Science.gov

Sample records for abrupt warming events

  1. North Pacific deglacial hypoxic events linked to abrupt ocean warming.

    PubMed

    Praetorius, S K; Mix, A C; Walczak, M H; Wolhowe, M D; Addison, J A; Prahl, F G

    2015-11-19

    Marine sediments from the North Pacific document two episodes of expansion and strengthening of the subsurface oxygen minimum zone (OMZ) accompanied by seafloor hypoxia during the last deglacial transition. The mechanisms driving this hypoxia remain under debate. We present a new high-resolution alkenone palaeotemperature reconstruction from the Gulf of Alaska that reveals two abrupt warming events of 4-5 degrees Celsius at the onset of the Bølling and Holocene intervals that coincide with sudden shifts to hypoxia at intermediate depths. The presence of diatomaceous laminations and hypoxia-tolerant benthic foraminiferal species, peaks in redox-sensitive trace metals, and enhanced (15)N/(14)N ratio of organic matter, collectively suggest association with high export production. A decrease in (18)O/(16)O values of benthic foraminifera accompanying the most severe deoxygenation event indicates subsurface warming of up to about 2 degrees Celsius. We infer that abrupt warming triggered expansion of the North Pacific OMZ through reduced oxygen solubility and increased marine productivity via physiological effects; following initiation of hypoxia, remobilization of iron from hypoxic sediments could have provided a positive feedback on ocean deoxygenation through increased nutrient utilization and carbon export. Such a biogeochemical amplification process implies high sensitivity of OMZ expansion to warming. PMID:26581293

  2. PALEOECOLOGY. Abrupt warming events drove Late Pleistocene Holarctic megafaunal turnover.

    PubMed

    Cooper, Alan; Turney, Chris; Hughen, Konrad A; Brook, Barry W; McDonald, H Gregory; Bradshaw, Corey J A

    2015-08-01

    The mechanisms of Late Pleistocene megafauna extinctions remain fiercely contested, with human impact or climate change cited as principal drivers. We compared ancient DNA and radiocarbon data from 31 detailed time series of regional megafaunal extinctions and replacements over the past 56,000 years with standard and new combined records of Northern Hemisphere climate in the Late Pleistocene. Unexpectedly, rapid climate changes associated with interstadial warming events are strongly associated with the regional replacement or extinction of major genetic clades or species of megafauna. The presence of many cryptic biotic transitions before the Pleistocene/Holocene boundary revealed by ancient DNA confirms the importance of climate change in megafaunal population extinctions and suggests that metapopulation structures necessary to survive such repeated and rapid climatic shifts were susceptible to human impacts. PMID:26250679

  3. A ``triple sea-ice state'' mechanism for the abrupt warming and synchronous ice sheet collapses during Heinrich events

    NASA Astrophysics Data System (ADS)

    Kaspi, Yohai; Sayag, Roiy; Tziperman, Eli

    2004-09-01

    Abrupt, switch-like, changes in sea ice cover are proposed as a mechanism for the large-amplitude abrupt warming that seemed to have occurred after each Heinrich event. Sea ice changes are also used to explain the colder-than-ambient glacial conditions around the time of the glacier discharge. The abrupt warming events occur in this mechanism, owing to rapid sea ice melting which warmed the atmosphere via the strong sea ice albedo and insulating feedbacks. Such abrupt sea ice changes can also account for the warming observed during Dansgaard-Oeschger events. The sea ice changes are caused by a weak (order of 5 Sv) response of the thermohaline circulation (THC) to glacier discharges. The main point of this work is therefore that sea ice may be thought of as a very effective amplifier of a weak THC variability, explaining the abrupt temperature changes over Greenland. Synchronous ice sheet collapses from different ice sheets around the North Atlantic, indicated by some proxy records, are shown to be possible via the weak coupling between the different ice sheets by the atmospheric temperature changes caused by the sea ice changes. This weak coupling can lead to a "nonlinear phase locking" of the different ice sheets which therefore discharge synchronously. It is shown that the phase locking may also lead to "precursor" glacier discharge events from smaller ice sheets before the Laurentide Ice Sheet discharges. The precursor events in this mechanism are the result rather than the cause of the major glacier discharges from the Laurentide Ice Sheet.

  4. Response to Comment on "Abrupt warming events drove Late Pleistocene Holarctic megafaunal turnover".

    PubMed

    Cooper, Alan; Turney, Chris; Hughen, Konrad

    2016-02-26

    Rasmussen and Svensson correctly point out that there is currently no satisfactory method to fully align the Greenland and Cariaco Basin records of climate change. However, our approach using interstadial onsets as tie-points allows direct comparison between radiocarbon dates and Greenland climate records. Crucially, both the standard Greenland and the merged Greenland-Cariaco time scales show that interstadial warming was associated with megafaunal genetic transitions. PMID:26917762

  5. New Measurements of 14C Provide Constraints on Sources of a Large Atmospheric Methane Increase During the Younger Dryas - Preboreal Abrupt Warming Event

    NASA Astrophysics Data System (ADS)

    Petrenko, V. V.; Severinghaus, J. P.; Smith, A.; Riedel, K.; Brook, E.; Schaefer, H.; Baggenstos, D.; Harth, C. M.; Hua, Q.; Buizert, C.; Schilt, A.; Fain, X.; Mitchell, L.; Bauska, T. K.; Orsi, A. J.; Weiss, R. F.

    2014-12-01

    Thawing permafrost and marine methane hydrate destabilization have been proposed as large sources of methane to the atmosphere in the future warming world. To evaluate this hypothesis it is useful to ask whether such methane releases happened during past warming events. The two major abrupt warming events of the last deglaciation, Oldest Dryas - Bølling (OD-B) and Younger Dryas - Preboreal (YD-PB), were associated with large (up to 50%) increases in atmospheric methane (CH4) concentrations. The sources of these large warming-driven CH4 increases remain incompletely understood, with possible contributions from tropical and boreal wetlands, thawing permafrost as well as marine CH4 hydrates. We present new measurements of 14C of paleoatmospheric CH4 over the YD-PB transition from ancient ice outcropping at Taylor Glacier, Antarctica. 14C can unambiguously identify CH4 emissions from "old carbon" sources, such as permafrost and CH4 hydrates. The only prior study of paleoatmospheric 14CH4 (from Greenland ice) suggested that wetlands were the main driver of the YD-PB CH4 increase, but the results were weakened by an unexpected and poorly understood 14CH4 component from in situ cosmogenic production directly in near-surface ice. In this new study, we have been able to accurately characterize and correct for the cosmogenic 14CH4 component. Preliminary analysis of the results indicates that ≈10% of the overall CH4 source to the atmosphere during the nearly-constant climate of the YD was attributable to 14C-free sources. This 14C-free source fraction increased slightly over the YD-PB transition, however, wetlands were nonetheless the main driver of the CH4 increase. Final analysis and interpretation of the 14CH4 data are currently in progress.

  6. Abrupt climate change and extinction events

    NASA Technical Reports Server (NTRS)

    Crowley, Thomas J.

    1988-01-01

    There is a growing body of theoretical and empirical support for the concept of instabilities in the climate system, and indications that abrupt climate change may in some cases contribute to abrupt extinctions. Theoretical indications of instabilities can be found in a broad spectrum of climate models (energy balance models, a thermohaline model of deep-water circulation, atmospheric general circulation models, and coupled ocean-atmosphere models). Abrupt transitions can be of several types and affect the environment in different ways. There is increasing evidence for abrupt climate change in the geologic record and involves both interglacial-glacial scale transitions and the longer-term evolution of climate over the last 100 million years. Records from the Cenozoic clearly show that the long-term trend is characterized by numerous abrupt steps where the system appears to be rapidly moving to a new equilibrium state. The long-term trend probably is due to changes associated with plate tectonic processes, but the abrupt steps most likely reflect instabilities in the climate system as the slowly changing boundary conditions caused the climate to reach some threshold critical point. A more detailed analysis of abrupt steps comes from high-resolution studies of glacial-interglacial fluctuations in the Pleistocene. Comparison of climate transitions with the extinction record indicates that many climate and biotic transitions coincide. The Cretaceous-Tertiary extinction is not a candidate for an extinction event due to instabilities in the climate system. It is quite possible that more detailed comparisons and analysis will indicate some flaws in the climate instability-extinction hypothesis, but at present it appears to be a viable candidate as an alternate mechanism for causing abrupt environmental changes and extinctions.

  7. Examining Risks, Extreme Events, and Abrupt Changes

    NASA Astrophysics Data System (ADS)

    Hargreaves, Julia; Keller, Klaus; Edwards, Tamsin

    2013-08-01

    Climate change research in Japan has shifted focus significantly in the past 2 years, with a greater emphasis on risks, extreme events, and abrupt changes. Two new national government-funded 5-year projects, Integrated Climate Assessment—Risks, Uncertainty and Society (ICA-RUS) and Program for Risk Information on Climate Change (SOUSEI) will focus on climate-induced risks and hazards and the possibility of fast climate changes. In light of the devastating Tohoku earthquake, tsunami, and consequent nuclear accident that occurred 2 years ago in Japan, there is also an increased interest in looking again at risks previously thought to be highly unlikely and in searching for potential risks that have not been considered.

  8. Abrupt pre-Bølling-Allerød warming and circulation changes in the deep ocean

    NASA Astrophysics Data System (ADS)

    Thiagarajan, Nivedita; Subhas, Adam V.; Southon, John R.; Eiler, John M.; Adkins, Jess F.

    2014-07-01

    Several large and rapid changes in atmospheric temperature and the partial pressure of carbon dioxide in the atmosphere--probably linked to changes in deep ocean circulation--occurred during the last deglaciation. The abrupt temperature rise in the Northern Hemisphere and the restart of the Atlantic meridional overturning circulation at the start of the Bølling-Allerød interstadial, 14,700 years ago, are among the most dramatic deglacial events, but their underlying physical causes are not known. Here we show that the release of heat from warm waters in the deep North Atlantic Ocean probably triggered the Bølling-Allerød warming and reinvigoration of the Atlantic meridional overturning circulation. Our results are based on coupled radiocarbon and uranium-series dates, along with clumped isotope temperature estimates, from water column profiles of fossil deep-sea corals in a limited area of the western North Atlantic. We find that during Heinrich stadial 1 (the cool period immediately before the Bølling-Allerød interstadial), the deep ocean was about three degrees Celsius warmer than shallower waters above. This reversal of the ocean's usual thermal stratification pre-dates the Bølling-Allerød warming and must have been associated with increased salinity at depth to preserve the static stability of the water column. The depleted radiocarbon content of the warm and salty water mass implies a long-term disconnect from rapid surface exchanges, and, although uncertainties remain, is most consistent with a Southern Ocean source. The Heinrich stadial 1 ocean profile is distinct from the modern water column, that for the Last Glacial Maximum and that for the Younger Dryas, suggesting that the patterns we observe are a unique feature of the deglacial climate system. Our observations indicate that the deep ocean influenced dramatic Northern Hemisphere warming by storing heat at depth that preconditioned the system for a subsequent abrupt overturning event during the

  9. Voluminous Icelandic Basaltic Eruptions Appear To Cause Abrupt Global Warming

    NASA Astrophysics Data System (ADS)

    Ward, P. L.

    2011-12-01

    Beginning on June 21, 1783, Laki volcano in southern Iceland erupted 14.7 km3 basalt, ejecting 24 Mt SO_{2} into the stratosphere where it was blown eastward and northward and 98 Mt into the troposphere where the jet stream transported it southeastward to Europe. The "dry fog" observed in Europe with an estimated mean concentration of 60 ppbv SO2, raised daytime temperatures as much as 3.3^{o}C, causing the warmest July in England from 1659 when measurements began until 1983. SO2, tropospheric O_{3}, NO2, and fine ash absorb ultraviolet energy from the sun that causes the bonds between and within their atoms to oscillate at 47 times higher frequency than the bonds in CO_{2} absorbing infrared radiation. Temperature is proportional to the kinetic energy of these oscillations, i.e. the frequency squared. Thus these gases are raised to much higher temperatures than greenhouse gases. The Stefan-Boltzmann law says that radiation from these molecules is a constant times temperature raised to the fourth power. As a result, SO2 and ash radiate far more energy back to earth than CO_{2}, causing warming. Another way to look at the energy involved shows that 15 ppbv SO2 in the 0.3-0.42 μm wavelength band absorbs as much solar energy per unit volume as 388,000 ppbv CO_{2} absorbs infrared energy in the 12.7-17.5 μm band. Basaltic volcanoes such as Laki emit 10 to 100 times more SO2 than more evolved magmas and are less explosive, leaving most of the SO_{2} in the troposphere. All 14 Dansgaard-Oeschger (DO) sudden warmings between 46 and 11 ka are contemporaneous with the highest levels of sulfate in the GISP2 drill hole near Summit Greenland. These DO events typically warmed the northern hemisphere out of the ice age within decades, but as volcanism waned, ocean temperatures cooled the world back into an ice age within centuries. The world finally exited the ice age when voluminous volcanism continued from 11.6 to 9.6 ka. Basaltic table mountains or tuyas in Iceland document

  10. Precise Interhemispheric Phasing of the Bipolar Seesaw during Abrupt Dansgaard-Oeschger Events

    NASA Astrophysics Data System (ADS)

    Buizert, C.; Baggenstos, D.; Brook, E.; Cuffey, K. M.; Fudge, T. J.; Markle, B. R.; McConnell, J. R.; Rhodes, R.; Severinghaus, J. P.; Sowers, T. A.; Steig, E. J.; Taylor, K.

    2014-12-01

    Late Pleistocene glacial periods exhibit abrupt Dansgaard-Oeschger (DO) climatic oscillations, evidence of which is preserved in a variety of northern hemisphere (NH) palaeoclimatic archives. Ice cores show Antarctica is cooling during the warm phases of the Greenland DO cycle and vice versa, suggesting an interhemispheric redistribution of heat through a mechanism dubbed the bipolar seesaw. While it is generally accepted that variations in the Atlantic meridional overturning circulation (AMOC) strength play an important role, great uncertainty remains regarding the dynamics and trigger of the abrupt events. Key information is contained in the relative phasing of hemispheric climate variations, yet the large and poorly constrained ice age-gas age difference (Dage) in Antarctic ice cores has precluded methane-based synchronization at the required sub-centennial precision. Here we present a new high accumulation deep Antarctic ice core, the West Antarctic Ice Sheet (WAIS)-Divide core, that is used to resolve the timing of the bipolar seesaw at unprecedented temporal resolution. We find that the abrupt Greenland warming phase leads the corresponding Antarctic cooling by 195 ± 59 years for DO-events, including the Bølling period; Greenland cooling leads the corresponding Antarctic warming by 179 ± 61 years. The centennial NH lead time shows that the abrupt phases of the DO cycle are initiated in the NH, after which the temperature anomaly is propagated to the southern hemisphere (SH) high latitudes via an oceanic teleconnection. The similar phasing of warming and cooling events suggests that to first order the transfer time of the climatic signal is independent of the AMOC background state. Our findings confirm the central role ocean circulation plays in the seesaw, and provide a clear criterion for testing hypotheses and model simulations of DO dynamics.

  11. Abrupt pre-Bølling-Allerød warming and circulation changes in the deep ocean.

    PubMed

    Thiagarajan, Nivedita; Subhas, Adam V; Southon, John R; Eiler, John M; Adkins, Jess F

    2014-07-01

    Several large and rapid changes in atmospheric temperature and the partial pressure of carbon dioxide in the atmosphere--probably linked to changes in deep ocean circulation--occurred during the last deglaciation. The abrupt temperature rise in the Northern Hemisphere and the restart of the Atlantic meridional overturning circulation at the start of the Bølling-Allerød interstadial, 14,700 years ago, are among the most dramatic deglacial events, but their underlying physical causes are not known. Here we show that the release of heat from warm waters in the deep North Atlantic Ocean probably triggered the Bølling-Allerød warming and reinvigoration of the Atlantic meridional overturning circulation. Our results are based on coupled radiocarbon and uranium-series dates, along with clumped isotope temperature estimates, from water column profiles of fossil deep-sea corals in a limited area of the western North Atlantic. We find that during Heinrich stadial 1 (the cool period immediately before the Bølling-Allerød interstadial), the deep ocean was about three degrees Celsius warmer than shallower waters above. This reversal of the ocean's usual thermal stratification pre-dates the Bølling-Allerød warming and must have been associated with increased salinity at depth to preserve the static stability of the water column. The depleted radiocarbon content of the warm and salty water mass implies a long-term disconnect from rapid surface exchanges, and, although uncertainties remain, is most consistent with a Southern Ocean source. The Heinrich stadial 1 ocean profile is distinct from the modern water column, that for the Last Glacial Maximum and that for the Younger Dryas, suggesting that the patterns we observe are a unique feature of the deglacial climate system. Our observations indicate that the deep ocean influenced dramatic Northern Hemisphere warming by storing heat at depth that preconditioned the system for a subsequent abrupt overturning event during the

  12. Abrupt Atmospheric Methane Increases Associated With Hudson Strait Heinrich Events

    NASA Astrophysics Data System (ADS)

    Rhodes, R.; Brook, E.; Chiang, J. C. H.; Blunier, T.; Maselli, O. J.; McConnell, J. R.; Romanini, D.; Severinghaus, J. P.

    2015-12-01

    The drivers of abrupt climate change during the Last Glacial Period are not well understood. While Dansgaard-Oeschger (DO) cycles are thought to be linked to variations in the strength of the Atlantic Meridional Ocean Circulation (AMOC), it is not clear how or if Heinrich Events—extensive influxes of icebergs into the North Atlantic Ocean that impacted global climate and biogeochemistry—are related. An enduring problem is the difficultly in dating iceberg rafted debris deposits that typically lack foraminifera. Here we present an ultra-high resolution record of methane from the West Antarctic Ice Sheet Divide ice core at unprecedented, continuous temporal resolution from 67.2-9.8 ka BP, which we propose constrains the timing of Heinrich events. Our methane record essentially mirrors Greenland ice core stable isotope variability across D-O events, except during Heinrich stadials 1, 2, 4 and 5. Partway through these stadials only, methane increases abruptly and rapidly, as at the onset of a D-O event but Greenland temperature exhibits no equivalent response. Speleothem records exhibit signatures of drought in the Northern extra-tropics and intensified monsoonal activity over South America at these times. We use a simple heuristic model to propose that cold air temperatures and extensive sea ice in the North, resulting from Heinrich events, caused extreme reorganization of tropical hydroclimate. This involved curtailment of the seasonal northerly migration of tropical rain belts, leading to intensification of rainfall over Southern Hemisphere tropical wetlands, thus allowing production of excess methane relative to a 'normal' Greenland stadial. We note that this mechanism can operate if AMOC is already in a slowed state when a Heinrich event occurs, as paleo-evidence suggests it was. Heinrich events and associated sea ice cover would therefore act to prolong the duration of this AMOC state. Our findings place the big four Heinrich events of Hudson Strait origin

  13. Fluvial response to abrupt global warming at the Palaeocene/Eocene boundary.

    PubMed

    Foreman, Brady Z; Heller, Paul L; Clementz, Mark T

    2012-11-01

    Climate strongly affects the production of sediment from mountain catchments as well as its transport and deposition within adjacent sedimentary basins. However, identifying climatic influences on basin stratigraphy is complicated by nonlinearities, feedback loops, lag times, buffering and convergence among processes within the sediment routeing system. The Palaeocene/Eocene thermal maximum (PETM) arguably represents the most abrupt and dramatic instance of global warming in the Cenozoic era and has been proposed to be a geologic analogue for anthropogenic climate change. Here we evaluate the fluvial response in western Colorado to the PETM. Concomitant with the carbon isotope excursion marking the PETM we document a basin-wide shift to thick, multistoried, sheets of sandstone characterized by variable channel dimensions, dominance of upper flow regime sedimentary structures, and prevalent crevasse splay deposits. This progradation of coarse-grained lithofacies matches model predictions for rapid increases in sediment flux and discharge, instigated by regional vegetation overturn and enhanced monsoon precipitation. Yet the change in fluvial deposition persisted long after the approximately 200,000-year-long PETM with its increased carbon dioxide levels in the atmosphere, emphasizing the strong role the protracted transmission of catchment responses to distant depositional systems has in constructing large-scale basin stratigraphy. Our results, combined with evidence for increased dissolved loads and terrestrial clay export to world oceans, indicate that the transient hyper-greenhouse climate of the PETM may represent a major geomorphic 'system-clearing event', involving a global mobilization of dissolved and solid sediment loads on Earth's surface. PMID:23128230

  14. Abrupt termination of the 2012 Pacific warming and its implication on ENSO prediction

    NASA Astrophysics Data System (ADS)

    Su, Jingzhi; Xiang, Baoqiang; Wang, Bin; Li, Tim

    2014-12-01

    In the summer of 2012, there was a clear signal of the developing El Niño over the equatorial Pacific, and many climate models forecasted the occurrence of El Niño with a peak phase in the subsequent winter. However, the warming was aborted abruptly in late fall. Here we show that the abrupt termination of the 2012 Pacific warming was largely attributed to the anomalous sea surface temperature (SST) cooling in the northeastern and southeastern subtropical Pacific. The anomalous SST cooling induced strong easterly and low-level divergence anomalies, suppressing the development of westerly and convection anomalies over the equatorial central Pacific. Thus, the surface warming over the equatorial Pacific was decoupled from the surface wind forcing and subsurface thermocline variability, inhibiting its further development into a mature El Niño in the winter of 2012-2013. This study highlights the importance of the SST anomaly in the subtropical Pacific in El Niño prediction.

  15. Paradox of the peak-PCIM (Paleocene Carbon Isotope Maxima; ~57.8Ma) and Abrupt Global Warming

    NASA Astrophysics Data System (ADS)

    Harper, D. T.; Hoenisch, B.; Zachos, J. C.

    2015-12-01

    The Paleocene Carbon Isotope Maxima (PCIM; ~57.8Ma) represents a major transition in global δ13C during the late Paleocene, when the long-term positive trend in δ13C reversed from positive to negative. The peak-PCIM (~57.7Ma) has been tightly resolved in new high-resolution, astronomically-tuned benthic isotope records from IODP Sites 1209 (Pacific) and 1262 (Atlantic), which show the final phase of δ13C enrichment as abrupt (~1‰ in <100kyrs) and coinciding with a 0.5‰ decline in benthic δ18O indicative of 2-3ºC of bottom water warming, effectively marking the onset of a gradual 8Myr long warming trend [Littler et al., EPSL 2014]. Typically, during the Paleogene on orbital time scales, warming is observed during intervals of δ13C depletion, consistent with release of isotopically light carbon to the atmosphere. This event, which has the appearance of a bifurcation in the long-term coupling of climate system and the carbon cycle, poses an interesting paradox as any rapid carbon release to the atmosphere should, in theory, create a negative excursion because all of the major carbon sources are isotopically light, whether volcanic outgassing, weathering/oxidation of organic carbon, or methane release [Dunkley-Jones et al., Phil. Trans. R. Soc. A 2010]. If global, there are several testable mechanisms that may explain the shift including increase in burial flux of light carbon, a reduction in heavy carbon burial flux, or a large-scale circulation change perhaps associated with the transition of a major oceanic gateway. Using trace metal (B/Ca and Mg/Ca) and stable isotope (δ11B, δ18O, and δ13C) geochemistry, here we establish the nature of the peak-PCIM at sites from 3 different ocean basins (IODP Sites 690, 1209, and 1262) and begin to test several of the possible mechanisms for change. Mg/Ca in mixed-layer planktonic foraminifera show 2-3°C of sea surface warming coinciding with, and abrupt as, the benthic carbon isotope enrichment at all sites. Bottom

  16. Linear sea-level response to abrupt ocean warming of major West Antarctic ice basin

    NASA Astrophysics Data System (ADS)

    Mengel, M.; Feldmann, J.; Levermann, A.

    2016-01-01

    Antarctica's contribution to global sea-level rise has recently been increasing. Whether its ice discharge will become unstable and decouple from anthropogenic forcing or increase linearly with the warming of the surrounding ocean is of fundamental importance. Under unabated greenhouse-gas emissions, ocean models indicate an abrupt intrusion of warm circumpolar deep water into the cavity below West Antarctica's Filchner-Ronne ice shelf within the next two centuries. The ice basin's retrograde bed slope would allow for an unstable ice-sheet retreat, but the buttressing of the large ice shelf and the narrow glacier troughs tend to inhibit such instability. It is unclear whether future ice loss will be dominated by ice instability or anthropogenic forcing. Here we show in regional and continental-scale ice-sheet simulations, which are capable of resolving unstable grounding-line retreat, that the sea-level response of the Filchner-Ronne ice basin is not dominated by ice instability and follows the strength of the forcing quasi-linearly. We find that the ice loss reduces after each pulse of projected warm water intrusion. The long-term sea-level contribution is approximately proportional to the total shelf-ice melt. Although the local instabilities might dominate the ice loss for weak oceanic warming, we find that the upper limit of ice discharge from the region is determined by the forcing and not by the marine ice-sheet instability.

  17. H4 abrupt event and late Neanderthal presence in Iberia

    NASA Astrophysics Data System (ADS)

    Sepulchre, Pierre; Ramstein, Gilles; Kageyama, Masa; Vanhaeren, Marian; Krinner, Gerhard; Sánchez-Goñi, María-Fernanda; d'Errico, Francesco

    2007-06-01

    Heinrich event 4 (H4) is well documented in the North Atlantic Ocean and the adjacent continents as a cooling event 39,000 yr before present (BP). To quantify the impact of this event with respect to climate and vegetation over the Iberian Peninsula, we perform numerical experiments using a high-resolution general circulation model forced by sea surface temperatures before and during H4. Our model simulates an expansion of aridity over the peninsula during H4, a desertification of the south, and a replacement of arboreal by herbaceous plants in the north, all of which are in agreement with contemporaneous pollen sequences from marine cores located off the Iberian Peninsula. Our simulations demonstrate that the H4 marine event imprinted drastic changes over Southern Iberia, which would not have favoured its occupation by Anatomically Modern Humans, therefore providing a plausible explanation for the delayed extinction of Neanderthals in this region inferred from the archaeological record.

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

  19. Paleoclimate. Synchronization of North Pacific and Greenland climates preceded abrupt deglacial warming.

    PubMed

    Praetorius, Summer K; Mix, Alan C

    2014-07-25

    Some proposed mechanisms for transmission of major climate change events between the North Pacific and North Atlantic predict opposing patterns of variations; others suggest synchronization. Resolving this conflict has implications for regulation of poleward heat transport and global climate change. New multidecadal-resolution foraminiferal oxygen isotope records from the Gulf of Alaska (GOA) reveal sudden shifts between intervals of synchroneity and asynchroneity with the North Greenland Ice Core Project (NGRIP) δ(18)O record over the past 18,000 years. Synchronization of these regions occurred 15,500 to 11,000 years ago, just prior to and throughout the most abrupt climate transitions of the last 20,000 years, suggesting that dynamic coupling of North Pacific and North Atlantic climates may lead to critical transitions in Earth's climate system. PMID:25061208

  20. Sea-level response to abrupt ocean warming of Antarctic ice shelves

    NASA Astrophysics Data System (ADS)

    Pattyn, Frank

    2016-04-01

    Antarctica's contribution to global sea-level rise increases steadily. A fundamental question remains whether the ice discharge will lead to marine ice sheet instability (MISI) and collapse of certain sectors of the ice sheet or whether ice loss will increase linearly with the warming trends. Therefore, we employ a newly developed ice sheet model of the Antarctic ice sheet, called f.ETISh (fast Elementary Thermomechanical Ice Sheet model) to simulate ice sheet response to abrupt perturbations in ocean and atmospheric temperature. The f.ETISh model is a vertically integrated hybrid (SSA/SIA) ice sheet model including ice shelves. Although vertically integrated, thermomechanical coupling is ensured through a simplified representation of ice sheet thermodynamics based on an analytical solution of the vertical temperature profile, including strain heating and horizontal advection. The marine boundary is represented by a flux condition either coherent with power-law basal sliding (Pollard & Deconto (2012) based on Schoof (2007)) or according to Coulomb basal friction (Tsai et al., 2015), both taking into account ice-shelf buttressing. Model initialization is based on optimization of the basal friction field. Besides the traditional MISMIP tests, new tests with respect to MISI in plan-view models have been devised. The model is forced with stepwise ocean and atmosphere temperature perturbations. The former is based on a parametrised sub-shelf melt (limited to ice shelves), while the latter is based on present-day mass balance/surface temperature and corrected for elevation changes. Surface melting is introduced using a PDD model. Results show a general linear response in mass loss to ocean warming. Nonlinear response due to MISI occurs under specific conditions and is highly sensitive to the basal conditions near the grounding line, governed by both the initial conditions and the basal sliding/deformation model. The Coulomb friction model leads to significantly higher

  1. Investigation of the Impact of a Heinrich-Event-like Abrupt Event Superimposed Onto the RCP 8.5 Scenario

    NASA Astrophysics Data System (ADS)

    Defrance, D.; Ramstein, G.; Dumas, C.; Charbit, S.

    2014-12-01

    The CMIP5/IPCC (AR5) projections of climate change showed the temperatures should increase by between 1.3 °C and 4.4 °C by 2100 and the sea level rise between 26 cm and 82 cm on average. Superimposed on these climatic and hydrologic trends associated with the RCP 8.5 most pessimistic scenario, it is important to investigate the possible effect of an abrupt event like an ice-sheet surge. This is first justified by the recent collapse of the Larsen B ice shelf which illustrates that a non-linear response of the cryosphere may occur in a warming world. Furthermore, in glacial periods, ice-sheets have been unstable and huge surges of icebergs did occur and deeply modified the climate. The aim of this presentation is to show the hypothetical climatic consequences of such a Heinrich-type event on future climate change. To achieve this goal, 3 scenarios of rapid ice-sheet deglaciation have been designed, corresponding to an additional sea level rise of around 3 m : - S1 corresponds to a contribution from Greenland only; - S2 from West-Antarctica only; - S3 from both ice-sheets. We use the global atmosphere-ocean general circulation model (OAGCM) IPSL-CM5A-LR. The freshwater perturbation is applied near the ice-sheet(s) during 20 years from 2050 to 2070 during an RCP8.5 perturbation. The RCP8.5 scenario is then continued until 2100 (without freshwater). For these types of scenarios, previous experiments for paleoclimatic cases help us diagnose the most vulnerable areas. The North Atlantic and the collapse of thermohaline circulation is one key issue, but far field teleconnections with the Asian monsoon will also be explored. We will investigate the timing and amplitude of the climate impacts due to the perturbations, which may be quite different in our 3 scenarios. These abrupt events consequences can be important for the populations and the consideration of rapid changes should improve the reliability of IPCC predictions.

  2. Gradual onset and recovery of the Younger Dryas abrupt climate event in the tropics

    PubMed Central

    Partin, J.W.; Quinn, T.M.; Shen, C.-C.; Okumura, Y.; Cardenas, M.B.; Siringan, F.P.; Banner, J.L.; Lin, K.; Hu, H.-M.; Taylor, F.W.

    2015-01-01

    Proxy records of temperature from the Atlantic clearly show that the Younger Dryas was an abrupt climate change event during the last deglaciation, but records of hydroclimate are underutilized in defining the event. Here we combine a new hydroclimate record from Palawan, Philippines, in the tropical Pacific, with previously published records to highlight a difference between hydroclimate and temperature responses to the Younger Dryas. Although the onset and termination are synchronous across the records, tropical hydroclimate changes are more gradual (>100 years) than the abrupt (10–100 years) temperature changes in the northern Atlantic Ocean. The abrupt recovery of Greenland temperatures likely reflects changes in regional sea ice extent. Proxy data and transient climate model simulations support the hypothesis that freshwater forced a reduction in the Atlantic meridional overturning circulation, thereby causing the Younger Dryas. However, changes in ocean overturning may not produce the same effects globally as in Greenland. PMID:26329911

  3. Gradual onset and recovery of the Younger Dryas abrupt climate event in the tropics

    NASA Astrophysics Data System (ADS)

    Partin, J. W.; Quinn, T. M.; Shen, C.-C.; Okumura, Y.; Cardenas, M. B.; Siringan, F. P.; Banner, J. L.; Lin, K.; Hu, H.-M.; Taylor, F. W.

    2015-09-01

    Proxy records of temperature from the Atlantic clearly show that the Younger Dryas was an abrupt climate change event during the last deglaciation, but records of hydroclimate are underutilized in defining the event. Here we combine a new hydroclimate record from Palawan, Philippines, in the tropical Pacific, with previously published records to highlight a difference between hydroclimate and temperature responses to the Younger Dryas. Although the onset and termination are synchronous across the records, tropical hydroclimate changes are more gradual (>100 years) than the abrupt (10-100 years) temperature changes in the northern Atlantic Ocean. The abrupt recovery of Greenland temperatures likely reflects changes in regional sea ice extent. Proxy data and transient climate model simulations support the hypothesis that freshwater forced a reduction in the Atlantic meridional overturning circulation, thereby causing the Younger Dryas. However, changes in ocean overturning may not produce the same effects globally as in Greenland.

  4. Gradual onset and recovery of the Younger Dryas abrupt climate event in the tropics.

    PubMed

    Partin, J W; Quinn, T M; Shen, C-C; Okumura, Y; Cardenas, M B; Siringan, F P; Banner, J L; Lin, K; Hu, H-M; Taylor, F W

    2015-01-01

    Proxy records of temperature from the Atlantic clearly show that the Younger Dryas was an abrupt climate change event during the last deglaciation, but records of hydroclimate are underutilized in defining the event. Here we combine a new hydroclimate record from Palawan, Philippines, in the tropical Pacific, with previously published records to highlight a difference between hydroclimate and temperature responses to the Younger Dryas. Although the onset and termination are synchronous across the records, tropical hydroclimate changes are more gradual (>100 years) than the abrupt (10-100 years) temperature changes in the northern Atlantic Ocean. The abrupt recovery of Greenland temperatures likely reflects changes in regional sea ice extent. Proxy data and transient climate model simulations support the hypothesis that freshwater forced a reduction in the Atlantic meridional overturning circulation, thereby causing the Younger Dryas. However, changes in ocean overturning may not produce the same effects globally as in Greenland. PMID:26329911

  5. Abrupt summer warming and changes in temperature extremes over Northeast Asia since the mid-1990s: Drivers and physical processes

    NASA Astrophysics Data System (ADS)

    Dong, Buwen; Sutton, Rowan T.; Chen, Wei; Liu, Xiaodong; Lu, Riyu; Sun, Ying

    2016-09-01

    This study investigated the drivers and physical processes for the abrupt decadal summer surface warming and increases in hot temperature extremes that occurred over Northeast Asia in the mid-1990s. Observations indicate an abrupt increase in summer mean surface air temperature (SAT) over Northeast Asia since the mid-1990s. Accompanying this abrupt surface warming, significant changes in some temperature extremes, characterized by increases in summer mean daily maximum temperature (Tmax), daily minimum temperature (Tmin), annual hottest day temperature (TXx), and annual warmest night temperature (TNx) were observed. There were also increases in the frequency of summer days (SU) and tropical nights (TR). Atmospheric general circulation model experiments forced by changes in sea surface temperature (SST)/sea ice extent (SIE), anthropogenic greenhouse gas (GHG) concentrations, and anthropogenic aerosol (AA) forcing, relative to the period 1964-93, reproduced the general patterns of observed summer mean SAT changes and associated changes in temperature extremes, although the abrupt decrease in precipitation since the mid-1990s was not simulated. Additional model experiments with different forcings indicated that changes in SST/SIE explained 76% of the area-averaged summer mean surface warming signal over Northeast Asia, while the direct impact of changes in GHG and AA explained the remaining 24% of the surface warming signal. Analysis of physical processes indicated that the direct impact of the changes in AA (through aerosol-radiation and aerosol-cloud interactions), mainly related to the reduction of AA precursor emissions over Europe, played a dominant role in the increase in TXx and a similarly important role as SST/SIE changes in the increase in the frequency of SU over Northeast Asia via AA-induced coupled atmosphere-land surface and cloud feedbacks, rather than through a direct impact of AA changes on cloud condensation nuclei. The modelling results also imply

  6. Deglacial abrupt climate change in the Atlantic Warm Pool: A Gulf of Mexico perspective

    NASA Astrophysics Data System (ADS)

    Williams, Carlie; Flower, Benjamin P.; Hastings, David W.; Guilderson, Thomas P.; Quinn, Kelly A.; Goddard, Ethan A.

    2010-12-01

    During the last deglaciation, Greenland ice core and North Atlantic sediment records exhibit multiple abrupt climate events including the Younger Dryas cold episode (12.9-11.7 ka). However, evidence for the presence of the Younger Dryas in the Gulf of Mexico (GOM) and the relationship between GOM sea surface temperature (SST) and high-latitude climate change is less clear. We present new Mg/Ca-SST records from two varieties of the planktonic foraminifer Globigerinoides ruber (white and pink) to assess northern GOM SST history from approximately 18.4-10.8 ka. Thirty-five accelerator mass spectrometry (AMS) 14C dates from Orca Basin core MD02-2550 provide excellent age control and document high sedimentation rates (˜40 cm/kyr). G. ruber (white and pink) Mg/Ca-SST data exhibit increases (˜4.6 ± 0.6°C and ˜2.2 ± 0.5°C, respectively) from at least 17.8-16.6 ka, with nearly decadal resolution that are early relative to the onset of the Bolling-Allerod interstadial. Moreover, G. ruber (white) SST decreases at 16.0-14.7 ka (˜1.0 ± 0.5°C) and 12.8-11.6 ka (˜2.4 ± 0.6°C) correlate to the Oldest and Younger Dryas in Greenland and Cariaco Basin. The G. ruber (pink) SST record, which reflects differences in seasonality and/or depth habitat, is often not in phase with G. ruber (white) and closely resembles Antarctic air temperature records. Overall, it appears that Orca Basin SST records follow Antarctic air temperature early in the deglacial sequence and exhibit enhanced seasonality during Greenland stadials.

  7. Consistent simulations of multiple proxy responses to an abrupt climate change event.

    PubMed

    LeGrande, A N; Schmidt, G A; Shindell, D T; Field, C V; Miller, R L; Koch, D M; Faluvegi, G; Hoffmann, G

    2006-01-24

    Isotope, aerosol, and methane records document an abrupt cooling event across the Northern Hemisphere at 8.2 kiloyears before present (kyr), while separate geologic lines of evidence document the catastrophic drainage of the glacial Lakes Agassiz and Ojibway into the Hudson Bay at approximately the same time. This melt water pulse may have been the catalyst for a decrease in North Atlantic Deep Water formation and subsequent cooling around the Northern Hemisphere. However, lack of direct evidence for ocean cooling has lead to speculation that this abrupt event was purely local to Greenland and called into question this proposed mechanism. We simulate the response to this melt water pulse using a coupled general circulation model that explicitly tracks water isotopes and with atmosphere-only experiments that calculate changes in atmospheric aerosol deposition (specifically (10)Be and dust) and wetland methane emissions. The simulations produce a short period of significantly diminished North Atlantic Deep Water and are able to quantitatively match paleoclimate observations, including the lack of isotopic signal in the North Atlantic. This direct comparison with multiple proxy records provides compelling evidence that changes in ocean circulation played a major role in this abrupt climate change event. PMID:16415159

  8. Competition between global warming and an abrupt collapse of the AMOC in Earth's energy imbalance.

    PubMed

    Drijfhout, Sybren

    2015-01-01

    A collapse of the Atlantic Meridional Overturning Circulation (AMOC) leads to global cooling through fast feedbacks that selectively amplify the response in the Northern Hemisphere (NH). How such cooling competes with global warming has long been a topic for speculation, but was never addressed using a climate model. Here it is shown that global cooling due to a collapsing AMOC obliterates global warming for a period of 15-20 years. Thereafter, the global mean temperature trend is reversed and becomes similar to a simulation without an AMOC collapse. The resulting surface warming hiatus lasts for 40-50 years. Global warming and AMOC-induced NH cooling are governed by similar feedbacks, giving rise to a global net radiative imbalance of similar sign, although the former is associated with surface warming, the latter with cooling. Their footprints in outgoing longwave and absorbed shortwave radiation are very distinct, making attribution possible. PMID:26437599

  9. Stratospheric predictability and sudden stratospheric warming events

    NASA Astrophysics Data System (ADS)

    Stan, Cristiana; Straus, David M.

    2009-06-01

    A comparative study of the limit of predictability in the stratosphere and troposphere in a coupled general circulation model is carried out using the National Center for Environmental Prediction (NCEP) Climate Forecast System Interactive Ensemble (CFSIE). In "identical twin experiments", we compare the forecast errors of zonal wind and potential temperature in the troposphere and stratosphere for various wave groups. The results show smaller intrinsic error growth in the lower stratosphere compared with troposphere. The limit of predictability of sudden stratospheric warming events, measured by the errors in the divergence of the Eliassen-Palm flux, is dominated by the amplification of small errors in the individual fields due to differences between the phase of the waves.

  10. Abrupt post-glacial climate events in West Asia and North Africa monsoon domains

    NASA Astrophysics Data System (ADS)

    Gasse, Françoise; Van Campo, Elise

    1994-09-01

    Regions beyond the present or past penetration of the Indian and African monsoons have experienced several large and abrupt climatic fluctuations over the past 13 14C kyr. Pollen and lake records from West Asia (Western Tibet and Rajasthan), East Africa (Ethiopia) and West Africa (Western Sahara, Sahel and subequatorial Africa) were selected on the basis of chronological control, sensitivity of both site and environmental indicators to climate change, the continuity of the record, and interdisciplinary control of the palaeoclimatic interpretation. Conditions wetter than those of today prevailed during the early-mid-Holocene period, but major dry spells are recorded at all sites during the intervals ˜ 11.0-9.5 kyr BP, ˜ 8-7 kyr BP and 3-4 kyr BP. Several records also suggest dry events of minor amplitude around 6 kyr BP. Potential boundary forcings of insolation and sea surface and tropical land surface conditions are discussed. The solar radiation accounts for the general envelop of the post-glacial monsoon fluctuations, but explains neither the timing nor the amplitude of the short-term changes. In spite of apparent covariation between fluctuations in sea surface conditions in the North Atlantic and the monsoon record, no direct mechanism could be found relating the intensity of the oceanic thermohaline conveyor belt to the monsoon strength. Changes in tropical land surface conditions (soil moisture negative feedback, and changes in CH 4 production from wetlands) provide a more satisfactory hypothesis for explaining abrupt reversal events.

  11. Synchronous centennial abrupt events in the ocean and atmosphere during the last deglaciation

    NASA Astrophysics Data System (ADS)

    Chen, Tianyu; Robinson, Laura F.; Burke, Andrea; Southon, John; Spooner, Peter; Morris, Paul J.; Ng, Hong Chin

    2015-09-01

    Antarctic ice-core data reveal that the atmosphere experienced abrupt centennial increases in CO2 concentration during the last deglaciation (~18 thousand to 11 thousand years ago). Establishing the role of ocean circulation in these changes requires high-resolution, accurately dated marine records. Here, we report radiocarbon data from uranium-thorium-dated deep-sea corals in the Equatorial Atlantic and Drake Passage over the past 25,000 years. Two major deglacial radiocarbon shifts occurred in phase with centennial atmospheric CO2 rises at 14.8 thousand and 11.7 thousand years ago. We interpret these radiocarbon-enriched signals to represent two short-lived (less than 500 years) “overshoot” events, with Atlantic meridional overturning stronger than that of the modern era. These results provide compelling evidence for a close coupling of ocean circulation and centennial climate events during the last deglaciation.

  12. Synchronous centennial abrupt events in the ocean and atmosphere during the last deglaciation.

    PubMed

    Chen, Tianyu; Robinson, Laura F; Burke, Andrea; Southon, John; Spooner, Peter; Morris, Paul J; Ng, Hong Chin

    2015-09-25

    Antarctic ice-core data reveal that the atmosphere experienced abrupt centennial increases in CO2 concentration during the last deglaciation (~18 thousand to 11 thousand years ago). Establishing the role of ocean circulation in these changes requires high-resolution, accurately dated marine records. Here, we report radiocarbon data from uranium-thorium-dated deep-sea corals in the Equatorial Atlantic and Drake Passage over the past 25,000 years. Two major deglacial radiocarbon shifts occurred in phase with centennial atmospheric CO2 rises at 14.8 thousand and 11.7 thousand years ago. We interpret these radiocarbon-enriched signals to represent two short-lived (less than 500 years) "overshoot" events, with Atlantic meridional overturning stronger than that of the modern era. These results provide compelling evidence for a close coupling of ocean circulation and centennial climate events during the last deglaciation. PMID:26404835

  13. An abrupt climate event in a coupled ocean-atmosphere simulation without external forcing.

    PubMed

    Hall, A; Stouffer, R J

    2001-01-11

    Temperature reconstructions from the North Atlantic region indicate frequent abrupt and severe climate fluctuations during the last glacial and Holocene periods. The driving forces for these events are unclear and coupled atmosphere-ocean models of global circulation have only simulated such events by inserting large amounts of fresh water into the northern North Atlantic Ocean. Here we report a drastic cooling event in a 15,000-yr simulation of global circulation with present-day climate conditions without the use of such external forcing. In our simulation, the annual average surface temperature near southern Greenland spontaneously fell 6-10 standard deviations below its mean value for a period of 30-40 yr. The event was triggered by a persistent northwesterly wind that transported large amounts of buoyant cold and fresh water into the northern North Atlantic Ocean. Oceanic convection shut down in response to this flow, concentrating the entire cooling of the northern North Atlantic by the colder atmosphere in the uppermost ocean layer. Given the similarity between our simulation and observed records of rapid cooling events, our results indicate that internal atmospheric variability alone could have generated the extreme climate disruptions in this region. PMID:11196636

  14. Projections of the pace of warming following an abrupt increase in atmospheric carbon dioxide concentration

    NASA Astrophysics Data System (ADS)

    Caldeira, K.; Myhrvold, N. P.

    2013-09-01

    The temperature response of atmosphere-ocean climate models is analyzed based on atmospheric CO2 step-function-change simulations submitted to phase 5 of the Coupled Model Intercomparison Project (CMIP5). From these simulations and a control simulation, we estimate adjusted radiative forcing, the climate feedback parameter, and effective climate system thermal inertia, and we show that these results can be used to predict the temperature response to time-varying CO2 concentrations. We evaluate several kinds of simple mathematical models for the CMIP5 simulation results, including single- and multiple-exponential models and a one-dimensional ocean-diffusion model. All of these functional forms, except the single-exponential model, can produce curves that fit most CMIP5 results quite well for both continuous and step-function CO2-change pathways. Choice of model for any particular application would include consideration of factors such as the number of free parameters to be constrained and the conception of the underlying mechanistic model. Smooth curve fits to the CMIP5 simulation results realize approximately half (range 38%-61%) of equilibrium warming within the first decade after a CO2 concentration increase, but approximately one quarter (range 14%-40%) of equilibrium warming occurs more than a century after the CO2 increase. Following an instantaneous quadrupling of atmospheric CO2, fits to four of the 20 simulation results reach 4 ° C of warming within the first decade, but fits to three of the 20 simulation results require more than a century to reach 4 ° C. These results indicate the need to reduce uncertainty in the temporal response of climate models and to consider this uncertainty when evaluating the risks posed by climate change.

  15. Response of atmospheric CO2 to the abrupt cooling event 8200 years ago

    NASA Astrophysics Data System (ADS)

    Ahn, J.; Brook, E.; Buizert, C.

    2013-12-01

    The abrupt cooling event 8200 years ago (8.2 ka event) is the most prominent centennial scale climate event during the Holocene and was likely caused by a reduction in the Atlantic meridional overturning circulation (AMOC). Atmospheric CO2 records for this event may help us understand climate-carbon cycle feedbacks under interglacial conditions, which are important for understanding future climate, but existing ice core records do not provide enough detail and natural smoothing of the CO2 time series by diffusion and gradual bubble close-off in the firn layer (unconsolidated snow layer in the top of ice sheets) limits their resolution. Studies of leaf stomata records suggest a CO2 decrease of up to ~25 ppm during the 8.2 ka event, but relatively large uncertainties in reconstructed CO2 levels from leaves and dating make firm conclusions difficult. Here we present a new CO2 record from the Siple Dome ice core, Antarctica, that covers 7.4-9.0 ka with 8- to 16-year resolution. The relatively high snow accumulation rate at Siple Dome results minimizes smoothing relative to other records and the timing of the 8.2 ka event is precisely constrained by a CH4 record from the same core. We observe a small, ~2 ppm, increase of atmospheric CO2 during the 8.2 ka event. The increase is not remarkable when compared to other centennial variations in the Holocene that are not linked to large temperature changes. Our results imply that the sensitivity of atmospheric CO2 to the primarily northern hemisphere cooling of the 8.2 ka event was limited.

  16. Abrupt climate change: Past, present and the search for precursors as an aid to predicting events in the future (Hans Oeschger Medal Lecture)

    NASA Astrophysics Data System (ADS)

    Mayewski, Paul Andrew

    2016-04-01

    The demonstration using Greenland ice cores that abrupt shifts in climate, Dansgaard-Oeschger (D-O) events, existed during the last glacial period has had a transformational impact on our understanding of climate change in the naturally forced world. The demonstration that D-O events are globally distributed and that they operated during previous glacial periods has led to extensive research into the relative hemispheric timing and causes of these events. The emergence of civilization during our current interglacial, the Holocene, has been attributed to the "relative climate quiescence" of this period relative to the massive, abrupt shifts in climate that characterized glacial periods in the form of D-O events. But, everything is relative and climate change is no exception. The demise of past civilizations, (eg., Mesopatamian, Mayan and Norse) is integrally tied to abrupt climate change (ACC) events operating at regional scales. Regionally to globally distributed ACC events have punctuated the Holocene and extreme events have always posed significant challenges to humans and ecosystems. Current warming of the Arctic, in terms of length of the summer season, is as abrupt and massive, albeit not as extensive, as the transition from the last major D-O event, the Younger Dryas into the Holocene (Mayewski et al., 2013). Tropospheric source greenhouse gas rise and ozone depletion in the stratosphere over Antarctica are triggers for the modern advent of human emission instigated ACCs. Arctic warming and Antarctic ozone depletion have resulted in significance changes to the atmospheric circulation systems that transport heat, moisture, and pollutants in both hemispheres. Climate models offer a critical tool for assessing trends, but they cannot as yet predict ACC events, as evidenced by the inability of these models to predict the rapid onset of Arctic warming and resulting changes in atmospheric circulation; and in the model vs past analog differences in projections for

  17. Abrupt onset and prolongation of aragonite undersaturation events in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Hauri, Claudine; Friedrich, Tobias; Timmermann, Axel

    2016-02-01

    Ocean acidification may lead to seasonal aragonite undersaturation in surface waters of the Southern Ocean as early as 2030 (ref. ). These conditions are harmful to key organisms such as pteropods, which contribute significantly to the pelagic foodweb and carbon export fluxes in this region. Although the severity of ocean acidification impacts is mainly determined by the duration, intensity and spatial extent of aragonite undersaturation events, little is known about the nature of these events, their evolving attributes and the timing of their onset in the Southern Ocean. Using an ensemble of ten Earth system models, we show that starting around 2030, aragonite undersaturation events will spread rapidly, affecting ~30% of Southern Ocean surface waters by 2060 and >70% by 2100, including the Patagonian Shelf. On their onset, the duration of these events will increase abruptly from 1 month to 6 months per year in less than 20 years in >75% of the area affected by end-of-century aragonite undersaturation. This is likely to decrease the ability of organisms to adapt to a quickly evolving environment. The rapid equatorward progression of surface aragonite undersaturation can be explained by the uptake of anthropogenic CO2, whereas climate-driven physical or biological changes will play a minor role.

  18. Agriculture, Settlement, and Abrupt Climate Change: The 4.2ka BP event in Northern Mesopotamia

    NASA Astrophysics Data System (ADS)

    Ristvet, L.

    2003-12-01

    An abrupt aridification event at 4200 BP has been recorded in 41 paleoclimate proxies in the Old World, from Kilmanjaro, Tanzania to Rajasthan, India, East Asia and the Pacific. This event is particularly well defined for Western Asia, where it has been associated with the abandonment of settlements across the Fertile Crescent and the collapse of states on the Levantine coast and in the dry-farming plains of Northern Mesopotamia, including the Akkadian Empire. Adaptations to climate change are constrained by both local environmental and social factors. Agriculturalists, especially those living in pre-industrial societies, are particularly susceptible to changes in precipitation. The Tell Leilan Regional Survey, which systematically studied sites in a 1650km2 area of Northeastern Syria, records one set of adaptations to this event in an area where dry-farming provided the subsistence base. The survey transect crosses ecotones, from the present 500mm isohyet in the North to the 250mm isohyet in the South, and contains diverse wadi systems, ground water resources, soil profiles, and an ancient marsh/lake-- all of which allow this region to be taken as a microcosm of Northern Mesopotamia. In order to contextualize our study of human response to abrupt climate change, it is necessary to consider how the economic and social systems that were previously in place were transformed by this event. This study attempts to quantify climate change and model its effects on agricultural, pastoral, and settlement systems in Northeastern Syria from 2400-1700 BC. From 2400-2300 BC, optimal climate conditions coincided with the consolidation of an indigenous state. The next century witnessed the Akkadian conquest and imperialization of the Habur plains, which resulted in both the intensification and extensification of agro-production. During the next 300 years, (2200-1900 BC), rainfall plummeted to 70% of the climatic optimum, triggering the abandonment of cities along with their

  19. Abrupt climatic events during OIS-3 recorded in terrestrial sediments in the Netherlands: a multi-proxy approach

    NASA Astrophysics Data System (ADS)

    Bos, J. A. A.; Bohncke, S. J. P.; Kasse, C.; van Huissteden, J.; Schokker, J.; Bunnik, F. P. M.; Wallinga, J.

    2009-04-01

    Abrupt climatic changes during Oxygen Isotope Stage 3 (OIS-3 or Weichselian Middle Pleniglacial) are revealed in the oxygen isotope records of the Greenland ice cores and in the North Atlantic marine cores. In the Greenland ice cores, these so-called D/O cycles start with a rapid warming of 5-10˚C within a few decades, followed by a phase of gradual cooling over several hundred to more than a thousand years and often end with a final reduction in temperature back to cold, stadial conditions. On the adjacent European continent, however, climatic variability during this time interval is poorly known. High-resolution terrestrial records are scarce and the discontinuous nature of sedimentation and repeated erosion on the continent combined with poor dating control often hampers a detailed study of the vegetation and climate. In this contribution, a Middle Weichselian sequence with shallow lacustrine deposits, intercalated by fluvial sediments with permafrost features, is presented from the Netherlands. Within this Middle Weichselian sequence, rapid warming events are assumed to have given rise to thawlake formation and/or deposition of organic-rich lacustrine sediments, while the extreme cooling events of the D/O cycles are probably represented in the sequences by clastic intervals during which periglacial features developed. In the sixties of the last century, two warming events or "interstadials" were first recognized and described from terrestrial Middle Weichselian sequences from the Hengelo basin in the Netherlands, the Hengelo- and Denekamp interstadials, respectively. The shift from a polar desert to shrub tundra (i.e. Hengelo interstadial) and tundra to shrub tundra (i.e. Denekamp interstadial), visible in the pollen diagrams of this area, was interpreted as a temporary amelioration of the climate and were therefore given the names of interstadials. In time the Hengelo- and Denekamp interstadials were also correlated with D/O cycles 12 respectively 8 in the

  20. Diatoms as Proxies for Abrupt Events in the Hudson River Estuary

    NASA Astrophysics Data System (ADS)

    Skorski, W.; Abbott, D. H.; Recasens, C.; Breger, D. L.

    2014-12-01

    The Hudson River estuary has been subject to many abrupt events throughout its history including hurricanes, droughts and pluvials. Hurricanes in particular are rare, discrete events that if fingerprinted can be used to develop better age models for Hudson River sediments. Proxies use observed physical characteristics or biological assemblages (e.g. diatom and foraminiferal assemblages) as tools to reconstruct past conditions prior to the modern instrumental record. Using a sediment core taken from the Hudson River (CDO2-29A), in New York City, drought and pluvial layers were selected based on Cs-137 dating while hurricane layers were determined from occurrences of tropical to subtropical foraminifera. Contrary to previous studies (Weaver, 1970, Weiss et al, 1978), more than sixty different diatom species have been identified using a scanning electron microscope (SEM). Cosmopolitan, hurricane and drought assemblages have begun to be identified after observing multiple layers (Table 1). Tropical foraminifera dominated by Globigerinoides ruber pink were also found in a hurricane layer that we infer was deposited during Hurricane Belle in 1976. More diatom abundance analyses and cataloged SEM pictures will provide further insight into these proxies. Table 1 Diatom Genera and Species Environment Clarification Cyclotella caspia Planktonic, marine-brackish Cosmopolitan Karayevia clevei Freshwater Cosmopolitan Melosira sp Planktonic, marine Cosmopolitan Thalassiosira sp Marine, brackish Cosmopolitan Staurosirella leptostauron Benthic, freshwater Cosmopolitan Actinoptychus senarius Planktonic or benthic, freshwater to brackish Hurricane and pluvial layers Amphora aff. sp Benthic, marine or freshwater Hurricane layers only Nitzschia sp Benthic, marine or freshwater Hurricane layers only Gomphonema sp Freshwater Hurricane layers only Surirella sp Marine-brackish Drought layer only Triceratium sp Marine Drought layer only Other Genera and species Environment Clarification

  1. North Atlantic warming during Dansgaard-Oeschger events synchronous with Antarctic warming and out-of-phase with Greenland climate

    PubMed Central

    Rasmussen, Tine L.; Thomsen, Erik; Moros, Matthias

    2016-01-01

    The precise reason for the differences and out-of-phase relationship between the abrupt Dansgaard-Oeschger warmings in the Nordic seas and Greenland ice cores and the gradual warmings in the south-central Atlantic and Antarctic ice cores is poorly understood. Termed the bipolar seesaw, the differences are apparently linked to perturbations in the ocean circulation pattern. Here we show that surface and intermediate-depth water south of Iceland warmed gradually synchronously with the Antarctic warming and out of phase with the abrupt warming of the Nordic seas and over Greenland. The hinge line between areas showing abrupt and gradual warming was close to the Greenland-Scotland Ridge and the marine system appears to be a ‘push-and-pull’ system rather than a seesaw system. ‘Pull’ during the warm interstadials, when convection in the Nordic seas was active; ‘push’ during the cold stadials, when convection stopped and warm water from the south-central Atlantic pushed northward gradually warming the North Atlantic and Nordic seas. PMID:26847384

  2. North Atlantic warming during Dansgaard-Oeschger events synchronous with Antarctic warming and out-of-phase with Greenland climate.

    PubMed

    Rasmussen, Tine L; Thomsen, Erik; Moros, Matthias

    2016-01-01

    The precise reason for the differences and out-of-phase relationship between the abrupt Dansgaard-Oeschger warmings in the Nordic seas and Greenland ice cores and the gradual warmings in the south-central Atlantic and Antarctic ice cores is poorly understood. Termed the bipolar seesaw, the differences are apparently linked to perturbations in the ocean circulation pattern. Here we show that surface and intermediate-depth water south of Iceland warmed gradually synchronously with the Antarctic warming and out of phase with the abrupt warming of the Nordic seas and over Greenland. The hinge line between areas showing abrupt and gradual warming was close to the Greenland-Scotland Ridge and the marine system appears to be a 'push-and-pull' system rather than a seesaw system. 'Pull' during the warm interstadials, when convection in the Nordic seas was active; 'push' during the cold stadials, when convection stopped and warm water from the south-central Atlantic pushed northward gradually warming the North Atlantic and Nordic seas. PMID:26847384

  3. North Atlantic warming during Dansgaard-Oeschger events synchronous with Antarctic warming and out-of-phase with Greenland climate

    NASA Astrophysics Data System (ADS)

    Rasmussen, Tine L.; Thomsen, Erik; Moros, Matthias

    2016-02-01

    The precise reason for the differences and out-of-phase relationship between the abrupt Dansgaard-Oeschger warmings in the Nordic seas and Greenland ice cores and the gradual warmings in the south-central Atlantic and Antarctic ice cores is poorly understood. Termed the bipolar seesaw, the differences are apparently linked to perturbations in the ocean circulation pattern. Here we show that surface and intermediate-depth water south of Iceland warmed gradually synchronously with the Antarctic warming and out of phase with the abrupt warming of the Nordic seas and over Greenland. The hinge line between areas showing abrupt and gradual warming was close to the Greenland-Scotland Ridge and the marine system appears to be a ‘push-and-pull’ system rather than a seesaw system. ‘Pull’ during the warm interstadials, when convection in the Nordic seas was active; ‘push’ during the cold stadials, when convection stopped and warm water from the south-central Atlantic pushed northward gradually warming the North Atlantic and Nordic seas.

  4. Abrupt Climatic Events Observed in Organic-Rich Sediments From Lake Tanganyika, Tropical East Africa, Over the Past 50 kyr

    NASA Astrophysics Data System (ADS)

    Burnett, A. P.; Weyhenmeyer, C. E.; Scholz, C. A.; Swart, P. K.

    2006-12-01

    Abrupt climate changes such as Dansgaard-Oeschger Cycles and Heinrich Events were first detected in high- latitude records, but an increasing number of studies suggest that these rapid changes are actually global events. The degree to which the tropics drive, control and/or respond to such rapid changes is still poorly understood due to a scarcity of data from low-latitude regions. A recently acquired sediment core from Lake Tanganyika, East Africa, provides a unique archive to study abrupt climate events in the tropics throughout the last glaciation. The core provides a continuous, undisturbed and high resolution climate record over the past 100 kyr. An age-depth model based on 25 new radiocarbon dates provides a solid, high-resolution chronology for the past 50 kyr. Throughout this time, several rapid changes in paleoclimate proxy data are observed along the core. Sedimentation rates remained fairly constant from the Holocene until the Last Glacial Maximum (LGM) but increased abruptly from ~80 mm/1000 yr to ~150 mm/1000 yr around 18 kyr BP. At the same time, the sediment record reveals a sudden increase in total organic carbon (TOC) from 4% to 12% indicating a rapid increase in organic matter contributions at the end of the LGM. Abrupt changes in TOC and δ13C values are also found at ~38 kyr, ~30 kyr and ~16 kyr BP, suggesting a possible link to Heinrich events 4, 3 and 1, respectively. Forthcoming very high-resolution analyses, to augment existing low-resolution data, include δ13C, δ15N, C/N ratios and TOC values. Furthermore, TEX86 measurements will be carried out to determine whether the observed changes in organic matter contributions are associated with changes in water temperatures. In combination with the solid 14C chronology, the new data will allow us to precisely determine the onset, timing and nature of abrupt changes and evaluate them in the global context.

  5. Warm-season severe wind events in Germany

    NASA Astrophysics Data System (ADS)

    Gatzen, Christoph

    2013-04-01

    A 15-year data set of wind measurements was analyzed with regard to warm season severe wind gusts in Germany. For April to September of the years 1997 to 2011, 1035 wind measurements of 26 m/s or greater were found. These wind reports were associated with 268 wind events. In total, 252 convective wind events contributed to 837 (81%) of the wind reports, 16 non-convective synoptic-scale wind events contributed to 198 reports (19%). Severe wind events were found with synoptic situations characterized by rather strong mid-level flow and advancing mid-level troughs. Severe convective wind events were analyzed using radar images and classified with respect to the observed radar structure. The most important convective mode was squall lines that were associated with one third of all severe wind gusts, followed by groups, bow echo complexes, and bow echoes. Supercells and cells were not associated with many wind reports. The low contribution of isolated cells indicates that rather large-scale forcing by synoptic-scale features like fronts is important for German severe wind events. Bow echoes were found to be present for 58% of all wind reports. The movement speed of bow echoes indicated a large variation with a maximum speed of 33 m/s. Extreme wind events as well as events with more than 15 wind reports were found to be related to higher movement speeds. Concentrating on the most intense events, derechos seem to be very important to the warm season wind threat in Germany. Convective events with a path length of more than 400 km contributed to 36% of all warm-season wind gusts in this data set. Furthermore, eight of nine extreme gusts exceeding 40 m/s were recorded with derecho events.

  6. Discrimination of a major stratospheric warming event in February-March 1984 from earlier minor warmings

    NASA Technical Reports Server (NTRS)

    Johnson, K. W.; Quiroz, R. S.; Gelman, M. E.

    1985-01-01

    As part of its responsibility for stratospheric monitoring, the Climate Analysis Center derives time trends of various dynamic parameters from NMC stratospheric analyses. Selected figures from this stratospheric monitoring data base are published in Climate Diagnostics Bulletin in March and October, after each hemispheric winter. During the Northern Hemisphere winter of December 1983-February 1984 several warming events may be seen in the plot of 60 deg. N zonal mean temperatures for 10 mb. Minor warmings may be noted in early December, late December, mid January and early February. A major warming with the 60 deg. N zonal mean temperatures reaching -40C is observed in late February, associated with a circulation reversal. In all of the minor warming episodes, there is a polarward movement of the Aleutian anticyclone; however, at 10 mb the North Pole remains in the cyclonic circulation of the stratospheric vortex which is not displaced far from its usual position. In the case of the later February major warming, the 10 mb circulation pattern over the North Pole is anticyclonic, and the cyclonic circulation has moved to the south and east with a considerable elongation. Cross sections of heat transport and momentum transport are not dramatically different for the minor and major warming episodes.

  7. Competition between global warming and an abrupt collapse of the AMOC in Earth’s energy imbalance

    PubMed Central

    Drijfhout, Sybren

    2015-01-01

    A collapse of the Atlantic Meridional Overturning Circulation (AMOC) leads to global cooling through fast feedbacks that selectively amplify the response in the Northern Hemisphere (NH). How such cooling competes with global warming has long been a topic for speculation, but was never addressed using a climate model. Here it is shown that global cooling due to a collapsing AMOC obliterates global warming for a period of 15–20 years. Thereafter, the global mean temperature trend is reversed and becomes similar to a simulation without an AMOC collapse. The resulting surface warming hiatus lasts for 40–50 years. Global warming and AMOC-induced NH cooling are governed by similar feedbacks, giving rise to a global net radiative imbalance of similar sign, although the former is associated with surface warming, the latter with cooling. Their footprints in outgoing longwave and absorbed shortwave radiation are very distinct, making attribution possible. PMID:26437599

  8. Comment on "Abrupt warming events drove Late Pleistocene Holarctic megafaunal turnover".

    PubMed

    Rasmussen, Sune O; Svensson, Anders M

    2016-02-26

    Cooper et al. (Research Article, 7 August 2015, p. 602) combined the annual-layer-counted Greenland Ice Core Chronology 2005 with chronological information from the Hulu Cave and Cariaco Basin records to produce a "revised" time scale. We argue that their time scale is incompatible with the nature of annual-layer-counted time scales and may lead to seriously flawed conclusions if used elsewhere at face value. PMID:26917761

  9. Global variations of zonal mean ozone during stratospheric warming events

    NASA Technical Reports Server (NTRS)

    Randel, William J.

    1993-01-01

    Eight years of Solar Backscatter Ultraviolet (SBUV) ozone data are examined to study zonal mean variations associated with stratospheric planetary wave (warming) events. These fluctuations are found to be nearly global in extent, with relatively large variations in the tropics, and coherent signatures reaching up to 50 deg in the opposite (summer) hemisphere. These ozone variations are a manifestation of the global circulation cells associated with stratospheric warming events; the ozone responds dynamically in the lower stratosphere to transport, and photochemically in the upper stratosphere to the circulation-induced temperature changes. The observed ozone variations in the tropics are of particular interest because transport is dominated by zonal-mean vertical motions (eddy flux divergences and mean meridional transports are negligible), and hence, substantial simplifications to the governing equations occur. The response of the atmosphere to these impulsive circulation changes provides a situation for robust estimates of the ozone-temperature sensitivity in the upper stratosphere.

  10. Southeast Atlantic warm events and southern african rainfall

    NASA Astrophysics Data System (ADS)

    Rouault, M.

    2003-04-01

    From January to May 2001, several countries of Southern Africa experienced above normal rainfall and floods. 23 000 people were displaced in Southern Angola after a flood in April. In March, an inundation killed several people and displaced 5,000 others in eastern Zambia's. The situation in Zambia was aggravated when authorities had to open the spillway gates at the Kariba Dam, the main source of electricity for Zambia and Zimbabwe. Water discharged from the Kariba dam ran into neighbouring Mozambique, aggravating floods in that country. At the same time warm sea surface anomalies were measured off the Angolan and Namibian coast. Warm events in the Southeast Tropical Atlantic off Angola and Namibia called "Benguela Nino" are known to affect the fisheries of the region but they also affect the rainfall. In 1995, the warmest recorded Benguela Nino happened with anomalies off up to 8°C extending 300 km offshore with a southward extension to 27°S. During the 1984, 1986, 1995 and 2001 warm events, above average rainfall occurred near the sea surface temperature anomalies and extended inland from the coast to an extent that appeared to depend on the intensity of the regional moisture convergence and atmospheric circulation anomalies. Rainfall over western Angola / Namibia is greatest for those events for which the local circulation anomalies act to strengthen the climatological westwards flux of Indian Ocean sourced moisture across low latitude southern Africa and which flow anticyclonically over the warmest SST off the northern coast. The significance of the warm events occurring during the February to April period is that this is the time when SST reaches its maximum in the annual cycle (up to 28oC off northern Angola) and this favours more intense local evaporation and convection and a greater impact on late austral summer rainfall.

  11. Changes in winter warming events in the Nordic Arctic Region

    NASA Astrophysics Data System (ADS)

    Vikhamar-Schuler, Dagrun; Isaksen, Ketil; Haugen, Jan Erik; Bjerke, Jarle Werner; Tømmervik, Hans

    2015-04-01

    In recent years winter warming events are frequently reported from Arctic areas. Extraordinarily warm weather episodes, occasionally combined with intense rainfall, cause severe ecological disturbance and great challenges for Arctic infrastructure. For example, the formation of ground ice due to winter rain or melting prevents reindeer from grazing, leads to vegetation browning, and impacts soil temperatures. The infrastructure may be affected by avalanches and floods resulting from intense snowmelt. The aim of our analysis is to study changes in warm spells during winter in the Nordic Arctic Region, here defined as the regions in Norway, Sweden and Finland north of the Arctic circle (66.5°N), including the Arctic islands Svalbard and Jan Mayen. Within this study area we have selected the longest available high quality observation series with daily temperature and precipitation. For studying future climate we use available regionally downscaled scenarios. We analyse three time periods: 1) the past 50-100 years, 2) the present (last 15 years, 2000-2014) and 3) the future (next 50-100 years). We define an extended winter season (October-April) and further divide it into three subseasons: 1) Early winter (October and November), 2) Mid-winter (December, January and February) and 3) Late-winter (March and April). We identify warm spells using two different classification criteria: a) days with temperature above 0°C (the melting temperature); and b) days with temperature in excess of the 90th percentile of the 1985-2014 temperature for each subseason. Both wet and dry warm spells are analysed. We compare the results for the mainland stations (maritime and inland stations) with the Arctic islands. All stations have very high frequency of warm weather events in the period 1930-1940s and for the last 15 years (2000-2014). For the most recent period the largest increase in number of warm spells are observed at the northernmost stations. We also find a continuation of this

  12. Global warming, drought events, and GPP performance (Invited)

    NASA Astrophysics Data System (ADS)

    Yi, C.; Jensen, K.; Wei, S.; Hendrey, G.

    2013-12-01

    The first decade of the 21st century was the warmest decade recorded since the start of modern measurements in 1850, according to a new report on July 3, 2013 by the World Meteorological Organization (WMO). Global warming may now be exacerbating droughts in the world, and leading to more reduction in crop production, plant growth and hence carbon fixation, and further warming climate. How do we quantify the relationship between drought event and ecosystem performance? Here, we developed a method called 'perfect-deficit approach' and a local dryness index based on eddy-flux measurements. We applied these concepts and mathematical method to remote sensing observations (MODIS) to examine the world ecosystem performance in the first decade of 21st century and identify the associated climate extremes. The initial results show that the deficits of ecosystem performances in lower latitudes were caused mainly by drought events, while at high latitudes cold/warm events also exert substantial influences on ecosystem performances, particularly in spring season. Acknowledgements This research was financially supported by PSC-CUNY Award (PSC-CUNY-ENHC-44-83)

  13. Response of atmospheric CO2 to the abrupt cooling event 8200 years ago

    NASA Astrophysics Data System (ADS)

    Ahn, Jinho; Brook, Edward J.; Buizert, Christo

    2014-01-01

    Atmospheric CO2 records for the centennial scale cooling event 8200 years ago (8.2 ka event) may help us understand climate-carbon cycle feedbacks under interglacial conditions, which are important for understanding future climate, but existing records do not provide enough detail. Here we present a new CO2 record from the Siple Dome ice core, Antarctica, that covers 7.4-9.0 ka with 8 to 16 year resolution. We observe a small, about 1-2 ppm, increase of atmospheric CO2 during the 8.2 ka event. The increase is not significant when compared to other centennial variations in the Holocene that are not linked to large temperature changes. Our results do not agree with leaf stomata records that suggest a CO2 decrease of up to ~25 ppm and imply that the sensitivity of atmospheric CO2 to the primarily Northern Hemisphere cooling of the 8.2 ka event was limited.

  14. Atlantic Warm Pool Trigger for the Younger Dryas Climate Event

    NASA Astrophysics Data System (ADS)

    Abdul, N. A.; Mortlock, R. A.; Wright, J. D.; Fairbanks, R. G.; Teneva, L. T.

    2011-12-01

    There is growing evidence that variability in the size and heat content of the tropical Atlantic Warm Pool impacts circum-North Atlantic climate via the Atlantic Multi-decadal Oscillation mode (Wang et al., 2008). The Atlantic Warm Pool spans the Gulf of Mexico, Caribbean Sea and the western tropical North Atlantic. Barbados is located near the center of the tropical Atlantic Warm Pool and coupled ocean models suggest that Barbados remains near the center of the tropical Atlantic Warm Pool under varying wind stress simulations. Measurements of the oxygen isotope paleothermometer in Acropora palmata coral species recovered from cores offshore Barbados, show a 3oC monotonic decrease in sea surface temperature from 13106 ± 83 to 12744 ± 61 years before present (errors given as 2 sigma). This interval corresponds to a sea level rise from 71.4 meters to 67.1 meters below present levels at Barbados. The 3oC temperature decrease is captured in eight A. palmata specimens that are in stratigraphic sequence, 230Th/234U dated, and analyzed for oxygen isotopes. All measurements are replicated. We are confident that this is the warm pool equivalent of the Younger Dryas climate event. The initiation of this temperature drop in the Atlantic Warm Pool predates the Younger Dryas start in Greenland ice cores, reported to start at 12896 ± 138 years (relative to AD 2000) (Rasmussen et al., 2006), while few other Younger Dryas climate records are dated with similar accuracy to make the comparison. Rasmussen, S.O., Andersen, K.K., Svensson, A.M., Steffensen, J.P., Vinther, B.M., Clausen, H.B., Siggaard-Andersen, M.L., Johnsen, S.J., Larsen, L.B., Dahl-Jensen, D., Bigler, M., Röthlisberger, R., Fischer, H., Goto-Azuma, K., Hansson, M.E., and Ruth, U., 2006, A new Greenland ice core chronology for the last glacial termination: J. Geophys. Res., v. 111, p. D06102. Wang, C., Lee, S.-K., and Enfield, D.B., 2008, Atlantic Warm Pool acting as a link between Atlantic Multidecadal

  15. Evidence of Abrupt Climatic Variability Across Heinrich Events from Multiple Bahamian Stalagmites

    NASA Astrophysics Data System (ADS)

    Arienzo, M. M.; Swart, P. K.; Pourmand, A.; Broad, K.; Clement, A. C.; Murphy, L.; Kakuk, B.

    2013-12-01

    Various types of paleoclimate data support the global nature and scale of Heinrich events. While a comprehensive picture of climate across Heinrich events is emerging for the North Atlantic, very few studies have been conducted in the subtropical western Atlantic, which may be an important area for investigating the global propagation of these events. In this study, we have attempted to further understand sub-tropical climate using geochemical records from multiple speleothems from a flooded cave in the Bahamas. These Bahamian stalagmites demonstrate increased aridity and temperature decrease associated with Heinrich events. Speleothems collected at depths ranging from 10-40 meters below modern sea level were dated using U-Th geochronometry with MC-ICP-MS at the Neptune Isotope Laboratory of University of Miami. Stable carbon and oxygen isotopes were measured at a resolution of 1 mm. In the subtropics, it has been demonstrated that higher volume rainfall events generally lead to a depleted δ18O signal, whereas heavier δ18O values are attributed to lower amounts of rainfall. Interpreting the δ18O of a carbonate is inherently difficult because the δ18O of a carbonate is dependent on both the variations in temperature and the δ18O of the cave water. In order to solve for the second unknown, an additional proxy is needed to provide information on one of the two unknowns. Fluid inclusion isotopic analysis provides information on the isotopic ratio of the formation water that can therefore be used to calculate paleo-temperature. Preliminary U-Th age results from multiple speleothems from Dan's Cave, Abaco Island, Bahamas demonstrate the stalagmite samples were forming from ~13 to 65 ka. The carbonate δ18O and δ13C results reveal significant isotopic excursions associated with Heinrich events. More positive carbon and oxygen isotopic values are observed leading into the Heinrich events, followed by more negative values at the terminations. In contrast to increased

  16. The glaciology of IRD events: warming and ice dynamics

    NASA Astrophysics Data System (ADS)

    Hindmarsh, R. C. A.

