization imaging detection technology increased the polarization information on the basis of the intensity imaging, which is extensive application in the military and civil and other fields, the research on the polarization characteristics of target is particularly important. The research of the polarization reflection model was introduced in this paper, which describes the scattering vector light energy distribution in reflecting hemisphere polarization characteristics, the target polarization characteristics test system solutions was put forward, by the irradiation light source, measuring turntable and camera, etc, which illuminate light source shall direct light source, with laser light sources and xenon lamp light source, light source can be replaced according to the test need; Hemispherical structure is used in measuring circumarotate placed near its base material sample, equipped with azimuth and pitching rotation mechanism, the manual in order to adjust the azimuth Angle and high Angle observation; Measuring camera pump works, through the different in the way of motor control polaroid polarization test, to ensure the accuracy of measurement and imaging resolution. The test platform has set up by existing laboratory equipment, the laser is 532 nm, line polaroid camera, at the same time also set the sending and receiving optical system. According to the different materials such as wood, metal, plastic, azimuth Angle and zenith Angle in different observation conditions, measurement of target in the polarization scattering properties of different exposure conditions, implementation of hemisphere space pBRDF measurement.

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.

Comparison of the sampling rates and partitioning behaviour of polar and non-polar contaminants in the polar organic chemical integrative sampler and a monophasic mixed polymer sampler for application as an equilibrium passive sampler.

PubMed

Jeong, Yoonah; Schäffer, Andreas; Smith, Kilian

2018-06-15

In this work, Oasis HLB® beads were embedded in a silicone matrix to make a single phase passive sampler with a higher affinity for polar and ionisable compounds than silicone alone. The applicability of this mixed polymer sampler (MPS) was investigated for 34 aquatic contaminants (log K OW -0.03 to 6.26) in batch experiments. The influence of flow was investigated by comparing uptake under static and stirred conditions. The sampler characteristics of the MPS was assessed in terms of sampling rates (R S ) and sampler-water partition coefficients (K SW ), and these were compared to those of the polar organic chemical integrative sampler (POCIS) as a reference kinetic passive sampler. The MPS was characterized as an equilibrium sampler for both polar and non-polar compounds, with faster uptake rates and a shorter time to reach equilibrium than the POCIS. Water flow rate impacted sampling rates by up to a factor of 12 when comparing static and stirred conditions. In addition, the relative accumulation of compounds in the polyethersulfone (PES) membranes versus the inner Oasis HLB sorbent was compared for the POCIS, and ranged from <1% to 83% depending on the analyte properties. This is indicative of a potentially significant lag-phase for less polar compounds within POCIS. The findings of this study can be used to quantitatively describe the partitioning and kinetic behaviour of MPS and POCIS for a range of aquatic organic contaminants for application in field sampling. Copyright © 2018 Elsevier B.V. All rights reserved.

[Polarization characteristic of Al + MgF2 film at VUV].

PubMed

Liu, Ying; Li, Zhi-gang; Li, Fu-tian

2002-10-01

Polarization characteristic of Al + MgF2 is researched theoretically and experimentally. According to the theory of electromagnetism, the reflectance perpendicular and parallel to the incident plane of Al + MgF2 is calculated in the way of matrix optics. The effect of incident conditions and thickness of MgF2 is considered on the reflectance of Al + MgF2 coatings. The MgF2 not only prevents the oxidation of aluminum but also increases the reflectance of Al + MgF2 by interference. The polarization of Al + MgF2 is analyzed using the concept of ratio of extinction based on above mentioned calculations. The polarization character of Al + MgF2 and single Al coating is compared. The reflectances perpendicular and parallel to the incident plane of Al + MgF2 film are measured at VUV range, using LiF polarizer as a VUV polarizer. So the polarization character of Al + MgF2 is researched experimentally. Both theoretical and experimental results of the polarization character of Al + MgF2 are coincident.

Applications of polarization speckle in skin cancer detection and monitoring

NASA Astrophysics Data System (ADS)

Lee, Tim K.; Tchvialeva, Lioudmila; Phillips, Jamie; Louie, Daniel C.; Zhao, Jianhua; Wang, Wei; Lui, Harvey; Kalia, Sunil

2018-01-01

Polarization speckle is a rapidly developed field. Unlike laser speckle, polarization speckle consists of stochastic interference patterns with spatially random polarizations, amplitudes and phases. We have been working in this exciting research field, developing techniques to generate polarization patterns from skin. We hypothesize that polarization speckle patterns could be used in biomedical applications, especially, for detecting and monitoring skin cancers, the most common neoplasmas for white populations around the world. This paper describes our effort in developing two polarization speckle devices. One of them captures the Stokes parameters So and S1 simultaneously, and another one captures all four Stokes parameters So, S1, S2, and S3 in one-shot, within milliseconds. Hence these two devices could be used in medical clinics and assessed skin conditions in-vivo. In order to validate our hypothesis, we conducted a series of three clinical studies. These are early pilot studies, and the results suggest that the devices have potential to detect and monitor skin cancers.

Responses of the deep ocean carbonate system to carbon reorganization during the Last Glacial-interglacial cycle

NASA Astrophysics Data System (ADS)

Yu, Jimin; Anderson, Robert F.; Jin, Zhangdong; Rae, James W. B.; Opdyke, Bradley N.; Eggins, Stephen M.

2013-09-01

We present new deep water carbonate ion concentration ([CO32-]) records, reconstructed using Cibicidoides wuellerstorfi B/Ca, for one core from Caribbean Basin (water depth = 3623 m, sill depth = 1.8 km) and three cores located at 2.3-4.3 km water depth from the equatorial Pacific Ocean during the Last Glacial-interglacial cycle. The pattern of deep water [CO32-] in the Caribbean Basin roughly mirrors that of atmospheric CO2, reflecting a dominant influence from preformed [CO32-] in the North Atlantic Ocean. Compared to the amplitude of ˜65 μmol/kg in the deep Caribbean Basin, deep water [CO32-] in the equatorial Pacific Ocean has varied by no more than ˜15 μmol/kg due to effective buffering of CaCO3 on deep-sea pH in the Pacific Ocean. Our results suggest little change in the global mean deep ocean [CO32-] between the Last Glacial Maximum (LGM) and the Late Holocene. The three records from the Pacific Ocean show long-term increases in [CO32-] by ˜7 μmol/kg from Marine Isotope Stage (MIS) 5c to mid MIS 3, consistent with the response of the deep ocean carbonate system to a decline in neritic carbonate production associated with ˜60 m drop in sea-level (the “coral-reef” hypothesis). Superimposed upon the long-term trend, deep water [CO32-] in the Pacific Ocean displays transient changes, which decouple with δ13C in the same cores, at the start and end of MIS 4. These changes in [CO32-] and δ13C are consistent with what would be expected from vertical nutrient fractionation and carbonate compensation. The observed ˜4 μmol/kg [CO32-] decline in the two Pacific cores at >3.4 km water depth from MIS 3 to the LGM indicate further strengthening of deep ocean stratification, which contributed to the final step of atmospheric CO2 drawdown during the last glaciation. The striking similarity between deep water [CO32-] and 230Th-normalized CaCO3 flux at two adjacent sites from the central equatorial Pacific Ocean provides convincing evidence that deep

Non-uniformity calibration for MWIR polarization imagery obtained with integrated microgrid polarimeters

NASA Astrophysics Data System (ADS)

Liu, Hai-Zheng; Shi, Ze-Lin; Feng, Bin; Hui, Bin; Zhao, Yao-Hong

2016-03-01

Integrating microgrid polarimeters on focal plane array (FPA) of an infrared detector causes non-uniformity of polarization response. In order to reduce the effect of polarization non-uniformity, this paper constructs an experimental setup for capturing raw flat-field images and proposes a procedure for acquiring non-uniform calibration (NUC) matrix and calibrating raw polarization images. The proposed procedure takes the incident radiation as a polarization vector and offers a calibration matrix for each pixel. Both our matrix calibration and two-point calibration are applied to our mid-wavelength infrared (MWIR) polarization imaging system with integrated microgrid polarimeters. Compared with two point calibration, our matrix calibration reduces non-uniformity by 30 40% under condition of flat-field data test with polarization. The ourdoor scene observation experiment indicates that our calibration can effectively reduce polarization non-uniformity and improve the image quality of our MWIR polarization imaging system.

Theoretical analysis of non-polarizing beam splitters with appropriate amplitude and phase

NASA Astrophysics Data System (ADS)

Shi, Jin Hui; Wang, Zheng Ping; Guan, Chun Ying

2009-04-01

When used at oblique angles of incidence, the reflectance and transmittance of thin films exhibit strong polarization effects, particularly for the films inside a glass cube. However, the polarization effects are undesirable in many applications. Novel non-polarizing beam splitter designs are shown. Non-polarizing beam splitters with unique optical thin films are achieved through the combination of interference and frustrated total internal reflection. The non-polarizing condition expressions based on frustrated total internal reflection are derived, and examples of the non-polarizing beam splitters are also presented with the optimization technique and the results of Rp=(50±0.5)%, Rs=(50±0.5)%, and Δr=(0±0.3) in the wavelength range of 400-700 nm are obtained.

Transmission of linearly polarized light in seawater: implications for polarization signaling.

PubMed

Shashar, Nadav; Sabbah, Shai; Cronin, Thomas W

2004-09-01

Partially linearly polarized light is abundant in the oceans. The natural light field is partially polarized throughout the photic range, and some objects and animals produce a polarization pattern of their own. Many polarization-sensitive marine animals take advantage of the polarization information, using it for tasks ranging from navigation and finding food to communication. In such tasks, the distance to which the polarization information propagates is of great importance. Using newly designed polarization sensors, we measured the changes in linear polarization underwater as a function of distance from a standard target. In the relatively clear waters surrounding coral reefs, partial (%) polarization decreased exponentially as a function of distance from the target, resulting in a 50% reduction of partial polarization at a distance of 1.25-3 m, depending on water quality. Based on these measurements, we predict that polarization sensitivity will be most useful for short-range (in the order of meters) visual tasks in water and less so for detecting objects, signals, or structures from far away. Navigation and body orientation based on the celestial polarization pattern are predicted to be limited to shallow waters as well, while navigation based on the solar position is possible through a deeper range.

Quantum dot spin-V(E)CSELs: polarization switching and periodic oscillations

NASA Astrophysics Data System (ADS)

Li, Nianqiang; Alexandropoulos, Dimitris; Susanto, Hadi; Henning, Ian; Adams, Michael

2017-09-01

Spin-polarized vertical (external) cavity surface-emitting lasers [Spin-V(E)CSELs] using quantum dot (QD) material for the active region, can display polarization switching between the right- and left-circularly polarized fields via control of the pump polarization. In particular, our previous experimental results have shown that the output polarization ellipticity of the spin-V(E)CSEL emission can exhibit either the same handedness as that of the pump polarization or the opposite, depending on the experimental operating conditions. In this contribution, we use a modified version of the spin-flip model in conjunction with combined time-independent stability analysis and direct time integration. With two representative sets of parameters our simulation results show good agreement with experimental observations. In addition periodic oscillations provide further insight into the dynamic properties of spin-V(E)CSELs.