    2003-04-01

    Heinrich events, the enormous glacial-period ice-rafting episodeshave been posited to be due to large-scale surges of the Laurentide ice-sheet (3). However, more frequent events such as the Bond events are difficult to explain this way. Recently acquired geological evidence (2,4) suggests that climatic perturbations are correlated with some N. Atlantic IRD events. A model (1) which show how climate perturbations can lead to IRD events is reviewed. The model shows how 20-50km retreats induced by ablation rates of 2 m/yr provide sufficient debris flux through the grounding line to produce large sedimentation events. Such ablation would reduce ice-shelf extent markedly, permitting debris to reach the calving front and be transported by icebergs leading to ice-rafted debris (IRD) events. Surges are not necessary conditions for the production of large IRD events. The glacial dynamics of this climate perturbation model is compared with the surge theory, with particular emphasis on the amount of sediment that either method can deliver to the oceans. Consideration of the non-exclusivety and consistency of the two mechanisms is emphasised. (1) R.C.A. Hindmarsh and A. Jenkins, Centurial-millenial ice-rafted debris pulses from ablating marine ice sheets, Geophys Res. Lett 22(12), 2477-2480, 2001; (2) Paul C. Knutz et al. G3 Multidecadal ocean variability and NW European ice sheet surges during the last deglaciation G3 3(12) 17 December 2002 1077, doi:10.1029/2002GC000351; (3) MacAyeal,D.R. Binge/purge oscillations of the Laurentide ice-sheet as a cause of the North-Atlantic's Heinrich events, Paleoceanography, 8(6), p.775-784, (1993); (4) M. Moros, et. al. Were glacial iceberg surges in the North Atlantic triggered by climatic warming?, Marine Geology, 192(4), 2002, p.393-417

  17. Imminent onset and abrupt increase in duration of low aragonite and calcite saturation state events in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Friedrich, T.; Hauri, C.; Timmermann, A.

    2015-12-01

    Rapid progression of ocean acidification is a threat to key organisms of the Southern Ocean ecosystem. While the severity of ocean acidification impacts is mainly determined by the duration, intensity, and spatial extent of low aragonite or calcite saturation state events, little is known about the nature of these events, their evolving attributes, and the timing of their onset. Using output of historical and RCP 8.5 simulations from ten Earth System Models from CMIP5, we found that aragonite undersaturation, which decreases the calcification rate of pteropods and causes dissolution of their aragonitic shell, will spread rapidly after 2035, covering 70 % of the Southern Ocean surface waters by 2095. Surface aragonite undersaturation events will last for about 5 months in areas south of 60°S by 2055, and for more than 8 months by the end of the century. Overall, the duration of these events increases from 1 month to more than 6 months within fewer than 20 years in >75 % of the affected area. This abrupt change in exposure duration to unfavorable conditions may be too fast for pteropods to adapt, as these chemical changes will occur within just a few generations. As a result of two month-long calcite undersaturation events projected for the end of this century, even organisms built of the more stable calcium carbonate mineral calcite will face prolonged chemical dissolution. The threat of ocean acidification to the Southern Ocean ecosystem may be more imminent than previously thought, and may spread quickly to the southern tips of New Zealand, South America, and South Africa, with potentially far-reaching consequences to fisheries, local economies, and livelihoods.

  18. Thermospheric meridional circulation during sudden stratospheric warming events

    NASA Astrophysics Data System (ADS)

    Laskar, F. I.; Duggirala, P. R.

    2014-12-01

    Oxygen dayglow emission intensities, at OI 557.7, OI 630.0, and OI 777.4 nm, over a low-latitude location showed systematic enhancements in intensities throughout the daytime hours during the four sudden stratospheric warming (SSW) events that occurred in the years 2010 - 2013. The arctic latitude lower thermospheric temperatures at around 120 km altitudes obtained from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument are found to be enhanced during SSW events and show a latitudinal gradient (temperature decreasing towards low-latitudes). Commensurately, the Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics (TIMED) Doppler Interferometer (TIDI) measurements showed equatorward winds in the mesosphere lower thermosphere (MLT) altitudes over high latitudes during these events. Both, the high-latitude lower thermospheric temperature enhancements and the MLT region equatorward winds occur simultaneously with the observed enhancements in the OI dayglow emission intensities at all the wavelengths. From these observations and other supporting observational and modeling results it is proposed that a new cell of meridional circulation in the MLT winds is set up during SSW events, which enables transport of atomic oxygen from high-to-low latitudes. Such an additional contribution of oxygen density over low-latitudes interacts with daytime lower thermospheric dynamics and is attributed to be the cause for the observed enhancement in the oxygen daytime optical emission intensities over low-latitudes. These results will presented in the light of experimental evidence to such circulation alluded to by earlier simulation studies.

  19. Abrupt Changes at the Permian/Triassic Boundary: Tempo of Events from High-Resolution Cyclostratigraphy

    NASA Technical Reports Server (NTRS)

    Rampino, M. R.; Prokoph, A.; Adler, A. C.

    2000-01-01

    the nearby Reppwand outcrop section, the same faunal changes occurs over only 0.8 m or about 8,000 years, close to the limit of time-resolution induced by bioturbation and reworking in these sediments. The sharp negative global carbon-isotope shift took place within less than or equal to 40,000 yr, and the isotope excursions persisted for approximately 480,000 yr into the Early Triassic. The results indicate that the severe marine faunal event that marks the P/Tr boundary was very sudden, perhaps less than the resolution window in the GK-1 core, and suggest a catastrophic cause. The wavelet-analysis approach to high-resolution cyclostratigraphy can be applied to other P/Tr boundary sections, and when combined with precise absolute dating and magnetostratigraphic methods promises a significant increase in resolution in determining the correlation and tempo of the end-Permian extinctions and related events worldwide.

  20. Millennial scale precipitation changes over Easter Island (Southern Pacific) during MIS 3: Inter-hemispheric connections during North Atlantic abrupt cold events

    NASA Astrophysics Data System (ADS)

    Margalef, Olga; Cacho, Isabel; Pla-Rabes, Sergi; Cañellas-Boltà, Núria; Pueyo, Juan Jose; Sáez, Alberto; Valero-Garcés, Blas L.; Giralt, Santiago

    2013-04-01

    Marine Isotope Stage (MIS) 3 climate has been globally characterized by the occurrence of millennial-scale climate variations defined over North Atlantic as Dansgaard-Oeschger and Heinrich events. Despite climate variability has been broadly explored over North Atlantic records, the response of the tropical and subtropical latitudes, especially in the Southern Hemisphere, still remains as a matter of debate. Rano Aroi peat record (Easter Island, Chile, 27°S) provides a unique opportunity to understand Southern Pacific atmospheric and oceanic changes during these stadial-interstadial transitions because of its exceptional location on the interplay of the South Pacific Convergence Zone (SPCZ), the Intertropical Convergence Zone (ITCZ), the South Pacific Anticyclone (SPA) and the Southern Westerlies (SW). Rano Aroi record contains 8 main enhanced precipitation events between 70 and 40 kyr BP that can be correlated with the timing of Heinrich events 5, 5a and 6 as well as other cold stadials. These humid events are also present in other Southern Hemisphere continental sites and correspond to dry periods on Northern Hemisphere records. This opposite hydrologic trend has been explained by the latitudinal migration of ITCZ and has been supported by several climatic models. As Easter Island precipitation is mainly dependent on SPCZ storm track belt activity, we suggest that the southern migration of the ITCZ is associated to an expansion of SPCZ to the east. This process should be intimately related to a weakening of the Walker circulation, which is further supported by an estimation of d18Osw gradient along the equator for the same time period. Consequently, atmospheric and oceanic responses during these cold stadials and Heinrich events might lead to a configuration that resembles the warm ENSO state over Southern Pacific, as previously suggested by some global climatic models. Rano Aroi record clearly points out that shifts in hydrological cycle in tropical Southern

  1. Tropical North Atlantic subsurface warming events as a fingerprint for AMOC variability during Marine Isotope Stage 3

    NASA Astrophysics Data System (ADS)

    Parker, Andrew O.; Schmidt, Matthew W.; Chang, Ping

    2015-11-01

    The role of Atlantic Meridional Overturning Circulation (AMOC) as the driver of Dansgaard-Oeschger (DO) variability that characterized Marine Isotope Stage 3 (MIS 3) has long been hypothesized. Although there is ample proxy evidence suggesting that DO events were robust features of glacial climate, there is little data supporting a link with AMOC. Recently, modeling studies and subsurface temperature reconstructions have suggested that subsurface warming across the tropical North Atlantic can be used to fingerprint a weakened AMOC during the deglacial because a reduction in the strength of the western boundary current allows warm salinity maximum water of the subtropical gyre to enter the deep tropics. To determine if AMOC variability played a role during the DO cycles of MIS 3, we present new, high-resolution Mg/Ca and δ18O records spanning 24-52 kyr from the near-surface dwelling planktonic foraminifera Globigerinoides ruber and the lower thermocline dwelling planktonic foraminifera Globorotalia truncatulinoides in Southern Caribbean core VM12-107 (11.33°N, 66.63°W, 1079 m depth). Our subsurface Mg/Ca record reveals abrupt increases in Mg/Ca ratios (the largest equal to a 4°C warming) during the interstadial-stadial transition of most DO events during this period. This change is consistent with reconstructions of subsurface warming events associated with cold events across the deglacial using the same core. Additionally, our data support the conclusion reached by a recently published study from the Florida Straits that AMOC did not undergo significant reductions during Heinrich events 2 and 3. This record presents some of the first high-resolution marine sediment derived evidence for variable AMOC during MIS 3.

  2. An Abrupt Centennial-Scale Drought Event and Mid-Holocene Climate Change Patterns in Monsoon Marginal Zones of East Asia

    PubMed Central

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

    2014-01-01

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

  3. Analysis of warm convective rain events in Catalonia

    NASA Astrophysics Data System (ADS)

    Ballart, D.; Figuerola, F.; Aran, M.; Rigo, T.

    2009-09-01

    steep slopes. These factors increase the number of flash floods and the risk indexes. In the present study it is showed the general characteristics of the warm rain events observed in Catalonia, using meteorological, pluviometric, thermodynamic, and remote sensing data. Beside this, other heavy rain events with different features have been analyzed with the purpose of identify the main differences and to improve the knowledge in order to provide enough information for surveillance tasks

  4. A stratigraphic framework for abrupt climatic changes during the Last Glacial period based on three synchronized Greenland ice-core records: refining and extending the INTIMATE event stratigraphy

    NASA Astrophysics Data System (ADS)

    Rasmussen, Sune O.; Bigler, Matthias; Blockley, Simon P.; Blunier, Thomas; Buchardt, Susanne L.; Clausen, Henrik B.; Cvijanovic, Ivana; Dahl-Jensen, Dorthe; Johnsen, Sigfus J.; Fischer, Hubertus; Gkinis, Vasileios; Guillevic, Myriam; Hoek, Wim Z.; Lowe, J. John; Pedro, Joel B.; Popp, Trevor; Seierstad, Inger K.; Steffensen, Jørgen Peder; Svensson, Anders M.; Vallelonga, Paul; Vinther, Bo M.; Walker, Mike J. C.; Wheatley, Joe J.; Winstrup, Mai

    2014-12-01

    Due to their outstanding resolution and well-constrained chronologies, Greenland ice-core records provide a master record of past climatic changes throughout the Last Interglacial-Glacial cycle in the North Atlantic region. As part of the INTIMATE (INTegration of Ice-core, MArine and TErrestrial records) project, protocols have been proposed to ensure consistent and robust correlation between different records of past climate. A key element of these protocols has been the formal definition and ordinal numbering of the sequence of Greenland Stadials (GS) and Greenland Interstadials (GI) within the most recent glacial period. The GS and GI periods are the Greenland expressions of the characteristic Dansgaard-Oeschger events that represent cold and warm phases of the North Atlantic region, respectively. We present here a more detailed and extended GS/GI template for the whole of the Last Glacial period. It is based on a synchronization of the NGRIP, GRIP, and GISP2 ice-core records that allows the parallel analysis of all three records on a common time scale. The boundaries of the GS and GI periods are defined based on a combination of stable-oxygen isotope ratios of the ice (δ18O, reflecting mainly local temperature) and calcium ion concentrations (reflecting mainly atmospheric dust loading) measured in the ice. The data not only resolve the well-known sequence of Dansgaard-Oeschger events that were first defined and numbered in the ice-core records more than two decades ago, but also better resolve a number of short-lived climatic oscillations, some defined here for the first time. Using this revised scheme, we propose a consistent approach for discriminating and naming all the significant abrupt climatic events of the Last Glacial period that are represented in the Greenland ice records. The final product constitutes an extended and better resolved Greenland stratotype sequence, against which other proxy records can be compared and correlated. It also provides a

  5. Investigating Potential Causes for An Abrupt Change of Thermal State in Earth's Upper Mantle During the Great Oxygenation Event

    NASA Astrophysics Data System (ADS)

    Li, M.; McNamara, A. K.

    2014-12-01

    The oxygenic photosynthesis might have well evolved about 3 billion years ago, but there seems no great increase of atmospheric oxygen until the great oxygenation event (GOE) at about 2.4 Ga. One possibility for the suppressing of atmospheric oxygen level before the GOE is through consumption of oxygen by reduced volcanic gasses. The amount of atmospheric oxygen that could be consumed by volcanic gases depends on the absolute amount of volcanic gases as well as the redox state of the upper mantle. Evidence from the redox sensitive V/Sc ratio have shown that the redox state of the upper mantle have remained constant for the last 3.5 billion years (e.g., Li and Lee, 2004). If so, abrupt changes in thermal state of Earth's upper mantle could explain the rapid changes of degassing rate at the time of GOE. The Earth's lowermost mantle has been shown to be compositionally heterogeneous, which could be caused by the presence of dense, primordial material resulting from early differentiation processes. An important question is how do chemical heterogeneities in the lowermost mantle influence the secular cooling of the upper mantle. Here, we performed numerical calculations to explore the effects of themochemical convection on the thermal evolution of Earth's upper mantle. A large parameter space is explored, with varying Rayleigh number, viscosity, internal heating and density of chemical heterogeneities. We start with an initially hot mantle with a layer of dense material in the lowermost mantle. We found that when the mantle is hot, the dense material remains layered and covers the entire CMB, leading to low CMB heat flux. In this stage, the upper mantle cools down rapidly. However, as the mantle cools, the dense material is swept into discrete thermochemical piles by cold downwellings, leading to increasing CMB heat flux. The cooling rate of the mantle is temporarily reduced as this transition occurs. This occurs at a time consistent with the GOE event. Li, Z. X. A. and

  6. Subsurface North Atlantic warming as a trigger of rapid cooling events: evidence from the early Pleistocene (MIS 31-19)

    NASA Astrophysics Data System (ADS)

    Hernández-Almeida, I.; Sierro, F.-J.; Cacho, I.; Flores, J.-A.

    2015-04-01

    Subsurface water column dynamics in the subpolar North Atlantic were reconstructed in order to improve the understanding of the cause of abrupt ice-rafted detritus (IRD) events during cold periods of the early Pleistocene. We used paired Mg / Ca and δ18O measurements of Neogloboquadrina pachyderma (sinistral - sin.), deep-dwelling planktonic foraminifera, to estimate the subsurface temperatures and seawater δ18O from a sediment core from Gardar Drift, in the subpolar North Atlantic. Carbon isotopes of benthic and planktonic foraminifera from the same site provide information about the ventilation and water column nutrient gradient. Mg / Ca-based temperatures and seawater δ18O suggest increased subsurface temperatures and salinities during ice-rafting, likely due to northward subsurface transport of subtropical waters during periods of weaker Atlantic Meridional Overturning Circulation (AMOC). Planktonic carbon isotopes support this suggestion, showing coincident increased subsurface ventilation during deposition of IRD. Subsurface accumulation of warm waters would have resulted in basal warming and break-up of ice-shelves, leading to massive iceberg discharges in the North Atlantic. The release of heat stored at the subsurface to the atmosphere would have helped to restart the AMOC. This mechanism is in agreement with modelling and proxy studies that observe a subsurface warming in the North Atlantic in response to AMOC slowdown during Marine Isotope Stage (MIS) 3.

  7. Subsurface North Atlantic warming as a trigger of rapid cooling events: evidences from the Early Pleistocene (MIS 31-19)

    NASA Astrophysics Data System (ADS)

    Hernández-Almeida, I.; Sierro, F.-J.; Cacho, I.; Flores, J.-A.

    2014-10-01

    Subsurface water column dynamics in the subpolar North Atlantic were reconstructed in order to improve the understanding of the cause of abrupt IRD events during cold periods of the Early Pleistocene. We used Mg / Ca-based temperatures of deep-dwelling (Neogloboquadrina pachyderma sinistral) planktonic foraminifera and paired Mg / Ca-δ18O measurements to estimate the subsurface temperatures and δ18O of seawater at Site U1314. Carbon isotopes on benthic and planktonic foraminifera from the same site provide information about the ventilation and water column nutrient gradient. Mg / Ca-based temperatures and δ18O of seawater suggest increased temperatures and salinities during ice-rafting, likely due to enhanced northward subsurface transport of subtropical waters during periods of AMOC reduction. Planktonic carbon isotopes support this suggestion, showing coincident increased subsurface ventilation during deposition of ice-rafted detritus (IRD). Warm waters accumulated at subsurface would result in basal warming and break-up of ice-shelves, leading to massive iceberg discharges in the North Atlantic. Release of heat and salt stored at subsurface would help to restart the AMOC. This mechanism is in agreement with modelling and proxy studies that observe a subsurface warming in the North Atlantic in response to AMOC slowdown during the MIS3.

  8. Work More? The 8.2 kaBP Abrupt Climate Change Event and the Origins of Irrigation Agriculture and Surplus Agro-Production in Mesopotamia

    NASA Astrophysics Data System (ADS)

    Weiss, H.

    2003-12-01

    The West Asian archaeological record is of sufficient transparency and resolution to permit observation of the social responses to the major Holocene abrupt climate change events at 8.2, 5.2 and 4.2 kaBP. The 8.2kaBP abrupt climate change event in West Asia was a three hundred year aridification and cooling episode. During this period rain-fed agriculture, established for over a millennium in northern Mesopotamia, suddenly collapsed. Irrigation agriculture, pastoral nomadism, or migration were the only subsistence alternatives for populations previously supported by cereal dry-farming. Irrigation agriculture was not, however, possible along the northern alluvial plains of the Tigris and Euphrates Rivers, where incised riverbeds were several meters below plain level. Exploitable plain-level levees were only accessible in southern-most alluvial plain, at the head of the present-day Persian Gulf. The archaeological data from this region documents the first irrigation agriculture settlement of the plain during the 8.2 kaBP event. Irrigation agriculture provides about twice the yield of dry-farming in Mesopotamia, but at considerable labor costs relative to dry-farming. With irrigation agriculture surplus production was now available for deployment. But why work more? The 8.2 kaBP event provided the natural force for Mesopotamian irrigation agriculture and surplus production that were essential for the earliest class-formation and urban life.

  9. Sea-ice switches and abrupt climate change.

    PubMed

    Gildor, Hezi; Tziperman, Eli

    2003-09-15

    We propose that past abrupt climate changes were probably a result of rapid and extensive variations in sea-ice cover. We explain why this seems a perhaps more likely explanation than a purely thermohaline circulation mechanism. We emphasize that because of the significant influence of sea ice on the climate system, it seems that high priority should be given to developing ways for reconstructing high-resolution (in space and time) sea-ice extent for past climate-change events. If proxy data can confirm that sea ice was indeed the major player in past abrupt climate-change events, it seems less likely that such dramatic abrupt changes will occur due to global warming, when extensive sea-ice cover will not be present. PMID:14558902

  10. Subsurface warming in the subpolar North Atlantic during rapid climate events in the Early and Mid-Pleistocene

    NASA Astrophysics Data System (ADS)

    Hernández-Almeida, Iván; Sierro, Francisco; Cacho, Isabel; Abel Flores, José

    2014-05-01

    A new high-resolution reconstruction of the temperature and salinity of the subsurface waters using paired Mg/Ca-δ18O measurements on the planktonic foraminifera Neogloboquadrina pachyderma sinistrorsa (sin.) was conducted on a deep-sea sediment core in the subpolar North Atlantic (Site U1314). This study aims to reconstruct millennial-scale subsurface hydrography variations during the Early and Mid-Pleistocene (MIS 31-19). These rapid climate events are characterized by abrupt shifts between warm/cold conditions, and ice-sheet oscillations, as evidenced by major ice rafting events recorded in the North Atlantic sediments (Hernández-Almeida et al., 2012), similar to those found during the Last Glacial period (Marcott et al, 2011). The Mg/Ca derived paleotemperature and salinity oscillations prior and during IRD discharges at Site U1314 are related to changes in intermediate circulation. The increases in Mg/Ca paleotemperatures and salinities during the IRD event are preceded by short episodes of cooling and freshening of subsurface waters. The response of the AMOC to this perturbation is an increased of warm and salty water coming from the south, transported to high latitudes in the North Atlantic beneath the thermocline. This process is accompanied by a southward shift in the convection cell from the Nordic Seas to the subpolar North Atlantic and better ventilation of the North Atlantic at mid-depths. Poleward transport of warm and salty subsurface subtropical waters causes intense basal melting and thinning of marine ice-shelves, that culminates in large-scale instability of the ice sheets, retreat of the grounding line and iceberg discharge. The mechanism proposed involves the coupling of the AMOC with ice-sheet dynamics, and would explain the presence of these fluctuations before the establishment of high-amplitude 100-kyr glacial cycles. Hernández-Almeida, I., Sierro, F.J., Cacho, I., Flores, J.A., 2012. Impact of suborbital climate changes in the North

  11. A high-resolution lake sediment record of glacier activity from SE Greenland defines abrupt Holocene cooling events

    NASA Astrophysics Data System (ADS)

    Balascio, N. L.; Bradley, R. S.; D'Andrea, W. J.

    2013-12-01

    warming. Excursions from this trend occur at c. 8.5 ka and 8.3 ka showing brief periods of readvance that are likely associated with freshwater inputs to the North Atlantic Ocean related to the ';8.2 kyr Event.' The interval from 7.7-4.1 ka is clearly defined by high organic content (>20%) and extremely low magnetic susceptibility values, which we interpret as a lack of glacial input and the complete disappearance of the glaciers in the catchment. From 4.1-1.3 ka indicators of glacial input show a step-wise pattern with significant increases in glacial activity at 4.1 ka, 3.1 ka, 1.4 ka, and 1.3 ka indicating a progressive cooling and regrowth of the glaciers. Over the last 1.3 ka, glacial input was more constant, sedimentation rates were higher (0.8 mm/yr), and the sediment is finely laminated. Analysis of the μ-XRF data shows that the laminations were deposited annually, providing a high-resolution record of changes in glacial activity over the last 1.3 ka that corresponds well with regional temperature reconstructions.

  12. Westerly Wind Bursts, El Nino Diversity, and the Warm Event of 2014

    NASA Astrophysics Data System (ADS)

    Hu, S.; Fedorov, A. V.

    2014-12-01

    Each El Nino event is unique. The still developing event of 2014 is not an exception - its evolution has already surprised many researchers who in May anticipated a likely development of a strong warm event perhaps analogous to that in 1997/1998; however, by June - July its development nearly stalled. Whether one should still expect a strong warm event is now much less certain. It is believed that the activity of westerly wind bursts (WWBs) that occur in the tropical Pacific and the varying response of the coupled system to those bursts are among the key reasons for such uncertainty and, in general, of the broad diversity of El Niño events. For instance, WWBs that occurred at the beginning of 1997 and 2014 were favorable for the potential El Nino development. However, in the latter case the subsequent ocean-atmosphere interactions, which involve the interplay between the warm pool changes in the western/central Pacific and the warming of the eastern equatorial Pacific, might have impeded further development. In this study, we consider the evolution of different El Niño events after strong westerly wind bursts in a comprehensive coupled climate model and in the observations, aiming to find analogues to the event of 2014 and several other significant events and determine critical elements, and precursors, that affected their evolution, thus contributing to El Nino diversity.

  13. Catalogue of abrupt shifts in Intergovernmental Panel on Climate Change climate models.

    PubMed

    Drijfhout, Sybren; Bathiany, Sebastian; Beaulieu, Claudie; Brovkin, Victor; Claussen, Martin; Huntingford, Chris; Scheffer, Marten; Sgubin, Giovanni; Swingedouw, Didier

    2015-10-27

    Abrupt transitions of regional climate in response to the gradual rise in atmospheric greenhouse gas concentrations are notoriously difficult to foresee. However, such events could be particularly challenging in view of the capacity required for society and ecosystems to adapt to them. We present, to our knowledge, the first systematic screening of the massive climate model ensemble informing the recent Intergovernmental Panel on Climate Change report, and reveal evidence of 37 forced regional abrupt changes in the ocean, sea ice, snow cover, permafrost, and terrestrial biosphere that arise after a certain global temperature increase. Eighteen out of 37 events occur for global warming levels of less than 2°, a threshold sometimes presented as a safe limit. Although most models predict one or more such events, any specific occurrence typically appears in only a few models. We find no compelling evidence for a general relation between the overall number of abrupt shifts and the level of global warming. However, we do note that abrupt changes in ocean circulation occur more often for moderate warming (less than 2°), whereas over land they occur more often for warming larger than 2°. Using a basic proportion test, however, we find that the number of abrupt shifts identified in Representative Concentration Pathway (RCP) 8.5 scenarios is significantly larger than in other scenarios of lower radiative forcing. This suggests the potential for a gradual trend of destabilization of the climate with respect to such shifts, due to increasing global mean temperature change. PMID:26460042

  14. Catalogue of abrupt shifts in Intergovernmental Panel on Climate Change climate models

    PubMed Central

    Drijfhout, Sybren; Bathiany, Sebastian; Beaulieu, Claudie; Brovkin, Victor; Claussen, Martin; Huntingford, Chris; Scheffer, Marten; Sgubin, Giovanni; Swingedouw, Didier

    2015-01-01

    Abrupt transitions of regional climate in response to the gradual rise in atmospheric greenhouse gas concentrations are notoriously difficult to foresee. However, such events could be particularly challenging in view of the capacity required for society and ecosystems to adapt to them. We present, to our knowledge, the first systematic screening of the massive climate model ensemble informing the recent Intergovernmental Panel on Climate Change report, and reveal evidence of 37 forced regional abrupt changes in the ocean, sea ice, snow cover, permafrost, and terrestrial biosphere that arise after a certain global temperature increase. Eighteen out of 37 events occur for global warming levels of less than 2°, a threshold sometimes presented as a safe limit. Although most models predict one or more such events, any specific occurrence typically appears in only a few models. We find no compelling evidence for a general relation between the overall number of abrupt shifts and the level of global warming. However, we do note that abrupt changes in ocean circulation occur more often for moderate warming (less than 2°), whereas over land they occur more often for warming larger than 2°. Using a basic proportion test, however, we find that the number of abrupt shifts identified in Representative Concentration Pathway (RCP) 8.5 scenarios is significantly larger than in other scenarios of lower radiative forcing. This suggests the potential for a gradual trend of destabilization of the climate with respect to such shifts, due to increasing global mean temperature change. PMID:26460042

  15. An unprecedented Leeuwin Current warming event in 2011

    NASA Astrophysics Data System (ADS)

    Feng, M.; McPhaden, M. J.; Xie, S.; Hafner, J.

    2012-12-01

    At the climax of the 2010-2011 La Niña, the Leeuwin Current, a poleward flowing eastern boundary current off the west coast of Australia, was unseasonably strong and transported anomalous amount of warm water southward along the coast, increasing the upper ocean heat content (sea level) and causing unprecedented sea surface temperature anomalies in February - March 2011 by more than four times typical interannual variations. Peak surface temperatures of 27-29°C, 5°C warmer than its summer climatology, were observed off the mid west coast of Australia during a 2-week period in late February - early March 2011 and had caused widespread coral bleaching and fish kills. The unseasonable occurrence of the Leeuwin Current was forced by easterly wind anomalies in the equatorial western Pacific through oceanic teleconnection, as well as by low sea level pressure anomalies off the west coast of Australia through atmospheric teleconnection of the La Niña condition in the Pacific. An atmospheric model forced by observed sea surface temperatures is used to understand the drivers of the low sea level pressure anomalies.

  16. Deglacial paleoclimate in the southwestern United States: an abrupt 18.6 ka cold event and evidence for a North Atlantic forcing of Termination I

    NASA Astrophysics Data System (ADS)

    Lachniet, Matthew S.; Asmerom, Yemane; Polyak, Victor

    2011-12-01

    We present a new U-series dated speleothem record (PC-1) from the Great Basin that documents deglacial climate variability between ca 20.1 and 15.6 ka. Our data show an abrupt 18.6 ka cold event preceding Heinrich event 1 that is consistent with expansion of the Laurentide Ice sheet during the 'binge' phase of ice growth. This event coincided with dessication of pluvial Lake Mojave suggesting cold and dry conditions in the southern Great Basin at this time. PC-1 δ 18O values before and during Heinrich event 1 are similar, but an increase in stalagmite growth rates suggests wetter conditions that coincided with deposition of spring deposits in southern Nevada. The time interval of our record is consistent with the timing of pluvial conditions in the Great Basin as evident from a comparison to regional wetness proxies. Our new speleothem record, recovered from the recharge area for Devils Hole, does not show a δ 18O increase coincident with the abrupt increase in Devils Hole δ 18O at c. 18 ka, challenging the view that the Great Basin experienced an early Termination I. This hypothesis is supported by two other southwest speleothem records that demonstrate deglaciation was synchronous with forcing from the North Atlantic Ocean. We suggest that Devils Hole speleothem δ 18O values may partly reflect source water changes in the regional aquifer. Further, Devils Hole δ 13C minima coincide with peak global glacial conditions and weak Asian monsoon periods, suggesting that they constrain better the timing of pluvial conditions in the Great Basin.

  17. Abrupt climate events 500,000 to 340,000 years ago: Evidence from subpolar North Atlantic sediments

    SciTech Connect

    Oppo, D.W.; McManus, J.F.; Cullen, J.L.

    1998-02-27

    Subpolar North Atlantic proxy records document millennial-scale climate variations 500,000 to 340,000 years ago. The cycles have an approximately constant pacing that is similar to that documented for the last glacial cycle. These findings suggest that such climate variations are inherent to the late Pleistocene, regardless of glacial state. Sea surface temperature during the warm peak of Marine Isotope Stage 11 (MIS 11) varied by 0.5{degree} to 1{degree}C, less than the 4{degree} to 4.5{degree}C estimated during times of ice growth and the 3{degree}C estimated for glacial maxima. Coherent deep ocean circulation changes were associated with glacial oscillations in sea surface temperature. 31 refs., 3 figs.

  18. Warming of surface waters in the mid-latitude North Atlantic during Heinrich events

    NASA Astrophysics Data System (ADS)

    Naafs, B. D. A.; Hefter, J.; Grützner, J.; Stein, R.

    2013-01-01

    During the six Heinrich events of the last 70 kyr, episodic calving from the circum-Atlantic ice sheets released large numbers of icebergs into the North Atlantic. These icebergs and associated meltwater flux are hypothesized to have led to a shutdown of Atlantic Meridional Overturning Circulation and severe cooling in large parts of the Northern Hemisphere. However, due to the limited availability of high-resolution records, the magnitude of sea surface temperature (SST) changes related to the impact of Heinrich events on the midlatitude North Atlantic is poorly constrained. Here we present a record of U37K'-based SSTs derived from sediments of Integrated Ocean Drilling Project Site U1313, located at the southern end of the ice-rafted debris (IRD) belt in the midlatitude North Atlantic (41°N). We demonstrate that all six Heinrich events are associated with a rapid warming of surface waters by 2-4°C in a few thousand years. The presence of IRD leaves no doubt about the simultaneous timing and correlation between rapid surface water warming and Heinrich events. We argue that this warming in the midlatitude North Atlantic is related to a northward expansion of the subtropical gyre during Heinrich events. As a wide range of studies demonstrated that in the central IRD belt Heinrich events are associated with low SSTs, these results thus identify an antiphased (seesaw) pattern in SSTs during Heinrich events between the midlatitude (warm) and northern North Atlantic (cold). This highlights the complex response of surface water characteristics in the North Atlantic to Heinrich events that is poorly reproduced by freshwater hosing experiments and challenges the widely accepted view that, within the IRD belt of the North Atlantic, Heinrich events coincide with periods of low SSTs.

  19. Response of the Antarctic Stratosphere to Warm Pool EI Nino Events in the GEOS CCM

    NASA Technical Reports Server (NTRS)

    Hurwitz, Margaret M.; Song, In-Sun; Oman, Luke D.; Newman, Paul A.; Molod, Andrea M.; Frith, Stacey M.; Nielsen, J. Eric

    2011-01-01

    A new type of EI Nino event has been identified in the last decade. During "warm pool" EI Nino (WPEN) events, sea surface temperatures (SSTs) in the central equatorial Pacific are warmer than average. The EI Nino signal propagates poleward and upward as large-scale atmospheric waves, causing unusual weather patterns and warming the polar stratosphere. In austral summer, observations show that the Antarctic lower stratosphere is several degrees (K) warmer during WPEN events than during the neutral phase of EI Nino/Southern Oscillation (ENSO). Furthermore, the stratospheric response to WPEN events depends of the direction of tropical stratospheric winds: the Antarctic warming is largest when WPEN events are coincident with westward winds in the tropical lower and middle stratosphere i.e., the westward phase of the quasi-biennial oscillation (QBO). Westward winds are associated with enhanced convection in the subtropics, and with increased poleward wave activity. In this paper, a new formulation of the Goddard Earth Observing System Chemistry-Climate Model, Version 2 (GEOS V2 CCM) is used to substantiate the observed stratospheric response to WPEN events. One simulation is driven by SSTs typical of a WPEN event, while another simulation is driven by ENSO neutral SSTs; both represent a present-day climate. Differences between the two simulations can be directly attributed to the anomalous WPEN SSTs. During WPEN events, relative to ENSO neutral, the model simulates the observed increase in poleward planetary wave activity in the South Pacific during austral spring, as well as the relative warming of the Antarctic lower stratosphere in austral summer. However, the modeled response to WPEN does not depend on the phase of the QBO. The modeled tropical wind oscillation does not extend far enough into the lower stratosphere and upper troposphere, likely explaining the model's insensitivity to the phase of the QBO during WPEN events.

  20. Implications of abrupt climate change.

    PubMed Central

    Alley, Richard B.

    2004-01-01

    Records of past climates contained in ice cores, ocean sediments, and other archives show that large, abrupt, widespread climate changes have occurred repeatedly in the past. These changes were especially prominent during the cooling into and warming out of the last ice age, but persisted into the modern warm interval. Changes have especially affected water availability in warm regions and temperature in cold regions, but have affected almost all climatic variables across much or all of the Earth. Impacts of climate changes are smaller if the changes are slower or more-expected. The rapidity of abrupt climate changes, together with the difficulty of predicting such changes, means that impacts on the health of humans, economies and ecosystems will be larger if abrupt climate changes occur. Most projections of future climate include only gradual changes, whereas paleoclimatic data plus models indicate that abrupt changes remain possible; thus, policy is being made based on a view of the future that may be optimistic. PMID:17060975

  1. ENSO and disaster: droughts, floods and El Niño/Southern Oscillation warm events.

    PubMed

    Dilley, M; Heyman, B N

    1995-09-01

    The connection between El Niño/Southern Oscillation (ENSO) events and precipitation and temperature variability worldwide is increasingly well understood. ENSO has been linked to droughts and flooding in some regions. This paper uses the disaster history database of the U.S. Agency for International Development's Office of U.S. Foreign Disaster Assistance to examine the link between ENSO events and droughts or floods of sufficient magnitude to trigger international disasters. Worldwide, disasters triggered by droughts are twice as frequent during year two of ENSO warm events than during other years. No such relationship is apparent in the case of flood disasters. Drought disasters occur during year two of ENSO warm events significantly more frequently than in other years in Southern Africa and Southeast Asia. No regional pattern emerges from a comparable analysis of flood disasters. Those places likely to be affected by ENSO-triggered droughts can take proactive measures to mitigate the impacts. PMID:7552108

  2. Millennial-scale precipitation variability over Easter Island (South Pacific) during MIS 3: inter-hemispheric teleconnections with North Atlantic abrupt cold events

    NASA Astrophysics Data System (ADS)

    Margalef, O.; Cacho, I.; Pla-Rabes, S.; Cañellas-Boltà, N.; Pueyo, J. J.; Sáez, A.; Pena, L. D.; Valero-Garcés, B. L.; Rull, V.; Giralt, S.

    2015-04-01

    Marine Isotope Stage 3 (MIS 3, 59.4-27.8 kyr BP) is characterized by the occurrence of rapid millennial-scale climate oscillations known as Dansgaard-Oeschger cycles (DO) and by abrupt cooling events in the North Atlantic known as Heinrich events. Although both the timing and dynamics of these events have been broadly explored in North Atlantic records, the response of the tropical and subtropical latitudes to these rapid climatic excursions, particularly in the Southern Hemisphere, still remains unclear. The Rano Aroi peat record (Easter Island, 27° S) provides a unique opportunity to understand atmospheric and oceanic changes in the South Pacific during these DO cycles because of its singular location, which is influenced by the South Pacific Anticyclone (SPA), the Southern Westerlies (SW), and the Intertropical Convergence Zone (ITCZ) linked to the South Pacific Convergence Zone (SPCZ). The Rano Aroi sequence records 6 major events of enhanced precipitation between 38 and 65 kyr BP. These events are compared with other hydrological records from the tropical and subtropical band supporting a coherent regional picture, with the dominance of humid conditions in Southern Hemisphere tropical band during Heinrich Stadials (HS) 5, 5a and 6 and other Stadials while dry conditions prevailed in the Northern tropics. This antiphased hydrological pattern between hemispheres has been attributed to ITCZ migration, which in turn might be associated with an eastward expansion of the SPCZ storm track, leading to an increased intensity of cyclogenic storms reaching Easter Island. Low Pacific Sea Surface Temperature (SST) gradients across the Equator were coincident with the here-defined Rano Aroi humid events and consistent with a reorganization of Southern Pacific atmospheric and oceanic circulation also at higher latitudes during Heinrich and Dansgaard-Oeschger stadials.

  3. Abrupt Changes in the Marmara Pelagic Ecosystem during the recent jellyfish Liriope tetraphylla invasion and mucilage events

    NASA Astrophysics Data System (ADS)

    Erkan Kideys, Ahmet; Yüksek, Ahsen; Sur, Halil Ibrahim

    2013-04-01

    In this study, meteorological and hydrographical conditions as well as chemical and biological parameters have been examined for the period 2005-2009 to determine the impact and cause of the massive mucilage phenomenon observed in the Sea of Marmara in October 2007. Results showed that there is a decrease pattern in chl concentration as well as both phytoplankton and zooplankton abundances from August till October in 2007 whilst the jellyfish Liriope tetraphylla had bloom levels. This period coincided with the maximum intensity of pelagic fishing throughout the years. Nitrogen/phosphate ratio increased prior to the mucilage formation. Invasive Liriope tetraphylla abundance increased exponentially in August and died in masses as a result of starvation and meteorological / oceanographic conditions. In October, following the mucilage matter production another new species for the region Gonyaulax fragilis was observed in high abundance through the basin. It is worthy to note that during basin wide samplings conducted in the Sea of Marmara in both 2005 and 2006, high abundances of Liriope tetraphylla have been detected particularly at the northern parts where no mucilage event was observed. We suggest that overfishing in the Sea of Marmara provided a ground for the establishment of the invasive jellyfish and accompanying mucilage event was due to by synergic combinations of several factors.

  4. Quantifying the influence of observed global warming on the probability of unprecedented extreme climate events

    NASA Astrophysics Data System (ADS)

    Diffenbaugh, N. S.; Rajaratnam, B.; Charland, A.; Haugen, M.; Horton, D. E.; Singh, D.; Swain, D. L.; Tsiang, M.

    2014-12-01

    Now that observed global warming has been clearly attributed to human activities, there has been increasing interest in the extent to which that warming has influenced the occurrence and severity of individual extreme climate events. However, although trends in the extremes of the seasonal- and daily-scale distributions of climate records have been analyzed for many years, quantifying the contribution of observed global warming to individual events that are unprecedented in the observed record presents a particular scientific challenge. We will describe a modified method for leveraging observations and large climate model ensembles to quantify the influence of observed global warming on the probability of unprecedented extreme events. In this approach, we first diagnose the causes of the individual event in order to understand which climate processes to target in the probability quantification. We then use advanced statistical techniques to quantify the uncertainty in the return period of the event in the observed record. We then use large ensembles of climate model simulations to quantify the distribution of return period ratios between the current level of climate forcing and the pre-industrial climate forcing. We will compare the structure of this approach to other approaches that exist in the literature. We will then examine a set of individual extreme events that have been analyzed in the literature, and compare the results of our approach with those that have been previously published. We will conclude with a discussion of the observed agreement and disagreement between the different approaches, including implications for interpretation of the role of human forcing in shaping unprecedented extreme events.

  5. Abrupt changes in rainfall during the twentieth century

    NASA Astrophysics Data System (ADS)

    Narisma, G.; Foley, J.; Licker, R.; Ramankutty, N.

    2007-12-01

    A sudden change in climate is brought about by complex interactions in the climate system, including interactions between land and atmosphere, that can give rise to strong positive feedback mechanisms. Paleoclimatic studies have shown that abrupt climate changes have happened in the geologic past. Studies of future climate change under global warming scenarios indicate the possibility of the sudden collapse of the thermohaline circulation, which will have major implications for the climate of Europe. However, abrupt climatic changes are not events of the geologic past or a computer-simulated future: they have occurred in recent history and have had serious consequences on society and the environment. The prolonged Sahel drought in the late 1960s and the Dust Bowl of the 1930s are examples of abrupt climatic changes of the twentieth century. Apart from these events, however, there has been no systematic survey of recent climate history to determine the prevalence of abrupt climatic changes. Given the potential cost of these abrupt changes, there is a need to investigate historical records for evidence of other sudden climatic changes in the more recent past. Here we analyze the Climate Research Unit global historical rainfall observations (covering the years 1901-2000) using wavelet analysis to detect regions that have undergone large, sudden decreases in rainfall. We show that in the twentieth century, aside from the Sahel and the US midwest, at least 30 regions in the world have experienced sudden climatic changes. These events are statistically significant at the 99 percent level, are persistent for at least ten years, and most have magnitudes of change that are 10 percent lower than the climatological normal (1901-2000 rainfall average). We also illustrate some of the potential consequences of these abrupt changes and show that these events had major impacts on social and environmental conditions. Interestingly, these regions of abrupt precipitation changes are

  6. Response of seafloor ecosystems to abrupt global climate change

    NASA Astrophysics Data System (ADS)

    Moffitt, Sarah E.; Hill, Tessa M.; Roopnarine, Peter D.; Kennett, James P.

    2015-04-01

    Anthropogenic climate change is predicted to decrease oceanic oxygen (O2) concentrations, with potentially significant effects on marine ecosystems. Geologically recent episodes of abrupt climatic warming provide opportunities to assess the effects of changing oxygenation on marine communities. Thus far, this knowledge has been largely restricted to investigations using Foraminifera, with little being known about ecosystem-scale responses to abrupt, climate-forced deoxygenation. We here present high-resolution records based on the first comprehensive quantitative analysis, to our knowledge, of changes in marine metazoans (Mollusca, Echinodermata, Arthropoda, and Annelida; >5,400 fossils and trace fossils) in response to the global warming associated with the last glacial to interglacial episode. The molluscan archive is dominated by extremophile taxa, including those containing endosymbiotic sulfur-oxidizing bacteria (Lucinoma aequizonatum) and those that graze on filamentous sulfur-oxidizing benthic bacterial mats (Alia permodesta). This record, from 16,100 to 3,400 y ago, demonstrates that seafloor invertebrate communities are subject to major turnover in response to relatively minor inferred changes in oxygenation (>1.5 to <0.5 mLṡL-1 [O2]) associated with abrupt (<100 y) warming of the eastern Pacific. The biotic turnover and recovery events within the record expand known rates of marine biological recovery by an order of magnitude, from <100 to >1,000 y, and illustrate the crucial role of climate and oceanographic change in driving long-term successional changes in ocean ecosystems.

  7. Response of seafloor ecosystems to abrupt global climate change

    PubMed Central

    Moffitt, Sarah E.; Hill, Tessa M.; Roopnarine, Peter D.; Kennett, James P.

    2015-01-01

    Anthropogenic climate change is predicted to decrease oceanic oxygen (O2) concentrations, with potentially significant effects on marine ecosystems. Geologically recent episodes of abrupt climatic warming provide opportunities to assess the effects of changing oxygenation on marine communities. Thus far, this knowledge has been largely restricted to investigations using Foraminifera, with little being known about ecosystem-scale responses to abrupt, climate-forced deoxygenation. We here present high-resolution records based on the first comprehensive quantitative analysis, to our knowledge, of changes in marine metazoans (Mollusca, Echinodermata, Arthropoda, and Annelida; >5,400 fossils and trace fossils) in response to the global warming associated with the last glacial to interglacial episode. The molluscan archive is dominated by extremophile taxa, including those containing endosymbiotic sulfur-oxidizing bacteria (Lucinoma aequizonatum) and those that graze on filamentous sulfur-oxidizing benthic bacterial mats (Alia permodesta). This record, from 16,100 to 3,400 y ago, demonstrates that seafloor invertebrate communities are subject to major turnover in response to relatively minor inferred changes in oxygenation (>1.5 to <0.5 mL⋅L−1 [O2]) associated with abrupt (<100 y) warming of the eastern Pacific. The biotic turnover and recovery events within the record expand known rates of marine biological recovery by an order of magnitude, from <100 to >1,000 y, and illustrate the crucial role of climate and oceanographic change in driving long-term successional changes in ocean ecosystems. PMID:25825727

  8. Response of seafloor ecosystems to abrupt global climate change.

    PubMed

    Moffitt, Sarah E; Hill, Tessa M; Roopnarine, Peter D; Kennett, James P

    2015-04-14

    Anthropogenic climate change is predicted to decrease oceanic oxygen (O2) concentrations, with potentially significant effects on marine ecosystems. Geologically recent episodes of abrupt climatic warming provide opportunities to assess the effects of changing oxygenation on marine communities. Thus far, this knowledge has been largely restricted to investigations using Foraminifera, with little being known about ecosystem-scale responses to abrupt, climate-forced deoxygenation. We here present high-resolution records based on the first comprehensive quantitative analysis, to our knowledge, of changes in marine metazoans (Mollusca, Echinodermata, Arthropoda, and Annelida; >5,400 fossils and trace fossils) in response to the global warming associated with the last glacial to interglacial episode. The molluscan archive is dominated by extremophile taxa, including those containing endosymbiotic sulfur-oxidizing bacteria (Lucinoma aequizonatum) and those that graze on filamentous sulfur-oxidizing benthic bacterial mats (Alia permodesta). This record, from 16,100 to 3,400 y ago, demonstrates that seafloor invertebrate communities are subject to major turnover in response to relatively minor inferred changes in oxygenation (>1.5 to <0.5 mL⋅L(-1) [O2]) associated with abrupt (<100 y) warming of the eastern Pacific. The biotic turnover and recovery events within the record expand known rates of marine biological recovery by an order of magnitude, from <100 to >1,000 y, and illustrate the crucial role of climate and oceanographic change in driving long-term successional changes in ocean ecosystems. PMID:25825727

  9. The Impact of Warm Pool El Nino Events on Antarctic Ozone

    NASA Technical Reports Server (NTRS)

    Hurwitz, Margaret M.; Newman, P. A.; Song, In-Sun; Frith, Stacey M.

    2011-01-01

    Warm pool El Nino (WPEN) events are characterized by positive sea surface temperature (SST) anomalies in the central equatorial Pacific in austral spring and summer. Previous work found an enhancement in planetary wave activity in the South Pacific in austral spring, and a warming of 3-5 K in the Antarctic lower stratosphere during austral summer, in WPEN events as compared with ENSO neutral. In this presentation, we show that weakening of the Antarctic vortex during WPEN affects the structure and magnitude of high-latitude total ozone. We use total ozone data from TOMS and OMI, as well as station data from Argentina and Antarctica, to identify shifts in the longitudinal location of the springtime ozone minimum from its climatological position. In addition, we examine the sensitivity of the WPEN-related ozone response to the phase of the quasi-biennial oscillation (QBO). We then compare the observed response to WPEN events with Goddard Earth Observing System chemistry-climate model, version 2 (GEOS V2 CCM) simulations. Two, 50-year time-slice simulations are forced by annually repeating SST and sea ice climatologies, one set representing observed WPEN events and the second set representing neutral ENSO events, in a present-day climate. By comparing the two simulations, we isolate the impact of WPEN events on lower stratospheric ozone, and furthermore, examine the sensitivity of the WPEN ozone response to the phase of the QBO.

  10. Observation of an abrupt disruption of the long-term warming trend at the Balearic Sea, western Mediterranean Sea, in summer 2005

    NASA Astrophysics Data System (ADS)

    López-Jurado, J.-L.; González-Pola, C.; Vélez-Belchí, P.

    2005-12-01

    The properties of the Western Mediterranean Deep Water in a wide area located at the western boundary of the Mediterranean Sea, including the Balearic Sea, have revealed intense changes when observed in summer 2005. Between February and June 2005, a temperature drop of 0.14°C reverted dramatically the progressive warming trend of 0.011°C yr-1 that had been observed since 1996, in the waters below 600 dbar north of the Balearic channels. A similar temperature drop has been observed east of the Minorca Island, below the Levantine Intermediate Water and down to 1500 dbar. In the deepest levels, a complex thermohaline structure, which implies different waters masses as sources, was tracked more than 400 km along the western boundary of the Mediterranean Sea, from Barcelona to the Algerian Basin. It is suggested that the changes may be linked to the severe 2004/2005 winter occurred at the northwestern Mediterranean Sea.

  11. Recent and future warm extreme events and high-mountain slope stability.

    PubMed

    Huggel, C; Salzmann, N; Allen, S; Caplan-Auerbach, J; Fischer, L; Haeberli, W; Larsen, C; Schneider, D; Wessels, R

    2010-05-28

    The number of large slope failures in some high-mountain regions such as the European Alps has increased during the past two to three decades. There is concern that recent climate change is driving this increase in slope failures, thus possibly further exacerbating the hazard in the future. Although the effects of a gradual temperature rise on glaciers and permafrost have been extensively studied, the impacts of short-term, unusually warm temperature increases on slope stability in high mountains remain largely unexplored. We describe several large slope failures in rock and ice in recent years in Alaska, New Zealand and the European Alps, and analyse weather patterns in the days and weeks before the failures. Although we did not find one general temperature pattern, all the failures were preceded by unusually warm periods; some happened immediately after temperatures suddenly dropped to freezing. We assessed the frequency of warm extremes in the future by analysing eight regional climate models from the recently completed European Union programme ENSEMBLES for the central Swiss Alps. The models show an increase in the higher frequency of high-temperature events for the period 2001-2050 compared with a 1951-2000 reference period. Warm events lasting 5, 10 and 30 days are projected to increase by about 1.5-4 times by 2050 and in some models by up to 10 times. Warm extremes can trigger large landslides in temperature-sensitive high mountains by enhancing the production of water by melt of snow and ice, and by rapid thaw. Although these processes reduce slope strength, they must be considered within the local geological, glaciological and topographic context of a slope. PMID:20403836

  12. Predictability of stratospheric sudden warming event: A case study of 2013 event

    NASA Astrophysics Data System (ADS)

    Song, Kanghyun; Son, Seok-Woo; Kim, Junsu; Koo, Myung-Seo

    2015-04-01

    The predictability of SSW event, which has occurred on January 7th of 2013, is examined by integrating an operational weather prediction model, GRIMs, for 30 days with varying vertical resolutions and surface boundary conditions. This event was preconditioned by vertical propagation of wavenumber-one wave across the tropopause and caused by subsequent amplification of wavenumber-two wave that results in vortex split. These features are well predicted in the model with 64 vertical levels , but significantly underestimated in the model with 42 or 28 levels. Quantitatively, the high-top model predicts the event at 10-day lead while the low-top model shows the maximum lead of 5 days. This result is only weakly sensitive to the surface boundary condition, indicating that precise initial condition with high vertical resolution is important for the extended prediction of SSW event. Overall findings are compared with the results from 5 operational weather prediction systems that have participated in the SPARC/SNAP project.

  13. Past extreme warming events linked to massive carbon release from thawing permafrost.

    PubMed

    DeConto, Robert M; Galeotti, Simone; Pagani, Mark; Tracy, David; Schaefer, Kevin; Zhang, Tingjun; Pollard, David; Beerling, David J

    2012-04-01

    Between about 55.5 and 52 million years ago, Earth experienced a series of sudden and extreme global warming events (hyperthermals) superimposed on a long-term warming trend. The first and largest of these events, the Palaeocene-Eocene Thermal Maximum (PETM), is characterized by a massive input of carbon, ocean acidification and an increase in global temperature of about 5 °C within a few thousand years. Although various explanations for the PETM have been proposed, a satisfactory model that accounts for the source, magnitude and timing of carbon release at the PETM and successive hyperthermals remains elusive. Here we use a new astronomically calibrated cyclostratigraphic record from central Italy to show that the Early Eocene hyperthermals occurred during orbits with a combination of high eccentricity and high obliquity. Corresponding climate-ecosystem-soil simulations accounting for rising concentrations of background greenhouse gases and orbital forcing show that the magnitude and timing of the PETM and subsequent hyperthermals can be explained by the orbitally triggered decomposition of soil organic carbon in circum-Arctic and Antarctic terrestrial permafrost. This massive carbon reservoir had the potential to repeatedly release thousands of petagrams (10(15) grams) of carbon to the atmosphere-ocean system, once a long-term warming threshold had been reached just before the PETM. Replenishment of permafrost soil carbon stocks following peak warming probably contributed to the rapid recovery from each event, while providing a sensitive carbon reservoir for the next hyperthermal. As background temperatures continued to rise following the PETM, the areal extent of permafrost steadily declined, resulting in an incrementally smaller available carbon pool and smaller hyperthermals at each successive orbital forcing maximum. A mechanism linking Earth's orbital properties with release of soil carbon from permafrost provides a unifying model accounting for the salient

  14. Increased frequency of extreme La Niña events under greenhouse warming

    NASA Astrophysics Data System (ADS)

    Cai, Wenju; Wang, Guojian; Santoso, Agus; McPhaden, Michael J.; Wu, Lixin; Jin, Fei-Fei; Timmermann, Axel; Collins, Mat; Vecchi, Gabriel; Lengaigne, Matthieu; England, Matthew H.; Dommenget, Dietmar; Takahashi, Ken; Guilyardi, Eric

    2015-02-01

    The El Niño/Southern Oscillation is Earth’s most prominent source of interannual climate variability, alternating irregularly between El Niño and La Niña, and resulting in global disruption of weather patterns, ecosystems, fisheries and agriculture. The 1998-1999 extreme La Niña event that followed the 1997-1998 extreme El Niño event switched extreme El Niño-induced severe droughts to devastating floods in western Pacific countries, and vice versa in the southwestern United States. During extreme La Niña events, cold sea surface conditions develop in the central Pacific, creating an enhanced temperature gradient from the Maritime continent to the central Pacific. Recent studies have revealed robust changes in El Niño characteristics in response to simulated future greenhouse warming, but how La Niña will change remains unclear. Here we present climate modelling evidence, from simulations conducted for the Coupled Model Intercomparison Project phase 5 (ref. ), for a near doubling in the frequency of future extreme La Niña events, from one in every 23 years to one in every 13 years. This occurs because projected faster mean warming of the Maritime continent than the central Pacific, enhanced upper ocean vertical temperature gradients, and increased frequency of extreme El Niño events are conducive to development of the extreme La Niña events. Approximately 75% of the increase occurs in years following extreme El Niño events, thus projecting more frequent swings between opposite extremes from one year to the next.

  15. Increased frequency of extreme Indian Ocean Dipole events due to greenhouse warming.

    PubMed

    Cai, Wenju; Santoso, Agus; Wang, Guojian; Weller, Evan; Wu, Lixin; Ashok, Karumuri; Masumoto, Yukio; Yamagata, Toshio

    2014-06-12

    The Indian Ocean dipole is a prominent mode of coupled ocean-atmosphere variability, affecting the lives of millions of people in Indian Ocean rim countries. In its positive phase, sea surface temperatures are lower than normal off the Sumatra-Java coast, but higher in the western tropical Indian Ocean. During the extreme positive-IOD (pIOD) events of 1961, 1994 and 1997, the eastern cooling strengthened and extended westward along the equatorial Indian Ocean through strong reversal of both the mean westerly winds and the associated eastward-flowing upper ocean currents. This created anomalously dry conditions from the eastern to the central Indian Ocean along the Equator and atmospheric convergence farther west, leading to catastrophic floods in eastern tropical African countries but devastating droughts in eastern Indian Ocean rim countries. Despite these serious consequences, the response of pIOD events to greenhouse warming is unknown. Here, using an ensemble of climate models forced by a scenario of high greenhouse gas emissions (Representative Concentration Pathway 8.5), we project that the frequency of extreme pIOD events will increase by almost a factor of three, from one event every 17.3 years over the twentieth century to one event every 6.3 years over the twenty-first century. We find that a mean state change--with weakening of both equatorial westerly winds and eastward oceanic currents in association with a faster warming in the western than the eastern equatorial Indian Ocean--facilitates more frequent occurrences of wind and oceanic current reversal. This leads to more frequent extreme pIOD events, suggesting an increasing frequency of extreme climate and weather events in regions affected by the pIOD. PMID:24919920

  16. The appearance of sustained equatorial surface westerlies during the 1982 pacific warm event.

    PubMed

    Harrison, D E

    1984-06-01

    In June 1982 a band of anomalous southerly surface wind, extending from the equator as far south as the Tasman Sea, formed east of Australia (150 degrees E to 160 degrees E). This flow crossed the equator just before the appearance of sustained westerly winds on the equator somewhat west of the date line. Because these westerly winds induced the initial strong equatorial warming of the ocean east of the date line during the 1982 El Niño-Southern Oscillation (ENSO) event, the southerly jet appears to be an important atmospheric component leading to the onset of the vigorous phase of this event. Some historical evidence suggests that anomalous southerly winds in the same region occurred prior to the appearance of sustained equatorial westerly winds in the major ENSO events of 1957, 1965, and 1972. PMID:17735247

  17. Warm and Saline Events Embedded in the Meridional Circulation of the Northern North Atlantic

    NASA Technical Reports Server (NTRS)

    Hakkinen, Sirpa; Rhines, Peter B.; Worthen, Denise L.

    2011-01-01

    Ocean state estimates from 1958 to 2005 from the Simple Ocean Assimilation System (SODA) system are analyzed to understand circulation between subtropical and subpolar Atlantic and their connection with atmospheric forcing. This analysis shows three periods (1960s, around 1980, and 2000s) with enhanced warm, saline waters reaching high latitudes, alternating with freshwater events originating at high latitudes. It complements surface drifter and altimetry data showing the subtropical -subpolar exchange leading to a significant temperature and salinity increase in the northeast Atlantic after 2001. The warm water limb of the Atlantic meridional overturning cell represented by SODA expanded in density/salinity space during these warm events. Tracer simulations using SODA velocities also show decadal variation of the Gulf Stream waters reaching the subpolar gyre and Nordic seas. The negative phase of the North Atlantic Oscillation index, usually invoked in such variability, fails to predict the warming and salinization in the early 2000s, with salinities not seen since the 1960s. Wind stress curl variability provided a linkage to this subtropical/subpolar gyre exchange as illustrated using an idealized two ]layer circulation model. The ocean response to the modulation of the climatological wind stress curl pattern was found to be such that the northward penetration of subtropical tracers is enhanced when amplitude of the wind stress curl is weaker than normal. In this case both the subtropical and subpolar gyres weaken and the subpolar density surfaces relax; hence, the polar front moves westward, opening an enhanced northward access of the subtropical waters in the eastern boundary current.

  18. Absorbing and reflecting sudden stratospheric warming events and their relationship with tropospheric circulation

    NASA Astrophysics Data System (ADS)

    Kodera, Kunihiko; Mukougawa, Hitoshi; Maury, Pauline; Ueda, Manabu; Claud, Chantal

    2016-01-01

    Sudden stratospheric warming (SSW) events have received increased attention since their impacts on the troposphere became evident recently. Studies of SSW usually focus on polar stratospheric conditions; however, understanding the global impact of these events requires studying them from a wider perspective. Case studies are used to clarify the characteristics of the stratosphere-troposphere dynamical coupling, and the meridional extent of the phenomena associated with SSW. Results show that differences in the recovery phase can be used to classify SSW events into two types. The first is the absorbing type of SSW, which has a longer timescale as well as a larger meridional extent due to the persistent incoming planetary waves from the troposphere. The absorbing type of SSW is related to the annular mode on the surface through poleward and downward migration of the deceleration region of the polar night jet. The other is the reflecting type. This is characterized by a quick termination of the warming episode due to the reflection of planetary waves in the stratosphere, which leads to an amplification of tropospheric planetary waves inducing strong westerlies over the North Atlantic and blocking over the North Pacific sector. Differences in the tropospheric impact of the absorbing and reflecting SSWs are also confirmed with composite analysis of 22 major SSWs.

  19. Tropospheric predictability around stratospheric warming events examined with an idealized forecast ensemble

    NASA Astrophysics Data System (ADS)

    Hörnqvist, E.; Körnich, H.

    2012-04-01

    By representing sudden stratospheric warming events (SSWs) in numerical weather prediction models, the predictability length could possibly be improved. It has been suggested that this improvement depends on the initial day of the forecast relative to the central date of the SSW. In this project this hypothesis is tested in the framework of an idealized general circulation model. Furthermore, it will be examined how uncertainties of the initial conditions and model errors in the forecast model affect the predictability around stratospheric warming events. Identical-twin forecast experiments are performed with the Kühlungsborn Mechanistic general Circulation Model KMCM that extends to the stratopause. In a 20-year truth run with perpetual January conditions, 21 SSWs are identified. Ensemble forecasts using random field perturbations in the initial conditions are conducted with initial dates from 20 days before to 20 days after each SSW central date. In four different experiments, we examine how the tropospheric predictability depends on perturbations in troposphere, stratosphere or both, and on model errors in the stratospheric radiative equilibrium temperature. The results show that a forecast initialised before the SSW central date has a greater forecast skill than after. On average useful forecast for the zonal mean zonal wind at 60N and 850 hPa are extended by 10 days, when initialized up to 12 days before the SSW. This extension is robust for the different perturbation experiments and also when a model error was introduced. Thus, the experiments confirm that the largest improvement of predictability is achieved, when the forecast is initialised before the sudden stratospheric warming event.

  20. Community impacts of mid-May frost event during an anomalously warm spring

    NASA Astrophysics Data System (ADS)

    Hufkens, K.; Sonnentag, O.; Keenan, T. F.; Richardson, A. D.; Melaas, E. K.; Bailey, A.; O'Keefe, J.; Friedl, M. A.

    2011-12-01

    Global land and ocean surface temperatures of 2010 have gone on record as one of the warmest of the last 131 years. In the northeastern US extraordinarily warm spring temperatures were recorded, averaging +3 °C above the long term mean, causing very early leaf development. However, the entire northeastern US region was hit by a severe frost event. Leveraging the coincidence of an anomalously warm spring and a late spring frost event we assess species specific responses of these combined extremes for three northern hardwood species(sugar maple, American beech, yellow birch) across an elevational gradient. We integrated ground observations with satellite and near-surface remote sensing data to address the following questions: 1) How did different species respond to a gradient in altitude / freezing temperatures? 2) How does phenological strategy influence this response? 3) To what extent were regional effects measurable? 4) How did the late spring frost event alter the carbon balance of a northern hardwood forest? 5) Finally, what changes do we foresee in community ecology? Our results show an early onset for all species, triggered by the anomalously warm spring. However, the three species responded differently to a late spring frost event. Where both yellow birch and American beech remained largely unaffected by frost, by comparison, sugar maple showed severe frost damage with increasing altitude resulting in leaf loss and delayed canopy development. Conservative estimates of gross carbon exchange losses due to the frost event ranged from 63 g C m-2 to 156 g C m-2, or ~5% to ~13 % of the annual gross carbon exchange of a northern hardwood forest. Our results suggest that the additional pressure on forest succession at high altitude range margins due to late spring frost events may provide a competitive advantage for yellow birch and American beech, at the expense of sugar maple. Consequently, a late spring frost does not only affect the short term carbon balance

  1. Towards Greenland Glaciation: cumulative or abrupt transition?

    NASA Astrophysics Data System (ADS)

    Tan, Ning; Dumas, Christophe; Ladant, Jean-Baptiste; Ramstein, Gilles; Contoux, Camille

    2016-04-01

    During the mid-Pliocene warming period (3-3.3 Ma BP), global annual mean temperature is warmer by 2-3 degree than pre-industrial. Greenland ice sheet volume is supposed to be a 50% reduction compared to nowadays [Haywood et al. 2010]. Around 2.7-2.6 Ma BP, just ~ 500 kyr after the warming peak of mid-Pliocene, there is already full Greenland Glaciation [Lunt et al. 2008]. How does Greenland ice sheet evolve from a half size to a glaciation level during 3 Ma - 2.5 Ma? Data show that there is a decreasing trend of atmospheric CO2 concentration from 3 Ma to 2.5 Ma [Seki et al.2010; Bartoli et al. 2011; Martinez et al. 2015]. However, a recent study [Contoux et al. 2015] suggests that a lowering of CO2 is not sufficient to initiate a perennial glaciation on Greenland and must be combined to low summer insolation, to preserve the ice sheet during insolation maximum, suggesting a cumulative process. In order to diagnose whether the ice sheet build-up is an abrupt event or a cumulative process, we carry on, for the first time, a transient simulation of climate and ice sheet evolutions from 3 Ma to 2.5 Ma. This strategy enables to investigate waxing and waning of the ice sheet during several orbital cycles. To reach this goal, we use a tri-dimensional interpolation method designed by Ladant et al. (2014) which combines the evolution of CO2 concentration, orbital parameters and Greenland ice sheet sizes in an off-line way by interpolating snapshots simulations. Thanks to this new method, we can build a transient like simulation through asynchronous coupling between GCM and ice sheet model. With this method, we may consistently answer the question of the build-up of Greenland: abrupt or cumulative process.

  2. Ice core measurements of 14CH4 show no evidence of methane release from methane hydrates or old permafrost carbon during a large warming event 11,600 years ago

    NASA Astrophysics Data System (ADS)

    Petrenko, Vasilii; Severinghaus, Jeffrey; Smith, Andrew; Riedel, Katja; Brook, Edward; Schaefer, Hinrich; Baggenstos, Daniel; Harth, Christina; Hua, Quan; Buizert, Christo; Schilt, Adrian; Fain, Xavier; Mitchell, Logan; Bauska, Thomas; Orsi, Anais

    2015-04-01

    Thawing permafrost and marine methane hydrate destabilization in the Arctic and elsewhere have been proposed as large sources of methane to the atmosphere in the future warming world. To evaluate this hypothesis it is useful to ask whether such methane releases happened during past warming events. The two major abrupt warming events of the last deglaciation, Oldest Dryas - Bølling (OD-B, ≈ 14,500 years ago) and Younger Dryas - Preboreal (YD-PB; ≈11,600 years ago), were associated with large (up to 50%) increases in atmospheric methane (CH4) concentrations. The sources of these large warming-driven CH4 increases remain incompletely understood, with possible contributions from tropical and boreal wetlands, thawing permafrost as well as marine CH4 hydrates. We present new measurements of 14C of paleoatmospheric CH4 over the YD-PB transition from ancient ice outcropping at Taylor Glacier, Antarctica. 14C can unambiguously identify CH4 emissions from "old carbon" sources, such as permafrost and CH4 hydrates. The only prior study of paleoatmospheric 14CH4 (from Greenland ice) suggested that wetlands were the main driver of the YD-PB CH4 increase, but the results were weakened by an unexpected and poorly understood 14CH4 component from in situ cosmogenic production directly in near-surface ice. In this new study, we have been able to accurately characterize and correct for the cosmogenic 14CH4 component. All samples from before, during and after the abrupt warming and associated CH4 increase yielded 14CH4 values that are consistent with 14C of atmospheric CO2 at that time, indicating a purely contemporaneous methane source. These new measurements rule out the possibility of large CH4 releases to the atmosphere from methane hydrates or old permafrost carbon in response to the large and rapid YD-PB warming. To the extent that the characteristics of the YD-PB warming are comparable to those of the current anthropogenic warming, our measurements suggest that large future

  3. Responses of sequential and hierarchical phenological events to warming and cooling in alpine meadows

    PubMed Central

    Li, Xine; Jiang, Lili; Meng, Fandong; Wang, Shiping; Niu, Haishan; Iler, Amy M.; Duan, Jichuan; Zhang, Zhenhua; Luo, Caiyun; Cui, Shujuan; Zhang, Lirong; Li, Yaoming; Wang, Qi; Zhou, Yang; Bao, Xiaoying; Dorji, Tsechoe; Li, Yingnian; Peñuelas, Josep; Du, Mingyuan; Zhao, Xinquan; Zhao, Liang; Wang, Guojie

    2016-01-01

    Organisms' life cycles consist of hierarchical stages, from a single phenological stage (for example, flowering within a season), to vegetative and reproductive phases, to the total lifespan of the individual. Yet phenological events are typically studied in isolation, limiting our understanding of life history responses to climate change. Here, we reciprocally transfer plant communities along an elevation gradient to investigate plastic changes in the duration of sequential phenological events for six alpine species. We show that prolonged flowering leads to longer reproductive phases and activity periods when plants are moved to warmer locations. In contrast, shorter post-fruiting leaf and flowering stages led to shorter vegetative and reproductive phases, respectively, which resulted in shorter activity periods when plants were moved to cooler conditions. Therefore, phenological responses to warming and cooling do not simply mirror one another in the opposite direction, and low temperature may limit reproductive allocation in the alpine region. PMID:27535205

  4. Responses of sequential and hierarchical phenological events to warming and cooling in alpine meadows.

    PubMed

    Li, Xine; Jiang, Lili; Meng, Fandong; Wang, Shiping; Niu, Haishan; Iler, Amy M; Duan, Jichuan; Zhang, Zhenhua; Luo, Caiyun; Cui, Shujuan; Zhang, Lirong; Li, Yaoming; Wang, Qi; Zhou, Yang; Bao, Xiaoying; Dorji, Tsechoe; Li, Yingnian; Peñuelas, Josep; Du, Mingyuan; Zhao, Xinquan; Zhao, Liang; Wang, Guojie

    2016-01-01

    Organisms' life cycles consist of hierarchical stages, from a single phenological stage (for example, flowering within a season), to vegetative and reproductive phases, to the total lifespan of the individual. Yet phenological events are typically studied in isolation, limiting our understanding of life history responses to climate change. Here, we reciprocally transfer plant communities along an elevation gradient to investigate plastic changes in the duration of sequential phenological events for six alpine species. We show that prolonged flowering leads to longer reproductive phases and activity periods when plants are moved to warmer locations. In contrast, shorter post-fruiting leaf and flowering stages led to shorter vegetative and reproductive phases, respectively, which resulted in shorter activity periods when plants were moved to cooler conditions. Therefore, phenological responses to warming and cooling do not simply mirror one another in the opposite direction, and low temperature may limit reproductive allocation in the alpine region. PMID:27535205

  5. Changes in Large Spatiotemporal Climatic Extreme Events Beyond the Mean Warming Signal

    NASA Astrophysics Data System (ADS)

    Sippel, S.; Mahecha, M. D.; Otto, F. E. L.

    2014-12-01

    Weather and climate extremes impose substantial impacts on human societies and ecosystems. In particular, events that are large in space (areal extent), time (duration) or both are likely to be associated with highly significant consequences. Hence, a better detection, characterization and understanding of such anomalous events is crucial. There is widespread consensus on a global and continental-scale warming trend, which leads to increases in the number, magnitude and frequency of temperature extremes (Hansen et al., 2012). It is less clear, however, if this warming also coincides with a broadening of temperature distributions (Huntingford et al., 2013). Moreover, the question whether other climate variables, such as large-scale precipitation deficits, likewise change, remains largely unanswered (Sheffield et al., 2012; Seneviratne 2012). In this study, we address this issue by investigating the characteristics of large extremes, using an algorithm that detects the n largest spatiotemporally connected climate extremes for any time period. The deployed algorithm detects, depending on the chosen time step and variable, major heat waves, cold spells or droughts. We find a robust increase in the magnitude of large hot temperature extremes on a global and European scale in observations and reanalysis products, whereas the duration and affected area of those extremes does not show any pronounced changes. These results reveal that there is a detectable signal in temperature distributions beyond the mean warming trend, which might imply a structural change in the making of large extreme events. Furthermore, we use the CMIP5 ensemble of models and an ensemble of 100+ members of a regional climate model for Europe (HadRM3P within the weather@home framework[1]) in order to conduct a global and continental-scale analysis of large extreme events in temperature and precipitation. The employment of those model ensembles allows to sample more reliably the tails of the

  6. CMIP5 Model Assessments of the Ongoing Global Warming Hiatus and Two Extreme 2012 Climate Events

    NASA Astrophysics Data System (ADS)

    Knutson, T. R.; Zhang, R.; Wittenberg, A. T.; Zeng, F. J.

    2013-12-01

    Several recent climate phenomena are assessed using a 23-model CMIP5 multi-model ensemble. The pause in global warming since 1998 represents an important ongoing test for climate models. We find that the observed global mean temperature trend (1998-2010) is still within the 5th to 95th percentile of the distribution of trends formed by the CMIP5 ensemble. The CMIP5 ensemble is also used to assess two extreme climate events that occurred in 2012. For Arctic sea ice extent, both the trend over 2000-2012 and the 2012 extreme low are outside the 5th to 95th percentile range of the multi-model CMIP5 ensemble that uses historical forcing. These changes are also far outside the corresponding range of the control runs alone, strongly suggesting a role for anthropogenic forcing in the ice loss. Potential causes of the under-prediction of 2012 Arctic ice loss by the models include: underestimation of natural variability in the Arctic; underestimation of the models' Arctic ice response to forcing; errors in or missing historical forcings; or the extreme ice loss may simply have been an extremely rare event. For the eastern U.S., 2012 produced record temperature anomalies in March-May (MAM), according to the HadCRUT4 gridded data set. Based on the CMIP5 model assessment, we find a significant anthropogenic component to a long-term (multi-decadal to century scale) warming in this region during MAM. According to the ensemble mean of the CMIP5 historical runs, and using a baseline period of 1881-1920, we estimate that about one third of the 2012 warm anomaly was attributable to external forcing (principally anthropogenic). Eastern U.S. MAM warm anomalies exceeding those of 2012 occur about 12 times more often in the CMIP5 historical runs than in the control runs, suggesting that external forcing (principally anthropogenic) has substantially increased the risk of occurrence of such an event.

  7. Communicating Climate Uncertainties: Challenges and Opportunities Related to Spatial Scales, Extreme Events, and the Warming 'Hiatus'

    NASA Astrophysics Data System (ADS)

    Casola, J. H.; Huber, D.

    2013-12-01

    Many media, academic, government, and advocacy organizations have achieved sophistication in developing effective messages based on scientific information, and can quickly translate salient aspects of emerging climate research and evolving observations. However, there are several ways in which valid messages can be misconstrued by decision makers, leading them to inaccurate conclusions about the risks associated with climate impacts. Three cases will be discussed: 1) Issues of spatial scale in interpreting climate observations: Local climate observations may contradict summary statements about the effects of climate change on larger regional or global spatial scales. Effectively addressing these differences often requires communicators to understand local and regional climate drivers, and the distinction between a 'signal' associated with climate change and local climate 'noise.' Hydrological statistics in Missouri and California are shown to illustrate this case. 2) Issues of complexity related to extreme events: Climate change is typically invoked following a wide range of damaging meteorological events (e.g., heat waves, landfalling hurricanes, tornadoes), regardless of the strength of the relationship between anthropogenic climate change and the frequency or severity of that type of event. Examples are drawn from media coverage of several recent events, contrasting useful and potentially confusing word choices and frames. 3) Issues revolving around climate sensitivity: The so-called 'pause' or 'hiatus' in global warming has reverberated strongly through political and business discussions of climate change. Addressing the recent slowdown in warming yields an important opportunity to raise climate literacy in these communities. Attempts to use recent observations as a wedge between climate 'believers' and 'deniers' is likely to be counterproductive. Examples are drawn from Congressional testimony and media stories. All three cases illustrate ways that decision

  8. Observations of planetary waves in the mesosphere-lower thermosphere during stratospheric warming events

    NASA Astrophysics Data System (ADS)

    Stray, N. H.; Orsolini, Y. J.; Espy, P. J.; Limpasuvan, V.; Hibbins, R. E.

    2015-05-01

    This study investigates the effect of stratospheric sudden warmings (SSWs) on planetary wave (PW) activity in the mesosphere-lower thermosphere (MLT). PW activity near 95 km is derived from meteor wind data using a chain of eight SuperDARN radars at high northern latitudes that span longitudes from 150° W to 25° E and latitudes from 51 to 66° N. Zonal wave number 1 and 2 components were extracted from the meridional wind for the years 2000-2008. The observed wintertime PW activity shows common features associated with the stratospheric wind reversals and the accompanying stratospheric warming events. Onset dates for seven SSW events accompanied by an elevated stratopause (ES) were identified during this time period using the Specified Dynamics Whole Atmosphere Community Climate Model (SD-WACCM). For the seven events, a significant enhancement in wave number 1 and 2 PW amplitudes near 95 km was found to occur after the wind reversed at 50 km, with amplitudes maximizing approximately 5 days after the onset of the wind reversal. This PW enhancement in the MLT after the event was confirmed using SD-WACCM. When all cases of polar cap wind reversals at 50 km were considered, a significant, albeit moderate, correlation of 0.4 was found between PW amplitudes near 95 km and westward polar-cap stratospheric winds at 50 km, with the maximum correlation occurring ∼ 3 days after the maximum westward wind. These results indicate that the enhancement of PW amplitudes near 95 km is a common feature of SSWs irrespective of the strength of the wind reversal.

  9. Detecting abrupt climate changes on different time scales

    NASA Astrophysics Data System (ADS)

    Matyasovszky, István

    2011-10-01

    Two concepts are introduced for detecting abrupt climate changes. In the first case, the sampling frequency of climate data is high as compared to the frequency of climate events examined. The method is based on a separation of trend and noise in the data and is applicable to any dataset that satisfies some mild smoothness and statistical dependence conditions for the trend and the noise, respectively. We say that an abrupt change occurs when the first derivative of the trend function has a discontinuity and the task is to identify such points. The technique is applied to Northern Hemisphere temperature data from 1850 to 2009, Northern Hemisphere temperature data from proxy data, a.d. 200-1995 and Holocene δ18O values going back to 11,700 years BP. Several abrupt changes are detected that are, among other things, beneficial for determining the Medieval Warm Period, Little Ice Age and Holocene Climate Optimum. In the second case, the sampling frequency is low relative to the frequency of climate events studied. A typical example includes Dansgaard-Oeschger events. The methodology used here is based on a refinement of autoregressive conditional heteroscedastic models. The key element of this approach is the volatility that characterises the time-varying variance, and abrupt changes are defined by high volatilities. The technique applied to δ18O values going back to 122,950 years BP is suitable for identifying DO events. These two approaches for the two cases are closely related despite the fact that at first glance, they seem quite different.