Polarized light sensitivity and orientation in coral reef fish post-larvae.

PubMed

Berenshtein, Igal; Kiflawi, Moshe; Shashar, Nadav; Wieler, Uri; Agiv, Haim; Paris, Claire B

2014-01-01

Recent studies of the larvae of coral-reef fishes reveal that these tiny vertebrates possess remarkable swimming capabilities, as well as the ability to orient to olfactory, auditory, and visual cues. While navigation according to reef-generated chemicals and sounds can significantly affect dispersal, the effect is limited to the vicinity of the reef. Effective long-distance navigation requires at least one other capacity-the ability to maintain a bearing using, for example, a sun compass. Directional information in the sun's position can take the form of polarized-light related cues (i.e., e-vector orientation and percent polarization) and/or non-polarized-light related cues (i.e., the direct image of the sun, and the brightness and spectral gradients). We examined the response to both types of cues using commercially-reared post-larvae of the spine-cheeked anemonefish Premnas biaculeatus. Initial optomotor trials indicated that the post-larval stages are sensitive to linearly polarized light. Swimming directionality was then tested using a Drifting In-Situ Chamber (DISC), which allowed us to examine the response of the post-larvae to natural variation in light conditions and to manipulated levels of light polarization. Under natural light conditions, 28 of 29 post-larvae showed significant directional swimming (Rayleigh's test p<0.05, R = 0.74±0.23), but to no particular direction. Swimming directionality was positively affected by sky clarity (absence of clouds and haze), which explained 38% of the observed variation. Moreover, post-larvae swimming under fully polarized light exhibited a distinct behavior of tracking the polarization axis, as it rotated along with the DISC. This behavior was not observed under partially-polarized illumination. We view these findings as an indication for the use of sun-related cues, and polarized light signal in specific, by orienting coral-reef fish larvae.

Polarized Light Sensitivity and Orientation in Coral Reef Fish Post-Larvae

PubMed Central

Berenshtein, Igal; Kiflawi, Moshe; Shashar, Nadav; Wieler, Uri; Agiv, Haim; Paris, Claire B.

2014-01-01

Recent studies of the larvae of coral-reef fishes reveal that these tiny vertebrates possess remarkable swimming capabilities, as well as the ability to orient to olfactory, auditory, and visual cues. While navigation according to reef-generated chemicals and sounds can significantly affect dispersal, the effect is limited to the vicinity of the reef. Effective long-distance navigation requires at least one other capacity–the ability to maintain a bearing using, for example, a sun compass. Directional information in the sun’s position can take the form of polarized-light related cues (i.e., e-vector orientation and percent polarization) and/or non-polarized-light related cues (i.e., the direct image of the sun, and the brightness and spectral gradients). We examined the response to both types of cues using commercially-reared post-larvae of the spine-cheeked anemonefish Premnas biaculeatus. Initial optomotor trials indicated that the post-larval stages are sensitive to linearly polarized light. Swimming directionality was then tested using a Drifting In-Situ Chamber (DISC), which allowed us to examine the response of the post-larvae to natural variation in light conditions and to manipulated levels of light polarization. Under natural light conditions, 28 of 29 post-larvae showed significant directional swimming (Rayleigh’s test p<0.05, R = 0.74±0.23), but to no particular direction. Swimming directionality was positively affected by sky clarity (absence of clouds and haze), which explained 38% of the observed variation. Moreover, post-larvae swimming under fully polarized light exhibited a distinct behavior of tracking the polarization axis, as it rotated along with the DISC. This behavior was not observed under partially-polarized illumination. We view these findings as an indication for the use of sun-related cues, and polarized light signal in specific, by orienting coral-reef fish larvae. PMID:24516662

Production of Highly Polarized Positrons Using Polarized Electrons at MeV Energies

NASA Astrophysics Data System (ADS)

Abbott, D.; Adderley, P.; Adeyemi, A.; Aguilera, P.; Ali, M.; Areti, H.; Baylac, M.; Benesch, J.; Bosson, G.; Cade, B.; Camsonne, A.; Cardman, L. S.; Clark, J.; Cole, P.; Covert, S.; Cuevas, C.; Dadoun, O.; Dale, D.; Dong, H.; Dumas, J.; Fanchini, E.; Forest, T.; Forman, E.; Freyberger, A.; Froidefond, E.; Golge, S.; Grames, J.; Guèye, P.; Hansknecht, J.; Harrell, P.; Hoskins, J.; Hyde, C.; Josey, B.; Kazimi, R.; Kim, Y.; Machie, D.; Mahoney, K.; Mammei, R.; Marton, M.; McCarter, J.; McCaughan, M.; McHugh, M.; McNulty, D.; Mesick, K. E.; Michaelides, T.; Michaels, R.; Moffit, B.; Moser, D.; Muñoz Camacho, C.; Muraz, J.-F.; Opper, A.; Poelker, M.; Réal, J.-S.; Richardson, L.; Setiniyaz, S.; Stutzman, M.; Suleiman, R.; Tennant, C.; Tsai, C.; Turner, D.; Ungaro, M.; Variola, A.; Voutier, E.; Wang, Y.; Zhang, Y.; PEPPo Collaboration

2016-05-01

The Polarized Electrons for Polarized Positrons experiment at the injector of the Continuous Electron Beam Accelerator Facility has demonstrated for the first time the efficient transfer of polarization from electrons to positrons produced by the polarized bremsstrahlung radiation induced by a polarized electron beam in a high-Z target. Positron polarization up to 82% have been measured for an initial electron beam momentum of 8.19 MeV /c , limited only by the electron beam polarization. This technique extends polarized positron capabilities from GeV to MeV electron beams, and opens access to polarized positron beam physics to a wide community.

Last Glacial-Interglacial Transition ice dynamics in the Wicklow Mountains, Ireland

NASA Astrophysics Data System (ADS)

Knight, Lauren; Boston, Clare; Lovell, Harold; Pepin, Nick

2017-04-01

Understanding of the extent and dynamics of former ice masses in the Wicklow Mountains, Ireland, during the Last Glacial-Interglacial Transition (LGIT; 15-10 ka BP) is currently unresolved. Whilst it is acknowledged that the region hosted a local ice cap within the larger British-Irish Ice Sheet at the Last Glacial Maximum (LGM; 27 ka BP), there has been little consideration of ice cap disintegration to a topographically constrained ice mass during the LGIT. This research has produced the first regional glacial geomorphological map, through remote sensing (aerial photograph and digital terrain model interrogation) and field mapping. This has allowed both the style and extent of mountain glaciation and ice recession dynamics during the LGIT to be established. This geomorphological mapping has highlighted that evidence for local glaciation in the Wicklow Mountains is more extensive than previously recognised, and that small icefields and associated outlet valley glaciers existed during the LGIT following disintegration of the Wicklow Ice Cap. A relative chronology based on morphostratigraphic principles is developed, which indicates complex patterns of ice mass oscillation characterised by periods of both sustained retreat and minor readvance. Variations in the pattern of recession across the Wicklow Mountains are evident and appear to be influenced, in part, by topographic controls (e.g. slope, aspect, glacier hypsometry). In summary, this research establishes a relative chronology of glacial events in the region during the LGIT and presents constraints on ice mass extent, dynamics and retreat patterns, offering an insight into small ice mass behaviour in a warming climate.

Population substructure and space use of Foxe Basin polar bears.

PubMed

Sahanatien, Vicki; Peacock, Elizabeth; Derocher, Andrew E

2015-07-01

Climate change has been identified as a major driver of habitat change, particularly for sea ice-dependent species such as the polar bear (Ursus maritimus). Population structure and space use of polar bears have been challenging to quantify because of their circumpolar distribution and tendency to range over large areas. Knowledge of movement patterns, home range, and habitat is needed for conservation and management. This is the first study to examine the spatial ecology of polar bears in the Foxe Basin management unit of Nunavut, Canada. Foxe Basin is in the mid-Arctic, part of the seasonal sea ice ecoregion and it is being negatively affected by climate change. Our objectives were to examine intrapopulation spatial structure, to determine movement patterns, and to consider how polar bear movements may respond to changing sea ice habitat conditions. Hierarchical and fuzzy cluster analyses were used to assess intrapopulation spatial structure of geographic position system satellite-collared female polar bears. Seasonal and annual movement metrics (home range, movement rates, time on ice) and home-range fidelity (static and dynamic overlap) were compared to examine the influence of regional sea ice on movements. The polar bears were distributed in three spatial clusters, and there were differences in the movement metrics between clusters that may reflect sea ice habitat conditions. Within the clusters, bears moved independently of each other. Annual and seasonal home-range fidelity was observed, and the bears used two movement patterns: on-ice range residency and annual migration. We predict that home-range fidelity may decline as the spatial and temporal predictability of sea ice changes. These new findings also provide baseline information for managing and monitoring this polar bear population.

Polarized γ source based on Compton backscattering in a laser cavity

NASA Astrophysics Data System (ADS)

Yakimenko, V.; Pogorelsky, I. V.

2006-09-01

We propose a novel gamma source suitable for generating a polarized positron beam for the next generation of electron-positron colliders, such as the International Linear Collider (ILC), and the Compact Linear Collider (CLIC). This 30-MeV polarized gamma source is based on Compton scattering inside a picosecond CO2 laser cavity generated from electron bunches produced by a 4-GeV linac. We identified and experimentally verified the optimum conditions for obtaining at least one gamma photon per electron. After multiplication at several consecutive interaction points, the circularly polarized gamma rays are stopped on a target, thereby creating copious numbers of polarized positrons. We address the practicality of having an intracavity Compton-polarized positron source as the injector for these new colliders.

Polarized electron sources

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

Prepost, R.

1994-12-01

The fundamentals of polarized electron sources are described with particular application to the Stanford Linear Accelerator Center. The SLAC polarized electron source is based on the principle of polarized photoemission from Gallium Arsenide. Recent developments using epitaxially grown, strained Gallium Arsenide cathodes have made it possible to obtain electron polarization significantly in excess of the conventional 50% polarization limit. The basic principles for Gallium and Arsenide polarized photoemitters are reviewed, and the extension of the basic technique to strained cathode structures is described. Results from laboratory measurements of strained photocathodes as well as operational results from the SLAC polarized sourcemore » are presented.« less

Promoting Diversity Through Polar Interdisciplinary Coordinated Education (Polar ICE)

NASA Astrophysics Data System (ADS)

McDonnell, J. D.; Hotaling, L. A.; Garza, C.; Van Dyk, P. B.; Hunter-thomson, K. I.; Middendorf, J.; Daniel, A.; Matsumoto, G. I.; Schofield, O.