  10. Characteristics and mechanisms of the sudden warming events in the nocturnal atmospheric boundary layer: A case study using WRF

    NASA Astrophysics Data System (ADS)

    Ma, Yuanyuan; Yang, Yi; Hu, Xiao-Ming; Gan, Ruhui

    2015-10-01

    Although sudden nocturnal warming events near the earth's surface in Australia and the United States have been examined in previous studies, similar events observed occasionally over the Loess Plateau of Northwest China have not yet been investigated. The factors that lead to these warming events in such areas with their unique topography and climate remain not clear. To understand the formation mechanisms and associated thermal and dynamical features, a nocturnal warming event recorded in Gansu Province (northwest of the Loess Plateau) in June 2007 was investigated by using observations and model simulations with the Weather Research and Forecasting (WRF) model. Observations showed that this near-surface warming event lasted for 4 h and the temperature increased by 2.5°C. During this event, a decrease in humidity occurred simultaneously with the increase of temperature. The model simulation showed that the nocturnal warming was caused mainly by the transport of warmer and drier air aloft downward to the surface through enhanced vertical mixing. Wind shear played an important role in inducing the elevated vertical mixing, and it was enhanced by the continuous development of the atmospheric baroclinicity, which converted more potential energy to kinetic energy.

  11. Ice-shelf collapse from subsurface warming as a trigger for Heinrich events.

    PubMed

    Marcott, Shaun A; Clark, Peter U; Padman, Laurie; Klinkhammer, Gary P; Springer, Scott R; Liu, Zhengyu; Otto-Bliesner, Bette L; Carlson, Anders E; Ungerer, Andy; Padman, June; He, Feng; Cheng, Jun; Schmittner, Andreas

    2011-08-16

    Episodic iceberg-discharge events from the Hudson Strait Ice Stream (HSIS) of the Laurentide Ice Sheet, referred to as Heinrich events, are commonly attributed to internal ice-sheet instabilities, but their systematic occurrence at the culmination of a large reduction in the Atlantic meridional overturning circulation (AMOC) indicates a climate control. We report Mg/Ca data on benthic foraminifera from an intermediate-depth site in the northwest Atlantic and results from a climate-model simulation that reveal basin-wide subsurface warming at the same time as large reductions in the AMOC, with temperature increasing by approximately 2 °C over a 1-2 kyr interval prior to a Heinrich event. In simulations with an ocean model coupled to a thermodynamically active ice shelf, the increase in subsurface temperature increases basal melt rate under an ice shelf fronting the HSIS by a factor of approximately 6. By analogy with recent observations in Antarctica, the resulting ice-shelf loss and attendant HSIS acceleration would produce a Heinrich event. PMID:21808034

  12. A Global Warming Event in Magnetochron C19r: New evidence from the Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    Roehl, U.; Westerhold, T.; Donner, B.; Kordesch, W.; Bohaty, S. M.

    2014-12-01

    The Chron C19r event in the late middle Eocene was first described at ODP Site 1260 in the equatorial Atlantic. It is characterized by strong dissolution expressed in a dark, clay-rich layer and a distinct peak in X-ray fluorescence (XRF) scanning Fe intensities as well as by a negative carbon isotope excursion (CIE) in bulk sediment. All similar to early Paleogene hyperthermal events - the Chron C19r event could also be a hyperthermal event but in the late middle Eocene. The dissolution of carbonate at Site 1260 prevented so far to retrieve a benthic stable isotope record with a typical CIE and warming of deep water. The C19r event occurred ~1.0 myr prior to the onset of the Middle Eocene Climate Optimum (MECO, 40.5 Ma) and several million years after the Early Eocene Climate Optimum (EECO, 51 Ma) during a slightly cooler climate. No significant CCD changes have been observed one million years before and after the event as expressed by regular Fe cycles at Site 1260. The duration of the event estimated by orbital calibration is in the order of 40-50 kyr, similar to other transient hyperthermals in the early to middle Eocene. Here we present new high-resolution bulk and benthic stable isotope data revealing the widespread nature of the event. We investigated ODP Sites 702B (~2200m) near the crest of the Islas Orcadas Rise in the southern South Atlantic, 1263 (~1800 m) on Walvis Ridge in the SE Atlantic, and 1051 (2100 m) on Blake Nose in the NW Atlantic. The position of the event was initially narrowed by careful analysis of magnetostratigraphy and XRF scanning data. First results of stable isotope data show a ~0.7 δ13C and ~0.4‰ δ18O excursion very similar to the pattern observed at Site 1260. Although the magnitude of the bulk δ13C excursion is comparable, the bulk δ18O excursion at Site 702B is only a third of that observed at Site 1260 which might be related to diagenetic and/or latitudinal effects. 702B benthic isotope data show a ~0.75 ‰ CIE and a ~0

  13. On the composite response of the MLT to major sudden stratospheric warming events with elevated stratopause

    NASA Astrophysics Data System (ADS)

    Limpasuvan, Varavut; Orsolini, Yvan J.; Chandran, Amal; Garcia, Rolando R.; Smith, Anne K.

    2016-05-01

    Based on a climate-chemistry model (constrained by reanalyses below ~50 km), the zonal-mean composite response of the mesosphere and lower thermosphere (MLT) to major sudden stratospheric warming events with elevated stratopauses demonstrates the role of planetary waves (PWs) in driving the mean circulation in the presence of gravity waves (GWs), helping the polar vortex recover and communicating the sudden stratospheric warming (SSW) impact across the equator. With the SSW onset, strong westward PW drag appears above 80 km primarily from the dissipation of wave number 1 perturbations with westward period of 5-12 days, generated from below by the unstable westward polar stratospheric jet that develops as a result of the SSW. The filtering effect of this jet also allows eastward propagating GWs to saturate in the winter MLT, providing eastward drag that promotes winter polar mesospheric cooling. The dominant PW forcing translates to a net westward drag above the eastward mesospheric jet, which initiates downwelling over the winter pole. As the eastward polar stratospheric jet returns, this westward PW drag persists above 80 km and acts synergistically with the return of westward GW drag to drive a stronger polar downwelling that warms the pole adiabatically and helps reform the stratopause at an elevated altitude. With the polar wind reversal during the SSW onset, the westward drag by the quasi-stationary PW in the winter stratosphere drives an anomalous equatorial upwelling and cooling that enhance tropical stratospheric ozone. Along with equatorial wind anomalies, this ozone enhancement subsequently amplifies the migrating semidiurnal tide amplitude in the winter midlatitudes.

  14. Vertical and Horizontal Coupling of Atmospheres During Sudden Stratospheric Warming Events

    NASA Astrophysics Data System (ADS)

    Laskar, Fazlul; Pallamraju, Duggirala; Chau, Jorge L.

    2016-07-01

    The dynamics of neutral behavior over low- mid- and high-latitudes and electrodynamic behavior over low-latitude middle and upper atmosphere during sudden stratospheric warming (SSW) events have been investigated in this study. Over a decade long datasets of equatorial electrojet (EEJ) and total electron content (TEC) from Indian longitudes at low-latitudes have been used for studying the electrodynamical behavior. From the amplitudes of quasi-16 day waves in these two datasets it has been observed that the vertical coupling is stronger during strong major SSW events and weaker but significant for the minor SSW events. The neutral dynamical behavior has been investigated using both optical and radio measurements. The oxygen dayglow emission intensities from low-latitudes showed enhancements in and around the duration of SSW occurrences. Evidences of equatorward winds at mesosphere lower thermosphere altitude from TIMED-TIDI and lower-thermospheric temperature enhancements from TIMED-SABER are observed in the duration of enhancement in dayglow emission intensities. The results from these three independent datasets and discrete results from earlier modeling and observational studies suggest that an equatorward circulation in the winds is set up in the MLT-region during SSW. The low-latitude oxygen intensity enhancements during SSW are attributed to be due to the transport of oxygen from high- to low-latitudes. Enhanced semi-diurnal tides are also observed during the SSW events in the low-latitude dayglow emission intensities and specular meteor radar-based mid- and high-latitude horizontal winds. These results will be presented in the context of neutral and wave dynamics of the mesosphere-thermosphere region during SSW events.

  15. Changes in the strength of Atlantic Ocean overturning circulation across repeated Eocene warming events

    NASA Astrophysics Data System (ADS)

    Kirtland Turner, S.; Sexton, P. F.; Norris, R. D.; Wilson, P. A.; Charles, C. D.; Ridgwell, A.

    2015-12-01

    The Paleogene Period (~65 to 34 Ma) was a time of acute climatic warmth, with deep ocean temperatures exceeding 12°C at the height of the Early Eocene Climatic Optimum (~53 to 50 Ma). Multiple rapid warming events, associated with transient deep sea temperature increases of 2 to 4°C (termed 'hyperthermals'), potentially related to orbital forcing of the carbon cycle and climate, occurred from the late Paleocene through at least the early middle Eocene and onset of long-term Cenozoic cooling (~47 Ma). While deep ocean circulation patterns associated with the great glaciations of the Plio-Pleistocene have been studied extensively, the behavior of the ocean's overturning circulation on orbital-timescales in the extreme warmth of the early Cenozoic is largely unknown. Here we present new evidence for changing patterns of ocean overturning in the southern hemisphere associated with four orbitally paced hyperthermal events in the early-middle Eocene (~50 to 48 Ma) based on a combination of multi-site bulk carbonate and benthic foraminiferal stable isotope measurements and Earth system modeling. Our results suggest that southern-sourced overturning weakens and shoals in response to modest atmospheric carbon injections and consequent warming, and is replaced by invasion of nutrient-rich North Atlantic-sourced deep water, leading to predictable spatial patterns in deep-sea carbon isotope records. The changes in abyssal carbon isotope 'aging' gradients associated with these hyperthermals are, in fact, two to three times larger than the change in aging gradient associated with the switch in Atlantic overturning between the Last Glacial Maximum and today. Our results suggest that the Atlantic overturning circulation was sensitive to orbital-scale climate variability during Eocene extreme warmth, not just to interglacial-glacial climatic variability of the Plio-Pleistocene.

  16. Precise interpolar phasing of abrupt climate change during the last ice age

    USGS Publications Warehouse

    WAIS Divide Project Members; Buizert, Christo; Adrian, Betty M.; Ahn, Jinho; Albert, Mary; Alley, Richard B.; Baggenstos, Daniel; Bauska, Thomas K.; Bay, Ryan C.; Bencivengo, Brian B.; Bentley, Charles R.; Brook, Edward J.; Chellman, Nathan J.; Clow, Gary D.; Cole-Dai, Jihong; Conway, Howard; Cravens, Eric; Cuffey, Kurt M.; Dunbar, Nelia W.; Edwards, Jon S.; Fegyveresi, John M.; Ferris, Dave G.; Fitzpatrick, Joan J.; Fudge, T. J.; Gibson, Chris J.; Gkinis, Vasileios; Goetz, Joshua J.; Gregory, Stephanie; Hargreaves, Geoffrey Mill; Iverson, Nels; Johnson, Jay A.; Jones, Tyler R.; Kalk, Michael L.; Kippenhan, Matthew J.; Koffman, Bess G.; Kreutz, Karl; Kuhl, Tanner W.; Lebar, Donald A.; Lee, James E.; Marcott, Shaun A.; Markle, Bradley R.; Maselli, Olivia J.; McConnell, Joseph R.; McGwire, Kenneth C.; Mitchell, Logan E.; Mortensen, Nicolai B.; Neff, Peter D.; Nishiizumi, Kunihiko; Nunn, Richard M.; Orsi, Anais J.; Pasteris, Daniel R.; Pedro, Joel B.; Pettit, Erin C.; Price, P. Buford; Priscu, John C.; Rhodes, Rachael H.; Rosen, Julia L.; Schauer, Andrew J.; Schoenemann, Spruce W.; Sendelbach, Paul J.; Severinghaus, Jeffrey P.; Shturmakov, Alexander J.; Sigl, Michael; Slawny, Kristina R.; Souney, Joseph M.; Sowers, Todd A.; Spencer, Matthew K.; Steig, Eric J.; Taylor, Kendrick C.; Twickler, Mark S.; Vaughn, Bruce H.; Voigt, Donald E.; Waddington, Edwin D.; Welten, Kees C.; Wendricks, Anthony W.; White, James W. C.; Winstrup, Mai; Wong, Gifford J.; Woodruff, Thomas E.

    2015-01-01

    The last glacial period exhibited abrupt Dansgaard–Oeschger climatic oscillations, evidence of which is preserved in a variety of Northern Hemisphere palaeoclimate archives1. Ice cores show that Antarctica cooled during the warm phases of the Greenland Dansgaard–Oeschger cycle and vice versa2, 3, suggesting an interhemispheric redistribution of heat through a mechanism called the bipolar seesaw4, 5, 6. Variations in the Atlantic meridional overturning circulation (AMOC) strength are thought to have been important, but much uncertainty remains regarding the dynamics and trigger of these abrupt events7, 8, 9. Key information is contained in the relative phasing of hemispheric climate variations, yet the large, poorly constrained difference between gas age and ice age and the relatively low resolution of methane records from Antarctic ice cores have so far precluded methane-based synchronization at the required sub-centennial precision2, 3,10. Here we use a recently drilled high-accumulation Antarctic ice core to show that, on average, abrupt Greenland warming leads the corresponding Antarctic cooling onset by 218 ± 92 years (2σ) for Dansgaard–Oeschger events, including the Bølling event; Greenland cooling leads the corresponding onset of Antarctic warming by 208 ± 96 years. Our results demonstrate a north-to-south directionality of the abrupt climatic signal, which is propagated to the Southern Hemisphere high latitudes by oceanic rather than atmospheric processes. The similar interpolar phasing of warming and cooling transitions suggests that the transfer time of the climatic signal is independent of the AMOC background state. Our findings confirm a central role for ocean circulation in the bipolar seesaw and provide clear criteria for assessing hypotheses and model simulations of Dansgaard–Oeschger dynamics.

  17. Precise interpolar phasing of abrupt climate change during the last ice age.

    PubMed

    2015-04-30

    The last glacial period exhibited abrupt Dansgaard-Oeschger climatic oscillations, evidence of which is preserved in a variety of Northern Hemisphere palaeoclimate archives. Ice cores show that Antarctica cooled during the warm phases of the Greenland Dansgaard-Oeschger cycle and vice versa, suggesting an interhemispheric redistribution of heat through a mechanism called the bipolar seesaw. Variations in the Atlantic meridional overturning circulation (AMOC) strength are thought to have been important, but much uncertainty remains regarding the dynamics and trigger of these abrupt events. Key information is contained in the relative phasing of hemispheric climate variations, yet the large, poorly constrained difference between gas age and ice age and the relatively low resolution of methane records from Antarctic ice cores have so far precluded methane-based synchronization at the required sub-centennial precision. Here we use a recently drilled high-accumulation Antarctic ice core to show that, on average, abrupt Greenland warming leads the corresponding Antarctic cooling onset by 218 ± 92 years (2σ) for Dansgaard-Oeschger events, including the Bølling event; Greenland cooling leads the corresponding onset of Antarctic warming by 208 ± 96 years. Our results demonstrate a north-to-south directionality of the abrupt climatic signal, which is propagated to the Southern Hemisphere high latitudes by oceanic rather than atmospheric processes. The similar interpolar phasing of warming and cooling transitions suggests that the transfer time of the climatic signal is independent of the AMOC background state. Our findings confirm a central role for ocean circulation in the bipolar seesaw and provide clear criteria for assessing hypotheses and model simulations of Dansgaard-Oeschger dynamics. PMID:25925479

  18. Pregnancy Complications: Placental Abruption

    MedlinePlus

    ... page It's been added to your dashboard . The placenta attaches to the wall of the uterus (womb) ... abruption is a serious condition in which the placenta separates from the wall of the uterus before ...

  19. Snow cover and extreme winter warming events control flower abundance of some, but not all species in high arctic Svalbard

    PubMed Central

    Semenchuk, Philipp R; Elberling, Bo; Cooper, Elisabeth J

    2013-01-01

    Abstract The High Arctic winter is expected to be altered through ongoing and future climate change. Winter precipitation and snow depth are projected to increase and melt out dates change accordingly. Also, snow cover and depth will play an important role in protecting plant canopy from increasingly more frequent extreme winter warming events. Flower production of many Arctic plants is dependent on melt out timing, since season length determines resource availability for flower preformation. We erected snow fences to increase snow depth and shorten growing season, and counted flowers of six species over 5 years, during which we experienced two extreme winter warming events. Most species were resistant to snow cover increase, but two species reduced flower abundance due to shortened growing seasons. Cassiope tetragona responded strongly with fewer flowers in deep snow regimes during years without extreme events, while Stellaria crassipes responded partly. Snow pack thickness determined whether winter warming events had an effect on flower abundance of some species. Warming events clearly reduced flower abundance in shallow but not in deep snow regimes of Cassiope tetragona, but only marginally for Dryas octopetala. However, the affected species were resilient and individuals did not experience any long term effects. In the case of short or cold summers, a subset of species suffered reduced reproductive success, which may affect future plant composition through possible cascading competition effects. Extreme winter warming events were shown to expose the canopy to cold winter air. The following summer most of the overwintering flower buds could not produce flowers. Thus reproductive success is reduced if this occurs in subsequent years. We conclude that snow depth influences flower abundance by altering season length and by protecting or exposing flower buds to cold winter air, but most species studied are resistant to changes. Winter warming events, often

  20. Ionospheric reaction on sudden stratospheric warming events in Russiás Asia region

    NASA Astrophysics Data System (ADS)

    Polyakova, Anna; Perevalova, Natalya; Chernigovskaya, Marina

    2015-12-01

    The response of the ionosphere to sudden stratospheric warmings (SSWs) in the Asian region of Russia is studied. Two SSW events observed in 2008-2009 and 2012-2013 winter periods of extreme solar minimum and moderate solar maximum are considered. To detect the ionospheric effects caused by SSWs, we carried out a joint analysis of global ionospheric maps (GIM) of the total electron content (TEC), MLS (Microwave Limb Sounder, EOS Aura) measurements of temperature vertical profiles, as well as NCEP/NCAR and UKMO Reanalysis data. For the first time, it was found that during strong SSWs, in the mid-latitude ionosphere the amplitude of diurnal TEC variation decreases nearly half compared to quiet days. At the same time, the intensity of TEC deviations from the background level increases. It was also found that at SSW peak the midday TEC maximum decreases, and night/morning TEC values increase compared to quiet days. It was shown that during SSWs, TEC dynamics was identical for different geophysical conditions.The response of the ionosphere to sudden stratospheric warmings (SSWs) in the Asian region of Russia is studied. Two SSW events observed in 2008-2009 and 2012-2013 winter periods of extreme solar minimum and moderate solar maximum are considered. To detect the ionospheric effects caused by SSWs, we carried out a joint analysis of global ionospheric maps (GIM) of the total electron content (TEC), MLS (Microwave Limb Sounder, EOS Aura) measurements of temperature vertical profiles, as well as NCEP/NCAR and UKMO Reanalysis data. For the first time, it was found that during strong SSWs, in the mid-latitude ionosphere the amplitude of diurnal TEC variation decreases nearly half compared to quiet days. At the same time, the intensity of TEC deviations from the background level increases. It was also found that at SSW peak the midday TEC maximum decreases, and night/morning TEC values increase compared to quiet days. It was shown that during SSWs, TEC dynamics was

  1. Subtropical influence on January 2009 major sudden stratospheric warming event: diagnostic analysis

    NASA Astrophysics Data System (ADS)

    Schneidereit, Andrea; Peters, Dieter; Grams, Christian; Wolf, Gabriel; Riemer, Michael; Gierth, Franziska; Quinting, Julian; Keller, Julia; Martius, Olivia

    2015-04-01

    In January 2009 a major sudden stratospheric warming (MSSW) event occurred with the strongest NAM anomaly ever observed at 10 hPa. Also stratospheric Eliassen-Palm flux convergence and zonal mean eddy heat fluxes of ultra-long waves at 100 hPa layer were unusually strong in the mid-latitudes just before and after the onset of the MSSW. Beside internal interactions between the background flow and planetary waves and between planetary waves among themselves the subtropical tropospheric forcing of these enhanced heat fluxes is still an open question. This study investigates in more detail the dynamical reasons for the pronounced heat fluxes based on ERA-Interim re-analysis data. Investigating the regional contributions of the eddy heat flux to the northern hemispheric zonal mean revealed a distinct spatial pattern with maxima in the Eastern Pacific/North America and the Eastern North Atlantic/ Europe in that period. The first region is related with an almost persistent tropospheric blocking high (BH) over the Gulf of Alaska dominating the upper-level flow and the second region with a weaker BH over Northern Europe. The evolution of the BH over the Gulf of Alaska can be explained by a chain of tropospheric weather events linked to and maintained by subtropical and tropical influences: MJO (phase 7-8) and the developing cold phase of ENSO (La Niña), which are in coherence over the Eastern Pacific favor enhanced subtropical baroclinicity. In turn extratropical cyclone activity increases and shifts more poleward associated with an increase of the frequency of warm conveyor belts (WCB). These WCBs support enhanced poleward directed eddy heat fluxes in Eastern Pacific/North-American region. The Eastern North Atlantic/European positive heat flux anomaly is associated with a blocking high over Scandinavia. This BH is maintained by an eastward propagating Rossby wave train, emanating from the block over the Gulf of Alaska. Eddy feedback processes support this high pressure

  2. The Science of Abrupt Climate Change

    NASA Astrophysics Data System (ADS)

    Overpeck, J. T.

    2002-12-01

    The issue of abrupt climate change has been highlighted by a recent National Academy of Sciences (NRC) study as one of the most troubling potential aspects of future global climate change. The science of abrupt climate change originated in the discovery and study of huge climatic shifts during the last glacial period, particularly in and around the North Atlantic. We now know that ocean thermohaline circulation and circum-North Atlantic climate can change in hard-to-anticipate non-linear ways, and that this type of threat is still very real for the future. At the same time, attention is increasingly being focused on other, equally serious, types of potential "warm climate" abrupt climate change. Worldwide, there is abundant paleoenvironmental evidence for decades-long "megadroughts" that, for example, seemingly occurred on average once or twice a millennium in North America. Dramatic shifts in El Nino - Southern Oscillation (ENSO) variability have also occurred in the past, and could be linked to the occurrence of past megadroughts. Evidence also exists that supports the assertion that the frequency of major floods, and/or landfalls by the largest tropical storms, can change significantly and abruptly. However, as with abrupt shifts in ENSO or drought frequency/duration, we still have only an imperfect observational record, and worse, little proven basis for prediction. This is one reason why abrupt change poses a significant threat to technologically-advanced, as well as developing countries. Major abrupt sea level rise is also a major threat, but again, the paleoclimate record indicates that our understanding of processes related to ice cap melting are not as good as we would like. Given that abrupt climatic changes could occur even in the absence of significant anthropogenic climate change, society should act soon to reduce vulnerabilities. However, the most troubling aspect of the issue is that global warming will likely act to increase the probability of

  3. Thermohaline instability and the formation of glacial North Atlantic super polynyas at the onset of Dansgaard-Oeschger warming events

    NASA Astrophysics Data System (ADS)

    Vettoretti, Guido; Peltier, W. Richard

    2016-05-01

    Late Quaternary rapid warming events inferred on the basis of oxygen isotopic data from Greenland ice cores are the most prominent characteristic of millennial-scale Dansgaard-Oeschger oscillations. In a coupled climate model simulation which has accurately reproduced this oscillatory behavior for the first time, we show that formation of a glacial North Atlantic super polynya characterizes the initial stage of transition from cold stadial to warm interstadial conditions. The winter polynya forms within the otherwise sea ice-covered North Atlantic as a consequence of the onset of a thermohaline convective instability beneath an extensive stadial sea ice lid. Early in the stadial period, the tendency for thermal convective instability of an extensive warm pool beneath the sea ice lid is strongly inhibited by a stabilizing vertical salinity gradient, which gradually diminishes until a thermohaline convective instability occurs that leads to polynya formation and the rapid retreat of North Atlantic sea ice cover.

  4. Does the trigger for abrupt climate change reside in the ocean or in the atmosphere?

    PubMed

    Broecker, W S

    2003-06-01

    Two hypotheses have been put forward to explain the large and abrupt climate changes that punctuated glacial time. One attributes such changes to reorganizations of the ocean's thermohaline circulation and the other to changes in tropical atmosphere-ocean dynamics. In an attempt to distinguish between these hypotheses, two lines of evidence are examined. The first involves the timing of the freshwater injections to the northern Atlantic that have been suggested as triggers for the global impacts associated with the Younger Dryas and Heinrich events. The second has to do with evidence for precursory events associated with the Heinrich ice-rafted debris layers in the northern Atlantic and with the abrupt Dansgaard-Oeschger warmings recorded in the Santa Barbara Basin. PMID:12791974

  5. Upper mesospheric lunar tides over middle and high latitudes during sudden stratospheric warming events

    NASA Astrophysics Data System (ADS)

    Chau, J. L.; Hoffmann, P.; Pedatella, N. M.; Matthias, V.; Stober, G.

    2015-04-01

    In recent years there have been a series of reported ground- and satellite-based observations of lunar tide signatures in the equatorial and low latitude ionosphere/thermosphere around sudden stratospheric warming (SSW) events. This lower atmosphere/ionosphere coupling has been suggested to be via the E region dynamo. In this work we present the results of analyzing 6 years of hourly upper mesospheric winds from specular meteor radars over a midlatitude (54°N) station and a high latitude (69°N) station. Instead of correlating our results with typical definitions of SSWs, we use the definition of polar vortex weaking (PVW) used by Zhang and Forbes. This definition provides a better representation of the strength in middle atmospheric dynamics that should be responsible for the waves propagating to the E region. We have performed a wave decomposition on hourly wind data in 21 day segments, shifted by 1 day. In addition to the radar wind data, the analysis has been applied to simulations from Whole Atmosphere Community Climate Model Extended version and the thermosphere-ionosphere-mesosphere electrodynamics general circulation model. Our results indicate that the semidiurnal lunar tide (M2) enhances in northern hemispheric winter months, over both middle and high latitudes. The time and magnitude of M2 are highly correlated with the time and associated zonal wind of PVW. At middle/high latitudes, M2 in the upper mesosphere occurs after/before the PVW. At both latitudes, the maximum amplitude of M2 is directly proportional to the strength of PVW westward wind. We have found that M2 amplitudes could be comparable to semidiurnal solar tide amplitudes, particularly around PVW and equinoxes. Besides these general results, we have also found peculiarities in some events, particularly at high latitudes. These peculiarities point to the need of considering the longitudinal features of the polar stratosphere and the upper mesosphere and lower thermosphere regions. For

  6. Can the GEOS CCM Simulate the Temperature Response to Warm Pool El Nino Events in the Antarctic Stratosphere?

    NASA Technical Reports Server (NTRS)

    Hurwitz, M. M.; Song, I.-S.; Oman, L. D.; Newman, P. A.; Molod, A. M.; Frith, S. M.; Nielsen, J. E.

    2010-01-01

    "Warm pool" (WP) El Nino events are characterized by positive sea surface temperature (SST) anomalies in the central equatorial Pacific. During austral spring. WP El Nino events are associated with an enhancement of convective activity in the South Pacific Convergence Zone, provoking a tropospheric planetary wave response and thus increasing planetary wave driving of the Southern Hemisphere stratosphere. These conditions lead to higher polar stratospheric temperatures and to a weaker polar jet during austral summer, as compared with neutral ENSO years. Furthermore, this response is sensitive to the phase of the quasi-biennial oscillation (QBO): a stronger warming is seen in WP El Nino events coincident with the easterly phase of the quasi-biennial oscillation (QBO) as compared with WP El Nino events coincident with a westerly or neutral QBO. The Goddard Earth Observing System (GEOS) chemistry-climate model (CCM) is used to further explore the atmospheric response to ENSO. Time-slice simulations are forced by composited SSTs from observed WP El Nino and neutral ENSO events. The modeled eddy heat flux, temperature and wind responses to WP El Nino events are compared with observations. A new gravity wave drag scheme has been implemented in the GEOS CCM, enabling the model to produce a realistic, internally generated QBO. By repeating the above time-slice simulations with this new model version, the sensitivity of the WP El Nino response to the phase of the quasi-biennial oscillation QBO is estimated.

  7. Can the GEOS CCM Simulate the Temperature Response to Warm Pool El Nino Events in the Antarctic Stratosphere?

    NASA Technical Reports Server (NTRS)

    Hurwitz, M. M.; Song, I.-S.; Oman, L. D.; Newman, P. A.; Molod, A. M.; Frith, S. M.; Nielsen, J. E.

    2011-01-01

    "Warm pool" (WP) El Nino events are characterized by positive sea surface temperature (SST) anomalies in the central equatorial Pacific. During austral spring, WP El Nino events are associated with an enhancement of convective activity in the South Pacific Convergence Zone, provoking a tropospheric planetary wave response and thus increasing planetary wave driving of the Southern Hemisphere stratosphere. These conditions lead to higher polar stratospheric temperatures and to a weaker polar jet during austral summer, as compared with neutral ENSO years. Furthermore, this response is sensitive to the phase of the quasi-biennial oscillation (QBO): a stronger warming is seen in WP El Nino events coincident with the easterly phase of the quasi-biennial oscillation (QBO) as compared with WP El Nino events coincident with a westerly or neutral QBO. The Goddard Earth Observing System (GEOS) chemistry-climate model (CCM) is used to further explore the atmospheric response to ENSO. Time-slice simulations are forced by composited SSTs from observed NP El Nino and neutral ENSO events. The modeled eddy heat flux, temperature and wind responses to WP El Nino events are compared with observations. A new gravity wave drag scheme has been implemented in the GEOS CCM, enabling the model to produce e realistic, internally generated QBO. By repeating the above time-slice simulations with this new model version, the sensitivity of the WP El Nino response to the phase of the quasi-biennial oscillation QBO is estimated.

  8. Abrupt glacial climate shifts controlled by ice sheet changes.

    PubMed

    Zhang, Xu; Lohmann, Gerrit; Knorr, Gregor; Purcell, Conor

    2014-08-21

    During glacial periods of the Late Pleistocene, an abundance of proxy data demonstrates the existence of large and repeated millennial-scale warming episodes, known as Dansgaard-Oeschger (DO) events. This ubiquitous feature of rapid glacial climate change can be extended back as far as 800,000 years before present (BP) in the ice core record, and has drawn broad attention within the science and policy-making communities alike. Many studies have been dedicated to investigating the underlying causes of these changes, but no coherent mechanism has yet been identified. Here we show, by using a comprehensive fully coupled model, that gradual changes in the height of the Northern Hemisphere ice sheets (NHISs) can alter the coupled atmosphere-ocean system and cause rapid glacial climate shifts closely resembling DO events. The simulated global climate responses--including abrupt warming in the North Atlantic, a northward shift of the tropical rainbelts, and Southern Hemisphere cooling related to the bipolar seesaw--are generally consistent with empirical evidence. As a result of the coexistence of two glacial ocean circulation states at intermediate heights of the ice sheets, minor changes in the height of the NHISs and the amount of atmospheric CO2 can trigger the rapid climate transitions via a local positive atmosphere-ocean-sea-ice feedback in the North Atlantic. Our results, although based on a single model, thus provide a coherent concept for understanding the recorded millennial-scale variability and abrupt climate changes in the coupled atmosphere-ocean system, as well as their linkages to the volume of the intermediate ice sheets during glacials. PMID:25119027

  9. Abrupt glacial climate shifts controlled by ice sheet changes

    NASA Astrophysics Data System (ADS)

    Zhang, Xu; Lohmann, Gerrit; Knorr, Gregor; Purcell, Conor

    2014-08-01

    During glacial periods of the Late Pleistocene, an abundance of proxy data demonstrates the existence of large and repeated millennial-scale warming episodes, known as Dansgaard-Oeschger (DO) events. This ubiquitous feature of rapid glacial climate change can be extended back as far as 800,000 years before present (BP) in the ice core record, and has drawn broad attention within the science and policy-making communities alike. Many studies have been dedicated to investigating the underlying causes of these changes, but no coherent mechanism has yet been identified. Here we show, by using a comprehensive fully coupled model, that gradual changes in the height of the Northern Hemisphere ice sheets (NHISs) can alter the coupled atmosphere-ocean system and cause rapid glacial climate shifts closely resembling DO events. The simulated global climate responses--including abrupt warming in the North Atlantic, a northward shift of the tropical rainbelts, and Southern Hemisphere cooling related to the bipolar seesaw--are generally consistent with empirical evidence. As a result of the coexistence of two glacial ocean circulation states at intermediate heights of the ice sheets, minor changes in the height of the NHISs and the amount of atmospheric CO2 can trigger the rapid climate transitions via a local positive atmosphere-ocean-sea-ice feedback in the North Atlantic. Our results, although based on a single model, thus provide a coherent concept for understanding the recorded millennial-scale variability and abrupt climate changes in the coupled atmosphere-ocean system, as well as their linkages to the volume of the intermediate ice sheets during glacials.

  10. The surface impact of stratospheric sudden warmings in a 1000 year control simulation: sensitivity to event definition and type

    NASA Astrophysics Data System (ADS)

    Maycock, Amanda

    2014-05-01

    Major sudden stratospheric warmings (SSWs) are characterised by large departures of the northern hemisphere winter-time circulation from climatology. Numerous studies have shown that on average these events impact on tropospheric weather patterns leading to a more negative North Atlantic Oscillation index; however, recent studies have suggested that the nature of this downward coupling may be sensitive to the type of SSW (vortex split or displacement). This study explores this issue using a 1000 year pre-industrial control simulation from the IPSL-CM5A-LR model taken from the CMIP5 archive. We identify SSW events using two distinct methods: the widely applied algorithm of Charlton and Polvani (2007) and a 2-D moments-based approach described by Seviour et al (2013). The long simulation offers a unique opportunity to analyse a very large sample of SSW events (~500). We evaluate the relative timing and frequency of SSWs identified by the two methods and examine their impact on the tropospheric state. In contrast to other recent studies, we do not find a significant difference between the impact of split and displacement SSWs on the troposphere in this model. We analyse the evolution of the SSWs that are not consistently identified by the two algorithms, and examine whether they have a significant role in determining the overall impact of SSWs on the troposphere. The large number of warming events enables a comprehensive assessment of the noise that may be associated with analysing stratosphere-troposphere coupling in smaller sample sizes.

  11. Modeling evidences for global warming, Arctic seawater freshening, and sluggish oceanic circulation during the Early Toarcian anoxic event

    NASA Astrophysics Data System (ADS)

    Dera, Guillaume; Donnadieu, Yannick

    2012-06-01

    The paleoecological disturbances recorded during the Early Toarcian warming event (183 Myr ago), including marine anoxia, sea level rise, seawater acidification, carbonate production crisis, and species extinctions, are often regarded as past examples of Earth's possible responses to the rapid emergence of super greenhouse conditions. However, physical mechanisms explaining both the global and local expressions of paleoenvironmental events are still highly debated. Here we analyze the paleoclimatic and paleoceanographic consequences of increases in atmospheric pCO2 levels at a multiscale resolution using a fully coupled ocean-atmosphere model (FOAM). We show that, in association with stronger high-latitude precipitation rates and enhanced continental runoff, the demise of polar sea ice due to the global warming event involved a regional freshening of Arctic surface seawaters. These disturbances lead to progressive slowdowns of the global oceanic circulation accountable for widespread ocean stratification and bottom anoxia processes in deep oceanic settings and epicontinental basins. In agreement with very negative oxygen isotope values measured on fossil shells from the NW Tethys, our simulations also show that recurrent discharges of brackish and nutrient-rich Arctic surface waters through the Viking Corridor could have led to both vertical and geographical gradients in salinity and seawater δ18O in the NW Tethyan seas. Locally contrasted conditions in water mass density and rises in productivity rates due to strong nutrient supplies could partly explain the regional severity of the anoxic event in the restricted Euro-boreal domains, as it has been previously suggested and modeled regionally.

  12. Changes in extreme temperature and precipitation events in the Loess Plateau (China) during 1960-2013 under global warming

    NASA Astrophysics Data System (ADS)

    Sun, Wenyi; Mu, Xingmin; Song, Xiaoyan; Wu, Dan; Cheng, Aifang; Qiu, Bing

    2016-02-01

    In recent decades, extreme climatic events have been a major issue worldwide. Regional assessments on various climates and geographic regions are needed for understanding uncertainties in extreme events' responses to global warming. The objective of this study was to assess the annual and decadal trends in 12 extreme temperature and 10 extreme precipitation indices in terms of intensity, frequency, and duration over the Loess Plateau during 1960-2013. The results indicated that the regionally averaged trends in temperature extremes were consistent with global warming. The occurrence of warm extremes, including summer days (SU), tropical nights (TR), warm days (TX90), and nights (TN90) and a warm spell duration indicator (WSDI), increased by 2.76 (P < 0.01), 1.24 (P < 0.01), 2.60 (P = 0.0003), 3.41 (P < 0.01), and 0.68 (P = 0.0041) days/decade during the period of 1960-2013, particularly, sharp increases in these indices occurred in 1985-2000. Over the same period, the occurrence of cold extremes, including frost days (FD), ice days (ID), cold days (TX10) and nights (TN10), and a cold spell duration indicator (CSDI) exhibited decreases of - 3.22 (P < 0.01), - 2.21 (P = 0.0028), - 2.71 (P = 0.0028), - 4.31 (P < 0.01), and - 0.69 (P = 0.0951) days/decade, respectively. Moreover, extreme warm events in most regions tended to increase while cold indices tended to decrease in the Loess Plateau, but the trend magnitudes of cold extremes were greater than those of warm extremes. The growing season (GSL) in the Loess Plateau was lengthened at a rate of 3.16 days/decade (P < 0.01). Diurnal temperature range (DTR) declined at a rate of - 0.06 °C /decade (P = 0.0931). Regarding the precipitation indices, the annual total precipitation (PRCPTOT) showed no obvious trends (P = 0.7828). The regionally averaged daily rainfall intensity (SDII) exhibited significant decreases (- 0.14 mm/day/decade, P = 0.0158), whereas consecutive dry days (CDD) significantly increased (1.96 days

  13. How did ocean warming affect Australian rainfall extremes during the 2010/2011 La Niña event?

    NASA Astrophysics Data System (ADS)

    Ummenhofer, Caroline C.; Sen Gupta, Alexander; England, Matthew H.; Taschetto, Andréa. S.; Briggs, Peter R.; Raupach, Michael R.

    2015-11-01

    Extreme rainfall conditions in Australia during the 2010/2011 La Niña resulted in devastating floods claiming 35 lives, causing billions of dollars in damages, and far-reaching impacts on global climate, including a significant drop in global sea level and record terrestrial carbon uptake. Northeast Australian 2010/2011 rainfall was 84% above average, unusual even for a strong La Niña, and soil moisture conditions were unprecedented since 1950. Here we demonstrate that the warmer background state increased the likelihood of the extreme rainfall response. Using atmospheric general circulation model experiments with 2010/2011 ocean conditions with and without long-term warming, we identify the mechanisms that increase the likelihood of extreme rainfall: additional ocean warming enhanced onshore moisture transport onto Australia and ascent and precipitation over the northeast. Our results highlight the role of long-term ocean warming for modifying rain-producing atmospheric circulation conditions, increasing the likelihood of extreme precipitation for Australia during future La Niña events.

  14. Sensitivity of the Atmospheric Response to Warm Pool El Nino Events to Modeled SSTs and Future Climate Forcings

    NASA Technical Reports Server (NTRS)

    Hurwitz, Margaret M.; Garfinkel, Chaim I.; Newman, Paul A.; Oman, Luke D.

    2013-01-01

    Warm pool El Nino (WPEN) events are characterized by positive sea surface temperature (SST) anomalies in the central equatorial Pacific. Under present-day climate conditions, WPEN events generate poleward propagating wavetrains and enhance midlatitude planetary wave activity, weakening the stratospheric polar vortices. The late 21st century extratropical atmospheric response to WPEN events is investigated using the Goddard Earth Observing System Chemistry-Climate Model (GEOSCCM), version 2. GEOSCCM simulations are forced by projected late 21st century concentrations of greenhouse gases (GHGs) and ozone-depleting substances (ODSs) and by SSTs and sea ice concentrations from an existing ocean-atmosphere simulation. Despite known ocean-atmosphere model biases, the prescribed SST fields represent a best estimate of the structure of late 21st century WPEN events. The future Arctic vortex response is qualitatively similar to that observed in recent decades but is weaker in late winter. This response reflects the weaker SST forcing in the Nino 3.4 region and subsequently weaker Northern Hemisphere tropospheric teleconnections. The Antarctic stratosphere does not respond to WPEN events in a future climate, reflecting a change in tropospheric teleconnections: The meridional wavetrain weakens while a more zonal wavetrain originates near Australia. Sensitivity simulations show that a strong poleward wavetrain response to WPEN requires a strengthening and southeastward extension of the South Pacific Convergence Zone; this feature is not captured by the late 21st century modeled SSTs. Expected future increases in GHGs and decreases in ODSs do not affect the polar stratospheric responses to WPEN.

  15. The examination of a downslope warming wind event over the Larsen Ice Shelf in Antarctica through modeling and aircraft observations.

    NASA Astrophysics Data System (ADS)

    Grosvenor, Daniel; Choularton, Thomas; King, John; Lachlan-Cope, Thomas

    2010-05-01

    During the last 50-60 years temperatures over the Antarctic Peninsula region have increased more rapidly than anywhere else in the southern hemisphere, at several times the global average rate. At one station, the near-surface warming between 1951 and 2004 was 2.94 oC compared to a global average of 0.52 oC. However, the seasonal pattern of this regional warming has varied with location, with the east side having warmed more than the west in the autumn and summer seasons. This is important since the process of surface melting on the Larsen ice shelves, which are located on the east side, predominately occurs in summer. Crevasse propagation due to the weight of accumulated melt water is currently thought to have been the major factor in causing the catastrophic near-total disintegration of the Larsen B ice shelf in 2002, representing a loss of ice of area 3200 km2. The larger and more southerly Larsen C ice shelf could also suffer a similar fate if the warming continues, with consequences for the ecology and for increased glacier flow, leading to sea level rise. The difference in warming between the east and west side in these seasons is thought to have been driven by circulation changes that have led to increases in the strength of westerly winds. The high mountains of the Antarctic Peninsula provide a climatic barrier between the warmer oceanic air of the west and the cold continental air of the east. It has been suggested that increased westerlies allow warm winds to cross to the east side more frequently. The warming of westerly flow can also be enhanced by latent heat release on the upslope side and/or adiabatic descent of air from above, on the downslope side. In January 2006 the British Antarctic Survey performed an aircraft flight over the Larsen C ice shelf on the east side of the Peninsula, which sampled a strong downslope warming wind event. Surface flux measurements over the ice shelf suggest that the sensible heat provided by the warm jets would be

  16. Warm Events At Summit, Greenland During 2012 Relative To An Evolving Climate Record

    NASA Astrophysics Data System (ADS)

    Shuman, C. A.; Schnaubelt, M. J.; Mefford, T. K.

    2012-12-01

    An evolving temperature record from the Greenland Summit Station, at approximately 3216 m in elevation, has documented unusual periods of near and above freezing air temperatures in July 2012. Since August 2005, data has been collected from well-calibrated and actively-ventilated temperature sensors at a NOAA-ESRL climate observatory. Comparison of these data from a nominal 2 m height above the ice sheet surface over the past seven summers reveals several periods of unusual warmth at the highest elevations of the ice sheet in 2012. Detailed analysis of the available data indicates that temperatures rose to or above freezing for almost 6.5 hours on July 11 at Summit Station. A maximum air temperature of 1 degree C was recorded repeatedly in the 1-minute averages during this period. NOAA's data also indicated brief periods at or above zero on July 12th and 29th as well. These anomalously warm air-temperature periods can now be compared and contrasted with equivalent-quality data from earlier records (automatic weather stations began operating in May 1987 during the GISP2 project) and used to calibrate indications of warm surface temperatures derived from multi-decadal satellite passive microwave and infrared sensors.

  17. Isotope modeling of a mid-Turonian warming event in the South Atlantic

    NASA Astrophysics Data System (ADS)

    Bice, K.; Pollard, D.; MacLeod, K.; Huber, B.

    2006-12-01

    Oxygen isotope data from very well preserved late Turonian planktonic foraminifera at DSDP Site 511 (Falkland Plateau, 60 S paleolatitude) exhibit a 2 per mil excursion to values as low as -4.7 per mil (PDB), apparently coincident with the warmest tropical temperature estimates yet obtained for the open ocean. However, local benthic foraminifer d18O show no coincident decrease. This suggests that local bottom waters experienced no temperature change while the upper ocean warmed by as much as 9C, that upper ocean waters because much more depleted due to a dramatic increase in freshwater delivery or decrease in d18O of precipitation and runoff, or that some combination of these three changes occurred. Using an isotope-capable general circulation model, we examine the likelihood that a significant upper ocean freshening or dw depletion occurred during a modest increase in local sea surface temperature during this period of overall warmer-than-modern climate. We also examine preliminary planktonic foraminiferal Mg/Ca data that support some late Turonian warming at Site 511.

  18. Nucleation events at a coastal city during the warm period: Kerbside versus urban background measurements

    NASA Astrophysics Data System (ADS)

    Siakavaras, D.; Samara, C.; Petrakakis, M.; Biskos, G.

    2016-09-01

    Number size distributions of atmospheric aerosol particles were simultaneously measured at a kerbside and an urban background site in the city of Thessaloniki, Greece, from June to October 2009. New particle formation events were observed ca. 27% of the days at the urban kerbside site and 29% of the days at the urban background site. In almost all the cases the events started between 10:00 and 12:00, and continued for several hours. The total number concentration (TNC) of the particles having diameters from 10 to ca. 500 nm during the events increased from 1.4 × 104 to 6.5 × 104 #/cm3 at the urban kerbside site, and from 0.2 × 104 to 2.4 × 104 #/cm3 at the urban background site. At the urban kerbside site, 9% of the days exhibited class I events (i.e., events followed by a clear growth of the newly formed particles), 10% class II (i.e., events during which the concentration of nucleation mode particles were high but their growth was not continuous), 67% were characterised as non-event days, and 14% of the days exhibited no clear particle formation pattern (undefined). At the urban background site, 15% of the days were classified as class I, 5% as class II, 75% of the days showed no nucleation, whereas only 5% of the days were undefined. While the fraction of event days (both class I and class II) at both sites was similar (ca. 20%), the higher fraction of class I events observed at Eptapyrgio can be attributed to the cleaner environment of the urban background site that allows better identification of the particle concentration increase. The nucleation bursts show a similar pattern at both sites, with the newly formed particles reaching a final size of ca. 80-100 nm. A distinct difference between the two stations was that the smallest particles observed during the new-particle formation events had a diameter of ca. 10 nm (i.e., the smallest particles we could observe) at the kerbside site and ca. 20 nm at the urban background site. This is an indication that

  19. Dynamic response of desert wetlands to abrupt climate change

    PubMed Central

    Springer, Kathleen B.; Manker, Craig R.; Pigati, Jeffrey S.

    2015-01-01

    Desert wetlands are keystone ecosystems in arid environments and are preserved in the geologic record as groundwater discharge (GWD) deposits. GWD deposits are inherently discontinuous and stratigraphically complex, which has limited our understanding of how desert wetlands responded to past episodes of rapid climate change. Previous studies have shown that wetlands responded to climate change on glacial to interglacial timescales, but their sensitivity to short-lived climate perturbations is largely unknown. Here, we show that GWD deposits in the Las Vegas Valley (southern Nevada, United States) provide a detailed and nearly complete record of dynamic hydrologic changes during the past 35 ka (thousands of calibrated 14C years before present), including cycles of wetland expansion and contraction that correlate tightly with climatic oscillations recorded in the Greenland ice cores. Cessation of discharge associated with rapid warming events resulted in the collapse of entire wetland systems in the Las Vegas Valley at multiple times during the late Quaternary. On average, drought-like conditions, as recorded by widespread erosion and the formation of desert soils, lasted for a few centuries. This record illustrates the vulnerability of desert wetland flora and fauna to abrupt climate change. It also shows that GWD deposits can be used to reconstruct paleohydrologic conditions at millennial to submillennial timescales and informs conservation efforts aimed at protecting these fragile ecosystems in the face of anthropogenic warming. PMID:26554007

  20. Dynamic response of desert wetlands to abrupt climate change.

    PubMed

    Springer, Kathleen B; Manker, Craig R; Pigati, Jeffrey S

    2015-11-24

    Desert wetlands are keystone ecosystems in arid environments and are preserved in the geologic record as groundwater discharge (GWD) deposits. GWD deposits are inherently discontinuous and stratigraphically complex, which has limited our understanding of how desert wetlands responded to past episodes of rapid climate change. Previous studies have shown that wetlands responded to climate change on glacial to interglacial timescales, but their sensitivity to short-lived climate perturbations is largely unknown. Here, we show that GWD deposits in the Las Vegas Valley (southern Nevada, United States) provide a detailed and nearly complete record of dynamic hydrologic changes during the past 35 ka (thousands of calibrated (14)C years before present), including cycles of wetland expansion and contraction that correlate tightly with climatic oscillations recorded in the Greenland ice cores. Cessation of discharge associated with rapid warming events resulted in the collapse of entire wetland systems in the Las Vegas Valley at multiple times during the late Quaternary. On average, drought-like conditions, as recorded by widespread erosion and the formation of desert soils, lasted for a few centuries. This record illustrates the vulnerability of desert wetland flora and fauna to abrupt climate change. It also shows that GWD deposits can be used to reconstruct paleohydrologic conditions at millennial to submillennial timescales and informs conservation efforts aimed at protecting these fragile ecosystems in the face of anthropogenic warming. PMID:26554007

  1. Dynamic response of desert wetlands to abrupt climate change

    USGS Publications Warehouse

    Springer, Kathleen; Manker, Craig; Pigati, Jeff

    2015-01-01

    Desert wetlands are keystone ecosystems in arid environments and are preserved in the geologic record as groundwater discharge (GWD) deposits. GWD deposits are inherently discontinuous and stratigraphically complex, which has limited our understanding of how desert wetlands responded to past episodes of rapid climate change. Previous studies have shown that wetlands responded to climate change on glacial to interglacial timescales, but their sensitivity to short-lived climate perturbations is largely unknown. Here, we show that GWD deposits in the Las Vegas Valley (southern Nevada, United States) provide a detailed and nearly complete record of dynamic hydrologic changes during the past 35 ka (thousands of calibrated 14C years before present), including cycles of wetland expansion and contraction that correlate tightly with climatic oscillations recorded in the Greenland ice cores. Cessation of discharge associated with rapid warming events resulted in the collapse of entire wetland systems in the Las Vegas Valley at multiple times during the late Quaternary. On average, drought-like conditions, as recorded by widespread erosion and the formation of desert soils, lasted for a few centuries. This record illustrates the vulnerability of desert wetland flora and fauna to abrupt climate change. It also shows that GWD deposits can be used to reconstruct paleohydrologic conditions at millennial to submillennial timescales and informs conservation efforts aimed at protecting these fragile ecosystems in the face of anthropogenic warming.

  2. Definition of Stratospheric Sudden Warming Events for Multi-Model Analysis and Its Application to the CMIP5

    NASA Astrophysics Data System (ADS)

    Kim, Junsu; Son, Seok-Woo; Park, Hyo-Seok

    2015-04-01

    The onset of major stratospheric sudden warming (SSW) events has been often defined as the date when the westerly at 10 hPa and 60°N turns to easterly during winter, corresponding to warmer polar stratosphere than mid latitudes. This simple definition effectively detects the observed characteristics of SSW, but its application to climate models, which have different background flow and temporal variability, is often challenging. For example, the model whose stratospheric mean wind is too weak tends to overestimate the frequency of zonal-wind reversal and SSW events. In this study we propose a simple definition of major SSW events that is applicable to multi-model analysis. Specifically, SSW events are defined when the tendency of zonal-mean zonal wind at 10 hPa at 60°N crosses -1 m/s/day within 30 to 40 days while growing in magnitude. This tendency-based definition, which is independent of mean wind, is applied to both ERA40 reanalysis and CMIP5 models. The models are further grouped into the high-top models with a well-resolved stratosphere and low-top models with a relatively simple stratosphere. A new definition successfully reproduces the mean frequency of SSW events that is identified by wind reversal approach, i.e., about 6 events per decade in ERA40. High-top models well capture this frequency. Although low-top models underestimate the frequency, in contrast to previous studies, the difference to high-top models is not statistically significant. Likewise, no significant difference is found in the downward coupling in the high-top and low-top models. These results indicate that model vertical resolution itself may not be a key factor in simulating SSW events and the associated downward coupling.

  3. Dynamics of 2013 Sudden Stratospheric Warming event and its impact on cold weather over Eurasia: Role of planetary wave reflection.

    PubMed

    Nath, Debashis; Chen, Wen; Zelin, Cai; Pogoreltsev, Alexander Ivanovich; Wei, Ke

    2016-01-01

    In the present study, we investigate the impact of stratospheric planetary wave reflection on tropospheric weather over Central Eurasia during the 2013 Sudden Stratospheric Warming (SSW) event. We analyze EP fluxes and Plumb wave activity fluxes to study the two and three dimensional aspects of wave propagation, respectively. The 2013 SSW event is excited by the combined influence of wavenumber 1 (WN1) and wavenumber 2 (WN2) planetary waves, which makes the event an unusual one and seems to have significant impact on tropospheric weather regime. We observe an extraordinary development of a ridge over the Siberian Tundra and the North Pacific during first development stage (last week of December 2012) and later from the North Atlantic in the second development stage (first week of January 2013), and these waves appear to be responsible for the excitation of the WN2 pattern during the SSW. The wave packets propagated upward and were then reflected back down to central Eurasia due to strong negative wind shear in the upper stratospheric polar jet, caused by the SSW event. Waves that propagated downward led to the formation of a deep trough over Eurasia and brought extreme cold weather over Kazakhstan, the Southern part of Russia and the Northwestern part of China during mid-January 2013. PMID:27051997

  4. Dynamics of 2013 Sudden Stratospheric Warming event and its impact on cold weather over Eurasia: Role of planetary wave reflection

    PubMed Central

    Nath, Debashis; Chen, Wen; Zelin, Cai; Pogoreltsev, Alexander Ivanovich; Wei, Ke

    2016-01-01

    In the present study, we investigate the impact of stratospheric planetary wave reflection on tropospheric weather over Central Eurasia during the 2013 Sudden Stratospheric Warming (SSW) event. We analyze EP fluxes and Plumb wave activity fluxes to study the two and three dimensional aspects of wave propagation, respectively. The 2013 SSW event is excited by the combined influence of wavenumber 1 (WN1) and wavenumber 2 (WN2) planetary waves, which makes the event an unusual one and seems to have significant impact on tropospheric weather regime. We observe an extraordinary development of a ridge over the Siberian Tundra and the North Pacific during first development stage (last week of December 2012) and later from the North Atlantic in the second development stage (first week of January 2013), and these waves appear to be responsible for the excitation of the WN2 pattern during the SSW. The wave packets propagated upward and were then reflected back down to central Eurasia due to strong negative wind shear in the upper stratospheric polar jet, caused by the SSW event. Waves that propagated downward led to the formation of a deep trough over Eurasia and brought extreme cold weather over Kazakhstan, the Southern part of Russia and the Northwestern part of China during mid-January 2013. PMID:27051997

  5. Improved predictability of stratospheric sudden warming events in an atmospheric general circulation model with enhanced stratospheric resolution

    NASA Astrophysics Data System (ADS)

    Marshall, Andrew G.; Scaife, Adam A.

    2010-08-01

    The impact of stratospheric resolution on the predictability of stratospheric sudden warming (SSW) events and their effect on European climate is cleanly assessed in two versions of the Hadley Center's atmospheric climate model, Hadley Center global environmental model. The standard 38-level version of the model extends to an altitude of 39 km (˜3 mbar) while the extended 60-level version has enhanced stratospheric resolution and reaches 84 km altitude (˜0.004 mbar). We show that the L60 model captures SSW events earlier than the L38 model (12 days before an event compared with 8 days) and influences the simulation of European surface winter cold spells at seasonal time scales, highlighting the benefit of high vertical resolution and daily initialization for seasonal forecasting. This is likely due to earlier initialization of the downward-propagating SSW signal in the higher-top L60 model. We suggest however that the increased lead time for predicting SSW events is unlikely to be improved much further by raising the model lid above the L60 model domain.

  6. Thermokarst processes in west-European loess series: new evidences for rapid climatic warming events during the Last Glacial

    NASA Astrophysics Data System (ADS)

    Antoine, Pierre; Moine, Olivier; Didier Rousseau, Denis; Hatté, Christine

    2013-04-01

    For a long time, the imprint of millennial climatic cycles (D/O cycles) in the Last Glacial loess sequences has been related to the alternation of loess layers and arctic brown soil horizons, especially between about 60 and 30 ka BP (± MIS 3). Nevertheless, owing to erosion gaps and strong reductions in the sedimentation rate, there are always less individual soil horizons than D/O cycles during the same period, which makes correlations very difficult. The discovery in the Nussloch loess sequence (Germany) of a thermokarst structure including well preserved vegetal remains, mollusc shells, and relicts of former ice wedge casts, provides new evidences for a rapid climatic warming at the origin of a major erosion event during the Middle Pleniglacial (±MIS 3). This elongated thermokarst erosion gully incised the underlying deposits. The presence of deformed ice-wedge relicts along its very sharp and irregular lower boundary indicates a formation by thermal erosion linked to a rapid melting of the permafrost ice. The analysis of the biological data (vegetal remains and mollusc shells) allows to evidence interstadial conditions strongly contrasting with the over- and underlying loess environments. Radiocarbon dates from wood remains (average 32.26 14C / ± 37.7 cal. BP) allow the correlation of the main thermokarst formation and infilling with GIS-8 from the GRIP ice core, following H4 event. Similar structures have been evidenced in other west-European loess sequences, most of them at the base of the Middle Pleniglacial formations. On the basis of a comparison with present day analogues from Alaska and Siberia permafrost areas, past "thermokarst events" are related to thermal erosion processes and proposed as markers for rapid warming periods in Last Glacial European loess sequences.

  7. Characteristics of the Dominant Frequency of West Pacific Warm Pool Subsurface Temperature in Response to ENSO Events.

    NASA Astrophysics Data System (ADS)

    Park, G. S.; Lee, D. K.; Jo, Y. H.

    2014-12-01

    West Pacific Warm Pool (WPWP) is the warm water body confined by Sea Surface Temperature (SST) over 28°C. The most important role of WPWP in response to air-sea interactions is that El-Niño and La-Niña events are determined by WPWP's zonal migration. Many researches have conducted to understand the relationship between ENSO events and WPWP changes, but research for Subsurface Temperature (ST) fluctuation by WPWP's movement does not well understood due to deficiency of observations, which is the main motivation of this research. This research based on ARGO's float profile subsurface data and TAO/TRITON's mooring subsurface data. Especially, our research results are based on ST from surface to 500m depth and estimated ST deviation in route of eastbound WPWP between north and south 10° by the Pacific equatorial line to identify ENSO events. The El-Niño and La-Niña events were defined by Multivariate ENSO Index (MEI) and then, we computed certain frequencies of ST under each condition, respectively. In order to understand the dominant frequency of ST, Ensemble Empirical Mode Decomposition (EEMD) was used. EEMD is analysis method to add Gaussian white noise in signal to redeem weak point of analysis method to non-linear and non-stationary signal. The research result shows that during normal condition, ST deviation values in Eastern Pacific (EP) had lower than those of Western Pacific (WP). During El-Niño condition, ST deviation values in the EP was higher than the normal condition, and ST deviation values in the WP was lower than normal condition and higher frequency in temperature fluctuation. During La-Niña condition, EP had similar ST amplitude with normal condition, but ST deviation values in the WP was so lower than the normal condition and fluctuation frequency was lower, too. So, we could understand that our estimations are resulting from intensified ST difference between high temperature of WPWP and low temperature of subsurface in location of WPWP

  8. Influence of external forcings on abrupt millennial-scale climate changes: a statistical modelling study

    NASA Astrophysics Data System (ADS)

    Mitsui, Takahito; Crucifix, Michel

    2016-07-01

    The last glacial period was punctuated by a series of abrupt climate shifts, the so-called Dansgaard-Oeschger (DO) events. The frequency of DO events varied in time, supposedly because of changes in background climate conditions. Here, the influence of external forcings on DO events is investigated with statistical modelling. We assume two types of simple stochastic dynamical systems models (double-well potential-type and oscillator-type), forced by the northern hemisphere summer insolation change and/or the global ice volume change. The model parameters are estimated by using the maximum likelihood method with the NGRIP Ca^{2+} record. The stochastic oscillator model with at least the ice volume forcing reproduces well the sample autocorrelation function of the record and the frequency changes of warming transitions in the last glacial period across MISs 2, 3, and 4. The model performance is improved with the additional insolation forcing. The BIC scores also suggest that the ice volume forcing is relatively more important than the insolation forcing, though the strength of evidence depends on the model assumption. Finally, we simulate the average number of warming transitions in the past four glacial periods, assuming the model can be extended beyond the last glacial, and compare the result with an Iberian margin sea-surface temperature (SST) record (Martrat et al. in Science 317(5837): 502-507, 2007). The simulation result supports the previous observation that abrupt millennial-scale climate changes in the penultimate glacial (MIS 6) are less frequent than in the last glacial (MISs 2-4). On the other hand, it suggests that the number of abrupt millennial-scale climate changes in older glacial periods (MISs 6, 8, and 10) might be larger than inferred from the SST record.

  9. Abrupt climate change: can society cope?

    PubMed

    Hulme, Mike

    2003-09-15

    Consideration of abrupt climate change has generally been incorporated neither in analyses of climate-change impacts nor in the design of climate adaptation strategies. Yet the possibility of abrupt climate change triggered by human perturbation of the climate system is used to support the position of both those who urge stronger and earlier mitigative action than is currently being contemplated and those who argue that the unknowns in the Earth system are too large to justify such early action. This paper explores the question of abrupt climate change in terms of its potential implications for society, focusing on the UK and northwest Europe in particular. The nature of abrupt climate change and the different ways in which it has been defined and perceived are examined. Using the example of the collapse of the thermohaline circulation (THC), the suggested implications for society of abrupt climate change are reviewed; previous work has been largely speculative and has generally considered the implications only from economic and ecological perspectives. Some observations about the implications from a more social and behavioural science perspective are made. If abrupt climate change simply implies changes in the occurrence or intensity of extreme weather events, or an accelerated unidirectional change in climate, the design of adaptation to climate change can proceed within the existing paradigm, with appropriate adjustments. Limits to adaptation in some sectors or regions may be reached, and the costs of appropriate adaptive behaviour may be large, but strategy can develop on the basis of a predicted long-term unidirectional change in climate. It would be more challenging, however, if abrupt climate change implied a directional change in climate, as, for example, may well occur in northwest Europe following a collapse of the THC. There are two fundamental problems for society associated with such an outcome: first, the future changes in climate currently being

  10. Simulating the vegetation response in western Europe to abrupt climate changes under glacial background conditions

    NASA Astrophysics Data System (ADS)

    Woillez, M.-N.; Kageyama, M.; Combourieu-Nebout, N.; Krinner, G.

    2013-03-01

    The last glacial period has been punctuated by two types of abrupt climatic events, the Dansgaard-Oeschger (DO) and Heinrich (HE) events. These events, recorded in Greenland ice and in marine sediments, involved changes in the Atlantic Meridional Overturning Circulation (AMOC) and led to major changes in the terrestrial biosphere. Here we use the dynamical global vegetation model ORCHIDEE to simulate the response of vegetation to abrupt changes in the AMOC strength. We force ORCHIDEE offline with outputs from the IPSL_CM4 general circulation model, in which the AMOC is forced to change by adding freshwater fluxes in the North Atlantic. We investigate the impact of a collapse and recovery of the AMOC, at different rates, and focus on Western Europe, where many pollen records are available for comparison. The impact of an AMOC collapse on the European mean temperatures and precipitations simulated by the GCM is relatively small but sufficient to drive an important regression of forests and expansion of grasses in ORCHIDEE, in qualitative agreement with pollen data for an HE event. On the contrary, a run with a rapid shift of the AMOC to a hyperactive state of 30 Sv, mimicking the warming phase of a DO event, does not exhibit a strong impact on the European vegetation compared to the glacial control state. For our model, simulating the impact of an HE event thus appears easier than simulating the abrupt transition towards the interstadial phase of a DO. For both a collapse or a recovery of the AMOC, the vegetation starts to respond to climatic changes immediately but reaches equilibrium about 200 yr after the climate equilibrates, suggesting a possible bias in the climatic reconstructions based on pollen records, which assume equilibrium between climate and vegetation. However, our study does not take into account vegetation feedbacks on the atmosphere.

  11. Continental warming preceding the Palaeocene-Eocene thermal maximum.

    PubMed

    Secord, Ross; Gingerich, Philip D; Lohmann, Kyger C; Macleod, Kenneth G

    2010-10-21

    Marine and continental records show an abrupt negative shift in carbon isotope values at ∼55.8 Myr ago. This carbon isotope excursion (CIE) is consistent with the release of a massive amount of isotopically light carbon into the atmosphere and was associated with a dramatic rise in global temperatures termed the Palaeocene-Eocene thermal maximum (PETM). Greenhouse gases released during the CIE, probably including methane, have often been considered the main cause of PETM warming. However, some evidence from the marine record suggests that warming directly preceded the CIE, raising the possibility that the CIE and PETM may have been linked to earlier warming with different origins. Yet pre-CIE warming is still uncertain. Disentangling the sequence of events before and during the CIE and PETM is important for understanding the causes of, and Earth system responses to, abrupt climate change. Here we show that continental warming of about 5 °C preceded the CIE in the Bighorn Basin, Wyoming. Our evidence, based on oxygen isotopes in mammal teeth (which reflect temperature-sensitive fractionation processes) and other proxies, reveals a marked temperature increase directly below the CIE, and again in the CIE. Pre-CIE warming is also supported by a negative amplification of δ(13)C values in soil carbonates below the CIE. Our results suggest that at least two sources of warming-the earlier of which is unlikely to have been methane-contributed to the PETM. PMID:20962843

  12. An observational analysis of warm-sector rainfall characteristics associated with the 21 July 2012 Beijing extreme rainfall event

    NASA Astrophysics Data System (ADS)

    Zhong, Lingzhi; Mu, Rong; Zhang, Dalin; Zhao, Ping; Zhang, Zhiqiang; Wang, Nan

    2015-04-01

    An observational analysis of the multiscale processes leading to the extreme rainfall event in Beijing on 21 July 2012 is performed using rain gauge records, Doppler radar, and satellite products, radiosondes, and atmospheric analysis. This rainstorm process included two heavy rainfall stages in the early afternoon [1300-1400 Beijing Standard time (BST) (0500-0600 UTC)] and the evening (1600-1900 BST), respectively. The first stage exhibited warm-sector rainfall characteristics as it occurred under low-level warm and moist southeasterly flows ahead of a synoptic-scale vortex and a cold front. When the southeasterly flows turned northeastward along a southwest-northeast oriented mountain range in western Beijing, mesoscale convergence centers formed on the windward side of the mountain range in the early afternoon, initiating moist convection. Radar echo showed a northeastward propagation as these flows extended northward. Despite the shallowness of moist convection in the warm sector, atmospheric liquid water content showed the rapid accumulation, and a large amount of supercooled water and/or ice particles was possibly accumulated above the melting level. These appeared to contribute to the occurrence of the largest rainfall rate. During the second stage, as the synoptic-scale vortex moved across Beijing, with southeastward intrusion of its northwesterly flows, the vortex-associated lifting caused the generation of strong updrafts aloft and formed deep convection. This facilitated the further accumulation of supercooled water and/or ice particles above the melting level. Radar echo propagated southeastward. Liquid water showed a decrease in the lower troposphere, and there were strong downdrafts due to evaporation of liquid water particles, which resulted in the relatively weak hourly rainfall rates.

  13. Linkage Between Hourly Precipitation Events and Atmospheric Temperature Changes over China during the Warm Season

    PubMed Central

    Miao, Chiyuan; Sun, Qiaohong; Borthwick, Alistair G. L.; Duan, Qingyun

    2016-01-01

    We investigated changes in the temporospatial features of hourly precipitation during the warm season over mainland China. The frequency and amount of hourly precipitation displayed latitudinal zonation, especially for light and moderate precipitation, which showed successive downward change over time in northeastern and southern China. Changes in the precipitation amount resulted mainly from changes in frequency rather than changes in intensity. We also evaluated the linkage between hourly precipitation and temperature variations and found that hourly precipitation extreme was more sensitive to temperature than other categories of precipitation. A strong dependency of hourly precipitation on temperature occurred at temperatures colder than the median daily temperature; in such cases, regression slopes were greater than the Clausius-Clapeyron (C-C) relation of 7% per degree Celsius. Regression slopes for 31.6%, 59.8%, 96.9%, and 99.1% of all stations were greater than 7% per degree Celsius for the 75th, 90th, 99th, and 99.9th percentiles for precipitation, respectively. The mean regression slopes within the 99.9th percentile of precipitation were three times the C-C rate. Hourly precipitation showed a strong negative relationship with daily maximum temperature and the diurnal temperature range at most stations, whereas the equivalent correlation for daily minimum temperature was weak. PMID:26931350

  14. Total Electron Content (TEC) disturbances over Brazilian region during the minor sudden stratospheric warming (SSW 2012) event of January 2012

    NASA Astrophysics Data System (ADS)

    Vieira, Francisco; Fagundes, Paulo Roberto; Kavutarapu, Venkatesh; Gil Pillat, Valdir

    2016-07-01

    The effects of Sudden Stratospheric Warming on ionosphere have been investigated by several scientists, using different observational techniques and model simulations. However, the 2011-2012 minor event is one of those that are less studied. Since, the zonal westward wind is slowed without reversing to eastward, this SSW was consider as a minor event. The stratospheric temperature started increasing on December 26, 2011, reached its peak on January 18, 2012, and afterwards started decreasing slowly. In addition, there was moderate geomagnetic storm on January 22-25, 2012, after the SSW temperature peak. In the present study, the GPS-TEC measurements from a network of 72 receivers over the Brazilian region are considered. This network of 72 GPS-TEC locations lies between 5 N and 30 S (35 degrees) latitudes and 35 W and 65 W (30 degrees) longitudes. Further, two chains of GPS receivers are used to study the response of Equatorial Ionization Anomaly (EIA) changes in the Brazilian East and West sectors, as well as its day-to-day variability before and during the SSW2012. It was noted that the TEC is depleted to the order of 30% all over the Brazilian region, from equator to beyond the EIA regions and from East to West sectors. It is also noticed that the EIA strengths at East and West sectors were suppressed after the stratospheric temperature peak. However, the Brazilian West sector was found to be more disturbed compared to the East sector during this SSW event.

  15. Heavy warm season precipitation events in northern Spain: ¿mediterranean processes in an oceanic temperate region?

    NASA Astrophysics Data System (ADS)

    García Codrón, J. C.; Rasilla Álvarez, D.; Garmendia Pedraja, C.

    2009-09-01

    The northern coast of the Iberian Peninsula is one of the wettest areas of Europe. Most of the coastal observatories receive exceed 1000mm, and the rainfall is higher than 1700mm along the basque coast. The contribution of late summer-early fall precipitation is remarkable (about 25 %), unusual taking in account the southern latitude of the region at continental scale (Cfb climate, following Köppen’s notation). One of the causes of this summertime wetness are the frequent heavy rainfall events, historically responsible of the most damaging floods in the region. The aim of this paper is to identify and investigate the spatial and temporal characteristics of those heavy rain events, improving the understanding of the dynamical mechanisms by means of a classification of the related atmospheric patterns. The role of the exchange of heat fluxes from a very warm pool of water around the vertex of the Gulf of Biscay, feeding the lowest atmospheric layers, is also discussed. Heavy rainfall events were analyzed using long-term daily rainfall records from 22 stations belonging to the spanish, portuguese and french meteorological networks. The 1000 hPa and 500 hPa geopotential heights (hereafter Z1000 and Z500), as well as the 850 hPa temperature (T850) were utilized to derive a typology of circulation pattern, combining principal components analysis (PCA) and cluster analysis (CA). Results show that most of those heavy precipitation events, whose atmospheric environment and spatial impacts remember some of the typical features of the heavy precipitation events in the Spanish Mediterranean coast, implicate convective systems, associated to upper level stationary disturbances ("cold lows"), which trigger a thermodynamic instability. Most of them affect a relatively restricted area, from Cantabria to the Basque Country, and, even within this area, most of the precipitation falls in the shorelines and the first orographic ridges. Finally, it is worth to mention that the

  16. The regional forcing of Northern hemisphere drought during recent warm tropical west Pacific Ocean La Niña events

    USGS Publications Warehouse

    Hoell, Andrew; Funk, Christopher C.; Mathew Barlow

    2014-01-01

    Northern Hemisphere circulations differ considerably between individual El Niño-Southern Oscillation events due to internal atmospheric variability and variation in the zonal location of sea surface temperature forcing over the tropical Pacific Ocean. This study examines the similarities between recent Northern Hemisphere droughts associated with La Niña events and anomalously warm tropical west Pacific sea surface temperatures during 1988–1989, 1998–2000, 2007–2008 and 2010–2011 in terms of the hemispheric-scale circulations and the regional forcing of precipitation over North America and Asia during the cold season of November through April. The continental precipitation reductions associated with recent central Pacific La Niña events were most severe over North America, eastern Africa, the Middle East and southwest Asia. High pressure dominated the entire Northern Hemisphere mid-latitudes and weakened and displaced storm tracks northward over North America into central Canada. Regionally over North America and Asia, the position of anomalous circulations within the zonal band of mid-latitude high pressure varied between each La Niña event. Over the northwestern and southeastern United States and southern Asia, the interactions of anomalous circulations resulted in consistent regional temperature advection, which was subsequently balanced by similar precipitation-modifying vertical motions. Over the central and northeastern United States, the spatial variation of anomalous circulations resulted in modest inter-seasonal temperature advection variations, which were balanced by varying vertical motion and precipitation patterns. Over the Middle East and eastern Africa, the divergence of moisture and the advection of dry air due to anomalous circulations enhanced each of the droughts.

  17. Response of a Habitat-Forming Marine Plant to a Simulated Warming Event Is Delayed, Genotype Specific, and Varies with Phenology

    PubMed Central

    Reynolds, Laura K.; DuBois, Katherine; Abbott, Jessica M.; Williams, Susan L.; Stachowicz, John J.

    2016-01-01

    Growing evidence shows that increasing global temperature causes population declines and latitudinal shifts in geographical distribution for plants living near their thermal limits. Yet, even populations living well within established thermal limits of a species may suffer as the frequency and intensity of warming events increase with climate change. Adaptive response to this stress at the population level depends on the presence of genetic variation in thermal tolerance in the populations in question, yet few data exist to evaluate this. In this study, we examined the immediate effects of a moderate warming event of 4.5°C lasting 5 weeks and the legacy effects after a 5 week recovery on different genotypes of the marine plant Zostera marina (eelgrass). We conducted the experiment in Bodega Bay, CA USA, where average summer water temperatures are 14–15°C, but extended warming periods of 17–18°C occur episodically. Experimental warming increased shoot production by 14% compared to controls held at ambient temperature. However, after returning temperature to ambient levels, we found strongly negative, delayed effects of warming on production: shoot production declined by 27% and total biomass decreased by 50% relative to individuals that had not been warmed. While all genotypes’ production decreased in the recovery phase, genotypes that grew the most rapidly under benign thermal conditions (control) were the most susceptible to the detrimental effects of warming. This suggests a potential tradeoff in relative performance at normal vs. elevated temperatures. Modest short-term increases in water temperature have potentially prolonged negative effects within the species’ thermal envelope, but genetic variation within these populations may allow for population persistence and adaptation. Further, intraspecific variation in phenology can result in maintenance of population diversity and lead to enhanced production in diverse stands given sufficient frequency of

  18. Response of a Habitat-Forming Marine Plant to a Simulated Warming Event Is Delayed, Genotype Specific, and Varies with Phenology.

    PubMed

    Reynolds, Laura K; DuBois, Katherine; Abbott, Jessica M; Williams, Susan L; Stachowicz, John J

    2016-01-01

    Growing evidence shows that increasing global temperature causes population declines and latitudinal shifts in geographical distribution for plants living near their thermal limits. Yet, even populations living well within established thermal limits of a species may suffer as the frequency and intensity of warming events increase with climate change. Adaptive response to this stress at the population level depends on the presence of genetic variation in thermal tolerance in the populations in question, yet few data exist to evaluate this. In this study, we examined the immediate effects of a moderate warming event of 4.5°C lasting 5 weeks and the legacy effects after a 5 week recovery on different genotypes of the marine plant Zostera marina (eelgrass). We conducted the experiment in Bodega Bay, CA USA, where average summer water temperatures are 14-15°C, but extended warming periods of 17-18°C occur episodically. Experimental warming increased shoot production by 14% compared to controls held at ambient temperature. However, after returning temperature to ambient levels, we found strongly negative, delayed effects of warming on production: shoot production declined by 27% and total biomass decreased by 50% relative to individuals that had not been warmed. While all genotypes' production decreased in the recovery phase, genotypes that grew the most rapidly under benign thermal conditions (control) were the most susceptible to the detrimental effects of warming. This suggests a potential tradeoff in relative performance at normal vs. elevated temperatures. Modest short-term increases in water temperature have potentially prolonged negative effects within the species' thermal envelope, but genetic variation within these populations may allow for population persistence and adaptation. Further, intraspecific variation in phenology can result in maintenance of population diversity and lead to enhanced production in diverse stands given sufficient frequency of warming

  19. Abrupt climate variability in the North Atlantic region: Did the icebergs do it?

    NASA Astrophysics Data System (ADS)

    Barker, S.; Chen, J.; Gong, X.; Jonkers, L.; Knorr, G.; Thornalley, D. J.

    2014-12-01

    We present high resolution records of temperature and ice rafted debris over the last ~440Kyr from a sediment core retrieved from the NE Atlantic. Our records reveal that episodes of ice rafting typically occurred after abrupt cooling at the site. Because the site is sensitive to the earliest phases of ice rafting as recorded by other sites across the wider Atlantic, this suggests that icebergs were not the trigger for North Atlantic cold events. Moreover we find a different relationship between cooling and the arrival of rafted ice at a site ~750km to the SE of ours. We suggest that asynchronous cooling between these locations can be explained by the more gradual southward migration of the North Atlantic polar front. We describe a mechanism that can explain the occurrence of abrupt stadial events over Greenland as a non-linear response as regional cooling continues beyond the threshold necessary for sustaining ocean circulation in its 'warm' mode with active convection north of Iceland. Thus while the freshwater derived from melting icebergs may provide a positive feedback for enhancing and prolonging stadial conditions, it is probably not the trigger for northern stadial events.

  20. The role of Southern Ocean winds and CO2 in glacial abrupt climate change

    NASA Astrophysics Data System (ADS)

    Banderas, R.; Alvarez-Solas, J.; Montoya, M.

    2011-12-01

    The last glacial period (ca. 110-10 kyr before present, hereafter kyr BP) is characterized by substantial climate instability, manifested as climatic variability on millennial timescales. Two types of events dominate this variability: Dansgaard-Oeschger (DO) events, which involve decadal-scale warming by more than 10K, and Heinrich events, massive iceberg discharges from the Laurentide Ice Sheet at intervals of ca. 10 kyr during peak glacial conditions. Both DO and Heinrich events are associated with widespread centennial to millennial scale climatic changes, including a synchronous temperature response over the North Atlantic and an anti-phase temperature relationship over Antarctica and most of the Southern Ocean, as revealed by a wealth of deep sea sediments and terrestrial record. Recent studies indicate CO2 changes during deglaciation and, possibly, during glacial abrupt climate changes were preceded by significant increases of Southern Ocean upwelling caused by an enhancement and/or a shift of surface winds over that region. The proposed hypothesis is that periods of halted or reduced North Atlantic deep water (NADW) formation resulted in warming of the Southern Ocean through the bipolar see-saw effect leading to a reorganization of Southern Hemisphere (SH) surface winds, and thereby enhanced upwelling and atmospheric CO2 concentrations. Here, the role of SH surface wind and CO2 changes in the Atlantic meridional overturning circulation (MOC) is analyzed in a coupled climate model of intermediate complexity. We investigate whether changes in the former could eventually trigger an intensification of the Atlantic overturning circulation and a northward shift of NADW formation, which would allow to explain glacial abrupt climate changes as the result of an oscillation which involves the MOC, CO2 and the winds.

  1. Antarctic Forcing of Abrupt Global Climate Change During Isotope Stage 3

    NASA Astrophysics Data System (ADS)

    Turney, Christian; Jones, Richard; Phipps, Steven; Thomas, Zoë; Hogg, Alan; Kershaw, Peter; Fogwill, Christopher; Palmer, Jonathan; Bronk Ramsey, Christopher; Adolphi, Florian; Muscheler, Raimund; Hughen, Konrad; Staff, Richard; Grosvenor, Mark; Golledge, Nicholas; Haberle, Simon

    2016-04-01

    Contrasting Greenland and Antarctic temperature trends during the late Pleistocene (60,000 to 11,650 years ago) are thought to be driven by imbalances in the rate of formation of North Atlantic and Antarctic Deep Water (the 'bipolar seesaw'), with millennial-scale cooling Dansgaard-Oeschger (D-O) events in the north leading warming in the south. An alternative origin for these abrupt climate shifts, however, is the Southern Hemisphere whereby changes are transmitted globally via atmospheric and/or oceanic teleconnections. Testing these competing hypotheses is challenging given the relatively large uncertainties associated with dating terrestrial, marine and ice core chronologies. Here we use a fully coupled climate system model to investigate whether freshening of the Southern Ocean has extra-regional climate impacts. Focusing on an Isotope Stage 3 cooling event preserved in Antarctic ice cores immediately prior to Antarctic Isotope Maximum 4 (AIM 4; around 29,000 years ago) we undertook an ensemble of transient meltwater simulations. We observe no impact on the Atlantic Meridional Overturning Circulation (AMOC) from freshwater hosing in the Southern Ocean but a dramatic warming over the North Atlantic and contrasting precipitation patterns across the low latitudes. Exploiting a new bidecadally-resolved 14C calibration dataset obtained from New Zealand kauri (Agathis australis) we undertook intensive radiocarbon dating and high-resolution multiproxy analysis of the tropical Australia Lynch's Crater terrestrial peat sequence spanning this same period and find a synchronous change in hydroclimate to the purported meltwater event in the Southern Ocean. Our results imply Southern Ocean dynamics played a significant role in driving global climate change across this period via atmospheric teleconnections, with implications for other abrupt events through the late Pleistocene.

  2. Approaching the Edge of Abrupt Climate Change

    NASA Astrophysics Data System (ADS)

    Ramadhin, C.; Yi, C.

    2015-12-01

    The phenomenon of Abrupt Climate Change (ACC) became evident as paleoclimate data analyses began revealing that Earth's climate has the ability to rapidly switch from one state to the next in just a few decades after thresholds are crossed. Previously paleo-climatologists thought these switches were gradual but now there is growing concern to identify thresholds and the dominant feedback mechanisms that propel systems toward thresholds. Current human civilization relies heavily on climate stability and ACC threatens immense disruption with potentially disastrous consequences for all ecosystems. Therefore, prediction of the climate system's approach to threshold values would prove vital for the resilience of civilization through development of appropriate adaptation strategies when that shift occurs. Numerous studies now establish that earth systems are experiencing dramatic changes both by system interactions and anthropogenic sources adding urgency for comprehensive knowledge of tipping point identification. Despite this, predictions are difficult due to the immensity of interactions among feedback mechanisms. In this paper, we attempt to narrow this broad spectrum of critical feedback mechanisms by reviewing several publications on role of feedbacks in initiating past climate transitions establishing the most critical ones and significance in current climate changes. Using a compilation of paleoclimate datasets we compared the rates of deglaciations with that of glacial inceptions, which are approximately 5-10 times slower. We hypothesize that the critical feedbacks are unique to each type of transition such that warmings are dominated by the ice-albedo feedback while coolings are a combination of temperature - CO2 and temperature-precipitation followed by the ice-albedo feedbacks. Additionally, we propose the existence of a commonality in the dominant trigger feedbacks for astronomical and millennial timescale abrupt climate shifts and as such future studies

  3. Rapid increases of CO and H2O in the tropical lower stratosphere during January 2010 stratospheric sudden warming event

    NASA Astrophysics Data System (ADS)

    Eguchi, Nawo; Kodera, Kunihiko; Ueyama, Rei; Li, Qian

    2014-05-01

    A potential transport mechanism of various tracers from the tropical troposphere to the lower stratosphere (LS) across the tropical tropopause layer (TTL) is the overshooting convective clouds which inject air with tropospheric characteristics (high CO, high H2O, low O3) into the LS over a period of a few days. Evidence of such convective intrusions extending up to the 90 hPa level are observed over the southern African continent at the end of January 2010 in MLS and CALIOP satellite measurements. Rapid increases of CO and water vapor concentrations over Africa are associated with increased convective activity over the region a few days prior to the onset of stratospheric sudden warming (SSW) event and contribute to enhancements in their zonal tropical mean concentrations during January and February 2010. The modulation of tropical upwelling by SSW appears to force stronger and deeper tropical convection, particularly in the Southern Hemisphere tropics. The January 2010 SSW event induced the lowest recorded LS temperature in MLS history (2004-13), allowing an unprecedented clear detection of stratosphere-troposphere exchange process by way of CO, H2O and O3 intrusions. The present study suggests that short duration, overshooting clouds can have a large impact on the zonally averaged fields of LS composition (zonally-averaged tracer fields in the tropical LS). In this presentation, we present the simulated CO, water vapor and ozone mixing ratios during Jan 2010 SSW using GEOS-Chem model. We further investigate the transport pathways based on trajectory analysis of air parcels in convective regions of the tropics.

  4. Proxy records of Late Holocene climate events in the eastern United States: Medieval Warm Period and Little Ice Age

    NASA Astrophysics Data System (ADS)

    Willard, D. A.; Cronin, T. M.; Hayo, K. M.

    2006-12-01

    We are conducting a multiproxy, regional reconstruction of climate variability during the last two millennia including the Medieval Warm Period (MWP) and Little Ice Age (LIA) in eastern North America. Pollen, benthic foraminifers, ostracodes, and other proxies were analyzed from high-resolution sampling of continuous sedimentary records from lakes, wetlands, and estuaries in Florida, North Carolina, Chesapeake Bay, and Lake Champlain. These records document multi-decadal changes in vegetation, temperature, precipitation, and estuarine salinity across a latitudinal transect. During both the MWP and LIA, decreased precipitation altered plant community composition and distribution in the southeastern United States, and the LIA triggered threshold changes in vegetation that persisted until anthropogenic land-cover change overwhelmed the climate signature. In the mid-Atlantic region, progressively cooler and wetter late Holocene springs culminated in a cool, wet LIA; this trend correlates with observed oceanic changes. Trend analysis of the data suggest that inter-regional correlation of multi-decadal and centennial-scale Holocene climate events will be forthcoming.

  5. Abrupt shifts in phenology and vegetation productivity under climate extremes

    NASA Astrophysics Data System (ADS)

    Ma, Xuanlong; Huete, Alfredo; Moran, Susan; Ponce-Campos, Guillermo; Eamus, Derek

    2015-10-01

    Amplification of the hydrologic cycle as a consequence of global warming is predicted to increase climate variability and the frequency and severity of droughts. Recent large-scale drought and flooding over numerous continents provide unique opportunities to understand ecosystem responses to climatic extremes. In this study, we investigated the impacts of the early 21st century extreme hydroclimatic variations in southeastern Australia on phenology and vegetation productivity using Moderate Resolution Imaging Spectroradiometer Enhanced Vegetation Index and Standardized Precipitation-Evapotranspiration Index. Results revealed dramatic impacts of drought and wet extremes on vegetation dynamics, with abrupt between year changes in phenology. Drought resulted in widespread reductions or collapse in the normal patterns of seasonality such that in many cases there was no detectable phenological cycle during drought years. Across the full range of biomes examined, we found semiarid ecosystems to exhibit the largest sensitivity to hydroclimatic variations, exceeding that of arid and humid ecosystems. This result demonstrated the vulnerability of semiarid ecosystems to climatic extremes and potential loss of ecosystem resilience with future mega-drought events. A skewed distribution of hydroclimatic sensitivity with aridity is of global biogeochemical significance because it suggests that current drying trends in semiarid regions will reduce hydroclimatic sensitivity and suppress the large carbon sink that has been reported during recent wet periods (e.g., 2011 La Niña).

  6. Abrupt shutdown of the Atlantic meridional overturning circulation and rainfall patterns in Mexico

    NASA Astrophysics Data System (ADS)

    Martinez-Lopez, B.; Garcia, C. Gay

    2010-03-01

    Abrupt shutdown of the Atlantic meridional overturning circulation and rainfall patterns in Mexico. Model simulations agree that the warming and the resulting freshening of the surface waters will significantly reduce deep water formation in the Labrador Sea during the next decades. A complete collapse of the Atlantic meridional overturning circulation (AMOC) would be associated with a strong cooling of several degrees in the North Atlantic region (Winton 2003). The future response of the AMOC, however, is predictable only within a broad range due to the existence of a critical threshold in the system and the large uncertainty about both the location of this threshold on the freshwater axis and the freshwater forcing (Zickfeld et al., 2007). According to Meehl et al. (2007), the probability of an abrupt slowdown or shutdown of the AMOC triggered by greenhouse gas forcing is low, but it is considered a high-impact event (Wood et al., 2003). An abrupt change in the AMOC could occur so unexpectedly and quickly that natural systems would have difficulty adapting to them (NRC, 2002). In this work we use coupled ocean-atmosphere models to asses the response of rainfall patterns in Mexico to an abrupt shutdown of the AMOC. First, a cooling pattern, triggered by a freshwater flux perturbation in the North Atlantic, is simulated by an isopycnic ocean model coupled to an atmospheric energy balance model. Then, this anomalous surface temperature pattern is used as a surface boundary condition for a numerical experiment performed using the simplified global atmospheric circulation model PUMA (Portable University Model of the Atmosphere; Fraedrich et al., 1998), which compute the perturbed rainfall patterns in Mexico.

  7. International policy implications of abrupt climate change scenarios

    SciTech Connect

    Molitor, M.R.

    1997-12-31

    New theoretical and empirical evidence supports the view that in the recent past [Holocene] abrupt climate changes occurred over very short [decadal] time periods. One leading possibility of future changes involves the North Atlantic Ocean conveyor that transfers warm surface waters from the equator to northern latitudes and helps maintain Europe`s climate. The predicted abrupt climate change scenario theorizes that the conveyor may be modified as a result of disruption of the thermohaline circulation driving North, Atlantic Deep Water. This would lead, the theory contends, to a rapid cooling of Europe`s climate. In light of the EPCC`s 1995 Second Assessment Report conclusion that there is a {open_quotes}discernible{close_quotes} human influence on the global climate system, there are many emerging questions concerning possible abrupt climate change scenarios.

  8. Sonographic spectrum of placental abruption.

    PubMed

    Nyberg, D A; Cyr, D R; Mack, L A; Wilson, D A; Shuman, W P

    1987-01-01

    Fifty-seven cases of placental abruption detected by sonography were retrospectively reviewed. The location of hemorrhage was subchorionic in 46 cases (81%), retroplacental in nine cases (16%), and preplacental in two cases (4%). Subchorionic hematomas were more frequently shown in the 33 patients presenting before 20 menstrual weeks (91%) than in the 24 patients presenting after 20 weeks (67%). The echogenicity of hemorrhage depended on the time the sonogram was performed relative to the onset of symptoms: Acute hemorrhage was hyperechoic to isoechoic compared with the placenta, while resolving hematomas became hypoechoic within 1 week and sonolucent within 2 weeks. Acute hemorrhage was occasionally difficult to distinguish from the adjacent placenta. This occurred in five retroplacental hematomas that showed only an abnormally thick and heterogeneous placenta. Nine cases of placental abruption were initially confused with other mass lesions. Placental abruption causes a wide spectrum of sonographic findings that may be overlooked or misdiagnosed. PMID:3538831

  9. Abrupt climate change and transient climates during the Paleogene: a marine perspective

    NASA Technical Reports Server (NTRS)

    Zachos, J. C.; Lohmann, K. C.; Walker, J. C.; Wise, S. W.

    1993-01-01

    Detailed investigations of high latitude sequences recently collected by the Ocean Drilling Program (ODP) indicate that periods of rapid climate change often culminated in brief transient climates, with more extreme conditions than subsequent long term climates. Two examples of such events have been identified in the Paleogene; the first in latest Paleocene time in the middle of a warming trend that began several million years earlier: the second in earliest Oligocene time near the end of a Middle Eocene to Late Oligocene global cooling trend. Superimposed on the earlier event was a sudden and extreme warming of both high latitude sea surface and deep ocean waters. Imbedded in the latter transition was an abrupt decline in high latitude temperatures and the brief appearance of a full size continental ice-sheet on Antarctica. In both cases the climate extremes were not stable, lasting for less than a few hundred thousand years, indicating a temporary or transient climate state. Geochemical and sedimentological evidence suggest that both Paleogene climate events were accompanied by reorganizations in ocean circulation, and major perturbations in marine productivity and the global carbon cycle. The Paleocene-Eocene thermal maximum was marked by reduced oceanic turnover and decreases in global delta 13C and in marine productivity, while the Early Oligocene glacial maximum was accompanied by intensification of deep ocean circulation and elevated delta 13C and productivity. It has been suggested that sudden changes in climate and/or ocean circulation might occur as a result of gradual forcing as certain physical thresholds are exceeded. We investigate the possibility that sudden reorganizations in ocean and/or atmosphere circulation during these abrupt transitions generated short-term positive feedbacks that briefly sustained these transient climatic states.

  10. Atmospheric forcing intensifies the effects of regional ocean warming on reef-scale temperature anomalies during a coral bleaching event

    NASA Astrophysics Data System (ADS)

    Zhang, Zhenlin; Falter, James; Lowe, Ryan; Ivey, Greg; McCulloch, Malcolm

    2013-09-01

    We investigate how local atmospheric conditions and hydrodynamic forcing contributed to local variations in water temperature within a fringing coral reef-lagoon system during the peak of a marine heat wave in 2010-2011 that caused mass coral bleaching across Western Australia. A three-dimensional circulation model Regional Ocean Modeling System (ROMS) with a built-in air-sea heat flux exchange module Coupled Ocean Atmosphere Experiment (COARE) was coupled with a spectral wave model Simulating Waves Nearshore (SWAN) to resolve the surface heat exchange and wave-driven reef circulation in Coral Bay, Ningaloo Reef. Using realistic oceanic and atmospheric forcing, the model predictions were in good agreement with measured time series of water temperature at various locations in the coral reef system during the bleaching event. Through a series of sensitivity analyses, we found that the difference in temperature between the reef and surrounding offshore waters (ΔT) was predominantly a function of both the daily mean net heat flux (Qnet>¯) and residence time, whereas diurnal variations in reef water temperature were dependent on the diurnal fluctuation in the net heat flux. We found that reef temperatures were substantially higher than offshore in the inner lagoon under normal weather conditions and over the entire reef domain under more extreme weather conditions (0.7°C-1.5°C). Although these temperature elevations were still less than that caused by the regional ocean warming (2°C-3°C), the arrival of peak seasonal temperatures in the summer of 2010-2011 (when net atmospheric heat fluxes were positive and abnormally high) caused substantially higher thermal stresses than would have otherwise occurred if offshore temperatures had reached their normal seasonal maxima in autumn (when net atmospheric heat fluxes were negative or cooling). Therefore, the degree heating weeks calculated based on offshore temperature substantially underestimated the thermal stresses

  11. Simulating the vegetation response to abrupt climate changes under glacial conditions with the ORCHIDEE/IPSL models

    NASA Astrophysics Data System (ADS)

    Woillez, M.-N.; Kageyama, M.; Combourieu-Nebout, N.; Krinner, G.

    2012-09-01

    The last glacial period has been punctuated by two types of abrupt climatic events, the Dansgaard-Oeschger (DO) and Heinrich (HE) events. These events, recorded in Greenland ice and in marine sediments, involved changes in the Atlantic Meridional Overturning Circulation (AMOC) and led to major changes in the terrestrial biosphere. Here we use the dynamical global vegetation model ORCHIDEE to simulate the response of vegetation to abrupt changes in the AMOC strength. To do so, we force ORCHIDEE off-line with outputs from the IPSL_CM4 general circulation model, in which we have forced the AMOC to change by adding freshwater fluxes in the North Atlantic. We investigate the impact of a collapse and recovery of the AMOC, at different rates, and focus on Western Europe, where many pollen records are available to compare with. The impact of an AMOC collapse on the European mean temperatures and precipitations simulated by the GCM is relatively small but sufficient to drive an important regression of forests and expansion of grasses in ORCHIDEE, in qualitative agreement with pollen data for an HE event. On the contrary, a run with a rapid shift of the AMOC to an hyperactive state of 30 Sv, mimicking the warming phase of a DO event, does not exhibit a strong impact on the European vegetation compared to the glacial control state. For our model, simulating the impact of an HE event thus appears easier than simulating the abrupt transition towards the interstadial phase of a DO. For both a collapse or a recovery of the AMOC the vegetation starts to respond to climatic changes immediately but reaches equilibrium about 200 yr after the climate equilibrates, suggesting a possible bias in the climatic reconstructions based on pollen records, which assume equilibrium between climate and vegetation. However, our study does not take into account vegetation feedbacks on the atmosphere.

  12. Ecological response of foraminifera to past warming events in Bartonian section of Western India using carbon isotope stratigraphy

    NASA Astrophysics Data System (ADS)

    Khanolkar, Sonal; Saraswati, Pratul Kumar; Rogers, Karyne

    2015-04-01

    The presence of warming event in the Middle Eocene known as the Middle Eocene Climatic Optimum (MECO), is marked by an increase in seawater temperatures by 5° to 6° C and a corresponding negative carbon isotope excursion. The MECO is biostratigraphically constrained to have lasted from the later part of P12 to P13. In this study, the carbon isotope stratigraphy and foraminiferal assemblage in the corresponding Bartonian section from a low- paleolatitude site in western India are studied to examine how foraminifera responded to warming during this interval. Litho-stratigraphically, the section is referred to as the Harudi Formation at the bottom, and the Fulra Limestone at the top. The base of the planktic foraminiferal zone P13, marked by the first appearance of Orbulinoides beckmanni, is recorded in the upper part of the Harudi Formation. The δ13Corg records a marked negative shift of ~1.5o (-24.5o to -26) at ~2 meters below the base of P13. A previous study on the same section indicated a strong depletion in δ13Ccarbonate ~ -3.5° and δ18O values ~ -0.5°. The negative excursion in δ13Corg also coincides with the appearance of Nummulites obtusus, N. vredenburgi, N. spectabilis and N. praediscorbinus. The smaller benthic foraminifera are dwarfed species of Nonion, Nonionella, Rotalia, Brizalina and Bulimina. The diversity of foraminifera is low (α ~ 1 - 8; H ~ 1 - 1.8). A bloom of triserial planktic foraminifer Jenkinsina (>40%) coincides with δ13C excursion indicating eutrophic conditions. It is followed upward by a highly fluctuating and distinct positive excursion of δ13Corg (-25.3o to -23.5) around the P12 - P13 boundary. This interval of about 1.5m is characterized by an increase in planktic and larger benthic foraminifera (LBF) numbers including Acarinina rohri, Acarinina topilensis, Orbulinoides beckmanni, Discocylina, Linderina, Halkyardia and Lockhartia. The diversity of foraminifera (α ~ 14 - 38; H ~ 2.2 - 3.4), abundance and their size

  13. Abrupt termination of Marine Isotope Stage 16 (Termination VII) at 631.5 ka in Santa Barbara Basin, California

    NASA Astrophysics Data System (ADS)

    Dean, Walter E.; Kennett, James P.; Behl, Richard J.; Nicholson, Craig; Sorlien, Christopher C.

    2015-10-01

    The Marine Isotope Stage 16-15 boundary (Termination VII) is the first deglacial warming step of the late Quaternary following the mid-Pleistocene transition (MPT), when 41 kyr climatic cycles shifted to strong 100 kyr cycles. The detailed structure of this important climatic event has remained unknown until now. Core MV0508-19JPC from Santa Barbara Basin, California, contains a decadal-scale climatic and geochemical sediment record of 4000 years duration that includes the early part of this deglacial episode. This record reveals that the climatic shift during the early deglacial occurred rapidly (<700 years), in a progression of three abrupt warming steps. The onset of Marine Isotope Stage (MIS) 15 was remarkably abrupt with 4-5°C sea surface warming in ~50 years. The deglacial sequence contains the well-dated Lava Creek tephra (631.3 ± 4 ka) from Yellowstone Caldera used to date the onset of Termination VII at 631.5 ka. The late MIS 16 and early MIS 15 interval exhibits multiple decadal-scale negative excursions in δ13C of planktic foraminifera, likely the result of repeated discharges of methane from methane hydrates associated with both ocean warming and low sea level. A warm interstadial that interrupts late MIS 16 is marked by elevated concentrations of redox-sensitive elements indicating sulfidic, oxygen-deficient bottom and pore-waters, and elevated concentrations of total organic carbon and Cd, reflecting increased surface productivity. Unlike younger sediments on the California margin, these indicators of increased productivity and low dissolved oxygen do not consistently correspond with each other or with preserved laminations, possibly reflecting instability of a still evolving ocean-atmosphere system following the MPT.

  14. Contribution of the land-use forcing to the increase in risk of warm extreme events since 1850 over North America from constrained CMIP5 simulations

    NASA Astrophysics Data System (ADS)

    Lejeune, Quentin; Davin, Edouard; Seneviratne, Sonia

    2016-04-01

    During the industrial period, large areas of North America experienced a reduction in forest cover and an expansion of agricultural areas. There is indication that this has affected the intensity and frequency of temperature extremes through changes in biophysical land surface properties (Christidis et al., 2013, Pitman et al., 2012). However, it has never been addressed in the context of a multi-model transient experiment ensemble. Here we intend to constrain CMIP5 models with observations in order to assess the contribution of historical land-cover changes (LCC) to changes in the risk of warm extreme events over North America. We have retained only six models from the CMIP5 ensemble that can reproduce the local warming effect of deforestation during daytime, which was identified in present-day observations of the impact of deforestation on mean summer temperature (Lee et al, 2011). As for its observed cooling effect during nighttime, we kept the sole model that is able to simulate it. Using a framework derived from the Fraction of Attributable Risk methodology, we have then quantified by how much the increase in risk of getting a particular extreme event driven by increased greenhouse gas concentrations (GHG) was damped or amplified over areas which were largely affected by LCC, compared to surrounding ones that experienced few LCC over the same period. We find that the constrained model ensemble indicates an amplification by between 10 and more than 100% by local LCC of the increase in risk of occurrence of a warm extreme event corresponding to the 90th percentile during the pre-industrial period, depending on the model. This amplification factor gets higher for more extreme events, rising to at least 20% for the 995th permille. Regarding nighttime temperatures, the retained model indicates that historical LCC have locally more than cancelled the effect of increased GHG concentrations on the frequency of warm extreme events corresponding to between the 90th

  15. Remote Detection and Modeling of Abrupt and Gradual Tree Mortality in the Southwestern USA

    NASA Astrophysics Data System (ADS)

    Muss, J. D.; Xu, C.; McDowell, N. G.

    2014-12-01

    Current climate models predict a warming and drying trend that has a high probability of increasing the frequency and spatial extent of tree mortality events. Field surveys can be used to identify, date, and attribute a cause of mortality to specific trees, but monetary and time constraints prevent broad-scale surveys, which are necessary to establish regional or global trends in tree mortality. This is significant because widespread forest mortality will likely lead to radical changes in evapotranspiration and surface albedo, which could compound climate change. While understanding the causes and mechanisms of tree mortality events is crucial, it is equally important to be able to detect and monitor mortality and subsequent changes to the ecosystem at broad spatial- and temporal-scales. Over the past five years our ability to remotely detect abrupt forest mortality events has improved greatly, but gradual events—such as those caused by drought or certain types of insects—are still difficult to identify. Moreover, it is virtually impossible to quantify the amount of mortality that has occurred within a mixed pixel. We have developed a system that fuses climate and satellite-derived spectral data to identify both the date and the agent of forest mortality events. This system has been used with Landsat time series data to detect both abrupt and general trends in tree loss that have occurred during the past quarter-century in northern New Mexico. It has also been used with MODIS data to identify pixels with a high likelihood of drought-caused tree mortality in the Southwestern US. These candidate pixels were then fed to ED-FRT, a coupled forest dynamics-radiative transfer model, to generate estimates of drought-induced. We demonstrate a multi-scale approach that can produce results that will be instrumental in advancing our understanding of tree mortality-climate feedbacks, and improve our ability to predict what forests could look like in the future.

  16. Drivers and Dynamics of Ecological Responses to Abrupt Environmental Change on the Early Miocene Oregon Shelf

    NASA Astrophysics Data System (ADS)

    Belanger, C. L.

    2012-12-01

    We know that the biosphere responds to abrupt climate change, but know less about the dynamics of those changes and their proximal drivers. Studies of well-preserved fossil time-series spanning past climate events that utilize multiple environmental proxies and examine multiple taxonomic groups can provide critical insight into (a) the specific environmental factors to which the biota respond, (b) the rate and tempo of those responses, and (c) whether taxonomic groups respond similarly or differently to the same stresses. I examine the drivers and dynamics of ecological changes in continental shelf benthic foraminifera and molluscs from the Early Miocene Newport Member of the Astoria Formation in Oregon (20.3-16.3 mya), which spans a time of global warming leading into the Middle Miocene Climate Optimum. Stable isotope (δ18O) data from three species of benthic foraminifera from the Astoria sediments indicate that the region abruptly warmed by 2-4°C approximately 19 mya. In addition, δ13C values from epifaunal and infaunal foraminifera indicate an increase in productivity and organic carbon flux over time. Further, an increase in δ15N from bulk sediment and an increase in sedimentary laminations suggest oxygen levels declined. Multivariate analyses demonstrate a strong correlation between foraminiferal community metrics and δ15N suggesting that the foraminiferal community is tracking oxygenation levels while correlations to productivity changes appear indirect. Molluscan community metrics also have an approximately linear relationship to δ15N. Temperature itself had little direct influence on community composition. Changes in community composition and structure of both the foraminifera and the molluscs are abrupt relative to the duration of community states, but each group responds differently to the climate change. The foraminiferal community increases in the number of species and the evenness of species abundances while the molluscan community decreases in

  17. Last Glacial warm events on Mount Hermon: the southern extension of the Alpine karst range of the east Mediterranean

    NASA Astrophysics Data System (ADS)

    Ayalon, Avner; Bar-Matthews, Miryam; Frumkin, Amos; Matthews, Alan

    2013-01-01

    This study focuses on warm Last Glacial episodes in the southernmost extension of the Alpine karst range of the Eastern Mediterranean (Levant) region through the study speleothems in Mizpe Shelagim Cave, located in Mt. Hermon. The Alpine karst range extends from Turkey through Syria and Lebanon, reaching its southern limit in Mt. Hermon at an elevation of more than 2000 m. Under present-day conditions, southern Mt. Hermon receives 1000-2000 mm precipitation, mostly as snow, that originates in the Eastern Mediterranean Sea. Speleothems deposition in this high altitude region was continuous during interglacials, but during the Last Glacial growth only occurred when average annual temperatures exceeded ˜3 °C as inferred from the study of speleothem fluid inclusions. Warming episodes occurred at: ˜65 ka, ˜56 ka, 54.5 ka, ˜52.5-51 ka, ˜49 ka, ˜42 ka, and ˜36 ka and are coincident with maximum insolation at 65 °N. The main depositional period from ˜56 ka to 51 ka coincides with Dansgaard-Oeschger interstadial 15 and 14, and warming in the northeastern basin of the Mediterranean Sea. Warming in the southern Alpine karst range of the Eastern Mediterranean was manifested by vegetation development, together with significant snow melting that resulted in the drainage of large amount of water to the Dead Sea Rift Valley.

  18. Warm water events in the southeast Atlantic and their impact on regional and large-scale atmospheric conditions in the CMIP5 model output

    NASA Astrophysics Data System (ADS)

    Ott, Irena; Lutz, Karin; Rathmann, Joachim; Jacobeit, Jucundus

    2013-04-01

    Two types of El Niño-like events are described in the South Atlantic: the Atlantic Niño in the equatorial Atlantic and the Benguela Niño off the Namibian and Angolan coast. These warm water events are known to be associated with rainfall anomalies at the West and Southwest African coastal region and harm marine ecosystems and fish populations. The two phenomena are handled separately so far, but the identification of warm water events in our study - via similar variabilities of sea surface temperatures (SST) - based on observed SST data (HadISST1.1) as well as global climate model output from CMIP5, involved the definition of an area mean index that includes both Niño types from the Atlantic region. A multi-model ensemble of the CMIP5 output is used to investigate the impact of Atlantic Niño events on regional atmospheric conditions. Based on the Atlantic SST index, composite analyses give information about anomalous precipitation, air pressure, humidity, evaporation, horizontal wind and vertical air motion patterns over the African continent and the South Atlantic. The Atlantic variability mode is similar to the Pacific El Niño system, but more irregular and less intense. However, recent studies show that the Atlantic influences the El Niño Southern Oscillation (ENSO) in the Pacific Ocean by the modification of the Walker and Hadley circulations and associated wind stress, thermocline and SST anomalies, further amplified by the Bjerknes positive feedback. As a result, an Atlantic Niño is followed by a La Niña-like phenomenon in the Pacific area with a lag of six months. In our study, the CMIP5 output is considered with respect to its ability of describing the complex connection between the Atlantic and Pacific variability modes. For that purpose, the inter-ocean teleconnection is studied with correlation analyses of the ensemble members of the CMIP5 output by means of the Atlantic index, the Southern Oscillation (SOI) and the Pacific El Niño indices (Ni

  19. Younger Dryas deglaciation of Scotland driven by warming summers.

    PubMed

    Bromley, Gordon R M; Putnam, Aaron E; Rademaker, Kurt M; Lowell, Thomas V; Schaefer, Joerg M; Hall, Brenda; Winckler, Gisela; Birkel, Sean D; Borns, Harold W

    2014-04-29

    The Younger Dryas Stadial (YDS; ∼ 12,900-11,600 y ago) in the Northern Hemisphere is classically defined by abrupt cooling and renewed glaciation during the last glacial-interglacial transition. Although this event involved a global reorganization of atmospheric and oceanic circulation [Denton GH, Alley RB, Comer GC, Broecker WS (2005) Quat Sci Rev 24:1159-1182], the magnitude, seasonality, and geographical footprint of YDS cooling remain unresolved and pose a challenge to our understanding of abrupt climate change. Here, we present a deglacial chronology from Scotland, immediately downwind of the North Atlantic Ocean, indicating that the Scottish ice cap disintegrated during the first half of the YDS. We suggest that stratification of the North Atlantic Ocean resulted in amplified seasonality that, paradoxically, stimulated a severe wintertime climate while promoting warming summers through solar heating of the mixed layer. This latter process drove deglaciation of downwind landmasses to completion well before the end of the YDS. PMID:24733909

  20. Abrupt changes in rainfall during the twentieth century

    NASA Astrophysics Data System (ADS)

    Narisma, Gemma T.; Foley, Jonathan A.; Licker, Rachel; Ramankutty, Navin

    2007-03-01

    Complex interactions in the climate system can give rise to strong positive feedback mechanisms that may lead to sudden climatic changes. The prolonged Sahel drought and the Dust Bowl are examples of 20th century abrupt climatic changes that had serious effects on ecosystems and societies. Here we analyze global historical rainfall observations to detect regions that have undergone large, sudden decreases in rainfall. Our results show that in the 20th century about 30 regions in the world have experienced such changes. These events are statistically significant at the 99% level, are persistent for at least ten years, and most have magnitudes of change that are 10% lower than the climatological normal (1901-2000 rainfall average). This analysis illustrates the extent and magnitude of abrupt climate changes across the globe during the 20th century and may be used for studying the dynamics of and the mechanisms behind these abrupt changes.

  1. Contribution of enhanced Antarctic Bottom Water formation to Antarctic warm events and millennial-scale atmospheric CO2 increase

    NASA Astrophysics Data System (ADS)

    Menviel, L.; Spence, P.; England, M. H.

    2015-03-01

    During Marine Isotope Stage 3, the Atlantic Meridional Overturning Circulation (AMOC) weakened significantly on a millennial time-scale leading to Greenland stadials. Ice core records reveal that each Greenland stadial is associated with a warming over Antarctica, so-called Antarctic Isotope Maximum (AIM), and that atmospheric CO2 increases with Antarctic temperature during the long Greenland stadials. Here we perform transient simulations spanning the period 50-34 ka B.P. with two Earth System Models (LOVECLIM and the UVic ESCM) to understand the possible link between changes in the AMOC, changes in high latitude Southern Hemispheric climate and evolution of atmospheric CO2. We find that oceanic carbon releases due to the AMOC resumption during stadial/interstadial transitions lead to an atmospheric CO2 increase. However, the atmospheric CO2 increases observed during the first parts of AIM12 (∼47.6 ka B.P.) and AIM8 (∼39.8 ka B.P.) occur during periods of weak AMOC (HS5 and HS4 respectively) and could instead be explained by enhanced Antarctic Bottom Water transport. Enhanced Antarctic Bottom Water formation is shown to effectively ventilate the deep Pacific carbon and lead to CO2 outgassing into the atmosphere. In addition, changes in the AMOC alone are not sufficient to explain the largest Antarctic Isotope Maxima (namely AIM12 and AIM8). Stronger formation of Antarctic Bottom Water during AIM12 and AIM8 would enhance the southern high latitude warming and lead to a better agreement with high southern latitude paleoproxy records. The robustness of this southern warming response is tested using an eddy-permitting coupled ocean sea-ice model. We show that stronger Antarctic Bottom Water formation contributes to Southern Ocean surface warming by increasing the Southern Ocean meridional heat transport.

  2. The role of the thermohaline circulation in abrupt climate change.

    PubMed

    Clark, Peter U; Pisias, Nicklas G; Stocker, Thomas F; Weaver, Andrew J

    2002-02-21

    The possibility of a reduced Atlantic thermohaline circulation in response to increases in greenhouse-gas concentrations has been demonstrated in a number of simulations with general circulation models of the coupled ocean-atmosphere system. But it remains difficult to assess the likelihood of future changes in the thermohaline circulation, mainly owing to poorly constrained model parameterizations and uncertainties in the response of the climate system to greenhouse warming. Analyses of past abrupt climate changes help to solve these problems. Data and models both suggest that abrupt climate change during the last glaciation originated through changes in the Atlantic thermohaline circulation in response to small changes in the hydrological cycle. Atmospheric and oceanic responses to these changes were then transmitted globally through a number of feedbacks. The palaeoclimate data and the model results also indicate that the stability of the thermohaline circulation depends on the mean climate state. PMID:11859359

  3. Redefining deuterium excess in ice cores: Antarctic-wide evidence for ITCZ and polar jet variability during abrupt climate change

    NASA Astrophysics Data System (ADS)

    Markle, B. R.; Steig, E. J.; Schoenemann, S. W.; Sowers, T. A.; Buizert, C.; Ding, Q.; Fudge, T. J.; White, J. W.

    2013-12-01

    We examine a new, high-resolution ice core record of water isotopes (δ18O and deuterium excess) and atmospheric methane from West Antarctica, focusing on the millennial events of the most recent glacial period. High temporal resolution and a small gas-age/ice-age difference enable unprecedented precision in the analysis of phasing between these records. Our analysis reveals large amplitude millennial variability in the deuterium excess, a proxy for moisture source conditions and atmospheric circulation, which is out of phase with local site temperatures. On the other hand, this variability is in phase with atmospheric methane, which likely records changes in tropical hydrology and co-varies with Greenland temperatures during abrupt millennial Dansgaard-Oeschger (DO) events. Using a logarithmic definition of the deuterium excess, we show that these changes were probably near symmetric around Antarctica; the historical (linear) definition of the parameter appears to misrepresent millennial to multi-millennial variability at high East Antarctic ice core sites. Modeling experiments show that asymmetric warming of the hemispheres, a defining characteristic of these millennial events, should shift the position of the Inter Tropical Convergence Zone (ITCZ) and in turn the Southern sub-polar jet. Postulated ITCZ shifts can, in principle, help to explain the rapid rise in methane that accompanies abrupt Northern Hemisphere warming events by varying tropical rainfall patterns. Our observations are the first to show that these tropical changes may have directly influenced moisture sources and atmospheric circulation in the high southern latitudes, as recorded by the deuterium excess. We support these paleoclimate observations with isotope tracing atmospheric modeling experiments.

  4. Contribution of enhanced Antarctic Bottom Water formation to Antarctic warm events and millennial-scale atmospheric CO2 increase

    NASA Astrophysics Data System (ADS)

    Menviel, L.; Spence, P.; England, M. H.

    2014-12-01

    During Marine Isotope Stage 3, the Atlantic Meridional Overturning Circulation (AMOC) weakened significantly on a millennial time-scale leading to Dansgaard-Oeschger (DO) and Heinrich stadials. Ice core records reveal that each Northern Hemisphere stadial is associated with a warming over Antarctica, so-called Antarctic Isotope Maximum (AIM), and that atmospheric CO2 varies in phase with Antarctic temperature. Here we perform transient simulations spanning the period 50-34 ka B.P. with two Earth System Models (LOVECLIM and the UVic ESCM) to understand the link between changes in the AMOC, changes in high latitude Southern Hemispheric climate and evolution of atmospheric CO2. Given the latest Antarctic ice core chronology, we find that part of the atmospheric CO2 increase occurring during AIM12 (DO12, ~48 ka B.P.) and at the end of AIM8 (DO8, 38 ka B.P.) can be attributed to the AMOC resumption. In contrast, the atmospheric CO2 increase observed at the beginning of AIM8 (~39.6 ka B.P.) occurs during a period of weak AMOC and can instead be explained by enhanced Antarctic Bottom Water production. Enhanced Antarctic Bottom Water formation is shown to effectively ventilate the deep Pacific carbon and thus lead to CO2 outgassing into the atmosphere. In addition, changes in the AMOC alone are not sufficient to explain the largest Antarctic Isotope Maxima (namely AIM12 and AIM8). Stronger formation of Antarctic Bottom Water during AIM12 and AIM8 enhances the southern high latitude warming and leads to a better agreement with high southern latitude paleoproxy records. The robustness of this southern warming response is tested using an eddy-permitting coupled ocean sea-ice model. We show that stronger Antarctic Bottom Water formation contributes to Southern Ocean surface warming by increasing the Southern Ocean meridional heat transport. Finally, our simulations also suggest that the Antarctic cooling should be in phase, or lag by a maximum of ~200 years, the North Atlantic

  5. Comparison of the dynamical response of low latitude middle atmosphere to the major stratospheric warming events in the Northern and Southern Hemispheres

    NASA Astrophysics Data System (ADS)

    Bhagavathiammal, G. J.; Sathishkumar, S.; Sridharan, S.; Gurubaran, S.

    2016-08-01

    This study presents comparison of low-latitude dynamical responses to boreal 2008/09 and austral 2002 winter Major Stratospheric Warming (MSW) events, as both events are of vortex split type. During these winters, planetary wave (PW) variability and changes in low-latitude circulation are examined using European Center for Medium Range Weather Forecasting (ECMWF) reanalysis (ERA)-interim data sets and mesospheric wind data acquired by the MF radars at Tirunelveli (8.7°N) and Rarotonga (22°S). Eliassen-Palm diagnostic is used to provide an evidence for the lateral PW energy propagation from high to low-latitudes during both the MSW events. The PW flux reaches much lower latitudes during the boreal event than during the austral event. The low-latitude westward winds at stratospheric heights are stronger (weaker) during the boreal (austral) MSW. Weak (strong) PW wave activity at low latitude mesospheric heights during boreal (austral) MSW indicates the influence of low-latitude stratospheric westward winds on the vertical propagation of PW to low-latitude mesosphere.

  6. Impacts of urban development on runoff event characteristics and unit hydrographs across warm and cold seasons in high latitudes

    NASA Astrophysics Data System (ADS)

    Sillanpää, Nora; Koivusalo, Harri

    2015-02-01

    The impacts of urbanization on catchment hydrology are widely studied by comparing how different urban catchments respond to storm events, but rarely by realizing long-term observations of hydrological changes during the construction process at urbanizing small catchments. In this study, the changes occurring in runoff generation were monitored in a developing catchment under construction and in two urban control catchments. As the imperviousness of the developing catchment increased from 1.5% to 37%, significant increases were observed in event runoff depths and peak flows during rainfall-runoff events. At the same time, the only statistically significant changes that were observed for the cold period runoff events were the shorter duration and smaller runoff depths. The effect of urbanization on event runoff dynamics was studied in terms of changes in the instantaneous unit hydrographs (IUH). Negative trends were detected in the gamma parameters of IUHs, which became more consistent across events and produced a sharper shape of the hydrograph as the construction works progressed. Because urban development caused the greatest relative changes in runoff during frequently occurring minor rainfall events, the study results underlined the importance of small storms in urban runoff management for maintaining the predevelopment water balance. During infrequent major rainfall events and the cold period snowmelt events the impacts of urbanization were less pronounced. The impact of urbanization on runoff was best detected based on peak flow rates, volumetric runoff coefficients, or mean runoff intensities. Control catchments were essential to distinguish the hydrological impact caused by catchment characteristics from those caused by changes in the meteorological conditions or season.

  7. The warming-induced increase of growing-season freezing event and its effect on the survival and growth of treeline seedlings in the Sergyemla Mountains, Southeast Tibet

    NASA Astrophysics Data System (ADS)

    Shen, W.; Zhang, L.; Liu, X.; Luo, T.

    2013-12-01

    Seedling establishment is important to the formation and dynamics of alpine treeline. How can we understand the limitation to the survival and growth of seedlings at and above treeline under a warmer climate? In this study, we conducted a 4-yr reciprocal transplant experiment of seed-based fir and root-sprouting juniper seedlings on opposite slopes of a valley in the Sergyemla Mountains, where annual mean air-temperature differed by 0.5-2.1 K and annual precipitation was similar. We aim to test the hypotheses that the warmer climate on the south-facing slope generally has more severe growing-season freezing events, and the seed-based fir seedlings are especially vulnerable to the warming-induced increase of freezing days in the early growing season. The frequency, intensity and duration of the growing-season freezing events across site habitats generally increased from north- to south-facing slopes. The freezing days in the early growing season (April-June) were mainly determined by daily minimum net radiation and relative humidity, and positively correlated with annual mean air-temperature across sites and years. The survival rates of transplanted fir seedlings on the south-facing slope greatly decreased by <60% in forested habitat and by <40% in non-forested habitat, while their survival rates on the north-facing slope did not change in forested habitat and slowly decreased by 85% in non-forested habitat. The survival rates of transplanted juniper seedlings decreased by 68%-84% with unclear change trends among different slopes and habitats. In pooled data across sites and years, annual top-shoot growth rates decreased in fir seedlings but varied little in juniper seedlings with increasing freezing days in the early growing season. The data supported our hypotheses. The warming-enhanced difficulty of seedling establishment above treeline can explain why the fir treeline position did not advance with climatic warming in past 200 years.

  8. Rain-on-snow events, floods and climate change in the Alps: Events may increase with warming up to 4°C and decrease thereafter.

    PubMed

    Beniston, Martin; Stoffel, Markus

    2016-11-15

    This paper focuses on the influence of mountain rain-on-snow (ROS) events that can on occasion trigger major floods in alpine catchments. In order to assess the evolution of these events in a recent past, and the potential changes that could be experienced in a changing climate over coming decades, we have focused on a small catchment in north-eastern Switzerland, the Sitter, well-endowed with both climate and hydrological data. Observations show that there has been an increase in the number of rain-on-snow events since the early 1960s related to the rise in atmospheric temperatures. Results from a simple temperature-based snow model show that the number of ROS events could increase by close to 50% with temperatures 2-4°C warmer than today, before declining when temperatures go beyond 4°C. The likelihood of more ROS events suggests that the risks of flooding in a future climate may indeed get worse before they improve. PMID:27476005

  9. Warm season heavy rainfall events over the Huaihe River Valley and their linkage with wintertime thermal condition of the tropical oceans

    NASA Astrophysics Data System (ADS)

    Li, Laifang; Li, Wenhong; Tang, Qiuhong; Zhang, Pengfei; Liu, Yimin

    2016-01-01

    Warm season heavy rainfall events over the Huaihe River Valley (HRV) of China are amongst the top causes of agriculture and economic loss in this region. Thus, there is a pressing need for accurate seasonal prediction of HRV heavy rainfall events. This study improves the seasonal prediction of HRV heavy rainfall by implementing a novel rainfall framework, which overcomes the limitation of traditional probability models and advances the statistical inference on HRV heavy rainfall events. The framework is built on a three-cluster Normal mixture model, whose distribution parameters are sampled using Bayesian inference and Markov Chain Monte Carlo algorithm. The three rainfall clusters reflect probability behaviors of light, moderate, and heavy rainfall, respectively. Our analysis indicates that heavy rainfall events make the largest contribution to the total amount of seasonal precipitation. Furthermore, the interannual variation of summer precipitation is attributable to the variation of heavy rainfall frequency over the HRV. The heavy rainfall frequency, in turn, is influenced by sea surface temperature anomalies (SSTAs) over the north Indian Ocean, equatorial western Pacific, and the tropical Atlantic. The tropical SSTAs modulate the HRV heavy rainfall events by influencing atmospheric circulation favorable for the onset and maintenance of heavy rainfall events. Occurring 5 months prior to the summer season, these tropical SSTAs provide potential sources of prediction skill for heavy rainfall events over the HRV. Using these preceding SSTA signals, we show that the support vector machine algorithm can predict HRV heavy rainfall satisfactorily. The improved prediction skill has important implication for the nation's disaster early warning system.

  10. Analysis of abrupt transitions in ecological systems

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The occurrence and causes of abrupt transitions, thresholds, or regime shifts between ecosystem states are of great concern and the likelihood of such transitions is increasing for many ecological systems. General understanding of abrupt transitions has been advanced by theory, but hindered by the l...

  11. Global warming

    NASA Astrophysics Data System (ADS)

    Houghton, John

    2005-06-01

    'Global warming' is a phrase that refers to the effect on the climate of human activities, in particular the burning of fossil fuels (coal, oil and gas) and large-scale deforestation, which cause emissions to the atmosphere of large amounts of 'greenhouse gases', of which the most important is carbon dioxide. Such gases absorb infrared radiation emitted by the Earth's surface and act as blankets over the surface keeping it warmer than it would otherwise be. Associated with this warming are changes of climate. The basic science of the 'greenhouse effect' that leads to the warming is well understood. More detailed understanding relies on numerical models of the climate that integrate the basic dynamical and physical equations describing the complete climate system. Many of the likely characteristics of the resulting changes in climate (such as more frequent heat waves, increases in rainfall, increase in frequency and intensity of many extreme climate events) can be identified. Substantial uncertainties remain in knowledge of some of the feedbacks within the climate system (that affect the overall magnitude of change) and in much of the detail of likely regional change. Because of its negative impacts on human communities (including for instance substantial sea-level rise) and on ecosystems, global warming is the most important environmental problem the world faces. Adaptation to the inevitable impacts and mitigation to reduce their magnitude are both necessary. International action is being taken by the world's scientific and political communities. Because of the need for urgent action, the greatest challenge is to move rapidly to much increased energy efficiency and to non-fossil-fuel energy sources.

  12. Warm Atlantic water drives Greenland Ice Sheet discharge dynamics

    NASA Astrophysics Data System (ADS)

    Christoffersen, P.; Heywood, K. J.; Dowdeswell, J. A.; Syvitski, J. P.; Benham, T. J.; Mugford, R. I.; Joughin, I.; Luckman, A.

    2008-12-01

    Greenland outlet glaciers terminating in fjords experience seasonal fluctuations as well as abrupt episodes of rapid retreat and speed-up. The cause of abrupt speed-up events is not firmly established, but synchronous occurrences suggest that it is related to Arctic warming. Here, we report major warming of water masses in Kangerdlugssuaq Fjord, East Greenland, immediately prior to the fast retreat and speed-up of Kangerdlugssuaq Glacier in 2004-05. Our hydrographic data show that this event occurred when Atlantic water entered the fjord and increased temperature of surface water by 4°C and deep water by 1°C. On the basis of meteorological records and satellite-derived sea surface temperatures, which fluctuate by up to 4°C in periods of 2-3 years, we infer that inflow of Atlantic water is controlled by the direction and intensity of prevailing winds that force coastal and offshore currents. Our results demonstrate that Greenland Ice Sheet discharge dynamics are modulated by North Atlantic climate variability, which is identified by shifts in the position of atmospheric low pressure over the Labrador and Irminger seas. A persisting westerly position of the Icelandic Low since 1999 may explain why winters in Greenland have been particularly mild during the last decade and it is feasible that widespread and synchronous discharge fluctuations from outlet glaciers, which resulted in high rates of ice loss in southeast Greenland, are a consequence of this synoptic condition.

  13. Abrupt Climate Change in the Arctic (and Beyond): An Update (Invited)

    NASA Astrophysics Data System (ADS)

    Alley, R. B.

    2013-12-01

    Our understanding of future Arctic change is informed by the history of past changes, which often have been both large and abrupt. The well-known ice-age events such as the Younger Dryas show how sea-ice changes can amplify forcing to produce very large responses, with wintertime sea ice especially important. These changes are increasingly seen to have played a central role in the ice-age cycling through their global impact on CO2 storage in the deep ocean. The Heinrich events reveal processes of ice-sheet/ocean interaction, some of which are being played out in Greenland and Antarctica now, and which may have large future effects on sea-level rise. The paleoclimatic record plus physical understanding greatly reduce the worst worries about instabilities from methane stored in cold places, but tend to support a role in amplifying future warming. Overall, the very large impacts of past Arctic changes, and the likelihood that future changes under business-as-usual fossil-fuel emissions will be unprecedented in combined size and speed, raise important questions.

  14. Global Warming and Energy Transition: A Public Policy Imperative

    NASA Astrophysics Data System (ADS)

    Stone, G. T.

    2006-12-01

    The historic transition from fossil fuels to alternative energy resources has begun. This development is commonly attributed to increasing energy costs and the need for energy security. Looming ever larger, however, is the issue that will soon drive the third energy revolution: global warming. A preponderance of evidence documents accelerating warming, enlarging impacts, and human causes -- principally combustion of fossil fuels. The carbon dioxide (C02) content of Earth's atmosphere has increased more than 35 percent since the beginning of the industrial revolution and is the highest in 650,000 years. This dramatic rise of C02 and attendant positive feedbacks are already forcing significant impacts worldwide. These include atmospheric warming with shifting climatic and habitat zones, spreading tropical disease, and more extreme weather events; rapid ice loss at high latitude and high altitude; ocean warming and acidification with coral reef bleaching and intensifying tropical storms; rising sea level; and accelerating extinction rates. The 2007 draft report of the Intergovernmental Panel on Climate Change (IPCC) predicts greater warming than in previous models. A tipping point to abrupt climate change may be imminent. It is incumbent upon geoscientists and geoscience educators to assume leadership in addressing this challenge through public outreach and general education. The following topics should be integrated into all appropriate courses: the evidence of global warming and its causes; observed present and predicted future impacts of global warming; mitigation and adaptation strategies; and implications for energy policies and economic opportunities. New entry-level science and general education courses -- such as Climate Change Fundamentals and Energy in Nature, Technology, and Society -- are proving to be effective should be widely developed In addition, by workshops and presentations to civic and business organizations and by demonstrated examples of

  15. Impact of Climate and Fires on Abrupt Permafrost Thaw in Alaskan Tundra

    NASA Astrophysics Data System (ADS)

    Chipman, M. L.; Reents, C.; Greenberg, J. A.; Hu, F.

    2015-12-01

    Thermo-erosion from abrupt permafrost thaw is a key pulse disturbance in the Arctic that may impact the global carbon cycle. Abrupt thaw can occur when the permafrost active layer expands in response to climate warming and/or increased wildfire activity. Understanding these drivers of thermo-erosion is necessary to anticipate feedbacks in the Arctic, where summer temperature and fire frequency are predicted to increase. We examine modern and late-Holocene thermo-erosion in high-fire (Noatak) and low-fire (North Slope) tundra ecoregions of Alaska using a combination of remote-sensing and paleo-records. Lakes with active thaw features were identified through Landsat-7 image classification and time-series analysis based on observed 0.52-0.60 μm reflectance peaks following slump formation. We identified 1067 and 1705 lakes with active features between CE 2000-2012 in the Noatak and North Slope ecoregions, respectively. The density of features was higher in the highly flammable Noatak (0.04 versus 0.01 features km-2, respectively), suggesting that warmer climate and/or fires likely promote high thermo-erosional activity at present. To assess modern signals of thermo-erosion and identify past events, we analyzed soil profiles and lake-sediment cores from both ecoregions using X-ray fluorescence. The ratios of Ca:K and Ca:Sr increased with depth in permafrost soils, were higher in soils from younger versus older slump surfaces, and were significantly correlated with the ratio of carbonate to feldspar and clay minerals in lake sediments (r=0.96 and 0.93, P<0.0001, n=15). We interpret past increases in Ca:K, Ca:Sr, and δ13C as enhanced weathering of carbonate-rich permafrost soils associated with thermo-erosion. At the North Slope site, we identified ten episodes of thermoerosion over the past 6000 years and found strong correspondence to summer temperature trends. Events were more frequent at the Noatak site, where 15 thermo-erosional episodes and 26 fires occurred over

  16. Discussion of “Deglacial paleoclimate in the southwestern United States: an abrupt 18.6 cold event and evidence for a North Atlantic forcing of Termination I” by M.S. Lachniet, Y. Asmerom and V. Polyak

    USGS Publications Warehouse

    Winograd, Isaac J.

    2012-01-01

    Utilizing a stable isotopic time series obtained from a speleothem (PC-1), which grew between 20.1 and 15.6 ka, Lachniet, Asmeron and Polyak (2011; hereafter LAP) present evidence for a significant cold event in the southern Great Basin at 18.6 ka, a finding that we accept. Supplementing this short record with a literature review, they go on to claim, as their central thesis, that the paleoclimate of the southwestern US was driven by “the transmission of atmospheric anomalies to the southwest…that coincided with deglacial climate changes in Greenland and the North Atlantic region”, not by a “dominant Pacific Ocean SST control” as suggested by SST time series off California and by the Devils Hole δ18O time series from the southern Great Basin. We do not find their central thesis supportable.

  17. Responses to Global Warming Over the Eastern and Central Tibetan Plateau as Reflected in Day-time and Night-time Temperatures, Extreme Temperature Events, and Growing Season Length During 1961-2003

    NASA Astrophysics Data System (ADS)

    Yin, Z.; Liu, X.; Shao, X.

    2006-12-01

    This study examines the trends and variation patterns in daily maximum (day-time) and minimum (night-time) temperatures (hereafter referred to as Tm and Tn), extreme events, and growing season lengths over the eastern and central Tibetan Plateau (TP), in comparison with the results from other regions. Data during the period 1961-2003 from 66 weather stations over the eastern and central TP with elevations above 2000 m are used in this study, after going through rigorous quality assessment/quality control procedures. Statistically significant warming trends are identified in various measures of the temperature regime, especially in night- time temperatures, extreme warm/cold events, and diurnal temperature range (DTR). We find that the trends in Tn and Tm display distinct spatial patterns in the study region. The warming trends in winter night-time temperatures are among the highest when compared with studies conducted in other regions. Our results also confirm the asymmetric pattern of greater warming trends in minimum or night-time temperatures as compared to the day-time temperatures, which reduces the DTR in the region. Based on the time-varying percentiles of Tn and Tm, prominent warming trends are found in Tn during cold season months across the relative temperature scale of both warm and cold events. The warming in night-time temperatures causes the number of frost days to decrease significantly and the number of warm days to increase. The mean length of growing season has increased by approximately 17 days during the 43-year study period for the region. Most of the record-setting months for cold events are found in the earlier part of the study period, while that of the warm events have occurred mostly in the later half, especially since the 1990s. The changes in the temperature regime in this region may have brought regional-specific impacts on the ecosystems. It is found that grain production in Qinghai Province, located in the northeastern part of the

  18. Impact of warming events on reef-scale temperature variability as captured in two Little Cayman coral Sr/Ca records

    NASA Astrophysics Data System (ADS)

    von Reumont, J.; Hetzinger, S.; Garbe-Schönberg, D.; Manfrino, C.; Dullo, W.-Chr.

    2016-03-01

    The rising temperature of the world's oceans is affecting coral reef ecosystems by increasing the frequency and severity of bleaching and mortality events. The susceptibility of corals to temperature stress varies on local and regional scales. Insights into potential controlling parameters are hampered by a lack of long term in situ data in most coral reef environments and sea surface temperature (SST) products often do not resolve reef-scale variations. Here we use 42 years (1970-2012) of coral Sr/Ca data to reconstruct seasonal- to decadal-scale SST variations in two adjacent but distinct reef environments at Little Cayman, Cayman Islands. Our results indicate that two massive Diploria strigosa corals growing in the lagoon and in the fore reef responded differently to past warming events. Coral Sr/Ca data from the shallow lagoon successfully record high summer temperatures confirmed by in situ observations (>33°C). Surprisingly, coral Sr/Ca from the deeper fore reef is strongly affected by thermal stress events, although seasonal temperature extremes and mean SSTs at this site are reduced compared to the lagoon. The shallow lagoon coral showed decadal variations in Sr/Ca, supposedly related to the modulation of lagoonal temperature through varying tidal water exchange, influenced by the 18.6 year lunar nodal cycle. Our results show that reef-scale SST variability can be much larger than suggested by satellite SST measurements. Thus, using coral SST proxy records from different reef zones combined with in situ observations will improve conservation programs that are developed to monitor and predict potential thermal stress on coral reefs.

  19. Abrupt climate change and collapse of deep-sea ecosystems

    USGS Publications Warehouse

    Yasuhara, Moriaki; Cronin, T. M.; Demenocal, P.B.; Okahashi, H.; Linsley, B.K.

    2008-01-01

    We investigated the deep-sea fossil record of benthic ostracodes during periods of rapid climate and oceanographic change over the past 20,000 years in a core from intermediate depth in the northwestern Atlantic. Results show that deep-sea benthic community "collapses" occur with faunal turnover of up to 50% during major climatically driven oceanographic changes. Species diversity as measured by the Shannon-Wiener index falls from 3 to as low as 1.6 during these events. Major disruptions in the benthic communities commenced with Heinrich Event 1, the Inter-Aller??d Cold Period (IACP: 13.1 ka), the Younger Dryas (YD: 12.9-11.5 ka), and several Holocene Bond events when changes in deep-water circulation occurred. The largest collapse is associated with the YD/IACP and is characterized by an abrupt two-step decrease in both the upper North Atlantic Deep Water assemblage and species diversity at 13.1 ka and at 12.2 ka. The ostracode fauna at this site did not fully recover until ???8 ka, with the establishment of Labrador Sea Water ventilation. Ecologically opportunistic slope species prospered during this community collapse. Other abrupt community collapses during the past 20 ka generally correspond to millennial climate events. These results indicate that deep-sea ecosystems are not immune to the effects of rapid climate changes occurring over centuries or less. ?? 2008 by The National Academy of Sciences of the USA.

  20. North Atlantic Meridional Overturning Circulation (AMOC) and Abrupt Climate Change through the Last Glaciation

    NASA Astrophysics Data System (ADS)

    Henry, G., III; McManus, J. F.; Curry, W. B.; Keigwin, L. D.; Giosan, L.

    2014-12-01

    The climate of the glacial North Atlantic was punctuated by catastrophic discharges of icebergs (Heinrich events), as well as by more mysterious, abrupt warming events associated with Dansgaard-Oeschger oscillations. These events are suspected to be related to changes in AMOC and its influence on heat transport and the regional and global heat budget. Investigation of these rapid oscillations is often limited by the resolution of sediment records. High accumulation rates at our study site (33.69°N, 57.58°W, 4583m water depth) on the Bermuda Rise allow improved resolution by one to two orders of magnitude. Cores CDH19 (38.81m) and CDH13 (36.70m), were recovered during KNR191, the initial deployment of the RV Knorr's long coring system developed at the Woods Hole Oceanographic Institution with support from the NSF. These cores contain high quality sediment sections that allow high resolution studies extending through the last glacial cycle at a key location for monitoring past oceanographic and climatic variability. Here we present detailed multi-proxy data from Bermuda Rise sediments reflecting deep ocean chemistry and dynamics of the last glaciation, and combine them with published data to produce a continuous, high resolution record spanning the last 70,000 years. CaCO3 burial fluxes, foraminifera stable isotopes, and sedimentary uranium-series disequilibria (including seawater-derived 231Pa /230Th), display coherent, complementary variability throughout the last glaciation. Glacial values in each proxy are consistent with reduced ventilation and overturning compared to the Holocene, with intervals that indicate substantial millennial reductions in each, and others when they briefly approach Holocene levels. In multiple instances, particularly spanning interstadials eight through twelve (IS8-IS12) our results are consistent with an abrupt, subcentennial acceleration in the export of excess 231Pa from the North Atlantic during stadial-interstadial transitions

  1. Prediction of fetal acidemia in placental abruption

    PubMed Central

    2013-01-01

    Background To determine the major predictive factors for fetal acidemia in placental abruption. Methods A retrospective review of pregnancies with placental abruption was performed using a logistic regression model. Fetal acidemia was defined as a pH of less than 7.0 in umbilical artery. The severe abruption score, which was derived from a linear discriminant function, was calculated to determine the probability of fetal acidemia. Results Fetal acidemia was seen in 43 survivors (43/222, 19%). A logistic regression model showed bradycardia (OR (odds ratio) 50.34, 95% CI 11.07 – 228.93), and late decelerations (OR 15.13, 3.05 – 74.97), but not abnormal ultrasonographic findings were to be associated with the occurrence of fetal acidemia. The severe abruption score was calculated for the occurrence of fetal acidemia, using 6 items including vaginal bleeding, gestational age, abdominal pain, abnormal ultrasonographic finding, late decelerations, and bradycardia. Conclusions An abnormal FHR pattern, especially bradycardia is the most significant risk factor in placental abruption predicting fetal acidemia, regardless of the presence of abnormal ultrasonographic findings or gestational age. PMID:23915223

  2. Stalagmite-inferred abrupt hydroclimate changes in the central Mediterranean over the past 6500 years

    NASA Astrophysics Data System (ADS)

    Hu, H. M.; Shen, C. C.; Jiang, X.; Wang, Y.; Mii, H. S.

    2015-12-01

    Mediterranean, as one of the global climate change "hot spots", was faced with severe drought over the recent decades. Investigation of regional paleo-hydroclimate evolution helps improve climate projection and adaption strategy. Here, we present a new decadal-resolved record documenting hydroclimate in the central Mediterranean from an Italian stalagmite since 6500 years ago. Eighty high-precision absolute U-Th dates with 2-sigma uncertainty better than ±20 years and 560 oxygen isotopic ratio data show several abrupt drying events with an average of 600 mm precipitation decrease in less than 80 years since the mid-Holocene. North Atlantic Oscillation (NAO) could dominantly govern the centennial-scale hydroclimate variability, especially for a period of 4500 to 2000 years ago. Total solar irradiance (TSI) also partially affected this regional precipitation. The obscure relationship between stalagmite and global/local mean surface temperature sequences, in contradict to previous studies, implies complex internal feedback of global warming and atmospheric circulation in the Mediterranean. Our result suggests that the twenty-first century Mediterranean drying trend is significant but not unprecedented in the past six thousand years.

  3. An incoherent scatter radar study of the midnight temperature maximum that occurred at Arecibo during a sudden stratospheric warming event in January 2010

    NASA Astrophysics Data System (ADS)

    Gong, Yun; Zhou, Qihou; Zhang, Shaodong; Aponte, Nestor; Sulzer, Michael

    2016-06-01

    We present an analysis of the thermospheric midnight temperature maximum, a large increment of temperature around midnight. The analysis is based on data collected from the Arecibo incoherent scatter radar during 14-21 January 2010. The experiment overlaps with a major sudden stratospheric warming (SSW) event which commenced on 18 January 2010. Throughout the observation, the ion temperature exhibited moderate increase around postmidnight during 14-17 January, while it showed more intense increment during 18-21 January. In particular, on 20 January, the amplitude of the midnight temperature maximum (MTM) is 310 K, which is seldom seen at Arecibo. During the SSW, the meridional wind reverses toward the pole just before the commencement of the MTM. Then, the poleward wind and the ion temperature maximize almost at the same time. The variation of meridional wind and the MTM are consistent with the Whole Atmosphere Model (WAM) studies, which suggested that the variation is due to effects from an upward propagating terdiurnal tide. On the nights of 18-19 January, the MTM showed clear phase variation at the heights of 265, 303, and 342 km. A strong terdiurnal tide has been observed during the SSW and it is likely generated from low atmosphere and propagating upward. Our results provide direct observational evidence that the propagating upward terdiurnal tide plays an important role in causing the MTM, which supports the WAM simulations.

  4. Abrupt shifts in ecosystem function and intensification of global biogeochemical cycle driven by hydroclimatic extremes

    NASA Astrophysics Data System (ADS)

    Ma, Xuanlong; Huete, Alfredo; Ponce-Campos, Guillermo; Zhang, Yongguang; Xie, Zunyi; Giovannini, Leandro; Cleverly, James; Eamus, Derek

    2016-04-01

    Amplification of the hydrologic cycle as a consequence of global warming is increasing the frequency, intensity, and spatial extent of extreme climate events globally. The potential influences resulting from amplification of the hydro-climatic cycle, coupled with an accelerating warming trend, pose great concerns on the sustainability of terrestrial ecosystems to sequester carbon, maintain biodiversity, provide ecosystem services, food security, and support human livelihood. Despite the great implications, the magnitude, direction, and carry-over effect of these extreme climate events on ecosystem function, remain largely uncertain. To address these pressing issues, we conducted an observational, interdisciplinary study using satellite retrievals of atmospheric CO2 and photosynthesis (chlorophyll fluorescence), and in-situ flux tower measures of ecosystem-atmosphere carbon exchange, to reveal the shifts in ecosystem function across extreme drought and wet periods. We further determine the factors that govern ecosystem sensitivity to hydroclimatic extremes. We focus on Australia but extended our analyses to other global dryland regions due to their significant role in global biogeochemical cycles. Our results revealed dramatic impacts of drought and wet hydroclimatic extremes on ecosystem function, with abrupt changes in vegetation productivity, carbon uptake, and water-use-efficiency between years. Drought resulted in widespread reductions or collapse in the normal patterns of vegetation growth seasonality such that in many cases there was no detectable phenological cycle during extreme drought years. We further identified a significant increasing trend (p < 0.001) in extreme wet year precipitation amounts over Australia and many other global regions, resulting in an increasing trend in magnitude of the episodic carbon sink pulses coupled to each La Niña-induced wet years. This finding is of global biogeochemical significance, with the consequence of amplifying

  5. Abrupt climate change in southeast tropical Africa influenced by Indian monsoon variability and ITCZ migration

    NASA Astrophysics Data System (ADS)

    Tierney, Jessica E.; Russell, James M.

    2007-08-01

    The timing and magnitude of abrupt climate change in tropical Africa during the last glacial termination remains poorly understood. High-resolution paleolimnological data from Lake Tanganyika, Southeast Africa show that wind-driven seasonal mixing in the lake was reduced during the Younger Dryas, Inter-Allerød Cool Period, Older Dryas, and Heinrich Event 1, suggesting a weakened southwest Indian monsoon and a more southerly position of the Inter-Tropical Convergence Zone over Africa during these intervals. These events in Lake Tanganyika, coeval with millennial and centennial-scale climate shifts in the high latitudes, suggest that changes in ITCZ location and Indian monsoon strength are important components of abrupt global climate change and that their effects are felt south of the equator in Africa. However, we observe additional events in Lake Tanganyika of equal magnitude that are not correlated with high-latitude changes, indicating the potential for abrupt climate change to originate from within tropical systems.

  6. Detection of abrupt changes in dynamic systems

    NASA Technical Reports Server (NTRS)

    Willsky, A. S.

    1984-01-01

    Some of the basic ideas associated with the detection of abrupt changes in dynamic systems are presented. Multiple filter-based techniques and residual-based method and the multiple model and generalized likelihood ratio methods are considered. Issues such as the effect of unknown onset time on algorithm complexity and structure and robustness to model uncertainty are discussed.

  7. Observations of Enhanced Semi Diurnal Lunar Tides in the Mesosphere and Lower Thermosphere at Mid and High Northern Latitudes during Sudden Stratospheric Warming Events

    NASA Astrophysics Data System (ADS)

    Chau, J. L.; Hoffmann, P.; Pedatella, N. M.; Matthias, V.

    2014-12-01

    In recent years, there have been a series of reported ground- and satellite-based observations of lunar tide signatures in the equatorial and low latitude ionosphere around sudden stratospheric warming (SSW) events. More recently, Pedatella et al. [2014], using the Whole Atmosphere Community Climate Model Extended version (WACCM-X) and the thermosphere-ionosphere-mesosphere electrodynamics general circulation model (TIME-GCM) has demonstrated that the semi-diurnal lunar tide (M2) is an important contributor to the ionosphere variability during the 2009 SSW. Although the model results were focused on the low-latitude ionosphere and compare with Jicamarca electric fields, Pedatella et al. [2014] also reported that the M2 was enhanced in the northern mid and high latitudes (between 30 and 70oN) at mesospheric and lower thermospheric altitudes during the 2009 SSW. Motivated by this finding, we have analyzed winds from 80 to 100 kms obtained with meteor radars from Juliusruh (54oN) and Andøya (69oN) stations during five SSWs (2008, 2009, 2010, 2012, and 2013). By fitting the usual solar components (diurnal and semidiurnal and M2, we have been able to identify clearly the enhancement of the M2 as well as the semi diurnal solar tide during all these SSWs. The qualitative agreement with the Pedatella et al. [2014] simulations is very good, i.e., stronger signature at 54oN than at 69oN and enhanced around SSW. The analysis of other SSWs not only show the clear relationship with SSWs, but also the different behaviors in strength, time of occurrence, duration, etc., that appear to be associated to the mean wind dynamics as well as the stratospheric planetary wave characteristics.

  8. Millennial-scale trends in west Pacific warm pool hydrology since the Last Glacial Maximum.

    PubMed

    Partin, Judson W; Cobb, Kim M; Adkins, Jess F; Clark, Brian; Fernandez, Diego P

    2007-09-27

    Models and palaeoclimate data suggest that the tropical Pacific climate system plays a key part in the mechanisms underlying orbital-scale and abrupt climate change. Atmospheric convection over the western tropical Pacific is a major source of heat and moisture to extratropical regions, and may therefore influence the global climate response to a variety of forcing factors. The response of tropical Pacific convection to changes in global climate boundary conditions, abrupt climate changes and radiative forcing remains uncertain, however. Here we present three absolutely dated oxygen isotope records from stalagmites in northern Borneo that reflect changes in west Pacific warm pool hydrology over the past 27,000 years. Our results suggest that convection over the western tropical Pacific weakened 18,000-20,000 years ago, as tropical Pacific and Antarctic temperatures began to rise during the early stages of deglaciation. Convective activity, as inferred from oxygen isotopes, reached a minimum during Heinrich event 1 (ref. 10), when the Atlantic meridional overturning circulation was weak, pointing to feedbacks between the strength of the overturning circulation and tropical Pacific hydrology. There is no evidence of the Younger Dryas event in the stalagmite records, however, suggesting that different mechanisms operated during these two abrupt deglacial climate events. During the Holocene epoch, convective activity appears to track changes in spring and autumn insolation, highlighting the sensitivity of tropical Pacific convection to external radiative forcing. Together, these findings demonstrate that the tropical Pacific hydrological cycle is sensitive to high-latitude climate processes in both hemispheres, as well as to external radiative forcing, and that it may have a central role in abrupt climate change events. PMID:17898765

  9. Understanding future projected changes and historical trends in extreme climate and streamflow events in warm boreal permafrost basins of Interior Alaska

    NASA Astrophysics Data System (ADS)

    Bennett, K. E.; Cherry, J. E.; Walsh, J. E.; Hinzman, L. D.

    2014-12-01

    Changes in future and historical extreme events may have disastrous consequences in vulnerable systems such as the warm- permafrost-dominated Interior region of Alaska. This paper presents a study examining extreme hydro-climate events (temperature, precipitation and streamflow) in Interior Alaskan watersheds, focused on results from Fairbanks, Alaska, located within the Chena River basin. Results are presented for an ensemble of global climate models (GCMs) and emission scenarios, run through to 2100. GCMs, selected for performance over the Alaskan domain, project the largest increases in minimum daily minimum temperature (TNn), compared to maximum daily maximum temperature (TXx), in the winter and spring at the Fairbanks Airport station. The increases in TNn and TXx are much larger (two to four times) than the across GCM standard deviations, indicating robustness in the projected changes. Statistically significant increases in five-day maximum precipitation are also projected to occur by the 2080s, with the largest increases expected for the summer and fall seasons. Streamflow projections provided by running the Sacramento Soil Moisture Accounting model, coupled with the SNOW17 snow model, are analyzed using a generalized extreme value (GEV) theorem and nonparametric trend approach. The Chena River basin exhibits linear nonstationary increases in maximum and minimum annual streamflow projected by the 2080s under both the RCP 4.5 and RCP 8.5 scenarios, minimized by the Akaike Information Criteria statistic, corrected for small sample sizes. Changes are indicative of increased flow volumes in the summer and fall, following precipitation changes projected to occur during these seasons. These changes are distinct from trends and GEV analysis performed on the historical streamflow series, which indicate declining flows associated with the loss of snowpack observed as a statistically significant reduction in relative flow volume (-49%, p-value 0.01) during the May

  10. Abrupt rise of new machine ecology beyond human response time

    PubMed Central

    Johnson, Neil; Zhao, Guannan; Hunsader, Eric; Qi, Hong; Johnson, Nicholas; Meng, Jing; Tivnan, Brian

    2013-01-01

    Society's techno-social systems are becoming ever faster and more computer-orientated. However, far from simply generating faster versions of existing behaviour, we show that this speed-up can generate a new behavioural regime as humans lose the ability to intervene in real time. Analyzing millisecond-scale data for the world's largest and most powerful techno-social system, the global financial market, we uncover an abrupt transition to a new all-machine phase characterized by large numbers of subsecond extreme events. The proliferation of these subsecond events shows an intriguing correlation with the onset of the system-wide financial collapse in 2008. Our findings are consistent with an emerging ecology of competitive machines featuring ‘crowds' of predatory algorithms, and highlight the need for a new scientific theory of subsecond financial phenomena. PMID:24022120

  11. Global warming elucidated

    SciTech Connect

    Shen, S.

    1995-03-01

    The meaning of global warming and its relevance to everyday life is explained. Simple thermodynamics is used to predict an oscillatory nature of the change in climate due to global warming. Global warming causes extreme events and bad weather in the near term. In the long term it may cause the earth to transition to another equilibrium state through many oscillation in climatic patterns. The magnitudes of these oscillations could easily exceed the difference between the end points. The author further explains why many no longer fully understands the nature and magnitudes of common phenomena such as storms and wind speeds because of these oscillations, and the absorptive properties of clouds. The author links the increase in duration of the El Nino to global warming, and further predicts public health risks as the earth transitions to another equilibrium state in its young history.

  12. Abruptness of Cascade Failures in Power Grids

    NASA Astrophysics Data System (ADS)

    Pahwa, Sakshi; Scoglio, Caterina; Scala, Antonio

    2014-01-01

    Electric power-systems are one of the most important critical infrastructures. In recent years, they have been exposed to extreme stress due to the increasing demand, the introduction of distributed renewable energy sources, and the development of extensive interconnections. We investigate the phenomenon of abrupt breakdown of an electric power-system under two scenarios: load growth (mimicking the ever-increasing customer demand) and power fluctuations (mimicking the effects of renewable sources). Our results on real, realistic and synthetic networks indicate that increasing the system size causes breakdowns to become more abrupt; in fact, mapping the system to a solvable statistical-physics model indicates the occurrence of a first order transition in the large size limit. Such an enhancement for the systemic risk failures (black-outs) with increasing network size is an effect that should be considered in the current projects aiming to integrate national power-grids into ``super-grids''.