2017-12-01

Polar Interdisciplinary Coordinated Education (ICE) is an education and outreach program designed to provide public access to the Antarctic and Arctic regions through polar data and interactions with the scientists. The program provides multi-faceted science communication training for early career scientists that consist of a face-to face workshop and opportunities to apply these skills. The key components of the scientist training workshop include cultural competency training, deconstructing/decoding science for non-expert audiences, the art of telling science stories, and networking with members of the education and outreach community and reflecting on communication skills. Scientists partner with educators to provide professional development for K-12 educators and support for student research symposia. Polar ICE has initiated a Polar Literacy initiative that provides both a grounding in big ideas in polar science and science communication training designed to underscore the importance of the Polar Regions to the public while promoting interdisciplinary collaborations between scientists and educators. Our ultimate objective is to promote STEM identity through professional development of scientists and educators while developing career awareness of STEM pathways in Polar science.

Polarization-independent broadband meta-holograms via polarization-dependent nanoholes.

PubMed

Zhang, Xiaohu; Li, Xiong; Jin, Jinjin; Pu, Mingbo; Ma, Xiaoliang; Luo, Jun; Guo, Yinghui; Wang, Changtao; Luo, Xiangang

2018-05-17

Composed of ultrathin metal or dielectric nanostructures, metasurfaces can manipulate the phase, amplitude and polarization of electromagnetic waves at a subwavelength scale, which is promising for flat optical devices. In general, metasurfaces composed of space-variant anisotropic units are sensitive to the incident polarization due to the inherent polarization dependent geometric phase. Here, we implement polarization-independent broadband metasurface holograms constructed by polarization-dependent anisotropic elliptical nanoholes by elaborate design of complex amplitude holograms. The fabricated meta-hologram exhibits a polarization insensitive feature with an acceptable image quality. We verify the feasibility of the design algorithm for three-dimensional (3D) meta-holograms with simulation and the feasibility for two-dimensional (2D) meta-holograms is experimentally demonstrated at a broadband wavelength range from 405 nm to 632.8 nm. The effective polarization-independent broadband complex wavefront control with anisotropic elliptical nanoholes proposed in this paper greatly promotes the practical applications of the metasurface in technologies associated with wavefront manipulation, such as flat lens, colorful holographic displays and optical storage.

Gravity with free initial conditions: A solution to the cosmological constant problem testable by CMB B -mode polarization

NASA Astrophysics Data System (ADS)

Totani, Tomonori

2017-10-01

In standard general relativity the universe cannot be started with arbitrary initial conditions, because four of the ten components of the Einstein's field equations (EFE) are constraints on initial conditions. In the previous work it was proposed to extend the gravity theory to allow free initial conditions, with a motivation to solve the cosmological constant problem. This was done by setting four constraints on metric variations in the action principle, which is reasonable because the gravity's physical degrees of freedom are at most six. However, there are two problems about this theory; the three constraints in addition to the unimodular condition were introduced without clear physical meanings, and the flat Minkowski spacetime is unstable against perturbations. Here a new set of gravitational field equations is derived by replacing the three constraints with new ones requiring that geodesic paths remain geodesic against metric variations. The instability problem is then naturally solved. Implications for the cosmological constant Λ are unchanged; the theory converges into EFE with nonzero Λ by inflation, but Λ varies on scales much larger than the present Hubble horizon. Then galaxies are formed only in small Λ regions, and the cosmological constant problem is solved by the anthropic argument. Because of the increased degrees of freedom in metric dynamics, the theory predicts new non-oscillatory modes of metric anisotropy generated by quantum fluctuation during inflation, and CMB B -mode polarization would be observed differently from the standard predictions by general relativity.

Demographic and temporal variations in immunity and condition of polar bears (Ursus maritimus) from the southern Beaufort Sea

USGS Publications Warehouse

Neuman-Lee, Lorin; Terletzky, Patricia; Atwood, Todd C.; Gese, Eric; Smith, Geoffrey; Greenfield, Sydney; Pettit, John; French, Susannah

2017-01-01

Assessing the health and condition of animals in their natural environment can be problematic. Many physiological metrics, including immunity, are highly influenced by specific context and recent events to which researchers may be unaware. Thus, using a multifaceted physiological approach and a context-specific analysis encompassing multiple time scales can be highly informative. Ecoimmunological tools in particular can provide important indications to the health of animals in the wild. We collected blood and hair samples from free-ranging polar bears (Ursus maritimus) in the southern Beaufort Sea and examined the influence of sex, age, and reproductive status on metrics of immunity, stress, and body condition during 2013–2015. We examined metrics of innate immunity (bactericidal ability and lysis) and stress (hair cortisol, reactive oxygen species, and oxidative barrier), in relation to indices of body condition considered to be short term (urea to creatinine ratio; UC ratio) and long term (storage energy and body mass index). We found the factors of sex, age, and reproductive status of the bear were critical for interpreting different physiological metrics. Additionally, the metrics of body condition were important predictors for stress indicators. Finally, many of these metrics differed between years, illustrating the need to examine populations on a longer time scale. Taken together, this study demonstrates the complex relationship between multiple facets of physiology and how interpretation requires us to examine individuals within a specific context.

Polarized and non-polarized leaf reflectances of Coleus blumei

NASA Technical Reports Server (NTRS)

Grant, Lois; Daughtry, C. S. T.; Vanderbilt, V. C.

1987-01-01

A polarization photometer has been used to measure the reflectance of three variegated portions of Coleus blumei, Benth. in five wavelength bands of the visible and near-infrared spectrum. The polarized component of the reflectance factor was found to be independent of wavelength, indicating that the polarized reflectance arises from the leaf surface. It is suggested that differences in the polarized component result from variations in surface features. The nonpolarized component of the reflectance factor is shown to be related to the internal leaf structure. The variation of the degree of polarization with wavelength was found to be greatest in the regions of the spectrum where absorption occurs.

Production of Highly Polarized Positrons Using Polarized Electrons at MeV Energies

DOE PAGES

Abbott, D.; Adderley, P.; Adeyemi, A.; ...

2016-05-27

The Polarized Electrons for Polarized Positrons experiment at the injector of the Continuous Electron Beam Accelerator Facility has demonstrated for the first time the efficient transfer of polarization from electrons to positrons produced by the polarized bremsstrahlung radiation induced by a polarized electron beam in a high-Z target. Positron polarization up to 82% have been measured for an initial electron beam momentum of 8.19~MeV/c, limited only by the electron beam polarization. We report that this technique extends polarized positron capabilities from GeV to MeV electron beams, and opens access to polarized positron beam physics to a wide community.

Polarization digital holographic microscopy using low-cost liquid crystal polarization rotators

NASA Astrophysics Data System (ADS)

Dovhaliuk, Rostyslav Yu

2018-02-01

Polarization imaging methods are actively used to study anisotropic objects. A number of methods and systems, such as imaging polarimeters, were proposed to measure the state of polarization of light that passed through the object. Digital holographic and interferometric approaches can be used to quantitatively measure both amplitude and phase of a wavefront. Using polarization modulation optics, the measurement capabilities of such interference-based systems can be extended to measure polarization-dependent parameters, such as phase retardation. Different kinds of polarization rotators can be used to alternate the polarization of a reference beam. Liquid crystals are used in a rapidly increasing number of different optoelectronic devices. Twisted nematic liquid crystals are widely used as amplitude modulators in electronic displays and light valves or shutter glass. Such devices are of particular interest for polarization imaging, as they can be used as polarization rotators, and due to large-scale manufacturing have relatively low cost. A simple Mach-Zehnder polarized holographic setup that uses modified shutter glass as a polarization rotator is demonstrated. The suggested approach is experimentally validated by measuring retardation of quarter-wave film.

Macrophage Polarization in Chronic Inflammatory Diseases: Killers or Builders?

PubMed Central

Baci, Denisa; Tremolati, Marco; Fanuli, Matteo; Farronato, Giampietro; Mortara, Lorenzo

2018-01-01

Macrophages are key cellular components of the innate immunity, acting as the main player in the first-line defence against the pathogens and modulating homeostatic and inflammatory responses. Plasticity is a major feature of macrophages resulting in extreme heterogeneity both in normal and in pathological conditions. Macrophages are not homogenous, and they are generally categorized into two broad but distinct subsets as either classically activated (M1) or alternatively activated (M2). However, macrophages represent a continuum of highly plastic effector cells, resembling a spectrum of diverse phenotype states. Induction of specific macrophage functions is closely related to the surrounding environment that acts as a relevant orchestrator of macrophage functions. This phenomenon, termed polarization, results from cell/cell, cell/molecule interaction, governing macrophage functionality within the hosting tissues. Here, we summarized relevant cellular and molecular mechanisms driving macrophage polarization in “distant” pathological conditions, such as cancer, type 2 diabetes, atherosclerosis, and periodontitis that share macrophage-driven inflammation as a key feature, playing their dual role as killers (M1-like) and/or builders (M2-like). We also dissect the physio/pathological consequences related to macrophage polarization within selected chronic inflammatory diseases, placing polarized macrophages as a relevant hallmark, putative biomarkers, and possible target for prevention/therapy. PMID:29507865

Quaternion Based Thermal Condition Monitoring System

NASA Astrophysics Data System (ADS)

Wong, Wai Kit; Loo, Chu Kiong; Lim, Way Soong; Tan, Poi Ngee

In this paper, we will propose a new and effective machine condition monitoring system using log-polar mapper, quaternion based thermal image correlator and max-product fuzzy neural network classifier. Two classification characteristics namely: peak to sidelobe ratio (PSR) and real to complex ratio of the discrete quaternion correlation output (p-value) are applied in the proposed machine condition monitoring system. Large PSR and p-value observe in a good match among correlation of the input thermal image with a particular reference image, while small PSR and p-value observe in a bad/not match among correlation of the input thermal image with a particular reference image. In simulation, we also discover that log-polar mapping actually help solving rotation and scaling invariant problems in quaternion based thermal image correlation. Beside that, log-polar mapping can have a two fold of data compression capability. Log-polar mapping can help smoother up the output correlation plane too, hence makes a better measurement way for PSR and p-values. Simulation results also show that the proposed system is an efficient machine condition monitoring system with accuracy more than 98%.

Polarity Control of Heteroepitaxial GaN Nanowires on Diamond.

PubMed

Hetzl, Martin; Kraut, Max; Hoffmann, Theresa; Stutzmann, Martin

2017-06-14

Group III-nitride materials such as GaN nanowires are characterized by a spontaneous polarization within the crystal. The sign of the resulting sheet charge at the top and bottom facet of a GaN nanowire is determined by the orientation of the wurtzite bilayer of the different atomic species, called N and Ga polarity. We investigate the polarity distribution of heteroepitaxial GaN nanowires on different substrates and demonstrate polarity control of GaN nanowires on diamond. Kelvin Probe Force Microscopy is used to determine the polarity of individual selective area-grown and self-assembled nanowires over a large scale. At standard growth conditions, mixed polarity occurs for selective GaN nanowires on various substrates, namely on silicon, on sapphire and on diamond. To obtain control over the growth orientation on diamond, the substrate surface is modified by nitrogen and oxygen plasma exposure prior to growth, and the growth parameters are adjusted simultaneously. We find that the surface chemistry and the substrate temperature are the decisive factors for obtaining control of up to 93% for both polarity types, whereas the growth mode, namely selective area or self-assembled growth, does not influence the polarity distribution significantly. The experimental results are discussed by a model based on the interfacial bonds between the GaN nanowires, the termination layer, and the substrate.

Dating Last Interglacial Coastal Systems Using New Feldspar Luminescence Technologies

NASA Astrophysics Data System (ADS)

Lamothe, M.

2017-12-01

The recent explosion in new luminescence dating technologies offers new opportunities to explore Quaternary marine coastal facies and landforms. However, tectonic and climatic processes controlling the development of Pleistocene coastal lithosomes are commonly obscured by their poorly constrained geological age. Luminescence dating of feldspar probes one order of magnitude deeper into geological time than radiocarbon and more than 5 times the current age range of quartz optically-stimulated luminescence, routinely used in luminescence dating. However, feldspar luminescence stimulated by infrared photons (eg IRSL) is hampered by anomalous fading. Successful correction methods developed by us over the last 15 years did produce sound chronologies but the fading-corrected ages carried large uncertainties. New approaches initiated by other laboratories, mainly in Europe, have isolated high temperature post-IRSL luminescence as this signal seems to be only slightly affected by fading. However, the gain in stability seems to be lessened due to bleachibility issues, generating age overestimations. We developed a novel protocol known as post-isothermal IRSL dating (Pit-IR) that focuses on a dual system of luminescence signals, probing low (50C) and medium (225C) temperature IRSL signals following isothermal treatments of various intensities. These protocols have been tested on Last interglacial coastal sediments in strikingly different GIA contexts along the Atlantic coastal areas of SE USA as well as from Morocco, Brazil and LIG sites in the Mediterranean basin. A systematic analysis of these results would suggest that a) falling-stages sequences are more commonly preserved as the OSL/IRSL ages are preferentially dating from the end of the MIS5e high stand and b) MIS5a marine sediments may be detectable away from areas generally thought to be affected by peripheral bulge collapse.

Polarization optics of the Brewster's dark patch visible on water surfaces versus solar height and sky conditions: theory, computer modeling, photography, and painting.

PubMed

Takács, Péter; Barta, András; Pye, David; Horváth, Gábor

2017-10-20

When the sun is near the horizon, a circular band with approximately vertically polarized skylight is formed at 90° from the sun, and this skylight is only weakly reflected from the region of the water surface around the Brewster's angle (53° from the nadir). Thus, at low solar heights under a clear sky, an extended dark patch is visible on the water surface when one looks toward the north or south quarter perpendicular to the solar vertical. In this work, we study the radiance distribution of this so-called Brewster's dark patch (BDP) in still water as functions of the solar height and sky conditions. We calculate the pattern of reflectivity R of a water surface for a clear sky and obtain from this idealized situation the shape of the BDP. From three full-sky polarimetric pictures taken about a clear, a partly cloudy, and an overcast sky, we determine the R pattern and compose from that synthetic color pictures showing how the radiance distribution of skylight reflected at the water surface and the BDPs would look under these sky conditions. We also present photographs taken without a linearly polarizing filter about the BDP. Finally, we show a 19th century painting on which a river is seen with a dark region of the water surface, which can be interpreted as an artistic illustration of the BDP.

Bandwidth broadening of a graphene-based circular polarization converter by phase compensation.

PubMed

Gao, Xi; Yang, Wanli; Cao, Weiping; Chen, Ming; Jiang, Yannan; Yu, Xinhua; Li, Haiou

2017-10-02

We present a broadband tunable circular polarization converter composed of a single graphene sheet patterned with butterfly-shaped holes, a dielectric spacer, and a 7-layer graphene ground plane. It can convert a linearly polarized wave into a circularly polarized wave in reflection mode. The polarization converter can be dynamically tuned by varying the Fermi energy of the single graphene sheet. Furthermore, the 7-layer graphene acting as a ground plane can modulate the phase of its reflected wave by controlling the Femi energy, which provides constructive interference condition at the surface of the single graphene sheet in a broad bandwidth and therefore significantly broadens the tunable bandwidth of the proposed polarization converter.

Dynamic Nuclear Polarization of 17O: Direct Polarization

PubMed Central

Michaelis, Vladimir K.; Corzilius, Björn; Smith, Albert A.; Griffin, Robert G.

2014-01-01

Dynamic nuclear polarization of 17O was studied using four different polarizing agents – the biradical TOTAPOL, and the monoradicals trityl and SA-BDPA, as well as a mixture of the latter two. Field profiles, DNP mechanisms and enhancements were measured to better understand and optimize directly polarizing this low-gamma quadrupolar nucleus using both mono- and bi-radical polarizing agents. Enhancements were recorded < 88 K and were > 100 using the trityl (OX063) radical and < 10 with the other polarizing agents. The > 10,000 fold savings in acquisition time enabled a series of biologically relevant small molecules to be studied with small sample sizes and the measurement of various quadrupolar parameters. The results are discussed with comparison to room temperature studies and GIPAW quantum chemical calculations. These experimental results illustrate the strength of high field DNP and the importance of radical selection for studying low-gamma nuclei. PMID:24195759

Dynamic nuclear polarization of 17O: direct polarization.

PubMed

Michaelis, Vladimir K; Corzilius, Björn; Smith, Albert A; Griffin, Robert G

2013-12-05

Dynamic nuclear polarization of (17)O was studied using four different polarizing agents: the biradical TOTAPOL and the monoradicals trityl and SA-BDPA, as well as a mixture of the latter two. Field profiles, DNP mechanisms, and enhancements were measured to better understand and optimize directly polarizing this low-gamma quadrupolar nucleus using both mono- and biradical polarizing agents. Enhancements were recorded at <88 K and were >100 using the trityl (OX063) radical and <10 with the other polarizing agents. The >10,000-fold savings in acquisition time enabled a series of biologically relevant small molecules to be studied with small sample sizes and the measurement of various quadrupolar parameters. The results are discussed with comparison to room temperature studies and GIPAW quantum chemical calculations. These experimental results illustrate the strength of high field DNP and the importance of radical selection for studying low-gamma nuclei.

Calibration of polarimetric radar systems with good polarization isolation

NASA Technical Reports Server (NTRS)

Sarabandi, Kamal; Ulaby, Fawwaz T.; Tassoudji, M. Ali

1990-01-01

A practical technique is proposed for calibrating single-antenna polarimetric radar systems using a metal sphere plus any second target with a strong cross-polarized radar cross section. This technique assumes perfect isolation between antenna ports. It is shown that all magnitudes and phases (relative to one of the like-polarized linear polarization configurations) of the radar transfer function can be calibrated without knowledge of the scattering matrix of the second target. Comparison of the values measured (using this calibration technique) for a tilted cylinder at X-band with theoretical values shows agreement within + or - 0.3 dB in magnitude and + or - 5 degrees in phase. The radar overall cross-polarization isolation was 25 dB. The technique is particularly useful for calibrating a radar under field conditions, because it does not require the careful alignment of calibration targets.

Polarization effects in cutaneous autofluorescent spectra

NASA Astrophysics Data System (ADS)

Borisova, E.; Angelova, L.; Jeliazkova, Al.; Genova, Ts.; Pavlova, E.; Troyanova, P.; Avramov, L.

2014-05-01

Used polarized light for fluorescence excitation one could obtain response related to the anisotropy features of extracellular matrix. The fluorophore anisotropy is attenuated during lesions' growth and level of such decrease could be correlated with the stage of tumor development. Our preliminary investigations are based on in vivo point-by-point measurements of excitation-emission matrices (EEM) from healthy volunteers skin on different ages and from different anatomical places using linear polarizer and analyzer for excitation and emission light detected. Measurements were made using spectrofluorimeter FluoroLog 3 (HORIBA Jobin Yvon, France) with fiber-optic probe in steady-state regime using excitation in the region of 280-440 nm. Three different situations were evaluated and corresponding excitation-emission matrices were developed - with parallel and perpendicular positions for linear polarizer and analyzer, and without polarization of excitation and fluorescence light detected from a forearm skin surface. The fluorescence spectra obtained reveal differences in spectral intensity, related to general attenuation, due to filtering effects of used polarizer/analyzer couple. Significant spectral shape changes were observed for the complex autofluorescence signal detected, which correlated with collagen and protein cross-links fluorescence, that could be addressed to the tissue extracellular matrix and general condition of the skin investigated, due to morphological destruction during lesions' growth. A correlation between volunteers' age and the fluorescence spectra detected was observed during our measurements. Our next step is to increase developed initial database and to evaluate all sources of intrinsic fluorescent polarization effects and found if they are significantly altered from normal skin to cancerous state of the tissue, this way to develop a non-invasive diagnostic tool for dermatological practice.

Separation of polar gases from nonpolar gases

DOEpatents

Kulprathipanja, S.

1986-08-19

The separation of polar gases from nonpolar gases may be effected by passing a mixture of nonpolar gases over the face of a multicomponent membrane at separation conditions. The multicomponent membrane which is used to effect the separation will comprise a mixture of a glycol plasticizer having a molecular weight of from about 200 to about 600 and an organic polymer cast on a porous support. The porous support is pretreated prior to casting of the mixture thereon by contact with a polyhydric alcohol whereby the pores of the support are altered, thus adding to the increased permeability of the polar gas.

Glacial-interglacial variations in sediment organic carbon accumulation and benthic foraminiferal assemblages on the Bermuda Rise (ODP Site 1063) during MIS 13 to 10

NASA Astrophysics Data System (ADS)

Poli, Maria Serena; Meyers, Philip A.; Thunell, Robert C.; Capodivacca, Marco

2012-09-01

We have determined organic carbon concentrations and isotopic compositions and benthic foraminiferal assemblages in sediments deposited between ˜500 and 340 ka at ODP Site 1063 on the northeastern flank of the Bermuda Rise. This time interval includes Marine Isotope Stage (MIS) 11, a particularly warm and long interglacial that was similar to today, and MIS 12, one of the most severe glacials of the last 600 kyr. During MIS 11.3, the peak of interglacial warming, organic carbon accumulation rates are low and benthic foraminiferal assemblages are dominated by Nuttallides umbonifera, a species indicative of oligotrophic environments. Higher accumulation rates during MIS 12 and 10 correspond with elevated sedimentation rates (33-36 cm/kyr). This pattern implies a combination of enhanced delivery and improved preservation of sediment organic matter during these glacial times. Organic δ13C values are less negative during MIS 12 and MIS 10 than during MIS 11, which is consistent with greater glacial-stage marine productivity. High relative abundances ofOridorsalis umbonatus during glacial intervals probably records a low but sustained flux of highly degraded organic material. Large, recurrent fluctuations in the abundance of Epistominella exiguaat the beginnings of the MIS 12 and MIS 10 glaciations suggest a marked increase in local phytoplankton blooms at these times and consequent delivery of phytodetritus to the seafloor. The most likely causes of these variations are changes in the position and strength of the Gulf Stream and its associated cold-ring eddies, combined with increased advection of terrigenous sediments from northerly locations during glacial lowstands.