  13. Abruptness of cascade failures in power grids.

    PubMed

    Pahwa, Sakshi; Scoglio, Caterina; Scala, Antonio

    2014-01-01

    Electric power-systems are one of the most important critical infrastructures. In recent years, they have been exposed to extreme stress due to the increasing demand, the introduction of distributed renewable energy sources, and the development of extensive interconnections. We investigate the phenomenon of abrupt breakdown of an electric power-system under two scenarios: load growth (mimicking the ever-increasing customer demand) and power fluctuations (mimicking the effects of renewable sources). Our results on real, realistic and synthetic networks indicate that increasing the system size causes breakdowns to become more abrupt; in fact, mapping the system to a solvable statistical-physics model indicates the occurrence of a first order transition in the large size limit. Such an enhancement for the systemic risk failures (black-outs) with increasing network size is an effect that should be considered in the current projects aiming to integrate national power-grids into "super-grids". PMID:24424239

  14. Abrupt percolation in small equilibrated networks

    NASA Astrophysics Data System (ADS)

    Matsoukas, Themis

    2015-05-01

    Networks can exhibit an abrupt transition in the form of a spontaneous self-organization of a sizable fraction of the population into a giant component of connected members. This behavior has been demonstrated in random graphs under suppressive rules that passively or actively attempt to delay the formation of the giant cluster. We show that suppressive rules are not a necessary condition for a sharp transition at the percolation threshold. Rather, a finite system with aggressive tendency to form a giant cluster may exhibit an instability at the percolation threshold that is relieved through an abrupt and discontinuous transition to the stable branch. We develop the theory for a class of equilibrated networks that produce this behavior and find that the discontinuous jump is especially pronounced in small networks but disappears when the size of the system is infinite.

  15. Relative timing of deglacial climate events in Antarctica and Greenland.

    PubMed

    Morgan, Vin; Delmotte, Marc; van Ommen, Tas; Jouzel, Jean; Chappellaz, Jérôme; Woon, Suenor; Masson-Delmotte, Valérie; Raynaud, Dominique

    2002-09-13

    The last deglaciation was marked by large, hemispheric, millennial-scale climate variations: the Bølling-Allerød and Younger Dryas periods in the north, and the Antarctic Cold Reversal in the south. A chronology from the high-accumulation Law Dome East Antarctic ice core constrains the relative timing of these two events and provides strong evidence that the cooling at the start of the Antarctic Cold Reversal did not follow the abrupt warming during the northern Bølling transition around 14,500 years ago. This result suggests that southern changes are not a direct response to abrupt changes in North Atlantic thermohaline circulation, as is assumed in the conventional picture of a hemispheric temperature seesaw. PMID:12228715

  16. Transient simulation of last deglaciation with a new mechanism for Bolling-Allerod warming.

    PubMed

    Liu, Z; Otto-Bliesner, B L; He, F; Brady, E C; Tomas, R; Clark, P U; Carlson, A E; Lynch-Stieglitz, J; Curry, W; Brook, E; Erickson, D; Jacob, R; Kutzbach, J; Cheng, J

    2009-07-17

    We conducted the first synchronously coupled atmosphere-ocean general circulation model simulation from the Last Glacial Maximum to the Bølling-Allerød (BA) warming. Our model reproduces several major features of the deglacial climate evolution, suggesting a good agreement in climate sensitivity between the model and observations. In particular, our model simulates the abrupt BA warming as a transient response of the Atlantic meridional overturning circulation (AMOC) to a sudden termination of freshwater discharge to the North Atlantic before the BA. In contrast to previous mechanisms that invoke AMOC multiple equilibrium and Southern Hemisphere climate forcing, we propose that the BA transition is caused by the superposition of climatic responses to the transient CO(2) forcing, the AMOC recovery from Heinrich Event 1, and an AMOC overshoot. PMID:19608916

  17. Transient Simulation of Last Deglaciation with a New Mechanism for B lling-Aller d Warming

    SciTech Connect

    Erickson, David J

    2009-01-01

    We conducted the first synchronously coupled atmosphere-ocean general circulation model simulation from the Last Glacial Maximum to the Boelling-Alleroed (BA) warming. Our model reproduces several major features of the deglacial climate evolution, suggesting a good agreement in climate sensitivity between the model and observations. In particular, our model simulates the abrupt BA warming as a transient response of the Atlantic meridional overturning circulation (AMOC) to a sudden termination of freshwater discharge to the North Atlantic before the BA. In contrast to previous mechanisms that invoke AMOC multiple equilibrium and Southern Hemisphere climate forcing, we propose that the BA transition is caused by the superposition of climatic responses to the transient CO{sub 2} forcing, the AMOC recovery from Heinrich Event 1, and an AMOC overshoot.

  18. Speed and Magnitude of Abrupt Climate Change at 8,200 yrs B.P. from the Greenland Ice Core (GISP2)

    NASA Astrophysics Data System (ADS)

    Kobashi, T.; Severinghaus, J. P.; Brook, E. J.; Grachev, A.

    2003-12-01

    At ˜8,200 years before present, an abrupt climate change occurred, which is believed to be the largest in the past 10,000 years. The scale of the event was probably global, as seen in reduced atmospheric methane concentration and paleoclimatic evidence around the globe indicating drying and cooling trends. The timing of the climate change also coincides with widespread abandonment of villages in southwestern Asia, which marks the end of the Pre-Pottery Neolithic B (PPNB) interval. Owing to the similarity between the warm early-Holocene and the projected warmer future climate, the 8.2 k event provides us an invaluable test case for a future potential abrupt climate change. We reconstructed the speed and magnitude of temperature change at the event, using argon and nitrogen isotopes in trapped air from the Greenland ice core coupled with the oxygen isotope record of ice. This method makes use of two isotopic fractionations, gravitational and thermal, which occur within the firn layer (snow layer above the air bubble close-off depth). The analyses of argon and nitrogen isotopes can separate the two effects, and allows us to directly retrieve temperature information (Severinghaus et al., Nature, v. 391, 141, 1998). The magnitude of temperature change in central Greenland at 8.2kyr B.P. is preliminarily estimated to be 5 +/- 2 ° C for the decadal average with the experimentally determined thermal diffusion constants (Grachev and Severinghaus, Geochim. et Cosmochim. Acta, v.67, 345, 2003; J. Phys. Chem., v.107, 4636, 2003), implying an oxygen isotope-temperature coefficient, α , of ˜0.4 permil/° C. Using oxygen isotope record of ice and α , we estimate that the abrupt cooling took place within ˜5 years with an 'instantaneous' magnitude of ˜8° C, and climate was locked in the cold phase for ˜60 years. In addition, we plan to measure methane concentration in trapped air, which will constrain the mechanisms of the abrupt climate change.

  19. Climatic warming and accompanying changes in the ecological regime of the Black Sea during 1990s

    NASA Astrophysics Data System (ADS)

    Oguz, Temel; Cokacar, Tulay; Malanotte-Rizzoli, Paola; Ducklow, Hugh W.

    2003-09-01

    The Black Sea ecosystem is shown to experience abrupt shifts in its all trophic levels from primary producers to apex predators in 1995-1996. It arises as a manifestation of concurrent changes in its physical climate introduced by intensive warming of its surface waters as well as abrupt increases in the mean sea level and the net annual mean fresh water flux. The warming is evident in the annual-mean sea surface temperature (SST) data by a continuous rise at a rate of ˜0.25°C per year, following a strong cooling phase in 1991-1993. The most intense warming event with ˜2°C increase in the SST took place during winters of the 1994-1996 period. It also coincides with 4 cm yr-1 net sea level rise in the basin, and substantial change in the annual mean net fresh water flux from 150 km3 yr-1 in 1993 to 420 km3 yr-1 in 1997. The subsurface signature of warming is marked by a gradual depletion of the Cold Intermediate Layer (characterized by T < 8°C) throughout the basin during the same period. Winters of the warming phase are characterized by weaker vertical turbulent mixing and upwelling velocity, stronger stratification and, subsequently, reduced upward nutrient supply from the nutricline. From 1996 onward, the major late winter-early spring peak of the classical annual phytoplankton biomass structure observed prior to mid-90s was, therefore, either weakened or disappeared altogether depending on local meteorological and oceanographic conditions during each of these years. The effect of bottom-up limited unfavorable phytoplankton growth is reflected at higher trophic levels (e.g., mesozooplankton, gelatinous macrozooplankton, and pelagic fishes) in the form of their reduced stocks after 1995.

  20. Younger Dryas deglaciation of Scotland driven by warming summers

    PubMed Central

    Bromley, Gordon R. M.; Putnam, Aaron E.; Rademaker, Kurt M.; Lowell, Thomas V.; Schaefer, Joerg M.; Hall, Brenda; Winckler, Gisela; Birkel, Sean D.; Borns, Harold W.

    2014-01-01

    The Younger Dryas Stadial (YDS; ∼12,900–11,600 y ago) in the Northern Hemisphere is classically defined by abrupt cooling and renewed glaciation during the last glacial–interglacial transition. Although this event involved a global reorganization of atmospheric and oceanic circulation [Denton GH, Alley RB, Comer GC, Broecker WS (2005) Quat Sci Rev 24:1159–1182], the magnitude, seasonality, and geographical footprint of YDS cooling remain unresolved and pose a challenge to our understanding of abrupt climate change. Here, we present a deglacial chronology from Scotland, immediately downwind of the North Atlantic Ocean, indicating that the Scottish ice cap disintegrated during the first half of the YDS. We suggest that stratification of the North Atlantic Ocean resulted in amplified seasonality that, paradoxically, stimulated a severe wintertime climate while promoting warming summers through solar heating of the mixed layer. This latter process drove deglaciation of downwind landmasses to completion well before the end of the YDS. PMID:24733909

  1. Abrupt climate shift in the Western Mediterranean Sea

    PubMed Central

    Schroeder, K.; Chiggiato, J.; Bryden, H. L.; Borghini, M.; Ben Ismail, S.

    2016-01-01

    One century of oceanographic measurements has evidenced gradual increases in temperature and salinity of western Mediterranean water masses, even though the vertical stratification has basically remained unchanged. Starting in 2005, the basic structure of the intermediate and deep layers abruptly changed. We report here evidence of reinforced thermohaline variability in the deep western basin with significant dense water formation events producing large amounts of warmer, saltier and denser water masses than ever before. We provide a detailed chronological order to these changes, giving an overview of the new water masses and following their route from the central basin interior to the east (toward the Tyrrhenian) and toward the Atlantic Ocean. As a consequence of this climate shift, new deep waters outflowing through Gibraltar will impact the North Atlantic in terms of salt and heat input. In addition, modifications in the Mediterranean abyssal ecosystems and biogeochemical cycles are to be expected. PMID:26965790

  2. Abrupt climate shift in the Western Mediterranean Sea.

    PubMed

    Schroeder, K; Chiggiato, J; Bryden, H L; Borghini, M; Ben Ismail, S

    2016-01-01

    One century of oceanographic measurements has evidenced gradual increases in temperature and salinity of western Mediterranean water masses, even though the vertical stratification has basically remained unchanged. Starting in 2005, the basic structure of the intermediate and deep layers abruptly changed. We report here evidence of reinforced thermohaline variability in the deep western basin with significant dense water formation events producing large amounts of warmer, saltier and denser water masses than ever before. We provide a detailed chronological order to these changes, giving an overview of the new water masses and following their route from the central basin interior to the east (toward the Tyrrhenian) and toward the Atlantic Ocean. As a consequence of this climate shift, new deep waters outflowing through Gibraltar will impact the North Atlantic in terms of salt and heat input. In addition, modifications in the Mediterranean abyssal ecosystems and biogeochemical cycles are to be expected. PMID:26965790

  3. Abrupt climate shift in the Western Mediterranean Sea

    NASA Astrophysics Data System (ADS)

    Schroeder, K.; Chiggiato, J.; Bryden, H. L.; Borghini, M.; Ben Ismail, S.

    2016-03-01

    One century of oceanographic measurements has evidenced gradual increases in temperature and salinity of western Mediterranean water masses, even though the vertical stratification has basically remained unchanged. Starting in 2005, the basic structure of the intermediate and deep layers abruptly changed. We report here evidence of reinforced thermohaline variability in the deep western basin with significant dense water formation events producing large amounts of warmer, saltier and denser water masses than ever before. We provide a detailed chronological order to these changes, giving an overview of the new water masses and following their route from the central basin interior to the east (toward the Tyrrhenian) and toward the Atlantic Ocean. As a consequence of this climate shift, new deep waters outflowing through Gibraltar will impact the North Atlantic in terms of salt and heat input. In addition, modifications in the Mediterranean abyssal ecosystems and biogeochemical cycles are to be expected.

  4. Diagnosis of Placental Abruption: Relationship between Clinical and Histopathological Findings

    PubMed Central

    Elsasser, Denise A.; Ananth, Cande V.; Prasad, Vinay; Vintzileos, Anthony M.

    2009-01-01

    Objective We evaluated the extent to which histologic lesions bearing a diagnosis of abruption conform to a diagnosis based on established clinical criteria. We further examined the profile of chronic and acute histologic lesions associated with clinical abruption. Methods Data from the New Jersey-Placental Abruption Study – a multi-center, case-control study – were utilized to compare the clinical and histologic criteria for abruption. The study was based on 162 women with clinically diagnosed abruption and 173 controls. We examined the concordance between clinical indicators for abruption with those of a histopathological diagnosis. The clinical criteria for a diagnosis of abruption included (i) evidence of retroplacental clot(s); (ii) abruption diagnosed on prenatal ultrasound; or (iii) vaginal bleeding accompanied by nonreassuring fetal status or uterine hypertonicity. The pathological criteria for abruption diagnosis included hematoma, fibrin deposition, compressed villi, and hemosiderin-laden histiocytes in cases with older hematomas. Acute lesions included chorioamnionitis, funisitis, acute deciduitis, meconium stained membranes, villous stromal hemorrhage, and villous edema. Chronic lesions included chronic deciduitis, decidual necrosis, decidual vasculopathy, placental infarctions, villous maldevelopment (delayed or accelerated maturation), hemosiderin deposition, intervillous thrombus, and chronic villitis. Results Of clinically diagnosed cases, the sensitivity and specificity for a histologic confirmation of abruption were 30.2% and 100%, respectively. Presence of retroplacental clots remained the single most common finding (77.1%) among clinically diagnosed cases. Among the acute lesions, chorioamnionitis and funisitis were associated with abruption. The only chronic histologic lesion associated with abruption was placental infarctions. Conclusions The concordance between clinical and pathologic criteria for abruption diagnosis is poor. The criteria

  5. Abrupt release of terrigenous organic carbon to the Laptev Sea at termination of the Younger Dryas

    NASA Astrophysics Data System (ADS)

    Tesi, T.; Muschitiello, F.; Smittenberg, R.; Jakobsson, M.; Vonk, J.; Hill, P.; Dudarev, O.; Semiletov, I. P.; Kirchner, N.; Noormets, R.; Andersson, A.; Gustafsson, O.

    2015-12-01

    Based on analysis of a piston core collected in 2014 from the Lena River paleo delta, now Laptev Sea, we show that rapid and massive organic carbon (OC) deposition took place into the marine system at the termination of the Younger Dryas when the Arctic region experienced a large and extremely fast climate change. The highly laminated strata with absence of bioturbation further confirm the rapid event-driven emplacement of this deposit which was largely dominated by terrigenous OC as indicated by depleted δ13C values and high concentrations of terrestrial fossil biomarkers (lignin phenols and cutin-derived products). Moreover, the hydrogen isotopic composition (δ2H) of HMW n-alkanes indicates that this terrestrially-derived translocated OC was produced in the watershed during a relatively cold period. The OC appears to be a few thousand years old at time of deposition (ca. 4-5000 radiocarbon years; reservoir age corrected), consistent with the radiocarbon age of pre-aged OC currently supplied by the Lena river. Altogether our results indicate that fast climate warming exerts first-order control on large-scale carbon redistribution. Because the Younger Dryas-Preboreal transition occurred within a few decades, we infer that the abrupt and large release of terrigenous OC was essentially driven by rapid changes in the permafrost stability (i.e., thermal collapse/thawing) and increase in precipitation over the Siberian watershed. Interestingly, only surface and sub-surface carbon pools (i.e., active layer) were remobilized while deep and old sources (radiocarbon dead) did not seem to have substantially contributed to the total land-to-ocean flux during the Younger Dryas-Preboreal transition.

  6. An abrupt weakening of the subpolar gyre as trigger of Little Ice Age-type episodes

    NASA Astrophysics Data System (ADS)

    Moreno-Chamarro, Eduardo; Zanchettin, Davide; Lohmann, Katja; Jungclaus, Johann H.

    2016-04-01

    We investigate the mechanism of a decadal-scale weakening shift in the strength of the subpolar gyre (SPG) that is found in one among three last millennium simulations with a state-of-the-art Earth system model. The SPG shift triggers multicentennial anomalies in the North Atlantic climate driven by long-lasting internal feedbacks relating anomalous oceanic and atmospheric circulation, sea ice extent, and upper-ocean salinity in the Labrador Sea. Yet changes throughout or after the shift are not associated with a persistent weakening of the Atlantic Meridional Overturning Circulation or shifts in the North Atlantic Oscillation. The anomalous climate state of the North Atlantic simulated after the shift agrees well with climate reconstructions from within the area, which describe a transition between a stronger and weaker SPG during the relatively warm medieval climate and the cold Little Ice Age respectively. However, model and data differ in the timing of the onset. The simulated SPG shift is caused by a rapid increase in the freshwater export from the Arctic and associated freshening in the upper Labrador Sea. Such freshwater anomaly relates to prominent thickening of the Arctic sea ice, following the cluster of relatively small-magnitude volcanic eruptions by 1600 CE. Sensitivity experiments without volcanic forcing can nonetheless produce similar abrupt events; a necessary causal link between the volcanic cluster and the SPG shift can therefore be excluded. Instead, preconditioning by internal variability explains discrepancies in the timing between the simulated SPG shift and the reconstructed estimates for the Little Ice Age onset.

  7. Conclusive evidence of abrupt coagulation inside the void during cyclic nanoparticle formation in reactive plasma

    NASA Astrophysics Data System (ADS)

    van de Wetering, F. M. J. H.; Nijdam, S.; Beckers, J.

    2016-07-01

    In this letter, we present scanning electron microscopy (SEM) results that confirm in a direct way our earlier explanation of an abrupt coagulation event as the cause for the void hiccup. In a recent paper, we reported on the fast and interrupted expansion of voids in a reactive dusty argon-acetylene plasma. The voids appeared one after the other, each showing a peculiar, though reproducible, behavior of successive periods of fast expansion, abrupt contraction, and continued expansion. The abrupt contraction was termed "hiccup" and was related to collective coagulation of a new generation of nanoparticles growing in the void using relatively indirect methods: electron density measurements and optical emission spectroscopy. In this letter, we present conclusive evidence using SEM of particles collected at different moments in time spanning several growth cycles, which enables us to follow the nanoparticle formation process in great detail.

  8. Abrupt plate accelerations shape rifted continental margins.

    PubMed

    Brune, Sascha; Williams, Simon E; Butterworth, Nathaniel P; Müller, R Dietmar

    2016-08-11

    Rifted margins are formed by persistent stretching of continental lithosphere until breakup is achieved. It is well known that strain-rate-dependent processes control rift evolution, yet quantified extension histories of Earth's major passive margins have become available only recently. Here we investigate rift kinematics globally by applying a new geotectonic analysis technique to revised global plate reconstructions. We find that rifted margins feature an initial, slow rift phase (less than ten millimetres per year, full rate) and that an abrupt increase of plate divergence introduces a fast rift phase. Plate acceleration takes place before continental rupture and considerable margin area is created during each phase. We reproduce the rapid transition from slow to fast extension using analytical and numerical modelling with constant force boundary conditions. The extension models suggest that the two-phase velocity behaviour is caused by a rift-intrinsic strength--velocity feedback, which can be robustly inferred for diverse lithosphere configurations and rheologies. Our results explain differences between proximal and distal margin areas and demonstrate that abrupt plate acceleration during continental rifting is controlled by the nonlinear decay of the resistive rift strength force. This mechanism provides an explanation for several previously unexplained rapid absolute plate motion changes, offering new insights into the balance of plate driving forces through time. PMID:27437571

  9. Abrupt climate-independent fire regime changes

    USGS Publications Warehouse

    Pausas, Juli G.; Keeley, Jon E.

    2014-01-01

    Wildfires have played a determining role in distribution, composition and structure of many ecosystems worldwide and climatic changes are widely considered to be a major driver of future fire regime changes. However, forecasting future climatic change induced impacts on fire regimes will require a clearer understanding of other drivers of abrupt fire regime changes. Here, we focus on evidence from different environmental and temporal settings of fire regimes changes that are not directly attributed to climatic changes. We review key cases of these abrupt fire regime changes at different spatial and temporal scales, including those directly driven (i) by fauna, (ii) by invasive plant species, and (iii) by socio-economic and policy changes. All these drivers might generate non-linear effects of landscape changes in fuel structure; that is, they generate fuel changes that can cross thresholds of landscape continuity, and thus drastically change fire activity. Although climatic changes might contribute to some of these changes, there are also many instances that are not primarily linked to climatic shifts. Understanding the mechanism driving fire regime changes should contribute to our ability to better assess future fire regimes.

  10. Climate oscillations and abrupt changes in C14 data

    NASA Astrophysics Data System (ADS)

    Kuznetsova, T. V.; Tsirulnik, L. B.

    2004-01-01

    The radiocarbon series are analysed by a method of non-linear spectral analysis to detect time intervals of appearance of non-stationary oscillations of large amplitude, and the times of abrupt changes of their oscillation regime. The analysis shows that the most powerful cycles of the spectra can be interpreted in terms of periods (and their respective higher harmonics) of astronomical origin. An intense stationary sinusoid from the spectrum with period T˜6500 yr, the 4th harmonic of the period of equinox precession, correlates with the time variations of the geomagnetic dipole moment. The most powerful non-stationary sinusoid with mean period T=2230 yr, reflects oscillations in C14 data related to the non-dipole part of the geomagnetic field, and correlates with periods of climate warming/cooling. The apparent regularities that can be inferred in the interaction of such two powerful cycles (i.e. stationary and non-stationary parts of the uniform mechanism of the geomagnetic field generation) permit to forecast a tendency of the climate changes. A possible physical mechanism is presented based on a possible transformation, of some signals caused by perturbation of the tidal forces of astronomical origin (that can arise along the orbit of the Earth), into effects that control geophysical systems through small variations of the dissipative parameters of a dynamo system.

  11. Topography's crucial role in Heinrich Events.

    PubMed

    Roberts, William H G; Valdes, Paul J; Payne, Antony J

    2014-11-25

    Heinrich Events, the abrupt changes in the Laurentide Ice Sheet that cause the appearance of the well-observed Heinrich Layers, are thought to have a strong effect on the global climate. The focus of most studies that have looked at the climate's response to these events has been the freshwater flux that results from melting icebergs. However, there is the possibility that the varying height of the ice sheet could force a change in the climate. In this study, we present results from a newly developed coupled climate/ice sheet model to show what effect this topographic change has both on its own and in concert with the flux of freshwater from melting icebergs. We show that the topographic forcing can explain a number of the climate changes that are observed during Heinrich Events, such as the warming and wettening in Florida and the warm sea surface temperatures in the central North Atlantic, which freshwater forcing alone cannot. We also find regions, for example the tropical Atlantic, where the response is a mixture of the two: Here observations may help disentangle the relative importance of each mechanism. These results suggest that the simple paradigm of a Heinrich Event causing climate change via freshwater inputs into the North Atlantic needs to be revised. PMID:25368154

  12. Topography's crucial role in Heinrich Events

    PubMed Central

    Roberts, William H. G.; Valdes, Paul J.; Payne, Antony J.

    2014-01-01

    Heinrich Events, the abrupt changes in the Laurentide Ice Sheet that cause the appearance of the well-observed Heinrich Layers, are thought to have a strong effect on the global climate. The focus of most studies that have looked at the climate’s response to these events has been the freshwater flux that results from melting icebergs. However, there is the possibility that the varying height of the ice sheet could force a change in the climate. In this study, we present results from a newly developed coupled climate/ice sheet model to show what effect this topographic change has both on its own and in concert with the flux of freshwater from melting icebergs. We show that the topographic forcing can explain a number of the climate changes that are observed during Heinrich Events, such as the warming and wettening in Florida and the warm sea surface temperatures in the central North Atlantic, which freshwater forcing alone cannot. We also find regions, for example the tropical Atlantic, where the response is a mixture of the two: Here observations may help disentangle the relative importance of each mechanism. These results suggest that the simple paradigm of a Heinrich Event causing climate change via freshwater inputs into the North Atlantic needs to be revised. PMID:25368154

  13. Observation and analysis of abrupt changes in the interplanetary plasma velocity and magnetic field.

    NASA Technical Reports Server (NTRS)

    Martin, R. N.; Belcher, J. W.; Lazarus, A. J.

    1973-01-01

    This paper presents a limited study of the physical nature of abrupt changes in the interplanetary plasma velocity and magnetic field based on 19 day's data from the Pioneer 6 spacecraft. The period was chosen to include a high-velocity solar wind stream and low-velocity wind. Abrupt events were accepted for study if the sum of the energy density in the magnetic field and velocity changes was above a specified minimum. A statistical analysis of the events in the high-velocity solar wind stream shows that Alfvenic changes predominate. This conclusion is independent of whether steady state requirements are imposed on conditions before and after the event. Alfvenic changes do not dominate in the lower-speed wind. This study extends the plasma field evidence for outwardly propagating Alfvenic changes to time scales as small as 1 min (scale lengths on the order of 20,000 km).

  14. Panic anxiety after abrupt discontinuation of mianserin.

    PubMed

    Kuniyoshi, M; Arikawa, K; Miura, C; Inanaga, K

    1989-06-01

    We observed a case of withdrawal after abrupt discontinuation of mianserin. A 41-year-old woman was treated according to a diagnosis of depression, which was her 6th episode. Mianserin 30 mg/day, etizolam 1 mg/day and flunitrazepam 1 mg/day were administered. When the patient discontinued taking the drugs by herself because of subsiding of these symptoms, severe panic anxiety appeared. This panic anxiety was not relieved by taking etizolam and flunitrazepam again, but subsided rapidly by the re-administration of mianserin 30 mg/day, and because of that the depressive symptom also disappeared. From these experiences panic anxiety seemed to be a withdrawal symptom, and involvement of the noradrenergic system in panic anxiety as well as serotonergic system was suggested. PMID:2796025

  15. Australasian monsoon response to Dansgaard-Oeschger event 21 and teleconnections to higher latitudes

    NASA Astrophysics Data System (ADS)

    Griffiths, Michael L.; Drysdale, Russell N.; Gagan, Michael K.; Hellstrom, John C.; Couchoud, Isabelle; Ayliffe, Linda K.; Vonhof, Hubert B.; Hantoro, Wahyoe S.

    2013-05-01

    Dansgaard-Oeschger (D-O) cycles were the most prominent, abrupt climate events of the last glacial period whose impact was most strongly felt in the high latitudes of the North Atlantic region. The climate links between the North Atlantic, the Asian and American tropics, and Antarctica during these cycles are well documented. However, the potential role of the Indo-Pacific Warm Pool and Australasian monsoon system in propagating climate impacts across the hemispheres is still unclear. Here, we use tandem measurements of oxygen isotopes in calcite and fluid inclusions, as well as carbon-isotope ratios, from multiple stalagmites from Liang Luar Cave, Flores (southern Indonesia) to examine the monsoon response to D-O event number 21 (~87,000-84,000 years ago), the longest and warmest event recorded in Greenland ice cores. The record shows that there was a rapid decline in monsoon rainfall in Indonesia during D-O21 warming in Greenland and cooling in Antarctica. At around the same time, the East Asian monsoon was intensified, indicating that the intertropical convergence zone (ITCZ) shifted abruptly to the north during this event. Our record also shows that there was a 2-3 °C increase in local air temperature, which would have acted to increase primary productivity and promote the generation of soil carbon for methanogenesis. Therefore, our findings indicate that ITCZ positioning in tropical Australasia—through its influence on large-scale oceanic-atmospheric circulation—played a key role in transmitting the abrupt climate signal between the hemispheres, thereby facilitating the rapid rise of atmospheric CO2 and CH4 concentrations during D-O21 that ultimately led to global warming and the demise of the MIS5b stadial.

  16. Modeling dust emission variations in Eastern Europe related to North-Atlantic abrupt climate changes of the last glacial period

    NASA Astrophysics Data System (ADS)

    Sima, A.; Kageyama, M.; Rousseau, D.; Ramstein, G.; Schulz, M.; Balkanski, Y.; Antoine, P.; Dulac, F.; Hatte, C.; Lagroix, F.; Gerasimenko, N.

    2010-12-01

    The European loess sequences of the last glacial period (~ 100-15 kyr BP) show periods of strong dust accumulation alternating with episodes of reduced (or no) sedimentation, allowing soil development. For the main loess sedimentation period (~ 40 - 15 kyr BP), data indicate a correlation between these variations and the North Atlantic rapid climate changes: the Dansgaard-Oeschger (DO) and Heinrich (H) events. We use numerical modeling to investigate the relationship between the North-Atlantic abrupt changes and the sedimentation variations in Europe. A first study (Sima et al, QSR, 2009) focused on western Europe, and addressed the impact on dust emission of North-Atlantic SST changes as those associated to DO and H events. It proposed that vegetation played a key role in modulating dust emission variations in western European source areas. Here we focus on eastern Europe, especially on the areas north and north-east of the Carpathian Mountains, where loess deposits have recorded DO and H events (Rousseau et al. Clim. Past D, 2010). As in the previous study, we use the LMDZ AGCM and the SECHIBA land-surface models to simulate a reference glacial state (“stadial”), a cold (“HE”) and a warm (“DO interstadial”) perturbation, all corresponding to Marine Isotope Stage 3 conditions. We follow the same protocol as for the study on the west-European sector to analyze the impact of the climate factors and surface conditions on dust emission. The simulated most active emission areas are compatible with the loess deposit distribution, and the key role of vegetation in stadial-interstadial dust emission variations is confirmed.

  17. Global Warming?

    ERIC Educational Resources Information Center

    Eichman, Julia Christensen; Brown, Jeff A.

    1994-01-01

    Presents information and data on an experiment designed to test whether different atmosphere compositions are affected by light and temperature during both cooling and heating. Although flawed, the experiment should help students appreciate the difficulties that researchers face when trying to find evidence of global warming. (PR)

  18. Cesarean Delivery for a Life-threatening Preterm Placental Abruption

    PubMed Central

    Okafor, II; Ugwu, EO

    2015-01-01

    Placental abruption is one of the major life-threatening obstetric conditions. The fetomaternal outcome of a severe placental abruption depends largely on prompt maternal resuscitation and delivery. A case of severe preterm placental abruption with intrauterine fetal death. Following a failed induction of labor with a deteriorating maternal condition despite resuscitation, emergency cesarean delivery was offered with good maternal outcome. Cesarean delivery could avert further disease progression and possible maternal death in cases of severe preterm placental abruption where vaginal delivery is not imminent. However, further studies are necessary before this could be recommended for routine clinical practice. PMID:27057388

  19. A GCM study on the mechanism of seasonal abrupt changes

    NASA Astrophysics Data System (ADS)

    Wang, Huijun; Zeng, Qingcun

    1994-02-01

    In this paper the observational studies and some related dynamical and numerical researches on seasonal abrupt changes were reviewed first. Then a speculation that the seasonal variation of insolation and the nonlinear dynamic interaction account for the abrupt changes was put forward and was asserted by a set of GCM sensitivity experiments. The results show that the abrupt changes would exist in case that all the earth surface was grass land and there was no topography. However, many factors may have influences on the abrupt changes. Hence this phenomenon is quite complicated and needs further investigations.

  20. The Arctic Grand Challenge: Abrupt Climate Change

    NASA Astrophysics Data System (ADS)

    Wilkniss, P. E.

    2003-12-01

    Trouble in polar paradise (Science, 08/30/02), significant changes in the Arctic environment are scientifically documented (R.E. Moritz et al. ibid.). More trouble, lots more, "abrupt climate change," (R. B. Alley, et al. Science 03/28/03). R. Corell, Arctic Climate Impact Assessment team (ACIA), "If you want to see what will happen in the rest of the world 25 years from now just look what's happening in the Arctic," (Arctic Council meeting, Iceland, 08/03). What to do? Make abrupt Arctic climate change a grand challenge for the IPY-4 and beyond! Scientifically:Describe the "state" of the Arctic climate system as succinctly as possible and accept it as the point of departure.Develop a hypothesis and criteria what constitutes "abrupt climate change," in the Arctic that can be tested with observations. Observations: Bring to bear existing observations and coordinate new investments in observations through an IPY-4 scientific management committee. Make the new Barrow, Alaska, Global Climate Change Research Facility a major U.S. contribution and focal point for the IPY-4 in the U.S Arctic. Arctic populations, Native peoples: The people of the North are living already, daily, with wrenching change, encroaching on their habitats and cultures. For them "the earth is faster now," (I. Krupnik and D. Jolly, ARCUS, 2002). From a political, economic, social and entirely realistic perspective, an Arctic grand challenge without the total integration of the Native peoples in this effort cannot succeed. Therefore: Communications must be established, and the respective Native entities must be approached with the determination to create well founded, well functioning, enduring partnerships. In the U.S. Arctic, Barrow with its long history of involvement and active support of science and with the new global climate change research facility should be the focal point of choice Private industry: Resource extraction in the Arctic followed by oil and gas consumption, return the combustion

  1. Laurentide Ice Sheet meltwater and abrupt climate change during the last glaciation

    SciTech Connect

    Hill, H W; Flower, B P; Quinn, T M; Hollander, D J; Guilderson, T P

    2005-10-02

    A leading hypothesis to explain abrupt climate change during the last glacial cycle calls on fluctuations in the margin of the North American Laurentide Ice Sheet (LIS), which may have routed freshwater between the Gulf of Mexico (GOM) and North Atlantic, affecting North Atlantic Deep Water (NADW) variability and regional climate. Paired measurements of {delta}O and Mg/Ca of foraminiferal calcite from GOM sediments reveal five episodes of LIS meltwater input from 28-45 thousand years ago (ka) that do not match the millennial-scale Dansgaard-Oeschger (D/O) warmings recorded in Greenland ice. We suggest that summer melting of the LIS may occur during Antarctic warming and likely contributed to sea-level variability during Marine Isotope Stage 3 (MIS 3).

  2. The Effect of Maternal Thrombophilia on Placental Abruption: Histologic Correlates

    PubMed Central

    Kinzler, Wendy L.; Prasad, Vinay; Ananth, Cande V.

    2011-01-01

    Objective To determine if the histology of placental abruption differs by maternal thrombophilia status. Study design This was a multicenter, case-control study of women with abruption and delivering at ≥20 weeks’ gestation, collected as part of the ongoing New Jersey-Placental Abruption Study. Women were identified by clinical criteria of abruption. Maternal blood was collected postpartum and tested for anticardiolipin antibodies, and mutations in the Factor V Leiden and prothrombin genes. Cases were comprised of women with an abruption and a positive thrombophilia screen. Controls were comprised of women with an abruption and a negative thrombophilia screen. All placental histology was systematically reviewed by two perinatal pathologists, blinded to the abruption status. Results A total of 135 women with placental abruption were identified, of which 63.0% (n=85) had at least one diagnosed maternal thrombophilia. There were increases in the rates of meconium-stained membranes (7.9% versus 2.1%, P=0.015) and decidual necrosis (4.5% versus 2.1%, P=0.023) when a maternal thrombophilia was diagnosed. Although there was no difference in the overall presence of infarcts between the 2 groups (27.0% versus 38.3%, P=0.064), the presence of an old infarct was more common among women with a positive thrombophilia screen (83.3% versus 44.4%, P=0.003). Conclusion Placental abruption with a positive maternal thrombophilia screen is associated with higher rates of old placental infarcts and decidual necrosis compared with abruption when thrombophilia is not diagnosed. These lesions suggest a chronic etiology of placental abruption in the presence of a maternal thrombophilia. PMID:19330709

  3. The role of synoptic-scale features and advection in prolonged warming and generation of different forms of precipitation at Dome Fuji station, Antarctica, following a prominent blocking event

    NASA Astrophysics Data System (ADS)

    Hirasawa, Naohiko; Nakamura, Hisashi; Motoyama, Hideaki; Hayashi, Masahiko; Yamanouchi, Takashi

    2013-07-01

    A blocking event over the East Antarctic ice sheet during June 1997 generated the highest surface air temperature (which increased from around -70°C to around -30°C) and pressure of that year at the Dome Fuji station (77.5°S, 40°E). Following the blocking event, the anomalously high air temperature (around -50°C to -60°C) and pressure were maintained at the surface for about 1 week. This study investigates how these warm conditions were maintained and documents the sequential occurrence of two forms of synoptic-scale high-pressure systems with conditions that produced precipitation by different processes in each case. In the first half of the warm period, a solitary high-pressure system (the Solitary High) formed over the Dome Fuji station and traveled west over East Antarctica after being cut off from the tip of the preceding blocking ridge. During this phase, tropospheric temperatures were higher, and surface-based temperature inversions were more intense than during the following period. While a dry-out developed in the troposphere below about 300 hPa, the precipitation of ice crystals in the surface-based temperature inversion layer was generated by deposition of moisture that had become trapped in the boundary layer after being transported onto the continent by the previous blocking ridge. This mechanism has not been previously reported elsewhere. During the second half of the warm period, a ridge of high pressure (the Transcontinental Ridge) traversed East Antarctica almost completely, and its western section was amplified by the merging of the Solitary High with a preceding quasi-stationary Rossby wave train propagating along the Southern Ocean. This ridge allowed an intrusion of warm, moist air from the Weddell Sea toward the station, which generated precipitation throughout the whole troposphere by orographic uplift once again, and ended the dry-out. This represents the typical mechanism of both moisture transportation and the generation of

  4. Going, Going, Gone: Localizing Abrupt Offsets of Moving Objects

    ERIC Educational Resources Information Center

    Maus, Gerrit W.; Nijhawan, Romi

    2009-01-01

    When a moving object abruptly disappears, this profoundly influences its localization by the visual system. In Experiment 1, 2 aligned objects moved across the screen, and 1 of them abruptly disappeared. Observers reported seeing the objects misaligned at the time of the offset, with the continuing object leading. Experiment 2 showed that the…

  5. Why were Past North Atlantic Warming Conditions Associated with Drier Climate in the Western United States?

    NASA Astrophysics Data System (ADS)

    Wong, C. I.; Potter, G. L.; Montanez, I. P.; Otto-Bliesner, B. L.; Behling, P.; Oster, J. L.

    2014-12-01

    Investigating climate dynamics governing rainfall over the western US during past warmings and coolings of the last glacial and deglaciation is pertinent to understanding how precipitation patterns might change with future global warming, especially as the processes driving the global hydrological reorganization affecting this drought-prone region during these rapid temperature changes remain unresolved. We present model climates of the Bølling warm event (14,500 years ago) and Younger Dryas cool event (12,200 years ago) that i) uniquely enable the assessment of dueling hypothesis about the atmospheric teleconnections responsible for abrupt temperature shifts in the North Atlantic region to variations in moisture conditions across the western US, and ii) show that existing hypotheses about these teleconnections are unsupported. Modeling results show no evidence for a north-south shift of the Pacific winter storm track, and we argue that a tropical moisture source with evolving trajectory cannot explain alternation between wet/dry conditions, which have been reconstructed from the proxy record. Alternatively, model results support a new hypothesis that variations in the intensity of the winter storm track, corresponding to its expansion/contraction, can account for regional moisture differences between warm and cool intervals of the last deglaciation. Furthermore, we demonstrate that the mechanism forcing the teleconnection between the North Atlantic and western US is the same across different boundary conditions. In our simulation, during the last deglaciation, and in simulations of future warming, perturbation of the Rossby wave structure reconfigures the atmospheric state. This reconfiguration affects the Aleutian Low and high-pressure ridge over and off of the northern North American coastline driving variability in the storm track. Similarity between the processes governing the climate response during these distinct time intervals illustrates the robust nature

  6. Investigating an Apparent Warming Event in the Southern Ocean During the Late Miocene (11.5-11.0 Ma): Foraminiferal and Geochemical Results from IODP Expedition 318 Site U1361 Wilkes Land, Antarctica

    NASA Astrophysics Data System (ADS)

    DeCesare, M.; Pekar, S. F.

    2012-12-01

    High-resolution isotope and foraminiferal biofacies records are being developed from samples obtained from IODP Expedition 318 Site U1361 to investigate a transient warming event that effected the Southern Ocean and Antarctica during the Late Miocene (11.5-11.0 Ma). The Pagodroma Group are proximal glaciomarine strata and provide evidence that the Lambert Glacier had receded up 300 km inland from its present-day grounding line between 12.1 and 8.5 Ma. Four cores, 34X-37X (311.6-349.99 mbsf), recovered from Site U1361 and dated at 11.5-11.0 Ma, contain a sedimentary archive suggestive of a transient warming event. With excellent core recovery and good preservation of foraminifers, it will be possible to document the extent and duration of this warming event. Integrated biostratigraphy and magnetostratigraphy, as well as high sedimentation rates of ~69 m/106 yr allow for excellent age control. These cores were drilled in 3,466 meters water depth on the continental rise, ~280km offshore from Wilkes Land. Foraminiferal abundances are variable, with specimens ranging from rare to relatively high abundances. Planktonic foraminifers are dominated by Globigerina bulloides, while benthic foraminiferal assemblages include Oridorsalis Umbonatus, Cibicidoides Wuellertorfi, Cibicidoides Bradyi, and Epistominella Exigua. Shipboard studies recognized apparent cyclicity in the sediments, which shows good correlation with 41-kyr obliquity cycles. This is supported by comparing foraminiferal abundances to sediment luminosity (total light reflectance or L*). These changes in foraminiferal abundances are interpreted to represent a periodic deepening of the lysocline and carbonate compensation depth. Stable isotope (δ18O and δ13C) records are being developed to reconstruct bottom and surface water conditions and place constraints on changes in Southern Ocean dynamics. Mg/Ca and Li/Ca ratio records are being obtained using laser ablation-inductively coupled plasma-mass spectrometry

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

    NASA Astrophysics Data System (ADS)

    Hearty, P. J.

    2005-12-01

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

  8. Icebergs not the trigger for North Atlantic cold events.

    PubMed

    Barker, Stephen; Chen, James; Gong, Xun; Jonkers, Lukas; Knorr, Gregor; Thornalley, David

    2015-04-16

    Abrupt climate change is a ubiquitous feature of the Late Pleistocene epoch. In particular, the sequence of Dansgaard-Oeschger events (repeated transitions between warm interstadial and cold stadial conditions), as recorded by ice cores in Greenland, are thought to be linked to changes in the mode of overturning circulation in the Atlantic Ocean. Moreover, the observed correspondence between North Atlantic cold events and increased iceberg calving and dispersal from ice sheets surrounding the North Atlantic has inspired many ocean and climate modelling studies that make use of freshwater forcing scenarios to simulate abrupt change across the North Atlantic region and beyond. On the other hand, previous studies identified an apparent lag between North Atlantic cooling events and the appearance of ice-rafted debris over the last glacial cycle, leading to the hypothesis that iceberg discharge may be a consequence of stadial conditions rather than the cause. Here we further establish this relationship and demonstrate a systematic delay between pronounced surface cooling and the arrival of ice-rafted debris at a site southwest of Iceland over the past four glacial cycles, implying that in general icebergs arrived too late to have triggered cooling. Instead we suggest that--on the basis of our comparisons of ice-rafted debris and polar planktonic foraminifera--abrupt transitions to stadial conditions should be considered as a nonlinear response to more gradual cooling across the North Atlantic. Although the freshwater derived from melting icebergs may provide a positive feedback for enhancing and or prolonging stadial conditions, it does not trigger northern stadial events. PMID:25877202

  9. Abrupt Climate Change Caused by Global Fires from a Large Meteor Impact

    NASA Astrophysics Data System (ADS)

    Bardeen, C.; Toon, O. B.; Garcia, R. R.; Otto-Bliesner, B. L.; Wolf, E. T.

    2015-12-01

    Global or near-global fires like those that are thought to have occurred after the Chicxulub asteroid impact are associated with abrupt climate change and the K-Pg mass extinction event. Using the Community Earth System Model (CESM), a three-dimensional coupled climate model with interactive chemistry, we have simulated the climate response to global fires assuming a burden of 70,000 Tg, as estimated from the K-Pg layer sediments by Wolbach et al. (1988). Soot aerosols are lofted by solar heating and remain in the atmosphere for about 6 years, warming the stratosphere by more than 240 K and suppressing completely solar radiation at the surface for 2 years. Global average land surface temperatures cool by -28 K after 3 years and ocean temperatures by -11 K after 4 years. Precipitation is reduced by 80 % for 5 years, and the ozone column is reduced by 80 % for 4 years. The tropical tropopause cold point disappears for a few years, leading to water vapor mixing ratios of > 1000 ppmv in the stratosphere. There is a rapid recovery around year 6, when the soot is removed by wet deposition as stratospheric water condenses and precipitates, but this is followed by a peak in the UV Index in the tropics of over 40 before stratospheric ozone recovers. Ocean temperature cools by more than -2 K to a depth of 300 m, and sea ice develops in the Black Sea, Caspian Sea, and Baltic Sea. Global fires, two years of darkness, extreme surface cooling, significant ocean cooling, increases in sea ice extent and a large short-term increase in UV Index would have been catastrophic for many life forms. This work is the first step in an effort to simulate the climatic effects of all of the aerosols and gases that may have been generated by the Chicxulub impact in a model that has been configured for late-Cretaceous conditions to help assess the role of the Chicxulub impact in the K-Pg extinction.

  10. Delayed flowering and global warming

    NASA Astrophysics Data System (ADS)

    Cook, B. I.; Wolkovich, E. M.; Parmesan, C.

    2011-12-01

    Within general trends toward earlier spring, observed cases of species and ecosystems that have not advanced their phenology, or have even delayed it, appear paradoxical, especially when made in temperate regions experiencing significant warming. The typical interpretation of this pattern has been that non-responders are insensitive to relatively small levels of warming over the past 40 years, while species showing delays are often viewed as statistical noise or evidence for unknown confounding factors at play. However, plant physiology studies suggest that when winter chilling (vernalization) is required to initiate spring development, winter warming may retard spring events, masking expected advances caused by spring warming. Here, we analyzed long-term data on phenology and seasonal temperatures from 490 species on two continents and demonstrate that 1) apparent non-responders are indeed responding to warming, but their responses to winter and spring warming are opposite in sign, 2) observed trends in first flowering date depend strongly on the magnitude of a given species' response to autumn/winter versus spring warming, and 3) inclusion of these effects strongly improves hindcast predictions of long-term flowering trends. With a few notable exceptions, climate change research has focused on the overall mean trend towards phenological advance, minimizing discussion of apparently non-responding species. Our results illuminate an under-studied source of complexity in wild species responses and support the need for models incorporating diverse environmental cues in order to improve predictability of species responses to anthropogenic climate change.

  11. Abrupt shifts in Horn of Africa hydroclimate and the influence of the Indian Ocean (Invited)

    NASA Astrophysics Data System (ADS)

    Tierney, J. E.; deMenocal, P. B.

    2013-12-01

    The timing and abruptness with which Northeast Africa transitioned into and out of the Early Holocene African Humid Period is a subject of ongoing debate, with direct consequences for our understanding of climate stability and paleoenvironments. Here we present a new proxy record of regional hydroclimate, based on the hydrogen isotopic composition of leaf waxes, from a marine core in the Gulf of Aden that documents rapid, century-scale transitions into and out of the African Humid Period across the Horn of Africa. The Gulf of Aden record also documents large drying events during the last deglacial, synchronous with Heinrich Event 1 and the Younger Dryas. Similar and generally synchronous abrupt transitions at other East African sites suggest that rapid shifts in hydroclimate are regionally coherent. In addition, the termination of the African Humid Period in East Africa is synchronous with the termination along the western Saharan margin. A probabilistic analysis of the abruptness of the transitions in East Africa suggests that they likely occurred within centuries, underscoring the sensitivity of northeast African hydroclimate to external forcings. We speculate that the non-linear behavior of hydroclimate in the Horn of Africa is related to convection thresholds in the western Indian Ocean, and test this hypothesis with preliminary SST proxy data.

  12. Agulhas salt-leakage oscillations during abrupt climate changes of the Late Pleistocene

    NASA Astrophysics Data System (ADS)

    Marino, Gianluca; Zahn, Rainer; Ziegler, Martin; Purcell, Conor; Knorr, Gregor; Hall, Ian R.; Ziveri, Patrizia; Elderfield, Henry

    2013-09-01

    An ensemble of new, high-resolution records of surface ocean hydrography from the Indian-Atlantic oceanic gateway, south of Africa, demonstrates recurrent and high-amplitude salinity oscillations in the Agulhas Leakage area during the penultimate glacial-interglacial cycle. A series of millennial-scale salinification events, indicating strengthened salt leakage into the South Atlantic, appear to correlate with abrupt changes in the North Atlantic climate and Atlantic Meridional Overturning Circulation (AMOC). This interhemispheric coupling, which plausibly involved changes in the Hadley Cell and midlatitude westerlies that impacted the interocean transport at the tip of Africa, suggests that the Agulhas Leakage acted as a source of negative buoyancy for the perturbed AMOC, possibly aiding its return to full strength. Our finding points to the Indian-to-Atlantic salt transport as a potentially important modulator of the AMOC during the abrupt climate changes of the Late Pleistocene.

  13. Globally synchronous ice core volcanic tracers and abrupt cooling during the last glacial period

    USGS Publications Warehouse

    Bay, R.C.; Bramall, N.E.; Price, P.B.; Clow, G.D.; Hawley, R.L.; Udisti, R.; Castellano, E.

    2006-01-01

    We perform a Monte Carlo pattern recognition analysis of the coincidence between three regional volcanic histories from ice coring of Greenland and Antarctica over the period 2 to 45 ka, using SO4 anomalies in Greenland and East Antarctica determined by continuous core chemistry, together with West Antarctic volcanic ash layers determined by remote optical borehole logging and core assays. We find that the Antarctic record of volcanism correlates with Glacial abrupt climate change at a 95% to >99.8% (???3??) significance level and that volcanic depositions at the three locations match at levels exceeding 3??, likely indicating that many common horizons represent single eruptive events which dispersed material world wide. These globally coincident volcanics were associated with abrupt cooling, often simultaneous with onsets or sudden intensifications of millennial cold periods. The striking agreement between sites implies that the consistency of current timescales obtained by isotopic and glaciological dating methods is better than estimated. Copyright 2006 by the American Geogphysical Union.

  14. The Role of the Tropics in Abrupt Climate Changes

    SciTech Connect

    Fedorov, Alexey

    2013-12-07

    Topics addressed include: abrupt climate changes and ocean circulation in the tropics; what controls the ocean thermal structure in the tropics; a permanent El Niño in paleoclimates; the energetics of the tropical ocean.

  15. The Sudden Stratospheric Warming Atlas

    NASA Astrophysics Data System (ADS)

    Sjoberg, J. P.; Butler, A. H.; Seidel, D. J.

    2015-12-01

    Sudden stratospheric warmings (SSWs) are large and rapid temperature increases in the polar stratosphere associated with a complete reversal of the climatological westerly winds in wintertime. These extreme events can have substantial impacts on wintertime surface climate, such as cold air outbreaks over North America and Eurasia, or anomalous warming over Greenland. Here we promote our progress towards a new atlas of historical SSW events and their impacts on the surface. The SSW atlas contains a variety of metrics, time series, maps, and animations for individual SSW events. The atlas will allow users to examine the structure and development of individual SSWs, the variability between events, the surface impacts in temperature and precipitation, and the impacts of SSWs during years with certain tropospheric signatures, like El Niño or La Niña winters.

  16. Status Cataplecticus Precipitated by Abrupt Withdrawal of Venlafaxine

    PubMed Central

    Wang, Janice; Greenberg, Harly

    2013-01-01

    Status cataplecticus is a rare manifestation of narcolepsy with cataplexy episodes recurring for hours or days, without a refractory period, in the absence of emotional triggers. This case highlights a narcoleptic patient who developed status cataplecticus after abrupt withdrawal of venlafaxine. Citation: Wang J; Greenberg H. Status cataplecticus precipitated by abrupt withdrawal of venlafaxine. J Clin Sleep Med 2013;9(7):715-716. PMID:23853567

  17. Simulated sudden stratospheric warming - Synoptic evolution

    NASA Technical Reports Server (NTRS)

    Blackshear, W. T.; Grose, W. L.; Turner, R. E.

    1987-01-01

    An analysis is presented of a sudden stratospheric warming event which occurred spontaneously during a general circulation model simulation of the global atmospheric circulation. Two separate warming pulses exhibit the same dynamical evolution with a 'cycle' of about two weeks. Two distinct phases of the warming cycle are apparent: (1) the generation of an intense localized warm cell in conjunction with significant adiabatic heating associated with cross-isobar flow which has been induced by vertically propagating long wave disturbances; and (2) the northward transport of that warm cell via advection by the essentially geostrophic windfield corresponding to an intense, offset polar cyclone, in conjunction with a strong Aleutian anticyclone. During the first warming pulse in January, a moderate Aleutian anticyclone was in place prior to the warming cycle and was intensified by interaction with an eastward traveling anticyclone induced by the differential advection of the warm cell. The second warming pulse occurred in early February with a strong Aleutian anticyclone already established. In contrast to the January event, the warming in February culminated with reversal of the zonal westerlies to easterlies over a significant depth of the stratosphere.

  18. Abrupt changes in the Northern Hemisphere large-scale flow in the summer to winter seasonal transition

    SciTech Connect

    Houghton, D.D.; Keller, L.M.

    1997-11-01

    The purpose of this study is to quantitatively identify the overall characteristics of the abrupt changes in atmospheric circulation patterns during the extratropical transition season from summer to winter. Both observations and comprehensive global atmospheric model simulations are examined. Emphasis is placed on the large scale and overall Northern Hemisphere circulation characteristics. A testing procedure for abrupt changes is developed, incorporating several established approaches. The analysis found significant abrupt change events in all the observational and model simulation years. The mean dates for the changes are September 7 and 22 for the observations and model, respectively, but there is considerable variability in the dates from year to year. The large scale patterns associated with the abrupt change have a hemispheric scope with centers of activity in the western Pacific and Atlantic sectors. The model captures the general nature of the abrupt shifts. However, the model simulations have smaller magnitudes in kinetic energy values and changes than observed, especially in the Atlantic Ocean and central Asia areas. These limitations should not negate the utility of the model for process studies. 17 refs., 7 figs.

  19. Carbon cycle: Global warming then and now

    NASA Astrophysics Data System (ADS)

    Stassen, Peter

    2016-04-01

    A rapid warming event 55.8 million years ago was caused by extensive carbon emissions. The rate of change of carbon and oxygen isotopes in marine shelf sediments suggests that carbon emission rates were much slower than anthropogenic emissions.

  20. Global Warming And Meltwater

    NASA Astrophysics Data System (ADS)

    Bratu, S.

    2012-04-01

    glaciers, permafrost and sea ice. Other likely effects of the warming include more frequent occurrences of extreme weather events including heat waves, droughts and heavy rainfall events, species extinctions due to shifting temperature regimes, and changes in agricultural yields. Meltwater is the water released by the melting of snow or ice, including glacial ice and ice shelves in the oceans. Meltwater is often found in the ablation zone of glaciers, where the rate of snow cover is reduced. In a report published in June 2007, the United Nations Environment Program estimated that global warming could lead to 40% of the world's population being affected by the loss of glaciers, snow and the associated meltwater in Asia. This is one of many activities of the physics laboratory that the students of our high school are involved in.

  1. Fungal decomposition of terrestrial organic matter accelerated Early Jurassic climate warming

    PubMed Central

    Pieńkowski, Grzegorz; Hodbod, Marta; Ullmann, Clemens V.

    2016-01-01

    Soils – constituting the largest terrestrial carbon pool - are vulnerable to climatic warming. Currently existing uncertainties regarding carbon fluxes within terrestrial systems can be addressed by studies of past carbon cycle dynamics and related climate change recorded in sedimentary successions. Here we show an example from the Early Jurassic (early Toarcian, c. 183 mya) marginal-marine strata from Poland, tracking the hinterland response to climatic changes through a super-greenhouse event. In contrast to anoxia-related enhanced carbon storage in coeval open marine environments, Total Organic Carbon (TOC) concentrations in the Polish successions are substantially reduced during this event. Increasing temperature favoured fungal-mediated decomposition of plant litter – specifically of normally resistant woody tissues. The associated injection of oxidized organic matter into the atmosphere corresponds to abrupt changes in standing vegetation and may have contributed significantly to the amplified greenhouse climate on Earth. The characteristic Toarcian signature of multiple warm pulses coinciding with rapidly decreasing carbon isotope ratios may in part be the result of a radical reduction of the terrestrial carbon pool as a response to climate change. PMID:27554210

  2. Fungal decomposition of terrestrial organic matter accelerated Early Jurassic climate warming.

    PubMed

    Pieńkowski, Grzegorz; Hodbod, Marta; Ullmann, Clemens V

    2016-01-01

    Soils - constituting the largest terrestrial carbon pool - are vulnerable to climatic warming. Currently existing uncertainties regarding carbon fluxes within terrestrial systems can be addressed by studies of past carbon cycle dynamics and related climate change recorded in sedimentary successions. Here we show an example from the Early Jurassic (early Toarcian, c. 183 mya) marginal-marine strata from Poland, tracking the hinterland response to climatic changes through a super-greenhouse event. In contrast to anoxia-related enhanced carbon storage in coeval open marine environments, Total Organic Carbon (TOC) concentrations in the Polish successions are substantially reduced during this event. Increasing temperature favoured fungal-mediated decomposition of plant litter - specifically of normally resistant woody tissues. The associated injection of oxidized organic matter into the atmosphere corresponds to abrupt changes in standing vegetation and may have contributed significantly to the amplified greenhouse climate on Earth. The characteristic Toarcian signature of multiple warm pulses coinciding with rapidly decreasing carbon isotope ratios may in part be the result of a radical reduction of the terrestrial carbon pool as a response to climate change. PMID:27554210

  3. An abrupt change in the African monsoon at the end of the Younger Dryas

    NASA Astrophysics Data System (ADS)

    Talbot, Michael R.; Filippi, Maria Letizia; Jensen, Niels Bo; Tiercelin, Jean-Jacques

    2007-03-01

    High-resolution studies of variations in the elemental and stable carbon- and nitrogen-isotope composition of organic matter in cores from Lakes Malawi, Tanganyika, and Bosumtwi (tropical Africa) indicate an abrupt change in the wind-driven circulation of these lakes that, within the limits of available chronologies, was contemporaneous with the end of the Younger Dryas in the northern hemisphere. The change was also coincident with shifts in surface winds recorded in cores from off the west and northeast coasts of Africa. A range of other proxies indicate that these changes in wind regime were accompanied by a marked increase in precipitation in the northern tropics. Africa south of ˜5°-10°S, on the other hand, initially suffered drought conditions. Together, the evidence suggests an abrupt northward translation of the African monsoon system at circa 11.5 ± 0.25 ka B.P. The data assembled here contribute to a growing body of work showing that the Younger Dryas was a major climatic excursion in tropical Africa. Furthermore, they add substance to recent suggestions that climatic events in the southern hemisphere may have played a significant role in the abrupt demise of the Younger Dryas.

  4. Controls on the abruptness of gravel-sand transitions

    NASA Astrophysics Data System (ADS)

    Venditti, J. G.; Church, M. A.; Lamb, M. P.; Domarad, N.; Rennie, C. D.

    2014-12-01

    As gravel-bedded rivers fine downstream, they characteristically exhibit an abrupt transition from gravel- to sand-bed. This is the only abrupt transition in grain-size that occurs in the fluvial system and has attracted considerable attention. A number of competing theories have been proposed to account for the abruptness of the transition, including base-level control, attrition of ~10mm gravel to produce sand, and sediment sorting processes. The prevailing theory for the emergence of abrupt transitions is size selective sorting of bimodal sediment wherein gravel deposits due to downstream declining shear stress, fining the bedload until a sand-bed emerges. We explored this hypothesis by examining grain-size, shear stress, gravel mobility and sand suspension thresholds through the gravel-sand transition (GST) of the Fraser River, British Columbia. The Fraser GST is an arrested gravel wedge with patches of gravel downstream of the wedge forming a diffuse extension. There is an abrupt change in bed slope through the transition that leads to an abrupt change in shear stress. The GST, bed-slope change and backwater caused by the ocean are all coincident spatially, which enhances the sharpness of the GST. Interestingly, the bimodal reach of the river occurs downstream of the GST and exhibits no downstream gradients in shear stress, suspended sediment flux, gravel mobility or sand suspension thresholds. This calls into question the prevailing theory for the emergence of an abrupt GST by size selective sorting. We provide evidence, both empirical and theoretical, that suggests the emergence of an abrupt GST is caused by rapid deposition of sand when fine gravel deposits. We argue that the emergence of gravel-sand transitions is a consequence of gravel-bedded rivers adopting a steeper slope than sand-bedded rivers. The abruptness arises because the bed slope required to convey the gravel load fixes the distal location of a terminal gravel wedge, and once the river has

  5. North Atlantic ocean circulation and abrupt climate change during the last glaciation.

    PubMed

    Henry, L G; McManus, J F; Curry, W B; Roberts, N L; Piotrowski, A M; Keigwin, L D

    2016-07-29

    The most recent ice age was characterized by rapid and hemispherically asynchronous climate oscillations, whose origin remains unresolved. Variations in oceanic meridional heat transport may contribute to these repeated climate changes, which were most pronounced during marine isotope stage 3, the glacial interval 25 thousand to 60 thousand years ago. We examined climate and ocean circulation proxies throughout this interval at high resolution in a deep North Atlantic sediment core, combining the kinematic tracer protactinium/thorium (Pa/Th) with the deep water-mass tracer, epibenthic δ(13)C. These indicators suggest reduced Atlantic overturning circulation during every cool northern stadial, with the greatest reductions during episodic Hudson Strait iceberg discharges, while sharp northern warming followed reinvigorated overturning. These results provide direct evidence for the ocean's persistent, central role in abrupt glacial climate change. PMID:27365315

  6. North Atlantic ocean circulation and abrupt climate change during the last glaciation

    NASA Astrophysics Data System (ADS)

    Henry, L. G.; McManus, J. F.; Curry, W. B.; Roberts, N. L.; Piotrowski, A. M.; Keigwin, L. D.

    2016-07-01

    The most recent ice age was characterized by rapid and hemispherically asynchronous climate oscillations, whose origin remains unresolved. Variations in oceanic meridional heat transport may contribute to these repeated climate changes, which were most pronounced during marine isotope stage 3, the glacial interval 25 thousand to 60 thousand years ago. We examined climate and ocean circulation proxies throughout this interval at high resolution in a deep North Atlantic sediment core, combining the kinematic tracer protactinium/thorium (Pa/Th) with the deep water-mass tracer, epibenthic δ13C. These indicators suggest reduced Atlantic overturning circulation during every cool northern stadial, with the greatest reductions during episodic Hudson Strait iceberg discharges, while sharp northern warming followed reinvigorated overturning. These results provide direct evidence for the ocean’s persistent, central role in abrupt glacial climate change.

  7. The abrupt climate change near 4,400 yr BP on the cultural transition in Yuchisi, China and its global linkage

    PubMed Central

    Wang, Jianjun; Sun, Liguang; Chen, Liqi; Xu, Libin; Wang, Yuhong; Wang, Xinming

    2016-01-01

    Extreme climatic events have profound impacts on human society. Here we present the results of a study of organic biomarkers within a sedimentary section at the archaeological site of Yuchisi, eastern China, in order to reconstruct climatic variability during the Dawenkou (5,050–4,400 yr BP) and Longshan (4,400–4,000 yr BP) cultures. At ~4,400 yr BP, within the cultural transition horizon, abrupt changes in biomarkers, such as the fatty acid ratio C18:2/C18:0, 2C31/(C27 + C29), n-C18-ol and n-C30-ol, indicate the occurrence of local climate changes over the course of a few decades. These changes occurred during the transition from the Holocene warm period to a subsequent cold period which lasted for the following 600 years. This climatic shift has been recorded at numerous sites worldwide, and it is likely to have been the main cause of the widespread collapse of many isolated cultures at that time. The palaeoclimatic and archaeological data from the Yuchisi sediments may provide new insights into the relationship between climate change and prehistoric cultural transitions. PMID:27283832

  8. The abrupt climate change near 4,400 yr BP on the cultural transition in Yuchisi, China and its global linkage.

    PubMed

    Wang, Jianjun; Sun, Liguang; Chen, Liqi; Xu, Libin; Wang, Yuhong; Wang, Xinming

    2016-01-01

    Extreme climatic events have profound impacts on human society. Here we present the results of a study of organic biomarkers within a sedimentary section at the archaeological site of Yuchisi, eastern China, in order to reconstruct climatic variability during the Dawenkou (5,050-4,400 yr BP) and Longshan (4,400-4,000 yr BP) cultures. At ~4,400 yr BP, within the cultural transition horizon, abrupt changes in biomarkers, such as the fatty acid ratio C18:2/C18:0, 2C31/(C27 + C29), n-C18-ol and n-C30-ol, indicate the occurrence of local climate changes over the course of a few decades. These changes occurred during the transition from the Holocene warm period to a subsequent cold period which lasted for the following 600 years. This climatic shift has been recorded at numerous sites worldwide, and it is likely to have been the main cause of the widespread collapse of many isolated cultures at that time. The palaeoclimatic and archaeological data from the Yuchisi sediments may provide new insights into the relationship between climate change and prehistoric cultural transitions. PMID:27283832

  9. The abrupt climate change near 4,400 yr BP on the cultural transition in Yuchisi, China and its global linkage

    NASA Astrophysics Data System (ADS)

    Wang, Jianjun; Sun, Liguang; Chen, Liqi; Xu, Libin; Wang, Yuhong; Wang, Xinming

    2016-06-01

    Extreme climatic events have profound impacts on human society. Here we present the results of a study of organic biomarkers within a sedimentary section at the archaeological site of Yuchisi, eastern China, in order to reconstruct climatic variability during the Dawenkou (5,050–4,400 yr BP) and Longshan (4,400–4,000 yr BP) cultures. At ~4,400 yr BP, within the cultural transition horizon, abrupt changes in biomarkers, such as the fatty acid ratio C18:2/C18:0, 2C31/(C27 + C29), n-C18-ol and n-C30-ol, indicate the occurrence of local climate changes over the course of a few decades. These changes occurred during the transition from the Holocene warm period to a subsequent cold period which lasted for the following 600 years. This climatic shift has been recorded at numerous sites worldwide, and it is likely to have been the main cause of the widespread collapse of many isolated cultures at that time. The palaeoclimatic and archaeological data from the Yuchisi sediments may provide new insights into the relationship between climate change and prehistoric cultural transitions.

  10. How warm days increase belief in global warming

    NASA Astrophysics Data System (ADS)

    Zaval, Lisa; Keenan, Elizabeth A.; Johnson, Eric J.; Weber, Elke U.

    2014-02-01

    Climate change judgements can depend on whether today seems warmer or colder than usual, termed the local warming effect. Although previous research has demonstrated that this effect occurs, studies have yet to explain why or how temperature abnormalities influence global warming attitudes. A better understanding of the underlying psychology of this effect can help explain the public's reaction to climate change and inform approaches used to communicate the phenomenon. Across five studies, we find evidence of attribute substitution, whereby individuals use less relevant but available information (for example, today's temperature) in place of more diagnostic but less accessible information (for example, global climate change patterns) when making judgements. Moreover, we rule out alternative hypotheses involving climate change labelling and lay mental models. Ultimately, we show that present temperature abnormalities are given undue weight and lead to an overestimation of the frequency of similar past events, thereby increasing belief in and concern for global warming.

  11. Abrupt climate-triggered lake ecosystem changes recorded in late glacial lake sediments in northern Poland

    NASA Astrophysics Data System (ADS)

    Slowinski, M. M.; Zawiska, I.; Ott, F.; Noryskiewicz, A. M.; Apolinarska, K.; Lutynska, M.; Michczynska, D. J.; Brauer, A.; Wulf, S.; Skubala, P.; Blaszkiewicz, M.

    2013-12-01

    The aim of this study was to better understand how local lake ecosystems responded to abrupt climate changes through applying multi-proxy sediment analyses. Therefore, we carried out a detailed and high-resolution case study on the late glacial sediment from the Trzechowskie palaeolake located in the eastern part of the Pomeranian Lakeland, northern Poland. We reconstructed climate induced environmental changes in the paleolake and its catchment using biotic proxies (macrofossils, pollen, cladocera, diatoms, oribatidae mite) and classical geochemical proxies (δ18O, δ13C, loss-on-ignition, CaCO3 content) in combination with high-resolution μ-XRF element core scanning. The core chronology has been established by means of biostratigraphy, AMS 14C-dating on plant macro remains, varve counting in laminated intervals and tephrochronology. The latter was possible by the discovery of the late Allerød Laacher See Tephra for the first time at such eastern location. Biogenic accumulation in the lake started rather late during the lateglacial interstadial at 13903×170 cal yrs BP. The rapid and pronounced cooling at the beginning of the Younger Dryas had a major impact on the lake and its catchment as clearly reflected by both, biotic and geochemical proxies. The depositional environment of the lake abruptly changed from a varved to massive gytjia. The pronounced warming at the demise of Younger Dryas cooling is well-reflected in all environmental indicators but with conspicuous leads and lags reflecting complex responses of lake ecosystems to climate warming. The research was supported by the National Science Centre Poland - NN306085037. This study is a contribution to the Virtual Institute ICLEA (Integrated Climate and Landscape Evolution Analysis) funded by the Helmholtz Association.

  12. Beam losses due to abrupt crab cavity failures in the LHC

    SciTech Connect

    Baer, T.; Barranco, J.; Calaga, R.; Tomas, R.; Wenninger, B.; Yee, B.; Zimmermann, F.

    2011-03-28

    A major concern for the implementation of crab crossing in a future High-Luminosity LHC (HL-LHC) is machine protection in an event of a fast crab-cavity failure. Certain types of abrupt crab-cavity amplitude and phase changes are simulated to characterize the effect of failures on the beam and the resulting particle-loss signatures. The time-dependent beam loss distributions around the ring and particle trajectories obtained from the simulations allow for a first assessment of the resulting beam impact on LHC collimators and on sensitive components around the ring. Results for the nominal LHC lattice is presented.

  13. Sensitivity and Thresholds of Ecosystems to Abrupt Climate Change

    NASA Astrophysics Data System (ADS)

    Peteet, D. M.; Peteet, D. M.

    2001-12-01

    Rapid vegetational change is a hallmark of past abrupt climate change, as evidenced from Younger Dryas records in Europe, eastern North America, and the Pacific North American rim. The potential response of future ecosystems to abrupt climate change is targeted, with a focus on particular changes in the hydrological cycle. The vulnerability of ecosystems is notable when particular shifts cross thresholds of precipitation and temperature, as many plants and animals are adapted to specific climatic "windows". Significant forest species compositional changes occur at ecotonal boundaries, which are often the first locations to record a climatic response. Historical forest declines have been linked to stress, and even Pleistocene extinctions have been associated with human interaction at times of rapid climatic shifts. Environmental extremes are risky for reproductive stages, and result in nonlinearities. The role of humans in association with abrupt climate change suggests that many ecosystems may cross thresholds from which they will find it difficult to recover. Sectors particularly vulnerable will be reviewed.

  14. Ocean surface conditions on the SE Greenland shelf during the last millennium - from abrupt changes to centennial variability

    NASA Astrophysics Data System (ADS)

    Miettinen, Arto; Divine, Dmitry; Husum, Katrine; Koç, Nalan; Jennings, Anne

    2016-04-01

    August sea surface temperatures (aSST) and April sea-ice concentrations (aSIC) covering the last 2900 years have been reconstructed in order to investigate the variability of summer surface conditions along possible forcing factors on the SE Greenland shelf. In this diatom-based study, we focus on the interval ca. 870-1910 Common Era (CE) reconstructed at a high temporal resolution of 3-8 years. The results demonstrate both abrupt changes and a clear centennial-bicentennial variability for the last millennium. The Medieval Climate Anomaly (MCA) between 1000 and 1200 CE represents the warmest ocean surface conditions of the SE Greenland shelf over the late Holocene (880 BCE-1910 CE). MCA in the current record is characterized by abrupt, decadal to multidecadal changes, such as an abrupt warming of ~2.4 °C in 55 years around 1000 CE. Temperature changes of these magnitudes are rarely observed in other proxy records from the North Atlantic. Compared to regional air temperature reconstructions, our results indicate a lag of about 50 years in ocean surface warming either due to increased freshwater discharge from the Greenland ice sheet or intensified sea-ice export from the Arctic as a response to atmospheric warming at the beginning of the MCA. A cool phase, from 1200-1890 CE, associated with the Little Ice Age (LIA), ends with the rapid warming of aSST and diminished aSIC in the early 20th century. The phases of warm aSST and aSIC minima on the SE Greenland shelf and solar minima of the last millennium are antiphased, suggesting that solar forcing possibly amplified by atmospheric forcing has been behind the aSST variability on the SE Greenland over the last millennium. The results might indicate decreased sea ice formation on the SE Greenland shelf due to diminished freshwater input from the Greenland Ice Sheet during the cold climate periods. The results show that the SE Greenland shelf is a climatologically sensitive area where extremely rapid changes are

  15. Abrupt variations of Indian and East Asian summer monsoons during the last deglacial stadial and interstadial

    NASA Astrophysics Data System (ADS)

    Hong, Bing; Hong, Yetang; Uchida, Masao; Shibata, Yasuyuki; Cai, Cheng; Peng, Haijun; Zhu, Yongxuan; Wang, Yu; Yuan, Linggui

    2014-08-01

    The phase relationship between the Indian summer monsoon (ISM) and the East Asian summer monsoon (EASM) during the last deglaciation remains controversial. Here, we reconstruct a 15,000-year plant cellulose δ13C proxy record for the ISM from the Yuexi peat bog in southwestern China. The record shows that the ISM abruptly decreases during the Younger Dryas (YD) stadial and abruptly increases during the Bølling-Allerød (BA) interstadial. A comparison of the Yuexi record with other related proxy climate records reveals two types of phenomena. First, the strengths of the two Asian monsoons are inversely related during the YD stadial, i.e., the ISM strength decreases and the EASM increases. During this period, the southern Chinese mainland consisted of a wide arid zone while the northern Chinese mainland was much wetter. The arid zone in southern China resulted from two different types of monsoon processes: the abnormal northward extension of the EASM rain belt, leading to less rainfall in southeast China, or an illusion that the EASM weakened. The other process is a real weakening of the ISM. Second, during the BA interstadial, the strengths of both the ISM and EASM clearly increased. However, the maximum strengths appear to have occurred in the Allerød period. During this period, the entire Chinese mainland, both northern and southern, experienced wet conditions. The abnormal climate pattern of wet in the north and dry in the south during the YD stadial occurs because of the combined effects of the strengthened EASM, intensified westerlies, and weakened ISM, which could be attributed to the response to the abrupt cooling in the high northern latitudes and to the El Niño-like activity in the equatorial Pacific. The widespread wet climate during the BA interstadial may be related to an abrupt increase in the greenhouse gases (GHGs) concentrations in the atmosphere and to the La Niña-like activity in the equatorial Pacific. These results contribute to a better

  16. Abrupt transitions to a cold North Atlantic in the late Holocene

    NASA Astrophysics Data System (ADS)

    Geirsdóttir, Áslaug; Miller, Gifford; Larsen, Darren; Florian, Christopher; Pendleton, Simon

    2015-04-01

    The Holocene provides a time interval with boundary conditions similar to present, except for greenhouse gas concentrations. Recent high-resolution Northern Hemisphere records show general cooling related to orbital terms through the late Holocene, but also highly non-linear abrupt departures of centennial scale summer cold periods. These abrupt departures are evident within the last two millennia (the transitions between the Roman Warm Period (RWP, ~2,000 yr BP), the Dark Ages Cold Period (DACP, ~500-900 years AD), the Medieval Warm Period (MWP, 1000-1200 years AD) and the Little Ice Age (LIA, ~1300-1900 AD). A series of new, high-resolution and securely dated lake records from Iceland also show abrupt climate departures over the past 2 ka, characterized by shifts to persistent cold summers and an expanded cryosphere. Despite substantial differences in catchment-specific processes that dominate the lake records, the multi-proxy reconstructions are remarkably similar. After nearly a millennium with little evidence of significant climate shifts, the beginning of the first millennium AD is characterized by renewed summer cooling that leads to an expanding cryosphere. Slow summer cooling over the first five centuries is succeeded by widespread substantial cooling, with evidence for substantial expansion of glaciers and ice caps throughout our field areas between 530 and 900 AD, and an accompanying reduction in vegetation cover across much of Iceland that led to widespread landscape instability. These data suggest that the North Atlantic system began a transition into a new cold state early in the first millennium AD, which was amplified after 500 AD, until it was interrupted by warmer Medieval times between ~1000 and 1250 AD. Although severe soil erosion in Iceland is frequently associated with human settlement dated to 871 ±2 AD our reconstructions indicate that soil erosion began several centuries before settlement, during the DACP, whereas for several centuries

  17. Abrupt climate change and thermohaline circulation: Mechanisms and predictability

    PubMed Central

    Marotzke, Jochem

    2000-01-01

    The ocean's thermohaline circulation has long been recognized as potentially unstable and has consequently been invoked as a potential cause of abrupt climate change on all timescales of decades and longer. However, fundamental aspects of thermohaline circulation changes remain poorly understood. PMID:10677464

  18. Abrupt Depletion Layer Approximation for the Metal Insulator Semiconductor Diode.

    ERIC Educational Resources Information Center

    Jones, Kenneth

    1979-01-01

    Determines the excess surface change carrier density, surface potential, and relative capacitance of a metal insulator semiconductor diode as a function of the gate voltage, using the precise questions and the equations derived with the abrupt depletion layer approximation. (Author/GA)

  19. Abrupt climate change and thermohaline circulation: mechanisms and predictability.

    PubMed

    Marotzke, J

    2000-02-15

    The ocean's thermohaline circulation has long been recognized as potentially unstable and has consequently been invoked as a potential cause of abrupt climate change on all timescales of decades and longer. However, fundamental aspects of thermohaline circulation changes remain poorly understood. PMID:10677464

  20. Abrupt changes in the dynamics of quantum disentanglement

    SciTech Connect

    Lastra, F.; Romero, G.; Lopez, C. E.; Retamal, J. C.; Franca Santos, M.