Middle Pleistocene interglacial Thames--Medway deposits at Clacton-on-Sea, England: Reconsideration of the biostratigraphical and environmental context of the type Clactonian Palaeolithic industry

NASA Astrophysics Data System (ADS)

Bridgland, David R.; Field, Michael H.; Holmes, Jonathan A.; McNabb, John; Preece, Richard C.; Selby, Ian; Wymer, John J.; Boreham, Steve; Irving, Brian G.; Parfitt, Simon A.; Stuart, Anthony J.

In 1987 an archaeological investigation was undertaken during redevelopment of the erstwhile Butlin's holiday camp at Clacton-on-Sea, on the grounds that the Middle Pleistocene Clacton Channel Deposits, containing the type-Clactonian Palaeolithic industry, were known to extend beneath the site. Excavations for a storm-drain allowed sampling at points along a longitudinal traverse of the main Clacton Channel. Analysis of these samples has provided new palaeontological information, including data pertaining to the rise in relative sea level during the interglacial represented. Systematic studies of molluscs and ostracods, the latter undertaken at Clacton for the first time, have been particularly valuable. Information from the Butlin's site supplements evidence previously gathered from the West Cliff section and from other localities at Clacton. The calcareous clay ('marl') that underlies the Clacton golf course extends beneath Butlin's, where it was found to be part of the Freshwater Beds, not the Estuarine Beds, as hitherto supposed. The Clacton Estuarine Beds, restricted to the eastern end of the site, have their base just below 2 m O.D., implying that their superposition upon the Clacton Freshwater Beds occurred when relative sea level in this area was close to present ordnance datum. Correlation of the Clacton Channel Deposits with the interglacial immediately following the Anglian/Elsterian Stage appears secure; equivalence with Oxygen Isotope Stage 11 of the oceanic sequence is most probable. A borehole survey and subsequent excavation revealed a Holocene sequence of unlithified tufa and organic sediments beneath part of the site.

A new method for geochemical characterization of atmospheric mineral dust from polar ice cores: preliminary results from Talos Dome ice core (East Antarctica, Pacific-Ross Sea sector)

NASA Astrophysics Data System (ADS)

Baccolo, Giovanni; Delmonte, Barbara; Clemenza, Massimiliano; Previtali, Ezio; Maggi, Valter

2015-04-01

Assessing the elemental composition of atmospheric dust entrapped in polar ice cores is important for the identification of the potential dust sources and thus for the reconstruction of past atmospheric circulation, at local, regional and global scale. Accurate determination of major and trace elements in the insoluble fraction of dust extracted from ice cores is also useful to better understand some geochemical and biogeochemical mechanisms which are linked with the climate system. The extremely reduced concentration of dust in polar ice (typical Antarctic concentrations during interglacials are in the range of 10 ppb), the limited availability of such samples and the high risk of contamination make these analyses a challenge. A new method based on low background Instrumental Neutron Activation Analysis (INAA) was specifically developed for this kind of samples. The method allows the determination of the concentration of up to 35 elements in extremely reduced dust samples (20-30 μg). These elements span from major to trace and ultra-trace elements. Preliminary results from TALDICE (TALos Dome Ice CorE, East Antarctica, Pacific-Ross Sea Sector) ice core are presented along with results from potential source areas in Victoria Land. A set of 5 samples from Talos Dome, corresponding to the last termination, MIS3, MIS4 and MIS6 were prepared and analyzed by INAA.

Visualizing molecular polar order in tissues via electromechanical coupling

PubMed Central

Denning, Denise; Alilat, Sofiane; Habelitz, Stefan; Fertala, Andrzej; Rodriguez, Brian J.

2015-01-01

Electron microscopy (EM) and atomic force microscopy (AFM) techniques have long been used to characterize collagen fibril ordering and alignment in connective tissues. These techniques, however, are unable to map collagen fibril polarity, i.e., the polar orientation that is directed from the amine to the carboxyl termini. Using a voltage modulated AFM-based technique called piezoresponse force microscopy (PFM), we show it is possible to visualize both the alignment of collagen fibrils within a tissue and the polar orientation of the fibrils with minimal sample preparation. We demonstrate the technique on rat tail tendon and porcine eye tissues in ambient conditions. In each sample, fibrils are arranged into domains whereby neighboring domains exhibit opposite polarizations, which in some cases extend to the individual fibrillar level. Uniform polarity has not been observed in any of the tissues studied. Evidence of anti-parallel ordering of the amine to carboxyl polarity in bundles of fibrils or in individual fibrils is found in all tissues, which has relevance for understanding mechanical and biofunctional properties and the formation of connective tissues. The technique can be applied to any biological material containing piezoelectric biopolymers or polysaccharides. PMID:22985991

Normalized Polarization Ratios for the Analysis of Cell Polarity

PubMed Central

Shimoni, Raz; Pham, Kim; Yassin, Mohammed; Ludford-Menting, Mandy J.; Gu, Min; Russell, Sarah M.

2014-01-01

The quantification and analysis of molecular localization in living cells is increasingly important for elucidating biological pathways, and new methods are rapidly emerging. The quantification of cell polarity has generated much interest recently, and ratiometric analysis of fluorescence microscopy images provides one means to quantify cell polarity. However, detection of fluorescence, and the ratiometric measurement, is likely to be sensitive to acquisition settings and image processing parameters. Using imaging of EGFP-expressing cells and computer simulations of variations in fluorescence ratios, we characterized the dependence of ratiometric measurements on processing parameters. This analysis showed that image settings alter polarization measurements; and that clustered localization is more susceptible to artifacts than homogeneous localization. To correct for such inconsistencies, we developed and validated a method for choosing the most appropriate analysis settings, and for incorporating internal controls to ensure fidelity of polarity measurements. This approach is applicable to testing polarity in all cells where the axis of polarity is known. PMID:24963926

Lunar true polar wander inferred from polar hydrogen.

PubMed

Siegler, M A; Miller, R S; Keane, J T; Laneuville, M; Paige, D A; Matsuyama, I; Lawrence, D J; Crotts, A; Poston, M J

2016-03-24

The earliest dynamic and thermal history of the Moon is not well understood. The hydrogen content of deposits near the lunar poles may yield insight into this history, because these deposits (which are probably composed of water ice) survive only if they remain in permanent shadow. If the orientation of the Moon has changed, then the locations of the shadowed regions will also have changed. The polar hydrogen deposits have been mapped by orbiting neutron spectrometers, and their observed spatial distribution does not match the expected distribution of water ice inferred from present-day lunar temperatures. This finding is in contrast to the distribution of volatiles observed in similar thermal environments at Mercury's poles. Here we show that polar hydrogen preserves evidence that the spin axis of the Moon has shifted: the hydrogen deposits are antipodal and displaced equally from each pole along opposite longitudes. From the direction and magnitude of the inferred reorientation, and from analysis of the moments of inertia of the Moon, we hypothesize that this change in the spin axis, known as true polar wander, was caused by a low-density thermal anomaly beneath the Procellarum region. Radiogenic heating within this region resulted in the bulk of lunar mare volcanism and altered the density structure of the Moon, changing its moments of inertia. This resulted in true polar wander consistent with the observed remnant polar hydrogen. This thermal anomaly still exists and, in part, controls the current orientation of the Moon. The Procellarum region was most geologically active early in lunar history, which implies that polar wander initiated billions of years ago and that a large portion of the measured polar hydrogen is ancient, recording early delivery of water to the inner Solar System. Our hypothesis provides an explanation for the antipodal distribution of lunar polar hydrogen, and connects polar volatiles to the geologic and geophysical evolution of the Moon

Mechanism and energetics of O and O{sub 2} adsorption on polar and non-polar ZnO surfaces

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

Gorai, Prashun; Seebauer, Edmund G.; Ertekin, Elif, E-mail: ertekin@illinois.edu

2016-05-14

Polar surfaces of semiconducting metal oxides can exhibit structures and chemical reactivities that are distinct from their non-polar surfaces. Using first-principles calculations, we examine O adatom and O{sub 2} molecule adsorption on 8 different known ZnO reconstructions including Zn-terminated (Zn–ZnO) and O-terminated (O–ZnO) polar surfaces, and non-polar surfaces. We find that adsorption tendencies are largely governed by the thermodynamic environment, but exhibit variations due to the different surface chemistries of various reconstructions. The Zn–ZnO surface reconstructions which appear under O-rich and H-poor environments are found to be most amenable to O and O{sub 2} adsorption. We attribute this to themore » fact that on Zn–ZnO, the O-rich environments that promote O adsorption also simultaneously favor reconstructions that involve adsorbed O species. On these Zn–ZnO surfaces, O{sub 2} dissociatively adsorbs to form O adatoms. By contrast, on O–ZnO surfaces, the O-rich conditions required for O or O{sub 2} adsorption tend to promote reconstructions involving adsorbed H species, making further O species adsorption more difficult. These insights about O{sub 2} adsorption on ZnO surfaces suggest possible design rules to understand the adsorption properties of semiconductor polar surfaces.« less

Polar Bears

USGS Publications Warehouse

Amstrup, Steven C.; Douglas, David C.; Reynolds, Patricia E.; Rhode, E.B.

2002-01-01

Polar bears (Ursus maritimus) are hunted throughout most of their range. In addition to hunting polar bears of the Beaufort Sea region are exposed to mineral and petroleum extraction and related human activities such as shipping road-building, and seismic testing (Stirling 1990).Little was known at the start of this project about how polar bears move about in their environment, and although it was understood that many bears travel across political borders, the boundaries of populations had not been delineated (Amstrup 1986, Amstrup et al. 1986, Amstrup and DeMaster 1988, Garner et al. 1994, Amstrup 1995, Amstrup et al. 1995, Amstrup 2000).As human populations increase and demands for polar bears and other arctic resources escalate, managers must know the sizes and distributions of the polar bear populations. Resource managers also need reliable estimates of breeding rates, reproductive intervals, litter sizes, and survival of young and adults.Our objectives for this research were 1) to determine the seasonal and annual movements of polar bears in the Beaufort Sea, 2) to define the boundaries of the population(s) using this region, 3) to determine the size and status of the Beaufort Sea polar bear population, and 4) to establish reproduction and survival rates (Amstrup 2000).

Low-Energy Electron Effects on the Polar Wind Observed by the POLAR Spacecraft

NASA Technical Reports Server (NTRS)

Horwitz, J. L.; Su, Y.-J.; Dors, E. E.; Moore, Thomas E.; Giles, Barbara L.; Chandler, Michael O.; Craven, Paul D.; Chang, S.-W.; Scudder, J.

1998-01-01

Large ion outflow velocity variation at POLAR apogee have been observed. The observed H+ flow velocities were in the range of 23-110 km/s and 0+ flow velocities were in the range of 5-25 km/s. These velocity ranges lie between those predicted by simulations of the photoelectron-driven polar wind and "baseline" polar wind. The electric current contributions of the photoelectrons and polar rain are expected to control the size and altitude of an electric potential drop which accelerates the polar wind at relatively high altitudes. In this presentation, we compare polar wind characteristics observed near 5000 km and 8 RE altitudes by the Thermal Ion Dynamics Experiment (TIDE) with measurements of low-energy electrons sampled by HYDRA, both from the POLAR spacecraft, to examine possible effects of the polar rain and photoelectrons on the polar wind. Both correlations and anti-correlations are found between the polar wind velocities and the polar rain fluxes at POLAR apogee during different polar cap crossings. Also, the low-altitude upward/downward photoelectron spectra are used to estimates the potential drops above the spacecraft. We interpret these observations in terms of the effects that both photoelectrons and polar rain may have on the electric potential and polar wind acceleration along polar cap magnetic field lines.

Partially coherent polarized atmospheric transmission characteristics and application technology research

NASA Astrophysics Data System (ADS)

Fu, Qiang; Gao, Duorui; Liu, Zhi; Chen, Chunyi; Lou, Yan; Jiang, Huilin

2014-11-01

Based on partially coherent polarized light transmission characteristics of the atmosphere, an intensity expression of completely coherent flashing light is derived from Andrews scale modulation method. According to the generalized Huygens-Fresnel principle and Rytov theory, the phase fluctuation structure function is obtained on condition that the refractive index profile in the atmosphere meet Von Karman spectrum, then get the arrival Angle fluctuation variance. Through the RMS beam width of gaussian beams in turbulent atmosphere, deviation angle formula of fully coherent gaussian beams in turbulence atmosphere is attained, then get the RMS beam width of partially coherent and derivation angle expression of GSM beam in turbulent atmosphere. Combined with transmission properties of radial polarized laser beam, cross spectral density matrix of partially coherent radially polarized light can be gained by using generalized huygens-fresnel principle. And light intensity and polarization after transmission can be known according to the unity of coherence and polarization theory. On the basis of the analysis model and numerical simulation, the simulation results show that: the light spot caused by atmospheric turbulence of partially coherent polarization will be superior to completely polarized light.Taking advantage of this feature, designed a new wireless suppression technology of atmospheric turbulence, that is the optimization criterion of initial degree of coherent light beam. The optimal initial degree of coherent light beam will change along with the change of atmospheric turbulence conditions,make control the beam's initial degree of coherence to realize the initial degree of coherence of light beam in real time and dynamic control. A spatial phase screen before emission aperture of fully coherent light is to generate the partially coherent light, liquid crystal spatial light modulator is is a preferable way to realize the dynamic random phase. Finally look

Why do horseflies need polarization vision for host detection? Polarization helps tabanid flies to select sunlit dark host animals from the dark patches of the visual environment

PubMed Central

Szörényi, Tamás; Pereszlényi, Ádám; Gerics, Balázs; Hegedüs, Ramón; Barta, András

2017-01-01

Horseflies (Tabanidae) are polarotactic, being attracted to linearly polarized light when searching for water or host animals. Although it is well known that horseflies prefer sunlit dark and strongly polarizing hosts, the reason for this preference is unknown. According to our hypothesis, horseflies use their polarization sensitivity to look for targets with higher degrees of polarization in their optical environment, which as a result facilitates detection of sunlit dark host animals. In this work, we tested this hypothesis. Using imaging polarimetry, we measured the reflection–polarization patterns of a dark host model and a living black cow under various illumination conditions and with different vegetation backgrounds. We focused on the intensity and degree of polarization of light originating from dark patches of vegetation and the dark model/cow. We compared the chances of successful host selection based on either intensity or degree of polarization of the target and the combination of these two parameters. We show that the use of polarization information considerably increases the effectiveness of visual detection of dark host animals even in front of sunny–shady–patchy vegetation. Differentiation between a weakly polarizing, shady (dark) vegetation region and a sunlit, highly polarizing dark host animal increases the efficiency of host search by horseflies. PMID:29291065

Why do horseflies need polarization vision for host detection? Polarization helps tabanid flies to select sunlit dark host animals from the dark patches of the visual environment.

PubMed

Horváth, Gábor; Szörényi, Tamás; Pereszlényi, Ádám; Gerics, Balázs; Hegedüs, Ramón; Barta, András; Åkesson, Susanne

2017-11-01

Horseflies (Tabanidae) are polarotactic, being attracted to linearly polarized light when searching for water or host animals. Although it is well known that horseflies prefer sunlit dark and strongly polarizing hosts, the reason for this preference is unknown. According to our hypothesis, horseflies use their polarization sensitivity to look for targets with higher degrees of polarization in their optical environment, which as a result facilitates detection of sunlit dark host animals. In this work, we tested this hypothesis. Using imaging polarimetry, we measured the reflection-polarization patterns of a dark host model and a living black cow under various illumination conditions and with different vegetation backgrounds. We focused on the intensity and degree of polarization of light originating from dark patches of vegetation and the dark model/cow. We compared the chances of successful host selection based on either intensity or degree of polarization of the target and the combination of these two parameters. We show that the use of polarization information considerably increases the effectiveness of visual detection of dark host animals even in front of sunny-shady-patchy vegetation. Differentiation between a weakly polarizing, shady (dark) vegetation region and a sunlit, highly polarizing dark host animal increases the efficiency of host search by horseflies.

Conditions for the formation of prominences as inferred from optical observations

NASA Technical Reports Server (NTRS)

Martin, Sara F.

1990-01-01

It is suggested that three conditions, if dynamically maintained for a sufficient period of time, will result in the formation of a solar prominence. These conditions are the presence of a coronal arcade that connects the magnetic fields on opposite sides of a prominence; the existence of a long-term (hours to days) converging flow of small patches of opposite-polarity magnetic flux toward a common-polarity inversion zone; and the cancellation of encountered patches of magnetic flux of opposite polarity at a photospheric polarity inversion boundary.

Study on Low Illumination Simultaneous Polarization Image Registration Based on Improved SURF Algorithm

NASA Astrophysics Data System (ADS)

Zhang, Wanjun; Yang, Xu

2017-12-01

Registration of simultaneous polarization images is the premise of subsequent image fusion operations. However, in the process of shooting all-weather, the polarized camera exposure time need to be kept unchanged, sometimes polarization images under low illumination conditions due to too dark result in SURF algorithm can not extract feature points, thus unable to complete the registration, therefore this paper proposes an improved SURF algorithm. Firstly, the luminance operator is used to improve overall brightness of low illumination image, and then create integral image, using Hession matrix to extract the points of interest to get the main direction of characteristic points, calculate Haar wavelet response in X and Y directions to get the SURF descriptor information, then use the RANSAC function to make precise matching, the function can eliminate wrong matching points and improve accuracy rate. And finally resume the brightness of the polarized image after registration, the effect of the polarized image is not affected. Results show that the improved SURF algorithm can be applied well under low illumination conditions.

Polarization of Narrowband VLF Transmitter Signals as an Ionospheric Diagnostic

NASA Astrophysics Data System (ADS)

Gross, N. C.; Cohen, M. B.; Said, R. K.; Gołkowski, M.

2018-01-01

Very low frequency (VLF, 3-30 kHz) transmitter remote sensing has long been used as a simple yet useful diagnostic for the D region ionosphere (60-90 km). All it requires is a VLF radio receiver that records the amplitude and/or phase of a beacon signal as a function of time. During both ambient and disturbed conditions, the received signal can be compared to predictions from a theoretical model to infer ionospheric waveguide properties like electron density. Amplitude and phase have in most cases been analyzed each as individual data streams, often only the amplitude is used. Scattered field formulation combines amplitude and phase effectively, but does not address how to combine two magnetic field components. We present polarization ellipse analysis of VLF transmitter signals using two horizontal components of the magnetic field. The shape of the polarization ellipse is unchanged as the source phase varies, which circumvents a significant problem where VLF transmitters have an unknown source phase. A synchronized two-channel MSK demodulation algorithm is introduced to mitigate 90° ambiguity in the phase difference between the horizontal magnetic field components. Additionally, the synchronized demodulation improves phase measurements during low-SNR conditions. Using the polarization ellipse formulation, we take a new look at diurnal VLF transmitter variations, ambient conditions, and ionospheric disturbances from solar flares, lightning-ionospheric heating, and lightning-induced electron precipitation, and find differing signatures in the polarization ellipse.

Convection flow structure in the central polar cap

NASA Astrophysics Data System (ADS)

Bristow, W. A.

2017-12-01

A previous study of spatially averaged flow velocity in the central polar cap [Bristow et al., 2015] observed under steady IMF conditions found that it was extremely rare for the average to exceed 850 m/s (less than 0.2 % of the time). Anecdotally, however it is not uncommon to observe line-of-sight velocities in excess of 100 m/s in the McMurdo radar field of view directly over the magnetic pole. This discrepancy motivated this study, which examines the conditions under which high-velocity flows are observed at latitudes greater than 80° magnetic latitude. It was found that highly structured flows are common in the central polar cap, which leads to the flow within regions to have significant deviation from the average. In addition, the high-speed flow regions are usually directed away from the earth-sun line. No specific set of driving conditions was identified to be associated with high-speed flows. The study did conclude that 1)Polar cap velocities are generally highly structured. 2)Flow patterns typically illustrate narrow channels, vortical flow regions, and propagating features. 3) Persistent waves are a regular occurrence. 3)Features are observed to propagate from day side to night side, and from night side to day side.. 4)Convection often exhibits significant difference between the two hemispheres. And 5)About 10% of the time the velocity somewhere in the cap exceeds 1 Km/s The presentation will conclude with a discussion of the physical reasons for the flow structure. Bristow, W. A., E. Amata, J. Spaleta, and M. F. Marcucci (2015), Observations of the relationship between ionospheric central polar cap and dayside throat convection velocities, and solar wind/IMF driving, J. Geophys. Res. Space Physics, 120, doi:10.1002/2015JA021199.

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.

Resveratrol regulates microglia M1/M2 polarization via PGC-1α in conditions of neuroinflammatory injury.