    2007-06-15

    The evolution of the lower bound of entanglement proposed by Chen et al. [Phys. Rev. Lett. 95, 210501 (2005)] in high-dimensional bipartite systems under dissipation is studied. Discontinuities for the time derivative of this bound are found depending on the initial conditions for entangled states. These abrupt changes along the evolution of the entanglement bound appear as precursors of sudden death.

  1. Meltwater and Abrupt Climate Change in the Gulf of Mexico During the Last Glacial Termination

    NASA Astrophysics Data System (ADS)

    Williams, C.; Flower, B.; Hastings, D.; Randle, N.

    2008-12-01

    During the Last Glacial Termination from 18,000-8,000 cal. yrs B.P., meltwater routing of the Laurentide Ice Sheet (LIS) may have been linked to abrupt climatic events, such as the Younger Dryas. Previous studies show episodic meltwater input from the LIS, via the Mississippi River to the Gulf of Mexico (GOM) several thousand years before the onset of the Younger Dryas until approximately 13,000 cal yrs B.P., when meltwater routing may have switched to a more northern spillway, causing an abrupt change in thermohaline circulation (THC). The exact timing and magnitude of this meltwater input to the GOM is poorly constrained due to the lack of high-resolution data. Also unknown are the detailed relationships between GOM sea surface temperature, sea surface salinity and ice volume, relative to Northern and Southern Hemisphere climate from Greenland and Antarctica ice core records. High sedimentation rates (~40 cm/kyr) from laminated, anoxic Orca Basin core MD02-2550 provide the necessary resolution to assess GOM paleoceanography. Paired Mg/Ca and δ18O values from planktonic Foraminifera species Globigerinoides ruber (pink and white varieties) provide the relative timing of meltwater input and temperature change in the GOM with nearly decadal resolution. δ18Ocalcite results show multiple cool and/or high salinity periods with isotopic excursions of at least 2‰ that coincide with abrupt climatic events in Greenland ice core records, including the Oldest Dryas from 16,200-15,000 cal. yrs B.P. and the Intra-Allerod Cold Period at 13,860-13,560 cal. yrs B.P. Meltwater input to the GOM is seen for several thousand years before the onset of the Younger Dryas with white G. ruber δ18Ocalcite values as low as -4‰. Thirty-three AMS radiocarbon dates and high-resolution δ18O results provide excellent temporal constraints on deglacial climate events, including an abrupt (<200 yrs) cessation of meltwater in the GOM centered at 10,970± 40 radiocarbon yrs B.P., with a δ18O

  2. Extreme temperatures, foundation species, and abrupt ecosystem change: an example from an iconic seagrass ecosystem.

    PubMed

    Thomson, Jordan A; Burkholder, Derek A; Heithaus, Michael R; Fourqurean, James W; Fraser, Matthew W; Statton, John; Kendrick, Gary A

    2015-04-01

    Extreme climatic events can trigger abrupt and often lasting change in ecosystems via the reduction or elimination of foundation (i.e., habitat-forming) species. However, while the frequency/intensity of extreme events is predicted to increase under climate change, the impact of these events on many foundation species and the ecosystems they support remains poorly understood. Here, we use the iconic seagrass meadows of Shark Bay, Western Australia--a relatively pristine subtropical embayment whose dominant, canopy-forming seagrass, Amphibolis antarctica, is a temperate species growing near its low-latitude range limit--as a model system to investigate the impacts of extreme temperatures on ecosystems supported by thermally sensitive foundation species in a changing climate. Following an unprecedented marine heat wave in late summer 2010/11, A. antarctica experienced catastrophic (>90%) dieback in several regions of Shark Bay. Animal-borne video footage taken from the perspective of resident, seagrass-associated megafauna (sea turtles) revealed severe habitat degradation after the event compared with a decade earlier. This reduction in habitat quality corresponded with a decline in the health status of largely herbivorous green turtles (Chelonia mydas) in the 2 years following the heat wave, providing evidence of long-term, community-level impacts of the event. Based on these findings, and similar examples from diverse ecosystems, we argue that a generalized framework for assessing the vulnerability of ecosystems to abrupt change associated with the loss of foundation species is needed to accurately predict ecosystem trajectories in a changing climate. This includes seagrass meadows, which have received relatively little attention in this context. Novel research and monitoring methods, such as the analysis of habitat and environmental data from animal-borne video and data-logging systems, can make an important contribution to this framework. PMID:25145694

  3. Impact of abrupt deglacial climate change on tropical Atlantic subsurface temperatures

    PubMed Central

    Schmidt, Matthew W.; Chang, Ping; Hertzberg, Jennifer E.; Them, Theodore R.; Ji, Link; Otto-Bliesner, Bette L.

    2012-01-01

    Both instrumental data analyses and coupled ocean-atmosphere models indicate that Atlantic meridional overturning circulation (AMOC) variability is tightly linked to abrupt tropical North Atlantic (TNA) climate change through both atmospheric and oceanic processes. Although a slowdown of AMOC results in an atmospheric-induced surface cooling in the entire TNA, the subsurface experiences an even larger warming because of rapid reorganizations of ocean circulation patterns at intermediate water depths. Here, we reconstruct high-resolution temperature records using oxygen isotope values and Mg/Ca ratios in both surface- and subthermocline-dwelling planktonic foraminifera from a sediment core located in the TNA over the last 22 ky. Our results show significant changes in the vertical thermal gradient of the upper water column, with the warmest subsurface temperatures of the last deglacial transition corresponding to the onset of the Younger Dryas. Furthermore, we present new analyses of a climate model simulation forced with freshwater discharge into the North Atlantic under Last Glacial Maximum forcings and boundary conditions that reveal a maximum subsurface warming in the vicinity of the core site and a vertical thermal gradient change at the onset of AMOC weakening, consistent with the reconstructed record. Together, our proxy reconstructions and modeling results provide convincing evidence for a subsurface oceanic teleconnection linking high-latitude North Atlantic climate to the tropical Atlantic during periods of reduced AMOC across the last deglacial transition. PMID:22908256

  4. Impact of abrupt deglacial climate change on tropical Atlantic subsurface temperatures.

    PubMed

    Schmidt, Matthew W; Chang, Ping; Hertzberg, Jennifer E; Them, Theodore R; Ji, Link; J, Link; Otto-Bliesner, Bette L

    2012-09-01

    Both instrumental data analyses and coupled ocean-atmosphere models indicate that Atlantic meridional overturning circulation (AMOC) variability is tightly linked to abrupt tropical North Atlantic (TNA) climate change through both atmospheric and oceanic processes. Although a slowdown of AMOC results in an atmospheric-induced surface cooling in the entire TNA, the subsurface experiences an even larger warming because of rapid reorganizations of ocean circulation patterns at intermediate water depths. Here, we reconstruct high-resolution temperature records using oxygen isotope values and Mg/Ca ratios in both surface- and subthermocline-dwelling planktonic foraminifera from a sediment core located in the TNA over the last 22 ky. Our results show significant changes in the vertical thermal gradient of the upper water column, with the warmest subsurface temperatures of the last deglacial transition corresponding to the onset of the Younger Dryas. Furthermore, we present new analyses of a climate model simulation forced with freshwater discharge into the North Atlantic under Last Glacial Maximum forcings and boundary conditions that reveal a maximum subsurface warming in the vicinity of the core site and a vertical thermal gradient change at the onset of AMOC weakening, consistent with the reconstructed record. Together, our proxy reconstructions and modeling results provide convincing evidence for a subsurface oceanic teleconnection linking high-latitude North Atlantic climate to the tropical Atlantic during periods of reduced AMOC across the last deglacial transition. PMID:22908256

  5. Deep-Sea Biodiversity Response to Abrupt Deglacial and Holocene Climate Changes

    NASA Astrophysics Data System (ADS)

    Yasuhara, M.

    2014-12-01

    High-resolution records of microfossil assemblages from deep-sea sediment cores covering the last 20,000 years in the North Atlantic Ocean were investigated to understand biotic responses to abrupt climate changes over decadal-centennial timescales. The results show pervasive control of deep-sea benthic species diversity by rapidly changing climate. Species diversity rapidly increased during abrupt stadial events during the last deglacial and the Holocene interglacial periods. These included the well-known Heinrich 1, the Younger Dryas, and the 8.2 ka events when the strength of Atlantic Meridional Overturning Circulation (AMOC) decreased. In addition, there is evidence for quasi-cyclic changes in biodiversity at a ~1500-year periodicity. Statistical analyses revealed that AMOC-driven bottom-water-temperature variability is a primary influence on deep-sea biodiversity. Our results may portend pervasive, synchronous and sudden ecosystem responses to human-induced changes to climate and ocean circulation in this century. Exceptionally highly resolved fossil records help us to understand past, present and future ecosystem responses to climate changes by bridging the gap between biological and palaeontological time-scales.

  6. Reducing abrupt climate change risk using the Montreal Protocol and other regulatory actions to complement cuts in CO2 emissions

    PubMed Central

    Molina, Mario; Zaelke, Durwood; Sarma, K. Madhava; Andersen, Stephen O.; Ramanathan, Veerabhadran; Kaniaru, Donald

    2009-01-01

    Current emissions of anthropogenic greenhouse gases (GHGs) have already committed the planet to an increase in average surface temperature by the end of the century that may be above the critical threshold for tipping elements of the climate system into abrupt change with potentially irreversible and unmanageable consequences. This would mean that the climate system is close to entering if not already within the zone of “dangerous anthropogenic interference” (DAI). Scientific and policy literature refers to the need for “early,” “urgent,” “rapid,” and “fast-action” mitigation to help avoid DAI and abrupt climate changes. We define “fast-action” to include regulatory measures that can begin within 2–3 years, be substantially implemented in 5–10 years, and produce a climate response within decades. We discuss strategies for short-lived non-CO2 GHGs and particles, where existing agreements can be used to accomplish mitigation objectives. Policy makers can amend the Montreal Protocol to phase down the production and consumption of hydrofluorocarbons (HFCs) with high global warming potential. Other fast-action strategies can reduce emissions of black carbon particles and precursor gases that lead to ozone formation in the lower atmosphere, and increase biosequestration, including through biochar. These and other fast-action strategies may reduce the risk of abrupt climate change in the next few decades by complementing cuts in CO2 emissions. PMID:19822751

  7. Combined effects of warming, acidification and changing ocean circulation on the marine carbon cycle during the PETM

    NASA Astrophysics Data System (ADS)

    Heinze, M.; Ilyina, T.

    2014-12-01

    We are studying the ocean biogeochemistry during the Paleocene-Eocene Thermal Maximum (PETM; 55 million years ago) with an Earth System Model (ESM). During this period of abrupt environmental change the climate underwent a significant transformation within short geological timescales (~10 ky). The PETM is globally recorded in proxy-data by a negative δ13C carbon isotope excursion and carbonate dissolution in the ocean, suggesting that the occurred warming was caused by massive carbon release. To investigate the marine biogeochemistry before and during the onset of the PETM we use the ESM of the Max Planck Institute for Meteorology to simulate scenarios with different rates of carbon release over several thousand years. Starting from an already warmer background climate than present, the atmospheric CO2 increase and concomitant warming lead to acidification and deoxygenation of mid and deep ocean waters. Our results indicate that a weakening of deep water formation, caused by global warming, plays a major role in producing inhospitable conditions for benthic organisms during the PETM. We show how the interaction between biological and physical responses to the carbon perturbation lead to the observed calcite sediment dissolution in the deep ocean. At the surface a weakening of the physical and biological carbon pump restricts the oceanic uptake capacity of atmospheric CO2 which helps to maintain elevated atmospheric CO2 concentrations and temperatures throughout the event.

  8. Spontaneous abrupt climate change due to an atmospheric blocking-sea-ice-ocean feedback in an unforced climate model simulation.

    PubMed

    Drijfhout, Sybren; Gleeson, Emily; Dijkstra, Henk A; Livina, Valerie

    2013-12-01

    Abrupt climate change is abundant in geological records, but climate models rarely have been able to simulate such events in response to realistic forcing. Here we report on a spontaneous abrupt cooling event, lasting for more than a century, with a temperature anomaly similar to that of the Little Ice Age. The event was simulated in the preindustrial control run of a high-resolution climate model, without imposing external perturbations. Initial cooling started with a period of enhanced atmospheric blocking over the eastern subpolar gyre. In response, a southward progression of the sea-ice margin occurred, and the sea-level pressure anomaly was locked to the sea-ice margin through thermal forcing. The cold-core high steered more cold air to the area, reinforcing the sea-ice concentration anomaly east of Greenland. The sea-ice surplus was carried southward by ocean currents around the tip of Greenland. South of 70 °N, sea ice already started melting and the associated freshwater anomaly was carried to the Labrador Sea, shutting off deep convection. There, surface waters were exposed longer to atmospheric cooling and sea surface temperature dropped, causing an even larger thermally forced high above the Labrador Sea. In consequence, east of Greenland, anomalous winds changed from north to south, terminating the event with similar abruptness to its onset. Our results imply that only climate models that possess sufficient resolution to correctly represent atmospheric blocking, in combination with a sensitive sea-ice model, are able to simulate this kind of abrupt climate change. PMID:24248352

  9. Spontaneous abrupt climate change due to an atmospheric blocking–sea-ice–ocean feedback in an unforced climate model simulation

    PubMed Central

    Drijfhout, Sybren; Gleeson, Emily; Dijkstra, Henk A.; Livina, Valerie

    2013-01-01

    Abrupt climate change is abundant in geological records, but climate models rarely have been able to simulate such events in response to realistic forcing. Here we report on a spontaneous abrupt cooling event, lasting for more than a century, with a temperature anomaly similar to that of the Little Ice Age. The event was simulated in the preindustrial control run of a high-resolution climate model, without imposing external perturbations. Initial cooling started with a period of enhanced atmospheric blocking over the eastern subpolar gyre. In response, a southward progression of the sea-ice margin occurred, and the sea-level pressure anomaly was locked to the sea-ice margin through thermal forcing. The cold-core high steered more cold air to the area, reinforcing the sea-ice concentration anomaly east of Greenland. The sea-ice surplus was carried southward by ocean currents around the tip of Greenland. South of 70°N, sea ice already started melting and the associated freshwater anomaly was carried to the Labrador Sea, shutting off deep convection. There, surface waters were exposed longer to atmospheric cooling and sea surface temperature dropped, causing an even larger thermally forced high above the Labrador Sea. In consequence, east of Greenland, anomalous winds changed from north to south, terminating the event with similar abruptness to its onset. Our results imply that only climate models that possess sufficient resolution to correctly represent atmospheric blocking, in combination with a sensitive sea-ice model, are able to simulate this kind of abrupt climate change. PMID:24248352

  10. Abrupt increases in Amazonian tree mortality due to drought-fire interactions.

    PubMed

    Brando, Paulo Monteiro; Balch, Jennifer K; Nepstad, Daniel C; Morton, Douglas C; Putz, Francis E; Coe, Michael T; Silvério, Divino; Macedo, Marcia N; Davidson, Eric A; Nóbrega, Caroline C; Alencar, Ane; Soares-Filho, Britaldo S

    2014-04-29

    Interactions between climate and land-use change may drive widespread degradation of Amazonian forests. High-intensity fires associated with extreme weather events could accelerate this degradation by abruptly increasing tree mortality, but this process remains poorly understood. Here we present, to our knowledge, the first field-based evidence of a tipping point in Amazon forests due to altered fire regimes. Based on results of a large-scale, long-term experiment with annual and triennial burn regimes (B1yr and B3yr, respectively) in the Amazon, we found abrupt increases in fire-induced tree mortality (226 and 462%) during a severe drought event, when fuel loads and air temperatures were substantially higher and relative humidity was lower than long-term averages. This threshold mortality response had a cascading effect, causing sharp declines in canopy cover (23 and 31%) and aboveground live biomass (12 and 30%) and favoring widespread invasion by flammable grasses across the forest edge area (80 and 63%), where fires were most intense (e.g., 220 and 820 kW ⋅ m(-1)). During the droughts of 2007 and 2010, regional forest fires burned 12 and 5% of southeastern Amazon forests, respectively, compared with <1% in nondrought years. These results show that a few extreme drought events, coupled with forest fragmentation and anthropogenic ignition sources, are already causing widespread fire-induced tree mortality and forest degradation across southeastern Amazon forests. Future projections of vegetation responses to climate change across drier portions of the Amazon require more than simulation of global climate forcing alone and must also include interactions of extreme weather events, fire, and land-use change. PMID:24733937

  11. Abrupt increases in Amazonian tree mortality due to drought–fire interactions

    PubMed Central

    Brando, Paulo Monteiro; Balch, Jennifer K.; Nepstad, Daniel C.; Morton, Douglas C.; Putz, Francis E.; Coe, Michael T.; Silvério, Divino; Macedo, Marcia N.; Davidson, Eric A.; Nóbrega, Caroline C.; Alencar, Ane; Soares-Filho, Britaldo S.

    2014-01-01

    Interactions between climate and land-use change may drive widespread degradation of Amazonian forests. High-intensity fires associated with extreme weather events could accelerate this degradation by abruptly increasing tree mortality, but this process remains poorly understood. Here we present, to our knowledge, the first field-based evidence of a tipping point in Amazon forests due to altered fire regimes. Based on results of a large-scale, long-term experiment with annual and triennial burn regimes (B1yr and B3yr, respectively) in the Amazon, we found abrupt increases in fire-induced tree mortality (226 and 462%) during a severe drought event, when fuel loads and air temperatures were substantially higher and relative humidity was lower than long-term averages. This threshold mortality response had a cascading effect, causing sharp declines in canopy cover (23 and 31%) and aboveground live biomass (12 and 30%) and favoring widespread invasion by flammable grasses across the forest edge area (80 and 63%), where fires were most intense (e.g., 220 and 820 kW⋅m−1). During the droughts of 2007 and 2010, regional forest fires burned 12 and 5% of southeastern Amazon forests, respectively, compared with <1% in nondrought years. These results show that a few extreme drought events, coupled with forest fragmentation and anthropogenic ignition sources, are already causing widespread fire-induced tree mortality and forest degradation across southeastern Amazon forests. Future projections of vegetation responses to climate change across drier portions of the Amazon require more than simulation of global climate forcing alone and must also include interactions of extreme weather events, fire, and land-use change. PMID:24733937

  12. What caused the 2009 cold event in the Atlantic cold tongue region?

    NASA Astrophysics Data System (ADS)

    Burmeister, Kristin; Brandt, Peter; Lübbecke, Joke F.

    2016-04-01

    The tropical Atlantic (TA) exhibits sea surface temperature (SST) variability on seasonal to inter-annual time scales. This variability is associated with changes of atmospheric dynamics, linking it to severe flooding or droughts in South America and West Africa. This study investigates processes in the TA that might have caused the extreme cold event in the Atlantic cold tongue (ACT) region in 2009. During boreal spring, a strong negative Atlantic meridional mode event developed in the TA associated with northwesterly wind anomalies along the equator. Contrary to what would be expected from ENSO-like dynamics, these wind anomalies did not lead to a warming in the eastern equatorial Atlantic in boreal summer. Instead, from May to August 2009, an abrupt cooling took place in the ACT region resulting in the coldest August ACT SST on record. In the literature, two processes - equatorial wave reflection and meridional advection of subsurface temperatures - are discussed as potential causes of such an event. Whereas previous studies are mainly based on satellite data, reanalysis products and model output, we here use in situ measurements (data from Argo floats, PIRATA buoys, and TACE moorings, as well as CTD data of various ship cruises) in addition to satellite and reanalysis products to investigate the contribution of both processes to the strong surface cooling in the ACT region in 2009. Results based on the Argo float data confirm previous findings that equatorial wave reflection contributed to the cold event in the ACT region in 2009. They further indicate that higher baroclinic mode waves played an important role. The analysis of in situ and reanalysis temperature and velocity data does not suggest a significant contribution of meridional advection of subsurface temperatures for the onset of the 2009 cold event. The results indicate an asymmetry in the importance of meridional advection for non-ENSO-like cold and warm events with warm events more strongly affected

  13. Warm Up with Skill.

    ERIC Educational Resources Information Center

    Hoyle, R. J.; Smith, Robert F.

    1989-01-01

    Too little time is often spent on warm-up activities in the school or recreation class. Warm-ups are often perfunctory and unimaginative. Several suggestions are made for warm-up activities that incorporate both previously learned and new skills, while preparing the body for more vigorous activity. (IAH)

  14. Recommended Experimental Procedures for Evaluation of Abrupt Wing Stall Characteristics

    NASA Technical Reports Server (NTRS)

    Capone, F. J.; Hall, R. M.; Owens, D. B.; Lamar, J. E.; McMillin, S. N.

    2003-01-01

    This paper presents a review of the experimental program under the Abrupt Wing Stall (AWS) Program. Candidate figures of merit from conventional static tunnel tests are summarized and correlated with data obtained in unique free-to-roll tests. Where possible, free-to-roll results are also correlated with flight data. Based on extensive studies of static experimental figures of merit in the Abrupt Wing Stall Program for four different aircraft configurations, no one specific figure of merit consistently flagged a warning of potential lateral activity when actual activity was seen to occur in the free-to-roll experiments. However, these studies pointed out the importance of measuring and recording the root mean square signals of the force balance.

  15. Abruptly autofocusing terahertz waves with meta-hologram.

    PubMed

    He, Jingwen; Wang, Sen; Xie, Zhenwei; Ye, Jiasheng; Wang, Xinke; Kan, Qiang; Zhang, Yan

    2016-06-15

    An abruptly autofocusing ring-Airy beam is demonstrated in the terahertz (THz) waveband with a meta-hologram. The designed meta-hologram is composed of gold C-shaped slot antennas, which can realize both phase and amplitude modulation of the incident THz wave. A THz holographic imaging system is utilized to measure the generated ring-Airy beam; an abrupt focus following a parabolic trajectory is subsequently observed. THz ring-Airy beams with different parameters are also generated and investigated. This method can be expanded to other wavebands, such as the visible band, for which the meta-hologram can replace traditional computer-generated holography to avoid undesirable multiple diffraction orders. PMID:27304289

  16. Complications of coronary intervention: abrupt closure, dissection, perforation

    PubMed Central

    Dash, Debabrata

    2013-01-01

    The introduction of drug-eluting stents (DESs) and superior anticoagulation has successfully improved the safety and patency rates of complex percutaneous coronary interventions (PCIs). The evolving techniques of contemporary PCI have been unable to completely eliminate coronary injury and mechanical complications. Primary causes for abrupt closure include dissection, thrombus formation and acute stent thrombosis. Initial treatment for abrupt closure includes balloon redilatation, optimisation of activated clotting time (ACT) and deployment of stent to stabilise a dissection. Coronary perforation is one of the most challenging and feared complications of PCI. It is most frequently due to distal wire or balloon/stent oversizing and should be fixed with balloon occlusion. Covered stent may be needed for large perforation in major proximal vessels. Perforations in small or distal vessels not resolving with balloon occlusion may be managed by coil or Gelfoam embolisation. Referral to emergency coronary artery bypass surgery (CABG) should be an option in case perforations do not seal.

  17. Ultra-wideband horn antenna with abrupt radiator

    DOEpatents

    McEwan, Thomas E.

    1998-01-01

    An ultra-wideband horn antenna transmits and receives impulse waveforms for short-range radars and impulse time-of flight systems. The antenna reduces or eliminates various sources of close-in radar clutter, including pulse dispersion and ringing, sidelobe clutter, and feedline coupling into the antenna. Dispersion is minimized with an abrupt launch point radiator element; sidelobe and feedline coupling are minimized by recessing the radiator into a metallic horn. Low frequency cut-off associated with a horn is extended by configuring the radiator drive impedance to approach a short circuit at low frequencies. A tapered feed plate connects at one end to a feedline, and at the other end to a launcher plate which is mounted to an inside wall of the horn. The launcher plate and feed plate join at an abrupt edge which forms the single launch point of the antenna.

  18. Ultra-wideband horn antenna with abrupt radiator

    DOEpatents

    McEwan, T.E.

    1998-05-19

    An ultra-wideband horn antenna transmits and receives impulse waveforms for short-range radars and impulse time-of flight systems. The antenna reduces or eliminates various sources of close-in radar clutter, including pulse dispersion and ringing, sidelobe clutter, and feedline coupling into the antenna. Dispersion is minimized with an abrupt launch point radiator element; sidelobe and feedline coupling are minimized by recessing the radiator into a metallic horn. Low frequency cut-off associated with a horn is extended by configuring the radiator drive impedance to approach a short circuit at low frequencies. A tapered feed plate connects at one end to a feedline, and at the other end to a launcher plate which is mounted to an inside wall of the horn. The launcher plate and feed plate join at an abrupt edge which forms the single launch point of the antenna. 8 figs.

  19. Not Just the 8.2 event: Dynamic Early Holocene Climate in Arctic Canada

    NASA Astrophysics Data System (ADS)

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

    2006-12-01

    Temperature reconstructions from a lake in the eastern Canadian Arctic indicate that peak warmth in the early Holocene was interrupted by two abrupt, short-lived temperature reversals at ~9.l and ~8.5 ka. Summer temperatures at Lake CF8, Baffin Island (~500 km west of Greenland) are inferred from subfossil midge (Chironomidae) assemblages. Our results indicate that the site, like others on Baffin Island, experienced exceptionally warm summers (almost 5°C warmer than present) through much of the early Holocene, presumably in response to enhanced summer insolation. After 1000 years of very warm, stable climate, warmth was interrupted by two discrete cold reversals at ~9.1 and ~8.5 ka, during which multiple cold-stenothermous midge taxa appeared in the lake and summer temperatures dropped more than 3°C. These two clearly-defined reversals, well beyond the range of background variability, were of similar amplitude and duration, and were separated by several centuries of near-peak warmth. The only Holocene events of comparable amplitude at this site are the rapid onset of Holocene warmth, and the more gradual Neoglacial cooling after 8 ka. Abrupt cooling events over the Baffin region are consistent with model simulations of the impacts of freshwater outbursts into the Labrador Sea, such as the Lake Agassiz outburst flood that occurred ~8.4 ka. That there are two discrete events recorded at this site indicates that the "8.2 event" was not uniquely significant in this region; rather, the period between approximately ~9.2 and 8 ka was characterized by repeated climate fluctuations forced by multiple outburst floods or other mechanisms. Thus global correlations among paleoclimate records need not assume that climate perturbations during this time period necessarily correlate with the draining of Lake Agassiz or the 8.2 ka cooling in central Greenland.

  20. A Rare Cause of Placental Abruption: Uterine Torsion

    PubMed Central

    Güneş, Muhammed Siraç; Kiran, Gürkan; Gülşen, Mehmet Serdar

    2016-01-01

    Uterine torsion is defined as a rotation on its long axis and it is a dangerous, unexpected obstetric emergency. We report a case of uterine torsion at 32 weeks of gestation in a singleton pregnancy. A 37-year-old woman with multiple prior cesarean deliveries referred to emergency unit of our hospital at 32 weeks of gestation with severe abdominal pain and mild vaginal bleeding. Ultrasonography showed a single fetus in vertex position, with a normal amniotic fluid. Fetal biometer was appropriate for 32 weeks of gestation. Placental location was anterior with a subchorionic hypoechogenic small area which was suspected to be a sign of placental abruption. An emergency cesarean section was performed under general anesthesia. The 180° uterine torsion was diagnosed and it was not possible to perform detorsion of the gravid uterus by exteriorization by pfannenstiel incision. Posterior hysterotomy was performed and a male baby of 1830 grams weight was delivered. The newborn was transported to Neonatal Intensive Care Unit (NICU) of another hospital and discharged within two weeks. Patient recovered well and was discharged on second postoperation day. Uterine torsion is a very rare and life threatening situation. In unexpected cases posterior low transuerse hysterotomy is generally performed and it is suggested as a safe choice when detorsion was not accomplished. It is not easy to keep in mind the possibility of uterine torsion in cases of abdominal pain during pregnancy. Because it generally causes abruption, management of abruption is vitally important to prevent fetal mortality. PMID:26894131

  1. Deep time evidence for climate sensitivity increase with warming

    NASA Astrophysics Data System (ADS)

    Shaffer, Gary; Huber, Matthew; Rondanelli, Roberto; Pepke Pedersen, Jens Olaf

    2016-06-01

    Future global warming from anthropogenic greenhouse gas emissions will depend on climate feedbacks, the effect of which is expressed by climate sensitivity, the warming for a doubling of atmospheric CO2 content. It is not clear how feedbacks, sensitivity, and temperature will evolve in our warming world, but past warming events may provide insight. Here we employ paleoreconstructions and new climate-carbon model simulations in a novel framework to explore a wide scenario range for the Paleocene-Eocene Thermal Maximum (PETM) carbon release and global warming event 55.8 Ma ago, a possible future warming analogue. We obtain constrained estimates of CO2 and climate sensitivity before and during the PETM and of the PETM carbon input amount and nature. Sensitivity increased from 3.3-5.6 to 3.7-6.5 K (Kelvin) into the PETM. When taken together with Last Glacial Maximum and modern estimates, this result indicates climate sensitivity increase with global warming.

  2. Abrupt state change of river water quality (turbidity): Effect of extreme rainfalls and typhoons.

    PubMed

    Lee, Chih-Sheng; Lee, Yi-Chao; Chiang, Hui-Min

    2016-07-01

    River turbidity is of dynamic nature, and its stable state is significantly changed during the period of heavy rainfall events. The frequent occurrence of typhoons in Taiwan has caused serious problems in drinking water treatment due to extremely high turbidity. The aim of the present study is to evaluate impact of typhoons on river turbidity. The statistical methods used included analyses of paired annual mean and standard deviation, frequency distribution, and moving standard deviation, skewness, and autocorrelation; all clearly indicating significant state changes of river turbidity. Typhoon Morakot of 2009 (recorded high rainfall over 2000mm in three days, responsible for significant disaster in southern Taiwan) is assumed as a major initiated event leading to critical state change. In addition, increasing rate of turbidity in rainfall events is highly and positively correlated with rainfall intensity both for pre- and post-Morakot periods. Daily turbidity is also well correlated with daily flow rate for all the eleven events evaluated. That implies potential prediction of river turbidity by river flow rate during rainfall and typhoon events. Based on analysis of stable state changes, more effective regulations for better basin management including soil-water conservation in watershed are necessary. Furthermore, municipal and industrial water treatment plants need to prepare and ensure the adequate operation of water treatment with high raw water turbidity (e.g., >2000NTU). Finally, methodology used in the present of this study can be applied to other environmental problems with abrupt state changes. PMID:26994797

  3. Geochemistry of oceanic anoxic events

    NASA Astrophysics Data System (ADS)

    Jenkyns, Hugh C.

    2010-03-01

    Oceanic anoxic events (OAEs) record profound changes in the climatic and paleoceanographic state of the planet and represent major disturbances in the global carbon cycle. OAEs that manifestly caused major chemical change in the Mesozoic Ocean include those of the early Toarcian (Posidonienschiefer event, T-OAE, ˜183 Ma), early Aptian (Selli event, OAE 1a, ˜120 Ma), early Albian (Paquier event, OAE 1b, ˜111 Ma), and Cenomanian-Turonian (Bonarelli event, C/T OAE, OAE 2, ˜93 Ma). Currently available data suggest that the major forcing function behind OAEs was an abrupt rise in temperature, induced by rapid influx of CO2 into the atmosphere from volcanogenic and/or methanogenic sources. Global warming was accompanied by an accelerated hydrological cycle, increased continental weathering, enhanced nutrient discharge to oceans and lakes, intensified upwelling, and an increase in organic productivity. An increase in continental weathering is typically recorded by transient increases in the seawater values of 87Sr/86Sr and 187Os/188Os ratios acting against, in the case of the Cenomanian-Turonian and early Aptian OAEs, a longer-term trend to less radiogenic values. This latter trend indicates that hydrothermally and volcanically sourced nutrients may also have stimulated local increases in organic productivity. Increased flux of organic matter favored intense oxygen demand in the water column, as well as increased rates of marine and lacustrine carbon burial. Particularly in those restricted oceans and seaways where density stratification was favored by paleogeography and significant fluvial input, conditions could readily evolve from poorly oxygenated to anoxic and ultimately euxinic (i.e., sulfidic), this latter state being geochemically the most significant. The progressive evolution in redox conditions through phases of denitrification/anammox, through to sulfate reduction accompanied by water column precipitation of pyrite framboids, resulted in fractionation of

  4. An Abrupt Change in the African Monsoon at the end of the Younger Dryas?

    NASA Astrophysics Data System (ADS)

    Talbot, M. R.; Filippi, M. L.; Jensen, N. B.; Tiercelin, J.

    2005-12-01

    A variety of proxy palaeoclimatic records from tropical Africa and the adjacent oceans suggest that a climatic event equivalent to the Younger Dryas (YD) also affected this region. To date however, little attention has been directed towards the end of the YD in Africa, even though it has been identified as a period of particularly rapid and profound climatic change in the circum-North Atlantic region. High-resolution studies of variations in the elemental and stable carbon- and nitrogen-isotope composition of organic matter in cores from Lakes Malawi, Tanganyika and Bosumtwi (tropical Africa) indicate an abrupt change in the wind-driven circulation of these lakes that, within the limits of available chronologies, was contemporaneous with the end of the YD in the northern hemisphere. The change was apparently coincident with the transition to humid conditions in the central Sahara, with shifts in surface winds recorded in cores from off the coasts of East and West Africa, and possibly also with the onset of the last phase of ice accumulation on Mt. Kilimanjaro. Together, the evidence suggests an abrupt northward translation of the African monsoon system at ca. 11.5 +/- 0.3 cal. ka BP.

  5. Extreme warm temperatures alter forest phenology and productivity in Europe.

    PubMed

    Crabbe, Richard A; Dash, Jadu; Rodriguez-Galiano, Victor F; Janous, Dalibor; Pavelka, Marian; Marek, Michal V

    2016-09-01

    Recent climate warming has shifted the timing of spring and autumn vegetation phenological events in the temperate and boreal forest ecosystems of Europe. In many areas spring phenological events start earlier and autumn events switch between earlier and later onset. Consequently, the length of growing season in mid and high latitudes of European forest is extended. However, the lagged effects (i.e. the impact of a warm spring or autumn on the subsequent phenological events) on vegetation phenology and productivity are less explored. In this study, we have (1) characterised extreme warm spring and extreme warm autumn events in Europe during 2003-2011, and (2) investigated if direct impact on forest phenology and productivity due to a specific warm event translated to a lagged effect in subsequent phenological events. We found that warmer events in spring occurred extensively in high latitude Europe producing a significant earlier onset of greening (OG) in broadleaf deciduous forest (BLDF) and mixed forest (MF). However, this earlier OG did not show any significant lagged effects on autumnal senescence. Needleleaf evergreen forest (NLEF), BLDF and MF showed a significantly delayed end of senescence (EOS) as a result of extreme warm autumn events; and in the following year's spring phenological events, OG started significantly earlier. Extreme warm spring events directly led to significant (p=0.0189) increases in the productivity of BLDF. In order to have a complete understanding of ecosystems response to warm temperature during key phenological events, particularly autumn events, the lagged effect on the next growing season should be considered. PMID:27152990

  6. Hydrological consequences of global warming

    SciTech Connect

    Miller, Norman L.

    2009-06-01

    The 2007 Intergovernmental Panel for Climate Change indicates there is strong evidence that the atmospheric concentration of carbon dioxide far exceeds the natural range over the last 650,000 years, and this recent warming of the climate system is unequivocal, resulting in more frequent extreme precipitation events, earlier snowmelt runoff, increased winter flood likelihoods, increased and widespread melting of snow and ice, longer and more widespread droughts, and rising sea level. The effects of recent warming has been well documented and climate model projections indicate a range of hydrological impacts with likely to very likely probabilities (67 to 99 percent) of occurring with significant to severe consequences in response to a warmer lower atmosphere with an accelerating hydrologic cycle.

  7. Defining Sudden Stratospheric Warmings

    NASA Astrophysics Data System (ADS)

    Butler, Amy; Seidel, Dian; Hardiman, Steven; Butchart, Neal; Birner, Thomas; Match, Aaron

    2015-04-01

    The general form of the definition for Sudden Stratospheric Warmings (SSWs) is largely agreed to be a reversal of the temperature gradient and of the zonal circulation polewards of 60° latitude at the 10 hPa level, as developed by the World Meteorological Organization (WMO) in the 1960s and 1970s. However, the details of the definition and its calculation are ambiguous, resulting in inconsistent classifications of SSW events. These discrepancies are problematic for understanding the observed frequency and statistical relationships with SSWs, and for maintaining a robust metric with which to assess wintertime stratospheric variability in observations and climate models. To provide a basis for community-wide discussion, we examine how the SSW definition has changed over time and how sensitive the detection of SSWs is to the definition used. We argue that the general form of the SSW definition should be clarified to ensure that it serves current research and forecasting purposes, and propose possible ways to update the definition.

  8. Zooplankton patch dynamics: daily gap formation over abrupt topography

    NASA Astrophysics Data System (ADS)

    Genin, Amatzia; Greene, Charles; Haury, Loren; Wiebe, Peter; Gal, Gideon; Kaartvedt, Stein; Meir, Eli; Fey, Connie; Dawson, Jim

    1994-05-01

    Net tow and acoustic surveys of zooplankton distributions were made over and around Sixtymile Bank (110 km southwest of San Diego, California). Gaps devoid of vertically migrating zooplankton were formed every evening above the summit of the bank. Interactions between the migrating animals, their predators, physical advection and the local topography appear to determine the gap formation and dynamics. Gaps were transported downstream during the night and appeared to disintegrate slowly through vertical swimming behavior, current shear and mixing processes. Patch dynamics following gap formation, mediated by both ocean currents and animal behavior, should augment the spatial heterogeneity of zooplankton and affect marine food webs in areas where abrupt topography features are common.

  9. Shock wave interaction with an abrupt area change

    NASA Technical Reports Server (NTRS)

    Salas, Manuel D.

    1991-01-01

    The wave patterns that occur when a shock wave interacts with an abrupt area changed are analyzed in terms of the incident shock wave Mach number and area-jump ratio. The solutions predicted by a semi-similar models are in good agreement with those obtained numerically from the quasi-one-dimensional time-dependent Euler equations. The entropy production for the wave system is defined and the principle of minimum entropy production is used to resolve a nonuniqueness problem of the self-similar model.

  10. Paleoecological evidence for abrupt cold reversals during peak Holocene warmth on Baffin Island, Arctic Canada

    NASA Astrophysics Data System (ADS)

    Axford, Yarrow; Briner, Jason P.; Miller, Gifford H.; Francis, Donna R.

    2009-03-01

    A continuous record of insect (Chironomidae) remains preserved in lake sediments is used to infer temperature changes at a small lake in Arctic Canada through the Holocene. Early Holocene summers at the study site were characterized by more thermophilous assemblages and warmer inferred temperatures than today, presumably in response to the positive anomaly in Northern Hemisphere summer insolation. Peak early Holocene warmth was interrupted by two cold reversals between 9.5 and 8 cal ka BP, during which multiple cold-stenothermous chironomid taxa appeared in the lake. The earlier reversal appears to correlate with widespread climate anomalies around 9.2 cal ka BP; the age of the younger reversal is equivocal but it may correlate with the 8.2 cal ka BP cold event documented elsewhere. Widespread, abrupt climate shifts in the early Holocene illustrate the susceptibility of the climate system to perturbations, even during periods of enhanced warmth in the Northern Hemisphere.

  11. Holocene Abrupt Climate Change Over NW Iran: The Hand That Rocked The Cradle Of Civilization?

    NASA Astrophysics Data System (ADS)

    Sharifi, A.; Pourmand, A.; Canuel, E. A.; Ferer-Tyler, E.; Peterson, L. C.; Aichner, B.; Feakins, S. J.; Daryaee, T.; Djamali, M.; Naderi Beni, A.; Lahijani, H. A. K.; Swart, P. K.

    2014-12-01

    Human civilizations around the globe have been influenced by abrupt climate change throughout the Holocene. The paucity of high-resolution palaeoclimate data from the "Cradle of Civilization" in West Asia, however, has limited our ability to evaluate the potential role of Holocene climate variability on early societies. We present a high-resolution, multi-proxy reconstruction of aeolian input and palaeoenvironmental conditions based on a 13-kyr record of ombrotrophic (rain fed) peat from Neor Lake in Northwest Iran. Variations in relative abundances of major and trace elements, total organic carbon (TOC), stable carbon isotopes of TOC (δ13CTOC) and compound-specific leaf wax hydrogen isotope (δD) compositions suggest dry and dusty conditions prevailed during the Younger Dryas, and a substantial increase in atmospheric dust loading and decrease in moisture availability occurred between the early and late Holocene. In addition, variations in radiogenic Sr-Nd-Hf isotopic composition and REE anomalies in samples from Neor peat core indicate significant shifts occurred in source contributions of eolian material to the study area between the Younger Dryas, early and late Holocene. Time-series analysis of aeolian input to NE Iran reveals periodicities at 540, 1050 and 2940 years that correspond with solar variability and internal climate feedbacks identified in other records of Holocene climate change from the northern hemisphere. Transitions in major Mesopotamian and Persian civilizations, including the collapse of the Akkadian empire at 4,200 yr BP, the fall of the Ur III empire at 3,955 yr BP, the fall of Elam empire at 2,500 yr BP and the demise of the Achaemenids around 2,280 BP overlap with major dust events from this study. Several other episodes of enhanced atmospheric dust, however, are not reflected in historical or archaeological accounts of the late Holocene. This indicates either abrupt climate change was not the sole driver of societal changes in the

  12. Links between early Holocene ice-sheet decay, sea-level rise and abrupt climate change

    NASA Astrophysics Data System (ADS)

    Törnqvist, Torbjörn E.; Hijma, Marc P.

    2012-09-01

    The beginning of the current interglacial period, the Holocene epoch, was a critical part of the transition from glacial to interglacial climate conditions. This period, between about 12,000 and 7,000 years ago, was marked by the continued retreat of the ice sheets that had expanded through polar and temperate regions during the preceding glacial. This meltdown led to a dramatic rise in sea level, punctuated by short-lived jumps associated with catastrophic ice-sheet collapses. Tracking down which ice sheet produced specific sea-level jumps has been challenging, but two events between 8,500 and 8,200 years ago have been linked to the final drainage of glacial Lake Agassiz in north-central North America. The release of the water from this ice-dammed lake into the ocean is recorded by sea-level jumps in the Mississippi and Rhine-Meuse deltas of approximately 0.4 and 2.1 metres, respectively. These sea-level jumps can be related to an abrupt cooling in the Northern Hemisphere known as the 8.2 kyr event, and it has been suggested that the freshwater release from Lake Agassiz into the North Atlantic was sufficient to perturb the North Atlantic meridional overturning circulation. As sea-level rise on the order of decimetres to metres can now be detected with confidence and linked to climate records, it is becoming apparent that abrupt climate change during the early Holocene associated with perturbations in North Atlantic circulation required sustained freshwater release into the ocean.

  13. Transonic Experimental Observations of Abrupt Wing Stall on an F/A-18E Model (Invited)

    NASA Technical Reports Server (NTRS)

    McMillin, S. Naomi; Hall, Robert M.; Lamar, John E.

    2003-01-01

    A transonic wind tunnel test of an 8% F/A-18E model was conducted in the NASA Langley Research Center (LaRC) 16 ft Transonic Tunnel (16-ft TT) to investigate on-surface flow physics during stall. The technical approach employed focused on correlating static (or time-averaged) and unsteady wind-tunnel test data to the unsteady wing-stall events using force, moment, pressure, and pressure-sensitive-paint measurements. This paper focuses on data obtained on the pre-production configuration of the F/A-18E aircraft at Mach number of 0.90. The flow unsteadiness occurring on the wing as the wing went through the stall process was captured using the time history of balance and pressure measurements and by calculating the root mean square (RMS) for a number of instrument signals. The second step was to gather global perspectives on the pressures influencing the wing stall process. The abrupt wing stall experienced by the 8% F/A-18E Model was observed to be an unsteady event triggered by the rapid advancement of separation, which had migrated forward from the trailing edge, to the leading-edge flap hingeline over a very small increment in angle of attack. The angle of attack at which this stall occurred varied, from run to run, over an 1 deg increment. The abrupt wing stall was observed, using pressure-sensitive-paint, to occur simultaneously on both wing panels or asymmetrically. The pressure-sensitive paint data and wingroot bending moment data were essential in providing insight to the flow structures occurring over the wing and the possible asymmetry of those flow structures. A repeatability analysis conducted on eight runs of static data provided a quick and inexpensive examination of the unsteady aerodynamic characteristics of abrupt wing stall. The results of the repeatability analysis agreed extremely well with data obtained using unsteady measurement techniques. This approach could be used to identify test conditions for more complex unsteady data measurements using

  14. Percolation Features on Climate Network under Attacks of El Niño Events

    NASA Astrophysics Data System (ADS)

    Lu, Z.

    2015-12-01

    Percolation theory under different attacks is one of the main research areas in complex networks but never be applied to investigate climate network. In this study, for the first time we construct a climate network of surface air temperature field to analyze its percolation features. Here, we regard El Niño event as a kind of naturally attacks generated from Pacific Ocean to attack its upper climate network. We find that El Niño event leads an abrupt percolation phase transition to the climate network which makes it splitting and unstable suddenly. Comparing the results of the climate network under three different forms of attacks, including most connected attack (MA), localized attack (LA) and random attack (RA) respectively, it is found that both MA and LA lead first-order transition and RA leads second-order transition to the climate network. Furthermore, we find that most real attacks consist of all these three forms of attacks. With El Niño event emerging, the ratios of LA and MA increase and dominate the style of attack while RA decreasing. It means the percolation phase transition due to El Niño events is close to first-order transition mostly affected by LA and MA. Our research may help us further understand two questions from perspective of percolation on network: (1) Why not all warming in Pacific Ocean but El Niño events could affect the climate. (2) Why the climate affected by El Niño events changes abruptly.

  15. The abrupt onset of the modern South Asian Monsoon winds

    PubMed Central

    Betzler, Christian; Eberli, Gregor P.; Kroon, Dick; Wright, James D.; Swart, Peter K.; Nath, Bejugam Nagender; Alvarez-Zarikian, Carlos A.; Alonso-García, Montserrat; Bialik, Or M.; Blättler, Clara L.; Guo, Junhua Adam; Haffen, Sébastien; Horozal, Senay; Inoue, Mayuri; Jovane, Luigi; Lanci, Luca; Laya, Juan Carlos; Mee, Anna Ling Hui; Lüdmann, Thomas; Nakakuni, Masatoshi; Niino, Kaoru; Petruny, Loren M.; Pratiwi, Santi D.; Reijmer, John J. G.; Reolid, Jesús; Slagle, Angela L.; Sloss, Craig R.; Su, Xiang; Yao, Zhengquan; Young, Jeremy R.

    2016-01-01

    The South Asian Monson (SAM) is one of the most intense climatic elements yet its initiation and variations are not well established. Dating the deposits of SAM wind-driven currents in IODP cores from the Maldives yields an age of 12. 9 Ma indicating an abrupt SAM onset, over a short period of 300 kyrs. This coincided with the Indian Ocean Oxygen Minimum Zone expansion as revealed by geochemical tracers and the onset of upwelling reflected by the sediment’s content of particulate organic matter. A weaker ‘proto-monsoon’ existed between 12.9 and 25 Ma, as mirrored by the sedimentary signature of dust influx. Abrupt SAM initiation favors a strong influence of climate in addition to the tectonic control, and we propose that the post Miocene Climate Optimum cooling, together with increased continentalization and establishment of the bipolar ocean circulation, i.e. the beginning of the modern world, shifted the monsoon over a threshold towards the modern system. PMID:27436574

  16. The abrupt onset of the modern South Asian Monsoon winds.

    PubMed

    Betzler, Christian; Eberli, Gregor P; Kroon, Dick; Wright, James D; Swart, Peter K; Nath, Bejugam Nagender; Alvarez-Zarikian, Carlos A; Alonso-García, Montserrat; Bialik, Or M; Blättler, Clara L; Guo, Junhua Adam; Haffen, Sébastien; Horozal, Senay; Inoue, Mayuri; Jovane, Luigi; Lanci, Luca; Laya, Juan Carlos; Mee, Anna Ling Hui; Lüdmann, Thomas; Nakakuni, Masatoshi; Niino, Kaoru; Petruny, Loren M; Pratiwi, Santi D; Reijmer, John J G; Reolid, Jesús; Slagle, Angela L; Sloss, Craig R; Su, Xiang; Yao, Zhengquan; Young, Jeremy R

    2016-01-01

    The South Asian Monson (SAM) is one of the most intense climatic elements yet its initiation and variations are not well established. Dating the deposits of SAM wind-driven currents in IODP cores from the Maldives yields an age of 12. 9 Ma indicating an abrupt SAM onset, over a short period of 300 kyrs. This coincided with the Indian Ocean Oxygen Minimum Zone expansion as revealed by geochemical tracers and the onset of upwelling reflected by the sediment's content of particulate organic matter. A weaker 'proto-monsoon' existed between 12.9 and 25 Ma, as mirrored by the sedimentary signature of dust influx. Abrupt SAM initiation favors a strong influence of climate in addition to the tectonic control, and we propose that the post Miocene Climate Optimum cooling, together with increased continentalization and establishment of the bipolar ocean circulation, i.e. the beginning of the modern world, shifted the monsoon over a threshold towards the modern system. PMID:27436574

  17. Usage leading to an abrupt collapse of connectivity

    NASA Astrophysics Data System (ADS)

    Stäger, D. V.; Araújo, N. A. M.; Herrmann, H. J.

    2014-10-01

    Network infrastructures are essential for the distribution of resources such as electricity and water. Typical strategies to assess their resilience focus on the impact of a sequence of random or targeted failures of network nodes or links. Here we consider a more realistic scenario, where elements fail based on their usage. We propose a dynamic model of transport based on the Bak-Tang-Wiesenfeld sandpile model where links fail after they have transported more than an amount μ (threshold) of the resource and we investigate it on the square lattice. As we deal with a new model, we provide insight on its fundamental behavior and dependence on parameters. We observe that, for low values of the threshold due to a positive feedback of link failure, an avalanche develops that leads to an abrupt collapse of the lattice. By contrast, for high thresholds the lattice breaks down in an uncorrelated fashion. We determine the critical threshold μ* separating these two regimes and show how it depends on the toppling threshold of the nodes and the mass increment added stepwise to the system. We find that the time of major disconnection is well described with a linear dependence on μ . Furthermore, we propose a lower bound for μ* by measuring the strength of the dynamics leading to abrupt collapses.

  18. The abrupt onset of the modern South Asian Monsoon winds

    NASA Astrophysics Data System (ADS)

    Betzler, Christian; Eberli, Gregor P.; Kroon, Dick; Wright, James D.; Swart, Peter K.; Nath, Bejugam Nagender; Alvarez-Zarikian, Carlos A.; Alonso-García, Montserrat; Bialik, Or M.; Blättler, Clara L.; Guo, Junhua Adam; Haffen, Sébastien; Horozal, Senay; Inoue, Mayuri; Jovane, Luigi; Lanci, Luca; Laya, Juan Carlos; Mee, Anna Ling Hui; Lüdmann, Thomas; Nakakuni, Masatoshi; Niino, Kaoru; Petruny, Loren M.; Pratiwi, Santi D.; Reijmer, John J. G.; Reolid, Jesús; Slagle, Angela L.; Sloss, Craig R.; Su, Xiang; Yao, Zhengquan; Young, Jeremy R.

    2016-07-01

    The South Asian Monson (SAM) is one of the most intense climatic elements yet its initiation and variations are not well established. Dating the deposits of SAM wind-driven currents in IODP cores from the Maldives yields an age of 12. 9 Ma indicating an abrupt SAM onset, over a short period of 300 kyrs. This coincided with the Indian Ocean Oxygen Minimum Zone expansion as revealed by geochemical tracers and the onset of upwelling reflected by the sediment’s content of particulate organic matter. A weaker ‘proto-monsoon’ existed between 12.9 and 25 Ma, as mirrored by the sedimentary signature of dust influx. Abrupt SAM initiation favors a strong influence of climate in addition to the tectonic control, and we propose that the post Miocene Climate Optimum cooling, together with increased continentalization and establishment of the bipolar ocean circulation, i.e. the beginning of the modern world, shifted the monsoon over a threshold towards the modern system.

  19. Responses of Antarctic Oscillation to global warming

    NASA Astrophysics Data System (ADS)

    Feng, S.

    2015-12-01

    The Antarctic Oscillation (AAO) is the major annular mode dominates the spatiotemporal variability of the atmospheric circulation in the Southern Hemisphere. This study examined the sensitivity of AAO to future warming by analyzing the outputs of 34 state-of-the-art climate models participating in phase 5 of the Coupled Model Intercomparion Project (CMIP5). The model simulations include the stabilized (RCP4.5) and business as usual (RCP8.5) scenarios as well as the idealized 1% per year increase in atmospheric CO2 to quadrupling (1pctCO2) and an instantaneous quadrupling of CO2 (abrupt4xCO2). We show that the CMIP5 models on average simulate increases in the AAO in every season by 2100 under the RCP4.5 and RCP8.5 scenarios. However, due to the impacts of ozone, aerosol and land use changes, the amplitudes of the projected changes in AAO to future climate scenarios are quit different on different seasons. After the impact of ozone, aerosol and land use changes were removed; it was found that the impact of greenhouse gases (GHGs) on AAO is similar on all seasons. The increases of AAO are accelerating following the increase of GHGs. Our results are also consistent with the simulations of 1pctCO2 and abrupt4xCO2.

  20. Warm-Up Activities.

    ERIC Educational Resources Information Center

    Mingguang, Yang

    1999-01-01

    Discusses how warm-up activities can help to make the English-as-a-foreign-language classroom a lively and interesting place. Warm-up activities are games carried out at the beginning of each class to motivate students to make good use of class time. (Author/VWL)

  1. Temperature and size variabilities of the Western Pacific Warm Pool

    NASA Technical Reports Server (NTRS)

    Yan, Xiao-Hai; Ho, Chung-Ru; Zheng, Quanan; Klemas, Vic

    1992-01-01

    Variabilities in sea-surface temperature and size of the Western Pacific Warm Pool were tracked with 10 years of satellite multichannel sea-surface temperature observations from 1982 to 1991. The results show that both annual mean sea-surface temperature and the size of the warm pool increased from 1983 to 1987 and fluctuated after 1987. Possible causes of these variations include solar irradiance variabilities, El Nino-Southern Oscillaton events, volcanic activities, and global warming.

  2. Cold to Warm and Warm to Cold: A Comparison of rates and signatures of climate change going into and out of the Younger Dryas

    NASA Astrophysics Data System (ADS)

    Popp, T.; White, J.; Sveinbjornsdottir, A.; Masson-Delmotte, V.; Johnsen, S.; Jouzel, J.

    2003-12-01

    The most recent, very large (15 degrees C change in mean annual temperature) and very abrupt (50 years or less) climate change recorded in Greenland ice cores is the end of the Younger Dryas (YD). While this cold to warm transition has been extensively studied in ice cores using tools such as stable isotopes in ice, gas concentrations, stable isotopes in gases, snow chemistry, snow accumulation, and electrical conductivity of ice, the start of the YD has received much less attention in ice core analyses. In contrast, we have better theories for how the YD began, than how it ended. We focus here on the Greenland ice core record of the beginning of the YD, with an eye to the speed and nature of this abrupt climate change, and what the ice evidence may tell us concerning the fingerprint, and thus potential processes, of climate change left by this event. The first challenge is identifying the beginning of the YD in the ice core. Warm to cold transitions in isotopes in ice cores can be muted if winter snows are lost as a result of the colder conditions. This appears to be the case in the Greenland cores. Deuterium excess, which records ocean conditions during moisture evaporation, on the other hand, retains its sharpness. At the beginning of the YD, XS changes in NorthGRIP in a matter of years, a signal similar in size and speed to that seen at the end of the YD, but opposite in sign. Other signals are not similar in size and speed, however. These differences between the beginning and end of the YD will be discussed, and can reveal clues to the nature and timing of the climate changes. For example, continental dust does not change (increase) rapidly at the beginning of the YD cold period, but rather is delayed by decades. This suggests that there may be is a lag in the production of dust as ecosystems slowly dry and transform in response to the climate change.

  3. The INTIMATE event stratigraphy of the last glacial period

    NASA Astrophysics Data System (ADS)

    Olander Rasmussen, Sune; Svensson, Anders

    2015-04-01

    The North Atlantic INTIMATE (INtegration of Ice-core, MArine and TErrestrial records) group has previously recommended an Event Stratigraphy approach for the synchronisation of records of the Last Termination using the Greenland ice core records as the regional stratotypes. A key element of these protocols has been the formal definition of numbered Greenland Stadials (GS) and Greenland Interstadials (GI) within the past glacial period as the Greenland expressions of the characteristic Dansgaard-Oeschger events that represent cold and warm phases of the North Atlantic region, respectively. Using a recent synchronization of the NGRIP, GRIP, and GISP2 ice cores that allows the parallel analysis of all three records on a common time scale, we here present an extension of the GS/GI stratigraphic template to the entire glacial period. In addition to the well-known sequence of Dansgaard-Oeschger events that were first defined and numbered in the ice core records more than two decades ago, a number of short-lived climatic oscillations have been identified in the three synchronized records. Some of these events have been observed in other studies, but we here propose a consistent scheme for discriminating and naming all the significant climatic events of the last glacial period that are represented in the Greenland ice cores. In addition to presenting the updated event stratigraphy, we make a series of recommendations on how to refer to these periods in a way that promotes unambiguous comparison and correlation between different proxy records, providing a more secure basis for investigating the dynamics and fundamental causes of these climatic perturbations. The work presented is a part of a newly published paper in an INTIMATE special issue of Quaternary Science Reviews: Rasmussen et al., 'A stratigraphic framework for abrupt climatic changes during the Last Glacial period based on three synchronized Greenland ice-core records: refining and extending the INTIMATE event

  4. The effect of abrupt climate changes and climate background conditions in Southern Europe during the last glacial

    NASA Astrophysics Data System (ADS)

    Knorr, Gregor; Martin-Puertas, Celia; Brauer, Achim; Lohmann, Gerrit

    2015-04-01

    The last glacial period is characterized by abrupt and large temperature shifts in Greenland and the North Atlantic realm. Pollen and sediment data from Lago Grande di Monticchio (MON) have demonstrated a clear imprint of these fluctuations operating at millennial time-scales. Interestingly, basic mean environmental condition changes with respect to temperature and precipitation occurred during MIS4, separating warm and dry conditions during MIS5 from relatively cold and humid conditions within MIS3. This general climate background shift is superposed by distinct millennial-scale variability at MON. Using a fully coupled atmosphere-ocean general circulation model applying boundary conditions at 32 ka BP and pre-industrial conditions as a surrogate for MIS3 and MIS5, we have simulated and analysed characteristic changes in Southern Europe during the last glacial. We find that changes in the mean state at MON are mainly related to a partial shift of the North Atlantic deep water (NADW) convection sites from the Nordic Seas to South of Iceland, the presence of the Fennoscandian ice sheet and lower greenhouse gas concentrations. These background characteristics provide the basis for enhanced zonal moisture transport from the eastern North Atlantic to Middle and Southern Europe. Furthermore, simulations of abrupt climate change scenarios show that a deactivation of the convection sites South of Iceland during MIS3 leads to cooler and dryer conditions at MON. Such temperature and precipitation changes are thought to provide a counter-acting effect on woody vegetation and associated pollen signals at MON. This is in contrast to the impact of abrupt climate perturbation scenarios during MIS5, where no significant precipitation changes are detected. Hence, the simulated changes and underlying mechanisms are largely consistent with the recorded proxy evidence with respect to both, mean state and millennial-scale changes.

  5. Fluvial system response to abrupt climate change: sedimentary record example of the Paleocene-Eocene Thermal Maximum (PETM) in the South-Pyrenean foreland basin, Spain

    NASA Astrophysics Data System (ADS)

    Chen, Chen; Castelltort, Sebastien; Foreman, Brady; Hassenruck-Gudipati, Hima J.

    2015-04-01

    The "Paleocene-Eocene Thermal Maximum" (PETM), is understood to be an extreme and short-lived (ca.150-220kya) global warming event that occurred 55.8 million years ago and during which global annual temperatures are estimated to have increased by ca. 5-8°C, with respect to sea surface temperatures and ca. 4-5°C, with respect to the deep sea. A remaining outstanding question is: in addition to the global increase in temperature, how was precipitation perturbed during the event, and how did fluvial surface processes respond to the perturbation? In the southern Spanish Pyrenees, the Paleocene succession of the Tremp-Graus Basin is made up of the Talarn (Danian) and Esplugafreda (Thanetian) red bed formations. The Esplugafreda section is composed of approximately 250m of reddish paleosols and contains numerous lenticular bodies of calcareous conglomerates, which are interpreted as braided channels. The Esplugafreda Formation is overlain by the Claret Conglomerate -- an extensive sheet-like unit which ranges in thickness between 1m and 4m of clast-supported calcareous conglomerate and pebbly calcarenites and is interpreted as marking the fluvial response to a dramatic climate change, in the form of the transformation of a braided river and floodplain system into an enormous conglomeratic braided plain (formed over at least 2000km2 conservatively) due to dramatic change in the hydrologic cycle. The conglomerate unit ends abruptly and is overlaid by fine-grained yellowish soils which are mainly made up of silty mudstones with abundant small size carbonate nodules suggesting another shift in the hydrological cycle after the PETM. Here we present paleo-channel geometry and grain size data collected in the southern Pyrenees (Tremp, Aren, and Serraduy sections) that we invert to reconstruct paleoflow conditions during the Paleocene and during the Paleocene-Eocene Thermal Event. We confront paleohydraulic results with sea level, isotope and lithological records in order to

  6. Is Europa's Subsurface Water Ocean Warm?

    NASA Technical Reports Server (NTRS)

    Melosh, H. J.; Ekholm, A. G.; Showman, A. P.; Lorenz, R. D.

    2002-01-01

    Europa's subsurface water ocean may be warm: that is, at the temperature of water's maximum density. This provides a natural explanation of chaos melt-through events and leads to a correct estimate of the age of its surface. Additional information is contained in the original extended abstract.

  7. A Common Mechanism of Multi-timescale Abrupt Global Change

    NASA Astrophysics Data System (ADS)

    Duke, J. H.

    2008-12-01

    The La Nina phase of the El Nino/Southern Oscillation (ENSO) is known to cause global cooling on inter- annual timescales through changes in deep convection patterns and reduced supply of water vapor to the tropical atmosphere. Two distinct means are presented here by which this mechanism may also act on timescales exceeding 100,000 years. Firstly, the hypothesis of millennial tidal forcing is revisited with the view that equatorial buoyancy frequencies and steep internal waves in the Pacific Equatorial Undercurrent make vertical mixing in the equatorial Pacific uniquely susceptible to incremental changes in tidal energy. Hourly Tropical Ocean Array subsurface temperature data show a resonant response to extreme tides associated with the 1997 and 2000 ENSO events. Complimenting the known 1,800 year peak tide cycle, a 550-600 year cycle of three-fold variation in the frequency of deep central eclipses (gamma < 0.05) is consistent with the timing of the Little Ice Age. Fortnightly eclipse triples (FET's) associated with this eclipse cycle are shown to coincide with both warm and cold phase Southern Oscillation Index (SOI) inflection points between 1876 and 2007, and notably the cold phase maxima of 1904 and 1917. In the second proposed trigger, southward migration of the intertropical convergence zone (ITCZ) in the central and eastern Pacific may periodically shift the rising branch of the Hadley circulation over the equatorial cold tongue. The resulting winter monsoon system develops an equatorially symmetric La Nina (ESLN) mode through a positive feedback between diverging surface winds and meridional rather than zonal SST gradients. Exchange of latent heat in the winter monsoon contracts the Hadley Cell, draws circumpolar westerly winds equatorward, and expands high latitude ice volume, as demonstrated in 1998. A three million year record of obliquity and August 10°N minus 10°S insolation (AUG10N-S) shows an ice volume dependence upon the mutual direction of

  8. Intrusion detection robust to slow and abrupt lighting changes

    NASA Astrophysics Data System (ADS)

    Makarov, Aleksej; Vesin, Jean-Marc; Reymond, Florian

    1996-03-01

    In this communication we present an image based object detection algorithm which is applied to intrusion detection. The algorithm is based on the comparison of input edges and temporally filtered edges of the background. It is characterized by very low computational and memory loads, high sensitivity to the presence of physical intruders and high robustness to slow and abrupt lighting changes. The algorithm is implementable on a cheap digital signal processor. It was tested on a data base of about one thousand gray-level CIF-format frames representing static scenes with various contents (light sources, intruders, lighting changes), and neither false alarm nor detection failure occurred. The number of parameters involved by the algorithm is very low, and their values do not require a fine tuning. The same set of parameters performs equally well in different conditions: different scenes, various lighting changes, various object sizes.

  9. Abrupt tectonics and rapid slab detachment with grain damage.

    PubMed

    Bercovici, David; Schubert, Gerald; Ricard, Yanick

    2015-02-01

    A simple model for necking and detachment of subducting slabs is developed to include the coupling between grain-sensitive rheology and grain-size evolution with damage. Necking is triggered by thickened buoyant crust entrained into a subduction zone, in which case grain damage accelerates necking and allows for relatively rapid slab detachment, i.e., within 1 My, depending on the size of the crustal plug. Thick continental crustal plugs can cause rapid necking while smaller plugs characteristic of ocean plateaux cause slower necking; oceanic lithosphere with normal or slightly thickened crust subducts without necking. The model potentially explains how large plateaux or continental crust drawn into subduction zones can cause slab loss and rapid changes in plate motion and/or induce abrupt continental rebound. PMID:25605890

  10. Abrupt tectonics and rapid slab detachment with grain damage

    PubMed Central

    Bercovici, David; Schubert, Gerald; Ricard, Yanick

    2015-01-01

    A simple model for necking and detachment of subducting slabs is developed to include the coupling between grain-sensitive rheology and grain-size evolution with damage. Necking is triggered by thickened buoyant crust entrained into a subduction zone, in which case grain damage accelerates necking and allows for relatively rapid slab detachment, i.e., within 1 My, depending on the size of the crustal plug. Thick continental crustal plugs can cause rapid necking while smaller plugs characteristic of ocean plateaux cause slower necking; oceanic lithosphere with normal or slightly thickened crust subducts without necking. The model potentially explains how large plateaux or continental crust drawn into subduction zones can cause slab loss and rapid changes in plate motion and/or induce abrupt continental rebound. PMID:25605890

  11. Accelerated Arctic land warming and permafrost degradation during rapid sea ice loss

    NASA Astrophysics Data System (ADS)

    Lawrence, D. M.; Slater, A. G.; Tomas, R. A.; Holland, M. M.; Deser, C.

    2008-12-01

    Coupled climate models and recent observational evidence suggest that Arctic sea ice may undergo abrupt periods of loss during the next fifty years. Here, we evaluate how rapid sea ice loss affects terrestrial Arctic climate and ground thermal state in the Community Climate System Model. We find that simulated western Arctic land warming trends during rapid sea ice loss are 3.5 times greater than secular 21st century climate- change trends. The accelerated warming signal penetrates up to 1500km inland and is apparent throughout most of the year, peaking in autumn. Idealized experiments using the Community Land Model, with improved permafrost dynamics, indicate that an accelerated warming period substantially increases ground heat accumulation. Enhanced heat accumulation leads to rapid degradation of warm permafrost and may increase the vulnerability of colder permafrost to degradation under continued warming. Taken together, these results imply a direct link between rapid sea ice loss and permafrost health.

  12. Accelerated Arctic land warming and permafrost degradation during rapid sea ice loss

    NASA Astrophysics Data System (ADS)

    Lawrence, David M.; Slater, Andrew G.; Tomas, Robert A.; Holland, Marika M.; Deser, Clara

    2008-06-01

    Coupled climate models and recent observational evidence suggest that Arctic sea ice may undergo abrupt periods of loss during the next fifty years. Here, we evaluate how rapid sea ice loss affects terrestrial Arctic climate and ground thermal state in the Community Climate System Model. We find that simulated western Arctic land warming trends during rapid sea ice loss are 3.5 times greater than secular 21st century climate-change trends. The accelerated warming signal penetrates up to 1500 km inland and is apparent throughout most of the year, peaking in autumn. Idealized experiments using the Community Land Model, with improved permafrost dynamics, indicate that an accelerated warming period substantially increases ground heat accumulation. Enhanced heat accumulation leads to rapid degradation of warm permafrost and may increase the vulnerability of colder permafrost to degradation under continued warming. Taken together, these results imply a link between rapid sea ice loss and permafrost health.

  13. An automatic abrupt information extraction method based on singular value decomposition and higher-order statistics

    NASA Astrophysics Data System (ADS)

    He, Tian; Ye, Wu; Pan, Qiang; Liu, Xiandong

    2016-02-01

    One key aspect of local fault diagnosis is how to effectively extract abrupt features from the vibration signals. This paper proposes a method to automatically extract abrupt information based on singular value decomposition and higher-order statistics. In order to observe the distribution law of singular values, a numerical analysis to simulate the noise, periodic signal, abrupt signal and singular value distribution is conducted. Based on higher-order statistics and spectrum analysis, a method to automatically choose the upper and lower borders of the singular value interval reflecting the abrupt information is built. And the selected singular values derived from this method are used to reconstruct abrupt signals. It is proven that the method is able to obtain accurate results by processing the rub-impact fault signal measured from the experiments. The analytical and experimental results indicate that the proposed method is feasible for automatically extracting abrupt information caused by faults like the rotor-stator rub-impact.

  14. Warm and Cool Dinosaurs.

    ERIC Educational Resources Information Center

    Mannlein, Sally

    2001-01-01

    Presents an art activity in which first grade students draw dinosaurs in order to learn about the concept of warm and cool colors. Explains how the activity also helped the students learn about the concept of distance when drawing. (CMK)

  15. Reconciling Warming Trends

    NASA Technical Reports Server (NTRS)

    Schmidt, Gavin A.; Shindell, Drew T.; Tsigaridis, Konstantinos

    2014-01-01

    Climate models projected stronger warming over the past 15 years than has been seen in observations. Conspiring factors of errors in volcanic and solar inputs, representations of aerosols, and El NiNo evolution, may explain most of the discrepancy.

  16. Dynamic vegetation modeling of tropical biomes during Heinrich events

    NASA Astrophysics Data System (ADS)

    Handiani, Dian Noor; Paul, André; Dupont, Lydie M.

    2010-05-01

    Heinrich events are thought to be associated with a slowdown of the Atlantic Meridional Overturning Circulation (AMOC), which in turn would lead to a cooling of the North Atlantic Ocean and a warming of the South Atlantic Ocean (the "bipolar seesaw" hypothesis). The accompanying abrupt climate changes occurred not only in the ocean but also on the continents. Changes were strongest in the Northern Hemisphere but were registered in the tropics as well. Pollen data from Angola and Brazil showed that climate changes during Heinrich events affected vegetation patterns very differently in eastern South America and western Africa. To understand the differential response in the terrestrial tropics, we studied the vegetation changes during Heinrich events by using a dynamic global vegetation model (TRIFFID) as part of the University of Victoria (UVic) Earth System-Climate Model (ESCM). The model results show a bipolar seesaw pattern in temperature and precipitation during a near-collapse of the AMOC. The succession in plant-functional types (PFTs) showed changes from forest to shrubs to desert, including spreading desert in northwest Africa, retreating broadleaf trees in West Africa and northern South America, but advancing broadleaf trees in Brazil. The pattern is explained by a southward shift of the tropical rainbelt resulting in a strong decrease in precipitation over northwest and West Africa as well as in northern South America, but an increase in precipitation in eastern Brazil. To facilitate the comparison between modeled vegetation results with pollen data, we diagnosed the distribution of biomes from the PFT coverage and the simulated model climate. The biome distribution was computed for Heinrich event 1 and the Last Glacial Maximum as well as for pre-industrial conditions. We used a classification of biomes in terms of "mega-biomes", which were defined following a scheme originally proposed by BIOME 6000 (v 4.2). The biome distribution of the Sahel region

  17. Abrupt decadal-to-centennial hydroclimate changes in the Mediterranean region since the mid-Holocene

    NASA Astrophysics Data System (ADS)

    Hu, Hsun-Ming; Shen, Chuan-Chou; Jiang, Xiuyang; Wang, Yongjin; Mii, Horng-Sheng; Michel, Véronique

    2016-04-01

    A series of severe drought events in the Mediterranean region over the past two decades has posed a threat on both human society and biosystem. Holocene hydrological dynamics can offer valuable clues for understanding future climate and making proper adaption strategy. Here, we present a decadal-resolved stalagmite record documenting various hydroclimatic fluctuations in the north central Mediterranean region since the middle Holocene. The stalagmite δ18O sequence shows dramatic instability, characterized by abrupt shifts between dry and wet conditions <50 years. The timing of regional culture demises, such as the Hittite Kingdom, Mycenaean Greece, Akkadian Empire, Egyptian Old Kingdom, and Uruk, occurred during the drought events, suggesting an important role of climate impact on human civilization. The unstable hydroclimate evolution is related to transferred North Atlantic Oscillation states. Rate of rapid transfer of precipitation patterns, which can be pin-pointed by our good chronology, improves the prediction to future climate changes in North Atlantic region. We also found that a strong correlation between this stalagmite δ18O and sea surface temperatures especially in Pacific Ocean. This agreement suggests a distant interregional climate teleconnection.

  18. Abrupt shifts in Horn of Africa hydroclimate since the Last Glacial Maximum.

    PubMed

    Tierney, Jessica E; deMenocal, Peter B

    2013-11-15

    The timing and abruptness of the initiation and termination of the Early Holocene African Humid Period are subjects of ongoing debate, with direct consequences for our understanding of abrupt climate change, paleoenvironments, and early human cultural development. Here, we provide proxy evidence from the Horn of Africa region that documents abrupt transitions into and out of the African Humid Period in northeast Africa. Similar and generally synchronous abrupt transitions at other East African sites suggest that rapid shifts in hydroclimate are a regionally coherent feature. Our analysis suggests that the termination of the African Humid Period in the Horn of Africa occurred within centuries, underscoring the nonlinearity of the region's hydroclimate. PMID:24114782

  19. Onset of deglacial warming in West Antarctica driven by local orbital forcing

    USGS Publications Warehouse

    WAIS Divide Project Members; Steig, Eric J.; Markle, Bradley R.; Schoenemann, Spruce W.; Ding, Qinghua; Taylor, Kendrick C.; McConnell, Joseph R.; Brook, Edward J.; Sowers, Todd; White, James W. C.; Alley, Richard B.; Chen, Hai; Clow, Gary D.; Cole-Dai, Jihong; Conway, Howard; Fitzpatrick, Joan J.; Hargreaves, Geoffrey; and others

    2013-01-01

    The cause of warming in the Southern Hemisphere during the most recent deglaciation remains a matter of debate. Hypotheses for a Northern Hemisphere trigger, through oceanic redistributions of heat, are based in part on the abrupt onset of warming seen in East Antarctic ice cores and dated to 18,000 years ago, which is several thousand years after high-latitude Northern Hemisphere summer insolation intensity began increasing from its minimum, approximately 24,000 years ago. An alternative explanation is that local solar insolation changes cause the Southern Hemisphere to warm independently. Here we present results from a new, annually resolved ice-core record from West Antarctica that reconciles these two views. The records show that 18,000 years ago snow accumulation in West Antarctica began increasing, coincident with increasing carbon dioxide concentrations, warming in East Antarctica and cooling in the Northern Hemisphere associated with an abrupt decrease in Atlantic meridional overturning circulation. However, significant warming in West Antarctica began at least 2,000 years earlier. Circum-Antarctic sea-ice decline, driven by increasing local insolation, is the likely cause of this warming. The marine-influenced West Antarctic records suggest a more active role for the Southern Ocean in the onset of deglaciation than is inferred from ice cores in the East Antarctic interior, which are largely isolated from sea-ice changes.

  20. Onset of deglacial warming in West Antarctica driven by local orbital forcing.

    PubMed

    2013-08-22

    The cause of warming in the Southern Hemisphere during the most recent deglaciation remains a matter of debate. Hypotheses for a Northern Hemisphere trigger, through oceanic redistributions of heat, are based in part on the abrupt onset of warming seen in East Antarctic ice cores and dated to 18,000 years ago, which is several thousand years after high-latitude Northern Hemisphere summer insolation intensity began increasing from its minimum, approximately 24,000 years ago. An alternative explanation is that local solar insolation changes cause the Southern Hemisphere to warm independently. Here we present results from a new, annually resolved ice-core record from West Antarctica that reconciles these two views. The records show that 18,000 years ago snow accumulation in West Antarctica began increasing, coincident with increasing carbon dioxide concentrations, warming in East Antarctica and cooling in the Northern Hemisphere associated with an abrupt decrease in Atlantic meridional overturning circulation. However, significant warming in West Antarctica began at least 2,000 years earlier. Circum-Antarctic sea-ice decline, driven by increasing local insolation, is the likely cause of this warming. The marine-influenced West Antarctic records suggest a more active role for the Southern Ocean in the onset of deglaciation than is inferred from ice cores in the East Antarctic interior, which are largely isolated from sea-ice changes. PMID:23945585

  1. Dansgaard-Oeschger Cycles in the Gulf of Mexico: A Clue to Abrupt Climate Change?

    NASA Astrophysics Data System (ADS)

    Hill, H. W.; Flower, B. P.; Quinn, T. M.