PubMed

Yang, Xiaodong; Xu, Shaoqing; Qian, Yiwei; Xiao, Qin

2017-08-01

Microglia are the primary cells that exert immune function in the central nervous system (CNS), and accumulating evidence suggests that microglia act as key players in the initiation of neurodegenerative diseases. It is now well recognized that microglia have functional plasticity and dual phenotypes, proinflammatory M1 and anti-inflammatory M2 phenotypes. Inhibiting the M1 phenotype while stimulating the M2 phenotype has been suggested as a potential therapeutic approach for the treatment of neuroinflammation-related diseases. Resveratrol has been demonstrated to exert anti-inflammatory effects by suppressing M1 microglia activation. However, the role of resveratrol in regulating microglia polarization and the molecular mechanisms involved have not been fully clarified. In this study, we tested whether resveratrol could suppress microglia activation by promoting microglia polarization toward the M2 phenotype via PGC-1α by measuring M1 and M2 markers in vitro and in vivo. Our study demonstrated that resveratrol reduced inflammatory damage and promoted microglia polarization to the M2 phenotype in LPS-induced neuroinflammation. In addition, resveratrol ameliorated LPS-induced sickness behavior in mice. The promoting effects of resveratrol on M2 polarization were attenuated by knocking down PGC-1α. PGC-1α not only suppressed LPS-evoked M1 marker expression by inhibition of NF-κB activity but also increased M2 marker expression by coactivation of the STAT6 and STAT3 pathways. We propose that overexpression PGC-1α by resveratrol could be a potential therapeutic approach to suppress neuroinflammation by regulating microglia polarization. Copyright © 2017 Elsevier Inc. All rights reserved.

Reconstruction of surface water conditions in the central region of the Okhotsk Sea during the last 180 kyrs

NASA Astrophysics Data System (ADS)

Khim, Boo-Keun; Sakamoto, Tatsuhiko; Harada, Naomi

2012-02-01

Core GC9A, a 6.7 m long gravity core collected from the central region of the Okhotsk Sea during Cruise YK0712 on R/V Yokosuka (JAMSTEC), was used to reconstruct the changes in surface water conditions by measuring biogenic components (biogenic opal, CaCO3, total organic carbon and δ15N of sediment organic matter) of sediment samples. The age of Core GC9A was determined indirectly by graphic correlation comparing the b* (psychometric yellow-blue chromaticness) values with those of well-dated Core MD01-2415, with complement to the tephra layer (K3; 50 ka). The bottom age of Core GC9A was estimated to be about 180 kyr; therefore it provides the history of surface water conditions from MIS 1 to MIS 6. The biogenic opal, CaCO3, and TOC contents were high during the interglacial periods as expected, indicating enhanced surface water production under warm climatic conditions. This condition resulted from sufficient nutrient supply to the surface waters by active vertical mixing, which was validated by low δ15N values of the sediment organic matter. In contrast, surface water productivity was depressed during the colder glacial periods, probably due to the expanded sea-ice distribution and limited nutrient supply. However, the glacial sediments had moderately high δ15N values, indicating enhanced nitrate utilization resulting from the limited nutrient supply caused by strong stratification of the surface water. High δ15N values were also observed during the deglaciation, which was attributed to the increased nitrate utilization during enhanced surface water productivity. However, the low δ15N values during the glacial and deglacial periods may be attributed to the increased supply of terrestrial organic matter. Diatom production was primarily responsible for surface water paleoproductivity during the interglacial periods rather than coccolithophores. However, the succession of glacial to early deglacial coccolithophore production and late deglacial to interglacial

The Snowmastodon Project: A view of the Last Interglacial Period from high in the Colorado Rockies

USGS Publications Warehouse

Pigati, Jeffery S.

2015-01-01

In North America, terrestrial records of biodiversity and climate change that span the Last Interglacial Period [or Marine Oxygen Isotope Stage (MIS) 5] are rare. In 2010-11, construction at Ziegler Reservoir near Snowmass Village, Colorado revealed a lacustrine/wetland sedimentary sequence that preserved evidence of past plant communities between ~140 and 55 ka, including all of MIS 5. At an elevation of 2705 m, the Ziegler Reservoir fossil site (ZRFS) also contained thousands of well-preserved bones and teeth of Pleistocene megafauna, including mastodons, mammoths, ground sloths, horses, camels, deer, bison, black bear, coyotes, and bighorn sheep. In addition, the site contained more than 26,000 bones from at least 30 species of small animals, including salamanders, otters, muskrats, minks, rabbits, beavers, frogs, lizards, snakes, fish, and birds. The combination of macro- and micro-vertebrates, invertebrates, terrestrial and aquatic plant macrofossils, a detailed pollen record, and a robust, directly dated stratigraphic framework, shows that high-elevation ecosystems in the Rocky Mountains of Colorado are climatically sensitive and varied dramatically throughout MIS 5.

Connecting Polar Literature with Contemporary Research

NASA Astrophysics Data System (ADS)

Pfirman, S.; Bell, R.; Fowler, C.

2006-12-01

The public is fascinated with polar research, especially when it is linked with exploration, discovery, adventure, isolation, self-reliance, hardship, and exotic landscapes and biota. A powerful way to engage the public in appreciating current research is to link it with accounts of historical expeditions. We have been doing this at Barnard College, Columbia University, since 2003 through "Exploring the Poles," a First Year Seminar. The class investigates polar exploration at the turn of the last century by reading "Farthest North" by Nansen about his adventure with the Fram, "The Last Place on Earth" by Huntford about Scott and Amundsen's race to the South Pole, and "Endurance" by Lansing about Shackleton's journey. To bring polar conditions home for the students, they are assigned to expedition teams for specific years and the fates of the student "expeditions" are based on the actual environmental conditions as well as their own decisions. For example, in the Arctic, student teams navigate satellite images of coastal ice and then freeze their ships into the sea ice north of Siberia, where they then drift with the ice across the pole, re-creating the transit of the Fram. Because the conditions are based on actual data, natural variability causes different outcomes for different years, creating an element of suspense. Fates of the teams vary tremendously: some teams emerge safely as Nansen did at Fram Strait or reach Elephant Island as happened with Shackleton, while others nearly become hopelessly lost in the Arctic Beaufort Gyre or drift out to sea into the Antarctic Circumpolar Current. Interweaving history, science, and stories of past and present expeditions provides a meaningful connection with the otherwise remote polar regions. Evaluation shows that combining historical texts with current data and simulations is an extremely powerful way of engaging non-scientists in science, and explaining the role of science and the environment in decision- making

Late-Quaternary changes of biogenic fluxes in the pacific sector of the Southern Ocean

NASA Astrophysics Data System (ADS)

Giglio, F.; Langone, L.; Capotondi, L.; Morigi, C.; Focaccia, P.; Frignani, M.; Ravaioli, M.

2003-04-01

During the last decade the research project BIOSESO of the Italian National Research Program for Antarctica (PNRA) has collected 13 gravity cores and 3 box-cores along a N-S transect at about 175^oE in the Southern Ocean. In this presentation we discuss the results from 6 sediment cores sampled between 62^oS and 71^oS. This area embraces the Polar Front and the Marginal Ice Zone. The data set includes the contents of organic carbon, biogenic silica, CaCO_3 and some metals (Ba, Al, Fe, Mn) involved in the biogeochemical cycles. Chronologies were based on 230Thex profiles and the boundaries of the isotope stages were set assuming that biological productivity was enhanced during periods of less ice cover. Then , 230Thex, organic carbon, biogenic silica and biogenic Ba distributions were compared to the glacial-interglacial stage boundaries and corresponding ages of the δ18O record of Martinson et al. (1987). At the sampling sites sediment accumulation rates range between 0.2 to 3.8 cm ka-1. The higher values characterize the interglacial stages and the southern stations. Processes of sediment redistribution at sea bottom were enlightened by a comparison of measured and expected fluxes of 230Thex . The Polar Front zone is characterized by winnowing, whereas sediments along the continental slope of the Ross Sea are mainly subject to focussing processes. The environmental factors that drive changes of biogenic particle fluxes during glacial-interglacial transitions have been investigated.

Applications of remanent supermirror polarizers

NASA Astrophysics Data System (ADS)

Böni, P.; Clemens, D.; Kumar, M. Senthil; Pappas, C.

1999-06-01

Recent developments in sputtering techniques allow the fabrication of multilayers with a high degree of perfection over large areas. We show, that using reactive sputtering, it is possible to adjust the index of refraction for neutrons, ni, of the individual layers. This property is particularly important for polarizing mirrors, where nnm for the non-magnetic layers can be matched to nm of the magnetic layers such that neutrons for one spin-eigenstate are not reflected by the coating, whereas the reflectivity is high for the other spin-eigenstate. In addition, by using anisotropic sputtering conditions it is possible to orient the easy axis of magnetization within the plane of the mirrors in any particular direction resulting in a simultaneous appearance of a pronounced remanence and coercivity. Remanent polarizers can be used as broad band spin selectors at continuous and in particular at pulsed neutron sources thus eliminating the need of spin flippers, whose performance depends on the wavelength of the neutrons and is often strongly influenced by stray magnetic fields from the sample environment. The possibility to operate remanent supermirrors in arbitrary small fields leads to attractive applications of polarizing devices in low field environments such as they occur in neutron-spin-echo or in spin selective neutron guides. We present applications, where several tasks like polarizing, focusing and spin selection are performed in one single device thus reducing the problem of phase space matching between different neutron optical components.

Polarization-sensitive color in butterfly scales: polarization conversion from ridges with reflecting elements.

PubMed

Zhang, Ke; Tang, Yiwen; Meng, Jinsong; Wang, Ge; Zhou, Han; Fan, Tongxiang; Zhang, Di

2014-11-03

Polarization-sensitive color originates from polarization-dependent reflection or transmission, exhibiting abundant light information, including intensity, spectral distribution, and polarization. A wide range of butterflies are physiologically sensitive to polarized light, but the origins of polarized signal have not been fully understood. Here we systematically investigate the colorful scales of six species of butterfly to reveal the physical origins of polarization-sensitive color. Microscopic optical images under crossed polarizers exhibit their polarization-sensitive characteristic, and micro-structural characterizations clarify their structural commonality. In the case of the structural scales that have deep ridges, the polarization-sensitive color related with scale azimuth is remarkable. Periodic ridges lead to the anisotropic effective refractive indices in the parallel and perpendicular grating orientations, which achieves form-birefringence, resulting in the phase difference of two different component polarized lights. Simulated results show that ridge structures with reflecting elements reflect and rotate the incident p-polarized light into s-polarized light. The dimensional parameters and shapes of grating greatly affect the polarization conversion process, and the triangular deep grating extends the outstanding polarization conversion effect from the sub-wavelength period to the period comparable to visible light wavelength. The parameters of ridge structures in butterfly scales have been optimized to fulfill the polarization-dependent reflection for secret communication. The structural and physical origin of polarization conversion provides a more comprehensive perspective on the creation of polarization-sensitive color in butterfly wing scales. These findings show great potential in anti-counterfeiting technology and advanced optical material design.