    2003-12-01

    events. The amplitude of the isotopic data and the very negative δ 18O values (-2 ‰ ) point to meltwater input as being the primary control on salinity. The presence of D-O cycles in the Gulf of Mexico has important implications for understanding abrupt climate change on the millennial time scale and for defining the relationship between high and low latitude climate variability, particularly as it relates to meltwater input from ice sheets. Defining the phasing of D-O cycles in the Gulf of Mexico relative to Greenland will make it easier to assess the relative importance of thermohaline circulation and greenhouse gas concentration changes on global climate change.

  2. Long range global warming

    SciTech Connect

    Rolle, K.C.; Pulkrabek, W.W.; Fiedler, R.A.

    1995-12-31

    This paper explores one of the causes of global warming that is often overlooked, the direct heating of the environment by engineering systems. Most research and studies of global warming concentrate on the modification that is occurring to atmospheric air as a result of pollution gases being added by various systems; i.e., refrigerants, nitrogen oxides, ozone, hydrocarbons, halon, and others. This modification affects the thermal radiation balance between earth, sun and space, resulting in a decrease of radiation outflow and a slow rise in the earth`s steady state temperature. For this reason the solution to the problem is perceived as one of cleaning up the processes and effluents that are discharged into the environment. In this paper arguments are presented that suggest, that there is a far more serious cause for global warming that will manifest itself in the next two or three centuries; direct heating from the exponential growth of energy usage by humankind. Because this is a minor contributor to the global warming problem at present, it is overlooked or ignored. Energy use from the combustion of fuels and from the output of nuclear reactions eventually is manifest as warming of the surroundings. Thus, as energy is used at an ever increasing rate the consequent global warming also increases at an ever increasing rate. Eventually this rate will become equal to a few percent of solar radiation. When this happens the earth`s temperature will have risen by several degrees with catastrophic results. The trends in world energy use are reviewed and some mathematical models are presented to suggest future scenarios. These models can be used to predict when the global warming problem will become undeniably apparent, when it will become critical, and when it will become catastrophic.

  3. Warm up to the idea: Global warming is here

    SciTech Connect

    Lynch, C.F.

    1996-07-01

    This article summarizes recent information about global warming as well as the history of greenhouse gas emissions which have lead to more and more evidence of global warming. The primary source detailed is the second major study report on global warming by the Intergovernmental Panel on climate change. Along with comments about the environmental effects of global warming such as coastline submersion, the economic, social and political aspects of alleviating greenhouse emissions and the threat of global warming are discussed.

  4. A High-Resolution Record of Meltwater Discharge and Deglacial Warming in the Gulf of Mexico

    NASA Astrophysics Data System (ADS)

    Gilbert, M. L.; Hastings, D. W.; Flower, B. P.; Quinn, T. M.

    2005-12-01

    Sea surface temperature (SST) and δ18Osw records from the Gulf of Mexico (GOM) during the last deglaciation will help distinguish different mechanisms for abrupt climate change. Orca Basin is an ideal location to study climate changes in the GOM and to record the timing of meltwater discharge events through the Mississippi River; the anoxic hypersaline bottom water prevents bioturbation and results in finely laminated sediments. We sampled core MD 02-2550 at 0.5 cm resolution which, given sedimentation rates of greater than 30 cm/ka, corresponds to ~20 yr resolution. We analyzed Mg/Ca ratios on Globigerinoides ruber (white) to generate a SST record using the calibration of Anand et al. (2003). The record presented here extends from ca. 13 to 10.4 ka BP. The average temperatures at the beginning of the record from 13 to 12.5 ka BP are 26.3°C, with a variability of 1.0°C (1 σ). A major SST decrease of 3.0°C is recorded in two steps at 12.5 ka and 12.2 that lasts ca. 500 years. Within this transition, a more rapid cooling of ~2.0°C in less than 100 years is observed starting at ca. 12.2 ka. A reciprocal warming is observed in three stages from 12.0 to 11.0 ka: first a warming of 1.3°C over 300 years, relatively constant temperatures for 400 years, and a final warming of 1.7°C over 300 years returning to the same average SST as before the cold period. These cooler temperatures persisted for ca. 1500 yrs and likely corresponds to the Younger Dryas stadial. The annual SST in the GOM today is the same as the average temperature preceding and following the cold period. These trends represent the most detailed Mg/Ca SST records of the B/A Younger Dryas oscillation observed in the GOM. Paired with the Mg/Ca-derived SST, δ18O data will be generated to produce a δ18Osw record. This will enable us to ascertain the timing and precise phasing of deglacial warming relative to Laurentide ice sheet meltwater input into the GOM.

  5. Abrupt drainage cycles of the Fennoscandian Ice Sheet

    PubMed Central

    Soulet, Guillaume; Ménot, Guillemette; Bayon, Germain; Rostek, Frauke; Ponzevera, Emmanuel; Toucanne, Samuel; Lericolais, Gilles; Bard, Edouard

    2013-01-01

    Continental ice sheets are a key component of the Earth’s climate system, but their internal dynamics need to be further studied. Since the last deglaciation, the northern Eurasian Fennoscandian Ice Sheet (FIS) has been connected to the Black Sea (BS) watershed, making this basin a suitable location to investigate former ice-sheet dynamics. Here, from a core retrieved in the BS, we combine the use of neodymium isotopes, high-resolution elemental analysis, and biomarkers to trace changes in sediment provenance and river runoff. We reveal cyclic releases of meltwater originating from Lake Disna, a proglacial lake linked to the FIS during Heinrich Stadial 1. Regional interactions within the climate–lake–FIS system, linked to changes in the availability of subglacial water, led to abrupt drainage cycles of the FIS into the BS watershed. This phenomenon raised the BS water level by ∼100 m until the sill of the Bosphorus Strait was reached, flooding the vast northwestern BS shelf and deeply affecting the hydrology and circulation of the BS and, probably, of the Marmara and Aegean Seas. PMID:23569264

  6. The Magnetospheric Response to Abrupt Variations in the IMF Orientation

    NASA Astrophysics Data System (ADS)

    Sibeck, D. G.

    2014-12-01

    We run the University of Michigan's BATS-R-US global magnetohydrodynamic model at NASA/GSFC's CCMCto study the magnetospheric response to abrupt variations in the IMF orientation but constant solar wind plasmaparameters. IMF rotations from southward to duskward orientations diminish reconnection rates and the flow ofplasma to the dayside magnetopause, launch Alfven waves that carry strong duskward magnetic field perturbationsto the cusp ionosphere, introduce a weak duskward magnetic field perturbation to the outer dayside magnetosphere, twistthe magnetotail current sheet counterclockwise when viewed from the Sun, flatten the north/south dimensions of the distant magnetotail, andgenerate a broad slow-mode fan on the magnetotail flanks. Southward IMF turnings strengthen the Region 1 Birkelandcurrents, prominently depressing magnetic field strengths in the inner dayside magnetosphere and to a lesserdegree those in the outer magnetosphere, consistent with inward dayside magnetopause erosion. The daysidemagnetopause becomes blunter. As evidenced by enhanced magnetosheath thermal and magnetosphericmagnetic pressures, the magnetopause therefore becomes subject to a greater fraction of the incident solar winddynamic pressure at locations away from the subsolar point.

  7. Abrupt drainage cycles of the Fennoscandian Ice Sheet.

    PubMed

    Soulet, Guillaume; Ménot, Guillemette; Bayon, Germain; Rostek, Frauke; Ponzevera, Emmanuel; Toucanne, Samuel; Lericolais, Gilles; Bard, Edouard

    2013-04-23

    Continental ice sheets are a key component of the Earth's climate system, but their internal dynamics need to be further studied. Since the last deglaciation, the northern Eurasian Fennoscandian Ice Sheet (FIS) has been connected to the Black Sea (BS) watershed, making this basin a suitable location to investigate former ice-sheet dynamics. Here, from a core retrieved in the BS, we combine the use of neodymium isotopes, high-resolution elemental analysis, and biomarkers to trace changes in sediment provenance and river runoff. We reveal cyclic releases of meltwater originating from Lake Disna, a proglacial lake linked to the FIS during Heinrich Stadial 1. Regional interactions within the climate-lake-FIS system, linked to changes in the availability of subglacial water, led to abrupt drainage cycles of the FIS into the BS watershed. This phenomenon raised the BS water level by ∼100 m until the sill of the Bosphorus Strait was reached, flooding the vast northwestern BS shelf and deeply affecting the hydrology and circulation of the BS and, probably, of the Marmara and Aegean Seas. PMID:23569264

  8. Detecting and isolating abrupt changes in linear switching systems

    NASA Astrophysics Data System (ADS)

    Nazari, Sohail; Zhao, Qing; Huang, Biao

    2015-04-01

    In this paper, a novel fault detection and isolation (FDI) method for switching linear systems is developed. All input and output signals are assumed to be corrupted with measurement noises. In the proposed method, a 'lifted' linear model named as stochastic hybrid decoupling polynomial (SHDP) is introduced. The SHDP model governs the dynamics of the switching linear system with all different modes, and is independent of the switching sequence. The error-in-variable (EIV) representation of SHDP is derived, and is used for the fault residual generation and isolation following the well-adopted local approach. The proposed FDI method can detect and isolate the fault-induced abrupt changes in switching models' parameters without estimating the switching modes. Furthermore, in this paper, the analytical expressions of the gradient vector and Hessian matrix are obtained based on the EIV SHDP formulation, so that they can be used to implement the online fault detection scheme. The performance of the proposed method is then illustrated by simulation examples.

  9. Abrupt climate change and the decline of Indus urbanism

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    Climate change has been suggested as a cause for the decline of the cities of the Indus Civilization, which is believed to have begun ~4.0 to 3.9 ky B.P. Previous studies have centered on paleoclimatic records obtained from areas outside the geographic limits of the Indus Civilization, raising questions about their suitability for evaluating past climate-cultural linkages. Here we report a detailed climate record from paleolake Kotla Dahar, Haryana (28°00'095'' N, 76°57'173'' E), located at the eastern edge of the distribution of Indus settlements and ~100km to the east of the city-site of Rakhigarhi in NW India. Regional hydrologic changes are inferred using oxygen-isotope measurements of gastropod aragonite from a 2.88-m sediment section. A permanent ~4‰ increase in δ18O of shell aragonite occurred at ~4.1±0.1 ky B.P., marking an abrupt increase in evaporation/precipitation in the lake catchment. These data provide evidence for a weakening of the monsoon and shift toward drier climate on the plains of northwest (NW) India at ~4.1±0.1 ky B.P. Decreased monsoon rainfall at this time may have been linked to increased ENSO variability, and supports a possible role of climate in the transformation of the Indus Civilization from an urbanized (mature or urban Indus) to a rural (post-urban) society.

  10. Anticipating abrupt shifts in temporal evolution of probability of eruption

    NASA Astrophysics Data System (ADS)

    Rohmer, Jeremy; Loschetter, Annick

    2016-04-01

    Estimating the probability of eruption by jointly accounting for different sources of monitoring parameters over time is a key component for volcano risk management. In the present study, we are interested in the transition from a state of low-to-moderate probability value and to the one of high probability value: the latter value generally supports the call for evacuation. By using the data of MESIMEX exercise at the Vesuvius volcano, we investigated the potential for time-varying indicators related to the correlation structure or to the variability of the probability time series for detecting in advance this critical transition. We found that changes in the power spectra and in the standard deviation estimated over a rolling time window both present an abrupt increase, which marks the approaching shift. Our numerical experiments revealed that the transition from an eruption probability of 10-15% to >70% could be identified up 4 hours in advance, ~2.5 days before the evacuation call (decided for an eruption probability >80% during the MESIMEX exercise). This additional lead time could be useful to place different key services (e.g., emergency services for vulnerable groups, commandeering additional transportation means, etc.) on a higher level of alert before the actual call for evacuation.

  11. Abrupt Schottky Junctions in Al/Ge Nanowire Heterostructures

    PubMed Central

    2015-01-01

    In this Letter we report on the exploration of axial metal/semiconductor (Al/Ge) nanowire heterostructures with abrupt interfaces. The formation process is enabled by a thermal induced exchange reaction between the vapor–liquid–solid grown Ge nanowire and Al contact pads due to the substantially different diffusion behavior of Ge in Al and vice versa. Temperature-dependent I–V measurements revealed the metallic properties of the crystalline Al nanowire segments with a maximum current carrying capacity of about 0.8 MA/cm2. Transmission electron microscopy (TEM) characterization has confirmed both the composition and crystalline nature of the pure Al nanowire segments. A very sharp interface between the ⟨111⟩ oriented Ge nanowire and the reacted Al part was observed with a Schottky barrier height of 361 meV. To demonstrate the potential of this approach, a monolithic Al/Ge/Al heterostructure was used to fabricate a novel impact ionization device. PMID:26052733

  12. Anticipating abrupt shifts in temporal evolution of probability of eruption

    NASA Astrophysics Data System (ADS)

    Rohmer, J.; Loschetter, A.

    2016-04-01

    Estimating the probability of eruption by jointly accounting for different sources of monitoring parameters over time is a key component for volcano risk management. In the present study, we are interested in the transition from a state of low-to-moderate probability value to a state of high probability value. By using the data of MESIMEX exercise at the Vesuvius volcano, we investigated the potential for time-varying indicators related to the correlation structure or to the variability of the probability time series for detecting in advance this critical transition. We found that changes in the power spectra and in the standard deviation estimated over a rolling time window both present an abrupt increase, which marks the approaching shift. Our numerical experiments revealed that the transition from an eruption probability of 10-15% to > 70% could be identified up to 1-3 h in advance. This additional lead time could be useful to place different key services (e.g., emergency services for vulnerable groups, commandeering additional transportation means, etc.) on a higher level of alert before the actual call for evacuation.

  13. Consistent Observational and Numerical Modeling Support for Ice Sheet Forcing of DOI event 8

    NASA Astrophysics Data System (ADS)

    Lu, S.; Jackson, C.; Marchal, O.; Thompson, W.; Stocker, T.

    2008-12-01

    The Binge/Purge (B/P) hypothesis of abrupt climate change (MacAyeal, 1993a,b, Paleoceanography) suggests that an instability and periodic collapse of the Laurentide ice sheet is responsible for the observed abrupt warmings of Greenland (Dansgaard-Oeschger Interstadials or DOIs) through the influence of ice sheet meltwater on ocean circulation and its poleward heat transport. If the B/P hypothesis is correct, then one should be able to use the Greenland paleotemperature data and a climate model to infer changes in global sea level associated with the DOIs. The B/P hypothesis could then be tested by comparing the inferred sea level changes with independent reconstructions based on marine records (corals and sediments). We use stochastic inversion of a seasonal resolving climate model (Schmittner and Stocker, 1999, J. Climate), composed of a zonally averaged ocean model (Wright and Stocker, 1992, J. Geophys. Res.) coupled to an energy and moisture balance model of the atmosphere, to infer the changes in ice sheet meltwater required to explain the Greenland paleotemperature record from 39 ka to 34 ka which include DOIs 8, 7, and 6. We found a compelling consistency between modeled and reconstructed sea level changes for DOI 8 (a particularly long interstadial following Heinrich Event 4), which tends to support the B/P hypothesis. On the other hand, the large estimated uncertainties in the inversion solution and sea level reconstructions do not permit a firm test of the B/P hypothesis for DOIs 7 and 6.

  14. Iceberg discharges and oceanic circulation changes during glacial abrupt climate changes

    NASA Astrophysics Data System (ADS)

    Alvarez-Solas, Jorge; Robinson, Alexander; Banderas, Rubén; Montoya, Marisa

    2015-04-01

    Proxy data reveal the existence of episodes of increased deposition of ice-rafted debris in the North Atlantic Ocean during the last glacial period. These are interpreted as massive iceberg discharges mainly from the Laurentide Ice Sheet. Although these have long been attributed to self-sustained ice sheet oscillations, growing evidence points to an active role of the oceanic circulation. Here we will present simulations of the last glacial period carried out with a hybrid ice sheet-ice shelf model. Two mechanisms producing iceberg discharges are compared. First, we reproduce the classic binge-purge by which the iceberg surges are produced thanks to the existence of an internal thermo-mechanical feedback that allows the ice sheet to behave under an oscillatory regime. Second, our ice-sheet model is forced by an oceanic warming index derived from proxy data that accounts for the impact of past ocean circulation changes on ocean temperatures. In this case, the model generates a time series of iceberg calving that agrees with ice-rafted debris records over the past 80 ka. We compare the two theories and discuss their advantages and weaknesses in terms of both the robustness of the physics on which they are based and their comparison with proxies. This comparison highlights the importance of considering past oceanic circulation changes in order to understand the ice-sheet dynamics. However, the ultimate processes determining abrupt changes in the Atlantic Meridional Overturning Circulation (AMOC) remain elusive. Therefore we will also analyze several proposed mechanisms that aims to explain such AMOC reorganizations, focusing on those that do not require freshwater flux forcing.

  15. Middle East coastal ecosystem response to middle-to-late Holocene abrupt climate changes

    PubMed Central

    Kaniewski, D.; Paulissen, E.; Van Campo, E.; Al-Maqdissi, M.; Bretschneider, J.; Van Lerberghe, K.

    2008-01-01

    The Holocene vegetation history of the northern coastal Arabian Peninsula is of long-standing interest, as this Mediterranean/semiarid/arid region is known to be particularly sensitive to climatic changes. Detailed palynological data from an 800-cm alluvial sequence cored in the Jableh plain in northwest Syria have been used to reconstruct the vegetation dynamics in the coastal lowlands and the nearby Jabal an Nuşayriyah mountains for the period 2150 to 550 B.C. Corresponding with the 4.2 to 3.9 and 3.5 to 2.5 cal kyr BP abrupt climate changes (ACCs), two large-scale shifts to a more arid climate have been recorded. These two ACCs had different impacts on the vegetation assemblages in coastal Syria. The 3.5 to 2.5 cal kyr BP ACC is drier and lasted longer than the 4.2 to 3.9 cal kyr BP ACC, and is characterized by the development of a warm steppe pollen-derived biome (1100–800 B.C.) and a peak of hot desert pollen-derived biome at 900 B.C. The 4.2 to 3.9 cal kyr BP ACC is characterized by a xerophytic woods and shrubs pollen-derived biome ca. 2050 B.C. The impact of the 3.5 to 2.5 cal kyr BP ACC on human occupation and cultural development is important along the Syrian coast with the destruction of Ugarit and the collapse of the Ugarit kingdom at ca. 1190 to 1185 B.C. PMID:18772385

  16. Abrupt along-strike change in tectonic style: San Andreas fault zone, San Francisco Peninsula

    USGS Publications Warehouse

    Zoback, M.L.; Jachens, R.C.; Olson, J.A.

    1999-01-01

    Seismicity and high-resolution aeromagnetic data are used to define an abrupt change from compressional to extensional tectonism within a 10- to 15-km-wide zone along the San Andreas fault on the San Francisco Peninsula and offshore from the Golden Gate. This 100-km-long section of the San Andreas fault includes the hypocenter of the Mw = 7.8 1906 San Francisco earthquake as well as the highest level of persistent microseismicity along that ???470-km-long rupture. We define two distinct zones of deformation along this stretch of the fault using well-constrained relocations of all post-1969 earthquakes based a joint one-dimensional velocity/hypocenter inversion and a redetermination of focal mechanisms. The southern zone is characterized by thrust- and reverse-faulting focal mechanisms with NE trending P axes that indicate "fault-normal" compression in 7- to 10-km-wide zones of deformation on both sides of the San Andreas fault. A 1- to 2-km-wide vertical zone beneath the surface trace of the San Andreas is characterized by its almost complete lack of seismicity. The compressional deformation is consistent with the young, high topography of the Santa Cruz Mountains/Coast Ranges as the San Andreas fault makes a broad restraining left bend (???10??) through the southernmost peninsula. A zone of seismic quiescence ???15 km long separates this compressional zone to the south from a zone of combined normal-faulting and strike-slip-faulting focal mechanisms (including a ML = 5.3 earthquake in 1957) on the northernmost peninsula and offshore on the Golden Gate platform. Both linear pseudo-gravity gradients, calculated from the aeromagnetic data, and seismic reflection data indicate that the San Andreas fault makes an abrupt ???3-km right step less than 5 km offshore in this northern zone. A similar right-stepping (dilatational) geometry is also observed for the subparallel San Gregorio fault offshore. Persistent seismicity and extensional tectonism occur within the San

  17. Permafrost thawing as a possible source of abrupt carbon release at the onset of the Bølling/Allerød

    PubMed Central

    Köhler, Peter; Knorr, Gregor; Bard, Edouard

    2014-01-01

    One of the most abrupt and yet unexplained past rises in atmospheric CO2 (>10 p.p.m.v. in two centuries) occurred in quasi-synchrony with abrupt northern hemispheric warming into the Bølling/Allerød, ~14,600 years ago. Here we use a U/Th-dated record of atmospheric Δ14C from Tahiti corals to provide an independent and precise age control for this CO2 rise. We also use model simulations to show that the release of old (nearly 14C-free) carbon can explain these changes in CO2 and Δ14C. The Δ14C record provides an independent constraint on the amount of carbon released (~125 Pg C). We suggest, in line with observations of atmospheric CH4 and terrigenous biomarkers, that thawing permafrost in high northern latitudes could have been the source of carbon, possibly with contribution from flooding of the Siberian continental shelf during meltwater pulse 1A. Our findings highlight the potential of the permafrost carbon reservoir to modulate abrupt climate changes via greenhouse-gas feedbacks. PMID:25409739

  18. An abrupt and prominent climatic reversal at 9.2 ka in the northeastern North America

    NASA Astrophysics Data System (ADS)

    Hou, J.; Huang, Y.; Shuman, B. N.; Oswald, W.; Foster, D. R.

    2008-12-01

    Continental climate during the early Holocene (from 10 to 7 ka) is characterized by multiple abrupt climatic reversals such as the well-known 8.2 ka event that has been observed worldwide and attributed to the terminal collapse of the Laurentide Ice Sheet (LIS) in the North American continent. However, many episodes of meltwater releases occurred prior to the final collapse of LIS, their impact on the continental climate is much less understood. We present in this paper decadal-scale hydrogen isotopic records of aquatic and terrestrial plant biomarkers from Blood Pond, Massachusetts during the early Holocene. Our isotopic records infer a cooling of 3~4 degree between 9.3 and 9.1 ka against the millennial scale climate background, mainly induced by changes in precipitation seasonality. In comparison, the 8.2 ka event displays smaller amplitude of temperature cooling of 1~2 degree at our southern New England site. We interpret our observed climatic reversal at ~ 9.2 ka as representing increased proportion of winter precipitation in conjunction with a drier and cooler summer, triggered by slowdown in thermohaline circulation as a result of freshwater release from the proglacial lakes. We attribute the difference in climate response at 8.2 ka and 9.2 ka events to the configuration of LIS, with 9.2 ka LIS having a much stronger blocking effect on the moisture from the Gulf of Mexico during the summer. Our data suggest that the seasonality of the precipitation at the southern New England was highly sensitive to meltwater releases, especially prior to the final collapse of the LIS.

  19. Wildfire responses to abrupt climate change in North America

    PubMed Central

    Marlon, J. R.; Bartlein, P. J.; Walsh, M. K.; Harrison, S. P.; Brown, K. J.; Edwards, M. E.; Higuera, P. E.; Power, M. J.; Anderson, R. S.; Briles, C.; Brunelle, A.; Carcaillet, C.; Daniels, M.; Hu, F. S.; Lavoie, M.; Long, C.; Minckley, T.; Richard, P. J. H.; Scott, A. C.; Shafer, D. S.; Tinner, W.; Umbanhowar, C. E.; Whitlock, C.

    2009-01-01

    It is widely accepted, based on data from the last few decades and on model simulations, that anthropogenic climate change will cause increased fire activity. However, less attention has been paid to the relationship between abrupt climate changes and heightened fire activity in the paleorecord. We use 35 charcoal and pollen records to assess how fire regimes in North America changed during the last glacial–interglacial transition (15 to 10 ka), a time of large and rapid climate changes. We also test the hypothesis that a comet impact initiated continental-scale wildfires at 12.9 ka; the data do not support this idea, nor are continent-wide fires indicated at any time during deglaciation. There are, however, clear links between large climate changes and fire activity. Biomass burning gradually increased from the glacial period to the beginning of the Younger Dryas. Although there are changes in biomass burning during the Younger Dryas, there is no systematic trend. There is a further increase in biomass burning after the Younger Dryas. Intervals of rapid climate change at 13.9, 13.2, and 11.7 ka are marked by large increases in fire activity. The timing of changes in fire is not coincident with changes in human population density or the timing of the extinction of the megafauna. Although these factors could have contributed to fire-regime changes at individual sites or at specific times, the charcoal data indicate an important role for climate, and particularly rapid climate change, in determining broad-scale levels of fire activity. PMID:19190185

  20. Introduction to the Abrupt Wing Stall (AWS) Program

    NASA Technical Reports Server (NTRS)

    Hall, Robert M.; Woodson, Shawn H.

    2003-01-01

    The Abrupt Wing Stall (AWS) Program has addressed the problem of uncommanded, transonic lateral motions, such as wing drop, with experimental, computational, and simulation tools. Background to the establishment of the AWS program is given as well as program objectives. In order to understand the fundamental flow mechanisms that caused the undesirable motions for a pre-production version of the F/A-18E, steady and unsteady flow field details were gathered from dedicated transonic wind-tunnel testing and computational studies. The AWS program has also adapted a free-to-roll (FTR) wind-tunnel testing technique traditionally used for low-speed studies of lateral dynamic stability to the transonic flow regime. This FTR capability was demonstrated first in a proof-of -concept study and then applied to an assessment of four different aircraft configurations. Figures of merit for static testing and for FTR testing have been evaluated for two configurations that demonstrated wing drop susceptibility during full-scale flight conditions (the pre-production F/A-18E and the AV-8B at the extremes of its flight envelope) and two configurations that do not exhibit wing drop (the F/A-18C and the F-16C). Design insights have been obtained from aerodynamic computational studies of the four aircraft configurations and from computations quantifying the impact of the various geometric wing differences between the F/A-18C and the F/A-18E wings. Finally, the AWS program provides guidance for assessing, in the simulator, the impact of experimentally determined lateral activity on flight characteristics before going to flight.

  1. Introduction to the Abrupt Wing Stall (AWS) Program

    NASA Technical Reports Server (NTRS)

    Hall, Robert M.; Woodson, Shawn H.

    2003-01-01

    The Abrupt Wing Stall (AWS) Program has addressed the problem of uncommanded, transonic lateral motions, such as wing drop, with experimental, computational, and simulation tools. Background to the establishment of the AWS program is given as well as program objectives. In order to understand the fundamental flow mechanisms that caused the undesirable motions for a pre-production version of the F/A-18E, steady and unsteady flow field details were gathered from dedicated transonic wind-tunnel testing and computational studies. The AWS program has also adapted a free-to- roll (FTR) wind-tunnel testing technique traditionally used for low-speed studies of lateral dynamic stability to the transonic flow regime. This FTR capability was demonstrated first in a proof-of-concept study and then applied to an assessment of four different aircraft configurations. Figures of merit for static testing and for FTR testing have been evaluated for two configurations that demonstrated wing drop susceptibility during full-scale flight conditions (the pre-production F/A-l8E and the AV-8B at the extremes of its flight envelope) and two configurations that do not exhibit wing drop (the F/A-l8C and the F-l6C). Design insights have been obtained from aerodynamic computational studies of the four aircraft configurations and from computations quantifying the impact of the various geometric wing differences between the F/A-18C and the F/A-l8E wings. Finally, the AWS program provides guidance for assessing, in the simulator, the impact of experimentally determined lateral activity on flight characteristics before going to flight.

  2. Relaxation Oscillations as a Mechanism of Abrupt Climate Change

    NASA Astrophysics Data System (ADS)

    Marchal, O.; Jackson, C.; Nilsson, J.; Paul, A.; Stocker, T.

    2007-12-01

    Climate variability at the millennial time scale is difficult to rationalize, as the frequency 0.001 1/yr falls near the middle of a wide gap in the spectrum of external forcing on the climate system (between the low-frequency orbital components and the high-frequency tidal components). This situation prompted interest in the possibility for the climate system to undergo self-sustained or self-excited oscillations. Our contribution will comprise two parts. First, we will review elements from the theory of non-linear vibrations that provide a framework for the discussion of the fundamental mechanisms responsible for millennial-scale climate variability. Particular emphasis will be put on the self-sustained oscillations that occur in physical systems with one degree of freedom. In such systems self-sustained oscillations arise from the nonlinear dependence of the damping force on velocity. In the limit of very large nonlinearity, the oscillator stores energy for a relatively long period of time and releases this energy in a relatively short time, i.e., the oscillations are strongly asymmetric (relaxation oscillations). Second, we will examine the self-sustained oscillations of the meridional overturning circulation simulated by an ocean circulation model when subject to large freshwater forcing (salt addition at low latitudes and salt extraction at high latitudes). A scaling analysis provides evidence that these oscillations can be fundamentally interpreted as relaxation oscillations : the model ocean stores potential energy in the form of an unstable vertical temperature gradient for a relatively long period of time (phase of reduced MOC) and converts this potential energy into kinetic energy (phase of intense MOC) when the unstable vertical temperature gradient dominates the stable vertical salinity gradient in the density stratification. The merits and weaknesses of the hypothesis of relaxation oscillations as a mechanism of abrupt climate change will be discussed.

  3. Warm and Cool Cityscapes

    ERIC Educational Resources Information Center

    Jubelirer, Shelly

    2012-01-01

    Painting cityscapes is a great way to teach first-grade students about warm and cool colors. Before the painting begins, the author and her class have an in-depth discussion about big cities and what types of buildings or structures that might be seen in them. They talk about large apartment and condo buildings, skyscrapers, art museums,…

  4. Abrupt reversal in emissions and atmospheric abundance of HCFC-133a (CF3CH2Cl)

    NASA Astrophysics Data System (ADS)

    Vollmer, Martin K.; Rigby, Matt; Laube, Johannes C.; Henne, Stephan; Rhee, Tae Siek; Gooch, Lauren J.; Wenger, Angelina; Young, Dickon; Steele, L. Paul; Langenfelds, Ray L.; Brenninkmeijer, Carl A. M.; Wang, Jia-Lin; Ou-Yang, Chang-Feng; Wyss, Simon A.; Hill, Matthias; Oram, David E.; Krummel, Paul B.; Schoenenberger, Fabian; Zellweger, Christoph; Fraser, Paul J.; Sturges, William T.; O'Doherty, Simon; Reimann, Stefan

    2015-10-01

    Hydrochlorofluorocarbon HCFC-133a (CF3CH2Cl) is an anthropogenic compound whose consumption for emissive use is restricted under the Montreal Protocol. A recent study showed rapidly increasing atmospheric abundances and emissions. We report that, following this rise, the atmospheric abundance and emissions have declined sharply in the past three years. We find a Northern Hemisphere HCFC-133a increase from 0.13 ppt (dry-air mole fraction in parts per trillion) in 2000 to 0.50 ppt in 2012-mid-2013 followed by an abrupt drop to ˜0.44 ppt by early 2015. Global emissions derived from these observations peaked at 3.1 kt in 2011, followed by a rapid decline of ˜0.5 kt yr-2 to reach 1.5 kt yr-1 in 2014. Sporadic HCFC-133a pollution events are detected in Europe from our high-resolution HCFC-133a records at three European stations, and in Asia from samples collected in Taiwan. European emissions are estimated to be <0.1 kt yr-1 although emission hot spots were identified in France.

  5. -induced continental warming

    NASA Astrophysics Data System (ADS)

    Kamae, Youichi; Watanabe, Masahiro; Kimoto, Masahide; Shiogama, Hideo

    2014-11-01

    In this the second of a two-part study, we examine the physical mechanisms responsible for the increasing contrast of the land-sea surface air temperature (SAT) in summertime over the Far East, as observed in recent decades and revealed in future climate projections obtained from a series of transient warming and sensitivity experiments conducted under the umbrella of the Coupled Model Intercomparison Project phase 5. On a global perspective, a strengthening of land-sea SAT contrast in the transient warming simulations of coupled atmosphere-ocean general circulation models is attributed to an increase in sea surface temperature (SST). However, in boreal summer, the strengthened contrast over the Far East is reproduced only by increasing atmospheric CO2 concentration. In response to SST increase alone, the tropospheric warming over the interior of the mid- to high-latitude continents including Eurasia are weaker than those over the surrounding oceans, leading to a weakening of the land-sea SAT contrast over the Far East. Thus, the increasing contrast and associated change in atmospheric circulation over East Asia is explained by CO2-induced continental warming. The degree of strengthening of the land-sea SAT contrast varies in different transient warming scenarios, but is reproduced through a combination of the CO2-induced positive and SST-induced negative contributions to the land-sea contrast. These results imply that changes of climate patterns over the land-ocean boundary regions are sensitive to future scenarios of CO2 concentration pathways including extreme cases.

  6. Gradual and abrupt changes during the Mid-Pleistocene Transition

    NASA Astrophysics Data System (ADS)

    Ford, Heather L.; Sosdian, Sindia M.; Rosenthal, Yair; Raymo, Maureen E.

    2016-09-01

    During the Mid-Pleistocene Transition (MPT), the dominant glacial-interglacial cyclicity as inferred from the marine δ18O records of benthic foraminifera (δ18Obenthic) changed from 41 kyr to 100 kyr years in the absence of a comparable change in orbital forcing. Currently, only two Mg/Ca-derived, high-resolution bottom water temperature (BWT) records exist that can be used with δ18Obenthic records to separate temperature and ice volume signals over the Pleistocene. However, these two BWT records suggest a different pattern of climate change occurred over the MPT-a record from North Atlantic DSDP Site 607 suggests BWT decreased with no long-term trend in ice volume over the MPT, while South Pacific ODP Site 1123 suggests that BWT has been relatively stable over the last 1.5 Myr but that there was an abrupt increase in ice volume at ∼900 kyr. In this paper we attempt to reconcile these two views of climate change across the MPT. Specifically, we investigated the suggestion that the secular BWT trend obtained from Mg/Ca measurements on Cibicidoides wuellerstorfi and Oridorsalis umbonatus species from N. Atlantic Site 607 is biased by the possible influence of Δ[CO32-] on Mg/Ca values in these species by generating a low-resolution BWT record using Uvigerina spp., a genus whose Mg/Ca values are not thought to be influenced by Δ[CO32-]. We find a long-term BWT cooling of ∼2-3°C occurred from 1500 to ∼500 kyr in the N. Atlantic, consistent with the previously generated C. wuellerstorfi and O. umbonatus BWT record. We also find that changes in ocean circulation likely influenced δ18Obenthic, BWT, and δ18Oseawater records across the MPT. N. Atlantic BWT cooling starting at ∼1.2 Ma, presumably driven by high-latitude cooling, may have been a necessary precursor to a threshold response in climate-ice sheet behavior at ∼900 ka. At that point, a modest increase in ice volume and thermohaline reorganization may have caused enhanced sensitivity to the 100 kyr

  7. Arctic Ocean freshwater as a trigger for abrupt climate change

    NASA Astrophysics Data System (ADS)

    Bradley, Raymond; Condron, Alan; Coletti, Anthony

    2016-04-01

    The cause of the Younger Dryas cooling remains unresolved despite decades of debate. Current arguments focus on either freshwater from Glacial Lake Agassiz drainage through the St Lawrence or the MacKenzie river systems. High resolution ocean modeling suggests that freshwater delivered to the North Atlantic from the Arctic Ocean through Fram Strait would have had more of an impact on Atlantic Meridional Overturning Circulation (AMOC) than freshwater from the St Lawrence. This has been interpreted as an argument for a MacKenzie River /Lake Agassiz freshwater source. However, it is important to note that although the modeling identifies Fram Strait as the optimum location for delivery of freshwater to disrupt the AMOC, this does not mean the freshwater source came from Lake Agassiz. Another potential source of freshwater is the Arctic Ocean ice cover itself. During the LGM, ice cover was extremely thick - many tens of meters in the Canada Basin (at least), resulting in a hiatus in sediment deposition there. Extreme ice thickness was related to a stagnant circulation, very low temperatures and continuous accumulation of snow on top of a base of sea-ice. This resulted in a large accumulation of freshwater in the Arctic Basin. As sea-level rose and a more modern circulation regime became established in the Arctic, this freshwater was released from the Arctic Ocean through Fram Strait, leading to extensive sea-ice formation in the North Atlantic (Greenland Sea) and a major reduction in the AMOC. Here we present new model results and a review of the paleoceanographic evidence to support this hypothesis. The bottom line is that the Arctic Ocean was likely a major player in causing abrupt climate change in the past, via its influence on the AMOC. Although we focus here on the Younger Dryas, the Arctic Ocean has been repeatedly isolated from the world ocean during glacial periods of the past. When these periods of isolation ended, it is probable that there were significant

  8. Response of dominant wind wave fields to abrupt wind increase

    NASA Astrophysics Data System (ADS)

    Caulliez, Guillemette

    2013-04-01

    Over the last decades, significant progress has been made in modelling wave field development by wind observed at sea, based on more elaborated numerical schemes and refined parametrizations of wind energy input and wave dissipation. In such models, the wind wave growth in space or time is generally governed by the average wind speed evaluated at one reference level and the natural wind speed variability is neglected. However, the impact of this assumption is not really known, mainly because of the lack of appropriate observations. To revisit this question, we report a detailed laboratory investigation aimed at describing the dominant wave field evolution resulting from an abrupt local wind speed increase. The experiments were conducted in the large Marseille-Luminy wind wave tank for moderate to high wind conditions. At 23 m fetch, a contraction of the wind tunnel section by a convergent profile created a spatial wind speed acceleration over a distance of about 2 m. Downwind, the wind speed, enhanced by a factor 1.4, was kept constant up to the end of the water tank. The wind wave field development induced by such a "wind gust" was investigated at successive fetches by wave probes and compared to those observed at similar fetches for homogeneous wind conditions. When wind increases, these observations first revealed no dramatic change in the evolution of the dominant spectral peak with fetch. The dominant wave energy which increases slowly for constant wind conditions, follows the wind speed but with a significant space lag. For well-established gravity wave fields, the space relaxation scales which describe this evolution do not depend noticeably on wind, all the curves collapse into a single one when wave quantities are normalized by their value observed just upstream the convergent profile. The wave growth rate observed for the new equilibrium state can be described by the Hasselman et al. (1973) relationship but with an "equivalent'' shorter fetch since, in

  9. Maternal Sleep Duration and Complaints of Vital Exhaustion during Pregnancy is Associated with Placental Abruption

    PubMed Central

    Qiu, Chunfang; Sanchez, Sixto E.; Gelaye, Bizu; Enquobahrie, Daniel A.; Ananth, Cande V.; Williams, Michelle A.

    2014-01-01

    OBJECTIVE Sleep disorders are associated with cardiovascular complications and preterm delivery (PTD). Insufficient sleep results in metabolic alterations and increased inflammation, both known to contribute to placental abruption (abruption), a determinant of PTD. We examined associations of abruption with sleep duration and complaints of vital exhaustion. METHODS The study included 164 abruption cases and 160 controls in a multicenter study in Peru. Data on habitual sleep duration and vital exhaustion during the first 6 months of pregnancy were elicited during interviews conducted following delivery. Women were categorized according to short, normal and long sleep duration (≤6, 7-8 and ≥9 h); and frequency of feeling exhausted. Odds ratios (OR) and 95% confidence intervals (CI) were calculated. RESULTS Short and long sleep durations were associated with increased odds of abruption. The ORs of abruption in relation to short (≤6 h) and long (≥9 h) sleep duration were 2.0 (95%CI 1.1-3.7) and 2.1 (95%CI 1.1-4.1), compared with normal sleep duration (7-8 h). Complaints of vital exhaustion were also associated with abruption (OR=2.37; 95%CI 1.46-3.85), and were independent of sleep duration. CONCLUSION We extend the existing literature and support the thesis that maternal sleep habits and disorders should be assessed among pregnant women. PMID:24749793

  10. Population age and initial density in a patchy environment affect the occurrence of abrupt transitions in a birth-and-death model of Taylor's law

    USGS Publications Warehouse

    Jiang, Jiang; DeAngelis, Donald L.; Zhang, B.; Cohen, J.E.

    2014-01-01

    Taylor's power law describes an empirical relationship between the mean and variance of population densities in field data, in which the variance varies as a power, b, of the mean. Most studies report values of b varying between 1 and 2. However, Cohen (2014a) showed recently that smooth changes in environmental conditions in a model can lead to an abrupt, infinite change in b. To understand what factors can influence the occurrence of an abrupt change in b, we used both mathematical analysis and Monte Carlo samples from a model in which populations of the same species settled on patches, and each population followed independently a stochastic linear birth-and-death process. We investigated how the power relationship responds to a smooth change of population growth rate, under different sampling strategies, initial population density, and population age. We showed analytically that, if the initial populations differ only in density, and samples are taken from all patches after the same time period following a major invasion event, Taylor's law holds with exponent b=1, regardless of the population growth rate. If samples are taken at different times from patches that have the same initial population densities, we calculate an abrupt shift of b, as predicted by Cohen (2014a). The loss of linearity between log variance and log mean is a leading indicator of the abrupt shift. If both initial population densities and population ages vary among patches, estimates of b lie between 1 and 2, as in most empirical studies. But the value of b declines to ~1 as the system approaches a critical point. Our results can inform empirical studies that might be designed to demonstrate an abrupt shift in Taylor's law.

  11. Regional Heterogeneity in the Rates of Warming from CO2 Emissions

    NASA Astrophysics Data System (ADS)

    Ricke, K.; Caldeira, K.

    2015-12-01

    While it is commonly understood that the magnitudes of global warming from anthropogenic emissions are and will be spatially heterogeneous, little work has been done exploring heterogeneity in the timing of effects from an emission of carbon dioxide (CO2). Using the results from the Coupled Model Intercomparison Project v5 (CMIP5) abrupt4xco2 experiment, we explore regional differences in the timing, as opposed to magnitude, of the warming from emissions of CO2. Our analysis reveals a surprisingly high amount of regional diversity in the pace of realization of the warming effect of a CO2 emission, with relatively accelerated warming for areas such as the eastern United States and Central Asia and a relatively long lag between emission and warming effect for Australia and Amazonia. Figure 1 shows the ratio of the ensemble median rate of warming in the first decade after a change in CO2 concentration to the rate of warming for the remainder of the first century. Because estimates of social cost of carbon implicitly assume similar timing of warming for all regions, the observed effects have important implications for climate policy.

  12. Grouped spindle and electromyographic responses to abrupt wrist extension movements in man

    PubMed Central

    Hagbarth, K.-E.; Hägglund, J. V.; Wallin, E. U.; Young, R. R.

    1981-01-01

    1. Different techniques were used to generate sudden ramp extension movements of the wrist while the subjects were either relaxed or maintaining a weak voluntary contraction in the wrist flexors. Afferent responses to the displacements were recorded with a tungsten micro-electrode inserted into a fascicle of the median nerve supplying one of the wrist flexor muscles, and e.m.g. responses were recorded with needle electrodes inserted into the same muscle. 2. With the wrist flexors either relaxed or contracting, extensions at 100-200°/sec for 60-70 msec (generated by either an hydraulic motor or a torque motor) produced segmented afferent responses with two to four afferent bursts, separated by intervals of 20-30 msec. The successive neural peaks, occuring during the stretch phase, were correlated to mechanical vibrations sensed by a strain gauge and sometimes also by a wrist goniometer. With the flexor muscles contracting, the successive peaks in the neurogram were followed by similar peaks in the e.m.g, the delay between neural and e.m.g. peaks being 20-25 msec. 3. Small abrupt extension movements of 1-2° lasting only 10-15 msec often produced segmented afferent responses with one neural burst occuring during the stretch phase and another 15-20 msec later, corresponding to a mechanical oscillatory event succeeding the stretch. The oscillation and the second neural burst were not present with small extension movements of smooth onset and halt. With the flexor muscles contracting, stimuli producing one afferent burst produced only one e.m.g. peak, whereas double-peaked afferent discharges produced double-peaked e.m.g. responses, the delay between individual neural e.m.g. peaks being 20-25 msec. 4. Similar segmentation of the neural stretch responses was seen when abrupt displacements were produced by electrically induced muscle twitches, by manual pulls on a spring attached to the hand or by the subject making fast voluntary wrist extensions. This grouping of

  13. Global Warming and Neotropical Rainforests: A Historical Perspective

    NASA Astrophysics Data System (ADS)

    Jaramillo, Carlos; Cárdenas, Andrés

    2013-05-01

    There is concern over the future of the tropical rainforest (TRF) in the face of global warming. Will TRFs collapse? The fossil record can inform us about that. Our compilation of 5,998 empirical estimates of temperature over the past 120 Ma indicates that tropics have warmed as much as 7°C during both the mid-Cretaceous and the Paleogene. We analyzed the paleobotanical record of South America during the Paleogene and found that the TRF did not expand toward temperate latitudes during global warm events, even though temperatures were appropriate for doing so, suggesting that solar insolation can be a constraint on the distribution of the tropical biome. Rather, a novel biome, adapted to temperate latitudes with warm winters, developed south of the tropical zone. The TRF did not collapse during past warmings; on the contrary, its diversity increased. The increase in temperature seems to be a major driver in promoting diversity.

  14. Tracking ocean heat uptake during the surface warming hiatus

    NASA Astrophysics Data System (ADS)

    Liu, Wei; Xie, Shang-Ping; Lu, Jian

    2016-03-01

    Ocean heat uptake is observed to penetrate deep into the Atlantic and Southern Oceans during the recent hiatus of global warming. Here we show that the deep heat penetration in these two basins is not unique to the hiatus but is characteristic of anthropogenic warming and merely reflects the depth of the mean meridional overturning circulation in the basin. We find, however, that heat redistribution in the upper 350 m between the Pacific and Indian Oceans is closely tied to the surface warming hiatus. The Indian Ocean shows an anomalous warming below 50 m during hiatus events due to an enhanced heat transport by the Indonesian throughflow in response to the intensified trade winds in the equatorial Pacific. Thus, the Pacific and Indian Oceans are the key regions to track ocean heat uptake during the surface warming hiatus.

  15. Tracking ocean heat uptake during the surface warming hiatus

    PubMed Central

    Liu, Wei; Xie, Shang-Ping; Lu, Jian

    2016-01-01

    Ocean heat uptake is observed to penetrate deep into the Atlantic and Southern Oceans during the recent hiatus of global warming. Here we show that the deep heat penetration in these two basins is not unique to the hiatus but is characteristic of anthropogenic warming and merely reflects the depth of the mean meridional overturning circulation in the basin. We find, however, that heat redistribution in the upper 350 m between the Pacific and Indian Oceans is closely tied to the surface warming hiatus. The Indian Ocean shows an anomalous warming below 50 m during hiatus events due to an enhanced heat transport by the Indonesian throughflow in response to the intensified trade winds in the equatorial Pacific. Thus, the Pacific and Indian Oceans are the key regions to track ocean heat uptake during the surface warming hiatus. PMID:27025666

  16. Tracking ocean heat uptake during the surface warming hiatus.

    PubMed

    Liu, Wei; Xie, Shang-Ping; Lu, Jian

    2016-01-01

    Ocean heat uptake is observed to penetrate deep into the Atlantic and Southern Oceans during the recent hiatus of global warming. Here we show that the deep heat penetration in these two basins is not unique to the hiatus but is characteristic of anthropogenic warming and merely reflects the depth of the mean meridional overturning circulation in the basin. We find, however, that heat redistribution in the upper 350 m between the Pacific and Indian Oceans is closely tied to the surface warming hiatus. The Indian Ocean shows an anomalous warming below 50 m during hiatus events due to an enhanced heat transport by the Indonesian throughflow in response to the intensified trade winds in the equatorial Pacific. Thus, the Pacific and Indian Oceans are the key regions to track ocean heat uptake during the surface warming hiatus. PMID:27025666

  17. Teaching Global Warming

    NASA Astrophysics Data System (ADS)

    Hobson, Art

    2004-05-01

    Every citizen's education should include socially relevant science courses because, as the American Association for the Advancement of Science puts it, "Without a scientifically literate population, the outlook for a better world is not promising." I have developed a conceptual liberal-arts physics course that covers the major principles of classical physics, emphasizes modern/contemporary physics, and includes societal topics such as global warming, ozone depletion, transportation, exponential growth, scientific methodology, risk assessment, nuclear weapons, nuclear power, and the energy future. The societal topics, occupying only about 15% of the class time, appear to be the main cause of the surprising popularity of this course among non-scientists. I will outline some ideas for incorporating global warming into such a course or into any other introductory physics course. For further details, see my textbook Physics: Concepts and Connections (Prentice Hall, 3rd edition 2003).

  18. Spatio-temporal analysis of warming in Bangladesh using recent observed temperature data and GIS

    NASA Astrophysics Data System (ADS)

    Rahman, Md. Rejaur; Lateh, Habibah

    2016-05-01

    This study focused on the annual and seasonal warming at local scale by analysing the trends, anomalies, change points and shifting of isotherm in temperature from 34 meteorological stations distributed over Bangladesh, spanning 40 years from the year 1971-2010. For trends, a linear regression using least square model was applied. Anomalies were calculated as a difference between the reference (1971-2000 mean) and actual occurrence value. Inverse distance weighted interpolation and GIS techniques were used to find out the spatial pattern of warming. Besides, the sequential version of the Mann-Kendall test was applied to detect the changing point of warming. Direction of shifting of warming was detected by the decadal distribution pattern of specific isotherms which were generated using GIS. The result reveals that the climate of Bangladesh undergone a significant warming during the period 1971-2010, 0.020 °C per year (for annual mean) and the maximum temperature warmed more than the minimum temperature (0.022 vs. 0.018 °C per year). On a seasonal basis, hot summer, humid summer and dry winter also show significant warming, 0.022, 0.026 and 0.011 °C per year, respectively. The warming of maximum temperature (0.032 °C per year) in humid summer was greater than other seasons, contributed more on annual warming. Spatial patterns indicate that geographically the warming varied significantly and some places warming exit 2.0 °C and reached up to 3.2 °C. The north western, north eastern, southern and south eastern parts of the country are more susceptible to rising temperature. In 2010, mean annual temperature was 0.84 °C warmer than the base period (1971-2000) mean. The significant warmest period was spread across the year 1995-2010, with 2010 being the warmest year. Statistically significant warming was began in early 1990's and the years 1990, 1994 and 1997 identified as important abrupt change points of warming. Moreover, a remarkably northward and north

  19. Abrupt Climate Change and the Atlantic Meridional Overturning Circulation: sensitivity and non-linear response to Arctic/sub-Arctic freshwater pulses. Collaborative research. Final report

    SciTech Connect

    Hill, Christopher

    2015-06-15

    This project investigated possible mechanisms by which melt-water pulses can induce abrupt change in the Atlantic Meridional Overturning Circulation (AMOC) magnitude. AMOC magnitude is an important ingredient in present day climate. Previous studies have hypothesized abrupt reduction in AMOC magnitude in response to influxes of glacial melt water into the North Atlantic. Notable fresh-water influxes are associated with the terminus of the last ice age. During this period large volumes of melt water accumulated behind retreating ice sheets and subsequently drained rapidly when the ice weakened sufficiently. Rapid draining of glacial lakes into the North Atlantic is a possible origin of a number of paleo-record abrupt climate shifts. These include the Younger-Dryas cooling event and the 8,200 year cooling event. The studies undertaken focused on whether the mechanistic sequence by which glacial melt-water impacts AMOC, which then impacts Northern Hemisphere global mean surface temperature, is dynamically plausible. The work has implications for better understanding past climate stability. The work also has relevance for today’s environment, in which high-latitude ice melting in Greenland appears to be driving fresh water outflows at an accelerating pace.

  20. PERENNIAL WARM-SEASON GRASSES

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Warm-season grasses and can be used to augment the forage supply for grazing livestock operations in the northeastern U.S. Much of what is known about warm season grass production and management in the northeastern US was obtained from a soil conservation or wildlife habitat perspective. Warm-seas...

  1. Abrupt Decline in the Arctic Winter Sea Ice Cover

    NASA Technical Reports Server (NTRS)

    Comiso, Josefino C.

    2007-01-01

    Maximum ice extents in the Arctic in 2005 and 2006 have been observed to be significantly lower (by about 6%) than the average of those of previous years starting in 1979. Since the winter maxima had been relatively stable with the trend being only about -1.5% per decade (compared to about -10% per decade for the perennial ice area), this is a significant development since signals from greenhouse warming are expected to be most prominent in winter. Negative ice anomalies are shown to be dominant in 2005 and 2006 especially in the Arctic basin and correlated with winds and surface temperature anomalies during the same period. Progressively increasing winter temperatures in the central Arctic starting in 1997 is observed with significantly higher rates of increase in 2005 and 2006. The Atlantic Oscillation (AO) indices correlate weakly with the sea ice and surface temperature anomaly data but may explain the recent shift in the perennial ice cover towards the western region. Results suggest that the trend in winter ice is finally in the process of catching up with that of the summer ice cover.

  2. Yangtze Delta floods and droughts of the last millennium: Abrupt changes and long term memory

    NASA Astrophysics Data System (ADS)

    Jiang, T.; Zhang, Q.; Blender, R.; Fraedrich, K.

    2005-09-01

    Climate variability and flood events in the Yangtze Delta, which is a low-lying terrain prone to flood hazards, storm tides and typhoons, are studied in terms of a trend and detrended fluctuation analysis of historical records. The data used in this paper were extracted from historical records such as local annuals and chronologies from 1000 1950 and supplemented by instrumental observations since 1950. The historical data includes frequencies of floods, droughts and maritime events on a decadal basis. Flood magnitudes increase during the transition from the medieval warm interval into the early Little Ice Age. Fluctuating climate changes of the Little Ice Age, which are characterised by arid climate events, are followed by wet and cold climate conditions with frequent flood hazards. For trend analysis, the Mann-Kendall test is applied to determine the changing trends of flood and drought frequency. Flood frequency during 1000 1950 shows a negative trend before 1600 A.D. and a positive trend thereafter; drought frequency increases after 1300. The detrended fluctuation analysis of the flood and drought frequencies reveals power law scaling up to centuries; this is related to long-term memory and is similar to the river Nile floods.

  3. Is the Perinatal Outcome of Placental Abruption Modified by Clinical Presentation?

    PubMed Central

    Furukawa, Seishi; Sameshima, Hiroshi; Ikenoue, Tsuyomu; Ohashi, Masanao; Nagai, Yoshio

    2011-01-01

    Objective. The purpose of this study was to elucidate the impact of the clinical presentation on perinatal outcome in placental abruption. Study Design. A retrospective study was performed in 97 placental abruptions. Placental abruptions were classified according to clinical presentation: pregnancy-induced hypertension (HT, n = 22), threatened premature labor and/or premature rupture of membranes (TPL/ROM, n = 35), clinically low risk (LR, n = 27), and others (n = 13). Perinatal outcomes were compared among the HT, TPL/ROM, and LR groups. Results. The HT had significantly higher incidence of IUGR, IFUD, and low fibrinogen. The TPL/ROM had less severe disease. However, the LR had significantly higher incidence of IUFD, low UA pH < 7.1, low Apgar score of <7 at 5 min, and low fibrinogen. Conclusion. Disease severity in placental abruption is likely to depend on the clinical presentation. PMID:21490793

  4. ABRUPT CHANGES OF THE PHOTOSPHERIC MAGNETIC FIELD IN ACTIVE REGIONS AND THE IMPULSIVE PHASE OF SOLAR FLARES

    SciTech Connect

    Cliver, E. W.; Petrie, G. J. D.; Ling, A. G.

    2012-09-10

    We compared time profiles of changes of the unsigned photospheric magnetic flux in active regions with those of their associated soft X-ray (SXR) bursts for a sample of 75 {>=} M5 flares well observed by Global Oscillation Network Group longitudinal magnetographs. Sixty-six of these events had stepwise changes in the spatially integrated unsigned flux during the SXR flares. In superposed epoch plots for these 66 events, there is a sharp increase in the unsigned magnetic flux coincident with the onset of the flare impulsive phase while the end of the stepwise change corresponds to the time of peak SXR emission. We substantiated this result with a histogram-based comparison of the timing of flux steps (onset, midpoint of step, and end) for representative points in the flaring regions with their associated SXR event time markers (flare onset, onset of impulsive phase, time of peak logarithmic derivative, maximum). On an individual event basis, the principal part of the stepwise magnetic flux change occurred during the main rise phase of the SXR burst (impulsive phase onset to SXR peak) for {approx}60% of the 66 cases. We find a close timing agreement between magnetic flux steps and >100 keV emission for the three largest hard X-ray (>100 keV) bursts in our sample. These results identify the abrupt changes in photospheric magnetic fields as an impulsive phase phenomenon and indicate that the coronal magnetic field changes that drive flares are rapidly transmitted to the photosphere.

  5. Global warming - A reduced threat

    SciTech Connect

    Michaels, P.J.; Stooksbury, D.E. )

    1992-10-01

    Issues associated with global warming are analyzed focusing on global and hemispheric temperature histories and trace gas concentrations; artificial warming from urban heat islands; high-latitude and diurnal temperatures; recent climate models; direct effects on vegetation of an increase in carbon dioxide; and compensatory cooling from other industrial products. Data obtained indicate that anthropogenerated sulfate emissions are mitigating some of the warming, and that increased cloudiness as a result of these emissions will further enhance night, rather than day, warming. It is noted that the sulfate emissions are not sufficient to explain all of the night warming. The sensitivity of climate to anthropogenerated aerosols, and the general lack of previously predicted warming, could drastically alter the debate on global warming in favor of less expensive policies. 61 refs.

  6. The applicability of research on moving cut data-approximate entropy on abrupt climate change detection

    NASA Astrophysics Data System (ADS)

    Jin, Hongmei; He, Wenping; Liu, Qunqun; Wang, Jinsong; Feng, Guolin

    2016-04-01

    In this study, the performance of moving cut data-approximate entropy (MC-ApEn) to detect abrupt dynamic changes was investigated. Numerical tests in a time series model indicate that the MC-ApEn method is suitable for the detection of abrupt dynamic changes for three types of meteorological data: daily maximum temperature, daily minimum temperature, and daily precipitation. Additionally, the MC-ApEn method was used to detect abrupt climate changes in daily precipitation data from Northwest China and the Pacific Decadal Oscillation (PDO) index. The results show an abrupt dynamic change in precipitation in 1980 and in the PDO index in 1976. The times indicated for the abrupt changes are identical to those from previous results. Application of the analysis to observational data further confirmed the performance of the MC-ApEn method. Moreover, MC-ApEn outperformed the moving t test (MTT) and the moving detrended fluctuation analysis (MDFA) methods for the detection of abrupt dynamic changes in a simulated 1000-point daily precipitation dataset.

  7. Abrupt spatiotemporal land and water changes and their potential drivers in Poyang Lake, 2000-2012

    NASA Astrophysics Data System (ADS)

    Chen, Lifan; Michishita, Ryo; Xu, Bing

    2014-12-01

    Driven by various natural and anthropogenic factors, Poyang Lake, the largest freshwater lake in China, has experienced significant land use/cover changes in the past few decades. The aim of this study is to investigate the spatial-temporal patterns of abrupt changes and detect their potential drivers in Poyang Lake, using time-series Moderate Resolution Imaging Spectroradiometer (MODIS) 16-day maximum value composite vegetation indices between 2000 and 2012. The breaks for additive seasonal and trend (BFAST) method was applied to the smoothed time-series normalized difference vegetation index (NDVI), to detect the timing and magnitude of abrupt changes in the trend component. Large part of Poyang Lake (98.9% for trend component) has experienced abrupt changes in the past 13 years, and the change patterns, including the distributions in timing and magnitudes of major abrupt trend changes between water bodies and land areas were clearly differentiated. Most water bodies had abrupt increasing NDVI changes between 2010 and 2011, caused by the sequential severe flooding and drought in the two years. In contrast, large parts of the surrounding land areas had abrupt decreasing NDVI changes. Large decreasing changes occurred around 2003 at the city of Nanchang, which were driven by urbanization. These results revealed spatial-temporal land cover changing patterns and potential drivers in the wetland ecosystem of Poyang Lake.

  8. Rapid response of Arctic land ice during Dansgaard-Oeschger events and variation in water exchange between the Atlantic and Arctic oceans

    NASA Astrophysics Data System (ADS)

    Rasmussen, T. L.; Thomsen, E.

    2014-12-01

    The climate of the last glaciation was interrupted by numerous abrupt millennial scale temperature fluctuations between cold stadials and warm interstadials, the so-called Greenland Dansgaard-Oeschger events. During the warm interstadials the Atlantic Meridional Overturning Circulation (AMOC) was active and warm water flowed north into the Nordic seas. During the cold stadials the northern oceans were partially ice covered and the AMOC disrupted. So far, very little is known of changes in the surrounding ice sheets and in the discharge of meltwater in response to abrupt warmings even though variation in meltwater production is regarded to be a major factor in the instability. Here we present results from sediment cores from the western slope of Svalbard in order to reconstruct the delivery of sediments and meltwater from the archipelago as in response to stadial/interstadial shifts during MIS 3. During interstadials the normal greenish silt was replaced by laminated, pink clay originating from Devonian Red Beds on Svalbard and transported in suspension by meltwater to the coring site. The large distance from the ice margin to the site indicates the outpourings of meltwater were substantial, probably comparable to some of the largest outbursts during the deglaciation. The concentration of ice rafted debris decreased as the meltwater production increased signifying that the ice margin retreated from the coastal area. In the study, we establish the precise chronology for eight major meltwater discharges during MIS 3 corresponding to Dansgaard-Oeschger warmings DO-11 to DO-3. The results are based on the Svalbard-Barents Sea ice sheet, but it is likely that the Scandinavian ice sheet reacted concurrently. Our observations indicate that the Eurasian ice sheet was much more dynamic than previously recognized with retreat and advances closely linked to the Greenland interstadials and stadials .Our findings also provide clear evidence of a significant northern component to

  9. FLATs: Warming Up

    NASA Astrophysics Data System (ADS)

    Calzetti, Daniela

    1997-07-01

    The purpose of this proposal is to monitor the flat fields during the interval between the end of science observations and the exhaustion of cryogen and subsequent warming of the dewar to > 100K. These flats will provide a monitor for particulate comtamination {GROT} and detector lateral position {from the coronagraphic spot and FDA vignetting}. They will provide some measure of relative {flat field} and absolute QE variation as a function of temperature. When stars are visible they might provide a limited degree of focus determination.

  10. FLATs: Warming Up - continuation

    NASA Astrophysics Data System (ADS)

    Calzetti, Daniela

    1997-07-01

    The purpose of this proposal is to monitor the flat fields during the interval between the end of science observations and the exhaustion of cryogen and subsequent warming of the dewar to > 100K. These flats will provide a monitor for particulate comtamination {GROT} and detector lateral position {from the coronagraphic spot and FDA vignetting}. They will provide some measure of relative {flat field} and absolute QE variation as a function of temperature. When stars are visible they might provide a limited degree of focus determination.

  11. Abrupt cooling associated with the oceanic Rossby wave and lateral advection during CINDY2011

    NASA Astrophysics Data System (ADS)

    Seiki, Ayako; Katsumata, Masaki; Horii, Takanori; Hasegawa, Takuya; Richards, Kelvin J.; Yoneyama, Kunio; Shirooka, Ryuichi

    2013-10-01

    The cooperative Indian Ocean experiment on intraseasonal variability in the Year 2011 (CINDY2011) was conducted to capture atmospheric and oceanic characteristics of the Madden-Julian Oscillation (MJO) in the central Indian Ocean from late 2011 to early 2012. During CINDY2011, the research vessel (R/V) MIRAI stayed at 8°S, 80.5°E for two months during the special observing period (SOP). Intraseasonal convection associated with the MJO was organized in the central Indian Ocean in late October and late November during the SOP. In the middle of November, both sea surface temperature (SST) and mixed layer temperature decreased suddenly when cold low salinity water intruded into the upper layer around the R/V MIRAI. This intrusion was accompanied by a surface current change from southwestward to westward/west-northwestward associated with the passage of the annual oceanic downwelling Rossby wave. The mixed layer heat budget analysis shows that horizontal advection plays an important role in the abrupt cooling whereas the net surface heat flux cannot account for the cooling. This is an interesting result because the associated downwelling Rossby wave is usually considered to increase SST through a reduction of entrainment cooling. In addition, for the second MJO event convection was activated around 20 November over the central north and equatorial Indian Ocean but not in the south. It is suggested that the cooler surface waters (as seen at the location of the R/V MIRAI) tended to suppress the initial atmospheric convection, resulting in the lagged convective onset in the end of November over the central south Indian Ocean.

  12. Reducing The Risk Of Abrupt Climate Change: Emission Corridors Preserving The Thermohaline Circulation

    NASA Astrophysics Data System (ADS)

    Zickfeld, K.

    Paleo-reconstructions have shown that large and abrupt climate changes have occurred throughout the last ice-age cycles. This evidence, supplemented by insights into the complex and nonlinear nature of the climate system, gives raise to the concern that anthropogenic forcing may trigger such events in the future. A prominent example for such a potential climatic shift is the collapse of the North Atlantic thermohaline circu- lation (THC), which would cause a major cooling of the northern North Atlantic and north-western Europe and considerable regional sea level rise, with possibly severe consequences on, e.g., fisheries, agriculture and ecosystems. In this paper we present emission corridors for the 21st century preserving the THC. Emission corridors embrace the range of future emissions beyond which either the THC collapses or the mitigation burden becomes intolerable. They are calculated along the conceptual and methodological lines of the tolerable windows approach. We investigate the sensitivity of the emission corridors to the main uncertain parame- ters (climate and North Atlantic hydrological sensitivities as well as emissions of non CO_2 greenhouse gases). Results show a high dependence of the size of the emis- sion corridors on hydrological and climate sensitivities. For the best-guess values of both parameters we find that the emission corridors are wider than the range spanned by the SRES emissions scenarios. Thus, no immediate mitigation seems necessary in order to preserve the THC. For high but still realistic values of the sensitivities, however, even the low SRES emissions scenarios transgress the corridor boundaries. These findings imply that under 'business as usual' a non-negligible risk of either a THC collapse or an intolerable mitigation burden exists.

  13. Abrupt transitions in the NAO control of explosive North Atlantic cyclone development

    NASA Astrophysics Data System (ADS)

    Gómara, Iñigo; Rodríguez-Fonseca, Belén; Zurita-Gotor, Pablo; Ulbrich, Sven; Pinto, Joaquim G.

    2016-02-01

    Explosive cyclones are intense extra-tropical low pressure systems featuring large deepening rates. In the Euro-Atlantic sector, they are a major source of life-threatening weather impacts due to their associated strong wind gusts, heavy precipitation and storm surges. The wintertime variability of the North Atlantic cyclonic activity is primarily modulated by the North Atlantic Oscillation (NAO). In this study, we investigate the interannual and multi-decadal variability of explosive North Atlantic cyclones using track density data from two reanalysis datasets (NCEP and ERA-40) and a control simulation of an atmosphere/ocean coupled General Circulation Model (GCM—ECHAM5/MPIOM1). The leading interannual and multi-decadal modes of variability of explosive cyclone track density are characterized by a strengthening/weakening pattern between Newfoundland and Iceland, which is mainly modulated by the NAO at both timescales. However, the NAO control of interannual cyclone variability is not stationary in time and abruptly fluctuates during periods of 20-25 years long both in NCEP and ECHAM5/MPIOM1. These transitions are accompanied by structural changes in the leading mode of explosive cyclone variability, and by decreased/enhanced baroclinicity over the sub-polar/sub-tropical North Atlantic. The influence of the ocean is apparently important for both the occurrence and persistence of such anomalous periods. In the GCM, the Atlantic Meridional Overturning Circulation appears to influence the large-scale baroclinicity and explosive cyclone development over the North Atlantic. These results permit a better understanding of explosive cyclogenesis variability at different climatic timescales and might help to improve predictions of these hazardous events.

  14. Abrupt Late Pleistocene Changes in Northern South American River Run-Off

    NASA Astrophysics Data System (ADS)

    Hoffmann, J.; Bahr, A.; Voigt, S.; Schönfeld, J.; Nuernberg, D.

    2014-12-01

    Paleoenvironmental studies as well as climate models demonstrate that fluvial run-off and moisture availability in the hinterland of the Caribbean react highly sensitively to climatic variations. Deglacial (Late Pleistocene) records document pronounced dry and wet spells over tropical South America which are mainly caused by shifts of the Intertropical Convergence Zone (ITCZ) coupled with South American monsoonal activity. Here we present a high-resolution foraminiferal Ba/Ca and δ18Oseawater record from a core located within the Orinoco outflow area, that give insights into abrupt changes of the hydrology of the Orinoco catchment area and, furthermore, enables us to reconstruct circulation patterns within the Caribbean during deglacial times. Our data, obtained from the surface-dwelling foraminifera Globigerinoides ruber (pink variety), show a distinct increase in Ba/Ca ratios during the Heinrich 1 (H1) interval, as well as during the Dansgaard-Oeschger cycles up to 36 kyr. Based on the multi-proxy evidence we largely attribute the Ba/Ca increase during H1 to enhanced Amazon river run-off, while Orinoco river discharge appears not to be significantly elevated. During Dansgaard-Oeschger cycles, the causal mechanism for enhanced Ba/Ca ratios is an insolation-driven shift of the ITCZ and/or enhanced South American summer monsoon activity. Interestingly, the H1 Ba/Ca shows strong similarities in shape and timing to published Ba/Ca data from Florida Straits.This leads us to the assumption that the South American run-off signal is transported directly into the Atlantic Ocean via Yukatan Strait and Florida Strait and therefore alter the salinity budget in the North Atlantic. The results point to immediate high to low latitude feedbacks which might help to re-inforce the weakening of the overturning circulation during Heinrich Events and Dansgaard-Oeschger cycles.

  15. Final Scientific Report for "The Interhemispheric Pattern in 20th Century and Future Abrupt Change in Regional Tropical Rainfall"

    SciTech Connect

    Chiang, John C. H.; Wehner, Michael F.

    2012-10-29

    This is the final scientific report for grant DOE-FG02-08ER64588, "The Interhemispheric Pattern in 20th Century and Future Abrupt Change in Regional Tropical Rainfall."The project investigates the role of the interhemispheric pattern in surface temperature – i.e. the contrast between the northern and southern temperature changes – in driving rapid changes to tropical rainfall changes over the 20th century and future climates. Previous observational and modeling studies have shown that the tropical rainband – the Intertropical Convergence Zone (ITCZ) over marine regions, and the summer monsoonal rainfall over land – are sensitive to the interhemispheric thermal contrast; but that the link between the two has not been applied to interpreting long-term tropical rainfall changes over the 20th century and future.The specific goals of the project were to i) develop dynamical mechanisms to explain the link between the interhemispheric pattern to abrupt changes of West African and Asian monsoonal rainfall; ii) Undertake a formal detection and attribution study on the interhemispheric pattern in 20th century climate; and iii) assess the likelihood of changes to this pattern in the future. In line with these goals, our project has produced the following significant results: 1.We have developed a case that suggests that the well-known abrupt weakening of the West African monsoon in the late 1960s was part of a wider co-ordinated weakening of the West African and Asian monsoons, and driven from an abrupt cooling in the high latitude North Atlantic sea surface temperature at the same time. Our modeling work suggests that the high-latitude North Atlantic cooling is effective in driving monsoonal weakening, through driving a cooling of the Northern hemisphere that is amplified by positive radiative feedbacks. 2.We have shown that anthropogenic sulfate aerosols may have partially contributed to driving a progressively southward displacement of the Atlantic Intertropical

  16. Is Global Warming Accelerating?

    NASA Astrophysics Data System (ADS)

    Shukla, J.; Delsole, T. M.; Tippett, M. K.

    2009-12-01

    A global pattern that fluctuates naturally on decadal time scales is identified in climate simulations and observations. This newly discovered component, called the Global Multidecadal Oscillation (GMO), is related to the Atlantic Meridional Oscillation and shown to account for a substantial fraction of decadal fluctuations in the observed global average sea surface temperature. IPCC-class climate models generally underestimate the variance of the GMO, and hence underestimate the decadal fluctuations due to this component of natural variability. Decomposing observed sea surface temperature into a component due to anthropogenic and natural radiative forcing plus the GMO, reveals that most multidecadal fluctuations in the observed global average sea surface temperature can be accounted for by these two components alone. The fact that the GMO varies naturally on multidecadal time scales implies that it can be predicted with some skill on decadal time scales, which provides a scientific rationale for decadal predictions. Furthermore, the GMO is shown to account for about half of the warming in the last 25 years and hence a substantial fraction of the recent acceleration in the rate of increase in global average sea surface temperature. Nevertheless, in terms of the global average “well-observed” sea surface temperature, the GMO can account for only about 0.1° C in transient, decadal-scale fluctuations, not the century-long 1° C warming that has been observed during the twentieth century.

  17. Warm Inflation Model Building

    NASA Astrophysics Data System (ADS)

    Bastero-Gil, Mar; Berera, Arjun

    We review the main aspects of the warm inflation scenario, focusing on the inflationary dynamics and the predictions related to the primordial spectrum of perturbations, to be compared with the recent cosmological observations. We study in detail three different classes of inflationary models, chaotic, hybrid models and hilltop models, and discuss their embedding into supersymmetric models and the consequences for model building of the warm inflationary dynamics based on first principles calculations. Due to the extra friction term introduced in the inflaton background evolution generated by the dissipative dynamics, inflation can take place generically for smaller values of the field, and larger values of couplings and masses. When the dissipative dynamics dominates over the expansion, in the so-called strong dissipative regime, inflation proceeds with sub-Planckian inflaton values. Models can be naturally embedded into a supergravity framework, with SUGRA corrections suppressed by the Planck mass now under control, for a larger class of Kähler potentials. In particular, this provides a simpler solution to the "eta" problem in supersymmetric hybrid inflation, without restricting the Kähler potentials compatible with inflation. For chaotic models dissipation leads to a smaller prediction for the tensor-to-scalar ratio and a less tilted spectrum when compared to the cold inflation scenario. We find in particular that a small component of dissipation renders the quartic model now consistent with the current CMB data.

  18. RHIC warm-bore systems

    SciTech Connect

    Welch, K.M.

    1994-07-01

    Pressure profiles, in time, are calculated as a consequence of anticipated outgassing of various beam components (e.g., rf cavities, etc.) and warm-bore beam pipes. Gold beam lifetimes and transverse beam emittance growth are given for calculated average pressures. Examples of undesirable warm-bore conditions are presented such as contaminated experimental beam pipes and warm-bore magnets (i.e., DX). These examples may prove instructive. The methods used in making these calculations are presented in Section 2. They are applicable to all linear systems. The calculations given apply to the RHIC accelerator and more specifically to warm-bore regions of the machine.

  19. Collective Behavior of Market Participants during Abrupt Stock Price Changes

    PubMed Central

    Maskawa, Jun-ichi

    2016-01-01

    Under uncertainty, human and animal collectives often respond stochastically to events they encounter. Human or animal individuals behave depending on others’ actions, and sometimes follow choices that are sub-optimal for individuals. Such mimetic behaviors are enhanced during emergencies, creating collective behavior of a group. A stock market that is about to crash, as markets did immediately after the Lehman Brothers bankruptcy, provides illustrative examples of such behaviors. We provide empirical evidence proving the existence of collective behavior among stock market participants in emergent situations. We investigated the resolution of extreme supply-and-demand order imbalances by increased balancing counter orders: buy and sell orders for excess supply and demand respectively, during times of price adjustment, so-called special quotes on the Tokyo Stock Exchange. Counter orders increase positively depending on the quantity of revealed counter orders: the accumulated orders in the book until then. Statistics of the coming counter order are well described using a logistic regression model with the ratio of revealed orders until then to the finally revealed orders as the explanatory variable. Results given here show that the market participants make Bayesian estimations of optimal choices to ascertain whether to order using information about orders of other participants. PMID:27513335

  20. Collective Behavior of Market Participants during Abrupt Stock Price Changes.

    PubMed

    Maskawa, Jun-Ichi

    2016-01-01

    Under uncertainty, human and animal collectives often respond stochastically to events they encounter. Human or animal individuals behave depending on others' actions, and sometimes follow choices that are sub-optimal for individuals. Such mimetic behaviors are enhanced during emergencies, creating collective behavior of a group. A stock market that is about to crash, as markets did immediately after the Lehman Brothers bankruptcy, provides illustrative examples of such behaviors. We provide empirical evidence proving the existence of collective behavior among stock market participants in emergent situations. We investigated the resolution of extreme supply-and-demand order imbalances by increased balancing counter orders: buy and sell orders for excess supply and demand respectively, during times of price adjustment, so-called special quotes on the Tokyo Stock Exchange. Counter orders increase positively depending on the quantity of revealed counter orders: the accumulated orders in the book until then. Statistics of the coming counter order are well described using a logistic regression model with the ratio of revealed orders until then to the finally revealed orders as the explanatory variable. Results given here show that the market participants make Bayesian estimations of optimal choices to ascertain whether to order using information about orders of other participants. PMID:27513335

  1. Surviving coral bleaching events: porites growth anomalies on the Great Barrier Reef.

    PubMed

    Cantin, Neal E; Lough, Janice M

    2014-01-01

    Mass coral bleaching affected large parts of the Great Barrier Reef (GBR) in 1998 and 2002. In this study, we assessed if signatures of these major thermal stress events were recorded in the growth characteristics of massive Porites colonies. In 2005 a suite of short (<50 cm) cores were collected from apparently healthy, surviving Porites colonies, from reefs in the central GBR (18-19°S) that have documented observations of widespread bleaching. Sites included inshore (Nelly Bay, Pandora Reef), annually affected by freshwater flood events, midshelf (Rib Reef), only occasionally affected by freshwater floods and offshore (Myrmidon Reef) locations primarily exposed to open ocean conditions. Annual growth characteristics (extension, density and calcification) were measured in 144 cores from 79 coral colonies and analysed over the common 24-year period, 1980-2003. Visual examination of the annual density bands revealed growth hiatuses associated with the bleaching years in the form of abrupt decreases in annual linear extension rates, high density stress bands and partial mortality. The 1998 mass-bleaching event reduced Porites calcification by 13 and 18% on the two inshore locations for 4 years, followed by recovery to baseline calcification rates in 2002. Evidence of partial mortality was apparent in 10% of the offshore colonies in 2002; however no significant effects of the bleaching events were evident in the calcification rates at the mid shelf and offshore sites. These results highlight the spatial variation of mass bleaching events and that all reef locations within the GBR were not equally stressed by the 1998 and 2002 mass bleaching events, as some models tend to suggest, which enabled recovery of calcification on the GBR within 4 years. The dynamics in annual calcification rates and recovery displayed here should be used to improve model outputs that project how coral calcification will respond to ongoing warming of the tropical oceans. PMID:24586377

  2. Modeling past abrupt climate changes: driven oscillators and synchronization phenomena in Paleoclimate theory

    NASA Astrophysics Data System (ADS)

    Marchionne, Arianna

    2014-05-01

    According to Milankovitch theory of ice ages, summer insolation at high northern latitudes drives the glacial cycles, i.e. the growth and reduction of Northern Hemisphere ice sheets, and there is evidence that astronomical forcing controls indeed the timing of Pleistocene glacial-interglacial cycles. However, the δ18Otime series (the δ18O is a proxy for global ice volume) available for the last few million years reveal a non-linear response of the climate to the external forcing: transitions from the glacial to the interglacial states occur more rapidly than the transitions from the interglacials to the glacials, resulting in the so-called saw-tooth shape of the signal. These terminations were very abrupt compared to the smooth changes in insolation. Moreover, insolation alone cannot explain the Mid-Pleistocene transition. During this event, occurred about one million years ago, the dominant 41 kyr glacial cycles, were replaced by longer saw-tooth shaped cycles with a time scale around 100 kyr. The asymmetry in the oscillations indicates a non-linear response to the orbital forcing, expressed through a bifurcation, or tipping point. As an introduction to the problem, we studied simple driven oscillators that can exhibit asymmetric oscillations between the glacial and interglacial states under the effect of the astronomical forcing, such as the Van der Pool and the Duffing oscillators. In order to understand how these simple low-dimensional models enter theories of ice ages and rapid events, we studied synchronization phenomena between simple driven oscillators and astronomical forcing, focusing on distinguishing between the so-called resonance scenario and the so-called phase locking scenario. We next examined the possible mechanisms for the Mid-Pleistocene transition. Here we show that the transition could be explained as a result of frequency-locking to the external forcing. This change can be interpreted as a result of an internal change in climate response

  3. Microbial Community Dynamics from Permafrost Across the Pleistocene-Holocene Boundary and Response to Abrupt Climate Change

    NASA Astrophysics Data System (ADS)

    Hammad, A.; Mahony, M.; Froese, D. G.; Lanoil, B. D.

    2014-12-01

    Earth is currently undergoing rapid warming similar to that observed about 10,000 years ago at the end of the Pleistocene. We know a considerable amount about the adaptations and extinctions of mammals and plants at the Pleistocene/Holocene (P/H) boundary, but relatively little about changes at the microbial level. Due to permafrost soils' freezing anoxic conditions, they act as microbial diversity archives allowing us to determine how microbial communities adapted to the abrupt warming at the end of P. Since microbial community composition only helps differentiate viable and extant microorganisms in frozen permafrost, microbial activity in thawing permafrost must be investigated to provide a clear understanding of microbial response to climate change. Current increased temperatures will result in warming and potential thaw of permafrost and release of stored organic carbon, freeing it for microbial utilization; turning permafrost into a carbon source. Studying permafrost viable microbial communities' diversity and activity will provide a better understanding of how these microorganisms respond to soil edaphic variability due to climate change across the P/H boundary, providing insight into the changes that the soil community is currently undergoing in this modern era of rapid climate change. Modern soil, H and P permafrost cores were collected from Lucky Lady II site outside Dawson City, Yukon. 16S rRNA high throughput sequencing of permafrost DNA showed the same trends for total and viable community richness and diversity with both decreasing with permafrost depth and only the richness increasing in mid and early P. The modern, H and P soils had 50.9, 33.9, and 27.3% unique viable species and only 14% of the total number of viable species were shared by all soils. Gas flux measurements of thawed permafrost showed metabolic activity in modern and permafrost soils, aerobic CH­­4 consumption in modern, some H and P soils, and anaerobic CH­­4 production in one H

  4. Pink marine sediments reveal rapid ice melt and Arctic meltwater discharge during Dansgaard-Oeschger warmings.

    PubMed

    Rasmussen, Tine L; Thomsen, Erik

    2013-01-01

    The climate of the last glaciation was interrupted by numerous abrupt temperature fluctuations, referred to as Greenland interstadials and stadials. During warm interstadials the meridional overturning circulation was active transferring heat to the north, whereas during cold stadials the Nordic Seas were ice-covered and the overturning circulation was disrupted. Meltwater discharge, from ice sheets surrounding the Nordic Seas, is implicated as a cause of this ocean instability, yet very little is known regarding this proposed discharge during warmings. Here we show that, during warmings, pink clay from Devonian Red Beds is transported in suspension by meltwater from the surrounding ice sheet and replaces the greenish silt that is normally deposited on the north-western slope of Svalbard during interstadials. The magnitude of the outpourings is comparable to the size of the outbursts during the deglaciation. Decreasing concentrations of ice-rafted debris during the interstadials signify that the ice sheet retreats as the meltwater production increases. PMID:24264767

  5. Global Warming on Triton

    NASA Technical Reports Server (NTRS)

    Elliot, J. L.; Hammel, H. B.; Wasserman, L. H.; Franz, O. G.; McDonald, S. W.; Person, M. J.; Olkin, C. B.; Dunham, E. J.; Spencer, J. R.; Stansberry, J. A.; Buie, M. W.; Pasachoff, J. M.; Babcock, B. A.; McConnochie, T. H.

    1998-01-01

    Triton, Neptune's largest moon, has been predicted to undergo significant seasonal changes that would reveal themselves as changes in its mean frost temperature. But whether this temperature should at the present time be increasing, decreasing or constant depends on a number of parameters (such as the thermal properties of the surface, and frost migration patterns) that are unknown. Here we report observations of a recent stellar occultation by Triton which, when combined with earlier results, show that Triton has undergone a period of global warming since 1989. Our most conservative estimates of the rate of temperature and surface-pressure increase during this period imply that the atmosphere is doubling in bulk every 10 years, significantly faster than predicted by any published frost model for Triton. Our result suggests that permanent polar caps on Triton play a c dominant role in regulating seasonal atmospheric changes. Similar processes should also be active on Pluto.

  6. Global warming challenge

    SciTech Connect

    Hengeveld, H. )

    1994-11-01

    Global warming will necessitate significant adjustments in Canadian society and its economy. In 1979, the Canadian federal government created its Canadian Climate Program (CCP) in collaboration with other agencies, institutions, and individuals. It sought to coordinate national efforts to understand global and regional climate, and to promote better use of the emerging knowledge. Much of the CCP-coordinated research into sources and sinks of greenhouse gases interfaces with other national and international programs. Other researchers have become involved in the Northern Wetlands Study, a cooperative United States-Canada initiative to understand the role of huge northern bogs and muskegs in the carbon cycle. Because of the need to understand how the whole, linked climate system works, climate modeling emerged as a key focus of current research. 35 refs., 4 figs.

  7. Warm waters, bleached corals

    SciTech Connect

    Roberts, L.

    1990-10-12

    Two researchers, Tom Goreau of the Discovery Laboratory in Jamaica and Raymond Hayes of Howard University, claim that they have evidence that nearly clinches the temperature connection to the bleached corals in the Caribbean and that the coral bleaching is an indication of Greenhouse warming. The incidents of scattered bleaching of corals, which have been reported for decades, are increasing in both intensity and frequency. The researchers based their theory on increased temperature of the seas measured by satellites. However, some other scientists feel that the satellites measure the temperature of only the top few millimeters of the water and that since corals lie on reefs perhaps 60 to 100 feet below the ocean surface, the elevated temperatures are not significant.

  8. Relative effectiveness of central, peripheral, and abrupt-onset cues in visual attention.

    PubMed

    Koshino, H; Warner, C B; Juola, J F

    1992-11-01

    The relative effectiveness of central arrow, peripheral arrow, and abrupt-onset cues was assessed in a character recognition task. On each trial, either a central or a peripheral arrow cue was presented 0, 100, or 200 msec before the appearance of a three-digit display. Two of the digits were "uncamouflaged" from previous figure-eight masks, whereas the third digit appeared abruptly in a previously empty space. Four different groups of subjects were run in factorial combinations of high or low expected validities for arrow and onset cues. In Experiment 1, arrow cues were located centrally, near the fixation point. Abrupt onsets showed larger cost-plus benefits than central arrows, except when subjects expected the central cues to have higher validity than the onsets. In Experiment 2, arrow cues were located peripherally, near the display digits, and abrupt onsets were again more effective in capturing attention except when peripheral cues had higher validity and led the onsets by 100 msec or more. In both experiments, the relative effectiveness of abrupt onsets decreased with arrow SOA. The results were consistent with a model in which automatic and voluntary processes interact in their control of attentional resources. PMID:1484975

  9. Interacting warm dark matter

    SciTech Connect

    Cruz, Norman; Palma, Guillermo; Zambrano, David; Avelino, Arturo E-mail: guillermo.palma@usach.cl E-mail: avelino@fisica.ugto.mx

    2013-05-01

    We explore a cosmological model composed by a dark matter fluid interacting with a dark energy fluid. The interaction term has the non-linear λρ{sub m}{sup α}ρ{sub e}{sup β} form, where ρ{sub m} and ρ{sub e} are the energy densities of the dark matter and dark energy, respectively. The parameters α and β are in principle not constrained to take any particular values, and were estimated from observations. We perform an analytical study of the evolution equations, finding the fixed points and their stability properties in order to characterize suitable physical regions in the phase space of the dark matter and dark energy densities. The constants (λ,α,β) as well as w{sub m} and w{sub e} of the EoS of dark matter and dark energy respectively, were estimated using the cosmological observations of the type Ia supernovae and the Hubble expansion rate H(z) data sets. We find that the best estimated values for the free parameters of the model correspond to a warm dark matter interacting with a phantom dark energy component, with a well goodness-of-fit to data. However, using the Bayesian Information Criterion (BIC) we find that this model is overcame by a warm dark matter – phantom dark energy model without interaction, as well as by the ΛCDM model. We find also a large dispersion on the best estimated values of the (λ,α,β) parameters, so even if we are not able to set strong constraints on their values, given the goodness-of-fit to data of the model, we find that a large variety of theirs values are well compatible with the observational data used.

  10. Tropospheric circulation during the early twentieth century Arctic warming

    NASA Astrophysics Data System (ADS)

    Wegmann, Martin; Brönnimann, Stefan; Compo, Gilbert P.

    2016-06-01

    The early twentieth century Arctic warming (ETCAW) between 1920 and 1940 is an exceptional feature of climate variability in the last century. Its warming rate was only recently matched by recent warming in the region. Unlike recent warming largely attributable to anthropogenic radiative forcing, atmospheric warming during the ETCAW was strongest in the mid-troposphere and is believed to be triggered by an exceptional case of natural climate variability. Nevertheless, ultimate mechanisms and causes for the ETCAW are still under discussion. Here we use state of the art multi-member global circulation models, reanalysis and reconstruction datasets to investigate the internal atmospheric dynamics of the ETCAW. We investigate the role of boreal winter mid-tropospheric heat transport and circulation in providing the energy for the large scale warming. Analyzing sensible heat flux components and regional differences, climate models are not able to reproduce the heat flux evolution found in reanalysis and reconstruction datasets. These datasets show an increase of stationary eddy heat flux and a decrease of transient eddy heat flux during the ETCAW. Moreover, tropospheric circulation analysis reveals the important role of both the Atlantic and the Pacific sectors in the convergence of southerly air masses into the Arctic during the warming event. Subsequently, it is suggested that the internal dynamics of the atmosphere played a major role in the formation in the ETCAW.

  11. Preoperative forced-air warming combined with intraoperative warming versus intraoperative warming alone in the prevention of hypothermia during gynecologic surgery.

    PubMed

    Adriani, Melissa Bucci; Moriber, Nancy

    2013-12-01

    Hypothermia in the perioperative setting can have serious consequences, including increased risk of infection or adverse cardiac events. Forced-air warming units commonly are used to prevent hypothermia. This study examined the impact of adding preoperative warming (Bair Paws, 3M) to conventional intraoperative forced-air warming modalities. Thirty patients received both preoperative and intraoperative forced-air warming, and 30 patients received intraoperative warming alone. Temperature readings were recorded across 3 time periods: preoperative, intraoperative, and postoperative. Data were analyzed using descriptive statistics, analysis of variance (ANOVA), and repeated-measures ANOVA. Demographics were similar in both groups with respect to age, body mass index, total intravenous fluids, and estimated blood loss. Statistically significant differences in temperature were seen over time (df = 2, P < .001), and for each intervention across all 3 time periods (P = .042). However, no statistically significant differences in temperature were demonstrated between groups over time. ASA status and type of procedure (laparoscopic vs open) also had no impact on results. These results suggest that preoperative warming with the Bair Paws gown offers no benefit over conventional therapy in maintaining normothermia in the perioperative period. PMID:24597006

  12. The Necessity of Awareness of Early Symptoms of Placental Abruption Among Pregnant Japanese Women

    PubMed Central

    Suzuki, Shunji; Shinmura, Hiroki

    2016-01-01

    Background In 2012, the recommendation for immediate contact and visit to obstetric institutions by pregnant women was emphasized by The Japan Obstetric Compensation System for Cerebral Palsy (JOCSC). In this study, we examined whether or not the increased awareness has led to the improvement of perinatal outcomes of placental abruption managed at private clinics. Methods We reviewed the obstetric records of 38 singleton pregnant women complicated by placental abruption that developed at home, and were managed at private clinics from April 2008 through April 2016. Results The perinatal outcomes, specifically the rate of cases with ≥ 1 hour time interval between symptom onset and clinic visit, have not changed significantly after the intervention. Conclusion The provision of information regarding the early clinical symptoms associated with placental abruption in pregnant women has not been well documented in Japan. PMID:27540442

  13. Abrupt Climate Change: the View from the Past, the Present and the Future

    NASA Astrophysics Data System (ADS)

    White, J. W. C.

    2014-12-01

    Climate is changing as humans put more and more greenhouse gases into the atmosphere. With CO2 levels today around 400ppm, we are clearly committed to far more climate change, both in the near term, and well beyond our children's future. A key question is how that change will occur. Abrupt climate changes are those that exceed our expectations, preparedness, and ability to adapt. Such changes challenge us economically, physically, and socially. This talk will draw upon results from ice core research over the past twenty years, as well as a new NRC report on abrupt climate change in order to address abrupt change, as seen in the past in ice cores, as seen today in key environmental systems upon which humans depend, and what is may be coming in the future.

  14. Microscopic Approaches to Decomposition and Burning Processes of a Micro Plastic Resin Particle under Abrupt Heating

    NASA Astrophysics Data System (ADS)

    Ohiwa, Norio; Ishino, Yojiro; Yamamoto, Atsunori; Yamakita, Ryuji

    To elucidate the possibility and availability of thermal recycling of waste plastic resin from a basic and microscopic viewpoint, a series of abrupt heating processes of a spherical micro plastic particle having a diameter of about 200 μm is observed, when it is abruptly exposed to hot oxidizing combustion gas. Three ingenious devices are introduced and two typical plastic resins of polyethylene terephthalate and polyethylene are used. In this paper the dependency of internal and external appearances of residual plastic embers on the heating time and the ingredients of plastic resins is optically analyzed, along with appearances of internal micro bubbling, multiple micro explosions and jets, and micro diffusion flames during abrupt heating. Based on temporal variations of the surface area of a micro plastic particle, the apparent burning rate constant is also evaluated and compared with those of well-known volatile liquid fuels.

  15. Formation of compositionally abrupt axial heterojunctions in silicon-germanium nanowires.

    PubMed

    Wen, C-Y; Reuter, M C; Bruley, J; Tersoff, J; Kodambaka, S; Stach, E A; Ross, F M

    2009-11-27

    We have formed compositionally abrupt interfaces in silicon-germanium (Si-Ge) and Si-SiGe heterostructure nanowires by using solid aluminum-gold alloy catalyst particles rather than the conventional liquid semiconductor-metal eutectic droplets. We demonstrated single interfaces that are defect-free and close to atomically abrupt, as well as quantum dots (i.e., Ge layers tens of atomic planes thick) embedded within Si wires. Real-time imaging of growth kinetics reveals that a low solubility of Si and Ge in the solid particle accounts for the interfacial abruptness. Solid catalysts that can form functional group IV nanowire-based structures may yield an extended range of electronic applications. PMID:19965471

  16. Policy implications of greenhouse warming

    NASA Astrophysics Data System (ADS)

    Coppock, Rob

    1992-03-01

    A study panel of the National Academy of Sciences, National Academy of Engineering, and Institute of Medicine recently issued the report Policy Implications of Greenhouse Warming. That report examined relevant scientific knowldeg and evidence about the potential of greenhouse warming, and assayed actions that could slow the onset of warming (mitigation policies) or help human and natural systems of plants and animals adapt to climatic changes (adaptation policies). The panel found that, even given the considerable uncertainties knowledge of the relevant phenomena, greenhouse warming poses a threat sufficient to merit prompt action. People in this country could probably adapt to the changes likely to accompany greenhouse warming. The costs, however, could be substantial. Investment in mitigation acts as insurance protection against the great uncertainties and the possibility of dramatic surprises. The panel found mitigation options that could reduce U.S. emissions by an estimated 10 to 40 percent at modest cost.

  17. Myocardial infarction complicated by left ventricular thrombus and fatal thromboembolism following abrupt cessation of dabigatran

    PubMed Central

    Weiler, Bethany; Marciniak, Ellen T; Reed, Robert M; McCurdy, Michael T

    2014-01-01

    Novel anticoagulants are increasingly utilised in lieu of warfarin to treat non-valvular atrial fibrillation. Their clinical use in other non-FDA approved settings is also increasing. We present a case in which a patient abruptly stopped taking dabigatran due to a small bowel obstruction and shortly thereafter suffered a myocardial infarction complicated by left ventricular thrombosis with fatal embolisation to the superior mesenteric artery. In this context, we discuss the possibility of a rebound phenomenon of hypercoagulability with abrupt cessation of novel anticoagulants. PMID:25100807

  18. Analysis of mode scattering from an abruptly ended dielectric slab waveguide by an accelerated iteration technique.

    PubMed

    Tigelis, I G; Manenkov, A B

    2000-12-01

    A new modification of the integral equation method using an iteration technique with "accelerating" parameters is presented to solve the problem of guided-mode scattering from an abruptly ended asymmetrical slab waveguide. The optimal choice of the parameters is shown to be closely connected with the variational principle. The electric-field distribution at the terminal plane, the reflection coefficient of the guided mode, and the far-field radiation pattern are computed. Numerical results are presented for several cases of abruptly ended waveguides, including the systems with constant and variable profiles of the refractive indices. The phenomenon of the radiation pattern rotation is examined in detail. PMID:11140485

  19. New evidence from the South China Sea for an abrupt termination of the last glacial period

    NASA Technical Reports Server (NTRS)

    Broecker, W. S.; Klas, M.; Andree, M.; Bonani, G.; Wolfli, W.

    1988-01-01

    Results demonstrating an abrupt change in the rate and character of sedimentation in the South China Sea at the close of the last glacial period are presented. Radiocarbon dating and its position in the oxygen isotope shift suggest that this change may be coincident with the abrupt change in climatic conditions seen at high latitudes in the North Atlantic and the Antarctic at 13 kyr BP. These results support the contention that a major global climatic change occurred between 14 and 13 kyr BP.

  20. On the warm/cold regime shift in the South China Sea: Observation and modeling study

    NASA Astrophysics Data System (ADS)

    Swapna, P.; Gan, Jianping; Lau, Alexis; Fung, Jimmy

    2009-07-01

    Remote sensing data sets and a high-resolution three-dimensional regional ocean model were utilized to investigate the shifting of warm/cold regime and the associated sea level variation in the South China Sea (SCS) during 2000-2003. Both the altimetry data and the model results showed an increase in the sea level (warm phase) followed by an abrupt decrease (cold phase) in the SCS during 2000-2003. Heat budget calculations performed with the model revealed excess heat advection from the western Pacific warm pool into the SCS during the warm phase than the cold phase. The warm phase, which occurred during La Niña episodes, resulted from the intrusion of abnormally warmer western Pacific water that increased the heat content and thus sea level in the SCS. The cold phase, which occurred during El Niño episodes, was triggered by a reduction in the net atmospheric heat flux followed by cold water advection into the SCS. Decrease in the rate of precipitation minus evaporation ( P-E) also accounted for the falling of sea level during cold phase. The present study integrated the available remote sensing data and advanced numerical model to identify the time-dependent three-dimensional dynamic and thermodynamic forcing that are important in governing the warm/cold regime shift in the SCS.

  1. Warming up for Planck

    NASA Astrophysics Data System (ADS)

    Bartrum, Sam; Berera, Arjun; Rosa, João G.

    2013-06-01

    The recent Planck results and future releases on the horizon present a key opportunity to address a fundamental question in inflationary cosmology of whether primordial density perturbations have a quantum or thermal origin, i.e. whether particle production may have significant effects during inflation. Warm inflation provides a natural arena to address this issue, with interactions between the scalar inflaton and other degrees of freedom leading to dissipative entropy production and associated thermal fluctuations. In this context, we present relations between CMB observables that can be directly tested against observational data. In particular, we show that the presence of a thermal bath warmer than the Hubble scale during inflation decreases the tensor-to-scalar ratio with respect to the conventional prediction in supercooled inflation, yielding r < 8|nt|, where nt is the tensor spectral index. Focusing on supersymmetric models at low temperatures, we determine consistency relations between the observables characterizing the spectrum of adiabatic scalar and tensor modes, both for generic potentials and particular canonical examples, and which we compare with the WMAP and Planck results. Finally, we include the possibility of producing the observed baryon asymmetry during inflation through dissipative effects, thereby generating baryon isocurvature modes that can be easily accommodated by the Planck data.

  2. Warm dense crystallography

    NASA Astrophysics Data System (ADS)

    Valenza, Ryan A.; Seidler, Gerald T.

    2016-03-01

    The intense femtosecond-scale pulses from x-ray free electron lasers (XFELs) are able to create and interrogate interesting states of matter characterized by long-lived nonequilibrium semicore or core electron occupancies or by the heating of dense phases via the relaxation cascade initiated by the photoelectric effect. We address here the latter case of "warm dense matter" (WDM) and investigate the observable consequences of x-ray heating of the electronic degrees of freedom in crystalline systems. We report temperature-dependent density functional theory calculations for the x-ray diffraction from crystalline LiF, graphite, diamond, and Be. We find testable, strong signatures of condensed-phase effects that emphasize the importance of wide-angle scattering to study nonequilibrium states. These results also suggest that the reorganization of the valence electron density at eV-scale temperatures presents a confounding factor to achieving atomic resolution in macromolecular serial femtosecond crystallography (SFX) studies at XFELs, as performed under the "diffract before destroy" paradigm.

  3. Warming up for Planck

    SciTech Connect

    Bartrum, Sam; Berera, Arjun; Rosa, João G. E-mail: ab@ph.ed.ac.uk

    2013-06-01

    The recent Planck results and future releases on the horizon present a key opportunity to address a fundamental question in inflationary cosmology of whether primordial density perturbations have a quantum or thermal origin, i.e. whether particle production may have significant effects during inflation. Warm inflation provides a natural arena to address this issue, with interactions between the scalar inflaton and other degrees of freedom leading to dissipative entropy production and associated thermal fluctuations. In this context, we present relations between CMB observables that can be directly tested against observational data. In particular, we show that the presence of a thermal bath warmer than the Hubble scale during inflation decreases the tensor-to-scalar ratio with respect to the conventional prediction in supercooled inflation, yielding r < 8|n{sub t}|, where n{sub t} is the tensor spectral index. Focusing on supersymmetric models at low temperatures, we determine consistency relations between the observables characterizing the spectrum of adiabatic scalar and tensor modes, both for generic potentials and particular canonical examples, and which we compare with the WMAP and Planck results. Finally, we include the possibility of producing the observed baryon asymmetry during inflation through dissipative effects, thereby generating baryon isocurvature modes that can be easily accommodated by the Planck data.

  4. Correlating Cordilleran Ice Sheet Collapse with North Atlantic Heinrich Events using Global Radiocarbon Plateaus.

    NASA Astrophysics Data System (ADS)

    Hendy, I. L.; Cosma, T.

    2006-12-01

    The small, ephemeral Cordilleran Ice Sheet, present in Alaska, British Columbia and northern Washington during the last glacial cycle is believed to have behaved differently than the larger Laurentice Ice Sheet to climate forcing. High quality chronology is required to understand the relationship between this ice sheet and global climate change. Presently MD02-2496 (48°58.47N: 127°02.14W; 1190m water depth) is the highest resolution paleoclimate record available for the last 50 Ka in the Pacific northwest and contains intervals of glacial-marine sedimentation. High resolution dating based on 36 radiocarbon dates provide a chronology that includes radiocarbon age plateaus, while planktonic foraminiferal stable isotopes offer a continuous record of climate change. Glacial-marine sediments collected from this site on the continental slope west of Vancouver Island, British Columbia, document three intervals of iceberg discharge during the last ~50 Ka. Gradually increasing quantities of ice rafted detritus (grains >250μm, g-1; IRD) followed by abrupt cessation within ~500 years is strongly suggestive of catastrophic iceberg discharge. The penultimate event is correlated to marine invasion of the Juan de Fuca Strait, and Puget Sound, while the final IRD event with that of Georgia Strait. We posit that these previously unknown IRD events represent repeated rapid iceberg discharge related to Cordilleran Ice Sheet collapse. The events occur near the end of radiocarbon plateaus at 13.35 ±90 and 14.05 ±70 14C Kyr BP (not reservoir corrected). If these plateaus correlate with the 12.2 and 13.3 14C Kyr BP plateaus recorded in Carriaco Basin and elsewhere, local reservoir ages can be calculated and vary between 1,150 and 1,550 years similar to those derived locally from glacial wood-shell pairs. Furthermore, if the plateaus result from reduced North Atlantic Deep Water export and consequently Heinrich Events, the Cordilleran IRD events are related to North Atlantic iceberg

  5. From drought to flooding: understanding the abrupt 2010-11 hydrological annual cycle in the Amazonas River and tributaries

    NASA Astrophysics Data System (ADS)

    Carlo Espinoza, Jhan; Ronchail, Josyane; Loup Guyot, Jean; Junquas, Clementine; Drapeau, Guillaume; Martinez, Jean Michel; Santini, William; Vauchel, Philippe; Lavado, Waldo; Ordoñez, Julio; Espinoza, Raúl

    2012-06-01

    In this work we document and analyze the hydrological annual cycles characterized by a rapid transition between low and high flows in the Amazonas River (Peruvian Amazon) and we show how these events, which may impact vulnerable riverside residents, are related to regional climate variability. Our analysis is based on comprehensive discharge, rainfall and average suspended sediment data sets. Particular attention is paid to the 2010-11 hydrological year, when an unprecedented abrupt transition from the extreme September 2010 drought (8300 m3 s-1) to one of the four highest discharges in April 2011 (49 500 m3 s-1) was recorded at Tamshiyacu (Amazonas River). This unusual transition is also observed in average suspended sediments. Years with a rapid increase in discharge are characterized by negative sea surface temperature anomalies in the central equatorial Pacific during austral summer, corresponding to a La Niña-like mode. It originates a geopotential height wave train over the subtropical South Pacific and southeastern South America, with a negative anomaly along the southern Amazon and the southeastern South Atlantic convergence zone region. As a consequence, the monsoon flux is retained over the Amazon and a strong convergence of humidity occurs in the Peruvian Amazon basin, favoring high rainfall and discharge. These features are also reported during the 2010-11 austral summer, when an intense La Niña event characterized the equatorial Pacific.

  6. Recent Warming of Lake Kivu

    PubMed Central

    Katsev, Sergei; Aaberg, Arthur A.; Crowe, Sean A.; Hecky, Robert E.

    2014-01-01

    Lake Kivu in East Africa has gained notoriety for its prodigious amounts of dissolved methane and dangers of limnic eruption. Being meromictic, it is also expected to accumulate heat due to rising regional air temperatures. To investigate the warming trend and distinguish between atmospheric and geothermal heating sources, we compiled historical temperature data, performed measurements with logging instruments, and simulated heat propagation. We also performed isotopic analyses of water from the lake's main basin and isolated Kabuno Bay. The results reveal that the lake surface is warming at the rate of 0.12°C per decade, which matches the warming rates in other East African lakes. Temperatures increase throughout the entire water column. Though warming is strongest near the surface, warming rates in the deep waters cannot be accounted for solely by propagation of atmospheric heat at presently assumed rates of vertical mixing. Unless the transport rates are significantly higher than presently believed, this indicates significant contributions from subterranean heat sources. Temperature time series in the deep monimolimnion suggest evidence of convection. The progressive deepening of the depth of temperature minimum in the water column is expected to accelerate the warming in deeper waters. The warming trend, however, is unlikely to strongly affect the physical stability of the lake, which depends primarily on salinity gradient. PMID:25295730

  7. Dynamics of climate and ecosystem coupling: abrupt changes and multiple equilibria.

    PubMed Central

    Higgins, Paul A T; Mastrandrea, Michael D; Schneider, Stephen H

    2002-01-01

    Interactions between subunits of the global climate-biosphere system (e.g. atmosphere, ocean, biosphere and cryosphere) often lead to behaviour that is not evident when each subunit is viewed in isolation. This newly evident behaviour is an emergent property of the coupled subsystems. Interactions between thermohaline circulation and climate illustrate one emergent property of coupling ocean and atmospheric circulation. The multiple thermohaline circulation equilibria that result caused abrupt climate changes in the past and may cause abrupt climate changes in the future. Similarly, coupling between the climate system and ecosystem structure and function produces complex behaviour in certain regions. For example, atmosphere-biosphere interactions in the Sahel region of West Africa lead to multiple stable equilibria. Either wet or dry climate equilibria can occur under otherwise identical forcing conditions. The equilibrium reached is dependent on past history (i.e. initial conditions), and relatively small perturbations to either climate or vegetation can cause switching between the two equilibria. Both thermohaline circulation and the climate-vegetation system in the Sahel are prone to abrupt changes that may be irreversible. This complicates the relatively linear view of global changes held in many scientific and policy communities. Emergent properties of coupled socio-natural systems add yet another layer of complexity to the policy debate. As a result, the social and economic consequences of possible global changes are likely to be underestimated in most conventional analyses because these nonlinear, abrupt and irreversible responses are insufficiently considered. PMID:12079526

  8. Dynamics of climate and ecosystem coupling: abrupt changes and multiple equilibria.

    PubMed

    Higgins, Paul A T; Mastrandrea, Michael D; Schneider, Stephen H

    2002-05-29

    Interactions between subunits of the global climate-biosphere system (e.g. atmosphere, ocean, biosphere and cryosphere) often lead to behaviour that is not evident when each subunit is viewed in isolation. This newly evident behaviour is an emergent property of the coupled subsystems. Interactions between thermohaline circulation and climate illustrate one emergent property of coupling ocean and atmospheric circulation. The multiple thermohaline circulation equilibria that result caused abrupt climate changes in the past and may cause abrupt climate changes in the future. Similarly, coupling between the climate system and ecosystem structure and function produces complex behaviour in certain regions. For example, atmosphere-biosphere interactions in the Sahel region of West Africa lead to multiple stable equilibria. Either wet or dry climate equilibria can occur under otherwise identical forcing conditions. The equilibrium reached is dependent on past history (i.e. initial conditions), and relatively small perturbations to either climate or vegetation can cause switching between the two equilibria. Both thermohaline circulation and the climate-vegetation system in the Sahel are prone to abrupt changes that may be irreversible. This complicates the relatively linear view of global changes held in many scientific and policy communities. Emergent properties of coupled socio-natural systems add yet another layer of complexity to the policy debate. As a result, the social and economic consequences of possible global changes are likely to be underestimated in most conventional analyses because these nonlinear, abrupt and irreversible responses are insufficiently considered. PMID:12079526

  9. A study of the early warning signals of abrupt change in the Pacific decadal oscillation

    NASA Astrophysics Data System (ADS)

    Wu, Hao; Hou, Wei; Yan, Peng-Cheng; Zhang, Zhi-Sen; Wang, Kuo

    2015-08-01

    In recent years, the phenomenon of a critical slowing down has demonstrated its major potential in discovering whether a complex dynamic system tends to abruptly change at critical points. This research on the Pacific decadal oscillation (PDO) index has been made on the basis of the critical slowing down principle in order to analyze its early warning signal of abrupt change. The chaotic characteristics of the PDO index sequence at different times are determined by using the largest Lyapunov exponent (LLE). The relationship between the regional sea surface temperature (SST) background field and the early warning signal of the PDO abrupt change is further studied through calculating the variance of the SST in the PDO region and the spatial distribution of the autocorrelation coefficient, thereby providing the experimental foundation for the extensive application of the method of the critical slowing down phenomenon. Our results show that the phenomenon of critical slowing down, such as the increase of the variance and autocorrelation coefficient, will continue for six years before the abrupt change of the PDO index. This phenomenon of the critical slowing down can be regarded as one of the early warning signals of an abrupt change. Through calculating the LLE of the PDO index during different times, it is also found that the strongest chaotic characteristics of the system occurred between 1971 and 1975 in the early stages of an abrupt change (1976), and the system was at the stage of a critical slowing down, which proves the reliability of the early warning signal of abrupt change discovered in 1970 from the mechanism. In addition, the variance of the SST, along with the spatial distribution of the autocorrelation coefficient in the corresponding PDO region, also demonstrates the corresponding relationship between the change of the background field of the SST and the change of the PDO. Project supported by the National Natural Science Foundation of China (Grant Nos

  10. Amplified Arctic warming by phytoplankton under greenhouse warming.

    PubMed

    Park, Jong-Yeon; Kug, Jong-Seong; Bader, Jürgen; Rolph, Rebecca; Kwon, Minho

    2015-05-12

    Phytoplankton have attracted increasing attention in climate science due to their impacts on climate systems. A new generation of climate models can now provide estimates of future climate change, considering the biological feedbacks through the development of the coupled physical-ecosystem model. Here we present the geophysical impact of phytoplankton, which is often overlooked in future climate projections. A suite of future warming experiments using a fully coupled ocean-atmosphere model that interacts with a marine ecosystem model reveals that the future phytoplankton change influenced by greenhouse warming can amplify Arctic surface warming considerably. The warming-induced sea ice melting and the corresponding increase in shortwave radiation penetrating into the ocean both result in a longer phytoplankton growing season in the Arctic. In turn, the increase in Arctic phytoplankton warms the ocean surface layer through direct biological heating, triggering additional positive feedbacks in the Arctic, and consequently intensifying the Arctic warming further. Our results establish the presence of marine phytoplankton as an important potential driver of the future Arctic climate changes. PMID:25902494

  11. Amplified Arctic warming by phytoplankton under greenhouse warming

    PubMed Central

    Park, Jong-Yeon; Kug, Jong-Seong; Bader, Jürgen; Rolph, Rebecca; Kwon, Minho

    2015-01-01

    Phytoplankton have attracted increasing attention in climate science due to their impacts on climate systems. A new generation of climate models can now provide estimates of future climate change, considering the biological feedbacks through the development of the coupled physical–ecosystem model. Here we present the geophysical impact of phytoplankton, which is often overlooked in future climate projections. A suite of future warming experiments using a fully coupled ocean−atmosphere model that interacts with a marine ecosystem model reveals that the future phytoplankton change influenced by greenhouse warming can amplify Arctic surface warming considerably. The warming-induced sea ice melting and the corresponding increase in shortwave radiation penetrating into the ocean both result in a longer phytoplankton growing season in the Arctic. In turn, the increase in Arctic phytoplankton warms the ocean surface layer through direct biological heating, triggering additional positive feedbacks in the Arctic, and consequently intensifying the Arctic warming further. Our results establish the presence of marine phytoplankton as an important potential driver of the future Arctic climate changes. PMID:25902494

  12. Coral Evidence for Abrupt Changes in Ocean-Atmosphere Dynamics in the SW Pacific since 1565 AD

    NASA Astrophysics Data System (ADS)

    Hendy, E. J.; Gagan, M. K.; McCulloch, M. T.; Lough, J. M.

    2004-12-01

    A coral-based multi-tracer approach can give an overview of the whole tropical ocean-atmosphere system. Key indicators are sea surface temperature (SST), which sets climate boundary conditions, sea surface salinity (SSS), which provides a measure of energy transfer through the evaporation-precipitation balance, and river runoff, which can establish the strength and variability of precipitation. We present palaeoenvironmental records from eight massive { \\it Porites} coral colonies, spanning 120 to 420 years of continuous growth, collected from the central Great Barrier Reef, Australia. Stable isotopes (\\delta18O and \\delta13C), Sr/Ca, U/Ca, and Ba/Ca ratios were measured in 5-year increments and a record of annual UV luminescence was developed. By replicating the measurements between colonies we demonstrate how faithfully corals record changes in their environment over decadal-to-centennial timescales, constructing composite records in a manner analogous to dendroclimatology and confidence intervals for each proxy. The competing environmental influences affecting a number of tracers can be distinguished by comparison between the SST-tracers (Sr/Ca, U/Ca, \\delta18O), the freshwater flux tracers (\\Delta\\delta18O, Ba/Ca and luminescence) and tracers of water mass characteristics (\\delta18O, \\delta13C, and \\Delta14C). The coral palaeothermometers Sr/Ca and U/Ca ratios, measured in tandem with \\delta18O, allow the separation of SST changes from changes in seawater \\delta18O, thereby resolving SSS. The composite Sr/Ca and U/Ca are in excellent agreement back to 1565, and capture the 20th century warming trend, up to the 1980s when the cores were collected. The most remarkable feature of the 420-year record is that SSTs were consistently as warm as the second half of the 20th century from the early 18th and through most of the 19th centuries. Changes in the evaporation-precipitation balance dominate the \\delta18O record. A striking 0.2\\permil\\ shift from the

  13. Constraining the trigger for an ancient warming episode

    NASA Astrophysics Data System (ADS)

    Schultz, Colin

    2011-08-01

    The Paleocene epoch (˜66-56 million years ago) was sandwiched between sudden climate shifts and mass extinctions. The boundary between the end of the Paleocene and the beginning of the Eocene (the P-E boundary) saw the global average temperature soar by 5°C over a few thousand years, leading to a pronounced reorganization of both terrestrial and oceanic plant and animal communities. The P-E boundary warming was triggered by an influx of atmospheric carbon dioxide, but the influx's ultimate trigger is still being debated. Other prominent warming events within the Paleogene (˜66-23 million years ago), the broad time span that encompasses the Paleocene and Eocene, have been linked to regularly recurring changes in the eccentricity of the Earth's orbit that take place on 100,000- and 405,000-year cycles. Proponents of this view suggest that an alignment of the two cycles could lead to the warming of deep ocean waters, melting frozen methane and triggering an increase in atmospheric carbon dioxide. However, some studies have suggested that the P-E boundary warming was instead the product of geological processes, where carbon-rich rocks were baked by injected magma, which eventually liberated the carbon to the atmosphere. Deciding between proposed explanations for the cause of the P-E warming, whether they are astronomical or geological, depends on accurately pinning the event in time. (Geochemistry, Geophysics, Geosystems, doi:10.1029/2010GC003426, 2011)

  14. Global warming: Perspectives from the Late Quaternary paleomammal record

    SciTech Connect

    Graham, R.W. )

    1993-03-01

    Global warming at the end of the Pleistocene caused significant environmental changes that directly and indirectly effected biotic communities. The biotic response to this global warming event can provide insights into the processes that might be anticipated for future climatic changes. The megafauna extinction may have been the most dramatic alteration of mammalian communities at the end of the Pleistocene. Late Quaternary warming also altered regional diversity patterns for some small mammal guilds without extinction. Reductions in body size for both small and large mammal species were also consequences of these environmental fluctuations. Geographic shifts in the distributions of individual mammal species resulted in changes in species composition of mammalian communities. The individualistic response of biota to environmental fluctuations define some boundary conditions for modeling communities. Understanding these boundary conditions is mandatory in planning for the preservation of biodiversity in the future. Finally, it is essential to determine how global warming will alter seasonal patterns because it is apparent from the paleobiological record that not all Quaternary warming events have been the same.

  15. Weird Warm Spot on Exoplanet

    NASA Video Gallery

    This animation illustrates an unexpected warm spot on the surface of a gaseous exoplanet. NASA's Spitzer Space Telescope discovered that the hottest part of the planet, shown here as bright, orange...

  16. The ecology of catastrophic events: understanding abrupt spatial transitions in susceptibility of grasslands and croplands to multi-year drought

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Much of the central grasslands region (CGR) of North America experienced a multi-year extreme drought in the 1930s that combined with land management practices to result in broad-scale plant mortality, massive dust storms, and losses of soil and nutrients. All grassland types in the CGR were affecte...

  17. Keeping Enceladus warm

    NASA Astrophysics Data System (ADS)

    Travis, B. J.; Schubert, G.

    2015-04-01

    Despite its small size, Enceladus emits considerable heat, especially at its south pole, even long after simple thermal models predict it should be frozen. Several sources of energy have been proposed as responsible for this heating, such as tidal dissipative heating (TDH), convection and shearing in the ice shell, and exothermic chemical reactions (e.g., serpentine formation). Crater relaxation simulations suggest that episodic heating events have occurred over long stretches of Enceladus' history. Thermal history and hydrothermal simulations reported here show that a combination of steady plus episodic TDH heating could maintain at least a polar ocean to the present time. Hydrothermal circulation can play a significant role in mining Enceladus' internal heat, facilitating the persistence of an ocean even to the present by focusing internal heat to the polar regions.

  18. The interaction of radiative and dynamical processes during a simulated sudden stratospheric warming

    NASA Technical Reports Server (NTRS)

    Pierce, R. B.; Blackshear, W. T.; Fairlie, T. D.; Grose, W. L.; Turner, R. E.

    1993-01-01

    An analysis of a spontaneous sudden stratospheric warming that occurred during a 2-year integration of the Langley Research Center (LaRC) Atmospheric Simulation Model is presented. The simulated warming resembles observed 'wave 1' warmings in the Northern Hemisphere stratosphere and provides an opportunity to investigate the radiative and dynamical processes occurring during the warming event. Isentropic analysis of potential vorticity sources and sinks indicates that dynamically induced departures from radiative equilibrium play an important role in the warming event. Enhanced radiative cooling associated with a series of upper stratospheric warm pools leads to radiative dampening within the polar vortex. Within the 'surf zone' large-scale radiative cooling leads to diabatic advection of high potential vorticity air from aloft. Lagrangian area diagnostics of the simulated warming agree well with Limb Infrared Monitor of the Stratosphere (LIMS) analyses. Dynamical mixing is shown to account for the majority of the decrease in the size of the polar vortex during the simulated warming. An investigation of the nonlinear deformation of material lines that are initially coincident with diagnosed potential vorticity isopleths is conducted to clarify the relationship between the Lagrangian area diagnostics and potential vorticity advection during wave breaking events.

  19. Pronounced warming in the Indian and Pacific sectors of the Southern Ocean during the 1970s

    NASA Astrophysics Data System (ADS)

    Turney, Chris; Fogwill, Chris; Palmer, Jonathan; van Sebille, Erik; Thomas, Zoë; McGlone, Matt; Richardson, Sarah; Wilmshurst, Janet; Fenwick, Pavla; Carter, Lionel; Jones, Richard; Harsch, Melanie; Wilson, Kerry-Jayne; Clark, Graeme; Marzinelli, Ezequiel; Rogers, Tracey; Rainsley, Eleanor; Ciasto, Laura; Waterman, Stephanie; Antarctic Expedition 2013-2014 Members, Australasian

    2015-04-01

    Occupying some 20% of the world's ocean surface, the Southern Ocean is home to a diverse and unique biota and plays a fundamental role in global oceanic circulation, climate variability, Antarctic ice sheet stability and carbon cycling. Significant warming has been observed over recent decades, most prominently in the Antarctic Circumpolar Current (ACC). The mechanism(s) behind this warming, however, remain uncertain. Here, we integrate historic ocean and atmospheric observations and climate-sensitive tree growth on subantarctic islands from the northern limit of the ACC to extend historic and satellite measurements to produce a unique proxy record of temperature across 4˚ of latitude in the southwest Pacific. We demonstrate a hitherto unobserved abrupt warming during the 1970s that is unprecedented over the past 130 years, coincident with a significant decline in marine vertebrate populations and wider warming across the Indian Ocean. Comparison between our reconstruction and high-resolution ocean modelling provides a possible mechanism, suggesting warmer waters resulted from a poleward migration of the subtropical and ACC fronts. Projected increases in the strength of westerly winds are likely to continue the fronts' migration, driving warming in the Southern Ocean (>50˚S), with significant impacts on biota.

  20. Suppressed midlatitude summer atmospheric warming by Arctic sea ice loss during 1979-2012

    NASA Astrophysics Data System (ADS)

    Wu, Qigang; Cheng, Luyao; Chan, Duo; Yao, Yonghong; Hu, Haibo; Yao, Ying

    2016-03-01

    Since the 1980s, rapid Arctic warming, sea ice decline, and weakening summer circulation have coincided with an increasing number of extreme heat waves and other destructive weather events in the Northern Hemisphere (NH) midlatitudes in summer. Recent papers disagree about whether such high-impact events are related to Arctic warming and/or ice loss. Here we use atmospheric model ensemble simulations to attribute effects of sea ice loss and other factors on observed summer climate trends during 1979-2012. The ongoing greenhouse gas buildup and resulting sea surface temperature warming outside the Arctic explains nearly all land warming and a significant portion of observed weakening zonal winds in the NH midlatitudes. However, sea ice loss has induced a negative Arctic Oscillation(AO)-type circulation with significant summer surface and tropospheric cooling trends over large portions of the NH midlatitudes, which reduce the warming and might reduce the probability of regional severe hot summers.

  1. Temperature and precipitation reconstruction in correspondence to Dansgaard-Oeschger events and glacial terminations from Turkey

    NASA Astrophysics Data System (ADS)

    Stockhecke, Mona; Bechtel, Achim; Peterse, Francien; Randlett, Marie-Eve; Schubert, Carsten J.; Timmermann, Axel

    2016-04-01

    Lacustrine records from deep closed lakes, such as the 600,000 yr-old sedimentary sequence from Lake Van (Turkey), can provide detailed insights into the mechanisms of past environmental changes in the continental interior. The Lake Van record is continues and has an excellent age control over the last 350 ka. Repetitive intervals of annually-laminated sections are reflected in a sub-annual resolved color record. The Lake Van color record documents lake-level rises for all Dansgaard-Oeschger (DO) interstadials synchronous to the NGRIP δ18O record of Greenland ice reflecting temperature increases. Comparison with model hindcasts from LOVECLIM experiments, supports the notion that the lake-level increases during the warm interstadials is caused by precipitation increases due to atmospheric changes as consequence of AMOC increase during a paucity of ice-sheet calving events. Quaternary quantitative temperature and precipitation changes in the Eastern Mediterranean are unknown over the last 150 ka although it covers a critical time and area in human and mammal evolution. We quantified temperature and hydroclimate changes within a multi-proxy biomarker study. Lipid biomarkers during several DO events from MIS 3 and over the last two terminations were extracted at centennial resolution. Mean air temperatures (MAT) based on down-core distributional changes in branched glycerol dialkyl glycerol tetraethers (brGDGTs), indicate a 1.5-3° warming at stadial/interstadial transitions and 2-4° warming for glacials/interglacial transitions. Simultaneous analysis of the leaf wax hydrogen isotopic composition (δ2Hwax) result in a reconstruction of changes in the source water due to variable precipitation/evaporation ratio. Isotopically 10 ‰ (20) lighter δD-values of leaf-wax n-alkane C29 argue for a significantly increased humidity during the interstadials (interglacials) compared to the stadials (glacials). Magnitudes of temperature and precipitation changes at the DO

  2. The Great Warming Brian Fagan

    NASA Astrophysics Data System (ADS)

    Fagan, B. M.

    2010-12-01

    The Great Warming is a journey back to the world of a thousand years ago, to the Medieval Warm Period. Five centuries of irregular warming from 800 to 1250 had beneficial effects in Europe and the North Atlantic, but brought prolonged droughts to much of the Americas and lands affected by the South Asian monsoon. The book describes these impacts of warming on medieval European societies, as well as the Norse and the Inuit of the far north, then analyzes the impact of harsh, lengthy droughts on hunting societies in western North America and the Ancestral Pueblo farmers of Chaco Canyon, New Mexico. These peoples reacted to drought by relocating entire communities. The Maya civilization was much more vulnerable that small-scale hunter-gatherer societies and subsistence farmers in North America. Maya rulers created huge water storage facilities, but their civilization partially collapsed under the stress of repeated multiyear droughts, while the Chimu lords of coastal Peru adapted with sophisticated irrigation works. The climatic villain was prolonged, cool La Niñalike conditions in the Pacific, which caused droughts from Venezuela to East Asia, and as far west as East Africa. The Great Warming argues that the warm centuries brought savage drought to much of humanity, from China to Peru. It also argues that drought is one of the most dangerous elements in today’s humanly created global warming, often ignored by preoccupied commentators, but with the potential to cause over a billion people to starve. Finally, I use the book to discuss the issues and problems of communicating multidisciplinary science to the general public.

  3. Distinguishing warming-induced drought from drought-induced warming

    NASA Astrophysics Data System (ADS)

    Roderick, M. L.; Yin, D.

    2015-12-01

    It is usually observed that temperatures, especially maximum temperatures are higher during drought. A very widely held public perception is that the increase in temperature is a cause of drought. This represents the warming-induced drought scenario. However, the agricultural and hydrologic scientific communities have a very different interpretation with drought being the cause of increasing temperature. In essence, those communities assume the warming is a surface feedback and their interpretation is for drought-induced warming. This is a classic cause-effect problem that has resisted definitive explanation due to the lack of radiative observations at suitable spatial and temporal scales. In this presentation we first summarise the observations and then use theory to untangle the cause-effect relationships that underlie the competing interpretations. We then show how satellite data (CERES, NASA) can be used to disentangle the cause-effect relations.

  4. Active Movement Warm-Up Routines

    ERIC Educational Resources Information Center

    Walter, Teri; Quint, Ashleigh; Fischer, Kim; Kiger, Joy

    2011-01-01

    This article presents warm-ups that are designed to physiologically and psychologically prepare students for vigorous physical activity. An active movement warm-up routine is made up of three parts: (1) active warm-up movement exercises, (2) general preparation, and (3) the energy system. These warm-up routines can be used with all grade levels…

  5. Warm Up to a Good Sound

    ERIC Educational Resources Information Center

    Tovey, David C.

    1977-01-01

    Most choral directors in schools today have been exposed to a variety of warm-up procedures. Yet, many do not use the warm-up time effectively as possible. Considers the factors appropriate to a warm-up exercise and three basic warm-up categories. (Author/RK)

  6. Warm summers during Younger Dryas cold reversal over Eurasia

    NASA Astrophysics Data System (ADS)

    Schenk, Frederik; Muschitiello, Francesco; Heikkilä, Miaja; Väliranta, Minna; Tarasov, Lev; Brandefelt, Jenny; Johansson, Arne; Näslund, Jens-Ove; Wohlfarth, Barbara

    2016-04-01

    The Younger Dryas cold reversal (GS-1) sticks out as a major stadial interrupting the mid to late deglaciation with a sharp temperature drop of several degrees around the North Atlantic with global teleconnections. The abrupt return to a very cold glacial-like ocean state introduces a strong temperature anomaly to the climate system contrasting the high solar radiation received by northern summers. Here we show that, in contrast to earlier coarse resolution climate simulations of the Younger Dryas, these competing factors result in rather warm summer conditions over Eurasia comparable to the preceding warm period of the late Allerød (GI-1a). Despite up to 10 K colder sea-surface-temperatures in summer, our high resolution simulation with the Community Earth System Model 1 (CESM1.0.5) suggests that the presence of large ice sheets over Scandinavia, Spitsbergen and the Kara Sea significantly modifies atmospheric flow in summer preventing cold westerly winds from the Atlantic to impact the continent. Instead, fluid dynamics around ice sheets deflect winds to the north or south along the coasts supported by divergent flow from ice domes, stratification and increased tendency to high pressure and atmospheric blocking. Consistent with our model simulation, we show that temperature reconstructions derived from an extended compilation of multi-proxy lake records (chironomids, aquatic pollen, macrofossils) suggest warm July conditions of 13-17° C for continental Europe with exception of coastal and high elevation sites. The analysis of simulated growing degree days, season length and first results from paleo lake modelling driven by climate model output suggests that severe winter to spring conditions significantly delay and shorten the vegetation season but do not produce cold summers as previously simulated.

  7. Characterizing abrupt changes in the stock prices using a wavelet decomposition method

    NASA Astrophysics Data System (ADS)

    Caetano, Marco Antonio Leonel; Yoneyama, Takashi

    2007-09-01

    Abrupt changes in the stock prices, either upwards or downwards, are usually preceded by an oscillatory behavior with frequencies that tend to increase as the moment of transition becomes closer. The wavelet decomposition methods may be useful for analysis of this oscillations with varying frequencies, because they provide simultaneous information on the frequency (scale) and localization in time (translation). However, in order to use the wavelet decomposition, certain requirements have to be satisfied, so that the linear and cyclic trends are eliminated by standard least squares techniques. The coefficients obtained by the wavelet decomposition can be represented in a graphical form. A threshold can then be established to characterize the likelihood of a short-time abrupt change in the stock prices. Actual data from the São Paulo Stock Exchange (Bolsa de Valores de São Paulo) were used in this work to illustrate the proposed method.

  8. Abrupt GaP/Si hetero-interface using bistepped Si buffer

    SciTech Connect

    Ping Wang, Y. Kuyyalil, J.; Nguyen Thanh, T.; Almosni, S.; Bernard, R.; Tremblay, R.; Da Silva, M.; Létoublon, A.; Rohel, T.; Tavernier, K.; Le Corre, A.; Cornet, C.; Durand, O.; Stodolna, J.; Ponchet, A.; Bahri, M.; Largeau, L.; Patriarche, G.; Magen, C.

    2015-11-09

    We evidence the influence of the quality of the starting Si surface on the III-V/Si interface abruptness and on the formation of defects during the growth of III-V/Si heterogeneous crystal, using high resolution transmission electron microscopy and scanning transmission electron microscopy. GaP layers were grown by molecular beam epitaxy on vicinal Si (001). The strong effect of the Si substrate chemical preparation is first demonstrated by studying structural properties of both Si homoepitaxial layer and GaP/Si heterostructure. It is then shown that choosing adequate chemical preparation conditions and subsequent III-V regrowth conditions enables the quasi-suppression of micro-twins in the epilayer. Finally, the abruptness of GaP/Si interface is found to be very sensitive to the Si chemical preparation and is improved by the use of a bistepped Si buffer prior to III-V overgrowth.

  9. Effects of comfort warming on preoperative patients.

    PubMed

    Wagner, Doreen; Byrne, Michelle; Kolcaba, Katharine

    2006-09-01

    THERMAL COMFORT IS ONE DIMENSION of overall patient comfort, and it usually is addressed by covering the patient with warmed cotton blankets. WARMING HELPS A PATIENT maintain normothermia and appears to decrease patient anxiety. AN STUDY WAS CONDUCTED in a preoperative setting to compare the effects of preoperative warming with warmed cotton blankets versus patient-controlled warming gowns on patients' perceptions of thermal comfort and anxiety. BOTH WARMING INTERVENTIONS had a positive effect on patients' thermal comfort and sense of well-being. Patients who used the patient-controlled warming gown also experienced a significant reduction in preoperative anxiety. PMID:17004666

  10. Climate warming and disease risks for terrestrial and marine biota.

    PubMed

    Harvell, C Drew; Mitchell, Charles E; Ward, Jessica R; Altizer, Sonia; Dobson, Andrew P; Ostfeld, Richard S; Samuel, Michael D

    2002-06-21

    Infectious diseases can cause rapid population declines or species extinctions. Many pathogens of terrestrial and marine taxa are sensitive to temperature, rainfall, and humidity, creating synergisms that could affect biodiversity. Climate warming can increase pathogen development and survival rates, disease transmission, and host susceptibility. Although most host-parasite systems are predicted to experience more frequent or severe disease impacts with warming, a subset of pathogens might decline with warming, releasing hosts from disease. Recently, changes in El Niño-Southern Oscillation events have had a detectable influence on marine and terrestrial pathogens, including coral diseases, oyster pathogens, crop pathogens, Rift Valley fever, and human cholera. To improve our ability to predict epidemics in wild populations, it will be necessary to separate the independent and interactive effects of multiple climate drivers on disease impact. PMID:12077394

  11. Climate warming and disease risks for terrestrial and marine biota

    USGS Publications Warehouse

    Harvell, C.D.; Mitchell, C.E.; Ward, J.R.; Altizer, S.; Dobson, A.P.; Ostfeld, R.S.; Samuel, M.D.

    2002-01-01

    Infectious diseases can cause rapid population declines or species extinctions. Many pathogens of terrestrial and marine taxa are sensitive to temperature, rainfall, and humidity, creating synergisms that could affect biodiversity. Climate warming can increase pathogen development and survival rates, disease transmission, and host susceptibility. Although most host-parasite systems are predicted to experience more frequent or severe disease impacts with warming, a subset of pathogens might decline with warming, releasing hosts from disease. Recently, changes in El Niño–Southern Oscillation events have had a detectable influence on marine and terrestrial pathogens, including coral diseases, oyster pathogens, crop pathogens, Rift Valley fever, and human cholera. To improve our ability to predict epidemics in wild populations, it will be necessary to separate the independent and interactive effects of multiple climate drivers on disease impact.

  12. Early emergence in a butterfly causally linked to anthropogenic warming.

    PubMed

    Kearney, Michael R; Briscoe, Natalie J; Karoly, David J; Porter, Warren P; Norgate, Melanie; Sunnucks, Paul

    2010-10-23

    There is strong correlative evidence that human-induced climate warming is contributing to changes in the timing of natural events. Firm attribution, however, requires cause-and-effect links between observed climate change and altered phenology, together with statistical confidence that observed regional climate change is anthropogenic. We provide evidence for phenological shifts in the butterfly Heteronympha merope in response to regional warming in the southeast Australian city of Melbourne. The mean emergence date for H. merope has shifted -1.5 days per decade over a 65-year period with a concurrent increase in local air temperatures of approximately 0.16°C per decade. We used a physiologically based model of climatic influences on development, together with statistical analyses of climate data and global climate model projections, to attribute the response of H. merope to anthropogenic warming. Such mechanistic analyses of phenological responses to climate improve our ability to forecast future climate change impacts on biodiversity. PMID:20236964

  13. Abrupt Onset of Mutations in a Developmentally Regulated Gene during Terminal Differentiation of Post-Mitotic Photoreceptor Neurons in Mice

    PubMed Central

    Sandoval, Ivette M.; Price, Brandee A.; Gross, Alecia K.; Chan, Fung; Sammons, Joshua D.; Wilson, John H.; Wensel, Theodore G.

    2014-01-01

    For sensitive detection of rare gene repair events in terminally differentiated photoreceptors, we generated a knockin mouse model by replacing one mouse rhodopsin allele with a form of the human rhodopsin gene that causes a severe, early-onset form of retinitis pigmentosa. The human gene contains a premature stop codon at position 344 (Q344X), cDNA encoding the enhanced green fluorescent protein (EGFP) at its 3′ end, and a modified 5′ untranslated region to reduce translation rate so that the mutant protein does not induce retinal degeneration. Mutations that eliminate the stop codon express a human rhodopsin-EGFP fusion protein (hRho-GFP), which can be readily detected by fluorescence microscopy. Spontaneous mutations were observed at a frequency of about one per retina; in every case, they gave rise to single fluorescent rod cells, indicating that each mutation occurred during or after the last mitotic division. Additionally, the number of fluorescent rods did not increase with age, suggesting that the rhodopsin gene in mature rod cells is less sensitive to mutation than it is in developing rods. Thus, there is a brief developmental window, coinciding with the transcriptional activation of the rhodopsin locus, in which somatic mutations of the rhodopsin gene abruptly begin to appear. PMID:25264759

  14. Abrupt onset of mutations in a developmentally regulated gene during terminal differentiation of post-mitotic photoreceptor neurons in mice.

    PubMed

    Sandoval, Ivette M; Price, Brandee A; Gross, Alecia K; Chan, Fung; Sammons, Joshua D; Wilson, John H; Wensel, Theodore G

    2014-01-01

    For sensitive detection of rare gene repair events in terminally differentiated photoreceptors, we generated a knockin mouse model by replacing one mouse rhodopsin allele with a form of the human rhodopsin gene that causes a severe, early-onset form of retinitis pigmentosa. The human gene contains a premature stop codon at position 344 (Q344X), cDNA encoding the enhanced green fluorescent protein (EGFP) at its 3' end, and a modified 5' untranslated region to reduce translation rate so that the mutant protein does not induce retinal degeneration. Mutations that eliminate the stop codon express a human rhodopsin-EGFP fusion protein (hRho-GFP), which can be readily detected by fluorescence microscopy. Spontaneous mutations were observed at a frequency of about one per retina; in every case, they gave rise to single fluorescent rod cells, indicating that each mutation occurred during or after the last mitotic division. Additionally, the number of fluorescent rods did not increase with age, suggesting that the rhodopsin gene in mature rod cells is less sensitive to mutation than it is in developing rods. Thus, there is a brief developmental window, coinciding with the transcriptional activation of the rhodopsin locus, in which somatic mutations of the rhodopsin gene abruptly begin to appear. PMID:25264759

  15. Warming early Earth and Mars

    SciTech Connect

    Kasting, J.F.

    1997-05-23

    Sagan and Chyba, in their article on page 1217 of this issue, have revived an old debate about how liquid water was maintained on early Earth and Mars despite a solar luminosity 25 to 30% lower than that at present. A theory that has been popular for some time is that greatly elevated concentrations of atmospheric COD produced by the action of the carbonate-silicate cycle, provided enough of a greenhouse effect to warm early Earth. However, Rye et al. have placed geochemical constraints on early atmospheric CO{sub 2} abundances that fall well below the levels needed to warm the surface. These constraints are based on the absence of siderite (FeCO{sub 3}) in ancient soil profiles-a negative and, hence, rather weak form of evidence- and apply to the time period 2.2 to 2.8 billion years ago, when Earth was already middle aged. Nonetheless, the soil data provide some indication that atmospheric CO{sub 2} levels may have been lower than previously thought. An even more serious problem arises if one tries to keep early Mars warm with CO{sub 2}. Model calculations predict that CO{sub 2} clouds would form on Mars in the upper troposphere, reducing the lapse rate and severely limiting the amount of surface warming. A suggestion that CO{sub 2} clouds may have warmed the planet radiatively has yet to be borne out by detailed calculations. 26 refs.

  16. Trends and abrupt changes in 104 years of ice cover and water temperature in a dimictic lake in response to air temperature, wind speed, and water clarity drivers

    NASA Astrophysics Data System (ADS)

    Magee, Madeline R.; Wu, Chin H.; Robertson, Dale M.; Lathrop, Richard C.; Hamilton, David P.

    2016-05-01

    abrupt changes in air temperature and wind speed. Average summer hypolimnetic temperature and fall turnover date exhibit significant differences between the third period and the first two periods. Changes in ice cover (ice-on and ice-off dates, ice cover duration, and maximum ice thickness) exhibit an abrupt change after 1994, which was related in part to the warm El Niño winter of 1997-1998. Under-ice water temperature, freeze-over water temperature, hypolimnetic temperature, fall turnover date, and stratification duration demonstrate a significant difference in the third period (1994-2014), when air temperature was warmest and wind speeds decreased rather abruptly. The trends in ice cover and water temperature demonstrate responses to both long-term and abrupt changes in meteorological conditions that can be complemented with numerical modeling to better understand how these variables will respond in a future climate.

  17. Flow Regime Study in a High Density Circulating Fluidized Bed Riser with an Abrupt Exit

    SciTech Connect

    Mei, J.S.; Shadle, L.J.; Yue, P.C.; Monazam, E.R.

    2007-01-01

    Flow regime study was conducted in a 0.3 m diameter, 15.5 m height circulating fluidized bed (CFB) riser with an abrupt exit at the National Energy Technology Laboratory of the U.S. Department of Energy. Local particle velocities were measured at various radial positions and riser heights using an optical fiber probe. On-line measurement of solid circulating rate was continuously recorded by the Spiral. Glass beads of mean diameter 61 μm and particle density of 2,500 kg/m3 were used as bed material. The CFB riser was operated at various superficial gas velocities ranging from 3 to 7.6 m/s and solid mass flux from 20 to 550 kg/m2-s. At a constant riser gas velocity, transition from fast fluidization to dense suspension upflow (DSU) regime started at the bottom of the riser with increasing solid flux. Except at comparatively low riser gas velocity and solid flux, the apparent solid holdup at the top exit region was higher than the middle section of the riser. The solid fraction at this top region could be much higher than 7% under high riser gas velocity and solid mass flux. The local particle velocity showed downward flow near the wall at the top of the riser due to its abrupt exit. This abrupt geometry reflected the solids and, therefore, caused solid particles traveling downward along the wall. However, at location below, but near, the top of the riser the local particle velocities were observed flowing upward at the wall. Therefore, DSU was identified in the upper region of the riser with an abrupt exit while the fully developed region, lower in the riser, was still exhibiting core-annular flow structure. Our data were compared with the flow regime boundaries proposed by Kim et al. [1] for distinguishing the dilute pneumatic transport, fast fluidization, and DSU.

  18. Abrupt PN junctions: Analytical solutions under equilibrium and non-equilibrium

    NASA Astrophysics Data System (ADS)

    Khorasani, Sina

    2016-08-01

    We present an explicit solution of carrier and field distributions in abrupt PN junctions under equilibrium. An accurate logarithmic numerical method is implemented and results are compared to the analytical solutions. Analysis of results shows reasonable agreement with numerical solution as well as the depletion layer approximation. We discuss extensions to the asymmetric junctions. Approximate relations for differential capacitance C-V and current-voltage I-V characteristics are also found under non-zero external bias.

  19. Abrupt increase in east Indonesian rainfall from flooding of the Sunda Shelf ˜9500 years ago

    NASA Astrophysics Data System (ADS)

    Griffiths, Michael L.; Drysdale, Russell N.; Gagan, Michael K.; Zhao, Jian-xin; Hellstrom, John C.; Ayliffe, Linda K.; Hantoro, Wahyoe S.

    2013-08-01

    We present a precisely dated, multi-proxy stalagmite record from Liang Luar Cave, Flores (southeast Indonesia) that reveals a rapid increase in Indonesian monsoon rainfall at ˜9.5 ka. A "ramp-fitting" method for detecting statistically significant inflections in a time-series was applied to the stalagmite δ18O, Mg/Ca, and Sr/Ca profiles to quantify the precise timing and magnitude of an abrupt increase in monsoon strength over a period of ˜350 years. Previously published lake-level records from the monsoon-affected Australian interior show a sudden intensification of the Australian monsoon at ˜14 ka. However, our records indicate that monsoon intensification in Flores occured ˜4-5 kyr later. The timing of the monsoon shift in Flores is synchronous with the rapid expansion of rainforest in northeast Australia and regional freshening of the southern Makassar Strait which, under present-day conditions, is sensitive to monsoon variability. The freshening of southern Makassar was coeval with an abrupt ˜1.5 °C cooling in the upper thermocline of the Timor Sea ˜9.5 ka, indicative of reduced surface heat transport by the Indonesian Throughflow (ITF) when the Java Sea opened during postglacial sea-level rise. This suggests that the abrupt increase in monsoon rainfall on Flores was not due to a change in the ITF - because a decrease in rainfall would be expected to accompany cooler local sea surface temperatures (SSTs) - but rather by the sudden increase in ocean surface area and/or temperature in the monsoon source region as the Sunda Shelf flooded during deglaciation. We propose that it was the abrupt intensification of the monsoon through the late deglaciation that maintained the subsequent structure of the ITF following the flooding of the Sunda Shelf at ˜9.5 ka.

  20. The abrupt changes in the yellowed fibril density in the Linen of Turin

    NASA Astrophysics Data System (ADS)

    Curciarello, F.; De Leo, V.; Fazio, G.; Mandaglio, G.

    2012-03-01

    The present investigation is an attempt to explain the abrupt changes in the yellowed fibril density (or image intensity) values in the dorsal part of the Shroud of Turin body image. The interested areas are the ones at the base of the shoulders and the buttocks. These rapid changes in the body image intensity are not anomalies of the linen manufacture. They can be explained with the original presence of aromas and/or burial ointments.

  1. Relationship between ATS-6 spacecraft-charging occurrences and warm plasma encounters

    NASA Technical Reports Server (NTRS)

    Reasoner, D. L.; Chappell, C. R.; Lennartsson, W.

    1976-01-01

    The occurrences in local time of spacecraft-charging and warm plasma events observed by the University of California at San Diego plasma detector on ATS-6 have been examined using data from 40 contiguous orbits. The local time distribution of charging events was found to maximize between local midnight and dawn and was also similar to the distribution of synchronous spacecraft anomalies reported by others. More than half of the charging events had potentials of -50 V or more, and potentials on the order of -1000 V were observed. All of the spacecraft charging events reported in this paper occurred during sunlit conditions. The warm plasma encounters were concentrated in the local noon-to-dusk sector, and the local-time distributions of charging events and warm plasma encounters were found to be anticorrelated.

  2. A Fast Framework for Abrupt Change Detection Based on Binary Search Trees and Kolmogorov Statistic.

    PubMed

    Qi, Jin-Peng; Qi, Jie; Zhang, Qing

    2016-01-01

    Change-Point (CP) detection has attracted considerable attention in the fields of data mining and statistics; it is very meaningful to discuss how to quickly and efficiently detect abrupt change from large-scale bioelectric signals. Currently, most of the existing methods, like Kolmogorov-Smirnov (KS) statistic and so forth, are time-consuming, especially for large-scale datasets. In this paper, we propose a fast framework for abrupt change detection based on binary search trees (BSTs) and a modified KS statistic, named BSTKS (binary search trees and Kolmogorov statistic). In this method, first, two binary search trees, termed as BSTcA and BSTcD, are constructed by multilevel Haar Wavelet Transform (HWT); second, three search criteria are introduced in terms of the statistic and variance fluctuations in the diagnosed time series; last, an optimal search path is detected from the root to leaf nodes of two BSTs. The studies on both the synthetic time series samples and the real electroencephalograph (EEG) recordings indicate that the proposed BSTKS can detect abrupt change more quickly and efficiently than KS, t-statistic (t), and Singular-Spectrum Analyses (SSA) methods, with the shortest computation time, the highest hit rate, the smallest error, and the highest accuracy out of four methods. This study suggests that the proposed BSTKS is very helpful for useful information inspection on all kinds of bioelectric time series signals. PMID:27413364

  3. Parameter estimation on compact binary coalescences with abruptly terminating gravitational waveforms

    NASA Astrophysics Data System (ADS)

    Mandel, Ilya; Berry, Christopher P. L.; Ohme, Frank; Fairhurst, Stephen; Farr, Will M.

    2014-08-01

    Gravitational-wave (GW) astronomy seeks to extract information about astrophysical systems from the GW signals they emit. For coalescing compact-binary sources this requires accurate model templates for the inspiral and, potentially, the subsequent merger and ringdown. Models with frequency-domain waveforms that terminate abruptly in the sensitive band of the detector are often used for parameter-estimation studies. We show that the abrupt waveform termination contains significant information that affects parameter-estimation accuracy. If the sharp cutoff is not physically motivated, this extra information can lead to misleadingly good accuracy claims. We also show that using waveforms with a cutoff as templates to recover complete signals can lead to biases in parameter estimates. We evaluate when the information content in the cutoff is likely to be important in both cases. We also point out that the standard Fisher matrix formalism, frequently employed for approximately predicting parameter-estimation accuracy, cannot properly incorporate an abrupt cutoff that is present in both signals and templates; this observation explains some previously unexpected results found in the literature. These effects emphasize the importance of using complete waveforms with accurate merger and ringdown phases for parameter estimation.

  4. Abrupt discontinuation of psychotropic drugs during pregnancy: fear of teratogenic risk and impact of counselling.

    PubMed Central

    Einarson, A; Selby, P; Koren, G

    2001-01-01

    OBJECTIVE: To assess the consequences to mother and baby of abruptly discontinuing antidepressant or benzodiazepine medication during pregnancy and to assess the impact of our counselling. PARTICIPANTS: All women who consulted the Motherisk Program between November 1996 and December 1997 and who stopped taking antidepressant or benzodiazepine medication when pregnancy was confirmed agreed to participate in the study. DESIGN AND INTERVENTIONS: Subjects were interviewed, received counselling, and completed a questionnaire 1 month after their initial call and after the birth of their baby. RESULTS: Of 36 women who completed the study, 34 discontinued their medication abruptly for fear of harming the fetus, 28 on the advice of their physician; 26 (70.3%) women reported physical and psychological adverse effects, 11 reported psychological effects only, and 11 reported suicidal ideation (4 were admitted to hospital). After counselling, 22 of 36 (61.1%) women resumed taking their medication, and 4 found that they no longer required it. One woman had a therapeutic abortion and 2 experienced spontaneous abortions; there were therefore 35 healthy babies (including 2 sets of twins) born to 33 women; 14 of 21 mothers breast-fed their babies while taking their psychotropic medication, with no adverse effects reported. CONCLUSIONS: When assessing the risks and benefits of taking psychotropic medication during pregnancy, women and their physicians should be aware that the abrupt discontinuation of psychotropic drugs can lead to serious adverse effects. Counselling is effective in reassuring women to adhere to therapy. PMID:11212593

  5. Abrupt intensification of ENSO forced by deglacial ice-sheet retreat in CCSM3

    NASA Astrophysics Data System (ADS)

    Lu, Zhengyao; Liu, Zhengyu; Zhu, Jiang

    2016-03-01

    The influence of ice-sheet retreat on the El Niño-Southern Oscillation (ENSO) variability is studied using a transient simulation in NCAR-CCSM3 forced only by variations in continental ice sheets during the last deglaciation. The most striking feature is an abrupt strengthening of ENSO (by ~25 %) at 14 thousand years before present (ka BP) in response to a significant retreat (an equivalent ~25 m sea-level rise) of the Laurentide ice sheet (LIS). This abrupt intensification of ENSO is caused mainly by a sudden weakening of the equatorial annual cycle through the nonlinear mechanism of frequency entrainment, rather than an increase in the coupled ocean-atmosphere instability. The weakened annual cycle corresponds to a reduced north-south cross-equatorial annual mean SST contrast in the eastern Pacific. This reduced interhemispheric SST gradient—significant cooling north of the equator—is forced predominantly by an anomalous easterly from an abrupt polarward shift of the jet stream in the Northern Hemisphere, which extends to the northeastern tropical Pacific Ocean surface and is reinforced by the wind-evaporation-SST feedback then propagates equatorward; it could also be contributed by a fast sea-ice expansion and a consequent cooling in the North Pacific and North Atlantic that is induced by the retreat of the LIS.

  6. A Fast Framework for Abrupt Change Detection Based on Binary Search Trees and Kolmogorov Statistic

    PubMed Central

    Qi, Jin-Peng; Qi, Jie; Zhang, Qing

    2016-01-01

    Change-Point (CP) detection has attracted considerable attention in the fields of data mining and statistics; it is very meaningful to discuss how to quickly and efficiently detect abrupt change from large-scale bioelectric signals. Currently, most of the existing methods, like Kolmogorov-Smirnov (KS) statistic and so forth, are time-consuming, especially for large-scale datasets. In this paper, we propose a fast framework for abrupt change detection based on binary search trees (BSTs) and a modified KS statistic, named BSTKS (binary search trees and Kolmogorov statistic). In this method, first, two binary search trees, termed as BSTcA and BSTcD, are constructed by multilevel Haar Wavelet Transform (HWT); second, three search criteria are introduced in terms of the statistic and variance fluctuations in the diagnosed time series; last, an optimal search path is detected from the root to leaf nodes of two BSTs. The studies on both the synthetic time series samples and the real electroencephalograph (EEG) recordings indicate that the proposed BSTKS can detect abrupt change more quickly and efficiently than KS, t-statistic (t), and Singular-Spectrum Analyses (SSA) methods, with the shortest computation time, the highest hit rate, the smallest error, and the highest accuracy out of four methods. This study suggests that the proposed BSTKS is very helpful for useful information inspection on all kinds of bioelectric time series signals. PMID:27413364

  7. The grain size gap and abrupt gravel-sand transitions in rivers due to suspension fallout

    NASA Astrophysics Data System (ADS)

    Lamb, Michael P.; Venditti, Jeremy G.

    2016-04-01

    Median grain sizes on riverbeds range from boulders in uplands to silt in lowlands; however, rivers with ~1-5 mm diameter bed sediment are rare. This grain size gap also marks an abrupt transition between gravel- and sand-bedded reaches that is unlike any other part of the fluvial network. Abrupt gravel-sand transitions have been attributed to rapid breakdown or rapid transport of fine gravel, or a bimodal sediment supply, but supporting evidence is lacking. Here we demonstrate that rivers dramatically lose the ability to transport sand as wash load where bed shear velocity drops below ~0.1 m/s, forcing an abrupt transition in bed-material grain size. Using thresholds for wash load and initial motion, we show that the gap emerges only for median bed-material grain sizes of ~1-5 mm due to Reynolds number dependencies in suspension transport. The grain size gap, therefore, is sensitive to material properties and gravity, with coarser gaps predicted on Mars and Titan.

  8. Rebound insomnia induced by abrupt withdrawal of hypnotics in sleep-disturbed rats.

    PubMed

    Hirase, Masahiro; Ishida, Takayuki; Kamei, Chiaki

    2008-11-12

    The present study was performed to examine whether or not rebound insomnia is caused by an abrupt withdrawal of benzodiazepine hypnotics and tandospirone in rats. Etizolam and triazolam caused a significant shortening of sleep latency, increase in non-REM sleep time, and decrease in wake time in a dose-dependent manner. Etizolam and triazolam caused a significant shortening of sleep latency during drug administration (for 7 days), whereas a significant prolongation of sleep latency was observed by the abrupt withdrawal of these drugs. Tandospirone caused a shortening of sleep latency, whereas no effect was observed on non-REM sleep time and wake time during drug administration (for 7 days). On the other hand, tandospirone showed no significant effect on sleep latency through its abrupt withdrawal, differing from etizolam and