Changes in aerobic performance, body composition, and physical activity in polar explorers during a year-long stay at the polar station in the Arctic

NASA Astrophysics Data System (ADS)

Maciejczyk, Marcin; Araźny, Andrzej; Opyrchał, Marta

2017-04-01

The aim of this study was to evaluate changes in physical activity, aerobic performance, and body composition in polar explorers during a 1-year stay at the polar station. The study group consisted of 10 people, including 8 men and 2 women. Aerobic performance (maximal oxygen uptake), physical activity, body mass, and composition were evaluated for the polar explores of the Polish Polar Station prior to departure, and then during their stay at the station for a period of 1 year. The measurements were performed every 3 months. Compared to the measurements taken before going to the polar station, aerobic performance significantly ( p = 0.02) increased in the first 3 months of residing at the polar station and then remained relatively stable for the following duration of the stay. In the first 3 months of the stay, we also observed the highest level of physical activity in participants. In the polar explorers, no significant ( p > 0.05) body fatness changes were noted. Nonetheless, lean body mass, body mass, and BMI significantly increased compared to the measurements taken before departure to the polar station. The greatest changes in aerobic performance, physical activity, and body composition were observed during the first 3 months after arrival to the Arctic and then, despite changing biometeorological conditions, they remained stable for the next months of the stay. We recommend the introduction of a physical preparation program before departing to the polar station to improve explorers' physical fitness, so that they can meet the physical challenges they are faced with immediately after arrival to the polar station.

Glacial-Interglacial Changes in the Position of the Intertropical Convergence Zone

NASA Astrophysics Data System (ADS)

Reimi Sipala, M. A.; Marcantonio, F.

2016-12-01

The Intertropical Convergence Zone (ITCZ) is a key component of tropical hydroclimate. It is associated with a zonally heterogeneous tropical precipitation maximum which affects the lives of billions. The Central Equatorial Pacific, near the Line Islands, is an ideal location to study ITCZ migration in response to global temperature fluctuations. Our study uses dust records recovered from five locations in the CEP. We address changes in dust provenance, and the response of the paleo-ITCZ to glacial-interglacial transitions around the penultimate termination (150 to 110 ka). Pb and Nd isotope ratios can be used as dust provenance tools, and lead to accurate reconstructions of paleo-ITCZ position, which are decoupled from rainfall intensity and dust flux. Five cores, along a meridional transect at approximately 160° W, give us access to unprecedented high spatial resolution records with core samples at: 0.48° N (ML1208-17PC), 1.27° N (ML1208-20BB), 2.97° N (ML1208-28BB), 4.68° N (ML1208-31BB), and 7.04° N (ML1208-31BB). Our preliminary data suggests that at the location of the equatorial core (17PC) dust is predominantly sourced from South America (average ɛNd = -4.4), but during Heinrich Stadial 11 ( 136-129 ka) there is a rapid isotopic excursion (-3 ɛNd units). This suggests an abrupt change in dust provenance to the CEP potentially associated with an increased influence of northern hemisphere dust. We will present Pb isotope data to further constrain this finding, and discuss the implications of the results for models of abrupt climate change.

A Last Interglacial pollen-temperature reconstruction, central North Island, New Zealand

NASA Astrophysics Data System (ADS)

Newnham, Rewi; Alloway, Brent; McGlone, Matt; Juchnowicz, Hannah; Rees, Andrew; Wilmshurst, Janet

2017-08-01

We present new pollen-temperature reconstructions for the Last Interglacial from central North Island, New Zealand using partial least squares regression (PLS) and modern analogue technique applied with the New Zealand pre-deforestation calibration pollen dataset. The pollen-bearing organic sequence includes numerous millimetre- to decimetre- thick tephra mostly from the adjacent Tongariro Volcanic Centre and is overlain by tephric cover-beds including the c. 25.4 ka cal BP Kawakawa/Oruanui Tephra. Fine-resolution pollen and preliminary diatom analyses above and below prominent tephra layers showed that significant vegetation impact followed only the thickest ashfall event (22 cm thickness), with vegetation recovery taking several hundred years. Apart from this, changes in the longer-term pollen record are likely to be related to climate oscillations that resemble the classic five-fold subdivision of MIS 5. The warmest interval, ascribed to MIS 5e, was characterised by tall, temperate rainforest, and occurs at the base of the sequence, with mean annual temperatures reaching around 1.1 °C higher than present. Mean annual temperatures declined to ∼4 °C below present during MIS 5d and MIS 5b and were within 1-2 °C of present during MIS 5c. The PLS temperature reconstructions are corroborated by estimates derived independently from elevational changes to vegetation communities, corresponding to modern temperature controls, inferred from the Karioi pollen spectra. Temperatures reconstructed quantitatively by the modern analogue technique were up to 1.3 °C higher for MIS 5e, MIS 5d and MIS 5b, possibly reflecting weaker modern vegetation analogues for these intervals.

Mixing and demixing of binary mixtures of polar chiral active particles.

PubMed

Ai, Bao-Quan; Shao, Zhi-Gang; Zhong, Wei-Rong

2018-05-17

We study a binary mixture of polar chiral (counterclockwise or clockwise) active particles in a two-dimensional box with periodic boundary conditions. Besides the excluded volume interactions between particles, the particles are also subjected to the polar velocity alignment. From the extensive Brownian dynamics simulations, it is found that the particle configuration (mixing or demixing) is determined by the competition between the chirality difference and the polar velocity alignment. When the chirality difference competes with the polar velocity alignment, the clockwise particles aggregate in one cluster and the counterclockwise particles aggregate in the other cluster; thus, the particles are demixed and can be separated. However, when the chirality difference or the polar velocity alignment is dominant, the particles are mixed. Our findings could be used for the experimental pursuit of the separation of binary mixtures of chiral active particles.

PolarHub: A Global Hub for Polar Data Discovery

NASA Astrophysics Data System (ADS)

Li, W.

2014-12-01

This paper reports the outcome of a NSF project in developing a large-scale web crawler PolarHub to discover automatically the distributed polar dataset in the format of OGC web services (OWS) in the cyberspace. PolarHub is a machine robot; its goal is to visit as many webpages as possible to find those containing information about polar OWS, extract this information and store it into the backend data repository. This is a very challenging task given huge data volume of webpages on the Web. Three unique features was introduced in PolarHub to make it distinctive from earlier crawler solutions: (1) a multi-task, multi-user, multi-thread support to the crawling tasks; (2) an extensive use of thread pool and Data Access Object (DAO) design patterns to separate persistent data storage and business logic to achieve high extendibility of the crawler tool; (3) a pattern-matching based customizable crawling algorithm to support discovery of multi-type geospatial web services; and (4) a universal and portable client-server communication mechanism combining a server-push and client pull strategies for enhanced asynchronous processing. A series of experiments were conducted to identify the impact of crawling parameters to the overall system performance. The geographical distribution pattern of all PolarHub identified services is also demonstrated. We expect this work to make a major contribution to the field of geospatial information retrieval and geospatial interoperability, to bridge the gap between data provider and data consumer, and to accelerate polar science by enhancing the accessibility and reusability of adequate polar data.

Polarization extinction ratio of the polarization crosstalk caused by point pressure force in the polarization-maintaining fiber

NASA Astrophysics Data System (ADS)

Mukhtubayev, Azamat B.; Aksarin, Stanislav M.; Strigalev, Vladimir E.

2017-11-01

A study of the orthogonal polarization modes crosstalk changes in the point of different mechanical actions (pressure force) in the polarization-maintaining fiber with straining elliptical cladding is presented. It was found that by increasing of the pressure force the polarization extinction ratio increases nonlinearly. Also revealed the dependence of the extinction coefficient and the angle between vector of the mechanical action and polarization axes of the test fiber, which leads to change the extinction coefficient variable from -57 dB to -25 dB under the pressure force of 0.7 N. Also it was found that the cross angle of the fiber axes doesn't influence on the extinction ratio value of the mechanical induced polarization crosstalk.

Polar Wind Measurements with TIDE/PSI and HYDRA on the Polar Spacecraft

NASA Technical Reports Server (NTRS)

Su, Y. J.; Horwitz, J. L.; Moore, Thomas E.; Giles, Barbara L.; Chandler, Michael O.; Craven, Paul D.; Chang, S.-W.; Scudder, J.

1998-01-01

The Thermal Ion Dynamics Experiment (TIDE) on the POLAR spacecraft has allowed sampling of the three-dimensional ion distributions with excellent energy, angular, and mass resolution. The companion Plasma Source Instrument, when operated, allows sufficient diminution of the electric potential to observe the polar wind at very high altitudes. In this presentation, we will describe the results of polar wind characteristics H+, He+, and 0+ as observed by TIDE at 5000 km and 8 RE altitudes. The relationship of the polar wind parameters with the solar zenith angle and with the day-night distance in the Solar Magnetic coordinate system will also be presented. We will compare these measurements with recent simulations of the photoelectron-driven polar wind using a couple fluid-semikinetic model. In addition, we will compare these polar wind observations with low-energy electrons sampled by the HYDRA experiment on POLAR to examine possible effects of the polar rain and photoelectrons and hopefully explain the large ion outflow velocity variations at POLAR apogee.

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.

Polarization and microstructural effects of ceramic hydroxyapatite electrets

NASA Astrophysics Data System (ADS)

Tanaka, Yumi; Iwasaki, Takeshi; Nakamura, Miho; Nagai, Akiko; Katayama, Keiichi; Yamashita, Kimihiro

2010-01-01

To provide bioelectrets with controlled electrical energy, the polarization and relaxation characteristics of hydroxyapatite (HA) ceramic electrets were investigated in terms of poling conditions and microstructures. HA electrets were prepared between 250 and 500 °C for 5-120 min under a 5 kV cm-1 dc electrical field. Poling conditions and grain size of HA ceramics significantly influenced the thermally stimulated depolarization current (TSDC) spectra and charge storage (Q). Under a poling field of 5 kV cm-1, varying the poling temperature from 250 to 500 °C drastically shifted the TSDC peak temperature from 250 to 620 °C and increased Q from 0.5 to 45 μC cm-2. The change in the average grain size from 2 to 11 μm increased the Q value from 15 to 60 μC cm-2 with a negligible shift in the TSDC peak position. The measured difference of the TSDC peak shapes and positions, as well as the Q values, was theoretically due to the four polarization states with different activation energies (Edr) of dipole relaxation and the pre-exponential factor of relaxation times (τ0). The dependences on the poling conditions and grain size indicated that the four states were due to the orientation polarization of absorbed water (state 1), the localizations of displaced protons around PO43- and OH- in the grains (states 2 and 3), and the localization of displaced protons in the grain boundaries (state 4).